using System;

using System.Collections.Generic;

using Newtonsoft.Json;

using System.Linq;

public class Program

{

    public static void Main()

    {

        string id = "1";

        string data = "1,2,3";

        string data2 = @"{

   ""personalizations"": [       

   {

      ""template_id"":""" + id + @""",

      ""data"": [" + data + @"]

    }]

}";

        var result = JsonConvert.DeserializeObject<Root>(data2);

        Console.WriteLine(result.personalizations.First().template_id);

    }

    public class Personalization

    {

        public string template_id { get; set; }

        public List<string> data { get; set; }

    }

​

    public class Root

    {

        public List<Personalization> personalizations { get; set; }

    }

}