通过cURL发送JSON后，Solr PHP错误请求

I am trying to update fields in my solr documents via cURL, because a partial update method is not available in Apache's Solr PHP Client. Before i tried the PHP cURL API, I tried it manually via terminal:

curl http://[server-ip]:8080/solr/collection1/update -H 'Content-type:application/json'd-d '[{"url":"https:\/\/hrz1.rz.htw-berlin.de\/oneNet\/NetStorage\/Common%20HRZ\/Dozent\/FB4\/Classen\/DAWeb\/crawling12.pdf","titel":"Crawling - Ingo Cla\u00dfen HTW Berlin-8-8-1","keywords":{"add":["cla\u00dfen","peter pan","htw-berlin"]},"bewertung":{"set":"5"},"schwierigkeit":{"set":"5"}}]'

Response:

{"responseHeader":{"status":0,"QTime":9}}

It works quiet well. After that i tried the PHP API.

$exampledata = array("url" => 'google.de', "titel" => "peter");
//make  a json file
$update = json_encode($exampledata);
pr($update);
//send json file to solr-server
$curlSolrUpdate = curl_init();
curl_setopt($curlSolrUpdate, CURLOPT_URL, "http://[server-ip]:8080/solr/collection1/update");

//curl_setopt($curlSolrUpdate, CURLOPT_POST, 1);
curl_setopt($curlSolrUpdate,CURLOPT_POST,true); 
curl_setopt($curlSolrUpdate, CURLOPT_POSTFIELDS, $update);
//curl_setopt($curlSolrUpdate, CURLINFO_HEADER_OUT, true);
curl_setopt($curlSolrUpdate, CURLOPT_RETURNTRANSFER, true);
curl_setopt($curlSolrUpdate, CURLOPT_HTTPHEADER, array('Content-Type:application/json'));
curl_setopt($curlSolrUpdate, CURLOPT_VERBOSE, true);


$verbose = fopen('php://temp', 'rw+');
curl_setopt($curlSolrUpdate, CURLOPT_STDERR, $verbose);


$result = curl_exec($curlSolrUpdate);

rewind($verbose);
$verboseLog = stream_get_contents($verbose);


echo "Verbose information:
<pre>", htmlspecialchars($verboseLog), "</pre>
";
//get server response

die(pr($result));

Server-Response:

 Verbose information:
 * About to connect() to [server-ip] port 8080 (#0)
 *   Trying [server-ip]...
 * connected
 * Connected to 1[server-ip] ([server-ip]) port 8080 (#0)
 > POST /solr/collection1/update HTTP/1.1
 Host: [server-ip]:8080
 Accept: */*
 Content-Type:application/json
 Content-Length: 35

 * upload completely sent off: 35 out of 35 bytes
 * HTTP 1.1 or later with persistent connection, pipelining supported
 < HTTP/1.1 400 Bad Request
 < Server: Apache-Coyote/1.1
 < Content-Type: text/plain;charset=UTF-8
 < Transfer-Encoding: chunked
 < Date: Sun, 02 Feb 2014 20:51:43 GMT
 < Connection: close
 < 
 * Closing connection #0

 {"responseHeader":{"status":400,"QTime":2},"error":{"msg":"Unknown command: url [6]","code":400}}

So why does Solr says bad request -> unknown command: url ? Does my file need to get escaped strings? I already validated the json format.

First i tried with a much more complex json file. I also tried to set the length of the content for header information. But this is being set automatically by cURL.

Thanks in advance for your help !!!