Command Block Issue

If I use this command:

setblock ~-3 ~ ~ minecraft:command_block 0 replace {Command:"testfor @p[r=5] {Inventory:[tag:{display:{Name:"Key"}}}]}"}

I get this output:

Data tag parsing failed: Unexpected token 'K' at: Key"}}}]}"

"Key" is used in the command to specify the item needed with a comparator to trigger the teleport command block. It needs to be used multiple times because it will be on a server so the command block that detects the item needs to be replaced. If there is another way I can do this without an error please report to me.