Vapor-phase impregnation and thermal equilibration of CpIr(CO)H2 in dehydrated M56Y (where M = H, Li, Na, K, Rb, and Cs) yields samples in which the guest displays two main anchoring modes. In Li56Y and Na56Y, a CpIrH2(CO)...M+ interaction is favored (type I), whereas in K56Y, Rb56Y, and Cs56Y the preferred-binding geometry involves CpIr(CO)H2...M+ (type II). The topology, spacial requirements, and ionic potential of the site II M+ cations appear to be mutually responsible for "lock-and-key" anchoring effects of CpIr(CO)H2 in the supercage of zeolite Y. The thermal and photochemical reactivities of CpIr(CO)H2-M56Y toward D2, HBr, CO, C6H6, and alkanes are investigated and compared with the situation known in solution. With D2, one finds only H/D exchange of the hydride ligands to yield intrazeolite CpIr(CO)D2-M56Y without hydride or Cp ring hydrogen scrambling, while exposure to CO yields the known intrazeolite species CpIr(CO)2-M56Y. In the case of both Bronsted acid H56Y and proton-loaded (HBr)8-Na56Y zeolites, one discovers a proton-induced, reductive-elimination, dimerization reaction, which yields the novel intrazeolite dimer Cp2Ir2(CO)2-M56Y anchored to a supercage Bronsted acid site via one of its bridge carbonyl ligands. By contrast to the situation found in solution, CpIr(CO)H2-M56Y so far appears to be photochemically and thermally inactive toward C-H bond activation chemistry with arenes and alkanes.