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

Abstract

A study has been made of reactions involving organometallic compounds containing ortho-Me{2}NCH{2} substituted aryl ligands. The single step syntheses of the new compounds [(2-Me{2}NCH{2}C{6}H{4}){2}TlCl], [ [{(S)-2-Me{2}NCH(Me)C{6}H{4}}{2}TlCl], [{(S)-2-Me{2}NCH(Me)C{6}H{4}}TlCl{2}], [{2, 6-(Me{2}NCH{2}){2}C{6}H{3}}TlClBr] and [{2,6-(Me{2}NCH{2}){2}C{6}H{3}}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-Me{2}NCH{2}C{6}H{4}){2}Hg] with Pd(O{2}CMe){2}, and also of the reverse reaction of cis-[(2-Me{2}NCH{2}C{6}H{4}){2}Pd] with Hg(O{2}CR){2} or Tl(O{2}CR){3}, gave transmetallation of one organo ligand and led to a single mono-organopalladium compound and corresponding by-products. Reaction of cis-[({2}-Me{2}NCH{2}C{6}H{4}){2}Pd] with Pd(O{2}CR){2} gave the dimeric compound [{(2-Me{2}NCH{2}C{6}H{4})Pd(O{2}CR)}{2}]. cis-[(2-Me{2}NCH{2}C{6}H{4}){2}Pt] did not react with Pd(O{2}CMe){2}, while reaction of trans-[(2-Me{2}NCH{2}C{6}H{4}){2}Pt] or cis-[(2-Me{2}NC{6}H{4}CH{2}){2}Pt] with Pd(O{2}CMe){2} resulted in decomposition. Upon heating, trans-[(2-Me{2}NCH{2}C{6}H{4}){2}Pt] was isomerized to cis-isomer. A redox reaction between [(2-Me{2}NCH{2}C{6}H{4}){2}Hg] and [Pt(COD){2}] (COD @? 1,5-cyclo-octadiene) and [Pd{2}(DBA){3}] (DBA @? dibenzylideneacetone) gave the cis-isomers of [(2-Me{2}NCH{2}C{6}H{4}){2}M] (M @? Pd, Pt).The results are discussed in terms of influence of internal coordination of the CH{2}NMe{2} group. It is concluded that although internal coordination of the CH{2}NMe{2} 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(O{2}CR){2} and Tl(O{2}CR){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.