Redox-state dependent activation of silanes and ammonia with reverse polarity (PC_carbeneP)Ni complexes: electrophilic vs. nucleophilic carbenes

Abstract

A rigidified PCalkylP ligand allowed for the synthesis and characterization of cationic and radical PCCarbeneP nickel complexes in which the carbene anchor of the pincer framework is electrophilic rather than nucleophilic.

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.…”

“…The 13 C{ 1 H} NMR spectra contain distinct singlets at 257.7 ppm for 2 Pd and 229.7 ppm (with observable 195 Pt satellites, J C‐Pt =1118 Hz) for 2 Pt . The carbene carbon in the isostructural Ni complex 2 Ni appears at 250.8 ppm …”

“…Thus, the carbene is only weakly electrophilic in this complex. Similar to 2 Ni , no reaction of 2 Pt with dihydrogen (1 atm.) was observed even after heating.…”

“…Cyclic voltammetry experiments in o ‐difluorobenzene show reduction events at −0.56 and −1.94 V vs. Fc/Fc + , potentials virtually unchanged from the nickel complex in the same solvent (Figure ). These events have been clearly demonstrated to belong to one electron, ligand‐centered reduction in both 2 Ni and related palladium analogues …”

“…Despite the change in oxidation state and geometry, the DFT‐calculated LUMO is similar to the ligand‐centered LUMO of 2M (Figure S4, Supporting Information). However, the cyclic voltammograms of 3 are markedly different than related carbenes in the +2 oxidation state . Two irreversible reduction events are observed at −1.11 and −1.49 V vs. Fc/Fc + (Figure S6), with all subsequent features matching the cyclic voltammogram for 2 Pt .…”