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

Abstract

In an effort to explore the coordination chemistry of the coordinative sulfur centers in arachno-ruthenaborane [(Cp*Ru)₂(B₃H₈)(CS₂H)] (arachno-1), we have thermolyzed arachno-1 with group-6 metal carbonyls [M(CO)₅·THF] (M = Cr, Mo and W). The reaction of arachno-1 with [Cr(CO)₅·THF] resulted in the formation of hetero-trimetallic triply bridging borylene [(Cp*Ru)₂(μ-CO)(μ₃-CH₂S₂-κ²S′:κ²S′′){Cr(CO)₃}(μ₃-BH)] (2), bridging boryl–borylene [(Cp*Ru)₂(μ-CO){(μ₃-BH(CH₂S₂)-κ²B:κ²S′:κ¹S′′)}{Cr(CO)₃}(μ₃-BH)] (3), and sulfido bridged hetero-trimetallic complex [(Cp*Ru)₂(μ-CO)₃{Cr(CO)₃}(μ₃-S)] (4). In 2, one side of Ru₂Cr-triangle features a μ₃-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 Ru₂Cr-triangle has a μ₃-BH ligand while the opposite side is bridged by a boryl ligand BH(CH₂S₂) in an unsymmetrical way (μ₃–κ²:κ²:κ¹) to the metal centers. Interestingly, when the similar reactions of arachno-1 were performed with heavier group-6 metal carbonyls [M(CO)₅·THF] (M = Mo and W), it led to the formation of methanedithiolato bridged hetero-trimetallic chain complexes, [{Cp*Ru(CO)}₂(μ-CO)₂(μ₃-CH₂S₂-κ²S′:κ²S′′){M(CO)₂}] (5, M = Mo; 6, M = W) and sulfido-bridged hetero-trimetallic complexes [(Cp*Ru)₂(μ-CO)₃{M(CO)₃}(μ₃-S)] (7, M = Mo; 8, M = W), analogous to 4. In complexes 5 and 6, a Ru₂M-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 μ₃-fashion. All the complexes have been characterized by ¹H NMR, ¹³C 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.