I think that you understand that by allowing this to take place, you have failed in your responsibility as a teacher. With 45 students in the class, you cannot allow a small group to interfere in any way with your command of the space. The very first day that this was a problem you should have held them after class. Then you should have specifically told them that you wanted them to sit apart, to not work in groups together, and to behave professional. If you assign groups or seating you should have immediately split them up. Then you needed to specifically keep an eye on them in the next few classes and immediately when they got out of line, used the most severe authority you have. In many university classes the instructor has the authority to remove a student from class if they are disruptive. One of this group should have been dismissed from class on the second day that they were disruptive.

This is not vindictive or cruel. You have a responsibility to the other 44 students to see that they are in a positive learning environment. And you have a responsibility to the disruptive students to see that they learn a new attitude. When everyone understands that you mean business and will not stand for any nonsense, then you will get cooperation. Also, I agree that if you have a personal relationship with the students you will get better cooperation. You should learn the names of the students as fast as possible. By the third or fourth class you should know the names, majors, hometowns, dorms, whatever information you can get, about any potential trouble makers. Turn them from troublemakers into guided students.

Teaching is not lecturing. It is a management skill. And, that skill can be learned by practice, and pedagogically. Talk to some good teachers in your department to get tips.

You can do this. But many of us who won teaching awards started out tearing our hair out over our 'bad' students.