F NMR in organometallic chemistry: Applications of fluorinated aryls

The applications of ¹⁹F NMR in the study of a number of problems in organometallic chemistry are illustrated with relevant cases, paying special attention to the case of molecules containing fluorinated aryls. These are used as reporter groups of molecular symmetry, fluxional processes, and chemical changes, and help in the study of many fundamental organometallic processes.     

Atomistic fibrillar architectures of polar prion-inspired heptapeptides

This article provides the computational prediction of the atomistic architectures resulting from self-assembly of the polar heptapeptide sequences NYNYNYN, SYSYSYS and GYGYGYG. Using a combination of molecular dynamics and a newly developed tool for non-covalent interaction analysis, we uncover the properties of a new class of bionanomaterials, including hydrogen-bonded polar zippers, and the relationship between peptide composition, fibril geometry and weak interaction networks. Our results, corroborated by experimental observations, provide the basis for the rational design of prion-inspired nanomaterials.

This article provides the computational prediction of the atomistic architectures resulting from self-assembly of the polar heptapeptide sequences NYNYNYN, SYSYSYS and GYGYGYG.     

Water-catalyzed isomerization of the glycine radical cation. From hydrogen-atom transfer to proton-transport catalysis

The isomerization reactions of the glycine radical cation, from [NH₂CH₂COOH]⁺, I, to [NH₃CHCOOH]⁺, II, or [NH₂CHC(OH)₂]⁺, III, in the presence of a water molecule have been studied theoretically. The water molecule reduces dramatically the energy barriers of the III and IIII tautomerizations owing to a change in the nature of the process. However, the role of the water molecule depends on the kind of isomerization, the catalytic effect being more important for the IIII reaction. As a consequence, the preferred mechanism for the interconversion of glycine radical cation I to the stablest isomer, III, is the direct one-step mechanism instead of the two step (III and IIIII) process found for isolated [NH₂CH₂COOH]⁺. When using ammonia as a solvent molecule, a spontaneous proton-transfer process from [NH₂CH₂COOH]⁺ to NH₃ is observed and so no tautomerization reactions take place. This behavior is the same as that observed in aqueous solution, as has been confirmed by continuum model calculations.Contribution to the Jacopo Tomasi Honorary Issue     

C(C6F4PPh2-o)NMe a C,P-chelate and C,N-bridging ligand. Crystal structure of

Addition of PPh₂H and base to cis-[{Pd₂(μ-Cl)₂[μ-C((C₆F₅)=N(Me)]₂}_n] results in formation of a CP bond at the expense of a CF bond to give the title complex, the crystal structure of which has been determined.     

Triplet (pi,pi) reactivity of the guanine-cytosine DNA base pair: benign deactivation versus double tautomerization via intermolecular hydrogen transfer

Ab initio computations (CASSCF/6-31G* supported by CAS-PT2 single-point calculations) are used to study the reactivity of the triplet excited state of the guanine-cytosine DNA base pair. When the triplet excitation is centered on cytosine there is a competition between benign deactivation to the ground state and a hydrogen transfer route that can trigger double tautomerization. The calculated barriers favor the benign deactivation, but this route goes through a singlet/triplet intersystem crossing with small spin-orbit coupling. Therefore, the potentially mutagenic, double tautomerization route cannot be ruled out completely, and the two paths are probably an alternative to the well-known cytidine photodimerization reaction.     

Rhodium complexes with the chelating and binucleating ligands P(CH2CH2Py)nPh3-n (Py = 2-pyridyl; n = 1,2): structures and fluxional behavior

Several rhodium(I) complexes of the type [RhX(CO)(PePy2)], [Rh(diene)(PePy)]+, and [Rh(diene)(PePy2)]+ (PePyn = P(CH2CH2Py)nPh3-n; Py = 2-pyridyl; n = 1, 2) have been prepared. The two former are square planar; the latter are pentacoordinated for diene = tetrafluorobenzobarrelene or norbornadiene (confirmed by X-ray diffraction), but an equilibrium of 4- and 5-coordinate isomers exists in solution for diene = 1,5-cyclooctadiene. The fluxional behavior of all these complexes is studied by NMR spectroscopy. The complex [Rh(NBD)(PePy2)]PF6.Cl2CH2 crystallizes in the monoclinic space group P21/n with a = 8.455(1) A, b = 18.068(3) A, c = 19.729(3) A, beta = 99.658(3)degrees, and Z = 4. The complexes [Rh(diene)(PePy2)]+ react with CO to give the dimeric complex [Rh2(CO)2[P(CH2CH2Py)2Ph]2](BF4)2 with the pyridylphosphine acting as P,N-chelating and P,N-bridging.     

Oxidative coupling of platinum arylamides: temperature dependent C-H or C-F cleavage

The oxidation of an arylamido platinum complex leads to C-C coupling with selective C-H versus C-F bond cleavage depending on the reaction temperature.     

Room‐Temperature Columnar Mesophases in Triazine–Gold Thiolate Metal–Organic Supramolecular Aggregates

Supramolecular mono‐ and dinuclear liquid‐crystalline gold(I) aggregates have been synthesized by means of hydrogen bond interactions of 2,4,6‐triarylamino‐1,3,5‐triazine with thiolate moities of gold metalloacids [Au(PR₃)(SC₆H₄COOH)] or [μ‐(binap){Au(SC₆H₄COOH)}₂], in 1:1 and 2:1 molar ratio, respectively. All of the supramolecular aggregates display a stable columnar hexagonal mesophase (Col_h) at room‐temperature. The supramolecular arrangement within the columns consists of the one‐dimensional stacking of triazine units, with the core of the attached metallic thioacid fragments acting as the fourth branch. The phosphine‐containing moieties of the metallic thioacid protrude out in the aliphatic continuum. These complexes do not show metallophilic interactions, but this strategy appears very promising for the future design of room‐temperature LC mesophases containing interacting metallic fragments.