1,2-AZABOROLYL COMPLEXES .30. PHOSPHANYL-SUBSTITUTED 1,2-AZABOROLES

1-tert-Butyl-2-methyl-1,2-azaborolyllithium (LiAb, 1) and TiCl equilibrate at -75-degrees-C in THF under action of light to TlAb (2) and LiCl. Compound 2 decomposes above -50-degrees-C with elimination of thallium and the neutral isomers 1-tert-butyl-2,5-dihydro-2-methyl-1H-1,2-azaborole and 1-tert-butyl-2,3-dihydro-2-methyl-1H-1,2-azaborole. Whilst 1 reacts with Ph2PCl in only very small amounts to give the expected Ph2P-substituted azaborole ring 3, TlAb (2) forms this compound by reaction with Ph2PCl in high yields. The yellow oily 3 is characterized by H-1-, B-11-, C-13-, and P-31-NMR data. The Me3Si-substituted derivative 1-tert-butyl-3-(diphenyl-phosphanyl)-2,3-dihydro-2-methyl-3-(trimethylsilyl)-1H-1,2-azaborole (5), available via 4, the Li salt of 3, and ClSiMe3, forms yellow crystals which could be used for an X-ray structure analysis. As expected, the Ph2P and Me3Si groups substitute the boron neighboring C3 atom of the planar ring framework. The crystal structure of 5 shows the two expected enantiomers.