REGIOSELECTIVITY OF THE INSERTION OF 4,4-DIMETHYL-2-PENTYNE INTO THE PD-C BOND OF CYCLOPALLADATED COMPLEXES

The mono-insertion of 4,4-dimethyl-2-pentyne into the Pd-C bond of a series of cyclopalladated complexes has been studied. In most cases these reactions were found to be highly regioselective, and stable organometallic complexes could often be isolated. Two basic trends were found for these reactions. When chelation of the donor atom to palladium was relatively important, the regioisomer obtained had the t-Bu fragment on the same carbon as the palladium atom. In the absence of such coordination, the opposite regiochemistry was observed. These results were interpreted by taking into account the pre-insertion scenario involving eta(2)-coordination of the alkyne to the metal. The X-ray crystal structures of [PdC-(t-Bu)=C(Me)C6H4-2-CH(2)SMe(C5H5N)Cl], 7a, [PdC(Me)=C(t-Bu)C6H4-2-CH2S-t-Bu(C5H5N)I], 7c, and [PdC(t-Bu)=C(Me)-2-C6H4C6H4-2'-SMe(C5H5N)Cl] 10b, were determined.