Covalent attachment of diphosphine ligands to glassy carbon electrodes via Cu-catalyzed alkyne-azide cycloaddition. Metallation with Ni(II)

Covalent tethering of P^Ph₂N^C6H4C≡CH₂ ligands (P^Ph₂N^C6H4C≡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 Cu^I-catalyzed alkyne-azide cycloaddition (CuAAC) coupling reaction, using a BH₃←P protection-deprotection strategy. Deprotected, surface-confined ligands were metallated using [Ni^II(MeCN)₆](BF₄)₂. X-ray photoelectron spectroscopic measurements demonstrate that metallation introduced 1.3 equivalents Ni^II per diphosphine onto the electrode surface. Exposure of the surface to a second diphosphine ligand, P^Ph₂N^Ph₂, 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 [Ni^II(diphosphine)₂]²⁺ complex.