Inorg. Chem. 1987, 26, 2943-2949 for X-ray work. To date, only one crystal structure of a metal complex with bzp has been reported.32 This compound contains the [ ( C ~ ( b z p ) ) , C ~ 0 , ] cation, ~' and bzp is bound to copper(I1) through the nitrogen atoms of both the pyridine ring and the imine group. It has already been reported that bzp can induce a spin transition in iron(I1) chemistry; indeed, Fe(bzp),(NCS)z presents such a transition around 235 K.33 In 3, the transition occurs at much the same temperature, but is more gradual and very incomplete since only 56% of the metal centers become low-spin upon cooling down. Another striking aspect of the phenomenon is that, below the transition temperature, the relative proportions of SS, QQ, and SQ species do not correspond at all to the statistical proportions. If 56% of the low-spin and 44% of the high-spin iron(I1) were statistically distributed among the SS, QQ, and SQ species, we would have 31.4% of SS (instead of 52%), 19.4% of QQ (instead of 40%) and 49.3% of SQ (instead of 8%). In fact, when an iron(I1) ion undergoes the transition within a dinuclear unit, the other iron(I1) ion of the same unit has a very high probability of undergoing the transition too, so that the formation of SQ species is unlikely. In a certain sense, the dinuclear unit (32) Real, J. A,; Borras, J.; Solans, X.; Font-Altaba, M . Transition Met. Chem. (Weinheim, Ger.), in press. (33) Real, J. A,; Borras, J.; Adler, P.; Giitlich, P., unpublished result.
2943
itself plays the role of a small domain in which the two metal ions have the same spin state. To conclude, we may attempt to sum up the results emerging from this study: (i) The high-spin state in the dinuclear species seems to 1 e stabilized with respect to what happens with mononuclear species in which the iron(I1) ion has much the same environment; (ii) the spin transition, when occurring, is apparently more gradual and very incomplete in the low-temperature range; (iii) the intramolecular interaction gives rise to a specific cooperativity within the dinuclear unit. In spite of the incomplete character of the transition, the proportion of electronically dissymmetric species SQ is very small. It would be quite unreasonable to generalize the results presented above to all of the polymetallic systems in which spin transition and exchange interaction coexist. Many investigations will be necessary before an overyiew can be obtained on this problem. Registry No. 1, 109584-92-1;2, 109584-93-2;3, 109612-95-5;Fe(py),(NCS),, 15 154-78-6. Supplementary Material Available: Listings of atomic parameters for hydrogen atoms (Table S1) and anisotropic thermal parameters for non-hydrogen atoms (Table S2) (2 pages); a table of calculated and observed structure factors (9 pages). Ordering information is given on any current masthead page.
Contribution from the Departments of Chemistry, Northwestern University, Evanston, Illinois 60208, and Oklahoma State University, Stillwater, Oklahoma 74078
Synthesis of Heterometallic Carbide Clusters Containing Three Iron Atoms: [PPN]2[MFe3(CO)13C](M = Cr, W), [PPNI2[Cr2Fe3(C0)&], Rh2Fe3(CO)&, and [PPNI[Rh3Fe3(CO) 1SCI Joseph A. Hriljac,+ Elizabeth M. Holt,*t and Duward F. Shriver*+ Received January 14, 1987 Redox-condensation reactions involving [PPN],[ Fe,(CO),(CCO)] and electrophilic transition-metal reagents lead to [PPN],[MFe3(C0)&] (M = Cr, W), [PPN],[Cr2Fe3(C0)&], Rh2Fe3(CO)&, and [PPN][Rh,Fe3(CO)1SC].Variable-temperature "C NMR spectroscopy was employed to assign the structures of the tetranuclear clusters and Rh2Fe3(CO),,Cin solution. An improved synthesis of [PPN][RhFe3(C0)&] and more complete variable-temperature (ca. -1 30 to +20 "C) "C NMR spectra of this cluster and [PPN] [MnFe,(CO)&] are discussed. All of the tetranuclear clusters are assigned butterfly metal geometries with the heterometals located at hinge sites. Attempts to prepare iron-molybdenum carbide clusters are discussed. The structure of [PPN][Rh,Fe3(CO),SC]was determined by a single-crystal X-ray diffraction study and was found to consist of a trigonalantiprismatic metal array with the carbide ligand within the metal polyhedron. The iron atoms define one of the trigonal faces and the rhodium atoms define the other. Crystal data for [PPN] [Rh3Fe3(CO)&]: monoclinic, space group P2,/n, a = 16.220 (6) A,b = 9.282 (3) A,c = 35.17 (3) A,i3 = 94.84 ( 5 ) O , Z = 4.
Introduction Transition-metal carbide clusters form a very interesting class of organometallic compounds. These clusters contain a carbon atom bonded only to metal atoms, and therefore their study plays a central role in defining the structural, bonding, and reactivity aspects of metal-carbon bonds. They may also be useful as models of the reactive carbide species that form on metal surfaces during C O hydrogenation reactions.'-2 The first report of reactivity at a carbide ligand was by Bradley and c o - ~ o r k e r swho , ~ demonstrated that the carbide ligand in a butterfly cluster with four metal atoms is subject to attack. This is in contrast to what had been found earlier for pentametallic cluster^.^^^ Studies of these butterfly cluster compounds by several research groups have demonstrated that reactions of the carbide ligands can lead to the formation of C-H and C-C bonds.2s6 Carbide reactivity is unique to the tetranuclear butterfly clusters. It was therefore of interest to study similar systems to try to
understand the factors that relate to this reactivitv and to trv and extend the known reaction pathways. This work isdirected toward the synthesis of new heterometallic carbide clusters, especially those that should contain reactive carbide ligands. The synthetic methodology that was chosen was to use the trimetallic cluster [Fe3(C0),(CCO)]*- in redox-condensation reactions.' We previously demonstrated that this ketenylidene cluster is a useful carbide p r e c ~ r s o r . ~ ~ ~ (1) Tachikawa, M.; Muetterties, E. L. Prog. Inorg. Chem. 1981, 28, 203 and references therein. (2) Bradley, J. S. Adu. Organomef. Chem. 1983, 22, 1 and references
therein.
(3) Bradley, J. S.; Ansell, G. B.; Hill, E.W. J. Am. Chem. SOC.1979, 101, 7417.
(4) Cooke, C. G.; Mays, M . J. J . Organomer. Chem. 1975, 88, 231. (5) Kolis, J. W.; Basolo, F.; Shriver, D. F. J . Am. Chem. SOC.1982, 104, 5626. (6) Bogdan, P. L.; Woodcock, C.; Shriver, D. F. Organomefallics, 1987, 6,
1377.
(7) Chini, P.; Heaton, B. T. Top. Curr. Chem. 1977, 71, 1. (8) Kolis, J. W.; Holt, E. M.; Hriljac, J. A,; Shriver, D. F. Organometallics 1984, 3, 496. (9) Hriljac, J. A,; Swepston, P. N.; Shriver, D. F. Organometallics 1985,
Northwestern University. *Oklahoma State University
4. 158.
0020-1669/87/1326-2943$01 .50/0
0 1987 American Chemical Society
2944 Inorganic Chemistry, Vol. 26, No. 18, 1987 This research led to the synthesis of tetra-, penta-, and hexametal cluster compounds. Details of the synthesis and characterization of several heterometallic carbide systems are discussed, and an improved synthesis of [PPN][RhFe,(C0),,Cl9 is described.
Experimental Section General Procedures and Materials. All of the compounds prepared in this work are moderately air- and moisture-sensitive, and therefore all manipulations were performed under an atmosphere of purified nitrogen by employing standard Schlenk and needlestock techniques.'0." Solids were manipulated in a Vacuum Atmosphere glovebox equipped with a recirculator and Dri-Train system. Solvents were refluxed over and then distilled from appropriate drying agents under nitrogen before use (THF, Et20, and hexane from Na/benzophenone; acetone and pentane from 4A molecular sieves; dichloromethane from P20,; methanol and 2-propanol from Mg/12; acetonitrile from CaH,). N M R solvents were freeze/ thaw-degassed and then vacuum-distilled from appropriate drying agents. The following starting materials were synthesized by literature methods (or minor variations thereof) and judged pure by IR spectroscopy: salts of [ Fe3(C0),(CCO)l2- and its "C-enriched analogues;I2 [Rh(CO),Clj2;l3 Rh(CO),(py)C1;I4 C r ( C O ) 3 ( N C M e ) 3 ; i S W ( C O ) , ( N C E t ) , . I 6 GLASSCLAD6C was purchased from Petrarch Chemicals. IR spectra were recorded with a Perkin-Elmer 283 spectrometer using 0.1 mm path length CaF, solution cells or Nujol mulls between KBr plates. "C N M R spectra were recorded with either a JEOL FX-270 or Varian XL-400 spectrometer operating at 67.8 and 100.577 MHz, respectively. All chemical shifts are reported positive if downfield from TMS, and the I3C resonance for CD,Cl2 (53.80 ppm) was used as the reference peak. Cr(acac)3 (acac = acetylacetonate) was added as a relaxation agent. Elemental analyses were performed by Galbraith Laboratories. Mass spectra were recorded by Dr. D. Hung of the Northwestern University Analytical Services Laboratory with a Hewlett-Packard HP5905A spectrometer using 70-eV ionization. Synthesis of [PPN)[RhFe,(CO),,C] ( P P N = Bis(tripheny1phosphine)nitrogen( l+)). All Schlenk flasks used in this preparation were treated with GLASSCLAD6C before use. A Schlenk flask was charged with 1.001 g (0.6514 mmol) of [PPN]2[Fe3(CO)9(CCO)],0.178 g (0.651 mmol) of Rh(CO),(py)CI (py = pyridine), 0.193 g (0.654 mmol) of [BzMe,N] [PF,], and a magnetic stirbar. A 10-mL portion of dichloromethane was added and the solution stirred. After 20 min. 50 mL of Et,O was added to the red-brown solution. The resulting precipitate was removed via filtration, the solution was cooled to 0 'C, and 50 mL of pentane was slowly introduced via syringe. The red microcrystalline solid was isolated and washed with pentane before drying under vacuum: 0.580 g isolated, 77% yield. Anal. Calcd (found) for C49H30NFe3Rh012P,:C, 50.86 (50.34); H, 2.61 (2.62); N, 1.21 (1.17); Fe, 14.48 (13.37); Rh, 8.89 (9.38). Synthesis of [PPN),[CrFe,(CO),,C]. A Schlenk flask was charged with 1.000 g (0.6507 mmol) of [PPN]2[Fe3(CO)9(CCO)],0.190 g (0.733 mmol) of Cr(CO),(NCMe),, and a magnetic stirbar. The flask was immersed in a -23 OC (CCI, slush) cold bath, and I O mL of acetone was slowly introduced via syringe. The solution was stirred 30 min and then 40 mL of 2-propanol added. Removing the cold bath and subsequent warming to room temperature produced a dark brown solid. The crude product was isolated by filtration and washed with three portions of methanol ( 5 mL each) and then thoroughly with E t 2 0 before vacuum drying. This material was recrystallized by the slow diffusion of Et,O (30 mL) into a dichloromethane solution (15 mL) of the cluster: 0.990 g isolated, 91% yield. Anal. Calcd (found) for C86H60N2Fe3CrOi,P,: C, 61.74 (61.34); H, 3.62 (3.96); N, 1.68 (1.88): Fe, 10.02 (9.88); Cr, 3.11 (2.22). Synthesis of [PPN],[WFe,(CO),,C]. A Schlenk flask was charged with 1.000 g (0.6507 mmol) of [PPN]2[Fe3(CO)9(CCO)],0.340 g (0.785 mmol) of W(CO),(NCEt),, and a magnetic stirbar. Addition of I O mL of acetone followed by 20 min of stirring produced a dark greenish brown solution. The crude product was precipitated by the addition of 40 mL of 2-propanol. The solids were isolated and washed with three portions of methanol (5 mL each) and Et,O before drying. Slow diffusion of Et,O (35 mL) into a dichloromethane solution (20 mL) produced black crystals: 0.943 g isolated, 80% yield. Anal. Calcd (found) for
(10)
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(12) (13) (14)
(15)
(16)
Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air-Sensitiw Compounds, 2nd ed.; Wiley: New York, 1986. Brown, H. C. Organic Synthesis via Boranes; Wiley: New York, 1975. Hriljac, J. A,; Shriver, D. F. J . Am. Chem. Soc., in press. McCleverty, J. A,: Wilkinson, G. Inorg. Synth. 1966, 8, 211. Lawson, D. N.; Wilkinson, G. J . Chem. SOC.1965, 1900. Tate, D. P.: Knipple, W. R.; Augl, J. M. Inorg. Chem. 1962,I , 433. Kubas, G. J. Inorg. Chem. 1983, 22, 692.
Hriljac et al. Table I. X-ray Crystal Structure Data for lPPN1 IRhqFeq(CO),,C1 formula 5276.2 (53) C S ~ H ~ O F ~ ~ N O v. I .SA3 P~R~~ mol wt 1.821 1446.97 dcalcd, g cm13 cryst ha bit 2848 needle F(OO0) cryst size,
