Casey Charles P, Kraft Stefan, Powell Douglas R
Department of Chemistry, University of Wisconsin, Madison, WI 53706, USA.
J Am Chem Soc. 2002 Mar 20;124(11):2584-94. doi: 10.1021/ja011962o.
Dimerization of the alkynylcarbene complex Cp(CO)(2)Re=C(Tol)C(triple bond)CCH(3) (8) occurs at 100 degrees C to give a 1.2:1 mixture of enediyne complexes Cp(CO)(2)Re[eta(2),eta(2)-TolC(triple bond)CC(CH(3))=C(CH(3))C(triple bond)CTol] (10-Eand 10-Z), showing no intrinsic bias toward trans-enediyne complexes. The cyclopropyl-substituted alkynylcarbene complex Cp(CO)(2)Re=C(Tol)C(triple bond)CC(3)H(5) (11) dimerizes at 120 degrees C to give a 5:1 ratio of enediyne complexes Cp(CO)(2)Re[eta(2),eta(2)-TolC(triple bond)C(C(3)H(5))C=C(C(3)H(5))C(triple bond)CTol] (12-E and 12-Z); no ring expansion product was observed. This suggests that if intermediate A formed by a [1,1.5] Re shift and having carbene character at the remote alkynyl carbon is involved, then interaction of the neighboring Re with the carbene center greatly diminishes the carbene character as compared with that of free cyclopropyl carbenes. The tethered bis-(alkynylcarbene) complex Cp(CO)(2)Re=C(Tol)C(triple bond)CCH(2)CH(2)CH(2)C(triple bond)CC(Tol)= Re(CO)(2)Cp (13) dimerizes rapidly at 12 degrees C to give the cyclic cis-enediyne complex Cp(CO)(2)Re[eta(2),eta(2)-TolC(triple bond)CC(CH(2)CH(2)CH(2))=CC(triple bond)CTol] (15). Attempted synthesis of the 1,8-disubstituted naphthalene derivative 1,8-Cp(CO)(2)Re=C(Tol)C(triple bond)CC(10)H(6) (16), in which the alkynylcarbene units are constrained to a parallel geometry, leads to dimerization to Cp(CO)(2)Re(eta(2),eta(2)-1,2-(tolylethynyl)acenaphthylene] (17). The very rapid dimerizations of both 13 and 16 provide compelling evidence against mechanisms involving cyclopropene intermediates. A mechanism is proposed which involves rate-determining addition of the carbene center of A to the remote alkynyl carbon of a second alkynylcarbene complex to generate vinyl carbene intermediate C, and rearrangement of C to the enediyne complex by a [1,1.5] Re shift.
炔基卡宾配合物Cp(CO)(2)Re=C(Tol)C(triple bond)CCH(3)（8）在100℃发生二聚反应，生成烯二炔配合物Cp(CO)(2)Re[eta(2),eta(2)-TolC(triple bond)CC(CH(3))=C(CH(3))C(triple bond)CTol]（10-E和10-Z）的1.2:1混合物，对反式烯二炔配合物没有内在偏向性。环丙基取代的炔基卡宾配合物Cp(CO)(2)Re=C(Tol)C(triple bond)CC(3)H(5)（11）在120℃发生二聚反应，生成烯二炔配合物Cp(CO)(2)Re[eta(2),eta(2)-TolC(triple bond)C(C(3)H(5))C=C(C(3)H(5))C(triple bond)CTol]（12-E和12-Z），比例为5:1；未观察到扩环产物。这表明，如果涉及通过[1,1.5]Re迁移形成且在远端炔基碳上具有卡宾特征的中间体A，那么与游离环丙基卡宾相比，相邻的Re与卡宾中心的相互作用会大大降低卡宾特征。连接的双（炔基卡宾）配合物Cp(CO)(2)Re=C(Tol)C(triple bond)CCH(2)CH(2)CH(2)C(triple bond)CC(Tol)=Re(CO)(2)Cp（13）在12℃迅速二聚，生成环状顺式烯二炔配合物Cp(CO)(2)Re[eta(2),eta(2)-TolC(triple bond)CC(CH(2)CH(2)CH(2))=CC(triple bond)CTol]（15）。尝试合成1,8-二取代萘衍生物1,8-Cp(CO)(2)Re=C(Tol)C(triple bond)CC(10)H(6)（16），其中炔基卡宾单元被限制为平行几何构型，导致二聚为Cp(CO)(2)Re(eta(2),eta(2)-1,2-（甲苯乙炔基）苊]（17）。13和16的非常快速的二聚反应提供了令人信服的证据，反对涉及环丙烯中间体的机理。提出了一种机理，该机理涉及速率决定步骤，即A的卡宾中心加到第二个炔基卡宾配合物的远端炔基碳上，生成乙烯基卡宾中间体C，然后C通过[1,1.5]Re迁移重排为烯二炔配合物。
