Organometallics 1995, 14, 3160-3162
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Magnetic Behavior in Cluster-Based Organometallic Materials: Synthesis and Characterization of the Novel 1,l'-Bis(dipheny1phosphino)ferrocene-CrippledCluster Derivative [Ru& (C0)15{p -Fe((C5 H 4 )PPh2)2} 1 Alexander J. Blake, Andrew Harrison, Brian F. G . Johnson,* Eric J . L. McInnes, Simon Parsons, Douglas S. Shephard, and Lesley J. Yellowlees Department of Chemistry, The University of Edinburgh, West Mains Road, Edinburgh EH9 3 J J ) U.K. Received January 12, 1995@ Summary: The hexaruthenium carbido cluster derivative [ R U S C ( C O ) I S { ~ - F ~ ( C ~ H ~3~,(has P ~ )been ~ ) ~synthe}/, sized by direct reaction of the parent cluster [Rust(CO)I 71, 1, with 1 1'- bis(dipheny1phosphino)ferrocene (dppfl. An X-ray crystallographic study revealed that the dppf ligand is coordinated in the vicinal form and the cluster core is greatly distorted from a regular octahedron. 31PN M R spectra of 3 at various temperatures show a high degree of stereochemically nonrigid behavior. Magnetic susceptibility measurements across a range of temperatures indicate that 3 is paramagnetic at all temperatures. An electrochemical study of 3 has demonstrated a significant degree of communication between the redox-active sites. )
cluster derivatives of dppf have been reported to date, and those are mainly of low nuclearity.12 Reports of paramagnetism in cluster complexes are also relatively few, and the phenomenon is poorly u n d e r s t o ~ d . ~ - ~ ~ The thermally initiated reaction of dppf with the parent cluster [Ru&(c0)171,1, in tetrahydrofuran yields [Ru6C(CO)~,@-dppf)],3, as the major product along with a smaller amount of [Ru&(CO)l6{dppf)], 2.1°b After separation by TLC using CHzCl&exane (1:4)as eluent, dark green 3 and red 21°b were tentatively identified on the basis of their IR spectra.loc The 'H
(10)( a ) Schneider, J. J.; Goddard, R.; Kruger, C.; Werner, S.; Metz, B. Chem. Ber. 1991, 124, 301. (b) [Ru&(CO)ledppfl will be described in full in a forthcoming paper. (c) Spectroscopic data for 3: IR (CH2Metallocenes, in particular ferrocene, possess properClz) v(CO)/cm-l: 2070 m, 2034 s, 2024 vs, 2012 s, 1997 m, 1969 w br; ties which have led to their use as 31PNMR (CDC13,298K): h 43.78 (br s) ppm; 'H NMR (CDC13,298K): molecular sens0rs,3-~and electrochemical agentsn6Clush 7.58 (br m, 20H), h 4.12 (br s, 8H) ppm. Anal. for found C, 37.43; H, 1.9 (calcd C, 37.32; H, ters have been shown to possess unusual m a g n e t i ~ ~ - ~ C50HzsFeO15P2Ru6.2CH2C12: ~ 1.78). (d) Crystal data for 3: C~oHzsFe015PzRug2CHzClz,M = 1762.8, and redox propertieslO which, as far as we are aware, monoclinic, space group Palin with a = 17.280(3)A, b = 18.488(4)A, C = 17.359(3)A, /j = 92.09(3)",u = 5542(2) A3, Dcaled = 2.101 g C l W 3 , have not been put to commercial use. The idea of 2 = 4, p = 2.512 mm-', T = 150.0(2)K. Diffraction amplitudes were combining the properties of these two sets of fascinating acquired using a Stoe-Stadi-4 four-circle diffractometer, graphitemolecules has significant appeal, and in this commonochromated Mo Ka X-radiation, and an Oxford Cryosystems lowtemperature device (Cosier,J.;Glazer, A. M. J . Appl. Crystallogr. 19M, munication we report the synthesis of the new cluster 19, 105-108). Of 8872 reflections collected to 20,,, = 45", 7213 were P (aP 1,l'~ ) ~ ) ~ ) Iunique , compound [ R U & ( C O ) ~ ~ ( ~ - F ~ ( C ~ H ~ 3, (RLnt= 0.064). The structure was solved by automatic direct bis(dipheny1phosphino)ferrocene (dppf)derivative of the methods (Ru) (SHELXS-86; Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467) and developed through iterative cycles of least-squares closo cluster [Ru&(C0)17], 1, which exhibits a major refinement and difference Fourier synthesis. Dichloromethane solvate cluster deformation, interesting redox chemistry, and molecules occupy channels between molecules of 1, and modeling of their substantial disorder was largely successful. Anisotropic refineparamagnetic behavior. ment was allowed for Ru, Fe, P, and 0 atoms and nonsolvent H atoms There are many reports in the literature of dppf were included in calculated positions and allowed to refine riding on coordinated to single transition-meta1s.l' Scme of these their respective carbon atoms. (SHELXL-93: G. M. Sheldrick, University of Gottingen, Germany.) At final convergence with R [F > 4aheterobimetallic complexes show interesting cooperative (I?)] = 0.074, wRp [P, 7161 datal = 0.1851, and S = 1.055 for 465 effects between the two metal sites. Few corresponding refined parameters, and the final A F synthesis showed no feature lay outside the range f1.44 to -1.02 e k 3 . (e) Electrochemical experiments were carried out using a DSL 286-D PC with General Purpose @Abstractpublished in Aduance ACS Abstracts, June 1, 1995. (1)Kollmar, C.; Couty, M.; Kahn, 0. J.Am. Chem. SOC.1991, 113, Electrochemical System (GPES) Version 3 software coupled to an Autolab system containing a PSTAT 10 potentiostat. A conventional 7994. ( 2 ) ( a ) Chi, K. M.; Calabrese, J. C.; Reiff, W. M.; Millar, J . S. three-electrode cell was employed with Pt counter and microworking electrodes and a Ag/AgCl reference electrode against which the Fcl Organometallics 1991, 10,668. (b)Millar, J. S.; Epstein, A. J. Angew. Fc' couple was measured at +0.55 V. Coulometric studies employed Chem., Int. Ed. Engl. 1994, 33, 385. (3)Wagner, R. W.; Brown, P. A.; Johnson, T. E.; Lindsey, J. S. J. a three-electrode H-type cell with a Pt basket working electrode. All Chem. SOC.,Chem. Commun. 1991, 1463. electrochemical experiments were performed under an atmosphere of (4) Constable, E. C. Angew. Chem., Int. Ed. Engl. 1991,30, 407. nitrogen. ( 0 Magnetic susceptibility measurements were performed on powder samples with a SQUID magnetometer (Quantum Design, (5)Beer, P. D.; Chen, Z.; Drew, M. G. B.; Pilgrim, A. J. Inorg. Chim. Acta 1994, 225, 137. model MPMSz) at temperatures between 1.8 and 310 K in an applied (6) Butler, I. R. Organometallic Chemistry; Abel, E. W., Ed.; Specialmagnetic field of 0.1 T. The data were corrected for the response of ist Periodic Reports 21; Royal Society of Chemistry: Letchworth, U.K., the sample holder and the diamagnetic contributions of all atoms.18 1992; p 338. (11)For examples, see: Millar, T. M; Ahmed, K. J.; Wrighton, M. (7) (a) Rosch, N.; Ackermann, L.; Pacchioni, G.; Dunlap, B. I. J. S. Inorg. Chem. 1989, 28, 2347. Housecroft, C. E.; Owen, S. 0.; Chem. Phys. 1991,95, 7005. (b) Williams, I. H.; Spangler, D.; Femec, Raithby, P. R.; Shaykh, B. A. M. Organometallics 1990, 9, 1617. D. A.; Maggiora, G. M.; Schowen, R. L. J . A m . Chem. SOC.1980,102, Butler, I. R.; Cullen, W. R.; Kim, T.-J.; Rettig, S. J.; Trotter, J. 6621. Organometallics 1985, 4, 972. Clemente, D. A,; Pillioni, G.; Corain, ( 8 ) Johnson, D. C.; Edwards, P. P.; Benfield, R. E.; Nelson, W. J. B.; Longato, B.; Tiripicchio-Camellini, M. Inorg. Chim. Acta 1986,115, H.; Vargas, M. D. Nature 1985, 314, 231. L9. (9)(a) Dahl, L. F.; Olsen, W. L.; Stacy, A. M. J . A m . Chem. SOC. 11211a) Draper, S. M.; Housecroft, C. E.; Rheingold, A. L. J . 1986,108,7646. (b) Dahl, L. F.; Olsen, W. L. J . A m . Chem. SOC.1986, Organomet. Chem. 1992, 435, 9. ( b ) Chacon, S. T.; Cullen, W. R.; 108, 7657. (c) Dahl, L. F.; Byers, L. R.; Uchtman, V. A. J . A m . Chem. Bruce, M. I.; Shawkataly, 0.;Einstein, F. W. B.; Jones, R. H.; Willis, SOC.1981, 103, 1942. A. C. Can. J . Chem. 1990, 68, 2001.
0276-733319512314-3160$09.00/0 0 1995 American Chemical Society
Organometallics, Vol. 14, No. 7, 1995 3161
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I
I
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0.5
+
01611
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Figure 1. The solid state molecular structure of 3 as determined by X-ray crystallography. The hydrogens and phenyl groups have been omitted for clarity. Selected bond lengths (A): Ru(l)-Ru(2), 2.968(1); Ru(l)-Ru(3), 2.912(1); Ru(l)-Ru(4), 2.870(1); Ru(~)-Ru(~), 2.767(1); Ru(2)Ru(~), 2.971(1);Ru(~)-Ru(~), 2.816(1);Ru(3)-Ru(4), 2.854(1);Ru(~)-Ru(~), 2.914(1); Ru(~)-Ru(~), 2.827(1); Ru(5)Ru(6),2.861(1);Ru(l)-P(2), 2.391(2);Ru(~)-P(1),2.389(2). NMR spectrum of 3 in CDCl3 showed exceptionally poor resolution of both the phenyl and cyclopentadienyl resonances at both room temperature and 223 K. This immediately suggested unusual behavior of the new cluster derivative. A 31PNMR spectrum of 3 obtained a t 298 K showed a single, slightly broadened signal at cu. 6 44 ppm. This may be attributed to stereochemically nonrigid behavior producing equivalence of the two phosphorus nuclei on the NMR time scale (vide infru). At 198 K, however the 31PNMR spectrum showed two signals at 6 41.07 and 52.96 ppm. The high-frequency signal was significantly broadened, possibly due to the presence of proximal unpaired electrons. The two signals observed at low temperature are consistent with the two phosphorus environments observed in the solid state structure of 3. These observations perhaps indicate the itinerant nature of the unpaired electrons at ambient temperatures (vide infra). A single-crystal X-ray analysis of 3 was undertaken to establish the molecular structure, and this is shown in Figure 1 along with some pertinent structural parameters.lod Of striking significance is the distorted R-C metal core. Two very long Ru-Ru distances [(Ru(1)-Ru(6), 3 . 1 7 ~ 1 ) and Ru(4)-Ru(6), 3.450(1)A)] are observed and show an "opening up" of the normally closo octahedron to give a hinged square-based pyramid. Ru(6) is hinged a t the basal metal atoms Ru(2) and Ru(5) and supported by P(1) of the bridging dppf ligand. All remaining Ru-Ru contacts are within the normal range. The carbido carbon atom is displaced from the centroid of the four metals constituting the base of the
I
,
-1.0
-0.5
I 1 .G 1.5
Potential / V Figure 2. Cyclic voltammogram of 3 in 0.5 M [NButn4][BF4J/CH&12solution at room temperature.
square-based pyramid by 0.217(8) %i and toward Ru(6). The distorted cluster is surrounded by 13 terminal carbonyls and 2 p-COS triangulating the Ru(2)-Ru(3) and Ru(3)-Ru(4) vectors. A single-crystal X-ray structural determination has shown that no comparable effect occurs in [R~sC(Co)ls(C1-dppm}]~~ or [H~RuC(CO)lo{p-diphos}1. l4 The dppf is ligated in the vicinal form, bridging the hinged metal Ru(6) and the basal metal Ru(1). The P atoms each occupy slightly distorted tetrahedral environments which, due to the bonding mode and rearrangement of the metal core, are nonequivalent. The relative orientations of the P atoms with respect to the ferrocene moiety show a twist of 73.7'. The cyclopentadienyl rings are parallel to within estimated error, eclipsed to within 2.04", and produce an average distance of 1.635(4)%i from their centroids to the iron. The crystal structure also contains highly disordered dichloromethane solvate molecules. Modeling of these was largely successful. Shifts in the redox potential of the dppf ligand and RUGcluster are of great interest and demonstrate in a complementary fashion electronic and/or electrostatic communication between redox-active sites.l5 Cyclic voltammetry of 3 in 0.5 M [NButn4][BF4YCH2C12solution at room temperature reveals a n irreversible twoelectron reduction at -0.65 V vs AglAgCl with associated daughter peaks at +0.07 V and +0.25 V (Figure 2).loe An irreversible oxidation is observed at cu. +1.15 V. Bulk electrolysis at -0.80 V confirms the reductive process as a two-electron step (n = 1.95e). Investigation is under way to characterize the daughter products of the reductive process. The parent cluster 1 exhibits no oxidative process but a two-electron reduction at -0.46 V to yield [RU&(CO)ls2-] which oxidizes at +0.45 V.16 Free dppf undergoes a quasi-reversible oxidation at ( 13) Gracey, B. P.; Evans, J.; Jones, A. G.; Webster, M. Acta Crystallogr. 1987, C43, 2286. (14) Churchill, R. M.; Lashewycz, R. A.; Shapeley, J. R.; Richter, S. I. Znorg. Chem. 1980,19, 1277. (15)Colbert, M. C. B.; Ingham, S. L.; Lewis, J.; Long, N. J.; Raithby, P.R. J . Chem. Soc., Dalton. Trans. 1994, 2215. (16) Drake, S.R.; Johnson, B. F. G.;Lewis, J. J. Chem. SOC., Dalton Trans. 1989, 243.
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3162 Organometallics, Vol. 14, No. 7, 1995
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coupling between the molecular units. The ESR spectrum of a solid sample of 3 appears silent at both 77 and 298 K. This is perhaps consistent with the high rate of relaxation that may be expected in both moieties.l 7 These results suggest that there is a strong interaction between the ferrocene and the cluster cage frontier orbitals. We propose the HOMO t o be primarily ferrocene-based but with significant cage character which results in its more difficult oxidation. Concomitantly the LUMO is primarily cage-based but with a significant ferrocene admixture. Increased electron density at the cluster leads to the structural deformation of the formally 86e closo cluster framework observed in the solid state. In the light of these results we have now begun a thorough investigation into a wide variety of systems designed to produce similar interactions between clusters and proximal redox-active centers.
E:::::tL 1 v
0
,
t t -
,
0.000 0
50 100 150 200 250 300 350 Temperature (K) Figure 3. Variation of the molar magnetic susceptibility of 3 with temperature. Superimposed on the data points is a line of best fit utilizing the Curie-Weiss expression.
+0.75 V. We therefore assign the 2e reduction of 3 as primarily cluster-based and the oxidation as primarily dppf-based. These results show that the cluster and dppf moieties are more difficult to reduce and oxidize, respectively, than in the parent cluster and free dppf. Variable temperature magnetic measurementslOf show 3 to be paramagnetic at all temperatures (Figure 3). The corrected data were fitted to both a Curie and a CurieWeiss expression plus a temperature independent paramagnetic (TIP) term. The quality of the fit was appreciably better when a small Curie-Weiss constant 0 of -0.50 K was included, and the corresponding values of the Curie constant C and TIP contributions were 0.12 emu K mol-l and O.O52C, respectively. The value of C corresponds to an effective magnetic moment of 0.99(5) Bohr magnetons at high temperatures. It appears therefore that the moment on the ferrocene/cluster unit is 35% of the moment that would arise from a spin triplet state and that there is a weak antiferromagnetic
Acknowledgment. We thank C. M. Grant and Dr. J. M. Rawson for magnetic data collection and processing, and also Dr. J. R. Galsworthy for helpful discussions. We gratefully acknowledge The University of Edinburgh and the EPSRC for financial support. Supporting Information Available: Tables giving crystal data and structure refinement details, atomic coordinates, bond distances and angles, and anisotropic thermal parameters for 3 (11pages). Ordering information is given on any current masthead page. OM9500230 (17)Prins, R.; Reinders, F. J. J.Am. Chem. SOC.1969, 91, 4929. (18)Konig, E. In Landholt-BornsteinNew Series, Group 2 Atomic and Molecular Physics; Hellwege, K. H. Ed.; Springer-Verlag, Berlin, 1966; Vol. 2.
