Nora Veldman

Catalytic enantioselective Michael addition reactions of α-nitroesters to α,β-unsaturated ketones

Abstract Enantioselective Michael additions of α-nitroesters 2a-d with α,β-unsaturated ketones were carried out in the presence of a catalytic amount of chiral Al-Li-(R,R′)-2,2′-dihydroxy-1,1′-binaphthyl (‘AlLiBINOL’) complex prepared in situ from LiAlH 4 and 2.45 equiv. of (R,R′)-BINOL. The enantioselectivity of the Michael addition proved to be extremely temperature dependent: Michael adduct 4a showed 7% e.e when the reaction was performed at RT, whereas 72% e.e. of the opposite enantiomer of 4a was found when the 1,4-addition was performed at −23°C. Solvent variation showed that tetrahydrofuran gave the highest selectivity (up to 80% e.e.), whereas the highest enantioselectivity for the opposite enantiomer was found in methylene chloride (up to 25%). X-Ray structure analysis of the AlLi 3 BINOL 3 complex 6 in combination with 27 Al NMR studies showed that ‘AlLiBINOL’ is a mixture of aluminium complexes in solution.

Three dinuclear copper(II) carboxylates with the paddle-wheel cage structure as intermediates in copper(II) catalyzed oxidations of carboxylic acids. X-ray crystal structures of [tetrakis(diphenyl acetato-μ-O,O′)bis(acetonitrile-N)dicopper(II)] tetrakis(acetonitrile), [] and [tetrakis(1-phenyl-1-carboxylato-μ-O,O′-cyclopentane)-bis(ethanol-O)dicopper(II)] bis (ethanol)

Abstract The synthesis spectroscopic magnetic and structural characterization of three new dinuclear copper(II) carboxylates are described. All compounds exhibit the typical dinuclear paddle-wheel type structure, consisting of two copper(II) ions in square-pyramidal geometry bridged by four carboxylate anions in the xy plane and O- or N-donor ligands at the apex. [tetrakis(diphenyl acetato-μ-O,O′)bis(acetonitrile-N dicopper(II)tetrakis(acetonitrile) (1, CnhCu2N2O8, crystallizes in the triclinic space group P 1 (No.2) with a=10.8941(17) b=11.140), c=13.346(3) A , α=69.9271(17), β=78.658(16), γ=86.819(14)°= Z=1, R=0.0438 and R w =0.0479 for 5188 observed reflections. The −2J value of this compounds is 330(17)cm−1, the triplet state exhibiting a rhombic zero-field splitting with D=0.353(11 cm1 and E=0.0022(2) cm−1, with g=2.03(1), g=2.05(1) and g=2.34(1). The compound [tetrakis(diphenylacetato-μ-O,O′)bis(acetone-O)dicopper(II)] (2). C62H50Cu2O10 crystallizes in the triclinic space group Pt (No. 2). The cell dimensions are a=10.8722(6), b=11.4003(8), c=11.6856(10) A , α=94.216(6), β=104.859(6), γ=111.193(5)°, Z=1, R1=0.0325 and wR2=0.0795 . The −2J value is 303(15) cm1, the triplet state exhibiting a rhombic zero-field splitting with D=0.345(10)cm−1 and E=0.0004cm1, with g1=2.06(1), g1=2.33(1) and g1=2.33(1). The dinuclear compound [tetrakis(1-phenyl-1-carboxylato-μ-O,O′-cyclopentane)bis(ethanol-O)dicopper(II)] bis(ethanol) (3). C56H76Cu2O12, crystallizes in the triclinic space group P 1 (No. 2). The cell dimensions for 3 are a=10.1013(6), b=11.6013(6), c=12.7596(5) A , α=64.908(4), β=70.116(4), γ=83.079(5)°, Z=1, R=0.0311 and R w =0.0253 . The structure forms an extended chain by hydrogen bonding from the axial ethanol, via a lattice ethanol to a carboxylate oxygen of another dicopper unit. The relatively small −2J value of this compound is 284(14) cm−1, the triplet state exhibiting a rhombic zero-field splitting with [D]=0.346(10) cm1 and relatively large [E]=0.0058 cm1, g1=2.04, g1=2.04 and g1=2.33, A1=0.065cm−1.

Extended structures in crystalline phyllosilicates: silica ring systems in lithium, rubidium, cesium, and cesium/lithium phyllosilicate

The crystal structure of lithium phyllosilicate, (Li2Si2O5) has been refined and those of rubidium (Rb2Si2O5), cesium (Cs2Si2O5) and cesium/lithium (Cs1.33Li0.67Si2O5) phyllosilicate have been determined. Lithium phyllosilicate is orthorhombic, Ccc2, a = 5.807(2), b = 14.582(7), c = 4.773(3) A with R = 0.042. Rubidium phyllosilicate is monoclinic, C2/c, a = 9.851(4), b = 8.3789(7), c = 14.753(4) A, β = 90.09(3)° and R = 0.121. Cesium phyllosilicate is monoclinic, P21/c, a = 10.061(5), b = 8.609(5), c = 18.414(6) A, β = 122376(4)° and R = 0.088. Cesium/lithium phyllosilicate is monoclinic, P21/m, a = 10.9547(9), b = 8.4281(7), c = 18.962(2), β = 90.314(7)°, R = 0.0501. A review of all crystalline alkali-alkaline earth phylloslicates known to date indicates that the topology of the silica sheets for lithium, α-, β-, δ-sodium and barium phyllosilicate consists of six-membered rings in chair, boat or mixed chair-boat conformations. The newly discovered rubidium and cesium phyllosilicate sheets consist of four- and eight-membered silica rings whereas the mixed cesium/lithium phyllosilicate sheet consists of four-, eight- and 12-membered rings.

Weak hydrogen bonding. Part 5. Experimental evidence for the long-range nature of CC–H ⋯π interactions: crystallographic and spectroscopic studies of three terminal alkynes

In the crystal structures of three terminal alkynes, long CC–H ⋯ CC contacts with H ⋯ C separations in the range 2.7–3.1 A are observed. Despite the long distances, these contacts possess the characteristic infrared spectroscopic features of weak hydrogen bonds. This provides direct evidence that the range of C–H ⋯π interactions donated by sufficiently acidic C–H groups extends beyond van der Waals separation. In two of the crystal structures, the C–H ⋯π interactions form interconnected systems CC–H ⋯ CC–H ⋯ CC–H.

Self-complementary hydrogen bonding of 1,1′-bicyclohexylidene-4,4′-dione dioxixe. Formation of a non-covalent polymer.

Abstract 1,1′-Bicyclohexylidene-4,4′-dione dioxime 2 self-assembles into a non-covalent polymer structure in the solid state due to intermolecular directional hydrogen bonding between the oxime functionalities.

FLUCTUATIONS BETWEEN SQUARE-PLANAR AND TETRAHEDRAL COORDINATION GEOMETRY WITH BIS(2-BENZIMIDAZOLYL)ALKANE LIGANDS. SYNTHESIS, SPECTROSCOPIC PROPERTIES AND X-RAY CRYSTAL STRUCTURE OF FOUR REPRESENTATIVE EXAMPLES

Abstract Several new transition-metal(II) coordination compounds with the formula [M(L)2(ClO4)2](sol)x(H2O)y (in which L=bis(2-benzimidazolyl)ethane, abbreviated as dbz or bis(2-benzimidazolyl)propane, abbreviated as tbz, M=Cu(II), Ni(II); sol=MeOH, EtOH, 1-PropOH, ButOH, x=1–4, y=0–1) have been prepared and characterized structurally and spectroscopically. Four representative compounds, i.e. [Cu(dbz)2](ClO4)2(C2H5OH)2 (1), [Cu(tbz)2](ClO4)2(C3H8O) (2), [Cu(tbz)2](ClO4)2(C3H8O)(H2O) (3) and [Ni(dbz)2](ClO4)2(C2H5OH)4 (4), were characterized structurally by X-ray diffraction. Structure 1 consists of a mononuclear Cu(II) ion surrounded by four nitrogen atoms of two dbz ligands, in a square planar geometry with trans angles of 180° and with one oxygen of a perchlorate molecule in an apical position with a distance of 2.9320(19) A. Structures 2 and 3 both consist of a mononuclear Cu(II) ion surrounded by four nitrogens of two tbz ligands, in which the trans angles of 144.3(3) and 146.9(3)° for structure 2 and 138.9(4) and 142.0(4)° for structure 3, indicate quite a distorted square-planar geometry. The difference between both structures is that structure 3 has, in addition to a 1-propanol molecule, a water molecule in the lattice, whereas structure 2 has only a 1-propanol molecule in the lattice. Structure 4 consists of mononuclear Ni(II) ions surrounded by four nitrogens of two dbz ligands with trans angles of 176.8(2) and 175.8(2)°, indicative of an almost perfect square-planar geometry. In the far-IR an absorption is observed in compound 3 at 384 cm−1 which is absent in compounds 2 and 4 and which is ascribed to the librational mode of the water molecule present in the lattice.

Versatile coordination behavior of (N-aryliminophosphoranyl) (thiophosphoranyl) methane and its anion to platinum(II)

Abstract A Staudinger reaction of bis(diphenylphosphino)methane (dppm) with 1 equiv. of aryl-azide, gave pure mono-phosphinimine Ph2PCH2PPh2N-aryl (1a, aryl = p-tolyl; 1b, aryl = p-anisyl), after column chromatography. A continuing reaction of 1 with sulfur afforded the new ligand, (thiophosphoranyl)(iminophosphoranyl)methane, CH2(PPh2S)(PPh2N-aryl) (dppmSn(aryl)] (2a,b). By using n-BuLi, deprotonation of 2 took place, but isolation of the organometallic derivatives M[CH(PPh2S) (PPh2N-aryl)] (3) failed. The reaction of a,b with Pt2Cl4(PEt3)2 resulted in the formation of two isomers 4 and 5. The major product, the four-membered platinacylcle trans-P-Pt-C [PtCl(PEt3) CH(PPh2S) (PPh2NH-aryl)-C,S]+ (Y)− (4a, aryl = p-tolyl, YCl; 4c, aryl = p-tolyl, YBF4; 4c, aryl = p-anisyl, Y  BF4; 4d, aryl = p-tolyl, Y  CF3CO2), contains a C,S-chelating ligand in which an H shift has taken place from the methylene group to the non-coordinated N. The minor product, the six-membered platinacycle [PtCl(PEt3) CH2(PPh2S) (PPh2N-aryl)-S,N] + (Y)− (5a-d), cannot be converted into 4a-d. The molecular structure of 4b, as determined by X-ray crystallography, shows that an intramolecular H bridge exists between the pendant PNH group and the Cl ligand on Pt cis to it. A deprotonation reaction of the product mixture 4/5 with NaH readily afforded the neutral four-membered platinacycle trans PPtN [PtCl(PEt3) CH(PPh2N-pTol) (PPh2S)-C,N] (6), containing a C,N-coordinated anionic ligand. Remarkably, protonation of 6 did not give 4 and 5 again, but afforded trans ClPtC [PtCl(PEt3) CH(PPh2S)(PPh2NH-aryl)-C,S]+ (Y)− (7), the geometric isomer of 4. The formation of the products 4–7, their geometry and relative (thermodynamic) stability is explained by comparing the relative σ-donor capacity of N versus S versus C within the neutral or anionic coordinated dppmSN(aryl) ligand, with earlier reported data of related platinum complexes.

A SIMPLE PROCEDURE FOR THE PREPARATION OF 1,8-BIS(DIPHENYLPHOSPHINO)NAPHTHALENE

Abstract 1,8-Bis(diphenylphosphino)naphthalene has been obtained in good yields from 1,8-dilithionaphthalene and chlorodiphenylphosphine.

Synthesis of a New Multidentate Phosphane Ligand C6H2(CH2PPh2)4-1,2,4,5 − X-ray Structure of a Dinuclear Ruthenium(II)-Bridged Complex: [{RuCl2(PPh3)}2{C6H2(CH2PPh2)4-1,2,4,5-P,P′,P′′,P′′′}]

The tetrakis(phosphane oxide) C6H2{CH2P(O)Ph2}4-1,2,4,5 (5), has been prepared in high yield from the Arbuzov reaction of C6H2(CH2Br)4-1,2,4,5 (4), with excess (7 equiv.) of Ph2POEt. Subsequent reduction of 5 with HSiCl3 (12 equiv.) in C6H4Cl2-1,2 afforded the new tetraphosphane C6H2(CH2PPh2)4-1,2,4,5 (6), in high yield. The reaction of 6 with [RuCl2(PPh3)4] in CH2Cl2 afforded the green dinuclear ruthenium(II) coordination complex [{RuCl2(PPh3)}2{C6H2- (CH2PPh2)4-1,2,4,5-P,P′,P′′,P′′′}]·0.5 CH2Cl2 (8), in 39% isolated yield. The solid-state molecular geometry of 8, determined by X-ray analysis, shows that the tetraphosphane is ortho-P,P′-chelated to each of the two [RuIICl2(PPh3)] units.

Synthesis and molecular structures of palladium and platinum complexes of PTFA: models of Grignard cross-coupling catalysts

Abstract A number of palladium(O) and palladium(II) as well as platinum(O) and platinum(II) complexes of (η5-cyclopentadienyl)-(η5-4-endo-N,N-dimethylamino-3-diphenylphosphino-4,5,6,7-tetrahydro-1H-idenyl)iron (PTFA) of the type (PTFA)M(0)(alkene) and (PTFA)M(II)(R)X, (M = Pd, Pt; alkene = dibenzylideneacetone, maleic anhydride, fumaronitrile and tetracyanoethylene; R = CH3, Ph and PhCH2; X = Cl, Br and I) have been synthesized as models of Grignard cross-coupling catalysts. All complexes were prepared either by proper ligand exchange or via oxidative addition reactions. A comparison of the X-ray structures of five complexes ((PTFA)Pd(fumaronitrile), 4, (PTFA)PdCl2, 8, (PTFA)Pd(Ph)I, 10, (PTFA)Pt(tetracyanoethylene), 6, and (PTFA)Pt(CH3)Cl, 13) showed that, in contrast to complexes of 2-(1-N,N-dimethylaminoethyl)-1-diphenylphosphino-ferrocene (PTFA), the overall molecular structures of PTFA complexes are comparable; they neither strongly depend on the oxidation state of the metal nor the type of additional ligands coordinated to the metal. Compound 4, C32H32FeN3PPd · CH2Cl2, crystallizes in the monoclinic space group P21/c (no. 14), with a = 19.237(2), b = 9.0737(10), c = 17.917(3), A , β = 96.458(11)°, V = 3107.6(7) A 3 , Z = 4 . The structure refinement converged to R1 = 0.0579 for 3832 F0 > 4q (F0) and wR2 = 0.1276 for all unique data, S = 0.94. Compound 6, C34H30FeN5PPt·C4H10, crystallizes in the triclinic space group P 1 , with a a = 11.845(3), b = 12.120(4), c = 12.979(3) A , α = 81.68(2)δ, β = 82.06(2)°, γ = 68.11(3)°, V = 1703.6(8) A 3 , Z = 2 . The structure refinement converged to R1 = 0.0402 for 6459 F0 > 4q(F0 and wR2 = 0.1076 for all 7235 unique data, S = 1.04. Compound 13, C29H33ClFeNPPt, crystallizes in the monoclinic space group P21/c (no. 14), with a = 16.122(2), b = 10.1608(11), c = 21.716(3) A , β = 132.202(11)°, V = 2635.2(5) A 3 , Z = 4 . The structure refinement converged to R1 = 0.0322 for 3846 F0 > 4q (F0) and wR2 = 0.0734 for all unique data, S = 1.03.