Co-ordination chemistry of macrocyclic compounds with dangling phosphines.Unusual NMR shifts in metallo-calix[4]arenes

The chelating behaviour of three polyphosphines, cone-5,11,17,23-tetra-tert -butyl-25,26,27,28-tetrakis(diphenylphosphinomethoxy)calix[4]arene L-1, con e-5,11,17,23-tetra-tert-butyl-25,26,27-tris(diphenylphosphinomethoxy)-28-me thoxycalix[4]arene L-2, and cone-5,11,17,23-tetra-tert-butyl-25,26-bis(diph enylphosphinomethoxy)-27,28-dihydroxycalix[4]arene L-3, has been investigat ed. When [Mo(CO)(3)(C7H8)] and tetraphosphine L-1 are heated together under reflux in tetrahydrofuran (THF) complex [Mo(CO)(3)L-1] 1 is formed, for wh ich the calixarene behaves as a fac-bonded tridentate ligand with one phosp hine remaining free. Similar fac-chelating behaviour is found with [Mo(CO)( 3)L-2] 2, which is obtained from triphosphine L-2. Formation of this latter complex is accompanied by the calixarene matrix adopting a partially flatt ened-cone conformation. In contrast, the conventional cone conformation is maintained in the trinuclear complex [(AuCl)(3)L-2] 3, obtained quantitativ ely by treating L-2 with [AuCl(THT)] (THT=tetrahydrothiophene). Reaction of L-1 with [RuCl2(DMSO)(4)] (DMSO=Me2SO) in CH2Cl2 results in selective form ation of the deep purple complex [RuCl2L2] 4 built around a fac-trigonal bi pyramidal RuCl2P3 structure. Complex 4 reacts reversibly and stepwise with two equivalents of CH3CN. The calculated stability constants, as determined from a spectrophotometric titration, are log beta(1)=9.1 and log beta(2)=1 2.4. The proximally substituted calixarene L-3 reacts with [PtCl2(COD)] (CO D=cycloocta-1,5-diene) to afford the chelate complex cis-[PtCl2L3] 5. As re vealed by an X-ray diffraction study, the P-Pt vectors point away from the calixarene axis in the solid state. The axial H atom of the C6H2CH2 group l ocated between the two phosphine units of L-3 undergoes a significant low-f ield shift upon complexation (delta 7.32 vs. 4.48 for free L-3) presumably due to interaction with the lone pairs of the two neighbouring O-atoms. Com plex 5 displays dynamic behaviour in solution, which can be rationalized as follows: (i) a fast flip-flop motion of the hydroxyl groups at low tempera ture, alternately forming hydrogen bonds with each of two neighbouring phen olic oxygens; (i) a reversible inversion of the phenol ring through the low er-rim annulus, triggered by breakage of the hydrogen bonds at higher tempe rature. Reaction of [PtCl2(COD)] with one equivalent of L-1, followed by in situ oxidation with NH2CONH2. H2O2, results in formation of a chelate comp lex, containing two proximal phosphines bonded to platinum as in 5 and two pending CH2P(O)Ph-2 phosphine oxides. Stepwise reaction of [PtCl2(COD)] wit h one equivalent of L-1 and two equivalents of [AuCl(THT)]gives a cis compl ex in which the platinum atom is again bonded to two proximal phosphines an d the two AuCl units to the other two phosphine arms. As in 5, an anomalous low-field shift is observed for the axial C6H2CH belonging to the platinoc ycle of these complexes.