Structural Diversity in the Reaction of Mono- and Disubstituted Pyrazoles with Titanium Tetrachloride. Importance of Hydrogen Bonding and Trends in cis/trans Geometry of Binary Adducts with Unidentate Ligands.

Treatment of titanium tetrachloride with 3,5-di-tert-butylpyrazole affords the complexes [3,5-(C(CH(3))(3))(2)C(3)H(3)N(2)](2)[TiCl(6)] and (3,5-(C(CH(3))(3))(2)C(3)HN(2))(2)TiCl(2) in 37 and 42% yields, respectively. An analogous reaction with 3,5-dimethylpyrazole, 3-methylpyrazole, 4-bromopyrazole, and 4-iodopyrazole leads to the formation of corresponding TiCl(4)L(2) binary adducts in 30-86% yields. Crystal structures of [3,5-(C(CH(3))(3))(2)C(3)H(3)N(2)](2)[TiCl(6)], (3,5-(C(CH(3))(3))(2)C(3)HN(2))(2)TiCl(2), TiCl(4)(3,5-(CH(3))(2)C(3)H(2)N(2))(2), and TiCl(4)(4-IC(3)H(3)N(2))(2) were determined. [3,5-(C(CH(3))(3))(2)C(3)H(3)N(2)](2)[TiCl(6)] crystallizes in the space group C2/c with a = 18.892(4) Å, b = 7.1200(10) Å, c = 24.461(6) Å, beta = 103.78(2) degrees, and Z = 4. (3,5-(C(CH(3))(3))(2)C(3)HN(2))(2)TiCl(2) crystallizes in the space group P2(1)/n with a = 12.283(10) Å, b = 17.891(8) Å, c = 12.580(6) Å, beta = 90.96(4) degrees, and Z = 4. TiCl(4)(3,5-(CH(3))(2)C(3)H(2)N(2))(2) crystallizes in the space group C2/c with a = 12.087(2) Å, b = 12.922(3) Å, c = 10.403(2) Å, beta = 92.08(2) degrees, and Z = 4. TiCl(4)(4-IC(3)H(3)N(2))(2) crystallizes in the space group C2/c with a = 9.252(2) Å, b = 8.660(2) Å, c = 19.652(4) Å, beta = 102.14(3) degrees, and Z = 4. An analysis of factors governing the cis/trans geometry of MCl(4)L(2) (M = Ti, Zr, Hf) complexes is offered.