Synthesis and optical activity analysis of chiral titanium(IV) sec-butoxide and its group IV analogues

The complete series of chiral group IV sec-butoxides has been obtained by the treatment of M(NMe2)4 (M = Ti, Zr, Hf) with resolved (R)-(−)- or (S)-(+)-2-butanol. These complexes were analyzed by polarimetry, revealing a decreasing trend in molar rotation down the group, from titanium to hafnium. Catalysis screenings showed that the resolved titanium sec-butoxides, in conjunction with the resolved BINOL (BINOL = 1,1′-bi-2-naphthol) of the opposite configuration designation, catalyzed the addition of dimethyl zinc to benzaldehyde with higher enanteoselectivity than that observed for resolved BINOL with titanium(IV) isopropoxide or with the titanium(IV) sec-butoxide of the same configuration designation.

Figure optionsDownload as PowerPoint slide

Titanium(IV) tetra-(R)-(−)-sec-butoxideC16H36O4Ti[α]D24=-83.1 (c 1.0, C6H6)Absolute configuration: (R)

Zirconium(IV) tetra-(R)-(−)-sec-butoxideC16H36O4Zr[α]D24=-20.9 (c 1.0, C6H6)Absolute configuration: (R)

Hafnium(IV) tetra-(R)-(−)-sec-butoxideC16H36O4Hf[α]D24=-11.75 (c 1.0, C6H6)Absolute configuration: (R)