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

Abstract

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)quinoxaline (DPQ) in ethanol were studied. With DPP as ligand, the monometallic complexes [MOCl₂(X)(DPP)] (M = Tc, Re; X = Cl, OEt) and the bimetallic compounds [MOCl₂(X)](μ-DPP) [MOCl₂(OEt)] (X = Cl for M = Tc; X = OEt for M = Re) were isolated. Infrared and ¹H NMR data suggest that coordination of DPP to the metals occurs in a bidentate manner through one pyrazine and one pyridine nitrogen atom to form a five-membered metallocycle. Only monometallic complexes of formulation [MOCl₂(X)(DPQ)] (X = Cl, OEt) could be isolated with DPQ as ligand, irrespective of the mol ratio of reactants. Experimental evidence suggests bidentate coordination of DPQ to the metals through the two pyridinic nitrogen atoms, with the two quinoxaline nitrogens not participating in bonding to the metals, to form a single seven-membered chelate ring.

Key Words:

• technetium(V)
• rhenium(V)
• diimines
• seven-membered chelate rings