Chemical and theoretical comparison between phosphido (X = PR2) and thiolato (X = SR) bent niobocenes of the type [Nb(cp)2L(X)][L = CO or P(OMe)3, cp =η-C5H5]. Structure of [Nb(cp)2(CO)(µ-SEt){Fe(CO)4}

Abstract

The hydrido complexes [Nb(cp)2H(L)][L = CO or P(OMe)3, cp =η-C5H5] reacted with Mel to afford the iodo derivatives [Nb(cp)2L(I)]1. The reaction of 1 with Na(SEt)led to the terminal thiolato complexes [Nb(cp)2L(SEt)]2. Compounds 2 were used to bind the metal carbonyl fragments Fe(CO)4 and M(CO)5 from [Fe2(CO)9] and [M(CO)5(thf)](thf = tetrahydrofuran) respectively. The corresponding monothiolato-bridged complexes [Nb(cp)2L(µ-SEt){M(CO)n}]3(M = Fe, n= 4; M = Mo or W, n= 5) were obtained only in the case of L = CO and no dibridged µ-SEt, µ-CO complex was formed. The new complexes 1–3 were characterized by IR, 1H and 31P NMR spectroscopies. The X-ray analysis of [Nb(cp)2(CO)(µ-SEt){Fe(CO)4}] showed an endo position of the ethyl group with respect to the CO ligand bound to the niobium. The results of extended-Huckel molecular orbital (EHMO) conformational calculations carried out on the model complexes [Nb(cp)2(CO)(PMe2)] and [Nb(cp)2(CO)(SMe)] are compared, and the imporatance of electronic and steric effects deducecd. An explanation for the non-formation of dibridged µ-SEt, µ-CO complexes is attempted on the basis of EHMO and X-ray results.