Tuning iridium (I) PCcarbeneP frameworks for facile cooperative N2O reduction

H/D exchange under mild conditions in arenes and unactivated alkanes with C6D6 and D2O using rigid, electron-rich iridium PCP pincer complexes

“…The sp 3 hybridization of the a-carbon is also indicated by the central Ir1-C1 bond length of 2.184(5)Å which is similar to other sp 3 hybridized Ir-C bonds we have observed with these NR 2 substituted ligand frameworks 44,45 and lengthened signicantly from the values of z1.93 A seen in PC carbene P complexes of this ligand. 44 Given the lack of crystallographic data concerning the iridium hydrides in Ir-H 4 , we turned to criteria developed by Halpern and co-workers 55 to shed some light on what form dominates the speciation of Ir-H 4 in solution. While it is typically difficult to unambiguously categorize the hydride bonding mode for these complexes, we were able to rule out the possibility that Ir-H 4 is a "non-classical" Ir(I) bis-dihydrogen species (Scheme 2).…”

“…43 We have shown that the rate of addition of N 2 O to the C]Ir bond 40 can therefore be tuned substantially. 44 Furthermore, the rigidication of the ligand tends to favor the PC carbene P form of the ligand vs. the PC sp 3 P form, while also providing greater protection against C-C bond cleavage reactions that destroy the integrity of the ligand in unlinked systems akin to V. 45 The ability of the carbon atom in these PCP pincers to engage in ligand cooperativity has been exploited in hydrogen, 35,46 silane [47][48][49] and other small molecule 40,[50][51][52][53] activations in various systems. Furthermore, in polyhydridic systems, the dibenzylic hydrogen is actively involved in exchange with the metal hydrides, 34,35 increasing the "hydrogen capacity" of these compounds relative to other (for example PNP) polyhydridic pincer complexes and potentially providing new pathways for catalysis.…”

“…reported Ir-Cl 44 to 120 C in toluene with an excess of CsOH for 24 hours (Scheme 1, red arrows). The resulting brown solution was ltered through Celite® and a brown powder was isolated in 80% yield aer removing all volatiles in vacuo.…”

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

“…Thus far, the cleavage of strong carbon‐element bonds, beyond carbon‐hydrogen bonds, has been little reported using PC carbene P complexes. Of course, strong C−O bonds must be cleaved in the hydrogen or alcohol driven reduction of a metal bound keto‐pincer ligand that forms a necessary step in the catalytic deoxygenation reactions of nitrous oxide or amine/pyridine N ‐oxides (described above) . Similarly, we have described the direct cleavage of keto‐pincer C−O bonds using phosphines as both cooperative ligands and reductants .…”

“…Heavier chalcogenide examples have also been reported using elemental sulfur, selenium and tellurium . Piers has demonstrated the step‐wise reactions necessary for the reduction of nitrous oxide to nitrogen and water in the presence of hydrogen, but has so far failed to reconcile these steps into a catalytic cycle . More recently, we reported on the catalytic deoxygenation of amine and pyridine N ‐oxides mediated by a rhodium PC carbene P complex and alcohol reductant …”