Isolobal analogies

Notice that the structure of Fc3(CO)i2 contains a pair of bridging carbonyls. However, in the isoclectronic Ru3fCO)i2 and Os3(CO)i2 all carbonyls are terminal.Again this implies a very small energy difference. The structure shown for Cp3Rh3fCO)3 is one of several possibilities that pass through an all-terminal CO structure. Mixed structures such as 21.37 and 21.38 also have been pre- 

The most simple, stable organic compound containing the CH2 group is ethylene. It is reasonable to expect that the compounds given by 21.40-21.43 can be 

A fascinating. series of organic compounds arc produced when the ML3 unit is replaced in polyene-MLs complexes with an isolobal analog. Consider butadiene- 

One needs to be adaptable in viewing the structures of molecules. Normally 21.74 is considered to be an acetylene coordinated to a trinuclear cluster. There 

Organic group Number of valence electrons Number of framework electrons Organometallic group 

The valence orbitals of the chain, cyclic, and cluster structures constructed from the isolobal groups also have the similar shapes. For example, the valence orbitals of Co2(CO)6 are similar to those of acetylene C2H2, the orbitals of the cyclic clusters Fe2(CO)i2 and Fe3(CO)9 are analogous to the MO s of the cyclopropane and cyclopropenium cation. Some other examples of isolobally related organic and organometallic compounds are represented by the structures 

Similarity of the orbital structure causes the similarities in the types and the mechanisms of organometallic and organic compounds constructed of isolobal fragments. 

Some typical examples will be considered below (see Sects. 6.2, 10.3). 

Woodward RB, Hoffmann R (1970) The conservation of orbital symmetry. VCH Acad Press Weinheim 

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Taking into account the isolobal analogy between RSb and 16-e ML fragments metallocycles, the complexes of type 25 may be considered as analogs of cyclo-tristibine systems. Type 26 is related to complexes with cyclo-tristibine ligands. 

Complex 27 is an isolobal analog of the manganese system 11 and like the latter exhibits rather large Si-H coupling constant of 80 Hz compared with the range... 

The compound [Ti(H)(SiXR2)(PMe3)Cp2] (99) is an isolobal analog of the ni-obocene compounds 83 with IHI, and is therefore expected to have the IHI too. By contrast, the compound [Ti(ri -H2SiPh2)(PMe3)Cp2] (20) discussed above is a stretched silane o-complex, i.e. it has an electronic structure intermediate between Ti(IV) and Ti(II). ... 

The isolobal analogy between the imido and Cp ligands makes the Cp/imido ancillary a potential platform to study the IHI (see 105 and Scheme 5). 

Schmidbaur and coworkers have prepared the pentaaurylated carbomonocation (4), an isolobal analog of CH and hexaaurylated carbodication (5), the isolobal analog of From X-ray crystallographic studies, it was shown that the... 

FABMS, 39 340-342 isolobal analogies, 39 378-381 ligand addition, elimination, and substitution reactions, 39 337-338 Mossbauer spectroscopic studies, 39 342-344... 

Further evidence comes from structural analyses of [Ph3PAuFeW(CO)9] and MeFeW(CO)9,11-12 which find Ph3PAu and Me groups, isolobal analogs to H, to be located solely on Fe. The Fe—W bond is regarded as a metallodonor-metalloacceptor interaction, Structure C.13,14... 

A theoretical approach addresses the question of alkynes bonded to PtL2 fragments in both parallel and perpendicular geometries. With each mode of alkyne coordination there is required a different coordination geometry at platinum. The authors use the isolobal analogy to calculate the electronic structures of complexes, and propose several unknown complexes to be stable.842... 

The addition of transition metal fragments ML (L = two-electron donor ligand) across formally unsaturated metal-metal or metal-carbon bonds is a well-developed synthetic route to heteronuclear clusters (1,2,11,12,27) and has received theoretical justification from Hoffmann s isolobal principle (46). The addition of a PtL2 fragment across an M=M double bond may be considered as analogous to the reaction of a carbene with an olefin, resulting in a cyclopropane. The use of isolobal analogies in the directed synthesis of heteronuclear clusters has been reviewed (11,12,27). 

In a number of ways the reactions of stable silylenes resemble those of phosphines, R3P, to which they are isolobal analogs. Examples are provided by the reactions of 59 with covalent azides. Phosphines are known to react with azides to give phosphineimines, Ph3P=NR. In similar fashion, 59 reacted with triphenylmethyl azide in THF to give the silanimine 72 as its THF complex (equation 109)148. This reaction provides a new method for synthesizing compounds containing Si=N double bonds, which have previously been made by salt elimination reactions375. 

The gold complexes were characterized by X-ray crystallography and represent isolobal analogs of L 02+. 

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