Trinuclear and Cyclometallated Organometallic Dinuclear Pt-Pyrazolato Complexes: A Combined Experimental and Theoretical Study

Two differently substituted pyrazole ligands have been investigated with regard to the topology of their Pt complexes: upon deprotonation, two mononuclear 1:2 Pt-II-pyrazole complexes-one of the sterically unhindered 4-Me-pzH and one of the bulky 3,5-Bu-t-pzH (pzH = pyrazole)-yield the corresponding 1:2 Pt-II-pyrazolato species; the former a triangular, trinuclear metallacycle (1), and the latter a dinuclear, half-lantern species (2) formed via the unprecedented cyclometallation of a butyl group. Stoichiometric oxidation of the colorless Pt-2(II) complex produces the deep-blue, metal-metal bonded Pt-2(III) analog (3) with a rarely encountered unsymmetrical coordination across the Pt-Pt bond. All three complexes have been characterized by single crystal X-ray structure determination, H-1-NMR, IR, and UV-vis-NIR spectroscopic methods. The XPS spectra of the Pt-2(II) and Pt-2(III) species are also reported. Density functional theory calculations were carried out to investigate the electronic structure, spectroscopic properties, and chemical bonding of the new complexes. The calculated natural population analysis charges and Wiberg bonding indices indicate a weak sigma-interaction in the case of 2 and a formal Pt-Pt single bond in 3.