discussed here and leaves little doubt as to the appropriateness Of the uncatalyzed reaction as a d e l . Omission from these calculations of the data for the p C F 3 compound results in p = 5.08 f 0.13, r = 0.998 for the correlation with u and p = 3.25 f 0.31, r = 0.986 for the correlation with u-. A. I. Biggs and R. A. Robinson, J. Chem. SOC..388 (1961). J. Miller, “Aromatic Nucleophilic Substitution,” Elsevier, New York, N.Y., 1968, p 146. J. Miller, !bid., p 78. 0. Exner il: “Advances in Linear Free Energy Relationships,” N. B. Chapman and J. Shorter, Ed., Plenum Press, New York, N.Y., 1972, p 26. P. Neta and R . H. Schuler, J. Am. Chem. Soc., 94, 1056 (1972). A p of -0.45 was observed. M. Mohammad and E. M. Kosower. J. Am. Chem. Soc., 93, 2709 (1971). A p of 4-14 was observed. D. J. Creighton, J. Hajdu, G. Mooser, and D. S. Sigman. J. Am. Chem. Soc.,95, 6855 (1973); J. J. Steffens and D. M. Chipman, J. Am. Chem. Soc., 93, 6694 (1971). A detailed investigation of isotope effects on the reactions reported here is in progress.
Linda C. Kurz, Carl Frieden* Department of Biological Chemistry Division of Biology and Biomedical Sciences Washington University St. Louis, Missouri 631 10 Received November 14, 1974
Table I Cp,Zr(H)CI 1
Di(~5-cyclopentadienyl)(chloro)alkylzirconium(IV) complexes have been shown to be useful intermediates in the transformation of olefins into a variety of organic derivatives. We have now observed that hydrozirconation of disubstituted acetylenes proceeds stereospecifically with high regioselectivity to yield vinylic Zr(1V) complexes which are, as well, valuable as precursors of trisubstituted olefins. The reaction of (v5-C5H~)ZrH(C1)(1) with I-butyne gives trans vinylic derivative 2 which establishes that Z-H addition to the acetylene occurs cis.3 We have found that addition of 1 to various unsypmetrically disubstituted acetylenes occurs readily4 to give mixtures of vinylic derivatives in which the steric bulk of the alkyl substituents dictates the direction of Zr-H cis &addition to the triple bond. Thus, for each unsymmetrical acetylene, two vinylzirconium(1V) compounds can be formed which differ only in the point of attachment of the metal to the double bond. We have also observed that, over a period of several hours, this initial mixture of vinylic species can be converted to one with higher regioselectivity, at room temperature, through catalysis with 1 (see Table I). In no case were products derived from allylic rearrangements ~ b s e r v e d .The ~ regioselectivity found was generally higher than that observed for hydroboration with hindered boranes6 The chemical reactivity of these vinylzirconium(1V) compounds renders them useful as intermediates in the facile and selective conversion of dialkylacetylenes to trisubstituted olefins. The two-step conversion of an acetylene to a functionalized olefin is illustrated as follows. 5-Methyl-2-hexyne (670 mg, 6.67 mmol) was stirred with 1.58 g (6.13 mmol) of 1 in benzenes for 2 hr. Removal of the solvent in vacuo gave the vinylic complex (2d and 3d, 55:45)’ as a pale red oil. The mixture of 2d and 3d was redissolved in benzene. Reanalysis of this mixture by N M R 7 after several hours at room temperature revealed that its composition had not changed. However, addition of several milligrams of 1 to this solution
Initially observed
Acetylene a, R = H; b, R = CH, ; C, R = CH, ; d, R = CH, ; e, R = C H , ; f, R = CH, ;
R’ = n-C,H,R’ = CH,CH,R’ = CH, CH, CH, R’ = (CH,), CHCH, R’=(CH,),CHR’ = (CH, 11-
Table I1
.e1
R
Sir:
-
RC-CR’
Product ratio (2:3)’
Cp2Zr’
Hydrozirconation. 111. Stereospecific and Regioselective Functionalization of Alkylacetylenes via Vinylzirconium(1V) Intermediates
+
679
I
H
/
R’
2a f 3a
>98:95:95:98:98: 2
--
3
Vinylic complex (ratio 2:3)
>98: 2 5 5 : 45 69 : 3 1
i-c”.:;;”
c1
R
R‘
2
After treatment with 1
-
R
R
’
R
R 5
4
X
NBS NCS NBS NCS NB S NCS NB S
Product composition’ (4:s) >98:98:95 :95:95% 2d and 6% 3de9Treatment of a solution of the vinylic complexes with N-bromosuccinimide gave, rapidly, the corresponding vinylic bromides in good yield, with retention of (C=C) stereochemistry10and with the same composition of positional isomers as that observed for the organometallic precursor (see Tables I and 11). In this way, vinylic chlorides were prepared from 2, 3 and NCS, and iodides from 2, 3, and Iz. The yield of vinylic halides so produced was at least as high as that reported for the hydrohalogenation of acetylenes via vinylalanes. I It is interesting to note that, whereas alkylzirconium(1V) complexes positionally rearrange rapidly,’ no such process occurs for their purified vinylic analogs. We believe that this rearrangement, observed to be catalyzed by 1, occurs through a dimetalated alkyl intermediate as shown in reaction 1. R R (zr) (zr) -1 (“’)_
