β‐Diketiminato–Alkaline Earth Cationic Complexes: Synthesis, Structures, Lactide Polymerization and Unusual Oxidative Reactivity of the Ancillary Ligand

Abstract

Well-defined (β-diketiminate)calcium and -strontium cationic complexes paired with weakly coordinating anions have been prepared in high yields by straightforward protocols. These highly electrophilic species are efficient catalysts [a] We postulated that on account of the exacerbated Lewis acidity of the metal center, well-defined solvent-free calcium cations with low coordination numbers of the type [{BDI iPr }Ca(L) n ] + (L = donor; n = 0-3) would constitute ideal precatalysts for immortal ROP reactions (iROP) performed in the presence of excess exogenous alcohol as a transfer agent. [18b,18c,19] A complex giving 1 H NMR spectroscopic data (recorded with the complex in CD 2 Cl 2 ) consistent with the formulation [{BDI iPr }Ca(THF)] + · [H 2 N{B(C 6 F 5 ) 3 } 2 ] -(1), was generated upon treatment of {BDI iPr }CaN(SiMe 3 ) 2 (THF) in Et 2 O with an equimolar amount of Bochmann's acid, [H(OEt 2 ) 2 ] + ·[H 2 N{B-(C 6 F 5 ) 3 } 2 ] -[20] (Scheme 1). 19 F{ 1 H} (δ = -132.9, -160.2 and -165.7 ppm; 2:1:2 ratio) and 11 B{ 1 H} (δ = -8.15 ppm) NMR spectroscopic data confirmed the integrity of the weakly coordinating [H 2 N{B(C 6 F 5 ) 3 } 2 ]anion. However, complex 1 was not stable in solution, and it spontaneously formed the doubly protonated proligand [{BDI iPr }HH] + · Scheme 1. www.eurjic.org

Macrocyclic Weakly Coordinating Anions

“…Because of the similar size and charge density,t here is strong potential that M-WCAs also form giant vesicle structures, which could be probed by static and dynamic light scatteringofM -WCA solutions in polar solvents. Self-assembled vesicle structures would open afurther dimension of M-WCA chemistry:E lectrolytes containingk nown weakly coordinating anions(e.g.,PF 6 À )form only simplehomogeneouss olutions. Solutionsc ontaining vesicles made of MWCAs would be an ovel type of liquid electrolyte.…”

“…Eur.J.2015, 21,[14258][14259][14260][14261][14262][14263][14264][14265][14266][14267] www.chemeurj.org sites and to achieve good solubility in organic solvents. [6] MWCAs offer additional opportunities for catalysis because the anion can act as the host for the cation. Such host-guest structures are expected to produce steric confinement for substrates,w hich may lead to enhanced or unusual regio-and stereoselectivities.…”

“…[1,2] For example, solutions of LiPF 6 are the state-of-the-art electrolytes in Li-ion batteries. [3] Polymeric WCAs are effective solid-state ion conductors.…”

“…For instance, Nafion is ap olymeric WCA with ap erfluorinatedb ackbone and sulfonica cid groups with an extraordinarilyh igh ion mobility, which is utilized in proton-exchange membranes of fuel cells. [4] Because of their low ability to coordinate to cations, WCAs are being used for the stabilization of highly electrophilico rganometallicc ations, such as [Fe(CO) 6 ] 2 + . [5] They can also function as counter ions of cationic organometallic catalysts due to their inability to coordinate to catalytically active Lewis acidic sites.…”

“…[5] They can also function as counter ions of cationic organometallic catalysts due to their inability to coordinate to catalytically active Lewis acidic sites. [6] WCAs with protons as counter ions are often superacids, which are ablet oa bstract H À from alkanes to yield carbocations,adiscovery that has been awarded aNobel prize. [7] The Concept…”