First direct structural comparison of complexes of the same metal fragment to ketenes in both C,C- and C,O-bonding modes

Article abstract of DOI:10.1021/ja004324z

Using a series of Ir(I) and Rh(I) ketene complexes, conclusions about the structure and bonding of complexes of the fundamentally important ketene ligand class are reached. In a unique comparison of X-ray structures of the same metal fragment to ketenes in both the η²-(C,C) and the η²-(C,O) binding mode, the Ir-C1 bond distances in complexes of trans-Cl(Ir)[P(i-Pr)_3]2 to phenylketene [4, η²-(C, C)] and diphenylketene [2a, η²-(C,O)] are 2.371(3) and 2.285 A, respectively. This would be consistent with greater trans influence of a ketene ligand bound to a metal through its C=C bond than one connected by its C=O bond. Backbonding of Ir(I) and Rh(I) to diphenylketene was assessed using trans-Cl(M)[P(i-Pr)3]2η²-(C,O)-diphenylketene] (2a and 2d). Most bond lengths and angles are identical, but slightly greater back-bonding by Ir(I) is suggested by the somewhat greater deformation of the ketene C=C=O system [C-C-O angles are 136.6(4) and 138.9(4) in the Ir and Rh cases 2a and 2d, respectively]. Syntheses of new labeled ketenes Ph²C= 13C=O and Ph₂C=C=¹⁸O and their RH(I) complexes are reported, along with the generation of an Ir(I) complex of PhCH=¹³C=O. The effects of isotopic substitution on infrared absorption data for ketene complexes are presented for the first time. Preliminary normal coordinate mode analysis allowed definitive assignment of absorptions ascribed to the C-O stretching frequencies of coordinated ketenes, which are near the absorptions for aromatic ring systems commonly found as substituents on ketenes. For free diphenylketene and four of its complexes and a phenylketene complex characterized by X-ray diffraction, the magnitude of the ¹³C-¹³C coupling between the two ketene carbons is correlated to carbon-carbon bond distance.

Full text of DOI:10.1021/ja004324z

8260
J. Am. Chem. Soc. 2001, 123, 8260-8270
First Direct Structural Comparison of Complexes of the Same Metal
Fragment to Ketenes in Both C,C- and C,O-Bonding Modes
Douglas B. Grotjahn,*,† Laura S. B. Collins,† Marcus Wolpert,† Galina A. Bikzhanova,†
H. Christine Lo,‡ David Combs,† and John L. Hubbard§
Contribution from the Department of Chemistry, 5500 Campanile DriVe, San Diego State UniVersity,
San Diego, California 92182-1030, and Department of Chemistry and Biochemistry, Utah State UniVersity,
Logan, Utah 84322-0300
ReceiVed December 22, 2000
Abstract: Using a series of Ir(I) and Rh(I) ketene complexes, conclusions about the structure and bonding of
complexes of the fundamentally important ketene ligand class are reached. In a unique comparison of X-ray
structures of the same metal fragment to ketenes in both the η2-(C,C) and the η2-(C,O) binding mode, the
Ir-Cl bond distances in complexes of trans-Cl(Ir)[P(i-Pr)3]2 to phenylketene [4, η2-(C,C)] and diphenylketene
[2a, η2-(C,O)] are 2.371(3) and 2.285(2) Å, respectively. This would be consistent with greater trans influence
of a ketene ligand bound to a metal through its CdC bond than one connected by its CdO bond. Back-
bonding of Ir(I) and Rh(I) to diphenylketene was assessed using trans-Cl(M)[P(i-Pr)3]2[η2-(C,O)-diphenylketene]
(2a and 2d). Most bond lengths and angles are identical, but slightly greater back-bonding by Ir(I) is suggested
by the somewhat greater deformation of the ketene CdCdO system [C-C-O angles are 136.6(4) and 138.9-
(4) in the Ir and Rh cases 2a and 2d, respectively]. Syntheses of new labeled ketenes Ph2Cd13CdO and
Ph2CdCd18O and their Ir(I) and Rh(I) complexes are reported, along with the generation of an Ir(I) complex
of PhCHd13CdO. The effects of isotopic substitution on infrared absorption data for ketene complexes are
presented for the first time. Preliminary normal coordinate mode analysis allowed definitive assignment of
absorptions ascribed to the C-O stretching frequencies of coordinated ketenes, which are near the absorptions
for aromatic ring systems commonly found as substituents on ketenes. For free diphenylketene and four of its
complexes and a phenylketene complex characterized by X-ray diffraction, the magnitude of the 13C-13C
coupling between the two ketene carbons is correlated to carbon-carbon bond distance.
Introduction
than observed directly. The lack of structural information makes
it difficult or impossible to explain results such as changes in
cyclization diastereoselectivity with changes in metal fragment.7
The work reported here is part of our program to understand
trends in structure, bonding,10 and reactivity11-14 of metal-
ketene complexes.
In one class of ketene complexes involving a single metal,
the metal imparts inertness to the ketene ligand.15-17 A second
class of ketene complexes are barely stable enough to be
isolated, forming at temperatures of -20 to +50 °C mixtures
of products that can be rationalized by cleavage of the ketene
CdC bond.18-21 Finally, a third kind of ketene complexes, too
Ketenes are versatile reaction partners in cycloadditions and
nucleophilic addition reactions.1-3 Coordination of a metal
fragment to the ketene leads to an even wider range of possible
structure and reactivity.4 Ketene-metal complexes have been
suggested as key intermediates in many of the applications of
carbene-CO complexes to organic synthesis, including ben-
zannulation reactions,5 â-lactam or cyclobutanone formation,6-8
and electrophilic substitution reactions.9 However, in the reac-
tions just cited, intermediate ketene complexes are inferred rather
† San Diego State University.
‡ Current address: Department of Molecular Biology, The Scripps
Research Institute, La Jolla, CA 92037.
(10) Grotjahn, D. B.; Lo, H. C. Organometallics 1995, 14, 5463-5465.
(11) Grotjahn, D. B.; Lo, H. C. J. Am. Chem. Soc. 1996, 118, 2097-
2098.
(12) Lo, H. C.; Grotjahn, D. B. J. Am. Chem. Soc. 1997, 119, 2958-
2959.
(13) Grotjahn, D. B.; Bikzhanova, G. A.; Hubbard, J. L. Organometallics
1999, 18, 5614-5619.
(14) Grotjahn, D. B.; Bikzhanova, G. A.; Collins, L. S. B.; Concolino,
T.; Lam, K.-C.; Rheingold, A. J. Am. Chem. Soc. 2000, 122, 5222-5223.
(15) Redhouse, A. D.; Herrmann, W. A. Angew. Chem., Int. Ed. Engl.
1976, 15, 615-616.
(16) Herrmann, W. A. Angew. Chem., Int. Ed. Engl. 1974, 13, 335-
336.
§ Utah State University.
(1) Tidwell, T. T. Acc. Chem. Res. 1990, 23, 273-279.
(2) Tidwell, T. T. Ketenes; Wiley: New York, 1995.
(3) Brady, W. T. Synthetic Uses of Ketenes and Allenes. In The
Chemistry of Ketenes, Allenes and Related Compounds, Part 1; Patai, S.,
Ed.; Wiley: Chichester, 1980; Chapter 8.
(4) Geoffroy, G. L.; Bassler, S. L. AdV. Organomet. Chem. 1988, 28,
1-83.
(5) Do¨tz, K. H. Angew. Chem., Int. Ed. Engl. 1984, 23, 587-608.
(6) Hegedus, L. S. Tetrahedron 1997, 53, 4105-4128.
(7) Kim, O. K.; Wulff, W. D.; Jing, W.; Ball, R. G. J. Org. Chem. 1993,
58, 5571-5573.
(8) Arrieta, A.; Coss´ıo, F. P.; Ferna´ndez, I.; Go´mez-Gallego, M.; Lecea,
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C. Organometallics 1988, 7, 1066-1073.
(18) Hoberg, H.; Korff, J. J. Organomet. Chem. 1978, 152, 255-264.
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10.1021/ja004324z CCC: $20.00 © 2001 American Chemical Society
Published on Web 08/03/2001

C,C- and C,O-Bonding Modes of Metal-Ketenes
J. Am. Chem. Soc., Vol. 123, No. 34, 2001 8261
reactive to be isolated or even detected, have been proposed as
reaction intermediates.5,22-24 In contrast, Ir(I) and Rh(I) ketene
complexes such as those reported here are unique in that they
are stable enough to be isolated and characterized fully,10 yet
reactive.11-14 In the work described here, we use the relative
stability of a series of complexes to explore the structural and
electronic effects of metal coordination at either the C,C or C,O
bond. Relatively strong absorptions for ketenes and their
complexes in infrared spectra make such data a useful tool in
identifying the position of the metal on the ketene ligand.4 These
data have relevance not only to organometallic chemistry but
also to surface science, where absorbed ketene has been
identified using infrared spectroscopies.25-27 As far as we are
aware, the studies here include the first verification of assign-
ments of C-O stretching frequencies, using isotopically labeled
compounds.
Scheme 1
Results and Discussion
Synthesis of Complexes. In 1995 we reported a preparation
of the first Ir(I) ketene complexes, including 2a and 4, by metal-
induced elimination reactions of 2-pyridyl esters 1 (Scheme 1).10
This route is unique, because there are only two previous reports
of ketene formation from transition metals and carboxylic acid
derivatives (acid chlorides), and in these cases the reactions led
to free ketenes,28,29 a net result that one also can obtain in many
cases by reaction of an acid chloride with a tertiary amine base.2
In contrast, the chemistry portrayed in the upper part of Scheme
1 leads to ketene complex 2a or 4,10 along with at least one
other Ir-containing product, pyridinato complex 3, the structure
of which has been determined by X-ray crystallography.30 The
fragmentation of 1 gives access to a variety of iridium-ketene
complexes, in which the ketene ligand has either two aryl
groups, one aryl and one alkyl group, or, albeit in lower yields,
only one aryl or alkyl group.31 Subsequently it was found that
a high yield of diphenylketene complex 2a also could be
obtained by a ligand substitution reaction (Scheme 1, eq 2) on
[(µ-Cl)Ir(cyclooctene)2]2 using (per iridium) 2 mol of phosphine
a Conditions: [Ir(µ-Cl)(cyclooctene)2]2, 4 P(i-Pr)3, C6D6, room
temperature. b Conditions: 0.5 [M(µ-Cl)(cyclooctene)2]2, 2 P(i-Pr)3,
C6H6 or C6D6, room temperature. c Conditions: Et3N, Et2O, 0 °C, 8 h.
d Conditions: 0.5 [Ir(µ-Cl)(cyclooctene)2]2, 2 P(i-Pr)3, C6H6, room
temperature, 10 min. To allow for consumption of phenylketene through
oligomerization, 9-10 mol of PhCH2COCl/mol of Ir was used.
(20) Miyashita, A.; Sugai, R.; Yamamoto, J. J. Organomet. Chem. 1992,
428, 239-247. Subsequently, the complex η2-(C,O)-(CH2dCdO)Ni-
(PCy3)2 was reported, albeit without description of its stability: Wright, C.
A.; Thorn, M.; McGill, J. W.; Sutterer, A.; Hinze, S. M.; Prince, R. B.;
Gong, J. K. J. Am. Chem. Soc. 1996, 118, 10305-10306.
(21) Miyashita, A.; Shitara, H.; Nohira, H. J. Chem. Soc., Chem.
Commun. 1985, 850-851.
and 1 mol of diphenylketene32 (which can be stored in the
glovebox freezer for months without decomposition). This direct
synthesis was used to make all six diphenylketene complexes
(2a-f, eq 2 and Table 1) reported in this paper, along with
several isotopomers, in yields of 70-96%. While this work was
progress, a similar synthesis of Rh complex 2d was reported.33
Unfortunately, direct synthesis by ligand exchange works well
only when stable ketenes and stable metal fragments or their
precursors are used. Therefore, as far as we can tell, no one
has used this route with monosubstituted ketenes.31 As a
demonstration of the difficulties encountered, phenylketene has
only been characterized when made in inert matrixes at
temperatures below 40 K,34,35 as a transient solution species in
flash photolysis reactions,36,37 or when generated in the gas
phase,38,39 because of its facile oligomerization reactions.40-42
When used preparatively, phenylketene is always generated in
(22) Do¨tz, K.-H. In Organometallics in Organic Synthesis; de Meijere,
A., tom Dieck, H., Eds.; Springer: Berlin, 1988.
(23) Wulff, W. D. Metal-Carbene Cycloadditions. In ComprehensiVe
Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon: New York,
1991; Vol. 5, pp 1065-1113.
(24) Wulff, W. D. Transition Metal Carbene Complexes: Alkyne and
Vinylketene Chemistry. In ComprehensiVe Organometallic Chemistry II;
Hegedus, L. S., Ed.; Pergamon: New York, 1995; Vol. 12, pp 469-547.
(25) McBreen, P. H.; Erley, W.; Ibach, H. Surf. Sci. 1984, 148, 292-
310.
(26) Mitchell, G. E.; Radloff, P. L.; Greenlief, C. M.; Henderson, M.
A.; White, J. M. Surf. Sci. 1987, 183, 403-426.
(27) de Jesu´s, J. C.; Zaera, F. J. Mol. Catal. A: Chem. 1999, 138, 237-
240.
(28) Hommeltoft, S. I.; Baird, M. C. J. Am. Chem. Soc. 1985, 107, 2548-
2549.
(29) Ishii, Y.; Kobayashi, Y.; Iwasaki, M.; Hidai, M. J. Organomet.
Chem. 1991, 405, 133-140.
(30) Grotjahn, D. B.; Lo, H. C.; Groy, T. L. Acta Crystallogr., Sect. C
1996, 300-302.
(31) One significant point about complexes of monoalkyl or monoaryl-
ketenes is that, before our synthesis of 4, complexes of monosubstituted
ketenes with simple binding through either the C,C or C,O bond were
unknown. Since our initial report, two examples of (η2-C,C)-(RCHdCd
O)Fe(CO)2(PEt3)2 complexes were published (R ) Me, SiMe3): Kandler,
H.; Bidell, W.; Janicke, M.; Knickmeier, M.; Veghini, D.; Berke, H.
Organometallics 1998, 17, 960-971.
(32) For preparation of 2a, see footnote 7 of ref 11.
(33) Bleuel, E.; Laubender, M.; Weberndo¨rfer, B.; Werner, H. Angew.
Chem., Int. Ed. Engl. 1999, 38, 156-159.
(34) West, P. R.; Chapman, O. L.; LeRoux, J.-P. J. Am. Chem. Soc. 1982,
104, 1779-1782.
(35) McMahon, R. J.; Abelt, C. J.; Chapman, O. L.; Johns, J. W.; Kreil,
C. L.; LeRoux, J.-P.; Mooring, A. M.; West, P. R. J. Am. Chem. Soc. 1987,
109, 2456-2469.
(36) Wagner, B. D.; Zgierski, M. Z.; Lusztyk, J. J. Am. Chem. Soc. 1994,
116, 6433-6434.
(37) Wagner, B. D.; Arnold, B. R.; Brown, G. S.; Lusztyk, J. J. Am.
Chem. Soc. 1998, 120, 1827-1834.

8262 J. Am. Chem. Soc., Vol. 123, No. 34, 2001
Grotjahn et al.
Table 1. Selected Spectroscopic Data for Complexes of Diphenylketene to Fragments trans-ClM(PR3)2 (δ in ppm, J in Hz)
1H of ortho protons of
Ph2C(2)dC(1)dO 13C{1H}
substituents (C6D6 solvent)
(CDCl3 or C6D6 solvent)a
31P{1H}
(C6D6 solvent)
Ph syn to M
(2 H)
Ph anti to M
(2 H)
d
M
PR3
C(2)
C(1)
IR (cm-1
)
b,c
2a Ir P(i-Pr)3
2b Ir PCy3
20.90 (s)
10.99 (s)
74.75 (s)
74.42 (s)
76.01 (s)
143.78 (t, J ) 3.2)
142.33 (t, J ) 3.7)
138.18 (t, J ) 3.9)
8.63 (d, J ) 7.2) 7.63 (d, J ) 7.2) 1636, 1589, 1493 (KBr)
8.66 (d, J ) 7.2) 7.84 (d, J ) 7.2) 1627, 1591, 1441 (C6D6)
8.42 (d, J ) 8.0) 7.64 (d, J ) 8.0) 1624, 1591, 1471 (C6D6)
2c Ir P(t-Bu)2Me 17.85 (s)
2d Rh P(i-Pr)3
32.55 (d, J ) 112.0) 77.06 (d, J ) 2.1) 167.77 (dt, J ) 20.1, 5.6) 8.76 (d, J ) 7.5) 7.65 (d, J ) 7)
1656, 1599, 1590, 1494,
1461, 1446 (KBr)
2e Rh PCy3
22.57 (d, J ) 107.1) 77.25 (d, J ) 3.0) 167.58 (dt, J ) 20.2, 4.6) 8.75 (d, J ) 7.6) 7.87 (d, J ) 7.6) 1645, 1589, 1444 (C6D6)
2f Rh P(t-Bu)2Me 31.97 (d, J ) 109.1) 79.17 (d, J ) 2.3) 165.13 (dt, J ) 20.7, 5.8) 8.57 (d, J ) 8.4) 7.64 (d, J ) 8.2) 1650, 1594, 1475 (C6D6)
a 2b and 2c in CDCl3, 2a, 2d-2f in C6D6. b Reference 10. c Reference 11. d See also Table 6.
the presence of the desired reactant.43,44 In this study, because
acid chlorides oxidatively add to Ir(I)-phosphine complexes,45,46
direct synthesis of phenylketene complex 4 required generation
of phenylketene in solution by allowing phenylacetyl chloride
to react with triethylamine at 0 °C for 4 h, followed by filtration
of the resulting mixture into a solution of the metal fragment.
While less efficient than the fragmentation of pyridyl ester 1
(R1 ) Ph, R2 ) H) route in terms of yield, this protocol was
significantly faster, allowing synthesis of phenylketene complex
4 within 1 day in 5% yield. After completion of this part of our
study, Tidwell and co-workers reported a promising alternative
method of making dilute solutions of phenylketene in hydro-
carbon solvent,47 which may be useful in improving the yield
of 4 and related species.
The identification of the ketene complexes was eventually
confirmed by X-ray diffraction (vide infra) but was suggested
by a combination of NMR and IR spectral data (Table 1). For
the diphenylketene complexes 2a-f, the 31P{1H} NMR spectra
show a single resonance, a singlet in the case of the Ir species
and a doublet (1JPRh ) 107.1-112.0 Hz) in the Rh cases. The
Figure 1. Molecular structure of 2a. See Table 2 for key bond lengths
and angles.
magnitude of the Rh-P coupling constant is consistent with a
Rh(I) species with mutually trans phosphines sharing the same
metal orbital. Two linkage isomers of these complexes are
possible,33 the η2-(C,O) complexes shown or alternative η2-(C,C)
In contrast, 4 was formulated as the η2-(C,C) isomer shown.
The 31P{1H) NMR spectrum of the complex showed two
doublets at δ 25.43 and 23.30 ppm, each with a large coupling
1
isomers. Particularly diagnostic is the fact that the H and 13C
NMR spectra of 2a-f show two inequivalent phenyl rings,
consistent with metal coordination to one side of the C,O bond.
Alternative η2-(C,C) isomers would feature equivalent phenyl
rings. The nuclei of the phenyl rings experience different
shielding: the ortho protons of the phenyl ring syn to the metal
resonate in the range δ 8.42-8.76 ppm whereas those anti
resonate upfield, between δ 7.63 and 7.87 ppm.48
2
constant JPP ) 323.5 Hz, consistent with the presence of
mutually trans phosphines. Only the η2-(C,C) isomer, which
features planar chirality, would have two inequivalent trans
phosphines; the two alternative η2-(C,O) isomers, one with the
phenyl group syn, the other anti to the metal fragment, would
be achiral and would contain equivalent phosphines.
The 13C NMR and IR spectral data for these species will be
discussed in detail below.
(38) Sammynaiken, R.; Westwood, N. P. C. J. Chem. Soc., Perkin Trans.
2 1989, 1987-1992.
X-ray Crystallography. X-ray diffraction studies verified
the assignments just described, but more significantly, gave
insight into metal-ketene bonding. The molecular structures
of 2a (Figure 1) and 2d have been communicated by us10 and
by Werner’s group,33 respectively. Because 2a and 2d feature
the same ligand set, most of this paragraph will compare these
two species. The structure of 2c is new (Figure 2). For all three
structures, selected bond lengths and angles are shown in Table
2. In each case, the complexes show essentially square planar
geometry. The square plane can be roughly defined by the metal
and the ligating atoms Cl, P, and P, with the O atom of the
ketene closest to that plane. In 2a and 2d the P-Ir-P angles
are 168.0(1) and 168.41(4)°, respectively, and a plane defined
(39) Werstiuk, N. H.; Muchall, H. M.; Ma, J.; Liu, M. T. H. Can. J.
Chem. 1998, 76, 1162-1173.
(40) Staudinger, H. Ber. Bunsen-Ges. Phys. Chem. 1911, 44, 533-541.
(41) Baldwin, J. E.; Roberts, J. D. J. Am. Chem. Soc. 1963, 85, 2444-
2445.
(42) Efremov, D. A.; Zavlin, P. M.; Essentseva, N. S.; Tebby, J. C. J.
Chem. Soc., Perkin Trans. 1 1994, 3163-3168.
(43) Hertenstein, U.; Hu¨nig, S.; Reichelt, H.; Schaller, R. Chem. Ber.
1982, 115, 261-287.
(44) Brady, W. T.; Shieh, C. H. J. Heterocycl. Chem. 1985, 22, 357-
360.
(45) Zizelman, P. M.; Stryker, J. M. Organometallics 1990, 9, 1713-
1715.
(46) Bennett, M. A.; Jeffery, J. C. Inorg. Chem. 1980, 19, 3763-3767.
(47) Allen, A. D.; Cheng, B.; Fenwick, M. H.; Huang, W.-w.; Missiha,
S.; Tahmassebi, D.; Tidwell, T. T. Org. Lett. 1999, 1, 693-696.
(48) Complexation of (phenyl)(methyl)ketene to ClIr[(P(i-Pr)3]2 leads to
a single complex, although in lower yield than in the case of diphenylketene,
probably because of some ketene polymerization (Grotjahn, D. B.; Lo, H.
C.; Bikzhanova, G. A., unpublished results). All NMR data for the single
product [also obtained by fragmentation of the appropriate pyridyl ester 1
(R1 ) Ph, R2 ) CH3)10] are consistent with formulation as the sterically
favored isomer, with the methyl group syn to the metal. For example, the
1H NMR resonance for the ortho protons of the single phenyl ring appears
as a two-proton doublet at 7.69 ppm. NOE experiments involving irradiation
of the ketene methyl group led to 11.3% enhancement of the signals for
the i-Pr methyls.10

C,C- and C,O-Bonding Modes of Metal-Ketenes
J. Am. Chem. Soc., Vol. 123, No. 34, 2001 8263
Figure 2. Molecular structure of 2c. See Table 2 for key bond lengths
and angles.
Figure 3. Molecular structure of 4. See Table 3 for key bond lengths
and angles.
great interest to obtain a structure for 4. A crystal of complex
4 suitable for X-ray diffraction studies was analyzed at -100
°C. The molecular structure of the compound is shown in Figure
3, and selected bond distances and angles are given in Table 3.
As far as we are aware, this is the first crystal structure of a
η2-(C,C)-monosubsituted ketene complex. The complex exhibits
slightly distorted square planar geometry about the Ir atom, as
revealed by a 359.6° sum of four angles between Cl, P(1), P(2),
and C(27) and the central Ir atom. Atoms P(1), P(2), Cl, and
C(27) lie in a plane with an average deviation on 0.070 Å.
Inclusion of the central Ir atom in this calculation gives almost
the same result, a deviation of 0.075 Å. Thus, in 4, the ketene
carbon atom C(27) is closest to the square plane, whereas in
2a, 2c, and 2d, it is the ketene oxygen that is closer. In 4, the
plane containing the CdCdO atoms is nearly perfectly per-
pendicular (92.3°) to the square plane defined above. The
P-Ir-P angle of 166.6(1)° and the direction of distortion from
the ideal 180° value suggest that the phosphines are oriented to
minimize steric interactions with the phenylketene ligand. This
impression is reinforced by the fact that the phosphine syn to
the phenyl ring [P(2)-Ir-C(27) angle, 99.8(3)°] appears to be
displaced more than the phosphine anti to the phenyl group
[P(1)-Ir-C(27) angle, 89.7(3)°]. The displacement of the
phosphine syn to the phenyl ring is also shown by the fact that
the distance between C(27) and P(2) is 3.476 Å, 0.265 Å greater
than the distance between C(27) and P(1), and the distance
between C(28) and P(2) (3.336 Å) is 0.211 Å greater than that
between C(28) and P(1). Finally, we note that in both 4 and
2a/2c/2d the metal-phosphorus bond lengths are similar,
whereas the metal-chlorine bond length in 4 is significantly
longer (2.371 vs 2.285-2.300 Å). This difference may be
attributed to a greater trans influence of the ketene when bound
at the C,C bond, assuming that the electronic perturbation of
one phenyl substituent is insignificant.
Table 2. Comparison of the Geometries of 2a, 2d, 2c, and
Ph2CdCdO (bond distances in Å, Angles in deg)
parametera
2ab
2dc
Ph2CdCdOd
2ce
C(1)-C(2)
C(1)-O
C(1)-M
O-M
1.348(6)
1.286(6)
1.972(5)
2.092(4)
2.285(2)
2.366(2),
1.349(6)
1.264(5)
1.971(4)
2.090(3)
2.298(1)
2.369(1),
2.382(1)
138.9(4)
144.0(3)
1.333
1.188
1.356(16)
1.295(12)
1.982(12)
2.099(8)
2.300(6)
2.362(3),
2.283(3)
134.3(10)
148.9(8)
M-Cl
M-P
2.381(2)
C(2)-C(1)-O 136.6(6)
C(2)-C(1)-M 146.7(5)
a Numbering of ketene atoms in parameter column same for all
structures [Ph2C(2)dC(1)dO]. b Reference 10. c Reference 33. d From
semiempirical AM1 calculations.38 e This work.
by the metal atom and the two phosphines passes through the
phenyl ring syn to the bulky metal fragment, consistent with
repulsive steric interactions between metal fragment and the
nearest ketene phenyl substituent. Key bond distances and angles
in these complexes are virtually identical (Table 2), showing
strong distortion from calculated values for the free ligand
diphenylketene.38 The slight differences between complexes of
the two metals would be consistent with mildly greater back-
bonding in the Ir complex than in the Rh analogue. The C-C-O
angle in the Ir(I) species is 136.6(4)°, whereas in the Rh
analogue, the deformation from linear geometry is less [138.9-
(4)°]. Moreover, the M-C-C angle in the Ir complex is 2.7°
greater than in the Rh analogue. The data are all within the
ranges shown by other metal complexes featuring diphen-
ylketene bound in an η2-(C,O) fashion.4,49-52 Finally, we observe
that the structure of 2c is similar to that of 2a, with the notable
difference that the phosphine ligands are oriented to place the
sterically unassuming methyl groups closer to the ketene ligand.
Because there is no example of crystal structures of the same
metal fragment to ketenes in different binding modes, it was of
Only theoretically calculated geometries are available for the
free phenylketene ligand,38,53 but it is clear that, in complex 4,
the C(27)-C(28) bond is elongated [1.468(17) Å in 4 vs 1.31138
or 1.31953 Å in phenylketene] and the CdCdO unit is bent
due to back-bonding (see below). The C-O bond distance is
not much different [1.165(13) vs 1.14538 or 1.19053 Å].
There are five other crystal structures of ketene complexes
featuring η2-(C,C) coordination, and these all involve di-
(49) Birk, R.; Berke, H.; Hund, H.-U.; Huttner, G.; Zsolnai, L.;
Dahlenburg, L.; Behrens, U.; Sielisch, T. J. Organomet. Chem. 1989, 372,
397-410.
(50) Antin˜olo, A.; Otero, A.; Fajardo, M.; Lopez-Mardomingo, C.; Lucas,
D.; Mugnier, Y.; Lanfranchi, M.; Pellinghelli, M. A. J. Organomet. Chem.
1992, 435, 55-72.
(51) Hofmann, P.; Perez-Moya, L. A.; Steigelmann, O.; Riede, J.
Organometallics 1992, 11, 1167-1176.
(52) Flu¨gel, R.; Gevert, O.; Werner, H. Chem. Ber. 1996, 129, 405-
410.
(53) McAllister, M. A.; Tidwell, T. T. J. Org. Chem. 1994, 59, 4506-
4515.

8264 J. Am. Chem. Soc., Vol. 123, No. 34, 2001
Grotjahn et al.
Table 3. Selected Bond Distances (Å) and Angles (deg) for Complex 4
Ir-Cl
2.371(3)
2.378(3)
2.370(3)
2.171(11)
1.935(11)
1.468(17)
C(28)-O
1.165(13)
166.6(1)
85.6(1)
84.5(1)
174.9(3)
89.7(3)
P(2)-Ir-C(27)
Cl-Ir-C(27)
Cl-Ir-C(28)
Ir-C(28)-O
99.8(3)
174.9(3)
140.9(4)
139.1(10)
142.6(12)
Ir-P(1)
P(1)-Ir-P(2)
Cl-Ir-P(1)
Cl-Ir-P(2)
Cl-Ir-C(27)
P(1)-Ir-C(27)
Ir-P(2)
Ir-C(27)
Ir-C(28)
C(27)-C(28)
C(27)-C(28)-O
Table 4. Structural Data for Known η2-(C,C)-Bound Ketene
Complexes [Bond Distances (Å) and Angles (deg), Ketene
Numbering R2C(2)dC(1)dO]
Scheme 2
com-
plex C(1)-C(2) C(1)-O C(2)-C(1)-O M-C(1) M-C(2) ref
5a
5b
5c
6
4
7
1.35(2)
1.21(2)
145
1.96(2)
2.17(2)
15
1.448(8)
1.401(9)
1.467(5)
1.468(17) 1.165(13)
1.488(7) 1.222(6)
1.194(8)
1.224(8)
1.208(4)
139.8(6)
142.5(7)
142.0(5)
142.6(12)
141.3(5)
1.976(6) 2.242(6) 54
1.940(7) 2.212(6) 55
1.936(5) 2.180(5) 33
1.935(11) 2.171(11)
1.986(5) 2.245(4) 14
a
a This work.
that there is an electronic preference for binding of the ketene
to the C,C bond, which may be overridden by steric factors
and lead to C,O-binding. Most significant, however, is the
observation of the longer Ir-Cl bond in 4 compared to that in
2a. Although the origins of the trans influence are a subject of
continuing debate,56 if one assumes that phenyl and diphen-
ylketene are electronically similar, our structures suggest that
a ketene is a better π-acid when bound through the C,C bond.
To investigate bonding in the complexes more fully, a series
of 13C NMR and IR spectroscopic investigations was performed.
For this work, new isotopically labeled ketenes and their
precursors were required, as described in the next section.
Syntheses of Isotopically Labeled Ketenes and Their
Complexes. Both 13C- and 18O-labeled ketenes were needed
for the IR and NMR studies conducted. The diphenylketene
isotopomer Ph2Cd13CdO was unknown. Ph2CdCd18O has
been reported once,57 but as a product of a rather indirect
synthesis and without spectroscopic data. Furthermore, the
sample produced had only 4% isotopic enrichment. However,
for our purposes we sought to prepare diphenylketene with a
high degree of isotopic enrichment. This in turn required highly
enriched samples of diphenylacetic acid as a precursor. The acid
Ph2CH13CO2H has been mentioned in the literature,58 but
without details of its preparation. In the present work (Scheme
2), diphenylmethane was deprotonated using BuLi-TMEDA
and the resulting mixture added to a flask containing 13CO2 at
1 atm pressure. Acid workup afforded Ph2CH13CO2H in 65%
yield. Similarly, monophenyl precursor PhCH213CO2H was
obtained in 67% yield or purchased. The sample of 13CO2 used
to make the two acids was 99% enriched in 13C but also
contained a few percent 18O, so in some NMR and IR spectra
of the products and subsequent intermediates, additional satel-
lites for the 13C18O isotopomer could be seen. Finally, isoto-
pomer Ph2CHC(18O)2H was produced by base-catalyzed hy-
dration of the nitrile Ph2CHCN in H218O. This and all other
isotopically labeled acids were converted to the ketenes using
SOCl2, followed by Et3N.59 Complexation proceeded as for the
unlabeled ketenes.
arylketenes (Table 4). From 1976 to 1984, three structures of
diarylketene complexes (5a-c) with metal fragments of the type
η5-(C5H4R)Mn(CO)2 were reported by Herrmann and co-
workers,15,54,55 and in 1999 a structure of η5-(indenyl)Rh[P(i-
Pr)3] coordinated to the C,C bond of diphenylketene (6) was
published by Werner and co-workers.33 (Although the C,O-
bound linkage isomer of 6 was prepared,33 its crystal structure
is unfortunately not available for comparison.) Finally, we
recently described the structure of complex 7.14 The reported
structures resemble that of 4 in that the CdC bond of the
coordinated diarylketenes are elongated and the CdCdO unit
is bent. The Rh(I) and Ir(I) examples exhibit the greatest degree
of deformation.
In summary, comparing the X-ray structure of complex η2-
(C,O)-phenylketene complex 4 with those of η2-(C,O)-diphen-
ylketene complexes 2a, 2c, and 2d reveals the following
similarities: (a) there is significant back-bonding from the metal
to the ketene π-system, with concomitant elongation of the
coordinated π-bond and bending of the ketene ligand away from
the metal; (b) distortions consistent with steric interactions
between ketene and phosphine substituents are seen. Differences
between the two types of complexes include (a) a longer metal-
chlorine bond when then ketene trans to Cl is bound at the C,C
bond and (b) a greater elongation of the attached multiple bond
in the case of the C,C bond than the C,O bond. These
observations do nothing to contradict our earlier conclusion10
(56) Huheey, J. E.; Keiter, E. A.; Keiter, R. L. Inorganic Chemistry
Principles of Structure and ReactiVity; 4th ed.; HarperCollins: New York,
1993.
(57) Ainsworth, C.; Chen, F.; Kuo, Y.-N. J. Organomet. Chem. 1972,
46, 59-71.
(58) Rajca, A.; Tolbert, L. M. J. Am. Chem. Soc. 1987, 109, 1782-
1789.
(54) Herrmann, W. A.; Plank, J.; Ziegler, M.; Weidenhammer, K. J. Am.
Chem. Soc. 1979, 101, 3133-3135.
(55) Herrmann, W. A.; Plank, J.; Kriechbaum, G. W.; Ziegler, M. L.;
Pfisterer, H.; Atwood, J. L.; Rogers, R. D. J. Organomet. Chem. 1984,
264, 327-352.
(59) Smith, L. I.; Hoehn, H. H. Organic Syntheses; Wiley: New York,
1955; Collect Vol. III, pp 356-358.

C,C- and C,O-Bonding Modes of Metal-Ketenes
J. Am. Chem. Soc., Vol. 123, No. 34, 2001 8265
Table 5. Comparison of Carbon-Carbon Coupling Constants and
Bond Distances
1JCC
(Hz)
C-C bond
ref for
C-C distance
species
distance (Å)a
Ph2CdCdO
107b
1.333
38
10
33
13
e
2a
2d
8
4
7
92.5b
93.0c
54.4d
45.7c
44.3d
1.348(6)
1.349(6)
1.442(6)
1.468(17)
1.488(7)
14
a Values from X-ray diffraction, except for Ph2CdCdO, which
comes from semiempirical AM1 calculations. b CDCl3, 30 °C. c C6D6,
30 °C. d CD2Cl2, -50 °C. e This work.
NMR Spectroscopy. The proton NMR shifts for related Ir
and Rh complexes are virtually identical, but significant
differences in 13C NMR chemical shifts of the ketene C(1)
carbon are seen (Table 1). The 13C NMR chemical shifts for
the C(1) carbon in the Rh complexes (δ 165.13-167.77 ppm)
are closer to that in the free ligand (δ 201.2 ppm)2,60,61 than
those of the Ir analogues (δ 138.18-143.39 ppm). As analyzed
above, the X-ray structures of Ir and Rh complexes 2a and 2d
suggested slightly greater back-bonding in the Ir congener.
However, examination of the literature suggests that differences
in 13C NMR data are due to some effect other than back-
bonding.62 Recent work on the effects of heavy atoms on NMR
chemical shifts suggests that the greater spin-orbit coupling
in the third-row metal may be responsible for the shielding
effect.63
1
Figure 4. Plot of JCC and C-C bond distance. All values are
experimentally determined, except for the calculated bond distance for
Ph2CdCdO. See Table 5 for data on ketene derivatives.
1
correlation between C-C bond distance and JCC has been
seen,64,66 but the data here are the first reported for ketene
complexes. For organic molecules, it is agreed that the
magnitude of 1JCC is dominated by the Fermi contact interaction,
which in turn depends on the electron densities at the two
carbons.66 Thus, as originally formulated by Frei and Bern-
stein,67 1JCC ) a(sC1 × sC2) + b, where sC1 and sC2 refer to the
amount of s character of the carbon atoms of the ketene ligand.
To characterize the degree of back-bonding further, the
1
magnitude of JC(1)-C(2) between the two ketene carbons was
determined. Although in principle natural abundance materials
could be analyzed in this way using the INADEQUATE pulse
sequence, the relatively low sensitivity obtainable has led in
other studies to the use of as much as 2 g of metal complex.64
In our work, the expense of Ir and Rh and the difficulty in
obtaining more than 100 mg of 4 for study prompted synthesis
of ketene complexes enriched with 13C (vide supra); moreover,
isotopically labeled materials were needed for IR spectroscopy
Our data would allow only for calculation of the product sC1
sC2.
×
To further probe how metal coordination to the ketene
π-system may change the hybridization of the carbons, the
spin-spin coupling between the terminal ketene carbon C(2)
and attached proton was considered. In other π-systems, the
effect of metal coordination on 1JCH values varies. In arene and
cyclopentadienyl compounds, 1JCH increases on metal coordina-
tion, whereas in η2-(C,C)-alkene complexes, it decreases. The
causes of the former change are unclear, but for the latter, a
reduction in carbon s-character through metal-ligand back-
bonding has been offered as explanation.65 Therefore, because
complex 4 featured a hydrogen on the ketene π-system, a gated
decoupling 13C NMR experiment was performed, allowing
1
(vide infra). Table 5 compares JCC values (all new data) and
CsC bond distances for Ph2CdCdO, for four of its complexes,
and for PhCHdCdO complex 4. Inspection of the data shows
that 1JCC decreases as the C-C bond distance increases, results
shown in Figure 4 along with literature data for ethane, ethene,
and ethyne.65 Among ethene and ethyne complexes, some
(60) Firl, J.; Runge, W. Angew. Chem., Int. Ed. Engl. 1973, 12, 668-
669.
(61) Firl, J.; Runge, W. Z. Naturforsch., B 1974, 29B, 393-398.
(62) For example, in alkyl complexes there is no back-bonding from
the metal to the alkyl ligand, yet in Cp*M(R)(H)(PMe3), where R )
cyclopentyl, the cyclopentyl carbon directly attached to the metal was shifted
upfield in the Ir case (δ 0.22 ppm)62a compared to the Rh case (7.21 ppm).62b
Similar effects were seen for the Cp* carbons attached to the metal (Ir,
92.37; Rh, 97.31 ppm) and for the phosphorus nuclei as well (Ir case, -44.83
ppm; Rh case, 9.5 ppm).62a,62b Furthermore, in hydride complexes (H)-
(Cl)2M[P(i-Pr)3]2, the hydride proton is more shielded in the Ir complex
than in the Rh analogue (Ir-H, δ -48.83 ppm;62c Rh-H, δ -31.2 ppm62d).
Similar trends have been noted (without comment) for metal carbonyls.62e
Thus, the effect appears general and applies to ligands of many types. (a)
Buchanan, J. M.; Stryker, J. M.; Bergman, R. G. J. Am. Chem. Soc. 1986,
108, 1537-1550. (b) Periana, R. A.; Bergman, R. G. J. Am. Chem. Soc.
1986, 108, 7332-7346. (c) Werner, H.; Wolf, J.; Ho¨hn, A. J. Organomet.
Chem. 1985, 287, 395-407. (d) Harlow, R. L.; Thorn, D. L.; Baker, R. T.;
Jones, N. L. Inorg. Chem. 1992, 31, 993-997. (e) Parish, R. V. NMR, NQR,
EPR, and Mo¨ssbauer Spectroscopy in Inorganic Chemistry; Ellis Hor-
wood: New York, 1990; p 72.
1
observation of JCH ) 158 Hz. Similar data on the free
phenylketene ligand are unavailable because of the cumulene’s
instability. As far as we are aware, the only data for ketenes in
the literature are JCH ) 171.5 and 184.4 for H2CdCdO60,61
1
and H(Cl)CdCdO,68,69 respectively. In comparison, we note
that, for η2-(C,C)-(H2CdCdO)Pt(PPh3)2, JCH ) 159 Hz.19
1
These values compare with 156.4 Hz in ethylene, 154.5 Hz for
the R C-H bond in styrene, and 167.8 Hz in allene.65 If the
(65) Kalinowski, H.-O.; Berger, S.; Braun, S. 13C NMR-Spektrokopie;
Thieme: Stuttgart, 1984. Pages 496-502 focus on 1JCC values and structure.
(66) Kamienska-Trela, K. Annu. Rep. NMR Spectrosc. 1995, 30, 131-
230.
(63) Kaupp, M.; Malkina, O. L.; Malkin, V. G.; Pyykko¨, P. Chem.-
(67) Frei, K.; Bernstein, H. J. J. Chem. Phys. 1963, 38, 1216.
(68) Lindner, E.; Steinwand, M.; Hoehne, S. Angew. Chem., Int. Ed. Engl.
1982, 21, 355-356.
(69) Lindner, E.; Steinwand, M.; Hoehne, S. Chem. Ber. 1982, 115,
2181-2191.
Eur. J. 1998, 4, 118-126.
(64) Abbenhuis, H. C. L.; Feiken, N.; Grove, D. M.; Jastrzebski, J. T.
B. H.; Kooijman, H.; van der Sluis, P.; Smeets, W. J. J.; Spek, A. L.; van
Koten, G. J. Am. Chem. Soc. 1992, 114, 9773-9781.

8266 J. Am. Chem. Soc., Vol. 123, No. 34, 2001
Grotjahn et al.
Table 6. IR Data for Isotopomers of Ir and Rh Ketene Complexes
species
conditions
12Cd16O
13Cd16O
12Cd18O
Ph2CdCdO
hexanes, NaCl cell, RT
2102 (s), 1599 (m), 1495(m),
1458 (s)
2046 (s), 1600 (m), 1494 (m)
2075 (s), 1599 (m),
1495 (m)
2a
2a
2d
CH2Cl2, -52 °C
KBr, RT
1632 (s), 1589 (s), 1494 (m),
1464 (m)
1636 (s), 1589 (s), 1493 (m),
1460 (m), 1445 (m)
1656 (s), 1599 (s), 1590 (s),
1494 (m), 1461 (m), 1446 (m)
1651 (s), 1591 (s), 1494 (s),
1468 (s), 1447 (s)
1610 (m), 1581 (s), 1567 (s),
1494 (m), 1463 (m)
1610 (m), 1582 (s), 1568 (s),
1494 (m), 1461 (m), 1443 (m)
1619 (s), 1590 (s), 1491 (m),
1463 (m)
1617 (s), 1587 (s), 1491 (m),
1452 (s)
1719 (s), 1710 (s), 1678 (s),
1597 (s), 1490 (m), 1462 (m)
1755 (s), 1737 (m), 1597 (w),
1476 (m), 1446 (m)
1626 (s), 1588 (s),
1493 (m), 1463 (m)
1631 (s), 1590 (s),
1494 (m), 1461 (m)
nda
KBr, RT
C6D6, NaCl cell, RT
CH2Cl2, -52 °C
C6D6, NaCl cell, RT
CH2Cl2, NaCl cell, RT
nd
nd
nd
nd
4
8
7
1752 (s), 1708 (m), 1597 (m),
1489 (m), 1465 (m)
1801 (s), 1620 (s), 1455 (s)
1728 (s), 1591 (m), 1483 (s)
1693 (s), 1595 (w), 1491 (s),
1473 (m)
a nd, not determined.
phenyl substituent on ketene has a similarly negligible effect
as it does on ethylene, we would anticipate the coupling constant
for phenylketene to be ∼171.5 Hz, whereas in the complexed
In the spectra of 2a, the intense band at 1632 cm-1 shifts to
1610 cm-1 upon 13C substitution using Ph2Cd13CdO; this peak
is assigned to the diphenylketene C-O stretching mode. In the
rhodium analogue, 2d, the C-O stretching mode is attributed
to the band at 1656 cm-1, which shifts down in energy (1617
cm-1) upon 13C substitution.79 When phenylketene is bound via
the CdC bond, as in 2, ν(CO) is found at 1752 cm-1 and
decreases 33 cm-1 upon 13C substitution using PhCHd13CdO.
Finally, substitution of the ketene oxygen with 18O in 2a also
leads to lowering of the band by 6 cm-1 to 1626 cm-1, which
at first glance seemed a very modest shift. However, in η2-
(C,O)-acetone complexes, 18O substitution lowers the C-O
stretching frequency only from 1330 to 1312 cm-1 80 or from
1
ligand it is 158 Hz. If the equation JCH ) 570(s) - 18.4 is
used,65 then in free and complexed phenylketene the s-character
of C(2) would be 0.332 and 0.309, respectively. However,
because of uncertainty regarding the theoretical meaning of
changes in 1JCH, the use of this equation for anything other than
hydrocarbons has been questioned.70
The clearest conclusions from our work are that a good
correlation between 1JC(1)-C(2) and the C(1)-C(2) bond distance
can be established and that the chemical shifts of C(1) in 13C
NMR spectra of Rh and Ir complexes are upfield in the Ir series,
probably because of relativistic effects.
1230 to 1220 cm-1 81
.
Infrared Spectroscopy. IR data for Rh- and Ir-ketene
complexes (Table 6) show the strong perturbation of the ketene
ligand by the metal regardless of the position of binding.
Whereas the C-O stretching frequency of coordinated ketenes
shown in Table 6 is in the range 1600-1800 cm-1, the
corresponding absorption for the free ketenes appears near 2100
cm-1,2 as assigned using 13C- and 2H-labeled ketene itself.71-75
However, IR data of the Rh- and Ir-ketene complexes show
a significant difference: the absorption assigned to the C-O
stretching appears in the range 1624-1636 (Ir) and 1645-1650
cm-1 (Rh). Although this band has been assigned routinely to
the C-O stretch in a variety of diphenyl- and (phenyl)(alkyl)-
ketene complexes in which a metal is coordinated to the C,O
bond, the wide variance in the value for this stretching frequency
To better understand the proposed assignments for the ketene
complexes, initial82 normal coordinate analyses83 of the vibra-
tional modes of the metal-diphenylketene fragments were
undertaken. Using calculated bond lengths and angles for
diphenylketene and treating each phenyl ring as a point mass,
the reported isotopic shifts of ν(CO) of free diphenylketene2
can be fit very well to an approximate force field using the
Wilson F and G matrix method.84 To reproduce the selected
vibrational frequency for Ph2CCO, Ph2C13CO, Ph2CC18O, and
Ph213CC18O, only two primary force constants are required
(Table 7) suggesting kinematic coupling via the shared carbon
atom but not necessarily electronic coupling of the C-C and
C-O stretching modes. Upon binding diphenylketene to iridium
via the CdO bond, the energy of the carbon-oxygen stretching
mode decreases dramatically. In our model studies (Table 7)
of the [M(η2-Ph2CCO)] (M ) Ir, Rh) fragments and isoto-
(from a low of 1548 cm-1 to a high of 1632 cm-1 18,49-52,76,77
)
and the overlap with absorptions of the aryl ring near 1580
cm-1 78 prompted us to perform the first study of isotopically
labeled ketene complexes.
(79) In all of the complexes, there are also strong absorptions in the
vicinity of 1590 cm-1. The difficulty of using IR spectroscopy to assign
metal position on highly substituted ketenes is shown by the recent
assignment of the absorption of 2d at 1590 cm-1 to the C-O stretching
mode.33 We have contacted Professor Werner, who agrees with our revised
assignment.
(70) Gil, V. M. S.; Geraldes, C. F. G. C. Uses and Misuses of 13C-H
Coupling Constants between Directly Bonded Nuclei. In NMR Spectroscopy
of Nuclei Other than Protons; Axenrod, T., Webb, G. A., Eds.; Wiley-
Interscience: New York, 1974; pp 219-231.
(71) Arendale, W. F.; Fletcher, W. H. J. Chem. Phys. 1957, 26, 793-
797.
(80) Harman, W. D.; Fairlie, D. P.; Taube, H. J. Am. Chem. Soc. 1986,
108, 8223-8227.
(72) Moore, C. B.; Pimentel, G. C. J. Chem. Phys. 1963, 38, 2816-
2829.
(81) Bryan, J. C.; Mayer, J. M. J. Am. Chem. Soc. 1990, 112, 2298-
2308.
(73) Duncan, J. L.; Ferguson, A. M.; Harper, J.; Tonge, K. J. Mol.
Spectrosc. 1987, 125, 196-213.
(82) For complex 2d, the limited vibrational data preclude the possibility
of a complete analysis of the vibrational modes. The reported force constants
reflect a self-consistent analysis, but a number of force fields are possible.
Refer to the Experimental Section for further details.
(83) Experimental data were fit using a nonlinear least-squares fitting
program (Program QCMPO12, Quantum Chemistry Program Exchange;
Indiana University, Bloomington, IN) that varied the primary force constants
identified in the F matrix of the generalized valence force field (GVFF).
(84) Wilson, E. B.; Decius, J. C.; Cross, P. C. Molecular Vibrations:
The Theory of Infrared and Raman Vibrational Spectra; McGraw-Hill: New
York, 1955.
(74) Duncan, J. L.; Ferguson, A. M.; Harper, J.; Tonge, K. H.; Hegelund,
F. J. Mol. Spectrosc. 1987, 122, 72-93.
(75) Leszczynski, J.; Kwiatkowski, J. S. Chem. Phys. Lett. 1993, 201,
79-83.
(76) Sugai, R.; Miyashita, A.; Nohira, H. Chem. Lett. 1988, 1403-1406.
(77) Okuda, J.; Herberich, G. E. J. Organomet. Chem. 1987, 320, C35-
C38.
(78) Silverstein, R. M.; Webster, F. X. Spectrometric Identification of
Organic Compounds; 6th ed.; Wiley: New York, 1998; p 86.

C,C- and C,O-Bonding Modes of Metal-Ketenes
Table 7. Experimentally Observed and Calculated Vibrational Frequencies and Calculated Force Constants
vibrational frequencies (cm-1 force constantsa (mdyn/Å)
J. Am. Chem. Soc., Vol. 123, No. 34, 2001 8267
% symmetry
coordinate
in ν(CO)
)
compd
CCO
C13CO
CC18O
C13C18O
fCO
fCC
fCC/CO
Ph2CCO
ν(CO)expt
ν(CO)calc
ν(CO)expt
ν(CO)calc
ν(CO)expt
ν(CO)calc
ν(CO)expt
ν(CO)calc
ν(CO)expt
ν(CO)calc
2102
2102
1632
1645
1656
1655
1728
1732
1752
1760
2046
2045
1610
1600
1617
1614
1694
1692
1719
1715
2075
2076
1626
1626
2019
2019
13.9
9.4
7.8
6.7
7.1
4.2
4.8
0.0
1.3
1.1
0.7
0.75
70 CO, 30 CC
60 CO, 40 CC
61 CO, 39 CC
97 CO, 2 CC
83 CO, 15 CC
2a
2d
7
8.8
11.7
11.4
4
a For each calculated set of force constants the M-L bond force constant was held to 1.5 mdyn/Å. Refer to Experimental Section for details.
tetramethylsilane and referenced to residual solvent resonances (1H
pomers, the C-O and C-C stretching force constants decrease,
NMR: δ 7.15 for C6HD5 and δ 7.27 for CHCl3. 13C NMR: δ 128.39
while the C-C/C-O interaction force constant in each model
1
for C6D6 and δ 77.23 for CDCl3), where H NMR chemical shifts are
followed (in parentheses) by multiplicity, coupling constants J in hertz,
is increased as a result of coordination to the metal. A positive
interaction force constant indicates that as the CdO bond is
and integration. For complex coupling patterns (e.g., dt, J ) 3.2, 7.6
lengthened, the strength of the CdC bond increases and,
Hz, 1 H), multiplicities and coupling constants are listed in the same
correspondingly, when the CdC bond is lengthened the CdO
bond strength increases. As shown by the potential energy
order, e.g., the doublet (d) is characterized by the smaller coupling,
and the triplet (t) by the larger coupling. The abbreviations br and sl
distributions of the carbon-oxygen stretching mode in the free
and η2-(C,O)-bound ketenes, the coupling of the C-C and C-O
symmetry coordinates increases in the metal-bound diphen-
ylketene fragment. When the CdC bond is coordinated to the
metal center, as in 4 and 7, the electronic coupling of the CdC
and CdO symmetry coordinates decreases and the vibrational
modes become more pure. As would be predicted by a simple
harmonic oscillator approximation, the CdO bond stretching
force constant increases in these complexes and the CdC bond
stretching force constant decreases.
br designate broad and slightly broad signals, respectively. 31P{1H}
1
NMR chemical shifts are referenced to external 85% H3PO4 (aq). H
and 13C chemical shifts for 2a and 4 are slightly different from those
reported earlier10 because of different reference values used in this work.
IR spectra at ambient temperatures were obtained on a Perkin-Elmer-
1600 FTIR spectrometer. Samples were examined in C6D6 solutions
in NaCl cells or in KBr pellets. Low-temperature spectra were acquired
on a Mattson Research Series FTIR equipped with an external
reflectance cell with a temperature sensor in the cell and a circulating
cooling bath to cool the cell. Samples were injected as solutions ∼5
mM in complex in dry CH2Cl2. Elemental analyses were performed at
NuMega Resonance Labs (San Diego, CA). High-resolution mass
spectra were observed at the UC Riverside Mass Spectrometry Facility.
Conclusions
The first crystal structure of a monosubstituted ketene in η2-
(C,C) binding mode is presented in phenylketene complex 4.
Significantly, by comparing its crystal structure with that of η2-
(C,O)-diphenylketene complex 2a, a longer Ir-Cl bond in 4 is
taken as evidence that a η2-(C,C)-bound ketene has a higher
trans influence than a η2-(C,O)-bound ketene. Five complexes
of diphenylketene-1-13C and one of phenylketene-1-13C were
made in order to analyze their IR and 13C NMR spectra. From
the structural and 13C NMR data, a correlation between increased
ketene C-C bond distance and decreased one-bond coupling
constant can be made. Moreover, for the first time, IR data for
coordinated ketenes were definitively assigned and normal
coordinate mode analysis was used to assess the mixing of
vibrational modes. These results should be useful in future
studies of ketenes both in organometallic chemistry and in
surface science, with impact on fields such as organic synthesis
and catalysis.
Representative Procedure for Preparation of trans-Cl(PR3)2(η2-
Ph2CdCdO)M (M ) Rh, Ir) (2a-f). trans-Chlorobis(tricyclohexyl-
phosphine)(η2-C,O-diphenylketene)rhodium (2e). A J. Young NMR
tube was charged with [(µ-Cl)Rh(cyclooctene)2]2 (71.3 mg, 0.099 mmol)
in a glovebox, and C6D6 (∼1.0 mL) was added to give a suspension.
To this was added Ph2CdCdO (49.0 mg, 0.252 mmol) via syringe.
P(Cy)3 (112.6 mg, 0.402 mmol) was then added. Upon the addition of
P(Cy)3, a clear red solution formed. The tube was sealed and shaken
to mix the contents well before removal from a glovebox, and the tube
was kept at room temperature, protected from light. The reaction was
1
followed by H and 31P{1H} NMR spectra and was considered to be
complete after 24 h. The mixture was concentrated on a vacuum line
and the residue recrystallized from hexanes to give 2e (170.6 mg, 96%)
as a deep orange solid: 1H NMR (C6D6, 500 MHz) δ 8.75 (d, J ) 7.6
Hz, 2 H), 7.87 (d, J ) 8.0 Hz, 2 H), 7.42 (t, J ) 7.6 Hz, 2 H), 7.32 (t,
J ) 7.6 Hz, 2 H), 7.11 (t, J ) 7.5 Hz, 1 H), 7.01 (t, J ) 7.5 Hz, 1 H),
2.26-2.34 (m, 6 H), 2.13 (br d, J ) 10 Hz, 6 H), 2.06 (br d, J ) 10
Hz, 6 H), 1.56-1.82 (m, 30 H), 1.06-1.28 ppm (m, 18 H); 13C{1H}
1
2
NMR (C6D6, 125.7 MHz) δ 167.58 (dt, JRhC ) 20.2 Hz, JPC ) 4.6
Hz, OdCdC), 141.05, 138.46, 129.43, 128.72, 128.66, 128.49, 124.48,
Experimental Section
1
124.29, 77.25 (d, JRhC ) 3.0 Hz, OdCdC), 32.54 (vt, N ) 17.9 Hz,
6 C), 30.52 (6 C), 30.23 (6 C), 28.58 (vt, N ) 10.4 Hz, 6 C), 28.55
(vt, N ) 9.4 Hz, 6 C), 27.26 ppm (6 C); 31P{1H} NMR (C6D6, 80.95
MHz) δ 22.57 ppm (d, 1JRhP ) 107.1 Hz); IR (NaCl, C6D6) 1645, 1589,
1444 cm-1. Anal. Calcd For C50H76ClRhOP2 (893.16): C, 67.23; H,
8.59. Found: C, 67.16; H, 8.99.
trans-Chlorobis(triisopropylphosphine)(η2-C,O-diphenylketene)-
iridium (2a): 1H NMR (C6D6, 300 MHz) δ 8.63 (d, J ) 7.2 Hz, 2 H),
7.63 (d, J ) 7.2 Hz, 2 H), 7.33 (t, J ) 7.6 Hz, 2 H), 7.29 (t, J ) 8.0
Hz, 2 H), 7.09 (app t, J ) 7.2 Hz, 1 H), 7.03 (app t, J ) 7.1 Hz, 1 H),
2.45 (m, 6 H, PC(H)CH3CH3), 1.19 (dvt, J ) 7.1 Hz, N ) 14 Hz, 18
H, PC(H)CH3CH3), 1.16 ppm (dvt, J ) 7.2 Hz, N ) 14 Hz, 18 H,
PC(H)CH3CH3); 13C{1H} NMR (C6D6, 75.5 MHz) δ 143.78 (t, J )
General Information. Reactions were performed in resealable NMR
tubes (J. Young or Wilmad Glass) under dry nitrogen, using a
combination of Schlenk line and glovebox techniques. C6D6 was
distilled from LiAlH4. Radial chromatography was carried out with a
Harrison Research Chromatotron under a N2 atmosphere; silica gel
(SiO2) and deoxygenated solvents were used. 13CO2 was obtained from
Cambridge Isotope Laboratories and contained 99% 13C but, according
to the manufacturer, also contained 5-7% 18O.
Unless otherwise specified, 1H, 13C, and 31P data were measured at
30 °C on a 200-MHz (50.3 MHz for 13C and 80 MHz for 31P) or nominal
1
1
500-MHz (499.9 MHz for H, 125.7 MHz for 13C) spectrometer. H
and 13C NMR chemical shifts are reported in ppm downfield from

8268 J. Am. Chem. Soc., Vol. 123, No. 34, 2001
Grotjahn et al.
3.2 Hz, O)C)C), 141.95 (ipso C), 138.60 (ipso C), 128.79, 128.76 [a
the vacuum line and the residue crystallized from hexanes to give 2f
(99.5 mg, 76%) as a deep red solid: 1H NMR (C6D6, 500 MHz) δ
8.57 (d, J ) 8.4 Hz, 2 H), 7.64 (d, J ) 8.2 Hz, 2 H), 7.33 (t, J ) 8.0
Hz, 2 H), 7.28 (t, J ) 8.2 Hz, 2 H), 7.10 (m, 2 H), 1.35 (vt, N ) 12.5
Hz, 18 H), 1.25 (vt, N ) 13.5 Hz, 18 H), 0.70 ppm (vt, N ) 5.0 Hz,
6 H); 13C{1H} NMR (C6D6, 125.7 MHz) δ 165.13 (dt, JRhC ) 20.7 Hz,
JPC ) 5.8 Hz, OdCdC), 140.11, 139.22, 129.03, 128.97, 128.94,
2
tall peak with an intensity greater than two C(sp )H carbons], 128.58,
124.97 (para C), 123.93 (para C), 74.75 (OdCdC), 21.20 (vt, N )
24.6 Hz), 19.43, 18.96 ppm; 31P{1H} NMR (C6D6, 202.3 MHz) δ 20.90
ppm; IR (KBr) 1636, 1589, 1493 cm-1. Anal. Calcd for C32H52ClIrOP2
(742.45): C, 51.76; H, 7.07. Found: C, 51.95; H, 7.04.
trans-Chlorobis(tricyclohexylphosphine)(η2-C,O-diphenylketene)-
iridium (2b). Following the general procedure, [(µ-Cl)Ir(cyclooctene)2]2
(89.6 mg, 0.100 mmol) in C6D6 (∼0.6 mL) was treated with Ph2Cd
CdO (39.5 mg, 0.203 mmol), followed by P(Cy)3 (115.1 mg, 0.410
mmol), whereupon a clear red solution formed. After 24 h, the mixture
was concentrated on a vacuum line and the residue recrystallized from
hexanes to give 2b as dark orange solid (196.5 mg, 94%): 1H NMR
(C6D6, 500 MHz) δ 8.66 (d, J ) 7.2 Hz, 2 H), 7.84 (d, J ) 7.2 Hz, 2
H), 7.39 (t, J ) 7.6 Hz, 2 H), 7.33 (t, J ) 7.8 Hz, 2 H), 7.14 (t, J )
7.8 Hz, 1 H), 7.07 (t, J ) 7.8 Hz, 1 H), 2.35-2.45 (m, 6 H), 2.13 (br
d, J ) 11.5 Hz, 6 H), 2.02 (br d, J ) 11.5 Hz, 6 H), 1.76 (br t, J ) 9.8
Hz, 12 H), 1.63 (br dd, J ) 2.5, 10.5 Hz, 18 H), 1.10-1.28 ppm (m,
18 H); 13C{1H} NMR (CDCl3, 125.7 MHz) δ 142.33 (t, J ) 3.7 Hz,
OdCdC), 141.17, 137.21, 128.81, 128.61, 127.68, 127.66, 123.41,
123.12, 74.42 (OdCdC), 31.04 (t, N ) 23.9 Hz, 6 C), 29.84 (6 C),
29.44 (6 C), 28.10 (vt, N ) 10.4 Hz, 12 C), 26.78 ppm (6 C); 31P{1H}
NMR (C6D6, 80.95 MHz) δ 10.99 ppm; IR (NaCl, C6D6) 1627, 1591,
1441 cm-1. Anal. Calcd for C50H76ClIrOP2 (982.52): C, 61.12; H, 7.81.
Found: C, 60.65; H, 8.08.
trans-Chlorobis(di-tert-butylmethylphosphine)(η2-C,O-diphenyl-
ketene)iridium (2c). Following the general procedure, to a suspension
of [(µ-Cl)Ir(cyclooctene)2]2 (179.2 mg, 0.200 mmol) in C6D6 (∼1.5
mL) was added Ph2CdCdO (78.6 mg, 0.405 mmol), followed by
P(C4H9)2(CH3) (128.2 mg, 0.800 mmol). The resulting clear red solution
was allowed to stand for 24 h before concentration and recrystallization
from hexane to give 2c (222.0 mg, 75%) as a deep red solid: 1H NMR
(C6D6, 500 MHz) δ 8.42 (d, J ) 8.0 Hz, 2 H), 7.64 (d, J ) 8.0 Hz, 2
H), 7.33 (t, J ) 8.6 Hz, 2 H), 7.27 (t, J ) 8.6 Hz, 2 H), 7.12 (t, J )
8.5 Hz, 1 H), 7.09 (t, J ) 7.5 Hz, 1 H), 1.32 (vt, N ) 12.5 Hz, 18 H),
1.26 (vt, N ) 13.5 Hz, 18 H), 0.71 ppm (vt, N ) 6.0 Hz, 6 H); 13C
NMR (CDCl3, 125.7 MHz) δ 138.18 (t, J ) 3.9 Hz, OdCdC), 140.25,
138.24, 128.23, 128.15, 127.88, 127.51, 124.56, 123.18, 76.01 (Od
CdC), 35.78 (vt, N ) 22.9 Hz, 2 C), 35.33 (vt, N ) 23.3 Hz, 2 C),
30.67 (6 C), 30.22 (6 C), -2.43 ppm (vt, N ) 25.5 Hz, 2 C); 31P{1H}
NMR (C6D6, 80.95 MHz) δ 17.85 ppm; IR (NaCl, C6D6) 1624, 1591,
1471 cm-1; FAB MS (m/z) 743 (15%), 742.282 00 (31%, calcd for
C32H52ClIrOP2, 742.281 14), 740 (15), 436 (21), 434 (12), 167 (22),
161 (100).
1
128.44, 125.20, 124.37, 79.17 (d, JRhC ) 2.3 Hz, OdCdC), 35.73
(vt, N )15.6 Hz, 2 C), 35.47 (vt, N ) 17.8 Hz, 2 C), 30.50 (6 C),
30.40 (6 C), -0.59 ppm (t, J ) 9.2 Hz, 2 C); 31P{1H} NMR (C6D6,
80.95 MHz) δ 31.97 ppm (d, J ) 109.1 Hz); IR (NaCl, C6D6) 1650,
1594, 1475 cm-1; FAB MS (m/z) 652.2268 (8%, calcd for C32H52-
ClRhOP2, 652.2237), 460 (33), 459 (21), 458 (100), 161 (74).
trans-Chlorobis(triisopropylphosphine)(η2-C,C-phenylketene)iri-
dium (4): 1H NMR (C6D6, 300 MHz) δ 7.76 (d, J ) 6.5 Hz, 2 H),
6.90-7.07 (m, 3 H), 3.51 [dd, J ) 6.5, 11.1 Hz, 1 H, OdCdC(H)-
4
(Ph)], 2.54 [octet of d, J ) 7.2 (3JHH ) JHP), 14.4 Hz (2JHP), 3 H,
PC(H)(CH3)2], 2.26 (octet of d, J ) 7.2 (3JHH ) 4JHP), 14.4 Hz (2JHP),
3 H, PC(H)CH3CH3), 1.27-1.33 ppm (m, 36 H); 13C{1H} NMR
(CDCl3, 125.7 MHz) δ 198.41 (t, J ) 2.9 Hz, OdCdC), 137.89 (dd,
J ) 2.1, 3.4 Hz, ipso C), 128.09, 125.49, 23.67 (dd, J ) 4.3, 21.7 Hz),
23.22 (dd, J ) 3.9, 21.6 Hz), 20.61, 20.57, 20.14, 19.92, -32.83 to
-32.77 ppm (not well-resolved dd, two slightly broad lines (δ -32.80,
-32.81 ppm) were observed with equal intensities, OdCdC), missing
one aryl carbon; 31P{1H} NMR (C6D6, 202.3 MHz) δ 25.43 (d, J )
323.5 Hz), 23.30 ppm (d, J ) 323.5 Hz); IR (KBr) 1763, 1460, 1248
cm-1. Anal. Calcd for C26H48ClIrOP2 (666.35): C, 46.86; H, 7.28.
Found: C, 46.63; H, 6.90.
X-ray Diffraction Study on 2c. A red block measuring 0.42 × 0.40
× 0.52 mm3 was mounted in an X-ray capillary and placed in a
precooled N2 stream at -100 °C using the Siemens LT 2a low-
temperature device on a Siemens P4 autodiffractometer. Centering of
23 randomly selected reflections between 3.0 and 30.0° 2θ revealed a
1
primitive orthorhombic cell. Data collection of /4 of the hemisphere
was completed, and an absorption correction was made using empirical
ψ scan data. No appreciable deterioration of the check reflections
occurred during data collection. Data reduction and analysis revealed
the space group Pna21. Structure solution using Patterson methods
revealed the position of the Ir, Cl, and P atoms, and the remaining
non-hydrogen atoms were located by subsequent cycles of least-squares
refinement, Fourier synthesis, and difference maps. Least-squares
refinement led to a successful anisotropic convergence for all non-
hydrogen atoms. The Siemens package of programs (SHELXTL PLUS)
was used throughout for solution and refinement. Formula C32H52-
ClIrOP2 (742.3), orthorhombic, space group Pna21, red color, a )
15.340(6) Å, b ) 18.825(7) Å, c ) 11.638(5) Å at 173 K, Z ) 4, final
R indices (observed data) R ) 2.88%, wR ) 3.52%, R indices (all
data) R ) 3.40%, wR ) 3.93%, and GOF ) 0.84.
X-ray Diffraction Study on 4. As for 2c, a suitable specimen 0.08
× 0.25 × 0.55 mm in size was analyzed at -100 °C. The Siemens
random search program located 25 reflections between 15 and 30° 2θ.
Centering these reflections indicated a monoclinic primitive cell.
Collection was conducted on 1/2 of the hemisphere. Data reduction gave
the unambiguous P21/c space group (No. 14). Direct methods success-
fully located the Ir, Cl, and P atoms, and the remaining non-hydrogen
atoms were located in subsequent difference maps and refined in least-
squares cycles. Hydrogen atoms were assigned a riding model on the
carbon atoms. The Siemens package of programs (P3, SHELXS,
SHELXL) was used exclusively for the structure determination and
refinement. Formula C26H48ClIrOP2 (666.2), monoclinic, space group
P21/c, yellow plate, a ) 11.723(4) Å, b ) 14.607(4) Å, c ) 17.573(5)
Å, â ) 107.48(2)° at 173 K, Z ) 4, final R indices (observed data) R
) 4.04%, wR ) 5.49%, R indices (all data) R ) 6.22%, wR ) 6.12%,
and GOF ) 1.28.
trans-Chlorobis(triisopropylphosphine)(η2-C,O-diphenylketene)-
rhodium (2d). In a slight modification of the general procedure, to a
suspension of [(µ-Cl)Rh(cyclooctene)2]2 (38.6 mg, 0.0538 mmol) and
C6D6 (∼0.5 mL) was added P(i-Pr)3 (37.5 mg, 0.234 mmol), followed
25 min later by Ph2CdCdO (20.8 mg, 0.113 mmol). By 1H and
especially 31P{1H} NMR it required ∼1 h for the ketene complex to
be formed, but the clear red solution was allowed to react for 14 h
before it was concentrated on the vacuum line and the residue
crystallized from toluene-petroleum ether to give 2d (49.0 mg, 70%)
as a red solid: 1H NMR (C6D6, 499.88 MHz) δ 8.76 (d, J ) 7.5 Hz,
2 H), 7.65 (d, J ) 7 Hz, 2 H), 7.37 (t, J ) 7.5 Hz, 2 H), 7.27 (t, J )
7.5 Hz, 2 H), 7.07 (t, J ) 7 Hz, 1 H), 7.02 (t, J ) 7 Hz, 1 H), 2.27-
2.39 (m, 6 H), 1.18 ppm (dvt, J ) 6.5 Hz, N ) 13.5 Hz, 36 H); 13C-
{1H} (C6D6, 125.7 MHz) δ 167.77 (dt, JRhC ) 20.1 Hz, JPC ) 5.6 Hz),
140.91 (1 C), 138.79 (1 C), 128.94 (2 CH), 128.92 (2 CH), 128.78 (2
CH), 128.71 (2 CH), 124.99 (1 CH), 124.28 (1 CH), 77.06 (d, 1JRhC
)
2.1 Hz), 22.63 (vt, N ) 18.9 Hz), 20.03, 19.75 ppm; 31P{1H} (C6D6,
202.3 MHz) δ 32.55 ppm (d, J ) 112.0 Hz); IR (KBr) 2958 (m), 2928
(m), 2871 (m), 1656 (s), 1599 (m), 1590 (m), 1494 (m), 1461 (m),
1446 (m), 1431 (m), 1242 (m) cm-1. Anal. Calcd for C32H52ClORhP2
(653.06): C, 58.85; H, 8.03. Found: C, 58.96; H, 8.29.
Phenylacetic Acid-1-13C. Toluene (65 mL, 56 g, 0.61mol) was
placed in a flask under N2 atmosphere. N,N′-Tetramethylethylenedi-
amine (TMEDA) (33 mL, 25.6 g, 220 mmol) and BuLi (80 mL of 2.5
M solution in hexane, 200 mmol) were added dropwise. The mixture
was heated to a gentle reflux for 30 min. After cooling, THF (140
mL) was added and the mixture was transferred to a 500-mL flask
containing 13CO2 (22 mmol). After stirring overnight, the reaction
trans-Chlorobis(di-tert-butylmethylphosphine)(η2-C,O-diphen-
ylketene)rhodium (2f). Following the general procedure, to a suspen-
sion of [(µ-Cl)Rh(cyclooctene)2]2 (72.2 mg, 0.101 mmol) and C6D6
(∼1.0 mL) was added Ph2CdCdO (39.0 mg, 0.243 mmol), followed
by P(C4H9)2(CH)3 (73.0 mg, 0.456 mmol). The resulting clear red
solution was allowed to react for 24 h before it was concentrated on

C,C- and C,O-Bonding Modes of Metal-Ketenes
J. Am. Chem. Soc., Vol. 123, No. 34, 2001 8269
mixture was quenched with water, and the resulting mixture was
extracted twice with aqueous NaOH (1 M). To the combined aqueous
layers was added aqueous HCl until the pH was less than 1, and the
product was extracted with ether. The combined organic layers were
dried with MgSO4, and the solvent was removed. The remaining solid
was purified via hot Soxhlet extraction with hexanes, to give 2.06 g
(15 mmol, 67%): 1H NMR (CDCl3, 500 MHz) δ 11.69 (s, br, 1 H,
OH), 7.30-7.33 and 7.25-7.27 (m, 5 H), 3.63 ppm (d, J ) 8 Hz, 2
H); 13C{1H} NMR (CDCl3, 125.7 MHz) δ 178.42 (13COOH), 133.43
(d, J ) 2 Hz, ipso C), 129.57 (d, J ) 2 Hz, 2 CH), 128.85 (2 CH),
127.56 (CH), 41.27 ppm (d, J ) 55 Hz, CH2) [satellites of COOH
peak: δ 178.40 (13C18OOH, 1.8% intensity), 178.42 ppm (d, J ) 55
Hz, Ph213CH13COOH, 1% intensity]; IR (KBr) 3063, 1661 (13CdO),
1499, 1454, 1408, 1339, 1232, 1181, 919, 751, 700, 676, 604, 479
and DEPT (CDCl3, 125.7 MHz) δ 179.11 (13COOH), 138.10 (d, J )
2 Hz, 2 C), 128.88 (d, J ) 2 Hz, 4 CH), 128.85 (4 CH), 127.69 (d, J
) 0.5 Hz, 2 CH), 57.25 ppm (d, J ) 55 Hz, CH) [satellites of the
COOH peak: δ 178.79 (Ph2CH13C18O18OH, 0.36% intensity), 179.09
(Ph2CH13C18OOH, 14% intensity), 179.10 ppm (Ph2CH13CH13COOH,
J ) 55 Hz, 1% intensity)]; IR (KBr) 3024, 2903, 2784, 2681, 1661,
1599, 1583, 1498, 1449, 1392, 1305, 1212, 1079, 1033, 933, 747, 727,
696, 636, 501 cm-1; MS (m/z, %) 215 (3), 214 (3), 213 (M+, 21), 169
(1), 168 (17), 167 (100), 165 (39), 163 (3), 153 (3), 152 (21), 141 (1),
139 (3), 128 (2), 115 (4), 91 (1), 89 (2), 83 (4), 82 (4), 77 (3), 76 (1),
65 (2), 63 (3), 62 (1), 51 (4), 50 (2). Anal. Calcd for 13CC13H12O2: C,
78.86; H, 5.67. Found: C, 78.63; H, 5.57.
Diphenylacetic Acid-1-13C Chloride. Diphenylacetic acid-1-13C
(1.00 g, 4.69 mmol) was dissolved in SOCl2 (10 mL). The reaction
mixture was heated to reflux for 1 h. Excess reagent was distilled off,
and the residue was distilled at reduced pressure (p < 1 Torr), giving
1.050 g (97%) of product: 1H NMR (CDCl3, 500 MHz) δ 7.24-7.42
(m, 10 H), 5.44 ppm (d, J ) 10 Hz, 1 H); 13C{1H} NMR (CDCl3,
125.7 MHz) δ 173.69 (13COCl), 136.46 (d, J ) 2 Hz, 2 C), 129.23 (4
CH), 128.95 (d, J ) 3 Hz, 4 CH), 128.39 (2 CH), 68.88 ppm (d, J )
52 Hz, CH).
cm-1
.
Phenylacetic Acid-1-13C Chloride. Phenylacetic-1-13C acid (2.06
g, 15 mmol) was dissolved in SOCl2 (10 mL), and the reaction mixture
was heated to reflux for 1 h. Excess reagent was distilled off, and the
residue was distilled under reduced pressure (∼10 Torr) to give the
acid chloride as a clear pungent liquid (1.35 g, 8.7 mmol, 60%): 1H
NMR (CDCl3, 500 MHz) δ 7.34-7.39 and 7.26-7.28 (m, 5 H), 4.14
ppm (d, J ) 8 Hz, 2 H); 13C{1H} NMR (CDCl3, 125.7 MHz) δ 172.02
(13COCl), 131.45 (d, J ) 4 Hz, C), 129.68 (d, J ) 2 Hz, 2 CH), 129.16
(2 CH), 128.32 (CH), 53.16 ppm (d, J ) 53 Hz, CH2).
Diphenylketene-1-13C. Diphenylacetic acid-1-13C chloride (1.00 g,
4.32 mmol) was dissolved in dry ether (10 mL). Triethylamine (437
mg, 4.32 mmol) was added. After 1 h, the heterogeneous mixture was
filtered. The ether was removed, and the residue was distilled at reduced
pressure (<1 Torr) to give a yellow oil (586 mg, 70%): 1H NMR
(CDCl3, 500 MHz) δ 7.34-7.40 and 7.19-7.25 ppm (m, 10 H); 13C-
{1H} NMR (CDCl3, 125.7 MHz) δ 201.28 (13CO), 132.72 (d, J ) 5
Hz, 2 C), 129.45 (4 CH), 127.91 (d, J ) 3 Hz, 4 CH), 126.41 (2 CH),
47.03 ppm (d, J ) 107 Hz, Cd13CdO) [satellite to 13CO peak δ 201.22
ppm (13C18O, 7% intensity)]; IR (hexane, NaCl) 2046 (s), 2019 (w,
13Cd18O), 1600 (m), 1494 (m), 1074 (w), 1032 (w), 756 (m), 693 (m)
4-(1-13C). Phenylacetyl chloride-1-13C (459.3 mg, 2.95 mmol) and
dry Et2O (10 mL) were stirred in an ice-cooled flask under nitrogen.
Triethylamine (318.8 mg, 3.15 mmol) was added dropwise by syringe
over 0.5 min. A thick white precipitate formed. The mixture was stirred
for 5.5 h while the flask was cooled in ice. Meanwhile, 10 min before
filtering the cold mixture containing acid chloride and base, to a separate
flask containing a stirred suspension of [(µ-Cl)Ir(cyclooctene)2]2 (146.3
mg, 0.163 mmol) and dry benzene (3 mL) was added P(i-Pr)3 (138.0
mg, 0.861 mmol) by syringe. An orange solution resulted. After 10
min under positive nitrogen pressure, a dry Schlenk filter was placed
between the two flasks, and the cold ethereal mixture was quickly
filtered into the benzene solution. The white filter cake was washed
with by injecting a few milliliters of dry Et2O through the Schlenk
flask sidearm under positive nitrogen pressure. A yellow-orange solution
resulted. As soon as filtration was complete, the reaction mixture was
concentrated on the vacuum line and the residue was applied to a 1-mm
SiO2 plate on the Chromatotron, using ∼1 mL of benzene to rinse the
flask before petroleum ether was applied as eluent. Once benzene was
washed onto the plate, EtOAc-petroleum ether (1:40) was used to elute
the plate. The desired ketene complex was the first colored band to
come off the plate. A second purification was necessary to remove
organic impurities. From two runs [using a total of 1.047 g of acid
chloride, 325.3 mg of [(µ-Cl)Ir(cyclooctene)2]2, and 303.2 mg of P(i-
Pr)3], 6.3 mg of pure 4-(1-13C) and 26.0 mg of less pure sample were
obtained (total yield, 5%): 13C{1H} (C6D6, 125.7 MHz) δ 197.20 (dd,
J ) 2.8, 3.1 Hz), 125.83, 24.14 (dd, J ) 4.2, 21.8 Hz), 23.42 (dd, J )
3.8, 21.8 Hz), 21.02 (3 C), 20.76 (3 C), 20.29 (6 C), -32.70 ppm (dd,
cm-1
.
2a-(1-13C). Diphenylketene-1-13C (43.5 mg, 0.223 mmol), P(i-Pr)3
(71.5 mg, 0.446 mmol), and [(µ-Cl)Ir(cyclooctene)2]2 (100 mg, 0.112
mmol) were dissolved in benzene (1 mL). The mixture was purified
using radial chromatography (SiO2, hexane/ethyl acetate 40:1) to give
a red product (52.1 mg, 0.070 mmol, 63%): 13C{1H} NMR (CDCl3,
125.7 MHz) δ 142.50 (t, J ) 4 Hz, 13CO), 141.27 (d, J ) 5 Hz, C),
137.77 (C), 128.37 (d, J ) 2 Hz, 2 CH), 128.11 (2 CH), 127.81 (d, J
) 4 Hz, 2 CH), 127.79 (2 CH), 124.35 (CH), 122.93 (CH), 73.97 (d,
J ) 92.5 Hz, Cd13CdO), 21.32 (vt, N ) 26 Hz, 6 CH), 19.77 (6 CH3),
19.30 ppm (6 CH3); 31P{1H} NMR δ 20.72 ppm (d, J ) 2 Hz); IR
(KBr) 2958, 2927, 2870, 1610, 1582, 1568, 1494, 1443, 1386, 1367,
1243, 1060, 932, 884, 757, 693, 667, 651, 526 cm-1; MS (m/z, %) 747
(0.1), 746 (0.2), 745 (0.2), 744 (1), 742 (0.4), 195 (23), 168 (13), 167
(22), 166 (24), 165 (59), 162 (10), 161 (100), 160 (40), 159 (24), 118
(39), 105 (13), 86 (13), 84 (14), 77 (16), 76 (48), 75 (25), 69 (11), 49
(17), 43 (50), 41 (34).
2d-(1-13C). Using a similar procedure with Rh dimer (51.3 mg, 0.071
mmol), P(i-Pr)3 (45.0 mg, 0.281 mmol) and Ph2Cd13CdO (31.8 mg,
0.164 mmol), labeled complex 2d-(1-13C) (86 mg, 95%) was obtained.
Signals affected by the presence of the 13C label: 13C{1H} (C6D6, 125.7
MHz) δ 167.76 (dt, J ) 19.9, 4.8 Hz, CdCdO), 140.92 (d, 2JCC ) 4.5
2
1JCC ) 45.7 Hz, JPC ) 2.1 Hz) (it was not possible to unequivocally
identify other peaks for aromatic C); 31P{1H} (C6D6, 80.95 MHz) δ
2
2
2
25.56 (dd, JPP ) 325.3 Hz, JPC ) 3.0 Hz), 23.41 ppm (dd, JPP
)
2
1
325.3 Hz, JPC ) 3.0 Hz).
Hz, ipso carbon of one phenyl ring), 77.05 ppm (dd, JCC ) 93.0 Hz,
1JRhC ) 2.0 Hz, CdCdO). 31P{1H} (C6D6, 80.95 MHz) δ 32.63 ppm
Diphenylacetic Acid-1-13C. To dry diphenylmethane (84.12 g, 512
mmol) was added TMEDA (21.23 g, 183 mmol), followed by BuLi
(76 mL of 2.5 M solution in hexane, 190 mmol). The resulting red
mixture was heated to reflux for 14 h. The cold solution was transferred
into a 1-L flask containing 13CO2 gas at 1 atm (44.6 mmol). The flask
was placed into a shaker for 20 h, after which time the reaction mixture
was quenched with water. The mixture was extracted with ether and
the organic layer was washed two times with aqueous NaOH solution
(1 M). To the combined aqueous layers was added aqueous HCl until
the pH became less than 1. The product was extracted with ether.
Combined organic layers were dried with MgSO4, and the solvent was
removed. The product was dissolved in CH2Cl2, MgSO4 was added to
the heterogeneous mixture. The drying reagent was filtered off and
the solvent removed, leaving the acid as colorless solid (6.26 g, 29
mmol, 65%): 1H NMR (CDCl3, 500 MHz) δ 11.0 (br s, 1 H, OH),
7.18-7.33 (m, 10 H), 5.03 ppm (d, J ) 8 Hz, 1 H); 13C {1H} NMR
1
2
(dd, JRhP ) 107.9 Hz, JCP ) 4.5 Hz); IR (C6D6) 1617 (s), 1587 (s),
1491 (m), 1452 (s), 1326 (s) cm-1
.
Diphenylacetic Acid-C(18O)2H. Sodium metal (25 mg, 1.09 mmol)
was added to H218O (0.5 mL, 25 mmol) in ethylene glycol (2 mL, twice
distilled under vacuum from sodium). Diphenylacetonitrile (193 mg,
1.00 mmol) was added, and the resulting mixture was heated at 150
°C for 17 h. To the cooled mixture was added aqueous HCl (0.2 M, 30
mL) and the solution was extracted with ether. The combined organic
layers were dried with MgSO4 and the solvent was removed, leaving
the acid as white solid (205.7 mg, 0.96 mmol, 95%).
Diphenylacetic Acid-18O Chloride and Diphenylketene-18O. The
procedure used to make 13C-labeled material was followed starting with
Ph2CHC18O2H (205.7 mg, 0.96 mmol) and SOCl2, affording after
vacuum distillation 235.7 mg (1.02 mmol, more than 106%) of Ph2-
CHC18OCl, which was then converted to Ph2CdCd18O (142 mg, 0.72

8270 J. Am. Chem. Soc., Vol. 123, No. 34, 2001
Grotjahn et al.
mmol, 75%): IR (hexane, NaCl) CdO 2075 cm-1. A second, smaller
band was seen at 2102 cm-1, suggesting incomplete 18O incorporation.
The ratio of integrated areas was 3.8 to 1.
addition, the energy of ν(CO) is unaffected by reasonable values of
fCR. This approximation was continued in the metal-containing frag-
ments, [M(η2-R2CCO)], where M ) Ir, Rh, and R ) phenyl group
point mass. The structural parameters used in the construction of the
G matrixes were taken from crystal structure data. Because no low-
energy vibrational data are currently available, the metal-ligand bond
stretching force constants were held constant in each of the calculations.
The M-C and M-O symmetry coordinates contribute less than 2% to
ν(CO) and so reasonably85 are included in the calculation for the sake
of completeness, but no conclusions can be drawn as to the accuracy
of this value.
2a-(18O). Diphenylketene-18O (50 mg, 0.255 mmol), P(i-Pr)3 (82 mg,
0.511 mmol), and [(µ-Cl)Ir(cyclooctene)2]2 (107.5 mg, 0.12 mmol) were
dissolved in benzene (1 mL). The mixture was purified using radial
chromatography (SiO2, hexane/ethyl acetate 40:1) to give a red product
(65 mg, 0.087 mmol, 73%).
Labeled Ketene Complex 7-(1-13C). Prepared using diphenylketene-
1-13C according to the reported procedure for the unlabeled material.14
Data influenced by 13C enrichment at C-1: 13C{1H} NMR (CD2Cl2,
2
1
125.7 MHz) δ 23.6 ppm (dd, JPC ) 47.5 Hz, JCC ) 44.3 Hz, Od
Acknowledgment. Acknowledgment is made to the donors
of the Petroleum Research Fund, administered by the ACS, for
partial support of this research, and to San Diego State
University. Professor Cliff Kubiak and Casey Londergan are
especially thanked for helping us to obtain low-temperature IR
data and for fruitful discussions. Cambridge Isotope Laboratories
donated some of the isotopically labelled precursors.
13CdC); IR (CH2Cl2) 1693 cm-1
.
Labeled Ketene Complex 8-(1-13C). The compound was prepared
using diphenylketene-1-13C according to the reported procedure for the
unlabeled material.13 Data influenced by 13C enrichment at C-1: 13C-
{1H} NMR (CD2Cl2, 125.7 MHz, -50 °C) δ 22.33 ppm (d, JCC
)
1
54.4 Hz); IR (C6D6, NaCl) 1755 (s), 1737 (m), 1597 (w), 1476 (m),
1446 (m) cm-1 31P{1H} (C6D6, 81.0 MHz, 30 °C) δ 59.47 ppm (dd,
;
2
1JRhC ) 228.2, JCP ) 4.0 Hz).
Supporting Information Available: Complete details of the
X-ray diffraction studies on 2c and 4. This material is available
free of charge via the Internet at http://pubs.acs.org. See any
current masthead page for ordering information and Web access
instructions.
Normal Coordinate Mode Analyses. Experimental vibrational data
were fit using a nonlinear least-squares fitting program that varied the
primary force constants identified in the F matrix of the generalized
valence force field (GVFF). The diphenylketene fragment was analyzed
using the R2CCO fragment where R is a point mass equal to a phenyl
ring, using calculated bond lengths and bond angles.38 Although this
calculation neglects electronic coupling to the phenyl CdC stretching
modes, it accurately reproduces the experimental vibrational frequencies,
suggesting that coupling of ν(CO) to these modes is negligible. In
JA004324Z
(85) Jegat, C.; Fouassier, M.; Mascetti, J. Inorg. Chem. 1991, 30, 1521-
1529.