Dinuclear Rare‐Earth Metal Alkyl Complexes Supported by Indolyl Ligands in μ‐η2:η1:η1 Hapticities and their High Catalytic Activity for Isoprene 1,4‐cis‐Polymerization

Two series of new dinuclear rare‐earth metal alkyl complexes supported by indolyl ligands in novel μ‐η²:η¹:η¹ hapticities are synthesized and characterized. Treatment of [RE(CH₂SiMe₃)₃(thf)₂] with 1 equivalent of 3‐(tBuN?CH)C₈H₅NH ( L₁ ) in THF gives the dinuclear rare‐earth metal alkyl complexes trans‐[(μ‐η²:η¹:η¹‐3‐{tBuNCH(CH₂SiMe₃)}Ind)RE(thf)(CH₂SiMe₃)]₂ (Ind=indolyl, RE=Y, Dy, or Yb) in good yields. In the process, the indole unit of L₁ is deprotonated by the metal alkyl species and the imino C?N group is transferred to the amido group by alkyl CH₂SiMe₃ insertion, affording a new dianionic ligand that bridges two metal alkyl units in μ‐η²:η¹:η¹ bonding modes, forming the dinuclear rare‐earth metal alkyl complexes. When L₁ is reduced to 3‐(tBuNHCH₂)C₈H₅NH ( L₂ ), the reaction of [Yb(CH₂SiMe₃)₃(thf)₂] with 1 equivalent of L₂ in THF, interestingly, generated the trans‐[(μ‐η²:η¹:η¹‐3‐{tBuNCH₂}Ind)Yb(thf)(CH₂SiMe₃)]₂ (major) and cis‐[(μ‐η²:η¹:η¹‐3‐{tBuNCH₂}Ind)Yb(thf)(CH₂SiMe₃)]₂ (minor) complexes. The catalytic activities of these dinuclear rare‐earth metal alkyl complexes for isoprene polymerization were investigated; the yttrium and dysprosium complexes exhibited high catalytic activities and high regio‐ and stereoselectivities for isoprene 1,4‐cis‐polymerization.     

Syntheses,structures and catalytic activities of low-coordinated rare-earth metal complexes containing 2,2′-pyridylpyrrolides

Reactions of the ligand precursors 2-(2′-pyridyl)-3,5-Me₂-pyrrole ( L ¹ H) and 2-(2-pyridyl)-3,4,5-Me₃-pyrrole ( L ² H) with [(Me₃Si)₂N]₃RE(μ-Cl)Li(THF)₃ in toluene afforded a series of low-coordinated rare-earth metal bis-amido complexes L ¹ RE[N(SiMe₃)₂]₂ [RE = Y ( 1a ), Dy ( 1b ), Er ( 1c ), Yb ( 1d )] and L ² RE[N(SiMe₃)₂]₂ [RE = Y ( 2a ), Dy ( 2b ), Er ( 2c ), Yb ( 2d )]. With the ionic radius of rare-earth metal increasing, the reaction of L ¹ H and [(Me₃Si)₂N]₃RE(μ-Cl)Li(THF)₃ gave dinuclear complexes ( L ¹ )₂RE(μ-Cl)(μ-η⁵:η¹:η¹- L ¹ )RE( L ¹ )[N(SiMe₃)₂]₂ [RE = Sm ( 1e ), Pr ( 1f )]; however, the reaction of L ² H and [(Me₃Si)₂N]₃Sm(μ-Cl)Li(THF)₃ afforded ( L ² )₂Sm[N(SiMe₃)₂]₂ ( 2e ). Results indicated that the ionic radius of rare-earth metal and subtle change in the ligands have substantial effects on the structure and bonding mode of complexes. The complexes showed a high catalytic activity for the ring-opening reaction of cyclohexene oxide with amines to afford various β-aminoalcohols under mild solvent-free conditions.     

Dinuclear Dysprosium and Ytterbium Complexes Incorporating N,N‐Bis(pyrrolyl‐α‐methyl)‐N‐methylamine Ligand: Syntheses and Structures

Reaction of DyCl₃ with two equivalents of NaN(SiMe₃)₂ in THF yielded {Dy(μ‐Cl)[N(SiMe₃)₂]₂(THF)}₂ ( 1 ). X‐ray crystal structure analysis revealed that 1 is a centrosymmetric dimer with asymmetrically bridging chloride ligands. The metal coordination arrangement can be best described as distorted trigonal bipyramid. The bond lengths of Ln–Cl and Ln–N showed a decreasing trend with the contraction of the size of Ln³⁺. Treatment of N,N‐bis(pyrrolyl‐α‐methyl)‐N‐methylamine (H₂dpma) with 1 and known compound {Yb(μ‐Cl)[N(SiMe₃)₂]₂(THF)}₂, respectively, led to the formations of [Dy(μ‐Cl)(dpma)(THF)₂]₂ ( 2 ) and {Yb(μ‐Cl)[N(SiMe₃)₂]₂(THF)}₂ ( 3 ). Compounds 2 and 3 were fully characterized by single‐crystal X‐ray crystallography, elemental analysis, and ¹H NMR spectroscopy. Structure determination indicated that 2 and 3 exhibit as centrosymmetric dimers with asymmetrically bridging chloride ligands. One pot reactions involving LnCl₃ (Ln = Dy and Yb), LiN(SiMe₃)₂, and H₂dpma were explored and desired products 2 and 3 were not yielded, which indicated that 1 and {Yb(μ‐Cl)[N(SiMe₃)₂]₂(THF)}₂ are the demanding precursors to synthesize Dysprosium and Ytterbium complexes supported by dpma^2– ligand. Compounds 2 and 3 are the first reported lanthanide complexes chelated by dpma^2– ligand.     

Isoprene polymerization with indolide‐imine supported rare‐earth metal alkyl and amidinate complexes

Reaction of 7‐{(N‐2,6‐R)iminomethyl)}indole ( HL¹ , R = dimethylphenyl; HL² , R = diisopropylphenyl) and rare‐earth metal tris(alkyl)s, Ln(CH₂SiMe₃)₃(THF)₂, generated new rare‐earth metal bis(alkyl) complexes LLn(CH₂SiMe₃)₂(THF) [L = L¹: Ln = Lu ( 1a ), Sc ( 1b ); L = L²: Ln = Lu ( 3a ), Sc ( 3b )] and mono(alkyl) complexes L²₂Lu(CH₂SiMe₃) ( 4a ). Treatment of alkyl complexes 1a and 4a with N,N′‐diisopropylcarbodiimide afforded the corresponding amidinates L¹Lu{iPr₂NC(CH₂SiMe₃)NiPr₂}₂ ( 2a ) and L²₂Lu{iPr₂NC(CH₂SiMe₃)NiPr₂} ( 5a ), respectively. These new rare‐earth metal alkyls and amidinates except 4a in combination with aluminum alkyls and borate generated efficient homogeneous catalysts for the polymerization of isoprene, providing high cis‐1,4 selectivity and high molar mass polyisoprene with narrow molar mass distribution (M_n = 2.65 × 10⁵, M_w/M_n = 1.07, cis‐1,4 98.2%, −60 °C). The environmental hindrance around central metals arising from the bulkiness of the ligands, the Lewis‐acidity of rare‐earth metal ions, the types of aluminum tris(alkyl)s and borate, and polymerization temperature influenced significantly on both the catalytic activity and the regioselectivity. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5251–5262, 2008     

Lutetium‐Methanediide‐Alkyl Complexes: Synthesis and Chemistry

The first four‐coordinate methanediide/alkyl lutetium complex (BODDI)Lu₂(CH₂SiMe₃)₂(μ₂‐CHSiMe₃)(THF)₂ (BODDI=ArNC(Me)CHCOCHC(Me)NAr, Ar=2,6‐iPr₂C₆H₃) ( 1 ) was synthesized by a thermolysis methodology through α‐H abstraction from a Lu–CH₂SiMe₃ group. Complex 1 reacted with equimolar 2,6‐iPrC₆H₃NH₂ and Ph₂C?O to give the corresponding lutetium bridging imido and oxo complexes (BODDI)Lu₂(CH₂SiMe₃)₂(μ₂‐N‐2,6‐iPr₂C₆H₃)(THF)₂ ( 2 ) and (BODDI)Lu₂(CH₂SiMe₃)₂(μ₂‐O)(THF)₂ ( 3 ). Treatment of 3 with Ph₂C?O (4 equiv) caused a rare insertion of Lu–μ₂‐O bond into the C?O group to afford a diphenylmethyl diolate complex 4 . Reaction of 1 with PhN=C?O (2 equiv) led to the migration of SiMe₃ to the amido nitrogen atom to give complex (BODDI)Lu₂(CH₂SiMe₃)₂‐μ‐{PhNC(O)CHC(O)NPh(SiMe₃)‐κ³N,O,O}(THF) ( 5 ). Reaction of 1 with tBuN?C formed an unprecedented product (BODDI)Lu₂(CH₂SiMe₃){μ₂‐[η²:η²‐tBuNC(=CH₂)SiMe₂CHC?NtBu‐κ¹N]}(tBuN?C)₂ ( 6 ) through a cascade reaction of N?C bond insertion, sequential cyclometalative γ‐(sp³)‐H activation, C?C bond formation, and rearrangement of the newly formed carbene intermediate. The possible mechanistic pathways between 1 , PhN?C?O, and tBuN?C were elucidated by DFT calculations.     

Organometallic Compounds of the Lanthanides. 157 [1] The Molecular Structure of Tris(trimethylsilylmethyl)samarium, ‐erbium, ‐ytterbium,and ‐lutetium

SmCl₃ reacts with Me₃SiCH₂Li in THF yielding Sm(CH₂SiMe₃)₃(THF)₃ ( 1 ). The single crystal X‐ray structural analyses of 1 , Er(CH₂SiMe₃)₃(THF)₂ ( 2 ), Yb(CH₂SiMe₃)₃(THF)₂ ( 3 ), and Lu(CH₂SiMe₃)₃(THF)₂ ( 4 ) show the Sm atom in a fac‐octahedral coordination and the heavier lanthanides Er, Yb, and Lu trigonal bipyramidally coordinated with the three alkyl ligands in equatorial and two THF molecules in axial positions.     

Lanthanide amido complexes incorporating amino-coordinate-lithium bridged bis(indolyl) ligands: synthesis, characterization, and catalysis for hydrophosphonylation of aldehydes and aldimines

Two series of new lanthanide amido complexes supported by bis(indolyl) ligands with amino-coordinate-lithium as a bridge were synthesized and characterized. The interactions of [(Me(3)Si)(2)N](3)Ln(III)(μ-Cl)Li(THF)(3) with 2 equiv of 3-(CyNHCH(2))C(8)H(5)NH in toluene produced the amino-coordinate-lithium bridged bis(indolyl) lanthanide amides [μ-{[η(1):η(1):η(1):η(1)-3-(CyNHCH(2))Ind](2)Li}Ln[N(SiMe(3))(2)](2)] (Cy = cyclohexyl, Ind = Indolyl, Ln = Sm (1), Eu (2), Dy (3), Yb (4)) in good yields. Treatment of [μ-{[η(1):η(1):η(1):η(1)-3-(CyNHCH(2))Ind](2)Li}Ln[N(SiMe(3))(2)](2)] with THF gave new lanthanide amido complexes [μ-{[η(1):η(1)-3-(CyNHCH(2))Ind](2)Li(THF)}Ln[N(SiMe(3))(2)](2)] (Ln = Eu (5), Dy (6), Yb (7)), which can be transferred to amido complexes 2, 3, and 4 by reflux the corresponding complexes in toluene. Thus, two series of rare-earth-metal amides could be reciprocally transformed easily by merely changing the solvent in the reactions. All new complexes 1-7 are fully characterized including X-ray structural determination. The catalytic activities of these new lanthanide amido complexes for hydrophosphonylation of both aromatic and aliphatic aldehydes and various substituted aldimines were explored. The results indicated that these complexes displayed a high catalytic activity for the C-P bond formation with employment of low catalyst loadings (0.1 mol?% for aldehydes and 1 mol?% for aldimines) under mild conditions. Thus, it provides a convenient way to prepare both α-hydroxy and α-amino phosphonates.     

Reactivity of TpMe2‐Supported Yttrium Alkyl Complexes toward Aromatic N‐Heterocycles: Ring‐Opening or CC Bond Formation Directed by CH Activation

Unusual chemical transformations such as three‐component combination and ring‐opening of N‐heterocycles or formation of a carbon–carbon double bond through multiple C–H activation were observed in the reactions of Tp^Me2‐supported yttrium alkyl complexes with aromatic N‐heterocycles. The scorpionate‐anchored yttrium dialkyl complex [Tp^Me2Y(CH₂Ph)₂(THF)] reacted with 1‐methylimidazole in 1:2 molar ratio to give a rare hexanuclear 24‐membered rare‐earth metallomacrocyclic compound [Tp^Me2Y(μ‐N,C‐Im)(η²‐N,C‐Im)]₆ ( 1 ; Im=1‐methylimidazolyl) through two kinds of C–H activations at the C2‐ and C5‐positions of the imidazole ring. However, [Tp^Me2Y(CH₂Ph)₂(THF)] reacted with two equivalents of 1‐methylbenzimidazole to afford a C–C coupling/ring‐opening/C–C coupling product [Tp^Me2Y{η³‐(N,N,N)‐N(CH₃)C₆H₄NHCH?C(Ph)CN(CH₃)C₆H₄NH}] ( 2 ). Further investigations indicated that [Tp^Me2Y(CH₂Ph)₂(THF)] reacted with benzothiazole in 1:1 or 1:2 molar ratio to produce a C–C coupling/ring‐opening product {(Tp^Me2)Y[μ‐η²:η¹‐SC₆H₄N(CH?CHPh)](THF)}₂ ( 3 ). Moreover, the mixed Tp^Me2/Cp yttrium monoalkyl complex [(Tp^Me2)CpYCH₂Ph(THF)] reacted with two equivalents of 1‐methylimidazole in THF at room temperature to afford a trinuclear yttrium complex [Tp^Me2CpY(μ‐N,C‐Im)]₃ ( 5 ), whereas when the above reaction was carried out at 55 °C for two days, two structurally characterized metal complexes [Tp^Me2Y(Im‐Tp^Me2)] ( 7 ; Im‐Tp^Me2=1‐methyl‐imidazolyl‐Tp^Me2) and [Cp₃Y(HIm)] ( 8 ; HIm=1‐methylimidazole) were obtained in 26 and 17 % isolated yields, respectively, accompanied by some unidentified materials. The formation of 7 reveals an uncommon example of construction of a C?C bond through multiple C–H activations.     

Synthesis and Structure of Lanthanide Sandwich Complexes with Mixed Cyclooctatetraenyl and Chelating Substituted‐indenyl Ligands

Two types of sandwich complexes (η⁵‐MeOCH₂CH₂C₉H₆) Ln (η⁸‐C₈H₈) (THF)_n [Ln=La (1), Nd(2), n=0; Sm(3), Dy (4) and Er (5). n = l] and (η⁵‐C₄H₇OCH₂C₉H₆)Ln(η⁸‐C₈H₈) (THF) [Ln = La (6), Nd(7). Sm(8). Dy (9) and Er (10)] were synthesized by the reactions of LnCl₃ with equivalent mole of K₂C₈H₈, followed by treatment with corresponding potassium salt of ether‐substituted indenide. The molecular structures of 3 and 8 were determined by single crystal X‐ray diffraction. (η⁵ ‐MeOCH₂CH₂C₉H₆) Sm (η⁸‐C₈H₈) (THF) (3) monoclinic. Pt₁/c, a = 1.4793(3) nm, b = 0.8716 (2) nm, c = 1.6149 (3) nm, β = 98. 17(3), V = 2.0612(7) nm³, Z = 4, R(F)=0.0362. (η⁵‐C₄H₇OCH₂C₉H₆)Sm(η⁸‐C₈H₈)(THF) (8) orthorhombic. p2₁2₁2₁. a = 0.8754(2) nm, b = 1.1000(2) nm, c = 2.3117 (5) nm, V = 2.2260(8) nm³, Z=4, R(F) =0.0497.     

Synthesis,structure, and catalytic activity of rare-earth metal amides with a neutral pyrrolyl-functionalized indolyl ligand

<正>1 Representation of complexes and selected bond distances and bond angles Figure S1 Structure of complex 4. Hydrogen atoms were omitted for clarity, ellipsoids set at the 30% probability level. Selected bond distances() and angles(°): Er(1)–Cl(1) 2.6180(18), Er(1)–N(1) 2.301(6), Er(1)–N(4) 2.232(6), Er(1)–N(5) 2.229(6), N(1)–Er(1)–Cl(1) 87.41(14), N(4)–Er(1)–Cl(1) 101.16(14), N(5)–Er(1)–Cl(1) 118.60(16), N(4)–Er(1)–N(1) 114.1(2), N(5)–Er(1)–N(1) 108.7(2), N(5)–Er(1)–N(4) 121.9(2).Figure S2 Structure of complex 5. Hydrogen atoms were omitted for clarity, ellipsoids set at the 30% probability level. Selected bond distances(o) and angles(°): Y(1)–Cl(1) 2.6212(12), Y(1)–N(1) 2.280(3), Y(1)–N(4) 2.214(3), Y(1)–N(5) 2.228(3), N(1)–Y(1)–Cl(1) 87.67(8), N(4)–Y(1)–Cl(1) 121.32(8), N(5)–Y(1)–Cl(1) 102.88(8), N(4)–Y(1)–N(1) 107.75(11), N(5)–Y(1)–N(1) 111.64(11), N(4)–Y(1)–N(5) 120.78(10).     

Dysprosiacarboranes as Organometallic Single‐Molecule Magnets

The dicarbollide ion, nido‐C₂B₉H₁₁^2? is isoelectronic with cyclopentadienyl. Herein, we make dysprosiacarboranes, namely [(C₂B₉H₁₁)₂Ln(THF)₂][Na(THF)₅] (Ln=Dy, 1Dy ) and [(THF)₃(μ‐H)₃Li]₂[{η⁵‐C₆H₄(CH₂)₂C₂B₉H₉}Dy{η²:η⁵‐C₆H₄(CH₂)₂C₂B₉H₉}₂Li] 3Dy and show that dicarbollide ligands impose strong magnetic axiality on the central Dy^III ion. The effective energy barrier (U_eff) for the loss of magnetization can be varied by the substitution pattern on the dicarbollide. This finding is demonstrated by comparing complexes of nido‐C₂B₉H₁₁^2? and nido‐[o‐xylylene‐C₂B₉H₉]^2?, which show a U_eff of 430(5) K and 804(7) K, respectively. The blocking temperature defined by the open hysteresis temperature of 3Dy reaches 6.8 K. Moreover, the linear complex [Dy(C₂B₉H₁₁)₂]^? is predicted to have comparable properties with the linear [Dy(Cp^Me3)₂]⁺ complex. As such, carboranyl ligands and their derivatives may provide a new type of organometallic ligand for high‐performance single‐molecule magnets.     

Synthesis and Characterization of donor‐functionalized ansa‐Cyclopentadienyl‐Indenyl and ansa‐Indenyl‐Indenyl Complexes of Yttrium,Samarium, Thulium,and Lutetium

The stepwise reaction of Me₂SiCl₂ with K[C₅H₃ ^tBuMe‐3] or Li[C₉H₇] and then with K[C₉H₆CH₂CH₂‐ NMe₂‐1] followed by double deprotonation with NaH or LiBu, yields the two dimethylsilicon bridged cyclopentadienyl‐indenyl and indenyl‐indenyl donor‐functionalized ligand systems K₂[(C₅H₂ ^tBu‐3‐Me‐5)SiMe₂(1‐C₉H₅CH₂CH₂NMe₂‐3)] ( 1 ), and Li₂[(1‐C₉H₆)SiMe₂(1‐C₉H₅CH₂CH₂NMe₂‐3)] ( 2 ), respectively. Treatment of 1 with YCl₃(THF)₃, SmCl₃(THF)_1.77, TmI₃(DME)₃, and LuCl₃(THF)₃ gives the mixed ansa‐metallocenes [(C₅H₂ ^tBu‐3‐Me‐5)SiMe₂(1‐C₉H₅CH₂CH₂NMe₂‐3)]LnX (X = Cl, Ln = Y ( 3 ), Sm ( 4 ), Lu ( 5 ); X = I, Ln = Tm ( 6 )), respectively. The reaction of 2 with LuCl₃(THF)₃ yields [(1‐C₉H₆)SiMe₂(1‐C₉H₅CH₂CH₂NMe₂‐3)]LuCl ( 7 ). Compound 4 reacts with LiMe to give the corresponding alkyl derivative [(C₅H₂ ^tBu‐3‐Me‐5)SiMe₂(1‐C₉H₅CH₂CH₂NMe₂‐3)]Sm(CH₃) ( 8 ). The new complexes were characterized by elemental analyses, MS spectrometry, and NMR spectroscopy. The molecular structures of 5 and 6 were determined by single crystal X‐ray diffraction.     

Mono‐ and Dinuclear Heteroleptic Cobalt Complexes with α‐Diimine and Polyarene Ligands

Reactions of the dimeric cobalt complex [(L^?Co)₂] ( 1 , L=[(2,6‐iPr₂C₆H₃)NC(Me)]₂) with polyarenes afforded a series of mononuclear and dinuclear complexes: [LCo(η⁴‐anthracene)] ( 2 ), [LCo(μ‐η⁴:η⁴‐naphthalene)CoL] ( 3 ), and [LCo(μ‐η⁴:η⁴‐phenanthrene)CoL] ( 4 ). The pyrene complexes [{Na₂(Et₂O)₂}{LCo(μ‐η³:η³‐pyrene)CoL}] ( 5 ) and [{Na₂(Et₂O)₃}{LCo(η³‐pyrene)}] ( 6 ) were obtained by treating precursor 1 with pyrene followed by reduction with Na metal. These complexes contain three potential redox active centers: the cobalt metal and both α‐diimine and polyarene ligands. Through a combination of X‐ray crystallography, EPR spectroscopy, magnetic susceptibility measurement, and DFT computations, the electronic configurations of these complexes were studied. It was determined that complexes 2 – 4 have a high‐spin Co^I center coupled with a radical α‐diimine ligand and a neutral polyarene ligand. Whereas, the ligand L in complexes 5 and 6 has been further reduced to the dianion, the cobalt remains in a formal (I) oxidation state, and the pyrene molecule is either neutral or monoanionic.     

Phosphido‐diphosphine pincer group 3 complexes as efficient initiators for lactide polymerization

New Group 3 metal complexes of the type [LM(CH₂SiMe₃)₂(THF)_n] supported by tridentate phosphido‐diphosphine ligands [(o‐C₆H₄PR₂) ₂ PH; L1‐H : R = iPr; L2‐H : R = Ph] have been synthesized by reaction of L1‐H and L2‐H with [M(CH₂SiMe₃)₃(THF)₂)] (M = Y and Sc). All the new complexes [(o‐C₆H₄PR₂) ₂ PM(CH₂SiMe₃)₂(THF)_n] [M = Y, R = iPr (1), R = Ph (2); M = Sc, R = iPr (3), R = Ph (4)] were studied as initiators for the ring opening polymerization of lactide. The yttrium complexes ( 1 and 2 ) exhibited high activity and good polymerization control, shown by the linear fits in the plot of number‐averaged molecular weight (M_n) versus the percentage conversion and versus the monomer/initiator ratio and by the low polydispersity index values. Interestingly, very good molar‐mass control was observed even when L ‐Lactide was polymerized in the absence of solvent at 130 °C. A good molar‐mass control but lower activities were observed in the polymerization reaction of lactide promoted by the analogous scandium complexes 3 and 4 . © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1374–1382, 2010     

Yttrium bis(alkyl) and bis(amido) complexes bearing N,O multidentate ligands. Synthesis and catalytic activity towards ring‐opening polymerization of L‐lactide

Methoxy‐modified β‐diimines HL ¹ and HL ² reacted with Y(CH₂SiMe₃)₃(THF)₂ to afford the corresponding bis(alkyl)s [L¹Y(CH₂SiMe₃)₂] ( 1 ) and [L²Y(CH₂SiMe₃)₂] ( 2 ), respectively. Amination of 1 with 2,6‐diisopropyl aniline gave the bis(amido) counterpart [L¹Y{N(H)(2,6‐iPr₂? C₆H₃)}₂] ( 3 ), selectively. Treatment of Y(CH₂SiMe₃)₃(THF)₂ with methoxy‐modified anilido imine HL ³ yielded bis(alkyl) complex [L³Y(CH₂SiMe₃)₂(THF)] ( 4 ) that sequentially reacted with 2,6‐diisopropyl aniline to give the bis(amido) analogue [L³Y{N(H)(2,6‐iPr₂? C₆H₃)}₂] ( 5 ). Complex 2 was “base‐free” monomer, in which the tetradentate β‐diiminato ligand was meridional with the two alkyl species locating above and below it, generating tetragonal bipyramidal core about the metal center. Complex 3 was asymmetric monomer containing trigonal bipyramidal core with trans‐arrangement of the amido ligands. In contrast, the two cis‐located alkyl species in complex 4 were endo and exo towards the O,N,N tridentate anilido‐imido moiety. The bis(amido) complex 5 was confirmed to be structural analogue to 4 albeit without THF coordination. All these yttrium complexes are highly active initiators for the ring‐opening polymerization of L ‐LA at room temperature. The catalytic activity of the complexes and their “single‐site” or “double‐site” behavior depend on the ligand framework and the geometry of the alkyl (amido) species in the corresponding complexes. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5662–5672, 2007     

Direct Evidence for a [4+2] Cycloaddition Mechanism of Alkynes to Tantallacyclopentadiene on Dinuclear Tantalum Complexes as a Model of Alkyne Cyclotrimerization

A dinuclear tantalum complex, [Ta₂Cl₆(μ‐C₄Et₄)] ( 2 ), bearing a tantallacyclopentadiene moiety, was synthesized by treating [(η²‐EtC?CEt)TaCl₃(DME)] ( 1 ) with AlCl₃. Complex 2 and its Lewis base adducts, [Ta₂Cl₆(μ‐C₄Et₄)L] (L=THF ( 3 a ), pyridine ( 3 b ), THT ( 3 c )), served as more active catalysts for cyclotrimerization of internal alkynes than 1 . During the reaction of 3 a with 3‐hexyne, we isolated [Ta₂Cl₄(μ‐η⁴:η⁴‐C₆Et₆)(μ‐η²:η²‐EtC?CEt)] ( 4 ), sandwiched by a two‐electron reduced μ‐η⁴:η⁴‐hexaethylbenzene and a μ‐η²:η²‐3‐hexyne ligand, as a product of an intermolecular cyclization between the metallacyclopentadiene moiety and 3‐hexyne. The formation of arene complexes [Ta₂Cl₄(μ‐η⁴:η⁴‐C₆Et₄Me₂)(μ‐η²:η²‐Me₃SiC?CSiMe₃)] ( 7 b ) and [Ta₂Cl₄(μ‐η⁴:η⁴‐C₆Et₄RH)(μ‐η²:η²‐Me₃SiC?CSiMe₃)] (R=nBu ( 8 a ), p‐tolyl ( 8 b )) by treating [Ta₂Cl₄(μ‐C₄Et₄)(μ‐η²:η²‐Me₃SiC?CSiMe₃)] ( 6 ) with 2‐butyne, 1‐hexyne, and p‐tolylacetylene without any isomers, at room temperature or low temperature were key for clarifying the [4+2] cycloaddition mechanism because of the restricted rotation behavior of the two‐electron reduced arene ligands without dissociation from the dinuclear tantalum center.     

Synthesis and Structures of Homoleptic Methyl‐ and Phenylthiomethylaluminium Complexes [Al(CH2SR)3](R = Me,Ph)

Sulfur‐substituted methylmercury compounds [Hg(CH₂SR)₂]( 1a, R = Me; 1b, R = Ph ) react with aluminium amalgam in refluxing toluene with transmetallation to give homoleptic tris(thiomethyl)aluminium complexes [Al(CH₂SR)₃]( 2a, R = Me; 2b, R = Ph ) (degree of conversion: >80%, isolated yields: 2a 63%, 2b 41%). Their identities were confirmed by NMR spectros‐copy (¹H, ¹³C) and X‐ray crystal structure analyses. In crystals of compound 2a the aluminium atoms possess a trigonal‐bipyramidal arrangement with the coordination polyhedron defined by three carbon and two sulfur atoms. Two of the three CH₂SMe ligands are bridging ligands (μ‐η²; 1kC:2kS), the third one is terminal bound (η¹; kC). The structure is polymeric. Crystals are threaded by helical chains built up of six‐membered Al₂C₂S₂ rings. Crystals of 2b are built up of centrosymmetrical dimers with six‐membered Al₂C₂S₂ rings having bridging CH₂SPh ligands (μ‐η²; 1kC:2kS). On each Al atom two terminal (η¹; kC)CH₂SPh ligands are bound. They exhibit quite different Al‐C‐S angles (116.7(4) and 106.5(3)?). Similar values (114.32115.7? and 109.52109.9?) were found in ab initio calculations of model compounds [{Al(CH₂SR)₃}₂]( 3a, R=H; 3b, R=Me; 3c, R=CH=CH₂ ). A conformational energy diagram for rotation of one of the terminal CH₂SH ligand in the parent compound 3a around the Al‐C bond is discussed in terms of repulsive interactions of lone electron pairs of sulfur atoms.     

Versatile Reactivity of Scorpionate‐Anchored Yttrium?Dialkyl Complexes towards Unsaturated Substrates

A series of unusual chemical‐bond transformations were observed in the reactions of high active yttrium? dialkyl complexes with unsaturated small molecules. The reaction of scorpionate‐anchored yttrium? dibenzyl complex [Tp^Me2Y(CH₂Ph)₂(thf)] ( 1 , Tp^Me2=tri(3,5‐dimethylpyrazolyl)borate) with phenyl isothiocyanate led to C?S bond cleavage to give a cubane‐type yttrium–sulfur cluster, {Tp^Me2Y(μ₃‐S)}₄ ( 2 ), accompanied by the elimination of PhN?C(CH₂Ph)₂. However, compound 1 reacted with phenyl isocyanate to afford a C(sp³)? H activation product, [Tp^Me2Y(thf){μ‐η¹:η³‐OC(CHPh)NPh}{μ‐η³:η²‐OC(CHPh)NPh}YTp^Me2] ( 3 ). Moreover, compound 1 reacted with phenylacetonitrile at room temperature to produce γ‐deprotonation product [(Tp^Me2)₂Y]⁺[Tp^Me2Y(N=C?CHPh)₃]^? ( 6 ), in which the newly formed N?C?CHPh ligands bound to the metal through the terminal nitrogen atoms. When this reaction was carried out in toluene at 120 °C, it gave a tandem γ‐deprotonation/insertion/partial‐Tp^Me2‐degradation product, [(Tp^Me2Y)₂(μ‐Pz)₂{μ‐η¹:η³‐NC(CH₂Ph)CHPh}] ( 7 , Pz=3,5‐dimethylpyrazolyl).     

Alternating copolymerization of cyclohexene oxide and carbon dioxide catalyzed by noncyclopentadienyl rare‐earth metal bis(alkyl) complexes

The syntheses of several dialkyl complexes based on rare‐earth metal were described. Three β‐diimine compounds with varying N‐aryl substituents (HL¹=(2‐CH₃O(C₆H₄))N?C(CH₃)CH?C(CH₃)NH(2‐CH₃O(C₆H₄)), HL² = (2,4,6‐(CH₃)₃ (C₆H₂))N?C(CH₃)CH?C(CH₃)NH(2,4,6‐(CH₃)₃(C₆H₂)), HL³ = PhN?C(CH₃)CH(CH₃) NHPh) were treated with Ln(CH₂SiMe₃)₃(THF)₂ to give dialkyl complexes L¹Ln (CH₂SiMe₃)₂ (Ln = Y ( 1a ), Lu ( 1b ), Sc ( 1c )), L²Ln(CH₂SiMe₃)₂(THF) (Ln = Y ( 2a ), Lu ( 2b )), and L³Lu(CH₂SiMe₃)₂(THF) (3). All these complexes were applied to the copolymerization of cyclohexene oxide (CHO) and carbon dioxide as single‐component catalysts. Systematic investigation revealed that the central metal with larger radii and less steric bulkiness were beneficial for the copolymerization of CHO and CO₂. Thus, methoxy‐modified β‐diiminato yttrium bis(alkyl) complex 1a , L¹Y(CH₂SiMe₃)₂, was identified as the optimal catalyst, which converted CHO and CO₂ to polycarbonate with a TOF of 47.4 h^?1 in 1,4‐dioxane under a 15 bar of CO₂ atmosphere (T_p=130 °C), representing the highest catalytic activity achieved by rare‐earth metal catalyst. The resultant copolymer contained high carbonate linkages (>99%) with molar mass up to 1.9 × 10⁴ as well as narrow molar mass distribution (M_w/M_n = 1.7). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6810–6818, 2008     

Cationic Allyl Complexes of the Rare‐Earth Metals: Synthesis,Structural Characterization,and 1,3‐Butadiene Polymerization Catalysis

Monocationic bis‐allyl complexes [Ln(η³‐C₃H₅)₂(thf)₃]⁺[B(C₆X₅)₄]^? (Ln=Y, La, Nd; X=H, F) and dicationic mono‐allyl complexes of yttrium and the early lanthanides [Ln(η³‐C₃H₅)(thf)₆]²⁺[BPh₄]₂^? (Ln=La, Nd) were prepared by protonolysis of the tris‐allyl complexes [Ln(η³‐C₃H₅)₃(diox)] (Ln=Y, La, Ce, Pr, Nd, Sm; diox=1,4‐dioxane) isolated as a 1,4‐dioxane‐bridged dimer (Ln=Ce) or THF adducts [Ln(η³‐C₃H₅)₃(thf)₂] (Ln=Ce, Pr). Allyl abstraction from the neutral tris‐allyl complex by a Lewis acid, ER₃ (Al(CH₂SiMe₃)₃, BPh₃) gave the ion pair [Ln(η³‐C₃H₅)₂(thf)₃]⁺[ER₃(η¹‐CH₂CH?CH₂)]^? (Ln=Y, La; ER₃=Al(CH₂SiMe₃)₃, BPh₃). Benzophenone inserts into the La? C_allyl bond of [La(η³‐C₃H₅)₂(thf)₃]⁺[BPh₄]^? to form the alkoxy complex [La{OCPh₂(CH₂CH?CH₂)}₂(thf)₃]⁺[BPh₄]^?. The monocationic half‐sandwich complexes [Ln(η⁵‐C₅Me₄SiMe₃)(η³‐C₃H₅)(thf)₂]⁺[B(C₆X₅)₄]^? (Ln=Y, La; X=H, F) were synthesized from the neutral precursors [Ln(η⁵‐C₅Me₄SiMe₃)(η³‐C₃H₅)₂(thf)] by protonolysis. For 1,3‐butadiene polymerization catalysis, the yttrium‐based systems were more active than the corresponding lanthanum or neodymium homologues, giving polybutadiene with approximately 90 % 1,4‐cis stereoselectivity.