Bromination and nitration reactions of metallated (Ru and Os) multiaromatic ligands and crystal structures of selected products

Abstract

Three nitrogen-containing aromatic heterocycles, 2-(1′-naphthyl)pyridine, 2-phenylquinoline, and 2,3-diphenylquinoxaline, have been mercurated in the naphthyl or phenyl ring 2-position and then symmetrised to form the mercury compounds Ar 2Hg (Ar=Nppy ( 3), Phqn ( 1) or Dpqx ( 5), respectively). These reagents are suitable for trans-metallation and reaction with MHCl(CO)(PPh 3) 3 affords the complexes M(η 2-C,NAr)Cl(CO)(PPh 3) 2, ( 6, M=Ru, Ar=Nppy; 7, M=Os, Ar=Nppy; 8, M=Ru, Ar=Phqn; 9, M=Os, Ar=Phqn; 10, M=Ru, Ar=Dpqx; 11, M=Os, Ar=Dpqx) in which each product features an aryl ligand that forms a strongly chelated five-membered ring through coordination of the heterocyclic N atom. The chloride ligand in each of the complexes 6– 11 can be replaced by dimethyl dithiocarbamate to give ultimately the mono-triphenylphosphine complexes, M(η 2-Ar)(η 2-S 2CNMe 2)(CO)(PPh 3) ( 12, M=Ru, Ar=Nppy; 13, M=Os, Ar=Nppy; 14, M=Ru, Ar=Phqn; 15, M=Os, Ar=Phqn; 16, M=Ru, Ar=Dpqx; 17, M=Os, Ar=Dpqx). Similarly, compound 10 when treated with Na(acac) gives Ru(η 2-Dpqx)(η 2-acac)(CO)(PPh 3) ( 18), while treatment with trifluoroacetic acid gives Ru(η 2-Dpqx)(O 2CCF 3)(CO)(PPh 3) 2 ( 19). Many of these complexes were found to be very robust, making them suitable for electrophilic aromatic substitution reactions under harsh conditions. In each case, the presence of the metal had both an activating and a directing effect on the aryl ring to which it was bonded. Bromination or nitration reactions, both of which are not normally possible with organometallic substrates, were carried out successfully, giving rise to monobrominated or dinitrated products, respectively. The following compounds were characterised, M(η 2-Ar-4-Br)Cl(CO)(PPh 3) 2 ( 20, M=Ru, Ar=Phqn; 21, M=Os, Ar=Phqn; 22, M=Ru, Ar=Dpqx; 24, M=Os, Ar=Dpqx), M(η 2-Dpqx-4-Br)(η 2-S 2CNMe 2)(CO)(PPh 3) ( 23, M=Ru; 25, M=Os), Os(η 2-Ar)Cl(CO)(PPh 3) 2 ( 26, Ar=Nppy-6,8-(NO 2) 2; 27, Ar=Phqn-4,6-(NO 2) 2). Crystal structures of compounds 7, 12, 15, 18, 19, 21, 23 and 25 have been determined.