H2 binding to and silane alcoholysis on an electrophilic Mn(I) fragment with tied-back phosphite ligands. X-ray structure of a Mn–CH2Cl2 complex

The solvent-coordinated cationic complex [mer-Mn(CO)3{P(OCH2)3CMe}2(ClCH2Cl)][BArF] (4), has been prepared by the reaction of the methyl precursor mer-Mn(Me)(CO)3{P(OCH2)3CMe}2 with [Ph3C][BArF]. The coordinated solvent, CH2Cl2, binds to Mn through one chloride atom in the X-ray crystal structure, which also exhibits novel interligand hydrogen bonding between an acidic hydrogen on CH2Cl2 and an oxygen of the phosphite. 4 binds H2 in equilibrium fashion, and the η2-H2 complex has a very high JHD of 34.5 Hz indicative of the high electrophilicity of the metal center. Silanes also displace the bound CH2Cl2 at low temperature, although the η2-SiH bond undergoes heterolytic cleavage on warming. 4 catalyzes reaction of SiHEt3 with phenol to give Et3SiOPh and H2. The bound CH2Cl2 in 4 is displaced irreversibly by olefins, ethers, and amines, to form stable adducts. The cationic [Mn(CO)3(P(OCH2)3CMe)2]+ fragment is more electrophilic than phosphine analogues, and the tied-back phosphites give less steric congestion and, importantly, cannot engage in agostic interactions that would compete with external ligand binding. The results in these and other related systems bring to the forefront the subtle balance between electronic and steric forces that occur on addition of sixth ligands to 16 e− metal fragments.