Aminoborylene complexes of group 6 elements and iron: A synthetic, structural, and quantum chemical study

Transition-metal-borylene complexes of the type [(OC)(5)M = BR] (NI = Cr, Mo, W; R = N(SiMe3)(2), 1a-3a, Si(SiMe3)(3) 4a) and [(OC)(4)Fe=B=N(SiMe3)(2)] (8) were prepared by salt elimination reactions. Synthesis of the latter complex was accompanied by the formation of substantial amounts of an unusual dinuclear iron complex [Fe-2{mu-C2O2(BN(SiMe3)(2))}(2)(CO)(6)] (9). The aminoborylene complexes of Group 6 metals were converted to trans-[(Cy3P)(CO)(4)M=B=N(SiMe3)(2)] (5a-7a) by irradiation in the presence of PCy3. Structural and spectroscopic parameters were discussed with respect to the trans-effect of the borylene ligand and the degree of M-B d(pi)-p(pi)-backbonding. Computational studies were performed on Group 6-borylene complexes. The population and topological analyses as well as the molecular orbital composition are consistent with the presence of both sigma- and pi-type interactions. There are, however, indications that the d(pi)-p(pi)-backbonding in the silylborylene complex is significantly more pronounced than in the aminoborylene complexes.