[Ni(cod) 2 ][Al(OR F ) 4 ], a Source for Naked Nickel(I) Chemistry

Isolation and Characterization of the Homoleptic Nickel(I) and Nickel(II) Bis‐benzene Sandwich Cations

A stable salt of the metalloradical [Ni(C₆ H₆ )₂ ]⁺ hitherto unknown in the condensed phase was synthesized from [Ni(CO)₄ ]⁺ [WCA]^- and benzene ([WCA]^- =[F{Al(OR^F )₃ }₂ ]^- ; R^F =C(CF₃ )₃ ). Single crystal XRD reveals a remarkable asymmetrically η³ ,η⁶ -slipped sandwich structure. The magnetic properties of the [Ni(C₆ H₆ )₂ ]⁺ cation were determined in solution and in the gas phase. Oxidation with the synergistic Ag⁺ /0.5 l₂ system led to the salt [Ni(C₆ H₆ )₂ ]²⁺ ([WCA]^- )₂ . All products were fully characterized by means of IR, Raman, NMR/EPR, single crystal and powder XRD.

Chasing the Mond Cation: Synthesis and Characterization of the Homoleptic Nickel Tetracarbonyl Cation and its Tricarbonyl-Nitrosyl Analogue

130 years after Mond discovered the first homoleptic carbonyl complex Ni(CO)₄, we report on a [Ni(CO)₄]^.+ salt as the first synthesis of any homoleptic nickel carbonyl cation in the condensed phase. It was prepared by oxidation of nickel metal with the synergistic oxidant Ag[F{Al(OR^F)₃}₂]/0.5 I₂ (R^F=C(CF₃)₃) in CO atmosphere. This D_2d‐symmetric metalloradical represents the last missing entry among the structurally characterized homoleptic carbonyl cations of Groups 6 to 11. Additionally, the nickel tricarbonyl‐nitrosyl cation [Ni(CO)₃(NO)]⁺ was obtained by usage of NO[F{Al(OR^F)₃}₂] and all products were fully characterized by means of IR, Raman, NMR/EPR, single crystal and powder XRD.

A Simple Homoleptic Gallium(I) Olefin Complex: Mimicking Transition-Metal Chemistry at a Main-Group Metal?

The earth-metal olefin complex [GaI (COD)2 ]+ [Al(ORF )4 ]- (COD=1,5-cyclooctadiene; RF =C(CF3 )3 ) constitutes the first homoleptic olefin complex of any main-group metal accessible as a bulk compound. It is straight forward to prepare in good yield and constitutes an olefin complex of a main-group metal that-similar to many transition-metals-may adopt the +1 and +3 oxidation states opening potential applications. Crystallographic-, vibrational- and computational investigations give an insight to the atypical bonding between an olefin and a main-group metal. They are compared to classical transition-metal relatives.

Taming the Cationic Beast: Novel Developments in the Synthesis and Application of Weakly Coordinating Anions

This Review gives a comprehensive overview of the most topical weakly coordinating anions (WCAs) and contains information on WCA design, stability, and applications. As an update to the 2004 review, developments in common classes of WCA are included. Methods for the incorporation of WCAs into a given system are discussed and advice given on how to best choose a method for the introduction of a particular WCA. A series of starting materials for a large number of WCA precursors and references are tabulated as a useful resource when looking for procedures to prepare WCAs. Furthermore, a collection of scales that allow the performance of a WCA, or its underlying Lewis acid, to be judged is collated with some advice on how to use them. The examples chosen to illustrate WCA developments are taken from a broad selection of topics where WCAs play a role. In addition a section focusing on transition metal and catalysis applications as well as supporting electrolytes is also included.

Synthesis, Characterisation and Reactions of Truly Cationic NiI -Phosphine Complexes

The recently published purely metallo-organic Ni^I salt [Ni(cod)₂ ][Al(OR^F )₄ ] (1, cod=1,5-cyclooctadiene, R^F =C(CF₃ )₃ ) provides a starting point for a new synthesis strategy leading to Ni^I phosphine complexes, replacing cod ligands by phosphines. Clearly visible colour changes indicate reactions within minutes, while quantum chemical calculations (PBE0-D3(BJ)/def2-TZVPP) approve exergonic reaction enthalpies in all performed ligand exchange reactions. Hence, [Ni(dppp)₂ ][Al(OR^F )₄ ] (2, dppp=1,3-bis(diphenylphosphino)propane), [Ni(dppe)₂ ][Al(OR^F )₄ ] (3, dppe=1,3-bis(diphenyl-phosphino)ethane), three-coordinate [Ni(PPh₃ )₃ ][Al(OR^F )₄ ] (4) and a remarkable two-coordinate Ni^I phosphine complex [Ni(PtBu₃ )₂ ][Al(OR^F )₄ ] (5) were characterised by single crystal X-ray structure analysis. EPR studies were performed, confirming a nickel d⁹ -configuration in complexes 2, 4 and 5. This result is supported by additional magnetization measurements of 4 and 5. Further investigations by cyclic voltammetry indicate relatively high oxidation potentials for these Ni^I compounds between 0.7 and 1.7 V versus Fc/Fc⁺ . Screening reactions with O₂ and CO gave first insights on the reaction behaviour of the Ni^I phosphine complexes towards small molecules with formation of mixed phosphine-CO-Ni^I complexes and oxidation processes yielding new Ni^I and/or Ni^II derivatives. Moreover, 4 reacted with CH₂ Cl₂ at RT to give a dimeric Ni^II ylide complex (4 c). As CH₂ Cl₂ is a rather stable alkyl halide with relatively high C-Cl bond energies, 4 appears to be a suitable reagent for more general C-Cl bond activation reactions.

A T-Shaped Nickel(I) Metalloradical Species

A T-shaped Ni^I complex was synthesized using a rigid acridane-based pincer ligand to prepare a metalloradical center. Structural data displays a nickel ion is embedded in the plane of a PNP ligand. Having a sterically exposed half-filled dx2-y2 orbital, this three-coordinate Ni^I species reveals unique open-shell reactivity including the homolytic cleavage of various σ-bonds, such as H-H, N-N, and C-C.