Physical Organic Chemistry of Transition Metal Carbene Complexes. 21.¹Kinetics and Mechanism of Hydrolysis of (CO)₅MC(SR)Ar (M = Cr and W; R = CH₃and CH₃CH₂CH₂; Ar = C₆H₅and 3-ClC₆H₄) in Aqueous Acetonitrile. Important Differences Relative to Complexes with Alkoxy Leaving Groups

Abstract

A kinetic study of the hydrolysis of (CO) 5 MdC(SMe)Ph (M ) Cr and W) in 50% MeCN-50% water (v/v) at 25°C over a pH range from 1.7 to 14.2 is reported. The reaction occurs in two stages: the first is formation of (CO) 5 MdC(O -)Ph or (CO) 5 MdC(OH)Ph while the second stage leads to the formation of PhCHdO and (CO) 5 MOH -. This paper is concerned with the first stage. The rate-pH profiles are complex and consistent with a mechanism (Scheme 1) that involves water/OH -addition to the substrate to form a tetrahedral intermediate (T OH -), followed by product formation via five potential pathways whose relative importance depends on the pH. A more limited study of the reactions of (CO) 5 MdC(SCH 2 CH 2 CH 3 )Ph (M ) Cr and W) and (CO) 5 MdC(SMe)C 6 H 4 -3-Cl (M ) Cr and W) with OH -is also reported. The main focus of the discussion is aimed at understanding the reactivity differences between (CO) 5 MdC(SMe)Ph and the corresponding methoxy analogues studied earlier. This understanding is in large measure based on an analysis of how the intrinsic rate constants are affected by the interplay of steric, inductive, and π-donor effects and the potential imbalances of these effects at the transition state. It is also shown that the much lower sensitivity to H + -catalysis of RS -compared to RO -leaving group departure from the tetrahedral intermediate is responsible for the more complex rate-pH profile for the hydrolysis of (CO) 5 MdC(SMe)Ph than for the hydrolysis of the methoxy analogue. IntroductionA kinetic study of the hydrolysis of the Fischer type transition metal carbene complexes 1-M, 2 2-M 2 , and 3-Cr in 50%

A new versatile binuclear seven-coordinate complex of molybdenum(II), [(μ-Cl)2{Mo(μ-Cl)(SnCl3)(CO)3}2]2−

“…In the presence of water, the norbornylidene ligand can be transformed to norborneol, which was detected in small amounts in our experiments as nbe-H 2 O adduct by GC-MS method (Scheme 2 and 3). Such formation of alcohol in reaction of a carbene ligand had been observed before [28][29][30][31][32]. In a similar way as with water, the carbene ligand interacts with alcohol [33][34].…”

Transition metal carbene chemistry 2: kinetic studies on the nucleophilic substitution reactions of (CO)5MC(SCH3)CH3 (M=Cr and W) with morpholine in aqueous acetonitrile

“…The higher reactivity of tungsten carbene complexes over the chromium is particularly true for thioalkyl carbene complexes, as is borne out by the results for the reaction of 2-M(S), 11-M(S) and 12-M(S) with OH À and water [3,18]. This is also expected to be valid for the reactions of 1-M(S) with morpholine.…”

Electronic Structure and Reactivity of Metal Carbenes

“…Both interactions have been found to be important for the correct description of the bond and the electrophilic character at the carbene carbon atom [86,88,93,94]. The kinetic and thermodynamic properties of Fischer-type carbene complexes have also been addressed by Bernasconi, who relates the strength of the p-donor substituent to the thermodynamic acidity [95-101] and the kinetics and mechanism of hydrolysis and reversible cyclization to differences in the ligand X [96,102].…”