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

Abstract

The addition of carbon monoxide (CO), carbon dioxide (CO2) and isoelectronic isocyanide and isocyanates to the nickel carbene bond in PCcarbeneP pincer complexes is reported. For CO and CNR, irreversible group transfer reactions are observed, while for CO2, a reversible 2 + 2 addition to the carbene moiety occurs. The course of the CO and CO2 reactions are strongly affected by the nature of the PCcarbeneP pincer ligand framework, and a new more rigid ligand based on a 10,10-dimethyl-9,10-dihydroanthracene core was designed in order to study these reactions, illustrating the profound effect of small changes in ligand structure on reaction outcomes.

C−N, C−S and S−S Bond Cleavage by Rhodium PCcarbeneP Pincer Complexes

“…Although the mechanism for this bond cleavage was not investigated, this example is rather unremarkable, as rhodium complexes in the presence of PPh 3 have long been known to generate thiocarbonyls from CS 2 . In contrast to CS 2 , Piers has shown that CO 2 and tert ‐butyl isocyanate react with a nucleophilic nickel PC carbene P pincer complex to form metallabutylcycles, in which the C−O bond of CO 2 and the C−N bond of OCN t Bu are activated, but not completely cleaved …”

“…31 P NMR analyses reveal that the half‐lives of these complexes to be a matter of hours at room temperature (t 1/2 2‐Int PPh3 <6 h, 2‐Int PPh2(C6F5) <1 h). These short half‐lives prevented structural characterization, however, PC carbene P pincer complexes have been shown to form adducts in a [2+2] fashion with isocyanates and carbon dioxide, and related sulfur tethered methandiide complexes reported by Gessner are known to also form [2+2] adducts with isocyanates and isothiocyanates . The identity of these short lived complexes prior to formation of 2‐L could presumably also be [2+2] ‘pre‐activation’ complexes.…”

Synthesis and Structures of Stable PtII and PtIV Alkylidenes: Evidence for π‐Bonding and Relativistic Stabilization

“…Given that both Pt II and Pt IV salts and complexes are effective π‐acid catalysts, we sought to isolate well‐defined examples of cationic Pt II and Pt IV carbene complexes to probe the bonding in these important species. Hypothesizing that a strong ligand chelate may be able to support these species, we employed the rigid, 10,10‐dimethyl‐9,10‐dihydroanthracene‐derived PCP ligand framework L 1 , which is competent in the stabilization of analogous nickel(II) complexes . For comparison, an isostructural Pd II species was also prepared and it was shown that the Pt−C bonds are indeed more stable due to stronger π bonding, attributable to relativistic effects.…”

Synthesis and Structures of Stable Pt(II) and (IV) Alkylidenes: Evidence for π-Bonding and Relativistic Stabilization

“…As both Pt(II) and Pt(IV) salts and complexes are effective π-acid catalysts, we sought to isolate well--defined examples of cationic Pt(II) and Pt(IV) carbene complexes to probe the bonding in these important species. Hypothesizing that a strong ligand chelate may be able to support these species, we employed the rigid, 10,10--dimethyl--9,10--dihydroanthracene-derived PCP ligand framework L 1 , 11 which is competent in the stabilisation of analogous nickel(II) complexes. 12 For comparison, an isostructural Pd(II) species was also prepared and it can be shown that the Pt--C bonds are indeed more stable due to stronger π bonding, attributable to relativistic effects.…”