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A new tetraphosphine, the cis-cis-cis-1,2,3,4-tetrakis(diphenylphosphinomethyl)cyclopentane (Tedicyp) 1 has been synthesized, characterized, and used in Pd-catalyzed allylic substitutions. The Tedicyp was easily prepared in seven steps from the commercially available himic anhydride. The structure of the complex Tedicyp-borane was determined by X-ray analysis. The tetraphosphine in combination with [Pd(eta(3)-C(3)H(5))Cl](2) affords a very efficient catalyst for allylic substitution of several allylic acetates. Under mild conditions, very high turnover numbers and turnover frequencies have been obtained.

The system combining the new ferrocenyl tetraphosphine 1,1′,2,2′-tetrakis(diphenylphosphino)-4,4′-di-tert-butylferrocene (called Fc(P) 4 t Bu, 1) and [PdCl(η 3 -C 3 H 5 )] 2 has been found to be an active catalyst for the cross-coupling of aryl halides with aryl boronic acids (i.e., Suzuki reaction) and for the vinylation of aryl halides with alkenes (Heck reaction). A variety of chlorides reacts in good yield with aryl boronic acids in the presence of 1-0.01% catalyst. The more reactive aryl bromides were reacted with aryl boronic acids or alkenes in the presence of 0.01-0.0001% catalyst. This system compares well with other catalytic systems that have been described for Suzuki or Heck reactions. 1 H, 13 C, and 31 P NMR studies in solution were conducted with the view to obtain a better understanding of the interaction involving the palladium dimeric precursor and the tetraphosphine. The initial formation of kinetic and then different thermodynamic species was evidenced. A dynamic evolution from labile Pd(π-allyl)/tetraphosphine species toward the well-defined, stable, and nonfluxional complexes [PdCl 2 {Fc(P) 4 t Bu}] (3) and [Pd 2 Cl 4 {Fc(P) 4 t Bu}] (4) is observed. This behavior is different from the other known active tetraphosphine Tedicyp [cis,cis,2,3,cyclopentane]. The palladium mononuclear 3 and dinuclear 4 complexes were isolated and fully characterized in the solid state by X-ray diffraction analysis and in solution by multinuclear NMR. The blocked conformation in solution of compounds 1, 3, and 4 respectively leads to original AA′BB′, ABMX, and A 2 B 2 31 P NMR spin-systems for the four phosphorus atoms.

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[structure: see text] The catalytic activity in Sonogashira cross-coupling reactions of alkynes with a variety of aryl halides (including chlorides) using a multidentate ferrocenyl phosphine is presented. The novel mixed ferrocenyl aryl/alkyl triphosphine is thermally stable and insensitive to air or moisture, and its robustness allows aryl alkynylation at 10(-1) to 10(-4) mol % catalyst loadings with TONs up to 250,000. Copper-free coupling using phenylacetylene is also accessible in good yield.

A system combining the tetraphosphine cis,cis, cis-1,2,3,4-tetrakis((diphenylphosphino)methyl)cyclopentane (Tedicyp) and [Pd(C 3 H 5 )Cl] 2 was found to promote the direct arylation of furans Via C-H functionalization in good yields using Very low catalyst loadings.The coupling reaction of furan derivatives with aryl halides provides an efficient method for the preparation of arylfurans. The classical method to perform this reaction is to employ an aryl halide with an organometallic derivative of furan (metal ) ZnX, 1 SnR 3 2 B(OR) 2 3 ) using a palladium catalyst (Scheme 1). However, these reactions require preparation of the furan organometallic derivative and provide either an organometallic or a salt (MX) as a byproduct.In the last few years, very interesting results for the coupling of aryl halides with aryl derivatives via C-H activation have been reported: for example, Fagnou has used simple palladium salts or Pd associated with monodentate ligands. 4 The direct coupling of furans with aryl halides via C-H activation/ functionalization of furans at low catalyst loadings would provide an economically and environmentally attractive procedure for the preparation of such compounds. A few results have already been reported for this coupling. To our knowledge, the first coupling of furans with aryl halides via C-H activation was described by Ohta et al. using tetrakis(triphenylphosphine)-palladium (5 mol %) and potassium acetate as base. 5a However, in general low to moderate yields of arylated products (0-60%) were obtained using this catalyst. This procedure was applied in a few syntheses of furan derivatives to give the arylated or biarylated furans in 13-73% yields. 5b,d,e The sterically hindered and electron-rich phosphine P(Cy) 3 (10 mol %) associated to PdCl 2 (5 mol %) also catalyzes the coupling of 2-furaldehyde with a variety of aryl iodides in good yields. 5c Finally, the coupling of 2-furaldehyde with bromobenzene using 10 mol % of Pd(OH) 2 /C as catalyst gave the coupling product in 75% yield. 5f Although monophosphine ligands have been successfully used for the coupling of furan derivatives with aryl halides via C-H activation, to the best of our knowledge, the efficiency of polydentate ligands for such couplings has not been demonstrated. Moreover, all of the reactions employing monophosphines as ligands were performed using high catalyst loadings (5-10 mol %). Therefore, an effective and selective method allowing high substrate/catalyst ratios for the coupling of these challenging substrates is still subject to significant improvement.The nature of phosphine ligands on complexes has an important influence on the rate of catalyzed reactions. In order to find more efficient palladium catalysts, we have prepared the tetrapodal phosphine ligand cis,cis,cis-1,2,3,4-tetrakis-((diphenylphosphino)methyl)cyclopentane (Tedicyp; Scheme 2), 6 in which the four diphenylphosphino groups are stereospecifically bound to the same face of the cyclopentane ring. A very high efficiency has been observed for Suz...

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