Phenylbenzothiazole-Based Platinum(II) and Diplatinum(II) and (III) Complexes with Pyrazolate Groups: Optical Properties and Photocatalysis

Abstract

Based on 2-phenylbenzothiazole (pbt) and 2-(4-dimethylaminophenyl)benzothiazole (Me 2 N-pbt), mononuclear [Pt(pbt)(R′ 2 -pzH) 2 ]PF 6 (R′ 2 -pzH = pzH 1a, 3,5-Me 2 pzH 1b, 3,5-i Pr 2 pzH 1c) and diplatinum (Pt II −Pt II ) [Pt(pbt)(μ-R′ 2 pz)] 2 (R′ 2pz = pz 2a, 3,5-Me 2 pz 2b, 3,5-i Pr 2 pz 2c) and [Pt(Me 2 N-pbt)(μ-pz)] 2 (3a) complexes have been prepared. In the presence of sunlight, 2a and 3a evolve, in CHCl 3 solution, to form the Pt III −Pt III complexes [Pt(R-pbt)(μ-pz)Cl] 2 (R = H 4a, NMe 2 5a).Experimental and computational studies reveal the negligible influence of the pyrazole or pyrazolate ligands on the optical properties of 1a−c and 2a,b, which exhibit a typical 3 IL/ 3 MLCT emission, whereas in 2c the emission has some 3 MMLCT contribution. 3a displays unusual dual, fluorescence ( 1 ILCT or 1 MLCT/ 1 LC), and phosphorescence ( 3 ILCT) emissions depending on the excitation wavelength. The phosphorescence is lost in aerated solutions due to sensitization of 3 O 2 and formation of 1 O 2 , whose determined quantum yield is also wavelength dependent. The phosphorescence can be reversibly photoinduced (365 nm, ∼ 15 min) in oxygenated THF and DMSO solutions. In 4a and 5a, the lowest electronic transitions (S 1 −S 3 ) have mixed characters (LMMCT/ LXCT/L'XCT 4a and LMMCT/LXCT/ILCT 5a) and they are weakly emissive in rigid media. The 1 O 2 generation property of complex 3a is successfully used for the photooxidation of p-bromothioanisol showing its potential application toward photocatalysis.

N,C,N-Pincers in Platinum Bimetallic Complexes: Influence of the Pincer and Bridging Ligands on the Metal–Metal Bond and the Photophysical Properties

“…The most common designs have been structures of the types [Pt­{κ 2 - C,N -[chelate]}­(μ-L 2 )] 2 and [Pt­{(κ 2 -C,C -[chelate]}­(μ-L 2 )] 2 . The first type is based on two platinum subunits, which contain an orthometalated phenyl- N -heterocycle, linked by a double bridge formed by two bidentate ligands resulting from the deprotonation of molecules type: thiazolthiol, quinolinyl- and pyridylthiol, hydroxyquinoline, hydroxypyridine, pyrazol, triazole, and terminal alkyne . The second one is constructed in a similar way, changing the N -donor heterocycle by an NHC group and using pyrazolate or formamidinate as bridges.…”