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

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-C4Ph4)·(CH3OH) (2etpb) (etpb = P(OCH2)3CEt) and Os3(CO)8-(P(OPh)3)(μ-C4Ph4)·(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.