Europium(II) and Ytterbium(II) Cyclic Organohydroborates:  An Europium(II) Complex with an Agostic Interaction

Lanthanide bis((cyclooctane-1,5-diyl)dihydroborate) complexes (THF)4Ln{(μ-H)2BC8H14}2 (Ln = Eu, 1; Yb, 2) were synthesized by a metathesis reaction between (THF) x LnCl2 and K[H2BC8H14] in THF in a 1:2 molar ratio. Attempts to prepare the monosubstituted lanthanide cyclic organohydroborates (THF) x LnCl{(μ -H)2BC8H14} were unsuccessful. On the basis of the molecular structure and IR spectrum of 1, there is an agostic interaction between Eu(II) and one of the α-C−H hydrogens from the {(μ-H)2BC8H14} unit. No such interaction was observed for 2. The coordinated THF in 1 and 2 can be removed under dynamic vacuum, but the solvent ligands remain bound to Yb when 2 is directly dissolved in Et2O or toluene. In strong Lewis basic solvents, such as pyridine or CH3CN, attack of the Yb−H−B bridge bonds results. Decomposition of 2 to the 9-BBN dimer in CD2Cl2 was observed by 11B and 1H NMR spectroscopies. Compound 2 was reacted with 2 equiv of the hydride ion abstracting reagent B(C6F5)3 to afford the solvent-separated ion pair [Yb(THF)6][HB(C6F5)3]2 (3). Complexes 1, 2, and 3 were characterized by single-crystal X-ray diffraction analysis. Crystal data: 1 is orthorhombic, Pna21, a = 21.975(1) Å, b = 9.310(1) Å, c = 16.816(1) Å, Z = 4; 2 is triclinic, P1̄, a = 9.862(1) Å, b = 10.227(1) Å, c = 10.476(1) Å, α = 69.87(1)°, β = 76.63(1)°, γ = 66.12(1)°, Z = 1; 3·Et2O is triclinic, P1̄, a = 13.708(1) Å, b = 14.946(1) Å, c = 17.177(1) Å, α = 81.01(1)°, β = 88.32(1)°, γ = 88.54(1)°, Z = 2.