J. Phys. Chem. 1992,96,9568-9571
9568
remains an intemting point that needs to be further clarified. We
HzFeOs3(C0)1z/Si02+ CO
(2) occurring on the surface of ~ i l i c a .It~ is worth pointing out that this is essentially the same as the reaction shown in eq 1. The initial photochemical process occurring in matrixes at 77 K,and on the surface of silica, involves the dissociation of one CO ligand. The matrix systems allow the photoproduct to be isolated and studied. In a similar manner, on the surface of silica the initial photoproduct HzFeOs3(C0)12appears to be stable and its spectra can be obtained. This stabilization in the silica system can be rationalized as involving the surface hydroxyl group which are the only functionality available to act as a stabilizing ligand" as mentioned in our previous paper.3 This stabilization prevents disproportionation of the tetranuclear photoproduct to smaller clusters. In addition, the dissociated CO is easily lost from the surface because there is no possibility for a cage effect on the open silica surface. The loss of CO from the surface p ~ ~ e natgeminate s recombination of the coordinatively unsaturated cluster HzFe O S ~ ( C Owith ) ~ ~the released CO. The formation of H2FeOs3(CO)12on the surface of silica and its observation are similar in many ways to the solid matrix systems at 77 K. H2FeOS3(C0)13/Si02
arenowstudyingfurtberthephotochemistryof~carbonyl clusters on the surface of silica and in solid matrixes to address this interesting point. The results will be published elsewhere. Acknowledgment. We thank Mr. H. Yao of the Central R e starch Institute of Mitsui Toatsu Chemicals, Inc., for preparation
of the polystyrene film sample.
Refemma urd Notes (1) Gam, B. C.; Guczi, L.;Knozinger, H. Metal Clwters in Catalysis; Elrevia: Amsterdam. 1986. (2) (a) Yamamoto, S.;Lewis,R. M.;Hotta, H.; Kuroda, H. Inorg. Chem. 1989.28, 3091. (b) Yamamoto, S.; Lewis, R. M.; Hotta, H.; Kuroda, H. Vacuum lm,41,65. (c) Yamamoto, S.;Lewis, R. M.;Nabata, Y.; Hotta, H.; Kuroda, H. Inorg. Chem. 1998,29,4342. (3) Yamamoto, S.;Miyamoto, Y.; Koizumi, M.;Lewis, R. M.;Morioka, Y .; Asakura, K.; Kuroda, H. to be published in J. P h y . Chem. (4) Burdett, J. K.; Pmtz, R. N.; Poliakoff, N.; Turner, J. J. Pure Appl. Chem. 1977,49,271. (5) (a) Hcpp, A. F.; Wnghton,M.S. J. Am. Chem. Soc. 1983,105,5934. (b) Bentsen, J. G.; Wnghton, M.S.J . Am. Chem.Soc.1S4,106,4041. (c) Bentsen, J. G.; Wrighton, M. S.J. Am. Chem. Sor. 1987,109,4518. (6) Hooker, R. H.; Mahmoud, K. A.; Rest, A. J. J. Chem. Soc., Chem. Commun. 1983, 1022. (7) Burkhardt, E. W.; Geoffroy, G. L. J. Organornet. Chem. 1980,198, 179. ( 8 ) Mum, S. L. H d M of Photorhemhtrv; Marcel D e b , Inc.: New York, 1973. (9) (a) Abrahamson, H. B.; Frada, C.; Ginley, D. S.;Gray, H. B.; Lilienthal, J.; Tyler, D. R.; Wrighton, M.S. Inorg. Chem. 1977, 16, 1554. (b) Tyler, D. R.; Levenson, R. A,; Gray, H. B. J. Am. Chem. Soc. 1978,100, 7888. (c) Delley, B.; Manning, M.C.; Ellis,D. E.; Berkowitz, J.; Trogler, W. C. Inorg. Chem. 1982,21,2247. (10) Foley, H. C.; Geoffroy, G. L. 1.Am. Chem. Soc. 1981,103,7176. (1 1) M m y , G. L.; Gladfclter, W. L. J. Am. Chem. Sor. 19n. 99,7565. (12) The photochemical reaction of H2FcCh3(C0),, a h b e d on the surface of silica ie independent of the loading of the metal carbonyl. Thus, we present here the spectrum of the photoproduct from 2 wt 96 H2FcCh3(C0),3 on silica becaw the spectral nsdutim of this -le with lowgcarbonyl load* b better than that for samples with higher carbonyl loadings. (13) ForwmpIe,thewcakpeakat2109~n-~ sceainthespaanunofthe polyltyrsacfhcannot hobraved in the spectra ofthe-on dica or in that of the 3-methylpentane matrix sample. The caw for the lack of the weak ahrption peak at 2109 cm-I is not clear. (14) JacLson, R. L.;Truaheim, M.R. J. Am. Chem. Soc. 1982,104,6590.
Conclrmion Using the matrix isolation technique, we were able for the first time to observe the W-visible and IR absorption spectra of the coordinatively unsaturated cluster H2FeOs3(CO)L2. FT-IR spectroscopy revealed that H2FeOs3(C0)12has the same two bridging CO ligands as the parent HzFeOs3(C0)13cluster. H2FeOs3(CO)lzhas a structure in which the unsaturated site is at the Os atom which does not have a bridging CO ligand. It was found that HzFeOs3(CO)lzis so reactive that it recombines with CO even at the low temperature of 180 K. From the similarity of the UV-visible and IR spectra of the matrix isolate photoproduct with the spectra of the photoproduct formed on silica, we can assign the photoproduct on silica as H2FeOs3(CO)11.This c o n f i i our previous postulate about the photochemical reaction of H2FeOs3(CO)13on the surface of silica. Finally, the nature of the stabilization of the coordinatively unsaturated cluster H2FeOs3(C0)1zby the silica surface, even at room temperature,
Estimation of Heats of Formation for Vinyl Derivatives Yu-Ran Luo and John L. Holmes* Department of Chemistry, University of Ottawa, Ottawa, Ontario, Canada KIN 6N5 (Received:May 7, 1992; In Final Form August 18, 1992) The heats of formation for vinyl compounds can be estimated by the following equation: AfHO(C2HsX)= AfHO(C6H5X)
- 7.1 (f1.5)kcal/mol. This new relationship provides a useful supplement to group additivity rules.
For X = H, CH3, and CzHSthe difference between the heats of formation were 6.9, 7.1, and 7.3 kcal mol-', respectively. Using the average value, 7.1 kcal mol-', and the AfW values for phenyl halides, AfW for CzH3F,CzH3C1,and CzH3Brwere estimated. The work was followed by a discussionof heterocycle aromaticity.' In another ampilation,8 George reported a similar mult, namely 1.0060&F[C6H&] -7.3 1.5 kcalmol-', A&P[CHzCHX] b a d upon 12 data points. However these earlier studies did not use all the available experimental data and did not consider possible discrepancies and uncertainties. The present work discusses the data from 37 molecular pairs.
Introduction There are relatively few experimental values for the standard heats of formation, A$P, for molecules containing the vinyl gr0up.I The recent difficulty in estimating 4W for vinyl iodid& has prompted us critically to evaluate all available data on vinylic molecules with the intent of finding an appropriate reliable additivity term or similar empirical relationship which can be widely used. Two approaches have been employed in this work. The first involves the use of a recently described electmmgativity (EN) scale and the correspondingcovalent potential V,.4J This has bcen used to correlate heats of formation and bond strengths for a wide range of compounds. The second a p c h involved the empirical comparison of the available experimental enthalpy data for molecules containing a formal vinyl group with their phenyl analogues. Some progress has been reported in two books. Six years ago Liebmand compared AfHO(CHzCH-X) with AfW(C6Hs-x). 0022-3654/92/2096-9568$03.00/0
*
R d Q urd Dbcuesion Table I gives the available experimental data for vinyl and phenyl derivatives, together with the estimated errors. In an earlier study by Luo and Benson4it was found that a linear correlation (8
1992 American Chemical Society
Heats of Formation for Vinyl Derivatives
The Journal of Physical Chemistry, Voi. 96, No. 23, 1992 9569
(1) Valid for Eq 1 X is an atom F
c1
Br H C-centered substituents CH3 CZH5 C3H7 i-Pr C4H9 sec-Bu i-Bu I-BU C2H3 C6H5 CHCHCHJ (trans) CHCHCH, (cis) C(CH3)CHZ CHZOH CH3COO CHO COOH CHzCl CH2Br CN 0-centered substituents OH OCZHS OC6H5 metal-centered substituents Sn(CH313 using AfHO(C2H3X)suggested
I NO2
-33.2 f 0.4 8.9 f 0.5 18.9 f 0.5 12.5 f 0.1
-27.7 f 0.4 13.0 f 0.2 25.2 f 1.0 19.7 f 0.2
-5.5 -4.1 -6.3 -7.2
f 0.6 f 0.7 f 1.2 f 0.3
4.8 f 0.2 0 f 0.3 -5.1 f 0.3 -6.6 f 0.2 -10.4 f 0.4 -11.8 f 0.4 -12.3 f 0.5 -14.5 f 0.4 26.3 f 0.3 35.3 f 0.2 19.4 f 0.2 18.2 f 0.1 18.6 f 0.3 -29.7 4 0.5 -75.3 f 0.2 -18 -77 -1.3 f 0.6 10.8 f 1.1 44
12.0 f 0.2 7.1 f 0.3 1.9 f 0.2 1.0 f 0.3 -3.1 f 0.3 -4.2 f 0.4 -5.1 f 0.4 -5.4 f 0.4 35.3 f 0.4 43.6 f 0.3 29 28 27 f 1.5 -24.0 f 0.4 -66.8 f 0.5 -8.8 f 0.7 -70.3 f 0.6 4.5 f 0.7 16 f 0.5 52
-7.2 -7.1 -6.9 -7.6 -7.3 -7.6 -7.2 -9.1 -9.0 -8.3 -9.6 -9.8 -9.0 -5.7 -8.5 -9.2 -6.7 -5.8 -5.2 -8
f 0.3 f 0.5 f 0.4 f 0.4 f 0.5 f 0.6 f 0.7
-3 0 -33.7 f 0.3 5.4 f 0.5
-23.0 f 0.3 -24.3 f 0.2 12.4 f 0.4
-7.0 f 1.0 -9.4 f 0.4 -7.0 f 0.7
a From refs 1 and 9 unless indicated. fReferencc 12.
27 f 1
-5 f 3.2
32Sb 9 f 2c
39.4 f 1.4 16.1 f 0.2
-6.9 f 2 -7.1 f 2d
0 -11.8 -11.4 -3.8 -1.2
f 2.1 f2 f 2.1 f2
From ref 3. 'Suggested by Benson; see ref 16. dCalculation based on ref 5 . 'See text for discussion.
-161
I
I
f 0.9 f 0.4 f2 f2 f 1.6 f 0.7 f 0.6 f 1.5 f 1.5 f 1.0 f 1.3 2
22 f 3
(2) Exceptions for Eq 1' 73 73 25.2 f 0.4 37 f 2 -32.18 f 2 -20.7 f 0.4 -143.2 f 0.3 -146.8 f 1.6 -23.8 25.0 f 1.4
CCH CHZCHCHZ COCHJ CF3 CHzI
f 0.6
40I
1
r
I
-4d5
-;5
-1;
-4 afH0(C6H,X),
d
1;
5:
35
4)5
kcaI/moI
Figure 2. Linear relation between AfW(c6H5x)and AfHO(C2H3X).
to saturated compounds. However, it is noteworthy that the points in Figure 1, although scattered, are similarly displaced for the two unsaturated grOupS, the C6H& points being always a . 7 kcal mol-' above their C2H3X counterparts.
AfH(C2H3X)= A#f(C&X)
- 7.1 k 1.5 kcal mol-'
(1)
Accordingly, the difference A~HO(CZH~X) - AfW(C6HSX)= AAf~(C2H3X/C6H5X) was found to be a constant, 7.1 f 1.5 kcal mol-', as illustrated in Figure 2 and also presented in Table I.
9570 The Journal of Physical Chemistry, Vol. 96, No. 23, 1992 TABLE II: Five Exceptions; from Table I AJZO,
expt'
3
TABLE IIk Valws for Apo(C2H&) or A,Ho(C&X) Estimated Using the A(ArHo) and Group Additivity (GA), kcal mol-' (1)
estd by GAb this worlf
73 73 CiH&H2CHCH2 37 k 2 C2H3CH2CHCH2 25.2 f 0.4 C6HsCOCHn -20.7 & 0.4 -32.1 f 2d -143.2 f 0.3 -146.8 f 1.6 25.0 f 1.4 23.E' f 1 .O
2
kcal mol-]
Luo and Holmes
78 69.2 32.4 25.4 -20.9 -29.4 -140.7
78.5 f 1.5 71.4 f 3 32 f 1 25.2 f 0.4 -20.7 f 0.4 -27.8 f 1.9 -143.2 f 0.3 -150.3 f 1.8
Arff(C2H3X) Estimated
N3
NHNHZ NHCHI NHCOCH.
30.4
