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Hydrogenation of substituted styrenes and unactivated aliphatic alkenes by molecular hydrogen has been achieved using a Mn catalyst with a non‐pincer, picolylphosphine ligand. This is the second reported example of alkene hydrogenation catalyzed by a Mn complex. Mechanistic studies showed that a Mn hydride formed by H2 activation in the presence of a base is the catalytically active species. Based on experimental and DFT studies, H2 splitting is proposed to occur via a metal‐ligand cooperative pathway involving deprotonation of the CH2 arm of the ligand, leading to pyridine dearomatization.

We report the synthesis and reactivity of RuII complexes with a new naphthyridinone-substituted phosphine ligand, 7-(diisopropylphosphinomethyl)-1,8-naphthyridin-2(1H)-one (L-H), which contains two reactive sites that can potentially be deprotonated by a strong base: an NH proton of naphthyridinone and a methylene arm attached to the phosphine. In the absence of a base, the stable bis-ligated complex Ru(L-H)2Cl2 (1) containing two NH groups in the secondary coordination sphere is formed. Upon further reaction with a base, a doubly deprotonated, dimeric complex is obtained, [Ru2(L*-H)2(L)2] (2), in which two of the four ligands undergo deprotonation at the NH (L), while the other two ligands are deprotonated at the methylene groups (L*-H) as confirmed by an X-ray diffraction study; intramolecular hydrogen bonding is present between the NH group of one ligand and an O-atom of another ligand in the dimeric structure, which stabilizes the observed geometry of the complex. Complex 2 reacts with protic solvents such as water or methanol generating aqua Ru(L)2(OH2)2 (3) or methanol complexes Ru(L)2(MeOH)2 (4), respectively, both exhibiting intramolecular H-bonded patterns with surrounding ligands at least in the solid state. These complexes react with benzyl alcohols to give aldehydes via base-free acceptorless dehydrogenation.

C–X bond reductive elimination and oxidative addition are key steps in many catalytic cycles for C–H functionalization catalyzed by precious metals; however, engaging first row transition metals in these overall 2e– processes remains a challenge. Although high-valent Mn aryl species have been implicated in Mn-catalyzed C–H functionalization, the nature and reactivity of such species remain unelucidated. In this work, we report rare examples of stable, cyclometalated monoaryl MnIII complexes obtained through clean oxidative addition of Ar–Br to MnI(CO)5Br. These isolated MnIII–Ar complexes undergo unprecedented 2e– reductive elimination of the Ar–X (X = Br, I, and CN) bond and MnII induced by 1e– oxidation, presumably via transient reactive MnIV species. Mechanistic studies suggest a nonradical pathway.

International audience; A growing and useful class of alkene coupling reactions involve hydrogen atom transfer (HAT) from a metal-hydride species to an alkene to form a free radical, which is responsible for subsequent bond formation. Here, we use a combination of experimental and computational investigations to map out the mechanistic details of iron-catalyzed reductive alkene cross-coupling, an important representative of the HAT alkene reactions. We are able to explain several observations that were previously mysterious. First, the rate-limiting step in the catalytic cycle is the formation of the reactive Fe–H intermediate, elucidating the importance of the choice of reductant. Second, the success of the catalytic system is attributable to the exceptionally weak (17 kcal/mol) Fe–H bond, which performs irreversible HAT to alkenes in contrast to previous studies on isolable hydride complexes where this addition was reversible. Third, the organic radical intermediates can reversibly form organometallic species, which helps to protect the free radicals from side reactions. Fourth, the previously accepted quenching of the postcoupling radical through stepwise electron transfer/proton transfer is not as favorable as alternative mechanisms. We find that there are two feasible pathways. One uses concerted proton-coupled electron transfer (PCET) from an iron(II) ethanol complex, which is facilitated because the O–H bond dissociation free energy is lowered by 30 kcal/mol upon metal binding. In an alternative pathway, an O-bound enolate-iron(III) complex undergoes proton shuttling from an iron-bound alcohol. These kinetic, spectroscopic, and computational studies identify key organometallic species and PCET steps that control selectivity and reactivity in metal-catalyzed HAT alkene coupling, and create a firm basis for elucidation of mechanisms in the growing class of HAT alkene cross-coupling reactions.

Utilization of hydroxy‐substituted bipyridine ligands in transition metal catalysis mimicking [Fe]‐hydrogenase has been shown to be a promising approach in developing new catalysts for hydrogenation. For example, MnI complexes with 6,6′‐dihydroxy‐2,2′‐bipyridine ligand have been previously shown to be active catalysts for CO2 hydrogenation. In this work, simple bipyridine‐based Mn catalysts were developed that act as active catalysts for transfer hydrogenation of ketones, aldehydes and imines. For the first time, Mn‐catalyzed transfer hydrogenation of N ‐heterocycles was reported. The highest catalytic activity among complexes with variously substituted ligands was observed for the complex bearing two OH groups in bipyridine. Deuterium labeling experiments suggest a monohydride pathway.

We report the synthesis and reactivity of RuII complexes with a new naphthyridinone-substituted phosphine ligand, 7-(diisopropylphosphinomethyl)-1,8-naphthyridin-2(1H)-one (L-H), which contains two reactive sites that can potentially be deprotonated by a strong base: an NH proton of naphthyridinone and a methylene arm attached to the phosphine. In the absence of a base, the stable bis-ligated complex Ru(L-H)2Cl2 (1) containing two NH groups in the secondary coordination sphere is formed. Upon further reaction with a base, a doubly deprotonated, dimeric complex is obtained, [Ru2(L*-H)2(L)2] (2), in which two of the four ligands undergo deprotonation at the NH (L), while the other two ligands are deprotonated at the methylene groups (L*-H) as confirmed by an X-ray diffraction study; intramolecular hydrogen bonding is present between the NH group of one ligand and an O-atom of another ligand in the dimeric structure, which stabilizes the observed geometry of the complex. Complex 2 reacts with protic solvents such as water or methanol generating aqua Ru(L)2(OH2)2 (3) or methanol complexes Ru(L)2(MeOH)2 (4), respectively, both exhibiting intramolecular H-bonded patterns with surrounding ligands at least in the solid state. These complexes react with benzyl alcohols to give aldehydes via base-free acceptorless dehydrogenation.

A [RuH(CO)(py-NP)(PPh3)2]Cl (1) catalyst is found to be effective for catalytic transformation of primary alcohols, including amino alcohols, to the corresponding carboxylic acid salts and two molecules of hydrogen with alkaline water. The reaction proceeds via acceptorless dehydrogenation of alcohol, followed by a fast hydroxide/water attack to the metal-bound aldehyde. A pyridyl-type nitrogen in the ligand architecture seems to accelerate the reaction.

International audience; The interaction of [IrCl(COD)]2 with PPh3 in isopropanol has been investigated for various P/Ir ratios, in the absence or presence of a strong base (KOtBu), at room temperature and at reflux. At room temperature, PPh3 adds to the metal center to yield [IrCl(COD)(PPh3)] and additional PPh3 only undergoes rapid degenerative ligand exchange. Subsequent addition of KOtBu affords [IrH(COD)(PPh3)2] as the main compound, even for high P/Ir ratios, although very minor amounts of products having a “HIr(PPh3)3” core are also generated. Warming to the solvent reflux temperature results in a rapid (< 1 h) and quantitative COD removal from the system as hydrogenated products (54.4% of cyclooctene plus 32.2% of cyclooctane according to a quantitative GC analysis) and in the eventual generation of [IrH3(PPh3)3]. The latter is observed as a mixture of the fac and mer isomers in solvent-dependent proportions. Other minor products, one of which is suggested to be mer-cis-[IrH2(OiPr)(PPh3)3] by the NMR characterization, are also generated. These results show that, contrary to certain previously published assumptions, systems of this kind are unlikely to function via a COD-containing active species in transfer hydrogenation catalyses conducted in hot isopropanol in the presence of a strong base.

International audience; The kinetics and mechanism of catalytic radical termination (CRT) of n-butyl acrylate (BA) in MeCN in the presence of Cu complexes with tridentate and tetradentate ligands was investigated both theoretically and experimentally. The tetradentate TPMA, TPMA*(1), TPMA*(2), TPMA*(3), and the newly synthesized tridentate N-propyl-N,N-bis(4-methoxy3,5-dimethylpyrid-2-ylmethyl)amine (BPMA*(Pr)) as well as tridentate BPMA(Me) were used as ligands. L/(CuX2)-X-II (X = Cl or OTf) complexs were characterized by cyclic voltammetry (CV), UV-vis-NIR, and X-ray diffraction. Polymerization of BA initiated by azobis(isobutyronitrile) (AIBN) in MeCN in the presence of a L/Cu-I complex showed higher rates of CRT for more reducing L/Cu-I complexes. The ligand denticity (tri- vs tetradentate) had a minor effect on the relative polymerization kinetics but affected the molecular weights in a way specific for ligand denticity. Quantification of the apparent CRT rate coefficients, kappa(app)(CRT) showed larger values for more reducing L/Cu-I complexes, which correlated with the L/Cu-II-R (R = CH(CH3)(COOCH3)) bond strength, according to DFT calculations. The bond strength is mostly affected by the complex reducing power and to a lesser degree by the ligand denticity. Analysis of kinetics and molecular weights for different systems indicates that depending on the ligand nature, the rate-determining step of CRT may be either the radical addition to L/Cu-I to form the L/Cu-II-R species or the reaction of the latter species with a second radical.

International audience; The investigations reported in this article probe the behavior of the RAFT polymerization of vinylidene fluoride (VDF) when degrees of polymerization higher than 50 are targeted: they demonstrate that higher molar mass PVDF (11 000 g mol–1) can indeed be prepared by RAFT polymerization, but only at rather low monomer conversions (

The diruthenium(II,II) complex [Ru2(L1)(OAc)3]Cl (1), spanned by a naphthyridine-diimine ligand and bridged by three acetates, has been synthesized. The catalytic efficacy of complex 1 has been evaluated for the acceptorless dehydrogenation (AD) of alcohols and for the dehydrogenative coupling reactions of alcohols with Wittig reagents. The diruthenium(II,II) complex is an excellent catalyst for AD of a diverse range of alcohols, and it is shown to be particularly effective for the conversion of primary alcohols to the corresponding aldehydes without undesired side products such as esters. Triphenylphosphonium ylides in a one-pot reaction with alcohols afforded the corresponding olefins in high yields with excellent E selectivity. The liberated dihydrogen gas was identified and measured to be 1 equiv with respect to alcohol. Deuteration studies with PhCD2OH revealed the absence of isotope scrambling in the product, indicating the involvement of a Ru-monohydride intermediate. Kinetic studies and DFT calcul...

International audience; Metal complexes stabilized by appropriate ligands, particularly CuI/L systems, have proven powerful for the controlled polymerization of acrylates and other monomers by atom transfer radical polymerization (ATRP). The polymerization of acrylates by CuI/L systems, however, is haunted by interference of catalyzed radical termination (CRT), which reduces the chain-end fidelity. Other monomers do not appear to be affected by this phenomenon to any significant extent. The phenomenon appears to involve the formation of an organometallic intermediate by reversible radical trapping, as in organometallic mediated radical polymerization (OMRP). We summarize here the current knowledge and the efforts made to elucidate the CRT pathway and products.

International audience; The X-C bond dissociation energies (BDEs) for five series of X-CH2-nFnCH3-mFm molecules (n = 0, 1, 2; m = 0, 1, 2, 3) with X = H, I, SC(S)OEt, Co(acac)2 or Mn(CO)5 were calculated using a DFT approach, yielding results in good agreement with the few experimentally determined values. Calculations were also carried out on the simpler (CO)5Mn-CFnH3-n molecules (n = 0, 1, 2, 3), for which experimental data are available. The BDE trends as n and m vary are different for different X groups: BDE increases as n increases (particularly from 0 to 1) for X = H, I and SC(S)OEt, but decreases (particularly from 1 to 2) for X = Co(acac)2 and Mn(CO)5. The effective charge analysis suggests that the effect of the bond polarity on the ionic component of the bond energy is a major contribution to these trends. These results rationalize the limited control, for the polymerization of vinylidene fluoride (VDF), by the iodine transfer polymerization (ITP) and reversible addition-fragmentation chain-transfer (RAFT) polymerization approaches. They also predict a better controlled process for this monomer by organometallic mediated radical polymerization (OMRP), mediated by Co(acac)2. They also allow predictions for the performance of the same processes for other fluorinated monomers. The results for X = Mn(CO)5 suggest that the (CO)5Mn-CH2-nFnCH3-mFm molecules cannot be thermally activated at significant rates. Therefore, these molecules either do not form or are photochemically reactivated during the Mn2(CO)10-assisted ITP polymerization of VDF.

Oxygenation of 1,5-cyclooctadiene (COD) is achieved on an iridium center using water as a reagent. A hydrogen-bonding interaction with an unbound nitrogen atom of the naphthyridine-based ligand architecture promotes nucleophilic attack of water to the metal-bound COD. Irida-oxetane and oxo-irida-allyl compounds are isolated, products which are normally accessed from reactions with H2O2 or O2. DFT studies support a ligand-assisted water activation mechanism.

International audience; A triflamide-tethered N-heterocyclic carbene (NHC)-bound Rh-I dicarbonyl catalyst was highly effective for both intermolecular hydroalkoxylation and intramolecular heteroannulation reactions. The involvement of both the amido nitrogen and triflato oxygen atoms of the triflamide functionality for alcohol activation and 1,2-hydrogen shift, respectively, was proposed.

International audience; Organometallic‐mediated radical polymerization (OMRP) has given access to well‐defined poly(vinyl acetate‐alt‐tert‐butyl‐2‐trifluoromethacrylate)‐b‐poly(vinyl acetate) and poly(VAc‐alt‐MAF‐TBE) copolymers composed of two electronically distinct monomers: vinyl acetate (VAc, donor, D) and tert‐butyl‐2‐trifluoromethacrylate (MAF‐TBE, acceptor, A), with low dispersity (≤1.24) and molar masses up to 57 000 g mol−1. These copolymers have a precise 1:1 alternating structure over a wide range of comonomer feed compositions. The reactivity ratios are determined as rVAc = 0.01 ± 0.01 and rMAF‐TBE = 0 at 40 °C. Remarkably, from a feed containing >50% molar VAc content, poly(VAc‐alt‐MAF‐TBE)‐b‐PVAc block copolymers are produced via a one‐pot synthesis. Such diblock copolymers exhibit two glass transition temperatures attributed to the alternating and homopolymer sequences. The OMRP of this fluorine‐containing alternating monomer system may provide access to a wide range of new polymer materials.

International audience; The decomposition of the diazo initiator dimethyl 2,2′‐azobis(isobutyrate) (V‐601), generating the Me2C.(CO2Me) radical, affords essentially the same fraction of disproportionation and combination in media with a large range of viscosity (C6D6, [D6]DMSO, and PEG 200) in the 25–100 °C range. This is in stark contrast to recent results by Yamago et al. on the same radical generated from Me2C(TeMe)(CO2Me) and on other X‐TeR systems (X=polymer chain or unimer model; R=Me, Ph). The discrepancy is rationalized on the basis of an unprecedented RTe.‐catalyzed radical disproportionation, with support from DFT calculations and photochemicaL V‐601 decomposition in the presence of Te2Ph2.

International audience; RAFT polymerization of vinylidene fluoride (VDF), leading to relatively well defined poly(vinylidenefluoride) (PVDF), is negatively affected by chain inversion resulting in less easily reactivatable PVDFT-XAdormant chains (terminated with the tail end of an inversely added VDF unit; XA = xanthate moiety).Although slow reactivation of these chains by PVDF• radicals (in contrast to general belief) was recentlydemonstrated, slow radical exchange leads to progressive loss of chain growth control. This article dealswith the possibility of synthesizing block copolymers from PVDF-XA macroCTAs by sequential addition.The investigations show that only PVDFH-XA (chains terminated with the head end of regularly addedVDF) can be reactivated by PNVP• (poly(N-vinylpyrrolidone)) radicals and that PVDFT-XA chains are completelyunreactive in the presence of PNVP•, PB• (poly(butylacrylate)) or PDM• (poly(N,N’-dimethylacrylamide)).However, both PVDFH-XA and PVDFT-XA can be reactivated by PVAc• (poly(vinyl acetate))radicals. The reactivation of the PVDFT-XA, albeit slower than that of the PVDFH-XA, is sufficiently fast toallow the synthesis of unprecedented well-defined PVDF-b-PVAc block copolymers with relatively highend-group fidelity. DFT calculations rationalize this behavior on the basis of faster radical exchange in theorder PVDFH-XA/VAc > PVDFH-XA/NVP > PVDFT-XA/VAc ≫ PVDFT-XA/NVP. The success of the chainextension also relies on faster activation relative to homopropagation of the chain extending monomer, aswell as fast addition of the released PVDF•H and PVDF•T to the monomer.

Reaction of 1,8-naphthyrid-2-yl-ferrocene (FcNP) with a variety of acids affords protonated salts at first, whereas longer reaction time leads to partial demetalation of FcNP resulting in a series of Fe complexes. The corresponding salts [FcNP·H][X] (X = BF(4) or CF(3)SO(3) (1)) are isolated for HBF(4) and CF(3)SO(3)H. Reaction of FcNP with equimolar amount of CF(3)CO(2)H for 12 h affords a neutral complex [Fe(FcNP)(2)(O(2)CCF(3))(2)(OH(2))(2)] (2). Use of excess acid gave a trinuclear Fe(II) complex [Fe(3)(H(2)O)(2)(O(2)CCF(3))(8)(FcNP·H)(2)] (3). Three linear iron atoms are held together by four bridging trifluoroacetates and two aqua ligands in a symmetric fashion. Reaction with ethereal solution of HCl afforded [(FcNP·H)(3)(Cl)][FeCl(4)](2) (4) irrespective of the amount of the acid used. Even the picric acid (HPic) led to metal extrusion giving rise to [Fe(2)(Cl)(2)(FcNP)(2)(Pic)(2)] (5) when crystallized from dichloromethane. Metal extrusion was also observed for CF(3)SO(3)H, but an analytically pure compound could not be isolated. The demetalation reaction proceeds with an initial proton attack to the distal nitrogen of the NP unit. Subsequently, coordination of the conjugate base to the electrophilic Fe facilitates the release of Cp rings from metal. The conjugate base plays an important role in the demetalation process and favors the isolation of the Fe complex as well. The 1,1'-bis(1,8-naphthyrid-2-yl)ferrocene (FcNP(2)) does not undergo demetalation under identical conditions. Two NP units share one positive charge causing the Fe-Cp bonds weakened to an extent that is not sufficient for demetalation. X-ray structure of the monoprotonated FcNP(2) reveals a discrete dimer [(FcNP(2)·H)](2)[OTf](2) (6) supported by two N-H···N hydrogen bonds. Crystal packing and dispersive forces associated with intra- and intermolecular π-π stacking interactions (NP···NP and Cp···NP) allow the formation of the dimer in the solid-state. The protonation and demetalation reactions of FcNP and FcNP(2) with a variety of acids are reported.

The reactions between [Ir(COD)(μ-OAc)]2 and the functionalized imidazolium salt 1-mesityl-3-(pyrid-2-yl)imidazolium bromide (MesIPy·HBr) or 1-benzyl-3-(5,7-dimethylnaphthyrid-2-yl)imidazolium bromide (BnIN·HBr) at room temperature afford the COD-activated IrIII–N-heterocyclic carbene (NHC) complexes [Ir(1-κ-4,5,6-η-C8H12)(κ2C,N-MesIPy)Br] (1) and [Ir(1-κ-4,5,6-η-C8H12)(κ2C,N-BnIN)Br] (2), respectively. In contrast, the methoxy analogue [Ir(COD)(μ-OMe)]2 on reaction with MesIPy·HBr under identical conditions affords the IrI–NHC complex [Ir(COD)(κ2C,N-MesIPy)Br]. Treatment of [Ir(COD)(κ2C,N-MesIPy)Br] with sodium acetate does not lead to COD activation. Further, use of 2,2′-bipyridine (bpy) with [Ir(COD)(μ-X)]2 (X = MeO or AcO) in the presence of [nBu4N][BF4] affords exclusively [Ir(bpy)(COD)][BF4] (3). Metal-bound acetate is shown to be an essential promoter for activation of the COD allylic C–H bond. An examination of products reveals the following transformations of the precursor components: cleavage of ...

Bubbling of CO into a dichloromethane solution of [Ir(COD)(CH3CN)2][BF4] followed by the addition of 2-phenyl-1,8-naphthyridine (LH) at room temperature results in the bis-cyclometalated IrIII comp...

Treatment of [Rh(COD)(μ-Cl)]2 with excess tBuOK and subsequent addition of 2 equiv of PIN·HBr in THF afforded [Rh(COD)(κC2-PIN)Br] (1) (PIN = 1-isopropyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)imidazol-2-ylidene, COD = 1,5-cyclooctadiene). The X-ray structure of 1 confirms ligand coordination to “Rh(COD)Br” through the carbene carbon featuring an unbound naphthyridine. Compound 1 is shown to be an excellent catalyst for the hydration of a wide variety of organonitriles at ambient temperature, providing the corresponding organoamides. In general, smaller substrates gave higher yields compared with sterically bulky nitriles. A turnover frequency of 20 000 h–1 was achieved for the acrylonitrile. A similar Rh(I) catalyst without the naphthyridine appendage turned out to be inactive. DFT studies are undertaken to gain insight on the hydration mechanism. A 1:1 catalyst–water adduct was identified, which indicates that the naphthyridine group steers the catalytically relevant water molecule to the active metal site...

Metallamacrocycles 1, 2, and 3 of the general formula [{Ir(ppy)(2)}(2)(μ-BL)(2)](OTf)(2) (ppyH = 2-phenyl pyridine; BL = 1,2-bis(4-pyridyl)ethane (bpa) (1), 1,3-bis(4-pyridyl)propane (bpp) (2), and trans-1,2-bis(4-pyridyl)ethylene (bpe) (3)) have been synthesized by the reaction of [{(ppy)(2)Ir}(2)(μ-Cl)(2)], first with AgOTf to effect dechlorination and later with various bridging ligands. Open-frame dimers [{Ir(ppy)(2)}(2)(μ-BL)](OTf)(2) were obtained in a similar manner by utilizing N,N'-bis(2-pyridyl)methylene-hydrazine (abp) and N,N'-(bis(2-pyridyl)formylidene)ethane-1,2-diamine (bpfd) (for compounds 4 and 5, respectively) as bridging ligands. Molecular structures of 1, 3, 4, and 5 were established by X-ray crystallography. Cyclic voltammetry experiments reveal weakly interacting "Ir(ppy)(2)" units bridged by ethylene-linked bpe ligand in 3; on the contrary the metal centers are electronically isolated in 1 and 2 where the bridging ligands are based on ethane and propane linkers. The dimer 4 exhibits two accessible reversible reduction couples separated by 570 mV indicating the stability of the one-electron reduced species located on the diimine-based bridge abp. The "Ir(ppy)(2)" units in compound 5 are noninteracting as the electronic conduit is truncated by the ethane spacer in the bpfd bridge. The dinuclear compounds 1-5 show ligand centered (LC) transitions involving ppy ligands and mixed metal to ligand/ligand to ligand charge transfer (MLCT/LLCT) transitions involving both the cyclometalating ppy and bridging ligands (BL) in the UV-vis spectra. For the conjugated bridge bpe in compound 3 and abp in compound 4, the lowest-energy charge-transfer absorptions are red-shifted with enhanced intensity. In accordance with their similar electronic structures, compounds 1 and 2 exhibit identical emissions. The presence of vibronic structures in these compounds indicates a predominantly (3)LC excited states. On the contrary, broad and unstructured phosphorescence bands in compounds 3-5 strongly suggest emissive states of mixed (3)MLCT/(3)LLCT character. Density functional theory (DFT) calculations have been carried out to gain insight on the frontier orbitals, and to rationalize the electrochemical and photophysical properties of the compounds based on their electronic structures.

Reaction of 2-imidazolyl-5,7-dimethyl-1,8-naphthyridine (L1) with [Rh(COD)Cl]2 (COD = 1,5-cyclooctadiene) affords the dinuclear complex [Rh(COD)Cl]2(μ-L1) (1). Elimination of chloride from the metal coordination sphere leads to a self-assembled tetranuclear macrocycle [Rh(COD)L1]4[ClO4]4 (2). A subtle alteration in the ligand framework results in the polymeric chain compound {Rh(COD)(L2)}n(PF6)n (3) (L2 = 2-imidazolyl-3-phenyl-1,8-naphthyridine). In all these complexes, the imidazole nitrogen and one of the naphthyridine nitrogen (away from the imidazole substituent) bind the metal. The ‘parallel’ and ‘perpendicular’ dispositions of nitrogens are observed in these compounds contributing to different Rh···Rh separations. The L1 ligand adopts planar configuration, whereas the naphthyridine–imidazole rings deviate from planarity in L2 yielding a polymeric structure. The extent of deviation is less in the polymeric structure {Mo2(OAc)4(L2)}n (4) in which the ligand exhibits weak axial interactions to the metal.

Base-assisted reduction of [Ru(CO) 3 Cl 2 ] 2 in the presence of NP-Me 2 (2,7-dimethyl-1,8-naphthyridine) in thf provides an unsupported diruthenium(I) complex [Ru 2 (CO) 4 Cl 2 (NP-Me 2 ) 2 ] ( 1 ). Two NP-Me 2 and four carbonyls bind at equatorial positions and two chlorides occupy sites trans to the Ru–Ru single bond. Reaction of [Ru(CO) 3 Cl 2 ] 2 , TlOTf, KOH and NP-Me 2 in acetonitrile, in a sealed container, affords a bicarbonate bridged diruthenium(I) complex [Ru 2 (CO) 2 ( μ -CO) 2 ( μ -O 2 COH)(NP-Me 2 ) 2 ](OTf) ( 2 ). The in situ generated CO 2 is the source for bicarbonate under basic reaction medium. Isolation of 2 validates the decarboxylation step in the base-assisted reduction of [Ru II (CO) 3 Cl 2 ] 2 → [Ru I 2 (CO) 4 ] 2+ .

Site-directed anchoring of naphthyridine-functionalized N-heterocylic carbene (NHC) is achieved on a metal−metal singly bonded diruthenium(I) platform. Room-temperature treatment of 1-isopropyl-3-(...

Reaction of cis -[Mo 2 (OAc) 2 (CH 3 CN) 6 ][BF 4 ] 2 with NP-Et,Me (2-ethyl-3-methyl-1,8-naphthyridine) in acetonitrile provides trans- [Mo 2 (NP-Et,Me) 2 (OAc) 2 (CH 3 CN)][BF 4 ] 2 ( 1 ). Partial protonation of 1 by HBF 4 ·Et 2 O in acetonitrile leads to trans- [Mo 2 (NP-Et,Me) 2 (OAc)(CH 3 CN) 3 ][BF 4 ] 3 ( 2 ). In both compounds, NP-R ligands are arranged in a head-to-head (HH) fashion leaving one of the axial sites vacant. Substitution of acetonitriles by NP-Me (3-methyl-1,8-naphthyridine) in trans -[Mo 2 (NP-tz) 2 (OAc)(CH 3 CN) 2 ][BF 4 ] 3 provides trans -[Mo 2 (NP-tz) 2 (OAc)(NP-Me)][BF 4 ] 3 ( 3 ) with retention of configuration. Fully solvated dimolybdenum(II) compound reacts with NP-NH 2 to provide [Mo 2 (NP-NH 2 ) 2 (NP-NH)(CH 3 CN) 2 ][BF 4 ] 3 ( 4 ) in which the NP-NH 2 ligands are trans and arranged in a HH fashion. The deprotonated ligand (NP-NH − ) binds the dimetal unit utilizing naphthyridine nitrogen and amido nitrogen. Treatment of [Mo 2 (NP-tz) 2 (CH 3 CN) 4 ][CF 3 SO 3 ] 4 with bpym (2,2 ′ -bipyrimidine) followed by crystallization in air provided an oxo complex [Mo 2 (NP-tz) 2 ( μ 2 -O) 2 (bpym) 2 ][CF 3 SO 3 ] 4 ( 5 ). Compounds 1 – 5 have been characterized by a variety of spectroscopic techniques and by X-ray crystallography. The reactivity pattern is rationalized based on ligand labilities and thermodynamic stabilities.

A newly synthesized diruthenium complex bridged by a naphthyridine-functionalized N-heterocyclic carbene ligand, is found to be active for the acceptorless dehydrogenation coupling of alcohols into aldehydes under base-free conditions.

Mononuclear complexes in- and out-[Ru(Cl)(trpy)(Hbpp)]+ (in-0, out-0; Hbpp is 2,2′-(1H-pyrazole-3,5-diyl)dipyridine and trpy is 2,2′:6′,2″-terpyridine) are used as starting materials for preparation of Ru–Zn heterodinuclear out-{[Ru(Cl)(trpy)][ZnCl2](μ-bpp)} (out-2) and heterotrinuclear in,in- and out,out-{[Ru(Cl)(trpy)]2(μ-[Zn(bpp)2])}2+ (in-3, out-3) constitutional isomers. Further substitution of the Cl ligand from the former complexes leads to Ru–aquaout,out-{[Ru(trpy)(H2O)]2(μ-[Zn(bpp)2])}4+ (out-4) and the oxo-bridged Ru–O–Ru complexin,in-{[RuIII(trpy)]2(μ-[Zn(bpp)2(H2O)]μ-(O)}4+ (in-5). All complexes are thoroughly characterized by the usual analytical techniques as well as by spectroscopy by means of UV–vis, MS, and when diamagnetic NMR. CV and DPV are used to extract electrochemical information and monocrystal X-ray diffraction to characterize complexes out-2, in-3, out-3, and in-5 in the solid state. Complex out-3 photochemically isomerizes toward in-3, as can be observed by NMR spectroscopy and rationalized by density functional theory based calculations.

Metalmetal singly-bonded diruthenium com- plexes, bridged by naphthyridine-functionalized N-hetero- cyclic carbene (NHC) ligands featuring a hydroxy appendage on the naphthyridine unit, are obtained in a single-pot reac- tion of (Ru2(CH3COO)2(CO)4) with 1-benzyl-3-(5,7-dimethyl- 1,8-naphthyrid-2-yl)imidazolium bromide (BIN·HBr) or 1-iso- propyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)imidazolium bro- mide (PIN·HBr), TlBF4, and substituted benzaldehyde contain- ing an electron-withdrawing group. The modified NHC- naphthyridine-hydroxy ligand spans the diruthenium unit in which the NHC carbon and hydroxy oxygen occupy the axial sites. All the synthesized compounds catalyze acceptorless dehydrogenation of alcohols to the corresponding alde- hydes in the presence of a catalytic amount of weak base 1,4-diazabicyclo(2.2.2)octane (DABCO). Further, acceptorless dehydrogenative coupling (ADHC) of the alcohol with amines affords the corresponding imine as the sole product. The substrate scope is examined with 1 (BIN, p-nitrobenzal- dehyde). A similar complex (Ru2(CO)4(CH3COO)(3-PhBIN))(Br), that is devoid of a hydroxy arm, is significantly less effective for the same reaction. Neutral complex 1a , obtained by de- protonation of the hydroxy arm in 1, is found to be active for the ADHC of alcohols and amines under base-free condi- tions. A combination of control experiments, deuterium la- beling, kinetic Hammett studies, and DFT calculations sup- port metal-hydroxyl/hydroxide and metal-metal coopera- tion for alcohol activation and dehydrogenation. The bridg- ing acetate plays a crucial role in allowing b-hydride elimina- tion to occur. The ligand architecture on the diruthenium core causes rapid aldehyde extrusion from the metal coordi- nation sphere, which is responsible for exclusive imine formation.

Two binuclear copper complexes [{Cu I (L 1 )} 2 ][OTf] 2 (1) and [{Cu II (L 2 )Cl} 2 ] (2) have been synthesized and structurally characterized. The reaction of [{(5,7-dimethyl-1,8-naphthyridin-2-yl)amino}carbonyl]ferrocene (L 1 ) with [Cu(CH 3 CN) 4 ][OTf] in dichloromethane afforded complex 1 in high yield and the dicopper(II) complex 2 was obtained by the overnight treatment of N-(5,7-dimethyl-1,8-naphthyridin-2-yl)-1-methylpyrrolidine-2-carboxamide (L 2 H) with [Cu(CH 3 CN) 4 ][BF 4 ] in dichloromethane. The two copper atoms in complex 1 are bridged by two L 1 ligands in a trans disposition; the naphthyridine nitrogen atoms bridge two copper centers and the carbonyl oxygen atoms occupy sites trans to the Cu···Cu vector. The metal···metal distance is 2.4594(6) A. In contrast, in complex 2, each of the two L 2 ligands bind to the two copper atoms through one naphthyridine nitrogen, a deprotonated amide, and a proline nitrogen atom to form an open-book geometry. Both dicopper complexes have been shown to be excellent catalysts for the cyclopropanation of various olefins with ethyl diazoacetate (EDA), with catalyst 1 found to be marginally superior to 2.

The trinuclear complex [{Ir(ppy)(2)}(3)(L(1))(2)](OTf)(3) (1) is a bright red luminophore whereas the monomer [Ir(ppy)(2)L(2)](OTf) (2) exhibits emission in the green region.

A binuclear Pd catalyst containing amide-tethered naphthyridinylferrocene ligands as well as a similar binuclear Ru catalyst are synthesized.

Dipalladium(I) and diruthenium(I) compounds bridged by two [{(5,7-dimethyl-1,8-naphthyridin-2-yl)amino}carbonyl]ferrocene (L) ligands have been synthesized. The X-ray structures of [Pd(2)L(2)][BF(4)](2) (1) and [Ru(2)L(2)(CO)(4)][BF(4)](2) (2) reveal dinuclear structures with short metal-metal distances. In both of these structures, naphthyridine bridges the dimetal unit, and the site trans to the metal-metal bond is occupied by weakly coordinating oxygen from the amido fragment. The catalytic utilities of these bimetallic compounds are evaluated. Compound 1 is an excellent catalyst for phosphine-free, Suzuki cross-coupling reactions of aryl bromides with arylboronic acids and provides high yields in short reaction times. Compound 1 is also found to be catalytically active for aryl chlorides, although the corresponding yields are lower. A bimetallic mechanism is proposed, which involves the oxidative addition of aryl bromide across the Pd-Pd bond and the bimetallic reductive elimination of the product. Compound 1 is also an efficient catalyst for the Heck cross-coupling of aryl bromides with styrenes. The mechanism for aldehyde olefination with ethyl diazoacetate (EDA) and PPh(3), catalyzed by 2, has been fully elucidated. It is demonstrated that 2 catalyzes the formation of phosphorane utilizing EDA and PPh(3), which subsequently reacts with aldehyde to produce a new olefin and phosphine oxide. The efficacy of bimetallic complexes in catalytic organic transformations is illustrated in this work.

The 1,8-naphthyridine-functionalized N-heterocyclic carbene 1-benzyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)imidazol-2-ylidene (BIN) has been successfully coordinated to Pd(II), W(0), Rh(I), and Ir(III), exhibiting its diverse binding modes. Reaction of BIN x HBr with Ag(2)O, followed by transmetalation with PdCl(2)(COD)(2) provides a cis complex PdCl(2)(kappaC(2)-BIN)(2) (1). Treatment of BIN x HBr with W(CO)(4)(piperidine)(2) in acetonitrile affords a chelate complex W(CO)(4)(kappa(2)C(2),N(1)'-BIN) (2). Reaction of {RhCl(COD)}(2) with KO(t)Bu and subsequent treatment with BIN x HBr in 1:2 and 1:1 ratio results in the mono and dinuclear complexes [Rh(COD)Br(kappaC(2)-BIN)] (3) and [{Rh(COD)Br}(2)(kappaN(8)':kappaC(2)-BIN)] (4), respectively. In complex 3, the "Rh(COD)Br" unit is coordinated to the carbene center, whereas an additional "Rh(COD)Br" unit is attached to naphthyridine nitrogen in complex 4 in an anti arrangement. Under identical reaction condition, a novel Ir(III) complex [Ir(kappa(2)C(2),N(1)'-BIN)(kappa(2)C(3)',C(2)-BIN)(H(2)O)Br]Br (5) has been synthesized. Complex 5 is proved to be catalytically active in hydrogen transfer reaction from (i)PrOH. All complexes have been characterized by spectroscopic methods and X-ray crystallography.

Oxidative additions of dichloromethanes to a diiridium(i) core, bridged by 2-ferrocenyl-1,8-naphthyridines (NP-Fc), provide an iridium(II) dimer, [IrCl2(CO)2(eta 1-NP-Fc)]2, featuring an unsupported Ir-Ir single bond (2.7121(8) A).

Reaction of cis-[Rh2(CH3COO)2(CH3CN)6](BF4)2 with two equivalents of 2-mesityl-1,8-naphthyridine (Mes-NP) affords trans-[Rh2(CH3COO)2(Mes-NP)2](BF4)2 (1). X-ray structure reveals weak Rh–C(ipso) interaction, and a short Rh–Rh distance. The same ligand, in contrast, oxidatively cleaves the Ru–Ru bond in cis-[Ru2(CO)4(CH3CN)6](BF4)2 and results in trans-[Ru(Mes-NP)2(CH3CN)2](BF4)2 (2). Both compounds adopt trans geometry to relieve the steric strain. Compound 2 exhibits moderate activity for the alcohol oxidation and aldehyde olefination reactions.

International audience; Complexes [M(P,SR)(diene)X] where (P,SR) = CpFe[1,2-C 5 H 3 (PPh 2)(CH 2 SR)] (M = Ir, R = tBu or Bn diene = cod, X = Cl; M = Rh, diene = cod or nbd; X = BF 4 or Cl) were used as precatalysts for the redox isomerization of various allylic alcohols (7a-e) to the corresponding saturated ketones (8a-e) and or hydrogenation to the saturated alcohol (9a-e). In optimization studies using 1-phenyl-2-propen-1-ol (7a) in THF and in iPrOH/MeONa, the only observed product was the saturated alcohol 1-phenyl-1-propanol (9a) when working under a 30 bar H 2 pressure, but activation for only 1 min under H 2 pressure and then continuation under 1 bar of H 2 or Ar led to increasing amounts of the allylic isomerization product propiophenone (8a). Continued reaction under H 2 converted (8a) into (9a). The Rh precatalysts were more active than the Ir analogues. For the rhodium precatalysts (3) and (4), the redox isomerization reaction could be carried out after precatalyst activation in iPrOH/MeONa under Ar at 82°C (without H 2) with complete conversion in 1 h (1% catalyst loading). However, longer reaction times resulted in slow transfer hydrogenation of (8a) leading to (9a) with low enantiomeric excess. Extension of the H 2-free activation of the Rh precatalysts in iPrOH to other allylic alcohol substrates (7b-d) yielded the corresponding ketones with good to excellent yields and excellent chemoselectivities under appropriate conditions.