Robin B. English

Synrotolide, an α-pyrone from Syncolostemon rotundifolius

Abstract The structure of synrotolide, a new α-pyrone isolated from Syncotostemon rotundifolius, has been established as 6R-[3R,6S-(diacetyloxy)-4R,5S-(dihydroxy)-1-heptenyl]-5,6-dihydro-2H-pyran-2-one. Oleanolic acid is the major component of both S. rotundifolius and S. densiflorus.

Ammonium di-μ-oxalatotitanate(III) dihydrate : an eight-coordinate polymeric titanium(III) complex

Abstract The preparation, magnetic and spectral properties and crystal structure of ammonium di-μ-oxalatotitanate(III) dihydrate are described. NH 4 [Ti(C 2 O 4 ) 2 ] · 2H 2 O, M r = 278.01, hexagonal, P 6 2 22, a = 8.935(3) c = 10.878(4) A, V = 752.1(7) A 3 , Z = 3; R = 0.045 for 426 absorption-corrected independent reflections and 48 parameters. The crystals are isomorphous with those of ammonium di-μ-oxalatoindate(III) dihydrate. The titanium atoms are coordinated by eight oxalate oxygen atoms in a square-antiprismatic arrangement, and bridging oxalate groups link the coordination polyhedra to form a right-handed spiral structure about 6 2 crystal axes.

Reactions of metal carbonyl derivatives. Part 22. The crystal and molecular structures of dicarbonyl(η-cyclopentadienyl)(ethylthio)iron and µ-ethylthio-bis[dicarbonyl(η-cyclopentadienyl)iron] tetrafluoro-borate, and a comparison of their molecular parameters

The solid-state structures of [Fe(cp)(CO)2(SEt)](1) and [{Fe(cp)(CO)2}2SEt][BF4]{[BF4]– salt of (2)}(cp =η-C5H5) have been determined by single-crystal X-ray analyses. Compound (1) crystallises in the orthorhombic space group Pnma with cell parameters a= 14.118(5), b= 9.822(5), c= 7.443(5)A, and Z= 4 while the [BF4]– salt of (2) crystallises in the triclinic space group P with a= 9.41 (1), b= 11.36(1), c= 10.04(l)A. α= 99.77(l), β= 104.40(l)γ= 67.83(1)°, and Z= 2. The structures have been solved by conventional Patterson and Fourier techniques and refined to R= 0.049 and 0.030 for 885 and 2 197 independent reflections respectively. Molecule (1) lies on a mirror plane of symmetry with the cyclopentadienyl group being disordered. The cation (2) has symmetry C1 and contains the two cyclopentadienyl groups cis disposed with respect to the Fe(1)SFe(2) plane. The ct(cp)–Fe(1)–Fe(2)–ct(cp)[ct(cp)= centroid of the cyclopentadienyl group] torsional angle τ′ is 58.2 °. The Fe–S bond distance and the Fe–S–C bond angle remain essentially unaltered on co-ordination of (1) to [Fe(cp)(CO)2]+ to give (2). The n.m.r. data for the salt of (2) are interpreted in terms of fluxional behaviour in solution.

Synthesis and crystal and molecular structure of [Fe2Rh2(µ-PPh2)4(µ-CO)2(CO)6], an unusual straight-chain tetranuclear compound

Reaction of [{Rh(η3-C3H5)2Cl}2] with [Fe(CO)4(PPh2H)] in alcohol in the presence of carbon monoxide affords an unusual straight-chain compound, [Fe2Rh2(µ-PPh2)4(µ-CO)2(CO)6], the structure of which has been determined by X-ray methods. The complex crystallizes in space group P21/c with a= 12.468(5), b= 13.354(5), c= 17.293(7)A, β= 95.43(1)°, and Z= 2. The metal-atom skeleton is a centrosymmetric Fe–Rh–Rh–Fe chain with the metal atoms being linked through closed Fe–P–Rh and Rh–P–Rh bridge bonds. The 31P-{1H} n.m.r. spectral data for the compound have been interpreted in terms of the presence of two isomeric forms in solution.

Reactions of metal carbonyl derivatives. Part 20. Synthesis, redox behaviour, and crystal and molecular structure of µ-ethylthio-bis-[dicarbonyl(η-methylcyclopentadienyl)manganese](Mn–Mn) perchlorate: an unusual monothio-bridged derivative of manganese

Treatment of [Mn(MeC5H4)(CO)2(SEt)]–, prepared in situ from [Mn(MeC5H4)(CO)2(thf)] and [SEt]–, with perchloric acid in aqueous tetrahydrofuran leads to the formation of the unusual monothio-bridged derivative [{Mn(MeC5H4)(CO)2}2(SEt)][ClO4], in which the manganese atoms are joined by a metal–metal bond (MeC5H4=η-methylcyclopentadienyl). A crystal structure determination by the heavy-atom method from diffractometer data of this complex reveals the cyclopentadienyl groups to be trans, and Mn–Mn 2.930(1)A. Crystals are monoclinic, space group P21/n, Z= 4, a= 8.676(5), b= 16.062(5), c= 15.872(5)A, β= 104.45(20)°, and the structure was refined to R 0.51 for 1 785 observed reflections. The compound undergoes two reversible one-electron reductions as established by cyclic voltammetry and polarography.

Synthesis and structural properties of a series of pentacoordinate rhodium nitrosyl complexes: Crystal and molecular structures of cis-dibromonitrosylbis(methoxydiphenylphosphine)rhodium and trans-dibromonitrosylbis(iso-propoxydiphenylphosphine)rhodium

Abstract The pentacoordinate rhodium nitrosyl complexes [RhBr2(NO)L2 [L = P(OPh)2Ph, P(OMe)Ph2 or P(OPri)Ph2] have been synthesized and the structures of [RhBr2(NO){P(OMe)Ph2}2] and [RhBr2(NO){P(OPri)Ph2}2] have been determined X-ray crystallographically. Both of these latter compounds are tetragonal pyramidal with the nitrosyl group apical. The methoxydiphenylphosphine ligands in [RhBr2(NO){P(OMe)Ph2}2] are cis-disposed whereas the larger cis-propoxydiphenylphosphine ligands in [RhBr2(NO){P(OPri)Ph2}2] are mutually trans. The nitrosyl group in trans-[RhBr2(NO){P(OPri)Ph2}2] eclipses an Rh-P axis but in cis-[RhBr2(NO){P(OMe)Ph2}2] it is staggered with respect to the P-Rh-P linkage. The isomeric behaviour of nitrosyl complexes of type [RhX2(NO)L2] (X = halogen, L = phosphorus donor ligand) is rationalized in terms of the size of the ligand L.

Synthesis and X-ray crystal and molecular structure of [{RhFe(µ-PPh2)2-(µ-CO)(CO)3}2], an unusual tetranuclear compound with a straight-chain structure

Treatment of [{Rh(η-C3H5)2Cl}2] with [Fe(CO)4-(PPh2H)] in benzene in the presence of CO affords the mixed metal tetranuclear derivative [{RhFe(µ-PPh2)2(µ-CO)(CO)3}2], the structure of which has been determined X-ray crystallographically.

The synthesis, reactivity, and crystal and molecular structure of [Rh3(µ-PPh2)3(µ-Cl)2(µ-CO)(CO)3], an unusual 50-electron closed trinuclear cluster derivative of rhodium

The reaction of [{Rh(µ-Cl)(CO)2}2] with PPh2H in benzene affords the mononuclear complex [RhCl(CO)(PPh2H)2] for a molar ratio of 1 : 4 and the trinuclear derivative [Rh3(µ-PPh2)3(µ-Cl)2(µ-CO)(CO)3], for a molar ratio of 1 : 2. The structure of the trinuclear derivative has been determined by X-ray crystallography. It crystallises in the monoclinic space group P21/n, with a= 12.461(5), b= 32.867(5), c= 11.149(5)A, β= 99.29(1)°, Z= 4, and R= 0.085. The metal atoms adopt a triangular configuration with each edge of the triangle being bridged by a diphenylphosphido-group as well as by either a chloro or a carbonyl group. In spite of this compound being a 50-electron system, all of the Rh–Rh distances correspond with those normally associated with a formal rhodium–rhodium bond. The chloro-groups in this compound can be extracted as radicals by the addition of NEt2H, affording, in the presence of CO, [Rh3(µ-PPh2)3(CO)5], or displaced as chloride ions by treatment of the complex with AgSbF6; the former reaction is a reversible process with dissolution of [Rh3(µ-PPh2)3(CO)5] in CCl4 resulting in the regeneration of the title complex. [Rh3(µ-PPh2)3(µ-Cl)2(µ-CO)(CO)3] is only moderately stable in solution and converts slowly to an insoluble species formulated as [{Rh(µ-PPh2)(µ-Cl)(CO)}n].

Benzodiazepine analogues. Part 22.1 Conformational analysis of benzodioxepine and benzoxathiepine derivatives

1H NMR spectroscopy, single crystal X-ray analysis and computer modelling have been used to explore the conformational preferences in five series of 1,5-benzodioxepine and 1,5- and 4,1-benzoxathiepine derivatives.

Bitter guaianolides from Eriocephalus punctulatus

Abstract A new, slightly bitter guaianolide, 8-isobutyloxycumambrin- B , occurs, together with the intensely bitter cumambrin-A, in Eriocephalus punctulatus ; its structure has been confirmed by X-ray crystallography. l -2- O -Methylchiroinositol was also isolated.