Zinc complexes of TtzR,Me with O and S donors reveal differences between Tp and Ttz ligands: acid stability and binding to H or an additional metal (TtzR,Me = tris(3-R-5-methyl-1,2,4-triazolyl)borate; R = Ph, tBu)
Alkylzinc complexes, (TtzR,Me)ZnR′ (R = tBu, Ph; R′ = Me, Et), show interesting reactivity with acids, bases and water. With acids (e.g. fluorinated alcohols, phenols, thiophenol, acetylacetone, acetic acid, HCl and triflic acid) zinc complexes of the conjugate base (CB), (TtzR,Me)ZnCB, are generated. Thus the B–N bonds in Ttz ligands are acid stable. (TtzR,Me)ZnCB complexes were characterized by 1H, 13C-NMR, IR, MS, elemental analysis, and, in most cases, single crystal X-ray diffraction. The four coordinate crystal structures included (TtzR,Me)Zn(CB) [where R = Ph, CB (conjugate base) = OCH2CF3 (2), OPh (6), SPh (8), p-OC6H4(NO2) (10); R = tBu, CB = OCH(CF3)2 (3), OPh (5), SPh (7)*, p-OC6H4(NO2) (9) (* indicates a rearranged Ttz ligand)]. The use of bidentate ligands resulted in structures [(TtzPh,Me)Zn(CB) (CB = acac (12), OAc (14))] in which the coordination geometries are five, and intermediate between four and five, respectively. Interestingly, three forms of (TtzPh,Me)Zn(p-OC6H4(NO2)) (10) were analyzed crystallographically including a Zn coordinated water molecule in 10H2O, a coordination polymer in 10CP, and a p-nitrophenol molecule hydrogen bonded to a triazole ring in 10Nit. Ttz ligands are flexible since they are capable of providing κ3 or κ2metal binding and intermolecular interactions with either a metal center or H through the four position nitrogen (e.g. in 10CP and HTtztBu,Me·H2O, respectively). Preliminary kinetic studies on the protonolysis of LZnEt (L = TtztBu,Me, TptBu,Me) with p-nitrophenol in toluene at 95 °C show that these reactions are zero order in acid and first order in the LZnEt.
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