conditionally add formGroup to another formGroup angular2

I am trying to add a formGroup to my overall form conditional on a specific field being of a certain type in my case. My function to add this formGroup looks like this:

  initSocial() {
      const group = <FormGroup>this.cardForm;
        group.addControl(
          'social': this._fb.group({
            'fb': new FormControl(this.currentCard.social.fb),
            'yt': new FormControl(this.currentCard.social.yt),
            'ig': new FormControl(this.currentCard.social.ig),
            'tw': new FormControl(this.currentCard.social.tw),
          })
        )
  }

Right now I am getting a typescript error under the colon after 'social' saying a ',' is expected. I haven't been able to test this to see if addControl() will even work.

My function to fire initSocial is in ngOnInit and looks like this:

      if(this.currentCard.cardType === "brand"){
        this.initSocial();
      }

Any help/tips/suggestions would be much appreciated.