ALKALI METAL DERIVATIVES OF GROUP IV ORGANOMETALLICS: MECHANISTIC ASPECTS OF REACTIONS WITH HALIDES
Organometallic derivatives of the Group IV elements have been known and used as synthetic intermediates for a half century, but little has been done by way of systematic investigation of the scope, and limitations of their reactions. And only recently have investigators turned their attentions to the study of mechanistic aspects of these reactions. An overview of the field reveals many highly useful facts, but it is also strewn with some contradictory observations, along with many others that are difficult to fit into a coherent overall conceptual scheme. This scheme lies beyond the present horizon and will be revealed only after completion of systematic studies on the various parameters affecting the scope, limitations, and mechanisms of these reactions. Delineation of these, in turn, will provide reliable guides to their synthetic utility. This report deals with our present understanding of the mechanisms of Group IV organometalalkalis with organic halides, with reference to other reactions as appropriate, and with some of the questions concerning these reactions, whose answers lie beyond the horizon. Experimental observations which are relevant for understanding of mechanisms will be first summarized; mechanisms consistent with these will be reviewed; and questions remaining to be answered will be raised. Because of the nature of the presently known facts, those concerning silicon, germanium, tin, and lead alkalis will be intermingled, and valid trends within the series will be indicated.
Mise en evidence d'un mecanisme de substitution arynique pour la reaction d'halogenures aromatiques avec le tributylstannyllithium
Abstract Evidence for a benzyne mechanism is observed when tributylstannyllithium reacts with aromatic fluorides and chlorides, however with the corresponding bromides the reaction fails to proceed by this mechanism.
Triphenyltinmagnesium bromide : Evidence for the occurrence of diphenylstannene stabilizied by coordination
Whereas organotin alkali metal derivatives have been widely investigated’ information on organotin mtignesium derivatives is restricted to a brief report on the solution chemistry of (Ph,Sn),Mg’. Evidence has been presented for the existence in solution of Ph,GeMgC13*4 and Ph,PbMgBr’, but these compounds have not been isolated. The isolation of triphenyltin derivatives of the Group IIB metals Zn and Cd has recently been reported6. The hydrostannolysis of reactive metal-carbon bonds offers a particularly useful route to compounds containing metal-tin bonds6-‘. This reaction has now been applied to a study of the triphenyltin Grignard reagent_ The reaction of triphenyltin hydride with an equimolecular amount of ethylmagnesium bromide-triethylamine complexQ*‘0 in diethyl ether at 15-O” results in selective hydrostannolysis of the Mg:C bond as evidenced by the quantitative formation of ethane :