Electrophiles aminocarbyne complex

Carvalho et al. reported molecular orbital calculations on the electron-rich rhenium isocyanide complex ReCl(CNH)(H2PCH2CH2PH2) and the aminocarbyne complex [ReCl(CNH2)(H2PCH2CH2PH2)] (37). They found that in the isocyanide complex a negative charge is accumulated on the Cl and N atoms. These two sites may therefore compete for electrophiles however, the product of N attack is thermodynamically favored. 

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... 

Electron-rich aminocarbyne complexes of the type Cp (CO)n(L)2-nWsCNEt2 (n = 0, 1 L = PMes, EtNC, BuNC) are susceptible to successive protonation by HX (X = Br, I, CN). The site of the electrophilic attack depends strongly on the ligand sphere allowing the selective synthesis of a variety of new compounds with high synthetic potential. 

The ran -aminocarbyne(iodo)tungsten complexes 125 react with CF3SO3CH3 to give the inflate derivatives 126 and methyl iodide [Eq. (106)] 138). This reaction is a rare example of direct attack of electrophiles at the trans halide ligand of a carbyne complex. 

Electrophilic addition to anionic molybdenum isocyanide derivatives [Na][Tp Mo(CNR)(CO)2] is dominated by direct attack at nitrogen to form alkylidyne products however, alkylation at the metal followed by isonitrile insertion can lead to j -iminoacyl complexes in some cases. The aminocarbyne products Tp Mo(=CNRMe)(CO)2 are formed in high yield for methyl and phenyl isocyanide reagents. However, the formation of the corresponding tcrt-butylamino-alkylidyne complex is accompanied by formation of f/ -acyl and / -iminoacyl complexes (Scheme 22). ... 

The ligating isocyanide is activated toward electrophilic attack and aminocarbyne-type species are formed by reactions with acids or alkylating agents. The nucleophilicity of the isocyanide ligand in those electron-rich complexes is in contrast to its usual electrophilic character " reported for this ligand when it binds a metal ion in its normal or higher oxidation states. 

ABSTRACT. Alkynes, when activated by an electron-rich d Re, Mo or W phosphinic centre, undergo hydrogen shift reactions (to give, e.g., vinylidene species) or oxidatively add to the metal (forming alkynyl--hydrido or alkynyl complexes). These alkyne-derived products undergo 3-protonation to afford a variety of carbyne-fluoro or -chloro complexes, whereas aminocarbynes are obtained upon 3-electrophilic attack (e.g., by a protic or a Lewis acid) at isocyanides when ligating such metal sites. Mechanistic studies, by stopped-flow spectrophotometry, are also indicated. 

Several types of reactivity for metal-bound nitriles and isocyanides should be recognized [1, 7, 8]. For instance, the nucleophilic addition to metal-bound nitriles allows the generation of imine complexes [1], electrophiUc addition produces metal-bound azavinylidenes [1], and the DCA results in coordinated heterocycUc imines (Route I, Scheme 13.1) [5, 6, 10]. With respect to the metal-ligated isocyanides, the addition of nucleophiles furnishes complexes with acycUc aminocarbenes [7, 9, 11], electrophilic addition gives aminocarbynes [8, 12], while the DCA brings about the formation of A-heterocyclic carbene derivatives (Route II, Scheme 13.1) [6, 10]. 

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