Syntheses and electrochemistry of (p-XC6H4O)6W (1-X, X=H, CH3, OCH3, Cl, Br, OH, OCH2Ph) and (p-XC6H4O)5W(OC6H4OH) (X=H, CH3, OCH3, Cl, Br): an approach to electrocatalytic CH bond activation

Alcoholysis of W(OMe)6 afforded (p-PhCH2OC6H4O)6W (1-OCH2Ph), which could be hydrogenated (10% Pd/C, 1 atm H2) to prepare (p-HOC6H4O)6W (1-OH). Related alcoholyses of WCl6 with HOC6H4-p-X provided the hexaphenoxides (p-XC6H4O)6W (1-X, X = H, CH3, OCH3, Cl, Br) through minor modifications of literature procedures. Acid catalyzed treatment of 1-X with p-HOC6H4OCH2Ph provided a mixture of substitution products (p-XC6H4O)6−xW(OC6H4OCH2Ph)x (x = 1, 5-X) that could be hydrogenated (10% Pd/C, 1 atm H2) to a mixture of hydroxylated products. Chromatography permitted isolation of (p-XC6H4O)5W(OC6H4OH) (6-X, X = H, 19%; Me, 29%; OCH3, 19%; Cl, 12%; Br, 11%) in modest yields. Hexaphenoxides 1-X and 6-X manifested two electrochemical reduction waves whose positions were a function of para-substituent. When oxidized, 6-X and 1-OH were proposed to behave as W(V)quinone mimics, albeit at potentials capable of oxidizing hydrocarbons as shown via a thermochemical cycle. If the proposed transients (p-XC6H4O)5W(OC6H4O) (7-X) were generated, degradation was apparently competitive with CH bond activation. The structure of oligomeric {K[(p-ClC6H4O)6W]}∞ (8-Cl) is addressed, and comments on the nature of radical CH bond activation in this and related systems are presented.