Metalloporphyrin, diamagnetic

Reactivity of compounds 1 and 2c with O2 is remarkably different from that of 5c, 5cCo, and 8 (Fig. 18.18). Metalloporphyrin 2c binds O2 reversibly at room temperature under anhydrous conditions to produce a diamagnetic ferric-superoxo/Cu adduct as demonstrated by resonance Raman spectroscopy using 2 and 2... 

The complex [Rh(TPP)(C02Et)] (reaction 42) is diamagnetic and monomeric in dichloromethane.195 The presence of an ethoxycarbonyl ligand was supported by the strong carbonyl stretch at 1700 cm-1, and the regeneration of [Rh(TPP)Cl(CO)] and ethanol via treatment with HC1. Related metalloporphyrins of the type [RhL-(Me2NH)2] (L = TPP or etioporphyrin) have been synthesized, and their structures... 

The phosphorescence of diamagnetic metalloporphyrins can be easily observed at 77 K. This is consistent with slower radiationless rates, and hence with the absence of metastable cis NH intermediates, but the heavy-atom effect exerted by the central metal ion can also contribute to enhance the phosphorescence rate. For example, the phosphorescence lifetimes in the series MgTPP, ZnTPP, and PdTPP decrease in the order 45, 26, and... 

The absorption spectrum of a diamagnetic metalloporphyrin consists of two electronic transitions, the Q-band (or a-band) in the region 550-600 nm, of lower intensity, corresponding to the mixture of one-electron transitions that involve partial cancallation of the dipole moments, and the other, the B-band (or Soret band), between —380 and 450 nm, of high intensity, which comprises the one-electron transition... 

Scm. Only the Scandium111 complex of OEP has been reported [Buckler (19)]. It is diamagnetic and produces a normal electronic spectrum [Sc OEP(OAc), 574 (16,600), 538 (12,300), 406 (332,000)]. This complex is interesting because it is the only metalloporphyrin, with a higher... 

Diamagnetic n dianions have also been obtained by reduction in aprotic solvents and surprisingly produce an electronic spectrum which resembles the normal spectra of metalloporphyrins [Closs (35), Peychal-Heiling (147, 148)]. 

Sflver(III).—To date the only reported Ag complexes are guanidine derivatives. However, oxidation of the known Ag octaethylporphinato-species with Fe( 104)3 in CHCl3-MeOH solution has yielded the corresponding Ag metalloporphyrin. The crystalline product is diamagnetic, as expected for a compound. In both this complex and previous guanidine species the extraordinary stabilization of the central d ion arises from the square-planar co-ordination to four N atoms. 

Most o-bonded alkyl (or aryl) metalloporphyrins exhibit typical H NMR features of diamagnetic metalloporphyrins. The o-alkyl (or aryl) iron(III) complexes have characteristic spectra of paramagnetic species. In addition, the NMR data for some o-bonded complexes correlate with the UV-visible data. The presence of an alkyl or aryl group coordinated to the metal is demonstrated by the appearance of a signal at very high fields. 

The isolation of a diamagnetic bridging methylene complex [(OEP-N-yx-CH2) Ru(CH3)](BF4) from decomposition of [(OEP - N - CH3)Ru(CH3)](BE4) was also possible. This complex has been characterized by H NMR and partially by an X-ray structure [145]. Unfortunately, reduction of this complex did not result in formation of an axial methylene carbene complex as was postulated by James and Dolphin [146]. Although M = CH2 species have been prepared [147,148], similar metalloporphyrin complexes are not yet known. Ruthenium carbene complexes which are involved in catalytic reactions will be discussed below. 

---