Synthesis and Structural Characterization of New Perfluoroacyl and

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1948

Organometallics 2010, 29, 1948–1955 DOI: 10.1021/om1001183

Synthesis and Structural Characterization of New Perfluoroacyl and Perfluoroalkyl Group 6 Transition Metal Compounds Hui Huang,† Russell P. Hughes,*,† and Arnold L. Rheingold‡ †

Department of Chemistry, 6128 Burke Laboratories, Dartmouth College, Hanover, New Hampshire 03755, and ‡Department of Chemistry, University of California, San Diego, California 92093 Received February 12, 2010

A series of perfluoroacyl group 6 transition metal complexes Cp*M(CO)3[C(O)RF] and CpM(CO)3[C(O)RF] (M = Cr, Mo, W; RF = CF3, CF2CF3, CF2CF2CF3) have been synthesized by treatment of M(CO)6 with Cp*Li or CpNa in DME under reflux, followed by reaction with [RFC(O)]2O at -78 °C. The molecular structures of Cp*M(CO)3[C(O)CF3] (M = Cr, Mo, W) and Cp*Mo(CO)3[C(O)RF] (RF = CF2CF3, CF2CF2CF3) have been determined crystallographically. The chromium and molybdenum perfluoroacyl complexes were readily converted to the corresponding perfluoroalkyl complexes by heating under N2 in the solid state. The tungsten perfluoroacyl complexes were decarbonylated in refluxing toluene or xylene. The molecular structures of Cp*M(CO)3(CF3) (M = Cr and W) and Cp*Mo(CO)3(RF) (RF = CF2CF3, CF2CF2CF3) have been determined crystallographically. Structural comparisons within these compounds and with previously reported analogues are presented, allowing the first evaluations of the effect of the metal (M = Cr, Mo, W) on the M-CF3 parameters and the effect of fluoroalkyl chain length in Mo-RF (RF = CF3, CF2CF3, and CF2CF2CF3) to be made.

Introduction We have recently shown that inner-sphere reductions of CF3 and other perfluoroalkyl groups attached to iridium provide an excellent route to perfluorinated carbene ligands,1 which are important intermediates in the activation and functionalization of C-F bonds R to transition metals.2 Likewise the known trifluoromethyl-molybdenum complex 1a could also be reduced by two electrons to afford the simple complex 2, containing the first example of a terminal CF ligand; conversion of 2 to the μ3CF cluster compound 3 was also described.3 There are relatively few examples of perfluoroalkyl complexes of the group 6 metals, and with a view to the eventual synthesis of other relatives of compounds 2 and 3 we sought a general route to trifluoromethyl and perfluoroalkyl analogues of 1. Previously reported routes the preparation of CpM(CO)3(CF3) (M = Mo, W) from CpM(CO)3Cl by using Cd(CF3)2 as a CF3 transfer reagent:4 a similar route to CpM(NO)2(CF3) [M = Cr, Mo] has been described.5 However, we wished to avoid the use of toxic cadmium reagents and settled on the route described originally by King et al., who successfully prepared CpMo(CO)3(RF) (RF = CF3, C3F7) by decarbonylation of the perfluoroacyl *To whom correspondence should be addressed. E-mail: rph@ dartmouth.edu. (1) (a) Hughes, R. P.; Laritchev, R. B.; Yuan, J.; Golen, J. A.; Rucker, A. N.; Rheingold, A. L. J. Am. Chem. Soc. 2005, 127, 15020–15021. (b) Bourgeois, C. J.; Hughes, R. P.; Yuan, J.; DiPasquale, A. G.; Rheingold, A. L. Organometallics 2006, 25, 2908–2910. (c) Yuan, J.; Hughes, R. P.; Rheingold, A. L. Eur. J. Inorg. Chem. 2007, 4723–4725. (2) Hughes, R. P. Eur. J. Inorg. Chem. 2009, 31, 4591–4606. (3) Huang, H.; Hughes, R. P.; Landis, C. R.; Rheingold, A. L. J. Am. Chem. Soc. 2006, 128, 7454–7455. (4) Naumann, D.; Varbelow, H.-G. J. Fluorine Chem. 1988, 41, 415–419. (5) Loizou, D. C.; Castillo, J.; Oki, A. R.; Hosmane, N. S.; Morrison, J. A. Organometallics 1992, 11, 4189–4193. pubs.acs.org/Organometallics

Published on Web 03/19/2010

complexes CpMo(CO)3[C(O)RF];6 this route was also used by the Roddick group to prepare Cp*Mo(CO)3(CF3) analogue 1a,7 but does not appear to have been utilized previously to prepare perfluoroalkyl chromium and tungsten analogues.

Results and Discussion Perfluoroacyl complexes were prepared as shown in Scheme 1, by refluxing M(CO)6 4 (M = Cr, Mo, W) with 1 equiv of Cp*Li in DME overnight to make the nucleophilic anion [Cp*M(CO)3];; cooling this solution to -78 °C and addition of 1 equiv of anhydride RFC(O)OC(O)RF afforded the desired perfluoroacyl products 5-7; Cp analogues 8-10 were similarly prepared; 9 and 10 have been prepared previously by this route.6 With perfluoroacyl complexes in hand, attention was then focused on their decarbonylation reactions. Thermal decarbonylation of solid perfluoroacyl precursors under N2 worked well for chromium and molybdenum perfluoroacyl complexes 5, 6, 8, and 9, affording the corresponding perfluoroalkyl complexes 1, 11, 12, and 13. However, the tungsten analogues 7 and 10 were more stable thermally and more resistant to this method of decarbonylation than their Cr (6) King, R. B.; Bisnette, M. B. J. Organomet. Chem. 1964, 2, 15–37. (7) Koola, J. D.; Roddick, D. M. Organometallics 1991, 10, 591–597. r 2010 American Chemical Society

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Scheme 1

and Mo analogues;6,7 the perfluoroacyl complexes simply sublime unchanged without undergoing decarbonylation. The photochemical decarbonylation method described by King et al. for the synthesis of CpFe(CO)2(RF) from CpFe(CO)2[RFC(O)]6 was likewise unsuccessful for tungsten, affording only copious amounts of dark intractable precipitate. Encouraged by observations that that third row metal (Ir and Pt) CF3 compounds could be prepared by refluxing perfluoroacyl precursors in benzene,8 we found that when the tungsten perfluoroacyl complex 7 was refluxed in xylene for 2 days the corresponding CF3 compound 14 was obtained in reasonable yield of 67%. Use of toluene instead of xylene required longer times (5 days) and gave poorer yields (50%). Likewise the Cp analogue 15 was obtained from the decarbonylation of 10 in xylene with acceptable yield (57%). The perfluoroacyl and perfluoroalkyl compounds were air stable, with the Cr-CF3 compounds being air sensitive over long periods of exposure. They were characterized spectroscopically and crystallographically. No structures of perfluoroacyl compounds of group 6 appear in the Cambridge Structure Database.9 Our perfluoroacyl compounds all formed crystals suitable for X-ray structure determination; Figures 1-5 show ORTEP representations of the structures of 5a, 5b, 5c, 6, and 7, respectively. Selected bond lengths and angles are presented in Table 1, with corresponding data for the perfluoroalkyl complexes 1b, 1c, 11, and 14 and previously published data for 1a7 and CpMo(CO)3(C3F7) (16).10 Details of the crystallographic determinations of all compounds in this paper are presented in Table 2. The perfluoroacyl complexes 5a, 5b, 5c, 6, and 7 adopt the expected four-legged piano-stool structures or Cp*(Cp)capped square pyramids, with the acyl group essentially bisecting the angle between its flanking CO ligands and with its perfluoroalkyl substituent disposed distally to the Cp* ring. The series provides the opportunity to compare structural parameters for varying perfluoroacyl ligands, keeping the metal constant (Mo), and for various metal centers, keeping the perfluoroalkyl group constant (CF3). For fourlegged piano-stool structures of general type CpM(CO)3L it (8) (a) Bennett, M. A.; Chee, H.-K.; Robertson, G. B. Inorg. Chem. 1979, 18, 1061–1070. (b) Blake, D. M.; Shields, S.; Wyman, L. Inorg. Chem. 1974, 13, 1595–1600. (9) Cambridge Structural Database (CSD), http://www.ccdc.cam.ac. uk/, September 2009 update. (10) Churchill, M. R.; Fennessey, J. P. Inorg. Chem. 1967, 6, 1213– 1220.

Figure 1. ORTEP diagram of 5a with ellipsoids drawn at the 30% probability level. Hydrogen atoms are omitted for clarity. Selected bond lengths and angles are presented in Table 1. The compound sits on a crystallographic plane that includes Mo1, C8, and C9.

Figure 2. ORTEP diagram of 5b with ellipsoids drawn at the 30% probability level. Hydrogen atoms are omitted for clarity. Selected bond lengths and angles are presented in Table 1.

has been suggested that the trans angle, L-M-CO, is an important feature that is determined by the bonding characteristics of L in comparison to those of CO.11,12,7 The HOMO of complex CpM(CO)3L is stabilized by decreasing the trans angle for π-acceptor ligands and is also stabilized by increasing the trans angle for π-donor ligands.12 For example, the trans angle of CF3-Mo-CO in 1a [130.2(2)o] is larger than that of OC-Mo-CO [113.3(1)o], implying that CO is a better π-acceptor than CF3. In contrast, the trans angle of F2CdMo-CO in the cationic carbene complex [Cp*Mo(CO)3(CF2)]þ [115.6(5)o]7 is smaller than that of the corresponding OC-Mo-CO [138.9(5)o], implying that CF2 is a better π-acceptor ligand than CO. For our perfluoroacyl complexes 5a, 5b, 5c, and 7, the trans angles, L-M-CO (11) Kubacek, P.; Hoffmann, R.; Havlas, Z. Organometallics 1982, 1, 180–188. (12) Poli, R. Organometallics 1990, 9, 1892–1900.

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Figure 3. ORTEP diagram of 5c with ellipsoids drawn at the 30% probability level. Hydrogen atoms are omitted for clarity. Selected bond lengths and angles are presented in Table 1.

Figure 4. ORTEP diagram of 6 with ellipsoids drawn at the 30% probability level. Hydrogen atoms are omitted for clarity. Selected bond lengths and angles are presented in Table 1. The fluorines of the CF3 group are disordered.

and OC-M-CO, fall within the ranges 126129° and 112-121°, respectively, similar to the normal ranges observed for CpM(CO)3(L) (L-M-CO, 125-133°; OCM-CO, 105-117°).7,11,12 The chromium compound 6 is a notable exception, with a CF3C(O)-Cr-CO trans angle of 120.08(14)o, which is significantly smaller than the trans angle OC-Cr-CO [127.98(15)o]. It is possible that this may be a result of steric effects overcoming the natural trans angle preferences; in the case of the small chromium center, a “normal” trans angle in the 125-133° range would cause unfavorable repulsion between the acyl oxygen atom and the Cp* ring. In the perfluoroacyl molybdenum complexes 5a, 5b, and 5c containing different perfluoroalkyl chains, the MoC(O)RF distances of 2.216(3) A˚ (in 5a), 2.225(3) A˚ (in 5b), and 2.229(2) A˚ (in 5c), are essentially identical. Within experimental error the average Mo-CO distances are the same for 5a (2.004 A˚), 5b (2.006 A˚), and 5c (1.997 A˚), as are the Mo-Cp* centroid distances of 2.015 A˚ (5a), 2.005 A˚ (5b), and 2.007 A˚ (5c). Likewise, the average C-O distances for 5a

Huang et al.

Figure 5. ORTEP diagram of 7 with ellipsoids drawn at the 30% probability level. Hydrogen atoms are omitted for clarity. Selected bond lengths and angles are presented in Table 1. There are two molecules in the asymmetric unit, each of which sits on a crystallographic plane that includes W1, C8, and C9; in each molecule, the fluorines of the CF3 group are also disordered about this plane.

(1.141 A˚), 5b (1.142 A˚), and 5c (1.144 A˚) are the same, as are the C(RF)-O distances for 5a (1.212(3) A˚), 5b (1.204(4) A˚), and 5c (1.208(3) A˚). Clearly changing the RF chain length from CF3 through C2F5 to C3F7 does not change in any significant way the structural features of the molybdenum coordination sphere. The trifluoroacetyl complexes 5a, 6, and 7 allow comparisons within the group 6 triad. The M-CO(average) and M-Cp*(centroid) distances of 5a(Mo) [2.004(3), 2.015(3) A˚] and 7(W) [1.997(9), 1.980(10); 2.007(9), 1.996(10) A˚] are identical within experimental error and longer than those of 6(Cr) [1.866(3), 1.852(3) A˚]. The M-C(O)CF3 distances in 7(W) [2.173(12); 2.220(11) A˚] are significantly longer than that in 6(Cr) [2.104(2) A˚] and essentially identical to that in 5a(Mo) [2.216(3) A˚]. Similarly, the perfluoroalkyl compounds 1b, 1c, 11, and 14 were subjected to crystallographic analysis. ORTEP diagrams are provided in Figure 6-9. Details of the crystallographic analysis are presented in Table 2, and selected bond distances and angles are given in Table 1, along with previously determined parameters for 1a7 and 16.10 The conformational properties of the fluoroalkyl groups 1b and 1c are such that the R-CF2 group lies proximal to Cp*, with the additional RF group distal. Trans angles of the perfluoroalkyl complexes 1b, 1c, 11, and 14, L-M-CO and CO-MCO, fall within the ranges 128-131° and 112-122o, respectively, within the normal ranges for reported CpM(CO)3L (L-M-CO, 125-133o; CO-M-CO, 105-117°).7,11,12 For the series of fluoroalkyl homologues 1a-c, the MoCF3 distance in 1a (2.248(5) A˚)7 is slightly shorter than those in 1b (2.2640(13) A˚) and 1c (2.2717(19) A˚). The Mo-Cp* distances of 2.001 A˚ (in 1a), 1.997 A˚ (in 1b), and 1.993 A˚ (in 1c) are essentially identical. The structures of the series of trifluoromethyl complexes 11, 1a, and 14 allow comparison of CF3 ligands bound to Cr, Mo, and W, respectively. The Cr-CF3 distance in 11 (2.129(2) A˚) is slightly shorter than the W-CF3 distance in 14 (2.189(19) A˚), and each is shorter than that in the Mo analogue 1a (2.248(5) A˚). Some slight

131.94(1) 116.91(1) 130.1(5) 112.8(4) 129.23(7) 118.96(7) 128.83(5) 120.36(5) 130.2(2) 113.3(1)

128.97(8) 121.76(8)

1.115(10) 1.143(12) 1.141(2) 1.140(5)

1.285(20) 1.152(13) 1.202(15) 127.3(5) 118.5(4)

16

1.372(11)

2.189(19) 1.994(12) 2.003(19) 1.384(17)

14 11

2.129(2) 1.8714(18) 1.843(2) 1.374(2)

2.2717(19) 2.005(2) 1.993(2) 1.394(2) 1.347(2) 1.144(2)

1c 1b

2.2640(13) 2.0076(14) 1.997(14) 1.3937(15) 1.3386(17) 1.1405(17) 2.248(5) 1.998(4) 2.001(5) 1.363(6)

1.273(20) 1.137(13) 1.225(15) 127.4(4) 115.7(4) a

Two independent molecules in the asymmetric unit.

1.334(20) 1.139(4) 1.201(4) 120.08(14) 127.98(15) 1.350(3) 1.144(4) 1.208(3) 127.80(10) 115.13(11) 1.309(4) 1.142(4) 1.204(4) 124.35(12) 119.94(14) 1.307(4) 1.141(3) 1.212(3) 126.50(10) 113.51(10)

2.104(3) 1.866(3) 1.851(3) 2.229(2) 1.997(3) 2.007(3) 2.225(3) 2.006(4) 2.005(4) 2.216(3) 2.004(3) 2.015(3)

M-X M-CO (average) M-Cp0 (centroid) CR-F (average) Cβ-F (average) C-O (average) C(RF)-O X-M-C(O) C(O)-M-C(O)

5a

5b

5c

6

2.173(11) 1.997(9) 2.007(11)

7a

2.220(11) 1.980(10) 1.996(10)

1a

2.282(9) 2.000(9)

Organometallics, Vol. 29, No. 8, 2010 Table 1. Selected Bond Lengths (A˚) and Angles (deg) for Cp*M(CO)3(X) (5, M = Mo; X = C(O)CF3 (a), C(O)C2F5 (b), C(O)C3F7 (c); 6, M = Cr; X = C(O)CF3; 7, M = W; X = C(O)CF3;a 1, M = Mo; X = CF3 (a),7 C2F5 (b), C3F7 (c); 11, M = Cr; X = CF3; 14, M = W; X = CF3) and CpMo(CO)3(C3F7) (16)10

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relativistic shortening of the W-CF3 bond relative to MoCF3 might be expected,13 but the Cr-CF3 bond length is surprisingly close to the W-CF3 distance. A similar trend is observed in the trifluoroacetyl analogues (vide supra). This may be a result of the crowded steric environment around the small chromium atom; by way of comparison the Cr-CF3 distance in the significantly less crowded CpCr(NO)2(CF3) (2.057(7)A˚)5 is substantially shorter than that in 11. The average CR-F distances in 1a (1.363 A˚), 11 (1.374 A˚), and 14 (1.384 A˚) are basically identical. A comparison of Cp*Mo complex 1c and its Cp analogue 16 reveals no significant differences in metric parameters, with the Mo-C3F7 distance in 1c (2.2717(19) A˚) similar to that of 16 (2.282 A˚). M-CO (2.005 A˚), CR-F (1.374 A˚), and C-O (1.144 A˚) distances of 1c are the same as M-CO (2.000 A˚), CR-F (1.372 A˚), and C-O (1.115 A˚) distances of 16. Carbon-fluorine bonds R to a transition metal center are usually found to be longer than those further removed from the metal,14 an observation often interpreted in terms of a weakening of these bonds, perhaps via a mechanism involving the C-F σ*-antibonding orbitals acting as π-acceptors.15 For example, in 1b the average R-C-F bond distance (1.3937 A˚) is significantly longer than the average β-C-F bond distance (1.3386 A˚). But the π-acceptor properties of CF3 ligands have been shown to be rather weak,16 and a more mundane explanation of this significant bond lengthening may simply involve application of Bent’s rule.17 A C-F bond R to an electropositive metal competes more effectively for carbon p-character and therefore exhibits a longer bond length than does a C-F bond R to F or CF3. The infrared data for the perfluoroacyl and perfluoroalkyl complexes 1a-c, 5a-c, and 6-15 are shown in Table 3 along with corresponding data for acyl and alkyl complexes. Perfluoroacyl complexes, in general, have two strong bands at 1943-2045 cm-1 in hexane that correspond to the stretches of the three terminal CO ligands. There are two bands at around 1650 and 1680 cm-1, which belong to the acyl stretches in 6 and 8, probably indicative of two conformers in solution, as observed previously for iron-acyl analogues.18 Only one acyl stretch is observed for other perfluoroacyl complexes. The CO stretching frequencies for the perfluoroalkyl complexes are higher than those of the corresponding perfluoroacyl complexes, indicative of a stronger electron-withdrawing property for the perfluoroalkyl ligands. However there is no significant effect of perfluoroalkyl chain length on CO stretches in 1a-c. Not surprisingly the CO stretches of 11 (2031, 1966, 1942 cm-1) are at higher frequencies than those of its CH3 derivative 16 (1998, 1926, 1918 cm-1).19 (13) Pyykk€ o, P. Chem. Rev. 1988, 88, 563–594. (14) (a) Hughes, R. P.; Smith, J. M.; Liable-Sands, L. M.; Concolino, T. E.; Lam, K.-C.; Incarvito, C.; Rheingold, A. L. J. Chem. Soc., Dalton Trans. 2000, 873–879. (b) Hughes, R. P. Adv. Organomet. Chem. 1990, 31, 183–267. (15) (a) Cotton, F. A.; McCleverty, J. A. J. Organomet. Chem. 1965, 4, 490. (b) Cotton, F. A.; Wing, R. M. J. Organomet. Chem. 1967, 9, 511– 517. (16) (a) Leyssens, T.; Peeters, D.; Orpen, A. G.; Harvey, J. N. Organometallics 2007, 26, 2637–2645. (b) Huang, H.; Hurubeanu, N. R.; Bourgeois, C. J.; Cheah, S.-M.; Yuan, J.; Rheingold, A. L.; Hughes, R. P. Can. J. Chem. 2009, 87, 151-160. (17) Bent, H. A. J. Chem. Phys. 1960, 33, 304–305. (18) King, R. B.; Kapoor, R. N.; Pannell, K. H. J. Organomet. Chem. 1969, 20, 187–193. (19) Jaeger, T. J.; Baird, M. C. Organometallics 1988, 7, 2074–2076. (20) King, R. B.; Bisnette, M. B. J. Organomet. Chem. 1967, 8, 287– 297. (21) King, R. B.; Efraty, A.; Douglas, W. M. J. Organomet. Chem. 1973, 60, 125–137.

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Table 2. Summary of Crystallographic Data for 1b, 1c, 5a, 5b, 5c, 6, 7, 11, and 14

formula fw space group a, A˚ b, A˚ c, A˚ β, deg V, A˚3 Z D(calc), g cm-3 μ(Mo KR), mm-1 temp, K diffractometer radiation cryst size, mm F(000) measd reflns indep reflns R (F), % R (wF2), %

1b

1c

5a

C15H15CrF3O4 368.27 P2(1)/c 14.438(3) 8.2587(17) 14.853(3) 115.79(3) 1594.6(6) 4 1.534 0.764 208(2)

C15H15F3MoO4 412.21 P2(1)/m 8.4631(9) 10.9118(12) 8.8831(10) 98.415(2) 811.50(15) 2 1.687 0.854 173(2)

C16H15F5MoO4 462.22 P2(1) 8.300(3) 9.727(4) 11.258(5) 102.624(5) 887.0(6) 2 1.731 0.807 100(2)

0.20  0.05  0.05 752 10 279 3622 0.0758 0.1433

0.40  0.40  0.30 412 6816 1969 0.0236 0.0642

0.20  0.20  0.10 460 10 268 3917 0.0282 0.0616

5b

5c

6

C14H15C17H15C15H15F7MoO4 F3O4W CrF3O3 512.23 500.12 340.26 P2(1)/n Pmc2(1) Pna2(1) 8.7600(7) 11.4088 16.457(4) 16.0940(14) 8.4128(11) 9.668(2) 13.7820(12) 16.984(2) 8.982(2) 93.1230(10) 1940.1(3) 1630.1(4) 1429.2(6) 4 4 4 1.754 2.038 1.581 0.762 7.132 0.840 208(2) 208(2) 100(2) Bruker Smart Apex CCD Mo KR (0.71073 A˚) 0.15  0.10 0.30  0.30 0.30  0.30  0.10  0.30  0.30 1016 952 696 9633 11 612 9011 4478 3503 3188 0.0393 0.0267 0.0244 0.0766 0.0633 0.0591

7

11

14

C15H15F5MoO3 434.21 P2(1)/c 14.6162(8) 8.4293(5) 15.0114(8) 118.1610(10) 1630.54(16) 4 1.769 0.868 100(2)

C16H15F7MoO3 484.22 P2(1)/n 8.5750(6) 16.7549(12) 12.8756(10) 96.3550(10) 1838.5(2) 4 1.749 0.794 100(2)

C14H15F3O3W 472.11 Pna2(1) 16.913(6) 9.751(4) 9.135(3)

0.30  0.30  0.20 864 13 367 3661 0.0202 0.0539

0.25  0.20  0.15 960 15 622 4278 0.0292 0.0679

0.28  0.10  0.10 896 4756 2571 0.0437 0.0793

1506.5(10) 4 2.081 7.706 213(2)

Figure 6. ORTEP diagram of 1b with ellipsoids drawn at the 30% probability level. Hydrogen atoms are omitted for clarity. Selected bond lengths and angles are presented in Table 1.

Figure 7. ORTEP diagram of 1c with ellipsoids drawn at the 30% probability level. Hydrogen atoms are omitted for clarity. Selected bond lengths and angles are presented in Table 1.

The 1H and 19F data for these perfluoroacyl and perfluoroalkyl complexes are summarized in Table 4. The 19F resonance of the CF3 group in trifluoromethyl complexes is shifted significantly to low field compared to that in trifluoroacetyl precursors or the CF3 groups in longer perfluoroalkyl ligands. In the W-CF3 compounds 2JW-F coupling was observed to be 36 and 42 Hz for Cp*W(CO)3(CF3) and CpW(CO)3(CF3), respectively. Selected 13C{1H} NMR spectra are provided in the Experimental Section. With this series of perfluoroalkyl complexes in hand, synthesis and reactivity studies concerning their conversion to perfluoroalkylidyne complexes are in progress.

atmosphere of nitrogen, which was deoxygenated over BASF catalyst and dried over Aquasorb, or in an MBraun drybox. Methylene chloride, hexanes, diethyl ether, tetrahydrofuran, and toluene were dried over an alumina column under nitrogen.26 DME was refluxed over sodium-benzophenone ketyl and vacuum-distilled prior to use. NMR spectra were recorded on a Varian Unity Plus 300 or 500 FT spectrometer. 19F NMR spectra were referenced to external CFCl3 (0.00 ppm). Coupling constants are reported in units of Hz and are absolute values. IR spectra were recorded on a Perkin-Elmer FTIR 1600 Series spectrophotometer. Elemental analyses were performed by Schwartzkopf (Woodside, NY), and X-ray crystallographic analyses at the University of California, San Diego. Mo(CO)6, Cr(CO)6, W(CO)6 (Aldrich), Cp*H (Strem), DME (dimethoxyethane), and [RFC(O)]2O (RF = CF3, C2F5, C3F7) (Acros) are commercially available. Cp*Li and CpNa was prepared by following literature procedures.27

Experimental Section General Data. Air-sensitive reactions were performed in ovendried glassware, using standard Schlenk techniques, under an (22) King, R. B.; Efraty, A. J. Am. Chem. Soc. 1972, 94, 3773–3779. (23) Alt, H. G. J. Organomet. Chem. 1977, 124, 167–174. (24) Adeyemi, O. G.; Coville, N. J. Organometallics 2003, 22, 2284– 2290.

(25) Davison, A.; McCleverty, J. A.; Wilkinson, G. J. Chem. Soc. 1963, 1133–1138. (26) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.; Timmers, F. J. Organometallics 1996, 15, 1518–1520.

Article

Figure 8. ORTEP diagram of 11 with ellipsoids drawn at the 30% probability level. Hydrogen atoms are omitted for clarity. Selected bond lengths and angles are presented in Table 1. CpCr(CO)3[C(O)CF3] (8). Cr(CO)6 (880 mg, 4.00 mmol) and CpNa (352 mg, 4.00 mmol) were refluxed in DME (80 mL) overnight to give a yellow solution, which was cooled to -78 °C. CF3C(O)OC(O)CF3 (0.6 mL, 4.00 mmol) was added to the solution by syringe. The solution was allowed to react overnight and warmed to room temperature gradually to give a brown-red solution. The solvent was removed to give a brown-red solid, which was extracted with hexane (50 mL) to give a yellow solution, which was concentrated to smaller amount (20 mL) and allowed to stand at -30 °C overnight to give yellow crystalline needles (600 mg, 50%). Anal. Calcd for C10H5CrF3O4: C, 40.28; H, 1.69. Found: C, 40.26; H, 1.89. 1H NMR (C6D6, 300 MHz, 25 °C): δ 3.99 (15H, s, C5(CH3)5). 19F NMR (C6D6, 282 MHz, 25 °C): δ -76.8 (F, s, CF3). IR (hexane, cm-1): 2034 (s); 1964 (vs); 1688 (m); 1654 (m). Cp*Cr(CO)3[C(O)CF3] (6). Cr(CO)6 (110 mg, 0.500 mmol) and Cp*Li (71 mg, 0.50 mmol) were refluxed in DME (20 mL) under N2 for 2 days to give a green-yellow solution, which was cooled to -78 °C. CF3C(O)OC(O)CF3 (0.15 g, 0.10 mL, 0.50 mmol) was added into the solution by syringe. The solution was allowed to react overnight and allowed to warm to room temperature gradually to give a green-yellow solution. The solvent was then removed in vacuo to give a green-yellow solid, which was extracted with hexane (20 mL) to give a green-yellow solution. The solution was concentrated to 2 mL and cooled at -30 °C overnight to give yellow crystals (140 mg, 69%). Anal. Calcd for C15H15CrF3O4: C, 48.88; H, 4.11. Found: C, 48.51; H, 4.09. 1H NMR (C6D6, 300 MHz, 25 °C): δ 1.37 (15H, s, C5(CH3)5). 19F NMR (C6D6, 282 MHz, 25 °C): δ -77.19 (F, s, CF3). IR (hexane, cm-1): 1947 (vs); 2016 (s); 1683 (s); 1648 (s). Cp*Mo(CO)3[C(O)C2F5] (5b). Mo(CO)6 (690 mg, 2.60 mmol) and Cp*Li (360 mg, 2.60 mmol) were refluxed in DME (50 mL) overnight to give a yellow solution, which was cooled to -78 °C. C2F5C(O)OC(O)C2F5 (1.6 g, 1.0 mL, 5.1 mmol) was added into the solution by syringe. The solution was allowed to react overnight and warm to room temperature gradually to give a red solution. The solvent was removed to give a brown-red solid, which was extracted with hexane (50 mL, 3 times) to give a yellow solution. The solution was concentrated to 10 mL and cooled at -30 °C overnight to give brown-yellow crystals (900 mg, 69%). Anal. Calcd for C15H15F3MoO4: C, 41.22; H, 3.24. Found: C, 41.73; H, 3.24. 1H NMR (C6D6, 300 MHz, 25 °C): δ 1.47 (15H, s, C5(CH3)5). 19F NMR (C6D6, 282 MHz, 25 °C): δ (27) (a) Yang, D. S.; Bancroft, G. M.; Puddephatt, R. J.; Bursten, B. E.; McKee, S. D. Inorg. Chem. 1989, 28, 872–877. (b) Panda, T. K.; Gamer, M. T.; Roesky, P. W. Organometallics 2003, 22, 877–878.

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Figure 9. ORTEP diagram of 14 with ellipsoids drawn at the 30% probability level. Hydrogen atoms are omitted for clarity. Selected bond lengths and angles are presented in Table 1. -79.92 (F, s, CF3); -113.54 (F, s, CF2). IR (hexane, cm-1): 2031 (s), 1954 (vs), 1649 (m). Cp*Mo(CO)3[C(O)C3F7] (5c). Mo(CO)6 (792 mg, 3.00 mmol) and Cp*Li (423 mg, 3.00 mmol) were refluxed in DME (50 mL) for 1 day to give a dark brown solution, which was cooled to -78 °C. C3F7C(O)OC(O)C3F7 (2.46 g, 6.00 mmol) was added into the solution by syringe. The solution was allowed to react overnight and warm to room temperature gradually to give a red solution. The solvent was removed to give a brown-red solid, which was extracted with hexane (50 mL, 3 times) to give a yellow solution. The solution was removed to give a yellow solid (1.2 g, 78%). The solid was recrystallized from hexane at -30 °C to give yellow crystals suitable for X-ray diffraction. Anal. Calcd for C17H15F7MoO4: C, 39.86; H, 2.95. Found: C, 40.27; H, 3.39. 1H NMR (C6D6, 500 MHz, 25 °C): δ 1.46 (15H, s, C5(CH3)5). 19F NMR (C6D6, 470 MHz, 25 °C): δ -80.95 (F, t, 3JFF = 9 Hz, CF3); -110.21 (F, tq, 3JFF = 9 Hz, 3JFF = 3 Hz, γ-CF2); -125.93 (F, tt, J = 7 Hz, 3JFF = 3 Hz, β-CF2). IR (hexane, cm-1): 2031 (s), 1954 (vs), 1652 (m). Cp*W(CO)3[C(O)CF3] (7). W(CO)6 (528 mg, 1.50 mmol) and Cp*Li (213 mg, 1.50 mmol) were refluxed in DME (80 mL) for two days to give a dark brown solution, which was cooled to -78 °C. CF3C(O)OC(O)CF3 (930 mg, 3.00 mmol) was added into the solution by syringe. The solution was allowed to react overnight and warm to room temperature gradually to give a dark brown solution. The solvent was removed to give a dark brown solid, which was extracted by hexane (60 mL) to give a yellow solution. The solvent was removed to give a green-yellow solid (550 mg, 74%). It was chromatographed (neutral deactivated Al2O3) with a column (2 cm  6 cm) under N2 to give a yellow solution, which was eluted with mixture of hexane/ether, 1: 1. The solvent was removed to give yellow crystals (525 mg, 70%). The solid was recrystallized from hexane at -30 °C to give yellow crystals. Anal. Calcd for C15H15F3O4W: C, 36.02; H, 3.02. Found: C, 35.75; H, 3.02. 1H NMR (C6D6, 300 MHz, 25 °C): δ 1.55 (15H, s, C5(CH3)5). 19F NMR (C6D6, 282 MHz, 25 °C): δ -79.66 (F, s, CF3). IR (hexane, cm-1): 2028 (s); 1943 (vs); 1649 (m). CpCr(CO)3(CF3) (12). CpCr(CO)3[C(O)CF3] (300 mg, 1.00 mmol) was heated at 70 °C under N2 for 30 min. It melted first, then turned to a yellow solid. Crystallization from hexanes afforded yellow crystals (260 mg, 96%). Anal. Calcd for C9H5CrF3O3: C, 40.00; H, 1.85. Found: C, 40.26; H, 1.89. 1H NMR (C6D6, 300 MHz, 25 °C): δ 4.11 (15H, s, C5(CH3)5). 19F NMR (C6D6, 282 MHz, 25 °C): δ 13.85 (F, s, CF3). 13C{1H} NMR (C6D6, 126 M, 25 °C): δ 90.4 (5C, s, C5H5), 160.9 (C, q, 1JCF = 375 Hz, CF3), 237.6 (2C, q, 3JCF = 5 Hz, CO cis to CF3), 246.2

1954

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Table 3. Comparison of CO Stretching Frequencies of Perfluoroacyl and Perfluoroalkyl Complexes with Selected Hydrocarbon Analogues perfluoroacyl complexes

IR (hexane, cm-1)

acyl complexes

IR (hexane, cm-1)

perfluoroalkyl complexes

IR (hexane, cm-1)

CpMo(CO)3(CF3) 13

2031 (s), 1966 (vs), 1942 (s) 2040 (s), 1963 (s), 1948 (s) 2040 (s), 1966 (vs), 1944 (s) 2040 (s), 1966 (vs), 1943 (s) 2036 (s), 1950 (s), 1939 (s) 2047 (w); 1985 (vs); 1967 (s) 2053 (s), 1976 (vs)

CpW(CO)3(CF3) 15

2049 (vs), 1963 (s)

Cp*Cr(CO)3[C(O)CF3] 6

2016 (s), 1947 (vs), 1683 (m), 1648 (m)

Cp*Cr(CO)3(CF3) 11

Cp*Mo(CO)3[C(O)CF3] 5a

2031 (s), 1955 (vs), 1647 (s)

Cp*Mo(CO)3(CF3) 1a

Cp*Mo(CO)3[C(O)C2F5] 5b

2031 (s), 1954 (vs), 1649 (m)

Cp*Mo(CO)3(C2F5) 1b

Cp*Mo(CO)3[C(O)C3F7] 5c

2031 (s), 1954 (vs), 1652 (m)

Cp*Mo(CO)3(C3F7) 1c

Cp*W(CO)3[C(O)CF3] 7

2028 (s), 1943 (vs), 1649 (m)

CpCr(CO)3[C(O)CF3] 8

2034 (s); 1964 (vs); 1688 (m); 1654 (m).

CpMo(CO)3[C(O)CF3] 9

2045 (s), 1965 (s), 1653 (s)

CpW(CO)3[C(O)CF3] 10

2041 (s), 1959 (vs), 1646 (s)

Cp*W(CO)3[C(O)CH3]21 (cyclohexane)

2005 (s), 1912 (s), 1639 (m)

Cp*W(CO)3(CF3) 14 CpCr(CO)3(CF3) 12

CpMo(CO)3[C(O)CH3]24 (CH2Cl2)

2006 (s), 1946 (s), 1665 (s)

alkyl complexes

IR (hexane, cm-1) 1998 (s), 1926 (vs), 1918 (s) 2014 (s), 1929 (vs)

Cp*Cr(CO)3(CH3)19 17 Cp*Mo(CO)3(CH3)20 (cyclohexane)

Cp*W(CO)3(CH3)22

2013 (s), 1920 (vs)

CpCr(CO)3(CH3)23 (pentane)

2012 (s); 1938 (vs);

CpMo(CO)3(CH3)20 (cyclohexane) CpW(CO)3(CH3)25 (CH2Cl2)

2028 (s), 1944 (vs) 2019 (vs), 1924 (s)

Table 4. 1H and 19F NMR Data for Perfluoroacyl and Perfluoroalkyl Complexes perfluoroacyl complex

1

H NMR δ (C6D6)

19

1

F NMR δ (C6D6)

perfluoroalkyl complex Cp*Cr(CO)3(CF3) 11 Cp*Mo(CO)3(CF3) 1a Cp*Mo(CO)3(C2F5) 1b

1.41 1.65 1.53

Cp*Mo(CO)3(C3F7) 1c

1.50

Cp*W(CO)3(CF3) 14

1.61

CpCr(CO)3(CF3) 12 CpMo(CO)3(CF3) 13 CpW(CO)3(CF3) 15

4.11 4.50 4.49

Cp*Cr(CO)3[C(O)CF3] 6 Cp*Mo(CO)3[C(O)CF3] 5a Cp*Mo(CO)3[C(O)C2F5] 5b

1.37 1.47 1.47

Cp*Mo(CO)3[C(O)C3F7] 5c

1.46

Cp*W(CO)3[C(O)CF3] 7

1.55

-77.2 -80.0 -79.9 (CF3); -113.5 (CF2). -81.0 (CF3); -110.2 (R-CF2); -125.9 (β-CF2) -79.7

CpCr(CO)3[C(O)CF3] 8 CpMo(CO)3[C(O)CF3] 9 CpW(CO)3[C(O)CF3] 10

3.99 4.44 4.44

-76.8 -79.1 -78.6

(C, s, CO trans to CF3). IR (hexane, cm-1): 2047 (w); 1985 (vs); 1967 (s). CpW(CO)3(CF3) (15). A yellow xylene (60 mL) solution of CpW(CO)3[C(O)CF3] (300 mg, 0.698 mmol) was refluxed at 150 °C for 2 days to give a brown-yellow solution with blackbrown precipitate. 19F in situ NMR showed the reaction had finished. The solution was filtered, and the solvent was removed to give a brown solid, which was extracted with hexane (50 mL) to give a yellow solution. It was concentrated to a small amount and cooled at -30 °C to give yellow crystals (160 mg, 57%). 1H NMR (C6D6, 500 MHz, 25 °C): δ 4.49 (5H, s, C5H5). 19F NMR (C6D6, 470 MHz, 25 °C): δ 9.61 (3F, s, CF3). 13C NMR (C6D6, 126 MHz, 25 °C): δ 91.5 (5C, s, C5H5), 133.6 (C, q, 1JCF = 372 Hz, CF3), 217.5 (2C, q, 3JCF = 6 Hz, CO cis to CF3), 226.2 (C, s, CO trans to CF3). The data are similar to those previously reported.4 Cp*Cr(CO)3(CF3) (11). Cp*Cr(CO)3[(CO)CF3] (40 mg, 0.10 mmol) was heated at 80 °C under N2 for 1 h to give a yellow solid (31 mg, 90%). The solid was recrystallized from hexane at -30 °C to give yellow crystals. Anal. Calcd for C14H15CrF3O3: C, 49.42; H, 4.44. Found: C, 49.55; H, 4.44. 1H NMR (C6D6, 300 MHz, 25 °C): δ 1.41 (15H, s, C5(CH3)5). 19F NMR (C6D6, 282 MHz, 25 °C): δ 4.54 (F, s, CF3). 13C{1H} NMR (C6D6, 126 MHz, 25 °C): δ 9.47 (5C, s, C5(CH3)5), 103.8 (5C, s, C5(CH3)5), 162.8 (C, q, 1JCF = 375 Hz, CF3), 240.7 (2C, q, 3JCF = 5 Hz, CO), 249.8 (C, s, CO). IR (hexane, cm-1): 2031 (s); 1966 (vs); 1942 (s).

H NMR δ (C6D6)

19

F NMR δ (C6D6)

4.54 0.7 -79.1 (CF2); -82.3 (CF3) -75.8 (R-CF2); -78.3 (CF3); -113.2 (CF2) 0.22 (s, 2 JW(183)F = 36 Hz) 13.9 12.7 9.61 (s, 2 JW(183)F = 42 Hz)

Cp*Mo(CO)3(C2F5) (1b). Cp*Mo(CO)3[C(O)C2F5] (900 mg, 1.80 mmol) was heated at 80 °C for 6 h to give a dark brown solid, which was extracted with hexane (40 mL, 3 times) to give a yellow solution. The solvent was removed in vacuo to give a yellow solid, which was recrystallized from ether/hexane to give yellow crystals (700 mg, 90%). Anal. Calcd for C15H15F5MoO3: C, 41.49; H, 3.48. Found: C, 41.51; H, 3.74. 1H NMR (C6D6, 500 MHz, 25 °C): δ 1.53 (15H, s, C5(CH3)5). 19F NMR (C6D6, 470 MHz, 25 °C): δ -79.07 (F, s, CF2); -82.27 (F, s, CF3). 13C{1H} NMR (C6D6, 126 MHz, 25 °C): δ 10.18 (5C, s, C5(CH3)5), 107.45 (5C, s, C5(CH3)5), 124.0 (C, tq, 1JCF = 284 Hz, 2JCF = 31 Hz, CF3), 145.8 (C, qt, 1JCF = 301 Hz, 2JCF = 43 Hz, CF2), 232.74 (C, s, CO), 242.18 (2C, m, CO). IR (hexane, cm-1): 2040 (s); 1966 (vs); 1944 (s). Cp*Mo(CO)3(C3F7) (1c). Cp*Mo(CO)3[CO(C3F7)] (1.20 g, 2.34 mmol) was heated at 75 °C for 6 h to give a dark tan solid, which was chromatographed [neutral Al2O3 (deactivated), hexane/ether, 1:1] with a column (2 cm  6 cm) to give a yellow solution. The solvent was removed to give a yellow solid (900 mg, 79%). The solid was recrystallized in hexane at -30 °C to give yellow crystals. Anal. Calcd for C16H15F7MoO3: C, 39.69; H, 3.12. Found: C, 39.99; H, 3.12. 1H NMR (C6D6, 500 MHz, 25 °C): δ 1.50 (15H, s, C5(CH3)5). 19F NMR (C6D6, 470 MHz, 25 °C): δ -75.82 (F, q, 4JFF = 10 Hz, R-CF2); -78.34 (F, t, 4JFF = 11 Hz, CF3); -113.24 (F, s, β-CF2). 13C{1H} NMR (C6D6, 126 MHz, 25 °C): δ 10.2 (5C, s, C5(CH3)5), 107.4 (5C, s, C5(CH3)5), 112.1 (C, qt,

Article JCF = 264 Hz, 2JCF = 34 Hz, β-CF2), 120.1 (C, tq, 1JCF = 290 Hz, 2JCF = 39 Hz, CF3), 150.8 (C, tt, 1JCF = 308 Hz, 2JCF = 50 Hz, R-CF2), 232.9 (2C, m, CO), 242.5 (C, s, CO). IR (hexane, cm-1): 2040 (s); 1966 (vs); 1943 (s). Cp*W(CO)3(CF3) (14). 1. A yellow toluene (60 mL) solution of Cp*W(CO)3[C(O)CF3] (500 mg, 1.00 mmol) was refluxed for 5 days to give a brown-red solution with black-brown precipitate. 19F in situ NMR showed the reaction was 95% complete. The solvent was removed to give a brown solid, which was extracted with hexane (50 mL) to give a red solution. It was concentrated to a small amount and cooled at -30 °C to give yellow crystals (236 mg, 50%). 2. A yellow xylene (50 mL) solution of Cp*W(CO)3[C(O)CF3] (500 mg, 1.00 mmol) was refluxed for 2 days to give a brown-red solution with black-brown precipitate. 19F in situ NMR showed the reaction had finished. The solvent was removed to give a brown solid, which was extracted with hexane (50 mL) to give a 1

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brown-yellow solution. It was concentrated to a small amount and cooled at -30 °C to give yellow crystals (300 mg, 64%). 1 H NMR (C6D6, 500 MHz, 25 °C): δ 1.61 (15H, s, C5(CH3)5). 19 F NMR (C6D6, 470 MHz, 25 °C): δ 0.22 (F, s, d, 2JW-F = 36 Hz, CF3). 13C{1H} NMR (C6D6, 126 M, 25 °C): δ 10.31 (5C, s, C5(CH3)5), 105.8 (5C, s, C5(CH3)5), 136.5 (C, q, 1JCF = 354 Hz, CF3), 222.9 (2C, q, 3JCF = 6 Hz, CO cis to CF3), 230.6 (C, s, CO trans to CF3). IR (CH2Cl2, cm-1): 2032 (s); 1939 (vs); (hexane, cm-1): 2036 (s), 1950 (s), 1939 (s).

Acknowledgment. R.P.H. is grateful to the U.S. National Science Foundation for generous financial support. Supporting Information Available: Crystallographic information files (CIF) for all structures reported here. This material is available free of charge via the Internet at http://pubs.acs.org.