Reactivity of hydroxo complexes of palladium(II) towards nitriles: formation of carboxamide and imino ether derivatives of palladium(II)

Abstract

The binuclear hydroxo complexes [Pd₂(C,N)₂(µ-OH)₂] [C,N = 2-(dimethylaminomethyl)phenyl (dmba) or 2-(phenylazo)phenyl (az)] have been prepared by addition of 2 equivalents of NBu₄OH to the corresponding di-µ-acetate complexes in acetone. The reactions of both hydroxo complexes with a number of nitriles, RCN, led to the formation of the carboxamide complexes [Pd₂(C,N)₂(µ-NHC(R)O)₂] (R = Me, Ph or CH₂CH) as well as the succinonitrile derivatives [(C,N)Pd{NHC(O)CH₂CH₂C(O)NH}Pd(C,N)]. The complexes [Pd₂(C,N)₂(µ-NHC(Me)O)₂] can also be prepared by reaction of [Pd₂(C,N)₂(µ-OH)₂] with acetamide. The hydroxo complex [Pd₂(C₆F₅)₄(µ-OH)₂]^2– reacted with nitriles in methanol or ethanol to give the imino ether complexes [Pd(C₆F₅)₂{NHC(OR′)R}₂] (R = Ph, R′ = Me or Et; R = Me, R′ = Me or Et) which in acetone solution are present as mixtures of EE, EZ and ZZ isomers. Similar reactions with 2-cyanopyridine and succinonitrile gave [Pd(C₆F₅)₂{NC₅H₄C(OR′)NH-2}] and [Pd(C₆F₅)₂{NHC(OR′)CH₂CH₂NH(OR′)}] (R′ = Me or Et) and the reaction with 2-cyanopyridine in acetone yielded [Pd(C₆F₅)₂{NC₅H₄C(O)NH-2}]. The crystal structures of [Pd₂(dmba)₂(µ-NHC(Ph)O)₂] and [Pd(C₆F₅)₂{NHC(OMe)Me}₂] have been determined by single-crystal X-ray diffraction.