Search

Two different methacrylate modified barium-titanium and barium-based oxoclusters are formed by reacting methacrylic acid with barium-titanium and barium-zirconium double alkoxides, respectively. The presence of methacrylate groups surrounding the two polynuclear compounds are exploited for the embedding of the oxoculster in inorganic-organic hybrid materials.

X-ray and neutron diffraction are used to examine the single crystals of [h.sub.8]-naphthalene over a wide range of temperatures and the anisotropic displacement parameters (ADPs) of carbons and hydrogens are measured. A considerable reduction is seen in the ratio of number of adjustable parameters/numbers of independent observations by applying the treatment to multi-temperate diffraction data.

A series of cationic and dicationic Ru-arene complexes with Binap (1a) and MeO-Biphep (1b) have been prepared. [sup.13]C NMR studies are shown to be useful in connection with recognising the 6e-bonding mode of 1a and 1b in the dications [Ru(1a or 1b)([[eta].sup.6]-arene)][(Sb[F.sub. 6]).sub.2] (8, 9). Reaction of 8, 9 with: (a) ([Bu.sub.4]N)([Ph.sub.3] Si[F.sub.2]) leads to a cyclometallated product which arises via P--C bond breaking and P--F bond making; (b) methanol provides a straightforward synthesis of the corresponding hydrides. [sup.13]C NMR p-cymene chemical shifts are reported. Key words: P--C bond cleavage, 6e donors, cyclometallation, hydrides, [sup.13]C NMR.

Single-crystal neutron diffraction method is used to investigate the crystal structure of N-methylacetamide at two temperature, 250 and 276 K. Result reported no evidence for proton transfer along the N-H...O hydrogen bond at either temperatures, but a short intramolecular contacts between the amide hydrogen atom and those on both neighboring methyls is found, which may affect the vibrational properties of the respective molecular groups.

Issues concerning the examination of the intramolecular dihydrogen/hydride exchange in the iridium complexes IrXH2(eta squared-H2)(PR3)2 (X=Cl, Br, I) using density functional theory are discussed. Calculations indicate that the oxidative-addition/reductive-elimination route is the preferred mechanism for this process.

The molecular and electronic structures of (Zn4(mu4-S)(mu-S2As(CH3)2)6) of the novel Cd complex (Cd4(mu4-S)(mu-S2As(CH3)2)6) have been studied with x-ray diffraction measurements, electrospray mass and UV absorption spectrometries and density functional computations. Results indicate that the unit cell has four independent molecules and four solvent molecules. Each independent unit has a central mu4-S coordinated to four Zn ions.

A study was undertaken to analyze the dinitrogen complex of zirconium [P2N2]Zr(mu-eta2-N2)Zr[P2N2] wherein P2N2 = PhP(CH2SiMe2NSiMe2CH2)2PPh reacted with 1-4 atm of H2 in toluene solution to form the [P2N2]Zr(mu-eta2-N2H)(mu-H)Zr[P2N2] (2) having an N-H bond and a bridging hydride. Results of the neutron studies and density functional theory revealed that the dinuclear dihydrogen complex, [P2N2]Zr(mu-eta2-N2)(mu-eta2-H2)Zr[P2N2], was an artifact of the X-ray analysis while solution 2 was identical to the solid-state structure.

A study was conducted on the reaction of [Pt(mu-PBut2)(H)(PBut2H)]2 (1) with tetracyanoethylene or other oxidants yielding the unsaturated cation [Pt2-(mu-PBut2)2(H)(PBu(super t)2H)2]+ (2+) which is formally obtained from the abstraction of a hydride ligand from complex 1. Crystallographic analysis showed that the molecular structure of cation 2+ was similar to the dipalladium cation [Pd2(mu-PBut2)(mu-PBu(super t)2H)(PBu(super t)2H)2]+ (4+). However, cations 2+ and 4+ differed significantly in the position of a single proton.

Hydrotris(pyrazolyl)borato compounds of iridium(I) are of particular interest, as some easily generate transient species activating C-H bonds. There is additional interest in the type (Tpsuper3R,4R,5RMLsub2) compounds, relating to the variable denticity of the Tp-type ligands. The preparation and characterization of (TPsuper3R,4R,5RIr(COD)) complexes is reported, with particular focus on their hydrolytic stabilities, static structures and equlibria between linking four- and five-coordinate species containing etasuper2- and etasuper3-bonded Tp-type ligands.

CS2 complex (Pd2(muPtBu2)(mu,eta2:eta2-CS2)(PPh3)2)BF4, BF4, reacted with Me4NI, yielding the neutral tetranuclear Pd(I) derivative Pd4(mu-PtBu2)2(mu4-CS2)(PPh3)2I, characterized by single crystal X-ray diffraction. The unusual molecular structure, with a formally hexacoordinate carbon atom, is explained on the basis of fragment MO considerations and EHMO models. The stepwise reaction proceeds with a fast substitution of CS2 by the iodide ion.

The MeO-BIPHEP was used in both the Pd-catalyzed enantioselective Heck and allylic alkylation reactions, and the new solid-state and solution structural chemistry for Ru and Pd complexes. Results reveal that the 3,5-di-tert-butyl substituents develop the enantioselectivity based on the Heck reaction and the allylic alkylation. Findings suggest that the entire chiral array is increasingly rigid with expected restricted rotations.

The conversion of the Pt(II) dinuclear derivative Pt2(mu-P(t-Bu)2)2(H)2(p(t-BU)2H)2 by carbon monoxide into the new Pt(super I)(sub 2)Pt(super II) triangulo cluster Pt3(mu-P(t-BU)2)3(H)(CO)2 in a stepwise reaction is reported. The triangulo cluster is formed through the slow CO-induced reductive elimination of P(t-BU)2H from the dinuclear derivative, affording an intermediate equilibrium mixture of the mononuclear Pt(0) carbonyl derivative Pt(P(t-Bu)2H)2(CO)2 and the carbonyl-bridged triangulo derivative Pt3(P(t-BU)2H)3(mu-CO)3.

X-ray crystallographic studies enable the determination of the structures of trans-(a2PtL(LH))+ (a = NH3 or CH3NH2; L = 2-pyridonate) and trans-(a2PtL2CuL2Pt(a2))2+ complexes prepared by the interaction of exocyclic oxygens of the L with protons or Cu(II) ions, respectively. Trans-(a2PtL(LH))+ has an extraordinary hydrogen bond between two oxygen of L and LH. All the three metals in trans-(a2PtL2CuL2Pt(a2))2+ exhibit distorted coordination geometry.

Reaction of zinc halides with dimethyl(aminomethyl)phosphine oxide (DMAO) produces polymeric compounds of the composition ZnX2(DMAO) (X = Cl, Br, I). The nature of the halide, reagent ratio and the order of the addition of the reagents influence the compositions of the complex. X-ray crystallographic studies reveal the presence of Zn-O-P-C-N-Zn-chains in ZnBr2(DMAO) and ZnI2(DMAO). Two bromide ions complete the Pseudoocatahedral coordination at zinc in the bromocomplex, while in the iodo complex, one iodide and a monodentate nitrogen-bonded DMAO molecule complete the coordination at zinc.

Structural studies of OsH5L(sub 3)(super +) (L=PMe2Ph) by neutron diffraction experiments reveal the compound to be a dodecahedral pentahydride with H/H separations as short as 1.49 angstroms. Labeling studies help determine the mechanism of olefin hydrogenation and the hydroformylation reactions of OsH5(sub 3)(super +). Variable-temperature spectroscopic studies and X-ray diffraction help determine the structure of OsH(C2H4)2L(sub 3)(super +). Extended Huckel calculations reveal the absence of trans influence on Os-C bond lengths in the olefin cation.

Single crystal neutron diffraction analysis of (Ru(H...H)(C5Me5)(dppm))BF4 shows that the crystal belongs to the monoclinic space group p2(1). H-H distance in the dihydrogen ligand is 1.10(1) angstrom. Decrease in 1J(H,D) coupling in the Ru(H-D) isotopomer with increasing temperatures suggests a lengthening of H-D bond at higher temperatures. Orientation of the dihydrogen bond parallel to the C5Me5 ligand inhibits rotation of the H-H unit.

1H and 15N NMR spectroscopy helped study the interactions between three-center N-H---Pt bonds, with respect to spin-spin couplings. The interactions between coordinated and uncoordinated three-center bonds, observed in cationic complexes that were generated from cyclometalated ligands, were weak. X-ray diffraction revealed the cyclometalated solid-state complex structure.

The presence of the binuclear cation (Ru2(mu-Cl)3(ETP)2)+ (ETP = bis(2-(diphenylphosphino)ethyl)phenylphosphine) and Cl- in a compound of composition RuCl2(ETP) is analyzed. The cation exists as a combination of staggered and eclipsed isomeric forms in CDCl3. Single crystals grown from CH2Cl2/CHCl3/PhMe have only an eclipsed form.

Gold cations reacted with (Ruh4(triars)) or (RuH(BH4)(triphos)) to produce ruthenium-gold clusters of varying structures. The presence of a RuAu3 tetrahedron, with the ruthenium atom capped by triphos, and one PPh3 controlling each gold atom were observed in the X-ray crystal structure of ((triphos)RuH3(Au(PPh3))3) (PF6)2. A single Ru-Au2 face had a hydride ligand in a bridging place above it, despite the displacement of the ligands in the direction of the Ru-Au edge. A tetrahedron of RuHAu2 revealed the static compositions of the complexes, which were fluxional in solution.

An economical source of hydrogen forms a metal hydride under wild conditions when the hydrogen is split heterolytically. The splitting is categorized by the presence of molecular H2 to be Bronsted-acidic. Coordinated H2 is known to quickly dissociate, disallowing the intracellular molecular rearrangement in d octahedra. Hydrogen binds with five-coordinate substructures, varying in equilibrium constants. The varying lengths of the bonding H2 are caused by a reduction in the strength of the sigma bond. The reducing power of the bonding fragments also vary.

Hydride ligands in cationic clusters were studied in terms of their structural and bonding characteristics. These included (triphos)MH2(Au(PPh3))3 2+ triphos = CH3C(CH2PPh2)3; M = Rh and Ir and (triphos)RuH3(Au(PPh3)3)2+. Spectral analysis showed that the phosphorus atoms of the triphos ligands and the PPh3 molecules are inequivalent while the corresponding donors in the trihydrido complex are equivalent. Mossbauer spectra showed distinct assymetry of measured doublet patterns which could possibly be due to the presence of overlapping doublets.

X-ray diffraction and nuclear magnetic resonance spectroscopy analyses were conducted on the chiral P,N-bidentate complexes of palladium(II) and platinum(II). The results identified the differences in the structures of the complexes both in solution and in solid-state conditions. Molecular mechanics calculations were also used to further characterize the complexes. In addition, the three-dimensional geometry of the complexes were readily obtained from nuclear Overhauser effects.

A study was done on the reactions of silver ions with two equivalent of the hydrides which produce trinuclear complex cations. The crystal structure of (PEt3)2(C6Cl5)Pt(mu-H)Ag(mu-H)Pt(C6Cl5)(PEt3)2(CF3SO3) were also given and the silver ion in the complex was found to be linear with two hydride ligands. The angle of H-Ag-H is ca. 152 degrees with significant occurrence of direct interactions between Pt and Ag.

The barrier to rotation of the complexes (MH(eta2-H2)PP3)1+, where M = Fe or Ru and which are crystallized as BPh4 salts, is investigated to derive evidence for the intensity of the back-bonding interaction. Results show that Ru's binding strength for the dihydrogen ligand is not consistent with its expected order in the periodic table. This is the result of the better back-donation properties of the Fe center as compared to Ru.

The iridium-gold hydride (triphos Ir H C2H4 Au PPh3)PF6 was prepared from the reaction of (Au THF PPh3)PF6 with a THf solution of (triphos)Ir(H)(C2H4). The digold adduct (triphos Cl Ir mu-H Au2 PPh3 2)PF6, on the other hand, was produced from AuCl(PPh3) and the hydride. Likewise, (triphos Cl Ir mu-H Au2 AsPh3 2)PF6 was afforded by the substitution of AuCl(AsPPh3) for AuCl(PPh3). (Triphos Cl Ir mu-H Au2 PPh3 2)PF6 possesses a crystal structure with a discrete (triphos Cl Ir mu-H Au2 PPh3 2)1+ cation, a PF6 anion and a clathrated THF molecule.

A single-crystal neutron diffraction study of (CO)5Re(mu-H)Mn(CO)4Mn(CO)5 was undertaken to probe the geometry of the Re(mu-H)Mn bridge. The complex is characterized by a relativelyweak Re-Mn bond and a hydride ligand asymmetrically positioned between the two metal atoms. (CO)5Re(mu-H)Mn(CO)4Re(CO)5 was found to have cocrystallized with the complex. The presence of this impurity was signified by an additional singlet at delta -19.24 in the 1H NMR spectrum assigned to the bridging hydrideof the major product.

The reactions of (tmeda)Pt(1-MeU)2, where tmeda = N,N,N'N'-tetramethylethylenediamine and 1-MeU = methyluracilate-N(super 3) with electrophiles were investigated via 1H NMR spectroscopy. The 1H NMR spectrum of (tmeda)Pt(1-MeU)2 was found to exhibit two sets of H5 and H6 resonances of the 1-MeU ligand which are attributed to two rotamers with Head-head and head-tail arranged 1-MeU rings. The xcompound (tmeda Pt 1-MeU 2 Cu 1-MeU 2 Pt tmeda)(ClO4)2 was produced from the crystallization of the former in the presence of Cu(ClO4)2.

Metal clusters with trigonal-bipyramidal structures of the type (HgX 2 Pt3 u2-CO 3 L3) were studied using nuclear magnetic resonance spectroscopy and X-ray crystallographic analysis. These complexes were formed from the reaction of (Pt3 u2-CO 3 L3) with mercury halides. The results revealed that the complexes in solution existed as monomers but in the solid state they take a dimeric structure with two Hg2Pt3 units.

The dihydrogen complex Ru(H2)2H2(P(C5H9)3)2 has been investigated, via ab initio accelerated molecular dynamics, to elucidate the H ligands dynamics and possible reaction paths for H2/H exchange. We have characterized the free energy landscape associated with the H atoms positional exchange around the Ru centre. From the free energy landscape, we have been able to estimate a barrier of 6 kcal mol−1 for the H2/H exchange process. We have also observed a trihydrogen intermediate as a passing state along some of the possible reaction pathways. [ABSTRACT FROM AUTHOR]