Synthesis and Reactivity of [(Amidosilyl)cyclopentadienyl]titanium and -zirconium Complexes. X-ray Molecular Structure of [Zr{η⁵:η¹-C₅H₄SiMe₂(μ-O)}Cl₂{H₂N(CHMe)Ph}]₂

Abstract

New half-sandwich (amidosilyl)cyclopentadienyl complexes of titanium(IV) and zirconium(IV) were synthesized from the chlorosilyl-substituted cyclopentadienyl precursors [M(η5-C5H4SiMe2Cl)Cl3] (M = Ti (1a), Zr (1b)). The reaction of [Ti(η5-C5H4SiMe2Cl)Cl3] (1a) with LiNHR in the presence of NEt3 gives the [Ti(η5:η1-C5H4SiMe2NR)Cl2] (R = tBu (2a), (±)-CH(Me)Ph (3a)) complexes. Similarly, the addition of 2 equiv of LiN(SiMe3)2 to complex 1a affords the diamido derivative [Ti(η5-C5H4SiMe2Cl)Cl{N(SiMe3)2}2] (4a). The amidotitanium complex [Ti(η5:η1-C5H4SiMe2NHtBu)Cl2(NHtBu)] (5a) is prepared, in low yield, by reacting 1a with NH2tBu in a 1:3 molar ratio. In this reaction, the presence of 2a is also detected. The same complexes 2a and 3a may also be obtained by reaction of the trichloro compound 1a with NH2R and NEt3 in a 1:1:2 molar ratio. The reaction of 2a with Tl(C5H5) gives the mixed-dicyclopentadienyl derivative [Ti(η5:η1-C5H4SiMe2NtBu)(η5-C5H5)Cl] (6a). The dialkyl derivatives [Ti(η5:η1-C5H4SiMe2NR)R‘2] (R = tBu, R‘ = CH3 (7a), CH2Ph (8a); R = CH(Me)Ph, R‘ = CH3 (9a), CH2Ph (10a)) have been isolated by reaction of 2 equiv of MgClMe or 1 equiv of Mg(CH2Ph)2·2THF with the dichlorides 2a and 3a. The analogous reaction of 2a with 1 equiv of MgCl(CH2Ph) affords the chloro alkyl derivative [Ti(η5:η1-C5H4SiMe2NtBu)(CH2Ph)Cl] (11a). The reaction of complexes 2a and 3a with CO2 leads to their conversion into the reported oxo derivative [Ti{μ-(η5-C5H4SiMe2O)}Cl2]2 with elimination of alkyl isocyanate OCNR (R = tBu, (±)-CH(Me)Ph) as the unique organic product. Addition of 1 equiv of LiN(SiMe3)2 to a diethyl ether solution of [Zr(η5-C5H4SiMe2Cl)Cl3] (1b) gives the monoamido derivative [Zr(η5-C5H4SiMe2Cl)Cl2{N(SiMe3)2}] (2b). The related reaction of the zirconium derivative 1b with LiNHtBu in the presence of NEt3 produces a mixture of two compounds, [Zr(η5:η1-C5H4SiMe2NtBu)Cl2] (3b) and [Zr(η5-C5H4SiMe2NHtBu)Cl3(NEt3)] (4b). Pure 3b can be isolated by recrystallization of this mixture, but attempts to isolate the pure compound 4b were unsuccessful. The analogous reaction of 1b with 1 equiv of LiNHCH(Me)Ph in the presence of NEt3 gives the related zirconium compound [Zr{η5-C5H4SiMe2[NH(CHMe)Ph]}Cl3(NEt3)] (5b), which cannot be obtained as an analytically pure solid and is identified by 1H NMR spectroscopy. When water-saturated toluene is used to prepare 5b, the oxo-zirconium derivative [Zr{η5:η1-C5H4SiMe2(μ-O)}Cl2{H2N(CHMe)Ph}]2 (6b) is obtained by slow precipitation. Compound 6b has been characterized by X-ray crystallography.