The reductive activation of [M5C(CO)15](M = Ru or Os) and subsequent reactions of the dianion [Os5C(CO)14]2–, carbonylation of [M5C(CO)15](M = Ru or Os), and the crystal structures of [Os5C(CO)16], [N(PPh3)2]2[Os5C(CO)14], and [Os5C(CO)14{Au(PPh3)}2]