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J . A m . Chem. SOC.1984, 106, 3484-3491
primarily 1-pentene. Polymerization o r extended oligomerization
does not occur in a n y of these reactions because the product olefins a r e less reactive than their precursors toward t h e dirhenium center, presumably for steric reasons. W e a r e currently exploring t h e chemistry of various phosphine-substituted (p-hydrido)(p-alkeny1)dirhenium carbonyl compounds, to vary the steric a n d electronic characteristics of t h e catalyst a n d t o address t h e problem of catalyst decomposition. W e a r e also investigating other polynuclear m e t a l systems with respect t o similar catalytic activity.
Acknowledgment. We t h a n k J. R. Shapley a n d K. S.Suslick for use of t h e g a s chromatographs. High-field NMR facilities
were provided by a g r a n t f r o m t h e National Science Foundation (NSF G r a n t CHE 79-16100).
Registry No. I, 82621-42-9; I d 4 , 88035-65-8; IIa, 82638-69-5; IIb, 88082-36-4; IIIa, 82621-39-4; IIIb, 88082-37-5; IIIc, 82621-43-0; IV, 89958-85-0; V, 90026-98-5; cis-V, 89958-86-1; Re2(CO)lo,14285-68-8; C2H4, 74-85-1; C2D4, 683-73-8; (p-H)(p-tr~ns-CH=CHPh)Re~(C0)~, 86244-50-0; ”CO, 1641-69-6; PPh3, 603-35-0; HRe(C0)4(PPh3), 25838-69-1; Re, 7440-15 - 5 ; frans-4-methyl-2-pentene,674-76-0; cis-2pentene, 627-20-3; frans-2-pentene, 646-04-8; 1-pentene, 109-67-1; cis2-butene, 118-03-6; trans-2-butene, 624-64-6; 2-hexene, 592-43-8; cis3-hexene, 7642-09-3; trans-3-hexene, 13269-52-8; methyl vinyl ether, 107-25-5; 1-hexene, 592-41-6; butene, 25167-67-3; styrene, 100-42-5; 1-butene, 106-98-9; propylene, 11 5-07-1.
Organoactinide Carbonylation and Carboxylation Chemistry. Structural, Electronic, Bond Energy, and Photochemical Effects on Migratory Insertion in the Tris(cyclopentadieny1)thorium Hydrocarbyl Series David C. Sonnenberger, Eric A. Mintz, and Tobin J. Marks* Contribution f r o m t h e D e p a r t m e n t of Chemistry, Northwestern University, Evanston, Illinois 60201. Received S e p t e m b e r 28, 1983
Abstract: This contribution reports a synthetic and kinetic study of C O migratory insertion for the series of thorium hydrocarbyls Th(v5-C5H5),R,R = i-C3H7, sec-C4Hg, neeC5H11,n-C4H9, CH2Si(CH3)3,CH3, and CH2C6H5. Under the conditions employed, the reaction was found to be first order in Th(C5H5)3Rand first order in CO. In the above order, the relative rates of migratory insertion were found to be 42:18:1.3:1.0:0.02:0.01: --
1.5
-
I. 0
-
0.5
-
u
0.0-
-0.5
-
-1.0
-
-1.5
-
-2.01, 0
,
, 200
,
,
,
,
I
60C
433
;]me
,
I
,
1959
833
,
,
1239
i fs9
imirr tins)
Figure 1. Kinetic plot for carbonylation (disappearance) of Th(C,HS),CH2C(CH3),at 23 O C and 680 torr CO.
\
S I ( C H ~ ) H~
3g is formulated as an enolate on the basis of infrared spectroscopy (vC4 = 1567 cm-') and 'H N M R (olefinic resonances at 6 4.45 and 4.87 J C 1 Hz). This type of product has been identified in closely analogous bis(pentamethylcyclopentadieny1)chemistry and has been connected with the facile rearrangement of an intermediate acyl (eq 9). Enolate 7 exhibits uM = 1576 cm-' (Ul3-
7
= 1538 cm-') and 'H N M R olefinic resonances of the proper intensities at 6 4.54 and 4.88 (singlets). The greater migratory aptitude of a third-row element such as silicon over that of hydrogen is well documented in carbene chemistry.20acv22 In the case of eq 8, compounds l g and 3g are the only species observed by 'H N M R during the course of the reaction at 70 OC. From these results and those in eq 9, it is inferred that the rate-limiting step in eq 8 is C O activation and that subsequent rearrangement of the resulting acyl 2g to 3g is comparatively rapid under these conditions. Cp ;Th-:CCHZSI(C
H313
2g
The benzyl compound l e is the least reactive of the thorium hydrocarbyls investigated. At 50 OC, 1 atm of CO, negligible carbonylation is observed after 3 days. At higher temperatures, the 'H N M R of the reaction mixture evidences a great multiplicity of resonances, suggesting that insertion is accompanied by a number of other chemical transformations. Th(C5HS),RCarbonylation Kinetics. Once the nature of the Cp,ThR carbonylation chemistry had been established, a detailed examination of reaction velocities was carried out by 'H NMR. The rate of disappearance of Cp,ThR resonances was monitored at various C O pressures under conditions which were pseudo first order in CO. In all cases, plots of In A, vs. time were linear over at least 3 half-lives. Some representative data for Cp3ThCH2C(22) (a) Kirmse, W.'Carbene Chemistry", 2nd ed.;Academic Press: New York, 1971; Chapter 12. (b) Robson, J. H.; Shechter, H. J . Am. Chem. SOC. 1967,89,7112.
Pressure o f
LO
(torr)
Figure 2. Dependence of the observed rate constant for the carbonylation
of Th(C,HS)3(i-C3H7) on CO pressure.
Table I. Kinetic Data for Cp,ThR Migratory CO Insertion" compd Cp3Th(i-C3H7)
T, O 23
C
pco, torr
1OSkobsdrb
47 77
8.8 (1.0)' 11 (2) 13 (2)' 14 (2)d 26 (3)' 3.2 (9) 3.5 (5) 2.6 (3) 0.23 (4) 0.12 (2)
17 82 148
S-1
130 (10)
55 (15) Cp3Th(sec-C4H9) 23 44 3.9 (6) Cp,Th(neo-C5H11) 23 680 2.9 (3) CP~T~(~-C,HSJ 23 690 0.25 (4) Cp3ThCH2Si(CH3)3 45 690 0.13 (2) CpiThCHi 45 700 aAll rates are the average of at least two separate trials. bError limits are 95% confidence interval. 'Obtained by using A,' in place of A,. dUsing 70% of normal spinning rate during the reaction.
(CH,), are shown in Figure 1. Fitting of these plots by standard linear-regression techniques yields observed reaction rate constants, koW, which are compiled in Table I. It was also found that the magnitude of koM was linearly dependent upon the CO pressure (Figure 2). Assuming that Henry's law is obeyed, these observations are consistent with the rate law shown in eq 10 where k o ~ rate = kobsd[Cp3ThR]= k[Cp,ThR][CO] (10)
= k[CO]. Table I also shows derived k values. From these data, it can be seen that the variation of migratory CO insertion with R functionality follows the ordering isopropyl > sec-butyl >> neopentyl > n-butyl >> CH2Si(CH3),> methyl > benzyl. The
J. Am. Chem. Soc.. Vol. 106, No. 12, 1984 3489
Organoactinide Carbonylation dispersion in these rates with alkyl group is significant. For example, there is a 103-fold decrease in rate on proceeding from R = isopropyl to R = methyl. Photoassisted Migratory CO Insertion. Migratory insertion of CO was also found to occur under conditions of photochemical excitation. Experiments with Cp3ThCHzSi(CH3),,which is not susceptible to photoinduced P-hydride elimination,* revealed that the photochemical insertion is not as clean as the thermal reaction, but that insertion/rearrangement product 3g is initially formed more rapidly (20% yield in 11 h for the photochemical reaction vs. no detectable reaction (
