Reactivity of Oxygen-Bridged Geminal Al/P and Si/P Frustrated Lewis Pairs towards Heterocumulenes.

The two oxygen-bridged geminal frustrated Lewis pairs (FLP) tBu 2 P-O-AlBis 2 (Bis=CH(SiMe 3 ) 2 ; 1) and tBu 2 P-O-Si(C 2 F 5 ) 3 (2) were reacted with the heterocumulenes PhNCO, PhOCN, PhNCS, CS 2 and PhNSO as well as SO 2 . With isocyanate and cyanate, both 1 and 2, form addition products under formation of five-membered rings. With CS 2 , isothiocyanate and sulfinylaniline, only 1 forms stable adducts, whereas 2 shows reactivity towards sulfinylaniline, but the product decomposed after a few minutes. The reaction of 1 with SO 2 led to partial cleavage of the P-O-Al and Al-C units, as confirmed by X-ray diffraction studies of a complex aggregate. The reaction of 2 with SO 2 affords the 1,2-addition product. All adducts were characterized by means of multinuclear NMR spectroscopy, X-ray crystallography and CHN analyses.