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Unexpected differences in reactivity between tin and lead organyl chlorides – crystal structures of their organylphosphonium salts
Inorganica Chimica Acta 357 (2004) 125–134 www.elsevier.com/locate/ica
Unexpected differences in reactivity between tin and lead organyl chlorides – crystal structures of their organylphosphonium salts q Dirk Weber a
a,*
, Sven H. Hausner b,1, Axel Eisengr€ aber-Pabst c, Sanghee Yun b, Jeanette A. Krause-Bauer b, Hans Zimmer b,2
Institut f€ ur Organische Chemie und Biochemie, Technische Universit€at M€unchen, Lichtenbergstr. 4, Garching 85747, Germany b Department of Chemistry, University of Cincinnati, ML 0172, Cincinnati, OH 45221-0172, USA c Fakult€at Chemie, Universit€at Stuttgart, Pfaffenwaldring 55, Stuttgart D-70569, Germany Received 14 May 2003; accepted 24 May 2003
Abstract Pentacoordinated tin is known since the late 1950s but little is known about the ability of lead to form similar structures. Originally we investigated the reaction between a number of tetraorganylphosphonium chlorides [PR4 ]þ Cl (R ¼ Me, Bun , and Ph) and several diorganyltin dichlorides SnR0 2 Cl2 (R0 ¼ Me, Et, Prn , Bun , Ph, o-, m-, p-Tol) between 100 and 240 °C. Novel pentacoordinated tin complexes, tetraorganylphosphonium diorganyltrichlorostannates [PR4 ][SnR0 2 Cl3 ] (1–19), were formed in good to excellent yields. In a second step, this synthetic approach was extended to include the reaction of diphenyllead dichloride Ph2 PbCl2 with [PR4 ]þ Cl (R ¼ Bun , Ph). Surprisingly, a two chloride transfer was observed to form the hexacoordinated lead species [PBun4 ]2 [PbPh2 Cl4 ] (20). Under similar conditions, the pentacoordinated [PPh4 ][PbPh3 Cl2 ] (21) was obtained by a phenyl transfer. Complexes 20 and 21 were characterised by NMR (1 H, 13 C, 31 P, and 207 Pb), IR, MS, and X-ray crystallography. The anion of 20 assumes a lightly distorted octahedral geometry with the phenyl substituents in trans-positions. In the anion of 21 the phenyl substituents occupy the equatorial positions of a lightly distorted trigonal bipyramid. A thorough spectroscopical investigation of the tin complexes 1–19, including X-ray structural studies, which were possible for complexes with R0 ¼ aryl, revealed that these complexes are monomeric with a distorted trigonal bipyramidal [SnR0 2 Cl3 ] anion. Both aryl groups occupy equatorial positions. Ó 2003 Elsevier B.V. All rights reserved. Keywords: Pentacoordinated tin; Hexacoordinated lead; Pentacoordinated lead; Phenyl transfer
1. Introduction Structures of pentacoordinated organotin compounds are known since the late 1950s [1,2]. Since then, numerous structural investigations on monomeric, dimeric, oligoor even polymeric pentacoordinate tin species employing such different techniques as X-ray diffraction, M€ ossbauer q Supplementary data associated with this article can be found, in the online version, at doi:10.1016/S0020-1693(03)00365-7. * Corresponding author. Tel.: +49-89-36037682; fax: +49-75318493514. E-mail address: [email protected] (D. Weber). 1 Present address: School of Medicine, Yale University, VA Medical Center/116A2, 950 Campbell Ave, West Haven, CT 06516, USA. 2 Deceased.
0020-1693/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0020-1693(03)00365-7
spectroscopy, conductivity measurements, IR and solidstate NMR spectroscopy have been reported (for a review see for example [3]). Besides their importance for stereochemical models and for the determination of cation–anion interactions, these studies may be useful for the understanding of the intermediate state of nucleophilic substitution reactions such as the Stille coupling during which the tin atom has been proposed to be pentacoordinated [4]. Although organotin has been studied extensively, there is a striking lack of data in the literature concerning organolead compounds. Little is known about the behaviour of lead in comparable reactions to tin or the ability to form similar structures. Despite their toxicity handicap, organolead compounds may have a greater potential for
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organic synthesis than currently recognised. One important step towards tailored applications is to elaborate the general differences concerning structure and reactivity in comparison to tin. Therefore our effort was directed towards a comparison of the behaviour of these two metals in a relatively simple reaction setup. In this paper we describe the discovery of interesting differences concerning the reactivity of these two metals. Our interest in organotin, as well as organophosphonium chemistry, originally led us to investigate the reaction between tetraorganylphosphonium chlorides and dialkyltin dichlorides. In contrast to other experimental conditions described for the reaction between diorganyltin dichlorides and various salts [5–10] we simply combined the dialkyltin dichloride with an equimolar amount of the appropriate tetraorganylphosphonium chloride without employing any solvent [11]. Initially, we prepared the alkyl complexes [PR4 ][SnR0 2 Cl3 ] (1)–(7) and (12)–(15) (R0 ¼ Me, Et, Prn , Bun ) [12]. For the complexes obtained we tentatively proposed, based on NMR studies, a trigonal bipyramidal structure [SnR0 2 Cl3 ] . We rationalised that, by further limiting the degree of flexibility of the R0 residues, we would obtain more crystalline structures, suitable for X-ray crystal analysis. It has been proposed that, for complexes [SnR02 Cl3 ] , the stability decreases in the order R0 ¼ Ph > Me > Et > Pr because of the decreasing electronegative character of these groups [6]. Based on this information, and because of the easy synthetic access, we decided to prepare the corresponding complexes with R0 ¼ aryl [13]. As a part of our work on pentacoordinated tin anions bearing a tetraorganylphosphonium counterion, we here present the crystal structures of [PBun4 ][SnPh2 Cl3 ] (8), [PBun4 ][Sn(o-Tol)2 Cl3 ] (9), [PPh4 ][SnPh2 Cl3 ] (16), [PPh4 ][Sn(o-Tol)2 Cl3 ] (17), [PPh4 ] [Sn(m-Tol)2 Cl3 ] (18), and [PPh4 ][Sn(p-Tol)2 Cl3 ] (19). The geometry and coordination of complexes 8, 9, and 16–19 are discussed. On the basis of a detailed characterisation by means of 1 H-, 13 C-, 31 P-, and 119 SnNMR spectroscopy their structures are compared with those of complexes 1–7 and 12–15. Furthermore, the extension of this synthetic approach to include the reaction of diphenyllead dichloride Ph2 PbCl2 with [PR4 ]þ Cl (R ¼ Bun , Ph) is presented [14]. Unexpectedly, the formation of complexes [PBun4 ]2 [PbPh2 Cl4 ] (20) and [PPh4 ][PbPh3 Cl2 ] (21) was observed. Their structures and structural differences to the aforementioned tin complexes, obtained from the corresponding reactions, will be discussed based on spectroscopic and crystallographic data.
tyl)phosphonium chloride was obtained from Fluka (Buchs, Switzerland). Diphenyllead dichloride and all diorganyltin dichlorides, except dimethyltin dichloride, were prepared in two steps by published methods [15]. Dimethyltin dichloride was provided by Morton International Incorporation (Cincinnati, OH). Reactions were carried out under an inert gas atmosphere (N2 or Ar). 207 Pb NMR spectra were recorded on a Bruker AC 250 spectrometer. The broad range of 207 Pb NMR shifts of about 16,000 ppm required acquisition at various frequencies [16–18]. The maximum shift-window size on the spectrometer used was 100,000 Hz (equivalent to about 1900 ppm). The signals of the lead complexes 20 and 21 were recorded in windows centred at 52.330, 52.320, and 52.280 MHz. Each signals was confirmed at the three different frequencies to insure that the signal seen is a real peak and not a ‘‘fold over’’ signal. 3 Further details, as well as NMR and IR experimental details are summarised in the supplementary material. 2.2. Preparations 2.2.1. Tetraorganylphosphonium diorganyltrichlorostannates [PR4 ][SnR0 2 Cl3 ] (1–19). General procedure Equimolar amounts, ranging between 0.8 and 2 mmol, of tetraorganylphosphonium chloride and the corresponding diorganyltin dichloride were heated until a homogeneous liquid was obtained (Table 1). The crude product (except for complexes 10 and 11) was recrystallised (Table 1). For complexes 8, 9, and 16–19 the slightly cloudy solution was pressed through a syringe microfilter. Slow evaporation of the solvent at room temperature yielded crystals suitable for X-ray analysis. Analytical and physical data are listed in Tables 2 and 3. 2.2.2. Di[tetra(n-butyl)phosphonium] diphenyltetrachloroplumbate [PBun4 ]2 [PbPh2 Cl4 ] (20) Diphenyllead dichloride (865 mg, 2.00 mmol) and tetra(n-butyl)phosphonium chloride (590 mg, 2.00 mmol) were heated to 180 °C for 1 h. The melt was cooled to room temperature, dissolved in hot ethanol, and filtered cold (syringe microfilter). Removal of the solvent in a rotary evaporator yielded brownish, waxy crystals. More impurities were removed with three times 50 ml of refluxing ether. A colourless, crystalline product (810 mg, 0.80 mmol, 80% o. Th.) was obtained after recrystallising twice from a small amount of THF
2. Experimental 2.1. Materials Unless stated otherwise, all chemicals were purchased from Aldrich Chemical (Milwaukee, WI). Tetra(n-bu-
3 The standard frequency for 207 Pb NMR spectra is the exact frequency determined for Pb(CH3 )4 (d 0 ppm). Pb(CH3 )4 has historically been used as a standard, but nowadays is avoided because of its toxicity and volatility. The standard frequency is defined as ‘‘20,920,597/100,000,000 times the frequency of SiMe4 ’’ [16,17]. For the 250.133000 MHz instrument used, it is 52.329317 MHz.
D. Weber et al. / Inorganica Chimica Acta 357 (2004) 125–134
127
Table 1 Reaction conditions for complexes 1–19 Complex
T (°C)
t (min)
Recrystallisation solvent
[PMe4 ][SnMe2 Cl3 ] (1) [PMe4 ][SnEt2 Cl3 ] (2) [PMe4 ][SnPrn2 Cl3 ] (3) [PBun4 ][SnMe2 Cl3 ] (4) [PBun4 ][SnEt2 Cl3 ] (5) [PBun4 ][SnPrn2 Cl3 ] (6) [PBun4 ][SnBun2 Cl3 ] (7) [PBun4 ][SnPh2 Cl3 ] (8) [PBun4 ][Sn(o-Tol)2 Cl3 ] (9) [PBun4 ][Sn(m-Tol)2 Cl3 ] (10) [PBun4 ][Sn(p-Tol)2 Cl3 ] (11) [PPh4 ][SnMe2 Cl3 ] (12) [PPh4 ][SnEt2 Cl3 ] (13) [PPh4 ][SnPrn2 Cl3 ] (14) [PPh4 ][SnBun2 Cl3 ] (15) [PPh4 ][SnPh2 Cl3 ] (16) [PPh4 ][Sn(o-Tol)2 Cl3 ] (17) [PPh4 ][Sn(m-Tol)2 Cl3 ] (18) [PPh4 ][Sn(p-Tol)2 Cl3 ] (19)
200 200 180 110 100 100 100 120 120 140 130 200 200 200 200 230 230 220 220
240 180 120 60 60 120 120 60 60 60 60 180 180 240 240 30 30 30 30
EtOH EtOH EtOH Et2 O Et2 O:EtOH ¼ 7:1 Et2 O Et2 O:EtOH ¼ 19:1 Et2 O:acetone:CH3 CN ¼ 45:2:few drops Et2 O:EtOH ¼ 1:1
a
a a
EtOH EtOH EtOH EtOH EtOH EtOH EtOH EtOH
Oil. Compound did not crystallise.
(Table 4). Crystals suitable for X-ray crystallography were obtained by slow evaporation of the THF at room temperature. 2.2.3. Tetraphenylphosphonium triphenyldichloroplumbate [PPh4 ][PbPh3 Cl2 ] (21) Diphenyllead dichloride (2.50 g, 5.78 mmol) and 2.17 g (5.78 mmol) tetraphenylphosphonium chloride were
combined in a 100 ml round bottom flask and placed onto a preheated oilbath (260–265 °C). The mixture was stirred until a thin melt was obtained and kept at this temperature for one additional minute. The mixture was removed from the oilbath and cooled to below 200 °C. The bath was allowed to cool, and the mixture was stirred for an additional one half hour at 205–215 °C. The mixture solidified readily upon cooling to room
Table 2 Analytical and physical data for tetraorganylphosphonium diorganyltrichlorostannates Complex
Mp (°C)
Appearance
Yieldb (%)
Analysis (%)e C
[PMe4 ][SnMe2 Cl3 ] (1) [PMe4 ][SnEt2 Cl3 ] (2) [PMe4 ][SnPrn2 Cl3 ] (3) [PBun4 ][SnMe2 Cl3 ] (4) [PBun4 ][SnEt2 Cl3 ] (5) [PBun4 ][SnPrn2 Cl3 ] (6) [PBun4 ][SnBun2 Cl3 ] (7) [PBun4 ][SnPh2 Cl3 ] (8) [PBun4 ][Sn(o-Tol)2 Cl3 ] (9) [PBun4 ][Sn(m-Tol)2 Cl3 ] (10) [PBun4 ][Sn(p-Tol)2 Cl3 ] (11) [PPh4 ][SnMe2 Cl3 ] (12) [PPh4 ][SnEt2 Cl3 ] (13) [PPh4 ][SnPrn2 Cl3 ] (14) [PPh4 ][SnBun2 Cl3 ] (15) [PPh4 ][SnPh2 Cl3 ] (16) [PPh4 ][Sn(o-Tol)2 Cl3 ] (17) [PPh4 ][Sn(m-Tol)2 Cl3 ] (18) [PPh4 ][Sn(p-Tol)2 Cl3 ] (19) a
a
>300 >280a 260a 92–93 80–81 92–93 79–81 64–66 95–96
197–198 177–178 130–131 109–110 230–233 230 149–150 153–154
Decomposition. Based on tin. c Yield not optimised. d Compound could not be recrystallised. e Calculated values in parentheses. f Not determined. b
colourless powder colourless powder colourless powder colourless plates colourless plates colourless plates colourless plates colourless crystals colourless crystals colourless oil colourless oil colourless powder colourless powder colourless powder colourless powder colourless crystals brownish crystals brownish crystals brownish crystals
66 72 88 82 81 96 91 92 24c quant.d quant.d 83 83 90 92 34c 57c 70c 31c
21.02 25.45 30.03 42.20 44.09 46.49 48.33 53.00 54.32 54.20 53.89 52.30 53.93 54.95 56.69 59.94 61.25 60.91 61.23
H (20.81) (25.67) (29.85) (42.02) (44.27) (46.30) (48.15) (52.66) (54.05) (54.05) (54.05) (52.53) (54.02) (55.38) (56.63) (60.17) (61.13) (61.13) (61.13)
5.32 5.67 6.39 8.19 8.35 8.61 8.97 7.15 7.70 7.55 7.38 4.39 4.98 5.24 5.58 4.19 4.61 4.36 4.40
Cl (5.24) (5.92) (6.51) (8.23) (8.55) (8.83) (9.09) (7.25) (7.55) (7.55) (7.55) (4.41) (4.86) (5.27) (5.64) (4.20) (4.59) (4.59) (4.59)
30.53 28.06 26.27 20.81 19.46 18.46 17.50
(30.72) (28.42) (26.43) (20.67) (19.60) (18.64) (17.76)
f f f f
17.76 17.23 15.89 15.80 f f f f
(17.89) (17.08) (16.35) (15.67)
128 Table 3 31 P- and
D. Weber et al. / Inorganica Chimica Acta 357 (2004) 125–134
119
Sn NMR data for tetraorganylphosphonium diorganyl-trichlorostannates (complexes 1–19) and some starting materialsa
Compound
31
Pb
119
Sn
DMSO-d6 SnMe2 Cl2 SnEt2 Cl2 SnPrn Cl2 SnBun Cl2 SnPh2 Cl2 Sn(m-Tol)2 Cl2 Sn(p-Tol)2 Cl2 [PBun4 ]Cl [PPh4 ]Cl [PMe4 ][SnMe2 Cl3 ] (1) [PMe4 ][SnEt2 Cl3 ] (2) [PMe4 ][SnPrn2 Cl3 ] (3) [PBun4 ][SnMe2 Cl3 ] (4) [PBun4 ][SnEt2 Cl3 ] (5) [PBun4 ][SnPrn2 Cl3 ] (6) [PBun4 ][SnBun2 Cl3 ] (7) [PBun4 ][SnPh2 Cl3 ] (8) [PBun4 ][Sn(o-Tol)2 Cl3 ] (9) [PBun4 ][Sn(m-Tol)2 Cl3 ] (10) [PBun4 ][Sn(p-Tol)2 Cl3 ] (11) [PPh4 ][SnMe2 Cl3 ] (12) [PPh4 ][SnEt2 Cl3 ] (13) [PPh4 ][SnPrn2 Cl3 ] (14) [PPh4 ][SnBun2 Cl3 ] (15) [PPh4 ][SnPh2 Cl3 ] (16) [PPh4 ][Sn(o-Tol)2 Cl3 ] (17) [PPh4 ][Sn(m-Tol)2 Cl3 ] (18) [PPh4 ][Sn(p-Tol)2 Cl3 ] (19)
CDCl3
)249.9 )225.7 )218.3 )211.6
141.5 128.3 126.3 126.5 )27.2 )25.4 )21.7
)246.7 )226.4 )206.4
d;e
d
33.7 23.6 26.16c 26.53c 24.17 33.54 33.54 33.54 33.49 34.91c 34.90c 34.86c 34.89c 23.80 23.81 23.81 23.81 23.46c 23.51c 23.46c 23.45c
d;e d;e
)98.7 )96.1 )106.2 )99.6 )248.2 )238.4 )247.3 )238.9
)387.7 )270.6 )384.6 )375.2 )243.4 )221.4 )195.9 )193.8 )387.2 )276.0 )381.0 )375.3
MeOH-d3
)92.9 )98.9 )58.7
d;e
)103.3 )112.0 )114.0 d;e d;e
)249.7d )240.5d
a
Chemical shift (d) in ppm. Spectra in CDCl3 unless otherwise stated. c Spectrum in DMSO-d6 . d Low solubility. e Unable to determine. b
temperature. It was extracted with 125 ml hot ethanol in several portions, followed by filtration (syringe microfilter). Removal of the solvent in a rotary evaporator yielded a partially viscous, light-brownish solid. It solidified upon addition of 150 ml water. The mixture was briefly treated with ultrasound, and the solid was allowed to settle overnight. The liquid was removed, and the treatment was repeated with another 150 ml water. The lightly cream coloured solid was dried under reduced pressure. It was taken up in 150 ml THF, briefly heated to reflux, ultrasonicated, and filtered warm (syringe microfilter). The solvent was removed in a rotary evaporator. Remaining impurities in the resulting resin were extracted with three times 1–5 ml refluxing THF. After drying, 0.78 g (0.919 mmol, 16% o. Th.) colourless, fine crystals were obtained (Table 4). Crystals suitable for X-ray crystallography were obtained by slow evaporation of the THF at room temperature. 2.3. X-Ray crystallographic analysis For X-ray examination and data collection, suitable crystals were coated with a light film of epoxy resin or
paratone-N and mounted on glass fibers. Data for [PPh4 ][SnPh2 Cl3 ] (16) and [PPh4 ][Sn(p-Tol)2 Cl3 ] (19) were collected at room temperature on a Siemens P3 diffractometer 4 with graphite-monochromated Mo Ka radiation. Lattice parameters were obtained from the angular settings from 40 reflections lying in a 2h range of 10–30°. Intensity data were collected using variable speed h 2h scans out to 55° in 2h. All data were corrected for decay (based on three standard reflections), Lorentz and polarisation effects as well as for absorption (based on measured w scans) [19]. Data for [PBu4 ][Sn(o-Tol)2 Cl3 ] (9), [PPh4 ][Sn(oTol)2 Cl3 ] (17), [PPh4 ][Sn(m-Tol)2 Cl3 ] (18), and [PBu4 ]2 [PbPh2 Cl4 ] (20) were collected at low temperature on a standard Siemens SMART 1K CCD diffractometer 4 with graphite-monochromated Mo Ka radiation and a detector distance of 5.0 cm. Data for 4
For the CCD diffractometer, SMART v4.05, v5.054 or v5.622 and SAINT v4.05, v5.A06 or v6.02A programs were used for data collection and processing, respectively. The P 3=P 4-PC Diffractometer Program v4.27 was used for data collection and reduction on the P 3 diffractometer. Siemens Analytical X-ray Instruments, Madison, WI.
D. Weber et al. / Inorganica Chimica Acta 357 (2004) 125–134
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Table 4 Analytical and physical data for tetraorganylphosphonium organylchloroplumbates Complex
[PBun4 ]2 [PbPh2 Cl4 ] (20)
[PPh4 ][PbPh3 Cl2 ] (21)
Mp (°C) Appearance Yielda (%) Analysisb (%)
166–168 colourless plates 80 51.74 (51.71)c 8.14 (8.09)c 0.90 (24H, t, J 6.9, PCH2 CH2 CH2 CH3 ), 1.30–1.50 (32H, m, PCH2 CH2 CH2 CH3 ), 2.10–2.30 (16H, m, PCH2 ), 7.31 (2H, t, J 7.0, p-CH), 7.46 (4H, t, J 7.4, 4 JPbH 20.7, m-CH), 8.34 (4H, d, J 7.9, 3 JPbH 106.8, o-CH) 13.37 (PCH2 CH2 CH2 CH3 ), 17.53 (d, 1 JPC 46.7, PCH2 ), 22.78 (d, 2 JPC 4.9, PCH2 CH2 ), 23.58 (PCH2 CH2 CH2 ), 128.38 (p-CH), 128.60 (3 JPbC 104.8, m-CH), 134.04 (2 JPbC 63.5, o-CH), 173.91 (PbC) 34.68 )520 682 m, 735 m, 844 w, 906 m, 992 m, 1017 m, 1095 m, 1231 w, 1313 w, 1380 w, 1414 s, 1436 s, 1472 s, 1566 m, 2871 s, 2931 s, 2956 s, 3045 w
212–214 colourless crystals 16 59.70 (59.43) 4.39 (4.16) 7.26–7.36 (3H, m, Pb p-CH), 7.44 (6H, t, J 7.3, 4 JPbH 21.0, Pb m-CH), 7.67–7.77 (8H, m, P o-CH), 7.77–7.85 (8H, m, P m-CH), 7.92–7.98 (4H, m, P pCH), 8.20 (6H, d, J 7.3, 4 JPbH 60.3, Pb o-CH)
NMRd
C H 1 H
13
C
31
P Pb
207
IRe (m/cm1 )
117.80 (d, 1 JPC 90.7, PC), 128.22 (bs, Pb p-CH), 129.11(t,3 JPbC 55.7, Pb m-CH), 130.56 (d, 3 JPC 13.4, P m-CH), 134.63 (d, 2 JPC 10.6, P o-CH), 135.47 (bs, P p-CH), 136.78 (t, 2 JPbC 44.7, Pb o-CH), 162.09 (PbC) 23.45 (1 JPC 89.3, 2 JPC 11.0) )237 536 s, 689 s, 724 s, 757 m, 857 w, 996 m, 1015 w, 1059 w, 1109 s, 1185 w, 1314 w, 1434 s, 1474 m, 1483 m, 1568 m, 1586 w, 3048 m
a
Isolated yield of pure product based on PbPh2 Cl2 , not optimised. Calculated values in parentheses. c Calculated for [PBun4 ]2 [PbPh2 Cl4 ]. d Chemical shift (d) in ppm, J values in Hz. Recorded in DMSO-d6 . Assignments are based on data published in the literature (for 13 C NMR of phenyl lead complexes, see for example [22], for 13 C NMR of phenylphosphonium salt complexes, see [25], for 1 H NMR data of [PbPh3 Cl2 ][NEt4 ], see [23]) [24]. e Sample in pressed KBr pellet. b
[PPh4 ][PbPh3 Cl2 ] (21) was collected at room temperature. Data for [PBu4 ][SnPh2 Cl3 ] (8) was collected at low temperature on a standard Siemens SMART 2K CCD diffractometer with graphite-monochromated Ag Ka radiation and a crystal-to-detector distance of 3.9 cm.
Crystallographic data for complexes 8, 20, and 21 are summarised in Table 5. Further details, as well as the refinements for all solved structures, with the crystallographic agreement factors, are available in the supplementary material.
Table 5 Crystal and refinement data for [PBun4 ][SnPh2 Cl3 ] (8), [PBun4 ]2 [PbPh2 Cl4 ] THF (20), and [PPh4 ][PbPh3 Cl2 ] (21) with estimated standard deviations in parentheses Compound
8
20
21
Formula Formula weight Crystal system Space group T (K) ) k (A ) a (A ) b (A ) c (A b (°) 3 ) V (A Z l(Mo Ka) (mm1 ) Collected reflections Independent reflections Rint R1 [I > 2rðIÞ] R1 (all data)
C28 H46 Cl3 PSn 638.66 orthorhombic Pna21 150(2) 0.56086 22.1430(4) 11.1633(2) 12.4882(2)
C44 H82 Cl4 P2 Pb C4 H8 O 1094.13 monoclinic P 21 =n 150(2) 0.71073 15.7749(7) 15.6298(7) 23.2054(10) 104.011(1) 5551.3(4) 4 3.320 57355 13672 0.0537 0.0340 0.0667
C42 H35 Cl2 PPb 848.76 orthorhombic Pbca 293(2) 0.71073 17.984(3) 16.658(2) 24.147(3)
3086.95(9) 4 0.608 32141 7426 0.0686 0.0329 0.0482
7234.0(18) 8 4.885 45441 8962 0.0819 0.0339 0.1166
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3. Results and discussion 3.1. Diorganyltrichlorostannates 3.1.1. Crystal structures of tetraorganylphosphonium diaryltrichlorostannates (8, 9, and 16–19) The crystal structures of 8, 9, and 16–19 consist of isolated [PPh4 ]þ or [PBun4 ]þ cations and [SnR0 2 Cl3 ] (R0 ¼ Ph, o-Tol, m-Tol, p-Tol) anions. As a typical example, an ORTEP view of complex 8 is shown in Fig. 1. Selected bond distances and angles are given in Table 6. For the structures reported here, the [SnR0 2 Cl3 ] anion adopts a distorted trigonal bipyramidal geometry about the central metal atom with both aryl groups occupying equatorial positions. As observed for related [SnR0 2 Cl3 ] trigonal bipyramidal species [5,7–10,20], the axial Sn–Cl bond distances in complexes 8, 9, and 16–19 are 0.15– (6.3–8.9%) longer than the equatorial Sn–Cl 0.21 A bond. This finding is consistent with the observation that the difference between axial and equatorial lengths increases markedly upon replacement of one or more of five identical ligands with more electropositive groups in a trigonal bipyramidal coordination [21]. The Sn–C bond lengths in our complexes are similar to those found in other trigonal bipyramidal tin complexes with either alkyl or aryl groups. The C–Sn–C and C–Sn–
Fig. 1. ORTEP plot of complex 8. (Hydrogens have been omitted for clarity.)
Table 6 ) and angles (°) for complex 8 with estimated Selected bond lengths (A standard deviations in parentheses Sn–Cl(1) Sn–Cl(2) Sn–Cl(3) Cl(1)–Sn–Cl(2) Cl(1)–Sn–Cl(3) Cl(2)–Sn–Cl(3) C(23)–Sn–C(17) Cl(1)–Sn–C(17)
2.541(1) 2.523(1) 2.371(1) 175.56(3) 88.24(3) 87.35(3) 122.6(1) 91.30(9)
Sn–C(17) Sn–C(23) Cl(1)–Sn–C(23) Cl(2)–Sn–C(17) Cl(2)–Sn–C(23) Cl(3)–Sn–C(17) Cl(3)–Sn–C(23)
2.152(3) 2.147(3) 91.4(1) 91.3(1) 90.3(1) 118.36(9) 119.08(9)
Clequatorial distortions from ideal trigonal bipyramidal geometry can be attributed to repulsions of the aryl groups in the equatorial plane and between the aryl groups and the equatorial halide, respectively. One notes that the C–Sn–C angles range from 134.7 to 143.5° for the [PPh4 ]þ salts 16–19 and are 122.6° and 135.3°, respectively, for the [PBun4 ]þ salts 8 and 9, while the Cl(3)– Sn–C angles range from 106.7° to 116.6° for the [PPh4 ]þ salts and are 109.3° and 119.1°, respectively, for the [PBun4 ]þ salts. The distortions appear to be dependent on the overall steric bulk of the aryl group, as well as the degree of non-coplanarity of the rings. Unlike the [SnR0 2 Cl3 ] anions in complexes such as [dbttf][SnEt2 Cl3 ] [10] [C9 H8 N][SnMe2 Cl3 ] [5] [Pt(S2 N2 H)(PEt3 )][SnMe2 Cl3 ] [8], and [ttf][SnMe2 Cl3 ] [9] which form loosely associated ), the complexes dimers (Sn Cl interactions of <4 A reported here are monomeric (Sn Cl interactions of ), such as [Et4 N][SnPh2 Cl3 ] [7] and [Me2 SnCl, >5 A terpyridyl][SnMe2 Cl3 ] [20]. 3.1.2. NMR data and structure of the tetraorganylphosphonium dialkyltrichlorostannates (1–7 and 12–15) Although we were unable to obtain X-ray crystal structures for the tin complexes [PR4 ][SnR0 2 Cl3 ] (R ¼ Me 1–3; Bun 4–7; Ph 12–15; R0 ¼ Me, Et, Prn , and Bun ), the analysis of the NMR data yielded distinct information about their structure. Comparing the 13 C chemical shift of CipsoSn (the carbon atom attached to the Sn atom) between the precursors, namely SnPrn2 Cl2 , SnBun2 Cl2 , SnPh2 Cl2 , and Sn(p-Tol)2 Cl2 , and complexes 6–8, 11, 14, and 15, it was found that there is a uniform downfield shift of about 10–11 ppm (Table 7). This can be explained by the transfer of a chlorine anion to the central tin atom, which, in case of the complexes with R0 ¼ aryl, was confirmed by X-ray crystallography. The deshielding effect caused by the additional covalently bound chlorine was found to be only effective for the nearest carbon atom, changes for carbon atoms further
Table 7 Comparison of 13 C chemical shifta of CipsoSn (the carbon atom attached to the tin atom) Compound
d
Ddb
SnPrn2 Cl2 [PBun4 ][SnPrn2 Cl3 ] (6) [PPh4 ][SnPrn2 Cl3 ] (14)
29.03 39.37 39.16
10.34 10.13
SnBun2 Cl2 [PBun4 ][SnBun2 Cl3 ] (7) [PPh4 ][SnBun2 Cl3 ] (15)
26.83 36.92 36.96
10.09 10.13
SnPh2 Cl2 [PBun4 ][SnPh2 Cl3 ] (8)
136.95 148.09
11.14
Sn(p-tol)2 Cl2 [PBun4 ][Sn(p-Tol)2 Cl3 ] (11)
133.47 144.30
10.83
a b
Chemical shift (d) in ppm, spectra in CDCl3 . Difference to the corresponding precursor.
D. Weber et al. / Inorganica Chimica Acta 357 (2004) 125–134
away were marginal. As shown in Table 3, 119 Sn NMR chemical shifts (in CDCl3 ) changed from about +125 ppm for the dialkyltin dichlorides SnR2 Cl2 (R ¼ Et, Prn , and Bun ) to about )100 to )110 ppm for their products, complexes 5–7 and 13–15. A similar change, i.e., about )220 to )230 ppm, is observed when comparing the diaryltin dichlorides SnR2 Cl2 (R ¼ Ph, m-Tol, and pTol) with their products, complexes 8, 10, 11, 18, and 19. On the other hand, changes of the 119 Sn NMR chemical shifts in DMSO-d6 were found to be relatively small (3–56 ppm) for the complexes studied. The reason for this observation most probably lies in the enhanced coordinating and polarising abilities of the solvent DMSO, compared to CDCl3 . The presence of this solvent effect is supported by the observation that increasing alkyl-chain lengths at the Sn atom correlate with an increasing change of the 119 Sn NMR chemical shift. The methyl group in compound 1 showed with Dd ¼ 3 ppm the smallest shielding of the Sn atom, the nbutyl group in compound 15 with Dd ¼ 56 ppm the greatest. 31 P NMR chemical shifts for the phosphonium cations remain almost unchanged by the complex salt formation (Table 3), which is in agreement with previous studies [25]. In summary, 13 C-, and 119 Sn NMR data indicated that the complex salt formation changed the chemical environment of the tin atom for both, compounds with R0 ¼ aryl and R0 ¼ alkyl. These results agree very well with the structural insights obtained from the crystal structures of complexes 8, 9, and 16–19 (Fig. 1, Tables 5 and 6). Based on these data it can be concluded that for complexes 1–7 and 12–15, for which no X-ray analysis was possible, most likely, also a [SnR0 2 Cl3 ] anion with distorted trigonal bipyramidal geometry was formed, as well. 3.2. Phenylchloroplumbates 3.2.1. Synthesis Compound 20, [PBun4 ]2 [PbPh2 Cl4 ], was formed by the same reaction seen for the tetraorganylphosphonium dialkyltrichlorostannates 1–19, in which the chloride ion formed a bond with the metal. In case of the tin complexes, one chloride was transferred, whereas for 20, two chlorides reacted with the metal (Fig. 2, Table 5). Given the high yield of 20, the two-chloride transfer was the preferred reaction of PbCl2 Ph2 with [PBun4 ]þ Cl . Considering the fact that the reaction conditions for this reaction, heating a neat mixture to 180 °C, and for the formation of many [SnCl3 R2 ] tin complexes are practically identical, it can be concluded that steric factors play an important role. As pointed out in the experimental section, the mixture of [PPh4 ]þ Cl and Ph2 PbCl2 had to be heated to
131
Fig. 2. ORTEP plot of complex 20. (Hydrogens and the THF molecule have been omitted for clarity.)
Fig. 3. ORTEP plot of complex 21. (Hydrogens have been omitted for clarity.)
260 °C for a short time in order to obtain a homogeneous melt. Prolonged heating at this temperature resulted in significant decomposition (i.e., gas development and the formation of some colourless, insoluble solid). The isolated product, [PPh4 ][PbPh3 Cl2 ] (21), did not result from a chloride transfer to the metal (Fig. 3, Table 5). Surprisingly, a phenyl transfer occurred instead. Tetraphenylphosphonium ions are stable even at relatively high temperatures. 5 Phenyl lead compounds, on the other hand, are known to undergo disproportionation reactions and phenyl transfers [15,26]. Based 5 The melting points of [PPh4 ]þ Cl and [PPh4 ]þ Br are 273–275 °C and 295–298 °C, respectively.
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on these facts, it is conceivable that 21 was formed from Ph2 PbCl2 in a phenyl transfer reaction. The relatively low yield and the observed partial decomposition at the high reaction temperature are consistent with the formation of a significant amount of by-products. 6 3.2.2. 207 Pb NMR spectroscopy The 207 Pb NMR shift of [PBun4 ]2þ [PbCl4 Ph2 ]2 (20) was determined as d ¼ 520 ( 5) ppm; the shift of [PPh4 ]þ [PbCl2 Ph3 ] (21) was observed at d ¼ 237 (5) ppm. Given the fact that the 207 Pb NMR shift values reflect the electron density at the metal [24] they indicate moderate shielding of the metal nucleus. The shift values fall in the range between those reported for PbPh4 (d 175 ppm) and for PbCl4 (d ¼ 768 ppm). 7 In fact, the shift of complex 20 is very close to the one of the hexacoordinated metal in anhydrous PbPh2 (OAc)2 (d ¼ 587 ppm) [27]. However, the dependence of the 207 Pb NMR shift on temperature, interaction with the solvent, and, to a lesser extend, concentration makes the direct comparison of the shift values difficult. 3.2.3. Crystal structures The tetraalkyl ammonium salts of [PbCl4 Ph2 ]2 and [PbCl2 Ph3 ] have been studied previously by means of IR- and Raman spectroscopy [28]. Based on these results, essentially isolated anions had been predicted, but there remained uncertainty about the precise structure and possible weak interactions between the anions. Fig. 2 depicts an ORTEP plot of 20. Selected bond distances and angles are given in Table 8. In the crystal, the [PbPh2 Cl4 ]2 anion assumes a lightly distorted octahedral geometry. The phenyl groups occupy trans positions. Compound 20 consists of isolated cations and anions. Based on the large distance of 6.890 A (Cl1 Cl3) between neighbouring anions, the formation of Pb–Cl chains can be ruled out. The dihedral angle between the planes of the phenyl groups is 85.4°. The crystal used for X-ray crystallographic studies was obtained from a THF solution by slow evaporation of the solvent. This crystal contains a THF molecule in the lattice. Compound 21 consists of isolated cations and anions, between two with a closest Pb Cl distance of 7.698 A anions. The anions do not form chains. Their geometry is trigonal bipyramidal with the chlorine atoms occupying the axial positions. An ORTEP view of 21 is shown in Fig. 3, selected bond distances and angles are listed in Table 9. The Pb–Cl distances in 20 and 21 are essentially identical, while the Pb–C distances in 20 are about 1% longer than those in 21. 6
These by-products were not analysed further. The exact values depend on solvent and concentration. For PbPh4 shift values of d ¼ 166 to )183 ppm have been reported. See [16]. 7
Table 8 ) and angles (°) for complex 20 with estimated Selected bond lengths (A standard deviations in parentheses Pb–Cl(1) Pb–Cl(2) Pb–Cl(3) Pb–Cl(4) Cl(1)–Pb–Cl(2) Cl(1)–Pb–Cl(3) Cl(1)–Pb–Cl(4) Cl(1)–Pb–C(33) Cl(1)–Pb–C(39) Cl(2)–Pb–Cl(3) Cl(2)–Pb–Cl(4) Cl(2)–Pb–C(33) Cl(2)–Pb–C(39)
2.7140(9) 2.6968(9) 2.7392(9) 2.7386(9) 90.99(3) 90.88(3) 179.00(3) 90.75(10) 90.96(9) 178.00(3) 88.01(3) 90.57(9) 91.43(9)
Pb–C(33) Pb–C(39)
Cl(3)–Pb–Cl(4) Cl(3)–Pb–C(33) Cl(3)–Pb–C(39) Cl(4)–Pb–C(33) Cl(4)–Pb–C(39) C(33)–Pb–C(39)
2.180(4) 2.179(9)
90.12(3) 88.68(10) 89.26(9) 89.16(10) 89.17(9) 177.35(13)
Table 9 ) and angles (°) for complex 21 with estimated Selected bond lengths (A standard deviations in parentheses Pb–Cl(1) Pb–Cl(2) Cl(1)–Pb–Cl(2) Cl(1)–Pb–C(25) Cl(1)–Pb–C(31) Cl(1)–Pb–C(37) Cl(2)–Pb–C(25) Cl(2)–Pb–C(31) Cl(2)–Pb–C(37)
2.7273(12) 2.7277(11) 177.70(4) 87.72(12) 88.86(12) 91.17(14) 90.74(12) 90.50(12) 91.01(13)
Pb–C(25) Pb–C(31) Pb–C(37) C(25)–Pb–C(31) C(25)–Pb–C(37) C(31)–Pb–C(37)
2.213(4) 2.221(4) 2.218(4) 121.84(15) 113.71(17) 124.39(15)
3.2.4. Mass spectroscopic studies In the case of the lead complexes 20 and 21 we were able to obtain mass spectra with a good S/N ratio and an excellent correspondence of observed to calculated isotope distribution. The mass spectrum for [PBun4 ]2þ [PbCl4 Ph2 ]2 (20) showed strong signals around m/z ¼ 1282. They are attributed to the cationic complex [PBun4 ]3þ [PbCl4 Ph2 ]2 (calc. m/z ¼ 1281.53) (Fig. 4). Other prominent signals in the MALDI-MS could be attributed to [PBun4 ]þ (m/ z ¼ 259); 2[PBun4 ]þ Cl (m/z ¼ 553); 3[PBun4 ]þ 2Cl (m/ z ¼ 847); 4[PBun4 ]þ [PbCl4 Ph2 ]2 Cl (m/z ¼ 1576). Anion and cation of [PPh4 ]þ [PbCl2 Ph3 ] (21) were observed separately. The [PPh4 ]þ ion was detected in ‘‘positive ionisation mode’’: m/z ¼ 339.1323 (C24 H20 P; deviation: 7.7 ppm). The [PbCl2 Ph3 ] ion was detected in ‘‘negative ionisation mode’’: m/z ¼ 509.0340 (C18 H15 Cl2 Pb; deviation: 4.5 ppm).
4. Summary The extension of a synthetic approach leading to novel complexes incorporating distorted trigonal bipyramidal [SnR0 2 Cl3 ] anions with both aryl groups in the equatorial position to include phenylchloroplumbates
D. Weber et al. / Inorganica Chimica Acta 357 (2004) 125–134
133
Fig. 4. Mass spectrum of 3[PBun4 ]þ [PbCl4 Ph2 ]2 . Insert: Calculated distribution.
unexpectedly yielded two complexes, [PBun4 ]2 [PbPh2 Cl4 ] (20) and [PPh4 ][PbPh3 Cl2 ] (21) with different geometry. In case of the reaction between [PBun4 ]þ Cl and PbCl2 Ph2 , a two chloride transfer was the favoured reaction, leading to the distorted octahedral [PbPh2 Cl4 ]2 anion. However when [PPh4 ]þ Cl was reacted with PbCl2 Ph2 at a higher temperature, a trigonal bipyramidal [PbCl2 Ph3 ] anion was formed.
Academic Exchange Service (DAAD) for financial support. SMART 1K CCD data were collected through the Ohio Crystallographic Consortium, funded by the Ohio Board of Regents 1995 Investment Fund (CAP-075), located at the University of Toledo, Instrumentation Center in A & S, Toledo, OH 43606. J.A. Krause-Bauer thanks Dr. A. Pinkerton (Department of Chemistry, University of Toledo) for use of his SMART 2K CCD diffractometer.
5. Supplementary material Cristallographic data for structural analysis of compounds 8, 9, and 16–19 have been deposited with the Cambridge Crystallographic Data Centre, CCDC (Nos. 183894–183901). These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44-1223-336033; e-mail: deposit@ccdc. cam.ac.uk). Further experimental details, 1 H and 13 C NMR spectroscopic data for complexes 1–19, IR spectroscopic data for complexes 8–11 and 16–19, and further HR-MS data of complexes 20 and 21 are available as supplementary material.
Acknowledgements We thank Dr. E. Brooks, Dr. G.P. Kreishman, Dr. K. Jayasimhulu (Department of Chemistry, University of Cincinnati) and Dr. M.-R. Dominic (Morton International Inc.) for their excellent technical assistance. D. Weber. and A. Eisengr€ aber-Pabst. thank the German
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[17] G. Neue, C. Dybovski, M.L. Smith, M.A. Hepp, D.L. Perry, Solid State Nucl. Mag. Res. 6 (3) (1996) 241. [18] E.S. Claudio, M.A. ter Horst, C.E. Forde, C.L. Stern, M.K. Zart, H.A. Godwin, Inorg. Chem. 39 (7) (2000) 1391. [19] An absorption correction based on measured psi scans was used for the P3 data A.C.T. North, D.C. Phillips, F.S. Matthews, Acta Cryst. A 24 (1968) 351. [20] F.W.B. Einstein, B.R. Penfold, J. Chem. Soc. A (1968) 3019. [21] E.L. Muetterties, R.A. Schunn, Quart. Rev. 20 (1966) 245. [22] (a) U. Edlund, T. Lejon, P. Pyykk€ o, T.K. Venkatachalam, E. Buncel, J. Am. Chem. Soc. 109 (1987) 5982; (b) E. Breitmaier, W. Voelter, in: H.F. Ebel (Ed.), Carbon-13 NMR Spectroscopy, third ed., VCH Verlagsgesellschaft, Weinheim, 1989, p. 297; (c) T.N. Mitchell, J. Gmehlin, F. Huber, J. Chem. Soc. Dalton (1978) 960. [23] A.C. Sau, R.R. Holmes, J. Organomet. Chem. 217 (1981) 157. [24] F. Huber, H. Preut, D. Scholz, M. Sch€ urmann, J. Organomet. Chem. 441 (1992) 227. [25] (a) R.M. Farmer, Y. Sasaki, A.I. Popov, Aust. J. Chem. 36 (1983) 1785; (b) B.V. Timokhin, V.K. Dimitriev, V.I. Dimitriev, B.I. Istomin, V.I. Donskikh, J. Gen. Chem. USSR (Engl. Transl.) 51 (1981) 1711. [26] M.E. Cucciolito, A. Derenzi, F. Giordano, F. Ruffo, Organometallics 14 (11) (1995) 5410. [27] M. Sch€ urmann, F. Huber, J. Organomet. Chem. 530 (1997) 121. [28] I. Wharf, R. Cuenca, E. Besso, M. Onyszchuk, J. Organomet. Chem. 277 (1984) 245.
Unexpected differences in reactivity between tin and lead organyl chlorides – crystal structures of their organylphosphonium salts q Dirk Weber a
a,*
, Sven H. Hausner b,1, Axel Eisengr€ aber-Pabst c, Sanghee Yun b, Jeanette A. Krause-Bauer b, Hans Zimmer b,2
Institut f€ ur Organische Chemie und Biochemie, Technische Universit€at M€unchen, Lichtenbergstr. 4, Garching 85747, Germany b Department of Chemistry, University of Cincinnati, ML 0172, Cincinnati, OH 45221-0172, USA c Fakult€at Chemie, Universit€at Stuttgart, Pfaffenwaldring 55, Stuttgart D-70569, Germany Received 14 May 2003; accepted 24 May 2003
Abstract Pentacoordinated tin is known since the late 1950s but little is known about the ability of lead to form similar structures. Originally we investigated the reaction between a number of tetraorganylphosphonium chlorides [PR4 ]þ Cl (R ¼ Me, Bun , and Ph) and several diorganyltin dichlorides SnR0 2 Cl2 (R0 ¼ Me, Et, Prn , Bun , Ph, o-, m-, p-Tol) between 100 and 240 °C. Novel pentacoordinated tin complexes, tetraorganylphosphonium diorganyltrichlorostannates [PR4 ][SnR0 2 Cl3 ] (1–19), were formed in good to excellent yields. In a second step, this synthetic approach was extended to include the reaction of diphenyllead dichloride Ph2 PbCl2 with [PR4 ]þ Cl (R ¼ Bun , Ph). Surprisingly, a two chloride transfer was observed to form the hexacoordinated lead species [PBun4 ]2 [PbPh2 Cl4 ] (20). Under similar conditions, the pentacoordinated [PPh4 ][PbPh3 Cl2 ] (21) was obtained by a phenyl transfer. Complexes 20 and 21 were characterised by NMR (1 H, 13 C, 31 P, and 207 Pb), IR, MS, and X-ray crystallography. The anion of 20 assumes a lightly distorted octahedral geometry with the phenyl substituents in trans-positions. In the anion of 21 the phenyl substituents occupy the equatorial positions of a lightly distorted trigonal bipyramid. A thorough spectroscopical investigation of the tin complexes 1–19, including X-ray structural studies, which were possible for complexes with R0 ¼ aryl, revealed that these complexes are monomeric with a distorted trigonal bipyramidal [SnR0 2 Cl3 ] anion. Both aryl groups occupy equatorial positions. Ó 2003 Elsevier B.V. All rights reserved. Keywords: Pentacoordinated tin; Hexacoordinated lead; Pentacoordinated lead; Phenyl transfer
1. Introduction Structures of pentacoordinated organotin compounds are known since the late 1950s [1,2]. Since then, numerous structural investigations on monomeric, dimeric, oligoor even polymeric pentacoordinate tin species employing such different techniques as X-ray diffraction, M€ ossbauer q Supplementary data associated with this article can be found, in the online version, at doi:10.1016/S0020-1693(03)00365-7. * Corresponding author. Tel.: +49-89-36037682; fax: +49-75318493514. E-mail address: [email protected] (D. Weber). 1 Present address: School of Medicine, Yale University, VA Medical Center/116A2, 950 Campbell Ave, West Haven, CT 06516, USA. 2 Deceased.
0020-1693/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0020-1693(03)00365-7
spectroscopy, conductivity measurements, IR and solidstate NMR spectroscopy have been reported (for a review see for example [3]). Besides their importance for stereochemical models and for the determination of cation–anion interactions, these studies may be useful for the understanding of the intermediate state of nucleophilic substitution reactions such as the Stille coupling during which the tin atom has been proposed to be pentacoordinated [4]. Although organotin has been studied extensively, there is a striking lack of data in the literature concerning organolead compounds. Little is known about the behaviour of lead in comparable reactions to tin or the ability to form similar structures. Despite their toxicity handicap, organolead compounds may have a greater potential for
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organic synthesis than currently recognised. One important step towards tailored applications is to elaborate the general differences concerning structure and reactivity in comparison to tin. Therefore our effort was directed towards a comparison of the behaviour of these two metals in a relatively simple reaction setup. In this paper we describe the discovery of interesting differences concerning the reactivity of these two metals. Our interest in organotin, as well as organophosphonium chemistry, originally led us to investigate the reaction between tetraorganylphosphonium chlorides and dialkyltin dichlorides. In contrast to other experimental conditions described for the reaction between diorganyltin dichlorides and various salts [5–10] we simply combined the dialkyltin dichloride with an equimolar amount of the appropriate tetraorganylphosphonium chloride without employing any solvent [11]. Initially, we prepared the alkyl complexes [PR4 ][SnR0 2 Cl3 ] (1)–(7) and (12)–(15) (R0 ¼ Me, Et, Prn , Bun ) [12]. For the complexes obtained we tentatively proposed, based on NMR studies, a trigonal bipyramidal structure [SnR0 2 Cl3 ] . We rationalised that, by further limiting the degree of flexibility of the R0 residues, we would obtain more crystalline structures, suitable for X-ray crystal analysis. It has been proposed that, for complexes [SnR02 Cl3 ] , the stability decreases in the order R0 ¼ Ph > Me > Et > Pr because of the decreasing electronegative character of these groups [6]. Based on this information, and because of the easy synthetic access, we decided to prepare the corresponding complexes with R0 ¼ aryl [13]. As a part of our work on pentacoordinated tin anions bearing a tetraorganylphosphonium counterion, we here present the crystal structures of [PBun4 ][SnPh2 Cl3 ] (8), [PBun4 ][Sn(o-Tol)2 Cl3 ] (9), [PPh4 ][SnPh2 Cl3 ] (16), [PPh4 ][Sn(o-Tol)2 Cl3 ] (17), [PPh4 ] [Sn(m-Tol)2 Cl3 ] (18), and [PPh4 ][Sn(p-Tol)2 Cl3 ] (19). The geometry and coordination of complexes 8, 9, and 16–19 are discussed. On the basis of a detailed characterisation by means of 1 H-, 13 C-, 31 P-, and 119 SnNMR spectroscopy their structures are compared with those of complexes 1–7 and 12–15. Furthermore, the extension of this synthetic approach to include the reaction of diphenyllead dichloride Ph2 PbCl2 with [PR4 ]þ Cl (R ¼ Bun , Ph) is presented [14]. Unexpectedly, the formation of complexes [PBun4 ]2 [PbPh2 Cl4 ] (20) and [PPh4 ][PbPh3 Cl2 ] (21) was observed. Their structures and structural differences to the aforementioned tin complexes, obtained from the corresponding reactions, will be discussed based on spectroscopic and crystallographic data.
tyl)phosphonium chloride was obtained from Fluka (Buchs, Switzerland). Diphenyllead dichloride and all diorganyltin dichlorides, except dimethyltin dichloride, were prepared in two steps by published methods [15]. Dimethyltin dichloride was provided by Morton International Incorporation (Cincinnati, OH). Reactions were carried out under an inert gas atmosphere (N2 or Ar). 207 Pb NMR spectra were recorded on a Bruker AC 250 spectrometer. The broad range of 207 Pb NMR shifts of about 16,000 ppm required acquisition at various frequencies [16–18]. The maximum shift-window size on the spectrometer used was 100,000 Hz (equivalent to about 1900 ppm). The signals of the lead complexes 20 and 21 were recorded in windows centred at 52.330, 52.320, and 52.280 MHz. Each signals was confirmed at the three different frequencies to insure that the signal seen is a real peak and not a ‘‘fold over’’ signal. 3 Further details, as well as NMR and IR experimental details are summarised in the supplementary material. 2.2. Preparations 2.2.1. Tetraorganylphosphonium diorganyltrichlorostannates [PR4 ][SnR0 2 Cl3 ] (1–19). General procedure Equimolar amounts, ranging between 0.8 and 2 mmol, of tetraorganylphosphonium chloride and the corresponding diorganyltin dichloride were heated until a homogeneous liquid was obtained (Table 1). The crude product (except for complexes 10 and 11) was recrystallised (Table 1). For complexes 8, 9, and 16–19 the slightly cloudy solution was pressed through a syringe microfilter. Slow evaporation of the solvent at room temperature yielded crystals suitable for X-ray analysis. Analytical and physical data are listed in Tables 2 and 3. 2.2.2. Di[tetra(n-butyl)phosphonium] diphenyltetrachloroplumbate [PBun4 ]2 [PbPh2 Cl4 ] (20) Diphenyllead dichloride (865 mg, 2.00 mmol) and tetra(n-butyl)phosphonium chloride (590 mg, 2.00 mmol) were heated to 180 °C for 1 h. The melt was cooled to room temperature, dissolved in hot ethanol, and filtered cold (syringe microfilter). Removal of the solvent in a rotary evaporator yielded brownish, waxy crystals. More impurities were removed with three times 50 ml of refluxing ether. A colourless, crystalline product (810 mg, 0.80 mmol, 80% o. Th.) was obtained after recrystallising twice from a small amount of THF
2. Experimental 2.1. Materials Unless stated otherwise, all chemicals were purchased from Aldrich Chemical (Milwaukee, WI). Tetra(n-bu-
3 The standard frequency for 207 Pb NMR spectra is the exact frequency determined for Pb(CH3 )4 (d 0 ppm). Pb(CH3 )4 has historically been used as a standard, but nowadays is avoided because of its toxicity and volatility. The standard frequency is defined as ‘‘20,920,597/100,000,000 times the frequency of SiMe4 ’’ [16,17]. For the 250.133000 MHz instrument used, it is 52.329317 MHz.
D. Weber et al. / Inorganica Chimica Acta 357 (2004) 125–134
127
Table 1 Reaction conditions for complexes 1–19 Complex
T (°C)
t (min)
Recrystallisation solvent
[PMe4 ][SnMe2 Cl3 ] (1) [PMe4 ][SnEt2 Cl3 ] (2) [PMe4 ][SnPrn2 Cl3 ] (3) [PBun4 ][SnMe2 Cl3 ] (4) [PBun4 ][SnEt2 Cl3 ] (5) [PBun4 ][SnPrn2 Cl3 ] (6) [PBun4 ][SnBun2 Cl3 ] (7) [PBun4 ][SnPh2 Cl3 ] (8) [PBun4 ][Sn(o-Tol)2 Cl3 ] (9) [PBun4 ][Sn(m-Tol)2 Cl3 ] (10) [PBun4 ][Sn(p-Tol)2 Cl3 ] (11) [PPh4 ][SnMe2 Cl3 ] (12) [PPh4 ][SnEt2 Cl3 ] (13) [PPh4 ][SnPrn2 Cl3 ] (14) [PPh4 ][SnBun2 Cl3 ] (15) [PPh4 ][SnPh2 Cl3 ] (16) [PPh4 ][Sn(o-Tol)2 Cl3 ] (17) [PPh4 ][Sn(m-Tol)2 Cl3 ] (18) [PPh4 ][Sn(p-Tol)2 Cl3 ] (19)
200 200 180 110 100 100 100 120 120 140 130 200 200 200 200 230 230 220 220
240 180 120 60 60 120 120 60 60 60 60 180 180 240 240 30 30 30 30
EtOH EtOH EtOH Et2 O Et2 O:EtOH ¼ 7:1 Et2 O Et2 O:EtOH ¼ 19:1 Et2 O:acetone:CH3 CN ¼ 45:2:few drops Et2 O:EtOH ¼ 1:1
a
a a
EtOH EtOH EtOH EtOH EtOH EtOH EtOH EtOH
Oil. Compound did not crystallise.
(Table 4). Crystals suitable for X-ray crystallography were obtained by slow evaporation of the THF at room temperature. 2.2.3. Tetraphenylphosphonium triphenyldichloroplumbate [PPh4 ][PbPh3 Cl2 ] (21) Diphenyllead dichloride (2.50 g, 5.78 mmol) and 2.17 g (5.78 mmol) tetraphenylphosphonium chloride were
combined in a 100 ml round bottom flask and placed onto a preheated oilbath (260–265 °C). The mixture was stirred until a thin melt was obtained and kept at this temperature for one additional minute. The mixture was removed from the oilbath and cooled to below 200 °C. The bath was allowed to cool, and the mixture was stirred for an additional one half hour at 205–215 °C. The mixture solidified readily upon cooling to room
Table 2 Analytical and physical data for tetraorganylphosphonium diorganyltrichlorostannates Complex
Mp (°C)
Appearance
Yieldb (%)
Analysis (%)e C
[PMe4 ][SnMe2 Cl3 ] (1) [PMe4 ][SnEt2 Cl3 ] (2) [PMe4 ][SnPrn2 Cl3 ] (3) [PBun4 ][SnMe2 Cl3 ] (4) [PBun4 ][SnEt2 Cl3 ] (5) [PBun4 ][SnPrn2 Cl3 ] (6) [PBun4 ][SnBun2 Cl3 ] (7) [PBun4 ][SnPh2 Cl3 ] (8) [PBun4 ][Sn(o-Tol)2 Cl3 ] (9) [PBun4 ][Sn(m-Tol)2 Cl3 ] (10) [PBun4 ][Sn(p-Tol)2 Cl3 ] (11) [PPh4 ][SnMe2 Cl3 ] (12) [PPh4 ][SnEt2 Cl3 ] (13) [PPh4 ][SnPrn2 Cl3 ] (14) [PPh4 ][SnBun2 Cl3 ] (15) [PPh4 ][SnPh2 Cl3 ] (16) [PPh4 ][Sn(o-Tol)2 Cl3 ] (17) [PPh4 ][Sn(m-Tol)2 Cl3 ] (18) [PPh4 ][Sn(p-Tol)2 Cl3 ] (19) a
a
>300 >280a 260a 92–93 80–81 92–93 79–81 64–66 95–96
197–198 177–178 130–131 109–110 230–233 230 149–150 153–154
Decomposition. Based on tin. c Yield not optimised. d Compound could not be recrystallised. e Calculated values in parentheses. f Not determined. b
colourless powder colourless powder colourless powder colourless plates colourless plates colourless plates colourless plates colourless crystals colourless crystals colourless oil colourless oil colourless powder colourless powder colourless powder colourless powder colourless crystals brownish crystals brownish crystals brownish crystals
66 72 88 82 81 96 91 92 24c quant.d quant.d 83 83 90 92 34c 57c 70c 31c
21.02 25.45 30.03 42.20 44.09 46.49 48.33 53.00 54.32 54.20 53.89 52.30 53.93 54.95 56.69 59.94 61.25 60.91 61.23
H (20.81) (25.67) (29.85) (42.02) (44.27) (46.30) (48.15) (52.66) (54.05) (54.05) (54.05) (52.53) (54.02) (55.38) (56.63) (60.17) (61.13) (61.13) (61.13)
5.32 5.67 6.39 8.19 8.35 8.61 8.97 7.15 7.70 7.55 7.38 4.39 4.98 5.24 5.58 4.19 4.61 4.36 4.40
Cl (5.24) (5.92) (6.51) (8.23) (8.55) (8.83) (9.09) (7.25) (7.55) (7.55) (7.55) (4.41) (4.86) (5.27) (5.64) (4.20) (4.59) (4.59) (4.59)
30.53 28.06 26.27 20.81 19.46 18.46 17.50
(30.72) (28.42) (26.43) (20.67) (19.60) (18.64) (17.76)
f f f f
17.76 17.23 15.89 15.80 f f f f
(17.89) (17.08) (16.35) (15.67)
128 Table 3 31 P- and
D. Weber et al. / Inorganica Chimica Acta 357 (2004) 125–134
119
Sn NMR data for tetraorganylphosphonium diorganyl-trichlorostannates (complexes 1–19) and some starting materialsa
Compound
31
Pb
119
Sn
DMSO-d6 SnMe2 Cl2 SnEt2 Cl2 SnPrn Cl2 SnBun Cl2 SnPh2 Cl2 Sn(m-Tol)2 Cl2 Sn(p-Tol)2 Cl2 [PBun4 ]Cl [PPh4 ]Cl [PMe4 ][SnMe2 Cl3 ] (1) [PMe4 ][SnEt2 Cl3 ] (2) [PMe4 ][SnPrn2 Cl3 ] (3) [PBun4 ][SnMe2 Cl3 ] (4) [PBun4 ][SnEt2 Cl3 ] (5) [PBun4 ][SnPrn2 Cl3 ] (6) [PBun4 ][SnBun2 Cl3 ] (7) [PBun4 ][SnPh2 Cl3 ] (8) [PBun4 ][Sn(o-Tol)2 Cl3 ] (9) [PBun4 ][Sn(m-Tol)2 Cl3 ] (10) [PBun4 ][Sn(p-Tol)2 Cl3 ] (11) [PPh4 ][SnMe2 Cl3 ] (12) [PPh4 ][SnEt2 Cl3 ] (13) [PPh4 ][SnPrn2 Cl3 ] (14) [PPh4 ][SnBun2 Cl3 ] (15) [PPh4 ][SnPh2 Cl3 ] (16) [PPh4 ][Sn(o-Tol)2 Cl3 ] (17) [PPh4 ][Sn(m-Tol)2 Cl3 ] (18) [PPh4 ][Sn(p-Tol)2 Cl3 ] (19)
CDCl3
)249.9 )225.7 )218.3 )211.6
141.5 128.3 126.3 126.5 )27.2 )25.4 )21.7
)246.7 )226.4 )206.4
d;e
d
33.7 23.6 26.16c 26.53c 24.17 33.54 33.54 33.54 33.49 34.91c 34.90c 34.86c 34.89c 23.80 23.81 23.81 23.81 23.46c 23.51c 23.46c 23.45c
d;e d;e
)98.7 )96.1 )106.2 )99.6 )248.2 )238.4 )247.3 )238.9
)387.7 )270.6 )384.6 )375.2 )243.4 )221.4 )195.9 )193.8 )387.2 )276.0 )381.0 )375.3
MeOH-d3
)92.9 )98.9 )58.7
d;e
)103.3 )112.0 )114.0 d;e d;e
)249.7d )240.5d
a
Chemical shift (d) in ppm. Spectra in CDCl3 unless otherwise stated. c Spectrum in DMSO-d6 . d Low solubility. e Unable to determine. b
temperature. It was extracted with 125 ml hot ethanol in several portions, followed by filtration (syringe microfilter). Removal of the solvent in a rotary evaporator yielded a partially viscous, light-brownish solid. It solidified upon addition of 150 ml water. The mixture was briefly treated with ultrasound, and the solid was allowed to settle overnight. The liquid was removed, and the treatment was repeated with another 150 ml water. The lightly cream coloured solid was dried under reduced pressure. It was taken up in 150 ml THF, briefly heated to reflux, ultrasonicated, and filtered warm (syringe microfilter). The solvent was removed in a rotary evaporator. Remaining impurities in the resulting resin were extracted with three times 1–5 ml refluxing THF. After drying, 0.78 g (0.919 mmol, 16% o. Th.) colourless, fine crystals were obtained (Table 4). Crystals suitable for X-ray crystallography were obtained by slow evaporation of the THF at room temperature. 2.3. X-Ray crystallographic analysis For X-ray examination and data collection, suitable crystals were coated with a light film of epoxy resin or
paratone-N and mounted on glass fibers. Data for [PPh4 ][SnPh2 Cl3 ] (16) and [PPh4 ][Sn(p-Tol)2 Cl3 ] (19) were collected at room temperature on a Siemens P3 diffractometer 4 with graphite-monochromated Mo Ka radiation. Lattice parameters were obtained from the angular settings from 40 reflections lying in a 2h range of 10–30°. Intensity data were collected using variable speed h 2h scans out to 55° in 2h. All data were corrected for decay (based on three standard reflections), Lorentz and polarisation effects as well as for absorption (based on measured w scans) [19]. Data for [PBu4 ][Sn(o-Tol)2 Cl3 ] (9), [PPh4 ][Sn(oTol)2 Cl3 ] (17), [PPh4 ][Sn(m-Tol)2 Cl3 ] (18), and [PBu4 ]2 [PbPh2 Cl4 ] (20) were collected at low temperature on a standard Siemens SMART 1K CCD diffractometer 4 with graphite-monochromated Mo Ka radiation and a detector distance of 5.0 cm. Data for 4
For the CCD diffractometer, SMART v4.05, v5.054 or v5.622 and SAINT v4.05, v5.A06 or v6.02A programs were used for data collection and processing, respectively. The P 3=P 4-PC Diffractometer Program v4.27 was used for data collection and reduction on the P 3 diffractometer. Siemens Analytical X-ray Instruments, Madison, WI.
D. Weber et al. / Inorganica Chimica Acta 357 (2004) 125–134
129
Table 4 Analytical and physical data for tetraorganylphosphonium organylchloroplumbates Complex
[PBun4 ]2 [PbPh2 Cl4 ] (20)
[PPh4 ][PbPh3 Cl2 ] (21)
Mp (°C) Appearance Yielda (%) Analysisb (%)
166–168 colourless plates 80 51.74 (51.71)c 8.14 (8.09)c 0.90 (24H, t, J 6.9, PCH2 CH2 CH2 CH3 ), 1.30–1.50 (32H, m, PCH2 CH2 CH2 CH3 ), 2.10–2.30 (16H, m, PCH2 ), 7.31 (2H, t, J 7.0, p-CH), 7.46 (4H, t, J 7.4, 4 JPbH 20.7, m-CH), 8.34 (4H, d, J 7.9, 3 JPbH 106.8, o-CH) 13.37 (PCH2 CH2 CH2 CH3 ), 17.53 (d, 1 JPC 46.7, PCH2 ), 22.78 (d, 2 JPC 4.9, PCH2 CH2 ), 23.58 (PCH2 CH2 CH2 ), 128.38 (p-CH), 128.60 (3 JPbC 104.8, m-CH), 134.04 (2 JPbC 63.5, o-CH), 173.91 (PbC) 34.68 )520 682 m, 735 m, 844 w, 906 m, 992 m, 1017 m, 1095 m, 1231 w, 1313 w, 1380 w, 1414 s, 1436 s, 1472 s, 1566 m, 2871 s, 2931 s, 2956 s, 3045 w
212–214 colourless crystals 16 59.70 (59.43) 4.39 (4.16) 7.26–7.36 (3H, m, Pb p-CH), 7.44 (6H, t, J 7.3, 4 JPbH 21.0, Pb m-CH), 7.67–7.77 (8H, m, P o-CH), 7.77–7.85 (8H, m, P m-CH), 7.92–7.98 (4H, m, P pCH), 8.20 (6H, d, J 7.3, 4 JPbH 60.3, Pb o-CH)
NMRd
C H 1 H
13
C
31
P Pb
207
IRe (m/cm1 )
117.80 (d, 1 JPC 90.7, PC), 128.22 (bs, Pb p-CH), 129.11(t,3 JPbC 55.7, Pb m-CH), 130.56 (d, 3 JPC 13.4, P m-CH), 134.63 (d, 2 JPC 10.6, P o-CH), 135.47 (bs, P p-CH), 136.78 (t, 2 JPbC 44.7, Pb o-CH), 162.09 (PbC) 23.45 (1 JPC 89.3, 2 JPC 11.0) )237 536 s, 689 s, 724 s, 757 m, 857 w, 996 m, 1015 w, 1059 w, 1109 s, 1185 w, 1314 w, 1434 s, 1474 m, 1483 m, 1568 m, 1586 w, 3048 m
a
Isolated yield of pure product based on PbPh2 Cl2 , not optimised. Calculated values in parentheses. c Calculated for [PBun4 ]2 [PbPh2 Cl4 ]. d Chemical shift (d) in ppm, J values in Hz. Recorded in DMSO-d6 . Assignments are based on data published in the literature (for 13 C NMR of phenyl lead complexes, see for example [22], for 13 C NMR of phenylphosphonium salt complexes, see [25], for 1 H NMR data of [PbPh3 Cl2 ][NEt4 ], see [23]) [24]. e Sample in pressed KBr pellet. b
[PPh4 ][PbPh3 Cl2 ] (21) was collected at room temperature. Data for [PBu4 ][SnPh2 Cl3 ] (8) was collected at low temperature on a standard Siemens SMART 2K CCD diffractometer with graphite-monochromated Ag Ka radiation and a crystal-to-detector distance of 3.9 cm.
Crystallographic data for complexes 8, 20, and 21 are summarised in Table 5. Further details, as well as the refinements for all solved structures, with the crystallographic agreement factors, are available in the supplementary material.
Table 5 Crystal and refinement data for [PBun4 ][SnPh2 Cl3 ] (8), [PBun4 ]2 [PbPh2 Cl4 ] THF (20), and [PPh4 ][PbPh3 Cl2 ] (21) with estimated standard deviations in parentheses Compound
8
20
21
Formula Formula weight Crystal system Space group T (K) ) k (A ) a (A ) b (A ) c (A b (°) 3 ) V (A Z l(Mo Ka) (mm1 ) Collected reflections Independent reflections Rint R1 [I > 2rðIÞ] R1 (all data)
C28 H46 Cl3 PSn 638.66 orthorhombic Pna21 150(2) 0.56086 22.1430(4) 11.1633(2) 12.4882(2)
C44 H82 Cl4 P2 Pb C4 H8 O 1094.13 monoclinic P 21 =n 150(2) 0.71073 15.7749(7) 15.6298(7) 23.2054(10) 104.011(1) 5551.3(4) 4 3.320 57355 13672 0.0537 0.0340 0.0667
C42 H35 Cl2 PPb 848.76 orthorhombic Pbca 293(2) 0.71073 17.984(3) 16.658(2) 24.147(3)
3086.95(9) 4 0.608 32141 7426 0.0686 0.0329 0.0482
7234.0(18) 8 4.885 45441 8962 0.0819 0.0339 0.1166
130
D. Weber et al. / Inorganica Chimica Acta 357 (2004) 125–134
3. Results and discussion 3.1. Diorganyltrichlorostannates 3.1.1. Crystal structures of tetraorganylphosphonium diaryltrichlorostannates (8, 9, and 16–19) The crystal structures of 8, 9, and 16–19 consist of isolated [PPh4 ]þ or [PBun4 ]þ cations and [SnR0 2 Cl3 ] (R0 ¼ Ph, o-Tol, m-Tol, p-Tol) anions. As a typical example, an ORTEP view of complex 8 is shown in Fig. 1. Selected bond distances and angles are given in Table 6. For the structures reported here, the [SnR0 2 Cl3 ] anion adopts a distorted trigonal bipyramidal geometry about the central metal atom with both aryl groups occupying equatorial positions. As observed for related [SnR0 2 Cl3 ] trigonal bipyramidal species [5,7–10,20], the axial Sn–Cl bond distances in complexes 8, 9, and 16–19 are 0.15– (6.3–8.9%) longer than the equatorial Sn–Cl 0.21 A bond. This finding is consistent with the observation that the difference between axial and equatorial lengths increases markedly upon replacement of one or more of five identical ligands with more electropositive groups in a trigonal bipyramidal coordination [21]. The Sn–C bond lengths in our complexes are similar to those found in other trigonal bipyramidal tin complexes with either alkyl or aryl groups. The C–Sn–C and C–Sn–
Fig. 1. ORTEP plot of complex 8. (Hydrogens have been omitted for clarity.)
Table 6 ) and angles (°) for complex 8 with estimated Selected bond lengths (A standard deviations in parentheses Sn–Cl(1) Sn–Cl(2) Sn–Cl(3) Cl(1)–Sn–Cl(2) Cl(1)–Sn–Cl(3) Cl(2)–Sn–Cl(3) C(23)–Sn–C(17) Cl(1)–Sn–C(17)
2.541(1) 2.523(1) 2.371(1) 175.56(3) 88.24(3) 87.35(3) 122.6(1) 91.30(9)
Sn–C(17) Sn–C(23) Cl(1)–Sn–C(23) Cl(2)–Sn–C(17) Cl(2)–Sn–C(23) Cl(3)–Sn–C(17) Cl(3)–Sn–C(23)
2.152(3) 2.147(3) 91.4(1) 91.3(1) 90.3(1) 118.36(9) 119.08(9)
Clequatorial distortions from ideal trigonal bipyramidal geometry can be attributed to repulsions of the aryl groups in the equatorial plane and between the aryl groups and the equatorial halide, respectively. One notes that the C–Sn–C angles range from 134.7 to 143.5° for the [PPh4 ]þ salts 16–19 and are 122.6° and 135.3°, respectively, for the [PBun4 ]þ salts 8 and 9, while the Cl(3)– Sn–C angles range from 106.7° to 116.6° for the [PPh4 ]þ salts and are 109.3° and 119.1°, respectively, for the [PBun4 ]þ salts. The distortions appear to be dependent on the overall steric bulk of the aryl group, as well as the degree of non-coplanarity of the rings. Unlike the [SnR0 2 Cl3 ] anions in complexes such as [dbttf][SnEt2 Cl3 ] [10] [C9 H8 N][SnMe2 Cl3 ] [5] [Pt(S2 N2 H)(PEt3 )][SnMe2 Cl3 ] [8], and [ttf][SnMe2 Cl3 ] [9] which form loosely associated ), the complexes dimers (Sn Cl interactions of <4 A reported here are monomeric (Sn Cl interactions of ), such as [Et4 N][SnPh2 Cl3 ] [7] and [Me2 SnCl, >5 A terpyridyl][SnMe2 Cl3 ] [20]. 3.1.2. NMR data and structure of the tetraorganylphosphonium dialkyltrichlorostannates (1–7 and 12–15) Although we were unable to obtain X-ray crystal structures for the tin complexes [PR4 ][SnR0 2 Cl3 ] (R ¼ Me 1–3; Bun 4–7; Ph 12–15; R0 ¼ Me, Et, Prn , and Bun ), the analysis of the NMR data yielded distinct information about their structure. Comparing the 13 C chemical shift of CipsoSn (the carbon atom attached to the Sn atom) between the precursors, namely SnPrn2 Cl2 , SnBun2 Cl2 , SnPh2 Cl2 , and Sn(p-Tol)2 Cl2 , and complexes 6–8, 11, 14, and 15, it was found that there is a uniform downfield shift of about 10–11 ppm (Table 7). This can be explained by the transfer of a chlorine anion to the central tin atom, which, in case of the complexes with R0 ¼ aryl, was confirmed by X-ray crystallography. The deshielding effect caused by the additional covalently bound chlorine was found to be only effective for the nearest carbon atom, changes for carbon atoms further
Table 7 Comparison of 13 C chemical shifta of CipsoSn (the carbon atom attached to the tin atom) Compound
d
Ddb
SnPrn2 Cl2 [PBun4 ][SnPrn2 Cl3 ] (6) [PPh4 ][SnPrn2 Cl3 ] (14)
29.03 39.37 39.16
10.34 10.13
SnBun2 Cl2 [PBun4 ][SnBun2 Cl3 ] (7) [PPh4 ][SnBun2 Cl3 ] (15)
26.83 36.92 36.96
10.09 10.13
SnPh2 Cl2 [PBun4 ][SnPh2 Cl3 ] (8)
136.95 148.09
11.14
Sn(p-tol)2 Cl2 [PBun4 ][Sn(p-Tol)2 Cl3 ] (11)
133.47 144.30
10.83
a b
Chemical shift (d) in ppm, spectra in CDCl3 . Difference to the corresponding precursor.
D. Weber et al. / Inorganica Chimica Acta 357 (2004) 125–134
away were marginal. As shown in Table 3, 119 Sn NMR chemical shifts (in CDCl3 ) changed from about +125 ppm for the dialkyltin dichlorides SnR2 Cl2 (R ¼ Et, Prn , and Bun ) to about )100 to )110 ppm for their products, complexes 5–7 and 13–15. A similar change, i.e., about )220 to )230 ppm, is observed when comparing the diaryltin dichlorides SnR2 Cl2 (R ¼ Ph, m-Tol, and pTol) with their products, complexes 8, 10, 11, 18, and 19. On the other hand, changes of the 119 Sn NMR chemical shifts in DMSO-d6 were found to be relatively small (3–56 ppm) for the complexes studied. The reason for this observation most probably lies in the enhanced coordinating and polarising abilities of the solvent DMSO, compared to CDCl3 . The presence of this solvent effect is supported by the observation that increasing alkyl-chain lengths at the Sn atom correlate with an increasing change of the 119 Sn NMR chemical shift. The methyl group in compound 1 showed with Dd ¼ 3 ppm the smallest shielding of the Sn atom, the nbutyl group in compound 15 with Dd ¼ 56 ppm the greatest. 31 P NMR chemical shifts for the phosphonium cations remain almost unchanged by the complex salt formation (Table 3), which is in agreement with previous studies [25]. In summary, 13 C-, and 119 Sn NMR data indicated that the complex salt formation changed the chemical environment of the tin atom for both, compounds with R0 ¼ aryl and R0 ¼ alkyl. These results agree very well with the structural insights obtained from the crystal structures of complexes 8, 9, and 16–19 (Fig. 1, Tables 5 and 6). Based on these data it can be concluded that for complexes 1–7 and 12–15, for which no X-ray analysis was possible, most likely, also a [SnR0 2 Cl3 ] anion with distorted trigonal bipyramidal geometry was formed, as well. 3.2. Phenylchloroplumbates 3.2.1. Synthesis Compound 20, [PBun4 ]2 [PbPh2 Cl4 ], was formed by the same reaction seen for the tetraorganylphosphonium dialkyltrichlorostannates 1–19, in which the chloride ion formed a bond with the metal. In case of the tin complexes, one chloride was transferred, whereas for 20, two chlorides reacted with the metal (Fig. 2, Table 5). Given the high yield of 20, the two-chloride transfer was the preferred reaction of PbCl2 Ph2 with [PBun4 ]þ Cl . Considering the fact that the reaction conditions for this reaction, heating a neat mixture to 180 °C, and for the formation of many [SnCl3 R2 ] tin complexes are practically identical, it can be concluded that steric factors play an important role. As pointed out in the experimental section, the mixture of [PPh4 ]þ Cl and Ph2 PbCl2 had to be heated to
131
Fig. 2. ORTEP plot of complex 20. (Hydrogens and the THF molecule have been omitted for clarity.)
Fig. 3. ORTEP plot of complex 21. (Hydrogens have been omitted for clarity.)
260 °C for a short time in order to obtain a homogeneous melt. Prolonged heating at this temperature resulted in significant decomposition (i.e., gas development and the formation of some colourless, insoluble solid). The isolated product, [PPh4 ][PbPh3 Cl2 ] (21), did not result from a chloride transfer to the metal (Fig. 3, Table 5). Surprisingly, a phenyl transfer occurred instead. Tetraphenylphosphonium ions are stable even at relatively high temperatures. 5 Phenyl lead compounds, on the other hand, are known to undergo disproportionation reactions and phenyl transfers [15,26]. Based 5 The melting points of [PPh4 ]þ Cl and [PPh4 ]þ Br are 273–275 °C and 295–298 °C, respectively.
132
D. Weber et al. / Inorganica Chimica Acta 357 (2004) 125–134
on these facts, it is conceivable that 21 was formed from Ph2 PbCl2 in a phenyl transfer reaction. The relatively low yield and the observed partial decomposition at the high reaction temperature are consistent with the formation of a significant amount of by-products. 6 3.2.2. 207 Pb NMR spectroscopy The 207 Pb NMR shift of [PBun4 ]2þ [PbCl4 Ph2 ]2 (20) was determined as d ¼ 520 ( 5) ppm; the shift of [PPh4 ]þ [PbCl2 Ph3 ] (21) was observed at d ¼ 237 (5) ppm. Given the fact that the 207 Pb NMR shift values reflect the electron density at the metal [24] they indicate moderate shielding of the metal nucleus. The shift values fall in the range between those reported for PbPh4 (d 175 ppm) and for PbCl4 (d ¼ 768 ppm). 7 In fact, the shift of complex 20 is very close to the one of the hexacoordinated metal in anhydrous PbPh2 (OAc)2 (d ¼ 587 ppm) [27]. However, the dependence of the 207 Pb NMR shift on temperature, interaction with the solvent, and, to a lesser extend, concentration makes the direct comparison of the shift values difficult. 3.2.3. Crystal structures The tetraalkyl ammonium salts of [PbCl4 Ph2 ]2 and [PbCl2 Ph3 ] have been studied previously by means of IR- and Raman spectroscopy [28]. Based on these results, essentially isolated anions had been predicted, but there remained uncertainty about the precise structure and possible weak interactions between the anions. Fig. 2 depicts an ORTEP plot of 20. Selected bond distances and angles are given in Table 8. In the crystal, the [PbPh2 Cl4 ]2 anion assumes a lightly distorted octahedral geometry. The phenyl groups occupy trans positions. Compound 20 consists of isolated cations and anions. Based on the large distance of 6.890 A (Cl1 Cl3) between neighbouring anions, the formation of Pb–Cl chains can be ruled out. The dihedral angle between the planes of the phenyl groups is 85.4°. The crystal used for X-ray crystallographic studies was obtained from a THF solution by slow evaporation of the solvent. This crystal contains a THF molecule in the lattice. Compound 21 consists of isolated cations and anions, between two with a closest Pb Cl distance of 7.698 A anions. The anions do not form chains. Their geometry is trigonal bipyramidal with the chlorine atoms occupying the axial positions. An ORTEP view of 21 is shown in Fig. 3, selected bond distances and angles are listed in Table 9. The Pb–Cl distances in 20 and 21 are essentially identical, while the Pb–C distances in 20 are about 1% longer than those in 21. 6
These by-products were not analysed further. The exact values depend on solvent and concentration. For PbPh4 shift values of d ¼ 166 to )183 ppm have been reported. See [16]. 7
Table 8 ) and angles (°) for complex 20 with estimated Selected bond lengths (A standard deviations in parentheses Pb–Cl(1) Pb–Cl(2) Pb–Cl(3) Pb–Cl(4) Cl(1)–Pb–Cl(2) Cl(1)–Pb–Cl(3) Cl(1)–Pb–Cl(4) Cl(1)–Pb–C(33) Cl(1)–Pb–C(39) Cl(2)–Pb–Cl(3) Cl(2)–Pb–Cl(4) Cl(2)–Pb–C(33) Cl(2)–Pb–C(39)
2.7140(9) 2.6968(9) 2.7392(9) 2.7386(9) 90.99(3) 90.88(3) 179.00(3) 90.75(10) 90.96(9) 178.00(3) 88.01(3) 90.57(9) 91.43(9)
Pb–C(33) Pb–C(39)
Cl(3)–Pb–Cl(4) Cl(3)–Pb–C(33) Cl(3)–Pb–C(39) Cl(4)–Pb–C(33) Cl(4)–Pb–C(39) C(33)–Pb–C(39)
2.180(4) 2.179(9)
90.12(3) 88.68(10) 89.26(9) 89.16(10) 89.17(9) 177.35(13)
Table 9 ) and angles (°) for complex 21 with estimated Selected bond lengths (A standard deviations in parentheses Pb–Cl(1) Pb–Cl(2) Cl(1)–Pb–Cl(2) Cl(1)–Pb–C(25) Cl(1)–Pb–C(31) Cl(1)–Pb–C(37) Cl(2)–Pb–C(25) Cl(2)–Pb–C(31) Cl(2)–Pb–C(37)
2.7273(12) 2.7277(11) 177.70(4) 87.72(12) 88.86(12) 91.17(14) 90.74(12) 90.50(12) 91.01(13)
Pb–C(25) Pb–C(31) Pb–C(37) C(25)–Pb–C(31) C(25)–Pb–C(37) C(31)–Pb–C(37)
2.213(4) 2.221(4) 2.218(4) 121.84(15) 113.71(17) 124.39(15)
3.2.4. Mass spectroscopic studies In the case of the lead complexes 20 and 21 we were able to obtain mass spectra with a good S/N ratio and an excellent correspondence of observed to calculated isotope distribution. The mass spectrum for [PBun4 ]2þ [PbCl4 Ph2 ]2 (20) showed strong signals around m/z ¼ 1282. They are attributed to the cationic complex [PBun4 ]3þ [PbCl4 Ph2 ]2 (calc. m/z ¼ 1281.53) (Fig. 4). Other prominent signals in the MALDI-MS could be attributed to [PBun4 ]þ (m/ z ¼ 259); 2[PBun4 ]þ Cl (m/z ¼ 553); 3[PBun4 ]þ 2Cl (m/ z ¼ 847); 4[PBun4 ]þ [PbCl4 Ph2 ]2 Cl (m/z ¼ 1576). Anion and cation of [PPh4 ]þ [PbCl2 Ph3 ] (21) were observed separately. The [PPh4 ]þ ion was detected in ‘‘positive ionisation mode’’: m/z ¼ 339.1323 (C24 H20 P; deviation: 7.7 ppm). The [PbCl2 Ph3 ] ion was detected in ‘‘negative ionisation mode’’: m/z ¼ 509.0340 (C18 H15 Cl2 Pb; deviation: 4.5 ppm).
4. Summary The extension of a synthetic approach leading to novel complexes incorporating distorted trigonal bipyramidal [SnR0 2 Cl3 ] anions with both aryl groups in the equatorial position to include phenylchloroplumbates
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Fig. 4. Mass spectrum of 3[PBun4 ]þ [PbCl4 Ph2 ]2 . Insert: Calculated distribution.
unexpectedly yielded two complexes, [PBun4 ]2 [PbPh2 Cl4 ] (20) and [PPh4 ][PbPh3 Cl2 ] (21) with different geometry. In case of the reaction between [PBun4 ]þ Cl and PbCl2 Ph2 , a two chloride transfer was the favoured reaction, leading to the distorted octahedral [PbPh2 Cl4 ]2 anion. However when [PPh4 ]þ Cl was reacted with PbCl2 Ph2 at a higher temperature, a trigonal bipyramidal [PbCl2 Ph3 ] anion was formed.
Academic Exchange Service (DAAD) for financial support. SMART 1K CCD data were collected through the Ohio Crystallographic Consortium, funded by the Ohio Board of Regents 1995 Investment Fund (CAP-075), located at the University of Toledo, Instrumentation Center in A & S, Toledo, OH 43606. J.A. Krause-Bauer thanks Dr. A. Pinkerton (Department of Chemistry, University of Toledo) for use of his SMART 2K CCD diffractometer.
5. Supplementary material Cristallographic data for structural analysis of compounds 8, 9, and 16–19 have been deposited with the Cambridge Crystallographic Data Centre, CCDC (Nos. 183894–183901). These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44-1223-336033; e-mail: deposit@ccdc. cam.ac.uk). Further experimental details, 1 H and 13 C NMR spectroscopic data for complexes 1–19, IR spectroscopic data for complexes 8–11 and 16–19, and further HR-MS data of complexes 20 and 21 are available as supplementary material.
Acknowledgements We thank Dr. E. Brooks, Dr. G.P. Kreishman, Dr. K. Jayasimhulu (Department of Chemistry, University of Cincinnati) and Dr. M.-R. Dominic (Morton International Inc.) for their excellent technical assistance. D. Weber. and A. Eisengr€ aber-Pabst. thank the German
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