6962
Kinetics and Mechanism of Sulfur Dioxide Insertion in Pentaha~to(substitutedand unsubstituted cyclopen tadienyl)alkyl( and -aryl)dicarbonyliron( 11) Complexes Stephen E. Jacobson and Andrew Wojcicki" Contribution from the McPherson Chemical Laboratory, The Ohio State University, Columbus, Ohio 43210. Received May 26, 1973
Abstract: The rates of the cleavage of the iron-carbon bond in h5-C5HhFe(CO)2R and related (K-ring)Fe(CO)?R complexes by SO2 have been investigated in neat sulfur dioxide. The reactions were followed by infrared spec-
trophotometry in the v(C0) region over the temperature range -70 to -23". For the h5-CSH5Fe(CO)zR alkyls, the reaction velocity generally decreases with an increasing value of the Taft u* and with increasing v(C0) of the reacting complex, e.g., R = CHZCHB> CH3 > CHZOCHB> CH2CN. However, as the bulkiness of R increases, or CH2CH2C(CH&> CH2Cthe rate of iron-carbon bond cleavage decreases, e . g . , R = CH3 > CHZCH(CH~)~ (CH3)3 > C(CH3)3. For the N-C5H5Fe(CO)?Raryls, the rate constant decreases as a function of increasing g+, ciz., R = P - C ~ H ~ O C>Hp-C6H4CH3 ~ > m-C6H4CH3 C&, with p = -4.3. Methyl substitution on the cyclo>> pentadienyl ring increases the rate of the insertion when R = CH2C6H5, ciz., [hj-(CH3)5C5]Fe(C0)2CH2C6H5 (h5-CH~CgH4)Fe(CO)2CHGH~ > N-C5H5Fe(C0)2CH2CcHS,but does not produce a regular trend when R is an aryl group. These insertion reactions have characteristically large and negative values of A S * (-62 to -43 eu) and low values of AH* (2.9-7.8 kcal/mol). The observed rate dependence on the nature of R demonstrates that the cleavage of the Fe-R bond is an electrophilic process. Fur the iron alkyls, the results are consistent with a backside attack of SO2on the cy carbon which leads to the heterolysis of the Fe-R bond and formation of a contact ion pair (h5-ring)Fe(CO)2+O2SR-. These ions appear to recombine rapidly to yield the 0-sulfinate, (hS-ring)FeThe 0-sulfinate then isomerizes (CO)20S(0)R,and, more slowly, to give the S-sulfinate, (/~~-ring)Fe(C0)~S(O)~R. to the S-sulfinate, which is the final product of the insertion.
-
C
onsiderable interest has been evidenced in recent years in insertion reactions involving transition metal complexes. Although much synthetic work has been done in this context, few kinetic studies have been carried out. The insertion of carbon monoxide into transition metal-carbon bonds has been the only reaction whose mechanism has received more than cursory a t t e n t i ~ n . ~ Since its discovery in 19644 the sulfur dioxide insertion has been also largely dominated by synthetic considerations5n6 More recently, however, active interest has developed in its mechanism. Spectroscopic (infrared and 'H nmr) studies have demonstrated' intermediacy of the oxygen-bonded sulfinates in the formation of the sulfur-bonded sulfinates from SO, and metal alkyls and aryls of the type h5-C5H,Fe(CO),R, hs-CjHjMO(CO)~R,and M(CO),R (M = Mn or Re). Stereochemical investigations on the insertion have been also r e p ~ r t e d ; the ~ , ~elegant experiment of Whitesidesg has demonstrated inversion of configuration at the cy carbon in the formation of h5-CjHjFe(CO)2S(0)2CHDCHDC(CH& from the corresponding metal alkyl and s02. We now report the kinetic results of our study on the SO, insertion involving some h6-CjH5Fe(CO)ZRand (1) M. F. Lappert and B. Prokai, Adcan. Organometal. Chem., 5 , 225 (1967). ( 2 ) R. F. Heck, Adcan. Chem. Ser.,No. 49, 181 (1965).
(3) A. Wojcicki, Adaan. Organometal. Chem., 1 1 , 8 7 (1973). and A. Wojcicki, J. Amer. Chem. Soc., 86,5051 (1964). (5) W. Kitching and C. W. Fong, Organometal. Chem. Reo., Sect. A , 5,281 (1970). (6) A. Wojcicki, Accounts Chem. Res., 4, 344(1971). (7) S. E. Jacobson, P. Reich-Rohrwig, and A. Wojcicki, Znorg. Chem., 12,717(1973). ( 8 ) J. J. Alexander and A. Wojcicki, Znorg. Chim.Acta, 5,655 (1971). (9) (a) G. M. Whitesides and D. J. Boschetto, J . Amer. Chem. Soc., 93, 1529 (1971); (b) G. M. Whitesides and P. L. Bock, private com-
other, structurally similar, iron complexes. Based on these and related previously reported a plausible mechanism is suggested for the insertion. This paper deals entirely with the reactions in neat SOs; communicated later will be our investigation on the insertion in organic solution. A preliminary account of this work was published earlier." Kinetic studies on insertion of SO2 into tin-carbon bonds have been also reported.'*
Experimental Section General Procedures. A nitrogen atmosphere was used routinely in all preparative and kinetic aspects of this work. Ventron and Florisil alumina, deactivated with distilled water ( 6 1 0 (60-100 mesh), from Fisher Scientific Co., were employed in chromatographic separations and purifications. Elemental analyses were performed by Dr. F. Pascher, Mikroanalytisches Laboratorium, Bonn, Germany. and by Galbraith Laboratories, Inc., Knoxville, Tenn. Physical Measurements. Except as noted in Table I, all infrared measurements were made with a Beckman Model IR-9 spectrophotometer. Solution spectra at 25" were obtained using NaCl sample cells of 0.05, 0.10, and 0.50 mm thickness in conjunction with matched reference cells. Solid-state spectra were obtained as Nujol mulls. Hydrogen-1 nmr spectra were obtained on a Varian Associates A-60 spectrometer using tetramethylsilane (TMS) as an internal standard. Melting points were measured either in capillaries using a mineral oil bath or with a Thomas-Hoover capillary melting point apparatus; they are uncorrected. Materials. Anhydrous grade SOs, from Matheson, was purified and dried as described elsewhere.' The compound [N(CH3)4]&0j
z),
(4) J. P. Bibler
munication.
(10) S. E. Jacobson and A. Wojcicki, in preparation. (11) S. E. Jacobson and A. Wojcicki, J . Amer. Chem. Soc., 93, 2535 (1971). Although it was shown subsequently (cf. ref 7) that the re-
action followed is not a one-step conversion, hj-CsHiFe(CO)nR SO2 /r~-C5HbFe(C0)TS(0)2R, this does not alter the correctness of the reported experimental data. (12) (a) C. W. Fong and W. Kitching, J . Amer. Chem. Soc., 93, 3791 (1971); (b) C. W. Fong and W. Kitching, J . Organometd Chem., in press; (c) C. J. Moore and W. Kitching, private communication.
+
Journal of the American Chemical Society 1 95:2I 1 October 17, 1973
-f
6963 Table I.
Melting Points and Infrared and lH Nmr Spectra of New (/~~-ring)Fe(CO)~R Complexes
____-
Compd---
Ring
Ir, cm-l----
7 -
R
MP, 'C
V(C0)b
C,H, C,H,
CH?C(CH313 CHsCsHaOCH3-p
011 69-71
2005, 1950 2007, 1955
C,H,
p-C sH4OCH3
63-64
2027, 1971
C,H,
0-C sH 4CH I
67-68
2024, 1968
C,H,
m-CsH4CH3
48-49
2027, 1970
CH3CaHa
CH2CsHa
011
2007, 1956
U
2024, 1967
50-5 1
2019, 1967
91-92 88-89 165-166 86-87
1993, 1943 2008, 1958 2001, 1950 2008, 1957
C H I C ~ H I CsH, CHIC,H.j
P-CsHaCHs
(CH3)jCj (CH8)jCj (CH3)jCj C9H7
CHzCsHj CHXN CsH; CHtCsHj
CjHj
S(O)G(cHd3
CjHj
S(O)zCHzC(CH3)3
145-146
CjHj
S(O)CHzCH(CHd2
103-105
C;Hj
S(0)zCHzCHzC(CH3)3 185-203 dec
CjHj
lH nmr,
V(S0)C
7.
C H 3 , 9 . 0 4 ~ ;C H 2 , 8 . 2 4 ~ ;CjHj,5.26S CHZ, 7.27 S ; CH3, 6.25 S ; CjHj, 5.27 S ; C6H4,3.43-3.22 m(2), 3.03-2.74 m(2) CH3, 6.36 S ; CjHs, 5 30 S ; CeH4; 3.75-3.21 m(2), 3.10-2.56 m(2)t CH3, 7.62 S ; CjHj, 5.29 S ; CeHa, 3.47-3.01 m(3), 2.71-2.43 m(l)J CsH4, 3.53CHI, 7.82 S ; CjHj, 5.58 CHI. 2.638.26 mf S ; CHI, 7.44 S ; CjH4, 5.70 S ; CsHs, 3.06 Sg CHI, 8.29 S ; CjHd, 5.42 m,5.31 m; CsHs, 3.17-2.87 m(3), 2.67-2 37 m(2) CjCH3, 8.35 S ; CeCHa, 7 . 7 9 s; C5H4, 5.49 m, 5.41 m ; C&, 3.34-3.08 m(2), 2.852 , 6 0 m(2) CHI, 8.25 S ; CH?, 7.79 S ; CsHj, 2.96 S U CH3, 8.36 S ; CeHj, 3.13-2.46 m
1178, 1033 1179, 1048
CH3, 8.83 S ; CHz, 6.87 s ; C&;, 4.85 s
1181, 1172 sh, 1050 1188, 1175 sh, 1049 1206, 1046
CH3, 8.93 d ( J = 6 Hz); CH, 7,9-7.2 m ; CH2, 6.97 d ( J = 6 Hz); CjHj, 4 . 8 5 s CHI, 9.07 s; CCHzC, 8.46-8.09 m ; SCH2, 7.12-6.77 t: CjHs. 4.85 s
S(O)?CH?CsHaOCHs-p 167-168
2059, 2049, 2012, 2000 2058, 2048, 2009-2001 br 2060, 2049, 2012, 2001 2059, 2050. 2014, 2005 2061, 2008
CHz, 7.93 S ; CsH3, 5.39 t ( J = 2 . 5 Hz)(l) 4.69 d ( J = 2 . 5 H2)(2); C&4, 2.92 S; CsHs, 3.00-2.64 m CHI, 8.73 S ; CjHj, 4.79 s
CjHj
S(O)pCH20CH3
2060, 2013
CiHa C;H: CjHj
S(O)zCHcSCH3 S( O)zCH2CH2CN S(0)2CsH4OCH3-p
114-116 163-164 dec
2062, 2021 2067, 2027 2059, 2010
1200, 1185 1046 1187, 1045 1186, 1047 1193, 1038 br
CjHj
S(0)2CsHdCHz-O
149.5
2056, 2011
1192, 1040
CjHj
S(O)zCsHiCH3-m
143
2060, 2011
1191, 1046
CH3CjH4
S(O),CH,C,Hj
111-1 12
2056, 2005
137-1 39
2055, 2005
1198, 1175, 1038 br 1192, 1038
2028, 1980 2029, 1983 2058, 2006
1173, 1030 1179, 1041d 1199. 1053
C H I C ~ H I S(O)zCsHaCH3-p (CH3)jCj (CHdjCs CgH7
S(O)zCH;CsHj s(o),CsH: S(O)zCHK6Hj
U
82.5 U
U
188-190 152 dec
CH2CH2,7.17-6.45 m ; CjHj, 4 74 s
U
CHD, 6 01 S ; CjHj, 4.82 S ; CsH4, 3.10-2.72 m, 2 . 3 c 2 . 0 6 m CHI, 7.19 S ; CjHj. 4.99 S ; C6H4. 2.87-2.56 m(3), 2.33-1.99 m(1) CH3, 7 54 S ; CjHr, 4.94 S ; CGH4, 2.752.25 m CH3, 8 , 0 2 s; CH2, 5.79 m ; CjHd, 5.25 m 5.13 m ; CsHj, 2.57 S CZCH3, 8.06 S ; CsCH3, 7.59 S ; CjHa, 5.18 m, 5.04 m; C&4, 2.86-2.53 m, 2.412.15 m CH3, 8 . 1 5 S ; CHc, 5.87 S ; CeHj, 2.69 s 5.79 S ; CjH3, 4.63 t ( J = 3 Hz)( I), CH2, U 4.30 d (J = 3 H2)(2); CGHI-CBHI,2.802.34 m
Cyclohexane solution of the alkyls and aryls, CHC13 solution of the S-sulfinates. All absorptions are very strong, a Not measured. Recorded on a Perkin-Elmer Model 337 spectrophotometer using, except as noted, Nujol mulls. Unless otherwise indicated, all absorptions are strong. Abbreviations: br = broad, sh = shoulder. CHC1, solution. e CDCl3 solution unless otherwise noted. For groups containing nonequivalent hydrogens, the number of absorbing protons is given in parentheses. Abbreviations: s = singlet, d = doublet, CSzsolution. t = triplet, m = complex multiplet. f CC14solution. c
(CsHj = indenyl) were prepared by literature procedures; [(/I5was prepared by the method of Jander and Hecht.13 Other chemiCjHj)Fe(CO)z]zwas purchased from Strem Chemical Co. cals were procured in reagent grade quality and used as received. The majority of the alkyls hs-CjHjFe(CO)zR,ciz., R = CH3,'j Organic solvents were purified by standard pr0cedures.j CzHj,'7 CH(CH3)z,18C(CH3)3,lSCH?CH(CH3)2," CHzCHzC(CH3)3,' Metal Alkyls (Aryls) and S-Sulfinates. The melting points and CHzCsHj," C H ( C H ~ ) C G HCHICN," ~,~ C H I O C H ~ , CHZSCHI,*~ '~ infrared and lH nmr spectra of all new alkyl (aryl) and S-sulfinato complexes are presented in Table I. Analytical data are provided in Supplementary Table Ia. l 4 (17) T.S.PiperandG. Wilkinson, J . Inorg.Nucl. Chem.,3,104(1956). The metal carbonyl starting compounds [(/z6-CH3CjH4)FeM. L. H. Green and P. L. I. Nagy, J . Organometal. Chem., 1, CO)212,15{ [/15-(CHI)jCj]Fe(CO)I] z , 1 6 a and [(/i5-C9H7)Fe(C0)z]z16b 58(18) (1963). (19) W. P. Giering and M. Rosenblum, J . Organometal. Chem., 25, C71 (1970). (1 3) G. Jander and H. Hecht, Z. Anorg. Allg. Chem., 250,304 (1943). (20) M. L.H. Greenand M. J. Smith,J. Chem. SOC.A , 3220(1971). (14) See paragraph at end of paper regarding supplementary ma(21) J. P. Bibler and A . Wojcicki,J. Amer. Chem. SOC., 88,4862(1966). terial. (1 5) D. A. Ross, Ph.D. Thesis, The Ohio State University, 1970. (22) J. I
