Double addition of phenylacetylene onto the mixed bridge phosphinito–phosphanido Pt(i) complex [(PHCy2)Pt(μ-PCy2){κ2P,O-μ-P(O)Cy2}Pt(PHCy2)](Pt–Pt)

Abstract

The reaction of the dinuclear phosphinito bridged complex [(PHCy₂)Pt(μ-PCy₂){κ²P,O-μ-P(O)Cy₂}Pt(PHCy₂)](Pt–Pt) (1) with phenylacetylene affords the η¹-alkenyl-μ,η¹:η²-alkynyl complex [(η¹-trans-(Ph)HCCH)(PHCy₂)Pt(μ-PCy₂)(μ,η¹:η²-PhCC)Pt{κP-P(O)Cy₂}(PHCy₂)] (4) displaying a σ-bonded 2-phenylethenyl ligand and an alkynyl (μ-κC^α:η²) bridge between the platinum atoms. Complex 4 was shown to form in two steps: initially, the attack of the first molecule of phenylacetylene gives the σ-acetylide complex [(PHCy₂)(η¹-PhCC)Pt¹(μ-PCy₂)Pt²(PHCy₂){κP-P(OH)Cy₂}](Pt–Pt) (5) featuring an intramolecular π-type hydrogen bond between the POH and the CC triple bond; fast reaction of 5 with a second molecule of phenylacetylene results in the oxidative addition of the terminal C–H bond of the second alkyne to Pt¹ that, after rearrangements, leads to 4. When left in solution for two weeks, complex 4 spontaneously isomerizes completely to [(PHCy₂)(η¹-trans-(Ph)HCCH)Pt(μ-PCy₂){κ²P,O-μ-P(O)Cy₂}Pt(η¹-PhCC)(PHCy₂)] (7) displaying a 2-phenylethenyl ligand and a phenylethynyl group both σ-bonded to the metal. Density functional calculations at the B3LYP/LACV3P++**//DFT/LACVP* level were carried out to study the thermodynamics of the formation of all considered complexes and to trace the mechanism of formation of the observed products.