Organometallics in Superacidic Media:  Generation of Highly Electrophilic (Fluoroalkyl)phosphine Pt(II) Cationic Complexes

Abstract

The chemistry of highly electrophilic late transition metal centers has received increasing attention in recent years. 1 In the context of "Shilov chemistry", the involvement of cationic Pt(II) centers in hydrocarbon activation has been recently demonstrated by several groups for L 2 Pt(R)X systems. 2,3 A key for electrophilic group 10 studies has been the use of weakly coordinating anions such as B[3,5-C 6 H 3 (CF 3 ) 2 ] 4 -and MeB(C 6 F 5 ) 3 -, which allows the incipient generation of reactive 14-electron metal centers. [2][3][4] Several years ago we reported the synthesis of very electronpoor (perfluoroalkyl)phosphine complexes (dfepe)Pt(Me)X (dfepe ) (C 2 F 5 ) 2 PCH 2 CH 2 P(C 2 F 5 ) 2 ; X ) O 2 CCF 3 , OTf, SO 3 H). 5 While these systems could, in principle, afford an extremely electrophilic (dfepe)Pt(Me) + moiety, simple anion dissociation is greatly disfavored, and ligand association reactions to form (dfepe)Pt(Me)(L) + products are not observed. 6 A different approach was suggested by the unusual stabilities of (dfepe)Pt(Me)X and (dfepe)Pt(X) 2 compounds in the protic superacids CF 3 SO 3 H and FSO 3 H, 5,7 together with Aubke's novel syntheses of unusual cationic metal polycarbonyl complexes, M(CO) n m+ , which exploit the inherently low nucleophilicity of superacidic media. 8,9 In this report we show that well-defined (dfepe)Pt(II) coordination compounds with accessible coordination sites may be generated in superacidic solvent systems, the utility of SbF 5 (SO 2 ) as a stoichiometric reagent for the generation of weakly associated L n M + [(X)(SbF 5 ) n ] -organometallics, and some initial observations regarding the stabilization of transition metalcarbon bonds in superacidic media.(dfepe)Pt(X) 2 (X ) OTf, FSO 3 ) complexes have very limited solubilities in aprotic solvents and do not react with CO. In fluorosulfonic acid, however, treatment of (dfepe)Pt(FSO 3 ) 2 with 1 atm CO cleanly generates a cationic monocarbonyl product [(dfepe)Pt(CO)(FSO 3 )] + (1) (ν(CO) ) 2214 cm -1 ) (eq 1). Under higher pressures of CO (>40 psi), the reversible appearance of an additional single 31 P resonance and two new ν(CO) bands at 2235 and 2222 cm -1 are attributed to generation of [(dfepe)Pt-(CO) 2 ] 2+ (2). In triflic acid, only [(dfepe)Pt(CO)(OTf)] + (3) (ν-(CO) ) 2210 cm -1 ) is observed under these conditions. 10 Both 1 and 3 in the absence of CO only slowly revert to (dfepe)Pt(X) 2 at 20°C over several days. This acid-dependent carbonylation behavior has been previously attributed to the formation of more weakly coordinating hydrogen-bonded anion aggregates, X(HX) n -. 11,12 Aubke has reported that dissolution of simple transition metal salts in the neat Lewis superacid SbF 5 in the presence of CO leads to X -abstraction and the formation of novel polycarbonyl polycations such as Pt(CO) 4 2+ , Ir(CO) 6 3+ , and Fe(CO) 6 2+ with Sb 2 F 11 -counteranions. 8,13 Treatment of the donor phosphine complex (dmpe)Pt(Me) 2 with SbF 5 at 20°C does not afford any identifiable soluble products. In contrast, both (d...

The Versatile Behavior of Platinum Alkyne Complexes towards XeF2: Formation of Fluorovinyl and Fluorido Complexes

“…There are no indications for an insertion of CO into the PtÀCb ond of the vinyl ligand. [93,95,96] The electron-poor natureo f the metal center in compound 6 is also in accordance with the high-field shifto ft he 13 CNMR carbonyl resonance at d = 172.73 ppm. The Pt,P coupling constant is comparable with those found for other literature-known cationic platinum(II) complexes.…”

“…The IR spectrum of compound 6 reveals a CO absorption band at =2125 cm −1 . The value is in agreement with those found for other cationic platinum carbonyl complexes . The electron‐poor nature of the metal center in compound 6 is also in accordance with the high‐field shift of the 13 C NMR carbonyl resonance at δ =172.73 ppm .…”

“…In the absence of CO complex 6 converted into [Pt(PhC=CFPh)(THF){k 2 -(P,N)-iPr 2 PC 2 H 4 NMe 2 }]BF 4 (5)a tr oom temperature over several days. [93,94] The P, Fc oupling constant was also observed in the 19 F{ 1 H} NMR spectrum, which reveals ad oublet at d = À91.3 ppm with 195 Pt satellites ( 3 J(Pt,F) = 150 Hz) for the b-fluorovinyl ligand. [92] The 31 P{ 1 H} NMR spectrum of compound 6 displays ad oublet at d = 49.9 ppm with 195 Pt satellites ( 4 J(P,F) = 3, 1 J(Pt,P) = 3347 Hz).…”

“…The value is in agreement with those found for other cationic platinum carbonyl complexes . The electron‐poor nature of the metal center in compound 6 is also in accordance with the high‐field shift of the 13 C NMR carbonyl resonance at δ =172.73 ppm . The signal appears as a doublet, due to the trans P,C coupling of 2 J (P,C)=132 Hz.…”

“…[92] The 31 P{ 1 H} NMR spectrum of compound 6 displays ad oublet at d = 49.9 ppm with 195 Pt satellites ( 4 J(P,F) = 3, 1 J(Pt,P) = 3347 Hz). [93,95,96] The signal appears as ad oublet, due to the trans P, Cc oupling of 2 J(P,C) = 132 Hz. [93,94] The P, Fc oupling constant was also observed in the 19 F{ 1 H} NMR spectrum, which reveals ad oublet at d = À91.3 ppm with 195 Pt satellites ( 3 J(Pt,F) = 150 Hz) for the b-fluorovinyl ligand.…”