Reactions of Square‐Planar d
            <sup>8</sup>
            Pincer Complexes with Oxygen and Hydrogen

Bailey, Wilson D.; Parkes, Marie Vernell; Kemp, Richard A.; Goldberg, Karen I.

doi:10.1002/9783527681303.ch11

Cited by 3 publications

(2 citation statements)

References 76 publications

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“…Notably, there are significantly fewer mononuclear late-transition-metal hydroxide, alkoxide, and amide complexes relative to their metal alkyl (M–C) analogues . However, such M–OR and M–NR 2 linkages are pertinent to catalysis, , and thus isolation and study of model metal hydroxide, alkoxide and amide complexes are of great value.…”

Section: Introductionmentioning

confidence: 99%

Pyrazole-Based PCN Pincer Complexes of Palladium(II): Mono- and Dinuclear Hydroxide Complexes and Ligand Rollover C–H Activation

et al. 2015

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Palladium complexes of the novel unsymmetrical phosphine pyrazole-containing pincer ligands PCN H (PCN H = 1-[3-[(di-tert-butylphosphino)methyl]phenyl]-1H-pyrazole) and PCN Me (PCN Me = 1-[3-[(di-tert-butylphosphino)methyl]phenyl]-5-methyl-1H-pyrazole) have been prepared and characterized through single-crystal X-ray diffraction and multinuclear 1 H, 13 C{ 1 H}, and 31 P{ 1 H} NMR spectroscopy. In preparations of the monomeric hydroxide species (PCN H )Pd(OH), an unexpected N detachment followed by C−H activation on the heterocycle 5-position took place resulting in conversion of the monoanionic {P,C − ,N} framework into a dianionic {P,C − ,C − } ligand set. The dinuclear hydroxide-bridged species (PCN H )Pd(μ-OH)Pd(PCC) was the final product obtained under ambient conditions. The "rollover" activation was followed via 31 P{ 1 H} NMR spectroscopy, and dinuclear cationic μ-OH and monomeric Pd II hydroxide intermediates were identified. DFT computational analysis of the process (M06//6-31G*, THF) showed that the energy barriers for the pyrazolyl rollover and for C−H activation through a σ-bond metathesis reaction are low enough to be overcome under ambient-temperature conditions, in line with the experimental findings. In contrast to the PCN H system, no "rollover" reactivity was observed in the PCN Me system, and the terminal hydroxide complex (PCN Me )Pd(OH) could be readily isolated and fully characterized. ■ INTRODUCTIONThe use of pincer-ligated transition-metal complexes as catalysts for organic transformations has grown dramatically in recent years. 1 The robust tridentate binding motif coupled with the tunability of the steric and electronic parameters of pincer ligands has proven highly effective in stabilizing and allowing isolation of a variety of uncommon types of metal complexes. For example, pincer ligands have been very useful in the preparation of mononuclear late-metal complexes bearing M−OR and M−NR 2 bonds. Notably, there are significantly fewer mononuclear late-transition-metal hydroxide, alkoxide, and amide complexes relative to their metal alkyl (M−C) analogues. 2 However, such M−OR and M−NR 2 linkages are pertinent to catalysis, 3,4 and thus isolation and study of model metal hydroxide, alkoxide and amide complexes are of great value.The variety of available pincer ligands has increased in recent years. While early pincer ligands were symmetric with respect to ligand "arms" (e.g., PCP, PNP, POCOP, etc.), 5 pincer-type complexes bearing unsymmetrical arms have begun to appear in greater numbers (NCC, PNN, PCO, PCS, etc.). 6 PCN-type systems in particular are intriguing, because in (PCN)M(L) n complexes (M = transition metal; L = ancillary ligand) the tridentate hybrid ligand contains both hard (N) and soft (P) donor functions, thus leading to novel and unprecedented chemical properties. 7 In such species, there is a marked difference in the trans effect between the two different donor arms. This difference results in the group with the weaker trans effect (N) being more likely to dissociate fro...

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Section: Introductionmentioning

confidence: 99%

Pyrazole-Based PCN Pincer Complexes of Palladium(II): Mono- and Dinuclear Hydroxide Complexes and Ligand Rollover C–H Activation

et al. 2015

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“…Although molecular oxygen is the most environmentally benign, abundant, and inexpensive oxidant, it has limited synthetic use due to over-oxidation and lack of selectivity. The use of organometallic catalysts with O 2 for selective oxidation of hydrocarbons is a growing field, pioneered by Hay and Shilov . The active species in the catalytic oxidation are superoxo or hydroperoxo complexes, although these are rarely directly observed.…”

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O₂ Activation by Metal–Ligand Cooperation with Ir^I PNP Pincer Complexes

et al. 2015

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A unique mode of molecular oxygen activation, involving metal-ligand cooperation, is described. Ir pincer complexes [((t)BuPNP)Ir(R)] (R = C6H5 (1), CH2COCH3 (2)) react with O2 to form the dearomatized hydroxo complexes [((t)BuPNP*)Ir(R)(OH)] ((t)BuPNP* = deprotonated (t)BuPNP ligand), in a process which utilizes both O-atoms. Experimental evidence, including NMR, EPR, and mass analyses, indicates a binuclear mechanism involving an O-atom transfer by a peroxo intermediate.

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Hydrogenolysis of Dinuclear PCN^R Ligated Pd^II μ‐Hydroxides and Their Mononuclear Pd^II Hydroxide Analogues

Bailey

Phearman

Luconi

et al. 2019

Chemistry A European J

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The hydrogenolysis of mono-and dinuclear Pd II hydroxidesw as investigated both experimentally and computationally.I tw as found that the dinuclear m-hydroxidereact with H 2 to form the analogous dinuclear hydride species {[(PCN R )Pd] 2 (m-H)}(OTf). The dinuclear m-hydride complexes were fully characterized, and are rare examples of structurally characterizedu nsupported singly bridged m-H Pd II dimers. The {[(PCN Me )Pd] 2 (m-OH)}(OTf) hydrogenolysis mechanism was investigated through experimentsa nd com-putations. The hydrogenolysis of the mononuclear complex (PCN H )Pd-OHr esulted in am ixed ligand dinuclears pecies [(PCN H )Pd](m-H)[(PCC)Pd] (PCC = ad ianionic version of PCN H boundt hrough phosphorus P, aryl C, and pyrazole Ca toms) generated from initial ligand "rollover" CÀHa ctivation. Further exposure to H 2 yields the bisphosphine Pd 0 complex Pd[(H)PCN H ] 2 .When the ligand was protected at the pyrazole 5-position in the (PCN Me )PdÀOH complex, no hydride formed under the same conditions;t he reactionp roceeded directly to the bisphosphine Pd 0 complex Pd[(H)PCN Me ] 2 .R eaction mechanisms for the hydrogenolysis of the monomeric and dimerichydroxides are proposed.[a] Dr.Supporting information (selected crystallographic parameters of the solved XRD structures, NMR spectra of all the described compounds, further computationald etails)a nd the ORCID identification number(s) for the author(s) of this article can be found under:h ttps://doi.

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Reactions of Square‐Planar d ⁸ Pincer Complexes with Oxygen and Hydrogen

Cited by 3 publications

References 76 publications

Pyrazole-Based PCN Pincer Complexes of Palladium(II): Mono- and Dinuclear Hydroxide Complexes and Ligand Rollover C–H Activation

Pyrazole-Based PCN Pincer Complexes of Palladium(II): Mono- and Dinuclear Hydroxide Complexes and Ligand Rollover C–H Activation

O₂ Activation by Metal–Ligand Cooperation with Ir^I PNP Pincer Complexes

Hydrogenolysis of Dinuclear PCN^R Ligated Pd^II μ‐Hydroxides and Their Mononuclear Pd^II Hydroxide Analogues

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Reactions of Square‐Planar d 8 Pincer Complexes with Oxygen and Hydrogen

Cited by 3 publications

References 76 publications

Pyrazole-Based PCN Pincer Complexes of Palladium(II): Mono- and Dinuclear Hydroxide Complexes and Ligand Rollover C–H Activation

Pyrazole-Based PCN Pincer Complexes of Palladium(II): Mono- and Dinuclear Hydroxide Complexes and Ligand Rollover C–H Activation

O2 Activation by Metal–Ligand Cooperation with IrI PNP Pincer Complexes

Hydrogenolysis of Dinuclear PCNR Ligated PdII μ‐Hydroxides and Their Mononuclear PdII Hydroxide Analogues

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Reactions of Square‐Planar d ⁸ Pincer Complexes with Oxygen and Hydrogen

O₂ Activation by Metal–Ligand Cooperation with Ir^I PNP Pincer Complexes

Hydrogenolysis of Dinuclear PCN^R Ligated Pd^II μ‐Hydroxides and Their Mononuclear Pd^II Hydroxide Analogues