They are not.
Can. 904 Remembering always that in the mystery of the eucharistic sacrifice the work of redemption is exercised continually, priests are to celebrate frequently; indeed, daily celebration is recommended earnestly since, even if the faithful cannot be present, it is the act of Christ and the Church in which priests fulfill their principal function.
Can. 906 Except for a just and reasonable cause, a priest is not to celebrate the Eucharistic sacrifice without the participation of at least some member of the faithful.
Can. 276 §1. In leading their lives, clerics are bound in a special way to pursue holiness since, having been consecrated to God by a new title in the reception of orders, they are dispensers of the mysteries of God in the service of His people.
§2. In order to be able to pursue this perfection:
1/ they are first of all to fulfill faithfully and tirelessly the duties of the pastoral ministry;
2/ they are to nourish their spiritual life from the two-fold table of sacred scripture and the Eucharist; therefore, priests are earnestly invited to offer the Eucharistic sacrifice daily and deacons to participate in its offering daily;
3/ priests and deacons aspiring to the presbyterate are obliged to carry out the liturgy of the hours daily according to the proper and approved liturgical books; permanent deacons, however, are to carry out the same to the extent defined by the conference of bishops
So, to review....
Liturgy of the Hours - Required
Daily Mass - Recommended