Aspects of transmetallation reactions of 2-Me2NCH2C6H4- and 2,6-(Me2NCH2)C6H3-Metal (Pd,Pt, Hg,Tl) complexes with metal carboxylates and low-valent metal (Pd,Pt) complexes

A study has been made of reactions involving organometallic compounds containing ortho-Me₂NCH₂ substituted aryl ligands. The single step syntheses of the new compounds (2-Me₂NCH₂C₆H₄)₂TlCl], {(S)-2-Me₂NCH(Me)C₆H₄}₂TlCl], {(S)-2-Me₂NCH(Me)C₆H₄}TlCl₂], {2,6-(Me₂NCH₂)₂C₆H₃}TlClBr] and {2,6-(Me₂NCH₂)₂C₆H₃}HgCl] are described. Stable internal NTl coordination at low temperatures has been established for the C-chiral thallium compounds. Reactions of the other Tl and Hg compounds and of (2-Me₂NCH₂C₆H₄)₂Hg] with Pd(O₂CMe)₂, and also of the reverse reaction of cis-(2-Me₂NCH₂C₆H₄)₂Pd] with Hg(O₂CR)₂ or Tl(O₂CR)₃, gave transmetallation of one organo ligand and led to a single mono-organopalladium compound and corresponding by-products. Reaction of cis-(₂-Me₂NCH₂C₆H₄)₂Pd] with Pd(O₂CR)₂ gave the dimeric compound {(2-Me₂NCH₂C₆H₄)Pd(O₂CR)}₂]. cis-(2-Me₂NCH₂C₆H₄)₂Pt] did not react with Pd(O₂CMe)₂, while reaction of trans-(2-Me₂NCH₂C₆H₄)₂Pt] or cis-(2-Me₂NC₆H₄CH₂)₂Pt] with Pd(O₂CMe)₂ resulted in decomposition. Upon heating, trans-(2-Me₂NCH₂C₆H₄)₂Pt] was isomerized to cis-isomer. A redox reaction between (2-Me₂NCH₂C₆H₄)₂Hg] and Pt(COD)₂] (COD  1,5-cyclo-octadiene) and Pd₂(DBA)₃] (DBA  dibenzylideneacetone) gave the cis-isomers of (2-Me₂NCH₂C₆H₄)₂M] (M  Pd, Pt).The results are discussed in terms of influence of internal coordination of the CH₂NMe₂ group. It is concluded that although internal coordination of the CH₂NMe₂ ligand can stabilize metal—carbon bonds it cannot prevent cleavage of such bonds by electrophiles. In this respect, there is no difference in the behaviour of Hg(O₂CR)₂ and Tl(O₂CR)₃. The reactions are influenced by the metal—nitrogen bond strength, which follows the order PtN > PdN > HgN, TlN. The reactivity of Pt compounds is greatly influenced by their structure and type of ligand. It is proposed that cleavege of PdC bonds occurs mainly by a mechanism involving direct electrophilic attack at the carbon centre.