Synthesis, structure and reactivity of Pd and Ir complexes based on new lutidine-derived NHC/phosphine mixed pincer ligands

Abstract

Coordination studies of new lutidine-derived hybrid NHC/phosphine ligands (CNP) to Pd and Ir have been performed. Treatment of the square-planar [Pd(CNP)Cl](AgCl) complex 2a with KHMDS produces the selective deprotonation at the CHP arm of the pincer to yield the pyridine-dearomatised complex 3a. A series of cationic [Ir(CNP)(cod)] complexes 4 has been prepared by reaction of the imidazolium salts 1 with Ir(acac)(cod). These derivatives exhibit in the solid state, and in solution, a distorted trigonal bipyramidal structure in which the CNP ligands adopt an unusual C-N-P coordination mode. Reactions of complexes 4 with CO and H yield the carbonyl species 5a(Cl) and 6a(Cl), and the dihydrido derivatives 7, respectively. Furthermore, upon reaction of complex 4b(Br) with base, selective deprotonation at the methylene CHP arms is observed. The, thus formed, deprotonated Ir complex 8b reacts with H in a ligand-assisted process leading to the trihydrido complex 9b, which can also be obtained by reaction of 7b(Cl) with H in the presence of KOBu. Finally, the catalytic activity of Ir-CNP complexes in the hydrogenation of ketones has been briefly assessed.

Hydroboration of carbon dioxide with catechol- and pinacolborane using an Ir–CNP* pincer complex. Water influence on the catalytic activity

“…Reaction of the carbonyl iridium complex 1(Cl) 25 with KO t Bu in THF yielded the formation of a mixture of the deprotonated "tautomeric" species 2a and 2b (Scheme 1). The ratio, as determined by 1 H NMR spectroscopy, between these species depends on the solvent.…”

Hydrogenation of an iridium-coordinated imidazol-2-ylidene ligand fragment

“…Recently, we have reported the synthesis of new iridium complexes based on lutidine-derived NHC/phosphine (CNP) pincer ligands, as exemplified by the pentacoordinated diolefin derivative 1 (Scheme 1). 17 As previously shown with protonresponsive lutidine-derived pincer complexes, 18 reaction of this complex with base produces the selective deprotonation of the methylene CH 2 P moiety. 17 Interestingly, prolonged heating of complex 1 in toluene resulted in the activation of the ortho C-H bond of the xylyl group to yield derivative 2.…”

“…17 As previously shown with protonresponsive lutidine-derived pincer complexes, 18 reaction of this complex with base produces the selective deprotonation of the methylene CH 2 P moiety. 17 Interestingly, prolonged heating of complex 1 in toluene resulted in the activation of the ortho C-H bond of the xylyl group to yield derivative 2. The 1 H NMR spectrum of this complex showed a doublet signal at -22.76 ppm with a small 2 J HP coupling constant of 17.4 Hz, indicative of the cis arrangement of the hydride and phosphine ligands.…”

“…After 40 min, a new major species characterized in the 1 H NMR spectrum by a doublet signal at -9.39 ppm ( 2 J HP = 20.0 Hz; 2H) was observed, in line with the generation of the dihydride complex 5, which formation likely involves a ligandassisted activation of dihydrogen after deprotonation of the CH 2 P or CH 2 N arms of the lutidine-derived ligand. [17][18][19] The 13 C{ 1 H} NMR spectrum of 5 exhibits two doublet signals at attributable to the meridional hydride ligand. In order to determine whether complex 7 is formed after hydrogenation of the imidazolylidene fragment of 6 or by reaction of 4 with H 2 , complex 6 was generated from the reaction of 1 with H 2 in the presence of KO t Bu in THF-d 8 and exposed to a H 2 atmosphere (4 bar) for 6 days.…”

Metalated Ir–CNP Complexes Containing Imidazolin‐2‐ylidene and Imidazolidin‐2‐ylidene Donors – Synthesis, Structure, Luminescence, and Metal–Ligand Cooperative Reactivity

“…Recently, some of us reported new iridium complexes stabilized by ligands having u NHC and phosphane side donors and a lutidine central fragment (CNP, Figure 1), and assessed their ability to adapt to different coordination geometries and participate in the ligand‐assisted activation of H 2 . [ 18,19 ] These non‐symmetric pincer ligands permit the tuning of two different side donors, thus allowing a larger electronic and steric diversity, [ 20 ] and serve for a direct comparison of the properties of the u NHC‐ and phosphane‐containing halves of the pincer. Furthermore, we have communicated the selective hydrogenation of the olefinic backbone of a coordinated imidazolin‐2‐ylidene fragment that occurs in an iridium complex based on a metalated κ 4 ‐(P,N,C uNHC ,C aryl ) lutidine‐derived ligand.…”