The docs for split on
http://docs.mongodb.org/manual/reference/command/split/#split-a-chunk-using-values-of-a-hashed-shard-key

seem incorrect. the contents of the "bounds" array should be documents that contain the key & value of the shard key, not just the value. The example provided should be something like :

db.runCommand( { split: "test.people" ,
               bounds : [ { _id: NumberLong("-5838464104018346494") },
                          { _id: NumberLong("-5557153028469814163") }] } )