Optically active transition-metal compounds. 93. X-ray determination of the structure and absolute configuration of (+) 578-C 5H 5Fe(CO) [P(C 6H 5) 3] COCH 3

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The structure and absolute configuration of (+) 578- C 5H 5Fe(CO)[P(C 6H 5) 3]COCH 3 have been determined by single crystal X-ray diffraction methods. The substance crystallizes in the monoclinic space group P2 1 with cell constants of a = 8.084(14), b = 8.527(2), c32.706(21) Å and β = 104.32(10)°; V 2184.18 Å 3 and D(calc: Z 4 mol/unit cell) = 1.381 g cm -3. There are two independent molecules in the asymmetric unit, which allowed us to gauge the effect of packing on the conformation of those groups able, in principle, to be twisted by crystalline forces. Only minor changes in conformations were observed, the largest being at the terminal CH 3 of the acetyl ligand (0.065 Å). All other differences in conformation are less than 0.036 Å. The plane of the acetyl ligand is close to being aligned with the FeC(CO) bond, making the acetyl oxygen point in the direction of the phosphorus atom. It is suggested that in phosphine exchange reactions this conformation persists in solution while the acetyl oxygen, intra- molecularly, attacks the adjacent phosphorus atom to form a dihapto acetyl species as the first intermediate, in which there is retention of configuration at Fe. With the priority of the ligand sequence as C 5H 5 > P(C 6H 5) 3 > CO > COCH 3, the absolute configuration at Fe is (S). So, the formation of (−) 578- C 5H 5Fe(CO)[P(C 6H 5) 3]COCH 3 by reaction of (+) 578- C 5 H 5 Fe(CO)[P(C 6H 5) 3] COOC 10H 19 and LICH 3 requires an inversion to occur at the Fe center.