The synthesis, molecular structure and supramolecular architecture of complexes between the ammonia adduct of tris(pentafluorophenyl)boron and a series of mono and polydentate hydrogen-bond acceptors.
The ammonia adduct of tris(pentafluorophenyl)boron, (C6F5)3B.NH3, is a potentially tri-functional hydrogen-bond donor. Co-crystallisation with the bases acetonitrile, pyridine, tetrahydrofuran, tetramethylethylenediamine, 15-crown-5, 1,4-diazabicyclo[2.2.2]octane (DABCO), pyrazine and 4,4'-bipyridine results, not in donor exchange, but in the formation of supermolecules assembled through hydrogen bonding to second coordination sphere acceptors. The complexes have been characterised by elemental analysis, multinuclear NMR and single-crystal diffraction methods. The solid-state architectures range in complexity, from the hydrogen bonded pairing of (C6F5)3B.NH3, with a single monodentate acceptor molecule (e.g. MeCN to form (C6F5)3B.NH3.NCMe), through complexation with all three N-H groups to the macrocycle 15-crown-5, to the formation of infinite one-dimensional chains with pyrazine and DABCO, and to two-dimensional networks with the divergent acceptor 4,4'-bipyridine.
Mechanistic studies on selectivity in the B(C6F5)3-catalyzed allylstannation of aldehydes: is hypercoordination at boron responsible?
[structure: see text] The selective, B(C6F5)3-catalyzed allylstannation of aldehydes with proximal donor groups is shown to proceed via borane abstraction of the allyl group from the tin reagent and activation of the substrate by "Bu3Sn+". This is supported by a number of 19F NMR experiments. The selectivity of the reaction is not attributable to hypercoordinate boron as proposed by the discoverers of this highly selective reaction but likely involves chelation at tin.
Pentacoordinate vs. Tetracoordinate complexation for alkoxycarbonyl compounds with dialkylboron triflates and trifluoroacetates
Abstract The implication of hitherto unknown pentacoordinate complex formation for alkoxycarbonyl compounds with Et2BX (X =OTf, OCOCF3) is presented by several reduction/allylation experiments and low-temperature 13C, 11B NMR spectroscopy.