Organometallics 1986,5, 263-270
263
Structure and Reactivity Studies of Bis(cyclopentadieny1) Ytterbium and Yttrium Alkyl Complexes Including the X-ray Crystal Structure of (C,H,),Yb(CH,)(THF)’ William J. Evans,** Raul Dominguez, and Timothy P. Hanusa Department of Chemistry, University of California at Imine, Imine, California 9271 7 Received May 20, 1985
(C,H,),Yb(CH,)(THF) crystallizes from T H F under hexane diffusion in space group P2,/a, with unit cell dimensions a = 14.518 (5) A, b = 13.063 (7) A, c = 8.141 (2) A, p = 105.96 (2)O, U = 1484 A3, and Dcalcd = 1.747 g cm-, for 2 = 4. Least-squares refinement on the basis of 1825 unique observed reflections converged to a final R = 0.035. T h e two ring centroids, the T H F oxygen atom, and the methyl carbon describe a distorted tetrahedron. The average Yb-C(ring) distance is 2.60 (2) A, the Yb-C(methy1) distance is 2.36 (1) A, and the Yb-O(THF) distance is 2.31 (1)A. Comparison of the Ln-C distances in (C5H5),Yb(CH,) (THF) and the (C5H5),LuR(THF) complexes (R = t-C4H9,CHzSiMe3,C6H4Me-4)suggests trends in steric crowding whose effects on reactivity were experimentally examined in hydrogenolysis reactions. Over 20 systems were examined in which the metal, the alkyl group, and the ring substituent in the formulas (C,H4R),LnR’(THF) and [(C5H4R),LnR’I2(R = H, CH3; Ln = Y, Er, Yb, Lu; R’ = C H , CH2SiMe3,t-C4H,) were varied as well as the solvent. Small changes in the size of the metal, the steric crowding caused by the alkyl group, and the solvent can have dramatic effects on reactivity. Using this new reactivity data, optimum conditions for isolating ytterbium hydrides were determined and the ytterbium analogues of were synthesized and characterized. [(C5H5)2LnH(THF)]2and ( [(C5H5)2LnH],H)(Li(THF)4) T h e first report in t h e literature of t h e hydrogenolysis of a n organolanthanide metal alkyl complex t o form a molecular organolanthanide hydride compound involved ytterbium3 (eq 1). T h e reaction proceeded slowly and was toluene
[(CH3C5H,),Yb(l*-CH3)]~ + 2H2 __* 2CH4 2[(CH,C5H4),YbH] (1)
+
complicated by t h e fact t h a t t h e trivalent ytterbium hydride was unstable with respect t o divalent ytterbium species (eq 2). To avoid t h e Ln(II1) Ln(I1) decompo-
-
[ ( C H ~ C ~ H J Z Y ~ H (I C H & ~ H ~ ) Z Y ~
(2)
sition, hydrogenolysis of alkyl complexes of Lu, Er, a n d Y, which d o not have readily accessible divalent oxidation states, were examined a n d provided fully characterizable hydride complexes4 (eq 3; R = CH,, H ; L n = Lu, E r , Y).
lanthanide methyl complex, (C5H5),Yb(CH3)(THF),which provides benchmark structural information useful in understanding t h e observed reactivity. I n this report, we describe the structure of the ytterbium methyl compound a n d t h e hydrogenolysis of this complex to form isolable ytterbium(II1) hydride complexes. In addition, we examine further the patterns of hydrogenolysis reactivity observed earlier by studying the reaction of several lanthanide a n d yttrium(II1) alkyl complexes with hydrogen under a variety of conditions. These studies demonstrate how small differences in the size of the metal, the size of the alkyl group, a n d t h e solvent can change reactivity substantially.
Experimental Section
The complexes described below are extremely air- and moisture-sensitive. Therefore, all syntheses and subsequent manipulations of these compounds were conducted under nitrogen with the rigorous exclusion of air and water using Schlenk, vacuum toluene 2(C5H4R),Ln(t-C4H9)(THF) 2H2 line, and glovebox (Vacuum/Atmospheres HE-553 Dri-Lab) techniques. [(C,H4R),Ln(l*-H)(THF)Iz + 2C4HI0 (3) Materials. Toluene and THF were distilled from potassium benzophenone ketyl. THF-d8 and benzene-d, were vacuum In the presence of lithium salts, trimeric hydride complexes transferred from potassium benzophenone ketyl. Anhydrous of formula ([(C5H5),Ln(l*-H)l2[(CSHs)zLn(~-X)I(l*3-H))ytterbium and yttrium trichlorides were prepared from the hy(Li(THF),) (X = H , C1) were d i s ~ o v e r e d . ~ Improved drates (Research Chemicals, Phoenix, Az) by the method of Taylor syntheses of both t h e dimers6 a n d t h e trimers7 have suband Carter.8 Hydrogen (Matheson, prep grade) was purified by sequently been developed. passage through an Alltech Oxytrap. Deuterium (Union Carbide, In t h e course of studying t h e above hydride complexes, CP grade) was used as received. LiCHzSiMe3was prepared acevidence for some general principles of organolanthanide cording to the literatureg from lithium shot and ClCH2SiMe, a n d organoyttrium reactivity has accumulated. We have (Aldrich). NaC5H4R (R = H, CH,) and [(CSH4R),LnC1],were recently obtained an X-ray diffraction structure of a simple prepared as previously de~cribed.~ Methyllithium (1.5 M in EbO, Aldrich) was used in the preparation of [(C6H4R),LnCH3],(Ln = Y ,Er, Yb, Lu) according to the literature.6 Literature proce(1)Part 8 of the series Organolanthanide and Organoyttrium Hydride dures were followed in the preparation of (C5H5),LnChemistry. Part 7: Evans, W. J.; Grate, J. W., Doedens, R. J. J. Am. (CH2SiMe3)(THF)l0(Ln = Y, Yb) and (CH,CSH4),Ln(CMe3)Chem. SOC.1986,107,1671-1679. (THF)4-11(Ln = Y, Lu). (2)Alfred P. Sloan Research Fellow.
+
-
(3) Zinnen, H. A,; Pluth, J. J.; Evans, W. J. J. Chem. SOC.,Chem. Commun. 1980,810-812. (4)Evans, W. J.; Meadows, J. H.; Wayda, A. L.; Hunter, W. E.; Atwood, J. L. J.Am. Chem. SOC.1982,104,2008-2014. (5)Evans, W. J.; Meadows, J. H.; Wayda, A. L.; Hunter, W. E.; Atwood,J. L. J. Am. Chem. SOC.1982,104,2015-2017. (6)Evans, W. J.: Meadows, J. H.: Hunter, W. E.: Atwood. J. L. J.Am. Chem. SOC.1984,106,1291-1300. (7) Evans, W. J.; Meadows, J. H.; Hanusa, T. P. J . Am. Chem. SOC. 1984,106,4454-4460.
(8)Taylor, M. D.; Carter, C. P. J. Inorg. Nucl. Chem. 1962, 24, 387-391. (9)Collier, M. R.; Lappert, M. F.; Pearce, R. J . Chem. Soc., Dalton Trans. 1973,445-451. (10)Schumann, H.; Genthe, W.; Bruncks, N.; Pickardt J. Organometallics 1982,1, 1194-1200. (11)Evans, W. J.;Wayda, A. L.;Hunter, W. E.; Atwood, J. L. J.Chem. Soc., Chem. Commun. 1981,292-293.
0276-7333/86/2305-0263$01.50/00 1986 American Chemical Society
264 Organometallics, Vol. 5, No. 2, 1986
Physical Measurements. Infrared spectra were obtained as previously de~cribed.~ 'H NMR spectra were recorded by using a Bruker 250 spectrometer and were referenced to residual (3methylene protons in C4D80(6 1.72) or to residual aryl protons in C6D6(6 7.15). Gas chromatographic analyses were performed on a Hewlett-Packard 5830A thermal conductivity gas chromain. column of 4A molecular tograph equipped with a 6 ft. X sieves pulverized to 40/60 mesh. Complete elemental analyses were obtained from Analytische Laboratorien, Engelskirchen, Germany. Complexometric analyses were obtained as previously described.12 GC/MS data were collected on a Finnigan 4000 mass spectrometer equipped with a gas inlet system. [(C5H5),YbCH3],. This modification of the original preparation of this compound13is included since slight variations in procedure can alter the purity of the product, particularly with respect to the presence of LiCl. In the glovebox, a 500-mL Schlenk flask was charged with [(C5H5)2YbCl]z(3.135 g, 4.63 mmol), 75 mL of THF, and a magnetic stirring bar and attached to an addition funnel containing CH3Li (7.8 mL of 1.5 M solution in EtzO, 11.7 mmol). The apparatus was removed to a double manifold and the Schlenk flask cooled to -78 "C. The CH3Li solution was added dropwise over 10 min, and the stirred solution was allowed to warm to room temperature overnight. The apparatus was returned to the glovebox, and the solvent was removed by rotary evaporation. The resulting orange oil was extracted with toluene (50 mL) and filtered. Removal of solvent from the filtrate gave an orange solid which was subsequently extracted with 50 mL of toluene heated to boiling. This solution was filtered hot and reduced in volume to ca. 10 mL by rotary evaporation. Hexane was layered over the toluene solution which was then cooled to -20 "C overnight. Bright orange crystals of [(C5H5),YbCH3],were isolated by filtration (1.01 g, 34%). Anal. Calcd for YbC11H13: Yb, 54.40; Li, 0.00; C1, 0.00. Found: Yb, 54.3; Li, 5 Following the procedure described above, [(C5H5)2YbCH3]2 (112 mg, 0.18 mmol) was treated with D2 to form the analogous deuteride in approximately 48% yield. The initial product of the hydrogenolysis was recrystallized from THF. IR (KBr): 3100 (m), 2950 (m), 2880 (m), 1440 (w), 1020 (sh w), 1010 (s), 920 (m br, sh), 870 (s), 770 (vs) cm-'. Decomposition of [ (C5H5)2YbH(THF)]2.This ytterbium hydride complex desolvates readily in the glovebox (cf. the facile and decomposes in THF desolvation of [ (C5H5)2LuH(THF)]~) within 48 h to form (C5H5)2Yb(THF).This decomposition could be followed by 'H NMR spectroscopy by monitoring the disappearance of the broad 0.4 ppm C5H5resonance of the hydride complex and the growth of the 5.8 ppm C5H5 resonance of (C5H5)2Yb(THF).'s ([(C,H,),YbH],H)(Li(THF),). (a) In a 250-mL flask quipped with a high vacuum Teflon stopcock and a Teflon stirring bar, a sample of [(C5H5)2YbCH3]z(0.765 g, 0.377 mmol) prepared without hot toluene extraction and containing a trace of LiCl (approximately 1:7 LiCl/Yb) was dissolved in a mixture of 45 mL of diethyl ether and 9 mL of hexane yielding a dark amber solution. The flask was attached to a vacuum line, cooled to -196 "C, and evacuated. An atmospheric pressure of H2was established as described above, and the vessel was sealed. The solution was stirred vigorously for 8 days over which time a yellow powder was slowly deposited. The solid was collected by filtration and was washed first with 10 mL of diethyl ether followed by 10 mL of hexane. A bright yellow powder (0.472 g, 65% based on a prewas isolated. Recryscursor formula of [ (C5H5)2YbCH3]7LiC1) tallization by hexane diffusion into THF yielded long transparent yellow needles. These crystals became opaque and brittle after 30 min under nitrogen presumably due to desolvation (cf. the ready desolvation of ( [(C5H5)zLuH],H)(Li(THF)4)5). The IR spectrum of a freshly recrystallized sample indicated the presence of T H F but the elemental analysis was consistent with a desolvated sample. Anal. Calcd for the desolvate C30H34LiYb3:C, 39.13; H, 3.70; Li, 0.76; Yb, 56.41. Found: C, 38.71; H, 4.25; Li, 0.57; Yb, 55.70. IR (KBr): 3090 (w), 2960 (m), 2880 (m), 1440 (w), 1350 (m), 1210 (vs), 1120 (w), 1035 (m), 1010 (s), 880 (s), 770 (vs), 730 (m), 685 (m) cm-'. 'H NMR (THF-d,): b 23 (s, C5H5). (0.031 g, 0.026 Freshly recrystallized I[ (C,H5)2YbH]3H)(Li(THF)4) mmol) was decomposed with H 2 0 in a Toepler pump system to give H2 (2.49 mL, 0.111 mmol, 94%) identified by GC. (b) In the glovebox, [(C5H5)2YbH(THF)]2 (100 mg, 0.13 mmol) was suspended in DME (10 mL) in an Erlenmeyer flask. Solid t-C4H,Li (7 mg, 0.109 mmol) was added to the solution causing a vigorous reaction to occur with formation of a yellow solid and a green solution. Toluene (10 mL) was added to the solution, and the yellow precipitate was isolated by filtration. Recrystallization by slow hexane diffusion into a saturated THF solution gave bright (50 mg, 47%) yellow plates of {[(C5H5)2YbH]3H)(Li(THF)4) identical with the hydride product described above by IR and 'H NMR. The green solution was identified to contain (C5H5)zYb(DME)19 by 'H NMR spectroscopy." { [(C5H5),YbDI3D)(Li(THF),J.In a manner analogous to (a) above, this substance was obtained as a yellow powder in 37% yield after 6 days under deuterium gas. It was recrystallized by hexane diffusion into a saturated T H F solution. 'H NMR (17) This yield assumes that the product is a DME solvate, [(C,H5)2YbH(DME)],,analogous to the yttrium system described later. (18) Calderazzo, F.; Pappalardo, R.; Losi, S. J. Znorg. Nucl. Chem. 1966, 28,987-999. (19) Deacon, G. B.; MacKinnon, P. I.; Hambley, T. W.; Taylor, J. C. J . Organomet. Chem. 1983,259, 91-97.
Organometallics, Vol. 5, No. 2, 1986 265 (THF-d8): 6 23 (s, C5H5). IR (KBr): 3090 (w), 2970 (m), 2950 (m), 2880 (m), 1440 (w), 1035 (m), 1010 (s), 965 (m), 880 (s), 850 (sh m), 775 (vs), 730 (9) cm-'. The complex was also prepared by route b above in 40% yield. Decomposition of ([(C5H5),YbHI3H)(Li(THF),J.The decomposition of this hydride to (C5H5)2Yb(THF)in THF was also followed by 'H NMR spectroscopy. The decomposition half-life was found to be approximately 50 days. (C5H5),Y[CH2Si(CH3)J(THF). In a Schlenk flask equipped with a magnetic stirring bar, YC13 (6.493 g, 33.25 mmol) was suspended in 100 mL of THF. Over 5 min NaC5H5(5.848 g, 66.439 mmol) was added. After being stirred for '/2 h, the solution was cooled to -78 "C, and LiCH2Si(CHJ3 (3.146 g, 33.41 mmol) in 30 mL of hexane was added dropwise. The mixture was allowed to warm to room temperature over several hours and then filtered. Solvent was removed from the filtrate by rotary evaporation to give an oil. This oil was twice extracted with 50 mL of roomtemperature toluene, filtered, and rotary evaporated to dryness. The pale yellow solid was recrystallized by diffusing hexane into a saturated toluene solution to yield large clear and colorless hexagonal prisms (3.321 g, 33% based on YCl,). 'H NMR (THF-d,): 6 6.37 (s, C5H5),-0.05 (9, CH,Si(CH,),), -0.93 (d, CH2Si(CH3)3, J = 3.2 Hz). lH NMR (benzene-d,): 6 6.12 (s, C S 5 ) 3.00 (m, THF), 0.95 (m, THF), 0.42 (s, CH2Si(CH3),),-0.66 (d, J = 2.6 Hz, CH2SiMe3). IR (KBr): 3080 (w), 2940 (s), 2880 (m), 1440 (w), 1247 (m), 1233 (s), 1010 (s), 905 (m), 860 (s), 780 (vs), 770 (vs), 715 (w), 660 (w) cm-'. Single crystals are orthorhombic with a = 17.39 (1)A, b = 12.37 (4) i\, c = 9.23 (5) A, and U = 1986 (2) A3 and are isomorphous with (C5H5)zL~(CH2SiMe3)(THF).lo (CH3C6H4),Y[CH2Si(CH3),](THF). This substance is synthesized as described above. After the second toluene extraction, the product is isolated in 55% yield based on YC13 'H NMR (benzene-&): 6 6.00 (5, 8, CH3C$Z4),3.03 (m, 4, THF), 2.15 (s, 7, CH3C5H4),0.97 (m, 4,THF), 0.45 (s, 9, CH2Si(CH3)J, -0.75 (d, J = 3.4 Hz, CH2SiMe3). T H F assignments were verified by exchanging the T H F with THF-d8 and retaking the spectrum. IR (KBr): 3090 (w), 2840 (m), 2880 (m), 1443 (m), 1387 (m), 1265 (m), 1020 (s), 830 (w), 820 (s), 760 (vs) cm-'. Hydrogenolysis Experiments. Procedure. The following standardized procedure was used in the hydrogenolysis studies of the (C5H4R)2LnX(R = H, CH,; Ln = Y, Er, Yb, Lu; X = CH,, CH2Si(CH3),,C(CH,),) compounds. The yttrium or lanthanide alkyl precursor (50-100 mg) was dissolved in 10 mL of the desired solvent system and placed into a tube of approximate volume 90 mL fitted with a high vacuum greaseless stopcock and a stirring bar. The flask was connected to a vacuum line, cooled to -196 "C, and evacuated. Hydrogen was admitted to the flask, and the vessel was warmed to room temperature. When the hydrogen pressure was 1 atm, the flask was sealed and the solution was stirred. After the desired interval of reaction time, the solids were isolated by filtration and washed with 10 mL of hexane, dried, and weighed. For those cases in which solids were not deposited, IR and/or NMR spectroscopy was used to detect the presence of hydrides or decomposition products in the reaction solutions. The results are given in Table 111. Identification of Products. For reactions carried out in THF, the [(C5H4R)2LnH(THF)]2 products (R = H, CH,; Ln = Y, Lu) were identified by their IR and 'H NMR ~ p e c t r a .[(C5H5)2Er~ H(THF)], was identified by IR spectro~copy.~ For yttrium reactions run in DME, the presence of a dimeric hydride product was indicated by the characteristic broad vy-H IR absorption in the 1300 cm-' region of the powdery product. IR (KBr): 3100 (m), 2950 (m), 2890 (w), 2720 (w), 1470 (m), 1447 (m), 1310 (s br), 1175 (s), 1090 (m), 1040 (m), 1010 (m), 860 (m), 780 (s),670 (m) cm-'. The DME-insoluble products were then dissolved in THF to give a 'H NMR spectrum characteristic of DME and [(C5H5),Y(p-H)(L)],(L = THF or DME). The Y-H-Y triplet due to ssY-lH coupling was observed in the usual r e g i ~ n .'H ~ NMR (THF-d,): 6 6.07 (s, 10, C5H5), 3.39 (s,4, (CH,OCH2),), 3.23 (s, 6, (CH,OCH,),), 2.18 (t,J = 20 Hz, 1,Y-H-Y). Hydrogenolysis reactions in dioxane gave a white powdery product with a broad IR absorption in the 1300 cm-' region. [ (C5H5),YH(dioxane)I2: IR (KBr) 3100 (m), 2970 (m), 2940 (m), 2870 (m), 2640 (w), 2620 (w), 1640 (w), 1460 (m), 1450 (m), 1300 (s), 1260 (s), 1120 (s), 1065 (4, 1010 (s), 970 (w), 890 (s), 880 (s), 850 (m), 820 (s), 770 (vs),
266 Organometallics, Vol. 5, No. 2, 1986
Evans et al. Table 111. Hydrogenolysis Results" % vield of hvdride
expt
substr" (CpzYCH3)z
1 2
3 4
5 6 7 8 9
10 11 12
13 14 15 16
17 18 19 20 21 22
23
'Cp = C6H5;Cp'
toluene toluene/THF THF DME dioxane hexane/THF THF toluene THF toluene THF toluene/THF THF toluene THF THF DME THF DME toluene toluene/THF THF DME
Results and D i s c u s s i o n Synthesis of (C,H,),Yb(CH,)(THF).
A standard method for preparing bis(cyclopentadieny1) lanthanide methyl complexes is the ionic metathesis reaction shown in eq 4.6J0J3320p21Separation of t h e LiCl byproduct can
+ 2CH3Li
THF
[ ( C S H S ) & ~ ( C H ~+) I2LiC1 ~ (4) (20) Evans, W. J. In "The Chemistry of the Metal-Carbon Bond"; Hartley, F. R., Patai, S., Eds.; Wiley: New York, 1982; Chapter 12, pp 489-537. (21) See also: Holton, J.; Lappert, M. F.; Ballard, D. G. H.; Pearce, R.; Atwood, J. L.; Hunter, W. E. J. Chem. SOC.,Dalton Trans. 1979, 54-61.
168 = 10
40 39 24 24
= 10
34 36
"
producib 0 85 60 80
30 85 50
72 120 24
70
24 48
72 24 40 24
0 85 55 0 0 20 52 0 0 0 0 6
24
10
= 10
24 72 24 336 24 96 = 10
50
70
= CH3C5H4. [(C5H4R)zLnH(ether),]z (R = H, CH3;Ln = Y, Er, Yb, Lu).
640 (s), 610 (s) cm-'; 'H NMR (THF-d,) 6 5.92 (5, 10, C5H5),3.61 (s, 10, dioxane), 2.05 (br m, H, a clean triplet was not resolved possibly due to exchange of THF for dioxane on the NMR time scale). Characterization of Some Incomplete Reactions. [ (C5H5)zL~CH3]2 (70 mg, 0.109 "01) in 10 mL of toluene was reacted with H2 for 24 h as described above. No precipitated [(C5H5)2LuH(THF)I2 was observed in this time period. The transparent solution was reduced to dryness by rotary evaporation and the resulting solid identified as starting material by 'H NMR spectroscopy. A reaction on the same scale was run in THF. The 'H NMR spectrum of the product contained primarily starting materials plus resonances of [ (C5H5),LuH(THF)J2accounting for an approximately 6% yield. Hydrogenolysis of [(C5H5)2LuCH3]2 (66 mg, 0.103 mmol) was also carried out for 24 h in 10 mL of DME. Addition of 20 mL of toluene generated a white precipitate which was collected by filtration, recrystallized from THF, and identified by 'H NMR spectroscopy as [(C5H5),LuH(THF)IZ(8 mg, 10%). The remaining solution was reduced to dryness and examined by 'H NMR spectroscopy which revealed it to be composed of starting material. Reaction of Hz with [(C5H5)zYbCH3]2(90 mg, 0.142 mmol) in 10 mL of THF for 24 h did not change the appearance of the dark auburn solution. Rotary evaporation of the solution gave an orange solid which had the IR spectrum of the starting material. Reaction of H2 with [(C5H&YbCH3], (136 mg, 0.214 mmol) in 10 mL of T H F for 336 h formed a yellow precipitate (30 mg, 20%) and a purple solution. The precipitate was identified as [ (C5H5),YbH(THF)I2by IR spectroscopy. The purple solution was reduced to dryness and identified as (C5H5),Yb(THF) by IR and 'H NMR spectroscopy.
[(C5H&LnC1I2
reactn time, h
soh
c.2 2- ~
c33
Figure 1. ORTEP view of (C5H5),Yb(CH3)(THF)with the atomnumbering scheme used in the tables. Thermal ellipsoids are drawn a t the 35% probability level. be achieved by removing the T H F solvent, extracting the soluble methyl complex into toluene, and filtering off the insoluble LiC1. Although room-temperature extraction removes a large percentage of lithium as LiCI, some lithium is carried along into the toluene, possibly as an adduct such as (C5H5),Ln(p-CH3)(p-C1)Li(THF),, a structural type which has ample precedent in the literature.22-28 In general, we find t h a t even after three cycles of extracting with toluene a t room temperature, filtering, removing the toluene, and reextracting with toluene, residual lithium may persist. We find it essential to extract the methyl product with hot toluene (or a t least t o heat t h e toluene extract solution) to remove all detectable lithium. Since for yt(22) Atwood, J. L.; Hunter, W. E.; Rogers, R. D.; Holton, J.; McMeeking, J.; Pearce, R.; Lappert, M. F. J. Chem. SOC., Chem. Com-
mun. 1978, 140-142. (23) Wayda, A. L.; Evans, W. J. Inorg. Chem. 1980, 19, 2190-2191. (24) Watson, P. L. J. Chem. Soc., Chem. Commun. 1980, 652-653. (25) Tilley, T. D.; Andersen, R. A. Inorg. Chem. 1981,20, 3267-3270. (26) Watson, P. L.; Whitney, J. F.; Harlow, R. L. Inorg. Chem. 1981, 20, 3271-3278.
(27) Lappert, M. F.; Singh, A.; Atwood, J. L.; Hunter, W. E. J. Chem. SOC.,Chem. Commun. 1981, 1191-1193. (28) Schumann, H.; Lauke, H.; Hahn, E.; Heeg, M. J.; van der Helm, D. Organometallics 1985, 4 , 321-324.
Ytterbium and Yttrium Alkyl Complexes
Organometallics, Vol. 5, No. 2, 1986 267
Table IV. Bond Distances (A) in (C,H,),Yb(CH,)(THF) Yb 0 2.311 (6) 2.362 (11) 2.588 (12) 2.613 (11) 2.598 (11) 2.553 (12) 2.588 (13) 2.612 (10) 2.607 (11) 2.600 (11) 2.620 (10) 2.621 (10) 2.399 2.336 1.281 (20) 1.310 (26) 1.328 (22) 1.364 (23) 1.360 (27) 1.340 (16) 1.365 (22) 1.405 (22) 1.399 (17) 1.353 (17) 1.397 (16) 1.456 (12) 1.448 (21) 1.488 (15) 1.446 (11)
Table V. Selected Bond Angles (deg) in (CxH,),Yb(CH,)(THF) 0 C(41) 94.1 (3) Yb Yb C(32) 123.2 (6) 0 Yb (335) 126.2 (6) 0 0 Yb cntrd 1 99.2 cntrd 2 107.5 0 Yb cntrd 1 95.2 C(4U Yb cntrd 2 106.7 ~(41) Yb cntrd 1 Yb cntrd 2 143.7 C(15) 110.1 (16) C(11) C(12) C(13) 109.1 (14) C(11) C(12) (314) 107.5 (15) ~(13) C(W C(13) 105.3 (15) ~(14) C(15) 107.9 (13) C(11) C(15) ‘(14) 109.3 (12) C(25) C(21) C(22) C(21) C(22) C(23) 107.2 (11) C(24 C(23) C(22) 106.1 (13) C(25) ~(24) C(23) 108.0 (12) C(21) C(25) ~(2.4) 109.4 (12) C(33) C(34) 108.6 (11) (333) (334) C(35) 105.9 (11) C(35) 0 C(32) 109.1 (8)
(29) Evans, W. J.; Dominguez, R.; Hanusa, T. P., submitted for publication. (30) The structure of the pentamethylcyclopentadienyl derivative (C5Me6)2Nd[CH(SiMe3)z] has been communicated: Mauermann, H.; Swepston, P. N.; Marks, T. J. Organometallics 1985, 4, 200-202. (31) ORTEP plots of structures of the pentamethylcyclopentadienyl derivatives (C5Me&Yb(CH3)(EhO)and (C5Me&Yb(CH3)(THF)have been released, but details of the structural analysis have not been reported: Watson, P. L.; Herskovitz, T. ACS S y m p . Ser. 1983, No. 212, 459-479. (32) Evans, W. J.; Wayda, A. L. J. Organomet. Chem. 1980,202, C6-
(35) Lauher, J. W.; Hoffmann, R. J . Am. Chem. SOC.1976, 98, 1729-1742 and references therein. (36) The thermal parameters of the cyclopentadienyl carbons are relatively large, reflecting either a slight disorder or considerable thermal motion. Such libration of cyclopentadienyl rings is fairly common in organometallic complexes, as exemplifed in the structures of (C5H&M compounds. See: Sailer, P.;Dunitz, J. D. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1979, B35, 1068-1074. (37) Baker, E. C.; Brown, L. D.; Raymond, K. N. Inorg. Chem. 1975, 14, 1376. (38) Shannon, R. D. Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. 1976, A32, 751-767. (39) Cotton, F. A.; Wilkinson,G. “Advanced Inorganic Chemistry”,4th ed.; Wiley: New York, 1980. (40) Holton, J.; Lappert, M. F.; Ballard, D. G. H.; Pearce, R.; Atwood, J. L.; Hunter, W. E. J. Chem. SOC., Dalton Trans. 1979,45-53.
~
The orientation of the THF ring with respect to the cyclopentadienyl rings and methyl group can be described by some dihedral angles involving the best least-squares “plane” of the five atoms in the THF ring. The THF “plane” makes an 85’ angle with the plane defined by the two cyclopentadienyl ring centroids and the ytterbium atom; i.e., it is almost perpendicular. The plane defined terbium, [(C,H4R),Yb(CH3)], complexes (R = H, CH3) can by the methyl carbon atom, ytterbium, and the THF oxthermally decompose to divalent (C5H4R),Ybcompounds3 ygen atom also makes a near perpendicular (90.7’) angle or in the presence of T H F to species such as with the centroid-Yb-centroid plane. The T H F ring is [(C5H4R)2Yb(OCH=CH2)]2,B the material in the final hot tipped to avoid being coplanar with the methyl group as toluene extract must be recrystallized before use. evidenced by the dihedral angle of 16.9’ between the THF X-ray Crystal S t r u c t u r e of (C,H5),Yb(CH3)(THF) “plane” and the methyl carbon-Yb-THF oxygen plane. (I). Although a number of bis(cyclopentadieny1) organoThe average ytterbium-cyclopentadienyl carbon dislanthanide and organoyttrium alkyl complexes have been tance, 2.60 (2) A,is similar to that found in the ytterbium crystallographically characterized, including [ (C5H,),Ln[ (C5H5)2Yb(p-CH3)]221 (V), 2.613 (13) A, and complexes (p-CH3)], (Ln = Yb, Y),2’(C5H5)2Er(p-CH3)2Li(TMEDA)28 [ (CH3C5H4)2Yb(p-C1)]2,37 2.585 (7) A. Taking into account (TMEDA = Me2NCH2CH2NMe2),(C,H5),Lu(t-C4Hg)that trivalent ytterbium is 0.00838-0.0139A larger than (THF)” (II), (C5H5),Lu(CH2SiMe3)(THF)’O (III), and trivalent lutetium, the average Yb-C(q5) distance in I is (C5H,)2Lu(C6H4CH3-4)(THF)10 (IV),no crystal studies of also very similar to those found in 111,2.61(3) A, and IV, a simple solvated bis(cyclopentadieny1)methyl complex, (C,H5),Ln(CH3)(THF),have previously been r e p ~ r t e d . ~ ? ~2.59 ~ (3) A. The analogous average in (C,H,),Lu(tC4H9)(THF),2.63 (2) A, is slightly larger as previously Since the (C,H,),Ln(CH,)(THF) complexes are common noted.” The ytterbium-oxygen (THF) distance in I, 2.31 precursors to a variety of organolanthanide complex(1) A, is similar to the analogous metal-oxygen (THF) es,6,12,32-34 full characterization of this class was desirable. distance in 11, 2.31 (2) A,111, 2.288 (10) A, and IV, 2.265 Single crystals of (C,H,),Yb(CH,)(THF) (I), obtained A. (28) by diffusing hexane into a THF solution at 0 ‘C, crystallize The most interesting distance in the structure of I is the in space group P2,/a. Figure 1illustrates the molecular Yb-C methyl distance of 2.36 (1) A. The ytterbiumstructure of I, and Table IV gives the important bond bridging methyl carbon distances in [ (C5H5)2Yb(p-CH3)]2, distances and angles. As in 11, 111, and IV, the two cy(17) and 2.536 (17) A, are considerably longer as 2.486 clopentadienyl ring centroids, the THF oxygen atom, and expected for a bridging alkyl compared to the identical the alkyl carbon coordinate to the metal in I in a roughly terminal alkyl. The Yb-(p-CH,) distances in (C5H5),Ybtetrahedral fashion. The structure is typical of bent me(p-CH3)2A1(CH3)2,40 2.562 (18) and 2.609 (2) A, are also tallocene species which contain two additional ligand^.^^^^ longer as expected. The Er-, Ho-, and Lu-(p-CH3) dis-
C8.
(33) Marks, T. J.; Ernst, R. D. In ‘Comprehensive Organometallic Chemistry”;Wilkinson, G., et al., Eds.;Pergamon Press: New York, 1982; Vol. 3, Chapter 21. (34) Evans, W. J. Adu. Organomet. Chem. 1985, 24, 131-177.
268 Organometallics, Vol. 5, No. 2, 1986
tances in Er(p-CH3)6Li3(TMEDA)3,41 2.57 (2) A, (C5HS)ZEr(p-CH3)2Li(TMEDA),28 2.458 (19) A, Ho(pCH3)6Li3(TMEDA)3,42 2.563 (18) A, and LU(p-CH3)&(MeOCH,CH20Me),,432.53 (2) A, are also longer when the differences in metallic radii are considered. The lutetium terminal alkyl carbon distances in I11 and IV, 2.376 (17) and 2.345 (39) A, are similar to the Yb-C distance in I, but the Lu-C distance in I1 is considerably and significantly longer, 2.471 (2) A. The Yb-C distance in I provides for the first time a Ln-C distance for an unsubstituted terminal alkyl ligand of modest size in a late lanthanide (C5H5I2LnR(THF) complex. This distance allows one to characterize the relative amount of steric crowding in other terminal organolanthanide alkyl complexes. Evidently, the steric bulk of the CH,SiMe3 and C6H4-4-CH3ligands in I11 and IV is not so large at the carbon atom coordinated to lutetium as to prevent “normal” Lu-C bond lengths. In contrast, the Lu-C bond in (C5H5)zLu(t-C4HS)(THF) is clearly long in comparison and suggests that this molecule is quite sterically crowded. Analysis of the relative degree of steric crowding is quite important in organolanthanide chemistry, since steric effects influence the structure, stability, and reactivity of the c ~ m p l e x e s . ~ Comparison ~-~~ of (C,H,),Yb(CH,)(THF) with the lutetium analogue (C5H5)zLu(CH,)(THF)’oconstitutes a clear example of how small changes in steric crowding can have large effects on stability. ( C 5 H 5 ) 2 L ~ ~ (CH,)(THF) is reported to decompose below 20 “C, whereas a room-temperature crystal structure of the ytterbium analogue was readily obtained. Although both compounds desolvate, the lutetium complex is much more susceptable to this decomposition reaction.47 The main difference between the complexes of these metals, which are adjacent in the periodic table, is the 0.0083s-0.0139A difference in the size of the metal. This small change in radius causes the lutetium derivative to be slightly more sterically crowded. This may enhance the THF extrusion process and cause the decomposition to occur more readily. Consistent with this, both [ (C5H5)2LuH(THF)]zand (CH3C,H4),Lu(t-C4HS)(THF)are less stable than the analogous erbium or yttrium complexe~.~ Hydrogenolysis Studies. We sought to examine the consequences in reactivity of the structural features discussed above. The hydrogenolysis reaction was chosen to probe Ln-C bond reactivity because the substrate is relatively small, the hydride products are well-characterized>6 and our earlier studies showed a wide range of rates for this r e a ~ t i o n . ~ ~ ~ , ~ ~ The structural data discussed above indicated that, for a given metal, (C5HS)zLn(t-C4HS)(THF) complexes were significantly more crowded than (C5H,),Ln(CHzSiMe3)(THF) or (C5H5),Ln(CH3)(THF)species. Consistent with the crystallographically established steric congestion in (CSHJ2Lu(t-C,HS)(THF) we have found that this species (41) Schumann, H.; Pickardt, J.; Bruncks, N. Angew. Chem., Int. Ed. Engl. 1981, 20, 120-121. (42) Schumann, H.; Muller, J.; Bruncks, N.; Lauke, H.; Pickardt, J.; Schwarz, H.; Eckart, K. Organometallics 1984, 3, 69-74. (43) Schumann, H.: Lauke, H.; Hahn, E.; Pickardt, J. J . Organomet. Chem. 1984, 263, 29-35. (44) For a more extensive discussion of the consequences of steric crowding in organolanthanide chemistry, see ref 34 and 45. (45) Evans, W. J.; Peterson, T. T.; Rausch, M. D.; Hunter, W. E.; Zhang, H.; Atwood, J. L. Organometallics 1985, 4, 554-559. (46) Quantitative analysis of the steric crowding is under development: Xing-Fu, Li; Fischer, R. D. Inorg. Chim. Acta 1983, 94, 50-52. (47) Freshly recrystallized clear crystals of (C,H,),Lu(CH,)(THF) s t a r t to become opaque within 10 min at room temperature and appear by ’H NMR spectroscopy to lose about one-third of their solvated THF in this time period
Evans e t al.
is rather unreactive to Hz in THF solvent where it is likely to be fully solvated6(eq 5). In contrast, in toluene a rapid
+ H2 (C5H5)2L~(t-C4HS)(THF)
THF
room temp 6h
no reaction
(5) hydrogenolysis is observed6 (eq 3) to give the [(C,H5)2LuH(THF)], product in good yield.4 The toluene reaction presumably differs from the THF reaction in that in toluene some dissociation of THF occurs to provide access to a highly reactive, sterically unsaturated species like (C,H5)zL~(t-C4H9).6 Consistent with these observations, we had found that the bridged dimer [(CH,C,H,),Yb(wCH,)], reacted slowly with hydrogen in toluene (eq l), but that [(CH,C,H,)2Y(p-CH,)12 and [(C,H5)2Y(~-CH3)Iz reacted rapidly in mixed 1:lO THF/alkane or 1:lO THF/ arene solvents.6 In these latter cases, the presence of the substoichiometric amounts of THF could effect a bridge cleavage leading to (C5H5)2Y (CH,)(THF) and (C5H5),YCH,, species more reactive than the doubly bridged dimer. Clearly, the solvent and degree of association of a complex can be as important as the size of the metal and the alkyl ligand. To more fully examine the previously observed trends in Ln-C bond reactivity to hydrogenolysis, we have examined several alkyl complexes in a variety of solvents. The widest range of reactions has been carried out with yttrium complexes since ‘H NMR spectroscopy is particularly informative with this metal due to the I = 1/2 nuclear spin of the metal.16 The degree of association of organoyttrium complexes in solution can often be determined from the Y-H coupling pattern^.^,^ The reactivity of yttrium complexes is compared with those of Er, Yb, and Lu by using a more limited range of alkyls and solvents. A summary of these results is shown in Table 111. Alkyl Yttrium Complexes. The methyl carbon yttrium bond in dimeric [(C5H5)2YCH3]2 fails to react with hydrogen in toluene under ambient conditions over a several day period as expected based on the ytterbium results (eq l)., With a mixed solvent of 101 toluene/THF, hydrogenolysis is efficient as previously reportede6 In the latter case, the (C5H5)2YCH3 complexes present would be expected to react with H2,but the reactivity of the solvated (C5H5)2Y (CHJ(THF) was less certain. Fully solvated (C,H5)zLu(t-C4Hg)(THF)in THF did not react with hydrogen (eq 4), but since the crystal structure of I indicated that (C,H,),Ln(CH,)(THF) complexes were less sterically crowded than (C5H5)2L~(t-C4H9)(THF), reactivity of the solvated methyl species toward hydrogen was feasible. As shown in entry 3 of Table I11 (C,H,),Y(CH,)(THF) does react readily with Hz in THF (eq 6) to form [(C5HJzY(pTHF
2(C,H5)2Y(CH,)(THF) + 2Hz [(C,H,)zY(p-H)(THF)Iz + 2CH4 (6) H)(THF)]; in good yield. DME is a better ethereal solvent than THF for the hydrogenolysis of a terminal Y-CH, bond, and dioxane is worse although the reaction still proceeds a t a reasonable rate. (C5H5)2Y(t-C4H9)(THF) readily undergoes hydrogenolysis in toluene, but in T H F no hydride is generated over 24 h. The inertness of (C5H5),Y(t-C4H,)(THF)compared to the reactivity of (C,H,),Y(CH,)(THF) in THF clearly demonstrates the importance of steric crowding in organolanthanide reactivity. Substitution of the larger t-C4H9 ligand for CH, drastically reduces reactivity. Substituting the CH3 ligand with CHzSiMe,, which is large but not as sterically bulky around the Ln-C bond as the t-C4Hgligand, does not stop the hydrogenolysis from occurring in __+
Ytterbium and Yttrium Alkyl Complexes
(C5H5)2YR(THF)complexes. This is consistent with the similar Ln-C bond distances in the (C5H5I2LnR(THF) complexes (R = CH3, CH2SiMe3) and the fact that (C5H5)2Y (CH2SiMe3)(THF)is a monomer in both toluene and T H F solution (by sgY-lH splitting in the IH NMR spectra). Monomethylation of the cyclopentadienyl rings of the yttrium methyl complexes (entries 5 and 6) does not greatly affect the hydrogenolysis reactivity. In summary, for bis(cyclopentadieny1) yttrium alkyl complexes, reactivity to hydrogenolysis depends mainly on access to an unsolvated monomeric complex, (C5H5)2LnR,or to a solvated species, (C5H5)2LnR(THF),in which R does not cause steric crowding close to the metal. Alkyl Complexes of Erbium, Ytterbium, and Lutetium. Since E$+ is almost identical in size with Y3+ (0.881 vs. 0.88 A, respe~tively~~), its chemistry is likely to be the same. Indeed, entries 12 and 13 show that the reactivity to hydrogenolysis in toluene/THF and of [(C5H5)2ErCH3]2 in T H F is very similar to that of the yttrium analogue. [(C5H5)2YbCH3]2 and [(C5H5)2LuCH,],in toluene are also similar to [(C5H5)2YCH3]2; i.e., no reaction occurs with H2. In THF, however, the reactivity of the ytterbium and lutetium complexes differs. Only small amounts of [(C5undergo hydrogenolysis H,),YbCH,], and [(C5H5)2LuCH,]2 after 24 h under H2 in THF. Neither reaction produces enough hydride to form a precipitate as is observed in the can yttrium reactions. A 6% yield of [(C5H5)2LuH(THF)]2 be detected by 'H NMR spectroscopy after 24 h, and, after many days, the ytterbium reaction gives detectable amounts of [(C5H5),YbH(THF)12as well as its decomposition product (C,H,),Yb(THF). Hence, the reactivity of (C5H5)2Ln(CH3) (THF) complexes differs substantially for Ln = Y and Er compared to Ln = Yb and Lu. If the observed difference in reactivity is due entirely to steric effects, it means that a change in metal radius as small as 0.02239-0.03438A can greatly effect reactivity. Dimethoxyethane, which was a better solvent for [ (C5H5)2YCH3]2hydrogenolysis than THF (entries 3 and 4), is also a better solvent for the ytterbium and lutetium reactions (entries 17 and 23), although [ (C5H5),LuCH3I2 still gives only a 10% yield of hydridic product. Comparison of the latter two reactions suggests that a radial difference of only 0.00838-0.0139A can change significantly the yield of the hydrogenolysis reaction. These data can be summarized with a few general statements. Bridged methyl dimers [ (C5H5)2Ln(p-R)]2 in non-coordinating solvents are clearly the least reactive toward hydrogenolysis. The reactivity of fully solvated terminal alkyl complexes (C5H5),LnR(THF)depends on the size of the alkyl group: R = CH, is more reactive than R = CHzSiMe, which is more reactive than R = t-C4Hg. Terminal alkyls on unsolvated, sterically unsaturated metal centers would be expected to be the most reacti~e.~s~~** In sterically crowded molecules, small changes in the radius of the metal can have significant effects on reactivity. Organoytterbium Hydrides. The principles of hydrogenolysis reactivity outlined above indicate why the original hydrogenolysis of the bridged ytterbium dimer [(CH3C5H4)zYbCH3]2 (eq 1) was so slow. Clearly, there were better precursors and solvents for the formation of ytterbium hydrides. Moreover, a reasonably rapid reaction was necessary in the ytterbium case to minimize the amount of Yb3+-H to Yb2+decomposition. The initially observed trends in hydrogenolysis reactivity4 suggested (48) Ample evidence for this is available from the reactivity of the (C5Me&Ln(p-Z)LnZ(C5Me5)z complexes (Ln = Lu, Yb; Z = H, CHJ: Watson, P. L.; Parshall, G. W. Acc. Chem. Res. 1985, 18, 51-56 and references therein.
Organometallics, Vol. 5, No. 2, 1986 269
that (C5H5)2Yb(t-C4H9)(THF) (VI) in toluene was likely to be a better precursor to ytterbium hydride complexes than [ (C5H5),YbCH3I2.Unfortunately, attempts to prepare VI from [(C5H5)2YbC1]2 and t-C4H,Li in THF gave the divalent reduction product (C5H5)zYb.11The reaction of (C5H5),YbC1(THF)l,6in toluene with t-C4H9Liin pentane has been reported to give VI, but the yield is only 15%.lo The major product of that reaction again is (C5H5)2Yb. Hence, VI is not accessible in high enough yield to be a viable precursor to ytterbium hydrides. The reaction of [ (C5H5),YbCH3I2in the presence of ethers was therefore studied. As shown in Table 111, the [(C5H5),YbCH3I2/ DME system has the necessary characteristics to allow isolation of an ytterbium hydride in a reasonably high yield and convenient time as described below.49 In DME, [(C5H5),YbCH3I2 reacts with H2 in 24 h to give an orange precipitate. This product dissolves in THF and can be recrystallized from THF as yellow plates. Complexometric ytterbium analysis is consistent with the empirical formula (C5H5)2YbH(THF).The IR spectrum exhibited a broad absorption centered around approximately 1350 cm-' in the region found for vh-H absorptions of other [ (C5H5),LnH(THF)I2complexe~.~ The IR spectrum of the analogous complex prepared from Dz lacked this 1350 cm-I band and had new broad absorptions in the frequency range expected for an Yb-D absorption. Decomposition of the freshly recrystallized hydride complex with H 2 0 generated a quantitative yield of the expected amount of H2. The instability of this hydride in solution precluded the usual isopiestic molecular weight determination, but this species is likely to be a dimer, [(C5H&YbH(THF)IZ, like the Y, Er, and Lu a n a l o g u e ~ . ~The J ~ complex desolvates readily in a glovebox atmosphere (as does [(C5H5),LuH(THF)]$),and X-ray diffraction analysis of solvated crystals has not yet been possible. When [(C5H5)2Yb(CH,)],was hydrogenolyzed in the presence of lithium salts, a different organoytterbium hydride complex was formed. With 5:l Et20/hexane as a solvent, a yellow precipitate was obtained which contained lithium. Complete elemental analysis of this species (cf. the suggested the formula [(C5H5)zLnH]3H]{Li(THF)4) Ln = Y,7 Er,,l and Lu5 analogues, VII, VIII, and IX, respectively). The IR spectrum of this material contained a strong broad band at 1210 cm-' compared to absorptions in the 1170-1205 cm-I region for VII-IX. The analogous ytterbium complex prepared with Dz lacks the 1210 cm-' absorption and has an additional band a t approximately 850 cm-' (ratio = 1.4). Hydrolysis of a freshly recrystallized sample of this organoytterbium hydride gave 95% of the hydrogen expected from the trimer { [ (C5H5)zYbH]3H]{Li(THF),). This ytterbium hydride could also be prepared from [ (C5H5)2YbH(THF)]2 described above and t-C4H9Li following the direct synthetic route recently developed for VI1 from [ (C5H5)2YH(THF)]27 Attempts to fully identify this complex by X-ray diffraction have been unsuccessful since crystals of this product have repeatedly desolvated (49) The characterization of trivalent ytterbium cyciopentadienyl hydride complexes is somewhat more difficult than the analysis of other lanthanide or yttrium systems. In addition to the problem of Yb3+-H to Yb2+decomposition, Yb3+has a room-temperature magnetic moment of 4.4-4.9 pg and is not likely to yield the definitive NMR evidence readily obtainable with the diamagnetic lutetium and yttrium systems. In general, it has proven difficult to obtain complete elemental analysis on solvated late lanthanide hydride complexes and those systems not accessible by NMR, e.g., the erbium systems, have usually been fully characterized only by X-ray ~rystallography.4,~ The success of the latter approach, particularly with solvated species, depends on the stability of the crystals." (50) Four different crystal systems were tried before a refinable X-ray data set on a [(CSH4R)2Ln(p-H)(THF)]* complex was obtained.* (51) Evans, W. J.; Meadows, J. H., unpublished results.
270
Organometallics 1986, 5, 270-274
and decomposed in the X-ray beam before a unit cell could be determined. Decomposition Studies. Both of the trivalent ytterbium hydride complexes described above decompose to (C5H5)2Yb(THF).3.52 Both decompositions can be followed by 'H Nh4R spectroscopy by monitoring the disappearance of the paramagnetically broadened C,H, absorption of the Yb3+hydride and the growth of the 5.8 ppm resonance of the diamagnetic Yb2+product. At room temperature the [ (C,H5)2YbH(THF)]2conversion to (C,H,),Yb(THF) in THF is nearly complete in 48 h. In contrast, the anionic {[(C,H,),YbH],H]{Li(THF),J has a half-life of almost 50 days in THF.
Conclusion These studies indicate that the reactivity of bis(cyc1opentadienyl) lanthanide and yttrium alkyl complexes is a sensitive function of the size of the metal, the size of the ligand, and the coordinating ability of the solvent. Three major classes of organolanthanide complexes can be differentiated on the basis of the relative size of the ligands and the metal: sterically unsaturated, sterically saturated, and sterically o v e r ~ a t u r a t e d .Each ~~~~ class ~ has its own distinctive type of reactivity. The results of this study on sterically saturated complexes show that within a single class, there can also be considerable variation in reactivity due to small changes in steric saturation and the degree of molecular association. Furthermore, the present results show that these factors can effect reactivity in different directions depending on the reaction considered. Hence, by increasing the steric saturation of a (C,H,),Ln(CH,)(THF) complex by changing from Ln = Y to Ln = Lu, reactivity toward hydrogen decreases. However, the same (52) T h e decomposition of the trivalent ytterbium complex [(CjMe&Yb(DME] [PF,] by K H has been reported.**
change in metal increases the reactivity to desolvation. In (C5H5),YR(THF)complexes, increasing steric saturation by changing from R = CH, to R = t-C,H9 decreases re(tactivity toward hydrogen. In contrast for (R'CSH4)2Y C4H9)(THF)complexes, increasing steric saturation by changing from R' = H to R' = CH3 increases decomposition reactivity. A similar dichotomy exists in solvent effects. Addition of THF to [(C5H5),LnCH,], dimers increases reactivity to hydrogen, but the presence of THF diminishes the reactivity of (C5H,)2Ln(t-C4H9)(THF) complexes. All of these effects can be correlated with access to a terminal alkyl ligand on a sterically unsaturated metal center as the most reactive species. Clearly, there are several ways to finely manipulate the reactivity of organolanthanide alkyl complexes, providing a level of control unusual in organometallic chemistry. The fact that the lanthanide elements constitute the largest series of metals with similar chemistry but a gradually changing radial size makes these metals ideal for this sterically based variation of reactivity.,,
Acknowledgment. For support of this research, we thank the Division of Basic Energy Sciences of the Department of Energy. We also thank the Alfred P. Sloan Foundation and the University of California, Irvine Faculty Mentor Program, for fellowships (to W.J.E. and R.D., respectively). We thank Professor R. J. Doedens for his help and advice with the crystal structure determination. Supplementary Material Available: Tables of thermal parameters, structure factor amplitudes,and least-squaresplanes (10 pages). Ordering information is given on any current masthead page. (53) Evans, W. J.; Engerer, S. C.; Piliero, P. A.; Wayda, A. L. In "Fundamental Research in Homogeneous Catalysis"; Tsutsui, M., Ed.; Plenum Press: New York, 1979; Vol. 3, pp 941-952.
Characterization of the Anion [(q5-C5H5)3U111-n-C4H9]-. Synthesis and Crystal Structure of Tricyclopentadienyl-n-butyluranium(I I I ) Lithium Cryptate: [( C ~ H ~ ) ~ U C ~ H ~ I4H28N2041+ -[L~CI Lucile Arnaudet, Pierrette Charpin, GQrard Folcher,* Monique Lance, Martine Nierlich, and Daniel Vigner SCM-CEA-IRDI, 9 119 1 GIF Sur Yvette C a e x , France Received March 19, 1985
The anion [(~5-C,H,)3U*-n-C,H,]-forms with lithium inserted in a macrocycle a solid crystalline compound of stoichiometry 1/1. [Cp,UC,H,]- Li-2.1.11' crystallizes in the centrosymmetric monoclinic space group P2,ln (no. 14) with a = 8.873 (6) , b = 26.594 (8) A, c = 14.175 (3) A, /3 = 93.01 (3)", and 2 = 4. The structure was refined to R = 4.18% for 1890 reflections with 6 = 2-20' and I > 3u(I). The two entities have no crystallography-imposed symmetry: the U"I anion is very similar to the neutral equivalent U"
A
compound, with distances significantly smaller between uranium and its carbon neighbors.
Introduction The organometallic chemistry of trivalent uranium offers a few examples of well-established compounds. The sbonded ligands' like C5H5- (hereafter Cp-) and C8Hs2(1) Marks, T. J.; Fischer, R. D. "Organometallics o f f Elements"; D. Reidel Publishing Co.: Dordrecht, 1979; Chapter 1 and Chapter 2.
stabilize the four oxidation state of uranium and render the reduction more difficult than in the case of simple hydrated ions. Strong reductants are required to achieve quantitative reduction, and consequently the resulting compounds are very reactive. For instance, the reduction of (C8Hs)2Ucan be obtained only with lithium naphthalenide,2and the expected anion (C8H8),U- has not yet
0276-7333/86/2305-02~0$01.50/0 0 1986 American Chemical Society
