Aromatic alkyne insertion into six-membered cyclometalated pyridine complexes of iridium: different insertion modes and structurally novel products.

Reactions of 2-benzoylpyridine or 2-benzylpyridine with [Cp*MCl] (M = Ir, Rh) have been carried out in the presence of NaOAc in refluxing methanol, which form the corresponding six-membered cyclometalated products (1-3) except for the reaction of 2-benzylpyridine with [Cp*RhCl]. Insertion reactions of two six-membered cyclometalated pyridine iridium complexes (1 and 2) with terminal or internal aromatic alkynes were studied. Terminal alkynes -XCHC[triple bond, length as m-dash]CH (X = H, MeO, and F) with 1 give the corresponding five- and seven-membered doubly cycloiridated complexes 4a-c, internal alkynes -XCHC[triple bond, length as m-dash]CCHX- (X = H, MeO, and Br) form the similar five- and seven-membered doubly cycloiridated complexes (5a,b) and/or di-insertion products (6a,c), whereas the acyl alkyne PhC[triple bond, length as m-dash]CCOPh affords the novel spiro-metalated complex 7. For complex 2, internal alkynes -XCHC[triple bond, length as m-dash]CCHX- (X = H, MeO, and Br) form similar five- and seven-membered doubly cycloiridated complexes (8a-c). However, in the case of PhC[triple bond, length as m-dash]CCOPh, the reaction gives the novel four-membered cyclometalated complex 9. These results suggest that the products formed by alkyne insertion reactions of the six-membered cycloiridated pyridine complexes are very diverse. Plausible pathways for the formation of these novel insertion products were proposed. Molecular structures of seven cyclometalated complexes were determined by X-ray diffraction.