Steric limitations in associative substitution reactions of Os3(CO)9(μ-C4Ph4)

Article abstract of DOI:10.1016/S0020-1693(97)05992-6

Reactions of the cluster Os₃(CO)₉(μ-C₄Ph₄) (1) with a large number of smaller P-donor nucleophiles (Tolman cone angle θ ≤ 143°) proceed rapidly in heptane at room temperature via associative adduct formation to form the monosubstituted products. However, reactions with several larger P-donor nucleophiles (θ ≤ 145°) in heptane at room temperature yield, in a single observable bimolecular step, a mixture of mononuclear and dinuclear products and it is therefore not possible to synthesize the monosubstituted clusters directly with these larger ligands. Crystallographic structures of Os₃(CO)₈(etpb)(μ-C₄Ph ₄)·(CH₃OH) (2etpb) (etpb = P(OCH₂)₃CEt) and Os₃(CO)₈-(P(OPh)₃)(μ-C₄Ph ₄)·(C₆H₁₄) (2P(OPh)₃) have been determined and show that the substituent has displaced a CO ligand from the Os(CO)₄ moiety in 1.