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 [Mn2(CO)10] and 2-chloro-N1,N3-bis­(diisopropylphosphanyl)-N1,N3-diethylbenzene-1,3-diamine (P­(C-Cl)­PNEt-iPr) in CH3CN under solvothermal conditions in a sealed microwave glass tube for 8 h at 140 °C. Protonation of this complex with HBF4·Et2O leads to the formation of the cationic Mn­(I) complex [Mn­(κ3P,CH,P-P­(CH)­PNEt-iPr)­(CO)3]­BF4, which features an η2-Caryl–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.