Porphyrin dimers, osmium

Alkyl and aryl systems - As already mentioned in Sect. 3.2, dialkyl ruthenium and osmium porphyrins have been synthesized according to Eq. (22) by the reaction of metalloporphyrin dianions [M(P)]2 with alkyl iodides [223, 260, 261,307]. These dianions have been obtained by reduction of porphyrin dimers [M(P)]2. 

Sanders went on to synthesise a second generation of porphyrin hosts using guest amine-type molecules as templates. This enabled cyclic porphyrin dimers and trimers to be prepared. The trimer recognises and binds large polyoxometalate anionic clusters (e.g. PWj2O40 ) and anionic metal-carbonyl clusters containing osmium and carbon (e.g. OSioC(CO)24 -).-2 ... 

Imamura (11,20,21) synthesized several similar perpendicular dimers exploiting axial coordination of the 4-pyridyl free-base porphyrin to Ru(II)CO (3) and Os(II)CO (4) porphyrins (Fig. 1). The pyridine-ruthenium and pyridine-osmium interactions are much stronger than the pyridine-zinc interaction, and the complexes are perfectly stable in solution and can be isolated by precipitation. One of the ruthenium dimers was characterized by FAB-MS (11). Complexation is accompanied by characteristic changes in JH NMR chemical shift, indicating... 

A number of /.t-oxo-osmium(IV) porphyrin complexes have been prepared by aerial oxidation of [Os OEP)(CO)(MeOH)] in the presence 2,3-dimethylindole in CH2Cl2. " Cyclic voltammetric studies show that [0s2(0)(0EP)2(0Me)2] can undergo reduction to give an Os —O—Os dimer. The X-ray crystal structure of [0s(0EP)(0Me)]2( -0) shows a linear Os—O—Os backbone with Os—O and Os—OCH3 distances of 1.808 A and 1.997 A, respectively. 

Carbene and silylene complexes - Carbene complexes of ruthenium [312] and osmium [313] porphyrins were formed from the neutral dimers [M(P)]2 with diazoalkanes (Eq. 26). 

Double bonded ruthenium and osmium homodimers have been synthesized by Coil-man . These two metals are inserted into the porphyrin free base by using the corresponding metal chlorocarbonyl dimer [MCl2(CO)3]2- Irradiation of the resulting carbonyl metal(II) porphyrin irradiated in pyridine solutions yields the bis(pyridine) metal(II) porphyrin and leads to the expected dimers by heating under vacuum. This is shown in Scheme 16. 

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