TRITIUM AND DEUTERIUM LABELING STUDIES OF ALKALI-METAL BOROHYDRIDES AND THEIR APPLICATION TO SIMPLE REDUCTIONS

Simple and facile syntheses of highly deuterated and tritiated LiBH4, NaBH4 and KBH4 were achieved by hydrogen isotope exchange with deuteri um or tritium gas at elevated temperatures. The exchange products were characterized by boron, proton and deuterium or tritium NMR spectrosc opy. The extent of isotope (H-2 or H-3) incorporation was calculated f rom the patterns of B-11 NMR spectra. Several samples of tritiated NaB H4 were treated with BF3-Et(2)O to produce tritiated borane-THF comple x, which is an electrophilic reducing agent. The utility of both the b orohydride reagents and borane-THF complex in labelling reactions was confirmed by exemplary reductions leading to specifically labelled pro ducts. The extent and orientation of labelling in the reduction produc ts was assessed by a combination of radio-HPLC analysis, H-1, H-2 or H -3 NMR and mass spectrometry.