37823-96-4Relevant academic research and scientific papers
Formation and reactions of tetracarbonyl intermediates of the Fischer carbene complex (CO)5WqqC(OMe)Ph. A laser flash photolysis study using time-resolved infrared and UV/vis spectroscopy
Gut, Hans-Peter,Welte, Nicolas,Link, Uwe,Fischer, Helmut,Steiner, Ulrich E.
, p. 2354 - 2364 (2000)
The results of nanosecond laser flash photolysis (XeCl excimer irradiation at 308 nm) of the Fischer carbene complex [(CO)5WqqC(OMe)Ph] (CZ) in di-n-butyl ether and n-hexane are reported. Spectrokinetical detection of the intermediates was based on transient absorptions simultaneously recorded in the UV/vis and the IR spectral regions. The primary photoproducts are the unstable isomer CE produced with a quantum yield of about 30% and a tetracarbonyl complex I-S, probably of structure [(CO)4(S)WqqC(OMe)Ph], where S is a solvent molecule. The quantum yield of CO photoelimination was estimated as 1.7%. The CE isomer was found to return to the stable CZ isomer within a few microseconds, confirming previous results of McGarvey and co-workers. The tetracarbonyl species reacts with cosolutes present in the solution such as N2, H2O, acetonitrile, and methyl trans-crotonate to form secondary complexes of cis-tetracarbonyl complex structure [(CO)4(L)WqqC(OMe)Ph] (I-L). The tetracarbonyl complexes react readily with CO. For I-N2 in n-hexane the rate constant is 3.5 × 108 M-1 s-1. The rate constants of the corresponding reactions with acetonitrile (MeCN) and the olefin are larger by a factor of 2. In the presence of CO the complexes I-MeCN and I-olefin revert to CZ in a dissociative reaction mechanism. The rate constants for the elimination of MeCN or olefin are 5 and 105 s-1, respectively. The I-olefin complex irreversibly decomposes with a rate constant of 8 × 103 s-1.
Physical organic chemistry of transition metal carbene complexes. 19. Kinetics of reversible alkoxide ion addition to substituted (methoxyphenylcarbene)pentacarbonylchromium(0) and (methoxyphenylcarbene)pentacarbonyltungsten(0) in methanol and aqueous ace
Bernasconi, Claude F.,Garcia-Rio, Luis
, p. 3821 - 3829 (2007/10/03)
Rate and equilibrium constants for the nucleophilic addition of MeO- in methanol and in 90% MeCN-10% MeOH, of HC≡CCH2O- and CF3CH2O- in 50% MeCN-50% water, and of OH- in 50% MeCN
Abstraction of methyl from neutral Fischer-type carbene complexes: A new site for nucleophilic attack
Toomey, Laurence M.,Atwood, Jim D.
, p. 490 - 493 (2008/10/08)
Reactions of Fischer-type carbene complexes, M(CO)5(C(OMe)Ph) (M = Cr, W), with metal carbonyl anions (M′- = CpFe(CO)2-, Re(CO)5-, Mn(CO)4PPh3-, Co(CO)3PPh3-, Cp*Cr(CO)3-, CpMo(CO)3-) result in demethylation of the carbene complexes. The products are M(CO)5C(O)Ph- and M′-Me, characterized by infrared and NMR spectroscopy. A slower rate for reaction with W(CO)5(C(OEt)Ph) in comparison to the methyl analogue is consistent with nucleophilic attack of the metal carbonyl anion on the methyl of the methoxy group of the carbene. This is a new type of nucleophilic attack on a Fischer-type carbene.
Physical organic chemistry of transition metal carbene complexes. 4. Kinetics and equilibria of methoxide ion addition to [methoxy(phenyl)carbene]pentacarbonylchromium(0) and [methoxy(phenyl)carbene]pentacarbonyltungsten(0)
Bernasconi, Claude F.,Flores, Francis X.,Gandler, Joseph R.,Leyes, Aquiles E.
, p. 2186 - 2193 (2008/10/08)
A stopped-flow kinetic study of the reversible addition of methoxide ion to [methoxy(phenyl)-carbene]pentacarbonylchromium(0) (2-Cr) and [methoxy(phenyl)carbene]pentacarbonyltungsten-(0) (2-W) in methanol at 25°C is reported. The reaction was investigated by approaching the equilibrium (eq 1) from either side; due to the rapid decomposition of the adduct, the reaction in the reverse direction had to be measured in a sequential stopped-flow apparatus a few milliseconds after the adduct had been generated. Evidence that the observed reaction refers to the formation of (CO)5M--C(Ph)(OCH3)2 (M = Cr, W) includes a comparison of the absorption spectrum of (CO)5W--C(Ph)(OCH3)2 with that of the ylide derived from 2-W and DABCO, low-temperature IR of the adducts, and demonstration of CH3O/CD3O exchange on the same time scale as the kinetic experiments. The following rate and equilibrium constants were obtained: k1 = 77.1 M-1 s-1, k-1 = 1.10 s-1, and K1 = 70.1 M-1 for 2-Cr and k1 = 186 M-1 s-1, k-1 = 1.68 s-1, and K1 = 111 M-1 for 2-W. Approximate intrinsic rate constants (k0 = k1 = k-1 when K1 = 1) were calculated from the experimental rate constants. The k0 values are substantially lower than those estimated for the addition of methoxide ion to methyl benzoate. This is consistent with significant charge delocalization in the methoxide ion adducts of the metal carbene complexes. Rate constants, k-1BH, for general acid catalyzed methoxide ion loss from the adducts by phenol and 3,5-dichlorophenol were also determined. They allow an estimate of a Br?nsted α value on the order of 0.9, suggesting a transition state in which proton transfer from the catalyst to the incipient methoxide ion is well advanced. The near-independence of K1 on the metal contrasts with the strong metal dependence (Cr vs W) of the pKa values of (η5-C5H5)M(CO)3H-type hydrido complexes and supports Norton's view that the acidity of these hydrido complexes is not governed by the stabilization of the negative charge in the respective anions.
Synthesis of carbyne complexes of chromium, molybdenum, and tungsten by formal oxide abstraction from acyl ligands
McDermott, Gregory A.,Dorries, Alison M.,Mayr, Andreas
, p. 925 - 931 (2008/10/08)
Reaction of the acyl metal complexes [NMe4][M(C(O)R)(CO)5] (R = C6H5, M = Cr, Mo, W; R = CH3, M = W) with the Lewis acids COCl2, C2O2Cl2, C2O2Br2, and ClC(O)OCCl3 in CH2Cl2 at low temperatures (≤-78°C) and subsequent warming of the solutions (≤0°C) lead to clean formation of trans-halo(carbyne)tetracarbonylmetal complexes, [M(CR)(X)(CO)4] (X = Cl, Br). The carbyne complexes [M(CR)X(CO)4] are transformed into stabilized derivatives [M(CR)X(CO)2L2] by the addition of donor ligands (L2 = (pyridine)2 (py), tetramethylethylenediamine (tmeda), bipyridine (bpy)). The complex [W-(CPh)(O2CCF3)(CO)2(tmeda)] is prepared in a similar reaction sequence from [NMe4][W(C(O)Ph)(CO)5], (CF3CO)2O, and tmeda. Reaction of [NMe4][W(C(O)Ph)(CO)5] with C2O2Br2 and 1 equiv of PPh3 gives [W(CPh)Br(CO)3(PPh3)]. The bis(pyridine)-substituted complexes [W(CPh)Cl(CO)2(py)2] undergo further substitution reactions with PMe3 and Ph2PCH2CH2PPh2 (dppe) to give [W(CPh)Cl(CO)2(PMe3)2] and [W(CPh)Cl(CO)2(dppe)].
Synthesis of Metal Carbene Complexes from Diazirines
Chaloner, Penny A.,Glick, Gary D.,Moss, Robert A.
, p. 880 - 881 (2007/10/02)
Reaction of methoxy(phenyl)diazirine (1a) with tungsten or chromium pentacarbonyl yields carbene complexes (2a) and (2b) by a mechanism not involving free carbene.
Photochemistry of >. Formation of Alkyne-Carbene Complexes and Studies of Their Decomposition Reactions
Foley, Henry C.,Strubinger, Leslie M.,Targos, Tom S.,Geoffroy, Gregory L.
, p. 3064 - 3073 (2007/10/02)
The photochemistry of > has been examined and been shown to involve CO loss as the only detectable photoreaction.Irradiation in acetonitrile solution leads smoothly to the formation of > in quantitative yield.The 366 and 313-nm quantum yields for disappearance of > in CH3CN solution are 0.009 and 0.011, respectively, but the quantum yield drops to -4 at 436 nm, even though the complex absorbs strongly at the latter wavelength.The lowest intense absorption band (λmax 402 nm) (εmax 10560 L mol-1 cm-1) has been assigned as a W -> carbene(?*) charge-transfer transition with ligand field bands lying at higher energy.The low-lying W -> carbene charge-transfer state is inactive with respect to CO loss, with the latter occuring from ligand field excited states.Low-temperature photolysis in the presence of PhC=*CPh, MeC=*CPh, MeC=*CMe, PhC=*CH, and n-BuC=*CH leads to spectroscopically observable alkyne-carbene adducts, with the diphenylacetylene complex > isolated as a crystalline solid.None of the alkyne adducts are stable at 25 deg C in solution, and they decompose to give products that depend markedly upon the nature of the alkyne.With terminal alkynes, only polyacetylenes form, whereas the PhC=*CPh and PhC=*CMe adducts decay exclusively to form 1-methoxy-2,3-diphenylindene and 1-methoxy-2-methyl-3-phenylindene, respectively.The MeC=*CMe adduct leads to both poly-2-butyne and 1-methoxy-2,3-dimethylindene.
