Activation of Water, Ammonia, and Other Small Molecules by PC_carbeneP Nickel Pincer Complexes

Abstract

Nickel complexes of a PC(carbene)P pincer ligand framework are described. Dehydrobromination of the precursor (PC(sp)(3)P)NiBr in the presence of a donor (PPh3 or NC(t)Bu) leads to the title complexes, which feature a rare nickel-carbene linkage as the pincer ligand anchor point. This strongly donating, nucleophilic carbene center engages in a variety of E-H bond activations (E = H, C, N, O), some of which are reversible. This represents a new mode of bond activation by ligand cooperativity in nickel pincer complexes.

Ammonia Activation by a Nickel NCN‐Pincer Complex featuring a Non‐Innocent N‐Heterocyclic Carbene: Ammine and Amido Complexes in Equilibrium

“…10 Piers recently disclosed the use of a carbenebased PCP-pincer complex of Ni 0 for the ligand-assisted activation of ammonia to give a terminal LNi II -NH2 product. 11 Noteworthy are also the remarkable progresses made in the activation of ammonia by main group systems. 12 The activation of the N-H bond in ammonia proved to be highly sensitive to the nature of the catalyst, 13 with the ammine-amide equilibrium being completely shifted upon changing the metal from rhodium (ammine) to iridium (amide) for the same ligand system.…”

Divergent Reactivity of CO2 and CO and Related Substrates at the Nickel Carbon Double Bond of (PCcarbeneP)Ni(II) Pincer Complexes

“…1 The proposed mechanism of action of (CODH) is believed to proceed via CO 2 binding to a square planar nickel center at the [NiFe 4 S 4 ] active site. 2 As such the coordination chemistry of CO 2 and CO at nickel centers supported by pincer ligands to rigorously enforce a square planar geometry is of particular interest, and has been widely explored. [3][4][5][6][7][8][9][10][11][12][13] Notably, the isolation of key proposed intermediates in selective reduction of CO 2 to CO, 3 and a closed synthetic cycle for the reduction CO 2 to CO have recently been realized using PNP pincer ligand supported nickel complexes.…”

“…[3][4][5][6][7][8][9][10][11][12][13] Notably, the isolation of key proposed intermediates in selective reduction of CO 2 to CO, 3 and a closed synthetic cycle for the reduction CO 2 to CO have recently been realized using PNP pincer ligand supported nickel complexes. 4,9 Despite the rich coordination chemistry of CO 2 , 14 there is a relative dearth of examples of CO 2 bonding and activation using metal-ligand cooperation. 15 Many of these examples consist of 1,3-activation of CO 2 at dearomatized PNP or PNN pincer complexes of second and third row transition metals, [16][17][18] though examples have been noted with Fe 19 and Ni, 20 and the formal 1,2-addition has been observed at pincer ligand supported Mo and W amides.…”

“…[31][32][33][34] However, there has been no investigation of the reactivity of CO 2 or CO with the PCP complexes of the group 10 metals. Here we present the reactivity of 1 L1 with with CO 2, CO and isoelectronic isocyanate and isocyanide analogues and introduce a key ligand modification that dictates the course of CO 2 and CO activation by these platforms.…”

“…of CO 2 or CO in C 6 D 6 immediately led to a color change from orange to brown-black. In the case of the CO 2 reaction, a marked loss of intensity in peaks Scheme 1.…”