Electrophilic addition to ligands

Nucleophilic or electrophilic addition to ligands, promoted by their coordination (see above), are the most typical and most studied reactions however, other kinds of reactivity can be illustrated. 

The effect of metal basicity on the mode of reactivity of the metal-carbon bond in carbene complexes toward electrophilic and nucleophilic reagents was emphasized in Section II above. Reactivity studies of alkylidene ligands in d8 and d6 Ru, Os, and Ir complexes reinforce the notion that electrophilic additions to electron-rich compounds and nucleophilic additions to electron-deficient compounds are the expected patterns. Notable exceptions include addition of CO and CNR to the osmium methylene complex 47. These latter reactions can be interpreted in terms of non-innocent participation of the nitrosyl ligand. 

Exposure of alkenes to a combination of 4 and trimethylsilyl isothiocyanate leads to the formation of 1,2-dithiocyanates [Eq. (8)] [28]. The reaction involves the formation of bis(thiocyanato)-A3-iodane by a ligand exchange. The decomposition of this iodane leads to the formation of thiocyanogen, which in turn undergoes the anti electrophilic addition to olefins. 

Recent structural and spectroscopic investigations of organometallic complexes bonding two carbons of an allenic ligand to one rhodium 50 72> 87,95) or platinum atom 58,87,98,132) may have some pertinence to possible bridged intermediates proposed for various electrophilic additions to allenes, and the cr-iron-jr-iron complexes derived from allene and diiron... 

Other hand, electrophilic addition to thiocarbonyl ligands is a well-established method for the synthesis of thiocarbyne complexes (5). Doyle and Angelici synthesized the cationic thiocarbyne complex 42 according to Eq. 

Lewis acid employed. The methyl abstraction occurs using fHCgFsL to give associated ion pair 353, whereas the use of A1(C6Fs)3 effects electrophilic addition to the methylene carbon on the enamide ligand backbone to give zwitterionic complex 354. The ion-paired complexes 353 are inactive for ethylene polymerization, but the zwitterionic complex 354, the remotely activated complex, rapidly consumes ethylene to form polyethylene. 

The Mo-Sx bonds (x = 1, 2, 4) within the Mo(OXSx) units react readily with SO2 to give various products that contain thiosulfite, thiosulfate, sulfite, or sulfate ligands (Tables V and VI). These reactions are best described as electrophilic additions to the Mo-S bond and in many instances may be subject to the effects of the spectator Mo=0 group (see Section III,B). 

Electrophilic addition to the alkyne ligand in ReCp (CO)2 ( -RC=CR) complexes leads to 1-metallacyclopropene cations similar to (80). These undergo a number of structural rearrangements eventually ending up in ReCp (CO)2( 7 -allyl) complexes. ... 

Electrophilic addition to the sulfur atom of terminal thiocarbonyl ligands is a well-established route to thiocarbyne complexes of Group VI metals [2, 18, 19]. A requirement for the success of this approach is that the thiocarbonyl ligand be bound to a very electron-rich metal centre, preferably in an anionic complex. A methyltellurocarbyne complex of tungsten, [L(CO)2W=CTeMe]... 

In many cases, complexes containing bridging carbyne ligands are formed via electrophilic addition to the oxygen atom of coordinated carbonyl group or to the carbon atom of carbide clusters [reactions (3.71)-(3.83), Section 3.10]. 

As a zero-electron reagent, an electrophile such as H" " or Me can attack the ligand, or the M-L bonds, or the metal—even in an 18e complex. Particularly in the case of the proton, initial attack may occur at one site, followed by rearrangement with transfer to a second site, so the location of the electrophile in the final product may be misleading. Electrophilic addition to metal complexes can therefore be mechanistically complexit is also less easily controllable and less often used than nucleophilic addition. 

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