Josefina Díez

Indenyl complexes of Group 8 metals

Abstract The present review article is concerned with the state of the art of the chemistry of indenyl Group 8 metal complexes which has undergone significant progress during the last decade. It deals mainly with complexes of the types: (a) bis(indenyl) sandwich compounds [M(η5-C9H7−xRx)2] (R=H, Me); (b) half-sandwich derivatives [M(η5-C9H7−xRx)(CO)2]2 and [M(η5-C9H7−xRx)XL2] (X=halides, H, alkyl, acetylide; L=two electron donor ligands); (c) cationic complexes [M(η5-C9H7−xRx)L2L′]+ (L, L′=two electron donor ligands). A detailed account of the synthesis, structural and reactivity aspects is presented including kinetic studies and catalytic processes. A discussion of the structural features and coordination modes of the indenyl group with special attention to its distortion parameters is presented. The reactivity studies include redox (chemical and electrochemical) processes, insertion reactions, ring transformations as well as ligand exchange processes in half-sandwich derivatives [M(η5-C9H7−xRx) XL2]. In particular, a detailed discussion of the ability of the moiety [M(η5-C9H7−xRx)L2] to stabilize unsaturated carbene groups such as vinylidene (CCR2, allenylidene CCCR2 and α,β-unsaturated alkenyl carbene C(H)C(R1)CRR′ complexes is presented. The influence of the indenyl ring on the regio- and stereoselective nucleophilic additions to these carbene groups allows selective synthesis leading to either allenyl or functionalized alkynyl complexes. A large number of the latter have been synthesized some of them showing excellent non-linear optical properties.

A highly efficient copper(I) catalyst for the 1,3-dipolar cycloaddition of azides with terminal and 1-iodoalkynes in water: regioselective synthesis of 1,4-disubstituted and 1,4,5-trisubstituted 1,2,3-triazoles

A new water soluble Cu(I) complex that exhibits a versatile and high catalytic activity in the Huisgen cycloadditions of azides and terminal alkynes in aqueous media under mild conditions is the first well-defined Cu(I) catalyst that is active with 1-iodoalkynes in water under aerobic conditions.

Bis(allyl)ruthenium(IV) Complexes Containing Water‐Soluble Phosphane Ligands: Synthesis, Structure, and Application as Catalysts in the Selective Hydration of Organonitriles into Amides

The novel mononuclear ruthenium(IV) complexes [RuCl(2)(eta(3):eta(3)-C(10)H(16))(L)] [L=(meta-sulfonatophenyl)diphenylphosphane sodium salt (TPPMS) (2a), 1,3,5-triaza-7-phosphatricyclo[3.3.1.1(3, 7)]decane (PTA) (2b), 1-benzyl-3,5-diaza-1-azonia-7-phosphatricyclo[3.3.1.1(3, 7)]decane chloride (PTA-Bn) (2c), 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane (DAPTA) (2d), and 2,4,10-trimethyl-1,2,4,5,7,10-hexaaza-3-phosphatricyclo[3.3.1.1(3, 7)]decane (THPA) (2e)] have been synthesized by treatment of the dimeric precursor [{RuCl(mu-Cl)(eta(3):eta(3)-C(10)H(16))}(2)] (C(10)H(16)=2,7-dimethylocta-2,6-diene-1,8-diyl) (1) with two equivalents of the corresponding water-soluble phosphane. Reaction of 1 with one equivalent of the cage-type diphosphane ligand 2,3,5,6,7,8-hexamethyl-2,3,5,6,7,8-hexaaza-1,4-diphosphabicyclo[2.2.2]octane (THDP) allowed also the high-yield preparation of the dinuclear derivative [{RuCl(2)(eta(3):eta(3)-C(10)H(16))}(2)(mu-THDP)] (2f). All these new complexes have been analytically and spectroscopically (IR and multinuclear NMR) characterized. In addition, the structure of 2b, 2c, 2d, and 2f was unequivocally confirmed by X-ray diffraction methods. Complexes 2a-f are active catalysts for the selective hydration of nitriles to amides in pure aqueous medium under neutral conditions. The wide scope of this catalytic transformation has been evaluated by using the most active catalysts [RuCl(2)(eta(3):eta(3)-C(10)H(16))(THPA)] (2e) and [{RuCl(2)(eta(3):eta(3)-C(10)H(16))}(2)(mu-THDP)] (2f). Advantages of using MW versus conventional thermal heating are also discussed.

Cycloisomerization versus Hydration Reactions in Aqueous Media: A Au(III)-NHC Catalyst That Makes the Difference

A novel water-soluble Au(III)-NHC complex has been synthesized and successfully applied in the intramolecular cyclization of γ-alkynoic acids into enol-lactones under biphasic toluene/water conditions, thus representing a rare example of an active and selective catalyst for this transformation in aqueous media. Remarkably, competing alkyne hydration processes were not observed, even during the desymmetrization reaction of challenging 1,6-diyne substrates. In addition, after phase separation, the water-soluble Au(III) catalyst could be recycled 10 times without loss of activity or selectivity.

Highly Efficient Redox Isomerisation of Allylic Alcohols Catalysed by Pyrazole‐Based Ruthenium(IV) Complexes in Water: Mechanisms of Bifunctional Catalysis in Water

The catalytic activity of ruthenium(IV) ([Ru(η(3):η(3)-C(10)H(16))Cl(2)L]; C(10)H(16) = 2,7-dimethylocta-2,6-diene-1,8-diyl, L = pyrazole, 3-methylpyrazole, 3,5-dimethylpyrazole, 3-methyl-5-phenylpyrazole, 2-(1H-pyrazol-3-yl)phenol or indazole) and ruthenium(II) complexes ([Ru(η(6)-arene)Cl(2)(3,5-dimethylpyrazole)]; arene = C(6)H(6), p-cymene or C(6)Me(6)) in the redox isomerisation of allylic alcohols into carbonyl compounds in water is reported. The former show much higher catalytic activity than ruthenium(II) complexes. In particular, a variety of allylic alcohols have been quantitatively isomerised by using [Ru(η(3):η(3)-C(10)H(16))Cl(2)(pyrazole)] as a catalyst; the reactions proceeded faster in water than in THF, and in the absence of base. The isomerisations of monosubstituted alcohols take place rapidly (10-60 min, turn-over frequency = 750-3000 h(-1)) and, in some cases, at 35 °C in 60 min. The nature of the aqueous species formed in water by this complex has been analysed by ESI-MS. To analyse how an aqueous medium can influence the mechanism of the bifunctional catalytic process, DFT calculations (B3LYP) including one or two explicit water molecules and using the polarisable continuum model have been carried out and provide a valuable insight into the role of water on the activity of the bifunctional catalyst. Several mechanisms have been considered and imply the formation of aqua complexes and their deprotonated species generated from [Ru(η(3):η(3)-C(10)H(16))Cl(2)(pyrazole)]. Different competitive pathways based on outer-sphere mechanisms, which imply hydrogen-transfer processes, have been analysed. The overall isomerisation implies two hydrogen-transfer steps from the substrate to the catalyst and subsequent transfer back to the substrate. In addition to the conventional Noyori outer-sphere mechanism, which involves the pyrazolide ligand, a new mechanism with a hydroxopyrazole complex as the active species can be at work in water. The possibility of formation of an enol, which isomerises easily to the keto form in water, also contributes to the efficiency in water.

[Ru(η3-2-C3H4Me)(CO)(dppf)][SbF6]: a mononuclear 16e− ruthenium(II) catalyst for propargylic substitution and isomerization of HCCCPh2(OH)

The 16e(-) derivative [Ru(eta3-2-C3H4Me)(CO)(dppf)][SbF6] catalyzes: (i) the propargylic substitution reaction of 1,1-diphenyl-2-propyn-1-ol with alcohols to produce propargylic ethers, and (ii) the formal isomerization of 1,1-diphenyl-2-propyn-1-ol into 3,3-diphenyl-2-propenal.

Alkali-metal-mediated zincation (AMMZn) meets N-heterocyclic carbene (NHC) chemistry: Zn–H exchange reactions and structural authentication of a dinuclear Au(I) complex with a NHC anion

Merging two evolving areas in synthesis, namely cooperative bimetallics and N-heterocyclic carbenes (NHCs), this study reports the isolation of the first intermediates of alkali-metal-mediated zincation (AMMZn) of a free NHC and a Zn–NHC complex using sodium zincate [(TMEDA)NaZn(TMP)(tBu)2] (1) as a metallating reagent. The structural authentication of (THF)3Na[:C{[N(2,6-iPr2C6H3)]2CHCZn(tBu2)}] (2) and [Na(THF)6]+[tBu2Zn:C{[N(2,6-iPr2C6H3)]2CHCZn(tBu2)}]− (4), resulting from the reactions of 1 with unsaturated free NHC IPr (IPr = 1,3-bis(2,6-di-isopropylphenylimidazole-2-ylidene) and NHC complex ZntBu2IPr (3) respectively demonstrates that in both cases, this mixed-metal approach can easily facilitate the selective C4 zincation of the unsaturated backbone of the NHC ligand. Furthermore, the generation of anionic NHC fragments enables dual coordination through their normal (C2) and abnormal (C4) positions to the bimetallic system, stabilising the kinetic AMMZn intermediates which normally go undetected and provides new mechanistic insights in to how these mixed-metal reagents operate. In stark contrast to this bimetallic approach when NHC-complex 3 is reacted with a more conventional single-metal base such as tBuLi, the deprotonation of the coordinated carbene is inhibited, favouring instead, co-complexation to give NHC-stabilised [IPr·LiZntBu3] (5). Showing the potential of 2 to act as a transfer agent of its anionic NHC unit to transition metal complexes, this intermediate reacts with two molar equivalents of [ClAu(PPh3)] to afford the novel digold species [ClAu:C{[N(2,6-iPr2C6H3)]2CHCAu(PPh3)}] (6) resulting from an unprecedented double transmetallation reaction which involves the simultaneous exchange of both cationic (Na+) and neutral (ZntBu2) entities on the NHC framework.

Highly water-soluble arene-ruthenium(II) complexes: application to catalytic isomerization of allylic alcohols in aqueous medium

Arene-ruthenium(II) derivatives [RuCl2(η6-C6H5OCH2CH2OH)(L)] (L = P(OMe)3 (2a), P(OEt)3 (2b), P(OiPr)3 (2c), P(OPh)3 (2d), PPh3 (2e)) have been prepared from the dimer [{RuCl(μ-Cl)(η6-C6H5OCH2CH2OH)}2] and the appropriate P-donor ligand. The hydroxyethoxy substituent on the arene induces water-solubility of the resulting complexes (up to 755 g L−1); in particular derivative 2a being one hundred times more soluble in water than its p-cymene congener [RuCl2(η6-p-cymene){P(OMe)3}]. Compounds 2a–e are active catalysts for isomerization of allylic alcohols into the corresponding ketones in aqueous medium. The best performances are obtained with derivatives 2a–c which have shown the highest activity reported to date for the isomerization of aromatic or disubstituted substrates in water.

Novel Copper(I) Complexes Containing 1,1‘-Bis(diphenylphosphino)ferrocene (dppf) as a Chelate and Bridging Ligand: Synthesis of Tetrabridged Dicopper(I) Complexes [Cu2(μ-η1-C⋮R)2(μ-dppf)2] and X-ray Crystal Structure of [Cu2(μ-η1-C⋮CC6H4CH3-4)2(μ-dppf)2]

Binuclear copper(I) complexes [Cu(κ2-P,P-dppf)(CH3CN)2][BF4] (1), [Cu(κ2-P,P-dppf)(bipy)][BF4] (2) containing the chelating dppf ligand (dppf = 1,1‘-bis(diphenylphosphino)ferrocene) have been prepared by substitution reactions of the acetonitrile ligands from the complexes [Cu(CH3CN)4][BF4] and (1) with dppf and bipy, respectively. Similarly, the treatment of the complex [Cu2(μ-dppm)2(CH3CN)2][BF4]2 with dppf in CH2Cl2 at room temperature gives the tetranuclear complex [Cu2(μ-dppm)2(κ2-P,P-dppf)2][BF4]2 (3). The analogous bridging chloride tetranuclear complex [Cu2(μ-Cl)2(κ2-P,P-dppf)2] (4) has been also prepared by the addition of dppf to a solution in THF containing an equimolar mixture of CuCl and tetramethylethylenediamine. Complex 4 has been used as a precursor for μ-η1-alkynyl bridging dicopper(I) complexes containing the framework [Cu2(μ-dppf)2]. Complexes [Cu2(μ-η1-C⋮CR)2(μ-dppf)2] (R = C6H4CH3-4 (5), C6H5 (6), CH2OCH3 (7), CH2CH2CH3 (8), (η5-C5H4)Fe(η5-C5H5) (9)) are obtained by the treatment of ...

Tuning N-Heterocyclic Carbenes in T-Shaped PtII Complexes for Intermolecular CH Bond Activation of Arenes†

Small change matters: T-shaped Pt(II) complexes with less flexible substituents, than, for example, isopropyl or tert-butyl groups, on N-heterocyclic carbene (NHC) ligands allow for C-H bond activation reactions of aromatic compounds (see scheme; BAr(f)(4)(-) =tetrakis[(3,5-trifluoromethyl)phenyl]borate; F yellow, Pt red). NHC substituents that are not highly branched prevent agostic interactions and reduce the barriers to achieve the C-H bond cleavage.