Synthesis and Characterization of New Biphenolate and Binaphtholate Rare‐Earth‐Metal Amido Complexes: Catalysts for Asymmetric Olefin Hydroamination/Cyclization

Abstract

Monomeric diolate amido yttrium complexes [Y[diolate][N(SiHMe(2))(2)](thf)(2)] can be prepared in good yield by treating [Y[N(SiHMe(2))(2)](3)(thf)(2)] with either 3,3'-di-tert-butyl-5,5',6,6'-tetramethyl-1,1'-biphenyl-2,2'-diol (H(2)(Biphen)), 3,3'-bis(2,4,6-triisopropylphenyl)-2,2'-dihydroxy-1,1'-dinaphthyl (H(2)(Trip(2)BINO)) or 3,3'-bis(2,6-diisopropylphenyl)-2,2'-dihydroxy-1,1'-dinaphthyl (H(2)(Dip(2)BINO)) in racemic and enantiopure form. The racemic complex [Y(biphen)[N(SiHMe(2))(2)](thf)(2)] dimerizes upon heating to give the heterochiral complex (R,S)-[Y(biphen)[N(SiHMe(2))(2)](thf)](2). The corresponding dimeric heterochiral lanthanum complex was the sole product in the reaction of H(2)(Biphen) with [La[N(SiHMe(2))(2)](3)(thf)(2)]. Single-crystal X-ray diffraction of both dimeric complexes revealed that the two Ln(biphen)[N(SiHMe(2))(2)](thf) fragments are connected through bridging phenolate groups of the biphenolate ligands. The two different phenolate groups undergo an intramolecular exchange process in solution leading to their equivalence on the NMR timescale. All complexes were active catalysts for the hydroamination/cyclization of aminoalkynes and aminoalkenes at elevated temperature, with [Y((R)-dip(2)bino)[N(SiHMe(2))(2)](thf)(2)] being the most active one giving enantioselectivities of up to 57 % ee. Kinetic resolution of 2-aminohex-5-ene proceeded with this catalyst with 6.4:1 trans selectivity to give 2,5-dimethylpyrrolidine with a k(rel) of 2.6.

Lanthanide Complexes Coordinated by N‐Substituted (R)‐1,1′‐Binaphthyl‐2,2′‐diamido Ligands in the Catalysis of Enantioselective Intramolecular Hydroamination

“…[16] At the same time as this work, Hultzsch and co-workers prepared new yttrium and lanthanum amides, coordinated by ancillary chiral biphenolate or binaphtholate ligands, that led to the cyclization of aminopentenes with up to 57 % ee. [17] An improvement in terms of activity and selectivity was reported by this team in preparing more sterically hindered yttrium complexes in order to favor a monomeric structure. [18] The 3,3'-bis(tris(aryl)silyl)-substituted binaphtholate ligands allow the isolation of an yttrium aryl complex that is active at room temperature and leads to an enantiomeric excess of 83 % for the hydroamination of aminopent-4-ene, the best enantiomeric excess obtained to date.…”

Synthesis and Crystal Structure Investigations of Trivalent Rare Earth (Y3+, Nd3+, Er3+) Thienyl‐Substituted Methoxides

“…This type of compound has found a variety of applications in catalysis, [1][2][3][4][5][6] ceramics and electronic materials. [7,8] Lanthanide derivatives are frequently screened to form precursors for MOCVD and for emitting layers in polymer-based light-emitting diodes [9,10] Recently, europium(3+) and terbium(3+) compounds containing thiophenyl-derivatized nitrobenzoic acid [9] and 2-nitro-4-(thiophen-3-yl)benzoic acid [11] ligands were reported.…”

Bis(phosphinimino)methanide Rare Earth Amides: Synthesis, Structure, and Catalysis of Hydroamination/Cyclization, Hydrosilylation, and Sequential Hydroamination/Hydrosilylation

“…[13] In addition to the well established cyclopentadienyl complexes, a number of non-cyclopentadienyl lanthanide complexes based on amido and alkoxide ligands are today also known to be active in hydroamination/cyclization catalysis. [14][15][16][17][18] The first non-cyclopentadienyl lanthanide catalyst for the hydroamination/cyclization reaction was developed by us, [14] while recently we have introduced the use of the bis(phosphinimino)methanide {CH(PPh 2 NSiMe 3 ) 2 } À , previously employed by a number of research groups in main group and transition metal chemistry, [19][20][21][22][23][24][25][26][27] into yttrium and lanthanide chemistry as a cyclopentadienyl replacement. [28][29][30] The obtained complexes were used as homogenous catalysts for a number of different catalytic applications.…”