Scandium half-metallocene-catalyzed syndiospecific styrene polymerization and styrene-ethylene copolymerization: unprecedented incorporation of syndiotactic styrene-styrene sequences in styrene-ethylene copolymers

On treatment with 1 equiv of [Ph3C][B(C6F5)4], the scandium half-sandwich bis(alkyl) complex (C5Me4SiMe3)Sc(CH2SiMe3)2(THF) showed extremely high activity (up to 1.36 x 104 kg of sPS/(mol Sc.h)) and syndiospecificity (rrrr > 99%) for the polymerization of styrene at room temperature in toluene. More remarkably, this catalyst system could also effect the syndiospecific copolymerization of styrene with ethylene to yield styrene-ethylene copolymers having syndiotactic styrene-styrene sequences. The styrene content in the copolymers could be easily controlled by changing the styrene feed and could reach higher than 80 mol %. This is the first example of formation of such types of styrene-ethylene copolymers, which are expected to show novel properties.     

Syndiotactic polymerization of styrene and copolymerization with ethylene catalyzed by chiral half-sandwich rare-earth metal dialkyl complexes

The syndiotactic polymerization of styrene(St) and the copolymerization of St with ethylene(E) were carried out by using a series of chiral half-sandwich rare-earth metal dialkyl complexes(Cp~x*) as the catalysts. The complexes are Ln(CH_2SiMe_3)_2(THF)(1-4: Ln = Sc(1), Ln = Lu(2), Ln = Y(3), Ln = Dy(4)) bearing chiral cyclopentadienyl ligand containing bulky cylcohexane derivatives in the presence of activator and AliBu_3. For the St polymerization, a high activity up to 3.1 × 10~6 g of polymer mol Ln~(-1)·h~(-1) and a high syndiotactic selectivity more than 99% were achieved. The resulting syndiotactic polystyrenes(sPSs) have the molecular weights(Mn) ranging from 3700 g·mol~(-1) to 6400 g·mol~(-1) and the molecular weight distributions(Mw/Mn) from 1.40 to 5.03. As for the copolymerization of St and E, the activity was up to 2.4 × 10~6 g of copolymer mol Sc~(-1)·h~(-1)·MPa~(-1), giving random St-E copolymers containing syndiotactic polystyrene sequences with different St content in the range of 15 mol%-58 mol%. These results demonstrate that the bulky cyclopentadienyl ligands of the chiral half-sandwich rare-earth metal complexes effectively inhibit the continued insertion of St monomers into the(co)polymer chain to some extent in comparison with the known half-sandwich rare-earth metal complexes.     

亚胺膦亚胺型稀土双烷基配合物对丁二烯1,2-选择性聚合

以三烷基钪Sc(CH2SiMe3)3(THF)2和胺基膦亚胺配体为原料,经烷基消去反应合成了胺基膦亚胺(NPN)型配体螯合钪烷基配合物。 其结构用1H NMR、13C NMR、元素分析和X射线衍射分析进行了表征。 在助催化剂有机硼盐和烷基铝的作用下,该配合物对丁二烯聚合表现出了较高的催化活性。 并且随着聚合温度的降低,催化剂的1,2-选择性也随之升高。 聚合温度为-75 ℃时,产物的1,2-结构含量高达98.0%,聚合物的分子量为2.95×104,分子量分布为1.65。     

Titanium "constrained geometry" complexes with pendant arene groups

The synthesis of the proligands C(5)Me(4)HSiMe(2)N(H)R) (R = CMe(2)Ph 1, 2-C(6)H(4)Ph 2) was accomplished via a straightforward salt metathesis reaction of the appropriate lithium amide and ClSiMe(2)(C(5)Me(5)H). Generation of the dilithio salt and reaction with TiCl(3)·(THF)(3) followed by oxidation gave C(5)Me(4)SiMe(2)N(C(6)H(4)Ph)TiCl(2) (3) in low yield. In contrast, deprotonation of 1 and 2 and reaction with (Me(2)N)(2)TiCl(2) afforded C(5)Me(4)(SiMe(2)NR)Ti(NMe(2))(2) (R = CMe(2)Ph 4, 2-C(6)H(4)Ph 5), respectively, in good yields Treatment with MeI gave the analogs C(5)Me(4)(SiMe(2)NR)TiI(2) (R = CMe(2)Ph 6, 2-C(6)H(4)Ph 7). Reduction of 7 with potassium graphite afforded C(5)Me(4)(SiMe(2)NC(6)H(4)Ph)Ti 8. Treatment of 6 and 7 with MeMgBr afforded C(5)Me(4)(SiMe(2)NR)TiMe(2) (R = CMe(2)Ph 9, 2-C(6)H(4)Ph 10). Complexes 9 and 10 in combination with the activator [Ph(3)C][B(C(6)F(5))(4)] catalyzed the polymerization of styrene and ethylene. Copolymerization was also investigated. While the catalyst derived from 10 showed poor activity, compound 9 showed markedly higher activity than 10 and (C(5)Me(4))SiMe(2)(NtBu)]TiMe(2).     

阳离子烷基钪配合物催化体系催化乙烯与丙烯共聚合的研究

双烷基钪配合物LSc(CH2SiMe3)2(L=(2,6-iPr2C6H3)NC(Me)CHPPh2N(2,6-Me2C6H3))在助催化剂[Ph3C][B(C6F5)4]的作用下能够高活性地催化乙烯和丙烯共聚.在反应温度30℃和乙烯与丙烯常压(1.0×105Pa)下聚合,共聚活性能够达到7.5×105g(PE)mol-1h-1(105Pa)-1.单体的竞聚率分别为rE=29.75和rP=0.015.13C-NMR和DSC分析表明所得到的乙丙共聚物是弹性体,且丙烯单体无规分布在共聚物链中.     

[O(S),O=P]型配体修饰的单氯单茂锆催化剂的高温乙烯聚合

以Ph3CB(C6F5)4/iBu3Al作为助催化体系,研究了单氯半茂型催化剂,ClCp′Zr[X-2-R1-4-R2-6-(Ph2P=O)C6H2]2(Cp′=C5H5,a:X=O,R1=Ph,R2=H;b:X=O,R1=F,R2=H;c:X=O,R1=tBu,R2=H;d:X=O,R1=R2=tBu;e:X=O,R1=SiMe3,R2=H;f:X=S,R1=SiMe3,R2=H;Cp′=C5Me5;g:X=O,R1=SiMe3,R2=H)的乙烯高温（50~125 ℃）聚合行为。 结果表明,催化剂a~d可在高温(50~100 ℃)下高效引发乙烯聚合,最佳反应温度为75 ℃。 适当增大R1取代基的位阻或引入吸电子取代基均有利于提高催化活性。 三甲基硅烷基取代的催化剂[WTHZ]e[WTBZ]耐高温性能较催化剂a~d大大提升,在100 ℃时,乙烯聚合活性可达5628 kg/(mol Zr·h)。 金属中心的配位原子及茂环上取代基团的改变对催化活性和聚合物的相对分子质量分布有一定的影响。     

Rare-earth-metal-hydrocarbyl complexes bearing linked cyclopentadienyl or fluorenyl ligands: synthesis, catalyzed styrene polymerization, and structure-reactivity relationship

A series of rare-earth-metal-hydrocarbyl complexes bearing N-type functionalized cyclopentadienyl (Cp) and fluorenyl (Flu) ligands were facilely synthesized. Treatment of [Y(CH(2)SiMe(3))(3)(thf)(2)] with equimolar amount of the electron-donating aminophenyl-Cp ligand C(5)Me(4)H-C(6)H(4)-o-NMe(2) afforded the corresponding binuclear monoalkyl complex [({C(5)Me(4)-C(6)H(4)-o-NMe(μ-CH(2))}Y{CH(2)SiMe(3)})(2)] (1a) via alkyl abstraction and C-H activation of the NMe(2) group. The lutetium bis(allyl) complex [(C(5)Me(4)-C(6)H(4)-o-NMe(2))Lu(η(3)-C(3)H(5))(2)] (2b), which contained an electron-donating aminophenyl-Cp ligand, was isolated from the sequential metathesis reactions of LuCl(3) with (C(5)Me(4)-C(6)H(4)-o-NMe(2))Li (1 equiv) and C(3)H(5)MgCl (2 equiv). Following a similar procedure, the yttrium- and scandium-bis(allyl) complexes, [(C(5)Me(4)-C(5)H(4)N)Ln(η(3)-C(3)H(5))(2)] (Ln=Y (3a), Sc (3b)), which also contained electron-withdrawing pyridyl-Cp ligands, were also obtained selectively. Deprotonation of the bulky pyridyl-Flu ligand (C(13)H(9)-C(5)H(4)N) by [Ln(CH(2)SiMe(3))(3)(thf)(2)] generated the rare-earth-metal-dialkyl complexes, [(η(3)-C(13)H(8)-C(5)H(4)N)Ln(CH(2)SiMe(3))(2)(thf)] (Ln=Y (4a), Sc (4b), Lu (4c)), in which an unusual asymmetric η(3)-allyl bonding mode of Flu moiety was observed. Switching to the bidentate yttrium-trisalkyl complex [Y(CH(2)C(6)H(4)-o-NMe(2))(3)], the same reaction conditions afforded the corresponding yttrium bis(aminobenzyl) complex [(η(3)-C(13)H(8)-C(5)H(4)N)Y(CH(2)C(6)H(4)-o-NMe(2))(2)] (5). Complexes 1-5 were fully characterized by (1)H and (13)C NMR and X-ray spectroscopy, and by elemental analysis. In the presence of both [Ph(3)C][B(C(6)F(5))(4)] and AliBu(3), the electron-donating aminophenyl-Cp-based complexes 1 and 2 did not show any activity towards styrene polymerization. In striking contrast, upon activation with [Ph(3)C][B(C(6)F(5))(4)] only, the electron-withdrawing pyridyl-Cp-based complexes 3, in particular scandium complex 3b, exhibited outstanding activitiy to give perfectly syndiotactic (rrrr >99%) polystyrene, whereas their bulky pyridyl-Flu analogues (4 and 5) in combination with [Ph(3)C][B(C(6)F(5))(4)] and AliBu(3) displayed much-lower activity to afford syndiotactic-enriched polystyrene.     

Synthesis and characterization of heterobimetallic oxo-bridged aluminum-rare earth metal complexes

Reaction of the aluminum hydroxide LAl(OH)[C(Ph)CH(Ph)] (1, L = HC[(CMe)(NAr)](2), Ar = 2,6-iPr(2)C(6)H(3)) with Y(CH(2)SiMe(3))(3)(THF)(2) yielded the oxo-bridged heterobimetallic yttrium dialkyl complex LAl[C(Ph)CH(Ph)](μ-O)Y(CH(2)SiMe(3))(2)(THF)(2) (2). Alkane elimination reaction of 2 with 2-(imino)pyrrole [NN]H ([NN]H = 2-(ArN═CH)-5-tBuC(4)H(2)NH) afforded the yttrium monoalkyl complex LAl[C(Ph)CH(Ph)] (μ-O)Y(CH(2)SiMe(3))[NN](THF)(2) (5). Alternatively, 5 can be prepared in high yield by reaction of 1 with [NN]Y(CH(2)SiMe(3))(2)(THF)(2) (3). The analogous samarium alkyl complex LAl[C(Ph)CH(Ph)](μ-O)Sm(CH(2)SiMe(3))[NN](THF)(2) (6) was prepared similarly. Reactions of 5 and 6 with 1 equiv of iPrOH yielded the corresponding alkoxyl complexes 7 and 8, respectively. The molecular structures of 3, 6, and 8 have been determined by X-ray single-crystal analysis. Complexes 2, 3, 5, 7, and 8 have been investigated as lactide polymerization initiators. The heterobimetallic alkoxyl 8 is highly active to yield high molecular weight (M(n) = 6.91 × 10(4)) polylactides with over 91% conversion at the lactide-to-initiator molar ratio of 2000.     

Scandium alkyl complex with phosphinimino-amine ligand: synthesis, structure and catalysis on ethylene polymerization

The THF-free scandium dialkyl complex LSc(CH(2)SiMe(3))(2) (L = (2,6-iPr(2)C(6)H(3))NC(Me)CHPPh(2)N(2,6-Me(2)C(6)H(3))) bearing the phosphinimino-amine ligand was prepared, which under the activation of [Ph(3)C][B(C(6)F(5))(4)] initiated the polymerization of ethylene with high activity.     

Syntheses and structures of structurally diverse potassium beta-diketiminates derived from the ligand [(N(SiMe3)C(Ph))2CH

The compounds [K((mu-N(SiMe3)C(Ph))2CH)(thf)2]infinity 1, [K(mu-N(SiMe3)C(Ph)C(H)C(Ph)NH)L]2 [L = (thf)2 2, tmen 3], [K(mu-NSi(Me)2C(Ph)C(H)C(Ph)N)(thf)3]2 4 and [K(N(H)C(Ph))2CH](thf)0.5 5 have been prepared from K[(N(SiMe3)C(Ph))2CH] and the X-ray structures of 1-4 are reported.     

Rare-earth metal bis(alkyl)s that bear a 2-pyridinemethanamine ligand: dual catalysis of the polymerizations of both isoprene and ethylene

New pyridinemethanamido-ligated rare-earth metal bis(alkyl) complexes [C(5)H(4)N-CH(Me)-NC(6)H(3)((i)Pr)(2)]Ln(CH(2)SiMe(3))(2)(THF) (Ln = Sc (1), Y (2), Lu (3)) have been prepared at 0 °C via a protonolysis reaction between rare-earth metal tris(alkyl)s and the corresponding 2-pyridinemethanamine ligand and fully characterized by NMR and X-ray diffraction analysis. Bis(alkyl) complexes 1-3 are analogous monomers of THF solvate, where the ligand bonds to the metal center in a κN:κN-bidentate mode. Complexes 1-3, in combination with [Ph(3)C][B(C(6)F(5))(4)], showed a good activity towards isoprene polymerization to give polyisoprene with a main 3,4-selectivity (60%-66%); in particular the yttrium catalyst system, 2/[Ph(3)C][B(C(6)F(5))(4)], displayed a living mode. By contrast, only the precatalyst 2 exhibited activity for isoprene polymerization in the presence of [PhNMe(2)H][B(C(6)F(5))(4)]. The influence of alkylaluminium (AlR(3), R = Me, Et, (i)Bu) and the metal center on the polymerization of isoprene was also studied, and it was found that addition of AlMe(3) to the catalyst systems could lead to a dramatic change in the microstructure of the polymer from 3,4-specific to 1,4-selective (89%-95%), but the ionic radius of the central metal had little influence on the selectivity. In addition, by using the 1(Sc)/[Ph(3)C][B(C(6)F(5))(4)]/10 Al(i)Bu(3), the polymerization of ethylene was also achieved with moderate activity (up to 3.2× 10(5) g (PE) mol(Sc)(-1) h(-1) bar(-1)) and narrow polydispersity (M(w)/M(n) = 1.19-1.28); while the effect of temperature on the activity was discussed. Such dual catalysis for the polymerizations of both isoprene and ethylene is rare.     

Synthetic and structural experiments on yttrium, cerium and magnesium trimethylsilylmethyls and their reaction products with nitriles; with a note on two cerium beta-diketiminates

The yttrium, cerium and magnesium bis(trimethylsilyl)methyls [Ln[CH(SiMe3)2]3][Ln = Y (1), Ce (2)], and the known compound Mg[[CH(SiMe3)2]2 (C) and [Mg(mu-Br)[CH(SiMe3)2](OEt2)]2 (D) formed the crystalline nitrile adducts [1(NCBut)2] (5), [2(NCPh)] (6), [C(NCR)2][R = But (8), Ph (9), C6H3Me2-2,6 (10)] and [Mg(mu-Br)[CH(SiMe3)2](NCR)]2 [R = But (11), Ph (12), C6H3Me2-2,6 (13)], rather than beta-diketiminato-metal insertion products. The beta-diketiminato-cerium complex [Ce[(N(SiMe3)C(C6H4But-4))2CH][N(SiMe3)2]2] (16) was obtained from [Ce[N(SiMe3)2]3] and the beta-diketimine H[[N(SiMe3)C(C6H4But-4)]2CH]]. The cerium alkyl 2 and [Ln[CH(SiMe3)(SiMe2OMe)]3][Ln = Y (3), Ce (4)] were obtained from the appropriate lithium alkyl precursor and [Ce(OC6H2But2-2,6-Me-4)3] or LnCl3, respectively. Heating complex 3 with benzonitrile in toluene afforded 2,2-dimethyl-4,6-diphenyl-5-trimethylsilyl-1,3-diaza-2-silahexa-1,3-diene (7), a member of a new class of heterocycles. The X-ray structures of the crystalline compounds, D, [Mg[CH(SiMe3)2]2(OEt2)2], the known [Ce(Cl)[(N(SiMe3)C(Ph))2CH]2] (E) and 16 are reported. The cerium alkyl (like 1) has one close Ce...C contact for each ligand, attributed to a gamma-C-Ce agostic interaction. The Ln alkyls and have a trigonal prismatic arrangement of the chelating ligands (each of the same chirality at Calpha) around the metal. In an arene solution at 313 K exists as two isomers, as evident from detailed NMR spectroscopic experiments.     

Synthesis, characterization and ethylene reactivity of 2-diphenylphosphanylbenzamido nickel complexes

Addition of primary amines to N-[2-(diphenylphosphanyl)benzoyloxy]succinimide affords 2-diphenylphosphanylbenzamides, Ph2PC6H4C(O)NHR (R = C(CH3)3, 3; R = H, 4; R = CH2CH2CH3, 5; R = CH(CH3)2, 6). Addition of NiCl(eta3-CH2C6H5)(PMe3) to the deprotonated potassium salts of the amides and subsequent treatment of two equivalents of B(C6F5)3 to the resulting products furnishes eta3-benzyl zwitterionic nickel(II) complexes, [Ph2PC6H4C(O)NR-kappa2N,P]Ni(eta3-CH2C6H5) (R = C6H5, 9; R = C(CH3)3, 10; R = H, 11; R = CH2CH2CH3, 12; R = CH(CH3)2, 13). Solid structures of 9, 11, 13 and the intermediate eta1-benzyl nickel(II) complexes, [Ph2PC6H4C(O)NR-kappa2N,P]Ni(eta1-CH2C6H5)(PMe3) (R = C6H5, 7; R = C(CH3)3, 8) were determined by X-ray crystallography. When ethylene is added to the eta3-benzyl zwitterionic nickel(II) complexes, butene is obtained by the complexes 9-12 but complex 13 provides very high molecular-weight branched polyethylene (Mw, approximately 1300000) with excellent activity (up to 5200 kg mol-1 h-1 at 100 psi gauge).     

Alkyl-eta2-alkene niobocene and tantalocene complexes with the allyldimethylsilyl-eta5-cyclopentadienyl ligand: synthesis, NMR studies and DFT calculations

Group 5 metal complexes [M(eta5-C5H5)[eta5-C5H4SiMe2(CH2-eta]2-CH=CH2)]X] (M = Nb, X = Me, CH2Ph, CH2SiMe3; M = Ta, X = Me, CH2Ph) and [Ta(eta5-C5Me5)[eta5-C5H4SiMe2(CH2-eta2-CH=CH2)]X] (X = Cl, Me, CH2Ph, CH2SiMe3) containing a chelating alkene ligand tethered to a cyclopentadienyl ring have been synthesized in high yields by reduction with Na/Hg (X = Cl) and alkylation with reductive elimination (X = alkyl) of the corresponding metal(iv) dichlorides [M(eta5-Cp)[eta5-C5H4SiMe2(CH2CH=CH2)]Cl2] (Cp = C5H5, M = Nb, Ta, Cp = C5Me5, M = Ta). These chloro- and alkyl-alkene coordinated complexes react with CO and isocyanides [CNtBu, CN(2,6-Me2C6H3)] to give the ligand-substituted metal(III) compounds [M(eta5-Cp)[eta5-C5H4SiMe2(CH2CH=CH2)]XL] (X = Cl, Me, CH2Ph, CH2SiMe3). Reaction of the chloro-alkene tantalum complex with LiNHtBu results in formation of the imido hydride derivative [Ta(eta5-C5Me5)[eta5-C5H4SiMe2(CH2CH=CH2)]H(NtBu)]. NMR studies for all of the new compounds and DFT calculations for the alkene-coordinated metal complexes are compared with those known for related group 4 metal cations.     

Effect of ligand substituents in olefin polymerisation by half-sandwich titanium complexes containing monoanionic iminoimidazolidide ligands-MAO catalyst systems

Various half-sandwich titanium complexes containing iminoimidazolidide ligands, CpTiCl(2)[1,3-R(2)(CH(2)N)(2)C=N] (1a-d) [R = Ph (a), 2,6-Me(2)C(6)H(3) (b), cyclohexyl (c), (t)Bu (d)], have been employed as the catalyst precursors for ethylene polymerisation, syndiospecific styrene polymerisation, and copolymerisation of ethylene with 1-hexene in the presence of MAO cocatalyst; 1d showed the highest catalytic activity for ethylene polymerisation whereas 1b showed the highest activity for syndiospecific styrene polymerisation.     

Catalytic Effect of Cobalt and Iron Complexes Incorporating Bis(2-aldiminoethyl)amine Ligands on Ethylene Oligomerization

IntroductionThe finding of a new promising family ofFe( ) - and Co( ) - based bis( imino) pyridyl cata-lysts for ethylene polymerization and oligomeriza-tion,discovered by Brookhart,Gibson andcoworkers[1— 3 ] ,has intrigued us into researchingthe preparation,the structure and the chemistry ofiron and cobalt complexes incorporating N,N ,N -tridentate ligands.The spectacular enhancement ofthe reactivity of iron and cobalt complexes towardsZiegler- Natta olefin polymerization has been re-po…     

Half-sandwich o-N,N-dimethylaminobenzyl complexes over the full size range of group 3 and lanthanide metals. synthesis, structural characterization, and catalysis of phosphine P--H bond addition to carbodiimides

The acid-base reactions between the rare-earth metal (Ln) tris(ortho-N,N-dimethylaminobenzyl) complexes [Ln(CH2C(H4NMe2-o)3] with one equivalent of the silylene-linked cyclopentadiene-amine ligand (C5Me4H)SiMe2NH(C6H2Me3-2,4,6) afforded the corresponding half-sandwich aminobenzyl complexes [{Me2Si(C5Me4)(NC6H2Me3-2,4,6)}Ln(CH2C6H4NMe2-o)(thf)] (2-Ln) (Ln=Y, La, Pr, Nd, Sm, Gd, Lu) in 60-87 % isolated yields. The one-pot reaction between ScCl(3) and [Me2Si(C5Me4)(NC6H2Me3-2,4,6)]Li2 followed by reaction with LiCH2C6H4NMe2-o in THF gave the scandium analogue [{Me2Si(C5Me4)(NC6H2Me3-2,4,6)}Sc(CH2C6H4NMe2-o)] (2-Sc) in 67 % isolated yield. 2-Sc could not be prepared by the acid-base reaction between [Sc(CH2C6H4NMe2-o)3] and (C5Me4H)SiMe2NH(C6H2Me3-2,4,6). These half-sandwich rare-earth metal aminobenzyl complexes can serve as efficient catalyst precursors for the catalytic addition of various phosphine P--H bonds to carbodiimides to form a series of phosphaguanidine derivatives with excellent tolerability to aromatic carbon-halogen bonds. A significant increase in the catalytic activity was observed, as a result of an increase in the metal size with a general trend of La>Pr, Nd>Sm>Gd>Lu>Sc. The reaction of 2-La with 1 equiv of Ph2PH yielded the corresponding phosphide complex [{Me2Si(C5Me4)(NC6H2Me3-2,4,6)}La(PPh2)(thf)2] (4), which, on recrystallization from benzene, gave the dimeric analogue [{Me2Si(C5Me4)(NC6H2Me3-2,4,6)}La(PPh2)]2 (5). Addition of 4 or 5 to iPrN=C=NiPr in THF yielded the phosphaguanidinate complex [{Me2Si(C5Me4)(NC6H2Me3-2,4,6)}La{iPrNC(PPh2)NiPr}(thf)] (6), which, on recrystallization from ether, afforded the ether-coordinated structurally characterizable analogue [{Me2Si(C5Me4)(NC6H2Me3-2,4,6)}La{iPrNC(PPh2)NiPr}(OEt2)] (7). The reaction of 6 or 7 with Ph2PH in THF yielded 4 and the phosphaguanidine iPrN=C(PPh2)NHiPr (3a). These results suggest that the catalytic formation of a phosphaguanidine compound proceeds through the nucleophilic addition of a phosphide species, which is formed by the acid-base reaction between a rare-earth metal o-dimethylaminobenzyl bond and a phosphine P--H bond, to a carbodiimide, followed by the protonolysis of the resultant phosphaguanidinate species by a phosphine P--H bond. Almost all of the rare earth complexes reported this paper were structurally characterized by X-ray diffraction studies.     

Enantiomerically pure phosphaalkene-oxazolines (PhAk-Ox): synthesis, scope and copolymerization with styrene

The design of a synthetic route to a class of enantiomerically pure phosphaalkene-oxazolines (PhAk-Ox) is presented. The condensation of a lithium silylphosphide and a ketone (the phospha-Peterson reaction) was used as the P=C bond-forming step. Attempted condensation of PhC(=O)Ox (Ox = CNOCH(iPr)CH(2)) and MesP(SiMe(3))Li gave the unusual heterocycle (MesP)(2)C(Ph)=CN-(S)-CH(iPr)CH(2)O (3). However, PhAk-Ox (S,E)-MesP=C(Ph)CMe(2)Ox (1?a) was successfully prepared by treating MesP(SiMe(3))Li with PhC(=O)CMe(2)Ox (52?%). To demonstrate the modularity and tunability of the phospha-Peterson synthesis several other phosphaalkene-oxazolines were prepared in an analogous manner to 1?a: TripP=C(Ph)CMe(2)Ox (1?b; Trip = 2,4,6-triisopropylphenyl), 2-iPrC(6)H(4)P=C(Ph)CMe(2)Ox (1?c), 2-tBuC(6)H(4)P=C(Ph)CMe(2)Ox (1?d), MesP=C(4-MeOC(6)H(4))CMe(2)Ox (1?e), MesP=C(Ph)C(CH(2))(4)Ox (1?f), and MesP=C(3,5-(CF(3))(2)C(6)H(3))C(CH(2))(4)Ox (1?g). To evaluate the PhAk-Ox compounds as prospective precursors to chiral phosphine polymers, monomer 1?a and styrene were subjected to radical-initiated copolymerization conditions to afford [{MesPC(Ph)(CMe(2)Ox)}(x){CH(2)CHPh}(y)](n) (9?a: x = 0.13n, y = 0.87n; GPC: M(w) = 7400?g mol(-1) , PDI = 1.15).     

Synthesis and structures of some new types of lithium beta-diketiminates

The tetracyclic dilithio-Si,Si'-oxo-bridged bis(N,N'-methylsilyl-beta-diketiminates) 2 and 3, having an outer LiNCCCNLiNCCCN macrocycle, were prepared from [Li{CH(SiMe(3))SiMe(OMe)(2)}](infinity) and 2 PhCN. They differ in that the substituent at the beta-C atom of each diketiminato ligand is either SiMe(3) (2) or H (3). Each of and has (i) a central Si-O-Si unit, (ii) an Si(Me) fragment N,N'-intramolecularly bridging each beta-diketiminate, and (iii) an Li(thf)(2) moiety N,N'-intermolecularly bridging the two beta-diketiminates (thf = tetrahydrofuran). Treatment of [Li{CH(SiMe(3))(SiMe(2)OMe)}](8) with 2Me(2)C(CN)(2) yielded the amorphous [Li{Si(Me)(2)((NCR)(2)CH)}](n) [R = C(Me)(2)CN] (4). From [Li{N(SiMe(3))C(Bu(t))C(H)SiMe(3)}](2) (A) and 1,3- or 1,4-C(6)H(4)(CN)(2), with no apparent synergy between the two CN groups, the product was the appropriate (mu-C(6)H(4))-bis(lithium beta-diketiminate) 6 or 7. Reaction of [Li{N(SiMe(3))C(Ph)=C(H)SiMe(3)}(tmeda)] and 1,3-C(6)H(4)(CN)(2) afforded 1,3-C(6)H(4)(X)X' (X =CC(Ph)N(SiMe3)Li(tmeda)N(SiMe3)CH; X' = CN(SiMe3)Li(tmeda)NC(Ph)=C(H)SiMe3)(9). Interaction of A and 2[1,2-C(6)H(4)(CN)(2)] gave the bis(lithio-isoindoline) derivative [C6H4C(=NH)N{Li(OEt2)}C=C(SiMe3)C(Bu(t))=N(SiMe3)]2 (5). The X-ray structures of 2, 3, 5 and 9 are presented, and reaction pathways for each reaction are suggested.     

Trialkyl imido niobium and tantalum compounds: synthesis, structural study and migratory insertion reactions

Trialkyl imido niobium and tantalum complexes [MR(3)(NtBu)] (M = Nb, R = Me 2, CH(2)CMe(3)3, CH(2)CMe(2)Ph 4, CH(2)SiMe(3)5; M = Ta, R = Me 6, CH(2)CMe(2)Ph 7, CH(2)SiMe(3)8) have been prepared by treatment of solutions containing [MCl(3)(NtBu)py(2)] (M = Nb 1a, Ta 1b) with three equivalents of magnesium reagent. By an unexpected hydrolysis reaction of the tris-trimethylsilylmethyl imido tantalum compound 8a, a μ-oxo derivative [(Me(3)SiCH(2)O)(Me(3)SiCH(2))(3)Ta(μ-O)Ta(CH(2)SiMe(3))(2)(NtBu)] (8a) was formed and its structure was studied by X-ray diffraction methods. Reactions of trialkyl imido compounds with two equivalents of isocyanide 2,6-Me(2)C(6)H(3)NC result in the migration of two alkyl groups, leading to the formation of a series of alkyl imido bisiminoacyl derivatives [MR(NtBu){C(R)NAr}(2)] (Ar = 2,6-Me(2)C(6)H(3); M = Nb, R = Me 9, CH(2)CMe(3)10, CH(2)CMe(2)Ph 11, CH(2)SiMe(3)12, CH(2)Ph 13; M = Ta, R = CH(2)CMe(3)14, CH(2)CMe(2)Ph 15, CH(2)SiMe(3)16). All compounds were studied by IR and NMR ((1)H, (13)C and (15)N) spectroscopy.