Iminophosphonamido-Supported Plumbylenes and Plumbyliumylidenes: Synthesis and Properties

A series of low-valent lead(II) species, i.e., plumbylenes and plumb­ylium­ylidenes supported by an <i>N</i>,<i>N</i>′-di-<i>tert</i>-butyl­imino­phosphon­amide ligand, have been synthesized. Chloroplumbylene [Ph₂P(N^<i>t</i>Bu)₂PbCl] (<b>1</b>) was readily prepared by the reaction of the corresponding lithium iminophos­phonamide and PbCl₂ in THF. The substitution reaction of <b>1</b> with KN(SiMe₃)₂ in THF afforded the corresponding aminoplumbylene [Ph₂P(N^<i>t</i>Bu)₂PbN(SiMe₃)₂] (<b>2</b>) 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, <b>1</b> adopts a nearly linear polymeric structure in the direction of the <i>c</i> axis via Pb–Cl bonds, with alternating four-membered PbN₂P rings. The chloride-abstraction reaction of <b>1</b> using Na[B(C₆F₅)₄] in fluorobenzene proceeded efficiently at ambient temperature to furnish plumb­yliumylidene [Ph₂P(N^<i>t</i>Bu)₂Pb:]⁺ (<b>3</b>⁺), which was isolated as the air-sensitive yellow borate salt <b>3</b>[B(C₆F₅)₄]. Plumb­yliumylidene <b>3</b>[B(C₆F₅)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.