Synthesis and Photophysical Properties of Cyclometallated Pt(II) 1,2-Benzenedithiolate Complexes and Heterometallic Derivatives Obtained from the Addition of [Au(PCy3)]+ Units

Abstract

The cyclometalated compounds [Pt(C^N)(HC^N)Cl] [HC^N = 2-phenylpyridine (Hppy; 1a), 1-(4-tert-butylphenyl)isoquinoline (Htbpiq; 1b)] react with 1,2-benzenedithiol, t-BuOK, and Bu4NCl in a 1:1:2:1 molar ratio in CH2Cl2/MeOH to give the complexes Bu4N[Pt(C^N)(bdt)] [bdt = 1,2-benzenedithiolate; C^N = ppy (Bu4N2a), tbpiq (Bu4N2b)]. In the absence of Bu4NCl, the same reactions afford solutions of K2a and K2b, which react with [AuCl(PCy3)] to give the neutral heterometallic derivatives [Pt(C^N)(bdt){Au(PCy3)}] [C^N = ppy (3a), tbpiq (3b)]. The cationic derivatives [Pt(C^N)(bdt){Au(PCy3)}2]ClO4 [C^N = ppy (4a), tbpiq (4b)] are obtained by reacting 3a and 3b with acetone solutions of [Au(OClO3)(PCy3)]. The crystal structures of 3b and 4b reveal the formation of short Pt···Au metallophilic contacts in the range 2.929–3.149 Å. Complexes 3b, 4a, and 4b undergo dynamic processes in solution that involve the migration of the [Au(PCy3)]+ units between the S atoms of the dithiolate. Complexes Bu4N2a and 2b display a moderately solvatochromic band in their electronic absorption spectra that can be ascribed to a transition of mixed ML′CT/LL′CT character (M= metal; L = bdt; L′ = C^N; CT = charge transfer), while their emissions are assignable to transitions of the same orbital parentage but from triplet excited states. The successive addition of [Au(PCy3)]+ units to the anions 2a and 2b results in an increase in the absorption and emission energies attributable to lower highest occupied molecular orbital energies. Additionally, the characteristics of the absorption and emission spectra of the heterometallic derivatives indicate a gradual loss of LL′CT character in the involved electronic transitions, with a concomitant increase of the L′C and ML′CT contributions.