Pyridinethiolate Titanocene Metalloligands and Their Self-Assembly Reactions To Yield Early–Late Metallamacrocycles

New titanocene pyridinethiolate compounds [(RCp)2Ti­(4-Spy)2] (R = H (1), Me (2); Cp = cyclopentadienyl; 4-Spy = pyridine-4-thiolate) and [Cp2Ti­(2-Spy)2] (3; 2-Spy = pyridine-2-thiolate) have been prepared by reaction of the corresponding Li­(Spy) salt with the appropriate compound [(RCp)2TiCl2]. Compounds 1 and 2 have been used as metalloligands in self-assembly reactions with the acceptor late-transition-metal compounds [M­(H2O)2(dppp)]­(OTf)2 (M = Pd (a) Pt (b); dppp = 1,3-bis­(diphenylphosphino)­propane), and the series of early–late tetranuclear metallamacrocycles [{(RCp)2Ti­(4-Spy)2}­{M­(dppp)}]2(OTf)4 (R = H, M = Pd (12a2); R = H, M = Pt (12b2); R = Me, M = Pd (22a2); R = Me, M = Pt (22b2)) arising from the anti isomer of the titanocene metalloligands have been obtained. Only ligand transfer reactions from Ti to either Pd or Pt atoms have been observed when the pyridine-2-thiolate derivative 3 has been assayed in self-assembly processes. The obtained species have been characterized by NMR spectroscopy and ESI­(+) mass spectrometry. The supramolecular assemblies have shown to be nonrigid in solution, and their fluxional behavior has been studied by VT 1H NMR spectroscopy. A DFT study including ab initio molecular dynamics in order to elucidate the structures and the relative stability of the isomers has been performed.

本研究合成了一系列吡啶硫醇盐二茂钛（titanocene）类化合物[(RCp)₂Ti(4-Spy)₂]（R = H（1）、Me（2）；Cp = 环戊二烯基（cyclopentadienyl）；4-Spy = 4-吡啶硫醇盐（pyridine-4-thiolate））与[Cp₂Ti(2-Spy)₂]（3；2-Spy = 2-吡啶硫醇盐（pyridine-2-thiolate）），合成方法为将相应的吡啶硫醇锂盐（Li(Spy)）与合适的[(RCp)₂TiCl₂]类化合物进行反应。以化合物1和2作为金属配体（metalloligand），与受体型后过渡金属化合物[M(H₂O)₂(dppp)](OTf)₂（M = Pd（a）、Pt（b）；dppp = 1,3-双(二苯基膦)丙烷（1,3-bis(diphenylphosphino)propane)）进行自组装（self-assembly）反应，得到了一系列由二茂钛金属配体反式异构体（anti isomer）形成的早-后过渡金属四核金属大环[{(RCp)₂Ti(4-Spy)₂}{M(dppp)}]₂(OTf)₄（R = H、M = Pd（12a2）；R = H、M = Pt（12b2）；R = Me、M = Pd（22a2）；R = Me、M = Pt（22b2））。当以2-吡啶硫醇盐衍生物3进行自组装实验时，仅观察到钛向钯或铂原子的配体转移反应。通过核磁共振波谱法（NMR spectroscopy）与电喷雾正离子模式质谱法（ESI(+) mass spectrometry）对所得产物进行了结构表征。该超分子组装体在溶液中呈现非刚性结构，通过变温氢核磁共振谱（VT ¹H NMR spectroscopy）研究了其流变行为。为阐明各异构体的结构与相对稳定性，本研究开展了包含从头算分子动力学（ab initio molecular dynamics）的密度泛函理论（DFT）计算研究。