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Conventional and Microwave Synthesis of 2‐Fluoro‐diazaborolidines and Their Reaction with Lithium Phosphanides
Author(s) -
Kaaz Manuel,
Bäucker Christian,
Deimling Max,
König Simon,
Schlindwein Simon H.,
Bender Johannes,
Nieger Martin,
Gudat Dietrich
Publication year - 2017
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201700559
Subject(s) - chemistry , ethylenediamine , lithium (medication) , boranes , base (topology) , amine gas treating , boron , boron trichloride , condensation , inorganic chemistry , medicinal chemistry , organic chemistry , medicine , mathematical analysis , physics , mathematics , thermodynamics , endocrinology
Condensation of N , N′ ‐disubstituted ethylenediamines with BF 3 · OEt 2 , in the presence or absence of an auxiliary base, gives mixtures of 2‐fluoro‐1,3,2‐diazaborolidines and ammonium tetrafluoroborates, respectively. Using BF 3 · NEt 3 as the reactant allows the introduction of the boron source and the auxiliary in a single component, but suffers from the inhibition of the cyclisation by an excess of free amine formed as a by‐product. In contrast, rapid and quantitative consumption of the starting materials is observed when the reaction is carried out with a 2:1 mixture of BF 3 · NEt 3 and BF 3 · OEt 2 per mol of ethylenediamine at elevated temperature. Extremely short reaction times are achieved by conducting the reaction in a superheated solution in a microwave reactor. The 2‐fluoro‐1,3,2‐diazaborolidines formed under these conditions are readily isolated in high yields, and their synthetic usability is demonstrated by reactions with lithium phosphanides to give 2‐phosphanyl‐1,3,2‐diazaborolidines. Both the F‐ and R 2 P‐substituted N‐heterocyclic boranes are fully characterised. In addition, the structural characterisation of an unprecedented BF 3 complex of Hünig's base ( i Pr 2 EtN) and of a 1,3,2‐diazaborolidine–BF 3 complex is reported.