Hetero-trimetallic complexes comprising bridging boryl and borylene ligands: an experimental and theoretical study.

In an effort to explore the coordination chemistry of the coordinative sulfur centers in -ruthenaborane [(Cp*Ru)(BH)(CSH)] (-1), we have thermolyzed -1 with group-6 metal carbonyls [M(CO)·THF] (M = Cr, Mo and W). The reaction of -1 with [Cr(CO)·THF] resulted in the formation of hetero-trimetallic triply bridging borylene [(Cp*Ru)(μ-CO)(μ-CHS-κS':κS''){Cr(CO)}(μ-BH)] (2), bridging boryl-borylene [(Cp*Ru)(μ-CO){(μ-BH(CHS)-κB:κS':κS'')}{Cr(CO)}(μ-BH)] (3), and sulfido bridged hetero-trimetallic complex [(Cp*Ru)(μ-CO){Cr(CO)}(μ-S)] (4). In 2, one side of RuCr-triangle features a μ-BH ligand while the other side is quadruply bridged by a methanedithiolato ligand in an unsymmetrical fashion. Unlike 2, in complex 3, one side of the RuCr-triangle has a μ-BH ligand while the opposite side is bridged by a boryl ligand BH(CHS) in an unsymmetrical way (μ-κ:κ:κ) to the metal centers. Interestingly, when the similar reactions of -1 were performed with heavier group-6 metal carbonyls [M(CO)·THF] (M = Mo and W), it led to the formation of methanedithiolato bridged hetero-trimetallic chain complexes, [{Cp*Ru(CO)}(μ-CO)(μ-CHS-κS':κS''){M(CO)}] (5, M = Mo; 6, M = W) and sulfido-bridged hetero-trimetallic complexes [(Cp*Ru)(μ-CO){M(CO)}(μ-S)] (7, M = Mo; 8, M = W), analogous to 4. In complexes 5 and 6, a RuM-chain is symmetrically bridged by a methanedithiolato ligand. On the other hand, in complexes 4, 7, and 8, a sulfido ligand coordinates to two ruthenium and one group-6 metal atoms in μ-fashion. All the complexes have been characterized by H NMR, C NMR, UV-vis, IR spectroscopy, and mass spectrometry and their structural architectures have been unambiguously established by single crystal X-ray diffraction studies. In addition, theoretical investigations provided valuable insights into their electronic structures and bonding properties.