Catalyst Activity and Selectivity in the Isomerising Alkoxycarbonylation of Methyl Oleate

The synthesis of unsymmetrical diphosphine ligands ( 3 a – g ) with an o‐tolyl backbone and tert‐butyl, adamantyl, cyclohexyl and isopropyl substituents on the phosphorus moiety is described (1,2‐(CH₂PR₂)(PR′₂)C₆H₄; 3 a : R=tBu, R′=tBu, 3 b : R=tBu, R′=Cy, 3 c : R=tBu, R′=iPr, 3 d : R=Ad, R′=tBu, 3 e : R=Ad, R′=Cy, 3 f : R=Cy, R′=Cy, 3 g : R=Ad, R′=Ad). The corresponding diphosphine–Pd^II ditriflate complexes [(P^P)Pd(OTf)₂] ( 5 a – g ) were prepared and structurally characterised by X‐ray crystallography. These new complexes were studied as catalyst precursors in the isomerising methoxycarbonylation of methyl oleate, and were found to convert methyl oleate into the corresponding linear α,ω‐diester ( L ) with 70–80 % selectivity. The products of this catalytic reaction with the known [{1,2‐(tBu₂PCH₂)₂C₆H₄}Pd(OTf)₂] complex ( 5 h ) were fully analysed, and revealed the formation of the linear α,ω‐diester ( L , 89.0 %), the methyl‐branched diester B1 (4.3 %), the ethyl‐branched diester B2 (1.0 %), the propyl‐branched diester B3 (0.6 %) and all diesters from butyl‐ to hexadecyl‐branched diesters B4 – B16 (overall 4.8 %) at 90 °C and 20 bar CO. The productivity of the catalytic conversion of methyl oleate with complexes 5 a – g varied with the steric bulk of the alkyl substituent on the phosphorus. Ligands with more bulky groups, like tert ‐ butyl or adamantyl (e.g., 5 a , 5 d , 5 g ), were more productive systems. The formation of the catalytically active hydride species [(P^P)Pd(H)(MeOH)]⁺ ( 6‐MeOH ) was investigated and observed directly for complexes 5 a – e and 5 g , respectively. These hydride species were isolated as the corresponding triphenylphosphine complexes ( 6‐PPh₃ ) and fully characterised, including by X‐ray crystallography. The catalytic productivity of 6 a‐PPh₃ was virtually identical to that of 5 a , thereby confirming the efficient hydride formation of 5 a under catalytic conditions.     

Pd‐Iminocarboxylate Complexes and Their Behavior in Ethylene Polymerization

Designing co‐catalyst‐free late transition metal complexes for ethylene polymerization is a challenging task at the interface of organometallic and polymer chemistry. Herein, a set of new, co‐catalyst‐free, single‐component catalytic systems for ethylene polymerization have been unraveled. Treatment of anthranilic acid with various aldehydes produced four iminocarboxylate ligands ( L1 – L4 ) in very good to excellent yield (75–92 %). The existence of 2‐((2‐methoxybenzylidene)amino) benzoic acid ( L1 ) has been unambiguously demonstrated using NMR spectroscopy, MS and single‐crystal X‐ray diffraction. A neutral Pd‐iminocarboxylate complex [{N O}PdMe(L1)] (N O=κ²‐N,O‐ArCHNC₆H₄CO₂ with Ar=2‐MeOC₆H₄) C1 was prepared by treating stoichiometric amount of L1.Na with palladium precursor. The identity of C1 was confirmed by 1–2D NMR spectroscopy and single‐crystal X‐ray diffraction studies. Along the same lines, palladium complexes C2 – C4 were prepared from ligands L2 – L4 respectively. In‐situ high‐pressure NMR investigations revealed that these Pd complexes are amenable to ethylene insertion and undergo facile β‐H elimination to produce propylene. These palladium complexes were then evaluated in ethylene polymerization reaction and various reaction parameters were screened. When C1 – C4 were exposed to ethylene pressures of 10–50 bar, formation of low‐molecular‐weight polyethylene was observed.     

Preparations of Saturated N‐P‐N Type Secondary Phosphine Oxides and their Applications in Cross‐Coupling Reactions

A series of cyclohexane‐1,2‐diamine ( 3a – 3d ) and benzene‐1,2‐diamine derivatives ( 3e – 3h ) were pre‐ pared. Followed by hydrolysis, the reaction of 3a – 3c with PCl₃ successfully led to the formation of cor‐ responding metastable saturated heteroatom‐substituted secondary phosphine oxides (HASPO 4a – 4c ), a tautomer of the saturated heteroatom‐substituted phosphinous acid (HAPA). Whereas ambient‐stable diamine‐coordinated palladium complexes were obtained, HAPA‐coordinated palladium complexes were not successfully synthesized. The molecular structures of HASPO 4c , Pd(OAc)₂(3a) , PdBr₂(3b) and Pd(OAc)₂(3c) and [Cu(NO₃)(3d)⁺][NO₃ ^? ] were determined by single‐crystal X‐ray diffraction method. Catalysis of in‐situ Suzuki‐Miyaura cross‐coupling reactions for aryl bromides and phenylboronic acid using diamine 3a as ancillary ligand showed that the optimized reaction condition at 60 °C is the combination of 2 mmol % 3a /3.0 mmol KOH/1.0 mL 1,4‐dioxane/1 mmol % Pd(OAc)₂. Moreover, moderate reactivity was observed when using aryl chlorides as substrates (supporting infor‐ mation). When diamine 3d was employed in Heck reaction, good tolerance of functional groups of aryl bromides were observed while using 4‐bromoanisole and styrene as substrates. The optimized condi‐ tion for Heck reaction at 100 °C is 3 mmol % 3d /3.0 mmol CsF/1.0 mL toluene/3 mmol % Pd(OAc)₂. In general, cyclohexane‐1,2‐diamine derivatives exhibited better catalytic properties than those of benzene‐1,2‐diamines.     

Efficient P‐Chiral Biaryl Bisphosphorus Ligands for Palladium‐Catalyzed Asymmetric Hydrogenation

A series of structurally novel P‐chiral biaryl bisphosphorus ligands L1‐L5 (BABIBOPs) are developed, providing high efficiency for the first time in palladium‐catalyzed asymmetric hydrogenation of β‐aryl and β‐alkyl substituted β‐keto esters. With the Pd‐ L3 (iPr‐BABIBOP) catalyst, a series of chiral β‐hydroxyl carboxylic esters are formed in excellent enantioselectivities (up to>99% ee) and yields at catalyst loading as low as 0.01 mol%.     

A Molecularly Defined Iron‐Catalyst for the Selective Hydrogenation of α,β‐Unsaturated Aldehydes

A selective iron‐based catalyst system for the hydrogenation of α,β‐unsaturated aldehydes to allylic alcohols is presented. Applying the defined iron–tetraphos complex [FeF(L)][BF₄] (L=P(PhPPh₂)₃) in the presence of trifluoroacetic acid a broad range of aldehydes are reduced in high yields using low catalyst loadings (0.05–1 mol %). Excellent chemoselectivity for the reduction of aldehydes in the presence of other reducible moieties, for example, ketones, olefins, esters, etc. is achieved. Based on the in situ detected hydride species [FeH(H₂)(L)]⁺ a catalytic cycle is proposed that is supported by computational calculations.     

Kinetico‐Mechanistic Insights on the Assembling Dynamics of Allyl‐Cornered Metallacycles: The PtNpy Bond is the Keystone

The square‐like homo‐ and heterometallamacrocycles [{Pd(η³‐2‐Me‐C₃H₄)( L ⁿ )₂}₂{M(dppp)}₂](CF₃SO₃)₆ (dppp=1,3‐bis(diphenylphosphino)propane) and [{Pd(η³‐2‐Me‐C₃H₄)( L¹ )₂}₂{M(PPh₃)₂}₂](CF₃SO₃)₆ [py=pyridine, M=Pd, Pt, L ^{n =}4‐PPh₂py ( L¹ ), 4‐C₆F₄PPh₂py ( L² )] containing allyl corners were synthesised by antisymbiotic self‐assembly of the different palladium and platinum metallic corners and the ambidentate N,P ligands. All the synthesised assemblies displayed a complex dynamic behaviour in solution, the rate of which is found to be dependent on the electronic and/or steric nature of the different building blocks. A kinetico‐mechanistic study by NMR line shape analysis of the dynamics of some of these assemblies was undertaken in order to determine the corresponding thermal activation parameters. Both an enhanced thermodynamic stability and slower dynamics were observed for platinum‐pyridine‐containing species when compared with their palladium analogues. Time‐dependent NMR spectroscopy in combination with ESI mass spectrometry was used to study the exchange between the assemblies and their building blocks, as well as that occurring between different metallamacrocycles. Preliminary studies were carried out on the activity of some of the metallamacrocyclic compounds as catalytic precursors in the allylic substitution reaction, and the results compared with that of the monometallic allylic corner [Pd(η³‐2‐Me‐C₃H₄)( L¹ )₂]⁺.     

Computational Study of the Palladium‐Catalyzed Carbonylative Synthesis of Aromatic Acid Chlorides: The Synergistic Effect of PtBu3 and CO on Reductive Elimination

We describe herein computational studies on the unusual ability of Pd(PtBu₃)₂ to catalyze formation of highly reactive acid chlorides from aryl halides and carbon monoxide. These show a synergistic role of carbon monoxide in concert with the large cone angle PtBu₃ that dramatically lowers the barrier to reductive elimination. The tertiary structure of the phosphine is found to be critical in allowing CO association and the generation of a high energy, four coordinate (CO)(PR₃)Pd(COAr)Cl intermediate. The stability of this complex, and the barrier to elimination, is highly dependent upon phosphine structure, with the tertiary steric bulk of PtBu₃ favoring product formation over other ligands. These data suggest that even difficult reductive eliminations can be rapid with CO association and ligand manipulation. This study also represents the first detailed exploration of all the steps involved in palladium‐catalyzed carbonylation reactions with simple phosphine ligands, including the key rate‐determining steps and palladium(0) catalyst resting state in carbonylations.     

Synthesis of α‐(Fluorophenyl)pyridine by Palladium‐Catalyzed Cross‐Coupling Reaction

A series of α‐(fluoro‐substituted phenyl)pyridines have been synthesized by means of a palladium‐catalyzed cross‐coupling reaction between fluoro‐substituted phenylboronic acid and 2‐bromopyridine or its derivatives. The reactivities of the phenylboronic acids containing di‐ and tri‐fluoro substituents with α‐pyridyl bromide were investigated in different catalyst systems. Unsuccessful results were observed in the Pd/C and PPh₃ catalyst system due to phenylboronic acid containing electron‐withdrawing F atom(s). For the catalyst system of Pd(OAc)₂/PPh₃, the reactions gave moderate yields of 55% –80%, meanwhile, affording 10% –20% of dimerisation (self‐coupling) by‐products, but trace products were obtained in coupling with 2,4‐difluorophenylboronic acids because of steric hinderance. Pd(PPh₃)₄ was more reactive for boronic acids with sterically hindering F atom(s), and the coupling reactions gave good yields of 90% and 91% without any self‐coupling by‐product.     

Magnetically recyclable palladium nanoparticles (Fe3O4‐Pd) for oxidative coupling between amides and olefins at room temperature

A convenient method for the synthesis of magnetically recyclable palladium nanoparticles (Fe₃O₄‐Pd) is described. The catalytic application of the Fe₃O₄‐Pd nanoparticles was explored for the first time in oxidative coupling between amides and olefins. p‐Toluenesulfonic acid plays a significant role in the oxidative amidation reaction. The reaction proceeds at room temperature, resulting in (Z)‐enamides under ambient air in the absence of co‐catalyst and ligand. The superparamagnetic nature of Fe₃O₄‐Pd facilitates easy, quantitative recovery of the catalyst from a reaction mixture, and it can be reused for up to three consecutive cycles with a slight decrease in catalytic activity.     

Aryl Phosphine Nickel(II) and Palladium(II) Complexes with N,O‐Amino‐carboxylate Chelate Ligands [(Aryl)(R3P)M(N,O‐α‐aminocarboxylate)](M = Ni,Pd). Catalysts for the Polymerization of Olefins

The title complexes [(Aryl)(R₃P)M(N,O‐α‐aminocarboxylate)] (M = Ni, Pd) were synthesized by reaction of [(o‐tolyl)(Ph₃P)₂NiBr] or of [(p‐Me₃CC₆H₄)(o‐tolyl₃P)Pd(μ‐Br)]₂ with the anions of α‐amino acids. The spectroscopic data indicate that the nickel complexes are formed as mixtures of isomers, whereas for the palladium complexes only one isomer is observed. The complex [(o‐tolyl)(Ph₃P)Ni(glycinate)] is – in the presence of AlEt₃ – a highly active catalyst for the polymerization of ethylene [up to 1800 kg PE / (mol Ni·h)] and gives polymers with remarkably high molecular weights (up to 900.000 g/mol) and with few branchings.     

Kohlenwasserstoffverbrückte Metallkomplexe. L Dicarbonyl‐cyclopentadienyl‐pyridoyl‐eisen‐Komplexe als Liganden

Hydrocarbon‐bridged Metal Complexes. L Dicarbonyl Cyclopentadienyl Pyridoyl Iron Complexes as Ligands Dicarbonyl‐cyclopentadienyl‐2‐ and 3‐pyridoyl‐iron (L¹, L²) and 2,6‐dicarbonyl‐pyridine‐bis(dicarbonyl‐cyclopentadienyl‐iron) (L³) function as ligands in metal complexes and the N,O‐chelates [(OC)₄M(L¹)] (M = Mo, W, 8 a, b ) and [(Ph₃P)₂Cu(L¹)]⁺BF₄^– ( 9 ) were prepared. Monodentate coordination of L¹ and L² through the pyridine N‐atom occurs in the palladium(II) complexes [Cl₂Pd(PnBu₃)(L¹)] ( 10 ), [Cl₂Pd(PnBu₃)(L²)] ( 11 ) and [Cl₂Pd(L²)₂] ( 12 ). Ligand L³ forms the O,N,O‐bis(chelate) [Cl₂Zn(L³)] ( 13 ). The crystal and molecular structures of L¹, 8 b (M = W), 9–11 and 13 were determined by X‐ray diffraction.     

Structural Aspects of Palladium and Platinum Complexes With Chiral Diphosphinoferrocenes Relevant to the Regio‐ and Stereoselective Copolymerization of CO with Propene

A series of chiral diphosphinoferrocene ligands 3a – i , derived from josiphos (=(2R)‐1‐[(1R)‐1‐(dicyclohexylphosphino)ethyl]‐2‐(diphenylphosphino)ferrocene, formerly called {(R)‐1‐[(S)‐2‐(diphenylphosphino)ferrocenyl]ethyl}dicycloxexylphosphine) where the electronic properties of the ligand are systematically varied, were prepared. X‐Ray studies of five of these new ligands confirmed that these compounds display very similar conformations in the solid state and that no structural criteria could be found indicating the modified electronic properties. These ligands find application in the Pd‐catalyzed highly regio‐ and stereoselective CO/propene copolymerization reaction, where the electronic properties of the ligand show a great impact on the catalyst activity. Coordination‐chemical aspects of these diphosphinoferrocenes relevant to the CO/propene copolymerization reaction were addressed by the preparation and characterization of Pd‐ and Pt‐complexes of the general formula [PdCl₂(P−P)] ( 5 ), [PdMe₂(P−P)] ( 6 ), [PdClMe(P−P)] ( 7 ), [PdMe(MeCN)(P−P)]PF₆ ( 8 ), and [PtClMe(P−P)] ( 9 ) (P−P=chiral diphosphinoferrocene ligand ( 3a – h ), four of which were characterized by X‐ray crystallography.     

The molecular structure of chlorothiomethoxymethyl-bis(triphenylphosphine)palladium(II) methylenechloride solvate at −160°C

The precise molecular structure of [PdCl(CH₂SCH₃)(PPh₃)₂] has been determined from three-dimensional X-ray diffraction data collected at ?160°C. The CH₂Cl₂ solvated crystal ([PdCl(CH₂SCH₃)(PPh₃)₂ · CH₂Cl₂]) belongs to the monoclinic system, space group P2₁/n, with four formula units in a cell of dimensions: a 14.973(3), b 15.333(3), c 17.377(3) Å and β 115.77(1)° at ?160°C. The structure was solved by the conventional heavy atom method and refined by the least-squares procedure to R = 0.035 for observed reflections. The geometry around the palladium atom is square-planar. The phosphorus atoms of the two triphenylphosphine ligands are mutually trans. The CH₂SCH₃ group is bonded to the palladium atom only through the PdC σ-bond and the sulfur atom is not bonded to the metal atom (PdC(1) 2.061(3), SC(1) 1.796(3), SC(2) 1.817(5), Pd?S 2.973(1) Å, PdC(1)S 100.64(14)° and C(1)SC(2) 101.28(18)°). The structure is in contrast to that of [PdCl(CH₂SCH₃)(PPh₃)], in which both the carbon and sulfur atoms of the CH₂SCH₃ group are bonded to the palladium atom.     

Novel Cs‐Symmetric 1,4‐Diphosphine Ligands in the Copolymerization of Propene and Carbon Monoxide: High Regio‐ and Stereocontrol in the Catalytic Performance

New C_s‐symmetric aryl 1,4‐diphosphine ligands were synthesized and tested in the copolymerization of carbon monoxide and propene. The electronic properties of the two different P‐atoms did not affect the high enantioselectivity of the catalyst precursors, thus resulting in high ‘regio’‐ and ‘stereoregular’ copolymers.     

Bond Formation and Coupling between Germyl and Bridging Germylene Ligands in Dinuclear Palladium(I) Complexes

The dinuclear palladium(I) complexes [L(Ar₂HGe)Pd(μ‐GeAr₂)₂Pd(GeHAr₂)L] (Ar=Ph, p‐Tol; L=PMe₃, tBuNC) contain terminal germyl and bridging germylene ligands with the experimentally observed Ge???Ge bond lengths of 2.8263(4) Å (L=PMe₃) and 2.928(1) Å (L=tBuNC), which are close to the longest Ge? Ge bond reported to date [2.714(1) Å]. Significant Ge???Ge interactions between the germylene and germyl ligands (PMe₃ complexes > tBuNC complexes) are supported by DFT calculations, Wiberg bond indices (WBI), and natural bond orbital (NBO) analyses. Exchanging tBuNC for PMe₃ ligands increases the Ge???Ge interaction, and simultaneously activates two Pd? Ge bonds. Adding the chelating diphosphine 1,2‐bis(diethylphosphino)ethane (depe) to the PMe₃ complexes results in the intramolecular coupling of germyl and germylene ligands followed by extrusion of a digermane.     

Magnetic nanoporous MCM‐41 supported ionic liquid/palladium complex: An efficient nanocatalyst with high recoverability

In this study, a novel magnetic mesoporous MCM‐41 silica supported ionic liquid/palladium complex (Fe₃O₄@MCM@IL/Pd) with core‐structure was prepared and characterized and its catalytic performance was developed under green conditions. The Fe₃O₄@MCM@IL/Pd was prepared via a post grafting method and was characterized using Fourier transform infrared spectroscopy, thermal gravimetric analysis, wide‐ and low‐angle powder X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, vibration sample magnetometer and energy‐dispersive X‐ray analyses. This was applied as an efficient and recoverable nanocatalyst for the one‐pot synthesis of pyrano[2,3‐d]pyrimidine derivatives under ultrasonic conditions. The catalyst was magnetically recovered and reused for 12 consecutive cycles without significant loss of its activity and selectivity.     

Towards Asymmetric Catalysis in the Major Groove of 1,1′‐Binaphthalenes

Four new diphosphane ligands, (R)‐ 4 , (R)‐ 5 , (S)‐ 6 , and (R)‐ 7 (Schemes 3, 4, 6, and 7), featuring metalcoordination sites located in the major groove of chiral 1,1′‐binaphthalene clefts, were prepared in enantiomerically pure form. The performance of this new class of ligands was tested in enantioselective, Pd‐catalyzed allylic alkylation reactions with acyclic and cyclic methyl carbonates 28 – 30 as substrates under various reaction conditions (Schemes 8 and 9). Using sodium phenyl sulfinate as a nucleophile, the reactivity of the catalysts formed with the new ligands and suitable palladium precursors was found satisfactory (>90%); however, the ee values were in all cases poor (<4%). Slightly better results were obtained using anions of dimethyl malonate as nucleophiles, but, also in these cases, the ee values never exceeded 17% (Table). ³¹P‐NMR‐Spectroscopic investigations revealed the formation of multiple‐catalyst species in solution (Fig. 2), and molecular modeling suggested a lack of embedding of the coordinated substrate in a `chiral pocket' (Fig. 3), which probably accounts for the observed low level of enantioselectvity.     

Higher α‐olefins carbonylation in aqueous media by Pd(II) catalysts modified with substituted diphosphine ligands: Aqueous polyketone latices with high solid contents and molecular weights

Water‐soluble palladium complexes cis‐[Pd(L)(OAc)₂] ( 1–8 ) (L represents a diphosphine ligands of the general formula CH₂(CH₂PR₂)₂, where for a : R ? (CH₂)₆OH; b–g : R ? (CH₂)_nP(O)(OEt)₂, n = 2–6 and n = 8; h : R ? (CH₂)₃NH₂) have been employed, after activation with a large excess of HBF₄, for emulsion polymerization of alkenes (propene, butene, and their equimolar mixtures) with carbon monoxide. Aliphatic polyketone lattices with a high solid content (21%), high molecular weight (6.3 × 10⁴ g mol^?1), and narrow polydispersities (M_w/M_n ≈ 2) were isolated. The catalytic activity of the dicationic palladium (II) based catalysts, C1–C8 is highly dependent on the length of the alkyl chain of the ligand. Catalyst 3 proved to be highly active for propene/CO copolymers, whereas 6 is active for butene/CO and propene/CO‐butene/CO systems. The presence of methyl β‐cyclodextrin, as a phase‐transfer agent, and undecenoic acid, as an emulsifier, increase the molar mass and the stability of the polyketones and finally the activity of the catalyst. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6715–6725, 2009     

Pd(II) complexes of Schiff bases and their application as catalysts in Mizoroki–Heck and Suzuki–Miyaura cross‐coupling reactions

Schiff bases of 2‐(phenylthio)aniline, (C₆H₅)SC₆H₄N?CR (R = (o‐CH₃)(C₆H₅), (o‐OCH₃)(C₆H₅) or (o‐CF₃)(C₆H₅)), and their palladium complexes (PdLCl₂) were synthesized. The compounds were characterized using ¹H NMR and ¹³C NMR spectroscopy and micro analysis. Also, electrochemical properties of the ligands and Pd(II) complexes were investigated in dimethylformamide–LiClO₄ solution with cyclic and square wave voltammetry techniques. The Pd(II) complexes showed both reversible and quasi‐reversible processes in the ?1.5 to 0.3 V potential range. The synthesized Pd(II) complexes were evaluated as catalysts in Mizoroki–Heck and Suzuki–Miyaura cross‐coupling reactions. Copyright © 2015 John Wiley & Sons, Ltd.     

Palladium(II) Complexes of New Bulky Bidentate Phosphanes: Active and Highly Regioselective Catalysts for the Hydroxycarbonylation of Styrene

The synthesis of four new bulky bidentate phosphines that possess both tert‐butyl and trifluoromethylphenyl substituents is described. Symmetric ligands were readily obtained by alkylation of phosphidoboranes of the type Li[P(BH₃)(tBu)(Ar)] with dihaloalkanes. Non‐symmetric ligands were prepared from a new stable precursor, tBu₂P(BH₃)(CH₂)₃Br, that should prove useful for other ligand syntheses. Palladium(II) complexes of the four new ligands were prepared and were characterised by spectroscopic methods, microanalysis and X‐ray crystallography. The new [PdCl₂(L)] complexes were evaluated as catalysts for the hydroxycarbonylation of styrene and found to give unprecedented regioselectivity and yields for a diphosphine‐based catalyst. A study on promoter effects reveals that the presence of acid and chloride is necessary to achieve such selectivities. It has been proposed in the literature that such conditions result in a new pathway in which styrene is converted into 2‐phenethyl chloride, with the latter being the real substrate in the reaction. However, a deuterium labelling study seems to rule out this mechanism, at least under the conditions used herein.