Hierarchical Assembly of Helicate-Type Dinuclear Titanium(IV) Complexes
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- 作者：Markus Albrecht ; Sebastian Mirtschin ; Marita de Groot ; Ingo Janser ; Jan Runsink ; Gerhard Raabe ; Michael Kogej ; Christoph A. Schalley ; and Roland Frö ; hlich
- 刊名：Journal of the American Chemical Society
- 出版年：2005
- 出版时间：July 27, 2005
- 年：2005
- 卷：127
- 期：29
- 页码：10371 - 10387
- 全文大小：444K
- 年卷期：v.127,no.29(July 27, 2005)
- ISSN：1520-5126
文摘
The ligands 4-7-H2 were used in coordination studies with titanium(IV) and gallium(III) ions toobtain dimeric complexes Li4[(4-7)6Ti2] and Li6[(4/5a)6Ga2]. The X-ray crystal structures of Li4[(4)6Ti2],Li4[(5b)6Ti2], and Li4[(7a)6Ti2] could be obtained. While these complexes are triply lithium-bridged dimers inthe solid state, a monomer/dimer equilibrium is observed in solution by NMR spectroscopy and ESI FT-ICR MS. The stability of the dimer is enhanced by high negative charges (Ti(IV) versus Ga(III)) of themonomers, when the carbonyl units are good donors (aldehydes versus ketones and esters), when thesolvent does not efficiently solvate the bridging lithium ions (DMSO versus acetone), and when stericalhindrance is minimized (methyl versus primary and secondary carbon substituents). The dimer isthermodynamically favored by enthalpy as well as entropy. ESI FT-ICR mass spectrometry provides detailedinsight into the mechanisms with which monomeric triscatecholate complexes as well as single catecholligands exchange in the dimers. Tandem mass spectrometric experiments in the gas phase show the dimersto decompose either in a symmetric (Ti) or in an unsymmetric (Ga) fashion when collisionally activated.The differences between the Ti and Ga complexes can be attributed to different electronic properties anda charge-controlled reactivity of the ions in the gas phase. The complexes represent an excellent examplefor hierarchical self-assembly, in which two different noncovalent interactions of well balanced strengthsbring together eleven individual components into one well-defined aggregate.