The Intra- and Intermolecular Oxidative Coupling of Ni(II)-meso-Octaethyl Mono(pyridine)-Tris(pyrrole) Complex Leading to C-C Bonds: Pathways to Oligomeric Porphyrinogens.
This paper reports the oxidative transformations of the unprecedented meso-octaalkyl mono(pyridine)-tris(pyrrole) macrocycle [Et(8)(C(5)H(3)N)(C(4)H(2)NH)(3)], 1, which was obtained by a homologation of the corresponding porphyrinogen, [Et(8)(C(4)H(2)NH)(4)], A. The metallation of 1 was obtained via its deprotonation with LiBu, followed by the reaction with MCl(2).thf(n)(), leading to the bimetallic complexes: [Et(8)(C(5)H(3)N)(C(4)H(2)N)(3)M{Li(thf)(2)}] [M = Fe, 3; M = Co, 4; M = Ni, 6; M = Cu, 7]. The cobalt derivative occurs also in the separated ion-pair form [Et(8)(C(5)H(3)N)(C(4)H(2)N)(3)Co](-)[{Li(thf)(4)}](+), 5. The reaction of 4 and 6 with an excess of Cp(2)FeBPh(4) led to the oxidation of the macrocycle with the formation of a cyclopropane functionality [Et(8)(C(5)H(3)N){(C(4)H(2)N)(3)(Delta)}Ni](+)BPh(4)(-), 8. The cyclopropane unit underwent reductive cleavage back to the initial macrocycle using lithium metal. The use of a Ni/Cp(2)Fe(+) 1:1 ratio allowed the identification of a dimer derived formally from the monoelectronic oxidation of the macrocycle 1, which formed a radical coupling to 9, [Et(8)(C(5)H(3)N)(C(4)H(2)N)(3)Ni](2). The same compound formed from a disproportionation redox reaction occurring between 6 and 8. The C-C bond across the two metallamacrocycles involved the beta position of the pyrrole. Deprotonation of 9 by LiBu led to a dianionic form 10 [Et(8)(C(5)H(3)N)(C(4)H(2)N)(3)Ni{Li(thf)(2)}]. The formation of the cyclopropane functionality was also achieved via the oxidation of [Et(8)(C(5)H(3)N)(C(4)H(2)N)(3)Li(3)(thf)(2)}], 2, forming [Et(8)(C(5)H(3)N){(C(4)H(2)N)(3)(Delta)}Li(thf)], 11, which was ready to be used in metallation reaction. The proposed structures were supported by X-ray analyses on 4, 7, 8, 9, and 11.
Crescenzi
Raffaella
R
Dipartimento di Chimica, Università di Parma, I-43100 Parma, Italy.
Solari
Euro
E
Floriani
Carlo
C
Chiesi-Villa
Angiola
A
Rizzoli
Corrado
C