Treatment of 4-MeO-C6H3-2,6-(CH2P t Bu2)2 with IrCl3·nH2O in i-PrOH/H2O gives a cyclometalated pincer chlorohydrido iridium complex. A second intramolecular oxidative addition reaction of one of the tert-butyl C−H bonds to the Ir(III) center followed by the reductive elimination of H2 gives a novel doubly metalated compound that is stable to air and water. X-ray crystallographic analysis revealed a chelated square-pyramidal iridium compound with two cyclometalated five-membered rings in the basal plane and the iridium bound methylene group of the four-membered ring in the apical position. The free coordination site is protected by an agostic C−H bond. While a phosphorus−phosphorus coupling constant of 351.1 Hz establishes the trans position of the phosphorus groups there is no indication of a hydridic or weakly bound hydrogen. Electrochemical studies establish an equilibrium between the pincer chlorohydrido compound and the doubly metalated complex and H2. A square scheme can be used to describe the relationship between the redox couples and solution equilibria. The unusual stability of the doubly metalated complex was supported by DFT calculations at different levels of theory on model compounds. They show the coordination of two hydrogen atoms best described as η2-coordinated dihydrogen and suggest an Ir(V) oxidation state as intermediate.

This work presents a new synthetic approach to aromatic and aliphatic polycarbonates by melt polycondensation of bisphenol A diacetates with alkylene-and arylenediphenyl dicarbonates. The diphenyl dicarbonates were prepared from phenyl chloroformate and the corresponding dihydroxy compounds. The process involved a precondensation step under a slow stream of dry argon with the elimination of phenyl acetate, followed by melt polycondensation at high temperature and under vacuum. The potential of this reaction is demonstrated by the successful synthesis of a series of aromatic-aromatic and aromatic-aliphatic polycarbonates having inherent viscosities from 0.19 to 0.43 dL/g. Thus low to intermediate molecular mass polymers were obtained. The 13 C-NMR spectra of the carbon of the carbonate group showed that the formed polycarbonates contain partial random sequence distribution of monomer residues in their chains. The polycarbonates were characterized by inherent viscosity, FTIR,

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