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

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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 CH2 CH) 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.