Palladium Catalysts Supported in Microporous Phosphine Polymer Networks

A new set of microporous organic polymers (POPs) containing diphosphine derivatives synthesized by knitting via Friedel-Crafts has been attained. These amorphous three-dimensional materials have been prepared by utilizing diphosphines, 1,3,5-triphenylbenzene, and biphenyl as nucleophile aromatic groups, dimethoxymethane as the electrophilic linker, and FeCl3 as a promoting catalyst. These polymer networks display moderate thermal stability and high microporosity, boasting BET surface areas above 760 m2/g. They are capable of coordinating with palladium acetate, using the phosphine derivative as an anchoring center, and have proven to be highly efficient catalysts in Suzuki-Miyaura coupling reactions involving bromo- and chloroarenes under environmentally friendly (using water and ethanol as solvents) and aerobic conditions. These supported catalysts have achieved excellent turnover numbers (TON) and turnover frequencies (TOF), while maintaining good recyclability without significant loss of activity or Pd leaching after five consecutive reaction cycles.

Problematic ArF-Alkynyl Coupling with Fluorinated Aryls. From Partial Success with Alkynyl Stannanes to Efficient Solutions via Mechanistic Understanding of the Hidden Complexity

The synthesis of aryl-alkynyl compounds is usually achieved via Sonogashira catalysis, but this is inefficient for fluorinated aryls. An alternative method reported by Shirakawa and Hiyama, using alkynylstannanes and hemilabile PN ligands, works apparently fine for conventional aryls, but it is also poor for fluorinated aryls. The revision of the unusual literature cycle reveals the existence and nature of unreported byproducts and uncovers coexisting cycles and other aspects that explain the reasons for the conflict. This knowledge provides a full understanding of the real complexity of these aryl/alkynylstannane systems and the deviations of their evolution from that of a classic Stille process, providing the clues to design several very efficient alternatives for the catalytic synthesis of the desired Ar^F-alkynyl compounds in almost quantitative yield. The same protocols are also very efficient for the catalytic synthesis of alkynyl-alkynyl' hetero- and homocoupling.

Ranking Ligands by Their Ability to Ease (C6F5)2NiIIL → Ni0L + (C6F5)2 Coupling versus Hydrolysis: Outstanding Activity of PEWO Ligands

The Ni^II literature complex cis-[Ni(C₆F₅)₂(THF)₂] is a synthon of cis-Ni(C₆F₅)₂ that allows us to establish a protocol to measure and compare the ligand effect on the Ni^II → Ni⁰ reductive elimination step (coupling), often critical in catalytic processes. Several ligands of different types were submitted to this Ni-meter comparison: bipyridines, chelating diphosphines, monodentate phosphines, PR₂(biaryl) phosphines, and PEWO ligands (phosphines with one potentially chelate electron-withdrawing olefin). Extremely different C₆F₅-C₆F₅ coupling rates, ranging from totally inactive (producing stable complexes at room temperature) to those inducing almost instantaneous coupling at 25 °C, were found for the different ligands tested. The PR₂(biaryl) ligands, very efficient for coupling in Pd, are slow and inefficient in Ni, and the reason for this difference is examined. In contrast, PEWO type ligands are amazingly efficient and provide the lowest coupling barriers ever observed for Ni^II complexes; they yield up to 96% C₆F₅-C₆F₅ coupling in 5 min at 25 °C (the rest is C₆F₅H) and 100% coupling with no hydrolysis in 8 h at -22 to -53 °C.

Experimental study of speciation and mechanistic implications when using chelating ligands in aryl-alkynyl Stille coupling

Neutral palladium(ii) complexes [Pd(Rf)X(P-L)] (Rf = 3,5-C6Cl2F3, X = Cl, I, OTf) with P-P (dppe and dppf) and P-N (PPh2(bzN)) ligands have chelated structures in the solid-state, except for P-L = dppf and X = Cl, were chelated and dimeric bridged structures are found. The species present in solution in different solvents (CDCl3, THF, NMP and HMPA) have been characterised by 19F and 31P{1H} NMR and conductivity studies. Some [Pd(Rf)X(P-L)] complexes are involved in equilibria with [Pd(Rf)(solv)(P-L)]X, depending on the solvent and X. The ΔH° and ΔS° values of these equilibria explain the variations of ionic vs. neutral complexes in the range 183-293 K. Overall the order of coordination strength of solvents and anionic ligands is: HMPA ≫ NMP > THF and I-, Cl- > TfO-. This coordination preference is determining the complexes participating in the alkynyl transmetalation from PhC[triple bond, length as m-dash]CSnBu3 to [Pd(Rf)X(P-L)] (X = OTf, I) in THF and subsequent coupling. Very different reaction rates and stability of intermediates are observed for similar complexes, revealing neglected complexities that catalytic cycles have to deal with. Rich information on the evolution of these Stille systems after transmetalation has been obtained that leads to proposal of a common behaviour for complexes with dppe and PPh2(bzN), but a different evolution for the complexes with dppf: this difference leads the latter to produce PhC[triple bond, length as m-dash]CRf and black Pd, whereas the two former yield PhC[triple bond, length as m-dash]CRf and [Pd(C[triple bond, length as m-dash]CPh)(SnBu3)(dppe)] or [Pd(C[triple bond, length as m-dash]CPh)(SnBu3){PPh2(bzN)}].

Novel phosphine sulphide gold(i) complexes: topoisomerase I inhibitors and antiproliferative agents

Gold(i) increases the cytotoxicity of phosphine sulfide quinolines against cancer cell lines, while heterocycles maintain the TopI inhibitory activity.

Microporous Polymer Networks for Carbon Capture Applications

A new generation of porous polymer networks has been obtained in quantitative yield by reacting two rigid trifunctional aromatic monomers (1,3,5-triphenylbenzene and triptycene) with two ketones having electron-withdrawing groups (trifluoroacetophenone and isatin) in superacidic media. The resulting amorphous networks are microporous materials, with moderate Brunauer-Emmett-Teller surface areas (from 580 to 790 m² g^-1), and have high thermal stability. In particular, isatin yields networks with a very high narrow microporosity contribution, 82% for triptycene and 64% for 1,3,5-triphenylbenzene. The existence of favorable interactions between lactams and CO₂ molecules has been stated. The materials show excellent CO₂ uptakes (up to 207 mg g^-1 at 0 °C/1 bar) and can be regenerated by vacuum, without heating. Under postcombustion conditions, their CO₂/N₂ selectivities are comparable to those of other organic porous networks. Because of the easily scalable synthetic method and their favorable characteristics, these materials are very promising as industrial adsorbents.

Promoting Difficult Carbon-Carbon Couplings: Which Ligand Does Best?

A Pd complex, cis-[Pd(C₆ F₅ )₂ (THF)₂ ] (1), is proposed as a useful touchstone for direct and simple experimental measurement of the relative ability of ancillary ligands to induce C-C coupling. Interestingly, 1 is also a good alternative to other precatalysts used to produce Pd⁰ L. Complex 1 ranks the coupling ability of some popular ligands in the order P^t Bu₃ >o-TolPEWO-F≈tBuXPhos>P(C₆ F₅ )₃ ≈PhPEWO-F>P(o-Tol)₃ ≈THF≈tBuBrettPhos≫Xantphos≈PhPEWO-H≫PPh₃ according to their initial coupling rates, whereas their efficiency, depending on competitive hydrolysis, is ranked tBuXPhos≈P^t Bu₃ ≈o-TolPEWO-F>PhPEWO-F>P(C₆ F₅ )₃ ≫tBuBrettPhos>THF≈P(o-Tol)₃ >Xantphos>PhPEWO-H≫PPh₃ . This "meter" also detects some other possible virtues or complications of ligands such as tBuXPhos or tBuBrettPhos.

Highly enantioselective addition of dimethylzinc to fluorinated alkyl ketones, and the mechanism behind it

Switching the solvent from toluene to dichloromethane results in a very important enhancement in the yield and enantiomeric excess of nucleophilic addition.

Polymer [Pd(CH2SO2C6H4Me)2]n, a precursor to remarkably stable Pd organometallics

Stable (arylsulfonyl)alkylpalladium complexes obtained from the polymer [Pd(CH₂SO₂C₆H₄Me)₂]_n undergo cis-to-trans isomerization in order to produce systems with stronger hydrogen bonds.

Study of the Replacement of Weak Ligands on Square-Planar Organometallic Nickel(II) Complexes. Organo-Nickel Aquacomplexes

When trans-[NiRf2L2] (Rf = 3,5-C6Cl2F3; L = group 15 soft monodentate weak ligand such as SbPh3 or AsPh3) is dissolved in wet (CD3)2CO, isomerization (to give cis-[NiRf2L2]) and subsequent substitutions of L by (CD3)2CO or by water occur, and several complexes containing acetone and aqua ligands are formed. The isomerization takes place in a few seconds at room temperature. The substitution reactions on the cis isomer formed are faster. The kinetics of the equilibria between all of the participating species have been studied by 19F exchange spectroscopy experiments at 217 K, and the exchange rates and rate constants have been calculated. These data reflect the weakness of acetone compared to water and AsPh3. The data obtained are the first available for square-planar nickel(II) aquacomplexes. The bulkier AsCyPh2 ligand slows down the exchange processes while the displacement of AsMePh2 is clearly disfavored. Activation entropy studies support an associative ligand substitution. All of these data fit well with the previously reported relative activity of these complexes as catalysts in norbornene polymerization.

Dinuclear azolato-bridged complexes of the nickel group metals with haloaryl ligands: a reinvestigation of their behavior in solution

A reinvestigation of the NMR spectra of the complexes (NBu4)2[M2(mu-LL)2R4] (M = Pd, Ni, Pt, LL = pyrazolate (pz), 3,5-dimethylpyrazolate (dmpz), 3-methylpyrazolate (mpz), indazolate (indz), R = C6F5; M = Pd, LL = pz, dmpz, mpz, indz, R = 2,4,6-C6F3H2) shows that the boat-shaped dimeric structures of their anions are quite stable in solution, and the previously proposed fast equilibria or dissociations to give species such as [R2M(N-N)(acetone)]-, [R2M(acetone)2] + 2dmpz-, or [R2M(N1-N2)(acetone)]- + [R2M(N2-N1)(acetone)]- in no case occur. A mixture of the two diastereoisomers (head-to-head, HH, and head-to-tail, HT) is present for the asymmetrically substituted azolates (mpz and indz), in a ratio ranging from 1:7 to 1:30 for the different complexes. Strong through-space coupling between the endo ortho fluorine nuclei of different MR2 fragments is observed in the 19F NMR spectra of these diastereoisomers whose boatlike structures place these atoms at short distances.

Oxidative Addition of Group 14 Element Hydrido Compounds to OsH(2)(eta(2)-CH(2)=CHEt)(CO)(P(i)Pr(3))(2): Synthesis and Characterization of the First Trihydrido-Silyl, Trihydrido-Germyl, and Trihydrido-Stannyl Derivatives of Osmium(IV)

The dihydrido-olefin complex OsH(2)(eta(2)-CH(2)=CHEt)(CO)(P(i)Pr(3))(2) (2) reacts with H(2)SiPh(2) to give OsH(3)(SiHPh(2))(CO)(P(i)Pr(3))(2) (3). The molecular structure of 3 has been determined by X-ray diffraction (monoclinic, space group P2(1)/c with a = 16.375(2) Å, b = 11.670(1) Å, c =18.806(2) Å, beta = 107.67(1) degrees, and Z = 4) together with ab initio calculations on the model compound OsH(3)(SiH(3))(CO)(PH(3))(2). The coordination geometry around the osmium center can be rationalized as a heavily distorted pentagonal bipyramid with one hydrido ligand and the carbonyl group in the axial positions. The two other hydrido ligands lie in the equatorial plane, one between the phosphine ligands and the other between the SiHPh(2) group and one of the phosphine ligands. Complex 3 can also be prepared by reaction of OsH(eta(2)-H(2)BH(2))(CO)(P(i)Pr(3))(2) (4) with H(2)SiPh(2). Similarly, the treatment of 4 with HSiPh(3) affords OsH(3)(SiPh(3))(CO)(P(i)Pr(3))(2) (5), while the addition of H(3)SiPh to 4 in methanol yields OsH(3){Si(OMe)(2)Ph}(CO)(P(i)Pr(3))(2) (6). Complex 2 also reacts with HGeR(3) and HSnR(3) to give OsH(3)(GeR(3))(CO)(P(i)Pr(3))(2) (GeR(3) = GeHPh(2) (7), GePh(3) (8), GeEt(3) (9)) and OsH(3)(SnR(3))(CO)(P(i)Pr(3))(2) (R = Ph (10), (n)Bu (11)), respectively. In solution, compounds 3 and 5-11 are fluxional and display similar (1)H and (31)P{(1)H} NMR spectra, suggesting that they possess a similar arrangement of ligands around the osmium atom.