Marcel Wesolek

Molecular complexes for efficient metathesis of olefins. The oxo-ligand as a catalyst–cocatalyst bridge and the nature of the active species

Three families of molecular complexes for the homogeneous metathesis of olefins are described; the role of the oxo-or imido-ligand as bridge for binding the Lewis acid and the nature of the active species in meta-thesis are discussed.

Synthesis and x-ray structure of monomeric aryloxide complexes of manganese(II) and chromium(II)

Abstract Two monomeric alkoxide complexes of manganese(II) and chromium(II) have been synthesized and their structure determined by X-ray methods. In both cases

X-ray crystal structure of W(OAlBr3)(CH2t-Bu)3Br, a model for catalyst−cocatalyst interaction

Abstract The crystal structure of the acid-base adduct obtained from WO(CH2t-Bu)3Br and AlBr3 is described. The interaction between the Lewis acid and the oxo ligand of the tungsten compound is discussed on the basis of bond distances and bond angles in the BrWOAl linkage. The role of the WOAl linkage in homogeneous catalysis and of such interactions modelling the catalyst-support interactions in heterogeneous catalysis are briefly considered.

Heterofunctionalised phosphites built on a calix[4]arene scaffold and their use in 1-octene hydroformylation. Formation of 12-membered P,O-chelate rings

The calixarene phosphites L1–L4 were obtained in high yield through reaction of PCl3/NEt3 with the monofunctionalised cone-calixarenes p-tert-butylcalix[4]arene(OH)3OR, in which the R substituents bear an oxygen donor ligand [R = CH2P(O)Ph2 (L1), CH2CO2Et (L2), CH2C(O)NEt2 (L3), CH2CH2OMe (L4)]. The calixarene core of the four ligands adopts a cone conformation and, hence, the phosphites become potential P,O-chelating systems. Phosphite L1 is remarkably stable towards aqueous NaOH, but the presence of slightly acidic water results in phosphonate formation. Slow oxidation of L1 in air afforded the corresponding mixed phosphine oxide–phosphate. In the complexes [RuCl2(p-cymene)L1], [cis-PtCl2(L1)2] (9), trans-[PdCl2(L1)2], [Pd(8-mq)Cl(Ln)] (8-mqH = 8-methylquinoline, n = 1–3), [Pd(dmba)Cl(L1)] (dmbaH = N,N-dimethylbenzylamine), [Pd(η3-C4H7)Cl(L2)], [Rh(acac)(CO)Ln] (n = 1–3) and [RhCl(CO)(L1)2], the phosphites behave as a monodentate phosphorus donor ligands. Owing to their steric crowding, the two cis-disposed ligands of complex 9 cannot freely rotate about their coordination axis. In the solid state, the calixarene backbones of complex 9 display a so-called ‘up-up-out-up’ conformation. Chelating phosphite behaviour was found in the cationic complexes [Pd(8-mq)Ln]BF4 (n = 1–3). In solution, the large, chelating P,O-loop of the latter complexes swings from one side of the metal plane to the other, the dynamics possibly being facilitated by the flexibility of the calixarene backbone. The four oxo-functionalised phosphites were tested as catalysts for 1-octene hydroformylation. The observed reaction rates lie in the range reported for other medium-bulky phosphites. Furthermore, the hydroformylation rate decreases as the donor strength of the side group increases, suggesting binding of the O-donor during catalysis. The L/B ratios lie in the range 1.4–3.6, the highest linear aldehyde selectivity being observed with the phosphite ester L3.

Tungsten (IV) carbenes for the metathesis of olefins. Direct observation and identification of the chain carrying carbene complexes in a highly active catalyst system

On addition of aluminium halides to the carbene complexes W(CHBut)(OCH2But)2X2 conversion into highly active catalysts for olefin metathesis occurs; the nature of the initiating and propagating species in olefin metathesis has been identified by n.m.r. spectroscopy.

Tungsten(VI) and molybdenumVI oxo-alkyl species. Their role in the metathesis of olefins

The complexes MOCl (neopentyl)3(M = Mo, W) can be isolated from solutions which are active in olefin metathesis, and although inactive alone, these species can be converted into very active catalysts; the syntheses of MO(neopentyl)4(M = Mo, W) are also reported.