Versatile Reactivity of a Four-Coordinate Scandium Phosphinidene Complex: Reduction, Addition, and CO Activation Reactions

摘要

The four-coordinate scandium phosphinidene complex, [LSc(μ-PAr)]_2 (L = (MeC(NDIPP)CHC(Me)-(NCH_2CH_2N('Pr)_2)), DIPP = 2,6-(~iPr)_2C_6H_3; Ar = 2,6-Me_2C_6H_3) (1), has been synthesized in good yield, and its reactivity has been investigated. Although 1 has a bis(μ-phosphinidene)discandium structural unit, this coordinatively unsaturated complex shows high and versatile reactivity toward a variety of substrates. First, two-electron reduction occurs when substrates as 2,2'-bipyridine, elemental selenium, elemental tellurium, Me_3P=S, or Ph_3P=E (E = S, Se) is used, resulting in the oxidative coupling of two phosphinidene ligands 2[PAr]~(2-) into a diphosphene ligand [ArP-PAr]~(2-). Complex 1 easily undergoes nucleophilic addition reactions with unsaturated substrates, such as benzylallene, benzonitrile, tert-butyl isocyanide, and CS_2. This complex also shows a peculiar reactivity to CO and Mo(CO)_6, that includes C-P bond formation, C-C coupling and C-O bond cleavage of CO, to afford novel phosphorus-containing products. In the last two types of reactivity, reaction profiles have been computed (for the insertion of ~tBuNC and the CO activation by 1) at the DFT level. The unexpected/surprising sequence of steps in the latter case is also revealed.