Simple, efficient synthetic route to 2-2 '-bipyrazine derivatives from bromopyrazine for making rhenium and ruthenium dyes

Abstract

A simple and efficient synthetic route for syntheses of 2-​2'-​bipyrazine (bpz) derivs. is described starting with 2-​chloropyrazine and 2-​methyl-​4-​carboxypyrazine resulting in 2,​2'-​bipyrazine, 4-​methyl-​2,​2'-​bipyrazine (mbpz)​, 4,​4'-​dimethyl-​2,​2'-​bipyrazine (dmbpz)​, 4,​4'-​dicarboxy-​2,​2'-​bipyrazine (dcbpz) and 2-​pyridyl-​2-​pyrazine (pypz)​. The bidentate ligands were ligated with Re (I) and Ru (II) to make dyes useful for harvesting solar energy and for potential therapeutic agents. The complexes to be described are: [Re(bpz)​(dppm)​(CO)​3]​+, [{Re(bpz)​(CO)​3}​2(dppe)​]​2+, Re(CO)​3(dcbpz)​Cl, Re(CO)​3(dmbpz)​Cl, Re(CO)​3(mbpz)​Cl, Re(CO)​3(pypz)​Cl and [Ru(bpz)​2(dcbpz)​]​2+ (where dppm is diphenylphosphinomethane, dppe is diphenylphosphinoethane)​. The bridged Re (I) complex was synthesized using diphenylphosphinoethane (dppe)​. These complexes were characterized by 1H NMR, mass spectra and elemental analyses. The Re (I) and Ru (II) complexes absorb in the near UV region of the spectrum and emit near 600 nm when excited into the lowest energy absorption band. Emission lifetimes detd. in a glassy matrix or in soln. varied from 100 to 400 ns.