A Simple Manganese(I) Catalyst for the Efficient and Selective Hydrophosphination of Olefins with PH3, Primary, and Secondary Phosphanes.

A tridentate ligand L with a P,NH,N donor motif was synthesized in few steps from commercially available precursors. Upon reaction with [MnBr(CO)5], an octahedral 18-electron complex [Mn(CO)3(L)]Br (1) is obtained in which L adopts a facial arrangement. Deprotonation of the NH group leads under loss of CO to a neutral Mn(I) amide complex [Mn(CO)2(L-H)] (2), which has a trigonal bipyramidal structure with the P and N donor centers are in trans position. Further deprotonation of 2 gives the deep-blue anion [Mn(CO)2(L-2H)]- (3). DFT calculations and QTAIM analyses show that 2 contains a Mn-N bond with partial double bond character and 3 an aromatic MnN2C2 ring. The anion [Mn(CO)2(L-2H)]- reacts with Ph2PH to give a phosphido complex, which serves as phosphide transfer reagent to activated olefins with low catalytic activity. However, the neutral amide complex 2 is an excellent catalyst and with 0.04 mol%, turn over frequencies of >40'000 h-1 can be achieved. Furthermore, secondary and primary alkyl phosphines as well as PH3 can be added in a catalytic hydrophosphination reaction to a wide range of activated olefins such as α,β-unsaturated aldehydes, ketones, esters, and nitriles. But also, vinyl pyridine and some styrene derivatives are converted into the corresponding phosphanes.

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