Crystallographic characterisation of Ti(IV) piperazine complexes and their exploitation for the ring opening polymerisation of rac-lactide

In this paper a series of eight Ti(IV) piperazine based complexes have been prepared and fully characterised in the solid-state by X-ray crystallography and in solution via NMR spectroscopy. In the solid-state either Ti(2)(L)(O(i)Pr)(6) or Ti(2)(L)(2)(O(i)Pr)(4) were observed depending upon the nature of the starting ligand. For complexes with less sterically demanding ligands (1H(2) and 2H(2)) an equilibrium was observed: 2 Ti(2)(L)(O(i)Pr)(6) ? Ti(2)(L)(2)(O(i)Pr)(4) + 2 Ti(O(i)Pr)(4). The thermodynamic properties (ΔG, ΔH and ΔS) have been investigated via variable temperature NMR spectroscopy. With more sterically demanding ligands (3-8H(2)) the Ti(2)(L)(O(i)Pr)(6) form was the most prevalent in the solid-state and in solution. These complexes have been tested for the production of polylactide under melt and solution conditions with high conversions being obtained.     

Tert-butylamidinate tin(ii) complexes: high activity, single-site initiators for the controlled production of polylactide

The tin(ii) coordination chemistry of two monoanionic N,N'-bis(2,6-diisopropylphenyl)alkylamidinate ligands is described. Complexation studies with the acetamidinate, [MeC(NAr)(2)](-), (Ar = 2,6-(i)Pr(2)C(6)H(3)) are complicated by the side formation of the bis(amidinate) tin(ii) compound, [MeC(NAr)(2)](2)Sn. By contrast, the bulkier tert-butylamidinate, [(t)BuC(NAr)(2)](-), allows tin(ii) mono-halide, -alkoxide and -amide complexes to be isolated cleanly in high yields. Thus, the reaction of [(t)BuC(NAr)(2)]H with (n)BuLi and subsequent treatment with SnCl(2) generates [(t)BuC(NAr)(2)]SnCl, in ca. 70% yield. Reactions of with LiO(i)Pr, LiNMe(2) and LiNTMS(2) afford [(t)BuC(NAr)(2)]Sn(O(i)Pr), [(t)BuC(NAr)(2)]Sn(NMe(2)), and [(t)BuC(NAr)(2)]Sn(NTMS(2)), respectively. The molecular structures of complexes are reported. Complexes, and have been investigated as initiators for the ring-opening polymerisation of rac-lactide: and display characteristics of well-controlled polymerisation initiators, but high molecular weight polymer is observed with due to inefficient initiation, a consequence of the steric bulk of the NTMS(2) unit. Polymerisations with and are faster than for the corresponding beta-diketiminate tin(ii) complexes, consistent with the more open nature of the tin(ii) coordination sphere.     

Interplay between lead carboxylate and Ti or Zr isopropoxides in solution routes to perovskites: synthesis, molecular structures and reactivity of single source non-oxo Pb-Zr and Pb-Ti carboxylatoalkoxides supported by 2-ethylhexanoate ligands

The reactions between Ti(O(i)Pr)(4) and Zr(2)(O(i)Pr)(8)(HO(i)Pr)(2), respectively, and lead 2-ethylhexanoate Pb(O(2)CC(7)H(15))(2) have been investigated at rt and by heating. The initial mixed-metal species, characterized by single-crystal X-Ray diffraction, were adducts namely Pb(4)Zr(4)(mu-O(2)CR')(8)(mu-OR)(6)(mu(3)-OR)(2)(OR)(8)(OHR)(2) and Pb(2)Ti(4)(mu-O(2)CR')(4)(mu-OR)(6)(mu(3)-OR)(2)(OR)(8) (R' = CHCH(Et)C(2)H(4)Me, R = (i)Pr) independently of the stoichiometry used. They are the first Pb-Ti and Pb-Zr non-oxo carboxylatoalkoxides reported. is also the first Pb-Zr species based on an alkoxide-carboxylate ligand set matching the PbZrO(3) stoichiometry. Both structures are centrosymmetric with six-coordinate transition metals, as required for the perovskite, and are based on triangular M(2)Pb cores (M = Zr, Ti). The lead centers display quite high coordination numbers, six and seven. The thermal and hydrolytic condensation reactions of and were investigated. Heat treatment of and elimination of the volatiles under vacuum afforded Pb(2)Ti(3)(mu(4)-O)(mu(3)-O)(mu-O(2)CC(7)H(15))(2)(mu-O(i)Pr)(6)(O(i)Pr)(4) resulting from extrusion of Ti(O(i)Pr)(4) and scrambling of carboxylate ligands. Characterization of the various compounds was achieved by elemental analysis, FT-IR, (1)H and (207)Pb NMR.     

New titanium complexes with symmetric or asymmetric cis-9,10-dihydrophenanthrenediamide ligands formed through sequential intramolecular C-C bond-forming reactions

A series of new titanium(IV) complexes with symmetric or asymmetric cis-9,10-dihydrophenanthrenediamide ligands, cis-9,10-PhenH(2)(NR)(2)Ti(O(i)Pr)(2) [PhenH(2) = 9,10-dihydrophenanthrene, R = 2,6-(i)Pr(2)C(6)H(3) (2a), 2,6-Et(2)C(6)H(3) (2b), 2,6-Me(2)C(6)H(3) (2c)], cis-9,10-PhenH(2)(NR(1))(NR(2))Ti(O(i)Pr)(2) [R(1) = 2,6-(i)Pr(2)C(6)H(3), R(2) = 2,6-Et(2)C(6)H(3) (2d); R(1) = 2,6-(i)Pr(2)C(6)H(3), R(2) = 2,6-Me(2)C(6)H(3) (2e)], and [cis-9,10-PhenH(2)(NR(1))(2)][o-C(6)H(4)(CH=NR(2))]TiO(i)Pr [R(1) = 2,6-(i)Pr(2)C(6)H(3), R(2) = 2,6-Et(2)C(6)H(3) (3a); R(1) = 2,6-(i)Pr(2)C(6)H(3), 2,6-Me(2)C(6)H(3) (3b)], have been synthesized from the reactions of TiCl(2)(O(i)Pr)(2) with o-C(6)H(4)(CH=NR)Li [R = 2,6-(i)Pr(2)C(6)H(3), 2,6-Et(2)C(6)H(3), 2,6-Me(2)C(6)H(3)]. The symmetric complexes 2a-2c were obtained from the reactions of TiCl(2)(O(i)Pr)(2) with 2 equiv of the corresponding o-C(6)H(4)(CH=NR)Li followed by intramolecular C-C bond-forming reductive elimination and oxidative coupling processes, while the asymmetric complexes 2d-2e were formed from the reaction of TiCl(2)(O(i)Pr)(2) with two different types of o-C(6)H(4)(CH=NR)Li sequentially. The complexes 3a and 3b were also isolated from the reactions for complexes 2d and 2e. All complexes were characterized by (1)H and (13)C NMR spectroscopy, and the molecular structures of 2a, 2b, 2e, and 3a were determined by X-ray crystallography.     

Titanium and niobium imido complexes stabilized by heteroscorpionate ligands

The reaction of [Ti(NR)Cl(2)(py)(3)](R = (t)Bu, p-tolyl, 2,6-C(6)H(3)(i)Pr(2)) with [{Li(bdmpza)(H(2)O)}(4)][bdmpza = bis(3,5-dimethylpyrazol-1-yl)acetate] and [{Li(bdmpzdta)(H(2)O)}(4)][bdmpzdta = bis(3,5-dimethylpyrazol-1-yl)dithioacetate] affords the corresponding complexes [Ti(NR)Cl(kappa(3)-bdmpzx)(py)](x = a, R = (t)Bu 1, p-tolyl 2, 2,6-C(6)H(3)(i)Pr(2) 3; x = dta, R =(t)Bu 4, p-tolyl , 2,6-C(6)H(3)(i)Pr(2) 6), which are the first examples of imido Group 4 complexes stabilized by heteroscorpionate ligands. The solid-state X-ray crystal structure of 1 has been determined. The titanium centre is six-coordinate with three fac-sites occupied by the heteroscorpionate ligand and the remainder of the coordination sphere being completed by chloride, imido and pyridine ligands. The complexes are 1-6 fluxional at room temperature. The pyridine ortho- and meta-proton resonances show evidence of dynamic behaviour for this ligand and variable-temperature NMR studies were carried out in order to study their dynamic behaviour in solution. The complexes [Nb(NR)Cl(3)(py)(2)](R = (t)Bu, p-tolyl, 2,6-C(6)H(3)(i)Pr(2)) reacted with [{Li(bdmpza)(H(2)O)}(4)] and (Hbdmpze)[bdmpze = 2,2-bis(3,5-dimethylpyrazol-1-yl)ethoxide], the latter with prior addition of (n)BuLi, to give the complexes [Nb(NR)Cl(2)(kappa(3)-bdmpzx)](x = a, R =(t)Bu 7, p-tolyl 8, 2,6-C(6)H(3)(i)Pr(2) 9; x = e, R = (t)Bu 10, p-tolyl 11, 2,6-C(6)H(3)(i)Pr(2)) 12 and these are the first examples of imido Group 5 complexes with heteroscorpionate ligands. The structures of these complexes have been determined by spectroscopic methods.     

Hybrid catalysts: the synthesis, structure and ethene polymerisation activity of (salicylaldiminato)(pyrrolylaldiminato) titanium complexes

The mono(salicylaldiminato) complexes Ti{3-tBu-2-(O)C6H3CH=N(R)}Cl3(THF)(where R = C6H5, C6F5) react with the metallated pyrrolylaldiminato ligand, K[2-(C6H5NCH)C4H3N], to afford the first examples of hybrid salicylaldiminato-ligated octahedral titanium complexes; the pre-catalysts give from very high to extremely high ethene polymerisation productivities when activated with MAO.     

Chiral fluorous dialkoxy-diamino zirconium complexes: synthesis and use in stereospecific polymerization of 1-hexene

New catalysts for the isospecific polymerization of 1-hexene based on cationic zirconium complexes incorporating the tetradentate fluorous dialkoxy-diamino ligands [OC(CF(3))(2)CH(2)N(Me)(CH(2))(2)N(Me)CH(2)C(CF(3))(2)O](2-) [(ON(2)NO)(2-)] and [OC(CF(3))(2)CH(2)N(Me)(1R,2R-C(6)H(10))N(Me)CH(2)C(CF(3))(2)O](2-) [(ON(Cy)NO)(2-)] have been developed. The chiral fluorous diamino-diol [(ON(Cy)NO)H(2), 2] was prepared by ring-opening of the fluorinated oxirane (CF(3))(2)COCH(2) with (R,R)-N,N'-dimethyl-1,2-cyclohexanediamine. Proligand 2 reacts cleanly with [Zr(CH(2)Ph)(4)] and [Ti(OiPr)(4)] precursors to give the corresponding dialkoxy complexes [Zr(CH(2)Ph)(2)(ON(Cy)NO)] (3) and [Ti(OiPr)(2)(ON(Cy)NO)] (4), respectively. An X-ray diffraction study revealed that 3 crystallizes as a 1:1 mixture of two diastereomers (Lambda-3 and Delta-3), both of which adopt a distorted octahedral structure with trans-O, cis-N, and cis-CH(2)Ph ligands. The two diastereomers Lambda-3 and Delta-3 adopt a C(2)-symmetric structure in toluene solution, as established by NMR spectroscopy. Cationic complexes [Zr(CH(2)Ph)(ON(2)NO)(THF)(n)](+) (n=0, anion=[B(C(6)F(5))(4)](-), 5; n=1, anion=[PhCH(2)B(C(6)F(5))(3)](-), 6) and [Zr(CH(2)Ph)(ON(Cy)NO)(THF)](+)[PhCH(2)B(C(6)F(5))(3)](-) (7) were generated from the neutral parent precursors [Zr(CH(2)Ph)(2)(ON(2)NO)] (H) and [Zr(CH(2)Ph)(2)(ON(Cy)NO)] (3), and their possible structures were determined on the basis of (1)H, (19)F, and (13)C NMR spectroscopy and DFT methods. The neutral zirconium complexes H and 3 (Lambda-3/Delta-3 mixture), when activated with B(C(6)F(5))(3) or [Ph(3)C](+)[B(C(6)F(5))(4)](-), catalyze the polymerization of 1-hexene with overall activities of up to 4500 kg PH mol Zr(-1) h(-1), to yield isotactic-enriched (up to 74 % mmmm) polymers with low-to-moderate molecular weights (M(w)=4800-47 200) and monodisperse molecular-weight distributions (M(w)/M(n)=1.17-1.79).     

含有烯丙基亚胺酚配体的ⅣB族烯烃聚合催化剂以及制备双峰分布聚乙烯(英)

选择含有烯丙基亚胺酚为辅助配体，设计合成了5个ⅣB族钛锆金属络合物[{CH₂=CHCH₂N=CH-C₆H₃(3-R)O}₂MCl₂](4a：R=t-Bu，M=Zr；4b：R=t-Bu，M=Ti；4c：R=Ph，M=Zr；4d：R=Ph，M=Ti)和[{(CH₃)₂CHCH₂N=CH-C₆H₃(3-t-Bu)O}₂ZrCl₂] (5)，对它们进行了红外光谱、核磁共振及元素分析表征。并用X-射线单晶衍射法测定了化合物4a和4d的晶体结构。部分配合物在助催化剂MMAO的作用下对烯烃聚合显示了较好的催化活性，其中自固载催化剂4a生成了双峰分布的聚烯烃产品 (M_w/M_n=15.3～31.9)。     

Titanium isopropoxide complexes of a series of sterically demanding aryloxo based [N2O2]2- ligands as precatalysts for ethylene polymerization

Several titanium isopropoxide complexes [N,N'-bis(2-oxo-3-R(1)-5-R(2)-phenylmethyl)-N,N'-bis(methylene-p-R(3)-C(6)H(4))-ethylenediamine]Ti(O(i)Pr)(2) [R(1) = t-Bu, R(2) = Me, R(3) = H (1b); R(1) = R(2) = t-Bu, R(3) = H, (2b); R(1) = R(2) = Cl, R(3) = H, (3b), R(1) = t-Bu, R(2) = Me, R(3) = Cl (4b); R(1) = R(2) = t-Bu, R(3) = Cl, (5b); R(1) = R(2) = R(3) = Cl, (6b)] supported over sterically demanding aryloxy based [N(2)O(2)]H(2) ligands have been designed as precatalysts for the ethylene polymerization. Specifically, the 1b-6b complexes, when treated with methylaluminoxane (MAO) under 88 ± 0.5 psi of ethylene at 30 °C for 3 h, produced polyethylene polymers of high molecular weight (M(w) = ca. 7.2-8.3 × 10(5) g mol(-1)) having broad molecular weight distribution (PDI = ca. 13.1-14.6). The 1b-6b complexes were conveniently synthesized from the direct reaction of the [N(2)O(2)]H(2) ligands, 1a-6a, with Ti(O(i)Pr)(4) in 69-86% yield.     

Latent low-coordinate titanium imides supported by a sterically encumbering beta-diketiminate ligand

Addition of an equal molar quantity of R- (R = Me, SiMe3) to complex (Nacnac)Ti=NAr(OTf) (Nacnac- =[ArNC(tBu)]2CH, Ar = 2,6-iPr2C6H3) forms the imido alkyl (Nacnac)Ti=NAr(R), which can be readily protonated to afford [(Nacnac)Ti=NAr(L)]+ (L = THF, Et2O, eta1-C6H5NMe2), or treated with B(C6F5)3 to afford the zwitterion (Nacnac)Ti=NAr(micro-CH3)B(C6F5)3.     

Heterobimetallic Bi(III)-Ti(IV) coordination complexes: synthesis and solid-state structures of BiTi4(sal)6(mu-OiPr)3(OiPr)4, and the cyclic isomers Bi4Ti4(sal)10(mu-OiPr)4(OiPr)4 and Bi8Ti8(sal)20(mu-OiPr)8(OiPr)8

The reaction of a 1:2 mixture of bismuth(III) salicylate with titanium(IV) isopropoxide in refluxing toluene has been investigated and found to proceed with ligand exchange to produce the new heterobimetallic complexes BiTi(4)(sal)(6)(mu-O(i)Pr)(3)(O(i)Pr)(4) (1), Bi(4)Ti(4)(sal)(10)(mu-O(i)Pr)(4)(O(i)Pr)(4) (2), and Bi(8)Ti(8)(sal)(20)(mu-O(i)Pr)(8)(O(i)Pr)(8) (3). Complex 1 is the major product, while 2 and 3 were identified as minor products from the reaction. Compound 1 is produced pure and in high yield by employing stoichiometric amounts of reagents; its crystal structure consists of a [Ti(4)(sal)(6)(O(i)Pr)(7)](3)(-) ion capped by a Bi(3+) ion. Complexes 2 and 3 exhibit cyclic ring structures of bismuth and titanium atoms showing crystallographically imposed inversion symmetry. Both structures occlude large quantities of lattice solvent. The compositional and structural parameters from the single crystal studies indicate that complexes 2 and 3 may represent sequential steps in a ligand exchange process between the two metal species, while the reactivity patterns that were observed provide clues about the solution state structure of bismuth(III) salicylate itself. The 2D COSY (1)H NMR spectrum of 1 indicates retention of the asymmetric structure in solution as evidenced by the presence of 14 diastereotopic isopropoxide methyl resonances.     

The synthesis, structure and ethene polymerisation catalysis of mono(salicylaldiminato) titanium and zirconium complexes

The silyl ethers 3-But-2-(OSiMe3)C6H3CH=NR (2a-e) have been prepared by deprotonation of the known iminophenols (1a-e) and treatment with SiClMe3 (a, R = C6H5; b, R = 2,6-Pri2C6H3; c, R = 2,4,6-Me3C6H2; d, R = 2-C6H5C6H4; e, R = C6F5). 2a-c react with TiCl4 in hydrocarbon solvents to give the binuclear complexes [Ti{3-But-2-(O)C6H3CH=N(R)}Cl(mu-Cl3)TiCl3] (3a-c). The pentafluorophenyl species 2e reacts with TiCl4 to give the known complex Ti{3-But-2-(O)C6H3CH=N(R)}2Cl2. The mononuclear five-coordinate complex, Ti{3-But-2-(O)C6H3CH=N(2,4,6-Me3C6H2)}Cl3 (4c), was isolated after repeated recrystallisation of 3c. Performing the dehalosilylation reaction in the presence of tetrahydrofuran yields the octahedral, mononuclear complexes Ti{3-But-2-(O)C6H3CH=N(R)}Cl3(THF) (5a-e). The reaction with ZrCl4(THF)2 proceeds similarly to give complexes Zr{3-But-2-(O)C6H3CH=N(R)}Cl3(THF) (6b-e). The crystal structures of 3b, 4c, 5a, 5c, 5e, 6b, 6d, 6e and the salicylaldehyde titanium complex Ti{3-But-2-(O)C6H3CH=O}Cl3(THF) (7) have been determined. Activation of complexes 5a-e and 6b-e with MAO in an ethene saturated toluene solution gives polyethylene with at best high activity depending on the imine substituent.     

Molecular precursors for the preparation of homogenous zirconia-silica materials by hydrolytic sol-gel process in organic media. Crystal structures of [Zr{OSi(O(t)Bu)3}4(H2O)2]·2H2O and [Ti(O(t)Bu){OSi(O(t)Bu)3}3

[Zr(OPr(i))(4)·Pr(i)OH] reacts with [HOSi(O(t)Bu)(3)] in anhydrous benzene in 1:1 and 1:2 molar ratios to afford alkoxy zirconosiloxane precursors of the types [Zr(OPr(i))(3){OSi(O(t)Bu)(3)}] (A) and [Zr(OPr(i))(2){OSi(O(t)Bu)(3)}(2)] (B), respectively. Further reactions of A or B with glycols in 1:1 molar ratio afforded six chemically modified precursors of the types [Zr(OPr(i))(OGO){OSi(O(t)Bu)(3)}] (1A-3A) and [Zr(OGO){OSi(O(t)Bu)(3)}(2)] (1B-3B), respectively [where G = (-CH(2)-)(2) (1A, 1B); (-CH(2)-)(3) (2A, 2B) and (-CH(2)CH(2)CH(CH(3)-)} (3A, 3B)]. The precursors A and B are viscous liquids, which solidify on ageing whereas the other products are all solids, soluble in common organic solvents. These were characterized by elemental analyses, molecular weight measurements, FAB mass, FTIR, (1)H, (13)C and (29)Si-NMR studies. Cryoscopic molecular weight measurements of all the products, as well as the FAB mass studies of 3A and 3B, indicate their monomeric nature. However, FAB mass spectrum of the solidified B suggests that it exists in dimeric form. Single crystal structure analysis of [Zr{OSi(O(t)Bu)(3)}(4)(H(2)O)(2)]·2H(2)O (3b) (R(fac) = 11.9%) as well as that of corresponding better quality crystals of [Ti(O(t)Bu){OSi(O(t)Bu)(3)}(3)] (4) (R(fac) = 5.97%) indicate the presence of a M-O-Si bond. TG analyses of 3A, B, and 3B indicate the formation of zirconia-silica materials of the type ZrO(2)·SiO(2) from 3A and ZrO(2)·2SiO(2) from B or 3B at low decomposition temperatures (≤200 °C). The desired homogenous nano-sized zirconia-silica materials [ZrO(2)·nSiO(2)] have been obtained easily from the precursors A and B as well as from the glycol modified precursors 3A and 3B by hydrolytic sol-gel process in organic media without using any acid or base catalyst, and these were characterized by powder XRD patterns, SEM images, EDX analyses and IR spectroscopy.     

New titanium and zirconium initiators for the production of polylactide

Two new group 4 initiators based on N,N′-Bis(2-hydroxybenzyl)ethylenediamine have been prepared and fully characterised via multi-nuclear NMR spectroscopy and single crystal X-ray diffraction studies. The complexes have been tested for the production of polylactide. The phenolate ligand complexes to Ti(IV) to generate the β-cis isomer in the solid-state. Whereas for Zr(IV) the isolated species (regardless of stoichiometery) is a diligated complex.     

Group 4 complexes of a tert-butylphosphine-bridged biphenolate ligand

The coordination chemistry of group 4 complexes supported by the tridentate, dianionic biphenolate phosphine ligand that carries a phosphorus-bound tert-butyl group, 2,2'-tert-butylphosphino-bis(4,6-di-tert-butylphenolate) ([(t)Bu-OPO](2-)), is described. Metathetical reactions of {[(t)Bu-OPO]Li(2)(DME)}(2) with 2 or 1 equiv of TiCl(4)(THF)(2) selectively produce [(t)Bu-OPO]TiCl(2)(THF) (1a) and Ti[(t)Bu-OPO](2) (2a), respectively. Protonolysis of Ti(O(i)Pr)(4) with 2 or 1 equiv of H(2)[(t)Bu-OPO] cleanly generates 2a and [(t)Bu-OPO]Ti(O(i)Pr)(2) (3a), respectively. Complex 1a can alternatively be prepared from comproportionation of 2a with 1 equiv of TiCl(4)(THF)(2). Treatment of 1a with 2 equiv of NaO(t)Bu affords [(t)Bu-OPO]Ti(O(t)Bu)(2) (4a). In contrast, reactions of {[(t)Bu-OPO]Li(2)(DME)}(2) with ZrCl(4)(THF)(2) or HfCl(4)(THF)(2), regardless of stoichiometry of the starting materials employed, selectively give bis-ligated M[(t)Bu-OPO](2) [M = Zr (2b), Hf (2c)]. Comproportionation of 2b,c with MCl(4)(THF)(2) (M = Zr, Hf) leads to the formation of [(t)Bu-OPO]MCl(2)(THF) [M = Zr (1b), Hf (1c)], which, upon being treated with 2 equiv of NaO(t)Bu, generates [(t)Bu-OPO]M(O(t)Bu)(2)(THF) (4b,c). These synthetic results are markedly different from those obtained from analogous reactions employing a biphenolate phosphine ligand bearing a phosphorus-bound phenyl group ([Ph-OPO](2-)), highlighting a profound phosphorus substituent effect on complex conformation. The alkoxide complexes 3a and 4a-c are all active initiators for catalytic ring-opening polymerization of ε-caprolactone. To assess the potential phosphorus substituent effect on catalysis, [Ph-OPO]Ti(O(i)Pr)(2) (5a) was prepared, and its reactivity was examined. Interestingly, polymers prepared from 3a are characterized by low polydispersities with molecular weights that are linearly dependent on the monomer-to-initiator ratio, thus featuring a living system. The polydispersitiy indexes of polymers prepared from 5a, however, are relatively larger, indicative of the significance of the phosphorus-bound tert-butyl group in 3a in view of discouraging the undesirable transesterification.     

Asymmetric [2 + 1] Cycloaddition Reactions of 1-Seleno-2-silylethene

The reaction of (E)-1-(phenylseleno)-2-(trimethylsilyl)ethene (1) and vinyl ketones 2a-d in the presence of a chiral Lewis acid prepared from TiCl(4), Ti(O(i)Pr)(4), (R)- or (S)-1,1'-binaphthol (BINOL), and MS4A gave enantiomerically enriched cis cyclopropane products 3a-d. The enantiomeric excess and chemical yield varied depending on the ratio of TiCl(4) and Ti(O(i)Pr)(4) to 1. Reproducible results (43-47% ee/33-41% yields) for cis-1-acetyl-2-[(phenylseleno)(trimethylsilyl)methyl]cyclopropane (3a) were obtained using 1.1 equiv of TiCl(4), 0.54-0.65 equiv of Ti(O(i)Pr)(4), and 1.65 equiv of BINOL. The observed enantioselectivity was explained by consideration of the structure of the postulated intermediates, alkoxy titanium-carbonyl complexes, via ab initio MO calculations.     

An arene-stabilized cobalt(I) aryl: reactions with CO and NO

The half-sandwich cobalt(I) complex (eta (6)-C 7H 8)CoAr*-3,5- ( i )Pr 2 (Ar*-3,5- ( i )Pr 2 = -C 6H-2,6-(C 6H 2-2,4,6- ( i )Pr 3) 2-3,5- ( i )Pr 2) was synthesized by reduction of [3,5- ( i )Pr 2Ar*Co(mu-Cl)] 2 in toluene. It reacts with CO or NO to afford the unusual complexes [3,5- ( i )Pr 2Ar*C(O)Co(CO)] or [3,5- ( i )Pr 2Ar*N(NO)OCo(NO) 2].     

Lanthanide chloride complexes of amine-bis(phenolate) ligands and their reactivity in the ring-opening polymerization of epsilon-caprolactone

Reaction of two equivalents of n-BuLi with sterically demanding amine-bis(phenol) compounds, H(2)O(2)NN'(R) (Me(2)NCH(2)CH(2)N{CH(2)-3,5-R(2)-C(6)H(2)OH}(2); R = t-Bu or t-Pe (tert-pentyl)) yields isolable lithium complexes, Li(2)(O(2)NN'(R)), in good yields. Upon reaction with one equivalent of LnCl(3)(THF)(x), the lithium salts afford rare earth amine-phenolate chloride complexes in good yields, Ln(O(2)NN'(R))Cl(THF); Ln = Y, Yb, Ho, Gd, Sm, Pr. Crystals of Y(O(2)NN'(t-Bu))Cl(THF), 1, and Sm(O(2)NN'(t-Bu))Cl(DME), 2, suitable for single crystal X-ray crystallographic analysis were obtained. In contrast to previously reported [{Gd(O(2)NN'(t-Pe))(THF)(micro-Cl)}(2)] and related La and Sm complexes, these species are monomeric. 1 contains Y in a distorted octahedral environment bonded to two amine, two phenolate, one THF and one chloride donor. 2 contains Sm in a distorted capped trigonal prismatic environment bonded to two amine, two phenolate, two DME oxygens and one chloride donor. The Ln(O(2)NN'(t-Pe))Cl(THF) complexes were active initators for the controlled ring-opening polymerization of epsilon-caprolactone with a tendency to form low molecular weight cyclic polyesters (M(n) 3000-5000). The conversion rates, although slower than related amido and alkyl species, were different for monomeric and dimeric initiators. The size of the metal centre also affected the conversions and the molecular weights achieved.     

Synthesis and Characterizations of Ti(O‐i‐Pr)Cl3(THF)(PhCOR) (R = H,Me, Ph) and Ti(O‐i‐Pr)Cl3(PhCOR)2 (R = Me,Ph). The Molecular Structure of Ti(O‐i‐Pr)Cl3(PhCOPh)2

A series of titanium(IV) complexes Ti(O‐i‐Pr)Cl₃(THF)(PhCOR) (R = H ( 1 ), CH₃ ( 2 ), or Ph ( 3 )) is prepared quantitatively from reactions of [Ti(O‐i‐Pr)Cl₂(THF)(μ‐Cl)]₂ with 2 molar equiv. PhCOR. Treatment of Ti(O‐i‐Pr)Cl₃ with 2 molar equiv. of PhCOR affords the disubstituted complexes Ti(O‐i‐Pr)Cl₃(PhCOR)₂ (R = CH₃ ( 4 ) or Ph ( 5 )). The ¹³C NMR study of these complexes shows that the relative bonding abilities are in the order of PhCOCH₃ > PhCHO > PhCOPh. The molecular structure of 5 reveals that one of the benzophenone ligands is trans to the strongest 2‐propoxide ligand with a long Ti‐O(carbonyl) distance of 2.193(5) Å which is much longer than the other Ti‐O(carbonyl) distance of 2.097(4) Å by ?0.1 Å. All ligands cis to the alkoxide ligand are bending away from the alkoxide ligand with the RO‐Ti‐L angles ranging from 93.6(2) to 99.0(2)°.     

New complexes of zirconium(IV) and hafnium(IV) with heteroscorpionate ligands and the hydrolysis of such complexes to give a zirconium cluster

A series of zirconium and hafnium heteroscorpionate complexes have been prepared by the reaction of MCl4 (M = Zr, Hf) with the compounds [[Li(bdmpza)(H2O)](4)] [bdmpza = bis(3,5-dimethylpyrazol-1-yl)acetate], [[Li(bdmpzdta)(H2O)](4)] [bdmpzdta = bis(3,5-dimethylpyrazol-1-yl)dithioacetate], and (Hbdmpze) [bdmpze = 2,2-bis(3,5-dimethylpyrazol-1-yl)ethoxide] (the latter with the prior addition of Bu(n)Li). Under the appropriate experimental conditions, mononuclear complexes, namely, [MCl3(kappa3-bdmpzx)] [x = a, M = Zr (1), Hf (2); x = dta, M = Zr (3), Hf (4); x = e, M = Zr (5), Hf (6)], and dinuclear complexes, namely, [[MCl2(mu-OH)(kappa3-bdmpzx)]2] [x = a, M = Zr (7), Hf (8); x = dta, M = Zr (9); x = e, M = Zr (10)], were isolated. A family of alkoxide-containing complexes of the general formula [ZrCl2(kappa3-bdmpzx)(OR)] [x = a, R = Me (11), Et (12), iPr (13), tBu (14); x = dta, R = Me (15), Et (16), iPr (17), tBu (18); x = e, R = Me (19), Et (20), (i)Pr (21), (t)Bu (22)] was also prepared. Complexes 11-14 underwent an interesting hydrolysis process to give the cluster complex [Zr6(mu3-OH)8(OH)8(kappa2-bdmpza)8] (23). The structures of these complexes have been determined by spectroscopic methods, and the X-ray crystal structures of 7, 8, and 23 were also established.