Metal-porphyrinogen organometallic chemistry:: The intramolecular reactivity of η2-acyls bonded to titanium( IV)-meso-octaethyl mono(pyridine)-tris(pyrrole) and to vanadium(III)-meso-octaethyl bis(pyridine)-bis(pyrrole) macrocycle

The organometallic chemistry of titanium- and vanadium-macrocycle was investigated using meso-octaethyl mono(pyridine)-tris(pyrrole), [Et-8(C5H3N)(C4H2NH3)(3)], 1, and meso-octaethyl cis-bis(pyridine)-bis(pyrrole), [Et(8)cis-(m-MeC5H2N)(C5H3N)(C4H2NH)(2)], 7, as ligands for titanium(IV) and vanadium(III), respectively. The metalation of 1 with LiBu followed by the reaction with TiCl4. thf(2) led to [Et-8(C5H3N)(C4H2N)(3)Ti-Cl], 3, which was alkylated to [Et-8(C5H3N)(C4H2N)(3)Ti-Me], 4. The Ti-C bond in 4 underwent a migratory insertion reaction with (BuNC)-N-t and carbon monoxide. In the former case the corresponding eta(2)-iminoacyl was isolated and structurally characterized as [Et-8(C5H3N)(C4H2N)(3)Ti(eta(2)-C(Me)NBut)], 6, while the reaction of 4 with carbon monoxide led to the homologation of one pyrrolyl anion, thus converting the mono(pyridine)-tris(pyrrole) into a cis-bis(pyridine)-bis(pyrrole) macrocycle and the oxotitanium(ni) functionality in [Et-8(m-MeC5H2N)(C5H3N)(C4H2N)(2)Ti=O], 5. The homologation occurs via a carbenium ion eta(2)-acyl which was not intercepted. The synthesis of [Et-8(m-MeC5H2N)(C5H8N)(C4H2N)(2)V-Cl], 9, was carried out from the lithiated form, 8, of 7 followed by reaction with VCl3. thf(3). Complex 9 was converted into the corresponding methyl derivative [Et-8(m-MeC5H2N)(C4H3N)(C4H2N)(2)V-Me], 10, which underwent a migratory insertion of CO and ButNC. The reaction of 10 with ButNC led to the expected eta(2)-iminoacyl [Et-8(m-MeC5H2N)(C5H3N)(C4H2N)(2)V{eta(2)-C(Me)=NBut}], 12, while in the case of CO, the intermediate eta(2)-acyl, behaving as a nucleophilic carbenoid, reacted preferentially with the pyridine alpha-position, leading to [Et-8(m-MeC5H3N)mu(O-CMe)(C4H2N)}(C4H2N)(C5H3N)V], 11. The proposed structures were supported by the X-ray analysis of 5, 6, 8, 9, and 11.