Complexation and selective cyclization of substituted oxalamidines

Crystallographic data for the acyclic benzylic substituted oxalamidine 3 an d the all;yl substituted oxalamidine 4 reveal different structures for comp ound 3 (s-trans(E/E)configuration and intramolecular hydrogen bridges) and compound 4 (s-cis(E/E)configuration without hydrogen bridges). On the basis of the different configurations of these isomeric oxalamidines, the comple xation on a (CO)(4)Mo-fragment varies remarkably: Complex formation of liga nd 3 takes place at the sp(2)-hybridized nitrogen atoms by rotation of the central C-C-axis, isomerisation of the C=N bonds, and by breaking of the hy drogen bridges. Because of the steric hindrance in 4, the initiating coordi nation should occur on the sp(3)-nitrogen atoms, followed by a intramolecul ar proton transfer and rehybridization. This complexation is favoured in th e cases of cyclic oxalamidines. The molecular structures of the oxalamidine s 3 and 4, their (CO)(4)Mo-complexes 5, 6, and of the coordination compound of the cyclic 2,3-bis(phenylamino)chinoxaline 8 were unambiguously clarifi ed by X-ray analysis. The cyclization of the different substituted oxalamid ines 3 and 4 by phosgene or thiophosgene in the presence of NaN[Si(CH3)(3)] (2) in THF proceeds regioselectively to the asymmetric 2-imidazolidinones a nd -thiones LI and 14, respectively. In contrast to 3, 4 cyclizes in toluen e selectively to the isomeric symmetric 2-imidazolidinthione 13. Furthermor e, the cyclization on the co-ordinated oxalamidines with oxalyl chloride pr ovides exclusively the co-ordinated 2-imidazolidinones 12 and 15, which ret ain the substituent pattern of the starting complexes 5 and 6 - the (CO)(4) Mo-fragment acts as a protecting group.