N,C,N-Pincers in Platinum Bimetallic Complexes: Influence of the Pincer and Bridging Ligands on the Metal–Metal Bond and the Photophysical Properties

Abstract

Precursors PtCl{κ 3 -N,C,N-[py-C 6 HMe 2 -py]} (1), PtCl{κ 3 -N,C,N-[py-O-C 6 H 3 -O-py]} (2), Pt(OH){κ 3 -N,C,N-[py-C 6 HMe 2 -py]} (3), and Pt(OH){κ 3 -N,C,N-[py-O-C 6 H 3 -O-py]} (4) were used to prepare d 8 -platinum bimetallic complexes. Precursors 1 and 2 react with AgBF 4 and 7-azaindole (Haz) to give [Pt{κ 3 -N,C,N-[py-C 6 HMe 2 -py]}{κ 1 -N-[Haz]}]BF 4 (5) and [Pt{κ 3 -N,C,N-[py-O-C 6 H 3 -O-py]}{κ 1 -N-[Haz]}]BF 4 (6) and 3 and 4 with indolo[2,3-b]indole (H 2 ii) to generate Pt{κ 1 -N-[Hii]}{κ 3 -N,C,N-[py-C 6 HMe 2 -py]} (7) and Pt{κ 1 -N-[Hii]}{κ 3 -N,C,N-[py-O-C 6 H 3 -O-py]} (8). Subsequent addition of 3 and 4 to 5-7 affords bimetallic derivatives [{Pt[κ 3 -N,C,N-(py-C 6 HMe 2py)]} 2 {μ-N,N-[az]}]BF 4 (9), [{Pt[κ 3 -N,C,N-(py-O-C 6 H 3 -O-py)]} 2 {μ-N,N-[az]}]BF 4 (10), and {Pt[κ 3 -N,C,N-(py-C 6 HMe 2py)]} 2 {μ-N,N-[ii]} (11). X-ray structures of 9-11 reveal separations between the metals in sequence 9 (3.0515(4) Å) < 10 (3.2689(9) Å) < 11 (3.2949(2) Å). DFT calculations support σ overlap of the dz 2 orbitals of platinum atoms, for 9 and 10. Accordingly, their absorption spectra show a MMLCT transition. Complex 9 is a red emitter. The excited state has 3 MMLCT characteristics and a Pt−Pt separation of 2.763 Å. Complex 11 is a dual emitter in the red and NIR regions, in solid. Both excited states have a 3 LC/LMCT characteristic and platinum−platinum separations of 3.290 and 3.202 Å. Intermediate 5 is a green emitter that achieves quantum yields close to unity, when diluted in PMMA and 1,2-dichloroethane at low concentrations.