Issue 17, 2010

Synthesis and characterization of group 4 metal amides with new C2-symmetric binaphthyldiamine-based ligands and their use as catalysts for asymmetric hydroamination/cyclization

Abstract

A new series of titanium(IV) and zirconium(IV) amides have been prepared from the reaction between M(NMe2)4 (M = Ti, Zr) and chiral ligands, (R)-2,2′-bis(p-toluenesulfonylamino)-1,1′-binaphthyl (1H2), (R)-2,2′-bis(diphenylphosphinoylamino)-1,1′-binaphthyl (2H2), (R)-2,2′-bis(mesitoylamino)-1,1′-binaphthyl (3H2), (R)-5,5′,6,6′,7,7′,8,8′-octahydro-2,2′-bis(pyrrol-2-ylmethyleneamino)-1,1′-binaphthyl (4H2), (R)-5,5′,6,6′,7,7′,8,8′-octahydro-2,2′-bis(mesitoylamino)-1,1′-binaphthyl (5H2), and (R)-5,5′,6,6′,7,7′,8,8′-octahydro-2,2′-bis(mesitylenesulfonylamino)-1,1′-binaphthyl (6H2), which are derived from (R)-2,2′-diamino-1,1′-binaphthyl. Reaction of M(NMe2)4 with 1 equiv of arylsulfonylamides 1H2 and 6H2, diphenylphosphoramide 2H2, mesitoylamides 3H2 and 5H2, or Schiff base ligand 4H2 at room temperature gives, after recrystallization from a benzene, toluene or n-hexane solution, the chiral titanium amides (1)Ti(NMe2)2·3C6H6 (7·3C6H6), (4)Ti(NMe2)2 (11), (5)Ti(NMe2)2 (13) and (6)Ti(NMe2)2 (15), and zirconium amides (1)Zr(NMe2)2 (8), (2)Zr(NMe2)2 (9), (3)Zr(NMe2)2 (10), (4)Zr(NMe2)2 (12), (5)Zr(NMe2)2 (14) and (6)Zr(NMe2)2·C7H8 (16·C7H8) respectively, in good yields. These amides are stable below 90 °C in toluene solution, but they degrade via ligand redistribution at a higher temperature. For example, treatment of (1)Zr(NMe2)2 (8) or (5)Zr(NMe2)2 (14) in refluxing toluene for three days leads to the isolation of the complexes (1)2Zr·C7H8 (17·C7H8) and (5)2Zr·3C7H8 (18·3C7H8) respectively, in moderate yields. These new compounds have been characterized by various spectroscopic techniques, and elemental analyses. The solid-state structures of compounds 7–9, 11–13, and 15–18 have further been confirmed by X-ray diffraction analyses. The titanium amide 13 and all the zirconium amides are active catalysts for the asymmetric hydroamination/cyclization of aminoalkenes, affording cyclic amines in moderate to excellent yields with moderate to excellent ee values (up to 93%). Theoretical studies reveal the interaction between the carbon chain of the substrate and the sterically demanding ligand groups plays a key role in the stereodirection of the enantioselection during the Zr[double bond, length as m-dash]N bond approaches to the C[double bond, length as m-dash]C bond.

Graphical abstract: Synthesis and characterization of group 4 metal amides with new C2-symmetric binaphthyldiamine-based ligands and their use as catalysts for asymmetric hydroamination/cyclization

Supplementary files

Article information

Article type
Paper
Submitted
09 Nov 2009
Accepted
23 Jan 2010
First published
23 Feb 2010

Dalton Trans., 2010,39, 4048-4061

Synthesis and characterization of group 4 metal amides with new C2-symmetric binaphthyldiamine-based ligands and their use as catalysts for asymmetric hydroamination/cyclization

G. Zi, F. Zhang, L. Xiang, Y. Chen, W. Fang and H. Song, Dalton Trans., 2010, 39, 4048 DOI: 10.1039/B923457H

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