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Organometallics 2010, 29, 2332–2342 DOI: 10.1021/om100105p
C-C Bond Activation of a Cyclopropyl Phosphine: Isolation and Reactivity of a Tetrameric Rhodacyclobutane Adrian B. Chaplin and Andrew S. Weller* Inorganic Chemistry Laboratory, Department of Chemistry, University of Oxford, OX1 3QR Oxford, U.K. Received February 10, 2010
Reaction of the functionalized phosphine PtBu2CH2(C3H5) with [Rh(C8H14)2Cl]2 (C8H14 = ciscyclooctene) resulted in selective C-C bond activation of the cyclopropyl group and formation of a tetrameric rhodacyclobutane, [RhCl(κ3-PtBu2CH2CH(CH2)2)]4, which was characterized in the solid state by X-ray crystallography. This complex acts as a latent source of the [Rh(κ3-PtBu2CH2CH(CH2)2)]þ fragment, forming a range of new complexes by salt metathesis with NaCp, [RhCp(κ3-PtBu2CH2CH(CH2)2)], chloride abstraction in the presence of arenes, [Rh(η6-arene)(κ3-PtBu2CH2CH(CH2)2)][BArF4] [arene = C6H5F, C6H3Me3; ArF = 3,5-C6H3(CF3)2], or fragmentation by addition of phosphine ligands, trans-[RhCl(PR3)(κ3-PtBu2CH2CH(CH2)2)] (R = iBu, Cy). In contrast, reaction with carbon monoxide results in the reductive elimination of the tethered cyclopropane, demonstrating reversible C-C bond activation, and formation of cis-[RhCl(CO)2(PtBuCH2(C3H5))]. These complexes were characterized in solution by NMR spectroscopy and in the solid state by X-ray diffraction. Chloride abstraction from [RhCl(PiBu3)(κ3-PtBu2CH2CH(CH2)2)] resulted in the regioselective isomerization of the tethered cyclopropane to a terminal alkene, viz., the formally 14-electron complex [Rh(PiBu3)(κ3-PtBu2CH2CH2CHdCH2)][BArF4], notable for the presence of a strong agostic interaction with a phosphine i Bu substituent, apparent both from the solid-state structure and in solution by 1H NMR spectroscopy. Addition of hydrogen to this complex resulted in hydrogenation of the alkene and formation of [Rh(H)2(PiBu3)(PtBu2nBu)][BArF4]. These steps overall correspond to selective C-C bond functionalization (hydrogenation) of the tethered cyclopropane and are of direct significance to a related catalytic process [J. Am. Chem. Soc. 2003, 125, 886] and, more generally, to the rhodium-mediated transformation of alkanes.
Introduction The transition-metal-mediated cleavage and subsequent fuctionalization of C-C single bonds is an area of significant contemporary interest.1 The selective activation of these traditionally unreactive bonds is a challenging aspect of organometallic chemistry owing to, in general, unfavorable kinetics and thermodynamics for oxidative addition and competing C-H activation processes.1 In spite of these limitations considerable progress has been made by use of substrates containing intrinsically strained C-C bonds (e.g., cyclopropanes and cyclobutanes), with the relief of ring strain and orbital directionality promoting oxidative addition, or by tight chelation control.1,2 Rhodium phosphine catalysts feature prominently in these processes and have been used for a wide range of transformations, including *Corresponding author. E-mail:
[email protected]. (1) (a) Jun, C.-H. Chem. Soc. Rev. 2004, 33, 610. (b) Rybtchinski, B.; Milstein, D. Angew. Chem., Int. Ed. 1999, 38, 870. (2) (a) Park, Y. J.; Park, J.-W.; Jun, C.-H. Acc. Chem. Res. 2008, 41, 222. (b) Perthuisot, C.; Edelbach, B. L.; Zubris, D. L.; Simhai, N.; Iverson, C. N.; M€ uller, C.; Satoh, T.; Jones, W. D. J. Mol. Catal. A 2002, 189, 157. (c) Jones, W. D. Nature 1993, 364, 676. (3) (a) Murakami, M.; Amii, H.; Shigeto, K.; Ito, Y. J. Am. Chem. Soc. 1996, 118, 8285. (b) Murakami, M.; Amil, H.; Ito, Y. Nature 1994, 370, 540. (4) Bart, S. C.; Chirik, P. J. J. Am. Chem. Soc. 2003, 125, 886. pubs.acs.org/Organometallics
Published on Web 04/23/2010
hydrogenolysis,3,4 ring-opening,4,5 ring expansion,6 alkene carboacylation,7 lactone formation,8 and C-C bond coupling with alkenes and alkynes.9 A notable recent highlight is the development of enantioselective ring expansion processes based on successive rhodium-mediated C-C and C-H bond activation.10 Key intermediates in the ring-opening of cyclopropanes are metallacyclobutanes, compounds further notable for their relevance to olefin metathesis.11 Metallacyclobutanes (5) (a) Simaan, S.; Goldberg, A. F. G.; Rosset, S.; Marek, I. Chem.; Eur. J. 2010, 16, 774. (b) Matsuda, T.; Makino, M.; Murakami, M. Org. Lett. 2004, 6, 1257. (6) (a) Crepin, D.; Dawick, J.; Aı¨ ssa, C. Angew. Chem., Int. Ed. 2010, 49, 620. (b) Hayashi, M.; Ohmatsu, T.; Meng, Y.-P.; Saigo, K. Angew. Chem., Int. Ed. 1998, 37, 837. (7) (a) Dreis, A. M.; Douglas, C. J. J. Am. Chem. Soc. 2009, 131, 412. (b) Murakami, M.; Itahashi, T.; Ito, Y. J. Am. Chem. Soc. 2002, 124, 13976. (8) (a) Matsuda, T.; Shigeno, M.; Murakami, M. J. Am. Chem. Soc. 2007, 129, 12086. (b) Murakami, M.; Tsuruta, T.; Ito, Y. Angew. Chem., Int. Ed. 2000, 39, 2484. (9) Iverson, C. N.; Jones, W. D. Organometallics 2001, 20, 5745. (10) (a) Winter, C.; Krause, N. Angew. Chem., Int. Ed. 2009, 48, 2460. (b) Seiser, T.; Cramer, N. Angew. Chem., Int. Ed. 2008, 47, 9294. (11) (a) Hoveyda, A. H.; Zhugralin, A. R. Nature 2007, 450, 243. (b) van der Eide, E. F.; Romero, P. E.; Piers, W. E. J. Am. Chem. Soc. 2008, 130, 4485. (c) Romero, P. E.; Piers, W. E. J. Am. Chem. Soc. 2007, 129, 1698. (d) Wenzel, A. G.; Grubbs, R. H. J. Am. Chem. Soc. 2006, 128, 16048. (e) Romero, P. E.; Piers, W. E. J. Am. Chem. Soc. 2005, 127, 5032. r 2010 American Chemical Society
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Organometallics, Vol. 29, No. 10, 2010 Chart 1
of transition metals are well established;12 platinacyclobutanes, in particular, constitute a well-known class since the first preparation in 1955 by Tipper of the tetrameric platinum(IV) metallacyclobutane [PtCl2(C3H6)]4 (A, Chart 1) from reaction of cyclopropane with H2[PtCl6].13 Wellcharacterized examples of rhodacyclobutanes, however, are comparatively rare. This is surprising, given both the isoelectronic relationship between Rh(III) and Pt(IV) and their important role as intermediates in C-C bond activation. A pertinent rhodium example is the metallacyclobutane B, prepared from reaction between the latent [RhCp*(PMe3)] fragment and cyclopropane at low temperature.14 A range of related rhodium cylcopentadienyl complexes are also known.15 The [RhCp*(PMe3)] fragment has, in addition, been shown to undergo insertion into the C-C bonds of cyclobutane and biphenylene.14a,16 Other notable, well-characterized rhodacyclobutane examples include the hydridotris(pyrazolyl)borate complex C,17 formed by rearrangement of a hydrido-cyclopropyl precursor, and the cationic rhodium phosphine complexes D.18 The latter are significant not only for the adoption of metallacyclobutane rings, but for additional stabilizing σ-C-C bonding interactions between the rhodium centers and adjacent cyclopropane groups of the coordinated BINOR-S ligands. These bonding interactions in D are found to be in rapid equilibrium at room temperature, demonstrating reversible C-C bond activation in solution, (12) (a) Jennings, P. W.; Johnson, L. J. Chem. Rev. 1994, 94, 2241. (b) Chappell, S. D.; Cole-Hamilton, D. J. Polyhedron 1982, 1, 739. (c) Puddephatt, R. J. Coord. Chem. Rev. 1980, 33, 149. (13) (a) Binns, S. E.; Cragg, R. H.; Gillard, R. D.; Heaton, B. T.; Pilbrow, M. F. J. Chem. Soc. A 1969, 1227. (b) Tipper, C. F. H. J. Chem. Soc. 1955, 2045. (14) (a) Periana, R. A.; Bergman, R. G. J. Am. Chem. Soc. 1986, 108, 7346. (b) Periana, R. A.; Bergman, R. G. J. Am. Chem. Soc. 1984, 106, 7272. (15) (a) Tjaden, E. B.; Stryker, J. M. Organometallics 1992, 11, 16. (b) Tjaden, E. B.; Stryker, J. M. J. Am. Chem. Soc. 1990, 112, 6420. (c) Andreucci, L.; Diversi, P.; Ingrosso, G.; Lucherini, A.; Marchatti, F.; Adovasio, V.; Nardelli, M. J. Chem. Soc., Dalton Trans. 1986, 477. (16) Perthuisot, C.; Jones, W. D. J. Am. Chem. Soc. 1994, 116, 3647. (17) Wick, D. D.; Northcutt, T. O.; Lachicotte, R. J.; Jones, W. D. Organometallics 1998, 17, 4484. (18) (a) Brayshaw, S. K.; Sceats, E. L.; Green, J. C.; Weller, A. S. Proc. Natl. Acad. Sci. 2007, 104, 6921. (b) Brayshaw, S. K.; Green, J. C.; Kociok-K€ ohn, G.; Sceats, E. L.; Weller, A. S. Angew. Chem., Int. Ed. 2006, 45, 452. (19) (a) Chaplin, A. B.; Weller, A. S. Angew. Chem., Int. Ed. 2010, 49, 581. (b) Chaplin, A. B.; Poblador-Bahamonde, A. I.; Sparkes, H. A.; Howard, J. A. K.; Macgregor, S. A.; Weller, A. S. Chem. Commun. 2009, 244.
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Scheme 1. Preparation of 1
while addition of Lewis bases results in irreversible reductive C-C bond elimination.18b,19 Similar σ-C-C bonding intermediates have been observed in solution during intramolecular C-C bond activation in rhodium and platinum systems.20 The presence of σ-C-C bonding interactions in cyclopropyl niobium complexes has also been discussed.21 As part of our investigations into C-C bond activation by rhodium phosphine compounds,18 we targeted the synthesis of rhodium complexes containing the cyclopropyl phosphine PtBu2CH2(C3H5)22 in an attempt to recreate the bonding modes observed in D. The synthesis and characterization of a tetrameric rhodacyclobutane, [RhCl(κ3-PtBu2CH2CH(CH2)2)]4 (1), resulting from C-C bond activation, is described along with related mononuclear derivatives. We also demonstrate the reversibility of this C-C bond cleavage, by reaction with CO, and isomerization of the metallacylobutane group to give a terminal alkene, which can be subsequently hydrogenated within the coordination sphere of the metal. Previous complexes containing PtBu2CH2(C3H5), and activated derivatives, have been described by Ibers, although limited to platinum,22 palladium,23 and iridium examples.24
Results and Discussion Reaction of the dimeric rhodium precursor [Rh(C8H14)2Cl]2 (C8H14 = cis-cyclooctene) with PtBu2CH2(C3H5) in pentaneheptane at 80 C resulted in the precipitation of a yellow microcrystalline solid, characterized as the tetrameric rhodacyclobutane [RhCl(κ3-PtBu2CH2CH(CH2)2)]4 (1, Scheme 1), in high yield (79%). Complex 1 could also be prepared at room temperature in pentane, but required long reaction times (ca. days) due to insolubility of the starting material. Formation of this complex is notable for the selective C-C bond activation of the tethered cyclopropane group, with ring-opening occurring at the least substituted position. Similar selective C-C bond activation of cyclopropanes has been demonstrated by Bergman by reaction of 1,1-dimethylcyclopropane with the [RhCp*(PMe3)] fragment.14a (20) (a) Madison, B. L.; Thyme, S. B.; Keene, S.; Williams, B. S. J. Am. Chem. Soc. 2007, 129, 9538. (b) Gandelman, M.; Vigalok, A.; Konstantinovski, L.; MIlstein, D. J. Am. Chem. Soc. 2000, 122, 9848. (21) (a) Boulho, C.; Keys, T.; Coppel, Y.; Vendier, L.; Etienne, M.; Locati, A.; Bessac, F.; Maseras, F.; Pantazis, D. A.; McGrady, J. E. Organometallics 2009, 28, 940. (b) Jaffart, J.; Cole, M. L.; Etienne, M.; Reinhold, M.; McGrady, J. E.; Maseras, F. Dalton Trans. 2003, 4057. (22) Youngs, W. J.; Ibers, J. A. Organometallics 1983, 2, 979. (23) Youngs, W. J.; Mahood, J.; Simms, B. L.; Swepston, P. N.; Ibers, J. A.; Maoyu, S.; Jinling, H.; Jiaxi, L. Organometallics 1983, 2, 917. (24) (a) Youngs, W. J.; Simms, B. L.; Ibers, J. A. J. Organomet. Chem. 1984, 272, 295. (b) Youngs, W. J.; Ibers, J. A. J. Am. Chem. Soc. 1983, 105, 639.
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Organometallics, Vol. 29, No. 10, 2010
Chaplin and Weller Table 1. Selected Bond Lengths (A˚) and Angles (deg) for 1a parameter (about Rh1)
Rh1
Rh2
Rh3
Rh4
Rh1-P1 Rh1-Cl1 Rh1-Cl2 Rh1-Cl4 Rh1-C3 Rh1-C4 C3 3 3 3 C4 P1-Rh1-Cl1 P1-Rh1-Cg(C3,C4) Cl1-Rh1-Cl2 Cl1-Rh1-Cl4 Cl2-Rh1-Cl4 C3-Rh1-C4 Rh1-P1-C1 P1-C1-C2 C3-C2-C4
2.2591(12) 2.4814(11) 2.6324(10) 2.6132(11) 2.078(4) 2.078(5) 2.261(7) 169.16(4) 80.26(11) 80.82(3) 86.70(3) 78.14(3) 65.91(8) 98.3(2) 102.3(3) 95.4(3)
2.2578(12) 2.4921(10) 2.613(5) 2.6205(11) 2.084(5) 2.056(4) 2.219(7) 170.23(4) 80.24(13) 80.51(3) 84.36(3) 78.53(3) 64.8(2) 98.3(2) 102.3(3) 94.6(4)
2.2609(11) 2.4877(10) 2.6327(10) 2.5917(11) 2.086(5) 2.076(4) 2.231(7) 169.23(4) 80.05(13) 79.82(3) 85.05(3) 78.82(3) 64.8(2) 98.0(2) 102.5(3) 95.2(4)
2.2640(12) 2.5079(11) 2.6243(11) 2.6271(10) 2.079(5) 2.067(4) 2.230(7) 169.44(4) 80.24(11) 80.53(4) 85.86(3) 77.50(3) 65.1(2) 97.9(2) 103.1(3) 94.1(4)
a
Figure 1. Solid-state structure of 1. Thermal ellipsoids are drawn at 50%; phosphine ligands are colored individually, and H atoms are omitted for clarity.
The solid-state structure of 1 is shown in Figure 1 and establishes the presence of four rhodium atoms, each bearing a chelating phosphine ligand bound through the phosphorus center and metalation of the tethered cyclopropane group (by C-C bond cleavage). The chelate bite angle of ca. 80 [P-Rh-Cg(Rh-C,Rh-C), Cg = centroid] is comparable to dppe (78).25 The metallacyclobutane rings are evident from short Rh-C bonds [2.056(4)-2.086(5) A˚] and elongated Rh(C 3 3 3 C) distances [2.219(7)-2.261(7) A˚] (Table 1). These parameters are in line with those of B-D, in which the values of Rh-C and Rh(C 3 3 3 C) are in the ranges 2.03-2.11 and 2.21-2.42 A˚, respectively.14,17,18 The four rhodium phosphine fragments are linked by bridging chloride ligands, in a similar manner to that suggested for Tipper’s tetrameric platinacyclobutane A,26 resulting in a distorted (noncrystallography imposed) S4 symmetrical framework. Long Rh 3 3 3 Rh distances (>3.6 A˚) rule out metal-metal bonding. The Rh-Cl bonds trans to metallacyclobutane rings are significantly lengthened in comparison to those trans to the coordinated phosphine group, as expected on the basis of the relative trans influences of these ligands [2.5917(11)-2.6327(10) vs 2.4814(11)-2.5079(11) A˚]. Closely related compounds to 1 include [RhCl(η4-C11H8F6)]4,27 [RhF(η2-C2H4)(η2-C2F4)]4,28 (25) van Leeuwen, P. W. N. M.; Kamer, P. C. J.; Reek, J. N. H.; Dierkes, P. Chem. Rev. 2000, 100, 2741. (26) The structure of A is supported by comparison to the platinium(IV) tetramer [PtMe3Cl]4, which has been characterised in the solid state by X-ray diffraction (Rundle, R. E.; Sturdivant, J. H. J. Am. Chem. Soc. 1947, 69, 1561). (27) The organic fragment in this complex results from the Diels-Alder addition of hexafluorobut-2-yne to norbornadiene and binds through coordination of an alkene and adoption of a metallocyclobutane ring (Evans, J. A.; Kemmitt, R. D. W.; Kimura, B. Y.; Russell, D. R. J. Chem. Soc., Chem. Commun. 1972, 509). (28) Burch, R. R.; Harlow, R. L.; Ittel, S. D. Organometallics 1987, 6, 982. (29) Herberich, G. E.; Eckenrath, H. J.; Englert, U. Organometallics 1997, 16, 4292. (30) Hodson, B. E.; Ellis, D.; McGrath, T. D.; Monaghan, J. J.; Rosair, G. M.; Welch, A. J. Angew. Chem., Int. Ed. 2001, 40, 715. (31) Fagan, P. J.; Mahoney, W. S.; Calabrese, J. C.; Williams, I. D. Organometallics 1990, 9, 1843.
Parameters grouped by metal center.
[RhI(η5-C4H4BR)]4 (R = Me, Ph),29 [Rh(η5-Ph2C2B9H9)(OH)]4,30 and [RuCp*Cl]4.31 The structure of 1 observed in the solid state appears to be retained in solution. The 31P{1H} NMR spectrum exhibits a single resonance at 113.1 ppm, which shows coupling to 103 Rh (1JRhP = 206 Hz), at significantly lower field than free ligand (28.5 ppm), consistent with chelation of the phosphine.32 Two environments, C3 and C4 (see Scheme 1 for NMR labeling), are observed for the coordinated carbon centers by 13C{1H} NMR spectroscopy, consistent with the S4 symmetry observed in the solid state. These resonances are shifted downfield from the free ligand (10.7, 12.1 ppm vs 7.2 ppm), and both show large coupling to 103Rh of ca. 20 Hz, confirming that they remain bound in solution. A downfield shift of similar magnitude is observed for the coordinated carbon resonances in D [R = iPr; 25.30 ppm (1JRhP = 22 Hz, 200 K) vs free ligand 16.9 ppm].18 For comparison, the corresponding signals in B [-22.9 ppm (1JRhC = 19 Hz)]14 and C [-16.4 ppm (1JRhC = 16 Hz)]17 are significantly upfield shifted from cyclopropane (-2.8 ppm), in accordance with trends observed for other metallacyclobutanes.12 The pseudoS4 symmetry seen in the solid-state structure of 1 is not apparent within resolution limits (500 MHz NMR spectrometer) for the H1 and tBu group resonances, which are observed as a single set of peaks by 1H and 13C{1H} NMR spectroscopy. An interesting feature to note for 1 is the large magnitude of the 3JPH coupling constant associated with H2 (66.5 Hz), presumably resulting from the enforced anti-conformation of H2 with the phosphorus center (av P-C1-C2-H2 dihedral =179.51) on formation of the chelate.32 Similar large coupling constants are observed for the new compounds described below, and the magnitude of this coupling correlates with the P-C1-C2-H2 dihedral angle, as measured in the solid state (Table 2). Complex 1 readily reacts in solution with a range of ligands (Cp-, C6H5F, C6H3Me3, PR3, CO), resulting in new complexes 2-5. These reactions are summarized in Scheme 2 and discussed in turn. Selected solution and solid-state data are compiled in Table 2. Reaction of 1 with a slight excess of NaCp in CH2Cl2 at room temperature resulted in the quantitative formation, by NMR spectroscopy, of the mononuclear cyclopentadienyl rhodacylobutane [RhCp(κ3-PtBu2CH2CH(CH2)2)] (2, Scheme 2). Complex 2 is an analogue of B and the closely related cyclopendienyl (32) Nelson, J. H. Nuclear Magnetic Resonance Spectroscopy; Pretence Hall: Upper Saddle River, NJ, 2003.
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Table 2. Selected Solution and Solid-State Data for 1-5a ligand 1 2 3a 3b 4a 4b 5
Cp C6H5F C6H3Me3 PiBu3 PCy3 CO
Rh(C3 3 3 3 C3)b/A˚
δ(H2)
2.219(7)-2.261(7) 2.249(10) 2.220(4) 2.213(6) -f 2.147(3) 1.483(5) 1.496(4)
3
JPH/Hz
2.76 3.77 3.10 3.38 3.38 3.27
66.5 55.6 66.7 64.4 56.5 58.7
0.88
-e
— DHc/deg d
179.51 178.38 179.87 179.08 -f 178.39 19.91 37.09
δ(C3) 10.7, 12.1 -0.9 10.2 12.8 -2.3 -2.1 8.9
1
0
JRhC/Hz
Δδ(H3, H3 )
δ(P)
20, 20 21 18 19 19 19
0.22, 0.64 0.47 -e 0.32 0.66 0.42
113.1 124.9 133.2 125.2 83.4 83.8
-
0.13
1
JRhP/Hz 206 196 194 194 129 132
58.1
127 4
NMR data recorded in C6D6 for 1, 2, 4, and 5; CD2Cl2 for 3. Refer to Schemes 1 and 2 for NMR labeling. For simplicity, data for H /C4 are combined with H3/C3 for 1. b Rh(C3 3 3 3 C4) for 1. c P-C1-C2-H2 dihedral angle measured in the solid state; H atoms in calculated positions. d Average value. e Not resolved ( 2σ(I)] wR2 [all data] GoF largest diff pk and hole [e A˚-3]
6595.36(11) 4 1.364 1.269 5.10 e θ e 26.37 25 221 0.0348 99.2% 13 376/0/565 0.0419 0.1202 1.070 1.089, -0.635
117.4577(5)
C48H100Cl4P4Rh4 1354.60 monoclinic P21/n 150(2) 24.6572(2) 11.80470(10) 25.5355(3)
1 C17H30PRh 368.29 triclinic P1 150(2) 8.8535(4) 10.5003(3) 12.5616(5) 66.733(2) 77.515(2) 89.703(2) 1043.25(7) 2 1.172 0.885 6.05 e θ e 25.02 11 080 0.0997 97.6% 3605/348/232 0.0775 0.2107 1.074 3.852, -1.179
2 C56H47BF26PRh 1358.63 triclinic P1 150(2) 13.8260(2) 13.8699(2) 15.2739(2) 76.8020(6) 88.5491(6) 79.7626(5) 2805.89(7) 2 1.608 0.458 5.11 e θ e 26.37 20 573 0.0199 99.1% 11 374/248/843 0.0396 0.1044 1.045 0.665, -0.669
3a C53H49BF24PRh 1286.61 triclinic P1 150(2) 13.0562(2) 14.1458(2) 16.8350(3) 71.5803(6) 67.3737(7) 83.7345(7) 2722.65(7) 2 1.569 0.462 5.12 e θ e 26.37 18 942 0.0322 98.9% 11 030/516/842 0.0456 0.1227 1.023 0.817, -0.646
3b
Table 3. Crystallographic Data for 1-6
6907.1(2) 8 1.300 0.690 5.13 e θ e 26.37 13 500 0.0294 99.2% 7003/30/367 0.0314 0.0685 1.029 0.449, -0.536
92.2748(5)
C33H60ClFP2Rh 676.11 monoclinic C2/c 150(2) 20.1059(2) 13.0009(2) 26.4447(4)
4b
3466.19(10) 8 (Z’ = 2) 1.513 1.228 3.09 e θ e 25.34 15 338 0.0291 97.8% 6193/0/355 0.0280 0.0601 1.080 0.581, -0.412
101.6478(5)
C14H25ClO2PRh 394.67 monoclinic P21/c 150(2) 30.0493(4) 8.12980(10) 14.4869(3)
5
6143.54(9) 4 1.480 0.439 5.11 e θ e 26.37 22 176 0.0218 99.0% 12 428/973/1018 0.0486 0.1220 1.014 0.774, -0.529
95.2368(4)
C56H64BF24P2Rh 1368.73 monoclinic P21/n 150(2) 12.66040(10) 24.8159(2) 19.6362(2)
6
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Organometallics, Vol. 29, No. 10, 2010
t
Bu{C}), 30.5 (d, 2JPC = 4, tBu{Me}), 24.2 (d, 1JPC = 20, C1), 9.3 (d, 2JPC = 2, C2), 8.9 (d, 3JPC = 6, C3). 31P{1H} NMR (C6D6, 202 MHz): δ 58.1 (d, 1JRhP = 127). IR (heptane, cm-1): ν(CO) 2089 (s), 1993 (s). Anal. Calcd for C14H25ClO2PRh (394.68 g mol-1): C, 42.60; H, 6.38. Found: C, 42.66; H, 6.35. Additional Experiments. Reaction of 3a with [Ph3PNPPh3]Cl. To a J Young NMR tube charged with 3a (0.0100 g, 0.008 mmol) and [Ph3PNPPh3]Cl (0.0046 g, 0.0008 mmol) was added C6H5F (0.4 mL). The resulting solution was immediately analyzed by 1H and 31P NMR spectroscopy and indicated quantitative formation of 1. Reaction of 1 with PtBu2CH2(C3H5). To a solution of 1 (0.005 g, 0.0037 mmol) in CD2Cl2 (0.4 mL) was added a pentane solution of PtBu2CH2(C3H5) (0.070 mL, 0.274 M, 0.019 mmol). The solution was monitored by 31P NMR spectroscopy at room temperature (293 K), which indicated the formation of an equilibrium mixture of 1:4c:PtBu2CH2(C3H5) in the ratio 1:18:10, corresponding to an equilibrium constant of 10.5. 31P{1H} NMR (CD2Cl2, 202 MHz): δ 82.1 [dd, 2JPP = 375, 1JRhP = 130, 1P, PtBu2CH2CH(CH2)2], 45.6 [dd, 2JPP = 375, 1JRhP = 126, 1P, PtBu2CH2(C3H5)]. Crystallography. Relevant details about the structure refinements are given in Table 3. Data were collected on an Enraf Nonius Kappa CCD diffractometer using graphite-monochromated Mo KR radiation (λ = 0.71073 A˚) and a low-temperature device;50 data were collected using COLLECT; reduction and cell refinement was performed using DENZO/SCALEPACK.51 An empirical absorption correction was applied to the data set of 2.52 The structures were solved by direct methods using SIR2004 (1, 2, 3a, 3b, 5, and 6)53 or SHELXS-97 (4b)54 and refined by full-matrix least-squares on F2 using SHELXL-97.54 All non-hydrogen atoms were refined anisotropically. Hydrogen (50) Cosier, J.; Glazer, A. M. J. Appl. Crystallogr. 1986, 19, 105. (51) Otwinowski, Z.; Minor, W. Methods in Enzymology. In Macromolecular Crystallography, part A; Carter, C. W., Jr., Sweet, R. M., Eds.; Academic Press: San Diego, 1997; Vol. 276, p 307. (52) Walker, N.; Stuart, D. Acta Crystallogr., Sect. A 1983, 39, 158. (53) Burla, M. C.; Caliandro, R.; Camalli, M.; Carrozzini, B.; Cascarano, G. L.; De Caro, L.; Giacovazzo, C.; Polidori, G.; Spagna, R. J. Appl. Crystallogr. 2005, 38, 381. (54) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.
Chaplin and Weller atoms were placed in calculated positions using the riding model. Problematic solvent disorder in the structures of 1 and 2 was treated using the SQUEEZE algorithm.55 Further details of disorder modeling are documented in the crystallographic information files under the heading _refine_special_ details. The overall quality of the data for 2 is poor, as evident in the high value of 1.4 for the mosaicity. Crystal degradation, presumably as a result of solvent loss on warming from -80 C, was observed during mounting. However, the model has been carefully checked and is believed to be correct. The structure is supported by correct microanalysis and characterization in solution by NMR spectroscopy. In addition arene analogues (3) have been characterized in the solid state and show similar structural metrics. The solution of 2 contains three large Fourier peaks close to the heavy atoms (3.9 e A˚-3, 0.97 A˚ from Rh1; 3.3 e A˚-3, 0.94 A˚ from Rh1; 2.3 e A˚-3, 1.00 A˚ from P1) attributed to Fourier truncation errors. If these peaks are excluded, the max./ min. residual density is 1.01/-1.23. Restraints to thermal parameters were applied where necessary in order to maintain sensible values. Centroids (Cg) were calculated using Platon.55 Graphical representations of the structures were made using ORTEP3.56
Acknowledgment. We thank the EPSRC, University of Oxford, and the John Fell Fund (University of Oxford) for support. We also thank Dr. Amber Thompson for useful advice on X-ray crystallography and Dr. Jon Rourke (University of Warwick) for exploratory NMR experiments. Supporting Information Available: NMR spectra of 6 and 7, additional details about the isomeristion of [4a - Cl] to 6, calculated structure of 6 using DFT, and CIF data. This material is available free of charge via the Internet at http:// pubs.acs.org.
(55) (a) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool; Utrecht University: The Netherlands, 2007. (b) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7. (56) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
