Frederick W. B. Einstein

The syntheses, 77Se CP-MAS solid state NMR spectra and crystal structures of adducts of the selenium coronand, 1,5,9,13-tetraselenacyclohexadecane, with copper(I) trifluoromethanesulfonate and mercury(II) cyanide

The preparation, characterization, X-ray crystal structures and 77Se CP-MAS solid state NMR spectra of adducts of 1,5,9,13-tetraselenacyclohexadecane with copper(I)trifluoromethansesulfonate and mercury(II)cyanide are reported. Crystal data: [(Cu(Se(CH2)3)4)][SO3CF3] (1); orthorhombic; space group B2212; a = 8.947 (2); b = 15.184(2); c = 15.918(2) A; V = 2162.2 A3; Z = 4; FW = 696.77; ϱc = 2.140 g cm−3; λ = 0.71069 A; R(F) = 0.044 for 622 data (I ⪖ 2.5σ(I)). (Hg(CN)2)3)4) (2); monoclinic; space group P21/c; a = 5.822(1); b = 12.457(2); c = 14.074(2) A; β = 99.07(1)°; V = 1008.1 A3; Z = 2; FW = 736.79; ϱc = 2.427 g cm−3; λ = 0.71069 A; R(F) = 0.038 for 1153 data (I ⪖ 2.5σ(I)). 1 displays orientational disorder of the SO3CF3− anion and correlated disorder of the complex cation. The refinement was stabilized using soft restraints. The cation is a three-dimensional polymeric complex with pseudo-tetrahedral coordination about copper to four distinct ligands. 2 consists of linear Hg(CN)2 molecules which interact weakly with four selenium atoms from different ligands to give a tetragonally distorted octahedral arrangement.

Synthesis and characterization of nitroimidazole complexes of platinum and palladium and the crystal and molecular structure of trans-dichlorobis-(misonidazole) platinum(II)

Abstract The synthesis and properties of some nitroimidazole complexes of platinum and palladium starting from the MCl42- salts are described. Both 5-NO2-imidazole and metronidazole give cis-[MCl2L2] complexes whereas trans-[MCl2L2] is obtained for 2-NO2-imidazole and misonidazole. The crystal structure of trans-dichlorobis(misonidazole)platinum(II) was determined by three-dimensional X-ray methods. The compound crystallized in space group P21/c in discrete monomeric units with a = 11.303(5), b = 13.002(5) and c = 8.125(3) A, B = 91.39(3)°, Z = 2 and the observed and calculated densities are 1.83 and 1.859 respectively. The final full-matrix least-squares refinement gave values of R1 = 0.037 and R2 = 0.045 for 142 variables. The complex is square-planar with Pt-Cl and Pt-N distances of 2.294(3) and 2.016(9) A respectively. The mean plane of the misonidazole ring is twisted 56° with respect to the PtCl2L2 square plane and the Cl-Pt-N angles are 89.4(3) and 90.6(3)°; the nitro group also lies out of the plane of the misonidazole ring. The closest nonbonded contact between non-hydrogen atoms in the unit cells is 2.80 A suggesting hydrogen bonding between the hydroxyl proton and the ether oxygen in the misonidazole side-chain, i.e. O-H⋯O. Aspects of the chemistry of these species in relation to their biological activity are discussed.

Synthesis of sulfur analogues of methyl and allyl kojibiosides and methyl isomaltoside and conformational analysis of the kojibiosides

Abstract The synthesis of methyl and allyl 5′-thio-α-D-kojibiosides and methyl 5′-thio-α-D-isomaltoside is described. The phenylselenoglycoside and trichloroacetimidate of 2,3,4,6-tetra- O -acetyl-5-thioglucose have been employed as glycosyl donors to glycosylate glucopyranosyl acceptors with 2-OH and 6-OH positions free. The disaccharides thus obtained are potential glucosidase inhibitors. The conformational preferences of allyl 5′-thiokojibioside ( 34 ) were studied by comparison of experimental NOE curves with the theoretical counterparts for the corresponding methyl glycoside 25 , derived from a Boltzmann-averaged grid search using the program PIMM91. Very good agreement of experimental NOE curves derived from selective NOE measurments with the theoretical curves is found. The data are consistent with the population of a global minimum structure (Φ=−43, Ψ=−39 degrees) to the extent of 90%, and a second local minimum (Φ=−36, Ψ=−173 degrees) to the extent of 6%. An X-ray crystal structure of 34 at 190 K (R=4.2%) indicates a conformation (Φ=−46, Ψ=−23 degrees) that is similar to that of the global minimum.

18-Electron complexes as ligands. Synthesis, structure, and stereochemical nonrigidity of (trimethylphosphine)tetracarbonylosmium-pentacarbonyltungsten complex ((Me3P)(OC)4OsW(CO)5)

Preparation et structure de (Me 3 P)(OC) 4 OsW(CO) 5 contenant une liaison donneur-accepteur non pontee entre differents atomes metalliques de transition; ce compose presente aussi une stereochimie non rigide en solution

XY–ZH systems as potential 1,3-dipoles. Part 2. Oxime cycloadditions: formation of 2 : 1 adducts

Cycloaddition of aldehyde and ketone oximes are shown to give mixtures of all possible isoxazolidine regioisomers and stereoisomers. The products are 2 : 1 adducts with the second molecule of the di-polarophile attached to the isoxazolidine N-atom. The stereochemistry of the major isomer from benzaldehyde oxime and acrylonitrile was established by an X-ray crystal structure analysis. The cycloaddition is shown to be weakly catalysed by 2,4-dinitrophenol and to proceed best in acetonitrile. More polar solvents slightly favour the 5-isoxazolidine regioisomer. The mechanism of the reaction is discussed.

Synthesis and structure of Ru(CO)4[P(OCH3)3]. The conformation of the trimethyl phosphite ligand in complexes

Abstract Two methods of preparation of Ru(CO)4[P(OCH3)3] from Ru3(CO)12 and P(OCH3)3 are described. The crystal structure of the compound has been determined from three-dimensional X-ray data collected by counter methods. The space group is P21/c with cell dimensions a 13.225(3), b 7.704(3), c 13.278(4) A and β 109.82(2)°. Intensity data for 1879 observed reflections were refined by conventional methods to R  0.044. The structure shows that the phosphite ligand does not have three fold symmetry. From a comparison of the infrared spectrum in the carbonyl region of Ru(CO)4[P(OCH3)3] with that of the corresponding P(OCH2)3CC2H5 derivative it is concluded that the asymmetry of the ligand is maintained on the infrared time scale. The13C and1H NMR spectra however indicate the methyl groups are all equivalent on the NM time scale, even at120°C. The NMR study also indicated there is rapid exchange of the axial and equatorial carbonyl groups in solution.

2′-fluoromaltose: Synthesis and properties of 4-O-(2-deoxy-2-fluoro-α-d-glucopyranosyl)-d-glucopyranose, and the crystal structure of 2,3-di-O-acetyl-1,6-anhydro-4-O-(3,4-tri-O-acetyl-2-deoxy-2-fluoro-α-d-glucopyranosyl)-β-d- glucopyranose

Abstract Coupling of 3,4,6-tri- O -acetyl-2-deoxy-2-fluoro-α- d -glucopyranosyl bromide and 3,4,6-tri- O -acetyl-2-deoxy-2-fluoro-α- d -galactopyranosyl bromide with 2,3-di- O -acetyl-1,6-anhydro-β- d -glucose, under Koenigs-Knorr reaction conditions gave, in both instances, only the corresponding α-(1→4)-linked disaccharides. In the first case, the linkage was verified by 1 H- and 19 F-n.m.r., and by X-ray crystallographic analysis of 2,3-di- O -acetyl-1,6-anhydro-4- O -(3,4,6-tri- O -acetyl-2-deoxy-2-fluoro-α- d -glucopyranosyl)-β- d -glucopyranose. Deprotection of this disaccharide gave 2′-deoxy-2′-fluoromaltose. Maltose and its fluorinated analogue displayed similar 1 H- and 13 C-n.m.r. spectra and optical rotations, indicating that these two sugars are isomorphous in solution and suggesting that 2′-deoxy-2′-fluoromaltose might be a suitable substrate for studies of α-glycosidases.

Selenium coronands. A novel conformational pair

The synthesis and characterization of the novel selenium coronands, 1,3,7,9-tetraselenacyclododecane 1a, 1,3,7,9,13,15-hexaselenacyclooctadecane 2a, the corresponding β-gem-dimethyl derivatives 1b, 2b, and 1,5,9,13-tetraselenacyclohexadecane 3, and 1,5,9,13,17,21-hexaselenacyclotetracosane 4 are described. X-ray crystallographic analysis of 1a reveals three independent molecules that exist in two distinct conformations, one molecule having approximate two-fold symmetry together with two molecules (of similar conformation) each having crystallographic symmetry. The conformations are denoted as [3333] or [66]. Whereas one resembles that of cyclododecane and tetrathia-12-crown-4 with respect to torsion angles, the other resembles that of tetraoxa-12-crown-4. The solid state CP-MAS 77Se and 13C nmr spectra are interpreted in light of the crystallographic information. Crystal structure: formula Se4C8H16; fw = 428.05; monoclinic, P21/c; Z = 8; a = 15.823(2) A, b = 5.534(1) A, c = 27.962(5) A, β = 92.26(1)°; V =...

Metal hydrides from cationic rhodium(I) catalyst precursors. X-Ray structure of [(L–L)HRh(µ-H)3RhH(L–L)]ClO4[L–L =rac-Fe(η5-C5H4PPhBut)2]

The hydrogenation catalyst precursor [(L–L)RhNBD]ClO4 reacts with H2(1 atm, 30 °C, MeOH) to yield [(L–L)HRh(µ-H)3RhH(L–L)]ClO4[L–L =rac-Fe(η5-C5H4PPhBut)2; NBD = norbornadiene].

A fluoroalicyclic-bridged ditertiary phosphine derivative of iron. the crystal structure of (π-C5H5)Fe(CO)(f6fos))SnMe3

Abstract The crystal structure of (π-C5H5)Fe(CO)(f6fos)SnMe3 where the ligand, fe6fos, is (PPh2) C=C(PPh 2 )(CF 2 ) 2 C F2 has been determined from three-dimensional X-ray data collected by counter methods. The structure has been refined by full-matrix least-squares techniques (tin, iron and three fluorine atoms with anisotropic thermal parameters) to a conventional R factor of 8.0 per cent of the 1703 observed reflections. The compound crystallizes in the triclinic space group A1 with four formula units in a cell of dimensions a=10.381 (1), b=22.382(4), c=15.459(2) A α=101.48(1), β=92.13(2), and γ=83.26(2)°. The hexacoordinate iron atom is bonded to a carbonyl group, a cyclopentadienyl group, a trimethyltin group and one phosphorus atom of the f6fos group. The iron-tin bond length of 2.562(4I A is slightly longer than the bonded distance in cyclopentadienyldicarbonyliron triphenyltin (average value of 2.536(3) A for the FeSn length). The conformation and structural properties of the five-membered fluorocarbon ring are compared to that found for the chelating f6fos ligand as found in the anion {cis-Rh(CO)2Cl2}–