Solid-state 11B NMR studies of coinage metal complexes containing a phosphine substituted diboraanthracene ligand

Abstract

Transition metal interactions with Lewis acids (M → Z linkages) are fundamentally interesting and practically important. The most common Z-type ligands contain boron, which contains an NMR active ¹¹B nucleus. We measured solid-state ¹¹B{¹H} NMR spectra of copper, silver, and gold complexes containing a phosphine substituted 9,10-diboraanthracene ligand (B₂P₂) that contain planar boron centers and weak M → BR₃ linkages ([(B₂P₂)M][BAr^F₄] (M = Cu (1), Ag (2), Au (3)) characterized by large quadrupolar coupling (C_Q) values (4.4–4.7 MHz) and large span (Ω) values (93–139 ppm). However, the solid-state ¹¹B{¹H} NMR spectrum of K[Au(B₂P₂)]⁻ (4), which contains tetrahedral borons, is narrow and characterized by small C_Q and Ω values. DFT analysis of 1–4 shows that C_Q and Ω are expected to be large for planar boron environments and small for tetrahedral boron, and that the presence of a M → BR₃ linkage relates to the reduction in C_Q and ¹¹B NMR shielding properties. Thus solid-state ¹¹B NMR spectroscopy contains valuable information about M → BR₃ linkages in complexes containing the B₂P₂ ligand.