Reductive Coupling of Xylyl Isocyanide Mediated by Low-Valent Uranium

Evidence for Carbene Intermediates in Isocyanide Homologation by Aluminium(I)

The C-C bond formation between C1 molecules plays an important role in chemistry as manifested by the Fischer-Tropsch (FT) process. Serving as models for the FT process, we report here the reactions between a neutral AlI complex (Me NacNac)Al (1, Me NacNac=HC[(CMe)(NDipp)]2 , Dipp=2,6-diisopropylphenyl) and various isocyanides. The step-by-step coupling mechanism was studied in detail by low-temperature NMR monitoring, isotopic labeling, as well as quantum chemical calculations. Three different products were isolated in reaction of 1 with the sterically encumbered 2,6-bis(benzhydryl)-4-Me-phenyl isocyanide (BhpNC). These products substantiate carbene intermediates. The reaction between 1 and adamantyl isocyanide (AdNC) generated a trimerization product, and a corresponding carbene intermediate could be trapped in the form of a molybdenum(0) complex. Tri-, tetra-, and even pentamerization products were isolated with the sterically less congested phenyl and p-methoxyphenyl isocyanides (PhNC and PMPNC) with concurrent construction of quinoline or indole heterocycles. Overall, this study provides evidence for carbene intermediates in FT-type chemistry of aluminium(I) and isocyanides.

Controlled reductive C-C coupling of isocyanides promoted by an aluminyl anion

We report the reaction of the potassium aluminyl, K[Al(NON)] ([NON]^2- = [O(SiMe₂NDipp)₂]^2-, Dipp = 2,6-iPr₂C₆H₃) with a series of isocyanide substrates (R-NC). In the case of tBu-NC, degradation of the isocyanide was observed generating an isomeric mixture of the corresponding aluminium cyanido-κC and -κN compounds, K[Al(NON)(H)(CN)]/K[Al(NON)(H)(NC)]. The reaction with 2,6-dimethylphenyl isocyanide (Dmp-NC), gave a C₃-homologation product, which in addition to C-C bond formation showed dearomatisation of one of the aromatic substituents. In contrast, using adamantyl isocyanide Ad-NC allowed both the C₂- and C₃-homologation products to be isolated, allowing a degree of control to be exercised over the chain growth process. These data also show that the reaction proceeds through a stepwise addition, supported in this study by the synthesis of the mixed [(Ad-NC)₂(Dmp-NC)]^2- product. Computational analysis of the bonding within the homologised products confirm a high degree of multiple bond character in the exocyclic ketenimine units of the C₂- and C₃-products. In addition, the mechanism of chain growth was investigated, identifying different possible pathways leading to the observed products, and highlighting the importance of the potassium cation in formation of the initial C₂-chain.

Metalation-Induced Denitrogenative Reductive Coupling of Isocyanides on a Silylene-Bridged Nickel Cluster

The denitrogenative reductive coupling of two molecules of CNtBu to afford a disilylketenimine with an aza-disilacyclobutane skeleton was achieved on a multinuclear silylene-bridged Ni cluster framework in the absence of...