Hi Andreas
As for if .NET 4.5 is compliant please review SAP KB 1678822 you will see that it references note 14 so scroll to the bottom of the KB for note 14 and see the hyperlink.
For the above error anytime a customer gets that error the solution Roberto provided 1866087 has always helped. If you have done this and are still having an issue then maybe the problem is your MS installer.
The error you are getting is actually an MS installer error. Are you able to install other software? Try installing office or somthing else just to test. Windows 2012 R2 should have MS installer 5.0 check to see if that is still the version and not replaced. You can check it by opening a command prompt and typing MSIExec it will give you the version and all. Also take a look at the operating system event logs application, system and security to see if anything gets generated.
April