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Complexes cis‐[Pd(ArF)2(NCMe)2] (A) and cis‐[Pd(ArF)2(THF)2] (B) (ArF=C6F3H2) are fast general precursors easy to prepare, store and handle, which allow in situ synthesis of tailor‐made [Pd(Ar)(X)(L)] catalysts for chosen Ar‐Nu couplings, provided that the L ligand (in this case PR2(2‐biaryl)) induces (ArF)2 coupling. This fluorinated byproduct is inert in the reaction conditions, and no other byproduct is expected because the Ar and X groups are the same in the catalyst, the intermediates and the products. The application of A or B in catalysis (e. g. with 1% catalyst) consists of a first step (formation of 1% tailor‐made catalyst) where 100 ArX+1 A (or B)+1 L in THF gives a solution with 99 ArX+1 [Pd(Ar)(X)(L)]+(ArF)2. The only other byproduct is THF or NCMe. In the second step, addition of the nucleophile, 100 Q(Nu), triggers and completes the catalytic cycle yielding 100 Ar‐Nu+100 Q(X)+1 [Pd0(L)]. The 100% yield is theoretical, but the tested catalysis (Ar‐Me Negishi coupling, C6F5‐alkynyl Stille coupling and Ar‐naphthyl Suzuki coupling) using A as precursor, SPhos as ligand, and 1000:1 reagents:catalyst ratio, afford 95–99% yield. In contrast, aryl‐amination requires 1000:5 ratio to give 96% yield (or 1000:50 for 99% yield) because PhNH2 eventually displaces the SPhos from Pd and blocks the catalyst. As a bonus, the presence of F in the precursors facilitates stepwise 19F NMR monitoring of the formation of [Pd(Ar)(X)(L)] with different phosphines, facilitating analysis of weaknesses or strengths of each of them to produce the catalyst, and helps in the choice of the most convenient one for the case. The in situ catalyst formation is ideal for serial two‐step catalysis with different phosphines or different nucleophiles. [ABSTRACT FROM AUTHOR]

An efficient Pd/Cu bimetallic cross-coupling catalysis of fluoroaryl halides and fluoroarenes is reported. In situ generation of the Cu nucleophile by rate determining C–H activation of highly fluorinated aryls (≥4 F atoms) leads to high cross-coupling selectivity with little formation of homocoupling products. [ABSTRACT FROM AUTHOR]

Several salen manganese(iii) complexes displaying stable columnar mesophases in a wide range of temperatures have been synthesized. In condensed phases the molecules are assembled into dimers through intermolecular manganese–oxygen interactions and the columnar structure of the mesophases consist of the stacking of supramolecular discs formed by the association of two or three dimers, depending on the number and location of alkoxy chains in the complex. The catalytic activity of the complexes in solution has been studied, and they behave as efficient homogeneous catalysts in the epoxidation of styrene with iodosylbenzene as oxidant. [ABSTRACT FROM AUTHOR]

Studies the mechanisms of catalyzed couplings of aryl triflates with vinyltributyltin. Acceleration of the rate-determining oxidative addition of the aryl triflate; Key intermediates undergoing transmetalation in the conditions and solvents; Common aspects of the Stille reaction with the Hiyama reaction.

Describes the development of an efficient catalytic system for the Heck reaction of fluoroaryls. Insertion into Pd-(perfluoro-organyl) bonds providing reaction conditions exempt of ligands other than halide, solvent and substrates needed for a fast coordination-insertion process; Efficiency of the catalyst system for other fluorinated aryls of the type p-C[sub 6]F[sub 4]XBr.

A bimetallic system of Pd/CuF2, catalytic in Pd and stoichiometric in Cu, is efficient and selective for the coupling of fairly hindered aryl silanes with aryl iodides of conventional size. [ABSTRACT FROM AUTHOR]

The complexity of the transmetalation step in a Pdcatalyzed Negishi reaction has been investigated by combining experiment and theoretical calculations. The reaction between trans-[PdMeCl(PMePh2)2] and ZnMe2 in THF as solvent was analyzed. The results reveal some unexpected and relevant mechanistic aspects not observed for ZnMeC1 as nucleophile. The operative reaction mechanism is not the same when the reaction is carried out in the presence or in the absence of an excess of phosphine in the medium. In the absence of added phosphine an ionic intermediate with THF as ligand ([PdMe(PMePhz)2(TfIF)]+) opens ionic transmetalation pathways. In contrast, an excess ofphosphine retards the reaction because of the formation ofa very stable cationic complex with three phosphines ([PdMe(PMePh2)3]+) that sequesters the catalyst. These ionic intermediates had never been observed or proposed in palladium Negishi systems and warn on the possible detrimental effect of an excess of good ligand (as PMePh2) for the process. In contrast, the ionic pathways via cationic complexes with one solvent (or a weak ligand) can be noticeably faster and provide a more rapid reaction than the concerted pathways via neutral intermediates. Theoretical calculations on the real molecules reproduce well the experimental rate trends observed for the different mechanistic pathways. [ABSTRACT FROM AUTHOR]

A DFT study of R-R reductive elimination (R = Me, Ph, vinyl) in plausible intermediates of Pd-catalyzed processes is reported. These include the square-planar tetracoordinated systems cis-[PdR2(PMe3)2] themselves, possible intermediates cis-[PdR2(PMe3)L] formed in solution or upon addition of coupling promoters (L = acetonitrile, ethylene, maleic anhydride (ma)), and tricoordinated intermediates cis-[PdR2(PMe3)] (represented as L = empty). he activation energy ranges from 0.6 to 28.6 kcal/mol in the gas phase, increasing in the order vinyl-vinyl < Ph-Ph < Me-Me, depending on R, and ma < "empty" ethylene < PMe3 ≈ MeCN, depending on L. The effect of added olefins was studied for a series of olefins, providing the following order of activation energy: p-benzoquinone < ma < trans-1,2-dicyanoethylene 3,5-dimethylcyclopent-1-ene < 2,5-dihydrofuran < ethylene < trans-2-butene. Comparison of the calculated energies with experimental data for the coupling of cis-[PdMe2(PPh3)2] in the presence of additives (PPh3, p-benzoquinone, ma, trans-1,2-dicyanoethylene, 2,5-dihydrofuran, and 1-hexene) reveals that: (1) There is no universal coupling mechanism. (2) The coupling mechanism calculated for cis-[PdMe2(PMe3)2] is direct, but PPh3 retards the coupling for cis-[PdMe2(PPh3)2], and DFT calculations support a switch of the coupling mechanism to dissociative for PPh3. (3) Additives that would provide intermediates with coupling activation energies higher than a dissociative mechanism (e.g., common olefins) produce no effect on coupling. (4) Olefins with electron-withdrawing substituents facilitate the coupling through cis-[PdMe2(PR3)(olefin)] intermediates with much lower activation energies than the starting complex or a tricoordinated intermediate. Practical consequences are discussed. [ABSTRACT FROM AUTHOR]

Complexes [AuCI{C(NHR)(NHPy-2)}] (Py-2 = 2-pyridyl; R = Me, 'Bu, 'Bu, 'Pr, 'heptyl) have been prepared in a modular way from [AuCI(CNPy-2)]. The carbene moiety has a hydrogen-bond supported heterocyclic structure similar to the nitrogen heterocyclic carbenes in the solid state, and in CH2CI2 or acetone solution, which is open in the presence of MeOH. The compounds are good catalysts for the skeletal rearrangement of enynes, and for the methoxycyclization of enynes. In contrast, the complexes [AuCI{C(NHR)(NHPy-4)}] are scarcely active due to the blocking effect of the coordination position required for the catalysis by the nitrogen of the NHPy-4 group. [ABSTRACT FROM AUTHOR]