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The Absolute Configuration of a Dissymmetric Pseudotetrahedral Coordination Compound Containing a Restricted Biphenyl. Molecular Structure of A-2,2’-Bis ( salicylidenaminato)(+),- (R)-6,6’-dimethylbiphenylcobalt(11)’ Louis H. Pignolet, Ronald P. Taylor, and William Dew. Horrocks, Jr. Contribution f r o m the Frick Chemical Laboratory, Princeton University, Princeton, N e w Jersey 08540. Received January 27, 1969 Abstract: The crystal and molecular structures of the dissymmetric molecule, A-2,2 ’-bis(salicylidenaminato)-(+)D(R)-6,6’-dimethylbiphenylcobalt(II), A-Co(sal)2-(R)-bmp,have been determined by single-crystal X-ray diffraction. The compound crystallizes in the orthorhombic space group P 212121with a = 17.978, b = 11.206, and c = 11.628 A. For 2 = 4 the measured and calculated densities are 1.35 i. 0.02 and 1.353 g/cm3, respectively. Counter data
were collected for 1745 independent reflections by the stationary-crystal-stationary-counter technique. The structure was solved using Patterson and Fourier methods and refined by least-squares techniques to a conventional R value of 0.098. The absolute configuration was determined from a comparison of 18 (hkf),(hki)pairs and found to be R for the biphenyl moiety. The R configuration of the diamine uniquely establishes the A configuration for the complex as a whole as predicted by O’Connor, Ernst, and Holm. The structure consists of discrete molecules wherein the ligand atoms surround the cobalt atom in a highly distorted tetrahedral fashion, The average bond distances involving the cobalt atom are Co-N = 2.09 =t0.01 A, and Co-0 = 1.90 f 0.01 A.
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n 1958 Mislow and coworkers determined the absolute configuration of 2,2’-diamino-6,6’-dimethylbiphenyl (bmp) by partial assymmetric synthesis. This molecule is a member of a configurationally related series of restricted biphenyls whose optical activity is of considerable interest.3 Prior to the present work4 no X-ray (Bijvoet) determination of the absolute configuration of any member of the restricted biphenyl series has been reported, although very recently the absolute configuration of a binaphthyl derivative has appeared5 which was subsequently6 chemically related to the biphenyl series confirming the original prediction. Furthermore the ORD spectra of tetradentate Schiff base complexes derived from the hindered biphenyl- and binaphthyldiamines (vide infra) served to establish the absolute configuration in the former ~ e r i e s . ~ In 1957 Lyons and Martin* prepared copper(I1) and beryllium(I1) complexes [Cu(sal)2bmp and Be(~al)~bmp] of the tetradentate ligand formed by the Schiff base reaction of salicylaldehyde, sal, on bmp. The expected distorted tetrahedral arrangement of ligand atoms was confirmed by a structure determinationg of the nonrestricted biphenyl analog, Cu(sal)2bp, bp = 2,2’-diaminobiphenyl. Recently O’Connor, Ernst, and Holm,7as part of an extensive series of investigations of diastereomeric four-coordinate complexes, have made use of
these and similar ligands to prevent the racemization of dissymmetric metal complexes, for example, M(sal)zbmp shown in I, where M = Co(II), Ni(II), Zn(II), and Pd(I1). These complexes are analogous to the bis-che-
CH, CH, I
late nickel(I1) complexes, Ni(A-B)2, which can exist in the A or A absolute configurations10but which are found to racemize rapidly on the nmr time scale. The present structure was undertaken t o confirm the absolute configuration of bmp predicted by Mislow2 and to show that it uniquely determines the configuration, A or A, of the coordination compound Co(sal)2bmp. This structure is the first direct determination of the absolute configuration of a pseudotetrahedral coordination compound. Experimental Section Deep red, long plate-like orthorhombic crystals of A-2,2’-bis-
(1) This research was supported by the Directorate of Chemical Sciences, Air Force Office of Scientific Research, through Contract A F 49(638)-1492. (2) F. A. McGinn, A. K. Lazarus, M. Siegel, J. E. Ricci, and K . Mislow, J . A m . Chem., Soc., 80, 476 (1958); cf. I
