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

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.