Ligand Substitution Reactions of W₆S₈L₆ with Tricyclohexylphosphine (L = 4-<i>tert</i>-Butylpyridine or <i>n</i>-Butylamine):  ³¹P NMR and Structural Studies of W₆S₈(PCy₃)<i>_n</i>(4-<i>tert</i>-butylpyridine)₆_-<i>_n</i> (0 < <i>n</i> ≤ 6) Complexes

Abstract

The substitution reactions by bulky tricyclohexylphosphine (PCy3) ligands on W6S8L6 (L = 4-tert-butylpyridine or n-butylamine) clusters were investigated to prepare clusters with mixed axial ligands for low-dimensional cluster linking. When 4−6 equiv of PCy3 are used to react with W6S8(4-tert-butylpyridine)6 (4) in THF, cis-W6S8(PCy3)4(4-tert-butylpyridine)2 (1) is preferentially formed. But when starting with W6S8(n-butylamine)6 (2), only W6S8(PCy3)6 (3) is produced with 6 equiv of PCy3. Other conditions with fewer equivalents of PCy3 led to mixtures of partially substituted complexes in the W6S8L6-n(PCy3)n (0 ≤ n ≤ 6, L = 4-tert-butylpyridine or n-butylamine) series. A significantly distorted structure for 1 helps to explain its preferential formation. 1H NMR spectra were collected for clusters 1 and 2 and 31P NMR spectra for 1 and W6S8(4-tert-butylpyridine)6-n(PCy3)n complexes. P−P coupling through P−W−W−P is reported for the first time in octahedral metal clusters and shown to be very useful in identifying nearly all the W6S8L6-n(PR3)n complexes and their stereoisomers in the mixtures even before individual species are isolated