Hydroamination Of Ethylene Research Articles

Dicoordinate Au(I)-Ethylene Complexes as Hydroamination Catalysts.

A series of gold(I)–ethylene π-complexes containing a family of bulky phosphine ligands has been prepared. The use of these sterically congested ligands is crucial to stabilize the gold(I)–ethylene bond and prevent decomposition, boosting up their catalytic performance in the highly underexplored hydroamination of ethylene. The precatalysts bearing the most sterically demanding phosphines showed the best results reaching full conversion to the hydroaminated products under notably mild conditions (1 bar of ethylene pressure at 60 °C). Kinetic analysis together with density functional theory calculations revealed that the assistance of a second molecule of the nucleophile as a proton shuttle is preferred even when using an extremely congested cavity-shaped Au(I) complex. In addition, we have measured a strong primary kinetic isotopic effect that is consistent with the involvement of X–H bond-breaking events in the protodeauration turnover-limiting step.

Hydroamination of ethylene with NH3 induced by non-thermal atmospheric plasma

We show here that non-thermal atmospheric plasma induces the cleavage of the N–H bond of NH3 to form aminium radicals, which then add onto ethylene to form ethylamine in 17% yield.

Pt-catalysed intermolecular hydroamination of non-activated olefins using a novel family of catalysts: Arbuzov-type phosphorus metal complexes

The catalytic system “PtBr2(0.3mol%)/2P(OR)3/10nBu4PBr” (R=alkyl) discovered recently in our group, allows good to excellent catalytic activities for the intermolecular hydroamination of ethylene and higher α-olefins (1-hexene) with aniline type amines to give the expected N-ethyl- (1) and N,N-diethyl-anilines (2) along with 2-methyl-quinoline (3). A poisoning effect of alkyl and aromatic phosphines has been observed. This effect could be minimised using small amounts of molecular iodide which reacts with phosphorus ligands to form non-coordinating well-described ionic species. Interestingly, beneficial effects of added P(OR)3 (R=alkyl) have been pointed out and further investigated. In this way, a new potential family of Arbuzov-type phosphorus-metal complexes has been suggested to be responsible for good catalytic activities found when using P(OR)3 alkyl phosphites rather than PR3 (R=alkyl, aromatic) and P(OPh)3 co-catalysts. [Display omitted]

Rhodium catalyzed hydroamination of C2H4 with NH3 with pincer derived PE(CH2CH2X)P ligands – Fighting the energy span

Density functional theory (DFT) calculations were carried out on a variety of rhodium complexes with a variety of pincer derived PE(CH2CH2X)P ligands (E = B, C, N; X = O, NH, CH2, PH, SiH2) to answer the question if computationally a catalyst for the as yet unresolved hydroamination of ethylene with ammonia can be designed. The influence of the different side arm donor groups X was studied with the central pincer backbone element E being carbon. Additionally to rhodium as the metal center cobalt and iridium were studied. Furthermore, the influence of solvation for four solvents (toluene, dichloromethane, tetrahydrofuran, acetonitrile) was investigated on an optimized system. While the majority of the study focuses on neutral catalysts the influence of the complex charge was also studied briefly. Anionic complexes generated by exchanging the backbone carbon E from C to B were studied as well as cationic complexes which were generated by replacing C with N. The variation of the calculated energy spans is large with many systems yielding spans of ca. 40 kcal/mol or above. The lowest energy span (ΔG = 28.7 kcal/mol) was identified for a neutral rhodium catalyst with E = C and X = NH in dichloromethane or tetrahydrofuran solution yielding a predicted TOF of 90 h−1 at 130 °C. Outer sphere mechanisms were studied briefly and cannot compete energetically with inner sphere mechanisms.

Analysis of Potential Molecular Catalysts for the Hydroamination of Ethylene with Ammonia: A DFT Study with [Ir(PCP)] and [Ir(PSiP)] Complexes

Very few cases of oxidative addition of NH(3) to transition-metal complexes forming terminal amide hydrides have been experimentally observed. Here, two examples with the iridium pincer complexes [Ir(PCP)(NH(3))] A1 with PCP = [κ(3)-(tBu(2)P-C(2)H(4))(2)CH](-) and [Ir(PSiP)(NH(3))] B1 with PSiP = [κ(3)-(2-Cy(2)P-C(6)H(4))(2)SiMe](-) were investigated by DFT calculations applying the M06L density functional to successfully reproduce the trend of the experimentally observed thermochemical stabilities. According to the calculations, the corresponding hydrido-amido complexes A2 and B2 are more stable than the corresponding ammine complexes by ΔG = -2.8 and -2.6 kcal mol(-1), respectively. Complexes such as A2 and B2 are ideally suited entry points to catalytic cycles for the hydroamination of ethylene with ammonia. Therefore, the relevant stationary points of the potentially available cycles were studied computationally to verify if these complexes can catalyze the hydroamination. As a result, complex A2 will clearly not catalyze the hydroamination as all energy spans calculated range close to 40 kcal mol(-1) or higher. The energy spans obtained with B2 are significantly lower in some cases and range around 35 kcal mol(-1), further indicating that no turnover can be expected. By systematically varying the structure of B2, the energy span could be reduced to 28.8 kcal mol(-1) corresponding to a TOF of 17 h(-1) at a reaction temperature of 140 °C. A reoptimization of relevant structures under the inclusion of cyclohexane as a typical solvent reduces the calculated TOF to 6.0 h(-1).

DFT study of the mechanism of hydroamination of ethylene with ammonia catalyzed by diplatinum(II) complexes: Inner‐ or outer‐sphere?

A detailed analysis of the reaction profiles of the hydroamination reaction between ethylene and ammonia catalyzed by the diplatinum(II) [{Pt(NH(2))(μ-H)(PPh(3))}(2)] complex is presented herein using density functional theory computational techniques. The coordinatively unsaturated 14e T-shaped [Pt(NH(2))(PPh(3))H] species resulted from the dissociation of the diplatinum [{Pt(NH(2))(μ-H)(PPh(3))}(2)] precatalyst are identified as the active catalytic species. All possible reaction pathways that constitute the entire catalytic cycle have exhaustively been investigated. Overall, the rate-determining step of all catalytic cycles constructed was found to be the oxidative addition of ammonia that leads to the regeneration of the catalyst. According to the energy span model, the outer-sphere mechanism for the hydroamination of ethylene with ammonia catalyzed by the diplatinum complexes is favored over the inner-sphere one, whereas TOF values are in favor of the inner-sphere mechanism.

Intermolecular Rhodium‐Catalysed Hydroamination of Non‐Activated Olefins: Effect of Olefin, Amine, Phosphine and Phosphonium Salt

AbstractThe catalytic system RhCl3⋅3H2O/2P(p‐CH3C6H4)3/65nBu4PI/2I2, which was discovered recently in our research group, allows the highest catalytic activity ever reported for the intermolecular hydroamination of ethylene, 1‐butene, and 1‐hexene with aniline‐type amines (0.3 mol % catalytic precursor) to give the expected N‐alkyl‐ (N‐ethyl‐, 1) and N,N‐dialkyl‐anilines (N,N‐diethyl‐, 2) along with 2‐methyl quinolines (3; in the case of ethylene). The effects of time and temperature, as well as the nature of the phosphonium salt, phosphine, and amine on the catalytic activity of this reaction have been studied. This system is particularly efficient for the hydroamination of ethylene with aniline in the presence of 2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthyl (CE*=460) and tri(p‐tolyl)phosphine (CE*=520). Good to excellent activities were also found by combining Wilkinson’s catalysts (RhI complexes) with nBu4PI and I2. The simple association of PPh3 and I2 has been shown to be a very efficient “in‐situ generated” source of I− promoters. *CE (catalytic efficiency)=TON1+2TON2+2TON3.

DFT and Experimental Studies on the PtX2/X–-Catalyzed Olefin Hydroamination: Effect of Halogen, Amine Basicity, and Olefin on Activity, Regioselectivity, and Catalyst Deactivation

A DFT/B3LYP study with inclusion of solvent and temperature effects has probed the olefin activation mechanism for the intermolecular hydroamination of ethylene and 1-hexene by aniline derivatives catalyzed by the PtX2/X– system on the basis of a variety of experimental results, including new experiments on catalyst deactivation. For ethylene and aniline, the calculated ΔG‡cycle between the resting state [PtX3(C2H4)]−, 1X, and the TOF-determining transition state of the C–H reductive elimination from [PtX3(H)(CH2CH2NHPh)]−, TS2X, is slightly smaller for X = Br than for Cl or I. The ΔG‡cycle decreases as the aniline basicity decreases. For the slightly less efficient hydroamination of 1-hexene, ΔG‡cycle is greater than that for the hydroamination of ethylene, with a preference for the Markovnikov addition, in agreement with experiment and with essentially equivalent ΔG‡cycle values for the Br and I systems. In general, the results of the calculations are in agreement with the experimental observation. A clear-cut comparison of trends is hampered by the small energy differences and by the possibility, proven in certain cases, that the reaction parameters under investigation affect the catalyst degradation rate in addition to its intrinsic activity. Extrapolation of the computational study to the fluoride system suggests that this should be even more active. However, experimental studies show that this is not the case. The reason for this anomaly has been traced to the basicity of the fluoride ion, which triggers more rapid catalyst decomposition. A bonding analysis of 1X indicates a significant push–pull π interaction between the C2H4 and the trans-F ligand.

Coordination and Organometallic Chemistry of Relevance to the Rhodium-Based Catalyst for Ethylene Hydroamination

The RhCl(3)·3H(2)O/PPh(3)/nBu(4)PI catalytic system for the hydroamination of ethylene by aniline is shown to be thermally stable by a recycle experiment and by a kinetic profile study. The hypothesis of the reduction under catalytic conditions to a Rh(I) species is supported by the observation of a high catalytic activity for complex [RhI(PPh(3))(2)](2). New solution equilibrium studies on [RhX(PPh(3))(2)](2) (X = Cl, I) in the presence of ligands of relevance to the catalytic reaction (PPh(3), C(2)H(4), PhNH(2), X(-), and the model Et(2)NH amine) are reported. Complex [RhCl(PPh(3))(2)](2) shows broadening of the (31)P NMR signal upon addition of PhNH(2), indicating rapid equilibrium with a less thermodynamically stable adduct. The reaction with Et(2)NH gives extensive conversion into cis-RhCl(PPh(3))(2)(NHEt(2)), which is however in equilibrium with the starting material and free Et(2)NH. Excess NHEt(2) yields a H-bonded adduct cis-RhCl(PPh(3))(2)(Et(2)NH)···NHEt(2), in equilibrium with the precursors, as shown by IR spectroscopy. The iodide analogue [RhI(PPh(3))(2)](2) shows less pronounced reactions (no change with PhNH(2), less extensive addition of Et(2)NH with formation of cis-RhI(PPh(3))(2)(NHEt(2)), less extensive reaction of the latter with additional Et(2)NH to yield cis-RhI(PPh(3))(2)(Et(2)NH)···NHEt(2). The two [RhX(PPh(3))(2)](2) compounds do not show any evidence for addition of the corresponding X(-) to yield a putative [RhX(2)(PPh(3))(2)](-) adduct. The product of C(2)H(4) addition to [RhI(PPh(3))(2)](2), trans-RhI(PPh(3))(2)(C(2)H(4)), has been characterized in solution. Treatment of the RhCl(3)·3H(2)O/PPh(3)/nBu(4)PI/PhNH(2) mixture under catalytic conditions yields mostly [RhCl(PPh(3))(2)](2), and no significant halide exchange, demonstrating that the promoting effect of iodide must take place at the level of high energy catalytic intermediates. The equilibria have also been investigated at the computational level by DFT with treatment at the full QM level including solvation effects. The calculations confirm that the bridge splitting reaction is slightly less favorable for the iodido derivative. Overall, the study confirms the active role of rhodium(I) species in ethylene hydroamination catalyzed by RhCl(3)·3H(2)O/PPh(3)/nBu(4)PI and suggest that the catalyst resting state is [RhCl(PPh(3))(2)](2) or its C(2)H(4) adduct, RhCl(PPh(3))(2)(C(2)H(4)), under high ethylene pressure.

Reactions of Diethylamine and Ethylene Catalyzed by PtII or Pt0 – Transalkylation vs. Hydroamination

AbstractPtBr2/nBu4PBr (without solvent) or K2PtCl4/NaBr (in water) have been shown to efficiently catalyze the hydroamination of ethylene by aniline and are poor catalysts for the hydroamination of ethylene by diethylamine. A DFT study on the hydroamination mechanism indicates that the energetic span of the C2H4/Et2NH catalytic cycle is close to that of the C2H4/PhNH2 cycle. The poor performance is attributed to rapid catalyst degradation with reduction to metallic platinum. Pt0, on the other hand, catalyzes a transalkylation process, partially transforming Et2NH into Et3N, EtNH2 and NH3. This process is inhibited by C2H4. Mechanistic considerations for the Pt0‐catalyzed transalkylation process are presented.

Modeling the platinum-catalyzed intermolecular hydroamination of ethylene: The nucleophilic addition of HNEt 2 to coordinated ethylene in trans-PtBr 2(C 2H 4)(HNEt 2)

Compound trans-PtBr 2(C 2H 4)(NHEt 2) ( 1) has been synthesized by Et 2NH addition to K[PtBr 3(C 2H 4)] and structurally characterized. Its isomer cis-PtBr 2(C 2H 4)(NHEt 2) ( 3) has been obtained from 1 by photolytic dissociation of ethylene, generating the dinuclear trans-[PtBr 2(NHEt 2)] 2 intermediate ( 2), followed by thermal re-addition of C 2H 4, but only in low yields. The addition of further Et 2NH to 1 in either dichloromethane or acetone yields the zwitterionic complex trans-Pt (−)Br 2(NHEt 2)(CH 2CH 2N (+)HEt 2) ( 4) within the time of mixing in an equilibrated process, which shifts toward the product at lower temperatures (Δ H° = −6.8 ± 0.5 kcal/mol, Δ S° = 14.0 ± 2.0 e.u., from a variable temperature IR study). 1H NMR shows that free Et 2NH exchanges rapidly with H-bonded amine in a 4·NHEt 2 adduct, slowly with the coordinated Et 2NH in 1, and not at all (on the NMR time scale) with Pt-NHEt 2 or –CH 2CH 2N (+)HEt 2 in 4. No evidence was obtained for deprotonation of 4 to yield an aminoethyl derivative trans-[PtBr 2(NHEt 2)(CH 2CH 2NEt 2)] − ( 5), except as an intermediate in the averaging of the diasteretopic methylene protons of the CH 2CH 2N (+)HEt 2 ligand of 4 in the higher polarity acetone solvent. Computational work by DFT attributes this phenomenon to more facile ion pair dissociation of 5·Et 2NH 2 +, obtained from 4·Et 2NH, facilitating inversion at the N atom. Complex 4 is the sole observable product initially but slow decomposition occurs in both solvents, though in different ways, without observable generation of NEt 3. Addition of TfOH to equilibrated solutions of 4, 1 and excess Et 2NH leads to partial protonolysis to yield NEt 3 but also regenerates 1 through a shift of the equilibrium via protonation of free Et 2NH. The DFT calculations reveal also a more favourable coordination (stronger Pt–N bond) of Et 2NH relative to PhNH 2 to the Pt II center, but the barriers of the nucleophilic additions of Et 2NH to the C 2H 4 ligand in 1 and of PhNH 2 to trans-PtBr 2(C 2H 4)(PhNH 2) ( 1a) are predicted to be essentially identical for the two systems.

A Computational Study of Rhodium Pincer Complexes with Classical and Nonclassical Hydride Centres as Catalysts for the Hydroamination of Ethylene with Ammonia

The catalytic hydroamination of ethylene with ammonia was investigated by means of density functional theory (DFT) calculations. An initial computational screening of key reaction steps (C-N bond formation, N-H bond cleavage), which are assumed to be part of a catalytic cycle, was carried out for complexes with the [M(L)]-complex fragment (M=Rh, Ir; L=NCN, PCP; NCN=2,5-bis(dimethylaminomethyl)benzene, PCP=2,5-bis- (dimethylphosphanylmethyl)benzene). Based on the evaluation of activation barriers, this screening showed the rhodium compound with the NCN ligand to be the most promising catalyst system. A detailed investigation was carried out starting with the hypothetical catalyst precursor [Rh(NCN)(H)(2)(H(2))] (1). A variety of activation pathways to yield the catalytically active species [Rh(NCN)(H)(NH(2))] (5), as well as [Rh(NCN)(C(2)H(5))(NH(2))] (17), were identified. With 5 and 17 several closed catalytic cycles could be calculated. One of the calculated cycles is favoured kinetically and bond-forming events have activation barriers low enough to be put into practice. The calculations also show that for experimental realisation the synthesis of 1 is not necessary, as the synthesis of 17 would establish an active catalyst directly without the need for activation. Oligomerisation of ethylene would be possible in principle and would be expected as a competitive side reaction. Accordingly not only ethylamine would be observed in an experimental system, as amines with longer carbon chains also can be formed.

Hydroamination of ethylene by aniline: catalysis in water

The platinum-catalyzed and halide-promoted hydroamination of ethylene with aniline is reported for the first time in the presence of simple sodium halides in water. Compounds K2PtX4 (X = Cl or Br), PtX2 or PtX4 (0.3% mol) in the presence of an aqueous solution of excess NaX and aniline under ethylene pressure (25 bar) affords N-ethylaniline with 60–85 turnovers after 10 h at 150 °C. The best result (TON = 85) was obtained in the presence of excess NaBr, whereas a slightly lower activity was observed with NaCl (60 cycles) and practically no activity with NaF or NaI (2–4 cycles). The reaction also produces N,N-diethylaniline (up to 1 cycle) and 2-methylquinoline (up to 8 cycles) as by-products. The influence of added H+ and different oxidizing agents was also examined.

Intermolecular Hydroamination of Ethylene and 1-Alkenes with Cyclic Ureas Catalyzed by Achiral and Chiral Gold(I) Complexes

Reaction of 1-methyl-imidazolidin-2-one (1) with 1-octene (10 equiv) catalyzed by a 1:1 mixture of (2b)AuCl [2b = 2-di-tert-butylphosphino-1,1'-binaphthyl] and AgSbF(6) in dioxane at 100 degrees C for 24 h led to isolation of 1-methyl-3-(octan-2-yl)imidazolidin-2-one in 96% yield as a single regioisomer. A range of unactivated 1-alkenes and ethylene underwent gold(I)-catalyzed intermolecular hydroamination at or below 100 degrees C in excellent yield with high regioselectivity. Reaction of 1-alkenes with substituted imidazolidin-2-ones catalyzed by chiral bis(gold) phosphine complexes led to enantioselective intermolecular hydroamination with up to 78% ee.

Platinum‐Catalyzed Intermolecular Hydroamination of Alkenes: Halide‐Anion‐Promoted Catalysis

AbstractTetraalkylphosphonium halides play the role of “promoters” for the previously unknown PtII‐catalyzed hydroamination of alkenes. The promoting effect of these “cocatalysts” depends only upon their anionic moiety. The PtII/nBu4PBr system exhibits an unprecedented catalytic activity (aerobic conditions) for the hydroamination of ethylene and 1‐hexene (regioselectivity > 95 %, Markovnikov).(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Rhodium-Catalyzed Hydroamination of Ethylene. Highly Promoting Effect of Iodide Ions

Association of the usual “RhCl3−3H2O−2PPh3” catalytic precursor (0.3%) with n-Bu4PI (65 equiv/Rh) and iodine (2 equiv/Rh) generates the most active catalytic system reported so far for the hydroamination of ethylene with aniline to give mixtures of N-ethyl- and N,N-diethylanilines. This system proved particularly efficient for the hydroamination of ethylene with N-ethylaniline (TON > 260 after 24 h).

Intermolecular hydroamination of non-activated alkenes catalyzed by Pt(II) or Pt(IV)- n-Bu 4PX (X = Cl, Br, I) systems: Key effect of the halide anion

Ionic liquids such as n-Bu 4PX salts (X = Cl −, Br −, I −) have a strong promoting effect for the Pt(II)-catalyzed hydroamination of ethylene and 1-hexene with aniline. In the case of ethylene, n-Bu 4PBr is the most efficient activator, whereas n-Bu 4PI is even more efficient in the case of 1-hexene. A special effect of molecular iodine has also been pointed out. Most notably, Pt(IV) precursors are also shown to be active for the hydroamination of ethylene. As for Pt(II) precursors, Pt(IV)- n-Bu 4PX associations exhibit enhanced catalytic activities.

Base-catalyzed hydroamination of ethylene with diethylamine

The catalytic hydroamination reaction of ethylene with diethylamine in the presence of lithium diethylamide has been reinvestigated to improve catalyst productivity. Various tertiary amines were synthesized and screened as ligands for the target reaction. Applying N, N, N′, N′-tetramethylethylenediamine (TMEDA) or N, N, N′, N″, N″-pentamethyldiethylentriamine (PMDTA) the rate of the reaction is increased, but also ligand degradation is observed. Using optimized parameters excellent yield (92%) and conversion (99%) were achieved under mild conditions. At higher temperature base-catalyzed hydroamination of higher olefins is also possible.

The First Platinum-Catalyzed Hydroamination of Ethylene

The platinum-catalyzed hydroamination of ethylene with aniline is reported for the first time. Using PtBr2 as a catalyst precursor in n-Bu4PBr under 25 bar of ethylene pressure affords N-ethylaniline with 80 turnovers after 10 h at 150 °C. The reaction simultaneously produces 2-methylquinoline in ca. 10 cycles. The catalytic activity is slightly improved by increasing the reaction temperature or the ethylene pressure and strongly depends on the aniline/platinum ratio. The beneficial effects of added P(OMe)3 (2 equiv/PtBr2) or of a proton source (3 equiv/PtBr2) have also been pointed out. A gradual poisoning by N-ethylaniline has been observed, which could be minimized by using biphasic systems. The best result for the hydroamination with aniline (TON = 145 after 10 h at 150 °C) has been obtained in a biphasic system (n-Bu4PBr/decane) in the presence of C6H5NH3+ (3 equiv/PtBr2). The basicity of the arylamine has been shown to play an important role: the lower the basicity, the higher the TON. Thus, the hy...

Ruthenium mediated hydroamination of ethylene

We investigated the potential of ruthenium complexes to mediate the hydroamination reaction, using piperidine and ethylene as model substrates. Our main approach was to activate the olefin towards nucleophilic attack by the amine. This might be achieved by co-ordination to a metal centre. We succeeded in identifying ruthenium complexes that mediate this reaction stoichiometrically. We showed that amine co-ordination to ruthenium is strong and that the co-ordinated amine does not take part in the desired reaction. Thus, we tentatively conclude that catalytic results were not achieved due to amine blockage of the essential metal sites. Reaction of higher olefins did not result in any aminated products at all. Dehydroalkylation of piperidine to 2-ethyl-1,2-dehydropiperidine 17 was observed as a side reaction with selected ruthenium compounds.