H2 Activation across Manganese(I)-C Bonds: Atypical Metal-Ligand Cooperativity in the Aromatization/Dearomatization Paradigm

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