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 arachno-ruthenaborane [(Cp*Ru)2(B3H8)(CS2H)] (arachno-1), we have thermolyzed arachno-1 with group-6 metal carbonyls [M(CO)5 center dot THF] (M = Cr, Mo and W). The reaction of arachno-1 with [Cr(CO)5 center dot THF] resulted in the formation of hetero-trimetallic triply bridging borylene [(Cp*Ru)2(mu-CO)(mu 3-CH2S2-kappa 2S ':kappa 2S ''){Cr(CO)3}(mu 3-BH)] (2), bridging boryl-borylene [(Cp*Ru)2(mu-CO){(mu 3-BH(CH2S2)-kappa 2B:kappa 2S ':kappa 1S '')}{Cr(CO)3}(mu 3-BH)] (3), and sulfido bridged hetero-trimetallic complex [(Cp*Ru)2(mu-CO)3{Cr(CO)3}(mu 3-S)] (4). In 2, one side of Ru2Cr-triangle features a mu 3-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 mu 3-BH ligand while the opposite side is bridged by a boryl ligand BH(CH2S2) in an unsymmetrical way (mu 3-kappa 2:kappa 2:kappa 1) to the metal centers. Interestingly, when the similar reactions of arachno-1 were performed with heavier group-6 metal carbonyls [M(CO)5 center dot THF] (M = Mo and W), it led to the formation of methanedithiolato bridged hetero-trimetallic chain complexes, [{Cp*Ru(CO)}2(mu-CO)2(mu 3-CH2S2-kappa 2S ':kappa 2S ''){M(CO)2}] (5, M = Mo; 6, M = W) and sulfido-bridged hetero-trimetallic complexes [(Cp*Ru)2(mu-CO)3{M(CO)3}(mu 3-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 mu 3-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. Triply bridging borylene and bridging boryl-borylene complexes in hetero-trimetallic template have been synthesized and structurally characterized by NMR, UV-vis, IR spectroscopy and mass spectrometry, and single crystal X-ray study.