Proton-detected fast-magic-angle spinning NMR of paramagnetic inorganic solids.

Fast (60 kHz) magic angle spinning solid-state NMR allows very sensitive proton detection in highly paramagnetic organometallic powders. We showcase this technique with the complete assignment of 1H and 13C resonances in a high-spin Fe(ii) polymerisation catalyst with less than 2 mg of sample at natural abundance.

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.

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.

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.

Sulfonamido-phosphoramidite ligands in cooperative dinuclear hydrogenation catalysis.

Sulfonamido-phosphoramidite ligands lead to the formation of Rh-Rh dinuclear complexes through the anionic P-N(-) bridging character. The resulting "boat-shaped" dinuclear catalysts activate molecular H(2) through a cooperative dinuclear endocyclic mechanism, resulting in one bridging and one classical hydride on the dinuclear complex. These new complexes are very active hydrogenation catalysts that operate via a new cooperative hydrogenation activation mechanism, as calculated with density functional theory, and they display unequaled high selectivities in the hydrogenation of hindered cyclic acetamidoalkenes.

Singly hydrogen bonded supramolecular ligands for highly selective rhodium-catalyzed hydrogenation reactions.

H bonds make the catalysts! A single hydrogen bond between ligands coordinated to a rhodium center is critical for the formation of pure supramolecular catalysts for asymmetric hydrogenation reactions. The ester group of the amidite ligand (see scheme) also forms a hydrogen bond with the coordinated substrate. Use of the heterocomplex afforded the highest enantioselectivity reported to date for the hydrogenation of several ester substrates.