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)

The reaction of the dinuclear phosphinito bridged complex [(PHCy2)Pt(mu-PCy2){kappa P-2,O-mu-P(O)Cy-2}Pt(PHCy2)](Pt-Pt) (1) with phenylacetylene affords the eta(1)-alkenyl-mu,eta(1):eta(2)-alkynyl complex [(eta(1)-trans-(Ph)HC=CH)(PHCy2)Pt(mu-PCy2)(mu,eta(1):eta(2)-PhC?C)Pt{kappa P-P(O)Cy-2}(PHCy2)] (4) displaying a sigma-bonded 2-phenylethenyl ligand and an alkynyl (mu-kappa C-alpha:eta(2)) 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 sigma-acetylide complex [(PHCy2)(eta(1)-PhC=C)Pt-1(mu-PCy2)Pt-2(PHCy2){kappa P-P(OH)Cy-2}](Pt-Pt) (5) featuring an intramolecular pi-type hydrogen bond between the POH and the C?C 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 Pt-1 that, after rearrangements, leads to 4. When left in solution for two weeks, complex 4 spontaneously isomerizes completely to [(PHCy2)(eta(1)-trans-(Ph)HC=CH)Pt(mu-PCy2){kappa P-2,O-mu-P(O)Cy-2}Pt(eta(1)-PhC=C)(PHCy2)] (7) displaying a 2-phenylethenyl ligand and a phenylethynyl group both sigma-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.