Reflectance infrared and UV–visible spectroelectrochemical studies on a series of [Ni3(µ3-L)(µ3-I)(µ2-dppm)3][PF6] (L = CO; CNR, R = alkyl, aryl; dppm = Ph2PCH2PPh2) clusters

Abstract

The trinuclear nickel clusters [Ni3(µ3-L)(µ3-I)(µ2-dppm)3]+ (L = CO (1); CNR, R = CH3 (2), i-C3H7 (3), C6H11 (4), t-C4H9 (5), CH2C6H5 (6), C6H5 (7), p-C6H4I (8), p-C6H4F (9), p-C6H4CH3 (10), p-C6H4CF3 (11), p-C6H4OCH3 (12), p-C6H4CN (13), 2,6-(CH3)2C6H3 (14); dppm = Ph2PCH2PPh2) all contain a triply bridging π-acceptor (carbonyl or isocyanide) ligand. Compounds 1–14 all undergo single electron reductions over a relatively narrow range of E1/2( +/0) (−1.08 V to –1.18 V vs. SCE in acetonitrile) and are known electrocatalysts for the reduction of carbon dioxide. Specular reflectance infrared spectroelectrochemical (SEC) measurements on 1–14 indicate that the capping isocyanide or carbonyl ligand remains triply bridging (µ3,η1) upon single electron reduction. The magnitude of the ν(C≡O) or ν(C≡N) absorption band shift upon reduction is related to both the electronic and steric properties of the capping π-acceptor ligand. Spectroelectrochemical studies with UV–visible detection revealed a hypsochromic shift upon reduction of the clusters. The SEC cell and spectrometer utilized are extremely versatile and allow for data from 600 to 22 000 cm−1 to be acquired without modifying the SEC cell and making only minor configuration changes to the spectrometer. Key words: nickel, cluster, carbonyl, isocyanide, spectroelectrochemical.