Coordination of Boron‐centered Lewis Acids by <i>organo</i>‐substituted Phosphanylboranes

The reactions of the monomeric phosphanylboranes Ph 2 P–BH 2 · NMe 3 ( 1a ) and t BuHP–BH 2 · NMe 3 ( 1b ) with the main group Lewis acids BH 3 and BBr 3 yield the adducts H 3 B · Ph 2 P–BH 2 · NMe 3 ( 2a ) and H 3 B · t BuHP–BH 2 · NMe 3 ( 2b ), Br 3 B · Ph 2 P–BH 2 · NMe 3 ( 3a ), and Br 3 B · t BuHP–BH 2 · NMe 3 ( 3b ). All these compounds were completely characterized by single‐crystal X‐ray structure analysis, NMR and IR spectroscopy as well as mass spectrometry and DFT computations. The secondary and tertiary phosphines 1a and 1b behave as classical Lewis bases to coordinate B X 3 ( X = H, Br) as terminal groups.