Formation of Stable<i>trans</i>-Dihydride Ruthenium(II) and 16-Electron Ruthenium(0) Complexes Based on Phosphinite PONOP Pincer Ligands. Reactivity toward Water and Electrophiles

Abstract

The synthesis of a series of new ruthenium complexes based on the new PONOP ligands 1 and 10 ((C5H3N-1,3-(OPR2)2: 1, R = iPr; 10, R = tBu) is presented, including the stable trans-dihydride complexes (iPr-PONOP)Ru(H)2(PPh3) (4) and (tBu-PONOP)Ru(H)2(CO) (12) and the stable Ru(0) complexes (R-PONOP)Ru(CO)2 (6, R = iPr; 15, R = tBu). A surprisingly stable 16-electron Ru(0) complex (13) was formed by deprotonation of 12 with KOtBu. Complex 13 reacts with H2 to afford the cis-dihydride complex 12a, which isomerized to the trans-dihydride 12. Complex 13 reacted with CO to afford the saturated Ru(0) complex 15. Reaction of complex 12 with water led to hydrolysis of the phosphinite PONOP ligand and rearrangement to a dimeric product (14). Reaction of the trans-dihydride complex 4 with the electrophiles PhCOCl, MeI, and MeOTf led to abstraction of one of the hydride ligands, forming the monohydride complexes (iPr-PONOP)Ru(H)(PPh3)(X) (X = Cl (2), I (8a), OTf (8b)) together with benzaldehyde in the case of 2. Similarly, 12 afforded the monohydride complexes (tBu-PONOP)Ru(H)(CO)(X) (X = Cl (11), OTf (17), I (18)). Reaction of the Ru(0) complexes 6 and 15 with water resulted in hydrolysis of the O−P bond and formation of the zwitterionic complexes 7 and 16. Treatment of 2 and 11 with MeOTf or MeI resulted in abstraction of the chloride ligand rather than the hydride, forming complexes 8a,b and 17, 18, respectively. Additional syntheses of complexes based on ligands 1 and 10 are presented.