Organometallics 1995, 14, 721-733
721
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 n
is afforded by the study of the reactions of the trimetallic species 01-H)013-r2-C=N(CH2)3)O S ~ ( C O(2) ) ~ with nitrogen donor ligands. The kinetic site of attack is the axial position on I
the unbridged osmium atom, syn to the p-imidoyl ligand in the products @-H)@-r2-C=N1
( C H ~ ) ~ ) O S ~ ( C O (3a, ) ~ ( LL) = 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 t o 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 B donor amines than the nitriles. The 13C-NMRof 3a, 3b, 4a, and 4c proved to be a valuable tool for relating solution n and solid state structures. Oxidation of CU-H)OL-r2-C=N(CH2)3)Os3(CO)~~ (1)with trimethylamine 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 n 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 (9,c = 8.543 (2) a = 80.16 (21, 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).
A,
Introduction
In recent years it has become increasingly obvious that nitrogen donor ligands can form relativelv stable Y
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 statecarbonyl complexes,moststudies have focused on traditional geometries in mononuclear complexes and on softer, kinetically stable ligands such as phosphines in the case of polymetallic ~pecies.~J @
Abstract published in Advance ACS Abstracts, December 15,1994.
0276-733319512314-0721$09.00/0
I
(1)(a) Twigg, M. V., Ed. Mechanisms of Inorganic and Organometallic 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.
0 1995 American Chemical Society
Kabir et al.
722 Organometallics, Vol. 14, No. 2, 1995
and kinetic aspects of a single “lightly stabilized’’ complexes with low oxidation state late transition metal osmium coordination site in a trimetallic species. In centers. In this same period their importance as ancilprevious studies, we reported the reactions of p3-imidoyl lary ligands in catalysis has Cone angles for clusters with various phosphines7d and i s o ~ y a n i d e s . ~ ~ amine ligands have been established for square planar We subsequently found that phosphine addition follows palladium complexe~.~In the case of polymetallic second order kinetics with the magnitude of the rate complexes, little information is available on the reactivconstants following the order expected for associative ity trends for nitrogen-based ligand additions to polyprocesses controlled by incoming ligand cone angle and metallic species. This is surprising in light of the fact donor ability (i.e., P(CH& > P(OCHd3 > P(CsH5)5).7c that the relatively labile species produced in these We also found that the structure and the number of additions have proved to be valuable synthetic interisomers present was quite sensitive to the structure of mediates such as the “lightly stabilized” cluster 0%the imidoyl ligand as well as the bulkiness of the donor (CO)~O(CH~CN We ) ~have . ~ recently been investigating ligand.7d We report here the results of our studies of a variation on the theme of “lightly stabilized clusters’’ the reactions of pus-imidoyl clusters with ammonia, in the chemistry of pus-imidoyl cluster^.^ This cluster RNH2 (R = n-Bu, i-Bu, s-Bu, t-Bu, benzyl, phenyl), Rzbonding mode has been known for some time, but we NH (R = Et, -(CH2)4-),R3N (R = Et), pyridine, and RCN have found that the reaction of certain secondary amines with the lightly stabilized cluster, OS~(CO)~O(CH~-(R = Me, phenyl). The thermal behavior of the pyrrolidine adduct is reported and a detailed examination of CN)2, provides a convenient entry to pimidoyls (eq 11.’ the dynamics at the initial site of coordination has been completed. These results in turn prompted us to examine the mechanism of tripodal motion in the initially formed phosphine derivatives of 2 as well as the regiochemistry of ligand addition to the lightly n
stabilized cluster @-H)@-C=N(CH~)~)OS~(CO)~(CH~CN) formed by amino oxide oxidation of 1 in acetonitrile.
Results A. Complexes with Ammonia and Amines. Solu1
2
The p-imidoyl @-H)@-32-~=N(CH~)3)0s3(C0)1~ (1)der carbonylates quantitatively to yield @-H)@3-r2-C=N1
( C H ~ ) ~ O S ~ ((2) C Owhich ) ~ reacts at room temperature with a variety of two-electron donors (eq 2).7 The
A
2
A
5a
reactions result in apparent displacement of the C=N n-bond by the two electron donor, but our experiments on related ruthenium systems indicate that in some cases initial attack may in fact be at the metal atom coordinated to the nitrogen lone pair.7c Regardless of the kinetic site of attack, this class of compounds provides the opportunity t o study the stereochemical (3) (a) Brodie, M. M. J.; Chen, L.; Poe, A. J. Int. J . Chem. Kinet. 1988, 20, 467. (b) Johnson, B. F. G.; Roberts, Y. V. J . Cluster Sci. 1993, 4, 231. (4)Togni, A.; Venanzi, L. M. Angew. Chem., Int. Ed. Engl. 1944, 33,497. (5) Trogler, W. C.;Seligson, A. L. J . Am. Chem. SOC.1991,113,2520. (6) (a) Tachikawa, M.; Shapley, J. R. J . Organometal Chem. 1977, 124, C19. (b) Shriver, D. F.;Kaesz, H. D.; Adams, R. D. The Chemistry ofMetaZ Cluster Complexes;VCH: New York, 1990; Chapter 1, 5. (7) (a) Day, M.; Espitia, D.; Hardcastle, K. I.; Kabir, S. E.; McPhillips, T.; Rosenberg, E.; Gobetto, R.; Milone, L.; Osella, D. Orgunometullics 1993,12, 2309. (b) Rosenberg, E.; Kabir, S. E.; Hardcastle, K. I.; Day, M.; Wolf, E. Organometallics 1990, 9, 2214. (c) Rosenberg, E.; Freeman, W.; Carlos, Z.; Hardcastle, K.; Yoo, Y. J.; Milone, L.; Gobetto, R. J . Cluster Sci. 1992, 3, 439. (d) Day, M.; Espitia, D.; Hardcastle, K.; Kabir, S. E.; Rosenberg, E.; Gobetto, R.; Milone, L.; Osella, D. Organometallics 1991, 10, 3550. (e) Rosenberg, E.; Kabir, S. E.; Irving, M.; Hardcastle, K.; Day, M. J . Cluster Sci. 1994,5,481.
tions of 2 in dichloromethane-d2 which are saturated with 10% 15N-enriched ammonia immediately show evidence of complex formation as seen from their lHNMR. Anew hydride resonance appears at -13.71 ppm along with the appearance of a new broad resonance at 2.99 ppm and the appearance of three relatively sharp methylene ring resonances at 3.40, 2.27, and 1.75 ppm which each integrate 2:3 with the new broad resonance at 2.99 ppm. A resonance observed at 0.5 ppm is due to free ammonia. Interestingly, the resonance assigned to the complexed NH3 shows two sharp satellites ( 1 J 1 5 ~ - 1 ~ = 69.5 Hz), while the resonance for free ammonia shows no such satellites. This is undoubtedly due to exchange moduation of the coupling in the free ammonia (aided by trace moisture). Slow proton exchange for the complexed ammonia is consistent with a relatively slow o d o f f rate for this ligand. The ~ slightly larger than observed magnitude of 1 J 1 6 ~ - i is for free ammonia under conditions of slow hydrogen exchange (61.5 Hz) as is the case for more conventional ammonia complexes.8 Over a 20 h period we observed a slight decrease in the relative intensity of the hydride resonance of 2 at -18.0 ppm relative to that of the complex (~-H)OL-32-C=N(CH)2)30s~(CO)~NH3 (3a)but more importantly a new hydride resonance at -14.03 ppm grows in while the original peak at -13.71 ppm decreases in intensity. Monitoring this conversion in l-h intervals for 20 h by lH-NMR affords a first order rate constant for this isomerization of 1.16 & 0.1 x m-l. After more than 20 h, the ratio of these isomeric forms of 3a continues to change until a final value of 6 : l is reached after -40 h. The ratio of 3a to 2 does not change further after 20 h in a sealed NMR tube and the formation constant for 3a is calculated to be 15 (Table 1). (8) Webb, G.; Witanouski, M. In Nitrogen NMR, Plenum Press: London, 1973.
Nitrogen Donors with ,us-Imidoyl Triosmium Clusters
Organometallics, Vol. 14,No. 2, 1995 723
Table 1. Formation Constants and Isomer Ratios for Amine Complexes of 2 ligand
compd
6A" (ppm)
NH3 n-BuNH2 i-BuNHz s-BuNH~ t-BuNH2 pyrrolidined BzNH2 pyridine"
3a 3b 3c 3d 3e 3f 3g 3h
-13.70 -13.80 -13.80 -13.80 -13.72 -13.79 -13.79 -13.62
6Ba (ppm) -14.03
-14.03 -14.03 -14.04 -13.83 - 14.33 - 14.03 -
A/B
Keab
6.0 3.2 3.0 2.1 0.50 0.21 1.41
15.0 1.25 1.25 0.37
-
cone ang1e:deg 94 106 106 113 123 120 106 -
0.005
0.18 0.11 0.04
T
a)
033A
012k 032A
a Chemical shifts re1 to TMS. f15%, moVdm3. Taken from ref 5. A third very minor isomer is detected at - 13.35 ppm (
