Since you have the active nitro group,you may end up with Grignard rgts as the following case: 1,2-Addition of Alkyl Grignard Reagents to the Nitro Group: Simple Access to

2-[Alkyl(hydroxy)amino]pyridine N-Oxides and 2-Alkylaminopyridine

N-Oxides;

You may need to change your strategy in achieving your desired target.

The preparation of the Grignard reagents successfully depends up on the use of moisture free solvent. Use double distilled dry ether .  3-nitrobenzyl bromide may be lacrimatory . During preparation of Grignard reagent  3-nitrobenzyl bromide should distilled under vacuum then it should be used to react with  fresh Mg metal get to good results.

Since you have the active nitro group,you may end up with Grignard rgts as the following case: 1,2-Addition of Alkyl Grignard Reagents to the Nitro Group: Simple Access to

2-[Alkyl(hydroxy)amino]pyridine N-Oxides and 2-Alkylaminopyridine

N-Oxides;

You may need to change your strategy in achieving your desired target.

In several Grignard reactions, initiation is problem; once initiated it can progress well. It also depends on MC of reagents & Mg quality.

Sometimes Grignard reactions can be initiated with small portion of bromo reagent at higher concentration of about 20-30%w/v in solvent at appropriate temp. in the presence of cat. I2. 

After initiation, remaining bromo reagent & solvent can be added under N2 and reagent can be prepared.

Nitro groups react with grignards unless there is some additional stabilisation present.

In which case they can be prepared by magnesium halogen exchange, using the likes of a Knochel transmetallation. However a benzylic bromide is too unreactive to generate in this fashion.

You most likely will not be able to prepare your desired grignard reagent. I suggest finding an alternative option. What did you intend to do with this grignard?

Keep it all dry and use 1,2-dibromoethane to activate. I have been dry stirring the Mg turnings for 20 mins. Then add 10% of the solvent/reactant mixture to the turnings. After this turn off the stirring and syringe the dibromoethane directly into the turnings. The turnings in the mixture should start evolving ethene gas off the surface when activated. Then syringe the other 90% into the reaction flask. Be careful of thermal runaway. Keep an ice bath close.

I agree with the view point of Dr. Chen and Harris that nitro group can react with grignard reagent but in my case i am getting only starting

 i want to react Grignard reagent  with chlorodiisopropylsilane and finally want to reduced nitro group

Thank every one for their nice suggestion