We also launched initiatives to put people to work upgrading our homes, businesses, and factories so that they waste less energy.
The expression work upgrading confuses me a little. Does the word work have an expression of the form work doing something? Why does the word upgrading use the form doing instead of to do?
Work and upgrading do not go together here; they should be parsed as
[to put people to work] [upgrading our homes, businesses, and factories]
To put sb to work or set sb to work is to give them work to do, as Macmillan has it, from the use of put to mean
to cause someone or something to be in a particular situation or state
e.g. put someone to work: He was put to work filing all the papers.
The phrase introduced by upgrading describes the nature of the work to be done.