DOES P-YLIDIC RADICAL FEATURE THE YLIDIC OR RADICAL CHARACTER TOWARD FORMALDEHYDE?

Abstract

Theoretical investigations are preformed on the model reaction of PH 3 CH + H 2 CO to unravel reactivity of PH 3 CH , so-called Ylide-like radical, at G3MP2 and CCSD(T)/aug-cc-pVDZ//MP2/6-311++G(d,p) level. The results indicate that P -Ylidic radical behaves differently from the P -Ylide or usual unsaturated radical toward formaldehyde. For the entrance channels, [2+2] cycloaddition to form oxaphosphetane radical INT1 is more favorable, which is an analogical process to Witting reaction of P -Ylide. So PH 3 CH shows P -Ylide character in entrance channel, which has found the support from the dual one-center frontier–orbital interaction based on Fukui's frontier–orbital theory. However, due to the radical character of INT1, it can competitively give P2 PH 3 CHCHO + H and INT2, but not Witting-type products of alkene and phosphine oxide. At last, INT2 almost can barrierlessly fragmentate to Corey-type products of ethene oxide radical and phosphine. The present study shows that PH 3 CH , Ylide-like radical, has duplicate reactivity of both P-Ylide and radical, and title reaction presents a completely new reaction mechanism, compared with previous well-known H -abstract or addition–elimination mechanism for radical- H 2 CO reactions.