Synthesis and Reactivity of a Vanadium(III)−Methyl Complex Stabilized by Hexamethylsilazanate Ligands

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.

Systematic reductive oligomerization of isocyanides with a vanadium(ii) complex

Using a V(ii) complex as a reducing reagent, we demonstrate controlled reduction of isocyanides, resulting in decyanation of alkyl isocyanides to form a V(iii) cyanide complex or oligomerization of aryl isocyanides to form trimers and a tetramer. The pathways leading to the trimers involve a divanadium ynediamido intermediate, which further reacts with the third isocyanide molecule to selectively produce a tri(imino)deltate or an indolenine complex, by altering the temperature and stoichiometry.

Reactions of (Arylimido)vanadium(V)-Trialkyl Complexes with Phenols: Effects of Arylimido Ligands and Phenols for Formation of the Vanadium Phenoxides

Reactions of a series of (arylimido)vanadium(V) trialkyl complexes, V(NAr')(CH₂SiMe₃)₃ (Ar' = C₆H₅, 2-MeC₆H₄, 2,6-Me₂C₆H₃, 2,6-Cl₂C₆H₃), with various phenols (ArOH, Ar = 2,6-F₂C₆H₃, 2,6-Cl₂C₆H₃, 2,6-Me₂C₆H₃, 2,6- ⁱ Pr₂C₆H₃, 2- ^t BuC₆H₄, 2,6- ^t Bu₂C₆H₃; 1.0 equiv) affording V(NAr')(CH₂SiMe₃)₂(OAr) were conducted in C₆D₆ at 25 °C, and the effects of both arylimido ligands and phenols on the substitution rate were explored. Sterically hindered arylimido ligands showed lower reactivity, and the reaction proceeded in the order: Ar' = 2,6-Me₂C₆H₃ < 2,6-Cl₂C₆H₃ < 2-MeC₆H₄ < C₆H₅. This order is somewhat different from that obtained from the chemical shifts in V(NAr')(CH₂SiMe₃)₃ in the ⁵¹V NMR spectra. The conversions with various disubstituted phenols increased in the order: 2,6- ⁱ Pr₂C₆H₃OH < 2,6-Me₂C₆H₃OH < 2,6-Cl₂C₆H₃OH < 2,6-F₂C₆H₃OH, irrespective of the kind of arylimido ligands. The reactions of V(NAr')(CH₂SiMe₃)₃ with 2,6- ^t Bu₂C₆H₃OH (1.0 or 3.0 equiv) did not take place even upon heating at 60 °C. These results suggest that the reactions proceed via coordination of ArOH toward vanadium, and the reactivity is highly dependent on steric bulk of both the arylimido ligand and the phenol.

Synthesis of a Vanadium(III) Tris(arylthiolato) Complex and Its Reactions with Azide and Azo Compounds: Formation of a Sulfenamide Complex via Cleavage of an Azo NN Bond

The tris(arylthiolate) vanadium(III) complex (1) has been synthesized in good yield. This complex is found to undergo CH activation across a V-S bond in the presence of TMEDA to give a cyclometalated species along with free arylthiol. Complex 1 behaves as a two-electron reductant toward Ad-N(3), yielding an imide complex. Treatment of 1 with azobenzene produces an imide-sulfenamide compound, in which an azo N=N bond cleavage takes place concomitant with formation of a V=N and an S-N bond.