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Abstract: Supported neodymium‐based Ziegler‐type catalysts are obtained by grafting homoleptic methylaluminate Nd(AlMe4)3 onto high‐surface silica materials including periodic mesoporous silicas MCM‐41, SBA‐15, and KIT‐6. Low [Et2AlCl]‐cocatalyst contents allow for the fabrication of polyisoprenes with ultrahigh molecular weight (UHMWPI). The synthetic rubbers display molecular weights as high as 3×106 g mol−1, polydispersity indices as low as 1.2, and microstructures with 99 % cis‐stereospecificity. Combined analysis of the organolanthanide/silica hybrid materials by nitrogen physisorption, FTIR and magic angle spinning NMR spectroscopies, and elemental (metal) analysis assist in elucidating the intrapore surface organometallic chemistry and suggest the formation of unprecedented organolanthanide species. [ABSTRACT FROM AUTHOR]

Two zirconium–organic frameworks were synthesized by exchanging the acetate ligands in [Zr12O8(OH)8(CH3COO)24] with polydentate linkers. Partial substitution of acetate groups by a phosphine based linker yielded a new porous framework with this unique dimeric Zr12 cluster unit as molecular building block. More exhaustive substitution of acetate resulted in cleavage of the Zr12 unit and formation of UiO-67. [ABSTRACT FROM AUTHOR]

Tetravalent zirconium complexes supported by tridentate bis-phenolate imidazolidin-2-ylidene (L1), imidazol-2-ylidene (L2) and benzimidazol-2-ylidene (L3) NHC ligands were synthesized and evaluated as precursors for the copolymerization of cyclohexene oxide (CHO) with CO2. While the reactivity of the imidazolidinium [H3L1] chloride salt with Zr(OiPr)4(HOiPr), and subsequent ligand exchanges with either (CH3)3SiCl or LiOiPr lead to a series of heteroleptic compounds (κ3-O,C,O-L1)Zr(X)2(THF) (X = Cl, OiPr), both imidazolium [H3L2] and benzimidazolium [H3L3] chloride salts give a mixture of homoleptic (κ3-O,C,O-NHC)2Zr and zwitterionic (κ2-O,O-HL)ZrCl2(OiPr) compounds along with traces or the absence of the heteroleptic intermediate (κ3-O,C,O-NHC)Zr(Cl)(OiPr)(THF). Such dissimilar reactivity between the unsaturated and saturated NHC ligands is predominantly ascribed to the increased acidity of azolium salts along with the π-donor strength of the Ccarbene in L2 and L3–Zr moieties. The reactivity with the more acidic azolium salts (H3L2/3) and the destabilized Zr–Xtrans to NHCcarbene bond results in a significant increase in the amount of homoleptic compounds generating HCl. The released HCl reacts preferentially with the heteroleptic intermediates having non-planar NHC ligands (i.e. L2/3) promoting the formation of zwitterionic complexes. The in situ deprotonation of the isolated zwitterionic (κ2-O,O-HL3)ZrCl2(OiPr) compound by using Ag2O gives the homoleptic complex as the major component along with a bimetallic hydroxo-bridged [(κ3-O,C,O-L3)Zr(μ-OH)(OiPr)]2 compound. Of particular interest is that only the heteroleptic NHC–Zr(iv) complexes were identified to be active and highly selective towards the copolymerization of CHO with CO2 independently of the co-catalysts used (both anionic and neutral) under mild conditions (PCO2 ＜ 1 bar, T = 60 °C), and gave atactic and completely alternating copolymers in a controlled manner (Mw/Mn≈ 1.3–1.8). In contrast, the isolated homoleptic, zwitterionic and bimetallic zirconium species were found to be inactive under similar reaction conditions. Although the activity found for NHC–Zr(iv) complexes is nearly of the same order of magnitude as that of the NHC–Ti(iv) analogues, these results are the first examples of tetravalent zirconium complexes achieving high selectivity (99% in PCHC) in the catalyzed copolymerization of CHO with CO2. [ABSTRACT FROM AUTHOR]

Titanium(iv) complexes bearing an unsubstituted tridentate bis(phenolate) N-heterocyclic carbene (NHC) were synthesized and structurally identified. While sterically unencumbered NHC–Ti(iv) complexes bearing chloro and alkoxy co-ligands tend to dimerize in solution and in solid-state, the use of a bulky aryloxy as co-ligand favors the monomeric species. Upon activation by onium salts, all these complexes were found to be highly selective towards the copolymerization of cyclohexene oxide (CHO) with CO2 under mild conditions (PCO2 ＜ 1 bar), albeit the sterically unencumbered NHC–Ti(iv) complexes are less stable and active than their structural analogues bearing bulkier substituents. [ABSTRACT FROM AUTHOR]

A new class of complexes based on titanium(IV) bearing a bisanionic mer-tridentate N-heterocyclic carbene ligand were investigated for the copolymerization of cyclohexene oxide with CO2. Upon addition of [PPN]X' salts, all complexes were found to be active and highly selective toward the formation of poly(cyclohexene oxide-alt-carbon dioxide). [ABSTRACT FROM AUTHOR]

Homoleptic rare-earth metal silylamide complexes Ln[N(SiMe3)2]3 (Ln = Y, La, Nd) were grafted onto a series of partially dehydroxylated periodic mesoporous silica (PMS) supports, SBA-15-500 (dp = 7.9 nm), SBA-15LP-500 (dp = 16.6 nm), and MCM-41-500 (dp = 4.1 nm). The hybrid materials Ln[N(SiMe3)2]3@PMS efficiently catalyze the intramolecular hydroamination/cyclization reaction of 2,2-dimethyl-4-penten-1-amine. Under the prevailing slurry conditions the metal size (Y> La > Nd), the pore size, and the particle morphology affect the catalytic performance. Material Y[N(SiMe3)2]3@SBA-15LR-500 displayed the highest activity (TOF = up to 420 h-1 at 60 °C), with the extralarge pores minimizing restrictive product inhibition and substrate diffusion effects. The catalytic activity of Y[N(SiMe3)2]3@SBA-15LP-500 is found to be much higher than that of the molecular counterpart (TOF = up to 54 h-1), and its recyclability is demonstrated. [ABSTRACT FROM AUTHOR]

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 °C (specific surface area as: 500 m2g−1; mesopore volume Vp: 1.06 cm3g−1; main pore diameter: 85 Å). The bimetallic materials [Ln(AlEt4)2]@KIT-6−500were 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 AlEt3@KIT-6−500since reaction of AlEt3with surface silanol groups is also a prominent reaction pathway when complexes [Ln(AlEt4)2]nare immobilized. Reaction of the Ln(ii) tetraalkylaluminates with tris(tert-butoxy)silanol HOSi(OtBu)3gave complexes Ln[(μ-OSi(OtBu)3)(μ-R)AlR2]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. [ABSTRACT FROM AUTHOR]

Silica and alumina supported tantalum and tungsten hydrides were tested in alkane metathesis, for comparison of their catalytic properties. In propane metathesis [W]–H/Al2O3 proves to be twice more efficient than the usual [Ta]–H/SiO2 catalyst which is still better than [Ta]–H/Al2O3 and [W]–H/SiO2. Tungsten based catalysts lead to a narrower distribution in the products selectivity and to a higher amount of linear products than [Ta]–H/SiO2. [W]–H/Al2O3 is also a better catalyst than [Ta]–H/SiO2 for butane metathesis but is less efficient with ethane. Whereas the results in the case of propane or butane can involve the higher initial activity and a lower deactivation of the tungsten catalyst, in the case of ethane, mechanistic or kinetic aspects can be envisaged in particular concerning the difficulty to dehydrogenate ethane into ethylene. [ABSTRACT FROM AUTHOR]

The reaction of [Ta(=CH(Bu)(CH2(Bu)3) or [Cp*Ta(CH3)4 with a silica partially dehydroxylated at 700 °C gives the corresponding monosiloxy surface complexes [(≡SiO)Ta(=CHtBu)(CH2tBu)2] and [(≡SiO)Ta(CH3)3Cp*] by eliminating a σ-bonded ligand as the corresponding alkane (H-CH2tBu or H-CH3). EXAFS data show that an adjacent siloxane bridge of the surface plays the role of an extra surface ligand, which most likely stabilizes these complexes as in [(≡SiO)Ta(≡CHtBu)(CH2/Bu)2(≡SiOSi≡)] (1a') and [(≡SiO)Ta(CH3)3Cp*(≡SiOSi≡)] (2a'). In the case of [(≡SiO)Ta(=CHtBu)(CH2tBu)2(≡SiOSi≡)], the structure is further stabilized by an additional interaction: a C-H agostic bond as evidenced by the small J coupling constant for the carbenic C-H (JC-H = 80 Hz), which was measured by J-resolved 2D solid-state NMR spectroscopy. The product selectivity in propane metathesis in the presence of [(≡SiO)Ta(=CHtBu)- (CH2tBu)2(≡SiOSi≡)] (1a') as a catalyst precursor and the inactivity of the surface complex [(≡SiO)Ta- (CH3)3Cp*(≡SiOSi≡)] (2a') show that the active site is required to be highly electrophilic and probably involves a metallacyclobutane intermediate. [ABSTRACT FROM AUTHOR]

A 0.9-V 1.2-mA fully integrated radio data system (RDS) receiver for the 88-108-MHz FM broadcasting band is presented. Requiring only a few external components (matching network, VCO inductors, loop filter components), the receiver, which has been integrated in a standard digital 0.18-µm CMOS technology, achieves a noise figure of 5 dB and a sensitivity of—86 dBm. The circuit can be configured and the RDS data retrieved via an I&sup2'C interlace so that it can very simply be used as a peripheral in any portable application. A 250-kHz low-IF architecture has been devised tn minimize the power dissipation of the baseband filters and FM demodulator. The frequency synthesizer consumes 250 µA, the RF front-end 450 µA while providing 40 dB of gain, the baseband filter and limiters 100 µA, and the FM and BPSK analog demodulators 300 µA. The chip area is 3.6 mm². [ABSTRACT FROM AUTHOR]

A series of hafnium complexes were structurally identified showing high activity (up to 500 h−1) in the selective alternated copolymerization of epoxides with CO2 under low pressure. [ABSTRACT FROM AUTHOR]

The reactivity of tridentate bis-aryloxy N-heterocyclic carbene (NHC) titanium complexes ([κ3-O,C,O]-NHC)Ti(X1)(X2) (X1 = X2 = Cl (1); X1 = X2 = OiPr (2)) via salt metathesis (with LiOBn, NaOAc), protonolysis (with (tBuO)3SiOH) and σ-bond metathesis (with Me3SiN3) were investigated, leading to a series of NHC titanium complexes bearing various X and XL type coligands, ([κ3-O,C,O]-NHC)Ti(X1)(X2) (X1 = X2 = OBn (3); X1 = Cl, X2 = OSi(OtBu)3 (4); X1 = OiPr, X2 = OSi(OtBu)3 (5); X1 = X2 = OAc (6); X1 = X2 = N3 (7)). The molecular structures of complexes 3 and 5 were identified by X-ray crystallographic studies, disclosing five-coordinate complexes, while complexes 4 and 7 crystallize only in the presence of THF, leading to the six-coordinate Ti-THF adducts ([κ3-O,C,O]-NHC)Ti(X1)(X2)(THF) (4-THF and 7-THF). In contrast, the structure of 6 reveals a rare example of a seven-coordinate Ti complex in which the tridentate NHC and two bidentate OAc ligands are coordinated in a pentagonal-bipyramidal fashion around the titanium atom. The reactivity of the 1,3-dipole Ti azide 7 was also further carried out via a [3 + 2] cycloaddition reaction with the dipolarophile dimethyl acetylenedicarboxylate, exhibiting a unique coordination mode for the newly formed triazolato (Tz) ligands to titanium 8 (i.e., as ([κ1-N1]-Tz)). Attempts to access NHC-Ti(III) species from the reduction of 1 with LiBEt3H·THF lead mainly to ([κ5-O,N,C,N,O]-imidazolidine)Ti(Cl)(THF) (9) via hydride transfer to the NHC carbene atom. The fully characterized NHC-Ti complexes 1-7 were evaluated for the copolymerization of cyclohexene oxide with CO2. Upon the addition of [PPN]X cocatalysts (with X = Cl, N3), all of the complexes are active at low CO2 pressure (<0.5 bar) and are highly selective (>99%) toward the formation of atactic poly(cyclohexene oxide-alt-carbonate). While the variation of the coligands has an overall moderate effect on the activity, the results mostly indicate that, in the presence of [PPN]Cl ([PPN] = (Ph3P=)2N), the sterically less hindered coligands in NHC-Ti(IV) isopropoxide, azide and acetate complexes show better activity with turnovers up to 930 in comparison to other bulky coligands. On the other hand, when the more nucleophilic [PPN]N3 salt is employed, the sterically more hindered complexes 2-6 show an increase in activity by approximatively 20%, whereas the less encumbered complexes 1 and 7 exhibit a decrease in activity. [ABSTRACT FROM AUTHOR]

Tetravalent zirconium complexes supported by tridentate bis-phenolate imidazolidin-2-ylidene (L1), imidazol-2-ylidene (L2) and benzimidazol-2-ylidene (L3) NHC ligands were synthesized and evaluated as precursors for the copolymerization of cyclohexene oxide (CHO) with CO2. While the reactivity of the imidazolidinium [H3L1] chloride salt with Zr(OiPr)4(HOiPr), and subsequent ligand exchanges with either (CH3)3SiCl or LiOiPr lead to a series of heteroleptic compounds (κ3-O,C,O-L1)Zr(X)2(THF) (X = Cl, OiPr), both imidazolium [H3L2] and benzimidazolium [H3L3] chloride salts give a mixture of homoleptic (κ3-O,C,O-NHC)2Zr and zwitterionic (κ2-O,O-HL)ZrCl2(OiPr) compounds along with traces or the absence of the heteroleptic intermediate (κ3-O,C,O-NHC)Zr(Cl)(OiPr)(THF). Such dissimilar reactivity between the unsaturated and saturated NHC ligands is predominantly ascribed to the increased acidity of azolium salts along with the π-donor strength of the Ccarbene in L2 and L3–Zr moieties. The reactivity with the more acidic azolium salts (H3L2/3) and the destabilized Zr–Xtrans to NHCcarbene bond results in a significant increase in the amount of homoleptic compounds generating HCl. The released HCl reacts preferentially with the heteroleptic intermediates having non-planar NHC ligands (i.e. L2/3) promoting the formation of zwitterionic complexes. The in situ deprotonation of the isolated zwitterionic (κ2-O,O-HL3)ZrCl2(OiPr) compound by using Ag2O gives the homoleptic complex as the major component along with a bimetallic hydroxo-bridged [(κ3-O,C,O-L3)Zr(μ-OH)(OiPr)]2 compound. Of particular interest is that only the heteroleptic NHC–Zr(iv) complexes were identified to be active and highly selective towards the copolymerization of CHO with CO2 independently of the co-catalysts used (both anionic and neutral) under mild conditions (PCO2 ＜ 1 bar, T = 60 °C), and gave atactic and completely alternating copolymers in a controlled manner (Mw/Mn≈ 1.3–1.8). In contrast, the isolated homoleptic, zwitterionic and bimetallic zirconium species were found to be inactive under similar reaction conditions. Although the activity found for NHC–Zr(iv) complexes is nearly of the same order of magnitude as that of the NHC–Ti(iv) analogues, these results are the first examples of tetravalent zirconium complexes achieving high selectivity (99% in PCHC) in the catalyzed copolymerization of CHO with CO2. [ABSTRACT FROM AUTHOR]

Titanium(iv) complexes bearing an unsubstituted tridentate bis(phenolate) N-heterocyclic carbene (NHC) were synthesized and structurally identified. While sterically unencumbered NHC–Ti(iv) complexes bearing chloro and alkoxy co-ligands tend to dimerize in solution and in solid-state, the use of a bulky aryloxy as co-ligand favors the monomeric species. Upon activation by onium salts, all these complexes were found to be highly selective towards the copolymerization of cyclohexene oxide (CHO) with CO2 under mild conditions (PCO2 ＜ 1 bar), albeit the sterically unencumbered NHC–Ti(iv) complexes are less stable and active than their structural analogues bearing bulkier substituents. [ABSTRACT FROM AUTHOR]