Organometallics最新文献

The Ni(0) methyl complex MeNiGaL was prepared and characterized by XRD, ¹H NMR, ¹³C NMR, ³¹P NMR, ESI-MS, and UV–vis. The compound can be prepared from the 16-valence electron complex NiGaL by addition of MeLi, yielding the corresponding lithium salt. NiGaL is a close derivative of a complex that has been previously reported by Lu et al. The title compound represents a rare example of a Ni(0) alkyl complex. The complex is based on a bimetallic, tripodal framework featuring a Ni–Ga bond. The methyl complex, isolated as its Li(THF)₄ salt, shows no interaction between the lithium cation and the methyl anion in the solid state. UV–vis titration experiments indicate reversible dissociation of MeLi in solution. Attempts to prepare the corresponding neopentyl or CH₂EMe₃ complexes (E = N, P), as possible intermediates or analogues thereof in the nickel catalyzed cyclopropanation of unactivated alkenes with NMe₄OTf/BuLi, were unsuccessful.

With an interest in chalcogen bonding, we use a rigid indazolium backbone to install a formally zero-valent Se center next to a divalent Te center, allowing us to investigate the effects of oxidation of the Se center on the observed Te···Se interaction. Through spectroscopic and computational comparison of the Se(0) species with its Se(II) counterpart and their monochalcogen analogues, we experimentally and computationally investigate the effect of modulating Se basicity on the resulting Te···Se interaction. Comparison with well-studied naphthalene and acenaphthene variants indicates that the increased basicity of the Se(0) center allows for a comparably strong Te···Se interaction despite longer peri distances and a larger splay angle. Finally, our study illuminates the potential non-innocence of cationic organic substituents in chalcogen-bonding catalysis of the transfer hydrogenation of quinolines.

Oxidative addition of PC(H)P pincer ligands at late transition metals typically occurs via C–H activation in the 2-position of the ligand, yielding [(PCP)MHX] type pincer complexes (X = monoanionic ligand). We present formation of the dinuclear Ir(III) complex [(^iPrPSCSP^iPr)Ir(H)(MeCN)₂]₂[OTf]₂ as a rare example of meta-C–H activation at a pincer ligand.

5-Hydroxymethylfurfural (HMF) is a biobased platform chemical with a lot of potential to be a key chemical in a future chemical industry. Oxidized derivatives of HMF are explored in many emerging chemical products. However, selective oxidation toward 5-hydroxymethyl-2-furan carboxylic acid (HMFCA) is challenging. Furthermore, this conversion has been hardly explored with homogeneous catalysts. We show here the selective oxidation toward HMFCA using the industrially relevant catalyst [Mn^IV₂(μ-O)₃(tmtacn)₂][(X)₂] (Mncat, X = CH₃COO/PF₆/SO₄). Moreover, this is achieved in water, under mild conditions (room temperature, pH 11), using low loadings of a nonprecious metal catalyst and hydrogen peroxide, reaching TONs of up to 200 mol_HMFCA/mol_Mncat. We show that the oxidation under these conditions behaves distinctively from the oxidation with Mncat in MeCN and allows selective oxidation of aldehydes in the presence of alcohols. Kinetic and ESI-MS studies were used to study the change in selectivity and to give an explanation for changes in catalytic behavior.

Radical-type carbene transfer catalysis is an efficient method for the direct functionalization of C–H and C═C bonds. However, carbene radical complexes are currently formed via high-energy carbene precursors, such as diazo compounds or iodonium ylides. Many of these carbene precursors require additional synthetic steps, have an explosive nature, or generate halogenated waste. Consequently, the utilization of carbene radical catalysis is limited by specific carbene precursors that access the carbene radical intermediate. In this study, we generate a cobalt(III) carbene radical complex from dimethyl malonate, which is commercially available and bench-stable. EPR and NMR spectroscopy were used to identify the intermediates and showed that the cobalt(III) carbene radical complex is formed upon light irradiation. In the presence of styrene, carbene transfer occurred, forming cyclopropane as the product. With this photochemical method, we demonstrate that dimethyl malonate can be used as an alternative carbene precursor in the formation of a cobalt(III) carbene radical complex.

KN(SiMe₃)₂, a non-nucleophilic strong base, rarely misses deprotonating an imidazolium-2-H to give its N-heterocyclic carbene (NHC). We report a rare case of a -CH₂-linked bifunctional imidazolium-phenol [HO-4,6-^tBu₂-C₆H₂-2-CH₂{CH(NCH═CHNAr)}]Br [LH₂Br; Ar = 2,6-ⁱPr₂–C₆H₃ (Dipp)], whose attempted double deprotonation by KN(SiMe₃)₂ majorly gives an unusual substitution product [(^DippImd)K{O-4,6-^tBu₂-C₆H₂-2-CH₂N(SiMe₃)₂}] (1; ^DippImd = CH{(NCH═CHN(Dipp)}). Apparently, the second KN(SiMe₃)₂, instead of deprotonating the imidazolium-2-H, substitutes the whole imidazolium moiety from the benzylic carbon. Control experiments indicate a S_N1-type mechanism. But the intermediate LH, seemingly a zwitterionic imidazolium aryloxide, also shows a steady self-fragmentation by releasing free ^DippImd to suggest a complex formative route for 1. Interestingly, LiN(SiMe₃)₂ in contrast favors the expected double deprotonation but further undergoes a 1,2-benzyl migration to give trimeric [Li(O-4,6-^tBu₂-C₆H₂-2-CH₂{C(NCH═CHNAr)}]₃ [4]₃. Two plausible routes for the substitution and deprotonation are proposed using DFT calculations. However, considering the complexities involved, a better clarity of the Li/K divergence would require a more accurate modeling of the reaction species and explicit solvent molecules.

Pincer-ligated iridium complexes have been widely developed, and (pincer)Ir(III) complexes, particularly five-coordinate, are central to their chemistry. Such complexes typically bear two formally anionic ligands in addition to the pincer ligand itself. Yet despite the prevalence of halides as anionic ligands in transition metal chemistry, there are relatively few examples in which both of these ancillary anionic ligands are halides or even other monodentate low-field anions. We report a study of the fragment (^iPrPCP)IrCl₂ (^iPrPCP = κ³-2,6-C₆H₃(CH₂PⁱPr₂)) and adducts thereof. These species are found to be thermodynamically disfavored relative to the corresponding hydridohalides. For example, DFT calculations and experiments indicate that one Ir–Cl bond of (^iPrPCP)IrCl₂ complexes will undergo reaction with H₂ to give (^iPrPCP)IrHCl or an adduct thereof. In the presence of aqueous HCl, (^iPrPCP)IrCl₂ adds a chloride ion to give an unusual example of an anionic transition metal complex ((^iPrPCP)IrCl₃^–) with a Zundel cation (H₅O₂⁺). (^iPrPCP)IrCl₂ is not stable as a monomer at room temperature but exists in solution as a mixture of clusters which can add various small molecules. DFT calculations indicate that dimerization and trimerization of (^iPrPCP)IrCl₂ are more favorable than the analogous reactions of (^iPrPCP)IrHCl, in accord with cluster formation being observed only for the dichloride complex.

We showed previously that the d¹⁰ nickel perfluorocarbene complex, P₃Ni═CF(CF₃) [P = P(OⁱPr)₃], 1, reacts with fluoroalkenes to produce both 4-membered nickelacycles and metathesis products via separate reaction pathways. Herein, we compare the reactivity of 1 with a variety of alkenes. The reaction of 1 with hexafluoropropene [CF₂═CF(CF₃), HFP] affords a single metallacycle, taking advantage of the diradical mechanism in which the carbene carbon adds to the CF₂ end of HFP. In contrast, 1 and perfluoro(methyl vinyl ether), CF₂═CF(OCF₃), yield both metallacycle and metathesis products, with preferential formation of the more stabilized difluorocarbene [P₃Ni═CF₂ vs P₃Ni═CF(OCF₃)] and a higher ratio of metathesis to metallacycle products than using tetrafluoroethylene or vinylidene difluoride. Attempts to form fluoropolymers via ring-opening metathesis polymerization of perfluorocyclobutene and hexafluorocyclopentene briefly gave new nickel carbenes but then yielded Ni fluoroalkene complexes with the loss of the CF(CF₃) unit. Surprisingly, both ethylene and styrene derivatives gave only metallacycles, although evidence was obtained for alkene coordination to nickel; computational studies are presented to identify the origin of these observations. Finally, insertion of ethylene into the ethylene-derived nickelacyclobutane afforded a new fluorinated alkene, CH₂═CHCH₂CH₂CHFCF₃, formed presumably via nickelacyclohexane through selective β-H and reductive eliminations.