82228-87-3Relevant academic research and scientific papers
Metathesis of nitrogen atoms within triple bonds involving carbon, tungsten, and molybdenum
Burroughs, Beth A.,Bursten, Bruce E.,Chen, Shentan,Chisholm, Malcolm H.,Kidwell, Andy R.
, p. 5377 - 5385 (2008)
(ButO)3Mo≡N and W2(OBu t)6(M≡M) react in hydrocarbons to form Mo 2(OBut)6(M≡M) and (ButO) 3W≡N via the reactive intermediate MoW(OBut) 6(M≡M). (ButO)3W≡N and CH 3C≡N15 react in tetrahydrofuran (THF) at room temperature to give an equilibrium mixture involving (ButO) 3W≡N15 and CH3C≡N. The (Bu tO)3W≡N compound is similarly shown to act as a catalyst for N15-atom scrambling between MeC13≡ N15 and PhC≡N to give a mixture of MeC13≡N and PhC≡N15. From studies of degenerate scrambling of N atoms involving (ButO)3W≡N and MeC13≡N in THF-d8 by 13C{1H} NMR spectroscopy, the reaction was found to be first order in acetonitrile and the activation parameters were estimated to be ΔH? = 13.4(7) kcal/mol and ΔS? = -32(2) eu. A similar reaction is observed for (ButO)3Mo≡N and CH3C≡N15 upon heating in THF-d8. The reaction is suppressed in pyridine solutions and not observed for the dimeric [(ButMe 2SiO)3W≡N]2. The reaction pathway has been investigated by calculations employing density functional theory on the model compounds (MeO)3M≡N and CH3C≡N where M = Mo and W. The transition state was found to involve a product of the 2 + 2 cycloaddition of M≡N and C≡N, a planar metalladiazacyclobutadiene. This resembles the pathway calculated for alkyne metathesis involving (MeO) 3W≡CMe, which modeled the metathesis of (ButO) 3W≡CBut. The calculations also predict that the energy of the transition state is notably higher for M = Mo relative to M = W.
Synthesis of Alkyne Metathesis Catalysts from Tris(dimethylamido)tungsten Precursors
àrias, òscar,Freytag, Matthias,Jones, Peter G.,Melcher, Daniel,Tamm, Matthias
supporting information, p. 4454 - 4464 (2020/12/01)
Benzylidyne tungsten systems bearing a combination of alkoxide and amide ligands were readily obtained by partial alcoholysis of amido-supported tungsten complexes. Benzylidyne tris(dimethylamido)tungsten was treated with fluorinated alcohols Me2(CF3)COH, Me(CF3)2COH, and (CF3)3COH, and also with silanols (tBuO)3SiOH, and Ph3SiOH, all of which resulted in complexes of the type [PhC≡W(NHMe2)(NMe2)(OR)2]. Full displacement of the amido ligands was also achieved in [PhC≡W(NHMe2){OC(CF3)2Me}{OSi(O-tBu)3}2] and [PhC≡W(NHMe2)(OSiPh3)3]. In addition, reaction of the three fluorinated alcohols with hexakis(dimethylamido)ditungsten yielded isomeric mixtures of bimetallic complexes [W2(NMe2)4(OR)2], which bear two electron-donating ligands and one electron-withdrawing ligand per tungsten atom. All amido-substituted compounds are active in the self-metathesis of 5-benzyloxy-2-pentyne, although [W2(OR)2(NMe2)4] complexes require longer initiation times depending on the degree of fluorination of the tert-butoxide ligand.
FURTHER STUDIES OF THE REACTIONS OF DITUNGSTEN HEXA-t-BUTOXIDE WITH ACETYLENES. ISOLATION AND CHARACTERIZATION OF WO(OCMe3)4(THF), 2 AND W(CPh)(OCMe3)3
Cotton, F. Albert,Schwotzer, Willi,Shamshoum, Edward S.
, p. 55 - 68 (2007/10/02)
Further studies of the reactions of W2(OCMe3)6 with acetylenes at 70 deg C in toluene for up to 12 h are reported.All acetylenes of the type PhCCR afford (Me3CO)2W(μ-CPh)2W(OCMe3)2 (1) in high yield.Purely aliphatic acetylenes, RCCR, give complex products containing tritungsten cluster units, one example from the reaction with 4-octyne being the dimer of trimers 2 (3b), whose structure has been determined by X-ray crystallography.It forms monoclinic crystals (P21/n) with unit cell dimensions of a 12.838(1), b 14.440(1), c 18.465(1) Angstroem, β 97.57(1) deg, and Z = 2.One half of the centrosymmetric dimer is the crystallographic asymmetric unit and it contains an approximately isosceles triangle of metal atoms (W-W 2.892(1), 2.901(1), 2.418(1) Angstroem) with one of the longer edges bridged by CC3H7 and the other by μ-O.There are then five terminal OCMe3 groups and the two trinuclear units are united by a pair of bridging oxygen atoms.From the reaction of W2(OCMe3)6 with 4-octyne it was also possible to isolate the mononuclear complex WO(OCMe3)4(THF) (4) as colorless or pale yellow crystals.The structure, which is disordered, was determined by X-ray crystallography and contains molecules with apparent C4 symmetry.The four Me3CO groups form a planar set of W-O bonds (1.905(8) Angstroem) and the W=O and W-OC4H8 bond lengths are 1.77(3) and 2.38(3) Angstroem), respectively.The refinement was conducted in space group I4 with Z = 2 and unit cell dimensions of a 11.707(1) and c 9.514(a) Angstroem.Aliphatic carbynes, (Me3CO)3WCR (R = Et, Pr), upon reactions with W2(OCMe3)6 in 1/1 ratio gave the dimer of trimers product (3), but the aromatic carbyne, (Me3CO)3WCPh, did not give the dinuclear species 1.The structure of W(CPh)(OCMe3)3 (5) was determined by X-ray crystallography.It forms monoclinnic crystals (P21/n) with unit cell dimensions a 10.011(3), b 21.041(7), c 10.064(2) Angstroem, β 94.66(2) deg and Z = 4.The tungsten atom has nearly regular tetrahedral coordination with WC 1.758(5), W-O(mean) 1.865(4) Angstroem, O-WC(mean) 107.8(11), W-O-C(mean) 141(1) and WC-C 175.8(4) deg.
A general route to tri-tert-butoxytungsten alkylidyne complexes. Scission of acetylenes by ditungsten hexa-tert-butoxide
Listemann, Mark L.,Schrock, Richard R.
, p. 74 - 83 (2008/10/08)
Alkylidyne complexes of the type W(CX)(OCMe3)3 can be prepared by reacting W2(OCMe3)6 with XC≡CX or RC≡CX (R = Me or Et; X = Me, Et, Pr, CMe3, Ph, CH=CH2, CH2NR2, CH2OMe, CH2OSiMe3, CH(OEt)2, CO2Me, CH2CO2Me, C(O)Me, SCMe3, or H). Several others have been prepared by reacting W(CMe)(OCMe3)3 with XC≡CX or RC≡CX (X = SiMe3, NEt2, CH2CN, C≡CEt, or CN). In one case a diacetylene (EtC≡CC≡CEt) reacts with W2(OCMe3)6 to give [(Me3CO)3W≡C]2. Approximately half of the compounds can be isolated only as adducts, W(CX)(OCMe3)3(B), where B = pyridine or quinuclidine. By analogy with WC3 tungstenacyclobutadiene and tungstenatetrahedrane (η3-cyclopropenyl) complexes it is proposed that alkylidyne complexes can form only from a molecule having a planar 1,3-W2C2 core and that added nitrogenous base can play a direct role in the scission reaction. Derivatized alkylidyne complexes that contain electron donors react most rapidly with 3-heptyne; those that contain electron acceptors directly attached to the α-carbon do not react with 3-heptyne to any significant extent at 25 °C. We conclude that the W≡C bond behaves as if it were polarized W(+)≡C(-).
Reactions of hexa-tert-butoxyditungsten( W≡W) with diphenylacetylene. Syntheses and structures of W2(OCMe3)4(μ-C6H 5C)2 and W2(OCMe3)4(C6H5CCC 6H5)2
Albert Cotton,Schwotzer, Willi,Shamshoum, Edwar S.
, p. 1167 - 1171 (2008/10/08)
Reaction of W2(OCMe3)6 with tolan, PhCCPh, at about 70°C in nonpolar solvents produces W2(OCMe3)4(μ-PhC)2 (1) and W2(OCMe3)4(PhCCPh)2 (2). Both of these new compounds have been characterized by X-ray crystallography. Compound 1 crystallizes in space group P21/c with a = 9.029 (3) A?, b = 19.769 (11) A?, c = 9.813 (5) A?, β = 107.67 (2)°, V = 1669 (2) A?3, and Z = 2. The molecule consists of two tetrahedra joined centrosymmetrically on a common edge formed by the μ-PhC groups. The tolan has been separated into two PhC units (C?C = 2.82 (2) A?), and the W-W distance is 2.665 (1) A?. There is structural evidence that the W-O bonds have appreciable O→W π character, and it is proposed that this is responsible for the rather long W-W bond. Compound 2 crystallizes in space group P1 with a = 10.206 (6) A?, b = 11.028 (3) A?, c = 20.763 (9) A?, a = 92.16 (3)°, β = 90.91 (5)°, γ = 104.40 (3)°, V = 2261 (2) A?3, and Z = 2. The molecules are dinuclear with two terminal Me3CO groups on each metal atom and two μ-η2-tolan molecules. The O2WWO2 group is planar and the four alkyne carbon atoms define approximately a plane that is perpendicular to it; however, this second plane is not perpendicular to the W-W axis. Each alkyne carbon atom forms a short W-C bond, 1.99 ± 0.03 A?, and a long one, 2.34 ± 0.10 A?, and the W-W distance, 2.677 (1) A?, is consistent with a bond order between 1 and 2. A resonance description that accounts for the structure is presented.
