Structural manipulation of organoantimony cations for tuneable Lewis acidity and reactivity of palladium organoantimony complexes

Coughlin, O. ORCID: 0000-0003-4528-9787, 2021. Structural manipulation of organoantimony cations for tuneable Lewis acidity and reactivity of palladium organoantimony complexes. PhD, Nottingham Trent University.

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Recent reports of novel organoantimony cations acting as Lewis acid catalysts as well as unprecedented bonding modes in transition metal complexes with trialkylantimony(III) ligands have yielded a newfound interest in historically neglected fields.

Triarylchlorostibonium salts of the form [Ar3SbCl][B(C6F5)4] (Ar = Ph, 3-FC6H4, 4-FC6H4, 3,5- F2C6H3, 2,4,6-F3C6H2) were synthesised and found to be active catalysts for the Friedel-Crafts dimerization of 1,1-diphenylethylene and Friedel-Crafts alkylation of benzene. This reactivity as well as structural and computational studies yielded a model for the Lewis acidity at the Sb centre which was proportional to the number of fluorine atoms on the aryl ring with a quenching effect from para fluorination.

Pentamethylcyclopentadienyl (Cp*) antimony(III) cations of the form [Cp*SbCl][B(C6F5)4], [Cp*2Sb][Y] (Y = B(C6F5)4, OTf) and Cp*Sb(OTf)2 were prepared and display diversity in both solid state structure and reactivity. The [Cp*SbCl]+ ion is moderately Lewis acidic. The [Cp*2Sb]+ ion shows no reactivity which can be attributed to Lewis acidity. [Cp*SbF][B(C6F5)4] could not be isolated due to thermal instability but was isolated as an NHC adduct. It was found to undergo chloride/fluoride exchange in chlorinated solvents; computational evidence suggests this occurs via a carbocation intermediate.

The potential for a ‘frustrated Lewis pair’, with both an organoantimony(III) base and an organoantimony(V) acid was explored, leading to the C-Cl bond activation of benzyl chloride (BnCl) with tBu3Sb and [(3,5-F2C6H3)4Sb][B(C6F5)4]. A novel stibinostibonium [(Bn2Sb)Bn3Sb][BF4] was isolated by serendipity when ‘one-pot’ routes to tetrabenzylstibonium salts ([Bn4Sb]+) were targeted.

[Pd4(Me3Sb)8] was found to have a range of reactivities with monodentate and bidentate phosphines. A novel Pd3 cluster, [Pd3(Me3Sb)3(μ2-(Me3Sb))3(μ3-(Me3Sb))], was structurally characterised, representing the first example of a homoleptic palladium(0) complex with terminal, μ2 and μ3 pnictine ligands.

A computational study investigated the mechanism by which alkyl/aryl groups exchange with chlorides between homoleptic stibines (Me3Sb and Ph3Sb) and SbCl3. This was found to occur via an intermediate containing a 3c-2e akyl/aryl bridge.

Item Type: Thesis
Creators: Coughlin, O.
Date: April 2021
Rights: The copyright in this work is held by the author. You may copy up to 5% of this work for private study, or personal, non-commercial research. Any re-use of the information contained within this document should be fully referenced, quoting the author, title, university, degree level and pagination. Queries or requests for any other use, or if a more substantial copy is required, should be directed to the author.
Divisions: Schools > School of Science and Technology
Record created by: Jeremy Silvester
Date Added: 08 Oct 2021 09:16
Last Modified: 08 Oct 2021 09:16

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