Osmium porphyrin preparation

The most significant and widely studied reactivity of the ruthenium and osmium porphyrin carbene complexes is their role in catalyzing both the decomposition of diazoesters to produce alkenes and the cyclopropanation of alkenes by diazoesters. Ethyl diazoacetate is used to prepare the carbene complex 0s(TTP)(=CHC02Et)... 

The first silylene complexes of osmium porphyrin, (TTP)Os=SiR2-THF, were prepared by treating K2[Os(TTP)] with Cl2SiR2 or the reaction of [Os(TTP)]2 with hexamethylsilacyclopropane (116). The molecular structure of (TTP)Os=SiEt2-2THF is stabilized by coordination of THF to the silicon, as shown by X-ray crystallography (Fig. 5). The measured Os—Si distance of 2.325(8) A is the shortest ever reported (116). 

Che and coworkers [152] were able to isolate and characterize a pure bis-carbene (TPFPP)Os(CPh2)2 (Fig. 3). The bis-carbene species represents the first structurally characterized fra s-bis-carbene metal complex whose carbene groups are not stabilized by heteroatoms. The related pentacoor-dinated mono-carbene complex was also prepared and characterized by an X-ray structure. A comparison of the reactivity of these complexes with olefins suggests that the bis-carbene species acts as an intermediate in cy-clopropanation. Thus, the inertness of the mono-carbene complex towards stoichiometric styrene cyclopropanation and the observation of an efficient cyclopropanation of styrene in the presence of the bis-carbene complex as a catalyst support this suggestion [152]. A recent X-ray structure determination for (TPFPP)Os(CPh2)(MeIm) revealed an Os = C distance of 1.902(3) A (Table 3) [141]. Recently, Che and coworkers [153] and Miyamoto and coworkers [154] reported oxo-bridged carbene complexes of osmium porphyrins (see Table 3). These compounds are rare examples of oxo-binuclear carbene complexes. 

Os(CO)4]2(p-CHMe) prepared by reaction of MeCH(OTf)2 on Na2lOs2(CO)gl.34 The dioxo-osmium porphyrins [Os(porX)2]> where por = octaethyl- or tetraphenyl-porphyrin, react with thionyl... 

Diazoalkanes are u.seful is precursors to ruthenium and osmium alkylidene porphyrin complexes, and have also been investigated in iron porphyrin chemistry. In an attempt to prepare iron porphyrin carbene complexes containing an oxygen atom on the /(-carbon atom of the carbene, the reaction of the diazoketone PhC(0)C(Ni)CH3 with Fe(TpCIPP) was undertaken. A low spin, diamagnetic carbene complex formulated as Fe(TpCIPP)(=C(CH3)C(0)Ph) was identified by U V-visible and fI NMR spectroscopy and elemental analysis. Addition of CF3CO2H to this rapidly produced the protonated N-alkyl porphyrin, and Bit oxidation in the presence of sodium dithionitc gave the iron(II) N-alkyl porphyrin, both reactions evidence for Fe-to-N migration processes. ... 

The first ruthenium porphyrin alkyls to be reported were prepared from the zerovalent dianion, [Ru(Por)] with iodomethane or iodocthane, giving the ruthe-nium(lV) dialkyl complexes Ru(Por)Me2 or Ru(Por)Et2 (Por = OEP, TTP). Alternatively, the Ru(lV) precursors Ru(Por)X2 react with MeLi or ArLi to produce Ru(Por)Mc2 or Ru(Por)Ar2 (Ar = / -C(,H4X where X = H, Me, OMe, F or Cl) 147-149 The osmium analogues can be prepared by both methods, and Os(Por)R2 where R = Me, Ph and CH2SiMe2 have been reported.Some representative structures are shown in Fig. 5, and the preparation and interconversion of ruthenium porphyrin alkyl and aryl complexes are shown in Scheme 10. 

A ruthenium porphyrin hydride complex was lirst prepared by protonation of the dianion, [Ru(TTP) in THF using benzoic acid or water as the proton source. The diamagnetic complex, formulated as the anionic Ru(If) hydride Ru(TTP)(H )(THF)l , showed by H NMR spectroscopy that the two faces of the porphyrin were not equivalent, and the hydride resonance appeared dramatically shifted upheld to —57.04 ppm. The hydride ligand in the osmium analogue resonates at —66.06 ppm. Reaction of [Ru(TTP)(H)(THF)j with excess benzoic-acid led to loss of the hydride ligand and formation of Ru(TTP)(THF)2. 

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. 

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 ... 

A series of osmium meso-tetra-p-tolyl-porphyrin carbene complexes, (TTP) Os(CRR )(R,R = p-tolyl R = H, R = SiMe3 or C02Et) were first prepared by Woo and Smith [ 149] by treating [(TTP)20s] with the appropriate diazoalkanes (Eq. 19). As an indirect method, one of these carbene complexes can also be prepared by reaction of the silylene complex (TTP)Os(SiEt2)(THF) (150) with di-p-tolyl diazomethane. 

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