Substituent effect on organotin Tp* compounds as the Tp* reagent for the preparation of mono Tp* complexes of group 4 - 6 metals (Tp* = tris(3,5-dimethylpyrazol-1-yl)hydroborate)

Organotin compounds [Tp*SnCl₃-(n)Bu(n)] (2: n = 1; 3: n = 2) having a Tp* ligand (Tp* = tris(3,5-dimethylpyrazol-1-yl)hydroborate) are useful reagents for introducing a Tp* ligand on Group 4 and 5 metals and chromium. The test reactions of these organotin compounds along with [Tp*SnCl₃] (1) with ZrCl₄, affording a known complex [Tp*ZrCl₃] (4), were examined. The reaction rates were in the order 3 > 2 >> 1. This tendency was understood by the average Sn-N(Tp* ligand) bond distance being longer in the order 3 > 2 > 1 as revealed by the crystallographic studies and the orbital interactions between the Tp* ligand and the SnCl₃-(n)Bu(n) fragments estimated by the ab initio calculations for 1 - 3. On the basis of the above findings, we applied the compound 3 to prepare Tp* complexes of Group 4 - 6 metals. Reactions of TiCl₄ with an equimolar amount of 3 afforded [Tp*TiCl₃] (7) in good yields after a simple rinse to remove the resulting tin compound, SnBu₂Cl₂. [Tp*HfCl₃] (8) was prepared in moderate yield by reaction of [HfCl₄(THF)₂] with 3 under severe conditions. Similarly, the reactions of 3 with a stoichiometric amount of [NbCl₄(THF)₂] or [NbCl₅(OEt)₂] and TaCl₅ in toluene gave [Tp*NbCl₃] (9) and [Tp*TaCl₃][TaCl₆] (10), respectively. We also applied our synthetic method to prepare Tp* complexes of vanadium, [Tp*VCl₂(THF)] (11), [Tp*VCl₂(DNAP)] (12) (DMAP = 4-dimethylaminopyridine), and [Tp*VCl₂(=NC₆H₃Me₂-2,6)] (13) and those of chromium, [Tp*CrCl₂(L)] (14: L = THF; 15: L = H₂O; 16: L = DMAP). Some of these Tp* complexes, 4, 8, 12, 13, 15, and 16 were crystallographically characterized to have discrete octahedral geometry containing the facial coordination of the Tp* ligand.