The 4-Electron Cleavage of a N═N Double Bond by a Trimetallic TiNi₂ Complex

The synthesis and reactivity of a new trimetallic complex Ti(NP)₄Ni₂ (NP = 2-diphenylphosphinopyrrolide) (3) is reported. Single-crystal X-ray diffraction and X-ray absorption studies point to a unique bonding motif: a d¹⁰-d¹⁰, Ni⁰-Ni⁰ bond stabilized by a proximal d⁰ Ti^IV metal center. The coordination chemistry of 3 with a variety of L (L = isocyanide and alkyne) donors has also been explored. In the case of isocyanide coordination, the Ni-Ni bond is broken, while diphenylacetylene binding results in a symmetric butterfly μ²-κ²-alkyne bridge across the Ni-Ni moiety. Finally, complex 3 is capable of the 4-electron cleavage of the N═N double bond in benzo[c]cinnoline, the first example of N═N bond cleavage by Ni. The resulting product, 7, has been characterized structurally and spectroscopically, and the mechanistic implications are discussed in the context of metal-metal cooperativity.