Cationic Phosphenium Complexes of Group 6 Transition Metals. Systematic Approach to Elucidation of Influence of Substituents of the Phosphenium Phosphorus on the Stability of the Complexes

Abstract

Abstract Group 6 transition-metal phosphite complexes, fac-[(bpy)(CO)3M{PXY(OMe)}] (M = Cr, Mo, and W; XY = (NEt2)2, 1a; N(Me)CH2CH2O, 2a; (NEt2)(OMe), 3a; OCMe2CMe2O, 4a; (OMe)2, 5a) have been prepared and subjected to the reaction with BF3·OEt2. In these reactions, cationic phosphenium complexes [(bpy)(CO)3M{PXY}]+ are formed by an OMe abstraction as an anion from the phosphorus ligand for 1a, 2a, and 3a (M = Mo, W). The reaction of 3a (M = Cr) yields fac-[(bpy)(CO)3Cr{P(OMe)2F}] (Cr-5c) and [(bpy)(CO)3Cr{P(NEt2)F2}] (Cr-7d). In the reaction of 4a and 5a for all group 6 congeners, an OMe/F substitution reaction takes place to give and fac-[(bpy)(CO)3M{P(OMe)2F}]. These results reveal that the stability of cationic phosphenium complexes increases with (i) going to a heavier congener, (ii) increasing the number of amino substituents on the phosphenium phosphorus, and (iii) adding an ethylene bridge between X and Y when at least one of X and Y is an amino substituent.