You need to re-frame the graph as the top-level object. You can use either:
{
"@context": ...,
"@type": "dcat:Distribution"
}
or
{
"@context": ...,
"@id": "http://example.com/datasets/1"
}
or
{
"@context": ...,
"example:props": {}
}
(i.e. object that contains any "example:props").