Metal-Mediated Addition of N-Nucleophiles to Isocyanides: Mechanistic Aspects

Despite the long history of the investigation of nucleophilic addition to metal-bound isocyanides, some important aspects of the reaction mechanism remain unclear even for the simplest systems. In this work, the addition of the sp(3)-N, sp(2)-N, and mixed sp(2)/sp(3)-N nucleophiles (i.e., HNMe(2), HN=CPh(2), and H(2)N–N=CPh(2), respectively) to isocyanides C≡NR coordinated to the platinum(II) centers in the complexes cis-[Pt(C≡NCy)(2-pyz)(dppe)](+) (2-pyz = 2-pyrazyl, dmpe = Me(2)PCH(2)CH(2)PMe(2)) and cis-[PtCl(2)(C≡NXyl)(C≡NMe)] was studied in detail by theoretical (DFT) methods. The mechanism of these reactions is stepwise associative rather than concerted and it includes the addition of a nucleophile to the isocyanide C atom, deprotonation of the nucleophilic moiety in the resulting intermediate, and protonation of the isocyanide N atom to give the final product. The calculated activation energy (ΔG(≠)) of all reactions is in the range of 19.8–22.4 kcal/mol.