Heterometallic Triply-Bridging Bis-Borylene Complexes

Triply-bridging bis-{hydrido(borylene)} and bis-borylene species of groups 6, 8 and 9 transition metals are reported. Mild thermolysis of [Fe-2(CO)(9)] with an in situ produced intermediate, generated from the low-temperature reaction of [Cp*WCl4] (Cp*=eta(5)-C5Me5) and [LiBH4.THF] afforded triply-bridging bis-{hydrido(borylene)}, [(mu(3)-BH)(2)H-2{Cp*W(CO)(2)}(2){Fe(CO)(2)}] (1) and bis-borylene, [(mu(3)-BH)(2){Cp*W(CO)(2)}(2){Fe(CO)(3)}] (2). The chemical bonding analyses of 1 show that the B-H interactions in bis-{hydrido (borylene)} species is stronger as compared to the M-H ones. Frontier molecular orbital analysis shows a significantly larger energy gap between the HOMO-LUMO for 2 as compared to 1. In an attempt to synthesize the ruthenium analogue of 1, a similar reaction has been performed with [Ru-3(CO)(12)]. Although we failed to get the bis-{hydrido(borylene)} species, the reaction afforded triply-bridging bis-borylene species [(mu(3)-BH)(2){WCp*(CO)(2)}(2){Ru(CO)(3)}] (2 '), an analogue of 2. In search for the isolation of bridging bis-borylene species of Rh, we have treated [Co-2(CO)(8)] with nido-[(RhCp*)(2)(B3H7)], which afforded triply-bridging bis-borylene species [(mu(3)-BH)(2)(RhCp*)(2)Co-2(CO)(4)(mu-CO)] (3). All the compounds have been characterized by means of single-crystal X-ray diffraction study; H-1, B-11, C-13 NMR spectroscopy; IR spectroscopy and mass spectrometry.