What investment do you mean exactly? CONFOTUR , an actual Business with employees or large enough CD deposit in a DR bank?
All that is through
migracion.gob.do
For citizenship that is the MIP
mip.gob.do
The MIP is in charge of naturalization to DR citizenship. As far as I know, you start with being a legal resident and then however long that takes from application and any wait period to then become naturalized. Probably not a short period of time, but you can contact the MIP directly on that.