If someone says krias shema on time before he is able to make the brachos for krias shema is that being mekyem the mitzvah lechatchilla? Sometimes shabbos minyan is later than the zeman for krias shema, so krias shema is said earlier, at home.
Lechatchilah, kerias shema should be recited together with the berachos. This is clear from the ruling of the Rambam (Keriyas Shema 3:13) and the Shulchan Aruch (67) whereby one who is in doubt concerning whether he recited kerias shema or not, should recite it again with the blessings. Although the blessings are not de’oraisah, one recites them as part of the kerias shema. See also Kessef Mishnah, citing from Rashba (320).
However, when the time for kerias shema is running out, one must recite kerias shema without the blessings, and repeat it later, in shul, with the blessings.
Indeed, according to the Shulchan Aruch (58:2) one should recite kerias shema as early as possible, even if this means reciting kerias shema without its berachos (see Mishnah Berurah 58:10; 58:3, citing from the Gaon).