Synthesis of cyclopentadienyl iron alkoxycarbene complexes via vinylidene intermediates: X-ray structures of [Fe{C(OMe)Me}(dppe)Cp][I] and [Fe{C(CH2)(3)O}(dppe)Cp][PF6]

摘要

The reaction of [FeI(dppe) Cp], 1 (dppe = Ph2PCH2CH2PPh2) with HC= CSiMe3 in refluxing methanol results in formation of a mixture of the vinylidene complex [Fe(=C=CH2)(dppe) Cp](+), 2 and the heteroatom stabilised alkoxycarbene [Fe{C(OMe) Me}(dppe) Cp](+), 3. The carbene 3 is formed by addition of the alcohol solvent to the reaction intermediate vinylidene 2, and prolonged reflux in methanol (4 days) resulted in complete conversion of 2 to 3. The methoxycarbene, 3 was isolated as a stable solid and fully characterised by spectroscopic and structural methods. Vinylidene 2 also reacts with ethanol to give the ethoxycarbene [Fe{C(OEt) Me}(dppe)Cp](+), 4 but no reaction was observed in refluxing isopropanol, thus providing a specific synthesis of vinylidene 2 from 1 and HC= CSiMe3. An example of an alcohol based, intramolecular nucleophilic addition to a mono-substituted vinylidene [Fe(=C=CHR)(dppe)Cp](+) was uncovered in the reaction of 1 with 3-butyn-1-ol which leads to the synthesis of the cyclic oxacarbene complex [Fe{C(CH2)(3)O}(dppe) Cp][PF6], 5. X-ray crystallographic investigations on 3[I] and 5[PF6] determine Fe-C alpha bonds lengths of 1.851(5) and 1.834(2) A rpectively, intermediate between previously reported Fe-C alpha distances for the amino carbene [Fe{C(NH2) Me}(dppe)Cp][PF6] and the alkylidene complex [Fe{=C(H) Me}(dppe) Cp*][PF6]. (C) 2016 Elsevier B.V. All rights reserved.