Alkynes clusters

The Cg ring in 172 has undergone dehydrogenation to form a cyclooctyne ligand that coordinates to a cluster face in the analogous bonding mode to that observed in the alkyne clusters 75-82. 

Reaction of the phosphaalkyne complex Pt(dppe)(f/2-P=CtBu) with either Fe2(CO)9 or Fe3(CO)12 affords high yields of the red cluster Fe2Pt-(A<3-( /2--L)-P=OBu)(CO)6(dppe) (55), which contains a novel /i3-(f/2-1) phosphaalkyne ligand (140,140a). This bonding mode is similar to the alkyne coordination observed in some alkyne clusters, such as Fe3(/i3-(f/2- )-PhC=CPh)(CO)9 (141), and the low value of J(195Pt-31P) = 128 Hz indicates that the P atom of the phosphaalkyne is not coordinated to the Pt... 

Tetranuclear alkyne clusters involving cobalt can adopt a variety of geometries. Reductive dehalogenation of ( Bu)(PhC=C)PCI by [Co2(CO)8] affords 39 in which a chain of four cobalt centers is supported by the functionalized alkyne, as shown in Eq, (15).146-147... 

The majority of tetranuclear alkyne clusters containing cobalt adopt butterfly geometries.151152 This is illustrated by the molecular structure of [Co4(/L4-r72-HC2H)(/L-CO)2(CO)8] (Fig. 16), which can be prepared by the... 

A variety of cobalt-containing mixed-metal butterfly alkyne clusters are known and will be described in approximate order of decreasing cobalt content. The dehalogenation of [RuCl2(Ph2PC=CBut)(p-cymene)] by [Co2(CO)8] followed by protonation affords fRuCo3(/x4-t -Bu QH)(/i-... 

The study of polynuclear cobalt-alkyne clusters has provided insight into the coordination, protection, and activation of the carbon-carbon triple bond. It is possible to draw analogies between alkynes coordinated to molecular species and those to surfaces. 

The area of alkyne cluster chemistry has been the subject of two previous review articles. The first is concerned largely with alkyne-cobalt chemistry (16), while the second provides a comprehensive, systematic review of alkyne-substituted homo- and heterome-tallic carbonyl clusters of the iron, cobalt, and nickel triads (17). This latter review covers the literature up to the end of 1981. The present work does not set out to be fully comprehensive, but rather reflects the authors own interests in the subject. A number of key examples are... 

The best example of chemical activation in cluster chemistry is the use of Me3NO which results in CO replacement under mild conditions (129). In an interesting example taken from alkyne-cluster chemistry, when Me3NO is used dry a monosubstituted cluster derivative is obtained, but with damp Me3NO a tetranuclear vinylidene complex is isolated (130, 131), as illustrated in Eqs. (4) and (5), respectively. 

Fig. 11. Alkyne clusters for which photoelectron spectroscopic data are available.

If these results are transferable to other alkyne cluster systems it appears that, in general, the ideas on cluster alkyne bonding developed over the last two decades from the work of Dahl and co-workers (26) are correct. 

Mixtures of alkynes and cyclopentadiene with Co atoms yield a variety of air-stable organometallics . These result from hydrogen transfer from cyclopentadiene, dimerization or trimerization of alkyne, clustering of Co atoms and simple addition. The nature of the products implies that a variety of reactive intermediates must be formed en route. Table 1 shows the major products that are formed. 

Hydrogenation of alkynes is catalyzed by alkyne cluster complexes Fe3(GO)9(RG2R ). In addition to hydrogenation, formation of metallacyclic byproducts such as Fe3(GO)8 (RG2R )(RG2R ) was observed, resulting in decreased catalytic activity. 

Historically speaking, the most studied reactions are those involving the formation of [M3( 3-CR)2Cp3] clusters where M = Co, Rh, Ir. This can be achieved from mononuclear units such as CpM(CO)2 or from preformed alkyne clusters M3(CO)(/ 3-C2R2)Cp3 in each case the scission step occurs at a trinuclear metal... 

Surprisingly, in several experiments carried out under a variety of conditions, formation of the / cyclohexyne derivative 19b from cyclohexene and la was never observed. This complex was prepared from cyclohexene with f(C5H5)2Co]/potassium. Reactions with this reagent usually do not proceed cleanly and generate a large amount of insoluble by-products. Nevertheless, separation of the products is usually less laborious, due to the absence of 3 and 4. As a second type of product, the tetranuclear /r4-alkyne cluster complexes 21 were formed in very low yield from the corresponding cycloalkenes and [(C5H5)2Co]/K. ° ... 

The tetranuclear alkyne clusters 21 have a rigid pseudo-octahedral C04C2 core. In contrast, fluxional behavior is displayed by the trinuclear complexes 15, 19, and 21. In these complexes, the //3-alkyne undergoes a windscreen-wiper type walk on the C03 frame. This is accompanied by a movement of the /12-hydrido ligand... 

Synthesis of Pd-alkyne clusters Pt carbonyl clusters Pt carbonyl cluster anions Triangular dppm-bridged Pt clusters Pt isocyanide clusters Polymetallic alkene complexes of Pt Polymetallic alkyne complexes of Pt... 

In addition, another case of affinity marking was found when a ferrocenyl group was attached at the 17a-position of estradiol. This metallocene is also commonly used to stabilize carbenium ions in the a-position while preserving good reactivity. The level of inactivation is comparable with that found with the small dicobalt-alkyne cluster (80%) [123]. 

The reaction of the symmetrical 1,3-diyne RCSCC5CR (R = Me, Et, Ph, Bu SiMe3) with [Os3(CO)io(MeCN)2] afforded [Os3(p-CO)(CO)9(lt3- n -PCCCCR)]. No exchange between uncoordinated and lis-Ti -coordinated alkyne moieties was observed. The synthesis, leactiviQr and electrochemical behaviour of triosmium alkyne clusters was reported and the X-ray crystal structure of [Os3(CO)8(p.3- n2-RCCR)(Ph2PCH2PPh2)] (R = Me, CF3) was determined. The synthesis, reactions and X-ray crystal structure of [Os3(CO)9(ii3- n2-MiCCPh)(ji-C(OMe)Ph)] have been reported. ... 

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