Your code have two problems:
1. Your rectangleShape is invalid, as below is the standard and a sample:
new RectangleShape(double minX, double maxY, double maxX, double minY)
new RectangleShape(-33.86000, 151.219389, -32.860000, 151.209389)
2. I think your currently map unit should be DecimalDegree, or else this rectangle shape will be very small in map.
But if you choose BingMap, please keep set iOSMap.MapUnit = GeographyUnit.Meter;