A cationic Rh(III) complex that efficiently catalyzes hydrogen isotope exchange in hydrosilanes.

The synthesis and structural characterization of a mixed-sandwich (η(5)-C(5)Me(5))Rh(III) complex of the cyclometalated phosphine PMeXyl(2) (Xyl = 2,6-C(6)H(3)Me(2)) with unusual κ(4)-P,C,C',C'' coordination (compound 1-BAr(f); BAr(f) = B(3,5-C(6)H(3)(CF(3))(2))(4)) are reported. A reversible κ(4) to κ(2) change in the binding of the chelating phosphine in cation 1(+) induced by dihydrogen and hydrosilanes triggers a highly efficient Si-H/Si-D (or Si-T) exchange applicable to a wide range of hydrosilanes. Catalysis can be carried out in an organic solvent solution or without solvent, with catalyst loadings as low as 0.001 mol %, and the catalyst may be recycled a number of times.

A new gadolinium-based MRI zinc sensor.

The properties of a novel Gd(3+)-based MRI zinc sensor are reported. Unlike previously reported Gd(3+)-based MRI contrast agents, this agent (GdL) differs in that the agent alone binds only weakly with human serum albumin (HSA), while the 1:2 GdL:Zn(2+) ternary complex binds strongly to HSA resulting in a substantial, 3-fold increase in water proton relaxivity. The GdL complex is shown to have a relatively strong binding affinity for Zn(2+) (K(D) = 33.6 nM), similar to the affinity of the Zn(2+) ion with HSA alone. The agent detects as little as 30 microM Zn(2+) in the presence of HSA by MRI in vitro, a value slightly more than the total Zn(2+) concentration in blood (approximately 20 microM). This combination of binding affinity constants and the high relaxivity of the agent when bound to HSA suggests that this new agent may be useful for detection of free Zn(2+) ions in vivo without disrupting other important biological processes involving Zn(2+).