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

Abstract

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 Ph 2 PO(CH 2 CH 2 O) 3 -2-C 12 H 8 -2‘-OPPh 2 and (2,2‘-O 2 C 12 H 8 )P(CH 2 CH 2 O) 3 -2-C 12 H 8 -2‘-P(2,2‘-O 2 C 12 H 8 ). These ligands react with Mo(CO) 4 (nbd) to form the monomeric cis -metallacrown ethers cis- Mo(CO) 4 {Ph 2 PO(CH 2 CH 2 O) 3 -2-C 12 H 8 -2‘-OPPh 2 } and cis- Mo(CO) 4 {(2,2‘-O 2 C 12 H 8 )P(CH 2 CH 2 O) 3 -2-C 12 H 8 -2‘-P(2,2‘-O 2 C 1 2 H 8 )}. The X-ray crystal structure of cis- Mo(CO) 4 {(2,2‘-O 2 C 12 H 8 )P(CH 2 CH 2 O) 3 -2-C 12 H 8 -2‘-P(2,2‘-O 2 C 1 2 H 8 )} 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 HgCl 2 but yield quite different products, cis- Mo(CO) 4 {Ph 2 PO(CH 2 CH 2 O) 3 -2-C 12 H 8 -2‘-OPPh 2 }·HgCl 2 and trans- Mo(CO) 4 {(2,2‘-O 2 C 12 H 8 )P(CH 2 CH 2 O) 3 -2-C 12 H 8 -2‘-P(2,2‘-O 2 C 12 H 8 )}·HgCl 2, when reacted with a stoichiometric amount of HgCl 2 . 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 {Ph 2 PO(CH 2 CH 2 O) 3 -2-C 12 H 8 -2‘-OPPh 2 ] 2 LiBPh 4 . In dichloromethane- d 2 solution, this complex very slowly isomerizes to form a mixture of [ trans- Mo(CO) 4 {Ph 2 PO(CH 2 CH 2 O) 3 -2-C 12 H 8 -2‘-OPPh 2 ]LiBPh 4 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.