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The reactions of the trihydride niobocene complex [NbCp’2H3] (Cp’ = η5-C5H4SiMe3) (1) with different α,β-unsaturated carboxylic acids have been studied. The reactions with fumaric and maleic acids (A and B) gave a new dinuclear carboxylato-containing niobocene derivative [(NbCp’2)2(μ-κ2O,O-OOC-CH2-CH2-COO-κ2O,O)] (2), due to the occurrence of two processes, dihydrogen elimination and hydrogenation of the C C bond of the α,β-unsaturated carboxylic acid. Likewise, the use of an α,β-unsaturated carboxylic acid derivative such as mono-methyl fumarate (ester) (C) gave the mononuclear [NbCp’2(OOC-CH2-CH2-COOMe-κ2O,O)] (3). When other α,β-unsaturated carboxylic acids with less activated alkenes were used, such as trans-cinnamic acid (F), (E)-2-methyl-3-phenylacrylic acid (G), cyclohex-1-ene-1-carboxylic acid (H), 3-methylbut-2-enoic acid (I), (E)-2-methylbut-2-enoic acid (J) or (E)-pent-2-enoic acid (K), only the complexes [NbCp’2(OOCR-κ2O,O)], (R = trans-CH=CHPh (4), trans-CMe = CHPh (5), 1-cyclohexenyl (6), (CH=CMe2) (7), (cis-CMe = CHMe) (8), (trans-C(H) = CH-Et) (9)), were isolated, respectively, resulting from a process with dihydrogen elimination and the hydrogenation of the C C bond do not takes place. Treatment of 2–9 with CO (3 atm) promote that the coordination mode of the carboxylate ligand changes from (κ2O,O-OOC-R) to (κ1O-OOC-R) and yielding new carbonyl derivatives [(NbCp’2)2(μ-κ1O-OOC-CH2-CH2-COO-κ1O) (CO)2] (10); and [NbCp’2(OOCR-κ1O) (CO)] (R = CH2-CH2-COOMe (11), trans-CH=CHPh (12), trans-CMe = CHPh (13), 1-cyclohexenyl (14), CH=CMe2 (15), cis-CMe = CHMe (16) and R = trans-CH CH-Et) (17)). Reaction of 2 with O2 afford a new diperoxo compound [{NbCp’2(O2-κ2O,O)}2 (μ−κ1O-OOC-CH2-CH2-COO-κ1O)](19), through a monoperoxo derivative [NbCp’2(O2-κ2O,O) (μ-κ1O-OOC-CH2-CH2-COO-κ2O,O)NbCp’2] (18). All the new complexes were characterized by usual IR and NMR spectroscopic methods and the crystal structure of 16 and 18 were determined by X-ray diffraction studies.

The reaction of [TiCp2Cl2] with dipotassium chelidamate yields the carboxylate derivative [TiCp2{(OOC)2PyOH}] (2), which is sparsely soluble in water at neutral pH but soluble in basic medium. [TiCp*Cl3] reacts with chelidamic acid in the presence of NEt3 to yield the dimetallic derivative [TiCp*{(OOC)2PyOH}]2O (5). The reaction of [TiCp*Cl3] with potassium chelidamate renders the hydroxide compound [TiCp*(OH){(OOC)2PyOH}] (6). Compound 6 evolves in DMSO solution to give the trimetallic derivative [TiCp*(DMSO){(OOC)2PyO}]3 (7). Complex 6 reacts with NaOH to render the heterometallic complex [TiCp*{(OOC)2PyONa(OH2)3}]2(O) (8). The structures of complexes 7 and 8b were determined by X-ray diffraction studies. The electrostatic potential surfaces, Mulliken population analysis, and frontier molecular orbitals were determined for complex 6, allowing us to infer its reactivity.

A series of inexpensive and sustainable amidinate aluminium complexes has been developed as catalysts for the chemical fixation of carbon dioxide into cyclic carbonates. The reactions using terminal epoxides as substrates were carried out at room temperature and one bar of carbon dioxide pressure in the presence of tetrabutylammonium iodide as cocatalyst in the absence of solvent. Under these reaction conditions, excellent conversions and selectivities were achieved for a broad range of terminal epoxides. Moreover, the optimal catalyst could be used for the synthesis of disubstituted cyclic carbonates from internal epoxides and carbon dioxide, highlighting the potential of these amidinate aluminium complexes as catalysts.

Highly efficient neutral and ionic imidazole-based organocatalysts have been developed for the synthesis of cyclic carbonates from epoxides and carbon dioxide. The ionic derivatives performed as bifunctional catalysts and exhibited improved activity for the fixation of CO2 compared to the neutral compounds. Mechanistic studies revealed that the hydroxyl group promoted the activation of the epoxide facilitating the epoxide ring-opening by nucleophilic attack of the iodide.

A new lanthanum heteroscorpionate complex has shown exceptional catalytic activity for the synthesis of cyclic carbonates from epoxides and carbon dioxide. This catalyst system also promotes the reaction of bio-based epoxides to give an important class of bis(cyclic carbonates) that can be further used for the production of bio-derived non-isocyanate polyurethanes. The catalytic process requires low catalyst loading and mild reaction conditions for the synthesis of a wide range of cyclic carbonates.

A series of new alkyl mono- and bimetallic aluminum complexes supported by novel amidinate ligands has been prepared in very high yields. These complexes were fully characterized by spectroscopic methods. Alkyl aluminum complexes 1–6 were investigated as catalysts for the ring-opening polymerization and copolymerization of e-caprolactone and L-lactide. Under the optimal reaction conditions, complex 5 acts as an efficient single-component initiator for the ring-opening polymerization and copolymerization of cyclic esters to yield biodegradable polyester materials with narrow polydispersities. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2397–2407

The reaction of the low sterically hindered heteroscorpionate lithium acetamidinates [Li(κ3-NNN)(thf)] {NNN = pbpamd (1) [pbpamd = N,N′-diisopropylbis(3,5-dimethylpyrazol-1-yl)acetamidinate], tbpamd (2) [tbpamd = N-ethyl-N′-tert-butylbis(3,5-dimethylpyrazol-1-yl)acetamidinate], ttbpamd (3) [ttbpamd = N,N′-di-tert-butylbis(3,5-dimethylpyrazol-1-yl)acetamidinate], phbpamd (4) [phbpamd = N,N′-di-p-tolylbis(3,5-dimethylpyrazol-1-yl)acetamidinate] and the highly sterically demanding [Li(κ3-phbptamd)(thf)] (5) [phbptamd = N,N′-di-p-tolylbis(3,5-di-tert-butylpyrazol-1-yl)acetamidinate] with the commercially available Grignard reagent tBuMgCl in an equimolecular ratio yielded the magnesium tert-butyl heteroscorpionates [Mg(tBu)(κ3-NNN)] [NNN = pbpamd (6), tbpamd (7), ttbpamd (8), and phbptamd (9)]. In addition, subsequent reaction of monoalkyls 6–8 with two additional equivalents of tBuMgCl gave rise to two different classes of chiral tetraalkyls, which contain apical methine C–H activated heteroscorpionates that...

The combination of an aluminium(heteroscorpionate) complex and tetrabutylammonium bromide acts as a highly efficient catalyst system for the synthesis of oxazolidinones from epoxides and isocyanates. Twenty two complexes were tested derived from a range of bispyrazole ligands and containing 1-3 aluminium atoms per complex. The optimal catalyst was found to be a bimetallic complex of a thioacetamidate ligand. Under the optimal reaction conditions (80°C in toluene for 24h using 5mol% of both aluminium catalyst and tetrabutylammonium bromide co-catalyst), six epoxides were reacted with six aromatic isocyanates, giving 25 oxazolidinones in moderate to excellent yields showing broad substrate scope. The regiochemistry of the reaction (to produce 3,4- or 3,5-oxazolidinones) is controlled by the substrate with epoxide ring opening occurring preferentially at the less hindered end of the epoxide unless a substituent on the epoxide can stabilise a positive charge.

The chiral, enantiopure bis(pyrazol-1-yl)methane-based NNO-donor scorpionate ligands in the form of the alcohol compounds bpzbeH (bpzbe = 1,1-bis(3,5-dimethylpyrazol-1-yl)-3,3-dimethyl-2-butoxide), bpzteH (bpzte = 2,2-bis(3,5-dimethylpyrazol-1-yl)-1-p-tolylethoxide), and (R,R)-bpzmmH ((R,R)-bpzmm = (1R)-1-{(1R)-6,6-dimethylbicyclo[3.1.1]-2-hepten-2-yl}-2,2-bis(3,5-dimethylpyrazol-1-yl)ethoxide) have been used to obtain new NNO-heteroscorpionate yttrium and lutetium complexes. The reactions of bpzbeH, bpzteH (racemic mixtures), and (R,R)-bpzmmH (enantiopure compound) with [M{N(SiHMe2)2}3(thf)2] (M = Y, Lu) in a 1:1 molar ratio in toluene afforded the mononuclear bis(silylamide) complexes [M{N(SiHMe2)2}2(κ3-NNO)(thf)] (M = Y, Lu; 1–6), respectively. When the reaction was carried out with a 2:1 molar ratio (ligand to metal precursor) or with excess ligand, homoleptic complexes of the type [Y(κ3-NNO)2(κ-O-NN)] (κ3-NNO = κ-O-NN = bpzbe (7), bpzte (8)) were obtained. Compounds 1 and 3 were used as convenient st...

A new and easy route to prepare “a la carte” bis(1,2,3-triazol-1-yl)methane compounds, namely bmtzm (1), bptzm (2), bttzm (3), bmtzpm (4), bptzpm (5), bttzpm (6), bmtzom (7), bptzom (8) and bttzom (9), with different functional groups is reported. The compounds were prepared by reaction between readily accessible alkynes and geminal diazides in a double Cu-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. These materials were used as starting materials for the synthesis of more elaborate compounds. Thus, the preparation of new bis(1,2,3-triazol-1-yl)methane-based heteroscorpionate neutral precursors pbptztamH (10), pbttztamH (11), (S)-mbptzamH (12) and (S)-mbttzamH (13) and a dinuclear zinc complex, [Zn{pbptztam}Et]2 (14), was achieved. The structures of the compounds were determined by spectroscopic methods, and the X-ray crystal structures of compounds 2, 3, 7, 8, 9 and 14 were established.

A series of new acetate and trifluroacetate bimetallic zinc complexes containing heteroscorpionate ligands have been prepared in very high yields. The structures of the complexes were determined by spectroscopic methods, and the single-crystal X-ray structure of complex 6 confirmed a κ3-NNO coordination mode of the scorpionate ligand in a dinuclear molecular arrangement. Bimetallic zinc complexes 6–11 were investigated as catalysts for the synthesis of polycarbonates from epoxides and carbon dioxide in the absence of a cocatalyst. Under the optimal reaction conditions, complex 10 acts as an efficient single-component initiator for the ring-opening copolymerisation of cyclohexene oxide and carbon dioxide, yielding polycarbonate materials with narrow polydispersities.

The reactivity of the activated alkynes RC≡CR (R = CO2Me, CO2tBu) with the Nb–H bond of the 18e– niobocene hydride trimethyl phosphite complex [Nb(η5-C5H4SiMe3)2(H)(P(OMe)3)] (1) has been studied, and the new (E)-niobocene alkenyl trimethyl phosphite complexes [Nb(η5-C5H4SiMe3)2(C(CO2R)═C(CO2R)H)(P(OMe)3)] (R = Me (2a), tBu (2b)) have been obtained. DFT studies were carried out to identify the lowest energy mechanism and the possible intermediates in the process. An unusual nucleophilic d2 Nb(III) center was identified as a σ-donor entity responsible for the nucleophilic attack on a carbon atom of the activated (electrophilic) alkyne molecules. A subsequent hydrogen transfer to the other carbon atom produces the final (E)-niobocene alkenyl trimethyl phosphite complexes, the stereochemistries of which were elucidated by NMR spectroscopy.

The titanium derivatives [TiCp * Me(κ3-ONO–OOCPhN CHPhO)] (1), [TiCp * Me(κ3-ONO–OCH2PhN CHPhO)] (2) and [TiCp * Me(κ3-ONS–SPhN CHPhO)] (3) have been synthesized by reaction of [TiCp * Me3] (Cp* = η5-C5Me5) with 2-(salicylideneamino)benzoic acid, 2-(hydroxybenzyl)salicylideneamino or 2-(salicylideneamino)thiophenol, respectively, in a 1:1 M ratio. The reaction of [TiCp * Me3] with and 2-(salicylideneamino)thiophenol in 1:2 M ratio yields the titanium compound [TiCp * Me(κ3-ONS–SPhN CHPhO)(κ1-O-PhCHNHPhS)] (5) Complexes 1, 2 and 3 react with tBuNC to yield the iminoacyl-containing compounds [TiCp * (η2-CN–MeC NtBu)(κ3-ONO–OOCPhN CHPhO)] (6), [TiCp * (η2-CN–MeC NtBu)(κ3-ONO–OCH2PhN CHPhO)] (7) and [TiCp * (η2-CN–MeC NtBu)(κ3-ONS–SPhN CHPhO)] (8). Compounds 7 and 8 can be protonated with triflic acid to yield the aminocarbene derivatives (9) and (10), respectively. Moreover, the reaction of complexes 1–3 with triflic acid renders the corresponding triflate compounds [TiCp * (κ3-ONO–OOCPhN CHPhO)(OTf)] (11), [TiCp * (κ3-ONO–OCH2PhN CHPhO)(OTf)] (12) and [TiCp * (κ3-ONS–SPhN CHPhO)(OTf)] (13). The reaction of 1 or 2 with B(C6F5)3 in a 1:1 M ratio yields the carboxylate adduct [TiCp * Me(κ3-ONO–OOCPhN CHPhO·B(C6F5)3)] (14) or the cationic derivative. [TiCp * (κ3-ONO–OCH2PhN CHPhO)]2[MeB(C6F5)3)]2 (15), respectively. The molecular structures of complexes 2, 5, 6, 13 and 15 have been established by X-ray diffraction methods.

Macromolecular engineering of cyclic polycaprolactones has been carried out by a ring-expansion procedure catalyzed by a series of alkyl-organoaluminum initiators. The single-site nature of the initiators allows a very well-controlled macrolactonization process to give moderate to high molecular weight cyclic polymers with narrow polydispersities. Cyclic architectures are supported by a combination of techniques such as viscosity measurements, NMR, and MALDI-TOF MS analysis.

The Spanish Ministerio de Ciencia e Innovacion (MICINN) [projects CTQ2010-20387 and Consolider Ingenio 2010, CSD2007-00006 and Juan de la Cierva contract (to A. B.), JCI-2009-03710], Fondos Europeos para el Desarrollo Regional (FEDER), the Generalitat Valenciana (PROMETEO 2009/039), and the University of Alicante are gratefully acknowledged for financial support.

The work described here represents the first example of an enantiopure hybrid scorpionate/cyclopentadiene ligand. The ligand was obtained in a one-pot synthetic procedure by an efficient and highly diastereoselective nucleophilic addition of an organolithium reagent to an electrophilically activated olefin in a new fulvene with a chiral substrate to control the stereochemistry of a newly created asymmetric center. We verified the potential utility of this ligand as a valuable scaffold that is able to induce chirality in organometallic/coordination chemistry. This was achieved through the preparation of a new enantiomerically pure zinc complex in which the ligand behaves in a tridentate manner with a κ2NN-η1(π)-Cp coordination mode. This alkylzinc complex constitutes the first example of an organozinc derivative which behaves as an efficient initiator for the ROP of rac-LA in the production of isotactic-enriched poly(lactides) with Pi = 0.77.

A series of new tantalum complexes containing the κ3O,S,O-type alkoxide ligand from 2,2′-thiodiethanol (tdgolH2) have been synthesized and characterized. The complexes [TaCp*Cl2{[O(CH2)2]2S-κ3O,S,O}] (1) and [TaCp*Me2{[O(CH2)2]2S-κ3O,S,O}] (2) were prepared by reaction of 2,2′-thiodiethanol with [TaCp*X4] (X = Cl, Me). The tantalum dihydride complex [TaCp*H2{[O(CH2)2]2S-κ3O,S,O}] (3) and its analogue containing the 2,2′-thiobis(6-tert-octylphenolate) ligand (4) were synthesized by reaction of the respective dichlorides with 2 equiv of NaBHEt3. In addition, [TaCp*Me(TfO){[O(CH2)2]2S-κ3O,S,O}] (5) and [TaCp*(TfO)2{[O(CH2)2]2S-κ3O,S,O}] (6; TfO = F3COSO2–) were synthesized by reaction of 2 with 1 and 2 equiv of triflic acid, respectively. The reactivity of this family of complexes with nucleophiles was also studied and, as a result, three azatantalacyclopropane complexes (7–9) and the carbene [TaCp*{C(Me)N(H)xylyl-κ1C}(OH){[O(CH2)2]2S-κ3O,S,O}] (10) were characterized. The single-crystal structures of 1 and ...

The synthesis of a stable hydride triphenylstibine derivative, Nb(η5-C5H4SiMe3)2(H)(SbPh3) (1), has been achieved through the formation of the transient coordinatively unsaturated 16-electron speci...

Preprint Reaction of chiral alcohol-scorpionate compoundbpzteH [bpzteH = 2,2-bis(3,5-dimethylpyrazol- 1-yl)-1-para-tolylethanol] with [ZnR2] (R = Me, CH2SiMe3) in a 1:2 molar ratio afforded the dinuclear chiral alkyl zinc complexes [Zn(R)(k2-NN μ-O)Zn(R)2] (1–2) [k2-NN μ-O= bpzte, R = Me 1, CH2SiMe32]. Using these trialkyl complexes in an alcoholysis reaction with ArOH (1 equiv; Ar = 2,6-C6H3Me2) yielded the chiral dinuclear zinc complexes [(ZnR)2(kN:kN- μ-O)( μ-EAr)] (3– 4) [kN:kN- μ-O= bpzte, R = Me 3, CH2SiMe34]. The structures of the different compounds were determined by spectroscopic methods and, in addition, the X-ray crystal structures of 1 and 3 confirmed a dinuclear structure in all complexes, with the alkoxide of the heteroscorpionate ligands in a μ-bridging mode between the two Zn(II) centers. Trisalkyl and alkyl-aryloxide-containing zinc complexes 1–4 can act as single-component initiators for the ring-opening homopolymerization of e-caprolactone and L-/rac-lactide, affording materials with low molecular weights and narrow monomodal molecular weight distributions under mild conditions in only a few hours. Microstructural analysis of poly(rac-lactide) revealed that the alkyl-aryloxide 3 exerts a moderate level of heteroselectivity (Ps= 0.68). More interestingly, this initiators 3 and 4 also allowed the well-controlled random copolymerization of ε-CL and LLA as indicated by both the values of the reactivity ratios of the two comonomers (rCL = 1.15 and 0.92, and rLA = 1.37 and 1.05, for 3 and 4, respectively), and the average lengths of the caproyl and lactidyl sequences (LCL ~ 2.0; LLA ~ 2.5, for both initiators). The copolymers also showed to possess monomer contents in close agreement with their composition in the initial monomer feed. Inspection by differential scanning calorimetry on the thermal properties such as Tg of various copolymers produced by 3 revealed a strong dependence on monomer content, as these values vary linearly with the molar percentage of L-lactide unit in the copolymer over a temperature range of -30 to 42 ºC.

The new diguanidinate-supported dibenzylzirconium complexes [Zr{κ2N,N′-(N-i-Pr)(NAr)CNH(i-Pr)}2(CH2Ph)2] (Ar = 4-t-BuC6H4 (1), 4-BrC6H4 (2)) and [Zr{κ2N,N′-(NEt)(N-t-Bu)CNMe2}2(CH2Ph)2] (3) have be...

The mechanism of the isocyanide migratory insertion into the metal–carbon bond of monocylopentadienyltantalum dimethyl derivatives with [OSO]2– tridentate phenolate ligands has been investigated with DFT calculations. The presence of both a cyclopentadienyl and a tridentate ligand complicates a usually simple reaction, the migratory insertion reaction being coupled with a fac → mer rearrangement of the tridentate ligand. Two routes have been explored for the overall migratory insertion process, depending on the order of the fac → mer and insertion steps. Calculations show that the dissociative (first fac → mer rearrangement, then migratory insertion) and the associative (first migratory insertion, then fac → mer rearrangement) pathways are in principle competitive. However, electronic effects of the phenyl substituents can favor one of the pathways. The study also points out the influence of the donor atom, due to the inversion at the donor atom required in order to achieve the fac → mer interconversion.

The reaction of the niobocene complex [Nb(η5-C5H4SiMe3)2(H)(CO)] (1) with α,β-unsaturated acids, namely, fumaric and maleic acids, and methylfumarate ester yielded the corresponding carboxylato-containing niobocene derivatives [Nb(η5-C5H4SiMe3)2(κ1-O-OOC-CH2-CH2-R)(CO)] (R = COOH (2); R = COOMe (3)), resulting from the hydrogenation of the C═C bond and the consequent coordination of a carboxylato moiety on the Nb center. The process represents the first reported example of the hydrogenation of α,β-unsaturated acids mediated by a hydride niobocene complex. Spectroscopic and theoretical studies at the DFT level have allowed for proposing a plausible reaction mechanism. Initial coordination of the C═C bond to the Nb center is followed by the insertion of this bond into the Nb–H bond, and the reaction is completed by a proton transfer from the carboxylic moiety to the α-carbon of the alkyl moiety, giving rise to the final κ1-carboxylato ligand.

The guanidines (HNi-Pr)2C NAr (Ar = 4-t-BuC6H4 1, 4-BrC6H4 2 and 2,4,6-Me3C6H2 3) have been used in the synthesis of the lithium salts [Li{i-PrN(HNiPr)C NAr}(THF)]2 4–6 and [Li2{(Ni-Pr)2C NAr}] 7–9. Complexes [Zr{κ2,N,N′-(Ni-Pr)(NAr)CNH(i-Pr)}2Cl2] (Ar = 4-t-BuC6H4 10, 4-BrC6H4 11, 2,4,6-Me3C6H2 12), which contain an asymmetrical monoanionic guanidinate ligand coordinated to the zirconium atom, were obtained by protonolysis of 1–3 in the presence of NEt3 or by a metathesis reaction of 4–6 with ZrCl4. The zirconocene complexes [Zr(η5-C5H5)2{κ2,N,N′-(Ni-Pr)(NAr)CNH(i-Pr)}Cl] (Ar = 4-t-BuC6H4 13, 4-BrC6H4 14, 2,4,6-Me3C6H2 15) and [Zr(η5-C5H5)2{κ2,N,N′-(Ni-Pr)2C NAr}] (Ar = 4-t-BuC6H4 16, 4-BrC6H4 17, 2,4,6-Me3C6H2 18) were synthesized by metathesis reactions of the corresponding lithium salts and Zr(η5-C5H5)2Cl2. Complexes 16–18 exhibit dynamic behavior in solution and this was studied by variable-temperature NMR experiments. The molecular structures of 4 and 10 were determined by single-crystal X-ray diffraction.

The chiral and the enantiopure bis(pyrazol-1-yl)methane-based NNO-donor scorpionate ligands in the form of the alcohol compounds (bpzbeH) [bpzbe = 1,1-bis(3,5-dimethylpyrazol-1-yl)-3,3-dimethyl-2-butoxide], (bpzteH) [bpzte = 2,2-bis(3,5-dimethylpyrazol-1-yl)-1-para-tolylethoxide], and (R,R)-bpzmmH {(R,R)-bpzmm = (1R)-1-[(1R)-6,6-dimethylbicyclo[3.1.1]-2-hepten-2-yl]-2,2-bis(3,5-dimethylpyrazol-1-yl)ethoxide} have been utilized to obtain new NNO-scorpionate zinc alkyl complexes. The reaction of bpzbeH, bpzteH (racemic mixture), or (R,R)-bpzmmH (enantiopure) with [ZnMe2] in a 1:1 molar ratio in toluene afforded the mononuclear and monoalkyl zinc complexes [Zn(Me)(κ3-NNO)] (1–3), respectively. However, when the same reaction was carried out with [ZnEt2], [ZntBu2], or [Zn(CH2SiMe3)2], new dinuclear complexes of the type [Zn(R)(κ-NNμ-O)]2 (κ-NNμ-O = bpzbe, R = Et 4, tBu 5, CH2SiMe36; bpzte, R = Et 7, tBu 8, CH2SiMe39; (R,R)-bpzmm, R = Et 10, tBu 11, CH2SiMe312) were obtained. The single-crystal X-ray structure...

The reactions of the hybrid scorpionate/cyclopentadiene compounds, as a mixture of regioisomers—1-[2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethyl]-1,3-cyclopentadiene and 2-[2,2-bis(3,5-dimeth...

A series of guanidine proligands, 2-(4-(tert-butyl)phenyl)-1,3-diisopropylguanidine (1), 2-(4-bromophenyl)-1,3-diisopropylguanidine (2), 2-(4-methoxyphenyl)-1,3-diisopropylguanidine (3), and 2,2′-(1,4-phenylene)bis(2′,3-diisopropylguanidine) (4), has been reacted with [NbBz3(NtBu)] (5) through a protonolysis reaction to obtain new monoguanidinate-supported dibenzyl niobium complexes, {NbBz2(NtBu)[(4-tBuC6H4)N═C(NiPr)(NHiPr)]} (6), {NbBz2(NtBu)[(4-BrC6H4)N═C(NiPr)(NHiPr)]} (7), {NbBz2(NtBu)[(4-MeOC6H4)N═C(NiPr)(NHiPr)]} (8), and the dinuclear complex {[NbBz2(NtBu)]2[(C6H4)(N═C(NiPr)(NHiPr))2]} (9). Complexes 6, 8, and 9 were structurally characterized. These neutral complexes contain a η2-benzyl ligand coordinated to the metal center. Insertion migratory reactions with isocyanides resulted in the formation of bis-κ2-iminoacyl species, {Nb(NtBu)(tBuN═CCH2Ph)2[(4-tBuC6H4)N═C(NiPr)(NHiPr)]} (10), {NbBz2(NtBu) (tBuN═CCH2Ph)2[(4-BrC6H4)N═C(NiPr)(NHiPr)]} (11), {Nb(NtBu)(tBuN═CCH2Ph)2[(4-MeOC6H4)N═C(NiPr)(NHiPr)...

The tantalum complex [TaCp*Me2(OOCPhN═CHPhO-κ3O,N,O)] (2) has been synthesized by reaction of [TaCp*Me4] (Cp* = η5-C5Me5) with 2-(salicylideneamino)benzoic acid. Complex 2 reacts with HOTf to yield...

Tantalum complexes [TaCp*Me{κ(4)-C,N,O,O-(OCH(2))(OCHC(CH(2)NMe(2))=CH)py}] (4) and [TaCp*Me{κ(4)-C,N,O,O-(OCH(2))(OCHC(CH(2)NH(2))=CH)py}] (5), which contain modified alkoxide pincer ligands, were synthesized from the reactions of [TaCp*Me{κ(3)-N,O,O-(OCH(2))(OCH)py}] (Cp* = η(5)-C(5)Me(5)) with HC≡CCH(2)NMe(2) and HC≡CCH(2)NH(2), respectively. The reactions of [TaCp*Me{κ(4)-C,N,O,O-(OCH(2))(OCHC(Ph)=CH)py}] (2) and [TaCp*Me{κ(4)-C,N,O,O-(OCH(2))(OCHC(SiMe(3))=CH)py}] (3) with triflic acid (1:2 molar ratio) rendered the corresponding bis-triflate derivatives [TaCp*(OTf)(2){κ(3)-N,O,O-(OCH(2))(OCHC(Ph)=CH(2))py}] (6) and [TaCp*(OTf)(2){κ(3)-N,O,O-(OCH(2))(OCHC(SiMe(3))=CH(2))py}] (7), respectively. Complex 4 reacted with triflic acid in a 1:2 molar ratio to selectively yield the water-soluble cationic complex [TaCp*(OTf){κ(4)-C,N,O,O-(OCH(2))(OCHC(CH(2)NHMe(2))=CH)py}]OTf (8). Compound 8 reacted with water to afford the hydrolyzed complex [TaCp*(OH)(H(2)O){κ(3)-N,O,O-(OCH(2))(OCHC(CH(2)NHMe(2))=CH(2))py}](OTf)(2) (9). Protonation of compound 8 with triflic acid gave the new tantalum compound [TaCp*(OTf){κ(4)-C,N,O,O-(OCH(2))(HOCHC(CH(2)NHMe(2))=CH)py}](OTf)(2) (10), which afforded the corresponding protonolysis derivative [TaCp*(OTf)(2){κ(3)-N,O,O-(OCH(2))(HOCHC(CH(2)NHMe(2))=CH(2))py}](OTf) (11) in solution. Complex 8 reacted with CNtBu and potassium 2-isocyanoacetate to give the corresponding iminoacyl derivatives 12 and 13, respectively. The molecular structures of complexes 5, 7, and 10 were established by single-crystal X-ray diffraction studies.

The reaction of the sterically hindered heteroscorpionate lithium acetamidinate [Li(κ3-pbptamd)(THF)] (pbptamd = N,N′-diisopropylbis(3,5-di-tert-butylpyrazol-1-yl)acetamidinate) and [Li(κ3-tbptamd)...

The synthesis, structures, and ring-opening polymerization (ROP) activity of heteroscorpionate aluminum alkyl and aryloxide complexes are reported. The reactions of the acetamide and thioacetamide heteroscorpionate protio ligands pbptamH (pbptamH = N-phenyl-2,2-bis(3,5-dimethylpyrazol-1-yl)thioacetamide), pbpamH (pbpamH = N-phenyl-2,2-bis(3,5-dimethylpyrazol-1-yl)acetamide), sbpamH (sbpamH = N-sec-butyl-2,2-bis(3,5-dimethylpyrazol-1-yl)acetamide), and (S)-mbpamH ((S)-mbpamH = (S)-(−)-N-α-methylbenzyl-2,2-bis(3,5-dimethylpyrazol-1-yl)acetamide) with 1 equiv of AlR3 (R = Me, Et, iBu) proceed in very high yields to give the neutral heteroscorpionate dialkyl aluminum complexes [AlR2{κ2-pbptam}] (R = Me (1), Et (2)), [AlR2{κ2-pbptam}] (R = Me (3), Et (4), iBu (5)), [AlR2{κ2-pbptam}] (R = Me (6), Et (7), iBu (8)), and [AlR2{κ2-(S)-mbpam}] (R = Me (9), Et (10)). In the solid state, complexes 1−10 adopt a tetrahedral structure with the heteroscorpionate ligands arranged in a κ2 coordination mode; in the case of t...

A series of new tantalum complexes containing a [NSN]-type amide ligand (2,2′-diamidophenyl sulfide) have been synthesized and characterized. The complexes [TaCp*Cl2{(N-C6H4)2S-κ3-N,S,N}] (1) and [TaCp*Me2{(N-C6H4)2S-κ3-N,S,N}] (2) were prepared by reaction of 2,2′-diaminophenyl sulfide with [TaCp*Cl4] and [TaCp*Me2Cl2], respectively. In addition, [TaCp*MeCl{(N-C6H4)2S-κ3-N,S,N}] (3) and [TaCp*(H)2{(N-C6H4)2S-κ3-N,S,N}] (4) were synthesized by reaction of 1 with AlMe3 and NaBEt3H, respectively. The reactivity of these complexes with nucleophiles and electrophiles was also studied, and complexes [TaCp*(tBuNCH2-κ2-C,N){(N-C6H4)2S-κ3-N,S,N}] (5) and [TaCp*Me{(N-C6H4)2S-κ3-N,S,N}][MeB(C6F5)3] (6) were isolated and characterized. The single-crystal structures of 1 and 4 were determined by X-ray diffraction methods. The NMR chemical shifts of the amidic protons in the complexes allowed us to evaluate the influence that the other ligands in the coordination sphere have on the electronic density of the metal.

A series of new cationic aminocarbene tantalum complexes have been synthesized and characterized. A significant contribution of the anion−cation interaction to the stability of the cationic moiety ...

The tantalum complex [TaCp*Me(OTf)((OOC)2py-κ3-O,N,O)] (1) has been synthesized by reaction of [TaCp*Me3(OTf)] (Cp* = η5-C5Me5, OTf = trifluoromethylsulfate) with 2,6-pyridinedicarboxylic acid. Com...

The allyl-substituted group 4 metal complexes [M{(R)CH(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )}Cl 2 ] [M = Ti, R = CH 2 CH CH 2 , ( 2 ); R = CH 2 C(CH 3 ) CH 2 ( 3 ); M = Zr, R = CH 2 CH CH 2 ( 4 ), R = CH 2 C(CH 3 ) CH 2 ( 5 )] have been synthesized by the reaction of allyl ansa -magnesocene derivatives and the tetrachloride salts of the corresponding transition metal. The dialkyl complexes [ M ( R ) CH ( η 5 - C 5 Me 4 ) ( η 5 - C 5 H 4 ) R 2 ′ ] [M = Ti, R = CH 2 =CHCH 2 , R′ = Me ( 6 ), R′ = CH 2 Ph ( 7 ); R = CH 2 C(CH 3 ) CH 2 , R′ = Me ( 8 ), R′ = CH 2 Ph ( 9 ); M = Zr, R = CH 2 CH CH 2 , R′ = Me ( 10 ), R′ = CH 2 Ph ( 11 ); R = CH 2 C(CH 3 ) CH 2 , R′ = Me ( 12 ), R′ = CH 2 Ph ( 13 )] have been synthesized by the reaction of the corresponding ansa -metallocene dichloride complexes 2–5 and two molar equivalents of the alkyl Grignard reagent. Compounds 2–5 reacted with H 2 under catalytic conditions (Wilkinson’s catalyst or Pd/C) to give the hydrogenation products [M{(R)CH(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )}Cl 2 ] [M = Ti and R = CH 2 CH 2 CH 3 ( 14 ) or R = CH 2 CH(CH 3 ) 2 ( 15 ); M = Zr and R = CH 2 CH 2 CH 3 ( 16 ) or R = CH 2 CH(CH 3 ) 2 ( 17 )]. The reactivity of 2–5 has also been tested in hydroboration and hydrosilylation reactions. The hydroboration reactions of 3 , 4 and 5 with 9-borabicyclo[3.3.1]nonane (9-BBN) yielded the complexes [M{(9-BBN)CH 2 CH(R)CH 2 CH(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )}Cl 2 ] [M = Ti and R = H ( 18 ); M = Zr and R = H ( 19 ) or R = CH 3 ( 20 )]. The reaction with the silane reagents HSiMe 2 Cl gave the corresponding [M{ClMe 2 SiCH 2 CHRCH 2 CH(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )}Cl 2 ] [M = Ti and R = H ( 21 ); M = Zr and R = H ( 22 ) or R = CH 3 ( 23 )]. The reaction of 22 with t -BuMe 2 SiOH produced a new complex [Zr{ t -BuMe 2 SiOSi(Me 2 )CH 2 CH 2 CH 2 CH(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )}Cl 2 ] ( 24 ) through the formation of Si–O–Si bonds. On the other hand, reactivity studies of some zirconocene complexes were carried out, with the insertion reaction of phenyl isocyanate (PhNCO) into the zirconium–carbon σ-bond of [Zr{( n -Bu)CH(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )} 2 Me 2 ] ( 25 ) giving [{( n -Bu)CH(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )]}Zr{Me{κ 2 -O,N-OC(Me)NPh}] as a mixture of two isomers 26a–b . The reaction of [Zr{( n -Bu)(H)C(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )}(CH 2 Ph) 2 ] ( 27 ) with CO also provided a mixture of two isomers [{( n -Bu)CH(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )]}Zr(CH 2 Ph){κ 2 -O,C-COCH 2 Ph}] 28a–b . The molecular structures of 4 , 11 , 16 and 17 have been determined by single-crystal X-ray diffraction studies.

A series of new compounds has been synthesised from an electron-rich olefin derived from cyclam (A). Thus, A reacts with oxygen gas to give the syn-bis(urea) 1 and with sulfur to yield the anti-bis(thiourea) 2. The reaction of A with triflic acid furnishes the bis(imidazolium) triflate 3, which gives the monoprotonated imidazolium salt 4 upon treatment with sodium tetraphenylborate in water. Theoretical calculations (DFT) predict the diprotonated species to be energetically disfavoured, thus demonstrating the importance of hydrogen-bonding interactions. Treatment of compound 3 with silver oxide affords the di- and monoprotonated cationic salts 5a and 5b in THF and dichloromethane, respectively. The molecular structures of compounds 1, 2, 3, 4, 5a and 5b have been established by X-ray diffraction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

A series of cationic rhodium(I) complexes of the type [Rh(N-N)(COD)][BPh4], containing the following iminopyridine-based bidentate nitrogen donor ligands (N-N): 2,6-diisopropyl-N-[1-(pyridin-2-yl)ethylidene]aniline (dipea, 1), 2,6-dimethyl-N-[1-(pyridin-2-yl)ethylidene]aniline (dmpea, 2), 2,4,6-tri-methyl-N-[1-(pyridin-2-yl)ethylidene]aniline (tmpea, 3) and 2,6-diisopropyl-N-[1-(4-methylpyridin-2-yl)-ethylidene]aniline] (dipmpea, 4), were synthesized and fully characterized. The intermolecular hydroamination of a terminal alkyne, such as 1-octyne, with primary aromatic amines in the presence of these cationic rhodium(I) catalysts occurred in an anti-Markovnikov fashion. The rhodium complexes catalyzed the regioselective formation of the E-isomer of the corresponding imine, without the formation of the Z-isomer or the Markovnikov product. These compounds are also presented as efficient regioselective catalysts for the hydroamination of anilines in the presence of air and/or water.

A series of new titanium pyridine−alkoxide complexes, [TiCp*Cl{2,6-(OCH2)2py-κ3-O,N,O}] (2), [TiCp*{2,6-(OCH2)py(CH2OH)-κ1-O}{2,6-(OCH2)2py-κ3-O,N,O}] (3), [TiCp*Me2{2-(OCH2)py-κ1-O}] (4), [TiCp*Me{2-(OCH2)py-κ1-O}2] (5), and [TiCp*(O){2-(OCH2)py-κ2-O,N})] (6), have been synthesized. All of these compounds were characterized by NMR spectroscopy. The single-crystal structures of [TiCp*Me{2,6-(OCH2)2py-κ3-O,N,O}] (1), 2, 3, and 4 were determined and revealed the presence of piano and nonpiano stool geometries. The molecular structures of 1, 2, and 3 were also studied by means of density functional theory (DFT) in an attempt to rationalize the possible reasons for the stabilization of one or other geometry., This work was supported by the Ministerio de Ciencia e Innovación (MCINN), Spain (Grant Nos. CTQ2005-08123-C02-01/BQU, CTQ2006-11845/BQU, and Consolider-Ingenio 2010 ORFEO CSD2007-00006) and the Junta de Comunidades de Castilla-La Mancha, Spain (Grant No. PCI08-0010).

The tantalum complex [TaCp*Cl2{2,6(OOC)2py-κ2O,O}] (1) has been synthesized by reaction of [TaCp*Cl4], Cp* = η5-C5Me5, with 2,6-pyridinedicarboxylic acid. Complex 1 reacts with AgOTf, OTf = trifluoromethylsulfate, to yield the new tantalum carboxylate derivative [TaCp*Cl(OTf){2,6(OOC)2py-κ2O,O}] (2) or with KOH to render the dinuclear oxo compound [TaCp*(μ-O){2,6(OOC)2py-κ2O,O}] 2 (3). The reaction of 3 with H2O and HOTf gives the dinuclear hydroxo derivative [{TaCp*{2,6(OOC)2py-κ2O,O}}2(μ-OH)3](OTf) (5). The structures of complexes 1, 2, 3, and 5 have been established by X-ray diffraction methods., This work was supported by the Ministerio de Ciencia e Innovación, Spain (Grant Nos CTQ2005-08123-C02-01/BQU and Consolider-Ingenio 2010 ORFEO CSD2007-00006) and the Junta de Comunidades de Castilla-La Mancha, Spain (Grant No. PCI08-0010).

A series of new tantalum-tbcp [tbcp = 2,2′-thiobis(4,6-dichlorophenolato)] and tantalum-tbop [tbop = 2,2′-thiobis(6-tert-octylphenolato)] complexes [TaCp*Cl2(κ3-tbop)] (1), [TaCp*Cl2(κ3-tbcp)] (2), [TaCp*Me2(κ3-tbop)] (3), [TaCp*Me2(κ3-tbcp)] (4), [TaCp*Me(κ3-tbop)(OTf)] (OTf = triflate) (5), [TaCp*Me(κ3-tbcp)(OTf)] (6), [TaCp*(κ3-tbop)(OTf)2] (7), and [TaCp*(κ3-tbcp)(OTf)2] (8) have been synthesized. Insertion processes into the methyl groups of complex 3 were not observed upon reaction with CO or isocyanides. In contrast, complex 4 reacted slowly with 1 equiv of xylyl isocyanide (xylyl = 2,6-dimethylphenyl) or tert-butyl isocyanide to yield complexes [TaCp*(κ2-Me2CNxylyl)(κ3-tbcp)] (9) and [TaCp*Me(κ2- MeCNtBu)(κ3-tbcp)] (10), respectively. All products were characterized by NMR spectroscopy and elemental analysis. The single-crystal structures of 2, 3, 6, and 9 were also determined.

The new tantalum siloxide complex [TaCp*Me3(OSiPh3)] (1; Cp* = η5-C5Me5) has been synthesized. The reaction of complex 1 with isocyanides yields the respective azatantalacyclopropanes [TaCp*(η2-Me2CNxylyl)Me(OSiPh3)] (2; xylyl = 2,6-dimethylphenyl) and [TaCp*(η2-Me2CNtBu)Me(OSiPh3)] (3). The molecular structure of complex 2 has been established by X-ray diffraction. Complex 2 reacts with a second mol-equiv. of 2,6-xylyl isocyanide to yield [TaCp*(Nxylyl)[N(xylyl)CMe=CMe2)(OSiPh3)] (4). The reaction of 1 with carbon monoxide gives [TaCp*(O)(OCMe=CMe2)(OSiPh3)] (5), whereas 1 reacts with B(C6F5)3 to give the corresponding cationic compound [TaCp*Me2(OSiPh3)][MeB(C6F5)3] (6). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

The reaction of bis(3,5-di-tert-butylpyrazol-1-yl)methane (bdtbpzm) with BunLi and carbodiimide derivatives, namely, N,N′-diisopropyl and 1-tert-butyl-3-ethyl carbodiimides, gives rise to the new sterically hindered lithium acetamidinate [Li(tbptamd)(THF)] (1) [tbptamd = N-ethyl-N′-tert-butylbis(3,5-di-tert-butylpyrazol-1-yl)acetamidinate] and [Li(pbptamd)(THF)] (2) [pbptamd = N,N′-diisopropylbis(3,5-di-tert-butylpyrazol-1-yl)acetamidinate]. Subsequent hydrolysis of 1 and 2, and the recently reported heteroscorpionate lithium salts [Li(tbpamd)(THF)] [tbpamd = N-ethyl-N′-tert-butylbis(3,5-dimethylpyrazol-1-yl)acetamidinate] and [Li(pbpamd)(THF)] [pbpamd = N,N′-diisopropylbis(3,5-dimethylpyrazol-1-yl)acetamidinate] with NH4Cl/H2O in ether cleanly affords the corresponding amidine ligands Htbpamd (3), Hpbpamd (4), Htbptamd (5), and Hpbptamd (6) in very good yields. The X-ray diffraction molecular structure of 3 was obtained. Reaction of the amidine-heteroscorpionate ligands 3–6 with 1 equiv of ZnR′2 proceeds...

The reaction of the heteroscorpionate lithium salts [Li(tbpamd)(THF)] [tbpamd = N-ethyl-N‘-tert-butylbis(3,5-dimethylpyrazol-1-yl)acetamidinate] and [Li(pbpamd)(THF)] [pbpamd = N,N‘-diisopropylbis(3,5-dimethylpyrazol-1-yl)acetamidinate] with 1 equiv of RMgCl proceeds to give very high yields of the neutral heteroscorpionate alkyl magnesium complexes [Mg(R)(NNN)] (NNN = tbpamd, R = C3H5 1, tBu 2, CH2SiMe3 3; NNN = pbpamd, R = C3H5 4, tBu 5, CH2SiMe3 6). On heating toluene solutions of complexes 1−3, 5, and 6, a ligand redistribution process occurs to give the corresponding 6-coordinated sandwich complexes [Mg(tbpamd)2] (7) and [Mg(pbpamd)2] (8). Interestingly, the allyl derivative 4 can be easily transformed to 8 at room temperature. In addition, the cationic sandwich complex [Mg(tbpamdH)2]Cl2 (9) [tbpamdH = N-ethyl-N‘-tert-butylbis(3,5-dimethylpyrazol-1-yl)acetamidine] was obtained from 7 by means of a protonation process. Finally, alkyl-containing complexes 1−6 can act as highly effective single-componen...

In this article, we have reviewed a series of insertion processes of different types of unsaturated reagents, namely carbon monoxide, carbon dioxide, isocyanates, isothiocyanates, isonitriles, alkenes and activated alkynes, in the Nb–X σ-bond, X = H, C and P, of “ Cp 2 ′ NbX ” moieties, Cp′ = η 5 -C 5 H 4 SiMe 3 .

The preparation of new hybrid scorpionate/cyclopentadienyl ligands in the form of the lithium derivatives [Li(bpzcp)(THF)] (1) [bpzcp = 2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethylcyclopenta...

The reaction under thermal conditions of [Cp′ 2 Nb(H) 3 ] ( 1 ), Cp′ = η 5 -C 5 H 4 SiMe 3 , with benzothiazole heterocycles, namely 2-aminobenzothiazole, bzta-NH 2 , 2-hydroxybenzothiazole, bzta-OH, 2-mercaptobenzothiazole, bzta-SH, benzoxazole, namely 2-mercaptobenzoxazole, bzoa-SH, and triazines, namely 1,3,5-triaminetriazine, 1,3,5-trihydroxytriazine, 1,3,5-trimercaptotriazine, (C 3 N 3 )-1,3,5-(XH) 3 , X = NH, O, S, yields a new family of niobocene complexes [Cp′ 2 Nb( κ 2 -X,S-Xbzta)], X = NH ( 2 ), O ( 3 ), S ( 4 ), [Cp′ 2 Nb( κ 2 -S,N-Sbzoa)] ( 5 ) and [(Cp′ 2 Nb) 3 ( κ 2 -X,N-X 3 C 3 N 3 )], X = NH ( 6 ), X = O ( 7 ), X = S ( 8 ). In the same way, the thermal treatment of complex [Cp′ 2 Nb(H)(CNXylyl)] ( 9 ), Xylyl = C 6 H 4 -2,6-Me 2 , with bzta-SH, bzoa-SH and (C 3 H 3 )-1,3,5-(SH) affords the complexes [Cp′ 2 Nb( κ 1 -S-Sbzta)(CNXylyl)] ( 10 ), [Cp′ 2 Nb( κ 1 -S-Sbzoa)(CNXylyl)] ( 11 ) and [{Cp′ 2 Nb(CNXylyl)} 3 ( κ 1 -S-S 3 C 3 N 3 )] ( 12 ). The reaction of compound 10 with an excess of MeI in toluene at room temperature leads to the ionic compound [Cp′ 2 Nb(CNXylyl) 2 ][I 3 ] ( 15 ), which contains two coordinated CNXylyl ligands and a non-coordinated I 3 − counteranion. All complexes were characterized by spectroscopic methods and the molecular structure of [Cp′ 2 Nb(CNXylyl) 2 ][I 3 ] ( 15 ) and [Cp′ 2 Nb(H)(P(OMe) 3 )] · (bzta)′-NH 2 ( 14 ), an adduct of the heterocycle with the hydride–niobocene, have been determined by X-ray molecular studies.

The organo-tin compounds, Me2Sn(C5H4R-1)2 (R = Me (1), Pri (2), But (3), SiMe3 (4)) and Me2Sn(C5Me4R-1)2 (R = H (5), SiMe3 (6)), were prepared by the reaction of Me2SnCl2 with the lithium or sodium derivative of the corresponding cyclopentadiene. Compounds 1–6 have been characterized by multinuclear NMR spectroscopy (1H, 13C, 119Sn). In addition the molecular structures of 5 and 6 were determined by single crystal X-ray diffraction studies. The transmetalation reaction of 1–6 with ZrCl4 or [NbCl4(THF)2] gave the corresponding metallocene complexes in high yields.

The heterometallic complex [TiCp*(O(2)Bz)(2)AlMe(2)] (2) has been synthesised by reaction of [TiCp*(O(2)Bz)(OBzOH)] (1) with AlMe(3) (Cp*=eta(5)-C(5)Me(5); Bz=benzyl). Complex 1 reacts with HOTf to yield the cationic derivative [TiCp*(OBzOH)(2)]OTf (3) (HOTf=HSO(3)CF(3)). Compound 3 reacts with [{M(mu-OH)(cod)}(2)] (M=Rh, Ir; cod=cyclooctadiene) to render the early-late heterometallic complexes [TiCp*(O(2)Bz)(2){M(cod)}(2)]OTf (M=Rh (4); Ir (5)). The molecular structure of complex 4 has been established by single-crystal X-ray diffraction studies.

New aluminium scorpionate based complexes have been prepared and used for the synthesis of cyclic carbonates from epoxides and carbon dioxide. Bimetallic aluminium(heteroscorpionate) complexes 9-14 were synthesised in very high yields. The single-crystal X-ray structures of 12 and 13 confirm an asymmetric κ(2)-NO-μ-O arrangement in a dinuclear molecular disposition. These bimetallic aluminium complexes were investigated as catalysts for the synthesis of cyclic carbonates from epoxides and carbon dioxide in the presence of ammonium salts. Under the optimal reaction conditions, complex 9 in combination with tetrabutylammonium bromide acts as a very efficient catalyst system for the conversion of both monosubstituted and internal epoxides into the corresponding cyclic carbonates showing broad substrate scope. Complex 9 and tetrabutylammonium bromide is the second most efficient aluminium-based catalyst system for the reaction of internal epoxides with carbon dioxide. A kinetic study has been carried out and showed that the reactions were first order in complex 9 and tetrabutylammonium bromide concentrations. Based on the kinetic study, a catalytic cycle is proposed.