ABSOLUTE-CONFIGURATION OF ORGANOMETALLIC COMPOUNDS .7. X-RAY STRUCTURAL STUDY OF (-)579-(+)436-(ETA-5-C5H5)MO(CO)2[(C5H5N)C(=S)NRSTAR] PREPARED FROM H2NRSTAR=(S)-(-)-ALPHA-PHENYLETHYLAMINE

The reaction of (η5-C5H5)Mo(CO)3Cl with pyridine-2-carboxylic acid [(S)-1-phenylethylthioamide] yields two diastereoisomers having composition (η5-C5H5)Mo(CO)2(thioami de) which are in equilibrium with one another in the ratio of 58/42 (toluene; 90°C). The diastereoisomers are separable by chromatography, and that (V; see text) whose CD spectrum shows (-) and (+)-bands, respectively, at 579 and 436 nm was used in the current crystallographic study. The space group isP212121 and the cell parameters are: a 6.950(4), b 14.038(4) and c 20.709(8) Å; V 2020.4 Å3; d(obs; flotation in aqueous ZnBr2) 1.51 g cm-3; d(calc; Z = 4) 1.507 g cm-3. A total of 3321 data were recorded in one octant of reciprocal space (2θmax 60.0°) of which 2134 were considered observed (I > 2σ(I)) and used in the solution of the structure and in the least-squares refinement. The molecules consist of a central Mo atom surrounded by an approximately square-pyramidal array of five ligands: the bidentate thioamide, two carbonyls and the Cp ring. The binding points of the thioamide are the nitrogen of the pyridine and the sulfur of the thioamide moiety. Thus, unlike previous examples of CpMo(CO)2(thioamides) studied here, the nitrogen of the thioamide is not part of the chelate ring; instead, it is part of an unusual, three atom, conjugated system (SCN) never observed before in thioamide-metal chelates. The SMoN, SMoC(O), NMoC(O) and (O)MoC(O) angles are 76.9(2), 75.2(3), 81.4(4) and 75.6(5)°, values which are typical of square-pyramidal compounds in which the metal is above the plane defined by the basal ligands. The bonds to the carbons of the C5H5 ring are normal but the two MoC(O) and the two CO distances are slightly different, and the differences make sense if we attribute them to inequalities in trans effect between S and N ligands opposite the carbonyls. The MoN(pyridine) bond (2.233(8) Å) is a little longer than those observed in thioamides but nearly the same as that observed in Schiff base derivatives of related CpMo(CO)2 compounds studied here earlier. Concomitantly, in V there is a shorter MoS bond than those observed in the thioamides containing normal, four-membered (MoSCN) chelate rings. Parallel with this, V contains longer SC bonds showing that an increase in the MoS bond order leads to a reduction of the SC π-bond order, which in this case is estimated to be only 0.47. Finally, the plane of the chelate ring (MoSCCN) and that of the pyridine ring make an angle of 8.7°, even though the two are fused to each other. The absolute configuration at the Mo site of the [(-)579, (+)436] diastereoisomer has been established as (S). © 1979.