PNNL

Abstract

Covalent tethering of PPh2NC6H4C=CH2 ligands (PPh2NC6H4C=CH2 = 1,5-di-(4-ethynylphenyl)-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane) to planar, azide-terminated glassy carbon electrode surfaces has been accomplished using a CuI-catalyzed alkyne-azide cycloaddition (CuAAC) as the coupling reaction, using a BH3?P protection-deprotection strategy. Deprotected, surface-confined ligands were metallated using [NiII(MeCN)6](BF4)2. X-ray photoelectron spectroscopic measurements demonstrate that metallation introduced 1.3 equivalents NiII per diphosphine onto the electrode surface. Exposure of the surface to a second diphosphine ligand, PPh2NPh2, resulted in the removal of Ni from the surface. Protection, coupling, deprotection, and metallation conditions were optimized using solution-phase model systems, with benzyl azide as a model for the azide-terminated carbon surface; these reactions generate a [NiII(diphosphine)2]2+ complex. Acknowledgment. This research was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. The XPS measurements were performed at the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the U. S. Department of Energy, Office of Science, Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. The x-ray crystal structure analysis was carried out by S.L., who was supported by a grant to Wendy J. Shaw from the Early Career Research Program through the U.S. Department of Energy, Office of Science. Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.