The synthesis and structural characterization of the sterically demanding tris(3,5-di-t-butylpyrazolyl) hydroborato ligand, [Tp(Bu-2(t))]: A highly twisted, propeller-like, ligand system

The synthesis of the new sterically demanding tris(3,5-di-t-butylpyrazolyl) hydroborato ligand, [Tp(Bu2t)], in which both the 3- and 5-positions of the pyrazolyl group are occupied by bulky t-butyl substituents is described. The structural characterization of several derivatives, namely K[Tp(Bu2t)], Cs [Tp(Bu2t)], Tl [Tp(Bu2t)], [Tp(Bu2t)] ZnI, and [Tp(Bu2t)] CdI, demonstrates that the [Tp(Bu2t)] ligand adopts a highly twisted propeller-like configuration, a consequence of intra-ligand repulsive interactions between the 5-t-butyl substituents. K[Tp(Bu2t)] (C6H6)(2) is monoclinic, P2(1)/c (No. 14), a=20.188(3)Angstrom, b=12.794(3)Angstrom, c=18.666(5)Angstrom, beta=98.43(2)degrees, b=17.430(4)Angstrom, c=18.437(3)Angstrom, beta=99.38(2)degrees, V=4283(2)Angstrom(3), Z=4. Tl[Tp(Bu2t)] is monoclinic, P2(1)/c (No. 14), a=18.644(4)Angstrom, b=10.366(3)Angstrom, c=20.883(4)Angstrom, beta=112.73(2)degrees, V=3733(2)Angstrom(3), Z=4. [Tp(Bu2t)] ZnI is triclinic, P (1) over bar (No. 2), a=11.095(2)Angstrom, b=13.236(4)Angstrom, c=13.302(5)Angstrom, alpha=95.15(3)degrees, beta=93.82(3)degrees, gamma=101.55(3)degrees, V=1899(1)Angstrom(3), Z=2. [Tp(Bu2t)] is monoclinic, P2(1)/c (No. 14), a=9.908(2)Angstrom, b=18.962(4)Angstrom, c=22.012(4)Angstrom, beta=100.84(2)degrees, V=4057(2)Angstrom(3), Z=4.