Aminocarbyne complexes

In certain cases, a bound cyanide ligand can participate in an oxidation-reduction reaction. For example, the electroreduction of the complex mans -[Mo(CN)Cl(dppe)2] in the presence of phenol reduces the cyanide ligand to the simplest aminocarbyne ligand, =CNH2, and gives trans-[(Mo=CNFl2)Cl(dppe)2]. The reduction of the cyanide is reversible, as oxidation of the aminocarbyne complex regenerates trans- [Mo(CN)Cl(dppe)2]. 

Certain pentacarbonyl carbene complexes of chromium rearrange spontaneously by loss of a CO ligand to give trans-substituted aminocarbyne complexes ... 

Secondary amines react with the same cationic, C- and S-coordinated mercaptocarbene complex to afford neutral aminocarbyne complexes in ca. 30% yield ... 

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. 

H. Fischer and co-workers synthesized several 2-azaallenylidene metal complexes by the a-alkoxide abstraction reaction shown in Eq. (4) (42,43). 2-Azaallenylidene complexes are closely related to aminocarbyne complexes [see, e.g., Eq. (80), Section IV,C]. 

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... 

A new class of aminocarbyne complexes was discovered by Filippou and Fischer. Oxidation of complexes 54 by iodine affords the triiodo monocarbonyl aminocarbyne complexes 55 [Eq. (46)] (83-85). Complexes 58 and... 

Several examples of CO substitution by halide ions in aminocarbyne complexes were reported by Fischer [Eq. (63)] 101). The halide ligand in... 

DIISOCYANIDE COMPLEXES OF MOLYBDENUM(O) AND TUNGSTEN(O) AND DERIVED AMINOCARBYNE COMPLEXES... 

The isocyanide-substituted complexes can be correspondingly obtained following thermal decarbonylation of the bromotetracarbonyl species with tert-butyl isonitrile to produce the cationic aminocarbyne complex [Cr(=CN Pr2)(CO)(CN Bu)4]. Subsequent treatment with Na[Cp] or K[Tp ] in tetrahydrofuran at 50 °C results in formation of LCr(=CN Pr2)(CO)(CN Bu) (L = Cp or Tp in 61 and 58% yield, respectively). In both reactions the minor product [Cr(=CN Pr2)(CN Bu)5] is formed by a competitive carbonyl-substitution reaction of the tetra(isonitrile) complex with liberated CN Bu. ... 

By following a related stepwise procedure, aminocarbyne complexes can be used to prepare rare examples of mononuclear bis(aminocarbyne) complexes. Oxidative decarbonylation of Tp W( = CNREt)(CO)2 (R = Me, Et) with Br2 or I2 affords the six-coordinate dihalido-aminocarbyne complexes Tp W( = CNREt) X2 (X = Br, I) in high yield. Subsequent reductive dehalogenation by Na/Hg in the presence of CNEt gives the electron-rich mono-aminocarbyne complexes Tp W( = CNREt)(CNEt)2. An unusually low-field chemical shift for the metal-bonded isonitrile carbons as well as low-frequency Vcn absorptions confirms the presence of a very electron-rich metal centre. Alkylation with [Et30][BF4] at one isocyanide nitrogen yields the bis(aminocarbyne) salts [Tp W( = CNREt) ( = CNEt2)(CNEt)][BF4] (Scheme 23). ... 

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