code: func (c *Client) SendToAddressCommentAsync(address btcutil.Address,
  	amount btcutil.Amount, comment,
  	commentTo string) FutureSendToAddressResult {
  
  	addr := address.EncodeAddress()
  	cmd := btcjson.NewSendToAddressCmd(addr, amount.ToBTC(), &comment,
  		&commentTo)
  	return c.sendCmd(cmd)
  }
docs: // SendToAddressCommentAsync returns an instance of a type that can be used to
  // get the result of the RPC at some future time by invoking the Receive
  // function on the returned instance.
  //
  // See SendToAddressComment for the blocking version and more details.