Formation of a manganese alkyl complex as an intermediate in the ring-opening hydroformylation of α-cyclopropylstyrene by HMn(CO)5

Article abstract of DOI:10.1016/0022-328X(92)83184-J

The reaction of α-cyclopropylstyrene (CPS) with HMn(CO)5 can result in either hydrogenation or hydroformylation.The hydrogenation occurs by a previously established pathway involving sequential hydrogen atom transfers from the metal hydride to the organic substrate, and is the predominant reaction observed with samples of HMn(CO)5 that have been thoroughly dried and purified using P2O5.With samples of HMn(CO)5 that have been not been treated with P2O5, the reaction that occurs with CPS is ring-opening hydroformylation, leading to the isolation of Mn2(CO)9(η¹-HCOCH2CH2CH=C(Ph)CH3).The detailed procedures for preparation and handling of HMn(CO)5 that are reported in this paper enable the hydroformylation reaction to be reproducibly observed as the predominant reaction.An induction period of a few hours is typically observed in the hydroformylation, but addition of Mn2(CO)9(η¹-tolualdehyde) eliminates the induction period.The hydroformylation reaction is inhibited by CO (1 atm).The manganese alkyl complex (CO)5MnCH2CH2CH=(Ph)CH3 is an intermediate in the hydroformylation.The details of the mechanism of formation of this alkyl complex from CPS and HMn(CO)5 are not completely understood, but several mechanistic possibilities are considered.