Germanium porphyrins complexes

Three publications deal with the synthesis of p-oxo-linked silicon phthalocyanine and porphyrin derivatives. The stepwise syntheses of p-oxo-linked hetero-chromophore arrays containing phthalocyanine, porphyrin, and sub phthalocyanine silicon and germanium complexes have been described [306, 307]. The p-oxo... 

Germanium(IV) forms well-defined porphyrin complexes, but they have not been accorded much... 

TABLE 12. Reduction potentials of porphyrin-iron carbonyl complexes of germanium and tin in CH2CI2 with TBA(PF<5), 0.1 M, on Au electrodes vs SCEa... 

The electrosynthesis of metalloporphyrins which contain a metal-carbon a-bond is reviewed in this paper. The electron transfer mechanisms of a-bonded rhodium, cobalt, germanium, and silicon porphyrin complexes were also determined on the basis of voltammetric measurements and controlled-potential electrooxidation/reduction. The four described electrochemical systems demonstrate the versatility and selectivity of electrochemical methods for the synthesis and characterization of metal-carbon o-bonded metalloporphyrins. The reactions between rhodium and cobalt metalloporphyrins and the commonly used CH2CI2 is also discussed. 

Germanium Porphyrins. The electrosynthesis of a-bonded mono-alkyl or mono-aryl germanium porphyrins involves the conversion of (P)Ge(R)2 to (P)Ge(R)X where X is an anionic ligand. A standard Grignard reaction between (P)Ge(Cl)2 and RMgX leads to the o-bonded bis-alkyl or bis-aryl complexes, (P)Gp(R)2. These complexes were initially synthesized as lH IWR shift reagents(28,29). However, almost no reactivity of these species was reported until several years later when it was shown that the... 

The range of organo-silicon, germanium, tin, and lead porphyrin complexes reported to date are given in Table Some mono- and dialkyltin... 

Ge(TPP)R2, Ge(TPP)(Fc)Ph, and Ge(TPP)Fc2) the spectrum after 2 /us was consistent with a triplet excited state, although this decayed much faster for the fer-rocenyl complexes. Addition of ferrocene to Ge(TPP)R2 also quenches triplet lifetimes. A similar situation was observed for the indium complexes In(Por)R, and the triplet-state quenching was attributed to an energy transfer process from the excited-state triplet to ferrocene. In the case of the germanium porphyrins, the longer-lived triplet state in Ge(TPP)R2 is responsible for the Ge—C bond homolysis, and both inter- and intramolecular quenching by ferrocene is observed. 

The stability of the germanium and silicon porphyrin alkylperoxide complexes contrasts with the lability of the corresponding iron porphyrin alkylperoxide complexes. For example, Fe(Por)(OOEt) was formed from the reaction of Fe(Por)Et with O2 and has been characterized only by spectroscopy as it decomposes to Fe(Por)OH and CH3CHO above —80°C. The key to the difference in stability is likely to be the availability of higher oxidation states in the iron porphyrins as... 

Por )=0 intermediates. Many metalloporphyrin complexes are bleached by peroxides, but the germanium porphyrins remain intact even in the presence of excess alkylhydroperoxide. This suggests that high oxidation state intermediates... 

The lack of adequate experimental data on chelates of germanium, boron, titanium, and vanadium prevents a similar comparison for these elements however, their high ionic potentials do indicate that they should form stable chelates. Vanadium does occur naturally in the very stable vanadium porphyrin complex. For similar reasons, molybdenum and tin are not discussed further. 

TABLE 84. Selected bond distances and angles for phyrazine complexes of germanium and tin some porphyrin, phthalocyanine and por-... 

Some new lanthanide porphyrin complexes of general formula Ln(iii)TAP(/i-diketonate), where TAP = tetraarylporphine, have been prepared (468,469) and their shift reagent capabilities assessed. The complexes of the early lanthanides (Pr, Nd, Sm, Eu) induce very small shifts whereas the complexes of Tb, Dy, and Ho produce quite large low frequency shifts in y-picoline. Analogous shift reagents based on silicon, germanium, low-spin iron, (517, 518) and cobalt (519) have been reported. 

In the absence of light, diorgano germanium porphyrin complexes are stable but have long been known to react with oxygen. The products of this oxidation process have been formulated speculatively as germanium-bound peroxyalkyl complexes " an assignment confirmed by the report of the crystal structure of (TPP)Ge(02R)2 (R = Et, Bu ). ... 

Porphyrin complexes, (porph)Ge and (porph)GeCl2, are known for the +2 and +4 oxidation states. Reaction of phthalocyanine with GeCl4 in quinoline gives the highly stable complex (phthalo)GeCl2 in which the two Cl atoms are necessarily trans. It sublimes without decomposition at 450 °C. Recently, the crystal structure of bis(acetato)(/He50-tetraphenylporphyrinato) germanium (IV), Ge (tpp) (0 Ac) 2... 

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