J. Am. Chem. SOC.1983, 105, 5804-581 1
5804
OC for the region 6 + I to -10. The sample was then removed from the probe and cooled to -78 "C. Solid PPh2(2-MeC6H4)(0.01I9 g) was added to this sample. The sample was then shaken for 30 s, returned to the probe at -20 OC, and allowed to equilibrate, and the NMR spectrum was recorded. The sample was removed and cooled to -78 OC, an additional amount of ligand (0.0108 g) was added, and the NMR spectrum was recorded. This was repeated several more times. The shift of the Pt2(p-H) proton was then used to calculate K from a nonlinear regressive fit of the observed shift vs. [L]a/[Ia]a curve.52 The value thus obtained was 3.2 L mol-I. This procedure was repeated at 0 OC to give K = 1.9 L mol-'. Kinetics of Dissociation of PPh3 from Complex IIIa. A sample of complex Ia in CD2CI2(0.18 M) in an NMR tube was cooled to -90 OC in the probe of the NMR spectrometer, and the spectrum was recorded. PPh3was added as a solid to give a 0.20 M solution. The cold tube was shaken to give a homogeneous solution, being careful to keep it cold, and was returned to the NMR probe at -90 "C. The spectrum was recorded, and further spectra were obtained at IO OC intervals as the probe was slowly warmed. Lifetimes were calculated from the spectra at each
temperature. A similar experiment was carried out by using 31PNMR spectroscopy.
Acknowledgment. W e thank NSERC (Canada) for financial support. Registry No. Ia, 6591 1-00-2; IIa, 77275-76-4; IIe, 86528-20-3; IIeCPF6-, 86528-26-9;IIf, 86528-21-4; IIt)PFC, 86528-27-0;IIg, 86528-28-1; IIg+PF6-,86528-29-2; IIIa, 86528-22-5; IIIc, 86528-23-6; IIId, 8652824-7; IIIf, 86528-25-8; H2, 1333-74-0; deuterium, 7782-39-0.
Supplementary Material Available: Table I, spectroscopic data for complexes I1 and Figures 3, Arrhenius plot for dissociation of IIIa, 5, observed points and best fit lines in graphs of absorbance vs. [Llo/[IaIo, 6, changes in absorption spectrum for reaction of Ia with PPh3 at 2 5 O C , 8, Arrhenius plots for reactions of eq 3, and 9, changes in absorption spectrum for reaction of Ia with PPh3 at 4 OC (8 pages). Ordering information is given on any current masthead page.
Syntheses, Properties, and X-ray Crystal Structures of Stable Methylidene Complexes of the Formula [ ( ~ p c ~ M e ~ ) R e ( NL)( o )=CH2)]+PF6( Alan T. Patton,l**bCharles E. Strouse,lb Carolyn B. Knobler,lb and J. A. Gladysz*',* Contribution from the Departments of Chemistry, University of Utah, Salt Lake City, Utah 84112, and University of California, Los Angeles, California 90024. Received February 24, I983
Abstract: Reaction of Re2(CO)lowith pentamethylcyclopentadiene at 150-210 "C yields (q-C5Mes)Re(CO)3(6). Treatment of 6 with NO'BF4- gives [(q-CsMe5)Re(NO)(CO)2]+BF4-(7). Reaction of 7 with C6H51+-O-/CH3CN yields [ ( q CsMes)Re(NO)(CO)(NCCH3)]+BF4(8), which is subsequently treated with L (a, L = PPh,; b, L = P(OPh),) to give [(q-C,Me,)Re(NO)(L)(CO)]+BF; (9a, 9b). Reduction of 9a and 9b with Li(C2H5)3BH/BH3and NaBH,, respectively, yields (q-C,Me,)Re(NO)(L)(CH3) (loa, lob). When 10a and 10b are treated with Ph3CtPF6-, the stable ( > l o 0 OC as solids) (4) and [(q-CsMe5)Re(NO)(P(OPh)3)(=CH2)] 'PF6- (5) methylidene complexes [(q-CSMes)Re(NO)(PPh3)(=CH2)]+PF6form. Properties of the =CH2 ligands in 4 and 5 are studied in detail: AG*mt(- 1 14 "C) 5 19 kcal/mol; IR uXH2: 4,2987/2972 and 2922 cm-I; 5,2987/2976 and 2920 cm-I; uND2: 4-d2, 2246/2239 and 2181 cm-'; 5-d,, 224512238 and 2187 cm-I; NMR 'hi@H(5) = 154 and 143 Hz. The -160 OC X-ray crystal structure of 4 shows =CH2/N0 disorder. The room-temperature X-ray crystal structure of 5 indicates space group P2'/c, a = 8.666 (3) A, b = 12.387 (5) A, c = 34.90 (1) A, p = 102.34 For. 3038 reflections ( I , 2 3.Ou(I:)), R = 0.057 and R, = 0.064. The (3)O, I/ = 3360 (2) A3, 2 = 4,pcald = 1.82 g ~ m - ~ Re=CH2 bond length is 1.898 (18) A, and the =CH2 plane is essentially parallel to the Re-NO bond. This provides optimal overlap with the d orbital HOMO on rhenium.
The synthesis, isolation, and characterization of transition-metal methylidene complexes, L,M=CH2, have been highly sought objectives of organometallic chemists over the past two decades. In addition to the intrinsic interest in stabilizing the normally ,~ species play key roles in reactive CH2 m ~ i e t y L,M=CHz metal-catalyzed olefin metathesis4 and olefin cyclopropanation.5 Some of the earliest attempts to prepare transition-metal methylidene complexes came from the laboratories of Pettit6 and University of Utah. (b) University of California, Los Angeles. (2) Address correspondence to this author at the Department of Chemistry, University of Utah, Salt Lake City, UT 841 12; Fellow of the Alfred P. Sloan Foundation (1980-1984) and Camille and Henry Dreyfus Teacher-Scholar Grant Recipient (1980-1985). (3) See references cited by: March, J. "Advanced Organic Chemistry", 2nd ed.; McGraw-Hill: New York, 1977; pp 178-181. (4) (a) Caldernon, N.; Lawrence, J. P.; Ofstead, E. A. Adu. Organomet. Chem. 1979, 17, 449 and earlier reviews cited therein. (b) Howard, T. R.; Lee, J. B.; Grubbs, R. H. J . Am. Chem. SOC.1980, 102, 6876. ( 5 ) (a) Nakamura, A,; Yoshida, T.; Cowie, M.; Otsuka, S.; Ibers, J. A. J . Am. Chem. SOC.1977, 99, 2108. (b) Nakamura, A,; Konishi, A,; Tatsuno, Y.; Otsuka, S. Zbid. 1978, 100, 3443. (c) Doyle, M. P.; Davidson, J. G. J . Org. Chem. 1980, 45, 1538. (d) Anciaux, A. J.; Hubert, A. J.; Noels, A. F.; Petiniot, N.; Teyssit, P. Zbid. 1980, 45, 695. (1) (a)
0002-7863/83/1505-5804$01,50/0
Green.' These investigators found that the addition of acid to (q-C5Hs)Fe(C0)2(CH20CH3) gave a species that could convert cyclohexene to norcarane. The intermediacy of [ (q-CsHs)Fe(CO),(=CH2)]+ (1) was proposed. However, workup of the reaction mixture afforded mainly ethylene complex [ (q-CsH5)Fe(C0)2(HzC=CH2)]+. Brookhart subsequently found that 1 was too unstable to be observed by 'H N M R a t -80 Herrmann has studied the reaction of (q-C5H4R)Mn(C0),(THF) with CH2N2.9 N o (q-C5H4R)Mn(C0)2(=CH2) was detected, but the plausible methylidene decomposition products (q-CSH4R)Mn(CO)2(H2C=CH2) and (&H,R)(CO),Mn-
-
CH,-Mn(C0)2(q-C5H,R) were isolated. The latter was the first example of a bridging CH2 complex. Such species are now relatively common.1° (6) Jolly, P. W.; Pettit, R. J . Am. Chem. SOC.1966, 88, 5044.
(7) Green, M. L. H.; Ishaq, M.; Whiteley, R. N. J . Chem. SOC.A 1967, 1508. (8) Brookhart, M.; Nelson, G. 0. J . Am. Chem. SOC.1977, 99, 6099. (9) Herrmann, W. A,; Reiter, B.; Biersack, H. J . Organomet. Chem. 1975, 97, 245.
0 1983 American Chemical Society
J . A m . Chem. Soc., Vol. 105, No. 18, 1983 5805
Stable Methylidene Complexes The first isolable methylidene complex, (q-CSH5)2Ta(CH3)(=CH,) (2), was reported in a landmark communication by Schrock in 1975.l' It was prepared by deprotonation of [(aCSH5)zTa(CH3)2]+ and exhibited reactivity indicative of a nucleophilic =CH2 moiety. This is characteristic of all early transition-metal alkylidene complexes synthesized to date. The has been unstable methylidene (q-C5H5)2Zr(PPh2Me)(=CHZ) briefly described by Schwartz.I2 Stable methylidene complexes of the middle and late transition metals have proven to be more e1u~ive.l~In 1980, Brookhart and Flood reported the generation of the labile methylidene [ ( q -
Scheme 1. Syntheses of Methylidene Complexes [(q-C,Me,)Re(NO)(L)(=CH,)I *PF;
CG
6
r
, , C5HS)FeP(C6H,)2CH2CH2P(c6Hs)2(=~H2)]+.14 Subse-
quently, spectroscopically detectable [ ( ~ - C , H , ) M O ( C O ) ~ ( L ) ( = CH2)]+and [(q-C,H,)W(CO),(L)(=CH,)I+ species were synthesized.15 In 1981, Schrock reported that methylidyne W(PMe,),(CI)(=CH) could be protonated to give the crystalline T-shaped methylidene [W(PMe3)4(CI)(=CH2)]+CF3S03-.'6 In 1979, we reported the synthesis and some chemical properties of the electrophilic rhenium methylidene [(q-CSHs)Re(NO)(PPh3)(=CH2)]+PF6-(3).17 Although 3 rapidly self-coupled to form ethylene complex [(q-C,H,)Re(NO)(PPh,)(H,C= CH2)]+PF; at room temperature,Is it proved isolable as a powder a t -23 OC.I9 The mechanism of this coupling is the subject of the following paper.18 In view of the demonstrated ability of the pentamethylcyclopentadienyl ligand to kinetically stabilize organometallic complexes,20we undertook a study of C5Me5 homologues of 3. In this paper we report (a) facile, high-yield syntheses of methylidene complexes [ (q-CsMe5)Re(NO)(L)(=CHz)]+PF6(4, L = PPh,; 5, L = P(OPh),), which are stable as solids to >lo0 "C, (b) X-ray crystal structures of 4 and 5, and (c) a thorough study of the physical properties of the =CH2 ligand in 4 and 5.
Results Synthesis of Methylidene Complexes. The preparation of methylidenes [(q-CSMeS)Re( NO) (PPh3)(=CH,)] +PF6- (4) and [ (q-CSMeS)Re(NO) (P( OPh),) (=CH,)] +PF6- (5) paralleled the route developed for the synthesis of [(q-CSH5)Re(NO)(PPh3)(=CH2)]+PF6- (3).19Direct reaction of Re2(CO)lowith pentamethylcyclopentadiene afforded (q-CSMeS)Re(CO),( 6 ) in 95% yield (Scheme I). This constituted a distinct improvement over the literature procedures." Addition of NO+BF4- to 6 gave the cation [(a-C5MeS)Re(NO)(CO)2]+BF4-(7) in 95% yield (Scheme I). While the crystallographic portion of this study was in progress, a similar synthesis of the PF6- salt of 7 was reported by Graham and Sweet." A CO ligand was oxidatively displaced from 7 with (IO) Herrmann, W. A. Adu. Orgunomet. Chem. 1982, 20, 159. (11) (a) Schrock, R. R. J . Am. Chem. SOC.1975, 97, 6577. (b) Guggenberger, L. J.; Schrock, R. R. Ibid. 1975, 97, 6578. (c) Schrock, R. R.; Sharp, P. R. Ibid. 1978, 100, 2389. (12) Schwartz, J.; Gell, K. I. J . Orgunomet. Chem. 1980, 184, C I . ( I 3) Some transformations that likely involve electrophilic L,M=CH2 intermediates have been reported by: (a) Hayes, J. C.; Pearson, G. D. N.; Cooper, N. J. J . Am. Chem. SOC.1981, 103, 4648. (b) Thorn, D. L.; Tulip, T. H. Ibid. 1981, 103, 5984. (14) Brookhart, M.; Tucker, J. R.; Flood, T. C.; Jensen, J. J . Am. Chem. SOC.1980, 102, 1203. (15) Kegley, S. E.; Brookhart, M.; Husk, G. R. Organometallics 1982, I , 760. (16) (a) Holmes, S. J.; Schrock, R. R. J. Am. Chem. SOC.1981, 103,4599. (b) Holmes, S. J.; Clark, D. N.; Turner, H. W.; Schrock, R. R. Ibid. 1982, 104,6322. (17) Wong, W.-K.; Tam, W.; Gladysz, J. A. J . Am. Chem. Soc. 1979,101, 5440. (18) Merrifield, J. H.; Lin, G.-Y.; Kiel, W. A,; Gladysz, J. A. J . Am. Chem. SOC.,following paper in this issue.
(19) Tam, W.; Lin, G.-Y.; Wong, W.-K.; Kiel, W. A,; Wong, V. K.; Gladysz, J. A. J . Am. Chem. SOC.1982, 104, 141. (20) Bercaw, J. E.; Marvich, R. H.; Bell, L. G.; Brintzinger, H. H. J . Am. Chem. SOC.1972, 94, 1219. (21) (a) (C0)5ReCI + LiCC5Me5-,4%: King, R. B.; Bisnette, M. B. J . Orgunomet. Chem. 1967,8,287. (b) (CO)SReCH3+ C5Me5H,26%: King, R. B.; Iqbal, M. Z.; King, A. D., Jr. Ibid. 1979, 171, 53. (22) Sweet, J. R.; Graham, W. A. G. J . Am. Chem. SOC.1982,104,2811.
&
&La ,L=PPh3
co
-a,
L=P(OPh)3
ON/T'NCCH;
-
C ~ H ~ I + O-
CH3CN
,Ret ON
co
NG+BFq-
1
CO
rn
L i (C2H5)38H/BH3 or NaBH4
CH3
_IO
P F6-
C6HSI+-O-/CH3CN. This gave [(q-C,Me,)Re(NO)(CO)(NCCH3)]+BF4-(8) in 91% yield. Reaction of 8 with P(OPh)3 in refluxing T H F gave [(q-C,Me,)Re(NO)(P(OPh)3)(CO)]+BF4(9b) in 76% yield. The PPh, complex [(q-C,Me,)Re(NO)(PPh,)(CO)]+BF,- (9a) was similarly prepared from 7 in 85% overall yield but without the isolation of intermediate 8. The CO ligand in 9 was reduced to a CH3 ligand by Li(C2H5),BH/BH3 (9a) or NaBH, in T H F (9b). Alkyls (7C5Me,)Re(NO)(PPh3)(CH3)(loa)and (q-C5MeS)Re(NO)(P(OPh),)(CH,) (lob)were isolated in 73% and 64% yields, respectively. The former reaction proceeds via the stable formyl (q-C5MeS)Re(NO)(PPh,) (CHO). Treatment of 10a and 10b with Ph3C+PF6-gave methylidenes 4 and 5 in 70% and 76% isolated yields, respectively. As solids, 4 and 5 were thermally stable to L 1 15 "C and were moderately air stable. In CD,CN, 5 (ca. 0.1 1 M) showed ca. 30% decomposition (relative to Ph3SiCH3 standard) after 1 h at 60 "C. Spectroscopic properties of 4 and 5, as well as precursors 7-10, are summarized in Table I. SpectroscopicProperties of Methylidene Ligands. Spectroscopic features of methylidenes 4 and 5 were studied in detail. Both 4 and 5 exhibited downfield ' H N M R resonances characteristic of electrophilic =CHR ~ o m p 1 e x e s ~ J and ~ J ~separate ~ ' ~ ~ ~resonances ~ for each of the =CH2 hydrogens. No coalescence or broadening of these resonances was observed at 114 "C in the 80-MHz spectrum of 4 in CDClzCDClZ.Similarly, there were no significant changes in the 90-MHz 'H NMR spectrum of 5 at 107 "C. These data bound the energy barrier for =CH2 rotation, AG*,,, ( 1 14 "C), as 219 kcal/mol. Selective saturation of one =CH2 resonance of 4 or 5 (87 "C) did not significantly affect the intensity of the other resonance (
