Synthesis and reactivity of PC(sp<sup>3</sup>)P-pincer iridium complexes bearing a diborylmethyl anion

Kishino, Masamichi; Takaoka, Satoko; Shibutani, Yuki; Kusumoto, Shuhei; Nozaki, Kyoko

doi:10.1039/d2dt00513a

Cited by 2 publications

(2 citation statements)

References 108 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The diborylcarbenoids 2 F and 2 Cl , possessing a five-membered ring skeleton of CB 2 N 2 , 56 were prepared from compound 3 following Scheme 1. 57 Single crystals for both 2 F and 2 Cl were obtained from tetrahydrofuran (THF)/hexane solutions at ambient temperature, and the structures were unambiguously determined using X-ray crystallography (Figure 2). This is the first reported isolation and characterization of diborylcarbenoid to the best of our knowledge.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Synthesis, Characterization, and Trapping of a Cyclic Diborylcarbene, an Electrophilic Carbene

2023

Self Cite

View full text Add to dashboard Cite

A carbene bearing two geminal boryl substituents, called diborylcarbene (DBC), has been predicted to be highly Lewis acidic in sharp contrast to the well-studied persistent carbenes stabilized by π-donating substituents. Studies on DBC have been limited to either the base-trapping or theoretical calculations. Herein, we developed chemical equivalents for DBC, namely, K/X-diborylcarbenoids 2 X (X = F or Cl). Treatment of 2 F with Al(C 6 F 5 ) 3 yielded [AlF(C 6 F 5 ) 3 ] − -stabilized DBC 1-FAl, which showed a significant low-field shift of the carbenoid carbon from 169 ppm (doublet, coupling with 19 F) to 242 ppm (singlet). The loss of halogen was also detected through electrospray ionization time-of-flight mass spectrometry analysis of 2 X only in the presence of Al(C 6 F 5 ) 3 . Generated DBC 1 from 1-FAl or 2 Cl was successfully trapped with excess amounts of trialkylphosphines (PR 3 , R = Me or Et), which afforded the corresponding DBC-PR 3 adducts. In addition, the Lewis acidity of DBC 1 was evaluated both experimentally and theoretically to reveal that 1 is one of the most Lewis acidic species among neutral molecules.

show abstract

Section: ■ Results and Discussionmentioning

confidence: 99%

Synthesis, Characterization, and Trapping of a Cyclic Diborylcarbene, an Electrophilic Carbene

2023

Self Cite

View full text Add to dashboard Cite

show abstract

“…The high thermostability and long lifetime of these pincer complexes play a major role in improving the catalytic performance as compared to the earlier iridium AD catalysts of monodentate phosphine ligands . Since then, many PCP-Ir and relevant complexes have been developed through tuning the substituents on the P atoms, the donors, the backbones, and the linkers between the donors and backbones (Figure B). ,− One interesting example is Brookhart’s O-bridging pincer complex ( t Bu P O C O P)Ir III HCl 4 : The CH 2 -to-O linker substitution enhances the turnover numbers (TONs) roughly by a factor of 2 in the benchmark TD reaction of cyclooctane (COA) with t -butylethene (TBE) . Inspired by the subtle linker effect, we have developed a series of hybrid pincer complexes with linkers of S/O, O/N, and S/N atoms, respectively .…”

Section: Introductionmentioning

confidence: 99%

A New Paradigm in Pincer Iridium Chemistry: PCN Complexes for (De)Hydrogenation Catalysis and Beyond

et al. 2022

View full text Add to dashboard Cite

The discovery and development of organometallic catalysts is of paramount importance in modern organic synthesis, among which the ligand scaffolds play a crucial role in controlling the activity and selectivity. Over the past several decades, d 8 transitionmetal complexes of pincer ligands have been developed extensively thanks to their easy structural modification, versatile reactivities, and high stability. One paradigm is the bis(phosphine)-based pincer iridium complexes PCP-Ir, which are highly active for alkane dehydrogenation, partly due to their high thermostability. However, except for alkane dehydrogenation and related transformations, few applications of pincer iridium catalysis have been seen in organic synthesis. This mainly arises from the low functional-group compatibility and poor substrate scope and the limited catalytic chemistry that invariably involves Ir(I/III) redox processes initiated by oxidative addition of substrates to 14-electron (PCP)Ir fragments (the proposed catalytically active intermediates). In this Account, we describe our endeavor on the development of a new family of PCN-Ir complexes with initial intention on creating more efficient alkane dehydrogenation catalysts. The replacement of a soft, σdonor phosphine arm in the PCP ligands by a harder, π-acceptor N-heteroarene (pyridine or oxazoline) not only provides an additional platform to modify the structural properties but also offers new modes of bond activation and novel reactivities and catalysis. One uniqueness of the PCN-Ir system lies in the formation, via ortho-C(sp 2 )−H cyclometalation of the pyridine unit in the PCN Py ligand, of the neutral monohydride (PCC)Ir III HL (L = neutral ligand), which catalyzes positional and stereoselective 1alkene-to-(E)-2-alkene isomerization. Moreover, the PCN-Ir catalysts effect ethanol dehydrogenation without decarbonylation, allowing for transfer hydrogenation of unactivated alkenes and trans-selective semihydrogenation of internal alkynes with userfriendly ethanol as the H-donor. Another feature originates from the ability of the pentacoordinate hydrido chloride complex (PCN)Ir III HCl to undergo reversible solvent-coordination-induced-ionization (SCII), furnishing a cationic monohydride [(PCN)Ir III H(Sol)] + Cl − bearing an uncoordinated Cl anion that effects selective hydrometalation of internal alkynes over the corresponding (Z)-alkenes; the resulting (PCN)Ir III (vinyl)Cl complex undergoes amine-assisted formal alcoholysis involving the protonation of the Cl anion by the activated Ir III -bound EtOH, again via the SCII pathway. Together these elementary reactions lay the foundation for cis-selective semihydrogenation of alkynes with EtOH. Further, the design of the oxazoline-containing chiral complexes (PCN Oxa )Ir III HCl enables asymmetric transfer hydrogenation of alkenes/ketones with ethanol. The efficient catalytic αalkylation of unactivated esters/amides with alcohols is another case showing the benefit that the PCN-Ir catalyst can offer. These examples illustrate the prof...

show abstract

Synthesis and reactivity of PC(sp³)P-pincer iridium complexes bearing a diborylmethyl anion

Abstract: PC(sp3)P-Ir complexes bearing two geminal boron atoms attached to the central carbon anion were synthesized. Strong σ-donation and unique back-donation to the boron atom at the β-position were observed.

Cited by 2 publications

References 108 publications

Synthesis, Characterization, and Trapping of a Cyclic Diborylcarbene, an Electrophilic Carbene

Synthesis, Characterization, and Trapping of a Cyclic Diborylcarbene, an Electrophilic Carbene

A New Paradigm in Pincer Iridium Chemistry: PCN Complexes for (De)Hydrogenation Catalysis and Beyond

Contact Info

Product

Resources

About

Synthesis and reactivity of PC(sp3)P-pincer iridium complexes bearing a diborylmethyl anion

Abstract: PC(sp3)P-Ir complexes bearing two geminal boron atoms attached to the central carbon anion were synthesized. Strong σ-donation and unique back-donation to the boron atom at the β-position were observed.

Cited by 2 publications

References 108 publications

Synthesis, Characterization, and Trapping of a Cyclic Diborylcarbene, an Electrophilic Carbene

Synthesis, Characterization, and Trapping of a Cyclic Diborylcarbene, an Electrophilic Carbene

A New Paradigm in Pincer Iridium Chemistry: PCN Complexes for (De)Hydrogenation Catalysis and Beyond

Contact Info

Product

Resources

About

Synthesis and reactivity of PC(sp³)P-pincer iridium complexes bearing a diborylmethyl anion