Dominique Matt

Confining Phosphanes Derived from Cyclodextrins for Efficient Regio- and Enantioselective Hydroformylation**

Two confining phosphane ligands derived from either α- or β-cyclodextrin produce singly P(III) -ligated metal complexes with unusual coordination spheres. High-pressure NMR studies have revealed that rhodium hydride complexes of the same type are also formed under hydroformylation conditions. This unique feature strongly favors the formation of the branched aldehyde at the expense of the linear one with high enantioselectivity in the rhodium-catalyzed hydroformylation of styrene.

Calix[4]arene daisychains

Generic calix[4]arenes became readily accessible in the late 70s. With their potential eight anchoring points, their utility for the production of sophisticated, highly functionalised macrocyclic molecules was rapidly recognised. While most studies in calixarene chemistry have focused on monocalixarene derivatives, there is now an increasing interest in developing multicalixarene compounds, especially those made of several linearly-arranged calix[4]arene units, the first examples of which were reported in 1989. This critical review will present the most important synthetic routes to such molecules together with an analysis of the properties that such cavity combinations may induce. In particular it will be shown that the nature of the links between the calixarene units plays a determinant role in the product properties and that singly-linked calixarenes can be exploited in varied applications, including those as efficient receptors of large molecules, as electrochemical and luminescent sensors in ion detection, or as new materials allowing capsule formation suitable for the storage of small guests (82 references).

Regioselective Double Capping of Cyclodextrin Scaffolds

Four different regioselective double capping reactions were applied either to α- or β-cyclodextrin (CD) scaffolds. The first, which relied on the use of a rigid, bulky dialkylating reagent containing two trityl-like subunits, gave access to an A,B,D,E-tetrafunctionalised β-CD regioisomer in large scale reactions. Two further capping reactions, involving the dianions PhP(2-) and S(2- , led to the synthesis of new C(1)-symmetrical β-cyclodextrins in which pairs of neighbouring glucose units are linked by very short spacers. The last double capping reaction described allowed the high-yield preparation of unprecedented α- and β-cyclodextrins containing two sulfate handles. Proximal capping turned out to be favoured for each of the above difunctional reagents. The structural characterisation of the capped species was achieved by thorough NMR investigations as well as by single-crystal X-ray diffraction studies.

Resorcinarene‐Functionalised Imidazolium Salts as Ligand Precursors for Palladium‐Catalysed Suzuki–Miyaura Cross‐Couplings

Three imidazolium salts based on a rigid resorcinarene platform (1–3) were synthesised and used as catalyst precursors in the Suzuki–Miyaura cross‐coupling of aryl halides with phenylboronic acid. In these pro‐carbene ligands, the heterocyclic moiety has one N atom connected to a C2 atom of a resorcinolic ring, and the other is substituted by an alkyl group (R=n‐propyl, iso‐propyl, benzyl). The methinic C atoms of the macrocyclic core are all substituted by a pentyl group. The best catalytic performances were obtained by using an imidazolium/Pd ratio of 1:1. The catalytic systems displayed high activities, which increased in the order R=n‐propyl (1)

First synthesis of a '1,2-diquinone-calix[4]arene'. Interaction of its reduced form with Ag+

Abstract Electrochemical oxidation of 5,11,17,23-tetra- tert -butyl-25,26-bis(diphenylphosphinoylmethoxy)-27,28-dihydroxycalix[4]arene ( 3 ), a calixarene with two phosphoryl units appended on proximal positions, affords the corresponding ‘1,2-diquinone-calix[4]arene’ ( 4 ). The formation of 4 results from nucleophilic attack of residual water on anodically generated diphenoxylium cations. Preliminary voltammetric experiments in CH 3 CN on a platinum electrode showed that 4 is suitable for electrochemical detection of the silver metal cation.

Nickel complexes with heterofunctionalized phosphine ligands. Catalytic oligomerization of ethylene with [Ni(C5Ph5){Ph2PCHC(O)Ph}]

Reaction of [Ni(C5Ph5)Br(CO)] with Ph2PCH2C(O)Ph in the presence of 1,8-bis(dimethylamino)naphthalene (proton sponge) gives the chelate complex [Ni(C5Ph5){Ph2PCHC(O)Ph}]1. The complexes [Ni(C5Ph5){Ph2PCHC(O)(C5H4)Fe(C5H5)}]2, [Ni(C5Ph5){Ph2PCHC(O)(1,3-C6H4)C(O)HCPPh2}Ni(C5Ph5)]3, [Ni(C5H5){Ph2PCHC(O)Ph}]4 and [Ni(C5H5){Ph2PCHC(O)(C5H4)Fe(C5H5)}]5 have been synthesised using the appropriate phosphine ligand and applying a procedure similar to that for 1. Complex 1, activated with NaBH4, exhibits catalytic activity in the low-pressure oligomerization of ethylene. At 130 °C, under 38 bar of ethylene, selectivities of up to 98% towards linear α-olefins were achieved. Protonation of the bimetallic complex 2 with HBF4 gave the cationic complex [Ni(C5Ph5){Ph2PCH2C(O)(C5H4)Fe(C5H5)}]BF46. Crystais of 6 belong to the orthorhombic space group Pbca with a= 19.427(6), b= 38.595(11), c= 13.001(4)A and Z= 8. The structure was refined to R= 0.049 (R′= 0.067). The bonding of C5Ph5 contrasts with the bonding modes usually found for cyclopentadienyl ligands. The ring contains two short [1.384(8) and 1.389(8)], two medium [1.444(8) and 1.443(8)], and one long [1.474(8)A] C–C bonds so that the C5Ph5 may be viewed as an (alkyl, diene) ligand. This unusual bonding is likely to result from the ‘chemical’ dissymmetry of the P,O ligand and the low trans influence of the oxygen atom. The extremely low ν, (CO) frequency of the co-ordinated ketone (1525 cm–1) reflects the strong electron-withdrawing effect of the Ni(C5Ph5)+ moiety.

Anodic oxidation of p-But-calix[4]arene-(OH)2-(OCH2CONEt2)2. Electrogeneration of a calixdiquinone in dichloromethane

The electrochemical oxidation of p-But-calix[4]arene-(OH)2-(OCH2CONEt2)2 1 has been investigated for the first time and was shown to result in the formation of the corresponding diquinone 3. The reaction proceeds via two successive two-electron irreversible oxidation steps both governed by an ECE mechanism. Alkali cations recognition can be realized by exhaustive oxidation of 1 in the presence of alkali salts.

Calix[4]arene-diphosphite rhodium complexes in solvent-free hydroaminovinylation of olefins

Under solvent-free conditions rhodium complexes containing hemispherical diphosphites based on a calix[4]arene skeleton catalyse efficiently the hydroaminovinylation of α-olefins, thereby leading to high proportions of linear enamines/amines (when starting from secondary amines) or imines (when starting from primary amines). When applying a Rh/olefin ratio of 1 : 5000, the reaction turned out to be ca. 15 times faster than when operating in toluene at the same Rh/olefin ratio and at an olefin concentration of 6.6 mol L−1. For example, in the hydroaminovinylation of 1-octene with piperidine using 5,11,17,23-tetra-tert-butyl-25,27-dipropyloxy-26,28-bis(1,1′binaphthyl-2,2′dioxyphosphanyloxy)calix[4]arene, TOFs up to 4640 mol(converted olefin).mol(Rh)−1.h−1 were observed (l/b ratio of 24.1).

Complexes of functional phosphines. Part 11. β-Ketophosphine complexes of nickel, palladium, and platinum. Crystal structures of trans-[NiX2(HL)2][X = Cl or I, HL = Ph2PCH2C(O)Ph]

The synthesis and spectroscopic properties (1H and 31P n.m.r., i.r.) of complexes containing the β-ketophosphine Ph2PCH2C(O)Ph (HL) are described. In [NiX2(HL)2][X = Cl (1), Br, or I (3)], [PdCl2(HL)2](4), [PtCl2(HL)2](5), and [{PdCl(µ-Cl)(HL)}2](6), HL behaves as a P-bonded monodentate ligand whereas in the cationic complexes [Pd(HL)2][BF4]2 and [{Pd(µ-Cl)(HL)}2][CF3SO3]2 it acts as a P,O chelate. The crystal structures of (1) and (3) have been determined using single-crystal X-ray diffraction methods. Compounds (1) crystallises in space group P21/n, with a= 10.079(3), b= 11.510(3), c= 15.411(3)A, β= 93.42(2)°, and Z= 2. Compound (3) crystallises in space group P21/c, with a= 9.283(1), b= 10.261(1), c= 19.318(1)A, β= 96.20(1)°, and Z= 2. The structures have been refined to R 0.050 (R′ 0.060) for (1) and to R 0.032 (R′ 0.041) for (3). The geometries of these complexes are essentially identical although the ν(CO) frequencies of these complexes are significantly different [1 662 cm–1 for (1) and 1 620 cm–1 for (3)]; the nickel atom occupies a centre of symmetry and has thus a square-planar environment. Although the ketone group is bent towards the nickel atom, no significant Ni–O bonding interaction occurs, as deduced from the Ni–O distances [3.230(4)A in (1) and 3.231(1)A in (3)]. In refluxing toluene (1), (4), or (5) lead to the phosphine–phosphinite complexes cis-[[graphic omitted]Ph2}](M = Ni, Pd, or Pt). Treatment of (1), (4), or (5) with base gives the enolato-complexes cis-[[graphic omitted]Ph}2](M = Ni, Pd, or Pt). Reaction of (6) with NaH affords the binuclear complex [{P[graphic omitted]Ph]}2]. The latter reacts with PPh3 to give cis-[P[graphic omitted]Ph}(PPh3)], and with Ph2PCH2CH2PPh2–TlPF6 to give [P[graphic omitted]Ph}(Ph2PCH2CH2PPh2)]PF6. The P–O coupling products [N[graphic omitted]R}](R = Cl or Ph) are obtained by reaction of the complex [N[graphic omitted]Ph}2] with PCl3 and PPhCl2 respectively, and shown to have a five-co-ordinate structure. The square-planar P,P,P complex [N[graphic omitted]Ph}]PF6 results from reaction of [N[graphic omitted]Ph}] with TIPF6.

Calixarene-monophosphines as supramolecular chelators

The calix[4]arenes 5-diphenylphosphino-17-R1-11,23-diR2-25,26,27,28-tetrapropoxycalix[4]arene (1, R1 = R2 = Br; 2, R1 = Br, R2 = H; 3, R1 = R2 = p-tolyl; 4, R1 = p-tolyl, R2 = H; 5, R1 = R2 = H; 20, R1 = p-tolyl, R2 = H), all bearing a diphenylphosphino group attached to the calixarene upper rim, have been synthesised starting from 5,11,17,23-tetrabromo-25,26,27,28-tetrapropoxycalix[4]arene. Reaction of 1-5 with [RuCl2(p-cymene)]2 leads quantitatively to monophosphine complexes, [RuCl2(p-cymene)L], in which the endo-oriented ruthenium atom unit sits inside the cone delineated by the four phenoxy rings. The particular orientation of the P-Ru vector appears to result from pi-pi interactions between the p-cymene ligand and two aromatic cavity walls. Overall, in each case the calixarene end of the ligand behaves as a supramolecular receptor towards the Ru(p-cymene) fragment. Formation of complexes with exo-oriented P-M bonds were observed in the complexes cis-[PtCl2 x 1(2)] and in [RuCl2(p-cymene) x 20]. As shown by a variable temperature study carried out on [RuCl2(p-cymene) x 3], in which the ruthenium is embedded in an expanded cone, the p-cymene ring undergoes a fast oscillation about the Ru-arene bond which can be frozen out at low temperatures. Reaction of [RuCl2(p-cymene) x 3] with AgBF4 in CH3CN results in an intra-cavity reaction, with one chloride ligand being replaced by acetonitrile.