Gold(I) complexes bearing phosphole ligands: Synthesis and antimalarial activity

A series of gold(I)-monophosphole complexes have been synthesized and characterized. The introduction of a nitrogen moiety in the complex structure was envisioned either by choosing the bis(trifluoromethanesulfonyl)imidate ligand as the X-ligand or by preparing a new pyrrolidinophosphole ligand as the L-ligand. All the complexes have been evaluated in vitro for their antimalarial activity. These gold–phosphole complexes showed moderate activities with IC₅₀ values ranging from 9.7 to 24 μM against Plasmodium falciparum chloroquine-resistant strains.     

Synthesis,structural characterization,and olefin polymerization behavior of vanadium(III) complexes bearing bidentate phenoxy‐phosphine ligands

Vanadium(III) complexes bearing phenoxy‐phosphine ligands ( 2a–g ) (2‐R₁‐4‐R₂‐6‐PPh₂‐C₆H₂O)VCl₂(THF)₂ ( 2a : R₁ = R₂ = H; 2b : R₁ = F, R₂ = H; 2c : R₁ = Ph, R₂ = H; 2d : R₁ = tBu, R₂ = H; 2e : R₁ = R₂ = Me; 2f : R₁ = R₂ = tBu; 2g : R₁ = R₂ = CMe₂Ph) were prepared from VCl₃(THF)₃ by treating with 1.0 equiv of the ligand in tetrahydrofuran (THF) in the presence of excess triethylamine (TEA). The reaction of VCl₃(THF)₃ with 2.0 equiv of the ligand in THF in the presence of excess TEA afforded vanadium(III) complexes bearing two phenoxy‐phosphine ligands ( 3c–f ). These complexes were characterized by FTIR and mass spectrum as well as elemental analyses. Structures of 2f and 3c were further confirmed by X‐ray crystallographic analyses. Complexes 2a–g and 3c–f were employed as the catalysts for ethylene polymerization under various reaction conditions. On activation with Et₂AlCl, these complexes exhibited high catalytic activities (up to 41.3 kg PE/mmol_V·h·bar) even at high temperature (70°C), and produced high molecular weight polymer with unimodal molecular weight distributions, indicating the polymerization took place in a single‐site nature. Complexes 3c–f displayed better thermal stability than the corresponding complexes 2a–g under similar conditions. In addition, copolymerizations of ethylene and 1‐hexene with precatalysts 2a–g were also explored in the presence of Et₂AlCl. Catalytic activity, comonomer incorporation, and properties of the resultant polymers can be controlled over a wide range by tuning catalyst structures and reaction parameters.© 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Electrochemical and catalytic properties of nickel(II) complexes with bis(imino)acenaphthene and diazadiphosphacyclooctane ligands

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Planar Chiral Phosphoramidites with a Paracyclophane Scaffold: Synthesis,Gold(I) Complexes,and Enantioselective Cycloisomerization of Dienynes

The key structural feature of the new phosphoramidites is a paracyclophane scaffold in which two aryl rings are tethered by both a 1,8‐biphenylene unit and a O?P?O bridge. Suitable aryl substituents generate planar chirality. The corresponding gold(I) complexes promote the cycloisomerization of prochiral nitrogen‐tethered dienynes. These reactions afford bicyclo[4.1.0]heptene derivatives displaying three contiguous stereogenic centers, with very high diastereoselectivity and up to 95 % ee.     

A Highly Efficient and Broadly Applicable Cationic Gold Catalyst

Gold catalysts capable of promoting reactions at low‐level loadings under mild conditions are the exception rather than the norm. We examined reactions where the regeneration of cationic gold catalyst (e.g., protodeauration) was the turnover limiting stage. By manipulating electron density on the substituents around phosphorus and introducing steric handles we designed a phosphine ligand that contains two electron‐rich ortho‐biphenyl groups and a cyclohexyl substituent. This ligand formed a gold complex that catalyzed common types of gold‐catalyzed reactions including intra‐ and intermolecular X? H (X=C, N, O) additions to alkynes and cycloisomerizations, with high turnover numbers at room temperature or slightly elevated temperatures (≤50 °C). Our new ligand can be prepared in one step from commercially available starting materials.     

Gold(I)‐Catalyzed Cycloisomerizations and Alkoxycyclizations of ortho‐(Alkynyl)styrenes

Indenes and related polycyclic structures have been efficiently synthesized by gold(I)‐catalyzed cycloisomerizations of appropriate ortho‐(alkynyl)styrenes. Disubstitution at the terminal position of the olefin was demonstrated to be essential to obtain products originating from a formal 5‐endo‐dig cyclization. Interestingly, a complete switch in the selectivity of the cyclization of o‐(alkynyl)‐α‐methylstyrenes from 6‐endo to 5‐endo was observed by adding an alcohol to the reaction media. This allowed the synthesis of interesting indenes bearing an all‐carbon quaternary center at C1. Moreover, dihydrobenzo[a]fluorenes can be obtained from substrates bearing a secondary alkyl group at the β‐position of the styrene moiety by a tandem cycloisomerization/1,2‐hydride migration process. In addition, diverse polycyclic compounds were obtained by an intramolecular gold‐catalyzed alkoxycyclization of o‐(alkynyl)styrenes bearing a nucleophile in their structure. Finally, the use of a chiral gold complex allowed access to elusive chiral 1H‐indenes in good enantioselectivities.     

Gold(I) complexes with tertiary phosphine sulfide ligands

Phosphine sulfides and their gold(I) complexes with general formula R₃P=S—Au—X (X = Cl^–, Br^– or CN^–) were prepared and characterized by elemental analyses, i.r. and ³¹P-n.m.r. spectroscopy. A decrease in the i.r. frequency of the P=S bond in the ligands upon complexation, is indicative of S coordination to gold (I). The ³¹P-n.m.r. spectra revealed that electronegativity of the substituents and angles between them were the two most important factors influencing the ³¹P-n.m.r. chemical shifts. The phosphorus resonance was observed to be more downfield in alkyl substituted phosphine sulfides as compared to the aryl substituted phosphine sulfides. Ligand scrambling in the Cy₃P=S—Au—CN complex in solution, to form [(Cy₃P=S)₂Au]⁺ and [Au(CN)₂]^–, was investigated by ¹³C and ¹⁵N-n.m.r. spectroscopy. Equilibrium constants (K _eq) for scrambling of the Cy₃P=S—Au—CN complex and for its analogue, Cy₃P=Se—Au—CN were measured by integrating the ¹³C-n.m.r. at 297 K and were found to be 0.147 and 1.81 respectively.     

Rare earth metal bis(alkyl) complexes bearing amino phosphine ligands: Synthesis and catalytic activity toward ethylene polymerization

Reactions of neutral amino phosphine compounds HL^1-3 with rare earth metal tris(alkyl)s, Ln(CH₂SiMe₃)₃(THF)₂, afforded a new family of organolanthanide complexes, the molecular structures of which are strongly dependent on the ligand framework. Alkane elimination reactions between 2-(CH₃NH)-C₆H₄P(Ph)₂ (HL¹) and Lu(CH₂SiMe₃)₃(THF)₂ at room temperature for 3 h generated mono(alkyl) complex (L¹)₂Lu(CH₂SiMe₃)(THF) (1). Similarly, treatment of 2-(C₆H₅CH₂NH)-C₆H₄P(Ph)₂ (HL²) with Lu(CH₂SiMe₃)₃(THF)₂ afforded (L²)₂Lu(CH₂SiMe₃)(THF) (2), selectively, which gradually deproportionated to a homoleptic complex (L²)₃Lu (3) at room temperature within a week. Strikingly, under the same condition, 2-(2,6-Me₂C₆H₃NH)-C₆H₄P(Ph)₂ (HL³) swiftly reacted with Ln(CH₂SiMe₃)₃(THF)₂ at room temperature for 3 h to yield the corresponding lanthanide bis(alkyl) complexes L³Ln(CH₂SiMe₃)₂(THF)_n (4a: Ln = Y, n = 2; 4b: Ln = Sc, n = 1; 4c: Ln = Lu, n = 1; 4d: Ln = Yb, n = 1; 4e: Ln = Tm, n = 1) in high yields. All complexes have been well defined and the molecular structures of complexes 1, 2, 3 and 4b-e were confirmed by X-ray diffraction analysis. The scandium bis(alkyl) complex activated by AlEt₃ and [Ph₃C][B(C₆F₅)₄], was able to catalyze the polymerization of ethylene to afford linear polyethylene.     

Gold(I)-catalyzed cyclizations of 1,6-enynes: alkoxycyclizations and exo/endo skeletal rearrangements

Gold(I) complexes are the most active catalysts for alkoxy- or hydroxycyclization and for skeletal rearrangement reactions of 1,6-enynes. Intramolecular alkoxycyclizations also proceed efficiently in the presence of gold(I) catalysts. The first examples of the skeletal rearrangement of enynes by the endocyclic cyclization pathway are also documented. Iron(III) is also able to catalyze exo and endo skeletal rearrangements of 1,6-enynes, although the scope of this transformation is more limited. The gold(I)-catalyzed endocyclic cyclization proceeds by a mechanism different from those followed in the presence of PdII, HgII, or RhI catalysts.     

Synthesis and characterisation of nonclassical ruthenium hydride complexes containing chelating bidentate and tridentate phosphine ligands

The synthesis and characterisation of nonclassical ruthenium hydride complexes containing bidentate PP and tridentate PCP and PNP pincer-type ligands are described. The mononuclear and dinuclear ruthenium complexes presented have been synthesised in moderate to high yields by the direct hydrogenation route (one-pot synthesis) or in a two-step procedure. In both cases [Ru(cod)(metallyl)(2)] served as a readily available precursor. The influences of the coordination geometry and the ligand framework on the structure, binding, and chemical properties of the M--H(2) fragments were studied by X-ray crystal structure analysis, spectroscopic methods, and reactivity towards N(2), D(2), and deuterated solvents.     

Synthesis, X-ray structures, and catalytic applications of palladium(II) complexes bearing N-heterocyclic iminocarbene ligands

Two new Pd(II) N-heterocyclic iminocarbene complexes (C-N)PdCl₂ that contain 5-membered chelate rings have been prepared by carbene transfer from a silver iminocarbene precursor to (COD)PdCl₂. The new Pd imonocarbene complexes, as well as two that have been previously reported (altogether three 5-membered and one 6-membered chelate ring complexes) have been evaluated as catalysts for the Suzuki-Miyaura coupling reaction. The complexes were found to be active in the reaction, but without exceptional catalytic performances. The 5-membered chelate ring complexes appeared to be more robust and remained active for a longer time than the 6-membered ring congener. The catalytic performance of the 5-membered chelate ring complexes appeared to be rather insensitive to the steric demands of the imine-N-aryl group. The X-ray structure of one of the Ag iminocarbene complexes reveals the κ¹(C) bonding of the iminocarbene moiety in a nearly linear Ag(I) complex; two monomeric units are associated through a weak Ag-Ag interaction. The X-ray structures of two new Pd iminocarbene complexes (C-N)PdCl₂ confirm the chelating κ²(C,N) nature of the iminocarbene moiety; in both complexes, the Pd-Cl distances trans to carbene-C are slightly longer than those trans to imine-N.     

Comparison of homogeneous and heterogeneous Ga(III) catalysis in the cycloisomerization of 1,6-enynes

We describe a study of the gallium(III)-catalyzed 1,6-enynes cycloisomerization reaction in both homogeneous and heterogeneous conditions. With GaBr₃ in homogeneous conditions, some particularities were observed in terms of selectivity compared to reported GaCl₃-catalyzed reactions. The transfer of the reaction in heterogeneous conditions was realized by supporting Ga(III) salts onto montmorillonite. Both systems were compared based on reaction times, conversion, and selectivity and showed complementary activities.     

Structural studies of two-coordinate complexes of tris(2-methoxylphenyl)phosphine and tris(4-methoxyphenyl)phosphine with gold(I) halides

A series of five gold(I) halide complexes with the two isomeric methoxy-substituted triarylphosphines, tris(2-methoxyphenyl)phosphine [P(oanis)₃], [AuP(oanis)₃X] [for X = Cl, (1); X = Br, (2) and X = I, (3)] and tris(4-methoxyphenyl)phosphine [P(panis)₃], [AuP(panis)₃X] [for X = Br (4) and X = I (5)] have been synthesized and characterized by single crystal X-ray diffraction and solution ³¹P{¹H} NMR spectroscopy. The structure determinations confirm the expected presence of linear two-coordination about the gold centres in all five complexes with bond distance and angle data typical of this type of compound [Au–P, 2.239(2)–2.259(3) Å; Au–Cl, 2.294(2) Å; Au–Br, 2.385(2)–2.402(2) Å; Au–I, 2.546(1)–2.554(1) Å; P–Au–X; 175.3(1)–180°]. All analogues except the iodo complex 5 crystallize with one complex molecule in the crystallographic asymmetric unit. The bromo and iodo complexes 2 and 3 constitute a trigonal isomorphous set while the bromo complex 4 is also isomorphous with the previously determined chloro complex [AuP(panis)₃Cl]. The 2-methoxy analogues are stabilized by significant methoxy-O?Au interactions.     

Palladium(0)-catalyzed cycloisomerization of enallenes

A novel palladium(0)-catalyzed cycloisomerization of enallenes has been developed. This reaction, catalyzed by [Pd(dba)2] (dba=dibenzylideneacetone) in acetic acid, results in the formation of cyclopentene derivatives and [n.3.0]bicyclic systems (n=3, 4) in good to high yields. The carbon-carbon bond-forming step is highly stereoselective to give cis-fused bicyclic systems. The presence of acetic acid as solvent and dba as ligand for palladium(0) turned out to be essential for the reaction in order to provide good reactivity and regioselectivity.