[SalesForce] Can you query new opportunity contact roles

As a start, the 'Leads__r' relationship is based on a custom field, as noted by the __r at the end, while convertedContactId is a standard field. Off the bat you're querying via the wrong relationship.

Looking at the schema it looks like there's no way to use a subquery (what your join is technically called in SOQL) as there's no relationship name. This is a quirk that can only happen with customer foreign-key (aka lookup) relationships. This means you'll need to change your logic to either

1. Query leads and their related contacts, like so: SELECT convertedContactId FROM Lead WHERE convertedContactId IN ('your id that isn't provided as text', 'and the other one I'm too lazy to transcribe')
2. Query the contacts, and then make a second query for any leads that reference them. As you're only querying the Id from the contact the first option makes sense, but I don't know your business case for this.

SOQL is odd in that it doesn't join in the traditional way, and instead uses subqueries in one direction and cross-object fields (e.g. querying lead for convertedContact.name) in the other. (there's also semi-joins and anti-joins, but that's getting longwinded)

1) Can you test running this code in an asynchronous method called by the trigger? I seem to recall Opportunity Contact Roles not being populated til Workflows normally would (after after update triggers fire).

2) I would strongly recommend querying the OpportunityContactRoles using trigger.newMap.keySet() outside of the loop instead, otherwise the trigger is not going to be bulk-safe.