The porphyrinogen-porphodimethene relationship leading to novel synthetic methodologies focused on the modification and functionalization of the porphyrinogen and porphodimethene skeletons

The general synthetic methods presented in this paper make available, on a preparative scale, unprecedented porphyrinogen-derived skeletons, including their functionalization at the meso positions. The stepwise dealkylation o f meso-octaalkylporphyrinogen R8N4H4 [R = Et, 1; R = Bu-n, 2] was chemicall y, mechanistically, and structurally followed until the formation of porpho methene and porphodimethene derivatives 5-13, obtained with a sequential us e of SnCl4. In particular, the porphodimethene derivative [(Et6N4)SnCl2], 9 , was reductively transmetalated using Li metal to Et6N4Li2. 14, subsequent ly hydrolyzed to Et6N4H2, 15. The porphodimethene-nickel complex [(Et6N4)Ni ], 16, was used for studying the reactivity and the ligand modification of the porphodimethene skeleton. The reactivity of 16 toward nucleophiles led to otherwise inaccessible meso-substituted-meso-functionalized porphyrinoge ns [(Et6N4R2)NiLi2], [R = H, 18; R = Bu-n, 19; R = CH2CN, 20], thus exempli fying a general methodology to meso-functionalized porphyrinogens. In addit ion, when [NMe2](-) was used as the nucleophile, 16 was converted into mono - and bis-vinylideneporphyrinogen derivatives [{Et-4(=CHMe)N-4}NiLi] 21, an d [{Et-5(=CHMe)(2)N-4}NiLi2], 22, through the intermediacy of meso-(dimethy lamino)-porphyrinogens undergoing an alpha-II elimination from the meso pos itions. Such intermediates were isolated and characterized in the stepwise reaction of 14 with LiNMe2 leading to [{Et-6(NMe2)(2)N-4}Li-4], 23, and [{E t-5(NMe2)(=CHMe)N-4}Li-4], 25. Both compounds, as a function of the reactio n solvent, undergo the thermal elimination of HNMe2 with the formation of [ {Et-4(=CHMe)(2)N-4}Li-4], 24, which is then protonated to [{Et-4(=CHMe)(2)N -4}H-4], 27. Transmetalation from 23 to 24 can be used as the methodology f or the synthesis of a remarkable variety of meso-substituted and functional ized porphyrinogen complexes. The deprotonation of 16 is reversible, theref ore 22 and 23 can be protonated back to their starting materials. We took a dvantage of the nucleophilicity of the vinylidene carbon in 21 and 22 fur e stablishing a general synthetic method to produce meso-functionalized porph odimethenes. This approach was exemplified with the alkylation and the benz oylation of 22 and 21 leading to [{(E4Pr2N4)-N-i)Ni], 28, [Et-4{CH(Me)(PhCO )}(2)N4Ni], 29, and [Et-5{CH(Me)(PhCO)}N4Ni], 30, respectively. Complex 21 displays a bifunctional behavior, as shown by the formation of 30, whereas in the reaction with LiBu, led to [{Et-5(Bu-n)(=CHMe)N-4}NiLi2], 31.