KINETISCHE UND MECHANISTISCHE UNTERSUCHUNGEN VON UEBERGANGS-METALLKOMPLEX-REAKTIONEN. X. KINETISCHE UNTERSUCHUNGEN DER INSERTION DES SCHWEFELS VON ORGANYLISOTHIOCYANATEN IN DIE METALL-CARBENKOHLENSTOFF-BINDUNG VON (ARYLPHENYLCARBEN)PENTACARBONYLWOLFRAM

Article abstract of DOI:10.1016/S0022-328X(00)89152-4

(Arylphenylcarbene)pentacarbonyltungsten complexes, (CO)5W (Ia, R = OCH3; Ib, R = CH3; Ic, R = H; Id, R = Br; Ie, R = CF3), react with organylisothiocyanates, R'NCS (IIa, R' = CH3; IIb, R' = C2H5; IIc, R' = C6H5), via insertion of the sulfur atom from R'NCS into the metal-carbene bond to yield (arylphenylthioketone)pentacarbonyltungsten complexes, (CO)5W (III).The decrease of the starting compound I in dibutyl ether follows a second-order rate law: -d/dt = k, but in octane, an additive law: -d/dt = k_I + k₂².Replacement of R = H in I by electron-withdrawing substituents (Br, CF3) results in an increase, by electron-donating groups (CH3, OCH3) in a decrease of the reaction rate.The rate constant k increases in the series R' = C6H5, R' = CH3, R' = C2H5.For the reaction of Ic with IIb in dibutyl ether the activation enthalpy is ΔH(excit.) = 40 kJ mol^-1, the activation entropy is ΔS(excit.) = -147 J mol^-1 K^-1.The results are discussed on the basis of an associative stepwise mechanism with a nucleophilic attack of the sulfur from R'NCS at the carbene carbon in the first reaction step.