Phosphorescent cyclometalated platinum complexes are highly attractive compounds for a variety of applications, including organic‐light emitting diodes (OLEDs), chemical and biological sensing and imaging, and photocatalysis. This review deals with the progress made in the last five years in the development of highly luminescent platinum complexes based on bidentate, tridentate, and tetradentate cyclometalating ligands. The ligand design and synthesis, general methods for the formation of cycloplatinated complexes, and their photophysical properties, in particular, the emission energy and photoluminescent quantum efficiency of the complexes, are discussed. The applications of the complexes in OLEDs, chemical sensing, biological imaging, and other fields are briefly covered.

Sphingosine kinase (SphK) is the major source of the lipid mediator and G protein-coupled receptor agonist sphingosine-1-phosphate (S1P). S1P promotes cell growth, survival, and migration and is a key regulator of lymphocyte trafficking. Inhibition of S1P signaling has been proposed as a strategy for treatment of inflammatory diseases and cancer. Two different formats of an enzyme-based high-throughput screen yielded two attractive chemotypes capable of inhibiting S1P formation in cells. The molecular combination of these screening hits led to compound 22a (PF-543) with 2 orders of magnitude improved potency. Compound 22a inhibited SphK1 with an IC of 2 nM and was more than 100-fold selective for SphK1 over the SphK2 isoform. Through the modification of tail-region substituents, the specificity of inhibition for SphK1 and SphK2 could be modulated, yielding SphK1-selective, potent SphK1/2 dual, or SphK2-preferential inhibitors.

The selective C−H bond activation of Nisopropyl-N-phenyl-2,2′-bipyridin-6-amine promoted by Pt(II) was complicated by the low selectivity of sp 2 C−H bond activation in acetonitrile and low yield of sp 3 C−H activation in acetic acid. The use of a base was found to effectively suppress the competing sp 3 C−H bond activation in acetonitrile, improving the selectivity of sp 2 C−H bond activation from 70% to 99%. In the reaction in acetic acid, the low yield was due to the competing C−N bond cleavage. The use of a base reduced the C−N bond cleavage, but not completely. The reaction of N-tert-butyl-Nphenyl-2,2′-bipyridin-6-amine with K 2 PtCl 4 in acetic acid produced the cyclometalated complex with complete C−N bond cleavage and its acylated derivative. These results indicated that the C−N bond cleavage might proceed via heterolytic C−N bond dissociation. The acylation following the C−N cleavage in the reaction in acetic acid is regioselective. Further experiments showed that the reaction of N-phenyl-2,2′-bipyridin-6-amine with K 2 PtCl 4 in acetic acid produced the cyclometalated complex, while the reaction in a mixture of acetic anhydride and acetic acid produced the acylated cyclometalated complex. An X-ray crystal structure study revealed strong intramolecular H bonding in the acylated complexes. The regioselectivity was explained in terms of H bonding and the electron distribution predicted by the DFT calculations.

Negishi coupling is an efficient and versatile tool for selective C–C bond formation in the synthesis of organic electronic, optical, electrochemical, and magnetic materials.

A series of platinum complexes based on the tridentate cyclometalating ligand derivatives 6-arylamino-2,2′-bipyridine, 6-phenoxy-2,2′-bipyridine, 6-phenylthio-2,2′-bipyridine, 6-benzyl-2,2′-bipyridine, and 6-benzoyl-2,2′-bipyridine were synthesized, and their acylation reactions were studied. Acylation of platinum complexes based on 6-(4-R-phenylamino)-2,2′-bipyridine derivatives (R = CH3O, CH3, Cl, COOEt) tolerates both electron-donating and electron-withdrawing substituents on the aryl ring that are para to the amino group. However, platinum complexes based on 6-(3-R′-phenylamino)-2,2′-bipyridine (R′ = CH3, Cl, Br) did not undergo the acylation reaction under the same conditions. Interestingly, the acylation of the platinum complexes based on 6-(3-fluorophenylamino)-2,2′-bipyridine proceeded smoothly, and the results indicate that the acylation is regiospecific and occurs at the metalated carbon. Complexes based on 6-phenoxy-2,2′-bipyridine, 6-phenylthio-2,2′-bipyridine, and 6-benzyl-2,2′-bipyridine are also regioselectively acylated. A cyclometalated platinum complex based on 6-benzoyl-2,2′-bipyridine, where the benzene is more electron deficient than those in other cyclometalated platinum complexes, failed to undergo the acylation reaction. The acylation can be carried out in acetic acid, 1,2-dichloroethane, benzonitrile, and acetonitrile. Other acyl halides such as benzoyl chloride and crotonyl chloride are also effective acylating reagents. On the basis of the fact that the reaction is discouraged by the electron deficiency of the phenyl ring and contrasting results of the acylation of platinum complexes based on 6-(3-R′-phenylamino)-2,2′-bipyridine (R′ = CH3, F, Cl, Br), an unprecedented electrophilic addition–platinum migration–rearomatization cascade mechanism is proposed for the regiospecific acylation reaction.