A synthetic cycle for the ruthenium-promoted formation of 1H-phosphindoles from phosphaalkynes

Article abstract of DOI:10.1021/ja0651198

Beginning with inexpensive and commercially available starting materials, a rational synthesis for the new phosphaalkyne Ph₃C-C≡P (1) is presented. Coordination of 1 to group 8 transition metal centers furnishes the η¹-complexes [MH(

Full text of DOI:10.1021/ja0651198

Published on Web 10/27/2006
A Synthetic Cycle for the Ruthenium-Promoted Formation of
1H-Phosphindoles from Phosphaalkynes
Joseph G. Cordaro, Daniel Stein, and Hansjo¨rg Gru¨tzmacher*
Contribution from the Department of Chemistry and Applied Biosciences, ETH-Zu¨rich,
HCI H131, CH-8093 Zu¨rich, Switzerland
Received July 18, 2006; E-mail: gruetzmacher@inorg.chem.ethz.ch
Abstract: Beginning with inexpensive and commercially available starting materials, a rational synthesis
for the new phosphaalkyne Ph3C-CtP (1) is presented. Coordination of 1 to group 8 transition metal
centers furnishes the η1-complexes [MH(dppe)2(Ph3CCtP)]OTf, where M ) Fe (3) or Ru (4) (dppe ) bis-
1,2-diphenylphosphinoethane). Treatment of 3 or 4 with a strong acid cyclizes the coordinated phospha-
alkyne and is the first example of an electrophilic aromatic substitution reaction in which the electrophile is
a low coordinate phosphorus. With the aid of DFT calculations, we were able to gain a more thorough
understanding of the energetics and mechanism of this new cyclization reaction. Thermolysis of the iron-
3,3-diphenyl-3H-phosphindole adduct (6) in CH3CN results in quantitative formation of the free 3H-
phosphindole (7). Alternatively, when ruthenium-3,3-diphenyl-3H-phosphindole adduct (5) is irradiated, a
photochemical rearrangement occurs furnishing 2,3-diphenyl-1H-phosphindole (9). Mechanistic work is
presented that provides an explanation for this transformation. Compounds 1, 3, 5, and 9 have been
characterized by single X-ray diffraction studies. Finally, a synthetic cycle for the conversion of 1 to 1H-
phosphindole 9 has been developed that recycles the ruthenium cation [RuH(dppe)2]+.
Chart 1
Introduction
Heterocycles containing a low-coordinated phosphorus center1-3
have found widespread applications ranging from ligands in
transition metal complexes4 to devices in material science.5
Specifically, phospholes I, phosphindoles (benzophospholes) II,
and dibenzophospholes III have been extensively studied (Chart
1). In view of the potential of these compounds, economic
synthetic routes are desirable with the ultimate goal of finding
catalytic pathways using readily available starting materials.
Some years ago, we studied the use of highly electrophilic
methylene phosphonium ions IV6-8 in electrocyclic ring closure
reactions leading to benzo-λ5-phosphetes and naphtho-λ5-
phosphetes V.9,10 Phosphavinylium ions VI are a class of highly
electrophilic and reactive low-valent phosphorus compounds that
are potentially suitable precursors for comparable electrocyclic
ring closures. Previously, these ions have been proposed as
intermediates in the protonation of phosphaalkynes under
superacidic conditions.11 Some donor-stabilized phospha-
vinylium ions include Ph3P f PdC(SiMe3)2 VII,12 the cyclic
intramolecularly stabilized aza-phosphirenylium ion VIII (gen-
erated in the gas-phase only), and the diphosphirenylium ion
IX.13,14 We report here the synthesis of phosphindoles via an
electrocyclic ring closure reaction using suitable and easily
accessible group 8 phosphaacetylene complexes as precursors.
Although not catalytic, we developed this reaction into a
complete synthetic cycle.
(1) Mathey, F. Phosphorus-Carbon Heterocyclic Chemistry: The Rise of a
New Domain; Elsevier Science: Oxford, 2001; p 856.
(2) Mathey, F. Chem. ReV. 1988, 88, 429.
(3) Dillon, K. B.; Mathey, F.; Nixon, J. F. Phosphorus: The Carbon Copy:
From Organophosphorus to Phospha-organic Chemistry; Wiley & Sons:
West Sussex, 1998.
(4) Weber, L. Angew. Chem., Int. Ed. 2002, 41, 563.
(5) Casado, J.; Reau, R.; Navarrete, J. T. L. Chem.-Eur. J. 2006, 12, 3759.
(6) Thomaier, J.; Alcaraz, G.; Gru¨tzmacher, H.; Hillebrecht, H.; Marchand,
C.; Heim, U. J. Organomet. Chem. 1997, 535, 91.
(7) Guerret, O.; Bertrand, G. Acc. Chem. ReV. 1997, 30, 486.
(8) Gru¨tzmacher, H.; Marchand, C. M. Coord. Chem. ReV. 1997, 163, 287.
(9) Heim, U.; Pritzkow, H.; Fleischer, U.; Gru¨tzmacher, H.; Sanchez, M.; Reau,
R.; Bertrand, G. Chem.-Eur. J. 1996, 2, 68.
(10) Heim, U.; Pritzkow, H.; Fleischer, U.; Gru¨tzmacher, H. Angew. Chem.,
Int. Ed. 1993, 32, 1359.
(11) Laali, K. K.; Geissler, B.; Regitz, M.; Houser, J. J. J. Org. Chem. 1995,
60, 6362.
(12) David, G.; Niecke, E.; Nieger, M.; Radseck, J.; Schoeller, W. W. J. Am.
Chem. Soc. 1994, 116, 2191.
(13) Soleilhavoup, M.; Canac, Y.; Polozov, A. M.; Baceiredo, A.; Bertrand, G.
J. Am. Chem. Soc. 1994, 116, 6149.
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4863.
9
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J. AM. CHEM. SOC. 2006, 128, 14962-14971
10.1021/ja0651198 CCC: $33.50 © 2006 American Chemical Society

Synthetic Cycle for Formation of 1H-Phosphindoles
A R T I C L E S
Scheme 1. Protonation of 1 Leading to 1-P-allyl or 3H-P-Indole;
Scheme 2. Calculated Formation of H-CP
Structures are Computed
Scheme 3. Synthesis of New Phosphaalkyne 1
Results and Discussion
Computational Studies. The protonation of various phospha-
alkynes, R-CtP (R ) H, alkyl, SiMe3, F, NO2), has been
computed prior to our own work, and with the exception of
H-CtP, hydrogen-bridged species were formed; R2N-CtP
species give P-protonated cations as minima.11,15
be exothermic by -15.5 kcal mol-1, and hence, this would be
an attractive new method to prepare the elusive H-CtP.21
However, a rather high activation barrier (25.3 kcal mol-1) is
predicted for this process so that 3H-phosphindole formation
may compete with trityl cation dissociation (d). In light of these
computational results, we decided to investigate synthetic meth-
ods for accessing phosphaalkyne 1. To prevent P-protonation
and rearrangement (a), we envisioned blocking this reaction
pathway by complexation to an inert metal fragment. The
following describes the outcome of our experimentation.
Synthesis of Phosphaalkyne 1. While the isolation of
numerous hydrocarbon-substituted phosphaalkynes, R-CtP (R
) tBu,22 adamantyl,23 Mes ) 2,4,6-Me3C6H2,24 Mes* ) 2,4,6-
tBu3C6H225) has been reported since the initial discovery of
H-CtP, their preparative methods can be cumbersome; isolated
yields are often low, and their stability toward oligomerization
For our purposes, we chose the triphenylmethyl substituted
phosphaalkyne, Ph3C-CtP 1, which is especially simple to
synthesize and isolate (vide infra). DFT calculations were carried
out by implementing the B3LYP exchange-correlation func-
tional16-18 with the 6-31G* basis set using Gaussian 03.19 The
results are shown in Scheme 1 (see SI for details). Protonation
of 1 at the terminal phosphorus center with H3O+ as acid did
not lead to a stable minimum structure of [Ph3C-CCPH]+.
Rather, minimization with a 2,1-phenyl shift gave a distorted
1-phosphaallyl cation, 1-P-allyl. Reaction (a) is exothermic by
∆Gr298 ) -66.6 kcal mol-1 (zero-point energies and thermal
corrections at 298 K were obtained from frequency calculations).
C-protonation of 1, reaction (b), is 20 kcal mol-1 less exothermic
but leads to a cyclic structure that is best described as an
intramolecular σ-complex between the phosphavinylium moiety
and one phenyl group. The calculated CdP distance (1.680 Å)
in σ-Ph3C-CHdP+ is rather long when compared to the above-
mentioned phosphavinylium ions (Chart 1, calculated distances
<1.60 Å) and more typical of a PdC double bond. The P‚‚‚
Carene interaction at 2.050 Å is considerably longer than usual
P-C bonds (∼1.86 Å, see also ref 10) but is not unusual for
comparable σ-type complexes.20 The stabilization provided by
the P‚‚‚Carene interaction likely contributes to the elongated PdC
double bond. Deprotonation of σ-Ph3C-CHdP+ gives the 3H-
phosphindole, 3H-P-indole, but reaction (c) is endothermic by
t
is poor. Even the syntheses of Bu-CP and Ad-CP require
multiple steps, expensive reagents, and arduous reaction condi-
tions. The conventional synthetic method for generating R-CtP
compounds utilizes P(SiMe3)3 and relies on a base-initiated
elimination of hexamethyldisiloxane from an R(Me3SiO)Cd
PSiMe3 phosphaalkene.26-28 Our attempts to synthesize the
corresponding triphenylmethyl substituted phosphaalkene from
the acid chloride Ph3CCOCl and P(SiMe3)3 were unsuccessful.
Alternatively, we explored a more economical, atom-efficient
route for accessing phosphaalkynes. Scheme 3 outlines our
approach, which exploits PCl3 rather than P(SiMe3)3 as an
abundant source of phosphorus.29 From inexpensive and readily
available reagents, two synthetic steps were required to access
28.9 kcal mol-1
.
The dissociation (d) of the triphenylmethyl (trityl) cation from
σ-Ph3C-CHdP+ is another reaction channel for this stabilized
phosphavinyl cation (Scheme 2). This reaction is calculated to
(21) Gier, T. E. J. Am. Chem. Soc. 1961, 83, 1769.
(22) Becker, G.; Gresser, G.; Uhl, W. Z. Naturforsch. 1981, 36B, 16.
(23) Allspach, T.; Regitz, M.; Becker, G.; Becker, W. Synthesis 1986, 31.
(24) Mack, A.; Pierron, E.; Allspach, T.; Bergstrasser, U.; Regitz, M. Synthesis
1998, 1305.
(15) Esteves, P. M.; Laali, K. K. Organometallics 2004, 23, 3701.
(16) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys. 1980, 58, 1200.
(17) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(18) Lee, C. T.; Yang, W. T.; Parr, R. G. Phys. ReV. B 1988, 37, 785.
(19) Pople, J. A.; et al. Gaussian 03, revision C.02; Gaussian, Inc.: Wallingford,
CT, 2004.
(20) Letzel, M.; Kirchhoff, D.; Gru¨tzmacher, H. F.; Stein, D.; Gru¨tzmacher, H.
J. Chem. Soc., Dalton Trans. 2006, 2008.
(25) Toyota, K.; Kawasaki, S.; Yoshifuji, M. J. Org. Chem. 2004, 69, 5065.
(26) Regitz, M.; Binger, P. Angew. Chem., Int. Ed. 1988, 27, 1484.
(27) Regitz, M. Chem. ReV. 1990, 90, 191.
(28) Markovski, L. N.; Romanenko, V. D. Tetrahedron 1989, 45, 6019.
(29) Phosphaalkynes have been synthesized via flash vacuum thermolysis of
alkyl-substituted dichlorophosphanes. See: Pellerin, B.; Denis, J. M.;
Perrocheau, J.; Carrie, R. Tetrahedron Lett. 1986, 27, 5723.
9
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A R T I C L E S
Cordaro et al.
While the dehydrohalogenation reaction of 2 to synthesize 1
must be carried out under inert conditions, the product itself is
stable and a sample of 1 in C6D6 showed no degradation after
more than two weeks when exposed to air. With respect to the
computed protonation reaction discussed above, reactions of 1
with various acids were studied. Remarkable was the inertness
of 1 toward a 1 M solution of HCl etherate, as determined by
the unchanged 1H and 31P NMR spectra. Reversion of 1 to the
alkyl phosphonous dichloride 2 or a chloro-substituted phospha-
alkene was never observed. Tosyl sulfonic acid (TsOH) was
also unreactive with 1. Protonation of 1 with stronger acids such
as trifluoromethanesulfonic acid (TfOH) gave inconclusive
results, even when the reaction was monitored in situ at low
temperature by NMR spectroscopy. Lewis acids such as
triphenyl- or perfluorophenyl borane showed no reactivity with
1, whereas GaCl3 reacted to give unidentifiable products.
Figure 1. Structure of 1. Thermal ellipsoids are drawn at 50% probability.
Selected bond lengths [Å] and angles [deg]: P1-C1, 1.538(2); C1-C2,
1.485(2); P1-C1-C2, 178.5(2); C10-C2-C20, 111.4(1); C20-C2-C30,
110.5(1); C10-C2-C30, 110.1(1).
(2,2,2-triphenylethyl) phosphonous dichloride (2) in moderate
yield (>58%) but on a multigram scale. Compound 2 was
characterized by multinuclear NMR, IR, and mass spec-
troscopies, and EA.
Synthesis of Metal-Phosphaalkyne Complexes. The com-
plexation of phosphaalkynes to transition metal centers is well-
documented, and various coordination modes have been re-
ported.34,35 Typically, η2-coordination to the metal via the
phosphorus-carbon π-bond is observed.36 Only when bulky
ligands surround the metal center is the less common η1- or
σ-coordination mode (via the lone pair of electrons at phos-
phorus) observed.37-40 We envisioned that by coordination of
1 to a metal, protonation would selectively occur at the carbon
center, thus eliminating undesired side reactions. The choice to
Various reaction conditions and bases were screened in order
to effect the dehydrochlorination of 2. Treatment of 2 with
anionic bases such as tert-butoxide or bis(trimethylsilyl)amide
resulted in chloride substitution rather than deprotonation. Both
n- and tert-butyl lithium reacted with 2 to give mixtures of
inseparable products. Tertiary amines showed varied reactivity.
While 1,9-bis(dimethylamino)-naphthalene (proton sponge) was
unreactive toward 2, the bicycloamines 1,5-diazabicyclo[4.3.0]-
non-5-ene (DBN) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)
reacted with 2 to give salts that were insoluble in nonpolar
organic solvents and decomposed upon attempted isolation
(similar reactivity has been reported30,31).
Treatment of 2 with 10 equiv of 1,8-diazabicyclo[2.2.2]octane
(DABCO) in hot acetonitrile furnished one new product with a
31P NMR chemical shift at δ ) -48.2 ppm, within the expected
range for a phosphaalkyne. No intermediate species were
observed when the reaction was monitored in situ by NMR
spectroscopy. Identification of this product as Ph3CCtP (1) was
made by multinuclear NMR spectroscopies, MS, and single-
crystal X-ray diffraction. Optimization of the reaction conditions
allowed for the isolation of phosphaalkyne 1 on a multigram
scale in approximately 64% yield.
Spectroscopic data for 1 are in accord with other known
phosphaalkynes. A doublet in the 13C NMR at δ ) 177.6 ppm
(1JC-P ) 40.6 Hz) was indicative of the alkynyl carbon. The
â-carbon (C2) was found at δ ) 64.0 ppm (2JCP ) 18.7 Hz)
while the aryl carbon resonances were located in the region
between 145 and 126 ppm. In the Raman spectrum, a strong
signal at 1512 cm-1 was observed for the CP triple bond.
Colorless crystals suitable for X-ray diffraction were grown
from a concentrated solution of 1 in toluene at -30 °C. A
molecular representation of 1 is shown in Figure 1. The
propeller-like orientation of the aryl substituents leaves the
phosphorus-carbon triple bond unhindered. With a nearly linear
P1-C2-C3 angle (178.50°) and a carbon-phosphorus bond
length of 1.538 Å, the structure of 1 is similar to those of other
phosphaalkynes.32,33
+
use the MH(dppe)2 fragment (dppe ) 1,2-bis(diphenylphos-
phino)ethane) was based upon the easily accessible starting
materials, convenience of having numerous NMR active nuclei
with which to monitor the reaction, and the sheltered pocket
around the metal created by the dppe ligands which leaves one
open coordination site when M has a d6 electronic configuration.
+
Furthermore, Nixon et al. previously employed FeH(dppe)2
t
to successfully isolate an η1-complex with Bu-CtP.40,41
Coordination of 1 to iron and ruthenium cations was
straightforward. Treatment of [MH(dppe)2]+ with 1 in dichloro-
methane42 furnished the desired iron(II) (3) and ruthenium(II)
(4) complexes in almost quantitative yield (Scheme 4). Con-
firmation that the phosphaalkyne coordinated to the metal center
was obtained via 31P{1H} NMR spectroscopy; a new quintet
was observed at a higher frequency relative to free 1 [3: δ )
0.94 ppm, (qnt, 2JPP ) 35.1 Hz). 4: δ ) -27.3 ppm, (qnt, 2JPP
) 27.5 Hz)]. Further evidence for the complexation of 1 to the
metal was seen by the AXY4 splitting pattern of the hydride
1
resonance in the H NMR spectrum. Coupling of the hydride
ligand to both the coordinated phosphaalkyne and four chemi-
cally equivalent phosphorus nuclei of the ancillary dppe ligands
resulted in the observed doublet of quintets and indicated that
(33) Arif, A. M.; Barron, A. R.; Cowley, A. H.; Hall, S. W. J. Chem. Soc.,
Chem. Commun. 1988, 171.
(34) Nixon, J. F. Coord. Chem. ReV. 1995, 145, 201.
(35) Nixon, J. F. Chem. ReV. 1988, 88, 1327.
(36) Burckett-St. Laurent, J. C. T. R.; Hitchcock, P. B.; Kroto, H. W.; Nixon,
J. F. J. Chem. Soc., Chem. Commun. 1981, 1141.
(37) Hitchcock, P. B.; Maah, M. J.; Nixon, J. F.; Zora, J. A.; Leigh, G. J.;
Abubakar, M. Angew. Chem., Int. Ed. 1987, 26, 474.
(38) Groer, T.; Baum, G.; Scheer, M. Organometallics 1998, 17, 5916.
(39) Bedford, R. B.; Hill, A. F.; Wilton-Ely, J. D. E. T.; Francis, M. D.; Jones,
C. Inorg. Chem. 1997, 36, 5142.
(40) Meidine, M. F.; Lemos, M. A. N. D. A.; Pombeiro, A. J. L.; Nixon, J. F.;
Hitchcock, P. B. J. Chem. Soc., Dalton Trans. 1998, 3319.
(41) Hitchcock, P. B.; Lemos, M. A. N. D. A.; Meidine, M. F.; Nixon, J. F.;
Pombeiro, A. J. L. J. Organomet. Chem. 1991, 402, C23.
(42) The Fe(II) cation was synthesized in situ after salt metathesis with KOTf.
See Experimental Section for details.
(30) Reed, R.; Reau, R.; Dahan, F.; Bertrand, G. Angew. Chem., Int. Ed. 1993,
32, 399.
(31) Bouhadir, G.; Reed, R. W.; Reau, R.; Bertrand, G. Heteroat. Chem. 1995,
6, 371.
(32) Oberhammer, H.; Becker, G.; Gresser, G. J. Mol. Struct. 1981, 75, 283.
9
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Synthetic Cycle for Formation of 1H-Phosphindoles
A R T I C L E S
Scheme 4. Coordination of 1 to Fe and Ru Cations
the phosphaalkyne was coordinated trans to the hydride [3: δ
) -12.03 ppm; 4: δ ) -9.44 ppm]. The magnitude of the
trans H-P coupling was significantly larger for ruthenium
complex 4 (trans-2JHP ) 129.6 Hz) compared to iron complex
3 (trans-2JHP ) 58.6 Hz); the latter being comparable to the
value reported for [FeH(dppe)2(tBu-CtP)]+.40 The cis couplings
showed the opposite behavior and are larger for 3 (cis-2JHP
52.8 Hz) when compared to 4 (cis-2JHP ) 17.4 Hz).
)
Figure 2. Structure of the cationic portion of 3. Hydrogen atoms are omitted
for clarity. Thermal ellipsoids are drawn at 30% probability. Selected bond
lengths [Å] and angles [deg]: P1-C1, 1.535(2); C1-C2, 1.495(3); Fe1-
P1, 2.1645(6); Fe1-P2, 2.2704(6); Fe1-P3, 2.2902(6); Fe1-P4, 2.2792(6);
Fe1-P5, 2.2683(6); P1-C1-C2, 174.6(2); C1-P1-Fe1, 172.95(9) C1-
C2-C20, 107.6(2); C20-C2-C30, 110.9(2); C10-C2-C30, 108.7(2); P1-
Fe1-P2, 97.57(2); P1-Fe1-P3, 96.95(2); P1-Fe1-P4, 95.05(2); P1-
Fe1-P5, 97.15(2); P2-Fe1-P3, 84.45(2); P3-Fe1-P5, 93.74(2); P5-
Fe1-P4, 83.71(2); P4-Fe1-P2, 95.01(2).
Both solids could be crystallized from CH2Cl2 layered with
hexane or THF layer with toluene at room temperature. Yellow
crystals of 3 suitable for X-ray analysis were obtained from a
supersaturated toluene solution. A molecular representation is
depicted in Figure 2. The results of the study confirm an η1-
coordination of 1 to iron. The Fe-P1 (phosphaalkyne) bond
length of 2.165(6) Å is slightly longer than in the analogous
[FeH(dppe)2(tBu-CtP)]+ complex.40 The PtC bond (1.535(2)
Å) does not change significantly upon coordination to iron. A
slight bend in the P-C-C bond angle of coordinated 1 is
observed in the solid state, although the overall geometry
remains linear.
Additional 2-D NMR experiments suggested that two aryl rings
of the coordinated phosphaalkyne ligand remained equivalent
while the third was significantly perturbed compared to 4 and
also lacked a fifth proton. All the NMR data suggested the
formation of a new phosphaalkene heterocycle in which one
aryl ring of the Ph3C group underwent an electrophilic aromatic
cyclization reaction to furnish a coordinated 3,3-diphenyl-3H-
phosphindole (7) in nearly quantitative yield.
By slow evaporation of a THF/toluene solution of 5, crystals
suitable for X-ray analysis were obtained. The results confirm
the structure of the new heterocyclic ligand coordinated to
ruthenium (Figure 3). The trigonal planar geometry around the
coordinated phosphorus is expected for such a phosphindole.
Selected bond lengths and angles are given in the caption.43
In view of the computational results discussed above, we
propose that the formation of 5 occurs upon protonation at the
alkynyl carbon C2, to give a highly electrophilic Ru-complexed
phosphavinylium ion (Scheme 5). As seen in the free ion
σ-Ph3C-CHdP+, stabilization of this intermediate phospha-
vinylium cation complex by π-arene interaction leads to an
electrophilic aromatic cyclization reaction. This reaction re-
sembles the Bischler-Napieralski ring closure, in which the
carbon atom of a nitrilium group is attacked by an internal
nucleophile.44
Complexes 3 and 4 were both found to be stable toward water.
Iron complex 3 reacted with TfOH or MeOTf to give large
amounts of unidentifiable paramagnetic products (vide infra).
The reactivity of ruthenium complex 4, however, was more
easily monitored due to the preferred low spin d6 electronic
configuration. Therefore, our initial focus was on this complex.
Phosphindole Synthesis. The reaction of 4 with strong acids
such as TfOH or TsOH at low temperature in CD2Cl2 resulted
in the formation of one new product, compound 5. A quintet at
δ ) 232 ppm accompanied by a doublet at δ ) 62 ppm was
observed by 31P{1H} NMR spectroscopy. In the 1H-coupled 31
P
NMR spectrum, the signal at δ ) 232 became a complex
multiplet with coupling to at least three hydrogen nuclei. The
1H NMR spectrum of this new product exhibited equally
complex resonances. While a doublet of quintets at δ ) -8.57
ppm indicated a hydride ligand cis to two dppe ligands and
trans to one additional phosphorus nucleus, numerous other
resonances ranging from δ ) 8.2 to 5.32 ppm did not give a
clear indication of the new product.
Attempts were made to isolate the free 3H-phosphindole 7.
Thermolysis of an acetonitrile solution of 5 gave no reaction
even with added chloride until above 120 °C, at which point
much decomposition occurred. However, photolysis of 5 in a
solution of CH3CN using a medium pressure Hg lamp gave
cleanly the acetonitrile adduct [RuH(dppe)2(CH3CN)]+ (8) and
a new phosphorus product (9) with a 31P NMR chemical shift
Multinuclear 2-D NMR experiments (HMQC, TOCSY,
NOESY) were used to elucidate the structure of 5. From the
1H-31P HMQC correlation experiment, strong coupling was
observed between the doublet at δ(1H) ) 8.2 ppm and the
multiplet at δ(31P) ) 232 ppm with JHP ) 26.8 Hz. Three aryl
proton resonances at δ ) 6.65, 6.00, and 5.38 ppm were also
found to have cross-peaks with the signal at δ(31P) ) 232 ppm.
1
On the basis of the H-13C correlation experiment, it was
(43) An uncoordinated 3,3-dimethyl-3H-phosphindole was reportedly synthesized
by gas-phase pyrolysis. See: Aitken, R. A.; Clasper, P. N.; Wilson, N. J.
Tetrahedron Lett. 1999, 40, 5271.
determined that the proton resonating at δ ) 8.2 ppm was
bonded to a carbon found at δ ) 172.4 ppm (JC-P ) 36.5 Hz).
(44) Fodor, G.; Phillips, B. A.; Gal, J. Angew. Chem., Int. Ed. 1972, 11, 919.
9
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A R T I C L E S
Cordaro et al.
Figure 4. Structure of 9. Thermal ellipsoids are drawn at 50% probability.
Selected bond lengths [Å] and angles [deg]: P1-C1, 1.830(2); C1-C2,
1.357(2); C2-C3, 1.467(2); C3-C4, 1.410(3); C4-P1, 1.808(2); P1-C1-
C2, 111.5(1); C1-C2-C3, 113.9(2); C2-C3-C4, 113.5(2); C3-C4-P1,
110.3 (1); C4-P1-C1, 90.36(8).
the ruthenium cation 8 was achieved by simply removing the
volatile materials under reduced pressure followed by extraction
with diethyl ether. Using 2-D NMR spectroscopy, the structure
of 9 was determined to be the rearranged 1H-phosphindole,
rather than the 3H-phosphindole 7, which would arise from
simple cleavage of the Ru-P bond. To confirm the identity of
9, single crystals suitable for X-ray analysis were grown from
a concentrated solution in diethyl ether at -30 °C. As predicted
from NMR spectroscopic data, the structure of 2,3-diphenyl-
1H-phosphindole (9) was confirmed by a single-crystal X-ray
diffraction study and, to the best of our knowledge, is the first
structurally characterized 1H-phosphindole (Figure 4).
Figure 3. Structure of the cationic portion of 5. Hydrogen atoms are omitted
for clarity. Thermal ellipsoids are drawn at 30% probability. Selected bond
lengths [Å] and angles [deg]: P1-C1, 1.664(4); C1-C2, 1.519(5); C2-
C3, 1.525(6); C3-C4, 1.392(6); C4-P1, 1.819(4); Ru1-P1, 2.327(2); Ru1-
P2, 2.351(1); Ru1-P3, 2.369(1); Ru1-P4, 2.370(1); Ru1-P5, 2.372(1);
P1-C1-C2, 116.5(3); C1-C2-C3, 105.1(3); C2-C3-C4, 114.9(4); C3-
C4-P1, 111.1(3); C4-P1-C1, 92.4(2); P1-Ru1-P2, 99.38(4); P1-Ru1-
P3, 97.38(4); P1-Ru1-P4, 94.90(4); P1-Ru1-P5, 92.07(4); P2-Ru1-
P3, 83.29(5); P3-Ru1-P5, 95.09(5); P5-Ru1-P4, 82.64(5); P4-Ru1-
P2, 96.51(5).
Note that, in the course of the remarkable 3H-phosphindole
f 1H-phosphindole transformation, the CdP bond, the C-
bonded hydrogen center, and one phenyl group are shifted. What
role does the Ru center play in this process and is this
exclusively a photochemical reaction? To address these ques-
tions, isolation of the uncomplexed 3H-phosphindole 7 was
required. Therefore, we repeated the protonation reaction of iron
phosphaalkyne complex 3 with TfOH in CH2Cl2 at -78 °C.
After removal of large amounts of paramagnetic material via
filtration through basic alumina, we were able to isolate the
desired iron-phosphindole adduct [FeH(dppe)2(7)]OTf (6) in
44% yield. Heating a CH3CN solution of 6 to 75 °C gave the
desired 3H-phosphindole 7 and [FeH(dppe)2(CH3CN)][OTf] in
quantitative yield after 18 h. In comparison to the Ru analogue,
this cleavage reaction was permissible due to the higher lability
of first row transition metal complexes.
Scheme 5. Proposed Mechanism for Electrophilic Aromatic
Cyclization Reaction
With pure 3,3-diphenyl-3H-phosphindole 7 in hand, we
investigated its photochemical reactivity. Irradiation of a CH2Cl2
solution of 7 for 10 min furnished a mixture of products,
including 1H-phosphindole 9 in less than 30% yield. This result
contrasts with the nearly quantitative photochemical reaction
of ruthenium adduct 5. Furthermore, irradiation of 7 in the
presence of 10 equiv of sensitizer (anthracene or benzophenone)
did not result in higher conversion to 9. Finally, when 7 was
added to a CD3CN solution of [RuH(dppe)2]OTf, only the
solvated ruthenium cation [RuH(dppe)2(CD3CN)]+ and free 7
were observed by NMR spectroscopy. Displacement of CD3CN
from ruthenium by 7 to furnish 5 did not occur. Irradiation of
this solution for 10 min resulted in partial consumption of 7.
Clean formation of 9 was not observed. Had irradiation of this
mixture resulted in complete conversion of free 3H-phosphindole
7 to 1H-phosphindole 9, we would have concluded that in the
original photochemical reaction (1) displacement of 7 from
Scheme 6. Release of 1H-Phosphindole from Ruthenium
Complex 5
1
of δ ) -50 ppm after only 15 min (Scheme 6). In the H-
coupled 31P NMR spectrum, this signal appeared as a doublet
1
with a large JH-P ) 205.5 Hz. Separation of product 9 from
9
14966 J. AM. CHEM. SOC. VOL. 128, NO. 46, 2006

Synthetic Cycle for Formation of 1H-Phosphindoles
A R T I C L E S
Scheme 7. Proposed Photochemical Rearrangement of 3H- to 1H-Phosphindole via Phenyl Migration
[RuH(dppe)2(7)]+ occurred followed by (2) rearrangement of
uncoordinated 7 to give 9 via a photoinduced energy transfer
from ruthenium. Since very little rearranged product was
observed when [RuH(dppe)2(CD3CN)]+ and 7 were irradiated,
we conclude that the photochemical rearrangement occurs when
the phosphindole is coordinated to ruthenium.
Our proposed mechanism for this rearrangement is based on
the known photoreactivity of 4,4-diphenylcyclohexanones,
extensively studied by Zimmerman and co-workers (Scheme
7).45-48 Upon irradiation of 5, the diradical is formed (i).
Migration of the adjacent phenyl ring (ii) gives the more stable
dibenzyl radical (iii). Collapse of the radical generates a
phosphirane (iv), which then ring opens simultaneously with
the 5,1-H-sigmatropic shift (v). (Phosphirane f vinyl phosphine
conversion has precedent, albeit at elevated temperatures.49-51
It is plausible that the metal center lowers the activation energy
for such a process or that it occurs from a photoexcited state.)
Last, displacement of 7 from the ruthenium cation with solvent
furnishes the observed 1H-phosphindole and the solvated species
[RuH(dppe)2(CH3CN)]+.
We calculated the structures of the 1H-phosphindole, 2H-
phosphindole, and 3H-phosphindole using DFT theory (B3LYP/
6-31+G*), and the results are shown in Figure 5.52,53 The
agreement between the experimental structure of 9 and the
computed parent 1H-phosphindole is very good with the
exception of the P1-C4 bond, which is about 0.03 Å shorter
in 9. Also, the agreement between the structural parameters of
the coordinated 3,3-diphenyl-3H-phosphindole in 4 and the
parent 3H-phosphindole is satisfactory. As expected, benz-
annulation of the phosphole changes the stability order from:
2H-phosphole > 1H-phosphole > 3H-phosphole53 to 1H-
phosphindole (0.0 kcal mol-1) > 3H-phosphindole (1.1 kcal
mol-1) > 2H-phosphindole (14.3 kcal mol-1). The latter is
especially high in energy because of severe perturbation of the
π-system of the benzo group by the exocyclic CdC and CdP
moieties in the five-membered ring. From these calculations, it
appears that the photochemical “Phospha-Zimmerman re-
arrangement” is nearly thermoneutral.
Last, we investigated whether the transformation of Ph3CCtP
to 7 or 9 could be achieved catalytically. While this has not yet
been realized, some preliminary results are notable: (1) A
stoichiometric amount of acid is required for the cyclization
reaction of ruthenium adduct 4 to the cyclized product 5. (2)
Irradiation of pure ruthenium-phosphindole adduct 5 in CH2Cl2
with added Ph3CCtP furnishes 1H-phosphindole 9 and ruthe-
nium-phosphaalkyne 4 quantitatively. (3) When a CH3CN (or
CD3CN) solution of Ph3CCtP, TsOH, and ruthenium-aceto-
nitrile adduct 8 is allowed to mix at ambient temperature for 2
days (or at 60 °C for 12 h), the cyclized product 5 is formed in
quantitative yield.54 (4) If this same sample containing 5 and
acid is then irradiated, only decomposition occurs. The acid must
first be removed from the reaction mixture before irradiation.
(5) Other soft Lewis acids (e.g., Ni2+, Pd2+, Cu+, Ag+, Au+)
either have shown no reactivity toward 1 or result in decom-
position of all starting materials with or without added acid.
Formally, however, the synthesis of 9 has been achieved through
(45) Zimmerman, H. E.; Wilson, J. W. J. Am. Chem. Soc. 1964, 86, 4036.
(46) Zimmerman, H. E.; Rieke, R. D.; Scheffer, J. R. J. Am. Chem. Soc. 1967,
89, 2033.
(47) Zimmerman, H. E.; Lewin, N. J. Am. Chem. Soc. 1969, 91, 879.
(48) Zimmerman, H. E.; Hancock, K. G. J. Am. Chem. Soc. 1968, 90, 3749.
(49) Pham-Tran, N. N.; Nguyen, H. M. T.; Veszpremi, T.; Nguyen, M. T. J.
Chem. Soc., Perkin Trans. 2 2001, 766.
(50) Huy, N. H. T.; Mathey, F. Synlett 1995, 353.
(51) Haber, S.; Lefloch, P.; Mathey, F. J. Chem. Soc., Chem. Commun. 1992,
1799.
(52) Computations of phospholes at the MP2/6-31G* level gave the stability
order: 2H-phosphole (0.0 kcal mol-1) > 3H-phosphole (3.7 kcal mol-1
)
> 1H-phosphole (6.5 kcal mol-1). See: Bachrach, S. M. J. Org. Chem.
1993, 58, 5414.
(53) Using B3LYP/6-31G*, we satisfactorily reproduced previous results
obtained for the comparable series of phospholes at the B3LYP/aug-cc-
pVTZ level. For these nonbenzannulated heterocycles, the stability order
follows: 2H-phosphole (0.0 (0.0) kcal mol-1) > 1H-phosphole [2.7 (2.2)
kcal mol-1] > 3H-phosphole (4.2 (3.9) kcal mol-1); values in italics at
B3LYP/aug-cc-pVTZ. See: Ozimi_ski, W. P.; Dobrowolski, J. C. Chem.
Phys. 2005, 313, 123.
Figure 5. Computed structures and relative energies of 1H-phosphindole,
3H-phosphindole, and 2H-phosphindole obtained from DFT using the
B3LYP functional at the 6-31+G* level of theory.
9
J. AM. CHEM. SOC. VOL. 128, NO. 46, 2006 14967

A R T I C L E S
Cordaro et al.
Scheme 8. Synthetic Cycle for the Conversion of Phosphaalkyne
1 to 1H-Phosphindole 9
agent and stored over 3 Å molecular sieves prior to use. Deuterated
solvents were purchased from Euriso-top, degassed and distilled from
the proper drying agent, and stored over 3 Å sieves. Silica gel, alumina,
and diatomaceous earth (Celite) used for chromatography or filtrations
were dried under vacuum at 240 °C for 2 days and stored in the
glovebox.
All NMR spectra were recorded on Bruker Avance spectrometers.
Chemical shifts (δ) are expressed in parts per million (ppm). 1H NMR
spectra were recorded at 500, 400, 300, or 250 MHz, and chemical
shifts were referenced to the residual protiated solvent peak. 13C NMR
spectra are proton-decoupled and were recorded at 75.5 MHz; chemical
shifts were referenced to the solvent. 19F NMR spectra were recorded
at 188 MHz, and chemical shifts are reported relative to an external
standard of CFCl3. 31P NMR spectra were recorded at 121.5 or 101.3
MHz; chemical shifts were referenced to an external standard of H3PO4.
Coupling constants J are given in hertz as absolute values, unless
specifically stated. Where a first-order analysis is appropriate, the
multiplicity of the signals is indicated as s, d, t, q, qnt, or m for singlets,
doublets, triplets, quartets, quintets, or multiplets, unless otherwise
specified.
a synthetic cycle by treating the isolated acetonitrile adduct 8
with Ph3CCtP in CH2Cl2 followed by addition of TfOH at low
temperature to give 3H-phosphindole adduct 5. After removal
of the volatile materials under reduced pressure and a quick
wash of the solid with diethyl ether, photolysis of 5 in CH3CN
furnished 8 and free heterocycle 9 in greater than 90% yield
(Scheme 8). Theoretically, this cycle could be repeated indefi-
nitely.
IR spectra were recorded on a Perkin-Elmer-Spectrum 2000 FT-IR
Raman spectrometer with KBr beam splitter (range 500-4000 cm-1
)
using the ATR technique. The absorption bands are described as
follows: very strong (vs), strong (s), medium (m), weak (w), or broad
(br). Mass spectra were recorded on a Finnigan MAT SSQ 7000 mass
spectrometer. Melting points were determined with a Bu¨chi melting
point apparatus and are not corrected. Samples were prepared in open
glass capillaries.
Conclusion
The following compounds were synthesized according to lit-
erature procedure: Ph3CCH2Cl,55 FeHCl(dppe)2,56 RuH2(dppe)2, and
[RuH(dppe)2][BF4].57 [RuH(dppe)2][OTf] was made via anion metath-
esis of [RuH(dppe)2][BF4] in THF using KOTf (1.2 mol equiv) followed
by filtration through diatomaceous earth to remove the precipitated
KBF4.
A straightforward synthesis of the sterically protected tri-
phenylmethyl substituted phosphaalkyne Ph3CCtP has been
presented. This crystalline compound was reacted with two
group 8 organometallic cations to furnish the η1-coordinated
complexes [MH(dppe)2(Ph3CCtP)]OTf, where M ) Fe (3) or
Ru (4). Both of these compounds reacted with strong acids to
give the first example of an electrophilic aromatic substitution
reaction in which the electrophile originated from a phos-
phaalkyne. Irradiation or thermolysis of the metal complexes
yielded the free phosphindole heterocycle, and in the former
case, a photochemical rearrangement occurred providing access
to the 1H-phosphole in nearly quantitative yield. With the aid
of DFT calculations, we were able to gain a more thorough
understanding of the energetics and mechanism of this new
cyclization reaction.
The phosphorus electrophilic aromatic cyclization reaction
and the photochemical “Phospha-Zimmerman reaction” pre-
sented in this article provide yet other examples of the carbon-
phosphorus analogy. The diagonal relationship between these
two elements demonstrates once again that “classic” organic
chemistry is not only reserved for carbon but can be extended
to other main group elements, especially phosphorus in its low
valence states. The potential of synthesizing other phosphorus
heterocycles from phosphaalkynes is yet to be realized, and
efforts into this field are sure to be rewarding.
(2,2,2-Triphenylethyl)phosphonous Dichloride (2). Following a
literature procedure, 1-chloro-2,2,2-triphenylethane (14.0 g, 0.0478 mol)
was converted to the Grignard reagent using freshly ground Mg turnings
(ca. 10 g) in THF.55 The Grignard was cannula transferred to a solution
of PCl3 (12.6 mL, 0.144 mol) in THF (75 mL) cooled to -15 °C over
1 h. The resulting mixture was allowed to warm to room temperature
over 4 h. The volatile materials were removed under reduced pressure,
giving a grayish-black solid. The product was extracted with diethyl
ether (ca. 300 mL) and filtered through diatomaceous earth on a
medium-pore fitted glass frit. The volatile materials were removed under
reduced pressure to give a yellow solid. The solid was dissolved in
hot toluene (ca. 50 mL) and cooled to -20 °C for crystallization. After
1 day, white microcrystals grew. The mother liquor was removed via
cannula and saved for further crops. The crystals were washed with
cold toluene, combining the toluene with the mother liquor. Excess
solvent was removed under reduced pressure. Crop 1 yield: 6.31 g
(36.6%). Further crops were obtained from the combined mother liquors.
1
Total yield: 10.0 g (57.5%). Mp 122-124 °C. H NMR (C6D6): δ
7.22 (d, 3J ) 7.2 Hz, 6H), 7.06 (m, 9H), 3.88 (d, 2JHP ) 4.12 Hz, 2H).
13C{1H} NMR (C6D6): δ 146.1 (d, 3JCP ) 3.8 Hz, Cipso), 129.2 (d, JCP
1
) 3.8 Hz, Caryl), 128.7 (Caryl), 127.1 (Caryl), 58.7 (d, JC-P ) 52.9 Hz,
-CH2-PCl2), 56.7 (d, 2JCP ) 17.7 Hz, Ph3C-CH2PCl2). 31P{1H} NMR
(C6D6): δ 185.8. IR (solid ATR): 3055 (w), 3018 (w), 1490 (s), 1440
(s), 1406 (m), 1189 (m), 1158 (m), 1085 (m), 1032 (m), 1001, 767 (s),
752 (s), 696 (s). Anal. Calcd for C20H17Cl2P: C, 66.87; H, 4.77.
Found: C, 67.04; H, 5.06. EI HRMS: m/z calcd for C20H17Cl2P,
358.04449 [M]+; found, 358.0443.
Experimental Section
General. All experiments were performed using standard Schlenk
and vacuum line techniques or in a Braun glovebox under an inert
atmosphere of Ar in 20-mL scintillation vials unless otherwise noted.
Glassware was dried at 120 °C overnight prior to use. All reagents
were used as received from commercial suppliers unless otherwise
noted. All solvents were distilled under Ar from the appropriate drying
(55) Eisch, J. J.; Kovacs, C. A.; Chobe, P. J. Org. Chem. 1989, 54, 1275.
(56) Giannoccaro, P.; Sacco, A.; Ittel, S. D.; Cushing, M. A., Jr. Inorg. Synth.
1977, 17, 69.
(57) Nolan, S. P.; Belderrain, T. R.; Grubbs, R. H. Organometallics 1997, 16,
(54) The analogous reaction with [FeH(dppe)2(CH3CN)]+ does not work.
5569.
9
14968 J. AM. CHEM. SOC. VOL. 128, NO. 46, 2006

Synthetic Cycle for Formation of 1H-Phosphindoles
A R T I C L E S
2,2,2-Triphenylmethylphosphaalkyne (1). A 300-mL flask equipped
with a resealable Teflon stopper and a stir bar was charged with 2 (2.9
g, 8.1 mmol) and CH3CN (150 mL). The solution was heated to just
below reflux (ca. 75 °C). A 150-mL flask equipped with a resealable
Teflon stopper was charged with DABCO (9.8 g, 81 mmol) and CH3CN
(50 mL). Both Teflon stoppers were replaced with rubber septa. The
solution of DABCO was heated until all DABCO dissolved. The
DABCO solution was then slowly added to the solution of 2 at 75 °C
via cannula, over 30 min. ReVersing the addition resulted in large
amounts of unidentified side products. Upon addition of DABCO, the
solution turned yellow and generated a white vapor. After stirring the
solution at 75 °C for 4 h, the volatile materials were removed under
reduced pressure to leave an orange-yellow solid. Toluene (50 mL)
and a saturated, O2-free aqueous solution of NH4Cl (50 mL) were added.
After 4 × 15 mL toluene extractions, the toluene extracts were
combined and the volatile materials were removed under reduced
pressure. The crude product was redissolved in toluene (ca. 20 mL)
and filtered through a pad of basic alumina (I) on a medium-pore fitted
glass frit eluting with 40 mL of toluene. The solvent was concentrated
to ca. 10 mL and cooled to -30 °C for crystallization. Faint yellow
microcrystals grew after 1 day. The mother liquor was decanted away
from the solid and saved. The solid was washed with cold toluene (2
× 5 mL) and then cold Et2O (3 × 5 mL), combining the washes with
the mother liquor. Excess solvent was removed from the solid under
reduced pressure to furnish analytically pure material. Yield: 1.98 g
(39.6.9%). Additional crops were isolated from the mother liquor.
was concentrated to approximately 8 mL, layered with 8 mL of toluene,
and let evaporate slowly. After 1 day, large crystals grew. The mother
liquor was removed via pipet, and the solid was washed with cold THF.
Excess solvent was removed under reduced pressure, furnishing
analytically pure colorless crystalline material. Yield: 0.237 g (93.3%).
1
Mp > 180 °C (dec). H NMR (CD2Cl2): δ 7.31-7.20 (m, 33H) 7.00
(m, 16H), 6.57 (d, J ) 6.9 Hz, 6H), 2.48 (br, 4H), 2.13 (br, 4H), -9.44
(dqnt, trans-2JHP ) 129.6, cis-2JHP ) 17.4 Hz, 1H). 13C{1H} NMR
1
1
(CD2Cl2): δ 171.3 (d, JC-P ) 122.8 Hz) 145.5 (d, JC-P ) 10.5 Hz),
134.2 (m), 134.0 (m) 132.9, 132.7, 130.6, 129.2, 128.7, 128.3, 128.0,
126.5, 65.5 (d, 3JCP ) 12.3 Hz), 31.2 (qnt, 1JC-P ) 12.6 Hz) (one aryl
carbon signal could not be resolved). 19F NMR (CD2Cl2): δ -78.5.
31P{1H} NMR (CD2Cl2): δ 60.2 (d, 2JPP ) 27.5 Hz), -27.3 (qnt, 2JPP
) 27.5 Hz). IR (solid ATR): 3057 (w), 1486 (m), 1435 (s), 1266 (vs),
1224 (s), 1151 (s), 1092 (s), 1030 (vs), 1000 (m), 878 (m), 819 (m),
742 (s), 692 (vs), 674 (s), 636 (vs). Anal. Calcd for C73H64F3O3P5RuS:
C, 65.71; H, 4.83. Found: C, 65.86; H, 5.02.
(The BF4 salt could be made in a similar fashion starting from
[RuH(dppe)2]BF4. Mp 195 °C.)
[RuH(dppe)2(3,3-diphenylphosphindole)]OTf (5). A 100-mL Schlenk
flask equipped with a stir bar was charged with 4 (0.257 g, 0.200 mmol)
and CH2Cl2 (ca. 25 mL). The solution was cooled to ca. -78 °C, and
TfOH (20 µL, 0.22 mmol) was added via a gastight syringe. The
resulting yellow solution was allowed to warm slowly to ambient
temperature. After being stirred for 18 h, the volatile materials were
removed under reduced pressure. The crude product was washed with
diethyl ether (3 × 20 mL), and excess solvent was removed under
reduced pressure. The solid was dissolved in CH2Cl2 (20 mL) and
cannula filtered to a narrow (ca. 4 cm diameter) Schlenk tube. The
volume was reduced to ca. 10 mL and then carefully layered with
hexane (ca. 20 mL). After 2 days, medium-sized colorless needles grew.
The mother liquor was removed via cannula, and excess solvent was
removed under reduced pressure. Yield: 0.241 g (89.3%). Mp 208 °C
1
Combined yields were typically > 60%. Mp 130-132 °C. H NMR
1
(C6D6): δ 7.40 (dd, J ) 7.5, 1.5 Hz, 6H), 7.04 (m, 9H). H NMR
(THF-d8): δ 7.30-7.20 (m, 15H). 13C{1H} NMR (THF-d8): δ 177.6
1
3
(d, JC-P ) 40.6 Hz), 145.2 (d, JCP ) 5.9 Hz), 129.5, 128.2, 127.2,
64.0 (d, JCP ) 18.7 Hz). 31P{1H} NMR (C6D6): δ -48.1. 31P{1H}
2
NMR (THF-d8): δ -47.8. IR (solid ATR): 3029 (w), 3056 (w), 1593
(m, PtC), 1489 (s), 1443 (s), 1181 (w), 1158 (w), 1080 (m), 1030
(m), 1002 (w), 763 (m), 746 (vs), 695 (vs), 635 (s). Anal. Calcd for
C20H15P: C, 83.90; H, 5.28. Found: C, 83.90; H, 5.38. EI HRMS:
m/z calcd for C20H15P, 286.09114 [M]+; found, 286.0905. Crystals
suitable for X-ray analysis were grown from a toluene solution at
-30 °C.
1
2
(dec). H NMR (CD2Cl2): δ 8.19 (d, JHP ) 26.4 Hz, 1H), 7.49-7.0
(m, 34H), 6.82-6.21 (m, 17H), 6.63 (t, JHH ) 7.4 Hz, 1H), 5.99 (dt,
JHH ) 7.4, 2.1 Hz, 1H), 5.32 (t, JHH ) 7.8 Hz, 1H), 3.02 (b, 4H), 2.51
2
(b, 4H), -8.56 (dqnt, JHP ) 87.2, 19.8 Hz, 1H). 13C{1H} NMR
1
3
(CD2Cl2): δ 172.4 (d, JC-P ) 36.3 Hz), 152.7 (d, JCP ) 5.6 Hz),
144.1 (d, JCP ) 10.3 Hz), 139.1 (d, 1JC-P ) 17.8 Hz), 135.9 (b), 134.8
[FeH(dppe)2(Ph3CCtP)]OTf (3). A 200-mL Schlenk flask was
charged with FeHCl(dppe)2 (0.811 g, 0.91 mmol), KOTf (0.206 g, 1.09
mmol), 1 (0.313 g, 1.09 mmol), and 60 mL of dichloromethane. The
dark purple-red solution was stirred for 18 h, at which point it turned
orange. The organic layer was washed with three 20 mL portions of
O2-free water and then dried with MgSO4. After filtration, the volatile
materials were removed under reduced pressure. The resulting red solid
was washed with diethyl ether (3 × 15 mL), and excess solvent was
removed under reduced pressure. Yield: 1.09 (91.2%). Mp 201-204
°C. 1H NMR (CD2Cl2): δ 7.4-7.2 (m, 33H), 7.1-6.95 (m, 14H), 6.93
(t, JH-H ) 7.5 Hz, 8H), 2.45 (b, 4H), 2.12 (b, 4H), -12.03 (dqnt, trans-
2JPH ) 58.2 Hz, cis-2JPH ) 52.8 Hz, 1H). 13C{1H} NMR (CD2Cl2): δ
173.3 (d, 1JC-P ) 136.1 Hz), 145.8 (d, 3JCP ) 9.8 Hz), 135.0 (m), 134.5
(m) 133.1, 131.1, 130.7, 130.4, 129.3, 128.4, 128.1, 128.0, 126.9, 66.4
2
(b), 132.7 (s), 132.2 (s), 130.2 (s), 128.8 (d, JCP ) 14.3 Hz), 128.6
(s), 128.2 (s), 128.1 (s), 128.0 (s), 127.2 (s), 126.4 (d, 4JCP ) 5.4 Hz),
3
3
2
126.0 (d, JCP ) 7.0 Hz), 124.8 (d, JCP ) 10.8 Hz), 72.5 (d, JCP
)
9.4 Hz), 33.5 (m, 1JC-P ≈ 13 Hz). 19F NMR (CD2Cl2): δ -78.8. 31P{1H}
2
2
NMR (CD2Cl2): δ 232.0 (qnt, JPP ) 24.5 Hz), 63.1 (d, JPP ) 24.5
Hz). IR (solid ATR): 3053 (w), 1485 (m), 1434 (s), 1260 (vs), 1222
(m), 1188 (m), 1148 (m), 1091 (s), 1029 (vs), 873 (w), 812 (m), 741
(s), 693 (vs), 670 (s), 635 (vs). Anal. Calcd for C73H64F3O3P5RuS: C,
65.71; H, 4.83. Found: C, 65.50; H, 5.01. Crystals suitable for X-ray
analysis were grown by slow evaporation of a THF/toluene solution
of 5.
[FeH(dppe)2(3,3-diphenylphosphindole)]OTf (6). A 100-mL Schlenk
flask equipped with a stir bar was charged with 3 (0.290 g, 0.223 mmol)
and CH2Cl2 (ca. 30 mL). The solution was cooled to ca. -78 °C, and
TfOH (20 µL) was added via a gastight syringe. The resulting solution
was slowly warmed to ambient temperature over 3 h. The volatile
materials were removed under reduced pressure, and the residue was
washed with diethyl ether (3 × 20 mL) to ensure all TfOH was
removed. The yellow solid was dissolved in THF (ca. 10 mL) and
filtered through a small plug of basic alumina (ca. 2 cm in a pasture
pipet), which removed the paramagnetic materials, into a 20-mL
scintillation vial. To the yellow THF solution was added toluene (5
mL), and the solution was allowed to slowly evaporate at room
temperature. After 1 day, bright, clear yellow crystals grew. The mother
liquor was removed via pipet and saved for further crops. The crystals
were washed with diethyl ether, and excess solvent was removed under
reduced pressure. Combined yield: 0.129 g (44.5%). Mp 230-232 °C.
2
1
(d, JCP ) 9.9 Hz), 32.6 (qnt, JC-P ≈ 12 Hz). 19F NMR (CD2Cl2):
δ -78.5. 31P{1H} NMR (CD2Cl2): δ 78.8 (d, JPP ) 35.1 Hz), 0.94
2
(qnt, 2JPP ) 35.1 Hz). IR (solid ATR): 3059 (w), 2977 (w), 1486 (m),
1433 (m), 1265 (vs), 1143 (m), 1031 (s), 1001 (m), 882 (m), 741 (s),
691 (vs), 635 (vs). X-ray quality crystals were grown from a solu-
tion of 3 in CH2Cl2 layered with hexane. Anal. Calcd for C77H74F3-
FeO4P5S (with 1 equiv of Et2O): C, 67.84; H, 5.42. Found: C, 67.25;
H, 5.22.
[RuH(dppe)2(Ph3CCtP)]OTf (4). A 20-mL vial equipped with a
stir bar was charged with [RuH(dppe)2]OTf (0.200 g, 0.19 mmol) and
THF (10 mL). To the resulting orange suspension was added 1 (0.057
g, 0.200 mmol), and the mixture was stirred. After 10 min, the solution
was filtered through diatomaceous earth eluting with THF. The solution
9
J. AM. CHEM. SOC. VOL. 128, NO. 46, 2006 14969

A R T I C L E S
Cordaro et al.
Table 1. Crystal Data and Structural Refinement for 1, 3, 5, and 9
compound
1
3
5
9
empirical formula
M
C20H15P
286.29
C87H80F3FeO3P5S
1473.28
C80H72F3O3P5RuS
1426.36
C20H15P
286.29
crystal system
space group
a/Å
b/Å
c/Å
R/deg
â/deg
monoclinic
C2/c (no. 15)
16.759(1)
10.517(1)
19.233(1)
triclinic
monoclinic
P21/c (no. 14)
17.285(7)
17.059(7)
23.96(1)
monoclinic
P21/c (no. 14)
6.033(1)
13.668(1)
17.873(2)
P1h (no. 2)
13.901(1)
16.803(1)
17.014(1)
83.666(1)
69.925(1)(2)
84.126(1)
3700.9(3)
0.399
113.844(1)
101.116(8)
91.428(2)
γ/deg
V/Å3
3100.6(3)
0.168
1.227
6932(5)
0.429
1.367
1473.4(2)
0.176
1.291
µ/mm-1
D
calcd/g cm-3
1.322
crystal dimensions/mm3
Z
0.51 × 0.33 × 0.29
0.32 × 0.28 × 0.17
0.30 × 0.20 × 0.13
0.39 × 0.29 × 0.07
8
2
4
4
T/K
150
200
200
200
2θmax/deg
56.68
13988
3857 (Rint ) 0.0249)
190/0
0.0613
0.1513
0.558/-0.305
56.56
38833
18240 (Rint ) 0.0310)
904/33
0.0518
0.1310
0.554/-0.379
52.84
36429
13977 (Rint ) 0.0682)
831/42
0.0469
0.1329
0.604/-0.832
56.62
16620
3648 (Rint ) 0.0300)
194/1
0.0588
0.1476
0.441/-0.225
reflns measured
reflns unique
parameters/restraints
R1 [I g 2σ(I)]
wR2 (all data)
max/min res electron
density/e Å-3
2
1H NMR (CD2Cl2): δ 8.50 (d, JHP ) 26.7 Hz, 1H), 7.45 (m, 6H),
7.34 (br, 8H), 7.26 (m, 4H), 7.12 (m, 8H), 6.83 (br, 8H), 6.79 (m, 8H),
6.67 (t, JHH ) 7.5 Hz, 1H), 6.03 (dt, JHH ) 7.5, 1.8 Hz, 1H), 5.32 (t,
JHH ) 7.5 Hz, 1H), 3.08 (br, 4H), 2.55 (br, 4H), -10.9 (qntd, cis-2JHP
) 51.9, trans-2JHP ) 31.5 Hz, 1H). 13C{1H} NMR (CD2Cl2): δ 178.9
glass frit and washed with diethyl ether (3 × 8 mL) to leave
phosphaalkyne adduct 4. The ether washes were combined, and the
volatile materials were removed under reduced pressure to furnish a
brightly colored yellow-green residue. While the yield of the photolysis
reaction was essentially quantitative by NMR spectroscopy, isolation
of pure 9 in high yield was unsuccessful. When the isolated material
was redissolved in nonpolar solvents such as C6D6 or diethyl ether, an
unidentifiable white insoluble material remained. However, in the solid
state at -30 °C 9 appeared stable toward decomposition for at least
one month. Crystals suitable for X-ray analysis were grown from a
diethyl ether solution of 9 at -30 °C. Mp 195-201 °C (dec). 1H NMR
(CD2Cl2): δ 7.86 (m, 1H), 7.4-7.16 (m, 13H), 5.40 (d, 1JH-P ) 207.6
Hz, 1H). 13C{1H} NMR (CD2Cl2): δ 149.7 (d, JCP ) 2.9 Hz), 146.1
(d, JCP ) 6.9 Hz), 141.0 (d, JCP ) 5.6 Hz), 137.5, 137.3, 137.1, 136.7
(d, JCP ) 1.8 Hz), 129.8 (d, JCP ) 1.8 Hz), 129.4 (d, JCP ) 8.7 Hz),
1
3
(d, JC-P ) 38.5 Hz), 152.3 (d, JCP ) 6.4 Hz), 144.3 (d, JCP ) 10.0
1
Hz), 140.4 (d, JC-P ) 20.0 Hz), 136.6 (br), 135.3 (br), 133.0, 132.7,
2
130.1, 129.2 (d, JCP ) 13.8 Hz), 128.7, 128.3, 128.1, 127.8, 127.2,
126.2, 126.1 (d, 4JCP ) 7.5 Hz), 124.8 (d, 3JCP ) 9.9 Hz), 72.5 (d, 2JCP
) 8.5 Hz), 34.1 (m, JC-P ≈ 11 Hz). 19F NMR (CD2Cl2): δ -78.8.
1
31P{1H} NMR (CD2Cl2): δ 250.3 (qnt, JPP ) 31.5 Hz), 80.3 (br). IR
2
(solid ATR): 3055 (w), 1456 (m), 1434 (m), 1279 (m), 1261 (s), 1223
(m), 1150 (s), 1091 (m), 1066 (m), 1031 (s), 916 (w), 874 (w), 811
(m), 758 (m), 742 (s), 694 (s). Anal. Calcd for C77H71F3FeO4P5S (1
equiv of THF): C, 67.99; H, 5.26. Found: C, 67.67; H, 5.46.
129.3 (d, JCP ) 20.0 Hz), 128.6, 128.1, 127.7, 127.5, 126.9 (d, JCP
)
3H-3,3-Diphenylphosphindole (7). In a resealable Schlenk flask
equipped with a stir bar, 6 (0.125 g, 0.096 mmol) was dissolved in
CH3CN and heated to 75 °C. After 18 h, the volatile materials were
removed under reduced pressure, and the orange residue was extracted
with diethyl ether (5 × 3 mL). The ether was filtered though a small
plug of diatomaceous earth into a 20-mL scintillation vial. The volatile
materials were removed under reduced pressure, leaving a yellow solid.
By NMR, the product was greater than 90% pure. Yield: 0.025 g (93%).
1.2 Hz), 125.6 (d, JCP ) 8.2 Hz), 123.9 (d, JCP ) 0.5 Hz). 31P{1H}
NMR (CD2Cl2): δ -51.1 (d, JP-H ) 207 Hz). IR (solid ATR): 3055
(w), 2963 (w), 1490 (m), 1442 (s), 1260 (s), 1077 (vs-br), 1030 (vs-
br), 798 (vs), 760 (vs), 747 (vs), 693 (vs). EI HRMS: m/z calcd for
C20H15P, 286.09114 [M]+; found, 286.0905.
X-ray Crystallography. Crystals suitable for X-ray analysis were
mounted in degassed perfluoropolyalkyether on top of a glass fiber
and then brought into the cold nitrogen stream of a low-temperature
device so that the oil solidified. Data collection for the X-ray structure
determinations was performed on Bruker SMART Apex diffractometer
system with CCD area detector by using graphite-monochromated Mo
KR (0.71073 Å) radiation and a low-temperature device. All calculations
were performed by using the SHELXTL (version 6.12) and SHELXL-
97 program packages.58 The structures were solved by direct methods
and successive interpretation of the difference Fourier map, followed
by full matrix least-squares refinement (against F2). Moreover, an
empirical absorption correction using SADABS (version 2.03) was
applied to all structures. All non-hydrogen atoms were refined aniso-
tropically. The locations of the hydrides were fixed at metal hydrogen
bond distances of 1.47 Å [Fe1-H1 (3)] and 1.59 Å [Ru1-H1 (5)].
2
1H NMR (CD2Cl2): δ 8.84 (d, JHP ) 34.3 Hz, 1H), 7.88 (m, 1H),
7.38-7.16 (m, 13H). 13C{1H} NMR (CD2Cl2): δ 191.9 (d, JCP ) 33.1
Hz), 154.7 (d, JCP ) 2.9 Hz), 146.2 (d, JCP ) 35.3 Hz), 143.6 (d, JCP
) 6.2 Hz), 130.5 (d, JCP ) 22.6 Hz), 128.4, 128.1 (d, JCP ) 2.9 Hz),
127.8, 127.4 (d, JCP ) 8.6 Hz), 127.0, 126.3 (d, JCP ) 2.6 Hz), 76.1
(d, JCP ) 14.0 Hz). 31P{1H} NMR (CD2Cl2): δ 222.7 (dd, JPH ) 34.2,
5.1 Hz). IR (solid ATR): 3058 (m), 1491 (s), 1442 (s), 1262 (w), 1155
(m), 1124 (w), 1086 (m), 1031 (m), 945 (w), 911 (m), 781 (s), 750
(vs), 696 (vs).
1H-2,3-Diphenylphosphindole (9). A 100-mL Schlenk tube equipped
with a stir bar was charged with 5 (0.750 g, 0.541 mmol), 1 (0.155 g,
0.541 mmol), and CH2Cl2 (25 mL). The Schlenk tube was immersed
in an ice bath, and the solution was irradiated using a Hg vapor arc
lamp (150 W), which was also cooled in the ice bath. After 1 h, the
volatile materials were removed under reduced pressure, leaving a
yellow-green solid. The solid was collected on a medium-pore fitted
(58) (a) SHELXTL, version 6.12; Bruker AXS: Madison, WI, 2002.
(b) Sheldrick, G. M. SHELXL-97, Program for the Refinement of
Crystal Structures; University of Go¨ttingen: Go¨ttingen, Germany,
1997.
9
14970 J. AM. CHEM. SOC. VOL. 128, NO. 46, 2006

Synthetic Cycle for Formation of 1H-Phosphindoles
A R T I C L E S
The toluene molecules included in the crystal lattices of (3) and (5)
are highly disordered on two positions, and a large number [33 for (3)
and 42 for (5)] of restraints had to be used to achieve a satisfactory
wR2. Table 1 shows crystal data and structural refinement for 1, 3, 5,
and 9.
analyses of compound 2. This work was supported by the ETH
Zu¨rich and the Swiss National Science Foundation (SNF).
Supporting Information Available: CIF files. Details of
computational results. Complete ref 19. This material is available
free of charge via the Internet at http://pubs.acs.org.
Acknowledgment. We thank Dr. Heinz Ru¨egger for as-
sistance with NMR spectroscopy and Dr. Frank Breher for X-ray
JA0651198
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J. AM. CHEM. SOC. VOL. 128, NO. 46, 2006 14971