Arynes transition metals

Jones, William M., and Klosin, Jerzy, Transition-Metal Complexes of Arynes,... 

The group R1 can be allyl, acyl, or alkynyl, and arynes can also act as the acceptors. The catalysts are usually Ni(cod)2, or ligated palladium. The mechanisms are not understood in detail, but a catalytic cycle involving the product of oxidative addition, Sn-M-R1, is thought to be involved. The stannylalkenes that are formed can then be subjected to reaction with electrophiles (e.g., AczO or RCH=0), or to coupling reactions in the presence of transition metals (e.g., the Stille reaction). 

An efficient, mild, transition metal-free method for the intermolecular C-N addition of amides and S-N addition of sulfinamides to arynes has been reported (Scheme 69).106... 

Most early transition-metal complexes of arynes have been prepared by thermally induced /3-hydrogen elimination from appropriately substituted aryl sigma complexes [Eq. (I)]2,8... 

Metal alkyls of late transition metals readily undergo decomposition by /3-hydrogen elimination.31 In principle, it should therefore be possible to prepare aryne complexes of dw metals by thermolysis of appropriately substituted late transition-metal aryl complexes. However, in practice this... 

The tantalum-benzyne complex (130) is much less reactive than other early transition-metal aryne complexes. It shows no reaction with acetone, benzophenone, benzaldehyde, acetonitrile, 3-hexyne, or methanol. The lack of reactivity of 130 was attributed to nonlability of the PMe3 ligand. Indeed, no phosphine exchange was observed when 130 was mixed with an excess of PMe3-d9. Refluxing 129 in a mixture of methanol and toluene (3 10 v/v) leads to clean formation of 131. This presumably results from reaction of a 16-electron benzyne complex with the alcohol. 

To date, no mononuclear transition metal complexes of three- or four-membered cycloalkynes have been reported. A number of polynuclear complexes of cyclobutyne have been prepared.90 However, since this article is limited to complexes in which the aryne, alkyne, or cumulene is coordinated to a single metal atom, a review of this topic is not included. 

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