Unusual Reactivity of “Proton Sponge” as a Hydride Donor to Transition Metals:  Synthesis and Structural Characterization of Fluoroalkyl(hydrido) Complexes of Iridium(III) and Rhodium(III)

Abstract

Attempts to prepare fluoroalkyl(hydrido) complexes of iridium by reactions of [Ir(C5Me5)(PMe3)(RF)I] {RF = CF2CF2CF3, CF(CF3)2} with either NaBH4 or LiAlH4 afford (inter alia) iridium hydrides [Ir(C5Me5)(PMe3)(CHCFCF3)H] or [Ir(C5Me5)(PMe3)(C{CF3}CF2)H], in which the fluoroalkyl groups are converted to unsaturated ligands via apparent α-CF activation and elimination of HF. A clean and selective route to desired saturated fluoroalkyl(hydrido) complexes [Ir(C5Me5)(PMe3)(RF)H] {RF = CF2CF2CF3, CF2CF3, CF(CF3)2} is afforded by treatment of the aqua cations [Ir(C5Me5)(PMe3)(RF)(H2O)]BF4 with 1,8-bis(dimethylamino)naphthalene (“Proton Sponge”). The reaction also affords the corresponding rhodium analogue [Rh(C5Me5)(PMe3)(CF2CF2CF3)H] from the corresponding aqua precursor. The source of the hydride is unambiguously defined as an N−CH3 group by using the perdeuteromethylated analogue of Proton Sponge, which provides clean routes to the corresponding fluoroalkyl(deutero) complexes of iridium. Triethylamine or cobaltocene also effect this reaction, though not as cleanly as Proton Sponge. The mechanism of this novel transformation is discussed. The fluoroalkyl(hydrido) complexes are thermally robust, but do react with chlorinated solvents to give the corresponding chlorides. Single-crystal X-ray diffraction studies of the structures of [Ir(C5Me5)(PMe3)(CF2CF2CF3)H], [Rh(C5Me5)(PMe3)(CF2CF2CF3)H], and [Rh(C5Me5)(PMe3)(CF2CF2CF3)Cl] are reported and compared.

Conversion of Carbon–Fluorine Bonds α to Transition Metal Centers to Carbon–Hydrogen, Carbon–Carbon, and Carbon–Heteroatom Bonds

“…[169] Displacement of water ligands by H 2 was well-established for other d 6 metal complexes, [170] and it seemed probable that a metal-dihydrogen complex was involved in this chemistry. We were fortunate enough to have serendipitously discovered a simple route to fluoroalkyl(H/D) complexes 14-H(D); [171] clearly reaction of 14-H with D + or reaction of 14-D with H + should afford the identical H/D complex 15. However, while no such intermediate could be observed directly, and C-F activation coupled with C-H bond formation was observed, unequivocal evidence for an H/D complex was obtained.…”

“…Specifically, treatment of the isotopically pure hydride complex 14-H [171] with CH 3 CO 2 D in CD 2 Cl 2 afforded a 90 % yield of a 2:1 mixture of the two diastereomers of 16-H contaminated with 10 % of the same diastereomeric mixture of 16-D. [172] Treatment of isotopically pure 14-D with CH 3 CO 2 H yielded 80 % of a 2:1 mixture of diastereomers Observation that only a small amount of label scrambling occurred indicated that the dominant process was the former; this is not the case for HCl, as discussed below. For each product isotopologue, the diastereoselectivity was about 2:1, the (R Ir ,R C )(S Ir S C ) diastereomer predominating.…”

Half-sandwich iridium complexes—Synthesis and applications in catalysis

“…Apparently ␣-CF bond activation takes place in both the reactions of 25 and 27, presumably followed by elimination of HF (Scheme 7) [24].…”

1,8-Bis(dimethylamino)naphthalene

“…[51][52][53] In the study of transition metal complexes containing a saturated fluorocarbon ligand, Hughes et al reduced aqua complexes to hydrido complexes. [51][52][53] In the study of transition metal complexes containing a saturated fluorocarbon ligand, Hughes et al reduced aqua complexes to hydrido complexes.…”

“…[51][52][53] In the study of transition metal complexes containing a saturated fluorocarbon ligand, Hughes et al reduced aqua complexes to hydrido complexes. 52 The resulting iridium hydride compound (18) was then converted into the first stable transition metal complex of tetrafluorobenzyne (19). Rapid loss of water follows the hydrogen atom abstraction from the amine methyl group by iridium to provide a metal-H bond and an iminium cation, which is trapped intramolecularly by the adjacent tertiary amine.…”