Electronic interactions in gold(I) complexes of 2,5-diferrocenyl-1-phenyl-1H-phosphole

•Synthesis of 2,5-diferrocenylphosphole gold(I) alkynyl complexes.•Gold(I) phosphole complexes exhibit IVCT absorptions of moderate strength.•Coordination of P to Au(I) leads to decreased electronic interactions.

The synthesis of gold(I) complexes of 2,5-diferrocenyl-1-phenyl-1H-phosphole (1) is presented. Chloro(2,5-diferrocenyl-1-phenyl-1H-phosphole)gold (3) has successfully been prepared by the reaction of 1 with AuCl(SMe2) (2). Treatment of 2 with arylethyne (aryl = ferrocenyl, phenyl) using catalytical amounts of [CuI] and 1 equiv. of 1 gave arylethynyl-(2,5-diferrocenyl-1-phenyl-1H-phosphole)gold 4a and 4b (aryl: a = ferrocenyl; b = phenyl). Compound [μ-(1,4-phenylenedi-2,1-ethynediyl)]bis(2,5-diferrocenyl-1-phenyl-1H-phosphole)digold (5) could be synthesized by a similar procedure using 0.5 equiv. of 1,4-diethynylbenzene. The electrochemical properties of 3, 4a,b and 5 were investigated by cyclic and square wave voltammetry. In 3, 4a and 4b each ferrocenyl unit shows one reversible redox event with redox separations of the ferrocenyl moieties in 2,5 position of approximately 260 mV. In 5 two redox events for the four ferrocenyl groups were observed. Spectroelectrochemical measurements of 3, 4a and 4b reveal IVCT absorptions with intensities of 1100–1300 L mol−1 cm−1 and a full-width-at-half-height of ≈3650 cm−1. In 5 two mixed-valent units are present per molecule and therefore, the intensity of the IVCT band is increased to 2700 L mol−1 cm−1. Compounds 3, 4a,b and 5 can be classified as moderately coupled class II systems according to Robin and Day. The complexation of the gold(I) fragment by the phosphorus atom leads to a decreased metal–metal interaction when compared to 1.

Graphical abstractThe reaction of 1 with different gold(I) compounds resulted in the formation of 2. Electrochemical measurements illustrate a decreased redox separation after coordination of P to Au. Spectroelectrochemical studies demonstrate a decreased metal–metal interaction in the gold(I) phospholes 2 compared to 1 showing that 2 can be classified as moderately coupled class II systems according to Robin and Day.Figure optionsDownload full-size imageDownload as PowerPoint slide