Models for reactions of acetylene on platinum(111): A vinyl(acetylene)triplatinum complex and evidence for an ethylidyne intermediate

Article abstract of DOI:10.1021/om00097a029

Reaction of [Pt₃(μ₃-H)(μ-dppm)₃]⁺ (1) with excess acetylene gives [Pt₃(CH=CH₂)(μ₃-η ²(∥)-HCCH)(μ-dppm)₃]⁺, where dppm = Ph₂PCH₂PPh₂. Deuterium-labeling studies indicate that H-D scrambling occurs within the vinyl group but not in the acetylene ligand. For example, [Pt₃(μ₃-D)(μ-dppm)₃]⁺ with HCCH gave [Pt₃(CH=CH₂-d₁)(μ₃-η ²(∥)-HCCH)(μ-dppm)₃]⁺, in which the deuterium label was distributed randomly in all three possible positions in the vinyl group. It is possible that this scrambling occurs by way of a short-lived ethylidyne intermediate. The complex is fluxional, due to rotation of the acetylene ligand, at room temperature. Similar reaction of 1 with excess propyne gives [Pt₃(CH=CHMe)(μ₃-η ²(∥)-MeCCH)(μ-dppm)₃]⁺, but this complex is not fluxional at room temperature and is formed selectively by cis insertion of propyne into the Pt-H group. There is a strong resemblance to the chemistry resulting from chemisorption of acetylene on a Pt(111) surface, thus providing a clear example of the value of coordinatively unsaturated clusters as mimics of metal surfaces.