Datensatz

Zusammenfassung

The complexes (R'₂PC₂H₄PR'₂)Pd(C₂H₄) (R' = ⁱPr, ^tBu) react with R₃SnH (R = Me, ⁿBu) by displacement of the ethene ligand and oxidative addition of the Sn−H bond to generate the chelating phosphane stabilized cis Pd^II hydrido stannyl complexes (R'₂PC₂H₄PR'₂)PdH(SnR₂) (R' = ⁱPr (1), ^tBu (2)). Complex 1a (R' = ⁱPr, R = Me), containing the smallest substituents, is only transiently formed but has been detected at −80 °C by NMR spectroscopy. It reacts further with Me₃SnH, even at −120 °C, by eliminating hydrogen to give (dⁱppe)Pd(SnMe₃)₂ (3). In contrast, the isolated (dⁱppe)PdH(SnⁿBu₃) (1b) is briefly stable at ambient temperature, whereas the sterically encumbered species (d^tbpe)PdH(SnR₃) (R = Me (2a), ⁿBu (2b)) are stable well above 100 °C. The molecular structure of 2a has been determined by X-ray crystallography. Complex 2a reacts with 2 equiv of C₂R''₂ (R'' = CO₂Me) to give (d^tbpe)Pd(C₂R''₂) (4) and predominantly the corresponding (E)-vinylstannane (E)-(R'')(H)CC(SnMe₃)(R'') (E-5). Since 2a also catalyzes the hydrostannation of the alkyne, the cis Pd^II hydrido stannyl complexes 1a,b and 2a,b represent trapped intermediates in the Pd-catalyzed hydrostannation of alkynes. The existence of the complexes also sheds light on the mechanism of the Pd-catalyzed degradation of R₃SnH into Sn₂R₆ and H₂.