- Tungsten-183 NMR study of cis-[W(CO)4(PPh3)(4-RC 5H4N)]; Effect of varying the σ donor strength of the pyridine
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Tungsten-183 NMR data are reported for the complexes cis-[W(CO) 4(PPh3)(4-RC5H4N)] (R = H, Me, Ph, COMe, COPh, OMe, NMe2, Cl, NO2). The 183W chemical shift (obtained by indirect detection using 31P) is found to correlate with the Hammett σ function for the group R, with 183W shielding increasing approximately linearly with the donor strength of the pyridine over a range of 93 ppm. The X-ray structures of cis-[W(CO)4(PPh3)(4-MeOC5H4N)] and cis-[W(CO)4(PPh3)(4-PhCOC5H4N)] are also reported. Copyright
- Carlton, Laurence,Mokoena, Lebohang V.,Fernandes, Manuel A.
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p. 199 - 202
(2013/05/09)
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- Thermodynamic hydride donor abilities of [HW(CO)4L]- complexes (L = PPH3, P(OMe)3, CO) and their reactions with [C5Me5Re(PMe3)(NO)(CO)]+
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Abstract: The thermodynamic hydride donor abilities of [HW(CO) 5]- (40 kcal/mol), [HW(CO)4P(OMe 3)]- (37 kcal/mol), and [HW(CO)4(PPh 3)]- (36 kcal/mol) have been measured in acet
- Ellis, William W.,Ciancanelli, Rebecca,Miller, Susie M.,Raebiger, James W.,DuBois, M. Rakowski,DuBois, Daniel L.
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p. 12230 - 12236
(2007/10/03)
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- The oxidative addition of SnCl4 to [W(CO)4(NCMe)(PPh3)]. The X-ray crystal structure of [WH(CO)3(NCMe)(PPh3)2]- [SnCl5·MeOH]
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The oxidative addition reaction of SnCl4 with [W(CO)4(NCMe)(PPh3)] in acetonitrile gives a mixture of seven-]coordinate tungsten(II) compounds: [WCl(SnCl3)(CO)3(NCMe)(PPh3)] (1), [WCl2(CO)3(NCMe)(PPh3)] (2), [WCl(SnCl3)(CO)2(NC-Me)2(PPh3)] (3), and [WCl2(CO)2(NCMe)2(PPh3)] (4) identified by IR and NMR (1H, 13C{1H}, and 31P{1H}) studies. Treatment of [W(CO)4(NCMe)(PPh3)] with 1 equiv. of SnCl4 in CH2Cl2 solution besides compounds 1 and 2 also gives ionic species such as [HPPh3]+ and [SnCl6]2- and cationic tungsten(II) complexes. The crystal structure of one of these, [WH(CO)3(NCMe)(PPh3)2][SnCl5 ·MeOH] (5), has been established by single-crystal X-ray diffraction. The IR, 1H, 13C{1H} and 31P{1H} spectra of 5 are also described and can be correlated with the crystallographically observed geometry. A notable feature of 5 is the presence of an agostic interaction of the hydride ligand with one of the carbonyl ligands.
- Szymańska-Buzar, Teresa,G?owiak, Tadeusz,Czelu?niak, Izabela
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p. 1817 - 1823
(2008/10/08)
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- Catalytic transformations of vinylthiiranes by tungsten carbonyl complexes. A new route to 3,6-dihydro-1,2-dithiins
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W(CO)5(NCMe) (1) has been found to transform vinylthiirane and a series of methyl-substituted vinylthiiranes into a series of 3,6-dihydro-1,2-dithiin compounds. Two equivalents of the vinylthiirane are required, and 1 equiv of a butadiene is formed by the transfer of its sulfur atom to the second vinythiirane, which is then transformed into the dihydrodithiin. The formation of 3,6-dihydro-1,2-dithiin (9) proceeds at 15 turnovers/h at 25°C using vinylthiirane (4) and 1 as the catalyst. The catalyst is long-lived (up to 2000 turnovers have been obtained without loss of activity) and relatively insensitive to air. Methyl substitutents on the vinyl group increase the rate of reaction while methyl substituents on the thiirane ring slow it considerably. The introduction of phosphine ligands to the catalyst also leads to significant increases in the rate of reaction. The dithiin complex W(CO)5(SSCH2CH=CHCH2) (13) was isolated from the catalytic reactions and was structurally characterized. The dihydrodithiin is coordinated to the tungsten atom through one of its two sulfur atoms. Compound 13 was shown to be a species in the catalytic cycle. A mechanism involving a vinylthiirane intermediate that undergoes spontaneous ring opening, followed by addition of a second vinylthiirane to the terminal carbon of the chain, elimination of 1 equiv of butadiene, and formation of a sulfur-sulfur bond leading to 13 is proposed. The vinylthiirane intermediate is regenerated by ligand substitution which releases the dihydrodithiin product. Compound 9 readily polymerizes when its pure form is exposed to visible light. If the polymerization is interrupted at an early stage, 1,2,7,8-tetrathiacyclododeca-4,10-diene (14), a dimer of 9, can be isolated. Compound 14 was obtained in 5.6% yield and was structurally characterized crystallographically.
- Adams, Richard D.,Perrin, Joseph L.
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p. 3984 - 3991
(2007/10/03)
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- Electron-Transfer Catalysis. Radical Chain Mechanism for the Ligand Substitution of Metal Carbonyls
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A novel chain process for the ligand substitution of metal complexes is revealed by bulk and transient electrochemical methods.The large turnover numbers that are obtained for the ligand substitution of the tris(acetonitrile) complexes of molybdenum and tungsten carbonyls with phosphines and isocyanides underscore the electrocatalytic phenomenon.The efficient chain process derives from the substitution lability of the cation radicals, which are formed by the one-electron oxidation of metal carbonyls and subsequently undergo rapid electron transfer, as in Scheme II.Th e driving force for ligand substitution is related to the relative stabilities of the cation radicals.Electron-transfer equilibria between these cation radicals can be evaluated from the standart reduction potentials E0 or the cyclic voltammetric peak potentials Ep.The initiation of the chain process is finely tuned to the value of E0 and Ep for the various metal carbonyls.The effectiveness of metal carbonyls as catalysts in the enhanced oxidation of nucleophiles such as triphenylphosphine is also described.
- Hershberger, J.W.,Klingler, R.J.,Kochi, J.K.
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p. 3034 - 3043
(2007/10/02)
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