Transition Metal Complexes of Optically Active Tris(pyrazolyl)hydroborates

The synthesis and characterization of a series of complexes of the recently reported (LeCloux, D. D.; Tokar, C. J.; Osawa, M.; Houser, R. P.; Keyes, M. C.; Tolman, W. B. Organometallics 1994, 13, 2855–2866) ligands tris(7(R)-isopropyl-4(R)-methyl-4,5,6,7-tetrahydroindazolyl)hydroborate (Tp^Menth) and tris(7(S)-tert-butyl-4(R)-methyl-4,5,6,7-tetrahydroindazolyl)hydroborate (Tp^Mementh) are presented. Specific complexes prepared are Tp^MenthM^IICl (M^II= Zn^II, Ni^II, Co^II, Cu^II, Mn_IIFe^II), Tp^MementhZn^IICl, Tp^MenthM^II(NO₃) (M^II = Cu^II,Ni^II), Tp^MenthM^II(OAc) (M^II = Cu^II, Ni^II), Tp^MenthRh^I(CO)₂) Tp^MenthTi^IV cl₃, and Tp^Menth*Ti^IVCl₃, where Tp^Menth* is an isomerized version of Tp^Menth in which one pyrazolyl group is attached to boron via the more, rather than the less, hindered N atom. Structural hypotheses are proposed on the basis of analytical and spectroscopic data for all compounds and X-ray crystal structures for Tp^MenthZnCl, Tp^MementhZnCl, Tp^MenthNi(OAc), and Tp^Menth*TiCl₃. Pseudooctahedral 4-coordinate (Tp^MenthMCl and Tp^MementhZnCl), distorted square pyramidal 5-coordinate [Tp^MenthM(OAc) and Tp^MenthM(NO₃)], and octahedral 6-coordinate (Tp^MenthTiCl₃ and Tp^Menth*TiCl₃) metal ion geometries were identified. IR and NMR data indicated that Tp^MenthRh(CO)₂ exists as a mixture of 4- and 5-coordinate isomers. The combined synthetic, spectroscopic, and structural data for the complexes we have synthesized suggest that the chiral Tp ligands have effective steric properties similar to those of achiral variants with 3-tert-butyl or 3-isopropyl substituents on the pyrazolyl rings. X-ray data for Tp^MenthZnCl: orthorhombic, space group P2₁2₁2₁ (No. 19), at −101 °C, a = 9.658(7) Å, b = 17.717(7) Å, c = 20.058(6) Å, V = 3444(5) ų, Z = 4, R = 0.063 and R_w = 0.049 for 4055 reflections with I > 2σ(I) and 379 parameters. X-ray data for Tp^MementhZnCl: orthorhombic, space group P2₁2₁2₁ (No. 19), at 24 °C, a = 11.170(4) Å, b = 14.829(9) Å, c = 23.063(9) Å, V = 3820(5) ų, Z = 4, R = 0.055 and R_w = 0.056 for 4566 reflections with I > 2σ(I) and 407 parameters. X-ray data for Tp^MenthNi(OAc): orthorhombic space group P2₁2₁2₁ (No. 19), at 24 °C, a = 10.139(5) Å, b = 18.248(8) Å, c = 19.700(8) Å,V= 3645(5) ų, Z = 4, R = 0.043 and R_w = 0.039 for 3721 reflections with I > 2σ(I) and 406 parameters. X-ray data for Tp^Menth*TiCl₃·CH₂Cl₂: orthorhombic, space group P2₁2₁2₁ (No. 19), at —100 °C, a = 10.335(8) Å, b = 15.430(7) Å, c = 25.11(1) Å, V= 4004(7) ų, Z = 4, R = 0.070 and R_w = 0.071 for 3831 reflections with I > 2σ(I) and 424 parameters.