The Synthesis and Structural Characterization of the Sterically Demanding Tris (3,5-di-t-butylpyrazolyl) hydroborato Ligand, [TpBut 2 ]: A Highly Twisted, Propeller-Like, Ligand System

The synthesis of the new stercially demanding tris(3,5-di-t-butylprazolyl) hydroborato ligand, [TpBut 2 ], 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[TpBut 2 ], Cs [TpBut 2 ], Tl [TpBut 2 ], [TpBut 2 ] ZnI, and [TpBut 2 ] CdI, demonstrates that the [TpBut 2 ] ligand adopts a highly twisted propeller-like configuration, a consequence of intra-ligand repulsive interactions between the 5-t-butyl substituents. K[TpBut 2 ] (C6H6)2 is monoclinic, P21/c (No. 14), a = 20.188(3) A, b = 12.794(3) A, c = 18.666(5)A, β = 98.43(2)°, V = 4769(2) A3, Z = 4. Cs [TpBut 2 ] (C6H6) is monoclinic, P21/c (No. 14), a = 13.513(3) A, b = 17.430(4) A, c = 18.437(3) A, β = 99.38(2)°, V = 4283(2) A3, Z = 4. [TpBut 2 ] is monoclinic, P21/c (No. 14), a = 18.644(4) A, b = 10.366(3) A, c = 20.883(4) A, β = 112.73(2)°, V = 3733(2) A3, Z = 4. [TpBut 2 ] ZnI is triclinic, P1 (No. 2), a = 11.095(2) A, b...