Synthesis, reactions and X-ray crystal structures of metallacrown ethers with unsymmetrical bis(phisphinite) and bis(phosphite) ligands derived from 2-hydroxy-2 '-(1,4-bisoxo-6-hexanol)-1,1 '-biphenyl

Chlorodiphenylphosphine and 2,2'-biphenylylenephosphorochloridite react wit h 2-hydroxy-2'-(1,4-bisoxo-6-hexanol)-1,1'-biphenyl to yield the new alpha, omega-bis(phosphorus-donor)-polyether ligands, 2-Ph2PO(CH2CH2O)(2)-C12H8-2' -OPPh2 (1) and 2-(2,2'-O2C12H8)P(CH2CH2O)(2)-C12H8-2'-P(2, 2'-O2C12H8) (2). These ligands react with Mo(CO)(4)(nbd) to form the monomeric metallacrown ethers, cis-Mo(CO)(4){2-Ph2PO(CH2CH2O)(2)-C12H8-2'-OPPh2} (cis-3) and cis- Mo(CO)(4){2-(2,2'-O2C12H8)P(CH2CH2O)(2)-C12H8-2'-P(2,2'-O2C12H8)} (cis-4), in good yields. The X-ray crystal structures of cis-3 and cis-4 are signifi cantly different, especially in the conformation of the metal center and th e adjacent ethylene group. The very different C-13-NMR coordination chemica l shifts of this ethylene group in cis-3 and cis-4 suggest that the solutio n conformations of these metallacrown ethers are also quite different. Both metallacrown ethers undergo cis-trans isomerization in the presence of HgC l2. Although the cis-trans equilibrium constants for the isomerization reac tions are nearly identical, the isomerization of cis-3 is more rapid. Pheny l lithium reacts with cis-3 to form the corresponding benzoyl complexes but does not react with either trans-3 or cis-4. Both the slower rate of cis-t rans isomerization of cis-l and its lack of reaction with PhLi are consiste nt with weaker interactions between the hard metal cations and the carbonyl oxygens in both trans-3 and cis-4. (C) 1999 Elsevier Science S.A. All righ ts reserved.