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A series of beta-diiminato complexes of the form (BDI-3)MX where (BDI-3) = [CH(CMeNC(6)H(4)-2-OMe)(2)]; M = Zn, Mg; X = O(i)()Pr, O(t)()Bu, or N(SiMe(3))(2) has been synthesized. The (BDI-3) ligand is bidentate in (BDI-3)ZnN(SiMe(3))(2) and tetradentate in (BDI-3)MgN(SiMe(3))(2). The alkoxide complexes are shown to be active for lactide polymerization. Polymerization of rac-lactide with (BDI-3)ZnO(i)Pr gives a moderate preference for heterotactic PLA. Polymerization of rac-lactide with [(BDI-3)MgO(t)Bu](2) shows a slight preference for heterotactic PLA in CH(2)Cl(2) but is highly stereoselective in THF in the production of heterotactic PLA.

From the reactions between diarylzinc compounds (Ar2Zn) and the alcohol (Pr(i)2CHOH) in toluene, the compounds [ArZn(OCHPr(i)2)]2 (Ar = C6H5, C6F5, p-CF3C6H4, and 2,4,6-Me3C6H2) have been isolated and shown to exist in equilibra with the trinuclear complexes Ar2Zn3(OCHPr(i)2)4 and Ar2Zn when Ar = C6H5, C6F5, and p-CF3C6H4. The trinuclear complexes have also been prepared from reactions of the Ar2Zn compounds with the alcohol, which reveals that the ease of Zn-C(aryl) bond cleavage is sensitive to the nature of the Ar group: C6H54-CF3C6H4C6F5. The molecular structures of Ar2Zn3(OCHPr(i)2)4 where Ar = p-CF3C6H4 and C6F5 and [ArZn(OCHPr(i)2)]2 where Ar = C6F5, p-CF3C6H4, and 2,4,6-Me3C6H2 are reported based on single-crystal X-ray diffraction studies. The X-ray structure of Zn(p-CF3C6H4)2 is also reported. The reactivity of these new compounds toward the polymerization of propylene oxide (PO) and the copolymerization of PO and CO2 have been investigated along with related reactions involving the partial hydrolysis of the Ar2Zn and R2Zn compounds, where R = t-Bu, n-Bu, and n-Oct. These results are compared with the previous studies employing Et2Zn as an organozinc precursor.

A series of monomeric amide or aryloxide complexes of the form LCaX, where L = CH[CMeNC(6)H(3)-2,6-](2), CH[CMeNC(6)H(4)-2-OMe](2), a bulky tris-pyrazolyl borate, Tp(iPr) or Tp(tBu) or 9-BBN-pz(2) and X = N(SiMe(3))(2) or OC(6)H(3)-2,6-, has been prepared and characterized and investigated in the ring-opening polymerizations of lactide. The compounds (Tp(tBu))CaX in THF are shown to be highly active and stereoselective. The propylene oxide complex (Tp(tBu))Ca(OC(6)H(3)-2,6-).(PO) has been isolated and structurally characterized (single-crystal X-ray) and shown to be inert to the polymerization of PO.

The preparation of the 3,6-dioxypyridazine-bridged tungsten complex, [W(2)(O(2)C(t)Bu)(3)](2)(mu-H(2)C(4)N(2)O(2)), I, is described, along with its single-electron oxidized cation, I(+), formed in the reaction between I and Ag(+)PF(6)(-). Compound I has been structurally characterized as a PPh(3) adduct, and I(+)PF(6)(-) as a THF solvate, by single-crystal X-ray studies. The geometric parameters of these compounds compare well with those calculated for the model compounds [W(2)(O(2)CH)(3)](2)(mu-H(2)C(4)N(2)O(2)) and [W(2)(O(2)CH)(3)](2)(micro-H(2)C(4)N(2)O(2))(+) by density functional theory employing the Gaussian 98 and 03 suite of programs. The calculations indicate that the two W(2) centers are strongly coupled by M(2) delta-to-bridge pi-bonding, and further coupled by direct M(2)...M(2) bonding. Compound I is purple and shows an intense absorption in the visible region due to a metal-to-bridge charge transfer and, with excitation within this absorption, compound I exhibits pronounced resonance Raman bands associated with symmetric vibrations of the bridge and the M(4) unit. The cyclic voltammogram of I in THF, the EPR spectrum of I(+)PF(6) in 2-MeTHF and the electronic absorption spectrum of I(+)PF(6)(-) in THF are consistent with electron delocalization over both W(2) units. These new data are compared with previous data for the molybdenum analogue, related oxalate-bridged compounds and closely related cyclic polyamidato-bridged Mo(4)-containing compounds. It is proposed that, while the electronic coupling occurs principally by an electron-hopping mechanism for oxalate-bridged compounds, hole-hopping contributes significantly in the cases of the amidate bridges and that this is more important for M = Mo than for M = W. Furthermore, for Class III fully delocalized mixed-valence compounds, the magnitude of K(c), determined from electrochemical methods, is not necessarily a measure of the extent of electron delocalization.

[reaction: see text] Apha,alpha'-dihydroxy ketones having two OH groups that can come into close proximity react with phosgene in the presence of DMAP to produce 1,3-dioxane-2,5-diones. When covalent bonding in this manner is prohibited, alternate reaction pathways can in principle be adopted. Of these, the generation of spiro epoxy carbonates is shown to be feasible in three examples. In other cases, the alpha-ketol rearrangement precedes diacylation.

A wide range of 2-(2-nitrophenyl)-1H-benzimidazoles undergo high-yielding intramolecular S(N)Ar of nitrite with N-pendant alkoxides under mild conditions (DMF, rt). When this operationally simple process is carried out at elevated temperatures in the presence of excess NaH, the initially formed S(N)Ar products are converted to the corresponding N-vinyl-substituted 2-(2-hydroxyphenyl)-1H-benzimidazoles via base-catalyzed isomerization. [reaction: see text]

[reaction: see text] The title compound 1, prepared from 1,4-cyclohexanedione monoethylene ketal, was treated with several reactive dienes, including diphenylisobenzofuran and 9,10-dihydro-11,12-dimethylene-9,10-ethanoanthracene. These [4 + 2] cycloadditions proceed with a strong kinetic bias for bonding to the dienophile from the direction syn to the tetrahydrofuranyl oxygen and consequently hold value in stereoselective synthesis.

Dimethyl-substituted bis(benzimidazole) (Me2BBZ) is a novel macrocyclic ligand that possesses an intrinsic nonplanarity. To examine how metal-ion binding affects the magnitude of this nonplanarity, we have determined the structures of a periodic series of Me2BBZ complexes bound to Mn(II), Fe(II), Co(II), Ni(II), and Cu(II). These studies demonstrate that the extent of ligand ruffling and metal doming is indeed influenced by the nature of the metal. Concomitant with the periodic decrease of the ionic radii of the encapsulated divalent metal ion, a decrease in the magnitude of both the ligand nonplanarity and the metal out-of-the-plane distance is observed. For the metal out-of-the-plane distance, this correlation persists until the metal finally moves into the mean ligand plane. For the nonplanar distortion, the extent of the nonplanarity decreases to a limiting value that is intrinsic to the Me2BBZ ligand due to steric factors. These observations indicate that the relative sizes of the metal ion and the Me2BBZ ligand cavity have profound effects on the structural features of the metal-ligand complex.

The structure of LiBrO 4 .3H 2 O consists of stacks, along z, of somewhat distorted face-sharing octahedra of water O atoms coordinating Li ions, with each stack surrounded by six stacks of virtually regular tetrahedral perbromate ions. This structure and that of LiClO 4 .3H 2 O are isomorphic. As in the perchlorate, the Br-O(1) (axial) bonds are oriented in the positive z direction. Location and isotropic refinement of the single type of H atom permitted detailed analysis of the hydrogen bonding, which occurs principally with perbromate O atoms and is best described as two-center bifurcated

In the title molecule, C24H21NO2, the dihedral angle between the carbazole ring system [with a maximum deviation of 0.052 (2) Å] and the benzene ring is 38.6 (1)°. In the crystal, weak bifurcated (C—H)2...O hydrogen bonds link the molecules into chains along [100].

The structural features most conducive to complexation of the alkali metal ions Li(+), Na(+), and K(+) in a series of constrained inositol orthoformate derivatives have been probed in solution, in the solid state, and in the gas phase by electrospray ionization mass spectrometry. The eight spirotricyclic polyethers differ in the size of the rings containing the potentially ligating oxygen atoms. Although the ring sizes have been limited to three to five atoms inclusively, the combinations of oxirane, oxetane, and tetrahydrofuran are rather extensive and consist of many options. The overall trend for lithium ion affinity is [5.5.5][ 5.5.4][4.4.4][5.5.3][5.4.3][4.4.3][1.1.1][3.3.1], an ordering that correlates with the differing polarizabilities of the oxygen atoms, ease of alignment of the nonbonded electron pairs, and the overall size of the ligand as gauged by nonbonded O......O distances.

[structure: see text] Preparation of the first rigid homoditopic tris(tetrahydrofuranyl) ligand with a pair of exotopic binding sites specifically tailored for effective coordination to lithium ions is described. The crystallographically defined structural parameters of the monomeric building block and a 1:2 complex of the dimer with lithium picrate reveal the unique features of these materials.

[formula: see text] First chiral bidentate bis-carbene complex of Pd(II) prepared from a bis-imidazolium salt derived from (S)-2,2'-bromomethyl-1,1'-binaphthyl exists in both cis- and trans-square planar geometry. These and the corresponding trans-Ni(II) complexes are remarkably resistant to high temperature, air, water, and silica gel chromatography. The Pd complexes catalyze Heck reactions.

Synthese de dihydroxy-5,5a perhydro tetramethyl-3a,6,6,9a benzo [e] indenedione a partir de decahydro tetramethyl-3a,6,6,9a benzo [e] indenedione, d'oxyde d'osmium et de methyl-4 N-oxyde morpholine via un complexe d'osmium VI

The mu-oxo dimer mu-oxo-bis[dichloro[(1,2,3,3a,7a-eta)- 4,5,6,7-tetrahydro-4,7-methano-1H-indenyl]titanium], [Ti2Cl4(mu-O)(C10H11)2], and the mu-oxo cyclic tetramer, cyclo-tetra-mu-oxo-tetrakis[chloro[(1,2,3,3a,7a-eta)-4,5,6,7-tetrahydro- 4,7-methano-1H-indenyl]titanium], [Ti4Cl4(mu-O)4(C10H11)4], have been synthesized by electrophilic attack of TiCl4 on the exo-trimethylsilyl derivative of isodiCp (isodiCp is the isodicyclopentadienide anion or 4,5,6,7-tetrahydro-4,7-methano-1H-indene) in the presence of trace amounts of moisture. Both structures are endo isomers, with each Ti atom bonded in a eta 5 manner to the Cp ring of the isodiCp ligand. Both display a slight bending of the isodiCp group about the bond common to the Cp ring and the norbornane fragment, such that the norbornane group is displaced in the direction away from the Ti atom. The dihedral angles which describe this bending are 9.0 (3) and 10.2 (3) degrees for the dimer, and 9.2 (2) degrees for the tetramer. The dimer contains a bent Ti-O-Ti angle of 159.5 (2) degrees. The tetramer forms tetragonal crystals, which are twinned by merohedry on the (110) plane. The tetramer molecule contains a crystallographic 4 axis, with the Ti atoms linked by the O atoms in a mu-oxo manner to form an eight-membered ring.

The diastereomeric endo and exo isomers of the title complex, [TiCl 3 (C 10 H 11 )], have been synthesized by electrophilic attack of TiCl 4 on the exo- or endo-tri-methylsilyl derivative of isodiCp (isodiCp = isodicyclo-pentadiene). This reaction proceeds with net inversion of configuration to give exclusively either the endo- or exo-(isodiCp)TiCl 3 compound. Although the two isomers have similar unit-cell constants, they crystallize in different space groups. The endo complex, (2), is in Pbcm with a crystallographic mirror plane, while the exo complex, (4), is in Pca21 with pseudo-mirror symmetry. Both molecules display a distorted tetrahedral geometry about the Ti atom. Each Ti atom is bonded in a η 5 manner to the Cp ring of the isodiCp ligand, with Ti-ring centroid distances of 2.031(2) and 2.013 (2) A for (2) and (4), respectively. A slight bending of the isodiCp ligand about the bond shared by the Cp ring and the norbornane fragment is observed in both structures. The determination of the absolute structure of (4) defines the directionality of the packing along the polar c axis.

The red title compound, [W2(C6H6NO)4]·1.5C7H8, contains isolated W2(hmp)4 molecules (hmp is 6-methyl­pyridin-2-olate) in which the W—W separation of 2.1617 (5) A is consistent with the expected tungsten–tungsten quadruple bond. The complex molecule cocrystallizes with 1.5 mol­ecules of toluene. One toluene mol­ecule is disordered about a crystallographic inversion center, and the other, in a general position, is also disordered.

Salen bismuth alkoxides, where the salen ligand contains 2,4-di-tert-butylphenoxy groups and one of ethylene, cyclohexane or ortho-phenyl as a backbone have been prepared from reactions involving Bi[N(SiMe₃)₂]₃ and the free salen ligand followed by alcoholysis (ButOH, PriOH and 2,6-But₂C₆H₃OH). The molecular structures of the salen ligand with the cyclohexyl back-bone have been determined for the complexes salenBiCl and salenBiOC₆H₃-2,6-But₂. The chloro compound is a dimer with chloride bridges while the phenoxide is monomeric with an unusually distorted five-coordinate geometry. The phenoxide and tert-butoxide complexes have been employed in the ring-opening polymerization of lactides (L- and rac-) to give polylactides, PLAs. With rac-LA heterotactic PLA is formed preferentially, Pr = ~0.9, in dichloromethane or toluene at room temperature. The reaction is first order in [Bi] and is notably faster than most aluminum and zinc initiators as well as tin(II) octanoate. These results are discussed in terms of a recent report on the polymerization of LA by Peptobismol® and bismuth subsalicylate.

Several new polyhydride complexes of rhenium containing the tridentate phosphine PhP(CH(2)CH(2)CH(2)PCy(2))(2) (Cyttp) were synthesized and characterized by (1)H and (31)P{(1)H} NMR and IR spectroscopy. The solid state structure of the previously reported ReH(5)(Cyttp) (1) was determined by X-ray crystallography. 1 crystallizes in the space group P2(1)/m with the following unit cell parameters: a = 8.582(2) Å, b = 19.690(2) Å, c = 10.800(2) Å, beta = 95.57(1) degrees, and Z = 2. The molecule adopts a classical polyhydride, triangulated dodecahedral structure, with the three phosphorus atoms and one hydrogen atom occupying the B sites, and the remaining hydrogen atoms occupying the A sites. 1 is protonated by HSbF(6) (or HBF(4)) to yield [ReH(4)(eta(2)-H(2))(Cyttp)]SbF(6) (3), which was shown by X-ray diffraction techniques (space group Ponemacr;, unit cell parameters: a = 9.874(2) Å, b = 14.242(4) Å, c = 16.198(2) Å, alpha = 99.12(2) degrees, beta = 98.85(2) degrees, gamma = 109.42(2) degrees, and Z = 2) to contain a nonclassical polyhydride cation with a triangulated dodecahedral structure in the solid. The same structure is suggested in solution by (1)H NMR data (including T(1) measurements). 3 is inert to loss of H(2) and is unaffected by CO, t-BuNC, and P(OMe)(3) at room temperature. In contrast, 1 reacts with a variety of reagents to afford classical tetrahydride complexes which are thought also to possess a triangulated dodecahedral structure, with the hydrogens in the A sites, from spectroscopic evidence. Accordingly, CS(2), p-O(2)NC(6)H(4)NCS, and EtOC(O)NCS (X=C=S) insert into an Re-H bond to yield ReH(4)(SCH=X)(Cyttp) (5-7, respectively). MeI cleaves one Re-H bond to afford ReH(4)I(Cyttp) (8), and [C(7)H(7)]BF(4) abstracts hydride in the presence of MeCN, t-BuNC, CyNC, or P(OMe)(3) (L) to give [ReH(4)L(Cyttp)]BF(4) (9-12, respectively). A related pentahydride, ReH(5)(ttp) (2, ttp = PhP(CH(2)CH(2)CH(2)PPh(2))(2)), also reacts with HSbF(6) to yield [ReH(6)(ttp)]SbF(6) (4), which appears to be a nonclassical polyhydride in solution by T(1) measurements.

The major product formed in the thermolysis of 5-diazouracil in thiophene at 423-433K has been identified as the unexpected compound (Z)-5-(2-thienylmethylene)-2,4-imidazolidinedione, C 8 H 6 N 2 O 2 S, by X-ray analysis. The molecule is a hydantoin derivative with a thienylmethylene group substituted at the 5-position. The structure is disordered in that the thiophene ring exists in two orientations which are related by an approximate 180° rotation about the C(6)-C(7) bond. All of the N and O atoms are involved in an intermolecular hydrogen-bonding network via N-H...O interactions. This network consists of an infinite chain along the a-axis direction and a cyclic trimer arrangement which branches from this chain. The molecules are arranged in the unit cell in pleated sheets which are approximately perpendicular to the c axis.

Amide and alkoxide coordination complexes of calcium supported by beta-diiminato and bulky trispyrazolylborate complexes are reported together with their activity in lactide ring-opening polymerization; some are amongst the most active systems discovered to date.

The crystal structures of an inorganic butane analogue, NH(3)BH(2)NH(2)BH(3) (DDAB), were determined using single crystal X-ray diffraction, revealing both anti and gauche conformations. The anti conformation is stabilized by intermolecular dihydrogen bonds in the crystal whereas two gauche conformations of DDAB observed in its 18-crown-6 adducts are stabilized by an intramolecular dihydrogen bond. The two gauche conformations show rotational isomerization but whether they are a pair of enantiomers is yet to be defined.

The compounds LMgBun(THF) and L′MgBun(THF) where L = 1,5,9-trimesityldipyrromethene and L′ = 2-[(2,6-diisopropylphenyl)amino]-4-[(2,6-diisopropylphenyl)imino]pent-2-ene have been prepared from reactions between MgBun2 and the protonated ligands LH and L′H, respectively. Single crystal X-ray crystallographic studies reveal that in each compound the Mg2+ ion is in a distorted tetrahedral environment and further that the ligand L is more sterically demanding with respect to access to the Mg–Bun group. Related alkyl complexes (R = Me, Et, Prn, Pri, n-hexyl and CH2CH2Ph) were prepared from reactions involving LLi(THF) or L′Li(THF) and the appropriate RMgX (X = Cl or Br) and characterized by 1H NMR spectroscopy. Those where R = CH2CH2X (X = alkyl or phenyl) have characteristic α-CH2 proton resonances which are the part of an AA′XX′ pattern. Reactions with alcohols ROH (1 equiv.) give the kinetic products LMg(OR)(THF) and L′Mg(OR)(THF) which are isolable and kinetically persistent when R = a bulky group such as But and the structure of LMg(OBut)(THF) is reported and compared with that of the known compound L′Mg(OBut)(THF). With less bulky groups the compounds are labile toward ligand scrambling and the compound L′MgBun(THF) reacts with alcohols (2 equiv.) to give L′H and Mg(OR)2. Reactions with amines and carbon dioxide are described which indicate the greater reactivity of the Mg–Bun group relative to both the L′ and L ligand. With PhCHO, Ph2CO and cyclohexanone both LMgBun(THF) and L′MgBun(THF) react via β-hydrogen atom transfer to generate the appropriate alkoxide with the elimination of 1-butene. Similarly L-lactide reacts by β-H transfer to give poly-L-lactide (P-L-LA) and 1-butene while rac-lactide yields atactic polylactide in toluene–dichloromethane solutions but in the presence of ≥10 equiv. of THF, heterotactic PLA is formed. The ring-opening polymerization of e-caprolactone also is initiated by β-H transfer and is about ten times faster than for lactide; kp(LA) = 10.7 M−1 s−1vs. kp(CL) = 110 M−1 s−1. Interestingly, the presence of lactide completely suppresses the polymerization of e-caprolactone.

Bis-2,2′-propargyl-1,1′-biphenyls undergo regio- and stereoselective bis-metallative cyclizations mediated by a [BSn] reagent, 1-trimethylstannyl-2,5-dimethyl-2,5-diazaborolidine, under Pd-catalysis. The cyclization yields axially chiral 1,2-bis-alkylidenes, whose configuration is controlled both by the resident chirality of the biphenyl moiety and a propargylic center that may be present in the tether. The propargylic center is installed by addition of lithium acetylides to 2′-substituted biphenyl-2-carbaldehydes. The stereoselectivity of this addition reaction depends on the nature of the 2′- and 6′-substituents. With an alkyl substituent or poorly coordinating groups (no coordination to the metal of the acetylide) at the 2′-position and a methoxy group at the 6′-position, a single product is formed via a metal chelate that involves the aldehyde oxygen and the methoxy group. Likewise, in biphenyl-2-carbaldehydes with a 2′-(1-oxazolinyl) and a 6′-methoxy substituents, the metal coordination to the oxazolinyl nitrogen and the aldehyde carbonyl controls the selectivity, and a highly selective reaction ensues. X-Ray crystallography reveals an extended pseudo-chair conformation for the 7,8-bis-alkylidenedibenzocyclooctadiene. Simple models based on steric arguments can be used to rationalize the stereochemical outcomes in successful cyclizations. Such models also explain why some substrates fail to cyclize. Among the various diastereomers of 2,2′-[1-(1-alkoxy-2-propynyl)biphenyls, only the diastereomer with (Sa*,Sc*,Sc*) configuration (Sc: configuration of the propargylic center) undergoes the cyclization. The products of the cyclization reactions are potentially useful for the synthesis of highly functionalized dibenzocyclooctadienes, an important class of natural products with wide-ranging biological activities.

Alkynes are found to react with [W2(OCH2tBu)8] (M = M) in hydrocarbon solvents at room temperature or 45 degrees C to give 1:1 adducts. These are shown to be either bridged (mu-PhCCH and mu-MeCCMe) or terminal-bound (eta2-PhCCMe) in the solid state by single-crystal X-ray crystallography. In solution NMR spectroscopy reveals that bridged and terminal species exist in equilibrium for MeCCH, MeCCMe, and PhCCMe. By NMR spectroscopy the PhCCH and Me3SiCCH adducts are present in solution in bridging and terminally bonded species, respectively. The interconversion of bridged and terminal-bound adducts is chemically rapid but slow on the NMR time scale even though each type of adduct shows fluxional behavior. Calculations employing density functional theory have been carried out on alkyne adducts of the model template W2(OCH3)8 and reveal very small differences in energy between a mu-skewed structure and one having a terminal eta2-alkyne.

Crystalline dibenzofuran-d8 has been found to exhibit disorder of the type described previously for dibenzofuran. The disordered molecules are related to the ordered molecules by a 180 degrees rotation about an axis passing through the molecular center of mass and perpendicular to the furan ring. In the present structure 11(2)% of the molecules were found to adopt this alternate orientation. The molecules are bisected by a mirror plane normal to the furan ring and containing the O atom. The average bond length in the benzenoid ring is 1.392 (10) A. The furan ring and the benzenoid ring are separately planar, but form a dihedral angle of 1.45 (9) degrees with each other.

A new ammine complex, Li2B12H12·7NH3, that can reversibly release all the NH3 at below 200 °C and reabsorb NH3 at room temperature and 0.5 bar was synthesized and investigated for reversible ammonia storage or indirect hydrogen storage.

The preparation and structure of Re(2)(dppm)(2)(O(2)CC(6)H(4)-p-NO(2))(2)Cl(2), where dppm = Ph(2)PCH(2)PPh(2), is reported together with its photophysical properties (absorption, steady state emission, fs- and ns-transient absorption spectroscopy) and electrochemistry. These data are compared with photophysical studies on the previously reported Re(2)(dppm)(2)(O(2)CCH(3))(2)Cl(2). The preparation of the complex Re(2)(O(2)CC(6)H(4)-p-NO(2))(4)Cl(2) is also reported together with its photophysical properties which allows for a comparison of the electronic structures and photophysical states of Re(2)(4+) and Re(2)(6+) containing complexes having MM configurations σ(2)π(4)δ(2)δ(*2) and σ(2)π(4)δ(2), respectively. An interesting comparison is also made with the related MM quadruply bonded complexes of molybdenum and tungsten.

1,2,3,4-Tetrahydro-7,12-dimethylbenz[a]anthracene (THDMBA) is an animal carcinogen which lacks an aromatic bay-region and shows promise as a model to investigate non-classical mechanisms of carcinogenesis. The fluorine-substituted derivatives at positions 5 and 6 on the B-ring exhibit a striking range of oncogenic potential wherein the 6F-THDMBA is twice as potent as the parent carcinogen, but the 5F-THDMBA is virtually inactive. To study structure-reactivity relationships for these fluorine regioisomers, we have determined the three-dimensional structures of the compounds by single-crystal X-ray diffraction. These crystal structures are the first such to be reported for any monofluoro anthracene (or pyrene) derivative. The partially-reduced A-ring exists in both enantiomeric half-chair conformers in the crystalline state, and the compounds have quasi-planar anthracene ring systems which exhibit a right-handed twist in the 'beta'-conformer, with the expected opposite twist in the other. A complete analysis of bond lengths, bond angles and torsion angles is presented. Preliminary electrostatic potentials have been derived from the X-ray data sets, and the results indicate significant differences in potential between 5F- and 6F-THDMBA at positions near the partially reduced bay region. Such results are likely to be of importance in the understanding of metabolic activation to reactive intermediates capable of bonding covalently to DNA.

Hexaaquaaluminium(III) bromate trihydrate, [Al(H2O)6](BrO3)3.3H2O, M(r) = 572.84, triclinic, P1, a = 9.536 (2), b = 11.095 (4), c = 9.291 (2) A, alpha = 106.58 (2), beta = 100.42 (2), gamma = 113.01 (2) degrees, V = 818.1 (4) A3, Z = 2, Dx = 2.33 g cm-3, lambda(Mo K alpha) = 0.71073 A, mu = 74.58 cm-1, F(000) = 560, T = 296 K, R = 0.050 for 3777 unique reflections having I greater than sigma 1. The single type of Al ion is coordinated by six inequivalent water O atoms which form a slightly distorted octahedron. The average Al--O distance within the octahedron is 1.872 (11) A. Each of the three inequivalent bromate groups has three inequivalent O atoms. The average Br--O distances and O--Br--O angles for these ions are: 1.652 (25) A and 104.1 (17) degrees for Br(1)O3; 1.650 (9) A and 104.4 (18) degrees for Br(2)O3; 1.643 (9) A and 103.6 (14) degrees for Br(3)O3. The aluminium-oxygen complex conformed to rigid-body behavior but the bromate groups did not. Corrected for rigid-body motion, the average Al--O distance becomes 1.880 (10) A. Least-squares refinement of the positional parameters of the 18 inequivalent H atoms permitted a detailed analysis of the hydrogen bonding.

C5H6N2O3, Mr = 142.11, monoclinic, P2(1)/n, a = 3.862 (1), b = 16.329 (2), c = 10.088 (1) A, beta = 98.77 (2) degrees, V = 628.7 (2) A3, Z = 4, Dx = 1.50 g cm-3, lambda(Mo K alpha) = 0.71069 A, mu = 1.18 cm-1, F(000) = 296, T = 296 K, R = 0.035 for 1124 independent reflections with I greater than 3 sigma(I). The structure is a hydantoin derivative with a methoxymethylene group substituted at the 5-position. Excluding the H atoms, the molecule is planar to within 0.032 A. All of the N and O atoms are involved in an intermolecular hydrogen-bonding network via N--H...O and C--H...O interactions. The packing arrangement is a linear ribbon motif with the ribbons stacked to form the short a axis.

C24H24O6, Mr = 408.45, triclinic, P1, a = 10.276 (2), b = 13.000 (2), c = 7.782 (1) A, alpha = 98.06 (1), beta = 97.63 (1), gamma = 84.43 (1) degree, V = 1017 A3, Z = 2, Dx = 1.33 g cm-3, lambda(Mo K alpha) = 0.71069 A, mu = 0.89 cm-1, F(000) = 432, T = 296 K, R = 0.048 for 3321 unique reflections with Fo2 greater than 3 sigma(Fo2). Both cyclopentenones are canted in the endo direction (6.0 and 7.9 degrees), the one syn to the ethoxy groups less so for steric reasons. When the ester groups are disregarded, the polyquinane portion of the molecule is seen to possess a non-crystallographic twofold axis. The overall molecular geometry is reconcilable with the absence of any significant alteration in the density maximum of the C--C pi bonds at this level of downward pyramidalization.

[Cu(H2O)4](ClO3)2, Mr = 302.51, orthorhombic, Pbca, lambda (Mo K alpha) = 0.71069 A, Z = 4, F(000) = 604; T = 296 K, a = 12.924 (3), b = 9.502 (2), c = 7.233 (1) A, V = 888.3 (3) A3, D chi = 2.26 g cm-3, mu = 31.04 cm-1, R = 0.041 for 1174 unique reflections with I greater than sigma (I); T = 223 K, a = 12.853 (2), b = 9.492 (2), c = 7.216 (2) A, V = 880.4 (3) A3, D chi = 2.28 g cm-3, mu = 31.28 cm-1, R = 0.033 for 1279 unique reflections with I greater than sigma (I). The single type of copper ion is octahedrally coordinated by four water oxygens and two chlorate ion oxygens; the complex is characterized by three distinct pairs of Cu-O distances (which we have previously described as '2 + 2 + 2' coordination), one of which is substantially larger than the remaining two. The nominal 90 degrees O-Cu-O angles of the complex differ from that value by at most +/- 1.8 degrees. The observed structure of the complex is typical for copper(II) and is consistent with the Jahn-Teller effect. The single type of chlorate ion shows the expected trigonal pyramidal geometry, with average Cl-O bond lengths 1.485 (13) and 1.490 (11) A and average O-Cl-O bond angles 106.8 (13) and 106.8 (13) degrees for 296 and 223 K, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Tetraaquacobalt(II) bromide dihydrate, [Co(H2O)4]Br2 x 2H2O, Mr = 326.83, monoclinic, C2/m, a = 11.0158(12), b = 7.1694(10), c = 6.9111(10) A, beta = 124.761(7)degrees, V = 448.4(1) A3, Z = 2, F(000) = 314, Dx = 2.420 g cm-3, lambda(Mo K alpha) = 0.71069 A, T = 296 K, mu = 107.13 cm-1, R = 0.022 for 532 unique reflections having I greater than 0. The single type of Co ion is octahedrally coordinated by four equivalent water-molecule O atoms at the observed distance 2.081(2) A and two equivalent Br ions at the observed distance 2.6048(5) A in an array which, with respect to its angles, departs only slightly from regular octahedral geometry. The cobalt-oxygen-bromine complex was found to manifest rigid-body behavior. The cobalt-oxygen distance corrected for rigid-body motion was found to be 2.088 A; the corrected cobalt-bromine distance, 2.6081 A. Associated with each complex are two water molecules of hydration. Assignment and refinement of the coordinates of the four non-equivalent H atoms permitted detailed analysis of the hydrogen bonding, which involves each of the four non-equivalent H atoms significantly. The structure as determined in this study differs markedly from that presented in the sole published single-crystal study [Stroganov, Andreev, Kozina & Solov'ev (1961). Vestn. Leningr. Univ. Ser. Mat. Fiz. Khim. 16, 114-119]. In particular, the space-group assignment differs and the pattern of bromine-oxygen distances is quite different. Contrary to Stroganov et al., this structure is isomorphic with that of cobalt chloride hexahydrate.

Mr = 200.25, orthorhombic, P2(1)2(1)2(1), a = 7.758(2), b = 20.506(3), c = 5.896(2) A, V = 938.0(4) A3, Z = 4, Dx = 1.42 g cm-3, lambda(Mo K alpha) = 0.71069 A, mu = 2.88 cm-1, F(000) = 416, T = 223 K, R = 0.044 for 1414 unique reflections having I greater than 3 sigma I. The phenoxathiin molecule is constituted of two very nearly regular planar hexagonal carbocyclic (benzenoid) rings joined to a non-planar heterocyclic ring. The heterocyclic ring geometry is described in terms of two intersecting planes between which the dihedral angle, the molecular fold angle, is 142.3 degrees. The angle at S (C-S-C) is 97.7(1) degrees, while the angle at O (C-O-C) is 117.4(2) degrees. The overall mean C-C distance in the carbocyclic rings is 1.387(7) A. The absence in this structure of the type of disorder previously found in the dibenzofuran structure is readily understandable since eight sets of close approaches involving each molecule were found in the present structure. These close approaches involve S and O atoms as well as H atoms.

When subjected to acetone-sensitized irradiation, the title compound undergoes near-quantitative self-coupling to give an uncommon [4+2] dimer, whose reaction with several oxidants demonstrated the enamide double bond of the photoproduct to be the more reactive.

The compounds M(2)(O(2)CMe)(4) and the lithium amidinates Li[(N(i)Pr)(2)CR] react to give the new compounds trans-M(2)(O(2)CMe)(2)[(N(i)Pr)(2)CR](2) where M = Mo or W and R = Me (M = Mo only), -C[triple bond]C(t)Bu, -C[triple bond]CPh and -C[triple bond]C-Fc where Fc = 1-ferrocenyl. The limitations of this type of reaction are described based on steric considerations together with the preparation and characterization of the compound Mo(2)(micro-O(2)C-9-anthracene)(2)[eta(2)-(N(i)Pr)(2)CMe](2). The electronic structures of the bis-amidinate-bis-carboxylate M(2) complexes are described based on model compounds employing density functional theory and are correlated with the experimental observations of their physicochemical properties and in particular their observed electronic absorption spectra which show intense MLCT absorption bands. Preliminary studies of the reactions of these bis-amidinate-bis-carboxylate complexes in the preparation of 1-D oligomers are also described along with the preparation and molecular structures of the compounds [Li(N(i)Pr)(2)CR.THF](2) where R = 2-thienyl or -C[triple bond]C-Ph. The kinetic lability of these new M(2)-containing compounds toward ligand exchange is also noted.

Ni(BrO4)2.6H2O, Mr = 454.61, trigonal, P3, a = 7.874 (1), c = 5.423 (2) A, V = 291.2 (1) A3, Z = 1, D chi = 2.59 g cm-3, lambda(Mo K alpha) = 0.71069 A, mu = 85.36 cm-1, F(000) = 222, T = 296 K, R = 0.029 for 457 unique reflections having I greater than 0. The room-temperature structure is very similar to that reported previously for a sample at 169 K. The water O atoms form a very slightly distorted octahedron about nickel while the perbromate-ion geometry is virtually regular tetrahedral. Both the coordination polyhedron and the perbromate ion were tested and found to behave as rigid bodies. Corrected for rigid-body motion, the Ni--O(2) distance is 2.064 (2) A and the mean Br--O distance in the perbromate ion is 1.629 (3) A. A detailed account of the hydrogen bonding is presented. The structure previously determined at 169 K is most probably not the stable structure at that temperature.

Hexaaquanickel(II) chlorate, [Ni(H2O)6]-(ClO3)2, Mr = 333.69, cubic, Pa3-, a = 10.3159 (5) A, V = 1097.80 (5) A3, Z = 4, F(000) = 680, Dx = 2.02 g cm-3, lambda(Mo K alpha-) = 0.71069 A, T = 296 K, mu = 23.13 cm-1, R = 0.026 for 388 unique reflections having I greater than sigma I. The single type of Ni ion is coordinated by six water-molecule O atoms, each at an observed distance 2.054 (1) A, in an almost regular octahedral array. The single type of chlorate ion has a Cl--O bond length 1.487 (1) A and O--Cl--O bond angle 106.45 (6) degrees. The Ni--O complex, but not the chlorate ion, manifested rigid-body behavior. The Ni--O distance corrected for rigid-body motion is 2.060 A. Location and refinement of the two inequivalent H atoms permitted a detailed analysis of hydrogen bonding, which occurs principally between the oxygen octahedra and the chlorate groups.

The complexes Na[(CO) 4 ReC(R)C(CO 2 Me)C (O)] ( 1a , R  CO 2 Me; 1b , R  Me) are formed in the reaction of Na[Re(CO) 5 ] with RCCCO 2 Me at room temperature. The structure of 1a has been shown by X-ray diffraction to contain a rhenacyclobutenone ring. Complex 1b is alkylated by Et 3 OPF 6 at the ketonic oxygen, as determined crystallographically.

Hexaaquanickel(II) chlorate, [Ni(H2O)6]-(ClO3)2, Mr = 333.69, cubic, Pa3-, a = 10.3159 (5) A, V = 1097.80 (5) A3, Z = 4, F(000) = 680, Dx = 2.02 g cm-3, lambda(Mo K alpha-) = 0.71069 A, T = 296 K, mu = 23.13 cm-1, R = 0.026 for 388 unique reflections having I greater than sigma I. The single type of Ni ion is coordinated by six water-molecule O atoms, each at an observed distance 2.054 (1) A, in an almost regular octahedral array. The single type of chlorate ion has a Cl--O bond length 1.487 (1) A and O--Cl--O bond angle 106.45 (6) degrees. The Ni--O complex, but not the chlorate ion, manifested rigid-body behavior. The Ni--O distance corrected for rigid-body motion is 2.060 A. Location and refinement of the two inequivalent H atoms permitted a detailed analysis of hydrogen bonding, which occurs principally between the oxygen octahedra and the chlorate groups.

The title compound, C15H22O3, was prepared via amino-acid-promoted Robinson annulation followed by tandem Pd/C-mediated hydrogenation and oxidative cyclization. This product was instrumental in determining the feasibility of a stereocontrolled hydrogenation in which the directing hydroxyl group is adjacent to the 6–7-ring network and its olefinic component. The asymmetric unit consists of a single molecule with normal geometric parameters. The absolute configuration was assigned based on the known enantiomeric prescursor. Intermolecular C—H...O interactions link each molecule with four neighboring molecules.