Thorium(IV) and uranium(IV) trans-calix[2]benzene[2]pyrrolide alkyl and alkynyl complexes: synthesis, reactivity, and electronic structure

Suvova, M., O’Brien, K. T.P., Farnaby, J. H. , Love, J. B., Kaltsoyannis, N. and Arnold, P. L. (2017) Thorium(IV) and uranium(IV) trans-calix[2]benzene[2]pyrrolide alkyl and alkynyl complexes: synthesis, reactivity, and electronic structure. Organometallics, 36(23), pp. 4669-4681. (doi: 10.1021/acs.organomet.7b00633)

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The first thorium(IV) and uranium(IV) hydrocarbyl complexes of a trans-calix[2]benzene[2]pyrrolide macrocycle can use ligand noninnocence to enable multiple C–H bond activation reactions at the metal. Both alkyl and alkynyl complexes supported by the L dianion and L–2H tetraanion are reported. The ThIV and UIV monoalkyl-ate complexes [M(L–2H)An(R)] (M = K for R = CH2Ph, M = Li for R = Me, CH2SiMe3), in which the ligand aryl groups are metalated, add C–H bonds of terminal alkynes across the metal and ligand, forming the AnIV-alkynyl complexes [(L)An(C≡CR′)2] (R′ = SiMe3, SiiPr3). This ligand reprotonation from (L–2H)4– to (L)2– is accompanied by a change in coordination mode of the ligand from η5:η1:η5:η1 to η5:η5. Alternatively, the original alkyl group can be retained if the ligand is reprotonated using [Et3NH][BPh4], affording the ThIV cations [(L)Th(R)][BPh4] (R = CH2Ph, N(SiMe3)2). Here, ligand rearrangement to the κ1:η6:κ1:η6 coordination mode occurs. These complexes provide rare examples of bis(arene) actinide sandwich geometry. The two η1-alkynides in [(L)Th(C≡CSiMe3)2] rearrange upon coordination of [Ni0], forming [(L)Th(C≡CSiMe3)2·Ni(PR″3)] (R″ = phenyl, cyclohexyl), featuring the shortest yet reported distance between Th and Ni and giving unprecedented insight into the changes in macrocyclic ligand coordination between κ1:η6:κ1:η6 and η5:η5 coordination modes. A computational study of this conformational change demonstrates the η5:η5 coordination mode to be more stable in the Th/Ni bimetallics (and hypothetical Pt analogues), an observation rationalized by detailed analysis of the Kohn–Sham orbital structure of the κ1:η6:κ1:η6 and η5:η5 conformers. Although remarkably inert to even high pressures of CO2 at room temperature, the bis(alkynyl) complexes [(L)An(C≡CSiMe3)2] completely cleave one CO bond of CO2 when they are heated under 1 bar pressure, resulting in the formation, and elimination from the metal, of a new, CO-inserted, bicyclic, carbonylated macrocycle with complete control over the C–C and C–N bond forming reactions.

Item Type:Articles
Additional Information:The EPSRC is also thanked for support through grants EP/H0048231 and EP/N022122/1.
Glasgow Author(s) Enlighten ID:Farnaby, Dr Joy
Authors: Suvova, M., O’Brien, K. T.P., Farnaby, J. H., Love, J. B., Kaltsoyannis, N., and Arnold, P. L.
College/School:College of Science and Engineering > School of Chemistry
Journal Name:Organometallics
Publisher:American Chemical Society
ISSN (Online):1520-6041
Published Online:16 October 2017
Copyright Holders:Copyright © 2017 American Chemical Society
First Published:First published in Organometallics 36(23):4669-4681
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher

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