Destiny of Transient Phosphenium Ions Generated from the Addition of Electrophiles to Phosphaalkenes: Intramolecular C-H Activation, Donor-Acceptor Formation, and Linear Oligomerization
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- 作者：Chi-Wing Tsang ; Crystal A. Rohrick ; Tejindra S. Saini ; Brian O. Patrick ; and Derek P. Gates
- 刊名：Organometallics
- 出版年：2004
- 出版时间：December 6, 2004
- 年：2004
- 卷：23
- 期：25
- 页码：5913 - 5923
- 全文大小：233K
- 年卷期：v.23,no.25(December 6, 2004)
- ISSN：1520-6041
文摘
The reaction of the phosphaalkenes MesP=CPh2 (Mes = 2,4,6-Me3C6H2) and Mes*P=CH2(Mes* = 2,4,6-tBu3C6H2) with Lewis (AlCl3, GaCl3, InCl3) and protic (HOTf) acids has beenexamined to evaluate the feasibility of cationic polymerization for P=C bonds. Addition ofGaCl3 to Mes*P=CH2 generates the adduct Mes*(Cl3Ga)P=CH2, which can be detectedspectroscopically at 193 K. At higher temperatures, GaCl3 migrates from phosphorus tocarbon to afford the fleeting phosphenium zwitterion Mes*PCH2GaCl3. This undetectedtransient species immediately oxidatively adds to a C-H bond of an o-tBu group in the P-Mes*substituent, resulting in a GaCl3-coordinated ylide that has been characterized crystallographically. The analogous reaction of GaCl3 with MesP=CPh2 gives stable Mes(Cl3Ga)P=CPh2, for which a crystal structure determination has been conducted. Significantly, treatinga highly concentrated solution of Mes*P=CH2 with substoichiometric quantities of GaCl3leads to linear dimerization following a cationic chain growth mechanism; however, theoligomerization is terminated by intramolecular C-H activation. The novel coordinated lineardimer (C-H activated Mes*)PCH2PH(Mes*)CH2GaCl3 has been characterized crystallographically. Interestingly, mechanistic studies reveal that the diphosphiranium ringMes*PCH2 P(Mes*)CH2GaCl3 derived from the reaction of Mes*PCH2GaCl3 with Mes*P=CH2 is an intermediate in this transformation. The reaction of phosphaalkenes withphosphenium species appears to be a general method to prepare diphosphiranium ions. Inone case, NMR spectroscopic data suggests that treating MesP=CPh2 with HOTf gives boththe diphosphiranium species [MesPCPh2 P(Mes)CPh2H]OTf and the adduct Ph2C=(Mes)P
P(Mes)(CHPh2)]OTf. Remarkably, treating concentrated Mes*P=CH2 solutions with HOTfresults in oligomers of up to six repeat units, as determined by ESI mass spectrometry.These results suggest that it may be possible to initiate the polymerization of P=C bondsusing cationic initiators and that the propagating species will be a cationic phospheniummoiety.
P(Mes)(CHPh2)]OTf. Remarkably, treating concentrated Mes*P=CH2 solutions with HOTfresults in oligomers of up to six repeat units, as determined by ESI mass spectrometry.These results suggest that it may be possible to initiate the polymerization of P=C bondsusing cationic initiators and that the propagating species will be a cationic phospheniummoiety.