ИСТИНА

Nowadays the design of well-defined Mn(I) catalysts for (de)hydrogenation-type processes became one of the most popular directions in homogeneous catalysis. Despite the Mn-based catalytic systems with pincer-type ligands still remain the most studied, some octahedral complexes fac-[(L−L')Mn(CO)3Br] bearing less structurally elaborated bidentate ligands could be competitive in terms of catalytic activity and/or substrate scope. In particular, we have recently shown that the association of phosphine and NHC donors in Mn(I) complex fac-[(Ph2PCH2NHC)Mn(CO)3Br] resulted in the development of catalytic system for ketone hydrogenation being one of the most active in Mn series. The mechanistic investigation of pre-catalyst activation step revealed the initial formation of cyclometallated form upon deprotonation, its isomerization to the non-classical ylide intermediate and cooperative H2 activation to form the corresponding hydride product. Inspired by our recent observation of easier H2 activation for the related Mn(I) dppm complexes fac-[(Ph2PCH(R)PPh2)Mn(CO)3Br] upon the ligand bridge substitution with phenyl group, we report herein that such modification of NHC-phosphine complex 1a significantly improved catalytic activity. Experimental and DFT studies of both stoichiometric H2 activation and catalytic cycle for acetophenone hydrogenation rationalizing the beneficial effect of the phenyl group will be also presented.