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 (B 3 H 8 )(CS 2 H)] ( 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)(μ 3 -CH 2 S 2 -κ 2 S':κ 2 S''){Cr(CO) 3 }(μ 3 -BH)] (2), bridging boryl-borylene [(Cp*Ru) 2 (μ-CO){(μ 3 -BH(CH 2 S 2 )-κ 2 B:κ 2 S':κ 1 S'')}{Cr(CO) 3 }(μ 3 -BH)] (3), and sulfido bridged hetero-trimetallic complex [(Cp*Ru) 2 (μ-CO) 3 {Cr(CO) 3 }(μ 3 -S)] (4). In 2, one side of Ru 2 Cr-triangle features a μ 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 Ru 2 Cr-triangle has a μ 3 -BH ligand while the opposite side is bridged by a boryl ligand BH(CH 2 S 2 ) in an unsymmetrical way (μ 3 -κ 2 :κ 2 :κ 1 ) 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 (μ 3 -CH 2 S 2 -κ 2 S':κ 2 S''){M(CO) 2 }] (5, M = Mo; 6, M = W) and sulfido-bridged hetero-trimetallic complexes [(Cp*Ru) 2 (μ-CO) 3 {M(CO) 3 }(μ 3 -S)] (7, M = Mo; 8, M = W), analogous to 4. In complexes 5 and 6, a Ru 2 M-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 3 -fashion. All the complexes have been characterized by 1 H NMR, 13 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.