New methoxo-, hydroxo-, and pyrazolate-bridged complexes of rhodium(III). Crystal structures of [{Rh(C5Me5)}2(mpz)(OMe)2][ClO4](mpz = 3-methylpyrazolate), [{Rh(C5Me5)}2(Hdmpz)2(OH)2][BF4]2(Hdmpz = 3,5-dimethylpyrazole), and [{Rh(C5Me5)}2(pz)2(OH)]-[ClO4](pz = pyrazolate)

Abstract

The tri-µ-hydroxo-dirhodium cation [{Rh(C₅Me₅)}₂(OH)₃][CIO₄](1) reacts with pyrazole type ligands (HL), in methanol, to give [{Rh(C₅Me₅)}₂(L)(OMe)₂][CIO₄] complexes, containing one bridging pyrazolate ligand and two bridging methoxo-groups. Reactions of complex (1) with an equimolecular amount of pyrazole (Hpz), in the absence of methanol, gave mixtures of the µ-hydroxo-µ-pyrazolate complexes [{Rh(C₅Me₅)}₂(pz)(OH)₂][ClO₄] and [{Rh(C₅Me₅)}₂(pz)₂(OH)][ClO₄], but only the latter was isolated. Di-µ-hydroxo-complexes [{Rh(C₅Me₅)}₂(HL)₂(OH)₂][A]₂[HL = 3,5-dimethylpyrazole (Hdmpz) or 3(5)-methyl,5(3)-phenylpyrazole (Hmppz); A = ClO₄ or BF₄] are obtained by addition of the appropriate pyrazole to [{Rh(C₅Me₅)}₂(OH)₃][ClO₄] in acetone or methanol, or the pyrazole and base to the solvated complex [Rh(C₅Me₅)(Me₂CO)₃][BF₄]₂, in acetone. However, the µ-hydroxo-di-µ-pyrazolate complexes [{Rh(C₅Me₅)}₂(L)₂(OH)][A] were obtained by addition of pyrazole itself and base to [Rh(C₅Me₅)(Me₂CO)₃][A]₂. Single-crystal X-ray structure determinations have been carried out on [{Rh(C₅Me₅)}₂(mpz)(OMe)₂][ClO₄](Hmpz = 3-methylpyrazole), [{Rh(C₅Me₅)}₂(Hdmpz)₂(OH)₂][BF₄]₂, and [{Rh(C₅Me₅)}₂(pz)₂(OH)][ClO₄]. They show two rhodium atoms per cation, each η⁵-bonded to a C₅Me₅ group, bridged by the proposed methoxo, hydroxo, or pyrazolate ligands. The rhodium–rhodium distances are 3.200(1), 3.360(1), and 3.488(1)Å, respectively.