Doubly cyclometalated pyridazines: Contrasting behavior with palladium andplatinum

The cyclometalation of 3,6-diphenylpyridazines with palladium and platinum has been studied. When palladium acetate is used as the metal source, two s equential cyclometalations are observed, with the first cyclometalation dea ctivating the system toward a second cyclometalation. Both monocyclopallada ted and dicyclopalladated species have been isolated and characterized as t heir acetylacetonate derivatives. When potassium tetrachloroplatinate is us ed as the metal source, only double cycloplatination is observed: the first cycloplatination activates the system toward a second cycloplatination thr ough a combination of nitrogen coordination and a chloride bridging two pla tinums. A doubly cycloplatinated compound has been isolated as its tripheny lphosphine derivative, which has been fully characterized: the single-cryst al X-ray structure shows that the two platinums are bridged by a chloride.