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摘要
The reactions of frustrated Lewis pairs (FLPs) derived from B(C(6)F(5))3 and the bulky Lewis bases 2,2,6,6-tetramethylpiperidine (TMP), tri-tert-butylphosphine, and lutidine (Lut) with terminal alkynes (acetylene, phenylacetylene, 3-ethynylthiophene) were investigated. The FLPs TMP center dot center dot center dot B(C(6)F(5))(3), t-Bu(3)P center dot center dot center dot B(C(6)F(5)) and Lut center dot center dot center dot(C(6)F(5)) reacted with acetylene (HC CH) to yield the apparently thermodynamically more stable E isomers [TMPH][(C(6)F(5))(2)B-C(C(6)F(5))=C(H)B(C(6)F(5))(3)] (1-E), t-Bu(3)PC(H)=C(H)B(C(6)F(5))(3) (2-E; 90%), and [t-Bu(3)PH][(C(6)F(5))(2)B-C(C(6)F(5))=C(H)B(C(6)F(5))(3)] (3-E; 10%),and LutC(H)=C(H)B(C(6)F(5))(3) (4-E), respectively. A mechanistic pathway for the reaction of acetylene is suggested to start with the formation of a weak B(C(6)F(5))(3)/acetylene adduct followed by it deprotonation of this species with any mentioned Lewis bases (LB), yielding the acetylicle salts [LBH][(C(6)F(5))(3)BC CH]. Alternatively, nucleophilic addition of the LB to this adduct occurs to yield LBC(H)=C(H)B(C(6)F(5))(3) compounds. Formation of 1 and 3-E is explained by the reactions of [LBH][B(C(6)F(5))(3)C CH] salts with a second equivalent of B(C(6)F(5))(3) to undergo clectrophilic addition, forming the vinylidene adduct (C(6)F(5))(3)B(-)C(+)=C(H)B(C(6)F(5))(3), which is subsequently stabilized by 1,2-migration Of a C(6)F(5) group to form [(C(6)F(5))(2)BC(C(6)F(5))=C(H)B(C(6)F(5))(3)]. The reaction between B(C(6)F(5))(3) and phenylacetylene yielded a mixture of (Z)- and (E)-PhC(H)=C(C(6)F(5))B(C(6)F(5))(2) (11-Z and 11-E), confirming that the reaction proceeds via an acetylene/vinylidene rearrangement and subsequent 1,2-shift of a C(6)F(5) group to the carbenic center. The FLPs TMP center dot center dot center dot B(C(6)F(5))(3) and tBu(3)P center dot center dot center dot B(C(6)F(5))(3) were converted with phenylacetylene or 3-ethynylthiophene to yield the acetylide products [TMPH][PhC CB(C(6)F(5))3] (5), [TMPH][SC(4)H(3)C CB(C(6)F(5))(3)] (6), [t-BU(3)PH][PhC CB(C(6)F(5))(3)] (7), and [t-Bu(3)PH][SC(4)H(3)C=CB(C(6)F(5))3] (8), where TMP and t-Bu(3)P acted as a base deprotonating the acetylenic proton. When the FLP Lut center dot center dot center dot B(C(6)F(5))(3) was reacted with phenylacetylene or 3-ethynylthiophene, the deprotonated product [LutH][PhC CB(C(6)F(5))(3)] (9; 47%) and the 1,2-addition compound LutC(SC(4)H(3)C)=C(H)B(C(6)F(5))(3) (10; 55%) were obtained. Compounds 1-E, 2-E, 5, and 6 were characterized by X-ray diffraction studies.
- 出版日期2010-1-11
