As shown by 31P NMR spectroscopy, addition of β‐cyclodextrin or randomly methylated β‐cyclodextrin to an aqueous solution of [HRh(CO){P(m‐C6H4SO3Na)3}3] has no effect on the organometallic complex. In contrast, [HRh(CO){(p‐tBuC6H4)P(m‐C6H4SO3Na)2}3] can be partially converted in the presence of the same β‐cyclodextrin derivatives into the hydroxy complex [HORh(CO){(p‐tBuC6H4)P(m‐C6H4SO3Na)2}2], under nitrogen, or to the hydrido complex [HRh(CO)2{(p‐tBuC6H4)P(m‐C6H4SO3Na)2}2] under carbon monoxide. This remarkable difference of behavior was attributed to the fact that the phosphane (p‐tBuC6H4)P(m‐C6H4SO3Na)2 forms more stable inclusion complexes with the β‐cyclodextrin derivatives than the phosphane P(m‐C6H4SO3Na)3. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)