Routes to Cyclobutadiene and Cycloallyl Pt(II) Complexes: Dicationic Bis(Alkyne) Species as Intermediates

Transition metal alkyne complexes can be crucial intermediates for a variety of transformations. Cyclobutadiene can be generated by metal‐mediated C–C coupling reactions, but this often requires an elaborate synthetic strategy. As a result, only a few examples of Pt(II) cyclobutadiene complexes have been described so far. Herein, we report on the development of a synthetic route to access cationic Pt(II) η 3 ‐cycloallyl complexes [Pt( η 3 ‐(C 2 H 5 C ) 3 C═C 2 H 4 )(L)][BF 4 ] bearing various chelating diphosphine ligands (L). Their generation and its dependence on the choice of L were studied using a combined experimental and quantum chemical approach. Dicationic bis(alkyne) BF 4 complexes are essential intermediates for the generation of η 3 ‐cycloallyl compounds. An investigation on the reactivity of Pt(II) η 3 ‐cycloallyl complexes toward the Br ø nsted acids HCl and HBF 4 ·Et 2 O led to the formation of cationic and dicationic Pt(II) η 4 ‐cyclobutadiene complexes.