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Constrained geometry aminooxazolinate ligands giving chiral zirconium guanidinates; catalytic cyclohydroamination

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Gott, Andrew L., Clarkson, Guy J., Deeth, Robert J., Hammond, Max L., Morton, Colin and Scott, Peter. (2008) Constrained geometry aminooxazolinate ligands giving chiral zirconium guanidinates; catalytic cyclohydroamination. Dalton Transactions (No.22). pp. 2983-2990. ISSN 1477-9226

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Official URL: http://dx.doi.org/10.1039/b803831g

Abstract

DFT calculations indicate that contrary to a prior report, N-heterocycle-augmented constrained geometry ligands e. g. Cp '-SiMe2-NR (Cp ' = Me4C5, R = 2-pyridine) should be capable of binding both atoms of the diazaallyl fragment at zirconium. This was confirmed by a molecular structure of a previously reported complex. Similar R = 2-oxazoline complexes were also shown to be feasible, although an additional N,O binding mode was accessible. The proligands HCp '-SiMe2-NHR (R = chiral non-racemic 2-oxazoline) were readily synthesised in high yield via base mediated reaction of 2-aminooxazolines and Cp '-SiMe2Cl. Subsequent reaction with Zr(NMe2)(4) gave, rather than the desired complexes, configurationally stable chiral-at-zirconum guanidinate/alkoxide chelate products; the aminooxazolinate units had undergone ring-opening and migratory insertion of -NMe2. Trends in the level diastereoselection follow the steric demand of the oxazoline substituent, with the larger groups (Bu-t, Pr-i) giving single diastereomers. The modest performance of these guanidinate compounds in enantioslective catalytic cyclohydroamination of aminoalkenes follows the expected trends for metal accessibility in a sigma-amido insertative mechanism.

Item Type:

Journal Article

Subjects:

Q Science > QD Chemistry

Divisions:

Faculty of Science > Chemistry

Library of Congress Subject Headings (LCSH):

Amination, Ligands, Ligand binding (Biochemistry), Catalysis, Zirconium, Chirality

Journal or Publication Title:

Dalton Transactions

Publisher:

Royal Society of Chemistry