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