Synthesis, NMR Characterization, and Cation Binding of Metallacrown Ethers with Asymmetric Bis(phosphinite) and Bis(phosphite) Ligands Derived from 2-Hydroxy-2‘-(1,4,7-trisoxo-9-nonanol)-1,1‘-biphenyl

Chlorodiphenylphosphine and 2,2‘-biphenylylenephosphorochloridite react with 2-hydroxy-2‘-(1,4,7-trisoxo-9-nonanol)-1,1‘-biphenyl to yield the new α,ω-bis(phosphorus-donor)polyether
ligands Ph2PO(CH2CH2O)3-2-C12H8-2‘-OPPh2 and (2,2‘-O2C12H8)P(CH2CH2O)3-2-C12H8-2‘-P(2,2‘-O2C12H8). These ligands react with Mo(CO)4(nbd) to form the monomeric cis-metallacrown ethers cis-Mo(CO)4{Ph2PO(CH2CH2O)3-2-C12H8-2‘-OPPh2} and cis-Mo(CO)4{(2,2‘-O2C12H8)P(CH2CH2O)3-2-C12H8-2‘-P(2,2‘-O2C12H8)}. The X-ray crystal structure of cis-Mo(CO)4{(2,2‘-O2C12H8)P(CH2CH2O)3-2-C12H8-2‘-P(2,2‘-O2C12H8)} indicates that in the solid
state three of the four metallacrown ether ring oxygens point away from the cavity in the
cis-metallacrown ether ring. Both metallacrown ethers undergo cis−trans isomerization in
the presence of catalytic amounts of HgCl2 but yield quite different products, cis-Mo(CO)4{Ph2PO(CH2CH2O)3-2-C12H8-2‘-OPPh2}·HgCl2 and trans-Mo(CO)4{(2,2‘-O2C12H8)P(CH2CH2O)3-2-C12H8-2‘-P(2,2‘-O2C12H8)}·HgCl2, when reacted with a stoichiometric amount of
HgCl2. NMR titrations of the cis-metallacrown ethers with lithium salts demonstrate that
the cis-metallacrown ethers form 2:1 complexes with Li+. The unexpected 2:1 ratio has been
confirmed by the isolation of [cis-Mo(CO)4{Ph2PO(CH2CH2O)3-2-C12H8-2‘-OPPh2]2LiBPh4. In
dichloromethane-d2 solution, this complex very slowly isomerizes to form a mixture of [trans-Mo(CO)4{Ph2PO(CH2CH2O)3-2-C12H8-2‘-OPPh2]LiBPh4 and the free cis-metallacrown ether,
indicating that the trans-metallacrown ether more strongly binds Li+ than does the cis-metallacrown ether. Neither 2:1 stoichiometries for Li+ complexes of cis-metallacrown ethers
nor complex formation by trans-metallacrown ethers have previously been reported.