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

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 (CF 3 ) 2 PtMe 3 ( 1; Tp (CF 3 ) 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 Tp Me 2 PtMe 3 ( 2; Tp Me 2 = 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−CH 3 bonds are slightly shorter in the fluorinated complex. These structural features are echoed in the relative magnitudes of the J Pt - H and J Pt - C coupling constants for the two complexes. The close spatial contact between the protons of the Pt IV −CH 3 group and fluorines of the 3-CF 3 group of the cis- pyrazole ring results in a formal 6 J H - F = 1.8 Hz. The nature of this coupling with the possible contribution of intramolecular hydrogen bonding is discussed.