[{"_id":ObjectId("5a934e000102030405000000"),"key":1},{"_id":ObjectId("5a934e000102030405000001"),"key":2},{"_id":ObjectId("5a934e000102030405000002"),"key":3},{"_id":ObjectId("5a934e000102030405000003"),"key":3},{"_id":ObjectId("5a934e000102030405000004"),"key":3}]

db.collection.aggregate([{$facet:{first:[{$match:{_id:{$gte:ObjectId("5a934e000102030405000002")}}},{$sort:{_id:1}},{$limit:2}],second:[{$match:{_id:{$lt:ObjectId("5a934e000102030405000002")}}},{$sort:{_id:-1}},{$limit:1}]}},{$project:{result:{$concatArrays:["$first","$second"]}}}])