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Kinetic and Mechanistic Investigations of Transition Metal Complex Reactions, XVIII. Insertion of Diorganylcyanamides into the Metal-Carbene Bond - Preparative and Kinetic Investigations
Fischer, Helmut,Maerkl, Robert
, p. 3683 - 3699 (2007/10/02)
Arylcarbene(pentacarbonyl) complexes, (CO)5M1> (M=Cr, Mo, W; R1=Ph, OMe), react with diorganylcyanamides, R2R3N-CN (R2,R3=Me, Et, Pr, iPr, Ph), via insertion of the CN group into the metal-carbene bond to give (diorganylamino)carbene>pentacarbonyl complexes, (CO)5M2R3)N=C(Ph)R1>.The reaction follows a second-order rate law, first order each in the concentrations of the complex and the cyanamide.The rate constant increases slightly with increasing ability of the amino substituents R2 and R3 to donate electron density.The activation enthalpies are small (ΔH*=37.5 to 40.4 kJ.mol-1), the activation entropies are strongly negative (ΔS*= -123 to -133 J.mol-1.K-1).The reaction is initiated by nucleophilic attack of the cyanamide via the nitrile nitrogen at the carbene carbon.
