Stereoselective Formation of Seven-Coordinate Titanium(IV) Monomer and Dimer Complexes of Ethylenebis(o-hydroxyphenyl)glycine
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- 作者：Maolin Guo ; Hongzhe Sun ; Shailja Bihari ; John A. Parkinson ; Robert O. Gould ; Simon Parsons ; and Peter J. Sadler
- 刊名：Inorganic Chemistry
- 出版年：2000
- 出版时间：January 24, 2000
- 年：2000
- 卷：39
- 期：2
- 页码：206 - 215
- 全文大小：142K
- 年卷期：v.39,no.2(January 24, 2000)
- ISSN：1520-510X
文摘
Reactions between the antitumor agent titanocene dichloride (Cp2TiCl2) and the hexadentate ligand N,N'-ethylenebis(o-hydroxyphenylglycine) (H4ehpg) have been investigated in aqueous solution and the solid state. The racemicligands give crystals of the monomer [Ti(ehpg)(H2O)]·(11/3)H2O (1), while the meso ligand gives the oxo-bridgeddimer [{Ti(Hehpg)(H2O)}2O]·13H2O (2). Complex 1 crystallizes in the monoclinic space group C2/c with a =24.149(4) Å, b = 14.143(3) Å, c = 19.487(3) Å, 
= 105.371(13)
, V = 6417.7(19) Å3, Z = 12, and R(F) =0.0499 for 4428 independent reflections having I > 2
(I), and contains seven-coordinate pentagonal-bipyramidalTiIV with two axial phenolate ligands (Ti-O, 1.869(2) Å). The pentagonal plane contains the two N-atoms at2.210(2) Å, two carboxylate O-atoms at 2.061(2) Å, and a water molecule (Ti-OH2, 2.091(3) Å). Complex 2crystallizes as an oxygen-bridged dimer in the triclinic space group P-1 with a = 12.521(6) Å, b = 14.085(7) Å,c = 16.635(8) Å, 
= 80.93(2), = 69.23(2), 
= 64.33(2), V = 2472(2) Å3, Z = 4, and R(F) = 0.0580 for5956 independent reflections having I > 2(I). Each seven-coordinate, pentagonal-bipyramidal TiIV has a bridgingoxide and a phenolate as axial ligands. The pentagonal plane donors are H2O, two carboxylate O-atoms, and twoNH groups, which form H-bonds to O-atoms both in the same half-molecule (O···N, 2.93-3.13 Å) and in theother half-molecule (O···N, 2.73-2.75 Å); the second phenoxyl group of each Hehpg ligand is protonated andnot coordinated to TiIV, but H-bonds to a nearby amine proton (O···N, 2.73-2.75 Å) from the same ligand andto a nearby H2O (O···O, 2.68 Å). In contrast to all previously reported crystalline metal-EHPG complexescontaining racemic ligands, in which the N(S,S)C(R,R) or N(R,R)C(S,S) form is present, complex 1 unexpectedlycontains the N(S,S)C(S,S) and N(R,R)C(R,R) forms. This is attributed to the presence of ring strain in seven-coordinate TiIV complexes. Moreover, the rac ligands selectively form crystals of monomeric 1, while the mesoligand selectively forms crystals of the dimer 2 (N(R,R)C(R,S) or N(S,S)C(S,R)). Complexes 1 and 2 exhibitphenolate-to-TiIV charge-transfer bands near 387 nm, and 2D NMR studies indicate that the structures of 1 and2 in solution are similar to those in the solid state. Complex 1 is stable over the pH range 1.0-7.0, while 2 isstable only between pH 2.5 and pH 5.5. Cp2TiCl2 reacts with EHPG at pH* 7.0 to give complex 1 with a t1/2 ofca. 50 min (298 K), but complex 2 was not formed at this pH* value. At pH* 3.7, the reaction is very slow: 1forms with a half-life of ca. 2.5 d, and 2 after ca. 1 week at ambient temperature. The relevance of these data tothe possible role of serum transferrin as a mediator for the delivery of TiIV to tumor cells is discussed.
= 105.371(13), V = 6417.7(19) Å3, Z = 12, and R(F) =0.0499 for 4428 independent reflections having I > 2(I), and contains seven-coordinate pentagonal-bipyramidalTiIV with two axial phenolate ligands (Ti-O, 1.869(2) Å). The pentagonal plane contains the two N-atoms at2.210(2) Å, two carboxylate O-atoms at 2.061(2) Å, and a water molecule (Ti-OH2, 2.091(3) Å). Complex 2crystallizes as an oxygen-bridged dimer in the triclinic space group P-1 with a = 12.521(6) Å, b = 14.085(7) Å,c = 16.635(8) Å, = 80.93(2), = 69.23(2), = 64.33(2), V = 2472(2) Å3, Z = 4, and R(F) = 0.0580 for5956 independent reflections having I > 2(I). Each seven-coordinate, pentagonal-bipyramidal TiIV has a bridgingoxide and a phenolate as axial ligands. The pentagonal plane donors are H2O, two carboxylate O-atoms, and twoNH groups, which form H-bonds to O-atoms both in the same half-molecule (O···N, 2.93-3.13 Å) and in theother half-molecule (O···N, 2.73-2.75 Å); the second phenoxyl group of each Hehpg ligand is protonated andnot coordinated to TiIV, but H-bonds to a nearby amine proton (O···N, 2.73-2.75 Å) from the same ligand andto a nearby H2O (O···O, 2.68 Å). In contrast to all previously reported crystalline metal-EHPG complexescontaining racemic ligands, in which the N(S,S)C(R,R) or N(R,R)C(S,S) form is present, complex 1 unexpectedlycontains the N(S,S)C(S,S) and N(R,R)C(R,R) forms. This is attributed to the presence of ring strain in seven-coordinate TiIV complexes. Moreover, the rac ligands selectively form crystals of monomeric 1, while the mesoligand selectively forms crystals of the dimer 2 (N(R,R)C(R,S) or N(S,S)C(S,R)). Complexes 1 and 2 exhibitphenolate-to-TiIV charge-transfer bands near 387 nm, and 2D NMR studies indicate that the structures of 1 and2 in solution are similar to those in the solid state. Complex 1 is stable over the pH range 1.0-7.0, while 2 isstable only between pH 2.5 and pH 5.5. Cp2TiCl2 reacts with EHPG at pH* 7.0 to give complex 1 with a t1/2 ofca. 50 min (298 K), but complex 2 was not formed at this pH* value. At pH* 3.7, the reaction is very slow: 1forms with a half-life of ca. 2.5 d, and 2 after ca. 1 week at ambient temperature. The relevance of these data tothe possible role of serum transferrin as a mediator for the delivery of TiIV to tumor cells is discussed.