Updating List Title Using REST

Hi,

I am trying to update a list title using the REST api and HttpClient. I have the following code but the StatusCode is returning BadRequest.

private async void UpdateTitle()
        {
            string webUrl = http://server;
            Uri uri = new Uri(webUrl + "/_api/web/lists/GetByTitle('Old')");
            //start replacement
            HttpClientHandler httpClientHandler = new HttpClientHandler();
            httpClientHandler.UseDefaultCredentials = true;
            HttpClient client = new HttpClient(httpClientHandler);
            client.DefaultRequestHeaders.Add("ContentType", "application/json;odata=verbose");
            string digest = await GetFormDigest("http://devsp13.dev.local/_api/contextinfo");
            client.DefaultRequestHeaders.Add("X-RequestDigest", digest);
            client.DefaultRequestHeaders.Add("X-HTTP-Method", "Merge");
            client.DefaultRequestHeaders.Add("IF-MATCH", "*");

            HttpContent content = new StringContent("{ '__metadata': { 'type': 'SP.List' }, 'Title': 'NewTitle' }");
            HttpResponseMessage response = await client.PostAsync(uri, content);
            response.EnsureSuccessStatusCode();
}

I'm guessing I've missed something in forming the HttpClient but I'm struggling to see what. Any help is much appreciated.

Cheers,

Geoff