Cationic Thorium Alkyl Complexes of Rigid NON- and NNN-Donor Ligands: π-Arene Coordination as a Persistent Structural Motif
作者:Carlos A. Cruz、David J. H. Emslie、Craig M. Robertson、Laura E. Harrington、Hilary A. Jenkins、James F. Britten
DOI:10.1021/om800624t
日期:2009.3.23
Reaction of the neutral dialkyl complex [(XA(2))Th(CH2SiMe3)(2)] 1; XA(2) = 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene} with [CPh3][B(C6F5)(4)] in benzene or toluene at room temperature resulted in the formation of [(XA(2))Th(CH2SiMe3)(eta(6)-arene)][B(C6F5)(4)] arene = C6H6 (5) and toluene (5B)}, which were characterized by H-1, C-13, and 2D NMR spectroscopy and by X-ray crystallography (for 5). In close analogy, reaction of [(XA(2))Th(CH2Ph)(2)] (3) with [CPh3][B(C6F5)(4)] in toluene at room temperature resulted in the formation of 1 equiv of Ph3CCH2R (R = Ph) and precipitation of an insoluble orange-brown oil, which upon layering with hexanes yielded crystals of [(XA(2))Th(eta(2)-CH2Ph)(eta(6)- C6H5Me)][B(C6F5)(4)] (6). NMR investigation of the reactions of 1 and 3 with substoichiometric amounts of [CPh3][B(C6F5)(4)] provided no evidence for dinuclear monocation formation. By contrast, reaction of [(BDPP)Th(CH2Ph)(2)] 4; BDPP = 2,6-bis(2,6-diisopropylanilidomethyl)pyridine) with 0.5 equiv of [CPh3][B(C6F5)(4)] resulted in the precipitation of an insoluble oil containing a mixture of a mononuclear and a dinuclear cation; the dinuclear cation was identified as [(BDPP)Th(eta(2)-CH2Ph)(mu-eta(1): eta(6)-CH2Ph)Th(eta(1)-CH2Ph)(BDPP)[B(C6F5)(4)] (7) by X-ray crystallography. Reaction of complex 3 with B(C6F5)(3) resulted in the formation of [(XA(2))Th(eta(1)-CH2Ph)] [eta(6)-PhCH2B(C6F5)(3)] (9), which was characterized in solution by NMR spectroscopy. Complexes 5, 5B, and 6 are rare examples of arene solvent-separated ion pairs, complex 9 exists as a tight contact ion pair, and dinuclear 7 exhibits a unique benzyl ligand bridging mode. The structures of cations 5-7 and 9 highlight a pronounced tendency for these systems to engage in arene pi-coordination.