Highly reduced organometallics XXVII. Synthesis, isolation and characterization of trisodium tricarbonylcobaltate(3 -), and initial studies on its derivative chemistry

Reduction of A[Co(CO)₄] by three equivalents of A (A = sodium or potassium) in liquid ammonia provides salts containing tricarbonylcobaltate(3 -). A satisfactorily pure sodium compound, Na₃[Co(CO)₃] is described for the first time. Reactions of A₃[Co(CO)₃] with two equivalents of Ph₃ECl (E = Ge, Sn, Pb) provides 50-70% yields of trans-(Ph₃E)₂Co(CO)₃^- which have been isolated as analytically pure Et₄N⁺ salts. Treatment of liquid ammonia slurries of K₃[Co(CO)₃] with three equivalents of NH₄Cl in the presence of PR₃ or CNR, results in evolution of hydrogen gas and the formation of Co(CO)₃L^-. In the case of L = t-BuNC, the first such isocyanide substituted carbonylcobaltate(1 -) species was prepared and isolated in a 67% yield by this procedure. A possible pathway for the formation of Co(CO)₃L^- from K₃[Co(CO)₃] is discussed in light of similar protonation reactions reported for other carbonylmetallate trianions.