Dicationic Palladium Research Articles

The Pd3(dppm)3(CO)2+ cluster: an efficient electrochemically assisted Lewis acid catalyst for the fluorination and alcoholysis of acyl chlorides.

The dicationic palladium cluster Pd3(dppm)3(CO)2+ (dppm = bis(diphenylphosphino)methane) reacts with acid chlorides RCOCl (R = n-C6H13, t-Bu, Ph) to afford quantitatively the chloride adduct Pd3(dppm)3(CO)(Cl)+ and the acyl cation RCO+ as the organic counterpart. The dicationic reactive cluster can be reformed by electrolyzing the chloride complex with a copper anode leaving CuCl as a byproduct. The combination of these two reactions provides an electrocatalytic way to form the acylium from the acid chloride. Indeed, in CH2Cl2, 0.2 M NBu4PF6, or NBu4BF4, the electrolysis of the acid chloride in the presence of a catalytic amount of the cluster (1%) gives in good yields the acid fluoride RCOF, arising from the coupling of the acylium with a F(-) issued from the fluorinated supporting electrolyte. Alternatively, in CH2Cl2 or 0.2 M NBu4ClO4, by operating with an alcohol R'OH as the nucleophile, the electrolysis gives the ester RC(O)OR' as the only final product.

Copolymerization of carbon monoxide with exo‐methylenecycloalkane and dienes: synthesis of functionalized aliphatic polyketones

AbstractSynthesis of functional aliphatic polyketones was achieved by co‐ and terpolymerization of the strained exo‐methylenecycloalkane, methylenecyclopropane (MCP), and also the dienes 1,5‐hexadiene, 1,7‐octadiene and 1,6‐heptadien‐4‐ol, with carbon monoxide and propene, using the dicationic palladium(II) phosphine complex [Pd(dppp) (NCCH3)2](BF4)2 (I) (dppp is 1,3‐bis(diphenyl‐phosphino)propane) as the catalyst precursor. The resulting MCP/CO copolymer contains both ring‐opened and cyclic microstructures. Ring‐opening copolymerization yields exo‐methylene functionalized polyketone. In contrast to hexadiene/carbon monoxide copolymer (Hx/CO), no ring structures were observed in the alternating octadiene/carbon monoxide (Oc/CO) and heptadien‐4‐ol/carbon monoxide (Hp‐ol/CO) copolymers. The remaining double bonds were left intact to yield polymers with olefinic functionalities in the side chains.© 2001 Society of Chemical Industry

Enantioselective Alternating Terpolymerization of Propene and Ethene with Carbon Monoxide

Optically active poly(1,4-ketone)s were synthesized by alternating terpolymerization of carbon monoxide with ethene and propene using the dicationic palladium(II) complexes [Pd(PΛP)(H 2 O) 2 ](OSO 2 CF 3 ) 2 1-3 (where PΛP is a chelate diphosphine ligand) modified with the optically pure ligands (R)(S p )-1-[2-(diphenylphosphino)-ferrocenyl]ethyl-dicyclohexylphosphine 1a, (R)-6,6'-(dimethoxybiphenyl-2,2'-diyl)bis(dicyclochexylphosphine) 2a and (S)-6,6'-(dimethoxybiphenyl-2,2'-diyl)bis-(diphenylphosphine) 3a as catalyst precursors. The influence of different ethene to propene ratios in the reaction mixture on the productivity of the catalyst systems as weel as on the composition and structure of the produced terpolymers was investigated. For all catalyst precursors, the distribution of the two olefin comonomers appears to be random. The productivity is more strongly increased by increasing the ethene concentration when the catalyst system is not regiospecific for propene, i.e. when 3 is used. The influence of the growing chain on the enantioface selection for propene appears to be of minor importance with respect to the enantioselectivity caused by the enantiomorphic site of the catalyst.

Homo- and Copolymerization of Strained Cyclic Olefins with New Palladium(II) Complexes Bearing Ethylene-Bridged Heterodonor Ligands

Amorphous and high molar mass polymers of norbornene and phenylnorbornene (endo/exo ratio of 80/20) were prepared by the use of new dicationic palladium(II) single-component catalysts of the general type [Pd(L∩L)(NCCH 3 ) 2 ](BF 4 ) 2 . [(L∩L) = 2-(diphenylarsino)-1-(methylthio)ethane (S∩As, 1) (4), 2-diphenylphosphino)-1-methylthio)ethane (S∩P, 2) (5), 1, 2-bis(diphenylphosphino)ethane (P∩P, 3) (6). With increasing the trans influence of the donor atom in the ligands (P>As>S) the polymerization activity of the catalysts towards polymerization of norbornene increases instantly. Both the molecular weight and the thermal behavior of the polymer can be tailored using ethene as chain transfer agent. Catalyst 4 is also active towards the alternating copolymerization of carbon monoxide and norbornene. The isolated copolymer is highly soluble in toluene, THF and chlorinated solvents. The DSC measurement of the norbornene-carbon monoxide copolymer showed a melting temperature (T m ) of 241°C (ΔH f = 47.3 J/g) and a glass transition temperature (T g ) of 161°C which is about 170°C lower compared to the homopolynorbornene (T g ≃ 330°C).

Olefins Coordinated at a Highly Electrophilic Site − Dicationic Palladium(II) Complexes and Their Equilibrium Reactions with Nucleophiles

Dicationic olefin palladium(II) complexes [Pd(PNP)(olefin)](BF4)2 [olefin = ethylene, propene, styrene, (Z)-2-butene, (E)-2-butene, norbornene; PNP = 2,6-bis(diphenylphosphanylmethyl)pyridine] have been prepared and characterized by 1H, 13C, and 31P NMR spectroscopy. The coordinated double bond in these complexes is strongly electrophilic, and easily adds a variety of nucleophiles NuH (H2O, MeOH, aliphatic and aromatic amines). This reaction competes with olefin displacement in a rapidly reversible equilibrium process, as a result of which the addition products can also be obtained starting from the substituted compounds [Pd(PNP)(NuH)](BF4)2 and the appropriate olefin. Equilibrium constants for the addition and substitution reactions have been determined in a number of cases. Proton abstraction from [Pd(PNP)(CHRCHR′NuH)]2+ by NaHCO3 quantitatively drives the equilibrium to β-functionalized alkyl complexes of the general formula [Pd(PNP)(CHRCHR′Nu)](BF4), which are unusually stable to β-H elimination.

Catalytic activity of cationic diphospalladium(II) complexes in the alkene/CO copolymerization in organic solvents and water in dependence on the length of the alkyl chain at the phosphine ligands

A series of diphos ligands CH2(CH2PR2)2 (1a–x) (a–g: R=(CH2)nOH, n=1, 3–8; h–k: R=(CH2)nCH(CH2OH)2, n=3–6; l–u: R=CnH2n+1, n=1–8, 10, 14; v–x: R=CH(CH3)2, (CH2)2CH(CH3)2, (CH2)3CH(CH3)2, (Scheme 1 ), provided with functionalities of different polarity, was prepared photochemically by hydrophosphination of the corresponding 1-alkenes with H2P(CH2)3PH2 or reaction of Grignard reagents with Cl2P(CH2)3PCl2. The water-soluble palladium complexes [(R2P(CH2)3PR2)Pd(OAc)2] (2a–k) were obtained by reaction of Pd(OAc)2 with the ligands 1a–k in ethanol–acetonitrile. Treatment of PdCl2(NCC6H5)2 with 1l–x afforded the dichloropalladium(II) complexes [(R2P(CH2)3PR2)PdCl2] (3l–x). Upon chloride abstraction with AgBF4 in dichloromethane–acetonitrile the dicationic palladium(II) complexes [(R2P(CH2)3PR2)Pd(NCCH3)2][BF4]2 (4l–x) are formed. The structure of 4n (R=n-Pr) was investigated by an X-ray structural analysis. In particular the water-soluble complexes 2c–k proved to be highly active in the carbon monoxide/ethene copolymerization under biphasic conditions (water–toluene). In the presence of an emulsifier and methanol as activator the catalytic activity increased by a factor of about three. Also higher olefins could be successfully incorporated into the copolymerization with CO and the terpolymerization with ethene and CO. The catalytic activity of the dicationic complexes 4l–x in the propene or 1-hexene/CO copolymerization strongly depends on the length of the alkyl chain R. At 25°C a maximum is achieved in the case of 4q (R=nHex) which is five times more active than the corresponding catalyst with the dppp-ligand. This maximum is shifted to 4t (R=n-C10H21) if the temperature is raised to 60°C. The 1-alkene/CO copolymers are distinguished by their regioregular microstructure and their ultra high molecular weights. Compared to the sulfonated dppp-SO3 catalyst the water-soluble complexes 2c,e,f,h are responsible for a higher 1-hexene incorporation in the terpolymerization of ethene with 1-hexene and CO.

Palladium(II) complexes with hemilabile etherdiphos ligands in the alternating copolymerization of carbon monoxide with olefins

The potentially hexadentate diphos ligands (ROCH 2CH 2) 2P(CH 2) 3P(CH 2CH 2OR) 2 ( 1a-d) (R=Et ( a), n-Bu ( b), t-Bu ( c), Cy ( d)) are accessible by photochemically induced hydrophosphination of the vinyl ethers CH 2CHOR with the diprimary phosphine H 2P(CH 2) 3PH 2. Treatment of 1a–d with (PhCN) 2PdCl 2 in CH 2Cl 2 leads to the dichlorodiphospalladium(II) complexes 2a–d, from which the dicationic palladium(II) complexes 3a–d were obtained by abstraction of the chlorides with AgBF 4 in CH 2Cl 2. In 3a–d the etherdiphos ligands are coordinated in a η 4(O,P;O′,P′) fashion. A rapid chemical exchange between the η 2-P ∩O chelated and the η 1-P coordinated part of the ligands in 3a–d was demonstrated by means of temperature-dependent 13C{ 1H} NMR spectroscopy. Both PdO bonds in 3a–d are easily cleaved by polar solvents such as acetonitrile and water resulting in the formation of the adducts 3b · 2CH 3CN, 3c · H 2O, and 3c · 2H 2O. The molecular structures of 2a and 3c · H 2O were determined by single crystal X-ray diffraction methods. Under a total pressure of 60 bar ethene/CO and propene/CO, respectively, 3a-d are highly active catalysts in the copolymerization of olefins with carbon monoxide. GPC measurements revealed high molecular weights of these polyketones.

Chiral palladium(II) complexes bearing tetradentate nitrogen ligands: synthesis, crystal structure and reactivity towards the polymerization of norbornene

A synthesis for a series of tetrapodal nitrogen ligands ( N,N′-dibenzyl- N,N′-di(quinoline-2-methyl)-1,2-ethylene diamine (DBQED, 1), N,N′-dimethyl- N,N′-di(quinoline-2-methyl)-1,2-ethylene diamine (DMQED, 2), (1 R,2 R)-(−)- N,N′-di(quinoline-2-methylene) diiminocyclohexane (DQEDC, 3), N,N′-di(quinoline-2-methylene)-1,2-phenylene diimine (DQPD, 4) and for their corresponding neutral and cationic palladium(II) complexes of the types [( 1, 2, 4)PdCl 2] ( 5a, 6a, 7) and [( 1, 2, 3, 4)Pd(NCCH 3) x ](Y) 2 ( 5b, 5c, 6b, 6c, 8, 9), x=0, 2; Y=BF 4 −, NO 3 − is reported. The dicationic palladium(II) complex [Pd(DBQED)(NO 3) 2·H 2O] ( 5c) crystallizes in the monoclinic space groups P2 1/ c (no. 14) with a=11.458(1), b=15.302(1) Å, c=20.644(2) Å, β=99.23(1)° and V=3572.7 Å 3, Z=4. All four nitrogen donors are attached to the Pd(II)-center in the chiral and C 2-symmetric complex 5c. The two quinoline nitrogen atoms of the more rigid Schiff bases (DQEDC, 3; DQPD, 4) do not coordinate coincidentally to Pd(II). A fluxional coordination behavior is suggested for these quinoline donors, which enables this new complex family to act as catalysts for norbornene polymerization, even when chloride is present as a counter ion. Introduction of an enantiomerically pure trans-1,2-cyclohexyl bridge into the Schiff base ligand systems afforded the formation of partially stereoregular polynorbornene.

Oxidative Addition of a Hypervalent Transannular Sulfur–Sulfur Bond to a Pd(0) Complex: Synthesis and Crystal Structures of 1,5-Dithiacyclooctanepalladium(II) Bis(trifluoromethanesulfonate) Having Phosphine Ligands

Abstract A hypervalent compound 1,5-bis(trifluoromethylsulfonyloxy)-1λ4,5λ4-dithiabicyclo[3.3.0]octane (1) oxidatively reacted with Pd2(dba)3 (dba = dibenzylidene acetone) in acetonitrile to give a dicationic complex [Pd(dtco)(CH3CN)2](OTf)2 (2) (DTCO = 1,5-dithiacyclooctane), in which the DTCO ligand coordinated in cis-chelation to the palladium metal. Acetonitrile in 2 was labile enough to be readily replaced by phosphine ligands to give dicationic DTCO-phosphine palladium complexes of the formula [Pd(dtco)(L)2](OTf)2 (3: L = PMe2Ph; 4: L = PPh3; 5: L2 = 1,2-bis(diphenylphosphino)ethane; 6: L2 = (R)-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl). Molecular structures of 5 and 6 have been characterized by X-ray analysis, indicating that each of these two complexes consists of a discrete dicationic palladium(II) species [Pd(dtco)L2]2+ and two trifluoromethanesulfonate ions without any cation–anion bonding interaction, and revealing that the DTCO is coordinated to the palladium center as a bidentate ligand and that two phosphorus atoms ultimately coordinated to the metal in cis-fashion.

A highly selective water-soluble dicationic palladium catalyst for the biphasic hydroxycarbonylation of alkenes

The application of a water-soluble diphosphine with a xanthene-type backbone in the biphasic palladium-catalysed hydroxycarbonylation reaction of alkenes leads to the selective formation of carboxylic acids.

Polyketone materials: control of glass transition temperature and surface polarity by co‐ and terpolymerization of carbon monoxide with higher 1‐olefins

AbstractHighly soluble alternating 1‐olefin/carbon monoxide copolymers with olefin monomers (H2CCHR) containing 4, 5, 6, 10, 14, 16 and 18 C‐atoms in the R‐substituents were prepared by the use of dicationic palladium(II) phosphine catalysts and an optimized amount of methanol as activator. In terpolymerization experiments the influence of icosene‐CO or octadecene‐CO units, distributed randomly along a propene‐CO or ethene‐CO copolymer backbone, on molecular weight, glass transition temperature and on the surface polarity of films casted from solution has been investigated. As the length of the α‐olefin side chain increases, the glass transition temperature (Tg) of the copolymer is reduced from room temperature to almost −60°C. For octadecene‐CO and icosene‐CO copolymers side chain crystallization occurs, leading to elastic materials. Contact angle measurements, performed on water drops located on the surface of selected co‐ and terpolymer films demonstrate the wide range of surface polarity which can be covered by simple copolymerization of polar CO groups with apolar alkenes.

Ultrahigh molecular weight alternating propene/ethene/carbon monoxide terpolymers with elastic properties

AbstractSoluble propene/ethene/CO terpolymers (EPEC) with ultrahigh molecular weight (up to 1.2 × 106 g/mol) were prepared by the use of dicationic palladium(II) phosphine catalysts and an optimized amount of water as activator. When the molar ratio of ethene/CO to propene/CO is below 50 mol‐%, the terpolymers are thermoplastic elastomers with excellent properties. Above this ratio the terpolymers are crystalline thermoplastics. The ultrahigh molecular weight elastomers are highly soluble in organic solvents such as CH2Cl2 and CHCl3.

Palladium(II) complexes of chiral tridentate nitrogen pybox ligands

A series of mono- and di-cationic palladium(II) complexes containing different chiral tridentate nitrogen ligands, pybox, have been prepared [pybox = 2,6-bis[4′-( S)- iPr (or Ph, or Bz or p-EtOC 6H 4)oxazoline-2′-yl]pyridine ( 1–4), respectively]. The molecular structures for two of these, [Pd(CH 3CN)( 2)](BF 4) 2 ( 6) and [Pd(PPh 3)( 3)](BF 4) 2 ( 21g), have been determined by X-ray diffraction and show no major steric hindrance in the fourth coordination position. In connection with the aldol reaction of CNCH 2CO 2Me with PhCHO, several new isonitrile Pd II complexes have also been prepared. It is shown that, under catalytic conditions, the chiral tridentate pybox ligand is completely displaced, thus explaining its failure as a chiral auxiliary. Preparative details for a series of chiral Pd(L)( 3) n+( BF 4) n ( 21) complexes [L = 4-methylpyridine, 2,6-dimethylpyridine, 4-methyl aniline, H 2NCH 2CH(OMe) 2, H 2NCH 2CH 2OH, H 2N(CH 2) 5CH 3, N 3 −, HCO 2 −] Cl −] are given, as are preparative details for some model Pd II acetonitrile complexes with chiral phosphorus and nitrogen chelating ligands. For 6, i.e. PdC 25H 22N 4O 2B 2F 8, the crystals are monoclinic with space group P2 1 (No. 4), a = 13.582(6) A ̊ , b = 13.826(6) A ̊ , c = 14.667(6) A ̊ , β = 97.28(3)°, V = 2732(2) A ̊ 3, Z = 4 . For 21g, i.e. C 43H 38B 2F 8N 3O 2P 2Pd, the crystals are orthorhombic with space group, P2 12 12 1, a = 10.616(4) A ̊ , b = 16.774(2) A ̊ , c = 23.086(4) A ̊ , V = 4111(3) A ̊ 3, Z = 4 .

α-Methylene Cyclic Carbonate as a Conjunctive Agent for Aromatic Aldehydes

Abstract α-Methylene cyclic carbonate underwent decarboxylative cycloaddition to aromatic aldehydes to yield dihydrofuranone derivatives in the presence of a dicationic palladium complex.