School census autumn 2017 : 16 to 19 reports : user guide

The synthesis of a series of cobalt NHC complexes of the types [Co­(NHC)₂(CO)­(NO)] (NHC = <i>i</i>Pr₂Im (<b>2</b>), <i>n</i>Pr₂Im (<b>3</b>), Cy₂Im (<b>4</b>), Me₂Im (<b>5</b>), <i>i</i>Pr₂ImMe (<b>6</b>), Me₂ImMe (<b>7</b>), Me<i>i</i>PrIm (<b>8</b>), Me<i>t</i>BuIm (<b>9</b>); R₂Im = 1,3-dialkylimidazolin-2-ylidene) and [Co­(NHC)­(CO)₂(NO)] (NHC = <i>i</i>Pr₂Im (<b>13</b>), <i>n</i>Pr₂Im (<b>14</b>), Me₂Im (<b>15</b>), <i>i</i>Pr₂ImMe (<b>16</b>), Me₂ImMe (<b>17</b>), Me<i>i</i>PrIm (<b>18</b>), Me<i>t</i>BuIm (<b>19</b>)) from the reaction of the NHC with [Co­(CO)₃(NO)] (<b>1</b>) is reported. These complexes have been characterized using elemental analysis, IR spectroscopy, multinuclear NMR spectroscopy, and in many cases by X-ray crystallography. Bulky NHCs tend to form the mono-NHC-substituted complexes [Co­(NHC)­(CO)₂(NO)], even from the reaction with an stoichiometric excess of the NHC, as demonstrated by the synthesis of [Co­(Dipp₂Im)­(CO)₂(NO)] (<b>11</b>), [Co­(Mes₂Im)­(CO)₂(NO)] (<b>12</b>), and [Co­(^MecAAC)­(CO)₂(NO)] (<b>20</b>). For <i>t</i>Bu₂Im a preferred coordination via the NHC backbone (“abnormal” coordination at the 4-position) was observed and the complex [Co­(<i>t</i>Bu₂^aIm)­(CO)₂(NO)] (<b>10</b>) was isolated. All of these complexes are volatile, are stable upon sublimation and prolonged storage in the gas phase, and readily decompose at higher temperatures. Furthermore, DTA/TG analyses revealed that the complexes [Co­(NHC)₂(CO)­(NO)] are seemingly more stable toward thermal decomposition in comparison to the complexes [Co­(NHC)­(CO)₂(NO)]. We thus conclude that the cobalt complexes of the type [Co­(NHC)­(CO)₂(NO)] and [Co­(NHC)₂(CO)­(NO)] have potential for application as precursors in the vapor deposition of thin cobalt films

From NHC to Imidazolyl Ligand: Synthesis of Platinum and Palladium Complexes d¹⁰-[M(NHC)₂] (M = Pd, Pt) of the NHC 1,3-Diisopropylimidazolin-2-ylidene

The widely held belief that N-heterocyclic carbenes (NHCs) act only as innocent spectator ligands is not always accurate, even in the context of well-explored reactions. Ligand exchange in the conversion of [Pt­(PPh₃)₂(η²-C₂H₄)] (<b>3</b>) to [Pt­(<i>i</i>Pr₂Im)₂] (<b>2</b>) depends critically on the particular reaction conditions employed, with slight changes leading to vastly different outcomes. In addition to [Pt­(<i>i</i>Pr₂Im)₂] (<b>2</b>), complexes [Pt­(<i>i</i>Pr₂Im)­(PPh₃)­(η²-C₂H₄)] (<b>5</b>) and <i>trans</i>-[Pt­(<i>i</i>Pr₂Im)₂(<i>i</i>Pr-Im*)­(H)] (<b>6</b>) were isolated and in the case of <b>6</b> fully characterized. Complex <b>5</b> represents the first mixed-olefin complex in transition metal chemistry containing both an NHC and a phosphine ligand. Chemical degradation of the NHC was shown to yield the new imidazole-2-yl <i>i</i>Pr-Im* in <b>6</b>. Therefore, the synthesis of [Pt­(<i>i</i>Pr₂Im)₂] (<b>2</b>) via metallic reduction of the ionic precursor [Pt­(<i>i</i>Pr₂Im)₃(Cl)]⁺Cl^– (<b>9</b>) is favorable, a procedure adaptable to analogous palladium compounds. While [Pd­(<i>i</i>Pr₂Im)₃(Cl)]⁺Cl^– (<b>8</b>) is the only product obtained from the reaction of <i>i</i>Pr₂Im and PdCl₂, neutral [Pt­(<i>i</i>Pr₂Im)₂(Cl)₂] (<b>10</b>), formed as a mixture of its two stereoisomers <i><b>cis</b></i><b>-10</b> and <i><b>trans</b></i><b>-10</b>, is available through precise control of the stoichiometry in the reaction of PtCl₂ and exactly 2 equiv of <i>i</i>Pr₂Im

Synthesis and Reactivity of Cyclic (Alkyl)(Amino)Carbene Stabilized Nickel Carbonyl Complexes

Cyclic (alkyl)­(amino)­carbenes cAAC^cy (<b>1b</b>) and cAAC^menthyl (<b>1c</b>) react with [Ni­(CO)₄] to give the 18 VE complexes [Ni­(CO)₃(cAAC^cy)] (<b>2b</b>) and [Ni­(CO)₃(cAAC^menthyl)] (<b>2c</b>). With these in hand, the donor-strength and the steric profile of the respective cAAC ligands were evaluated. CAAC^cy and cAAC^menthyl possess similar overall-donating properties (Tolman electronic parameter (TEP) = 2046 (<b>1b</b>) and 2042 (<b>1c</b>)) as common NHCs, though they are also known to be better π-acceptors. 3,3-Diamino-2-aryloxyacrylimidamide <b>3b</b>, arising from the reaction of cAAC^cy (<b>1b</b>) with released CO molecules, was obtained as side-product of CO substitution reactions at nickel carbonyls. In contrast to cAAC^menthyl (%<i>V</i>_bur = 42), the sterically less encumbered cAAC^cy (%<i>V</i>_bur = 38) undergoes a subsequent CO substitution at [Ni­(CO)₃(cAAC^Cy)] (<b>2b</b>) to afford the 16 VE complex [Ni­(CO)­(cAAC^cy)₂] (<b>4b</b>). Treatment of both [Ni­(CO)₃(cAAC^methyl)] (<b>2a</b>) and [Ni­(CO)­(cAAC^methyl)₂] (<b>4a</b>) with allyl bromides led to the formation of cAAC-stabilized allyl nickel complexes [NiBr­(η³-H₂<i>C</i><i>C</i>H–<i>C</i>H₂)­(cAAC^methyl)] (<b>5a</b>) and [NiBr­(η³-H₂<i>C</i><i>C</i>H–<i>C</i>Me₂)­(cAAC^methyl)] (<b>5b</b>). The chloro complex [NiCl­(η³-H₂<i>C</i><i>C</i>Me–<i>C</i>H₂)­(cAAC^methyl)] (<b>6</b>) was synthesized from [Ni­(COD)₂] (COD = 1,5-cyclooctadiene) by consecutive treatment with allyl chloride and cAAC. The allyl halide complexes <b>5</b> and <b>6</b> are thermally labile and decompose in solution already within a few hours at room temperature. One of the decomposition products, the dinuclear nickel complex [Ni₂(μ-Br)₂(η³-(<i>cAAC</i>^methyl)<i>C</i>H–<i>C</i>H­(CH₃))₂] (<b>7</b>), was crystallographically characterized

Synthesis and Reactivity of Cyclic (Alkyl)(Amino)Carbene Stabilized Nickel Carbonyl Complexes

Cyclic (alkyl)­(amino)­carbenes cAAC^cy (<b>1b</b>) and cAAC^menthyl (<b>1c</b>) react with [Ni­(CO)₄] to give the 18 VE complexes [Ni­(CO)₃(cAAC^cy)] (<b>2b</b>) and [Ni­(CO)₃(cAAC^menthyl)] (<b>2c</b>). With these in hand, the donor-strength and the steric profile of the respective cAAC ligands were evaluated. CAAC^cy and cAAC^menthyl possess similar overall-donating properties (Tolman electronic parameter (TEP) = 2046 (<b>1b</b>) and 2042 (<b>1c</b>)) as common NHCs, though they are also known to be better π-acceptors. 3,3-Diamino-2-aryloxyacrylimidamide <b>3b</b>, arising from the reaction of cAAC^cy (<b>1b</b>) with released CO molecules, was obtained as side-product of CO substitution reactions at nickel carbonyls. In contrast to cAAC^menthyl (%<i>V</i>_bur = 42), the sterically less encumbered cAAC^cy (%<i>V</i>_bur = 38) undergoes a subsequent CO substitution at [Ni­(CO)₃(cAAC^Cy)] (<b>2b</b>) to afford the 16 VE complex [Ni­(CO)­(cAAC^cy)₂] (<b>4b</b>). Treatment of both [Ni­(CO)₃(cAAC^methyl)] (<b>2a</b>) and [Ni­(CO)­(cAAC^methyl)₂] (<b>4a</b>) with allyl bromides led to the formation of cAAC-stabilized allyl nickel complexes [NiBr­(η³-H₂<i>C</i><i>C</i>H–<i>C</i>H₂)­(cAAC^methyl)] (<b>5a</b>) and [NiBr­(η³-H₂<i>C</i><i>C</i>H–<i>C</i>Me₂)­(cAAC^methyl)] (<b>5b</b>). The chloro complex [NiCl­(η³-H₂<i>C</i><i>C</i>Me–<i>C</i>H₂)­(cAAC^methyl)] (<b>6</b>) was synthesized from [Ni­(COD)₂] (COD = 1,5-cyclooctadiene) by consecutive treatment with allyl chloride and cAAC. The allyl halide complexes <b>5</b> and <b>6</b> are thermally labile and decompose in solution already within a few hours at room temperature. One of the decomposition products, the dinuclear nickel complex [Ni₂(μ-Br)₂(η³-(<i>cAAC</i>^methyl)<i>C</i>H–<i>C</i>H­(CH₃))₂] (<b>7</b>), was crystallographically characterized

Symmetrical P₄ Cleavage at Cobalt: Characterization of Intermediates on the Way from P₄ to Coordinated P₂ Units

Degradation of white phosphorus (P₄) in the coordination sphere of transition metals is commonly divided into two major pathways depending on the P_<i>x</i> ligands obtained. Consecutive metal-assisted P–P bond cleavage of four bonds of the P₄ tetrahedron leads to complexes featuring two P₂ ligands (symmetric cleavage) or one P₃ and one P₁ ligand (asymmetric cleavage). A systematic investigation of the degradation of white phosphorus P₄ to coordinated μ,η^2:2-bridging diphosphorus ligands in the coordination sphere of cobalt is presented herein as well as isolation of each of the decisive intermediates on the reaction pathway. The olefin complex [Cp*Co­(^<i>i</i>Pr₂Im)­(η²-C₂H₄)], <b>1</b> (Cp* = η⁵-C₅Me₅, ^<i>i</i>Pr₂Im = 1,3-di-isopropylimidazolin-2-ylidene), reacts with P₄ to give [Cp*Co­(^<i>i</i>Pr₂Im)­(η²-P₄)], <b>2</b>, the insertion product of [Cp*Co­(^<i>i</i>Pr₂Im)] into one of the P–P bonds. Addition of a further equivalent of the Co^I complex [Cp*Co­(^<i>i</i>Pr₂Im)­(η²-C₂H₄)], <b>1</b>, induces cleavage of a second P–P bond to yield the dinuclear complex [{Cp*Co­(^<i>i</i>Pr₂Im)}₂(μ,η^2:2-P₄)], <b>3</b>, in which a kinked cyclo-P₄^4– ligand bridges two cobalt atoms. Consecutive dissociation of the N-heterocyclic carbene with concomitant rearrangement of the cyclo-P₄ ligand and P–P dissociation leads to complexes [Cp*Co­(μ,η^4:2-P₄)­Co­(^<i>i</i>Pr₂Im)­Cp*], <b>4</b>, featuring a P₄ chain, and [{Cp*Co­(μ,η^2:2-P₂)}₂], <b>5</b>, in which two isolated P₂^2– ligands bridge two [Cp*Co] fragments. Each of these reactions is quantitative if performed on an NMR scale, and each compound can be isolated in high yields and large quantities

Symmetrical P₄ Cleavage at Cobalt: Characterization of Intermediates on the Way from P₄ to Coordinated P₂ Units

Degradation of white phosphorus (P₄) in the coordination sphere of transition metals is commonly divided into two major pathways depending on the P_<i>x</i> ligands obtained. Consecutive metal-assisted P–P bond cleavage of four bonds of the P₄ tetrahedron leads to complexes featuring two P₂ ligands (symmetric cleavage) or one P₃ and one P₁ ligand (asymmetric cleavage). A systematic investigation of the degradation of white phosphorus P₄ to coordinated μ,η^2:2-bridging diphosphorus ligands in the coordination sphere of cobalt is presented herein as well as isolation of each of the decisive intermediates on the reaction pathway. The olefin complex [Cp*Co­(^<i>i</i>Pr₂Im)­(η²-C₂H₄)], <b>1</b> (Cp* = η⁵-C₅Me₅, ^<i>i</i>Pr₂Im = 1,3-di-isopropylimidazolin-2-ylidene), reacts with P₄ to give [Cp*Co­(^<i>i</i>Pr₂Im)­(η²-P₄)], <b>2</b>, the insertion product of [Cp*Co­(^<i>i</i>Pr₂Im)] into one of the P–P bonds. Addition of a further equivalent of the Co^I complex [Cp*Co­(^<i>i</i>Pr₂Im)­(η²-C₂H₄)], <b>1</b>, induces cleavage of a second P–P bond to yield the dinuclear complex [{Cp*Co­(^<i>i</i>Pr₂Im)}₂(μ,η^2:2-P₄)], <b>3</b>, in which a kinked cyclo-P₄^4– ligand bridges two cobalt atoms. Consecutive dissociation of the N-heterocyclic carbene with concomitant rearrangement of the cyclo-P₄ ligand and P–P dissociation leads to complexes [Cp*Co­(μ,η^4:2-P₄)­Co­(^<i>i</i>Pr₂Im)­Cp*], <b>4</b>, featuring a P₄ chain, and [{Cp*Co­(μ,η^2:2-P₂)}₂], <b>5</b>, in which two isolated P₂^2– ligands bridge two [Cp*Co] fragments. Each of these reactions is quantitative if performed on an NMR scale, and each compound can be isolated in high yields and large quantities

C–Br Activation of Aryl Bromides at Ni⁰(NHC)₂: Stoichiometric Reactions, Catalytic Application in Suzuki–Miyaura Cross-Coupling, and Catalyst Degradation

Complex [Ni₂(^<i>i</i>Pr₂Im)₄(COD)] (<b>1</b>) (^<i>i</i>Pr₂Im = 1,3-diisopropylimidazolin-2-ylidene) is a very efficient catalyst for the Suzuki–Miyaura cross-coupling reaction of 4-bromotoluene with phenylboronic acid and also mediates the Ullmann-type homo-cross-coupling reaction of bromobenzene with a moderate efficiency. Stoichiometric reactions of complex <b>1</b> with aryl bromides (ArBr) at room temperature lead to mixtures of aryl bromo complexes of the type <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(Br)­(Ar)] and the bis­(bromo) complex <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(Br)₂] <b>2</b>. The complexes <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(Br)­(Ar)] (for Ar = Ph <b>3</b>, 4-MeC₆H₄ <b>4</b>, 4-Me­(O)­CC₆H₄ <b>5</b>, 4-MeOC₆H₄ <b>6</b>, 4-MeSC₆H₄ <b>7</b>, 4-Me₂NC₆H₄ <b>8</b>, 2-C₅NH₄ <b>9</b>) can be selectively synthesized by working at low temperatures and using a high dilution of the starting materials. A major deactivation pathway for <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(Br)­(Ar)] was identified in the presence of aryl bromides. This deactivation process includes (i) the formation of <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(Br)₂] from <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(Br)­(Ar)] (<b>2</b>) and ArBr and (ii) the formation of an imidazolium salt of the type 2­[^<i>i</i>Pr₂Im-Ar]⁺[NiBr₄]^2– from <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(Br)₂] (<b>2</b>) and ArBr. The reactions of complex <b>2</b> with a series of aryl halides at higher temperatures lead to the decomposition of the bis­(carbene) nickel moiety with formation of the imidazolium salts 2­[ⁱPr₂Im-Ar]⁺[NiBr₂X₂]^2– (for X = I, Ar = Ph <b>10</b> and X = Br, Ar = Ph <b>11</b>, 4-MeC₆H₄ <b>12</b>, 4-FC₆H₄ <b>13</b>, 4-OSi­(CH₃)₃-C₆H₄ <b>14</b>) in high yields

Decisive Steps of the Hydrodefluorination of Fluoroaromatics using [Ni(NHC)₂]

The hydrodefluorination reaction of perfluorinated arenes using [Ni₂(^<i>i</i>Pr₂Im)₄(COD)] (<b>1</b>; ^<i>i</i>Pr₂Im = 1,3-bis­(isopropyl)­imidazolin-2-ylidene) as a catalyst as well as stoichiometric transformations to elucidate the decisive steps for this reaction are reported. The reaction of hexafluorobenzene with 5 equiv of triphenylsilane in the presence of 5 mol % of <b>1</b> affords 1,2,4,5-tetrafluorobenzene after 48 h at 60 °C and 1,4-difluorobenzene after 96 h at 80 °C; the reaction of perfluorotoluene and 5 equiv of Et₃SiH for 4 days at 80 °C results in the selective formation of 1-(CF₃)-2,3,5,6-C₆F₄H. Stoichiometric transformations of the complexes <i>cis</i>-[Ni­(^<i>i</i>Pr₂Im)₂(H)­(SiPh₃)] and <i>cis</i>-[Ni­(^<i>i</i>Pr₂Im)₂(H)­(SiMePh₂)] with hexafluorobenzene at room temperature lead to the formation of <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(F)­(C₆F₅)] (<b>2</b>) and <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(H)­(C₆F₅)] (<b>4</b>) with elimination of the corresponding silane or fluorosilane. The reactions of the C–F activation products <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(F)­(C₆F₅)] (<b>2</b>) and <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(F)­(4-(CF₃)­C₆F₄)] (<b>3</b>) with PhSiH₃ and Ph₂SiH₂ afford the hydride complexes <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(H)­(C₆F₅)] (<b>4</b>) and <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(H)­(4-(CF₃)­C₆F₄)] (<b>5</b>), which convert into the compounds <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(F)­(2,3,5,6-C₆F₄H)] (<b>7</b>), <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(F)­(3-(CF₃)-2,4,5-C₆F₃H)] (<b>9a</b>), and <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(F)­(2-(CF₃)-3,4,6-C₆F₃H)] (<b>9b</b>), respectively. In the case of the rearrangement of <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(H)­(4-(CF₃)­C₆F₄)] (<b>5</b>) the intermediate [Ni­(^<i>i</i>Pr₂Im)₂(η²-<i>C</i>,<i>C</i>-(CF₃)­C₆F₄H)] (<b>8</b>) was detected. Reaction of <b>8</b> with perfluorotoluene gave the C–F activation product <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(F)­(4-(CF₃)­C₆F₄)] (<b>3</b>). All these experimental findings point to a mechanism for the HDF by [Ni­(^<i>i</i>Pr₂Im)₂] via the “fluoride route” involving C–F activation of the polyfluoroarene, H/F exchange of the resulting nickel fluoride, reductive elimination of the polyfluoroaryl nickel hydride to an intermediate with a η²-C,C-coordinated arene ligand, subsequent ligand exchange with the higher fluorinated polyfluoroarene, and renewed C–F activation of the polyfluoroarene. Without additional reagents, [Ni­(^<i>i</i>Pr₂Im)₂(η²-<i>C</i>,<i>C</i>-(CF₃)­C₆F₄H)] (<b>8</b>) rearranges to the isomers <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(F)­(3-(CF₃)-2,4,5-C₆F₃H)] (<b>9a</b>; major) and <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(F)­(2-(CF₃)-3,4,6-C₆F₃H)] (<b>9b</b>; minor) in a ratio of 80:20. DFT calculations performed on conversion of <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(H)­(4-(CF₃)­C₆F₄)] <b>5</b> into the two products <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(F)­(3-(CF₃)-2,4,5-C₆F₃H)] <b>9a</b> and <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(F)­(2-(CF₃)-3,4,6-C₆F₃H)] (<b>9b</b>) using the commonly accepted intramolecular concerted pathway via η²-C,F-σ-bound transition states predict <b>9b</b> to be the major product. We thus propose that this reaction mechanism is not valid for the [Ni(NHC)₂]-mediated C–F activation of partially fluorinated arenes with special substitution patterns

Decisive Steps of the Hydrodefluorination of Fluoroaromatics using [Ni(NHC)₂]

The hydrodefluorination reaction of perfluorinated arenes using [Ni₂(^<i>i</i>Pr₂Im)₄(COD)] (<b>1</b>; ^<i>i</i>Pr₂Im = 1,3-bis­(isopropyl)­imidazolin-2-ylidene) as a catalyst as well as stoichiometric transformations to elucidate the decisive steps for this reaction are reported. The reaction of hexafluorobenzene with 5 equiv of triphenylsilane in the presence of 5 mol % of <b>1</b> affords 1,2,4,5-tetrafluorobenzene after 48 h at 60 °C and 1,4-difluorobenzene after 96 h at 80 °C; the reaction of perfluorotoluene and 5 equiv of Et₃SiH for 4 days at 80 °C results in the selective formation of 1-(CF₃)-2,3,5,6-C₆F₄H. Stoichiometric transformations of the complexes <i>cis</i>-[Ni­(^<i>i</i>Pr₂Im)₂(H)­(SiPh₃)] and <i>cis</i>-[Ni­(^<i>i</i>Pr₂Im)₂(H)­(SiMePh₂)] with hexafluorobenzene at room temperature lead to the formation of <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(F)­(C₆F₅)] (<b>2</b>) and <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(H)­(C₆F₅)] (<b>4</b>) with elimination of the corresponding silane or fluorosilane. The reactions of the C–F activation products <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(F)­(C₆F₅)] (<b>2</b>) and <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(F)­(4-(CF₃)­C₆F₄)] (<b>3</b>) with PhSiH₃ and Ph₂SiH₂ afford the hydride complexes <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(H)­(C₆F₅)] (<b>4</b>) and <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(H)­(4-(CF₃)­C₆F₄)] (<b>5</b>), which convert into the compounds <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(F)­(2,3,5,6-C₆F₄H)] (<b>7</b>), <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(F)­(3-(CF₃)-2,4,5-C₆F₃H)] (<b>9a</b>), and <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(F)­(2-(CF₃)-3,4,6-C₆F₃H)] (<b>9b</b>), respectively. In the case of the rearrangement of <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(H)­(4-(CF₃)­C₆F₄)] (<b>5</b>) the intermediate [Ni­(^<i>i</i>Pr₂Im)₂(η²-<i>C</i>,<i>C</i>-(CF₃)­C₆F₄H)] (<b>8</b>) was detected. Reaction of <b>8</b> with perfluorotoluene gave the C–F activation product <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(F)­(4-(CF₃)­C₆F₄)] (<b>3</b>). All these experimental findings point to a mechanism for the HDF by [Ni­(^<i>i</i>Pr₂Im)₂] via the “fluoride route” involving C–F activation of the polyfluoroarene, H/F exchange of the resulting nickel fluoride, reductive elimination of the polyfluoroaryl nickel hydride to an intermediate with a η²-C,C-coordinated arene ligand, subsequent ligand exchange with the higher fluorinated polyfluoroarene, and renewed C–F activation of the polyfluoroarene. Without additional reagents, [Ni­(^<i>i</i>Pr₂Im)₂(η²-<i>C</i>,<i>C</i>-(CF₃)­C₆F₄H)] (<b>8</b>) rearranges to the isomers <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(F)­(3-(CF₃)-2,4,5-C₆F₃H)] (<b>9a</b>; major) and <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(F)­(2-(CF₃)-3,4,6-C₆F₃H)] (<b>9b</b>; minor) in a ratio of 80:20. DFT calculations performed on conversion of <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(H)­(4-(CF₃)­C₆F₄)] <b>5</b> into the two products <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(F)­(3-(CF₃)-2,4,5-C₆F₃H)] <b>9a</b> and <i>trans</i>-[Ni­(^<i>i</i>Pr₂Im)₂(F)­(2-(CF₃)-3,4,6-C₆F₃H)] (<b>9b</b>) using the commonly accepted intramolecular concerted pathway via η²-C,F-σ-bound transition states predict <b>9b</b> to be the major product. We thus propose that this reaction mechanism is not valid for the [Ni(NHC)₂]-mediated C–F activation of partially fluorinated arenes with special substitution patterns

Aryldihydroborane Coordination to Iridium and Osmium Hydrido Complexes

A series of iridium dihydroborate complexes [(^tBuPOCOP)­IrH­(κ²-H₂BHR)] (^tBuPOCOP = κ³-C₆H₃-1,3-[OP^tBu₂]₂; R = Mes = 2,4,6-Me₃C₆H₂; R = Dur = 2,3,5,6-Me₄C₆H) and [LIrH­(κ²-H₂BHDur)] (L = ^tBuPCP = κ³-C₆H₃-1,3-[CH₂P^tBu₂]₂, L = η⁵-C₅Me₅) and an osmium dihydroborate compound [OsH­(κ²-H₂BHDur)­(CO)­(PⁱPr₃)₂] have been prepared by using two different synthetic strategies. The first approach is based on direct borane coordination to the metal center, whereas the second is based on a salt-elimination protocol using the lithium salts Li­[H₃BR] (R = Mes or Dur) and the corresponding metal halides. The compounds have been characterized by multinuclear NMR and IR spectroscopy and X-ray diffraction analysis. The results constitute the first syntheses of κ²-σ:σ-dihydroborate complexes featuring bulky aryl groups