Binuclear gold(I) and mercury(II) derivatives of diethynylfluorenes

A new series of bis(alkynyl) gold(I) and mercury(II) d10 complexes incorporating fluorenyl-based based linking units are reported. The binuclear complexes [LAuC≡CRC≡CAuL] and their isoelectronic mercury(II) congeners [R′HgC≡CRC≡CHgR′] (L = tertiary phosphines; R = fluorene-2,7-diyl, dihexylfluorene-2,7-diyl, 9-((ferrocenylphenylene)methylene)fluorene-2,7-diyl, fluoren-9-one-2,7-diyl, 9-(dicyanomethylene)fluorene-2,7-diyl; R′ = Me, Ph) were prepared in very good yields by the base-catalyzed dehydrohalogenation reaction of the corresponding metal chloride precursors with the appropriate diethynylfluorene derivatives HC≡CRC≡CH at room temperature. All the compounds have been fully characterized by FTIR, NMR and electronic absorption spectroscopies and FAB mass spectrometry. The solid-state molecular structures of [Ph3PAuC≡CRC≡CAuPPh3] (R = 9,9-dihexylfluorene-2,7-diyl, fluoren-9-one-2,7-diyl) and [MeHgC≡CRC≡CHgMe] (R = fluoren-9-one-2.7-diyl) have been determined crystallographically, the last of which represents the first dimercury diacetylide to be structurally characterized. Absorption studies suggest that it is possible to fine-tune the optical gap of this class of materials by modifying the electronic properties of the substituent at the 9-position of the central fluorene spacer. The solution redox chemistry of these fluorene-linked binuclear complexes as revealed by cyclic voltammetry indicates some degree of electronic communication between the 9-substituent of the fluorenyl ring and the terminal metal groups via the conjugated alkynyl bridge. Most of the complexes in this study have been shown to exhibit rich photophysical behavior, and a discussion on their emission properties in terms of the nature of metal groups and their auxiliary ligands as well as the fluorene spacer was made.