Structural elucidation of a mononuclear titanium methylidene

Grant, L.,Ahn, S.,Manor, B.,Baik, M. H.,Mindiola, D. Royal Society of Chemistry 2017 Chemical communications Vol.53 No.24

<P>The first example of a structurally characterized titanium methylidene, (PN)(2)Ti=CH2, has been prepared via one-electron oxidation of (PN)(2)Ti(CH3) followed by deprotonation or by H-atom abstraction using an aryloxyl radical. The Ti=C distance was found to be 1.939(3) angstrom, and variable temperature, multinuclear, and multidimensional NMR spectroscopic experiments revealed the methylidene to engage in long range interactions with protons on the ligand framework. Computational studies showed that the Ti=C bond, which until now has eluded structural studies, displays all the hallmarks of a prototypical Schrock-carbene.</P>

Conversion of methane to ethylene using an Ir complex and phosphorus ylide as a methylene transfer reagent

Zatsepin, Pavel,Ahn, Seihwan,Pudasaini, Bimal,Gau, Michael R.,Baik, Mu-Hyun,Mindiola, Daniel J. The Royal Society of Chemistry 2019 Chemical communications Vol.55 No.13

<P>Cp*(Me3P)Ir(CH3)(OTf), a complex known to reversibly activate CH4 and other hydrocarbons under mild conditions, reacts with the phosphorus ylide H2CPPh3 in THF to afford two major species [Cp*(Me3P)(Ph3P)Ir(CH2CH3)][OTf] and [Cp*(Me3P)Ir(H)(η<SUP>2</SUP>-CH2CH2)][OTf]. Insertion of the ylide methylene group can also occur with Cp*(Me3P)Ir(Ph)(OTf) to afford the benzyl [Cp*(Me3P)(Ph3P)Ir(CH2Ph)][OTf]. Theoretical studies suggest the intermediacy of an Ir(iii)CH2 species.</P>

Room temperature olefination of methane with titanium–carbon multiple bonds

Kurogi, Takashi,Won, Joonghee,Park, Bohyun,Trofymchuk, Oleksandra S.,Carroll, Patrick J.,Baik, Mu-Hyun,Mindiola, Daniel J. Royal Society of Chemistry 2018 Chemical Science Vol.9 No.13

<▼1><P>C–H activation of methane followed by dehydrocoupling at room temperature led ultimately to the formation of the olefin H<SUB>2</SUB>C 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 CH<SUP><I>t</I></SUP>Bu <I>via</I> the addition of redox-active ligands (L) such as thioxanthone or 2,2′-bipyridine (bipy) to (PNP)Ti 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 CH<SUP><I>t</I></SUP>Bu(CH<SUB>3</SUB>) (<B>1</B>).</P></▼1><▼2><P>C–H activation of methane followed by dehydrocoupling at room temperature led ultimately to the formation of the olefin H<SUB>2</SUB>C 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000

A new and selective cycle for dehydrogenation of linear and cyclic alkanes under mild conditions using a base metal

Solowey, Douglas P.,Mane, Manoj V.,Kurogi, Takashi,Carroll, Patrick J.,Manor, Brian C.,Baik, Mu-Hyun,Mindiola, Daniel J. Nature Publishing Group 2017 Nature chemistry Vol.9 No.11

Selectively converting linear alkanes to α-olefins under mild conditions is a highly desirable transformation given the abundance of alkanes as well as the use of olefins as building blocks in the chemical community. Until now, this reaction has been primarily the remit of noble-metal catalysts, despite extensive work showing that base-metal alkylidenes can mediate the reaction in a stoichiometric fashion. Here, we show how the presence of a hydrogen acceptor, such as the phosphorus ylide, when combined with the alkylidene complex (PNP)Ti=CH<SUP>t</SUP>Bu(CH<SUB>3</SUB>) (PNP=N[2-P(CHMe<SUB>2</SUB>)<SUB>2</SUB>-4-methylphenyl]<SUB>2</SUB><SUP>−</SUP>), catalyses the dehydrogenation of cycloalkanes to cyclic alkenes, and linear alkanes with chain lengths of C<SUB>4</SUB> to C<SUB>8</SUB> to terminal olefins under mild conditions. This Article represents the first example of a homogeneous and selective alkane dehydrogenation reaction using a base-metal titanium catalyst. We also propose a unique mechanism for the transfer dehydrogenation of hydrocarbons to olefins and discuss a complete cycle based on a combined experimental and computational study.

Catalytic borylation of methane

Smith, Kyle T.,Berritt, Simon,Gonzá,lez-Moreiras, Mariano,Ahn, Seihwan,Smith III, Milton R.,Baik, Mu-Hyun,Mindiola, Daniel J. American Association for the Advancement of Scienc 2016 Science Vol.351 No.6280

<P>Despite steady progress in catalytic methods for the borylation of hydrocarbons, methane has not yet been subject to this transformation. Here we report the iridium-catalyzed borylation of methane using bis(pinacolborane) in cyclohexane solvent. Initially, trace amounts of borylated products were detected with phenanthroline-coordinated Ir complexes. A combination of experimental high-pressure and high-throughput screening, and computational mechanism discovery techniques helped to rationalize the foundation of the catalysis and identify improved phosphine-coordinated catalytic complexes. Optimized conditions of 150 degrees C and 3500-kilopascal pressure led to yields as high as similar to 52%, turnover numbers of 100, and improved chemoselectivity for monoborylated versus diborylated methane.</P>

Room-Temperature Ring-Opening of Quinoline, Isoquinoline, and Pyridine with Low-Valent Titanium

Baek, Seung-yeol,Kurogi, Takashi,Kang, Dahye,Kamitani, Masahiro,Kwon, Seongyeon,Solowey, Douglas P.,Chen, Chun-Hsing,Pink, Maren,Carroll, Patrick J.,Mindiola, Daniel J.,Baik, Mu-Hyun American Chemical Society 2017 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.139 No.36

<P>The complex (PNP)Ti=(CHBu)-Bu-t((CH2Bu)-Bu-t) (PNP = N[2-P(i)p(r2)-4-methylphenyl](2-)) dehydrogenates cyclohexane to cyclohexene by forming a transient low-valent titanium-alkyl species, [(PNP)Ti((CH2Bu)-Bu-t)], which reacts with 2 equiv of quinoline (Q) at room temperature to form (H3CBu)-Bu-t and a Ti(IV) species where the less hindered C-2=N-1 bond of Qis ruptured and coupled to another equivalent of Q, The product isolated from this reaction is an imide with a tethered cycloamide group, (PNP)Ti=N[C18H13N] (1). Under photolytic conditions, intramolecular C-H bond activation across the imide moiety in 1 occurs to form 2, and thermolysis reverses this process. The reaction of 2 equiv of isoquinoline (Iq) with intermediate [(PNP)Ti((CH2Bu)-Bu-t)] results in regioselective cleavage of the C-I=N-2 and C-1-H bonds, which eventually couple to form complex 3, a constitutional isomer of 1. Akin to 1, the transient [(PNP)Ti((CH2Bu)-Bu-t)] complex can ring-open and couple two pyridine molecules, to produce a close analogue of 1, complex (PNP)Ti=N[C10H9N] (4). Multinudear and multidimensional NMR spectra confirm structures for complexes 1-4, whereas solid-state structural analysis reveals the structures of 2, 3, and 4. DFT calculations suggest an unprecedented Mechanism for ring-opening of Q wheat the reactive intermediate in the low-spin manifold crosses over to the high-spin surface to access a low-energy transition state but returns to the low-spin surface immediately. This double spin-crossover constitutes a rare example of a two-state reactivity, which is key for enabling the reaction at room temperature. The regioselective behavior of Iq ring-opening is found to be due to electronic effects, where the aromatic resonance of the bicycle is maintained during the key C-C coupling event.</P>

C-H Bond Addition across a Transient Uranium-Nitrido Moiety and Formation of a Parent Uranium Imido Complex

Mullane, Kimberly C.,Ryu, Ho,Cheisson, Thibault,Grant, Lauren N.,Park, Ji Young,Manor, Brian C.,Carroll, Patrick J.,Baik, Mu-Hyun,Mindiola, Daniel J.,Schelter, Eric J. American Chemical Society 2018 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.140 No.36

<P>Uranium complexes in the +3 and +4 oxidation states were prepared using the anionic PN<SUP>-</SUP> (PN<SUP>-</SUP> = (<I>N</I>-(2-(diisopropylphosphino)-4-methylphenyl)-2,4,6-trimethylanilide) ligand framework. New complexes include the halide starting materials, (PN)<SUB>2</SUB>U<SUP>III</SUP>I (<B>1</B>) and (PN)<SUB>2</SUB>U<SUP>IV</SUP>Cl<SUB>2</SUB> (<B>2</B>), which both yield (PN)<SUB>2</SUB>U<SUP>IV</SUP>(N<SUB>3</SUB>)<SUB>2</SUB> (<B>3</B>) by reaction with NaN<SUB>3</SUB>. Compound <B>3</B> was reduced with potassium graphite to produce a putative, transient uranium-nitrido moiety that underwent an intramolecular C-H activation to form a rare example of a parent imido complex, [K(THF)<SUB>3</SUB>][(PN)U<SUP>IV</SUP>(═NH)[<SUP><I>i</I></SUP>Pr<SUB>2</SUB>P(C<SUB>6</SUB>H<SUB>3</SUB>Me)N(C<SUB>6</SUB>H<SUB>2</SUB>Me<SUB>2</SUB>CH<SUB>2</SUB>)]] (<B>4</B>). Calculated reaction energy profiles strongly suggest that a C-H insertion becomes unfavorable when a reductant is present, offering a distinctively different reaction pathway than previously observed for other uranium nitride complexes.</P> [FIG OMISSION]</BR>