Neutral and Cationic Zinc Complexes with N- and S‑Donor-Functionalized Cyclopentadienyl Ligands

The synthesis of neutral and cationic
zinc cyclopentadienyl (Cp)
complexes with amino and thio donor groups that are attached to the
Cp ring via a side chain is reported. The amino-functionalized zincocene
[ZnCp3N2] (3; Cp3N =
C5Me4(CH2)3NMe2) was prepared in a salt metathesis reaction from KCp3N and ZnCl2. In the solid-state structure of 3, which was determined by single-crystal X-ray diffraction, one of
the Cp3N ligands is coordinated as a chelating ligand through
a ring carbon atom and through the amino group, whereas the other
Cp3N ligand is bound in a monodentate mode through the
Cp ring only. A reaction of 3 with ZnEt2,
[ZnCp*2] (Cp* = C5Me5), and [ZnCp2N2] (2; Cp2N = C5Me4(CH2)2NMe2) gave the
heteroleptic complexes [ZnEtCp3N] (4), [ZnCp*Cp3N] (5), and [ZnCp3NCp2N] (6), respectively. The incorporation of a second amino
group in the same side chain led to the formation of the mononuclear
zinc chlorido complex [ZnClCptmeda] (7; Cptmeda = C5Me4(CH2)2NMe­(CH2)2NMe2), in which the Cptmeda ligand is bound in a tridentate coordination mode. In
addition, the thio-functionalized zincocene [ZnCp2S2] (8; Cp2S = C5Me4(CH2)2SMe) was obtained and shown to exhibit
an intramolecular coordination by the sulfur atoms. Starting from
the neutral complexes 2, 3, and 8, the cationic compounds [ZnCpD(py)2]+[BArF4]− (CpD =
Cp2N (9), Cp3N (10), Cp2S (11); py = pyridine; BArF4 = B­{3,5-(CF3)2C6H3}4) were obtained either by protonation or upon
reaction with an electrophile in the presence of pyridine. In these
cationic complexes the highly electrophilic zinc center is stabilized
by intramolecular coordination through the donor groups.