N-methyl-2,2′-bipyridylium ion (bpyMe) complexes: Synthesis and cyclometallation of [Pd(bpyMe)2Cl2]2+

On prolonged heating in water Pd(bpyMe)Cl₃ (bpyMe = N-methyl-2,2′-bipyridylium cation) cyclometallates to give monomeric Pd(bpyMe-H)Cl₂, whereas the immediate products are a mixture of trans-[Pd(bpyMe)₂Cl₂]²⁺ and anionic palladium species. [Pd(bpyMe)₂Cl₂]²⁺ was synthesised directly from Na₂PdCl₄ and on heating gives Pd(bpyMe-H)Cl₂ with the elimination of bpyMe and H⁺.     

Palladium(II) halide complexes with 2,5-dimethyl-, 2-amino-, 2-amino-5-methyl-, 2-ethylamino- and 2-mercapto-5-methyl-1,3,4-thiadiazole

Some palladium(II) halide complexes with 2,5-dimethyl- (DTZ), 2-amino- (ATZ), 2-amino-5-methyl- (MATZ), 2-ethylamino- (EATZ) and 2-mercapto-5-methyl-1,3,4-thiadiazole (MTTZ) have been prepared and studied: PdX₂ · 2L (L = DTZ, ATZ, MATZ : X = Cl, Br, I; L = EATZ: X = Br, I; L = MTTZ: X = I), PdCl₂ · 2.5EATZ, PdCl₂ · 3MTTZ, PdBr₂ · 1.5MTTZ and PdX₂ · L (L = DTZ, ATZ, MATZ, EATZ: X = Cl, Br; L = MTTZ: X = Cl(H₂O), Br). In the PdX₂ · 2L, PdCl₂ · 2.5EATZ and PdCl₂ · 3MTTZ complexes the palladium ions are cis-(2X, 2L)-coordinated, the coordination sites being N_ring for DTZ, NR₂ for ATZ, MATZ, EATZ and C = S for MTTZ. PdBr₂ · 1.5MTTZ may be formulated as cis[PdBr₂-2L] · [PdBr₂ · L]. In the PdX₂ · L complexes the ligand very likely acts as bidentate by using a ring-nitrogen atom as the second coordination site.     

Polypyrrole-palladium systems prepared in PdCl2 aqueous solutions

In the work, reactions of a partially deprotonated polypyrrole doped with hydroxide ions (PPyOH) in various PdCl₂ aqueous solutions which differed in acidity were studied. Using X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy it was established that in the PdCl₂ solutions of lower acidity PPyOH was oxidatively doped and Pd⁰ and Pd²⁺ were incorporated into the polymer matrix. Pd²⁺ formed palladium(II) hydroxy-and/or aquochlorocomplex dopant anions and/or was coordinated by nitrogen atoms of the polymer (Pd-N bond). Additionally, deprotonation of PPyOH occurred in the PdCl₂ solutions of lower acidity. It was proposed that deprotonation of PPyOH was caused by nucleophilic attack of [PdCl₃(H₂O)]⁻ on the positively charged, doped polymer chain. By comparison of the PPyOH and chloride-doped polypyrrole (PPyCl)-palladium systems prepared in similar PdCl₂ solutions of lower acidity it was shown that the type of the counterion in the starting polymer has a decisive effect on the deprotonation process.PPyOH was less reactive towards palladium species in the PdCl₂ solutions of higher acidity where [PdCl₄]²⁻ was the dominant complex. PPy-palladium systems containing exclusively Pd²⁺ were obtained in this case. It was proposed that incorporation of palladium species in these conditions proceeded via an acid-base reaction or coordination of palladium ions by the polymer chain (Pd-N bond formation).Results of the studies may serve as the basis for the preparation of a variety of polypyrrole-supported palladium catalysts.     

Highly regio- and stereoselective PdCl2(MeCN)2-catalyzed cross coupling of 1,2-allenylic sulfoxides with allyl bromide

2-Allyl-1(E),3(E)-dienyl sulfoxides were prepared highly stereoselectively via the PdCl₂(MeCN)₂-catalyzed coupling reaction of 1,2-allenylic sulfoxides and allyl bromide. A rationale was proposed for this transformation.     

A mild and efficient selective tetrahydropyranylation of primary alcohols and deprotection of THP ethers of phenols and alcohols using PdCl2(CH3CN)2 as catalyst

Primary alcohols were selectively tetrahydropyranylated in good to excellent yields at room temperature using PdCl₂(CH₃CN)₂ as catalyst in tetrahydrofuran (THF) in the presence of phenols, secondary, and tertiary alcohols. The tetrahydropyranyl (THP) group could be efficiently removed using PdCl₂(CH₃CN)₂ as catalyst in CH₃CN, while other protection groups such as p-toluenesulfonyl (Ts), tert-butyldiphenylsilyl (TBDPS), benzyloxycarbonyl (Cbz), allyl, benzyl (Bn), and benzoyl (Bz) remained intact under these conditions.     

Palladium(II) saccharinate complexes trans-[Pd(sac)2(LH)2] with amino- and acetylamino-pyridine co-ligands: molecular structures of trans-[PdCl2(2-ampyH)2].2dmf (2-ampyH = 2-amino-3-methylpyridine) and trans-[Pd(κ2-2-acmpy)2] (2-acmpyH = 2-acetylamino-3-methylpyridine)

Reaction of Na₂[PdCl₄] with two equivalents of amino- or acetylamino-pyridines (LH) affords trans-[PdCl₂-(LH)₂] {LH = 2-amino-3-methylpyridine (2-ampyH), 3-aminopyridine (3-apyH), 2-acetylamino-3-methylpyridine (2-acmpyH), 3-acetylamino-pyridine (3-acpyH)}. An X-ray crystal structure of trans-[PdCl₂(2-ampyH)₂] shows that the 2-ampy-H ligands are coordinated in a monodentate fashion via the nitrogen atoms of the pyridine rings. Treatment of trans-[PdCl₂(2-acmpyH)₂] with NEt₃ affords the cyclometalated complex, trans-[Pd(κ²-2-acmpy)₂], the X-ray structure of which shows that the 2-acmpy ligand is coordinated to palladium in a bidentate fashion via the nitrogen atom of the pyridine ring and oxygen. Reaction of trans-[PdCl₂(LH)₂] with two equivalents of sodium saccharinate affords the bis(saccharinate) complexes, trans-[Pd(sac)₂(LH)₂], in which the saccharinate anions are coordinated via the amide nitrogen atom.     

Synthesis of a new class of unsymmetrical PCP′ pincer ligands and their palladium (II) complexes: X-ray structure determination of PdCl{C6H3-2-CH2PPh2-6-CH2PBu2}

The unsymmetrical PCP′ pincer ligands {C₆H₄-1-CH₂PPh₂-3-CH₂PBu^t₂} and {C₆H₄-1-CH₂PPh₂-3-CH₂PPrⁱ₂} and the corresponding palladium complexes: PdCl{C₆H₃-2-CH₂PPh₂-6-CH₂PBu^t₂} and PdCl{C₆H₃-2-CH₂PPh₂-6-CH₂PPrⁱ₂} have been synthesized in good yields. The molecular structure of PdCl{C₆H₃-2-CH₂PPh₂-6-CH₂PBu^t₂} was determined through a single crystal X-ray diffraction study. The palladium center was found to be located into a slightly distorted square planar environment in which the {C₆H₄-1-CH₂PPh₂-3-CH₂PBu^t₂} ligand is coordinated as a tridentate, PCP pincer type chelate. The complex, PdCl{C₆H₃-2-CH₂PPh₂-6-CH₂PPrⁱ₂} catalyzes the Heck coupling of iodobenzene with styrene.     

Crystal structure of <Emphasis Type="Italic">cis</Emphasis>-[PdCl<Subscript>2</Subscript>(CNMes)<Subscript>2</Subscript>]

The interaction between PdCl₂(CH₃CN)₂ and 2,4,6-Me₃C₆H₂NC (MesNC) proceeds with the substitution of acetonitrile ligands and leads to the synthesis of a cis-[PdCl₂(MesNC)₂] complex. The structure of this compound is determined by single crystal X-ray diffraction (XRD). The complex has a slightly distorted square-planar structure of the metal center with two cis-positioned isocyanide ligands. In both CN isocyanide moieties the triple bonds have lengths similar to the lengths of the respective bonds in other isocyanide complexes. In the structure, the cis-[PdCl₂(MesNC)₂] complexes are bound by weak С–H???Cl hydrogen bonds and π-stacking interactions.     

Preparation and coordination chemistry of Ph2P(CH2)nNHPiPr2 (n=2, 3)

Unsymmetrical diphosphine ligands of the type Ph₂P(CH₂)_nNHPPrⁱ ₂ [n=2 (1), 3 (2)] have been obtained by reacting the appropriate (diphenylphosphino)alkylamine, Ph₂P(CH₂)_nNH₂ with chlorodi-iso-propylphosphine, in the presence of triethylamine. Reaction of Ph₂P(CH₂)₂NHPPrⁱ ₂ with PdCl₂(PhCN)₂, PtCl₂(PhCN)₂, PtMe₂(cod) and PtClMe(cod), NiCl₂·6H₂O and Fe(CO)₂(η⁵-C₅H₅)I gives the corresponding chelate complexes, PdCl₂L, PtX₂L, NiCl₂L and Fe(CO)(η⁵-C₅H₅)L. Reaction of Ph₂P(CH₂)₃NHPPrⁱ ₂ with PtCl₂(PhCN)₂, PtMe₂(cod) and PdCl₂(PhCN)₂ yields the chelate complexes and reaction with PtClMe(cod) led to a 50:50 mixture of chelate isomers.     

A new catalytic system for the copolymerization of dicyclopentadiene with CO: PdCl2/phen/M(CF3SO3)n

A new three-component catalytic system, PdCl₂/phen/M(CF₃SO₃)_n, was studied in the copolymerization of dicyclopentadiene (DCPD) with CO. It was found that the PdCl₂/phen/CF₃SO₃H catalytic system gave a very low catalytic activity, and the PdCl₂/phen/M(CF₃SO₃)_n catalytic system exhibited high activity when M(CF₃SO₃)_n was introduced instead of CF₃SO₃H. The resultant cooligomer was analyzed using various techniques such as FT-IR, ¹H NMR, ¹³C NMR, DSC and TGA. The results indicated that the copolymer was a polyspiroketal (PS) of CO and DCPD. Due to the tension of the ring of DCPD, the degree of copolymerization is low and the degree of crystallinity is also not high. The effects of ligands, M(CF₃SO₃)_n, solvents, 1,4-benzoquinone/PdCl₂ molar ratio, and temperatures on the copolymerization have been discussed in detail. The results showed that this novel catalytic system exhibited highly efficient activity, especially when 1,10-phenanthroline (phen) was used as ligand and Cu(CF₃SO₃)₂ was used as cocatalyst. The corresponding reaction rate was 49 000 g PS/molPd h when the reaction was carried out at 60 °C and 3.0 MPa of CO. The weight average molecular weight (M_w) and the number average molecular weight (M_n) of the resultant cooligomer were 1180 g/mol and 564 g/mol, respectively.     

Complex formation of PdCl<Subscript>2</Subscript> with 1-substituted 3,5-dimethylpyrazoles

Herein the synthesis of 3-(3,5-Dimethyl-1H-pyrazol-1-yl)butanal oxime (L) and its complex formation with PdCl₂ is studied. IR and 1Н NMR spectroscopic methods as well as X-ray diffraction analysis (СIF file CCDC no. 1531058) elucidate that the nitrogen atoms N(4) and N(15) from pyrazole and imine group of oxime respectively, participate in coordination with PdCl₂. Moreover, primarily thermal stability test shows that [PdCl₂(L)] complex (I) is quite stable at moderate temperatures and intense decomposition of latter occurs ca 200–210°C. As a consequence of thermal decomposition, both volatile ligand and its dehydration by-product 3-(3,5-dimethyl-1H-pyrazol-1-yl)butanenitrile are formed. Afterwards, the anticonvulsant properties of PdCl₂, L, and I are of interest and well studied in this section.     

SnCl2-mediated carbonyl allylation in fully aqueous media

Systematic studies were performed on SnCl₂-mediated carbonyl allylation reaction between aldehydes and allyl halides in fully aqueous media. Totally three valuable reaction systems were discovered, which were SnCl₂/CuCl₂, SnCl₂/TiCl₃, and SnCl₂/PdCl₂. They all provided good to excellent yields in the allylation of aliphatic and aromatic aldehydes under very mild and convenient conditions. SnCl₂, by itself, was also found to be effective for the allylation reaction when allyl bromide was employed. However, the SnCl₂-only reaction could only tolerate very small amount of water as the solvent. The SnCl₂/CuCl₂, SnCl₂/TiCl₃, and SnCl₂/PdCl₂-mediated reactions exhibited good regioselectivity favoring the γ-adduct when cinnamyl halides were employed as the allylation reagent. The same reactions with cinnamyl halides also showed good diastereoselectivity favoring the anti-product. Mechanistic studies using proton NMR techniques suggested that the additive (i.e., CuCl₂, TiCl₃, PdCl₂) could accelerate the formation of allyltin intermediate, but this step was shown not to be the most important for the allylation. Thus we proposed that the Lewis acid catalysis effect exerted by the additive was the main reason for the observed reactivity enhancement.     

Regiospecific synthesis of symmetrical (1E,3E) 2,3-difluoro-1,4-diphenyl-buta-1,3-dienes via palladium-catalyzed cross-coupling of (Z) 2-bromo-2-fluoroethenylbenzenes in presence of bis(pinacolato)diboron

The cross-coupling reaction of (Z) 1-bromo-1-fluoroalkenes catalyzed by PdCl₂(PPh₃)₂-2PPh₃ (3%) and CsF in Tetrahydrofuran (THF) in presence of bis(pinacolato)diboron led to (1E,3E) 2,3-difluoro-1,4-disubstituted-buta-1,3-dienes in high yields.     

Syntheses and structures of bowl-shaped triarylphosphines and their palladium(II) complexes

Novel bowl-shaped triarylphosphines, tris(2,2″,6,6″-tetraalkyl[1,1′:3′,1″-terphenyl]-5′-yl)phosphines (TRMP: alkyl = methyl; TRIP: alkyl = isopropyl), were prepared by lithiation of the corresponding m-terphenyl bromides followed by reaction with PCl₃. X-ray crystallographic analysis revealed that the phosphorus center of TRMP is embedded in the shallow bowl-shaped cavity of 16 Å diameter and 2.1 Å depth formed by three radially extended m-terphenyl units. Its cone angle was estimated to be as large as 174°. In the crystal structure of TRIP, the depth of the cavity and cone angle increased to 3.3 Å and 206°, respectively, because of the different arrangement of the m-terphenyl units. In contrast with TRMP, which can form the mononuclear complex, PdCl₂(TRMP)₂ (6), in the reaction with PdCl₂, treatment of TRIP (1 or 3 eq.) with PdCl₂ produced the trinuclear palladium(II) chloride complex, [(PdCl₂)₃(TRIP)₂] (8), as a single product. X-ray crystallography established the structure of 8, where the trimer of PdCl₂ is terminated by two TRIP ligands. The formation of the different types of PdCl₂ complexes was explained in terms of the difference in the cavity shape of TRMP and TRIP.     

Use of highly reactive, versatile and air-stable palladium-phosphinous acid complex [(t-Bu)2P(OH)]2PdCl2 (POPd) as a catalyst for the optimized Suzuki-Miyaura cross-coupling of less reactive heteroaryl chlorides and arylboronic acids

Using highly reactive air-stable palladium-phosphinous acid complex [(t-Bu)₂P(OH)]₂PdCl₂ (POPd) as a catalyst, synthesis of heteroaryl-aryl cross-coupled products via palladium-catalyzed Suzuki-Miyaura coupling of less reactive substituted 3-chloropyridines with arylboronic acids was achieved in high yields.     

Solvent,ligand and temperature effects on the rates of reactions of cis-[PdCl2(CNR)(L)] with secondary amines

The kinetics of the reaction of cis-[PdCl₂(CN-p-C₆H₄Cl)(PPh₃)] with N-methylaniline yielding the carbene derivative cis-[PdCl₂ {C(NH-p-C₆H₄Cl)NMePh} (PPh₃)] have been studied in various solvents such as acetone, 1, 4-dioxane, 1,2-dichloroethane, and benzene. Overall rates for the stepwise process increase with decreasing ability of the solvent to form hydrogen bonds with the attacking amine. A kinetic study is also reported for the reactions of N-methylaniline with cis- [PdCl₂(CN-p-C₆H₄Me)(L)] in 1,2-dichloroethane (L = P(OMe)₃, P(OMe)₂Ph, PPh₃. PMePh₂, PMe₂Ph, PEt₃, PCy₃). The cis ligand L affects reaction rates through both steric and electronic factors. The nucleophilic attack of the amine on the CN carbon atom of coordinated isocyanide is favoured by low steric requirements and high π-acceptor ability of L. The activation parameters for the bimolecular nucleophilic attack when L = PPh₃ are △H^≠₂ = 9.8 ± 0.7 kcal/mol and △S^≠₂ = — 30 ± 2 e.u.     

Conversion of pentynol to pentanone catalysed by Pd(II) metal centres

The cyclization of 3- or 4-pentyn-1-ol is catalysed by PdCl₂ or trans-[PdCl₂L₂] (L = R-camphorimine; R = Ph; Prⁱ; NMe₂) complexes at room temperature affording heterocyclic compounds, respectively, 2-methyl-2-pent-3-ynyloxy-tetrahydrofuran or 2-methyl-2-pent-4-ynyloxy-tetrahydrofuran which subsequently add water to give selectively 5-(2-methyl-tetrahydrofuran-2-yloxy)-pentan-2-one from both starting materials. By hydrolysis 5-(2-methyl-tetrahydrofuran-2-yloxy)-pentan-2-one undergoes ring cleavage to form 5-hydroxy-2-pentanone. The catalytic activity and selectivity of complexes trans-[PdCl₂L₂] (L = R-camphorimine) depend on the characteristics of the R group (NMe₂ > Prⁱ > Ph). The catalytic activity of PdCl₂ is comparable to that of trans-[PdCl₂L₂] (L = Ph-camphorimine) which is the less efficient catalyst.     

Phenoxide-assisted P-C bond cleavage in PdCl2(PPh3)2 under very mild conditions

PdCl₂(PPh₃)₂ reacted with NaOAr (Ar = Ph, p-tolyl) at 0 °C to afford PdCl(Ph)(PPh₃)₂, instead of PdCl(OAr)(PPh₃)₂, in 12-16% isolated yields based on Pd. The structure was confirmed by NMR and X-ray crystallography. GC-MS analysis of the reaction solution revealed that OPPh₂(OAr), OPPh(OAr)₂, and OP(OAr)₃ are formed, while NMR studies indicated that PdCl(Ph)(PPh₃)₂ is produced when PdCl(OAr)(PPh₃)₂ decomposes. The reaction of PdCl₂(PPh₃)₂ with Bu₃Sn(OC₆H₄-p-OMe) also gave PdCl(Ph)(PPh₃)₂ in 8% isolated yield. These results suggest that PdCl(OAr)(PPh₃)₂ is highly labile and the aryloxy ligand exchanges with the phenyl groups in triphenylphosphine even under very mild conditions.     

Synthesis of a new bidentate ferrocenyl N-heterocyclic carbene ligand precursor and the palladium (II) complex trans-[PdCl2(CfcC)], where (CfcC) = 1,1′-di-tert-butyl-3,3′-(1,1′-dimethyleneferrocenyl)-diimidazol-2-ylidene

A new ferrocenyl-N-heterocyclic carbene ligand precursor 1,1′-bis[(1-tert-butylimidazolium)-3-methyl]ferrocene dichloride has been synthesised and structurally characterised. The imidazolium salt was readily deprotonated in situ with KN(SiMe₃)₂ and reacted with [PdCl₂ (cod)] to afford the structurally characterised palladium (II) complex trans-[PdCl₂(C^∧fc^∧C)], where (cod) = 1,5-cyclooctadiene and (C^∧fc^∧C) = 1,1′-di-tert-butyl-3,3′-(1,1′-dimethyleneferrocenyl)-diimidazol-2-ylidene.     

Synthesis and evaluation of substituted pyrazoles palladium(II) complexes as ethylene polymerization catalysts

The substituted pyrazole palladium complexes, (3,5-^tBu₂pz)₂PdCl₂ (1) (3,5-Me₂pz)₂PdCl₂ (2), (3-Mepz)₂PdCl₂ (3) and (pz)₂PdCl₂ (4) (pzH=pyrazole), can be prepared from the reaction of (COD)PdCl₂ with the appropriate pyrazole. The chloromethyl derivative, (3,5-^tBu₂pz)₂PdCl(Me) (5), was prepared from (COD)PdClMe and ^tBu₂pzH. X-ray crystal structure determination of 1 and 5 established their structures in the solid state to be the trans-isomer. After activation of 1-4 and 5 with methylaluminoxane (MAO) the resulting palladium complexes were used as catalysts in ethylene polymerization, yielding linear high-density polyethylene (HDPE). The highest activity was observed for (3,5-^tBu₂pz)PdClMe.