Highly Substituted Tris(pyrazolyl)methane Ligands and Some Zinc Complexes Thereof

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Abstract
Tris(pyrazolyl)methane ligands in which two or three of the pyrazole carbon atoms bear organic substituents (L1‐L7) were synthesized from chloroform and the corresponding pyrazole under phase transfer conditions. Their behavior towards zinc salts was found to span the range from no reaction at all to hydrolytic destruction. One hydrolysis product isolated and structurally characterized was the perchlorate complex [(HPz5)3Zn‐OClO3]ClO4 (1), other ones were the 2:1 complexes (HPz3)2ZnBr2 (2) and (HPz6)2Zn(NO3)2 (3, HPzn = substituted pyrazole). Zinc perchlorate and tris(trimethylpy‐razolyl)methane (L2) formed the octahedral binary complex [L22Zn](ClO4)2 (4) as evidenced by a structure determination. Zinc halides produced the 1:1 complexes L1 · ZnBr2 (5), L4 · ZnCl2 (6), and L4 · ZnBr2 (7), which according to the structure determinations of 6 and 7 contain tetrahedral ZnN2Hal2 units with only bidentate tris(pyrazolyl)methane ligands. In contrast, the zinc nitrate complex L4 · Zn(NO3)2 (8) was found to have an octahedral structure with mono‐ and bidentate nitrate and tridentate L4. The bromide complex 7 was converted by silver perchlorate hydrate into the labile compound [L4 · ZnBr]ClO4 (9) and then into the unstable product [L4 · Zn‐OH2](ClO4)2 (10), both presumed to contain zinc in a tetrahedral ZnN3Br or ZnN3O environment, respectively. The ease of hydrolytic self‐destruction prevented the exploitation of the reactivity of 9 and 10 in analogy to that of the corresponding tris(pyrazolyl)borate zinc complexes.

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