Less is more: three-coordinate c,n-chelated distannynes and digermynes

We report here the synthesis of new C,N-chelated chlorostannylenes and germylenes L(3) MCl (M=Sn(1), Ge (2)) and L(4) MCl (M=Sn(3), Ge (4)) containing sterically demanding C,N-chelating ligands L(3, 4) (L(3) =[2,4-di-tBu-6-(Et2 NCH2 )C6 H2 ](-) ; L(4) =[2,4-di-tBu-6-{(C6 H3 -2',6'-iPr2 )N=CH}C6 H2 ](-) ). Reductions of 1-4 yielded three-coordinate C,N-chelated distannynes and digermynes [L(3, 4) M]2 for the first time (5: L(3) , M=Sn, 6: L(3) , M=Ge, 7: L(4) , M=Sn, 8: L(4) , M=Ge). For comparison, the four-coordinate distannyne [L(5) Sn]2 (10) stabilized by N,C,N-chelate L(5) (L(5) =[2,6-{(C6 H3 -2',6'-Me2 )NCH}2 C6 H3 ](-) ) was prepared by the reduction of chlorostannylene L(5) SnCl (9). Hence, we highlight the role of donor-driven stabilization of tetrynes. Compounds 1-10 were characterized by means of elemental analysis, NMR spectroscopy, and in the case of 1, 2, 5-7, and 10, also by single-crystal X-ray diffraction analysis. The bonding situation in either three- or four-coordinate distannynes 5, 7, and 10 was evaluated by DFT calculations. DFT calculations were also used to compare the nature of the metal-metal bond in three-coordinate C,N-chelating distannyne [L(3) Sn]2 (5) and related digermyme [L(3) Ge]2 (6).