COMPLEXES OF TECHNETIUM(V) AND RHENIUM(V) WITH 2,3-BIS(2-PYRIDYL)PYRAZINE (DPP) AND 2,3-BIS(2-PYRIDYL)QUINOXALINE (DPQ) - EVIDENCE FOR 7-MEMBERED CHELATE RING FORMATION IN DPQ COMPLEXES

Complexes formed by the reaction of (n-BU4N)[MOCl4] (M = Re. Tc) with the diimines 2,3-bis(2-pyridyl)pyrazine (DPP) and 2,3-bis(2-pyridyl)qu inoxaline (DPQ) in ethanol were studied. With DPP as ligand, the monom etallic complexes [MOCl2(X)(DPP)] (M = Tc, Re; X = Cl, OEt) and the bi metallic compounds [MOCl2(X)](mu-DPP) [MOCl2(OEt)] (X = Cl for M = Tc; X = OEt for M = Re) were isolated. Infrared and H-1 NMR data suggest that coordination of DPP to the metals occurs in a bidentate manner th rough one pyrazine and one pyridine nitrogen atom to form a five-membe red metallocycle. Only monometallic complexes of formulation [MOCl2(X) (DPQ)] (X = Cl, OEt) could be isolated with DPQ as ligand, irrespectiv e of the mol ratio of reactants. Experimental evidence suggests bident ate coordination of DPQ to the metals through the two pyridinic nitrog en atoms, with the two quinoxaline nitrogens not participating in bond ing to the metals, to form a single seven-membered chelate ring.