Selective C-C bond formation on the first ketene-alkyne complexes

Full text of DOI:10.1021/ja963750a

2958
J. Am. Chem. Soc. 1997, 119, 2958-2959
facile regiospecific C-H activation of the ketene phenyl
substituent and ultimately, coupling of ketene and alkyne to
give 8.
Selective C-C Bond Formation on the First
Ketene-Alkyne Complexes
H. C. Lo and Douglas B. Grotjahn*
Warming of either diphenylketene complex 18 (Scheme 1)
with alkyne 2 or of diphenylketene 4 with alkyne complex 59
led to a mixture containing free P(i-Pr)3 and the monophosphine
complex 3 in a molar ratio of 1:1.10 A series of NMR
experiments implicate the formulation shown for 3.11 For
example, by using 2D NMR, resonances for all 10 aryl protons
of 3a could be found between 6.98 and 8.25 ppm, showing that
C-H activation (Vide infra) had not yet occurred. Inequivalent
alkyne CH3 groups were revealed by sharp three-proton singlets
at δ 1.95 and 2.33 ppm. HMBC (1H, 13C) showed that the
acetylenic carbons resonated at 164.79 (d, J ) 9.1 Hz) and
144.07 (s) ppm.12 These data and a second narrow 13C{1H}
doublet at 118.74 (d, J ) 4.9 Hz) due to a ketene carbon verify
the presence of one phosphine, cis to both ketene and alkyne.12
The acetylenic carbons in 3a appear far downfield from those
in 5a (δ 56.83), consistent with replacement of trans-Cl in 5a
with the π-acid ketene. Binding of the ketene to Ir in 3a is
implicated by a significant cross peak in the HMBC spectrum
between the C)C)O carbon at 204.87 ppm and the alkyne
protons at 1.95 ppm, and the chemical shifts of the CdCdO
carbons are more consistent with coordination to the CdC
bond.13 Finally, and most significantly, η2-binding of the metal
to the ipso and ortho carbons of one ketene C6H5 substituent is
indicated by two sets of data: (1) the upfield shifts of the ortho
proton resonances [δ 6.98 Vs 8.25 ppm for those on the
uncoordinated ring]; (2) the upfield shifts and splitting of the
ipso and ortho carbon resonances [coordinated ring, ipso δ
118.42-118.60 (narrow unresolved m), ortho 118.74 (d, J )
4.9 Hz); uncoordinated ring, ipso 142.82 (s) and ortho 130.99
(s)]. The equivalence of the ortho and meta protons and carbons
on the coordinated C6H5 ring implies a rapid rotation of the
ring, as documented in some other η2-arene complexes.14
Similar spectroscopic properties were seen for other ketene-
alkyne complexes 3. As alkyne displaces P(i-Pr)3 from 1 to
give 3, the profound change in ketene binding, particularly η2-
arene coordination, presages regiospecific C-H bond activa-
tion15 of the ketene at an ortho position.
Department of Chemistry and Biochemistry
Arizona State UniVersity
Box 871604, Tempe, Arizona 85287-1604
ReceiVed October 28, 1996
Metal π-complexes of alkynes1 and of ketenes2 are key
intermediates in reactions capable of constructing synthetically
challenging organic molecules.3,4 Metal-mediated redox ho-
mocoupling of alkynes (to give metallacyclopentadienes A) is
a reaction of wide scope at the heart of syntheses of dienes,
arenes, heterocycles, and other organic products.3a,b Only two
isolated reports of ketene homocoupling exist [B, M ) Ti or
Ni, R1-R4 ) Ph].5 Even rarer is ketene-alkyne heterocou-
pling: the clearest example is limited to the parent compounds,
giving C (M ) Ti, R1-R4 ) H),6 but organic products were
not liberated from metallacycle C. Certain organic products
from reactions of chromium carbene complexes and alkynes
could be explained by invoking ketene-alkyne coupling as in
C7a or as in D,7b although these metallacycles were not observed.
Here we report the chemo-, regio-, and stereoselective coupling
of diphenylketene with internal alkynes on Ir(I) to give irida-
benzopyrans 8 rather than C or D. In these reactions, the first
ketene-alkyne complexes 3 are formed chemoselectively.
Spectral features of 3 point to η2-arene coordination, explaining
(1) Lewandos, G. S. In The Chemistry of the Metal-Carbon Bond;
Hartley, F., Patai, S., Eds.; Wiley: New York, 1982; Vol. 1, Chapter 7, pp
287-323.
(2) (a) Geoffroy, G. L.; Bassler, S. L. AdV. Organomet. Chem. 1988,
28, 1. (b) Hofmann, P.; Perez-Moya, L. A.; Steigelmann, O.; Riede, J.
Organometallics 1992, 11, 1167 and references therein.
(8) Grotjahn, D. B.; Lo, H. C. Organometallics 1995, 14, 5463.
(9) Complexes of terminal alkynes to ClIr[P(i-Pr)3]2: Ho¨hn, A.; Werner,
H. J. Organomet. Chem. 1990, 382, 255.
(10) The combination of 4 and 5 produced 3 much more rapidly than
when 1 and 2 were mixed. Isolation of 3 was not possible because of its
further reactions.
(3) (a) Cyclotrimerization: Grotjahn, D. B. In ComprehensiVe Organo-
metallic Chemistry II; Hegedus, L. S., Ed.; Pergamon; Oxford, 1995; Vol.
12, Chapter 7.3, pp 741-770. (b) Reductive dimerization of alkynes:
Broene, R. D. In ComprehensiVe Organometallic Chemistry II; Hegedus,
L. S., Ed.; Pergamon; Oxford, 1995; Vol. 12, Chapter 3.7, pp 323-348.
(c) Pauson-Khand cyclization: Schore, N. E. In ComprehensiVe Organo-
metallic Chemistry II; Hegedus, L. S., Ed.; Pergamon; Oxford, 1995; Vol.
12, Chapter 7.2, pp 703-740.
(4) Ketene complexes from carbene complexes: (a) Wulff, W. D. In
ComprehensiVe Organometallic Chemistry II; Hegedus, L. S., Ed.; Perga-
mon; Oxford, 1995; Vol. 12, Chapter 5.3, pp 469-548. (b) Hegedus, L. S.
In ComprehensiVe Organometallic Chemistry II; Hegedus, L. S., Ed.;
Pergamon; Oxford, 1995; Vol. 12, Chapter 5.4, pp 549-576. (c) Do¨tz, K.-
H. In Organometallics in Organic Synthesis; de Meijere, A., tom Dieck,
H, Eds.; Springer: Berlin, 1988. (d) Harvey, D.F.; Grenzer, E. M.; Gantzel,
P. K. J. Am. Chem. Soc. 1994, 116, 6719. (e) Merlic, C. A.; Xu, D.;
Gladstone, B. G. J. Org. Chem. 1993, 58, 538.
(11) See Supporting Information.
(12) (a) In (η3-P,P,P-triphos)Ir(H)(PhCCH),12b the alkyne is clearly a two-
electron donor and trans to one phosphine: 13C NMR δ 155.0 [ddd,
2J(CPtrans) ) 80.2 Hz, 2J(CPcis) ) 9.9, 6.3 Hz] and 153.3 [dt, 2J(CPtrans) )
82.7 Hz, 2J(CPcis) ) 6.3 Hz]. (b) Bianchini, C.; Barbaro, P.; Meli, A.;
Peruzzini, M.; Vacca, A.; Vizza, F. Organometallics 1993, 12, 2505. Cf.
Marinelli, G.; Streib, W. E.; Huffman, J. C.; Caulton, K. G.; Gagne´, M. R.;
Takats, J.; Dartiguenave, M. Polyhedron 1990, 9, 1867.
(13) Taken alone, the 13C NMR data for the OdCdC unit of 3a are
consistent with coordination to either double bond or with none at all.
Compare data for the OdC(1)dC(2) unit in 3a, 4,13e and 1,8 respectively:
for C(1) ) δ 204.87 (s), 201.2 (s), and 143.39 (t, J ) 3.2 Hz); C(2) ) δ
55.03 (s), 47.6 (s), and 74.26 (s); (C,C)-bound ketene complexes2a,8 appear
to have C(1) ) 166.8-255.7 and C(2) ) -33.0 to 74.7 ppm. (e) Tidwell,
T. T. Ketenes; Wiley: New York, 1995; p 34.
(5) (a) Fachinetti, G.; Biran, C.; Floriani, C.; Chiesi-Villa, A.; Guastini,
C. J. Am. Chem. Soc. 1978, 100, 1921. (b) Hoberg, H.; Korff, J. J.
Organomet. Chem. 1978, 152, C39.
(6) Straus, D. A.; Grubbs, R. H. J. Am. Chem. Soc. 1982, 104, 5499.
Vinylketene complexes of other metals can react with alkynes: Huffman,
M. A.; Liebeskind, L. S. J. Am. Chem. Soc. 1990, 112, 8617. Anderson, B.
A.; Wulff, W. D.; Rheingold, A. L. Ibid., 1990, 112, 8615.
(7) (a) Bao, J.; Wulff, W. D.; Dragisch, V.; Wenglowsy, S.; Ball, R. S.
J. Am. Chem. Soc. 1994, 116, 7616. (b) Xu, Y.-C.; Challener, C. A.;
Dragisch, V.; Brandvold, T. A.; Peterson, G. A.; Wulff, W. D.; Willard, P.
G. J. Am. Chem. Soc. 1989, 111, 7269. We thank a reviewer for bringing
these examples to our attention.
(14) (a) Upfield carbon shifts and fluxionality in η2-arene complexes:
Li, C.-S.; Jou, D.-C.; Cheng, C.-H. Organometallics 1993, 12, 3945 and
references therein. (b) NOE experiments11 showed saturation transfer14c
between ortho protons on the coordinated and noncoordinated C6H5 rings,
suggesting movement of the ketene ligand on Ir. Moreover, a negative NOE
effect14d from protons of 3d with those on 5d suggests the equilibria shown
at the top of Scheme 1. (c) Neuhaus, D.; Williamson, M. P. The Nuclear
OVerhauser Effect in Structural and Conformational Analysis; VCH: New
York, 1989; Chapters 5, pp 141-148. (d) The Nuclear OVerhauser Effect
in Structural and Conformational Analysis; VCH: New York, 1989;
Chapters 5, pp 175-180.
(15) Jones, W. D.; Feher, F. J. Acc. Chem. Res. 1989, 22, 91.
S0002-7863(96)03750-X CCC: $14.00 © 1997 American Chemical Society

Communications to the Editor
J. Am. Chem. Soc., Vol. 119, No. 12, 1997 2959
Scheme 1
Indeed, on further gentle warming 3 disappeared, giving
alkyne-ketene coupling product 8 (41-55%).16a,b The irida-
benzopyran core of 8 was implicated by spectral data.11 The
13C NMR spectrum of 8a, for example, showed one downfield
triplet (δ 113.83, J ) 7.0 Hz), suggesting bonding of only one
carbon to Ir. HMBC and HMQC data pointed to connectivity
of a diene unit and a vinylic proton, and NOE data11 showed
that exocyclic double bond substituents R1 ) R2 ) CH3 are cis
to each other.18 Identification of 8c and its regioisomer 8c′ in
an inseparable mixture (ratio 2:1) was secured by the multiplici-
ties of the 1H NMR resonances of the vinylic protons (8c, qt, J
) 1.0 and 7.0 Hz; 8c′, q, J ) 6.5 Hz). In 8d and 8e, the vinylic
proton resonance appears as a singlet. One consequence of
coordinative unsaturation in complexes 8 is that CO adds within
seconds at 1 atm, stereospecifically giving hexacoordinate
adducts in which the CO ligand is trans to the aryl carbon.19
Formation of 8 can be viewed as a consequence of η2-arene
complexation in 3, leading to C-H activation product 6, in
which the number of ligands on Ir is undetermined, hence the
symbol [Ir] is used.20 Subsequent alkyne insertion18 could give
7, and insertion of the ketene CdO bond into the Ir-vinyl bond
would give 8.21 Notable features of the oVerall process from 3
to 8 are the regio- and stereoselectiVe functionalizations of both
the ketene and the alkyne. On the basis of exclusive formation
of regioisomers 8d,e and the 2:1 ratio of regioisomers 8c and
8c′, we note that the larger group tends to emerge as the terminal
diene substituent R1.18,22 Successful production of 8e shows
that the reaction tolerates an ether functionality at an activated
position.
The unique structure and reactivity of ketene-alkyne complex
3 gives rise to polycyclic organometallic products unobtainable
either from ketene-alkyne cycloadditions16d or from other
metal-mediated processes. Studies of stereospecific elaborations
of the extensive π-system in 8 and demetalations are underway
and will be reported in due course.
Acknowledgment. We thank Johnson Matthey Aesar Alfa for a
loan of iridium salts and Cambridge Isotope Labs for a grant of 13CO.
(16) (a) Better yields (41-55%) of 8 were obtained by adding 4 (0.6
Supporting Information Available: Preparations, spectral data,
spectra, and combustion analyses of 16 compounds (33 pages). See
any current masthead page for ordering information and Internet access
instructions.
o
equiv) to 5, heating at 60 C for 2-3 h, adding a second portion of 4 (0.6
equiv), and heating until 5 was consumed; total time, 14-26 h.11 A minor
byproduct was 1017 (ca. 5%). From reactions of 1 and 2, isolation of 5
shows ketene-alkyne substitution occurs. (b) Spectral data suggest that a
chromatographically unstable component, perhaps related to C or D, is
derived from metal, alkyne, and ketene.11 Its amount is negligible for R1
and R2 ) alkyl but rivals that of 8 when R1 ) Ph. Efforts continue to
convert the compound to an isolable product. (c) Homocoupling of ketene
or alkyne on Ir(I) is excluded by control experiments: (i) 5d does not react
JA963750A
(19) The stereochemistry of CO addition was secured in part by use of
13CO on 8d and observation of 2JC-C ) 33.7 Hz between the CO and aryl
C across the metal in the resulting adduct.11,17
(20) Compound 6 is drawn with (C,O)-coordinated ketene because this
explains the course of subsequent insertions leading to 8, but Ir could be
coordinated to the C,C bond or not at all. However, we favor an 18-electron
species with [Ir] ) IrCl[P(i-Pr)3] bound to ketene.
(21) Diphenylketene insertion into a Ni-CH3 bond shows the same
regiochemical sense as transformation of 7 to 8: Jeffery, E. A.; Meisters,
A. J. Organomet. Chem. 1974, 82, 315.
o
with 2d (60 C, 2 d), excluding formation of A; (ii) warming of 1 in the
presence of 4 gives 10, not B (as reported earlier, 9 and 4 give 10);17 (iii)
free ligands 2d and 4 do not give [2 + 2] cycloadducts16d after 40 h at 60
oC. (d) Reference 13e, pp 514-518 and Houben-Weyl Methoden der
Organischen Chemie, Vol. E15, Part 2, pp 2472-2474.
(17) C-H activation on 1 leads to 9; 9 and 4 give 10. At no point in
these studies did we find evidence for η2-arene complexation as in 3:
Grotjahn, D. B.; Lo, H. C. J. Am. Chem. Soc. 1996, 118, 2097.
(18) Both cis- and trans-products from alkyne insertion into Ni-C
bonds: Huggins, J. M.; Bergman, R. G. J. Am. Chem. Soc. 1979, 101, 4410.
See also Alexander, J. J. In The Chemistry of the Metal-Carbon Bond, Vol.
2; Hartley, F., Patai, S., Eds.; Wiley: New York, 1985; pp 339-400.
(22) Under the conditions used to form 8a-e, 5f rearranged to trans-
[P(i-Pr)3]2Ir[CdC(CH3)(SiMe3)]Cl,11 a reaction known on Rh: Werner, H.;
Baum, M.; Schneider, D.; Windmu¨ller, B. Organometallics 1994, 13, 1089.
Terminal alkynes also give vinylidenes or products therefrom.