Immobilisation of η³‐Allyldicarbonyl Complexes of Mo^II with Bidentate Nitrogen Ligands within Aluminium‐Pillared Clays

Abstract

Molybdenum(II) complexes [MoX(CO)2(η3‐allyl)(CH3CN)2] (X = Cl or Br) were encapsulated in an aluminium‐pillared natural clay or a porous clay heterostructure and allowed to react with bidentate diimine ligands. All the materials obtained were characterised by several solid‐state techniques. Powder XRD, and 27Al and 29Si MAS NMR were used to investigate the integrity of the pillared clay during the modification treatments. 13C CP MAS NMR, FTIR, elemental analyses and low‐temperature nitrogen adsorption showed that the immobilisation of the precursor complexes was successful as well as the in situ ligand‐substitution reaction. The new complex [MoBr(CO)2(η3‐allyl)(2‐aminodipyridyl)] was characterised by single‐crystal X‐ray diffraction and spectroscopic techniques, and NMR studies were used to investigate its fluxional behaviour in solution. The prepared materials are active for the oxidation of cis‐cyclooctene using tert‐butyl hydroperoxide as oxidant, though the activity of the isolated complexes is higher. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Molybdenum(II) catalyst precursors in olefin oxidation reactions

“…[Mo(η 3 -C 3 H 5 )(CO) 2 X(NCMe) 2 ] is present in solution as the two main isomers shown in Chart 2 and some more obtained by allyl rotation may be observed, sometimes even at low temperatures. [42,43,44] Large L-L ligands stabilize the equatorial isomer, which is also the more interesting, since the metal environment is chiral. [7,42,43] [Mo (CO) 3 X 2 (NCMe) 2 ] is another18 electron Mo(II) d 4 complex with coordination number seven as [Mo(η 3 -C 3 H 5 )(CO) 2 X(NCMe) 2 ], where the allyl has been substituted by two monodentate ligands (X and CO).…”

“…They are obtained from the starting complexes with L = NCMe, since the nitrile ligand can be easily substituted by a wide range of ligands, with N, O and other donor atoms. [42,43,44] The X ligand may also be substituted by a neutral ligand, affording cationic complexes. Both can be functionalized with groups that will allow a fine tuning of the catalytic activity of the complex, but also with groups that make easy the reaction with material surfaces, in order to design new heterogeneous catalysts.…”

“…4-Cl-iPr2dab converted 88 (1st run) and 83 % (2nd run) of cy8 and similar numbers were obtained for 4-X-NCMe, 4-Cl-Me2Me-dab and others. [7,44] …”

“…Only one complex 4-Br-Me2Medab was intercalated in a PCH (porous clay heterostructures). [44] The results of catalytic studies are given in Table 5. The performance of some catalysts remains very similar when they are intercalated in HTC (4-Brpyim, 4-Br-pybzim, 5-Br-picH, 5-Br-pydcH2, 5-I-trp, 5-I-phe, and 4-X-dpa for cy8, for instance), while 4-Cl-Me2Medab loses activity in the PILC.…”

“…Other clays such as PILCs (pillared interlayered clays) are obtained from cationic clays where large polyoxo cations (aluminum in this work) form metal oxide structures after calcination, affording a two dimensional arrangement where molecules can intercalate. The clay was impregnated with complex [Mo(η 5 -C 3 H 5 )X(CO) 2 (NCMe) 2 ] (4), which then reacted with both dpa and Me2Medab [44]. …”