The ligands 2,4,6-tris(4-methylpyrazol-1-yl)-1,3,5-triazine (Me-TPzT), 2,4,6-tris(4-bromopyrazol-1-yl)-1,3,5-triazine (Br-TPzT), and 2-methoxy-4,6-bis(4-methylpyrazol-1-yl)-1,3,5-triazine (Me-BPzTOMe) have been synthesized and their reactions with some palladium derivatives explored. The palladium fragment [Pd(eta(3)-2-Me-C(3)H(4))(S)(2)](+), S = acetone, reacts in acetone with Me-TPzT or Br-TPzT in a 3:1 molar ratio to generate new complexes in which two allylpalladium fragments are present and the TPzT ligands have been partially hydrolyzed: [{Pd(eta(3)-C(4)H(7))}(2)(X-BPzTO)]A, X-BPzTO = 4,6-bis[4-methyl(or bromo)pyrazol-1-yl]-1,3,5-triazin-2-olate (X = Me, A = BF(4), 1; A = PF(6), 2; A = CF(3)SO(3), 3; A = p-MeC(6)H(4)SO(3), 4; X = Br, A = CF(3)SO(3), 5). When the ligand Me-BPzTOMe is made to react with only 1 equiv of the palladium solvate, compound 6, [Pd(eta(3)-2-Me-C(3)H(4))(Me-BPzTOMe)]CF(3)SO(3), is isolated. Reaction of 6 with another 1 equiv of the palladium derivative leads to 3. The intermediate 7, [{Pd(eta(3)-2-Me-C(3)H(4))}(2)(Me-BPzTOMe)]CF(3)SO(3), has been isolated as an almost pure compound. The reaction of Me-BPzTOMe with 1 equiv of [Pd(C(6)F(5))(2)(cod)] (cod = 1,5-cyclooctadiene) leads to the complex [Pd(C(6)F(5))(2)(Me-BPzTOMe)], 8. Attention has been focused on the dynamic behavior, related with metallotropic phenomena, of the new complexes. (1)H NMR variable-temperature studies of complexes 1, 6, and 8 have been carried out. For 8, only one static species is observed, while, for 1 and 6, two isomers are detected at low temperature. Different DeltaG(c)() activation energies at the coalescence temperature have been determined and are ascribed to processes implying Pd-N bond ruptures. For 6, two different barriers are detected, corresponding to Pd-N(triazine) or Pd-N(pyrazole) bond ruptures. From the DeltaG(c)() data, it is concluded that the main driving force of the hydrolysis process is the formation of a better coordinating ligand. The molecular structure of 4 has been determined by X-ray diffraction. The meso isomer, in which the two C-Me axes of the allylic groups are oriented in the same direction, is found in the solid state.

The (aminoferrocenyl)phosphine ligand 1-diphenylphosphino-2,1‘-(1-dimethylaminopropanediyl)ferrocene, 1, was used to synthesize new palladium(0) and -(II) complexes. The reaction of Pd2(dba)3·CHCl3 with 1 in the presence of the electron-withdrawing olefins dimethylfumarate (DMFU) and maleic anhydride (MA) gave the new complexes Pd(1)(DMFU) (2) and Pd(1)(MA) (3). The allyl complex [Pd(η3-2-Me-C3H4)(1)]Tf (4) was obtained from the reaction of 1 with [Pd(η3-2-Me-C3H4)(Cl)]2 in the presence of AgTf. In solution all these compounds exist as mixtures of two diastereomers, with either the alkene or the allyl group differently oriented with respect to the aminophosphine ligand. The orientation of these ligands in the major isomers has been determined by means of NOEs. Alkene rotation takes place in complexes 2 and 3 with free energies of activation ΔG 340 ⧧ = 73.1 kJ mol-1 (2) and ΔG 368 ⧧ = 79.9 kJ mol-1 (3), respectively. These barriers are compared with those of some analogous ferrocenyl aminophosphine ligands, PPFA (2-(1-dimethylaminoethyl)-1-diphenylphosphinoferrocene) and PTFA (1-diphenylphosphino-2,3-endo-(α-dimethylamino)tetramethyleneferrocene) complexes. For 3, the alkene rotation leads to isomer interconversion, while the observed isomerization of 2 must proceed via an olefin face exchange. Some experiments in relation to the nature of this process are discussed. Starting from PdRR‘L‘ precursors and 1 or PPFA, other Pd(II) derivatives of formulas PdRR‘(1), R = Cl, R‘ = Me, L‘ = cod, 5; R = R‘ = Me, L‘ = tmeda, 6; R = R‘ = C6F5, L‘ = cod, 7, or PdClMe(PPFA), 8, were prepared. For 5 and 8, only the isomers with the methyl group trans to nitrogen were obtained. The Pd−N bond rupture in the new complexes of 1 and in similar derivatives of PPFA and PTFA has been analyzed by variable-temperature 1H NMR studies, and in some cases a line shape analysis has been carried out. The influence of the ferrocenyl aminophosphine and ancillary ligands as well as of the oxidation state of the palladium center on this process is discussed. The molecular structures of both rotamers of 3, present in the same crystal, were determined by X-ray structure analysis.

The ligands 4,6-bis(pyrazol-1-yl)pyrimidine (bpzpm) and 4,6-bis(4-methylpyrazol-1-yl)pyrimidine (Me-bpzpm) were synthesized and their reactions with some palladium derivatives explored. Mononuclear or dinuclear neutral or cationic complexes were obtained by reaction of the ligands with 1 or 2 equiv of Pd(C6XF4)2(cod) (cod = 1,5-cyclooctadiene; X = F, H) or the palladium fragment [Pd(eta 3-2-Me-C3H4)(S)2]+ (S = acetone). The reaction of the dinuclear derivatives with 1 equiv of the respective free ligand immediately led to the regeneration of the mononuclear complexes. Except in the case of the synthesis of [[Pd(C6HF4)2][Pd(C6F5)2](bpzpm)], where two similar metallic groups are present, all attempts to obtain dinuclear asymmetric complexes with two different palladium fragments failed. Instead, the dinuclear symmetric complexes were formed. This result could be considered as an example of molecular recognition with the ligand acting as a ditopic receptor. This behavior is comparable to chemical symbiosis but in this case applied to the ligand rather than to the metal center as occurs normally. The polyfluorophenyl rings are situated on average in a perpendicular orientation with respect to the coordination plane. Their restricted rotation results in several atropoisomers for the complexes with m-C6HF4. Different cross-reaction experiments were carried out, and these showed the mobility of the metallic fragments, with the more difficult process being that involving the more strongly bonded polyfluorophenyl palladium groups. By means of 1H NMR variable temperature studies, the interconversion of the two isomers of [[Pd(eta 3-C4H7)]2-(bpzpm)]Tf2 (Tf = CF3SO3) was analyzed. In the case of [[Pd(eta 3-C4H7)](bpzpm)]Tf the existence of two processes, an intramolecular apparent allyl rotation and an intermolecular exchange of the allylpalladium fragments, has been demonstrated. Different delta Gc++ values at the coalescence temperatures have also been determined. An X-ray single-crystal analysis was carried out on [[Pd(eta 3-C4H7)]2(bpzpm)]Tf2, which crystallizes in the monoclinic system, space group I2/m, with a = 9.368(2), b = 16.191(3), c = 20.228(6) A, beta = 101.26(3), and Z = 4. Compound [[Pd(C6HF4)2](bpzpm)] crystallized in the triclinic system, space group P1, with a = 8.845(6), b = 12.6609(9), c = 12.826(3) A, alpha = 88.45(2), beta = 74.36(3), gamma = 89.32(2), and Z = 2.

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New examples of the fluxional behavior of (q3-ally1)palladium complexes are described. Variable-temperature experiments and line-shape analysis of two (q3-allyl)palladium complexes containing 2-( 1H-pyrazol-1-y1)azine ligands were performed in order to determine the activation free energies, enthalpies and entropies of the process. A dissociative mechanism pointing to a selective Pd-N cleavage is proposed on the basis of these results and NOE experiments above and below the coalescence temperature.The synthesis and catalytic reactivity of (q3-ally1)palladium complexes have been widely studied [']. For instance, the catalytic allylation is a process of synthetic interest[le-"I. When a chiral group, for example a chelating nitrogen or a phosphorus-nitrogen ligand, is involved, relatively high enantiomeric excesses are obtainedr21. There is a growing interest in understanding the solution structures ['] and the fluxional behaviorL41 of allylpalladium compounds as they may be related with the catalytic results. Some of us reported recently[5a] on the stabilization of PF; hydrolysis intermediates by the [2-methylallylpalladium]+ fragment. This unsaturated species may be stabilized in solutions of coordinating solvents such as acetone and reacts with different polypyrazolylmethane and borate ligands to give cationic complexes with interesting fluxional The fluxionality phenomena are very common in palladium(I1) chemistry and, in many cases, the dynamic behavior is explained as a result of preliminary ligand dissociations enabling different processes to occud6I. For instance, in complexes with N-donor chelating ligands, the Pd-N bond breaking is at this moment an accepted path to explain different interconversion processes. In this paper we study the fluxional behavior of new ally1 complexes containing asymmetric N-donor ligands. In this case, the equivalence of the two halves of the allylic group would be an indication of a fluxional process and, if a dissociative mechanism was found, the selectivity towards the Pd-N bond cleavage could be explored. Another aim in our work was to investigate if the study of NOE effects between the allylic group and the ligand could be a way to test the existence of a Pd-N bond cleavage. Results and DiscussionIn this paper we report on the preparation and dynamic behavior of (2-methyla1lyl)palladium complexes with asymmetric ligands such as 2-( lH-pyrazol-l-y1)pyridine (PzPy) and 2-( 1H-pyrazol-1 -yl)pyrimidine (PzPm). The new complexes [Pd(q3-2-Me-C3H4)PzPy]Tf (1) and [Pd(q3-2-Me-C3H4)PzPm]Tf (2) (Tf = CF3S0,, Scheme 1) were prepared by treatment of the dimer complex [Pd(q3-C4H7)C1I2 with AgCF3S03. The addition of the ligands to the filtered solutions allowed the isolation of complexes 1 and 2.Complexes 1 and 2 were characterized by their NMR spectra, elemental analyses and MS FAB. 'H-NMR and 13C-NMR spectra of 1 and 2 (Tables 1-2) at 293 K were assigned by comparison with the spectra of the ligdnd and with several related c0mplexes[~1. Coordination with the (q3-allyl)palladium fragme...

Novel palladium complexes with BPPFA (N,N-dimethyl-1-[2,1′-bis(diphenylphosphino)ferrocenyl]ethylamine) and the newly prepared ligand 1,1′-bis(diphenylphosphino)-2-methylferrocene (BPPFMe, 1) have been synthesized. Racemic BPPFA reacts with Pd 2 (dba) 3 ‚ CHCl 3 in the presence of electron-withdrawing alkenes to give palladium(0) complexes Pd(BPPFA)(alkene), where alkene ) dimethyl fumarate (2), maleic anhydride (3). Displacement of weak donor ligands from the appropriate palladium(II) precursors leads to the derivatives [Pd(η 3 -2-Me-C 3 H 4 )(BPPFA)]TfO (4), Pd(C 6 F 5 ) 2 (BPPFA) (5), Pd(C 6 F 5 ) 2 (BPPFMe) (6), PdMe 2 (BPPFA) (7), and PdClMe(BPPFA) (8). Complexes 2-4 and 8 each exist in solution as two diastereomers that do not interconvert at room temperature on the NMR time scale. In all mononuclear complexes BPPFA is P,P-coordinated to palladium. When PdClX(cod) (X ) Cl, Me) is reacted with (R C ,S P )-BPPFA in a Pd:L ratio higher than 1:1, polynuclear species are formed. A Pd:L ratio of 2:1 leads to the tetranuclear derivatives {cis-PdClX(µ-κ 3 -BPPFA)} 2 -{PdX(µ-Cl) 2 PdX} (X ) Me (9), Cl (10)), while a ratio of 1.5:1 gives the trinuclear complexes {cis-PdClX(µ-κ 3 -BPPFA)} 2 (trans-PdClX) (X ) Me (11), Cl ( 12)) along with the corresponding tetra-and mononuclear derivatives. Mechanistic studies concerning the formation of the tetranuclear complexes have shown that a P,P to P,N coordination shift and Pd-P bond rupture are feasible processes. Variable-temperature 1 H NMR studies have provided evidence of Pd-N interactions in complexes 2, 5, 7, and 8 that involve an unprecedented terdentate κ 3 N,P,P chelate coordination of BPPFA to palladium. The pentafluorophenyl complexes 5 and 6 each exist in solution as two conformers that are interconvertible by torsional twisting of the Cp rings. In the case of complex 5 this interconversion process is slowed at low temperature to such an extent that both conformers can be observed separately by NMR spectroscopy. This phenomenon is presumably due to the Pd-N interaction. The molecular structures of 2M and 8M (M ) major isomer) have been determined by X-ray diffraction.

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