Methylpalladium Complexes Research Articles

Synthesis of anionic methylpalladium complexes with phosphine–sulfonate ligands and their activities for olefin polymerization

Reaction of diarylphosphinobenzene-2-sulfonic acids with tertially amines, followed by addition of [PdMeCl(cod)], provided anionic methylpalladium(II) complexes with bidentate phosphine-sulfonate ligands, which show high activity for copolymerization of ethylene with methyl acrylate.

Methyl-palladium(II) complexes of pyridine-bridged bis(nucleophilic heterocyclic carbene) ligands: Substituent effects on structure, stability, and catalytic performance

A series of discrete, mononuclear palladium(II)–methyl complexes, together with several palladium(II)–chloro analogues, of pyridine-functionalised bis-NHC ligands have been prepared via ligand transmetallation from the silver(I)-NHC complexes. The reported complexes comprise examples with both the methylene-bridged 2,6-bis[(3-R-imidazolin-2-yliden-1-yl)methyl]pyridine ( RC ∧N ∧C; R = Mes, dipp, t Bu) and planar 2,6-bis(3-R-imidazolin-2-yliden-1-yl)pyridine ( RCNC; R = Mes, dipp) ligands and, when combined with the previously reported MeC ∧N ∧C/ MeCNC examples, cover a broad spectrum of ligand substituent steric and electronic properties, including the bulky Mes and dipp groups frequently used in catalytic applications. The palladium(II) complexes have been characterised by a variety of methods, including single crystal X-ray crystallography, with the shielding of the Pd– Me groups in the proton NMR spectra of some of the N-aryl substituted examples correlated with the proximity of the aryl rings to the methyl group in the solid state structures. The [PdMe( RC ∧N ∧C/ RCNC)] + complexes undergo thermal degradation via reductive methyl-NHC coupling to give 2-methyl-3-R-imidazolium-1-yl species with relative stabilities in the order of [PdMe( MesC ∧N ∧C)]BF 4 > [PdMe( MeC ∧N ∧C)]BF 4 ≈ [PdMe( MesCNC)]BF 4 > [PdMe( MeCNC)]BF 4 > [PdMe( tBu C ∧N ∧C)]BF 4 ≫ [PdMe( tBu CNC)]BF 4 (not isolable). A comparison of the activity of the complexes as precatalysts in a model Heck coupling reaction shows greatest activity in those species bearing bulkier N-substituents, with complexes bearing RC ∧N ∧C ligands generally more efficient precatalysts than those bearing RCNC ligands.

Fesulphos-Palladium(II) Complexes as Well-Defined Catalysts for Enantioselective Ring Opening of Meso Heterobicyclic Alkenes with Organozinc Reagents

The air-stable and readily available cationic methyl palladium(II) complexes of planar chiral Fesulphos ligands [(Fesulphos)Pd(Me)(PhCN)]+ X- are highly efficient catalysts for the alkylative ring opening of oxa- and azabicyclic alkenes with dialkylzinc reagents, showing broad scope with regards to both the bicyclic substrate and the dialkylzinc reagent. Catalyst loading as low as 0.5 mol % is sufficient to achieve good yields and enantioselectivities ranging 94 --> 99% ee in most cases. {Fesulphos = (1-phosphino-2-sulfenylferrocene); X- = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate or PF6(-)].} The origin of the high asymmetric induction has been rationalized by mechanistic studies combining computational calculations and X-ray structural analysis.

Rapid methylation on carbon frameworks leading to the synthesis of a PET tracer capable of imaging a novel CNS-type prostacyclin receptor in living human brain

To develop novel short-lived 11C radionuclide-incorporated PET tracers with high metabolic tolerance, we performed rapid methylation using 11CH 3I, a frequently used precursor for 11C-labeled tracers, on sp- and sp 2-carbon frameworks. Methyl iodide was trapped using an excess of tributylphenylstannane for 5 min at 60 °C in the presence of Pd[P( o-tolyl) 3] 2, a copper(I) salt (CuCl or CuBr), and K 2CO 3, resulting in a greater than 90% yield of toluene. A trapping reaction with tributyl-1-hexynylstannane for 5 min at 60 °C in the presence of Pd[P( t-C 4H 9) 3] 2 and a fluoride ion (KF or CsF) gave a high yield (>90%) of 2-heptyne. Since these reactions are applicable to a wide range of organic molecules, we synthesized 15 R-[ 11C]TIC methyl ester, a PET tracer targeting the CNS-specific prostacyclin receptor (IP 2), by rapid sp 2–sp 3 coupling with some modifications. Radiolabeled 11CH 3I was trapped with the methyl ester of the corresponding stannyl precursor via two steps. In the first, 11CH 3I and Pd[P( o-tolyl) 3] 2 were mixed to form a methylpalladium complex, and in the second, the methylpalladium complex was mixed with the other reagents necessary for the coupling reaction. The yield of radiolabeled 15 R-[ 11C]TIC methyl ester was 80–90%, and it had a radioactivity of 2.0–2.5 GBq, sufficient for an in vivo human PET study with high reproducibility. We used this tracer in PET studies imaging the IP 2 receptor in living monkey and human brains. Following its penetration of the blood–brain barrier, the tracer underwent ester hydrolysis and bound to its specific receptor in the brain. A protocol for sp–sp 3 coupling would be used to synthesize [ 11C]iloprost methyl ester, a PET tracer for the peripheral-type prostacyclin receptor (IP 1). A methyl group is the least bulky, unpolarized organic group, suggesting that it would have little effect on the biological activity of its parent compound. Thus, [ 11C]methylated compounds may be applicable to a wide range of biologically active molecules, converting them to PET tracers that can be utilized for in vivo molecular imaging.

Cationic planar chiral palladium P,S complexes as highly efficient catalysts in the enantioselective ring opening of oxa- and azabicyclic alkenes.

Open plan: Cationic methylpalladium(II) complexes of planar chiral Fesulphos ligands (Fesulphos=1-phosphanyl-2-sulfenylferrocene) show excellent performance in the alkylative ring opening of oxa- and azabicyclic alkenes with dialkyl zinc reagents (see scheme, Cy=cyclohexyl, ArF=3,5-bis(trifluoromethyl)phenyl). Catalyst loadings as low as 0.5 mol % are normally sufficient to achieve high enantioselectivities (94–>99 % ee).

Effect of 5-Me substituent(s) on the catalytic activity of palladium(II) 2,2 ′-bipyridine complexes in CO/4- tert-butylstyrene copolymerization

The coordination of two 5-substituted-2,2 ′-bipyridines L (L 1=5-methyl-2,2 ′-bipyridine, L 2=5,5 ′-dimethyl-2,2 ′-bipyridine) to palladium was studied. The neutral complexes [Pd(L)Cl 2] and [Pd(L)(Me)Cl], and the cationic complexes obtained after chlorine abstraction [Pd(L) 2][BAr ′ 4] 2 and [Pd(L)(Me)(NCMe)][BAr ′ 4] (Ar ′=3,5-(CF 3) 2-C 6H 3), respectively, were isolated and characterized by NMR and FAB mass spectroscopy. The complex [Pd(L 2)(L 3)][BAr ′ 4] 2 (L 3=2,2 ′-bipyridine) bearing different ligands, was prepared for comparison purposes. The activity of the monocationic and dicationic complexes as catalytic precursors in the CO/4- tert-butylstyrene copolymerization was compared with that of related well-known catalysts containing the unsubstituted 2,2 ′-bipyridine as nitrogen ligand, to evaluate the influence of the substituents in 5- and 5,5 ′-position. The presence of one or two substituents on the nitrogen ligand has a positive effect on productivity using both types of precursors. No influence was observed on the polymer properties in terms of molecular weight and tacticity. Analysis of the reactivity of the methyl–palladium complexes towards carbon monoxide shows further differences depending on the nitrogen ligand.

Carbon−Oxygen Bond Formation at Organopalladium Centers: The Reactions of PdMeR(L2) (R = Me, 4-tolyl; L2 = tmeda, bpy) with Diaroyl Peroxides and the Involvement of Organopalladium(IV) Species

The group 16 oxidants dibenzoyl- and bis(4-trifluoromethylbenzoyl)-peroxide react with dimethylpalladium(II) and methyl(4-tolyl)palladium(II) complexes of the bidentate nitrogen donor ligands 2,2'-bipyridine and N,N,N'N'-tetramethylethylenediamine in discrete stepwise processes as the temperature is raised from -70 °C. Carbon-oxygen bonds are formed during this reaction sequence but not from those Pd(IV) complexes detected spectroscopically. The initial reaction gives undetected “PdIV(O2CAr)2MeR(L2)” (Ar = Ph, ArF; R = Me, Tol; L2 = bpy, tmeda), which immediately undergo methyl aroate exchange with PdIIMeR(L2) to give PdII(O2CAr)R(L2) and PdIV(O2CAr)Me2R(L2), where all products except for PdIV(O2CAr)Me2- Tol(tmeda) were detected by 1H NMR spectroscopy. On raising the temperature, the PdIVMe3 complexes reductively eliminate Me-Me, and the PdIVMe2Tol complexes eliminate Me- Me and Tol-Me. The resultant Pd(II) complexes PdII(O2CAr)R(L2) react with (ArCO2)2 at higher temperatures to form PdII(O2CAr)2(L2) and R-O2CAr (R = Me, Tol), except for PdII(O2- CAr)Tol(tmeda), which forms PdII(O2CAr)2(tmeda) and 4,4'-bitolyl. Each reaction step has been confirmed by the independent synthesis of intermediates PdII(O2CAr)2(L2) and PdII(O2- CAr)R(L2) (Ar =Ph, ArF; R=Me, Tol; L2 = bpy, tmeda) and PdIV(O2CR)Me2R(L2) (R = Ph, ArF; R= Me, Tol; L2 = bpy) by metathesis reactions of halogeno complexes with Ag[O2CAr], followed by temperature-dependent studies of both the decomposition of Pd(IV) complexes and reactions of Pd(II) complexes with (ArCO2)2. Attempts to prepare “PdIV(O2CAr)2MeR- (bpy)” in a similar manner (and thus in the absence of PdMeR(bpy) with which they undergo exchange reactions) were unsuccessful, but the complexes PdIVI2MeR(bpy) (R=) Me, Tol) that formed on reaction of diiodine with PdMeR(L2) were detected and found to reductively eliminate iodomethane. X-ray structural studies are reported for the square-planar palladium( II) complexes Pd(O2CPh)2(bpy), Pd(O2CAr)2(tmeda) (Ar = Ph, ArF), and Pd(O2CPh)-

Palladium(II) complexes of new OPN phosphine ligands and their application in homogeneously catalysed reactions of CO with alkenes or alkynes.

Palladium complexes of a series of functionalised phosphines bearing the OPN donor set [2-pyCH(2)P(Ph)CH(2)(CHOCH(2)CH(2)CH(2)), 1; 2-py CH(2)P(Ph)-CH(2)CH(2)(CHOCH(2)CH(2)O), 2; 2-pyCH(2)P(Ph)CH(2)CH(2)CO(2)Me, 3; 2-pyP(Ph)CH(2)(CHOCH(2)CH(2)CH(2)), 4; 2-py = 2-pyridyl] have been prepared and characterised. Ligands 1-3 form five membered P-N chelates which is confirmed for PdCl(2) complexes of and by X-ray crystallography. O-coordination appears to be generally disfavoured although there is evidence of transient O-coordination for selected Pd complexes of 4. Palladium methyl and acetate complexes of all four ligands have been tested for catalytic activity in ethene/CO copolymerisation as well as alkoxy-carbonylation of propyne. Complexes of 1 and 4 show some activity in the copolymerisation reaction and complexes of 4 are active in the methoxy carbonylation of propyne. Unlike related pyridyl(diaryl)phosphines, 4 produces a much more stable catalyst system that does not require large excesses of ligand to maintain activity.

Reactivity of palladium(II) methyl complexes towards CO2: formation of carbonate complexes

Treatment of a benzene solution of (tmeda)PdMe2 or (dppe)PdMe2 with carbon dioxide gives the corresponding methyl bicarbonate complex, (L–L)PdMe(O2COH). These were characterised by NMR spectroscopy and elemental analysis. Under strictly dry conditions no reaction was observed. Recrystallisation of the tmeda bicarbonate complex from acetone yields the corresponding η2-carbonate complex, which was characterised by X-ray crystallography. The reaction probably proceeds through attack by free carbonic acid on the dimethyl complex.

New Bulky Phosphino−Pyridine Ligands. Palladium and Nickel Complexes for the Catalytic Polymerization and Oligomerization of Ethylene

Two bulky phosphino−pyridine ligands (6-mesityl-2-((diarylphosphino)methyl)pyridine, P∼N) were successfully prepared by means of Suzuki coupling of mesitylboronic acid with 6-bromo-2-picoline followed by phosphinylation. These ligands readily form the palladium and nickel complexes upon treatment with (COD)PdMeCl and (DME)NiBr2, respectively. These P∼N chelating Pd(II) and Ni(II) complexes were characterized by both spectral data and X-ray crystallography. The coordination geometry around the metal center is square planar for the Pd(II) complexes and tetrahedral for the Ni(II) complexes. The cationic methylpalladium(II) complexes showed poor activity in the catalytic polymerization of ethylene, but the nickel complexes were highly active with the activation of MAO. The nickel complexes catalyzed the polymerization of ethylene with an Al/Ni ratio of 150, whereas di- and trimerization was observed when the Al/Ni ratio is 500. The obtained polyethylenes are highly crystalline.

Palladium(II) Complexes Containing a Pyridinyliminophosphorane Ligand

AbstractA series of new pyridinyliminophosphorane bidentate ligands with different steric environments [(2‐C6H4N)PPh2=NAr (NPN)] and their methylpalladium complexes [PdClMe(NPN)] were prepared. From the crystal structure analysis it is evident that the alkyl ligands are always trans to the pyridinyl nitrogen donor, revealing a σ‐donating ability of the iminophosphorane. However, the two Pd−Cl bonds in [PdCl2(NPN)] are essentially the same length. Cationic palladium complexes catalyzed the copolymerization of norbornene/ethylene as well as CO/norbornene. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Chloride-Modulated Insertion Reactions of Dimethylallene across the Pd−C Bond in Palladium Methyl Complexes Bearing Potentially Terdentate Pyridylthioether Ligands

Palladium methyl complexes with potentially terdentate pyridylthioether (S−N−S(R) = 2,6-bis(R-thiomethyl)pyridine, R = Me, t-Bu, Ph; N−S−N = 2[(2-pyridylmethylthio)methyl]pyridine) ligands have been prepared and characterized. Both the bidentate chloride [Pd(Me)(S−N−S(R))]Cl and the terdentate chloride-free [Pd(Me)(S−N−S(R))]+ species are present in solution and display a substantially different reactivity toward allene insertion across the Pd−C bond. The structures of the complexes [Pd(Me)(S−N−S(t-Bu))]OTf and [Pd(Me)(S−N−S(t-Bu))]Cl were determined by X-ray diffraction. The chloride methyl substrates [Pd(Me)(S−N−S(R))]Cl display an enhanced reactivity in solution with respect to the allene insertion, and this reactivity was traced back to the distortion of the main coordination plane induced by the presence of an uncoordinated −CH2−S−R group in position 6 of the coordinating pyridine. The equilibrium position between the terdentate and the bidentate species can be modulated by addition of chloride ion, which therefore controls the overall reactivity of the system.

Insertion of 1,1-Me 2propadiene across the Pd–C bond of pyridyl–thioether methyl complexes. A mechanistic study

Novel neutral and cationic palladium methyl complexes containing pyridylthioethers (R′N–SR) as ancillary ligands and different leaving groups were synthesised and characterised by spectroscopic methods and elemental analysis. The reactivity of these complexes toward allene (allene=DMA=1,1-Me 2propadiene) insertion across the Pd–C bond was studied under different conditions. The influence of steric and electronic parameters, solvents and leaving groups was explored and an overall mechanistic picture is proposed. The distortion promoted by the ancillary ligand geometry together with the nature of the leaving group proved to be of primary importance in determining the reactivity of the complexes under study. The observed rate constants span several orders of magnitude. On the contrary, only a modest effect is observed when solvents with increasing dielectric constants are employed. The complex [Pd(PPh 3)(Me)(MeN–S tBu)] + shows a reactivity modulated by the presence of the phosphine which imparts to the substrate a peculiar reactivity owing to the scarce tendency of the phosphine itself to act as a leaving group.

Synthesis and reactivity of bimetallic palladium(ii) methyl complexes with new functional phosphine ligands

Bimetallic palladium(II) methyl complexes, [Pd(dppmpH)(CH3)(μ-Cl)]2 (1) and [Pd(dippmpH)(CH3)(μ-Cl)]2 (2) were synthesized by the reaction of (COD)Pd(CH3)(Cl) (COD = 1,5-cyclooctadiene) with the new functional phosphine ligands 2-diphenylphosphino-4-methylphenol (dppmpH) and 2-diisopropylphosphino-4-methylphenol (dippmpH). The homolytic cleavage of the CH3–Pd bond was found to occur when complexes 1 and 2 were heated or photolyzed to form a methyl radical and the corresponding oxygen-bridged bimetallic palladium(II) complexes, [Pd(dppmp)(Cl)]2 (3) and [Pd(dippmp)(Cl)]2 (4), respectively. The molecular structures of complexes 1, 3 and 4 were determined by single-crystal X-ray diffraction. Reaction of small molecules, such as CO, SO2 and CH2CH2, with complexes 1 and 2 was observed and characterized by IR, 1H, 13C and 31P{1H} NMR spectroscopy.

Potentially Tridentate Ligands in the Synthesis of Methyl- and Acetylpalladium(II) Complexes

The two protic tridentate ligands HNN′O (1) and HNN′S (2) were treated with [(COD)Pd(Me)Cl], and the corresponding methylpalladium(II) complexes [Pd(η2-HNN′)(Me)Cl] (1a and 2a) were isolated. The neutral ligands in these complexes coordinated the metal in an NN′ bidentate mode, through the pyridine and imine nitrogens, excluding the O or S atom from the coordination. This behavior was confirmed by X-ray diffraction analysis of the dichloro complex of 1, [Pd(η2-HNN′)Cl2] (1c). Complexes 1a and 2a easily transformed quantitatively into the corresponding three-coordinate complexes [Pd(η3-NN′X)(Me)] (1b: X = O, 2b: X = S) in basic medium, with elimination of HCl. The complexes 1a and 1b were treated with PPh3 and P(CD3)3, respectively, resulting in 1e and 1h; 1a reacted further with a double quantity of PPh3 to give rise to the diphosphane complex [trans-(PPh3)2Pd(Me)Cl] (1g) and free 1. The three-coordinate complexes 1b and 2b were subjected to CO bubbling at room temperature. In the case of 1b, acylation of the ligand on the phenolic oxygen was observed, with the formation of an organic acetate and release of palladium black. In the case of 2b, besides the acylated ligand on the thiolic sulfur, the acetylpalladium(II) complex [Pd(η3-NN′S)(MeCO)] (2c) was isolated. The X-ray structures of 1c·THF, 1b·1/2C6H6O2, 2b, 2c·1/2CH2Cl2, and 1g have been solved. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Palladium Complexes of a Novel Family of P,N-Chelates, the 2-(2-Pyridyl)phospholes: Synthesis, Structural Characterization, and Catalytic Activity for Olefin/CO Copolymerization

2-(2-Pyridyl)phospholes bearing phenyl or cyclohexyl substituents on the phosphorus atom and 2-pyridyl, phenyl, or 2-thienyl groups on the C 5 atom were prepared according to the Fagan-Nugent route. They reacted with (cod)PdClCH 3 , giving rise to stable complexes 3a-c and 3a'-c' as single diastereoisomers in excellent yields. An X-ray diffraction study performed on complex 3b featuring a 1-phenyl-2-(2-pyridyl)phosphole ligand revealed a cis configuration of the phosphorus atom and the methyl group. The geometry of the coordinated P atom is highly distorted due to the rigidity of the 1,4-P,N chelate backbone. Complexes 3a,a', featuring 2,5-bis(2-pyridyl)phosphole ligands, display fluxional behavior. NMR studies revealed an intramolecular exchange between the pendant and coordinated pyridyl groups, showing that 2-(2-pyridyl)phospholes can behave as hemilabile ligands. Treatment of complexes 3a-c and 3a'-c' with 1 equiv of AgSbF 6 in CH 3 CN afforded the corresponding cationic derivatives 4a-c and 4a'-c' as single diastereoisomers. Complexes possessing no pendant pyridyl moiety are air-stable solids that can be isolated in high yield. They are active for the copolymerization of ethylene and CO in CH 2 Cl 2 , whereas complex 4a, bearing the 2-(2-pyridyl)phosphole ligand 2a, is reduced quantitatively to give the dinuclear [Pd 2 (2a) 2 ] 2 + complex 6. The catalytic activities obtained with complexes 4b,c and 4b',c' are among the highest obtained with P,N chelates. The substitution pattern of the 2-(2-pyridyl)-phosphole ligands has an impact on the productivity of the Pd catalysts. P-cyclohexylphospholes are more efficient ligands than their P-phenyl analogues. Complex 4c, featuring a 2-(2-pyridyl)-5-(2-thienyl)phosphole ligand, catalyzed the copolymerization of CO and norbornene at 85 °C, affording oligomers with a narrow molecular weight distribution. In methanol, the cationic palladium methyl complex 4c afforded the bis-chelate [Pd(2c) 2 ] 2 + complex 5, which has been characterized by an X-ray diffraction study. Although the geometry around the palladium atom is distorted, the metric data of complex 5 are similar to those of 3b.

Ligand effects on palladium complex catalyzed copolymerization of ethylene/carbon monoxide

Several neutral and cationic methyl palladium complexes with bidentate ligands of phosphorus–nitrogen (P∼N) donors which form five- or six-membered chelates have been synthesized and characterized. Carbonylation of these complexes generates the corresponding stable Pd–acetyl complexes. The ligands that form a five-membered chelating ring appear to confer better activity towards carbonylation as well as copolymerization of ethylene/CO than do the six-membered analogues. Crystal structures of several inserted intermediates are provided.

Structure and Reactivity of (η3-Indolylmethyl)palladium Complexes Generated by the Reaction of Organopalladium Complexes with o-Alkenylphenyl Isocyanide

The reaction of methylpalladium complexes with o-alkenylphenyl isocyanides results in the successive intramolecular insertion of the alkenyl and isocyano groups followed by the 1,3-migration of hydrogen to give (η3-indolylmethyl)palladium complexes (4) in good yields. Treatment of 4 with diethylamine causes nucleophilic attack at the exo methylene carbon to give 2-methyl-3-(aminomethyl)indole, whereas the reactions with HCl produce 2,3-dimethylindole derivatives.

Cationic and neutral palladium(ii) methyl complexes of di-N-heterocyclic carbenes

Cationic and neutral methyl complexes of Pd(II) incorporating di-N-heterocyclic carbenes, tBuCCmeth and tBuCCeth (where tBuCCmeth = 1,1′-methylene-3,3′-di-tert-butyldiimidazol-2,2′-diylidene and tBuCCeth = 1,2-ethylene-3,3′-di-tert-butyldiimidazol-2,2′-diylidene), have been prepared. The complexes [Pd(tBuCCmeth)Me2] (1) and [Pd(tBuCCeth)Me2] (2) have been isolated and 2 has been characterised by single crystal X-ray diffraction. When 1 and 2 are dissolved in deuterated methanol in the presence of pyridine or bipyridine the four coordinate cations [Pd(tBuCCmeth)Me(py)]+ (3), [Pd(tBuCCeth)Me(py)]+ (4), [Pd(tBuC(D)-η-Cmeth)Me(η2-bipy)]+ (5), and [Pd(tBuC(D)-η-Ceth)Me(η2-bipy)]+ (6), are observed spectroscopically.

Synthesis, Structural Preference and Catalytic Activity of Neutral and Cationic Methylpalladium(II) Complexes Containing N-Arylpyridine-2-carbaldimine Chelating Ligands

The syntheses and structures of neutral complexes [PdCl(Py-2-CH=NAr)(Me)] (Ar = 4-MeC6H4, 4-MeOC6H4, 4-CF3C6H4) and cationic complexes [Pd(Py-2-CH=NAr)(Me)(MeCN)]SbF6 (Ar = 4-MeC6H4, 4-MeOC6H4, 4-CF3C6H4) are described. The preference for the trans-isomers in the cationic complexes and for the cis-isomers in the neutral complexes is discussed on the basis of electronic arguments and supported by DFT calculations. The observed preference seems to follow the maximum hardness principle (MHP) introduced by Pearson. On the basis of the application of this principle to square planar complexes of palladium(II) and platinum(II) we propose the trans choice, which means that the hardest ligand arranges trans to the softest one. The synthesis and crystal structure of the related neutral complex trans-[Pd(CF3COO)(Py-2-CH=NC6H4-4-OMe)(Me)] is also described and allows to rule out the charge of the complex as the cause of isomeric preference. We also report our preliminary studies dealing with the catalytic activity of the cationic complexes in alkene oligomerization and copolymerization with CO.