Michael A. Bruck

Syntheses of highly constrained β-aryl isohexanoic acid derivatives via asymmetric Michael addition

A series of enantiomerically pure highly sterically hindered β-branched isohexanoic acid derivatives have been synthesized with high diastereoselectivity via asymmetric Michael addition. The X-ray crystal structure of (4S,3′S)-3-[3′-(2,6-dimethylphenyl)isohexanyl]-4-phenyl-2-oxazolidinone demonstrated that the β-configuration was induced from the Si-face, and that the torsional angle χ2 was restricted by the bulky β-isopropyl group to the range expected from molecular modeling.

QUINOLINE BINDING MODE AS A FUNCTION OF OXIDATION STATE IN ARYLOXIDE-SUPPORTED TANTALUM COMPLEXES: MODELS FOR HYDRODENITROGENATION CATALYSIS

Abstract The heterocyclic complexes [η 1 ( N )-QUIN]Ta(OAr) 3 Cl 2 ( 1 ) and [η 1 ( N )-6MQ] Ta(OAr) 3 Cl 2 ( 2 ) (where Ar = 2,6-diisopropylphenyl, QUIN = quinoline, and 6MQ = 6-methylquinoline) are prepared from Ta(OAr) 3 Cl 2 (OEt 2 ) and QUIN or 6MQ in pentane. [η 1 ( N )-6MQ]Ta(OAr) 2 Cl 3 ( 4 ) is prepared similarly from Ta(OAr) 2 Cl 3 (OEt 2 ). Upon rapid, two-electron reduction of these complexes, an η 1 ( N ) → η 2 ( N,C ) bonding rearrangement is effected and the thermally sensitive, d 2 species [η 2 ( N,C )-QUIN]Ta(OAr) 3 ( 5 ), [η 2 ( N,C )-6MQ]Ta(OAr) 3 ( 6 ), and [η 2 ( N,C )-6MQ]Ta(OAr) 2 Cl(OEt 2 ) ( 9 ) can be isolated. Alternatively, [η 2 ( N,C )-6MQ]Ta(OAr) 2 Cl(OEt 2 ) ( 9 ) can be prepared in higher yield from (η 6 -C 6 Me 6 )Ta(OAr) 2 Cl and 6MQ. The trimethylphosphine adducts [η 2 ( N,C )-QUIN] Ta(OAr) 3 (PMe 3 ) ( 7 ) and [η 2 ( N,C )-6MQ]Ta(OAr) 3 (PMe 3 ) ( 8 ) can be prepared by simple coordination of PMe 3 to the base-free compounds 5 and 6 . When Ta(OAr) 2 Cl 3 (OEt 2 ) is reduced by one electron in the presence of QUIN, 6MQ, or pyridine, the d 1 bis(ligand) complexes [η 1 ( N )-QUIN] 2 Ta(OAr) 2 Cl 2 ( 10 ), [η 1 ( N )-6MQ] 2 Ta(OAr) 2 Cl 2 ( 11 ), and [η 1 ( N )-py] 2 Ta(OAr) 2 Cl 2 ( 12 ) can be isolated. Complexes 10 and 11 are not readily converted to the η 2 ( N,C ) analogues 5 and 6 by further reduction. Under mild hydrogenation conditions, the only heterocyclic ligands which are hydrogenated are those bound in the η 2 ( N,C ) mode to a d 2 metal. Structural studies on [η 2 ( N,C )-6MQ]Ta(OAr) 3 (PMe 3 ) ( 8 ) and [η 2 ( N,C )-6MQ]Ta(OAr) 2 Cl(OEt 2 ) ( 9 ) have been undertaken. [η 2 ( N,C )-6MQ]Ta(OAr) 3 (PMe 3 ) ( 8 ) crystallizes in the monoclinic space group C 2 1 / c (No. 15), with a = 32.849 (3) A, b = 19.579 (2) A, c = 23.822 (2) A, β = 135.69 (49)°, and V = 10702 (2) A 3 with Z = 8 and ρ caled = 1.16 g cm −3 . [η 2 ( N,C )-6MQ]Ta(OAr) 2 Cl(OEt 2 ) ( 9 ) crystallizes in the monoclinic space group P 2 1 / n (No. 14) with a = 12.059 (9) A, b = 17.975 (14) A, c = 17.949 (13) A, β = 100.29 (3)°, and V = 3828 (9) A 3 with Z = 4 and ρ caled = 1.37 g cm −3 . Both structures indicate an interruption of aromaticity to the heterocyclic ring only when bound in this fashion, consistent with the observation of 1,2,3,4-tetrahydroquinoline as the principal hydrogenation product of [η 2 ( N,C )-QUIN]Ta(OAr) 3 ( 5 ) with no decahydroquinoline being observed.

Syntheses of new 15-membered and 16-membered macrocyclic ligands with three pendant acetato groups and the structures of the gadolinium(III) complexes

Abstract A condensation of diethylenetriaminepentaacetic dianhydride with ethylenediamine gave a 15-membered macrocyclic ligand with three pendant acetato groups, (15-dtpa-en)H3C10H18N5O2(CH2CO2H)3; a l6-membered analogue, (l6-dtpa-pn)H3 C11H20N5O2(CH2CO2H)3, was obtained by the use of propanediamine instead of ethylenediamine. The structures of their gadolinium(III) complexes, Gd2(15-dtpa-en)2·16H2O and Gd(16-dtpa-pn)·4H2O, were determined by X-ray analyses. Gd2(15-dtpa-en)2·16H2O crystallized in the orthorhombic space group Pbca with: a=18.205(1), b=18.930(1) and c=15.609(1) A. Two Gd(III) ions are located between two ligand molecules, forming a binuclear metal chelate molecule with a center of inversion. The coordination geometry around a metal ion is described as a distorted tricapped trigonal prism that consists of nine coordinated atoms. Gd(l6- dtpa-pn)·4H2O crystallized in the monoclinic space group P21/c with: a =8.246(2), b = 14.995(3), c= 19.367(4) A and β = 90.258(2)°. In this compound, a water molecule and a single ligand molecule are coordinated to a Gd(III) ion, forming a mononuclear chelate with a tricapped trigonal prism. The structural differences between the two Gd(III) complexes are a result of the differences in the favorable conformations assumed by the two macrocyclic ligands.

A new bis(ethylenedithio)tetrathiafulvalene chloride: (BEDT-TTF)2Cl·3H2O

A new BEDT-TTF chloride (BEDT-TTF)2Cl·3H2O was obtained by electrochemical oxidation of the donor in dichloroethane solution containing K2[Cu(OX2−)2]·2H2O (OX2−: oxalate ion). The compound crystallized in the space group Pcca with a = 32.621(1), b = 6.720(3) and c = 14.894(6) A. The unit cell contained four units of the compound formula. Close side-by-side contacts of adjacent donor molecules formed a one-dimensional array that was parallel to the b-axis. In this array, the shortest SS distance of 3.47 A was less than the van der Waals contact of 3.70 A. The donor molecules were also stacked face-to-face along the c-axis. The shortest SS distance in the stack, however, was 3.76 A; there was no SS pair closer than the van der Waals contact. The electrical conductivity along the b-axis was c. 90 S cm− at 300 K, and exhibited metallic temperature dependence down to c. 120 K; around this temperature, a metal-insulator transition occurred. One-dimensional charge transport is attributed to the isolated array of BEDT-TTF molecules. When K2(OX2−)·H2O was used as an electrolyte instead of the bis(oxalato)cuprate(II), the known chloride, (BEDT-TTF)3Cl2·2H2O, was obtained.

Products of complete oxidative decarbonylation of tricarbonyl{hydrotris(3,5-dimethyl-1-pyrazolyl)borato}tungstate(0) by tetraalkylthiuram disulfides: {HB(Me2C3N2H)3}WS(S2CNEt2), W2(.mu.-S)2(S2CNEt2)4, and [W(S2CNEt2)4]+

The final products of the reaction of NEt 4 [{HB(Me 2 pz) 3 }W(CO) 3 ] and tetraethylthiuram disulfide in refluxing acetonitrile the red, diamagnetic, air-stable thiotungsten (IV) complex {HB(Me 2 pz) 3 }WS(S 2 CNEt 2 ) (1) and known W 2 (μ-S) 2 (S 2 CNEt 2 ) 4 (4) and [W(S 2 CNEt 2 ) 4 ] + isolated as chloride salt 3)

95Mo NMR investigation on cationic [C5H5Mo(CO)2L2]BF4 complexes (L = group 15 donor ligands ☆

Abstract Photochemically-initiated oxidative fission of the MoMo bond in [C5H5Mo(CO)3]2 by the ferricenium salt [(C5H5)2Fe]BF4 in the presence of four equivalents of L affords a good yield of [C5H5Mo(CO)2L2]BF4 (L = group 15 donor ligands). 95Mo NMR data are reported and discussed together with the NMR and IR data of new complexes. Decomposition of the title cations in polar solvents affords low yields of the corresponding [C5H5MO(CO)3L]BF4 complexes. The X-ray crystal structure of [C5H5Mo (CO)3{P(C6H5)3}]BF4 is reported. The cation has the CpML4 piano-stool geometry.

Novel bonding geometry and valence tautomerism of 4-(N,N-dimethyldithiocarbamato)-2-dimethyliminio-1,3-dithietane tetraphenylborate, [Me2NCS2·CH·S2CNMe2]+Ph4B–

A ring-opening/ring-closing tautomerism in solution of the title compound is deduced from the temperature dependence of the 1H NMR spectra; the molecular structure found by X-ray crystal analysis is favourably oriented for this tautomerism.

Crystal structure of tris(quinoxaline-2,3-dithiolato)molybdate(V); a distorted trigonal prismatic complex

The anion [Mo(qdt)3]–(qdt = quinoxaline-2,3-dithiolate) has been prepared by iodine dioxidation of the corresponding dianion. The compound [PPh4][Mo(qdt)3] crystallizes in triclinic space group P with a= 12.077(5), b= 12.519(5), c= 15.297(6)A, α= 89.76(3), β= 81.09(3), γ= 80.50(3)°, and Z= 2. The complex has a distorted trigonal prismatic MoS6 core with a mean Mo–S distance of 2.393(1)A and a mean twist angle of 14.6°. This monoanion is more significantly distorted from ideal trigonal-prismatic geometry than is the dianion, [Mo(qdt)3]2–, contrary to the results expected on the basis of previous molecular orbital calculations for tris(dithiolene) complexes.

Crystal and molecular structure of [SnLCl3]]. The single-crystal electron paramagnetic resonance spectra of [MoE(L)Cl2] and [MoO(L)(NCS)2] diluted in [SnLCl3] [E=O or S;L=tris(3,5-dimethylpyrazolyl)hydroborate]

The crystal structure of [SnLCl3] has been determined and shown to consist of discrete distorted fac-octahedral molecules [L = tris(3,5-dimethylpyrazolyl)hydroborate]. The single-crystal EPR spectra, at room temperature and Q-band frequencies, of [MoE(L)Cl2] and [MoO(L)(NCS)2], E = O or S, diluted in the structurally similar [SnLCl3] have been recorded. The data from the different possible diluent sites in [SnLCl3] are consistent with exact, or nearly exact, monoclinic EPR symmetry for each of the molybdenum compounds which involves a rotation of the g and A tensors about an axis perpendicular to the mirror plane in each molecule. The angles of rotation are in the range 30–38° and are in good agreement with those obtained via simulation of the frozen-solution X-band EPR spectra of the compounds. The relationships between the g and A tensors, the molecular geometries, and the electronic structures are discussed.

Structure of bis(ethylenedithio)tetrathiafulvalenium tribromodicuprate(I), (BEDT-TTF+)CuI2Br3: coordination of the organic radical cation to the metal ions

X-Ray crystal analysis has revealed that two sulfur atoms of a bis(ethylenedithio)tetrathiafulvalene radical cation, BEDT-TTF+, are coordinated to copper(I) atoms in a –Cu–Br–Cu–(µ-Br)2–Cu– chain, in which each copper atom has a distorted tetrahedral coordination with a sulfur atom and three bromine atoms.