Conventional and Microwave Synthesis of 2‐Fluoro‐diazaborolidines and Their Reaction with Lithium Phosphanides

Abstract

Condensation of N,N′‐disubstituted ethylenediamines with BF3·OEt2, in the presence or absence of an auxiliary base, gives mixtures of 2‐fluoro‐1,3,2‐diazaborolidines and ammonium tetrafluoroborates, respectively. Using BF3·NEt3 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 BF3·NEt3 and BF3·OEt2 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 R2P‐substituted N‐heterocyclic boranes are fully characterised. In addition, the structural characterisation of an unprecedented BF3 complex of Hünig's base (iPr2EtN) and of a 1,3,2‐diazaborolidine–BF3 complex is reported.

Cyclolinear Oligo‐ and Poly(iminoborane)s: The Missing Link in Inorganic Main‐Group Macromolecular Chemistry

“…The reaction of 7 a with either 2 a or 8 a was performed in different chlorinated nondonor solvents (CH 2 Cl 2 , CD 2 Cl 2 , and CDCl 3 ) and at various temperatures (Scheme and Table ). In a typical experiment (e.g., entry 2 in Table ), compounds 7 a and 2 a were mixed in dichloromethane at ambient temperature to give a 1 m starting concentration of the reactants.…”

Diaminophosphinoboranes: effective reagents for phosphinoboration of CO2

“…Hence, we focused on monomeric phosphinoboranes, which are another type of ambiphilic P,B-based molecules. 30,31 A recent very comprehensive review 31 by Pringle et al classies these species containing a single P-B bond with a pyramidal P atom and the general formula R 2 P-BR 2 as borylphosphines 30,32,33 and those with a double P]B bond and trigonal planar P atom and the general formula R 2 P]BR 0 2 as phosphinoboranes. [34][35][36] Notably, we found that there are a limited number of reports on the reactivity of P-B bond systems towards small molecules.…”

Phosphines with N‐Heterocyclic Boryl‐Substituents: Ligands for Coordination Chemistry and Catalysis

“…The studies described in this work were performed using NHB‐phosphines carrying both CC‐unsaturated 1,3,2‐diazaborolyl substituents ( 5a – d , Scheme ) and CC‐saturated 1,3,2‐diazaborolidinyl substituents ( 6a , b ) on phosphorus. Ligands 5a – c and 6a , b had been reported previously and were synthesized as described. The P‐alkyl derivative 5d was newly prepared by analogy to 5a , b from the appropriate 2‐bromo‐1,3,2‐diazaborole and lithium dimethyl phosphide, and characterized by multinuclear NMR spectroscopy.…”

“…The P‐alkyl derivative 5d was newly prepared by analogy to 5a , b from the appropriate 2‐bromo‐1,3,2‐diazaborole and lithium dimethyl phosphide, and characterized by multinuclear NMR spectroscopy. Like its congeners,, the new NHB‐phosphine is thermally stable in solution and the solid state, and can be shortly handled in air without decomposition.…”