The addition of HSiMe2Cl to the unsaturated compound Cp*(iPr3P)RuCl gives an unstable adduct which, according to NMR (J(H-Si)= 33.5 Hz), X-ray crystal structure and DFT evidence, is a silane sigma-complex Cp*(iPr3P)Ru(Cl)(eta2-HSiMe2Cl) supported by an unprecedented, simultaneous inter-ligand RuCl...SiCl hypervalent interaction between the chloride ligand on ruthenium and the SiMe2Cl group.

[Structure: see text]. A DFT calculation study of the addition reaction between molecular bromine and the number of symmetrical or unsymmetrical substituted alkynes 1 (R-CC-R'), where R = R' = H (1a), Me (1b), t-Bu (1c), or Ph (1d), or R = H and R' = Me (1e), t-Bu (1f), or Ph (1g), was performed. Two possible reactions were checked: (a) the reactions suitable for the gas-phase interactions, which start from a 1:1 Br2-alkyne pi-complex and do not enter into a 2:1 Br2-alkyne pi-complex; and (b) the processes passing through a 2:1 Br2-alkyne pi-complex, which look more realistic for the reactions in solutions. The structures of the starting reactants and the final products as well as the possible stable intermediates have been optimized. The transition states of the predicted process have been found. Both trans- and cis-dibromoalkenes (2 and 3) may ensue without the formation of ionic intermediates from a pi-complex of two bromine molecules with the alkyne (solution reactions). The geometry around the double bond forming in dibromoalkenes strongly depends on the nature of the substituents at the triple bond. The "cluster model" was also used for the prediction of solvent influence on the value of the activation barrier of the but-2-yne (1b) bromination reaction.

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.

A series of arene-ruthenium 11-vertex complexes 3-Cl-1-(η6-arene)-isonido-1,2,4-RuC2B8H9 (4a-4h) and 6-Cl-1-(η6-arene)-isonido-1,2,4-RuC2B8H9 (5a, 5b, 5f, 5g) (arene = p-xylene (a), mesitylene (b), p-cymene (c), benzene (d), toluene (e), hexamethylbenzene (f), 1,2,4,5-tetramethylbenzene (g), 1,2,4-trimethylbenzene (h)) have been obtained as isomeric mixtures 4a, 4b, 4f, 4g and 5a, 5b, 5f, 5g or, predominantly, as single isomers 4c-4e, 4h by the treatment of nido-5,6-C2B8H12 (1) with [RuCl2(PPh3)3] (2), either in the corresponding arene solvents at 80-85 °C (in the case of 4a-4e and 5a, 5b) or in the arene/1,2-dichloroethane solution under reflux (in the case of 4f-4h and 5f, 5g) in the presence of N,N,N',N'-tetramethylnaphthalene-1,8-diamine. The compounds prepared were characterized by combination of analytical, IR and multinuclear NMR data, including a crystallographic study of 4b. A possible pathway for the formation of isomeric complexes 4 and 5 is discussed.

Phosphanyl-substituted cyclopentadienes of the type [RnCp-PR((NRR2)-R-1/Cl)] (1-22) (R = Alk, Ar; R-1, R-2 = H, Alk, Ar, SiR3; RnCp = tBuCp, Me4Cp, Ind, Me(6)Ind, Flu) can be synthesised by reaction of alkyldichlorophosphanes and alkyl(amino)chlorophosphanes with alkali metal cyclopentadienides. The method used is a general one and provides high isolated yields of the target compounds. The phosphanylcyclopentadienes can easily be deprotonated by strong bases (e.g. nBuLi, PhCH2K, Ph2CHK) and the potassium salts [RnCp-PR((NRR2)-R-1)]K (25-28) are efficiently transmetallated by Me3SnCl. A subsequent reaction with TiCl4(L)2 and ZrCl4(L)(2) (L = THF, tetra-hydrothiophene, Me3P) affords new half-sandwich complexes [{Me4Cp-PtBu(NEt2)}TiCl3] (36), [{Me4Cp-PtBu(NEt2)}TiCl3] (37) and [{tBuCp-PtBu(NEt2)}TiCl3] (38) in moderate yields. The reaction of [tBuCp-PtBu(Cl)] (6) with TiCl4 in the presence of Et3N at low temperature yields the half-sandwich complex [{tBuCp-PtBu(Cl)}TiCl3] (39) quantitatively; [(Cp-PtBu(Cl)](2)CMe2] (11) reacts similarly and gives, dependent on the reagent ratio, either the homobimetallic derivative [{(Cp-PtBu(Cl)(2)CMe2}(TiCl3)(2)] (40) (1:2 ratio) or the ansa complex [((Cp-PtBu(Cl)](2)CMe2)TiCl2] (41) (1:1 ratio). The scope of this reaction could not be extended to sterically more demanding cyclopentadienyl derivatives. Treatment of [(tBuCp-PtBu(Cl)}TiCl3] (39) by LiN(H)tBu in the presence of Et3N leads to the formation of the constrained geometry complex [{tBuCp-PtBu(NtBu)}TiCl2] (42) in a high yield, All synthesised compounds were characterised by NMR spectroscopy, mass spectrometry and elemental analyses. The crystal structures of the ligand precursor [Me(6)Ind-PtBu(NHtBu)] (15) and that of [{Me4Cp-PtBu(NEt2)}TiCl3] (36) have been determined by X-ray diffractometry. The complexes described in this work are active in the MAO-mediated polymerisation of ethylene.

Reactions of Cp(NAr)NbMe2 with H2 and HSiMe2Cl are described. With H2 (1 atm) an apparent σ-bond metathesis process is accompanied by reduction to form the binuclear, metal–metal bonded species [CpNb(μ-NAr)Me]2 (NbNb=2.6852(4) Å). With HSiMe2Cl (excess) Cp(NAr)NbMeCl is obtained in quantitative yield.

[Cp-R(RPNEt2)]NI (Cp-R = t-BuC5H3, C-5(CH3)(4), indenyl, fluorenyl; M = Li, K) smoothly react with VCl3(Me3P)(2) and CrCl3(THF)(3) Systems giving paramagnetic complexes [Cp-R((RPNEt2)-P-1)]MCl2 (M = V(Me3P)(2), Cr). After reaction with MAO these complexes are active in the polymerisation of ethylene yielding highly crystalline, high-density products of high molecular weight (M-w ranging from 100 000 to 4.5 x 10(6) g mol(-1), 20 less than or equal to T-p less than or equal to 100 degreesC). Polymerisation with chromium complexes leads to the formation of polyethylenes with broad molecular weight distribution. (C) 2001 Elsevier Science B.V. All rights reserved.

Abstract The reduction behavior of the novel zirconocene dichlorides, (h5-C5Me5) (h5-C 5Me4CH2CH2ER 2) ZrCl2 (ER2 = NMe2, PMe2, PPh2) , (h5-C5Me4CH2 CH2PMe2) 2ZrCl 2, and (h5-C5Me4CH2 CH2PPh2) (h5-C 5Me4CH2CH2PMe 2) ZrCl2, together with the new types of intramolecular activation of inert C-H and C-heteroatom bonds are presented and discussed. A remarkably thermally stable zirconocene alkylhydryde type framework complex (h5-C5Me5) [h5 ,s-C5Me4CH2CH 2N (Me) CH2-]ZrH, zirconocene arylhydryde complex (h5-C5Me5) [h5 ,s-C5Me4CH2CH 2P (Ph) -o-C6H4-]ZrH, tetramethylfulvene hydride-type complexes (h5-C5Me5) [h6 :h1- (CH2C5Me3 ) CH2CH2PR2]ZrH (R = Me, Ph) and (h5-C5Me4CH2 CH2PPh2) [h6:h 1- (CH2C5Me3) CH 2CH2PMe2]ZrH are reported. The first unusually thermally stable zirconocene (h5,h1-C5Me4 CH2CH2PMe2) 2 Zr with the Zr (II) center stabilized by intramolecular coordination of two Me2P-groups is described.

A new system based on the addition of the Ni-2 Cluster to a mononuclear phthalocyanine complex with an energy stability of about 26 kcal mol(-l) was suggested for the barrierless activation of the H-H bond.

Reaction of the niobium diphosphine compound [NbCp(NAr)(PMe3)2] (Ar = 2,6-C6H3Pri2) with HSiMe2Cl gives the formally d2 silylamido derivative [NbCp{η3-N(Ar)SiMe2-H}Cl(PMe3)] 6. X-Ray diffraction and NMR studies of this compound show that it has a stretched β-agostic Si–H → Nb interaction. Reaction of the related precursor [NbCp(NAr′)(PMe3)2] (Ar′ = 2,6-C6H3Me2) with HSiMe2Cl gives an isomeric structure [NbCp{η3-N(Ar′)SiMe2-H}(PMe3)(Cl)] 7 differing from 6 in that the phosphine rather than chloride lies trans to the co-ordinated Si–H bond. A preliminary X-ray study and large 1J(Si–H) coupling constant of 116 Hz suggest that this compound is best described as an unstretched β-agostic (Si–H⋯M) d2 silylamide complex. Reaction of the tantalum diphosphine compound [TaCp(NAr)(PMe3)2] with HSiMe2Cl affords the d0 silylhydride derivative [TaCp(NAr)(H)(SiMe2Cl)(PMe3)] 8 which, according to an X-ray diffraction study and NMR data, has an interligand hypervalent interaction (IHI) between the silyl and hydride ligands. Reactions of 6 and 8 with Me3SiX (X = I, OTf) lead to the corresponding iodido and triflate derivatives [NbCp{η3-N(Ar)SiMe2-H}X(PMe3)] (X = OTf 11 or I 12) and [TaCp(NAr)(H)(SiMe2X)(PMe3)] (X = OTf 14 or I 15). Reaction of 8 with AgOTf gives [TaCp(NAr)(PMe3)2Cl]OTf 13, the crystal structure of which has been determined. Density functional theory calculations on models of the compounds 6 and 7 showed that the experimental geometries are only correctly reproduced when the phosphine ligands are adequately modelled. The extent of oxidative addition of the Si–H bond to the metal in 6 mainly depends on the basicity of the phosphine ligand. With PH3 in place of PMe3 the calculated structures are better described as silanimine-hydrido derivatives. The formation of isomeric type 6versus7 is determined by an interplay of the steric and electronic effects of the ligand environment.

The kinetic parameters of the synthesis of iso-, syndio-, hemiisotactic, and stereoblock PP in a liquid propylene using a series of ansa-metallocenes with C-1, C-2, and C-s symmetries activated by methylaluminoxane were studied. For several metallocenes, the effect of hydrogen on the activity and molecular mass characteristics of PP was assessed. The microstructure of the polymer chains, as well as the molecular mass characteristics and thermal, mechanical, and optical properties of the produced polymers, were investigated.

This review discusses the design and structure of coordination polymers derived from Ag(I) with N-donor ligands and their role in the investigation of weak non-covalent interactions in the solid state. These forces include arene–arene, metal–anion, metal–arene and metal–metal interactions. The main purpose of this review is to classify and discuss the supramolecular forces which define the overall observed structure (topology, geometry and packing arrangement) of coordination polymers by comparison of a series of structurally related compounds when one parameter of the multi-component system (choice of anion, ligand or solvent) is varied. Design criteria for one-dimensional polymers are given and discussed with respect to the fundamental importance of these compounds for understanding and further development of supramolecular synthetic strategies.

Bulk polymerization of propylene was studied over four ansa-zirconocene catalysts, viz., Me(2)SiInd(2)ZrCl(2) (1), Me2Si(4-Ph-2-Et-Ind)(2)ZrCl2 (2) (rac:meso = 1:2), Ph2C(CpFlu)ZrCl2 (3), and Me2C(3-Me-CpFlu)ZrCl2 (4), which were characterized by different symmetries (C-1, C-2, C-s). The structure of the metallocene affected the structure of PP. Upon reactions with methylaluminoxane (MAO) or triisobutylaluminum (TIBA), compounds 1-4 produced very active catalytic systems which catalyzed the polymerization to yield various structures of PP. Catalysts 1 and 2 gave isotactic PP, catalyst 3 gave syndiotactic PP and catalyst 4 gave hemiisotactic PP. Hemiiso-PP was similar in structure to amorphous PP and had no melting point. The catalytic activity of the system and molecular weight and stereospecificity of PP were studied in relation to the mode of preparation of the catalyst. Kinetic parameteres were evaluated, viz., time of insertion of the propylene molecule (0.001-0.0001 s) and the time of growth of a single PP macromolecule (3-6 s), and from these data the minimum degree of polymerization was determined. Activation energies were evaluated for the polymerization carried out over each catalyst system. Young's modulus, molecular weight and stereoregularity of the PP prepared were determined.

Reaction of [CpM(NAr)(PMe3)(2)] (M = Nb, Ta; Ar = 2,6-C(6)H(3)iPr(2)) With HSiClMe2 gives two remarkably different nonclassical Si...H...M products depending only on the identity of M; [CpTa(NAr)(H)(SiMe2Cl)(PMe3)] possesses an unusual electron-rich M-H Si interligand hypervalent interaction while [CpNb{eta(3)-N(Ar)SiMe2-H}Cl(PMe3)] is the first example of a beta-agostic silylamine Si-H...M interaction showing a "stretched" Si-H bond.

The influence of anions and intermolecular aromatic interactions on the orientation of one dimensional silver(I) co-ordination polymers has been studied. Reaction of AgX with 2,7-diazapyrene (diaz) (X=BF4- or NO3-), 1,4-bis(4-pyridyl)butadiyne (pybut) (X=BF4-, NO3-, PF6- or MeCO2-), 4,4'-bipy (X=BF4-) or 1,4-bis(4-pyridylethynyl)phenylene (pyphe) (X=PF6-) afforded products of general formula {[Ag(ligand)]X}(infinity). All of the products have been structurally characterised by single crystal X-ray diffraction confirming that they exist as one-dimensional linear chain co-ordination polymers. The arrangement of the chains with respect to each other in the solid state is discussed and evaluated in terms of the relative co-ordinating ability of the anion used and the tendency of the N-donor ligand to adopt intermolecular aromatic interactions. For the complexes of diaz the overriding force in controlling chain orientation was shown to be pi-pi interactions between diaz ligands on adjacent chains. In the case of the pybut complexes the most dominant forces were shown to be metal-anion interactions with aromatic pi-pi interactions and Ag . . . Ag interactions playing a less influential role. In the case of {[Ag(pyphe)]PF6}(infinity) Ag . . . aromatic interactions are important in the overall arrangement of adjacent chains.

In terms of the reaction-path Hamiltonian formalism, tunnelling has been found to make the major contribution to the rate constant of methane activation by the title complex at T < 270 K.

Racemic planar chiral metallocenes bis(2-methoxyethylindenyl) yttrium and lanthanum tetrahydroborates (MeOCH2CH2C9H6)2Ln(μ2-H)nBH4−n (Ln=Y, n=2 (1); Ln=La, n=3, (2)) have been stereoselectively isolated in high yield by reaction of the corresponding lanthanocene chlorides with sodium borohydride in THF at room temperature. The two complexes have been fully characterized by elemental analyses, MS, 1H NMR and IR spectra. The tetrahydroborate ion has been identified as slipped bidentate (μ2-H)2BH2 and tridentate (μ2-H)3BH ligands in 1 and 2, respectively.

In terms of the reaction-path Hamiltonian formalism, the catalytic cycle of ethylene hydrogenation by the Pd-2 cluster has been found to involve 5 reactions with 10 stationary points on the potential-energy surface.

The phosphinophosphido niobocene complex Cp2Nb(PHPh2)(PPh2) (2) was prepared by deprotonation of the cationic diphosphino complex [Cp2Nb(PHPh2)2]Cl (3). Complex 2 is thermally unstable and readily dissociates phosphine to give the ortho-metallated complex Cp2Nb(PHPhC6H4−). Crystal structure determination of 2 supported its formulation as the phosphinophosphido compound. The Nb–P(1) (phosphino) bond length is 2.524(2) Å and Nb–P(2) (phosphido) bond length is 2.610(2) Å.

Reaction of [Cp2NbBH4] with tertiary silanes HSiR3 (R-3 =(OEt)(3), Me2Ph, Me2Cl) in the presence of an amine affords monosilyl complexes [Cp2NbH2SiR3] (R-3 = (OEt)(3) (1), Me2Ph (2), Me2Cl (3)). Complex 3 was obtained as a mixture of two isomers. with the silyl ligand in the lateral (3b) and central (3a) positions. The more sterically strained isomer 3b was obtained in a slightly greater amount than 3a, signifying the presence of an additional stabilizing electronic factor. Complex 3b was shown to be a thermodynamic product of the reaction. Thermal reaction of [Cp2NbH3] with HSiMe2Cl at 50 degrees C gives initially a mixture of 3a and 3b, but under more severe conditions (at 90 degrees C) unprecedented dihydrogen elimination occurs to yield thebis(silyl) complex [Cp2NbH(SiMe2Cl)(2)]. Complexes [Cp2NbH(SiMe2X)(2)] (X = Cl (4), Ph (6)) were obtained by reaction of [Cp2NbH(C2H3Ph)] with the corresponding silanes HSiMe2X. Reduction of complex 4 by LiAlH4 gives a high yield of [Cp2NbH(SiMe2H)(2)], which reacts with [Ph3C]PF6 and Br-2.dioxane to afford bis(silyl) complexes [Cp2NbH(Si-Me2F)(2)] (8) and [Cp2NbH(SiMe2X)(2)] (9), respectively. Compounds 3b, 4, 6, 8 and 9 were studied by NMR and IR spectroscopy and X-ray diffraction analysis. The X-ray data for 3b, 4, 8 and 9, together with some reactivity trends, suggest a nonclassical nature of these complexes due to the presence of interligand interaction between the silyl and hydride ligands. The observed trends in structural parameters are different from those predicted for three-center, two-electron (3c-2e) interactions of silanes with transition metals. This new type of nonclassical bonding was rationalizedas a hypervalent interaction at the silicon centre due to the overlap of the Nb-H bonding orbital and the Si-CI antibonding orbital. The main structural trends as well as the occurrence of an Nb-H-->Si-Cl* electron density transfer were supported by natural bond orbital (NBO) analysis. The calculation results show stronger interligand interactions in the chlorosilyl complexes than in the corresponding SiH3 complexes. However, a correlation between the structural and NMR parameters for the niobocene silyl hydrides was not established because of the unfavourable influence of the quadrupolar niobium nucleus.