Synthesis, structure and metal compounds of a novel chromophoric cyanamide ligand

Abstract

The novel compound 2-cyanaminofluoren-9-one (HL) has been synthesized, and is readily deprotonated to form the corresponding cyanamide anion L^–. This has been isolated as the Tl⁺L^– and AsPh₄⁺L^– salts. The UV/visible spectra of HL and AsPh₄⁺L^– show the same amine to carbonyl charge transfer transition seen in other aminofluorenones, although at longer wavelengths. The compound AsPh₄⁺L^– undergoes the reversible one electron reduction typical of fluorenones, whilst HL undergoes an irreversible reduction. The crystal structure of AsPh₄⁺L^– was determined and related to the solvatochromic behaviour of the L^– anion. Some simple EHMO calculations have been carried out on the L^– anion of AsPh₄⁺L^–, which show the cyanamide based HOMO and carbonyl based LUMO involved in the aforementioned CT transition. The thallium salt Tl⁺L^– has also been used as a transmetallating agent in reaction with trimethyltin chloride to produce the corresponding tin cyanamide complex [SnMe₃L], and in reaction with (triphenylphosphine)gold chloride to produce the first reported gold cyanamide compound [AuL(PPh₃)], whose crystal structure has been determined.