RestSharp - Unable to cast object of System.String to type System.Generic.IDictionary
===

I am new to RestSharp. I have a Restful Service writtein in python which returns a Json message. I wrote a C# client using RestSharp to deserialize the json message to object.  

The response content is 
"\"[{\\\"coupon\\\": 4.5, \\\"cusip\\\": \\\"912810QB7\\\", \\\"currface\\\": 1000000, \\\"origface\\\": 1000000}]\"" 

response.data is null. 

The inner Exception in response object is
"Unable to cast object of type 'System.String' to type 'System.Collections.Generic.IDictionary`2[System.String,System.Object]'."

Below are my code:

    public class QuartzServiceAdapter
    {
        const string BaseUrl = "http://localhost:7666/ahs/";

        public QuartzServiceAdapter() { }

        public T Execute<T>(RestRequest request) where T : new()
        {
            var client = new RestClient();
            client.BaseUrl = BaseUrl;
            var response = client.Execute<T>(request);
            return response.Data;
        }

        public List<RootObject> GetBond()
        {
            var request = new RestRequest(Method.GET);
            request.OnBeforeDeserialization = resp => { resp.ContentType = "application/json"; };
            request.Resource = "getabond";
            //request.RootElement = "RootObject";
            return Execute<List<RootObject>>(request);
        }
    }

i created the following object using http://json2csharp.com/

    public class RootObject
    {
        public double coupon { get; set; }
        public string cusip { get; set; }
        public int currface { get; set; }
        public int origface { get; set; }
    }

Any ideas on why the deserialization is failing?
Thank you in advance!
