Rhodium and Iridium Complexes Derived from trans-[MCl(CO)(PPh3)2] (M = Rh, Ir) and Pyridine-2-thiolate or 4,6-Dimethylpyrimidine-2-thiolate Ligands: S-Monodentate Coordination versus S,N-Chelation and S,N-Bridging; Reactivity of trans-[Ir(‘Spy’)(CO)(PPh3)2] and trans-[Ir(‘SpymMe2’)(CO)(PPh3)2] towards Acid