Hybrid Phosphine/Amino-Acid Ligands Built on Phenyl and Ferrocenyl Platforms: Application in the Suzuki Coupling of o-Dibromobenzene with Fluorophenylboronic Acid.

We describe the synthesis and characterization of two classes of hybrid phosphino ligands functionalized with amino ester or amino acid groups. These compounds are built either on a rigid planar phenyl platform or on a functionalized - conformationally controlled - rotational ferrocene backbone. Modifications at the -PR2 phosphino groups (R=aryl and alkyl, with various steric bulk, Ph, Mes, i-Pr, Cy) and at the amino acid/amino ester functions are reported, showing a valuable high modularity. The coordination chemistry of these compounds regarding palladium and gold was investigated, in particular with respect to the coordination mode of the phosphino groups and the preferred interaction with metals for the amino ester and amino acid functions. For all the hybrid ligands, based either on ferrocenyl or phenyl platforms, the (P,N)-chelating effect dominates in solution for coordination to Pd(II), while linear P-Au(I) complexes without interaction with the amino groups are assumed. The investigation of the catalytic activity of these new ligands in the demanding palladium-catalyzed Suzuki-Miyaura coupling of o-dibromoarenes with fluorophenylboronic acid underlined the importance of the amino ester dicyclohexylphosphinoferrocene for avoiding the deleterious homocoupling and arene oligomerization side-reactions that were otherwise observed with the other phosphine ligands.

C-H Bond Arylation of Pyrazoles at the ß-Position: General Conditions and Computational Elucidation for a High Regioselectivity.

Direct arylation of most five-membered ring heterocycles are generally easily accessible and strongly favored at the α-position using classical palladium-catalysis. Conversely, regioselective functionalization of such heterocycles at the concurrent ß-position remains currently very challenging. Herein, we report general conditions for regioselective direct arylation at the ß-position of pyrazoles, while C-H α-position is free. By using aryl bromides as the aryl source and a judicious choice of solvent, the arylation reaction of variously N-substituted pyrazoles simply proceeds via ß-C-H bond functionalization. The ß-regioselectivity is promoted by a ligand-free palladium catalyst and a simple base without oxidant or further additive, and tolerates a variety of substituents on the bromoarene. DFT calculations revealed that a protic solvent such as 2-ethoxyethan-1-ol significantly enhances the acidity of the proton at ß-position of the pyrazoles and thus favors this direct ß-C-H bond arylation. This selective pyrazoles ß-C-H bond arylation was successfully applied for the straightforward building of π-extended poly(hetero)aromatic structures via further Pd-catalyzed combined α-C-H intermolecular and intramolecular C-H bond arylation in an overall highly atom-economical process.

Gold(I) Complexes Nuclearity in Constrained Ferrocenyl Diphosphines: Dramatic Effect in Gold-Catalyzed Enyne Cycloisomerization.

Di-tert-butylated-bis(phosphino)ferrocene ligands bearing phosphino substituents R (R=phenyl, cyclohexyl, iso-propyl, mesityl, or furyl) allow tuning the selective formation of Au(I) halide complexes. Thus, dinuclear linear two-coordinate, but also rare mononuclear trigonal three-coordinate and tetrahedral four-coordinate complexes were formed upon tuning of the conditions. Both Au(I) chloride and rarer Au(I) iodide complexes were synthesized, and their X-ray diffraction analysis are reported. The significance of the control of structure and nuclearity in Au(I) complexes is further illustrated herein by its strong effect on the efficiency and selectivity of gold-catalysed cycloisomerization. Cationic linear digold(I) bis(dicyclohexylphosphino) ferrocenes outperform other catalysts in the demanding regioselective cycloisomerization of enyne sulphonamides into cyclohexadienes. Conversely, tetrahedral and trigonal cationic monogold(I) complexes were found incompetent for enyne cycloaddition. We used the two-coordinate linear electron-rich Au(I) complex 2 b (R=Cy) to extend the scope of selective intramolecular cycloaddition of different 1,6-enyne sulfonylamines with high activity and excellent selectivity to the endo cyclohexadiene products.

C-H Halogenation of Pyridyl Sulfides Avoiding the Sulfur Oxidation: A Direct Catalytic Access to Sulfanyl Polyhalides and Polyaromatics.

Palladium-catalyzed oxidative C-H halogenation and acetoxylation reactions of S-unprotected sulfides, selectively directed by pyridinyl groups, allows the formation of C-X bonds (X = I, Br, Cl, OAc) by using simple halosuccinimide or phenyliodine diacetate (PIDA) oxidants. The undesired formation of sulfoxides and/or sulfones, which are usually observed under oxidative conditions, is fully obviated. Under the solvent-dependent conditions that we proposed, sulfide C-H functionalization is achieved in less than 1 h without any direct electrophilic halogenation at the pyridine moiety. N-Directed ortho-C-H activation of aryl also facilitates dibromination reactions which are hardly accessible with sulfone and sulfoxide counterparts because of their higher structural rigidity. This general method gives a straightforward access to polyhalide sulfides, without an organosulfur reduction step or protection-deprotection sequence. Polyhalide sulfides are valuable synthons that give a practical entry to new constrained polyaromatic and biphenyl sulfides, including synthetically challenging unsymmetrical examples.

A sterically congested 1,2-diphosphino-1'-boryl-ferrocene: synthesis, characterization and coordination to platinum.

A new class of tritopic ferrocene-based ambiphilic compounds has been prepared by assembling diphosphino- and boryl-substituted cyclopentadienides at iron. The presence of five sterically demanding substituents on the ferrocene platform induces conformational constraints, as is apparent from XRD and NMR data, but does not prevent the chelating coordination to platinum. The Lewis acid moiety is pendant in both the free ligand and the platinum complex.

A general diastereoselective synthesis of highly functionalized ferrocenyl ambiphiles enabled on a large scale by electrochemical purification.

A general synthesis of highly functionalized ferrocenes, which include (P,B)- and (N,B)-ambiphiles, has been developed at a multigram scale. Diastereoselective stepwise modification of di-tert-butylated ferrocenes included the unprecedented separation of electroactive species. Bulky alkyl groups on ferrocenes ensure planar chirality of ambiphiles and enforce closer proximity of antagonist Lewis functions.

Gold-Catalyzed Suzuki Coupling of ortho-Substituted Hindered Aryl Substrates.

A method that allows hindered ortho-substituted aryl iodides to be efficiently coupled to phenylboronic acid using a gold-catalyzed C-C bond formation is presented. The use of a molecularly-defined dinuclear gold chloride catalytic precursor that is stabilized by a new tetradentate (N,N')-diamino-(P,P')-diphosphino ferrocene hybrid ligand in a Suzuki-type reaction is described for the first time. Electron-rich isopropyl groups on phosphorus were found essential for a superior activity, while the performances of a set of analogous gold dinuclear complexes that were fully characterized by multinuclear NMR spectroscopy and XRD analysis, were investigated. Therefore, arylation of para and ortho-substituted iodoarenes bearing electron-rich, electron-poor functional groups, and even hindered polycyclic aromatic compounds is described.

Selective formation of a unique diphosphonium-diphosphine from a tetraphosphine double protonation induced by zirconium salts.

A mixed ferrocenyl diphosphonium-diphosphine cation, associated with two [ZrCl(5).thf](-) anions, is obtained from a ferrocenyl tetraphosphine, as a unique didentate ionic metalloligand in a perfectly selective reaction induced by ZrCl(4) in THF.

"Through-space" nuclear spin-spin J(PP) coupling in tetraphosphine ferrocenyl derivatives: a (31)P NMR and X-ray structure correlation study for coordination complexes.

Herein, we report on (31)P(31)P solution-phase "through-space" nuclear spin-spin coupling constants (J(PP)) from a novel family of organometallic tetraphosphine nickel and palladium complexes. These J(PP) constants were accurately determined through NMR iterative simulation based on the second-order spectra obtained for the compounds. The corresponding solid-state X-ray structures of the complexes were determined, and the "through-space" P.P distances are reported. Due to the blocked conformation of the species in solution, a qualitative and semiquantitative experimental correlation is obtained, which links the geometric parameters and the intensity of the corresponding P.P coupling constant. The lone-pair overlap theory developed for (19)F(19)F and (15)N(19)F "through-space" couplings in organic compounds [J. Am. Chem. Soc. 1973, 95, 7747-7752; 2000, 122, 4108-4116] appears to be a reliable foundation on which to account for our results. Based on the reported observations, the lone-pair overlap model is extended to "through-space" (31)P(31)P coupling, and the model is broadened to encompass metal orbital contributions for coordination complexes. Some of the predictions and consequences of the proposed theory are discussed.

Isolation, dynamic NMR study and X-ray characterisation of a bis sulfonium zirconocene-ate dimer.

The novel dimer [Cp(2)Zr[upper bond start]([minus sign in circle])S([plus sign in circle])CH(Ph)CH[double bond]C[upper bond end]PPh(2)](2), the first example of a structurally characterised sulfur-bridged binuclear zirconathiolane complex, was prepared, characterised by NMR spectroscopy and X-ray crystallography, and some aspects of its solution behaviour were studied.

ansa-[(tert-Butylamino)(isodicyclopentadienyl)dimethylsilane]Zr(NMe2)2 prepared by an amine-elimination reaction.

An amine-elimination reaction was used to obtain the title compound, i.e. (N-tert-butyl-N-[[(1,2,3,3a,7a-eta)-4,5,6,7-tetrahydro-4,7-methano-1H-inden-2-yl]dimethylsilyl]amido-kappaN)bis(N-methylmethanaminato-kappaN)zirconium(IV) or [isodiCpSiMe(2)N-tert-butyl]Zr(NMe(2))(2) (Cp is cyclopentadienyl), [Zr(C(16)H(25)NSi)(C(2)H(6)N)(2)], in very good yield. Treatment of isodiCpHSiMe(2)NH-tert-butyl with Zr(NMe(2))(4) leads to the formation of a yellow solid that can be purified by sublimation. The single-crystal structure of the product shows the exo complexation of the isodicyclopentadienyl ligand to the Zr atom. The Cp portion of this ligand is bonded to the Zr atom in a eta(5) manner, with a Zr-Cg (Cg is the ring centroid) distance of 2.2352 (10) A. The isodiCpSiMe(2)N-tert-butyl ligand has a constrained geometry, which is exhibited by the small angle of 95.55 (10) degrees for N-Si-C(Cp).

A doubly bridged isodicyclopentadienyl zirconium complex: bis[N-(3,5-dimethylphenyl)-N-[(eta5-isodicyclopentadien-2-yl)dimethylsilyl]amido-kappaN]zirconium(II) diethyl ether solvate.

Transmetallation of the dilithium salt of (3,5-dimethyphenylamino)(isodicyclopentadienyl)dimethylsilane by treatment with zirconium tetrachloride in a 2:1 ratio leads to the substitution of all four chloride ligands. With the applied stoichiometry, the title complex, [Zr(C(20)H(25)NSi)(2)].C(4)H(10)O, was obtained and crystallized from diethyl ether. X-ray diffraction characterization showed that both isodicyclopentadienyl ligands (alternatively called 4,5,6,7-tetrahydro-4,7-methano-1H-indene) are complexed to the metal on their exo face in a completely stereoselective manner and that they are eta(5)-bonded to the Zr atom.