Synthesis of the Tridentate Pyridine Donor 2,6-Bis[l-phenyl-1-(pyridin-2-yl)ethyl]pyridine (L), including Separation of meso and rac Diastereoisomers via Methylmercury(II) Derivatives, and an X-Ray Structural Study of [HgMe (meso-L)]N03.2H2O

Abstract

A synthesis of the new tridentate pyridine donor ligand 2,6-bis[l-phenyl-1-(pyridin-2-yl)ethyl]pyridine, L, by reaction of 2,6-dichloropyridine with lithiated 2-(1-phenylethyl)pyridine is described. The ligand reacts with methylmercury(II) nitrate to form complexes of the meso and rac diastereoisomers of L, [HgMe(L)]NO3.2H2O, which may be readily separated by fractional crystallization. The ligands meso-L and rac-L may be liberated from the complexes by reaction with cyanide ion in water. The crystal structure of the meso complex has been determined by single crystal X-ray diffraction at 295 K and refined by least-squares methods to R = 0.046 for 2600 'observed' reflections [monoclinic, space group P21/n, with a = 20.946(9), b = 14.767(4), c = 9.81 7(3) A, beta = 91.12(2), and Z = 41. The [HgMe(meso-L)]+ cations have irregular co-ordination geometry for the mercury atom 'HgCN3' with the ligand present as a tripodal tridentate. The central nitrogen forms the strongest bond to mercury [2.283(9)A] with C-Hg-N 166.3(5), with the other nitrogen donors 2.546(11) and 2.595(10) A from mercury and forming C-Hg-N angles of 113.3(5) and 113.7(5), respectively. 1H N.m.r. spectra for the complexes suggest that the ligand is at least bidentate in methanol.