Hydrolysis of (η5-C5Me5)MMe4 (M = Mo, W) and the Formation of Organometallic Oxides with μ3-CH Methylidyne and μ-CH2 Methylidene Groups: Model Compounds for Catalysis on Metal Oxide Surfaces

Mechanism of Coupling of Methylidene to Ethylene Ligands in Dimetallic Assemblies; Computational Investigation of a Model for a Key Step in Catalytic C1 Chemistry

Methylidene complexes often couple to ethylene complexes, but the mechanistic insight is scant. The path by which two cations [(η⁵-C₅H₅)Re(NO)(PPh₃)(═CH₂)]⁺ (5⁺) transform (CH₂Cl₂/acetonitrile) to [(η⁵-C₅H₅)Re(NO)(PPh₃)(H₂C═CH₂)]⁺ (6⁺) and [(η⁵-C₅H₅)Re(NO)(PPh₃)(NCCH₃)]⁺ is studied by density functional theory. Experiments provide a number of constraints such as the second-order rate in 5⁺; no prior ligand dissociation/exchange; a faster reaction of (S)-5⁺ with (S)-5⁺ than with (R)-5⁺ ("enantiomer self-recognition"). Although dirhenium dications with Re(μ-CH₂)₂Re cores represent energy minima, they are not accessible by 2 + 2 cycloadditions of 5⁺. Transition states leading to ReCH₂CH₂Re linkages are prohibitively high in energy. However, 5⁺ can give non-covalent S_Re/S_Re or S_Re/R_Re dimers with π interactions between the PPh₃ ligands but long ReCH₂···H₂CRe and H₂CRe···H₂CRe distances (3.073-3.095 Å and 3.878-4.529 Å, respectively). In rate-determining steps, these afford [(η⁵-C₅H₅)Re(NO)(PPh₃)(μ-η²:η²-H₂C···CH₂)(Ph₃P)(ON)Re(η⁵-C₅H₅)]²⁺ (13²⁺), in which one rhenium binds the bridging ethylene more tightly than the other (2.115-2.098 vs 2.431-2.486 Å to the centroid). In the S_Re/R_Re adduct, Dewar-Chatt-Duncanson optimization leads to unfavorable PPh₃/PPh₃ contacts. Ligand interactions are further dissected in the preceding transition states via component analyses, and ΔΔG^‡ (1.2 kcal/mol, CH₂Cl₂) favors the S_Re/S_Re pathway, in accordance with the experiment. Acetonitrile then displaces 6⁺ from the more weakly bound rhenium of 13²⁺. The formation of similar μ-H₂C···CH₂ intermediates is found to be rate-determining for varied coordinatively saturated M═CH₂ species [M = Fe(d⁶)/Re(d⁴)/Ta(d²)], establishing generality and enhancing relevancy to catalytic CH₄ and CO/H₂ chemistry.

Beyond Takai's Olefination Reagent: Persistent Dehalogenation Emerges in a Chromium(III)-μ3 -Methylidyne Complex

Reaction of CHI3 with six equivalents of CrCl2 in THF at low temperatures affords [Cr3 Cl3 (μ2 -Cl)3 (μ3 -CH)(thf)6 ] as the first isolable high-yield CrIII μ3 -methylidyne complex. Substitution of the terminal chlorido ligands via salt metathesis with alkali-metal cyclopentadienides generates isostructural half-sandwich chromium(III)-μ3 -methylidynes [CpR 3 Cr3 (μ2 -Cl)3 (μ3 -CH)] (CpR =C5 H5 , C5 Me5 , C5 H4 SiMe3 ). Side and decomposition products of the Cl/CpR exchange reactions were identified and structurally characterized for [Cr4 (μ2 -Cl)4 (μ2 -I)2 (μ4 -O)(thf)4 ] and [(η5 -C5 H4 SiMe3 )CrCl(μ2 -Cl)2 Li(thf)2 ]. The Cl/CpR exchange drastically changed the ambient-temperature effective magnetic moment μeff from 9.30/9.11 μB (solution/solid) to 3.63/4.32 μB (CpR =C5 Me5 ). Reactions of [Cr3 Cl3 (μ2 -Cl)3 (μ3 -CH)(thf)6 ] with aldehydes and ketones produce intricate mixtures of species through oxy/methylidyne exchange, which were partially identified as radical recombination products through GC/MS analysis and 1 H NMR spectroscopy.

Hydrolysis of organometallic and metal–amide precursors: synthesis routes to oxo-bridged heterometallic complexes, metal-oxo clusters and metal oxide nanoparticles

Organometallic and metal amide reagents react with –OH groups to generate metal–oxygen connectivity, yielding metal-oxo heterobimetallics, clusters and nanoparticles.

Reactions of d(0) tungsten alkylidyne complexes with O2 or H2O. Formation of an oxo siloxy complex through unusual silyl migrations

(Me3SiCH2)3(Me3SiC≡)W←O=PMe3 (1), an adduct between (Me3SiCH2)3W≡CSiMe3 (2) and O=PMe3, reacts with O2 to give O=W(OSiMe3)(CH2SiMe3)3 (3) and CO2. Reaction of 2 with H2O yields 3 and the trimer [(μ-O)W(CH2SiMe3)2(=O)(THF)]3 (4). In the reaction of D2O with 2, 3-d(n) and methane isotopologues CH2D2, CHD3 and CD4 have been observed.

Is water a friend or foe in organometallic chemistry? The case of group 13 organometallic compounds

This Account summarizes the recent developments in the hydrolysis chemistry of Group 13 trialkyl and triaryl compounds. Emphasis has been placed on the results obtained by us on (a) 1H NMR investigations of controlled hydrolyses of AlMes3 and GaMes3, (b) low-temperature isolation of water adducts of triaryl compounds of aluminum and gallium, (c) synthesis and structural characterization of new polyhedral alumoxanes and galloxanes, and (d) the search for an easy way to synthesize well-defined crystalline methylalumoxanes by deprotonation of the hydroxides with alkyllithium reagents. The systematic studies on the hydrolysis of tBu3Al carried out by Barron et al. are also discussed in order to elucidate the roles of (i) reaction temperature, (ii) solvent medium, and (iii) source of water molecules, in building up hitherto unknown alumoxane clusters. The role of water impurity in organometallic reactions involving a Group 13 alkyl and other ligands (such as silanetriols and phosphorus acids) to build molecular clusters has also been discussed.