Helical Oxidovanadium(IV) Salen‐Type Complexes: Synthesis, Characterisation and Catalytic Behaviour

Abstract

Chiral [VO(salen)] complexes (R,R)‐7 and (R,R)‐8 were synthesised by ligand replacement from [VO(acac)2] with the resolved (1R,2R)‐cyclohexyl ligands 3,3′‐[(1R,2R)‐1,2‐cyclohexane‐diylbis(nitrilomethylidyne)]bis‐4‐phenanthrenol [(R,R)‐3] and 3,3′‐[(1R,2R)‐1,2‐cyclohexanediylbis(nitrilomethylidyne)]bisbenz[a]anthracen‐1‐ol [(R,R)‐4], respectively. Similarly, complexes (R)‐9 and (R)‐10 were synthesised using the (R)‐binaphthyl ligands 3,3′‐[(1R)‐(1,1′‐binaphthalene)‐2,2′‐diylbis(nitrilomethylidyne)]bis‐4‐phenanthrenol [(R)‐5] and 3,3′‐[(1R)‐(1,1′‐binaphthalene)‐2,2′‐diylbis(nitrilomethylidyne)]bis‐benz[a]anthracen‐1‐ol [(R)‐6], respectively. These complexes were characterised by IR spectroscopy, ESI‐TOF‐MS, electronic absorption spectroscopy and circular dichroism (CD). Single crystal X‐ray analysis of (R,R)‐7 and (R,R)‐8 revealed distorted square pyramidal geometries and a 1:1 ratio of diastereomeric M and P helical conformers. Solution CD studies in THF combined with DFT calculations indicate that the M conformer dominates in solution for (R,R)‐7. Preliminary catalytic oxidation of thioanisole with H2O2 and 1 % [VO(salen)] showed good selectivity for sulfoxides over sulfones but low enantioselectivities (8 to 33 %) which are solvent dependent but insensitive to the catalyst used.

Assemblies of salen-type oxidovanadium(iv) complexes: substituent effects and in vitro protein tyrosine phosphatase inhibition

“…catalysis and molecular sensing. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] Vanadium is a very important transition metal in biological systems due to its ability to exist at different oxidation states and its affinity to oxygen. 16 Salen type oxidovanadium complexes were found to exhibit insulin-mimetic and proteintyrosine phosphatase (PTP) inhibiting behavior.…”

Dynamic Helicity Control of Oligo(salamo)-Based Metal Helicates

“…In particular, the 1,2-disubstituted ethylene bridge in the chiral salen unit facilitated the synthesis of dynamic helical structures in which the preferred helicity is rationally predicted from the structure of the organic framework. In addition to the oligo(salamo) helical structures reported in this article, there have already been a number of reports on various kinds of helical structures based on the monomeric [31][32][33][34][35][36][37][38][39][40][41], dimeric [42,43] and polymeric [44][45][46] salen-type ligands, as well as the tris(saloph) triple-helical cages [93,94] and single-helix with different types of donor sets [90,[95][96][97]. It has already been demonstrated that the oligo(salamo) helical complexes show unique physical properties and reactivities [98][99][100][101], and the dynamic helicity control would be useful for switching of the chiroptical properties of the helical structures.…”

“…As one of the possible candidates of dynamic helical complexes, we designed metal complexes having a series of acyclic oligo(salen)-type ligands (H 2 salen = N,N'-disalicylideneethylenediamine) ( Figure 5a) [25][26][27][28][29][30], while there are several types of related helical structures based on monomeric [31][32][33][34][35][36][37][38][39][40][41], dimeric [42,43] and polymeric [44][45][46] salen-type ligands. We employed salamo derivatives, the oxime analog of salen, as the constituent of the oligomers (H 2 salamo = 1,2-bis(salicylideneaminooxy)ethane) [47,48].…”

Catalytic Applications of Vanadium: A Mechanistic Perspective

“…New reports of catalysts containing salen, salan, and salophen ligands were also found. − Nonradical mechanisms similar to that in Scheme are proposed in these systems as well . Vanadium thiolate compounds containing SNS ([VO 2 L NS2 ]­[HNEt 3 ], where L NS2 = 2,2′-(pyridine-2,6-diyl)­bis­(1,1′-diphenylethanethiolate)) and SNNS (VOL N2S2 , where L N2S2 = 2,2′-(2,2′-bipyridine-6,6′-diyl)­bis­(1,1′-diphenylethanethiolate)) binding modes were also shown to be active for this transformation and are proposed to proceed via a nonradical mechanism .…”