[HttpPost]
public ActionResult Asociar(int? id, int proveedorId)
{

    return PartialView("Companies");
}

<a class='asociar' style='color: #004881' href='/administrador/asociar/@item.CompañiaId' id='@item.CompañiaId' title='Asociar al Proveedor'>

$('.asociar').click(function () {
    var proveedorId = $("#proveedorId");
    $.ajax({
        url: this.href,
        type: "post",
        data: proveedorId,
        success: function (result) {
            if (result.success) {
                //Refresh
                window.location.reload();
            }
        }
    });
});