Organometallics 1996, 14,2145-2147
2145
Insertion Reactions of Isocyanides with Dioxodimesitylmolybdenum(VI): Crystal and Molecular Structure of the pox0 q2-IminoacylDinuclear Complex [(C6H2Me3-2,4,6)Mo[C(CsHzMe3-2,4,6)=~~~](0)]2~-0) Richard Lai',*vt Olivier Desbois,+ Florence Zamkotsian,? Robert Faure,: Janine Feneau-Dupont ,*and Jean-Paul Declercqt ENSSPICAM URA CNRS 1410,Facultd des Sciences ISaint-Jdrame, 13013 Marseille, France, and Laboratoire de Chimie Physique et de Cristallographie, Universitd Catholique de Louvain la Neuve, 1348 Louvain, Belgium Received February 21, 199P Summary: Isocyanides react with dioxodimesitylmolybdenumWI), Mo(0)zmesz (mes = mesityl = Ca2Me;l2,4,6),affording three different compounds identified as dimesityl imine mes2C=NR, mesityl amide mesCONHR, and dinuclear p-oxo 9-iminoacyl complexes [(C&l2Me32 , 4 , 6 ) M o ~ C ~ C ~ ~ M e ~ - 2 , 4 , 6 ) = N R l ( O(R) l ~=~ But, -O) C&I, CH2C6Hd. These new complexes which have been characterized by spectroscopic methods and by X-ray crystallography in the case of R = But represent the first examples of compounds in which bound to a high-valent metal is a n 9-iminoacyl group together with terminal and oxo-bridged ligands. Furthermore, they constitute a new structural type for the M o ~ O systems ~ ~ + in which an oxo-bridged complex possesses a metal-metal bond and one terminal oxo group on each metal atom. Insertion of isonitriles into metal-alkyl bonds leads t o ql- or y2-iminoacyls,and this is comparable with CO reactivity.1,2 However, in contrast t o the extensive studies reported on the spectroscopic and structural properties of the +acyl function, the study of the isoelectronic q2-iminoacylligand formed by the migration insertion of isocyanides into metal-carbon bonds is much less t h ~ r o u g h ,and ~ sometimes more complicated reactions can occur by way of multiple insertion and coupling reaction^.^,^ Although the chemistry of complexes of the d-transition elements containing multiple-bonded ligands constitutes a rapidly expanding area of research,6 apart from a few exception^,^,^ these complexes do not give stable compounds with z-acid ligands. Indeed, in such species, d z*back-bonding is very weak or totally absent because of the high oxidation state of the metal. Consequently, in spite of the growing number of examples of do CO complexes only very few have been i s ~ l a t e d . ~Furthermore, J~ only
-
ENSSPICAM, Marseille, France.
* Universite de Louvain, Louvain, Belgium. +
@Abstractpublished in Advance ACS Abstracts, April 15, 1995. (1)Durfee, L. D.; Rothwell, I. P. Chem. Reu. 1988, 88, 1059. (2) Braterman, P. S. Reactions of Coordinated Ligands; Plenum Press: New York, 1986. (3)Chamberlain, L. R.; Durfee, L. D.; Fanwick, P. E.; Kobriger, L.; Latesky, S. L.; McMullen, A. K.; Rothwell, I. P.; Folting, K.; Huffman, J. C.; Streib, W. E.; Wang, R. J . A m . Chem. SOC.1987, 109, 390. (4) Chiu, K. W.; Jones, R. A.; Wilkinson, G.; Galas, A. M. R.; Hursthouse, M. B. J . Chem. SOC.,Dalton Trans. 1981, 2088. (5) Chiu, K. W.; Jones, R. A,; Wilkinson, G.; Galas, A. M. R.; Hursthouse, M. B. J . A m . Chem. SOC.1980, 102, 7978. (6) Nugent, W. A,; Mayer, J. M. Metal-Ligand Multiple Bonds; Wiley: New York, 1988. (7) Sullivan, A. C.; Wilkinson, G.; Motevalli, M.; Hursthouse, M. B. J. Chem. SOC.,Dalton Trans. 1988, 53. (8) Su, F.-M.; Cooper, C.; Geib, S. J.; Rheingold, A. L.; Mayer, J . M. J. A m . Chem. SOC. 1986, 108, 3545.
two examples of high-valent y2-iminoacyl complexes containing multiple-bonded ligands have been reported until n 0 w . 7 ~ ~ ~ We have recently shown that Mo(0)zmesz (mes = mesityl = CsHzMe3-2,4,6)reacts with CO in the presence of pyridines affording dihydropyridine dimer@ and tentatively explained this reactivity via electrophilic v2acyl species. In this context we thought it could be of interest to compare the reactivity of carbon monoxide with isoelectronic isonitriles. The reaction of Mo(0)zmesz with 1equiv of tert-butyl isocyanide in pyridine at 0 "C results in an immediate color change from yellow to brown. After stirring of the mixture overnight at room temperature, the brown residue left after pyridine removal under reduced pressure is chromatographed under nitrogen on a silica gel column affording three principal fractions. The first and the third ones have been identified by IR, NMR, and mass spectroscopic means as a dimesityl imine mes2C=NBut (3a)(55%) and a mesityl amide mesCONHBut (6a)(15%),respectively. The second fraction is a red-brick solid (4a) (25%) which exhibits a strong absorption band around 1678 cm-l ( Y C N ) and one at 954 cm-' (YMO-0)in the IR spectrum. The absorption at 1678 cm-l and a peak a t 6 207.4 ppm in the l3C(lH} NMR spectrum (CsDs) are consistent with a n V2-iminoacyl f ~ n c t i o n a l i t y . ~ J ~This J ~ complex 4a appears through the FAB' mass spectrum to be dimeric (mlz 884 , its struccorresponding to MH+ for isotope 9 6 M ~ )and ture, solved by a n X-ray diffraction study,15 confirmed this observation. A view of the molecule is depicted in (9) Guram, A. S.; Swenson, D. C.; Jordan, R. F. J . A m . Chem. SOC. 1992,114, 8991. (10) h t o n e l l i , D. M.; Tjaden, E. B.; Stryker, J. M. Organometallics 1994, 13, 763. (11)Vivanco, M.; Ruiz, J.; Floriani, C.; Chiesi-Villa, A,; Rizzoli, C. Organometallics 1993, 12, 1802. (12) Lay, R.; Le Bot, S.; Djafri, F. J . Organomet. Chem. 1991, 410, 335. (13)Carmona, E.; Palma, P.; Paneque, M.; Poveda, M. L. Organometallics 1990, 9, 583. (14)Adams, R. D.; Chodosh, D. F. Inorg. Chem. 1978,17, 41. (15) Crystal data for Mo~N20&&2: prallelepiped red crystals, 0.15 x 0.17 x 0.35 mm, monoclinic space group P21/c, Q = 10.927(5)A, b = 18.560(6)A, c = 23.863(11) A, p = 99.69(5)",V = 4770(3) A3, Z = 4, D, = 1.23 g cm-3,,p = 5.56 cm-'. X-ray diffraction data were collected on a Huber four-circle diffractometer using graphite-monochromatized Mo K a radiation ( I = 0.710 69 8). A total of 8383 independent reflections were collected ((sin O)/A 5 0.60 A-l). A total of 4035 reflections with Z 2 2.5dI) were used in the structure solution. The structure was solved by direct methods using SHELXS86.16 H atoms were placed in computed positions. Anisotropic least squares refinement (SHELX7617)using F led to R = 0.063 and R, = 0.062. Atomic scattering factors were taken from International Tables for X-ray Crystallography.
0276-733319512314-2 145$09.00/0 0 1995 American Chemical Society
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2146 Orgunometullics, Vol. 14, No. 5, 1995
concerns a rhenium(F.7) species.21 When Mo(Ohmes2 was reacted with C~HIINCor C6H&H2NC, the same reactivity was observed and the corresponding compounds were isolated and characterized. The NMR spectroscopic properties of 4 are consistent with the solid-state structurez2 (see Figure 2 for the numbering scheme), and the presence of only one absorption around 954 cm-' in the IR spectrum is well in accord with terminal oxo groups with a trans structure.lg Restricted rotation about the mesityl-molybdenum bond and about the mesityl-carbon bond of the iminoacyl functionality was shown by variable-temperature NMR experiments. The fact that neither coalescence nor line broadening was observed up to 110 "Cindicated barriers to rotation about the mesityl-Mo and mesitylCN bonds higher than 75 kJ-mol-l. Figure 1. ORTEP drawing of 4a. Selected bond distances (A) and angles (deg) are as follows: Mol01 = 1.671(7), Mol0 1.928(6), MolMo2 = 2.772(1), MolCl = 2.131(10), MolNl = 2.093(8), MolC3 = 2.176(9), ClNl = 1.254(12), Mo202 = 1.682(7), Mo20 = 1.926(6), Mo2C2 = 2.105(9), Mo2N2 = 2.104(8),Mo2C4 = 2.199(10), C2N2 = 1.260(14); MolOMo2 = 92.0(2), OMolMo2 44.0(2), OMo2Mol = 44.0(2), Mo2MolOl = 102.5(2), MolMo202 = 104.0(2), C2Mo2N2 = 34.8(4), C2N2Mo2 = 72.6(6), N2C2Mo2 = 72.5(6), 02Mo2C2 = 107.4(4), 02Mo20 = 109.6(3), 02Mo2N2 = 110.1(3), ClMolNl = 34.5(3), ClNlMol = 74.4(6),NlClMol = 71.1(6),OlMolCl = 108.8(3),OlMolO = 108.9(3), OlMolNl = 108.8(3).
Figure 1 with the most relevant bond distances and angles. This complex is formed by two equivalent molybdenum moieties bound by a bent oxo bridge and a metalmetal bond, the Mo-Mo distance of 2.772(1) 8, being consistent with a single bond. Each moiety contains one molybdenum atom, one terminal oxo ligand, and one mesityl group as well as a n v2-iminoacyl ligand. The terminal oxo ligands at each molybdenum atom are in the anti position with respect t o each other, and they are sitting symmetrically on each side of the Mo-OMo plane. The usual conventions indicate a MOW)dl formulation to each molybdenum atom, the diamagnetism of the complex being explained by spin-pairing between the two molybdenum atoms. The distances in two Mo-V2-iminoacyl linkages are identical within experimental error and lie in the range generally found for v2-iminoacyl ligand^.^ They are also very similar to those reported for the only v2-iminoacylimido do chromium ~ o m p l e x . ~ Complex 4 is remarkable for two reasons: first, it constitutes the unique example of an y2-iminoacyl functionality linked to a metal bearing terminal and bridging oxo groups, and, second, to our knowledge, the bent oxo-bridged complex possessing a molybdenummolybdenum bond and one terminal oxo group on each metal atom represents a completely new structural type for the Mo20s4+ systems.18-20 The only example of a complex containing such a framework reported t o date ~~~~~
~~
~~
(16) Sheldrick, G. M. SHELX86. Program for the Solution of Crystal Structures, 1985. (17) Sheldrick, G. M. SHELX76, Program for crystal structure determination, 1976. (18)West, B. 0. Polyhedron 1989, 8, 219.
(19) Stiefel, E. I. Progress in Inorganic Chemistry; Lippard, S. G., Ed.; Wiley: New York, 1977. (20) Holm, R. H. Chem. Rev. 1967,87,1401. (21) Herrmann, W. A.; Felixberger, J. IC;Kuchler, J. G.; Herdtweck, E. 2.Naturforsch. 1990,456, 876. (22) Selected NMR data for 4a: As far as mesityl I and I1 are concerned, lH and l3C assignments have been determined using a combination of inverse detection techniques. These techniques are the 1H detected one-bond (C,H) heteronuclear multiple quantum coherence (HMQC) and the long-range (two and three bonds) (C,H)heteronuclear quantum bond connectivity (HMBC) experiment^.^^ lH (CDCl3): 6 1.06 (s, 18 H, 'Bu),1.07 (s, Me(6) mes II), 1.43 ( s , 6 H, Me(6) mes I), 1.93 (s, 6 H, Me(2) mes II),2.23 ( s , 6 H, Me(4) me8 II), 2.42 (s, 6 H, Me(4) mes I), 2.64 ( 6 , 6 H, Me(2) mes I), 6.48 (s, 2 H, CH(5) mes 111, 6.49 ( 8 , 2 H, CH(5) mes I), 6.81 (s, 2 H, CH(3) mes 111, 6.97 ( 6 , 2 H, CH(3), mes I). 13C{lH}: 6 19.5 (Me(6) mes 11),20.8 (Me(2) mes 111, 21.0 (Me(4) mes II), 21.3 (Me(4)mes I), 22.4 (Me(6) mes I), 28.5 ((CH3)3C),29.5 (Me(2) mes I), 65.4 ((CH3)3C),126.9 (CH(3)mes I), 128.0 (CH(3)mes 11),128.2 (CH(5)mes I), 129.0 (CH(5)mes 11),132.1 (Cqu(4)mes II), 133.1 (Cqu(6) mes 11), 133.7 (Cqu(4)mes I), 134.0 (Cqu(1)mes II), 137.8 (Cqu(2) mes 11), 137.9 (Cqu(2) mes I), 143.3 (Cqu(6)mes I), 172.7 (Cqu(1) mes I), 206.5 (C-N). One can assume that for mesityl I the most shielded ortho methyl group (Me(6))is in the proximity of the shielding cone of the MoOMo ring, whereas the other one (Me(2))is deshielded because of the anisotropic effect of the Mo-0 bond. In the case of mesityl I1 one ortho methyl (Me(2))has a normal 6 value, whereas the other one (Me(6))being located in the shielding cone of mesityl I1 bound to the other molybdenum atom is shielded at higher field in the 'H NMR spectrum. We have also noticed that when C & j is used as a solvent, important differences are shown in the 'H NMR spectra which are due to the AIS effect.24 'H (C6D6): 6 0.99 (s, 18 H, 'Bu), 1.51 (s, 6 H, Me(6) mes 11), 1.53 ( 6 , 6 H, Me(6) mes I), 2.06 ( 6 , 6 H, Me(2) mes 111, 2.26 (s, 6 H, Me(4) mes II), 2.33 (s, 6 H, Me(4) mes I), 3.18 (s, 6 H, Me(2) mes I), 6.51 (s, 2 H, CH(5) mes 111, 6.66 (s, 2 H, CH(5) mes I), 6.70 (s, 2 H, CH(3) mes 11), 7.30 (s, 2 H, CH(3), mes I). 13C{lH]: 6 19.5 (Me(6)mes 11),20.9 (Me(2)mes 111,21.1 (Me(4)me8 II), 21.2 (Me(4) mes I), 23.4 (Me(6)mes I), 28.4 ((CH3)3C),30.1 (Me(2)mes I), 65.3 ((CH3)3C),127.7 (CH(3)mes I), 128.5 (CH(3)mes II), 128.8 (CH(5)mes I), 129.1 (CH(5) mes 111, 132.7 (Cqu(4) mes II), 133.3 (Cqu(6) mes II), 134.1 (Cqu(4)mes I), 134.6 (Cqu(1)mes 111,137.9(Cqu(2)mes II), 138.3 (Cqu(2)mes I), 143.9 (Cqu(6)mes I), 173.0 (Cqu(1)mes I), 207.4 (C=N). Data for 4b are as follows. lH (CDC13): 6 1.10 (s, 6H, Me, mes), 1.14 ( 6 , 6H, Me, mes), 1.80 ( 6 , 6H, Me, mes), 2.20 (s, 6H, Me, mes), 2.30 (s, 12 H, Me, mes), [4.47 (d, 2 H, JHH = 11 Hz),4.70 (d, 2 H, JHH = 11 Hz), CH2C6H5 AB type spectrum], 6.45-7.27 (m, 10 H, C & , ) . l3C{IH}: 6 18.9 (Me(6) mes 11), 20.0 (Me(2) mes II), 21.0 (Me(4) mes 111, 21.3 (Me(4) mes I), 21.6 (Me(6) mes I), 29.3 (Me(2) me8 I), 54.6 ( C H ~ C G H127.0-141.1 ~), (CH and Cqu C6H5 and mes), 172.9 (C ipso mes I, 209.8 (C-N). Data for 4c are as follows. 'H (C6D6): 6 0.59 (m, 4 H, CH2 in C&ll), 0.87 (m, 4 H, CH2 in C&11), 1.09 (m, 4 H, CH2 in C6H11), 1.24 (m, 4 H, CH2 in C&11), 1.55 (s, 6 H, Me(2) mes II), 1.61 (s, 6 H, Me(6) mes I), 1.63 (m, 4 H, CH2 in C&ll), 2.11 (s, 6 H, Me(2) mes 11), 2.18 (s, 6 H, Me(4) mes II),2.33 (s, 6 H, Me(4) mes I), 3.13 (s, 6 H, Me(2) mes I), 3.82 (m, 2 H, CHN), 6.46 (s, 2 H, CH(5) mes II), 6.65 ( 6 , 2 H, CH(5) mes I), 6.69 (s, 2 H, CH(3) mes 11, 7.27 (s, 2 H, CH(3), mes I). 13C{lH}: 6 19.5 (Me(6) mes 111, 20.8 (Me(2) mes 111, 21.0 (Me(4)mes 11),21.3 (Me(4)mes I), 21.8 (Me(6)mes I), 24.7 (CH2, cyclohexyl), 25.0 (CH2, cyclohexyl), 29.6 (Me(2) mes I), 30.5 (CH2, cyclohexyl), 30.8 (CH2, cyclohexyl), 62.7 (CHN), 127.0 (CH(3) mes I), 128.0 (CH(3)mes 11),128.4 (CH(5)mes I), 128.8 (CH(5)mes 111,131.5142.0 (Cqu mes), 171.5 (C ipso mes I), 207.9 (C=N). (23) Martin, G. E.; Zekter, A. S. Two-Dimensional NMR methods for establishing molecular Connectiuity; VCH Publishers, Inc.: New York, 1988. (24) Gunther, H. La Spectroscopie de RMN, Masson: Pans, 1994.
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Organometallics, Vol. 14, NO.5, 1995 2147
Scheme 1
%;les
OsM~+CNR I
I
Les
J
Figure 2. Adopted numbering scheme for the mesityl groups of 4. When the above reaction was effected in the presence of a n excess of isocyanide, only monoinserted products were isolated. A terminal isocyanide complex Mo(0)z(mes)2(CNBut)(la),which is likely intermediate in the reaction leading to 4a, can, however, be isolated as a dark-violet solid (YCN 2190 cm-l and YM~=O 910 and 924 cm-') by treating Mo(0)zmesz with 1equiv of ButNC in Et20 a t -50 "C and precipitation with hexane. This species is stable in the solid state, but in contrast with its osmium analogue,25it evolves rapidly in solution to form compounds 3a,4a,and 6a,respectively. When Mo(0)zmesz is reacted with ButNC in a sealed NMR tube in C5D5N, spectral changes occur as the temperature is raised from -33 to 25 "C. At -33 "C, in the 13Ci1H} NMR spectrum, a singlet is shown at 204.8 ppm. At 25 "C, this peak disappears and new peaks characteristic of 3a and 4a appear at 162.9 and 207 ppm. The signal at 204.8 ppm can possibly be assigned to a n unstable intermediate mononuclear $iminoacyl2 complex which could be at the origin of the different products found in this reaction (Scheme 1). Although this study has unambiguously established the structure of compound 4,both in the solid state and in solution, the precise mechanism of the reaction leading to 4 and 6 remains to be clarified and Scheme 1 can be seen as a rationalization rather than a true mechanism. Formation of the imine 3 can be easily explained via a double migration of mesityl g r o u p ~ lfollowed ,~~ by a reductive elimination pathway. Complex 4 is the result of the dimerization of the mononuclear y2-iminoacyl moiety with loss of a n oxygen. Insertion of oxygen into the molybdenum carbon bond of the iminoacyl function of 2 could afford a n oxazametallacycle 5 which upon hydrolysis would then generate the amide. Insertion of oxygen in a metal-carbon bond followed by amide formation has been reported once.27 Further(25) McGilligan, B. S.; Arnold, J.;Wilkinson, G.; Hussain-Bates, B.; Hursthouse, M. B. J . Chem. SOC.,Dalton Trans. 1990,2465. (26) Koschmieder, S. U.; Hussain-Bates, B.; Hursthouse, M. B.; Wilkinson, G.J . Chem. SOC.,Dalton Trans. 1991,2785.
"R
mes I
I mes
,NHR
mes
'$
0
6
more, such metallacycles as 5 could be common intermediates in reactions between CO and imido complexes7J2 or between isocyanates and imido- and oxomolybdenum complexes. In this last case they have been characterized by NMR.28
Acknowledgment. We are grateful to Dr. G. Salmon a and Dr. D. Nuel for helpful discussions and valuable cooperation. Supplementary Material Available: A fully labeled ORTEP diagram and tables of positional parameters, thermal
parameters, bond lengths, bond angles, torsion angles, and crystal data for 4a (7 pages). This material is contained in many libraries on microfiche, immediately follows this article in the microfilm version of the journal, and can be ordered from the ACS; see any current masthead page for ordering information. OM950134Z (27) Vivanco, M.; Ruiz, J.; Floriani, C.; Chiesi-Villa, A,; Guastini, C. Organometallics 1990,9, 2185. (28) Lai, R.; Mabille, S.; Croux, A.; Le Bot, S.Polyhedron 1991,10, 463.
