Isocyanide, coordinated ligands, nucleophilic addition

II = Nucleophilic addition to coordinated isocyanide and vinylidene ligands. 

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. 

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)]. 

A cyclopentadienylcopper-fcr/-butyl isocyanide complex catalyzes the Michael addition of dimethyl methylmalonate to acrylonitrile at room temperature to give an S6% yield of the adduct 249). As the CU2O—BNC complex can also catalyze the addition of indene to methyl acrylate, the intermediate is most likely an organocopper complex. The reactions and kinetic data support the mechanism given by Eq. (118) to (120), involving metalation and nucleophilic attack by the carbanion on the olefin within the complex. Displacement of a solvent ligand by the olefin and coordination of the latter to the copper species are essential features of the mechanism. The rate of reaction is decreased if the compound with the... 

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). 

While the advent of NHC ligands brought much new activity to the field of nickel carbene chemistry, important progress was also made with more traditional Fischer-type carbene complexes. The typical route to methoxy(amino) or bis(amino) Fischer-type carbene complexes is the nucleophilic attack of alcohols or amines on coordinated isocyanides. " A new and efficient route to heteroatom-stabilized carbene nickel(ii) complexes was recently reported to occur by a protonation reaction of the nickel(O) complex Ni(GNXyl)(triphos)." Addition of 2 equiv. of HBF4 to solution of Ni(CNXyl)(triphos) in THF affords the stable dicationic nickel carbene complex [Ni C(H)N(H)Xyl (triphos)]2+(BF4-)2 (Equation (16)). 

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