Effects of Trifluoromethyl Substituents in a Tris(pyrazolyl)borate Ligand: A Structural and Spectroscopic Study of Analogous Platinum(IV) Trimethyl Complexes

Abstract

To gain insight into how fluorination of the popular hydridotris(pyrazolyl)borate (Tp) ligands modifies the properties of organometallic compounds containing metal-bound alkyls, the novel Pt(IV) complex Tp(CF3)2PtMe3 (1; Tp(CF3)2 = hydridotris(3,5-bis(trifluoromethyl)pyrazolyl)borate) was synthesized and fully characterized. X-ray crystallographic studies were carried out on 1 and on the nonfluorinated analogue TpMe2PtMe3 (2; TpMe2 = hydridotris(3,5-dimethylpyrazolyl)borate). The structural and NMR spectral data for the complexes are compared and provide strong evidence for substantially weaker coordination of the fluorinated Tp ligand. The Pt−N bonds are significantly longer and the Pt−CH3 bonds are slightly shorter in the fluorinated complex. These structural features are echoed in the relative magnitudes of the JPt-H and JPt-C coupling constants for the two complexes. The close spatial contact between the protons of the PtIV−CH3 group and fluorines of the 3-CF3 group of the cis-pyrazole ring results in a formal 6JH-F = 1.8 Hz. The nature of this coupling with the possible contribution of intramolecular hydrogen bonding is discussed.