Boosting 2000‐Fold Hypergolic Ignition Rate of Carborane by Substitutes Migration in Metal Clusters

Hypergolic propellants rely on fuel and oxidizer that spontaneously ignite upon contact, which fulfill a wide variety of mission roles in launch vehicles and spacecraft. Energy‐rich carboranes are promising hypergolic fuels, but triggering their energy release is quite difficult because of their ultrastable aromatic cage structure. To steer the development of carborane‐based high‐performance hypergolic material, carboranylthiolated compounds integrated with atomically precise copper clusters are presented, yielding two distinct isomers, Cu14B‐S and Cu14C‐S, both possessing similar ligands and core structures. With the migration of thiolate groups from carbon atoms to boron atoms, the ignition delay (ID) time shortened from 6870 to 3 ms when contacted with environmentally benign oxidizer high‐test peroxide (HTP, with a H2O2 concentration of 90%). The extraordinarily short ignition ID time of Cu14B‐S is ranking among the best of HTP‐active hypergolic materials. The experimental and theoretical findings reveal that benefitting from the migration of thiolate groups, Cu14B‐S, characterized by an electron‐rich metal kernel, displays enhanced reducibility and superior charge transfer efficiency. This results in exceptional activation rates with HTP, consequently inducing carborane combustion and the simultaneous release of energy. This fundamental investigation shed light on the development of advanced green hypergolic propulsion systems. Two carboranylthiolate‐protected isometric copper clusters (Cu14B‐S and Cu14C‐S) show distinctly different ID times (three orders of magnitude difference) upon environmentally benign oxidizer high‐test peroxide (HTP) ignition. Based on the isomeric platform, the significantly boosted ignition rate with HTP is attributed to their distinct electronic structure, which leads to different activation rate toward triggering carborane “open face” and release of energy.