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

Three complexes of cyclotricatechylene (H ctc), [{PtL} (μ -ctc)], have been synthesised: (L = 1,2-bis(diphenylphosphino)benzene {dppb}, ; L = 1,2-bis(diphenylphosphino)ethane {dppe}, ; L = 4,4'-bis( -butyl)-2,2'-bipyridyl { Bu bipy}, ). The complexes show three low-potential, chemically reversible voltammetric oxidations separated by 180 mV, corresponding to stepwise oxidation of the [ctc] catecholato rings to the semiquinonate level. The redox series and 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 and has been delineated by cw EPR, ENDOR and HYSCORE spectroscopies, with the aid of two monometallic model compounds [PtL(DBsq˙)] (DBsqH = 3,5-bis( -butyl)-1,2-benzosemiquinone; L = dppe or Bu bipy). DF and time-dependent DF calculations confirm these interpretations, and demonstrate changes to spin-delocalisation in the ctc macrocycle as it is sequentially oxidised.