GCD, Threads, Program Flow and UI Updating

I'm having a hard time figuring out how to put this all together. I have a puzzle solving app on the mac. You enter the puzzle, press a button, and while it's trying to find the number of solutions, min moves and such I would like to keep the UI updated. Then once it's finished calculating, re-enable the button and change the title.

Below is some sample code from the button selector, and the solving function: ( Please keep in mind I copy/paste from Xcode so there might be some missing {} or some other typos.. but it should give you an idea what I'm trying to do.

Basicly, user presses a button, that button is ENABLED=NO, Function called to calculate puzzle. While it's calculating, keep the UI Labels updated with moves/solution data. Then once it's finished calculating the puzzle, Button is ENABLED=YES;

Called when button is pressed:

- (void) solvePuzzle:(id)sender{
    solveButton.enabled = NO;
    solveButton.title = @"Working . . . .";

    // I've tried using this as a Background thread, but I can't get the code to waitTilDone before continuing and changing the button state.
    [self performSelectorInBackground:@selector(createTreeFromNode:) withObject:rootNode];

    // I've tried to use GCD but similar issue and can't get UI updated.
    //dispatch_queue_t queue = dispatch_queue_create("com.gamesbychris.createTree", 0);
    //dispatch_sync(queue, ^{[self createTreeFromNode:rootNode];});

    }

    // Need to wait here until createTreeFromNode is finished.
    solveButton.enabled=YES;
    if (numSolutions == 0) {
    solveButton.title = @"Not Solvable";
    } else {
        solveButton.title = @"Solve Puzzle";
    }
}

Needs to run in background so UI can be updated:

-(void)createTreeFromNode:(TreeNode *)node
{
   // Tried using GCD
   dispatch_queue_t main_queue = dispatch_get_main_queue();

 ...Create Tree Node and find Children Code...

if (!solutionFound){
    // Solution not found