The study of the reactions of IrH5(PiPr3)2 (1) with 2,6-diphenylpyridine and 2-phenoxy-6-phenylpyridine and the photophysical characterization of some of the resulting compounds, as well as their osmium counterparts, reveal that the bite angle of dianionic C,N,C-pincer ligands has a marked influence on the chemical and photophysical properties of iridium(III) and osmium(IV) hydride complexes. Complex 1 promotes a double o-CH bond activation of both disubstituted pyridines. The reaction with 2,6-diphenylpyridine directly leads to IrH{κ3-C,N,C-(C6H4-py-C6H4)}(PiPr3)2 (2), whereas the activation of 2-phenoxy-6-phenylpyridine is sequential and slower. Initially, the phenyl activation gives IrH2{κ2-C,N-(C6H4-py-OPh)}(PiPr3)2 (3), which subsequently evolves to IrH{κ3-C,N,C-(C6H4-py-OC6H4)}(PiPr3)2 (4). Complexes 2 and 4 are Brønsted bases, which react with HBF4·OEt2. The protonation of the hydride position is elusive; the proton of the acid is selectively added to one of the metalated substituents. Thus, the reaction with 2 affords [IrH{κ3-C,N,(C–H)-(C6H4-py-Ph)}(PiPr3)2]BF4 (5), in which the C–H bond formed remains coordinated. The protonation of 4 selectively occurs at the phenoxy substituent to give the five-coordinate cationic complex [IrH{κ2-C,N-(C6H4-py-OPh)}(PiPr3)2]BF4 (6) bearing a free OPh group. In contrast to 5, complex 6 inserts acetylene and phenylacetylene into the Ir–H bond to yield [Ir{(E)-CH═CHR}{κ2-C,N-(C6H4-py-OPh)}(PiPr3)2]BF4 (R = H (7), Ph (8)). Complexes 2 and 4 and their osmium(IV) counterparts OsH2{κ3-C,N,C-(C6H4-py-C6H4)}(PiPr3)2 (A) and OsH2{κ3-C,N,C-(C6H4-py-OC6H4)}(PiPr3)2 (B) are phosphorescent emitters, which display emission wavelengths between 473 and 619 nm and quantum yields between 0.03 and 0.96 depending upon the metal center and the presence or absence of an oxygen atom in the pincer ligand.

Financial support from the MINECO of Spain (Project CTQ2017-82935-P (AEI/FEDER, UE)), Gobierno de Aragón (Group E06_17R and project LMP148_18), FEDER, and the European Social Fund is acknowledged.

Peer reviewed