Correlations and Contrasts in Homo- and Heteroleptic Cyclic (Alkyl)(amino)carbene-Containing Pt(0) Complexes.

An improved synthetic route to homoleptic complex [Pt(CAAC(Me))2] (CAAC = cyclic (alkyl)(amino)carbenes) and convenient routes to new heteroleptic complexes of the form [Pt(CAAC(Me))(PR3)] are presented. Although the homoleptic complex was found to be inert to many reagents, oxidative addition and metal-only Lewis pair (MOLP) formation was observed from one of the heteroleptic complexes. The spectroscopic, structural, and electrochemical properties of the zero-valent complexes were explored in concert with density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations. The homoleptic [Pt(CAAC)2] and heteroleptic [Pt(CAAC)(PR3)] complexes were found to be similar in their spectroscopic and structural properties, but their electrochemical behavior and reactivity differ greatly. The unusually strong color of the CAAC-containing Pt(0) complexes was investigated by TD-DFT calculations and attributed to excitations into the LUMOs of the complexes, which are predominantly composed of bonding π interactions between Pt and the CAAC carbon atoms.