Heterobimetallic carbene and allenylidene complexes; syntheses and crystal structures of iron(II)–chromium(>0>) cycloheptatrienylidene and (cycloheptatrienylidene)ethenylidene complexes†

The heterobimetallic iron(II)–chromium(>0>) complexes [(OC)2CpFe(µ-η1∶η7-C7H6)Cr(CO)3]+ and [(OC)2CpFe(µ-η1∶η7-C2C7H6)Cr(CO)3]+ containing the bridging carbene ligand cycloheptatrienylidene C7H6 and the cumulogous allenylidene ligand (cycloheptatrienylidene)ethenylidene C2C7H6 have been prepared and their properties studied. The former has been prepared by hydride abstraction from the heterobimetallic µ-η1∶η6-cyclohepta-1,3,5-trien-2-yl complex obtained by lithiation of 2-trimethylstannyl-cyclohepta-1,3,5-triene followed by reaction with [FeCp(CO)2Br] and [Cr(CO)3(NCEt)3]. Treatment of 7-ethynyl-cyclohepta-1,3,5-triene with LiBun and consecutive reaction with [FeCp(CO)2Br] and [Cr(CO)3(NCEt)3] led to the formation of endo-[(OC)2CpFe(µ-η1∶η6-CC–C7H7)Cr(CO)3] which was treated with [Ph3C][BF4] to give [(OC)2CpFe(µ-η1∶η7-C2C7H6)Cr(CO)3][BF4]. The crystal structures of [(OC)2CpFe(µ-η1∶η6-C7H7)Cr(CO)3], [(OC)2CpFe(µ-η1∶η7-C7H6)Cr(CO)3][PF6]·0.25CH2Cl2 and [(OC)2CpFe(µ-η1∶η7-C2C7H6)Cr(CO)3]+[BF4]·CH2Cl2 have been determined.

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