C# Deserialize JSON string into object using Newtonsoft.Json

I am trying to convert a json string to an object using Newtonsoft.json, but I am having some problems with the following conversion. I wonder if some one can explain this. thanks.

AddFaceResponse ir = JsonConvert.DeserializeObject<AddFaceResponse>(responseContentStr);

this is the json string responseContentStr

[{
    "faceId": "1fe48282-a3b0-47d1-8fa8-67c4fac3d984",
    "faceRectangle": {
        "top": 80,
        "left": 50,
        "width": 147,
        "height": 147
    }
}]

This is my model object.

public class AddFaceResponse
    {
        public class Face
        {
            public class FaceRectangle
            {
                public int top, left, width, height;
                public FaceRectangle(int t, int l, int w, int h)
                {
                    top = t;
                    left = l;
                    width = w;
                    height = h;
                }
            }
            public string faceId;
            public FaceRectangle faceRectangle;
            public Face(string id, FaceRectangle fac)
            {
                faceId = id;
                faceRectangle = fac;
            }
        }

        Face[] faces;
        public AddFaceResponse(Face[] f)
        {
            faces = f;
        }
    }

this is the error I am getting from visual studio.

Newtonsoft.Json.JsonSerializationException: Cannot deserialize the current JSON array (e.g. [1,2,3]) into type 'App2.AddFaceResponse' because the type requires a JSON object (e.g. {"name":"value"}) to deserialize correctly