Inorg. Chem. zyxwvu 1986, zyxwvu 25, zyxwvut 3489-3497 3489 Contribution from the Department of Chemistry, Emory University, Atlanta, Georgia 30322, and Dipartimento di Scienze Chimiche, Universita di Trieste, 34127 Trieste, Italy Structures, NMR Spectra, and Ligand-Exchange Properties of Costa-Type Organocobalt B12 Models with N-Donor Ligands Wallace 0. Parker, Jr.,t Ennio Zangrando,f Nevenka Bresciani-Pahor,f Lucio Randaccio,*f and Luigi G. Marzilli*+ Received January 27, 1986 In this report, we describe the first extensive characterization of ligand-exchange rates and 'H NMR spectral properties of the Costa-type organocobalt BIZ model system [LCo((DO)(DOH)pn)CH,]X, where L zyxwvu = N-donor ligand, X = C104 or PF6, and (DO)(DOH)pn = zyxwvuts fl,M"-propanediylbis(2,3-butanedione 2-imine 3-oxime). The three-dimensional structures of [PhNH2Co- ((DO)(DOH)pn)R]PF,, with R = CH3 (I) and R = CHZCO2CH3 (II), were determined. Crystallographic details follow. I: C18H29C~F6N502P, P2,/n, a = 13.912 (3) A, zyxwvutsrq b = 20.996 (3) A, c = 8.048 (1) A, 0 = 93.38 (2)O, D(calcd) = 1.56 g cm-,, Z = 4, R = 0.054 for 3640 independent reflections. 11: Cz0H31C~F6N504P, PI, a = 8.052 (3) A, b = 8.077 (2) A, c = 10.699 (2) A, a = 71.30 (2)'. /3 = 74.05 (2)O, y = 85.95 (2)O, D(calcd) = 1.60 g Z = 1, R = 0.035 for 3008 independent reflections. The only other complexes of the type [LCo((DO)(DOH)pn)R]X (L = N-donor ligand) that have been structurally characterized contain L = py (pyridine). In these compounds, the orientation of the py ligand is rotated by 90° relative to the 0-H-0 moiety in comparison to related cobaloximes, (py)Co(DH),R (where DH = monoanion of dimethylglyoxime). In contrast, the aniline ligand, PhNH,, occupies a similar orientation in the two series of B,, models. The axial Co-N bond distances, 2.147 (3) (I) and 2.126 (3) (11) A, are not significantly different from those expected from comparisons to cobaloxime structures. However, the rate of PhNHz dissociation is actually smaller than that in cobaloximes. These data and an analysis of 'H and "C NMR spectral shifts suggest that the Co center in [LCo((DO)(DOH)pn)R]X compounds is more electrophilic than that in analogous LCO(DH)~R species. In contrast, the magnetic anisotropy of the Co((DO)(DOH)pn)R+ moiety appears to be greater than that of the Co(DH),R moiety. These results, in conjunction with previous findings, support the view that the Costa-type compounds are not significantly different from cobaloximes as models for BIZ. Introduction We have previously listed reasons for studying in more detail the coordination chemistry of BIZ model compounds.'-5 Many questions remain about the coordination number and structural features of coenzyme BIZ both when it is in solution and when it is incorporated into Blz-dependent enzymes.5 In particular, the Costa-type model (see scheme has not been extensively studied in terms of its coordination chemistry, but it exhibits many interesting properties, which have led Finke's group to examine a related system in detail as a BIZ mode1.16-z2 In this report, we describe a continuation of our studies on this sy~tem.'~J~~~~ One unifying theme of these previous studies has been to draw direct comparisons with the cobaloxime model systems LCo(DH),R (DH = monoanion of dimethylglyoxime). As can be seen from the Chart I, the planarity of the equatorial (DO)(DOH)pn ligand is disrupted by the pucker of the propylene bridge. In a previous study, which focused on a comparison of pyridine complexes in the two B,, model series, we discovered that the relative orientations of the pyridine (py) ligand were different with respect to the 0-H--0 group(s).14 This finding was at- tributed to the steric interaction of the py with the propylene bridge, which led to a rotation of 90° by the py ligand with respect to its orientation in the cobaloxime series. We felt that structural data on complexes with an N-donor ligand that has a smaller effective bulk in the vicinity of the Co would permit a more direct comparison between the model systems. Complexes with aniline (PhNH2) met this requirement. In addition, for complexes with several other N-donor ligands (Zaminopyridine (2NHzpy), 2- amino-6-methylpyridine (2NHz6MePy), 4-cyanopyridine (4CNpy), 3,5-lutidine (3,5LUT), 4-(dimethy1amino)pyridine (4Me,NPy), quinoline (QUIN), 1,5,6-trimethylbenzimidazole (Me3Bzm), I-methylimidazole (NMeImd), 1-acetylimidazole (AcImd), 1 ,2-dimethylimidazole ( 1,2MezImd), thiazole (THIAZ), aminoacetaldehyde dimethyl acetal (DEA), tert-butylamine (tBuNH,), p-anisidine (MeOPhNH,), N,N-dimethyl-1,4- phenylenediamine (MqNPhNH,), and NH,), we have compared complexes in the two series to assess factors influencing L dis- sociation rates and 'H NMR chemical shifts. Experimental Section Reagents. PhNHz was purchased from Fisher and distilled under vacuum before use. Me3Bzm was prepared by a procedure similar to that 'Emory University. *Universita di Trieste. Chart I t given for 1 -ethyl-5,6-dimethylben~imidazoIe.*~ Ethyldiphenylphosphine was from Strem. All other ligands and reagents were obtained from (1) Bresciani-Pahor, N.; Forcolin, M.; Marzilli, L. G.; Randaccio, L.; Summers, M. F.; Toscano, P. J. Coord. Chem. Reu. 1985, 63, 1. (2) Toscano, P. J.; Marzilli, L. G. Prog. Inorg. Chem. 1984, 31, 105. (3) Summers, M. F.; Toscano, P. J.; Bresciani-Pahor, N.; Nardin, G.; Randaccio, L.; Marzilli, L. G. J. Am. Chem. SOC. 1983, 105, 6259. (4) Summers, M. F.; Marzilli, L. G.; Bresciani-Pahor, N.; Randaccio, L. J. Am. Chem. SOC. 1984, 106,4478. (5) Marzilli, L. G.; Summers, M. F.; Bresciani-Pahor, N.; Zangrando, E.; Charland, J.-P.; Randaccio, L. J. Am. Chem. SOC. 1985, zyx 107, 6880. (6) Costa, G.; Mestroni, G.; Savorgnani, E. Inorg. Chim. Acta 1969,3, 323. (7) Pellizer, G.; Tauszik, G. R.; Costa, G. J. Chem. SOC., Dalton Trans. 1973, 317. (8) Bigotto, A.; Costa, G.; Mestroni, G.; Pellizer, G.; Puxeddu, A,; Reis- enhofer, E.; Stefani, L.; Tauzher, G. Inorg. Chem. 1970, 4, 41. (9) Costa, G.; Mestroni, G.; Licari, T.; Mestroni, E. Inorg. Nucl. Chem. Lett. 1969, 5, 561. (10) Pellizer, G.; Tauszik, G. R.; Tauzher, G.; Costa, G. Inorg. Chim. Acta 1973, 7, 60. (11) Fox, J. P.; Banninger,R.; Proffitt, R. T.; Ingraham, L. L. Inorg. Chem. 1972, zyxwvuts 11, 2379. (12) Guschl, R. J.; Brown, T. L. Inorg. Chem. 1974, 13, 959. (13) Costa, G. Pure Appl. Chem. 1972, 30, 335. (14) Parker, W. O., Jr.; Bresciani-Pahor, N.; Zangrando, E.; Randaccio, L.; Marzilli, L. G. Inorg. Chem. 1985, 24, 3908. (15) Parker, W. O., Jr.; Bresciani-Pahor, N.; Zangrando, E.; Randaccio, L.; Marzilli, L. G. Inorg. Chem. 1986, 25, 1303. (16) Finke, R. G.; Schiraldi, D. A,; Mayer, B. J. Coord. Chem. Rev. 1984, 54, 1. (17) Finke, R. G.; Schiraldi, D. A. J. Am. Chem. SOC. 1983, 105, 7605 and references therein. (18) Finke, R. G.; McKenna, W. P.; Schiraldi, D. A,; Smith, B. L.; Pierpoint, C. J. Am. Chem. SOC. 1983, 105, 1592. (19) Finke, R. G.; Smith, B. L.; Mayer, B. J.; Molinero, A. A. Inorg. Chem. 1983, 22, 3677. 0020-1669/86/1325-3489$01.50/0 0 1986 American Chemical Society