The ortho-metalated complex [Pd 2 {κ 2 (C,N)-C 6 H 4 CH 2 CH 2 NHMe-2} 2 (μ-Br) 2 ] (1) can be prepared by refluxing a 1:1 mixture of Pd(OAc) 2 and N-methylphenethylamine in acetonitrile, followed by addition of an excess of NaBr. Complex 1 reacts with PPh 3 to give the mononuclear derivative [Pd{κ 2 (C,N)-C 6 H 4 CH 2 CH 2 NHMe-2}Br(PPh 3 )] (2). The cationic complex [Pd{κ 2 (C,N)-C 6 H 4 CH 2 CH 2 NHMe-2}(py) 2 ]-ClO 4 (3) can be obtained by reacting 1 with AgClO 4 and pyridine. The previously reported com- Et (4b)). These dimers react with neutral ligands (L=PPh 3 , t BuNC) in a 2:1 molar ratio to afford the monomeric complexes R=Et (7a), Ph (7b); X=F, R=Et (8a), Ph (8b); X=NO 2 , R=Ph (9)) through a double insertion of the alkyne into the Pd-C bond. Complexes A and D react with PhCtCCO 2 R in molar ratio 1:6-7 to afford a mixture of di-inserted head-to-tail and tail-to-tail isomersR 00 =Ph (12b)). CO further inserts into the Pd-C bond of complexes 7a,b and 8a,b to give the 10-membered palladacycles [Pd 2 {κ 2which contain a cyclopentadienyl unit. Complex 18 reacts with TlOTf and neutral ligands to give [Pd{κ 3 (O, C,N)-OdC(OMe){C 5 (CO 2 Me) 4 }C(CO 2 Me)C 6 H 4 CH 2 NHCH 2 Ph-2}(L)]OTf (L = H 2 O (22), py ( 23)). Reaction of complex A with an excess of 2-butyne for long periods of time affords the coordination derivative 24, probably emerging from tri-insertion of the alkyne into the Pd-C bond, followed by an internal cyclization and β-hydrogen abstraction. When complex G reacts with an excess of 2-butyne and TlOTf, the tri-inserted product 25 is obtained, which also contains a C 5 R 5 unit, although in this case, coordination around the palladium atom is completed by one CdC bond of the cyclopentadienyl unit. The crystal structures of complexes 2, 5a, 6b, 7a, 7b 3 3DMSO, 9, 14a 3 2DMSO, 18, 21, 24, and 25 have been solved by X-ray diffraction. In all these structures, the palladium atom shows a distorted or slightly distorted square-planar environment, except in complex 14a, where Pd(II) exhibits a distorted trigonalbipyramidal geometry.

The competition between π- and dual σ,π-gold-activation modes is revealed in the gold(I)-catalyzed heterocyclization of 1-(o-ethynylaryl)urea. A noticeable effect of various ligands in gold complexes on the choice of these activation modes is described. The cationic [Au(IPr)](+) (IPr=2,6-bis(diisopropylphenyl)imidazol-2-ylidene) complex cleanly promotes the π activation of terminal alkynes, whereas [Au(PtBu3 )](+) favors intermediate σ,π species. In this experimental and mechanistic study, which includes kinetic and cross-over experiments, several σ-gold, σ,π-gold, and other gold polynuclear reaction intermediates have been isolated and identified by NMR spectroscopy, X-ray diffraction, or MALDI spectrometry. The ligand control in the simultaneous or alternative π- and σ,π-activation modes is also supported by deuterium-labeling experiments.

Nucleobases team up: the efficient and selective preparation of purine-derived metallanucleosides, metallanucleotides, and metalladinucleotides having M-C bonds (M=Ir(III), Rh(III)) is reported for the first time. The results presented may be applied to the synthesis of functionalized nucleic acids, or DNA/RNA-modified segments.

The application of organoboron compounds as light-absorbing or light-emitting species in areas as relevant as organic electronics or biomedicine has motivated the search for new materials which contribute to the progress of those applications. This article reports the synthesis of four-coordinate boron complexes based on the unexplored 7-(azaheteroaryl)indole ligands. An easy synthetic approach has enabled the fine-tuning of the electronic structure of the organoboron species by modifying a heteroaromatic component in the conjugated system. Furthermore, a comprehensive characterization by X-ray diffraction, absorption and emission spectroscopy, both in solution and in the solid state, cyclic voltammetry, and computational methods has evidenced the utility of this simple strategy. Large Stokes shifts have been achieved in solid thin-films which show a range of emitted light from blue to orange. The synthesized compounds have been used as biocompatible fluorophores in cell bioimaging.

Partially modified retro- (PMR) and retro-inverso (PMRI) psi[NHCH(CF(3))]Gly peptides, a conceptually new class of peptidomimetics, have been synthesized in wide structural diversity and variable length by aza-Michael reaction of enantiomerically pure alpha-amino esters and peptides with enantiomerically and geometrically pure N-4,4,4-trifluorocrotonoyl-oxazolidin-2-ones. The factors underlying the observed moderate to good diastereocontrol have been investigated. The conformations of model PMR-psi[NHCH(CF(3))]Gly tripeptides have been studied in solution by (1)H NMR spectroscopy supported by MD calculations, as well as in the solid-state by X-ray diffraction. Remarkable stability of turn-like conformations, comparable to that of parent malonyl-based retropeptides, was evidenced, as a likely consequence of two main factors: 1) severe torsional restrictions about sp(3) bonds in the [CO-CH(2)-CH(CF(3))-NH-CH(R)-CO] module, which is biased by the stereoelectronically demanding CF(3) group and the R side chain; 2) formation of nine-membered intramolecularly hydrogen-bonded rings, which have been clearly detected both in CHCl(3) solution and in some crystal structures. The former factor seems to be more important, as turn-like conformations were found in the solid-state even in the absence of intramolecular hydrogen bonding. The relative configuration of the -C*H(CF(3))NHC*H(R)- stereogenic centers has a major effect on the stability of the turn-like conformation, which seems to require a syn stereochemistry. X-ray diffraction and ab initio computational studies showed that the [-CH(CF(3))NH-] group can be seen as a sort of hybrid between a peptide bond mimic and a proteolytic transition state analogue, as it combines some of the properties of a peptidyl -CONH- group (low NH basicity, CH(CF(3))-NH-CH backbone angle close to 120 degrees, C-CF(3) bond substantially isopolar with the C=O) with some others of the tetrahedral intermediate [-C(OX)(O(-))NH-] involved in the protease-mediated hydrolysis reaction of a peptide bond (high electron density on the CF(3) group, tetrahedral backbone carbon).