Catalyst-free and catalysed addition of P(O)-H bonds to allenyl/alkynyl-phosphonates and-phosphane oxides: Use of a robust, recoverable dinuclear palladium(I) catalyst

Article abstract of DOI:10.1002/ejoc.201100197

An effective, recoverable, dinuclear palladium(I) catalyst [(OCH ₂CMe₂CH₂O)PSPd(PPh₃)]₂ has been explored and compared with other traditional palladium catalysts (e.g., [Pd(PPh₃)₄]) in the phosphonylation/phosphanylation ofallenes (OCH₂CMe₂CH₂O)P(O)CH=C=CH₂ (1), Ph₂P(O)CH=C=CH₂ (2), (EtO)₂P(O)CH=C= CH₂ (3) (OCH₂CMe₂CH₂O)P(O)CH=C= CMe₂ (4), Ph₂P(O)CH=C=CMe₂ (5), (OCH ₂CMe₂CH₂O)P(O)C(Ph)=C=CH₂ (6) and Ph₂P(O)C(Ph)=C=CH₂ (7). The phosphonylation/ phosphanylation, in general, occurred at the carbon β to the phosphorus atom, but the concomitant proton addition took place at the α or γ positions leading to either allyl-or vinyl-phosphonates. The use of P(nBu) ₃ as catalyst led to geminal and bis-phosphonylation/phosphanylation with less substituted =CH₂ terminal allenes 1 and 2. In conjunction with the use of the corresponding isomeric alkynes 8 and 9, as many as five different types of phosphonylated products have been synthesized. The reactions with the more substituted allenes 4-7 gave single products in most cases. Several examples of catalyst-free, solvent-free phosphanylation reactions are also described. The reactivity of the phosphonylating/phosphanylating agents was found to be (OCH₂CMe₂CH₂O)P(O)H (10) < (OCH₂CMe₂CH₂O)P(S)H (11) < Ph ₂P(O)H (12) ≈ Ph₂P(S)H (13). The catalytic activity of the recoverable dinuclear palladium(I) complex [(OCH₂CMe ₂CH₂O)PSPd(PPh₃)]₂ (14), which poses interesting questions about the mechanistic pathway, is briefly highlighted. Structures of the dinuclear palladium(I) catalyst 14 and the key products were determined by X-ray crystallography.