Yttrium Alkyl Research Articles

Versatility of a diamidosilylether ligand supporting yttrium complexes: Synthesis, structure and reactivity

Yttrium alkyl complex [NONDippY(CH2SiMe3)(THF)], 1 (NONDipp = (DippNSiMe2)2O, Dipp = 2,6-iPr-C6H3) can be prepared in high yields by a σ-bond metathesis reaction between [Y(CH2SiMe3)3(THF)2] and the free bis(aminosilyl)ether. The reaction of 1 with one equivalent of PhSiH3 generates the hydride bridged yttrium dimer [μ-NONDippY(μ-H)(THF)]22, however, each diamidosilylether ligand does not chelate each yttrium centre but instead bridges to both yttrium atoms in a “flyover” fashion. This ligand rearrangement maybe reversed by the addition of a strong Lewis base to give the dimeric yttrium hydride [NONDippY(μ-H)(DMAP)]23, where each diamidosilylether ligand now chelate to each yttrium center respectively. The effect of the different diamidosilylether bonding modes on the reactivity of the yttrium complexes is examined with heterocumulenes.

Yttrium tris(trimethylsilylmethyl) complexes grafted onto MCM-48 mesoporous silica nanoparticles.

A series of tris(trimethylsilylmethyl) yttrium donor adduct complexes was synthesized and fully characterized by X-ray diffraction, 1H/13C/29Si/31P/89Y heteronuclear NMR and FTIR spectroscopies as well as elemental analyses. Treatment of Y(CH2SiMe3)3(thf)x with various donors Do led to complete (Do = TMEDA, DMAP) and partial displacement of THF (Do = NHCiPr, DMPE). Exceptionally large 89Y NMR shifts to low field were observed for the new complexes. Complexes Y(CH2SiMe3)3(tmeda) and Y(CH2SiMe3)3(dmpe)(thf) were chosen to perform surface organometallic chemistry, due to a comparatively higher thermal stability and the availability of the 31P nucleus as a spectroscopic probe, respectively. Mesoporous nanoparticles of the MCM-48-type were synthesized and used as a 3rd generation silica support. The parent and hybrid materials were characterized using X-ray powder diffraction, solid-state-NMR spectroscopy, DRIFTS, elemental analyses, N2-physisorption, and scanning electron microscopy (SEM). The presence of surface-bound yttrium alkyl moieties was further proven by the reaction with carbon dioxide. Quantification of the surface silanol population by means of HN(SiHMe2)2-promoted surface silylation is shown to be superior to titration with lithium alkyl LiCH2SiMe3.

Early Metal Di(pyridyl) Pyrrolide Complexes with Second Coordination Sphere Arene-π Interactions: Ligand Binding and Ethylene Polymerization.

Early metal complexes supported by hemilabile, monoanionic di(pyridyl) pyrrolide ligands substituted with mesityl and anthracenyl groups were synthesized to probe the possibility of second coordination sphere arene−π interactions with ligands with potential for allosteric control in coordination chemistry, substrate activation, and olefin polymerization. Yttrium alkyl, indolide, and amide complexes were prepared and structurally characterized; close contacts between the anthracenyl substituents and Y-bound ligands are observed in the solid state. Titanium, zirconium, and hafnium tris(dimethylamido) complexes were synthesized, and their ethylene polymerization activity was tested. In the solid state structure of one of the Ti tris(dimethylamido) complexes, coordination of Ti to only one of the pyridine donors is observed pointing to the hemilabile character of the di(pyridyl) pyrrolide ligands.

Self-Activated Coordination Polymerization of Alkoxystyrenes by a Yttrium Precursor: Stereocontrol and Mechanism

Coordination–insertion polymerization of polar vinyl monomers has always been a challenging subject since the Lewis basic polar groups are usually poisonous to the Lewis acidic metal centers of the catalysts. In this paper, we report the coordination polymerization of the unmasked polar alkoxystyrenes (AOS), including o-methoxystyrene (oMOS), o-ethoxystyrene (oEOS), o-n-propoxystyrene (oPOS), o-n-butoxystyrene (oBuOS), o-benzyloxystyrene (oBnOS), and 5-phenyl-2-methoxystyrene (Ph-MOS), by using the cationic quinolyl anilido yttrium alkyl species that was inert to styrene polymerization. In addition, the styrenic monomer bearing two polar groups, 4-fluoro-2-methoxystyrene (FMOS), was also polymerized since the presence of the additional polar fluorine group did not block the interaction between the ortho-oxygen and yttrium center. In contrast, the o-(tert-butyldimethyl)silyloxystyrene (oSiOS), where the ortho-oxygen atom was prevented from coordinating to the yttrium center by the sterically bulky −SiMe2tB...

Origin of Product Selectivity in Yttrium-Catalyzed Benzylic C–H Alkylations of Alkylpyridines with Olefins: A DFT Study

DFT studies have been conducted for the direct benzylic C(sp3)–H alkylation of alkylpyridines with olefins catalyzed by a cationic half-sandwich yttrium alkyl complex. It has been found that, in th...

Highly cis‐1,4 Selective Living Polymerization of Unmasked Polar 2‐(2‐Methylidenebut‐3‐enyl)Furan and Diels–Alder Addition

The polymerization of a new polar diene-based monomer 2-(2-methylidenebut-3-enyl)furan (MBEF) without masking is achieved by using the bis(phosphino)carbazoleide-ligated yttrium (Y) alkyl complex upon the activation of [Ph3 C][B(C6 F5 )4 ]. Under mild conditions, the polymerizations under the monomer-to-Y ratios ranging from 100:1 to 500:1 perform fluently in high yields. The afforded polydienes bearing pendant terminal furan groups have high cis-1,4-regularity up to 98.6% and molecular weights close to the theoretic values and narrow polymer dispersity index(PDI) (1.13-1.17) suggesting a livingness polymerization mode. In addition, this novel polydiene is an excellent building block for preparing functional rubber materials. For example, via Diels-Alder addition of furan groups under mild conditions, hydroxyl groups are successfully introduced on the side chains efficiently in a 75% conversion. Furthermore, the copolymerization of polar MBEF and nonpolar isoprene is also successfully realized by the bis(phosphino) carbazoleide-ligated scandium analog to access furan-modified cis-1,4 (>97%) polyisoprene with different MBEF contents (5.3%, 8.7%).

Facile Construction of Yttrium Pentasulfides from Yttrium Alkyl Precursors: Synthesis, Mechanism, and Reactivity.

Treatment of the yttrium dialkyl complex TpMe2Y(CH2Ph)2(THF) (TpMe2 = tri(3,5 dimethylpyrazolyl)borate, THF = tetrahydrofuran) with S8 in a 1:1 molar ratio in THF at room temperature afforded a yttrium pentasulfide TpMe2Y(κ4-S5) (THF) (1) in 93% yield. The yttrium monoalkyl complex TpMe2CpYCH2Ph(THF) reacted with S8 in a 1:0.5 molar ratio under the same conditions to give another yttrium pentasulfide [(TpMe2)2Y]+[Cp2Y(κ4-S5)]- (10) in low yield. Further investigations indicated that the S52- anion facilely turned into the corresponding thioethers or organic disulfides, and released the redundant S8, when it reacted with some electrophilic reagents. The mechanism for the formation of the S52- ligand has been investigated by the controlling of the reaction stoichiometric ratios and the stepwise reactions.

Highly Cis-1,4-Selective Living Polymerization of 3-Methylenehepta-1,6-diene and Its Subsequent Thiol–Ene Reaction: An Efficient Approach to Functionalized Diene-Based Elastomer

Living polymerization of 3-methylenehepta-1,6-diene (MHD) catalyzed by bis(phosphino)carbazoleide-ligated yttrium alkyl complex afforded a new product bearing pendant terminal vinyl groups with high stereotacticity (cis-1,4-selectivity up to 98.5%), proved by the NMR (1H, 13C, and 1D ROESY) spectroscopic analyses, which demonstrates overwhelmingly favorable chemoselectivity toward conjugated diene over α-olefin moieties. High cis-1,4 random copolymers of MHD and isoprene could also be obtained with pendant vinyl groups ranging from 10% to 90%. These vinyl groups in every chain unit can be cleanly and quantitatively converted into various functionalities via light-mediated thiol–ene reaction, resulting in homo- and copolymers of various functional butadiene derivatives, which display versatile thermal properties.

Selective Intermolecular C–H Bond Activation: A Straightforward Synthetic Approach to Heteroalkyl Yttrium Complexes Containing a Bis(pyrazolyl)methyl Ligand

The reactions of bis(pyrazolyl)methanes CH2(C3HN2R2-3,5)2 (R = Me, tBu) with Y(CH2SiMe3)3(THF)2 and LY(CH2SiMe3)2(THF)n (L = amidopyridinate (Ap′), amidinate (Amd), tridentate amidinate bearing 2-methoxyphenyl pendant in a side arm (AmdOMe) and pentamethylcyclopentadienyl (Cp*); n = 0, 1) were investigated. CH2(C3HN2tBu2-3,5)2 turned out to be inert in these reactions, while less bulky CH2(C3HN2Me2-3,5)2 easily undergoes metalation by yttrium alkyls. The reaction of Y(CH2SiMe3)3(THF)2 with CH2(C3HN2Me2-3,5)2 regardless of the molar ratio of the reagents affords a homoleptic tris(alkyl) species, Y[CH(C3HN2Me2-3,5)2]3 (1). However, the reactions of equimolar amounts of LY(CH2SiMe3)2(THF)n and CH2(C3HN2Me2-3,5)2 occur selectively with replacement of a sole CH2SiMe3 fragment and afford the related heteroalkyl complexes LY(CH2SiMe3)[CH(C3HN2Me2-3,5)2](THF)n (L = Ap′, n = 1 (6); Amd, n = 0 (7); AmdOMe, n = 1 (8); Cp*, n = 1 (9)) in good yields. The second equivalent of CH2(C3HN2Me2-3,5)2 does not react with heteroalkyl yttrium complexes. The X-ray studies revealed that in complexes 1 and 6–9 the bis(pyrazolyl)methyl ligands are bound to the yttrium centers in a similar fashion via one covalent Y–C and two coordination Y–N bonds. Thermal decomposition of complexes 6–9 (C6D6, 80 °C) as evidenced by 1H NMR spectroscopy resulted in SiMe4 elimination, while no activation of the C–H bonds of bis(pyrazolyl)methyl ligands was detected. When 6 was treated with an equimolar amount of PhSiH3, only the YCH2SiMe3 bond selectively underwent σ-bond metathesis and a dimeric yttrium alkyl-hydrido complex, {Ap′Y[CH(C3HN2Me2-3,5)2](μ2-H)}2 (10), was formed. The reaction of 6 with 2,6-diisopropylaniline also resulted in the selective protonation of the YCH2SiMe3 bond and cleanly afforded alkyl-anilido complex Ap′Y(NHC6H3iPr2-2,6)[CH(C3HN2Me2-3,5)2](THF) (11). The ternary catalytic systems 6–9/borate/AliBu3 (borate = [HNMe2Ph][B(C6F5)4], [Ph3C][B(C6F5)4]; [Ln]:[borate]:[AliBu3] = 1:1:10) demonstrated moderate catalytic activity in isoprene polymerization; they allow quantitative conversion into polymer of up to 1000 equiv of monomer in 2–4 h. The best activity and 1,4-cis selectivity (83.5%) were demonstrated by amidinato complex 8.

Polymerization of conjugated dienes with a homogeneous Ziegler–Natta catalytic system based on a carbon-bridged bis(phenolate) yttrium alkyl complex

1,3-Diene polymerization with some controllable characteristics was carried out and catalyzed by a triisobutylaluminum modified MAO activated complex [(EDBP)Y(CH2SiMe3)(THF)3].

Yttrium-Alkyl Complexes Supported by a Ferrocene-Based Phosphinimine Ligand

The synthesis and characterization of two yttrium alkyl complexes supported by a bisphosphinimine ferrocene ligand, NPfc (1,1′-di(2,4-di-tert-butyl-6-diphenylphosphiniminophenoxy)ferrocene), were accomplished. Although (NPfc)Y(CH2Ph) and (NPfc)Y(CH2SiMe3) could be structurally characterized, these compounds are thermally sensitive and decompose at ambient temperature within hours. Their characterization was accomplished by NMR spectroscopy, electrochemical measurements, and elemental analysis. Reactivity studies were also carried out; however, the lack of prolonged thermal stability at ambient temperature of these molecules led to decomposition before a clean transformation to reaction products could be observed.

Metallacyclic yttrium alkyl and hydrido complexes: synthesis, structures and catalytic activity in intermolecular olefin hydrophosphination and hydroamination.

Metallacyclic neutral and ionic yttrium alkyl complexes coordinated by a dianionic ene-diamido ligand ([2,6-iPr2C6H3NC(Me)=C(Me)NC6H3iPr2-2,6] = L(1)) [L(1)]Y(CH2SiMe3)(THF)2 (2), {[L(1)]Y(CH2SiMe3)2}(-){Li(THF)4}(+) (3), [L(1)]Y(OEt2)(μ-Me)2Li(TMEDA) (4) were synthesized using a salt-metathesis approach starting from the related chloro complex [L(1)]Y(THF)2(μ-Cl)2Li(THF)2 (1) in 70, 85 and 72% yields respectively. The reactions of 2 with H2 or PhSiH3 afford the dimeric hydride {[L(1)]Y(THF)(μ-H)}2(μ-THF) (5) containing two μ-bridging hydrido and one μ-bridging THF ligands (91 and 85% yields). The X-ray studies of complexes 2, 3 and 5 revealed η(2)-coordination of the C=C fragment of an ene-diamido ligand to a Y cation. DFT calculations were carried out to give an insight into the metal-ligand bonding and especially the interaction between the metal and the ene-diamido ligand. The observed bonding of the ene-diamido fragment is found to reflect the acidity of the metal center in the complex that is partially overcome by a better donation from the double bond (better overlap with an empty d orbital at the yttrium center). The treatment of complex 4 with DME resulted in the C-O bond cleavage of DME and afforded a three nuclear methoxide oxide complex [{[L(1)]Y}3(μ(2)-OMe)3(μ(3)-O)](2-)[Li(DME)3](+)2 (6). Complexes 2, 3, 5 and 7 proved to be efficient precatalysts for the intermolecular hydrophosphination of styrene, 4-vinylpyridine, and 1-nonene with PhPH2 and Ph2PH as well as hydroamination of styrene and pyrrolidine.

Cationic Tropidinyl Scandium Catalyst: A Perfectly Acceptable Substitute for Cationic Half-Sandwich Scandium Catalysts in cis-1,4-Polymerization of Isoprene and Copolymerization with Norbornene

Different nonmetallocene rare earth metal alkyl complexes such as monotropidinyl (Trop) scandium dialkyl complex (Trop)Sc(CH2SiMe3)2(THF) (1), ditropidinyl yttrium alkyl complex (Trop)2Y(CH2SiMe3)(THF) (3) as well as binuclear lutetium alkyl complex bearing one tetradentate dianionic 6-N-methyl-1,4-cycloheptadienyl (NMCH) ligand [(NMCH)Lu(CH2SiMe3)(THF)]2 (2) have been synthesized in high yields via one-pot acid–base reaction by using of the tris(trimethylsilylmethyl) rare earth metal complexes with the readily available natural product tropidine. The polymerization experiments indicate that the monotropidinyl scandium dialkyl complex 1 displays reactivity akin to that of the analogous monocyclopentadienyl scandium dialkyl complexes. In the presence of activator and a small amount of AlMe3, complex 1 exhibits similar activities (up to 1.6 × 106 g molSc–1 h–1) but higher cis-1,4-selectivities (up to 100%) than (C5H5)Sc(CH2SiMe3)2(THF) (cis-1,4-selectivity as 95%) in the isoprene polymerization, yielding the pure cis-1,4-PIPs with moderate molecular weights (Mn = 0.5–11.2 × 104 g/mol) and bimodal molecular weight distributions (Mw/Mn = 1.48–6.07). Moreover, the complex 1/[Ph3C][B(C6F5)4/AliBu3 ternary system also shows good comonomer incorporation ability in the copolymerization of isoprene and norbornene similar to the [C5Me4(SiMe3)]Sc(η3-CH2CHCH2)2/activator binary system, affording the random isoprene/norbornene copolymers with a wide range of isoprene contents around 57–91 mol % containing cis-1,4 configuration up to 88%.

Alkane Elimination Reactions between Yttrium Alkyls and Tungsten Hydrides

AbstractAlkane elimination of the yttrium monoalkyl [Cp2Y(CH2SiMe3)(thf)] (Cp = cyclopentadienyl, thf = tetrahydrofuran, Me = methyl) with the tungsten hydrido carbonyl complex [HW(CO)3Cp] in THF gave rise to the trinuclear complex [{CpW(CO)2(μ‐CO)}2YCp(thf)3] (1). In the course of the reaction, one Cp ligand per yttrium was redistributed, thus leading to the formation of [Cp3Y] as a side product. To avoid the observed ligand redistribution, other solvents were investigated. The reaction of [Cp2Y(CH2SiMe3)(thf)] with [HW(CO)3Cp] in acetonitrile afforded the dinuclear complex [{CpW(CO)2(μ‐CO)}YCp2(NCMe)2] (2). The reaction of the yttrium dialkyl complex [Y(CH2SiMe3)2(OC6H3tBu2‐2,6)(thf)2] with [HW(CO)3Cp] in toluene gave the polymeric compound [{CpW(CO)2(μ‐CO)}2Y(OC6H3tBu2‐2,6)]n (3), whereas reaction in THF gave the molecular compound [{CpW(CO)2(μ‐CO)}2Y(OC6H3tBu2‐2,6)(thf)3] (4). The reaction of the yttrium trialkyl complex [Y(CH2SiMe3)3(thf)2] with [HW(CO)3Cp] in THF led to the formation of [{CpW(CO)2(μ‐CO)}3Y(thf)5] (5). Reaction of [(Ap*)Y(CH2SiMe3)2(thf)] {Ap*H = (2,6‐diisopropylphenyl)‐[6‐(2,4,6‐triisopropylphenyl)pyridin‐2‐yl]amine} with [HW(CO)3Cp] in THF was unexpectedly accompanied by the loss of the Ap* ligand and resulted in the formation of 5 too. Isocarbonyl linkage is the dominating interaction between the Y and the W complex moieties. All compounds were characterized by NMR and IR spectroscopy as well as elemental analysis. Complexes 1, 2, 4, and 5 were additionally characterized by X‐ray crystal structure analysis (X‐ray diffraction).

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(Me2) Y(CH2 Ph)2 (THF)] reacted with 1-methylimidazole in 1:2 molar ratio to give a rare hexanuclear 24-membered rare-earth metallomacrocyclic compound [Tp(Me2) Y(μ-N,C-Im)(η(2) -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(Me2) Y(CH2 Ph)2 (THF)] reacted with two equivalents of 1-methylbenzimidazole to afford a C-C coupling/ring-opening/C-C coupling product [Tp(Me2) Y{η(3) -(N,N,N)-N(CH3 )C6 H4 NHCHC(Ph)CN(CH3 )C6 H4 NH}] (2). Further investigations indicated that [Tp(Me2) Y(CH2 Ph)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-η(2) :η(1) -SC6 H4 N(CHCHPh)](THF)}2 (3). Moreover, the mixed Tp(Me2) /Cp yttrium monoalkyl complex [(Tp(Me2) )CpYCH2 Ph(THF)] reacted with two equivalents of 1-methylimidazole in THF at room temperature to afford a trinuclear yttrium complex [Tp(Me2) CpY(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(Me2) Y(Im-Tp(Me2) )] (7; Im-Tp(Me2) =1-methyl-imidazolyl-Tp(Me2) ) and [Cp3 Y(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.

Reactivity of Scorpionate-Anchored Yttrium Alkyl Primary Amido Complexes toward Carbodiimides. Insertion Selectivity of Y–NHAr and Y–CH2Ph Bonds

The TpMe2-supported yttrium dialkyl TpMe2Y(CH2Ph)2(THF) (TpMe2 = tri(3,5-dimethylpyrazolyl)borate) reacted with 1 equiv of ArNH2 in THF at room temperature to afford the yttrium alkyl primary amido complexes TpMe2YNHAr(CH2Ph)(THF) (Ar = Ph (1), C6H3-iPr2-2,6 (2)) in 84% and 88% isolated yields, respectively. Complex 1 reacted with iPrN═C═NiPr in THF at room temperature to give a yttrium dianionic guanidinate complex, TpMe2Y[(iPrN)2C═NPh](THF)2 (3, 74%). However, the reaction of 1 with ArN═C═NAr (Ar = C6H3-iPr2-2,6) in the same conditions produced a Y–C bond insertion product, TpMe2Y[(ArN)2CCH2Ph](NHPh) (4, 87%). Moreover, treatment of 2 with 1 equiv of iPrN═C═NiPr in THF at room temperature afforded two yttrium complex, TpMe2Y[(iPrN)C═NAr](THF) (5) and TpMe2Y[(iPrN)2CCH2Ph](NHAr) (6), in 58% and 19% isolated yields, respectively. These results indicated that carbodiimide can selectively insert into the Y–CH2Ph and Y–NHAr σ-bonds of TpMe2-supported yttrium alkyl primary amido complexes TpMe2YNHAr(CH2Ph)(THF), and this selectivity depends on the steric hindrance of the substituent groups R of cabodiimides and the primary amido ligands. All these new complexes were characterized by elemental analysis and spectroscopic methods, and their solid-state structures except 1 were also confirmed by single-crystal X-ray diffraction analysis.

1-Methyl Boratabenzene Yttrium Alkyl: A Highly Active Catalyst for Dehydrocoupling of Me2NH·BH3

Catalytic activity of rare-earth metal complexes for dehydrocoupling of Me2NH center dot BH3 is deeply ligand- and metal ion-dependent, and 1-methyl boratabenzene yttrium alkyl shows very high activity for the reaction (TOF > 1000 h(-1)). The transformati

Synthesis and Catalytic Isoprene Polymerization of Rare-Earth Alkyl Complexes Supported by An Arylimine-amidinate Ligand

Reaction of the arylimine-amidinate ligand (NNN)H (1) ((NNN)=(2-C(H)NDippC6H3NHC(Ph)NDipp), Dipp= 2,6-i-Pr2C6H3) with Ln(CH2SiMe3)3(THF)2 (Ln=Y, Sm) in n-hexane at -78 ℃ followed by stirring the mixture for 3 h at room temperature afforded (NNN)Ln(CH2SiMe3)2 (Ln=Y, 2; Ln=Sm, 3) in 75% and 50% yields after work up. 2 and 3 have been characterized by 1 H NMR, 13 C NMR, IR spectroscopy, elemental analysis. The molecular structure of 2 has been confirmed by X-ray analysis. Complexes 2 and 3 catalyzed the polymerization of isoprene in the presence of (Ph3C)(B(C6F5)4) (1 equiv.) and AlEt3 (10 equiv.) at 25 ℃. 2 converted 250 equivalents of isoprene into polyisoprene with a narrow molecular weight distribution (Mw/Mn=1.20) and a 3,4-rich microstructure (3,4-selectivity: 78%, rr=50%) in 12 h. A significant increase of 3,4-selectivity was observed in the presence of one equivalent of AlEt3 (3,4-selectivity: 87%). When i-Bu2AlH (10 equiv.) was used instead of AlEt3, the catalytic activity and selectivity did not change noticeably while the re- sulting polyisoprenes feature a broad molecular weight distribution (Mw/Mn=2.45). When the amounts of i-Bu2AlH de- creased from 5 to 1 equivalent, a significant increase of 3,4-selectivity and number-average molecular weight have been ob- served while the molecular distributions became small. The catalyst is active within a wide range of temperatures from low temperature to 40 ℃. At 40 ℃, a similar selectivity (3,4-selectivity: 78%, Mw/Mn=1.43) to that found at 25 ℃ but the increased reaction rate has been observed. High stereo- and regioselectivity and narrow molecular weight distributions were obtained at -20 ℃ (3,4-selectivity: 88%, rr=52%, Mw/Mn=1.15). The samarium alkyl 3 exhibited a high activity but low selectivity (25 ℃, 3 h, 3,4-selectivity: 67%, Mw/Mn=1.71) compared to the yttrium alkyl 2. Keywords rare-earth metal; alkyl complex; arylimine-amidine; isoprene polymerization; 3,4-selectivity

Reactivity of the Yttrium Alkyl Carbene Complex [Y(BIPM)(CH2C6H5)(THF)] (BIPM = {C(PPh2NSiMe3)2})2–: From Insertions, Substitutions, and Additions to Nontypical Transformations

The yttrium alkyl carbene complex [Y(BIPM)(CH2Ph)(THF)] (1; BIPM = {C(PPh2NSiMe3)2})2–) was treated with a series of unsaturated organic substrates, a bulky primary amine, and a group 1 metal alkyl to gauge and compare the reactivity of the Y═Ccarbene and Y–Calkyl bonds. Treatment of 1 with tert-butyl nitrile and 1-adamantyl azide gave the 1,2-migratory insertion products [Y(BIPM){NC(But)(CH2Ph)}(THF)] (2) and [Y(BIPM){N3Ad-1,Bn-3-κ2N1,3}(THF)] (3), respectively, with no reactivity observed at the Y═C double bond even when an excess of the relevant organic substrate was added. In contrast, the heteroallenes N,N′-dicyclohexylcarbodiimide and tert-butyl isocyanate reacted at both the Y═Ccarbeneand Y–Calkyl bonds of 1 to afford [Y{C(PPh2NSiMe3)2[C(NCy)2]-κ4C,N,N′,N″}{C(NCy)2(CH2Ph)-κ2N,N′}] (4) and [Y{C(PPh2NSiMe3)2[C(O)(NBut)]-κ4C,N,N′,O}{C(O)(NBut)(CH2Ph)-κ2N,O}] (5), respectively. 4 and 5 form regardless of the molar ratio of 1 to heteroallene, with no intermediates observed; thus, it is not clear if the [2 + 2]-cycloaddition or the 1,2-migratory insertion reaction occurs first. The addition of 2 equiv of tert-butyl isothiocyanate to 1 yields dimeric [Y(BIPMH){C(S)2(NBut)-1-κS,2-κN:μ,κS′}]2 (6), benzyl nitrile, and isobutylene by desulfurization and carbene-mediated deprotonation of a tert-butyl group of 1 equiv of heteroallene. The reaction between 1 and the bulky amine DippNH2 (Dipp = C6H3Pri2) gave [Y(BIPM)(NHDipp)(THF)] (7) by alkane elimination, with no reactivity observed at the Y═Ccarbene bond. Finally, the addition of benzylpotassium to 1 afforded the yttriate polymer [Y(BIPM)(μ-η1:η6-CH2Ph)(μ-η1:η2-CH2Ph)K]∞ (8) by a formal carbopotassiation across the Y═Ccarbene bond. Complexes 2–8 have been characterized by X-ray crystallography, multielement NMR spectroscopy, FTIR spectroscopy, and CHN microanalyses.

Reactivity of Scorpionate-Anchored Yttrium Alkyl Complex toward Organic Nitriles

The mixed TpMe2/Cp-supported yttrium monoalkyl (TpMe2)CpYCH2Ph(THF) (1) reacted with 1 equiv of PhCN in THF at room temperature to afford the imine–enamine tautomer (TpMe2)CpY(N(H)C(Ph)═CHPh)(THF) (2) and the insertion product (TpMe2)CpY(N═C(CH2Ph)Ph)(THF) (3), in 61% and 12% isolated yields, respectively. 2 further reacted with PhCN in toluene at 120 °C to give the N–H bond addition product (TpMe2)CpY(N(H)C(Ph)NC(Ph)═CHPh) (4). Treatment of 1 with 1 equiv of anthranilonitrile produced the dimer [(TpMe2)CpY(μ-NHC6H4CN)]2 (5). The monomer product (TpMe2)CpY(NHC6H4CN)(HMPA) (6) can be obtained through the coordination of HMPA (hexamethylphosphoric triamide). The reaction of 5 with 1 in THF at room temperature gave the cyano group insertion product [(TpMe2)CpY(THF)]2(μ-NHC6H4C(CH2Ph)═N) (7). However, this reaction under the heating conditions gave an unexpected rearrangement product, (TpMe2)CpY(THF)(η2-NHC6H4C(CH2Ph)═NH) (8). 5 further reacted with o-aminobenzonitrile at 120 °C to afford the nucleophilic addition/cyclization product TpMe2Y[κ3-(4-NH═(C8N2H4)(2-NHC6H4)](HMPA) (9), accompanied with the elimination of the Cp ring. These results indicated that the yttrium alkyl complex exhibits high activity toward organic nitriles and reveals some unusual transformations during the insertion process. All these new complexes were characterized by elemental analysis and spectroscopic methods, and their solid-state structures were also confirmed by single-crystal X-ray diffraction analysis.