Difluorobis(pentafluoroethyl)phosphoranide: A Promising Building Block for Phosphoranidometal Complexes

Abstract

Despite the fact that different metal tetrafluorophosphoranides, M [PF 4 ] (M = Cs, Ag, K), decompose readily, we successfully enhanced the stability of such species by the replacement of two fluorine atoms with electron withdrawing pentafluoroethyl groups. Thus, AgF adds to P(C 2 F 5 ) 2 F, yielding Ag[P(C 2 F 5 ) 2 F 2 ], which served as a starting material for the synthesis of mono-, bis-, and tris[difluorobis(pentafluoroethyl)phosphoranido]silver complexes. Addition of 2,2′-bipyridine allowed for the isolation of stable [Ag(bipy)-{P(C 2 F 5 ) 2 F 2 }], whereas the reaction with the chlorides [NMe 4 ]Cl and CoCl 2 afforded the bis-and trisphosphoranidoargentates, respectively. Altogether, the difluorobis(pentafluoroethyl)phosphoranido moiety serves as a novel, small, noncyclic phosphoranido ligand. It provided access to the first homoleptic phosphoranidometal complex, [Co(NCMe) 6 ][Ag{P(C 2 F 5 ) 2 F 2 } 3 ]•2MeCN, which itself features the unusual structural motif of an [AgX 3 ] 2− ion.

Free Difluorobis(pentafluoroethyl)phosphoranide Ion and Its Ligand Properties

“…As for the hydrolysis of [P­(C 2 F 5 ) 2 F 2 ] − salts, we briefly described it in the Supporting Information of an earlier work . [P­(C 2 F 5 ) 2 F 2 ] − salts react with water under the formation of [P­(C 2 F 5 ) 2 O] − salts and hydrogen fluoride.…”

“…Since strongly electron-withdrawing substituents should enhance the stability of phosphoranide salts, our attention was directed toward perfluoroalkyl groups. Previously, Röschenthaler and Shyshkov synthesized different trifluoromethylphosphoranide salts. − [K­(18-crown-6)]­[P­(CF 3 ) 3 F], for example, was obtained by the addition of KF to tris­(trifluoromethyl)­phosphane in the presence of 18-crown-6. , Since pentafluoroethylphosphanes exhibit a higher fluoride ion affinity and are safer to handle than trifluoromethylphosphanes, pentafluoroethyl derivatives were placed in the center of our research. , The addition of CsF to P­(C 2 F 5 ) 3 yielded Cs­[P­(C 2 F 5 ) 3 F] at temperatures below −30 °C . The reaction of P­(C 2 F 5 ) 2 F with Ishikawa’s reagent, Et 2 N–CF 2 –CHF–CF 3 , as well as fluorotrimethyl­[( Z )-pentafluoropropen-1-yl]­phosphorane, PMe 3 (CFCF–CF 3 )­F, yielded [P­(C 2 F 5 ) 2 F 2 ] − salts intermediately.…”

“…Thus, in oxidative addition reactions, the zwitterionic compounds [Et 2 NCF­{PF 3 (C 2 F 5 ) 2 }–CHF–CF 3 ] and [Me 3 P–CFC­(CF 3 )–PF 3 (C 2 F 5 ) 2 ] were formed. , Reaction of P­(C 2 F 5 ) 2 F with AgF led to the formation of Ag­[P­(C 2 F 5 ) 2 F 2 ], eventually. This silver salt served as a precursor for mono-, bis-, and trisphosphoranido silver complexes (Figure , top) …”

“…29,30 Since pentafluoroethylphosphanes exhibit a higher fluoride ion affinity and are safer to handle than trifluoromethylphosphanes, pentafluoroethyl derivatives were placed in the center of our research. 32,33 The addition of CsF to P(C 2 F 5 ) 3 yielded Cs[P(C 2 F 5 ) 3 F] at temperatures below −30 °C. 34 The reaction of P(C 2 F 5 ) 2 F with Ishikawa's reagent, Et 35,36 Reaction of P(C 2 F 5 ) 2 F with AgF led to the formation of Ag[P(C 2 F 5 ) 2 F 2 ], eventually.…”

“…This silver salt served as a precursor for mono-, bis-, and trisphosphoranido silver complexes (Figure 1, top). 32 In the present work, we would like to focus on the preparation and the ligand properties of the free [P(C 2 F 5 ) 2 F 2 ] − ion, utilizing the weakly coordinating phosphazenium cation [{(Et 2 N) 3 P�N} 3 P�NHC(CH 3 ) 3 ] + ([EtP 4 H] + ) which recently provided access to noncoordinated anions, such as the first free phenolate ion 3 7 and the reactive tris-(pentafluoroethyl)silanide ion. 38 Furthermore, we would like to prepare different phosphoranido transition metal complexes featuring the P(C 2 F 5 ) 2 F 2 moiety.…”