The abstraction of the Lewis acid from [W(CO)(5)(PH2BH2-NMe3)] (1) by an excess of P(OMe3)(3) leads to the quantitative, formation of the first Lewis base stabilized monomeric parent compound of phosphanylborane [H2PBH2-NMe3] 2. Density functional theory (DFT) calculations have shown a low energetic difference between the crystallographically determined anti-periplanar arrangement of the lone pair and the trimethylamine group relative to the P-B core and the synperi-planar conformation. Subsequent reactions with the main-group Lewis acid BH3 as well as with an [Fe(CO),] unit as a transition-metal Lewis acid led to the formation of [(BH3)(PH2BH2NMe3)-N-.] (3), containing a central H3B-PH2-BH2 unit, and [Fe(CO)(4)-(PH2BH2-NMe3)] (4), respectively. In oxidation processes with O-2, Me3NO, elemental sulfur, and selenium, the boranylphosphine chalcogenides [H2P(Q)(BH2NMe3)-N-.] (Q = S 5b; Se 5c) as well as the novel boranyl phosphonic acid [(HO)(2)P(O)BH2-NMe3] (6a) are formed. All products have been characterized by spectroscopic as well as by single-crystal X-ray structure analysis.