Tantalocenehydridephosphorus chemistry.: Some new complexes and crystal structures of [CpCp′TaH2(PMe2H)]PF6 (Cp=C5H5, Cp′=C5H2tBu(Me)2) and Cp2Ta(H)(μ-PPh2,H)Fe(CO)3

Abstract The aim of this paper is to look for a better knowledge of the behaviour of bent tantalocenes that bear hydrides, phosphorus PR 2 X (R=Me, Ph; X=H, lone pair) and cyclopentadienyl (Cp=C 5 H 5 , Cp′=C 5 H 2 t Bu(Me) 2 , Cp*=C 5 Me 5 ) ligands. An orbital control of regioselectivity of insertion of the PR 2 phosphide fragment of chlorophosphines PR 2 Cl into the central TaH bond of trihydrides Cp 2 TaH 3 leading to the formation of metallophosphonium cations is discussed. Neutralisation of cationic complexes with strong bases leads either to the Ta(V)–phosphide or to the Ta(III)–phosphine species depending on the nature of the cyclopentadienyl ligand; good electron donor Cp′ and Cp* rings favour the formation of Ta(V)–phosphide species, while C 5 H 5 orients neutralisation towards Ta(III)–phosphine ones. These trends are roughly confirmed by DFT calculations. The X-ray structure of the first tantalocene phosphonium ionic compound [CpCp′TaH 2 (PMe 2 H)]PF 6 (Cp′=C 5 H 2 t Bu(Me) 2 ) as well as that of the bimetallic complex Cp 2 Ta(H)(μ-PPh 2 ,H)Fe(CO) 3 are also reported.