Insights into the Formation Process of Yttrium–Aluminum Bimetallic Alkyl Complexes Supported by a Bulky Phosphazene Ligand

The reaction of the yttrium dialkyl precursor [N[Ph2PNC6H3(iPr)2]2Y(CH2SiMe3)2] (1) with more than 3 equiv of trimethylaluminum or triethylaluminum afforded the dinuclear heterometallic complexes N[Ph2PNC6H3(iPr)2]2Y{(μ-R)2AlR2}R (R = Me (2), Et (3)). When trimethylaluminum loading was reduced to 2 equiv, the same reaction gave the product N[Ph2PNC6H3(iPr)2]2Y{(μ-Me)2(μ-CH2SiMe3)AlMe}Me (4), with quite a different bonding mode. All of these complexes were characterized by NMR spectra, X-ray crystallography, and elemental analysis. We elucidated the step-reaction mechanism between the yttrium dialkyl complex based on bulky phosphazene ligand and trialkylaluminum, which might shed new light on the formation process of active species in organoaluminum-dependent Ziegler–Natta catalytic systems.