Regioselectivity with hemispherical chelators: increasing the catalytic efficiency of complexes of diphosphanes with large bite angles.
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Journal Article↗
Biomedical subjects
Catherine Jeunesse
Publications and source records attributed to Catherine Jeunesse.
Ethylene oligomerisation and polymerisation with nickel phosphanylenolates bearing electron-withdrawing substituents: Structure-reactivity relationships.
Three SHOP-type catalysts, in which the C=C(O) double bond was substituted by electron-withdrawing substituents, [Ni{Ph2PC(R1)=C(R2)O}Ph(PPh3)] (2: R1,R2 = -C(Me)=NN(Ph)-; 3: R1 = CO2Et, R2 = Ph; 4: R1 = CO2Et, R2 = CF3), were assessed as ethylene-oligomerisation and -polymerisation catalysts and compared to Keim's complex, [Ni{Ph2PCH=C(Ph)O}Ph(PPh3)] (1). A rationale for the influence of the double-bond substituents of the P,O-chelate unit on the catalytic properties is proposed, on the basis of X-ray diffraction studies, spectroscopic data and DFT-B3 LYP calculations. Whatever their relative electron-withdrawing strength, the R1 and R2 substituents induce an increase in activity with respect to catalyst 1. For those systems in which the basicity of the oxygen atom is decreased relative to that of the phosphorus atom, the chain-propagation rate increases with respect to that for catalyst 1. Reduction of the basicity of the P relative to that of the O, however, induces higher chain-termination rates.
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Catalytic applications of keto-stabilised phosphorus ylides based on a macrocyclic scaffold: calixarenes with one or two pendant Ni(P,O)-subunits as ethylene oligomerisation and polymerisation catalysts.
Four calix[4]arenes containing either one or two ylidic -C(O)CH=PPh3 moieties anchored at p-phenolic carbon atoms were prepared starting from cone-25,27-dipropoxycalix[4]arene (1): 1,3-alternate-5,17-bis(2-triphenylphosphoranylideneacetyl)-25,26,27,28-tetrapropoxycalix[4]arene (12), 1,3-alternate-5-(2-triphenylphosphoranylideneacetyl)-25,26,27,28-tetrapropoxycalix[4]arene (13), cone-5-(2-triphenylphosphoranylideneacetyl)-25,27-dihydroxy-26,28-dipropoxycalix[4]arene (14), cone-5,17-bis(2-triphenylphosphoranylideneacetyl)-25,27-dihydroxy-26,28-dipropoxycalix[4]arene (15). All the ylides were shown to be suitable for the preparation of SHOP-type complexes, i.e. of molecules containing [NiPh{Ph2PCH=C(O)R}(PPh3)] subunits (R = calixarene fragment). The monometallic complexes, namely those obtained from the monophosphorus ylides 13 and 14, proved to be efficient ethylene oligomerisation or polymerisation catalysts. At 80 degrees C, they displayed significantly better activities than the prototype [NiPh{Ph(2)PCH=C(O)Ph}(PPh3)], hence reflecting the beneficial role of the bulky calixarene substituent. The systems derived from the two ylides 12 and 15, both containing two convergent ylidic moieties, resulted in lower activities, the proximity of the two catalytic centres facilitating an intramolecular deactivation pathway during the period of catalyst activation. For the first time, the solid-state structure of a complex containing two "NiPh(P,O)(PPh3)" units as well as that of a SHOP-type complex having two linked phosphorus units were determined.
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Playing with podands based on cone-shaped cavities. How can a cavity influence the properties of an appended metal centre?
The potential of molecules that combine the properties of a conical cavity with those of a covalently-linked transition-metal centre is highlighted through the assessment of cyclodextrin- and calixarene-derived podands ("cavitand" ligands) in coordination chemistry and catalysis. Metallocavitands with coordination sites directed towards the interior of the generic cavity provide interesting systems for studying host-guest complexation processes, their enhanced strength of metal-ion binding allowing for regioselective catalysis in a confined environment, and stabilisation of coordination complexes of unusual forms. Where cavitands have exo-oriented podand arms, the intrinsic dynamics of the cavity can dramatically modify metal chelation behaviour and the catalytic properties of the complexes. Such functionalised cavities are also useful as metal-ion transporters.
Calixarenes↗
Bis-phosphites and bis-phosphinites based on distally-functionalised calix[4]arenes: coordination chemistry and use in rhodium-catalysed, low-pressure olefin hydroformylation.
Six calix[4]arenes each bearing two non-cyclic PR2 units attached at distal phenolic oxygen atoms, p-Bu t-calix[4]arene-25,27-(OPR2)2-26,28-(OR')2(R = OPh; R'= Prn, L1; R = OPh; R'= CH2CO2Et, L2; R= OPh; R'= CO2 cholesteryl, L3; R = Ph; R'= Prn, 4; R = Ph; R'= CH2CO2Et, L5; R = Ph; R'= CO2cholesteryl, L6) have been synthesized and their coordinative properties investigated. The diphosphites L1-L3, where the P centres are separated by 12 bonds, readily form chelate complexes provided the complexation reaction is achieved either by using a starting complex that possesses good leaving groups or by operating under high dilution in order to avoid oligomer formation. Thus, the cationic complexes [Rh(COD)L1]BF4 and [Rh(COD)L3]BF4 were both formed in high yield by reacting the appropriate diphosphite with either [Rh(COD)(THF)2]BF4 or [Rh(COD)2]BF4. At high dilution, reaction of L3 with the neutral complex [PdCl2(COD)] afforded the chelate complex [PdCl2L3] in 90% yield. The reaction of one equiv. of L1 with [Rh(acac)(CO)2] resulted in the formation of [Rh(acac)L1] without requiring high dilution conditions. When the latter reaction was carried out with 0.5 equiv. of L1, the bimetallic complex [{Rh(acac)(CO)}2(eta]1-P,eta1-P'-L1)] was formed instead. Reaction at high dilution of with the cyclometallated complex [Pd(o-C6H4CH2NMe2)(THF)2]BF4 gave the expected chelate complex [Pd(o-C6H4CH2NMe2)]BF4. The latter slowly converts in solution to an oligomer in which the ligand behaves as a (eta1-P,eta1-P') bridging ligand, thus leading to a less strained structure. All six ligands, when mixed with [Rh(acac)CO2], effectively catalyse the hydroformylation of octene and styrene. In the hydroformylation of octene, the linear aldehyde selectivities observed with L2 and L3 are significantly higher (linear : branched =ca. 10) than those obtained with the other 4 ligands of this study and also with respect to PPh3. Molecular modelling shows that the lower rim substituents of and form tighter pockets about the metal centre than do the other ligands and so sterically favour the formation of Rh(n-alkyl) intermediates over that of Rh(i-alkyl) ones. In styrene hydroformylation, all ligands result in the formation of unusually high amounts of the linear aldehyde, the b : l ratios being all close to 65 : 35. The highest activities were found when using an L/Rh ratio of 1/1.
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Diphosphines with expandable bite angles: highly active ethylene dimerisation catalysts based on upper rim, distally diphosphinated calix[4]arenes.
The binding properties of two large diphosphines, cone-5,17-dibromo-11,23-bis(diphenylphosphino)-25,26,27,28-tetrapropoxycalix[4]arene (1) and cone-5,17-bis(diphenylphosphino)-25,26,27,28-tetrapropoxycalix[4]arene (2) toward Ni(II) centres have been investigated. Whatever the starting complex, NiBr2 or [NiCp]BF4, quantitative formation of a chelate complex was observed, illustrating the preorganisation of the ligands. An X-ray structure determination was carried out for [NiCp1]BF4 which revealed that the nickel atom is positioned to one side of the calixarene axis, the PNiP plane being roughly parallel to the calixarene reference plane. The molecule has C(1) symmetry in the solid state, a feature which is also observed in solution at low temperature. As shown by variable-temperature 1H and 31P NMR studies, the complex undergoes two distinct motions: 1) a fan-like swinging of the coordination plane which displaces the metal from one side of the calixarene axis to the other, a motion during which the PNiP angle is likely to undergo a significant enlargement; 2) a rapid oscillation of each PPh2 unit about the corresponding Ni--P bond. In the latter dynamics the two endo-oriented PPh rings alternately occupy the calixarene entry. The two flexible ligands were assessed in ethylene oligomerisation. Activation with methylaluminoxane of the paramagnetic complexes [NiBr2.(1 or 2)] afforded highly active ethylene dimerisation catalysts, with turnover frequencies up to 10(6) (mol C2H4) (mol Ni)(-1) h(-1). The selective formation of 1-butene can be rationally controlled by using low catalyst concentrations.
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