Selective Transformation of Nickel‐Bound Formate to CO or C−C Coupling Products Triggered by Deprotonation and Steered by Alkali‐Metal Ions

Abstract

The complexes [LtBuNi(OCO‐κ2O,C)]M3[N(SiMe3)2]2 (M=Li, Na, K), synthesized by deprotonation of a nickel formate complex [LtBuNiOOCH] with the corresponding amides M[N(SiMe3)2], feature a NiII−CO22− core surrounded by Lewis‐acidic cations (M+) and the influence of the latter on the behavior and reactivity was studied. The results point to a decrease of CO2 activation within the series Li, Na, and K, which is also reflected in the reactivity with Me3SiOTf leading to the liberation of CO and formation of a Ni−OSiMe3 complex. Furthermore, in case of K+, the {[K3[N(SiMe3)2]2}+ shell around the Ni−CO22− entity was shown to have a large impact on its stabilization and behavior. If the number of K[N(SiMe3)2] equivalents used in the reaction with [LtBuNiOOCH] is decreased from 3 to 0.5, the deprotonated part of the precursor enters a complex reaction sequence with formation of [LtBuNiI(μ‐OOCH)NiILtBu]K and [LtBuNi(C2O4)NiLtBu]. The same reaction at higher concentrations additionally led to the formation of a unique hexanuclear NiII complex containing both oxalate and mesoxalate ([O2C‐CO2‐CO2]4−) ligands.

Alkali Metal Amide Salts of a Bulky Nitrogen Tethered Phosphonium Fluorenide Ligand

“…The crystal structure of each alkali metal complex gave rise to a wide range of (ipso-Dipp)-N-metal bond angles, highlighting dual aryl interactions, pronounced with the larger alkali metals Na and K. 34 A nitrogen atom with a trigonal planar configuration would ideally possess 120-degree bond angles; however, the angle between atoms C4−N1−metal significantly lowers with increasing alkali metal mass and size from roughly 114.87(6)°and 111.51 (14)°for lithium complexes 4a and 4• (THF, 0.5 C 6 D 6 ), 100.66 (10)°for sodium complex 5a, and 95.13 (11)°or 94.37 (8)°for potassium complexes 6a and 6• (0.5 n-C 6 H 14 ). This is notable as unique molecular structure has been observed reliant on this sort of aryl interaction with NacNac ligands including Co(I) spin-isomerism 35 and stabilizing a diamagnetic Ni(II) cation, 36 possibly indicating a specific niche for ligands like the one we present here for enabling this situational additional aryl electron donation.…”

Molecular Nickel Thiolate Complexes for Electrochemical Reduction of CO2 to C1–3 Hydrocarbons

“…Although complexes that couple CO 2 or CO to form multiple C−C bonds at a single metal site are rare, [21] there are examples showing that C−C coupled products can be generated intermolecularly by monometallic Ni complexes [10a,e, 22] . Based on the square planar geometry of 5 , we propose that the C 3 products are generated from two or more Ni centers (Scheme 1).…”