Synthesis and tunable reactivity of N-heterocyclic germylene.

Modifying the β-diketimine ligand LH 1 (LH=[ArN=C(Me)-CH=C(Me)-NHAr], Ar=2,6-iPr(2)C(6)H(3)) through replacement of the proton in 3-position by a benzyl group (Bz) leads to the new (Bz)LH ligand 2, which could be isolated in 77% yield. According to (1) H NMR spectroscopy, 2 is a mixture of the bis(imino) form (ArN=C(Me)CH(Bz) 2a and its tautomer [ArN=C(Me)-C(Bz)=C(Me)NHAr] 2b. Nevertheless, lithiation of the mixture of 2a and 2b affords solely the N-lithiated β-diketiminate [ArN=C(Me)-C(Bz)=C(Me)-NLiAr], (Bz)LLi 3. The latter reacts readily with GeCl(2)· dioxane to form the chlorogermylene (Bz)LGeCl 4, which serves as a precursor for a new zwitterionic germylene by dehydrochlorination with LiN(SiMe(3))(2). This reaction leads to the zwitterionic germylene (Bz)L'Ge: 5 ((Bz)L'=ArNC(=CH(2))C(Bz)=C(Me)NAr) which could be isolated in 83% yield. The benzyl group has a distinct influence on the reactivity of zwitterionic 5 in comparison to its benzyl-free analogue, as shown by the reaction of 5 with phenylacetylene, which yields solely the 1,4-addition product 6, that is, the alkynyl germylene (Bz)LGeCCPh. Compounds 2-6 have been fully characterized by multinuclear NMR spectroscopy, mass spectrometry, elemental analyses, and single-crystal X-ray diffraction analyses.