I would expect no problem running the mojoPortal .NET 4 packages under .NET 4.5.1 but have not tried it yet.
I did a quick google for ".NET 4.5.1 problem" to see if anyone is having problems with it and found a link about the 4.x framework installation stalling which may be relevant to solving what you encountered with .NET .4.5.
The google results also show some people having IE 11 problems even with .NET 4.5.1.
I have not had IE 11 problems using any fully patched installation of .NET 4.5 but have seen problems on servers that don't have all the windows updates.