Select2 en yii2

sudo composer require kartik-v/yii2-widget-select2 "*"

agregar

use yii\helpers\Html;
use yii\helpers\ArrayHelper;
use yii\widgets\ActiveForm;
use app\models\CatMatyreact;
use kartik\select2\Select2;

   <?= $form->field($model, 'id_catmat')->widget(Select2::classname(), [

       'data'=> ArrayHelper::map(CatMatyreact::find()->all(),'id','nombre'),

       'language'=> 'es',

       'options'=> ['placeholder' => 'Seleciona'],

       'pluginOptions' => [

       'allowClear' => true

       ],

    ]); ?>