I've always heard, wrt clematis, that they like their feet in the shade and their head in the sun. Also, they tend to be temperamental about being moved. My plant that now blooms freely and has for years, gets direct sun about two hours per day and gets filtered or indirect light for the rest of the time. Is totally shaded from morning through early afternoon and then from about 2:30 p.m. on is shaded under the canopy of a huge oak tree. The plant gives a hundred or more blooms per year, and in peak bloom you can barely see the leaves for the blossoms. So IMO mostly filtered light should be o.k. but dense shade or mostly shade would be a problem.