Hydrogen-transfer catalysis with Cp*Ir^III complexes:The influence of the ancillary ligands

Fourteen Cp*IrIII complexes, bearing various combinations of N- and C-spectator ligands, are assayed in hydrogen-transfer catalysis from isopropyl alcohol to acetophenone under various conditions to investigate ligand effects in this widely used reaction. The new cationic complexes bearing monodentate pyridine and N-heterocyclic carbene (NHC) ligands were characterized crystallographically and by variable-temperature nuclear magnetic resonance (VT-NMR). Control experiments and mercury poisoning tests showed that iridium(0) nanoparticles, although active in the reaction, are not responsible for the high activity observed for the most active precatalyst [Cp*Ir(IMe) 2Cl]BF4 (6). For efficient catalysis, it was found necessary to have both NHCs in monodentate form; tying them together in a bis-NHC chelate ligand gave greatly reduced activity. The kinetics of the base-assisted reaction showed induction periods as well as deactivation processes, and H/D scrambling experiments cast some doubt on the classical monohydride mechanism. © 2013 American Chemical Society

Organometallic half-sandwich iridium anticancer complexes

The low-spin 5d6 IrIII organometallic half-sandwich complexes [(η5-Cpx)Ir(XY)Cl]0/+, Cpx = Cp*, tetramethyl(phenyl)cyclopentadienyl (Cpxph), or tetramethyl(biphenyl)cyclopentadienyl (Cpxbiph), XY = 1,10-phenanthroline (4−6), 2,2′-bipyridine (7−9), ethylenediamine (10 and 11), or picolinate (12−14), hydrolyze rapidly. Complexes with N,N-chelating ligands readily form adducts with 9-ethylguanine but not 9-ethyladenine; picolinate complexes bind to both purines. Cytotoxic potency toward A2780 human ovarian cancer cells increases with phenyl substitution on Cp*: Cpxbiph > Cpxph > Cp*; Cpxbiph complexes 6 and 9 have submicromolar activity. Guanine residues are preferential binding sites for 4−6 on plasmid DNA. Hydrophobicity (log P), cell and nucleus accumulation of Ir correlate with cytotoxicity, 6 > 5 > 4; they distribute similarly within cells. The ability to displace DNA intercalator ethidium bromide from DNA correlates with cytotoxicity and viscosity of Ir−DNA adducts. The hydrophobicity and intercalative ability of Cpxph and Cpxbiph make a major contribution to the anticancer potency of their IrIII complexes

First Cp*-Functionalized N-Heterocyclic Carbene and Its Coordination to Iridium. Study of the Catalytic Properties

The Food Stamp Program provides assistance to households with incomes and assets below fixed thresholds. Although it is the largest entitlement program in the social safety net, little is known about the effect of food stamps on stabilizing fluctuations in household income and consumption. To estimate the volatility of income and the attendant reduction in volatility due to food stamps we use data from the Panel Study of Income Dynamics over 1980-1999 along with a model of income that admits permanent and transitory components as well as random growth rate heterogeneity. We then specify a model relating income changes to consumption changes for use in a variance decomposition. This decomposition highlights the role of food stamps in stabilizing food consumption volatility. We estimate the income and food consumption models across a host of samples that vary in the degree of ‘risk’ of food stamp takeup, ranging from all families to those families that lie below the gross income threshold for food stamp eligibility. We find that across all families food stamps reduced income volatility by about 3 percent and consumption volatility by about 4 percent, but this stabilizing role is a much more pronounced 12 and 14 percent among families at high ex ante risk of food stamp participation. Despite the positive role of the Food Stamp Program in smoothing income and consumption shocks there was a marked decline of nearly two-thirds in the income and consumption smoothing benefits of the program in the early 1990s relative to the 1980s. This stabilizing role improved only modestly by the end of the 1990s