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 [Fe2(CO)9] with an in situ produced intermediate, generated from the low-temperature reaction of [Cp*WCl4] (Cp*=η5-C5Me5) and [LiBH4⋅THF] afforded triply-bridging bis-{hydrido(borylene)}, [(μ3-BH)2H2{Cp*W(CO)2}2{Fe(CO)2}] (1) and bis-borylene, [(μ3-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 [Ru3(CO)12]. Although we failed to get the bis-{hydrido(borylene)} species, the reaction afforded triply-bridging bis-borylene species [(μ3-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 [Co2(CO)8] with nido-[(RhCp*)2(B3H7)], which afforded triply-bridging bis-borylene species [(μ3-BH)2(RhCp*)2Co2(CO)4(μ-CO)] (3). All the compounds have been characterized by means of single-crystal X-ray diffraction study; 1H, 11B, 13C NMR spectroscopy; IR spectroscopy and mass spectrometry.