Interactions with acetylenes and allyl ligands

7t-Bonding to acetylenic moieties has been reported in several organometallic compoimds of the alkaline earth metals. For example, short Be-C distances in dimeric [Be CHCMe)2(NMe3)]2, 10, indicate self-assembly via 7i-interactions [8]. 

A series of heterometallic alkynylmagnesates has been prepared and structurally characterized. In these compounds the alkali metal cations connect the acetylenic moieties of the [Mg(C=CR)3] fragments by Ti-contacts. Typical examples are Li2[Mg(CsCPh)3(tmeda)]2, 11 [9], Na2[Mg(CHCBu )3(tmeda)]2, 12, and Na2[Mg(CsCBu )3(pmdta)]2, 13 [10]. Ti-Coordination has been shown to be present in the organomagnesium acetylide [(MgEt)2(C=CBu )3(tmeda)]2-C6H6, 14 [11]. 

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