The reaction of tetrasulfonated calixarene (trioctylammonium salt) with P(NMe2)(3) followed by treatment with gaseous NMe2H gave a zwitterionic six-coordinate phosphorus(V) species 1 containing a P(H)(NHMe2) group which can be stored for months without decomposition. In water, 1 loses NHMe2 and rearranges to form the water soluble phosphite L-c. Phosphite L-c has a half-life in water of ca. 5 h decomposing to H3PO3 and free tetrasulfonated calix arene. Compound 1 serves as a convenient precursor to L-c and complexes of L-c are formed by dissolving 1 in water in the presence of labile metal complexes. The products have been identified by comparison of their 31 P NMR data with well established analogues of calix arene derived phosphites. In this way the water soluble complexes [Rh(acac)(CO)(L-c)(2)] (2c) [Rh2Cl2(CO)(2)(L-c)(2)] (3c), [Pt2Cl4(L-c)(2)] (4c) and [PtCl2(L-c)(2)] have been tentatively identified. The rhodium complex 3c has a half-life in water of 4 months. Two-phase (water/toluene) hydroformylation of 2-methylpentenoate with 2c as a catalyst has been investigated and the results compared with the same reaction in toluene with lipophilic analogues of 2c. Under mild conditions, with 2c catalyst, branched aldehydes are the only products of hydroformylation and one of the branched aldehydes is selectively hydrogenated to give the lactone derivative.