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Organometallics 1995, 14, 4980-4982
Synthesis of the Quatercyclopentadienyl Ligand and Its Half-Sandwich Tetratungsten Complexes Cristina G. de Azevedo,la Roland Boese,lb David A. Newman,lc and K. Peter C. Vollhardt*Jc Department of Chemistry, University of California at Berkeley, and Chemical Sciences Division, Lawrence Berkeley Laboratory, Berkeley, California 94720, and Institut f i r Anorganische Chemie der Universitat-GH Essen, Universitatsstrasse 3-5, 0-45117 Essen, Germany Received August 23, 1995@ Summary: Double 3-oxocyclopentenylation of the fulvalene dianion, followed by metalation, results i n the four isomeric bis(enones) 1 which were elaborated via the bis(cyc1opentadienes) 2 to the four regio- and stereoisomeric forms of (quatercyclopentadieny1)tetratungsten (connectivity 1,1‘,2‘,1‘‘,3‘‘,1 “‘ (3a,b and 4a,b) and 1,1’,3’,1’’,~,1‘’’ (3c,d and &,d)). The molecular structures of l a and l b have been determined by X-ray analysis. The tetramethyl complex 5 is obtained from 2d by a metalation-methylation sequence involving deprotonation of the intermediate bidtungsten hydride) with Ki(-OC(CH3)3). Half-sandwicholigocyclopentadienyl complexes can be viewed as cyclopentadienylmetal analogs of the corresponding fulvalene dimetals2 and as such constitute attractive molecules with which to explore the basic chemical potential of rigidly held acyclic3metal arrays, in particular with respect to organic substrate activation, intrachain ligand migration, electron transfer, and ultimately, synergistic catalysis. The series contrasts topologically with that of the analogous and extensively investigated sandwich oligometall~cenes~ and has up to now been extended only once, t o the two isomers of Abstract published in Advance ACS Abstracts, November 1, 1995. (1)(a) Permanent address: Centro de Quimica Estrutural, Instituto Superior Technico, Av. Rovisco Pais, 1096 Lisboa, Portugal. (b) Universitat-GH Essen. ( c ) University of California at Berkeley. (2)For leading references, see: (a) Tilset, M.; Vollhardt, K. P. C.; Boese, R. Organometallics 1994, 13, 3146. (b) McGovern, P. A.; Vollhardt, K. P. C. Synlett 1990,493. (3)For recent work on “linear” oligometals, see, inter alia: (a) Herberhold, M.; Jin, G.-X.; Rheingold, A. L. Angew. Chem., Int. Ed. Engl. 1995,34,656. (b) Sundermeyer, J.;Runge, D. Angew. Chem., Int. Ed. Engl. 1994,33, 1255.( c ) Sundermeyer, J.; Runge, D.; Field, J. S. Angew. Chem., Int. Ed. Engl. 1994,33, 678. (d) Laguna, A.; Laguna, M.; Jimenez, J.; Lahoz, F. J.; Olmos, E. Organometallics 1994, 13,253.(e) Mashima, K.;Nakano, H.; Nakamura, A. J. Am. Chem. SOC.1993,115,11632. (0Yamamoto, Y.; Yamazaki, H. Organometallics 1993,12,933. (g) Herrmann, W. A.; Albach, R. W.; Behm, J. J . Chem. SOC.,Chem. Commun. 1991, 367. (h) Cazanoue, M.; Dahan, F.; Mathieu, R. Inorg. Chem. 1990,29, 563. (i) Rardin, R. L.; Bino, A.; Poganiuch, P.; Tolman, W. B.; Liu, S.; Lippard, S. J. Angew. Chem., Int. Ed. Engl. 1990,29,812.(i) Firfiray, D. B.; Irving, A,; Moss, J. R. J . Chem. Soc., Chem. Commun. 1990,377.(k) Ferrer, M.; Perales, A.; Rossell, 0.; Seco, M. J . Chem. SOC.,Chem. Commun. 1990,1447.(1) Davies, S.J.; Howard, J. A. K.; Musgrove, R. J.;Stone, F. G. A. Angew. Chem., Int. Ed. Engl. 1989,28,624. (4)For recent work, see, inter alia: (a) Dong, T.-Y.; Huang, C.-H.; Chang, C.-K.; Hsieh, H.-C.; Peng, S.-M.; Lee, G.-H. Organometallics 1995,14,1776.(b) Dong, T.-Y.; Lee, T.-Y.; Lee, S.-H.; Lee, G.-H.; Peng, S.-M. Organometallics 1994,13,2337.( c ) Lai, L.-L.; Dong, T.-Y. J. Chem. Soc., Chem. Commun. 1994,2347. (d) Jaitner, P.; Schottenberger, H.; Gamper, S.; Obendorf, D. J . Organomet. Chem. 1994,475, 113.(e) Foucher, D. A.; Honeyman, C. H.; Nelson, J . M.; Tang, B. Z.; Manners, 1.Angew. Chem., Znt. Ed. Engl. 1993,32,1709. (0Oelckers, B.; Chavez, I.; Mann’quez, J . M.; Romhn, E. Organometallics 1993, 12,3396.(g) Dong, T.-Y.; Huang, C.-H.; Chang, C.-K.; Wen, Y.-S.; Lee, S.-L.; Chen, J.-A.; Yeh, W.-Y.; Yeh, A. J . Am. Chem. SOC.1993,115, 6357.(h) For early work, see: Gmelin Handbook of Inorganic Chemistry; Springer-Verlag: Berlin, 1977;Vol. 41,Pt. A, Ferrocene 6. @
0276-7333/95/2314-4980$09.00l0
trimetalated ter~yclopentadienyl.~ We report now the synthesis of the next higher cyclopentadiene analog, quatercyclopentadienyl, complexed to four tungsten units. The free ligand can exist in three regioisomeric forms with connectivities designated as 1,1’”’,1~”2,1’’’; 1,1‘”‘,1’’,”,1‘’’;and 1,1’,3’,1”,3”,1’’’,6of which only the last two are described here. Transition-metal complexation renders the two center rings chiral and, depending on the presence and location of metal-metal (M-M) bonds, may give rise to a number of additional stereoisomers and (M-M) regioisomers, providing a unique opportunity t o explore the influence of topology on the physical and chemical properties of these complexes. Scheme 1depicts the assembly of the target molecules patterned after the strategy used in the construction of (tercyc10pentadienyl)trimetals.~Thus, double 3-oxocy,~ by clopentenylation of the fulvalene d i a n i ~ nfollowed metalation, gave the four purple isomers la-d, separated initially by careful chromatography on silica (CH2Cl2-acetone gradient) into the two pairs of purple la,b ( l : l , 36.7%)and lc,d ( l : l , 34%),which could be conveniently carried on as such through the scheme or separated further into the pure components by fractional crystallization. Complex Id was subjected to the sequence in Scheme 1 in pure form. The multiple organic and inorganic functionalities present in 1-4 render them extremely light, air, heat, acid, and base sensitive, sometimes to the detriment of isolated yields. Rigorous and self-consistent structural assignments were made primarily by IH NMR techniques, which readily corroborated the substitution patterns of the central rings (1,2 vs 1,3), symmetry (series a,b vs c,d), location of the tungsten-tungsten bond,8 proximity of hydrogens (NOESY),and connectivity (TOCSY). Confirmation was obtained by the execution of X-ray crystal analyses on l a and l b (from CHzCl.2-hexane by vapor diffusion; Figures 1 and 2).9 The structures of la,b can be viewed as being composed of FvWn(CO)6 modified by cyclopentenone substitution. In la, the planes defined by rings 1((27C11) and 2 (C12-Cl6) form an angle of 25.9”,distortion from planarity occurring in the direction of the respective two attached metals W1 and W2. For lb, this angle is 22.3’. These values are similar to those observed for related compounds; in (~5:~5:~5-1,1’,3’,1’’-tercyclo(5)Boese, R.; Myrabo, R.; Newman, D. A,; Vollhardt, K. P. C. Angew. Chem., Int. Ed. Engl. 1990,29,549. (6)IUPAC Nomenclature of Organic Chemistry; Rigaudy, J., Klesney, S. P., Eds.; Pergamon Press: Oxford, U.K., 1979;Rules A-52,p 42; A-54, p 44;c-71;p 128. (7)Smart, J . C.; Curtis, C. J. Inorg. Chem. 1977,16, 1788. (8) Meverhoff, D. J.: Nunlist, R.: Tilset, M.: Vollhardt. K. P. C. M u m . Reson. Ckem. 1986,24,709. I
0 1995 American Chemical Society
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Organometallics, Vol. 14,No.11, 1995 4981
3c
4a 4b 4c 4d Legend: (a) 3-chloro-2-cyclopentenone(1 equiv), 10 min, -78 "C, THF; (b) BuLi (2 equiv), 5 min, -78'C; (c) 3-chloro-2cyclopentenone (2 equiv), 10 min, -78 "C; (d) BuLi (1 equiv), -78 "C to room temperature; (e) W(COMNCEt)3 (2 equiv), 5.5 h, 2 SH, room temperature; (DAgBF4 (2 equiv), -78 "C to room temperature; (g) i-BuAlH, 2 h, 0 "C, CH2C12; (h) cat. ~ - C H ~ C ~ H ~ S O min, 60 "C,C6Hs; (i) W(C0)dNCEth (5 equiv), 3 days at room temperature, 3 h at 50 "C, THF; (j) LiN(TMS)Z (2.5 equiv), 7 min, room temperature; (k)CH3I (10equiv), -78 "C for 1 h, room temperature for 1 h; Yield for the conversion of pure 2b to 3b and 4b.
pentadienyl)[W(CO)31[W(C0)31'[W(CO)~CH~l''5the angle is 22.5". The two rings are also somewhat twisted to avoid eclipsing strain associated with the carbonyl groups, which become approximately staggered by this distortion. For la, the torsion angle is 21.0", and for lb it is 13.4". Cycles C7-Cll and C17-C21 are more nearly coplanar, with dihedral angles of 9.3" (la) and 9.1" (lb),respectively. The fourth ring (C22-C26) is twisted with respect to the second, the dihedral angle between the planes C7-Cll and C22-C26 being 46.0" (la) and 33.4" (lb). The twisting distortion observed for the a-bonded cyclopentenone is not unexpected and can be ascribed to steric hindrance to achieving coplanarity. In contrast, in the /3-bonded analog this effect is absent. Presumably, these distinctive structural (9) (a) Crystallographic data for la: triclinic, Pi,2 = 2, a = 8.955(1) = 80.82(1)",y = 86.76 (l)", V = 1184.3(2) peale = 1.801 g/cm3. Nicolet R3mN diffractometer, Mo Ka radiation ( I = 0.710 69 6362 unique reflections, of which 4791 were observed (F, 2 4dF)); R = 0.0277, R, = 0.0273. (b) Crystallographicdata for lbCHzC12: monoclinic,P21/c, 2 = 4, u = 14.095(2)A, b = 13.604(2)A, c = 14.290(3)A, a = go",p = 96.20(1)",y =go", V = 2723.4(7)A3,pealc= 2.115 &m3; Nicolet R 3 m N diffractometer, Mo Ka radiation ( I = 0.71069 A); 5011 unique reflections, of which 3513 were observed 3513 (F,2 4dF)); R = 0.0594, R, = 0.0601.
A, b = 9.434(1)A, c = 14.271(1)A, a = 84.98(1F',p
#,
h);
characteristics are present along the series 1-4 as exemplified by the crystal structures of (q5:~5:75-1,1',3',1''t e r c y c l o p e n t a d i e n y l ~ [ W ( C 0 ) ~ l [ W ~ C 0 ) ~ land ~~CO~~C~~ (45:95:q5-1 ,1',2',1''-tercyclopentadienyl)[Re(C0)~1[Ru(C0)~l'[Ru(CO)zl"! The shorter Wl-W2 bond of 3.252(2) 8, for la, compared with 3.286(2) 8, for lb, is in agreement with the higher torsion and bending angle for the former; the carbonyls in l a are perhaps more staggered, allowing for a shorter W-W distance. The W-W separations in l a and l b are closer t o that in cp2wz(co)6 (3.222(1) A),'' than to that in ??VWz(C0)6 (3.347(1)8,),11 again reflecting the eclipsed configuration of the carbonyls in the latter. The enone functions in 1 (either as the pairs la,b and lc,d or as pure Id) were elaborated initially by reduction to diastereomeric mixtures of the corresponding allylic alcohols and subsequently by acid-catalyzed dehydration to mixtures of the desired 1,3- and 1,4cyclopentadiene isomers 2 (only the former are shown in Scheme 1). It was possible t o separate 2a from 2b a t this stage by chromatography (silica, ethyl acetate(10)Adams, R. D.; Collins, D. M.; Cotton, F. A. Inorg. Chem. 1974, 13, 1086. (11) Abrahamson, H. B.; Heeg, M . J. Inorg. Chem. 1984,23,2281.
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4982 Organometallics, Vol. 14, No. 11, 1995
l,l1,2',1''-connected portion of 34b and 44b is sterically prevented from achieving the required coplanarization of the three rings.5 Interestingly, subjecting pure 2d to the sequence i-k (Scheme 1) but using K+(-OC(CH&) as a base in j furnished none of the expected 3d and 4d but rather the yellow tetramethyltungsten derivative 5 (22%) as the sole isolable product.
08
0
5
C
\
oc'
oc'
C
5 04
Figure 2. Molecular structure of lb in the crystal. Selected distances (A): Wl-W2,3.286(2); Wl-C1,1.939(21); Wl-C2, 2.004(18);W1-C3, 1.985(17);W2-C4, 1.995(19); W2-C5, 1.963(19);W2-C6,1.970(24); C7-C12,1.444(21); C10-C17, 1.489(26); C13-C22, 1.508(26). hexane, gradient), allowing for the later conversion of pure 2b to 3b and 4b. Finally permetalation proceeded through the bidtungsten hydrides) as intermediates (observed by 'H NMR from pure 2d: 6 -6.91 (8,J183W-H = 39.5 Hz, 2H) ppm), which were deprotonated to the corresponding dianions and then methylated (with CH31; in the case of pure 2b with CF3S03CH3) to give not only the purple (quatercyclopentadieny1)tungsten species 3 but also the rearranged purple complexes 4 (ratio 3,b:4a,b = 4:l; 3c,d:4c,d = 3:1), separable by careful chromatography (silica, ethyl acetate-hexane, gradient). Migration of the W-W bond can be most readily envisioned to occur at the dianion stage by invoking attack of a charged metal center on the linked dinuclear core,12 resulting in equilibration along a (tercyclopentadieny1)trimetal subunit. The regioselectivity of this process has topological origin, as the (12)Corraine, M.S.;Atwood, J. D. Organometallics 1991,10,2315.
c
cn,
I"C0
CO
5
Figure 1. Molecular structure of la in the crystal. Selected distances (A): Wl-W2,3.252(2); W1-C1, 1.999(7); Wl-C2, 1.969(7);Wl-C3,1.984(6); W2-C4,1.978(7); W2C5, 1.976(7);W2-C6,1.983(5); C7-Cl2, 1.458(7);C9-Cl7, 1.468(7);C13-C22, 1.464(8).
0
-1
w,-
w.lfCO co 6
Evidently, reduction of the W-W bond to produce 6 (or its functional equivalent) occurs under these conditions, perhaps by electron transfer-disproportionation before or during the methylation sequence. This explanation is plausible in light of the relatively facile electrochemical reduction of (fulvalene)ditungsten hexacarbonyl13 and related literature reports.14 In summary, we have demonstrated that organometallic methodology can be applied to doubly extend the fulvalene nucleus to tetrametallic quatercyclopentadienyls. Application of the rich chemistry of the component subunits of these systems215to the whole should be a fruitful area of investigation, currently in progress.
Acknowledgment. This work was supported by the director, Office of Energy Research, Office of Basic Energy Sciences, Materials Science Division, of the U.S. Department of Energy under Contract DE-AC-03 76SF00098. C.G.A. is grateful to INVOTAN, FLAD, and the Fulbright Scholarship Program for financial support. Supporting Information Available: Text and tables giving experimental details and spectral (including lH NMR spectral assignments of la-d, 3b-d, and 4c,d), analytical, and X-ray (for la,b) data for new compounds (39 pages). Ordering information is given on any current masthead page. OM950655M (13)(a) Moulton, R.;Weidman, T. W.; Vollhardt, K. P. C.; Bard, A. J. Inorg. Chem. 1986,25, 1846.(b) Kadish, K. M.; Lacombe, D. A,; Anderson, J. E. Inorg. Chem. 1988,25,2246. (14)(a) Bergman, R. G.; Yang, G. K. J. Am. Chem. SOC.1983,105, 6045.(b)Schore, N.E.; Ilenda, C.; Bergman, R. G. J.Am. Chem. SOC. 1976,98,7436.
