Organometallics 1996, 14, 2931-2936
2931
Structural Characterization of Intermediates in the Rhodium-CatalyzedReductive Carbonylation of Methanol: Rh(COCH~)(1)2(dppp) and [Rh(H)(I)~-I)(dppp)lz Kenneth G. Moloy* Union Carbide Corporation, P.O. Box 8361, South Charleston, West Virginia 25303-0361
Jeffrey L. Petersen Department of Chemistry, West Virginia University, Morgantown, West Virginia 26505-6045 Received February 21, 1995@ X-ray structural analyses of Rh(COCHs)(I)z(dppp) (1) and [Rh(H>(I>gl-I>(dppp)l~ (2) are reported. Complex 1 is converted to hydride 2 with Ha, and this reaction is believed to be the critical step in the conversion of methanol to acetaldehyde, catalyzed by 1. Unsaturated complex 1 possesses a distorted five-coordinate geometry that is intermediate between sbp and tbp structures. Complex 2 achieves coordinative saturation via formation of iodo bridges. Hz activation by 1 is discussed in view of these structural results. Complex 1 further is found to heterolytically activate HZin the presence of base.
Introduction In a previous report1 we described a rhodium catalyst for the reductive carbonylation of methanol to acetaldehyde. This catalyst is unique in that it gives good rates and selectivities (80%)under much milder temperatures and pressures (140 "C, 1000 psig) than previously reported catalysts (typically cobalt-based, =200 "C, 3000-5000 psig). The rhodium acetyl complex Rh(COCHs)(I)a(dppp)(1, dppp = 1,3-bis(diphenylphosphino)propane) is isolable in essentially quantitative yield from spent catalyst solutions. This observation, the demonstration that 1 can be reused for catalysis and again be recovered, and also kinetic and mechanistic studies led us t o postulate that 1 is a key intermediate in the catalytic reaction. The catalytic cycle proposed for this transformation is shown in Scheme 1. In what appears to be the ratedetermining step, l reacts with H2 to produce acetaldehyde and hydride 2. In a separate catalytic cycle (not shown) 1 is believed t o add a CO ligand; the resulting carbonyl complex then reductively eliminates CH3CO1, forming Rh(I)(CO)(dppp). Liberated CH3COI is rapidly converted to HOAc/MeOAc, resulting in the major inefficiency (ca. 20%) with this catalyst. If these hypotheses are correct, 1 is seen t o play a pivotal role in this catalysis, governing both the rate- and selectivity-determining steps. Due to the importance of the conversion of 1 to 2 in the catalytic cycle, we became interested in understanding the mechanism of this step. The hydrogenolysis of Rh-C bonds is a well-studied transformation owing to its importance in rhodium-catalyzed olefin hydroformy* Author to whom correspondence should be addressed. Current
address: E. I. du Pont de Nemours and Company, Central Research and Development, Experimental Station E328/215A, P.O. Box 80328, Wilmington, DE 19880-0328.E-mail:
[email protected]. @Abstractpublished in Advance ACS Abstracts, May 1, 1995. (1)(a)Moloy, K. G.; Wegman, R. W. Organometallics 1989,8, 2883. (b) Moloy, K. G.; Wegman, R. W. In Homogeneous Transition Metal Catalyzed Reactions; Moser, W. R., Slocum, D. W., Eds.; Advances in Chemistry Series 230; American Chemical Society: Washington, D.C., 1992; p 323.
Q276-7333I95/2314-2931$09.QQlQ
Scheme 2 c-m(I) + Hz
+
C-,RP(III) H H
_ . )
H-Rh(1) + C-H
lation and hydrogenation.2 The Rh-C intermediates in these latter transformations involve Rh(I), and the hydrogenolysis is believed to involve oxidative addition of Hz, followed by reductive elimination of C-H from the resulting Rh(II1) dihydride (Scheme 2). Complex 1,however, presents a possible dilemma in that it contains Rh(II1). In our previous report1 we demonstrated the reaction of 1 with HZto liberate CH3CHO and 2. The lack of reactivity of 1 toward hydride or proton donors, as well as kinetic evidence, suggested that the catalytic reaction may involve direct reaction of 1 with Hz. While many potential mechanisms for this transformation can be envisioned, an intriguing possibility is the a-bond metathesis shown in eq 1. Rhod1
+ H2
'.
,CFH3 ,' (dp~p)(IkRh,, H + ,*'
2 + CH3CHO (1) ium in 1 is d6, 16 e, and therefore unsaturated. It is
(2) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles a n d Applications of Organotransition Metal Chemistry; University Science Books: Mill Valley, CA, 1987, p 524, 625.
0 1995 American Chemical Society
Moloy and Petersen
2932 Organometallics, Vol. 14, No. 6, 1995
Table 1. Selected Interatomic Distances (A> and Bond Angles (deg) in Rh[Ph2P(CH2)3PPhzl(COCH,)Iz(1)" Interatomic Distances 2.6768(5) Rh-I2 2.299(1) Rh-P2 1.817(6) P2-C5 1.821(5) P2-Cl8 1.806(5) P2-C24 1.981(6) 0-C1 1.513(9) C3-C4 1.526(8)
Rh-I1 Rh-P1 Pl-C3 Pl-C6 Pl-Cl2 Rh-C1 C1-C2 c4-c5
2.7263(5) 2.276(1) 1.829(6) 1.830(5) 1.834(5) 1.182(7) 1.527(8)
Range of C-C distances in phenyl rings: 1.350(11)-1.399(9)
Figure 1. Perspective (ORTEP) drawing of complex 1 showing the atom-labeling scheme.
possible that the empty coordination site may be available t o activate H2 in such a manner, possibly via a Rh(r2-H2)intermediate.3 A concern with this proposal is that, by analogy with related structurally characterized complexes R ~ P ~ X Z is Y presumed , ~ , ~ ~ t o possess the sbp geometry shown in Scheme 1. This places the empty orbital available for H2 activation in a position trans to the acetyl ligand. Although five-coordinate molecules are characteristically fluxional, we sought to determine if 1 indeed possesses a sbp geometry. The solid state structure of hydride 2 is also described, which shows that this complex is actually a dimer. This result corrects our previous structural assignmentla for 2 and also serves to underscore the unsaturated nature of 1. Finally, we report a preliminary observation on the heterolytic activation of H2 by 1. Results and Discussion The solid state structure of complex 1 was determined by X-ray crystallography, and an ORTEP drawing of the molecule is shown in Figure 1;important bond lengths and angles are provided in Table 1. As expected, the complex contains a five-coordinate Rh(II1) ion. The dppp bite angle of 90.5" is within the range found for other complexes of this ligand. The conformation of the chelate ring is that of a "flattened boat" as generally found for this particular ligand.6 The bonding parameters involving the acetyl group are not unusual. The Rh-C bond length, 1.981(6)A, is within the range observed for similar acyl complexes of the type Rh(COR)X2P2 (X = halideh4 While previous reports of related acyl complexes have suggested that these Rh-C bond lengths (1.95-2.0 A) are unusually short and indicative of substantial metal to ligand backbonding, we disagree with this conclusion. The Rh-C bond length in 1 is slightly shorter than that recently (3)(a)Kubas, G. J. Acc. Chem. Res. 1988,21,120. (b) Jessop, P. G.; Morris, R. H. Coord. Chem. Rev. 1992,121,155. (4) (a) Shie, J.-Y.; Lin, Y.-C; Wang, Y. J . Organomet. Chem. 1989, 371,383. (b) McGuiggan, M. F.; Doughty, D. H.; Pignolet, L. H. J . Organomet. Chem. 1980,185, 241. (c) Slack, D. A,; Epplestone, D. L.; Ba'rd, M. C. J . Organomet. Chem. 1978,146, 71. (dTEgglestone, D. L.; Baird, M. C.; Lock, C. J. L.; Turner, G. J . J . Chem. SOC.Dalton 1977,1576.(e) Cheng, C.-H.; Eisenberg, R. Inorg. Chem. 1979,18, 1418.(D Cheng, C.-H.; Spivack, B. D.; Eisenberg, R. J . Am. Chem. SOC. 1977,99,3003. (5)(a) Fawcett, J.; Holloway, J. H.; Saunders, G. C. Inorg. Chim. Acta 1992,202,111. (b) The structure of Rh(CH3)(1)2(PPh& has also been reported (Rh-CHS = 2.081 A): Troughton, P. G. H.; Skapski, A. C. J . Chem. SOC.,Chem. Commun. 1968,575. (6) Andrews, M.A.; Voss, E. J.;Gould, G . L.; Klooster, W. T.; Koetzle, T. F. J . A m . Chem. SOC.1994,116,5730.
Bond Angles 89.15(2) P1-Rh-P2 179.36(4) I2-Rh-P2 90.15(3) 12-Rh-P1 90.4(2) C1-Rh-I2 89.7(2) C1-Rh-P2 113.6(2) Rh-P2-C5 115.6(2) Rh-P2-C18 115.7(2) Rh-P2-C24 102.4(3) C5-P2-C18 103.3(2) C5-P2-C24 104.6(2) C18-P2-C24 114.5(4) P2-C5-C4 115.0(4) Rh-C1-01 113.1(4) C2-'21-0
11-Rh-I2 I 1 -Rh-P1 11-Rh-P2 C1-Rh-I1 C1-Rh-P1 Rh-P1-C3 Rh-P1-C6 Rh-Pl-Cl2 C3-Pl-C6 C3-Pl-Cl2 C6-Pl-Cl2 Pl-C3-C4 c3-c4-c5 Rh-C1-C2
90.49(5) 156.79(4) 90.23(4) 108.6(2) 94.6(2) 118.4(2) 119.8(2) 105.3(2) 100.1(2) 107.0(2) 105.1(2) 117.3(4) 125.7(5) 121.1(6)
range of C-C-C
bond angles: 117.8(5)-121.2(7)
range of P-C-C
bond angles: 117.9(4)-122.7(4)
a The esd's for t h e interatomic distances and bond angles were calculated from t h e standard errors of the fractional coordinates of t h e corresponding atomic parameters.
Clll
I121
Figure 2. ORTEP view of 1 showing the coordination environment about rhodium.
reported for trans-Rh(Ph)(Cl)z(PPh3)2 (2.016(3)Ai).5aIn addition, the carbonyl stretching frequency for 1(1698 cm-l) is found at the high end of the range for +acyl complexes, which more commonly are found t o absorb at or below ca. 1650 ~ m - l .Also, ~ we reported previously that 1 is unreactive toward even very potent acids. For example, the IR spectrum of 1 is unchanged upon the addition of HOTf. Together, these results lead us t o disfavor a significant resonance contribution involving metal to ligand back-bonding such as that shown by B.
--
OYR Rh A
OKR Rh'
B
While the gross structural features are within expectations, close inspection reveals a significant distortion (7)(a) Reference 2, p 107.(bj Hitam, R. B.; Narayanaswamy, R.; Rest, A. J. J . Chem. SOC.,Dalton Trans. 1983,615.
Rh-Catalyzed Reductive Carbonylation of MeOH
of the molecular structure of 1 from an ideal sbp geometry. Most notable is the linear (179.4') P(l)-RhI(1) arrangement, which may be compared with the P(2)-Rh-I(2) angle of 156.8'. As a result of this disparity the four basal donor atoms of the ideal square base pyramid (P(1), P(2), Ul), and I(2)) no longer lie in a plane. Figure 2 depicts clearly this distortion of the rhodium coordination sphere. This structural feature should be compared and contrasted with the related complexes Rh(COPh)Cla(dppp) (P-Rh-C1 = 163.5', 169.8')4b and C ~ S - R ~ ( C O C H Z C H ~ ) C W(P-Rh-C1 PP~~)Z = 166.7', 161.2'),4a in which each pair of corresponding angles are much more similar and the four basal donor atoms nearly form a plane. Related structurallycharacterized complexes of the type trans-Rh(R)(X)z(PPh3)2 also exhibit nearly ideal sbp ge~metries.~ The structure of 1 appears t o be approaching that of a trigonal bipyramid. This distortion does not lie on the Berry coordinate, however.8 Such interconversions involve a concerted movement of ligands, and this is not observed in 1. The deviation from the "tbp" geometry is reflected by the varied bond angles in the equatorial plane passing through C(1), P(2), and I(2). Although the sum of these angles is 360', the individual values vary widely from 94.6" (C(l)-Rh-P(2)) to 108.6"(C(1)Rh-I(2)) to 156.8' (P(2)-Rh-I(2)). Similar distortions have been reportedg for five-coordinate, d6 complexes with bulky, mutually trans monodentate phosphine ligands. It is not yet clear how or if the electronic explanations for the distortions in the trans structures apply to 1,where the phosphines are cis. Although rhodium in complex 1 is 16 e we find no evidence for an additional donor interaction to alleviate this unsaturation. Inspection of the crystal-packing diagram shows that there are no intermolecular distances within bonding range. It has been reported5a that the sbp complex trans-Rh(Ph)Clz(PPh3)2possesses agostic interactions with ortho hydrogens on two of the phosphine phenyl groups (Rh---H = 2.87, 2.84 A). Although two of the dppp phenyl rings flank the empty coordination site trans to the acetyl ligand, the shortest Rh-H contact involving the dppp ligand in 1 is 2.99 A. We do not attribute this to a bonding interaction. The shortest intramolecular contact of this type in 1 involves the acetyl methyl group with a Rh-H distance of 2.85 A. Agostic interactions with acetyl ligands have been observed previously.1° However, they are accompanied by significant angular distortions about the carbonyl carbon. The acetyl ligand in 1 is tilted slightly so as to move the methyl group closer to rhodium, but this distortion is significantly smaller than that previously found for agostic acyls. The absence of a significant decrease in the Rh-C-0 angle of 1 further demon(8)Holmes, R. R. Progress in Inorganic Chemistry; Lippard, s. J., Ed.; John Wiley & Sons: New York, 1984; Vol. 32, p 119. (9) (a)Albinati, A.; Bakhmutov, V. I.; Caulton, K. G.; Clot, E.; Eckert, J.; Eisenstein, 0.;Gusev, D. G.; Grushin, V. V.; Hauger, B. E.; Klooster, W. T.; Koetzle, T. F.; McMullan, R. K.; OLoughlin, T. J.; PBlissier, M.; Ricci, J . S.; Sigalas, M. P.; Vymenits, A. B. J. Am. Chem. SOC.1993, 115, 7300. (b) Riehl, J.-F.; Jean, Y.; Eisenstein, 0.; PBlissier, M. Organometallics 1992,11, 729. ( c ) Rachidi, I. E.-I.; Jean, Y.; Eisenstein, 0.New J . Chem. 1990,14,671. (d) Harlow, R. L.; Thorn, D. L.; Baker, R. T.; Jones, N. L. Inorg. Chem. 1992,31,993. (10)(a) Contreras, L.; Monge, A,; Pizzano, A,; Ruiz, C.; Sanchez, L.; Carmona, E. Organometallics 1992,11, 3971. (b) Carmona, E.; Contreras, L.; Poveda, M. L.; Sanchez, L. J. Am. Chem. SOC.1991,113, 4322.
Organometallics, Vol. 14, No. 6, 1995 2933 strates the lack of an v2-acetylinteraction.ll This result is perhaps surprising considering that the related complexes Ru(COR)(Cl)(CO)(PPh3)2achieve saturation via formation of an v2 acyl linkage (in fact, these are the first y2-acylcomplexes t o have been reported).12It is possible that rhodium, being less oxophilic than ruthenium, prefers Jt-donation from the iodide ligands13 to alleviate this unsaturation as an alternative to r2acetyl formation. The unsaturated nature of the rhodium center in complex 1 is nicely demonstrated by the structure of hydride 2. An ORTEP drawing of the molecule is shown in Figure 3, and selected bond distances and angles are provided in Table 2. X-ray crystallography shows that 2 is actually a centrosymmetric dimer, correcting our previous structural assignment. This dimeric structure resembles that assigned by Osborn to related iridium ~omp1exes.l~ Thus, simply replacing the acetyl ligand with a sterically less demanding hydride ligand is sufficient to allow the formation of iodo bridges and a more stable 18 e configuration at rhodium.15 Bond distances and angles for 2 are all within the expected ranges , The structural data presented here demonstrate the unsaturated nature of 1. Moreover, the distorted nature of this complex suggests the potential for an open coordination site cis to the acetyl ligand as the limiting tbp geometry places this vacant coordination site in the equatorial plane defined by C(1), P(2), and I(2). Extensive NMR studies have to date failed t o detect any interaction between 1 and Hz (e.g., Rh-(r2-Hz)). It is known, however, that such species are very acidic and that they may often be intercepted with base.3, 9a,16 To test this possibility we examined the reactivity of 1 with HZ in the presence of amine bases such as Et3N and
DMAP. Complex 1 reacts with Hz only under forcing conditions (120 'C, 120 psi) to generate 2 and CH3CHO. These conditions approach those employed in the catalytic reaction, consistent with the conclusion that hydrogenolysis of 1 to 2 is the catalytic rate-determining step. In the presence of base (DMAP, Et3N), however, 1 activates Hz at significantly reduced temperature. NMR and IR spectral monitoring show the formation of Et3NH+ and a new rhodium complex. This new complex exhibits an acetyl band in the IR a t 1708 cm-l, which is shifted to a slightly higher frequency than 1. (11)Durfee, L. D.; Rothwell, I. P. Chem. Rev. 1988,88,1059. (12) (a) Roper, W. R.; Taylor, G. E.; Waters, J. M.; Wright, L. J. J.
Organomet. Chem. 1979,182,C46. (b) Hitch, R. R.; Gondal, S. K.; Sears, C. T. J. Chem. SOC.,Chem. Commun. 1971,777. (13) (a) Poulton, J. T.; Sigalas, M. P.; Eisenstein, 0.;Caulton, K. G. Inorg. Chem. 1993,32,5490. (b) Poulton, J. T.; Folting, K.; Streib, W. E.; Caulton, K. G. Inorg. Chem. 1992,31,3190. (14) (a)Ng Cheong Chan, Y.; Osborn, J. A. J . Am. Chem. SOC.1990, 112,9400. (b) RhHClz(dppp)has been formulated as both a dimer and a monomer: Faraone, F.; Bruno. G.; Schiavo, S. L.; Tresoldi, G.; Bombieri, G. J . Chem. SOC.,Dalton Trans. 1983,433. (15)The unsaturated nature of 1 is also demonstrated by the reports that the Rh(II1) acyl complexes R ~ ( C O R ) X Z ( C O ) ( Pand R ~[MesPhNIz~~~ [ R ~ ~ I ~ ( C O C H ~ ) Z ( Care O )dimeric, Z ] ' ~ ~ achieving saturation through the formation of halide bridges. (a)Doyle, M. J.; Mayanza, A.; Bonnet, J.J.; Kalck, P.; Poilblanc, R. J. Organomet. Chem. 1978,146,293. (b) Adamson, G. W.; Daly, J . J.; Forster, D. J . Organmet. Chem. 1974, 71, C17. (16)(a) Cappellani, E. P.; Drouin, S. D.; Jia, G.; Maltby, P. A.; Morris, R. H.; Schweitzer, C. T. J . Am. Chem. SOC.1994,116,3375. (b) Chinn, M. S.; Heinekey, D. M. J . Am. Chem. SOC.1987,109,5865. ( c ) Kristjansdottir, S. S.; Norton, J. R. In Transition Metal Hydrides: Recent Advances in Theory and Experiment; Dedieu, A., Ed.; VCH: New York, 1991; Chapter 10.
2934
Organometallics, Vol. 14, No. 6, 1995 Q
Moloy and Petersen
C13
V
Figure 3. ORTEP drawing of hydride 2 (molecule 1). Table 2. Selected Interatomic Distances (A) and Bond Angles (deg) in (Rh[PhzP(CHz)sPPhzl (H)I@-I))2 Molecule A Interatomic Distances Rh * * * Rh* Rh-I1 Rh-I1* Rh-I2 Rh-P1 Rh-P2 11.. I1* P1 ' * P2
.
P1-c1 Pl-C4 P1-c10 P2-C3 P2-Cl6 P2-C22 C1-C2 C2-C3 I 1-Rh-I 1* 11-Rh-I2 11-Rh-P1 11-Rh-P2 I2-Rh-I1* 12-Rh-P1 I2-Rh-P2 P1-Rh-11* P1-Rh-P2 P2-Rh-I1* Rh-11-Rh* Cl-Pl-C4 c1-P1-c10 C4-Pl-ClO C3-P2-C16 C3-P2-C22 C16-P2-C22 c2-c1-P1 Cl-C2-C3 C2-C3-P2
4.085(2) 2.709(1) 2.712(1) 2.861(2) 2.261(4) 2.259(3) 3.564(2) 3.185(4) 1.82(2) 1.83(1) 1.82(1) 1.82(2) 1.81(1) 1.83(1) 1.53(2) 1.57(2)
Molecule B 4.085(2) 2.710(1) 2.71 l(2) 2.859(1) 2.264(3) 2.261(4) 3.563(2) 3.194(6) 1.84(1) 1.82(2) 1.83(1) 1.81(1) 1.83(1) 1.84(2) 1.54(3) 1.56(2)
Bond Angles 82.20(4) 91.19(4) 172.8(1) 94.4(1) 93.78(4) 94.8(1) 91.1(1) 93.3(1) 89.6(1) 174.1(1) 97.80(4) 105.2(7) 102.6(7) 103.4(5) 105.7(7) 102.1(7) 102.1(6) 112(1) 115(1) 115(9)
82.19(4) 91.25(4) 172.6(1) 94.4(1) 93.88(4) 94.7(1) 91.1(1) 93.1(1) 89.8(1) 174.0(1) 97.81(4) 105.2(7) 102.6(7) 103.6(7) 105.8(6) 102.4(6) 102.3(7) 112.6(9) 113(1) 116.4(9)
This new complex has been identified as t h e dichloiide Rh(COCHs)Cls(dppp) (3). Confirmation of this assignm e n t was obtained through an alternate synthesis of 3 (reaction of 1 with C1-). Reaction of 1 with DZ in t h e presence of Et3N cleanly produces Et3ND+ a n d 3. Presumably, a rhodium hydride is generated which abstracts chloride from t h e CHzC12 solvent, generating
Rh-C1 bonds and CH3C1; formation of t h e latter has not yet been confirmed.l' These preliminary results reveal t h a t 1 is indeed able t o participate i n t h e heterolytic activation of Hz. Although cleavage of Rh-I bonds, r a t h e r than RhCOCH3, occurs under t h e conditions reported here, these observations suggest that t h e vacant coordination site on 1 may be an important consideration in t h e catalytic conversion of methanol to acetaldehyde. F u r t h e r studies of t h e activation of Hz by 1, as well as careful consideration of other potential mechanisms for t h e conversion of 1 to 2, a r e required to more fully unders t a n d t h e chemistry of t h i s pivotal intermediate. Experimental Section General Considerations. The syntheses and spectroscopic properties of 1 and 2 have been reported previously. Crystals suitable for X-ray diffraction were grown by slowly cooling saturated methanol (1) or toluene (2) solutions of the complex. All manipulations were routinely conducted under an inert atmosphere (N2) using Schlenk or glovebox techniques. Solvents were Aldrich anhydrous grade material and used as received. DMAP (4-(dimethylamino)pyridine)and Et3N were obtained from commercial sources. Proton and phosphorus NMR data were collected in the Union Carbide Corp. NMR Skill Center using General Electric GN-300NB and QE-300 spectrometers (each are 300 MHz IH). lH NMR spectra were referenced to TMS via solvent peaks, and the 31Pspectra were referenced externally to 85% phosphoric acid. Infrared spectra were recorded on a Nicolet 205 FTIR spectrometer as solutions in CaF2 cells. X-ray Structural Analyses of Rh[PhzP(CHz)sPPhzI(COCIWIz and {R~[P~S(CHZ)~PP~Z](H)IC~-I)}Z. The same general procedures were utilized to perform the X-ray structural analyses of Rh[PhzP(CH2)3PPh&COCH3)12 and (Rh[P~ZP(CH~)~PP~~](H)IO~-I)}~. Crystalline samples of these two ~~
(17) In related chemistry the complexes LzRh(H)ClZ (L = P'Pr3, PCy3) have been reported to catalyze the hydrogenolysis of chloroarenes to arenes. It has been suggested that these reactions may proceed through Rh-($-Hz) intermediates. See: (a) Grushin, V. V.; Alper, H. Chem. Reu. 94, 1047. (b) Grushin, V. V.; Alper, H. Organometallics 1991, I O , 1620. (c) Grushin, V. V. Acc. Chem. Res. 1993, 26, 279.
Rh-Catalyzed Reductive Carbonylation of MeOH
Organometallics, Vol. 14, No. 6, 1995 2935
Table 3. Crystallographic Data for the X-ray Diffraction Analysis of Rh[Ph2P(CH2)sPPh2l(COCH& CRh[PhzP(CHz)sPPhzI(H)(I)b-1)12 empirical formula color cryst dimens, mm3 temp, K cryst syst space group a,A b, A
c,A a,deg
A deg
Crystal Data CmH29RhIzOPz red-orange
CdhRh214P4 red
0.125 x 0.325 x 0.55 295(2)
0.140 x 0.210 x 0.275 295(2)
monoclinic
teclinic
P2dn (Cw5,No. 14) 10.339(2) 10.238(2) 27.269(6)
P 1 (CG1, No. 2) 10.037(3) 15.108(4) 20.131(5) 78.87(2) 75.59(2) 70.60(2) 2768.3(9) 2 1540.34 1.848 30.13 784
95.17(2)
Y,deg
v, A 3
,
z
fw, amu calcd density, g/cm3 p , cm-l F(000)
2874.6(11) 4 812.21 1.876 29.215 1088
Data Collection and Structuiral Analyses 8-28, fmed
scan type scan rate, deg/min scan width 28 range, deg index ranges no. of reflns collected agreement between equiv data, R,,(Fo) total no. of unique data obsd data criteria no. of obsd data abs corr range of transmissn coeff P
refinement method discrepancy indices R(Fo) R(Fa2) Rw(Fo2)
Fo > d F o ) 5466
face-indexed
face-indexed
0.534-0.785 0.03
0.57-0.70 0.03
full matrix on F
0.044 0.050
0.056 0.072 0.116 2.23 577 9.51
1.67 408 12.5:l
compounds were sealed in glass capillary tubes under a nitrogen atmosphere and then optically aligned on a Picker full-circle goniostat under computer control by a Krisel Control diffractometer automation system. After the indexing18 of a series of low-angle reflections and the calculation of a preliminary set of lattice parameters, the orientation angles of 20 higher order reflections were optimized by an automatic peak-centering routinelg and then least-squares fitted to provide the corresponding refined lattice parameters and the orientation matrix. Intensity data were measured with Zr-filtered Mo K a radiation with a take-off angle of 2". Peak scans employed a fured scan rate and a variable scan width. The integrated intensity, I , and its standard deviation, uc(I),for each measured reflection were calculated from the expressions I = w(S/t, B/tb) and s ( I ) = w(S/tS2+ B/tb2)1/2,where is the total scan count measured in time t, and B is the combined background count in time tb. The standard deviation of the square of each ) [acstructure factor, Fo2= AZ/Lp, was calculated from d F O 2= (F,2I2 (pF,2)211'2. The observed data were corrected for sample decay, absorption,20and Lorentz-polarization effects. Duplicate reflections were averaged. Additional crystallographic information is provided in Table 1. The initial coordinates for the Rh and I atoms of Rh[ P ~ ~ P ( C H ~ ) ~ P P ~ ~ ] ( Cand O C{Rh[Ph2P(CH2)3PPh2l(H)I(pH~)IZ
s
+
(18)This automatic reflection-indexing algorithm is based upon Jacobson's procedure: Jacobson, R. A. J.Appl. Crystallogr. 1976, 9,
115.
+
full matrix on F
0.080
GOF no. of variables data to param ratio UI,
8-28, fixed 4.00 1.1 0.8 tan 8 5.0-45.0 -12 i h i 12; -17 5 k i 17; 0 i 1 5 32 8460 0.019
2.00 1.1 0.9 tan t9 5.0-50.0 -12 i h i 12; 0 i k i 12; 0 i I i 32 5218 0.035 5103 Fa > d F o ) 4508
+
(191This peak-centering algorithm is similar to that described by Busing: Busing, W. R. Crystallographic Computing;Ahmed, F. R., Ed.; Munksgaard: Copenhagen, Denmark, 1970; p 319. The (u, x , and 20 angles were optimized with respecr to the Ka, peak (i = 0.709 26 A).
and
1 ) )were ~ interpolated from an E-map calculated on the basis of the initial phases determined by MULTAN78.21 Approximate coordinates for the remaining non-hydrogen atoms were obtained by Fourier methods and then refined with anisotropic thermal parameters. The hydrogen atoms were initially located using difference Fourier calculations based on only lowangle data with (sin O/l) < 0.40 A-l and then later adjusted with the aid of MIRAGE.22 During the refinement of Rh[PhzP(CH2)3PPhz](COCH3)12,it became apparent that the sample contained a detectable amount of Rh[PhzP(CH2)3PPh& A small residual peak in the difference Fourier map is located at ca. 2.7 A from the central Rh atom and occupies the same general coordination site as the acyl ligand. A correction for the residual iodide was introduced by reducing the occupancy factors of 0, C1, C2, H1, H2, and H3 from 1.000 to 0.977 and introducing a third iodine atom with an occupancy of 0.023. The position and occupancy factor of the residual iodine atom were refined with an isotropic thermal model. Full-matrix refinementz3of the positional and anisotropic thermal parameters for the 35 non-hydrogen atoms, the coordinated and isotropic temperature factors for the residual iodide, and the positional para(20) The absorption correction was performed with the use of the general polyhedral shape routine of DTALIB. The distance from the crystal center to each face and the orientation angles ($ and x ) used to place each face in diffractingposition are required to define the crystal's shape, size, and orientation with respect to the diffractometer's coordinate system. (21) Declerq, J. P.; Germain, D.; Main, P.; Woolfson, M. M. Acta Crystallogr. Sect. A 19'
Moloy and Petersen
2936 Organometallics, Vol. 14, No. 6, 1995 meters with fixed isotropic contributions for the 29 hydrogen atoms converged with final discrepancy indices of R(FJ = 0.044, R(Fo2)= 0.050, and R,(Fo2) = 0.080 with u1 = 1.67 for the 4508 reflections with F,2 > 45'2). The final difference map contained no additional regions of significant electron density. Selected interatomic distances and bond angles and their esd's for the non-hydrogen atoms are given in Table 2. In the crystallographic setting used to collect the X-ray data for {R~[P~~P(CHZ)~PP~Z~(H)I@-I)}~, the two molecular dimers lie on different crystallographic centers of inversion. Therefore, the asymmetric unit consists of two independent Rh[ P ~ ~ P ( C H Z ) ~ P P ~molecular ~ ] ( H ) I ~fragments. The terminal hydride ligand, H27, was located but not varied. Full-matrix refinement23(based on Fa2)of the positional and anisotropic thermal parameters for the 64 non-hydrogen atoms with fmed isotropic contributions for the 54 hydrogen atoms converged with final discrepancy indices ofR(F,) = 0.056, R(F,2) = 0.072, and R,(F,2) = 0.116 with 01 = 2.23 for the 5466 reflections with Fo2> u(Fo2).The final difference map contained a residual peak a t ca. 1.0 A from the terminal iodine atom, 12, and was lying nearly along the Rh-I2 vector. Interatomic distances and bond angles and their esd's for the non-hydrogen atoms are given in Table 3. Preparation of Rh(dppp)(COCHs)(Cl)2(3) from 1, H2, and Base. A glass pressure reactor (Fischer-Porter bottle) was charged with 1.03 g (1.27 mmol) of 1,0.200 g (1.63 mmol) of DMAP, 55 mL of CH2C12, and a magnetic stir bar. The bottle was connected to a high-pressure gas manifold. After purging, the vessel was charged with 80 psi of H2 and then immersed in a 70 "C oil bath. After ca. 15 h the solution turned from yellow-orange to yellow. A small amount of precipitate was removed by filtration, and the solvent was removed under vacuum. The residue was washed with MeOH, and the solid product was dried. Recrystallization from CH2(23)The least-squares refinementsz4of the X-ray diffraction data were based upon the minimization of 20,1Foz - SzFC2l2,where w1 is the individual weighting factor and S is the scale factor. The discrepancy indices were calculated from the expressions R(Fo)= ZllFol IFc!!EIFol, R(Foz)= W o 2 FczlEFoz,and R,(Fo2)= [P(w,!Fo2- FcZl2)/ ZW,F,~)I"~. The standard deviation of an observation of unit weight (GOF)was computed from [Z(w,lFoz- Fczlz)/(n- p)11'2,where n is the number of reflections a n d p is the number of parameters varied during the last refinement cycle. (24) The scattering factors employed in all of the structure factor calculations were those of Cromer and MannZ4"for the non-hydrogen atoms and those of Stewart et aZ.24bfor the hydrogen atoms with corrections included for anomalous dispersi0n.~4f(a) Cromer, D. T.; Mann, J. B. Acta Crystallogr., Sect. A 1968,A24,321. (b) Stewart, R. F.; Davidson, E. R.; Simpson, W. T. J . Chem. Phys. 1966,42,3175. (c) Cromer, D.T.; Liberman, D. J. J . Chem. Phys. 1970, 53, 1891.
Cl2 provided yellow crystals of 3 contaminated with small amounts of Rh(COCH3)(Cl)(I)(dppp)(see below). Yield: 0.40 g, 50%. 31PNMR (CDzClz): 6 24.3, d, J R h - p = 136 Hz. 'H NMR (CD2C12): 6 7.8-7.2 (m, 20H), 2.93 (s, 3H), 2.44 (m, 4H), 1.64 (m, 2H). These data are consistent with those previously reported4' for 3. Analysis (IR, NMR) of the MeOH extracts showed the presence of [DMAPHl[Il and unreacted DMAF'. Similar results are obtained with Et3N. A control experiment, omitting base, resulted in recovery of intact 1after the above treatment. Preparation of 3 From 1 and Et4NC1. Solutions of 1 (0.095 g, 0.12 mmol, in 6 mL) and Et4NCl(O.O55g, 0.33 mmol, in 2 mL) were prepared in CHZC12. The Et4NC1 solution was added to the solution of 1in 0.5 mL aliquots, and the reaction was monitored by IR. The solution turned from yellow-orange to yellow during the titration, and the carbonyl absorption attributable to the acetyl ligand shifted from 1698 to 1708 cm-'. The solvent was then removed in vacuo, and the resulting product was washed well with MeOH. 31PNMR (CD2C12)showed the product to be complex 3. In a separate experiment, 1 was treated with 1 equiv of Et4NCl, and the product was isolated as described above. 31P NMR showed, in addition to resonances attributable to 1 and 3, an ABX spectrum assignable t o the mixed halide Rh(COCH3)(Cl)(I)(dppp):Pad 21.3, dd, J R h - p , % 169 Hz; Pb 6 20.2, dd, J R h - p h * 162 HZ; Jp,-pb 22 HZ.25
Acknowledgment. Helpful discussions with Professor K. G. Caulton are gratefully acknowledged. T. L. Fortin is thanked for laboratory assistance. This work was partially funded by the U.S. Department of Energy under Contracts DE-AC22-84PC70022 and DE-AC2286FC90013. We thank Union Carbide Corporation for permission t o publish these results. SupplementaryMaterial Available: Tables of positional parameters, thermal parameters, and bond distances and angles, for complexes 1 and 2 (14 pages). Ordering information is given on any current page. OM950139W (25)The observation of inequivalent phosphorus resonances in the
31PNMR of 3, while 1 shows equivalent phosphorus resonances,
indicates that in solution this class of compounds adopt rigid (on the NMR time scale) sbp geometries or that any fluxional processes that are occurring involve pairwise motion of transoid phosphorus and halogen ligands. We have not conducted variable temperature 31PNMR measurements on either complex to investigate this in more detail.
