Carbonyl complexes of manganese, rhenium and molybdenum with ethynyliminopyridine ligands

[MBr(CO)5] reacts with m-ethynylphenylamine and pyridine-2-carboxaldehyde in refluxing tetrahydrofuran to give, fac-[MBr(CO)3(py-2-CHdouble bond; length as m-dashN-C6H4-m-(Ctriple bond; length of mdashCH))] (M = Mn, 1a; Re, 2a). The same method affords the tetracarbonyl [Mo(CO)4{py-2-CHdouble bond; length as m-dashN-C6H4-m-(Ctriple bond; length of mdashCH)}] (3a) starting from [Mo(CO)4(piperidine)2]; and the methallyl complex [MoCl(η3-C3H4Me-2)(CO)2{py-2-CHdouble bond; length as m-dashN-C6H4-m-(Ctriple bond; length of mdashCH)}] (4a) from [MoCl(η3-C3H4Me-2)(CO)2(NCMe)2]. The use of p-ethynylphenylamine gives the corresponding derivatives (1b, 2b, 3b, and 4b) with the ethynyl substituent in the para-position at the phenyl ring of the iminopyridine. All complexes have been isolated as crystalline solids and characterized by analytical and spectroscopic methods. X-ray determinations, carried out on crystals of 1a, 1b, 2a, 2b, 3b, 4a, and 4b, reveals the same structural type for all compounds with small variations due mainly to the different size of the metal atoms. The reaction of complexes 1a or 2a with dicobalt octacarbonyl affords the tetrahedrane complexes [MBr(CO)3{py-2-CHdouble bond; length as m-dashN-C6H4-m-{(μ-Ctriple bond; length of mdashCH)Co2(CO)6}}] (M = Mn, 5; Re, 6), the structures of which have been confirmed by an X-ray determination on a crystal of compound 5.