HYDROTRIS(3-NEOPENTYLPYRAZOL-1-YL)BORATES - A NEW TYPE OF STERICALLY HINDERED POLY(PYRAZOLYL)BORATE

The new ligand hydrotris(3-neopentylpyrazol-1-yl)borate (=L*) was synthesized and found useful in preparing heteroleptic L*ML compounds, by the reaction of its stable L*MCI derivatives with L-. Examples of L included pseudohalides,in which case L*ML complexes were tetrahedral, various tris(pyrazolyl)borates, which led to octahedral complexes of C3, symmetry, and H2B(3,5-Me2pz)2, which yielded complexes containing five N-bonds to the metal, plus an agostic B-H-M bond. L*2M complexes (M = Co, Ni, Fe) were also obtained, as were the complexes L*Mo(CO)2(pi-methallyl) and L*Rh(CO)2. Structures of the compounds Co[HB(3-neopentylpyrazol-1-yl)3]NCO and Ni[HB(3-neopentylpyrazol-1-yl)3]2 were established by X-ray crystallography. The former complex, CoON7C25BH40, crystallizes in the monoclinic space group P2(1)/n (No. 14), with four molecules per unit cell of dimensions a = 12.240 (2) angstrom, b = 10.496 (2) angstrom, c = 23.103 (6) angstrom, and beta = 94.52 (2)-degrees, at -70-degrees-C. Least-squares refinement of 316 variables led to a value of the conventional R index (on F) of 0.053 and a value of R(w) = 0.051 for 3591 reflections with I > 3.0sigma(I). The Co(II) ion is coordinated to three pyrazolyl nitrogens of L* and one nitrogen of the linear NCO ligand. The L*2Ni complex, NiCl2N12C49B2H82, crystallizes on the triclinic space group P1BAR (No. 2), with one molecule per unit cell of dimensions a = 10.211 (2) angstrom, b = 12.327 (4) angstrom, c = 12.932 (2) angstrom, alpha = 107.55-degrees, beta = 10 1.49 (1)-degrees, and gamma = 106.80 (2)-degrees, at -70-degrees-C. Least-squares refinement of 304 variables led to a value of the conventional R index (on F) of 0.068 and a value of R(w) = 0.065 for 3831 reflections with I > 3.0sigma(I). The Ni(II) ion is coordinated to six pyrazolyl nitrogens of two L* ligands. This complex is five-coordinate in solution, while L*2Co is five-coordinate in the solid state but tetrahedral in solution. Both compounds rearrange on heating to high-melting, octahedral complexes containing the mixed ligand HB(3-neopentyl-pz)2(5-neopentyl-pz).