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

The synthesis and structural elucidation of a series of ruthenium diborane and triborane compounds are described. Treatment of [CpRu(PPh)Cl] () (Cp = 1,2,3,4,5-pentamethylcyclopentadienyl; PPh = triphenylphosphine) with [BH·THF] (THF = tetrahydrofuran) at 60 °C led to the formation of the hydrogen-rich ruthena-octahydrotetraborane -[2-{CpRu(PPh)BH}] (). The chemistry of is explored with [Fe(CO)] at room temperature, which resulted in the formation of a metal-stabilized triborane species, [{CpRu(PPh)}(μ-η:η:η-BH){Fe(CO)}] (). Compound can be considered as a triborane analogue [BH] that stabilizes in the coordination sphere of two iron and one ruthenium atoms. Further, the photolysis of -[1,2-(CpRu)(μ-H)(BH)] () with [M(CO)·THF] (M = Mo and W) afforded an -[1,2-(CpRu)(CpRuCO)(μ-H)(BH)] (), in which the [M(CO)·THF] acted as a CO source. In an attempt to convert - into a or species, we have pyrolyzed - in toluene at 90 °C for 20 h that afforded -[2,3-(CpRu)(μ-CO)(μ-H)(BH)] () having two ruthenium atoms at the basal position. Irradiation of - with an intermediate generated from CS and [LiBH·THF] in THF afforded the diborane(5) species [(CpRuCO)(CpRu)(μ-H)(μ-η:η-BH)(CSH)] () in which a dithioformato ligand (SHC═S) is attached to one Ru-B bond. Compound 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 , , , and 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.