Synthesis, Structures, and Reactivity of Cyclometalated Complexes Formed by Insertion of Alkynes into M–C (M = Ir and Rh) Bonds

Reactions of three aryl-substituted phosphines with [Cp*MCl2]2 (M = Ir and Rh) have been carried out in the presence of sodium acetate. Aryl-substituted phosphine is cyclometalated readily to give the corresponding five-membered metallacycle complex via an intramolecular activation of C­(sp2)–H or C­(sp3)–H bond. Competition reaction indicates that the aromatic C­(sp2)–H bond is more likely to be activated than C­(sp3)–H bond under the same conditions. As representatives of cyclometalated complexes containing an M–C­(sp2) bond, cycloiridated complex 1 and cyclorhodated complex 3 reacted with DMAD to afford corresponding seven-membered cyclometalated complexes 13 and 14 via 1,2-insertion of alkyne into M–C bond. However, the reaction of 1 with diphenylacetylene or phenylacetylene resulted in five-membered and six-membered doubly cycloiridated complexes 15 or 16, the formation of which presumably went through the vinylidene rearrangement of alkynes followed by 1,1-insertion; while the reaction of 3 with diphenylacetylene or phenylacetylene mainly gave normal seven-membered cyclorhodated complexes 17 or 18 by 1,2-insertion. For two representatives of cyclometalated complexes comprising an M–C­(sp3) bond, cycloiridated complex 4 and cyclorhodated complex 6 reacted with DMAD to form corresponding seven-membered cyclometalated complexes 20 and 21 by 1,2-insertion. Interestingly, the reactions of 4 and 6 with phenylacetylene generated six-membered metallacycle complexes 22 and 23, and a plausible formation pathway is the similar 1,1-insertion of vinylidene ligand into the M–C bond followed by the isomerization of the C–C double bond. Molecular structures of five-membered cyclometalated complexes 4 and 5 and insertion products 13, 15–19, 21, and 22 were determined by X-ray diffraction.