Remarkable Influence of the Cyclometalating Ligand on the Nuclearity and Properties of Heterobridged (μ-X)(μ-C≡CR) Platinum(II) Complexes

Abstract

Partial dehalogenation reaction of [Pt(C ∧ N)(μ-Cl)] 2 [C ∧ N = 2,6-diphenylpyridinate (dppyH), 7,8-benzoquinolate (bzq)] with NaCtC t Bu (or HCtC t Bu/NEt 3 /CuI) proceeds with formation of binuclear ([{Pt(dppyH)} 2 (μ-Cl)(μ-CtC t Bu)], 1) or tetranuclear ([Pt 2 (bzq) 2 (μ-Cl)(μ-CtC t Bu)] 2 , 4) complexes, depending on the nature of the cyclometalated ligand. Similar halide-bridged complexes 2, 3, 5, and 6 have also been prepared. The X-ray structures of 1, 4, and 5 reveal the selective formation in all cases of the isomer having the bridging chlorine atom located in a trans position to the metalated carbon atoms of two Pt(C ∧ N) units. In 4 and 5, the tetrahedral Pt 4 core is additionally stabilized by short Pt 3 3 3 Pt and π 3 3 3 π intramolecular bonding interactions, which have influence on their photophysical properties. The lower lying absorption bands are ascribed to mixed 1 MLCT [PtfdppyH]/ 1 LL 0 CT [CtCR/XfdppyH] (complexes 1-3) or to 1 MMLL 0 CT transitions (L = CtCR, L 0 = bzq) (complexes 4-6, TD-DFT). Complexes 1-3 are nonemissive. By contrast, the tetranuclear clusters are brightly emissive at 77 K (solid state, frozen CH 2 Cl 2 ), exhibiting an unstructured orange emission (560-580 nm). This emission has been attributed, according to computational studies of the frontier orbitals in the optimized T 1 state of 5, to an excited state of large [Pt(d)/π(CtCR)/Pt(d)fbzq/bzq] character, with the LUMO delocalized on the adjacent Pt(bzq) fragments. In frozen CH 2 Cl 2 , an additional low-energy shoulder (∼640-675 nm) is also detected, probably due to the presence of close distinct emissive states originating in small modifications in the ground-state structure in frozen solution.

Synthesis, Characterization, and Properties of Doubly Alkynyl Bridging Dinuclear Cyclometalated Iridium(III) Complexes

“…Following our successful work on alkynyl bridging homo and heteropolynuclear cycloplatinated complexes, ,,,,, we sought to explore the design of homo- and heteromultinuclear iridium cyclometalating systems based on alkynyl bridging ligands. In this contribution, we describe the synthesis of the first examples of cyclometalated dinuclear Ir III complexes [Ir­(ppy) 2 (μ-CCR)] 2 (R = Tol 1 , C 6 H 4 OMe-4 2 , 1-Np 3 , SiMe 3 4 , and t Bu 5 ), stabilized by a double σ:η 2 alkynyl bridging system.…”

Synthesis, Structural, and Photophysical Studies of Phenylquinoline and Phenylquinolinyl Alkynyl Based Pt(II) Complexes

“…The synthesis of these complexes required the use of appropriate LiCCR as alkynylating agent and subsequent precipitation of the in situ formal anionic species with tetrabutylamonium. By contrast, treatment of the binuclear [Pt(C ∧ N)­(μ-Cl)] 2 precursors with HCCR in the presence of NaOMe (or HCCR/​NEt 3 /CuI) evolves with formation of the binuclear [{Pt­(dppyH)} 2 ­(μ-Cl)­(μ-CC t Bu)] or unusual tetranuclear clusters [Pt 2 (bzq) 2 ­(μ-Cl)­(μ-CCR) 2 ] 2 (R = t Bu, Ph, C 6 H 4 CF 3 -4), depending on the nature of the cyclometalating ligand . Aiming to expand the family of anionic precursors of the type bis(alkynyl)cycloplatinate systems [Pt(C ∧ N)(CCR) 2 ] − , we decided to study the reactions of the phenylquinolinyl derivative [Pt(pq)­(μ-Cl)] 2 with LiCCR.…”