A Tripodal Benzylene-Linked Trisamidophosphine Ligand Scaffold: Synthesis and Coordination Chemistry with Group(IV) Metals

A new
tripodal trisamidophosphine ligand (1) based
on the trisbenzylphosphine backbone has been synthesized in three
steps starting from NaPH2 and phthaloyl-protected 2-aminobenzyl
bromide. At elevated temperatures, 1 reacts directly
with M­(NMe2)4 (M = Zr, Hf) to afford the dimethylamido
complexes [PN3]­M­(NMe2) (M = Zr,
Hf) (2), which are easily converted into the corresponding
triflates [PN3]­MOTf (M = Zr, Hf) (3)
via reaction with triethylsilyl trifluoromethanesulfonate. The related
titanium chloro complex [PN3]­TiCl (4-Ti) is obtained from 1 and Bn3TiCl via protonolysis.
Triple deprotonation of 1 with n-butyllithium
affords the tris-lithium salt Li3­[PN3]
(1-Li), which serves as a common starting material for
the preparation of all the group­(IV) chlorides [PN3]­MCl
(M = Ti, Zr, Hf) (4). Upon treatment of 4-Ti with Bn2Mg­(thf)2, formation of a benzyltitanium
species is observed, which is converted cleanly into a ligand-CH-activated
species (5-Ti).