Palladium Complexes Of General Formula Research Articles

Highly Recoverable Pd(II) Catalysts for the Mizoroki–Heck Reaction Based on N-Heterocyclic Carbenes and Poly(benzyl ether) Dendrons

Two series of bis(imidazolylidene)palladium complexes of general formula [PdBr2(NHC)2] have been prepared. The molecular weight of the complexes was enlarged by bonding poly(benzyl ether) dendrons of increasing size (G0 to G3) at the nitrogen atom of the NHC ligands. Complexes 1–4 contain monodentate NHC ligands coordinated in a trans mode, whereas complexes 9–12 contain a chelating ethylene-bridged bis(NHC) ligand. The complexes were recovered from the product stream of a Mizoroki–Heck reaction by nanofiltration through thermally and chemically stable ceramic membranes. The recoverability is better for larger complexes and chelate ligands. In particular, chelate G3 complex 12 maintained a constant activity during the 13 recovery cycles performed, affording an accumulated turnover number (TON) of 13 000. On average, around 99.5% of the metal is recovered in each recovery cycle, and contamination by palladium is only 3 mg per kg of product. Several models to explain the efficiency of the recovery are discu...

A convenient route to prepare mono- and dinuclear 2-benzoylpyridine palladacycles with imidate ligands

New dinuclear cyclometallated palladium complexes of general formula [{Pd(μ-NCO)(CˆN)} 2] (CˆN = 2-benzoylpyridine (bzpy) I; NCO = saccharinate (sacc) a, Phthalimidate (phthal) b or 4,5-dichlorophthalimidate (DiClphthal) c have been synthesized by a simple acid-base reaction involving the di-μ-hydroxo-precursor [{Pd(μ-OH)(bzpy)}2] recently reported. Analogous to Ic, complex IIc with CˆN = 2-phenylpyridine (phpy) II has also been prepared, meaning the first examples reported to date of complexes including 4,5-dichlorophthalimidate as ligand coordinating a metal centre. The reaction of bridged imidato precursors against triphenylphosphine to form the mononuclear N-bonded imidato derivatives of general formula [Pd(CˆN)(N-imidate)(PPh3)] IaP, IbP, IcP and IIcP has been achieved under mild conditions. The new complexes were characterized by partial elemental analyses and spectroscopic methods. Structural characterization by X-ray diffraction of Ib and IIcP, the first crystal structure of a complex containing 4,5-diClphthal that has been deposited to date on the Cambridge Structural Database, have confirmed the proposed formulae.

N-Heterocyclic-Carbene Complexes Readily Prepared from Di-μ-hydroxopalladacycles Catalyze the Suzuki Arylation of 9-Bromophenanthrene

New cyclometalated palladium complexes of general formula [Pd(Bmim)(X)(C∧N)] have been synthesized by a novel reaction route involving di-μ-hydroxo-palladacycles [{Pd(μ-OH)(C∧N)}2] (C∧N = 2-benzoylpyridine (Bzpy), I, previously unreported, or C∧N = 2-phenylpyridine (Phpy), II)] and 1,3-butylmethylimidazolium salts [HBmim]X (X: Cl, Br, I, or saccharinate (Sacc); a, b, c, or d complexes, respectively). This simple acid–base reaction could not be achieved under identical conditions when corresponding di-μ-acetate complexes were used as starting materials. An alternative pathway to NHC/imidate complexes has also been explored by reacting IIb with [Ag(Phthal)(SMe2)]2 (Phthal = phthalimidate, e) to obtain [Pd(Bmim)(Phthal)(Phpy)], IIe. Structural characterization by X-ray diffraction of complexes Id, IIb, IId, and IIe has confirmed the proposed formulas. The mononuclear complexes have shown to catalyze the scalable Suzuki–Miyaura cross-coupling of 9-bromophenanthrene with a wide scope of aryl boronic acids, irr...

An effective route for the synthesis of cationic palladium complexes of general formula [(Acac)PdL 1L 2] +A −

A series of palladium complexes of general formula [(Acac)PdL 1L 2] +A −, where L 1, L 2 = phosphines and A = BF 4, CF 3SO 3, were synthesized. Preliminary studies show that the complexes are active in selective dimerization of styrene and addition polymerization of norbornene.

Chiral, bridged bis(imidazolin-2-ylidene) complexes of palladium

Varieties of chiral, bridged bisimidazolium salts as well as the synthesis of palladium complexes of general formula [ bridge { NC(H) C(H)N ( R ∗ ) C ¯ } 2 PdBr 2 ] with the corresponding chelating N-heterocyclic carbene ligands is reported. This is the first systematic study of chiral bis(imidazolin-2-ylidene)palladium(II) complexes bearing chiral groups on the endocyclic nitrogens. Structural proof of such a chiral palladium(II) complex is presented by way of an X-ray diffraction study of complex 3a.

Bridged Imidazolium Salts Used as Precursors for Chelating Carbene Complexes of Palladium in the Mizoroki-Heck Reaction

A variety of chiral and achiral imidazolium salts is synthesized. Methylene-, ethylene-, propylene- and pyridinyl-bridged bis(imidazolium) halides are used to generate the respective free chelating carbenes. The synthesis of palladium complexes of general formula [cis-CH 2 {NC(H)=C(H)N(R)C} 2 PdX 2 ] with these chelating N-heterocyclic carbene ligands is reported. Structural proofs of complexes 28 and 46 are represented by X-ray diffraction studies. Catalytic applications in the Mizoroki-Heck reaction are presented.

Long‐Lived Palladium Catalysts for CO/Vinyl Arene Polyketones Synthesis: A Solution to Deactivation Problems

A series of cationic palladium complexes of general formula [Pd(Me)(MeCN)(N-N)][PF(6)] (N-N = (phen) 1 a, 4,7-dichloro-1,10-phenanthroline (4,7-Cl(2)-phen) 2 a, 4,7-diphenyl-1,10-phenanthroline (4,7-Ph(2)-phen) 3 a, 4-methyl-1,10-phenanthroline (4-Me-phen) 4 a, 4,7-dimethyl-1,10-phenanthroline (4,7-Me(2)-phen) 5 a, 5,5,6,6-tetrafluoro-5,6-dihydro-1,10-phenanthroline (F(4)-phen) 6 a, containing different substituted phenanthroline ligands, have been prepared from the corresponding neutral chloro derivatives [Pd(Me)(Cl)(N-N)], (1 b-6 b). The X-ray crystal structure of [Pd(Cl)(2)(4,7-Cl(2)-phen)] (2 b') was determined. DFT calculations show that the electron density on the metal is tuned by the substituents on the ligands. The catalytic behavior of complexes 1 a-6 a in the CO/styrene and CO/p-Me-styrene copolymerizations was studied in detail, showing that the generated catalysts are active for at least 90 h, yielding copolymers of high molecular weight. A firm correlation between the electron density on palladium on the one hand and the catalytic activity of the complexes and the molecular weight and the stereochemistry of the polyketones synthesized on the other hand has been established: the catalyst containing the F(4)-phen is thus far the most active among those tested, yielding the syndiotactic CO/styrene copolymer with a stereoregularity of 96 % (uu triad) and with an M(w) value of 1 000 000.

Carbosilane Dendrons as Solubilizers of Metal Complexes in Supercritical Carbon Dioxide

Palladium complexes of general formula [PdCl2(L)2], 3a−c, were synthesized by reaction of [PdCl2(COD)] (COD = 1,5-cyclooctadiene) with the appropriate functionalized phosphine L = [P(C6H5)n((C6H4CH2CH2Si(CH2CH2CH2SiEtMe2)3)3-n)] (n = 2, 2a; 1, 2b; 0, 2c, respectively), which integrated carbosilane dendritic wedges attached to the para-carbon atom of the phenyl group. As a result of the inclusion of the carbosilane dendrons, the solubility of the corresponding palladium complexes 3 in supercritical carbon dioxide (scCO2) was increased in comparison with the palladium complex containing a PPh3 ligand, which showed negligible solubility. The employment of these complexes as precatalysts in a selected Heck coupling reaction in scCO2 was investigated. Good activities were found for 3a−c in such a medium due to the acquired solubility, in contrast with the palladium complex containing PPh3, which showed no activity.

Allylpalladium(II) Complexes with Aminophosphane Ligands: Solution Behaviour and X‐ray Structure of cis‐[Pd(η3‐CH2CHCHPh){Ph2PCH2CHPhNH(2,6‐C6H3iPr2)}][PF6

AbstractA new β‐aminophosphane L2 [Ph2PCH2CH(Ph)NH(2,6‐C6H3iPr2)], bearing an asymmetric carbon atom and a vicinal prochiral nitrogen centre and (η3‐allyl)palladium complexes of general formula [Pd(η3‐C3H4R){η2‐Ph2PCH2CH(Ph)NHAr}][PF6] (1−6) (R = H, Me or Ph and Ar = Ph or 2,6‐C6H3iPr2) have been synthesised. NMR spectroscopic studies and a crystal structure analysis of complex 6 (R = Ph, Ar = 2,6‐C6H3iPr2) confirmed the highly diastereoselective coordination of the nitrogen atom. Because of the allyl fluxionality and the presence of asymmetric centres, all the complexes exist in solution as mixtures of up to four diastereomers. For the monosubstituted allyl complexes [Pd(η3‐C3H4R){Ph2PCH2CH(Ph)NHAr}][PF6] (3−6, R = Me or Ph) only cis/trans‐P and endo/exo isomers with syn‐oriented allyl substituents have been observed in solution. The diastereomeric distribution is subject to a steric control since a modification of the steric bulk of the allyl substituents and/or N‐aryl groups strongly affect the isomers ratio. An X‐ray diffraction study of compound 6 reveals a mixture of endo and exo cis‐P syn isomers and corresponds to the first cis‐P isomer crystal structure for an N,P‐ligand allyl complex. A phase‐sensitive 2‐D NOESY NMR analysis showed that complex 1 undergoes a selective syn‐anti exchange isomerisation, involving exclusively a trans‐P opening of the η3‐allyl moiety. Therefore, η3‐η1‐η3 rearrangements in allylic complexes 1−6 were assumed to occur via the regioselective formation of a σ‐allyl intermediate. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Mixed ligand palladium(II) complexes of oxalate and malonate with vitamin-B6 molecules: synthesis, crystal structure and kinetics

The synthesis of six mononuclear palladium complexes of general formula [Pd(ox)/(mal)L2] and [Pd(ox)/(mal)L′] (ox = oxalate, mal = malonate, both L and L′ are vitamin-B6 molecules (I), L = pyridoxine, pyridoxal and L′ = pyridoxamine) has been achieved. The structures of these compounds were established by elemental analysis, i.r. and 13C-n.m.r. [Pd(oxalate)(pyridoxine)2] was analyzed by single crystal X-ray diffraction. It exhibits square planar coordination with bond lengths 2.015 (2) A for Pd—N and 2.010 (2) A for Pd—O. The interaction of [Pd(ox)2]2− and [Pd(mal)2]2− with L has been followed kinetically in order to look into the nature of products and the mechanism of formation under the conditions [PdII-chelate] ≫ [L] and [L′].

Allylpalladium Complexes of Mixed-Donor Diphosphazane Ligands Bearing a Stereogenic Phosphorus Centre: Structure and Stereodynamics

( 3-Allyl)palladium complexes of general formula [Pd( 3-R C3H4){ 2-Ph2PN(R)PPh(N2C3HMe2-3,5)}](PF6) (3-6) and [Pd( 3-R C3H4){ 2-Ph2P(S)N(CHMe2)PPh(N2C3HMe2-3,5)}](PF6) (7-8), containing pyrazolyl-substituted diphosphazane ligands bearing a stereogenic phosphorus centre, have been synthesised. NMR spectroscopic and X-ray diffraction studies showed that the diphosphazane ligand in [Pd( 3-R C3H4){ 2-Ph2PN(R)PPh(N2C3HMe2-3,5)}](PF6) [R = Me or Ph; R = CHMe2 (3 and 5) or (S)-*CHMePh (4 and 6)] displayed unprecedented P,N-coordination instead of the hitherto observed P,P-coordination. These complexes existed in solution as mixtures of endo,syn,trans, exo,syn,trans, and endo,syn,cis diastereomers. In the solid state, only the endo,syn,trans isomer was observed for complex 5. Phase-sensitive 2-D NOESY and ROESY spectra showed that the complexes 3-5 underwent syn,anti isomerisation; the NMR spectroscopic data were consistent with a mechanism involving the opening of the 3-allyl group at the trans position with respect to the phosphorus centre. The isomerisation thus appeared to be electronically controlled. The complexes [Pd( 3-MeC3H4){ 2-Ph2P(S)N(CHMe2)PPh(N2C3HMe23,5)}](PF6) (7) and [Pd( 3-PhC3H4){ 2-Ph2P(S)N(CHMe2)PPh(N2C3HMe2-3,5)}](PF6) (8), bearing the diphosphazane monosulfide Ph2P(S)N(CHMe2)PPh(N2C3HMe2-3,5) (1c), displayed P,S-coordination and existed in solution as six and four isomers, respectively. Exchange was observed among four of the six isomers of 7 and among all the four isomers of 8 at 298 K, through the opening of the 3-allyl moiety, which appeared to be subject to both electronic and steric control.

Ethylenediamine-palladium(II) complexes with pyridine and its derivatives: synthesis, molecular structure and initial antitumor studies

The synthesis of four mononuclear palladium complexes of general formula [Pd(en)Cl(L)]NO 3(en = ethylenediamine; L = pyridine ( I), 4-methylpyridine ( II), 4-hydroxypyridine ( III) or 4-aminopyridine ( IV)) has been achieved. The structure of these compounds was studied by elemental analysis, IR, far-IR and 1H NMR; complex I was analyzed by X-ray diffraction. The crystal of [Pd(en)(pyridine)Cl]NO 3 is monoclinic, space group P2 1/ c ( a = 7.990(2), b = 16.058(3), c = 9.846(2) Å, β = 103.81(3)°, Z = 4, R = 0.067, R w = 0.066). The Pd(II) atom exhibits an approximately square planar coordination with bond lengths in the range 2.017–2.042 Å for Pd-N and 2.320 Å for Pd-Cl. In order to determine the donor strength of the aromatic pyridine ligands, the stability constants of binary complex ML 2+ (M = [Pd(en)(H 2O) 2] 2+; L = pyridine, 4-Me-pyridine, 4-OH-pyridine and 4-NH 2-pyridine) were determined by potentiometric pH titration in aqueous solution ( T = 25°C, I = 0.1 mol 1 −1 NaNO 3). The results show that the stability constants of the binary complexes systematically increase with increasing p K a of the pyridines. The above four palladium complexes, [Pt(en)(pyridine)Cl]NO 3 and cis-diamminedichloroplatinum(II) ( cis-DDP) were assayed for cytotoxicity in vitro against the human leukemia cell line HL-60, and compounds I, II, III and cis-DDP show significant cytotoxic activity against HL-60.

SYNTHESIS AND SPECTROSCOPIC STUDIES OF COMPLEXES OF 1,2-BIS-(2-PYRIDYLMETHYLENEIMINO)BENZENE WITH PLATINUM(II) AND PALLADIUM(II)

The Synthesis and characterization of new square planer platinum and palladium complexes of general formula [ML]Cl, [M = Pt(II) and Pd(II), L = 1, 2−bis (2−pryidylmethyleneimino) benzenal are reported. By using high resolution 1 H NMR spectroscopy it has been shown that the ligand L acts as a tetradentate through all four nitrogen atoms and prefers the syn orientation for both pyridine rings.