Side-On Bonded Beryllium Dinitrogen Complexes

The preparation and spectroscopic identification of the complexes NNBe(η²-N₂) and (NN)₂Be(η²-N₂) and the energetically higher lying isomers Be(NN)₂ and Be(NN)₃ are reported. NNBe(η²-N₂) and (NN)₂Be(η²-N₂) are the first examples of covalently side-on bonded N₂ adducts of a main-group element. The analysis of the electronic structure using modern methods of quantum chemistry suggests that NNBe(η²-N₂) and (NN)₂Be(η²-N₂) should be classified as π complexes rather than metalladiazirines.     

Ansa‐Bridged Bis(benzene) Titanium Complexes

Taking advantage of an improved synthesis of [Ti(η⁶‐C₆H₆)₂], we report here the first examples of ansa‐bridged bis(benzene) titanium complexes. Deprotonation of [Ti(η⁶‐C₆H₆)₂] with nBuLi in the presence of N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine (pmdta) leads to the corresponding 1,1′‐dilithio salt [Ti(η⁶‐C₆H₅Li)₂] ? pmdta that enables the preparation of the first one‐ and two‐atom‐bridged complexes by simple salt metathesis. The ansa complexes were fully characterized (NMR spectroscopy, UV/Vis spectroscopy, elemental analysis, and X‐ray crystallography) and further studied electrochemically and computationally. Moreover, [Ti(η⁶‐C₆H₆)₂] is found to react with the Lewis base 1,3‐dimethylimidazole‐2‐ylidene (IMe) to give the bent sandwich complex [Ti(η⁶‐C₆H₆)₂(IMe)].     

Diimido‐, Imido(oxo)‐, Dioxo‐ und Imido(alkyliden)‐Halbsandwich‐Verbindungen über selektive Hydrolyse und α—H‐Abstraktion an Organylkomplexen des sechswertigen Molybdäns und Wolframs

Diimido, Imido Oxo, Dioxo, and Imido Alkylidene Halfsandwich Compounds via Selective Hydrolysis and α—H Abstraction in Molybdenum(VI) and Tungsten(VI) Organyl Complexes Organometal imides [(η⁵‐C₅R₅)M(NR′)₂Ph] (M = Mo, W, R = H, Me, R′ = Mes, tBu) 4 — 8 can be prepared by reaction of halfsandwich complexes [(η⁵‐C₅R₅)M(NR′)₂Cl] with phenyl lithium in good yields. Starting from phenyl complexes 4 — 8 as well as from previously described methyl compounds [(η⁵‐C₅Me₅)M(NtBu)₂Me] (M = Mo, W), reactions with aqueous HCl lead to imido(oxo) methyl and phenyl complexes [(η⁵‐C₅Me₅)M(NtBu)(O)(R)] M = Mo, R = Me ( 9 ), Ph ( 10 ); M = W, R = Ph ( 11 ) and dioxo complexes [(η⁵‐C₅Me₅)M(O)₂(CH₃)] M = Mo ( 12 ), M = W ( 13 ). Hydrolysis of organometal imides with conservation of M‐C σ and π bonds is in fact an attractive synthetic alternative for the synthesis of organometal oxides with respect to known strategies based on the oxidative decarbonylation of low valent alkyl CO and NO complexes. In a similar manner, protolysis of [(η⁵‐C₅H₅)W(NtBu)₂(CH₃)] and [(η⁵‐C₅Me₅)Mo(NtBu)₂(CH₃)] by HCl gas leads to [(η⁵‐C₅H₅)W(NtBu)Cl₂(CH₃)] 14 und [(η⁵‐C₅Me₅)Mo(NtBu)Cl₂(CH₃)] 15 with conservation of the M‐C bonds. The inert character of the relatively non‐polar M‐C σ bonds with respect to protolysis offers a strategy for the synthesis of methyl chloro complexes not accessible by partial methylation of [(η⁵‐C₅R₅)M(NR′)Cl₃] with MeLi. As pure substances only trimethyl compounds [(η⁵‐C₅R₅)M(NtBu)(CH₃)₃] 16 ‐ 18 , M = Mo, W, R = H, Me, are isolated. Imido(benzylidene) complexes [(η⁵‐C₅Me₅)M(NtBu)(CHPh)(CH₂Ph)] M = Mo ( 19 ), W ( 20 ) are generated by alkylation of [(η⁵‐C₅Me₅)M(NtBu)Cl₃] with PhCH₂MgCl via α‐H abstraction. Based on nmr data a trend of decreasing donor capability of the ligands [NtBu]^2— > [O]^2— > [CHR]^2— ? 2 [CH₃]^— > 2 [Cl]^— emerges.     

Beryllium Atom Mediated Dinitrogen Activation via Coupling with Carbon Monoxide

The reactions of laser‐ablated beryllium atoms with dinitrogen and carbon monoxide mixtures form the end‐on bonded NNBeCO and side‐on bonded (η²‐N₂)BeCO isomers in solid argon, which are predicted by quantum chemical calculations to be almost isoenergetic. The end‐on bonded complex has a triplet ground state while the side‐on bonded isomer has a singlet electronic ground state. The complexes rearrange to the energetically lowest lying NBeNCO isomer upon visible light excitation, which is characterized to be an isocyanate complex of a nitrene derivative with a triplet electronic ground state. A bonding analysis using a charge‐ and energy decomposition procedure reveals that the electronic reference state of Be in the NNBeCO isomers has an 2s⁰2p² excited configuration and that the metal‐ligand bonds can be described in terms of N₂→Be←CO σ donation and concomitant N₂←Be→CO π backdonation. The results demonstrate that the activation of N₂ with the N?N bond being completely cleaved can be achieved via coupling with carbon monoxide mediated by a main group atom.     

Synthesis of 2‐(N‐arylimino)pyrrolide nickel complexes and polymerization of methyl methacrylate

The synthesis, characterization and methyl methacrylate polymerization behaviors of 2‐(N‐arylimino)pyrrolide nickel complexes are described. The nickel complex [NN]₂Ni ( 1 , [NN] = [2‐C(H)NAr‐5‐tBu‐C₄H₂N]^?, Ar = 2,6‐iPr₂C₆H₃) was prepared in good yield by the reaction of [NN]Li with trans‐[Ni(Cl)(Ph)(PPh₃)₂] in THF. Reaction of [NN]Li with NiBr₂(DME) yielded the nickel bromide [NN]Ni(Br)[NNH] ( 2 ). Complexes 1 and 2 were characterized by ¹H NMR and IR spectroscopy and elemental analysis, and by X‐ray single crystal analysis. Both complexes, upon activation with methylaluminoxane, are highly active for the polymerization of methyl methacrylate to give high molecular weight polymethylmethacrylate with narrow molecular distributions. Copyright © 2009 John Wiley & Sons, Ltd.     

The Influence of Substituents at C2 Carbon Atom of Thiosemicarbazones {R(H)C2=N3‐N2(H)‐C1(=S)‐N1H2} on their Dentacy in PtII/PdII Complexes: Synthesis,Spectroscopy, and Crystal Structures

The coordination chemistry of platinum(II) with a series of thiosemicarbazones {R(H)C²=N³‐N²(H)‐C¹(=S)‐N¹H₂, R = 2‐hydroxyphenyl, H₂stsc; pyrrole, H₂ptsc; phenyl, Hbtsc} is described. Reactions of trans‐PtCl₂(PPh₃)₂ precursor with H₂stsc (or H₂ptsc) in 1 : 1 molar ratio in the presence of Et₃N base yielded complexes, [Pt(η³‐ O, N³, S‐stsc)(PPh₃)] ( 1 ) and [Pt(η³‐ N⁴, N³, S‐ptsc)(PPh₃)] ( 2 ), respectively. Further, trans‐PtCl₂(PPh₃)₂ and Hbtsc in 1 : 2 (M : L) molar ratio yielded a different compound, [Pt(η²‐ N³, S‐btsc)(η¹‐S‐btsc)(PPh₃)] ( 3 ). Complex 1 involved deprotonation of hydrazinic (‐N²H‐) and hydroxyl (‐OH) groups, and stsc^2? is coordinating via O, N³, S donor atoms, while complex 2 involved deprotonation of hydrazinic (‐N²H‐) and ‐N⁴H groups and ptsc^2? is probably coordinating via N⁴, N³, S donor atoms. Reaction of PdCl₂(PPh₃)₂ with Hbtsc‐Me {C₆H₅(CH₃)C²=N³‐N²(H)‐C¹(=S)‐N¹H₂} yielded a cyclometallated complex [Pd(η³‐C, N³, S‐btsc‐Me)(PPh₃)] ( 4 ). These complexes have been characterized with the help of analytical data, spectroscopic techniques {IR, NMR (¹H, ³¹P), U.V} and single crystal X‐ray crystallography ( 1 , 3 and 4 ). The effects of substituents at C² carbon of thiosemicarbazones on their dentacy and cyclometallation are emphasized.     

On the Electronic Structure and Photochemistry of Coordinatively Unsaturated Complexes: The Case of Nickel Bis‐dinitrogen,Ni(N2)2

The electronic ground and excited states of the coordinatively unsaturated complex Ni(η¹‐N₂)₂, isolated in an Ar matrix, are analyzed in detail by vibrational and electronic absorption and emission spectroscopies allied with quantum chemical calculations. The bond force constants are determined from a normal coordinate analysis and compared with those of the isoelectronic carbonyl complex. The consequences for the bond properties are discussed, and the trend in the force constants is compared with the standard formation enthalpies. The linear complex Ni(η¹‐N₂)₂ with two terminal dinitrogen ligands can be photoisomerized to two isomeric, metastable forms Ni(η¹‐N₂)(η²‐N₂) and Ni(η²‐N₂)₂, with one and two side‐on coordinated dinitrogen ligands, respectively.     

2H‐Azirines as Ligands: Structural Characterization of the First Neutral and Cationic (η5‐C5Me5)Rh(III) 2H‐Azirine Complexes

The synthesis and structural characterization of two azirine rhodium(III ) complexes are described. The stabilization, N‐coordination and phenylgroup π‐stacking of the highly reactive and strained 3‐phenyl‐2H‐azirine by transition metal coordination is observed. The reaction of the dimeric complex [(η⁵‐C₅Me₅)RhCl₂]₂ with 3‐phenyl‐2H‐azirine (az) in CH₂Cl₂ at room temperature in a 1:2 molar ratio afforded the neutral mono‐azirine complex [(η⁵‐C₅Me₅)RhCl₂(az)]. The subsequent reaction of [(η⁵‐C₅Me₅)RhCl₂]₂ with six equivalents of az and 4 equivalents of AgOTf yielded the cationic tris‐azirine complex [(η⁵‐C₅Me₅)Rh(az)₃](OTf)₂. After purification, all complexes have been fully characterized. The molecular structures of the novel rhodium(III ) complexes exhibit slightly distorted octahedral coordination geometries around the metal atoms.     

Activation of Molecular Hydrogen by Bis(η5,η1‐pentafulvene)‐titanium Complexes – Efficient Formation of Titanium(III)hydrides

The synthesis and crystal structures of two dinuclear titanocene hydride complexes are reported. Both complexes, namely bis(η⁵‐(di‐para‐tolylmethyl)cyclopentadienyl)titanium hydride dimer, [(η⁵‐C₂₀H₁₉)₂Ti(μ‐H)]₂ ( 2a ), and bis(η⁵‐2‐adamantylcyclopentadienyl)‐titanium hydride dimer, [(η⁵‐C₁₅H₁₉)₂Ti(μ‐H)]₂ ( 2b ), are formed via activation of molecular hydrogen by the corresponding bis(η⁵,η¹‐pentafulvene)titanium complexes 1a and 1b at ambient temperatures and pressures in high yields. The hydride complexes 2a and 2b exhibit planar [Ti₂H₂] cores and, as a result of the heterolytic cleavage of molecular hydrogen, substituted Cp Ligands were formed during the reaction.     

Experimental and Computational Studies on the Reactivity of a Terminal Thorium Imidometallocene towards Organic Azides and Diazoalkanes

The reaction of the base‐free terminal thorium imido complex [{η⁵‐1,2,4‐(Me₃C)₃C₅H₂}₂Th?N(p‐tolyl)] ( 1 ) with p‐azidotoluene yielded irreversibly the tetraazametallacyclopentene [{η⁵‐1,2,4‐(Me₃C)₃C₅H₂}₂Th{N(p‐tolyl)N?N? N(p‐tolyl)}] ( 2 ), whereas the bridging imido complex [{[η⁵‐1,2,4‐(Me₃C)₃C₅H₂]Th(N₃)₂}₂{μ‐N(p‐tolyl)}₂][(n‐C₄H₉)₄N]₂ ( 3 ) was isolated from the reaction of 1 with [(n‐C₄H₉)₄N]N₃. Unexpectedly, upon the treatment of 1 with 9‐diazofluorene, the NN bond was cleaved, an N atom was transferred, and the η²‐diazenido iminato complex [{η⁵‐1,2,4‐(Me₃C)₃C₅H₂}₂Th{η²‐[N?N(p‐tolyl)]}{N?(9‐C₁₃H₈)}] ( 4 ) was formed. In contrast, the reaction of 1 with Me₃SiCHN₂ gave the nitrilimido complex [{η⁵‐1,2,4‐(Me₃C)₃C₅H₂}₂Th{NH(p‐tolyl)}{N₂CSiMe₃}] ( 5 ), which slowly converted into [{η⁵‐1,2,4‐(Me₃C)₃C₅H₂}{η⁵:κ‐N‐1,2‐(Me₃C)₂‐4‐CMe₂(CH₂NN?CHSiMe₃)C₅H₂}Th{NH(p‐tolyl)}] ( 6 ) by intramolecular C? H bond activation. The experimental results are complemented by density functional theory (DFT) studies.     

Mirror‐Image Organometallic Osmium Arene Iminopyridine Halido Complexes Exhibit Similar Potent Anticancer Activity

Four chiral Os^II arene anticancer complexes have been isolated by fractional crystallization. The two iodido complexes, (S_Os,S_C)‐[Os(η⁶‐p‐cym)(ImpyMe)I]PF₆ (complex 2 , (S)‐ImpyMe: N‐(2‐pyridylmethylene)‐(S)‐1‐phenylethylamine) and (R_Os,R_C)‐[Os(η⁶‐p‐cym)(ImpyMe)I]PF₆ (complex 4 , (R)‐ImpyMe: N‐(2‐pyridylmethylene)‐(R)‐1‐phenylethylamine), showed higher anticancer activity (lower IC₅₀ values) towards A2780 human ovarian cancer cells than cisplatin and were more active than the two chlorido derivatives, (S_Os,S_C)‐[Os(η⁶‐p‐cym)(ImpyMe)Cl]PF₆, 1 , and (R_Os,R_C)‐[Os(η⁶‐p‐cym)(ImpyMe)Cl]PF₆, 3 . The two iodido complexes were evaluated in the National Cancer Institute 60‐cell‐line screen, by using the COMPARE algorithm. This showed that the two potent iodido complexes, 2 (NSC: D‐758116/1) and 4 (NSC: D‐758118/1), share surprisingly similar cancer cell selectivity patterns with the anti‐microtubule drug, vinblastine sulfate. However, no direct effect on tubulin polymerization was found for 2 and 4 , an observation that appears to indicate a novel mechanism of action. In addition, complexes 2 and 4 demonstrated potential as transfer‐hydrogenation catalysts for imine reduction.     

Photochemically Induced Reductive Elimination as a Route to a Zirconocene Complex with a Strongly Activated N2 Ligand

The zirconocene dinitrogen complex [{(η⁵‐C₅Me₄H)₂Zr}₂(μ₂,η²,η²‐N₂)] was synthesized by photochemical reductive elimination from the corresponding zirconium bis(aryl) or aryl hydride complexes, providing a high‐yielding, alkali metal‐free route to strongly activated early‐metal N₂ complexes. Mechanistic studies support the intermediacy of zirconocene arene complexes that in the absence of sufficient dinitrogen promote C? H activation or undergo comproportion to formally Zr^III complexes. When N₂ is in excess arene displacement gives rise to strong dinitrogen activation.     

Well-Defined Aminophenolate Zinc and Magnesium Complexes as Excellent Inhitiators for the ROP of Lactides

A series of molecular homo and heteroleptic zinc and magnesium compounds with aminophenolate ligands [(µ,η²-L²)ZnEt]₂ ( 1 ), [(η²-L²)Zn(µ-BnO)]₂ ( 2 ), [Zn(η²-L²)₂] ( 3 ), [Zn(η²-L³)₂] ( 4 ), [Mg(η²-L³)₂] ( 5 ) (L²-H = N-[methylene(2-hydroxy-3,5-di-tert-butylphenyl)]-N-methyl-N-cyclohexylamine, L³-H = N-[methylene(2-hydroxy-3,5-di-tert-butylphenyl)]-N-methyl-N-methyl-1,3-dioxolaneamine) have been prepared and characterized. The homoleptic complexes 3–5 are most probably a mixture of diastereoisomers that in solution show an interesting dynamics which plays an important role in their catalytic behavior. The complexes 2 – 5 are efficient initiators in ring-opening polymerization (ROP) of lactides to produce polymers with desired molecular weight and narrow polydispersity.     

The Thermally Stable Silylene Si[(NCH2But)2C6H4‐1,2]: Reactions with ButCN,AdCN, ButNC,AdN3, and Me3SiN3 (Ad = 1‐Adamantyl)

The crystalline compounds NSi(NN)Si(NN)CR [R = Bu^t ( 2 a ), Ad ( 2 b )], (NN)Si(Bu^t)CN ( 3 ), Bu^tSi(NN)Si(NN)CN ( 4 ), AdNSi(NN)Si(NN) ( 5 ), AdNN=NN(Ad)Si(NN) ( 6 ), (NN)Si(N₃)N(SiMe₃)₂ ( 7 ) and Me₃SiNSi(NN)Si(NN)(thf) ( 8 ) were obtained in good yield under mild conditions from Si[(NCH₂Bu^t)₂C₆H₄‐1,2] [≡ Si(NN)] and the appropriate reagent RCN, Bu^tNC and R′N₃. The compounds 2 – 8 were characterised by microanalysis, multinuclear NMR and (not 8 ) mass spectra, as well as for 2 a , 4 and 7 single crystal X‐ray diffraction data. The results are placed in context of data in the literature on reactions of especially Si[N(Bu^t)CH=]₂, (SiBu^t₂)₃, Mes₂Si=SiMes₂ with (where available) a nitrile, isonitrile or azide. Reaction pathways are discussed.     

Tuning the Excited State of Water‐Soluble IrIII‐Based DNA Intercalators that are Isostructural with [RuII(NN)2(dppz)] Light‐Switch Complexes

The synthesis of two new Ir^III complexes which are effectively isostructural with well‐established [Ru(NN)₂(dppz)]²⁺ systems is reported (dppz=dipyridophenazine; NN=2,2′‐bipyridyl, or 1,10‐phenanthroline). One of these Ir^III complexes is tricationic and has a conventional N₆ coordination sphere. The second dicationic complex has a N₅C coordination sphere, incorporating a cyclometalated analogue of the dppz ligand. Both complexes show good water solubility. Experimental and computational studies show that the photoexcited states of the two complexes are very different from each other and also differ from their Ru^II analogues. Both of the complexes bind to duplex DNA with affinities that are two orders of magnitude higher than previously reported Ir(dppz)‐based systems and are comparable with Ru^II(dppz) analogues.     

Stabilization of a Silaaldehyde by its η2 Coordination to Tungsten

Treatment of pyridine‐stabilized silylene complexes [(η⁵‐C₅Me₄R)(CO)₂(H)W?SiH(py)(Tsi)] (R=Me, Et; py=pyridine; Tsi=C(SiMe₃)₃) with an N‐heterocyclic carbene ^MeIⁱPr (1,3‐diisopropyl‐4,5‐dimethylimidazol‐2‐ylidene) caused deprotonation to afford anionic silylene complexes [(η⁵‐C₅Me₄R)(CO)₂W?SiH(Tsi)][H^MeIⁱPr] (R=Me ( 1‐Me ); R=Et ( 1‐Et )). Subsequent oxidation of 1‐Me and 1‐Et with pyridine‐N‐oxide (1 equiv) gave anionic η²‐silaaldehydetungsten complexes [(η⁵‐C₅Me₄R)(CO)₂W{η²‐O?SiH(Tsi)}][H^MeIⁱPr] (R=Me ( 2‐Me ); R=Et ( 2‐Et )). The formation of an unprecedented W‐Si‐O three‐membered ring was confirmed by X‐ray crystal structure analysis.     

Enantioselective Synthesis and Application to the Allylic Imidate Rearrangement of Amine‐Coordinated Palladacycle Catalysts of Cobalt Sandwich Complexes

The reaction of (η⁵‐(N,N‐dimethylaminomethyl)cyclopentadien‐yl)(η⁴‐tetraphenylcyclobutadiene)cobalt with sodium tetrachloropalladate and (R)‐N‐acetylphenylalanine gave planar chiral palladacycle di‐μ‐chloridebis[(η⁵‐(S_p)‐2‐(N,N‐dimethylaminomethyl)cyclopentadienyl,1‐C,3′‐N)(η⁴‐tetraphenylcyclobutadiene)cobalt]dipalladium [(S_p)‐Me₂‐CAP‐Cl] in 92 % ee and 64 % yield. Enantiopurity (>98 % ee) was achieved by purification of the monomeric (R)‐proline adducts and conversion back to the chloride dimer. Treatment with AgOAc gave (S_p)‐Me₂‐CAP‐OAc which was applied to asymmetric transcyclopalladation (up to 78 % ee). The (R)‐N‐acetylphenylalanine mediated palladation methodology was applicable also to the corresponding N,N‐diethyl (82 % ee, 39 % yield) and pyrrolidinyl (>98 % ee, 43 % yield) cobalt sandwich complexes. A combination of 5 mol % of the latter [(S_p)‐Pyrr‐CAP‐Cl] and AgNO₃ (3.8 equiv) is a catalyst for the allylic imidate rearrangement of an (E)‐N‐aryltrifluoroacetimidate (up to 83 % ee), and this catalyst system is also applicable to the rearrangement of a range of (E)‐trichloroacetimidates (up to 99 % ee). This asymmetric efficiency combined with the simplicity of catalyst synthesis provides accessible solutions to the generation of non‐racemic allylic amine derivatives.     

Facile Access to Silicon‐Functionalized Bis‐Silylene Titanium(II) Complexes

A series of unprecedented bis‐silylene titanium(II) complexes of the type [(η⁵‐C₅H₅)₂Ti(LSiX)₂] (L=PhC(NtBu)₂; X=Cl, CH_3, H) has been prepared using a phosphane elimination strategy. Treatment of the [(η⁵‐C₅H₅)₂Ti(PMe₃)₂] precursor ( 1 ) with two molar equivalents of the N‐heterocyclic chlorosilylene LSiCl ( 2 ), results in [(η⁵‐C₅H₅)₂Ti(LSiCl)₂] ( 3 ) with concomitant PMe₃ elimination. The presence of a Si? Cl bond in 3 enabled further functionalization at the silicon(II) center. Accordingly, a salt metathesis reaction of 3 with two equivalents of MeLi results in [(η⁵‐C₅H₅)₂Ti(LSiMe)₂] ( 4 ). Similarly, the reaction of 3 with two equivalents of LiBHEt₃ results in [(η⁵‐C₅H₅)₂Ti(LSiH)₂] ( 5 ), which represents the first example of a bis‐(hydridosilylene) metal complex. All complexes were fully characterized and the structures of 3 and 4 elucidated by single‐crystal X‐ray diffraction analysis. DFT calculations of complexes 3 – 5 were also carried out to assess the nature of the titanium–silicon bonds. Two σ and one π‐type molecular orbital, delocalized over the Si‐Ti‐Si framework, are observed.     

Catalytic diversity of diene complexes of niobium and tantalum on polymerizations of ethylene,norbornene, and methyl methacrylate

Half‐metallocene diene complexes of niobium and tantalum catalyzed three‐types of polymerization: (1) the living polymerization of ethylene by niobium and tantalum complexes, MCl₂(η⁴‐1,3‐diene)(η⁵‐C₅R₅) ( 1‐4 ; M = Nb, Ta; R = H, Me) combined with an excess of methylaluminoxane; (2) the stereoselective ring opening metathesis polymerization of norbornene by bis(benzyl) tantalum complexes, Ta(CH₂Ph)₂(η⁴‐1,3‐butadiene)(η⁵‐C₅R₅) ( 11 : R = Me; 12 : R = H) and Ta(CH₂Ph)₂(η⁴‐o‐xylylene)(η⁵‐C₅Me₅) ( 16 ); and (3) the polymerization of methyl methacrylate by butadiene‐diazabutadiene complexes of tantalum, Ta(η²‐RN=CHCH=NR)(η⁴‐1,3‐butadiene)(η⁵‐C₅Me₅) ( 25 : R = p‐methoxyphenyl; 26 : R = cyclohexyl) in the presence of an aluminum compound ( 24 ) as an activator of the monomer.     

Synthesis and characterization of new complexes of the type [Ru(CO)2Cl2 (2‐phenyl‐1,8‐naphthyridine‐kN) (2‐phenyl‐1,8‐naphthyridine‐kN′)]. Preliminary applications in homogeneous catalysis

Novel ruthenium (II) complexes were prepared containing 2‐phenyl‐1,8‐naphthyridine derivatives. The coordination modes of these ligands were modified by addition of coordinating solvents such as water into the ethanolic reaction media. Under these conditions 1,8‐naphthyridine (napy) moieties act as monodentade ligands forming unusual [Ru(CO)₂Cl₂(η¹‐2‐phenyl‐1,8‐naphthyridine‐ kN )(η¹‐2‐phenyl‐1,8‐naphthyridine‐kN′)] complexes. The reaction was reproducible when different 2‐phenyl‐1,8‐naphthyridine derivatives were used. On the other hand, when dry ethanol was used as the solvent we obtained complexes with napy moieties acting as a chelating ligand. The structures proposed for these complexes were supported by NMR spectra, and the presence of two ligands in the [Ru(CO)₂Cl₂(η¹‐2‐phenyl‐1,8‐naphthyridine‐ kN )(η¹‐2‐phenyl‐1,8‐naphthyridine‐kN′)] type complexes was confirmed using elemental analysis. All complexes were tested as catalysts in the hydroformylation of styrene showing moderate activity in N,N′‐dimethylformamide. Copyright © 2008 John Wiley & Sons, Ltd.