An Isolable Terminal Imido Complex of Palladium and Catalytic Implications

Grünwald, Annette; Orth, Nicole; Scheurer, Andreas; Heinemann, Frank W.; Pöthig, Alexander; Munz, Dominik

doi:10.1002/anie.201809152

Cited by 39 publications

(27 citation statements)

References 79 publications

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“…C-H insertion by L n M-NR species has been associated with electrophilic subvalent nitrene ( 3 NR) 23 or imidyl ( 2 NR − ) [24][25][26] character that arises from low lying d orbitals of late transition met-als. This strongly reduces the imido ( 1 NR 2− ) contribution 27,28 . Similar considerations might apply for metallonitrene (L n M-N) or nitridyl (L n M=N • ) versus nitrido (L n M≡N) species (Fig.…”

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A platinum(ii) metallonitrene with a triplet ground state

et al. 2020

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ational synthetic method development is driven by the ability to relate reactivity to the electronic structures of key transient intermediates. For example, organic nitrenes (R-N) are generally highly reactive monovalent nitrogen species and detailed spectroscopic studies have enabled the assignment of their diverse reaction pathways, such as C-H insertion or N-N coupling, to the accessibility of triplet versus (open shell) singlet spin states 1,2 . In comparison, the well-established class of nitrido complexes (L n MN) commonly features trivalent nitrogen with significant covalent components of M-N σand π-bonding (Fig. 1a) 3 . Increased radical and electrophilic nitrogen character can be formally represented by divalent nitridyl all the way to monovalent metallonitrene contributions 4 . Formal nitrido complexes with predominant subvalent metallonitrene (L n M-N) character, which can be regarded as metal analogues of organic nitrenes, have been proposed as key intermediates in stoichiometric intramolecular [5][6][7][8][9] and intermolecular 10-15 nitrogen atom transfer reactions. However, in contrast to organic nitrenes 16 , authentic metallonitrenes with a monovalent atomic nitrogen ligand remain elusive, which impedes the development of new nitrogen transfer reactions based on electronic structure/reactivity relationships.The emergence of C-H amination and amidation via nitrene transfer as a powerful synthetic tool was fuelled by the development of group 9-11 transition metal catalysts that facilitate selective insertion of coordinated nitrene fragments (Fig. 1b) [17][18][19] . Late transition metals are also instrumental as anode materials in electrocatalytic amine oxidation for synthetic and fuel cell applications [20][21][22] . The dominance of late transition metals in redox transformations of nitrogenous species stimulated fundamental interest in M-N(R) bonding 3 . C-H insertion by L n M-NR species has been associated with electrophilic subvalent nitrene ( 3 NR) 23 or imidyl ( 2 NR − ) [24][25][26] character that arises from low lying d orbitals of late transition met-als. This strongly reduces the imido ( 1 NR 2− ) contribution 27,28 . Similar considerations might apply for metallonitrene (L n M-N) or nitridyl (L n M=N • ) versus nitrido (L n M≡N) species (Fig. 1a). However, intermolecular C-H activation has not been reported for the few known late transition metal nitrido or nitridyl complexes [29][30][31] . The exploitation of nitrogen atom insertion reactivity (Fig. 1b) is still in its infancy; as of yet, catalytic protocols are not known and systematic advances suffer from the lack of well-defined metallonitrene platforms.In this contribution, a formal nitrido complex beyond group 9 is reported. Crystallographic, spectroscopic, magnetic and computational characterization shows a triplet electronic ground state with a predominantly single-bonded metallonitrene (L n Pt ii -N) and nitrogen-centred diradical character. Facile N-atom insertion into C-H, B-H and B-C bonds is demonstrated. In contrast to the...

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A platinum(ii) metallonitrene with a triplet ground state

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“…We recently used a palladium(0) complex with an ancillary cyclic (alkyl)(amino)carbene (CAAC) ligand [15] as a reactive intermediate [16] . The solid state structure reveals now that 1 is a mononuclear, pyridine‐coordinate 14‐electron complex without interaction of the metal with the pendant imino group (Figure 1, left).…”

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Oxidative Addition of Water, Alcohols, and Amines in Palladium Catalysis

2020

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The homolytic cleavage of O−H and N−H or weak C−H bonds is a key elementary step in redox catalysis, but is thought to be unfeasible for palladium. In stark contrast, reported here is the room temperature and reversible oxidative addition of water, isopropanol, hexafluoroisopropanol, phenol, and aniline to a palladium(0) complex with a cyclic (alkyl)(amino)carbene (CAAC) and a labile pyridino ligand, as is also the case in popular N‐heterocyclic carbene (NHC) palladium(II) precatalysts. The oxidative addition of protic solvents or adventitious water switches the chemoselectivity in catalysis with alkynes through activation of the terminal C−H bond. Most salient, the homolytic activation of alcohols and amines allows atom‐efficient, additive‐free cross‐coupling and transfer hydrogenation under mild reaction conditions with usually unreactive, yet desirable reagents, including esters and bis(pinacolato)diboron.

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“…37 We became interested in carbazolyl bridged pincer-type NHC ligands [38][39][40][41] as promising candidates to stabilize multiple bonded late transition metal complexes. [41][42][43][44] Similar ligands, which had been studied mainly as NNN pincers (Fig. 1 II), [45][46][47][48][49][50][51][52][53][54][55][56][57] have been pioneered by Bezuidenhout [58][59][60][61][62] (CNC pincer, C: mesoionic carbene MIC; III and IV) and Kunz [63][64][65][66][67][68] (CNC pincer, C: N-heterocyclic carbene NHC; V).…”

Section: Introductionmentioning

confidence: 99%