Kinetic addition of nucleophiles to η3-propargyl rhenium complexes occurs at the central carbon to produce rhenacyclobutenes

Article abstract of DOI:10.1021/ja9729847

Kinetic addition of nucleophites occurs at the center carbon of η³-propargyl rhenium complexes to produce rhenacyclobutenes. Reaction of P(CH₃)₃ with C₅Me₅(CO)₂Re[η³-CH₂C≡CC(CH₃)₃]⁺BF₄^- (3a) gave the metallacyclobutene C₅Me₅(CO)₂ReCH₂C(PMe₃)=CC(CH₃)₃⁺BF₄^- (4a), which was characterized by X-ray crystallography. Malonate and acetylide nucleophiles reacted with C₅Me₅(CO)₂Re[η³-CH₂C≡CCH₃]⁺PF₆^- (3b) to give metallacyclobutene complexes. Pyridine added to the central propargyl carbon of 3b at low temperature to produce the metastable metallacyclobutene C₅Me₅(CO)₂ReCH₂C(NC₅H₅)=CCH₃⁺PF₆^- (14b) which rearranged to the η²-allene complex C₅Me₅(CO)₂Re[η₂-H₂C=C=C(NC₅H₅)CH₃]⁺PF₆^- (15K) at room temperature. 4-(Dimethylamino)pyridine (DMAP) added to the central carbon of the tert-butyl-substituted η³-propargyl complex 3a below -38°C to give the rhenacyclobutene complex C₅Me₅(CO)₂ReCH₂C-C(NC₅H₄NMe₂)=CC(CH₃)₃⁺BF₄^- (22a) which rearranged to the η²-alkyne complex C₅Me₅(CO)₂Re[η²-(CH₃)₃-CC≡CCH₂NC₅H₄NMe₂]⁺BF₄^- (23) at room temperature. Reaction of water with C₅Me₅(CO)₂Re[η³-CH₂C≡CH]⁺BF₄^-(3c) gave the hydroxyallyl complex C₅Me₅(CO)₂Re[η³-CH₂C(OH)CH₂]⁺BF₄^- (29) by a process proposed to involve nucleophilic addition of water to the central propargyl carbon of 3c followed by protonation of the metallacyclobutene intermediate.

Full text of DOI:10.1021/ja9729847

722
J. Am. Chem. Soc. 1998, 120, 722-733
Kinetic Addition of Nucleophiles to η3-Propargyl Rhenium
Complexes Occurs at the Central Carbon to Produce
Rhenacyclobutenes
Charles P. Casey,* John R. Nash, Chae S. Yi, Anthony D. Selmeczy, Steven Chung,
Douglas R. Powell, and Randy K. Hayashi
Contribution from the Department of Chemistry, UniVersity of Wisconsin, Madison Wisconsin 53706
ReceiVed August 25, 1997
Abstract: Kinetic addition of nucleophiles occurs at the center carbon of η3-propargyl rhenium complexes to
produce rhenacyclobutenes. Reaction of P(CH3)3 with C5Me5(CO)2Re[η3-CH2CtCC(CH3)3]+BF4- (3a) gave
the metallacyclobutene C5Me5(CO)2ReCH2C(PMe3)dCC(CH3)3+BF4- (4a), which was characterized by X-ray
crystallography. Malonate and acetylide nucleophiles reacted with C5Me5(CO)2Re[η3-CH2CtCCH3]+PF6
-
(3b) to give metallacyclobutene complexes. Pyridine added to the central propargyl carbon of 3b at low
-
temperature to produce the metastable metallacyclobutene C5Me5(CO)2ReCH2C(NC5H5)dCCH3+PF6 (14b)
which rearranged to the η2-allene complex C5Me5(CO)2Re[η2-H2CdCdC(NC5H5)CH3]+PF6- (15K) at room
temperature. 4-(Dimethylamino)pyridine (DMAP) added to the central carbon of the tert-butyl-substituted
η3-propargyl complex 3a below -38 °C to give the rhenacyclobutene complex C5Me5(CO)2ReCH2C-
(NC5H4NMe2)dCC(CH3)3+BF4- (22a) which rearranged to the η2-alkyne complex C5Me5(CO)2Re[η2-(CH3)3-
CCtCCH2NC5H4NMe2]+BF4 (23) at room temperature. Reaction of water with C5Me5(CO)2Re[η3-
-
CH2CtCH]+BF4 (3c) gave the hydroxyallyl complex C5Me5(CO)2Re[η3-CH2C(OH)CH2]+BF4 (29) by a
process proposed to involve nucleophilic addition of water to the central propargyl carbon of 3c followed by
protonation of the metallacyclobutene intermediate.
-
-
Introduction
those of η3-allyl metal complexes (Scheme 1). Synthetic
methods include protonation of η2-propargyl alcohol com-
plexes,6 halide abstraction from η1-propargyl or η1-allenyl metal
halide complexes,7 reaction of metal halides with propargyl
nucleophiles,8 reaction of propargyl ether complexes with Lewis
acids,9 addition of a metal acetylide to a vinylidene,4,10 rear-
rangement of η1-homopropargyl metal complexes,11 and oxida-
tive addition of propargyl halides or tosylates to metal com-
plexes.12
η3-Propargyl transition metal complexes are the triple-bond
analogues of the well-studied η3-allyl complexes,1 which have
found great utility in organic synthesis. η3-Propargyl metal
complexes may be involved as transient intermediates in
catalytic cycles,2,3 and have recently been detected and isolated.
Since Werner’s first report of the isolation of an η3-propargyl
metal complex in 1985,4 there have been rapid developments
in the synthesis and detection of η3-propargyl metal complexes.5
Syntheses of η3-propargyl metal complexes often parallel
Our group has extended the η2-propargyl alcohol complex
protonation methodology to the regiospecific synthesis of a
variety of rhenium η3-propargyl complexes (Scheme 2).13 In
addition, we have developed hydride abstraction from rhenium
η2-alkyne complexes as a new route to η3-propargyl com-
plexes.13,14 These methods have proven to be versatile and
reliable ways of synthesizing η3-propargyl compounds.
In a preliminary communication, we reported that nucleo-
philes attacked the center carbon atom of the η3-propargyl
ligand.14 Here, we report the scope of these nucleophilic
additions and more complete studies of their regiochemistry.
(1) (a) Hegedus, L. S. Transition Metals in the Synthesis of Complex
Organic Molecules; University Science Books: Mill Valley, CA, 1994. Ch.
9. (b) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles
and Applications of Organotransition Metal Chemistry; University Science
Books: Mill Valley, CA, 1987; pp 175-182, 417-420, 881-919. (c)
Harrington, P. J.; Oppolzer, W.; Krysan, D. J. In ComprehensiVe Organo-
metallic Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.;
Elsevier: Oxford, U.K., 1995; Vol. 12, Chapter 8.2-8.5. (d) Trost, B. M.;
Verhoeven, T. R. In ComprehensiVe Organometallic Chemistry; Wilkinson,
G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon: Oxford, U.K., 1982;
Vol. 8, Chapter 57. (e) Tsuji, J. Tetrahedron 1986, 42, 4361. (f) Trost, B.
M. Angew. Chem., Int. Ed. Engl. 1986, 25, 1. (g) Trost, B. M.; Van Vranken,
D. L. Chem. ReV. 1996, 96, 395.
(2) (a) Keinan, E.; Bosch, E. J. Org. Chem. 1986, 51, 4006. (b)
Wakatsuki, Y.; Yamazaki, H.; Kumegawa, N.; Satoh, T.; Satoh, J. Y. J.
Am. Chem. Soc. 1991, 113, 9604.
(3) (a) Tsuji, J.; Mandai, T. Angew. Chem., Int. Ed. Engl. 1995, 34, 2589.
(b) Minami, I.; Yuhara, M.; Watanabe, H.; Tsuji, J. J. Organomet. Chem.
1987, 334, 225. (c) Tsuji, J.; Watanabe, H.; Minami, I.; Shimizu, I. J. Am.
Chem. Soc. 1985, 107, 2196. (d) Shimizu, I.; Ohashi, Y.; Tsuji, J.
Tetrahedron Lett. 1984, 25, 5183.
(6) Krivykh, V. V.; Taits, E. S.; Petrovskii, P. V.; Struchkov, Y. T.;
Yanovskii, A. I. MendeleeV Commun. 1991, 103.
(7) (a) Blosser, P. W.; Schimpff, D. G.; Gallucci, J. C.; Wojcicki, A.
Organometallics 1993, 12, 1993. (b) Huang, T.-M.; Chen, J.-T.; Lee, G.-
H.; Wang, Y. J. Am. Chem. Soc. 1993, 115, 1170. (c) Huang, T.-M.; Hsu,
R.-H.; Yang, C.-S.; Chen, J.-T.; Lee, G.-H.; Wang, Y. Organometallics
1994, 13, 3, 3657. (d) Ogoshi, S.; Tsutsumi, K.; Kurosawa, H. J. Organomet.
Chem. 1995, 493, C19. (e) Baize, M. W.; Blosser, P. W.; Plantevin, V.;
Schimpff, D. G.; Gallucci, J. C.; Wojcicki, A. Organometallics 1996, 15,
164.
(4) Gotzig, J.; Otto, H.; Werner, H. J. Organomet. Chem. 1985, 287,
247.
(8) Blosser, P. W.; Gallucci, J. C.; Wojcicki, A. J. Am. Chem. Soc. 1993,
115, 2994.
(9) Weng, W.; Arif, A. M.; Gladysz, J. A. Angew. Chem., Int. Ed. Engl.
1993, 32, 891.
(5) For reviews of η3-propargyl complexes, see: (a) Wojcicki, A. New.
J. Chem. 1994, 18, 61. (b) Doherty, S.; Corrigan, J. F.; Carty, A. J. AdV.
Organomet. Chem. 1995, 37, 39.
S0002-7863(97)02984-3 CCC: $15.00 © 1998 American Chemical Society
Published on Web 01/20/1998

Kinetic Addition to Rhenium Complexes
J. Am. Chem. Soc., Vol. 120, No. 4, 1998 723
Scheme 1
Scheme 3
Scheme 2
Results
Metallacyclobutenes from Addition of Nucleophiles to η3-
Propargyl Complexes. The kinetic addition of phosphorus,
carbon, and nitrogen nucleophiles to the central carbon of η3-
propargyl complexes gives high yields of rhenacyclobutene
complexes. These complexes were completely characterized
by spectroscopy and in one case by X-ray crystallography.
PMe3 Addition to C5Me5(CO)2Re[η3-CH2CtCC(CH3)3]+-
BF4- (3a). Excess PMe3 was vacuum-transferred into a yellow
solution of C5Me5(CO)2Re[η3-CH2CtCC(CH3)3]+BF4- (3a) in
CH2Cl2 at -78 °C, and the sample was examined immediately
by 1H NMR spectroscopy at -53 °C. The only species observed
was the phosphine-substituted rhenacyclobutene complex
C5Me5(CO)2ReCH2C(PMe3)dCC(CH3)3+BF4- (4a) (Scheme 3).
Evaporation of solvent and excess PMe3 led to the isolation of
4a as an air-stable yellow powder in quantitative yield. The
structure of 4a was established spectroscopically and confirmed
by X-ray crystallography.
We have found that while kinetic addition of nucleophiles occurs
at the center carbon of the η3-propargyl ligand to give
rhenacyclobutene complexes, this addition is sometimes revers-
ible and can be followed by addition at either of the other two
metal-bound carbon atoms to give η2-allene or η2-alkyne
complexes. In addition, we report that η3-allyl complexes can
be obtained by protonation of the metallacyclobutenes derived
from nucleophilic attack at the center carbon of the η3-propargyl
complexes.
Spectral signatures for rhenacyclobutenes include (a) two low-
frequency H NMR resonances for the diastereotopic ReCH2
1
(10) (a) Alcock, N. W.; Hill, A. F.; Melling, R. P.; Thompsett, A. R.
Organometallics 1993, 12, 641. (b) Hills, A.; Hughes, D. L.; Jimenez-
Tenorio, M.; Leigh, G. J.; McGeary, C. A.; Rowley, A. T.; Bravo, M.;
McKenna, C. E.; McKenna, M.-C. J. Chem. Soc., Chem. Commun. 1991,
522. (c) McMullen, A. K.; Selegue, J. P.; Wang, J.-G. Organometallics
1991, 10, 3421. (d) Field, L. D.; George, A. V.; Hambley, T. W. Inorg.
Chem. 1990, 29, 4565. (e) Wakatsuki, Y.; Yamazaki, H.; Kumegawa, N.;
Satoh, T.; Satoh, J. Y. J. Am. Chem. Soc. 1991, 113, 9604. (f) Hsu, D. P.;
Davis, W. M.; Buchwald, S. L. J. Am. Chem. Soc. 1993, 115, 10394. (g)
Bianchini, C.; Bohanna, C.; Esteruelas, M. A.; Frediani, P.; Meli, A.; Oro,
L. A.; Peruzzini, M. Organometallics 1992, 11, 3837. (h) Bianchini, C.;
Peruzzini, M.; Zanobini, F.; Frediani, P.; Albinati, A. J. Am. Chem. Soc.
1991, 113, 5453. (i) Albertin, G.; Amendola, P.; Antoniutti, S.; Ianelli, S.;
Pelizzi, G.; Bordignon, E. Organometallics 1991, 10, 2876. (j) Wakatsuki,
Y.; Yamazaki, H.; Maruyama, Y.; Shimizu, I. J. Chem. Soc., Chem.
Commun. 1991, 261. (k) Hughes, D. L.; Jimenez-Tenorio, M.; Leigh, G.
J.; Rowley, A. T. J. Chem. Soc., Dalton Trans. 1993, 3151. (l) Jia, G.;
Rheingold, A. L.; Meek, D. W. Organometallics 1989, 8, 1378.
(11) Stang, P. J.; Crittell, C. M.; Arif, A. M. Organometallics 1993, 12,
4799.
protons with a 11-13 Hz geminal coupling, (b) 13C NMR
resonances for the ReCH2 carbon at very low frequency (near
δ -25), and (c) 13C NMR resonances for the ReCdC carbon
near δ 170 and for the ReCdC carbon near δ 120 (Table 1). In
the 1H NMR spectrum of 4a, the diastereotopic ReCH2 protons
were observed at δ 1.52 and 0.18, with a large 12 Hz geminal
coupling. The 13C NMR resonance of the ReCH2 carbon
appeared at very low frequency at δ -28.3. Similar NMR
parameters have been observed for other metallacyclobutenes;
Thorn assigned a 1H NMR resonance at δ 1.16 and a 13C NMR
resonance at δ -18.0 to the for IrCH2 group in (PMe3)3-
BrIrCH2C(p-tolyl)dC(p-tolyl).15 The 13C NMR resonances of
the alkene carbons of 4a appeared at δ 178.3 (JPC ) 6 Hz) for
ReCdCP and at δ 120.8 (JPC ) 15 Hz) for ReCdCP. Two
strong carbonyl bands were observed at 1994 and 1914 cm-1
in the IR spectrum of 4a in THF.
(12) Baize, M. W.; Blosser, P. W.; Plantevin, V.; Schimpff, D. G.;
Gallucci, J. C.; Wojcicki, A. Organometallics 1996, 15, 164.
(13) Casey, C. P.; Selmeczy, A. D.; Nash, J. R.; Yi, C. S.; Powell, D.
R.; Hayashi, R. K. J. Am. Chem. Soc. 1996, 118, 6698.
(14) Casey, C. P.; Yi, C. S. J. Am. Chem. Soc. 1992, 114, 6597.
(15) Calabrese, J. C.; Roe, D. C.; Thorn, D. L.; Tulip, T. H. Organo-
metallics 1984, 3, 1223.

724 J. Am. Chem. Soc., Vol. 120, No. 4, 1998
Casey et al.
Table 1. Characteristic Spectroscopic Data of Rhenacyclobutenesa
1H NMR (δ)
13C NMR (δ)
CH213CdC
compd
CH2CdC
other
13CH2CdC
CH2Cd13C
IR νCO (cm-1
)
4a
1.52, 0.18b
-28.3i
120.8
JPC ) 15 Hz
128.0
JPC ) 33.2 Hz
138.0
JPC ) 38 Hz
115.9
JPC ) 15 Hz
120.4
JPC ) 20 Hz
133.9
JPC ) 19 Hz
131.0
JPC ) 14 Hz
128.0
178.3
JPC) 6 Hz
157.7
1994, 1914
1991, 1915
1994, 1914
1993, 1914
1993, 1919
1994, 1914
1999, 1926
1981, 1905
1979, 1903
Jgem ) 12 Hz
4b
1.45, 0.30c
-31.7j
-27.0i
-27.2i
-26.8i
-27.3j
-30.0k
-21.7
-25.7l
Jgem ) 11.5 Hz
1.36, 0.09b
4c
dCH 8.18
JPH ) 12 Hz
142.8
Jgem ) 13 Hz
5a
1.51, 0.30b
178.0
JPC ) 5 Hz
168.9
Jgem ) 13 Hz
1.52, 0.17d
5b
Jgem ) 12 Hz
5c
1.86, 0.81e
dCH 8.32
JHP ) 11 Hz
154.7
179.1
150.2
140.3
Jgem ) 12 Hz
1.54, 0.28b
10b
11b
12b
13b
14b
16b
18c
22a
Jgem ) 12 Hz
1.37, 0.20g
Jgem ) 11 Hz
2.00, 0.50f
119.0
Jgem ) 11 Hz
1.79, 0.66b
Jgem ) 12 Hz
obscd, 0.62d
Jgem ) 12 Hz
obscd, 0.61d
Jgem ) 13 Hz
1.72, 0.58h
Jgem ) 12 Hz
dCH 7.41
-26.0m
-17.7m
111.3
105.6
185.7
140.9
1.80, 0.34h
Jgem ) 12 Hz
a 1H and 13C NMR resonances were referenced to solvent peaks. IR spectra were recorded in THF and displayed strong bands of approximately
equal intensity. b At 300 MHz in CD2Cl2. c At 200 MHz in CD2Cl2. d At 500 MHz in CD2Cl2. e At 500 MHz in acetone-d6. f At 200 MHz in
THF-d8. g At 200 MHz in C6D6. h At 360 MHz in CD2Cl2. i At 125 MHz in CD2Cl2. j At 125 MHz in CD2Cl2. k At 75 MHz in acetone-d6. l At 125
MHz in THF-d8. m At 90 MHz in CD2Cl2.
Table 2. Selected Bond Lengths (Å) and Bond Angles (deg) for
Table 3. Structural Comparison of Bond Lengths (Å) for
Metallacyclobutenes
-
C5Me5(CO)2ReCH2C(PMe3)dCC(CH3)3+BF4 (4A)
Bond Lengths (Å)
4a
6
7
8
ResC(1)
ResC(3)
C(2)dC(3)
1.92 (1)
2.19 (1)
1.33 (1)
C(1)sC(2)
C(3)sC(7)
C(2)sP(1)
1.52 (1)
1.51 (2)
1.79 (1)
MsC(1)
MsC(3)
C(1)sC(2)
C(2)dC(3)
1.92(1)
2.19(1)
1.52(1)
1.33(1)
2.04(1)
2.30(1)
1.47(1)
1.35(1)
2.13(1)
2.17(1)
1.53(1)
1.34(1)
2.10(1)
2.12(1)
1.54(1)
1.34(1)
Bond Angles (deg)
C(1)sResC(3)
ResC(1)sC(2)
C(1)sC(2)sC(3)
61.2 (3)
100 (1)
104 (1)
ResC(3)sC(2)
C(2)sC(3)sC(7)
C(11)sResC(12)
93.3 (6)
129 (1)
81.0 (4)
deviation from planarity is 0.039 Å, and Re is only 0.27 Å out
of the plane defined by the three carbons. The ring is slightly
puckered with the plane of the three carbons tilted 8.1° toward
the Cp* ring relative to the C(1)-Re-C(2) plane. The 104
(1)° C-CdC angle of the metallacyclobutene ring of 4a is
similar to those observed for other third-row metallacycles:
104.7 (7)° for (PPh3)2Pt(C3F4) (6)16 and 106.1 (5)° for (PMe3)3-
(Br)IrCH2C(p-tolyl)dC(p-tolyl) (7).15 The analogous angle in
Tebbe’s first-row metallacycle (C5H5)2TiCH2C(Ph)dC(Ph) (8)17
is 112.8 (6)°. Bond length comparisons of 4a and other
metallacyclobutenes show remarkable consistency (Table 3). All
of the metallacycles have a shorter M-C distance to the
formally sp2 carbon than to the sp3 carbon.
Metallacyclobutenes and η3-vinylcarbene complexes are
valence isomers. The η3-vinylcarbene provides two more
valence electrons to the metal center than a metallacyclobutene.
Compared with nearly planar metallacyclobutenes, η3-vinylcar-
bene complexes have geometries more similar to π-allyl
complexes with the metal center strongly interacting with all
Figure 1. X-ray Structure of C5Me5(CO)2ReCH2C(PMe3)dCC-
-
(CH3)3+BF4 (4a).
(16) (a) Hemond, R. C.; Hughes, R. P.; Robinson, D. J.; Rheingold, A.
L. Organometallics 1988, 7, 2239. (b) Hughes, R. P.; King, M. E.; Robinson,
D. J.; Spotts, J. M. J. Am. Chem. Soc. 1989, 111, 8919.
(17) (a) Tebbe, F. N.; Harlow, R. L. J. Am. Chem. Soc. 1980, 102, 6149.
(b) McKinney, R. J.; Tulip, T. H.; Thorn, D. L.; Coolbaugh, T. S.; Tebbe,
F. N. J. Am. Chem. Soc. 1981, 103, 5584.
The metallacyclobutene formulation of 4a was confirmed by
X-ray crystallography (Table 2, Figure 1). The metallacycle
atoms Re-C(1)-C(2)-C(3) are nearly coplanar. The mean

Kinetic Addition to Rhenium Complexes
J. Am. Chem. Soc., Vol. 120, No. 4, 1998 725
Scheme 4
5
three carbon centers. Several η3-vinylcarbene complexes have
been characterized by X-ray crystallography,18,19 including the
rhenium complex C5Me5Cl2Re[η3-C(CH3)CCldCH2] (9),20 which
can be compared directly to 4a. In contrast to the near planarity
of 4a, rhenium lies 1.7 Å above the plane of the carbons of the
η3-vinylcarbene ligand of 9 and all three carbons are bonded to
Re. In contrast to the low-frequency 1H NMR resonances and
large geminal coupling observed for the ReCH2 protons of 4a,
the diastereotopic protons of 9 appear at δ 4.31 and 3.27, with
a small 3 Hz geminal coupling, consistent with sp2 hybridization.
A short RedC distance of 1.97 Å in 9 and a δ 265 13C NMR
resonance provide support for a vinylcarbene formulation.
Addition of PMe3 to the methyl-substituted η3-propargyl
doublet of quartet resonances (Jgem ) 12 Hz, J ) 2 Hz) at δ
1.54 and 0.28 in the 1H NMR spectrum and to a low-frequency
resonance in the 13C{1H} NMR spectrum at δ -30.0 (d, JPC
)
9 Hz).
Rhenacyclobutenes from Reaction of η3-Propargyl Com-
plexes with Carbon Nucleophiles. The methyl-substituted η3-
propargyl complex 3b reacted with carbon nucleophiles to form
metallacyclobutene complexes.21 When LiCtCC(CH3)3 was
added to a yellow THF solution of C5Me5(CO)2Re[η3-
CH2CtCCH3]+PF6- (3b), an orange-red solution was produced
in less than 10 min. Chromatography led to the isolation of
the neutral rhenacyclobutene C5Me5(CO)2ReCH2C[CtCC-
(CH3)3]dCCH3 (11b) in 47% yield as a dark orange-red liquid
(Scheme 4). The rhenacyclobutene structure was established
by the observation of 1H NMR resonances for the diastereotopic
ReCH2 protons of 11b at δ 1.37 and 0.20 (Jgem ) 11 Hz) and
a low-frequency 13C NMR resonance at δ -21.7 (Table 1).
Similarly, addition of solid NaCH(CO2Et)2 to a THF solution
of 3b led to the isolation of C5Me5(CO)2ReCH2C[CH(CO2-
Et)2]dCCH3 (12b) in 56% yield as a red-orange oil. In addition
to characteristic resonances for a rhenacyclobutene (Table 1),
the 13C NMR spectrum of 12b exhibited resonances for two
diastereotopic Et groups. Complexes 11b and 12b were
thermally less stable than the phosphine-substituted metallacy-
clobutenes and decomposed in solution at room temperature over
several days to give predominantly η3-allyl complexes. (The
reactivity of rhenacyclobutenes toward acid will be described
below.)
-
complex C5Me5(CO)2Re[η3-CH2CtCCH3]+BF4 (3b) and to
the unsubstituted η3-propargyl complex C5Me5(CO)2Re[η3-
CH2CtCH]+BF4 (3c) also proceeded by phosphine attack at
-
the central propargyl carbon and led to the formation of
rhenacyclobutenes. For example, when excess PMe3 was added
to a yellow solution of 3b in CH2Cl2, a white precipitate formed
gradually over 30 min at room temperature. The rhenacy-
clobutene C5Me5(CO)2ReCH2C(PMe3)dCCH3+BF4- (4b) was
isolated as a white powder in 72% yield. The low-frequency
1H NMR resonances of the diastereotopic ReCH2 protons at δ
1.45 and 0.3 (Jgem ) 12 Hz) and the low-frequency 13C NMR
resonance of the ReCH2 carbon at δ -31.7 helped to establish
the presence of the metallacyclobutene substructure of 4b.
Similarly, addition of PMe3 to C5Me5(CO)2Re[η3-CH2CtCH]+-
-
BF4 (3c) gave a 93% yield of C5Me5(CO)2ReCH2C(PMe3)d
CH+BF4 (4c), which was characterized spectroscopically
-
Addition of excess tert-butyl isocyanide to a CD2Cl2 solution
of 3b at -78 °C led to the immediate formation of a bright
yellow solution whose 1H NMR spectrum at -55 °C was
consistent with formation of the rhenacyclobutene C5Me5-
(CO)2ReH2CC(CtNCMe3)dCCH3+PF6- (13b). In particular,
two doublets of quartets were observed at δ 1.76 and 0.63 (Jgem
(Table 1).
PPh3 also added to the central carbon of η3-propargyl
complexes 3a-c to produce rhenacyclobutenes. When solid
PPh3 was added to a yellow CD2Cl2 solution of 3a at room
1
temperature, H NMR spectroscopy revealed the formation of
5
a
single new product C5Me5(CO)2ReCH2C(PPh3)dCC-
) 11 Hz, J ) 2 Hz). When the solution was warmed above
(CH3)3+BF4 (5a) with the resonances characteristic of a
rhenacyclobutene (Table 1). Complex 5a was isolated as a light
yellow powder in 91% yield. Similarly, addition of PPh3 to
3b and 3c led to the isolation of C5Me5(CO)2ReCH2C-
(PPh3)dCCH3+BF4- (5b) in 46% yield and C5Me5(CO)2ReCH2-
-
5 °C, further reaction with excess isocyanide ensued, leading
to an unidentified mixture of products. Species 13b was isolated
as an orange solid by evaporation of volatile material under
high vacuum at 0 °C.
Addition of malonates and acetylides to the tert-butyl-
substituted and unsubstituted η3-propargyl complexes 3a and
3c failed to give observable rhenacyclobutenes under conditions
that worked adequately for the methyl-substituted η3-propargyl
complex 3b. The unsubstituted η3-propargyl complex 3c
decomposed to uncharacterizable products upon warming solu-
tions containing either sodium diethyl malonate or LiCtCC-
(CH3)3. Due to its thermal instability above -20 °C, 3c
apparently decomposes before nucleophilic attack occurs. The
tert-butyl-substituted η3-propargyl complex 3a is not only
thermally sensitive but also failed to react with these carbon
nucleophiles to produce rhenacyclobutenes. 1H NMR spectra
C(PPh3)dCH+BF4 (5c) in 91% yield.
-
Trimethyl phosphite added to the central carbon of η3-
propargyl complex 3b to give the rhenacyclobutene complex
C5Me5(CO)2ReCH2C[P(OMe)3]dCCH3+BF4- (10b) as a yellow
solid in 55% yield. The ReCH2 unit of 10b gave rise to two
(18) (a) Mayr, A.; Asaro, M. F.; Glines, T. J. J. Am. Chem. Soc. 1987,
109, 2215. (b) Garrett, K. E.; Sheridan, J. B.; Pourreau, D. B.; Feng, W.
C.; Geoffroy, G. L.; Staley, D. L.; Rheingold, A. L. J. Am. Chem. Soc.
1989, 111, 8383.
(19) (a) Klimes, J.; Weiss, E. Angew. Chem., Int. Ed. Engl. 1982, 21,
205. (b) Nakatsu, K.; Mitsudo, T.; Nakanishi, H.; Watanabe, Y.; Takegami,
Y. Chem. Lett. 1977, 1447.
(20) (a) Herrmann, W. A.; Fischer, R. A.; Herdtweck, E. Angew. Chem.,
Int. Ed. Engl. 1987, 26, 1263. (b) Fischer, R. A.; Fischer, R. W.; Herrmann,
W. A.; Herdtweck, E. Chem. Ber. 1989, 122, 2035.
(21) Extension of this methodology to the tert-butyl-substituted and the
unsubstituted propargyl complexes 3a and 3c was unsuccessful.

726 J. Am. Chem. Soc., Vol. 120, No. 4, 1998
Casey et al.
Scheme 5
Table 4. Characteristic Spectroscopic Data of Rhenium Allene Complexesa
1H NMR (δ)
13C NMR (δ)
H2Cd13CdCRR′
148.1
compd
H2CdCdCRR′
other
H213CdCdCRR′
H2CdCd13CRR′
IR νCO (cm-1
)
15K
1.94, 1.19b
Jgem ) 8 Hz
1.91, 1.19b
Jgem ) 8 Hz
1.5 (br)b
R ) Me 2.59
-1.7e
132.0
1983, 1911
15T
R ) Me 2.73
-2.9e
153.8
125.7
1997, 1914
17
19
R ) Me 2.59
R ) Me 2.23
2.16, 1.44c
Jgem ) 9 Hz
1.69, 0.89c
Jgem ) 7 Hz
1.74, 0.95c
Jgem ) 8 Hz
3.4f
0.0g
147.0
142.2
140.6
123.0
99.0
1979, 1909
1975, 1906
20
21
R ) Me 2.37
R ) Me 2.25
-1.0g
111.9
a 1H and 13C NMR resonances were referenced to solvent peaks and observed at ambient temperature unless otherwise noted. IR spectra were
recorded in THF, and displayed strong bands of approximately equal intensity. b At 500 MHz in CD2Cl2. c At 500 MHz in CD2Cl2, -40 °C. d At
300 MHz in CD2Cl2. e At 125 MHz in CD2Cl2, -60 °C. f At 125 MHz in CD2Cl2. g At 75 MHz in CD2Cl2.
of the reaction mixtures showed no reaction between 3a and
the nucleophile over a day at room temperature. Perhaps steric
hindrance from the tert-butyl group of 3a prevents nucleophilic
addition.
Kinetic Formation of Metallacyclobutenes from Addition
of Nitrogen Nucleophiles to η3-Propargyl Complexes. At low
temperature, nitrogen nucleophiles kinetically add to the central
carbon of η3-propargyl complexes to give rhenacyclobutenes.
Upon warming, the rhenacyclobutenes dissociated the nitrogen
nucleophile which then re-added to the η3-propargyl complex
at one of the terminal sites to give either an allene or an alkyne
complex.
510, consistent with addition of pyridine to the π-propargyl
complex 3b. The H NMR spectrum of 15K at -40 °C had
1
resonances for inequivalent terminal allene protons at δ 1.94
and 1.18 (dq, shoulders not resolved, J ) 8, 2 Hz, 1H each)
and a triplet CH3 resonance (J ) 2 Hz) at δ 2.64 in addition to
resonances for C5Me5 and bound pyridine. At room tempera-
ture, the resonances for the inequivalent terminal allene protons
coalesced to a broad feature at δ 1.6. This coalescence is due
to interchange of the environments of the CH2dCdC protons
by rotation about the Re-allene bond. In the coupled 13C NMR
spectrum, the 13CH2dCdC resonance appeared at δ -1.70 (t,
J ) 164 Hz), the CH2d13CdC resonance at δ 148.8 (s), and
the CH2dCd13C resonance at 133.2 (s). These resonances are
characteristic of allene complexes (Table 4).
Addition of excess pyridine to a CD2Cl2 solution of 3b at
-78 °C followed by warming to -40 °C resulted in the rapid
formation of the metallacyclobutene complex C5Me5(CO)2-
Slow equilibration of the kinetically formed >10:1 mixture
of allene complexes 15K:15T occurred over several weeks (t1/2
≈ 14 d) to give a final 1:9 ratio of 15K:15T. The spectroscopic
properties of thermodynamically favored complex 15T were
very similar to those of the kinetically favored isomer 15K.
The low-temperature (-60 °C) 1H NMR spectrum of 15T
showed the decoalescence of two methylene protons at δ 1.91
and 1.18 (br d, J ) 8 Hz). The 13C{1H} NMR spectrum of
15T exhibited a resonance at δ -2.9, assigned to the
13CH2dCdC carbon.
-
ReCH2C(NC5H5)dCCH3+PF6 (14b) (Scheme 5). The 1H
NMR spectrum of 14b at -40 °C provided evidence of the
formation of a metallacyclobutene. Resonances were observed
at δ 2.29 (br s, CH3), 1.97 (s, C5Me5), and 0.62 (dq, shoulders
not resolved, J ) 12, 2 Hz, Re-CHH); the other Re-CHH
resonance was not observed and is presumably buried under
the C5Me5 resonance.
Conversion of a Metallacyclobutene to an Allene Complex.
When the CH2Cl2 solution of 14b was warmed to room
temperature, formation of a >10:1 ratio of η2-allene complexes
To determine whether the conversion of the metallacycle 14b
to allene complex 15K occurs via an intra- or intermolecular
mechanism, the conversion of the pyridine substituted metal-
lacycle 14b was carried out in the presence of 4-picoline.
Excess 4-picoline was added to a CD2Cl2 solution of 14b at
-
C5Me5(CO)2Re[η2-H2CdCdC(NC5H5)CH3]+PF6 (15K and
15T) was observed (Scheme 5). Addition of ether brought about
the precipitation of the allene complexes which were isolated
in 61% yield. The mass spectrum (LSIMS) showed a peak at

Kinetic Addition to Rhenium Complexes
J. Am. Chem. Soc., Vol. 120, No. 4, 1998 727
-78 °C. Inspection of the 1H NMR spectrum at -40 °C showed
the complete disappearance of 14b and formation of a new
material (16b) having resonances for a bound 4-picoline ligand
and a new ReCHH resonance at δ 0.61 (br d, Jgem ) 13 Hz)
characteristic of a metallacyclobutene. Apparently, loss of
pyridine is rapid and reversible at -40 °C. This provides a
dissociative mechanism for exchange of 4-picoline for pyridine
at the metallacyclobutene stage. When the solution was warmed
to room temperature, a complicated mixture of η2-allenyl
products incorporating both pyridine and 4-picoline was ob-
served. Resonances attributed to one isomer of the 4-picoline
η2-allene adduct C5Me5(CO)2Re[η2-H2CdCdC(p-CH3-C5H5N)-
Scheme 6
Scheme 7
CH3]+PF6 (17) were seen.
-
To determine whether the interconversion of allene isomers
15K and 15T occurs intramolecularly or by a dissociative
mechanism through η3-propargyl complex 3b, the equilibration
of an initial 2:1 mixture of 15K:15T was carried out in the
presence of a 3-fold excess of 4-picoline. After 24 h at room
temperature, no formation of 4-picoline η2-allene adduct 17 was
seen by 1H NMR spectroscopy and isomerization to a 1:2
mixture of 15K:15T had taken place. After 5 days, only 15T
was seen and no 4-picoline adducts were observable. This
experiment establishes that conversion of 15K to 15T is
intramolecular and that formation of the allene complexes from
η3-propargyl complex 14b is irreversible.
The similarity of the spectra of 15K and 15T requires that
these isomers differ only in the relative stereochemistry at the
allene terminus. We cannot assign the absolute stereochemistry
of the two allene complexes. However, examination of mo-
lecular models indicates that attack on an η3-propargyl complex
should occur preferentially from the side opposite the metal. It
is more difficult to assess which isomer is more thermodynami-
cally stable, but since the CdCdC angle in allene complexes
is about 140°,22 the isomer with pyridine syn to rhenium may
be more stable. The stereochemistry of the kinetic isomer is
arbitrarily drawn as having pyridine anti to rhenium. The
intramolecular rearrangement of allene complex 15K to 15T
probably occurs by migration of rhenium from the less-
substituted allene π-bond to the more-substituted allene π-bond
and then back to the opposite enantioface of the less-substituted
allene π-bond.23
broadened at -47 °C, suggesting the possibility of a fluxional
process involving inequivalent Et groups. Further cooling of
the solution to -80 °C resulted in the decoalescence of the NEt3
peaks into three distinct CH3 peaks between δ 0.92 and 1.27
(each a broad triplet) and six diastereotopic CH2 resonances
between δ 3.21 and 3.65 (all multiplets). Remarkably, rotation
about the C-NR3 bond has been frozen out at -80 °C.
The solution of 19 was monitored over several weeks at room
temperature but no evidence for a second allene isomer (as seen
for the pyridine case) was observed. We do not know whether
the NEt3 group is syn or anti to rhenium, but the observation of
a slow NEt3 rotation suggests that the NEt3 group is in a very
crowded environment. The NEt3 group is arbitrarily drawn anti
to rhenium.
Halide attack on the methyl-substituted η3-propargyl complex
3b also led to the formation of allene complexes. Addition of
Ph4PBr to a CD2Cl2 solution of 3b led to the isolation of C5-
Me5(CO)2Re[η2-H2CdCdC(Br)CH3] (20) in 60% yield. Simi-
larly, reaction of Ph4PCl with 3b gave C5Me5(CO)2Re[η2-
H2CdCdC(Cl)CH3] (21) in 58% yield. The 1H and 13C NMR
spectra of 20 and 21 support their formulation as allene
complexes (Table 4).
Pyridine added to the central carbon of the unsubstituted η3-
propargyl complex 3c below -43 °C to give the metallacy-
clobutene C5Me5(CO)2ReCH2C(NC5H5)dCH+PF6- (18c) as the
only observable product (Table 1). This metallacycle decom-
posed when warmed to -20 °C to give a mixture of more than
10 C5Me5-containing products.
The reaction of NEt3 with η3-propargyl complex 3b at room
temperature led to the isolation of a single isomer of the allene
complex C5Me5(CO)2Re[η2-H2CdCdC(NEt3)CH3]+PF6- (19)
as a yellow powder in 60% yield (Scheme 6). A key spectral
feature that led to the assignment of the allenyl structure of 19
was the appearance of a low-frequency 13C NMR resonance at
δ 3.4 for the 13CH2dCdC carbon. At -47 °C, rotation of the
allene ligand was frozen out and separate resonances were seen
for the two CH2dCdC protons at δ 2.16 and 1.44 (each a broad
doublet, Jgem ) 9 Hz, 1H). Surprisingly, the NEt3 resonances
Conversion of a Metallacyclobutene to an Alkyne Com-
plex. The tert-butyl-substituted η3-propargyl complex 3a was
attacked by 4-(dimethylamino)pyridine (DMAP) at the central
propargyl carbon below -38 °C to give the rhenacyclobutene
-
complex C5Me5(CO)2ReCH2C(NC5H4NMe2)dCC(CH3)3+BF4
(22a). This compound was characterized by its H and 13C
1
NMR spectra (Table 1).
When warmed to -20 °C, 22a rearranged to give the alkyne
complex C5Me5(CO)2Re[η2-(CH3)3CCtCCH2NC5H4NMe2]+-
-
BF4 (23) which was isolated as a stable yellow solid in 96%
yield (Scheme 7). In the 1H NMR spectrum of 23, the
diastereotopic propargyl protons of the CH2N group appeared
as two doublets at δ 5.45 and 5.09 with a geminal coupling of
16 Hz. Rotation about the rhenium-alkyne bond of this
sterically crowded alkyne is evidently slow at room temperature.
The observation of two carbonyl resonances at δ 209.6 and
208.3 in the 13C{1H} NMR spectrum provide further evidence
for slow rotation about the rhenium-alkyne bond. The 13C
(22) (a) Foxman, B. M. J. Chem. Soc., Chem. Commun. 1975, 221. (b)
Yasuoka, N.; Morita, M.; Kai, Y.; Kasai, N. J. Organomet. Chem. 1975,
90, 111. (c) Werner, H.; Schwab, P.; Mahr, N.; Wolf, J. Chem. Ber. 1992,
125, 2641. (d) Werner, H.; Schneider, D.; Schulz, M. J. Organomet. Chem.
1993, 451, 175. (e) Binger, P.; Langhauser, F.; Wedemann, P.; Gabor, B.;
Mynott, R.; Kru¨ger, C. Chem. Ber. 1994, 127, 39.
(23) (a) Ben-Shoshan, R.; Pettit, R. J. Am. Chem. Soc. 1967, 89, 2231.
(b) Foxman, B.; Marten, D.; Rosan, A.; Raghu, S.; Rosenblum, M. J. Am.
Chem. Soc. 1977, 99, 2160.

728 J. Am. Chem. Soc., Vol. 120, No. 4, 1998
Casey et al.
Table 5. Characteristic Spectroscopic Data of Rhenium Alkyne Complexesa
1H NMR (δ)
13C NMR (δ)
13
compd
CH2C≡C
13CH2C≡C
CH213C≡C
71.6
CH2C≡ C
IR νCO (cm-1
)
23
24
25
26
5.45, 5.09c
66.0f
101.3
1950, 1867
Jgem ) 16 Hz
4.48, 4.24b
Jgem ) 16 Hz
3.97, 3.58b
Jgem ) 16 Hz
4.03, 3.71b
Jgem ) 16 Hz
4.72, 4.60c
Jgem ) 15 Hz
4.69, 4.41d
Jgem ) 10 Hz
4.57, br se
1949, 1865
1951, 1869
1951, 1868
1945, 1863
1950, 1862
1951, 1867
25.2f
57.8
JPC ) 12 Hz
61.3
JPC ) 9 Hz
77.0
97.0
96.5
96.3
76.5
64.9
JPC ) 51 Hz
27.1f
JPC ) 50 Hz
59.0f
(C5Me5)(CO)2Re[η2-(CH3)3CC≡CCH2OH]
(C5Me5)(CO)2Re(η2-CH3C≡CCH2OH)13
(C5Me5)(CO)2Re(η2-HC≡CCH2OH)13
59.2g
59.1g
75.9
89.4
a 1H and 13C NMR resonances were referenced to solvent peaks. IR spectra were recorded in THF and displayed strong bands of approximately
equal intensity. b At 360 MHz in CD2Cl2. c At 300 MHz in CD2Cl2. d At 300 MHz in C6D6. e At 200 MHz in in C6D6. f At 90 MHz in CD2Cl2.g At
125 MHz in C6D6.
Scheme 8
NMR resonances of the propargyl unit provide a distinctive
spectral signature for this class of compounds (Table 5) that
allows them to be readily distinguished from metallacy-
clobutenes and allene complexes. The two alkyne carbons
appeared at δ 101.3 and 71.6 (C≡C), and the CH2N resonance
appeared at δ 66.0.
The conversion of metallacyclobutene 22a to alkyne complex
23 can be explained by dissociation of DMAP from 22a to
regenerate η3-propargyl complex 3a, followed by re-addition
of DMAP to the terminal CH2 carbon of the propargyl complex
to produce the alkyne complex 23. Apparently, the bulky tert-
butyl substituent prevents attack at the CtC-CMe3 terminal
Scheme 9
carbon which would have produced a sterically crowded allene
complex.24
The addition of NEt3 to tert-butyl-substituted η3-propargyl
complex 3a at -53 °C led directly to the alkyne complex C5-
Me5(CO)2Re[η2-(CH3)3CCtCCH2NEt3]+BF4- (24) which was
stable at room temperature. The structure of 24 was assigned
on the basis of characteristic 1H and 13C NMR resonances (Table
5). No metallacyclobutene intermediate was detected even at
-53 °C. Apparently, the sterically large Et3N nucleophile is
too large to attack either the CdCsCMe3 terminal carbon or
the central carbon of 3a.
Rearrangement of Phosphorus-Substituted Metallacy-
clobutenes. The low-temperature rearrangements of nitrogen-
substituted metallacyclobutenes led us to explore possible
rearrangements of analogous phosphorus-substituted metalla-
cycles. While these phosphorus analogues were stable enough
in 96% yield. The observation of two 1H NMR resonances for
to isolate as solids at room temperature, slow rearrangement of
the diastereotopic CH2P hydrogens at δ 4.03 and 3.71 with Jgem
) 16 Hz supported the formulation of 26 as an alkyne complex
(Table 5).
the sterically congested metallacycle C5Me5(CO)2ReCH2C-
(PMe3)dCC(CH3)3+BF4- (4a) occurred over 2 days in CH2Cl2
solution to give the alkyne complex C5Me5(CO)2Re[η2-(CH3)3-
η3-Allyl Complexes from Protonation of Metallacy-
clobutenes. The thermal instability of the alkynyl-substituted
rhenacyclobutene 11b was traced in part to protonation by acidic
-
CCtCCH2(PMe3)]+BF4 (25) in 90% yield (Scheme 8). The
assignment of 25 as an alkyne complex was made spectroscopi-
cally (Table 5). Slow rotation about the rhenium-alkyne bond
1
media.
When isolated, C5Me5(CO)2ReCH2C[CtCC-
was indicated by the observation of two H NMR resonances
(CH3)3]dCCH3 (11b) was treated with excess CF3CO2H (5
equiv) in CD2Cl2 at room temperature, and the cationic η3-allyl
rhenium complex C5Me5(CO)2Re[η3-CH2C[CtCC(CH3)3]-
for the diastereotopic CH2P hydrogens at δ 3.97 and 3.58 with
Jgem ) 16 Hz.
Similarly, the PPh3-substituted metallacycle C5Me5(CO)2-
CHCH3]+CF3CO2 (27) was immediately observed by H and
13C NMR spectroscopies (Scheme 9). In the 1H NMR spectrum,
resonances at δ 4.05 (d, Jgem ) 2.5 Hz) and 1.95 (d, Jgem ) 2.5
Hz) were assigned to syn and anti hydrogens on the same allylic
carbon, and a resonance at δ 2.9 (q, J ) 9 Hz) was assigned to
an anti allylic hydrogen on a terminal allylic carbon bearing a
methyl group. The absence of W-coupling expected for syn
-
1
-
ReCH2C(PPh3)dCC(CH3)3+BF4 (5a) rearranged slowly over
2 days at room temperature to the alkyne complex C5Me5(CO)2-
Re[η2-(CH3)3CCtCCH2(PPh3)]+BF4- (26) which was isolated
(24) Reaction of pyridine with the tert-butyl-substituted η3-propargyl
complex 3a did not produce products with NMR resonances consistent with
the formation of a metallacyclobutene and/or an alkyne complex analogous
to the DMAP complexes 22a or 23.

Kinetic Addition to Rhenium Complexes
J. Am. Chem. Soc., Vol. 120, No. 4, 1998 729
Scheme 10
mixture of exo and endo isomers.26 The 1H NMR spectrum of
29 in CD2Cl2 showed predominantly one compound (9:1). The
major compound was assigned the endo configuration on the
basis of the observation of a nuclear Overhauser enhancement
(NOE) between the C5Me5 protons and the Hanti protons of the
allyl unit, which are proximal in an endo isomer. Saturation
of the C5Me5 resonance resulted in a 5% NOE enhancement of
the Hanti resonance and no enhancement of the Hsyn resonance.
To probe the stereochemistry of water addition to η3-
propargyl complex 3c, the reaction was repeated using D2O in
place of water. Reaction of 3c with D2O in CD2Cl2 resulted in
the clean formation of C5Me5(CO)2Re[η3-HDCC(OD)CH2]+-
allylic hydrogens on opposite ends of an allylic system was
crucial in assigning a syn orientation of the Me group relative
to the CtC(CH3)3 group on the central allylic carbon. In the
13C NMR spectrum, a carbon resonance at δ 102.8 was assigned
to the central allyl carbon and resonances at δ 44.6 and 67.7
were assigned to the unsubstituted and methyl-substituted
terminal allyl carbons, respectively. Protonation of metallacycle
11b with CF3CO2D (99%) placed deuterium only on the methyl-
substituted allylic carbon of 27.
-
BF4 (29-d2) as a red solid in 30% yield (Scheme 10). The
chemical shifts of the protons of this complex were very similar
to that of the nondeuterated complex 29. The resonance for
Hsyn appeared at δ 4.27 as a broad doublet (J ) 4 Hz) that
integrated to 1.7 hydrogens vs the 15 hydrogens of the C5Me5
ligand. The Hanti resonance was also a broad 4 Hz doublet at
δ 1.85. This signal integrated to only 0.9 hydrogens, indicative
of the replacement of one of the anti hydrogen atoms by
deuterium. These data suggest that the addition of water and
D2O to 3c occurs stereospecifically to place the additional proton
in the anti position of the generated η3-allyl complex. The same
stereochemistry of addition was observed by Wojcicki for
addition of MeOH to (PPh3)2Pt(η3-CH2CtCCH3)+.7e
When η3-propargyl complex 3b was treated with LiCtCC-
(CH3)3 followed by H2O and CF3CO2H, the PF6 salt of the
η3-allyl complex was isolated in 45% yield.
-
In a related reaction, addition of LiCu(CH3)2 to η3-propargyl
complex 3b at -78 °C followed by treatment with wet ether
led to the isolation of the η3-allyl complex C5Me5(CO)2Re[η3-
Similarly, when the propargyl alcohol complex 3c was treated
with acid in the presence of methanol, the methoxy-substituted
-
η3-allyl complex C5Me5(CO)2Re[η3-H2CC(OCH3)CH2]+BF4
CH2C(CH3)CHCH3]+PF6 (28).
-
1
(31) was formed as a red solid in 73% yield. In the H NMR
η3-Allyl Complexes from Addition of Alcohols to η3-
Propargyl Complexes. Addition of water or methanol to η3-
propargyl complexes did not produce observable metallacy-
clobutenes. Instead, oxygen-substituted η3-allyl complexes were
the first species detected. The formation of these η3-allyl
complexes can be explained by initial attack of the oxygen
nucleophile at the central propargyl carbon to give an oxygen-
substituted metallacyclobutene followed by protonation of a
Re-C bond of the metallacycle (Scheme 10).
Addition of water to a yellow CH2Cl2 solution of the
unsubstituted η3-propargyl complex 3c at 0 °C led to isolation
of the 2-hydroxyallyl complex C5Me5(CO)2Re[η3-H2CC(OH)-
CH2]+BF4- (29) as a red solid in 35% yield. When the reaction
spectrum, AA′XX′ multiplets were seen at δ 4.23 for Hsyn and
δ 1.94 for Hanti. The endo configuration of the allyl unit was
established by the observation of a 15% NOE enhancement of
the Hanti multiplet upon saturation of the C5Me5 resonance.
Discussion
Kinetic Preference for Attack at the Central Carbon of
η3-Propargyl Rhenium Complexes. Phosphorus, nitrogen, and
carbon nucleophiles all attacked the central carbon of η3-
propargyl rhenium complexes to produce rhenacyclobutene
complexes. This reactivity pattern stands in contrast to that of
η3-allyl complexes, which “normally” undergo nucleophilic
attack at a terminal allyl carbon. Density functional molecular
orbital calculations on η3-propargyl complexes27 support this
mode of attack through both charge control and frontier
molecular orbital control.
For nitrogen and phosphorus nucleophiles, the initially formed
rhenacyclobutene complexes undergo rearrangement to give
products resulting from nucleophilic attack at the two different
terminal carbons of the propargyl unit. The addition of pyridine
to the central carbon of methyl-substituted η3-propargyl complex
3b was found to be reversible. The initially formed metalla-
cyclobutene 14b reacted with picoline below -40 °C to form
the picoline-substituted metallacyclobutene 16b, presumably by
pyridine dissociation to regenerate η3-propargyl complex 3b.
When warmed to room temperature, the metallacyclobutene 14b
was converted to a thermodynamically more stable allene
complex 15K. The higher stability of allene complexes is
reasonable on the basis of the strain inherent in the metallacy-
clobutene structure. The inability of picoline to exchange with
1
was monitored by H NMR spectroscopy in CD2Cl2 at -20
°C, 29 was observed immediately and no evidence for a
metallacyclobutene intermediate was seen. A higher yield
(80%) of 29 was obtained by addition of HBF4‚Et2O to an
acetone solution containing propargyl alcohol complex C5-
Me5(CO)2Re(η2-HCtCCH2OH) (30)13 and 0.1 mL of H2O. This
procedure was designed to generate the unsubstituted η3-
propargyl complex 3c in the presence of H2O as a trapping
agent.
Complex 29 was characterized spectroscopically. The protons
on the terminal allyl carbons appeared in the 1H NMR spectrum
as AA′XX′ multiplets at δ 4.28 (Hsyn) and δ 1.89 (Hanti) with
Jgem ) 4 Hz, Jsyn,syn′ ) 4 Hz, and Janti,anti′ ) 0 Hz.25 The13C
NMR spectrum supports the Cs symmetry of 29: only one
carbonyl resonance at δ 195 and one CH2 resonance at δ 33.3
were observed. η3-Allyl complexes are often observed as a
(25) The NMR shifts are similar to those observed by Sutton for the
endo rotamer of C5Me5(CO)2Re(η3-CH2CHCH2)+BF4-, whose terminal allyl
protons were observed at δ 3.83 (Hsyn) and δ 1.77 (Hanti). (a) Batchelor, R.
J.; Einstein, F. W. B.; Zhuang, J.-M.; Sutton, D. J. Organomet. Chem.
1990, 397, 69. (b) Batchelor, R. J.; Einstein, F. W. B.; He, Y.; Sutton, D.
J. Organomet. Chem. 1994, 468, 183. (c) He, Y.; Batchelor, R. J.; Einstein,
F. W. B.; Sutton, D. J. Organomet. Chem. 1996, 509, 37.
(26) (a) King, R. B. Inorg. Chem. 1966, 5, 2242. (b) Davison, A.; Rode,
W. C. Inorg. Chem. 1967, 6, 2124. (c) Faller, J. W.; Incorvia, M. J. Inorg.
Chem. 1968, 7, 840. (d) Faller, J. W.; Jakubowski, A. J. Organomet. Chem.
1971, 31, C75. (e) Faller, J. W.; Rosan, A. M. J. Am. Chem. Soc. 1976, 98,
3388.
(27) Casey, C. P.; Nash, J. R.; Boller, T. M. unpublished results.

730 J. Am. Chem. Soc., Vol. 120, No. 4, 1998
Casey et al.
Scheme 11
Scheme 12
Ba¨ckvall experimentally confirmed that ligand effects could alter
the regiochemistry of nucleophilic addition to η3-allyl palladium
complexes: σ-donor ligands (TMEDA) directed nucleophilic
attack toward the central carbon, while π-acceptor ligands (PPh3)
directed attack toward the terminal carbon.35 Their MP2 ab
initio calculations confirmed the ligand dependence of the
energy ordering of the two lowest-lying empty orbitals. With
σ-donor ligands, the LUMO is localized on the central carbon,
but with π-acceptor ligands, the LUMO is localized on the
terminal carbons.
the pyridine bound to allene complex 15K established the
irreversibility of allene complex formation.
The sterically more congested tert-butyl-substituted η3-
propargyl complex 3a was also attacked by nucleophiles at the
central propargyl carbon to give metastable metallacyclobutenes.
However, the nitrogen- and phosphorus-substituted metallacy-
clobutenes rearranged to η2-alkyne complexes instead of η2-
allene complexes. Apparently, attack at the carbon bearing the
bulky tert-butyl group is strongly disfavored. Thus, when the
allene-forming pathway is blocked, nucleophilic attack can occur
at the third propargyl carbon to form a lower energy alkyne
structure. Again, the greater stability of alkyne complexes
compared with that of metallacyclobutenes can be ascribed to
ring strain.
Access to Metallacyclobutenes. The addition of nucleo-
philes to the central carbon of cationic η3-propargyl rhenium
complexes provides a new and efficient way to generate
metallacyclobutenes. Other routes to metallacyclobutenes in-
clude (1) coupling of alkyne ligands with carbene,15,17,36 CO,37,38
and isonitrile ligands,39 (2) ring opening of cyclopropenes16,40
and cyclopropenones,41,42 and (3) rearrangement reactions
involving ring contraction of metallacycles.43
Comparison with η3-Allyl Systems. In contrast to the
predominate attack of nucleophiles at the central carbon of η3-
propargyl complexes, the normal mode of attack on nucleophiles
is at a terminal carbon of η3-allyl complexes.1 Nevertheless, a
growing number of examples of nucleophilic attack at the central
allyl carbon have been reported for cationic η3-allyl complexes
of Mo,28 W,28 Rh,29 and Pt.30 In several rare cases, kinetic attack
of nucleophiles at the central allyl carbon produced metallacy-
clobutanes that then rearranged to more stable products of net
terminal allyl carbon attack. Stryker and co-workers31,32
reported that enolate addition to rhodium η3-allyl complex 32
initially occurred at the central allyl carbon to give metallacy-
clobutane 33 which subsequently rearranged to alkene complex
34, the product of terminal carbon attack (Scheme 11).
The regioselectivity of nucleophilic addition to η3-allyl
complexes has been the subject of several theoretical investiga-
tions. Davies, Green, and Mingos stressed the importance of
charge control, and they predicted central-carbon nucleophilic
attack on π-allyl complexes with very electron-releasing metal
fragments.33 Curtis and Eisenstein emphasized the role of
frontier orbital control and pointed out that the energy ordering
of the two lowest-lying empty orbitals could affect the regio-
chemistry of nucleophilic addition to η3-allyl complexes.34
Addition of Nucleophiles to Other η3-Propargyl Systems.
While other reported nucleophilic additions to η3-propargyl
complexes have not resulted in isolable or even observable
metallacyclobutenes, the observed η3-allyl or η3-trimethylene-
methane products are consistent with initial kinetic attack at
the center carbon of the η3-propargyl ligand. Chen reported
that the reaction of (PPh3)2Pt(η3-H2CCtCH)+BF4 (35) with
-
a range of nucleophiles generated η3-allyl complexes (Scheme
12).44 The Wojcicki group found that the substituted η3-
propargyl platinum complex (PPh3)2Pt(η3-H2CCtCPh)+ (and
its palladium analog) reacted with nucleophiles to form η3-allyl
complexes.12,45 These products are consistent with nucleophilic
addition to the central propargyl carbon to form a transient
platinacyclobutene, followed by protonation of the metallacy-
clobutene to give the observed η3-allyl complexes. We observed
a similar reactivity pattern in the reactions of water with the
unsubstituted propargyl complex 3c which led to the isolation
of hydroxy-substituted η3-allyl complex 29.
Parallel work in the laboratories of Wojcicki and Chen
explored the conversion of η3-propargyl platinum complexes
(35) Aranyos, A.; Szabo´, K. J.; Castan˜o, A. M.; Ba¨ckvall, J.-E.
Organometallics 1997, 16, 1058.
(36) O’Connor, J. M.; Ji, H.; Iranpour, M.; Rheingold, A. L. J. Am. Chem.
Soc. 1993, 115, 1586.
(37) Burt, R.; Cooke, M.; Green, M. J. Chem. Soc. A 1970, 2981.
(38) (a) Padolik, L. L.; Gallucci, J.; Wojcicki, A. J. Organomet. Chem.
1990, 383, C1. (b) Padolik, L. L.; Gallucci, J. C.; Wojcicki, A. J. Am. Chem.
Soc. 1993, 115, 9986.
(39) Wakatsuki, Y.; Miya, S.-y.; Ikuta, S.; Yamazaki, H. J. Chem. Soc.,
Chem. Commun. 1985, 35.
(28) (a) Ephritikhine, M.; Francis, B. R.; Green, M. L. H.; Mackenzie,
R. E.; Smith, M. J. J. Chem. Soc., Dalton Trans. 1977, 1131. (b)
Ephritikhine, M.; Green, M. L. H.; Mackenzie, R. E. J. Chem. Soc., Chem.
Commun. 1976, 619.
(29) Periana, R. A. Bergman, R. G. J. Am. Chem. Soc. 1984, 106, 7272.
(30) Benyunes, S. A.; Brandt, L.; Green, M.; Parkins, A. W. Organo-
metallics 1991, 10, 57.
(31) (a) Tjaden, E. B.; Stryker, J. M. J. Am. Chem. Soc. 1990, 112, 6420.
(b) Wakefield, J. B.; Stryker, J. M. J. Am. Chem. Soc. 1991, 113, 7057. (c)
Tjaden, E. B.; Stryker, J. M. Organometallics 1992, 11, 16. (d) Tjaden, E.
B.; Casty, G. L.; Stryker, J. M. J. Am. Chem. Soc. 1993, 115, 9814.
(32) For reversible addition of nucleophiles to a Pt complex, see: (a)
Carfagna, C.; Galarini, R.; Linn, K.; Lo´pez, J. A.; Mealli, C.; Musco, A.
Organometallics 1993, 12, 3019. (b) Carfagna, C.; Mariani, L.; Musco,
A.; Sallese, G.; Santi, R. J. Org. Chem. 1991, 56, 3924. (c) Carfagna, C.;
Galarini, R.; Musco, A.; Santi, R. J. Mol. Catal. 1992, 72, 19. (d) Carfagna,
C.; Galarini, R.; Musco, A.; Santi, R. Organometallics 1991, 10, 3956.
(33) Davies, S. G.; Green, M. L. H.; Mingos, D. M. P. Tetrahedron 1978,
34, 3047.
(40) Donovan, B. T.; Egan, J. W., Jr.; Hughes, R. P.; Spara, P. P.; Trujillo,
H. A.; Rheingold, A. L. Isr. J. Chem. 1990, 30, 351.
(41) (a) Visser, J. P.; Ramakers-Blom, J. E. J. Organomet. Chem. 1972,
44, C63. (b) Wong, W.; Singer, S. J.; Pitts, W. D.; Watkins, S. F.; Baddley,
W. H. J. Chem. Soc., Chem. Commun. 1972, 672.
(42) Song, L.; Arif, A. M.; Stang, P. J. Organometallics 1990, 9, 2792.
(43) O’Connor, J. M.; Pu, L.; Woolard, S.; Chadha, R. K. J. Am. Chem.
Soc. 1990, 112, 6731.
(44) Tsai, F.-Y.; Hsu, R.-H.; Huang, T.-M.; Chen, J.-T.; Lee, G.-H.;
Wang, Y. J. Organomet. Chem. 1996, 520, 85.
(45) Some nucleophiles add to the metal center to form σ-allenyl and
σ-propargyl complexes. Blosser, P. W.; Schimpff, D. G.; Gallucci, J. C.;
Wojcicki, A. Organometallics 1993, 12, 1993.
(34) Curtis, M. D.; Eisenstein, O. Organometallics 1984, 3, 887.

Kinetic Addition to Rhenium Complexes
J. Am. Chem. Soc., Vol. 120, No. 4, 1998 731
Scheme 13
Scheme 16
Scheme 14
Scheme 15
In Stille coupling reactions, vinyl palladium intermediates
(which are good models for η1-allenyl species) react with
nucleophiles at the metal center and not at the â-vinyl carbon.50
On the basis of the reactivity patterns we have observed for
η3-propargyl complexes, we propose an alternative mechanism
for the double nucleophilic addition (Scheme 16). In our
proposed mechanism, oxidative addition of the propargyl
carbonate leads to an η3-propargyl intermediate. The first
nucleophilic addition occurs to the central carbon of the
propargyl ligand to produce a metallacyclobutene. This is
followed by a precedented protonation of the metallacyclobutene
to generate the same η3-allyl complex as proposed in Tsuji’s
mechanism.
to η3-trimethylenemethane complexes.46 The addition of sodium
dimethylmalonate to palladium47 and platinum48 η3-propargyl
complexes produced η3-trimethylenemethane (η3-TMM) com-
plexes (Scheme 13).
Comments on the Mechanism of Palladium-Catalyzed
Reactions of Propargyl Carbonates. Tsuji and co-workers
have developed many useful palladium-catalyzed reactions of
propargyl carbonates.3 The reactions of carbon nucleophiles
with propargyl carbonates produce double nucleophilic addition
products where nucleophiles have added to both the central and
a terminal carbon of the propargyl unit (Scheme 14). These
reactions are related to the well-studied palladium-catalyzed
reaction of allyl carbonates with nucleophiles.49
Conclusions
A clear picture of the nature of nucleophilic attack on η3-
propargyl complexes is emerging from the results reported by
our group and the other groups in this actively researched area.
It seems clear that kinetic attack of nucleophiles on the center
carbon of the propargyl ligand is almost always favored. After
this initial metallacyclobutene-forming attack, subsequent trans-
formations can lead to a variety of products, including η3-allyl
complexes, η3-trimethylenemethane complexes, η2-allene com-
plexes, and η2-alkyne complexes.
In Tsuji’s proposed mechanism (Scheme 15), oxidative
addition of the propargyl carbonate produces an η1-allenyl
complex (A) which is attacked by the first nucleophile at the
center allene carbon to produce a palladium carbene complex
(B) that is then protonated to give a η1-allyl intermediate.
Conversion of the η1- to an η3-allyl complex is then followed
by addition of a second nucleophile to a terminal allyl carbon.
Tsuji has provided convincing evidence for an η3-allyl inter-
mediate in these double nucleophilic additions. However, both
the addition of a nucleophile to the central carbon of an η1-
allenyl complex (A) and the protonation of a Pd carbene
complex (B) at carbon are unprecedented processes. Chen
observed nucleophilic attack on a platinum η1-allenyl complex
to occur at the metal;7c the η1-allenyl ligand was found be far
less reactive toward nucleophiles than an η3-propargyl ligand.
(46) For related syntheses of η3-oxatrimethylenemethane complexes,
see: (a) Baize, M. W.; Furilla, J. L.; Wojcicki, A. Inorg. Chim. Acta 1994,
223, 1. (b) Baize, M. W.; Plantevin, V.; Gallucci, J. C.; Wojcicki, A. Inorg.
Chim. Acta 1995, 235, 1.
(47) Su, C.-C.; Chen, J.-T.; Lee, G.-H.; Wang, Y. J. Am. Chem. Soc.
1994, 116, 4999.
(48) Plantevin, V.; Blosser, P. W.; Gallucci, J. C.; Wojcicki, A.
Organometallics 1994, 13, 3651.
(49) (a) Tsuji, J. Tetrahedron 1986, 42, 4361. (b) Trost, B. M.;
Verhoeven, T. R. in ComprehensiVe Organometallic Chemistry; Wilkinson,
G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon: Oxford, 1982; Vol. 8,
p 799.
Experimental Section
General. For details, see the Supporting Information. C5Me5(CO)2-
Re(η2-HCtCCH2OH), C5Me5(CO)2Re(η3-H2CCtCH)+BF4-, and C5-
-
Me5(CO)2Re(η3-H2CCtCCH3)+PF6 were prepared as described ear-
lier.13,14
C5Me5(CO)2ReCH2C(PMe3)dCC(CH3)3+BF4- (4a). Excess PMe3
(0.5 mL) was vacuum transferred into a yellow solution of 3a (60 mg,
0.105 mmol) in CH2Cl2 (1 mL) at -78 °C. The mixture was stirred
and allowed to warm to 25 °C over 30 min. Volatiles were evaporated
under high vacuum to give 4a (68 mg, 100%) as a light yellow air-
stable solid. 1H NMR (CD2Cl2, 300 (MHz): δ 1.98 (s, C5Me5), 1.88
(d, JPH ) 13 Hz, PMe3), 1.52 (d, J ) 12 Hz, CHH), 1.16 [s, C(CH3)3],
0.18 (d, J ) 12 Hz, CHH). 13C{1H} NMR (CD2Cl2, 125 (MHz): δ
212.9 (CO), 212.2 (CO), 178.3 (d, JPC ) 6 Hz, CdCPMe3), 120.8 (d,
JPC ) 15 Hz, CdCPMe3), 102.8 (C5Me5), 41.9 [C(CH3)3], 32.8
[C(CH3)3], 12.1 (d, JPC ) 53 Hz, PMe3), 10.5 (C5Me5), -28.3 (CH2).
IR (THF): 1994 (s), 1914 (s) cm-1. MS (MALDI-TOF) calcd (obsd):
for C22H35O2PRe+ (M+) 547.19 (547.41), for C21H35OPRe+ (M+ - CO)
519.20 (519.47), for C19H26O2Re+ (M+ - PMe3) 471.15 (471.41).
X-ray Crystallographic Determination of C5Me5(CO)2-
ReCH2C(PMe3)dCC(CH3)3+BF4- (4a). Single crystals of 4a suitable
(50) (a) Stille, J. K. Angew. Chem., Int. Ed. Engl. 1986, 25, 508. (b)
Scott, W. J.; Crisp, G. T.; Stille, J. K. J. Am. Chem. Soc. 1984, 106, 4630.
(c) Jeffery-Luong, T.; Linstrumelle, G. Synthesis 1983, 32. (d) Gueugnot,
S.; Linstrumelle, G. Tetrahedron Lett. 1993, 34, 3853. (e) Loar, M. K.;
Stille, J. K. J. Am. Chem. Soc. 1981, 103, 4174.

732 J. Am. Chem. Soc., Vol. 120, No. 4, 1998
Table 6. X-ray Crystal Structure Data for
Casey et al.
(CO), 102.4 (C5Me5), 150.2 (ReCdC), 128.0 (ReCdC), 92.2 and 83.1
(CtC), 31.9 [C(CH3)3], 31.2 [C(CH3)3], 21.1 (dCCH3), 10.1 (C5Me5),
-21.7 (CH2). IR (Et2O): 1981 (s), 1905 (s) cm-1. HRMS (EI) calcd
(obsd) for C22H29O2Re 512.1728, obsd (512.1731).
-
C5Me5(CO)2ReCH2C(PMe3)dCC(CH3)3+BF4 (4A)
empirical form
color; habit
cryst syst
space group
unit cell dimens
C22H35BF4O2PRe
yellow transparent prism
monoclinic
Cc
a ) 25.6741(2) Å
b ) 11.9960(3) Å
c ) 16.6122(3) Å
â ) 101.218(2)°
5018.6 Å3
C5Me5(CO)2ReCH2C[CH(CO2Et)2]dCCH3 (12b). Solid NaCH-
(CO2Et)2 (9.5 mg, 52 µmol) dissolved over 10 min as it reacted with
3b (30 mg, 52 µmol) in THF. Solvent was evaporated under high
vacuum, and the residue was dissolved in Et2O. The solution was
filtered and evaporated to give 12b (30 mg, 54% yield, >90% pure by
1H NMR) as a dark orange-red oil. 1H NMR (C6D6, 200 MHz): δ 4.5
[s, CH(CO2Et)2], 4.0 (m, OCH2CH3), 2.1 (t, J ) 2 Hz, dCCH3), 2.0
(dq, J ) 11, 2 Hz, CHH), 1.61 (s, C5Me5), 1.0 (m, OCH2CH3), 0.5
(dq, J ) 11, 2 Hz, CHH). 13C NMR (THF-d8, 126 MHz): δ 216.9 (s,
CO), 214.5 (s, CO), 168.3 (s, CO2R), 167.4 (s, CO2R), 140.3 (s,
dCCH3), 119.0 (s, CdCCH3), 102.1 (s, C5Me5), 61.3 (t, JCH ) 149
Hz, OCH2), 61.1 (t, JCH ) 144 Hz, OC′H2), 59.2 (d, JCH ) 130 Hz,
CH(CO2Et)2), 18.8 (q, JCH ) 125 Hz, dCCH3), 14.4 (q, J ) 127 Hz,
OCH2CH3), 14.2 (q, J ) 127 Hz, OCH2C′H3), 10.1 (q, J ) 128 Hz,
C5Me5), -25.7 (t, J ) 141 Hz, ReCH2): IR (Et2O) 1979 (s), 1903 (s),
vol.
Peaks to determine cell
θ range of cell peaks
Z
form wt
density (calcd)
abs coeff
8192
3.0 to 25.0°
8
635.48
1.682 Mg/m3
4.952 mm-1
2512
F(000)
R (F)a
3.16%
7.85%
wR (F2)a
1736 (m) cm-1
(590.1681).
.
HRMS calcd (obsd): for C23H31O6Re 590.1681
a R factors are defined as follows: R(F) ) {∑|Fo - kFc|}/∑|Fo| and
wR(F2) ) ({∑w(Fo - Fc2)2}/∑[w(Fo )2])1/2
.
2
2
C5Me5(CO)2ReCH2C(NC5H5)dCCH3+PF6 (14b). Pyridine (2
drops, 0.5 mmol) was added to a resealable NMR tube containing a
CD2Cl2 solution of 3b (15 mg, 0.09 mmol) frozen in liquid nitrogen.
The tube was evacuated, warmed to -78 °C, inverted several times to
mix the components, and placed in a pre-cooled NMR probe at -73
°C. 1H NMR spectra of the bright yellow solution showed the formation
of 14b. 1H NMR (CD2Cl2, -53 °C, 500 (MHz): δ 8.51 (d, J ) 6 Hz,
o-C5H5N), 8.31 (t, J ) 8 Hz, p-C5H5N), 8.02 (t, J ) 7 Hz, m-C5H5N),
2.29 (br s, CH3), 1.97 (s, C5Me5), 0.62 (dq, J ) 12, 2 Hz, dCHH),
remaining CdCHH obscured by C5Me5.
-
for X-ray analysis were obtained by slow diffusion of Et2O into a
saturated CH2Cl2 solution of pure compound at room temperature over
the course of 3 days. A crystal of 4a was coated in epoxy and mounted
on the tip of a thin glass fiber. Diffraction data were obtained with
graphite-monochromated Mo KR radiation on a Siemens P4/CCD
diffractometer at 133 K. Intensity data were collected in the range
1.62 e θ e 25° using φ scan frames. Standard reflections for the data
set showed a maximum variation of 0.32% throughout acquisition.
Systematic absences and statistical analyses were consistent with the
space group Cc. The 11 098 reflections collected produced 5029
independent reflections. The initial positions for Re atoms were found
by direct methods, and all non-hydrogen atoms were located from
successive difference Fourier maps. All non-hydrogen atoms were
refined anisotropically; hydrogen atoms were refined from initial
idealized positions with a riding model using isotropic displacement
parameters of 1.2× isotropic equivalent of the bonded atom. In the
riding model, hydrogens are fixed a set distance and geometry from
the heavy atom and “ride” the motions of the heavy atom during
refinement. A semiempirical absorption correction from ψ-scans was
applied to each data set. Crystallographic computations were performed
using the SHELXTL-PLUS51 software on a Silicon Graphics Indigo
computer. Crystallographic data is summarized in Table 6.
C5Me5(CO)2ReCH2C(PMe3)dCCH3+PF6- (4b). Excess PMe3 (10
equiv) was vacuum transferred into a CH2Cl2 solution of 3b (50 mg,
0.087 mmol). A white precipitate gradually formed over 1 h at room
temperature. The precipitate was filtered and washed with Et2O to
give 4b (41 mg, 72%) as a white powder. 1H NMR (acetone-d6, 200
MHz): δ 2.36 (q, J ) 2 Hz, CCH3), 2.05 (s, C5Me5), 1.95 (d, JPH ) 14
Hz, PMe3), 1.45 (dqd, J ) 12, 2 Hz, JPH ) 0.7 Hz, CHH), 0.3 (dq, J
) 12, 2 Hz, CHH). 13C NMR (acetone-d6, 126 MHz): δ 213.5 (s,
CO), 207.0 (s, CO), 157.7 (s, dCCH3), 128.0 (d, JPC ) 33 Hz, CPMe3),
103.3 (s, C5Me5), 24.8 (q, JCH ) 130 Hz, dCCH3), 9.9 (q, JCH ) 128
Hz, C5Me5), 9.2 (qd, JCH ) 133 Hz, JPC ) 53.0 Hz, PMe3), -31.7 (t,
JCH ) 145 Hz, ReCH2). 31P{1H} NMR (acetone-d6, 202.5 MHz): δ
3.3 (s, PMe3). IR (acetone): 1991 (s), 1915 (s) cm-1. Anal. Calcd
for C19H29O2ReP2F6: C, 35.02; H, 4.49. Found: C, 35.31; H, 4.36.
C5Me5(CO)2ReCH2C[CtCC(CH3)3]dCCH3 (11b). LiCtCC-
(CH3)3 (8 mg, 87 µmol) was added to 3b (50 mg, 87 µmol) in THF at
room temperature. After 10 min, solvent was evaporated under high
vacuum, and Et2O was added. The Et2O solution was filtered and
chromatographed (silica gel, 3:1 hexane/Et2O) to give 11b (29 mg, 47%
yield, >90% pure by 1H NMR) as a dark orange-red liquid. 1H NMR
(THF-d8, 200 MHz): δ 2.03 (t, J ) 2 Hz, dCCH3), 1.96 (s, C5Me5),
1.37 (dq, J ) 11, 2 Hz, CHH), 1.19 [s, C(CH3)3], 0.20 (dq, J ) 11, 2
Hz, CHH). 13C{1H} NMR (THF-d8, 126 MHz): δ 216.9 (CO), 214.2
C5Me5(CO)2Re[η2-H2CdCdC(NC5H5)CH3]+PF6 (15K) and
-
C5Me5(CO)2Re[η2-H2CdCdC(CH3)NC5H5]+PF6- (15T). Complex
3b (50 mg, 0.09 mmol) and pyridine (0.54 mmol) were stirred in 5
mL of CH2Cl2 for 15 min. Most of the solvent was evaporated from
the bright yellow solution, and 10 mL of Et2O was added. The resulting
yellow precipitate was filtered off, washed with Et2O, and dried under
vacuum to give a 10:1 mixture of 15K/15T (36 mg, 61%) as a yellow
powder. MS (LSIMS) calcd (obsd): for C21H25O2NRe 510.1 (510.2).
Anal. Calcd for C21H25O2NRePF6: C, 38.50; H, 3.96. Found: C,
38.20; H, 3.61.
Major Kinetic Isomer 15K. 1H NMR (CD2Cl2, -40 °C, 500
MHz): δ 8.73 (d, J ) 6 Hz, o-C5H5N), 8.39 (t, J ) 8 Hz, p-C5H5N),
8.02 (br t, J ) 8 Hz, m-C5H5N), 2.59 (br s, CH3), 2.00 (s, C5Me5),
1.94 (dq, shoulders not resolved, J ) 9, 2 Hz, dCHH), 1.19 (dq,
shoulders not resolved, J ) 8, 2 Hz, dCHH). 13C{1H} NMR (CD2-
Cl2, -60 °C, 126 MHz): δ 205.8 (CO), 202.4 (CO), 148.1 (CdCdC),
146.1 (br, p-C5H5N), 143.4 (br, o-C5H5N), 132.0 (dC(CH3)NC5H5),
126.9 (m-C5H5N), 100.1 (C5Me5), 26.4 (CH3), 9.7 (C5Me5), -2.5
(dCH2). 13C{1H} NMR (CD2Cl2, 22 °C, 126 MHz): δ 204 (br, CO),
148.9 (CdCdC), 145.8 (p-C5H5N), 144.4 (o-C5H5N), 133.3 (dC(CH3)-
NC5H5), 128.5 (m-C5H5N), 101.7 (C5Me5), 26.9 (CH3), 10.2 (C5Me5),
-1.7 (dCH2). 13C NMR (CD2Cl2, 22 °C, 126 MHz): δ 204 (br, CO),
148.8 (s), 145.7 (d, J ) 164 Hz), 144.4 (d, J ) 176 Hz), 133.2 (s),
128.5 (d, J ) 189 Hz), 101.1 (s), 26.9 (q, J ) 139 Hz), 10.2 (q, J )
126 Hz), -1.8 (t, J ) 164 Hz). IR (THF): 1983 (s), 1911 (s) cm-1
.
A solution of 15K (6 mg, 9.2 µmol) in CD2Cl2 solution slowly
equilibrated (t1/2 ≈14 d) to a 1:9 mixture of 15K/15T. After 2 months,
evaporation of solvent gave a yellow solid which was washed with
ether to give a 1:9 mixture of 15K/15T (6 mg, 100%).
Minor Kinetic Isomer 15T. 1H NMR (CD2Cl2, 213 K, 500 MHz):
δ 8.73 (d, J ) 6 Hz, o-C5H5N), 8.52 (t, J ) 6 Hz, p-C5H5N), 8.09 (br
t, J ) 6 Hz, m-C5H5N), 2.73 (br s, CH3), 1.91 (br d, J ) 8 Hz, dCHH),
1.81 (s, C5Me5), 1.19 (br d, J ) 8 Hz, dCHH). 13C{1H} NMR (CD2-
Cl2, 213 K, 126 (MHz): δ 203.7 (CO), 203.0 (CO), 153.8 (CdCdC),
144.0 (br, C5H5N), 140.8 (br, C5H5N), 126.7 (C5H5N), 125.7
(dC(CH3)NC5H5), 100.1 (C5Me5), 19.9 (CH3), 9.9 (C5Me5), -2.9
(dCH2). IR (THF): 1997 (s), 1914 (s) cm-1
.
-
Reaction of C5Me5(CO)2ReCH2C(NC5H5)dCCH3+PF6 (14b)
with 4-Picoline. A CD2Cl2 solution of 14b was prepared from pyridine
(7 µL, 9 µmol) and 3b (15 mg, 2.6 µmol) at -78 °C in a resealable
(51) Sheldrick, G. M. SHELXTL Version 5 Reference Manual, 1994;
Siemens Analytical X-ray Instruments, 6300 Enterprise Dr., Madison, WI
53719-1173.

Kinetic Addition to Rhenium Complexes
J. Am. Chem. Soc., Vol. 120, No. 4, 1998 733
NMR tube. 1H NMR spectra at -30 °C showed formation of 14b
along with excess pyridine. 4-Picoline (30 µL, 310 µmol) was added
to the solution at -78 °C. 1H NMR spectra at -40 °C showed complete
formation of C5Me5(CO)2ReCH2C(NC5H4-p-CH3)dCCH3+PF6- (16b)
along with excess pyridine and 4-picoline. 16b. 1H NMR (CD2Cl2,
-40 °C, 500 MHz): δ 8.39 (d, J ) 6 Hz, o-C5H4N), 7.79 (d, J ) 6
Hz, m-C5H4N), 2.58 (s, CH3), 1.98 (s, C5Me5), 0.61 (br d, J ) 13 Hz,
CHH), CH3 and CHH resonances buried under excess 4-picoline and
C5Me5 resonances.
(dd, Jgem ) 16 Hz, JPH ) 19 Hz, CHHP), 3.58 (dd, Jgem ) 16 Hz, JPH
) 15 Hz, CHHP), 2.01 (s, C5Me5), 1.92 (d, JPH ) 15 Hz, PMe3), 1.30
(s, C(CH3)3). 13C{1H} NMR (CD2Cl2, 90 MHz): δ 205.9 (CO), 204.8
(CO), 97.0 (CtCCH2), 100.9 (C5Me5), 57.8 (d, JPC ) 12 Hz, CtCCH2),
32.8 [C(CH3)3], 30.7 [C(CH3)3], 25.2 (d, JPC ) 51 Hz, CH2P), 10.4
(C5Me5). IR (THF): 1951 (s), 1869 (s) cm-1
. MS (MALDI-TOF)
calcd (obsd): for C22H35O2PRe+ (M+) 547.19 (547.38).
C5Me5(CO)2Re{η3-CH2C[CtCC(CH3)3]CHCH3}+PF6- (27). H2O
(2 equiv) was vacuum transferred into a THF solution of 3b (50 mg,
87 µmol). After 10 min at 25 °C, excess CF3CO2H (10 equiv) was
added, and volatile materials were evaporated under vacuum. The
residue was washed with wet Et2O and filtered to give 27 (26 mg,
45%) as a pale-brown solid. 1H NMR (acetone-d6, 200 MHz): δ 4.07
(d, Jgem ) 3 Hz, CHH), 2.90 (q, J ) 9.0 Hz, CHCH3), 2.27 (s, C5Me5),
2.11 (d, J ) 9 Hz, CHCH3), 1.95 (br d, Jgem ) 3 Hz, CHH), 1.24 [s,
C(CH3)3]. 13C{1H} NMR (acetone-d6, 126 MHz): δ 195.0, 193.1 (CO);
104.9 (C5Me5) 102.8 (CH2C) 90.6, 73.2 (CtC) 67.7 (CHCH3) 44.6
(CH2) 31.1 [C(CH3)3], 16.9 (CHCH3) 10.1 (C5Me5). IR (acetone): 2045
At 9 °C, new resonances for C5Me5(CO)2Re[η2-H2CdCdC-
(CH3)(NC5H4-p-CH3)]+PF6 (17) grew in slowly. After 8 h at room
-
temperature, volatile materials were evaporated under vacuum and fresh
CD2Cl2 was added. 1H NMR showed a complex mixture of η2-allenyl
adducts from both pyridine and 4-picoline. For 17. (CD2Cl2, 300
MHz): δ 8.58 (d, J ) 7 Hz, o-C5H4N), 7.82 (d, J ) 7 Hz, m-C5H4N),
2.68 (s, CH3), 2.59 (s, CH3), 2.05 (s, C5Me5), 1.5 (br, dCH2).
C5Me5(CO)2Re[η2-H2CdCdC(NEt3)CH3]+PF6- (19). Addition of
NEt3 (20 mg, 170 µmol) to C5Me5(CO)2Re(η3-CH2CtCCH3)+PF6- (55
mg, 9.6 µmol) in CD2Cl2 produced a bright yellow solution. Volatile
materials were evaporated under vacuum, and the resulting dark yellow
solid was washed with Et2O and dried under vacuum to give
C5Me5(CO)2Re[η2-H2CdCdC(NEt3)CH3]+PF6- (19) (14 mg, 60%) as
a yellow powder. 1H NMR (CD2Cl2, 24 °C, 500 MHz): δ 3.53 (q, J
) 8 Hz, NCH2CH3), 2.32 (t, J ) 2 Hz, CH3), 2.04 (s, C5Me5), 1.23 (t,
J ) 8 Hz, NCH2CH3), dCH2 resonances broadened by allene rotation.
The CH2d resonances decoalesced at -47 °C. 1H NMR (CD2Cl2, -47
°C, 500 MHz): δ 3.4 (br, NCH2CH3), 2.23 (br s, CH3), 2.16 (br d,
Jgem ) 9 Hz, dCHH), 1.96 (s, C5Me5), 1.44 (br d, Jgem ) 9 Hz, dCHH),
1.25 (br, NCH2CH3). 1H NMR (CD2Cl2, -80 °C, 500 MHz): additional
resonances observed for decoalesced Et groups at δ 3.65 (br, 1H), 3.52
(br, 1H), 3.41 (br, 1H), 3.29 (br, 2H), 3.21 (br, 1H), 1.27 (br t, J ) 6
Hz, 3H), 1.11 (br t, J ) 7 Hz, 3H), 0.92 (br t, J ) 5 Hz, 3H). 13C{1H}
NMR (CD2Cl2, 126 (MHz): δ 203.4 (CO), 147.0 (CdCdC), 123.0
(dC(CH3)NEt3), 101.1 (C5Me5), 53.2 (NCH2CH3), 18.9 (dC(CH3)-
NEt3), 10.5 (C5Me5), 8.4 (NCH2CH3), 3.4 (dCH2). IR (THF): 1979
(s), 1990 (s) cm-1
.
C5Me5(CO)2Re[η3-H2CC(OH)CH2]+BF4- (29). Addition of HBF4‚
Et2O (10 µL, 85%) to a yellow solution of C5Me5(CO)2Re(η2-
HCtCCH2OH) (25 mg, 58 µmol) and distilled water (0.1 mL) in
acetone (2 mL) produced an orange-red solution. The red precipitate
which formed upon addition of Et2O (15 mL) was separated, washed
twice with 10 mL of Et2O, and dried under vacuum to give 29 (20 mg,
80%) as a red air-stable powder as a 9:1 ratio of endo and exo isomers.
1H NMR (CD2Cl2, 300 MHz): endo isomer: δ 8.35 (br s, OH), 4.28
(AA′XX′, JAX ) -4 Hz, JXX ) 4 Hz, Hsyn),52 2.09 (s, C5Me5), 1.89
(AA′XX′, JAX ) 4 Hz, JXX ) 4 Hz, Hanti). 1H NMR (CD2Cl2, 300
MHz) exo isomer: δ 8.35 (br s, OH), 4.07 (m, Hsyn), 2.05 (s, C5Me5),
1.68 (m, Hanti). 13C{1H} NMR (CD2Cl2, 90 MHz): δ 195.0 (CO), 134.0
(COH), 104.2 (C5Me5), 33.3 (CH2), 10.4 (C5Me5). IR (CH2Cl2): 2045
(s), 1986 (s) cm-1. MS (MALDI-TOF) calcd (obsd): for C15H20O3-
Re+ 433.09 (433.23).
(s), 1909 (s) cm-1
.
MS (LSIMS) calcd (obsd): for C22H35O2NRe+
532.2 (532.2). Anal. Calcd for C22H35O2NRePF6: C, 39.05; H, 5.21.
Found: C, 39.22; H, 5.17.
-
C5Me5(CO)2ReCH2C(NC5H4NMe2)dCC(CH3)3+BF4 (22a). 4-
Reaction of 3c with D2O. HBF4‚Et2O (10 µL, 85%) was added to
a yellow solution of 30 (20 mg, 46 µmol) in CD2Cl2 (1 mL) at room
temperature to generate 3c. D2O (0.1 mL, excess) was immediately
added to the resulting orange solution, which reddened upon mixing.
Et2O (5 mL) was added to precipitate C5Me5(CO)2Re[η3-HDCC-
(Dimethylamino)pyridine (DMAP, 5 mg, 0.040 mmol) was added to a
yellow solution of 3a (20 mg, 0.035 mmol) in CD2Cl2 (1 mL) in a
resealable NMR tube at -78 °C. The tube was inverted to mix the
reactants and immediately inserted into a pre-cooled NMR probe at
1
-38 °C. Complex 22a was the only product observed by H NMR
(OD)CH2]+BF4 (29-d2) as a red solid (7 mg, 30%). 1H NMR (CD2-
-
spectroscopy. Rearrangement to 23 occurred at -20 °C. 1H NMR
(CD2Cl2, 360 MHz, -38 °C): δ 7.74 (d, J ) 7 Hz, CHN), 6.77 (d, J
) 7 Hz, CHCHN), 3.20 (s, NMe2), 1.99 (s, C5Me5), 1.80 (d, Jgem ) 12
Hz, CHH), 0.91 [s, C(CH3)3], 0.34 (d, Jgem ) 12 Hz, CHH). 13C{1H}
NMR (CD2Cl2, 90 MHz, -38 °C): δ 214.2, 213.6 (CO); 140.9
(CdCDMAP); 155.6, 136.9, 130.4 (DMAP aromatic carbons); 105.6
(CdCDMAP), 101.8 (C5Me5), 40.3 (NMe2), 37.5 [C(CH3)3], 32.0
[C(CH3)3], 10.2 (C5Me5), -17.7 (CH2).
Cl2, 300 MHz): δ 4.27 (br d, J ) 4 Hz, 1.7 H, Hsyn), 2.05 (s, 15 H,
C5Me5), 1.85 (br d, J ) 4 Hz, 0.9 H, Hanti).
Acknowledgment. Financial support from the National
Science Foundation is gratefully acknowledged.
C5H5(CO)2Re[η2-(CH3)3CCtCCH2(NC5H4NMe2)]+BF4- (23). A
yellow solution of DMAP (10 mg, 38 µmol) and 3a (17 mg, 35 µmol)
in CH2Cl2 (5 mL) was stirred at room temperature for 15 min. Volatiles
were evaporated under high vacuum, and the resulting yellow residue
was washed with 10 mL of diethyl ether to give 23 (25 mg, 96%) as
a yellow solid. 1H NMR (CD2Cl2, 300 MHz): δ 7.87 (d, J ) 7 Hz,
NCH), 6.85 (d, J ) 7 Hz, NCCH), 5.45 (d, Jgem ) 16 Hz, CHH), 5.09
(d, Jgem ) 16 Hz, CHH), 3.22 (s, NMe2), 2.02 (s, C5Me5), 1.18 [s,
C(CH3)3]. 13C{1H} NMR (CD2Cl2, 90 (MHz): δ 209.6, 208.3 (CO);
147.7, 141.2, 141.0 (DMAP aromatic carbons); 101.3 (CtC), 101.1
(C5Me5), 71.6 (C≡C), 66.0 (CH2), 40.5 (NMe2), 33.9 [C(CH3)3], 31.7
[C(CH3)3], 10.7 (C5Me5). IR (THF): 1950 (s), 1867 (s) cm-1. MS
(MALDI-TOF) calcd (obsd): for C26H36O2N2Re+ (M+) 593.23 (593.30),
for M+ - CO 565.24 (565.31), for M+ - DMAP 471.15 (471.29).
C5Me5(CO)2Re[η2-(CH3)3CCtCCH2(PMe3)]+BF4- (25). A CH2-
Cl2 solution of 4a (50 mg, 0.077 mmol) was stirred at room temperature
for 2 days. Volatiles were evaporated under high vacuum, and the
yellow residue was washed with 10 mL of diethyl ether to give 25 (45
mg, 90%) as a yellow solid. 1H NMR (CD2Cl2, 360 MHz): δ 3.97
Supporting Information Available: General experimental
methods and experimental details and characterization for C5-
Me5(CO)2Re[η2-(CH3)3CCtCCH2OH], 3a, 4c, 5a, 5b, 5c, 10b,
13b, 18c, 20, 21, 24, 26, 28, and 31 and X-ray crystallographic
data for 4a (19 pages). An X-ray crystallographic file, in CIF
format, is available through the Internet only. See any current
masthead page for ordering and Internet access instructions.
JA9729847
(52) The AA′XX′ pattern was modeled using the program WinDNMR
(v.1.4 Reich, H. J. J. Chem. Educ. Software, 1996) and is consistent with
JAA′ ) 0 Hz, JAX ) 4 Hz, and JXX′ ) 4 Hz, where “A”is Hsyn and “X”is
H
anti. Coupling constants between remote η3-allyl protons are generally
small,26 and the assignment of the Hsyn-Hsyn coupling as larger than the
Hanti-Hanti coupling is consistent with the “W” relative geometry of the
syn protons, which is more favorable for the transmission of coupling
information.