Kinetics and Mechanism of Alkaline Hydrolysis of [(Methoxy)(p-substituted styryl)-carbene] Pentacarbonyl Chromium(0) Complexes in Aqueous Acetonitrile

摘要: Kinetic studies have been performed for alkaline hydrolysis of a series [(methoxy)(p-substituted styryl)carbene]pentacarbonyl chromium(0) complexes ((CO) 5 Cr=C(OCH3)CH=CHC6H4X, X = p-OCH 3 , p-CH H, p-Cl, p-NO 2 ). Second-order rate constants (k O H -) the in 50% acetonitrile-water (v/v) were determined spectrophotometrically at various temperatures. At low pH region (pH 9.5), k o b s increases linearly with increasing medium. The second-order - ) increase as substituent changes from strong electron donating group to withdrawing group. Hammett plot obtained is consisted two intersecting straight lines. nonlinear might be interpreted change rate-determining step. However, fact that corresponding Yukawa-Tsuno linear p and r values 0.71 1.14, respectively indicates not due rate-determing step but ground-state stabilization through resonance interaction. positive value suggests nucleophilic attack by OH form tetrahedral addition intermediate large negative ΔS ≠ present system consistent proposed mechanism.