Diborane and Triborane Species in the Coordination Sphere of Group-8 Transition Metals

Abstract

The synthesis and structural elucidation of a series of ruthenium diborane and triborane compounds are described. Treatment of [Cp*Ru(PPh 3 ) 2 Cl] (1) (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl; PPh 3 = triphenylphosphine) with [BH 3 •THF] (THF = tetrahydrofuran) at 60 °C led to the formation of the hydrogen-rich ruthena-octahydrotetraborane arachno-[2-{Cp*Ru(PPh 3 )B 3 H 8 }] (2). The chemistry of 2 is explored with [Fe 2 (CO) 9 ] at room temperature, which resulted in the formation of a metal-stabilized triborane species, [{Cp*Ru(PPh 3 )}(μ 3η 1 :η 2 :η 2 -B 3 H 6 ){Fe 2 (CO) 7 }] (3). Compound 3 can be considered as a triborane analogue [B 3 H 6 ] 3− that stabilizes in the coordination sphere of two iron and one ruthenium atoms. Further, the photolysis of nido-[1,2-(Cp*Ru) 2 (μ-H) 2 (B 3 H 7 )] (4) with [M(CO) 5 •THF] (M = Mo and W) afforded an arachno-[1,2-(Cp*Ru)(Cp*RuCO)(μ-H)(B 3 H 8 )] (5), in which the [M(CO) 5 •THF] acted as a CO source. In an attempt to convert arachno-5 into a closo or nido species, we have pyrolyzed arachno-5 in toluene at 90 °C for 20 h that afforded nido-[2,3-(Cp*Ru) 2 (μ-CO)(μ 3 -H)(B 3 H 6 )] (6) having two ruthenium atoms at the basal position. Irradiation of arachno-5 with an intermediate generated from CS 2 and [LiBH 4 •THF] in THF afforded the diborane(5) species [(Cp*RuCO)(Cp*Ru)(μ-H)(μ-η 1 :η 2 -B 2 H 4 )(CS 2 H)] ( 7) in which a dithioformato ligand (SHC�S) is attached to one Ru−B bond. Compound 7 can be considered as a diborane(5) species, which is stabilized by a dithioformato ligand. All the synthesized compounds have been characterized by employing electrospray ionization-mass spectrometry, multinuclear NMR, and IR spectroscopy techniques. The single-crystal X-ray diffraction studies of compounds 2, 3, 6, and 7 helped to establish the structural integrity of these compounds. Further, density functional theory studies were performed to provide insight into the bonding of these metal-stabilized diborane and triborane species.

Metal Rich Metallaboranes: Synthesis, Structure and Bonding of pileo-[(Cp*Ru)2M(CO)3(µ-H)(µ-E)(µ3-BH)B2H5] (M = Mo, W, E = CO, and M = Mn, E = H) Clusters

“…The solution was subjected to evaporation under reduced pressure and subjected to thin-layer chromatography using silica gel TLC plates for the separation of the reaction mixture. Elution with CH 2 Cl 2 /hexane (10:90 v/v) yielded air-stable pure orange solid 2 (0.037 g, 26%) and known yellow I (0.019 g, 19%) [50] and II (0.009 g, 7%) [46]. Note that the treatment of nido-1 with [W(CO) 5 •THF] (UV irradiation of W(CO) 6 (0.07 g) in 10 mL of THF for 20 min) afforded orange 3 (0.035 g, 22%) along with clusters I (0.019 g, 19%) and II (0.009 g, 7%).…”