Homoleptic carbonyl cations of palladium(I), palladium(II), platinum(II), and gold(I)—simplified synthetic routes to their fluoroantimonate(V) salts

Abstract

The original synthetic routes to the new noble metal carbonyl cations [Au(CO)2]+ and [M(CO)4]2+, M = Pd or Pt, as [Sb2F11]−salts are multi-step procedures that involve corrosive reagents and require commercially unavailable starting materials. We report here two general simplifications: (i) the sole use of liquid antimony(V) fluoride as reaction medium in a single-step carbonylation process, and (ii) the use of the commercially available chlorides AuCl3 and MCl2, M = Pd or Pt, as starting materials, in addition to the binary fluorosulfates Au(SO3F)3, Pd[Pd(SO3F)6], and Pt(SO3F)4. The simplified routes developed here for [Au(CO)2][Sb2F11] and [M(CO)4][Sb2F11]2, M = Pd or Pt, should make these new reagents more easily available for wider use in synthesis. In addition, these routes are found suitable for the generation of new carbonyl cations of electron-rich metals. Key words: metal carbonyl cations of Au(I), Pd(I), Pd(II), and Pt(II); solvolysis reactions in liquid SbF5, reductive carbonylation in liquid SbF5; carbonylations in strong acidic media.

Homoleptic Metal Carbonyl Cations of the Electron‐Rich Metals: Their Generation in Superacid Media Together with Their Spectroscopic and Structural Characterization

“…These highly reactive cations are present in an acidic matrix and function as strong Lewis acids with respect to CO. The acceptor strength of M"+ increases with increasing n, and carbonyl cations with classical coordination geometries 21 Carbonylation reactions in superacid media have in the meantime found broad application (Tables 2 and 3). CO addition to metal complexes is only sensible to apply in the case of metals that form no thermally stable carbonyl cations.…”

Palladium(I) Carbonyl Cation-Catalyzed Carbonylation of Olefins and Alcohols in Concentrated Sulfuric Acid

“…Formation of Palladium(I) Carbonyl Cation, [ c -Pd 2 ( μ -CO) 2 ] 2+ (1), in Concentrated H 2 SO 4 . So far, three palladium carbonyl complexes, [Pd(CO) 4 ][Sb 2 F 11 ] 2 , cis -Pd(CO) 2 (SO 3 F) 2 , and [ c -Pd 2 ( μ -CO) 2 ](SO 3 F) 2 , have been prepared in superacidic media and well characterized by Willner et al The reductive carbonylation of the mixed-valency compound Pd II Pd IV (SO 3 F) 6 at 25 °C produces almost exclusively cis -Pd(CO) 2 (SO 3 F) 2 9b. When the reaction is carried out in fluorosulfuric acid, an isomer mixture of the composition Pd(CO) 2 (SO 3 F) 2 is obtained 9d…”

“…So far, three palladium carbonyl complexes, [Pd(CO) 4 ][Sb 2 F 11 ] 2 , cis -Pd(CO) 2 (SO 3 F) 2 , and [ c -Pd 2 ( μ -CO) 2 ](SO 3 F) 2 , have been prepared in superacidic media and well characterized by Willner et al The reductive carbonylation of the mixed-valency compound Pd II Pd IV (SO 3 F) 6 at 25 °C produces almost exclusively cis -Pd(CO) 2 (SO 3 F) 2 9b. When the reaction is carried out in fluorosulfuric acid, an isomer mixture of the composition Pd(CO) 2 (SO 3 F) 2 is obtained 9d 9c,d The cyclic and completely planar cation with symmetrically bridging carbonyl ligands, [ c -Pd 2 ( μ -CO) 2 ] 2+ , has also been recently isolated as the salt of [Sb 2 F 11 ] - 9e.…”

“…Our knowledge of relatively stable neutral carbonyl complexes has been dramatically enriched by the synthesis of the first metalloidal and alkaline earth metal carbonyls, [Cp*Si(CO)] and [Cp*Ca(CO)], respectively, in solution and by the isolation and X-ray structural characterization of the first f -block carbonyl complex, [(C 5 Me 4 H) 3 U(CO)] . In particular, the focus of much attention for the past years has been a new and very intriguing class of late-metal carbonyl complexes: homoleptic carbonyl cations and their cationic derivatives of the electron-rich metals in groups 8−12 isolated in superacidic media, − including [Pd(CO) 4 ][Sb 2 F 11 ] 2 , 9a,e cis -Pd(CO) 2 (SO 3 F) 2 , 9b,d and [ c -Pd 2 ( μ -CO) 2 ](SO 3 F) 2 9c. In contrast to typical metal carbonyl complexes, the new family of metal carbonyls has a distinguishing characteristic in that the CO vibrational frequencies are considerably higher than that of free CO, for which the term nonclassical metal carbonyl was previously proposed, and its definition has recently been revised. 13d,e Although there is an argument on the classification of classical and nonclassical metal carbonyls, 8h,13b,e there is no doubt that the metal carbonyl cations have remarkably reduced π -back-bonding.…”

Heterocations in Superacid Systems

“…The SeÀSe bonds of di-and tricoordinate selenium atoms alternate significantly [average Se(1)-Se(2) and Se(2)-Se(3) bond lengths are 2.475 and 2.227 A , respectively]. 1006 The stable, isolable salts have been thoroughly characterized by vibrational and 13 C NMR spectroscopy, and molecular structures have also been elucidated. 988 Both salts contain polymeric strands of (Se 6 I þ ) n species.…”