Allylboronic esters with various structures were synthesized for the first time based on [2.2]paracyclophane derivatives containing one or two hydroxy groups. It was demonstrated that these esters can be used as chiral inductors in the asymmetric allylboration of benzaldehyde. The highest enantiomeric excess of 1-phenylbut-3-en-1-ol (60%) was achieved in the reactions with acyclic bis-O,O′-(paracyclophanyl) allylboronates based on (S)-4-hydroxy-and (S)-12-bromo-4-hydroxy[2.2]paracyclophanes. (S)-4-Hydroxy[2.2]paracyclophane was studied by X-ray diffraction.

We report here the first examples of the regioselective double electrophilic substitution of chiral C-2-symmetric pseudometa-disubstituted [2.2]paracyclophanes. Thus, the double acylation of 4,15-dihydroxy[2.2]paracyclophane occurs ortho-regioseleclively, whereas the double acylation of its respective dimethyl ether is completely para-regioselective. Double bromination of ,15dicarbomethoxy[2.2] paracyclophane regioselectively generates the pseudo-gem-substitution pattern. The approaches elaborated allow the synthesis of all three possible types of chiral bis-bifunctional compounds, which have two independent, although chemically and stereochemically equal, functional fragments with pseudo-meta mutual orientation of both pairs of identical substituents. (c) 2006 Elsevier Ltd. All rights reserved.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

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The TiCl4/Zn-mediated intermolecular pinacol coupling of the planar chiral carbonyl compounds [2.2]paracyclophane-4-carbaldehyde, 4-acetyl[2.2]paracyclophane (ketone) and the four regioisomeric 5-, 7-, 12- and 13-methoxy[2.2]paracyclophane-4-carbaldehydes as well as the pTosOH-Zn/Cu-promoted coupling of their N-substituted imines is described. Coupling of the enantiomerically pure substrates (most of carbonyl compounds and all imines) occurs stereoselectively giving rise to diastereomerically pure 1,2-diols and 1,2-diamines. Racemic aldehydes and ketone react with different degrees of stereoselectivity (depending on the substituents in certain positions) and produce one to three diastereomers. 7-methoxy[2.2]paracyclophane-4-carbaldehyde undergoes a tandem pinacol coupling-pinacol rearrangement to yield bis-(7-methoxy[2.2]paracyclophane-4-yl)acetaldehyde. Coupling of the racemic imines produces a mixture of single racemic D,L-diamine and single meso-diamine in each case. The stereoselective formation of the asymmetric centres is governed by the planar chiral [2.2]paracyclophanyl moiety. The techniques elaborated are extended to the intramolecular coupling of [2.2]paracyclophane-4,13-dicarbaldehyde and its bis-N-phenylimine, resulting in stereoselective formation of the chiral triply-bridged diol and exclusive formation of the meso-diamine. X-Ray investigations of several diols and diamines have been carried out and the structural features of these derivatives are discussed.

Cyclopalladation of the Schiff bases of general formula McCH=N-CH(Me)Fc (Mc=Fc, Ru) (1a,b) with a chiral centre leads to the mixtures of three products, two of which (2 and 3) are planar chiral diastereomers formed from homoannular substitution into the aldehyde fragment. The third product 4 is a result of the unusual heteroannular palladation of the amine fragment in starting aldimine. This ansa-structure 4 having 3-atomic C-N-Pd bridge is without precedent in metallocenes. The molecular structures of all organopalladium compounds obtained have been proved using X-ray analysis of single crystals. (c) 2005 Elsevier B.V. All rights reserved.

Diastereoselective synthesis of new NiII complexes of Schiff bases of (S)-2-[N-(N-benzylprolyl)amino]benzophenone with (2S,4R)-4-bromoglutamic, (1S,2R)- and (1S,2S)-1-aminocyclopropane-1,2-dicarboxylic acid monoesters was performed.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The reactions of a complex [(η4-C7H8)RhCl]2 (C7H8 is norbornadiene) with salts of substituted nido-dicarbaundecaborates, [K][nido-7-R1-8-R2-7,8-C2B9H10] (R1 = R2 = H (a); R1 = R2 = Me (b); R1, R2 = 1′,2′-(CH2)2C6H4 (c); R1 = Me, R2 = Ph (d)), in CH2Cl2 afforded new closo-(η2,η3-(4-vinylcyclopenten-3-yl))rhodacarboranes. The structures of the compounds were studied by multinuclear NMR spectroscopy. A probable mechanism of the rearrangement of the norbornadiene ligand is discussed.

A series of new α-substituted acrolein dimethylhydrazones containing an acetal group were synthesized. These hydrazones react with acrylonitrile or methyl acrylate according to the Diels—Alder reaction pattern to give substituted tetrahydropyridines. An unusual [2+4]- and [2+3]-cycloaddition cascade reaction involving α-diethoxymethylacrolein dimethylhydrazone was discovered.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The monocarbon carborane [Cs][nido-7-CB(10)H(13)] reacts with the 16-electron [RuCl(2)(PPh(3))(3)] in a solution of benzene/methanol in the presence of N,N,N',N'-tetramethylnaphthalene-1,8-diamine as the base to give a series of 12-vertex monocarbon arene-biruthenacarborane complexes of two types: [closo-2-[7,11-exo-RuClPPh(3)(mu,eta(6)-C(6)H(5)PPh(2))]-7,11-(mu-H)(2)-2,1-RuCB(10)H(8)R] (5, R = H; 6, R = 6-MeO; 7, R = 3-MeO) and [closo-2-(eta(6)-C(6)H(6))-10,11,12-[exo-RuCl(PPh(3))(2)]-10,11,12-(mu-H)(3)-2,1-RuCB(10)H(7)R(1)] (8a, R(1) = 6-MeO; 8b, R(1) = 3-MeO, inseparable mixture of isomers) along with trace amounts of 10-vertex mononuclear hypercloso/isocloso-type complexes [2,2-(PPh(3))(2)-2-H-3,9-(MeO)(2)-2,1-RuCB(8)H(7)] (9) and [2,5-(Ph(3)P)-2-Cl-2-H-3,9-(MeO)(2)-2,1-RuCB(8)H(6)] (10). Binuclear ruthenacarborane clusters of both series were characterized by a combination of analytical and multinuclear NMR spectroscopic data and by single-crystal X-ray diffraction studies of three selected complexes, 6-8. In solution, isomers 8a,b have been shown to undergo the isomerization process through the scrambling of the exo-[RuCl(PPh(3))(2)] fragment about two adjacent triangular cage boron faces B(7)B(11)B(12) and B(8)B(9)B(12).

The present contribution reports experimental and computational investigations of the interaction between [Cp*Fe(dppe)H] and different proton donors (HA). The focus is on the structure of the proton transfer intermediates and on the potential energy surface of the proton transfer leading to the dihydrogen complex [Cp*Fe(dppe)(H2)]+. With p-nitrophenol (PNP) a UV/Visible study provides evidence of the formation of the ion-pair stabilized by a hydrogen bond between the nonclassical cation [Cp*Fe(dppe)(H2)]+ and the homoconjugated anion ([AHA]-). With trifluoroacetic acid (TFA), the hydrogen-bonded ion pair containing the simple conjugate base (A-) in equilibrium with the free ions is observed by IR spectroscopy when using a deficit of the proton donor. An excess leads to the formation of the homoconjugated anion. The interaction with hexafluoroisopropanol (HFIP) was investigated quantitatively by IR spectroscopy and by 1H and 31P NMR spectroscopy at low temperatures (200-260 K) and by stopped-flow kinetics at about room temperature (288-308 K). The hydrogen bond formation to give [Cp*Fe(dppe)H]HA is characterized by DeltaH degrees =-6.5+/-0.4 kcal mol(-1) and DeltaS degrees = -18.6+/-1.7 cal mol(-1) K(-1). The activation barrier for the proton transfer step, which occurs only upon intervention of a second HFIP molecule, is DeltaH(not equal) = 2.6+/-0.3 kcal mol(-1) and DeltaS(not equal) = -44.5+/-1.1 cal mol(-1) K(-1). The computational investigation (at the DFT/B3 LYP level with inclusion of solvent effects by the polarizable continuum model) reproduces all the qualitative findings, provided the correct number of proton donor molecules are used in the model. The proton transfer process is, however, computed to be less exothermic than observed in the experiment.

Agostic (C−H···M) complexes [closo-3,3-(σ,η2-C8H13)-1,2-μ-(ortho-xylylene)-3,1,2-IrC2B9H9] (5) and [closo-3,3-(σ,η2-C8H13)-1,2-μ-(ortho-xylylene)-3,1,2-RhC2B9H9] (9), stable in the solid state, have been prepared via the reaction of [M(η4-COD)Cl]2 (M = Ir, Rh) with the K+ salt of the [nido-7,8-μ-(ortho-xylylene)-7,8-C2B9H10]- anion and characterized by a combination of analytical (in the case of 5) and multinuclear NMR data, including a single-crystal X-ray diffraction study of 5. The crystallographic study confirmed the agostic structure of 5 and revealed that the orientation of the σ,η2-cyclooctenyl moiety relative to the carborane ligand is substantially influenced by the specific intramolecular C−H···π interaction between the agostic hydrogen and the π-system of the cage aromatic substituent. In solution, 5 exhibited both "side-to-side" agostic hydrogen migration and reversible interconversion with [closo-3-(η3-C8H13)-1,2-μ-(ortho-xylylene)-3,1,2-IrC2B9H9] (8). The agostic rhodium complex (9), in contrast, converts irreversibly both in the solid state and in solution to its η3-cyclooctenyl isomer [closo-3-(η3-C8H13)-1,2-μ-(ortho-xylylene)-3,1,2-RhC2B9H9] (11), which thus could be obtained as a pure solid. In solution, complex 11 is fluxional and shows an agostic C−H···Rh interaction. The fluxional process involves the exchange between the endo hydrogen atoms, on one hand, and the exo and allyl hydrogens of the C8-ring, on the other hand, confirmed by 2D [1H−1H]-EXSY spectroscopy. Solution structures of the agostic complexes obtained are discussed in detail on the basis of normal and low-temperature 1H and 13C/13C{1H} NMR spectroscopic data.

Palladium P,C,P pincer complexes based on ferrocene were synthesized for the first time. The reaction of the 1,3-bis((dialkylphosphino)methyl)ferrocenes {1,3-(R2PCH2)(2)C5H3}Fe(C5H5) (2a, R = Pr-i; 2b, R = Bu-t) with PdCl2(NCPh)(2) in refluxing 2-methoxyethanol leads to the corresponding pincer complexes PdCl[{2,5-(R2PCH2)(2)C5H2}Fe(C5H5)] (3a,b). The ferrocene-based binuclear compound 3b reacts with [Cp2Fe]PF6 to form the ferrocenium-based pincer complex {PdCl[{2,5-((Bu2PCH2)-P-t)(2)C5H2}Fe(C5H5)]}PF6 (4b), and this is the first example of ferrocene-based phosphine chelate oxidation centered on the iron atom. Treatment of complexes 3a,b with NaBH4 in refluxing ethanol affords the complexes Pd(BH4)[{2,5-(R-2-PCH2)(2)C5H2}Fe(C5H5)] (5a, R = Pr-i; 5b, R = Bu-t), containing a BH4- group coordinated to the metal in the rarely occurring unidentate mode. The structures of 3a,b and 5b were confirmed by X-ray analyses. Cyclic voltammetric investigations of complexes 2b and 3a,b are also reported. The structural and spectroscopic features of the palladium ferrocene-based pincer complexes are discussed and compared with those of related compounds.

Ethyl 4,4-difluoro-4-phenoxyacetoacetate was obtained and studied as a precursor to new heterocyclic compounds. 6-Hydroxypyrimidine, 1,3-dihydro-1,5- benzodiazepin-2-one, quinolin-2-one and 6-hydroxypyrazolo[3,4-b]pyridine derivatives containing phenoxydifluoromethyl groups were synthesized. These results make it possible to introduce aryloxydifluoromethyl substituents for the design of biologically active heterocycles.

The interaction of [NbCp(2)H(3)] with fluorinated alcohols to give dihydrogen-bonded complexes was studied by a combination of IR, NMR and DFT methods. IR spectra were examined in the range from 200-295 K, affording a clear picture of dihydrogen-bond formation when [NbCp(2)H(3)]/HOR(f) mixtures (HOR(f) = hexafluoroisopropanol (HFIP) or perfluoro-tert-butanol (PFTB)) were quickly cooled to 200 K. Through examination of the OH region, the dihydrogen-bond energetics were determined to be 4.5+/-0.3 kcal mol(-1) for TFE (TFE = trifluoroethanol) and 5.7+/-0.3 kcal mol(-1) for HFIP. (1)H NMR studies of solutions of [NbCp(2)H(2)(B)H(A)] and HFIP in [D(8)]toluene revealed high-field shifts of the hydrides H(A) and H(B), characteristic of dihydrogen-bond formation, upon addition of alcohol. The magnitude of signal shifts and T(1) relaxation time measurements show preferential coordination of the alcohol to the central hydride H(A), but are also consistent with a bifurcated character of the dihydrogen bonding. Estimations of hydride-proton distances based on T(1) data are in good accord with the results of DFT calculations. DFT calculations for the interaction of [NbCp(2)H(3)] with a series of non-fluorinated (MeOH, CH(3)COOH) and fluorinated (CF(3)OH, TFE, HFIP, PFTB and CF(3)COOH) proton donors of different strengths showed dihydrogen-bond formation, with binding energies ranging from -5.7 to -12.3 kcal mol(-1), depending on the proton donor strength. Coordination of proton donors occurs both to the central and to the lateral hydrides of [NbCp(2)H(3)], the former interaction being of bifurcated type and energetically slightly more favourable. In the case of the strong acid H(3)O(+), the proton transfer occurs without any barrier, and no dihydrogen-bonded intermediates are found. Proton transfer to [NbCp(2)H(3)] gives bis(dihydrogen) [NbCp(2)(eta(2)-H(2))(2)](+) and dihydride(dihydrogen) complexes [NbCp(2)(H)(2)(eta(2)-H(2))](+) (with lateral hydrides and central dihydrogen), the former product being slightly more stable. When two molecules of TFA were included in the calculations, in addition to the dihydrogen-bonded adduct, an ionic pair formed by the cationic bis(dihydrogen) complex [NbCp(2)(eta(2)-H(2))(2)](+) and the homoconjugated anion pair (CF(3)COO...H...OOCCF(3))(-) was found as a minimum. It is very likely that these ionic pairs may be intermediates in the H/D exchange between the hydride ligands and the OD group observed with the more acidic alcohols in the NMR studies.