Site selectivity and competitive CO attack in Co4(CO)10(μ4-PPh)2 using methanolic [Et4N][OH

Abstract

The reaction between the tetracobalt cluster Co4(CO)10(μ4-PPh)2 (1) and [Et4N][OH] (1.1 equivalents of a 1.3 M solution in MeOH) has been examined in THF at -78°C. Low-temperature IR analysis reveals the presence of both the hydroxycarbonyl cluster [Co4(CO)9(μ4-PPh)2(CO2H)-] [2-] and the methoxycarbonyl cluster [Co4(CO)9(μ4-PPh)2(CO2Me)-] [3-] as a result of hydroxide and methoxide attack, respectively, on a terminal carbonyl group in 1. IR band-shape analysis indicates that [2-] and [3-] exist in a 77:23 ratio at -72°C. Addition of excess [Li+] (as [CF3SO3][Li]) to solutions of [2-] and [3-] affords [3-] in quantitative yield at -72°C. The thermal stability and reactivity of these anionic clusters are discussed and comparisons made to the structural similar formyl and acetyl clusters derived from 1.