Metal–Ligand Cooperation as Key in Formation of Dearomatized Ni^II–H Pincer Complexes and in Their Reactivity toward CO and CO₂

Abstract

The unique synthesis and reactivity of [(RPNP*)NiH] complexes (1a,b), based on metal–ligand cooperation (MLC), are presented (RPNP* = deprotonated PNP ligand, R = iPr, tBu). Unexpectedly, the dearomatized complexes 1a,b were obtained by reduction of the dicationic complexes [(RPNP)Ni(MeCN)](BF4)2 with sodium amalgam or by reaction of the free ligand with Ni0(COD)2. Complex 1b reacts with CO via MLC, to give a rare case of a distorted-octahedral PNP-based pincer complex, the Ni(0) complex 3b. Complexes 1a,b also react with CO2 via MLC to form a rare example of η1 binding of CO2 to nickel, complexes 4a,b. An unusual CO2 cleavage process by complex 4b, involving C–O and C–P cleavage and C–C bond formation, led to the Ni–CO complex 3b and to the new complex [(PiPr2NC2O2)Ni(P(O)iPr2)] (5b). All complexes have been fully characterized by NMR and X-ray crystallography.

Facile C=O Bond Splitting of Carbon Dioxide Induced by Metal–Ligand Cooperativity in a Phosphinine Iron(0) Complex

“…Amore dramatic outcome is revealed by the second major reaction product, 3-s.I nt his case,t he molecular structure in Figure 3. Solid-state molecular structure of 2; [24] 11] Again, this can be attributed to the use of an unsaturated phosphinine moiety in place of am ore conventional phosphine donor.T his reaction represents the first example of full CO 2 C = O cleavage mediated by as ingle well-defined Fe centre.T hat the activation is achieved under ambient conditions using only earth-abundant elements renders this system ah ighly attractive starting point for further investigations into productive CO 2 utilization.…”

Phosphines and N‐Heterocycles Joining Forces: an Emerging Structural Motif in PNP‐Pincer Chemistry

“…The ease of preparing these hydrides via oxidative addition (vide supra) starting from Ni(cod) 2 , certainly enhanced the progress that has been made in this area. Similar to CbzC ( R PNP)NiH (compound 13 shown in Scheme ), the nickel complexes 50‐E (E = CH, N), 51 , and 52 (see Scheme ) have all been prepared via this route.…”

Beyond the PN3(P) system: Synthesis of non‐symmetrical PONNP‐pincer ligands and a unique Ni–Ag bimetallic complex containing a short Ag–Ag distance

“…Pincer ligand systems are well known for their flexibility to modify the electronic and steric properties by replacing the ligand backbone, spacers, donor atom, and substituents (Figure (a)) . Symmetrical PCP or PNP pincer ligand systems have been widely studied (Figure (b) A ) . With either CH 2 or NH spacers, the new mode of metal–ligand cooperation was demonstrated via deprotonation of either the C‐H or N‐H proton .…”