why dry ether is needed for reaction containing grignard reagents i thought because grignard reagent may react with H2O but R^- ​ may react with R-O-R to give R-R AND R-O^- SINCE R^- is better base and Nu ^- than R-O^-

Dear Student,

Ether is used as a solvent for reactions involving grignard reagents because it is aprotic in nature and can solvate the magnesium ion.

Ether has no acidic protons thus it is not energetically feasible for the R^- nucleophile to react with the ether as the partial positive charge is less on the carbons bonded with the oxygen molecule due to equal distribution of the electron density.
 
Also, because of the polar nature of the C-O bond, the oxygen atoms can solvate and stabilize the R-Mg⁺ ions.
Thus, ether is used as the solvent of choice for reactions involving Grignard reagents.

Regards