Computational Studies of Carboxylate-Assisted C-H Activation and Functionalization at Group 8-10 Transition Metal Centers

Computational studies on carboxylate-assisted C-H activation and functionalization at group 8-10 transition metal centers are reviewed. This Review is organized by metal and will cover work published from late 2009 until mid-2016. A brief overview of computational work prior to 2010 is also provided, and this outlines the understanding of carboxylate-assisted C-H activation in terms of the "ambiphilic metal-ligand assistance" (AMLA) and "concerted metalation deprotonation" (CMD) concepts. Computational studies are then surveyed in terms of the nature of the C-H bond being activated (C(sp(2))-H or C(sp(3))-H), the nature of the process involved (intramolecular with a directing group or intermolecular), and the context (stoichiometric C-H activation or within a variety of catalytic processes). This Review aims to emphasize the connection between computation and experiment and to highlight the contribution of computational chemistry to our understanding of catalytic C-H functionalization based on carboxylate-assisted C-H activation. Some opportunities where the interplay between computation and experiment may contribute further to the areas of catalytic C-H functionalization and applied computational chemistry are identified

Computational Studies of Carboxylate-Assisted C-H Activation and Functionalization at Group 8-10 Transition Metal Centers

Computational studies on carboxylate-assisted C-H activation and functionalization at group 8-10 transition metal centers are reviewed. This Review is organized by metal and will cover work published from late 2009 until mid-2016. A brief overview of computational work prior to 2010 is also provided, and this outlines the understanding of carboxylate-assisted C-H activation in terms of the "ambiphilic metal-ligand assistance" (AMLA) and "concerted metalation deprotonation" (CMD) concepts. Computational studies are then surveyed in terms of the nature of the C-H bond being activated (C(sp(2))-H or C(sp(3))-H), the nature of the process involved (intramolecular with a directing group or intermolecular), and the context (stoichiometric C-H activation or within a variety of catalytic processes). This Review aims to emphasize the connection between computation and experiment and to highlight the contribution of computational chemistry to our understanding of catalytic C-H functionalization based on carboxylate-assisted C-H activation. Some opportunities where the interplay between computation and experiment may contribute further to the areas of catalytic C-H functionalization and applied computational chemistry are identified

<i>N</i>,<i>N</i>′-Bis(diphenylphosphino)diaminophenylphosphine Ligands for Chromium-Catalyzed Selective Ethylene Oligomerization Reactions

Reaction of 1 or 2 equiv of Ph2PCl with PhP(N(H)R)2 (R = n-propyl) yields Ph2PN(R)P(Ph)N(R)H (1) or Ph2PN(R)P(Ph)N(R)PPh2 (2), respectively. In contrast, reaction of 1 or 2 equiv of Ph2PCl with PhP(N(H)R)2 (R = isopropyl) yields exclusively Ph2PN(R)P(Ph)N(R)H (3), even under more forcing conditions. Low-temperature NMR spectroscopy and a conformational analysis of Ph2PN(iPr)P(Ph)N(iPr)H (3) reveal the lowest energy conformer to have a close N−H···P interaction of 2.95 Å, which we speculate may hinder further reactivity of this molecule. Reaction of 3 with [Cr(CO)6] yields [Cr(3)(CO)4] (5), which has been structurally characterized. Coordination of ligand 3 facilitates its conversion to Ph2PN(iPr)P(Ph)N(iPr)PPh2 (4) while bound to chromium, yielding the complex [Cr(4)(CO)4] (6), which has also been structurally characterized. Ligands 1 and 2, when reacted in situ with [Cr(acac)3] (acac = acetylacetonate) and modified methylalumoxane, and complexes 5 and 6, when activated with Ag[Al(OC4F9)4] and triethylaluminum, are moderately active and selective catalysts for the selective oligomerization of ethene to 1-hexene and 1-octene

<i>N</i>,<i>N</i>′-Bis(diphenylphosphino)diaminophenylphosphine Ligands for Chromium-Catalyzed Selective Ethylene Oligomerization Reactions

Reaction of 1 or 2 equiv of Ph2PCl with PhP(N(H)R)2 (R = n-propyl) yields Ph2PN(R)P(Ph)N(R)H (1) or Ph2PN(R)P(Ph)N(R)PPh2 (2), respectively. In contrast, reaction of 1 or 2 equiv of Ph2PCl with PhP(N(H)R)2 (R = isopropyl) yields exclusively Ph2PN(R)P(Ph)N(R)H (3), even under more forcing conditions. Low-temperature NMR spectroscopy and a conformational analysis of Ph2PN(iPr)P(Ph)N(iPr)H (3) reveal the lowest energy conformer to have a close N−H···P interaction of 2.95 Å, which we speculate may hinder further reactivity of this molecule. Reaction of 3 with [Cr(CO)6] yields [Cr(3)(CO)4] (5), which has been structurally characterized. Coordination of ligand 3 facilitates its conversion to Ph2PN(iPr)P(Ph)N(iPr)PPh2 (4) while bound to chromium, yielding the complex [Cr(4)(CO)4] (6), which has also been structurally characterized. Ligands 1 and 2, when reacted in situ with [Cr(acac)3] (acac = acetylacetonate) and modified methylalumoxane, and complexes 5 and 6, when activated with Ag[Al(OC4F9)4] and triethylaluminum, are moderately active and selective catalysts for the selective oligomerization of ethene to 1-hexene and 1-octene

<i>N</i>,<i>N</i>′-Bis(diphenylphosphino)diaminophenylphosphine Ligands for Chromium-Catalyzed Selective Ethylene Oligomerization Reactions

Reaction of 1 or 2 equiv of Ph2PCl with PhP(N(H)R)2 (R = n-propyl) yields Ph2PN(R)P(Ph)N(R)H (1) or Ph2PN(R)P(Ph)N(R)PPh2 (2), respectively. In contrast, reaction of 1 or 2 equiv of Ph2PCl with PhP(N(H)R)2 (R = isopropyl) yields exclusively Ph2PN(R)P(Ph)N(R)H (3), even under more forcing conditions. Low-temperature NMR spectroscopy and a conformational analysis of Ph2PN(iPr)P(Ph)N(iPr)H (3) reveal the lowest energy conformer to have a close N−H···P interaction of 2.95 Å, which we speculate may hinder further reactivity of this molecule. Reaction of 3 with [Cr(CO)6] yields [Cr(3)(CO)4] (5), which has been structurally characterized. Coordination of ligand 3 facilitates its conversion to Ph2PN(iPr)P(Ph)N(iPr)PPh2 (4) while bound to chromium, yielding the complex [Cr(4)(CO)4] (6), which has also been structurally characterized. Ligands 1 and 2, when reacted in situ with [Cr(acac)3] (acac = acetylacetonate) and modified methylalumoxane, and complexes 5 and 6, when activated with Ag[Al(OC4F9)4] and triethylaluminum, are moderately active and selective catalysts for the selective oligomerization of ethene to 1-hexene and 1-octene

Controlling Al–<b>M</b> Interactions in Group 1 Metal Aluminyls (<b>M</b> = Li, Na, and K). Facile Conversion of Dimers to Monomeric and Separated Ion Pairs

The aluminyl compounds [M{Al­(NONDipp)}]2 (NONDipp = [O­(SiMe2NDipp)2]2–, Dipp = 2,6-iPr2C6H3), which exist as contacted dimeric pairs in both the solution and solid states, have been converted to monomeric ion pairs and separated ion pairs for each of the group 1 metals, M = Li, Na, and K. The monomeric ion pairs contain discrete, highly polarized Al–M bonds between the aluminum and the group 1 metal and have been isolated with monodentate (THF, M = Li and Na) or bidentate (TMEDA, M = Li, Na, and K) ligands at M. The separated ion pairs comprise group 1 cations that are encapsulated by polydentate ligands, rendering the aluminyl anion, [Al­(NONDipp)]− “naked”. For M = Li, this structure type was isolated as the [Li­(TMEDA)2]+ salt directly from a solution of the corresponding contacted dimeric pair in neat TMEDA, while the polydentate [2.2.2]­cryptand ligand was used to generate the separated ion pairs for the heavier group 1 metals M = Na and K. This work shows that starting from the corresponding contacted dimeric pairs, the extent of the Al–M interaction in these aluminyl systems can be readily controlled with appropriate chelating reagents

Seven-Membered Cyclic Diamidoalumanyls of Heavier Alkali Metals: Structures and C–H Activation of Arenes

Like the previously reported potassium-based system, rubidium and cesium reduction of [{SiNDipp}­AlI] ({SiNDipp} = {CH2SiMe2NDipp}2) with the heavier alkali metals [M = Rb and Cs] provides dimeric group 1 alumanyl derivatives, [{SiNDipp}­AlM]2. In contrast, similar treatment with sodium results in over-reduction and incorporation of a formal equivalent of [{SiNDipp}­Na2] into the resultant sodium alumanyl species. The dimeric K, Rb, and Cs compounds display a variable efficacy toward the C–H oxidative addition of arene C–H bonds at elevated temperatures (Cs > Rb > K, 110 °C) to yield (hydrido)­(organo)­aluminate species. Consistent with the synthetic experimental observations, computational (DFT) assessment of the benzene C–H activation indicates that rate-determining attack of the Al­(I) nucleophile within the dimeric species is facilitated by π-engagement of the arene with the electrophilic M+ cation, which becomes increasingly favorable as group 1 is descended

C–H Functionalization Reactivity of a Nickel–Imide

We report bifunctional reactivity of the β-diketiminato Ni­(III)–imide [Me3NN]­NiNAd (1), which undergoes H-atom abstraction (HAA) reactions with benzylic substrates R–H (indane, ethylbenzene, toluene). Nickel–imide 1 competes with the nickel–amide HAA product [Me3NN]­Ni–NHAd (2) for the resulting hydrocarbyl radical R• to give the nickel–amide [Me3NN]­Ni–N­(CHMePh)­Ad (3) (R–H = ethylbenzene) or aminoalkyl tautomer [Me3NN]­Ni­(η2-CH­(Ph)­NHAd) (4) (R–H = toluene). A significant amount of functionalized amine R–NHAd is observed in the reaction of 1 with indane along with the dinickel imide {[Me3NN]­Ni}2(μ-NAd) (5). Kinetic and DFT analyses point to rate-limiting HAA from R–H by 1 to give R•, which may add to either imide 1 or amide 2, each featuring significant N-based radical character. Thus, these studies illustrate a fundamental competition possible in C–H amination systems that proceed via a HAA/radical rebound mechanism

Rhodium Complexes of Cyclopropenylidene Carbene Ligands: Synthesis, Structure, and Hydroformylation Catalysis

Rhodium(III) cyclopropenylidene complexes of the type [RhCl3(PPh3)2(2,3-di(aryl)cyclopropenylidene)] (Aryl = C6H5, 4-C6H4F) are synthesized via oxidative addition of 1,1-dichloro-2,3-diarylcyclopropene fragments to rhodium(I) precursors. The molecular structure of these complexes has been determined. Attempted hydroformylation of 1-hexene with these complexes leads to catalysis results which are strongly suggestive of decomposition of the carbene complex

Seven-Membered Cyclic Diamidoalumanyls of Heavier Alkali Metals: Structures and C–H Activation of Arenes

Like the previously reported potassium-based system, rubidium and cesium reduction of [{SiNDipp}­AlI] ({SiNDipp} = {CH2SiMe2NDipp}2) with the heavier alkali metals [M = Rb and Cs] provides dimeric group 1 alumanyl derivatives, [{SiNDipp}­AlM]2. In contrast, similar treatment with sodium results in over-reduction and incorporation of a formal equivalent of [{SiNDipp}­Na2] into the resultant sodium alumanyl species. The dimeric K, Rb, and Cs compounds display a variable efficacy toward the C–H oxidative addition of arene C–H bonds at elevated temperatures (Cs > Rb > K, 110 °C) to yield (hydrido)­(organo)­aluminate species. Consistent with the synthetic experimental observations, computational (DFT) assessment of the benzene C–H activation indicates that rate-determining attack of the Al­(I) nucleophile within the dimeric species is facilitated by π-engagement of the arene with the electrophilic M+ cation, which becomes increasingly favorable as group 1 is descended