Platinum‐Catalyzed Hydrofluorination of Alkynes: Hydrogen Bonding to Indolylphosphine Ligands to Provide Fluoride Reactivity

Abstract

The reaction of the Pt complexes cis-[Pt-(CH 3 ) 2 {R 2 P(Ind)} 2 ] (Ind = 2-(3-methyl)indolyl, R = Ph (1 a), 4-FC 6 H 4 (1 b), 4-CF 3 C 6 H 4 (1 c)) with HF afforded the fluorido complexes trans-[Pt(F(HF) 2 )(CH 3 ){R 2 P-(Ind)} 2 ] 2 a-c, which can be converted into trans-[Pt(F)-(CH 3 ){R 2 P(Ind)} 2 ] (3 a-c) by treatment with CsF. Addition of 3-hexyne to 2 a-c gave alkyne complexes trans-[Pt(C,C-η 2 -C 2 H 5 C�CC 2 H 5 )(CH 3 ){R 2 P(Ind)} 2 {F(HF) 2 }] (4 a-c) at which a fluoride is stabilised as polyfluoride in the coordination sphere by hydrogen bonding to the indolyl-substituted phosphine ligands. Subsequent heating of a solution of 4 a in the presence of PVPHF led to fluoroalkene formation. Selective catalytic hydrofluorination of alkynes to yield (Z)-fluoroalkenes were developed. The ability of hydrogen bonding to polyfluoride favours the fluorination step as demonstrated by studies with complexes bearing no indolyl groups at the phosphine ligands.

Trendbericht Anorganische Chemie 2023: Nebengruppen, Bioanorganik und Koordinationschemie

“…Sie nutzten milde HF-Quellen wie (HF) 3 •NEt 3 , und es entstehen die entsprechenden Z-Alkene (Abbildung 9a). 27) Für die Reaktion sind die flankierenden Indolsubstituenten der Phosphanliganden entscheidend. Diese stabilisieren und aktivieren die gebundenen Polyfluoride über Wasserstoffbrückenbindungen.…”

Hydrogen Bonding in Platinum Indolylphosphine Polyfluorido and Fluorido Complexes

“…Both complexes, 1 d and 1 e, possess a slightly distorted square-planar coordination geometry of the two phosphines, the aryl and methyl ligands bound to Pt. They exhibit P1 À Pt1 À P2 bond angles of 96.09(2) and 102.82(3), while the C43 À Pt1 À C44 bond angle between the methyl and aryl ligand are smaller with values of 84.90(11) and 82.65 (12), respectively. For each complex the Pt1 À P1 bond length in a trans position to the methyl ligand is slightly shorter (2.3022 (7) for 1 d, 2.3105(8) for 1 e) compared to the Pt1 À P2 bond length that is located trans to the aryl ligand (2.3255 (7) (1 d), 2.3208(8) (1 e)).…”

“…[7] The hydrogen bonds of NH groups to the fluorido ligand provided unprecedented reactivities. [12] Most notably, the strength of a metal-ligand bond is affected by the trans influence of the trans coordinated ligand. For platinum complexes there is a well described correlation between PtÀ P bond lengths and 1 J(P,Pt) coupling constants [13] that enabled the early estimation of a ligand's transinfluence.…”

Hydrogen and Halogen Bonding to Au(I) Fluorido Complexes

“…In general, nucleophilic outer-sphere fluorination at transition-metal complexes requires control of fluoride reactivity in the metal coordination sphere. [5] The balance between nucleophilicity and basicity can be influenced by hydrogen bonding, [6] substrate interaction or interaction with the solvent. Thus, the properties of fluorido ligands in hydrogen bonding can differ significantly when compared to those of heavier halogenido ligands.…”

“…While Au(I) fluorido complexes are scarce, [2a,4] their high reactivity makes them good candidates for fluorination reactions. In general, nucleophilic outer‐sphere fluorination at transition‐metal complexes requires control of fluoride reactivity in the metal coordination sphere [5] . The balance between nucleophilicity and basicity can be influenced by hydrogen bonding, [6] substrate interaction or interaction with the solvent.…”