Annalisa Bisello

Synthesis, structure and reactivity of homobimetallic Rh(I) and Ir(I) complexes of s- and as-indacene-diide

Abstract The Rh(COD) and Ir(COD) homobimetallic complexes of s-indacene-diide, 2,6-dimethyl-s-indacene-diide, as-indacene-diide, and 2,7-dimethyl-as-indacene-diide have been synthesized from the di-lithium salts of the dianions and metal dimers [M(μ-Cl)L2]2 (M = Rh, Ir; L2 = COD, NBD, (ethylene)2, (CO)2 as mixtures of syn and anti isomers. The syn/anti ratio depends on the nature of the ancillary ligands at the metal and on the s or as geometry of the bridging ligand. In the reaction of the 2,7-dimethyl-as-indacene-diide-[M(COD)]2 species with CO, the higher reactivity of the syn isomers has been justified on the basis of a greater instability of the ground state due to steric interactions between the COD groups. Bis-η1 metal-bonded intermediates have been identified in the carbonylation of iridium derivatives; on the other hand, the formation of the bis-η5 mixed complexes syn and anti-{2,7-dimethyl-as-indacene-diide-[Rh(COD)][Rh(CO)2]} and their reactivity strongly support the existence of metalmetal interaction in the rhodium derivatives.

Charge Mapping in 310-Helical Peptide Chains by Oxidation of the Terminal Ferrocenyl Group

Two series of 3(10)-helical peptides of different lengths and rigidity, based on the strongly foldameric α-aminoisobutyric acid and containing a terminal ferrocenyl unit, have been synthesized. Oxidation-state sensitive spectroscopic tags of helical peptides, the N-H groups, allowed mapping of the charge delocalization triggered by oxidation of the terminal ferrocenyl moiety and were monitored by IR spectroelectrochemistry.

Low hapticity intermediates in the carbonylation of (η5-2,6-dimethyl-5-hydro-s-indacenide)-Ir(η4-COD)

Abstract The isomeric (η1-5-hydro-2,6-dimethyl-s-indacenide)-Ir(η4-COD)(CO)2 and (η1-7-hydro-2,6-dimethyl-s-indacenide)-Ir(η4-COD)(CO)2) complexes are produced in a 1/1 ratio in the first step of the carbonylation reaction of (η5-2,6-dimethyl-5-hydro-s-indacenide)-Ir(η4-COD) at 233 K. At 243 K, in the presence of excess CO, they slowly convert into the isomeric (η1-5-hydro-2,6-dimethyl-s-indacenide)-Ir[η2-COD)(CO)3) and (η1-7-hydro-2,6-dimethyl-s-indacenide]-Ir(η2-COD)(CO)3. The unprecedented η2-coordination of COD towards iridium has been detected both by conventional variable temperature 1D 1H NMR spectroscopy and by a single-temperature 2D EXSY experiment.

Synthesis, properties and reactivity of mononuclear Rh(I) and Ir(I) complexes of s- and as-hydroindacenide ligands

The monometallic complexes with Rh(COD) and Ir(COD) of 1,5- and 1,7-dihydro- s -indacene, 2,6-dimethyl-1,5-dihydro- s -indacene and 2,7-dimethyl-1,6-dihydro- as -indacene have been synthesized and characterized spectroscopically and structurally. Deprotonation and further complexation of these compounds afforded mixtures of syn and anti homobimetallic isomers. The syn / anti ratio depends on the structure of the ion pairs of the salt and on the s or as geometry of the bridging ligand.

New bis‐ferrocenyl end‐capped peptides: synthesis and charge transfer properties

In this article, the successful preparation of a new series of 3(10) -helical peptides of different length containing two terminal ferrocenyl (Fc) units and based on the strongly foldameric α-aminoisobutyric (Aib) acid is reported. The synthesis of the Fc-CO-(Aib)(n) -NH-Fc (n = 1-5) homo-peptides was performed by solution methods. Moderate to good yields (26-85%) were obtained in each of the difficult coupling steps of Fc-COOH and the corresponding H-(Aib)(n)-NH-Fc compounds by C-activation with the 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide/7-aza-1-hydroxy-1,2,3-benzotriazole method. Information on the C=O···H-N intramolecularly hydrogen-bonded networks was initially obtained from FT-IR absorption measurements. The N-H stretching (amide A) region allowed us to distinguish which amide protons are involved in intramolecular hydrogen bonds and indicates the formation of an incipient 3(10) -helix structure for peptides containing at least two Aib residues. This conclusion was confirmed by (1)H NMR titrations of the N-H groups of the peptides in CDCl(3) with dimethylsulfoxide and by crystallographic analysis of the N(α) -acylated Fc-CO-(Aib)(5)-NH-Fc pentapeptide amide. The two redox-active Fc groups covalently bound to the termini of the foldameric peptide architectures were used as electrochemical probes. The end-to-end effects of electron holes generated by single and double oxidations were analyzed by means of electrochemical and spectroelectrochemical techniques. The results of these studies indicate that charge transfer across the peptide main chain does occur in the five peptides. In particular, in the pentapeptide 5, charge is transferred through an intramolecular Fe···Fe separation of 14 Å.

CCDC 879903: Experimental Crystal Structure Determination

Related Article: Alessandro Donoli, Vanessa Marcuzzo, Alessandro Moretto, Marco Crisma, Claudio Toniolo, Roberta Cardena, Annalisa Bisello and Saverio Santi|2013|Biopolymers|100|14|doi:10.1002/bip.22197