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

Abstract

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.