C3 Symmetrical ligands

Fig. 29 Extension of the face bridging, C3-symmetric ligand 44 that forms M4L4 tetrahedron 47. Introduction of rigid phenyl bridges in ligand 50 preserves the necessary rigidity to form tetrahedron 51 [154], whereas introduction of a flexible methylene bridge results in the formation of mononuclear M1L1 complex 52 [156]...

The second example of how a tetrahedron could be built demonstrates once again that four metal ions with the same requirements as in the first one are needed. However, in this case the six linear ligands are replaced by four C3 symmetric ligands (covering the faces) which can connect a metal at each comer. The resulting stmcture exhibits M4L4 topology. 

The group of M. Fujita synthesised coordination cages of this shape while reacting a triazin ligand (L16-L18) with different Pd2+ or Pt2+ compounds. Two of the coordination sites in the square planar environment of these metal atoms are blocked by a coligand, like ethylene diamine, A,A,/V, /V -tetramethylethylene diamine or 2,2 -bipyridine, while the other two sites are used for coordination bonds to the C3 symmetric ligand. In the resulting tetrahedra, compounds could be... 

In 1992, Nugent [12] reported a significant advance in the Lewis acid-promoted opening of meso epoxides (Scheme 2). A novel chiral zirconium complex catalyses epoxide opening with hindered silyl azides iii excellent ee. The catalyst is derived from zirconium tert-h xi-oxide and the tetradentate C3-symmetric ligand 1, available by combination of (5)-pro-pene oxide with (S)-l-aminopropan-2-ol. Al-... 

Matloka, K., Gelis, A., Regalbuto, M., Vandegriff, G., Scott, M. 2006. C3-symmetric tripodal thio/diglycolamide-based ligands for trivalent f-element separations. Sep. Sci. Technol. 41 (10) 2129-2146. 

La(L4)]3+ isomerisation process on the NMR time scale. Compared to the parent complexes [La(L3)3]3+ which display enantiotopic methylene protons for T > 233 K (see sect. 3.1.3), the introduction of the covalent TREN tripod in [La(L4)]3+ significantly slows down the helical interconversion process. Protonation of the apical nitrogen atom produces the C3-symmetrical podates [R(L4+H)]4+ which display only marginally faster racemisation processes. Although some steric constraints induced by the tripod limit the thermodynamic stability of the podates [f (L4)]3+ and [/J(L4+H)]4+, stability constants confirm their quantitative formation for a total ligand concentration of 0.05 mol dm-3 and a stoichiometric ratio R L4 = 1.0 (Renaud etal., 1999 fig. 17). 

Markus Albrecht and co-workers synthesised three M4L4 tetrahedra based on different C3-symmetric imine type ligands. The ligands are shown in Fig. 16. For the formation of these ligands, 2,3-dihydroxybenzaldehyde was reacted with the product of the reduction of the corresponding trinitro derivative (L21) or with a tris-amine derivative (L22, L23) [30, 135-141]. 

An improved ligand design by Manioka, Saito and Yamamoto has led to a catalyst that is effective for allyl vinyl ethers that are unsubstituted on the vinyl group [27]. This was a serious limitation of the BINOL-derived catalyst 98 which induced only C-O bond cleavage with these substrates (Table 1, entry 1). The ligand (f )-115 was prepared in six steps from (/ )-BINOL and was reacted with trimethylaluminum to give C3 symmetrical Lewis acid Five substituted catalysts were prepared and as... 

Heterogenous metal tartrates were screened for their efficacy in the catalysis of the asymmetric ring opening of me o-2,3-disubstituted epoxides with thiols, aniline, and trimethylsilyl azide [72]. Whereas the enantioselectivity of Zn(II) tartrates is in the 15-85 % ee range, selectivity with the Mn(II), Fe(II), and Co(II) tartrates was lower (< 40 % ee). With Nugent s Zr(Of-Bu)4/C3-symmetric tetradentate ligand catalyst... 

Optically active and C3-symmetric tris(pyrazolyl)phosphine oxide ligands such as 0=P(Menthpz)3 were prepared by procedures analogous to those reported for achiral variants (Scheme 31).109... 

The use of C3-symmetric tripodal ligands in crystal engineering has been reviewed.172... 

The enantiopure C3 symmetric trisoxazoline 173 proved to be a suitable supporting ligand for scandium-catalyzed olefin polymerization whilst invoking sufficient stereocontrol over the substrate to induce a high level of tacticity in the polymer microstructure <05AG(E)1668>. 

Hexahomotrioxacalix[3]arene a scaffold for a C3-symmetric phosphine ligand that traps a hydrido-rhodium fragment inside a molecular funnel, C. B. Dieleman, D. Matt, I. Neda, R. Schmutzler, A. Harriman and R. Yaftian, Chem. Commun., 1999, 1911. 

Ward and coworkers reported the synthesis of a chiral C3-symmetric hexadentate tripodal ligand tris[3- 2-(pinene[4,5]pyridyl) pyrazolyl]-... 

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