Synthesis and Structure Determination of Rh−diene Complexes with the Hydridotris(3,5-diisopropylpyrazolyl)borate Ligand, TpiPrRh(diene) (diene = cod, nbd): Dependence of the ν(B−H) Values on the Hapticity of the TpiPrLigand (κ2vs κ3)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(μ-Cl)(diene)] 2 with KTp iPr or TlTp iPr . The structure of 1, characterized by X-ray crystallography, contains the κ 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 κ 2 -coordinated Tp iPr ligand similar to 1 and a trigonal-bipyramidal one with a κ 3 -coordinated Tp iPr ligand. Although 1 H and 13 C 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 ν(B−H) value can be used as an indicator of the hapticity of a Tp iPr ligand (κ 2 (∼2470 cm - 1 ) vs κ 3 (>2530 cm - 1 )) as compared with related Tp iPr ML n -type complexes.