Summary: The neodymium trisborohydride Nd(BH4)3(THF)3 (THF = tetrahydrofuran) has been used as a catalyst precursor for isoprene polymerization for the first time. Associated to an excess of Al(Et)3, the resulting catalyst is moderately active, giving a mixture of cis‐ and trans‐ polymer. Addition of a stoichiometric amount of MgBu2 to Nd(BH4)3(THF)3 affords a stereospecific catalyst providing trans‐1,4‐polyisoprene, more than 96% regular. That dual component Nd/Mg system also shows a better efficiency and good control of the molecular weights. A molecular structure is tentatively attributed to a bimetallic active species, based on 1H NMR experiments.
Possible Nd/Al and Nd/Mg active initiating species. 相似文献
Contributions to Organolanthanide Chemistry. II. Cyclopentadienyllanthanide 1,3-Butadiene Complexes – Synthesis, Properties, and Reactions From cyclopentadienyllanthanide dihalides and “magnesium butadiene” Cp*La(C4H6) · MgI2 · 3 THF ( I ), Cp*Ce(C4H6) · MgBr2 · 2 THF ( II ), Cp*Nd(C4H6) · MgCl2 · 2 THF ( III ), (1,3-(t-C4H9)2C5H3)Nd(C4H6) · MgCl2 · 2 THF ( IV ), CpEr(C4H6) · MgCl2 · 2 THF ( V ) and (1,3-(t-C4H9)2C5H3)Lu(C4H6) · MgCl2 · 2 THF ( VI ) were obtained as highly air sensitive complexes which react easily with proton active compounds and molecules with multible bonds. The reaction products with diphenylamine and carbon dioxide Cp*Nd(NPh2)2 · NHPh2 ( VII ) and Cp*Ce(O2CC4H6CO2) ( VIII ) are discribed. I–VIII were characterized by elementary analysis, i.r., 1H and 13C n.m.r., and EI-MS spectra. 相似文献
Reaction of [CpnMCl4?x] (M=V: n=x=2; M=Nb: n=1, x=0) or [Cp*TaCl4] (Cp=η5‐C5H5, Cp*=η5‐C5Me5), with [LiBH4?thf] at ?70 °C followed by thermolysis at 85 °C in the presence of [BH3?thf] yielded the hydrogen‐rich metallaboranes [(CpM)2(B2H6)2] ( 1 : M=V; 2 : M = Nb) and [(Cp*Ta)2(B2H6)2] ( 3 ) in modest to high yields. Complexes 1 and 3 are the first structurally characterized compounds with a metal–metal bond bridged by two hexahydroborate (B2H6) groups forming a symmetrical complex. Addition of [BH3?thf] to 3 results in formation of a metallaborane [(Cp*Ta)2B4H8(μ‐BH4)] ( 4 ) containing a tetrahydroborate ligand, [BH4]?, bound exo to the bicapped tetrahedral cage [(Cp*Ta)2B4H8] by two Ta‐H‐B bridge bonds. The interesting structural feature of 4 is the coordination of the bridging tetrahydroborate group, which has two B? H bonds coordinated to the tantalum atoms. All these new metallaboranes have been characterized by mass, 1H, 11B, and 13C NMR spectroscopy and elemental analysis and the structural types were established unequivocally by crystallographic analysis of 1 – 4 . 相似文献
Summary: Isoprene polymerisation performed under microwave irradiation with [Nd(BH4)3(THF)3]/Mg(Bu)2 and [Nd(BH4)3(THF)3]/Al(Et)3 showed an enhancement in reactivity, with selectivity being only slightly modified. An explanation of the observed effect is proposed based on our current knowledge of the catalytic mechanism and by considering the alkylated complex as an ion pair. An analogy is proposed with the pseudoanionic polymerisation of oxygenated monomers. Finally, depolymerisation is observed under microwave irradiation at high temperature.
Postulated mechanism for the polymerisation of isoprene with [Nd(BH4)3(THF)3]/Mg(Bu)2. 相似文献
The reaction of potassium 2,5‐bis[N‐(2,6‐diisopropylphenyl)iminomethyl]pyrrolyl [(dip2‐pyr)K] with the borohydrides of the larger rare‐earth metals, [Ln(BH4)3(thf)3] (Ln=La, Nd), afforded the expected products [Ln(BH4)2(dip2‐pyr)(thf)2]. As usual, the trisborohydrides reacted like pseudohalide compounds forming KBH4 as a by‐product. To compare the reactivity with the analogous halides, the dimeric neodymium complex [NdCl2(dip2‐pyr)(thf)]2 was prepared by reaction of [(dip2‐pyr)K] with anhydrous NdCl3. Reaction of [(dip2‐pyr)K] with the borohydrides of the smaller rare‐earth metals, [Sc(BH4)3(thf)2] and [Lu(BH4)3(thf)3], resulted in a redox reaction of the BH4? group with one of the Schiff base functions of the ligand. In the resulting products, [Ln(BH4){(dip)(dip‐BH3)‐pyr}(thf)2] (Ln=Sc, Lu), a dinegatively charged ligand with a new amido function, a Schiff base, and the pyrrolyl function is bound to the metal atom. The by‐product of the reaction of the BH4? anion with the Schiff base function (a BH3 molecule) is trapped in a unique reaction mode in the coordination sphere of the metal complex. The BH3 molecule coordinates in an η2 fashion to the metal atom. The rare‐earth‐metal atoms are surrounded by the η2‐coordinated BH3 molecule, the η3‐coordinated BH4? anion, two THF molecules, and the nitrogen atoms from the Schiff base and the pyrrolyl function. All new compounds were characterized by single‐crystal X‐ray diffraction. Low‐temperature X‐ray diffraction data at 6 K were collected to locate the hydrogen atoms of [Lu(BH4){(dip)(dip‐BH3)‐pyr}(thf)2]. The (DIP2‐pyr)? borohydride and chloride complexes of neodymium, [Nd(BH4)2(dip2‐pyr)(thf)2] and [NdCl2(dip2‐pyr)(thf)]2, were also used as Ziegler–Natta catalysts for the polymerization of 1,3‐butadiene to yield poly(cis‐1,4‐butadiene). Very high activities and good cis selectivities were observed by using each of these complexes as a catalyst in the presence of various cocatalyst mixtures. 相似文献
Zincocene Cp*2Zn reacts with carbodiimides C(NR)2 with insertion into the Zn–Cp* bond and formation of [(Cp*C(NR)2]2Zn [R = Et ( 1 ), iPr ( 2 ), Cy ( 3 )]. In addition, the reaction of Cp*2Zn with CS2 under dry conditions gives (Cp*CS2)2Zn ( 4 ), whereas in the presence of a small amount of water [Zn4(μ4‐O)(S2CCp*)6] ( 5 ) is obtained. Compounds 1 – 4 were characterized by NMR (1H, 13C) and IR spectroscopy as well as elemental analysis and single‐crystal X‐ray diffraction ( 2 – 4 , 5 of poor quality). The solid‐state structure of 5 is comparable to the carboxylate complex previously obtained from the reaction of Cp*2Zn with CO2. 相似文献
The reactions of LnI2 (Ln = Nd (1) or Dy (2)) with cyclopentadiene (CpH) in THF at 0 °C afforded the CpLnI2(THF)3 complexes in 65—67% yields. The reaction of thulium diiodide (3) with an excess of CpH at 60 °C produced CpTmI2(THF)3, Cp2TmI(THF)2, and TmI3(THF)3 in 21, 58, and 63% yields, respectively. The reactions of 1 and 2 with pentamethylcyclopentadiene (Cp*H) in THF were accompanied by disproportionation giving rise to the Cp*2LnI(THF)2 and LnI3(THF)x complexes. Neodymium triiodide was isolated in the ionic form [NdI2(THF)5]+[NdI4(THF)2]–. Its structure and the structure of CpTmI2(THF)3 were established by X-ray diffraction analysis. 相似文献
Statistical copolymerization of ethylene and isoprene was achieved by using a borohydrido half‐lanthanidocene complex. Under copolymerization conditions, activation of [(Cp*)(BH4)2Nd(thf)2] (Cp*=η5‐C5Me5) by an appropriate alkylating agent affords trans‐1,4‐poly‐isoprene‐co‐ethylene. Analysis of the microstructure of the copolymer revealed the presence of successive short sequences of ethylene/ethylene, trans‐1,4‐isoprene/ethylene, and trans‐1,4‐isoprene/trans‐1,4‐isoprene. A small amount of 1,2‐insertion of isoprene was observed, and no cyclic structures within the chain were characterized. Test runs showed that these catalysts are unable to copolymerize α‐olefins (such as hex‐1‐ene) with isoprene. The probable initial steps in the copolymerization have been computed at the DFT level of theory. Analysis of the energy profile provides insight into the catalyst’s activity and selectivity. Our theoretical results highlight the key role played by the allyl intermediate, in which diene insertion, and to a lesser extent olefin insertion, is the rate‐determining step of the process. These results also illustrate the coordination behavior of the allyl ligand during the insertion of an incoming monomer, which directly inserts, after pre‐coordination to the metal center, into the η3‐allyl ligand without inducing an η3 to η1 haptotropic shift. Finally, the inactivity of this family of catalysts towards the copolymerization of hex‐1‐ene was rationalized on the basis of the free‐energy profile of the copolymerization. 相似文献
Reaction of potassium salt of N‐aryliminopyrrole ligand [2‐(2, 6‐iPr2C6H3N=CH)–C4H3NK] ( 1 ) with samarium tris‐boro‐hydride [Sm(BH4)3(THF)3] gave a samarium ate complex [η2‐{2‐(2, 6‐iPr2C6H3N=CH)–C4H3N}3Sm(η1‐BH4){K(THF)6] ( 2 ); whereas similar treatment with erbium borohydride [Er(BH4)3(THF)3] afforded the mono(iminopyrrolyl) complex [η2‐{2‐(2, 6‐iPr2C6H3N=CH)–C4H3N}Er(η3‐BH4)2(THF)2] ( 3 ). In the solid‐state structures, the samarium complex 2 shows a rarely observed η1 and the erbium complex 3 shows a usual η3 coordination mode of the borohydrido ligand. 相似文献
A series of agostic σ‐borane/borate complexes have been synthesized and structurally characterized from simple borane adducts. A room‐temperature reaction of [Cp*Mo(CO)3Me], 1 with Li[BH3(EPh)] (Cp*=pentamethylcyclopentadienyl, E=S, Se, Te) yielded hydroborate complexes [Cp*Mo(CO)2(μ‐H)BH2EPh] in good yields. With 2‐mercapto‐benzothiazole, an N,S‐carbene‐anchored σ‐borate complex [Cp*Mo(CO)2BH3(1‐benzothiazol‐2‐ylidene)] ( 5 ) was isolated. Further, a transmetalation of the B‐agostic ruthenium complex [Cp*Ru(μ‐H)BHL2] ( 6 , L=C7H4NS2) with [Mn2(CO)10] affords a new B‐agostic complex, [Mn(CO)3(μ‐H)BHL2] ( 7 ) with the same structural motif in which the central metal is replaced by an isolobal and isoelectronic [Mn(CO)3] unit. Natural‐bond‐orbital analyses of 5–7 indicate significant delocalization of the electron density from the filled σB?H orbital to the vacant metal orbital. 相似文献
Room temperature photolysis of a triply‐bridged borylene complex, [(μ3‐BH)(Cp*RuCO)2(μ‐CO)Fe(CO)3] ( 1 a ; Cp*=C5Me5), in the presence of a series of alkynes, 1,2‐diphenylethyne, 1‐phenyl‐1‐propyne, and 2‐butyne led to the isolation of unprecedented vinyl‐borylene complexes (Z)‐[(Cp*RuCO)2(μ‐CO)B(CR)(CHR′)] ( 2 : R, R′=Ph; 3 : R=Me, R′=Ph; 4 : R, R′=Me). This reaction permits a hydroboration of alkyne through an anti ‐ Markovnikov addition. In stark contrast, in the presence of phenylacetylene, a metallacarborane, closo‐[1,2‐(Cp*Ru)2(μ‐CO)2{Fe2(CO)5}‐4‐Ph‐4,5‐C2BH2] ( 5 a) , is formed. A plausible mechanism has been proposed for the formation of vinyl‐borylene complexes, which is supported by density functional theory (DFT) methods. Furthermore, the calculated 11B NMR chemical shifts accurately reflect the experimentally measured shifts. All the new compounds have been characterized in solution by mass spectrometry and IR, 1H, 11B, and 13C NMR spectroscopies and the structural types were unequivocally established by crystallographic analysis of 2 , 5 a , and 5 b . 相似文献
The reaction of one equivalent of Nd(BH4)3(THF)3 with an half equivalent of dialkylmagnesium in the presence of a stoichiometric amount of pentamethylcyclopentadiene cleanly affords a new kind of half-sandwich of neodymium that is stable toward comproportionation. This strategy can be advantageously applied to generate in situ catalysts allowing the controlled polymerisation of isoprene. 相似文献
Treatment of [Cp*MoCl4], 1 (Cp* = η5-C5Me5), with [LiBH4.thf] in toluene at −40 °C, followed by thermolysis with [(thf)Li{CH(PPh2–BH3)2}] results in the formation of a new class of phosphido bridged molybdaborane [(Cp*Mo)2B4H7(μ-PPh2)], 2 which has been characterized crystallographically. In addition, the above reaction also produces known [(Cp*Mo)2B5H9], 3 and an unusual molybdaborane [(Cp*Mo)2B5H8(OiPr)], 4 (iPr = –CH(CH3)2). All the new compounds have been characterized in solution by 1H, 11B, 13C, 31P NMR spectroscopy and the structural types were unambiguously established by X-ray crystallographic analysis of compounds
2 and 4. 相似文献
Rare‐earth‐metal borohydrides are known to be efficient catalysts for the polymerization of apolar and polar monomers. The bis‐borohydrides [{CH(PPh2NSiMe3)2}La(BH4)2(THF)] and [{CH(PPh2NSiMe3)2}Ln(BH4)2] (Ln=Y, Lu) have been synthesized by two different synthetic routes. The lanthanum and the lutetium complexes were prepared from [Ln(BH4)3(THF)3] and K{CH(PPh2NSiMe3)2}, whereas the yttrium analogue was obtained from in situ prepared [{CH(PPh2NSiMe3)2}YCl2]2 and NaBH4. All new compounds were characterized by standard analytical/spectroscopic techniques, and the solid‐state structures were established by single‐crystal X‐ray diffraction. The ring‐opening polymerization (ROP) of ε‐caprolactone initiated by [{CH(PPh2NSiMe3)2}La(BH4)2(THF)] and [{CH(PPh2NSiMe3)2}Ln(BH4)2] (Ln=Y, Lu) was studied. At 0 °C the molar mass distributions determined were the narrowest values (M?w/M?n=1.06–1.11) ever obtained for the ROP of ε‐caprolactone initiated by rare‐earth‐metal borohydride species. DFT investigations of the reaction mechanism indicate that this type of complex reacts in an unprecedented manner with the first B? H activation being achieved within two steps. This particularity has been attributed to the metallic fragment based on the natural bond order analysis. 相似文献
We report a detailed study of the reactions of the Ti?NNCPh2 alkylidene hydrazide functional group in [Cp*Ti{MeC(NiPr)2}(NNCPh2)] ( 8 ) with a variety of unsaturated and saturated substrates. Compound 8 was prepared from [Cp*Ti{MeC(NiPr)2}(NtBu)] and Ph2CNNH2. DFT calculations were used to determine the nature of the bonding for the Ti?NNCPh2 moiety in 8 and in the previously reported [Cp2Ti(NNCPh2)(PMe3)]. Reaction of 8 with CO2 gave dimeric [(Cp*Ti{MeC(NiPr)2}{μ‐OC(NNCPh2)O})2] and the “double‐insertion” dicarboxylate species [Cp*Ti‐{MeC(NiPr)2}{OC(O)N(NCPh2)C(O)O}] through an initial [2+2] cycloaddition product [Cp*Ti{MeC(NiPr)2}{N(NCPh2)C(O)O}], the congener of which could be isolated in the corresponding reaction with CS2. The reaction with isocyanates or isothiocyanates tBuNCO or ArNCE (Ar=Tol or 2,6‐C6H3iPr2; E=O, S) gave either complete NNCPh2 transfer, [2+2] cycloaddition to Ti?Nα or single‐ or double‐substrate insertion into the Ti?Nα bond. The treatment of 8 with isonitriles RNC (R=tBu or Xyl) formed σ‐adducts [Cp*Ti{MeC(NiPr)2}(NNCPh2)(CNR)]. With ArF5CCH (ArF5=C6F5) the [2+2] cycloaddition product [Cp*Ti{MeC(NiPr)2}{N(NCPh2)C(ArF5)C(H)}] was formed, whereas with benzonitriles ArCN (Ar=Ph or ArF5) two equivalents of substrate were coupled in a head‐to‐tail manner across the Ti?Nα bond to form [Cp*Ti{MeC(NiPr)2}{N(NCPh2)C(Ar)NC(Ar)N}]. Treatment of 8 with RSiH3 (R=aryl or Bu) or Ph2SiH2 gave [Cp*Ti{MeC(NiPr)2}{N(SiHRR′)N(CHPh2)}] (R′=H or Ph) through net 1,3‐addition of Si? H to the N? N?CPh2 linkage of 8 , whereas reaction with PhSiH2X (X=Cl, Br) led to the Ti?Nα 1,2‐addition products [Cp*Ti{MeC(NiPr)2}(X){N(NCPh2)SiH2Ph}]. 相似文献
Reaction of [1,2‐(Cp*RuH)2B3H7] ( 1 ; Cp*=η5‐C5Me5) with [Mo(CO)3(CH3CN)3] yielded arachno‐[(Cp*RuCO)2B2H6] ( 2 ), which exhibits a butterfly structure, reminiscent of 7 sep B4H10. Compound 2 was found to be a very good precursor for the generation of bridged borylene species. Mild pyrolysis of 2 with [Fe2(CO)9] yielded a triply bridged heterotrinuclear borylene complex [(μ3‐BH)(Cp*RuCO)2(μ‐CO){Fe(CO)3}] ( 3 ) and bis‐borylene complexes [{(μ3‐BH)(Cp*Ru)(μ‐CO)}2Fe2(CO)5] ( 4 ) and [{(μ3‐BH)(Cp*Ru)Fe(CO)3}2(μ‐CO)] ( 5 ). In a similar fashion, pyrolysis of 2 with [Mn2(CO)10] permits the isolation of μ3‐borylene complex [(μ3‐BH)(Cp*RuCO)2(μ‐H)(μ‐CO){Mn(CO)3}] ( 6 ). Both compounds 3 and 6 have a trigonal‐pyramidal geometry with the μ3‐BH ligand occupying the apical vertex, whereas 4 and 5 can be viewed as bicapped tetrahedra, with two μ3‐borylene ligands occupying the capping position. The synthesis of tantalum borylene complex [(μ3‐BH)(Cp*TaCO)2(μ‐CO){Fe(CO)3}] ( 7 ) was achieved by the reaction of [(Cp*Ta)2B4H8(μ‐BH4)] at ambient temperature with [Fe2(CO)9]. Compounds 2 – 7 have been isolated in modest yield as yellow to red crystalline solids. All the new compounds have been characterized in solution by mass spectrometry; IR spectroscopy; and 1H, 11B, and 13C NMR spectroscopy and the structural types were unequivocally established by crystallographic analysis of 2 – 6 . 相似文献
