The Ambiphilicity of 1,1‐Diethoxy‐4,4,4‐trifluoro‐3‐(trifluoromethyl)‐1,2‐butadiene

Abstract

A position intermediate between allenes and carbenes is occupied by the donor/acceptor‐substituted allene (2), which was synthesized from (1) by flash thermolysis. The central C atom of (2) can be attacked by both electrophiles and nucleophiles.

Roots: From carbenes to allenes and coordination polymers : Ever present never twice the same

“…Reaction of hexafluoroacetone with cumulated phosphorane 2 31 affords the surprisingly thermally-stable oxaphosphetane 26. 32,33 Similarly, with non-enolizable 1,2-diketones the oxaphosphetanes 27 are accessible. 33,34 The 13 C NMR spectra of 26 and 27 display three equivalent phenyl groups, indicating fast regular ligand exchange processes, even at 240 uC.…”

Wittig-olefination via an yttrium-coordinated betaine

“…While in related work, kinetically stabilized oxaphosphetanes have been isolated under ambient conditions and shown to be competent for alkene and phosphine oxide formation at elevated temperatures. [5][6][7][8][9][10][11] Although the abscence of salt-free betaines as long-lived intermediates under standard Wittig-olefination conditions 12,13 is supported by extensive experimental and theoretical data, [13][14][15][16] a number of reports suggest that metal-coordinated betaines may be isolated upon precipitation from the reaction mixture (Scheme 1, II). 2,17,18 Along with the observed salt-effects on the stereochemical outcome of the reaction of pro-chiral ylides with pro-chiral carbonyls, 19,20 this finding argues for a more complicated mechanistic picture under conditions where Lewis acidic cations such as lithium are present.…”

“…The reaction of [Y{N(SiMe 3 ) 2 } 3 ] with [Ph 3 PMe]I occurred upon heating of 0.35 M d 6 -benzene solutions to 80 1C and could be monitored by 31 P NMR spectroscopy (see ESI,w Fig. S1).…”

“…Consumption of the phosphonium salt was observed over a 24 h period with concomitant formation of 1 (d 31 P = +30.9 ppm). A control sample of [CH 2 PPh 3 ], synthesised by deprotonation of the phosphonium iodide with [KOtBu] followed by filtration away from potassium iodide, demonstrated different data in d 6 -benzene (d 31 P = +22.0 ppm) suggesting that 1 contained a metal coordinated ylide.…”

“…39 Consistent with the perturbation of the ylide's structure due to metal coordination, the P-C bond length of 1.728(6) A ˚in 1 is considerably longer than the average value of 1.661 A ˚found in [CH 2 PPh 3 ], 40 and lies within the range of 1.71-1.75 A ˚established for [{C 5 H 4 R} 3 Ln(CH 2 PPh 2 Me)] complexes (Ln = Nd, Sm; R = H, t-Bu). 41,42 Compound 1 reacts cleanly with benzophenone in d 6 -benzene solution to form the metal-coordinated betaine 2 (d 31 P = +16.0 ppm).z The reaction proceeds via insertion of the ketone into the ylidic Y-C bond (Scheme 2). Similar addition reactions across M-C bonds are known for rare-earth N-heterocyclic carbene complexes, where parallels have been drawn with the reactivity of frustrated Lewis-acid Lewis-base pairs, 43,44 and more classical rare-earth alkyl complexes.…”