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)

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 (μeff=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 (μeff=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.