C−H Activation Induced by Water. Monocyclometalated to Dicyclometalated:  C∧N∧C Tridentate Platinum Complexes

Abstract

Metalation of 2,6-diphenylpyridine (1) by potassium tetrachloroplatinate in acetic acid gives a monocyclometalated chloride-bridged dimer 4. This dimer is split with CO to give a kinetic product 9t with the incoming CO trans to the orthometalated carbon. The kinetic product of cleavage is shown to be 16 kJ mol -1 higher in energy than the thermodynamic product 9c, which has the CO trans to the pyridine nitrogen. The isomerization of 9t to 9c is shown not to take place via an associative mechanism and, with analogue 11, is effectively suppressed when excess chloride is added, implying that it takes place via a chloride dissociation. The monocyclometalated 9 undergoes a second cyclometalation to give the C∧N∧C dicyclometalated complex 15 in high yield. This second cyclometalation is brought about by the simple expedient of adding water to the monocyclometalated precursor. The addition of water is rationalized on the basis of needing to ionize the HCl byproduct of the reaction. Using a substituted pyridine (5) analogous chemistry is observed. Single-crystal X-ray structures of one of the intermediates (6) and one of the final products (15) have been solved. Density functional theory calculations are used to rationalize the isomerizations of the monocyclometalated intermediates and the need to ionize HCl in the second cyclometalation.

Luminescent PtII Complexes of Tridentate Cyclometalating 2,5‐Bis(aryl)‐pyridine Ligands

“…The complexes were prepared according to a literature method. [23] [1][2][3][4][5][6] )} 2 (μ-Cl) 2 ] [23] or monomers [Pt(HL [1][2][3][4][5][6] )Cl], with S coordination through the thiophene moiety, as has been suggested earlier for the reaction of HL 1 with K 2 [PtCl 4 ]. [33] Our detailed 2D Pt-H NMR spectroscopy, searching for evidence of x J Pt,H coupling of the thiophene protons through extensive variation of the assumed coupling constant, was not successful (for spectra, see Supporting Information).…”

“…Consequently, the idea arose of using tridentate dicarbanionic cyclometalating ligands of the 2,6-di(phen-2-yl)pyridine ( -PhPyPh -, see Scheme 1) type with Pt II . [21][22][23][24][25][26][27][28][29][30][31][32] Recently, Che et al employed several derivatives of this ligand type, with the aim of providing suitable excited states through variation of the 2,5-aryl groups at the central pyridine unit, and they achieved very efficient triplet emitters, which show phosphorescence, even at room temperature. One crucial move in their ligand design was the use of thiophene as one of their pending metalated aryl groups, with complex 4 in Scheme 2 being the most efficient triplet emitter.…”

Platinum(ii) N-heterocyclic carbene complexes: coordination and cyclometallation.

“…However, relatively large (around 70 Hz) three bond couplings from the central platinum to the protons ortho to both the Pt and the F in cyclometallated ring are seen in complexes 6. Previously we have seen couplings in the range of 24-55 Hz [31][32][33][34] for this type of proton, with coupling this large only when the cyclometallated ring is trans to an agostic interaction. 35 The coupling of the platinum to the fluorine is also larger than normal, 34 again similar to that seen in agostic complex.…”

Synthesis and Antimicrobial Screening 6-Aryl-2-(Amino/Methoxy)-4-[(4′-Difluoro Methoxy) (3′-Hydroxy) Phenyl] Nicotinonitrile

“…Pyridine functionalities have been widely studied [1,2] and widely used [3][4][5][6] but still generate much interest due to their wide range of application in medicinal chemistry [7][8][9][10][11]. The naturally occurring B6-vitamins pyridoxine, pyrodoxal, pyridoxamine and codecarbaxylase contain a pyridine nucleus [12].…”