Reversible Ligand Protonation of a Mn(I) PCP Pincer Complex To Afford a Complex with an η2-Caryl-H Agostic Bond

The first manganese PCP pincer complex, [Mn(PCPNEt-iPr)(CO)(3)], was obtained by treating [Mn-2(CO)(10)] and 2-chloro-N-1,N-3-bis(diisopropylphosphany1)-N-1,N-3-diethylbenzene-1,3-diamine (P(C-Cl)PCPNEt-iPr) in CH3CN under solvothermal conditions in a sealed microwave glass tube for 8 h at 140 degrees C. Protonation of this complex with HEF4 center dot Et2O leads to the formation of the cationic Mn(I) complex [Mn((KP)-P-3,CH,P-P(CH)P-NEt-iPr)(CO)(3)]BF4, which features an eta(2)-C-aryl-H agostic bond. There was no evidence for the formation of a Mn(III) hydride species. The agostic C-H bond is comparatively acidic, and even relatively weak bases, such as NEt3, deprotonate this bond to re-form the starting material [Mn(PCPNEt-iPr)(CO)(3)]; protonation is fully reversible. Substitution of one CO ligand was achieved upon treatment with NO+, affording the cationic complex [Mn(PCPNEt-iPr)(CO)(2)(NO)](+), where the two CO ligands are trans to one another.