Hydroboration of CO2 using HBpin has also been successful with germanium and stannylene hydrides, thereby forming methanol and formic acid equivalents. HBpin is needed as a hydride source to restore the metallylene hydride catalyst. The reactions with stannylene hydride were faster than the ones with its germylene analogue. The mechanism and increased reactivity of the hydroboration of CO2 when going from a germylene hydride to a stannylene hydride was studied with DFT. The CO 2 activation barrier decreases when going to the larger Sn, which was traced back to an increased polar character Please do not adjust margins Please do not adjust margins of the E-H bond that needs to be broken. Other hydride sources besides HBpin have been used to convert CO2 into methanol by germylene hydrides, such as ammonia borane and aluminium hydride. 55d In addition to activating CO2, germylene and stannylene hydrides have also shown activity towards ketones and alkynes. A diborylstannylene was able to diborate CO2. In addition to hydroboration, silylation of ketones and aldehydes has also been reported. Cyanosilylation by an Nheterocyclic germylene and stannylene has been performed. The computational study by Takagi and Sakaki suggested beforehand that the hydrosilylation of ketones by a germylene hydride was likely to succeed, whereas the reaction barrier for the hydrogenation of ketones is too high. Dasgupta et al. propose the following catalytic cycle of an N-heterocyclic germylene (Scheme 6): the nitrogen atom from the cyano group of TMSCN coordinates to the tetrel center of the germylene, followed by coordination of the aldehyde to TMSCN and forming the cyanosilylation product, regaining the germylene. Hydrosilylation of aldehydes and ketones has been achieved by Inoue and coworkers using an amido stannylene, where the stannylene is stabilized by coordination of an NHC to Sn. 80c Scheme 6. A proposed mechanism for the cyanosilylation of aldehydes.