Co> 8 PPh

According to the 18-electron rule, a valence electron count of 120 would be required for clusters with a cubic shape and this condition is fulfilled by e. g. [Ni8(CO)8(PPh)6]. [20] The aforementioned compounds, however, often display appreciable deviations from this criterion if PPhj and Q are considered as 2e donors and jU4-PPh as a 4e donor, then 2 and 3 contain 116 and 112 valence electrons respectively. 

For example, with the Co-I-PPh catalyst, methyl acetate reacts with synthesis gas to form ethyl acetate. All of the primary and secondary alcohols tested (C thru C ) decompose during long-term operation. The major decomposition products include aldehydes, alkyl iodides, and ethers. Ketones are readily hydrogenated and the resulting alcohols decompose. Good solvents in terms of stability are diphenyl ether and alkanes. The acetaldehyde rate is somewhat low (1.8 M/hr) in diphenyl ether, and the selectivity is low in alkanes. In addition, these solvents do not have good solubility properties, especially in product refining. 

L = P(OPh)3 and PPh(OMe)2, the tetra-substituted RuPt2 species RuPt2-(ji-CO)3(CO)(L)4 (69) are also observed (37). With the reagent Pt(dppe)2, phosphine transfer between Pt and Ru does not occur, and the cluster Ru2Pt(CO)8(dppe) (70), structurally analogous to the Fe-Pt species 50, is obtained (57). 

Fig. 25. Arrangements of the Au atoms in the clusters [Au3Ru3(M3-COMe)(CO)9-(PPhsU [AusRu4(Mj-H)(CO)12(PPh,),]p [Au3CoRu3(CO)12(PPh3)3], and [Au3Ru3-(M3-C12H]5)(CO)8(PPh3)3].

The trimetallic complex [Fe3(CO)8(p-PPh)2(PF3)] has been obtained from the corresponding [Fe3(CO)8(p-PPh)2(MeCN)J compound by displacement of MeCN (method G). The structure, which is based on a square-pyramidal array of three iron and two phosphorus atoms, consists of isomers whose interconversion has been studied by variable-temperature 19F and 31P NMR spectroscopy. A trimetallic PF3 complex containing mercury bonded to two metals results from the reactions... 

Clusters, particularly those described in Section 2.2 as orbitally rich, can act as Lewis acids. Addition of a Lewis base formally adds two electrons to the cluster bonding system. For some clusters, this causes an opening of the cluster, for example, closo to nido interconversion of B3HgMn(CO)3 and B3Fl8Mn(CO)4 by the addition and loss of CO (equation 7). If the cluster is formally unsaturated with respect to the electron counting mles, no change in the core structure takes place, for example, the interconversion of Fe4(CO)n(PPh)2 and Fe4(CO)i2(PPh)2 (equation 8). The base pair may be supplied by a conventional Lewis base (equation 7 or 8), but also can come from bond pairs, for example, H2 (equation 9). The latter is equivalent to oxidative addition in mononuclear... 

---