The reaction of ketenylidenetriphenylphosphorane (Ph 3PCCO) with acidic HE (EO, N) Bonds

Article abstract of DOI:10.1080/10426507.2012.710674

The reactivity of ketenylidenetriphenylphosphorane (1) with the protic reagents 2,4,6-trimethylphenol (7), 2,6-di-tert-butyl-4-methylphenol (8), and diphenylamine (9) has been explored. Three novel carbonyl-stabilized ylides have been synthesized and characterized. Crystal structures were obtained for Ph3PCHC(O)O(C6H2Me3) (11), Ph3PCHC(O)O(C6H2t-Bu2Me) (12), and Ph3PCHC(O)NPh2 (13), respectively. These products were then methylated in an attempt to develop a new route to low-valent carbon compounds. Crystals of [Ph3PCH(CH3)C(O) O(C6H2Me3)]I (14) were isolated and characterized but this route did not prove to be synthetically useful, at least toward the goal of preparing low-valent carbon-centered materials. Finally, 1 was also reacted with the bulky tin reagent, bis[bis(trimethylsilyl)amido]tin(II), in the presence of 2,4,6-trimethylphenol. A complex mixture of products was obtained, from which crystals of an unusual chelated tin compound (15) were isolated and characterized using X-ray crystallography.

Full text of DOI:10.1080/10426507.2012.710674

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The Reaction of
Ketenylidenetriphenylphosphorane
(Ph3P˭C˭C˭O) with Acidic H‒E (E˭O, N)
Bonds
Miller G. Makramalla a , Monica T. Diab a , Cody N. Sherren a , Arthur
D. Hendsbee a , Jason D. Masuda a , Katherine N. Robertson a
Jason A. C. Clyburne a
&
a Maritimes Centre for Green Chemistry , Department of Chemistry,
Saint Mary's University , Halifax , Nova Scotia , Canada
Published online: 10 Sep 2012.
To cite this article: Miller G. Makramalla , Monica T. Diab , Cody N. Sherren , Arthur D. Hendsbee ,
Jason D. Masuda , Katherine N. Robertson & Jason A. C. Clyburne (2012) The Reaction of
Ketenylidenetriphenylphosphorane (Ph3P˭C˭C˭O) with Acidic H‒E (E˭O, N) Bonds, Phosphorus, Sulfur,
and Silicon and the Related Elements, 187:12, 1537-1554, DOI: 10.1080/10426507.2012.710674
To link to this article: http://dx.doi.org/10.1080/10426507.2012.710674
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Phosphorus, Sulfur, and Silicon, 187:1537–1554, 2012
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2012.710674
THE REACTION OF
KETENYLIDENETRIPHENYLPHOSPHORANE
(Ph3P C C O) WITH ACIDIC H E (E O, N) BONDS
Miller G. Makramalla, Monica T. Diab, Cody N. Sherren,
Arthur D. Hendsbee, Jason D. Masuda,
Katherine N. Robertson, and Jason A. C. Clyburne
Maritimes Centre for Green Chemistry, Department of Chemistry, Saint Mary’s
University, Halifax, Nova Scotia, Canada
GRAPHICAL ABSTRACT
Abstract The reactivity of ketenylidenetriphenylphosphorane (1) with the protic reagents
2,4,6-trimethylphenol (7), 2,6-di-tert-butyl-4-methylphenol (8), and diphenylamine (9) has
Received 20 April 2012; accepted 6 July 2012.
Funding was provided by the Natural Sciences and Engineering Council of Canada (NSERC) through the
Discovery Grants Program to J.D.M. and J.A.C.C. J.A.C.C. acknowledges generous support from the Canada
Research Chairs Program, the Canadian Foundation for Innovation, and the Nova Scotia Research and Innovation
Trust Fund. The authors are also grateful to NMR-3 (Dalhousie University) for NMR data acquisition.
Address correspondence to Katherine N. Robertson or Jason A. C. Clyburne, Maritimes Centre for Green
Chemistry, Department of Chemistry, Saint Mary’s University, Halifax, NS B3H 3C3, Canada. E-mail: katherine.
robertson@smu.ca
1537

1538
M. G. MAKRAMALLA ET AL.
been explored. Three novel carbonyl-stabilized ylides have been synthesized and characterized.
Crystal structures were obtained for Ph3PCHC(O)O(C6H2Me3) (11), Ph3PCHC(O)O(C6H2t-
Bu2Me) (12), and Ph3PCHC(O)NPh2 (13), respectively. These products were then
methylated in an attempt to develop a new route to low-valent carbon compounds.
Crystals of [Ph3PCH(CH3)C(O)O(C6H2Me3)]I (14) were isolated and characterized but
this route did not prove to be synthetically useful, at least toward the goal of preparing
low-valent carbon-centered materials. Finally, 1 was also reacted with the bulky tin reagent,
bis[bis(trimethylsilyl)amido]tin(II), in the presence of 2,4,6-trimethylphenol. A complex
mixture of products was obtained, from which crystals of an unusual chelated tin compound
(15) were isolated and characterized using X-ray crystallography.
Keywords X-ray crystallography; ketenylidenetriphenylphosphorane; phenols; dipheny-
lamine; 1,2-addition; stabilized P-ylide
INTRODUCTION
The chemistry of low-valent carbon is extremely relevant to catalysis and fundamental
main group chemistry.1,2 We have been interested in this area for some time, especially
in the role such compounds play in the chemistry of ionic liquids.3–5 Here, we report the
attempted use of ketenylidenetriphenylphosphorane (1) as a precursor to new low-valent
carbon centers.
Ketenylidenetriphenylphosphorane is a stable crystalline material and can be stored
at room temperature for months under an atmosphere of dry argon without decomposi-
tion. It is soluble in many organic solvents but in chlorinated solvents it undergoes slow
decomposition.6 It is a valuable commercial synthon with utility in a variety of reactions
including cycloaddition, multicomponent reactions, and domino reactions. Chapter 3, Cu-
mulene Ylides, in the book, Phosphorus Ylides: Chemistry and Application in Organic
Synthesis, by O. I. Kolodiazhnyi is a useful introduction to the chemistry of ketenyliden-
etriphenylphosphorane.7 More recently, it has also been utilized in a polystyrene-bound
form, as described by Schobert et al.8 However, its application in the generation of active
catalyst systems has been relatively unexplored.
There are four possible resonance structures that can be drawn to represent the
bonding in 1 (Scheme 1). The crystal structure of 1, as well as reactivity studies, clearly
indicates the dominance of 1B. In the crystal structure of compound 1, the P C C angle
is not linear, but rather is 145.5(7)◦, suggesting the importance of the ylide resonance
contribution.9 The bond length of phosphorus to the ylidic carbon is 1.648(7) Å, shorter
than the average bond length of phosphorus to the phenyl carbons (1.805 Å with a standard
deviation of 0.011 Å). This indicates that there is double bond character in the P–C bond,
thus giving credence to the importance of the ylene structure (1A). However, this bond
shortening could also be due to the coulombic forces arising from the charge difference
between P and C (1B). Finally, an alternative and much less common way of looking at the
compound is to see it as a triphenylphosphine adduct of :C C O (1D).
Scheme 1

REACTION OF Ph3P
C
C
O WITH ACIDIC H O/N BONDS
1539
Although 1 is formally a ketene, its reactivity is distinctly different. This is due
to the fact that its electronic structure features an orthogonal pair of filled π-systems.
Hence, Ph3P C C O does not dimerize like other ketenes.6 It does not enter readily into
Wittig alkenation reactions, which is a very common chemistry of phosphorus ylides.10 The
electronic nature of 1 suggests that it should undergo facile addition reactions to produce
novel phosphorane salts. For an extensive overview of this type of reactivity, refer to the
review by Bestmann.11 It is this reactivity that we have attempted to exploit in this work.
Ketenylidenetriphenylphosphorane can act as a ligand or a base. When 1 functions
as a base, it should react with Lewis acids, transition metals, or protic reagents. If a
transition metal acts as an isolated electrophilic site, assuming that it is not already co-
ordinatively saturated, attack by the ylidic carbon of 1 will result in an easily isolated
metal-substituted ketene.12 For example, see Scheme 2, which shows its reaction with bis-
2,4,6-tris(trifluoromethyl)phenyltin(II). The properties of these unique ketenes have been
discussed by Bertani.6
Scheme 212
The basicity of the ylidic carbon allows 1 to react with electrophile–nucleophile-type
compounds, as illustrated in Scheme 3. Such a reaction can take place via different mech-
anisms under certain circumstances. If the nucleophile is strong enough, as in the case of
protic nucleophiles, attack on the carbonyl carbon will occur resulting in the formation of
a carbonyl-stabilized ylide. Using this general procedure, a number of groups have iso-
lated carbonyl-stabilized ylides, compounds that otherwise would have been synthetically
challenging to prepare.9,13,14
Scheme 3
Stable metal-substituted ketenes have been produced using a variety of transition
metals, including Cr(0), Mo(0), Mn(I), and W(II).6 In contrast, there have only been a few

1540
M. G. MAKRAMALLA ET AL.
reports of the interaction of 1 with main group metals. In fact, in the literature, there has
only been one account of the reactivity of 1 with a main group metal compound, if its
reactions with Grignard reagents are excluded. More specifically, the reaction of 1 with
bis-2,4,6-tris(trifluoromethyl)phenyltin(II) gives rise to an unstable adduct formed through
the coordination of the ylidic carbon to the tin metal center (Scheme 2). This intermediate
◦
compound, on standing at 25 C for 6 h, transforms into compound 2, the X-ray crystal
structure of which has also been reported.12
Can compounds such as 3 be used to develop a new synthetic route to low-valent car-
bon centers? A possible retrosynthetic approach for the methylation of carbonyl-stabilized
ylides is shown in Scheme 4. Various resonance structures may be drawn to represent the
bonding in 6, itself a specific example of a type 3 compound. Reactivity studies indicate
that structure 6C will be dominant since oxygen is most electronegative and thus has a
larger charge density. Methylation of 6C will occur, as shown, to yield compounds 4 and
5. Structures such as compound 4, which can be used as new ligands for transition metal
catalysts, are rare in the current literature.
Scheme 415
In this paper, we report the reaction of ketenylidenetriphenylphosphorane with the
phenols 7 and 8, and then explore the methylation reactions of the new derivatives formed.
We also explore the reaction of 1 with diphenylamine (9), as well as its reaction with
the bulky reagent (10), bis[bis(trimethylsilyl)amido]tin(II). The results are summarized in
Scheme 5.
RESULTS AND DISCUSSION
The first stage of this project involved the reaction of the protic nucleophiles (7,
8, and 9) with 1 to form carbonyl-stabilized phosphorus ylides (Scheme 5). Under an
argon atmosphere, a solution of 1.0 mmol of 1 dissolved in dichloromethane was prepared,
followed by an addition of 1.0 mmol of the protic nucleophile. The solution was swirled
and a small amount of benzene was added to prevent evaporation to dryness. Overnight
evaporation yielded clear, beige X-ray quality crystals in high to excellent yields for all
three products.
Their structures were characterized using a combination of NMR, IR, elemental
analysis, and X-ray crystallography. Reaction of 1 with 2,4,6-trimethylphenol (7) gave

REACTION OF Ph3P
C
C
O WITH ACIDIC H O/N BONDS
1541
Scheme 5
Ph3PCHC(O)O(C6H2Me3) (11) as the isolated product (Figure 1). With 2,6-di-tert-butyl-
4-methylphenol (8), 1 reacted to give Ph3PCHC(O)O(C6H2t-Bu2Me) (12, Figure 2), while
with diphenylamine (9), the product obtained was Ph3PCHC(O)NPh2 (13, Figure 3). In each
case, the anticipated product was in fact isolated, after addition of the proton to the ylidic
Figure 1 Thermal ellipsoid plot (50% probability ellipsoids) of 11. Hydrogen atoms (except for H19) have been
omitted for clarity. Only one of two unique molecules in the asymmetric unit is shown.

1542
M. G. MAKRAMALLA ET AL.
Figure 2 Thermal ellipsoid plot (50% probability ellipsoids) of 12. Hydrogen atoms (except for H19) have been
omitted for clarity.
carbon atom and coordination of the remaining fragment of the reagent to the carbonyl
carbon atom (Scheme 3).
The IR spectra were clearly indicative of the formation of new products. The charac-
teristic peak in the spectrum of the starting material (∼2110 cm−1) disappeared, while new
peaks in the range 1500–1700 cm−1, assigned to the C O stretch, appeared in the spectra
1
of the products. Furthermore, in the 31P{ H} NMR spectra, the peak observed at ∼5 ppm
(CD2Cl2 and CDCl3) in the starting material was shifted downfield (∼20 ppm) in the prod-
ucts. In addition, after coordination of a proton to the ylidic carbon center of the starting
1
material, the signal appears in the H NMR spectra of the products. Compounds 11, 12,
and 13 were fully characterized by NMR and in each the expected doublet was observed.
Peak broadening has been observed before in protonated ylides but in these compounds the
signals were well separated and relatively sharp.16 The identifying spectral characteristics
of the products are summarized in Table 1.
The NMR spectra of compound 11 consistently showed a mixture of two products
in the CDCl3 solution. At room temperature the ratio was always the same and could
1
be determined by examining peak integrations. In the 31P{ H} spectrum, two peaks were
observed, at 19.1 and 15.4 ppm, and integration showed them to always occur in a ratio of
60% to 40%, respectively. Integration of pairs of peaks identified as belonging to the two
products in the 1H NMR also occurred in the same roughly 60%:40% ratio. For example,
the signal for the Cylide H proton in 11 was observed as a pair of doublets at 3.18 ppm
(2JP H = 21.7 Hz) and 3.11 ppm (2JP = 20.0 Hz), in a ratio of 58% to 42%.
H

REACTION OF Ph3P
C
C
O WITH ACIDIC H O/N BONDS
1543
Figure 3 Thermal ellipsoid plot (50% probability ellipsoids) of 13. Hydrogen atoms (except for H19) have been
omitted for clarity. Only one of two unique molecules in the asymmetric unit is shown.
There is ample evidence in the literature to explain these observations. The best
explanation is found in the 1969 publication of Zeliger et al.17 and Figure 4, which is shown
below, summarizes their results. These authors found that reversible proton exchange can
operate simultaneously with sterically hindered rotation to give a dynamic NMR system
for some α-carbonyl-stabilized phosphorus ylides.
Under normal conditions, the partial double bond character of the Cylide Ccarbonyl
enolate bond hinders free rotation and in the case of bulky ligands bound to Ccarbonyl results
in adoption of a trans arrangement of the ligand relative to the bulky triphenylphosphine.
This is in fact the structural arrangement that is observed crystallographically for all the
solids isolated and is the single conformation present in the NMR spectra of compounds
12 and 13. Compound 11 is different, most likely because of the greater acidity of 2,4,6-
trimethylphenol relative to the other reagents used. In this case, similar to that observed
by Zeliger et al.17 for methoxycarbonylmethylenetriphenylphosphoranes, a mixture of two
Table 1 Identifying characteristics of the synthesized products
1
Product
C
O stretch (cm−1
1638
)
1H ylide proton (ppm)
31P{ H} (ppm)
11 isomer 1
isomer 2
12
3.18 (2JH = 21.7 Hz)
19.1 (60%)
15.4 (40%)
18.8
P
3.11 (2JH = 20.0 Hz)
P
1653
1550
3.36 (2JH = 23.5 Hz)
P
13
2.81 (2JH = 20.9 Hz)
17.7
P
Phosphonium salt
7.32 (HSQC)
14
1740
27.8

1544
M. G. MAKRAMALLA ET AL.
Figure 4 Mechanism for the dynamic solution processes (hindered steric rotation and reversible proton exchange)
that result in the observation of both cis and trans isomers in the NMR spectra of 11.
different isomers (cis and trans) is observed in the NMR spectra because of the two
competing solution processes. The trans isomer is still expected to be the major form in
solution with the cis form present in a lesser but still substantial amount.
The crystallographic details of all the refinements carried out are summarized in
Table 2, while Tables 3 and 4 list relevant bond lengths and angles, respectively. Comparison
of the bond lengths and angles in the first three compounds isolated is broadly instructive.
The P Cylide bond lengths are all significantly shorter than the corresponding P Cphenyl
bonds indicative of their double bond character. The CC bond in the ketene portion of the
molecules has been labeled as Cylide Ccarbonyl since the C O bond lengths to the terminal
oxygen atoms are all characteristic of double bonds. The Cylide Ccarbonyl bonds, which
range from 1.393(4) Å in 11 to 1.416(6) Å in 13, may retain a small amount of double bond
character, if the same bond in compound 14 (1.493(6) Å) is used for comparison. The bond
is longest in compound 13, which may be a result of the electron withdrawing ability of
the diphenylamine group. The Cylide H bond lengths were refined in all three structures
and found to lie quite reasonably between 0.89(3) and 0.94(2) Å. The Ccarbonyl O/N and
N/O Cligand bonds all have distances typical of single bonds, but with the N/O Cligand
bond always being slightly longer in a given compound. The bond angles also reflect
these assignments, with the angles around Cylide and Ccarbonyl being consistent with sp2-type
carbon centers. The bond angles around Ccarbonyl are influenced by the lone pairs on oxygen,
being consistently smallest for Cylide Ccarbonyl N/O (112.9(2) to 118.2(4)◦) and larger for
Cylide Ccarbonyl O (123.1(4) to 127.1(3)◦) and N/O Ccarbonyl O (118.5(4) to 120.3(2)◦)
type angles.
The next stage of this project was to investigate the methylation reactions of the
synthesized ylides. A 1.0 mmol quantity of the desired compound (11, 12, or 13) was
dissolved in dichloromethane and 1.0 mmol of methyl iodide added. A solid product was
isolated only from the reaction of 11 with CH3I. Again, it is possible to speculate as to
why this might be so. 2,4,6-Trimethylphenol is the most acidic of the three reagents used
in the original syntheses, which, in turn, means that it has the weakest conjugate base. The
coordinated ligand, OC6H2(CH3)3, is least likely to withdraw electron density from the
Cylide carbon atom. Maximizing the electron density at this carbon in the trimethylphenol
adduct makes it the most reactive nucleophile when it comes to reaction with methyl iodide

1545

1546
M. G. MAKRAMALLA ET AL.
Table 3 Bond lengths [Å] for the compounds studied
Compound
Bond
11
12
13
14
15
Molecule 1 Molecule 2
Molecule 1 Molecule 2
P
P
P
P
Cph1
Cph2
Cph3
Cylide
1.819(3)
1.801(3)
1.814(3)
1.696(3)
0.91(2)
1.812(3) 1.8168(17) 1.813(4)
1.800(3) 1.8126(19) 1.817(4)
1.807(3) 1.8195(18) 1.818(4)
1.701(3) 1.7116(18) 1.710(4)
1.818(4) 1.799(4) 1.810(2)
1.827(4) 1.788(5) 1.808(2)
1.814(4) 1.801(4) 1.811(2)
1.712(4) 1.825(5) 1.718(2)
Cylide
Cylide CH3
Cylide Ccarbonyl 1.393(4)
Ccarbonyl
Ccarbonyl
H
0.89(3)
0.937(18)
0.90(6)
0.91(6)
0.96(4)
0.9500
1.535(6)
1.397(4) 1.399(2)
1.410(6)
1.416(6) 1.493(6) 1.386(3)
1.249(5) 1.187(5) 1.268(2)
1.350(6) 1.365(2)
O
O
1.227(3)
1.397(3)
1.402(3)
1.223(3) 1.2351(19) 1.245(5)
1.391(3) 1.4011(19)
1.409(3) 1.4068(19)
O
Cligand
1.415(5) 1.451(2)
Other
13 (molecule1/molecule2) Ccarbonyl–N = 1.408(5)/1.402(5); N–Cph1 = 1.431(5)/1.433(5); N–Cph2 =
1.438(5)/1.434(5).
15 Sn Cl = 2.4765(9); Sn O = 2.2326(15); Sn Cring = 2.160(2); Sn N1 = 2.0377(17); Sn N2 =
2.0354(17).
and could explain why only in this case was a solid product isolated. In the reaction of 11
with CH3I, overnight evaporation yielded clear beige X-ray quality crystals. The structure
of the product, [Ph3PCH(CH3)C(O)O(C6H2Me3)]I (14), was confirmed by IR, NMR, and
X-ray crystallography (Figure 5).
Table 4 Bond angles [◦] for the compounds studied
Compound
Angle
11
12
13
14
15
Molecule 1 Molecule 2
Molecule 1 Molecule 2
Cylid
Cylid
Cylid
Cph1
Cph1
Cph2
P
P
P
P
P
P
Cph1
Cph2
Cph3
Cph2
Cph3
Cph3
112.86(13)
108.59(13)
115.42(15)
107.75(13)
106.35(12)
105.37(12)
117.7(2)
112.75(13) 114.83(9)
110.21(13) 109.71(8)
114.76(14) 112.81(8)
106.36(13) 106.89(7)
106.14(12) 105.99(7)
106.07(12) 106.09(8)
105.6(2)
118.1(2)
113.5(2)
106.19(18)
107.9(2)
104.89(19)
114.7(2)
119.2(2)
105.3(2)
103.65(19) 109.3(2)
107.3(2) 108.1(2)
105.82(19) 110.6(2)
107.1(2)
109.3(2)
112.3(2)
114.00(10)
106.77(10)
114.49(10)
106.42(9)
107.67(10)
106.97(9)
125.93(16)
117.0
P
Cylide Ccarbonyl
Cylide
116.4(2)
115.22(12) 116.9(3)
118.2(3)
116(3)
110.5(3)
106(2)
P
H
118.1(16)
119.0(18)
122.7(11)
116(3)
P
H
H
Cylide CH3
Cylide Ccarbonyl
Cylide CH3
111.6(3)
105(2)
114(2)
123.1(16)
124.2(18)
121.8(11)
127(3)
125(3)
117.0
CH3 Cylide Ccarbonyl
110.6(4)
126.4(4)
109.8(4)
Cylide Ccarbonyl
Cylide Ccarbonyl
O
O
127.1(3)
112.9(2)
119.9(2)
116.71(19)
126.3(3)
113.4(2)
120.3(2)
126.53(15) 123.3(4)
113.19(13)
120.28(14) 123.8(4)
123.1(4)
124.24(18)
116.05(17)
O
Ccarbonyl
O
119.71(18)
Ccarbonyl
O
Cligand
115.90(19) 114.53(11) 116.5(3)
Other
13 (molecule1/molecule2) Cylid Ccarbonyl N = 118.2(4)/118.0(4); O=Ccarbonyl N = 118.5(4)/118.9(4);
Ccarbonyl Cph2 = 122.4(3)/120.5(3); Cph1 Cph2 =
Cph1 = 120.7(3)/122.8(3); Ccarbonyl
116.9(3)/116.7(3).
15 Ccarbonyl
Sn = 113.62(12); N2 Sn N1 =
N
N
N
O
Cring = 118.04(15); O Cring Sn = 110.68(13); Ccarbonyl
O
123.76(7); N1 Sn1 Cring = 111.87(8); N2 Sn1 Cring = 121.74(8); N2 Sn O = 89.43(6); N1 Sn O = 88.51(6);
Cring Sn O = 75.30(6); N1 Sn Cl = 97.84(5); N2 Sn Cl = 93.77(5); Cring Sn Cl = 94.67(5); O Sn Cl =
169.63(4).

REACTION OF Ph3P
C
C
O WITH ACIDIC H O/N BONDS
1547
The X-ray crystallographic results for compound 14 are all in keeping with the
addition of a methyl group at the ylidic carbon center. The bonds Cylide H, Cylide P,
Cylide CH3, and Cylide Ccarbonyl all have lengths characteristic of single bonds, with the
first two types having increased significantly from those observed in 11, 12, and 13. In fact,
the P Cylide bond in 14 is now longer than the P Cphenyl bonds, likely as a result of the
electron donating effect of the methyl group. The change from sp2 to sp3 carbon at the ylidic
carbon is also reflected in its bond angles in 14 (105(2) to 111.6(3)◦), which are closer to
109◦ than 120◦. In contrast, the bonds and angles at Ccarbonyl of 14 are very similar to those
found in the first three products, suggesting it remains an sp2-type center.
A priori calculation of the highest occupied molecular orbital (HOMO) of compound
11 (DFT, B3LYP/6-31+g∗) displayed a large amount of charge density around the ylidic
carbon. However, it also displayed a reasonably large localized electron density on the
carbonyl oxygen (Figure 6). It had been hoped that this charge density would be enough to
result in methylation occurring at the carbonyl oxygen site. This would have resulted in the
more labile hydrogen being coordinated to the formerly ylidic carbon (Scheme 4), instead
of the methyl group actually observed in compound 14. This result limited the synthetic
utility of compound 14 and its chemistry was not pursued any further.
In the final stage of this project, the reactivity of 1 toward a bulky metal reagent,
bis[bis(trimethylsilyl)amido]tin(II) (10), was examined. In an initial step, 1.0 mmol of
ketenylidenetriphenylphosphorane (1) dissolved in dichloromethane was added to 1.0 mmol
of 2,4,6-trimethylphenol (7) in benzene, which was stirred and left to sit for 20 min to
Figure 5 Thermal ellipsoid plot (50% probability ellipsoids) of 14. Hydrogen atoms (except for H19) have been
omitted for clarity. The C(19)–H(19). . . I(1) hydrogen bond (dashed line) has distances of C(19)–H(19) = 0.96(4)
Å, H(19). . . I(1) = 2.97(5) Å, and C(19). . . I(1) = 3.932(6) Å and a C(19)–H(19). . . I(1) angle of 178(3)◦, while
the distance P(1) . . . I(1) is 4.874(3) Å.

1548
M. G. MAKRAMALLA ET AL.
Figure 6 HOMO of 11 calculated at the density functional B3LYP/6-31+g∗ level using Spartan ’06 for Win-
dows.18
generate Ph3PCHC(O)O(C6H2Me3) (11) in situ. Next, 1.0 mmol of the tin reagent (10) was
added to the stirred solution, which was then left uncapped overnight. Slow evaporation
yielded orange X-ray quality crystals. The product was characterized using IR, NMR, and
X-ray crystallography.
The disappearance of the 2110 cm−1 peak from the IR spectrum of the starting
material and the emergence of a new peak at 1564 cm−1 (ν(C O)) confirmed the presence
of a carbonyl group in the product(s). The frequency was notably downshifted, which is
in agreement with the formation of a C O Sn bonding system, where the sigma-donor
1
effect of the electropositive tin atom affects the observed carbonyl frequency. The 31P{ H}
NMR spectrum of the product showed multiple peaks, four specifically, indicating that it
was not pure.
Crystals of one of the possible products were isolated from the solution. The crystallo-
graphic analysis showed that this one product had a somewhat unexpected structure, where
the ketenylidenetriphenylphosphorane plus atoms from the solvent and adventitious water
had combined to form a bidentate, five-membered ring chelated to the tin reagent (Figure 7).
In addition, the tin center had also coordinated a chloride ligand, again likely provided by
the solvent, dichloromethane. In an obvious first step, the ArOH fragment must be lost, fol-
lowed by a complex reaction between the regenerated ketenylidenetriphenylphosphorane,
water, solvent, and tin reagent.
The geometry at the five-coordinate tin center in the isolated complex is quite a regular
trigonal bipyramid, with Cl(1) and O(1) occupying the trans axial positions (169.63(4)◦)
and N(1), N(2), and C(21) lying in the equatorial plane. This geometry is likely favored for
a combination of electronic and steric reasons. Within the chelated ring, the C(20) O(1)
and C(20) O(2) bond lengths are substantially different, leading to the assignment of
C(20) O(1) as the carbonyl group from the original starting material. The bond angles
increase from 75.30(6)◦ at the tin center to 119.71(8)◦ at C(20), at the opposite end of
the ring away from the strong directional influence of the tin. The chelated ring is itself
relatively planar; the mean deviation from the plane defined by Sn(1), Cl(1), O(1), O(2),
C(20), and C(21) is 0.073 Å. However, no other region of the molecule is coplanar with the
ring, limiting potential interactions between different regions.

REACTION OF Ph3P
C
C
O WITH ACIDIC H O/N BONDS
1549
Figure 7 Thermal ellipsoid plot (50% probability ellipsoids) of 15. Hydrogen atoms (except for those on C19
and C21) have been omitted for clarity.
It appears that the tin amide has been inserted into a carbon–chlorine bond of the
CH2Cl2 solvent, as a first step in the reaction sequence. This oxidative addition would be
expected to give the tin(IV) complex, Sn(CH2Cl)Cl(NR2)2 (where R = Si(CH3)3), and in
fact this same compound was previously synthesized by Lappert et al.19 in 1987 and its
crystal structure reported by Dickie et al.20 in 2007. The latter authors report that “care
must be taken in the preparation . . . to ensure that a large excess of Sn[N(SiMe3)2]2 is not
used in the reaction. In the absence of other reagents . . . Sn[N(SiMe3)2]2 will react with the
CH2Cl2 solvent to give the insertion product Sn(CH2Cl)Cl(NR2)2.” In this complex, the
coordinated CH2Cl ligand is available for nucleophilic attack at the carbon atom bearing
the chloride leaving group.
It seems reasonable to suggest that some amount of free Ph3P C C O and 2,4,6-
trimethylphenol remain in the solution. Drawing from the work of Benetollo et al.21 on
the reaction of Ph3P C C O with water, we speculate on what might occur if there
were some adventitious water present in the reaction mixture. Benetollo et al. describe the
addition of one equivalent of water to Ph3P C C O, in the usual El-Nu-type reaction
(Scheme 3), as giving [Ph3PC(H) C O]+OH− with its possible subsequent rearrangement
to the zwitterionic Ph3P+C(H) C(O−)OH.
With both species, Sn(CH2Cl)Cl(NR2)2 and Ph3P+C(H) C(O−)OH, present in the
solution, one can envision a subsequent reaction occurring between the negatively charged
oxygen of the hydrated Ph3P C C O and the CH2Cl ligand on the modified tin reagent,
with an elimination of Cl− from the ligand and a formation of an O C bond joining the

1550
M. G. MAKRAMALLA ET AL.
two fragments together. This would give [Ph3PC(H) C(OH)OCH2Sn(NR2)Cl]Cl, which
could eliminate HCl and rearrange to give the crystalline product that was isolated.
Consistent with this speculation, the reaction between Ph3P C C O and
Sn(CH2Cl)Cl(NR2)2 with no added 2,4,6-trimethylphenol returned only starting materials.
This could have been due to a lack of sufficient water in this particular case (unlikely
in view of our usual observance of hydrolysis products) or because the trimethylphenol
(a weak acid) actually plays a role in the proposed reaction sequence. The reaction was
repeated with Ph3P C C O, Sn(CH2Cl)Cl(NR2)2, and added water, and again none of
the crystalline products were obtained, suggesting that the presence of trimethylphenol is
necessary for the reaction to proceed. It seems likely that the acid helps to promote the
initial hydrolysis of Ph3P C C O.
In any event, multiple attempts to crystallize more of this product (or other products
in the reaction mixture) have failed, giving only gel-like semisolids. We speculate that this
is due to a hydrolysis process, which, in fact, is in agreement with Grutzmacher’s obser-
vations after multiple attempts to crystallize their product from Scheme 2 (as mentioned
previously).12
EXPERIMENTAL
General Experimental
An argon atmosphere dry box (MBraun Unilab, Stratham, NH) was used for the
manipulation and preparation of these compounds. UltraHighPurity 5.0 GP-529323 type
argon gas was used in all syntheses. Anhydrous solvents were dispensed directly from
an MBraun MB-SPS solvent system. IR spectra were obtained using a Bruker Vertex 70
infrared spectrophotometer (Bruker Optics, Billerica, MA) as either potassium bromide
pellets or as dichloromethane solutions between potassium bromide plates. NMR spectra
were obtained using Bruker Avance 500 MHz or AC-250 spectrometers. All melting points
(mps) were determined using a Barnstead Mel-Temp apparatus (Sybron Corp., Milwaukee,
WI). Elemental analyses were performed using a Perkin Elmer CHN analyzer (Waltham,
MA).
The NMR spectra were obtained at the Nuclear Magnetic Resonance Research Re-
1
source (NMR-3), Dalhousie University, Halifax, Canada. 1H and 13C{ H}/DEPTQ spectral
shifts are reported in relation to either known residual solvent peaks or tetramethylsilane
1
(TMS), where available. 31P{ H} spectral shifts were taken without internal calibration.
Synthetic Methods
Synthesis of 11 (Ph3PCCO (1) + TMP (7)). To a solution of (triphenylphos-
phoranylidene)ketene (302 mg, 1 mmol) in anhydrous dichloromethane (3 mL), was added
2,4,6-trimethylphenol (136 mg, 1 mmol). The solution was stirred and slow evaporation of
the solvent yielded beige, X-ray quality crystals. Yield = 0.41 g, 94%. mp = 159–161 ◦C.
1H NMR (500 MHz, CDCl3) δ (ppm): 7.81 (m, 4H, PPh3 Cortho H isomer 2), 7.69 (m,
6H, PPh3 Cortho H isomer 1), 7.56 (m, 5H, PPh3 Cpara H isomers 1 and 2), 7.48 (m, 10H,
PPh3 Cmeta H isomers 1 and 2), 6.80 (s, 2H, ligand Cmeta H isomer 1), 6.70 (s, 4/3H,
ligand Cmeta H isomer 2), 3.18 (d, 1H, Cylide H, 2JP = 21.7 Hz, isomer 1), 3.11 (d,
H
2/3H, Cylide H, 2JP
= 20.0 Hz, isomer 2), 2.23 (s, 6H, ligand CH3 ortho isomer 1),
H
2.22 (s, 3H, ligand CH3 para isomer 1), 2.18 (s, 2H, ligand CH3 para isomer 2), 1.73 (s,
4H, ligand CH3 ortho isomer 2). 13C{ H} NMR (500 MHz, CDCl3) δ (ppm): 169.8 (d,
1

REACTION OF Ph3P
C
C
O WITH ACIDIC H O/N BONDS
1551
2JP = 15.9 Hz), 134.0 (s), 133.6 (d, 2JP = 9.8 Hz), 133.0 (d, 2JP = 9.8 Hz), 132.3
C
C
C
(s), 131.5 (s), 131.3 (s), 129.1 (d, 3JP C = 12.4 Hz), 129.0 (s), 128.9 (s), 128.1 (d, 1JP
=
C
93 Hz), 127.9 (d, 1JP = 92 Hz), 31.1 (d, Cylide H, 1JP = 121 Hz, isomer 2), 30.7 (d,
C
C
1
Cylide H, 1JP = 128 Hz, isomer 1), 21.1 (s), 21.0 (s), 17.0 (s), 16.9 (s). 31P{ H} NMR
C
(500 MHz, CDCl3) δ (ppm): 19.11 (s, 1.00, isomer 1), 15.39 (s, 0.64, isomer 2). IR (KBr,
cm−1): 3063(w), 2921(w), 1639(s), 1583(s), 1478(s), 1442(s), 1345(s), 1307(w), 1203(w),
1086(s), 1022(w), 887(s), 741(s), 691(s), 539(w), 517(w). E.A. C29H27O2P: calculated C
79.43, H 6.21. Found C 78.90, H 6.07.
Synthesis of 12 (Ph3PCCO (1) + BHT (8)). To a solution of (triphenylphospho-
ranylidene)ketene (302 mg, 1 mmol) in anhydrous dichloromethane (3 mL), was added
2,6-di-tert-butyl-4-methylphenol (220 mg, 1 mmol). The solution was stirred and slow
evaporation of the solvent yielded beige, X-ray quality crystals. Yield = 0.43 g, 82%. mp =
168–170 ◦C. 1H NMR (500 MHz, CDCl3) δ (ppm): 7.74 (m, 6H, PPh3 Cortho H), 7.56 (m,
3H, PPh3 Cpara H), 7.45 (m, 6H, PPh3 Cmeta H), 7.04 (s, 2H, ligand Cmeta H), 3.36 (d,
1
1H, Cylide H, 2JP = 23.5 Hz), 2.27 (s, 3H, CH3), 1.39 (s, 18H, CH3 t-butyl). 13C{ H}
H
NMR (500 MHz, CDCl3) δ (ppm): 171.1 (d, 2JP C = 15.7 Hz), 147.9 (d, 4JP C = 2.8 Hz),
2
4
143.3 (s), 133.4 (d, JP = 10.3 Hz), 132.6 (s), 132.0 (d, JP = 1.8 Hz), 128.7 (d,
C
C
3JP C = 12.2 Hz), 127.9 (d, 1JP C = 92.5 Hz), 126.4 (s), 35.5 (s), 33.6 (d, Cylide H, 1J =
129 Hz), 31.7 (s), 30.5 (s), 21.7 (s). 31P{ H} NMR (500 MHz, CDCl3) δ (ppm): 18.8. IR
1
(KBr, cm−1): 3633(br), 3062(w), 3007(m), 2909(w), 2864(w), 1630(s), 1482(w), 1437(m),
1335(s), 1259(w), 1187(m), 1103(s), 890(s), 748(m), 717(m), 693(w), 570(m), 543(m),
518(m). E.A. C35H39O2P: calculated C 80.43, H 7.52, N 0.00. Found C 78.95, H 7.37, N
0.01.
Synthesis of 13 (Ph3PCCO (1) + Ph2NH (9)). To a solution of (triphenylphos-
phoranylidene)ketene (302 mg, 1 mmol) in anhydrous dichloromethane (3 ml), was added
diphenylamine (170 mg, 1 mmol). Slow evaporation of the solvent yielded light brown, X-
ray quality crystals. Yield = 0.42 g, 89%. mp = 134–138 ◦C. 1H NMR (500 MHz, CDCl3)
δ (ppm): 7.65 (m, 6H, PPh3 Cortho H), 7.52 (m, 3H, PPh3 Cpara H), 7.44 (m, 6H, PPh3
Cmeta H), 7.31 (m, 4H, NPh2 Cmeta H), 7.25 (m, 4H, NPh2 Cortho H), 7.06 (m, 2H, NPh2
1
Cpara H), 2.82 (d, 1H, Cylide H, 2JP = 23.7 Hz). 13C{ H} NMR (500 MHz, CDCl3) δ
H
(ppm): 171.8 (d, 2JP C = 11.4 Hz), 146.2 (s), 133.2 (d, 2JP C = 10.1 Hz), 131.8 (d, 4JP
=
C
2.0 Hz), 128.8 (d, 3JP C = 12.2 Hz), 128.2 (d, 1JP C = 127 Hz), 128.2 (s), 127.7 (s), 124.2
(s), 37.7 (d, Cylide H, 1JP C = 128 Hz). 31P{ H} NMR (500 MHz, CDCl3) δ (ppm): 17.7.
1
IR (KBr, cm−1): 3266(w), 3118(w), 2095(w), 1590(s), 1550(s), 1493(s), 1435(m), 1363(s),
1315(m), 1239(m), 1176(w), 1138(w), 1103(s), 1071(w), 1024(w), 945(m), 878(m), 747(s),
692(s), 521(s). E.A. C32H26NOP: calculated C 81.51, H 5.56, N 2.97. Found C 80.71, H
5.77, N 3.30.
Synthesis of 14 (Ph3PCCO (1) + TMP (7) + CH3I). To a solution of 11 (440 mg,
1 mmol) in anhydrous dichloromethane (15 mL), was added iodomethane (140 mg, 1 mmol)
dissolved in anhydrous dichloromethane (5 mL). Subsequently, 1 mL of benzene was added.
The solution was stirred and slow evaporation of the solvent yielded beige, X-ray quality
crystals. Yield = 0.36 g, 79%. mp = 172–176 ◦C. 1H NMR (500 MHz, CDCl3) δ (ppm):
8.00 (m, 6H, PPh3 Cortho H), 7.69 (m, 3H, PPh3 Cpara H), 7.60 (m, 6H, PPh3 Cmeta H),
7.32 (m, 1H, C(CH3) H), 6.68 (s, 2H, ligand Cmeta H), 2.13 (s, 3H, ligand CH3 ortho),
2.11 (s, 3H, ligand CH3 ortho), 1.84 (s, 3H, ligand CH3 para), 1.82 (q, 3H, C(H) CH3,
1
3JH = 7.3 Hz). 13C{ H} NMR (500 MHz, CDCl3) δ (ppm): 167.6 (s), 145.6 (s), 136.3
H
4
2
3
(s), 135.2 (d, JP = 2.4 Hz), 134.6 (d, JP = 9.8 Hz), 130.5 (d, JP = 12.8 Hz),
C
C
C
129.5 (s), 117.8 (d, 1JP = 87 Hz), 38.0 (d, C(CH3) H, 1JP = 57 Hz), 25.2 (s), 20.9
C
C

1552
M. G. MAKRAMALLA ET AL.
2
1
(s), 16.8 (d, JP = 40 Hz), 16.23 (s), 13.5 (s). 31P{ H} (500 MHz, CDCl3) δ (ppm):
C
27.8. IR (CH2Cl2 solution, cm−1): 3054(s), 2986(s), 2306(w), 1740(s), 1589(w), 1484(s),
1440(s), 1266(s), 1187(m), 1110(m), 998(w), 896(s), 856(w), 747(s), 527(w).
Synthesis of 15 (Ph3PCCO (1) + TMP (7) + Sn[N(TMS)2]2 (10)). To a
mixed solution of (triphenylphosphoranylidene)ketene (302 mg, 1 mmol) in anhydrous
dichloromethane (5.0 mL) and 2,4,6-trimethylphenol (136 mg, 1 mmol) in benzene
(5.0 mL), bis[bis(trimethylsilyl)amido]tin(II) (2.3 mL, 1 mmol) was added slowly with
stirring. Slow evaporation of the solvent yielded light orange, X-ray quality crystals. Yield
1
= 0.54 g. mp = 163–166 ◦C. Isolated as a mixture as indicated by the 1H and 31P{ H} NMR
studies, which are ongoing. Sample also possibly wet. IR (KBr, cm−1): 3423(w), 3055(w),
2954(w), 2176(w), 1721(w), 1585(m), 1563(m), 1546(m), 1484(m), 1437(s), 1339(w),
1311(w), 1260(w), 1245(w), 1190(m), 1118(s), 1026(w), 997(w), 903(m), 836(m), 749(m),
721(s), 694(s), 542(s), 507(m).
X-ray Crystallography. In all studies, the crystals were attached to the tip of a
nylon loop with paratone-N oil. All measurements were made on a Bruker APEXII CCD-
equipped diffractometer (30 mA, 50 mV) using monochromated Mo Kα radiation (λ =
0.71073 Å) at 100 K (13, 14), 130 K (15), or 150 K (11, 12).22 The initial orientation
and unit cell were indexed using a least-squares analysis of a random set of reflections
collected from three series of 0.5◦ ω-scans, 10 s per frame and 12 frames per series, that
were well distributed in reciprocal space. For data collection, four ω-scan frame series were
collected with 0.5◦ wide scans, 30 s frames and 606 frames per series at varying ϕ angles
(ϕ = 0◦, 90◦, 180◦, 270◦). The crystal to detector distance was set to provide a complete
6 cm sphere of data. Cell refinement and data reduction were performed with the Bruker
SAINT software,23 which corrects for beam inhomogeneity, possible crystal decay, Lorentz
and polarization effects. A multiscan absorption correction was applied (SADABS).24 The
structures were solved using direct methods (SHELXS-97)25 and refined by full-matrix
least-squares method on F2 with SHELXL-97.25 The nonhydrogen atoms were refined
anisotropically. For the most part, hydrogen atoms bonded to carbon were included at
geometrically idealized positions and were not refined. The isotropic thermal parameters
of the hydrogen atoms were fixed at 1.2Ueq of the parent carbon atom, 1.5Ueq for methyl
hydrogens. The only exceptions were the hydrogen atoms bonded to the ylidic carbon atom
of the ketene in the substituted products (11, 12, 13, and 14). These atoms were located
in the Fourier difference map and refined isotropically. In structure 15, which contains the
heavy tin atom, the results were better when all of the hydrogen atoms were fixed rather
than refined. There was nothing unusual observed in any of these refinements although,
in general, the crystals were rather weak diffractors. Details of the individual refinements
are listed in Table 2. Selected bond lengths and bond angles are listed in Tables 3 and 4,
respectively.
Supplementary Data
CCDC 873916–873920 contain the supplementary crystallographic data for this
paper: 873916 for Ph3PCHC(O)O(C6H2Me3) (11), 873917 for Ph3PCHC(O)O(C6H2t-
Bu2Me) (12), 873918 for Ph3PCHC(O)NPh2 (13), 873919 for [Ph3PCH(CH3)C(O)O(C6H2
Me3)]I (14), and 873920 for the chelated tin compound (15). These data can be obtained
free of charge via www.ccdc.cam.ac.uk/retrieving.html (or from the Cambridge Crystallo-
graphic Data Centre, 12, Union Road, Cambridge, B2 1EZ, UK; fax +44 1223 336033; or
deposit@ccdc.cam.ac.uk).

REACTION OF Ph3P
C
C
O WITH ACIDIC H O/N BONDS
1553
CONCLUSIONS
Three novel carbonyl ylide derivatives of ketenylidenetriphenylphosphorane—11, 12,
and 13—have been successfully synthesized in high yields and subsequently characterized.
The disappearance of the C C O peak (∼2110 cm−1) from the IR of the starting material
and the appearance of ν(C O) peaks (∼1600 cm−1) in the spectra of the products, along
1
with the observed 31P{ H} NMR signal shift, provided evidence that new compounds
had been formed. The structure of each of the new derivatives was confirmed by X-ray
crystallography. In addition, attempts were made to methylate these products; however, this
was only successful for the reaction of 11 with CH3I, where 14 was successfully isolated
and characterized. Unfortunately, the methylation did not occur at the carbonyl oxygen site
as had been desired. Instead, it occurred at the ylidic carbon as calculations had suggested
it might. This limits the synthetic utility of these compounds as precursors to low-valent
carbon species. Finally, the reaction of 12 (generated in situ from 1 and 7) with a bulky metal
center gave a somewhat unanticipated product(s). NMR results suggested that a mixture of
compounds had been formed. Crystals of one product (15) were isolated and structurally
characterized using X-ray crystallography. Elimination of ArOH must be followed by the
reaction of the ketenylidenetriphenylphosphorane, water, solvent (CH2Cl2), and tin reagent
to give the isolated chelated ring structure. Several attempts to obtain more crystals of the
product(s) failed due to the high moisture sensitivity of the reagents. This we think is due
to a hydrolysis process, which will be investigated further.
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