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1.
From the N‐Heterocyclic Carbene‐Catalyzed Conjugate Addition of Alcohols to the Controlled Polymerization of (Meth)acrylates 下载免费PDF全文
Winnie Nzahou Ottou Damien Bourichon Dr. Joan Vignolle Anne‐Laure Wirotius Dr. Fredéric Robert Prof. Yannick Landais Dr. Jean‐Marc Sotiropoulos Dr. Karinne Miqueu Prof. Daniel Taton 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(26):9447-9453
Among various N‐heterocyclic carbenes (NHCs) tested, only 1,3‐bis(tert‐butyl)imidazol‐2‐ylidene (NHCtBu) proved to selectively promote the catalytic conjugate addition of alcohols onto (meth)acrylate substrates. This rather rare example of NHC‐catalyzed 1,4‐addition of alcohols was investigated as a simple means to trigger the polymerization of both methyl methacrylate and methyl acrylate (MMA and MA, respectively). Well‐defined α‐alkoxy poly(methyl (meth)acrylate) (PM(M)A) chains, the molar masses of which could be controlled by the initial [(meth)acrylate]0/[ROH]0 molar ratio, were ultimately obtained in N,N‐dimethylformamide at 25 °C. A hydroxyl‐terminated poly(ethylene oxide) (PEO‐OH) macro‐initiator was also employed to directly access PEO‐b‐PMMA amphiphilic block copolymers. Investigations into the reaction mechanism by DFT calculations revealed the occurrence of two competitive concerted pathways, involving either the activation of the alcohol or that of the monomer by NHCtBu. 相似文献
2.
Understanding the Subtleties of Frustrated Lewis Pair Activation of Carbonyl Compounds by N‐Heterocyclic Carbene/Alkyl Gallium Pairings 下载免费PDF全文
Marina Uzelac Dr. David R. Armstrong Dr. Alan R. Kennedy Prof. Eva Hevia 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(44):15826-15833
This study reports the use of the trisalkylgallium GaR3 (R=CH2SiMe3), containing sterically demanding monosilyl groups, as an effective Lewis‐acid component for frustrated Lewis pair activation of carbonyl compounds, when combined with the bulky N‐heterocyclic carbene 1,3‐bis(tert‐butyl)imidazol‐2‐ylidene (ItBu) or 1,3‐bis(tert‐butyl)imidazolin‐2‐ylidene (SItBu). The reduction of aldehydes can be achieved by insertion into the C=O functionality at the C2 (so‐called normal) position of the carbene affording zwitterionic products [ItBuCH2OGaR3] ( 1 ) or [ItBuCH(p‐Br‐C6H4)OGaR3] ( 2 ), or alternatively, at its abnormal (C4) site yielding [aItBuCH(p‐Br‐C6H4)OGaR3] ( 3 ). As evidence of the cooperative behaviour of both components, ItBu and GaR3, neither of them alone are able to activate any of the carbonyl‐containing substrates included in this study NMR spectroscopic studies of the new compounds point to complex equilibria involving the formation of kinetic and thermodynamic species as implicated through DFT calculations. Extension to ketones proved successful for electrophilic α,α,α‐trifluoroacetophenone, yielding [aItBuC(Ph)(CF3)OGaR3] ( 7 ). However, in the case of ketones and nitriles bearing acidic hydrogen atoms, C?H bond activation takes place preferentially, affording novel imidazolium gallate salts such as [{ItBuH}+{(p‐I‐C6H4)C(CH2)OGaR3}?] ( 8 ) or [{ItBuH}+{Ph2C=C=NGaR3}?] ( 12 ). 相似文献
3.
Polly L. Arnold Ian J. Casely Sergey Zlatogorsky Claire Wilson 《Helvetica chimica acta》2009,92(11):2291-2303
The use of tetravalent cerium alkoxides, nitrates, and triflates was studied as a direct route to [CeIV(carbene)] complexes. Protonolysis reactions between 1H‐imidazolium‐ or imidazoline (=4,5‐dihydro‐1H‐imidazole)‐containing alkoxide proligands HL (L=OCMe2CH2[1‐C(NCHCHNiPr)]) and HLS (LS=OCMe2CH2[1‐C(NCH2CH2NiPr)]) and CeIV tert‐butoxide, triflate, and nitrate compounds were studied to target [CeIV(N‐heterocyclic carbene)] complexes (of unsaturated and saturated carbenes, resp.). Instead, tetravalent cerium imidazolium [(OtBu)3Ce(μ‐OtBu)2(μ‐HL)Ce(OtBu)3], or imidazolinium adducts [(OtBu)3Ce(μ‐OtBu)2(μ‐HLS)Ce(OtBu)3] were isolated. However, the salt metathesis of cerium triflate with KL provided a simple route to [CeL4], which was significantly improved if an external oxidant, benzoquinone, was included in the mixture to maintain oxidation‐state integrity. Likewise, the salt metathesis of cerium triiodide with KL and added benzoquinone provided a straightforward route to [CeL4]. 相似文献
4.
Reaction of the cyclodiphosphazane [(OC4H8N)P(μ‐N‐t‐Bu)2P(HN‐t‐Bu)] ( 1 ) with an equimolar quantity of diisopropyl azodicarboxylate afforded the phosphinimine product [(OC4H8N)P(μ‐N‐t‐Bu)2P=N‐t‐Bu)(N(CO2 ‐i‐Pr)NHCO2‐i‐Pr] ( 6 ) having a PIII‐N‐PV skeleton. Similar products [(t‐BuNH)P(μ‐N‐t‐Bu)2P=N‐t‐Bu)(N(CO2Et)NHCO2Et] ( 7 ) and [(CO2‐i‐Pr)HNN(CO2‐i‐Pr)](t‐BuN=P(μ‐N‐t‐Bu)2POCH2CMe2CH2O[P(μ‐N‐t‐Bu)2P=N‐t‐Bu)(N(CO2‐i‐Pr)NH(CO2‐i‐Pr)] ( 8 ) were spectroscopically characterized in the reaction of [(t‐BuNH)P‐N‐t‐Bu]2 ( 2 ) and [(t‐BuNH)P(μ‐N‐t‐Bu)2POCH2CMe2CH2OP(μ‐N‐t‐Bu)2P(NH‐t‐Bu)] ( 3 ) with diethyl‐ and diisopropyl azodicarboxylate, respectively. By contrast, the reaction of [(μ‐t‐BuN)P]2[O‐6‐t‐Bu‐4‐Me‐C6H2]2CH2 ( 4 ) and [(C5H10N)P‐μ‐N‐t‐Bu]2 ( 5 ) with diisopropyl azodicarboxylate afforded the mono‐ and bis‐oxidized compounds [(O)P(μ‐N‐t‐Bu)2P][O‐6‐t‐Bu‐4‐Me‐C6H2]2CH2 ( 9 ) and [(C5H10N)(O)P‐μ‐N‐t‐Bu]2 ( 10 ), respectively. Oxidative addition of o‐chloranil to 7 and its DIAD analogue [(t‐BuNH)P(μ‐N‐t‐Bu)2P=N‐t‐Bu)(N(CO2‐i‐Pr)NHCO2‐i‐Pr] ( 11 ) afforded [(C6Cl4‐1, 2‐O2)(t‐BuNH)P(μ‐N‐t‐Bu)2P=N‐t‐Bu)(N(CO2R)NHCO2R] [R = Et ( 12 ) and i‐Pr ( 13 )] containing tetra‐ and pentacoordinate PV atoms in the cyclodiphosphazane ring. The structures of 6 , 9 , 12 and 13 have been confirmed by X‐ray structure determination. For comparison, the X‐ray structure of the double cycloaddition product [(C6Cl4‐1, 2‐O2)(t‐BuNH)PN‐t‐Bu]2 ( 14 ), obtained from the reaction of 2 with two mole equivalents of o‐chloranil is also reported. 相似文献
5.
The Mechanism of CO2 Insertion into Iridium(I) Hydroxide and Alkoxide Bonds: A Kinetics and Computational Study 下载免费PDF全文
Dr. Byron J. Truscott Hedi Kruger Dr. Paul B. Webb Prof. Dr. Michael Bühl Prof. Dr. Steven P. Nolan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(18):6930-6935
The facile insertion of CO2 into iridium(I) hydroxide, alkoxide, and amide bonds was recently reported. In particular, [Ir(cod)(IiPr)(OH)] (IiPr=1,3‐bis(isopropyl)imidazol‐2‐ylidene) reacted with CO2 in solution and in the solid state in a matter of minutes to give the novel [{Ir(cod)(IiPr)}2(μ‐κ1O:κ2O,O‐CO3)] complex. In the present study, this reaction is probed using kinetics and theoretical studies, which enabled us to analyse its facile nature and to fully elucidate the reaction mechanism with excellent correlation between the two methods. 相似文献
6.
Sathiyamoorthy Murugesan Berthold Stger Ernst Pittenauer Günter Allmaier Luis F. Veiros Karl Kirchner 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2016,128(9):3097-3100
The synthesis and reactivity of a CoI pincer complex [Co(ϰ3P,CH,P‐P(CH)PNMe‐iPr)(CO)2]+ featuring an η2‐ Caryl−H agostic bond is described. This complex was obtained by protonation of the CoI complex [Co(PCPNMe‐iPr)(CO)2]. The CoIII hydride complex [Co(PCPNMe‐iPr)(CNtBu)2(H)]+ was obtained upon protonation of [Co(PCPNMe‐iPr)(CNtBu)2]. Three ways to cleave the agostic C−H bond are presented. First, owing to the acidity of the agostic proton, treatment with pyridine results in facile deprotonation (C−H bond cleavage) and reformation of [Co(PCPNMe‐iPr)(CO)2]. Second, C−H bond cleavage is achieved upon exposure of [Co(ϰ3P,CH,P‐P(CH)PNMe‐iPr)(CO)2]+ to oxygen or TEMPO to yield the paramagnetic CoII PCP complex [Co(PCPNMe‐iPr)(CO)2]+. Finally, replacement of one CO ligand in [Co(ϰ3P,CH,P‐P(CH)PNMe‐iPr)(CO)2]+ by CNtBu promotes the rapid oxidative addition of the agostic η2‐Caryl−H bond to give two isomeric hydride complexes of the type [Co(PCPNMe‐iPr)(CNtBu)(CO)(H)]+. 相似文献
7.
A Cobalt(I) Pincer Complex with an η2‐Caryl−H Agostic Bond: Facile C−H Bond Cleavage through Deprotonation,Radical Abstraction,and Oxidative Addition 下载免费PDF全文
Sathiyamoorthy Murugesan Dr. Berthold Stöger Dr. Ernst Pittenauer Prof. Dr. Günter Allmaier Prof. Dr. Luis F. Veiros Prof. Dr. Karl Kirchner 《Angewandte Chemie (International ed. in English)》2016,55(9):3045-3048
The synthesis and reactivity of a CoI pincer complex [Co(?3P,CH,P‐P(CH)PNMe‐iPr)(CO)2]+ featuring an η2‐ Caryl?H agostic bond is described. This complex was obtained by protonation of the CoI complex [Co(PCPNMe‐iPr)(CO)2]. The CoIII hydride complex [Co(PCPNMe‐iPr)(CNtBu)2(H)]+ was obtained upon protonation of [Co(PCPNMe‐iPr)(CNtBu)2]. Three ways to cleave the agostic C?H bond are presented. First, owing to the acidity of the agostic proton, treatment with pyridine results in facile deprotonation (C?H bond cleavage) and reformation of [Co(PCPNMe‐iPr)(CO)2]. Second, C?H bond cleavage is achieved upon exposure of [Co(?3P,CH,P‐P(CH)PNMe‐iPr)(CO)2]+ to oxygen or TEMPO to yield the paramagnetic CoII PCP complex [Co(PCPNMe‐iPr)(CO)2]+. Finally, replacement of one CO ligand in [Co(?3P,CH,P‐P(CH)PNMe‐iPr)(CO)2]+ by CNtBu promotes the rapid oxidative addition of the agostic η2‐Caryl?H bond to give two isomeric hydride complexes of the type [Co(PCPNMe‐iPr)(CNtBu)(CO)(H)]+. 相似文献
8.
An alkylperoxonickel(II) complex with hydrotris(3,5‐diisopropyl‐4‐bromo‐1‐pyrazolyl)borate, [NiII(OOtBu)(TpiPr2,Br)] ( 3a ), is synthesized, and its chemical properties are compared with those of the prototype non‐brominated ligand derivative [NiII(OOtBu)(TpiPr2)] ( 3b ; TpiPr2=hydrotris(3,5‐diisopropyl‐1‐pyrazolyl)borate). Same synthetic procedures for the prototype 3b and its precursors can be employed to the synthesis of the TpiPr2,Br analogues. The dimeric nickel(II)‐hydroxo complex, [(NiIITpiPr2,Br)2(μ‐OH)2] ( 2a ), can be synthesized by the base hydrolysis of the labile complexes [NiII(Y)(TpiPr2,Br)] (Y=NO3 ( 1a ), OAc ( 1a′ )), which are obtained by the metathesis of NaTpiPr2,Br with the corresponding nickel(II) salts, and the following dehydrative condensation of 2a with the stoichiometric amount of tert‐butylhydroperoxide yields 3a . The unique structural characteristics of the prototype 3b , that is, highly distorted geometry of the nickel center and intermediate coordination mode of the O O moiety between η1 and η2, are kept in the brominated ligand analogue 3a . The introduction of the electron‐withdrawing substitutents on the distal site of TpR affects the thermal stability and reactivity of the nickel(II)‐alkylperoxo species. 相似文献
9.
This article deals that the rare earth metal complexes along with Al(i'-Bu),can catalyze the polymerization of methyl-methacrylate (MMA) into high molecular weight poly(MMA) along with narrow molecular weight distributions (MWD).A typical example was mentioned in the case of {Cp(Cl) Sm-Schiff-base(THF)} which expresses maximum (conv.% = 55.46 and Mn=354×103) efficiency along with narrow MWD (Mw/Mn<2) at 60℃.The resulting polymer was partially syndiotactic (>60%).The effect of the catalyst,temperature,catalyst/MMA molar ratio,catalyst/Al( i-Bu)3 molar ratio on the polymerization of MMA at 60℃ were also investigated. 相似文献
10.
W. Kuchen D. Langsch W. Peters 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):55-61
Abstract P.P-Dialkylthiophosphinsäureamide R2P(S)NHR' (R=Me, 'Pr, 'Bu; R'=Me, Et, iPr. cHex. tBu. Ph. etc.) wurden erhalten durch Umsetzung von R2PNHR' mit Schwefel oder durch Reaktion von Me2P(S)CI mit primaren Aminen. Ihre 31P- und 13C-NMR-Spektren werden diskutiert. Insbesondere die Di-t-butylthiophosphinsäureamide sind auszilg;ergewöhnlich stabil gegen Hydrolyse und Luftsauerstoff. P,P-Dialkylthiophosphinic acid amides R2P(S)NHR' (R=Me. iPr. tBu; R'=Me, Et, iPr, cHex. tBu, Ph. etc.) have been obtained by reaction of the corresponding aminophosphines with sulfur or by reaction of dimethylthiophosphorylhalides with primary amines. Their 31P- and 13C-NMR spectra are discussed. The di-t-butylthiophosphinic compounds proved to be remarkably stable against moisture and oxygen. 相似文献
11.
Normal‐to‐Abnormal NHC Rearrangement of AlIII,GaIII, and InIII Trialkyl Complexes: Scope,Mechanism, Reactivity Studies,and H2 Activation 下载免费PDF全文
Dr. Gilles Schnee Prof. Olalla Nieto Faza Dr. David Specklin Dr. Béatrice Jacques Dr. Lydia Karmazin Prof. Richard Welter Prof. Carlos Silva López Dr. Samuel Dagorne 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(49):17959-17972
The present contribution reports experimental and theoretical mechanistic investigations on a normal‐to‐abnormal (C2‐to‐C4‐bonded) NHC rearrangement processes occurring with bulky group 13 metal NHC adducts, including the scope of such a reactivity for Al compounds. The sterically congested adducts (nItBu)MMe3 (nItBu=1,3‐di‐tert‐butylimidazol‐2‐ylidene; M=Al, Ga, In; 1 a – c ) readily rearrange to quantitatively afford the corresponding C4‐bonded complexes (aItBu)MMe3 ( 4 a – c ), a reaction that may be promoted by THF. Thorough experimental data and DFT calculations were performed on the nNHC‐to‐aNHC process converting the Al‐nNHC ( 1 a ) to its aNHC analogue 4 a . A nItBu/aItBu isomerization is proposed to account for the formation of the thermodynamic product 4 a through reaction of transient aItBu with THF–AlMe3. The reaction of benzophenone with (nItBu)AlMe3 afforded the zwitterionic species (aItBu)(CPh2‐O‐AlMe3) ( 6 ), reflecting the unusual reactivity that such bulky adducts may display. Interestingly, the nItBu/Al(iBu)3 Lewis pair behaves like a frustrated Lewis pair (FLP) since it readily reacts with H2 under mild conditions. This may open the way to future reactivity developments involving commonly used trialkylaluminum precursors. 相似文献
12.
[(IPent)PdCl2(morpholine)]: A Readily Activated Precatalyst for Room‐Temperature,Additive‐Free Carbon–Sulfur Coupling 下载免费PDF全文
Jennifer L. Farmer Matthew Pompeo Dr. Alan J. Lough Prof. Michael G. Organ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(48):15790-15798
A series of new, easily activated NHC–PdII precatalysts featuring a trans‐oriented morpholine ligand were prepared and evaluated for activity in carbon‐sulfur cross‐coupling chemistry. [(IPent)PdCl2(morpholine)] (IPent=1,3‐bis(2,6‐di(3‐pentyl)phenyl)imidazol‐2‐ylidene) was identified as the most active precatalyst and was shown to effectively couple a wide variety of deactivated aryl halides with both aryl and alkyl thiols at or near ambient temperature, without the need for additives, external activators, or pre‐activation steps. Mechanistic studies revealed that, in contrast to other common NHC–PdII precatalysts, these complexes are rapidly reduced to the active NHC–Pd0 species at ambient temperature in the presence of KOtBu, thus avoiding the formation of deleterious off‐cycle PdII–thiolate resting states. 相似文献
13.
Dr. David Schmidt David Bialas Prof. Dr. Frank Würthner 《Angewandte Chemie (International ed. in English)》2015,54(12):3611-3614
The unexpected introduction of a cationic imidazolium substituent in the 2‐position of a tetrachloro‐substituted perylene‐3,4:9,10‐tetracarboxylic acid bisimide (PBI) by the reaction of PBI‐Cl4 1 with the N‐heterocyclic carbene 1,3‐di‐iso‐propyl‐imidazolin‐2‐ylidene (iPr2Im 2 ) enables the isolation of an ambient stable zwitterionic radical. The remarkable stability of this unprecedented PBI‐centered radical facilitates the complete characterization by several spectroscopic methods as well as single crystal structure analysis. Redox studies revealed that iPr2Im‐PBI‐Cl4 4 can be transferred reversibly to the corresponding anion and cation, respectively, even on a preparative scale. 相似文献
14.
Byron J. Truscott Dr. David J. Nelson Dr. Cristina Lujan Prof. Dr. Alexandra M. Z. Slawin Prof. Dr. Steven P. Nolan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(24):7904-7916
A family of iridium(I) hydroxides of the form [Ir(cod)(NHC)(OH)] (cod=1,5‐cyclooctadiene, NHC=N‐heterocyclic carbene) is reported. Single‐crystal X‐ray analyses and computational methods were used to explore the structural characteristics and steric properties of these new complexes. The model complex [Ir(cod)(IiPr)(OH)] (IiPr=1,3‐(diisopropyl)imidazol‐2‐ylidene) undergoes reaction with a wide variety of substrates including boronic acids and silicon compounds. In addition, O? H, N? H and C? H bond activation was achieved with alcohols, carboxylic acids, amines and various sp‐, sp2‐ and sp3‐hybridised carbon centres, giving access to a wide range of new IrI complexes. These studies have allowed us to explore the exciting reactivity of this motif, revealing a versatile and useful synthon capable of activating important chemical bonds under mild (typically room temperature) conditions. No additives were required and, in the case of X? H bond activation, water was the only waste product, rendering this an atom efficient procedure for bond activation. This system has great potential for the construction of new catalytic cycles for organic synthesis and small‐molecule activation. 相似文献
15.
Prof. Dr. Stephan Schulz Raphaela Schäper Daniel Krech Daniella Schuchmann Dieter Bläser Roland Boese 《无机化学与普通化学杂志》2011,637(1):83-86
Lewis acid‐base adducts of the general type R2Zn(4‐tBuPy)x (R = Me 1 , iPr 2 , tBu 3 , Cp* 4 ; x = 1, 2) were obtained in high yields from reactions of ZnR2 with the Lewis base 4‐tBu‐Pyridine. Compounds 1 – 4 were characterized by multinuclear NMR (1H, 13C) and IR spectroscopy and elemental analyses, 1 and 4 also by X‐ray diffraction at single crystals. 相似文献
16.
The Use of (−)‐Sparteine/Organolithium Reagents for the Enantioselective Lithiation of 7,8‐Dipropyltetrathia[7]helicene: Single and Double Kinetic Resolution Procedures 下载免费PDF全文
Dr. Julien Doulcet Dr. G. Richard Stephenson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(51):18677-18689
The effect of organolithium reagent (RLi: R=nBu, iPr, sBu, tBu), solvent (diethyl ether, diethyl ether/THF and MTBE), and stoichiometry on the (?)‐sparteine‐mediated silylation of 7,8‐dipropyltetrathia[7]helicene shows that, unusually, substantially more than 0.5 equivalent of RLi (R=iPr, sBu, tBu) and a large excess of (?)‐sparteine (R=nBu, sBu) is often needed to achieve substantial conversions and good ee values. With nBuLi, however, just one equivalent of the organolithium reagent is sufficient to obtain high conversions. Our best results were obtained using the convenient tBuLi/(?)‐sparteine adduct with which the need for a high (?)‐sparteine/RLi ratio can be avoided. Single‐ and double‐kinetic resolution (KR) procedures give enantiopure samples of 2‐trimethylsilyl‐ and 2,13‐di(trimethylsilyl)‐7,8‐dipropyltetrathia[7]helicene and two‐step double‐KR combining (?)‐sparteine/sBuLi and chiral formamides affords the synthetically valuable 2‐formyl‐7,8‐dipropyltetrathia[7]helicene. This is the first use of (?)‐sparteine for the enantioselective lithiation of helicenes and the first report of tBuLi outperforming sBuLi in a (?)‐sparteine‐mediated procedure. 相似文献
17.
Ring Opening and Bidentate Coordination of Amidinate Germylenes and Silylenes on Carbonyl Dicobalt Complexes: The Importance of a Slight Difference in Ligand Volume 下载免费PDF全文
Prof. Javier A. Cabeza Dr. Pablo García‐Álvarez Dr. Enrique Pérez‐Carreño Diego Polo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(28):8654-8663
The reactions of [Co2(CO)8] with one equiv of the benzamidinate (R2bzam) group‐14 tetrylenes [M(R2bzam)(HMDS)] (HMDS=N(SiMe3)2; 1 : M=Ge, R=iPr; 2 : M=Si, R=tBu; 3 : M=Ge, R=tBu) at 20 °C led to the monosubstituted complexes [Co2{κ1M?M(R2bzam)(HMDS)}(CO)7] ( 4 : M=Ge, R=iPr; 5 : M=Si, R=tBu; 6 : M=Ge, R=tBu), which contain a terminal κ1M–tetrylene ligand. Whereas the Co2Si and Co2Ge tert‐butyl derivatives 5 and 6 are stable at 20 °C, the Co2Ge isopropyl derivative 4 evolved to the ligand‐bridged derivative [Co2{μ‐κ2Ge,N‐Ge(iPr2bzam)(HMDS)}(μ‐CO)(CO)5] ( 7 ), in which the Ge atom spans the Co?Co bond and one arm of the amidinate fragment is attached to a Co atom. The mechanism of this reaction has been modeled with the help of DFT calculations, which have also demonstrated that the transformation of amidinate‐tetrylene ligands on the dicobalt framework is negligibly influenced by the nature of the group‐14 metal atom (Si or Ge) but is strongly dependent upon the volume of the amidinate N?R groups. The disubstituted derivatives [Co2{κ1M?M(R2bzam)(HMDS)}2(CO)6] ( 8 : M=Ge, R=iPr; 9 : M=Si, R=tBu; 10 : M=Ge, R=tBu), which contain two terminal κ1M–tetrylene ligands, have been prepared by treating [Co2(CO)8] with two equiv of 1 – 3 at 20 °C. The IR spectra of 8 – 10 have shown that the basicity of germylenes 1 and 3 is very high (comparable to that of trialkylphosphanes and 1,3‐diarylimidazol‐2‐ylidenes), whereas that of silylene 2 is even higher. 相似文献
18.
A series of cationic rare‐earth aryloxide complexes, i.e., [LREOAr']+[B(C6F5)4]– (L = CH3C(NAr)CHC(CH3)(NCH(R)CH2PPh2); RE = Y, Lu; Ar' =2,6‐tBu2‐C6H3, 2,6‐(PhCMe2)2‐4‐Me‐C6H2; Ar = 2,6‐iPr2‐C6H3, 2,6‐(Ph2CH)2‐4‐iPr‐C6H2; R = H, CH3, iPr, Ph), were prepared and applied to the Lewis pair polymerization of methyl methacrylate (MMA). The stereoregularity of the resulting PMMA was significantly affected by the R substituent on the pendant arm of the tridentate NNP ligand, and was found to increase with increase in the steric hindrance of R. When using a Ph group as R, the Y complex produced a highly isotactic polymer with an mm value of 95% and a Tg of 54.6 oC. In contrast, the steric hindrance of the Ar and Ar' groups had no effect on the tacticity of the resulting polymer, presumably because these two substituents were situated such that they pointed outward from the cyclic intermediates. Kinetics studies demonstrated that the polymerization was a first‐order process with regard to the monomer concentration prior to catalyst deactivation. End group analysis indicated that the polymerization was accompanied by two possibly competing chain‐termination side reactions that proceeded via intramolecular backbiting cyclization. 相似文献
19.
Volodymyr Sashuk Lars H. Peeck Herbert Plenio 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(13):3983-3993
Imidazolium salts (NHCewg ? HCl) with electronically variable substituents in the 4,5‐position (H,H or Cl,Cl or H,NO2 or CN,CN) and sterically variable substituents in the 1,3‐position (Me,Me or Et,Et or iPr,iPr or Me,iPr) were synthesized and converted into the respective [AgI(NHC)ewg] complexes. The reactions of [(NHC)RuCl2(CHPh)(py)2] with the [AgI(NHCewg)] complexes provide the respective [(NHC)(NHCewg)RuCl2(CHPh)] complexes in excellent yields. The catalytic activity of such complexes in ring‐closing metathesis (RCM) reactions leading to tetrasubstituted olefins was studied. To obtain quantitative substrate conversion, catalyst loadings of 0.2–0.5 mol % at 80 °C in toluene are sufficient. The complex with the best catalytic activity in such RCM reactions and the fastest initiation rate has an NHCewg group with 1,3‐Me,iPr and 4,5‐Cl,Cl substituents and can be synthesized in 95 % isolated yield from the ruthenium precursor. To learn which one of the two NHC ligands acts as the leaving group in olefin metathesis reactions two complexes, [(FL‐NHC)(NHCewg)RuCl2(CHPh)] and [(FL‐NHCewg)(NHC)RuCl2(CHPh)], with a dansyl fluorophore (FL)‐tagged electron‐rich NHC ligand (FL‐NHC) and an electron‐deficient NHC ligand (FL‐NHCewg) were prepared. The fluorescence of the dansyl fluorophore is quenched as long as it is in close vicinity to ruthenium, but increases strongly upon dissociation of the respective fluorophore‐tagged ligand. In this manner, it was shown for ring‐opening metathesis ploymerization (ROMP) reactions at room temperature that the NHCewg ligand normally acts as the leaving group, whereas the other NHC ligand remains ligated to ruthenium. 相似文献
20.
Iron Dicarbonyl Complexes Featuring Bipyridine‐Based PNN Pincer Ligands with Short Interpyridine CC Bond Lengths: Innocent or Non‐Innocent Ligand? 下载免费PDF全文
Dr. Thomas Zell Dr. Petr Milko Kathlyn L. Fillman Dr. Yael Diskin‐Posner Dr. Tatyana Bendikov Dr. Mark A. Iron Dr. Gregory Leitus Yehoshoa Ben‐David Prof. Michael L. Neidig Prof. David Milstein 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(15):4403-4413