Nucleophilic addition of phosphines to rhenium allenylidenes. Unprecedented double P–H bond activation to give an η1-P-phospha-1-butadienyl ligand

Abstract

Tertiary phosphines PMe_3−xPh_x (x = 0–2) react with the rhenium allenylidene [(triphos)(CO)₂Re(CCCPh₂)]OTf (1) yielding γ-phosphonioalkynyl complexes [(triphos)(CO)₂Re{CCCPh₂(PMe_3−xPh_x)}]OTf [x = 0, (2); 1, (4); 2 (7)] which convert into the α-phosphonioallenyl derivatives [(triphos)(CO)₂Re{C(PMe_3−xPh_x)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.