Unexpected Photodegradation of a Phosphaketenyl-Substituted Germyliumylidene Borate Complex

The first zwitterionic borata-bis(NHC)-stabilized phosphaketenyl germyliumylidene [(L₂ (O=C=P)Ge:] 2 (L₂ =(p-tolyl)₂ B[1-(1-adamantyl)-3-yl-2-ylidene]₂ ) has been synthesized by salt-metathesis reaction of [L₂ (Cl)Ge:] 1 with sodium phosphaethynolate [(dioxane)_n NaOCP]. Unexpectedly, its exposure to UV light affords, after reductive elimination of the entire PCO group, the unprecedented [L₂ Ge-GeL₂ ] complex 3 in 54 % yields bearing the Ge₂²⁺ ion with Ge in the oxidation state +1. In addition, the 1,3-digermylium-2,4-diphosphacyclobutadiene [L₂ Ge(μ-P)₂ GeL₂ ] 4 and bis(germyliumylidenyl)-substituted diphosphene [(L₂ Ge-P=P-GeL₂ )] 5 could also be obtained in moderate yields. The formation of 3-5 and their electronic structures have been elucidated with DFT calculations.