Desclaven is a powerful verb formed from des- (un-) and clavar (to nail), so it literally means "to un-nail". It creates a dramatic and almost visceral image that isn't found in everyday conversation.
In the song, Alejandro Sanz sings, "Que nos desclaven" (May they un-nail us), using it as a potent metaphor. He's describing a relationship so intertwined and painful that it feels like they've been nailed together, and he's pleading for a separation from this agonizing bond.
Alejandro Sanz is fed up. In "No Me Compares," he's talking to a lover who just can't stop comparing him to someone else. The song opens with a scene of things falling apart: the TV has snow, the rocking chair creaks, and it's even raining inside the living room. It's in this moment of decay that he decides it's time for some real talk. He's ready to show his true self, even the damaged parts, singing, "Ahora te enseño de donde vengo / Y las piezas rotas del motor" (Now I'll show you where I come from / And the broken pieces of the engine).
He's not just some new guy; he argues that he's a fundamental part of her life. He makes this beautiful claim: "Vengo del aire / Que te secaba a ti la piel mi amor" (I come from the air / that dried your skin, my love). He's the very atmosphere around her, while the other guy is just someone she met on a street that he is. The central message is a powerful demand: "No me compares" (Don't compare me). He insists he's unique, telling her it's "Imperdonable" (Unforgivable) to think he's like the other man, "Ni a él ni a nadie" (Not like him or anyone). The song builds from this quiet frustration into a huge, passionate chant, daring anyone to try and separate them because, as he sees it, "Yo soy tu alma, tú eres mi aire" (I am your soul, you are my air).