Can my boss agree to a pay raise then later tell me that he’s not sure whenI will get it?

Unfortunately, it is in fact most likely legal. An employer has the right to determine or set compensation more or less at will, and the law does not generally enforce promises. For the promise of a raise to be enforceable, one or both of the following would need to apply--

1) There was an actual contract or agreement for the raise; this would require that you provided consideration--that is that you voluntarily chose to do or give up something of value which your boss asked for you to do or give up, in order to bind the contract (similar to putting a deposit on a car or house to make the contract of sale enforceable). If a promise was made to you but you did not have to give anything to get it, that is an unenforceable promise, not a contract. For example: say you accepted the transfer to the different division in exchange for getting a raise (and that you had a choice--you could have refused the transfer); that could make a contract.

2) Or even if you did not do or give something required by the agreement, but nonetheless, in reasonable reliance on the promise, took some action to your detriment, and your boss knew or should have known you would do this; in that case, the fact that you relied on the promise to your disadvantage may make it enforceable. For example: say your boss knew you were looking for a different job and had or may have had a job offer; he then offered you a raise in hopes you would stay; if you gave up the other opportunity in reliance on the promise of a raise, that promise might be enforceable.

However, apart from 1) and 2), your boss may change his mind or go back on his word.