Synthesis of phthalide derivatives using nickel-catalyzed cyclization of o-haloesters with aldehydes

The reaction of o-bromobenzoate (1 b) with benzaldehyde (2 a) in the presence of [NiBr(2)(dppe)] (dppe=1,2-bis(diphenylphosphino)ethane) and zinc powder in THF (24 hours, reflux temperature), afforded 3-phenyl-3H-isobenzofuran-1-one (3 a) in an 86 % yield. Similarly, o-iodobenzoate reacts with 2 a to give 3 a, but in a lower yield (50 %). A series of substituted aromatic and aliphatic aldehydes (2 b, 4-MeC(6)H(4)CHO; 2 c, 4-MeOC(6)H(4)CHO; 2 d, 3-MeOC(6)H(4)CHO; 2 e, 2-MeOC(6)H(4)CHO; 2 f, 4-CNC(6)H(4)CHO; 2 g, 4-(Me)(3)CC(6)H(4)CHO; 2 h, 4-C(6)H(5)C(6)H(4)CHO; 2 i, 4-ClC(6)H(4)CHO; 2 j, 4-CF(3)C(6)H(4)CHO; 2 k, CH(3)(CH(2))(5)CHO; 2 l, CH(3)(CH(2))(2)CHO) also underwent cyclization with o-bromobenzoate (1 b) producing the corresponding phthalide derivatives in moderate to excellent yields and with high chemoselectivity. Like 1 b, methyl 2-bromo-4,5-dimethoxybenzoate (1 c) reacts with tolualdehyde (2 b) to give the corresponding substituted phthalide 3 m in a 71 % yield. The methodology can be further applied to the synthesis of six-membered lactones. The reaction of methyl 2-(2-bromophenyl)acetate (1 d) with benzaldehyde under similar reaction conditions afforded six-membered lactone 3 o in a 68 % yield. A possible catalytic mechanism for this cyclization is also proposed.     

Mono- and dinuclear complexes of chiral tri- and tetradentate Schiff-base ligands derived from 1,1'-binaphthyl-2,2'-diamine

The synthesis and characterization of the bis(bidentate) Schiff-base ligand [(R)-2] formed by the condensation reaction of (R)-1,1'-binaphthyl-2,2'-diamine [(R)-BINAM] with pyridine-2-carboxaldehyde is presented. The coordination chemistry of (R)-2 with Ni(ClO(4))(2).6H(2)O, Co(ClO(4))(2).6H(2)O, CuCl(2), and CuSO(4) has been investigated. Reaction of (R)-2 with the first two metal salts leads to complexes of the type [M((R)-4)(2)](ClO(4))(2) (M = Ni(II), Co(II)), where (R)-4 is a tridentate ligand resulting from the hydrolytic cleavage of one of the pyridyl groups from (R)-2. Both complexes were characterized by X-ray crystallography, which showed that the Lambda absolute configuration of the metal center is favored in both cases. (1)H NMR spectroscopy suggests that the high diastereoselectivity of Lambda-[Co((R)-4)(2)](ClO(4))(2) is maintained in solution. The reaction of (R)-2 with CuCl(2) leads to the dinuclear complex [Cu(2)((R)-2)Cl(4)], which has a [Cu(2)(mu(2)-Cl(2))] core. The reaction of CuSO(4) with (R)-2 gives a dimeric complex, [Cu((R)-4)SO(4)](2), which features a [Cu(2)(mu(2)-(SO(4))(2))] core. This complex can be prepared directly by the reaction of (R)-BINAM with pyridine-2-carboxaldehyde and CuSO(4). The use of rac-BINAM in this synthetic procedure leads to the heterochiral dimer [Cu(2)((R)-4)((S)-4)(SO(4))(2)]; that is, the ligands undergo a self-sorting (self/nonself discrimination) process based on chirality. The reaction of rac-BINAM, pyridine-2-carboxaldehyde, and Co(ClO(4))(2).6H(2)O proceeds via a homochiral self-sorting pathway to produce a racemic mixture of [Co((R)-4)(2)](2+) and [Co((S)-4)(2)](2+). The variable-temperature magnetic susceptibilities of the bimetallic complexes [Cu(2)((R)-2)Cl(4)], [Cu((R)-4)(mu(2)-SO(4))](2), and [Cu(2)((R)-4)((S)-4)(mu(2)-SO(4))(2)] all show weak antiferromagnetic coupling with J = -1.0, -0.40, and -0.67 cm(-)(1), respectively.     

Synthesis and characterization of octa- and hexanuclear polyoxomolybdate wheels: role of the inorganic template and of the counterion

Eight new compounds based on [O3PCH2PO3]4- ligands and {MoV2O4} dimeric units have been synthesized and structurally characterized. Octanuclear wheels encapsulating various guests have been isolated with different counterions. With NH4+, a single wheel was obtained, as expected, with the planar CO32- guest, (NH4)12[(MoV2O4)4(O3PCH2PO3)4(CO3)2].24H2O (1a), while with the pyramidal SO32- guest, only the syn isomer (NH4)12[(MoV2O4)4(O3PCH2PO3)4(SO3)2].26H2O (2a) was characterized. The corresponding anti isomer was obtained with Na+ as counterions, Na12[(MoV2O4)4(O3PCH2PO3)4(SO3)2]39H2O (2b), and with mixed Na+ and NH4(+) counterions, Na+(NH4)11[(MoV2O4)4(O3PCH2PO3)4(SO3)2].13H2O (2d). With [O3PCH2PO3]4- extra ligands, the octanuclear wheel Li12(NH4)2[(MoV2O4)4(O3PCH2PO3)4(HO3PCH2PO3)2].31H2O (4a) was isolated with Li+ and NH4+ counterions and Li14[(MoV2O4)4(O3PCH2PO3)4(HO3PCH2PO3)2].34H2O (4c) as a pure Li+ salt. A new rectangular anion, formed by connecting two MoV dimers and two MoVI octahedra via methylenediphosphonato ligands with NH4+ as counterions, (NH4)10[(MoV2O4)2(MoVIO3)2(O3PCH2PO3)2(HO3PCH2PO3)2].15H2)O (3a), and Li9(NH4)2Cl[(MoV2O4)2(MoVIO3)2(O3PCH2PO3)2]. 22H2O (3d) as a mixed NH4+ and Li+ salt have also been synthesized. The structural characterization of the compounds, combined with a study of their behavior in solution, investigated by 31P NMR, has allowed a discussion on the influence of the counterions on the structure of the anions and their stability. Density functional theory calculations carried out on both isomers of the [(MoV2O4)4(O3PCH2PO3)4(SO3)2]12- anion (2), either assumed isolated or embedded in a continuum solvent model, suggest that the anti form is favored by approximately 2 kcal mol(-1). Explicit insertion of two solvated counterions in the molecular cavity reverses this energy difference and reduces it to less than 1 kcal mol(-1), therefore accounting for the observed structural versatility.     

Solvent extraction of the ion-pairs of chromium(VI) and molybdenum(VI) with trioctylmethylammonium chloride and benzyldimethylcetylammonium chloride

The number of capriquat molecules per chromium(VI) atom in the chromate-capriquat ion-association complex has been found to be between one and two. The distribution ratio in the extraction of chromium(VI) with capriquat is dependent on the dielectric constant of the organic solvent, with a minimum at a dielectric constant of about 8. The absorption spectra of the ion-pair extracted into cyclohexane, carbon tetrachloride, benzene and n-butanol are very similar to that of chromate in aqueous solution. The absorption spectra of the chromium(VI)-capriquat extracts in these organic solvents gradually change to an absorption spectrum similar to that of HCrO(4)(-) in aqueous solution. Chromium(VI)-capriquat extracted into chloroform and 1,2-dichloroethane gives absorption spectra similar to that of HCrO(4)(-)in aqueous medium. The chromium(VI)-capriquat species extracted into 1,2-dichloroethane may be (Q(+))(2).CrO(4)(2-)(H(2)O)(n). In contrast, chromium(VI) is extracted with capriquat into the other organic solvents from ammoniacal medium as a mixture of (Q(+))(2).CrO(4)(2-)(H(2)O)(n) and Q(+).NH(4)(+).CrO(4)(2-)(H(2)O)(n). The spectral change is ascribed to the change of the extracted species from (Q(+))(2).CrO(4)(2-)(H(2)O)(n) and Q(+)NH(4)(+).CrO(4)(-)(H(2)O)(n) to Q(+).HCrO(4)(2-)(H(2)O)(n-1). The chromium(VI)-zephiramine species extracted is formulated as (Q(+), NH(4)(+))(2)CrO(4)(2-)(H(2)O)(n).(Q(+).Cl(-))(m). Molybdenum(VI) is extracted with capriquat into the same organic solvents as a mixture of (Q(+))(2).MoO(4)(2-)(H(2)O)(n) and Q(+).NH(4)(+).MoO(4)(2-).(H(2)O)(n).     

Self-assembly, reorganization, and photophysical properties of silver(I)-Schiff-base molecular rectangle and polymeric array species

A self-assembly of AgClO(4) with a Schiff-base ligand N,N'-bis(pyridin-2-ylmethylene)benzene-1,4-diamine (1) gave a 1D zigzag polymeric array [[Ag(2)(C(18)H(14)N(4))(2)](ClO(4))(2)(CH(3)CN)](n) (3), while the self-assembly of AgClO(4) with 3,3'-dimethyl-N,N'-bis(pyridin-2-ylmethylene)biphenyl-4,4'-diamine (2) afforded the molecular rectangle [[Ag(2)(C(26)H(22)N(4))(2)](ClO(4))(2)] (4). The structures of 3 and 4 were characterized by single-crystal X-ray diffraction analysis. Structural data for 3 indicate that the Ag(I) ion is coordinated by two ligands of 1 in a distorted tetrahedral fashion thereby leading to a 1D zigzag polymeric array. The zigzag chains are interdigitated with weak pi-pi stacking interactions. The structure of 4 consists of a discrete molecular rectangle where the silver atom has a distorted square-planar coordination with the pyridyl ligands and azomethine nitrogen atoms of 2. An intramolecular pi-pi interaction between the phenyl rings of adjacent Schiff-base 2 functions to stabilize the rectangular architecture. The Ag(I)-Schiff-base coordination polymer 3 is not stable in solution. The degradation and reorganization of 3 to form a [2 x 2] grid architecture [[Ag(4)(C(26)H(22)N(4))(4)](ClO(4))(4)] (3g) was supported in a FAB-MS study. The rectangular structure of 4 remains intact in solution at ambient temperature. The complexes 3g and 4 exhibit unusual luminescence behavior in solution at room temperature with significantly red-shifted emission in the visible region.     

Further study of the reaction of Fe2+ with CN-: synthesis and characterization of cis and trans [FeII,III(CN)4L2]n- complexes

The reaction of Fe2+ with CN-, which was first performed in 1704, has been used to synthesize a new series of basic [FeII,III(CN)4L2]n- complexes, where L is a monodentate ligand. trans-Na2[FeII(CN)4(DMSO)2] and cis-[NEt4]2[FeII(CN)4(pyridine)2] are synthesized by the direct reaction of FeCl2 with 4 equiv of CN- in DMSO or pyridine. Air oxidation of the latter compound gives cis-[NEt4][FeIII(CN)4(pyridine)2]. The non-cyanide ligands in these complexes undergo facile ligand exchange reactions with solvent. Reaction of cis-[NEt4]2[FeII(CN)4(pyridine)2] with CO at room temperature gives trans-[NEt4]2[FeII(CN)4(pyridine)(CO)].     

Synthesis, structure, and reactivity of a stabilized calcium carbene: R(2)CCa

Attempted 2-fold deprotonation of the bis(iminophosphorano)methane ligand, H(2)C(Ph(2)P=NSiMe(3))(2) (4-H(2)), with a calcium amide led only to mono-deprotonation. The crystal structure of (4-H)(2)Ca shows two tridentate ligands with short Ca-N and a rather long Ca-C bond. Reaction of 4-H(2) with a dibenzylcalcium complex gave the desired 2-fold deprotonation and formation of 4-Ca, which crystallized as a dimeric complex. Analysis of the calculated atomic and group charges in 4-H(2), (4-H)(2)Ca, and [4-Ca](2) showed that the negative charge at the imine nitrogens only slightly increases upon successive deprotonation of 4-H(2). The electron density at the central carbon, however, increases considerably: the charge on the carbene carbon in [4-Ca](2) is ca. -1.8. The negative charge in 4(2)(-) is therefore mainly located on the carbon. Reaction of [4-Ca](2) with benzophenone in benzene gave the remarkably stable adduct [4-Ca](2) x O=CPh(2), which was characterized by X-ray diffraction. Reaction of [4-Ca](2) with adamantylcyanide gave exclusive formation of the adduct [4-Ca](2) x (N identical withCR)(2), which did not react further, even at higher temperatures. Addition of cyclohexyl isocyanate to a benzene solution of [4-Ca](2) gave immediate [2 + 2]-cycloaddition and formation of a dianionic tetradentate ligand that binds to Ca(2+) through two nitrogens, the central carbon, and an oxygen. This product crystallized as a dimer with bridging oxygen atoms.     

Metamorphosis of a butterfly: synthesis, structural, thermal, magnetic and DFT characterisation of a ferromagnetically coupled tetranuclear copper(II) complex

The reaction in water of Cu(OH)(2) with 2,2'-bipyridine (bipy) and (NH(4))(2)HPO(4) in a 4 : 4 : 2 molar ratio under an inert atmosphere leads to the formation of a tetranuclear copper(II) complex of formula {[(H(2)O)(2)Cu(4)(bipy)(4)(mu(4)-PO(4))(2)(mu(2)-OH)] x 0.5 HPO(4) x 15.5 H(2)O}, 1, with butterfly topology. The structure of the tetranuclear core in 1 consists of four crystallographically unique copper(II) ions in approximate square-pyramidal geometry with each coordinated to a bipy ligand and interacting through two mu(4)-O,O',O'-phosphate bridges. Additional bridging between Cu(3) and Cu(4) is provided by a hydroxide ligand, whereas two water molecules cap the Cu(1) and Cu(2) square pyramids to yield a N(2)O(3) chromophore at each copper atom. Adjacent tetranuclear units align in anti-parallel fashion where proximate metal-bound water molecules interact with each other through both intra- and inter-molecular H-bonding to link two such clusters. These pairs then further associate through pi[...]pi interactions between bipy ligands to form a 2D sheet with neighbouring sheets separated by H-bonded lattice water molecules, which form a 2D H-bonded network. Variable-temperature magnetic susceptibility measurements performed upon 1 reveal net intramolecular ferromagnetic coupling between the copper(II) ions and this is supported and rationalized by a DFT study.     

Transformations of aryl isothiocyanates on tetraphosphine tungsten complexes and reactivity of the resulting dithiocarbonimidate ligand

Treatment of [WH(4)(κ(4)-P4)] (3: P4 = meso-o-C(6)H(4)(PPhCH(2)CH(2)PPh(2))(2)) with aryl isothiocyanate ArNCS at 50 °C afforded the dithiocarbonimidate-isocyanide complex [W(κ(2)-S(2)CNAr)(CNAr)(κ(4)-P4)] (4) in moderate yields. The reaction also produced ArNHCH(3) and a small amount of ArNH(2). The yield of the hydrodesulfurization product ArNHCH(3) increased when the reaction was conducted under H(2) (up to 0.65 equiv. to 3 for Ar = p-MeC(6)H(4) (Tol)). Complex 4 was proposed to be formed via reductive disproportionation of two ArNCS molecules on a zero-valent W species generated by dissociation of H(2) from 3. The reaction of W(0) complex [W(dppe)(κ(4)-P4)] (dppe = Ph(2)PCH(2)CH(2)PPh(2)) with ArNCS also yielded 4 accompanied by free dppe, in contrast to that of [Mo(dppe)(κ(4)-P4)], which had been previously reported to undergo sulfur-atom transfer to phosphine ligands. The dithiocarbonimidate ligands in 4a (Ar = Tol) received the addition of electrophiles [PhMe(2)NH][BF(4)], MeI, and PhCOCl selectively at the N atom to afford the cationic dithiocarbamate complexes [W(κ(2)-S(2)CNHTol)(CNTol)(κ(4)-P4)][BF(4)] (6), [W{κ(2)-S(2)CN(Me)Tol}(CNTol)(κ(4)-P4)]I (7), and [W{κ(2)-S(2)CN(COPh)Tol}(CNTol)(κ(4)-P4)]Cl (8). Complexes 4a, 6, 7, and 8 have been characterized by spectroscopic and crystallographic methods, and the donor strengths of their κ(2)-dithio ligands are discussed.     

Self-assembly and redox modulation of the cavity size of an unusual rectangular iron thiolate aryldiisocyanide metallocyclophane

The decarbonylation reaction of ferric carbonyl dicationic [Cp(2)Fe(2)(μ-SEt)(2)(CO)(2)](BF(4))(2) [1(BF(4))(2)] carried out in refluxing acetonitrile affords a binuclear iron-sulfur core complex [Cp(2)Fe(2)(μ-SEt)(2)(CH(3)CN)(2)](BF(4))(2) [2(BF(4))(2)] containing two acetonitrile coordinated ligands. The treatment of 2(BF(4))(2) with 2 equiv of the 1,4-diisocyanobenzene (1,4-CNC(6)H(4)NC) results in the formation of the diisocyanide complex [Cp(2)Fe(2)(μ-SEt)(2)(1,4-CNC(6)H(4)NC)(2)](BF(4))(2) [3(BF(4))(2)]. The rectangular tetranuclear iron thiolate aryldiisocyanide metallocyclophane complex [Cp(4)Fe(4)(μ-SEt)(4)(μ-1,4-CNC(6)H(4)NC)(2)](BF(4))(4) [4(BF(4))(4)] has been synthesized by a self-assembly reaction between equimolar amounts of 2(BF(4))(2) and 1,4-diisocyanobenzene or by a stepwise route involving mixing of a 1:1 molar ratio of complexes 2(BF(4))(2) and 3(BF(4))(2). Chemical reduction of 4(BF(4))(4) by KC(8) was observed to produce the reduction product 4(BF(4))(2). The spectroscopic and electrochemical properties of the iron-sulfur core complexes 1(PF(6))(2), 3(BF(4))(2), 4(BF(4))(4), and 4(BF(4))(2) were determined. Finally, differences between the redox control cavities of rectangular tetranuclear iron thiolate aryldiisocyanide complexes are revealed by a comparison of the X-ray crystallographically determined structures of complexes 4(BF(4))(4) and 4(BF(4))(2).     

Reaction paths of tautomerization between hydroxypyridines and pyridones

Tautomerization paths of 2(and 4)-hydroxypyridine (called here HP) to 2(and 4)-pyridone (called here PY) with water molecules were investigated by the use of density functional theory calculations. Potential energies were compared for a number of water molecules. The 2-HP molecule was found to be isomerized most readily and concertedly to the 2-PY one via proton relays with two water molecules. The reaction pattern is invariant even when outer water molecules are added. The 4-HP(H(2)O)(n) --> 4-PY(H(2)O)(n) reaction model did not give small activation energies. However, a reaction of (4-HP)(2)(H(2)O)(2) --> (4-PY)(2)(H(2)O)(2) was found to occur readily through a transient ion-pair intermediate. The conversion processes of (2-PY)(2) to the tautomerization reacting system were discussed. The hydrogen-bond directionality regulates the tautomerization paths.     

One-pot conditional self-assembly of multicopper metallacycles

The self-assembly of supramolecular metallacycles via the coordination-driven directional bonding approach can be modified to produce some unexpected structural variations. The combination of a flexible ligand-capped dinuclear transition-metal acceptor like [Cu(2)(dppm)(2)(NCMe)(2)]X(2) (1X(2); dppm = Ph(2)PCH(2)PPh(2); X(-) = BF(4)(-), PF(6)(-), or BPh(4)(-)) with monodentate-bidentate donors like 2-, 3-, and 4-pyridylcarboxylates produced oligomeric compounds [{Cu(2)(dppm)(2)}(μ-(2-PyCO(2)))](2)X(2) (2X(2)), [{Cu(2)(dppm)(2)}(μ-(3-PyCO(2)))](2)X(2) (3X(2)), and [{Cu(2)(dppm)(2)}(μ-(4-PyCO(2)))](4)X(4) (4X(4)), respectively, as the thermodynamically stable products in one-pot reactions. However, the modified self-assembly is still subject to steric hindrance. The reaction of complex 1(BF(4))(2) with 6-Me-3-PyCO(2)H did not produce a polygonal dimeric metallacycle but a simple dinuclear complex, [Cu(2)(dppm)(2)(6-Me-3-PyCO(2))](BF(4)) (5(BF(4))). The crystal structures of complexes 2(PF(6))(2), 3(PF(6))(2), 4(BF(4))(4), and 5(BF(4)) were determined using X-ray diffraction.     

Reactivity of a palladium fluoro complex towards silanes and Bu3SnCH=CH2: Catalytic derivatisation of pentafluoropyridine based on carbon-fluorine bond activation reactions

The chloro and azido complexes trans-[PdCl(4-C5NF4)(PiPr3)2] (3) and trans-[Pd(N3)(4-C5NF4)(PiPr3)2] (4) can be prepared by reaction of [PdF(4-C5NF4)(PiPr3)2] (2) with Et3SiCl or MeSiN3, respectively. In contrast, reactions of 2 with Ph3SiH or Me2FSiSiFMe2 give the products of reductive elimination 2,3,5,6-tetrafluoropyridine (5) or 4-(fluorodimethylsilyl)tetrafluoropyridine (6) as well as [Pd(PiPr3)2] (1). In a catalytic experiment, pentafluoropyridine can be converted with Ph3SiH into 5 in 62% yield, when 10% of 2 is employed as catalyst. Treatment of trans-[PdF(4-C5NF4)(PiPr3)2] (2) with Bu3SnCH=CH2 in THF at 50 degrees C results in the formation of [Pd(PiPr3)2] (1) and 4-vinyltetrafluoropyridine (7). Complex 2 is also active as a catalyst towards a Stille cross-coupling reaction of pentafluoropyridine with Bu3SnCH=CH2 to give 4-vinyltetrafluoropyridine (7) with a TON of 6. The molecular structure of the complex 3 has been determined by X-ray crystallography.     

助剂前体ZnSO_4浓度对苯选择加氢制环己烯Ru-Zn催化剂性能的影响

共沉淀法制备了Ru-Zn催化剂,在ZrO_2作分散剂下考察了助剂前体ZnSO_4浓度对苯选择加氢制环己烯Ru-Zn催化剂性能的影响.并用X-射线衍射(XRD)、X-射线荧光光谱(XRF)、N_2-物理吸附、透射电镜(TEM)和X-射线光电子能谱(XPS)等手段对催化剂进行了表征.结果表明,当ZnSO_4前体浓度低于0.10 mol/L时,Ru-Zn催化剂中Zn以ZnO形式存在,在加氢过程中ZnO可以与反应修饰剂ZnSO_4反应生成(Zn( OH)_2)_3(ZnSO_4)(H_2O)_3盐.继续增加ZnSO_4前体浓度,催化剂中Zn以ZnO和NaZn_4(SO_4)(Cl)(OH)_6·6H_2O盐存在,在加氢过程中ZnO和NaZn_4(SO_4)(Cl)(OH)_6·6H_2O盐可以与反应修饰剂ZnSO_4反应生成(Zn( OH)_2)_3(ZnSO_4)(H_2O)_5.(Zn( OH)_2)_3(ZnSO_4)(H_2O)_x(x=3或5)盐的Zn~(2+)可以转移金属Ru的部分电子.因此,随ZnSO_4前体浓度的增加,(Zn( OH)_2)_3(ZnSO_4)(H_2O)_x的量逐渐增加,金属Ru失电子越多,催化剂活性越低,环己烯选择性越高.0.08 mol/L ZnSO_4前体制备Ru-Zn催化剂给出了59.1%的环己烯收率,而且该催化剂具有良好的重复使用性能和稳定性.     

The use of 1,2-dipiperidinoacetylene for the preparation of monometallic diaminoacetylene and homo- or heterobimetallic diaminodicarbene ruthenium(II) complexes

The reaction of the ynediamine 1,2-dipiperidinoacetylene (1) with [(η(2)-COE)Cr(CO)(5)], [(THF)W(CO)(5)] and [RuCl(2)(η(6)-cymene)](2) afforded homobimetallic complexes 2a, 2b and 3, in which the diaminoacetylene 1 acts as a bis(aminocarbene) ligand by bridging two complex fragments Cr(CO)(5) (in 2a), W(CO)(5) (in 2b) and RuCl(2)(η(6)-cymene) (in 3). The reaction of 1 with [RuCl(2)(PPh(3))(3)] gave trans-[(1)RuCl(PPh(3))(2)]Cl, [4]Cl, in which the alkyne 1 coordinates as a 4-electron donor ligand. The cation 4 represents a rare example of a square-planar Ru(II) complex with a low-spin ground state (S = 0), and its stability can be ascribed to the strong alkyne-metal π-interaction as confirmed by DFT calculations. Treatment with one or two equivalents of NaBPh(4) in acetonitrile gave [4]BPh(4) and the dicationic [(1)Ru(PPh(3))(2)(CH(3)CN)(2)](BPh(4))(2), [5](BPh(4))(2). [4]Cl can be used for the preparation of heterobimetallic Ru-Pd bis(aminocarbene) complexes by reaction with [(MeCN)(2)PdCl(2)], resulting in the formation of bimetallic 6 and tetrametallic 7.     

Reduction of bis

The reduction of symmetric, fully-substituted titanocene dichlorides bearing two pendant omega-alkenyl groups, [TiCl2(eta5-C5Me4R)2], R = CH(Me)CH= CH2 (1a). (CH2)2CH=CH2 (1b) and (CH2)3CH=CH2 (1c), by magnesium in tetrahydrofuran affords bis(cyclopentadienyl)titanacyclopentanes [Ti(IV)[eta1:eta1: eta5:eta5-C5Me4CH(Me)CH(Ti)CH2CH(CH2(Ti))CH(Me)C5Me4]] (2a), [Ti(IV)[eta1:eta1:eta5: eta5-C5Me4(CH2)2CH(Ti)(CH2)2CH(Ti)(CH2)2C5Me4]] (2b) and [Ti(IV)[eta1:eta1:eta5:eta5-C5Me4(CH2)2CH(Ti)CH(Me)CH(Me)CH(Ti)(CH2)2C5Me4]](2c), respectively, as the products of oxidative coupling of the double bonds across a titanocene intermediate. For the case of complex 1c, a product of a double bond isomerisation is obtained owing to a preferred formation of five-membered titanacycles. The reaction of the titanacyclopentanes with PbCl2 recovers starting materials 1a from 2a and 1b from 2b, but complex 2c affords, under the same conditions, an isomer of 1c with a shifted carbon - carbon double bond, [TiCl[eta5-C5Me4(CH2CH2CH=CHMe)]2] (1c'). The titanacycles 2a-c can be opened by HCl to give ansa-titanocene dichlorides ansa-[[eta5:eta5-C5Me4CH(Me)CH2CH2CH(Me)CH(Me)C5Me4]TiCl2] (3a), ansa-[[eta5:eta5-C5Me4(CH2)8C5Me4]TiCl2] (3b), along with a minor product ansa-[[eta5:eta5-C5Me4CH2CH=CH(CH2)5C5Me4]TiCl2] (3b'), and ansa-[[eta5:eta5-CsMe4(CH2)3CH(Me)CH(Me)CH=CHCH2C5Me4]TiCl2] (3c), respectively, with the bridging aliphatic chain consisting of five (3a) and eight (3b, 3b' and 3c) carbon atoms. The course of the acidolysis changes with the nature of the pendant group; while the cyclopentadienyl ring-linking carbon chains in 3a and 3b are fully saturated, compounds 3c and 3b' contain one asymetrically placed carbon-carbon double bond, which evidently arises from the beta-hydrogen elimination that follows the HCl addition.     

Syntheses and reactivity studies of solvated dirhenium acetonitrile complexes

Fully and partially solvated triply-bonded [Re2]4+ complexes have been synthesized and their X-ray structures are described. A fully solvated dirhenium salt with BArf [tetrakis(3,5-bis(trifluoromethyl)phenyl)borate] as the counter anion [Re2(CH3CN)10][BArf]4 () has been characterized. The solubility of the complex in CH2Cl2 and THF in addition to CH3CN offers the possibility of improved reactivity. The structure of [Re2(micro-O)(CH3CN)10][BF4]4 () that possesses a linear [Re(III)-O-Re(III)]4+ unit is reported. Protonation reactions of cis-Re2Cl2(dppm)2(O2CCH3)2 and trans-Re2Cl4(dppm)2 with HBF4.Et2O in acetonitrile afforded cis and trans [Re2(dppm)2(CH3CN)6][BF4]4 ( and ), respectively. Prolonging the reaction time, however, does not lead to fully solvated complex [Re2(CH3CN)10][BF4]4. The neutral nitrogen donor ligands pynp (2-(2-pyridyl)-1,8-naphthyridine) and tznp (2-(2-thiazolyl)-1,8-naphthyridine) react readily with [Re2(CH3CN)10][BF4]4 to provide trans-[Re2(pynp)2(CH3CN)4][BF4]4 and trans-[Re2(tznp)2(CH3CN)4][BF4]4. The X-ray structures trans-[Re2(pynp)2(CH3CN)4][BF4]4 () and trans-[Re2(tznp)2(CH3CN)4][BF4]3[PF6] () have been determined.     

Role of axial donors in the ligand isomerization processes of quadruply bonded dimolybdenum(II) compounds

Quadruply bonded dimolybdenum(II) complexes with NP-R (2-(2-R)-1,8-naphthyridine; R = thiazolyl (NP-tz), furyl (NP-fu), thienyl (NP-th)) and 2,3-dimethyl-1,8-naphthyridine (NP-Me 2) have been synthesized by reactions of cis-[Mo2(OAc)2(CH3CN)6][BF4]2 with the corresponding ligands. The products cis-[Mo2(NP-tz)2(OAc)2][BF4]2 (1), trans-[Mo2(NP-fu)2(OAc)2][BF4]2 (2), trans-[Mo2(NP-th)2(OAc)2][BF4]2 (3), and trans-[Mo2(NP-Me2)2(OAc)2][BF4]2 (4) were isolated and characterized. The NP-R ligands with stronger R = pyridyl and thiazolyl donors result in cis isomers whereas the weaker furyl and thienyl appendages lead to compounds having a trans orientation of the ligands. The use of NP-Me2 leads to a trans structure with a tetrafluoroborate anion occupying one of the axial sites. Complete replacement of two acetate groups by acetonitrile in 1 and 2 resulted in the cis isomers [Mo2(NP-tz)2(CH3CN)4][OTf]4 (5) and [Mo2(NP-fu)2(CH3CN)4][OTf]4 (6) respectively. The combination of one acetate and two acetonitriles as ancillary ligands, however, yields trans-[Mo2(NP-tz)2(OAc)(CH3CN)2][BF4]3 (7) in the solid state as determined by X-ray crystallography. (1)H NMR spectra of the products are diagnostic of the cis and trans dispositions of the ligands. Solution studies reveal that the ligand arrangements observed in the solid state are mostly retained in the acetonitrile medium. The only exception is 7, for which a mixture of cis and trans isomers are detected on the NMR time scale. The isolation of trans compounds 2- 4 from the cis precursor [Mo2(OAc)2(CH3CN)6][BF4]2 indicates that an isomerization process occurs during the reactions. The mechanism involving acetate migration through axial coordination has been invoked to rationalize the product formation. Compounds 1- 7 were structurally characterized by single-crystal X-ray methods.     

Convenient synthesis of aluminum and gallium phosphonate cages

The reactions of AlCl 3.6H 2O and GaCl 3 with 2-pyridylphosphonic acid (2PypoH 2) and 4-pyridylphosphonic acid (4PypoH 2) afford cyclic aluminum and gallium phosphonate structures of [(2PypoH) 4Al 4(OH 2) 12]Cl 8.6H 2O ( 1), [(4PypoH) 4Al 4(OH 2) 12]Cl 8.11H 2O ( 2), [(2PypoH) 4Al 4(OH 2) 12](NO 3) 8.7H 2O ( 3), [(2PypoH) 2(2Pypo) 4Ga 8Cl 12(OH 2) 4(thf) 2](GaCl 4) 2..8thf ( 4), and [(2PypoH) 2(2Pypo) 4Ga 8Cl 12(OH 2) 4(thf) 2](NO 3) 2.9thf ( 5). Structures 1- 3 feature four aluminum atoms bridged by oxygen atoms from the phosphonate moiety and show structural resemblance to the secondary building units found in zeolites and aluminum phosphates. The gallium complexes, 4 and 5, have eight gallium atoms bridged by phosphonate moieties with two GaCl 4 (-) counterions present in 4 and nitrate ions in 5. The cage structures 1- 3 are interlinked by strong hydrogen bonds, forming polymeric chains that, for aluminum, are thermally robust. Exchange of the phosphonic acid for the more flexible 4PyCH 2PO 3H 2 afforded a coordination polymer with a 1:1 Ga:P ratio, {[(4PyCH 2PO 3H)Ga(OH 2) 3](NO 3) 2.0.5H 2O} x ( 6). Complexes 1- 6 were characterized by single-crystal X-ray diffraction, NMR, and mass spectrometry and studied by TGA.     

Hydration of pyridylketenes: formation of acid enol and dihydropyridine (eneaminone) transients

2-, 3-, and 4-Pyridylketenes 4 formed in water by photochemical Wolff rearrangements using flash photolysis undergo rapid hydration forming transient intermediates observed by UV spectroscopy. 3-Pyridylketene (3-4) formed the acid enol intermediate 3-10 which was converted to the acid 3-11, and phenylketene gave similar behavior. 4-Pyridylketene (4-4) reacted with a similar initial rate constant of 5.0 x 10(4) s(-1) for decay of an absorption at 275 nm, with concomitant formation of a strong absorption at 370 nm with the same rate constant. The intermediate absorbing at 370 nm decayed with a lifetime 2.4 x 10(3) fold longer than that of the ketene, and is identified as 4-(carboxymethylene)-1,4-dihydropyridine (4-13), resulting from conjugate 1,6-addition of H(2)O to 4-4. 2-Pyridylketene (2-4) underwent hydration with a similar rate constant of 1.1 x 10(4) s(-1) forming a transient with a UV absorption with maxima at 310 and 380 nm that decayed with biexponetial kinetics, with rate constants slower than the rate of formation by factors of 5.2 and 110, respectively. These results are interpreted as indicating the presence of two species, namely Z- and E-2-(carboxymethylene)-1,2-dihydropyridines (2-13), resulting from conjugate 1,4-addition of H(2)O to 2-4. The identifications of the 1,2- and 1,4-(carboxymethylene)dihydropyridines 2- and 4-13 were confirmed by comparison of their UV spectra with those of the corresponding N-methyl derivatives. The amination of 2-pyridylketene in CH(3)CN was reinvestigated, and spectroscopic evidence, computational studies, and preparation of the N-methyl analogue demonstrated formation of the 1,2-dihydropyridine Z-2-8f as the long-lived intermediate.