Synthesis and structure determination of Rh-diene complexes with the hydridotris(3,5-diisopropylpyrazolyl)borate ligand, Tp(iPr)Rh(diene) (diene = cod, nbd): Dependence of the nu(B-H) values on the hapticity of the Tp(iPr) ligand (kappa(2) vs kappa(3))(1)

Rhodium-diene complexes with the Tp(iPr) ligand, Tp(iPr)Rh(diene) (Tp(iPr) = hydridotris(3,5-diisopropylpyrazolyl)borate; diene = 1,5-cyclooctadiene (cod) (1), norbornadiene (nbd) (2)), are prepared by treatment of [Rh(mu-Cl)(diene)](2) with KTp(iPr) or TlTp(iPr), The structure of 1, characterized by X-ray crystallography, contains the kappa(2)-coordinated Tp(iPr) ligand, and its central Rh atom adopts a square-planar geometry, whereas the unit cell of 2 contains two independent molecules: a square-planar structure with a kappa(2)-coordinated Tp(iPr) ligand similar to 1 and a trigonal-bipyramidal one with a kappa(3)-coordinated Tp(iPr) ligand, Although H-1 and C-13 NMR spectroscopy does not provide any information concerning the coordination geometry due to the interconversion between the square-planar and trigonal-bipyramidal structures, which occurs at a rate much faster than the NMR time scale, IR analysis reveals that the bands observed around 2470 and 2540 cm(-1) are assigned to the B-H stretching vibrations of the square-planar and trigonal-bipyramidal structures, respectively, Thus, the nu(B-H) value can be used as an indicator of the hapticity of a Tp(iPr) ligand (kappa(2) (similar to 2470 cm(-1)) us kappa(3)(>2530 cm(-1))) as compared with related Tp(iPr)ML(n)-type complexes.