H₂Activation across Manganese(I)-C Bonds: Atypical Metal-Ligand Cooperativity in the Aromatization/Dearomatization Paradigm

Dehydrohalogenation of fac-Mn(κ2-N,P-PicP)(CO)3Br (1H) and fac-Mn(κ2-N,P-LutP)(CO)3Br (1Me) with equimolar K[N(SiMe3)]2 afforded the reactive, aromatized 18-electron complexes fac-Mn(κ3-N,C,P-PicP)(CO)3 (2H) and fac-Mn(κ3-N,C,P-LutP)(CO)3 (2Me), respectively, with atypical binding modes. 2H and 2Me activate H2 across the Mn(I)-C bond to furnish hydride complexes fac-Mn(κ2-N,P-PicP)(CO)3H (4H) and fac-Mn(κ2-N,P-LutP)(CO)3H (4Me), respectively. Both 2H and 2Me were observed to produce dearomatized 18-electron complexes Mn(κ2-N,P-PicP*)(CO)4 (3H) and Mn(κ2-N,P-LutP*)(CO)4 (3Me), respectively, when reacted with CO. The reactive Mn(I)-C moiety of 2H and 2Me reacts with a variety of electrophiles: benzyl cyanide to form fac-Mn(κ3-N,N′,P-(LutP-BnCN))(CO)3 (6), E-chalcone to form fac-Mn(κ3-N,C,P-LutP-chalcone)(CO)3 (7), and AlCl3 to form fac-Mn(κ3-N,Cl,P-PicP-AlCl3)(CO)3 (8H) and fac-Mn(κ3-N,Cl,P-LutP-AlCl3)(CO)3 (8Me) featuring a rare intramolecular Mn-(μ-Cl)-Al moiety. Mn(I)-catalyzed Michael addition was explored. Dehydrohalogenation of 1H with alkoxides afforded the substituted complex fac-Mn(κ2-N,P-PicP)(OR)(CO)3 (10H) that was also reactive toward H2 forming 4H. Under identical conditions with alkoxide bases, 1Me affords 2Me demonstrating dichotomous behavior. We also explored the iPr-substituted analogues of 1H and 1Me (11H and 11Me, respectively) and found them to be essentially identical in behavior. Complexes 1R and 11R were found to be excellent catalysts for styrene hydrogenation. The relevance of the κ3-N,C,P binding mode discovered herein to catalysis is briefly discussed.