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Organolanthanides—XVI. Preparation and structure of bis(η5-cyclopentadienyl)bis(triphenylphosphine oxide)ytterbium(II)—the first X-ray crystal structure of a phosphine oxideorganolanthanide(II) complex
0277~5387/89 s3.00+.00 @$I1989 Maxwell Rrgamal Maanillaa plc
Po/yk&cw~ Vol. 8, No. 15, pp. 198~1987,1989 Printed in Great Britain
ORGANOLANTHANIDES.* PREPARATION AND STRUCTURE OF BIS($-CYCLOPENTADIENYL)BIS(TRIPHENYLPHOSPHINE OXIDE)YTI’ERBIUM( FIRST X-RAY CRYSTAL STRUCTURE OF A PHOSPI-IINE OXIDEORGANOLANTHANIDE(II) COMPLEX G. B. DEACON,?
B. M. GATEHOUSE
and P. A. WHITE
Chemistry Department, Monash University, Clayton, Victoria 3 168, Australia (Received
17 January 1989; accepted 16 March 1989)
Abstract-Reaction of Cp ,Yb@ME) (Cp = cyclopentadienyl ; DME = 1,2dimethoxyethane) with triphenylphosphine oxide yields Cp,Yb(OPPh3)z. The X-ray crystal structure shows eight-coordinate ytterbium with a pseudo-tetrahedral arrangement of two oxygen donor atoms and the centroids of two eclipsed $-cyclopentadienyl rings. Surprisingly short Yb-0 distances (2.30(2); 2.33(2) A) and the absence of major inter-ligand contacts indicate an uncrowded arrangement.
Triphenylphosphine oxide complexes of the oxophilic lanthanide(II1) ions are well-known,’ and phosphine oxides have been used in solvent extraction of lanthanides.3 Thus, it is surprising that few triphenylphosphine oxide (or other phosphine oxide) complexes of organolanthanides have been prepared. &* The sole crystal structures are those of cis- and trans-[(CSMe,),Sm”‘OPPh3]Z~-OCH= CHO) (I and II), where the presence of the phosphine oxide results from attempts to crystallize the novel product(s) of the redox reaction between bis(q5 - pentamethylcyclopentadienyl)samarium(II) and carbon monoxide.6 There are only two known organolanthanide(I1) complexes with triphenylphosphine oxide, viz. (C5Me5),M(THF)(OPPh3) (M=Sm7 or Yb;* THF = tetrahydrofuran), and these have been characterized spectroscopically. We now report the preparation and crystal structure of Cp,Yb(OPPh3)z (Cp = cyclopentadienyl). The sole previous X-ray structure of an unsubstituted cyclopentadienyllanthanide(I1) complex is that of Cp,Yb(DME) (DME = 1,2-dimethoxyethane), in which the sites of the cyclopentadienyl ligands are disordered.g Organolanthanide(I1) X-ray structures are dominated by those of bis(q5-pentamethylcyclopentadienyl)deri* For Part XIII, see ref. 1. t Author to whom correspondence should be addressed.
vatives, probably owing to their ease of crystallization. RESULTS Preparation
AND DISCUSSION
and spectroscopic
data
of bis(q 5-cyclopentadienyl)( 1,2-diReaction methoxyethane)ytterbium(II) with triphenylphosphine oxide (mole ratio, 1: 2) in DME, gave a black precipitate of bis(q5-cyclopentadienyl)bis (triphenylphosphine oxide)ytterbium(II) in good yield : Cp,Yb(DME)+2Ph3POCp,Yb(OPPh,),J
+DME.
(1)
Although oxidation of Cp,Yb(DME) by trimethylamine oxide giving (Cp,Yb)sO has been observed,” a similar reaction was not expected with triphenylphosphine oxide, since (C,Me,), Sm(THF)(OPPh,) has been prepared7 and (C5Me5)2Sm is a much more powerful reductant5g” than Cp*Yb. ” However, an attempt to prepare an analogous triphenylarsine oxide complex resulted in oxidation presumably in accordance with reaction (2) : 2CpYb(DME) + Ph3As0 -
1983
Ph,As+(CpzYi&O+2DME.
(2)
1984
G. B. DEACON
Table 1. IR absorption frequencies and assignments for CpzYb(OPPh& Frequency (cm- ‘)
Assignment”
157ow 1435s 1195s 1175s 1125s 107ow 101om 745(sh), 740s 725s 695s
1, v(CC) (a,), Ph n, v(CC) (b,), Ph v(p---o) v(P=O) q, X-sensitive (a,), Ph d, B&H), (bz), Ph B(CH) CP y(CH) CP +A y&I-I) @I), Ph r, X-sensitive (a J 0, &CC) (b I)
“Based on those for coordinated triphenylphosphine oxide13 (terminology is that of Whiffen”) and q5-cyclopentadienyl ligands. ’ 5
’ H NMR and mass spectra confirmed the presence of both ligands in Cp,Yb(OPPh3)z. The IR
spectrum (Table 1) was of considerable interest, showing two v(P=O) frequencies. One corresponds to that (1193 cm-‘)‘3 of free triphenylphosphine oxide, whilst the other is lowered from the free ligand value, as expected16 on coordination. This suggests either that solid CpzYb(OPPh3)a contains seven-coordinate Cp,Yb(OPPh3) and a molecule of uncoordinated triphenylphosphine oxide,* or the two v(F’=O) bands are the antisymmetric and symmetric stretching modes of an eight-coordinate complex with only a small average shift (8 cm- ‘) from the free ligand value. A crystal structure was needed to resolve the structural alternatives. The black crystals dissolve in THF to give a purple-brown solution with the visible maximum shifted only 9 nm from that of Cp,Yb in THF. l8 This result and the insolubility of the complex in DME suggest that dissolution in THF involves at least partial dissociation of triphenylphosphine oxide : Cp,Yb(OPPh3)2+THFe Cp2Yb(THF)(OPPh3) + Ph3P0. X-ray crystal structure Single crystals of CpzYb(OPPh& were obtained on partial evaporation of a solution in THF. The
* See, e.g. LiI(OPPh,), which contains [Li(OPPh,),]+ and a molecule of uncoordinated Ph 3P0. ”
et al.
crystal structure (Fig. 1) is the first of an organolanthanide(IIkphosphine oxide complex or any Ph,PGlanthanide(II) ion complex. It shows eightcoordinate ytterbium with a distorted pseudotetrahedral arrangement of two oxygen donor atoms and the centroids (CT) of two eclipsed cyclopentadienyl rings. Selected bond lengths and angles are given with Fig. 1. All 0-Yb-CT angles are near 109”, but CT( l)-Yb-CT(2) and O(l)-Yb-O(2) are markedly larger and smaller than tetrahedral, respectively, as is observed in CP;M(THF)~ (Cp’ = Me3SiC5H4, M = Yb; Cp’ = C5Mes, M = Sm).5 However, O-M-O and CT-M-CT angles of the present complex are larger and smaller, respectively, than those’ of CP;M(THF)~, owing to greater steric repulsion between the substituted cyclopentadienyl groups. The presence of $-cyclopentadienyl groups in CpzYb(OPPh3)z is indicated by the small variation in Yb-C bond lengths. Greater bond length differences are observed for the $-bonded Cp;M(THF), complexes’ and Cp,Yb(DME).’ Further support for q5-bonding is provided by the 90” Yb-CT-C angles. Predominantly ionic cyclopentadienyl-metal bonding is indicatedg*” by the value (1.62 A) for the effective ionic cyclopentadienyl radius” (the average Yb-C distance minus the ionic radius of eight-coordinate Yb2+ (1.14 A)‘“). The Yb-0 distances (Fig. 1) are markedly shorter (by 0.16 A,,) than those of Cp,Yb(DME),’ the only other crystallographicallydetermined structure of a Cp,Yb complex. In I and II (see Introduction), the Sm”‘-OPPh, distances are ca 0.08 8, shorter than average Sm”‘-O(THF) bond lengths.6 The distance (d), obtained by subtraction of the appropriate lanthanide ionic radii2’ from lanthanideoxygen bond distances, also illustrates the shortness of the Yb-0 bonds. For most Ph,PO-M3+ (M = lanthanide) complexes2 and the organometallics I and II,6 d = 1.29 f 0.03 A (cf. 1.34 f 0.06 A for most organolanthanide(I1 or III) complexes with ethersg). Exceptions are two highly hindered tris(bis(trimethylsilyl)amido)lanthanum (III) complexes, 2’ for which d = 1.50 and 1.52 A, and the uncrowded Ce(N0,),(OPPh3)2,22 for which d = 1.15 A. Values for Cp,Yb(OPPh,), (1.19, 1.16 A) approach the last, indicating a relatively uncrowded structure and/or some covalency in the Yb-0 bonds. The sum of the solid cone angle factors (Cc.a.f.) for Cp,Yb(OPPh,), (0.61), calculated from the X-ray structure parameters using the first-order cone angle mode1,23 is within the stable region (0.57-0.77) for organolanthanide(I1) complexes.24 Although significant second-order repulsion23 involving Ph,PO molecules may be expected, the
1985
Organolanthanides-XIV
Fig. 1. Crystal structure of Cp,Yb(OPPh,),. Selected bond lengths (A) and angles (“) : Yb-O( 1) Yb-O(2) Yb-CT( 1) Yb-CT(2)
0(1)-Y@(2) CT( l)-Yb-CT(2) CT(l)-Yb-O(l) CT( l)-Yb-O(2) CT(2)-Yb-O( 1)
2.30(2) 2.33(2) 2.48(3) 2.49(3) 90.4(6) 128.3(10) 108.0(7) 105.9(7) 108.7(8)
location is well displaced from the metal ion and the donor atom owing to the spear-like nature of the ligand. There are no significant inter-ligand contacts (cf. La(N(SiMe3)2)3(0PPhJ2’), and the phenyl rings are well separated from the cyclopentadienyl groups (Fig. 1). Since Zc.a.f. for Cp2Yb(OPPh3)2 is at the low end of the stable range, second-order effects are not expected to lead to overcrowding. A meaningful value for the second-order cone angle factor cannot be calculated owing to the substantial variation in 0-Yb-o-H angles (23-61”). Despite the short Yb-0 bonds, the P-O distances (Fig. 1) are close to the free ligand value (1.46( 1) A)25 and correlate with the very small shift of v(m) from that of free Ph3P0. This contrasts with Ce(N03)4(0PPh3)2,22 for which the short Cc--O distances are (more expectedly) associated with a large shift in v(m) and larger P-O distances (1.531(8), 1.526(8) A). In fact, the present P-O distances are shorter than those of all crystallographically characterized Ph,PO-lanthanide complexes. 2*6Although many of the differences are
Yb-c
2.72(2)-2.79(3)
P--o(l) P--o(2)
2.76(2) 1.47(2) 1.48(2)
w-% CT(2)-Y&O(2) W-W>-Yb P(2W(2t_Yb W---CT-C),
108.9(8) 163.9(11) 165.9(10) 90.0(12)
within experimental error, the overall trend is clear. Metal-O--P angles in triphenylphosphine oxide complexes are generally near 150”,26which is midway between the value (120”) for full covalent bonding and that (180”) for electrostatic bonding and minimum steric repulsion.26 In lanthanidc--OPPh, complexes, larger angles are usually observed2 and approach linear in the highly hindered La(N(SiMe3)2)3(0PPh3).2’ The values for Cp2Yb(OPPh3)2 (Fig. 1) are relatively small for lanthanide complexes, and contrast with the larger values2’ for Ce(N0J4(0PPh3)2 [169.2(5), 173.2(4)“]. EXPERIMENTAL General
Syntheses were carried out in greaseless Schlenk apparatus under purified (BASF R3/11 oxygenremoval catalyst and molecular sieves) nitrogen. Solids were handled under purified nitrogen or argon in a recirculating atmosphere drybox
1986
G. B. DEACON et al.
(Vacuum Atmospheres HE43-2 Drilab or MillerHowe 100). Details of solvent purification, handling procedures and spectroscopic methods have been given in previous papers. 18~27-2g The IR spectrum (Table 1) was recorded on a mull of the compound in dry degassed Nujol. For mass spectrometry, the complex was briefly exposed to the atmosphere (with resulting decomposition), before insertion into the spectrometer. For ‘H NMR spectroscopy, perdeuterotetrahydrofuran was degassed and distilled from sodium-benzophenone. It contained an aromatic impurity, probably benzene from decomposition of Ph,CO, hence meaningful integration could not be obtained. Chemical shifts are in ppm downfield from internal TMS. When Cp,Yb(OPPh3)2 was analysed for ytterbium by the reported method (H2SOJHN03 digestion, followed by titration with disodium dihydrogen ethylenediaminetetraacetate),27-2g a satisfactory titrimetric end point could not be obtained. Accordingly, accurately weighed samples (ca 0.2 g) were dissolved in pure THF (5 cm3) and were decomposed with dilute sulphuric acid (2 M, 5 cm’). The solution was extracted with dichloromethane and the organic layer separated and washed with water. The aqueous layer and washings were heated under a stream of nitrogen. Aliquots of this solution were than buffered to pH 4.5 with hexamethylenetetraamine, and titrated by the standard methods.*‘-*’ The method was validated by analysis of Cp,Yb(DME). Reagents
Triphenylphosphine oxide (K&K) was sublimed under vacuum to decompose any hydrate26 present, and triphenylarsine oxide (from a modification of the reported preparation3’) was dehydrated by azeotropic distillation. Both compounds were shown to be anhydrous by IR spectroscopy. Cp,Yb(DME) was obtained by the reported method. ‘* Preparation of bis(q’-cyclopentadienyl)bis(triphenyfphosphine oxide)ytterbium(II)
Bis(q 5- cyclopentadienyl)( 1,2 - dimethoxyethane) ytterbium(I1) (0.15 g, 0.38 mmol) and triphenylphosphine oxide (0.22 g, 0.79 mmol) reacted immediately on addition of 1,2_dimethoxyethane (5 cm’) to give a black, highly air- and water-sensitive crystalline precipitate of the title complex, which was filtered off and washed with the solvent (yield, 0.20 g, 61%) (Found: Yb, 20.7. C46H4002P2Yb requires : Yb, 20.1 “A). ‘H NMR : 5.60, s, Cp ; 7.4
7.7, m, Ph. Mass spectrum: m/z 277 [loo%, C,eH,,OP+], 201 [19, Ph,PO+], 185 [IO, Ph2P+], 183 [15, C,2HsP+], 152 [lo, C,,H$], 77 [24, Ph+], 66 [12, C,Hz], 51 [16, C,H:]. UV-vis-nearIR(300-1100 nm) : Ama&) 382(sh), 516(13O)nm. The filtrate from the synthesis was virtually colourless, suggesting near quantitative precipitation. A similar preparation in THF (25 cm3) yielded a purple solution, which, on partial evaporation of the solvent, gave black crystals of the title complex (yield, 24%) (Found: Yb, 20.7%), with spectroscopic properties identical with those of the product from the first preparation. Reaction between Cp,Yb(DME) oxide
and triphenylarsine
Dissolution of triphenylarsine oxide (0.82 g, 2.5 mmol) and Cp,Yb(DME) (0.50 g, 1.3 mmol) in THF (20 cm3) gave an immediate yellow solution, followed (after ca 1 min) by formation of a white precipitate, which redissolved on further stirring. After 12 h, the solution had turned brown, and the vis-near-IR spectrum : &,,, 870,916,925,950,986, 1021, 1032 nm, was indicative31 of ytterbium(II1). X-ray crystallography
Crystals of Cp2Yb(OPPh3)2 were grown by slow distillation of solvent from a solution in THF in a sealed double Schlenk tube, and were stored under dry, degassed Nujol. Selected crystals were mounted under purified argon in 0.8 mm Lindemann capillaries and held in place by high vacuum grease. Crystal data YbC46H.&2P2 : monoclinic, space group P2,/c, a = 10.925(8), b = 21.942(12), c = 16.839(10) A, /I = 99.83(15)“, V = 3977.32 A3, Z = 4, D, (air-sensitive material, density not measured), D, 1.44 g cm- 3; MO-& radiation (0.7107 A), p = 24.8 cm- ’ ; Philips PW 1100 diffractometer, graphite monochromator, ~28 scans at a scan speed of 0.25” s- ’ (the relatively high speed was used due to a high decomposition rate of several crystals in the X-ray beam) with 6 < 28 < 40” and scan width (1.20+0.2 tan 0)’ at 22°C. 3698 unique reflections, 1656 observed [FO2 60(F0)], absorption correction based on indexed crystal faces (min-max transmission = 0.478/0.673). Solution by Patterson method and subsequent difference Fourier techniques, refinement by full-matrix least-squares methods. Hydrogen atoms inserted in geometrically calculated positions and refinement of position and thermal parameters (anisotropic for ytterbium, phosphorus and oxygen and a single isotropic parameter for hydrogen atoms) resulted in R = 0.057,
OrganolanthanideeXIV and R, = 0.051. All calculations were carried out with SHELX76.32 Atomic scattering factors for neutral atoms33 were corrected for anomalous dispersion. Full details of the crystal structure results are available on request from the Editor. Atomic coordinates have also been deposited at the Cambridge Crystallographic Data Centre. Acknowledgement-We
are grateful to the Australian
Research Council for support.
REFERENCES 1. G. B. Deacon and D. L. Wilkinson, Znorg. Chim. Actu 1988,142, 329. 2. F. A. Hart, Scandium, yttrium and the lanthanides, Chap. 39 in Comprehensive Coordination Chemistry (Edited by G. Wilkinson, R. D. Gillard and J. A. McCleverty), Vol. 3. Pergamon Press, Oxford (1987). 3. Gmelin Handbook of Inorganic Chemistry; System No. 39, Part D6, pp. 121-123. Springer, Berlin (1983). 4. H. Schumann and W. Genthe, Organometallic compounds of the rare earths, Chap. 53 in Handbook of the Physics and Chemistry of Rare Earths (Edited by K. A. Gschneidner and L. Eyring), Vol. 7. Elsevier, Amsterdam (1984). 5. W. J. Evans, Polyhedron 1987,6,803. 6. W. J. Evans, J. W. Grate and R. J. Doedens, .Z.Am. Chem. Sot. 1985,107, 1671. 7. W. J. Evans, J. W. Grate, I. Bloom, W. E. Hunter and J. L. Atwood, J. Am. Chem. Sot. 1985,107,405. 8. T. D. Tilley, PhD thesis. University of California, Berkeley (1982). 9. G. B. Deacon, P. I. MacKinnon, T. W. Hambley and J. C. Taylor, J. Organomet. Chem. 1983,259,91. 10. D. L. Wilkinson, PhD thesis. Monash (1987) ; G. B. Deacon and D. L. Wilkinson, unpublished results. 11. P. L. Watson, unpublished results in footnote 5 of R. G. Finke, S. R. Keenan, D. A. Schiraldi and P. L. Watson, Organometallics 1986,5, 598. 12. A. M. Bond, G. B. Deacon and R. H. Newnham, Organometallics
1986, 5,2312.
1987
13. G. B. Deacon and J. H. S. Green, Spectrochim. Acta 1968, UA, 845. 14. D. H. Whiffen, J. Chem. Sot. 1956, 1350. 15. R. T. Bailey and A. H. Curran, J. Mol. Struct. 1970, 6, 391. 16. F. A. Cotton, R. D. Barnes and E. Bannister, J. Chem. Sot. 1960,2199. 17. A. R. Hands and A. J. H. Mercer, J. Chem. Sot. A 1968,449. 18. G. B. Deacon, A. J. Koplick and T. D. Tuong, Aust. J. Chem. 1984,37,517. 19. K. N. Raymond and C. W. Eigenbrot Jr, Accts Chem. Res. 1980, 13, 276. 20. R. D. Shannon, Acta Cryst. 1976, A32, 751.
21. D. C. Bradley, J. S. Ghotra, F. A. Hart, M. B. Hursthouse and P. R. Raithby, J. Chem. Sot., Dalton Trans. 1977, 1166. 22. M-UL-Haque, C. N. Caughlan, F. A. Hart and R. VanNice, Znorg. Chem. 1971,10, 115. 23. R. D. Fischer and Li Xing-Fu, J. Less Common Metals 1985, 112, 303.
24. P. I. MacKinnon, PhD thesis. Monash (1985). 25. G. Bandoli, G. Bortolozzo, D. A. Clemente, U. Croatto and C. Panattoni, J. Chem. Sot. A 1970, 2778. 26. P. I,. Goggin, Sulfoxides, amides, amine oxides and related ligands, Section 15.8 in Comprehensive Coordination Chemistry (Edited by G. Wilkinson, R. D. Gillard and J. A. McCleverty), Vol. 2. Pergamon Press, Oxford (1987). 27. G. B. Deacon, C. M. Forsyth, R. H. Newnham and T. D. Tuong, Aust. J. Chem. 1987,40,895. 28. G. B. Deacon, W. D. Raverty and D. G. Vince, J. Organomet. Chem. 1977,135,103. 29. G. B. Deacon, A. J. Koplick, W. D. Raverty and D. G. Vince, J. Organomet. Chem. 1979,182,121. 30. R. L. Shriner and C. N. Wolf, Org. Synth. 1963, 4, 911.
31. F. Calderazzo, R. Pappalardo and S. Losi, J. Znorg. Nucl. Chem. 1966,28,987.
32. G. M. Sheldrick, SHELX76, Program for Crystal Structure Determination. University of Cambridge, U.K. (1976). 33. International Tables for X-ray Crystallography, Vol. IV. Kynoch Press, Birmingham (Present distributor, D. Reidel, Dordrecht) (1974).
Po/yk&cw~ Vol. 8, No. 15, pp. 198~1987,1989 Printed in Great Britain
ORGANOLANTHANIDES.* PREPARATION AND STRUCTURE OF BIS($-CYCLOPENTADIENYL)BIS(TRIPHENYLPHOSPHINE OXIDE)YTI’ERBIUM( FIRST X-RAY CRYSTAL STRUCTURE OF A PHOSPI-IINE OXIDEORGANOLANTHANIDE(II) COMPLEX G. B. DEACON,?
B. M. GATEHOUSE
and P. A. WHITE
Chemistry Department, Monash University, Clayton, Victoria 3 168, Australia (Received
17 January 1989; accepted 16 March 1989)
Abstract-Reaction of Cp ,Yb@ME) (Cp = cyclopentadienyl ; DME = 1,2dimethoxyethane) with triphenylphosphine oxide yields Cp,Yb(OPPh3)z. The X-ray crystal structure shows eight-coordinate ytterbium with a pseudo-tetrahedral arrangement of two oxygen donor atoms and the centroids of two eclipsed $-cyclopentadienyl rings. Surprisingly short Yb-0 distances (2.30(2); 2.33(2) A) and the absence of major inter-ligand contacts indicate an uncrowded arrangement.
Triphenylphosphine oxide complexes of the oxophilic lanthanide(II1) ions are well-known,’ and phosphine oxides have been used in solvent extraction of lanthanides.3 Thus, it is surprising that few triphenylphosphine oxide (or other phosphine oxide) complexes of organolanthanides have been prepared. &* The sole crystal structures are those of cis- and trans-[(CSMe,),Sm”‘OPPh3]Z~-OCH= CHO) (I and II), where the presence of the phosphine oxide results from attempts to crystallize the novel product(s) of the redox reaction between bis(q5 - pentamethylcyclopentadienyl)samarium(II) and carbon monoxide.6 There are only two known organolanthanide(I1) complexes with triphenylphosphine oxide, viz. (C5Me5),M(THF)(OPPh3) (M=Sm7 or Yb;* THF = tetrahydrofuran), and these have been characterized spectroscopically. We now report the preparation and crystal structure of Cp,Yb(OPPh3)z (Cp = cyclopentadienyl). The sole previous X-ray structure of an unsubstituted cyclopentadienyllanthanide(I1) complex is that of Cp,Yb(DME) (DME = 1,2-dimethoxyethane), in which the sites of the cyclopentadienyl ligands are disordered.g Organolanthanide(I1) X-ray structures are dominated by those of bis(q5-pentamethylcyclopentadienyl)deri* For Part XIII, see ref. 1. t Author to whom correspondence should be addressed.
vatives, probably owing to their ease of crystallization. RESULTS Preparation
AND DISCUSSION
and spectroscopic
data
of bis(q 5-cyclopentadienyl)( 1,2-diReaction methoxyethane)ytterbium(II) with triphenylphosphine oxide (mole ratio, 1: 2) in DME, gave a black precipitate of bis(q5-cyclopentadienyl)bis (triphenylphosphine oxide)ytterbium(II) in good yield : Cp,Yb(DME)+2Ph3POCp,Yb(OPPh,),J
+DME.
(1)
Although oxidation of Cp,Yb(DME) by trimethylamine oxide giving (Cp,Yb)sO has been observed,” a similar reaction was not expected with triphenylphosphine oxide, since (C,Me,), Sm(THF)(OPPh,) has been prepared7 and (C5Me5)2Sm is a much more powerful reductant5g” than Cp*Yb. ” However, an attempt to prepare an analogous triphenylarsine oxide complex resulted in oxidation presumably in accordance with reaction (2) : 2CpYb(DME) + Ph3As0 -
1983
Ph,As+(CpzYi&O+2DME.
(2)
1984
G. B. DEACON
Table 1. IR absorption frequencies and assignments for CpzYb(OPPh& Frequency (cm- ‘)
Assignment”
157ow 1435s 1195s 1175s 1125s 107ow 101om 745(sh), 740s 725s 695s
1, v(CC) (a,), Ph n, v(CC) (b,), Ph v(p---o) v(P=O) q, X-sensitive (a,), Ph d, B&H), (bz), Ph B(CH) CP y(CH) CP +A y&I-I) @I), Ph r, X-sensitive (a J 0, &CC) (b I)
“Based on those for coordinated triphenylphosphine oxide13 (terminology is that of Whiffen”) and q5-cyclopentadienyl ligands. ’ 5
’ H NMR and mass spectra confirmed the presence of both ligands in Cp,Yb(OPPh3)z. The IR
spectrum (Table 1) was of considerable interest, showing two v(P=O) frequencies. One corresponds to that (1193 cm-‘)‘3 of free triphenylphosphine oxide, whilst the other is lowered from the free ligand value, as expected16 on coordination. This suggests either that solid CpzYb(OPPh3)a contains seven-coordinate Cp,Yb(OPPh3) and a molecule of uncoordinated triphenylphosphine oxide,* or the two v(F’=O) bands are the antisymmetric and symmetric stretching modes of an eight-coordinate complex with only a small average shift (8 cm- ‘) from the free ligand value. A crystal structure was needed to resolve the structural alternatives. The black crystals dissolve in THF to give a purple-brown solution with the visible maximum shifted only 9 nm from that of Cp,Yb in THF. l8 This result and the insolubility of the complex in DME suggest that dissolution in THF involves at least partial dissociation of triphenylphosphine oxide : Cp,Yb(OPPh3)2+THFe Cp2Yb(THF)(OPPh3) + Ph3P0. X-ray crystal structure Single crystals of CpzYb(OPPh& were obtained on partial evaporation of a solution in THF. The
* See, e.g. LiI(OPPh,), which contains [Li(OPPh,),]+ and a molecule of uncoordinated Ph 3P0. ”
et al.
crystal structure (Fig. 1) is the first of an organolanthanide(IIkphosphine oxide complex or any Ph,PGlanthanide(II) ion complex. It shows eightcoordinate ytterbium with a distorted pseudotetrahedral arrangement of two oxygen donor atoms and the centroids (CT) of two eclipsed cyclopentadienyl rings. Selected bond lengths and angles are given with Fig. 1. All 0-Yb-CT angles are near 109”, but CT( l)-Yb-CT(2) and O(l)-Yb-O(2) are markedly larger and smaller than tetrahedral, respectively, as is observed in CP;M(THF)~ (Cp’ = Me3SiC5H4, M = Yb; Cp’ = C5Mes, M = Sm).5 However, O-M-O and CT-M-CT angles of the present complex are larger and smaller, respectively, than those’ of CP;M(THF)~, owing to greater steric repulsion between the substituted cyclopentadienyl groups. The presence of $-cyclopentadienyl groups in CpzYb(OPPh3)z is indicated by the small variation in Yb-C bond lengths. Greater bond length differences are observed for the $-bonded Cp;M(THF), complexes’ and Cp,Yb(DME).’ Further support for q5-bonding is provided by the 90” Yb-CT-C angles. Predominantly ionic cyclopentadienyl-metal bonding is indicatedg*” by the value (1.62 A) for the effective ionic cyclopentadienyl radius” (the average Yb-C distance minus the ionic radius of eight-coordinate Yb2+ (1.14 A)‘“). The Yb-0 distances (Fig. 1) are markedly shorter (by 0.16 A,,) than those of Cp,Yb(DME),’ the only other crystallographicallydetermined structure of a Cp,Yb complex. In I and II (see Introduction), the Sm”‘-OPPh, distances are ca 0.08 8, shorter than average Sm”‘-O(THF) bond lengths.6 The distance (d), obtained by subtraction of the appropriate lanthanide ionic radii2’ from lanthanideoxygen bond distances, also illustrates the shortness of the Yb-0 bonds. For most Ph,PO-M3+ (M = lanthanide) complexes2 and the organometallics I and II,6 d = 1.29 f 0.03 A (cf. 1.34 f 0.06 A for most organolanthanide(I1 or III) complexes with ethersg). Exceptions are two highly hindered tris(bis(trimethylsilyl)amido)lanthanum (III) complexes, 2’ for which d = 1.50 and 1.52 A, and the uncrowded Ce(N0,),(OPPh3)2,22 for which d = 1.15 A. Values for Cp,Yb(OPPh,), (1.19, 1.16 A) approach the last, indicating a relatively uncrowded structure and/or some covalency in the Yb-0 bonds. The sum of the solid cone angle factors (Cc.a.f.) for Cp,Yb(OPPh,), (0.61), calculated from the X-ray structure parameters using the first-order cone angle mode1,23 is within the stable region (0.57-0.77) for organolanthanide(I1) complexes.24 Although significant second-order repulsion23 involving Ph,PO molecules may be expected, the
1985
Organolanthanides-XIV
Fig. 1. Crystal structure of Cp,Yb(OPPh,),. Selected bond lengths (A) and angles (“) : Yb-O( 1) Yb-O(2) Yb-CT( 1) Yb-CT(2)
0(1)-Y@(2) CT( l)-Yb-CT(2) CT(l)-Yb-O(l) CT( l)-Yb-O(2) CT(2)-Yb-O( 1)
2.30(2) 2.33(2) 2.48(3) 2.49(3) 90.4(6) 128.3(10) 108.0(7) 105.9(7) 108.7(8)
location is well displaced from the metal ion and the donor atom owing to the spear-like nature of the ligand. There are no significant inter-ligand contacts (cf. La(N(SiMe3)2)3(0PPhJ2’), and the phenyl rings are well separated from the cyclopentadienyl groups (Fig. 1). Since Zc.a.f. for Cp2Yb(OPPh3)2 is at the low end of the stable range, second-order effects are not expected to lead to overcrowding. A meaningful value for the second-order cone angle factor cannot be calculated owing to the substantial variation in 0-Yb-o-H angles (23-61”). Despite the short Yb-0 bonds, the P-O distances (Fig. 1) are close to the free ligand value (1.46( 1) A)25 and correlate with the very small shift of v(m) from that of free Ph3P0. This contrasts with Ce(N03)4(0PPh3)2,22 for which the short Cc--O distances are (more expectedly) associated with a large shift in v(m) and larger P-O distances (1.531(8), 1.526(8) A). In fact, the present P-O distances are shorter than those of all crystallographically characterized Ph,PO-lanthanide complexes. 2*6Although many of the differences are
Yb-c
2.72(2)-2.79(3)
P--o(l) P--o(2)
2.76(2) 1.47(2) 1.48(2)
w-% CT(2)-Y&O(2) W-W>-Yb P(2W(2t_Yb W---CT-C),
108.9(8) 163.9(11) 165.9(10) 90.0(12)
within experimental error, the overall trend is clear. Metal-O--P angles in triphenylphosphine oxide complexes are generally near 150”,26which is midway between the value (120”) for full covalent bonding and that (180”) for electrostatic bonding and minimum steric repulsion.26 In lanthanidc--OPPh, complexes, larger angles are usually observed2 and approach linear in the highly hindered La(N(SiMe3)2)3(0PPh3).2’ The values for Cp2Yb(OPPh3)2 (Fig. 1) are relatively small for lanthanide complexes, and contrast with the larger values2’ for Ce(N0J4(0PPh3)2 [169.2(5), 173.2(4)“]. EXPERIMENTAL General
Syntheses were carried out in greaseless Schlenk apparatus under purified (BASF R3/11 oxygenremoval catalyst and molecular sieves) nitrogen. Solids were handled under purified nitrogen or argon in a recirculating atmosphere drybox
1986
G. B. DEACON et al.
(Vacuum Atmospheres HE43-2 Drilab or MillerHowe 100). Details of solvent purification, handling procedures and spectroscopic methods have been given in previous papers. 18~27-2g The IR spectrum (Table 1) was recorded on a mull of the compound in dry degassed Nujol. For mass spectrometry, the complex was briefly exposed to the atmosphere (with resulting decomposition), before insertion into the spectrometer. For ‘H NMR spectroscopy, perdeuterotetrahydrofuran was degassed and distilled from sodium-benzophenone. It contained an aromatic impurity, probably benzene from decomposition of Ph,CO, hence meaningful integration could not be obtained. Chemical shifts are in ppm downfield from internal TMS. When Cp,Yb(OPPh3)2 was analysed for ytterbium by the reported method (H2SOJHN03 digestion, followed by titration with disodium dihydrogen ethylenediaminetetraacetate),27-2g a satisfactory titrimetric end point could not be obtained. Accordingly, accurately weighed samples (ca 0.2 g) were dissolved in pure THF (5 cm3) and were decomposed with dilute sulphuric acid (2 M, 5 cm’). The solution was extracted with dichloromethane and the organic layer separated and washed with water. The aqueous layer and washings were heated under a stream of nitrogen. Aliquots of this solution were than buffered to pH 4.5 with hexamethylenetetraamine, and titrated by the standard methods.*‘-*’ The method was validated by analysis of Cp,Yb(DME). Reagents
Triphenylphosphine oxide (K&K) was sublimed under vacuum to decompose any hydrate26 present, and triphenylarsine oxide (from a modification of the reported preparation3’) was dehydrated by azeotropic distillation. Both compounds were shown to be anhydrous by IR spectroscopy. Cp,Yb(DME) was obtained by the reported method. ‘* Preparation of bis(q’-cyclopentadienyl)bis(triphenyfphosphine oxide)ytterbium(II)
Bis(q 5- cyclopentadienyl)( 1,2 - dimethoxyethane) ytterbium(I1) (0.15 g, 0.38 mmol) and triphenylphosphine oxide (0.22 g, 0.79 mmol) reacted immediately on addition of 1,2_dimethoxyethane (5 cm’) to give a black, highly air- and water-sensitive crystalline precipitate of the title complex, which was filtered off and washed with the solvent (yield, 0.20 g, 61%) (Found: Yb, 20.7. C46H4002P2Yb requires : Yb, 20.1 “A). ‘H NMR : 5.60, s, Cp ; 7.4
7.7, m, Ph. Mass spectrum: m/z 277 [loo%, C,eH,,OP+], 201 [19, Ph,PO+], 185 [IO, Ph2P+], 183 [15, C,2HsP+], 152 [lo, C,,H$], 77 [24, Ph+], 66 [12, C,Hz], 51 [16, C,H:]. UV-vis-nearIR(300-1100 nm) : Ama&) 382(sh), 516(13O)nm. The filtrate from the synthesis was virtually colourless, suggesting near quantitative precipitation. A similar preparation in THF (25 cm3) yielded a purple solution, which, on partial evaporation of the solvent, gave black crystals of the title complex (yield, 24%) (Found: Yb, 20.7%), with spectroscopic properties identical with those of the product from the first preparation. Reaction between Cp,Yb(DME) oxide
and triphenylarsine
Dissolution of triphenylarsine oxide (0.82 g, 2.5 mmol) and Cp,Yb(DME) (0.50 g, 1.3 mmol) in THF (20 cm3) gave an immediate yellow solution, followed (after ca 1 min) by formation of a white precipitate, which redissolved on further stirring. After 12 h, the solution had turned brown, and the vis-near-IR spectrum : &,,, 870,916,925,950,986, 1021, 1032 nm, was indicative31 of ytterbium(II1). X-ray crystallography
Crystals of Cp2Yb(OPPh3)2 were grown by slow distillation of solvent from a solution in THF in a sealed double Schlenk tube, and were stored under dry, degassed Nujol. Selected crystals were mounted under purified argon in 0.8 mm Lindemann capillaries and held in place by high vacuum grease. Crystal data YbC46H.&2P2 : monoclinic, space group P2,/c, a = 10.925(8), b = 21.942(12), c = 16.839(10) A, /I = 99.83(15)“, V = 3977.32 A3, Z = 4, D, (air-sensitive material, density not measured), D, 1.44 g cm- 3; MO-& radiation (0.7107 A), p = 24.8 cm- ’ ; Philips PW 1100 diffractometer, graphite monochromator, ~28 scans at a scan speed of 0.25” s- ’ (the relatively high speed was used due to a high decomposition rate of several crystals in the X-ray beam) with 6 < 28 < 40” and scan width (1.20+0.2 tan 0)’ at 22°C. 3698 unique reflections, 1656 observed [FO2 60(F0)], absorption correction based on indexed crystal faces (min-max transmission = 0.478/0.673). Solution by Patterson method and subsequent difference Fourier techniques, refinement by full-matrix least-squares methods. Hydrogen atoms inserted in geometrically calculated positions and refinement of position and thermal parameters (anisotropic for ytterbium, phosphorus and oxygen and a single isotropic parameter for hydrogen atoms) resulted in R = 0.057,
OrganolanthanideeXIV and R, = 0.051. All calculations were carried out with SHELX76.32 Atomic scattering factors for neutral atoms33 were corrected for anomalous dispersion. Full details of the crystal structure results are available on request from the Editor. Atomic coordinates have also been deposited at the Cambridge Crystallographic Data Centre. Acknowledgement-We
are grateful to the Australian
Research Council for support.
REFERENCES 1. G. B. Deacon and D. L. Wilkinson, Znorg. Chim. Actu 1988,142, 329. 2. F. A. Hart, Scandium, yttrium and the lanthanides, Chap. 39 in Comprehensive Coordination Chemistry (Edited by G. Wilkinson, R. D. Gillard and J. A. McCleverty), Vol. 3. Pergamon Press, Oxford (1987). 3. Gmelin Handbook of Inorganic Chemistry; System No. 39, Part D6, pp. 121-123. Springer, Berlin (1983). 4. H. Schumann and W. Genthe, Organometallic compounds of the rare earths, Chap. 53 in Handbook of the Physics and Chemistry of Rare Earths (Edited by K. A. Gschneidner and L. Eyring), Vol. 7. Elsevier, Amsterdam (1984). 5. W. J. Evans, Polyhedron 1987,6,803. 6. W. J. Evans, J. W. Grate and R. J. Doedens, .Z.Am. Chem. Sot. 1985,107, 1671. 7. W. J. Evans, J. W. Grate, I. Bloom, W. E. Hunter and J. L. Atwood, J. Am. Chem. Sot. 1985,107,405. 8. T. D. Tilley, PhD thesis. University of California, Berkeley (1982). 9. G. B. Deacon, P. I. MacKinnon, T. W. Hambley and J. C. Taylor, J. Organomet. Chem. 1983,259,91. 10. D. L. Wilkinson, PhD thesis. Monash (1987) ; G. B. Deacon and D. L. Wilkinson, unpublished results. 11. P. L. Watson, unpublished results in footnote 5 of R. G. Finke, S. R. Keenan, D. A. Schiraldi and P. L. Watson, Organometallics 1986,5, 598. 12. A. M. Bond, G. B. Deacon and R. H. Newnham, Organometallics
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