Organometallics 1995, 14, 5708-5710
5708
Synthesis and Characterization of the First Ruthenium-Lead Clusters, [Rus01-PbR2)01-C0)2(CO)gI and [ R U ~ @ - P ~ R ~ ) & - C(CO)s]. O) Single-Crystal X-ray Structure of [RU~~~-P~R~)~~~-CO)(CO)S] Nicolas C. Burton,t Christine J. Cardin,+David J. Cardin,*3t Brendan Twamley,'>Sand Yan Zubavichust78 Chemistry Department, University of Reading, Whiteknights, Reading, Berkshire RG6 6AD, U.K., and Chemistry Department, Trinity College, University of Dublin, Dublin 2, Ireland Received June 14, 1995@ Summary: Reaction of PbR2 [R = CH(SiMe3)d with [Ru3(C0)ld at 60 "C afforded the first ruthenium-lead (1)and LRu3(p-PbRZ)zclusters [Ru3(p-PbR2)(p-CO)dCO)sJ (p-CO)(CO)g](2). After separation the compounds were characterized by ' H a n d I3C N M R and I R spectroscopies, FAB-MS, and, for 2, by a single-crystal X-ray study. The structure gives the first reported Ru-Pb bond lengths and shows the cluster to have a planar pentametallic array with two PbR2 and one CO bridging the three sides of a n Ru3 triangle. A greatly improved yield for the preparation of PbR2 is also reported. -Compound 2 crystallizes i n the triclinic space group P1 with unit cell dimensions a = 12.279(6) A,b = 15.406(6) A, c = 20.775(5) A,a = 99.54(6)", = 107.47(6)", y = 109.59(6)", U = 3373.1(10) A3, and Z = 2. A total of 10179 unique observations gave a merging R of 0.038 and a conventional R of 0.0756.
Introduction We report the synthesis of the first ruthenium-lead clusters and the first structural data for lead-transition metal clusters, apart from two reports on Pb-Fe compounds.la2 We also report a higher-yield synthesis for our starting material, the lead(I1) compound [Pb{ CH(SiMe3)2}21, previously reported to be obtained in very low yield.3 There is extensive literature on heterometallic clusters incorporating main-group metal^,^ but very little relates to clusters having lead atoms in the framework. The published work is restricted to lead-iron systems, which were prepared from lead(lV) species using hydride or halide elimination reaction^.^ We have reported on a number of transition metal clusters in which University of Reading.
* University of Dublin. +
e Present address: Higher Chemical College, Russian Academy of Sciences, Miusskaya Sq. 9, Moscow, Russia. Abstract published in Advance ACS Abstracts, October 15, 1995. (1)Lagrone, C. B.; Whitmire, K. H.; Churchill, M. R.; Fettinger, J. C. Inorg. Chem. 1986,25,2080. (2)Whitmire, K.H.; Lagrone, C. B.; Churchill, M. R.; Fettinger, J. C.; Robinson, B.H. Inorg. Chem. 1987,26,3491. (3)Davidson, P. J.; Harris, D. H.; Lappert, M. F. J . Chem. Soc., Dalton Trans. 1976,2268. (4)For a leading review see: Whitmire, K H. J . Coord. Chem. 1987, 17., 95. -(5) (a) Cotton, J. D.; ~ O X S., A. R.; Paul, I.; Stone, F. G. A. J . Chem. SOC.A 1967,264.(b) Dalton, J.;Paul, I.; Stone, F. G . A. J . Chem. SOC. A 1968,1215. (c) Marks, T.J.; Newmann, A. R. J . A m . Chem. SOC. 1973,95,769. @
~
tin has been introduced using a variety of tin(I1) reagents.6 In these reactions, the nucleophilicity of the tin(I1) species is exploited t o displace either a carbonyl group (for the lighter metals) or a more labile group, such as acetonitrile (for heavy elements, e.g., osmium). This approach has led to a range of cluster nuclearities from M3Sn through M3Sn3 (M = Fe, Ru, or Os) to IrqSn5.'jC To date, no analogous reactions with clusters have been reported for the lead(I1) species, though [Pb{CH(SiMe3)2}21 (PbR2) has been shown in a single instance t o ligate to a metal center in the species [(OC)sMoPb(CH(SiMe3)2}21, obtained in 4% yield from the parent carbonyl and PbR2 under ultraviolet irradiat i ~ n The . ~ other reported chemistry for the lead species relates principally to oxidative additions or, for the case of the isoelectronic amide, t o insertion into the Pt-C1 bonds of [{PtC12(PEt3)}21to give [{Pt(ClPb(N(SiMe3)2)2)C1(PEt3)121.7 We now report that the plumbylene reacts thermally with ruthenium carbonyl t o afford two clusters and discuss the structure of one of them.
Results and Discussion The published synthesis of PbR2 quotes a yield of ca. 3%.3f8We find that following sublimation of the lead(11) chloride starting material, the procedure reported gives essentially quantitative yields. The compound was obtained as an extremely air-sensitive purple solid after recrystallization from hexane at low temperature. Where the analogous stannylene, SnR2 reacts rapidly with [RUQ(CO)~SI in hexane at room temperature, the lead reagent is a less effective nucleophile, failing t o react under these conditions. On heating in hexanes (60 "C, 1.5 h) two products were obtained and separated by fractional crystallization from hexanes. Chromatography (silica columrhexanes) is not the preferred (6)See for example: (a) Cardin, C. J.; Cardin, D. J.; Convery, M. A.; Devereux, M. M. J. Chem. SOC.,Chem. Commun. 1991,687. (b) Cardin, C. J.;Cardin, D. J.; Lawless, G. A.; Power, M. B.; Hursthouse, M. B. J.Organomet. Chem. 1987,325,203and references therein. (c) Cardin, C. J.; Cardin, D. J.; Power, M. B. J . Organomet. Chem. 1993, 462. C27. (7) Cotton, J. D.; Davidson, P. J.; Lappert, M. F. J . Chem. SOC., Dalton Trans. 1976,2275. (8)Davidson, P. J.; Lappert, M. F. J . Chem. Soc., Chem. Commun. 1973,317.
0276-733319512314-5708$09.00/0 0 1995 American Chemical Society
Notes
Organometallics, Vol. 14, No. 12, 1995 5709
Figure 1. Structure diagram of a single molecule of 2 with the atoms numbered as in Table 1. Hydrogen atoms are omitted for clarity. method of purification since 1 survives only in low yield and 2 decomposes on the column. Both compounds are R \ /PbR
1
co
w3 2
sensitive to air and light in solution, though they are moderately air-stable in the solid state.
The IR spectrum of 2 shows terminal CO stretches together with a characteristic single bridging carbonyl band at 1846 cm-l. Since in related reactions of the analogous stannylene, S ~ R Zthe , ~tin ~ group almost invariably bridges two transition metal centers, maintaining the 48-electron count for the metal triangle, this strongly suggests the presence of two bridging PbR2 groups. In contrast, two bridging carbonyl bands are observed in the IR spectrum of 1 at 1877 and 1833 cm-l, implying the addition of a single PbR2 group. lH and 13C NMR spectroscopy indicate the presence of the ligand CH(SiMe312 in both 1 and 2. Both lH and 13C spectra showed inequivalence of the methyl groups, as observed previously in the tin analogue.6b The compounds do not survive electron impact mass spectrometry and react with most common matrices employed in the FAB technique. Using meta-nitrobenzyl alcohol and FAB, the highest ions were detected at m l z 927, equal to the mass of the fragment [Ru3(CO)gPbRI+ (corresponding to the loss of an R group and two CO groups) for compound 1 and, a t mlz 1476, equal to the mass of the fragment [ R U ~ ( C O ) I O P ~(corresponding ~R~I+ to loss of a single R group) for compound 2. A single-crystal structure determination was carried out for compound 2, confirming the formulation suggested by the spectroscopic data above. The molecule consists of a pentanuclear metal array, with two sides of an Ru3 triangle bridged by PbR2 groups, see Figure 1. The substituents on the lead atoms are oriented essentially perpendicular to the metal plane with slight deviations l1.74" at Pbl and 4.47" at Pb21, similar to the geometries found for tin groups bridging ruthenium, osmium, iron, or iridium frameworks.6 The lead atoms thus have a highly distorted tetrahedral environment with Ru-Pb-Ru angles of 64.12(4) and 64.55(4)" and C-Pb-C angles of 96.7(10) and 102.2(10)"for Pbl and
Notes
5710 Organometallics,Vol. 14, No. 12, 1995 Table 1. Selected Bond Lengths (deg)
(A>and Angles
Pbl -Rul Pbl-Ru2 Pb2-Rul Pb2-Ru3 Rul-Ru2 Ru2-Ru3 Ru3-Rul
2.777(2) 2.790(2) 2.765(2) 2.787(2) 2.955(2) 2.852(2) 2.965(2)
Pbl-C1 Pbl-C2 Pb2-C3 Pb2-C4 Ru2-C25 Ru3-C25 C25-025
2.31(2) 2.27(2) 2.31(2) 2.30(2) 2.06(2) 2.08(2) 1.17(2)
C1-Pbl-C2 Rul-Pbl-Ru2 Pbl-Rul-Ru2 Rul-Ru2-Pbl Ru2-Rul-Ru3 Rul-Ru2-Ru3 Rul-Ru3-Ru2
96.7(10) 64.12(4) 58.15(4) 57.72(4) 57.60(5) 61.37(4) 61.02(4)
C25-Ru2-Ru3 Ru2-C25-R~3 C25-Ru3-Ru2 Rul-Pb2-Ru3 Pb2-Rul-Ru3 Pb2-Ru3-Rul C3-Pb2-C4
46.7(5) 87.0(7) 46.3(5) 64.55(4) 58.08(4) 57.38(4) 102.2(10)
Pb2, respectively. As with the tin analogue, the metalbridged Ru-Ru vectors are significantly longer than those of the parent carbonyl. The distances in (a) [RUB(C0)1~1,(b) CRU~C~-S~RZ)ZC~-CO)(C~)~I, and (c) [Ru&PbR2)z@-CO)(CO)gIare (a) 2.854(4), (b) 2.950(2) and 2.963(2), and (c) 2.955(2) and 2.965(2) A; thus the lengthening produced by both SnRz and PbRz is remarkably similar. The Ru-Pb distances, the first such to be reported, are given in the table of selected bond lengths and angles (Table 1). These bridges are significantly asymmetrical, the longer Pb-Ru separations in each case being adjacent to the bridging carbonyl. The probable interpretation of this is that the Pb-Ru vector is pseudo trans to the (in-plane) bridging carbonyl, which exerts a comparably larger trans influence. It is noteworthy that the SnRz bridges of the tin analogue (b above) are not significantly asymmetrical, possibly reflecting a greater trans influence for the Sn ligand. We have already noted above that the tin reagent is appreciably more reactive in displacing CO from the parent carbonyl.
Experimental Section The syntheses and subsequent manipulations of the compounds described here were conducted under inert atmosphere conditions using standard Schlenk, vacuum line, and glovebox techniques. Solvents were dried and distilled prior to use. NMR spectra were recorded on a Bruker AM250 instrument, and IR data were obtained using a Perkin-Elmer 1720-X FT instrument. [Pb{CH(SiMe&}2].8 Bis(trimethylsily1)lithium(20 mL, 6.6 mmol, 0.33 M in EtzO) was added over 1h t o a suspension of freshly sublimed anhydrous PbClz (0.92 g, 3.3 mmol) in diethyl ether (50 mL) a t -10 "C, and during the addition the slurry became yellow and quickly darkened to a deep purple. The mixture was stirred for 0.5 h at 0 "C and then for 1h a t room temperature, after which time solvent was removed under vacuum. The remaining purple solid was redissolved in hexane (50 mL), and the solution was filtered. The solution
was concentrated and cooled, (-25 "C), and the product was collected (1.65 g, 95%).
[RUS(~C-P~R~)(~C-CO)Z(CO)SI (1) and [Rus(lC-PbRz)&CO)(C0)9] (2). A purple solution of PbR2 (1.65 g, 3.1 mmol) in hexane (30 mL) was added to a suspension of [Ru3(C0)1~1 (0.33 g, 0.53 mmol) in hexane (50 mL), and the mixture was heated a t 60 "C for 1.5 h. The reaction was monitored by TLC until completion. After concentration of the solvent and 2 (0.18 g, 21%) was filtration to remove unreacted [Ru~(CO)IZI, obtained by crystallization a t -25 "C in hexane. Mp 135 "C (decomp). IR (CsI), v ( C 0 ) (cm-'1: 2090 s, 2059 s, 2038 s, 2022 s, 2009 s, 1981 s br, 1846 s br. FT-Raman (cm-I): 2954,2901, 2089,2051,2037,2028,2005,1983,1973,1841,460,448,149. 'H NMR (400 MHz, C6D6): 6 0.37, 0.39, 0.41, 0.43 (s, 72H), 1.59 (br, 4H). I3C NMR (10 MHz, CDC13): 6 5.98, 6.07, 6.42, 131.64, 199.64, 204.29. FAB MS: m / z 1476 (M+ - 156). Subsequent recrystallization from the mother liquor gave 1 (0.06 g, 11%).Mp 137 "C (decomp). IR (CsI), v(C0) (cm-I): 2113 s, 2051 s, 2031 s, 1996 s, 1877 s br, 1831 s br. 'H NMR (250 MHz, CDC13): 6 0.29 ( ~ , 3 6 H1.19 ) (s, 2H). I3C NMR (100 MHz, CDC13): 6 4.8, 128.22,205.2. FAB MS: m / z 927 (M+ 213). The light- and air-sensitivity preclude obtaining accurate elemental analytical data for these compounds. Crystal Data: C ~ ~ H W O I O P ~ Z M R U=~ 1635.30. S ~ ~ . Triclinic, space group Pi. a = 12.279(6) 8, b = 15.406(6) 8,c = 20.775(5) A, a = 99.54(6)", /3 = 107.47(6)", y = 109.59(6)", U = 3373.1(10) A3, 2 = 2, D,= 1.610 / ~ m - p(Mo ~ , Ka) = 5.81 mm-', F(OO0) = 1584, A. = 0.710 73 . A crystal of approximate dimensions 0.1 x 0.2 x 0.2 mm3 was mounted on a glass fiber, and intensity data in the range 2.77 z 0 z 25.02' were measured using a MAR Imageplate Scanner. Ninety-five frames were measured with a 2" rotation and an exposure time of 2 min per frame. Data were processed with the XDS package9 t o give a total of 10 179 unique observations with a merging R of 0.038. The structure was solved by Patterson synthesis using SHELX 86 and refined with SHELXL. The final conventional R factor is 0.0756 based on 7 150 observations for which IF1 > 4(aF) and 549 parameters, but the structure was refined using all 10 179 observations. SHELX 86 and SHELXL were used by kind permission of Professor G. M. Sheldrick (University of Gottingen, Gottingen, Germany).
1
Acknowledgment. We thank the EPSRC and the SERC for support, the Research Endowment fund (University of Reading) and the Krieble fund (Trinity College Dublin) for maintenance grants, Dr. P. Turner (Bruker, U.K.) for running the FT Raman spectra, Sun Microsystems, and Caversham Rotary Club (to Y.Z.). Supporting Information Available: Tables of crystal data, positional and thermal parameters, and distances and angles (16 pages). Ordering information is given on any current masthead page. OM9504563 (9)Kabsch, W. J . Appl. Crystallogr. 1993,26,795.
