Zirconocene Dichloride Catalyzed Hydrodefluorination of CF bonds

Abstract

Man nehme zwei Metalle: Vierfach koordinierte Aluminiumdihydride wie 1 sind das Reduktionsmittel in der selektiven Titelreaktion. Der Heterodimetallkomplex 2 wurde isoliert und als katalytisch aktive Spezies identifiziert.

Reactions of Fluoroalkenes with an Aluminium(I) Complex

“…While 2-E, 2-Z, 4b,a nd 5 were found to be stable at high temperatures for prolonged periods of time (353 K; > 1week), both 3 and 4a fragmented when heated to 353 K. Theo rganic fragments were identified as 1,1-difluoroallene (from 3)and tetrafluoroallene (from 4a); both form alongside the expected aluminium difluoride 1-F 2 ,w hich has also been isolated and fully characterised (Scheme 4). [49][50][51] Thenet pathway from 1 is adouble CÀFactivation of the fluoroalkenes leading to new fluorinated allenes.I nt he case of 3 and 4a,the second CÀFbond cleavage step is extremely slow.At353 K, 4a has ahalf-life of approximately 6days.For comparison, the first C À Fbond cleavage is fast and 4a forms from 1 and hexafluoropropene within minutes at 298 K. A further reaction between 1 and 1,1,1,4,4,4-hexafluoro-2butene (10 equiv;HFO-1336-mzz) did not allow the isolation of an ew organoaluminium compound but instead led to the formation of an s-trans isomer of 1,1,4,4-tetrafluorobutadiene and 1-F 2 . [52,53] While the unambiguous assignment of this pathway will have to await afull mechanistic study,itappears that, in this case,t he rate of the second CÀFb ond cleavage step is either similar to or faster than the first, possibly due to the ease of 1,3-diene formation over allene formation, leading directly to the organic product.…”

Synthese fluorierter Bausteine durch Übergangsmetall‐vermittelte Hydrodefluorierungsreaktionen

“…Angesichts der bekanntermaßen hohen Affinität früher Übergangsmetalle zu Fluoridoliganden ist es nicht verwunderlich, dass dieses Reaktionsprofil häufig bei Metallkomplexen der Gruppe 4 beobachtet wird. Aromatische, [10] vinylische [11] [12] wodurch die katalytische HDF von Pentafluorpyridin bei Raumtemperatur mçglich wird (Schema 2).…”

Isomerization of Cyclooctadiene to Cyclooctyne with a Zinc/Zirconium Heterobimetallic Complex

“…Theh eterobimetallic complexes M·Zr (M = Zn, Mg, Al(H) [9] )a re products of the simple addition of the known hydrides ( Figure 2). Following isolation, their solution and solid-state structures were confirmed and correlated by single-crystal X-ray diffraction, multinuclear and variabletemperature (VT) NMR, DFT studies,a nd CHN analysis.…”

“…[13] Thebridging hydrides H m and H m' in Mg·Zr are chemically and magnetically inequivalent, and at 298 Ki n[ D 8 ]toluene they resonate at d = À2.00 (dd, 2 J H-H = 13.0, 6.6 Hz) and À2.87 (dd, 2 J H-H = 6.6, 6.6 Hz) ppm, respectively. [14,15] Both couple to the terminal hydride (H t )f ound at d = 1.55 (dd, 2 J H-H = 13.0, [9] Ther eaction of Zn·Zr with 1,5-COD in C 6 D 6 at 80 8 8C resulted in more than 50 %c onversion of the hydrocarbon within 24 ha nd formation of 1,3-COD (22 %b ased on 1,5-COD), cyclooctene (80 %b ased on Zn·Zr), the heterobimetallic complex 1 (85 %b ased on Zn·Zr), and trace cyclooctane (Scheme 1). Following ap reparative-scale experiment, 1 was isolated as single crystals from an n-hexane solution at À35 8 8C.…”

“…[14,15] Both couple to the terminal hydride (H t )f ound at d = 1.55 (dd, 2 J H-H = 13.0, 8 ]toluene (273-353 K) provide no evidence for disintegration of the heterobimetallic complexes in solution, site exchange between the terminal hydride (H t )a nd the distal bridging hydride (H m' )w as observed at all temperatures.I nc ontrast, Al·Zr forms reversibly and readily establishes an equilibrium with the parent hydrides. [9] Ther eaction of Zn·Zr with 1,5-COD in C 6 D 6 at 80 8 8C resulted in more than 50 %c onversion of the hydrocarbon within 24 ha nd formation of 1,3-COD (22 %b ased on 1,5-COD), cyclooctene (80 %b ased on Zn·Zr), the heterobimetallic complex 1 (85 %b ased on Zn·Zr), and trace cyclooctane (Scheme 1).…”