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Iminophosphonamido-Supported Plumbylenes and Plumbyliumylidenes: Synthesis and Properties

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posted on 2022-09-21, 12:36 authored by Kazuki Nakaya, Shintaro Takahashi, Akihiko Ishii, Norio Nakata
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 [Ph2P(NtBu)2PbCl] (1) was readily prepared by the reaction of the corresponding lithium iminophos­phonamide and PbCl2 in THF. The substitution reaction of 1 with KN(SiMe3)2 in THF afforded the corresponding aminoplumbylene [Ph2P(NtBu)2PbN(SiMe3)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 PbN2P rings. The chloride-abstraction reaction of 1 using Na[B(C6F5)4] in fluorobenzene proceeded efficiently at ambient temperature to furnish plumb­yliumylidene [Ph2P(NtBu)2Pb:]+ (3+), which was isolated as the air-sensitive yellow borate salt 3[B(C6F5)4]. Plumb­yliumylidene 3[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.