A Terminal Yttrium Phosphinidene

Abstract

Terminal, nondirectional ionic "multiple" bond interactions between group 15 elements and rare-earth metals (Ln) have remained a challenging target until present. Although reports on terminal imide species have accumulated in the meantime, examples of terminal congeners with the higher homologue phosphorus are yet elusive. Herein, we present the synthesis of the first terminal yttrium organophosphinidene complex, Tp^tBu,MeY(═PC₆H₃iPr₂-2,6)(DMAP)₂, according to a double-deprotonation sequence previously established for organoimides of the smaller rare-earth metals. Subsequent deprotonation of the primary phosphane H₂PC₆H₃iPr₂-2,6 (H₂PAr^iPr) with discrete dimethyl compound Tp^tBu,MeYMe₂ in the presence of DMAP under simultaneous methane elimination generated a terminal multiply bonded phosphorus. The primary phosphide intermediates Tp^tBu,MeYMe(HPAr^iPr) and Tp^tBu,MeYMe(HNPAr^iPr)(DMAP) are isolable species and were also obtained and fully characterized for holmium and dysprosium. The Lewis acid-stabilized yttrium phosphinidene Tp^tBu,MeY[(μ₂-PAr^iPr)(μ₂-Me)AlMe₂] was obtained by treatment of H₂PAr^iPr with Tp^tBu,MeYMe(AlMe₄) but could not be converted into a terminal phosphinidene via cleavage of trimethylaluminum. The corresponding reaction of H₂PAr^iPr with Tp^tBu,MeYMe(GaMe₄) led to adduct [GaMe₃(PH₂Ar^iPr)] rather than to the formation of a yttrium phosphinidene. The yttrium-phosphorus interaction in the obtained organophosphide and phosphinidene complexes was scrutinized by ³¹P/⁸⁹Y NMR spectroscopy and DFT calculations, unambiguously supporting the existence of multiple bonding.