Halogen-free water-stable aluminates as replacement for persistent fluorinated weakly-coordinating anions

Abstract

Cost-efficient aluminates successfully replace expensive and persistent counterions in transition-metal catalyses such as Bolm's stereoselective enone hydrogenation.

Organic Azide and Auxiliary-Ligand-Free Complexes of Coinage Metals Supported by N-Heterocyclic Carbenes

“…The sulfur center adopts a very noticeable trigonal-pyramidal shape (sum of the angles at sulfur 307.8°). Key structural parameters such as Au–C and Au–S bond distances (2.007(3) and 2.3113(7) Å, respectively), and C–Au–S bond angle (173.62(7)°) of [(SIPr)­Au­(SMe 2 )]­[SbF 6 ] match well to the corresponding parameters of a previously reported IPr analogue involving an aluminate anion, [(IPr)­Au­(SMe 2 )] + (1.957(10) and 2.313(3) Å and 177.3(3)°, respectively) …”

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

“…[132] Equally important in the application of aluminate WCAsisthe facile conversion of the lithium salts into anumber of other starting materials of synthetic importance through multigram meta- [6,7,[133][134][135] Of particular note is the ready formation of the donor-free Ag[Al(OR F ) 4 ]s alt, as tarting material not available with many WCA classes (Scheme 1). [139][140][141] These anions do not show the same tolerance towards Brønsted acids as their fluorinated counterparts;h owever,t hey have been utilized as supporting WCAsi nt he iridium-catalyzed asymmetric hydrogenation of imines and enones. In agreement with this,as trong decrease in the rate of reaction for the asymmetric hydrogenation of (E)-1,2-diphenyl-1-propene by ac hiral iridiumphosphinooxazoline complex is observed in the series [Al- 4 ] À also imparting greater tolerance towards oxygen and moisture.…”

“…[133] As ar esult of the aforementioned stability and the commercially available synthetic precursors the [Al(OR F ) 4 ] À anion represents at rue alternative to the more traditional borate-based anions,particularly in the field of homogeneous catalysis,w here very weak interactions between the cation and anion are beneficial. [141] [136] Thei ncreased stability of the [Al(OR F ) 4 ] À ion under catalytic conditions has been demonstrated through the use of aC r-PNP complex for ethylene oligomerization as well as the use of [Ph 3 C][Al-(OR F ) 4 ]/Et 3 Al to activate ethylene polymerization rather than the traditional modified aluminoxane (MMAO).…”

“…[137,138] In contrast to the highly fluorinated aluminates described above,aseries of halogen-free and "lipophilic" aluminate anions based on as ubstituted biphenol moiety have recently been developed by Straub and co-workers. [139][140][141] These anions do not show the same tolerance towards Brønsted acids as their fluorinated counterparts;h owever,t hey have been utilized as supporting WCAsi nt he iridium-catalyzed asymmetric hydrogenation of imines and enones. [141] 2.6.…”

“…[139][140][141] These anions do not show the same tolerance towards Brønsted acids as their fluorinated counterparts;h owever,t hey have been utilized as supporting WCAsi nt he iridium-catalyzed asymmetric hydrogenation of imines and enones. [141] 2.6. Bridged WCAs Theformation of large complex anions,inwhich aparent anion binds to another equivalent of the corresponding Lewis acid, is well-established in the literature.S alts of the higher order such as [Al 2 X 7 ] À and [Sb 2 F 11 ] À have been known for decades.However,the formation of abridged anion, in which two large Lewis acid residues derived from modern WCAs, are bridged by asingle monoanionic ligand has the potential to permit delocalization of the negative charge over an even greater number of atoms,t hereby further reducing the coordinative strength.…”