Structural variation, dynamics, and catalytic application of palladium(II) complexes of di-N-heterocyclic carbene-amine ligands

A series of palladium(II) complexes incorporating di-NHC-amine ligands has been prepared and their structural, dynamic and catalytic behaviour investigated. The complexes [trans-(k(2)-(CN)-C-tBu(Bn)CN(Bn)C-tBu)PdCl2] (12) and [trans-(kappa(2)-(CN)-C-Mes(H)C-Mes)PdCl2] (13) do not exhibit interaction between the amine nitrogen and palladium atom respectively. NMR spectroscopy between - 40 and 25 degrees C shows that the di-NHC-amine ligand is flexible expressing C-s symmetry and for 13 rotation of the mesityl groups is prevented. In the related C-1 complex [(kappa(3)-(CN)-C-tBu(H)C-tBu)PdCl][CI] (14) coordination of NHC moieties and amine nitrogen atom is observed between -40 and 25 degrees C. Reaction between 12 - 14 and two equivalents of AgBF4 in acetonitrile gives the analogous complexes [trans-(kappa(2)-(CN)-C-tBu(Bn)C-tBu)PdCl2] (12) and [trans-(kappa(CN)-C-2Mes(H)C-Mes)PdCl2] (13) do not exhibit interaction between the amine nitrogen and palladium atom respectively. NMR spectroscopy between -40 ans 25 degrees C shows the di-NHC-amine ligand is flexible expressing C-s symmetry and for 13 rotation of the mesityl groups is prevented. In the related C-1 complex [kappa(3)-(CN)-C-tBu(H)C-tBu)PdCI][CI] (14) coordination of NHC moieties and amine nitrogen atom is observed between -40 and 25 degrees C.Reaction between 12-14 and two equivalents of AgBF4 in acetonitrile gives the analogous complexes [trans-(kappa(2)-(CN)-C-tBu(H)(CPd)-Pd-tBu(MeCN)(2)][BF4](2) (15), [trans-(kappa(CN)-C-2Mes(H)C-Mes)Pd(MeCN)(2)[BF4](2 (16)) and [(kappa(3)-(CN)-C-tBu(H)C-tBu)Pd(MeCN)][BF4](2) (17) indicating that ligand structure determines amine coordination. The single crystal X-ray structures of 12, 17 and two ligand imidazolium salt precursors C-tBu(H)N(Bn)C(H) (tBu)][CI](2) (2) and [C-tBu(H) N(H)C(H)(tBu)][BPh4](2) (4) have been determined. Complexes 12-14 and 15-17 have been shown to be active precatalysts for Heck and hydroamination reactions respectively

Rhodium-Catalyzed Asymmetric Intramolecular Hydroamination of Unactivated Alkenes

One for the Rh(oad): The first rhodium-catalyzed asymmetric intramolecular hydroamination of unactivated olefins was developed by using dialkylbiaryl phosphine ligands (see scheme; cod=1,5-cyclooctadiene, Cy=cyclohexyl). A variety of 2-methylpyrrolidines have been synthesized with high enantioselectivities.National Institutes of Health (U.S.) (Grant GM46059)Merck & Co.Boehringer Ingelheim PharmaceuticalsNational Institutes of Health (U.S.) (GM 1S10RR13886-01

The Catalytic Enantioselective Total Synthesis of (+)-Liphagal

Ring a ding: The meroterpenoid natural product (+)-liphagal has been synthesized enantioselectively in 19 steps from commercially available materials. The trans-homodecalin system was achieved by ring expansion followed by stereoselective hydrogenation

Mild, aqueous α-arylation of ketones : towards new diversification tools for halogenated metabolites and drug molecules

The authors thank the European Research Council (FP7/2007-2013/ERC grant agreement no 614779 to RJMG) and (FP7 2009-2014/ERC agreement no 227817 to SPN) for generous funding.The palladium-catalyzed aqueous α-arylation of ketones was developed and tested for a large variety of reaction partners. These mild conditions enabled the coupling of aryl/ alkyl-ketones with N-protected halotryptophans, heterocyclic haloarenes, and challenging base-sensitive compounds. The synthetic potential of this new methodology for the diversification of complex bioactive molecules was exemplified by derivatising prochlorperazine. The methodology is mild, aqueous and flexible, representing a means of functionalizing a wide range of halo-aromatics and therefore has the potential to be extended to complex molecule diversification.PostprintPeer reviewe

Bifunctional acid-base ionic liquid for the one-pot synthesis of fine chemicals: thioethers, 2H-chromenes and 2H-quinoline derivatives

A bifunctional organocatalyst with ionic liquid properties and with an optimized distance between the acid and basic sites efficiently activates electron deficient olefins for 1,4 conjugated addition, which can be incorporated in different one-pot transformations for the preparation of cyclic and acyclic compounds of biological and synthetic interest. More specifically, the catalyst can be successfully applied for different carbon–carbon (Csingle bondC) and carbon–heteroatom (Csingle bondN, Csingle bondO, Csingle bondS) bond forming reactions integrated in a cascade sequence. The activity of the organocatalyst has been compared with that of structurally related monofunctional and bifunctional catalysts. The most attractive features of this procedure are the high atom economy and the use of inexpensive starting materials as well as the use of an environmentally friendly catalyst that can be easily recovered due to its ionic liquid properties.Financial support by Consolider-Ingenio 2010 (project MULTICAT), Spanish MICINN (Projects MAT2011-28009 and CTQ-201127550) and Program Severo Ochoa are gratefully acknowledged.Climent Olmedo, MJ.; Iborra Chornet, S.; Sabater Picot, MJ.; Vidal Castro, JD. (2014). Bifunctional acid-base ionic liquid for the one-pot synthesis of fine chemicals: thioethers, 2H-chromenes and 2H-quinoline derivatives. Applied Catalysis A: General. 481:27-38. https://doi.org/10.1016/j.apcata.2014.05.004S273848

Phosphorus-containing gradient (block)copolymers via RAFT polymerization and post-polymerization modification

Reversible addition‐fragmentation chain transfer (RAFT) copolymerization of styrene (St) and 4‐(diphenylphosphino)styrene (DPPS) is explored to establish the statistical distribution of the phosphine‐functional monomer within the copolymer. RAFT copolymerization of St and DPPS at a variety of feed ratios provides phosphine‐functional copolymers of low dispersity at moderate monomer conversion (Ð 60%). In all cases, the fraction of DPPS in the resulting polymers is greater than that in the monomer feed. Estimation of copolymerization reactivity ratios indicates DPPS has a strong tendency to homopolymerize while St preferentially copolymerizes with DPPS (rDPPS = 4.4; rSt = 0.31). The utility of the copolymers as macro‐RAFT agents in block copolymer synthesis is demonstrated via chain extension with hydrophilic acrylamide (N,N‐dimethylacrylamide (DMAm)) and acrylate (poly(ethylene glycol) methyl ether acrylate (mPEGA), and di(ethylene glycol) ethyl ether acrylate (EDEGA)) monomers. Finally, access to polymers containing phosphine oxide and phosphonium salt functionalities is shown through postpolymerization modification of the phosphine‐containing copolymers

Cross-Dehydrogenative Couplings between Indoles and β-Keto Esters : Ligand-Assisted Ligand Tautomerization and Dehydrogenation via a Proton-Assisted Electron Transfer to Pd(II)

Cross-dehydrogenative coupling reactions between -ketoesters and electron-rich arenes, such as indoles, proceed with high regiochemical fidelity with a range of -ketoesters and indoles. The mechanism of the reaction between a prototypical -ketoester, ethyl 2-oxocyclopentanonecarboxylate and N-methylindole, has been studied experimentally by monitoring the temporal course of the reaction by 1H NMR, kinetic isotope effect studies, and control experiments. DFT calculations have been carried out using a dispersion-corrected range-separated hybrid functional (B97X-D) to explore the basic elementary steps of the catalytic cycle. The experimental results indicate that the reaction proceeds via two catalytic cycles. Cycle A, the dehydrogenation cycle, produces an enone intermediate. The dehydrogenation is assisted by N-methylindole, which acts as a ligand for Pd(II). The compu-tational studies agree with this conclusion, and identify the turnover-limiting step of the dehydrogenation step, which involves a change in the coordination mode of the -keto ester ligand from an O,O’-chelate to an C-bound Pd enolate. This ligand tautom-erization event is assisted by the -bound indole ligand. Subsequent scission of the ’-C–H bond takes place via a proton-assisted electron transfer mechanism, where Pd(II) acts as an electron sink and the trifluoroacetate ligand acts as a proton acceptor, to pro-duce the Pd(0) complex of the enone intermediate. The coupling is completed in cycle B, where the enone is coupled with indole. Pd(TFA)2 and TFA-catalyzed pathways were examined experimentally and computationally for this cycle, and both were found to be viable routes for the coupling step