Journal of the Chemical Society, Dalton Transactions p. 3441 - 3450 (1994)
Update date:2022-08-02
Topics:
Abel, Edward W.
Orrell, Keith G.
Osborne, Anthony G.
Pain, Helen M.
Sik, Vladimir
et al.
2,2':6',2 -Terpyridine reacted with trans-a bidentate chelate ligand.In solution these complexes are fluxional with the terpyridine oscillating between equivalent bidentate modes by a mechanism consisting of a 'tick-tock' twist of the metal moiety through an angle equal to the N-M-N angle of the metal centre.Rates of this fluxion were measured by NMR spectroscopy from the exchange effects on the 1H signals of the aromatic hydrogens and in the 19F signals of two C6F5 groups.The ΔG(excit) values for the fluxion were ca. 71 and 94 kJ mol-1 for the complexes of Pd(II) and Pt(II) respectively.At below-ambient temperatures further changes in the 19F NMR spectra of both complexes were interpreted in terms of varying rates of rotation of the unco-ordinated pyridine ring, with the rates of rotation of the C6F5 rings being substantially slower at all temperatures and not separately measurable.The lowest-temperature spectra suggested the presence of a pair of degenerate rotamers each having the planes of both C6F5 rings and the unco-ordinated pyridine ring closely parallel and orthogonal to the remainder of the ligand ring system.The crystal structure of a N-Pd-N angle of 77.9 deg, and the pendant ring oriented at an angle of 46 deg to the adjacent co-ordinated ring.
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