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 (C 5 H 3 N)(C 4 H 2 NH) 3 ], 1, and meso -octaethyl cis -bis(pyridine)−bis(pyrrole), [Et 8 cis -( m -MeC 5 H 2 N)(C 5 H 3 N)(C 4 H 2 NH) 2 ], 7, as ligands for titanium(IV) and vanadium(III), respectively. The metalation of 1 with LiBu followed by the reaction with TiCl 4 ·thf 2 led to [Et 8 (C 5 H 3 N)(C 4 H 2 N) 3 Ti−Cl], 3, which was alkylated to [Et 8 (C 5 H 3 N)(C 4 H 2 N) 3 Ti−Me], 4 . The Ti−C bond in 4 underwent a migratory insertion reaction with Bu t NC and carbon monoxide. In the former case the corresponding η 2 -iminoacyl was isolated and structurally characterized as [Et 8 (C 5 H 3 N)(C 4 H 2 N) 3 Ti(η 2 -C(Me)NBu t )], 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(IV) functionality in [Et 8 ( m -MeC 5 H 2 N)(C 5 H 3 N)(C 4 H 2 N) 2 Ti O], 5 . The homologation occurs via a carbenium ion η 2 -acyl which was not intercepted. The synthesis of [Et 8 ( m -MeC 5 H 2 N)(C 5 H 3 N)(C 4 H 2 N) 2 V−Cl], 9, was carried out from the lithiated form, 8, of 7 followed by reaction with VCl 3 ·thf 3 . Complex 9 was converted into the corresponding methyl derivative [Et 8 ( m -MeC 5 H 2 N)(C 5 H 3 N)(C 4 H 2 N) 2 V−Me], 10, which underwent a migratory insertion of CO and Bu t NC. The reaction of 10 with Bu t NC led to the expected η 2 -iminoacyl [Et 8 ( m -MeC 5 H 2 N)(C 5 H 3 N)(C 4 H 2 N) 2 V{η 2 -C(Me) NBu t }], 12, while in the case of CO, the intermediate η 2 -acyl, behaving as a nucleophilic carbenoid, reacted preferentially with the pyridine α-position, leading to [Et 8 ( m -MeC 5 H 3 N)μ(O−CMe)(C 4 H 2 N)}(C 4 H 2 N)(C 5 H 3 N)V], 11 . The proposed structures were supported by the X-ray analysis of 5, 6, 8, 9, and 11 .