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 (CO) ] with an in situ produced intermediate, generated from the low-temperature reaction of [Cp*WCl ] (Cp*=η -C Me ) and [LiBH ⋅THF] afforded triply-bridging bis-{hydrido(borylene)}, [(μ -BH) H {Cp*W(CO) } {Fe(CO) }] (1) and bis-borylene, [(μ -BH) {Cp*W(CO) } {Fe(CO) }] (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 (CO) ]. Although we failed to get the bis-{hydrido(borylene)} species, the reaction afforded triply-bridging bis-borylene species [(μ -BH) {WCp*(CO) } {Ru(CO) }] (2'), an analogue of 2. In search for the isolation of bridging bis-borylene species of Rh, we have treated [Co (CO) ] with nido-[(RhCp*) (B H )], which afforded triply-bridging bis-borylene species [(μ -BH) (RhCp*) Co (CO) (μ-CO)] (3). All the compounds have been characterized by means of single-crystal X-ray diffraction study; H, B, C NMR spectroscopy; IR spectroscopy and mass spectrometry.