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 [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.