Electrophilic bis-fluorophosphonium dications: Lewis acid catalysts from diphosphines

Abstract

A series of electrophilic bis-fluorophosphonium dications dervied from diphosphines with naphthalene- and (oligo)methylene-linkers is presented. The resulting Lewis acidity is demonstrated to depend on the spatial proximity between the P moieties as evidenced in several Lewis acid catalyzed transformations.

Reductive Catenation of Phosphine Antimony Complexes

“…[13] In the 19 FNMR spectrum, asignal for the Sb À F moiety of 6(OTf) 2 at d F = À117.5 ppm is significantly shielded compared to that of free FSb(OTf) 2 (À95.3 ppm), but deshielded compared to those for derivatives of [(R 3 P) 2 SbF] 2+ (R = Me,E t, Pr,B u; range of d F = À173.4 to À187.1 ppm), [4b] likely as aresult of the relatively low basicity of PPh 3 .T he 19 FNMR resonance signal for the triflate substituents in 6(OTf) 2 (d F = À78.8 ppm) is comparable to that of [PPh 4 ][OTf] (À79.4 ppm) and we therefore conclude that the triflate anions are dissociated, giving [(Ph 3 P) 2 SbF] 2+ , denoted [6] 2+ ,inM eCN solutions of 6(OTf) 2 .…”

“…[6] Upon heating (82 8 8C) for 90 min, an intensely orange-colored solution is observed. The 31 PNMR spectrum of this solution ( Figure 3b)i ndicates that [6] 2+ has been consumed with substantial formation of [Ph 3 PF] + ,anunassigned broad signal and three prominent broad resonances (1:2:1 intensity).…”

“…[9] Twor outes from [(Ph 3 P)Sb] + to [4] 4+ are proposed in Scheme 1. Route A involves catenation of six equivalents to give the cyclo-hexaantimony intermediate [(Ph 3 P) 6 Sb 6 ] 6+ (A 1 ,S cheme 1), whose significant molecular charge prompts asubsequent 2-electron reductive elimination of ad iphosphonium cation [Ph 3 PPPh 3 ] 2+ ,e nabling formation of at ransannular Sb À Sb bond to give [4] 4+ .A nalogous conversion of phosphine ligands into diphosphonium cations at electron-deficient phosphine metal complexes has been reported. [10] As pacefilling view of the molecular structure of [4] 4+ ( Figure S4) shows that limited space is available to accommodate two additional PPh 3 ligands and an optimization of the gas-phase geometry of A 1 failed because of excessive steric stress between the phosphines.…”

Non-conventional Lewis Acids and Bases in Frustrated Lewis Pair Chemistry

“…Applying a similar strategy to phosphonium cations was readily accomplished by the oxidation of 1,8-bis(diphenylphosphino)naphthalene by XeF 2 and fluoride abstraction to generated the bis-fluorophosphonium dicationic salt 54 (Scheme 35). This species is significantly more Lewis acidic than the analogous triphenylfluorophosphonium cation [114]. In a similar fashion, the corresponding derivative of (Ph 2 P) 2 CH 2 is also an effect Lewis acid (55).…”

Main Group Lewis Acids in Frustrated Lewis Pair Chemistry: Beyond Electrophilic Boranes

“…101 The structural variety of EPCs is not limited to cations with highly electron-withdrawing substituents. We have recently reported the synthesis of the formally dicationic species 103 As opposed to their monocationic analogues, these species are active in hydrosilylation catalysis, demonstrating the impact of proximal Lewis acid sites and thus further broadening the range of Lewis acidic EPCs.…”