Oxo-metal catalysed reactions of unsaturated alcohols

Smith, Graham J. (1981) Oxo-metal catalysed reactions of unsaturated alcohols. Doctoral thesis, Polytechnic of North London.


The use of oxo-transition metal complexes (particularly molybdenum and vanadium) as catalysts for a number of synthetically important reactions is described.

The ability of alkyl hydroperoxides to epoxidise alkenes in the presence of transition metal catalysts is well known and is reviewed here along with the more conventional methods of preparing epoxides in the laboratory, with particular emphasis on their application in asymmetric epoxidations.

In this work a number of novel oxo-vanadium and oxo-molybdenum complexes containing bulky and/or chiral ligand systems have been prepared and their application as potential catalysts for regio and/or asymmetric epoxidation has been studied.

A synthesis of the oxo-vanadium complex of the known ligand NN''-ethylenebis(iminomethylCcunphof ) was developed and the complex characterised. The synthesis and structure of oxo-molybdenum complexes containing novel tridentate ligands derived from substituted salicylaldéhydes and chiral 2-aminoalcohols are also described along with a D(-)-2,3- butandiol complex of dioxomolybdeniam(VI ). As in a number of examples recently reported in the literature, epoxidation of geraniol and related compounds in the presence of these catalysts showed regioselectivity with exclusive reaction of the allylic double bond. The latter complex was also found to give low asymmetric induction in epoxidations of geraniol.

In addition to using pre-formed chiral complexes as asymmetric epoxidation catalysts the possibility of using chiral catalysts prepared in situ from simple molybdenum complexes and an excess of the chiral ligand has also been studied. Some of these systems appeared to give the highest asymmetric inductions in epoxidations of geraniol.

During the studies of the epoxidation reaction it was found that some of the oxo-vanadium and oxo-molybdenum complexes were very efficient catalysts for the isomerization of allylic alcohols. The scope of rearrangement reactions of this type was examined for ten structurally different allylic alcohols. It was shown that in most cases isomerization leads to an equilibrium mixture and in some cases the position of equilibria differ from that which would be predicted from classical considerations. Several attempts were also made to prepare more reactive isomerization catalysts by synthesising oxo-vanadium complexes with fluorine containing ligands.

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