A hydrogen deposition tool

Several of the preceding reactions used a hydrogen abstraction tool (the ethynyl radical). As a consequence, we must refresh this tool without using tools which require the hydrogen abstraction tool for their production. At the same time, we wish to create a hydrogen deposition tool -- a tool with a weakly bonded hydrogen. When used, the hydrogen deposition tool will transfer a hydrogen to a specific site. After use, the hydrogen deposition tool will have to be refreshed by transferring a hydrogen to it.

The obvious solution to both these problems is to transfer the hydrogen from the abstraction tool to the deposition tool.

As noted earlier, there are many possible structures that would serve as a hydrogen deposition tool. One candidate is tin, which forms a weak bond to hydrogen. One reaction to transfer a hydrogen from the abstraction tool to the depsosition tool is shown:

Reaction 15

This is similar to the proposal by (Drexler, 1992) and simultaneously refreshes both the hydrogen abstraction tool and the hydrogen deposition tool.

While this reaction is most useful, the tin radical is quite weak. While AM1 suggests that the H-C bond is weakened to 3 × 10^-19 J (~45 kcal/mol) by the radical addition, there might still be a barrier to abstraction by tin (and the AM1 estimate might itself be seriously in error, see below). On the other hand, positional control can be used to weaken the H-C bond by, e.g., straightening the C#C-C angle; and can also be used to overcome any barrier by the use of an applied force. It will be necessary to examine this reaction more carefully to determine if transfer of the hydrogen to tin can be performed in one step. If not, the hydrogen could be transferred to a somewhat stronger radical as an intermediate step.