Application of the Redox-Transmetalation Procedure to Access Divalent Lanthanide and Alkaline-Earth NHC Complexes*

Tridentate NacNac Stabilized Tin and Nickel Complexes: Access to a Monomeric Nickel Hydride and Its Catalytic Application

The transmetalation reaction of picolyl-supported tridentate nacnac germylene monochloride [2,6-iPr₂-C₆H₃NC(Me)CHC(Me)NH(CH₂py)]GeCl (1) (py = pyridine) with SnCl₂ results in an analogous stannylene chloride (2). The three-coordinated stannylenium cation [{2,6-iPr₂-C₆H₃NC(Me)CHC(Me)NH(CH₂py)}Sn]⁺ with SnCl₃^- as a counteranion (3) has been generated through the abstraction of chloride ligand from 2 using an additional equivalent of SnCl₂. Instead of forming a donor-acceptor complex, 2 undergoes a facile redox transmetalation reaction with Ni(COD)₂ (COD = cyclooctadiene) and CuCl to afford analogous nickel and copper complexes [2,6-iPr₂-C₆H₃NC(Me)CHC(Me)NH(CH₂py)]MCl [M = Ni (4) and Cu (5)]. The reactions of 4 with potassium tri-sec-butylborohydride (commonly known as K-selectride) and AgSbF₆ provide access to monomeric Ni(II) hydride, [2,6-iPr₂-C₆H₃NC(Me)CHC(Me)NH(CH₂py)]NiH (6) and a Ni(II) cation, [{2,6-iPr₂-C₆H₃NC(Me)CHC(Me)NH(CH₂py)}Ni][SbF₆] (7), respectively. 6 was found to be an effective catalyst for the hydroboration of amides.

Solid-state and solution-phase characterization of SmII-aza[2.2.2]cryptate and its methylated analogue

Two new Sm^II-azacryptates are reported that differ in steric hindrance and Lewis basicity of donor atoms. The sterically hindered complex has a smaller coordination number and a more negative electrochemical potential than the complex with less steric hindrance.

Rare Earth Starting Materials and Methodologies for Synthetic Chemistry

The number of rare earth (RE) starting materials used in synthesis is staggering, ranging from simple binary metal-halide salts to borohydrides and "designer reagents" such as alkyl and organoaluminate complexes. This review collates the most important starting materials used in RE synthetic chemistry, including essential information on their preparations and uses in modern synthetic methodologies. The review is divided by starting material category and supporting ligands (i.e., metals as synthetic precursors, halides, borohydrides, nitrogen donors, oxygen donors, triflates, and organometallic reagents), and in each section relevant synthetic methodologies and applications are discussed.

Europium is Different: Solvent and Ligand Effects on Oxidation State Outcomes and C-F Activation in Reactions Between Europium Metal and Pentafluorophenylsilver

Unique outcomes have emerged from the redox transmetallation/ protolysis (RTP) reactions of europium metal with [Ag(C₆ F₅ )(py)] (py=pyridine) and pyrazoles (RR'pzH). In pyridine, a solvent not normally used for RTP reactions, the products were mainly Eu^II complexes, [Eu(RR'pz)₂ (py)₄ ] (RR'pz=3,5-diphenylpyrazolate (Ph₂ pz) 1; 3-(2-thienyl)-5-trifluoromethylpyrazolate (ttfpz) 2; 3-methyl-5-phenylpyrazolate (PhMepz) 3). However, use of 3,5-di-tert-butylpyrazole (tBu₂ pzH) gave trivalent [Eu(tBu₂ pz)₃ (py)₂ ] 4, whereas the bulkier N,N'-bis(2,6-difluorophenyl)formamidine (DFFormH) gave divalent [Eu(DFForm)₂ (py)₃ ] 5. In tetrahydrofuran (thf), the usual solvent for RTP reactions, C-F activation was observed for the first time with [Ag(C₆ F₅ )(py)] in such reactions. Thus trivalent [{Eu₂ (Ph₂ pz)₄ (py)₄ (thf)₂ (μ-F)₂ }{Eu₂ (Ph₂ pz)₄ (py)₂ (thf)₄ (μ-F)₂ }] (6), [Eu₂ (ttfpz)₄ (py)₂ (dme)₂ (μ-F)₂ ] (7), [Eu₂ (tBu₂ pz)₄ (dme)₂ (μ-F)₂ ] (8) were obtained from the appropriate pyrazoles, the last two after crystallization from 1,2-dimethoxyethane (dme). Surprisingly 3,5-dimethylpyrazole (Me₂ pzH) gave the divalent cage [Eu₆ (Me₂ pz)₁₀ (thf)₆ (μ-F)₂ ] (9). This has a compact ovoid core held together by bridging fluoride, thf, and pyrazolate ligands, the last including the rare μ₄ -1η⁵ (N₂ C₃ ): 2η² (N,N'): 3κ(N): 4κ(N') pyrazolate binding mode. With the bulky N,N'-bis(2,6-diisopropylphenyl)formamidine (DippFormH), which often favours C-F activation in RTP reactions, neither oxidation to Eu^III nor C-F activation was observed and [Eu(DippForm)₂ (thf)₂ ] (10) was isolated. By contrast, Eu reacted with Bi(C₆ F₅ )₃ and Ph₂ pzH or tBu₂ pzH in thf without C-F activation, to give [Eu(Ph₂ pz)₂ (thf)₄ ] (11) and [Eu(tBu₂ pz)₃ (thf)₂ ] (12) respectively, the oxidation state outcomes corresponding to that for use of [Ag(C₆ F₅ )(py)] in pyridine.