Synthesis and reactions of novel dipalladium(II) complexes of the type [{Pd[PPh2CHC(R)–N–NC(R) CHPPh2]}2] (R = But or Ph). Crystal structure of the tert-butyl complex containing two Pd–C bonds and five fused chelate rings

Abstract

Treatment of the neutral chloropalladium(II) complexes [PdCl{PPh ₂ CHC(R)–N–NC(R)+ + CH ₂ PPh ₂ }] (R = Bu ^t 1a or Ph 1b) with two equivalents of Li[N(SiMe ₃ ) ₂ ] gave the novel dipalladium(II) complexes [{Pd[PPh ₂ CHC(R)–N–NC(R) CHPPh ₂ ]} ₂ ] (R = Bu ^t 2a or Ph 2b) containing two palladium–carbon bonds, five fused chelate rings and enamine type (CC–N) moieties. Treatment of the chloroplatinum(II) complex [PtCl{PPh ₂ CHC(Bu ^t )–N–+ + NC(Bu ^t )CH ₂ PPh ₂ }] 1c with an excess of KOBu ^t in dimethyl sulfoxide (dmso) gave what was probably the species [Pt{PPh ₂ CHC(Bu ^t )–N–N C(Bu ^t )CHPPh ₂ }(dmso)] 3 containing both a co-ordinated and an unco-ordinated phosphine. The dipalladium(II) complex 2a or 2b underwent electrophilic attack at the enamine carbon with acids (HX) to give salts of type [{Pd[PPh ₂ CH ₂ C(R)N–NC+ + (R)CHPPh ₂ ]} ₂ ]X ₂ 4 (R = Bu ^t or Ph; X = trifluoroacetate, chloride or picrate); these, when treated with sodium methoxide, deprotonated at the methylene carbon to give the neutral complex 2a or 2b. Treatment of 2a with less than 2 equivalents of trifluoroacetic acid gave the monoprotonated complex [Pd{PPh ₂ CHC(Bu ^t )N–NC+ + (Bu ^t )CHPPh ₂ }{PPh ₂ CH ₂ C(Bu ^t )N–NC(Bu ^t ) CHPPh ₂ }][O ₂ CCF ₃ ] 5a, mixed with 2a and 4a. Complex 2a with Br ₂ or MeI underwent attack at the enamine carbon CC–N to give the corresponding bromo or methyl derivatives [{Pd[PPh ₂ CH(R)CBu ^t N–N C(Bu ^t )CHPPh ₂ ]} ₂ ]X ₂ (R = Br, X = Br 6a; R = Me, X = I 6b) respectively. When the methyl-substituted salt was treated with KOBu ^t it gave the neutral dipalladium(II) complex [{PdCl[PPh ₂ C(Me) C(Bu ^t )–N–NC(Bu ^t )CHPPh _{+ + 2} ]} ₂ ] 7. The crystal structure of 2a was determined.