Protecting-Group-Free Access to a Three-Coordinate Nickel(0) Tris-isocyanide

Details are presented regarding a convenient synthesis of the nickel tris-isocyanide complex Ni(CNArDipp2)3 (ArDipp2 = 2,6-(2,6-[i-Pr]2C6H3)2C6H3). A previous synthesis of a Ni tris-isocyanide complex relied on a Tl(I) coordination-site protection strategy to discourage the formation of a tetrakis-isocyano complex. However, protecting-group-free access to Ni(CNArDipp2)3 is enabled by the encumbering m-terphenyl isocyanide CNArDipp2. Treatment of Ni(COD)2 with CNArDipp2 affords Ni(COD)(CNArDipp2)2, which is readily oxidized to NiI2(CNArDipp2)2 upon addition of I2. Reduction of NiI2(CNArDipp2)2 with Mg metal generates Ni(CNArDipp2)3 and does not require the addition of a third equivalent of CNArDipp2. Tris-isocyanide Ni(CNArDipp2)3 is active toward Lewis acid binding and oxidative addition reactions. Treatment of Ni(CNArDipp2)3 with TlOTf (OTf = [O3SCF3]−) generates the salt [TlNi(CNArDipp2)3]OTf, in which the Ni center functions as a Lewis base toward Tl. The Ni center in Ni(CNArDipp2)3 also oxidatively adds across C–X bonds in a number of alkyl, aryl, and main-group halides and is accompanied by varying degrees of CNArDipp2 ligand loss. Formation of η2-iminoacyl complexes deactivates the Ni center toward additional reactivity.