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} σ‐orbital lone pair donor NBO to acceptor NBOs on Al 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.