Chelating assistance of P-C and P-H bond activation at palladium and nickel: Straightforward access to diverse pincer complexes from a diphosphine-phosphine oxide

cited By 19International audienceThe diphosphine-phosphine oxide (DPPO) [o-i-Pr2P-(C 6H4)]2P(O)Ph (1) reacts with [Ni(cod) 2] (cod = 1,4-cyclooctadiene) to give the diphosphine-phosphide oxide κP,P(O),P pincer complex 3. According to DFT calculations, the Ph-P(O) bond activation involves a three-center P,Cipso,Ni transition state. Reaction of the DPPO ligand 1 with [(nbd)Pd(ma)] (nbd = 2,5-norbornadiene and ma = maleic anhydride) affords the [(DPPO)Pd(ma)] complex 4. Upon heating, the ma coligand is displaced and the κP,P(O),P palladium pincer complex 2 is obtained. The dinuclear complex (DPPO)[Pd(ma)]2 (6) has also been authenticated. X-ray diffraction analysis showed an original situation in which the oxygen atom of the central phosphine oxide moiety bridges the two palladium centers. Addition of trifluoromethanesulfonic acid to DPPO 1 affords the trifunctional phosphine-phosphine oxide-phosphonium derivative 7. Upon reaction with [Pd 2(dba)3], the palladium hydride κP,O(P),P pincer complex 8 is cleanly formed as the result of P+-H bond activation. Complex 8 is readily deprotonated by DBU (DBU = 1,8- diazabicycloundec-7-ene), and spontaneous oxidative addition of the Ph-P(O) bond gives the diphosphine-phosphide oxide κP,P(O),P pincer complex 2. Conversely, addition of trifluoromethanesulfonic acid on 2 does not give back the palladium hydride 8 but leads to the diphosphine-hydroxy phosphine κP,P(OH),P pincer complex 9. © 2013 American Chemical Society