Organometallics 1996, 14, 2 5 7 5 - 2 5 8 4
2575
Synthesis and Chemistry of Chiral Tetraphenylcyclopentadienes: X-ray Structures of Rh(p5-C5Ph4R*)(p4-CgH12) (R*= Menthyl, Neomenthyl) James A. Ramsden, David J. Milner,l Harry Adams, Neil A. Bailey, Arnold J. Smith, and Colin White* Department of Chemistry, The University, Shefield 53 7HF, England Received August 4, 1994@ The syntheses of the homochiral cyclopentadienes C5Ph4R*H (R* = menthyl; R* = neomenthyl) are reported together with those of the corresponding rhodium complexes Rh(C5Ph&*)(COD) (Sa,R* = menthyl; Zb, R* = neomenthyl). Both complexes react with bromine to give the corresponding species [Rh(CsPLR*)Br212(3a,R* = menthyl; 3b,R* = neomenthyl). The X-ray structures of Rh(C5Ph4menthyl)(COD)and Rh(C5Phmeomenthyl)(COD) have been determined at room temperature with use of Mo K a radiation ( A = 0.710 69 A). Compound 2a crystallizes in the orthorhombic space group P212121 (D24,No. 19)with a = 12.762(35)A, b = 17.953(39)A, c = 31.91(14)A , V = 7311(42)Hi3, 2 = 8, and D,= 1.306 g and was refined to R = 0.1349 on the basis of 1267 independent reflections. The analogous neomenthyl compound 2b crystallizes in the hexagonal space group P62 (Cs4,No. 171)with a = 27.034(78)A, c = 9.540(19)A, V = 6041(27)A3, 2 = 6,and D,= 1.246g and was refined to R = 0.0671 on the basis of 2310 independent reflections. A correlation between the CD spectra of 2a and 2b and their solid-state structures is discussed.
Introduction Metal complexes containing a chiral cyclopentadienyl ligand have attracted considerable interest in recent years.2 In part this is because of their potential in catalytic enantioselective synthesis; chiral cyclopentadienyl ligands are spatially and electronically very different from chiral bis(phosphine1ligands, and hence they are attractive alternatives in cases where chiral bidphosphine) ligands give poor results. For example, nonfunctionalized alkenes are typically hydrogenated in I30% ee with rhodium(I)his(phosphine) catalyst^,^ whereas chiral bis(cyclopentadieny1)metal complexes give up to 96% ee.4 To date, however, high optical yields (i.e. '80% ee) have only been achieved with chiral cyclopentadienyl ligands using bis(cyclopentadieny1)metal complexes: especially those having the cyclopentadienyl ligands linked together,4I6 In contrast, chiral monocyclopentadienyl complexes have given at best modest optical yields.'~~There are several obvious Abstract published in Advance ACS Abstracts, December 15,1994. (1) Present address: Zeneca Specialties, P.O. Box 42, Hexagon House, Blackley, Manchester M9 3DA, England. (2)Halterman, R. L. Chem. Rev. 1992,92,965. ( 3 )(a) Dumont, W.; Poulin, J. C.; Dang, T. P.; Kagan, H. B. J. Am. Chem. SOC.1973, 95, 8295. (b) Hayashi, T.; Tanaka, M.; Ogata, I. Tetrahedron Lett. 1977,295. (c) Samuel, 0.; Couffignal,R.; Lauer, M.; Zhang, S. Y.; Kagan, H. B. Nouv. J. Chim. 1981,5, 15. (4) Conticello, V. P.; Brard, L.; Giarrdello, M. A.; Tsuji, Y.; Sabat, M.; Stem, C. L.; Marks, T. J. J.Am. Chem. SOC.1992, 114, 2761. (5) (a) Halterman, R. L.; Vollhardt, K. P. C.; Welker, M. E.; Blaser, D.; Boese, R. J. Am. Chem. SOC.1987,109,8105. (6) (a) F'ino, P.; Cioni, P.; Wei, J. J. J.Am. Chem. SOC.1987, 109, 6189. (b) Chen, Z.; Haltermann, R. L. J.Am. Chem. SOC.1992, 114, 2276. (7) (a) Schofield,P. A.; Adams, H.; Bailey, N. A.; Cesarotti, E.; White, C. J. Organomet. Chem. 1991,412, 273. (b) Adams, H.; Bailey, N. A.; Colley, M.; Schofield, P. A.; White, 6. J. Chem. SOC.,Dalton Trans. 1994, 1445. (8) One exception is the Zr(dibomaCp)CL complex, which catalyzes the coupling of 1-naphthol with ethyl pyruvate in 580% ee: Erker, G.; van der Zeijden, A. A. H. Angew. Chem., Int. Ed. Engl. 1990,29, 512. @
reasons for this; for example in a mono- rather than a bis(cyclopentadieny1)complex it is clearly easier for the substrate to avoid interaction with a bulky chiral substituent. Further, in contrast to linked bis(cyc1opentadienyl) ligands, rotation about the metal-cyclopentadienyl bond reduces the chiral directing influence of the mono(cyclopentadieny1)ligand. There are, however, a number of attractive mono(cyclopentadieny1) catalysts known. For example, whereas hydrogenation catalysts of the type Ti(Cp')zClz need to be activated by the controlled addition of a reducing agent, are only really effective for the reduction of C-C bonds, have a limited turnover number, and are very sensitive to moisture and reaction condition^,^ [Rh(C5Me5)C1212suffers from none of these disadvantages.l0 We therefore set out to synthesize an effective chiral mono(cyc1opentadienyl) ligand in order t o develop chiral analogues of [Rh(C5Me5)C1212and other attractive catalysts. With this objective in mind, we considered the fact that a wide variety of chiral bis(phosphines) of the type (Ar)2PnP(Ar)2are successful despite the fact that the chiral center is ofien remote from the metal center. This is because the chiral center dictates the conformation of the chelate phosphorus ring, which in turn dictates the orientation of the propeller arrangement of the aryl groups on the phosphorus atoms; in this way the chirality is transmitted to the environment around the metal.ll In a pentaphenylcyclopentadienyl ligand the five phenyl rings cannot lie coplanar and must adopt a ~
(9) Kagan, H. B. In Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon: Oxford, U.K.,1982; Vol. 8, p 479. (10) (a) Russell, M. J. H.; White, C.; Maitlis, P. M. J. Chem. SOC., Chem. Commun. 1977,427. (b) Gill,D. S.; White, C.; Maitlis, P. M. J . Chem. Soc., Dalton Trans. 1978, 617. (11) (a) Knowles, W. S.; Vineyard, B. D.; Sabacky, M. J.; Stuls, B. R. In Fundamental Research in Homogeneous Catalysis; Ishii,Y., Tsutsui, M., Eds.;Plenum: New York, 1979;Vol. 3, p 537. (b) MacNeil, P. A.; Roberts, N. K.; Bosnich, B. J . Am. Chem. SOC.1981,103,2273.
Q276-7333/95I2314-2575$Q9.QQIQ 0 1995 American Chemical Society
Ramsden et al.
2576 Organometallics, Vol. 14,No. 5, 1995
Figure 1. Chiral arrays of tetraphenyl substituents.
I
I
-
-
Ph
Ph
la
lb
Figure 2. chiral array; further, we and others have shown that in metal-pentaphenylcyclopentadienyl compounds rotation about the phenyl-cyclopentadienyl bonds is sufficiently restricted that this chiral array can, in the presence of another chiral center, give rise to diastereoisomers.12J3 We therefore wondered whether with a chiral tetraaryl cyclopentadienyl ligand it would be possible to mimic bis(phosphine) ligands by having a bulky chiral group which dictated the chiral orientation of the four aryl groups (Figure 1). This would produce a chiral "umbrella') over the metal and in this way transmit the chirality t o the metal environment. To our knowledge the only chiral tetraarylcyclopentadienyl compounds reported to date are those reported by us several years ago containing an (-1-0-methyl mandelate group as the chiral directing unit, i.e. [M(C5Ph40COCH(OMe)Ph}In(where n = 1, M = Rh(CO12 or Ru(C0)2Cl; n = 2, M = RhC12).14 In these cases, however, the chiral center is too remote to have any significant effect upon the orientations of the four phenyl substituents and we reasoned that to do this it was necessary to locate the chiral center immediately adjacent to the cyclopentadienylring. We report herein the synthesis of such ligands, namely menthyltetraphenylcyclopentadiene (la) and neomenthyltetraphenylcyclopentadiene (lb) (Figure 2) together with the synthesis and X-ray structures of their rhodium complexes.
Results and Discussion Ligand Syntheses. The synthetic route to the chiral ligands involved the reaction of menthyl or neomenthyl tosylate with lithium tetraphenylcyclopentadienide (eq 1). This procedure has several attractive features: not Li[C5Ph4H]
+ R*Ts - C5Ph4HR*+ LiTs
R* = menthyl, neomenthyl
(1)
only is it straightforward but also the tetraphenylcy~lopentadienel~ and the chiral tosylates16J7are readily (12)Adams, H.; Bailey, N. A.; Browning, A. F.; Ramsden, J. A.; White, C. J. Organomet. Chem. 1990, 387, 305 (13)Li, L.; Decken, A.; Sayer, E. G.; McGlinchey, M. J.; Brbgaint, P.; Thbpot, J.-Y.; Toupet, L.; Hamon, J.-R.; Lapinte, C. Organometallics 1994,13, 682. (14)Bailey, N. A.; Jassel, V. S.; Vefghi, R.; White, C. J.Chem. SOC., Dalton Trans. 1987 2815.
available and the stereochemical course of the reaction is well defined with the addition proceeding with inversion of configuration at the chiral carbon center. Thus, the chiral unit is introduced in one step so that multigram quantities of the optically pure ligands can readily be prepared and no resolution is required at any stage. The products were purified by liquid chromatography and found to be a mixture of the 1,3-, 2,4-, and 3,5-dienes. The yield of neomenthyltetraphenylcyclopentadiene (lb; 16%)was significantly lower than that obtained in the menthyl analogue l a (64%);this can be rationalized by the relative ease of the sN2 displacement of the tosylate group. Neomenthyl tosylate can adopt a chair conformation where the leaving group is axial and the approach of the nucleophile is not hindered by any of the other substituents on the cyclohexyl ring. Menthyl tosylate can also adopt a conformation with an axial leaving group, but the approach of the bulky tetraphenylcyclopentadienidenucleophile is then hindered by the adjacent isopropyl group. The increased reactivity of neomenthyl tosylate over menthyl tosylate with respect to S Ndisplacement ~ is also reflected in the relative rates of hydrolysis of these t0sy1ates.l~ Rhodium Complexes. Reaction of Li(C5Ph4R") (R* = menthyl(men), or neomenthylheomen)) with [Rh(COD)C1]2 in xylene a t 125-135 "C yielded the corresponding Rh(C5PbR*)(COD)complex (2a, R* = menthyl; 2b, R* = neomenthyl) in near-quantitative yield. No product was observed when the same reaction was carried out in boiling tetrahydrofuran, dioxane, or toluene. Presumably, the high reaction temperature necessary reflects the considerable steric hindrance experienced by the ligand. Both 2a and 2b are airstable compounds which have been fully characterized and whose X-ray crystal structures and CD spectra are reported below. In an attempt to synthesize Rh(CsPh4neomen)(COD) (2b) under milder conditions, neomenthyltetraphenylcyclopentadiene and [Rh(COD)C112were heated under reflux in methanol in the presence of sodium carbonate; this is the procedure reported for the synthesis of the corresponding Rh(q5-C5H5)(COD)complex.l* In the case of neomenthyltetraphenylcyclopentadiene,however, no cyclooctadienecomplex was obtained but a blue compound was isolated in low yield (4%). The infrared spectrum of the product contains a strong signal at 1735 cm-l indicative of a bridging carbonyl ligand, and positive ion FAJ3 mass spectroscopy indicated the presence of the [Rh(C5Pbneomen)(CO)I+moiety. The compound proved t o be unstable as a solid and in solution, but it has been tentatively assigned as his@-carbonyl)bis(q5-neomenthyltetraphenylcyclopentadienyl~dirhodium. It is pertinent to note that the analogous C5Me5 complexlg is also blue with YCO a t 1732 cm-l and (15) (a) Castellani, M. P.; Wright, J. M.; Geib, S. J.; Rheingold, A. L.; Trogler, W. C. Organometallics 1986, 5, 1116. (b) Cava, M. P.; Narashiman, K. J. Org. Chem. 1969,34, 3641. (16) Phillips, H. J. Chem. SOC.1925,127,2566. (17) Winstein, S.;Morse, E. K.; Grunwald, E.; Jones, H. W.; Corse, J.; Trifan, D.; Marshall, H. J. Am. Chem. SOC.1952, 74, 1127 and references therein. (18)Kang, J . W.; Moseley, R; Maitlis, P. M. J.Am. Chem. SOC.1969, 91,5970. (19) Nutton, A,; Maitlis, P. M. J.Organomet. Chem. 1979,166, C21.
Chiral Tetraphenylcyclopentadienes that [Rh(C5Ph5)(C0)12,which has been isolated as an impure solid, is dark green with vco at 1767 cm-l (CH2C12).20 There are two possible sources of the carbonyl ligand in [Rh(C5Pbneomen)(CO)l~.One is from the sodium carbonate used in the reaction as a base, but we know of no precedent for carbonate acting as a source of carbon monoxide for the formation of a metal carbonyl. However, under acidic conditions carbonate gives rise to water and carbon dioxide and the latter is k n o w n to be a source of carbon monoxide.21 An alternative source of carbon monoxide is from decarbonylation of the solvent methanol, and we tend to prefer this explanation given that complexes such as [Rh(C5Me5)C1212are k n o w n to catalyze methanol decarbonylation.22 The complexes Rh(C5Ph&*)(COD)(2a,R* = menthyl; 2b, R* = neomenthyl) readily reacted with bromine to displace the COD ligand and to give the corresponding [Rh(CsPbR*)Brz]z (3a, R* = menthyl; 3b, R* = neomenthyl). Again, these are both air-stable solids which have been stored at room temperature for months with no apparent change. One beneficial effect of the large chiral substituent is that they appear to be more soluble in a wide range of solvents compared to [Rh(C5P h 5 ) B r ~ I z .The ~ ~ analogous compound [Rh(C5Me5)Br212 is an active hydrogenation catalyst,1° and preliminary experiments indicate that the complexes 3a and 3b also catalyze alkene hydrogenation. Their ability to catalyze enantioselective reductions is being actively investigated. X-ray Crystallographic Structures of 2a and 2b. The unit cell of Rh(C5Pbmenthyl)(COD) (2a) consists of two crystallographically independent molecules which are illustrated in Figure 3. Tables 2 and 3 give bond lengths and angles with estimated standard deviations. If the menthyl unit is disregarded, the remainder of the molecule is almost centrosymmetrically related through the origin of the unit cell. In contrast to the normal conformation adopted by a phenyl-substituted ~yclopentadienyl,l~J~J~,~~ the phenyl groups do not adopt a propeller arrangement. The two phenyls adjacent to the menthyl site are tilted in opposite directions to form an asymmetric "cup" with its open side directed away from the metal; within this cup is encapsulated the menthyl substituent, the bulky isopropyl group of which is situated on the side of the cyclopentadienyl away from the rhodium. The four phenyl groups in this cup arrangement still form a chiral array. The orientational change from propeller to cup is due to the fact that one of the two remote phenyl substituents lies almost perpendicular t o the cyclopentadienyl ring; i.e., the interplanar angles between the phenyl rings and the cyclopentadienyl ring are 55" (C(l)-phenyl), 51" ((32)phenyl), 90" (C(3)-phenyl), and 112" (C(4)-phenyl) for molecule 1and 78" (C(51)-phenyl), 36" (C(52)-phenyl), 91" (C(53)-phenyl), and 129" (C(54)-phenyl) for molecule 2. Both menthyl units adopt the chair conformation with three equatorial substituents, and in the two (20)Connerley, N. G.;Raven, S. J. J. Chem. SOC.,Dalton Trans. 1986,1613. (21)Sneeden, R.P.A. In Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon: Oxford, U.K., 1982;V O ~8, . pp 262-265. (22)Smith, T.A.; Maitlis, P. M. J. Organomet. Chem. 1986,166, 385. (23)Baghdadi, J.;Bailey, N. A.; Dowding, A. S.; White, C.,J. Chem. SOC.,Chem. Commun., 1992, 170.
Organometallics, Vol. 14, No. 5, 1995 2577 forms, the menthyl groups only differ in a slight twist in the torsion angle between the menthyl group and the cyclopentadienyl ring; torsion angles C(l)-C(5)-C(30)C(31), C(4)-C(5)-C(3O)-C(31), C(51)-C(55)-C(80)C(81), and C(54)-C(55)-C(80)-C(Bl) are -44, +120, +136, and -32", showing that equivalent (but not pseudo-symmetry-related) torsion angles differ by only about 14". The cyclopentadienyl rings are planar (rms deviations 0.014 and 0.008 A) and display no loss of aromaticity; the rhodium atoms lie 1.92 and 1.99 A from these planes for molecules 1 and 2, respectively. The X-ray crystal structure of Rh(C5Pbneomen)(COD) (2b;Figure 4) shows that the neomenthyl group is much bulkier than the menthyl group. The c6 ring adopts a chair conformation with two of the substituents, methyl and isopropyl, occupying axial positions, while the bulkier tetraphenylcyclopentadienyl group is in an equatorial position. This conformation contrasts with that found in the less sterically hindered complexes [Ru(C5H4neomen)(CO)(PPh3)Lln+ ( n = 0 , L = I,24L = Me, S O Z M ~n; = ~ ~1, L = NCMe26 ) and [Rh(C5H4ne0men)C1232,~~ where the methyl and isopropyl substituents are equatorial and the cyclopentadienylgroup is in an axial position. Also, in contrast to the menthyl analogue, the phenyl groups in 2b adopt a propeller array (left-hand screw) around the cyclopentadienyl ring and are inclined to the plane of the C5 ring by 56.7" (C(S)-phenyl), 48.7" (C(lS)-phenyl), 45.1" (C(12)-phenyl), and 74.7" (C(l1)phenyl). Clearly the steeper pitch of the C(ll)-phenyl ring is a result of the adjacent neomenthyl group. The cyclopentadienyl ring shows no loss of aromaticity, and the bond lengths (Table 2b) and bond angles (Table 3b) are unexceptional. The X-ray crystal structures can only give an approximate guide to the conformational behavior of the ligand. The solution behavior of the complexes can, however, be probed by means of circular dichroism spectroscopy. Circular Dichroism. Comparison of the CD spectra of Rh(y5-C5R4neomen)(COD)(R= H, Ph) (Figure 5) reveals that although both complexes display Cotton effects, they are clearly very different. The most intense maximum observed in the CD spectrum of Rh(y5-CsH4neomen)(COD)is associated with a strong W absorption at 239 nm, whereas the CD spectrum of Rh(y5C5Pbneomen)(COD) (2b) shows a considerably more intense maximum at 287 nm (A€ = 42.1) and a shoulder at 258 nm which are associated with the maxima at 285 and 248 nm, respectively, in the W spectrum for the metal complex 2b. Clearly, therefore, these intense Cotton effectsfor 2b are associated with the presence of the four phenyl substituents. They are also probably associated with metal-ligand charge-transfer transitions, since the absorptions at 248 and 285 nm are absent in the W spectrum of the free ligand C5Phr(neomen)H (Figure 6). The free ligand C5Pb(neomen)H does have a large positive Cotton effect at 242 nm (A€ = +28), which is associated with a W transition at 239 nm ( E = 42 000). This transition is (24)Cesarotti, E.; Chiesa, A.; Ciani, G. F.; Sironi, A,; Vefghi, R.; White, C. J . Chem. SOC.,Dalton Trans. 1984,653. (25)Lindsay, C.; Cesarotti, E.; Adams, H.; Bailey, N. A.; White, C. Organometallics 1990,9, 2594. (26)Cesarotti, E.; Angoletta, M.; Walker, N. P. C.; Hursthouse, M. B.; Vefghi, R.;White, C. J . Organomet. Chem. 1986,286,343.
Ramsden et al.
2578 Organometallics, Vol. 14,No. 5, 1995
19 33
Figure 3. Structures of t h e two crystallographically independent molecules of Rh(CsPh4men)(COD) (2a).
Organometallics,Vol. 14,No.5, 1995 2579
Chiral Tetraphenylcyclopentadienes
Table 1. Atom Coordinates ( x lo4) and Temperature Factors (Azx 103) ~~
atom
X
142(6) -216(6) 280(12) 831(12) lOl(12) -885(12) -779(12) 760(21) 1272(21) 1641(21) 1499(21) 987(21) 617(21) 1987(13) 2339(13) 3409(13) 4128(13) 3776(13) 2706(13) 333(23) 733(23) 1019(23) 906(23) 505(23) 219(23) -1910(15) -2620(15) -3584(15) -3839(15) -3129(15) -2165(15) -1691(14) - 1746(14) -2790(14) -2908(14) -2890(14) - 1840(14) -1613(14) -1291(57) -2646(27) -3015(14) 454(33) -421(31) -883(19) -539(18) 661(15) 1121(26) 1583(28) 8079(1) 7622(4) 7844(5) 8368(5) 8910(4) 8885(4) 8665(4) 8379(6) 7863(5) 7517(4) 7406(4) 7921(4) 8335(4) 8092(4) 7073(4) 6986(4) 6585(4) 6247(5) 6321(5) 6742(4) 6816(3) 6354(4) 5780(4) 5738(4) 6199(4) 6787(4) 8013(4)
Y
1461(5) -1323(5) 551(6) 1208(6) 1811(6) 1530(6) 747(6) -198(9) -564(9) -1288(9) -1647(9) -1282(9) -557(9) 1235(16) 1575(16) 1608(16) 1300(16) 959(16) 927(16) 2584(9) 3104(9) 3812(9) 3999(9) 3478(9) 2771(9) 1910(16) 2054(16) 2383(16) 2566(16) 2421(16) 2093(16) 239(11) -368(11) -795(11) - 1130(11) -500(11) -80( 11) -47(11) -673(18) 307(38) -831(11) 2568(25) 2286(15) 1594(20) 1157(22) 1153(31) 1076(10) 1690(16) 2090(1) 1938(4) 1590(4) 1683(5) 2213(5) 2523(4) 2866(4) 2962(6) 2463(5) 2105(4) 1527(4) 1514(4) 2084(4) 2446(4) 2283(4) 2509(4) 2675(4) 2607(4) 2380(4) 2225(4) 1044(4) 896(4) 503(4) -38(4) 94(4) 494(4) 1023(4)
X Ueqa atom (a) Rh(CsPhmen)(COD)(2a) 1707(2) 1514(31) -1767(2) -492( 14) 1154(5) -1011(14) 1036(5) -234(14) 1039(5) 769(14) 1179(5) 606(14) 1239(5) -952(23) 1232(9) -1197(23) 905(9) -1473(23) 962(9) -1504(23) -1258(23) 1345(9) 1672(9) -982(23) 1616(9) -2181(15) 950(10) -2598(15) 583(10) -3643t15) -4273( 15) 496(10) 776(10) -3856( 15) 1143(10) -2810(15) 1230(10) -448(23) 887(9) -509(23) 1169(9) -614(23) 1030(9) -658(23) 608(9) -596(23) -491(23) 326(9) 465(9) 1798(17) 1082(9) 2552(17) 1404(9) 3463(17) 1314(9) 3620(17) 2866(17) 902(9) 1955(17) 579(9) 1412(19) 670(9) 1277(7) 2343(19) 946(7) 2988(19) 977(7) 3386(19) 1419(7) 2449(19) 1746(7) 1804(19) 1717(7) 1957(19) 504(7) 1442(56) 2887(27) 200(9) 355(12) 2846(19) 2188(7) -271( 16) 2404(15) 483(21) 2137(11) 772(18) 2223(9) 427(32) 2601(11) -590(28) 2628(9) -1133(33) 2198(10) -1470(26) 2003(8) -1316(19)
2449(11) -415(11) -1082(11) -1627(11) -1299(11) -556(11) 354(13) 695(13) 1447(13) 1857(13) 1516(13) 764(13) -1134(18) -1506(18) -1398(18) -918(18) -546(18) -654(18) -2393(12) -2992(12) -3716(12) -3841(12) -3243( 12) -2519(12) -1680(18) -1707(18) -2125(18) -2515( 18) -2488(18) -2071(18) 31(15) 15(15) 736(15) 793(15) 801(15) 81(15) -48(15) 685(25) -229(43) 855(15) -2728(10) -2213(12) -1533(10) -1309(25) -861(32) -971(11) - 1667(13) -2353(12)
-2194(22) -1275(6) - 1149(6) -1056(6) -1122(6) -1265(6) -1269(10) -889(10) -880(10) -1251(10) -1631(10) -1640( 10) -1098(11) -753(11) -641(11) -875(11) -1221(11) - 1333(11) -887(9) -1165(9) - 1012(9) -581(9) -303(9) -456(9) -1049(11) - 1365(11) - 1308(11) -936(11) -620(11) -677(11) - 1318(7) -1016(7) - 1069(7) - 1524(7) -1827(7) -1772(7) -562(7) -421(12) -272(9) -2281(7) -2306(15) -2106(7) -2280(7) -2708(9) -2690(16) -2281(13) -2148( 11) -2402(14)
(b) Rh(CnHmeomen)(COD)(2b) 4i(lj* 8911(4) 59(6)* 9394(4) 62(6)* 9922(5) 9991(5) 96(9)* 9512(5) 85(7)* 8997(4) 60(7)* 8352(4) 66(6)* 89(9)* 8276(4) 91(9)* 8469(5) 41(5)* 8733(5) 29(4)* 8810(4) 42(5)* 8598(4) 36(5)* 6114(4) 6453(4) 40(5)* 6857(4) 40(5)* 59(7)* 5899(4) 81(8)* 1054(55) 84(7)* 669 77(7)* 524 57(6)* 93 38(5)* 200 36(5)* 1507(37) 44(5)* 1089 56(6)* 683 47(5)* 573 42(5)* 238 45(5)* 561(41)
2253(4) 2765(4) 2931(5) 2584(5) 2075(5) 1920(4) 3057(4) 3428(4) 3988(4) 4183(4) 3814(5) 3253(4) 334(4) 669(4) 1164(4) 308(4) 1179(53) 933 1343 1076 648 977(52) 751 941 1086 536 1762(32)
2820(11) 2397(12) 2943(14) 3915(16) 4329(15) 3787(11) 2547(12) 1743(14) 2112(13) 3374(15) 4249(13) 3832(11) -1457(12) 3684(10) 4605(10) 4509(11) 308(120) 1607 2114 3166 3990 -608(107) 640 501 1860 2729 3509(84)
2
0 -1925(11) -1896(11) -2654(14) -2331(14) - 1056(11) - 1045(12) -2290(13) -2803(15) 1717(13) 1512(10) 1863(12) 2260(11) 2185(11) 1761(14) 2961(14) 3013(15) 1890(15) 692(15) 576(13) 1154(11) 2305(11) 1569(12) 973(11) -63(12) 629(11) 1911(13)
'
Y
Z
uqa
43(5)* 57(6)* 73(8)* 81(8)* 83(8)* 54(6)* 45(6)* 57(6)* 74(7)* 79(7)* 67(7)* 53(6)* 72(6)* 43(5)* 54(6)* 62(7)* 212(17) 179(14) 163(13) 179(14) 212(17) 212(17) 179(14) 163(13) 179(14) 212(17) 212(17)
2580 Organometallics, Vol. 14, No. 5, 1995
Ramsden et al.
Table 1 (Continued) atom C(27) C(28) C(29) C(30) C(31) a
X
7797(4) 7899(5) 8240(6) 8452(6) 8359(5)
Y
623(4) 184(5) 140(5) 510(6) 971(5)
U$
z
(b) Rh(C&beomen)(COD) 2972(12) 50(6)* 3065(16) 90(8)* 2096(17) 103(10)* 1026(17) 102(11)* 971(13) 74(7)*
atom
X
Y
z
U,,Q
451 86 210 5
1154 919 518 435
3242 2050 1389 - 142
179(14) 163(13) 179(14) 212(17)
(2b)(Continued) C(72) O(3) (373) C(74)
Asterisks denote equivalent isotropic U values defined as one-third of the trace of the orthogonalized Ut tensor.
Table 2. Selected Bond Lengths (A) with Estimated Standard Deviations (Esd’s)
Rh(l)-C(l) Rh(l)-C(3) Rh(l)-C(5) Rh(l)-C(41) Rh(l)-C(45) C(l)-C(2) C(2)-C(3) C(4)-C(5) Rh(2)-C(51) Rh(2)-C(53) Rh(2)-C(55) Rh(2)-C(91) Rh(2)-C(95) C(51)-C(52) C(52)-C(53) C(54)-C(55) Rh( 1)-C(1) Rh(l)-C(5) Rh(1)-C(9) Rh(l)-C(ll) Rh(l)-C(13) C(l)-C(8) C(3)-C(4) C(5)-C(6) C(7)-C(8) C(9)-C(13) C(ll)-C(12)
(a) Rh(CsHlmen)(COD)(2a) Molecule 1 2.411(18) Rh(l)-C(P) 2.225(19) Rh(l)-C(4) 2.293(18) Rh(l)-Cp(l) 2.143(33) Rh(l)-C(42) 2.119(32) Rh(l)-C(46) 1.425(4) C(1)-C(5) 1.427(4) C(3)-C(4) 1.424(4) Molecule 2 2.289(22) Rh(2)-C(52) 2.333i2ij ~hi2j-ci54j 2.358(22) Rh(2)-Cp(2) 2.126(26) Rh(2)-C(92) 2.112(41) Rh(2)-C(96) 1.426(4) C(51)-C(55) 1.425(4) C(53)-C(54) 1.426(4) (b) Rh(C5Ph4(neomen)(Cod)(2b) 2.136(11) Rh(l)-C(2) 2.140(10) 2.249(12) 2.260(11) 2.292(11) 1.489(17) 1.479(13) 1.327(20) 1.455(16) 1.424(13) 1.428(12)
2.358(19) 2.139(19) 1.92 2.116(29) 2.107(35) 1.422(4) 1.428(4)
2.260(21) 2.412(21) 1.99 2.103(24) 2.103(35) 1.424(4) 1.425(4) 2.156(10) 2.138(9) 2.222(8) 2.270(10) 1.343(21) 1.497(19) 1.499(18) 1.510(19) 1.449(14) 1.448(15) 1.429(19)
also visible in the CD spectrum of the metal complex 2b, although it has the opposite sign and is less intense. Inspection of the CD spectra of Rh(CsPLR*)(COD) complex (2a, R* = menthyl; 2b, R* = neomenthyl) shows that they exhibit pseudoenantiomorphic CD spectra (Figure 7). A simplistic explanation for this is that it reflects the fact that 2a contains a menthyl substituent, whereas 2b contains a neomenthyl substituent. Given, however, that it has been demonstrated above that the intense CD maxima of Rh(C5Ph4R*)(COD) (2a, R* = menthyl; 2b, R* = neomenthyl) are associated with the four phenyl substituents, this is obviously not the total explanation. Clearly the two arrangements of the phenyl groups, i.e. the asymmetric cup of the menthyl complex and the propeller arrangement of the neomenthyl complex, are not mirror images. The arrangement adopted is, however, determined by the nature of the chiral fifth substituent in the cyclopentadienyl ring, and therefore in this sense the arrangements do reflect the chirality of this substituent. The enantiomorphic CD spectra of 2a and 2b suggests that the different chiral orientations of these four phenyl substituents are maintained in solution and that these different chiral orientations convey the epimeric relationship between the menthyl and neomenthyl substituents. In terms of developing chiral cyclopentadienyl ligands which are effective in enanantioselective syn-
Table 3. Selected Bond Angles (deg) with Estimated Standard Deviations (Esd’s) (a) Rh(CsPhrmen)(COD) (2a) Molecule 1 Bond Angles C(2)-C(l)-C(5) 108.3(2) C(l)-C(2)-C(3) C(2)-C(3)-C(4) 108.1(2) C(3)-C(4)-C(5) C(l)-C(5)-C(4) 108.0(2) Torsion Angles -44 C(4)-C(5)C(l)-C(5)C(30)-C(31) C(30)-C(31) C(5)-C(l)-48 C(l)-C(2)C(12)-C(17) C(6)-C(ll) -90 C(3)-C(4)C(2)-C(3)C(24)-C(25) C(18)-C(19) Molecule 2 Bond Angles C(52)-C(51)-C(55) 107.6(2) C(51)-C(52)-C(53) C(52)-C(53)-C(54) 108.1(2) C(53)-C(54)-C(55) C(51)-C(55)-C(54) 108.4(2) Torsion Angles 136 C(54)-C(55)C(51)-C(55)C(80)-C(81) C(80)-C(81) 80 C(51)-C(52)C(55)-C(51)C(62)-C(67) C(56)-C(61) 96 C(53)-C(54)C(52)-C(53)C(74)-C(75) C(68)-C(69) (b)Rh(CbPhdneomen)(COD)(2b) C(2)-C(l)-C(8) 122.8(11) C(l)-C(2)-C(3) 117.1(11) C(3)-C(4)-C(5) C(2)-C(3)-C(4) C(4)-C(5)-C(6) 123.9(11) C(5)-C(6)-C(7) C(6)-C(7)-C(8) 116.2(11) C(l)-C(8)-C(7) C(lO)-C(9)-C(l3) 108.1(10) C(9)-C(lO)-C(ll) C(lO)-C(ll)-C(l2) 106.2(10) C(ll)-C(l2)-C(l3) C(9)-C(13)-C(12) 107.3(8) C(21)-C(2O)-C(25) C(2O)-C(21)-C(22) 104.9(8) C(2O)-C(21)-C(45) C(22)-C(21)-C(45) 115.6(7) C(21)-C(22)-C(23) C(22)-C(23)-C(24) 111.7(7) C(23)-C(24)-C(25) C(23)-C(24)-C(44) 113.0(10) C(25)-C(24)-C(44) C(ZO)-C(25)-C(24) 110.6(9) C(21)-C(45)-C(46) C(21)-C(45)-C(47) 112.8(9) C(46)-C(45)-C(47)
107.7(2) 107.8(2) 120 -49 -130
108.2(2) 107.6(2) -32 27 127 126.1(10) 114.4(10) 124.0(11) 116.9(12) 108.1(7) 110.2(9) 109.6(7) 115.6(9) 113.4(9) 109.0(9) 112.9(7) 109.9(8) 107.9(8)
thesis, this is a promising result, suggesting that the influence of the chiral substituent is transmitted via the phenyl groups to the whole region around the cyclopentadienyl group.
Experimental Section All reactions of moisture-sensitive reagents were performed under nitrogen. THF was heated under reflux over sodium benzophenone ketyl and distilled under nitrogen. Xylene and diethyl ether were heated under reflux over sodium and distilled under nitrogen, whereas methanol was used without purification. 1,2,3,4-Tetraphenyl~yclopenta-1,3-diene,~~ [Rh(COD)C1]2,27and [Rh(CsH4neomer1)12]2~~ were all prepared by literature procedures. NMR spectra were recorded on a Bruker AM250 spectrometer. Low-resolution mass spectra were obtained on a Kratos MS80 fitted with a FAB source operating through a DS55 data (27) Giordano, G.; Crabtree, R. H. Inorg. Synth. 1990,28, 88.
Organometallics, Vol. 14, No. 5, 1995 2581
+ 50
60 50
40
0 AE
30 EX 103
20
- 50
10
0
240
v 3 5 1
280
360
400
AI nm
Figure 4. Structure of Rh(C5Pbeomen)(COD) (2b).
+ 50
320
60
uv
-.-.-.
CD
.___.___._._. CD
50 40
0 A&
30
uv
--
Figure 6. Rh(CsPkneomen)(COD) (2b): (-) CD spectrum; (--) UV spectrum. CsPkH(neomen): ( - - - ) CD spectrum; (- -1 W spectrum.
Ex103
20
- 50
10
+50 -
0
240
280
320
360
400
klnm
n
A
uv
-.-.-.
CD
.-.-....-....
uv CD
- -
Figure 6. Rh(C~,Pkneomen)(COD)(2b): (-) CD spectrum; (- -) UV spectrum. Rh(CsH4neomen)(COD): (- - -) CD spectrum; (- -) UV spectrum.
-
system; E1 denotes electron impact, CI, chemical ionization; and +FAB (argon), positive fast atom bombardment with argon. IR spectra were recorded on a Perkin-Elmer 1710 IRFT spectrometer and UV spectra on a Perkin-Elmer 559 UV/vis spectrophotometer. Optical rotations were measured on a Perkin-Elmer 141 polarimeter, and CD spectra were obtained by the National CD Service, SERC, Birkbeck College, University of London. Elemental analyses were performed by the University of Sheffield Microanalysis Service.
220
Xfnm
400
Figure 7. CD spectra of Rh(CsPkmen)(COD) (2a)(--) and Rh(C5Pkneomen)(COD) (2b)(- - -1. (-)-Menthyl Tosylate [(1R,2S,SR)-(-)-2-Isopropyl-Smethylcyclohexyl g-Toluenesulfonatel. This was prepared by the literature method.16 Anal. Calcd for C17H2603S: C, 65.8; H, 8.4; S, 10.3. Found: C, 65.6; H, 8.3; S, 10.5. [ a l ~ (20 "C, 1 = 1.0, c = 2.45, EtOH): -66.71'. 'H NMR (CDC13): 6 0.57 (d, JHH7 Hz, 3 H, CHs), 0.78 (d, JHH7 Hz, 3 H, CH3), 0 . 8 2 (d, JIM7 Hz, 3 H, CH3), 0.65-2.17 (m, 9 H, CH2, CH menthyl), 2.38 (s, 3 H, CH&), 4.37 (m, 1 H, CHOTs), 7.33
2582 Organometallics, Vol. 14, No. 5, 1995 and 7.81(m, 4 H, CH aromatic). 13C NMR (CDC13): 6 15.0, 20.5,and 21.1 (CH3), 22.7,33.4,and 41.6 (CHz), 21.5,25.1, 31.2,and 47.3(CH menthyl), 83.1(CH&), 127.2and 129.3 (CHAr), 134.6 and 144.0(CAr). (+)-NeomenthylTosylate [(lS,2S,5R)-(+)-2-1sopropyl5-methylcyclohexylp-Toluenesulfonatel. This was prepared by the following modification of the literature procedure.17 Powdered toluenesulfonyl chloride (32.5g, 0.17mol) was added over 5 min to a solution of (+)-neomenthol(25.0 g, 0.16mol) in pyridine (35 cm3) in an ice-water bath and the mixture stored at 10 "C for 14 days but shaken daily. The mixture was then shaken with ice water (500 cm3)and left t o stand at 10 "C for a further 7 days; during this time large crystals formed. The crystals were filtered off and recrystallized from light petroleum ether to give (+I-neomenthyl tosylate (24g, 52%). Anal. Calcd for C17H2603S: C, 65.8;H, 8.4;S,10.3.Found: C, 65.7;H, 8.6;S,10.4. [ah (20"C, 1 = 1.0, c = 2.57,CHC13) +20.6". 'H NMR (CDC13): 6 0.68(d, JHH 7 Hz, 3 H, CH3), 0.74(d, JHH 7 Hz, 3 H, CH3); 0.77(d, JHH7 Hz, 3 H, CH3),0.70-2.04(m, 9H, CH2, CH neomenthyl), 2.38 (s, 3 H, CH&), 4.98(s (br), 1 H, CHOTs), 7.32and 7.81(m, 4 H, CH aromatic). (+)-l-Neomenthyl-2,3,4,5-tetraphenylcyclopenta-2,4-
diene (lb). A solution of n-butyllithium (2.5M in hexanes) (64mmol) was added under nitrogen t o a solution of 1,2,3,4tetraphenylcyclopenta-1,3-diene(21.6g, 60mmol) in dry THF (240cm3) over 30 min at room temperature. This solution of lithium 1,2,3,4-tetraphenylcyclopentadienide was transferred to a pressure-equalized dropping funnel under nitrogen and then added drop-wise t o a solution of (-)-menthyl tosylate (19.2g, 60 mmol) in dry THF (100 cm3). The mixture was heated under reflux under nitrogen for 17 h and then cooled to room temperature. After THF was removed in uucuo, the solid was extracted into petroleum ether (bp 60-80 "C) at room temperature. The petroleum ether was removed in uucuo to give a red oil, and chromatography (silica, petroleum ether bp 60-80 "C) yielded a white powder (4.5g, 16%), mp 50-56 "C. Anal. Calcd for C39H40: C, 92.1;H, 7.9. Found: C, 91.6; H, 8.3.[a](20"C, 1 = 1.0,c = 1.055,CHC13): (589nm) +239.8", (578nm) +256.9",(546nm) +295.7",(436nm) +601.9";c39&0, m l e 508 (M+). MS (EI): m l e 508 [(M)+, loo%], 370 [(M CloHlg)+, 87%]. lH NMR (CDC13): 6 0.33-2.38 (m, 18 H, menthyl), 3.27-3.38(m, 1 H, menthyl), 4.84(s, 1 H, cyclopentadiene), 6.58-7.51(m, 20 H, aromatic). 13C NMR (CDC13): 6 21.0,22.8,27.0,30.2,37.0,48.7,and 62.4(CWCH3 nonaroand 42.3(CHz), 125.9-130.2(CH aromatic), matic), 26.3,35.3, 135.7,136.3,136.9,138.5,140.7,147.4,148.2,and 151.1(C aromatic and olefinic).
Ramsden et al. dirhodium (500 mg, 2 mmol) was added against a stream of nitrogen, and after it was stirred for 1 h a t 125 "C, the mixture was cooled t o room temperature and filtered. Removal of the xylene in uucuo gave a yellow powder. Chromatography (alumina, petroleum ether bp 40-60"C followed by ether) gave the product as a bright yellow powder (290mg, 98%),mp '240 "C. Anal. Calcd for C47H&h: C, 78.5;H,7.2. Found: C, 78.4;H, 7.5.[ a](20 "C, 1 = 0.1,c = 1.230,CHC13): (589 nm) -340.7",(578 nm) -360.1",(546 nm) -425.2",(436 nm) -865.gxb0"; C47HS1Rh,m l e 718 (M+). MS (FAB argon): m l e 718 [(M)+,loo%], 608 [(M - COD)+, 54%1. 'H NMR (CDC13): 6 0.2-2.6(m, 27 H, menthyl and COD), 3.73-3.95(m, 4 H, olefinic COD), 6.75-7.44(m, 20 H,CH aromatic). 13C NMR (CDC13): 6 15.7,21.4,and 22.7(CH3),24.7,34.9,and 48.8(CH2 menthyl), 31.4and 33.0(CH2 COD), 27.6,33.8,39.2,and 44.5 (CH menthyl), 71.6 and 72.4,(JC-Rh 14 Hz, CH COD), 102.8, 105.7,106.0,106.3,and 114.2,( J c - 13.4 ~ Hz, C cyclopentadienyl), 125.7-127.3and 132.0-133.0(CH aromatic), 134.5135.8(C aromatic). (+)-(~4-Cycloocta-l,5-diene)[~s~l-neomenthyl-2,3,4,5tetraphenylcyclopentadienyl]rhodium (2b). This was
prepared as a bright yellow powder in 88% yield by the procedure described above for the menthyl analogue but with l-neomenthyl-2,3,4,5-tetraphenylcyclopenta-2,4-diene (800 mg, 1.6mmol). Mp: 168-171 "C. Anal. Calcd for C47H51Rh: C, c= 78.5;H, 7.2.Found: C, 78.5;H, 7.1. [a](20 "C, 1 = 0.1, 1.175,CHC13): (589nm) +612.8",(578nm) +644.2",(546nm) +761.7",and (436nm) +1600.0";C ~ ~ H S ImRl e~ 718 , (M+).MS (FAB argon): m l e 719 [(M)+,loo%], 608 [(M - COD)+,40%1, 580 [(M - CloH19)+,40%]. lH NMR (CDC13): 6 0.5-1.8 (m, 22 H, neomenthyl), 1.8-2.2and 2.3-2.6 (m, 8 H, methylene COD), 2.93(m, 1H, methine neomenthyl), 3.7(m, 4H, olefinic COD), 6.9-7.3(m, 20 H, aromatic). 13CNMR (CDC13): 6 17.9, 21.6,24.6,24.7,27.6,34.2, and 42.4(CH3 and CH neomenthyl), 23.8,26.8,and 32.8(CH2 neomenthyl), 31.7and 33.1 (CH2 COD), 72.4and 73.2(JW-C14 Hz, COD), 106.8,106.9,107.6, 109.0,and 109.1(C cyclopentadienyl),125-133 (CH aromatic), 133.9,134.1,136.5,and 136.7(C aromatic). ( -)-Bis~-bromo)dibrom0bis(~~-l-menthyl-2,3,4,5-tetraphenylcyclopentadieny1)dirhodium (3a). (-)-(q4-Cycloocta-1,5-diene)[q5-l-menthyl-2,3,4,5-tetraphenylcyclopentadienyllrhodium (215 mg, 0.3mmol) was dissolved in ether (15cm3),and a solution of bromine in ether (0.035M, 10 cm3, 0.35mmol) was added dropwise to give the product as a deep
red precipitate. The product was filtered off, and the filtrate was evaporated to dryness in uacuo and redissolved in the minimum amount of dichloromethane; addition of pentane (-)- l-Menthyl-2,3,4,5-tetraphenyl~yclopenta-2,4-di- gave additional product (total yield 190mg, 82%). Anal. Calcd ene (la). This was prepared in 64% yield by a procedure for C78H78Br4Rhz: C, 60.8;H, 5.1;Br, 20.7. Found: C, 60.2; similar to that used for the neomenthyl analogue, except that H, 5.1;Br, 20.0.[a](20"C, 1 = 0.1, c = 0.0948,CHC13): (589 the product was extracted from the reaction mixture using nm) -316.5",(578 nm) -295.4",(546nm) -200.4",(436nm) diethyl ether. The product was isolated after chromatography -1054.9". 'H NMR (CDC13): 6 -0.07(6H, d, JHH 7 Hz, CH3), as a clear oil which solidified upon drying under vacuum: mp 0.76(12H, d, JHH7 Hz, CH3), 0.32-1.56(16 H, m, CH2 and 58-61 "C. Anal. Calcd for C39H40: C, 92.1;H, 7.9. Found: CH menthyl), 2.41-2.53(2 H, m), 2.65-2.75(1 H, m), 6.91C, 92.1;H, 8.2. [a](20 "C, 1 = 0.1,c = 1.025,CHC13): (589 7.13and 7.22-7.51(40H, m, aromatic). 13CNMR (CDC13): 6 nm) -137.6",(578nm) -147.3",(546 nm) -167.8",(436nm) 15.4,21.4,and 22.1 (CH3), 24.3,34.3,and 41.8(CHz), 29.2, -319.0",C39H40, m l e 508 (M+). MS (EI): m l e 508 [(M)+, 32.9, 38.6,and 43.9 (CH), 101.3,102.0,and 106.4(C cycloloo%], 370 [(M - CloH19)+ 96%]. 'H NMR (CDCl3) 6 0.18pentadienyl), 126.9-127.3 (C aromatic), 127.7-132.6 (CH 2.66(m, 19 H, menthyl), 4.50-5.29(m, 1H, cyclopentadienyl), aromatic). 6.7-7.9(m, 20 H, aromatic). 13CNMR (CDC13): 6 14.1-16.0,
(+)-Bis~-bromo)dibrom0bis[~~-l-neomenthyl-2,3,4,5tetraphenylcyclopentadienylldirhodium(3b). This was prepared from (q4-cycloocta-1,5-diene)[qs-l-((+)-neomenthyl)2,3,4,5-tetraphenylcyclo-pentadienyllrhodium (100 mg, 0.14 mmol) as a red powder in 75% yield using the procedure (-)-(~4-Cycloocta-l,5-diene)[~5-l-menthyl-2,3,4,5-tetdescribed above for the menthyl analogue. Mp: 230-234 "C. raphenylcyclopentadienyl]rhodium (2a). 1-(( -)-Menthyl)Anal. Calcd for C78H~~Br4Rhz: C, 60.8;H, 5.1; Br, 20.7. 2,3,4,5-tetraphenylcyclopenta-2,4-diene (210 mg, 0.4mmol) Found: C, 59.4;H, 5.5; Br, 20.1.[a](20"C, 1 = 0.1, c = 0.118, was dissolved in dry xylene (18 cm3) and heated t o 125 "C CHC13): (589nm) +99.3",(578nm) +36.1",(546nm) -54.2", under nitrogen. n-Butyllithium solution (2.5M in hexanes, (436nm) +2400.7". MS (+FAB argon):,mle 1461 [(M - Br)+, 0.84mmol) was added dropwise and the mixture stirred at 120-135 "C for 2 h. Bis~-chloro)bis(cycloocta-1,5-diene)- 57%], 1383 [(M - 2Br)+, 8%], 691 [(CpRhBr)+,16%1, and 609
20.9-22.8,26.5-28.3,32.6-33.2,40.4-43.6,and 61.3-62.6 (CWCH3 menthyl), 24.1-24.5,34.9-35.3, and 42.8-44.6(CH2 menthyl), 125.8-130.5(CH aromatic), 135.5-139.1,144.6147.8,and 151.5-152.3(C aromatic).
Organometallics,Vol. 14, No.5, 1995 2583
Chiral Tetraphenylcyclopentadienes
Table 4. CrystallographicData for Diffraction Studies of Rh(C&'h&*)(COD) Neomenthyl)
(2a, R* = Menthyl; 2b, R* =
2a
2b (A) Crystal Parameters
empirical formula mol wt color solvent cryst size, mm habit cryst syst space group a, A b, c,
A
v, A3
Z
D(calcd),g ~ m - ~ p , cm-l
F(OO0)
C47H51Rh.0.5C4HioO 755.89 yellow dichloromethane/pentane/diethylether 0.3 x 0.3 x 0.5 plates hexagonal P62(Cs4,NO.171) 27.034(78)
C47HsiRh 718.8 yellow dichloromethane/pentane 0.25 x 0.25 x 0.06 diamond plates orthorhombic P212121(DZ4,No. 19) 12.762(35) 17.953(39) 31.91(14) 7311(42) 8 1.306 4.89 3023.66
9.540(19) 6041(27) 6 1.246 4.48 2393.73
(B)Intensity Data diffractometer I ( M o & radiation), A monochromator rflns measured 28 range, deg temp, "C scan type scan range, deg bkgd measurement std rflns no. of rflns collected no. of rflns used acceptance criterion min transmissn coeff max transmissn coeff abs method method progams computer scattering factors R
Nicolet R3 4-circle 0.710 69 graphite, incident beam +h,+k,+l 3.5-50 20
Nicolet R3 4-circle 0.710 69 graphite, incident beam +h,+k,+l 3.5-48 20
w
w
2.0 50% of scan time 1check every 200 rflns, no decay cor necessary 7069 1267 IFVdIFI)> 4.0 0.699 0.792 empirical, I/J scans (5 rflns, 180 measurements) (C) Structure Solution PattersodFourier SHEIXTLa Data General Nova 3 ref 28 0.1349
2.0 50% of scan time 1 check every 200 rflns, no decay cor necessary 4071 2310 IFlIdlFI) > 3.0 0.867 0.942 empirical, q~scans (10 rflns, 360 measurements)
RV? weighting scheme H refinement
unit weights riding mode
I
.
I
PattersodFourier SHELXTL" Data General Nova 3 ref 28 0.0671 0.0491 w = [UZ(F) 0.0002F]-' riding mode
+
a Sheldrick, G. M. SHEIXTL: An integrated System for Solving, Refining and Displaying Crystal Structures and Diffraction Data; University of Gottingen, Gottingen, Germany, 1978; revision 4.1, Aug 1983.
[(CpRh)+, loo%]. lH NMR (CDC13): 6 0.7-2.3 (m, 36 H, menthyl), 3.3-3.5 (m, 2 H, menthyl), 7.0-8.9 (m, 40 H, aromatic).
BisOl-carbonyl)bis[qs-l-( (+)-neomenthyl)-2,3,4,54etraphenylcyclopentadienylldirhodium. Bis@chloro)bis(q4-cycloocta-l,5-diene)dirhodium(200 mg, 0.4 mmol), anhydrous sodium carbonate (200 mg, 2 mmol), and l-neomenthyl2,3,4,5-tetraphenylcyclopenta-2,4-diene(410 mg, 0.8 mmol) were heated under reflux together in methanol (20 cm3) for 66 h under nitrogen. Extensive decomposition in the mixture was apparent. After the mixture was cooled, a black solid was filtered off and then extracted into THF to give a pale blue solution. The solvent was removed in uacuo,and chromatography (alumina, petroleum ether bp 60-80 "C followed by ether) gave a blue glassy solid (20 mg, 4%). Ms (FAB): m l e 638 [(W2)+, 12%1, 608 [(W2 - CO)', loo%]. IR (KBr, cm-'1: ztco 1765. 13CNMR (CDCl3): 6 14.1,21.0,22.7,23.1,27.0, 30.2, 30.4, 37.0, 48.7, and 62.4 (CWCH3),26.3, 29.7, 35.3, and 42.3 (CH2), 125.5-131.2 and 135.8-151.1 (CH aromatic). The carbonyl and cyclopentadienyl nuclei were not visible. (+)-(q4-Cycloocta1,5-diene)(qs-neomenthylcyclopentadieny1)rhodium. A mixture of [Rh(CsH4neomen)I2]2(0.08 g, 0.071 mmol), cycloocta-1,5-diene (0.5 cm3, 4.15 mmol), and sodium carbonate (0.20 g, 1.89 mmol) in ethanol (95%) was heated under reflux for 1h. After the mixture was cooled t o room temperature, solvent was removed in uacuo and the
residue chromatographed (alumina, hexane) t o yield a yellow oil which solidified on standing (50 mg, 85%). Anal. Calcd for C23H35Rh: C, 66.7; H, 8.5. Found: C, 66.6; H, 8.5. lH N M R (CDC13): 6 0.71 (3 H, d, JHH7 Hz, CH3), 0.86 (3 H, d, J w 7 Hz, CH3), 0.90 (3 H, d, JHH7 Hz, CH3), 1.04-1.87 (8 H, m, CH2 and CH neomenthyl), 1.89 (4 H, m, COD CH2), 2.20 (4H, m, COD CHz), 2.37 (1 H, m, neomenthyl), 2.83 (1 H, m, neomenthyl), 3.88 (4H, m, COD CH), 4.10 (1 H, m), 4.98 (2 H, m), 5.22 (1H, m) [Cpl. Crystal Structure Determinations. Experimental details of X-ray data collection and solution and refinement of the structures are summarized in Table 4. Unfortunately, despite several attempts at growing crystals, only poor-quality crystals were obtained for the menthyl derivative 2a and this limited the accuracy of this structure. The data for 2a were corrected for Lorentz and polarization effects and for absorption by analysis of azimuthal scans. The positions of the rhodium atoms were determined by standard Patterson techniques and were found to be consistent with space group Pbca (of which P212121 is a subgroup). Initially, structure solution was continued in this higher symmetry space group, since the positions of the phenyl groups, and of the cycloocta-1,5-diene seemed also to be essentially consistent with it. At this stage, (28)International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, U.K., 1974; Vol. 4.
2584 Organometallics, Vol. 14, No. 5, 1995 the atoms of the chiral menthyl group were ill-defined, but an acceptable model was derived which accounted well for the electron density and showed disorder of the two optical isomers in different rotational conformations about the bond linking the group to the cyclopentadienyl ring. The geometries of the menthyl groups were idealized with only the isopropyl substituent given some rotational freedom. T h e space group symmetry was lowered to the non-centrosymmetric P212121, and two independent (COD)Rh(men-cp)fragments, each containing a menthyl of the correct chirality, were inserted. The omitted phenyl rings were redetermined from difference electron density syntheses: their positions were little changed. The overall structure still possessed approximate Pbca symmetry with the two crystallographically independent molecules approximately centrosymmetrically related, and correlation coefficients were very high. Sensible and controlled refinement could only be achieved after all phenyl groups had been given constrained Dsh symmetry and the geometries of the cyclopentadienyl ring and the cycloocta-1,5-dieneligands had also been restricted in terms of both bond lengths and angles. Refinement then proceeded by blocked-cascade least-squares methods. Hydrogen atoms were placed in predicted positions and refined in the riding mode, with isotropic thermal parameters related t o those of the supporting carbon atoms. Refine-
Ramsden et al. ment converged a t a final R = 0.1349 with allowance for coupled anisotropic thermal motion of rhodium atoms only and related isotropic thermal parameters for each pseudo-centrosymmetrically related pair of ligands. The crystal of 2b contained a disordered half-molecule of solvent, EtzO; the most successful model has this solvent disordered over three sets of positions.
Acknowledgment. We thank the SERC for a postgraduate studentship (to J.A.R.) and for the purchase of the diffractometer. Financial support from IC1 Specialties is gratefully acknowledged, and we are indebted to Dr. Alex F. Drake and colleagues at the SERC Chiroptical Spectroscopy service for recording the CD spectra. Supplementary Material Available: Tables of complete bond lengths and angles, thermal parameters, and hydrogen atom positional parameters for 2a and 2b and a table of leastsquares planes and interplanar angles for 2b (13 pages). Ordering information is given on any current masthead page. OM9406207
