Hello Henrique,

Try this:

create fields in python file :

'contact_person_many': fields.many2many('dispatch.contact.person', string='Contact Persons', required=True),        'contact_person_one': fields.many2one('dispatch.contact.person', string='Contact Person'),

def onchange_contact_person_many(self, cr, uid, ids, contact_person_many, context=None):
        if contact_person_many:
            li_emp = []

            for i in contact_person_many[0][2]:
                li_emp.append(i)           

            emp = tuple(li_emp)     

           return {'domain': {'contact_person_one': [('id', 'in', emp)]}}

     In xml file:

<field name="contact_person_many" widget="many2many_tags" on_change="onchange_contact_person_many(contact_person_many)"/>                      

<field name="contact_person_one"/>