Isomeric hypho-boranes. Properties and molecular structures of the adducts B5H9·L (L = Ph2PCH2PPh2, Ph2PCH2CH2PPh2, or Me2NCH2CH2NMe2) and B4H8·L (L = Me2NCH2CH2NMe2)
Abstract
The air-stable adducts B5H9·L [L = bis(diphenylphosphino)methane (dppm), 1,2-bis(diphenylphosphino)ethane (dppe), and NNN′N′-tetramethylethylenediamine (tmen)] and B4H8˙tmen are formed by the action of the ligand on the borane at room temperature; no cleavage of the B5 group to form BH3·L species occurs, even with an excess of ligand. The B5H9 complexes, which may be regarded as derivatives of the hypho-B5H112– ion, have been fully characterised by X-ray methods; for B4H8˙tmen an approximate structure is reported. The dppm and dppe structures both show the phosphorus atoms bridging the apical and basal atoms of a flattened pyramidal B5 framework (with rearrangement of the hydrogen atoms). The tmen complexes differ markedly; each has the ligand chelating one of the originally basal boron atoms, which becomes singly bonded to the apical boron atom and is separated from the remaining basal atoms by typical non-bonded contact distances.