The field of diborinane is sparsely explored area, and not many compounds are structurally characterized. The room-temperature reaction of [{Cp*RuCl­(μ-Cl)}2] (Cp* = η5-C5Me5) with Na­[BH3(SCHS)] yielded ruthenium dithioformato [{Cp*Ru­(μ,η3-SCHS)}2], 1, and 1-thioformyl-2,6-tetrahydro-1,3,5-trithia-2,6-diborinane complex, [(Cp*Ru)­{(η2-SCHS)­CH2S2(BH2)2}], 2. To investigate the reaction pathway for the formation of 2, we carried out the reaction of [(BH2)4(CH2S2)2], 3, with 1 that yielded compound 2. To the best of our knowledge, it appears that compound 2 is the first example of a ruthenium diborinane complex where the central six-membered ring [CB2S3] adopts the chair conformation. Furthermore, room temperature reaction of 1 with [BH3·thf] resulted in the isolation of agostic-bis­(σ-borate) complex, [Cp*Ru­(μ-H)2BH­(S-CHS)], 4. Thermolysis of 4 with trace amount of tellurium powder led to formation of bis­(bridging-boryl) complex, [{Cp*Ru­(μ,η2-HBS2CH2)}2], 5, via dimerization of 4 followed by dehydrogenation. Compound 5 can be considered as a bis­(bridging-boryl) species, in which the boryl units are connected to two ruthenium atoms. Theoretical studies and chemical bonding analyses demonstrate the reason for exceptional reactivity and stability of these complexes.

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All the syntheses were carried out under an argon atmosphere with standard Schlenk line and glove box techniques. Compounds, such as, [Cp*TaCl4], [1] S2CPPh3, [2,3] and the external reference for the 11 B{ 1 H} NMR, [Bu4N][B3H8] [4] were synthesized according to the literature methods. Thin-layer chromatography was carried out on 250 mm aluminum supported silica gel TLC plates. NMR spectra were recorded in a 500 MHz Bruker FT-NMR spectrometer. Chemical shifts are referenced to (residual) solvent signals ( 1 H/ 13 C{ 1 H}; CDCl3: δ = 7.26/77.16 ppm) or external [Bu4N][B3H8] ( 11 B: δ = 30.07 ppm). Mass spectra were recorded in a Bruker Micro TOF-II mass spectrometer in ESI ionization mode. I.1 Synthesis and CharacterizationsScheme S1. Synthesis of compound 1. Synthesis of 1:A suspension of [Cp*TaCl4] (0.100 g, 0.22 mmol) in 8 mL toluene at -78 ºC was charged dropwise with lithium borohydride solution 2.0 M in THF (0.7 mL) in toluene (10 mL) over 15 min and kept under constant stirring for 1 hour. Then freshly prepared solution of excess S2CPPh3 (0.075 g of PPh3 dissolved in 6 mL of CS2) was added in the reaction mixture over 5 min and kept under constant stirring for 24h at room temperature.The colour of the reaction mixture changed from yellow to brown. The solvent was evaporated in vacuum; residue was extracted into hexane/CH2Cl2 (60:40 v/v) and passed through Celite. After the removal of the solvent from the filtrate, the residue was subjected to chromatographic workup using silica-gel TLC plates. Elution with hexane/CH2Cl2 (60:40 v/v) yielded orange [(Cp*Ta)2(µ,η 2 :η 2 -B2H5)(μ-H)(κ 2 ,µ-S2CH2)2], 1 (0.0125g, 14.02 %) along with known compound 2 (0.025 g, 33.30 %).

We have recently reported the perchlorinated diniobaborane species [(Cp*Nb)2(B2H4Cl2)2] from [(Cp*Nb)2(B2H6)2] using CCl4 as chlorinating agent. In an attempt to isolate the vanadium analogue, we have isolated [(Cp*V)2(B2H6)2], 1 from the reaction of (Cp*VCl2)3 with [LiBH4•THF] followed by thermolysis with excess [BH3•THF]. Subsequently, the thermolysis of 1 with CCl4 for a prolonged period of time afforded perchlorinated divanadaborane [(Cp*V)2(B2H4Cl2)2], 2 along with the formation of bichlorinated divanadaborane [(Cp*V)2(B2H5Cl)2], 3 and trichlorinated divanadaborane [(Cp*V)2(B2H4Cl2)(B2H5Cl)], 4. Similarly, in order to functionalize the terminal B-H by {SePh} group, thermolysis of 1 was carried out with Ph2Se2 that yielded persubstituted divanadaborane [(Cp*V)2{B2H4(SePh)2}2], 5 in parallel to the formation of [(Cp*V)2{B4H11(SePh)}], 6. Compound 5 is very fascinating in which all the terminal B-H hydrogens of 1 have been substituted by {SePh} ligands. All the compounds have been characterized by 1 H, 11 B, 13 C NMR spectroscopy; mass spectrometry; IR spectroscopy and single crystal X-ray analysis. Density functional theory (DFT) and TD-DFT calculations provided further understanding regarding the electronic structures, bonding and electronic transitions of these persubstituted vanadaborane species.