Organomercury Compounds. XXXI. Preparations and ¹⁹⁹Hg N.M.R. Spectra of Organomercury Derivatives of 2-Phenylpyridine, Benzo[h]quinoline, 1-Phenylpyrazole and 3,4,5-Trimethyl-1-phenylpyrazole, and the X-Ray Crystal Structure of Bis[2-(pyridin-2'-yl)phenyl]mercury

Abstract

2-(Pyridin-2'-yl) phenylmercuric acetate has been prepared by mercuration of 2-phenylpyridine. Symmetrization of the corresponding chloride by alkaline sodium stannite gave bis [2-(pyridin-2'-yl)phenyl]mercury, which was also prepared from 2-(2'-aminophenyl)pyridine by the diazo method and treatment of the initial product with copper powder and aqueous ammonia. Mercuration of benzo [h] quinoline and 3,4,5-trimethyl-1-phenylpyrazole with mercuric acetate followed by treatment with lithium chloride yielded benzo [h]quinolin-10-ylmercuric chloride and 2-(3',4',5'-trimethylpyrazol-1'-yl) phenylmercuric chloride respectively. Treatment of the former product with tribromide ions gave 10-bromobenzo[h] quinoline. The exchange Grignard reaction between 1-phenylpyrazole and ethylmagnesium bromide to give 2-(pyrazol-1'-yl) phenylmagnesium bromide has been monitored by reactions with benzonitrile and D₂O to establish optimum conditions for reaction with mercuric bromide giving bis [2-(pyrazol-1'-yl)phenyl]mercury. The ¹⁹⁹Hg n.m.r. chemical shifts of the majority of mercurials are shifted substantially downfield relative to the corresponding simple phenylmercurials consistent with weak intramolecular coordination by the heterocyclic nitrogen donor atoms, but a small upfield shift is observed for bis [2-(pyrazol-1'-yl)phenyl]mercury. The X-ray crystal structure of bis [2-(pyridin-2′-yl)phenyl]mercury [monoclinic, space group P2₁/n, a 12.746(2), b 11.660(2), c 5.698(1) Ǻ, β 92.81(1)′, V 845.8 Ǻ³] shows a centrosymmetric molecule with strong linear two coordination [Hg-C 2.098(8) Ǻ; C-Hg-C 180.0°] and significant but much weaker Hg-N interactions [Hg-N 2.798(7) Ǻ; N-Hg-N 180.0°] giving overall distorted square planar stereochemistry. The phenyl rings are mutually coplanar, whilst the two pyridin-2'-yl rings are parallel and inclined at 10.8° to the phenyl groups.