Cyclorhenated compounds derived from 1,4-diaryl-1-azabutadienes: preparation, structures and reactions

PhCH2Re(CO)5 reacted with 1,4-diaryl-1-azabutadienes to give cyclometallated (η2-(C,N)-azabutadiene)Re(CO)4 (4) together with the substituted derivatives (η1-(N)-azabutadiene)(η2-(C,N)-azabutadiene)Re(CO)3 (6 and 7) The substituted product was shown by NMR and X-ray crystal structure analysis to be an inseparable mixture of isomers differing in the conformation of the η1-ligand about the Ndouble bond; length as m-dashC bond—trans for (6) and cis for (7). Reaction of the mixture of 6 and 7 from 1,4-diphenyl-1-azabutadiene with phenyl acetylene gave η5-(1,2,4-triphenyl-1-aza-cyclohexadienyl)Re(CO)3.