The allyl complex di-&mgr;-chloro-bis

The title compound, di-&mgr;-chloro-bis[(2,3,4-eta)-ethyl 6, 6-dimethyl-5-oxohept-2-enoato]palladium(II), [Pd(2)Cl(2)(C(11)H(17)O(3))(2)], is a binuclear chloro-bridged palladium allyl complex that was obtained serendipitously From the reaction of 6,6-dimethyl-2-hepten-4-ynoate with Na(2)PdCl(4) in water-containing alcohol. The allyl group is substituted with an ester and a tert-butylcarboxy group. The dimeric molecules link via C-H.O contacts into a two-dimensional network parallel to the bc plane.

Chlorobis(triphenylphosphine)nickel(I) tetrahydrofuran solvate and an unsolvated trigonal phase of chlorotris(triphenylphosphine)nickel(I)

In [NiCl(C(18)H(15)P)(2)].C(4)H(8)O, the Ni atom is coordinated by three ligands in a distorted trigonal-planar configuration, with a P-Ni-P angle of 111.52 (2) degrees. In [NiCl(C(18)H(15)P)(3)], there are three independent molecules in the asymmetric unit, with each Ni-Cl bond on a crystallographic threefold rotation axis. Each Ni centre is tetrahedrally bound. The Ni atoms in both compounds have a d(9) configuration and a formal oxidation state of Ni(I). A comparison is made between the form of [NiCl(PPh(3))(3)] presented here and that of a known toluene solvate.

(2R,3R,5R)-2-

The molecular structures of two chiral cyclohexanones based on R-(-)-carvone, C(17)H(26)O(3), (I), and C(17)H(23)NO, (II), are reported here. The six-membered ring in (I) is in a chair conformation with the two fused five-membered rings of the furofuranyl substituent in a cis configuration. Compound (II) contains a decalin group; one ring has the chair form whilst the other is in a half-boat conformation. Both products have been characterized spectroscopically, however, neither NMR nor IR results could prove the stereochemistry at each chiral centre unambiguously. The crystal analyses were used to examine conformational properties of the compounds.

Organoplatinum crystals for gas-triggered switches

Considerable effort is being devoted to the fabrication of nanoscale devices. Molecular machines, motors and switches have been made, generally operating in solution, but for most device applications (such as electronics and opto-electronics), a maximal degree of order and regularity is required. Crystalline materials would be excellent systems for these purposes, as crystals comprise a vast number of self-assembled molecules, with a perfectly ordered three-dimensional structure. In non-porous crystals, however, the molecules are densely packed and any change in them (due, for example, to a reaction) is likely to destroy the crystal and its properties. Here we report the controlled and fully reversible crystalline-state reaction of gaseous SO2 with non-porous crystalline materials consisting of organoplatinum molecules. This process, including repetitive expansion-reduction sequences (on gas uptake and release) of the crystal lattice, modifies the structures of these molecules without affecting their crystallinity. The process is based on the incorporation of SO2 into the colourless crystals and its subsequent liberation from the orange adducts by reversible bond formation and cleavage. We therefore expect that these crystalline materials will find applications for gas storage devices and as opto-electronic switches.

Long-range sigma-pi interactions in tetrahydro-4H-thiopyran end-capped oligo(cyclohexylidenes). Photo-electron spectroscopy, ab initio SCF MO calculations, and natural bond orbital analyses

Long-range sigma-pi interactions in tetrahydro4H-thiopyran end-capped oligo(cyclohexylidenes) were identified by He(I) photoelectron spectroscopy (PES) and ab initio RHF/6-31G* calculations. The vertical ionization energies Ivj of the highest occupied molecular orbitals (MO's) were assigned using Koopmans' theorem (Iv,j = -epsilonj) and by correlation with the ionizations of related reference compounds. The experimental (PES) and theoretical (RHF/6-31G*) results are in good agreement. For tercyclohexylidene derivatives which contain two nonconjugated pi-bonds splittings deltaIv,j of the pi-bands in the range from approximately 0.5 to 0.7 eV (delta-epsilonj approximately 0.6 to 0.9 eV). For the bi- and tercyclohexylidene compounds containing two sulfur atoms at their alpha- and omega-end positions the pi-type sulfur lone pair bands [Lppi(S)] split significantly by deltaIvj approximately 0.3 to 0.4 eV (delta-epsilonj approximately 0.3 to 0.4 eV), i.e. sigma-pi interactions over distances of ca. 8 and 12 A, respectively, occur. The magnitude of the interactions and the observed splittings are independent of the anti and syn conformations of the oligo(cyclohexylidene) hydrocarbon skeletons. RHF/6-31G* Natural Bond Orbital analyses reveal that the Hax-C-C-Hax precanonical MO's (PCMO's) centered on the cyclohexyl-type rings are paramount for the relay of the through-bond sigma-pi interactions; no through-space sigma-pi interactions were identified.

Hydrogenation of

The course of the hydrogenation of [5]- and [6]metacyclophane (1b and 1c) and their thermochemistry is described. Both compounds are hydrogenated rapidly (within 10 s) to furnish the bridgehead olefins 13b and 12c. The accompanying hydrogenation enthalpies are -220 and -141 kJmol(-1), respectively. Strain energies (SE) and olefinic strains (OS) of a number of bridgehead olefins have been evaluated by DFT calculations; it was concluded that 13b belongs to the class of hyperstable olefins which correlates nicely with its reluctance to undergo hydrogenation. By combining experimental hydrogenation enthalpies and DFT calculations, SE of 187 and 121 kJmol(-1) were derived for 1b and 1c.

Diagnostic organometallic and metallodendritic materials for SO2 gas detection: reversible binding of sulfur dioxide to arylplatinum(II) complexes

A series of square-planar platinum(II) complexes of the N,C,N'-terdentate-coordinating monoanionic "pincer" ligand, [PtX(4-E-2,6-[CH2NRR']2-C6H2](X=Cl, Br, I, tolyl; R, R'=Et, Me; E=H, OH, OSiMe2tBu) has been prepared. In the presence of sulfur dioxide, these complexes spontaneously adsorb this gas to form penta-coordinated adducts. Solid-state crystal-structure analyses of the SO2 adducts 8c (X=I, R=R=Me, E=OSiMe2tBu) and 11 (X=Cl, R=R'=Me, E=OH) show a square-pyramidal geometry around the metal center with SO2 in the apical position. Most interestingly. the adduct 11 forms similar Pt-Cl... H-O hydrogen-bonded alpha-type networks as the corresponding SO2-free complex 5. The conservation of the supramolecular information (hydrogen-bonded self-assembly) throughout a reaction (SO2 adsorption) is unprecedented in crystal engineering. Adduct formation in the solid state or in solution is fast and reversible and is indicated by a characteristic color change of the material from colorless to bright orange. Since facile methods have been developed to remove SO2 from the adducts and to regenerate the square-planar starting complexes, these complexes fulfill several essential prerequisites of sensor materials for repeated diagnostic SO2 detection. The platinum sensors have been found to be highly selective for sulfur dioxide and particularly sensitive for submilimolar to molar gas quantities. Their response capacity is tuneable by electronic and steric modifications of the ligand array by introduction of, for example, different substituents on the nitrogen donors. The periphery of dendrimers is shown to be an appropriate macromolecular support for anchoring the detection-active sites, thus allowing full recovery of the sensor materials for repeated use. By using this concept, metallo-dendrimers 3 and 15 have been prepared. Owing to the dendritic connectivity, these sensors are suitable for repetitive qualitative and quantitative detection of small amounts of SO2.

Aminosulf(ox)ides as ligands for Iridium(I)-catalyzed asymmetric transfer hydrogenation

A new class of efficient catalysts was developed for the asymmetric transfer hydrogenation of unsymmetrical ketones. A series of chiral N,S-chelates (6-22) was synthesized to serve as ligands in the iridium(I)-catalyzed reduction of ketones. Both formic acid and 2-propanol proved to be suitable as hydrogen donors. Sulfoxidation of an (R)-cysteine-based aminosulfide provided a diastereomeric ligand family containing a chiral sulfur atom. The two chiral centers of these ligands showed a clear effect of chiral cooperativity. In addition, aminosulfides containing two asymmetric carbon atoms in the backbone were synthesized. Both the sulfoxide-containing beta-amino alcohols and the aminosulfides derived from 1,2-disubstituted amino alcohols gave rise to high reaction rates and moderate to excellent enantioselectivities in the reduction of various ketones. The enantioselective outcome of the reaction was favorably affected by selecting the most appropriate hydrogen donor. Enantioselectivities of up to 97% were reached in the reduction of aryl-alkyl ketones.

A Robust, Environmentally Benign Catalyst for Highly Selective Hydroformylation.

By a sol-gel process a rhodium complex containing a diphosphane with a large natural P-Rh-P bite angle is covalently anchored in a silica matrix (see picture). The immobilized catalyst is a very selective hydroformylation catalyst that is completely and conveniently separated from the product and can be reused in numerous cycles.

Olefin Cycloadditions of the Electrophilic Phosphinidene Complex

Highly strained methylenephosphiranes are formed in the reaction of the new electrophilic phosphinidene complex [iPr(2)N-P=Fe(CO)(4)] with allenes. Remarkably, reaction with diallenes at 0 degrees C also leads to a phosphirane, which rearranges upon warming to room temperature to a bis-isopropylidenephospholene (see scheme).

Design of Novel Hexametallic Cartwheel Molecules from Persubstituted Benzene Compounds.

The cartwheel complexes A are novel, nano-sized hexametallic species available from persubstituted benzenes C(6)[3,5-(CH(2)Y)(2)C(6)H(3)] (Y=NMe(2), P(O)Ph(2), PPh(2), SPh). The molecular structure of A (Y=SPh, ML(n)=PdCl) shows C(3) symmetry with adjacent radial Pd-Pd separations of 7.339(2) and 8.006(2) Å and a diametrically opposed Pd-Pd separation of 15.340(2) Å. Because of their size hexametallic species such as A are potential homogeneous catalysts in organic reactions which can be recovered by nanomembrane filtration techniques.