A crystalline stannyne.

The synthesis of heteronuclear alkyne analogues incorporating heavier group 14 elements (R 1 -C≡E-R 2 , E = Si, Ge, Sn, Pb) has posed a long-standing challenge. Neutral silynes (R 1 -C≡Si(L)-R 2 ) and germynes (R 1 -C≡Ge(L)-R 2 ) stabilized by a Lewis base have achieved sufficient stability for structural characterization at low temperatures. Here we show the isolation of a base-free stannyne (R 1 -C≡Sn-R 2 ) at room temperature, achieved through the strategic use of a bulky cyclic phosphino ligand in combination with a bulky terphenyl substituent. Despite an allenic structure with strong delocalization of π-electrons, this compound exhibits adjacent ambiphilic carbon and tin centres, forming a carbon-tin multiple bond with ionic character. The stannyne demonstrates reactivity similar to carbenes or stannylenes, reacting with 1-adamantyl isocyanide and 2,3-dimethyl-1,3-butadiene. Additionally, its carbon-tin bond can be saturated by Et 3 N·HCl or cleaved by isopropyl isocyanate.