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

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 B-11 nucleus. We measured solid-state B-11{H-1} 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][BAr4F] (M = Cu (1), Ag (2), Au (3)) characterized by large quadrupolar coupling (C-Q) values (4.4-4.7 MHz) and large span (omega) values (93-139 ppm). However, the solid-state B-11{H-1} NMR spectrum of K[Au(B2P2)](-) (4), which contains tetrahedral borons, is narrow and characterized by small C-Q and omega values. DFT analysis of 1-4 shows that C-Q and omega 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 B-11 NMR shielding properties. Thus solid-state B-11 NMR spectroscopy contains valuable information about M -> BR3 linkages in complexes containing the B2P2 ligand.

Automated summary

Interactions between transition metals and Lewis acids (M -> Z linkages) are of academic significance and practical importance. The study examined solid-state B-11{H-1} NMR spectra of metal complexes containing a phosphine substituted 9,10-diboraanthracene ligand (B2P2), revealing differences in C-Q and omega values between planar and tetrahedral boron environments. The presence of a M -> BR3 linkage was found to relate to the reduction in C-Q and B-11 NMR shielding properties.