Evidence for Cu---H Interactions in Dinuclear Cu(I) Complexes of Hindered Hydrotris (pyrazolyl) Borate Ligands

The structures of the synthetically useful Cu(I) compounds [Tpt-Bu,MeCuI]2·0.5toluene (1) (C51.5H84B2Cu2N12, a=13.2425(2), b=13.9201(2), c=17.6033(3) Å, α =105.137(1), β =106.730(1), γ =103.548(1)°, V=2826.73(8) Å3, triclinic, P1-, Z=2) (TpR,R′ = [HB(3-R,5-R′ pz)3]; pz=pyrazolyl) and [Tpt-Bu,i-PrCuI]2 (2) (C60H104B2Cu2N12, a=23.3168(2), b=14.3594(2), c=20.2819(2) Å, β =99.05(1)°, V=6706.2(1) Å3, monoclinic, P21/c, z=4) have been examined by X-ray analysis as well as by IR and NMR to reveal a complex pattern of B-H---Cu interactions that persist in solution. As opposed to the structures of the pseudo-tetrahedral carbonyl adducts [Tpt-Bu,MeCu(CO)] (3) (C25H40BCuN6O, a=15.502(4), b=9.681(2), c=19.049(6) Å, β =95.94(2)°, V=2843(1) Å3, monoclinic, Pc, Z=4) and [Tpt-Bu,i-PrCu(CO)] (4), the structures of 1 and 2 display an \u27inverted\u27 configuration at the boron atom that directs the B-H units towards the dicopper(I) core at a position suitable for a three-center, two-electron B-H---Cu bonding interaction