Organometallics zyxwvu 1995, 14, zyxwvu 721-733 721 zyxwvutsrqp Chemistry of Nitrogen Donors with pa-Imidoyl Triosmium Clusters: Dynamics of a Monometallic Site in a Trimetallic Cluster Shariff E. Kabir and Edward Rosenberg" Department of Chemistry, The University of Montana, Missoula, Montana 59812 Mike Day, Kenneth Hardcastle," Erich Wolf, and Tim McPhillips Department of Chemistry, California State University, Northridge, California 91330 Received July 25, 1994@ A detailed view of the ligand dynamics and coordination chemistry of a monometallic site is afforded by the study of the reactions of the trimetallic species 01-H)013-r2-C=N(CH2)3)- OS~(CO)~ (2) with nitrogen donor ligands. The kinetic site of attack is the axial position on the unbridged osmium atom, zyxwvuts syn to the p-imidoyl ligand in the products @-H)@-r2-C=N- (CH~)~)OS~(CO)~(L) (3a, L zyxwvuts = NH3, 3b-e, L = RNH2, R = n-Bu, i-Bu, s-Bu, t-Bu; 3f, L = pyrrolidine; 3g, L = BzNH2; 3h, L = pyridine; 4a,b, L = RCN, R = Me, Ph; 4c, isomer of 4a; 5a-c, L = PR3, R = Ph, Me, OMe). The initially formed syn-adducts isomerize to antzlsyn mixtures. This isomerization is shown to be a first order process whose rate as well as the final antilsyn ratio is sensitive to the stereoelectronic properties of L. The mechanism of this isomerization process is shown to be a dissociative process for the amine and nitrile ligands. The formation constants for the complexes have been measured; they show a clear dependence on ligand cone angle and are much larger for the pure zyxw B donor amines than the nitriles. The 13C-NMR of 3a, 3b, 4a, and 4c proved to be a valuable tool for relating solution and solid state structures. Oxidation of CU-H)OL-r2-C=N(CH2)3)Os3(CO)~~ zyx (1) with trimethyl- amine N-oxide in acetonitrile leads to formation of the regioisomer of 4a, 4c which allows for subsequent regiospecific phosphine substitution. The primary products of the thermolysis of 3a-h, are 2 and free amine; however, in the case of 3f, activation of the pyrrolidine ring leads to a bis-p-imidoyl complex, 01-H)201-r2-C=N(CH2)3)20s3(CO)s (6) as the major product. Solid state studies of 3a, 3f, 4a, and 6 are reported and discussed in light of the dynamics studies. Compound 3a crystallizes in the triclinic space group P1 with unit cell parameters a = 17.472 (6), b = 20.915 zyxwvut (9, c = 8.543 (2) zyxwv A, a = 80.16 (21, zyxw B = 78.24 (21, y = 75.96 (2>O, V = 29.40 (2) Hi3 and 2 = 6. Least squares refinement of 6345 observed reflections gave a final agreement factor of R = 0.080 (R, = 0.087). Compound 3f crystallizes in the orthorhombic space group Pea21 with unit cell parameters a = 16.530 (4), b = 17.249 (3), c = 15.955 (5) A, V = 4549 (3) A3 and 2 = 8. Least squares refinement of 4972 observed reflections gave a final agreement factor R = 0.061 (R, = 0.057). Compound 4a crystallizes in the triclinic space group P1 with unit cell parameters a = 9.586 (2), b = 13.510 (3), c = 9.504 (2) A, a = 70.26 (2), B = 62.30 (l), y = 77.66 (2)O, V = 1023 (1) A3, and 2 = 2. Least squares refinement of 4872 observed reflections gave a final agreement factor of R = 0.058 (R, = 0.061). Compound 6 crystallizes in the monoclinic space group P21lc with unit cell parameters a = 16.634 (2), b = 8.872 (2), c = 16.201 (2) A, B = 119.03 (2)", V = 2091 (1) and 2 = 4. Least squares refinement of 4714 observed reflections gave a final agreement factor R = 0.040 (R, = 0.041). n I 1 n n Introduction In recent years it has become increasingly obvious that nitrogen donor ligands can form relativelv stable Y I There has .been considerable study of the factors controlling the rates of the associative Components of ligand substitution at transition metal centers.1 For the lower state carbonyl complexes, most studies have focused on traditional geometries in mononuclear complexes and on softer, kinetically stable ligands such (1) (a) Twigg, M. V., Ed. Mechanisms of Inorganic and Organo- metallic Reactions, Plenum Press: New York, 1983-9; Vols. 1-6. (b) Jorden, R. B. Reaction Mechanism of Inorganic and Organometallic Systems; Oxford University Press: New York, 1991. (e) Langford, C. H., Gray, H. B. Ligand Substitution Processes; W. A. Benjamin: New York, 1966. (d) Atwood, J. D. Inorganic and Organometallic Reaction Mechanisms; Brooks-Co1e: Montereyi CA, lga5. (2) (a) Darensbourg, D. J. Adu. Organometal Chem. 1982,21, 113. (b) Darensbourg, D. J. In The Chemistry of Metal Cluster Complexes; Shriver, D. F., Kaesz, H. D., Adams, R. D.; VCH: New York, 1990; Ch. 4. (c) Johnson, B. F. G.; Roberts, Y. V.; Parsini, E. J. Chem. SOC. Dalton Trans. 1992, 2573. as phosphines in the case of polymetallic ~pecies.~J @ Abstract published in Advance ACS Abstracts, December 15,1994. 0276-733319512314-0721$09.00/0 0 1995 American Chemical Society