2,2′ : 6′,2″-Terpyridine (terpy) acting as a fluxional bidentate ligand. Part 3. Ruthenium carbonyl halide complexes, [RuX 2 (CO) 2 (terpy)](X = Cl, Br or I) and metal tetracarbonyl complexes [M(CO) 4 (terpy)](M = Cr, Mo or W): nuclear magnetic resonance studies of their solution dynamics and synthesis of trans-[RuX 2 (CO)(terpy)](X = Cl, Br or I)

Under mild conditions 2,2′ : 6′,2″-terpyridine reacted with [{RuX2(CO)2}n](X = Cl, Br or I) and with [M(CO)4(nbd)][M = Cr, Mo or W; nbd = norbornadiene (bicyclo[2.2.1]hepta-2,5-diene)] to form the octahedral complexes trans, cis-[RuX2(CO)2(terpy)] and [M(CO)4(terpy)], respectively, in which the terpyridine acts as a bidentate chelate ligand. In solution these complexes are fluxional with the terpyridine oscillating between equivalent bidentate modes. Heating trans,cis-[RuX2(CO)2(terpy)](X = Cl, Br or I) in a high boiling solvent formed trans-[RuX2(CO)(terpy)] whereas cis-[RuX2(CO)(terpy)] was formed by heating the solid dicarbonyl complex.