Models for B12-conjugated radiopharmaceuticals. Cobaloxime binding to new fac-[Re(CO)3(Me2bipyridine)(amidine)]BF4 complexes having an exposed pyridyl nitrogen

Re(CO)3-Templated Synthesis of α-Amidinoazadi(benzopyrro)methenes

α-Amidinoazadi(benzopyrro)methenes were synthesized using the Re(CO)₃ unit as a templating agent. The products of these template reactions are six-coordinate rhenium complexes, with a facial arrangement of carbonyls, a noncoordinating anion, and a tridentate α-amidinoazadi(benzopyrro)methene ligand. The tridentate ligand shows the conversion of one diiminoisoindoline sp² carbon to a sp³ carbon, which has been seen in the "helmet" and bicyclic phthalocyanines. The bidentate diiminoisoindoline fragment tilts out of the plane of coordination. Five examples of α-amidinoazadi(benzopyrro)methenes produced from these reactions using different nitrile solvents, including the nitrile activation of acetonitrile, propionitrile, butyronitrile, cyclohexanecarbonitrile, and benzonitrile.

Synthesis and Characterization of Pt(II) Complexes with Pyridyl Ligands: Elongated Octahedral Ion Pairs and Other Factors Influencing 1H NMR Spectra

Our goal is to develop convenient methods for obtaining trans-[Pt^II(4-Xpy)₂Cl₂] complexes applicable to 4-substituted pyridines (4-Xpy) with limited volatility and water solubility, properties typical of 4-Xpy, with X being a moiety targeting drug delivery. Treatment of cis-[Pt^II(DMSO)₂Cl₂] (DMSO = dimethyl sulfoxide) with 4-Xpy in acetonitrile allowed isolation of a new series of simple trans-[Pt^II(4-Xpy)₂Cl₂] complexes. A side product with very downfield H2/6 signals led to our synthesis of a series of new [Pt^II(4-Xpy)₄]Cl₂ salts. For both series in CDCl₃, the size of the H2/6 Δδ [coordinated minus "free" 4-Xpy H2/6 shift] decreased as 4-Xpy donor ability increased from 4-CNpy to 4-Me₂Npy. This finding can be attributed to the greater synergistic reduction in the inductive effect of the Pt(II) center with increased 4-Xpy donor ability. The high solubility of [Pt^II(4-Xpy)₄]Cl₂ salts in CDCl₃ (a solvent with low polarity) and the very downfield shift of the [Pt^II(4-Xpy)₄]Cl₂ H2/6 signals for the solutions provide evidence for the presence of strong {[Pt^II(4-Xpy)₄]²⁺,2Cl^-} ion pairs that are stabilized by multiple CH···Cl contacts. This conclusion gains considerable support from [Pt^II(4-Xpy)₄]Cl₂ crystal structures revealing that a chloride anion occupies a pseudoaxial position with nonbonding (py)C-H···Cl contacts (2.4-3.0 Å). Evidence for (py)C-H···Y contacts was obtained in NMR studies of [Pt^II(4-Xpy)₄]Y₂ salts with Y counterions less capable of forming H-bonds than chloride ion. Our synthetic approaches and spectroscopic analysis are clearly applicable to other nonvolatile ligands.