- Email: [email protected]
Synthesis of tetrakis(alkylisocyanide)bis(triphenylstibine)cobalt(II) and tetrakis(alkylisocyanide)bis(triphenylstibine oxide)cobalt(III) complexes: ligand substitution and oxidation in pentakis(alkylisocyanide)cobalt(II)
Inorganica Chimica Acta 334 (2002) 327 /333 www.elsevier.com/locate/ica
Synthesis of tetrakis(alkylisocyanide)bis(triphenylstibine)cobalt(II) and tetrakis(alkylisocyanide)bis(triphenylstibine oxide)cobalt(III) complexes: ligand substitution and oxidation in pentakis(alkylisocyanide)cobalt(II) Clifford A.L. Becker *, Galaletsang S. Sebobi, Ntshekelang Tostic Simane Department of Chemistry, University of Botswana, P/Bag 0022, Gaborone, Botswana Received 16 October 2001; accepted 13 February 2002
Abstract The complexes, [Co(CNC4H9-n )4(SbPh3)2](ClO4)2, [Co(CNC6H11)4(SbPh3)2](ClO4)2, [Co(CNC6H11)4(OSbPh3)2](ClO4)3, and [Co(CNCH2Ph)4(OSbPh3)2](BF4)3, have been synthesized by reaction of excess SbPh3 with the Co(II) /alkylisocyanide salts. With CNC6H11, the Co(II) complex can be isolated, continued reaction in solution producing the Co(IIl) complex. With CNCH2Ph, reaction proceeds more rapidly through a Co(II) complex directly to the Co(III) complex isolated. With CNC4H9-n , only the Co(II) complex is observed; attempted further reaction causes decomposition to OSbPh3. Characterization of the complexes is primarily in the solid state due to limited stability in solution. Coordination stereochemistries for both Co(II) and Co(III) complexes appear to be trans -substituted octahedral. Magnetic moments for [Co(CNC4H9-n )4(SbPh3)2](ClO4)2 and [Co(CNC6H11)4(SbPh3)2](ClO4)2 are low-spin (meff /1.94 BM, 2.27 BM, respectively), as expected, while [Co(CNCH2Ph)4(OSbPh3)2](BF4)3 and [Co(CNC6H11)4(OSbPh3)2](C1O4)3 are intermediate-spin (meff /3.30, 3.70 BM, respectively), as expected. Six-coordinate Co(III) complexes, in which both Co(II) and SbPh3 have been oxidized in the reaction, appear to be favored over the six-coordinate Co(II) complexes. Reactions of SbPh3 with pentakis (alkylisocyanide)cobalt(II) complexes are thus drastically different from reactions with PPh3 and even AsPh3. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Alkylisocyanide; Triphenylstibine; Triphenylstibine oxide; Cobalt(II) complexes; Cobalt(III) complexes; Ligand-substitution reactions
1. Introduction Triarylphosphine reactions with alkylisocyanide /cobalt(II) complexes are characterized by reduction/ligand-substitution reactions. The reactions of [Co(CNCMe3)4H2O](ClO4)2 and [Co2(CNCHMe2)10](ClO4)4 ×/5H2O with excess triarylphosphines have produced the disubstituted Co(I) complexes, [Co(CNR)3(PR3?)2]ClO4, in good yields [1,2]. The [Co(CNR)3(PR3?)2]X, X /ClO4, BF4, complexes have also been prepared with the CNC6H11, CNCH2Ph, and CNC4H9n ligands in analogous reactions [3]. A Co(II) complex, [Co(CNCHMe2)3{P(C6H4OMe-p )3}2](ClO4)2, was recovered in one instance, but this was only as a minor
* Corresponding author. Tel.: /267-355 2482; fax: /267-355 2836. E-mail address: [email protected] (C.A.L. Becker).
product and under restricted reaction conditions [4]. Five-coordinate Co(II) complexes with alkylisocyanide and triarylphosphine ligands, [Co(CNR)3(PR3?)2]X2, X /ClO4, BF4, have been synthesized by ligand-substitution reactions in [Co(CNR)4(AsR3?)2]X2 complexes and by AgClO4/AgBF4 oxidation of the [Co(CNR)3(PR3?)2]X complexes [5,6], but these reactions are not the characteristic reaction for alkylisocyanide /Co(II) complexes with triarylphosphine ligands. A six-coordinate Co(II) complex with alkylisocyanide and triarylphosphine ligands, [Co(CNC6H11)4(PPh3)2](ClO4)2, has even been recovered [7], but it has limited stability. Triarylarsine reactions with alkylisocyanide /cobalt(II) complexes are characterized by ligand-substitution of only one alkylisocyanide ligand and increase of the coordination number, resulting in six-coordinate Co(II) complexes, trans -[Co(CNR)4(AsR3?)2](ClO4)2, CNR / CNC6H11, CNCHMe2, CNCH2Ph, CNC4H9-n (but
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 0 8 5 8 - 7
328
C.A.L. Becker et al. / Inorganica Chimica Acta 334 (2002) 327 /333
not CNCMe3), AsR3? /AsPh3, As(C6H4Me-p)3, Ph2AsCH2CH2AsPh2 [8,9]. These complexes are prone to ligand-oxidation in solution [9,10] and solid state [9], leading to the tetrahedral Co(II) complexes, [Co(OAsR3?)4]X2, R?/Ph, C6H4Me-p; X /ClO4, BF4; and in one instance both ligand and Co(II) oxidation is observed, resulting in the Co(III) complex, [Co(CNCH2Ph)4{OAs(C6H4Me-p )3}2](BF4)3 [11], but no indication of Co(II) reduction to Co(I) was observed in any of these reactions. Preliminary investigation [12] indicated that both Co(II) complexes, [Co(CNR)4(SbPh3)2](ClO4)2, and Co(III) complexes, [Co(CNR)4(OSbPh3)2](ClO4)3, can be formed in triphenylstibine reactions with alkylisocyanide /cobalt(II) complexes. This present work investigates these SbPh3 reactions. What is especially significant in this study is the systematic changes in reaction observed for the group V donor-atoms in the homologous series of ligands, PPh3, AsPh3, and SbPh3.
2. Experimental 2.1. Materials and measurements Commercially available alkylisocyanides, CNC6H11, CNCHMe2, CNC4H9-n, CNCMe3, and CNCH2Ph (Strem Chemicals, Fluka and Aldrich), were used without re-distillation. [Co(CNCMe3)4H2O](C1O4)2, [Co2(CNCHMe2)10](ClO4)4 ×/5H2O, and [Co2(CNCH2Ph)10](BF4)4 ×/H2O were synthesized as previously reported [1,11,13]. Commercially available triphenylstibine (Fluka) was used without recrystallization. Co(ClO4)2 ×/ 6H2O and Co(BF4)2 ×/6H2O were obtained from Strem Chemicals. Anhydrous diethyl ether was filtered through an alumina column before use. IR spectra were recorded on a Perkin /Elmer 2000 FT-IR spectrophotometer in Nujol mull or solution using a single NaCl cell. Solution electronic spectra were recorded on a Shimadzu UV-2501PC spectrometer over the range 1100/200 nm. Diffuse reflectance spectra of solid samples were measured using an integrating sphere (model ISR-240A) over the range 800 /240 nm. Magnetic susceptibilities were measured at room temperature (r.t.) using a Johnson Matthey Alfa magnetic susceptibility balance. Effective magnetic moments were calculated assuming Curie’s law behavior. C, H and N elemental analyses were performed using a Carlo Erba CHN-O/S elemental analyzer, model 1106. Some of the complexes reported in this paper have been prepared as perchlorate salts, because Co(II) / alkylisocyanide complexes of CNC6H11 and CNC4H9n (as well as CNCHMe2, CNCMe3, and CNCMe2CH2CMe3) crystallize better with the ClO4 anion than the BF4 (while CNCH2Ph complexes crystallize better as BF4 salts). Although the complexes reported in this
paper have shown no explosive tendency, all perchlorate salts must be considered as potentially explosive. Please see the author’s comments regarding the use of perchlorate salts in Ref. [5]. 2.2. Synthesis of [Co(CNC4H9-n )4(SbPh3)2](ClO4)2 Co(ClO4)2 ×/6H2O (522 mg, 1.43 mmol), dissolved in EtOH (3.0 ml) and filtered through cotton with EtOH (0.5 ml) rinse, was chilled in ice. CNC4H9-n (593 mg, 7.13 mmol, neat; 5:1 RNC:Co mol ratio) was then added dropwise, with EtOH (0.5 ml) rinse, while the Co(II) solution was stirred at 0 8C. Solution color changed from pink to dark blue during ligand addition, with a mixture of suspended maroon solid and dark blue tar. SbPh3 (1.259 g, 3.566 mmol; 2.5:1 Sb:Co mol ratio), dissolved in CH2Cl2 (1.0 ml) and filtered through cotton, was added dropwise while the reaction mixture continued being stirred at 0 8C. The solution became dark green in color, with the formation of a solid. The mixture was filtered cold, and the product was washed twice with 2.5 ml portions of diethyl ether. Addition of 10.0 ml of diethyl ether to the filtrate and extensive chilling produced only a red/brown tar. Yield of dark green to yellow /green microcrystalline product: 1.403 g, 76%. Anal . Found: C, 51.90; H, 5.12; N, 4.26. Calc. for CoC56H66Cl2N4O8Sb2 [fw /1296.5 g mol1]: C, 51.88; H, 5.13; N, 4.32%. Solid state: m.p. 156/164 8C (dec.). IR: n(/N/C), 2221 vs, :/2190 br(sh) cm 1 (Nujol). Electronic spectrum: :/765 w(sh) (A /1.197), 610 (1.447), /436(1.864), /337 (1.986) nm. Magnetic susceptibility: xg /7629/15/109 (cgs), meff /1.949/0.02 BM. Solution: IR, n(/N/C), 2240 vs, :/2220 w(sh), 2156 m, 2135 m cm 1 (CH2Cl2); 2243 vs, :/2224 w(sh), 2156 m, 2136 m cm 1 (CH3NO2); 2241 vs, :/2228 m(sh), /2135 vw cm 1 (CF3CH2OH). Electronic spectra: 759 (o /180), /480 sh (160), 398 (765), :/275 w(sh) (1800), 256 (26 000), 229 (48 000) nm (CH2Cl2); 730 br (o /150), /252 br (22 000), /230 br (23 000) nm (CH3CN); 870 br (o /180), :/470 sh (490), 340 (3900), :/265 sh (6500), /250 sh (8400), 226 (19 400) nm (CF3CH2OH). 2.3. Synthesis of [Co(CNCH2Ph)4(OSbPh3)2](BF4)3 [Co2(CNCH2Ph)10](BF4)4 ×/H2O (750 mg, 0.453 mmol), dissolved in CH2C12 (5.0 ml), was filtered through cotton and chilled in ice. SbPh3 (800 mg, 2.27 mmol, neat; 2.5:1 Sb:Co mole ratio) was then added, small spatula-fulls at a time, with stirring. No color change in the dark yellow /brown solution was observed. The reaction mixture was allowed to stand at r.t. for 15 min., after which it was filtered through cotton, using 0.5 ml of CH2Cl2 as rinse. Dropwise addition of 1.5 ml of diethyl ether effected initial precipitation of a
C.A.L. Becker et al. / Inorganica Chimica Acta 334 (2002) 327 /333
golden yellow solid. A total volume of 5.0 ml of diethyl ether was added, and the solution was chilled in ice for 30 min. The yellow solid was filtered and washed twice with 1.5 ml portions of diethyl ether, but a greenish tint remained. The filtrate became dark green in color, and addition of excess diethyl ether and overnight refrigeration produced only a dark green tar. The crude product (346 mg) was dissolved in CH2Cl2 (18.0 ml), filtered through cotton using CH2Cl2 (0.5 ml) as rinse, and precipitated by dropwise addition of diethyl ether (20.0 ml) (initial precipitation, as a fine suspension, commenced after addition of 2.0 ml of diethyl ether). After chilling in ice for 20 min, the pale lemon-yellow microcrystalline product was filtered and washed twice with 1.5 ml portions of diethyl ether. Yield: 290 mg, 84% recovery, 21% overall yield. Anal . Found: C, 53.79; H, 3.85; N, 3.61. Calc. for CoC68H58B3F12N4O2Sb2 [fw / 1526.1 g mol 1]: C, 53.52; H, 3.83; N, 3.67%. Solid state: m.p. l85 /190 8C (dec.). IR: n (/N/C), 2243 vs, /2210 vw(sh) cm 1 (Nujol). Electronic spectrum: :/460 sh (A $/0.95), /335 br (1.76), :/270 sh (1.64) nm. Magnetic susceptibility: xg /2.629/0.15 / l0 6 (cgs), meff /3.309/0.08 BM. Solution: IR, n (/N/ C), 2240 m, 2173 s, 2136 vs cm 1 (CH2Cl2); 2243 vs (CH3NO2); 2236 vs, :/2215 vw(sh) cm 1 (CF3CH2OH). Electronic spectra: :/850 br (o /40), 403 (33 000), /244 sh (27 000), 232 sp (32 000) nm (CH2Cl2); 700 (o /75), :/390 vw(sh) (135), :/310w(sh) (680), :/275 sh (10 000), 256 (21 000), /222 sh (68 000) nm (CH3CN); /850 br (o /65), 340 (4200), :/265 sh (8000), /258 sh (9400), 254 (9600), 219 (44 000) nm (CF3CH2OH).
2.4. Synthesis of [Co(CNC6H11)4(OSbPh3)2](ClO4)3 [Co(CNC6H11)4(SbPh3)2](ClO4)2 (950 mg, 0.678 mmol) was dissolved in CH2Cl2 (4.0 ml), filtered through cotton, and rinsed with CH2Cl2 (1.0 ml). Working at 25 /28 8C, dropwise addition of 3.0 ml of diethyl ether effected initial precipitation of a greenishyellow solid. A total volume of 10.0 ml of diethyl ether was added, and the reaction mixture was chilled in ice for 20 min. The yellow solid was filtered and washed twice with 1.5 ml portions of diethyl ether. This product (391 mg) was dissolved in CH2Cl2 (8.0 ml) and filtered through cotton with CH2Cl2 (0.5 ml) rinse. Precipitation was achieved by dropwise addition of diethyl ether; initial precipitation commenced after addition of 4.0 ml, and a total of 12.0 ml was added. After chilling in ice for 20 min, the bright yellow microcrystalline product was filtered and washed twice with 1.5 ml portions of diethyl ether. Yield: 300 mg, 77% recovery, 29% overall yield (based on Co). Anal . Found: C, 49.89; H, 4.90; N, 3.66. Calc. for CoC64H74Cl3Cl3N4O14Sb2 [fw /1532.11 g mol 1]: C, 50.17; H, 4.87; N, 3.66%.
329
Solid state: m.p. 178/182 8C (dec.). IR: n(/N/C), 2229 vs cm 1 (Nujol). Electronic spectrum: /640 (A / 0.285), :/600 sh (0.272), /425 br (1.575), /358 br (1.736), :/272 sh (1.636) nm. Magnetic susceptibility: xg /3.389/0.04 /106 (cgs), meff /3.709/0.03 BM. Solution: IR, n(/N/C), 2231 vs (CH2Cl2); 2231 vs, :/2140 br (CH3NO2); 2229 vs, /2208 w(sh) cm 1 (CF3CH2OH). Electronic spectra: :/650 vw(sh) (o / 130), 404 (27 000), /285 sh (7500), :/243 w(sh) (24 000), 228 (62 000) nm (CH2Cl2); 715 br (o /100), :/340 w(sh) (420), :/275 sh (12 000), 253 (22 000), :/ 223 sh (71 000) nm (CH3CN); :/525 sh (o :/100), 405 (1260), 341 (780), 218 (5100) nm (CF3CH2OH).
2.5. Alternate synthesis of [Co(CNC6H11)4(SbPh3)2](ClO4)2 Co(ClO4)2 ×/6H2O (916 mg, 2.50 mmol) was dissolved in EtOH (4.0 ml), filtered through cotton with EtOH (0.5 ml) rinse, and chilled in ice for 5 min. CNC6H11 (1.095 g, 10.0 mmol, neat; 4:1 RNC:Co mol ratio) was then added dropwise to the stirred Co(II) solution in an ice bath. The reaction mixture changed color from pink to dark blue immediately upon addition of CNC6H11 but no solid precipitated. SbPh3 (1.949 g, 5.52 mmol; 2.2:1 Sb:Co mol ratio), dissolved in CH2Cl2 (3.0 ml) and filtered through cotton, was then added dropwise to the stirred Co(II) solution in an ice bath. The reaction mixture changed color from dark blue to dark green, with precipitation of a solid, during addition of the SbPh3 solution. Diethyl ether (12.0 ml) was added in small aliquots, to increase precipitation, and the dark yellow-green microcrystalline product was filtered without additional chilling in ice and washed twice with 2.0 ml portions of diethyl ether. Yield: 2.803 g, 80%. Anal . Found: C, 54.85; H, 5.32; N, 3.98. Calc. for CoC64H74Cl2N4O8Sb2 [fw /1400.66 g mol1]: C, 54.88; H, 5.33; N, 4.00%. Solid state: m.p. 167/173 8C (dec.). IR: n(/N/C), 2207 vs, /2168 vw(sh) cm 1 (Nujol). Electronic spectrum: 765 w (A /0.92), 590 (1.03), /415 sh (1.79), /375 sh (1.86), 346 (1.97), 274 (1.75) nm. Magnetic susceptibility: xg /1.099/0.07 /106 (cgs), meff /2.279/0.06 BM. Solution: IR, n( /N /C), 2228 vs, /2202 m(sh) cm 1 (CH2Cl2); 2231 vs, /2141 m(sh), /2125 m(sh) cm1 (CH3NO2); /2229 m(sh), 2215 vs, :/2204 w(sh), /2144 m(sh), 2131 m cm 1 (CF3CH2OH). Electronic spectra: 737 (o /140), 400 (460), /320 sh (830), :/276 w(sh) (18 000), 257 (30 000), 228 (50 000) nm (CH2Cl2); 721 (o /85), :/ 420 vw(sh) (70), :/265 sh (17 000), 253 (23 000), :/220 sh (54 000), 210 (69 500) nm (CH3CN); /880(o /170), :/470 sh(400), 343 (2500), /314 sh(2300), /253 (9200)nm (CF3CH2OH).
330
C.A.L. Becker et al. / Inorganica Chimica Acta 334 (2002) 327 /333
3. Results and discussion 3.1. Synthesis of the complexes Reactions of alkylisocyanide /Co(II) complexes (pentakis (alkylisocyanide)cobalt(II) in solution), with triphenylstibine produce both tetrakis (alkylisocyanide)bis (triphenyl-stibine)cobalt(II), [Co(CNR)4(SbPh3)2]X2, and tetrakis (alkylisocyanide)bis (triphenylstibine oxide)cobalt(III), [Co(CNR)4(OSbPh3)2]X3, X /ClO4, BF4; depending on the reaction conditions and the particular alkylisocyanide, 2SbPh3
[Co(CNR)5 ]2 0 [Co(CNR)4 (SbPh3 )2 ]2
Continued
0 [Co(CNR)4 (OSbPh3 )2 ]3
reaction
If the product can be isolated rapidly (synthesis of [Co(CNC4H9-n)4(SbPh3)2](ClO4)2), a Co(II) product is obtained. If the Co(II) complex remains in solution for a longer time period (the synthesis of [Co(CNCH2Ph)4(OSbPh3)2](BF4)3 and the recrystallization of [Co(CNC6H11)4(SbPh3)2](ClO4)2), however, reaction may proceed to a Co(III) complex. Only with the CNC6H11 ligand have both complexes been isolated in the pure state. With CNCH2Ph reaction proceeds through an apparent Co(II) complex to the Co(III) complex, while with CNC4H9-n the Co(II) complex decomposes upon continued reaction. With CNCHMe2 a mixture of apparent Co(II) and Co(III) complexes, with unreacted Co(II) starting material, was obtained. Reactions of [Co(CNC6H11)5]2 in EtOH with SbPh3 have not always been reproducible. In some instances, the reaction was analogous to that reported for CNC4H9-n. Then pure [Co(CNC6H11)4(SbPh3)2](ClO4)2 was obtained. In other instances the Co(II) product did not precipitate during SbPh3 addition, but required addition of diethyl ether and vigorous trituration of the solution to induce precipitation. In extreme cases the product first separated as a dark green tar which could be converted to crystalline material within 8/10 min of trituration. Here, the product was contaminated with the Co(III) complex. Better results were obtained with the alternate synthesis reported, in which a deficiency of CNC6H11 was added (4.0 mol ratio, instead of the stoichiometric 5.0 needed for complete conversion to [Co(CNR)5]2) so upon reaction with SbPh3 there was less free CNC6H11. Then [Co(CNC6H11)4(SbPh3)2](ClO4)2 precipitates more easily. Synthesis of [Co(CNC4H9-n)4(SbPh3)2](ClO4)2 was straightforward, but recrystallization from CH2Cl2 or continued reaction in EtOH leads to yellow /brown solutions from which only free OSbPh3 slowly precipitates after addition of diethyl ether and prolonged refrigeration, suggesting decomposition of any Co(III) complex that may have been formed in solution.
In the synthesis of [Co(CNCH2Ph)4(OSbPh3)2](BF4)3 there is evidence for the presence of a Co(II) complex, presumably formed as a precursor for the Co(III) complex. IR spectra taken on crude Co(III) samples revealed additional (unresolved) absorption at /2220 cm 1, suggesting a Co(II) minor product subsequently removed in recrystallization. Since precipitation from CH2Cl2 by addition of diethyl ether is a slower process than direct crystallization from EtOH, this synthesis would allow a Co(II) complex initially formed to react further to the Co(III) complex before isolation is achieved. Synthesis of [Co(CNC6H11)4(OSbPh3)2](ClO4)3 through double recrystallization of [Co(CNC6H11)4(SbPh3)2](ClO4)2 from CH2Cl2/diethyl ether illustrates that Co(II) and SbPh3 are oxidized when the Co(II) complex is allowed to remain in solution for a relatively short time period. The mechanism is not presently understood. IR spectra taken after one recrystallization show a weak shoulder /2210 cm 1, suggesting the presence of some Co(II) remaining unoxidized. If the Co(III) complex is left in solution for a more extended period of time, there is decomposition to a dark brownish-yellow solution with finely-divided OSbPh3 slowly precipitating. Similar behavior is seen with [Co(CNCH2Ph)4(OSbPh3)2](BF4)3. Reaction of SbPh3 with [Co2(CNCHMe2)10](ClO4)4 ×/ 5H2O in CH2Cl2 failed to produce a pure complex, but rather a mixture of complexes. Initial reaction produced a maroon-red solid, a yellow solid, and a dark green tar, which upon prolonged refrigeration converted into massive green crystals mixed with a microcrystalline yellow powder. IR spectra of crudely-separated crystals suggested the green compound could be a Co(II) complex (n(/N/C) /2206 cm 1) and the yellow compound could be Co(III) (n(/N/C) /2222 cm 1), but separation was incomplete, and attempted fractional recrystallization failed. The maroon-red compound could have been [Co2(CNCHMe2)10](ClO4)4 ×/5H2O [13] that reacted slowly in the freezer. Reactions with CNCHMe2 thus appear most similar to those with CNC6H11 in that both Co(II) and Co(III) complexes are observed, although reaction is apparently slower. Decreased reaction rate is possibly due to steric hindrance in CNCHMe2, since reaction with the CNCMe3 ligand (i.e. with [Co(CNCMe3)4H2O](ClO4)2) is not observed with AsPh3 or SbPh3. 3.2. Characterization of the complexes Solution IR and electronic spectra for these new complexes have been included for their routine basic characterization, but structural interpretation will be based primarily on solid state measurements, due to the limited stabilities in solution. The n (/N/C) IR patterns for [Co(CNC4H9-n )4(SbPh3)2](ClO4)2 and [Co(CNCH2-
C.A.L. Becker et al. / Inorganica Chimica Acta 334 (2002) 327 /333
Fig. 1. The n ( /N/C) IR pattern for [Co(CNC4H9n )4(SbPh3)2](ClO4)2 (top) and [Co(CNCH2Ph)4(OSbPh3)2](BF4)3 (bottom) in Nujol mull.
Ph)4(OSbPh3)23(BF4)3 in Nujol are pictured in Fig. 1; other data have been included with the syntheses. 3.2.1. IR spectra The n (/N /C) IR patterns for the Co(II) and Co(III) complexes in the solid state are compatible with tetragonal coordination; i.e. trans -[Co(CNR)4(SbPh3)2](ClO4)2 and trans -[Co(CNR)4(OSbPh3)2]X3. This pattern of one strong band with a lower-energy (unresolved) shoulder is typical of tetragonal complexes with known or assumed square /planar arrangement of four organoisocyanide ligands around Co(II) [7 /9,14 / 18]. Rigorous D4h symmetry for the Co(CNR)4 unit would require a single (strong) n (/N /C) (Eu), so the weak shoulder suggests slight distortion in the solid state. Distorted structures have been confirmed in X-ray analyses [16,19]. The n( /N /C) IR pattern for the Co(III) complexes is analogous to that seen for [Co(CNCH2Ph)4{OAs(C6H4Me-p )3}2](BF4)3 [11] and for the [Co(CNR)4(PR3)2]X3complexes [2,20,21], which have been assigned tetragonal structures. The frequencies of n( /N /C) for the [Co(CNR)4(SbPh3)2](ClO4)2 complexes are similar to,
331
but systematically lower than, the values for the and [Co(CN[Co(CNR)4(AsPh3)2](ClO4)2 R)4{As(C6H4Me-p)3}2](ClO4)2 complexes [9]. With CNC6H11, the values are 2207, 2211, and 2210, respectively, with CNC4H9-n , 2222, 2226, and 2225 cm 1, respectively. This can be understood in terms of the slightly increasing s-donating ability (and/or decreasing p*-accepting ability) of the ligands, AsPh3 B/ As(C6H4Me-p )3 B/SbPh3. n( /N /C) for [Co(CNCH2Ph)4(OSbPh3)2](BF4)3 (2243 cm 1) is lower than the frequency for [Co(CNCH2Ph)4{OAs(C6H4Mep )3}2](BF4)3 (2258 cm 1) [11]. First, both frequencies are lower than might have been expected for RNC ligands coordinated to Co(III), but this is due to the change of the soft p*-accepting As and Sb atoms for the hard s-donating, p-donating O atoms in the oxides. The Ph3Sb-moiety, being a better electron-releasing group than R3As-, then tends to make the stibine oxide a stronger s-donor than the arsine oxide. Solution IR spectra show evidence of extensive decomposition. For the Co(II) complexes, stability apparently decreases for the solvents in the order, CF3CH2OH /CH2Cl2 /CH3NO2, and for the complexes, in the order, [Co(CNC4H9-n)4(SbPh3)2]/ (ClO4)2 /[Co(CNC6H11)4(SbPh3)2](ClO4)2. Bands attributable to the Co(II) complexes are observed close to their frequencies in Nujol, but higher energy and lower energy bands, often more intense, suggest the formation of Co(III) and Co(I) species, respectively. High Co(III), medium Co(I), and relatively low Co(II) concentrations are apparent for [Co(CNC4H9-n )4(SbPh3)2](ClO4)2 in CH2Cl2 and CH3NO2; and for [Co(CNC6H11)4(SbPh3)2](ClO4)2 in CH2Cl2 and CF3CH2OH. Absence of Co(II) for [Co(CNC6H11)4(SbPh3)2](ClO4)2 in CH3NO2, and Co(I) for [Co(CNC4H9-n )4(SbPh3)2]/ (ClO4)2 in CF3CH2OH is observed. The Co(III) complexes show better solution stabilities, with [Co(CNCH2Ph)4(OSbPh3)2](BF4)3 indicating some reduction to Co(I) inCH2Cl2,and [Co(CNC6H11)4(OSbPh3)2](ClO4)3, in CH3NO2. Co(II) n (/N/C) values in solution are close to those in Nujol. 3.2.2. Magnetic moments The magnetic moments of these four complexes are of particular interest. Effective magnetic moments were calculated from room temperature magnetic susceptibilities assuming Curie Law behavior and using diamagnetic corrections from the literature [20,22] or directly measured (xM //589/3 /l06 cgs for SbPh3). [Co(CNC4H9-n )4(SbPh3)2](ClO4)2, meff /1.949/0.02 BM (where s/9/0.02, the standard deviation [23] reflecting precision of three independent measurements on the same bulk sample), and [Co(CNC6H11)4(SbPh3)2](ClO4)2, meff /2.279/0.06 BM, are both clearly low-spin, i.e. one-electron paramagnetic, as expected for tetragonal coordination by strong field ligands. These
332
C.A.L. Becker et al. / Inorganica Chimica Acta 334 (2002) 327 /333
values are within the range for low-spin Co(II) complexes in general, 1.8 /2.7 BM [22,24], and within the ranges reported for tetragonally-substituted six-coordinate Co(II) with four alkylisocyanide ligands and two triarylarsines, 1.83 /2.31 BM [9], and two aromatic or cyclic aliphatic amines, 1.8 /2.5 BM [14]. Assuming a tetragonal elongation, i.e. that CNR is a stronger-field ligand than SbPh3, an electronic ground state of 2A1g [(eg)4(b2g)2(alg)1] would be anticipated. [Co(CNCH2Ph)4(OSbPh3)2](BF4)3, meff /3.309/0.08 BM, and [Co(CNC6H11)4(OSbPh3)2](ClO4)3, meff / 3.709/0.03 BM, are both clearly intermediate-spin, i.e. two-electron paramagnetic, as anticipated by analogy with [Co(CNCH2Ph)4{OAs(C6H4Me-p )3}2](BF4)3 (meff /3.58) [11]. As previously discussed [11], an electronic ground state of 3B2g [(eg)4(b2g)1(alg)1] or 3B2g [(eg)4(alg)1(b2g)1] is anticipated. The separation energy between the alg and b2g one-electron levels, jE(alg)/ E(b2g)j must be less than the electron-pairing energy. Square planar Co(III) complexes with the ligands h4HMPA-DMP, where H4HMPA-DMP /2,4-bis (2-hydroxy-2-methylpropanamido)-2,4-dimethyl-3-oxopentane, and h4-HMPA-B, where H4HMPA-B /2,4-bis (2hydroxy-2-methylpropanamido)benzene, and their alkylated derivatives, have meff values of 2.9, 3.0, 3.2, 3.5, and 3.6 BM [25]. meff values for isoelectronic Fe(II) complexes may also be useful comparison. Complexes of the types, [Fe(L /L)2ox] and [Fe(L /L)2mal], L /L /o phen, bipy; ox /oxalato, mal /maleato; have meff :/ 3.90 BM [26], with a temperature-independent paramagnetic component. Values of 3.30 and 3.70 BM thus appear reasonable for intermediate-spin, six-coordinate Co(III) complexes (mso /2.83 BM). 3.2.3. Electronic spectra Electronic spectra for the two Co(II) complexes, in diffuse reflectance and solution, appear to exhibit at least two crystal field (d/d) transitions, plus high energy, high intensity charge transfer and/or intraligand bands. In solid state, the weak band observed /765 nm (reported absorption values are misleading due to an effective ‘baseline absorption’ of 0.915, 1.18 for [Co(CNC6H11)4(SbPh3)2](ClO4)2, [Co(CNC4H9n )4(SbPh3)2](ClO4)2, hereafter discussed in this order) and stronger band at 590, 610 nm are most probably d / d bands, with charge transfer bands above 400 nm. In solution, stability is solvent dependent, stability varying as CF3CH2OH ]/CH2C12 /CH3CN, so the intense UV bands could be intra-ligand transitions, from dissociated ligands, as well as charge transfer bands. In CF3CH2OH and CH3CN there appear to be two d/d bands, 880, 470 (i.e. for [Co(CNC6H11)4(SbPh3)2](ClO4)2 in CF3CH2OH); 870, 470 (for [Co(CNC4H9-n )4(SbPh3)2](ClO4)2) and 721, 420; 730 (in CH3CN) nm; with possibly three bands in CH2Cl2, 737, 400, 320; 759, 480, 398 nm. Following Lever’s highly informative discussion for
weak tetragonal elongation of the strong field d7 configuration [27], the first d /d band could be 2 A1g 0/2B1g within the split 2Eg (octahedral) state. Two additional bands could be 2A1g 0/2Eg, 2A1g 0/2B2g, transitions into components of the 2T2g (octahedral) excited state. Electronic spectra for the Co(III) complexes are mainly charge transfer, and possibly also some intraligand, bands in the UV, but two closely-spaced d /d bands are clearly observed for [Co(CNC6H11)4(OSbPh3)2](ClO4)3(s) and one broad, possibly doubled, d /d band is observed for both complexes in CH2Cl2 and CF3CH2OH solution. For [Co(CNCH2Ph)4(OSbPh3)2](BF4)3(s) there could be an unresolved, weak band under the long wavelength ‘tail’ of the intense charge transfer band. Both complexes appear to be reduced to Co(II) in CH3CN; possibly the [Co(CNR)4(OSbPh3)2]2 species are being formed. Intermediatespin square planar Fe(II) complexes exhibit two d /d bands [27], and the square planar Co(III) complexes previously noted [25] had only one band, 738 nm (o / 800), that could be interpreted as a possible d /d transition (all other bands above 500 nm, o ]/2000), but no spectral assignment was offered. Two transitions, 3 3 B2g, [(eg)4(b2g, a1g)2]0/3A2g [(eg)4(b2g)1(blg)1], Blg 4 1 1 [(eg) (alg) (b1g) ], would be anticipated for these sixcoordinate Co(III) complexes, but the relative order is unknown. 3.3. Significance of the results Two significant results have been observed from this work: the intermediate-spin nature of the [Co(CNR)4(OSbPh3)2]X3 complexes and the dissimilarity in reaction patterns of PPh3, AsPh3, and SbPh3 with Co(II) /alkylisocyanide complexes. The Co(III) complexes could have been anticipated to be two-electron paramagnetic by analogy with [Co(CNCH2Ph)4{OAs(C6H4Me-p )3}2](BF4)3, but this, nevertheless, increases the very small number of Co(III) complexes having this rare magnetic ground state. The labile nature of these complexes with regard to ligand-substitution reactions, like the labile character already established for [Co(CNCH2Ph)4{OAs(C6H4Me-p )3}2](BF4)3 [28], is currently under investigation [29]. While stability of transition metal complexes with ligands containing Group V donor atoms is well known to decrease in the order P /As /Sb, whether the metal is class (a) (hard) or class (b) (soft), analogous coordination compounds with phosphines, arsines, and stibines have, nevertheless, been reported for about 150 years [30]. Compounds having PPh3, AsPh3, and SbPh3 ligands in similar coordination environments, as, for example, V(CO)4(EPh3)2, Cr(CO)5EPh3, cis -Mo(CO)3(EPh3)2, Mn(CO)4EPh3, MnX(CO)3(EPh3)2, MnX(CO)4EPh3, FeX2(CO)2(EPh3)2, NiI(NO)(EPh3)2,
C.A.L. Becker et al. / Inorganica Chimica Acta 334 (2002) 327 /333
Ni(CO)3EPh3, RuI2(CO)2(EPh3)2, Co(CO)2(NO)EPh3, [Co(CO)3(EPh3)2][Co(CO)4], cis -PtCl2(EPh3)2 [30], Fe(CO)4EPh3 [31]; where EPh3 /PPh3, AsPh3, SbPh3; X /Cl, Br, I; are so common and so strikingly analogous that the present major dissimilarities in reaction patterns of PPh3, AsPh3, and SbPh3 with alkylisocyanide /Co(II) complexes are difficult to comprehend. Clearly more investigation is needed to explain why these drastic dissimilarities exist.
Acknowledgements The authors wish to thank the Faculty of Science Research and Publications Committee of the University of Botswana for a grant supporting this research.
References [1] C.A.L. Becker, A. Anisi, G. Myer, J.D. Wright, Inorg. Chim. Acta 111 (1986) 11. [2] C.A.L. Becker, S.A. Al-Qallaf, J.C. Cooper, Inorg. Chim. Acta 188 (1991) 99. [3] C.A.L. Becker, K.R. Barqawi, J. Coord. Chem. 34 (1995) 273. [4] C.A.L. Becker, Synth. React. Inorg. Met.-Org. Chem. 22 (1992) 99. [5] C.A.L. Becker, Synth. React. Inorg. Met.-Org. Chem. 27 (1997) 1527. [6] C.A.L. Becker, J. Coord. Chem. 50 (2000) 89. [7] C.A.L. Becker, Synth. React. Inorg. Met.-Org. Chem. 28 (1998) 1145. [8] C.A.L. Becker, Synth. React. Inorg. Met.-Org. Chem. 24 (1994) 855. [9] C.A.L. Becker, J. Coord. Chem. 31 (1994) 337.
333
[10] C.A.L. Becker, O. Al-Jowder, Synth. React. Inorg. Met.-Org. Chem. 26 (1996) 1719. [11] C.A.L. Becker, Inorg. Chim. Acta 203 (1993) 175. [12] C.A.L. Becker, 204th National ACS Meeting, Washington, DC, Paper no. 381, Division of Inorganic Chemistry, 1992. [13] C.A.L. Becker, J. Coord. Chem. 28 (1993) 147. [14] C.A.L. Becker, J. Coord. Chem. 26 (1992) 231. [15] C.A.L. Becker, J.C. Cooper, Inorg. Chim. Acta 158 (1989) 141. [16] C.A.L. Becker, J.C. Cooper, Inorg. Chim. Acta 182 (1991) 25. [17] C.A.L. Becker, Synth. React. Inorg. Met.-Org. Chem. 25 (1995) 1455. [18] C.A.L. Becker, M.A.S. Biswas, Synth. React. Inorg. Met.-Org. Chem. 25 (1995) 269. [19] C.J. Gilmore, S.F. Watkins, P. Woodward, J. Chem. Soc. A (1969) 2833. [20] C.A.L. Becker, M.A.S. Biswas, J. Coord. Chem. 29 (1993) 277. [21] C.A.L. Becker, M.A.S. Biswas, J.C. Cooper, Inorg. Chim. Acta 188 (1991) 191. [22] B.N. Figgis, J. Lewis, in: J. Lewis, R.G. Wilkins (Eds.), Modern Coordination Chemistry (Ch. 6), Interscience, New York, 1960. [23] D.A. Skoog, D.M. West, F.J. Holler, Fundamentals of Analytical Chemistry, 6th ed., 6th ed. (Ch. 2), Saunders College Publishing, New York, 1992. [24] JM Magnetic Susceptibility Balance Instruction Manual, Johnson Matthey Chemicals, York Way, Royston, Hertfordshire, UK. [25] J.C. Brewer, T.J. Collins, M.R. Smith, B.D. Santarsiero, J. Am. Chem. Soc. 110 (1988) 423. [26] F.A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, 5th ed. (Ch. 18), Wiley-Interscience, New York, 1988. [27] A.B.P. Lever, Inorganic Electronic Spectroscopy, 2nd ed. (Ch. 6), Elsevier, New York, 1984. [28] C.A.L. Becker, S. Motladiile, Synth. React. Inorg. Met.-Org. Chem. 31 (2001) 1545. [29] C.A.L. Becker, 8th International Chemistry Conference in Africa (ICCA) Meeting, Dakar, Senegal, 2001. [30] G. Booth, Adv. Inorg. Chem. Radiochem. 6 (1964) 1. [31] M.O. Albers, E. Singleton, N.J. Coville, Inorg. Synth. 28 (1990) 168.
Synthesis of tetrakis(alkylisocyanide)bis(triphenylstibine)cobalt(II) and tetrakis(alkylisocyanide)bis(triphenylstibine oxide)cobalt(III) complexes: ligand substitution and oxidation in pentakis(alkylisocyanide)cobalt(II) Clifford A.L. Becker *, Galaletsang S. Sebobi, Ntshekelang Tostic Simane Department of Chemistry, University of Botswana, P/Bag 0022, Gaborone, Botswana Received 16 October 2001; accepted 13 February 2002
Abstract The complexes, [Co(CNC4H9-n )4(SbPh3)2](ClO4)2, [Co(CNC6H11)4(SbPh3)2](ClO4)2, [Co(CNC6H11)4(OSbPh3)2](ClO4)3, and [Co(CNCH2Ph)4(OSbPh3)2](BF4)3, have been synthesized by reaction of excess SbPh3 with the Co(II) /alkylisocyanide salts. With CNC6H11, the Co(II) complex can be isolated, continued reaction in solution producing the Co(IIl) complex. With CNCH2Ph, reaction proceeds more rapidly through a Co(II) complex directly to the Co(III) complex isolated. With CNC4H9-n , only the Co(II) complex is observed; attempted further reaction causes decomposition to OSbPh3. Characterization of the complexes is primarily in the solid state due to limited stability in solution. Coordination stereochemistries for both Co(II) and Co(III) complexes appear to be trans -substituted octahedral. Magnetic moments for [Co(CNC4H9-n )4(SbPh3)2](ClO4)2 and [Co(CNC6H11)4(SbPh3)2](ClO4)2 are low-spin (meff /1.94 BM, 2.27 BM, respectively), as expected, while [Co(CNCH2Ph)4(OSbPh3)2](BF4)3 and [Co(CNC6H11)4(OSbPh3)2](C1O4)3 are intermediate-spin (meff /3.30, 3.70 BM, respectively), as expected. Six-coordinate Co(III) complexes, in which both Co(II) and SbPh3 have been oxidized in the reaction, appear to be favored over the six-coordinate Co(II) complexes. Reactions of SbPh3 with pentakis (alkylisocyanide)cobalt(II) complexes are thus drastically different from reactions with PPh3 and even AsPh3. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Alkylisocyanide; Triphenylstibine; Triphenylstibine oxide; Cobalt(II) complexes; Cobalt(III) complexes; Ligand-substitution reactions
1. Introduction Triarylphosphine reactions with alkylisocyanide /cobalt(II) complexes are characterized by reduction/ligand-substitution reactions. The reactions of [Co(CNCMe3)4H2O](ClO4)2 and [Co2(CNCHMe2)10](ClO4)4 ×/5H2O with excess triarylphosphines have produced the disubstituted Co(I) complexes, [Co(CNR)3(PR3?)2]ClO4, in good yields [1,2]. The [Co(CNR)3(PR3?)2]X, X /ClO4, BF4, complexes have also been prepared with the CNC6H11, CNCH2Ph, and CNC4H9n ligands in analogous reactions [3]. A Co(II) complex, [Co(CNCHMe2)3{P(C6H4OMe-p )3}2](ClO4)2, was recovered in one instance, but this was only as a minor
* Corresponding author. Tel.: /267-355 2482; fax: /267-355 2836. E-mail address: [email protected] (C.A.L. Becker).
product and under restricted reaction conditions [4]. Five-coordinate Co(II) complexes with alkylisocyanide and triarylphosphine ligands, [Co(CNR)3(PR3?)2]X2, X /ClO4, BF4, have been synthesized by ligand-substitution reactions in [Co(CNR)4(AsR3?)2]X2 complexes and by AgClO4/AgBF4 oxidation of the [Co(CNR)3(PR3?)2]X complexes [5,6], but these reactions are not the characteristic reaction for alkylisocyanide /Co(II) complexes with triarylphosphine ligands. A six-coordinate Co(II) complex with alkylisocyanide and triarylphosphine ligands, [Co(CNC6H11)4(PPh3)2](ClO4)2, has even been recovered [7], but it has limited stability. Triarylarsine reactions with alkylisocyanide /cobalt(II) complexes are characterized by ligand-substitution of only one alkylisocyanide ligand and increase of the coordination number, resulting in six-coordinate Co(II) complexes, trans -[Co(CNR)4(AsR3?)2](ClO4)2, CNR / CNC6H11, CNCHMe2, CNCH2Ph, CNC4H9-n (but
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 0 8 5 8 - 7
328
C.A.L. Becker et al. / Inorganica Chimica Acta 334 (2002) 327 /333
not CNCMe3), AsR3? /AsPh3, As(C6H4Me-p)3, Ph2AsCH2CH2AsPh2 [8,9]. These complexes are prone to ligand-oxidation in solution [9,10] and solid state [9], leading to the tetrahedral Co(II) complexes, [Co(OAsR3?)4]X2, R?/Ph, C6H4Me-p; X /ClO4, BF4; and in one instance both ligand and Co(II) oxidation is observed, resulting in the Co(III) complex, [Co(CNCH2Ph)4{OAs(C6H4Me-p )3}2](BF4)3 [11], but no indication of Co(II) reduction to Co(I) was observed in any of these reactions. Preliminary investigation [12] indicated that both Co(II) complexes, [Co(CNR)4(SbPh3)2](ClO4)2, and Co(III) complexes, [Co(CNR)4(OSbPh3)2](ClO4)3, can be formed in triphenylstibine reactions with alkylisocyanide /cobalt(II) complexes. This present work investigates these SbPh3 reactions. What is especially significant in this study is the systematic changes in reaction observed for the group V donor-atoms in the homologous series of ligands, PPh3, AsPh3, and SbPh3.
2. Experimental 2.1. Materials and measurements Commercially available alkylisocyanides, CNC6H11, CNCHMe2, CNC4H9-n, CNCMe3, and CNCH2Ph (Strem Chemicals, Fluka and Aldrich), were used without re-distillation. [Co(CNCMe3)4H2O](C1O4)2, [Co2(CNCHMe2)10](ClO4)4 ×/5H2O, and [Co2(CNCH2Ph)10](BF4)4 ×/H2O were synthesized as previously reported [1,11,13]. Commercially available triphenylstibine (Fluka) was used without recrystallization. Co(ClO4)2 ×/ 6H2O and Co(BF4)2 ×/6H2O were obtained from Strem Chemicals. Anhydrous diethyl ether was filtered through an alumina column before use. IR spectra were recorded on a Perkin /Elmer 2000 FT-IR spectrophotometer in Nujol mull or solution using a single NaCl cell. Solution electronic spectra were recorded on a Shimadzu UV-2501PC spectrometer over the range 1100/200 nm. Diffuse reflectance spectra of solid samples were measured using an integrating sphere (model ISR-240A) over the range 800 /240 nm. Magnetic susceptibilities were measured at room temperature (r.t.) using a Johnson Matthey Alfa magnetic susceptibility balance. Effective magnetic moments were calculated assuming Curie’s law behavior. C, H and N elemental analyses were performed using a Carlo Erba CHN-O/S elemental analyzer, model 1106. Some of the complexes reported in this paper have been prepared as perchlorate salts, because Co(II) / alkylisocyanide complexes of CNC6H11 and CNC4H9n (as well as CNCHMe2, CNCMe3, and CNCMe2CH2CMe3) crystallize better with the ClO4 anion than the BF4 (while CNCH2Ph complexes crystallize better as BF4 salts). Although the complexes reported in this
paper have shown no explosive tendency, all perchlorate salts must be considered as potentially explosive. Please see the author’s comments regarding the use of perchlorate salts in Ref. [5]. 2.2. Synthesis of [Co(CNC4H9-n )4(SbPh3)2](ClO4)2 Co(ClO4)2 ×/6H2O (522 mg, 1.43 mmol), dissolved in EtOH (3.0 ml) and filtered through cotton with EtOH (0.5 ml) rinse, was chilled in ice. CNC4H9-n (593 mg, 7.13 mmol, neat; 5:1 RNC:Co mol ratio) was then added dropwise, with EtOH (0.5 ml) rinse, while the Co(II) solution was stirred at 0 8C. Solution color changed from pink to dark blue during ligand addition, with a mixture of suspended maroon solid and dark blue tar. SbPh3 (1.259 g, 3.566 mmol; 2.5:1 Sb:Co mol ratio), dissolved in CH2Cl2 (1.0 ml) and filtered through cotton, was added dropwise while the reaction mixture continued being stirred at 0 8C. The solution became dark green in color, with the formation of a solid. The mixture was filtered cold, and the product was washed twice with 2.5 ml portions of diethyl ether. Addition of 10.0 ml of diethyl ether to the filtrate and extensive chilling produced only a red/brown tar. Yield of dark green to yellow /green microcrystalline product: 1.403 g, 76%. Anal . Found: C, 51.90; H, 5.12; N, 4.26. Calc. for CoC56H66Cl2N4O8Sb2 [fw /1296.5 g mol1]: C, 51.88; H, 5.13; N, 4.32%. Solid state: m.p. 156/164 8C (dec.). IR: n(/N/C), 2221 vs, :/2190 br(sh) cm 1 (Nujol). Electronic spectrum: :/765 w(sh) (A /1.197), 610 (1.447), /436(1.864), /337 (1.986) nm. Magnetic susceptibility: xg /7629/15/109 (cgs), meff /1.949/0.02 BM. Solution: IR, n(/N/C), 2240 vs, :/2220 w(sh), 2156 m, 2135 m cm 1 (CH2Cl2); 2243 vs, :/2224 w(sh), 2156 m, 2136 m cm 1 (CH3NO2); 2241 vs, :/2228 m(sh), /2135 vw cm 1 (CF3CH2OH). Electronic spectra: 759 (o /180), /480 sh (160), 398 (765), :/275 w(sh) (1800), 256 (26 000), 229 (48 000) nm (CH2Cl2); 730 br (o /150), /252 br (22 000), /230 br (23 000) nm (CH3CN); 870 br (o /180), :/470 sh (490), 340 (3900), :/265 sh (6500), /250 sh (8400), 226 (19 400) nm (CF3CH2OH). 2.3. Synthesis of [Co(CNCH2Ph)4(OSbPh3)2](BF4)3 [Co2(CNCH2Ph)10](BF4)4 ×/H2O (750 mg, 0.453 mmol), dissolved in CH2C12 (5.0 ml), was filtered through cotton and chilled in ice. SbPh3 (800 mg, 2.27 mmol, neat; 2.5:1 Sb:Co mole ratio) was then added, small spatula-fulls at a time, with stirring. No color change in the dark yellow /brown solution was observed. The reaction mixture was allowed to stand at r.t. for 15 min., after which it was filtered through cotton, using 0.5 ml of CH2Cl2 as rinse. Dropwise addition of 1.5 ml of diethyl ether effected initial precipitation of a
C.A.L. Becker et al. / Inorganica Chimica Acta 334 (2002) 327 /333
golden yellow solid. A total volume of 5.0 ml of diethyl ether was added, and the solution was chilled in ice for 30 min. The yellow solid was filtered and washed twice with 1.5 ml portions of diethyl ether, but a greenish tint remained. The filtrate became dark green in color, and addition of excess diethyl ether and overnight refrigeration produced only a dark green tar. The crude product (346 mg) was dissolved in CH2Cl2 (18.0 ml), filtered through cotton using CH2Cl2 (0.5 ml) as rinse, and precipitated by dropwise addition of diethyl ether (20.0 ml) (initial precipitation, as a fine suspension, commenced after addition of 2.0 ml of diethyl ether). After chilling in ice for 20 min, the pale lemon-yellow microcrystalline product was filtered and washed twice with 1.5 ml portions of diethyl ether. Yield: 290 mg, 84% recovery, 21% overall yield. Anal . Found: C, 53.79; H, 3.85; N, 3.61. Calc. for CoC68H58B3F12N4O2Sb2 [fw / 1526.1 g mol 1]: C, 53.52; H, 3.83; N, 3.67%. Solid state: m.p. l85 /190 8C (dec.). IR: n (/N/C), 2243 vs, /2210 vw(sh) cm 1 (Nujol). Electronic spectrum: :/460 sh (A $/0.95), /335 br (1.76), :/270 sh (1.64) nm. Magnetic susceptibility: xg /2.629/0.15 / l0 6 (cgs), meff /3.309/0.08 BM. Solution: IR, n (/N/ C), 2240 m, 2173 s, 2136 vs cm 1 (CH2Cl2); 2243 vs (CH3NO2); 2236 vs, :/2215 vw(sh) cm 1 (CF3CH2OH). Electronic spectra: :/850 br (o /40), 403 (33 000), /244 sh (27 000), 232 sp (32 000) nm (CH2Cl2); 700 (o /75), :/390 vw(sh) (135), :/310w(sh) (680), :/275 sh (10 000), 256 (21 000), /222 sh (68 000) nm (CH3CN); /850 br (o /65), 340 (4200), :/265 sh (8000), /258 sh (9400), 254 (9600), 219 (44 000) nm (CF3CH2OH).
2.4. Synthesis of [Co(CNC6H11)4(OSbPh3)2](ClO4)3 [Co(CNC6H11)4(SbPh3)2](ClO4)2 (950 mg, 0.678 mmol) was dissolved in CH2Cl2 (4.0 ml), filtered through cotton, and rinsed with CH2Cl2 (1.0 ml). Working at 25 /28 8C, dropwise addition of 3.0 ml of diethyl ether effected initial precipitation of a greenishyellow solid. A total volume of 10.0 ml of diethyl ether was added, and the reaction mixture was chilled in ice for 20 min. The yellow solid was filtered and washed twice with 1.5 ml portions of diethyl ether. This product (391 mg) was dissolved in CH2Cl2 (8.0 ml) and filtered through cotton with CH2Cl2 (0.5 ml) rinse. Precipitation was achieved by dropwise addition of diethyl ether; initial precipitation commenced after addition of 4.0 ml, and a total of 12.0 ml was added. After chilling in ice for 20 min, the bright yellow microcrystalline product was filtered and washed twice with 1.5 ml portions of diethyl ether. Yield: 300 mg, 77% recovery, 29% overall yield (based on Co). Anal . Found: C, 49.89; H, 4.90; N, 3.66. Calc. for CoC64H74Cl3Cl3N4O14Sb2 [fw /1532.11 g mol 1]: C, 50.17; H, 4.87; N, 3.66%.
329
Solid state: m.p. 178/182 8C (dec.). IR: n(/N/C), 2229 vs cm 1 (Nujol). Electronic spectrum: /640 (A / 0.285), :/600 sh (0.272), /425 br (1.575), /358 br (1.736), :/272 sh (1.636) nm. Magnetic susceptibility: xg /3.389/0.04 /106 (cgs), meff /3.709/0.03 BM. Solution: IR, n(/N/C), 2231 vs (CH2Cl2); 2231 vs, :/2140 br (CH3NO2); 2229 vs, /2208 w(sh) cm 1 (CF3CH2OH). Electronic spectra: :/650 vw(sh) (o / 130), 404 (27 000), /285 sh (7500), :/243 w(sh) (24 000), 228 (62 000) nm (CH2Cl2); 715 br (o /100), :/340 w(sh) (420), :/275 sh (12 000), 253 (22 000), :/ 223 sh (71 000) nm (CH3CN); :/525 sh (o :/100), 405 (1260), 341 (780), 218 (5100) nm (CF3CH2OH).
2.5. Alternate synthesis of [Co(CNC6H11)4(SbPh3)2](ClO4)2 Co(ClO4)2 ×/6H2O (916 mg, 2.50 mmol) was dissolved in EtOH (4.0 ml), filtered through cotton with EtOH (0.5 ml) rinse, and chilled in ice for 5 min. CNC6H11 (1.095 g, 10.0 mmol, neat; 4:1 RNC:Co mol ratio) was then added dropwise to the stirred Co(II) solution in an ice bath. The reaction mixture changed color from pink to dark blue immediately upon addition of CNC6H11 but no solid precipitated. SbPh3 (1.949 g, 5.52 mmol; 2.2:1 Sb:Co mol ratio), dissolved in CH2Cl2 (3.0 ml) and filtered through cotton, was then added dropwise to the stirred Co(II) solution in an ice bath. The reaction mixture changed color from dark blue to dark green, with precipitation of a solid, during addition of the SbPh3 solution. Diethyl ether (12.0 ml) was added in small aliquots, to increase precipitation, and the dark yellow-green microcrystalline product was filtered without additional chilling in ice and washed twice with 2.0 ml portions of diethyl ether. Yield: 2.803 g, 80%. Anal . Found: C, 54.85; H, 5.32; N, 3.98. Calc. for CoC64H74Cl2N4O8Sb2 [fw /1400.66 g mol1]: C, 54.88; H, 5.33; N, 4.00%. Solid state: m.p. 167/173 8C (dec.). IR: n(/N/C), 2207 vs, /2168 vw(sh) cm 1 (Nujol). Electronic spectrum: 765 w (A /0.92), 590 (1.03), /415 sh (1.79), /375 sh (1.86), 346 (1.97), 274 (1.75) nm. Magnetic susceptibility: xg /1.099/0.07 /106 (cgs), meff /2.279/0.06 BM. Solution: IR, n( /N /C), 2228 vs, /2202 m(sh) cm 1 (CH2Cl2); 2231 vs, /2141 m(sh), /2125 m(sh) cm1 (CH3NO2); /2229 m(sh), 2215 vs, :/2204 w(sh), /2144 m(sh), 2131 m cm 1 (CF3CH2OH). Electronic spectra: 737 (o /140), 400 (460), /320 sh (830), :/276 w(sh) (18 000), 257 (30 000), 228 (50 000) nm (CH2Cl2); 721 (o /85), :/ 420 vw(sh) (70), :/265 sh (17 000), 253 (23 000), :/220 sh (54 000), 210 (69 500) nm (CH3CN); /880(o /170), :/470 sh(400), 343 (2500), /314 sh(2300), /253 (9200)nm (CF3CH2OH).
330
C.A.L. Becker et al. / Inorganica Chimica Acta 334 (2002) 327 /333
3. Results and discussion 3.1. Synthesis of the complexes Reactions of alkylisocyanide /Co(II) complexes (pentakis (alkylisocyanide)cobalt(II) in solution), with triphenylstibine produce both tetrakis (alkylisocyanide)bis (triphenyl-stibine)cobalt(II), [Co(CNR)4(SbPh3)2]X2, and tetrakis (alkylisocyanide)bis (triphenylstibine oxide)cobalt(III), [Co(CNR)4(OSbPh3)2]X3, X /ClO4, BF4; depending on the reaction conditions and the particular alkylisocyanide, 2SbPh3
[Co(CNR)5 ]2 0 [Co(CNR)4 (SbPh3 )2 ]2
Continued
0 [Co(CNR)4 (OSbPh3 )2 ]3
reaction
If the product can be isolated rapidly (synthesis of [Co(CNC4H9-n)4(SbPh3)2](ClO4)2), a Co(II) product is obtained. If the Co(II) complex remains in solution for a longer time period (the synthesis of [Co(CNCH2Ph)4(OSbPh3)2](BF4)3 and the recrystallization of [Co(CNC6H11)4(SbPh3)2](ClO4)2), however, reaction may proceed to a Co(III) complex. Only with the CNC6H11 ligand have both complexes been isolated in the pure state. With CNCH2Ph reaction proceeds through an apparent Co(II) complex to the Co(III) complex, while with CNC4H9-n the Co(II) complex decomposes upon continued reaction. With CNCHMe2 a mixture of apparent Co(II) and Co(III) complexes, with unreacted Co(II) starting material, was obtained. Reactions of [Co(CNC6H11)5]2 in EtOH with SbPh3 have not always been reproducible. In some instances, the reaction was analogous to that reported for CNC4H9-n. Then pure [Co(CNC6H11)4(SbPh3)2](ClO4)2 was obtained. In other instances the Co(II) product did not precipitate during SbPh3 addition, but required addition of diethyl ether and vigorous trituration of the solution to induce precipitation. In extreme cases the product first separated as a dark green tar which could be converted to crystalline material within 8/10 min of trituration. Here, the product was contaminated with the Co(III) complex. Better results were obtained with the alternate synthesis reported, in which a deficiency of CNC6H11 was added (4.0 mol ratio, instead of the stoichiometric 5.0 needed for complete conversion to [Co(CNR)5]2) so upon reaction with SbPh3 there was less free CNC6H11. Then [Co(CNC6H11)4(SbPh3)2](ClO4)2 precipitates more easily. Synthesis of [Co(CNC4H9-n)4(SbPh3)2](ClO4)2 was straightforward, but recrystallization from CH2Cl2 or continued reaction in EtOH leads to yellow /brown solutions from which only free OSbPh3 slowly precipitates after addition of diethyl ether and prolonged refrigeration, suggesting decomposition of any Co(III) complex that may have been formed in solution.
In the synthesis of [Co(CNCH2Ph)4(OSbPh3)2](BF4)3 there is evidence for the presence of a Co(II) complex, presumably formed as a precursor for the Co(III) complex. IR spectra taken on crude Co(III) samples revealed additional (unresolved) absorption at /2220 cm 1, suggesting a Co(II) minor product subsequently removed in recrystallization. Since precipitation from CH2Cl2 by addition of diethyl ether is a slower process than direct crystallization from EtOH, this synthesis would allow a Co(II) complex initially formed to react further to the Co(III) complex before isolation is achieved. Synthesis of [Co(CNC6H11)4(OSbPh3)2](ClO4)3 through double recrystallization of [Co(CNC6H11)4(SbPh3)2](ClO4)2 from CH2Cl2/diethyl ether illustrates that Co(II) and SbPh3 are oxidized when the Co(II) complex is allowed to remain in solution for a relatively short time period. The mechanism is not presently understood. IR spectra taken after one recrystallization show a weak shoulder /2210 cm 1, suggesting the presence of some Co(II) remaining unoxidized. If the Co(III) complex is left in solution for a more extended period of time, there is decomposition to a dark brownish-yellow solution with finely-divided OSbPh3 slowly precipitating. Similar behavior is seen with [Co(CNCH2Ph)4(OSbPh3)2](BF4)3. Reaction of SbPh3 with [Co2(CNCHMe2)10](ClO4)4 ×/ 5H2O in CH2Cl2 failed to produce a pure complex, but rather a mixture of complexes. Initial reaction produced a maroon-red solid, a yellow solid, and a dark green tar, which upon prolonged refrigeration converted into massive green crystals mixed with a microcrystalline yellow powder. IR spectra of crudely-separated crystals suggested the green compound could be a Co(II) complex (n(/N/C) /2206 cm 1) and the yellow compound could be Co(III) (n(/N/C) /2222 cm 1), but separation was incomplete, and attempted fractional recrystallization failed. The maroon-red compound could have been [Co2(CNCHMe2)10](ClO4)4 ×/5H2O [13] that reacted slowly in the freezer. Reactions with CNCHMe2 thus appear most similar to those with CNC6H11 in that both Co(II) and Co(III) complexes are observed, although reaction is apparently slower. Decreased reaction rate is possibly due to steric hindrance in CNCHMe2, since reaction with the CNCMe3 ligand (i.e. with [Co(CNCMe3)4H2O](ClO4)2) is not observed with AsPh3 or SbPh3. 3.2. Characterization of the complexes Solution IR and electronic spectra for these new complexes have been included for their routine basic characterization, but structural interpretation will be based primarily on solid state measurements, due to the limited stabilities in solution. The n (/N/C) IR patterns for [Co(CNC4H9-n )4(SbPh3)2](ClO4)2 and [Co(CNCH2-
C.A.L. Becker et al. / Inorganica Chimica Acta 334 (2002) 327 /333
Fig. 1. The n ( /N/C) IR pattern for [Co(CNC4H9n )4(SbPh3)2](ClO4)2 (top) and [Co(CNCH2Ph)4(OSbPh3)2](BF4)3 (bottom) in Nujol mull.
Ph)4(OSbPh3)23(BF4)3 in Nujol are pictured in Fig. 1; other data have been included with the syntheses. 3.2.1. IR spectra The n (/N /C) IR patterns for the Co(II) and Co(III) complexes in the solid state are compatible with tetragonal coordination; i.e. trans -[Co(CNR)4(SbPh3)2](ClO4)2 and trans -[Co(CNR)4(OSbPh3)2]X3. This pattern of one strong band with a lower-energy (unresolved) shoulder is typical of tetragonal complexes with known or assumed square /planar arrangement of four organoisocyanide ligands around Co(II) [7 /9,14 / 18]. Rigorous D4h symmetry for the Co(CNR)4 unit would require a single (strong) n (/N /C) (Eu), so the weak shoulder suggests slight distortion in the solid state. Distorted structures have been confirmed in X-ray analyses [16,19]. The n( /N /C) IR pattern for the Co(III) complexes is analogous to that seen for [Co(CNCH2Ph)4{OAs(C6H4Me-p )3}2](BF4)3 [11] and for the [Co(CNR)4(PR3)2]X3complexes [2,20,21], which have been assigned tetragonal structures. The frequencies of n( /N /C) for the [Co(CNR)4(SbPh3)2](ClO4)2 complexes are similar to,
331
but systematically lower than, the values for the and [Co(CN[Co(CNR)4(AsPh3)2](ClO4)2 R)4{As(C6H4Me-p)3}2](ClO4)2 complexes [9]. With CNC6H11, the values are 2207, 2211, and 2210, respectively, with CNC4H9-n , 2222, 2226, and 2225 cm 1, respectively. This can be understood in terms of the slightly increasing s-donating ability (and/or decreasing p*-accepting ability) of the ligands, AsPh3 B/ As(C6H4Me-p )3 B/SbPh3. n( /N /C) for [Co(CNCH2Ph)4(OSbPh3)2](BF4)3 (2243 cm 1) is lower than the frequency for [Co(CNCH2Ph)4{OAs(C6H4Mep )3}2](BF4)3 (2258 cm 1) [11]. First, both frequencies are lower than might have been expected for RNC ligands coordinated to Co(III), but this is due to the change of the soft p*-accepting As and Sb atoms for the hard s-donating, p-donating O atoms in the oxides. The Ph3Sb-moiety, being a better electron-releasing group than R3As-, then tends to make the stibine oxide a stronger s-donor than the arsine oxide. Solution IR spectra show evidence of extensive decomposition. For the Co(II) complexes, stability apparently decreases for the solvents in the order, CF3CH2OH /CH2Cl2 /CH3NO2, and for the complexes, in the order, [Co(CNC4H9-n)4(SbPh3)2]/ (ClO4)2 /[Co(CNC6H11)4(SbPh3)2](ClO4)2. Bands attributable to the Co(II) complexes are observed close to their frequencies in Nujol, but higher energy and lower energy bands, often more intense, suggest the formation of Co(III) and Co(I) species, respectively. High Co(III), medium Co(I), and relatively low Co(II) concentrations are apparent for [Co(CNC4H9-n )4(SbPh3)2](ClO4)2 in CH2Cl2 and CH3NO2; and for [Co(CNC6H11)4(SbPh3)2](ClO4)2 in CH2Cl2 and CF3CH2OH. Absence of Co(II) for [Co(CNC6H11)4(SbPh3)2](ClO4)2 in CH3NO2, and Co(I) for [Co(CNC4H9-n )4(SbPh3)2]/ (ClO4)2 in CF3CH2OH is observed. The Co(III) complexes show better solution stabilities, with [Co(CNCH2Ph)4(OSbPh3)2](BF4)3 indicating some reduction to Co(I) inCH2Cl2,and [Co(CNC6H11)4(OSbPh3)2](ClO4)3, in CH3NO2. Co(II) n (/N/C) values in solution are close to those in Nujol. 3.2.2. Magnetic moments The magnetic moments of these four complexes are of particular interest. Effective magnetic moments were calculated from room temperature magnetic susceptibilities assuming Curie Law behavior and using diamagnetic corrections from the literature [20,22] or directly measured (xM //589/3 /l06 cgs for SbPh3). [Co(CNC4H9-n )4(SbPh3)2](ClO4)2, meff /1.949/0.02 BM (where s/9/0.02, the standard deviation [23] reflecting precision of three independent measurements on the same bulk sample), and [Co(CNC6H11)4(SbPh3)2](ClO4)2, meff /2.279/0.06 BM, are both clearly low-spin, i.e. one-electron paramagnetic, as expected for tetragonal coordination by strong field ligands. These
332
C.A.L. Becker et al. / Inorganica Chimica Acta 334 (2002) 327 /333
values are within the range for low-spin Co(II) complexes in general, 1.8 /2.7 BM [22,24], and within the ranges reported for tetragonally-substituted six-coordinate Co(II) with four alkylisocyanide ligands and two triarylarsines, 1.83 /2.31 BM [9], and two aromatic or cyclic aliphatic amines, 1.8 /2.5 BM [14]. Assuming a tetragonal elongation, i.e. that CNR is a stronger-field ligand than SbPh3, an electronic ground state of 2A1g [(eg)4(b2g)2(alg)1] would be anticipated. [Co(CNCH2Ph)4(OSbPh3)2](BF4)3, meff /3.309/0.08 BM, and [Co(CNC6H11)4(OSbPh3)2](ClO4)3, meff / 3.709/0.03 BM, are both clearly intermediate-spin, i.e. two-electron paramagnetic, as anticipated by analogy with [Co(CNCH2Ph)4{OAs(C6H4Me-p )3}2](BF4)3 (meff /3.58) [11]. As previously discussed [11], an electronic ground state of 3B2g [(eg)4(b2g)1(alg)1] or 3B2g [(eg)4(alg)1(b2g)1] is anticipated. The separation energy between the alg and b2g one-electron levels, jE(alg)/ E(b2g)j must be less than the electron-pairing energy. Square planar Co(III) complexes with the ligands h4HMPA-DMP, where H4HMPA-DMP /2,4-bis (2-hydroxy-2-methylpropanamido)-2,4-dimethyl-3-oxopentane, and h4-HMPA-B, where H4HMPA-B /2,4-bis (2hydroxy-2-methylpropanamido)benzene, and their alkylated derivatives, have meff values of 2.9, 3.0, 3.2, 3.5, and 3.6 BM [25]. meff values for isoelectronic Fe(II) complexes may also be useful comparison. Complexes of the types, [Fe(L /L)2ox] and [Fe(L /L)2mal], L /L /o phen, bipy; ox /oxalato, mal /maleato; have meff :/ 3.90 BM [26], with a temperature-independent paramagnetic component. Values of 3.30 and 3.70 BM thus appear reasonable for intermediate-spin, six-coordinate Co(III) complexes (mso /2.83 BM). 3.2.3. Electronic spectra Electronic spectra for the two Co(II) complexes, in diffuse reflectance and solution, appear to exhibit at least two crystal field (d/d) transitions, plus high energy, high intensity charge transfer and/or intraligand bands. In solid state, the weak band observed /765 nm (reported absorption values are misleading due to an effective ‘baseline absorption’ of 0.915, 1.18 for [Co(CNC6H11)4(SbPh3)2](ClO4)2, [Co(CNC4H9n )4(SbPh3)2](ClO4)2, hereafter discussed in this order) and stronger band at 590, 610 nm are most probably d / d bands, with charge transfer bands above 400 nm. In solution, stability is solvent dependent, stability varying as CF3CH2OH ]/CH2C12 /CH3CN, so the intense UV bands could be intra-ligand transitions, from dissociated ligands, as well as charge transfer bands. In CF3CH2OH and CH3CN there appear to be two d/d bands, 880, 470 (i.e. for [Co(CNC6H11)4(SbPh3)2](ClO4)2 in CF3CH2OH); 870, 470 (for [Co(CNC4H9-n )4(SbPh3)2](ClO4)2) and 721, 420; 730 (in CH3CN) nm; with possibly three bands in CH2Cl2, 737, 400, 320; 759, 480, 398 nm. Following Lever’s highly informative discussion for
weak tetragonal elongation of the strong field d7 configuration [27], the first d /d band could be 2 A1g 0/2B1g within the split 2Eg (octahedral) state. Two additional bands could be 2A1g 0/2Eg, 2A1g 0/2B2g, transitions into components of the 2T2g (octahedral) excited state. Electronic spectra for the Co(III) complexes are mainly charge transfer, and possibly also some intraligand, bands in the UV, but two closely-spaced d /d bands are clearly observed for [Co(CNC6H11)4(OSbPh3)2](ClO4)3(s) and one broad, possibly doubled, d /d band is observed for both complexes in CH2Cl2 and CF3CH2OH solution. For [Co(CNCH2Ph)4(OSbPh3)2](BF4)3(s) there could be an unresolved, weak band under the long wavelength ‘tail’ of the intense charge transfer band. Both complexes appear to be reduced to Co(II) in CH3CN; possibly the [Co(CNR)4(OSbPh3)2]2 species are being formed. Intermediatespin square planar Fe(II) complexes exhibit two d /d bands [27], and the square planar Co(III) complexes previously noted [25] had only one band, 738 nm (o / 800), that could be interpreted as a possible d /d transition (all other bands above 500 nm, o ]/2000), but no spectral assignment was offered. Two transitions, 3 3 B2g, [(eg)4(b2g, a1g)2]0/3A2g [(eg)4(b2g)1(blg)1], Blg 4 1 1 [(eg) (alg) (b1g) ], would be anticipated for these sixcoordinate Co(III) complexes, but the relative order is unknown. 3.3. Significance of the results Two significant results have been observed from this work: the intermediate-spin nature of the [Co(CNR)4(OSbPh3)2]X3 complexes and the dissimilarity in reaction patterns of PPh3, AsPh3, and SbPh3 with Co(II) /alkylisocyanide complexes. The Co(III) complexes could have been anticipated to be two-electron paramagnetic by analogy with [Co(CNCH2Ph)4{OAs(C6H4Me-p )3}2](BF4)3, but this, nevertheless, increases the very small number of Co(III) complexes having this rare magnetic ground state. The labile nature of these complexes with regard to ligand-substitution reactions, like the labile character already established for [Co(CNCH2Ph)4{OAs(C6H4Me-p )3}2](BF4)3 [28], is currently under investigation [29]. While stability of transition metal complexes with ligands containing Group V donor atoms is well known to decrease in the order P /As /Sb, whether the metal is class (a) (hard) or class (b) (soft), analogous coordination compounds with phosphines, arsines, and stibines have, nevertheless, been reported for about 150 years [30]. Compounds having PPh3, AsPh3, and SbPh3 ligands in similar coordination environments, as, for example, V(CO)4(EPh3)2, Cr(CO)5EPh3, cis -Mo(CO)3(EPh3)2, Mn(CO)4EPh3, MnX(CO)3(EPh3)2, MnX(CO)4EPh3, FeX2(CO)2(EPh3)2, NiI(NO)(EPh3)2,
C.A.L. Becker et al. / Inorganica Chimica Acta 334 (2002) 327 /333
Ni(CO)3EPh3, RuI2(CO)2(EPh3)2, Co(CO)2(NO)EPh3, [Co(CO)3(EPh3)2][Co(CO)4], cis -PtCl2(EPh3)2 [30], Fe(CO)4EPh3 [31]; where EPh3 /PPh3, AsPh3, SbPh3; X /Cl, Br, I; are so common and so strikingly analogous that the present major dissimilarities in reaction patterns of PPh3, AsPh3, and SbPh3 with alkylisocyanide /Co(II) complexes are difficult to comprehend. Clearly more investigation is needed to explain why these drastic dissimilarities exist.
Acknowledgements The authors wish to thank the Faculty of Science Research and Publications Committee of the University of Botswana for a grant supporting this research.
References [1] C.A.L. Becker, A. Anisi, G. Myer, J.D. Wright, Inorg. Chim. Acta 111 (1986) 11. [2] C.A.L. Becker, S.A. Al-Qallaf, J.C. Cooper, Inorg. Chim. Acta 188 (1991) 99. [3] C.A.L. Becker, K.R. Barqawi, J. Coord. Chem. 34 (1995) 273. [4] C.A.L. Becker, Synth. React. Inorg. Met.-Org. Chem. 22 (1992) 99. [5] C.A.L. Becker, Synth. React. Inorg. Met.-Org. Chem. 27 (1997) 1527. [6] C.A.L. Becker, J. Coord. Chem. 50 (2000) 89. [7] C.A.L. Becker, Synth. React. Inorg. Met.-Org. Chem. 28 (1998) 1145. [8] C.A.L. Becker, Synth. React. Inorg. Met.-Org. Chem. 24 (1994) 855. [9] C.A.L. Becker, J. Coord. Chem. 31 (1994) 337.
333
[10] C.A.L. Becker, O. Al-Jowder, Synth. React. Inorg. Met.-Org. Chem. 26 (1996) 1719. [11] C.A.L. Becker, Inorg. Chim. Acta 203 (1993) 175. [12] C.A.L. Becker, 204th National ACS Meeting, Washington, DC, Paper no. 381, Division of Inorganic Chemistry, 1992. [13] C.A.L. Becker, J. Coord. Chem. 28 (1993) 147. [14] C.A.L. Becker, J. Coord. Chem. 26 (1992) 231. [15] C.A.L. Becker, J.C. Cooper, Inorg. Chim. Acta 158 (1989) 141. [16] C.A.L. Becker, J.C. Cooper, Inorg. Chim. Acta 182 (1991) 25. [17] C.A.L. Becker, Synth. React. Inorg. Met.-Org. Chem. 25 (1995) 1455. [18] C.A.L. Becker, M.A.S. Biswas, Synth. React. Inorg. Met.-Org. Chem. 25 (1995) 269. [19] C.J. Gilmore, S.F. Watkins, P. Woodward, J. Chem. Soc. A (1969) 2833. [20] C.A.L. Becker, M.A.S. Biswas, J. Coord. Chem. 29 (1993) 277. [21] C.A.L. Becker, M.A.S. Biswas, J.C. Cooper, Inorg. Chim. Acta 188 (1991) 191. [22] B.N. Figgis, J. Lewis, in: J. Lewis, R.G. Wilkins (Eds.), Modern Coordination Chemistry (Ch. 6), Interscience, New York, 1960. [23] D.A. Skoog, D.M. West, F.J. Holler, Fundamentals of Analytical Chemistry, 6th ed., 6th ed. (Ch. 2), Saunders College Publishing, New York, 1992. [24] JM Magnetic Susceptibility Balance Instruction Manual, Johnson Matthey Chemicals, York Way, Royston, Hertfordshire, UK. [25] J.C. Brewer, T.J. Collins, M.R. Smith, B.D. Santarsiero, J. Am. Chem. Soc. 110 (1988) 423. [26] F.A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, 5th ed. (Ch. 18), Wiley-Interscience, New York, 1988. [27] A.B.P. Lever, Inorganic Electronic Spectroscopy, 2nd ed. (Ch. 6), Elsevier, New York, 1984. [28] C.A.L. Becker, S. Motladiile, Synth. React. Inorg. Met.-Org. Chem. 31 (2001) 1545. [29] C.A.L. Becker, 8th International Chemistry Conference in Africa (ICCA) Meeting, Dakar, Senegal, 2001. [30] G. Booth, Adv. Inorg. Chem. Radiochem. 6 (1964) 1. [31] M.O. Albers, E. Singleton, N.J. Coville, Inorg. Synth. 28 (1990) 168.