Competition between N , C , N -Pincer and N , N -Chelate Ligands in Platinum(II).

Replacement of the chloride ligand of PtCl{κ 3 - N , C , N -[py-C 6 HR 2 -py]} (R = H ( 1 ), Me ( 2 )) and PtCl{κ 3 - N , C , N -[py-O-C 6 H 3 -O-py]} ( 3 ) by hydroxido gives Pt(OH){κ 3 - N , C , N -[py-C 6 HR 2 -py]} (R = H ( 4 ), Me ( 5 )) and Pt(OH){κ 3 - N , C , N -[py-O-C 6 H 3 -O-py]} ( 6 ). These compounds promote deprotonation of 3-(2-pyridyl)pyrazole, 3-(2-pyridyl)-5-methylpyrazole, 3-(2-pyridyl)-5-trifluoromethylpyrazole, and 2-(2-pyridyl)-3,5-bis(trifluoromethyl)pyrrole. The coordination of the anions generates square-planar derivatives, which in solution exist as a unique species or equilibria between isomers. Reactions of 4 and 5 with 3-(2-pyridyl)pyrazole and 3-(2-pyridyl)-5-methylpyrazole provide Pt{κ 3 - N , C , N -[py-C 6 HR 2 -py]}{κ 1 - N 1 -[R'pz-py]} (R = H; R' = H ( 7 ), Me ( 8 ). R = Me; R' = H ( 9 ), Me ( 10 )), displaying κ 1 - N 1 -pyridylpyrazolate coordination. A 5-trifluoromethyl substituent causes N 1 -to-N 2 slide. Thus, 3-(2-pyridyl)-5-trifluoromethylpyrazole affords equilibria between Pt{κ 3 - N , C , N -[py-C 6 HR 2 -py]}{κ 1 - N 1 -[CF 3 pz-py]} (R = H ( 11a ), Me ( 12a )) and Pt{κ 3 - N , C , N -[py-C 6 HR 2 -py]}{κ 1 - N 2 -[CF 3 pz-py]} (R = H ( 11b ), Me ( 12b )). 1,3-Bis(2-pyridyloxy)phenyl allows the chelating coordination of the incoming anions. Deprotonations of 3-(2-pyridyl)pyrazole and its substituted 5-methyl counterpart promoted by 6 lead to equilibria between Pt{κ 3 - N , C , N -[pyO-C 6 H 3 -Opy]}{κ 1 - N 1 -[R'pz-py]} (R' = H ( 13a ), Me ( 14a )) with a κ- N 1 -pyridylpyrazolate anion, keeping the pincer coordination of the di(pyridyloxy)aryl ligand, and Pt{κ 2 - N , C -[pyO-C 6 H 3 (Opy)]}{κ 2 - N,N -[R'pz-py]} (R' = H ( 13c ), Me ( 14c )) with two chelates. Under the same conditions, 3-(2-pyridyl)-5-trifluoromethylpyrazole generates the three possible isomers: Pt{κ 3 - N , C , N -[pyO-C 6 H 3 -Opy]}{κ 1 - N 1 -[CF 3 pz-py]} ( 15a ), Pt{κ 3 - N , C , N -[pyO-C 6 H 3 -Opy]}{κ 1 - N 2 -[CF 3 pz-py]} ( 15b ), and Pt{κ 2 - N , C -[pyO-C 6 H 3 (Opy)]}{κ 2 - N , N -[CF 3 pz-py]} ( 15c ). The N 1 -pyrazolate atom produces a remote stabilizing effect on the chelating form, pyridylpyrazolates being better chelate ligands than pyridylpyrrolates. Accordingly, reactions of 4 - 6 with 2-(2-pyridyl)-3,5-bis(trifluoromethyl)pyrrole yield Pt{κ 3 - N , C , N -[py-C 6 HR 2 -py]}{κ 1 - N 1 -[(CF 3 ) 2 C 4 (py)HN]} (R = H ( 16 ), Me ( 17 )) or Pt{κ 3 - N , C , N -[pyO-C 6 H 3 -Opy]}{κ 1 - N 1 -[(CF 3 ) 2 C 4 (py)HN]} ( 18 ), displaying κ 1 - N 1 -pyrrolate coordination. Complexes 7 - 10 are efficient green phosphorescent emitters (488-576 nm). In poly(methyl methacrylate) (PMMA) films and in dichloromethane, they experience self-quenching, due to molecular stacking. Aggregation occurs through aromatic π-π interactions, reinforced by weak platinum-platinum interactions.