Optically active transition-metal compounds. Stereochemistry and crystal structure determination of [η5-C5H5)CoI-NC5H4C(R)NCH(CH3)(C6H5)]+I−, R = CH3

Abstract The crystal structures and absolute configurations of (η 5 -C 5 H 5 )-CoI(NC 4 H 3 -C(R)=N( S )-CH(CH 3 )(C 6 H 5 )) (R = H, compound I; R = CH 3 , compound II) have been determined by single crystal X-ray diffraction. Crystals of compound I are orthorhombic, with a 11.084(6), b 12.107(6) and c 13.121(7) A, space group P 2 1 2 1 2 1 and d (calcd, Z = 4) 1.69 g cm −3 The structure was solved by the Patterson technique and refined with use of full matrix least-squares methods to R ( F ) = 0.031 and R w ( F ) = 0.028. Compound II is nearly isomorphous and isostructural; a 11.246(6), b 11.923(6) and c 13.370(7) A, d (calc., Z = 4) 1.71 g cm −3 and was refined to the final agreement factors of R ( F ) = 0.044 and R w ( F ) = 0.035. The Co atom has a distorted tetrahedral coordination, with Co-I 2.595(2) for I and 2.607(2) A for II; Co-(η 5 -C 5 H 5 ring centroid) 1.681(4) and 1.703(5) A; Co-N(pyrrole) 1.905(9) and 1.885(9) A; Co-N(imine) 1.971(8) and 2.003(9) A, all the parameters being well within values found in the literature. The configuration around the chiral carbon of the phenylethylamine is S for both compounds, whereas the configuration around the metal is R in I and S in II. The different metal configurations in I and II have their origin in the two different substituents (R = H, CH 3 ) at the imine carbon atoms of the chelate ring, which induce completely different conformations of the ( S )-CH(CH 3 )(C 6 H 5 ) moiety in the two complexes. For both compounds the thermodynamically less stable isomer is enriched upon crystallization. Also, for compound I the solution and solid state conformations are almost opposite to each other, the conformation in the solid reflecting intramolecular interactions (phenyl/C 5 H 5 attraction).