Zinc Halide and Alkylzinc Complexes of a Neutral Doubly Base-Stabilized Diborane(4)

The doubly base-stabilized diborane(4) [HB(mu-hpp)](2) (hpp = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-alpha]pyrimidinate) was used as a ligand in the first authenticated example of a dialkylzinc complex and the second example of a zinc halide complex featuring a neutral boron hydride as ligand. The three complexes [ZnCl(2){HB(mu-hpp)}(2)] (2), [ZnBr(2){HB(mu-hpp)}(2)] (3), and [ZnMe(2){HB(mu-hpp)}(2)] (4) were fully characterized. The bonding properties were analysed in detail. This analysis indicated a complex bonding situation involving not only the two hydrogen atoms, but also the two boron atoms of the [HB(mu-hpp)](2) ligand.