Synthesis and solid-state characterization of platinum complexes with hexadentate amino- and iminophosphine ligands.

Hexadentate ligands cis,cis-C(6)H(9)(N[double bond, length as m-dash]CHC(6)H(4)(PPh(2)))(3) () and cis,cis-C(6)H(9)(NHCH(2)C(6)H(4)(PPh(2)))(3) () were synthesized starting from cis,cis-1,3,5-triaminocyclohexane, and characterized using NMR spectroscopy and single-crystal X-ray diffraction. These ligands can bind both Pt(0) and Pt(II) metal centers using either or both of the soft phosphine moieties and the hard amine/imine moieties. In many cases the resulting complexes are negligibly soluble; hence, (31)P and (195)Pt solid-state NMR (SSNMR) spectroscopy was applied to analyse the bonding modes of the hexadentate ligands. The (195)Pt SSNMR spectroscopy of these complexes is particularly challenging, since (1)H-(195)Pt cross polarization is extremely inefficient, the (195)Pt longitudinal relaxation times are extremely long and the (195)Pt powder patterns are expected to be quite broad due to platinum chemical shift anisotropy. It is demonstrated that the ultra-wideline (195)Pt SSNMR spectra can be efficiently acquired with a combination of frequency-stepped piecewise acquisitions and cross-polarization/Carr-Purcell Meiboom-Gill (CP/CPMG) NMR experiments. The (195)Pt and (31)P SSNMR data are correlated to important structural features in both Pt(0) and Pt(II) species.