6533b7d8fe1ef96bd12697f0

RESEARCH PRODUCT

Organometallic nucleophiles. Mechanism of halide displacement at saturated carbon by 2-pyridyl and 4-Pyridyl complexes [M(dmtc)(C5H4N-Cn)(L)] (M  Pd, Pt; dmtc  dimethyldithiocarbamate; n  2,4; L 

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Abstract A mechanistic study is reported of nucleophilic halide substitution by pyridyl complexes [M(dmtc)C 5 H 4 N- C 2 )(L)] (M  Pd or Pt; L  PMe 3 , PEt 3 or PPh 3 ) and [Pd(dmtc)C 5 H 4 N- C 4 )(L)] (L  PMe 3 or PPh 3 ) on organic halides XCH 2 R (X  Cl or Br; R  CHCH 2 , COMe, Ph, or CN) in various solvents, yielding the pyridylium derivatives [M(dmtc)1-CH 2 R)C 5 H 4 N- C 2 (L)] + and [Pd(dmtc)(1-CH 2 R)(C 5 H 4 N- C 4 (L)] + , respectively. The kinetics obey a second-order rate law: rate  k 2 [XCH 2 R][Complex]. A similar rate law is observed for the analogous reactions involving 4-dimethyl-aminopyridine (4-dmapy) as the nucleophile. The effects of solvent and leaving group, and the largely negative activation entropies, are in line with S N 2 substitution at saturated carbon. Tle nucleophilic power ( k 2 ) generally increases with increasing basicity (p K 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-NMe 2 > 4-Pd(dmtc)(L). The electron-release of the metal-containing groups appears to be essentially inductive.