Iminophosphonamido-Supported Plumbylenes and Plumbyliumylidenes: Synthesis and Properties.

A series of low-valent lead(II) species, i.e., plumbylenes and plumbyliumylidenes supported by an N , N '-di- tert -butyliminophosphonamide ligand, have been synthesized. Chloroplumbylene [Ph 2 P(N t Bu) 2 PbCl] ( 1 ) was readily prepared by the reaction of the corresponding lithium iminophosphonamide and PbCl 2 in THF. The substitution reaction of 1 with KN(SiMe 3 ) 2 in THF afforded the corresponding aminoplumbylene [Ph 2 P(N t Bu) 2 PbN(SiMe 3 ) 2 ] ( 2 ) in the form of colorless crystals. The structures of these plumbylenes in the solid state and in solution were exhaustively characterized using multinuclear NMR spectroscopy and X-ray diffraction analysis. In the crystalline state, 1 adopts a nearly linear polymeric structure in the direction of the c axis via Pb-Cl bonds, with alternating four-membered PbN 2 P rings. The chloride-abstraction reaction of 1 using Na[B(C 6 F 5 ) 4 ] in fluorobenzene proceeded efficiently at ambient temperature to furnish plumbyliumylidene [Ph 2 P(N t Bu) 2 Pb:] + ( 3 + ), which was isolated as the air-sensitive yellow borate salt 3 [B(C 6 F 5 ) 4 ]. Plumbyliumylidene 3 [B(C 6 F 5 ) 4 ] acts as a Lewis acid catalyst for the hydroboration of benzophenone and benzaldehyde at catalyst loadings of as low as 0.1 mol % under ambient conditions. Furthermore, the details of the reaction mechanism are discussed on the basis of the results of DFT calculations.