Osmium alkyne-substituted clusters

Of special relevance to the investigation of alkyne-substituted clusters is the observation of a low-field resonance, generally in the range —1 to + 1.5t, for a proton attached to a carbon atom which is either a or n bonded to the metals. Values of the chemical shift for this signal for 23 tri- and tetranuclear osmium clusters were presented by... 

The simplest bonding mode found in trinuclear hydrocarbon-substituted clusters of osmium and ruthenium is the 7 -vinyl coordination in which one carbon center is formally cr-bound to one metal atom in the triangular core and the alkene/alkyne unit is formally vr-bound to an adjacent metal, so that the ligand donates three electrons to the cluster. Vinyl complexes are generally prepared by alkyne insertion into [Os3(/U-H)2(GO)io] or by the oxidative addition of an alkene to [Os3(GO)io(NGMe)2l or [Os3(GO)i2], and may be considered to be intermediates in reactions to other hydrocarbon-containing cluster products. A list of reported 77 -vinyl- and the related 77 -acetylide-substituted complexes is presented in Table 1. The related 77 -vinylidene-substituted clusters, in which one carbon atom of the ligand is cr-bonded to two metal centers and the alkene unit is formally vr-bound to the third metal center, can be prepared by the thermal conversion of an 77 -vinyl cluster (Scheme 3). The 77 -vinylidene formally donates four electrons to the cluster core. 

The addition of a phosphine group to the organic fragment has been studied in some detail in compounds with cluster-bound vinyl ligands. The zwitterionic adducts which are formed can then undergo nucleophilic addition reactions (411, 461, 462). A reaction of this type also occurs with amine-substituted alkynes coordinated to osmium and ruthenium complexes (117). 

Reactions of ruthenium and osmium cluster carbonyls with heteroatom-substituted and functionalized alkynes (metallocycles) 00IZV1. 

Alternative indirect methods have been used in the synthesis of (3,3-dimethylcyclopen-tyne)Cp2Zr(PMe3> [52] and (cyclohexyne)[CpMo(CO)2]2 [53]. The smallest cycloalkyne stabilized by complexation is cyclobutyne, incorporated by Adams into tri- and tetrametallic ruthenium and osmium clusters as a P3-ligand 30 using 1-Br and -SPh substituted cyclobutene precursors (Scheme 4-11) [54]. Liberation of these strained alkynes from their metallic bondage has not been reported but some have been shown to be reactive towards insertion of unsaturated substrates, as illustrated in Scheme 4-12 with the Zr-cyclohexyne derivative 31 [55]. 

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