Chalcogen osmium

Scheme 8.20 Preparation of the five-coordinate osmium carbynes 75a,b and their reactions with chalcogens, HCI and chlorine to afford the six-coordinate carbene osmium(II) complexes 76a,b, 77a,b, and 78a,b (a R = Me, b R = Ph E = S, Se, Te)...

Electrophilic attack at carbyne complexes may ultimately place the electrophile on either the metal or the (former) carbyne carbon, the two possibilities being related in principle by a-elimination/migratory insertion processes (Figure 5.39). The reactions of the osmium carbyne complex are suggestive of an analogy with alkynes. Each of these reactions (hydro-halogenation, chlorination, chalcogen addition, metal complexation see below) have parallels in the chemistry of alkynes. 

The pattern of chemical reactions observed for these compounds clearly sets them apart from "Fischer-type" carbyne complexes of GroupVI e.g., W(hCR)X(CO)4. Whereas the "Fischer-type" complexes typically react with nucleophiles at the carbyne carbon all of the reactions observed for the five coordinate mthenium and osmium complexes, including the cationic examples, are electrophilic additions to the MsC bond. The following sections deal individually with, protonation, addition of halides of the coinage metals, addition of chlorine and chalcogens, and finally an attempted nucleophilic addition where the nucleophile is directed to a remote site on the aryl ring of the carbyne substituent. 

Finally, the stereodynamics of two mercury-containing metal clusters have been reported. The mercury-bridged osmium cluster [ (ju-H)(/i3-S) (C0)90s3 2(/i4-Hg)] exhibits variable-temperature NMR spectra which are attributed to movements of both fi-Hg and /i-H moieties at comparable rates. Mercury halides form adamantane-like anions with chalcogen bridges. The resulting structures [( i-ER)6(HgX)4] (E = S, Se, Te X = C1, Br, I) have been examined in solution by Se, Te, and Hg NMR spectroscopy. The species tend to dissociate in solution. Pyramidal inversions at Se and Te atoms are slow on the NMR time scale at reduced temperatures, but tend to become rapid at ambient temperatures. ... 

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