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Addition of lithium amides (LiNR2) to carbodiimides/nitriles was achieved in sustainable solvents, under air, allowing the synthesis of guanidines/amidines.

Highly-efficient and selective one-pot/two-step modular double addition of different highly polar organometallic reagents (RLi/RMgX) to nitriles en route to asymmetric tertiary alcohols (without the need for isolation/purification of any halfway reaction intermediate) has been studied, for the first time, in the absence of external/additional organic solvents (neat conditions), at room temperature and under air/moisture (no protecting atmosphere is required), which are generally forbidden reaction conditions in the field of highly-reactive organolithium/organomagnesium reagents. The one-pot modular tandem protocol demonstrated high chemoselectivity with a broad range of nitriles, as no side reactions (Li/halogen exchange, ortho-lithiations or benzylic metalations) were detected. Finally, this protocol could be scaled up, thus proving that this environmentally friendly methodology is amenable for a possible applied synthesis of asymmetric tertiary alcohols under bench type reaction conditions and in the absence of external organic solvents.

We report here the use of commercially available ZnEt

We report the reactivity of N-phosphinoguanidines of the formula (HNR)(Ph2PNR)C(NAr) (R = iPr and Ar = 2,6-iPr2C6H3 [Dipp] for 1a, R = iPr and Ar = 2,4,6-Me3C6H2 [Mes] for 1b, and R = Cy and Ar = D...

We study two metal-free catalysts for the reduction of CO2 with four different hydroboranes and try to identify mechanistically relevant intermediate species. The catalysts are the phosphinoborane Ph2P(CH2)2BBN (1), easily accessible in a one-step synthesis from diphenyl(vinyl)phosphine and 9-borabicyclo[3.3.1]nonane (H-BBN), and its formaldehyde adduct Ph2P(CH2)2BBN(CH2O) (2), detected in the catalytic reduction of CO2 with 1 as the catalyst but properly prepared from compound 1 and p-formaldehyde. Reduction of CO2 with H-BBN gave mixtures of CH2(OBBN)2 (A) and CH3OBBN (B) using both catalysts. Stoichiometric and kinetic studies allowed us to unveil the key role played in this reaction by the formaldehyde adduct 2 and other formaldehyde-formate species, such as the polymeric BBN(CH2)2(Ph2P)(CH2O)BBN(HCO2) (3) and the bisformate macrocycle BBN(CH2)2(Ph2P)(CH2O)BBN(HCO2)BBN(HCO2) (4), whose structures were confirmed by diffractometric analysis. Reduction of CO2 with catecholborane (HBcat) led to MeOBcat (C) exclusively. Another key intermediate was identified in the reaction of 2 with the borane and CO2, this being the bisformaldehyde-formate macrocycle (HCO2){BBN(CH2)2(Ph2P)(CH2O)}2Bcat (5), which was also structurally characterized by X-ray analysis. In contrast, using pinacolborane (HBpin) as the reductant with catalysts 1 and 2 usually led to mixtures of mono-, di-, and trihydroboration products HCO2Bpin (D), CH2(OBpin)2 (E), and CH3OBpin (F). Stoichiometric studies allowed us to detect another formaldehyde-formate species, (HCO2)BBN(CH2)2(Ph2P)(CH2O)Bpin (6), which may play an important role in the catalytic reaction. Finally, only the formaldehyde adduct 2 turned out to be active in the catalytic hydroboration of CO2 using BH3·SMe2 as the reductant, yielding a mixture of two methanol-level products, [(OMe)BO]3 (G, major product) and B(OMe)3 (H, minor product). In this transformation, the Lewis adduct (BH3)Ph2P(CH2)2BBN was identified as the resting state of the catalyst, whereas an intermediate tentatively formulated as the Lewis adduct of compound 2 and BH3 was detected in solution in a stoichiometric experiment and is likely to be mechanistically relevant for the catalytic reaction.

MCIN/AEI [PID2020-117353GB-I00, PGC2018-097366-B-I00, RED2018-102387-T]; Junta de Comunidades de Castilla-La Mancha & ERDF, EU [2021-AYUDA-32015]

A synthetically useful approach of catalytic intramolecular cyclization and oxidation of 2′,2′-(1,4-phenylene)bis(1,3-dialkyl)guanidines (Alkyl = isopropyl 1 or cyclohexyl 2) catalyzed by copper acetate in acetonitrile under air was studied by on line monitoring of the reaction by ESI-MS. All-important intermediates organic species were intercepted during the experiment confirming for the first time the stepwise (1,4-phenylene)bisguanidines cyclization and oxidation mechanism. Moreover, performed collision-induced dissociation (CID) experiments were also applied as a structure elucidation tool. Bimetallic copper intermediates Cu1 ([C28H48Cu2N6O10 + H]+) of m/z 755 and Cu2 [C22H36Cu2N6O4 + H]+ of m/z 575 were documented. The plausible key mechanistic steps involving the formation of organic and inorganic intermediates detected by in situ monitoring of the reaction are presented.

A set of alkyl aluminum complexes supported by non-symmetric ferrocenyl amidine ligands were used as catalysts for the preparation of cyclic carbonates from epoxides and carbon dioxide using Bu4NI as a co-catalyst. A modified method for the synthesis of aminoferrocene allowed us to obtain this precursor in quantitative yield. Treatment of aminoferrocene with the corresponding acetimidoyl chloride afforded the desired ferrocenyl amidine ligands L1H, (E)-N-(2,6-diisopropylphenyl)-N’-(ferrocenyl)acetimidamide, and L2H, (E)-N-(2,6-dimethylphenyl)-N’-(ferrocenyl)acetimidamide. The reaction of these ligands with 1.0 or 0.5 equiv. of AlMe3 led to the synthesis of aminoferrocene based aluminum complexes ((L1)AlMe2 (1), (L2)AlMe2 (2), (L1)2AlMe (3), and (L2)2AlMe (4)) in excellent yields, which were characterized by spectroscopic and X-ray diffraction methods. In addition, we have studied their electrochemical properties and complex 1 was found to be the most active catalyst for the formation of cyclic carbonates 6a–j from their corresponding epoxides 5a–j and CO2.

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.

This work was supported by FONDECYT, Project No. 1200748. Y.R.Y. acknowledges funding from Pontificia Universidad Catolica de Chile via a VRI 2015 -2017 fellowship and Ph.D. CONICYT 2018 fellowship No. 21182120. A.M.-S. acknowledges funding from Ph.D. CONICYT fellowship No. 51150322. The authors also gratefully acknowledge financial support from the Ministerio de Ciencia e Innovacion, Spain (grant numbers CTQ2016-77614-P and RED2018-102387-T) and "Plan Propio de I + D + i" of the Universidad Castilla-La Mancha (grant number 2020-GRIN29078)., A set of trisubstituted guanidine ligands L1H2-L4H2 with general formula (PrHN)(2)CNR (R = Ph (L1H2), R = 2,4,6-Me3C6H2(L2H2), R = p-BrC6H4(L3H2), R = (C5H4)Fe(C5H5), Fc (L4H2)) was employed to synthesize a family of mono- and dinuclear asymmetric methyl aluminum guanidinato compounds ((L2H)AlMe2 (1), (L4H)AlMe2 (2), (L-1)Al2Me4 (3), (L-2)Al2Me4 (4), (L-3)Al2Me4 (5), (L-4)Al2Me4 (6), (L1H)(2)AlMe (7), (L2H)(2)AlMe (8), and (L4H)(2)AlMe (9)) that were characterized by NMR spectroscopy (1-9) and single-crystal X-ray diffraction (4 and 8). These compounds were tested as catalysts for the fixation of carbon dioxide with epoxides to give cyclic carbonates, using tetrabutylammonium iodide (TBAI) as cocatalyst. The reactions were performed under solvent-free conditions at 70 degrees C and 1 bar CO2 pressure. Complexes 1-9 were more active than their respective free guanidines under the same experimental conditions for the synthesis of styrene carbonate (11a). The dinuclear complex 6 was the most efficient and active catalyst for the synthesis of several monosubstituted carbonates (11a-1) with excellent conversions and selectivities. Furthermore, the formation of some disubstituted cyclic carbonates (13a-c) using this dinuclear aluminum catalyst was also studied., Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) CONICYT FONDECYT 1200748, Pontificia Universidad Catolica de Chile, Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) 51150322 21182120, Spanish Government CTQ2016-77614-P RED2018-102387-T, "Plan Propio de I + D + i" of the Universidad Castilla-La Mancha 2020-GRIN29078

We report the reactivity of

We study two metal-free catalysts for the reduction of CO

We have synthesised a set of aromatic mono- and bis(guanidines) which are highly effective binary catalytic systems (guanidine/cocatalyst) for the formation of cyclic carbonates. The presence of multiple N–H bonds causes a modification in the traditional mechanism proposed for the synthesis of cyclic carbonates catalysed by guanidines through the formation of hydrogen bonds between the oxygen atom of the epoxide and the N–H groups of the guanidines. This change allows a considerable reduction of the reaction temperature and CO2 pressure employed in this process.

Novel N-phosphinoguanidines (HNiPr)(Ph2PNiPr)C(NAr) (Ar = 2,6-iPr2C6H3, 2,4,6-Me3C6H2) react with AlMe3 to afford phosphinimine-amidinato derivatives, via an unprecedented rearrangement of an initial N-phosphinoguanidinato intermediate. A reasonable mechanism has been proposed for this transformation, supported by DFT calculations, involving carbodiimide de-insertion followed by a [3+2] cycloaddition.

A selective three-component coupling was employed to fix carbon dioxide to boron guanidinato compounds. The one-pot reaction of carbon dioxide, carbodiimides, and borylamines (ArNH)BC8H14 afforded the corresponding 1,2-adducts {R(H)N}C{N(Ar)}(NR)(CO2)BC8H14. Alternatively, the reaction with p-MeOC6H4NC or 2,6-Me2C6H3NC gave the corresponding isocyanide 1,1-adducts {i-PrHN}C{N(p-Me-C6H4)}(Ni-Pr){CNAr}BC8H14. The molecular structures of products (2,6-i-Pr2C6H3NH)BC8H14 7, {i-Pr(H)N}C{N(p-MeC6H4)}(Ni-Pr)(CO2)BC8H14 9, {Cy(H)N}C{N(p-MeC6H4)}(Cy)(CO2)BC8H14 13, and {i-PrHN}C{N(p-MeC6H4)}(Ni-Pr){CNR″}BC8H14 (R″ = p-MeOC6H4, 2,6-Me2C6H3) 14 and 15 were established by X-ray diffraction. Density functional theory calculations at the M05-2X level of theory revealed that CO2 fixation and formation of the corresponding adduct is exothermic and proceeds via a nonchelate boron guanidinato intermediate.

The excited-state intermolecular proton transfer process (ESPT) in aqueous solution is achieved and controlled by the incorporation of guanidine groups in a fluorescent structure. The bisguanidine under investigation exhibits a dual fluorescence emission with a very high Stokes shifts in water, ≈86 (7890) and 210 (14 500) nm (cm–1), and an excited-stated deprotonation coupled to an intramolecular charge transfer (ICT) process contributes to this emission. The study demonstrates that the emission properties of the different protonation states are strongly dependent on the solvent environment, which also allows luminescence of the molecule to be tuned. The results of this work show the potential utility of guanidine substitution for the stabilization of ESPT–ICT processes in water and allow the subsequent logical design of new stimulus-responsive fluorophores.

Carbodiimides catalyse the reduction of CO2 with H-BBN or BH3·SMe2 to give either mixtures of CH2(OBBN)2 and CH3OBBN or (MeOBO)3 and B(OMe)3 under mild conditions (25–60 °C, 1 atm CO2). Stoichiometric reactions and theoretical calculations were performed to unveil the mechanism of these catalytic processes.

A set of alkyl aluminum complexes supported by non-symmetric ferrocenyl amidine ligands were used as catalysts for the preparation of cyclic carbonates from epoxides and carbon dioxide using Bu4NI as a co-catalyst. A modified method for the synthesis of aminoferrocene allowed us to obtain this precursor in quantitative yield. Treatment of aminoferrocene with the corresponding acetimidoyl chloride afforded the desired ferrocenyl amidine ligands L1H, (E)-N-(2,6-diisopropylphenyl)-N'-(ferrocenyl)acetimidamide, and L2H, (E)-N-(2,6-dimethylphenyl)-N'-(ferrocenyl)acetimidamide. The reaction of these ligands with 1.0 or 0.5 equiv. of AlMe3 led to the synthesis of aminoferrocene based aluminum complexes ((L1)AlMe2 (1), (L2)AlMe2 (2), (L1)2AlMe (3), and (L2)2AlMe (4)) in excellent yields, which were characterized by spectroscopic and X-ray diffraction methods. In addition, we have studied their electrochemical properties and complex 1 was found to be the most active catalyst for the formation of cyclic carbonates 6a-j from their corresponding epoxides 5a-j and CO2.

The discovery of a reaction which allows preparation of boroxide complexes of platinum group metals and study of their behavior under CO atmosphere is described. The trihydride-osmium(IV)-hydroxo complex OsH3(OH){κ3-P,O,P-[xant(PiPr2)2]} (1, xant(PiPr2)2 = 4,5-bis(diisopropylphosphino)xanthene) reacts with the amino-boranes iPr(H)NBCy2 and iPr(H)NBBN to give the osmium(IV)-boroxide derivatives OsH3(OBR2){κ3-P,O,P-[xant(PiPr2)2]} (BR2 = BCy2 (2), BBN (3); BBN = 9-borabicyclo[3.5.1]nonane) and iPrNH2 as a consequence of the addition of the O–H bond of the hydroxo ligand of 1 to the B–N bond of the amino-boranes. At room temperature under CO atmosphere, complexes 2 and 3 eliminate H2 to afford the osmium(II)–boroxide compounds OsH(OBR2)(CO)2{κ2-P,P-[xant(PiPr2)2]} (BR2 = BCy2 (4), BBN (5)) bearing a κ2-P,P-coordinated ether-diphosphine. The subsequent reductive elimination of the borinic acids R2BOH needs heating and a long duration and leads to the tricarbonyl-osmium(0) derivative Os(CO)3{κ2-P,P-[xant(PiPr2)2]} (6) with the phosphorus atoms of the diphosphine lying in the equatorial plane of a pentagonal bypyramid of donor atoms around the metal center. In contrast to 2 and 3, under CO atmosphere, precursor 1 eliminates water to initially give the trans-dihydride OsH2(CO){κ3-P,O,P-[xant(PiPr2)2]} (7), which subsequently evolves to the cis-dihydride-cis-dicarbonyl derivative OsH2(CO)2{κ2-P,P-[xant(PiPr2)2]} (8) and finally into the tricarbonyl 6., Financial support from the MINECO of Spain (Projects CTQ2017-82935-P, CTQ2016-77614-P and Red de Excelencia Consolider CTQ2016-81797-REDC), the Diputación General de Aragón (E06_17R), FEDER, and the European Social Fund is acknowledged. A.R. acknowledges a postdoctoral contract funded by the “Plan Propio de I + D + i” of the Universidad de Castilla-La Mancha.

We report here a series of new adducts incorporating arylguanidines Ar*NC(NiPrH)2 (Ar* = C6H5, (p-CN-C6H4), (p-CF3-C6H4) and (2,4,6-(CH3)3-C6H2)) bearing donor or acceptor substituents in the phenyl rings, and bispentafluorophenylborane [HB(C6F5)2]. The spectroscopic and structural features of the new compounds [(C6F5)2HBNAr*C(NiPrH)2] (Ar* = C6H5 1, (2,4,6-(CH3)3-C6H2) 2, (p-CN-C6H4) 3 and (p-CF3-C6H4) 4) have been studied by multinuclear NMR and X-ray diffraction techniques. The structural differences between 1 and 2–4 compounds have been explained using electronic structure descriptors based on DFT calculations at the B3LYP/6–31 + G(d,p) level in the gas phase.

Expanding the possibilities of the use of simple and available ZnEt2 as a catalyst, the hydroalkynylation of carbodiimides with a variety of alkynes to obtain unsaturated substituted amidines is described in this work. Different stoichiometric studies allow proposing that amidinate complexes are intermediates in this catalytic process, produced by easy activation of the C-H bond of the alkyne and formation of alkynyl derivatives followed by a carbodiimide insertion step. Kinetics studies allowed the generation of a rate law for the hydroalkynylation of N,N'-diisopropylcarbodiimide with phenylacetylene which is second order in [carbodiimide], first order in [catalyst] and zero order in [alkyne], with a negligible PhC[triple bond, length as m-dash]CH/PhC[triple bond, length as m-dash]CD isotopic effect, consistent with a rate-determining state involving carbodiimide insertion. The hydroalkynylation reaction has been coupled with isocyanate (and isothiocyanate) insertion and intramolecular hydroamination to obtain imidazolidin-2-ones (or thione). The structures of different plausible intermediates have been determined by X-ray diffraction studies.

The commercial 9-borabicyclo[3.3.1]nonane dimer is used as the first example of a metal-free catalyst for the monohydroboration of carbodiimides with pinacol borane. Stoichiometric reactions, kinetic studies, and DFT calculations have allowed us to propose a plausible mechanism involving a heterocyclic amidinate intermediate with a three center-two electron B-H-B bond.

A selective three-component coupling was employed to fix carbon dioxide to boron guanidinato compounds. The one-pot reaction of carbon dioxide, carbodiimides, and borylamines (ArNH)BC

Carbodiimides catalyse the reduction of CO2 with H-BBN or BH3·SMe2 to give either mixtures of CH2(OBBN)2 and CH3OBBN or (MeOBO)3 and B(OMe)3 under mild conditions (25-60 °C, 1 atm CO2). Stoichiometric reactions and theoretical calculations were performed to unveil the mechanism of these catalytic processes.

Tris(pentafluorophenyl)borane, [B(C6F5)3], has been used as an efficient catalyst in the guanylation reaction of amines with carbodiimide under mild conditions. A combined approach involving NMR spectroscopy and DFT calculations was employed to gain a better insight into the mechanistic features of this process. The results allowed us to propose a new Lewis acid-assisted Brønsted acidic pathway for the guanylation reaction. The process starts with the interaction of tris(pentafluorphenyl)borane and the amine to form the corresponding adduct, [(C6F5)3B-NRH2] , followed by a straightforward proton transfer to one of the nitrogen atoms of the carbodiimide, (i)PrN[double bond, length as m-dash]C[double bond, length as m-dash]N(i)Pr, to produce, in two consequent steps, a guanidine-borane adduct, [(C6F5)3B-NRC(N(i)PrH)2] . The rupture of this adduct liberates the guanidine product RNC(N(i)PrH)2 and interaction with additional amine restarts the catalytic cycle. DFT studies have been carried out in order to study the thermodynamic characteristics of the proposed pathway. Significant borane adducts with amines and guanidines have been isolated and characterized by multinuclear NMR in order to study the N-B interaction and to propose the existence of possible Frustrated Lewis Pairs. Additionally, the molecular structures of significant components of the catalytic cycle, namely 4-tert-butylaniline-[B(C6F5)3] adduct and both free and [B(C6F5)3]-bonded 1-(phenyl)-2,3-diisopropylguanidine, and respectively, have been established by X-ray diffraction.

The novel guanidinate–osmium(II) complexes [OsCl{2-(N,N′)-C(NR)(NiPr)NHiPr}(6-p-cymene)] [R = Ph (3a), 4-C6H4F (3b), 4-C6H4Cl (3c), 4-C6H4CF3 (3d), 3-C6H4CF3 (3e), 3,5-C6H3(CF3)2 (3f), 4-C6H4CN (3g), 4-C6H4Me (3h), 3-C6H4Me (3i), 2-C6H4Me (3j), 4-C6H4tBu (3k), 2,6-C6H3iPr2 (3l), 2,4,6-C6H2Me3 (3m)] have been synthesized in high yields (70–88 %) by treatment of THF solutions of the dimeric precursor [{OsCl(µ-Cl)(6-p-cymene)}2] (1) with 4 equivalents of the corresponding guanidine (iPrHN)2C=NR (2a–m) at room temperature. The easily separable guanidinium chloride salts [(iPrHN)2C(NHR)]Cl (4a–m) were also formed in these reactions. The structures of 3a, 3d, and 3h were unequivocally confirmed by X-ray diffraction methods. Complexes 3a–m proved to be active in the catalytic dehydration of aldoximes. The best results were obtained with [OsCl{2-(N,N′)-C(N-4-C6H4CF3)(NiPr)NHiPr}(6-p-cymene)] (3d; 5 mol-%), which, in acetonitrile at 80 °C, was able to convert selectively a large variety of aromatic, heteroaromatic, ,-unsaturated, and aliphatic aldoximes into the corresponding nitriles in high yields and short reaction times.

The potential of structurally new ferrocene-functionalized guanidines as redox-active precursors for the synthesis of heterometallic platinum(II)–guanidine complexes with anticancer activity was studied. To this end, an atom-economical catalytic approach was followed by using ZnEt2 to catalyze the addition of aminoferrocene and 4-ferrocenylaniline to N,N′-diisopropylcarbodiimide. Furthermore, reaction of a platinum(II) source with the newly obtained guanidines Fc–N═C(NHiPr)2 (3) and Fc(1,4-C6H4)–N═C(NHiPr)2 (4) provided access to the heterometallic complexes [PtCl2{Fc–N═C(NHiPr)2}(DMSO)] (5), [PtCl2{Fc(1,4-C6H4)–N═C(NHiPr)2}(DMSO)] (6), and [PtCl2{Fc(1,4-C6H4)–N═C(NHiPr)2}2] (7). Electrochemical studies evidence the remarkable electronic effect played by the direct attachment of the guanidine group to the ferrocene moiety in 3, making its one-electron oxidation extremely easy. Guanidine-based Fe–Pt complexes 5 and 6 are active against all human cancer cell lines tested, with GI50 values in the range 1.4–2...

The novel bis(allyl)ruthenium(IV) guanidinate complexes [RuCl{κ2(N,N′)-C(NR)(NiPr)-NHiPr}(η3:η3-C10H16)] (C10H16 = 2,7-dimethylocta-2,6-diene-1,8-diyl; R = Ph (3a), 4-C6H4F (3b), 4-C6H4Cl (3c), 4-C6H4Me (3d), 3-C6H4Me (3e) 4-C6H4tBu (3f)) have been synthesized by treatment of the dimeric precursor [{RuCl(μ-Cl)(η3:η3-C10H16)}2] (1) with 4 equiv of the corresponding guanidine (iPrHN)2C═NR (2a–f). The easily separable guanidinium chloride salts [(iPrHN)2C(NHR)][Cl] (4a–f) are also formed in these reactions. Attempts to generate analogous Ru(IV) guanidinate complexes from (iPrHN)2C═NR (R = 2-C6H4Me (2g), 2,4,6-C6H2Me3 (2h), 2,6-C6H3iPr2 (2i)) failed, due probably to the steric hindrance associated with the aryl group in these guanidines. On the other hand, the reaction of the dimer [{RuCl(μ-Cl)(η3:η3-C10H16)}2] (1) with (iPrHN)2C═N-4-C6H4C≡N (2j) led to the selective formation of the mononuclear derivative [RuCl2(η3:η3-C10H16){N≡C-4-C6H4-N═C(NHiPr2)2}] (5), in which the guanidine coordinates to ruthenium thro...

A combined experimental and quantum chemical study has been performed on rac- and meso-[Zr{1-Me2 Si(3-η5 -C9 H5 Et)2 }Cl2 ] (rac- and meso-1) and their hydrogenated forms (rac- and meso-2) to understand ligand effects and guide ligand design for more active ansa-bis(indenyl) zirconocenes for the polymerisation of ethylene. The rac-ansa-zirconocene rac-[Zr(1-Me2 Si{3-Et-(η5 -C9 H9 )}2 )Cl2 ] (rac-2) has been prepared and fully characterised by NMR spectroscopy and elemental analysis. The molecular structure of rac-2 has also been determined by single-crystal XRD. The behaviour of the catalysts was analysed in the polymerisation of ethylene and higher activities were obtained for rac-1 and its hydrogenated form rac-2. The influence of the stereochemistry and hydrogenation of the indenyl ligand on the experimental activities has been evaluated by computational studies. The differences along the reaction pathway are dominated by changes in the relative stabilities of the catalytic intermediates. A hybrid density functional B3LYP study, in the presence of toluene as the solvent, indicates that the rac forms give rise to more active species than their meso counterparts. The hydrogenation of the rac forms is a very promising approach to increase activities in polymerisation, in contrast to the meso forms. Finally, the global mechanism rate constants for the polymerisation reaction for each metallocene were calculated by using the thermodynamic formulation of transition-state theory to complement the computational study.

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.

Expanding the possibilities of the use of simple and available ZnEt

We report here 1,1- and 1,2-insertion reactions of small unsaturated molecules in the N–B bonds of two boron guanidinates, (Me2N)C(NiPr)2BCy2 (1) and {iPr(H)N}C(NiPr){N(p-tBu-C6H4)}BCy2 (2), and two bisboron guanidinates(2–), {iPr(BCy2)N}C(NiPr){N(p-tBu-C6H4)}BCy2 (3) and {iPr(C8H14B)N}C(NiPr){N(p-Me-C6H4)}BC8H14 (4), the latter being prepared for the first time by double deprotonation of the corresponding guanidine with the 9-borabicyclo[3.3.1]nonane dimer, (H-BC8H14)2. Compounds 1–4 easily insert aromatic isonitriles, XylNC (Xyl = 2,6-Me2-C6H3) and (p-MeO-C6H4)NC, to give the expected diazaboroles 5–12, some of them being structurally characterised by X-ray diffraction. Interestingly, the BC8H14 derivatives 11 and 12 are in a fast temperature-dependent equilibrium with the de-insertion products, whose thermodynamic parameters are reported here. A correlation between these equilibria and the puckered heterocyclic structure found in the solid state for 11, and confirmed by DFT calculations, is also established. Reactions of the aforementioned guanidinates with CO are more sluggish or even precluded, and only one product, {iPr(H)N}C{N(p-tBu-C6H4)}(NiPr)(CO)BCy2 (13), could be isolated in moderate yields. The 1,2-insertions of benzaldehyde in compounds 1, 2 and 4 are reversible reactions in all cases, and only one of the insertion products, {iPr(H)N}C{N(p-tBu-C6H4)}(NiPr)(PhHCO)BCy2 (16a), was isolated and diffractrometrically characterised. Likewise, CO2 reversibly inserts into a N–B bond of 2 to give {iPr(H)N}C{N(p-tBu-C6H4)}(NiPr)(CO2)BCy2 (19) with a conversion of ca. 9%. In all these equilibria, de-insertion is always favoured upon increasing the temperature.

The synthesis of the new zirconium complex [Zr(η5-C5H5){NC-amidine}Cl2] (1) has been achieved by reaction of the amidine (E)-N-(4-cyanophenyl)-N′-(2,6-diisopropylphenyl)acetimidamide with [Zr(η5-C5H5)Cl3] and the new complex has been characterized by spectroscopic methods. The reaction of one equivalent of B(C6F5)3 with compound 1 produces the adduct [Zr(η5-C5H5){(C6F5)3B-NC-amidine}]Cl2 (2). Complexes 1 and 2 have been tested as homogeneous catalysts in olefin polymerization using MAO as cocatalyst. The grafting of 1 and the previously reported complex [Zr(η5-C5H5)(NC-NacNac)Cl2] (3) on to several inorganic solid supports, namely dehydroxylated silica (SiO2(TEMP)) (S1), dehydroxylated silica modified with O(SiMe3)2 (S2) or MAO (S3), and MgCl2 (S4) has been carried out by addition of a freshly prepared solution of 1 or 3 to the corresponding inorganic solid. FT-IR studies of the new materials showed that the links between complexes 1 or 3 and S1 and S2 occur through the zirconium center, whereas with S3 and S4 the links involve the CN functional group of the ligand. These new materials have been studied as catalysts in olefin polymerization reactions in the presence of MAO. A UV–vis study was carried out in order to identify the minimum amount of MAO necessary to produce the active species. A preliminary study into the activity in olefin polymerizations was also carried out.

The guanidine proligands {2-[4-(tert-butyl)phenyl]-1,3-diisopropylguanidine} (1), [2-(4-methoxyphenyl)-1,3-diisopropylguanidine] (2) and [2-(4-bromophenyl)-1,3-diisopropylguanidine] (3) have been prepared by guanylation of anilines with diisopropylcarbodiimide, using [MgBz2(thf)2] as the catalyst at room temperature. These proligands react with the complex {[Nb(CH2SiMe3)3(CH3CN)]2(μ-1,4-NC6H4N)} (4) to afford new guanidinate-supported dialkyl niobium dinuclear complexes [{Nb(CH2SiMe3)2[(4-tBuC6H4)N=C(NiPr)(NHiPr)]}2(μ-1,4-NC6H4N)] (5), [{Nb(CH2SiMe3)2[(4-MeOC6H4)N=C(NiPr)(NHiPr)]}2(μ-1,4-NC6H4N)] (6) and [{Nb(CH2SiMe3)2[(4-BrC6H4)N=C(NiPr)(NHiPr)]}2(μ-1,4-NC6H4N)] (7). Treatment of compounds 5–7 with 2 equiv. of 2,6-dimethylphenyl isocyanide gave the imido bis(iminoacyl) compounds [{Nb(Me3SiCH2C=Nxylyl)2[(4-tBuC6H4)N=C(NiPr)(NHiPr)]}2(μ-1,4-NC6H4N)] (8), [{Nb(Me3SiCH2C=Nxylyl)2[(4-MeOC6H4)N=C(NiPr)(NHiPr)]}2(μ-1,4-NC6H4N)] (9) and [{Nb(Me3SiCH2C=Nxylyl)2[(4-BrC6H4)N=C(NiPr)(NHiPr)]}2(μ-1,4-NC6H4N)] (10). The molecular structures of compound 2 and complex 9 have been determined.

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...

To advance the catalytic applications of s-block mixed-metal complexes, sodium magnesiate [NaMg(CH2SiMe3)3] (1) is reported as an efficient precatalyst for the guanylation of a variety of anilines and secondary amines with carbodiimides. First examples of hydrophosphination of carbodiimides by using a Mg catalyst are also described. The catalytic ability of the mixed-metal system is much greater than that of its homometallic components [NaCH2SiMe3 ] and [Mg(CH2SiMe3)2]. Stoichiometric studies suggest that magnesiate amido and guanidinate complexes are intermediates in these catalytic routes. Reactivity and kinetic studies imply that these guanylation reactions occur via (tris)amide intermediates that react with carbodiiimides in insertion steps. The rate law for the guanylation of N,N'-diisopropylcarbodiimide with 4-tert-butylaniline catalyzed by 1 is first order with respect to [amine], [carbodiimide], and [catalyst], and the reaction shows a large kinetic isotopic effect, which is consistent with an amine-assisted rate-determining carbodiimide insertion transition state. Studies to assess the effect of sodium in these transformations denote a secondary role with little involvement in the catalytic cycle.

The synthesis of novel dialkylboron guanidinates is reported: the symmetrical compounds, (Me2N)C(NR)2BR′2 [R = iPr, R′ = Nrb (1); R = Cy, R′ = Nrb (2); R = iPr, R′ = Cy (3); R = R′ = Cy (4); R = 2,6-iPr2-C6H3; R′ = Cy (5); Nrb = exo-2-norbornyl] and the asymmetrically coordinated {iPr(H)N}C(NiPr)(NAr)BCy2 [Ar = Ph (6), 4-Me-C6H4 (7), 4-tBu-C6H4 (8)] were prepared by the salt metathesis method from the appropriate lithium guanidinates and chloroboranes. Moreover, the bis(dicyclohexylboron)guanidinate(−2) {iPr(Cy2B)N}C(NiPr){N(4-tBu-C6H4)}BCy2 (9) was also prepared from the corresponding dilithium guanidinate Li2[{N(4-tBu-C6H4)}C(NiPr)2] and ClBCy2. The structures of compounds 1, 3, 6 and 9 were confirmed by X-ray diffraction and all displayed a chelate coordination of the guanidinate ligand to the BR′2 fragment, the latter displaying an additional BCy2 attached to the exocyclic N atom. Solutions of compounds 1–4 reached an equilibrium with the aminoboranes Me2NBR′2 [R′ = Nrb (10), Cy (11)] and the corresponding carbodiimides, which was slow at 25 °C. The thermodynamic parameters for these equilibria are also reported. The activation parameters for the equilibrium for compound 1 have been calculated after a kinetic study. Compounds 5–8, with one or two N-aryl fragments bound to a B centre, are more robust and need higher temperatures (80 °C) and prolonged times to give similar carbodiimide de-insertion reactions.

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 ruthenium(II) arene dimer [{RuCl(μ-Cl)(η6-p-cymene)}2] readily reacted with 4 equiv of guanidines (iPrHN)2C═NR (R = iPr (1a), 4-C6H4tBu (1b), 4-C6H4Br (1c), 2,4,6-C6H2Me3 (1d), 2,6-C6H3iPr2 (1e...

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.

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 second polyhydridoniobocene complex that was characterized by X-ray diffraction is reported. On the basis of H–H distances and H–Nb–H angles, [Nb(η5-C5H4SiMe3)2(H)3] (1) is classified as a “compressed hydride”. Compound 1 acts as an efficient single-component initiator for the ring-opening polymerization of ϵ-caprolactone and δ-valerolactone. ϵ-Caprolactone and δ-valerolactone are both polymerized within a few hours to yield high-to-medium-molecular-weight polymers with medium to broad polydispersities. Polymer end-group analysis showed that the polymerization proceeds through a coordination–insertion mechanism based on the cleavage of the ring between the oxygen atom and the acyl carbon atom.

New C- ansa -zirconocene complexes containing methoxythiophenolate and mercaptophenolate ligands have been synthesized and characterized. The reaction of (HSC 6 H 4 - n -OMe) ( n = 2, 3 or 4) with [Zr{( t -Bu)HC(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )}Me 2 ] ( 1 ) led to the formation of monosubstituted complexes [Zr{( t -Bu)HC(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )}Me(κ,S-SC 6 H 4 - n -OMe)] ( n = 2 ( 2 ); n = 3 ( 3 )) and the disubstituted complex [Zr{( t -Bu)HC(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )}(κ,S-SC 6 H 4 -4-OMe) 2 ] ( 4 ). The complexes [Zr{(R)HC(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )}(κ,O-OC 6 H 4 -4-SH) 2 ] (R = t -Bu ( 6 ); R = CH 2 CH CH 2 ( 7 )) and [Zr(η 5 -C 5 H 4 ) 2 (OC 6 H 4 - n -SH) 2 ] ( n = 3 ( 9 ); n = 4 ( 10 )) have been synthesized using the corresponding dimethyl zirconocene and mercaptophenol. However, the reaction of [Zr{( t -Bu)HC(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )}Cl 2 ] ( 11 ) with 4-mercaptophenol in the presence of NEt 3 led to the formation of the first example of a homoleptic six-coordinate mercaptophenolate complex of zirconium, namely [HNEt 3 ] 2 [Zr(κ,O-OC 6 H 4 -4-SH) 6 ] ( 12 ). Complex 12 can be obtained in higher yield by the reaction of ZrCl 4 with six equivalents of 4-mercaptophenol and NEt 3. The reaction of 12 with [Zr(η 5 -C 5 H 4 ) 2 Cl 2 ] gave the unexpected disubstituted complex [Zr(η 5 -C 5 H 4 ) 2 (OC 6 H 4 -4-SH) 2 ] ( 10 ). The molecular structures of 4 and 12 have been determined by single-crystal X-ray diffraction studies.

The synthesis of the new cationic functionalized phosphane niobocene complexes [Nb(η 5 -C 5 H 4 SiMe 3 ) 2 (P(CH 2 CO(C 6 H 5 ))Ph 2 )(L)]Cl, L CO ( 3 ) or CNXylyl ( 4 ), and new phosphamido-niobocene complexes [Nb(η 5 -C 5 H 4 SiMe 3 ) 2 (P{CO(C 6 H 5 )}Ph 2 )(L)]Cl, L CO ( 5 ), CNXylyl ( 6 ), [Nb(η 5 -C 5 H 4 SiMe 3 ) 2 (P(COCH(C 6 H 5 ) 2 )Ph 2 )(L)]Cl, L CO ( 7 ) or CNXylyl ( 8 ), has been achieved. The complexes were prepared by reaction of the Lewis base niobocene complexes [Nb(η 5 -C 5 H 4 SiMe 3 ) 2 (PPh 2 )(L)], L CO ( 1 ) or CNXylyl ( 2 ), with the appropriate RX (PhCOCH 2 Cl, chloroacetophenone) and RCOX (PhCOCl, benzoyl chloride, Ph 2 CHCOCl, diphenylacetyl chloride) reagents through the formation of new P–C bonds in the corresponding nucleophilic substitution reactions. These processes afforded new metallophosphanes in which one of the substituents on the phosphorus atom contains a ketonic moiety. The presence of the carbonyl group in the coordination sphere of phosphorus increases the coordination possibilities of the phosphane and enriches the applications of these complexes.

The reactivity of hybrid scorpionate/cyclopentadienyl ligand-containing trichloride zirconium complexes [ZrCl 3 (bpzcp)] ( 1 ) [bpzcp = 2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethylcyclopentadienyl] and [ZrCl 3 (bpztcp)] ( 2 ) [bpztcp = 2,2-bis(3,5-dimethylpyrazol-1-yl)-1- tert -butylethylcyclopentadienyl] toward several lithium alkoxides has been carried out. Thus, alkoxide-containing complexes [ZrCl 2 (OR)(bpzcp)] (R = Me, 3 ; Et, 4 ; i Pr, 5 ; ( R )-2-Bu, 6 ), [ZrCl 2 (OR)(bpztcp)] (R = Me, 7 ; Et, 8 ; i Pr, 9 ; ( R )-2-Bu, 10 ) and [Zr(OR) 3 (bpztcp)] (R = Et, 11 ; i Pr, 12 ) were prepared by deprotonation of the appropriate alcohol group with Bu n Li followed by reaction with 1 or 2 . In addition, the imido-complex [Ti(N t Bu)Cl(bpztcp)(py)] ( 13 ) were also prepared. The structures of these complexes have been proposed on basis of spectroscopic and DFT methods.

Activation of ansa-zirconocenes of the type Rac [Zr{1-Me2Si(3-R-(η5-C9H5))(3-R′-(η5-C9H5))}Cl2] [R = Et, R′ = H (1); R = Pr, R′ = H (2); and R = Et, R′ = Pr (3), R, R′ = Me (4) and R, R′ = Bu (5)] by MAO has been studied by UV–visible spectroscopy. Compounds 1–3 have been tested in the polymerization of ethylene at different Al:Zr ratios. UV–vis spectroscopy was used to determine a correlation between the electronic structures of (1–5) and their polymerization activity. Copyright © 2009 John Wiley & Sons, Ltd.

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.

Bis(imino)piridyl vanadium(III) complexes have been synthesized and characterized by NMR, FT-IR and UV–vis spectroscopy. The activation reaction of these complexes in solution with methylalumoxane (MAO) was followed by UV–vis spectroscopy. The reactions of the complexes with the surface of silica were monitored by FT-IR spectroscopy. The resulting materials were activated with MAO or triisobutylaluminium (TIBA) and the catalytic systems were evaluated in the polymerization of ethylene. Characterization of the catalysts was accomplished by elemental analysis and by UV–vis spectroscopy. The effects caused by the nature of the support in the fixing reaction of the complex, as well as the catalytic activities of the resulting materials compared with those of the molecular precursors, are presented and discussed.