Flexible interactions of the rare-earth elements Y, La, and Lu with phosphorus in metallacyclohexane rings

Abstract

A geometrically flexible bifunctional (bis)aminophosphine ligand was synthesized in a three-component, one-pot Kabachnik–Fields reaction using ^tertbutylphosphine, paraformaldehyde, and 3,5-dimethyl aniline. The product, bis((3,5-dimethylphenyl)aminomethyl)^tertbutylphosphine (^ArBiAMP^tBu), containing two secondary amines and a tertiary phosphine, was isolated in good yields. Deprotonation of both N–H groups with (trimethylsilyl)methylpotassium (K-CH₂SiMe₃), followed by salt metathesis with LaI₃, YI₃, and LuI₃ generated the corresponding MI(^ArBiAMP^tBu)(thf)₃ complexes (M = Y (1), La (2), and Lu (3)) in good yields. A sterically encumbered indene, 1,3-diisopropyl-4,7-dimethyl-1H-indene, ^iPrMeInd, was deprotonated in situ and installed via salt-metathesis to generate the organometallic series of η⁵-indenide complexes, M(^ArBiAMP^tBu)(η^5-iPrMeInd)(thf) (M = Y (4), La (5), and Lu (6)). ¹H, ³¹P, ¹³C, and ⁸⁹Y NMR experiments, IR spectroscopy, and single crystal X-ray diffraction (SC-XRD), were used to characterize these complexes. The Y–P coupling constant was found to be variable depending on the modifiable coordination environment of the metal center, indicating potential as both a spectroscopic handle as well as providing insight into the influence of additional ligands on the metal center.