Gravar-mail: Crystal structure of (2-{[3,5-bis­(1,1-di­methyl­eth­yl)-4-hy­droxy­phen­yl](5-methyl-2H-pyrrol-2-yl­idene)meth­yl}-5-methyl-1H-pyrrolido-κ(2) N,N′)di­fluoridoboron