Cu-Catalyzed P-C bond formation/cleavage: straightforward synthesis/ring-expansion of strained cyclic phosphoniums.

Upon reaction with copper(i), peri-halo naphthyl phosphines readily form peri-bridged naphthyl phosphonium salts. The reaction works with alkyl, aryl and amino substituents at phosphorus, with iodine, bromine and chlorine as a halogen. It proceeds under mild conditions and is quantitative, despite the strain associated with the resulting 4-membered ring structure and the naphthalene framework. The transformation is amenable to catalysis. Under optimized conditions, the peri-iodo naphthyl phosphine 1-I is converted into the corresponding peri-bridged naphthyl phosphonium salt 2b in only 5 minutes at room temperature using 1 mol% of CuI. Based on DFT calculations, the reaction is proposed to involve a Cu(i)/Cu(iii) cycle made of P-coordination, C-X oxidative addition and P-C reductive elimination. This copper-catalyzed route gives a general and efficient access to peri-bridged naphthyl phosphonium salts for the first time. Reactivity studies could thus be initiated and the possibility to insert gold into the strained P-C bond was demonstrated. It leads to (P,C)-cyclometallated gold(iii) complexes. According to experimental observations and DFT calculations, two mechanistic pathways are operating: (i) direct oxidative addition of the strained P-C bond to gold,(ii) backward-formation of the peri-halo naphthyl phosphine (by C-P oxidative addition to copper followed by C-X reductive elimination), copper to gold exchange and oxidative addition of the C-X bond to gold. Detailed analysis of the reaction profiles computed theoretically gives more insight into the influence of the nature of the solvent and halogen atom, and provides rationale for the very different behaviour of copper and gold in this chemistry.

Simplified and versatile access to low valent Ni complexes by metal-free reduction of NiII precursors.

The reduction of [Ni(DME)Cl2] with 2 equiv. of bis(trimethylsilyl)-1,4-tetramethyldihydropyrazine in the presence of a ligand L and an excess of olefin cleanly leads to [Ni(L)(alkene)2] complexes. When reduction is performed in the presence of 1,5-cyclooctadiene (COD), [Ni(COD)2] is obtained. Such an approach also allows access to the NiI dimer [Ni(bis(dicyclohexylphosphino)propane)Cl]2.

Formation of a peri-Bridged Phosphonio-Naphthalene by Cu-Mediated Phosphine-Aryl Coupling.

The peri-iodo naphthyl phosphine 1 reacts with CuI to give the peri-bridged phosphonio-naphthalene 2, which has been fully characterized (multi-nuclear NMR, MS, XRD). The outcome of the reaction differs markedly from that observed with gold. A two-step pathway involving P-assisted C-I oxidative addition to copper, followed by P-C reductive elimination is shown to be energetically feasible by DFT calculations.

Outer-Sphere Reactivity Shift of Secondary Phosphine Oxide-Based Nickel Complexes: From Ethylene Hydrophosphinylation to Oligomerization.

A new dimension for secondary phosphine oxide (SPOs) ligands is described in this article. Demonstrated on original π-allylic nickel structures, these self-assembled complexes trigger catalytic hydrophosphinylation reactions. Addition of a Lewis acid B(C6 F5 )3 switches the reactivity towards migratory insertion and thus ethylene oligomerization through an unprecedented outer-sphere interaction with the coordinated SPO ligand. NMR experiments and X-ray analyses allowed for the observation of the formation of zwitterionic active species as well as their degradation pathway.

A Straightforward Access to Stable, 16 Valence-electron Phosphine-Stabilized Fe0 Olefin Complexes and their Reactivity.

The use of the dialkene divinyltetramethyldisiloxane (dvtms) allows easy access to the reactive 16 valence-electron complexes [Fe0(L-L)(dvtms)], (L-L) = dppe (1,2-bis(diphenylphosphino)ethane), (1), dppp (1,2-bis(diisopropylphosphino)propane), (2), pyNMeP(iPr)2 (N-(diisopropylphosphino)-N-methylpyridin-2-amine), (4), dipe (1,2-bis(diisopropylphosphino)ethane), (5), and [Fe0(L)2(dvtms)], L = PMe3, (3), by a mild reductive route using AlEt2(OEt) as reducing agent. In contrast, by the same methodology, the 18 valence-electron complexes [Fe0(L-L)2(ethylene)], (L-L) = dppm (1,2-bis(diphenylphosphino)methane), 6, (L-L) = dppa (1,2-bis(diphenylphosphino)amine) 7 or (L-L)=dppe, 8, were obtained, which do not contain dvtms. In addition, a combined DFT and solid-state paramagnetic NMR methodology is introduced for the structure determination of 5. A comparative study of the reactivity of 1,2,4-6 and 8 with 3-hexyne highlights emerging mechanistic implications for C-C coupling reactions using these complexes as catalysts.

Alternative aluminum-based cocatalysts for the iron-catalyzed oligomerization of ethylene.

Multinuclear aluminum cocatalysts have been obtained by the reaction of various phenols, alcohols or diols with trimethylaluminum and were used in situ or as isolated, well-defined species, for the activation of an iron(ii) or an iron(iii) pre-catalyst for the oligomerization of ethylene. The best cocatalyst candidate involves 2,2'-biphenol () in a /AlMe3 ratio of 2/3.

Synthesis and characterization of palladium(II) and nickel(II) alcoholate-functionalized NHC complexes and of mixed nickel(II)-lithium(I) complexes.

The synthesis of Pd(II) and Ni(II) alcohol-functionalized N-heterocyclic carbene (NHC) complexes was explored to examine the possible influence of the functional arm attached to the NHC backbone on their structure and reactivity and, in the case of a Ni(II) complex, on its catalytic properties in ethylene oligomerization. Starting from the alcohol-functionalized imidazolium salt [ImDiPP(C2OH)]Cl (2), the new functionalized NHC palladium(II) complex [PdCl(acac){ImDiPP(C2OH)-CNHC}] (3) was synthesized and fully characterized. Two byproducts, [PdCl{µ-ImDiPP(C2O)-CNHC,O}]2 (4) and trans-[PdCl2{ImDiPP(C2OH)-CNHC}2] (5), formed during the synthesis of 3, were also fully characterized. Acids promoted the transformation of 3 into the new CNHC-bound complex [PdCl(µ-Cl){ImDiPP(C2OH)-CNHC}]2 (6), unveiling the lability of the acac ligand and the resistance of the Pd-NHC bond to acids. Complex 6 reacted with a base to afford complex 4, in which alkoxide coordination to Pd(II) has occurred to generate a CNHC,O chelate. The stability of 3 was also assessed under basic conditions, and the new complex [Pd(acac){ImDiPP(C2O)-CNHC,O}] (7) was characterized. The new nickel(II) alcoholate-functionalized NHC complex [NiCl{µ-ImDiPP(C2O)-CNHC,O}]2 (8) was synthesized by the reaction of the imidazolium salt 2 with n-BuLi and [NiCl2(dme)]. The reaction of 8 with HCl regenerates the imidazolium and alcohol functions to give [ImDiPP(C2OH)]2[NiCl4] (9). The mixed-metal Ni(II)-Li(I) complexes [Ni2{µ-ImDiPP(C2O)-CNHC,µ-O}4Li]BF4 (10), [Ni2{µ-ImDiPP(C2O)-CNHC,µ-O}4Li]Cl (11), and [Ni{ImDiPP(C2O)-CNHC,µ-O}2LiBr] (12) were isolated and characterized. However, it was not possible to synthesize a Ni(II) alcohol-functionalized NHC complex in high yield. Small amounts of the square-planar complex [NiCl2{ImDiPP(C2OH)-CNHC}2] (13) could be isolated, and this complex was characterized by single-crystal X-ray diffraction. In 13, only the CNHC atom of the alcohol-functionalized NHC ligand is bound to the metal. The structures of the imidazolium salt 2·2H2O and of the complexes 3, 4, 4-polymorph, 5, 6·CH2Cl2, and 8-13 were established by single-crystal X-ray diffraction.

Cycloalkyl-based unsymmetrical unsaturated (U2)-NHC ligands: flexibility and dissymmetry in ruthenium-catalysed olefin metathesis.

Air-stable Ru-indenylidene and Hoveyda-type complexes bearing new unsymmetrical unsaturated N-heterocyclic carbene (U2-NHC) ligands combining a mesityl unit and a flexible cycloalkyl moiety as N-substituents were synthesised. Structural features, chemical stabilities and catalytic profiles in olefin metathesis of this new library of cycloalkyl-based U2-NHC Ru complexes were studied and compared with their unsymmetrical saturated NHC-Ru homologues as well as a set of commercially available Ru-catalysts bearing either symmetrical SIMes or IMes NHC ligands.

Synthesis and characterization of oxygen-functionalised-NHC silver(I) complexes and NHC transmetallation to nickel(II).

The new alcohol- and ether-functionalised-NHC silver(I) complexes bis(1-(2,6-diisopropylphenyl)-3-(2-hydroxyethyl)-1H-imidazol-2(3H)-ylidene)silver(I) chloride, [Ag{ImDiPP(C2OH)}2]Cl (4), bis(1-(2-hydroxyethyl)-3-mesityl-1H-imidazol-2(3H)-ylidene)silver(I) chloride, [Ag{ImMes(C2OH)}2]Cl (5), bis(1-(2-hydroxyethyl)-3-methyl-1H-imidazol-2(3H)-ylidene)silver(I) chloride, [Ag{ImMe(C2OH)}2]Cl (6), bis(1-(2,6-diisopropylphenyl)-3-(2-hydroxyethyl)-1H-imidazol-2(3H)-ylidene)silver(I) tetrafluoroborate, [Ag{ImDiPP(C2OH)}2]BF4 (9), and bis(1-(2,6-diisopropylphenyl)-3-(2-methoxyethyl)-1H-imidazol-2(3H)-ylidene)silver(I) chloride, [Ag{ImDiPP(C2OMe)}2]Cl (13), were synthesized and fully characterized by NMR spectroscopy and single crystal X-ray diffraction. For some complexes, an uncommon heteronuclear coupling (4)J((107/109)Ag-H) was unveiled. Their ability to transfer the NHC ligand to Ni(II) was assessed in the presence of different nickel(II) sources; the bis-NHC Ni(II) complex bis(1-(2,6-diisopropylphenyl)-3-(2-methoxyethyl)-1H-imidazol-2(3H)-ylidene)nickel(II) chloride, [NiCl2{ImDiPP(C2OMe)}2] (15), was obtained from 13 and shown by X-ray diffraction study to have a trans-arrangement of the two NHC ligands. However, in contrast to other Ag(I) NHC complexes the transmetallation reaction failed with the hydroxyl-functionalised silver complexes, possibly due to the acidity of the alcohol OH function, leading overall to reprotonation of the C(NHC) and isolation of the corresponding imidazolium salts.

Ethylene oligomerization using iron complexes: beyond the discovery of bis(imino)pyridine ligands.

Since the discovery that bis(imino)pyridine ligands are able to confer high activities in ethylene oligomerization and polymerization to their iron complexes, considerable attention has been focused on catalyst design for these reactions and this research constitutes an ever-growing area in molecular catalysis. The tuning of the ligand structures and properties, and thus of catalysts, generally represents the basis for subsequent work contributing to process development and industrialization. Significant effort is therefore devoted to generate structural diversity in order to access the required catalyst stability and selectivity. This feature article outlines nitrogen-containing ligands that have been developed for the iron-catalyzed oligomerization of ethylene since the seminal discovery of the properties of bis(imino)pyridine ligands.

A new stable C(NHC)--CH--C(NHC)N-heterocyclic dicarbene ligand: its mono- and dinuclear Ir(I) and Ir(I)-Rh(I) complexes.

The ligand [(1,3-phenylene)bis(methylene)]bis(1-ethyl-imidazol-2-ylidene) ( 2) (abbreviated as EtCNHC--CH--CNHC with CH = central aromatic ring, -- = CH2 spacer) has been synthesised, and isolated, by deprotonation of [(1,3-phenylene)bis(methylene)]bis(1-ethyl-imidazolium) dichloride, Et(CHimid.--CH--CHimid.)Cl2 ( 1) with LiN(SiMe3)2. This new, remarkably stable NHC dicarbene ligand is quantitatively protonated with HBr to form [(1,3-phenylene)bis(methylene)]bis(1-ethyl-imidazolium) dibromide Et(CHimid.--CH--CHimid.)Br2 ( 3) and reprotonated slowly enough in MeOH to allow observation of the monoprotonated intermediate 4. Dicarbene 2 reacts with S8 to give the dithione compound [(1,3-phenylene)bis(methylene)]bis(1-ethyl-imidazol-2-thione) Et[(SC)--CH--(CS)] ( 6). Reaction of 2 with [IrCl(CO)(PPh3)2] and [Ir(mu-Cl)(cod)]2 yielded the mononuclear [Ir(CO)(PPh3)2Et(CHimid.--CH--CNHC)(PF6)](PF6) ( 8) and [IrCl(cod)Et(CHimid.--CH--CNHC)](PF6) ( 10) complexes, respectively, and the dinuclear complexes [{Ir(CO)(PPh3)2}2Et(mu-CNHC--CH--CNHC)](PF6)2 ( 7) and [{IrCl(cod)}2Et(mu-CNHC--CH--CNHC)] ( 9), respectively, in which 2 acts as a bridging, non-pincer type ligand. Only one other Ir(I) complex has been reported before containing a CNHC--CH--CNHC ligand. The structures of 6 and 9 were determined by X-ray diffraction and depict different conformations of the (1,3-phenylene)bis(methylene) (or xylylene) moiety. The mononuclear Ir complex 9 reacted smoothly with [Rh(mu-Cl)(cod)]2 and Cs2CO3 to generate a rare example of a heteronuclear NHC complex, [IrRhCl2(cod)2Et(mu-CNHC--CH--CNHC)] ( 11).

Direct synthesis of a new class of N,N,N ligands based on 1,2-dihydro-1,10-phenanthroline backbone and their coordination to Pd complexes.

Reactions of acetylpyridine derivatives with 8-aminoquinolines provide a general and simple access to an unexpected class of versatile N,N,N ligands, which offer interesting perspectives in coordination chemistry.

Unprecedented cubane-type silver cluster with a novel phosphinite functionalized N-heterocyclic carbene ligand.

A novel heterodifunctional phosphinite imidazolium salt was synthesized and reacted with Ag(I) to afford an unusual tetrasilver cubane-type cluster with two P-NHC ligands bridging between the Ag(I) centres of opposite Ag(2)I(2) faces.

An unprecedented, figure-of-eight, dinuclear iridium(I) dicarbene and new iridium(III) 'pincer' complexes.

An unusual dinuclear Ir(I) complex bridged by two N-heterocyclic biscarbene ligands, forming a 20-membered, figure-of-eight dimetallacycle, and new CNHCCCNHC pincer complexes of Ir(III) have been obtained directly from the bis(imidazolium) precursors and [Ir(micro-Cl)(cod)]2.

Rhodium nanocatalysts stabilized by various bipyridine ligands in nonaqueous ionic liquids: influence of the bipyridine coordination modes in arene catalytic hydrogenation.

Rhodium nanoparticles stabilized by 2,2'-, 3,3'-, 4,4'-bipyridine ligands were prepared in various ionic liquids according to a chemical reduction approach. Zerovalent nanospecies in the size range of 2.0-2.5 nm were characterized. The nature of the bipyridine and its influence on the coordination environment of rhodium nanoparticles were investigated in various nonaqueous ionic liquids according to the cation and anion. The hydrogenation of various aromatic compounds by these colloidal suspensions was carried out at 80 degrees C and under 40 bar of H 2. A first structural explanation based on bipyridine coordination modes is proposed to justify the observed different activities.

Ethenolysis of methyl oleate in room-temperature ionic liquids.

Unsaturated vegetable oils are an attractive renewable feedstock, and the selective cleavage of unsaturated fatty esters is an important transformation in this respect. The efficient and selective cross-metathesis of methyl oleate with ethylene was achieved under mild conditions with ruthenium-alkylidene catalysts in toluene and room-temperature ionic liquids (RTILs) to give two important chemical intermediates, 1-decene and methyl 9-decenoate, without double-bond migration. As recovery of the catalyst is an important target with respect to industrial applications, catalyst recycling studies were also carried out in RTILs with the first-generation Hoveyda catalyst.

A selective synthesis of hydroxyborate anions as novel anchors for zirconocene catalysts.

A new family of hydroxytris(pentafluorophenyl)borate anions [B(C6F5)3OH](-) associated with organic and aprotic cations c+ (imidazolium, pyrrolidinium and phosphonium) has been prepared by a general one-pot synthesis that implies the chloride borate analogues [B(C6F5)3Cl](-)[c]+. The [c]+[B(C6F5)3OH](-) salts have been isolated and fully characterized. The borate anion [B(C6F5)3OH](-) has been shown to protonate the Zr-Me bond in the Cp2ZrMe2 complex forming CH4 and the first published example of anionic [Cp2Zr(Me)OB(C6F5)3](-) species. Standard spectroscopic methods demonstrate the covalent character of the Zr metal center and the anionic character of the boron atom. This protonolysis methodology using [B(C6F5)3OH](-) anion affords a new route for the incorporation of a covalently bonded anionic functionality on organometallic complexes. This provides a new way to immobilize transition metal complexes in ionic liquids.

Unexpected reduction pathway of a Co(2+) salt to [HCo(CO)(4)] via [Co(2)(CO)(8)] in an ionic liquid.

In the 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ionic liquid ([BMI][NTf(2)]), [Co(NTf(2))(2)] is reduced under 5.5 MPa of H(2)-CO to [Co(2)(CO)(8)] prior to [HCo(CO)(4)], provided a pyridine ligand is present in the medium.