The all-trans to mono-cis isomerizations of polyenes and two C40H56 carotenes, beta-carotene and lycopene, at the ground singlet (S0) and triplet (T1) states are studied by means of quantum chemistry computations. At the S0 state of polyenes containing n acetylene units (Pn), we find that the energy barrier of the central C=C rotation decreases with n. In contrast, however, at the T 1 state, the rotational barrier increases with n. For the C40H56 carotenes, the rotational barriers of lycopene are lower than those of their beta-carotene counterparts. This difference renders the rotational rates of lycopene to be 1-2 orders of magnitude higher than those of beta-carotene at room temperature. For both these carotenes, the barrier is lowest for the rotation toward the 13-cis isomer. The relative abundances are in the following order: all-trans > 9-cis > 13-cis > 15-cis. Although the 5-cis isomer of lycopene has the lowest energy among the cis isomers, its formation from the all-trans form is restricted, owing to a very large rotational barrier. The possible physiological implications of this study are discussed.

The imidazolium ligand precursors [L1H1H2]Cl and [L2H1 2H2]Cl (H1 = NHCO, H2 = NCHN) for the potentially bidentate and pincer-type amido-NHC ligands were synthesized in 66−78% yields. Selective deprotonation of H2 in these salts with pyridine in the presence of palladium chloride resulted in the monodentate palladium(II) complexes Pd(L1H1)(py)Cl2 and Pd(L2H1 2)(py)Cl2. The use of K2CO3 in pyridine or DMF led to the double and triple deprotonations of the ligand precursors, giving the bis-bidentate and pincer-type palladium(II) complexes PdL1 2 and PdL2(py), respectively. Intriguingly, in certain cases, both the cis and the trans isomers of PdL1 2 were formed and isolated in pure forms. A theoretical study indicates that the trans-PdL1 2 is thermodynamically more stable than the cis isomer (ca. 5.8 kcal mol-1). All the new complexes are characterized by NMR (1D and 2D) and single-crystal X-ray diffraction studies. A systematic study of the new complexes in Suzuki coupling reactions revealed the following order of activities:  Pd(L1H1)(py)Cl2 > PdL2(py) > PdL1 2.

Theoretical study of the enthalpies of formation (DeltaHf) for polyenes up to nine ethylene units and for several C40H56 carotenes including beta-carotene, alpha-carotene, lycopene, and prolycopene is presented. For polyenes and small branched alkenes, we used G2, G3, and G3MP2B3 theories, and the DeltaHf values were evaluated with the atomization, isodesmic bond separation, and homodesmic schemes. The applicability of six DFT functionals were evaluated by comparing their predictions with those obtained using G3 theory within the atomization scheme. Additivity approaches, including atom equivalents and group equivalents using DFT and semiempirical theories, were explored. We found that group equivalents associated with isodesmic reactions are able to provide the most accurate predictions within the test set. The predictions from the six functionals are in good agreement with the G3 results. Among them, B3LYP performs the best, with an average absolute deviation of only 0.30 kcal/mol. The application of DFT in the prediction for the DeltaHf value of C40H56 carotenes is promising.

A unique trithiol macromolecule, with an intrinsic conformational propensity for dimerization (cage) instead of oligomerization upon oxidation, was prepared straightforwardly through rational design. The quantitative conversion and the reversibility between the cage and trithiols through redox reactions were assayed by 1 H NMR spectroscopic analysis. The

The reactions of AlMe3 with the tridentate pyrrole ligand precursor C4H3NH(2‐CH=NCH2Py) and subsequent treatment of the derivatives with small organic molecules such as 2,6‐diisopropylphenol or dibenzoylmethane were conveniently performed, and the products were characterized. The reaction between 1 equiv. of AlMe3 and 1 equiv. of a pyrrole–imine–pyridine ligand in toluene affords [Al{C4H3N(CHNCH2Py)Me2}] (1) in high yield. In addition, the use of 2 equiv. of AlMe3 with the same tridentate precursor results in the formation of a dialuminum compound [AlMe3{C4H3N(CHNCH2‐Py)AlMe2}] (2) in moderate yield. Furthermore, the combination of 1 with either 1 or 2 equiv. of 2,6‐diisopropylphenol or 2 equiv. of dibenzoylmethane in toluene yields aluminum monophenoxide or diphenoxide compounds [Al{C4H3N(CHNCH2‐Py)Me(O‐2,6‐iPr2C6H3)}] (3) and [Al{C4H3N(CHNCH2‐Py)}(O‐2,6‐iPr2C6H3)2] (4), respectively, as well as an aluminum bis‐diketonate compound, [Al{C4H3N(CHNCH2‐Py)}(PhCOCHCOPh)2] (5). All of the aforementioned derivatives were characterized by 1H and 13C NMR spectroscopy, and their solid‐state molecular structures were determined by single‐crystal X‐ray diffraction. The geometries of 1–5 show that the pyrrole ligand exists in the pyrrolyl–imine and azafulvene–amido resonance forms. Compounds 1, 3, 4 and 5 were used in the ring‐opening polymerization of ϵ‐caprolactone in the presence of BnOH and in the catalytic Meerwein–Ponndorf–Verley (MPV) reaction of 1‐naphthalenemethanol and 2‐naphthalenecarbaldehyde.