Stabilization of Pentaphospholes as η5-Coordinating Ligands

Electrophilic functionalisation of [Cp*Fe(eta(5)-P-5)] (1) yields the first transition-metal complexes of pentaphospholes (cyclo-P5R). Silylation of1with [(Et3Si)(2)(mu-H)][B(C6F5)(4)] leads to the ionic species [Cp*Fe(eta(5)-P5SiEt3)][B(C6F5)(4)] (2), whose subsequent reaction with H2O yields the parent compound [Cp*Fe(eta(5)-P5H)][B(C6F5)(4)] (3). The synthesis of a carbon-substituted derivative [Cp*Fe(eta(5)-P5Me)][X] ([X](-)=[FB(C6F5)(3)](-)(4 a), [B(C6F5)(4)](-)(4 b)) is achieved by methylation of1employing [Me3O][BF4] and B(C6F5)(3)or a combination of MeOTf and [Li(OEt2)(2)][B(C6F5)(4)]. The structural characterisation of these compounds reveals a slight envelope structure for the cyclo-P5R ligand. Detailed NMR-spectroscopic studies suggest a highly dynamic behaviour and thus a distinct lability for2and3in solution. DFT calculations shed light on the electronic structure and bonding situation of this unprecedented class of compounds.