Neutral and Anionic Monomeric Zirconium Imides Prepared via Selective C=N Bond Cleavage of a Multidentate and Sterically Demanding β‐Diketiminato Ligand

2019 ◽  
Vol 14 (15) ◽  
pp. 2629-2638 ◽  
Author(s):  
Takashi Kurogi ◽  
Jiaxiang Chu ◽  
Yaofeng Chen ◽  
Daniel J. Mindiola
Keyword(s):  
Bond Cleavage ◽  
Sterically Demanding

Reactions of alkali metal and yttrium alkyls with a sterically demanding bis(aryloxysilyl)methane: Formation of aryloxide complexes by Si-O bond cleavage

2010 ◽  
Vol 13 (6-7) ◽  
pp. 593-602 ◽  
Author(s):  
Andrew D. Cornish ◽  
David P. Mills ◽  
William Lewis ◽  
Alexander J. Blake ◽  
Stephen T. Liddle
Keyword(s):  
Alkali Metal ◽  
Bond Cleavage ◽  
Methane Formation ◽  
Sterically Demanding

Formation of Silaimines from a Sterically Demanding Iminophosphonamido Chlorosilylene via intramolecular N–P bond Cleavage

2021 ◽  
Author(s):  
Shintaro Takahashi ◽  
Akihiko Ishii ◽  
Norio Nakata
Keyword(s):  
Nmr Spectroscopy ◽  
Bond Cleavage ◽  
Substitution Reactions ◽  
X Ray ◽  
X Ray Crystallography ◽  
Sterically Demanding

The sterically demanding iminophosphonamido chlorosilylene [Ph2P(DipN)2]SiCl (Dip = 2,6-diisopropylphenyl) was synthesized and fully characterized using NMR spectroscopy and X-ray crystallography. Substitution reactions of [Ph2P(DipN)2]SiCl with N- and Fe-nucleophiles led to...

scholarly journals Low Oxidation State Heavy P-Block Metal Compounds Supported by Di(amido) Chelating Ligands

2021 ◽  
Author(s):  
◽  
Ryan Schwamm
Keyword(s):  
Oxidation State ◽  
Bond Cleavage ◽  
Reducing Agents ◽  
Oxidation States ◽  
Cluster Compound ◽  
Single Bond ◽  
Reaction Products ◽  
Chloride Complexes ◽  
Sterically Demanding ◽  
Low Oxidation State

<p>The work presented in this thesis describes the synthesis and stabilisation of heavy p-block elements (defined herein as being those with 5s/p and 6s/p valence electrons) in low oxidation states using sterically demanding ligands based on a di(amido)siloxane framework ([(O{SiMe2N(R)}2]2-, abbrev. [(NONR)]2-).  Chapter 1 gives a general introduction to the heavy p-block elements and discusses a number of concepts that define the molecular chemistry of these elements. A brief introduction into low oxidation state main group chemistry is provided and the importance of sterically demanding ligands in this field of research is introduced. The di(amido)siloxane ligand framework utilised in this work is introduced, with common coordination modes and characteristic properties discussed.  Chapter 2 discusses the chemistry of low oxidation state bismuth complexes and follows a recent report by our group on the first structurally authenticated bismuth(II) radical •Bi(NONAr). The synthesis of a series of bismuth(III) monochloride species Bi(NONR)Cl (R = tBu, Ph, 2,6-Me2C6H3 (Ar’), 2,6-iPr2C6H3 (Ar) and 2,6-(CHPh2)2-4-tBu-C6H2 (Ar‡)) is discussed, and the steric properties of the ligand systems evaluated. In the case of the R = tBu and Ar‡ derivatives, reduction of the bismuth(III) monochloride gave the dibismuthane [Bi(NONtBu)]2 and bismuth(II) radical •Bi(NONAr‡), respectively. Further reduction of the bismuth centres resulted in the formation of rare and unprecedented multimetallic bismuth compounds containing [Bin]n+ cores. These include the Bi4 cluster compound Bi4(NONAr)2, in which the bismuth atoms exist in an unprecedented mixed valent arrangement and may be assigned oxidation states of 0, +1 or +2, and the tribismuthane cluster [Bi3(NONtBu)2]-, which features the first structurally characterised Bi3 chain. The utility of the di(amido) ligand plays a key role in the formation of many of these compounds, with Bi-N bond cleavage suggested to be a key step in many of the reaction pathways.  Chapter 3 discusses the reactivity of the bismuth(II) complexes [Bi(NONtBu)]2, •Bi(NONAr) and •Bi(NONAr‡) which feature either a Bi-Bi bond or a bismuth-centred radical. Initial experiments parallel reported reactivity with halogen radical sources (N-bromosuccinimide or iodine), chalcogens (S, Se, Te) and the stable nitroxyl radical (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), resulting in oxidative addition to generate bismuth(III) complexes. In the latter case, the isolated reaction products, Bi(NONR)(OTEMP), were used to access the catalytic coupling of TEMPO and phenylsilane. Subsequent investigations into the reactivity of the bismuth(II) species revealed the selective activation of white phosphorus (P4) and terminal aromatic alkynes by •Bi(NONAr), generating the bismuth(III) complexes [Bi(NONAr)]2(P4) and [Bi(NONR)]2(HC=C(C6H4-4-X)), respectively. In both cases, a temperature dependent equilibrium is observed. In contrast, the dibismuthane [Bi(NONtBu)]2 and more encumbered bismuth radical •Bi(NONAr‡) do not react with these substrates, demonstrating the importance of the nature of the bismuth centre (i.e. dibismuthane vs. bismuth radical) and ligand bulk on the reactivity of these systems.  Chapter 4 describes the synthesis and characterisation of a series of low oxidation state antimony compounds. A series of distibanes supported by the (NONR)-framework were prepared from the reaction of antimony(III) chloride species Sb(NONR)Cl with magnesium(I) reducing agents [(BDIAr§)Mg]2 (Ar§ = 2,4,6-Me3C6H3 or Ar). When R = tBu, Ph or 2,6-Me2C6H3 (Ar’), a distibane [Sb(NONR)]2 is obtained, featuring a Sb-Sb single bond. While the tBu and Ph derivatives contained typical Sb-Sb single bonds, the bonding in the Ar’ derivative is elongated, significantly longer than in all other reported distibanes. The weakness of this bond is highlighted in a reaction with P4, which shows activation of the P4 tetrahedron and P-P bond cleavage. In contrast, reduction of the bulkier Ar derivative (Ar = 2,6-iPr2C6H3) with the magnesium(I) reagents results in formation of the distibene [Sb(NONR)Mg(BDIAr§)]2, featuring a Sb=Sb bond.  Chapter 5 describes the synthesis and characterisation of low oxidation state indium compounds supported by the (NONAr)-ligand. A number of indium(III) chloride species supported by either the (NONAr)-ligand or the retro-Brook rearranged (NNOAr)-ligand (NNOAr = [RN{Me2SiO}{Me2SiN(R)}) were synthesised. In all cases, an equivalent of lithium chloride was retained in the molecular structure, allowing isolation of the indate complexes In(NONAr)(μ-Cl)2Li(Et2O)2, [Li(THF)4][In(NONAr)Cl2] and In(NNOAr.Li(THF)3)Cl2. Attempts to reduce these complexes using a hydride source were unsuccessful, instead yielding the corresponding indium(III) hydride species [Li(THF)4][In(NONAr)H2] and In(NNOAr.Li(THF)3)H2, respectively. Reduction of the (NONAr)-supported indium(III) chloride complexes using alkali reducing agents allowed access to the diindane [In(NONAr)]2, featuring an In-In single bond, and the first example of an anionic N-heterocyclic indene. The latter species is isovalent with N-heterocyclic carbenes and is a potential pre-cursor for indium-metal bonding formation. In addition, this compound is of interest as a source of nucleophilic indium.  Finally, Chapter 6 provides a summary of the results presented in this thesis and a brief overview of the future direction of this field of research.</p>

scholarly journals Low Oxidation State Heavy P-Block Metal Compounds Supported by Di(amido) Chelating Ligands

2021 ◽  
Author(s):  
◽  
Ryan Schwamm
Keyword(s):  
Oxidation State ◽  
Bond Cleavage ◽  
Reducing Agents ◽  
Oxidation States ◽  
Cluster Compound ◽  
Single Bond ◽  
Reaction Products ◽  
Chloride Complexes ◽  
Sterically Demanding ◽  
Low Oxidation State

<p>The work presented in this thesis describes the synthesis and stabilisation of heavy p-block elements (defined herein as being those with 5s/p and 6s/p valence electrons) in low oxidation states using sterically demanding ligands based on a di(amido)siloxane framework ([(O{SiMe2N(R)}2]2-, abbrev. [(NONR)]2-).  Chapter 1 gives a general introduction to the heavy p-block elements and discusses a number of concepts that define the molecular chemistry of these elements. A brief introduction into low oxidation state main group chemistry is provided and the importance of sterically demanding ligands in this field of research is introduced. The di(amido)siloxane ligand framework utilised in this work is introduced, with common coordination modes and characteristic properties discussed.  Chapter 2 discusses the chemistry of low oxidation state bismuth complexes and follows a recent report by our group on the first structurally authenticated bismuth(II) radical •Bi(NONAr). The synthesis of a series of bismuth(III) monochloride species Bi(NONR)Cl (R = tBu, Ph, 2,6-Me2C6H3 (Ar’), 2,6-iPr2C6H3 (Ar) and 2,6-(CHPh2)2-4-tBu-C6H2 (Ar‡)) is discussed, and the steric properties of the ligand systems evaluated. In the case of the R = tBu and Ar‡ derivatives, reduction of the bismuth(III) monochloride gave the dibismuthane [Bi(NONtBu)]2 and bismuth(II) radical •Bi(NONAr‡), respectively. Further reduction of the bismuth centres resulted in the formation of rare and unprecedented multimetallic bismuth compounds containing [Bin]n+ cores. These include the Bi4 cluster compound Bi4(NONAr)2, in which the bismuth atoms exist in an unprecedented mixed valent arrangement and may be assigned oxidation states of 0, +1 or +2, and the tribismuthane cluster [Bi3(NONtBu)2]-, which features the first structurally characterised Bi3 chain. The utility of the di(amido) ligand plays a key role in the formation of many of these compounds, with Bi-N bond cleavage suggested to be a key step in many of the reaction pathways.  Chapter 3 discusses the reactivity of the bismuth(II) complexes [Bi(NONtBu)]2, •Bi(NONAr) and •Bi(NONAr‡) which feature either a Bi-Bi bond or a bismuth-centred radical. Initial experiments parallel reported reactivity with halogen radical sources (N-bromosuccinimide or iodine), chalcogens (S, Se, Te) and the stable nitroxyl radical (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), resulting in oxidative addition to generate bismuth(III) complexes. In the latter case, the isolated reaction products, Bi(NONR)(OTEMP), were used to access the catalytic coupling of TEMPO and phenylsilane. Subsequent investigations into the reactivity of the bismuth(II) species revealed the selective activation of white phosphorus (P4) and terminal aromatic alkynes by •Bi(NONAr), generating the bismuth(III) complexes [Bi(NONAr)]2(P4) and [Bi(NONR)]2(HC=C(C6H4-4-X)), respectively. In both cases, a temperature dependent equilibrium is observed. In contrast, the dibismuthane [Bi(NONtBu)]2 and more encumbered bismuth radical •Bi(NONAr‡) do not react with these substrates, demonstrating the importance of the nature of the bismuth centre (i.e. dibismuthane vs. bismuth radical) and ligand bulk on the reactivity of these systems.  Chapter 4 describes the synthesis and characterisation of a series of low oxidation state antimony compounds. A series of distibanes supported by the (NONR)-framework were prepared from the reaction of antimony(III) chloride species Sb(NONR)Cl with magnesium(I) reducing agents [(BDIAr§)Mg]2 (Ar§ = 2,4,6-Me3C6H3 or Ar). When R = tBu, Ph or 2,6-Me2C6H3 (Ar’), a distibane [Sb(NONR)]2 is obtained, featuring a Sb-Sb single bond. While the tBu and Ph derivatives contained typical Sb-Sb single bonds, the bonding in the Ar’ derivative is elongated, significantly longer than in all other reported distibanes. The weakness of this bond is highlighted in a reaction with P4, which shows activation of the P4 tetrahedron and P-P bond cleavage. In contrast, reduction of the bulkier Ar derivative (Ar = 2,6-iPr2C6H3) with the magnesium(I) reagents results in formation of the distibene [Sb(NONR)Mg(BDIAr§)]2, featuring a Sb=Sb bond.  Chapter 5 describes the synthesis and characterisation of low oxidation state indium compounds supported by the (NONAr)-ligand. A number of indium(III) chloride species supported by either the (NONAr)-ligand or the retro-Brook rearranged (NNOAr)-ligand (NNOAr = [RN{Me2SiO}{Me2SiN(R)}) were synthesised. In all cases, an equivalent of lithium chloride was retained in the molecular structure, allowing isolation of the indate complexes In(NONAr)(μ-Cl)2Li(Et2O)2, [Li(THF)4][In(NONAr)Cl2] and In(NNOAr.Li(THF)3)Cl2. Attempts to reduce these complexes using a hydride source were unsuccessful, instead yielding the corresponding indium(III) hydride species [Li(THF)4][In(NONAr)H2] and In(NNOAr.Li(THF)3)H2, respectively. Reduction of the (NONAr)-supported indium(III) chloride complexes using alkali reducing agents allowed access to the diindane [In(NONAr)]2, featuring an In-In single bond, and the first example of an anionic N-heterocyclic indene. The latter species is isovalent with N-heterocyclic carbenes and is a potential pre-cursor for indium-metal bonding formation. In addition, this compound is of interest as a source of nucleophilic indium.  Finally, Chapter 6 provides a summary of the results presented in this thesis and a brief overview of the future direction of this field of research.</p>

Metal-Metal Cooperative Bond Activation by Heterobimetallic Alkyl, Aryl, and Acetylide PtII/CuI Complexes

2020 ◽  
Author(s):  
Shubham Deolka ◽  
Orestes Rivada Wheelaghan ◽  
Sandra Aristizábal ◽  
Robert Fayzullin ◽  
Shrinwantu Pal ◽  
...  
Keyword(s):  
Alkyl Group ◽  
Bond Activation ◽  
Bond Cleavage ◽  
Terminal Alkyne ◽  
Alkyl Aryl ◽  
Metal Metal ◽  
The Stability ◽  
Selective Formation ◽  
Organoplatinum Compounds

We report selective formation of heterobimetallic PtII/CuI complexes that demonstrate how facile bond activation processes can be achieved by altering reactivity of common organoplatinum compounds through their interaction with another metal center. The interaction of the Cu center with Pt center and with a Pt-bound alkyl group increases the stability of PtMe2 towards undesired rollover cyclometalation. The presence of the CuI center also enables facile transmetalation from electron-deficient tetraarylborate [B(ArF)4]- anion and mild C-H bond cleavage of a terminal alkyne, which was not observed in the absence of an electrophilic Cu center. The DFT study indicates that the role of Cu center acts as a binding site for alkyne substrate, while activating its terminal C-H bond.

Regioselective Gas-Phase n-Butane Transfer Dehydrogenation via Silica-Supported Pincer-Iridium Complexes

2020 ◽  
Author(s):  
Boris Sheludko ◽  
Cristina Castro ◽  
Chaitanya Khalap ◽  
Thomas Emge ◽  
Alan Goldman ◽  
...  
Keyword(s):  
Gas Phase ◽  
Active Site ◽  
Lower Cost ◽  
Open Systems ◽  
Iridium Complexes ◽  
Terminal Olefin ◽  
Molecular Precursors ◽  
Sterically Demanding ◽  
Olefin Production ◽  
Steam Cracking

<b>Abstract:</b> The production of olefins via on-purpose dehydrogenation of alkanes allows for a more efficient, selective and lower cost alternative to processes such as steam cracking. Silica-supported pincer-iridium complexes of the form [(≡SiO-<sup>R4</sup>POCOP)Ir(CO)] (<sup>R4</sup>POCOP = κ<sup>3</sup>-C<sub>6</sub>H<sub>3</sub>-2,6-(OPR<sub>2</sub>)<sub>2</sub>) are effective for acceptorless alkane dehydrogenation, and have been shown stable up to 300 °C. However, while solution-phase analogues of such species have demonstrated high regioselectivity for terminal olefin production under transfer dehydrogenation conditions at or below 240 °C, in open systems at 300 °C, regioselectivity under acceptorless dehydrogenation conditions is consistently low. In this work, complexes <a>[(≡SiO-<i><sup>t</sup></i><sup>Bu4</sup>POCOP)Ir(CO)] </a>(<b>1</b>) and [(≡SiO-<i><sup>i</sup></i><sup>Pr4</sup>PCP)Ir(CO)] (<b>2</b>) were synthesized via immobilization of molecular precursors. These complexes were used for gas-phase butane transfer dehydrogenation using increasingly sterically demanding olefins, resulting in observed selectivities of up to 77%. The results indicate that the active site is conserved upon immobilization.

Room Temperature Alkali Metal Reduction of Carbon Dioxide

2020 ◽  
Author(s):  
Lucas A. Freeman ◽  
Akachukwu D. Obi ◽  
Haleigh R. Machost ◽  
Andrew Molino ◽  
Asa W. Nichols ◽  
...  
Keyword(s):  
Alkali Metal ◽  
Alkali Metals ◽  
Room Temperature ◽  
Chemical Reduction ◽  
Bond Cleavage ◽  
Open Shell ◽  
Metal Reduction ◽  
One Pot ◽  
Earth Abundant ◽  
Electron Reduction

The reduction of the relatively inert carbon–oxygen bonds of CO<sub>2</sub> to access useful CO<sub>2</sub>-derived organic products is one of the most important fundamental challenges in synthetic chemistry. Facilitating this bond-cleavage using earth-abundant, non-toxic main group elements (MGEs) is especially arduous because of the difficulty in achieving strong inner-sphere interactions between CO<sub>2</sub> and the MGE. Herein we report the first successful chemical reduction of CO<sub>2</sub> at room temperature by alkali metals, promoted by a cyclic(alkyl)(amino) carbene (CAAC). One-electron reduction of CAAC-CO<sub>2</sub> adduct (<b>1</b>) with lithium, sodium or potassium metal yields stable monoanionic radicals clusters [M(CAAC–CO<sub>2</sub>)]<sub>n</sub>(M = Li, Na, K, <b> 2</b>-<b>4</b>) and two-electron alkali metal reduction affords open-shell, dianionic clusters of the general formula [M<sub>2</sub>(CAAC–CO<sub>2</sub>)]<sub>n </sub>(<b>5</b>-<b>8</b>). It is notable that these crystalline clusters of reduced CO<sub>2</sub> may also be isolated via the “one-pot” reaction of free CO<sub>2</sub> with free CAAC followed by the addition of alkali metals – a reductive process which does not occur in the absence of carbene. Each of the products <b>2</b>-<b>8</b> were investigated using a combination of experimental and theoretical methods.<br>

Oxygen-Oxygen Bond Cleavage and Formation in Co(II) Mediated Stoichiometric O2 Reduction via the Potential Intermediacy of a Co(IV) Oxyl Radical

2018 ◽  
Author(s):  
Lucie Nurdin ◽  
Denis M. Spasyuk ◽  
Laura Fairburn ◽  
Warren Piers ◽  
Laurent Maron
Keyword(s):  
Bond Cleavage ◽  
Peroxo Complex ◽  
Oxygen Oxygen ◽  
O2 Reduction ◽  
Oxygen Bond ◽  
Pentadentate Ligand

Diprotonation of a remarkably stable, toluene soluble cobalt peroxo complex supported by a neutral, dianionic pentadentate ligand leads to facile O-O bond cleavage and production of a highly reactive Co(IV) oxyl cation intermediate that dimerizes and releases O<sub>2</sub>. These processes are relevant to both O<sub>2</sub> reduction and O<sub>2</sub> evolution and the mechanism was probed in detail both experimentally and computationally.

Electron Donation by Low-Crystalline Ba-La-Ce Oxygen-Deficient Composite Oxide Accumulating on Ru Nanoparticles for Ammonia Synthesis under Mild Conditions

2019 ◽  
Author(s):  
Katsutoshi Sato ◽  
Shin-ichiro Miyahara ◽  
Yuta Ogura ◽  
Kotoko Tsujimaru ◽  
Yuichiro Wada ◽  
...  
Keyword(s):  
Ammonia Synthesis ◽  
Bond Cleavage ◽  
Synthesis Process ◽  
Strong Electron ◽  
Mild Conditions ◽  
Ru Nanoparticles ◽  
Rate Determining Step ◽  
Highly Active ◽  
Composite Oxides ◽  
Low Crystalline

<p>To mitigate global problems related to energy and global warming, it is helpful to develop an ammonia synthesis process using catalysts that are highly active under mild conditions. Here we show that the ammonia synthesis activity of Ru/Ba/LaCeO<i><sub>x</sub></i> pre-reduced at 700 °C is the highest reported among oxide-supported Ru catalysts. Our results indicate that low crystalline oxygen-deficient composite oxides, which include Ba<sup>2+</sup>, Ce<sup>3+</sup> and La<sup>3+</sup>, with strong electron-donating ability, accumulate on Ru particles and thus promote N≡N bond cleavage, which is the rate determining step for ammonia synthesis.</p>

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