22430-49-5Relevant academic research and scientific papers
Preparation of tert-Butyl-Capped Polyenes Containing up to 15 Double Bonds
Knoll, Konrad,Schrock, Richard R.
, p. 7989 - 8004 (1989)
7,8-Bis(trifluoromethyl)tricyclo2,5>deca-3,7,9-triene (TCDT) can be ring-opened in a controlled manner by W(CH-t-Bu)(NAr)(O-t-Bu)2 (Ar = 2,6-C6H3-i-Pr2) to give living oligomers from which the metal can be removed in a Wittig-like reaction with pivaldehyde or 4,4-dimethyl-trans-2-pentenal.Heating the oligomer yields a distribution of tetr-butyl-capped polyenes, (t-Bu)(CH=CH)n(t-Bu), where n is odd if pivaldehyde is used in the cleavage reaction or even if 4,4-dimethyl-trans-2-pentenal is used.Mixtures of odd and even polyenes have been analyzed byreserved-phase HPLC methods, and those having as many as 13 double bonds have been isolated by column chromatography on silica gel under dinitrogen at -40 deg C and characterized by (1)H and (13)C NMR and UV-vis studies.The 17-ene has been observed by HPLC.Polyenes containing more than 17 double bonds are relatively unstable under the reaction and subsequent isolation conditions; those containing between 11 and 15 double bonds decompose thermally progressively more readily.The initial isomer in the odd-ene series has largely the trans(cis,trans)x geometry as a result of stereospecific trans initiation, stereoselective trans propagation, stereospecific trans cleavage, and stereospecific cis retro-Diels-Alder reactions.The even-ene series is more complex since the Wittig-like reaction involving 4,4-dimethyl-trans-2-pentenal is not selective.UV-vis and (13)C and (1)H NMR data have been collected and analyzed in detail for the trans(cis,trans)x isomers for x = 1-5 (up to 11 double bonds) and for the odd and even all-trans forms containing up to nine double bonds.Extrapolation of a plot of the energy of the 1Bu 1Agg(0-0) transition versus 1/n (for up to the 13-ene) predicts that the HOMO-LUMO gap will be 1.79-1.80 eV for an infinite all-trans-polyene; in carbon disulfide it will be 1.56 eV.For the trans(cis,trans)x forms the 1Bu 1Agg(0-0) energy gap is predicted to be 1.95 eV for an infinite polyene in a mixture of acetonitrile, dichloromethane, and water (90:5:5).The ease of thermal cis-to-trans isomerization (ultimately to the all-trans form) correlates directly with chain length, isomerization to the all-trans form being especially facile for the 13-ene and beyond.The all-trans-polyenes are significantly less soluble than forms that contain one or more cis double bonds, although cross-linking cannot be ruled out as a contributor to insolubility for polyenes longer than the 13-ene.The retro-Diels-Alder reaction in the first unit away from the metal in living polyTCDT is accelerated 10 times relative to that in the second unit away from the metal.Heating polyTCDT gives living polyenes that are stable at 50 deg C for 45 min in solution; no benzene is formed.
Preparation and properties of tantalum imido complexes and their reactions with alkynes. Coordination control through multiple metal-ligand bonding
Chao, Yuan-Wei,Wexler, Pamela A.,Wigley, David E.
, p. 3860 - 3868 (2008/10/08)
The reaction of TaCl5 with Me3SiNHAr (NAr = N-2,6-C6H3-i-Pr2), in the presence of donor solvents, provides the imido complexes Ta(NAr)Cl3L2 (L = tetrahydrofuran (THF, 1), 1/2 dimethoxyethane (dme, 2), pyridine (py, 3), tetrahydrothiophene (THT, 4)) in high yield. These adducts are shown to exhibit a cis,mer geometry. The reaction of these compounds with 1 equiv of lithium alkoxides produces the imido alkoxide metathesis products Ta(NAr)(OR)Cl2L2 (5, OR = O-2,6-C6H3-i-Pr2 (DIPP), L = THF; 6, OR = DIPP, L = 1/2 dme; 7, OR = DIPP, L = py; 8, OR = O-2,6-C6H3Me2 (DMP), L = py). The reaction of Me3SiNEt2 with TaCl5 in toluene/diethyl ether gives a high yield of dimeric [Ta(NEt2)2Cl3]2 (9), from which the imido amide Ta(NAr)(NEt2)Cl2(py)2 (11) can be prepared by the reaction of 9 with LiNHAr. Dimeric 9 can be converted easily to the monomeric adduct Ta(NEt2)2Cl3(py) (10) upon reaction with pyridine. When these tantalum imides are reduced in the presence of alkynes, either alkyne adducts or metallacyclopentadienes are isolated. Thus, the compounds (EtC≡CEt)Ta(NAr)Cl(py)2 (12), (PhC≡CPh)Ta(NAr)Cl(py)2 (13), (Me3SiC≡CMe)Ta(NAr)Cl(py)2 (14), (C(CMe3)=CHCH=C(CMe3))Ta(NAr)Cl(py)2 (15), (EtC≡CEt)Ta(NAr)(DIPP)(py)2 (16), and (PrC≡CPr)Ta(NAr)(DIPP)(py)2 (17) are prepared from the two-electron reduction of either Ta(NAr)Cl3(py)2 (3) or Ta(NAr)(DIPP)Cl2(py)2 (7) in the presence of the appropriate alkyne. Crystals of the imido alkoxide Ta(N-2,6-C6H3-i-Pr2)(O-2,6-C6H 3Me2)Cl2(C5H5N) 2 (8) belong to the monoclinic space group P21/c with a = 9.547 (2) ?, b = 17.089 (3) ?, c = 19.135 (3) ?, β = 91.86 (1)°, and V = 3120.4 ?3 for Z = 4 with ρ(calcd) = 1.50 g/cm3. The X-ray structural study on 8 reveals a six-coordinate structure with cis-phenylimide and alkoxide ligands and mutually trans-chloride ligands. The imido linkage features a Ta-N bond of 1.769 (5) ? and Ta-N-Cipso angle of 179.1 (5)°, suggesting a Ta-N bond order between 2 and 3 and emphasizing the additional π donation of the nitrogen lone pair to an empty metal orbital. The phenoxide ligand is characterized by a Ta-O distance of 1.905 (5) ? and Ta-O-Cipso angle of 145.1 (5)°.
Mercury in Organic Chemistry. 36. Synthesis of (?-Allyl)palladium Compounds and 1,4-Dienes via Vinylpalladation of Monocyclic Alkenes
Larock, Richard C.,Takagi, Kentaro
, p. 4329 - 4332 (2007/10/02)
The reaction of vinylmercuric chlorides, cyclic alkenes, and Li2PdCl4 in tetrahydrofuran affords (?-allyl)palladium compounds 1.When the reaction is run in the presence of triethylamine, the corresponding 1,4-dienes 2 are obtained instead.These reactions
Palladium- or Nickel-Catalyzed Reactions of Alkenylmetals with Unsaturated Organic Halides as a Selective Route to Arylated Alkenes and Conjugated Dienes: Scope, Limitations, and Mechanism
Negishi, Ei-ichi,Takahashi, Tamotsu,Baba, Shigeru,Horn, David E. Van,Okukado, Nobuhisa
, p. 2393 - 2401 (2007/10/02)
Stereo- and regiodefined alkenylmetals containing Al, Zr, and Zn react with aryl and alkenyl iodides and bromides in the presence of catalytic amounts of Pd or Ni complexes containing phosphine ligands, such as PPh3, to give the corresponding cross-coupled products.Palladium catalysts permit nearly 100 percent stereospecificity in both alkenyl-aryl and alkenyl-alkenyl coupling reactions, whereas nickel catalysts lead to partial stereochemical scrambling in the alkenyl-alkenyl coupling.Although many other metals including Li, Mg, Cd, Hg, B, Si, Sn, Ti, and Ce were also used, the results were inferior to those obtained with Al, Zr, and Zn under the conditions used in the present study.The turnover numbers for the palladium-catalyzed reactions of PhI with (E)-1-octenylmetals containing Al, Zr, and Zn were 2,3, and > 2000 mmol of (E)-1-octenylbenzene (8) per mmol of Pd(PPh3)4 per hour at room temperature, respectively.The stoichiometric reaction of PhPd(PPh3)2I (6) with 1.2 equiv of (E)-1-octenylzinc chloride (7) in a 2:1 mixture of CD2Cl2 and THF was examined in detail.The reaction follows second-order konetics (k2 = 2.9 L/(mol.min) at 0 deg C) to give 8 without the buildup of any intermediate.The results are consistent with a slow formation of 9 via transmetalation followed by its rapid reductive elmination to give 8 and "Pd(PPhe3)2".Addition of PhI to the reaction mixture rapidly gives 6 in 98 percent yield, supporting the plausibility of the proposed oxidative addition step.These results are consistent with the proposed mechanism consisting of oxidative addition of Pd(0) complexes, rate-determining transmetalation involving Pd(II) complexes, and rapid decomposition of diorganopalladium(II) species to produce the coupling products in one or more subsequent steps.The rate-determining transmetalation step provides an explanation for the effect of metals in organometallic reagents used stoichiometrically.
