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The synthesis, structure and reactivity of B(C6F5)(3)-stabilised amide (M-NH2) complexes of the Group 4 metals

Record type: Article

Treatment of the homoleptic titanium amides [Ti(NR2)4] (R=Me or Et) with the Brønsted acidic reagent H3NB(C6F5)3 results in the elimination of one molecule of amine and the formation of the four-coordinate amidoborate complexes [Ti(NR2)3{NH2B(C6F5)3}], the identity of which was confirmed by X-ray crystallography. The reaction with [Zr(NMe2)4] proceeds similarly but with retention of the amine ligand to give the trigonal-bipyramidal complex [Zr(NMe2)3{NH2B(C6F5)3}(NMe2H)]. Cyclopentadienyl (Cp) amidoborate complexes, [MCp(NR2)2{NH2B(C6F5)3}] (M=Ti, R=Me or Et; M=Zr, R=Me) can be prepared from [MCp(NR2)3] and H3NB(C6F5)3, and exhibit greater thermal stability than the cyclopentadienyl-free compounds. H3NB(C6F5)3 reacts with nBuLi or LiN(SiMe3)2 to give LiNH2B(C6F5)3, which complexes with strong Lewis acids to form ion pairs that contain weakly coordinating anions. The attempted synthesis of metallocene amidoborate complexes from dialkyl or diamide precursors and H3NB(C6F5)3 was unsuccessful. However, LiNH2B(C6F5)3 does react with the highly electrophilic reagents [MCp2Me(-Me)B(C6F5)3] to give [MCp2Me(-NH2)B(C6F5)3] (M=Zr or Hf). Comparison of the molecular structures of the Group 4 amidoborate complexes reveals very similar BN, TiN and ZrN bond lengths, which are consistent with a description of the bonding as a dative interaction between an {M(L)n(NH2)} fragment and the Lewis acid B(C6F5)3. Each of the structures has an intramolecular hydrogen-bonding arrangement in which one of the nitrogen-bonded hydrogen atoms participates in a bifurcated FHF interaction to ortho-F atoms.

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Citation

Mountford, A.J., Clegg, W., Coles, S.J., Harrington, R.W., Horton, P.N., Humphrey, S.M., Hursthouse, M.B., Wright, J.A. and Lancaster, S.J. (2007) The synthesis, structure and reactivity of B(C6F5)(3)-stabilised amide (M-NH2) complexes of the Group 4 metals Chemistry - A European Journal, 13, (16), pp. 4535-4547. (doi:10.1002/chem.200601751).

More information

Published date: 2007
Keywords: polymerization catalysts, monocyclopentadienyl tantalum complexes, noncovalent interactions, boranes, polymerization, nitrido complexes, lewis acids, dot-f-c, hydrogen bonds, olefin, perfluorophenyl derivatives, zirconium complexes, amine elimination, lewis-acid, titanium, crystal-structure

Identifiers

Local EPrints ID: 54348
URI: http://eprints.soton.ac.uk/id/eprint/54348
ISSN: 0947-6539
PURE UUID: 7f9eb503-7106-4e06-8bb8-4e04add1cefc
ORCID for S.J. Coles: ORCID iD orcid.org/0000-0001-8414-9272
ORCID for P.N. Horton: ORCID iD orcid.org/0000-0001-8886-2016

Catalogue record

Date deposited: 31 Jul 2008
Last modified: 17 Jul 2017 14:35

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Contributors

Author: A.J. Mountford
Author: W. Clegg
Author: S.J. Coles ORCID iD
Author: R.W. Harrington
Author: P.N. Horton ORCID iD
Author: S.M. Humphrey
Author: M.B. Hursthouse
Author: J.A. Wright
Author: S.J. Lancaster

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