Platinum(ii) complexes of mixed-valent radicals derived from cyclotricatechylene, a macrocyclic tris-dioxolene

Jonathan J Loughrey; Nathan J Patmore; Amgalanbaatar Baldansuren; Alistair J Fielding; Eric J L McInnes; Michaele J Hardie; Stephen Sproules; Malcolm A Halcrow

doi:10.1039/c5sc02776d

Platinum(ii) complexes of mixed-valent radicals derived from cyclotricatechylene, a macrocyclic tris-dioxolene

Chem Sci. 2015 Dec 1;6(12):6935-6948. doi: 10.1039/c5sc02776d. Epub 2015 Aug 20.

Authors

Jonathan J Loughrey¹, Nathan J Patmore², Amgalanbaatar Baldansuren³, Alistair J Fielding³, Eric J L McInnes³, Michaele J Hardie¹, Stephen Sproules⁴, Malcolm A Halcrow¹

Affiliations

¹ School of Chemistry , University of Leeds , Woodhouse Lane , Leeds LS2 9JT , UK . Email: m.a.halcrow@leeds.ac.uk.
² Department of Chemistry , University of Sheffield , Brook Hill , Sheffield S3 7HF , UK.
³ School of Chemistry and Photon Science Institute , University of Manchester , Oxford Road , Manchester M13 9PL , UK.
⁴ WestCHEM , School of Chemistry , University of Glasgow , Glasgow G12 8QQ , UK . Email: stephen.sproules@glasgow.ac.uk.

Abstract

Three complexes of cyclotricatechylene (H₆ctc), [{PtL}₃(μ₃-ctc)], have been synthesised: (L = 1,2-bis(diphenylphosphino)benzene {dppb}, 1; L = 1,2-bis(diphenylphosphino)ethane {dppe}, 2; L = 4,4'-bis(tert-butyl)-2,2'-bipyridyl { ^t Bu₂bipy}, 3). The complexes show three low-potential, chemically reversible voltammetric oxidations separated by ca. 180 mV, corresponding to stepwise oxidation of the [ctc]^6- catecholato rings to the semiquinonate level. The redox series [1]^0/1+/2+/3+ and [3]^0/1+/2+/3+ have been characterised by UV/vis/NIR spectroelectrochemistry. The mono- and di-cations have class II mixed valent character, with reduced radical delocalisation compared to an analogous bis-dioxolene system. The SOMO composition of [1˙]⁺ and [3˙]⁺ has been delineated by cw EPR, ENDOR and HYSCORE spectroscopies, with the aid of two monometallic model compounds [PtL(DBsq˙)]⁺ (DBsqH = 3,5-bis(tert-butyl)-1,2-benzosemiquinone; L = dppe or ^t Bu₂bipy). DF and time-dependent DF calculations confirm these interpretations, and demonstrate changes to spin-delocalisation in the ctc macrocycle as it is sequentially oxidised.