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 sp3-N, sp2-N, and mixed sp2/sp3-N nucleophiles (i.e., HNMe2, HN=CPh2, and H2N–N=CPh2, 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 = Me2PCH2CH2PMe2) and cis-[PtCl2(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