Heterolytic CH-bond activation in the synthesis of Ni{(2-aryl-κC2)pyridine-κN}2 and derivatives

Thermolysis of Ni(OTf)2 in 2-phenyl-pyridine or 2-tolyl-pyridine afforded the cationic chelate derivatives, [bis(2-aryl-pyridine)Ni{(2-aryl-κC2)pyridine-κN}]OTf (aryl = phenyl, 1a; tolyl, 1b). Addition of KBr to 1a and LiBr to 1b provided the bromides, (2-aryl-pyridine)BrNi{(2-aryl-κC2)pyridine-κN} (aryl = phenyl, 2a; tolyl, 2b). When subjected to KOtBu in Et2O, the bromides generated the entitled bis-cyclometalated compounds, Ni{(2-aryl-κC2)pyridine-κN}2 (aryl = phenyl, 3a; tolyl, 3b). These compounds insert diphenylacetylene into one cyclometalate arm to produce [(2-aryl-κC2)pyridine-κN]Ni[2-(2-(1,2-diphenylethenyl-κC2)aryl)pyridine-κN] (aryl = phenyl, 4a; p-tolyl, 4b). X-ray crystallographic studies were conducted on 1a, 2a, 3a and 4a, and a brief DFT study of 3a confirmed its low spin configuration and rippled geometry.

Graphical abstractWhen subjected to KOtBu in Et2O, the bromides (2-aryl-pyridine)BrNi{(2-aryl-κC2)pyridine-κN} (aryl = phenyl, 2a; tolyl, 2b) generated the entitled bis-cyclometalated compounds, Ni{(2-aryl-κC2)pyridine-κN}2 (aryl = phenyl, 3a; tolyl, 3b), whose low spin configuration and rippled geometry were confirmed by X-ray crystallography and a DFT study.Figure optionsDownload full-size imageDownload as PowerPoint slide