Acenaphtho[5,6-cd]-1,2-dichalcogenoles and their platinum complexes

A related series of bis(phosphine) platinum complexes 1–5 and 6–8 bearing dichalcogenate acenaphthylene ligands have been synthesised. The chalcogen–chalcogen bonds in the parent acenaphtho[5,6-cd]-1,2-dichalcogenoles (AcenapylE₂; L1 E = S, L2 E = Se; Acenapyl = acenaphthylene-5,6-diyl) were reduced with two equivalents of lithium triethylborohydride to form the dilithio-species. Metathetical addition of the lithium dichalcogenate species to a suspension of the appropriate cis-dichlorobis(phosphine)platinum in THF resulted in the formation of platinum(II) complexes [Pt(5,6-AcenapylE₂)(PR₃)₂] (1 E = S, R₃ = Ph₃; 2 E = S, R₃ = Ph₂Me; 3 E = S, R₃ = PhMe₂; 4 E = S, R₃ = Me₃; 6 E = Se, R₃ = Ph₃; 7 E = Se, R₃ = Ph₂Me; 8 E = Se, R₃ = PhMe₂). The dilithio-species of L1 and L2 were also reacted with (1,5-cyclooctadiene)platinum(II) dichloride. This reaction was successful with L1 resulting in the formation of platinum complex [Pt(5,6-AcenapylS₂)(COD)] (5). Complexes 1–3 and 5–8 have been fully characterised, principally by multinuclear magnetic resonance spectroscopy, IR and MS. Secondary isotopomer effects create complex satellite systems observed in both the ³¹P{¹H} NMR and ⁷⁷Se NMR spectra of selenium complexes 6–8. X-ray structures were determined for L1, 1, 3 and 6 and analysed, where appropriate, by measuring the peri-distance, splay angle magnitude, peri-atom displacement, central naphthalene ring torsions and the geometry around the platinum centre. Platinum was found to adopt a distorted square-planar geometry in all three complexes. Complex 1 was found to have the greatest molecular distortion of all three complexes, showing that changing the phosphine group and also the chalcogen has a noticeable effect. Comparisons were made between 6 and our previously reported [Pt(NapSe₂)(PPh₃)₂] and [Pt(AcenapSe₂)(PPh₃)₂] complexes; the level of distortion was found to decrease as the backbone is altered from naphthalene to acenaphthylene.