Bolin Zhu

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*MCl2]2 (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*RhCl2]2. Insertion reactions of two six-membered cyclometalated pyridine iridium complexes (1 and 2) with terminal or internal aromatic alkynes were studied. Terminal alkynes p-XC6H4CCH (X = H, MeO, and F) with 1 give the corresponding five- and seven-membered doubly cycloiridated complexes 4a–c, internal alkynes p-XC6H4CCC6H4X-p (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 PhCCCOPh affords the novel spiro-metalated complex 7. For complex 2, internal alkynes p-XC6H4CCC6H4X-p (X = H, MeO, and Br) form similar five- and seven-membered doubly cycloiridated complexes (8a–c). However, in the case of PhCCCOPh, 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.

Synthesis, structures and catalytic activity of cyclometalated rhenium complexes

Thermal reactions of aryl-substituted phosphines or phosphinites with Re2(CO)10 in chlorobenzene resulted in the corresponding five-membered cyclometalated rhenium complexes (1–5) via an intramolecular activation of the C(sp2)–H or C(sp3)–H bond. The only exception occurred in the case of (1-naphthyl)diisopropylphosphinite, which gave a diphosphinite-substituted dinuclear rhenium complex 6. Competition reaction indicated that the aromatic C(sp2)–H bond is more likely to be activated than the C(sp3)–H bond under the same conditions. Photolysis of 1 or 2 in CHX3 led to the cleavage of the Re–C σ bond to yield corresponding phosphine-substituted tetracarbonyl rhenium halides 7–10. Complex 1 reacted with CF3COOH in CH2Cl2 to give addition product 11. Photolysis of cyclorhenated complexes 1–3 with a series of aryl halides in benzene resulted in the stoichiometric formation of biphenyl, together with corresponding phosphine-substituted tetracarbonyl rhenium halides (7, 9, 10, 12, and 13). When base was introduced into the above reaction, a catalytic system was established. Under optimized conditions, complex 1 provided moderate yield of biphenyl in a couple of hours at a [Re] : substrate ratio of 1 : 200. Molecular structures of complexes 1, 6, 9, and 11 were determined by X-ray diffraction.

Reactions of pyridine-2-ethyl/methyl cyclopentadienes with metal carbonyls

Abstract Thermal treatment of pyridine-2-ethyl cyclopentadiene (1) with Fe(CO)5 and Ru3(CO)12 gave novel intramolecular C–H activated dinuclear products (3 and 5). In the case of Fe(CO)5, the reaction also afforded the normal bis(cyclopentadienyl) diiron complex (4). However, similar reaction of pyridine-2-methyl cyclopentadiene (2) with Fe(CO)5 and Ru3(CO)12 only afforded the normal bis(cyclopentadienyl) dinuclear metal complexes (7 and 8). For Ru3(CO)12, the reaction also yielded a pendant η1-pyridyl-coordinated product (9). In addition, the reactions of 1 and 2 with Re2(CO)10 formed the corresponding pyridylethyl/pyridylmethyl cyclopentadienyl rhenium tricarbonyl complexes 10 and 11, which further underwent pyridine to rhenium cyclization via photoirradiation to provide the rhenium dicarbonyl complexes 12 and 13. The molecular structures of 3, 5, 6, 7, 8, 9, and 12 were determined by X-ray diffraction.