13643-02-2Relevant articles and documents
A Series of Crystallographically Characterized Linear and Branched σ-Alkane Complexes of Rhodium: From Propane to 3-Methylpentane
Bukvic, Alexander J.,Burnage, Arron L.,Tizzard, Graham J.,Martínez-Martínez, Antonio J.,Mckay, Alasdair I.,Rees, Nicholas H.,Tegner, Bengt E.,Kr?mer, Tobias,Fish, Heather,Warren, Mark R.,Coles, Simon J.,Macgregor, Stuart A.,Weller, Andrew S.
, p. 5106 - 5120 (2021)
Using solid-state molecular organometallic (SMOM) techniques, in particular solid/gas single-crystal to single-crystal reactivity, a series of σ-alkane complexes of the general formula [Rh(Cy2PCH2CH2PCy2)(ηn:ηm-alkane)][BArF4] have been prepared (alkane = propane, 2-methylbutane, hexane, 3-methylpentane; ArF = 3,5-(CF3)2C6H3). These new complexes have been characterized using single crystal X-ray diffraction, solid-state NMR spectroscopy and DFT computational techniques and present a variety of Rh(I)···H-C binding motifs at the metal coordination site: 1,2-η2:η2 (2-methylbutane), 1,3-η2:η2 (propane), 2,4-η2:η2 (hexane), and 1,4-η1:η2 (3-methylpentane). For the linear alkanes propane and hexane, some additional Rh(I)···H-C interactions with the geminal C-H bonds are also evident. The stability of these complexes with respect to alkane loss in the solid state varies with the identity of the alkane: from propane that decomposes rapidly at 295 K to 2-methylbutane that is stable and instead undergoes an acceptorless dehydrogenation to form a bound alkene complex. In each case the alkane sits in a binding pocket defined by the {Rh(Cy2PCH2CH2PCy2)}+ fragment and the surrounding array of [BArF4]- anions. For the propane complex, a small alkane binding energy, driven in part by a lack of stabilizing short contacts with the surrounding anions, correlates with the fleeting stability of this species. 2-Methylbutane forms more short contacts within the binding pocket, and as a result the complex is considerably more stable. However, the complex of the larger 3-methylpentane ligand shows lower stability. Empirically, there therefore appears to be an optimal fit between the size and shape of the alkane and overall stability. Such observations are related to guest/host interactions in solution supramolecular chemistry and the holistic role of 1°, 2°, and 3° environments in metalloenzymes.
Steric Acceleration in the Pyrolysis Kinetics of 2-Substituted Ethyl Acetates
Martin, Ignacio,Chuchani, Gabriel
, p. 3902 - 3904 (1981)
The rates of elimination of several cyclo and branched alkyl substituents at the β carbon of ethyl acetates have been determined in a static system over the temperature range of 360-420 deg C and pressure range of 34-337 torr.The reactions are homogeneous in both clean and seasoned vessels, follow a first-order rate law, and are unimolecular.The rate coefficients are given by the following Arrhenius equations: for 2-cyclohexylethyl acetate, log k1 (s-1)=(13.30+/-0.28)-(208.1+/-3.4) kJ mol-1 (2.303RT)-1; for 2-cyclopentylethyl acetate, log k1 (s-1)=13.20+/-0.26)-(207.4+/-3.2) kJ mol-1 (2.303RT)-1; for 3-methyl-1-pentyl acetate, log k1 (s-1)=(13.62+/-0.09)-(211.9+/-1.2) kJ mol-1 (2.303RT)-1; for 4-methyl-1-pentyl acetate, log k1 (s-1)=12.82+/-0.05)-(203.1+/-0.6) kJ mol-1 (2.303RT)-1.The present data together with those reported in the literature give a good correlation line only, when plotting log k/k0 against Hancock's Esc values (r=0.916, δ=-0.121, and intercept=-0.020 at 400 deg C).This work ratifies that steric acceleration is responsible for the rate of elimination of alkyl and several polar substituents interposed by at least three methylene groups with respect to Cα-O bond of ethyl acetates.Unreported Esc values of several substituents are defined.
Asymmetric Synthesis in the Nickel-complex-catalysed Formation of Olefins from Allyl Alcohols and Grignard Reagents
Cherest, Marc,Felkin, Hugh,Umpleby, J. David,Davies, Stephen G.
, p. 681 - 682 (1981)
The reaction of three isomeric pentenols with methyl magnesium bromide catalysed by (-)DIOP nickel dichloride leads to optically active 3-methylpent-1-ene, with the optical yield and product configuration related to the configuration of the initially formed (η3-allyl)nickel intermediates.
NNNO-Heteroscorpionate nickel (II) and cobalt (II) complexes for ethylene oligomerization: the unprecedented formation of odd carbon number olefins
Zubkevich, Sergey V.,Tuskaev, Vladislav A.,Gagieva, Svetlana Ch.,Kayda, Anatoliy S.,Khrustalev, Victor N.,Pavlov, Alexander A.,Zarubin, Dmitry N.,Bulychev, Boris M.
, (2020/07/04)
The unprecedented observation of odd carbon number olefins is reported during nickel- catalyzed ethylene oligomerization. Two complexes based on Co (II) and Ni (II) with novel tetradentate heteroscorpionate ligand have been synthesized and fully characterized. These complexes showed the ability to oligomerize ethylene upon activation with various organoaluminum compounds (Et2AlCl, Et3Al2Cl3, EtAlCl2, MMAO). Ni (II) based catalytic systems were sufficiently more active (up to 1900 kg·mol (Ni)?1·h?1·atm?1) than Co (II) analogs and have been found to be strongly dependent on the activator composition. The use of PPh3 as an additive to catalytic systems resulted in the increase of activity up to 4,150 kg·mol (Ni)?1·h?1·atm?1 and in the alteration of selectivity. All Ni (II) based systems activated with EtAlCl2 produce up to 5 mol. percent of odd carbon number olefins; two probable mechanisms for their formation are suggested – metathesis and β-alkyl elimination.
Iminobisphosphines to (Non-)symmetrical diphosphinoamine ligands: Metal-induced synthesis of diphosphorus nickel complexes and application in ethylene oligomerisation reactions
Boulens, Pierre,Lutz, Martin,Jeanneau, Erwann,Olivier-Bourbigou, Hlne,Reek, Joost N. H.,Breuil, Pierre-Alain R.
, p. 3754 - 3762 (2015/05/05)
We describe the synthesis of a range of novel iminobisphosphine ligands based on a sulfonamido moiety [R1SO2N=P(R2)2-P(R3)2]. These molecules rearrange in the presence of nickel by metal-induced breakage of the P-P bond to yield symmetrical and nonsymmetrical diphosphinoamine nickel complexes of general formula Ni{[P(R2)2]N(SO2R1)P(R3)2}Br2. The complexes can be isolated and are very stable. Upon activation by MAO, these complexes oligomerise ethylene to small chain oligomers (mainly C4-C8) with high productivity. Surprisingly fast codimerisation reactions of ethylene with butenes is observed, leading to a high content of branched C6 products.
Z -selective alkene isomerization by high-spin cobalt(II) complexes
Chen, Chi,Dugan, Thomas R.,Brennessel, William W.,Weix, Daniel J.,Holland, Patrick L.
supporting information, p. 945 - 955 (2014/02/14)
The isomerization of simple terminal alkenes to internal isomers with Z-stereochemistry is rare, because the more stable E-isomers are typically formed. We show here that cobalt(II) catalysts supported by bulky β-diketiminate ligands have the appropriate kinetic selectivity to catalyze the isomerization of some simple 1-alkenes specifically to the 2-alkene as the less stable Z-isomer. The catalysis proceeds via an "alkyl" mechanism, with a three-coordinate cobalt(II) alkyl complex as the resting state. β-Hydride elimination and [1,2]-insertion steps are both rapid, as shown by isotopic labeling experiments. A steric model explains the selectivity through a square-planar geometry at cobalt(II) in the transition state for β-hydride elimination. The catalyst works not only with simple alkenes, but also with homoallyl silanes, ketals, and silyl ethers. Isolation of cobalt(I) or cobalt(II) products from reactions with poor substrates suggests that the key catalyst decomposition pathways are bimolecular, and lowering the catalyst concentration often improves the selectivity. In addition to a potentially useful, selective transformation, these studies provide a mechanistic understanding for catalytic alkene isomerization by high-spin cobalt complexes, and demonstrate the effectiveness of steric bulk in controlling the stereoselectivity of alkene formation.
Iminobisphosphines to (Non-)symmetrical diphosphinoamine ligands: Metal-induced synthesis of diphosphorus nickel complexes and application in ethylene oligomerisation reactions
Boulens, Pierre,Lutz, Martin,Jeanneau, Erwann,Olivier-Bourbigou, Hélène,Reek, Joost N. H.,Breuil, Pierre-Alain R.
, p. 3754 - 3762 (2015/04/27)
We describe the synthesis of a range of novel iminobisphosphine ligands based on a sulfonamido moiety [R1SO2N=P(R2)2-P(R3)2]. These molecules rearrange in the presence of nickel by metal-induced breakage of the P-P bond to yield symmetrical and nonsymmetrical diphosphinoamine nickel complexes of general formula Ni{[P(R2)2]N(SO2R1)P(R3)2}Br2. The complexes can be isolated and are very stable. Upon activation by MAO, these complexes oligomerise ethylene to small chain oligomers (mainly C4-C8) with high productivity. Surprisingly fast codimerisation reactions of ethylene with butenes is observed, leading to a high content of branched C6 products. Alkyl-substituted symmetrical and nonsymmetrical diphosphinoamine nickel complexes have been prepared by using sulfonamido-based iminobisphosphines as ligand promoters. The complexes with basic substituents, activated by methylaluminoxane, oligomerise ethylene to short oligomers (C4-C8) with high activity. Fast codimerisation is observed, leading to highly branched C6 product distribution.
Iminobisphosphines to (non-)symmetrical diphosphinoamine ligands: Metal-induced synthesis of diphosphorus nickel complexes and application in ethylene oligomerisation reactions
Boulens, Pierre,Lutz, Martin,Jeanneau, Erwann,Olivier-Bourbigou, Hélène,Reek, Joost N. H.,Breuil, Pierre-Alain R.
, p. 3754 - 3762 (2014/08/18)
We describe the synthesis of a range of novel iminobisphosphine ligands based on a sulfonamido moiety [R1SO2N=P(R 2)2-P(R3)2]. These molecules rearrange in the presence of nickel by metal-induced breakage of the P-P bond to yield symmetrical and nonsymmetrical diphosphinoamine nickel complexes of general formula Ni{[P(R2)2]N(SO2R 1)P(R3)2}Br2. The complexes can be isolated and are very stable. Upon activation by MAO, these complexes oligomerise ethylene to small chain oligomers (mainly C4-C 8) with high productivity. Surprisingly fast codimerisation reactions of ethylene with butenes is observed, leading to a high content of branched C6 products. Copyright
Mechanism of ethylene dimerization catalyzed by Ti(OR′) 4/AlR3
Suttil, James A.,McGuinness, David S.
, p. 7004 - 7010,7 (2020/09/15)
Ti-alkoxide-based catalysts in combination with AlEt3 are responsible for the production of a significant proportion of the world's 1-butene supply, via the dimerization of ethylene. A metallacycle mechanism is normally presumed to operate with this system. However, despite its importance, the catalyst is not mechanistically well understood. The mechanism of dimerization has been studied through a series of C2H 4/C2D4 co-oligomerization experiments and comparison of theoretical and experimental mass spectra. The results obtained show that the textbook metallacycle mechanism is most likely not responsible for dimerization with this catalyst. Instead, an excellent fit between the theoretical and experimental mass spectra is obtained when a conventional Cossee-type mechanism (insertion/β-hydride elimination) is modeled. The formation of both the primary product 1-butene and the secondary reaction products (ethylene/1-butene co-dimers) is best explained by this mechanism.
Mono(aryloxido)titanium(IV) Complexes and their application in the selective dimerization of ethylene
Cazaux, Jean-Benoit,Braunstein, Pierre,Magna, Lionel,Saussine, Lucien,Olivier-Bourbigou, Helene
scheme or table, p. 2942 - 2950 (2011/05/13)
We report on the synthesis of mono(aryloxido)titanium(IV) complexes of general formula [Ti[O(o-R)Ar]X3), with X = OiPr, ArO = 2-ie.rr-but:yl-4-methylphenoxy and. R = CMe3 (2a), CMe2Ph (2b) and CH2NMe2 (2c). Attempts to reach pure mono(aryloxido) complexes when R = CH2NMe(CH2Ph) (2d) or CH2N(CH2Ph)2 (2e) were unsuccessful, When R = CH2OMe, the analogous mononuclear complex was not obtained, and instead, a dinuclear complex [(2-ieri-butyl-4methyl-6- methoxymethylphenoxy) TiCl(OiPr)(H2-OiPr)2TiCl(OiPr) 2] (3) was formed. Complexes 2b and 3 were characterized by single-crystal X-ray diffraction, The former contains a tetrahedrally coordinated. TiIV centre, whereas in the latter the aryloxido ligand behaves as a chelating-bridging ligand between the two, chemically very different metal centres that form two face-sharing octahedra, Different synthetic approaches starting from. [Ti(OiPr)4] or [TiCl(OiPr) 3] were evaluated and are discussed, The hemllabile behaviour of the aryloxido ligand. resulting from, reversible coordination of its side arm was studied by variable-temperature 1H NMR spectroscopy for 2c (R = CH 2NMe2). Complexes 2a-d were contacted, with ethylene and AlEt3 as cocatalyst, When activated with AlEt3 (3 equiv.) at 20 bar and 60 ° C, complex 2c exhibits interesting activity (2100 g/gTi/h) for the selective dimerization of ethylene to 1-butene (92% C 4"=; 99+% C4=1), Noticeable differences in catalyst activity were observed when the R group was modified,
