Hi @George_Kamel ,
I think latest compass aggregation tab have an “Export to Language” for Go. Also maybe the beta has also advanced language syntax 
It recommends me to use:
bson.D{
{"$regexMatch",
bson.D{
{"input", "$name"},
{"regex", primitive.Regex{Pattern: "ron"}},
{"options", "i"},
},
},
},
Have you tried the compass syntax?
Thanks
Pavel