Alkane Elimination Research Articles

Synthesis and Structural Characterization of Zinc Complexes that Contain Chelating Phenolate Phosphane Ligands

AbstractThe preparation and characterization of zinc complexes supported by potentially tridentate biphenolate phosphane ligands are reported. The in situ prepared dilithium complexes of 2,2′‐tert‐butylphosphanylbis(4,6‐di‐tert‐butylphenolate) ([LtBu]2–) and 2,2′‐phenylphosphanylbis(4,6‐di‐tert‐butylphenolate) ([LPh]2–) react with ZnCl2 in tetrahydrofuran (THF) to produce lithium zincates Zn[LtBuLi(THF)]2 and Zn[LPhLi(THF)]2, respectively, regardless of the stoichiometry of the starting materials. Alkane elimination reactions of ZnEt2 with one equiv. of H2LtBu or H2LPh in THF generate Zn2(LtBu)2(THF) or Zn2(LPh)2(THF)2, whereas those employing two equiv. of the protio ligands afford Zn(LtBuH)2(MeCN) or Zn(LPhH)2(MeCN), respectively. The X‐ray structures of Zn[LtBuLi(THF)]2, Zn2(LtBu)2(THF), Zn2(LPh)2(THF)2, and Zn(LtBuH)2(MeCN) are presented.

LaAl3Et12: A Homoleptic Ethyllanthanum Complex

They do exist after all: Molecular [La(AlEt4)3] of high purity can be obtained from the reaction of [La(NMe2)3(LiCl)3] with excess triethylaluminum. Although kinetically labile—the title complex decomposes gradually through β-H abstraction and release of ethane—alkane elimination reactions are feasible, as shown for the synthesis of metallocene complex [(C5Me5)2La(AlEt4)].

Synthesis of Bis(amino)pyridines by the Stepwise Alkylation of Bis(imino)pyridines: An Unexpected and Selective Alkylation of the Aminoiminopyridine by AlMe3

Bis(imino)pyridines 2-[2,6-(R1)2C6H3N═C(CH3)]-6-[2,6-(R2)2C6H3N═C(CH3)](C5H3N) (1a, R1 = R2 = i-Pr; 1b, R1 = i-Pr, R2 = CH3; 1c, R1 = R2 = CH3) were first alkylated by AlMe3 and then hydrolyzed to aminoiminopyridines 2-[2,6-(R1)2C6H3N═C(CH3)]-6-[2,6-(R2)2C6H3NHC(CH3)2](C5H3N) (3a, R1 = R2 = i-Pr; 3b, R1 = i-Pr, R2 = CH3; 3c, R1 = R2 = CH3). When the aminoiminopyridines were treated with AlMe3, the expected methane elimination was not found; alkylation at the imine functional group led to the aluminum complexes {2-[2,6-(R1)2C6H3NC(CH3)2]-6-[2,6-(R2)2C6H3NHC(CH3)2](C5H3N)}AlMe2 (4a, R1 = R2 = i-Pr; 4b, R1 = i-Pr, R2 = CH3; 4c, R1 = R2 = CH3), which were further hydrolyzed to the bis(amino)pyridines 2-[2,6-(R1)2C6H3NHC(CH3)2]-6-[2,6-(R2)2C6H3NHC(CH3)2](C5H3N) (5a, R1 = R2 = i-Pr; 5b, R1 = i-Pr, R2 = CH3; 5c, R1 = R2 = CH3). The selective alkylation over elimination may come from the noninnocent property of the conjugated iminopyridine group. New magnesium, yttrium, and zirconium complexes supported by 5a ({2,6-[2,6-(i-Pr)2C6H3NC(CH3)2]2(C5H3N)}Mg(THF) (6), {2,6-[2,6-(i-Pr)2C6H3NC(CH3)2]2(C5H3N)}Y(CH2SiMe3)(THF) (7), and {2,6-[2,6-(i-Pr)2C6H3NC(CH3)2]2(C5H3N)}Zr(CH2SiMe3)2 (8)) were formed via the alkane elimination method.

Toward Stereoselective Lactide Polymerization Catalysts: Cationic Zinc Complexes Supported by a Chiral Phosphinimine Scaffold

The P-stereogenic phosphinimine ligands (dbf)MePhP═NAr (7: Ar = Dipp; 8: Ar = Mes; dbf = dibenzofuran, Dipp = 2,6-diisopropylphenyl, Mes = 2,4,6-trimethylphenyl) were synthesized as racemates via reactions of the parent phosphines (rac)-(dbf)MePhP (6) with organoazides. The ligands 7 and 8 were protonated by Brønsted acids to afford the aminophosphonium borate salts [(7)-H][BAr(4)] (9: Ar = C(6)F(5); 11: Ar = Ph) and [(8)-H][BAr(4)] (10: Ar = C(6)F(5); 12: Ar = Ph). The protonated ligands 9 and 10 were active toward alkane elimination reactions with diethylzinc and ethyl-[methyl-(S)-lactate]zinc to give the heteroleptic complexes [{(dbf)MePhP═NAr}ZnR][B(C(6)F(5))(4)] (Ar = Dipp, 13: R = Et; 15: R = methyl-(S)-lactate; Ar = Mes, 14: R = Et; 16: R = methyl-(S)-lactate). By contrast, reaction of the tetraphenylborate derivative 11 with diethylzinc yielded a phenyl transfer product, [(dbf)MePhP═NDipp]ZnPh(2) (17). Complex 15 was found to catalyze the ring-opening polymerization of rac-lactide.

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.

Ammonia Activation by μ3-Alkylidyne Fragments Supported on a Titanium Molecular Oxide Model

Ammonolysis of the μ(3)-alkylidyne derivatives [{Ti(η(5)-C(5)Me(5))(μ-O)}(3)(μ(3)-CR)] [R = H (1), Me (2)] produces a trinuclear oxonitride species, [{Ti(η(5)-C(5)Me(5))(μ-O)}(3)(μ(3)-N)] (3), via methane or ethane elimination, respectively. During the course of the reaction, the intermediates amido μ-alkylidene [{Ti(η(5)-C(5)Me(5))(μ-O)}(3)(μ-CHR)(NH(2))] [(R = H (4), Me (5)] and μ-imido ethyl species [{Ti(η(5)-C(5)Me(5))(μ-O)}(3)(μ-NH)Et] (6) were characterized and/or isolated. This achievement constitutes an example of characterization of the three steps of successive activation of N-H bonds in ammonia within the same transition-metal molecular system. The N-H σ-bond activation of ammonia by the μ(3)-alkylidyne titanium species has been theoretically investigated by DFT method on [{Ti(η(5)-C(5)H(5))(μ-O)}(3)(μ(3)-CH)] model complex. The calculations complement the characterization of the intermediates, showing the multiple bond character of the terminal amido and the bridging nature of imido ligand. They also indicate that the sequential ammonia N-H bonds activation process goes successively downhill in energy and occurs via direct hydron transfer to the alkylidyne group on organometallic oxides 1 and 2. The mechanism can be divided into three stages: (i) coordination of ammonia to a titanium center, in a trans disposition with respect to the alkylidyne group, and then the isomerization to adopt the cis arrangement, allowing the direct hydron migration to the μ(3)-alkylidyne group to yield the amido μ-alkylidene complexes 4 and 5, (ii) hydron migration from the amido moiety to the alkylidene group, and finally (iii) hydron migration from the μ-imido complex to the alkyl group to afford the oxo μ(3)-nitrido titanium complex 3 with alkane elimination.

Synthesis, Structure, and Ring‐Opening Polymerization Catalysis of Zinc Complexes Containing Amido Phosphinimine Ligands

AbstractA series of amido phosphinimine ligands of the type [(NAr1)‐o‐(Ph2P=NAr2)C6H4]– (2a: Ar1 = 2,6‐C6H3iPr2, Ar2 = 2,6‐C6H3iPr2; 2b: Ar1 = 2,6‐C6H3iPr2, Ar2 = 2,4,6‐C6H2Me3; 2c: Ar1 = 2,6‐C6H3Me2, Ar2 = 2,4,6‐C6H2Me3), which are electronic variations of monoanionic β‐diketiminates, have been employed to examine the coordination chemistry of zinc. Alkane elimination reactions of ZnR2 (R = Me, Et) with H[2a–c] in toluene or ethereal solutions at –35 °C afforded cleanly the corresponding organozinc complexes [2a–c]ZnMe (3a–c) and [2a–c]ZnEt (4a–c). Deprotonation of H[2a–c] with nBuLi at –35 °C generated [2a–c]Li (5a–c), which may be isolated as either solvent‐free complexes or solvated adducts depending on the reaction solvents employed (toluene, OEt2, or THF). Metathetical reactions of 5a·OEt2 with Zn(OAc)2 in THF at –35 °C produced [2a]Zn(OAc) (6a). These amido phosphinimine derivatives all display solution Cs symmetry on the NMR timescale. The mononuclear nature of the three‐coordinate alkyls 3–4 and four‐coordinate acetate 6a was confirmed by single‐crystal X‐ray diffraction analyses. Interestingly, the alkyl complexes 3a–c and 4a–c are all active initiators for the catalytic ring‐opening polymerization of ϵ‐caprolactone, whereas the acetate 6a is comparatively inactive.

An Unsupported Uranium–Rhenium Complex Prepared by Alkane Elimination

An unsupported uranium–rhenium bond has been prepared by alkane elimination by treatment of a cyclometallated alkyl uranium triamidoamine complex with rhenocene hydride (see scheme). DFT analysis reveals σ and π combinations in the URe bond, but the rhenium contributions dominate and an atoms-in-molecules analysis reveals a closed-shell, predominantly ionic uranium–rhenium interaction.

Bimetallic amidinate aluminum methyl complexes: Synthesis, crystal structure and activity for ε-caprolactone polymerization

Four novel bridged-amidines H2L (1,4-R1[C(NR2)(NHR2)]2 (R1=C6H4, R2=2,6-iPr2C6H3 (H2L1), R1=C6H4, R2=2,6-Me2C6H3 (H2L2), R1=C6H10, R2=2,6-iPr2C6H3 (H2L3), R1=C6H10, R2=2,6-Me2C6H3 (H2L4)) were prepared in 65–78% isolated yields by the condensation reaction of dicarboxylic acid with four equimolar amounts of amines in the presence of PPSE (polyphosphoric acid trimethylsilyl ester) at 180°C. Alkane elimination reaction of AlMe3 with 0.5 equivalent of the bridged-amidines (H2L) in THF at room temperature afforded the corresponding bimetallic aluminum methyl complexes Me2AlLAlMe2 (L1 (1), L2 (2), L3 (3), L4 (4)) in 83–93% isolated yields. In order to understand whether the bimetallic complexes could show cooperative effect in the polymerization, their related mononuclear analogues LAlMe2 (L5 (5), L6 (6), L7 (7), L8 (8)) had also been synthesized in 85–91% isolated yields by treatment of AlMe3 with 1 equivalent of amidines HL ([PhC(N-2,6-iPr2C6H3)2]H (HL5), [PhC(N-2,6-Me2C6H3)2]H (HL6), [CyC(N-2,6-iPr2C6H3)2]H (HL7), [CyC(N-2,6-Me2C6H3)2]H (HL8)) in THF at room temperature. All these complexes were characterized by elemental analysis, FT-IR, and NMR spectroscopy. The crystal structures of H2L3, 1, 3, 5 and 7 were determined by X-ray diffraction. In all these amidinate aluminum methyl complexes, Al is four-coordinated by two nitrogen atoms from the dihapto-amidinate ligand and two methyl groups to adopt a distorted tetrahedral geometry. These complexes showed activity towards the ring-opening polymerization of ε-caprolactone at room temperature to give unimodal molecular weight distribution polyesters.

Highly trans-1,4 selective (co-)polymerization of butadiene and isoprene with quinolyl anilido rare earth metal bis(alkyl) precursors

The N-R-quinolinyl-8-amino ligands HL(1-3) (R = 2,6-(i)Pr(2)C(6)H(3) (HL(1)), 2,6-Et(2)C(6)H(3) (HL(2)), 2,6-Me(2)C(6)H(3) (HL(3))) have been prepared, which reacted readily with one equiv. of rare earth metal tris(alkyl)s to afford the corresponding bis(alkyl) complexes L(1)Y(CH(2)SiMe(3))(2)(THF) (1) and L(1-3)Lu(CH(2)SiMe(3))(2)(THF) (2-4) via alkane elimination. Contrastingly, treatment of the in situ generated neodymium tri(alkyl)s with HL(1) afforded a mono(alkyl) neodymium complex (5). Complexes 1, 2 and 5 in combination with aluminium alkyls and organoborates established homogenous ternary systems that exhibited versatile catalytic activities and trans-1,4 selectivities for the polymerization of butadiene, depending on the types of aluminium alkyl, organoborate and rare earth metal used. Furthermore, the trans-1,4 selective copolymerization of butadiene and isoprene was achieved by using the ternary system of 1/AlMe(3)/[Ph(3)C][B(C(6)F(5))(4)]. Both the kinetics of copolymerization and the thermal behavior of the copolymers were investigated.

Monoalkyl and monoanilide yttrium complexes containing tridentate pyridyl-1-azaallyl dianionic ligands

A series of pyridyl-1-azaallyl ligand precursors (HL1-HL5) were synthesized via condensation of pyridine ketones with anilines. The alkane elimination reactions between Y(CH(2)SiMe(3))(3)(THF)(2) and HL4 or HL5 gave the monoalkyl complexes (L4-H)YCH(2)SiMe(3)(THF) (1) and (L5-H)YCH(2)SiMe(3)(THF) (2) supported by new tridentate pyridyl-1-azaallyl dianionic ligands. The reactions of monoalkyl complexes, 1 and 2, with one equivalent of 2,6-diisopropylaniline produced the corresponding monoanilide complexes, (L4-H)YNHAr(THF) (3) and (L5-H)YNHAr(THF) (4) (Ar = 2,6-((i)Pr)(2)C(6)H(3)), via highly selective protonolysis of the terminal alkyl Y-CH(2)SiMe(3) bond. Complexes 1-4 are active for intramolecular hydroamination of aminoalkenes.

Lanthanide Alkyl Complexes Supported by a Piperazidine-Bridged Bis(phenolato) Ligand: Synthesis, Structural Characterization, and Catalysis for the Polymerization of l-Lactide and rac-Lactide

A series of lanthanide alkyl complexes supported by a piperazidine-bridged bis(phenolato) ligand were synthesized, and their catalytic activity for the polymerization of l-lactide was explored. The alkane elimination reaction of Ln(CH2SiMe3)3(THF)2 with H2[ONNO] {H2[ONNO] = 1,4-bis(2-hydroxy-3,5-di-tert-butylbenzyl)piperazidine} in a 1:1 molar ratio in THF gave the neutral lanthanide alkyl complexes [ONNO]Ln(CH2SiMe3)(THF) [Ln = Y (1), Lu (2), Yb (3), Gd (4)] in high isolated yields. Treatment of a gadolinium tris(alkyl) complex formed in situ from the reaction of anhydrous GdCl3 with 3 equiv of Li(CH2SiMe3) in THF gave a novel “ate” gadolinium alkyl complex, {[ONNO]Gd(CH2SiMe3)(μ-Li)(μ-Cl)}2 (5). All of these complexes are fully characterized including X-ray structural determination. Complexes 1−4 are isomorphous, monomeric, and THF-solvated. The coordination geometry around the lanthanide metals can be best described as a distorted trigonal bipyramid. Complex 5 is dimeric and unsolvated, and each [ONNO]...

Highly Volatile Alkaline Earth Metal Fluoroalkoxides

The synthetic strategies, structural comparison, and thermal gravimetric analyses for a novel family of alkaline earth metal perfluoro-tert-butoxides (PFTB) are presented. The isolated complexes follow the general formula, [Ae(PFTB)(2)(d)(x)]; (1a, Ae = Mg, d = THF, x = 2; 1b, Ae = Ca, d = THF, x = 4; 1c, Ae = Sr, d = THF, x = 4; 1d, Ae = Ba, d = THF, x = 4; 2a, Ae = Mg, d = DME, x = 1; 2b, Ae = Ca, d = DME, x = 2; 2c, Ae = Sr, d = DME, x = 2; 2d, Ae = Ba, d = DME, x = 3; 3a, Ae = Mg, d = diglyme, x = 1; 3b, Ae = Ca, d = diglyme, x = 2; 3c, Ae = Sr, d = diglyme, x = 2; 3d, Ae = Ba, d = diglyme, x = 2; THF = tetrahydrofuran, DME = 1,2-dimethoxyethane) where the crystallographically characterized compounds display either a cis or trans conformations in octahedral or pseudo-octahedral environments. Alkane elimination (Mg), direct metalation via ammonia activation (Ca, Sr, Ba), and transamination (Ca, Sr, Ba) methods yielded the target compounds in moderate to good yields. Structural studies of select compounds showed all compounds to be monomeric with varying degrees of co-ligand coordination, possibly explaining some of the observed physical properties. Thermal gravimetric analyses of the compounds shows sublimation at low temperatures, associated with minimal residue, making this family of fluoroalkoxides promising candidates for metal organic chemical vapor deposition (MOCVD).

Aminopyridinate‐Stabilized Lanthanoid Complexes: Synthesis, Structure and Polymerization of Ethylene and Isoprene

AbstractA series of aminopyridinate‐stabilized dialkyl‐lanthanoid complexes has been synthesized and characterized. The complexes were prepared by alkane elimination reacting [Ln(CH2SiMe3)3(thf)2] (Ln = Er, Yb, Lu) or [Ln(CH2Ph)3(thf)3] (Ln = Y, Er, Lu) with one equivalent of the bulky aminopyridine (2,6‐diisopropylphenyl)‐[6‐(2,4,6‐triisopropylphenyl)pyridin‐2‐yl]amine. Single‐crystal X‐ray analyses were carried out for all of the benzyl derivatives. The reaction of these compounds with ammonium borate leads to the elimination of one of the two alkyl functions and affords organolanthanoid cations. The aminopyridinate‐stabilized dialkyl‐lanthanoid compounds can initiate the polymerization of isoprene after activation with perfluorinated tetraphenyl borates. The obtained polymers have a 3,4‐content of 60–95 %. The metal ion size as well as the addition of alkylaluminium compounds influences the microstructure of the obtained polymer. Aminopyridinate‐stabilized organolanthanoid cations of Sc, Lu, Er and Y can polymerize ethylene in the presence of alkylaluminium compounds. The Lu, Er and Y complexes act as a CCTP catalyst and the erbium compound exhibits the highest activity.

Half-Sandwich Rare Earth Metal Complexes as Novel Catalysts for Olefin Polymerization and Other Chemical Transformations

Abstract This article describes our recent studies on the synthesis and chemistry of mono(cyclopentadienyl)-ligated rare earth metal alkyl and hydride complexes. The half-sandwich mono- and dialkyl rare earth metal complexes are prepared either by alkane elimination reactions between trialkyl rare earth complexes and the neutral cyclopentadiene derivatives or by metathetical reactions of rare earth trichlorides with the alkali metal salts of the corresponding ligands. The reaction of the dialkyl complexes with an equivalent of a borate compound such as [Ph3C][B(C6F5)4] or [PhNMe2H][B(C6F5)4] generates easily the corresponding cationic monoalkyl species, which serve as excellent catalysts for the polymerization and copolymerization of a variety of olefins to yield a new family of polymer materials that show novel properties but are difficult to prepare by other catalysts. The half-sandwich monoalkyl rare earth complexes bearing the silylene-linked cyclopentadienyl–arylamido ligands act as excellent catalysts for the catalytic dimerization of terminal alkynes, cross coupling of terminal alkynes with isocyanides, and the catalytic addition of terminal alkyne C–H, amine N–H, and phosphine P–H bonds to carbodiimides. The hydrogenolysis of the dialkyl rare earth complexes with H2 affords a new class of polynuclear rare earth metal polyhydride complexes, which show unique features in both structure and reactivity.

Novel polymerization catalysts and hydride clusters from rare-earth metal dialkyls

This Review gives an overview on recent progress in the synthesis and chemistry of rare-earth metal dialkyl complexes bearing monoanionic ancillary ligands, with an emphasis on novel polymerization catalysts. These structurally well-defined and highly reactive compounds are prepared either by alkane elimination reactions between trialkyl rare-earth complexes and acidic neutral ligands, or by the metathetical reactions of rare-earth trihalides with the alkali metal salts of the corresponding ligands. On treatment with an appropriate borate compound, the dialkyl complexes are converted into the corresponding cationic monoalkyl species, which serve as excellent catalysts for the polymerization and copolymerization of a variety of olefins to yield a series of new polymer materials that exhibit novel properties. Alternatively, hydrogenation of the dialkyl rare-earth complexes with H(2) affords a new class of rare-earth polyhydride complexes with unique features in terms of both their structure and reactivity.

Heteroleptic iminopyrrolidinates of aluminium

A series of iminopyrrolidine (ip) compounds were synthesized with excellent yields as potential ligands for novel organometallic precursors for atomic layer deposition. The idea behind these ligands was that carbodiimide (CDI) deinsertion would not occur as the quaternary carbon was tethered to one chelate nitrogen. To our advantage a melting point trend was evident within the ip ligands and reflected in the family of heteroleptic aluminium species when the ip ligands were reacted with TMA or TEA. The alkane elimination reaction occurred at room temperature yielding clean products with high yields. Crystal structures were collected for compounds 7 [ipipAlMe(2)], 12 [tbipAlMe(2)], and 14 [sbipAlEt(2)] demonstrating that the heteroleptic aluminium species were dimers. This was also evident in the mass spectra collected for each compound as the parent peak was that of the dimer minus a methyl. Thermolysis studies were carried out on all the ipAlMe(2) species to observe the decomposition at an isotherm over several days. The decay of the methyl peak was monitored as a ratio against TMS within the solution and was shown to be a first order decomposition. From these studies it was clear that nbip (9), iso-bip (10), and tbip (12) were the most stable complexes with half-lives of 24.8, 9.00, and 10.3 days, respectively.

Aluminium complexes of bidentate N,O- and N,N-ligands derived from oxidative functionalization of amido phosphines: synthesis, structure and reactivity

A series of amido phosphinoxide and amido phosphinimine ligands that are electronic variations of monoanionic N,O- and N,N-ketiminates have been prepared and employed to examine the coordination chemistry of aluminium. Oxidation of the previously established N-(2-diphenylphosphinophenyl)-2,6-dialkylaniline in the presence of H(2)O(2) or organic azides RN(3) (R = 2,6-C(6)H(3)(i)Pr(2), SiMe(3)) led to phosphinoxides (H[NO] 1a-b) and phosphinimines (H[NN] 1c-d), respectively. Alkane elimination reactions of these protio-ligand precursors with trialkylaluminium in toluene or pentane solutions afforded cleanly the corresponding organoaluminium complexes, including dimethyl 2a-d, diethyl 3a-d and diisobutyl derivatives 4a-b and 4d. Solution NMR studies revealed Cs symmetry for these organoaluminium species, in which the α-hydrogen atoms are all diastereotopic. The correlation between the steric congestion of these molecules and the degree of resolution of the multiplet signals corresponding to the diastereotopic α-hydrogen atoms observed by the (1)H NMR spectroscopy is of particular interest. Dichloroaluminium complexes 5c-d were prepared in high yields by protonolysis of MeAlCl(2) with 1c-d. Single-crystal X-ray diffraction analyses of 2c-d, 3a, 3d, 4a, and 4d elucidated a mononuclear, distorted tetrahedral core for all of these aluminium species. Interestingly, complexes 2c-d are active initiators for catalytic ring-opening oligomerization of ε-caprolactone, whereas 2a-b are rather inactive, highlighting the significance of the steric hindrance imposed by the amido phosphinimine ligands, as compared to that imposed by the phosphinoxide counterparts.

Grafting of peralkylated LnIIAlIII heterobimetallic complexes onto periodic mesoporous silica KIT-6

Tetraethylaluminates of the divalent lanthanides ytterbium and samarium were grafted onto large-pore cubic periodic mesoporous silica (PMS) KIT-6, which had been dehydroxylated at 500 degrees C (specific surface area a(s): 500 m(2)g(-1); mesopore volume V(p): 1.06 cm(3)g(-1); main pore diameter: 85 A). The bimetallic materials [Ln(AlEt(4))(2)]@KIT-6(-500) were analysed by DRIFT spectroscopy, elemental analysis, nitrogen physisorption and solid-state NMR. Upon heterogenization the surface area and pore volume of the KIT-6 materials dropped by 30-35% and 25%, respectively. The hybrid materials were compared to AlEt(3)@KIT-6(-500) since reaction of AlEt(3) with surface silanol groups is also a prominent reaction pathway when complexes [Ln(AlEt(4))(2)](n) are immobilized. Reaction of the Ln(II) tetraalkylaluminates with tris(tert-butoxy)silanol HOSi(OtBu)(3) gave complexes Ln[(mu-OSi(OtBu)(3))(mu-R)AlR(2)](2) (Ln = Yb, Sm; R = Et; Ln = Yb; R = Me) which can be seen as molecular model complexes, evidencing alkane elimination, trialkylaluminium adduct formation, and Ln(II)-O(siloxane) bonding.

Bimetallic Rare Earth Alkyl Complexes Bearing Bridged Amidinate Ligands: Synthesis and Activity for L‐Lactide Polymerization

AbstractFour novel bridged‐amidines H2L {1,4‐R1[C(=NR2)(NHR2)]2 [R1=C6H4, R2=2,6‐iPr2C6H3 (H2L1); R1=C6H4, R2=2,6‐Me2C6H3 (H2L2); R1=C6H10, R2=2,6‐iPr2C6H3 (H2L3); R1=C6H10, R2=2,6‐Me2C6H3 (H2L4)]} were synthesized in 65%–78% isolated yields by the condensation reaction of dicarboxylic acid with four equimolar amounts of amines in the presence of PPSE at 180°C. Alkane elimination reaction of Ln(CH2SiMe3)3(THF)2 (Ln=Y, Lu) with 0.5 equiv. of amidine in THF at room temperature afforded the corresponding bimetallic rare earth alkyl complexes (THF)(Me3SiCH2)2LnL1Ln(CH2SiMe3)2(THF) [Ln=Y (1), Lu (2)], (THF)(Me3SiCH2)2LnL2Ln‐ (CH2SiMe3)2(THF) [Ln=Y (3), Lu (4)], (THF)(Me3SiCH2)2YL3Y(CH2SiMe3)2(THF) (5), (THF)(Me3SiCH2)2YL4‐ Y(CH2SiMe3)2(THF) (6) in 72% –80% isolated yields. These neutral complexes showed activity towards L‐lactide polymerization in toluene at 70°C to give high molecular weight (M>104) and narrow molecular weight distribution (Mw/Mn≦1.40) polymers