title: Biphenolate phosphine complexes of tantalum.
abstract: The preparation and structural characterization of tantalum complexes supported by 2,2'-phenylphosphino-bis(4,6-di-tert-butylphenolate) ([OPO](2-)) are described. The reaction of Li(2)[OPO] with TaCl(5), regardless of the molar ratio employed, in diethyl ether at -35 degrees C led to high-yield isolation of yellow crystalline [OPO](2)TaCl. Alkylation of [OPO](2)TaCl with MeMgBr or EtMgCl in diethyl ether at -35 degrees C generated the corresponding alkyl complexes [OPO](2)TaR (R = Me, Et). Thermolysis of [OPO](2)TaEt in benzene led to quantitative formation of [OPO](2)TaH, which could also be prepared by treatment of [OPO](2)TaCl with LiHBEt(3) in diethyl ether at -35 degrees C. Hydrolysis of [OPO](2)TaCl or [OPO](2)TaR (R = H, Me, Et) generated [OPO](2)TaOH. The reaction of [OPO](2)TaOH with Me(3)SiCl in diethyl ether at room temperature afforded quantitatively [OPO](2)TaCl. The solution structures of these complexes were all characterized by multinuclear NMR spectroscopy. The solid-state structures of [OPO](2)TaCl, [OPO](2)TaH, and [OPO](2)TaOH were determined by X-ray crystallography. The spectroscopic and crystallographic data are all indicative of the coordination of both phosphorus donors to tantalum in these 7-coordinate complexes. Interestingly, the structure of [OPO](2)TaH is markedly different from those of [OPO](2)TaX (X = Cl, OH, Me, Et) on the basis of NMR and X-ray studies. Density functional theory computations reveal that the hydride structure found by X-ray crystallography is lower in energy by about 7 kcal/mol than that analogous to the established X-ray structures of [OPO](2)TaCl and [OPO](2)TaOH.
authors.affiliation: Department of Chemistry and Center for Nanoscience & Nanotechnology, National Sun Yat-sen University, Kaohsiung 80424, Taiwan. lcliang@mail.nsysu.edu.tw
authors.forename: Lan-Chang
authors.initials: LC
authors.lastname: Liang
authors.forename: Liang-Chien
authors.initials: LC
authors.lastname: Cheng
authors.forename: Tzung-Ling
authors.initials: TL
authors.lastname: Tsai
authors.forename: Ching-Han
authors.initials: CH
authors.lastname: Hu
authors.forename: Wen-Hsin
authors.initials: WH
authors.lastname: Guo