Rhenium(VII) monoimido alkylidyne complexes. The importance of face selectivity in the metathesis of acetylenes via rhenacyclobutadiene intermediates

Abstract

Re(NAr){sub 2}(CH-t-Bu)Cl (Ar = 2,6-C{sub 6}H{sub 3}-i-Pr{sub 2}) reacts with 3 equiv of HCl in diethyl ether to give (ArNH{sub 3})(Re-(C-t-Bu)(NHAr)Cl{sub 4}) (1a) as an insoluble orange powder. (NEt{sub 4})(Re(C-t-Bu)(NHAr)Cl{sub 4}) (1b) can be prepared from 1a by cation exchange. Addition of ZnCl{sub 2} to 1b yields (Re(C-t-Bu)(NHAr)Cl{sub 3}){sub 2} (2a), an x-ray study of which shows it to be a dimer in which each Re is a square pyramid with the neopentylidyne {alpha}-carbon atom in the apical position and a weakly bound bridging chloride ligand trans to it. Adducts of the type Re(C-t-Bu)(NHAr)Cl{sub 3}(L) (L = THF, py) can be prepared from 2a. Addition of DBU to Re(C-t-Bu)(NHAr)Cl{sub 3}(py) in the presence of pyridine gives Re(C-t-Bu)(NAr)Cl{sub 2}(py){sub 2} (4a). A more useful analogue, Re(C-t-Bu)(NAr)Cl{sub 2}(DME) (4b), can be prepared by adding ZnCl{sub 2} to 1b followed by NEt{sub 3} in DME. Complexes of the type Re(C-t-Bu)(NAr)(OR){sub 2} (OR = O-t-Bu (5a), OCMe{sub 2}(CF{sub 3}) (5b), O-2,6-C{sub 6}H{sub 3}-i-Pr{sub 2} (5c), OC(CF{sub 3}){sub 2}Me (5d), or OC(CF{sub 3}){sub 2}H (as a diethyl ether adduct, 5e)) can be prepared from 1b or 4b. Reactions of 5d and 5e with symmetric internal acetylenes give fluxional rhenacyclobutadiene complexes. Re(NAr)(C{sub 3}R{sub 3})(OC(CF{sub 3}){sub 2}Me){submore » 2} and Re(NAr)(C{sub 3}R{sub 3})(OC(CF{sub 3}){sub 2}H){sub 2} for R = Et, n-Pr, i-Bu, and i-Pr.« less