Effects of ligand and metal on the reductive elimination of dihydrogen by dinuclear complexes of chromium and manganese

Abstract

Six new dinuclear complexes of the form ( η 6 , η 6 - C 6H 5C 6H 4R)Cr 2(CO) 4-μ-L 2, where R  H, L 2  (CH 3) 4P 2, [(CH 3) 2] 2CH 2, [(CH 3O) 2P] 2NCH 3, (F 2P) 2NCH 3, [(CF 3CH 2O) 2P] 2CH 2 and R  CH 3, L  [(C 6H 5) 2P] 2CH 2 have been prepared and are fully characterized by their elemental analyses and spectral properties. The reactions of several dinuclear chromium compounds and ( η 5 , η 5 -C 5H 4C 5H 4)Mn 2- (CO) 4-μ-[(C 6H 5) 2P] 2CH 2 with strong acids have been examined. Dihydrogen evolution has been observed with all but one of the dinuclear chromium compounds. The relative rate of dihydrogen formation by the chromium compounds was found to be dependent upon the metal basicity which is dictated by the electronic character of the diphosphine ligand. The manganese derivative slowly eliminates dihydrogen under strong acid conditions. Deuterated acids have been shown to react with the dinuclear compounds to liberate mostly, but not exclusively, D 2 suggesting that some hydrogen exchange with either the arene rings or with the ligands is occurring prior to dihydrogen elimination. In no case has it been possible to recover the dinuclear compound intact after the reductive elimination of dihydrogen.