Synthesis, molecular structure, and dynamic behaviour in solution of octakis(t-butyl isocyanide)dicobalt

Abstract

Reduction of [Co(CNBut)5][PF6] with potassium amalgam in tetrahydrofuran affords red air-sensitive crystals of octakis(t-butyl isocyanide)dicobalt. Crystals of [Co2(CNBut)8] are orthorhombic, space group P21212, with two molecules in a cell of dimensions a= 18.017(4), b= 12.149(4), and c= 11.382(5)A. The structure has been solved by conventional techniques and refined by least squares to R 0.085 for 2 376 reflection intensities recorded on a four-circle diffractometer. The molecular geometry resembles that of [CO2(CO)8], but is substantially distorted, especially with respect to one of the basal isocyanide functions. Non-bonded contacts calculated for an idealized molecular geometry strongly suggest the importance of intermolecular contacts in the adopted distortions. The cobalt–cobalt distance is 2.4567(20)A. The 13C n.m.r. spectrum of an enriched (10%) sample of [Co2(CNBut)8] shows one resonance at ambient temperature collapsing (coalescence temperature –60 °C) to three resonances (1 : 1 : 2) at –90 °C. Evidence is presented for an intramolecular exchange process. Reaction of [Co2(CNBut)8] with CO, NO, and diphenylacetylene affords respectively [Co(CNBut)5][Co(CO)4], [Co(CNBut)3-(NO)], and [Co2{µ-(η2-PhC2Ph)}(CNBut)6].