Tungsten allenylidenes

Otherwise, treatment of the chromium complex 10 with an excess of [W (C0)5(THF)] afforded the tungsten allenylidene 61 by transmetallation of the cumulenic ligand and further addition of W(CO)s to the A-atom of the heterocyclic substituent (Scheme 18) [30]. The related chromium complexes [Cr... 

Unlike the chromium and tungsten allenylidenes 46, the coupling of the indenyl-ruthenium(II) allenylidene SO with ynamine MeC=CNEt2 takes place regioselectively... 

Scheme 2.20 Coupling between chromium and tungsten allenylidene complexes and ynamines.

In the reaction of chromium and tungsten allenylidene complexes with the alkyynyl complexes Cp(CO)2FeC=CR, only the [2+2] cycloadducts 38 are obtained... 

Scheme 18 Transmetallation of an allenylidene ligand from chromium to tungsten...

Reverse processes, that is reactions of propargyl or allenylidene ligands coordinated to mononuclear centers with water, methanol, amines, and other ligands are known. Tungsten l and platinum complexes give a series of reactions (some of which are mediated by surfaces) comparable with those discussed for clusters. 

Allenylidene complexes also undergo [2+2] cycloaddition reactions with alkynes, but in addition to the cycloadducts linear insertion products are also obtained. For example, diarylallenylidene complexes of chromium and tungsten react with MeC NEth2 or PhCMI NEt2 to give both linear adducts 36 and cycloadducts 37. The linear adducts are formed via an initial cycloaddition of the ynamine to the C =C bond in the allenylidene complex, followed by cycloreversion. The cyclobutenylidene complexes are formed by [2+2] cycloaddition of the ynamine to the C =C double bond . 

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