p tert Butylcalix[4]arene Tetrakis(diphenylphosphinite) and Tetrakis(dimethyl¬phosphinite) Acting as Phosphorus Binding Surfaces for Monometallic and Homo and Heterodimetallic Fragments

p-tert-Butylcalix[4]arene tetrakis(diphenylphosphinite), calix[4]-(PPh(2))(4) (1), and tetrakis(dimethylphosphinite), calix[4]-(PMe(2))(4) (2), provide a phosphorus surface consisting of four coplanar trivalent phosphorus atoms for binding two metal ions into a close geometrical proximity. Homodimetallic complexes have been obtained in the reaction of 1 with [(COD)MCl(2)] [COD = cycloocta-1,5-diene], namely, [{calix[4]-(PPh(2))(4)}(MCl(2))(2)] [M = Pd (3), Pt(4)]. Characterizations by H-1 and P-31 NMR were particularly informative and showed how the bridging methylene of the calix[4]arene skeleton may function as a spectroscopic probe, A dimeric complex was obtained by reacting 1 with [Rh(CO)(2)Cl](2) to give [{calix[4]-(PPh(2))(4)}{Rh(CO)Cl}(2)] (5). Reaction of 1 with excess NiCl2 gave exclusively the monometallic complex, [{calix[4]-(PPh(2))(4)}NiCl2] (6), regardless of the stoichiometry used. The analogous Pd monometallic complex (7) undergoes a ligand disproportionation reaction, while the corresponding Pt analogue does not exist under the same conditions. Complex 6 represents a good entry to dinuclear heterodimetallic complexes. In fact, its reaction with [(NBD)Mo(CO)(4)] [NBD = norbomadiene] led to [{calix[4](PPh(2))(4)}NiCl2{Mo(Co)(4)}] (8). The use of the more basic and less sterically demanding ligand 2 led to the synthesis of homonuclear bimetallic complexes [{calix[4]-(PMe(2))(4)}(MCl(2))(2)] [M = Ni (9), Pd (10), Pt (11)].