purchase_print_report/views/qweb.xml

<?xml version="1.0" encoding="utf-8"?>
 <!--<templates id="template" xml:space="preserve">
  <t t-extend="ListView.buttons">

    <t t-jquery="button.oe_list_add" t-operation="after">

    <t t-if="widget.model=='account.invoice'">

    <button class="oe_button oe_list_add_planing_daily oe_highlight"

    type="button">Create Planing Daily</button>

    <button class="oe_button oe_list_view_current_session oe_highlight"

    type="button">Current Session</button>

    </t>

    </t>

    </t>


</templates>  -->

<template id="template" xml:space="preserve">
<t t-extend="ListView.buttons">
            <t t-jquery="button.oe_list_add" t-operation="replace">
                    <button t-if="widget.model == 'purchase.order'"  class="oe_button oe_new_button oe_highlight" type="button">Boton</button>

    </t>
</t>
</template>