Could not cast or convert from System.String to System.Type

I am getting error on System defined types. When I pass custom defined type, it works:

_backgroundJobClient.Enqueue(() => _emailSender.SendEmail(emailParams)); <- This works.
_backgroundJobClient.Enqueue(() => _emailSender.SendEmail(“string”)); <- This doesn’t work.

Any insights from expert on this is highly appreciated. Thank you!