Abstract Various functionally-substituted methylidynetricobalt nonacarbonyl derivatives, RCCo 3 (CO) 9, where R is D, Me 3 Si, PhMe 2 Si,(MeO) 2 P (O),(EtO) 2 P (O), Me 3 COC (O), Me 3 SiOC (O), Et 2 NC (O), CH 3 C (O), C 2 H 5 C (O), nC 3 H 7 C (O), Me 2-CHC (O), nC 4 H 9 C (O), Me 3 C (O), PhC (O), p-CH 3 C 6 H 4 C (O), p-BrC 6 H 4 C (O), HOCH 2, HC (O), CH 3 O and Me 2 N, have been prepared by reaction of dicobalt octacarbonyl with the ...