Cleavage of a PN Bond in a Urea-Containing (Ph2P(R)PPh2)-Bridged Dinuclear Gold(I) Thiolate Complex by Fluoride and a Mechanistic Insight

A urea-containing, (Ph2P(R)PPh2)-bridged, dinuclear, gold(I) thiolate complex, [Au2{Ph2PN(C6H4OMe-4)PPh2}(SC6H4NHCONHC6H5)2] (1) was designed and synthesized and its photophysical and anion recognition properties studied. The results show that 1 has a high selectivity toward F−. Upon addition of F−, the yellow solution was decolorized, and drastic changes of emission and 1H and 31P{1H} NMR signals were observed. Interestingly, these changes are attributed to fluoride-assisted PN bond hydrolysis, instead of the expected hydrogen-bonding interactions with the urea receptor. Similar changes were observed for two other basic anions, AcO− and H2PO4−, but to a much lesser extent; and these anions were found to bind to the urea receptor at the same time. On the other hand, Cl− was found to only bind to the urea moiety through hydrogen-bonding interactions. Further studies with the control complex [Au2{Ph2PN(C6H4OMe-4)PPh2}Cl2] (2) indicate that F− assists the hydrolysis process via cleavage of the PN bond. DFT calculations were performed to study the reaction mechanism for the fluoride-assisted PN bond hydrolysis of 2; these provide a better insight into the role of fluoride in the hydrolysis.