biostudies-literatureUchida DJapan Science and Technology AgencyJapan Society for the Promotion of Science22597-22602https://www.ebi.ac.uk/biostudies/studies/S-EPMC12560044biostudies-literatureUnknown16(47)We report the synthesis of the first neutral homoaromatic heavy allene, stabilized by a methylene-bridged four-membered framework. Single-crystal X-ray diffraction and DFT calculations reveal a cyclic three-center-two-electron (3c-2e) π interaction, a short bridgehead distance, a delocalized HOMO, and a strongly negative NICS(-1) value (-16.9 ppm), collectively establishing pronounced homoaromaticity. Coordination of 4-dimethylaminopyridine (DMAP) induces a clean and selective transformation into a germylene-coordinated digermavinylidene, without substituent migration. This reactivity originates from LUMO localization at the bridgehead Ge atom supported by Wiberg bond indices and NBO analyses. Our findings highlight neutral homoaromaticity as a structural platform for programmable bonding Chemical scienceA neutral homoaromatic heavy allene as a platform for selective conversion to a germylene-coordinated digermavinylidene.PMC12560044JPMJFS2123JP18H01963JP25H02026JP24K01496Mizuhata YYamada HUchida DfalseA neutral homoaromatic heavy allene as a platform for selective conversion to a germylene-coordinated digermavinylidene.We report the synthesis of the first neutral homoaromatic heavy allene, stabilized by a methylene-bridged four-membered framework. Single-crystal X-ray diffraction and DFT calculations reveal a cyclic three-center-two-electron (3c-2e) π interaction, a short bridgehead distance, a delocalized HOMO, and a strongly negative NICS(-1) value (-16.9 ppm), collectively establishing pronounced homoaromaticity. Coordination of 4-dimethylaminopyridine (DMAP) induces a clean and selective transformation into a germylene-coordinated digermavinylidene, without substituent migration. This reactivity originates from LUMO localization at the bridgehead Ge atom supported by Wiberg bond indices and NBO analyses. Our findings highlight neutral homoaromaticity as a structural platform for programmable bonding 2025-01-01T00:00:00Z2025 Dec2026-07-15T13:26:51.118Z2026-07-05T03:08:18.251ZS-EPMC125600444116430510.1039/d5sc07177a