Frustrated Lewis Pairs from Al−E^{14} Bonds (E^{14}=Ge, Sn, Pb)

The potassium aluminyl K[Al(NON)] ([NON]²⁻=[O(SiMe₂NDipp)₂]²⁻, Dipp=2,6-iPr₂C₆H₃) reacts with group 14 chloroamidinates E^{14}(Am)Cl (E^{14}=Ge, Sn, Pb. [Am]⁻=[tBuC(NDipp)₂]⁻) to form (NON)Al−E^{14}(Am) Lewis pairs with unsupported Al−E^{14} bonds, including the first structurally authenticated Al−Pb bond. Analysis using spectroscopic (NMR, UV-vis and Mössbauer for E^{14}=Sn), X-ray diffraction and computational (DFT, QTAIM, TD-DFT) methods conclude an Al−E^{14} σ-bond derived from a Lewis basic Al and a Lewis acidic tetrylene, with back-donation from the E^{14} s-orbital lone pair donor NBO to acceptor NBOs on Al that are derived from s/p-orbitals. The reaction of the Al−Ge compound with CO₂ forms the dioxocarbene (NON)Al(μ-O₂C)Ge(Am), whilst under the same conditions the Al−Sn compound reacts with additional CO₂ to form the carbonate, (NON)Al(μ-CO₃)Sn(Am). Addition of ethene to the Al−E^{14} (E^{14}=Ge, Sn) compounds introduces an ethylene bridge between the aluminium and group 14 atoms forming a frustrated Lewis pair (FLP). Reaction of the (Al/Ge) FLP with CO₂ forms an activation product with new Al−O and Ge−C bonds, whilst reaction with iPrN=C=NiPr proceeds with insertion into the Al−C bond to form an aluminium amidinate.