- Email: [email protected]
Synthesis and characterization of sterically hindered tris(pyrazolyl)borate Ni complexes
Inorganica Chimica Acta 360 (2007) 3335–3340 www.elsevier.com/locate/ica
Synthesis and characterization of sterically hindered tris(pyrazolyl)borate Ni complexes David J. Harding a
a,*
, Phimphaka Harding a, Harry Adams b, Thawatchai Tuntulani
c
Molecular Technology Unit Cell, Department of Chemistry, Walailak University, Thasala, Nakhon Si Thammarat 80161, Thailand b Department of Chemistry, University of Sheffield, Brook Hill, Sheffield S3 7HF, England, United Kingdom c Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand Received 24 October 2006; received in revised form 28 March 2007; accepted 31 March 2007 Available online 10 April 2007
Abstract Addition of KTpPh2 to a solution of NiX2 (X = Cl, Br, NO3, OAc and acac) or NiBr(NO)(PPh3)2 in THF yields the structurally characterized series [NiCl(HpzPh2)TpPh2] (1) and [NiXTpPh2] (X = Br 2, NO 3, NO3 4, OAc 5 and acac 6) including the first example of a tris(pyrazolyl)borate nickel nitrosyl complex. IR spectroscopy confirms that all the TpPh2 ligands are j3 coordinated and that the NO ligand in 3 is linearly bound. Electronic spectra are consistent with four- or five-coordinate species in solution. NMR spectroscopic studies indicate that the complexes are paramagnetic, with the exception of 3. This is confirmed by magnetic susceptibility studies, which suggest that complexes 1, 2 and 4–6 are paramagnetic with two unpaired electrons. X-ray crystallographic studies of 5 reveal a distorted trigonal bipyramidal nickel centre with a symmetrically coordinated acetate ligand. 2007 Elsevier B.V. All rights reserved. Keywords: Nickel complexes; Tris(pyrazolyl)borates; Nitrosyl complexes; X-ray crystal structures
1. Introduction Tris(pyrazolyl)borate, Tp and tris(3,5-dimethylpyrazolyl)borate, Tp* are the simplest and most frequently encountered members of the scorpionate family but with first row transition metals have a tendency to form inert sandwich complexes, [Tp2M] [1]. In contrast, second generation scorpionates with large alkyl or aryl groups at the 3-position of the pyrazole ring allow the preparation of synthetically useful half-sandwich compounds [2]. Despite this, metal complexes of sterically hindered scorpionates are prone to 1,2-borotropic shifts thereby providing steric relief to the metal centre [3]. Such a structural rearrangement may be prevented by using scorpionates which are symmetrically substituted in the 3- and 5-positions of the pyrazole ring. In addition, large *
Corresponding author. Tel.: +66 0 75 672 094; fax: +66 0 75 672 004. E-mail address: [email protected] (D.J. Harding).
0020-1693/$ - see front matter 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2007.03.046
R groups in the 5-position protect the sometimes troublesome B–H bond [4]. Nickel TpR {TpR = substituted tris(pyrazolyl)borate ligands} complexes have previously been synthesized with a view to preparing alkene polymerization/oligomerization catalysts [5], enzyme mimics [6] and magnetic materials [7,8]. In most cases these studies have focused on second generation scorpionate ligands with few examples of the more substituted TpR2 (R = alkyl or aryl) ligands [1]. In an attempt to expand this area of chemistry we have selected tris(3,5-diphenylpyrazolyl)borate (TpPh2) as a supporting ligand as it is of intermediate steric bulk and electronically very different from the previously studied TpiPr2 [9]. Herein we describe the successful synthesis of six NiTpPh2 compounds including the first example of a nickel nitrosyl complex supported by a tris(pyrazolyl)borate ligand. The complexes have been studied by IR, NMR, UV–Vis spectroscopy, mass spectrometry and in some cases X-ray crystallography.
3336
D.J. Harding et al. / Inorganica Chimica Acta 360 (2007) 3335–3340
2. Experimental 2.1. General All manipulations were performed using standard Schlenk-line techniques under a nitrogen atmosphere. n-Hexane, CH2Cl2 and MeCN were distilled from CaH2, and THF was distilled from sodium benzophenone. Tris(3,5-diphenylpyrazolyl)borate (KTpPh2) [21] and [NiBr(NO)(PPh3)2] [26] were prepared by literature procedures. All other chemicals were purchased from Fluka Chemical Company and used as received. Infrared spectra (as KBr discs) were recorded on a Perkin–Elmer Spectrum One infrared spectrophotometer in the range 400–4000 cm1. Electronic spectra were recorded in CH2Cl2 or DMSO on a Unicam UV300 UV–Vis spectrometer. 1H NMR spectra were recorded on a Bruker 300 MHz FT-NMR spectrometer at 25 C in CDCl3 or DMSO with SiMe4 added as an internal standard. Elemental analyses and ESI-MS were carried out by the staff of the School of Chemistry, University of Bristol, UK. 2.2. Synthesis of [NiCl(HpzPh2)TpPh2] (1) NiCl2 Æ 6H2O (52 mg, 0.22 mmol) was dissolved in THF:MeOH (5:1 ml) giving a lime green solution and then stirred for 5 min. KTpPh2 (142 mg, 0.2 mmol) was dissolved in THF (5 ml) giving a pale yellow solution. Addition of the KTpPh2 solution to the Ni solution resulted in an orange solution. The solution was stirred overnight. The solution was reduced to dryness, redissolved in CH2Cl2 (2 ml) and filtered through celite. The red solution was layered with hexane (10 ml). After two days green crystals appeared. These were washed with EtOH (3 · 3 ml) and Et2O (2 · 5 ml) (87 mg, 44%). mmax(KBr)/cm1 3169 br (mNH), 3060 m (mCH), 2632 m (mBH). dH(300 MHz; CDCl3; SiMe4) 7.14 (br s, Ph, 7H), 7.25 (br s, Ph, 4H), 7.44 (br s, Ph, 5H), 7.72 (br s, Ph, 4H), 7.88 (br m, Ph, 15H), 8.50 (br s, Ph, 5H). UV–Vis kmax(CH2Cl2)/nm 490 (e/dm3 mol1 cm1 420), 812 (52), 922 (85). m/z (ESI) 947 [MCl]+, 727 [MCl-HpzPh2]+. Magnetic moment (leff/lB, 294 K): 2.73. Anal. Calc. for C60H46N8BClNi: C, 73.38, H 4.72, N 11.41; Found: C, 73.10, H 4.90, N 11.30%. Complexes 2–5 were synthesized by essentially the same procedures as described for 1 using appropriate starting materials and were crystallized from the solvents indicated (see below). 2.3. Synthesis of [NiBrTpPh2] (2) Pink-purple crystals (crystallized from THF-hexane). 54% yield. mmax(KBr)/cm1 3059w, 2966w, 2854w (mCH), 2626w (mBH). dH (300 MHz; CDCl3; SiMe4), 7.63 (br m, mand p-Ph, 18H), 8.53 (br s, o-Ph, 6H), 8.86 (br s, o-Ph, 6H). UV–Vis kmax(CH2Cl2)/nm 318 (e/dm3 mol1 cm1 3140), 502 (600), 828 (120), 926 (160). m/z (ESI) 800 [MBr+H+THF]+, 745 [MBr+H2O]+, 727 [MBr]+.
Magnetic moment (leff/lB, 294 K): 2.81. Anal. Calc. for C45H36N6BBrONi [2 Æ (H2O)]: C, 65.42; H, 4.39; N 10.17. Found: C, 65.42; H, 4.69; N, 10.17%. 2.4. Synthesis of [Ni(NO)TpPh2] (3) Blue crystals (crystallized from THF-hexane). 24% yield. mmax(KBr)/cm1 3061m, 2955w, (mCH), 2629w (mBH), 1803vs (mNO). dH (300 MHz; DMSO; SiMe4), 6.85–6.90 (m, Ph, 12 H), 7.25–7.35 (m, Ph and pz-CH, 5H), 7.43 (m, Ph, 10 H), 7.60 (m, Ph, 2H), 8.07 (d, J = 6.7 Hz, Ph, 4H). UV–Vis kmax(DMSO)/nm 612 (e/dm3 mol1 cm1 230). m/z (ESI) 758 [M+H]+, 745 [MNO+H2O]+, 727 [MNO]+. Magnetic moment (leff/lB, 294 K): 0.02. Anal. Calc. for C45H34N7BONi: C, 71.28; H, 4.52; N, 12.93. Found: C, 71.05; H, 4.76; N 12.74%. 2.5. Synthesis of [Ni(NO3)TpPh2] (4) Green crystals (crystallized from CH2Cl2-hexane). 38% yield. mmax(KBr)/cm1 3060w, 2980w, 2898w (mCH), 2612br (mBH), 1523 s ðmNO2 Þ, 1275s ðmNO2 Þ. dH(300 MHz; CDCl3; SiMe4), 6.81 (br s, Ph, 6H), 7.25 (br s, Ph, 9H), 7.53 (br s, Ph, 4H), 8.00 (br s, Ph, 6H), 8.67 (br s, Ph, 5H). UV–Vis kmax(CH2Cl2)/nm 420 (e/dm3 mol1 cm1 þ 230), 686 (60). m/z (ESI) 800 ½M NO3 þ H þ THF , þ 745 ½M NO3 þ H2 O . Magnetic moment (leff/lB, 294 K): 3.07. Anal. Calc. for C45H34N7BO3Ni: C, 68.39; H, 4.34; N, 12.41. Found: C, 68.42; H, 4.86; N, 12.14%. 2.6. Synthesis of [Ni(OAc)TpPh2] (5) Green-yellow crystals (crystallized from CH2Cl2-hexane). 38% yield. mmax(KBr)/cm1 3058 m, 3041 (mCH), 2648 m (mBH). dH(300 MHz; CDCl3; SiMe4), 6.76 (br s, Ph, 7H), 7.06 (br s, Ph, 8H), 7.46 (t, Ph, 5H), 7.78 (br s, Ph, 6H), 8.74 (br s, Ph, 4H). UV–Vis kmax(CH2Cl2)/nm 416 (e/dm3 mol1 cm1 270), 708 (70). m/z (ESI) 787 [M+H]+, 727 [MOAc]+. Magnetic moment (leff/lB, 294 K): 2.96. Anal. Calc. for C47H39N6BO3Ni [5 Æ (H2O)]: C, 70.09; H, 4.88; N, 10.44. Found: C, 69.70; H, 4.70; N, 10.20%. 2.7. Synthesis of [Ni(acac)TpPh2] (6) Green crystals (crystallized from CH2Cl2-hexane). 17% yield. mmax(KBr)/cm1 3062w (mCH), 2611br (mBH), 1594 s ðmCO2 Þ. dH(300 MHz; CDCl3; SiMe4), 1.66 (s, acac-Me, 6H), 3.75 (sp, acac-CH, 1H), 6.06 (br s, Ph, 8H), 6.72 (br s, Ph, 9H), 7.25 (br s, Ph, 9H), 9.03 (br s, Ph, 4H),. UV–Vis kmax(CH2Cl2)/nm 304 (e/dm3 mol1 cm1 8300), 404 (440). m/z (ESI) 827 [M+H]+, 745 [Macac+ H2O]+, 607 [MacacHpzPh2]+. Magnetic moment (leff/lB, 294 K): 2.94. Anal. Calc. for C50H41N6BO2Ni: C, 72.58; H, 4.99; N, 10.16. Found: C, 72.41; H, 5.14; N 10.24%.
D.J. Harding et al. / Inorganica Chimica Acta 360 (2007) 3335–3340
3. Results and discussion The reaction of appropriate Ni starting materials with KTpPh2 in THF yields green (X = Cl, NO3, OAc and acac), pink-purple (X = Br) or blue (X = NO) solutions. Purification by recrystallization gives highly crystalline products [NiCl(HpzPh2)TpPh2] (1) or [NiXTpPh2] (X = Br 2, NO 3, NO3 4, OAc 5 and acac 6) in moderate to good yields (Scheme 1). The solids are soluble in polar organic solvents such as, CH2Cl2 and DMSO, although complex 3 decomposes in CH2Cl2. By comparison the cobalt analogues, once crystallized, are almost insoluble [10]. In contrast to results reported by Yin et al. [11], [NiCl(HpzPh2)TpPh2], and not [NiClTpPh2], was the only product from the reaction between KTpPh2 and NiCl2. Our synthesis differs from that reported only in the method of crystallization {CH2Cl2/hexane cf. CH2Cl2:MeCN (2:1)/hexane}. It would appear that the presence of a coordinating solvent is essential to cleanly isolate [NiClTpPh2]. Although, [NiClTpPh2] may coordinate a further donor, complex 2 shows
3337
no such tendency. We hypothesize that the larger ionic radius of the bromide anion prevents coordination of additional ligands. Recently, we reported [10] the synthesis of [Co(OAc)(HpzPh2)TpPh2] from Co(OAc)2 and KTpPh2 and were therefore surprised to find that the analogous reaction with Ni(OAc)2 yielded 5 as the only product. This difference in reactivity may be due to the tendency of cobalt towards a monodentate acetate coordination mode in contrast to the bidentate coordination mode preferred by nickel [12,13]. It follows that for the cobalt metal to achieve coordination number five an additional ligand will be required, in this case by decomposition of the TpPh2 ligand. Characterization of complexes 1–6 by IR spectroscopy reveal B–H stretches between 2611 cm1 and 2648 cm1 indicative of j3 coordinated TpPh2 ligands (Table 1) [14]. This compares well with [NiClTpPh2] in which the B–H stretch is at 2612 cm1. The difference between the asymmetric and symmetric stretches of the acetate and nitrate groups is a useful probe for the coordination mode [15].
Scheme 1.
3338
D.J. Harding et al. / Inorganica Chimica Acta 360 (2007) 3335–3340
Table 1 IR and UV–Vis spectroscopic and mass spectrometric data for NiXTpPh2 complexes Complex Ph2
Ph2
[NiCl(Hpz )Tp [NiBrTpPh2] [Ni(NO)TpPh2] [Ni(NO3)TpPh2] [Ni(OAc)TpPh2] [Ni(acac)TpPh2] a b
]
Colour
% Yield
IR,amBH/cm1
green pink-purple blue green green-yellow green
44 54 24 38 39 17
2632 2626 2629 2612 2648 2611
IR,a mX=O/cm1
kmax/nm (e)
ESI MS
1803 1523, 1275 no 1593
490 318 612 420 416 304
947 745 758 800 787 827
(420), 812 (52), 922 (85) (3140), 502 (600), 828 (120), 926 (160) (230) (230), 686 (60) (270), 708 (70) (8300), 404 (440)
As KBr discs. In CH2Cl2 or DMSO see text, no = not observed, X = C or N.
For 4, the large Dm(NO2) value is consistent with a bidentate coordination mode [11,15]. Unfortunately, the asymmetric and symmetric stretches of the acetate ligand in 5 are masked by other IR bands making a determination of the coordination mode impossible. The CO stretch of the acac ligand in 6 is observed at 1593 cm1, characteristic of a chelating acac group and thus a five-coordinate nickel centre [13]. The IR spectrum of 3 also shows an NO band at 1803 cm1 exhibiting a shift of 79 cm1 to higher wavenumber compared with [NiBr(NO)(PPh3)2] and consistent with a linear nitrosyl ligand [16]. It follows that the nitrosyl ligand is best described as NO+ and consequently the metal centre is Ni(0). Interestingly, [Ni(NO)TpPh2] is isoelectronic with the previously reported carbonyl compound [Cu(CO)TpPh2]. Moreover, an analogous cyclopentadienyl Ni complex [Ni(NO)Cp] has previously been synthesized and exhibits a nitrosyl stretch at 1830 cm1 suggesting that TpPh2 is a better net donor than Cp [17]. The [NiXTpPh2] (X = Br, NO, NO3, OAc and acac) complexes and [NiCl(HpzPh2)TpPh2] are all green except for 2 which is pink-purple and 3 which is blue. The UV–Vis spectra of 1, 2 and 4–6 were recorded in CH2Cl2, while 3 was recorded in DMSO (see Table 1). The spectrum of 2 has four absorptions at 318, 502, 828 and 926 nm. The absorption at 318 nm has a large extinction coefficient (3140 M1 cm1) and by comparison with [Ni(SC6F5)TpiPr2], is tentatively assigned to a Br to Ni LMCT band [8,18]. The three absorptions at 502, 828 and 926 nm are typical of tetrahedral Ni(II) and compare well with those observed for [NiBrTp*] (kmax = 500, 810 and 894 nm) [19]. The spectrum of 1 resembles that of 2 indicating dissociation of the HpzPh2 ligand in CH2Cl2 to give tetrahedral [NiClTpPh2]. Similar observations have been made for [CoCl(HpzPh,Me)TpPh,Me] [20]. Uniquely the UV–Vis spectrum of the nitrosyl complex, 3 reveals a single broad band centred at 612 nm. The UV– Vis spectra of [NiXTpPh2] (NO3, OAc and acac) have a principle absorption between 404–420 nm, and in the case of 4 and 5 a further absorption at 686 nm and 708 nm respectively. The spectra are characteristic of five coordinate Ni(II) complexes and closely resemble those of the related complexes [Ni(NO3)TpMe3] and [Ni(OAc)TpR] (R = Me3; Me2 and Me2,Br) which exhibit two absorptions at between 413–442 and 676–682 nm [12]. In addition, to these metal centred absorptions complex 6 has a further band at 304 nm due to a ligand centred p to p* transition.
As with the related TpiPr2 complexes, the [NiXTpPh2] (X = Br, NO3, OAc and acac) complexes and [NiCl(HpzPh2)TpPh2] appear paramagnetic as evidenced by their NMR spectra [9]. The 1H NMR spectra of 1, 2 and 4–6 are relatively broad providing little or no structural information. Furthermore, despite repeated attempts we were unable to locate the pyrazole-CH and the acetate protons of 5, presumably due to broadening. Similar observations have been noted by Akita et al. [12] and Kitajima et al. [21]. The spectrum of 2 exhibits three resonances and closely resembles that of [NiClTpPh2] [11]. The NMR spectrum of 1 is markedly different from 2 and the previously reported [NiClTpPh2] confirming the presence of pyrazole. The spectra of 4 and 5 show five resonances consistent with their lower symmetry compared with 2. As expected, the spectrum of 6 shows four resonances in the aromatic region and two further peaks for the methine and methyl protons of the acac ligand. In contrast to other members in this series, the 1H NMR spectrum of [Ni(NO)TpPh2] reveals sharp resonances a doublet at 8.04 ppm and four multiplets between 7.60 and 6.90 ppm for the aromatic phenyl and pyrazole-CH protons. The significantly better resolution of the spectrum clearly suggests a diamagnetic Ni metal complex supporting earlier conclusions based upon IR spectroscopy. The NMR spectra of 1, 2 and 4–6 indicate that all the complexes are paramagnetic and this is confirmed by magnetic susceptibility measurements, which are consistent with paramagnetic species containing two unpaired electrons [16]. However, the nitrosyl complex, 3, exhibits a magnetic susceptibility close to zero consistent with a Ni(0) metal centre. Crystals suitable for an X-ray diffraction study were obtained by allowing n-hexane to diffuse into a concentrated solution of 5 in CH2Cl2. The structure of 5 is shown in Fig. 1 with bond lengths and angles given in Table 2. The compound crystallizes in a trigonal space group with two disordered water molecules per unit cell. The X-ray structure of 5 represents the first structurally characterized NiTpR acetate compound with a sterically hindered Tp ligand. The TpPh2 ligand is j3 coordinated with the phenyl rings arranged in a propeller-like conformation [22]. As such, the phenyl and pyrazolyl rings of the TpPh2 are not co-planar. The Ni–Npz bond lengths are typical for nickel ˚ for 5) [23]. Moreover, the complex TpR complexes (2.036 A
D.J. Harding et al. / Inorganica Chimica Acta 360 (2007) 3335–3340
3339
Table 3 Crystallographic data for 5 Complex
5
C47H39BN6NiO3 821.36 trigonal p3 12.8805(11) 12.8805(11) 13.799(2) 90 90 120 1982.6(4) 2 1.429 0.550 150(2) 3044 2345(0.0489) 0.0804, 0.2698 0.1020, 0.3026 hP i1=2 P P P 2 R1 ¼ jjF o j jF c jj= jF o j; wR2 . wðF 2o F 2c Þ = wðF 2o Þ2
Chemical formula Mr Crystal system Space group ˚) a (A ˚) b (A ˚) c (A a () b () c () ˚ 3) V (A Z Dc (g cm3) l(Mo Ka) (mm1) T (K) Reflections collected Independent reflections (Rint) R1, wR2 [I > 2r(I)]a R1, wR2 (all data) a
Fig. 1. The molecular structure of [Tpph2Ni(OAc)] 5. Ellipsoids are drawn at the 50% probability level and hydrogen atoms have been omitted for clarity.
Table 2 Selected bond lengths and angles of 5 ˚) Complex Bond lengths (A 5
Ni–O(1) Ni–N(1) O(1)–C(16) O(1A)–C(16) O(1B)–C(16) C(16)–C(17) Ni C(16)
2.036(3) 2.041(5) 1.281(7) 1.281(7) 1.281(7) 1.456(13) 2.364(11)
Bond angles () O(1)–Ni–O(1A) O(1)–Ni–N(1) O(1A)–Ni–N(1) O(1B)–Ni–N(1) N(1)–Ni–N(1A) Ni–O(1)–C(16)
55.9(2) 107.71(17) 100.46(16) 155.59(18) 92.31(12) 87.6(5)
exhibits Npz–Ni–Npz angles close to 90 as observed in other NiTpR complexes [23]. The presence of a crystallographically imposed C3 axis makes it appear that there are three acetate oxygen atoms (see Fig. 1). Despite this the acetate ligand is still best thought of as a j2 coordinated ˚ ) is similar ligand. The nickel-acetate bond length (2.041 A to the short Ni–O bond observed in [Ni(OAc)Tp*] ˚ , 2.131 A ˚ ) [12] but in contrast, to the structure of (2.014 A [Ni(OAc)Tp*] the acetate ligand of 5 is symmetrically coordinated. Similar symmetrically coordinated bidentate O-donor ligands have previously been reported in [NiTptBu(NO3)] [24] and [{NiTpiPr2}2(l-j2:j2-CO3)] [25]. The symmetric coordination of the acetate ligand should result in complete delocalization of the p electrons over the O–C–O linkage and thus identical C16–O1, C16–O1A and C16–O2A bond lengths, as indeed is observed (see Table 2). Interestingly, the bite angle of the acetate ligand is far smaller than that observed in [Ni(OAc)Tp*] (55.9 cf. 60.5) (see Table 3).
4. Conclusions In summary, the first tris(pyrazolyl)borate nickel nitrosyl complex and a range of other half-sandwich Ni complexes supported by the TpPh2 ligand have been synthesized and characterized. The nitrosyl ligand exhibits a linear coordination mode as evidenced by IR spectroscopy. The complexes have been shown to be four or fivecoordinate in solution depending on the nature of the anion. A solid state structure of the acetate complex as determined by X-ray crystallography reveals a distorted trigonal bipyramidal nickel centre. The use of tris(3,5-diphenylpyrazolyl)borate in the preparation of other first-row transition metal complexes is currently under way in these laboratories. Acknowledgements We gratefully acknowledge the Thailand Research Fund (MRG4680139) for financial support of this research. Assoc. Prof. Dr. Sujittra Youngme (Khon Kaen University) is thanked for magnetic susceptibility measurements. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at doi:10.1016/ j.ica.2007.03.046. References [1] (a) S. Trofimenko, Scorpionates: The Coordination Chemistry of Polypyrazolylborate Ligands, Imperial College Press, London, 1999; (b) S. Trofimenko, Chem. Rev. 93 (1993) 943.
3340
D.J. Harding et al. / Inorganica Chimica Acta 360 (2007) 3335–3340
[2] (a) S. Trofimenko, J.C. Calabrese, P.J. Domaille, J.S. Thompson, Inorg. Chem. 26 (1987) 1507; (b) S. Trofimenko, J.C. Calabrese, J.S. Thompson, Inorg. Chem. 28 (1989) 1091. [3] See for example: (a) O.M. Reinaud, A.L. Rheingold, K.H. Theopold, Inorg. Chem. 33 (1994) 2306; (b) J.C. Calabrese, S. Trofimenko, Inorg. Chem. 31 (1992) 4810; (c) A. Looney, G. Parkin, Polyhedron 9 (1990) 265. [4] C. Pattinari, C. Santini, Comprehensive Coordination Chemistry II, vol. 1, Elsevier, New York, 2004, pp. 159–210. [5] (a) F.A. Kunrath, R.F. de Souza, O.L. Casagrande Jr., N.R. Brooks, V.G. Young Jr., Organometallics 22 (2003) 4739; (b) R. Santi, A.M. Ramano, A. Sommazzi, M. Grande, C. Bianchini, G. Mantovani, J. Mol. Catal. 229 (2005) 191. [6] (a) Y.-J. Sun, P. Cheng, S.-P. Yan, Z.-H. Jiang, D.-Z. Liao, P.-W. Shen, Inorg. Chem. Commun. 3 (2000) 289; (b) Y.-J. Sun, W.-Z. Shen, P. Cheng, S.-P. Yan, D.-Z. Liao, Z.-H. Jiang, P.-W. Shen, Polyhedron 23 (2004) 211. [7] A.S. Yakovenko, S.V. Kolotilov, A.W. Addison, S. Trofimenko, G.P.A. Yap, V. Lopushanskaya, V.V. Pavlishchuk, Inorg. Chem. Commun. 8 (2005) 932. [8] Y. Matsunaga, K. Fujisawa, N. Ibi, Y. Miyashita, K. Okamoto, Inorg. Chem. 44 (2005) 325. [9] Examples of NiTpiPr2: (a) S. Hikichi, M. Yoshizawa, Y. Sasakura, H. Komatsuzaki, Y. Moro-oka, M. Akita, Chem. Eur. J. 7 (2001) 5011; (b) K. Uehara, S. Hikichi, M. Akita, J. Chem. Soc., Dalton Trans. (2002) 3529; (c) M. Kujime, S. Hikichi, M. Akita, J. Chem. Soc., Dalton Trans. (2003) 3506; (d) M. Akita, J. Organomet. Chem. 689 (2004) 4540, and references therein. [10] D.J. Harding, H. Adams, T. Tuntulani, Acta Cryst., Sec. C C61 (2005) m301. [11] S. Guo, E. Ding, Y. Yin, K. Yu, Polyhedron 17 (1998) 3841. [12] S. Hikichi, Y. Sasakura, M. Yoshizawa, Y. Ohzu, Y. Moro-oka, M. Akita, Bull. Chem. Soc. Jpn. 75 (2002) 1255. [13] A. Kremer-Aach, W. Kla¨ui, R. Bell, A. Strerath, H. Wunderlich, D. Mootz, Inorg. Chem. 36 (1997) 1552.
[14] M. Akita, K. Ohta, Y. Yakamashi, S. Hikichi, Y. Moro-oka, Organometallics 16 (1997) 4121. [15] K. Nakamoto, in: Infrared and Raman Spectra of Inorganic and Coordination Compounds, fourth ed., Wiley, New York, 1986, pp. 257–285. [16] F.A. Cotton, G. Wilkinson, C.A. Murillo, M. Bochmann, Advanced Inorganic Chemistry, sixth ed., Wiley, New York, 1999. [17] Ch. Elschenbroich, A. Salzer, Organometallics, second ed., VCH Publishers Inc., New York, 1992. [18] S.I. Gorelsky, L. Basumallick, J. Vura-Weis, R. Sarangi, K.O. Hodgson, B. Hedman, K. Fujisawa, E.I. Solomon, Inorg. Chem. 44 (2005) 4947. [19] P.J. Desrochers, S. LeLievre, R.J. Johnson, B.T. Lamb, A.L. Phelps, A.W. Cordes, W. Gu, S.P. Cramer, Inorg. Chem. 42 (2003) 7945. [20] S.V. Kolotilov, A.W. Addison, S. Trofimenko, W. Dougherty, V.V. Pavlishchuk, Inorg. Chem. Commun. 7 (2004) 485. [21] N. Kitajima, K. Fujisawa, C. Fujimoto, Y. Moro-oka, S. Hashimoto, T. Kitagawa, K. Toriumi, K. Tatsumi, A. Nakamura, J. Am. Chem. Soc. 114 (1992) 1277. [22] A.L. Rheingold, L.M. Liable-Sands, S. Trofimenko, Inorg. Chem. 40 (2001) 5609. [23] Examples of NiTpR complexes include: (a) P.J. Desrochers, R.W. Cutts, P.K. Rice, M.L. Golden, J.B. Graham, T.M. Barclay, A.W. Cordes, Inorg. Chem. 38 (1999) 5690; (b) S. Trofimenko, J.C. Calabrese, J.K. Kochi, S. Wolowiec, F.B. Hulsbergen, J. Reedijk, Inorg. Chem. 31 (1992) 3943; (c) S. Hikichi, M. Yoshizawa, Y. Sasakura, M. Akita, Y. Moro-oka, J. Am. Chem. Soc. 120 (1998) 10567; (d) G. Bandoli, D.A. Clemente, G. Paolucci, L. Doretti, Cryst. Struct. Commun. 8 (1979) 965. [24] A. Looney, R. Han, K. McNeill, G. Parkin, J. Am. Chem. Soc. 113 (1991) 9707. [25] N. Kitajima, S. Hikichi, M. Tanaka, Y. Moro-oka, J. Am. Chem. Soc. 115 (1993) 5496. [26] A.W.G. Platt, J.F. Gibson, in: J.D. Woolins (Ed.), Inorganic Experiments, second ed., Wiley–VCH Verlag GmbH & Co., Weinheim, 2003, pp. 127–129.
Synthesis and characterization of sterically hindered tris(pyrazolyl)borate Ni complexes David J. Harding a
a,*
, Phimphaka Harding a, Harry Adams b, Thawatchai Tuntulani
c
Molecular Technology Unit Cell, Department of Chemistry, Walailak University, Thasala, Nakhon Si Thammarat 80161, Thailand b Department of Chemistry, University of Sheffield, Brook Hill, Sheffield S3 7HF, England, United Kingdom c Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand Received 24 October 2006; received in revised form 28 March 2007; accepted 31 March 2007 Available online 10 April 2007
Abstract Addition of KTpPh2 to a solution of NiX2 (X = Cl, Br, NO3, OAc and acac) or NiBr(NO)(PPh3)2 in THF yields the structurally characterized series [NiCl(HpzPh2)TpPh2] (1) and [NiXTpPh2] (X = Br 2, NO 3, NO3 4, OAc 5 and acac 6) including the first example of a tris(pyrazolyl)borate nickel nitrosyl complex. IR spectroscopy confirms that all the TpPh2 ligands are j3 coordinated and that the NO ligand in 3 is linearly bound. Electronic spectra are consistent with four- or five-coordinate species in solution. NMR spectroscopic studies indicate that the complexes are paramagnetic, with the exception of 3. This is confirmed by magnetic susceptibility studies, which suggest that complexes 1, 2 and 4–6 are paramagnetic with two unpaired electrons. X-ray crystallographic studies of 5 reveal a distorted trigonal bipyramidal nickel centre with a symmetrically coordinated acetate ligand. 2007 Elsevier B.V. All rights reserved. Keywords: Nickel complexes; Tris(pyrazolyl)borates; Nitrosyl complexes; X-ray crystal structures
1. Introduction Tris(pyrazolyl)borate, Tp and tris(3,5-dimethylpyrazolyl)borate, Tp* are the simplest and most frequently encountered members of the scorpionate family but with first row transition metals have a tendency to form inert sandwich complexes, [Tp2M] [1]. In contrast, second generation scorpionates with large alkyl or aryl groups at the 3-position of the pyrazole ring allow the preparation of synthetically useful half-sandwich compounds [2]. Despite this, metal complexes of sterically hindered scorpionates are prone to 1,2-borotropic shifts thereby providing steric relief to the metal centre [3]. Such a structural rearrangement may be prevented by using scorpionates which are symmetrically substituted in the 3- and 5-positions of the pyrazole ring. In addition, large *
Corresponding author. Tel.: +66 0 75 672 094; fax: +66 0 75 672 004. E-mail address: [email protected] (D.J. Harding).
0020-1693/$ - see front matter 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2007.03.046
R groups in the 5-position protect the sometimes troublesome B–H bond [4]. Nickel TpR {TpR = substituted tris(pyrazolyl)borate ligands} complexes have previously been synthesized with a view to preparing alkene polymerization/oligomerization catalysts [5], enzyme mimics [6] and magnetic materials [7,8]. In most cases these studies have focused on second generation scorpionate ligands with few examples of the more substituted TpR2 (R = alkyl or aryl) ligands [1]. In an attempt to expand this area of chemistry we have selected tris(3,5-diphenylpyrazolyl)borate (TpPh2) as a supporting ligand as it is of intermediate steric bulk and electronically very different from the previously studied TpiPr2 [9]. Herein we describe the successful synthesis of six NiTpPh2 compounds including the first example of a nickel nitrosyl complex supported by a tris(pyrazolyl)borate ligand. The complexes have been studied by IR, NMR, UV–Vis spectroscopy, mass spectrometry and in some cases X-ray crystallography.
3336
D.J. Harding et al. / Inorganica Chimica Acta 360 (2007) 3335–3340
2. Experimental 2.1. General All manipulations were performed using standard Schlenk-line techniques under a nitrogen atmosphere. n-Hexane, CH2Cl2 and MeCN were distilled from CaH2, and THF was distilled from sodium benzophenone. Tris(3,5-diphenylpyrazolyl)borate (KTpPh2) [21] and [NiBr(NO)(PPh3)2] [26] were prepared by literature procedures. All other chemicals were purchased from Fluka Chemical Company and used as received. Infrared spectra (as KBr discs) were recorded on a Perkin–Elmer Spectrum One infrared spectrophotometer in the range 400–4000 cm1. Electronic spectra were recorded in CH2Cl2 or DMSO on a Unicam UV300 UV–Vis spectrometer. 1H NMR spectra were recorded on a Bruker 300 MHz FT-NMR spectrometer at 25 C in CDCl3 or DMSO with SiMe4 added as an internal standard. Elemental analyses and ESI-MS were carried out by the staff of the School of Chemistry, University of Bristol, UK. 2.2. Synthesis of [NiCl(HpzPh2)TpPh2] (1) NiCl2 Æ 6H2O (52 mg, 0.22 mmol) was dissolved in THF:MeOH (5:1 ml) giving a lime green solution and then stirred for 5 min. KTpPh2 (142 mg, 0.2 mmol) was dissolved in THF (5 ml) giving a pale yellow solution. Addition of the KTpPh2 solution to the Ni solution resulted in an orange solution. The solution was stirred overnight. The solution was reduced to dryness, redissolved in CH2Cl2 (2 ml) and filtered through celite. The red solution was layered with hexane (10 ml). After two days green crystals appeared. These were washed with EtOH (3 · 3 ml) and Et2O (2 · 5 ml) (87 mg, 44%). mmax(KBr)/cm1 3169 br (mNH), 3060 m (mCH), 2632 m (mBH). dH(300 MHz; CDCl3; SiMe4) 7.14 (br s, Ph, 7H), 7.25 (br s, Ph, 4H), 7.44 (br s, Ph, 5H), 7.72 (br s, Ph, 4H), 7.88 (br m, Ph, 15H), 8.50 (br s, Ph, 5H). UV–Vis kmax(CH2Cl2)/nm 490 (e/dm3 mol1 cm1 420), 812 (52), 922 (85). m/z (ESI) 947 [MCl]+, 727 [MCl-HpzPh2]+. Magnetic moment (leff/lB, 294 K): 2.73. Anal. Calc. for C60H46N8BClNi: C, 73.38, H 4.72, N 11.41; Found: C, 73.10, H 4.90, N 11.30%. Complexes 2–5 were synthesized by essentially the same procedures as described for 1 using appropriate starting materials and were crystallized from the solvents indicated (see below). 2.3. Synthesis of [NiBrTpPh2] (2) Pink-purple crystals (crystallized from THF-hexane). 54% yield. mmax(KBr)/cm1 3059w, 2966w, 2854w (mCH), 2626w (mBH). dH (300 MHz; CDCl3; SiMe4), 7.63 (br m, mand p-Ph, 18H), 8.53 (br s, o-Ph, 6H), 8.86 (br s, o-Ph, 6H). UV–Vis kmax(CH2Cl2)/nm 318 (e/dm3 mol1 cm1 3140), 502 (600), 828 (120), 926 (160). m/z (ESI) 800 [MBr+H+THF]+, 745 [MBr+H2O]+, 727 [MBr]+.
Magnetic moment (leff/lB, 294 K): 2.81. Anal. Calc. for C45H36N6BBrONi [2 Æ (H2O)]: C, 65.42; H, 4.39; N 10.17. Found: C, 65.42; H, 4.69; N, 10.17%. 2.4. Synthesis of [Ni(NO)TpPh2] (3) Blue crystals (crystallized from THF-hexane). 24% yield. mmax(KBr)/cm1 3061m, 2955w, (mCH), 2629w (mBH), 1803vs (mNO). dH (300 MHz; DMSO; SiMe4), 6.85–6.90 (m, Ph, 12 H), 7.25–7.35 (m, Ph and pz-CH, 5H), 7.43 (m, Ph, 10 H), 7.60 (m, Ph, 2H), 8.07 (d, J = 6.7 Hz, Ph, 4H). UV–Vis kmax(DMSO)/nm 612 (e/dm3 mol1 cm1 230). m/z (ESI) 758 [M+H]+, 745 [MNO+H2O]+, 727 [MNO]+. Magnetic moment (leff/lB, 294 K): 0.02. Anal. Calc. for C45H34N7BONi: C, 71.28; H, 4.52; N, 12.93. Found: C, 71.05; H, 4.76; N 12.74%. 2.5. Synthesis of [Ni(NO3)TpPh2] (4) Green crystals (crystallized from CH2Cl2-hexane). 38% yield. mmax(KBr)/cm1 3060w, 2980w, 2898w (mCH), 2612br (mBH), 1523 s ðmNO2 Þ, 1275s ðmNO2 Þ. dH(300 MHz; CDCl3; SiMe4), 6.81 (br s, Ph, 6H), 7.25 (br s, Ph, 9H), 7.53 (br s, Ph, 4H), 8.00 (br s, Ph, 6H), 8.67 (br s, Ph, 5H). UV–Vis kmax(CH2Cl2)/nm 420 (e/dm3 mol1 cm1 þ 230), 686 (60). m/z (ESI) 800 ½M NO3 þ H þ THF , þ 745 ½M NO3 þ H2 O . Magnetic moment (leff/lB, 294 K): 3.07. Anal. Calc. for C45H34N7BO3Ni: C, 68.39; H, 4.34; N, 12.41. Found: C, 68.42; H, 4.86; N, 12.14%. 2.6. Synthesis of [Ni(OAc)TpPh2] (5) Green-yellow crystals (crystallized from CH2Cl2-hexane). 38% yield. mmax(KBr)/cm1 3058 m, 3041 (mCH), 2648 m (mBH). dH(300 MHz; CDCl3; SiMe4), 6.76 (br s, Ph, 7H), 7.06 (br s, Ph, 8H), 7.46 (t, Ph, 5H), 7.78 (br s, Ph, 6H), 8.74 (br s, Ph, 4H). UV–Vis kmax(CH2Cl2)/nm 416 (e/dm3 mol1 cm1 270), 708 (70). m/z (ESI) 787 [M+H]+, 727 [MOAc]+. Magnetic moment (leff/lB, 294 K): 2.96. Anal. Calc. for C47H39N6BO3Ni [5 Æ (H2O)]: C, 70.09; H, 4.88; N, 10.44. Found: C, 69.70; H, 4.70; N, 10.20%. 2.7. Synthesis of [Ni(acac)TpPh2] (6) Green crystals (crystallized from CH2Cl2-hexane). 17% yield. mmax(KBr)/cm1 3062w (mCH), 2611br (mBH), 1594 s ðmCO2 Þ. dH(300 MHz; CDCl3; SiMe4), 1.66 (s, acac-Me, 6H), 3.75 (sp, acac-CH, 1H), 6.06 (br s, Ph, 8H), 6.72 (br s, Ph, 9H), 7.25 (br s, Ph, 9H), 9.03 (br s, Ph, 4H),. UV–Vis kmax(CH2Cl2)/nm 304 (e/dm3 mol1 cm1 8300), 404 (440). m/z (ESI) 827 [M+H]+, 745 [Macac+ H2O]+, 607 [MacacHpzPh2]+. Magnetic moment (leff/lB, 294 K): 2.94. Anal. Calc. for C50H41N6BO2Ni: C, 72.58; H, 4.99; N, 10.16. Found: C, 72.41; H, 5.14; N 10.24%.
D.J. Harding et al. / Inorganica Chimica Acta 360 (2007) 3335–3340
3. Results and discussion The reaction of appropriate Ni starting materials with KTpPh2 in THF yields green (X = Cl, NO3, OAc and acac), pink-purple (X = Br) or blue (X = NO) solutions. Purification by recrystallization gives highly crystalline products [NiCl(HpzPh2)TpPh2] (1) or [NiXTpPh2] (X = Br 2, NO 3, NO3 4, OAc 5 and acac 6) in moderate to good yields (Scheme 1). The solids are soluble in polar organic solvents such as, CH2Cl2 and DMSO, although complex 3 decomposes in CH2Cl2. By comparison the cobalt analogues, once crystallized, are almost insoluble [10]. In contrast to results reported by Yin et al. [11], [NiCl(HpzPh2)TpPh2], and not [NiClTpPh2], was the only product from the reaction between KTpPh2 and NiCl2. Our synthesis differs from that reported only in the method of crystallization {CH2Cl2/hexane cf. CH2Cl2:MeCN (2:1)/hexane}. It would appear that the presence of a coordinating solvent is essential to cleanly isolate [NiClTpPh2]. Although, [NiClTpPh2] may coordinate a further donor, complex 2 shows
3337
no such tendency. We hypothesize that the larger ionic radius of the bromide anion prevents coordination of additional ligands. Recently, we reported [10] the synthesis of [Co(OAc)(HpzPh2)TpPh2] from Co(OAc)2 and KTpPh2 and were therefore surprised to find that the analogous reaction with Ni(OAc)2 yielded 5 as the only product. This difference in reactivity may be due to the tendency of cobalt towards a monodentate acetate coordination mode in contrast to the bidentate coordination mode preferred by nickel [12,13]. It follows that for the cobalt metal to achieve coordination number five an additional ligand will be required, in this case by decomposition of the TpPh2 ligand. Characterization of complexes 1–6 by IR spectroscopy reveal B–H stretches between 2611 cm1 and 2648 cm1 indicative of j3 coordinated TpPh2 ligands (Table 1) [14]. This compares well with [NiClTpPh2] in which the B–H stretch is at 2612 cm1. The difference between the asymmetric and symmetric stretches of the acetate and nitrate groups is a useful probe for the coordination mode [15].
Scheme 1.
3338
D.J. Harding et al. / Inorganica Chimica Acta 360 (2007) 3335–3340
Table 1 IR and UV–Vis spectroscopic and mass spectrometric data for NiXTpPh2 complexes Complex Ph2
Ph2
[NiCl(Hpz )Tp [NiBrTpPh2] [Ni(NO)TpPh2] [Ni(NO3)TpPh2] [Ni(OAc)TpPh2] [Ni(acac)TpPh2] a b
]
Colour
% Yield
IR,amBH/cm1
green pink-purple blue green green-yellow green
44 54 24 38 39 17
2632 2626 2629 2612 2648 2611
IR,a mX=O/cm1
kmax/nm (e)
ESI MS
1803 1523, 1275 no 1593
490 318 612 420 416 304
947 745 758 800 787 827
(420), 812 (52), 922 (85) (3140), 502 (600), 828 (120), 926 (160) (230) (230), 686 (60) (270), 708 (70) (8300), 404 (440)
As KBr discs. In CH2Cl2 or DMSO see text, no = not observed, X = C or N.
For 4, the large Dm(NO2) value is consistent with a bidentate coordination mode [11,15]. Unfortunately, the asymmetric and symmetric stretches of the acetate ligand in 5 are masked by other IR bands making a determination of the coordination mode impossible. The CO stretch of the acac ligand in 6 is observed at 1593 cm1, characteristic of a chelating acac group and thus a five-coordinate nickel centre [13]. The IR spectrum of 3 also shows an NO band at 1803 cm1 exhibiting a shift of 79 cm1 to higher wavenumber compared with [NiBr(NO)(PPh3)2] and consistent with a linear nitrosyl ligand [16]. It follows that the nitrosyl ligand is best described as NO+ and consequently the metal centre is Ni(0). Interestingly, [Ni(NO)TpPh2] is isoelectronic with the previously reported carbonyl compound [Cu(CO)TpPh2]. Moreover, an analogous cyclopentadienyl Ni complex [Ni(NO)Cp] has previously been synthesized and exhibits a nitrosyl stretch at 1830 cm1 suggesting that TpPh2 is a better net donor than Cp [17]. The [NiXTpPh2] (X = Br, NO, NO3, OAc and acac) complexes and [NiCl(HpzPh2)TpPh2] are all green except for 2 which is pink-purple and 3 which is blue. The UV–Vis spectra of 1, 2 and 4–6 were recorded in CH2Cl2, while 3 was recorded in DMSO (see Table 1). The spectrum of 2 has four absorptions at 318, 502, 828 and 926 nm. The absorption at 318 nm has a large extinction coefficient (3140 M1 cm1) and by comparison with [Ni(SC6F5)TpiPr2], is tentatively assigned to a Br to Ni LMCT band [8,18]. The three absorptions at 502, 828 and 926 nm are typical of tetrahedral Ni(II) and compare well with those observed for [NiBrTp*] (kmax = 500, 810 and 894 nm) [19]. The spectrum of 1 resembles that of 2 indicating dissociation of the HpzPh2 ligand in CH2Cl2 to give tetrahedral [NiClTpPh2]. Similar observations have been made for [CoCl(HpzPh,Me)TpPh,Me] [20]. Uniquely the UV–Vis spectrum of the nitrosyl complex, 3 reveals a single broad band centred at 612 nm. The UV– Vis spectra of [NiXTpPh2] (NO3, OAc and acac) have a principle absorption between 404–420 nm, and in the case of 4 and 5 a further absorption at 686 nm and 708 nm respectively. The spectra are characteristic of five coordinate Ni(II) complexes and closely resemble those of the related complexes [Ni(NO3)TpMe3] and [Ni(OAc)TpR] (R = Me3; Me2 and Me2,Br) which exhibit two absorptions at between 413–442 and 676–682 nm [12]. In addition, to these metal centred absorptions complex 6 has a further band at 304 nm due to a ligand centred p to p* transition.
As with the related TpiPr2 complexes, the [NiXTpPh2] (X = Br, NO3, OAc and acac) complexes and [NiCl(HpzPh2)TpPh2] appear paramagnetic as evidenced by their NMR spectra [9]. The 1H NMR spectra of 1, 2 and 4–6 are relatively broad providing little or no structural information. Furthermore, despite repeated attempts we were unable to locate the pyrazole-CH and the acetate protons of 5, presumably due to broadening. Similar observations have been noted by Akita et al. [12] and Kitajima et al. [21]. The spectrum of 2 exhibits three resonances and closely resembles that of [NiClTpPh2] [11]. The NMR spectrum of 1 is markedly different from 2 and the previously reported [NiClTpPh2] confirming the presence of pyrazole. The spectra of 4 and 5 show five resonances consistent with their lower symmetry compared with 2. As expected, the spectrum of 6 shows four resonances in the aromatic region and two further peaks for the methine and methyl protons of the acac ligand. In contrast to other members in this series, the 1H NMR spectrum of [Ni(NO)TpPh2] reveals sharp resonances a doublet at 8.04 ppm and four multiplets between 7.60 and 6.90 ppm for the aromatic phenyl and pyrazole-CH protons. The significantly better resolution of the spectrum clearly suggests a diamagnetic Ni metal complex supporting earlier conclusions based upon IR spectroscopy. The NMR spectra of 1, 2 and 4–6 indicate that all the complexes are paramagnetic and this is confirmed by magnetic susceptibility measurements, which are consistent with paramagnetic species containing two unpaired electrons [16]. However, the nitrosyl complex, 3, exhibits a magnetic susceptibility close to zero consistent with a Ni(0) metal centre. Crystals suitable for an X-ray diffraction study were obtained by allowing n-hexane to diffuse into a concentrated solution of 5 in CH2Cl2. The structure of 5 is shown in Fig. 1 with bond lengths and angles given in Table 2. The compound crystallizes in a trigonal space group with two disordered water molecules per unit cell. The X-ray structure of 5 represents the first structurally characterized NiTpR acetate compound with a sterically hindered Tp ligand. The TpPh2 ligand is j3 coordinated with the phenyl rings arranged in a propeller-like conformation [22]. As such, the phenyl and pyrazolyl rings of the TpPh2 are not co-planar. The Ni–Npz bond lengths are typical for nickel ˚ for 5) [23]. Moreover, the complex TpR complexes (2.036 A
D.J. Harding et al. / Inorganica Chimica Acta 360 (2007) 3335–3340
3339
Table 3 Crystallographic data for 5 Complex
5
C47H39BN6NiO3 821.36 trigonal p3 12.8805(11) 12.8805(11) 13.799(2) 90 90 120 1982.6(4) 2 1.429 0.550 150(2) 3044 2345(0.0489) 0.0804, 0.2698 0.1020, 0.3026 hP i1=2 P P P 2 R1 ¼ jjF o j jF c jj= jF o j; wR2 . wðF 2o F 2c Þ = wðF 2o Þ2
Chemical formula Mr Crystal system Space group ˚) a (A ˚) b (A ˚) c (A a () b () c () ˚ 3) V (A Z Dc (g cm3) l(Mo Ka) (mm1) T (K) Reflections collected Independent reflections (Rint) R1, wR2 [I > 2r(I)]a R1, wR2 (all data) a
Fig. 1. The molecular structure of [Tpph2Ni(OAc)] 5. Ellipsoids are drawn at the 50% probability level and hydrogen atoms have been omitted for clarity.
Table 2 Selected bond lengths and angles of 5 ˚) Complex Bond lengths (A 5
Ni–O(1) Ni–N(1) O(1)–C(16) O(1A)–C(16) O(1B)–C(16) C(16)–C(17) Ni C(16)
2.036(3) 2.041(5) 1.281(7) 1.281(7) 1.281(7) 1.456(13) 2.364(11)
Bond angles () O(1)–Ni–O(1A) O(1)–Ni–N(1) O(1A)–Ni–N(1) O(1B)–Ni–N(1) N(1)–Ni–N(1A) Ni–O(1)–C(16)
55.9(2) 107.71(17) 100.46(16) 155.59(18) 92.31(12) 87.6(5)
exhibits Npz–Ni–Npz angles close to 90 as observed in other NiTpR complexes [23]. The presence of a crystallographically imposed C3 axis makes it appear that there are three acetate oxygen atoms (see Fig. 1). Despite this the acetate ligand is still best thought of as a j2 coordinated ˚ ) is similar ligand. The nickel-acetate bond length (2.041 A to the short Ni–O bond observed in [Ni(OAc)Tp*] ˚ , 2.131 A ˚ ) [12] but in contrast, to the structure of (2.014 A [Ni(OAc)Tp*] the acetate ligand of 5 is symmetrically coordinated. Similar symmetrically coordinated bidentate O-donor ligands have previously been reported in [NiTptBu(NO3)] [24] and [{NiTpiPr2}2(l-j2:j2-CO3)] [25]. The symmetric coordination of the acetate ligand should result in complete delocalization of the p electrons over the O–C–O linkage and thus identical C16–O1, C16–O1A and C16–O2A bond lengths, as indeed is observed (see Table 2). Interestingly, the bite angle of the acetate ligand is far smaller than that observed in [Ni(OAc)Tp*] (55.9 cf. 60.5) (see Table 3).
4. Conclusions In summary, the first tris(pyrazolyl)borate nickel nitrosyl complex and a range of other half-sandwich Ni complexes supported by the TpPh2 ligand have been synthesized and characterized. The nitrosyl ligand exhibits a linear coordination mode as evidenced by IR spectroscopy. The complexes have been shown to be four or fivecoordinate in solution depending on the nature of the anion. A solid state structure of the acetate complex as determined by X-ray crystallography reveals a distorted trigonal bipyramidal nickel centre. The use of tris(3,5-diphenylpyrazolyl)borate in the preparation of other first-row transition metal complexes is currently under way in these laboratories. Acknowledgements We gratefully acknowledge the Thailand Research Fund (MRG4680139) for financial support of this research. Assoc. Prof. Dr. Sujittra Youngme (Khon Kaen University) is thanked for magnetic susceptibility measurements. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at doi:10.1016/ j.ica.2007.03.046. References [1] (a) S. Trofimenko, Scorpionates: The Coordination Chemistry of Polypyrazolylborate Ligands, Imperial College Press, London, 1999; (b) S. Trofimenko, Chem. Rev. 93 (1993) 943.
3340
D.J. Harding et al. / Inorganica Chimica Acta 360 (2007) 3335–3340
[2] (a) S. Trofimenko, J.C. Calabrese, P.J. Domaille, J.S. Thompson, Inorg. Chem. 26 (1987) 1507; (b) S. Trofimenko, J.C. Calabrese, J.S. Thompson, Inorg. Chem. 28 (1989) 1091. [3] See for example: (a) O.M. Reinaud, A.L. Rheingold, K.H. Theopold, Inorg. Chem. 33 (1994) 2306; (b) J.C. Calabrese, S. Trofimenko, Inorg. Chem. 31 (1992) 4810; (c) A. Looney, G. Parkin, Polyhedron 9 (1990) 265. [4] C. Pattinari, C. Santini, Comprehensive Coordination Chemistry II, vol. 1, Elsevier, New York, 2004, pp. 159–210. [5] (a) F.A. Kunrath, R.F. de Souza, O.L. Casagrande Jr., N.R. Brooks, V.G. Young Jr., Organometallics 22 (2003) 4739; (b) R. Santi, A.M. Ramano, A. Sommazzi, M. Grande, C. Bianchini, G. Mantovani, J. Mol. Catal. 229 (2005) 191. [6] (a) Y.-J. Sun, P. Cheng, S.-P. Yan, Z.-H. Jiang, D.-Z. Liao, P.-W. Shen, Inorg. Chem. Commun. 3 (2000) 289; (b) Y.-J. Sun, W.-Z. Shen, P. Cheng, S.-P. Yan, D.-Z. Liao, Z.-H. Jiang, P.-W. Shen, Polyhedron 23 (2004) 211. [7] A.S. Yakovenko, S.V. Kolotilov, A.W. Addison, S. Trofimenko, G.P.A. Yap, V. Lopushanskaya, V.V. Pavlishchuk, Inorg. Chem. Commun. 8 (2005) 932. [8] Y. Matsunaga, K. Fujisawa, N. Ibi, Y. Miyashita, K. Okamoto, Inorg. Chem. 44 (2005) 325. [9] Examples of NiTpiPr2: (a) S. Hikichi, M. Yoshizawa, Y. Sasakura, H. Komatsuzaki, Y. Moro-oka, M. Akita, Chem. Eur. J. 7 (2001) 5011; (b) K. Uehara, S. Hikichi, M. Akita, J. Chem. Soc., Dalton Trans. (2002) 3529; (c) M. Kujime, S. Hikichi, M. Akita, J. Chem. Soc., Dalton Trans. (2003) 3506; (d) M. Akita, J. Organomet. Chem. 689 (2004) 4540, and references therein. [10] D.J. Harding, H. Adams, T. Tuntulani, Acta Cryst., Sec. C C61 (2005) m301. [11] S. Guo, E. Ding, Y. Yin, K. Yu, Polyhedron 17 (1998) 3841. [12] S. Hikichi, Y. Sasakura, M. Yoshizawa, Y. Ohzu, Y. Moro-oka, M. Akita, Bull. Chem. Soc. Jpn. 75 (2002) 1255. [13] A. Kremer-Aach, W. Kla¨ui, R. Bell, A. Strerath, H. Wunderlich, D. Mootz, Inorg. Chem. 36 (1997) 1552.
[14] M. Akita, K. Ohta, Y. Yakamashi, S. Hikichi, Y. Moro-oka, Organometallics 16 (1997) 4121. [15] K. Nakamoto, in: Infrared and Raman Spectra of Inorganic and Coordination Compounds, fourth ed., Wiley, New York, 1986, pp. 257–285. [16] F.A. Cotton, G. Wilkinson, C.A. Murillo, M. Bochmann, Advanced Inorganic Chemistry, sixth ed., Wiley, New York, 1999. [17] Ch. Elschenbroich, A. Salzer, Organometallics, second ed., VCH Publishers Inc., New York, 1992. [18] S.I. Gorelsky, L. Basumallick, J. Vura-Weis, R. Sarangi, K.O. Hodgson, B. Hedman, K. Fujisawa, E.I. Solomon, Inorg. Chem. 44 (2005) 4947. [19] P.J. Desrochers, S. LeLievre, R.J. Johnson, B.T. Lamb, A.L. Phelps, A.W. Cordes, W. Gu, S.P. Cramer, Inorg. Chem. 42 (2003) 7945. [20] S.V. Kolotilov, A.W. Addison, S. Trofimenko, W. Dougherty, V.V. Pavlishchuk, Inorg. Chem. Commun. 7 (2004) 485. [21] N. Kitajima, K. Fujisawa, C. Fujimoto, Y. Moro-oka, S. Hashimoto, T. Kitagawa, K. Toriumi, K. Tatsumi, A. Nakamura, J. Am. Chem. Soc. 114 (1992) 1277. [22] A.L. Rheingold, L.M. Liable-Sands, S. Trofimenko, Inorg. Chem. 40 (2001) 5609. [23] Examples of NiTpR complexes include: (a) P.J. Desrochers, R.W. Cutts, P.K. Rice, M.L. Golden, J.B. Graham, T.M. Barclay, A.W. Cordes, Inorg. Chem. 38 (1999) 5690; (b) S. Trofimenko, J.C. Calabrese, J.K. Kochi, S. Wolowiec, F.B. Hulsbergen, J. Reedijk, Inorg. Chem. 31 (1992) 3943; (c) S. Hikichi, M. Yoshizawa, Y. Sasakura, M. Akita, Y. Moro-oka, J. Am. Chem. Soc. 120 (1998) 10567; (d) G. Bandoli, D.A. Clemente, G. Paolucci, L. Doretti, Cryst. Struct. Commun. 8 (1979) 965. [24] A. Looney, R. Han, K. McNeill, G. Parkin, J. Am. Chem. Soc. 113 (1991) 9707. [25] N. Kitajima, S. Hikichi, M. Tanaka, Y. Moro-oka, J. Am. Chem. Soc. 115 (1993) 5496. [26] A.W.G. Platt, J.F. Gibson, in: J.D. Woolins (Ed.), Inorganic Experiments, second ed., Wiley–VCH Verlag GmbH & Co., Weinheim, 2003, pp. 127–129.