Metallacrown ethers with trans-tetracarbonylmolybdenum(0) centers. X-ray crystal structures of trans-Mo(CO) 4{Ph 2P(CH 2CH 2O) nCH 2CH 2PPh 2- P, P′} ( n=3, 5) and trans-Mo(CO) 4{Ph 2P(CH 2CH 2O) 2-1-C 6H 4-2-(OCH 2CH 2) 2PPh 2- P, P′}

Abstract

Photolysis of the cis-Mo(CO) 4{Ph 2P(CH 2CH 2O) n CH 2CH 2PPh 2- P, P′}, ( 1, n=3; 2, n=4; 3, n=5) metallacrown ethers in tetrahydrofuran under nitrogen gives moderate yields of the corresponding trans-Mo(CO) 4{Ph 2P(CH 2CH 2O) n CH 2CH 2PPh 2- P, P′} ( 4, n=3; 5, n=4; 6, n=5) metallacrown ethers. The trans-metallacrown ethers are also obtained when catalytic amounts of HgCl 2 are added to chloroform solutions of the cis-metallacrown ethers. The 1⇄ 4 and 2⇄ 5 equilibria are established within 3 min at ambient temperature and approximately equal amounts of the cis- and trans-metallacrown ethers are present in the equilibrium mixtures. The 3⇄ 6 equilibrium is more complicated because HgCl 2 complexation by 3 also occurs in these solutions. Addition of excess HgCl 2 to the equilibrium mixture of 3 and 6 results in the formation of the previously reported cis-Mo(CO) 4{μ-Ph 2P(CH 2CH 2O) 5CH 2CH 2PPh 2- P, P′, O, O′, O″, O‴, O⁗}HgCl 2. Comparison of the X-ray crystal structures of the trans-metallacrown ethers 4– 6 and trans-Mo(CO) 4{Ph 2P(CH 2CH 2O) 2-1-C 6H 4-2-(OCH 2CH 2) 2PPh 2- P, P′} ( 7) indicates that both ring size and flexibility affect the conformations of the metallacrown ether rings. The larger oxygen–oxygen distances in the trans-metallacrown ethers, compared with those in the corresponding cis-metallacrown ethers 1, 3 and cis-Mo(CO) 4{Ph 2P(CH 2CH 2O) 2-1-C 6H 4-2-(OCH 2CH 2) 2PPh 2- P, P′} ( 8), may explain why the trans-metallacrown ethers have not been observed to bind strongly the hard metal cations.