Question about C# covariance

In the code below:

interface I1 { }
class CI1: I1 { }

List<CI1> listOfCI1 = new List<CI1>();

IEnumerable<I1> enumerableOfI1 = listOfCI1; //this works

IList<I1> listofI1 = listOfCI1; //this does not

I am able to assign my "listOfCI1" to an IEnumerable<I1> (due to covariance)

But why am I not able to assign it to an IList<I1>? For that matter, I cannot even do the following:

List<I1> listOfI12 = listOfCI1;

Shouldn't covariance allow me to assign a derived type to a base type?