RESUMEN
Treatment of NaW2Cl7(THF)5 with 4 equiv of (t)Bu3SiNHLi afforded the C2 W(III) dimer [((t)Bu3SiNH)2WCl]2 (1, d(W triple bond W) = 2.337(2) A), which is a rare, primary amide M2X4Y2 species. Its degradation provided evidence of NH bond activation by the ditungsten bond. Addition of 2 equiv of (t)Bu3SiNHLi or TlOSi(t)Bu3 to 1 yielded H2 and hydride ((t)Bu3SiN)2((t)Bu3SiNH)WH (2, d(WH) = 1.67(3) A) or ((t)Bu3SiN)2((t)Bu3SiO)WH (3). Thermolysis (60 degrees C, 16 h) of 1 in py gave ((t)Bu3SiN)2WHCl(py) (4-py, 40-50%), ((t)Bu3SiN)2WCl2(py) (6-py, 10%), and ((t)Bu3SiN)2HW(mu-Cl)(mu-H)2W(NSi(t)Bu3)py2 (5-py2, 5%), whereas thermolysis in DME produced ((t)Bu3SiN)2WCl(OMe) (7, 30%), ((t)Bu3SiN)2WCl2 (6, 20%), and ((t)Bu3SiN)2HW(mu-Cl)(mu-H)2W(NSi(t)Bu3)DME (5-DME, 3%). Compound 7 was independently produced via thermolysis of 4-py and DME (-MeOEt, -py), and THF and ethylene oxide addition to hydride 2 gave ((t)Bu3SiN)2((t)Bu3SiNH)WO(n)Bu (8) and ((t)Bu3SiN)2((t)Bu3SiNH)WOEt (9), respectively. Dichloride 6 was isolated from SnCl4 treatment of 1 with the loss of H2. Sequential NH bond activations by the W2 core lead to "((t)Bu3SiN)2WHCl" (4) and subsequent thermal degradation products. Thermolysis of 1 in the presence of H2C=CH(t)Bu and PhC triple bond CPh trapped 4 and generated ((t)Bu3SiN)2W((neo)Hex)Cl (10) and a approximately 6:1 mixture of ((t)Bu3SiN)2WCl(cis-CPh=CPhH) (11-cis) and ((t)Bu(3)SiN)2WCl(trans-CPh=CPhH) (11-trans), respectively. Thermolysis of the latter mixture afforded ((t)Bu3SiNH)((t)Bu3SiN)WCl(eta2-PhCCPh) (12) as the major constituent. Alkylation of 1 with MeMgBr produced ((t)Bu3SiN)2W(CH3)2 (13), as did addition of 2 equiv of MeMgBr to 6. X-ray crystal structure determinations of 1, 2, 5-py2, 6-py, 11-trans, and 12 confirmed spectroscopic identifications. A general mechanism that features a sequence of NH activations to generate 4, followed by chloride metathesis, olefin insertion, etc., explains the formation of all products.
RESUMEN
The insertion of H2C=CHX (X = OR; R = Me, Et, nPr, (i)Pr, CH=CH2, Ph) into (tBu3SiO)3TaH2 (1) afforded (tBu3SiO)3HTaCH2CH2X (2-CH2CH2X), which beta-X-eliminated to give ethylene and (tBu3SiO)3HTaX (3-X). beta-X-elimination rates were inversely proportional to the size of R. An X-ray crystallographic study of (tBu3SiO)3HTaCH2CH2O(t)Bu (2-CH2CH2O(t)Bu) revealed a distorted trigonal bipyramidal structure with an equatorial plane containing the hydride and a -CH2CH2O(t)Bu ligand with a staggered disposition. erythro- and threo-(tBu3SiO)3HTaCHDCHDOEt (2-CHDCHDOEt) are staggered in solution, according to (1)H NMR spectroscopic studies, and eliminated cis- and trans-HDC=CHD, respectively, helping verify the four-centered transition state for beta-OEt-elimination. When X = F, Cl, or Br, 2-CH2CH2X was not observed en route to 3-X, signifying that olefin insertion was rate-determining. Insertion rates suggested that substantial positive charge on the substituted carbon was incurred. The reactivity of other H2C=CHX with 1, and a discussion of the observations and their ramifications on the incorporation of functionalized monomers in Ziegler-Natta copolymerizations, are presented.
RESUMEN
Treatment of ((i)PrO)4Ti with 2,7-dihydroxynaphthalene at 100 degrees C afforded the one-dimensional ladder [cis-Ti(mu(2,7)-OC10H6O)2py2]n (1: C30H22N2O4Ti, orthorhombic, P2(1)2(1)2(1), a = 9.866(2) A, b = 15.962(3) A, c = 16.223(3) A, Z = 4), in pyridine, and the stacked ladder, two-dimensional [Ti(mu(2,7)-OC10H6O)2(4-picoline)2.(4-picoline)(0.5)]n (2: C70H59N5O8Ti2, triclinic, P1, a = 10.814(2) A, b = 16.785(3) A, c = 18.020(4) A, alpha = 93.88(3) degrees, beta = 107.31(3) degrees, gamma = 108.77(3) degrees, Z = 2), in 4-picoline. A disruption of intramolecular edge-to-face and intermolecular face-to-face pi-stacking interactions in 1 by the Me group of the 4-picoline causes the structural change to 2. These derivatives and related two- and three-dimensional covalent metal organic networks (CMON) were assayed for ethylene and propylene polymerization activity via the addition of methylaluminoxane. CMON are mediocre Ziegler-Natta catalysts that generate polydisperse, linear polyethylene and atactic polypropylene. The data are best accommodated by viewing the degradation of CMON into numerous active sites of differing activity.
RESUMEN
Thermolysis of (iPrO)4V and 2,6-dihydroxynaphthalene in 4-(3-phenylpropyl)pyridine afforded [mer-V(mu 2,6-OC10H6O)1.5(4-(3-phenylpropyl)py)3]n (1; C57H54N3O3V, triclinic, P1, a = 10.450(2) A, b = 14.098(3) A, c = 16.765(3) A, alpha = 100.09(3) degrees, beta = 103.85(3) degrees, gamma = 103.08(3) degrees, Z = 2) and oxidation product bis-2,6-dinaphthol. Paramagnetic (S = 1) 1 adopts a bricklike motif of aryldioxide-connected V(III) centers whose channels are filled with the bound 4-(3-phenylpropyl)py. A similar procedure involving (iPrO)3VO provided the linear chain [(mu 2,6-OC10H6O)(4-(3-phenylpropyl)py)2VO]n (2; C38H36N2O3V, monoclinic, P2(1)/c, a = 10.6172(2) A, b = 9.4477(3) A, c = 31.8129(8) A, beta = 95.20(3) degrees, Z = 4). Interchain pyridine ring-edge to phenyl-face interactions generate a sheet of like-oriented oxos, but adjacent sheets are oriented in opposition so that no net dipole exists. Another 1-dimensional chain, [(mu 1,4-OC6H4O)(py)2VO]n (3; C16H14N2O3V, monoclinic, P2(1)/c, a = 8.377(2) A, b = 16.675(3) A, c = 11.061(2) A, beta = 103.91(3) degrees, Z = 4), was prepared by heating (iPrO)4V and hydroquinone in pyridine. Pyridines of adjacent chains interpenetrate to form a sheet, but oxos in adjacent chains are now in opposition.
RESUMEN
Treatment of M(OiPr)4 (M = Ti, V) and [Zr(OEt)4]4 with excess 1,4-HOC6H4OH in THF afforded [M(OC6H4O)a(OC6H4OH)3.34-1.83a(OiPr)0.66-0.17a(THF)0.2]n (M = Ti, 1-Ti; V, 1-V, 0.91 < or = a < or = 1.82) and [Zr(1,4-OC6H4O)2-x(OEt)2x]n (1-Zr, x = 0.9). The combination of of 1-M (M = Ti, V, Zr) or M(OiPr)4 (M = Ti, V), excess 1,4- or 1,3-HOC6H4OH, and pyridine or 4-phenylpyridine at 100 degrees C for 1 d to 2 weeks afforded various 2-dimensional covalent metal-organic networks: [cis-M(mu 1,4-OC6H4O)2py2] infinity (2-M, M = Ti, Zr), [trans-M(mu 1,4-OC6H4O)2py2.py] infinity (3-M, M = Ti, V), solid solutions [trans-TixV1-x(mu 1,4-OC6H4O)2py2.py] infinity (3-TixV1-x, x approximately 0.4, 0.6, 0.9), [trans-M(mu 1,4-OC6H4O)2(4-Ph-py)2] infinity (4-M, M = Ti, V), [trans-Ti(mu 1,3-OC6H4O)2py2] infinity (5-Ti), and [trans-Ti(mu 1,3-OC6H4O)2(4-Ph-py)2] infinity (6-Ti). Single-crystal X-ray diffraction experiments confirmed the pleated sheet structure of 2-Ti, the flat sheet structure of 3-Ti, and the rippled sheet structures of 4-Ti, 5-Ti, and 6-Ti. Through protolytic quenching studies and by correspondence of powder XRD patterns with known titanium species, the remaining complexes were structurally assigned. With py or 4-Ph-py present, aggregation of titanium centers is disrupted, relegating the building block to the cis- or trans-(ArO)4Tipy2 core. The sheet structure types are determined by the size of the metal and the interpenetration of the layers, which occurs primarily through the pyridine residues and inhibits intercalation chemistry.
RESUMEN
Ultraviolet irradiation (351, 364 nm) of the n-type semiconductor TiO(2) as the single crystal electrode of an aqueous electrochemical cell evolves O(2) at the TiO(2) electrode and H(2) at the Pt electrode. The gases are typically evolved in a two: one (H(2):O(2)) volume ratio. The photoassisted reaction seems to require applied voltages, but values as low as 0.25 V do allow the photoassisted electrolysis to proceed. Prolonged irradiation in either acid or base evolves the gaseous products in amounts which clearly demonstrate that the reaction is catalytic with respect to the TiO(2). The wavelength response of the TiO(2) and the correlation of product yield and current are reported. The results support the claim that TiO(2) is a true photoassistance agent for the electrolysis of water. Minimum optical storage efficiencies of the order of 1% can be achieved by the production of H(2).
