Organometallic Complexes of Bulky, Optically Active, <i>C</i>₃-Symmetric Tris(4<i>S</i>-isopropyl-5,5-dimethyl-2-oxazolinyl)phenylborate (To^P*)

Abstract

A bulky, optically active monoanionic scorpionate ligand, tris(4 S -isopropyl-5,5-dimethyl-2-oxazolinyl)phenylborate (To P *), is synthesized from the naturally occurring amino acid l -valine as its lithium salt, Li[To P *] ( 1 ). That compound is readily converted to the thallium complex Tl[To P *] ( 2 ) and to the acid derivative H[To P *] ( 3 ). Group 7 tricarbonyl complexes To P *M(CO) 3 (M = Mn ( 4 ), Re ( 5 )) are synthesized by the reaction of MBr(CO) 5 and Li[To P *] and are crystallographically characterized. The ν CO bands in their infrared spectra indicate that π back-donation in the rhenium compounds is greater with To P * than with non-methylated tris(4 S -isopropyl-2-oxazolinyl)phenylborate (To P ). The reaction of H[To P *] and ZnEt 2 gives To P *ZnEt ( 6 ), while To P *ZnCl ( 7 ) is synthesized from Li[To P *] and ZnCl 2 . The reaction of To P *ZnCl and KO t Bu followed by addition of PhSiH 3 provides the zinc hydride complex To P *ZnH ( 8 ). Compound 8 is the first example of a crystallographically characterized optically active zinc hydride. We tested its catalytic reactivity in the cross-dehydrocoupling of silanes and alcohols, which provided Si-chiral silanes with moderate enantioselectivity.