Deprotonated P-ylides As Templates for Novel Cyclopentadienyl Phosphonioalkyl, -alkylidene, and -alkylidyne (CpPC) Constrained-Geometry Complexes

Abstract

Cyclopentadienylidene phosphoranes of the general formula Cpx-PR2-CH3 (1a–d) and anionic derivatives thereof have been investigated as ligands in the coordination sphere of zirconium (R = NMe2, tBu, Ph; Cpx = C5H4, C5Me4, C5H2(CMe2)2CH2). The ligand set includes a full series of neutral and mono-, di-, and trianionic phosphonium ylides, which are formed by successive deprotonation of the PCH3 group. The degree of deprotonation can be controlled by choice of the ylides 1a–d and the zirconium precursor. The resulting zirconium complexes have been analyzed by NMR spectroscopy, elemental analyses, and single-crystal X-ray diffraction analyses. Our findings include the first fully characterized zirconium complex bearing a neutral cyclopentadienylidene phosphorane ligand, [Zr(H3C-P(NMe2)2-C5Me4)(CH2SiMe3)Cl3] (3a). New constrained-geometry complexes with chelating Cpx-phosphonio-alkyl ([Zr(CH2-PtBu2-C5H4)R′3]: 4b, R′ = Bn; 4b′, R′ = CH2SiMe3)) and Cpx-phosphonio-alkylidene ligands ([Zr(CH-PR2-Cpx)(CH2SiMe3)2]: 5a, R = NMe2, Cpx = C5Me4; 5c, R = Ph, Cpx = C5H2(CMe2)2CH2; 5d, R = Ph, Cpx = C5Me4) have been isolated and characterized. [Zr(C-PR2-C5Me4)Bn]2 (6a, R = NMe2) is a rare example of a compound featuring a bridging trianionic phosphonium ylide (phosphonio-alkylidyne) ligand.