Heterobimetallic Indenyl Complexes. The Trans-Cis Isomerization of

Publication Date: May 1995 ... A. Reingold, Kurtis L. Virkaitis, Gene B. Carpenter, Shouheng Sun, Dwight A. Sweigart, Paul T. Czech, and Kenneth R. Ov...
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Organometallics 1995, 14, 2430-2434

2430

Heterobimetallic Indenyl Complexes. The trans-cis Isomerization of Cr(CO)3@,q:q=indenyl)Rh(NBD) Chiara Bonifaci, Albert0 Ceccon," Alessandro Gambaro, Paolo Ganis,? and Saverio Santi Dipartimento di Chimica Fisica, Universita di Padova, Via Loredan 2, 35131 Padova, Italy

Alfonso Venzo CNR, Centro di Studio sugli Stati Molecolari, Radicalici ed Eccitati, Via Loredan 2, 35131 Padova, Italy Received October 11, 1994@ Reaction of trans-[Cr(C0)~+,q:q7-indeny1)Rh(C0)~1 at room temperature in CHzClz with l)Rh(NBD)I, 3. X-ray analysis for norbornadiene (NBD) yields trans-[Cr(C0)3+,q:q-inden 3 shows a = 8.200(5) b = 11.388(5) c = 17.868 = 92.1", space group P21Ic. In contrast with the cis-[Cr(CO)&qppindenyl)Rh(NBD)I, 2, isomer, the indenyl moiety in 3 is far less distorted, and the planes defined by [CI, CZ,C31 of the indenyl frame and by [ C ~ I , (212, c14, C151 of NBD are almost exactly parallel to each other, showing a n undistorted coordination about the rhodium atom. Under suitable conditions (THF as solvent in the presence of the tetrafluoroborate salt of [Rh(NBD)I+,or a similar cation species) 3 undergoes a fast intramolecular rearrangement to give the isomer cis-[Cr(C0)3+,q:q-indenyl)Rh(NBD)I, 2. The process exhibits a relatively low activation enthalpy (m= 11.7 f 0.9 kcal mol-l) and a very negative activation entropy (AS' = -30 f 3 cal mol-l K-l).

A,

A,

Introduction

The synthesis of dinuclear complexes in which two inorganic units are coordinated t o the same ligand ("bridging ligand") has been achieved successfully in recent years. Usually, the two metals reside on the same side of the ligand plane (i.e. in a cis stereochemistry) that often results in the formation of a metalmetal b0nd.l Some binuclear complexes of trans stereochemistry were also obtained, with either monoor b i c y c l i ~ ~ bridging -~ ligands. cyclic1aJb~2 Recently, we were able to synthesize trans-[Cr(CO)~1, by reacting the (q6-indenyl)@,q:~pindenyl)Rh(COD)], Cr(C0)3 potassium salt with [Rh@-Cl)COD12in THF a t -30 "C.4 Surprisingly, when the same anion was quenched with [Rh@-Cl)NBD12under identical conditions, the only product isolated was cis-[Cr(C0)3@,q:q-

* To whom correspondance should be addressed.

+ On sabbatical leave from University of Napoli, Italy. @Abstractpublished in Advance ACS Abstracts, March 15, 1995. (1) (a) Geiger, W. E.; Salzer, A.; Edwin, J.; von Philipsborn, W.; Piantini, U.; Rheingold, A. L. J . A m . Chem. SOC.1990,112, 7113. (b) Bieri, J. H.; Egolf, T.; von Philipsborn, W.; Piantini, U.; Prewo, R.; Ruppli, U.; Salzer, A. Organometallics, 1986, 5, 2413. (c) Heck, J.; Rist, G. J.Organomet. Chem. 1986,286,183. (d) Astley, S. T.; Takats, J. J. Organomet. Chem. 1989,363, 167. (e) Edelmann, F.; Kiel, G.-Y.; Takats, J.; Vasudevamurthy, A.; Yeung, M.-Y. J . Chem. SOC.,Chem. Commun. 1988,296. (0 Edelmann, F.; Takats, J. J . Orgummet. Chem. 1988, 344, 351. (g) Ball, R. G.; Edelmann, F.; Kiel, G.-Y.; Takats, J.; Drwes, R. Organometallics 1986, 5, 829. (h) Bennet, M. J.; Prat, J. L.; Simpson, K. A.; LiShing Man, L. K. K.; Takats, J. J . Am. Chem. SOC.1976,98,4810. (i) Jonas, K.; Koepe, G.; Schieferstein, L.; Mynott, R.; Kriiger, C.; Tasy, Y.-H. Angew. Chem., Int. Ed. Engl. 1983,22,620. Angew. Chem. Suppl. 1983,920. (j) Duff, A. W.; Jonas, K.; Goddard, R.; Kraus, H.-J.; Kriiger, C. J.A m . Chem. SOC.1983, 105, 5479. (k) Jonas, K.; Wiskamp, V.; Tsay, Y.-H.; Kruger, C. J . A m . Chem. SOC. 1983, 105, 5480. (1) Jonas, K.; Riisseler, W.; Angermund, K.; Kriiger, C. Angew. Chem., Int. Ed. Engl. 1986,25,927. (m) Behrens, U.; Heck, J.; Maters, M.; Frenzen, G.; Roelofsen, A.; Sommerdijk, H. T. J . Organomet. Chem. 1994, 475, 233. (n) Airoldi, M.; Deganello, G.; Gennaro, G.; Moret, M.; Sironi, A. Organometallics 1993, 12, 3964. (2) Jonas, K. Pure Appl. Chem. 1990, 62, 1169 and references therein.

indenyl)Rh(NBD)I,2,5showing that the structure of the ancillary ligand at rhodium plays an important role in determining the stereochemistry of the reaction product. Compounds 1 and 2 may now serve as starting materials for the preparation of other trans and cis complexes, respectively, as ligand exchange at rhodium occurs without changing the molecular stere~chemistry.~,~ In this paper we report the preparation of the new complex trans-[Cr(C0)3@,q:q-indenyl)Rh(NBD)],3, i .e., the trans isomer of 2. The availability of this compound allowed us t o make a direct comparison between the structural characteristics of the trans and those of the cis isomer. In addition, we found that the trans isomer rearranges intramolecularly to the cis isomer, and we have studied the kinetics of this rearrangement. The results are reported below. Results and Discussion

Bubbling CO through a CHzClz solution of 1 at room temperature produced trans-[Cr(C0)3@,~ppindenyl)Rh( C 0 ) ~ lin quantitative yield.6 This compound was converted quantitatively into 3 within a few minutes by treating a CHzClz solution with excess NBD at room temperature, as indicated by IR, NMR, and mass spectrometric measurements (see Experimental Sec(3) (a) Green, M. L. H.; Lowe, N. D.; OHare, D. J . J . Chem. SOC., Chem. Commun. 1986, 1547. (b) Bennett, M. A,; Neumann, H.; Thomas, M.; Wang, X. Organometallics 1991, 10, 3237. (c) Schulz, H.; Pritzkow, H.; Siebert, W. Chem. Ber. 1992,125,987. (d) Klein, H. F.; Hammerschmitt, B.; Lull, G.; Florke, U.; Haupt, H. J., Inorg. Chim. Acta 1994,218, 143. (e) Kudinov, A. R.; Petrovskii, P. V.; Struchkov, Yu. K ; Yanovskii, A. I.; Rybinskaya, M. I. J . Organomet. Chem. 1991, 412, 91. (4) Ceccon, A.; Gambaro, A.; Santi, S.; Valle, G.; Venzo, A. J . Chem. SOC.,Chem. Commun. 1989, 51. (5) Bonifaci, C.; Ceccon, A.; Gambaro, A.; Ganis, P.; Santi, S.; Valle, G . ;Venzo, A. Organometallics 1993, 12, 4211. (6) Ceccon,A,; Gambaro, A,; Santi, S.;Venzo, A. J . Mol. Catal. 1991, 69, Ll-L6.

0 1995 American Chemical Society

Heterobimetallic Indenyl Complexes

Organometallics, Vol. 14,No.5, 1995 2431

Table 1. Selected Bond Distances (A) and Angles (deg) of cis-[Cr(CO)~IndRh(NBD)], 2, trans-[Cr(CO)~InaRh(NBD)l,3, and IndRh(NBD),4 Rh-C1,sa 2g

3h 49

2.244 2.253 2.226

Rh-Cf

Rh-C3a,ia' 2.560 2.339

2.164 2.248 2.240

2.395

Cr-C4,7a

Cr-C5,8

Cr-C3a,ia

2.264 2.246

2.202 2.226

2.468 2.320

r-17

AGEb

AMC*

HA (Cp)d

HA (Bzy

ef

1.456

0.316 0.087

0.342 0.088 0.164

-12

e11 -6 -1

-23 -3

1.469 1.42

0.169

010 08

Figure 1. ORTEP view of 3. Selected bond lengths (A): Rh-Ci 2.270(4),Rh-CZ 2.248(5),Rh-Cs 2.235(5),Rh-C3, 2.334(5),%-Cia 2.344(4),Cr-C3,2.351(5), Cr-Cd 2.237(5))Cr-CS 2.214(5),Cr-Cs 2.197(5),Cr-C7 2.255(4), CrC7a 2.359(4), Ci-Cz 1.397(7), cz-c3 1.425(7), C3-C3a 1.446(7), C3a-C7a 1.469(6), Cl-CTa 1.454. Bond angles (deg): Cs-Cr-Cg 88.2(2),Cs-Cr-C10 87.9(2),Cg-Cr-Clo 89.3(2),Cr-Cs-08 178.7(4),Cr-Cg-09 178.9(6),Cr-Clo0 1 0 178.0(5). Torsion angles (deg): Cg-Cr-P-C6 11.8,CsCr-P-C4 14.0, Clo-Cr-P-C7, 10.7 (P designates the location of the center of the benzene ring).

tion). Orange crystals suitable for X-ray analysis were obtained from CHzClz-pentane solutions. Figure 1shows the molecular structure of complex 3, together with some relevant geometrical parameters. The distances from rhodium to the carbon atoms of the five-membered ring of the indenyl ligand indicate a distorted q5-coordination of rhodium similar to that found for several monometallic (q-indeny1)RhLz comhis distortion arises from the puckering of the p l e ~ e s .T~ [CI, C2, C31 plane with respect to the remainder of the (7) (a)Al-Obaidi, Y. N.; Baker, P. K.; Green, M.; White, N. D.; Taylor, G. E. J . Chem. Soc., Dalton Trans. 1981,2321. (b) Barr, R. D.; Green, M.; Marder, T. B.; Stone, F. G. A. J . Chem. Soc., Dalton Trans. 1984, 1261. (c) Baker, R. T.; Tulip, T. H. Organometallics 1986,5, 839. (d) Mlekuz, M.; Bougeard, P.; Sayer, B. G.; McGlinchey, M. J.; Rodger, C. A.; Churchill, M. R.; Ziller, J. W.; Kanz, S. W.; Albright, T. A. Organometallics 1986,5,1656. (e) O'Connor, J . M.; Casey, C. P. Chem. Rev. 1987,87,307 and references therein. (0 Marder, T. B.; Calabrese, J. C.; Roe, D. C.; Tulip, T. H. Organometallics 1987,6,2012. (g) Carl, R. T.; Hughes, R. P.; Rheingold, A. L.; Marder, T. B.; Taylor, N. J. Organometallics 1988, 7, 1613. (h) Kakkar, A. K.; Taylor, N. J.; Calabrese, J. C.; Nugent, W. A,; Roe, D. C.; Connaway, E. A,; Marder, T. B. J . Chem. Soc., Chem. Commun. 1989, 990. (i) Kakkar, A. K.; Jones, S.; Taylor, N. J.;Collins, S.; Marder, T. B. J. Chem. Soc., Chem. Commun. 1989, 1454. (i)Merola, S.; Kacmarcik, R. T. Organometallics 1989, 8, 778.

-6 -10

-1

indenyl group, the corresponding hinge angle being ca. 6". The distances Rh-Csa = 2.334(5) A and Rh-CTa = 2.344(4) A are about 0.1 A longer than the distances Rh-C1 = 2.270(4) A, Rh-C2 = 2.248(5) A, and Rh-C3 = 2.235(5)A. As a consequence, the A m parameter7c,d,i(AM-C = [(Rh-C3a) (Rh-C7a)1/2 - [(RhC1) (Rh-C3)Y2}, ) amounts to 0.087 A, and most of the distortion can be traced to ring folding rather than "slippage". The planes defined by [Cl, CZ,C31 of the indenyl frame and by [CII, C12, c14, C151 of NBD are approximately parallel to each other, showing an undistorted coordination about the Rh atom. Also, the distances from chromium to the ringjunction carbons C3a and C7a ,are longer than those from chromium t o the other carbon atoms of the benzene ring. The plane defined by [C4, C5, c6, C71 forms a hinge angle of ca. 6" with the planar , showing, therefore, that frame [C3, C3al Cq, C7, C T ~C11, the puckering of the benzene ring due to its coordination with Cr(C0)3 is comparable in magnitude with that induced by rhodium coordination t o the five-membered ring. The comparison between the structural characteristics of cis and trans isomers is instructive. Selected parameters and bond distances of 2 and 3 are listed in Table 1, together with the corresponding data for monometallic IndRh(NBD),4. The data in Table 1show that ( i ) the Rh-Cl and Rh-C3 distances in the three complexes are quite similar; on the other hand, the RhC2 distance, which is almost equal for 3 and 4, appears to be markedly shorter in the case of the cis isomer 2. The slippage of rhodium toward the C2 carbon atom is, therefore, more pronounced when the two metals are coordinated to the same side of the ligand plane. The cis arrangement of the metals is also responsible for the longer average distance of rhodium from the Csa and C7a atoms observed (2.560(5)A) in comparison with that found in the trans isomer 3 (2.350(6) A) and in the monometallic complex 4 (2.394(9)A). The ring slippage parameter AM-C describes well these structural differences in the indenyl complexes. It can be seen from data reported in column 9 of Table 1 that the the AM-C values change in the order 2 >> 4 > 3,indicating that rhodium coordination to the Cp ring is the least distorted in the trans complex and that the distortion is noticeably increased in the case of the cis isomer, as confirmed by the values of the hinge angles (columns 11 and 12). Taking into account also the Rh-Cz bond distance, the new parameter can be defined AM-C* = {[(Rh-Cs,) (Rh-C7,)]/2 - [(Rh-CI) (Rh-CZ) (Rh-C3)Y3} - (A); it exhibits practically the same value of AM-C in the case of 3 and 4, while it is noticeably - = greater in the case of 2 (AM-C" = 0.342, AM-C 0.316) because of the higher sensitivity of AM-C* to

s

+

09

-

C3a-Cia

+

+

+

+

Bonifaci et al.

2432 Organometallics, Vol. 14, No. 5, 1995 the slippage of the metal toward C2. Table 1also shows that (ii)the distortion of the coordination about rhodium evidenced in 2 by the large dihedral angle (23")between the planes [Cl, C2, C31 of the indenyl frame and [ C I ~ , C12, C14, C151 of NBD is practically absent in the case of the trans isomer 3 as well as in the monometallic complex 4 and (iii) the coordination with Cr(C013 of IndRh(NBD) causes the bending of the benzene ring which is larger in the cis complex (11")than in the trans one (6"). Analogously t o the AM-C parameter defined for the Cp ring, we have calculated the AM-CbenZene parameter (AM-Cbenzene= {[(CT-C~~)(Cr-C7a)Y2 [(Cr-C4) (Cr-C7)1/2}, A) which is much higher for 2 (0.184 A) than for 3 (0,109 A). Again, the distortion in the cis species is substantially larger than that in the trans isomer, indicating a pronounced shift of chromium from the ideal q6 hapticity toward an q4 one. This conclusion is corroborated by the NMR results which indicate that the difference between the structural features of 2 and 3 also persists in solution. As reported previ~usly,~ the most relevant effects caused by the coordination of the benzene ring with Cr(C0)3 to form the cis isomers, Ad(13C), are the tetrahedralization of the C1,C3 and C4,C7 carbon atoms as indicated by their very high upfield shiftsand the low coordinative engagement of Csa and C7a as suggested by the low-field position of their resonance. Conversely, the complexation effects observed for the same carbon nuclei in the trans isomer 3 are quite different, i.e., lower Ad(13C) values for C1, C3, C4, and C7, and higher for Csa and C7a, and they are very close to those previously reported for a series of trans-[Cr(C0)3(indenyl)Rh(COD)lderivatives.8 These features indicate that the structure of the cis isomer is characterized by severe molecular constraints which could make this isomer less stable than the trans one. In fact, we have found that the reaction between the (q6-indenyl)Cr(C0)3potassium salt and [Rhh-Cl)(NBD112 in THF affords quantitatively the trans isomer which, however, is stable only at temperatures below -30 "C. The stereochemistry of this product was established by lH (see Figure 2A) and 13C NMR measurements, as the spectra of the reaction mixture proved to be identical to those recorded for solutions of the authentic trans complex, 3. When the temperature was raised above -20 "C, the IR, NMR, and TLC analyses indicated that the trans species isomerizes quantitatively to the cis one (see Figure 2C), which is the sole product isolated at room temperature after the workup of the crude reaction mixture. Thus, in contrast to what would be anticipated on the basis of the structural evidence, the cis isomer 2 is thermodynamically more stable than the trans isomer 3, the formation of which is in turn kinetically favored under preparative conditions. The unexpected stability of the cis isomer 2 seems to trace both t o Rh-Cr bond interaction and to important stabilizing interactions between the NBD hydrogen atoms H11 and H15 and the facing carbonyl groups, as suggested by the experimental evidences reported and discussed in a previous paper.5 Attempts to accomplish the trans cis isomerization starting from a pure sample of complex 3 in THF, with added KC1 and [Rh@-Cl)NBDIzin order to simulate the preparative conditions, failed. As a matter of fact, we

+

+

-

(8) Ceccon, A.; Elsevier, C. J.; Ernsting, J. M.; Gambaro, A,; Santi, S.; Venzo, A. Inorg. Chim. Acta 1993, 204,15.

7

6

5

6

4

Figure 2. Changes in the lH NMR spectrum of complex 3 in THF-ds at 268 Kin the presence of 16.8%[Rh(NBD)]BF4 (Me4Si as internal standard, v,, 80.13 MHz): (A) spectrum after 3 min; (B) spectrum after ca. 24 min; (C) final spectrum (t ca. 90 min).

found that trans-3 isomerizes to cis-2 at room temperature in THF only in the presence of [F&(NBD)]+BF4-. The process takes place at a reasonable rate only when the amount of the salt overcomes a threshold value (ea. 5%),and a strong dependence of the isomerization rate on the catalyst concentration was qualitatively observed. The catalytic effect is not peculiar only to the [Rh(NBD)I+ species, but it was observed with other cations as well, uiz., [Rh(COD)l+, [Rh(COD)21+, [Ir(COD)]+,or [Rh(NBD-ds)l+. Both with deuterated [Rh(NBD-ddl+and with the other cations, careful 'H NMR analysis of the well-resolved signals of the CH2 protons of NBD allowed us t o rule out the occurrence of scrambling between the coordinated Rh(NBD) group and the cation used as catalyst. These results seem to favor a concerted intramolecular rather than a dissociative pathway for the rearrangement. As [Rhb-Cl)NBDl2 induces the isomerization in the preparative and not in the simulated conditions, we believe that only in the former medium is a sufficient catalyst concentration produced. In a quantitative study, the kinetics of the 3 2 isomerization in THF-ds in the presence of 16.8% [Rh(NBD)I+BF4-was monitored by lH NMR spectroscopy between 248 and 267 K, and an intermediate situation of the experiment carried out at 267 K is shown in Figure 2B. Use of the first-order kinetic equation for an irreversible process gave satisfactory plots ( r 1. 0.998) up to 95% reaction, and the calculated values (f5%) of the rate constants are 104k,b, = 0.75 (at 248 K), 1.03 (253 K), 1.70 (258 K), and 4.64 (267 K) = 11.7 f 0.9 kcal s-l. The activation parameters

-

Heterobimetallic Indenyl Complexes

Organometallics, Vol. 14, No. 5, 1995 2433

d ;/2 Rh

I

M+

Figure 3. Proposed mechanism of trans-3

-

Ill cis-2 isomerization (Rh*

mol-' and AS' = -30 k 3 cal mol-l K-l were calculated from the Eyring plot. A likely reaction pathway involving an intramolecular isomerization process assisted by rhodium- or iridiumolefin cations is presented in Figure 3. The ratedetermining step is proposed to be the interaction of the incoming cation M+ (the catalyst) with the n electron cloud of the Cp ring t o produce species I involving a crowded transition state. The Rh(NBD) and the Cr(CO)3units are still in the trans arrangement and the rhodium atom is a-bonded to the indene frame. This associative step is in agreement with the strongly negative activation entropy value; moreover, the low enthalpy barrier allows us to rule out a dissociative route. A cis stereochemistry of Rh(NBD) and cr(co)3 can be achieved through two fast [1,3]-hydrogen shifts I 11and II I11 necessary to invert the configuration a t the indene carbon atom a-bonded t o Rh(NBD). Removal of M+ restores the n coordination of rhodium to the five-membered ring, giving 2. The proposed mechanism is based on the stepwise formation of several ql-indenyl rhodium(1) intermediates. Even though this kind of coordination of rhodium to a cyclopentadienyl residue is very scarcely documented (we are aware of the existence of only a few (qlindenyl)Rh(CNR)r complexesg), we believe that for metals of d8 electronic configuration the existence of species such as 1-111 is reasonable. For example, we have demonstrated the remarkable ability of Ir(1) to form rather stable +indeny1 complexes in the reaction between carbon monoxide and the closely related (indenyl)Ir(COD)lOa and Cr(C0)3-(indenyl)Ir(COD) species.lob The formation of (yl-indenyl)IPintermedi-

-

-

(9) Caddy, P.; Green, M.; OBrien, E.; Smart, L. E.; Woodward, P. Angew. Chem., Int. Ed. Engl. 1977,16, 648.

Rh(Nl3D)).

ates was recently reported by Foo and Bergmaall Moreover, it is worth noting that the isomerization must be carried out in a coordinating solvent such as THF, which seems to be necessary to stabilize the intermediates with coordinatively unsaturated rhodium centers of low hapticity. As far as we are aware, this kind of isomerization in which the metal moves through the Cp plane of the bridging ligand is unprecedented. A nondissociative exchange of the C=C enantioface bound to the metal has been recently reported,12 where the metal is suggested to traverse through the alkene n nodal plane via a carbon-hydrogen a bond complex. Finally, the occurrence of the [1,3]-hydrogen shifts I I1 and 11 I11 as fast steps is in agreement with the previous finding that such procebses in indene derivatives are strongly favored when inorganic units such as Cr(C0)3 are present.13

-

-

Experimental Section General Comments. All reactions were carried out under a blanket of purified argon, and oxygen-free solvents and reagents were used. Solvents were purified according to standard procedures,14distilled, and purged with argon before use. Commercial grade norbornadiene (Aldrich) was dried over MgSOI and distilledjust before use. [F&(NBD)lfBF4-and (10) (a) Bellomo, S.; Ceccon, A.; Gambaro, A.; Santi, S.; Venzo, A.

J. Organomet. Chem. 1993, 453, C4. (b) Bonifaci, C.; Ceccon, A.; Gambaro, A.; Manoli, F.; Santi, S.; Venzo, A. Abstracts of XVIth International Conference on Organometallic Chemistry, Brighton (U.K.), July 10-15, 1994; OA.9. (11) Foo, T.; Bergman, R. G. Organometallics 1992, 11, 1811 and references therein. (12) Peng, T.-S.; Gladysz, J . A. J.Am. Chem. SOC.1992,114,4174. (13)Berno, P.; Ceccon, A,; Gambaro, A,; Daprh., F.; Venzo, A. Tetrahedron Lett. 1988,29, 3489. (14) Perrin, D. D.; Armageo, W. L. F. Purification of Laboratory Chemicals, 3rd ed.; Pergamon Press: Oxford, England, 1988.

Bonifaci et al.

2434 Organometallics, Vol. 14,No. 5, 1995

Table 2. Summary of Crystal Data and Intensity Data Collection for trans3 formula M

aIA blA CIA

Z

Ddg F(000) space group cryst dimenstmm

TIK radiation (AlA) ptcm-1 scan speeddeg min-' takeoff angletdeg 20 rangetdeg unique reflns used reflns (with Fn2> 2u(Fo2)) soln method Rn (on F0Ia RWb

GOP residual @/eA-3

C19H15Cr03Rh 446.22 8.200(5) 11.388(5) 17.868(5) 92.1 1667.4 4 1.78 888 P2 1lc 0.15 x 0.20 x 0.20 298 graphite monochromated Mo Ka (0.710 73) 17.42 2.0 in the 28 scan mode 3 3.0 5 e 5 45 3086 2904 Patterson 0.044 0.045 0.059 0.68

Table 3. Fractional Coordinates with Equivalent Isotropic Thermal Parameters (k> for the Complex trans-[Cr(CO)aIndRh(NBD)la atom Rh Cr CS c9

ClO

OS 09 010

c1 c2

c3 C3a c4 c5

c6

c7 Cla

c11

Cl2 c13 c14 c15 cl6 c17

a

the other used salts were obtained from the corresponding dimers according to literature methods.15 Instruments: mass spectrum, 70 eV-EI, VG-16 MicroMass; IR, Perkin-Elmer 1600 FT-IR; NMR, Bruker AM-400 (IH, 400.133 MHz; 13C, 100.614 MHz) and UP-80 SY (IH, 80.13 MHz). The 'H and 13C NMR spectra were recorded in CDzClz solution at 298 K and are in units of ppm referenced t o internal Me4Si. IR spectra were run as CHzCl2 solutions within CaF2 windows. Preparation of 3. Complex 3 was obtained in quantitative yield by reacting a solution of tran~-[Cr(CO)3(indenyl)Rh(CO)2]~ in CHzClz with a large excess of NBD for 10 min at room temperature. Removal of the solvent and excess NBD in uacuo gave an orange-brown residue which was crystallized from CHzClz/pentane. Mp = 168-172 "C dec. Anal. Calcd for C19H15C103Rh: C, 51.14; H, 3.39. Found: C, 51.01; H, 3.52. MS: m/z 446, M+ (calcd: 446). IR v(C=O) 1949 (vs) and 1872 (vs) cm-l. 'H NMR (CD2C12, 25 "C, assignments confirmed by {'H}-IH NOE): 6 = 6.29 (m, lH, J(lo3Rh-lH) = 2.1 Hz, Hz), 5.22 and 6.12 (m, 2H each, AA'BB', H5,6 and H4,7, respectively), 5.05 (m, 2H, (NBD resonances) 6 = 3.69 (m, 4H, olefin protons), 3.26 (m, 2H, bridgehead protons), 0.99 (m, 2H, CH2). 13CNMR (CD2C12,25"C, assignments made by selective lH-decoupling): 6 = 234.84 (Cr-C=O), 85.51 (d, J('03Rh-13C) = 2.3 Hz, C3a,7a),102.36 (J(13C-1H) = 176 Hz, J(103Rh-13C)= 6.3 Hz, Cz), 90.37 (J(13C-'H) = 173 Hz, C S , ~ ) , 83.33 (J(13C-1H) = 176 Hz, C4,7, 73.29 (J(13C-'H) = 175 Hz, J(lo3Rh-13C) = 4.0 Hz, c1,3);(NBD resonances) 6 = 59.91 (J(13C-lH) = 134 Hz, J(103Rh-13C) = 7.2 Hz, methylene carbon), 48.58 (J(13C--'H) = 152 Hz, J(103Rh-13C) = 2.0 Hz, bridgehead carbons), 43.621 (J(13C-'H) = 176 Hz, J(lo3Rh13C)= 9.0 Hz, olefin carbons). Crystallography. Crystal data, intensity data collection, and processing details for 3 are presented in Table 2. The data were obtained with a Philips PW-100 four-cycle diffractometer with graphite monochromator. Intensity data were collected at 25 "C using the 20 scan method. Two reference reflections, monitored periodically, showed no significant variation in intensity. Data were corrected for Lorentz and polarization effects and an empirical absorption correction was applied t o the intensities. The positions of Cr and Rh atoms were determined from the three-dimensional Patterson function. All the remaining atoms, including hydrogens, were located from (15) Schrock, R. R.; Osborn, J. A. J.Am. Chem. SOC. 1971,93,3089.

X

Y

0.40742(4) 0.08838(7) -0.1295(5) 0.0350(6) 0.1117(5) -0.2661(4) 0.0039(6) 0.1216(6) 0.3803(5) 0.2809(7) 0.1612(5) 0.1747(5) 0.0876(6) 0.1442(6) 0.2758(6) 0.3581(5) 0.3137(5) 0.6131(5) 0.6578(7) 0.6270(9) 0.4400(9) 0.3931(7) 0.5535(7) 0.6652(9)

0.17322(3) 0.23993(5) 0.2025(4) 0.3189(4) 0.1049(4) 0.1795(4) 0.3692(4) 0.0195(4) 0.0643(4) 0.0165(4) 0.0982(5) 0.1991(4) 0.3081(4) 0.3965(4) 0.3740(4) 0.2666(4) 0.1791(3) 0.2902(4) 0.1792(4) 0.1800(6) 0.1812(7) 0.2940(8) 0.3598(5) 0.3088(7)

2

uequiv

~

0.12896(2) 0.31992(4) 0.3056(3) 0.4046(3) 0.3754(2) 0.2981(2) 0.4580(2) 0.4103(3) 0.2341(3) 0.1767(3) 0.1496(3) 0.1986(2) 0.2025(3) 0.2521(3) 0.3025(3) 0.3059(2) 0.2513(2) 0.1244(3) 0.0988(4) 0.0143(4) 0.0115(3) 0.0373(3) 0.0547(3) -0.0057(3)

0.0362(1) 0.0307(2) 0.039(1) 0.043(1) 0.042(1) 0.062(2) 0.071(2) 0.077(2) 0.040(1) 0.051(2) 0.047(1) 0.036(1) 0.047(1) 0.052(2) 0.050(2) 0.038(1) 0.031(1) 0.038(1) 0.055(2) 0.079(3) 0.078(3) 0.073(2) 0.054(2) 0.075(2)

Uequivis defined as one-third of the trace of the orthogonalized

Ui tensor. successive Fourier maps using SHELX-76.16 Anisotropic thermal parameters were used for all the non-hydrogen atoms. Blocked-cascade least-squares refinements converged to R 0.043. The positional parameters of the non-hydrogen atoms are listed in Table 3. The anisotropic thermal parameters of the non-hydrogen atoms, the positional parameters of the hydrogen atoms, and full lists of bond lengths and angles are available as supplementary material. Kinetic Measurements. A 3 mL aliquot of a THF-& mol) solution prepared by dissolving 52.2 mg of 3 (1.17 x in 0.2 mL of a THF-da solution containing 0.39 x mol of [Rh(NBD)]+BF4-(obtained from 4.63 mg of [Rh(u-Cl)NBD]2 and 3.83 mg of AgBF4 as reported in ref 14) were mixed a t M in 3 and 6.14 -70 "C. The resulting mixture (3.65 x x M in [Rh(NBD)]+BFd-,i.e. (mol catalyst)/(mol 3) = 0.168) was stored a t liquid nitrogen temperature. Aliquots of the solution were transferred into precooled 5 mm NMR sample tubes for the kinetic runs. The isomerization reaction was followed a t different temperatures by 80 MHz 'H NMR spectroscopy,the time variation of the concentration of the two isomers being estimated ,by integration of the corresponding signals. Rate constants, kobs, were obtained by plotting the function ln([3Y[3]0)us time. It was possible to use directly the ratio [ n / [ f l o of the signal integrals instead of the concentration ratio, [3Y[3]0, since it was verified that at the end of the reaction [31, = [I],= 0. The sample kinetic plots obtained at four temperatures and the Eyring plot are available as supplementary material.

Acknowledgment. This work was supported in part by CNR through its Centro di Studi sugli Stati Molecolari Radicalici ed Eccitati, Padova, Italy, and through its Progetto Finalizzato Chimica Fine 11. Supplementary Material Available: Full lists of bond distances and bond angles, anisotropic thermal parameters, and fractional coordinates of the H atoms and sample kinetic plot at different temperatures and the Eyring plot (7 pages). Ordering information is given on any current masthead page. OM940781A (16) Sheldrick, G. M. SHELX-76, A System of Computer Programs for X-ray Crystal Structure Determination. Cambridge University, England, 1976.