Isocyanide ligands electrophilic addition

Addition of an electrophile (see Electrophile) to metal-bound cyanides will often form an isocyanide ligand (see Electrophile), -CsN-R. For example, the compound [Fe P(OMe)3 (NO)2(j7 -C3H4R)], which is a source of the allyl cation ( -C3H4R)+, reacts with trans-[Mn(CN)(CO)(dppm)2] to alkylate the cyanide, giving an allyl isocyanide ligand (equation 8). The tungsten alkyne... 

The parent TMM complex (190 R = H) undergoes photochemical ligand substitution with trifluorophosphine or trimethylamine Al-oxide assisted substitution with tertiary phosphines or t-butyl isocyanide (Scheme 5A) Trimethylamine A-oxide assisted substitution using isoprene as the incoming ligand results in C-C bond formation to afford the bis-TT-allyl complex (197). An intramolecular version of this reaction is also known.The parent complex (190 R = H) reacts with electrophiles. Addition of HCl or Br2 gives the methallyl complexes (192) and (198), respectively. Tetrafluoroethylene adds across the Fe bond to afford (199) under photochemical conditions. Complex (190) undergoes Friedel-Crafts-type acylation with... 

Alkylidenes have been prepared by reduction of alkyli-dynes, by C H oxidative addition from alkyls, and by treatment of unsaturated metal clusters with diazoalkanes. In most instances, the alkylidene adopts a /r2-h coordination mode. However, alkylidenes with heteroatom substituents may also be found in terminal coordination modes. The latter are typically prepared by the Fischer-type carbene route (see Fischer-type Carbene Complexes) (sequential addition of nucleophilic and electrophilic alkylating agents to carbonyl or isocyanide ligands), by condensation of metal fragments with mono- or dimetallic carbene complexes, or by C-H activation of alkylamines. These heteroatom substituted carbenes may also bind in a p3-ri mode, as in (12). 

XPS spectra " show that coordination of the RNC ligand causes a decrease of the electron density on the isocyanide carbon atom. Therefore, addition of nucleophiles to the carbon atom and addition of electrophiles to the nitrogen atom represent characteristic reactions of the isocyanide ligands. Reactions of metal isocyanide complexes with compounds of the type RXH (RX = RO, RNH, RS, etc.) lead to the formation of metal carbene complexes [Section 5.8.b, reactions (5.13)-(5.19)]. 

Replacement of the olefin in the complexes [Rh(/r-pz )(C2Fl4)2]2 (pz =pyrazolate (pz), 3-methylpyrazolate (Mepz), 3,5-dimethylpyrazolate (Mc2pz)) by / /Z-butyl isocyanide gave [Rh(/r-pz )(CN Bu)2]2 51. These complexes oxidatively added Mel, as a consequence of the metal basicity induced by the isocyanide ligands. The mechanisms of the oxidative addition of other electrophiles of the type RCFI2CI were also studied. 

The electron-rich ruthenium center can render the bound X ligand nucleophilic as has been demonstrated by the reactions of (rj5-C5H5)-(PPh3)2Ru—C=N (30) with a variety of electrophiles. Baird and Davies have shown, for example, that addition of alkyl halides to 30 gives the corresponding isocyanides in moderate yield [Eq. (32)] (29). Other... 

Isocyanides, when bound to weak tt-donor metal centers, can also undergo addition of protic nucleophiles (HNu) to form aminocarbene M=C(Nu)NHR species. Hence, a parallelism of behavior is observed for nitriles and isocyanides. In both ligands, either the electrophilic or the nucleophilic addition occurs at the unsaturated atom at the jS-position that exhibits a higher reactivity than the metal coordinated terminal atom. 

Addition of electrophiles to electron-rich isocyanide complexes is a proven synthetic method for the synthesis of aminocarbyne complexes (5,6). Reaction of the trimethylsilyl isocyanide rhenium complex 34 with HBF4 was reported by Pombeiro and co-workers (68). It leads to loss of the trimethylsilyl group and formation of the parent aminocarbyne ligand CNHj [Eq. (28)]. The CNHj ligand is easily interconverted to the CNH... 

With the exception of direct insertion into CO and isocyanides [51], carbon-carbon bond formation from organozirconocenes requires the use of metal salts for transmetalation or (chloride) ligand abstraction. The former protocol has been successfully applied for many carbonyl additions and crosscouplings, whereas the latter strategy is particularly useful for conversions with electrophiles such as epoxides and aldehydes. 

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