Martin Lamač

Palladium Catalysts Supported on Mesoporous Molecular Sieves Bearing Nitrogen Donor Groups: Preparation and Use in Heck and Suzuki CC Bond‐Forming Reactions

A series of supported catalysts is prepared by treatment of SBA-15-type mesoporous molecular sieve bearing [triple chemical bond]SiCH(2)CH(2)CH(2)NHCH(2)CH(2)NEt(2) groups with palladium(II) acetate. These catalysts are studied in Suzuki biaryl couplings and in Heck reactions to establish the influence of metal loading and innocent surface modifications (trimethylsilylation). The Suzuki reaction proceeded efficiently with model and practically relevant substrates; the catalyst performance increasing with an increasing degree of metalation (decreasing N/Pd ratio). Catalyst poisoning tests revealed that the reaction takes place in the liquid phase with the catalyst serving as a reservoir of active metal species and also as a stabilizing support once the reaction is performed. In the Heck reactions, on the other hand, the catalyst performance strongly changed with the reaction temperature and with the N/Pd ratio. The material with the lowest metal loading (0.01 mmol palladium per gram of material, N/Pd ratio ca. 100:1) proved particularly attractive in the Heck coupling, being highly active at elevated temperatures, recyclable, and capable of acting as a bifunctional catalyst (i.e., functioning without any external base.

Preparation, coordination and catalytic use of planar-chiral monocarboxylated dppf analogues

A novel polar dppf derivative possessing only planar chirality, 1′,2-bis(diphenylphosphino)-ferrocene-1-carboxylic acid (Hdpc), has been synthesised in racemic form and resolved into enantiomers via esters with D-glucose diacetonide ((Rp)- and (Sp)-3). (Rp)-Hdpc was further converted to a series of N-substituted amides that were studied as ligands for Pd-catalysed enantioselective allylic alkylation of racemic (E)-1,3-diphenylprop-2-en-1-yl acetate or ethyl carbonate with malonate esters, showing high activity and good enantioselectivity (er up to 10 : 90). The catalytic results were correlated with the structural data (X-ray diffraction and solution NMR) for (η3-allyl)palladium(II) complex (Rp)-[Pd(η3-1,3-Ph2C3H3){Fe(η5-C5H3-1-(C(O)NHCH2Ph)-2-(PPh2-κP))(η5-C5H4PPh2-κP)}]ClO4 (16) as a model of the plausible reaction intermediate. A further study into the coordination properties of Hdpc led to isolation of chelate complex [PdCl2(Hdpc-κ2P,P′)] (12). The crystal structures of rac-Hdpc, methyl ester of (Rp)-Hdpc, glycoside (Rp)-3, and 12·Me2CO suggested a close structural relationship between dppf and Hdpc.

Effects of the Linking of Cyclopentadienyl and Ketimide Ligands in Titanium Half-Sandwich Olefin Polymerization Catalysts

The role of the ketimide ligand geometry in Ti half‐sandwich complexes and the consequent effects in olefin polymerization catalysis (ethylene, styrene, 1‐hexene polymerization, and ethylene/1‐hexene copolymerization) were investigated under various conditions. [CpTiCl2(N=CtBu2)] (1; Cp=η5‐cyclopentadienyl) was used as a reference compound for comparison with the recently described complex [{η5‐C5H4CMe2CMe2C(tBu)=N‐κN}TiCl2] (2 a) and a new derivative that has a longer linker between Cp and the ketimide, [{η5‐C5H4CH2CH2CMe2C(tBu)=N‐κN}TiCl2] (9). The presence of a distorted intramolecularly tethered ketimide moiety reduces the polymerization activity significantly in systems that contain Al‐based cocatalysts (methylaluminoxane, triisobutylaluminum). However, in Al‐free systems both types of compounds provided active polymerization catalysts. Notably, the recently reported activation system Et3SiH/B(C6F5)3 was for the first time demonstrated to activate Ti complexes for ethylene and 1‐hexene (co)polymerization catalysis by hydride transfer.

Crystal structure of chlorido{[3-(η5-cyclopenta-dienyl)-2,2,3-trimethyl-1-phenylbutylidene] azanido-κN}[η2(N,O)-N,N-dimethylhydroxylaminato]titanium(IV), C20H27ClN2OTi

Abstract C20H27ClN2OTi, monoclinic, P21/c (no. 14), a = 9.4006(2) Å, b = 10.8185(3) Å, c = 19.4821(5) Å, β = 97.941(1)°, V = 1962.34(9) Å3, Z = 4, Rgt(F) = 0.0270, wRref(F2) = 0.0731, T = 150(2) K.

1,2:5,6-Di-O-isopropyl-idene-α-d-3-glucofuranosyl (R(p))-2-(diphenyl-phosphino)ferrocene-1-carboxyl-ate.

The title compound, [Fe(C5H5)(C30H32O7P)], which is an intermediate in the synthesis of (R p)-2-(diphenylphosphino)ferrocene-1-carboxylic acid, crystallizes in the common chiral space group P212121. In general, the molecular geometry is very similar to that of the corresponding 2,1′-bis(diphenylphosphino) congener. The ferrocene unit assumes a regular geometry with the proximal bulky substituents efficiently avoiding mutual spatial contacts. In the crystal, the molecules participate in weak intra- and intermolecular C—H⋯O interactions.