Syntheses, structures, and bonding of boron containing niobium and ruthenium clusters stabilized by chalcogens

Abstract

In an effort to synthesize niobaheteroboranes and ruthenaheteroboranes, two different synthetic methods are developed. The reactions of [Cp*NbCl4] (1) with chalcogenaborate ligands [LiBH2E3] (E = S, Se) were carried out under reflux conditions. The reaction with sulfur yielded a triniobium polysulfide cluster [(Cp*Nb)3(μ3-S)3{B(OCH3)}(μ-S)3] (2) in which a trithiaborate ligand [S3B(OCH3)]− is coordinated to Nb3 framework in a cubane-type geometry. While the reaction with selenium generated a diniobium polyselenide cluster [(Cp*NbCl)2(μ-Se2-κ1Se:κ2Se')2(μ-O)] (3) in which two diselenide ligands {[Se2]2−} are coordinated with both the metal centres in an unsymmetrical κ1:κ2 fashion. On the other hand, efforts were directed towards expliciting the coordinative sulfur centres of a preformed arachno‑ruthenaborane [(Cp*Ru)2(B3H8)(CS2H)] (arachno‑4), by carrying out the pyrolysis of arachno‑4 with excess [BH3⋅THF]. The reaction led to the formation of sulfido stabilized pileo cluster nido‑ruthenathiaborane [2,3-(Cp*Ru)2(μ-H)(B3H6)S] (5), nido‑ruthenaborane [2,3-(Cp*Ru)2(μ-H)(B4H5Me)] (6) and thiomethyl bridged nido‑ruthenaborane [2,3-(Cp*Ru)2(μ-SMe)(B3H6)] (7). One of the key features of complex 5 is the presence of an unusual pentacoordinated sulfido ligand(μ5-S). All the complexes have been characterized by multinuclear NMR, 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 the electronic structures and bonding of these clusters.