- Co(CO)4M(C6H3)s (M = Sn and Pb) and Fe(CO)4P(C6H3)3 are found to react with phenyllithium and methyllithium to yield stable trans-carbene complexes after ethylation. For metal carbonyls, it is proposed that there is a direct correlation between the apparent CO stretching force constant and the charge residing on the carbonyl carbon atom. The use of these force constants in predicting the reactivity at carbon by attacking nucleophiles is proposed. It is found that when there is a choice of carbonyl groups within a molecule, nucleophilic attack always occurs at the CO group with the greater stretching force constant. This proposal is substantiated by all known reactions of organolithium compounds with metal carbonyls. 1970, American Chemical Society. All rights reserved.