808
Organometallics 1982, 1, 808-812
C-0 Bond Cleavage of Esters Promoted by RhH(PPh3), and RUH2(PPh3)4
Takakazu Yamamoto, Satoshi Miyashita, Yoshiyuki Naito, Sanshiro Komiya, Takashi Ito, and Akio Yamamoto Research Laboratory of Resources Utilization, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 227, Japan Received November 24, 198 1
Reactions of RCOOC6H4X (R = CH3, CzH5; X = H, p-OCH,) with RhH(PPh3), at 80-110 O C cause bond and C OCH, ) ((R P P=~ ~ ) ~ cleavage between RCO- and -OC6H4X groups to afford ~ ~ ~ ~ S - R ~ ( O C ~ H ~ X ) ( CH3) or a mixture of C&, CZH4, and Hz (R = CzH5). The rate of the reaction of CH3COOC6H5with RhH(PPh3), is first order with respect to the concentration of the remaining RhH(PPh3)4. The pseudo+ first-order rate constant, k , of the reaction at 90 "C is expressed as k = (1.5 X 10-3)[CH3COOC6H5]/(1 1.1[CH3COOC6H5]+ 87[PPh3])s-l, indicating that the reaction proceeds through a mechanism involving predissociation of PPh3 from RhH(PPhJ4 and competitive coordination of CH3COOC6H5and PPh3 to the vacant site on Rh. The activation energy of the reaction is 46 f 13 kJ/mol. Substitution of H in the phenyl ring of CH3COOC&15by m-CF3,an electron-withdrawinggroup, facilititates the C-O bond cleavage, whereas the substitution by electron-donating groups such as 0-OCH, and p-Et decreases the reaction rate. RuH2(PPh3),promotes similar bond cleavage of esters including RCOOC6H5and alkyl carboxylates such as n-C3H7COO-n-C4H9.
Introduction Carbon-oxygen bond cleavage caused by a transitionmetal complex has been attracting somewhat belated but growing attention compared with the much more studied carbon-halogen bond cleavage reaction which has found considerable utility in organic synthesis.' Although the decarbonylation reaction has been observed in formation of the Vaska's complex from alcohols and IrC132 and cleavage of the a l l y l 4 bond in allyl carboxylates3and allyl ethers4 was noted about a decade ago, no systematic effort has been directed toward exploring the reaction courses, utility, and scope of the C-0 bond cleavage promoted by transition-metal complexes until very recently." Previous papers from our group have revealed the courses of the selective cleavage of the C-0 bond in aryl carboxylates promoted by Ni(0) complexes,7 alkenyl carboxylates by Ni,B Pd,9 and Ru'O complexes, and allyl ethers by Ni complexes.8 As extension of these studies we now report on the interactions of hydridorhodium and -ruthenium complexes, RhH(PPhJ4 and RuHZ(PPh3),, with esters. (1) (a) Heck, R. F. "Organotransition Metal Chemistry", Academic Press: New York, 1974. (b) Tsuji, J. "Organic Synthesis by Means of Transition Metal Complexes"; Springer-Verlag: Berlin, 1975. (c) Hagih a , N.; Joh, T. Kagaku, Zokan (Kyoto) 1972,54,57. (d) Kuroaawa, H. Kagaku Sosetsu 1981,32, 75. (2) (a) Vaeka, J. J. Am. Chem. Soc. 1964, 86, 1943. (b) Vaska, L.; DiLuzio, J. W. Ibid. 1961,83, 2784. (3) (a) Dawans, F.; Marechal, J. C.; Teyssie, P. J. Organomet. Chem. 1970, 21, 259. (b) Dawans, F.; Teyssie, P. J. Polym. Sei. 1969, B7, 111. (c) Chiusoli, G. P. Acc. Chem. Res., 1973,6,422; Pure Appl. Chem. 1980, 52, 635. (4) Clark, H. C.; Kurosawa, H. Inorg. Chem. 1973, 12, 357. (5) (a) Tatsumi, T.; Tominaga, H.; Hidai, M.; Uchida, Y. Chem. Lett. 1977,37. (b) Maki, S.; Tataumi, T.; Kodama, T.; Hidai, M.; Uchida, Y. J.Am. Chem. SOC.1978,100,4447. (c) Tabumi, T.; Tominaga, H.; Hidai, M.; Uchida, Y. J. Organomet. Chem. 1981, 215, 67. (6) Ittel, S. D.; Tolman, C. A.; English, A. D.; Jesson, J. P. J. Am. Chem. SOC.1978,100,7577. (7) (a) Ishizu, J.; Yamamoto, T.; Yamamoto, A. Chem. Lett. 1976, 1091. (b) Yamamoto, T.; Ishizu, J.; Yamamoto,A. J. Am. Chem. SOC. 1980, 102,3758. (8) Yamamoto, T.; Ishizu, J.; Yamamoto, A. J. Am. Chem. SOC.1981, 103, 6863. (9) Yamamoto, T.; Saito, 0.;Yamamoto, A. J. Am. Chem. SOC.1981. 103, 5600. (10) Komiya, S.; Yamamoto, A. J. Organomet. Chem. 1975, 87, 333.
0276-7333/82/2301-0808$01.25/0
Results a n d Discussion Products. Table I shows products of the reactions of RhH(PPh3), and RuH2(PPh,), with esters. The C-O bond cleavage of RCOOC6H4(R = CH,, CzH,; X = H, p-OCH,) by RhH(PPh,), does not proceed at room temperature. It starts only a t about 80 "C, a considerably higher temperature than that required for similar C-0 bond cleavage of aryl carboxylates by Ni(0) c ~ m p l e x e s .The ~ products of the reaction of RhH(PPh3), and CH&OOC&X (CHI and trans-Rh(OC6H4X)(CO)(PPh3)2, 1) indicate that the CH3CO-OC6H4Xbond is cleaved in the reaction according to the stoichiometry given in eq 1. Complexes la" and CH3COOC6H4X + RhH(PPh3)4 ~ ~ ~ ~ s - R ~ ( O C ~ H , X ) (+ C OCH, ) (+P 2P PPh, ~~)~ la, X = H lb, X = p-OCH, (1)
-
1b were characterized by means of elemental analysis as well as IR and NMR spectroscopy (see Experimental Section). Employment of other substituted phenyl acetates, CH3COOC6H4X(X = m-CF,, m-Me, p-Me, p-Et, p-OMe, o-OMe), in the reaction with RhH(PPh,), a t 90 "C also leads to evolution of a quantitative amount of CHI. Although in these cases isolation of analytically pure Rh(OC6H4X)(CO)(PPh3)2 type complexes such as la and l b was not feasible, the IR spectra of all the complexes obtained in the reactions showed v(C=O) and v ( C - 0 ) bands characteristic of the ~ h ( ~ ~ 6 H 4 X ) ( ~ ~ ) (type P P hcom3), plexes" a t about 1960 and 1280 cm-', respectively. We believe that reactions similar to that expressed by eq 1also proceed with the other substituted phenyl acetates. In contrast to the reaction of the aryl carboxylates, reactions of alkyl carboxylates with RhH(PPh3), did not lead to the C-0 bond cleavage under similar conditions. The two mechanisms (Mechanisms I and 11) are consistent with the products and stoichiometry of the reaction. In both Mechanisms I and I1 we assume predissociation of one PPh, ligand from RhH(PPh3), (eq 2a) and coordination of CH3COOC6H4Xto the vacant site of the co(11) (a) Vaska, L.; Jun, J. P. J . Chem. Soc., Chem. Commun. 1971,418. (b) Vizi Orosz, A.; Palyi, G.; Marko, L. J. Organomet. Chem. 1973, 57, 379.
1982 American Chemical Society
C-0 Bond Cleavage of Esters
no. 1
2 3
4
5 6 7 8
Organometallics, Vol. 1, No. 6, 1982 809
Table I. Reactions of Esters with RhH(PPh,), and RuH,(PPh,), product (%/Rh (or Ru)) teomp, time, ester a solvent C h gas or liquid complex b RhH(PPh,), CH,COOC,H, none 100 1 l a (70) CH,COOC,H, CH,Ph, 90 2 lac CH,COO-p-C,H,OMe CH,Ph, 90 3 l b (51) C,H,COOC,H, none 95 5 l a (50)
CH,COO-o-C,H,OMe CH,COO-p-C,H,CN CH, COOC,H, n-C,H, COOC, H,
RuH2(PPh3)4 100 4 104 4 100 5 5 110
none toluene toluene toluene
2 (67) 2c 2,c 3 c 2 (30),3 (30)
. ,
butadiene (4), H, (39) 2(50),3‘ nonene, C,H,OH 10 95 2,c 3c C6H6 (25),H2 (15) 11 110 “4 (2), C3H6 (18) 2 (30) C,H,OH (trace) 12 none n-C,H,COO-n-C,H, 110 20 C,H, (50), H, (trace) 2 (30) 13 C, H, COO-n-C, H, none 8 120 2c C,H, (71, C,H, (41, H2 (27) a Excess amounts (molar ratio to the complex = 6-130) of the esters were added. Volume of solvent/volume of ester = 3-10. CH,Ph, = diphenylmethane. For l a , lb, 2, and 3, see text. The value in the parentheses shows the isolated yield. Formation of the compound was confirmed by GLC, IR, and/or NMR spectroscopy, but its amount was not measured. 9
n-C,H,,COOC,H, C,H, COOC,H, n-C,H,COOC,H,
none toluene none
95
ordinatively unsaturated rhodium complex (eq 2b). This assumption is consistent with the kinetic results (vide infra). Mechanism I RhHL4
2
RhHL3
t L
(2a)
L=PPh3
*-I
CH3COOC6H4X
t RhHL3
kP e
[ R ~ H L J ( C H ~ C O O C ~ H1 ~ (2b) X)
h- 2
[RhHL3(CH3COOC6H4X) 1
k3
CCH3CO-RhL3-OC6
I H
H4XI
-
unambiguous evidence to prove or disprove Mechanisms 11. However, we favor Mechanism I as the more probable one because of the similarity of the reaction patterns with those of the C-O bond cleavage caused by Ni(0) complexes bearing no hydride ligand. Mechanism I1 is less straightforward than Mechanism I because of the necessity of invoking the ensuing reaction 7 after the rate-determining step. Mechanism I1 RhHL4
(3)
&
I I
e
(2a)
[RhHL3(CH3COOC6H,X)
I
(2b)
k- 2
(4)
[RhHL3CH3COOC&X)I
OC6H4X
-
I I H
k3
CCH3C--O-RhL3
H
CH4
L
k2
f RhHL3
co [ C H ~ - R ~ L Z - O C ~ H ~ X1
RhHL3 t
k- I
CH$mC6H4X
A -L
3 3 5
t 1
1
(6)
(5) Mechanism I resembles the mechanism proposed for the C-O bond cleavage of aryl carboxylates promoted by Ni(0) complexes and involves oxidative addition of the ester to Rh (eq 3) followed by decarbonylation (eq 4) and reductive elimination of CHI (eq 5 ) . In mechanism I1 insertion of the carbonyl group in the aryl acetate into the Rh-H bond to form a b-(aryloxy)alkoxo intermediate “B”is assumed. In the ensuing reaction abstraction of the OC6H4Xgroup a t the &position by Rh liberates acetaldehyde and Rh(0C&l4X)L3 (eq 7), which on further interaction with each other cause decarbonylation of aldehyde liberating CHI and 1. Although there are ample precedents of decarbonylation of aldehydes to give alkanes and metal carbonyl complexes by Rh and Ir complexes,12there have been only few reports concerning C=O bond insertion into the metal-hydride bond.13 A t the moment we do not have
When C2H&OOC,& is employed as the reactant, the reaction gives not only the coupling product of the ethyl group and H of RhH(PPh3)4,C2H6, but also &elimination products from the ethyl group, C2H4, and H2, as the gaseous product (no. 4 in Table I) with formation of la. The C-0 bond cleavage of aryl carboxylates proceeds also with R U H ~ ( P Pat~ about ~ ) ~ 100 “C(no.’s 5-10) as well as with the rhodium hydride. The reactions of RCOOC6H5 with RuH2(PPh3)4liberate alkane, olefin, and H2 leaving a mixture of the previously reported R u H , ( C O ) ( P P ~ ~ ) ~ , 2,14 and R U H ( ~ ~ - O C ~ H ~ ) 3.15 ( P P Complexes ~~)~, 2 and 3
(12) Tsuji, J. “Organic Synthesis via Metal Carbonyls”;Wender, I.; Pino, P. Eds.;Wiley: New York, 1977; Vol. 2. (13) (a) Schrock, R. R.; Osbom, J. A. J. C h m . SOC.,Chem. Commun. 1970,567. (b) Calas, R.; Valade, J.; Pommier, J.-C. C. R. Hebd. Seances Acad. Sci. 1962,%5, 1450. (c) Spencer, A. J . Organomet. Chem. 1980, 194,113. (d) Fahey, D. R. J. Am. Chem. SOC.1981,103, 136.
(14) (a) Hallman, P. S.; McGarvey, B. R.; Wilkinson, G. J. Chem. SOC. A 1968,3143. (b) Robinson, S. D. Chem. Ind. (London) 1969,1514. (c) Ito, T.; Horino, H.; Koshiro, Y.; Yamamoto, A. Bull. Chem. SOC.Jpn. 1982,55,504. (15) Cole-Hamilton, D. J.; Young, R. J.; Wilkinson, G. J. Chem. SOC., Dalton Trans. 1976, 1995.
8-OCgHqX
-
obstract~on
B CH3CHO
t
Rh(OCeH4XIL3
(7)
1
(8)
-Ll
CH4
t
810 Organometallics, Vol. 1, No. 6, 1982
Yamamoto et al.
L 1 2 3 4 x,03s Time
I
Figure 1. Time course of the evolution of CHI in the reaction of CH3COOC6H5(neat) with RhH(PPh3), at 90 "C.
0
I
I
0.5
1 .o
,
,L
0
1
"r'
--
Figure 3. Plots of l / k against 1/[CH3COOC6H5]using data given in Figure 2.
0
2
4 I
0
2
4
6
0
6 /
8
r r "
Figure 4. Dependence of k on the concentration of CH3COOC& at various temperatures: [PPh3] = 0 mol/dm3; solvent = diphenylmethane; temperature = 110 "C (O),100 OC (a),90 OC (O), and 80 "C (A).
[CHJC@OC6H5 1 /nol/dr3
Figure 2. Dependence of the pseudo-first-order rate constant, k , on the concentrations of CH3COOC6H5and PPh3 at 90 OC: solvent = diphenylmethane; [PPh3] = 0 mol/dm3 ( O ) , 0.009 mol/dm3 (@),0.035mol/dm3 (e),or 0.078 mol/dm3 (A); [RhH(PPh3),linitial = 0.011-0.013 mol/dm3. were separated by recrystallization and characterized by comparing their IR and NMR data with reported data. Employment of CH3C00-o-C6H40Meand CH,COO-pC6H4CN gives similar results, although in these cases isolation of analytically pure ruthenium-s5-aryloxo-type complexes was not feasible. In contrast to the poor reactivity of RhH(PPh,), against alkyl carboxylates, RuH2(PPh3),promotes also the RC(O)-OR' bond cleavage of the saturated esters, RCOOR', giving gaseous products derived from R and the carbonyl complex, 2 (no.%11-13). Kinetics of the C - 0 Bond Cleavage of CH3COOC6H4XPromoted by RhH(PPh3),. Kinetic (16) The assumption of the competitive coordination of PPh3 and CH3COOCeH6to RhH(PPh& as shown in Mechanisms I and I1 leads to the rate equation rate = -d[RhH(PPh,),]/dt - k&2[CH3COOCeHh] [RhH(PPh3)4] 1 + KI[PPh3] + K2[CH&OOCeH6]
-
aspects of the C-0 bond cleavage have been investigated for the decarbonylation reaction of CH3COOC6H5by RhH(PPh3)4,which proceeds most cleanly among the reactions listed in Table I forming 1 and CHI almost quantitatively. Measurement of the time course of the evolution of CHI (Figure 1) reveals a linear correlation between time, t , and In [(CH,), - (CH,),] ((CH,), = amount of CHI evolved at infinite time; (CH,), = amount of CHI evolved at time t ) ,giving the first-order rate equation concerning the remaining RhH(PPh,), d(CH,)/dt = -d[RhH(PPh,),] /dt = k[RhH(PPh,),] (9)
In [(CH,), - (CH4),I = In [(CH,),] - kt
Figure 2 shows dependence of the pseudo-first-order rate constant, k, on the concentrations of CH3COOC6H5and PPh3 added a t 90 "C. As shown in Figure 2 the k value increases with increase in [CH3COOC6H5],reaching a limiting value of 1.5 X s-l. Plots of l / k against 1/ [CH3COOC6H5]afford straight lines as shown in Figure 3. The slope of the line in Figures 3 increases linearly with increase in [PPh3], and consequently the pseudo-first-order rate constant at 90 "C is expressed as
+
1 b[PPh3] -=- l + k kmax akmax[CH3COOC6H51
k&2ICHsCOOCeHd k = 1 + KI[PPhS] + K2[CH&OOCeHJ where K1 and K2 stand for the formation constants for RhH(PPh,), and RhH(PPh&(CH3COOCeHJ (K,= k-,/kl; K2 = k2/k,), respectively, and correspond to the b and a values in eq 11 and 12. An assumption that the dissociation of PPh3 from RhH(PPh3), (step k,) is rate determining ( S Nmechanism) ~ also leads to a paeudc-firsborder rate equation in which the rate constant is given by an equation similar to eq 12, but the 31P N M R data (see text) indicating occurrence of a rapid exchange between free PPha and PPh3 ligand in RhH(PPh3), on the NMR time scale exclude the possibility that the step k, is the rate-determining one.
(10)
(11)
or k = k,
akm,[CH3COOC6H5] 1 + a[CH3COOC6H5]+ b[PPh3l
= 1.5 X
lo-,
s-l
a = 1.1dm3/mol
b = 87 dm3/mol
(12)
Organometallics, Vol. 1 , No. 6, 1982 811
C - 0 Bond Cleavage of Esters
Experimental Section
log k
-0.2
0
0.2
0.4
0.6
e-value
Figure 5. Hammett plot of the reaction of RhH(PPh3), with CH3COOC6H4Xat 90 "c. The rate constant, k, is given in s-l ([CH3COOC6H4X]= 0.98 i 0.04 mol/dm3 in diphenylmethane).
The Michaelis-Menten-type rate equation suggests that there exists competitive coordination of CH3COOC6H5and PPh3 to RhH(PPh3), formed by the dissociation of one PPh3 from RhH(PPh3), (eq 2a),'6 the relative coordinating ability of CH3COOC&5 to PPh3estimated from the a and b values in eq 11 and 12 (relative coordinating ability = a / b ) being ca. 1/80. The dissociation of one PPh3ligand from RhH(PPh3)4 in the solution is supported by the 31P NMR spectrum of RhH(PPh3)4 in diphenylmethane at 25 O C , 1 7 which shows a broad (half-width = ca.500 Hz) signal at 35 ppm downfield from external PPh3,indicating that the PPh3ligands in RhH(PPh3I3 formed by the dissociation is exchanged rapidly with PPh3 in solution. T h e position of the broad signal shifts to upfield on addition of PPh3according to the equilibrium expressed by eq 2a. Figure 4 shows the pseudo-first-order rate constants measured at different temperatures. T h e MichaelisMenten-type rate equation holds at the temperature range shown in Figure 4,and the ,k values at 110 "C, 100 "C, and 80 "C are measured as 3.2 X s-l, 2.0 X s-l, and 0.7 X s-l, respectively. The Arrhenius plot of the ,k values gives an activation energy of 46 f 13 kJ/mol, the value being considerably smaller than the activation energy for the C-0 bond cleavage of C2H5COOC6H5by Ni(0) complexes (E, = 92 kJ/mol).' The time course of the evolution of CHI in the reaction of the substituted phenyl acetates, CH3COOC6H4X(X = m-CF3, m-Me, p-Me, p-Et, p-OMe, o-OMe), also obeys the first-order rate law with respect to the concentration of RhH(PPh,),, and logarithms of the pseudo-first-order rate constants measured at 90 O C are plotted against Hammett's u value in Figure 5. It is seen from Figure 5 that there exists a trend that the ester having the more electron-withdrawing C6H4Xgroup reacts with RhH(PPhJ4 at the higher rate. A similar trend has been observed in the C-O bond cleavage of C2H5COOC6H4X promoted by Ni(0) complexes,' which is considered to proceed through oxidative addition of C2H5COOC6H4X to Ni. Observation of the similar trend for the C-0 bond cleavage of RCOOC6H4X promoted by both the Ni(0) complexes having no metal-hydrogen bond and the present rhodium(1) hydride complex may be taken as an indication that the present C-0 bond cleavage proceeds by a similar mechanism observed in the Ni(0)-promoted reaction. Use of solvents having a high coordinating ability (e.g., quinoline and (methylsulfiny1)methane)retards the reactions between CH3COOC6H4Xand RhH(PPh3), in accordance with the assumption that the reaction proceeds through coordination of CH3COOC6H4Xat the vacant site of
General Procedures and Materials. Manipulation of complexes was carried out under deoxygenation nitrogen or argon or and RUH~(PP~~),'~>'~ were prepared under vacuum. R~IH(PP~J,'~ as described in the literature. PPh3, CH3COOC6H5,C2H&OOC$15, C$I&OOC$15, saturated esters, alcohols, and ethers were purchased from Tokyo Kasei Co., Ltd., and purified by recrystallization or distillation. Substituted phenyl acetates, CH3COOC6H4X, as well as n-C4H9COOC6H5 and nC&lgCOOC6H5,were synthesized according to methods given in 1iterat~re.l~Solvents were dried by usual procedures, distilled, and stored under argon or nitrogen. Reactions of RCOOC6H,X with RhH(PPh3)4(cf. Table I). No. 1. Phenyl acetate (5.1 cm3,40 mmol) was added to a Schlenk tube containing 430 mg (0.37 mmol) of RhH(PPh3)4. After evacuation of the gas in the tube, the mixture was heated at 100 "C for 1 h. Evolution of 0.34 mlnol(92% /Rh) of CHI in the gas phase was observed as measured by means of a Toepler pump. Phenyl acetate was recovered by trap-to-trap distillation of the reaction mixture and identified by GLC analysis. The remaining solid was washed with diethyl ether twice to yield 190 mg (0.26 mmol, 70%) of a yellow solid, which was characterized as ~~U~~-R~(CO)(OC~H~)(PP~~)~, la," by elemental analysis,u ( C = O ) (1960 cm-') and u(C-0) (1290 cm-') bands in the IR spectrum," 'H NMR (6 6.5-7.9, PPh3 + OC6H5),and 31P(1H)NMR showing a doublet at 65.2 ppm (J(31P-103Rh)= 139 Hz) downfield from external PPh3 at 25 "c in C6Ds. The reaction of CH3C00-p-C6H40Me(no. 3) was carried out analogously, and lb was characterized by elemental analysis (Calcd C, 67.9; H, 4.8. Found: C, 68.2; H, 4.8) and IR spectrum showing u(C=O) and u(C-0) bands characteristic of the Rh(CO)(OC6H4X)(PPh3),-type complexes'l at 1960 and 1300 cm-', respectively. The reaction of CzH5COOC6H5 was carried out analogously. Reactions of RuH2(PPh3), (cf. Table I). No. 5. CH3C00-o-C6H40Me(3.0 g, 1.8 mmol) was added to a Schlenk tube containing R U H ~ ( P P(300 ~ ~mg, ) ~ 0.26 mmol). After the system was evacuated, the mixture was heated at 100 "C for 4 h. Gas chromatographic analysis of the gas phase showed evolution of CH4and H2 The precipitate formed in the reaction was collected by filtration, washed with ether three times, and dried under vacuum to yield 190 mg (67%)of a white solid, which was 2,', by comparing its IR (1940 characterized as RUH~(CO)(PP~~)~, cm-', u ( C 4 ) ) and 'H NMR (6 -7.2 (1 H, dtd, J = 69, 27, 6 Hz, Ru-Ha), -5.4 (1 H, tdd, J 28, 16, 6 Hz, Ru-Hb), ca. 7 (45 H, m, PPh3)) data with the reported data.', The crude precipitate initially obtained from the reaction seems to contain RuH(q5OC6H40Me)(PPh3)z, since its IR spectrum shows u(Ru-H) and u(-) bands characteristic of the R ~ ( ~ 5 - o c 6 ~ x ) ( P P h 3 ) z - t y p e complex*4at 1980 and 1580 cm-', respectively. However, isolation of the complex was not feasible since the proportion of the complex contained in the crude product was too small as judged from weak u(Ru-H) and v(C=O) bands in the IR spectrum of the crude product. The other reactions of RuH2(PPh3),were carried out analogously. Usually the solid products obtained in the reactions comcontained both 2 and the RUH(?~-OC~H,X)(PP~~),-~~~~ plexes as judged by their IR spectra. In the case of no. 8 in Table 3,'5 was formed I, a considerable amount of RuH(~5-oc6Hd(PPh3), and 3 was isolated by crystallization from toluene. RuH(q5OC6H,)(PPh3)zthus isolated was characterized by comparing its IR (1980 cm-', u(Ru-H)) and 'H NMR (6 -10.2 (1 H, t, J = 31 Hz Ru-H), 3.9 (1 H, t, J = 5 Hz, p-phenoxo-H), 4.8 (2 H, d, J = 7 Hz), o-phenoxo-H), 5.1 (2 H, dd, J = 7 , 5 Hz, m-phenoxo-H)) data with the reported data. Kinetic Studies. A Schlenk tube containing RhH(PPh3I4, CH3COOC&X, and solvent (CH2Ph2) was evacuated, and a measured amount of CZH6 was added into the Schlenk tube as a reference. The Schlenk tube was immersed in an oil bath
RhH(PPh3)3. ~~~
~
~
(17) (a) Levison, J. J.; Robinson, S.D. J. C h m . SOC.A 1970,2497. (b) Strauss, S. H.; Diamond, S. E.; Mares, F.; Shriver, D. F. Znorg. Chem. 1978, 17, 3064.
(18) (a) Ito, T.; Kitazume, S.;Yamamoto, A.; Ikeda, S. J. Am. Chem. SOC.1970,92, 3011. (b) Harris, R. 0.; Hob,N. K.; Sadavoy, L.; Yuen, J. M. C. J. Organomet. Chem. 1973,54,259.
(19) Kato, N. "Shin Jikken Kagaku Koza"; Maruzen: Tokyo, 1977; Vol. 14, p 1OOO.
Organometallics 1982,1, 812-819
812
thermostated to fl O C . The amount of CHI evolved at time t was calculated from a relative peak area of CHI to that of the reference by gas chromatography. Spectral Measurement and Analysis. IR and N M R spectra were recorded on a Hitachi 295 spectrometer and JEOL PS-100 spectrometer, respectively. The analysis of gaseous and liquid products were carried out with a Shimadzu GC-3BT or GC-3BF gas chromatograph. Amounts of gases were measured by a Toepler pump. The microanalysis of carbon, hydrogen, and nitrogen was performed by Mr. T. Saito of our laboratory with a Yanagimoto
CHN Autocorder Type MT-2. Registry No. la, 32354-35-1; lb, 80976-38-1; 2, 25360-32-1; 3,
RhH(PPhS)r, 18284-36-1; RuHZ(PPhJ4, 19529-00-1; CHSCOOC$16,122-79-2; CH3COO-p-C6H40Me, 1200-06-2; C,H6COOC&,, 637-27-4; CH3COO-o-C6H40Me,613-70-7; CH3COO-pC&dCN, 13031-41-9; n-CdHgCOOC6H6, 20115-23-5; nCgHigCOOC6H6, 14353-75-4; C6HsCOOCeH6, 93-99-2; nC3H7COOC~H~,105-54-4; n-C3H7COO-n-ClHB,109-21-7; CZHSCOOn-C3H7, 106-36-5. 61817-37-6;
Syntheses of Cationic and Zwitterionic Cyclobutadiene Compounds of Cobalt( I). Crystal and Molecular Structure of Tricarbonyl( 7-1-methoxy-3-methyl-2-phenylcyclobutadiene)cobalt( 1+) Hexafluorophosphate William A. Donaldson,laRussell P. Hughes,*”Vb Raymond E.
D a v i s , + l Cand
Steven M. Gadol’cgd
Departments of Chemistty, Dartmouth College, Hanover, New Hampshire 03755, and the Universiv of Texas at Austin, Austin, Texas 78712 Received December 21. 1982
The (~3-cyclobutenonyl)cobalt complexes 1 react with triallryloxonium salts to yield cationic cyclobutadiene compounds 2, which have been characterized by IR, ‘HNMR, and I3C NMR spectroscopy. Compounds 1 also react with BF3.0Et2 to afford the zwitterionic cyclobutadiene derivatives 4. Reactions of l b with PhCO+SbF,- or (CF3SOz)20produce 6 and 7, respectively. The CO ligands in 2a are displaced in refluxing benzene, affordingthe cationic sandwich complex 8, and the unstable zwitterion 4g can be trapped in refluxing benzene to give the zwitterionic sandwich complex 9. An X-ray crystallography investigation of 2i at -100 “C revealed a monoclinic crystal with space group E 1 / c (No. 14): a = 14.689 (5)A, b = 8.444 (2)A, c = 14.865 (5) A, @ = 109.32 (3)O, 2 = 4,R = 0.087,R, = 0.051. The cyclobutadiene ring is planar, and substituent atoms bound to the ring are displaced away from the metal. The carbon-carbon distances within the cyclobutadiene ring are unequal, as are the cobalt-carbon distances.
Introduction Cyclobutadiene, the simplest cyclic polyene, has intrigued, chemists for decades. Its structural simplicity is deceptive, however, and this prototype antiaromatic molecule usually can only be isolated at low temperatures in a noble-gas matrix,2unless equipped with highly bulky substituent^.^ While the square D4h geometry of cyclobutadiene is predicted to be a triplet diradical ground state, theoretical studies agree in predicting that the molecule will distort to a DS rectangular singlet;* spectroscopic5and chemical6 evidence has also been presented to this effect. (1) (a) Dartmouth College. (b) Alfred P. Sloan Research Fellow 1980-1982. (c) University of Texas at Austin. (d) Robert A. Welch
Foundation Undergraduate Scholar. (2) (a) Lin, C. Y.; Krantz, A. J. Chem. SOC.,Chem. Commun. 1972, 1111-1112. (b) Chapman, 0. L.; McIntosh, C. L.; Pacarsky, J. J . Am. Chem. SOC.1973,95, 614-617. (3) (a) Irngartinger, H.; Rodewald, H. Angew. Chem., Int. Ed. Engl. 1974, 13, 740-741. (b) Delbaere, L. T. J.; James, M. N. G.; Nakamura, N.; Masamune, S. J. Am. Chem. SOC.1975,97,1973-1974. (c) Maier, G.; Pfriem, S.; Schiifer, U.; Matusch, R. Angew. Chem., Int. Ed. Engl. 1978, Schneider, 17, 520-521. (d) Irngartinger, H.; Riegler, N.; Malsch, K.-D.; K.-A,; Maier, G. Ibid. 1980,19, 211-212. (4) (a) Buenker, R. J.; Peyerimhoff, S. D. J.Am. Chem. SOC.1969,91, 4342-4346. (b) Dewar, M. J. S.; Kohn, M. C.; Trinajstio, N. Ibid. 1971, 93, 3437-3440. (c) Haddon, R. C.; Williams, R. J. Ibid. 1976, 97, 6582-6584. (5) Masamune, S.; Souto-Bachiller, F. A.; Machiguchi, T.; Bertie, J. E. J . Am. Chem. SOC.1978, 100, 4889-4891.
0276-7333/82/2301-0812$01.25/0
Since the original prediction that cyclobutadiene should be stabilized by interaction with a transition-metal center,’ the organometallic chemistry of this ligand has been explored extensively.8 There are two methods generally available for the synthesis of a coordinated cyclobutadiene ligand. The first involves the use of a preformed fourmembered ring in the form of 3,4-dihalocyclobutenes,9J0 1,2,3,4-tetrahalocy~lobutanes,~~ or photo a-pyrones,12while the second forms the cyclobutadiene within the coordination sphere of the metal by the cyclodimerization of two alkyne^.'^-'^ We have described a convenient synthesis (6) Whitman, D. W.; Carpenter, B. K.J.Am. Chem. SOC.1980,102, 4272-4274. (7) LonguetHiggins, H. C.; Orgel, L. E. J. Chem. SOC.1956,1969-1972. (8) Efraty, A. Chem. Rev. 1977, 77,691-744. (9) Criegee, R.; Schroder, G. Angew. Chem. 1969, 71, 70-71. (10) (a) Emerson, G. F.; Watts, L.; Pettit, R. J . Am. Chem. SOC.1965, 87, 131-133. (b) Fitzpatrick, J. D.; Watts, L.; Emerson, G. F.; Pettit, R. Ibid. 1965,87, 3254-3255. (11) Berens, G.; Kaplan, F.; Rimerman, R.; Roberts, B. W.; Wissner, J. J . Am. Chem. SOC.1975,97,7076-7085. (12) Rosenblum, M.; Gataonis, C. J . Am. Chem. SOC. 1967, 89, 5074-5075. (13) Hiibel, W.; Braye, E. H. J.Inorg. Nucl. Chem. 1969,10,250-268. (14) Rausch, M. D.; Genetti, R. A. J . Am. Chem. SOC.1967, 89, 5502-5503. (15) Ville, G.; Vollhardt, K. P. C.; Winter, M. J. J . Am. Chem. SOC. 1981,103, 5267-5269.
0 1982 American Chemical Society
