[3] It has a huge expansion ratio on the nozzle and uses a unique propellant combination to achieve an extremely high isp of 352 s for a semi-cryogenic gas-generator engine.

But Sergei Korolev's refusal to use such a toxic combination shelved the project.

The critical issue was the low specific impulse of the first stage, and thus a very high-efficiency upper-stage engine was needed.

[3] It flew some very important missions on the Kosmos-2 launch vehicle, with about 165 engines produced.

Kosmonavtika Entsiklopediya - Cosmonautic Encyclopedia (Russian) - Космонавтика Энциклопедия (PDF).