Organometallic nucleophiles. Mechanism of halide displacement at saturated carbon by 2-pyridyl and 4-pyridyl complexes n)(L)> (M = Pd, Pt; dmtc = dimethyldithiocarbamate; n = 2,4; L = tertiary phosphine)

Article abstract of DOI:10.1016/0022-328X(92)88023-C

A mechanistic study is reported of nucleophilic halide substitution by pyridyl complexes 2)(L)> (M = Pd or Pt; L = PMe3, PEt3 or PPh3) and 4)(L)> (L = PMe3 or PPh3) on organic halides XCH2R (X = Cl or Br; R = CH=CH2, COMe, Ph, or CN) in various solvents, yielding the pyridylium derivatives 2>(L)>⁺ and 4>(L)>⁺, respectively.The kinetics obey a second-order rate law; rate = k₂.A similar rate law is observed for the analogous reactions involving 4-dimethylaminopyridine (4-dmapy) as the nucleophile.The effects of solvent and leaving group, and the largely negative activation entropies, are in line with S_N2 substitution at saturated carbon.The nucleophilic power (k₂) generally increases with increasing basicity (pK_a) of the pyridine nitrogen.Both these parameters depend on the position and nature of the substituent in the pyridine ring, in the order 2-M(dmtc)(L) > 4-NMe2 > 4-Pd(dmtc)(L).The electron-release of the metal-containing groups appears to be essentially inductive.