1,721,151 research outputs found
The reactivity and catalytic activity of bidentate indenyl-phosphine tethered complexes of rhodium and ruthenium
No full textA higher-yielding route to racemIC ligand 2-cyclohexyl-2-(3' H-I '-indenyl)ethyl diphenylphosphine has been adapted from the known route to the chiral phosphine. Protection via formation of the borane adduct allows easy handling of the air-sensitive phosphine and has improved overall yields of known complexes (l{lJl-indenyl-CH(CY) CH2PPh2)Rh(CO) and (lJ5:lJl-indenyl-CH(Cy)-CH2PPh2)RuCI(PPh3). Tetrahydroindenyl and cationic derivatives have been synthesised from the ruthenium complex and all the complexes have been tested for catalytic activity, along with (lJ5:lJl-indenyl-CH(CY) CH2CH2PPh2)RuCI(PPh3) and [(lJ5:lJl-indenyl-CH(Cy)-CH2CH2PPh2)Ru(PPh3)t[PF6r (from P. Wright). Catalytic activity was seen for the transfer hydrogenation of acetophenone, but the resulting alcohol was racemic. It was also seen for the hydrogenation of iminium tetrafluroroborate salts, though the amount of reduction seen was too small to observe a reproducible e.e. The complexes were catalytically inactive for the nucleophilic displacement of allylic acetates, the cyclopropanation of styrene and the Diels-Alder reaction between cyclopentadiene and methacrolein. It has also been shown that displacement of PPh3 from ruthenium complex (lJ5:lJl-indenyl CH(Cy)-CH2PPh2)RuCl(PPh3) with more electron-rich phosphines occurs with retention of stereochemistry at the metal centre. X-ray structures of the tetrahydroindenyl and cationic ruthenium complexes, as well as the complexes formed by phosphine displacement, have been obtained.</p
Transition metal complexes of bis(carbene)pyridine 'pincer' ligands : synthesis and reactivity
No full textA new (CNC) pmcer ligand, (2,6-bis(2,6-diisopropylphenyl)imidazol-2-ylidene)-3,5dimethylpyridine, has been synthesised. the previously reported ligand (2,6bis( 2,6-diisopropylphenyl)imidazol-2-ylidene)pyridine, (CNC) pincer complexes of transition metals across the from titanium to iridium, have been synthesised, fully characterised and investigated. NHCs, trialkylphosphines and imines as canied out. complexes of (CNC) and (PNP) were better a-donors than tpJI,;TP) ligands, in complexes of (CNC), (PNP) and (NNN) better a-donors, contrary to literature reports. keeping ligands A comparison of the cr-dlon:ltlnlg nroDlerties part of pincer ligands ligands revealed to coordinated vinyl groups have been observed (CNC) ligands. Proposed mechanisms indicate the to the CNHC followed by base-catalysed thougflt the latter occurs via a 4-membered nitrogenbinding mode for NnCs also been un:suullrated backbone of an imidazol-2-ylidene ring bonds in an 172 is centre.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Phosphine and diphosphine complexes of silicon(IV) halides
No full textThe reaction of SiX4 (X = Cl or Br) with PMe3 in anhydrous CH2Cl2 forms trans-[SiX4(PMe3)2], while the diphosphines, Me2P(CH2)2PMe2, Et2P(CH2)2PEt2, and o-C6H4(PMe2)2 form cis-[SiX4(diphosphine)], all containing six-coordinate silicon centers. With Me2PCH2PMe2 the product was trans-[SiCl4(?(1)-Me2PCH2PMe2)2]. The complexes have been characterized by X-ray crystallography, microanalysis, IR, and multinuclear ((1)H, (13)C{(1)H}, and (31)P{(1)H}) NMR spectroscopies. The complexes are stable solids and not significantly dissociated in nondonor solvents, although they are very moisture and oxygen sensitive. This stability conflicts with the predictions of recent density functional theory (DFT) calculations (Wilson et al. Inorg. Chem. 2012, 51, 7657-7668) which suggested six-coordinate silicon phosphines would be unstable, and also contrasts with the failure to isolate complexes with SiF4 (George et al. Dalton Trans. 2011, 40, 1584-1593). No reaction occurred between phosphines and SiI4, or with SiX4 and arsine ligands including AsMe3 and o-C6H4(AsMe2)2. Attempts to make five-coordinate [SiX4(PR3)] using the sterically bulky phosphines, P(t)Bu3, P(i)Pr3, or PCy3 failed, with no apparent reaction occurring, consistent with predictions (Wilson et al. Inorg. Chem. 2012, 51, 7657-7668) that such compounds would be very endothermic, while the large cone angles of the phosphines presumably preclude formation of six-coordination at the small silicon center. The reaction of Si2Cl6 with PMe3 or the diphosphines in CH2Cl2 results in instant disproportionation to the SiCl4 adducts and polychlorosilanes, but from hexane solution very unstable white [Si2Cl6(PMe3)2] and [Si2Cl6(diphosphine)] (diphosphine = Me2P(CH2)2PMe2 or o-C6H4(PMe2)2) precipitate. The reactions of SiHCl3 with PMe3 and Me2P(CH2)2PMe2 also produce the SiCl4 adducts, but using Et2P(CH2)2PEt2, colorless [SiHCl3{Et2P(CH2)2PEt2}] was isolated, which was characterized by an X-ray structure which showed a pseudo-octahedral complex with the Si-H trans to P. Attempts to reduce the silicon(IV) phosphine complexes to silicon(II) were unsuccessful, contrasting with the isolation of stable N-heterocyclic carbene adducts of Si(II
Imidazolium-based ionic liquids with large weakly coordinating anions
Full text linkEight imidazolium-based salts with the weakly-coordinating anions [BArF]− and [Al(OtC4F9)4]− ([BArF]− = tetrakis{3,5-bis(trifluoromethyl)phenyl}borate) have been synthesized. Characterization by 1H NMR spectroscopy shows that the salts are fully dissociated in solution. Six examples have been further characterized by X-ray crystallography, revealing that weak hydrogen bonds do occur in the solid phase between the imidazolium cations and weakly coordinating anions. Comparison with the bulky [IDiPPH] imidazolium cation (IDiPPH = 1,3-bis{2,6-bis(diisopropyl)phenyl}imidazolium) shows that large steric bulk close to the imidazolium protons can preclude hydrogen bonds from forming. Differential scanning calorimetry of the salts reveal that all are thermally stable up to 200 °C which renders them as potentially suitable background electrolytes for electrochemical processes which take place at elevated temperatures
Hexahalometallate salts of trivalent scandium, yttrium and lanthanum: cation–anion association in the solid state and in solution
No full textThe hexahalide salts, [NnBu4]3[LaCl6], [BMPYRR]3[LaCl6] (BMPYRR = 1-butyl-1-methylpyrrolidinium), [EMIM]3[MX6] (EMIM = 1-ethyl-3-methylimidazolium; M = La, X = Cl, Br, I; M = Sc, Y, Ce, X = Cl) and [EDMIM]3[MX6] (EDMIM = 1-ethyl-2,3-dimethylimidazolium; M = Y, X = Cl; M = La, X = Cl, I) have been prepared and X-ray crystal structures determined for several of them, with a view to probing the effect of varying the trivalent metal ion, the halide and the counter-cation on the structures adopted in the solid state. The crystal structures of the EMIM and EDMIM salts show extensive H-bonding between the halide ligands and organic cations; based upon the H-bonding distances, this appears to be strongest for the [EMIM]3[MCl6] salts, becoming progressively weaker for heavier metal ion or halide. In terms of the cations, changing from EMIM to EDMIM also reduces the strength of the H-bonding. The strength of the cation–anion pairing in solution has also been probed in solution via NMR spectroscopy where possible (45Sc, 89Y and 189La) and, for the EMIM salts, via the shift of ?(H2) relative to [EMIM]Cl at a standard concentration. The trends observed in solution mirror those determined in the solid state
Complexes of Group 2 dications with soft thioether- and selenoether-containing macrocycles
No full textA new route to cationic complexes of Mg, Ca, Sr and Ba with 18-membered ring O4S2, O4Se2 and O2S4 donor macrocycles from metal acetonitrile complexes with weakly coordinating [BArF]? anions is described. The precursors used were [M(MeCN)x][BArF]2 (M = Mg, x = 6; M = Ca, x = 8) and [M?(acacH)(MeCN)5][BArF]2 (M? = Sr or Ba). Reaction of these with the heterocrowns, [18]aneO4S2 (1,4,10,13-tetraoxa-7,16-dithiacyclooctadecane), [18]aneO4Se2 (1,4,10,13-tetraoxa-7,16-diselenacyclooctadecane) or [18]aneO2S4 (1,10-dioxa-4,7,13,16-tetrathiacyclooctadecane) in anhydrous CH2Cl2 solution gave [M(heterocrown)(MeCN)2][BArF]2 for M = Mg, Ca or Sr, whilst the larger Ba forms [Ba(heterocrown)(acacH)(MeCN)][BArF]2. The complexes have been characterised by microanalysis, IR, 1H and 13C{1H} NMR spectroscopy. X-ray crystal structures are reported for [Ca([18]aneO2S4)(MeCN)2][BArF]2, [Ca([18]aneO4Se2)(MeCN)2][BArF]2, [Sr([18]aneO4S2)(MeCN)2][BArF]2, and [Sr([18]aneO4Se2)(MeCN)2][BArF]2 which contain 8-coordinate metal centres with trans-nitrile ligands and ?6-heterocrowns, and for the 9-coordinate [Ba([18]aneO4Se2)(acacH)(MeCN)][BArF]2. Adventitious hydrolysis of the magnesium complexes in solution results in six-coordinate complexes, [Mg(?3-[18]aneO4Se2)(OH2)2(MeCN)][BArF]2 and [Mg(?3-[18]aneO4S2)(OH2)2(MeCN)][BArF]2, whose structures were determined. X-ray crystal structures are also reported for [Mg(MeCN)6][BArF]2, [M(MeCN)8][BArF]2 (M = Ca, Sr) and [Ca(18-crown-6)(MeCN)2][BArF]
'Pincer' dicarbene complexes of some early transition metals and uranium
No full textThe complexes [(C-N-C)MXn(thf)(m)] with the 'pincer' 2,6-bis(imidazolylidene)pyridine, (C-N-C) = 2,6-bis(arylimidazol-2-ylidene)pyriditie, aryl = 2,6-(Pr2C6H3)-C-1, M = V, X = Cl, n = 2, to = I 1a; M = Cr, X = Cl, n = 2, m = 0, 2a, X = Br, 2b; M = Mn, X = Br, n = 2, m = 0, 3; M = Nb, X = Cl, n = 3, m = 0, 4; and M = U, X = Cl, n = 4, m = 0, 5, were synthesised by (a) substitution of labile tined (1a), thf (2a, 3, 5) or dine (4) by free (C-N-C) or by (b) reaction of the bisimidazolium salt (CH-N-CH)Br-2 with {Cr[N(SiMe3)(2)](2)(thf)(2)} followed by amine elimination (2b). Attempted alkylation of 1a, 2, 3a and 4 with Grignard or alkyl lithiums gave intractable mixtures, and in one case [reaction of 1a with (mesityl)MgBr] resulted in exchange of Cl by Br (1b). Oxidation of 1a or [(C-N-C)VCl3] with 4-methylmorpholine N-oxide afforded the trans-V(C-N-C)(=O)Cl-2, 6, which by reaction with AgBF4 in MeCN gave trans-[V(C-N-C)(=O)(MeCN)(2)][BF4](2), 7. Reaction of 1a with p-tolyl azide gave trans-V(C-N-C)(=N-p-tolyl)Cl-2 8. The complex trans-Ti(C-N-C)(=NBu1)Cl-2, 9, was prepared by substitution of the pyridine ligands in Ti(NBu1)Cl-2(py)(3) by C-N-C
Neutral thioether and selenoether macrocyclic coordination to Group 1 cations (Li–Cs) – synthesis, spectroscopic and structural properties
No full textThe complexes [M(L)][BArF] (BArF = tetrakis{3,5-bis(trifluoromethyl)-phenyl}borate), L = [18]aneO4S2 (1,4,10,13-tetraoxa-7,16-dithiacyclooctadecane): M = Li–Cs; L = [18]aneO2S4 (1,10-dioxa-4,7,13,16-tetrathiacyclooctadecane): M = Li, Na, K; L = [18]aneO4Se2 (1,4,10,13-tetraoxa-7,16-diselenacyclooctadecane): M = Na, K, as well as [Na(18-crown-6)][BArF], are obtained in good yield as crystalline solids by reaction of M[BArF] with the appropriate macrocycle in dry CH2Cl2. X-ray crystallographic analyses of [Li([18]aneO4S2)][BArF] and [Li([18]aneO2S4)][BArF] show discrete distorted octahedral cations with hexadentate coordination to the macrocycle. The heavier alkali metal complexes all contain hexadentate coordination of the heterocrown, supplemented by M?F interactions via the anions, producing extended structures with higher coordination numbers; Na: CN = 7 or 8; K: CN = 8; Rb: CN = 9; Cs: CN = 8 or 10. Notably, all of the structures exhibit significant M–S/Se coordination. The crystal structures of the potassium and rubidium complexes show two distinct [M(heterocrown)]+ cations, one with M?F interactions to two mutually cis [BArF]? anions, and the other with mutually trans [BArF]? anions, giving 1D chain polymers. Solution multinuclear (1H, 13C, 7Li, 23Na, 133Cs) NMR data show that the macrocyclic coordination is retained in CH2Cl2 solution
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