As much as he's a Garden favorite, Robinson has often been a headache for D'Antoni and was benched for 14 straight games earlier this season. During that time Robinson's agent, Aaron Goodwin, wanted the Knicks to trade Robinson because he felt that D'Antoni's problems with his client were personal.
But Robinson rejoined the rotation Jan.1 and has helped the Knicks in recent weeks. So if they were to deal him by next month's trading deadline, they'd want to get a player back who also has an expiring contract - Robinson has a one-year deal at $4 million - and who also would help them make the playoffs. The Celtics can't offer the Knicks any such player.
UPDATE: According to The Hoops Forum, the deal is almost done and it involves Eddie House and Bill Walker. This will not work straight up (according to RealGM's trade checker).
(h/t Celtics Blog)