One-Pot and Step-by-Step N-Assisted CPh−H Activation in 2-(4-Bromophenyl)imidazol[1,2-a]pyridine: Synthesis of a New C,N-Cyclometalated Compound [{Pt(C∧N)(μ-Cl)}2] as Precursor of Luminescent Platinum(II) Compounds

Abstract

The activation of a CPh−H bond in the phenyl ring of 2-(4-bromophenyl)imidazol[1,2-a]pyridine (HC∧N) by [{Pt(η3-C4H7)(μ-Cl)}2] (η3-C4H7 = η3-2-methylallyl) renders the new cyclometalated complex [{Pt(C∧N)(μ-Cl)}2] (2) with high yield and selectivity. Complex 2 can be achieved directly in a one-pot reaction or step by step through the intermediate [Pt(η3-C4H7)Cl(HC∧N-κN)] (1). Compound 1 could be isolated and fully characterized. The X-ray structure shows the coordination of HC∧N through only the N and the existence of a weak Pt···H−C hydrogen bridging bond (Pt···H1 = 2.78 A, Pt···C1 = 3.365(3) A, Pt−H1−C1 = 120.9°). Hence, the formation of this intermediate could be considered the first step in the cyclometalation process. The mononuclear complexes [PtCl(C∧N)L] (L = tht (3), PPh3 (4), CN-Xyl (5), CN-tBu (6)) were obtained by cleavage of the bridging system in [{Pt(C∧N)(μ-Cl)}2] (2) by the neutral ligands, L. The resulting geometry (trans C, Cl) is that expected from the electronic preferences, taking into...