NON‐Ligated N‐Heterocyclic Tetrylenes

We report on the synthesis of N-heterocyclic tetrylenes ligated by the NON-donor framework 4,5-bis(2,6-diisopropylphenyl-amino)-2,7-di-tert-butyl-9,9-dimethylxanthene. The molecular structures of the germylene (3), stannylene (4) and plumbylene (5) where determined by X-ray diffraction studies. Furthermore, we present quantum chemical studies on the sigma-donor and pi-acceptor properties of 3-5. Additionally, we report on the reactivity of the tetrylenes towards the transition metal carbonyls [Rh(CO)(2)Cl](2), [W(CO)(6)] and [Ni(CO)(4)]. The isolated complexes (6 and 7) show the differing reactivity of NHTs compared to NHCs. Instead of just forming the anticipated complex [(NON)Sn-Rh(CO)(2)Cl], 4 inserts into the Rh-Cl bond to afford [(NON)Sn(Cl)Rh(CO)(C6H6)] (6, additional CO/C6H6 exchange) and [(NON)Sn(Cl)Rh-2(CO)(4)Cl] (7). By avoiding halogenated transition metal precursors in order to prevent insertion reactions, germylene 3 shows "classical" coordination chemistry towards {Ni(CO)(3)} forming the complex [(NON)Ge-Ni(CO)(3)] (8)

Applications of Transition Metal-Catalyzed ortho-Fluorine-Directed C–H Functionalization of (Poly)fluoroarenes in Organic Synthesis

The synthesis of organic compounds efficiently via fewer steps but in higher yields is desirable as this reduces energy and reagent use, waste production, and thus environmental impact as well as cost. The reactivity of C–H bonds ortho to fluorine substituents in (poly)fluoroarenes with metal centers is enhanced relative to meta and para positions. Thus, direct C–H functionalization of (poly)fluoroarenes without prefunctionalization is becoming a significant area of research in organic chemistry. Novel and selective methodologies to functionalize (poly)fluorinated arenes by taking advantage of the reactivity of C–H bonds ortho to C–F bonds are continuously being developed. This review summarizes the reasons for the enhanced reactivity and the consequent developments in the synthesis of valuable (poly)fluoroarene-containing organic compounds

Nickel boryl complexes and the nickel-catalyzed alkyne borylation

The first nickel bis-boryl complexes cis [Ni(iPr2ImMe)2(Bcat)2], cis [Ni(iPr2ImMe)2(Bpin)2] and cis [Ni(iPr2ImMe)2(Beg)2] are reported, which were prepared via the reaction of a source of [Ni(iPr2ImMe)2] with the diboron(4) compounds B2cat2, B2pin2 and B2eg2 (iPr2ImMe = 1,3-di-iso-propyl-4,5-dimethylimidazolin-2-ylidene; B2cat2 = bis(catecholato)diboron; B2pin2 = bis(pinacolato)diboron; B2eg2 = bis(ethylene glycolato)diboron). X-ray diffraction and DFT calculations strongly suggest that a delocalized, multicenter bonding scheme dictates the bonding situation of the NiB2 moiety in these square planar complexes, reminiscent to the bonding situation of “non-classical” H2 complexes. [Ni(iPr2ImMe)2] also efficiently catalyzes the diboration of alkynes using B2cat2 as the boron source under mild conditions. In contrast to the known platinum-catalyzed diboration, the nickel system follows a different mechanistic pathway, which not only provides the 1,2 borylation product in excellent yields, but also provides, additionally, an efficient approach to other products such as C–C coupled borylation products or rare tetra-borylated compounds. The mechanism of the nickel-catalyzed alkyne borylation was examined by means of stoichiometric reactions and DFT calculations. Oxidative addition of the diboron reagent to nickel is not dominant; the first steps of the catalytic cycle are coordination of the alkyne to [Ni(iPr2ImMe)2] and subsequent borylation at the coordinated and, thus, activated alkyne to yield complexes of the type [Ni(NHC)2(η2-cis-(Bcat)(R)C=C(R)(Bcat))], exemplified by the isolation and structural characterization of [Ni(iPr2ImMe)2(η2-cis-(Bcat)(Me)C=C(Me)(Bcat))] and [Ni(iPr2ImMe)2(η2-cis-(Bcat)(H7C3)C=C(C3H7)(Bcat))]

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

[Ni(NHC)2] as a scaffold for structurally characterized trans [H-Ni-PR2] and trans [R2P-Ni-PR2] complexes

The addition of PPh(2)H, PPhMeH, PPhH(2), P(para‐Tol)H(2), PMesH(2) and PH(3) to the two‐coordinate Ni(0) N‐heterocyclic carbene species [Ni(NHC)(2)] (NHC=IiPr(2), IMe(4), IEt(2)Me(2)) affords a series of mononuclear, terminal phosphido nickel complexes. Structural characterisation of nine of these compounds shows that they have unusual trans [H−Ni−PR(2)] or novel trans [R(2)P−Ni−PR(2)] geometries. The bis‐phosphido complexes are more accessible when smaller NHCs (IMe(4)>IEt(2)Me(2)>IiPr(2)) and phosphines are employed. P−P activation of the diphosphines R(2)P−PR(2) (R(2)=Ph(2), PhMe) provides an alternative route to some of the [Ni(NHC)(2)(PR(2))(2)] complexes. DFT calculations capture these trends with P−H bond activation proceeding from unconventional phosphine adducts in which the H substituent bridges the Ni−P bond. P−P bond activation from [Ni(NHC)(2)(Ph(2)P−PPh(2))] adducts proceeds with computed barriers below 10 kcal mol(−1). The ability of the [Ni(NHC)(2)] moiety to afford isolable terminal phosphido products reflects the stability of the Ni−NHC bond that prevents ligand dissociation and onward reaction

N‐Heterocyclic Silylene Main Group Element Chemistry: Adduct Formation, Insertion into E−X Bonds and Cyclization of Organoazides

Investigations concerning the reactivity of the N‐heterocyclic silylene Dipp$_{2}$NHSi (1, 1,3‐bis(2,6‐diisopropylphenyl)‐1,3‐diaza‐2‐silacyclopent‐4‐en‐2‐ylidene) towards selected alanes and boranes, elemental halides X$_{2}$ (X=Br, I), selected halide containing substrates such as tin chlorides and halocarbons, as well as organoazides are presented. The NHSi adducts Dipp$_{2}$NHSi⋅AlI$_{3}$ (2), Dipp$_{2}$NHSi⋅Al(C$_{6}$F$_{5}$)$_{3}$ (3), and Dipp$_{2}$NHSi⋅B(C$_{6}$F$_{5}$)$_{3}$ (4) were formed by the reaction of Dipp$_{2}$NHSi with the corresponding Lewis acids AlI$_{3}$, Al(C$_{6}$F$_{6}$)$_{3}$ and B(C$_{6}$F$_{5}$)$_{3}$. Adducts 3 and 4 were tested with respect to their ability to activate small organic molecules, but no frustrated Lewis pair reactivity was observed. Reactions of Dipp$_{2}$NHSi with Br$_{2}$, I$_{2}$, Ph$_{2}$SnCl$_{2}$ and Me$_{3}$SnCl led to formation of Dipp$_{2}$NHSiBr$_{2}$ (5), Dipp$_{2}$NHSiI$_{2}$ (6), Dipp$_{2}$NHSiCl$_{2}$ (7) and {(Me$_{3}$Sn)N(Dipp)CH}$_{2}$ (8), respectively. The reaction with the halocarbons methyl iodide, benzyl chloride, and benzyl bromide afforded the insertion products Dipp$_{2}$NHSi(I)(CH$_{3}$) (9), Dipp$_{2}$NHSi(Cl)(CH$_{2}$Ph) (10) and Dipp$_{2}$NHSi(Br)(CH$_{2}$Ph) (11). Reaction of Dipp$_{2}$NHSi with the organoazides Ad‐N$_{3}$ (Ad=adamantyl) and TMS‐N$_{3}$ (TMS=trimethylsilyl) led to the formation of 1‐Dipp$_{2}$NHSi‐2,5‐bis(adamantyl)‐tetrazoline (12) and bis(trimethylsilyl)amido azido silane (13), respectively. For 2,6‐(diphenyl)phenyl‐N$_{3}$ C−H activation occurs and a cyclosilamine 14 was isolated

Organometallic imido complexes - higher valent derivatives of the d-metal acids. 3. Synthesis and reactions of pentamethylcyclopentadienyl imido complexes of molybdenum and tungsten and an efficient strategy for the synthesis of the organometallates

A convenient and new entry into the chemistry of highvalent pentamethylcyclopentadienyl halfsandwich complexes of molybdenum and tungsten is described. The reaction of Mo-(NtBu)$_2$Cl$_2$ or W(NtBu)$_2$Cl$_2$(py)$_2$ with Cp*Li (Cp* = $\eta^5$-C$_5$Me$_5$) provides a high-yield route to new complexes Cp*Mo-(NtBu)$_2$CI (la) and Cp*W(NtBu)$_2$Cl (1 b) which are converted into a variety of diimido, monoimido, and oxo derivatives. Treatment of 1 a, b with MeLi yields the highly volatile methyl derivatives Cp*Mo(NtBu)$_2$Me (2a) and Cp*W(NtBu)$_2$Me (2b), while protolysis of 1 a, b with an excess of HCI gas leads to selective cleavage of only one imido function with formation of Cp*Mo(NtBu)Cl$_3$ (3a) and Cp*W(NtBu)Cl$_3$ (3b). In contrast, protolysis of 1 a, b with aqueous HCI provides a high-yield route to the well-known organometallic oxides [Cp*MoO$_2$](μ-0) (4a) and [Cp*WO$_2$]($\mu$-0) (4b). These two key compounds are easily converted into the organomolybdate and organotungstate salts NBu$_4$[Cp*MoO$_3$] (5a) and NBu$_4$[Cp*WO$_3$] (Sb) by cleavage of the M - 0 - M bridge with NBu$_4$[OH]. The Xray structure of 3a is reported

1,3-bis(tricyanoborane)imidazoline-2-ylidenate anion - a ditopic dianionic N-heterocyclic carbene ligand

The 1,3-bis(tricyanoborane)imidazolate anion 1 was obtained in high yield from lithium imidazolate and B(CN)$_3$−pyridine adduct. Anion 1 is chemically very robust and thus allowed the isolation of the corresponding H$_5$O$_2$$^+$ salt. Furthermore, monoanion 1 served as starting species for the novel dianionic N-heterocyclic carbene (NHC), 1,3-bis(tricyanoborane)imidazoline-2-ylidenate anion 3 that acts as ditopic ligand via the carbene center and the cyano groups at boron. First reactions of this new NHC 3 with methyl iodide, elemental selenium, and [Ni(CO)$_4$] led to the methylated imidazolate ion 4, the dianionic selenium adduct 5, and the dianionic nickel tricarbonyl complex 6. These NHC derivatives provide a first insight into the electronic and steric properties of the dianionic NHC 3. Especially the combination of properties, such as double negative charge, different coordination sites, large buried volume and good σ-donor and π-acceptor ability, make NHC 3 a unique and promising ligand and building block

A Versatile Route To Cyclic (Alkyl)(Amino)Carbene–Stabilized Stibinidenes

A convenient route for the synthesis of the cAAC$^{Me}$ (cAAC=cyclic (alkyl)(amino)carbene, cAAC$^{Me}$=1-(2,6-di-iso-propylphenyl)-3,3,5,5-tetramethyl-pyrrolidin-2-ylidene) and cAAC$^{Cy}$ (cAAC$^{Cy}$=2-azaspiro[4.5]dec-2-(2,6-diisopropylphenyl)-3,3-dimethyl-1-ylidene) stabilized stibinidenes cAAC$^{Me}$⋅SbMes (2a) (Mes=2,4,6-trimethylphenyl) and cAAC$^{Cy}$⋅SbMes (2b) is reported. A mechanism for the formation of [cAAC$^{R}$Cl][SbCl$_{3}$Mes] 1 and cAAC$^{R}$⋅SbMes 2 from the reaction of cAAC with the antimony(III) precursor SbCl$_{2}$Mes, which proceeds via the isolable intermediate [cAAC$^{R}$SbClMes][SbCl$_{3}$Mes] (3), is proposed