Oxidative Coordination versus C3 -C(O)Me Bond Cleavage in Acetylacetonate Iridium Complexes.

Iridabicycles [Ir{κ3 -N,C,O-(pyC(H)=C(C(O)Me)2 }(Cl)(L-L)](L-L=cod (cod=1,5-cyclooctadiene), 1 a; bipy (bipy=2,2'-bipyridine), 1 b) have been obtained by oxidative coordination of 3-(pyridine-2-yl-methylene)pentane-2,4-dione L1, to the complexes [{Ir(µ-Cl)(cod)}2 ] and [{Ir(µ-Cl)(coe)2 }2 ] (coe=cis-cyclooctene), the latter in the presence of bipy. Remarkably, cleavage of the C3 -C(O)Me bond of L1 has instead been achieved in the reaction with [Ir(Cl)(dmb)2 ] (dmb=2,3-dimethylbutadiene), yielding a compound formulated as [Ir{κ2 -N,C-(pyC(H)C(C(O)Me))}(CO)(µ-Cl)(Me)]2 , 2. Treatment of dimer 2 with DMSO or PMe3 produced the complexes[Ir{κ2 -N,C-(pyC(H)C(C(O)Me)}(CO)Cl(Me)L] (L=DMSO, 3 a; PMe3 , 3 b). Plausible mechanisms for the reactions leading to complexes 1 and 2 are proposed by means of DFT calculations.

A second generation MRI contrast agent for imaging zinc ions in vivo.

A Zn2+ specific GdDOTA derivative containing two bis-(3-pyrazolyl) units was prepared and characterized. Unlike a previously reported Zn2+ binding agent, the new agent binds to human albumin both in the presence and absence of Zn2+.

New seven membered palladacycles: C-Br bond activation of 2-bromo-pyridine derivative by Pd(II).

C-Br bond activation followed by a C-C coupling reaction of the 2-bromo-pyridyl unit of [1-phenyl-2-(6-bromopyridin-2-yl)-benzoimidazole] was performed by Pd(CH(2)CMe(2)-o-C(6)H(4))(η(4)-COD). Two new seven membered palladacycles were obtained. A combined experimental and theoretical DFT study elucidates the mechanism for this reaction.

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+).