Synthesis, Structural Characterization, and Catalytic Properties of Group 4 Metal Complexes Incorporating a Phosphorus-Bridged Indenyl-Carboranyl Constrained-Geometry Ligand

Interaction of iPr2NP(C9H7)(C2B10H11) with 1 equiv of M(NR2)4 in toluene gave constrained-geometry group 4 metal amides [η5:σ-iPr2NP(C9H6)(C2B10H10)]M(NMe2)2 (R = Me, M = Ti
(1), Zr (2), Hf (3); R = Et, M = Hf (4)) in good yields. Compound 2 reacted with 3 equiv of
PhNCO to produce the tri-insertion product [η5:σ-iPr2NP(C9H6)(C2B10H10)]Zr[η2-OC(NMe2)NPh][η2-OC(NMe2)N(Ph)C(NPh)O] (5). No further insertion reaction occurred with another
equivalent of PhNCO. Instead, the trimer (PhNCO)3 was isolated. Compound 2 reacted with
2 equiv of n-BuLi in toluene to afford, after recrystallization from DME/toluene, the dilithium
salt [Li(DME)3][η5:σ-iPr2NP(C9H6)(C2B10H10)Li(DME)] (6). An equimolar reaction of 2 with
acetylacetone resulted in the formation of Zr(acac)4. 2 exhibited an ethylene polymerization
activity of 3.7 × 103 g PE mol-1 atm-1 h-1 upon activation with MMAO. Furthermore, 2 was
also able to efficiently initiate the polymerization of ε-caprolactone to give polymers of high
molecular weights (Mn > 40 000) and low polydispersities (Mw/Mn < 1.4) through the action
of the nucleophilic amido-nitrogen atom, which represents the first example of the
polymerization of ε-caprolactone catalyzed by group 4 metal amides.