COMPARISON OF CHARACTERISTIC STRUCTURAL FEATURES AMONG THE TRIAD OF TRIS(CYCLOPENTADIENYL)(GROUP-4 METAL) COMPLEX CATIONS - A COMBINED THEORETICAL AND EXPERIMENTAL-STUDY
H. Jacobsen et al., COMPARISON OF CHARACTERISTIC STRUCTURAL FEATURES AMONG THE TRIAD OF TRIS(CYCLOPENTADIENYL)(GROUP-4 METAL) COMPLEX CATIONS - A COMBINED THEORETICAL AND EXPERIMENTAL-STUDY, Helvetica chimica acta, 81(9), 1998, pp. 1692-1709
A density functional theory computational chemistry study has revealed
a fundamental structural difference between [Ti(Cp)(3)](+) and its co
ngeners [Zr(Cp)(3)](+) and [WT(Cp)(3)](+)/(Cp = cyclopentadienyl). Whe
reas the latter two are found to contain three uniformely eta(5)-coord
inated Cp ligands (3 eta(5)-structural type), [Ti(Cp)(3)](+) is shown
to prefer a 2 eta(5)eta(2) structure. [Ti(Cp)(3)](+)[B(C6F5)(3)(Me)](-
) (10 .[B(C6F5)(3)(Me)](-)) was experimentally generated by treatment
of [Ti(Cp)(3)(Me)] (7a) with B(C6F5)(3) (Scheme 3). Low-temperature H-
1-NMR spectroscopy in CDFCl2 (143 K, 600 MHz; Fig. 8) showed a splitti
ng of the Cp resonance into five lines in a 2:5:2:5:1 ratio which woul
d be in accord with the theoretically predicted 2 eta(5)eta(2)-type st
ructure of [Ti(Cp)(3)](+). The precursor [Ti(Cp)(3)(Me)] (7a) exhibits
two H-1-NMR Cp resonances in a 10:5 ratio in CD2Cl2 at 223 K. Treatme
nt of [HfCl(Cp)(2)(Me)] (6c) with sodium cyclopentadienide gave [Hf(Cp
)(3)(Me)] (7c) (Scheme 1). Its reaction with B(C6F5)(3) furnished the
salt [Hf(Cp)(3)](+)[B(C6F5)(3)(Me)](-) (8 .[B(C6F5)(3)(Me)](-)), which
reacted with tert-butyl isocyanide to give the cationic complex [Hf(C
p)(3)(C=N-CMe3)](+) (9a; with counterion [B(C6F5)(3)(Me)](-) (Scheme 2
). Complex cation I)a was characterized by X-ray diffraction (Fig. 7).
Its Hf(Cp-3) moiety is of the 3 eta(5)-type. The structure is distort
ed trigonal-pyramidal with an average D-HI-D angle of 118.8 degrees an
d an average D-Hf-C(1) angle of 96.5 degrees (D denotes the centroids
of the Cp rings; Table 6). Cation 9a is a typical d(0)-isocyanide comp
lex exhibiting structural parameters of the C=N-CMe3 group (d(C(1)-N(2
))= 1.146(5) Angstrom; IR: <(nu)over bar>(C=N) 2211 cm(-1)) very simil
ar to free uncomplexed isonitrile. Analogous treatment of 8 with carbo
n monoxide yielded the carbonyl (d(0)-group-4-metal) complex [Hf(Cp)(3
)(CO)](+) (9b; with counterion [B(C6F5)(3)(Me)](-)) (Scheme 2) that wa
s also characterized by X-ray crystal-structure analysis (Fig. 6). Com
plex 9b is also of the 3 eta(5)-structural type, similar to the peviou
sly described cationic complex [Zr(Cp)(3)(CO)](+), and exhibits proper
ties of the CO ligand (d(C-O)=1.11(2) Angstrom; IR: <(nu)over bar>(C=O
) 2137 cm(-1)) very similar to the free carbon monoxide molecule.