Azaborolyl-Komplexe, 27 / Azaborolyl Complexes, 27 : Der 1-tert-Butyl-2-methyl-3-(4-penten-1-y1)-1H-1,2-azaborolyl-Ring als bifunktioneller Ligand in Rhodiumkomplexen / The 1-tert-Butyl-2-methyl-1H-1,2-azaborolyl Ring as a Bifunctional Ligand in Rhodium Complexes

Alkenyl substituted 1H-1,2-azaborolyl (Ab) complexes are promising candidates for stereoselective reactions, due to the chirality of the AbM moiety and the intramolecular coordination of the alkenyl group to the metal atom. The synthesis of [1-tert-butyl-2-methy1-3-(4-penten- l -y1)-η⁵-1H-1,2-azaborolyl]-bis(triphenylphosphine)rhodium (3) is achieved by the reaction of AbLi (2) [from AbH (1)] with (Ph₃P)₃RhCl. In benzene solution one PPh₃ ligand of 3 is substituted by the C=C group of the pentenyl substituent. Simultaneously the η⁵-coordination of the Ab ring changes to an allylic η³-coordination forming 4. Steric reasons seem to be responsible for this intramolecular 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- l -yl)-η⁵-1H-1,2-azaborolyl]-bis(triphenylphosphine)rhodium (7). Mass spectrometry, ¹H, ¹¹B and ³¹P NMR data were used to characterize the novel complexes.