Bow-tie clusters

The yellow and red isomers of [Os6(CO)i6(CHNMe2)(7<4-S)(7/3-S)(//-H)2] characterized by X-ray analysis both contain seven Os-Os bonds the former is a spiked bow-tie cluster (36, see Scheme 5) and the latter a 2-atom-spiked butterfly cluster (37). 36 is partially converted to 37 by heating under reflux in octane in a CO atmosphere. 

With Nucleophiles The addition of nucleophiles adds 2e to the cluster, and so it must either rearrange or lose a 2e ligand. Equation 13.27 shows an interesting example of the reversible conversion of the trigonal bipyramidal Os5(CO)i6 to the bow tie cluster Os5(CO)i9 with CO, and Eq. 13.28 shows rearrangement of the dicapped tetrahedral Os6(CO),g to the raft cluster Os6(CO)i7L4 with P(OMe)3 (= L). In each case the addition of CO or of L, which adds 2e to the cluster, causes breakage of an Os—Os bond, which absorbs the two electrons. 

Compared to the chalcogenido clusters, very few examples of organochalcogenato clusters have been reported except for the bow-tie clusters with the Fe2(/i- R) end groups, which were discussed in the previous section. 

When 0s3(C0)j2 is heated in a sealed tube to 190 C, Os (CO)ig is formed, together with OSg, Os and OSg species (Fig. 11.11). The pentaosmium cluster 0s5(C0)jg and the anion Os5(CO)j which is derived from it by reduction possess trigonal bipyramidal structures (p.e.c. 72). This figure can be viewed either as a doso-deltahedron (14t -h 2) or as a capped tetrahedron (2 tetrahedra sharing one face p.e.c. 60 + 60 — 48). 085(00)3 reacts with carbon monoxide to form 085(00)35 which has the fascinating bow-tie arrangement of five metal atoms all lying in a plane. 

Fig. 2.17. Types of geometries in pentanuclear clusters, (a) Trigonal bipyramid (b) Square pyramid (c) Edge-bridged tetrahedron (d) Bow-tie geometry (e) Diminished pentagonal bipyramid or bridged-butterfly geometry...

Q=E bond cleavage is an alternative synthetic method for chalcogenido cluster compounds. Treatment of the thiophene-substituted thiosemicarbazone, ThGH=NGHG(=S)NH2 (Th = 2-thienyl), with Fe2(GO)9 at RT gives the carbene complex 149 together with the carbene complex 150 with the bow-tie core, 121a, and a mononuclear complex. ... 

A related pentanuclear / 3-oxo species 146 with a highly distorted bow-tie structure was isolated in low yield. " The mixed-metal clusters [Ru2Mo2(/i3-S)2(/ -SR)(/i-X)(GO)4Gp2] [X = SR, R = Et, Pf 147 or PPh2 148 ] were prepared by the treatment of 149 or 150 with Ru3(GO)i2, which involved the dealkylation of the thiol ligand at the dimolybdenum center. 

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