Nicotine, the addictive chemical in tobacco smoke, initiates its actions in brain through nicotinic acetylcholine receptors (nAChRs). In particular, nAChRs containing ␤ 2 -subunits (␤ 2 *-nAChRs) the most prevalent subtype, mediate the reinforcing properties of nicotine. We hypothesized that abnormal numbers of ␤ 2 *-nAChRs during early abstinence contribute to the perpetuation of addiction to tobacco smoking. Using molecular imaging, specifically single-photon emission computed tomography with the nAChR agonist radiotracer ]5-IA uptake was significantly higher throughout the cerebral cortex (26 -36%) and in the striatum (27%) than in nonsmokers, suggesting higher ␤ 2 *-nAChR in recently abstinent smokers. ␤ 2 *-nAChR availability in recently abstinent smokers correlated with the days since last cigarette and the urge to smoke to relieve withdrawal symptoms but not the severity of nicotine dependence, severity of nicotine withdrawal, or the desire to smoke. Higher brain ␤ 2 *-nAChR during early abstinence indicates that, when smokers quit smoking, they do so in the face of a significant increase in the receptors normally activated by nicotine. Greater ␤ 2 *-nAChR availability during early abstinence may impact the ability of smokers to maintain abstinence.

The use of an in situ generated Ni(0) catalyst associated with 2,2'-bipyridine or N,N'-bis(2,6-diisopropylphenyl)dihydroimidazol-2-ylidene (SIPr) as a ligand and NaO-t-Bu as the base for the intramolecular coupling of aryl chlorides with amines is described. The procedure has been applied to the formation of five-, six-, and seven-membered rings. [reaction: see text]

Neutral pentamethylcyclopentadienyl nickel complexes of general formula [Ni(NHC)X(η5-C5Me5)] [NHC = 1,3-dimethylimidazol-2-ylidene (Me-NHC), 1,3-bis(2,4,6,-trimethylphenyl)imidazol-2-ylidene (Mes-NHC), 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (iPr-NHC); X = Cl, I] were prepared from the reaction of pentamethylcyclopentadienyl acetylacetonate nickel(II) with 1 equiv of the corresponding imidazolium salt (NHC·HX). The new complexes [Ni(Me-NHC)I(η5-C5Me5)] 1a, [Ni(Mes-NHC)Cl(η5-C5Me5)] 2, and [Ni(iPr-NHC)Cl(η5-C5Me5)] 3 were obtained in moderate to good yields and were fully characterized by 13C and 1H NMR spectroscopy, and in the cases of 1a and 2 by single-crystal X-ray crystallography. The related cyclopentadienyl complex [Ni(Me-NHC)I(η5-C5H5)] 1b was also synthesized and structurally characterized; its geometry and spectroscopic data are comparable to those of complex 1a. The variable-temperature (VT) 1H NMR spectra of the sterically constrained complexes 2 and 3 are consistent with restricted rotation about the nickel−carbene carbon bond. The free energy of activation for the dynamic processes, in both cases, was determined to be on the order of 65−67 kJ mol−1 by VT NMR experiments.

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