The synthesis of new weakly coordinating diborate anions: anion stability as a function of linker structure and steric bulk

Hannant, Mark H., Wright, Joseph A. ORCID: https://orcid.org/0000-0001-9603-1001, Lancaster, Simon J., Hughes, David L., Horton, Peter N. and Bochmann, Manfred ORCID: https://orcid.org/0000-0001-7736-5428 (2006) The synthesis of new weakly coordinating diborate anions: anion stability as a function of linker structure and steric bulk. Dalton Transactions (20). pp. 2415-2426. ISSN 1477-9234

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Abstract

The successive addition of KCN and Ph3CCl to B(C6F4-C6F5-2)3 (PBB) affords triphenylmethyl salts of the [NC-PBB]- anion. By contrast, the analogous reaction with sodium dicyanamide followed by treatment with Ph3CCl leads to the zwitterionic aminoborane H2NB(C12F9)2C12F8, via nucleophilic attack on an o-F atom, together with CPh3[F-PBB]. Whereas treatment of [NC-PBB]- with either PBB or B(C6F5)3 fails to give isolable cyano-bridged diborates, the reaction of Me3SiNC-B(C6F5)3 with PBB in the presence of Ph3CCl affords [Ph3C][PBB-NC-B(C6F5)3]. Due to steric hindrance this anion is prone to borane dissociation. The longer linking group N(CN)2- gives the very voluminous anions [N{CNB(C6F5)3}2]- and [N(CN-PBB)2]-. A comparison of propylene polymerisations with rac-Me2Si(Ind)2ZrMe2 activated with the various boranes or trityl borates gives an anion-dependent activity sequence, in the order [NC-PBB]- < [MeB(C6F5)3]- < [MePBB]- ˜ [PBB-NCB(C6F5)3]- ˜ [N{CNB(C6F5)3}2]- < [F-PBB]- « [B(C6F5)4]- < [N(CN-PBB)2]-. The anion [N(CN-PBB)2]- gives a catalyst productivity about 2500 times higher than that of [NC-PBB]- and exceeds that of [B(C6F5)4]- based catalysts. The van der Waals volumes and surface areas of the anions have been calculated and provide a rationale for the observed reactivity trends in polymerisation reactions.

Item Type: Article
Faculty \ School: Faculty of Science > School of Chemistry
Depositing User: Rachel Smith
Date Deposited: 02 Nov 2010 17:48
Last Modified: 13 Aug 2022 01:40
URI: https://ueaeprints.uea.ac.uk/id/eprint/10525
DOI: 10.1039/b515548g

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