In Search of the Elusive Open-Faced Triangulo Nickel Cluster:  Insertion of Thallium(I) into a μ₃-I Capping Ligand

Thallium(I) inserts into the Ni−I bonds on one face of the 52e triangulo cluster [Ni₃(μ₃-I)₂(μ-dppm)₃] to form the new electron-deficient cluster cation [Ni₃(μ₃-TlI)(μ₃-I)(μ-dppm)₃]⁺. A single-crystal X-ray diffraction study revealed a triangulo cluster containing a symmetrically face-capping TlI ligand and having average Ni−Ni, Ni−Tl, and Ni−I distances of 2.509(14), 2.580(16), and 2.624(14) Å, respectively. Thallium ion can be removed from this cationic cluster by various reagents to regenerate the starting cluster but will not eliminate as TlI and yield an open-faced cluster.