Osmium complexes carbon donors

The crystal structure of yellow metallacyclic-osmium(iv) complex 9 was also reported <20030M414>. The distribution of ligands around the osmium atom can be described as a four-legged piano-stool geometry with the carbon atom C-5 of the metallated phenyl group disposed transoid to the hydride ligand. The bidentate carbon donor... 

This hydride-dihydrogen complex allows the access of methyl propiolate and 1,1-diphenyl-2-propyn-l-ol into the osmium atom, and the carbon-carbon coupling between the resulting carbon-donor ligands [75] (Scheme 50). 

Intermediate Cases In the Os complex 11.12, Roper has a carbene with character intermediate between the Fischer and Schrock extremes because it reacts both with electrophiles [e.g., SO2 (Eq. 11.36) or H ] and with nucleophiles [e.g., CO (Eq. 11.37) or CNR]. This is reasonable based on our bonding picture. The osmium has ir-donor (Cl) as well as ir-acceptor (NO) ligands, the metal is in an intermediate oxidation state [Os(II) if we count the carbene as L, Os(IV) if X2], and the carbene carbon has non-ir-donor substituents (H). 

Complexes with other Carbon-donor Ligands. The naphthyl hydrido Complexes of the type [MH(CioH,)(MejP CHg CHa-PMe2)2] (46), where M = Ru or Os , are isomorphous and isostructural. They are octahedral and contain a naphthyl ligand o-bonded to the metal atom and in a position cis to the hydrido hydrogen. The respective Ru-C, Os-C, and Ru-H distances are 2.16(1), 2.13(2), and 1.7 A in the osmium compound the hydrido hydrogen atom has not been located. The M-P distances range... 

Instead of adding 4-substituted pyridine ligands trans to the carbene ligand, the complexes Os(CHR XTTP) (R = SiMe3, C02Et) add these donors to the carbene carbon atom with formation of an ylide species. This reaction is not observed for Os(CR2XTTP) with R = Ph [313c]. Nevertheless, the diphenylcar-bene or trimethylsilylmethylene osmium porphyrins crystallize as Os(CRR )-(TTP)THF with a THF molecule in trans position. 

The osmium hydride (CO)ioOs3H2 reacts with isonitriles to give monosubstituted products (CO)io(RNC)Os3H(/2-H), which react further via insertion to give (CO)io(ju-ri -RNCH))(/i-H)Os3. In weak donor solvents, hydride attacks at the carbon whereas strong donor solvents result in hydride attack at nitrogen. The latter reaction results from deprotonation of the hydride complex, followed by reprotonation at nitrogen. 

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