Organometallics 1995, 14, 4625-4634
4625
Photochemically Activated Phosphorus-Carbon Bond Cleavage in the Binuclear Ruthenium Complex Ru2(CO)6(bpcd).Redox Reactivity, Molecular Orbital Properties, and X-ray Diffraction Structures of Ru2(CO)6(bpcd) and I
I
Huafeng Shen, Simon G. Bott," and Michael G. Richmond* Department of Chemistry, Center for Organometallic Research and Education, University of North Texas, Denton, Texas 76203 Received April 26, 1995@ The reaction between the redox-active diphosphine ligand 4,5-bis(diphenylphosphino)4-cyclopenten-l,3-dione (bpcd) and RU~(CO)IZ has been examined under a variety of conditions. Thermolysis of Ru3(C0)12with bpcd affords the binuclear compounds Ruz(C0)~(bpcd) (2) and R U Z ( C O ) ~ ~ - C = C ( P P ~ Z ) C ( O ) C H Z C ( ~(3) ) I ~as Z -the P P ~major ~ ) and minor (1)has been synthesized products, respectively. The disubstituted cluster Rus(CO)~o(bpcd) and shown to contain a chelating bpcd ligand, on the basis of IR and 31PNMR data. The cluster Ru3(CO)lo(bpcd) (chelating isomer) undergoes cluster fragmentation at ambient temperatures in the dark to give the binuclear compound Ruz(CO)6(bpcd) and R u ~ ( C O ) ~ S , with no evidence for the formation of 3. Both 2 and 3 have been isolated and fully characterized in solution by IR and NMR spectroscopy, and the solid-state structure of each new binuclear compound has been established by X-ray diffraction analysis. The bpcd ligand in 2 bridges adjacent Ru(C013 centers via the PPhz groups and the alkene bond of the dione moiety, and this gives rise to a formal dative Ru-Ru bond where the phosphine-substituted ruthenium center acts as the two-electron-donor ligand and the alkene-substituted ruthenium center as the acceptor site. P-C(dione) bond cleavage and n bond decoordination highlight the key structural features of 3. Independent experiments reveal that binuclear 2 is converted to 3 by 366 nm light with a quantum efficiency of 0.035. Comparative photochemical experiments with the known binuclear compound Ruz(CO)g[(Z)-PhzPCH=CHPPhzI (4) provide no evidence for P-C bond cleavage, underscoring the overall importance of the nature of the ancillary diphosphine in controlling the course of reactivity in this genre of compound. The redox properties of 1-4 were explored by cyclic voltammetry, which revealed the presence of a n irreversible oxidation process (metal based) for each of these compounds. Whereas 2 and 4 do not exhibit any reductive electrochemistry in CHZClz, compounds 1 and 3, with their available dione z* acceptor orbital, undergo a reversible one-electron reduction at relatively low potential. The orbital composition of the HOMO and LUMO levels in 1-4 has been examined by carrying out extended Huckel MO calculations on the model compounds Ru3(CO)lo(H*-bpcd),Ruz(CO)6(&-bpcd), Ruz(CO)&-
~ = C ( P H ~ ) C ( O ) C H ~ ~ ( O ) ~ and ~ Z -RUZ(CO)~[(Z)-HZPCH=CHPHZ~, PH~), and the results are discussed relative t o the observed electrochemistry. The P-C bond cleavage that accompanies the conversion 2 3 is proposed to occur at one of the resulting biradical
-
ruthenium centers, which are formed by the photochemically induced homolysis of the donoracceptor ruthenium-ruthenium bond in 2.
Introduction
thenium cluster involved the controlled pyrolysis of Ru3(CO)g(PR3)3derivatives. Here several ortho-metalated The thermal and catalyst-mediated substitution chemphenyl-, phosphido-, and benzyne-containing clusters istry of RUQ(CO)~Z with phosphines has been extensively were isolated and characterized by solution method^.^ explored over the last several In several cases In fact, the controlled degradation of a wide variety of novel products derived from C-H and P-C bond activacluster-bound ligands has proved to be a convenient tion have been isolated and structurally ~haracterized.~ method into the mechanistic study of bond-breaking and For example, one the very first reports dealing with the bond-making processes at polynuclear ensembles.6 Condegradation of a tertiary phosphine ligand at a trirutinued research in this area of metal cluster chemistry is critical if new hybrid catalysts are to be exploited for Abstract published in Advance ACS Abstracts, September 1,1995. their synthetic potential. @
0276-733319512314-4625$09.00/0 0 1995 American Chemical Society
Shen et al.
4626 Organometallics, Vol. 14,No.10,1995 We have recently embarked on a program designed to study the reactivity of polynuclear clusters with redox-active phosphines in an effort t o prepare new ligandkluster redox systems. It is our hope that such compounds will display superior electron reservoir capabilities, as a result of the cooperative mixing of ligand and cluster orbitals. The two redox-active diphosphine ligands that we have concentrated on are 2,3-bis(dipheny1phosphino)maleic anhydride (bma) and 4 3 bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd).
accession on going from neutral fac-ReBr(CO)s(bma)t o the corresponding 18 6 complex [fac-ReBr(CO)a(bma)l-,ll no other reactivity studies with these unique ligands exist, to our knowledge. Given the complete absence of polynuclear reactivity with the ligands bma and bpcd, our first study involved the reaction using the tricobalt cluster PhCCo3(CO)s, which initially proceeds to give the expected bmasubstituted cluster PhCCoa(COh(bma). This latter cluster was subsequently shown to exhibit exceptional liability with respect to P-C(malei&nhydride) bond scission, coupled with C-C bond reductive elimination
+
,
PhzP
PPh,
bma
Ph2P
to give CO~(~~)~[~LZ-)~~:)~~-C(P~)C=C(PP~Z)C(O @2-PPh2),as shown in eq l.12J3
PPhz
bpcd
Ph
These two particular diphosphines, which were first prepared by Becher and F e n ~ k e have , ~ been used as ligands in the synthesis and redox investigation of sundry mononuclear compounds by the same groups, with the bma ligand receiving the most attention.8 Extensive studies pertaining to the EPR properties and the enhanced substitutional reactivity of the 18 6 complex Co(CO)a(bma)have been published by Tyler and Rieger,sJo and with the exception of our recent report on the redox pair of [fac-ReBr(C0)3(bma)lo’-, which dealt with the structural aspects of electron
- co
+
~~~
~
0
~
(1)(a) Karel, K. J.; Norton, J. R. J . Am. Chem. Soc. 1974,96,6812. (b) Shen, J.-K.; Shi, Y.-L.; Gao, Y.-C.; Shi, &.-Z.; Basolo, F. J . Am. Chem. SOC.1988,110,2414. (c) Po&,A. J. Pure Appl. Chem. 1988,60, 1209. (d) Brodie, N. M. J.; Poe, A. J. J. Organomet. Chem. 1990,383, 531. (e) Chin-Choy, T.; Keder, N. L.; Stucky, G. D.; Ford, P. C. J . Organomet. Chem. 1988, 346, 225. (0 Bruce, M. I.; Liddell, M. J.; Hughes, C. A.; Skelton, B. W.; White, A. H. J . Organomet. Chem. 1988, 347, 157. (g) Corrigan, J. F.; Doherty, S.; Taylor, N. J.; Carty, A. J.; Boroni, E.; Tiripicchio, A. J . Organomet. Chem. 1993, 462, C24. (2) (a)Lavigne, G.; Kaesz, H. D. J. Am. Chem. SOC.1984,106,4647. (b) Lavigne, G.; Lugan, N.; Bonnet, J.-J.Inorg. Chem. 1987,26, 2345. (c) Bruce, M. I.; Kehoe, D. C.; Matisons, J. G.; Nicholson, B. K.; Rieger, P. H.; Williams, M. L. J . Chem. Soc., Chem. Commun. 1982, 442. (d) Bruce, M. I.; Hambley, T. W.; Nicholson, B. K.; Snow, M. R. J. Organomet. Chem. 1982,235,83. (3) For other examples of RudCO)12activation by catalyst mediation, see: (a)Darensbourg, D. J.; Gray, R. L.; Pala, M. Organometallics 1984, 3,1928. (b)Day, M. W.; Hajela, S.; Kabir, S.E.; Irving, M.; McPhillips, T.; Wolf, E.; Hardcastle, K. I.; Rosenberg, E.; Milone, L.; Gobetto, R.; Osella, D. Organometallics 1991,10,2743.(c) Rivomanana, S.; Lavigne, G.; Lugan, N.; Bonnet, J.-J.; Yanez, R.; Mathieu, R. J. Am. Chem. SOC. 1989,111,8959. (4) (a)Lugan, N.; Lavigne, G.; Bonnet, J.-J.Inorg. Chem. 1987,26, 585. (b) Deeming. A. J.: Smith. M. B. J. Chem. Soc.. Dalton Trans. 1993,2041. ( c ) LLgan, N.;Bonnet, J.-J.; Ibers, J. A. J . Am. Chem. Soc. 1986,107,4484.(d) Nucciarone, D.; MacLaughlin, S. A.; Taylor, N. J.; Carty, A. J . Organometallics 1988, 7,106. (e) b o x , S. A. R.; Lloyd, B. R.; Morton, D. A. V.; Nicholls, S. M.; Orpen, A. G.; Vifias, J. M.; Weber, M.; Williams, G. K J . Organomet. Chem. 1990,394,385.(0 ManojloviCMuir, L.; Brandes, D. A.; Puddephatt, R. J. J . Organomet. Chem. 1987, 332, 201. (g) Bruce, M. I.; Williams, M. L.; Patrick, J. M.; Skelton, B. W.; White, A. H. J . Chem. Soc., Dalton Trans. 1986, 2557. (5) Bruce, M. I.; Shaw, G.; Stone, F. G. A. J . Chem. Soc., Dalton Trans. 1972, 2094. (6) (a) Lavigne, G. In The Chemistry of Metal Cluster Complexes; Shriver, D. F., Kaesz, H. D., Adams, R. D., Eds.; VCH New York, 1990; Chapter 5. (b) Deeming, A. J. In Transition Metal Clusters Johnson, B. F. G., Ed.; Wiley: New York, 1980; Chapter 6. (7)(a) Fenske, D.; Becher, H. J. Chem. Ber. 1974, 107, 117. (b) Fenske, D. Chem. Ber. 1979,112, 363. ( 8 ) (a) Becher, H. J.; Bensmann, W.; Fenske, D. Chem. Ber. 1977, 110, 315. (b) Fenske, D. Angew. Chem., Int. Ed. Engl. 1976, 15, 381. ( c ) Bensmann, W.; Fenske, D. Angew. Chem., Int. Ed. Engl. 1978,17, 462; 1979, 18, 677. (d) Fenske, D.; Christidis, A. Angew. Chem., Int. Ed. Engl. 1981,20, 129. (9) (a) Mao, F.; Tyler, D. R.; Keszler, D. J . Am. Chem. SOC.1989, 111, 130. (b) Mao, F.; Philbin, C. E.; Weakley, T. J. R.; Tyler, D. R. Organometallics 1990, 9, 1510. ( c ) Fei, M.; Sur, S. K.; Tyler, D. R. Organometallics 1991, 10, 419. (10) (a) Mao, F.; Tyler, D. R; Rieger, A. L.; Rieger, P. H. J . Chem. Soc., Faraday Trans. 1991,87, 3113. (b) Mao, F.; Tyler, D. R.; Bruce, M. R. M.; Bruce, A. E.; Rieger, A. L.; Rieger, P. H. J.Am. Chem. SOC. 1992, 114, 6418.
The full scope of the reactivity of these and related ligands with other cluster compounds is under consideration by our groups,14J5and for this reason we decided to investigate the substitution reaction between Ru3(C0)12 and bpcd. Herein we report our data on the synthesis and reactivity studies of Rw(CO)dbpcd), RUZI
(CO)s(bpcd),and Ru~(CO)B[~L-C=C(PP~Z)C(O)CHZ~(O)~@z-PPhz),in addition to the X-ray diffraction structures of the last two binuclear compounds. Included are the cyclic voltammetry data and extended Hiickel MO calculations on these new compounds. The importance of the bpcd ligand in promoting the observed P-C(dione) bond cleavage is discussed relative to the parent binuclear compound Ruz(CO)s[(Z)-PhzPCH=CHPPh21.
Results and Discussion
I. Synthesis and Characterization of Compounds 1-3. The reaction between RudC0)1z and bpcd was explored under different conditions as a route t o the bpcd-substituted cluster Rw(CO)lo(bpcd). Refluxing Ru~(C0)12 with bpcd in either 1,2-&chloroethane or toluene led only to the isolation of the binuclear I
complexes Ruz(CO)s(bpcd) (2) and Ru2(CO)&-C=C-
(PP~~)C(O)CHZC(O)I@~-PP~~) (3),with the former com(11)Yang, K.; Bott, S. G.; Richmond, M. G. Organometallics 1996, 14, 2387. (12)Yang, K.; Smith, J. M.; Bott, S. G.; Richmond, M. G. Organometallics 1993, 12, 4779. (13) Reaction of PhCCoS(C0)g with bpcd proceeds in an analogous
fashion: Shen, H.; Bott, S. G.; Richmond, M. G. Unpublished results. (14) Xia, C.-G.; Bott, S. G.; Richmond, M. G. Inorg. Chim. Acta 1995,
230, 45.
(15)Shen, H.; Williams, T. J.; Bott, S. G.; Richmond, M. G. J . Organomet. Chem., in press.
P-C Bond Cleavage in an Ruz Complex
Organometallics, Vol. 14, No. 10, 1995 4627
Scheme 1
Chart 1
Q
(a) thermolysis
197.66
or (b) M q N O
t
0
Table 1. X-RayCrystallographic and Data Processing Parameters for Ru~(CO)&pcd)(2) and I
I
Ru~(CO)&-C=C(PP~~)C(O)CH&(O)I (lr2-PPh2)6,Hlt, (3) 1
2
space group cell const a, A b, A c, A
A deg
v, A3
mol formula
fw
pound always predominating. When the thermolysis reactions were monitored by IR spectroscopy, traces of the desired cluster were observed, but the facile fragmentation of 1 t o 2 and Ru3(C0)12 precluded any possible isolation of 1. Analogous cluster fragmentation behavior has already been noted in other phosphinesubstituted triruthenium clusters.16 Activation of RUB(CO)IP in MeCNXH2C12 using the oxidative-decarbonylation reagent Me3NO (2 equiv)17in the presence of bpcd (1equiv) led t o cluster 1 in low yield ( 35". Intensity data in Ordering information is given on any current masthead page. the range 2.0 5 2 6 544" were collected at room temperature OM9503048 using the 8/26 scan technique in the variable-scan-speed mode and were corrected for Lorentz, polarization, and absorption (DIFABS). Three reflections (600,080,0010) were measured (47)Ryan, M.F.;Richardson, D. E.; Lichtenberger, D. L.; Gruhn, N. E.Organometallics 1994, 13, 1190. after every 3600 s of exposure time as a check of crystal (48)(a) Hoffmann, R.; Lipscomb, W. N. J. Chem. Phys. 1962,36, stability ( ~ 2 % ) The . structure was initially solved by using a 2179.(b) Hoffmann, R. J. Chem. Phys. 1963,39,1397. Patterson map, and all of the non-hydrogen atoms were located (49)Handbook of Chemistry and Physics, Weast, R. C., Ed.; 56th with difference Fourier maps and refined by using full-matrix ed.; CRC: Cleveland, OH, 1975.
