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Insertion Reactions of (Benzyne)nickel(0) Complexes with Carbon Monoxide:  X-ray Structure of a (Phthalato)nickel(II) Complex Formed by Oxidation of an η11-Phthaloyl Intermediate

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journal contribution
posted on 06.02.1996, 00:00 by Martin A. Bennett, David C. R. Hockless, Mark G. Humphrey, Madeleine Schultz, Eric Wenger
The reaction of (benzyne)nickel(0) complexes Ni(η2-C6H4)(dcpe) (1) and Ni((1,2-η)-4,5-F2C6H2)(dcpe) (2) [dcpe = 1,2-bis(dicyclohexylphosphino)ethane, (C6H11)2PCH2CH2P(C6H11)2] with carbon monoxide at low concentration gives Ni(CO)2(dcpe) (3) and, as the main organic products, 9H-fluoren-9-one (4) and 2,3,6,7-tetrafluoro-9H-fluoren-9-one (5), 2,3,6,7-X4C12H4CO (X = H, F), respectively, resulting from monoinsertion into the nickel−benzyne bond. Higher concentrations of CO give rise to bis(acyl) intermediates, one of which, Ni(CO-4,5-F2C6H2CO-2)(dcpe) (9), has been observed by 31P and 19F NMR spectroscopy. These intermediates reversibly form 3 and the corresponding benzocyclobutenediones OC-4,5-X2C6H2CO [X = H (12), F (13)] by reductive elimination and react readily with oxygen to form the stable (phthalato)nickel(II) complexes Ni(OCOC6H4COO-2)(dcpe) (6) and Ni(OCO-4,5-F2C6H2COO-2)(dcpe) (7). On treatment with iodine, the latter give the corresponding phthalic anhydrides C6H4C2O3 (10) and 4,5-F2C6H2C2O3 (11), respectively. According to a single-crystal X-ray study, 7 is a planar nickel(II) complex containing a seven-membered chelate ring with monodentate carboxylato groups, the average Ni−O and Ni−P distances being 1.904(4) and 2.152(2) Å, respectively.