Azaborolyl complexes. 27. The 1-tert-butyl-2-methyl-1H-1,2-azaborolyl ring as a bifunctional ligand in rhodium complexes.
Alkenyl substituted 1H-12-azaborolyl (Ab) complexes are promising candidates for stereoselective reactions, due to the chirality of the AbM moiety and the intramol. coordination of the alkenyl group to the metal atom. The synthesis of azaborolyl rhodium complex I was achieved by the reaction of AbLi with (Ph3P)3RhCl. In benzene soln. one PPh3 ligand of I is substituted by the C:C group of the pentenyl substituent. Simultaneously the h5-coordination of the Ab ring changes to an allylic h5-coordination forming complex II. Steric reasons seem to be responsible for this intramol. rearrangement. The shorter 2-propen-1-yl substituent is unable to act in the same way and therefore only forms the stable complex [1-tert-butyl-2-methyl-3-(2-propen-1-yl)-h5-1H-1,2-azaborolyl]-bis(triphenylphosphine)rhodium. Mass spectrometry, 1H, 11B and 31P NMR data were used to characterize the novel complexes.
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