Nucleophilic addition of phosphines to rhenium allenylidenes. Unprecedented double P–H bond activation to give an η 1 -P-phospha-1-butadienyl ligand

Tertiary phosphines PMe3−xPhx (x = 0–2) react with the rhenium allenylidene [(triphos)(CO)2Re(CCCPh2)]OTf (1) yielding γ-phosphonioalkynyl complexes [(triphos)(CO)2Re{CCCPh2(PMe3−xPhx)}]OTf [x = 0, (2); 1, (4); 2 (7)] which convert into the α-phosphonioallenyl derivatives [(triphos)(CO)2Re{C(PMe3−xPhx)CCPh2}]OTf [x = 0, (3); 1, (5); 2 (6)] at higher tempereature. The reactions of 1 with secondary, PHPh2, and primary, PH2CH2Fc (Fc = ferrocenyl), phosphines proceed with a similar mechanism, followed by single or double P–H bond cleavage. The γ-phosphonioalkynyl [(triphos)(CO)2Re{CCCPh2(PHPh2)}]OTf (9) and the α-phosphonioallenyl [(triphos)(CO)2Re{C(PHPh2)CCPh2}]OTf (10) have been intercepted by insitu NMR spectroscopy. On increasing the temperature, 10 undergoes a selective 1,3-P,C-H shift to give the α-phosphoniobutadienyl derivative [(triphos)(CO)2Re{C(PPh2)CHCPh2}]OTf (8). With the primary phosphine PH2CH2Fc, the initially formed α-phosphoniobutadienyl complex [(triphos)(CO)2Re{C(PHFc)CHCPh2}]OTf (11) transforms into the η1-P-phospha-1-butadienyl complex [(triphos)(CO)2Re{P(CH2Fc)CHCHCPh2}]OTf (12) upon heating at 50 °C.