I'm interested to know what the bits between the [ ]'s are?
It seems you have a MultiSig wallet of some description (either normal MultiSig or perhaps 2FA). Unfortunately, you cannot recreate a MultiSig wallet from only one private key... it needs all the keys that were originally used to create the wallet.
Also, with Electrum you should not need to save private keys... you should only be using "seeds" to restore wallets... that is the whole point of having seeds!
Electrum 3.0.1 - default_wallet [2fa]
I need that private key for my exact BTC address
what to do now?