Conformationally restrained octahedral metallacrown ethers with 1,2-(Ph2P(CH2CH2O)2)2C6H4 ligands.: X-ray crystal structure of cis-Mo(CO)4{1,2-(Ph2P (CH2CH2O)2)2C6H4-P,P′}

A new alpha,omega-bis(phosphine)-polyether ligand, 1,2-(Ph2P(CH2CH2O)(2))(2)C6H4, has been synthesized and used to prepare a number of conformationally restrained metallocrown ethers. The reaction of 1,2-(Ph2P(CH2CH2O)(2))(2)C6H4 and Mo(CO)(4)(nbd) gives a good yield of cis-Mo(CO)(4) {1,2-(Ph2P(CH2CH2O)(2))(2)C6H4-P,P'}. This complex has been isomerized to trans-Mo(CO)(4) {1,2-(Ph2P(CH2CH2O)(2))(2)C6H4-P,P'} using both UV light and HgCl2 catalysis. The reaction of 1,2-(Ph2P(CH2CH2O)(2))(2)C6H4 with fac-RuCl2(CO)(3)(THF) initially yields a mixture of monomeric and oligomeric cis,cis, trans-[RuCl2(CO)(2){1,2-(Ph2P(CH2CH2O)(2))(2)C6H4-P,P'}](n) metallacrown ethers. Surprisingly, the oligomeric metallacrown ethers slowly convert into the monomeric metallacrown ether at ambient temperature in a chloroform-d solution. This does not occur with the conformationally mobile [cis,cis, trans-RuCl2(CO)(2){Ph2P(CH2CH2O)(4)CH2CH2PPh2-P,P'}](n) metallacrown ethers. The X-ray crystal structure of cis-Mo(CO)(4){1,2(Ph2P(CH2CH2O)(2))(2)C6H4-P, P'} has also been determined. The four ether oxygens lie in a plane, and the average cross-ring oxygen-oxygen distance is slightly larger than those in metallacrown ethers containing Ph2P(CH2CH2O)(4)CH2CH2PPh2 ligands.