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Reduction of metal(II) tetraphenylporphyrins, where metal(II) is copper, nickel or iron, has been performed in toluene solution using cesium anthracenide as a reductant in the presence of cryptand. Crystalline salts...

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The new method for the reduction of free‐base porphyrins has been developed and crystalline {cryptand[2.2.2](Cs+)}{H2TPP·–} (1) and {cryptand[2.2.2](Cs+)}{H2T(F5Ph)P·–}·C6H5CH3 (2) salts containing porphyrin radical anions [TPP is tetraphenylporphyrin, T(F5Ph)P is tetrakis(pentafluorophenyl)porphyrin] have been obtained. The Cs+ cations partially come out of the cryptand cage in {cryptand[2.2.2](Cs+)} approaching close to negatively charged porphyrin surface. As a result, one porphyrin radical anion forms close contacts with two Cs+ cations with the Cs···P(plane) distances of 2.83–2.86 Å for 1 and 3.42 Å for 2 but another radical anion is positioned rather far from these cations. The salts have effective magnetic moments of 1.63–1.67 µB at 300 K indicating the contribution of one S = 1/2 spin per radical anion. Salt 2 shows paramagnetic behaviour indicating the preservation of H2T(F5Ph)P·– down to 2 K. Magnetic moment of 1 is preserved down 240 K and below this temperature decrease of magnetic moment is observed. This can be attributed to charge disproportionation accompanied by electron transfer between H2TPP·– with different cationic surrounding and the formation of diamagnetic H2TPP0 and H2TPP2–. This transfer is a thermally activated process with estimated energy of 200 ± 2 K. The effects of freezing of the disproportionation at low temperatures and shift of the equilibrium to paramagnetic H2TPP·– in magnetic field have been found. EPR spectra of 1 and 2 are also presented and discussed.

Metal complexes of trithiadodecaazahexaphyrin (Hhp) that contain M II 3 O clusters inside a π-extended trianionic (Hhp 3− ) macrocycle have been prepared. Studies of the magnetic properties of Ni II 3 O(Hhp) and Cu II 3 O(Hhp) reveal a diamagnetic and EPR-silent trianionic (Hhp 3− ) macrocycle and diamagnetic Ni II 3 (O 2− ) or paramagnetic Cu II 3 (O 2− ) tetracations. The positive charge of M II 3 O(Hhp) is compensated by one acetate anion {M II 3 O(Hhp)} + (CH 3 CO 2 − ). The three-electron reduction of {M II 3 O(Hhp)} + yields {cryptand 2) crystalline salts. The magnetic properties of 1 reveal the formation of Hhp 5− and the reduction of nickel(II) to the paramagnetic Ni I ion (S = 1/2), which is accompanied by the formation of the {Ni II 2 Ni I O(Hhp 5− )} 2− dianion. As a result, the magnetic moment of 1 is 1.68 μ B in the 20−220 K range, and a broad EPR signal of Ni I was observed. The Hhp 5− macrocycle has a singlet ground state, but the increase in the magnitude of the magnetic moment of 1 above 220 K is attributed to the population of the triplet excited state in Hhp 5− . The {Ni II 2 Ni I O(Hhp 5− )} 2− dianion is transferred from the doublet excited state to the quartet excited state with an energy gap of 1420 ± 50 K. Salt 1 also shows an unusually strong low-energy NIR absorption, which was observed at 1000−2200 nm. In 2, a highly reduced Hhp •6− radical hexaanion (S = 1/2) coexists with a Cu II 3 (O 2− ) cluster (S = 1/2) in the {Cu II 3 O(Hhp •6− )} 2− dianions. The dianions have a triplet ground state with antiferromagnetic exchange between two S = 1/2 spins with J = −6.4 cm −1 . The reduction of Hhp in both salts equalizes the initially alternated C−N bonds, supporting the increase in the Hhp macrocycle electron delocalization.