Allyl and μ-allyl complexes from reactions of a hydrido-bridged molybdenum-manganese complex with dienes: Crystal structures of (η-C 5H 5)(CO) 2Mo(μ-PPh 2)Mn(η 3-C 3H 5)(CO) 3 and (η-C 5H 5)(CO)Mo(μ-σ:η 4-C 5H 9)(μ-PPh 2)Mn(CO) 3

Abstract

The complex (η-C 5H 5)(CO) 2Mo(μ-H)(μ-PPh 2)Mn(CO) 4 reacts under photolysis with the dienes allene, 1,1-dimethylallene, 1,3-butadiene and 2-methyl- 1,3-butadiene to give heterodimetallic allyl complexes in which the allyl ligand is bonded to either the Mn atom, the Mo atom or, alternatively, to both metal atoms. The crystal structure of two of these complexes, (η-C 5H 5)(CO) 2Mo(μ-PPh 2)Mn(η 3-C 3H 5)(CO) 3 and (η-C 5H 5)(CO)Mo(μ-σ: η 4-C 5H 9)(μ-PPh 2)Mn(CO) 3, have been determined by X-ray diffraction. In the former the allyl ligand is η 3bonded to the manganese atom, which is also coordinated by three CO groups, the bridging PPh 2 group and the Mo atom [MoMn = 3.038(1) Å]. In the latter complex the syn-CH 3CHC(CH 3)CH 2 allyl ligand is η 3bonded to the Mo atom and also via coordination of one CH bond of the CH 2 group to the Mn atom. The Mo atom is additionally coordinated by an η-C 5H 5 ligand, a CO group, the PPh 2 group and the Mn atom [MoMn = 2.800(1) Å]. In the presence of CO, the μ-allyl complexes are in equilibrium in solution with complexes of proposed formula (η-C 5H 5)(CO)(η 3-allyl)Mo(μ-PPh 2)Mn(CO) 4, containing the allyl ligand bonded exclusively to the Mo atom, but these latter complexes lose CO and revert to the μ-allyl complexes readily on attempted isolation. The μ-allyl complex (η-C 5H 5)(CO)Mo(μ-σ: η 4-C 4H 7)Mn(CO) 3 gives a 1:1 adduct with P(OMe) 3 in which the coordination of the allyl CH bond to the Mn atom is replaced by bonding of the P(OMe) 3 group. The μ-allyl complexes can be deprotonated with LIBu n giving anionic species which are postulated to contain μ-allylidene ligands. One such species, [(η-C 5H 5)(CO)Mo(μ-σ:η 3-CH 3CHCHCH)(η-PPh 2)Mn(CO) 3] −, has been reacted with CD 3COOD to regenerate the corresponding allyl complex; the added deuterium atom is located exclusively at the site involved in the interaction with the Mn atom.