Stabilization of Pentaphospholes as η(5)‐Coordinating Ligands

Electrophilic functionalisation of [Cp*Fe(η(5)‐P(5))] (1) yields the first transition‐metal complexes of pentaphospholes (cyclo‐P(5)R). Silylation of 1 with [(Et(3)Si)(2)(μ‐H)][B(C(6)F(5))(4)] leads to the ionic species [Cp*Fe(η(5)‐P(5)SiEt(3))][B(C(6)F(5))(4)] (2), whose subsequent reaction with H(2)O yields the parent compound [Cp*Fe(η(5)‐P(5)H)][B(C(6)F(5))(4)] (3). The synthesis of a carbon‐substituted derivative [Cp*Fe(η(5)‐P(5)Me)][X] ([X](−)=[FB(C(6)F(5))(3)](−) (4 a), [B(C(6)F(5))(4)](−) (4 b)) is achieved by methylation of 1 employing [Me(3)O][BF(4)] and B(C(6)F(5))(3) or a combination of MeOTf and [Li(OEt(2))(2)][B(C(6)F(5))(4)]. The structural characterisation of these compounds reveals a slight envelope structure for the cyclo‐P(5)R ligand. Detailed NMR‐spectroscopic studies suggest a highly dynamic behaviour and thus a distinct lability for 2 and 3 in solution. DFT calculations shed light on the electronic structure and bonding situation of this unprecedented class of compounds.