| Abstract
| - Monometalation of 2,6-diphenylpyridines by potassium tetrachloroplatinate gives chloride-bridged cyclometalated dimers, which then undergo a second cyclometalation to give the C∧N∧C dicyclometalated complexes in high yield. This second cyclometalation is brought about by the simple expedient of adding water to the monocyclometalated precursor.
- Metalation of 2,6-diphenylpyridine (1) by potassium tetrachloroplatinate in acetic acidgives a monocyclometalated chloride-bridged dimer 4. This dimer is split with CO to give akinetic product 9t with the incoming CO trans to the orthometalated carbon. The kineticproduct of cleavage is shown to be 16 kJ mol-1 higher in energy than the thermodynamicproduct 9c, which has the CO trans to the pyridine nitrogen. The isomerization of 9t to 9cis shown not to take place via an associative mechanism and, with analogue 11, is effectivelysuppressed when excess chloride is added, implying that it takes place via a chloridedissociation. The monocyclometalated 9 undergoes a second cyclometalation to give theC∧N∧C dicyclometalated complex 15 in high yield. This second cyclometalation is broughtabout by the simple expedient of adding water to the monocyclometalated precursor. Theaddition of water is rationalized on the basis of needing to ionize the HCl byproduct of thereaction. Using a substituted pyridine (5) analogous chemistry is observed. Single-crystalX-ray structures of one of the intermediates (6) and one of the final products (15) have beensolved. Density functional theory calculations are used to rationalize the isomerizations ofthe monocyclometalated intermediates and the need to ionize HCl in the second cyclometalation.
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