Jean-Cyrille Hierso

Progress in palladium-based catalytic systems for the sustainable synthesis of annulated heterocycles: a focus on indole backbones

A survey highlighting the most recent palladium catalytic systems produced and their performances for progress in direct synthesis of indole backbones by heterocarbocyclization of reactive substrates is provided. The discussion is developed in relation with the principles of sustainable chemistry concerning atom and mass economy. In this respect, the general convergent character of the syntheses is of particular interest (one-pot, domino, cascade or tandem reactions), and the substrates accessibility and reactivity, together with the final waste production, are also important. This critical review clearly indicates that the development of ligand chemistry, mainly phosphines and carbenes, in the last few decades gave a significant impetus to powerful functionalization of indoles at virtually all positions of this ubiquitous backbone (118 references).

Structural diversity in coordination chemistry of tridentate and tetradentate polyphosphines of Group 6 to 10 transition metal complexes

Abstract Tridentate and tetradentate polyphosphines offer a huge variety of coordination modes to transition metals which lead, depending on the metal, to very different structural features in the resulting complexes. Steric effects being crucial in metal–phosphine complexes reactivity, a good knowledge of the molecular structures of the species is required both in the solid state and in solution. This article reviews from a structural point of view the monometallic and symmetrical homobimetallic complexes of the transition elements of Group 6 to 10 with tridentate and tetradentate phosphines. Concerning the classical triphosphines and tetraphosphines, emphasis was put on advances reported after the year 1994, since comprehensive reviews have covered the former period. Several anterior relevant results are, however, briefly mentioned when necessary. A second part is devoted to nitrogen- and sulfur-containing derivatives potentially tridentate and tetradentate ligands, and their coordination to the above-mentioned metals. The last part describes the complexes obtained with the less classical ferrocenyl polyphosphine ligands or their nitrogen-containing derivatives: each ligand having a potential tridentate or tetradentate coordination from either phosphorus or nitrogen donor atoms. The literature cutoff date was during the second half of 2000, but in a few cases, references to important work appearing during 2001 were made; however such coverage should be completed in a future compilation. An exhaustive quoting of catalytic applications and reaction chemistry was beyond the scope of this article mainly devoted to structural works. Nevertheless, in order to illustrate the importance of this chemistry, efforts were made to provide the reader with recent references that have marked the field, even in the absence of X-ray structural characterization.

Diamondoids: functionalization and subsequent applications of perfectly defined molecular cage hydrocarbons

The term “diamondoid” describes cage hydrocarbon molecules that are superimposable on the diamond lattice. Diamondoids that are formally built by face-fusing of adamantane units, namely diamantane, triamantane, tetramantane, etc., have fascinated chemists since the beginning of the last century. The functionalization of these perfectly defined (C,H)-molecules is described here. Thus, diamondoid halides and diamondoid alcohols are first rank precursors for amino and phosphine-substituted diamondoids that have proved to be highly useful in therapeutic applications and metal catalysis, respectively. The extent of functionalization and polyfunctionalization achieved for adamantane and diamantane, and the synthesis and applications of the resulting organohybrids are illustrated, revealing their high potential in fields such as organocatalysis, polymers, molecular electronics and mechanics.

MOCVD of rhodium, palladium and platinum complexes on fluidized divided substrates: Novel process for one-step preparation of noble-metal catalysts

A new one-step method, entitled fluidized-bed metal-organic chemical vapor deposition (FBMOCVD) of preparing highly dispersed metal-supported catalysts is reported. The following complexes were studied and used as CVD precursors in presence of H2: [Rh(m-Cl)(CO)2]2, Rh(allyl)3, Rh(acac)(CO)2, Pd(allyl)(hfac), Pd(allyl)(Cp), Pt(COD)(CH3)2. (acac, acetylacetonato; hfac, hexafluoroacetylacetonato; Cp, cyclopentadienyl; COD, cyclooctadienyl). In a first approach, depositions on planar substrates were carried out to establish the best experimental conditions to obtain good-quality deposits. X-ray diffraction, X-ray photo-electron spectroscopy and electron microprobe studies were realized on the resulting thin films. Analyses of the products contained in the gas phase after and during deposition were performed by mass spectrometry and GC‐MS. Finally, catalysts prepared by FBMOCVD were characterized by transmission electron microscopy‐energy dispersion spectroscopy (TEM‐ EDS), metal-loading determinations and specific-surface measurements (BET). Dispersed nanosized aggregates were obtained, showing high activities in alkene hydrogenation and alcohol hydrocarbonylation. # 1998 John Wiley & Sons, Ltd.

Direct Arylation of Heteroaromatic Compounds with Congested, Functionalised Aryl Bromides at Low Palladium/Triphosphane Catalyst Loading

A new ferrocenyl triphosphane ligand associated to palladium was found to be an efficient catalyst for the direct coupling of highly congested, functionalised aryl bromides with a variety of heteroarenes. These coupling reactions can generally be performed by using a low-loading (0.1-0.5 mol%) of the catalyst. The present protocol tolerates important and useful functional groups, which allows for further elaboration into more sophisticated heterocyclic molecules. The straightforward arylation of heteroaromatic compounds with congested ortho-substituted aryl bromides may permit further convergent syntheses of diverse ligands, biologically active molecules and molecular materials in only a few steps.

Platinum, palladium and rhodium complexes as volatile precursors for depositing materials

Abstract This article reviews the transition-metal complexes of rhodium, palladium and platinum which were described in the literature as volatile. A classification has been adopted according to the ligands borne by each metal center, and the preparation procedures have been given. As the general aim of the review is to use the most convenient complexes for chemical vapor deposition, the yields of the syntheses and the stability and/or sensitivity of the complexes have been emphasized. When appropriate, their use in CVD and a detailed description of the resulting deposits have been reported. Challenges for researchers in the field are discussed.

Metal-organic chemical vapor deposition in a fluidized bed as a versatile method to prepare layered bimetallic nanoparticles

Abstract Bimetallic supported layered nanoparticles, with an inner nucleus of platinum and an outer shell of palladium were synthesized by two successive chemical vapor deposition runs in a fluidized bed from Pt(Me)2(COD) at 120°C and Pd(η3-C3H5)(hfacac) at 60°C, these remarkable mild conditions allowing in the presence of H2 to reach pure metal particles sized between 5 and 15 nm. Both TEM and EDX analyses evidenced the layered structure. The preliminary studies on catalytic dehydrogenation showed the great activity and stability of these bimetallic materials.

Direct Arylation of Heterocycles: The Performances of Ferrocene-Based Polyphosphane Ligands in Palladium-Catalyzed CH Bond Activation

The palladium‐catalyzed direct arylation of alkylated‐ furan, thiophene, and thiazole and benzoxazole heterocycles with electronically and sterically deactivated bromoarenes was selectively and efficiently promoted by ferrocenyl polyphosphanes. In this CH bond activation reaction of heteroaromatics, the performances of polydentate di‐, tri‐, and tetraphosphane ligands were compared, showing that the triphosphane 1,1′,2‐tris(diphenylphosphino)‐4‐tert‐butylferrocene 3 was the most effective for the coupling. The introduction of more electron‐donating (iPr) or electron‐withdrawing (furyl) groups on the phosphorus atoms did not improve the ligand performances. The coordination behavior of 3 towards palladium(II) and other group 10 metals, NiII and PtII, was studied and the corresponding 1,2‐P chelating phosphorus complexes were isolated in high yields and fully characterized by multinuclear 1H, 13C, 31P NMR (3⋅PdCl2, 3⋅PtCl2) and X‐ray structures (3⋅NiBr2). It was found that the triphosphane ligand 3 was able to accommodate bidentate chelating cis coordination to group 10 metals, and additionally a much rarely described bis monodentate trans configuration. The combination of these two modes of coordination in a multimetallic species was clearly evidenced for the first time for a ferrocenyl polyphosphane. This versatility in bonding is a clear difference of coordination potential of this catalytically more efficient triphosphane compared to analogous ferrocenyl di‐ or tetraphosphanes.

Ortho-Functionalized Aryltetrazines by Direct Palladium-Catalyzed C-H Halogenation: Application to Fast Electrophilic Fluorination Reactions.

A general catalyzed direct C-H functionalization of s-tetrazines is reported. Under mild reaction conditions, N-directed ortho-C-H activation of tetrazines allows the introduction of various functional groups, thus forming carbon-heteroatom bonds: C-X (X=I, Br, Cl) and C-O. Based on this methodology, we developed electrophilic mono- and poly-ortho-fluorination of tetrazines. Microwave irradiation was optimized to afford fluorinated s-aryltetrazines, with satisfactory selectivity, within only ten minutes. This work provides an efficient and practical entry for further accessing highly substituted tetrazine derivatives (iodo, bromo, chloro, fluoro, and acetate precursors). It gives access to ortho-functionalized aryltetrazines which are difficult to obtain by classical Pinner-like syntheses.

Alkyne[hydrotris(pyrazolyl)borato]tantalum Complexes – An Ethyl Group is a Better α-Agostic Donor Than a Methyl Group

The synthesis of unprecedented alkyne hydrotris(3,5-dimethylpyrazolyl)borato (TpMe2) tantalum(III) complexes is reported. The parent dichloro complex TpMe2TaCl2(PhC≡ CCH3) (2) is obtained from TaCl3(DME)(PhC≡CCH3) and KTpMe2. 2 reacts with methyllithium to give the dimethyl complex TpMe2Ta(CH3)2(PhC≡CCH3) (3) and with ethylmagnesium chloride to give the X-ray characterized α-agostic ethyl complex TpMe2Ta(Cl)(μ-H–CHCH3)(PhC≡CCH3) (4). Reaction of 4 with methyllithium generates the mixed methyl ethyl complex TpMe2Ta(CH3)(μ-H–CHCH3)(PhC≡CCH3) (5) in solution. Spectroscopic data indicate that 5 is α-agostic at the ethyl group only.