Structure of a Novel Rhodium Phosphinite Compound: Agostic Interactions as a Model for an Oxidative Addition Intermediate

Pincer ligand metalation is presumed to proceed via initial coordination to the phosphorus atoms followed by C–H oxidative addition. Few isolated intermediates in this process are known. A rhodium phosphinite complex has been isolated and structurally characterized that exhibits a strong agostic interaction with a C–H bond in the ligand backbone. The [(^tBuPOCOP)­Rh­(CO)­H]⁺ system exhibits greater acidity and reactivity than the analogous iridium species (^tBuPOCOP = κ³-C₆H₃-1,3-[OP­(<i>t</i>Bu)₂]₂)

Structure and Solution Reactivity of (Triethylsilylium)triethylsilane Cations

Reaction of triphenylmethylium tetrakis­(pentafluorophenyl)­borate, [Ph₃C]­[B­(C₆F₅)₄], with excess neat triethylsilane affords triethylsilylium­(triethylsilane) tetrakis­(pentafluorophenyl)­borate, [(Et₃Si)₂(μ-H)]­[B­(C₆F₅)₄] (<b>1</b>), identified by X-ray crystallography. In chlorobenzene and fluorobenzene, <b>1</b> is observed in solution. When <b>1</b> is dissolved in benzene or toluene, the evolved gas was shown to be hydrogen. Isotope labeling experiments demonstrate that the hydrogen arises from the reaction of Et₃SiH with the silylium complex of the arene solvent

Structure of a Novel Rhodium Phosphinite Compound: Agostic Interactions as a Model for an Oxidative Addition Intermediate

Pincer ligand metalation is presumed to proceed via initial coordination to the phosphorus atoms followed by C–H oxidative addition. Few isolated intermediates in this process are known. A rhodium phosphinite complex has been isolated and structurally characterized that exhibits a strong agostic interaction with a C–H bond in the ligand backbone. The [(^tBuPOCOP)­Rh­(CO)­H]⁺ system exhibits greater acidity and reactivity than the analogous iridium species (^tBuPOCOP = κ³-C₆H₃-1,3-[OP­(<i>t</i>Bu)₂]₂)

η⁶‑Tetramethylfulvene and μ‑η³:η³‑Benzene Complexes of Iridium

The reaction of Cp*Ir­(NHC)­Me₂ (<b>Ir-Me</b>_<b>2</b>) with [CPh₃]⁺[B­(C₆F₅)₄]^ in dichloromethane resulted in conversion of the Cp* ligand to an η⁶-tetramethylfulvene ligand via apparent hydride abstraction (Cp* = η⁵-C₅Me₅; NHC = 1,3-<i>N</i>,<i>N</i>-dimethylimidazol-2-ylidene). The products of this reaction are triphenylmethane and the η⁶-tetramethylfulvene complex [(η⁶-C₅Me₄CH₂)­Ir­(NHC)­(Me₂)]⁺[B­(C₆F₅)₄]^ (<b>fulv-Ir</b>^<b>+</b>). When dichloromethane solutions of the related complex [Cp*Ir­(NHC)­(Ph)­(solv)]⁺[MeB­(C₆F₅)₃]⁻ were allowed to stand at room temperature, crystals of the unusual sandwich complex [{Cp*Ir­(NHC)}₂(μ-η³:η³-C₆H₆)]²⁺ (<b>Ir-C</b>_<b>6</b><b>H</b>_<b>6</b><b>-Ir</b>^<b>2+</b>) were obtained. Complexes <b>fulv-Ir</b>^<b>+</b> and <b>Ir-C</b>_<b>6</b><b>H</b>_<b>6</b><b>-Ir</b>^<b>2+</b> represent unique architectures in the Cp*Ir­(NHC) family. Both compounds were characterized by spectroscopic methods as well as by single-crystal X-ray diffraction

Regeneration of an Iridium(III) Complex Active for Alkane Dehydrogenation Using Molecular Oxygen

(^<i>dm</i>Phebox)­Ir­(OAc)₂(OH₂) (<b>1a</b>) has previously been found to promote stoichiometric alkane dehydrogenation, affording alkene, acetic acid, and the corresponding Ir hydride complex (^<i>dm</i>Phebox)­Ir­(OAc)­(H) (<b>2a</b>) in high yield. In this study, we describe the use of oxygen to quantitatively regenerate <b>1a</b> from <b>2a</b> and HOAc. Distinct reaction intermediates are observed during the conversion of <b>2a</b> to <b>1a</b>, depending upon the presence or absence of 1 equiv of acetic acid, highlighting potential mechanistic implications regarding alkane dehydrogenation catalysis and the use of oxygen as an oxidant in such systems

Alkane Dehydrogenation by C–H Activation at Iridium(III)

Stoichiometric alkane dehydrogenation utilizing an Ir^III pincer complex, (^<i>dm</i>Phebox)­Ir­(OAc)₂(OH₂) (<b>1a</b>), has been described. The reaction between <b>1a</b> and octane resulted in quantitative formation of (^<i>dm</i>Phebox)­Ir­(OAc)­(H) (<b>3a</b>) and octene. At early reaction times 1-octene is the major product, indicative of terminal C–H activation by <b>1a</b>. In contrast to prior reports of alkane dehydrogenation with Ir, C–H bond activation occurs at Ir^III and the dehydrogenation is not inhibited by nitrogen, olefin, or water

Regeneration of an Iridium(III) Complex Active for Alkane Dehydrogenation Using Molecular Oxygen

(^<i>dm</i>Phebox)­Ir­(OAc)₂(OH₂) (<b>1a</b>) has previously been found to promote stoichiometric alkane dehydrogenation, affording alkene, acetic acid, and the corresponding Ir hydride complex (^<i>dm</i>Phebox)­Ir­(OAc)­(H) (<b>2a</b>) in high yield. In this study, we describe the use of oxygen to quantitatively regenerate <b>1a</b> from <b>2a</b> and HOAc. Distinct reaction intermediates are observed during the conversion of <b>2a</b> to <b>1a</b>, depending upon the presence or absence of 1 equiv of acetic acid, highlighting potential mechanistic implications regarding alkane dehydrogenation catalysis and the use of oxygen as an oxidant in such systems

An Improved Synthesis of ^Me4PCP and DMPE

We present a new synthetic method for the bis­(dimethyl)­phosphines ^Me4PCP (C₆H₄-2,6-(CH₂P­(CH₃)₂)₂) and DMPE ((CH₃)₂PCH₂CH₂P­(CH₃)₂) that starts from an aminophosphine, Et₂NPMe₂. Two equivalents of Et₂NPMe₂ react with the corresponding bis­(alkyl bromide) to afford an oxygen- and moisture-stable aminophosphonium salt. NaAlH₄ selectively reduces the aminophosphonium salt to the desired phosphine. Each step is high yielding and requires minimal purification

Alkane Dehydrogenation by C–H Activation at Iridium(III)

Stoichiometric alkane dehydrogenation utilizing an Ir^III pincer complex, (^<i>dm</i>Phebox)­Ir­(OAc)₂(OH₂) (<b>1a</b>), has been described. The reaction between <b>1a</b> and octane resulted in quantitative formation of (^<i>dm</i>Phebox)­Ir­(OAc)­(H) (<b>3a</b>) and octene. At early reaction times 1-octene is the major product, indicative of terminal C–H activation by <b>1a</b>. In contrast to prior reports of alkane dehydrogenation with Ir, C–H bond activation occurs at Ir^III and the dehydrogenation is not inhibited by nitrogen, olefin, or water

η⁶‑Tetramethylfulvene and μ‑η³:η³‑Benzene Complexes of Iridium

The reaction of Cp*Ir­(NHC)­Me₂ (<b>Ir-Me</b>_<b>2</b>) with [CPh₃]⁺[B­(C₆F₅)₄]^ in dichloromethane resulted in conversion of the Cp* ligand to an η⁶-tetramethylfulvene ligand via apparent hydride abstraction (Cp* = η⁵-C₅Me₅; NHC = 1,3-<i>N</i>,<i>N</i>-dimethylimidazol-2-ylidene). The products of this reaction are triphenylmethane and the η⁶-tetramethylfulvene complex [(η⁶-C₅Me₄CH₂)­Ir­(NHC)­(Me₂)]⁺[B­(C₆F₅)₄]^ (<b>fulv-Ir</b>^<b>+</b>). When dichloromethane solutions of the related complex [Cp*Ir­(NHC)­(Ph)­(solv)]⁺[MeB­(C₆F₅)₃]⁻ were allowed to stand at room temperature, crystals of the unusual sandwich complex [{Cp*Ir­(NHC)}₂(μ-η³:η³-C₆H₆)]²⁺ (<b>Ir-C</b>_<b>6</b><b>H</b>_<b>6</b><b>-Ir</b>^<b>2+</b>) were obtained. Complexes <b>fulv-Ir</b>^<b>+</b> and <b>Ir-C</b>_<b>6</b><b>H</b>_<b>6</b><b>-Ir</b>^<b>2+</b> represent unique architectures in the Cp*Ir­(NHC) family. Both compounds were characterized by spectroscopic methods as well as by single-crystal X-ray diffraction