Covalently Bound Paramagnetic Shift Reagents. 1. A Versatile Lithium Reagent Derived from Biscobalt(II)

Article abstract of DOI:10.1021/ja00370a016

A versatile precursor for the attachment of covalently bound paramagnetic probes has been prepared.Sodium (4-bromophenyl)tris(1-pyrazolyl)borate, 4-BrC6H4B(pz)3Na, was converted to the 4-lithio derivative via a metal-halogen exchange with butyllithium in THF at -70 deg C.Deuteration of this lithium reagent could be effected by treatment with D2O; carbonation, however, led to decomposition.Conversion of (4-BrC6H4B(pz)3)2Co^II to the corresponding 4-lithio compound followed by deuteration, coupling with 1-iodobutane, or carbonation gave (4-RC6H4B(pz)3)2Co^II, with R = D, n-Bu, or CO2H, respectively.The latter compound was converted to the methyl ester by reaction with diazomethane.The large isotropic shifts observed for protons on the phenyl ring and its substituents can be accurately predicted by using conventional expressions for the dipolar shifts.