New precursors in the chemistry of IVB transition metal alkoxides V. Synthesis and molecular structure of Zr3Fe(μ4-O)(μ2-OC3H7)6-(OC3H7)4(acac)3

The reaction of iron(III) acetylacetonate with zirconium(IV) n-propanolate in n-propanol leads to a tetranuclear species Zr₃FeO(OC₃H₇)₁₀(acac)₃. This compound crystallizes in the triclinic system (space group P ): a = 12.426(2), b = 12.977(2), c = 20.129(4) Å, α = 91.55(1), β = 97.90(1), γ = 100.53(1)°. The structure consists of discrete tetranuclear molecules. The metal atoms design an almost perfect tetrahedron around a four-fold coordinated oxygen atom. The zirconium atoms are in a seven-fold coordination and the iron atom in a five-fold coordination.     

Binuclear complexes of a new hexadentate macrocyclic ligand. The crystal and molecular structure of [LCu2(CH3CO2)2](ClO4)2·5H2O

The 30-membered hexaaza macrocylic ligand, L (L=3,7,11,18,22,26-hexaazatricyclo-[26.2.2.2^13,16]tetratriaconta-1(31),13(33),14,16(34),28(32),29-hexaene), is capable of forming binuclear complexes with the divalent transition metal ions Ni, Cu and Zn. The two metal ions are bound by the two dipropylenetriamine units of the macrocycle. Extra coordination sites on the metal ions can be occupied by exogenous ligands such as acetate, chloride and thiocyanate. The crystal structure of one of the di-copper complexes is described: [LCu₂(CH₃CO₂)₂](ClO₄)₂·5H₂O crystallizes in the monoclinic space group P2₁/c (No. 14), with a=9.369(2), b=17.644(3), c= 27.466(3) Å, β=92.90(1)°, U=4534.7 ų and Z=4. The Cu1···Cu2 separation is 8.40(3) Å. The access for potential exogenous bridging ligands, to the cavity between the copper ions, is somewhat restricted by the two phenyl units of the macrocycle which appear almost parallel in the structure. The redox potential of the couple L(Cu²⁺)₂/L(Cu⁺)₂, recorded by cyclic voltammetry for the chloride adduct, [LCu₂Cl₂]Cl₂·5H₂O, is −0.061 V versus SCE in DMF.     

Synthesis and structure of an organosamarium aryloxide complex, (C5 Me5)2 Sm(OC6HMe4-2,3,5,6)

Bis(pentamethylcyclopentadienyl)samarium bis- (tetrahydrofuranate), (C₅Me₅)₂Sm(THF)₂, reacts with 2,3,5,6-tetramethylphenol in toluene to yield (C₅Me₅)₂Sm(OC₆HMe₄-2,3,5,6). The compound crystallizes in the space group P2₁/c with a = 8.725(3) Å, b=18.821(6) Å, c=18.461(6) Å, β= 111.17(2)°, V = 2827(2) ų and D_c=1.340 g cm⁻³ for Z = 4. Molecules of the aryloxide complex are monomeric and exhibit a bent metallocene structure with a nearly linear Sm---O---C(aryloxide) linkage: Sm---O = 2.13(1) Å, O---C = 1.29(2) Å, and Sm---O---C = 172.3(13)°. Reaction of the samarium complex with phenyllithium produces the previously- characterized species (C₅Me₅)₂Sm(C₆H₅)(THF).     

Preparation, X-ray structure and solution behavior of [Ag(9-EtGH-N7)2]NO3·H2O (9-EtGH=9-ethylguanine)

The preparation and X-ray structure of [Ag(9-EtGH-N7)₂]NO₃·H₂O(9-EtGH=neutral 9-ethylguanine) is reported. The compound crystallizes in the triclinic system, space group P with a=7.063(6), b=7.153(3), c=11.306(10) Å, α=83.36(6), β=76.66(7), γ=81.44(6)°. The cation is centrosymmetric with Ag(I) coordinated via two N7 positions and Ag---N7 bond lengths of 2.11(1) Å. Applying ¹⁰⁹Ag NMR spectroscopy, complex formation constants for both the 1:1 complex (log β₁=0.6) and the title compound (log β₂=1.6) in Me₂SO have been determined.     

Synthesis and crystal structure of the MgCl2(CH3COOC2H5)2· (CH3COOC2H5) adduct

The reaction of α-MgCl₂ with boiling ethyl acetate affords MgCI₂(CH₃COOC₂H₅)₂· (CH₃COOC₂H₅), which is obtained as crystals suitable for X-ray analysis only from the mother liquor. M=315.5, orthorhombic, space group P2₁22₁ (No. 18), a=25.077(3), b=8.616(1), c=7.345(1) Å, V=1587.0(3) ų, Z=4, D_x=1.32 g cm⁻³,λ A(Mo Kα)=0.71069 Å, μ=4.17 cm⁻¹, F(000)=664, T=298 K, observed reflections: 1667, R=0.059 and R_w=0.069. The structure is composed of polymeric chains of MgCl₂(CH₃COOC₂H₅₎₂ and the ethyl acetate molecules occupy a mutually trans position.     

Synthesis of bent titanocene metalloligands with the (diphenylphosphino)tetramethylcyclopentadienyl moiety. X-ray structure of [(η-C5Me4 2)2TiCl2]Mo(CO)4

The reactions of lithium(diphenylphosphino)tetramethylcyclopentadienide with CpTiCl₃ and secondly with TiCl₃ followed by CCl₄ oxidation lead to the formation of two titanocene phosphines: (η⁵-C₅H₅)[η⁵-C₅Me₄P(C₆H₅)₂]TiCl₂ (2) and [η⁵-C₅Me₄P(C₆H₅)₂]₂TiCl₂ (3), respectively. The metalloligand 3 reacts readily with Mo(CO)₄cod, Mo(CO)₅THF and Mo(CO)₆ to give in each case [(η⁵-C₅Me₄ o(CO)₄ (6) as a sole product. The structure of 6 has been determined by X-ray diffraction. Crystal data: P , a = 11.716(1), b = 11.753(2), c = 16.110(2) Å, α = 99.06(1), β = 92.61(1), γ = 104.20(1)°, Z = 2. The molybdenum-titanium distance of 5.194(1) Å rules out any metal-metal interaction. The chlorine substitution reactions by CO in 2 and 3 and by thiolate group (pH₃C-C₆H₄-S) in 16 are reported.     

Anomalous carbonylation of [Pd(dppm)(O2CCF3)]2 to give an asymmetric μ-CO complex

The reactive palladium dimer, [Pd(dppm)(O₂CCF₃)]₂, is carbonylated to [Pd(dppm)(O₂CCF₃)]₂(μ-CO) in a reversible reaction with K = c. 7.2(2)x10⁴ atm⁻¹ (P_1/2 = c. 2.4 Torr). This is significantly larger than is expected based on the λ_max = 280 nm in the electronic spectrum. The product can be isolated in analytically pure form by crystallization under a CO atmosphere. It forms crystals in the monoclinic space group Cc with a = 18.584(5), b = 28.65(1), c = 11.164(3) Å and β = 95.16(2)°. The structure is significantly distorted. The bonding about the two palladium atoms is quite asymmetric. While one is close to a square planar geometry with a Pd---C(O) distance of 1.90(2) Å, the other is significantly pyramidalized and has a longer (2.00(2) Å) bond to the bridging CO. The Pd---Pd distance is only 2.896(2) Å, much shorter than that usually observed for formally non-bonded Pd atoms.     

N7 and C8 coordinated purine complexes of [(NH3)5Os]. Crystal structures of 7-[9MeHyp(NH3)5Os]Cl3·H2O and 8-[1,3,7Me3Xan(NH3)5Os]Cl3·2H2O

Pentaammineosmium(III) coordinates to both the N7 and C8 positions of purine rings. The compound 7-[9MeHyp(NH₃)₅Os]Cl₃·H₂O crystallizes in the orthorhombic space group Pnma (No. 62) with the unit cell parameters: a=11.542(2), b=6.9841(8), c=21.960(3) Å and Z=4. The compound 8-[1,3,7Me₃Xan(NH₃)₅Os]Cl₃·2H₂O crystallizes in the monoclinic space group P2₁/c (No. 14) with the unit cell parameters: a=7.1228(X), b=14.613(1), c=19.667(1) Å, β=91.782(9)° and Z=4. The Os---C bond in the latter structure is 2.039(9) Å and the imidazolylidine ligand exerts a slight trans influence seen in the lengthening of the Os---N_ax distance (2.172(8) Å) by about 0.05 Å relative to the average of the equatorial Os---N_eq value of 2.123(8) Å. The spectroscopic, electrochemical and structural properties of these and additional N-bound purine complexes are compared with those of similar N7 and C8 ruthenium(III) species.     

trans-Bis[(thiocyanato-S)(1-methylimidazoline-2(3H)-thione)-μ2-(1-methylimidazoline-2(3H)-thione)copper(I)]: preparation, thermal analysis and crystal structure

1-Methylimidazoline-2(3H)-thione (mimtH) and copper(I) thiocyanate in refluxing ethanolacetonitrile produce a colourless, diamagnetic complex, [Cu₂(mimtH)₄(SCN)₂], which crystallises in an orthorhombic cell (a=8.0724(3), b=15.9545(6), c=21.3357(8) Å), space GROUP=Pbca, Z=4, final R=0.0319 from 2427 observed reflections F>4σ_c(F)). In the dimeric complex the copper(I) atoms are pseudo-tetrahedrally coordinated by pairs of, respectively, asymmetrically μ₂-S bridging mimtH, terminal monodentate-S mimtH, (Cu---S=2.290(1) Å), and terminal monodentate-S thiocyanate, (Cu---S=2.332(1) Å). Each pair of ligands is trans-related to its partner across crystallographic centres of symmetry, consequently, each copper(I) atom has an identical S₄ donor set with angles at the metal ranging from 95.9(1)° to 121.8(1)°. The centro-symmetric Cu₂S₂ core is rhomboid with Cu---S=2.377(1) and 2.457(1) Å, Cu---S_br---Cu=72.6(1)° and Cu---Cu, S_br---S_br separation distances of 2.861(1) and 3.897(2) Å, respectively. Thermal decomposition of the complex in flowing air, (133–1000 °C), involves de-sulfurisation of mimtH and thiocyanate with concomitant production of copper(II) sulfide followed by oxidation to copper(II) oxide.     

Molybdenum complexes with sterically-hindered thiolate ligands. The synthesis and structure of a seven coordinate complex with a molybdenum-diazenido core, [Mo(NNC6H5)(2-SC5H3N-3-SiMe3)3]

The reaction of [Mo₂Cl₄(μ-S₂)(μ-2-SC₅H₃NH-3-SiMe₃)(2-SC₅H₃N-3-SiMe₃)₂] with phenylhydrazine yields [Mo(NNPh)(2-SC₅H₃N-3-SiMe₃)₃] (1). Complex 1 adopts a pentagonal bipyramidal geometry with the phenyldiazenido group occupying an axial position. The structural parameters exhibited by 1 are similar to those of other members of the class of seven coordinate Mo-hydrazido and Mo-diazenido species. Crystal data for C₃₀H₄₁N₅Si₃S₃Mo (1): monoclinic space group P2₁n, a = 11.600(2), b = 14.880(3), c = 21.681(3) Å, β = 90.46(1)°, V = 3242.2(12) ų, Z = 4; 5690 reflections, R = 0.049.     

X-ray crystal structures of the copper(II), nickel(II) and silver(I) complexes of a 17-membered dibenzo macrocycle with a N3S2 donor set

The copper(II), nickel(II) and silver(I) complexes of the pentadentate 17-membered macrocycle 1, 12, 15-triaza-3, 4:9, 10-dibenzo-5,8-dithiacycloheptadecane (L¹) have been prepared as perchlorates and characterized by X-ray crystallography. The N₃S₂ ligand uses all donor atoms for complexation. The copper coordination is square pyramidal with one sulfur atom in the axial site. Ni(II) displays an octahedral coordination by an interaction with a water molecule. The Ag(I) coordination is best described as a distorted pentagonal bipyramid. In [CuL¹]²⁺ the 1, 4, 7-triazaheptane fragment of L¹ is meridionally coordinated, but facially in [NiL¹(H₂O)]²⁺ and intermediate in [AgL¹](ClO₄). Crystal data for [CuL¹](ClO₄)₂: monoclinic, space group P2₁/n, a = 13.153(8), b = 11.951(5), c = 17.880(8)Å, β = 110.29(4)°, Z = 4, R = 0.086 for 2732 independent reflections with I 2σ(I); [NiL¹(H₂O)](ClO₄)₂: monoclinic, P2₁/a, a = 10.771(2), b= 16.157(2), c = 15.286(2) Å, β =93.08(1)°, Z = 4, R = 0.085 for 1464 independent reflections with I 2σ(I); [AgL¹](ClO₄): monoclinic, P2₁/n, a = 12.708(9), b = 9.483(7), c = 19.569(13) Å, β= 103.95(6)°, Z = 4, R = 0.039 for 3600 independent reflections with I 2σ(I).     

Metal dependent coordination of biomolecular ligand: X-ray crystal structures of copper, cobalt and calcium complexes of (3-hydroxy-5-(hydroxymethyl)-2-methylisonicotinic acid) 5-phosphate, an oxidized pyridoxal 5-phosphate

X-ray crystal analyses of divalent copper, cobalt and calcium complexes of monoanionic (3-hydroxy-5-(hydroxymethyl)-2-methylisonicotinic acid) 5-phosphate (L₁C₈H₉NO₇P⁻) revealed the chemical compositions of Cu ---L·3H₂O(1), Co ---L·5H₂O(2) and Ca·L₂·7H₂O (3) and the coordination structures which depend on the coordination abilities and chemical properties of the respective metal ions. Although 1 and 2 crystals showed similar features, i.e., presence of the metal ion at the crystallographic center of symmetry and octahedral six-coordination, the patterns of coordination with the ligand molecules differed. While direct coordination to the L carboxyl oxygen was observed in 1 crystals, all ligation positions in 2 crystals were occupied by water molecules. On the other hand, 3 crystals formed a pentagonal bipyramidal structure (seven-coordination), where oxygens of L phosphates and water molecules coordinated to the calcium ion. Each of the complex structures showed characteristic molecular packing depending on the pattern of coordination to the respective metal ion. L is monoanionic in all complex crystals, where the phosphate and carboxyl groups are deprotonated and pyridine nitrogen is protonated, and is neutralized by each metal ion. Crystal data: 1, monoclinic, space group P2₁/c, A = 5.4129(6), B = 10.515(2), C = 22.770(2) Å, β = 91.853(9)°, Z = 4, R = 0.0404 for 1834 observed reflections; 2, triclinic, space group

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, c = 6.789(3) Å, α = 96.84(3), β = 109.10(3), γ = 100.50(2)°, Z = 2, R = 0.0684 for 1605 observed reflections; 3, triclinic, , a = 10.069(2), B = 14.501(3), c = 10.051(1) Å, α = 100.75(1), β = 97.28(2), γ = 76.18(2)°, Z = 2, R = 0.0540 for 3637 observed reflections.     

New Crystal Forms of the Motile Major Sperm Protein (MSP) ofAscaris suum

We have obtained two new crystal forms of theAscarismajor sperm protein (MSP) that mediates amoeboid cell motility in nematode sperm. We obtained crystals with C2 symmetry from bacterially expressed α-MSP witha= 216.5 Å,b= 38.6 Å,c= 32.5 Å, γ = 93.1° and also crystals with P2₁symmetry from native β-MSP witha= 63.1 Å,b= 91.7 Å,c= 72.5 Å, γ = 91.3°. A full native data set has been collected for each crystal form using synchrotron radiation. Both crystal forms diffract to 2 Å and are suitable for high-resolution structural investigation.     

A new structural type for a binuclear chloride-bridged copper(II) complex. Structural and magnetic characterization of di-μ-chloro-chloropentakis(benzimidazole) dicopper(II) monochloride tetrahydrate, [Cu2Cl3(C7H6N2)5]Cl·4H2O

The synthesis, crystal structure determination and magnetic properties of a new five-coordinated unsymmetrical copper(II) dinuclear complex [Cu₂Cl₃(C₇H₆N₂)₅]Cl·4H₂O are reported. The crystals are orthorhombic, space group Pnma with 4 formula units in a cell of dimensions: a = 19.506(3), b = 17.384(4), C = 11.940(2) Å. The structure was solved by direct methods. Least-squares refinement using 2138 independent reflections with I3σ(I) has led to a final value of the conventional R factor (on F) of 0.047 and R_w of 0.049. The complex cation consists of pairs of deformed trigonal-bipyramidal copper(II) centers which share an edge by two equatorial chloride ions. The equatorial coordination sites of the Cu(1) atom are occupied by three chloride ligands, while of the Cu(2) atom by two chloride and one benzimidazole ligands. The axial sites are occupied by the nitrogen atoms from four benzimidazole ligands. The Cu atoms and equatorial ligands are located on the symmetry plane. The Cu---Cu non-bonding distance in the complex is 3.386(1) Å; the two shorter bridging Cu(1)---Cl(1) and Cu(2)---Cl(1) distances are 2.402(2) and 2.424(2) Å; the two longer Cu(1)---Cl(2) and Cu(2)---Cl(2) are 2.620(2) and 2.551(2) Å. The Cu(1)---Cl(1)---Cu(2) and Cu(1)---Cl(2)---Cu(2) angles are 89.1(1) and 81.8(1)°. The structure is the first example of a bibridged binuclear complex with two non-equivalent Cu---Cl---Cu bridges. Comparison to other binuclear bis(μ-halide)-bridged copper complexes of similar structure has been made. Magnetic susceptibility measurements indicate ferromagnetic coupling of the copper(II) centers, the intramolecular exchange parameter, 2J, being 5.6 cm⁻¹ and the intermolecular one J′ = −0.6 cm⁻¹. The investigation of the electronic structure of the complex and the orbital interpretation of the magnetic coupling based on extended Hückel molecular orbital calculations are also presented.     

Synthesis of 5,6-dihydro-4H-1,3-oxazines from neutral and cationic platinum(II) nitrile complexes. X-ray structure of trans-[Pt(CF3){ H2CH2}(PPh3)2]BF4

The 1,3-oxazine complexes cis- and trans-[PtCl₂{ C(R)OCH₂CH₂C}H₂₂] (cis: R=CH₃ (1a), CH₂CH₃ (2a), (CH3)₃C (3a), C₆H₅ (4a); trans:R =CH₃ (1b), C₆H₅ (4b)) were obtained in 51-71% yield by reaction in THF at 0 °C of the corresponding nitrile complexes cis- and trans-[PtCl2(NCR)₂] with 2 equiv. of ⁻OCH₂CH₂CH₂Cl, generated by deprotonation of 3-chloro-1-propanol with n-BuLi. The cationic nitrile complexes trans-[Pt(CF₃)(NCR)(PPh₃)₂]BF₄ (R=CH3, C₆H₅) react with 1 equiv, of ⁻ OCH2CH2CH2Cl to give a mixture of products, including the corresponding oxazine derivatives trans-[Pt(CF₃){ CH₂}(PPh₃)₂]BF₄ (5 and 6), the chloro complex _trans- [Pt(CF₃)Cl(PPh₃)₂] and free oxazine H2. For short reaction times (c. 5–15 min) the oxazine complexes 5 and 6 could be isolated in modest yield (37–49%) from the reaction mixtures and they could be separated from the corresponding chloro complex (yield 40%) by taking advantage of the higher solubility of the latter derivative in benzene. For longer reaction times (> 2 h), trans-[Pt(CF₃)Cl(PPh₃)₂] was the only isolated product. Complex 6 was crystallographically characterized and it was found to contain also crystals of trans- [PtCl{ H₂}(PPh₃)₂]BF₄, which prevented a more detailed analysis of the bond lengths and angles within the metal coordination sphere. The 1,3-oxazine ring, which shows an overall planar arrangement, is characterized by high thermal values of the carbon atoms of the methylene groups indicative of disordering in this part of the molecule in agreement with fast dynamic ring processes suggested on the basis of ¹H NMR spectra. It crystallizes in the trigonal space group P , with a=22.590(4), b=15.970(3) Å, γ=120°, V=7058(1) ų and Z=6. The structure was refined to R=0.059 for 3903 unique observed (I3σ(I)) reflections. A mechanism is proposed for the conversion of nitrile ligands to oxazines in Pt(II) complexes.     

An X-ray crystallographic study of α-d-allopyranosyl α-d-allopyranoside · CaCl2 · 5H2O (a pentadentate complex)

Three-dimensional, single-crystal, X-ray diffraction methods were used to determine the structure of the calcium chloride complex of α-d-allopyranosyl α-d-allopyranoside. The crystal is monoclinic with cell dimensions: a = 16.262(5), b = 8.345(5), c = 8.298(5)Å, β = 98.428(5)Å, and z = 2. The space group is P2₁. The structure was solved by three-dimensional Patterson and Fourier methods, and was refined by least-squares techniques to give a conventional discrepancy factor of R = 0.026; 2435 diffractometer-read reflections were used. The cation was found to be in 9-fold co-ordination to O-1, O-2, O-3, O-2′, O-3′, and four water molecules.     

CO substitution and diphosphine ligand chelation in the reaction between 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) and Re(2(CO)8(μ-H)(μ-η,η-C CPh)

The reaction between the redox-active diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) and the dirhenium compound Re₂(CO)₈(μ-H)(μ-η¹,η²-C CPh) in CH₂Cl₂ at room temperature proceeds by CO loss to give the dirhenium complex Re₂(CO)₇(bpcd)(μ-H)(η¹-C CPh) (1). This new complex was characterized in solution by IR and NMR (¹H and ³¹P) spectroscopy and in the solid state by X-ray diffraction analysis. Re₂(CO)₇(bpcd)(μ-H)(η¹-C CPh) crystallizes in the triclinic space group

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γ = 69.240(6)°, V = 2024.9(3) ų, Z = 2, d_calc = 1.862 g cm⁻³ R = 0.0221, R_w = 0.243 for 4066 observed reflections. The bpcd ligand in 1 adopts a chelating mode with a linear phenylacetylide ligand being located on the adjacent rhenium center cis to the bpcd ligand. This complex represents the first structurally characterized example of a hydrido-bridged dirhenium complex possessing both a linear acetylide ligand and a chelating diphosphine ligand.     

Heterocyclic compounds containing antimony 1. Synthesis, physicochemical properties, crystal and molecular structure of 2-(β-hydroxyethylthio) 1,3,2-oxathiastibolane

The compound (HOCH₂CH₂S) ) (1) has been prepared by the reaction of antimony(III) isopropoxide and 2-mercaptoethanol in a 1:2 molar ratio. Reaction of 1 with MOCH₃ (where M = Li, Na and K) yields bimetallic products of the type, M[(OCH₂CH₂S) )]. All these derivatives have been characterized by elemental analysis, IR, NMR (¹H and ¹³C) spectra and molar conductivity measurements. Crystals of 1 are triclinic, space group P , with a = 6.449(2), b = 10.285(2), c = 13.494(1) Å, α = 78.08(1), β = 75.99(1), γ = 71.54(2)°, V = 815.48 ų, Z = 4, D_calc = 2.239 g cm⁻³, (Mo Kα) λ = 0.7107 Å, μ = 3.55 mm₋₁, F(000) = 528, T = 295 K, final R = 0.0189 for 2344 reflections. One of the two mercaptoethanol moieties in 1 forms a five-membered chelate ring with antimony, Sb(1)---O(11) = 2.023(2) Å and Sb(1)---S(11) = 2.434(1) Å, while the other is bonded through the S atom only, Sb(1)---S(12) = 2.434(1) Å. The angles between these primary bonds with a mean value of 90.2° suggest a basically pyramidal, or pseudo tetrahedral structure if the stereochemically active lone pair is included in the coordination sphere. Two molecules are linked by intermolecular hydrogen bridges. The presence of weak intermolecular secondary bonding, Sb(1)---O(12) = 2.567(3) Å, in the complex indicates that the overall coordination polyhedron is best described in terms of a distorted trigonal bipyramidal arrangement.     

Molecular conformation of prostaglandin A1 monoclinic cyrstalline polymorph

The molecular conformation of the monoclinic crystalline polymorph of prostaglandin A₁ has been determined by X-ray diffraction techniques. The space group is P2₁ with a = 13.637 (2), b = 7.567 (1), I c = 10.576 (2) Å, β = 107.37 (3)°; D_c = 1.073 g·cm⁻³ for Z = 2. The molecular conformation is characterized by the nearly parallel arrangement of the C₁–C₇ and C₁₃–C₂₀ side chains, with a general flattening of the overall structure when compared with the orthorhombic polymorph. The cyclopentenone moiety assumes a C₈ envelope conformation with C₈ and O₉ displaced +0.29 Å and −0.18 Å from the C₉–C₁₀=C₁₁–C₁₂ plane respectively. Concerted, small variations of the torsion angles, primarily about the C₈–C₁₂, C₁₄–C₁₅ and C₁₆–C₁₇ bonds, bring the monoclinic and orthorhombic conformations into coincidence.     

A study of the reactivity and structure of cyclic α,β-unsaturated Fischer-type carbene complexes

Cycloaddition reactions with α,β-unsaturated carbene complexes of the Fischer-type bearing the carbene carbon atom and the double bond incorporated in the same ring are described. Pentacarbonyl(2H-benzopyran-2- ylidene)chromium(0) complexes (2a-c) and pentacarbonyl(4-methoxy-3,3-dimethyl-2-oxacyclopentylidene)- chromium(0) (3) show a rather low reactivity towards 1,3-dipoles and 1,3-dienes. The reactions with diazomethane are regioselective but not chemoselective; compounds 2 and 3 show two sites of attack: the α,β carbon-carbon and the carbon-metal double bond. The crystal and molecular structures of 2a and 3 have been elucidated by single crystal X-ray analysis. Crystals of 2a are monoclinic, space group P2₁/c, a=7.614(3), b=14.033(3), c=12.766(3) Å, β=95.24°, V=1358.3(7) Å Z=4; crystals of 3 are triclinic, space group P , a=6.553(1), b=9.408(1), c=10.620(1) Å α=92.70(1), β=92.30(1), γ=92.12(1)°, V=653.0(1), ų, Z=2. Final agreement indices for 2a and 3 are R=0.034 and 0.033, respectively. Vibrational properties of the Cr(CO)₅ moiety were interpreted by FT-IR and FT-Raman spectroscopy. Electronic spectra and π electron distribution were interpreted by resonance Raman spectroscopy.