Organometallics 1996,14, 1085- 1086
1085
Oxy Functionalization of Metal-Coordinated Heterocyclic Carbenest98 Wolfgang A. Herrmann,* Peter W. Roesky,§Martina Elison, Georg Artus, and Karl Ofele Anorganisch-chemisches Institut der Technischen Universitat Miinchen, Lichtenbergstrasse 4, 0-85747 Garching bei Miinchen, Germany Received December 6, 1994@ Summary: Metal-coordinated 1,3-dimethylimidazolin-2ylidene ligands undergo osmylation by means of osmium tetraoxide to yield a new type of bimetallic, redox-stable complexes with metals in very different oxidation states (e.g. W l 0 s w ) . This oxy functionalization does not influence the metal-carbene bond in a significant way (IR and NMR spectra, single-crystal X-ray diffraction structure). Carbenes which are derived from imidazolium and pyrazolium salts have long been known as ligands in transition-metal chemistry.2 The isolation of the free monomeric ligand l3has spurred renewed interest in H
R
H-N.
H-N'
I
3ac
' CH3
I
R 1
this subject. The attractiveness of these ligands is due both to their easy availability and to their stability. Acting as strongly nucleophilic ligands, heterocyclic carbenes behave in metal coordination chemistry like the widely used phosphines,lv4 with n-back-bonding being of little or no importance. In the present paper, we describe the osmylation of metal-attached carbenes. Treatment of an ether solution of the metal complexes 2a-c of the CC-unsaturated carbene 1 (R= CH3) with osmium tetraoxide in the presence of pyridine results in the bimetallic complexes 3a-c as brown precipitates The products are stable in air and (yields '80%). dissolve in polar solvents (eq 1). The crystallographically determined structure of the chromium derivative + Heterocyclic Carbenes. 2. Part 1: Reference 1.
Dedicated to Professor Herbert W. Roesky on the occasion of his 60th birthday. Kekul6 Fellow of the Verband der Chemischen Industrie, Frankfurt am Main, Germany, 1993-1994. Abstract published in Advance ACS Abstracts, February 1, 1995. (1) Ofele, K.; Herrmann, W. A.; Mihalios, D.; Elison, M.; Herdtweck, E.; Scherer, W.; Mink, J. J . Organomet. Chem. 1993, 459, 177-184. ( 2 )(a) Ofele, K. J. Orgunomet. Chem. 1968, 12, 42-43. (b) Ofele, K.; Kreiter, C. G. Chem. Ber. 1972, 105, 529-540. (c) Ofele, K.; Herberhold, M. 2. Naturforsch. 1973, 28B, 306-309. (d) Ofele, K.; Herberhold, M. Angew. Chem. 1970,82,775-777;Angew. Chem., Int. Ed. Engl. 1970, 9 , 739-740. (e) Wanzlick, H.-W.; Schijnhem, H.-J. Angew. Chem. 1968, 80, 154;Angew. Chem., Int. Ed. Engl. 1968, 7 , 141. ( 3 )(a) Arduengo, A. J., 111; Harlow, R. L.; Kline, M. J. Am. Chem. SOC.1991,113,361-363. (b) Dixon, D. A.; Arduengo, A. J., 111.J. Phys. Chem. 1991, 95, 4180-4182. (c) Arduengo, A. J., 111; Rasika Dias, H. V.; Harlow, R. L.; Kline, M. J.Am. Chem. SOC.1992,114,5530-5534. ( 4 )Herrmann, W. A.; Ofele, K.; Elison, M.; Kiihn, F. E.; Roesky, P. W. J . Organomet. Chem. 1994,480, C7-C9.
3a (single-crystal X-ray diffraction) and the spectroscopic data reveal a cis addition of osmium tetraoxide across the C-C bond of the heterocyclic carbene. An osmate e ~ t e f l and - ~ a metal carbene,*both of which are known as separate molecules, are connected in 3a-c by oxy-functionalized 1,3-dimethylimidazolin-2-ylidene ligands (Figure 1). Obviously, the metal carbonyl fragment is kinetically resistant against oxidation; no interaction is observed in the system OsVII1/Cro,with the cyclic voltammetry El12 data amounting to f1.4 V (irreversible) and -1.1 V (irreversible) vs AgIAgC1 for 3b. The individual molecular structures of the components (CrO-carbonyl and Osv-ester) differ only slightly from the monomolecular examples. The shorter C(carbene)-N bond and the elongated N-C(3,4) bondg may be explained by the disappearance of a certain n-delocalization within the planar carbene moiety of 2a or by changes in the hybridization a t C3 and C4 as a consequence of the CC cross addition of osmium tetraoxide. The C-C distance (1.523(6)A) is in the normal
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(5)Herrmann, W. A.; Eder, S. J.; Scherer, W. Chem. Ber. 1993,126, 39-43. ( 6 )(a)Criegee, R. Justus Liebigs Ann. Chem. 1936,522, 75-96. (b) Criegee, R. Angew. Chem. 1937,50, 153-155. (c) Criegee, R.; Marchand, B.; Wannowius, H. Justus Liebigs Ann. Chem. 1942, 550, 99133. ( 7 )(a) Hentges, S. G.; Sharpless, K B. J.Am. Chem. Soc. 1980,102, 4263-4365. (b) Johnson, R. A.; Sharpless, K. B. In Catalytic Asymmetric Synthesis; Ojima, I., Ed.; VCH: Weinheim, Germany, 1993; pp 227-272. ( 8 )Kuhn, N.; Kratz, T.; Boese, R.; Bltiser, D. J . Orgunomet. Chem. 1994,470, C8-Cll. (9)Ackermann,K.; Hofmann, P.; KiShler, F. H.; Kratzer, H.; Krist, H.; Ofele, K.; Schmidt, H. R. 2. Nuturforsch. 1983, 38B, 1313-1324.
0276-733319512314-1085$09.00/0 0 1995 American Chemical Society
Communications
1086 Organometallics, Vol. 14, No. 3, 1995
Figure 1. PLATON drawing of the crystal and molecular structure of 3a. Thermal ellipsoids are drawn at the 50% probability level. Selected distances (A) and angles (deg): Osl-01, 1.966(3); Osl-02, 1.955(3); Crl-C1, 2.129(4); Crl-C8, 1.879(5); 01-C3, 1.411(5); 02-C4,1.405(5); N1C1, 1.342(5); Nl-C3, 1.468(5); N2-C1, 1.349(5); N2-C4, 1.470(5); C3-C4,1.523(6); 02-0sl-01,83.8(1); C8-CrlC1, 177.6(2); C3-01-Osl, 111.5(2); C4-02-Osl, 112.5(2); C3-Nl-C1, 114.2(3); C4-N2-C1, 113.8(3);N1-C1Crl, 126.7(3);N2-Cl-Crl,126.8(3); N2-Cl-Nl,106.5(3); Nl-C3-01, 110.9(4); C4-C3-01, 112.6(4); C4-C3-N1, 102.5(3); N2-C4-02, 110.1(3); C3-C4-02,113.2(4); C3C4-N2, 102.3(3).
range of single bonds. It is much shorter in 2c (1.355(13) AI8 and in the free carbene 1 (1.338(3) A, R = a d a m a n t ~ l ~ The ~ ) ) . osmate ester fragment shows the typical trans O=Os=O structure. The osmacycle adopts an envelope conformation (Os a t a distance of 0.547 A off the plane of 01,02,C3,C4). This results in a boat-shaped conformation of the molecule.1° CYOS electron transfer is blocked by the bending of the complex at the C-C bond (Nl-C3-01 angle 110.9(4)"; N2-C4-02 angle 110.1(3)").10 The structure of 3a-c is retained in solution as shown by IR and NMR spectra. The reduction of the symmetry of the M(C0)5 fragment which is caused by the Os04 addition results in three (instead of two) CO valence vibrations.ll The new oxygenated carbene ligand is (10) X-ray crystal structure determination: the chromiudosmium complex 3a of formula CzoH18CrN40@s crystallized from chloroform at 25 "C in the triclinic space group P1 with a = 8.184(2) A, b = 11.979(3) A, c = 12.227(3)A, a = 93.91(2)", B = 95.77(2)", y = 93.22(2)", V = 1187.46) A3,2 = 2, ecdc= 1.96 g ~ m T-=~-50 i 3 "C, Fa00 = 676, Mo Ka radiation, CAD4 Enraf-Nonius, o-scan (maximum 60 s), 4381 measured reflections (1" 0 < 25.0"), 240 with negative intensity (I < O.OlO(n), 378 reflections merged, 3943 independent reflections, 3943 of which with I > 0.0dnused for the refinement. The structure solution was obtained by Patterson methods.ls All hydrogen atoms were detected from difference Fourier syntheses and were freely refined.14 No intensity correction was used; the empirical absorption correction is based on +-scan data o( = 58.7 cm-'1: w = l/uz(Fo),R = Z(IIF,I ~Fc~~)LZIFo~ = 0.026; R, = Zw(lF,, - ~Fcl)zLZw~Fo~z = 0.020, residual electron density f1.31 e -3 (1.01 A near Osl), minimum -0.87 e A-3. For further details of the crystal structure determination, the Fachinformationszentrum Karlsruhe, Gesellschaft fiir wissenschaftlichtechnische Information mbH, D-76344 Eggenstein-Leopoldshafen, Germany, may be contacted; quote the reference number of this paper, the names of the authors, and the registration number CSD-58805. (11)Adams, D. M. Metal-Ligand and Related Vibrations; Edward Arnold: London, 1960.
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seen to be slightly more C-nucleophilic than its precursor 1: the trans-coordinated CO group is less involved in the back-bonding to the zerovalent metal centers (IR data). The addition of Os04 to the C=C bond of the carbene ligands results in a high-field shift of the NMR signals as a consequence of the new CH-0 bonds in 3 (lH NMR: 2a 6(CH) 7.11, 3a &CH) 5.30; 13C NMR: 2a 6(CHI 124.29,3a 6 (CHI 103.18). The number of NMR signals shows the symmetrical bonding of the osmate ester to the metal-coordinated carbene ligand. The oxy derivatization has only a small influence on the WI vis spectra.12
Acknowledgment. This work received generous support by the Verband der Chemischen Industrie (Ph.D. Fellowship for P.W.R.) and the Deutsche Forschungsgemeinschaft. Supplementary Material Available: Text giving a description of the crystal structure determination and tables giving positional and thermal parameters and bond distances and angles for 3a (8 pages). Ordering information is given on any current masthead page.
OM940929Q (12) Pentacarbonyl[O,O-((bis(pyridine)dioxooemium)-1,3dimethyl-4,5-dioxoiazolidin-2-ylidenelchromium (3a): 88 mg (0.35 mmol) of 0 5 0 4 and 0.06 mL (0.70 mmol) of dry pyridine are dissolved in 10 mL of ether. To this solution are added 100 mg of 2a (0.35 mmol) in 10 mL of ether. The mixture is stirred for 12 h. During the reaction a brown microcrystalline solid precipitate is obtained. After the solvent is decanted, the solid is washed with ether and then dried in vacuo. Yield: 203 mg (83%).IR (KBr; cm-I): 2052 (m, v(CO)), 1969 (s. v(C0)). 1912 (vs. v(C0)). 1431 (m). 1048 (m). 843 ( 6 . v(O=Os=O)). 1H-NMR (CDi3, 270 MHz,' 20 "C): 6'3.32 (8,6H, NCH3), 5.30 (8,2H, NCH), 7 50 (t, 4H, py H-31, 7.92 (t, 2H, PY H-4), 8.81 (4 4H9 PY H-2). '3C{'H} NMR (CDC13, 67.6 MHz, 20 "'2): 6 = 35.30 (NCHd, 103.18 (NCH)-l25.65 (py C-31, 141.17 (py (2-41, 149.31 (PY C-2), 188.34 (C carbene), 218.44 (CO), 222.27 (CO). W/vis (CHzClZ 20 "C: I,,, nm (E, L mol-' cm-I)): 246 (20 3501,346 (2400). Mp: '320 "C. Anal. Found (calcd) for C20H18CrN40908 (700.58): C, 34.29 (33.80); H, 2.59 (2.63); N, 8.00 (7.76). Pentacarbonyl[O,O-((bie(pyridine)dioxoosdum)1,3-dimethyl-4,S-dioxoimidazolidin-2-ylidenelmolybdenw.1 (3b). , Yield: 80%. IR (KBr; cm-'): 2061 (m, v(Co)), 1974 ( 8 , ~ ( c o ) )1916 (VS, v(CO)), 1451 (m), 1048 (m), 842 ( 8 , Y(O=Os-O)), 603 (4. 'H NMR (CDClq. 270 MHz. 20 "C): 6 3.29 (5. 6H. NCHq). 5.34 ( 8 . 2H. NCH). 7.51 (
