Photoredox Reaction of [Hg(cyclam)|2+[Co(CO)4r Induced by Outer Sphere Charge Transfer Excitation

Photoredox processes induced by metal-tometal charge transfer (MMCT) excitation have a t­ tracted much attention in recent years [1-4]. These processes may be exploited for applications in arti­ ficial photosynthesis and photocatalysis [5, 6], They also facilitate our understanding of optical and thermal electron transfer in general [7, 8], A point of particular interest is the relationship be­ tween inner-sphere (IS) and outer-sphere (OS) CT interaction of closely related donor/acceptor sys­ tems such as suitable binuclear complexes (e.g. [(NH3)5Ru(III)<>NC)Ru(II)(CN)5-] [9]) and the corresponding ion pairs (e.g. [Ru(II)(NHj)6]3*[Ru(H)(CN)J-[10,11]). iS MMCT transitions are not restricted to ligandbridged complexes. They also occur if a reducing and an oxidizing metal center are connected by a direct, but polar m etal-m etal bond such as H g (II)-C o (-I) in [HgCo2(CO)8] [12]. Here, we describe the CT interaction and the resulting photoactivity of the ion pair [Hg(cyclam)]2+[Co(CO)4]“ with cyclam = 1,4,8,11tetraazacyclotetradecane. This example demon­ strates that under suitable conditions the CT inter­ action which is present in a polar m etal-m etal bond can still be observed if both metal centers are separated in an ion pair. Our observation does not only represent the first case of an OS CT interac­ tion involving Hg2+ as an acceptor, it is also a val­ uable contribution to the photochemistry of mer­ cury compounds which is receiving considerable interest in recent years [12—16].