Dual nucleophilic substitution at a W() η-coordinated diiodo acetylene leading to an amidinium carbyne complex

The synthesis and reactivity of a W( ii ) C 2 I 2 complex towards various nucleophiles are described. Soft, aprotic nucleophiles like 4-dimethylaminopyridine (DMAP) lead to substitution of one CO at tungsten, whereas reaction with an excess of benzylamine results in a dual nucleophilic substitution at the alkyne moiety involving the rearrangement to a novel cationic amidinium carbyne complex. The reactivity of side-on coordinated diiodo acetylene at the [Tp′W(CO) 2 ] + complex building block towards various nucleophiles is described. Introduction of two primary amines involved a side-on to end-on rearrangement, which is rather unexpected for 4e donor alkyne complexes.