Polyhedron Vol. 8, No. 15, pp. 2003-2006, 1989 Printed in Great Britain
OZll-5381189 $3.00+.00 0 1989 MaxwU Peqamon MacmiUm plc
COMMUNICATION
ROTATION OF THE ACETYLIDE LIGAND ON THE TRIANGULAR FACE OF TUNGSTEN-DIRUTHENIUM CLUSTERS. CRYSTAL STRUCTURE AND SOLUTION DYNAMICS OF LWM,(CO),(CCPh), L = C,H,, CSMeS AND
M=Os, Ru
YUN CHI* and BANGJI LIU
Department of Chemistry, National Tsing Hua University, Hsinchu 30043, Taiwan, R.O.C.
and
GEN-HSIANG LEE and SHIEMING PENGt
Department of Chemistry, National Taiwan University, Taipei 10764, Taiwan, R.O.C.
(Received 31 January 1989 ; accepted 31 March 1989)
Abstract-Reaction of CpW(CO),aPh with OS~(CO)~~(CH~CN)~ or Ru~(CO),~ in refluxing toluene gives trinuclear mixed-metal acetylide clusters, CpWOs,(CO),(~Ph)
(1) and CpWRUz(CO)8(c%CPh) (3) ; the acetylide ligands of these two complexes are related to each other by a 120” rotation as indicated by X-ray diffraction studies. In solution, the variable temperature ‘H and 13C NMR spectra suggest that the acetylide ligand of 3 undergoes a 360” rotation on the face of the WRu2 triangle.
The C2 hydrocarbyl ligands hold a key position in the development of dinuclear, trinuclear and poly- nuclear organometallic chemistry. This position is in part due to a belief that the chemistry of the C2 hydrocarbyl ligands in the organometallic com- plexes is analogous to those adsorbed on metal surfaces. Among the many interesting properties of the C2 ligands is their fluxionality and mobility on the coordination sphere of the transition metal complexes. Related studies on the C2 hydrocarbyl ligands have attracted the attention of many theor- etical and synthetic chemists. Schilling and Hoffmann’ have reported the extended Htickel cal- culation of some hydrocarbyl ligands on the tri- *Author to whom correspondence should be addressed. t Author to whom enquiries concerning the X-ray crystallographic work should be addressed.
angular face of homonuclear transition metal com- plexes. For the C2 vinylidene complex, CO~(CO)~(CCHR)+, Norton and co-workers2 have reported the disrotatory correlated rotation about the CO~(CO)~-C vector and C-CHR bond by variable-temperature ’ 3C NMR studies. Stone and co-workers3 and Shapley and co-workers4 have both described the so-called “windscreen-wiper” type of motion of a coordinated alkyne ligand on a W20s triangular face. For the closely related C2 acetylide ligand, although the syntheses of many transition metal acetylide clusters have been reported in the literature,’ no paper has ever focused on the subject of site selectivity and solution fluxionality. We now report the structural and NMR studies of a series of acetylide complexes, which permit an analysis of the solution dynamics of the acetylide ligand.
2004 Communication LWM2(C0)&J-q2-C=CPh) M L Yield (I) OS C5H5 9% (2) OS CSMeS 2% (3) Ru CsHS 50% (4) Ru CSMes 57%
Treatment of LW(CO)3MPh6 with the sub- stance Os,(CO), ,,(CH 3CN)Z in refluxing toluene (1 10°C 30 min) provided, in addition to a red tetranuclear complex LWOs,(CO) I ,(C=CPh),’ a pale yellow trinuclear complex (L = CSHS, 1;
L = C,Me,, 2)* in low yield. The 13C-{ ‘H} NMR spectrum of 1 showed two signals at 6 137.5 and 73.8, reminiscent of those reported for the two ace- tylide carbon nuclei (6 172.9 and 112.7) in the anal- ogous CpWFe2(CO)8(C=CTol).8 The latter is a mixed-metal cluster in which the acetylide ligand
* Selected spectroscopic data 1: IR (&Hi J v(C0)
2077(s), 2043(vs), 2005(vs), 1995(s), 1965(s), 1924(m); ‘H NMR (CD&l*, RT): 6 7.68 (d, 2H), 7.37 (t, 2H), 7.20 (t, lH), 5.29 (s, 5H) ; “C-(‘H} NMR (CD,&, RT): 6 208.3 (Jw_c = 165 Hz, W-CO), 204.1 (Jw_c = 157 Hz, W-CO), 179.4 (OS-CO), 137.5 (CCPh), 73.8 (CCPh, Jwx = 16 Hz). 2 : IR (C6H ,J v(C0) 2076(s), 2041(vs), 2004(vs), 1991(s), 1963(m), 1905(w); ‘H NMR (CDCI,): 6 7.62 (d, 2H), 7.31 (t, 2H), 7.20 (t, lH), 1.93 (s, 15H).
t Crystal data for 1: Cz,H,oOsW ,Os,, M = 1104.27, monoclinic, space group P2,/c, a = 8.332(3), b = 14.543(4), c = 17.819(S) 8, /5 = 94.46(3)“, I’= 2152.71 AS, Z= 4, DC = 2.945 g cmT3, I;(OOO) = 1703.33, Nonius diffractometer with graphite-monochromated MO-K, radiation, 1= 0.70930 A, ~(Mo-KJ = 17.28 mm- ‘. $ scan absorption correction made, 3777 unique reflections were measured and 2980 reflections with Z > 2a(Z) were used in refinement. Refinement of 42 atoms and 145 parameters converged to RF = 0.068 and R, = 0.090, G.O.F. = 1.768.
$ Selected spectroscopic data. 3 : IR (&Hi *) v(C0) 2076(s), 2069(m), 2044(vs), 2033(vs), 2OlO(vs), 2003(m), 1994(m), 1975(m), 1966(w), 1952(vw), 193O(vw), 1918(vw) cm-‘; ‘H NMR (CDCl,, RT): 67647.24 (m, Ph), 5.56 (s, Cp, 3b), 5.25 (s, Cp, 3a) ; ‘3C-(‘H} NMR (d,-THF, RT): 6 210.8 (J,, = 160 Hz, W-CO, 3a), 210.7 (J,, = 165 Hz, W-CO, 3a), 207.6 (Jw_c = 169 Hz, W-CO, 3b), 197.0 (Ru-CO, 3b), 196.6 (Ru-CO,
3a), 168.9 (CCPh, Jw__c = 139 Hz, 3b), 168.6 (CCPh, 3a), 98.3 (CCPh, Jwx = 22 Hz, 3b), 85.6 (CCPh, Jwq = 21 Hz, 3a). 4 : IR (&HI 2) v(C0) 2071(m), 2064(vs), 2038(s), 2024(vs), 2005(s), 2001(vs), 1986(m), 1970(w), 1965(w), 1955(w), 1936(vw), 1913(vw) cm-‘; ‘H NMR (CD#J,, 273 K): 6 7.65-7.27 (m, Ph), 2.30 (s, Me, 4b), 1.93 (s, Me, 4a); 13C-{ ‘H} NMR(d*-THF, 226K) : 6 218.5 (W-CO,
4a), 217.3 (W-CO, 4a), 214.5 (J,, = 169 Hz, W-CO,
4b), 175.3 (CCPh, 4b), 173.0 (CCPh, Jw4 = 141 Hz, 4a), 100.1 (CCPh, J,, = 23 Hz, 4b), 90.2 (CCPh, 4a).
C(3)
8 O(3)
Fig. 1. The ORTEP diagram of 1. Bond lengths (A) : W---OS(~), 2.8294(19); W--OS(~), 2.9160(18); OS(~)-- OS(~), 2.8114(18); W-C(15), 2.20(3); Os(l)-C(15), 2.16(3); Os(2)--C(15), 1.96(3); Os(l)-C(14), 2.17(4); W-C(14), 2.36(4); C(14)-C(15), 1.23(5); C(16)-C(14),
1.47(5). Bond angles (“): Os(2)-C(15)-C(14), 159(3); C(15)-C(14)--C(16), 148(4).
functions as a five-electron donor, a-bonded to the tungsten atom, while employing its two orthogonal alkyne n-bonds to bridge the unique Fe-Fe edge. However, since the colour, as well as the IR spectra of these osmium complexes in the region of CO absorption are substantially different from the com- plex of iron triads, an X-ray diffraction study was carried out on 1.t
The molecular structure of 1 is shown in Fig. 1, together with some important bond parameters. The molecule has a triangular WOs, core structure in which the tungsten atom is coordinated to a Cp ring and two CO ligands, while each of the osmium atoms is linked to three, mutually orthogonal, ter- minal CO ligands. The most important feature is the orientation of the phenyl acetylide moiety, which is a-bonded to an osmium atom and at the same time forms a transverse bridge across the second W-OS bond. Therefore, the structure of 1 is related to CpWFe,(CO),(C=C!Tol) by a 120” rotation of the acetylide ligand.
In order to further study the preferred orientation of the acetylide ligand over the triangular face of the trinuclear mixed-metal complexes, we have carried out the syntheses and structural determination of the tungsten-diruthenium analogues. Complexes 3 and 4$ were similarly obtained in good yield using Ru~(CO),~ as reagent. Crystals of 3 suitable for X-ray structural determination were obtained by recrystallization from CH,Cl,-hexane at room temperature. The structure of 3 is shown in Fig. 2
Communication 2005
Fig. 2. The ORTEP diagram of 3. Bond lengths (A): W-Ru(l), 2.9976(10); W-Ru(2), 2.9651(10); Ru(l)- Ru(2), 2.6612(11); W-C(15), 1.976(8); Ru(l)---C(lS), 2.128(8); Ru(2)-C(15), 2.195(7); Ru(l)-C(14), 2.297(8); Ru(2)-C(14), 2.188(8); C(14)-C(15), 1.314(11); C(16)-C(14), 1.470(11). Bond angles (“): W-C(15)-
C(l4), 162.5(6); C(15)-C(14)-C(16), 142.5(8).
with selected structural parameters.* The WRu2 triangle is near-isosceles and the phenyl acetylide moiety is now a-bonded to the W atom and, quasi- symmetrically, x-bonded to the two ruthenium atoms. Therefore, we conclude that complex 3 is not isostructural with 1 but rather with the iron- containing complexes.
The solution dynamics of these WRu, complexes is of particular interest. Both the ‘H NMR and IR spectra in the region of CO absorption suggest the presence of two isomers. Based on the structural information, we proposed that the isomerization is due to a 360“ rotation of the acetylide ligand over
(3a : 3b = 1: 1.2) the WRuz triangle (Scheme 1). The assignment of each individual isomer is identified by its characteristic 13C NMR data.
The 13C NMR spectrum of 3 at 205 K exhibits three W-CO signals at 6 210.8, 210.5 and 207.3 in the ratio of 1 : 1 : 2.4. Therefore, the first two resonance lines are assigned to the “asymmetric”
*Crystal data for 3: C2,H,,0,W ,Ruz, M = 776.29, monoclinic, space group P2,/n, a = 12.4756(13), b = 13.216(4), c = 13.395(4) A, B = 97.993(17)“,
V= 2186.95 i%‘, Z= 4, DC = 2.358 g ~rn-~, P(OO0) = 1447.68, Nonius diffractometer with graphite- monochromated MO-K, radiation, 1= 0.70930 8, ~(Mo-
KJ = 6.74 mm-‘. JI scan absorption correction made,
3840 unique reflections were measured and 2851 reflec- tions with I > 2a(Z) were used in refinement. Refinement of 42 atoms and 290 parameters converged to R, = 0.029 and R, = 0.027, G.O.F. = 1.583.
3a'
Scheme 1.
3a
isomer (3a, acetylide C-C bond is orthogonal to the W-Ru bond) and the third one to the “sym- metric” isomer (3b, acetylide C-C bond is ortho- gonal to the Ru-Ru bond). This assignment is not unreasonable because the free rotation of the CPW(CO)~ unit in the asymmetric isomer would be expected to encounter the steric interaction of the phenyl group, whereas in isomer 3b this process should have a smaller activation energy. Fur- thermore, five signals at 6 202.5,200.8, 196.0, 194.2 and 192.4 with an intensity ratio of 1 : 1 : 1: 1 : 2 can be assigned to the Ru-CO resonances of 3a to support the assignment; the signal at 6 192.4 is double the intensity of the other four signals and therefore corresponds to two coincident signals.
The Ru-CO signals of 3b were not observed in this spectrum. However, while the temperature was decreasing to 190 K, its W-CO signal broadened and collapsed, suggesting the slow-down of the CpW(CO)r rotation, and three very broad Ru-CO signals at 6 203, 198.5 and 189 appeared in the spectrum, consistent with the symmetric nature of
3b, as suggested by the solid-state structural studies. Interpretation of the ’ ‘C NMR data for 4 followed similar studies. From the relative intensities of the methyl signals in the ‘H NMR spectrum at room temperature, it is deduced that an isomer ratio
4a : 4b of 1 : 5.5 prevails.
The kinetic parameters of the acetylide ligand rotation have also been calculated from the data of the variable-temperature 13C and ‘H NMR spec- troscopies. The racemization process of 3a consists
of a simultaneous correlated rotation of the CpW(CO), moiety around an axis through tungsten and a 120” rotation of the acetylide ligand over the tungsten atom (step A, 3a++3a’, Scheme 1). Therefore, the coalescence of the two W-CO res- onances, as well as the coalescence of the six
2006 Comrmmication Ru-CO resonances in 3a, would provide the appropriate kinetic data for step A. In fact, both the W-CO and the Ru-CO resonance lines have broadened and merged into single lines during the temperature rise to 300 K. A free energy of acti- vation (AG*), calculated from the dynamic behav- iour of the W-CO resonance lines, is estimated to be 62 kJ mol- I.*
In contrast to the racemization of 3a, iso- merization between 3a and 3b is consistent with a
120” rotation from a W-Ru edge to the Ru-Ru edge (steps B, 3a t* 3b or 3a’ c* 3b). Because only two Cp signals were observed in the ‘H NMR spec- trum at 300 K, we conclude that the energy barrier of rotation of the CPW(CO)~ unit is much too small to affect the energy barrier of steps B. The free energy of activation (AGf), calculated from the coalescence of the Cp signals, is 67 kJ mol- ’ at 338 K, providing an estimate of the energy barrier of steps B.
Interestingly, the acetylide ligand of the WOs, complexes is static on the time scale of 13C NMR spectroscopy. THe 13C NMR spectrum of 1 at 295 K (d*-toluene) exhibits two W-CO signals at 6 208.6 and 204.0, a sharp Os(CO), line at 6 179.7, and two very broad OS-CO signals at 6 178.8 and 173.4. The exchange of the OS-CO resonances is not due to the rotation of the acetylide ligand, but to a localized Os(CO), rotation around an axis through the two different osmium atoms. When the temperature is increased to 350 K, the sharp Os(C0) 3 signal remained unchanged and the broad *The free energy of activation AGf calculated from the 13C NMR data recorded on d,-toluene solution is 70 KJ mol- ‘. This data suggests that the rotation of the acetylide ligand possibly involves a transition state in which the acetylide C-C bond is perpendicular to the WRuz triangle.
OS-CO signals became a relatively sharp signal at 6 176.5, confirming that the racemization of 1 has not occurred at this temperature.
Acknowledgement-We thank the National Science
Council of the Republic of China for generous financial support of this research.
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