(R2PC2H4PR2)Pd 0-1-alkyne complexes

Article abstract of DOI:10.1021/om9702035

Displacement of the ethene ligand in (d¹PPe)Pd(C₂H₄) (dⁱppe = ⁱPr₂PC₂H₄P_iPr ₂) by 1-alkynes RC≡CH affords the mononuclear complexes (dⁱPPe)Pd(RC≡CH) (R = Me (2a), Ph (3a), CO₂-Me (4), SiMe₃ (5)). The molecular structure of 3a has been determined by X-ray crystallography. Mononuclear 2a and 3a have been reacted with stoichiometric amounts of (dⁱPPe)Pd(η¹-C₃H₅)₂ as a source for [(dⁱppe)Pd⁰] to yield the dinuclear derivatives {(dⁱppe)-Pd}₂(RC≡=CH) (R = Me (2b), Ph (Sb)). By the reaction Of (dⁱPPe)Pd(C₂H₄) with difunctional vinylacetylene the mononuclear complex (dⁱppe)Pd{(l,2-η²)-RC≡CH} (R = CH=CH₂ (6a)) is formed, which is in equilibrium with isomeric (dⁱppe)Pd{(3,4-η²)-H₂C=CHC≡CH}(6b). Addition of [dⁱPPe)Pd⁰] to 6a,b yields dinuclear {(dⁱPPe)Pd}₂(μ-RC≡CH) (R = CH≡CH₂ (6c)). Reaction of (dⁱppe)Pd(C₂H₄) with butadiyne affords (dⁱppe)Pd(η²-HC≡=CC≡CH) (7c). From dippe, Pt(cod)₂, and C₄H₂ the Pt homologue has also been synthesized and thus, together with the already known Ni derivative, the series (dⁱppe)M(η²-HC≡CC≡CH) (M = Ni (7a), Pd (7c), Pt (7f)) is now complete. When 7c and [(dⁱppe)Pd⁰] are combined, the dinuclear complex {(dⁱppe)Pd}₂(γ-RC≡CH) (R = C≡CH (7e)) is formed in solution, whereas isomeric {(dⁱppe)Pd}₂{μ(l,2-η²):(3,4-η ²)-HC≡CC≡CH} (7d) is present in the solid state. The preparation of the Pd⁰-1-alkyne complexes refutes the conventional wisdom that this type of compound is inherently unstable. By reaction of (dⁱppe)Pd(C₂H₄) with internal alkynes C₂R₂ the complexes (dⁱPPe)Pd(RC≡CR) (R = Me (8a), Ph (9), CO₂Me (10), SiMe₃ (11)) have also been prepared. Combining 8a with [(dⁱPPe)Pd⁰] affords dinuclear {(dⁱppe)Pd}₂(μ-MeC≡CMe) (8b). Finally, solution thermolysis of 2b and 8b gives rise to dinuclear alkyne-free Pd₂(dⁱPPe)₂ (12).