Marc Stchedroff

Intramolecular hydrogen bonding in transition metal clusters: NMR evidence for an Os–H⋯H–S interaction in H(μ-H)Os3(CO)10(HSR) (R=ethyl, cyclopentyl)

Abstract The reaction of H 2 Os 3 (CO) 10 with RSH (R=CH 2 CH 3 , cyclopentylthiol) at low temperatures in CD 2 Cl 2 affords three H(μ-H)Os 3 (CO) 10 (RSH) adducts, where, by the 13 C NMR carbonyl spectrum, it can be shown that the thiol ligand occupies an axial position. The presence of an intermolecular MH⋯HS interaction in the main isomer has been determined by longitudinal relaxation time measurements. The isolation of the H,H dipolar contribution to the terminal hydride relaxation affords a value of 1.97 A for the ‘unconventional’ hydrogen–hydrogen interaction in H(μ-H)Os 3 (CO) 10 (RSH) (R=cyclopentylthiol). An intramolecular proton transfer from the thiol ligand RSH to the terminal hydride, via a dihydrogen bonded species, ultimately losing an H 2 molecule. leading to the formation of the stable product (μ-H)Os 3 (CO) 10 (μ-SR) is proposed.

The effect of ligand basicity on the unconventional hydrogen-bond in H(μ-H)Os3(CO)10L (L=amine) derivatives

Abstract The reaction of amine ligands with the unsaturated 46 e − cluster Os 3 (μ-H 2 )(CO) 10 yields a series of complexes of formula Os 3 H(μ-H)(CO) 10 (amine). In these derivatives the presence of an unconventional hydrogen-bond MH⋯HN is detected by the evaluation of proton spin-lattice relaxation times. In order to elucidate the relationship between p K b and H⋯H length, the MH⋯HN distances were quantified for amines of known p K b . In practice, this was achieved by comparing the T 1 values of the terminal hydride resonances of the protonated isotopomer with the T 1 values of the corresponding derivative containing selectively deuterated amine. A nice correlation between the MH⋯HN distances and the p K b of the amine ligands was found. DFT calculations were carried out for the cluster on Os 3 H(μ-H)(CO) 10 (Benzylamine) to gain a fuller understanding of the possible coordination geometries of an amine ligand on the surface of a tri-osmium cluster.

Preparation and structure of homochiral tetrahydro-2H-1,3-oxazines

The synthesis, and structural elucidation using NMR and X-ray crystallography, of homochiral N-tert-butoxycarbonyl-tetrahydro-2H-1,3-oxazines are described.

Enhanced mobility of the cluster Ru3(CO)12 in the solid state formed in situ by the reaction of CO and Ru3(CO)6(μ-CO)(μ3∶η2∶η3∶η5-C12H8) on silica

The reaction of Ru3(CO)6(μ-CO)(μ3∶η2 ∶η3∶η5-C12H 8) (physisorbed on SiO2) with CO in the solid state leads to Ru3(CO)12 and acenaphthylene in quantitative yields; the Ru3(CO)12 generated in situ is highly mobile leading to a reduced chemical shielding anisotropy.

Orientational isomerism in bridging 2-pyridyl complexes: orthometallation of (S)-nicotine and (R)-1-(4-pyridyl)ethanol in triosmium clusters

Diastereomeric orthometallated products, formed by treating [Os3(CO)10(MeCN)2] with (S)-nicotine or (R)-1-(4-pyridyl)ethanol, have been partially separated by TLC but completely so by HPLC. The two diastereomers of [Os3(µ-H){µ-(R)-NC5H3CH(OH)Me-4}(CO)10] 1 and 2 and four isomers of [Os3(µ-H){µ-(S)-NC5H3C4H7NMe}(CO)10], 3 to 6, two diastereomers each for the products of metallation at the 2 and 6 positions respectively, have been separated and characterized by circular dichroism (CD) spectra to obtain their relative configurations. The CD spectra in the 230–500 nm wavelength range are totally characteristic of the configuration of the Os3CN group at atoms. A crystal structure determination for isomer 2 has allowed absolute configurations of all isomers to be established. There is little enantioselection in the orthometallation process and no detectable interconversion of isomers. The compound [Os3(µ-H)2{µ-(S)-NC5H3C4H7NMe}2(CO)8] was also obtained as a complex isomeric mixture which was not separated.