Structural elucidation of supported Rh complexes derived from RhCl (PPh3)3 immobilized on surface-functionalized SBA-15 and their catalytic performance for C-heteroatom (S, O) bond formation

The local structures of rhodium complexes derived from the immobilization of Wilkinson's complex, RhCI (PPh3)(3), on SBA-15 silica functionalized with primary-amine, secondary-amine, or diphenylphosphine groups within the mesoporous channels were characterized by a series of techniques including XRD, HR-TEM, multinuclear ((13)c/(29)si/P-31) solid-state NMR, 2D P-31{H-1) HETCOR NMR, XPS, and Rh K-edge EXAFS. Immobilization of RhCI(PPh3)(3) through covalent bond formation with different functional groups grafted to the silica surface lead to variations in the local structure of the Rh center that has important implications for catalysis. The immobilized Rh complexes demonstrated high activity for the addition of alkynes with thiols (hydrothiolation) or sulfonic acids (hydrosulfonation) with excellent regio- and stereoselectivity under mild reaction conditions. This work demonstrates the elucidation of the local structure of the immobilized Rh complexes requires a complimentary multi-technique characterization approach that probes both the metal center itself and surrounding ligands. (C) 2018 Elsevier Inc. All rights reserved.