1259031-29-2Relevant academic research and scientific papers
Activation of an aryl C-H bond converts chelating diphenolate ligands bound to zirconium into trianionic pincer ligands: σ-Donor ligand effects versus thermolysis
Kuppuswamy, Subramaniam,Ghiviriga, Ion,Abboud, Khalil A.,Veige, Adam S.
, p. 6711 - 6722 (2011/03/16)
This report describes the synthesis and characterization of new zirconium benzyl complexes supported by a trianionic pincer ligand. Treating Zr(CH 2Ph)4 with the terphenyldiol [tBuOCO]H 3 (1) in benzene affords [tBuOCHO]Zr(CH 2Ph)2 (2). Thermolysis of 2 leads to formation of dinuclear {[tBuOCO]ZrCH2Ph}2 (3), which contains a five-coordinate zirconium center in a trigonal-bipyramidal (tbp) geometry. Adding 2 equiv of PMe3 to 2 affords [tBuOCO] ZrCH2Ph(PMe3)2 (4-PMe3). X-ray crystallographic analysis reveals strong agostic interactions for the benzyl ligand in both 3 and 4-PMe3. Treatment of 2 with 2 equiv of THF results in hydrocarbon-soluble [tBuOCO]ZrCH2Ph(THF) 2 (5). NMR spectroscopic measurements indicate a C 2v-symmetric molecule that is isostructural with 4-PMe3. Addition of the larger phosphine PMe2Ph to 2 provides the corresponding mono-PMe2Ph complex in solution, but a small amount of the bis-diphenolate [tBuOCHO]2Zr (6) also forms. Complex 6 was independently synthesized by treating Zr(CH2Ph)4 with 2 equiv of 1. When 2 equiv of pyridine (py) is added to 2, the intermediate [tBuOCHO]ZrCH2Ph(η2-C5H 4N)py (7) results from pyridine o-C-H bond activation. After 48 h, complex 7 releases another 1 equiv of toluene by activation of the pincer C ipso-H bond to produce the trianionic pincer complex [ tBuOCO]Zr(η2-C5H4N)(py) 2 (8). Multinuclear and 2D NMR spectroscopic experiments and combustion analysis support the molecular assignment of 8. Addition of α-picoline to 2 provides different results compared to py. Initially, the α-picoline adduct [tBuOCHO]Zr(CH2Ph) 2(α-picoline) (9) forms. Addition of another 1 equiv of α-picoline provides the mixed η2(N,C)-6-Me-pyridyl)/ η2(N,C-CH2)-pyrid-2-yl complex [tBuOCHO] Zr(η2(N,C)-6-Me-pyridyl)(η2(N,C-CH 2)-pyrid-2-yl) (10).
