A Remarkable Solvent Effect on the Nuclearity of Neutral Titanium(IV)‐Based Helicate Assemblies

Abstract

The spontaneous self-assembly of a neutral circular trinuclear Ti(IV) -based helicate is described through the reaction of titanium(IV) isopropoxide with a rationally designed tetraphenolic ligand. The trimeric ring helicate was obtained after diffusion of n-pentane into a solution with dichloromethane. The circular helicate has been characterized by using single-crystal X-ray diffraction study, (13) C CP-MAS NMR and (1) H NMR DOSY solution spectroscopic, and positive electrospray ionization mass-spectrometric analysis. These analytical data were compared with those obtained from a previously reported double-stranded helicate that crystallizes in toluene. The trimeric ring was unstable in a pure solution with dichloromethane and transformed into the double-stranded helicate. Thermodynamic analysis by means of the PACHA software revealed that formation of the double-stranded helicates was characterized by ΔH(toluene)=-30 kJ mol(-1) and ΔS(toluene)=+357 J K(-1) mol(-1) , whereas these values were ΔH(CH2 Cl2 )=-75 kJ mol(-1) and ΔS(CH2 Cl2 )=-37 J K(-1) mol(-1) for the ring helicate. The transformation of the ring helicate into the double-stranded helicate was a strongly endothermic process characterized by ΔH(CH2 Cl2 )=+127 kJ mol(-1) and ΔH(n-pentane)=+644 kJ mol(-1) associated with a large positive entropy change ΔS=+1115 J K(-1) ⋅mol(-1) . Consequently, the instability of the ring helicate in pure dichloromethane was attributed to the rather high dielectric constant and dipole moment of dichloromethane relative to n-pentane. Suggestions for increasing the stability of the ring helicate are given.

A Bowl‐Shaped Circular Trinuclear Helicate Generated from a TiO4N2 Motif by a Multicomponent Self‐Assembly Approach

“…The selection of these building blocks to pre‐program the formation of a helicate‐type structure was motivated by the following facts: 1) It has been shown that the pro‐ligand LH 4 in presence of [Ti(O i Pr) 4 ] generates either a double‐stranded dinuclear helicate or a circular trinuclear helicate ([Ti 3 (L) 3 (HO i Pr) 6 ]) in solid‐state depending on the solvent medium used to isolate the species. Interestingly, the spontaneous rearrangement of the circular species into double‐stranded architecture was observed in solution 9. 2) A novel family of heteroleptic monomeric octahedral TiO 4 N 2 complexes with well‐defined geometries was recently developed: these complexes incorporate two phenyl‐substituted biphenolate ligands and one nitrogenated bidentate chelate 10.…”

“…[15] This observation definitively confirms the structural stability of the complex in solution, whereas for the recently reported [Ti 3 (L) 3 (HOiPr) 6 ] helicate, a spontaneous transformation into a dinuclear helicate was characterized upon dissolution. [9] The bowl shape of [Ti 3 (L) 3 (bpym) 3 ] explains the four doublet of doublets resonance of the bpym proton Ha a , Ha b , Ha c , Ha d as observed in the 1 H NMR spectrum (Figure 3 B). By 1 H NMR spectroscopy, we also notice the absence of interaction between the toluene molecules and the helicate in solution, probably owing to the replacement of toluene by more polar chloroform molecules.…”

“…The selection of these building blocks to pre-program the formation of a helicate-type structure was motivated by the following facts: 1) It has been shown that the pro-ligand LH 4 observed in solution. [9] 2) A novel family of heteroleptic monomeric octahedral TiO 4 N 2 complexes with well-defined geometries was recently developed: these complexes incorporate two phenyl-substituted biphenolate ligands and one nitrogenated bidentate chelate. [10] By taking into account these information highlighted by these preliminary studies, the formation of a circular helicate constructed from a TiO 4 N 2 motif was tested if an equimolar ratio of [Ti(OiPr) 4 ]/LH 4 /bpym was used as presented in Equation (1).…”

Progress in Helicates Directed by Metal Coordination

“…而 61 与 Ti 4＋ 配位后在二氯甲烷与正戊烷中扩散则形成三 核的环状螺旋结构, Ti 4＋ 分别与两个配体分子上的四个 酚基 O 原子及两个异丙氧基形成八面体型配位. 此外, 在二氯甲烷溶液中环状螺旋结构还可以转化为双核的 双螺旋结构 [108] . 61 还可以与半径更大的 Zr 4＋ 络合, 在乙 醚及二氯甲烷溶液中形成四核的三螺旋结构 [110] .…”

Mono- and di-anionic coordination modes of arylazosalicylates in their bis(η5-cyclopentadienyl)titanium(IV) complexes: Syntheses and crystal structures

“…Organometallic and coordination titanium(IV) compounds are of interest due to their reactivity and uses including as reagents for catalytic enantioselective processes [1], organic transformations [2], as initiators for polymerization reactions [3], polymerisation catalysts [4][5][6][7][8][9][10] to metal organic frameworks [11][12][13] and metallo-supramolecular chemistry [14][15][16][17][18][19]. Other applications include the use of alkoxides or aryloxides precursors for the generation of titaniumbased materials [20][21][22][23][24][25][26] and their uses as photo-sensitisers and photo-catalysts [27,28], titaniumbased drugs [29][30][31][32][33][34][35][36][37][38][39] and cell imaging [40][41].…”