PdCl2 Complexes Research Articles

Reactions of chiral phosphoramidites with complexes Pd(COD)Cl2 and Pt(COD)Cl2

Reactions of phosphoramidites based on (−)-ephedrine and [(1S)-endo]-(−)-borneol with the complexes M(COD)Cl2 (M is Pd or Pt, and COD is cycloocta-1,5-diene) were studied. The formation ofcis andtrans complexes of the general formulas MCl2L2 and M2Cl2(μ-Cl)2L2 was observed. The structures of the resulting compounds were established by31P,13C, and195Pt NMR and IR spectroscopy and by plasma desorption mass spectrometry.

Cyclometalated Compounds. XI.1 Single and Double Cyclometalations of Poly(pyrazolylmethyl)benzenes

Six ligands containing 1,3-bis(pyrazol-1-ylmethyl)benzene subunits are shown to readily undergo cyclometalation reactions. 1,3-Bis(pyrazol-1-ylmethyl)-4,6-dimethylbenzene (1) is cyclopalladated to form the complex PdCl[C6HMe2(CH2pz)2-N,C,N] (3), containing two fused-ring six-membered metallocycles, for which the X-ray crystal structure of the DMSO solvate is described. The tetramethyl-substituted derivative C6H2Me2(CH2Me2pz)2 (2) and the 1,3,5-tris(pyrazol-1-ylmethyl)benzenes C6HMe2(CH2pz)3 (7) and C6HMe2(CH2Me2pz)3 (8) behave similarly. Reaction of 1 with a (terpyridine)ruthenium reagent ultimately produces the cycloruthenated derivative (tpy)Ru[C6HMe2(CH2pz)2-N,C,N]+ (6), the hexafluorophosphate salt of which is also crystallographically characterized. This reaction proceeds by way of a novel intermediate dication (tpy)Ru[C6H2Me2(CH2pz)2-N,N]2+ (5) that is shown, by detailed NMR studies, to contain an aryl C−H···Ru interaction. The 1,2,4,5-tetrakis(pyrazol-1-ylmethyl)benzenes C6H2(CH2pz)4 (12) and C6H2(...

A new method for the synthesis of nitrogen heterocycles via palladium catalyzed intramolecular hydroamination of allenes

The intramolecular hydroamination of certain allenes, bearing amine or sulfonyl amide groups at the terminus of the carbon chain, proceeded smoothly in the presence of catalytic amounts of palladium complex ([( η 3-C 3H 5)PdCl] 2-dppf) under weakly acidic conditions (0.15-1.0 equivalent of acetic acid) to give the corresponding 2-vinylpyrrolidines and 2-vinylpiperidines in good to high yield.

Pd(gly- l-his- l-lys)Cl: Solution structure and ternary complex formation with mono- and tetranucleotides

The tripeptide complex Pd(gly- l-his- l-lys)Cl (Pd(GHK)Cl. 1) has been studied by a variety of NMR techniques ( 1H, 1H E.COSY, 1H NOESY, 1H, 13C HMQC), by ESI-MS, as well as simulated annealing and molecular dynamics methods. Reactions of 1 with isolated 5′-deoxynucleotides of guanine, cytidine, adenine and thymine, alone and in competition, have been carried out in water and followed by 1H NMR spectroscopy. They reveal preferential binding of Pd(GHK) + to guanine N7 in weakly to moderately acidic solution and slow rotation of the Pd tripeptide entity about the metal-N7 bond below 276 K. The self-complementary tetranucleotide 5′-d(GTAC) reacts with 1 in D 2O, pD 3.5, at guanine N7.

Retention of Regiochemistry of Allylic Esters in Palladium-Catalyzed Allylic Alkylation in the Presence of a MOP Ligand

In the palladium-catalyzed allylic alkylation of (E)-3-substituted-2-propenyl acetates (1), 1-substituted-2-propenyl acetates (2), and 1- or 3-deuterio-2-cyclohexenyl acetate (5), which proceeds through 1,3-unsymmetrically substituted π-allylpalladium intermediates, selective substitution at the position originally substituted with acetate was observed by use of a sterically bulky monodentate phosphine ligand, 2-(diphenylphosphino)-2‘-methoxy-1,1‘-binaphthyl (MeO-MOP). Studies of the structure of π-allylpalladium complexes generated by mixing [PdCl(π-cyclohexenyl)]2 with 1 or 2 equiv of MeO-MOP (L*) revealed that cationic bisphosphine complex [Pd(L*)2(π-cyclohexenyl)]+Cl- is not formed even in the presence of excess ligand but neutral monophosphine complex PdCl(L*)(π-cyclohexenyl) (11) is formed, leaving excess ligand free, and that the exchange of the coordination site of Cl and L* in 11 is much slower than that in triphenylphosphine complex PdCl(PPh3)(π-cyclohexenyl) (13). The slow exchange can rationalize the retention of regiochemistry in the allylic alkylation catalyzed by palladium/MeO-MOP complex.

Bis{(2-diphenylphosphino)phenyl}mercury: a novel bidentate ligand and transfer reagent for the o-C6H4PPh2 group

The compound [Hg(o-C6H4PPh2)2] behaves as a trans-spanning bidentate ditertiary phosphine in its PdCl2 complex, the two metal atoms being forced into close contact; the palladium(0) complex [Pd{(o-Ph2PC6H4)2Hg}2] undergoes reductive elimination on heating with formation of the coupled product o-Ph2PC6H4C6H4PPh2-o.

Non-covalent synthesis of multiporphyrin systems

Non-covalent synthesis was used in the controlled assembly of metallodendrimers containing up to 12 porphyrins on the surface. A porphyrin containing four Pd-Cl complexes was synthesized to assemble dendrimers with a porphyrin in the nucleus. 1H NMR, ES-MS and MALDI-TOF mass spectrometry were used to characterize the nanometer-size assemblies.

Insertion reactions into palladium–carbon bonds of complexes containing new rigid bidentate nitrogen ligands

The neutral complexes Pd(Me)Cl(DPIA) ( 3) and Pd(Me)Cl(DQIA) ( 4), containing the novel rigid bidentate nitrogen ligands (5,6-dihydro-[1]pyrindin-7-ylidene)-isopropylamine (DPIA) and (6,7-dihydro-5 H-quinolin-8-ylidene)-isopropylamine (DQIA), respectively, have been synthesized. Complexes 3 and 4 react quantitatively with CO to give the neutral acylpalladium complexes Pd(C(O)Me)Cl(DPIA) ( 6) and Pd(C(O)Me)Cl(DQIA) ( 7), respectively. Complexes 3, 4, 6, and 7, which were present as mixtures of the cis and trans isomers, were fully characterized, and in the case of complexes 6 and 7 single crystal X-ray structures have been determined. The molecular structure of 6 and 7 show a square planar geometry with the α-diimine ligands coordinated in a bidentate fashion with comparable bite angles of about 78°. The acylpalladium complexes 6, 7, and Pd(C(O)Me)Cl( iPr–PyCa) ( 5), containing the nitrogen ligand 2-( N-2-propanecarbaldimino)pyridine ( iPr–PyCa), which is the flexible analogue of DPIA and DQIA, react with norbornadiene to yield the ionic alkyl complexes [Pd(C 7H 8C(O)Me)(DPIA)]Cl ( 9a), [Pd(C 7H 8C(O)Me)(DQIA)]Cl ( 10a), and [Pd(C 7H 8C(O)Me)( iPr–PyCa)]Cl ( 8a), respectively. Interestingly, the nature of the α-diimine ligand influences the reaction rate of the norbornadiene insertion in the order N–N=DQIA≪ iPr–PyCa<DPIA. Competition experiments and comparison of the crystal data from 6 and 7 indicate that the complexation strength of the α-diimine ligand is exactly opposite to the reactivity of the corresponding acylpalladium complexes toward norbornadiene, which suggest a mechanism via intermediates containing a unidentate coordinated α-diimine ligand.

Synthesis and reactivity of new palladium alkyl complexes containing PMe 3 ligands: Insertion reactions and formation of bis(pyrazolyl)borate derivatives

The complex PdCl 2(cod) (cod = 1,4-cyclooctadiene) reacts with one equivalent of R(Mg)Cl (R = CH 2CMe 2Ph, CH 2SiMe 3, CH 2C 6H 4- o-Me) to yield monoalkyl derivatives of composition Pd(R)Cl(cod). The cyclooctadiene ligand is readily displaced by dmpe (dmpe = 1,2-bis(dimethylphosphino)ethane) and PMe 3 to generate Pd(R)Cl(L 2) (L 2 = (PMe 3) 2, dmpe) of which, the complex Pd(CH 2CMe 2Ph)Cl(PMe 3) 2 thermally isomerizes to the palladium aryl Pd(C 6H 4- o-CMe 3)Cl(PMe 3) 2 in the presence of catalytic amounts of NEt 3. Carbonylation of the alkyl derivatives affords acyl complexes Pd(COR)Cl(L 2) and related iminoacyl derivatives have also been obtained by the analogous reaction with tert-butyl-isocyanide. New alkyl and acyl species containing bis(pyrazolyl)borate ligands have been prepared by halide metathesis in the Pd(R/COR)Cl(PMe 3) 2 complexes. During the course of these reactions one equivalent of PMe 3 is liberated. The complex Bp ∗Pd(CH 2SiMe 3)(PMe 3) has been structurally characterized by X-ray crystallography.

Palladium(II) complexes with polyphosphazene

AbstractAn allylphenoxy‐substituted polyphosphazene has been modified via inorganic chemical concepts. The transition metal salt is bis(acetonitrile)dichloropalladium(II). The coordination complexes have been characterized using acid‐base solution chemistry, sol‐gel phase transitions, thermomechanical property measurements and infrared spectroscopy. Solid complexes of polyphosphazene and PdCl2 cannot be dissolved in the original solvent (i.e., tetrahydrofuran) used during sample preparation. These polymeric palladium complexes also cannot be disrupted by a stronger base, like triphenylphosphine. There is a monotonic increase in the glass transition temperature at higher concentrations of palladium chloride. Tg of the pure polymer increases by 21°C in the presence of 10 mol% palladium chloride. The increase in high‐strain mechanical properties cannot be explained solely by a “filler effect.” At higher PdCl2 concentrations, there is a direct correlation between the enhancement in Tg, higher mechanical fracture stress, and increased infrared absorbance @ 1092 cm−1 because of the formation of a palladium‐π‐complex with allylic substituents in the phenoxy sidegroup. Palladium chloride relinquishes its acetonitrile ligands after dissolution in THF, and the vacant sites in the first‐shell coordination sphere of the transition metal are occupied by these allylic substituents in the sidegroup. This produces interchain coordination crosslinks, which modify the thermomechanical properties of polyphosphazene/ PdCl2 complexes.

Isocyanide Insertion into the Palladium−Carbon Bond of Complexes Containing Bidentate Nitrogen Ligands: A Structural and Mechanistic Study

Insertion of the isocyanides 2,6-dimethylphenyl isocyanide (DIC), tert-butyl isocyanide (TIC) and tosylmethyl isocyanide (TosMIC) into the Pd−Me bond of complexes (N⌒N)Pd(Me)Cl (N⌒N = 2,2‘-bipyridine (bpy), 1,10-phenanthroline (phen), 2,2‘-bipyrimidine (bpm)) afforded quantitatively (N⌒N)Pd(C(NR)Me)Cl (R = 2,6-Me2C6H3, t-Bu, CH2Tosyl). The course of the reaction has been shown to proceed via the intermediates [(N⌒N)Pd(CN−R)(Me)]Cl (N⌒N = bpy, phen; R = 2,6-Me2C6H3, t-Bu, CH2Tosyl), which have been characterized at 250 K by NMR and IR spectroscopies and conductivity measurements. The mechanism of the insertion reaction involves substitution of the halide by the isocyanide followed by a rate-determining methyl migration to the precoordinated isocyanide. Kinetic measurements of the isocyanide insertion reaction, which provided the reaction rate constants of the isocyanide association (k1), isocyanide dissociation (k-1), and methyl migration reaction (k2), have demonstrated that the migration rate of the meth...

?-Conjugated soluble palladium poly-ynes: Synthesis and fluorescence properties

Insertion of thiophene-2,5-diyl, or 1,4-phenylene into palladium poly-ynes by the polycondensation of dihalide complexes PdCl2(PR3)2 (R = Ph o γ n-butyl) with a di-yne monomer (obtained from the reaction of equimolar quantities of p-diethynyl-benzene with 2,5-diiodothiophene or 1,4-diiodobenzene) affords a series of palladium poly-ynes 1–6. The polymers/oligomers, soluble in common organic solvents, exhibit strong fluorescence at the excitation of UV-visible light at room temperature. The emission intensity of the polymers/oligomers with thiophene-2,5-diyl is 3–17 times stronger than that of the analogous polymers without thiophene-2,5-diyl. Polymers with phenyl substituted phosphine ligands emit stronger emission than those only with n-butyl phosphine ligands. The effects of molecular weight, ligands, solvents, and concentration on the fluorescence properties are also investigated. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1657–1665, 1997

Diastereospecific Dimerization in Bridging Amido Complexes of Dipalladium

Chirality is conserved in the deprotonation of the complex PdCl2(La) (La = 2-[(N-p-tolylamino)methyl]pyridine; 1a) leading to the folded diastereomer of [PdCl(μ-La-H)]2 (2a), where the p-tolyl groups are syn exo and the same enantiomer of 1a shapes both halves of the amido-bridged dimer. The dimerization of different enantiomers of 1a (R with S), which should lead to the achiral unfolded diastereomer of 2a where p-tolyl groups would arrange anti, is not observed.

Synthesis of 1-methyl-2-diphenylphosphino-3-(1′-isoquinolyl)indole; an easily racemised ligand giving insights into catalytic asymmetric allylation

Abstract The synthesis of the title compound is described, involving 2-lithiation and phosphinylation of the coupled heterocycle in the final step. Attempts to resolve the phosphine by previously described methods led to its immediate racemisation, also observed more slowly in the PdCl2 complex, for which the X-ray structure is described. The phosphinamine formed a cationic Pd(1,3-diphenylallyl) complex with high diastereoselectivity. By analysis of the solution stucture using NMR techniques, in comparison with the X-ray structure, some inferences about the mechanism of allylic alkylation with related heterotopic ligands can be drawn.

Insertions of Allenes into Palladium−Carbon Bonds of Complexes Containing Bidentate Nitrogen Ligands. Structural and Mechanistic Studies

The insertion reactions of the allenes propadiene and 1,2-heptadiene in the Pd−C bond of complexes (N⌒N)Pd(R)X (N⌒N = 8-PQ, p-An-BIAN, i-Pr-DAB, p-An-DAB, i-Pr-PyCa; R = Me, C(O)Me, C(O)Ph, C(O)i-Pr; X = Cl, Br) have been investigated. An X-ray crystal structure determination of (8-PQ)Pd{(1−3-η)-2-methylpropenyl}Cl exhibited the unexpected monodentate coordination of the nitrogen ligand. The monodentate coordination in apolar solvents and bidentate coordination in polar solvents was demonstrated by means of NOE NMR experiments. Kinetic measurements revealed that the reactions are first order in the palladium concentration and occur via an allene concentration independent and dependent pathway. Reactions of complexes containing flexible bidentate nitrogen ligands were retarded by additional free bidentate nitrogen ligand indicating that initial dissociation of a nitrogen donor is an important step in the reaction. We have strong indications that the migration of the R group to the precoordinated allene is the rate-determining step. Instead of mass-law retardation by excess X- (X = Cl-, Br-), an enhancement of the reaction has been observed in case of the complexes (8-PQ)Pd(Me)Cl, (8-PQ)Pd(Me)Br, and (i-Pr-DAB)Pd(C(O)Me)Cl. Flexible bidentate nitrogen ligands greatly enhance the reaction, owing to the easy formation of an accessible site on the metal center. The insertion of allenes into the Pd−C bonds of complexes containing rigid bidentate nitrogen ligands probably proceeds via initial allene association followed by either halide or nitrogen dissociation and subsequent migration of the R group to the precoordinated allene.

Divalent Palladium and Platinum Complexes Containing Rigid Bidentate Nitrogen Ligands and Electrochemistry of the Palladium Complexes1

The synthesis and characterization of divalent palladium and platinum complexes of the type PdX2(Ar-BIAN) (X = Cl, Br, I, OC(O)Me), PdCl2(Ph-BIC) and PtCl2(Ar-BIAN) is described. These complexes contain the rigid bidentate nitrogen ligands bis(arylimino)acenaphthene (Ar-BIAN; Ar = Ph, p-MeC6H4, p-MeOC6H4, o,o‘-Me2C6H3, o,o‘-i-Pr2C6H3) or bis(phenylimino)camphane (Ph-BIC), which act as σ-donor ligands to the metal center, as was deduced from the observed shifts in the IR and NMR spectra of the complexes. Electrochemical reduction of PdCl2(Ar-BIAN) complexes in THF or DMF occurs via two one-electron reductions and affords the complex PdICl(Ar-BIAN)•-, which slowly produces some Pd0(Ar-BIAN) complex. PdICl(Ar-BIAN)•- reacts with iodomethane, whereas with iodobenzene or bromobenzene no reaction was observed. PdICl(Ar-BIAN)•- reacts with free Ar-BIAN or the alkenes dimethyl fumarate, dimethyl maleate, and methyl acrylate, giving complexes of the formulas PdICl(Ar-BIAN)2•- and PdICl(Ar-BIAN)(alkene)•-, respectively. A two-electron reduction of the latter afforded Pd0(Ar-BIAN)22- and Pd0(Ar-BIAN)(alkene)2-, respectively, whose further oxidation in two one-electron steps produces Pd0(Ar-BIAN)2 and Pd0(Ar-BIAN)(alkene). The Pd0(Ar-BIAN) complex which is slowly formed from PdICl(Ar-BIAN)•- reacts with alkene but directly affords the complexes Pd0(Ar-BIAN)(alkene)•- because Pd0(Ar-BIAN)(alkene) complexes are formed at a potential more negative than their first reduction potential. Reoxidation of Pd0(Ar-BIAN)(alkene)•- affords Pd0(Ar-BIAN)(alkene) complexes. The results of the electrochemical experiments corroborate earlier mechanistic proposals of exchange of Ar-BIAN ligands in Pd0(Ar-BIAN)(alkene) complexes and homogeneous hydrogenation of electron-poor alkenes by Pd0(Ar-BIAN)(alkene) complexes.

New chiral phosphetanes: Synthesis and use in the palladium-catalyzed allylic alkylation

The new chiral phosphetane—acetals 4a–d and 10a–d were synthesized and evaluated as coligands for the palladium-catalyzed allylic alkylation of 1,3-diphenyl-2-propenyl acetate with sodium malonate. For each set of epimeric phosphetanes, the enantiomeric excesses are highly dependent on the relative configurations of the various chiral centers. The highest asymmetric induction was observed with phosphetane 4a. An X-ray crystal structure of the complex (allyl)PdCl( 4a) is also reported.

Palladium catalyzed intramolecular hydrocarbonation of allenes leading to carbocycles

The intramolecular hydrocarbonation of certain allenes ( 1 and 3), bearing active methyne groups at the terminus of the carbon chain, proceeded smoothly in the presence of catalytic amounts of palladium complex ([( η 3-C 3H 5)PdCl] 2-dppf) to give the corresponding carbocycles ( 2 and 4, respectively) in good to high yields.

Coordination modes of the novel bifunctional nitrogen ligands 8-(2-pyridyl)quinoline and 8-(6-methyl-2-pyridyl)quinoline towards palladium and platinum. X-ray crystal structures of (8-(2-pyridyl)quinoline)Pd(Me)Cl, (8-(2-pyridyl)quinoline)-Pd(C(O)Me)Cl and (8-(2-pyridyl)quinoline)Pd(PEt 3)Cl 2

The coordination chemistry of the new bidentate nitrogen ligands 8-(2-pyridyl)quinoline (8-PQ) and 8-(6-methyl-2-pyridyl)quinoline (Me-8-PQ) towards palladium and platinum has been studied. Several (N⌢N)Pd(R)Cl and (N⌢N)Pd(alkene) complexes have been synthesized. The complex (8-PQ)Pd(Me)Cl has been characterised by a single crystal X-ray determination (crystal data triclinic space group P l with a=8.513(5), b=9.338(4), c=10.219(2) A ̊ , α=108.11(2), β=89.82(3), γ=116.81(4)°, V=680.1(6) A ̊ 3, R=0.033, Z=2 ). A fast CO insertion occurs into the palladium-carbon bond of the complexes (N⌢N)Pd(Me)Cl providing the (N⌢N)Pd(C(O)Me)Cl complexes. For (8-PQ)Pd(C(O)Me)Cl an X-ray structure determination has been carried out (crystal data: monoclinic space group P2 1/ c with a=9.084(4), b=10.179(3), c=16.400(3) A ̊ , β=95.59(2)°, V=1509.2(9) A ̊ 3, R=0.043, Z=4 ). Unexpected in both molecular structures is the large dihedral angle between the plane of the bidentate nitrogen ligand and the coordination plane of the palladium. Both bidentate coordinating ligands 8-PQ and Me-8-PQ show a relatively large bite angle. A monodentate coordination mode has been observed for the complexes (N⌢N)M(PEt 3)Cl 2 (M=Pd, Pt), as the pyridyl group of the ligand is coordinated to the metal while the quinoline group is dissociated from the metal, which is shown in the X-ray structure determination for the complex (8-PQ)Pd(PEt 3)Cl 2 (crystal data: monoclinic space group P2 1/a with a=15.736(2), b=7.782(1), c=18.255(3) A ̊ , β=102.98(1)°, V=2178.3(6) A ̊ 3, R=0.062, Z=4 ).

Cyclopalladation of N-( p-thiotoluoyl)pyrrolidine and -piperidine

Reaction of N-( p-thiotoluoyl)pyrrolidine (Hpr) with lithium tetrachloropalladate(II) in methanol at room temperature resulted in an ortho C—H activation of the benzene ring and a benzene ring- orthopalladated complex PdCl (bpr) was obtained. Another reaction in hexamethylphosphoric triamide at 80°C resulted in an α-CH 2 activation of the pyrrolidine ring to form PdCl (ppr) with an aliphatic α-C—Pd bond. Under the latter reaction conditions N-( p-thiotoluoyl)piperidine (Hpi) was similarly cyclopalladated at α-CH 2 of the piperidine ring to give PdCl (ppi) but under the former experimental conditions no cyclopalladation occurred. These complexes and some of their derivatives were characterized spectroscopically. The results suggested that the steric bulk of the thioamide-N substituents was of prime importance to cyclopalladation-reactivity of thioamides. To verify the facts, the structures of N-(2-thionaphthoyl)pyrrolidine, Pd(acac) (bpr) (acac = acetylacetonate ion), and {l,3-bis(1-pyrrolidinothiocarbonyl)-phenyl-C 2,S,S′} chloropalladium(II) were determined by X-ray analysis. A pyrrolidino group is a sterically more favorable thioamide-substituent than a dimethylamino group to fulfil the requirements of aromatic ring cyclopalladation of tertiary thioamides with palladium(II).