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Article: Stereoselective formation of seven-coordinate titanium(IV) monomer and dimer complexes of ethylenebis(o-hydroxyphenyl)glycine

TitleStereoselective formation of seven-coordinate titanium(IV) monomer and dimer complexes of ethylenebis(o-hydroxyphenyl)glycine
Authors
Issue Date2000
PublisherAmerican Chemical Society. The Journal's web site is located at http://pubs.acs.org/ic
Citation
Inorganic Chemistry, 2000, v. 39 n. 2, p. 206-215 How to Cite?
AbstractReactions between the antitumor agent titanocene dichloride (Cp 2TiCl 2) and the hexadentate ligand N,N'-ethylenebis-(o-hydroxyphenylglycine) (H 4ehpg) have been investigated in aqueous solution and the solid state. The racemic ligands give crystals of the monomer [Ti(ehpg)(H 2O)]·(11/3)H 2O (1), while the meso ligand gives the oxo-bridged dimer [{Ti(Hehpg)(H 2O)} 2O]·13H 2O (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, β = 105.371(13)°, V = 6417.7(19) Å 3, Z = 12, and R(F) 0.0499 for 4428 independent reflections having I > 2σ(I), and contains seven-coordinate pentagonal-bipyramidal Ti(IV) with two axial phenolate ligands (Ti-O, 1.869(2) Å). The pentagonal plane contains the two N-atoms at 2.210(2) Å, two carboxylate O-atoms at 2.061(2) Å, and a water molecule (Ti-OH 2, 2.091(3) Å). Complex 2 crystallizes 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, α = 80.93(2)°, β = 69.23(2)°, γ = 64.33(2)°, V = 2472(2) Å 3, Z = 4, and R(F) = 0.0580 for 5956 independent reflections having I > 2σ(I). Each seven-coordinate, pentagonal-bipyramidal Ti(IV) has a bridging oxide and a phenolate as axial ligands. The pentagonal plane donors are H 2O, two carboxylate O-atoms, and two NH groups, which form H-bonds to O-atoms both in the same half-molecule (O···N, 2.93-3.13 Å) and in the other half-molecule (O···N, 2.73-2.75 Å); the second phenoxyl group of each Hehpg ligand is protonated and not coordinated to Ti(IV), but H-bonds to a nearby amine proton (O···N, 2.73-2.75 Å) from the same ligand and to a nearby, H 2O (O···O, 2.68 Å). In contrast to all previously reported crystalline metal-EHPG complexes containing racemic ligands, in which the N(S,S)C(R,R) or N(R,R)C(S,S) form is present, complex 1 unexpectedly contains 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 Ti(IV) complexes. Moreover, the rac ligands selectively form crystals of monomeric 1, while the meso ligand selectively forms crystals of the dimer 2 (N(R,R)C(R,S) or N(S,S)C(S,R)). Complexes 1 and 2 exhibit phenolate-to-Ti(IV) charge-transfer bands near 387 nm, and 2D NMR studies indicate that the structures of 1 and 2 in solution are similar to those in the solid state. Complex 1 is stable over the pH range 1.0-7.0, while 2 is stable only between pH 2.5 and pH 5.5. Cp 2TiCl 2 reacts with EHPG at pH* 7.0 to give complex 1 with a t 1/2 of ca. 50 min (298 K), but complex 2 was not formed at this pH* value. At pH* 3.7, the reaction is very slow: 1 forms with a half-life of ca. 2.5 d, and 2 after ca. 1 week at ambient temperature. The relevance of these data to the possible role of serum transferrin as a mediator for the delivery of Ti(IV) to tumor cells is discussed.
Persistent Identifierhttp://hdl.handle.net/10722/69803
ISSN
2015 Impact Factor: 4.82
2015 SCImago Journal Rankings: 1.873
ISI Accession Number ID
References

 

DC FieldValueLanguage
dc.contributor.authorGuo, Men_HK
dc.contributor.authorSun, Hen_HK
dc.contributor.authorBihari, Sen_HK
dc.contributor.authorParkinson, JAen_HK
dc.contributor.authorGould, ROen_HK
dc.contributor.authorParsons, Sen_HK
dc.contributor.authorSadler, PJen_HK
dc.date.accessioned2010-09-06T06:16:59Z-
dc.date.available2010-09-06T06:16:59Z-
dc.date.issued2000en_HK
dc.identifier.citationInorganic Chemistry, 2000, v. 39 n. 2, p. 206-215en_HK
dc.identifier.issn0020-1669en_HK
dc.identifier.urihttp://hdl.handle.net/10722/69803-
dc.description.abstractReactions between the antitumor agent titanocene dichloride (Cp 2TiCl 2) and the hexadentate ligand N,N'-ethylenebis-(o-hydroxyphenylglycine) (H 4ehpg) have been investigated in aqueous solution and the solid state. The racemic ligands give crystals of the monomer [Ti(ehpg)(H 2O)]·(11/3)H 2O (1), while the meso ligand gives the oxo-bridged dimer [{Ti(Hehpg)(H 2O)} 2O]·13H 2O (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, β = 105.371(13)°, V = 6417.7(19) Å 3, Z = 12, and R(F) 0.0499 for 4428 independent reflections having I > 2σ(I), and contains seven-coordinate pentagonal-bipyramidal Ti(IV) with two axial phenolate ligands (Ti-O, 1.869(2) Å). The pentagonal plane contains the two N-atoms at 2.210(2) Å, two carboxylate O-atoms at 2.061(2) Å, and a water molecule (Ti-OH 2, 2.091(3) Å). Complex 2 crystallizes 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, α = 80.93(2)°, β = 69.23(2)°, γ = 64.33(2)°, V = 2472(2) Å 3, Z = 4, and R(F) = 0.0580 for 5956 independent reflections having I > 2σ(I). Each seven-coordinate, pentagonal-bipyramidal Ti(IV) has a bridging oxide and a phenolate as axial ligands. The pentagonal plane donors are H 2O, two carboxylate O-atoms, and two NH groups, which form H-bonds to O-atoms both in the same half-molecule (O···N, 2.93-3.13 Å) and in the other half-molecule (O···N, 2.73-2.75 Å); the second phenoxyl group of each Hehpg ligand is protonated and not coordinated to Ti(IV), but H-bonds to a nearby amine proton (O···N, 2.73-2.75 Å) from the same ligand and to a nearby, H 2O (O···O, 2.68 Å). In contrast to all previously reported crystalline metal-EHPG complexes containing racemic ligands, in which the N(S,S)C(R,R) or N(R,R)C(S,S) form is present, complex 1 unexpectedly contains 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 Ti(IV) complexes. Moreover, the rac ligands selectively form crystals of monomeric 1, while the meso ligand selectively forms crystals of the dimer 2 (N(R,R)C(R,S) or N(S,S)C(S,R)). Complexes 1 and 2 exhibit phenolate-to-Ti(IV) charge-transfer bands near 387 nm, and 2D NMR studies indicate that the structures of 1 and 2 in solution are similar to those in the solid state. Complex 1 is stable over the pH range 1.0-7.0, while 2 is stable only between pH 2.5 and pH 5.5. Cp 2TiCl 2 reacts with EHPG at pH* 7.0 to give complex 1 with a t 1/2 of ca. 50 min (298 K), but complex 2 was not formed at this pH* value. At pH* 3.7, the reaction is very slow: 1 forms with a half-life of ca. 2.5 d, and 2 after ca. 1 week at ambient temperature. The relevance of these data to the possible role of serum transferrin as a mediator for the delivery of Ti(IV) to tumor cells is discussed.en_HK
dc.languageengen_HK
dc.publisherAmerican Chemical Society. The Journal's web site is located at http://pubs.acs.org/icen_HK
dc.relation.ispartofInorganic Chemistryen_HK
dc.titleStereoselective formation of seven-coordinate titanium(IV) monomer and dimer complexes of ethylenebis(o-hydroxyphenyl)glycineen_HK
dc.typeArticleen_HK
dc.identifier.openurlhttp://library.hku.hk:4550/resserv?sid=HKU:IR&issn=0020-1669&volume=39&spage=206&epage=215&date=2000&atitle=Stereoselective+formation+of+seven-coordinate+titanium(IV)+monomer+and+dimer+complexes+of+ethylenebis(o-hydroxyphenyl)glycineen_HK
dc.identifier.emailSun, H:hsun@hkucc.hku.hken_HK
dc.identifier.authoritySun, H=rp00777en_HK
dc.description.naturelink_to_subscribed_fulltext-
dc.identifier.doi10.1021/ic990669aen_HK
dc.identifier.pmid11272527-
dc.identifier.scopuseid_2-s2.0-0034707525en_HK
dc.identifier.hkuros53575en_HK
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-0034707525&selection=ref&src=s&origin=recordpageen_HK
dc.identifier.volume39en_HK
dc.identifier.issue2en_HK
dc.identifier.spage206en_HK
dc.identifier.epage215en_HK
dc.identifier.isiWOS:000085010500009-
dc.publisher.placeUnited Statesen_HK
dc.identifier.scopusauthoridGuo, M=7201564747en_HK
dc.identifier.scopusauthoridSun, H=7404827446en_HK
dc.identifier.scopusauthoridBihari, S=6507257944en_HK
dc.identifier.scopusauthoridParkinson, JA=54402144900en_HK
dc.identifier.scopusauthoridGould, RO=7201353942en_HK
dc.identifier.scopusauthoridParsons, S=7202703236en_HK
dc.identifier.scopusauthoridSadler, PJ=7103024488en_HK

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