Addition of excess HOSO2CF3 (HOTf) to CpRu(L)H (1) (L = dfepe = PR2CH2CH2PR2, R = C2F5) in CD2Cl2 under N2 produces a mixture of [CpRu(L)(H)2]+ (2a), [CpRu(L)(H2)]+ (2b), and CpRu(L)(OTf) (3) in a ratio of 1:5:2. Salts of the acid [HOEt2]+ are not strong enough to protonate 1. Complexes 2 slowly eliminate H2 to give 3; this reaction is slowed by adding excess HOTf. Of all such complexes [CpRu(PR2CH2CH2PR2)(H2)]+, R = alkyl and aryl, the dihydrogen complex 2b has the greatest acidity (similar to that of HOTf) and the related HD complex has the greatest J HD (29.1 Hz) because of the electron-withdrawing substituents R = C2F5. The reaction of 3 with 1 atm H2(g) proceeds much faster in the presence than in the absence of 1 equiv of HOTf to produce 1 and HOTf. This is a rare example of the production of a strong acid from H2(g) where the intermediate dihydrogen complex has been characterized. Reaction of Cp*Ru(L)Cl (4), Cp* = C5Me5, in dry CH2Cl2 at −78 °C with AgX salts under H2(g) (1 atm) gives mixtures of Cp*Ru(L)H (5) and [Cp*Ru(L)(H)2]+ (6), which have been identified by 1H NMR. 6 is deprotonated by traces of water or by PPh3 to give Cp*Ru(L)H (5). The addition of excess HOTf to mixtures of 5 and 6 under H2(g) produces 6. Complexes 3, 4, and 5 have been characterized by single-crystal X-ray diffraction. Complexes CpRu(L)Cl, 1, 4, and 5 have very positive redox potentials that indicate that the dfepe ligand has the electron-withdrawing power close to that of two carbonyl ligands.

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 cationic iridium(III) complex [IrCF(3)(CO)(dppe)(DIB)][BARF](2) where DIB = o-diiodobenzene, dppe = 1,2-bis(diphenylphosphino)ethane, and BARF = B(3,5-(CF(3))(2)C(6)H(3))(4)(-) undergoes reaction in the presence of dihydrogen to form [IrH(2)(CO)(2)(dppe)](+) as the major product. Through labeling studies and (1)H and (31)P[(1)H] NMR spectroscopies including parahydrogen measurements, it is shown that the reaction involves conversion of the coordinated CF(3) ligand into carbonyl. In this reaction sequence, the initial step is the heterolytic activation of dihydrogen, leading to proton generation which promotes alpha-C-F bond cleavage. Polarization occurs in the final [IrH(2)(CO)(2)(dppe)](+) product by the reaction of H(2) with the Ir(I) species [Ir(CO)(2)(dppe)](+) that is generated in the course of the CF(3) --> CO conversion.

The reaction of hydrogen with iridium and rhodium µ-S A-frame complexes has been investigated using parahydrogen-induced polarization (PHIP) NMR spectroscopy. The reaction of Ir 2 (µ-S)(CO) 2 (dppm) 2 where dppm ) bis(diphenylphosphino)methane with hydrogen proceeds by two addition pathways corresponding to oxidative addition inside (endo) and outside (exo) the pocket of the A-frame complex. The exo addition pathway yields a kinetically significant dihydride that has not been previously reported. This species is a key intermediate in the formation of the thermodynamic product of the reaction system. Also present are polarized resonances for the addition of hydrogen to the mixed metal A-frame, IrRh(µ-S)(CO) 2 (dppm) 2 , formed as a contaminant from rhodium present in the iridium trichloride starting material. To confirm this observation, IrRh(µ-S)(CO) 2 (dppm) 2 was prepared independently and its reaction with parahydrogen was investigated, leading to results supporting endo addition H 2 as the major pathway and exo addition as a minor reaction channel. The complex Rh 2 (µ-S)(CO) 2 (dppm) 2 , which had not previously been found to react with dihydrogen, generates polarized hydride signals under para-enriched hydrogen, showing that an equilibrium is established between the complex and its H 2 adduct. In all of these cases, PHIP is used to detect species not readily seen by normal NMR spectroscopy and to investigate the mechanism of these reactions.