A (μ-hydrido)diborane(4) anion and its coordination chemistry with coinage metals

Doubly Base-Stabilized Diborane(4) and Borato-Boronium Species and Their Chemistry with Chalcogens

In an effort to isolate diborane(4) derivatives, we have developed an efficient and uncatalyzed approach using [BH3·THF] and the mercaptopyridine ligand. Thermolysis of 2-mercaptopyridine, in the presence of [BH3·THF], afforded a doubly base-stabilized diborane(4) species 1, [HB(μ-C5H4NS)]2, along with the formation of its isomeric species 2, [HB(μ-C5H4NS)]2, albeit in less yield. Based on the coordination of the boron with the mercaptopyridine ligand in 2 and its spectroscopic data, compound 2 has been designated as a borato-boronium species, in which the anionic borate and cationic boronium units are covalently bonded to each other. Furthermore, we have demonstrated the oxidative insertion of chalcogen atoms (S and Se) through the B-B bond of the base-stabilized diborane(4), 1, that yielded chalcogenido-diboron species, 3(S) and 4(Se).

Diboriranide σ-Complexes of d- and p-Block Metals

Diboriranides are the smallest conceivable monoanionic aromatic cycles, yet only limited examples have been reported and their reactivity and complexation behavior remain completely unexplored. We report a straightforward synthesis of the first peraryl diboriranide c-(DurB)2 CPh- as its lithium salt in three steps via the corresponding non-classical diborirane from a readily available 1,2-dichlorodiborane(4) (Dur=2,3,5,6-tetramethylphenyl). With the preparation and complete characterization of representative complexes with tin, copper, gold and zinc, we demonstrate the strong preference of the diboriranide for σ-type coordination modes towards main group and transition metal centers under unperturbed retention of the three-membered B2 C-ring's 2e- π-system.

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 [Cp*Ru(PPh3)2Cl] (1) (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl; PPh3 = triphenylphosphine) with [BH3·THF] (THF = tetrahydrofuran) at 60 °C led to the formation of the hydrogen-rich ruthena-octahydrotetraborane arachno-[2-{Cp*Ru(PPh3)B3H8}] (2). The chemistry of 2 is explored with [Fe2(CO)9] at room temperature, which resulted in the formation of a metal-stabilized triborane species, [{Cp*Ru(PPh3)}(μ3-η1:η2:η2-B3H6){Fe2(CO)7}] (3). Compound 3 can be considered as a triborane analogue [B3H6]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(B3H7)] (4) with [M(CO)5·THF] (M = Mo and W) afforded an arachno-[1,2-(Cp*Ru)(Cp*RuCO)(μ-H)(B3H8)] (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)(μ3-H)(B3H6)] (6) having two ruthenium atoms at the basal position. Irradiation of arachno-5 with an intermediate generated from CS2 and [LiBH4·THF] in THF afforded the diborane(5) species [(Cp*RuCO)(Cp*Ru)(μ-H)(μ-η1:η2-B2H4)(CS2H)] (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.