The reactivity of the Lewis acid/base stabilized complex of phosphanylalane [(CO)5W(H2PAlH2·NMe3)] (1) towards the Lewis bases THF and NMe3 has been investigated. The reaction with THF leads to decomposition of the complex. One of the decomposition products was identified as containing the anion [{(CO)5W}2PH2]- (2). This anion could be synthesized independently by reaction of [(CO)5WPH3] with KH in the presence of [(CO)5W(THF)] and was isolated as the tetraphenylphosphonium salt [Ph4P][{(CO)5W}2PH2] (2a). The treatment of 1 with NMe3 leads to the formation of [(CO)5W(H2PAlH2·2 NMe3)] (3) containing a five-coordinate aluminum atom. Compound 3 exhibits a fast exchange of the NMe3 ligands in solution containing an excess of NMe3. The products were characterized by spectroscopic methods and X-ray crystallography.