THE EFFECT OF THE TRIMETHYLSILYL GROUP ON ELECTROPHILIC CYCLOPALLADATION - A STUDY OF C-ARYL-SI VERSUS C-ARYL-H SELECTIVE BOND ACTIVATION WITH 2,6(ME2NCH2)(2)C6H3R (R=H OR SIME3)

The site selectivity of electrophilic palladation has been studied by using two bis(aminomethyl)-substituted benzenes 1,3-(Me2NCH2)(2)C6H4 ( 6) and 2,6-(Me2NCH2)(2)C6H3(SiMe3) (7) and Li-2[PdCl4] or Pd(OAc)(2) i n solution in MeOH or CH2Cl2. The major product of direct palladation of 6 in both solvents is the polymeric cyclopalladated organometallic complex [1,5-{PdCl}(2)-2,4-(Me2NCH2)(2)C6H2](n), which was characteriz ed as its dinuclear pyridine derivative [1,5-{PdCl(C5H5)}(2)-2,4-(Me2N CH2)(2)C6H2] (9). The effect of the trimethylsilyl group present at th e 1-position in 7 leads to inversion of the site selectivity in compar ison to that observed for 6, and to activation of the C-Si bond when M eOH is used as solvent; the major product of this direct palladation i s the known monomeric cyclopalladated complex [{PdCl}2,6-(Me2NCH2)(2)C 6H3] (8). However, using CH2Cl2 instead of MeOH in the palladation rea ction of 7 leads to the major product arising from C-H rather than C-S i bond activation.