Rhodium and iridium were discovered independently in the same year and also share many resemblances in their chemistry [1–10]. They form a wide range of conventional complexes as well as those of π-bonding ligands. Both metals exhibit an extensive chemistry, principally in the +3 oxidation state, with +1 also being important, and a significant chemistry of iridium +4 existing. Few compounds are known in the +2 state, in contrast to the situation for cobalt, their lighter homologue (factors responsible include the increased stability of the +3 state consequent upon the greater stabilization of the low spin d6 configuration as 10 Dq increases).