James D. Korp

Germacranolides from Helianthus californicus

Abstract Five germacranolide sesquiterpene lactones and a trachylobane diterpene were isolated from the hexaploid species Helianthus californicus . Four of the sesquiterpene lactones are new, including a 1-oxo-3,10-diol without any carbon-carbon double bonds in the main ring whose structure was confirmed by X-ray crystallography. These results require revision of the structures of several previously published compounds. Two of the germacranolides have alkyl ether functions at a position β to a ketone and are believed to be artifacts of the isolation process. Based on terpenoid chemistry, there are no obvious progenitors of H. californicus among the diploid species of Helianthus examined to date.

Germacranolides from Viguiera microphylla

Abstract Three new germacranolides, including two heliangolides (niveusin C-2′,3′-epoxide and 1,2-dehydroniveusin C-2′,3′-epoxide) and a germacrolide (3β-hydroxy-8β-epoxyangeloyloxycostunolide-1β,10α-epoxide) were isolated from Viguiera microphylla. Their structures were established by spectroscopic analyses, including extensive 1H NMR and 13C NMR decoupling experiments and chemical transformations. X-ray diffraction analysis confirmed the structure of niveusin C-2′,3′-epoxide.

Structural, spectroscopic, and electrochemical characterization of tetrakis-µ-(2-pyrrolidinonato)-dirhodium(II) and tetrakis-µ-(δ-valerolactamato)-dirhodium(II)

The structure, chemical properties, and electrochemistry of two tetralactamato bridged dirhodium(II) complexes is reported. These complexes were formed by a ligand-exchange reaction involving 2-pyrrolidinone (Hpyro) and δ-valerolactam (Hvall)(2-piperidinone) with the acetate groups of [Rh2(O2CCH3)4]. Compound [Rh2(pyro)4(Hpyro)2]·2CH2Cl2(1a) crystallizes in space group P(triclinic) with cell constants a= 9.186(1), b= 9.569(1), c= 10.458(1)A, α= 107.28(1), β= 99.15(1), γ= 95.07(1)°, and Z= 1. The structure refinement converged to R= 0.032 and R′= 0.038. Compound [Rh2(vall)4(Hvall)2]·2Hvall (2a) crystallizes in the monoclinic space group C2/c with cell constants a= 19.990(3), b= 10.567(1), c= 21.784(7)A, β= 99.47(2)°, and Z= 4. The sample decayed rapidly, which limited the amount of available data, but the refined model converged at R= 0.035 indicating good accuracy. The prominent feature common to compounds (1a) and (2a) is the ‘cis’ arrangement of the bridging ions, where two cis nitrogens and two cis oxygens are bound to each Rh ion. The Rh–Rh bond lengths are 2.445(1) and 2.392(1)A, respectively. The oxidation potentials for [Rh2(pyro)4](1) and [Rh2(vall)4](2) in CH3CN are +0.15 and +0.04 V vs. s.c.e. Carbon monoxide binding to (1) and (2) is rapid and reversible in binding solvents such as CH3CN. However, in non-bonding solvents CO adduct formation is fast but CO dissociation is very slow. Formation constants for CO binding to (1) and (2) in CH3CN were log(Kco/atm–1)= 1.63 ± 0.05 and 2.11 ± 0.06, respectively.

Hexacarbonyl complexes of dirhenium(I) containing E2Ph4(E = P, As, or Sb) ligands; X-ray crystal structure of [Re2Br2(CO)6(Sb2Ph4)]

The E2Ph4 complexes of rhenium(I), [Re2X2(CO)6(E2Ph4)](X = Br, E = As or Sb; X = I, E = P, As, or Sb), have been prepared by the reactions of [Re2Br2(CO)6(thf)2](thf = tetrahydrofuran) or [Re2I2(CO)8] with the appropriate E2Ph4. The crystal and molecular structure of one of the compounds, namely [Re2Br2(CO)6(Sb2Ph4)], has been solved by X-ray diffraction methods. The crystals are monoclinic, space group P21/n, with a= 16.585(8), b= 22.036(13), c= 19.764(19)A, β= 109.34(6)°, and Z= 8. Data collection yielded 2 197 observed reflections, R= 0.040. The molecule consists of two pseudo-octahedral rhenium(I) centres joined by bromide and Sb2Ph4 bridges. Average distances include Re–Br 2.663(4), Sb ⋯ Br 3.640(3), Re ⋯ Re 3.970(2), and Sb–Sb 2.826(4)A. The rhenium–P2Ph4 complex undergoes nucleophilic attack by PPh2– to form an anionic rhenium(I) carbonyl species. The small angle of folding along the Br ⋯ Br vector produces the appearance of the number of i.r. carbonyl stretches expected for the local C2v symmetry of the Re2(CO)6 core, presumably due to a better coupling of the two Re(CO)3 moieties. Chemical evidence and mass spectral data indicate that the stability of the rhenium(I) complexes decreases with increasing atomic weight of the Group 5 donor atom.

The crystal structure, absolute configuration, and circular dichroism of (R)-(–)546-8,8′-(2-thiatrimethylene)-1,1′-binaphthyl

The crystal structure of (–)546-(2-thiatrimethylene)-1,1′-binaphthyl has been examined by the Bijvoet X-ray method using Cu radiation: the orthorhombic crystals are of space group P212121 with four molecules in a unit cell of dimensions a= 8.442(7), b= 9.491(3), c= 20.075(9)A. The structure was solved using MULTAN, and refined to a final R value of 2.3%. The molecules are found to have axial chirality R(helicity M), while each individual naphthalene unit is twisted with P helicity. The angle between the main planes of the naphthalene pairs is 92.5° and they are badly buckled, as predicted earlier on the basis of the low optical stabilities of related but unbridged compounds. The pattern of naphthalene bond lengths is unusual, all bonds adjacent to the strained points of connection of two naphthalene rings to each other and to the 2-thiatrimethylene bridge being longer than normal. The two six-membered rings adjacent to the 2-thiatrimethylene bridge are more distorted from planarity than the other two. The C–S and C–C bond lengths in the bridge average 1.830 and 1.496 A, while the naphthyl–naphthyl C–C distance is 1.503 A. The C–S–C angle is 103.8°. C.d. spectra of this and related compounds are presented, compared, and discussed. Chemical correlation through synthesis extends the assignment of absolute configuration to many other 8,8′-disubstituted 1,1′-binaphthyls.

Crystal and molecular structure of the {2,6-bis[1-(2-imidazol-4-ylethylimino)ethyl]pyridine}-zinc(II) and -copper(II) cations: five-co-ordinate relatives of a copper(I) oxygen carrier

The crystal and molecular structures of the two title compounds are reported and discussed as they relate to the analogous copper(I) derivative which reacts reversibly with O2 in solution under ambient conditions. The five-co-ordinate [CuII(imep)][CIO4]2 and [ZnII(imep)][CIO4]2 complexes are isomorphous and isostructural, being derived from a single quinquedentate ligand {imep = 2,6-bis[1-(2-imidazol-4-ylethylimino)ethyl]pyridine} containing one pyridine nitrogen atom, two imine nitrogen atoms, and two imidazole nitrogen-donor atoms to give MN5 primary co-ordination spheres. The co-ordination about CuII and ZnII is best described as intermediate between an idealized trigonal bipyramid and a square pyramid, with a potential sixth site lying trans to the pyridine nitrogen-donor atom (and between the imidazole rings) where a small molecule like O2 is most likely to bind in the copper(I) species. Crystal data for [CuII(imep)][ClO4]2: space group C2/c, Z= 8, a= 19.065(9), b= 11.370(4), c= 23.802(12)A, and R= 0.043 for 1 939 reflections. Crystal data for [ZnII(imep)][CIO4]2: space group C2/c, Z= 8, a= 19.414(8), b= 11.313(4), c= 24.012(6)A, and R= 0.051 for 2 551 reflections.

Crystal and molecular structure of 1,4-epoxy-4-(4-nitrophenylmethyl)-1-phenyl-1H-2,3-benzodioxepin-5(4H)-one

The title compound (I), an ozonide, crystallizes in a monoclinic unit cell, space group P21/c, with a= 8.205(9), b= 14.585(7), c= 15.925(5)A, β= 100.05(8)°, and Z= 4. The structure was determined by single crystal X-ray diffraction methods. The phase problem was solved by direct methods and refined by full-matrix least-squares techniques to R 0.052 for 1 150 unique reflections. The five-membered ring is in an epoxide-oxygen pure envelope conformation with Cs symmetry and the six-membered ring of the bicyclic system also has an envelope or half-boat configuration.

Studies on organometallic compounds with hetero multiple bridges. X-Ray crystal and molecular structure of Mn2Br2(CO)6P2Ph4, the product resulting from co-ordinative addition of P2Ph4 to manganese(I)

The P2Ph4- and Br-bridged compound Mn2Br2-(CO)6P2Ph4(3) is the product of the reaction between MnBr(CO)5 and P2Ph4 at reflux temperature in benzene.

Synthesis, properties, and crystal and molecular structure of [Re2Br2(CO)6(Se2Ph2)], a binuclear rhenium(I) complex containing a diphenyl diselenide bridge

The tetrahydrofuran (thf) adduct, [Re2Br2(CO)6(thf)2], reacts with diphenyl diselenide in toluene at room temperature to give the orange-red [Re2Br2(CO)6(Se2Ph2)]. Three-dimensional X-ray analysis has shown this to be the first known example of a complex containing a Se2R2 unit bridging two metal atoms. The substance crystallises from toluene in the monoclinic system, space group C2/c with cell constants a= 11.813(3), b= 10.645(2), c= 19.593(5)A, and β= 106.92(2)°, U= 2 357.15 A3, and Dc= 2.85 g cm–3, M= 1 012.41 and Z= 4. Solution and refinement of the structure proved the compound to be isostructural with the diphenyl disulphide analogue reported previously and to consist of two ReI atoms linked by two bromines and by a Se–Se bridge. The six carbonyl groups are distributed around the two rhenium atoms in two groups of three, each in a fac arrangement, thus completing the six co-ordination. The normals to the planes defined by Re(1)–Br(1)–Br(2) and by Re(2)–Br(1)–Br(2) intersect at an angle of 31°, a result which is similar to that found for the diphenyl disulphide, the dimethyl disulphide, and the tetraphenyldiphosphine derivatives. The Re–Se and Se–Se distances and the Re–Se–Se angle are 2.604(4) and 2.411(23)A, and 106.2(1)°, respectively. The Re–Se–C(phenyl) angle is 109.9(8)°, while the Re ⋯ Re and Br ⋯ Br contacts are 3.90(4) and 3.462(20)A. The Se(1) atom is 0.92 A above the plane defined by Re(1)–Se(2)–C(phenyl) and the Re atoms are almost exactly in the plane defined by the two bromines and the two carbonyl carbon atoms; the torsional angle around the Se–Se bond is –121.4°. Similar to the dimethyl disulphide and the diphenyl disulphide derivatives, the diphenyl diselenide ligand of [Re2Br2(CO)6(Se2Ph2)] is displaced by thf.

Molecular structure of two derivatives of the germacranolide sesquiterpene lactone melnerin

Two biomodified esters (1) and (2) of a new germacranolide sesquiterpene lactone, melnerin, have been isolated from the leaves of Melapodium cinereum. Their structures have been characterized by 1H and 13C n.m.r. spectroscopy, and gas chromatography–mass spectrometry of trimethylsilyl-derivatives, and single-crystal X-ray diffraction. Melnerin A, (1), C20H28O7, with an isobutyrate side-chain, and melnerin B, (2), C21H30O7 with a 2-methylbutyrate side-chain, co-crystallize in ca. 4 : 1 ratio, in the orthorhombic space group P212121, with a= 9.322(2), b= 11.655(2), c= 19.032(4)A, Z= 4. The crystal structure, which is disordered in the ester side-chain, was solved by direct phasing procedures and refined by weighted full-matrix least-squares to R 8.2% 1 711 reflections. The Δ1(10)-cis-germacrene ring has the same conformation as cis-cyclodecene. Substituents at C(4)(hydroxymethylene) and C(10)(methoxycarbonyl) are syn and α-oriented, while the ester group attached to C(8) is β-oriented. The α-methylene-γ-lactone, trans-fused at C(6) and C(7), is non-planar with right-handed chirality. The absolute configuration is assigned from biogenetic considerations and correlation with known structures.