Preparation and Reactivity of Zirconium(III), Niobium(III), and Molybdenum(III) Complexes Stabilized by a Cyclopentadienyl Unit with Pendant Phosphine Donors

Abstract

This paper deals with the organometallic chemistry of the trivalent second-row transition metals of groups 4−6, namely, Zr, Nb, and Mo, with the cyclopentadienyldiphosphine ligand [η5-C5H3-1,3-(SiMe2CH2PR2)2], abbreviated as [RP2Cp] (where R = i-Pr and Ph). The Zr(IV) complex [i-PrP2Cp]ZrCl3 undergoes reduction with Na/Hg to form the trivalent Zr derivative, [i-PrP2Cp]ZrCl2, which undergoes a metathetical reaction with MeMgBr to yield the monomethyl derivative [i-PrP2Cp]Zr(CH3)Cl. The reaction of the Zr(III) complex [i-PrP2Cp]ZrCl2 with excess carbon monoxide results in disproportionation to the Zr(IV) complex, [i-PrP2Cp]ZrCl3, and the Zr(II) compound [i-PrP2Cp]Zr(CO)2Cl. This reaction is reversible, and upon removal of CO the starting material, [i-PrP2Cp]ZrCl2 is formed. The preparation of the diamagnetic Nb(III) complex [RP2Cp]NbCl2 is achieved by the reaction of NbCl3(DME) with [RP2Cp]Li. [RP2Cp]NbCl2 complexes react with excess CO to form the CO adducts whose solid-state structures have been determined. The Nb(IV) derivatives [RP2Cp]NbCl3 are formed via the reaction of [RP2Cp]NbCl2 with PbCl2. These complexes can also be produced when Nb(O)Cl3(THF)2 is allowed to react with excess [RP2Cp]Li. These Nb(IV) derivatives are ESR active, and their solid-state molecular structures show distorted octahedral geometries around the Nb center. MoCl3(THF)3 reacts with [RP2Cp]Li to generate the corresponding Mo(III) complexes [RP2Cp]MoCl2. These compounds are low-spin, paramagnetic complexes as evidenced by their ESR spectra.