New complexes of methyldiphenylphosphonium cyclopentadienylide, representative of a class of ligands heretofore much neglected

Article abstract of DOI:10.1021/om070018j

Methyldiphenylphosphonium cyclopentadienylide, C₅H ₄PMePh₂ (II), has been synthesized and characterized spectroscopically and crystallographically and has been found to exhibit properties consistent with the zwitterionic structure IIb. The new group 6 coordination complexes (η⁵-C₅H₄PMePh ₂)M(CO)₃ have been synthesized via substitution reactions of II with M(CO)₆ (M = Cr, Mo) or W(CO)₃(MeCN) ₃. Comparisons of ν(CO) values of these complexes with those of the isoelectronic (η⁶-C₆H₆)M(CO) ₃ and [(η⁵-C₅H₅)M(CO) ₃]^- suggest that the electron-donating ability of the ylide is less than that of the cyclopentadienyl anion but much greater than that of benzene. Thermal and photochemical substitutions of the CO ligands of (η⁵-C₅H₄PMePh₂)M(CO) ₃ (M = Cr, Mo) by equimolar amounts of PMe₃ and PPh ₃ were not observed, but the ylide is displaced photochemically from (η⁵-C₅H₄PMePh₂)Mo(CO) ₃ by excess PMe₃ to form fac-Mo(CO)₃(PMe ₃)₃, while (η⁵-C₅H ₄PMePh₂)Mo(CO)₃ reacts with I₂ to form [(η⁵-C₅H₄-PMePh₂)Mo(CO) ₃I]I. The crystal structures of the free ylide and all four of its coordination complexes show that in each case one of the ylide phenyl rings not only eclipses the C₅H₄ ring but also is oriented toward it in an edge-on fashion. The intramolecular edge-face orientations involve interactions of an aromatic hydrogen atom with the C₅H₄ aromatic π systems and are rationalized in terms of electrostatic attractive forces between the slightly positive phenyl hydrogen atom and the negatively charged C₅H₄ ring. The electronic structures of II and of (η⁵-C₅H₄PMePh₂)Cr(CO) ₃ have been investigated using ab initio methodologies; it is found that the near-degenerate HOMO and HOMO-1 orbitals of the free ylide exhibit symmetries very similar to those of the corresponding, doubly degenerate HOMO of the cyclopentadienyl anion (E₁ symmetry) and that a lower energy, almost fully symmetric orbital corresponds to the fully symmetric bonding A ₁ MO of the cyclopentadienyl anion. In none of these three orbitals does there appear to be significant π involvement of an orbital on the phosphorus atom, consistent with the low P-C bond order implicit in the zwitterionic structure IIb. The primary ylide-metal interactions in (η⁵-C₅H₄PMePh₂)Cr(CO) ₃ involve donation of the HOMO and HOMO-1 orbitals into the d _xz and d_yz orbitals of the chromium, while the calculated ylide-Cr(CO)₃ bond dissociation energy is about 30% higher than the analogous ring-metal bond dissociation energy of (η⁶-C ₆H₆)Cr(CO)₃.

Full text of DOI:10.1021/om070018j

Organometallics 2007, 26, 1433-1443
1433
New Complexes of Methyldiphenylphosphonium
Cyclopentadienylide, Representative of a Class of Ligands
Heretofore Much Neglected
John H. Brownie and Michael C. Baird*
Department of Chemistry, Queen’s UniVersity, Kingston, Canada K7L 3N6
Hartmut Schmider
The High Performance Computing Virtual Laboratory, Queen’s UniVersity, Kingston, Canada K7L 3N6
ReceiVed January 8, 2007
Methyldiphenylphosphonium cyclopentadienylide, C5H4PMePh2 (II), has been synthesized and
characterized spectroscopically and crystallographically and has been found to exhibit properties consistent
with the zwitterionic structure IIb. The new group 6 coordination complexes (η5-C5H4PMePh2)M(CO)3
have been synthesized via substitution reactions of II with M(CO)6 (M ) Cr, Mo) or W(CO)3(MeCN)3.
Comparisons of ν(CO) values of these complexes with those of the isoelectronic (η6-C6H6)M(CO)3 and
[(η5-C5H5)M(CO)3]- suggest that the electron-donating ability of the ylide is less than that of the
cyclopentadienyl anion but much greater than that of benzene. Thermal and photochemical substitutions
of the CO ligands of (η5-C5H4PMePh2)M(CO)3 (M ) Cr, Mo) by equimolar amounts of PMe3 and PPh3
were not observed, but the ylide is displaced photochemically from (η5-C5H4PMePh2)Mo(CO)3 by excess
PMe3 to form fac-Mo(CO)3(PMe3)3, while (η5-C5H4PMePh2)Mo(CO)3 reacts with I2 to form [(η5-C5H4-
PMePh2)Mo(CO)3I]I. The crystal structures of the free ylide and all four of its coordination complexes
show that in each case one of the ylide phenyl rings not only eclipses the C5H4 ring but also is oriented
toward it in an edge-on fashion. The intramolecular edge-face orientations involve interactions of an
aromatic hydrogen atom with the C5H4 aromatic π systems and are rationalized in terms of electrostatic
attractive forces between the slightly positive phenyl hydrogen atom and the negatively charged C5H4
ring. The electronic structures of II and of (η5-C5H4PMePh2)Cr(CO)3 have been investigated using ab
initio methodologies; it is found that the near-degenerate HOMO and HOMO-1 orbitals of the free ylide
exhibit symmetries very similar to those of the corresponding, doubly degenerate HOMO of the
cyclopentadienyl anion (E1 symmetry) and that a lower energy, almost fully symmetric orbital corresponds
to the fully symmetric bonding A1 MO of the cyclopentadienyl anion. In none of these three orbitals
does there appear to be significant π involvement of an orbital on the phosphorus atom, consistent with
the low P-C bond order implicit in the zwitterionic structure IIb. The primary ylide-metal interactions
in (η5-C5H4PMePh2)Cr(CO)3 involve donation of the HOMO and HOMO-1 orbitals into the dxz and dyz
orbitals of the chromium, while the calculated ylide-Cr(CO)3 bond dissociation energy is about 30%
higher than the analogous ring-metal bond dissociation energy of (η6-C6H6)Cr(CO)3.
Triphenylphosphonium cyclopentadienylide (cyclopentadi-
enylidene triphenylphosphorane) (I) was first reported in 1956
by Ramirez and Levy,1a who also explored its chemistry.1b-f
attributed this unusual stability to the charge delocalization
implied by resonance structure Ib, consistent with the relatively
high dipole moment of 7.0 D.1c
Further evidence for extensive delocalization of the π-electron
density was found in the crystal structure, which showed
significant shortening of the P-C5H4 bond,1g and in the 13C
NMR spectrum, which showed an unusually high field chemical
shift for the ylide carbon and a P-C(ylide) coupling constant
typical of an aliphatic carbon-P bond.1h
Wilkinson noted soon after the initial Ramirez report that,
since Ib would be isoelectronic with benzene, the ylide might
be expected to form compounds of the type (η5-C5H4PPh3)M-
(CO)3 (M ) Cr, Mo, W), analogous to the known arene
compounds (η6-C6H6)M(CO)3. Successful attempts to prepare
the group 6 compounds were carried out, and the molybdenum
compound was obtained analytically pure,2a although the
structures and chemistry of these compounds were only explored
many years later.2b-g Analogous carbonyl complexes of man-
ganese and rhenium, of the type [(η5-C5H4PPh3)M(CO)3]+ (M
They found, inter alia, that I is unusually inert, for instance
being unreactive with ketones, unlike ylides normally. They
(1) (a) Ramirez, F.; Levy, S. J. Org. Chem. 1956, 21, 488. (b) Ramirez,
F.; Levy, S. J. Org. Chem. 1956, 21, 1333. (c) Ramirez, F.; Levy, S. J.
Am. Chem. Soc. 1957, 79, 67. (d) Ramirez, F.; Dershowitz, S. J. Org. Chem.
1957, 22, 41. (e) Ramirez, F.; Levy, S. J. Am. Chem. Soc. 1957, 79, 6167.
(f) Ramirez, F.; Levy, S. J. Org. Chem. 1958, 23, 2035. (g) Ammon, H.
L.; Wheeler, G. L.; Watts, Jr., P. H. J. Am. Chem. Soc. 1973, 95, 6158. (h)
Gray, G. A. J. Am. Chem. Soc. 1973, 95, 7736. (i) For a recent computational
study, see: Laavanya, P.; Krishnamoorthy, B. S.; Panchanatheswaran, K.;
Manoharan, M. J. Mol. Struct. THEOCHEM 2005, 716, 149.
10.1021/om070018j CCC: $37.00 © 2007 American Chemical Society
Publication on Web 02/15/2007

1434 Organometallics, Vol. 26, No. 6, 2007
Brownie et al.
) Mn, Re),3 and a cobalt complex, [(η5-C5H4PPh3)Co(CO)2]+,4
have subsequently been reported, as have a few satisfactorily
characterized complexes of I with ruthenium,5a rhodium,5b,c
nickel,5d palladium,5e-h platinum,5h and mercury.5i,j However,
a number of attempts to prepare complexes of metal halides
generally resulted in poorly soluble species of indefinite
constitution.6
PClPh2 + NaCp f PCpPh2
(1)
(2)
PCpPh2 + MeI f [PMeCpPh2]I
C H PMePh
2
[PMeCpPh2]I + BuLi f
(3)
5
4
II
We quickly found that II had been prepared previously via
a similar route in which TlCp was used instead of NaCp9 but
that the free ylide had been neither thoroughly characterized
nor investigated with respect to its coordination chemistry. We
have therefore developed a reliable synthetic procedure for II
and report here the complete spectroscopic and crystallographic
characterization of this compound. We also describe the
syntheses and characterization and some chemistry of the group
6 compounds (η5-C5H4PMePh2)M(CO)3 (M ) Cr, Mo, W), a
series chosen for our initial study because the group 6 tricarbonyl
complexes of I are known2 and we wished to be able to make
direct comparisons of the coordination chemistry of I and II.
We have also investigated, via ab initio calculations, the nature
of the bonding in II and of its complex (η5-C5H4PMePh2)Cr-
(CO)3.
In part, perhaps, because of difficulties in characterizing many
of the compounds obtained, research in this area stagnated and
virtually no publications dealing with the coordination chemistry
of I have appeared in over two decades.2-6 However, the donor
properties of I and similar ligands are expected to fall between
those of benzene and the cyclopentadienyl (Cp) ligand and,
given the enormous importance of Cp and related complexes,7
this lack of interest seems quite surprising. Furthermore, while
complexes of I have been found to contain the ligand bound to
the metal in an η5 fashion, coordination in an η1 fashion has
been demonstrated5i and coordination could in principle also
occur in the η2, η3, and η4 modes. Thus, tertiary phosphine based
cyclopentadienylidene ligands offer the possibility of exhibiting
a range of interesting structures and catalytic reactivities, and
we have embarked on a program to reopen the chemistry of
this class of ligand.
Experimental Section
Hoping to avoid the solubility problems apparently limiting
development of the chemistry of I, we have chosen to investigate
mixed alkyl-aryl cyclopentadienylidene derivatives which
would also be more amenable to characterization by NMR
spectroscopy. Since the original Ramirez synthetic procedure1
turned out not to be generally applicable to other phosphines,8
we are working initially with C5H4PMePh2 (II), which we
anticipated synthesizing from commercially available starting
materials as in eqs 1-3.
All syntheses were carried out under a dry, deoxygenated argon
atmosphere using standard Schlenk line techniques. Argon was
deoxygenated by passage through a heated column of BASF copper
catalyst and then dried by passing through a column of 4A
molecular sieves. Handling and storage of air-sensitive organome-
tallic compounds was done using an MBraun Labmaster glovebox.
NMR spectra were recorded using Bruker AV 300, AV 500, and
1
AV 600 spectrometers. All H and 13C{1H} NMR spectra were
referenced to carbons or residual protons present in the deuterated
solvents with respect to TMS at δ 0. 31P NMR was referenced to
external 85% H3PO4. Elemental analyses were conducted by
Canadian Microanalytical Service Ltd., Delta, BC, Canada.
Anhydrous methylene chloride, THF, diethyl ether, hexanes, and
toluene were purchased from Aldrich in 18 L reservoirs packaged
under nitrogen and were dried by passage through columns of
activated alumina (Innovative Technology Solvent Purification
System). THF, Et2O, and CH2Cl2 were then stored over 4A
molecular sieves to result in residual water concentrations that were
lower than 20 ppm. NMR solvents used for organometallic
compounds were degassed under vacuum and dried by passage
through a small column of activated alumina before being stored
over 4A molecular sieves. All deuterated solvents were purchased
from Cambridge Isotope Laboratories, Inc., or CDN Isotopes. Most
chemicals were obtained from Aldrich or Strem and were used as
received or purified by established procedures.
X-ray crystal structure determinations were performed by Dr.
Ruiyao Wang in the X-ray Crystallography Laboratory at Queen’s
University. Crystals were mounted on glass fibers with epoxy glue,
and data collection was performed on a Bruker Smart CCD 1000
X-ray diffractometer with graphite-monochromated Mo KR radia-
tion (λ ) 0.710 73 Å) controlled with a Cryostream Controller 700.
No significant decay was observed during data collections. Data
were processed on a Pentium PC using the Bruker AXS Crystal
Structure Analysis Package, Version 5.10.10a Neutral atom scattering
factors were taken from Cromer and Waber.10b The raw intensity
data were converted (including corrections for scan speed, back-
(2) (a) Abel, E. W.; Singh, A.; Wilkinson, G. Chem. Ind. (London) 1959,
1067. (b) Kotz, J. C.; Pedrotty, D. G. J. Organomet. Chem. 1970, 22, 425.
(c) Cashman, D.; Lalor, F. J. J. Organomet. Chem. 1970, 24, C29. (d)
Cashman, D.; Lalor, F. J. J. Organomet. Chem. 1971, 32, 351. (e)
Zdanovitch, V. I.; Yurtanov, A. I.; Zhakaeva, A. Zh.; Setkina, V. N.;
KursanoV, D. N. IzV. Akad. Nauk SSSR, Ser. Khim. 1973, 6, 1375. (f)
Setkina, V. N.; Zhakaeva, A. Zh.; Panosyan, G. A.; Zdanovitch, V. I.;
Petrovskii, P. V.; Kursanov, D. N. J. Organomet. Chem. 1977, 129, 361.
(g) Debaerdemaeker, T. Z. Kristallogr. 1980, 153, 221.
(3) (a) Nesmeyanov, A. N.; Kolobova, N. E.; Zdanovitch, V. I.; Zhakaeva,
A. Zh. J. Organomet. Chem. 1976, 107, 319. (b) Zdanovitch, V. I.;
Kolobova, N. E.; Vasyukova, N. I.; Nekrasov, Yu. S.; Panosyan, G. A.;
Petrovskii, P. V.; Zhakaeva, A. Zh. J. Organomet. Chem. 1978, 148, 63.
(4) (a) Holy, N, L.; Baenziger, N, C.; Flynn, R. M. Angew. Chem., Int.
Ed. Engl. 1978, 17, 686. (b) Baenziger, N, C.; Flynn, R. M.; Holy, N, L.
Acta Crystallogr. 1979, B35, 741.
(5) (a) Blake, A. J.; Johnson, B. F. G.; Parsons, S.; Shephard, D. S. J.
Chem. Soc., Dalton Trans. 1995, 495. (b) Tresoldi, G.; Recca, A.;
Finocchiaro, P.; Faraone, F. Inorg. Chem. 1981, 20, 3103. (c) Bombieri,
G.; Tresoldi, G.; Faraone, F.; Bruno, G. Inorg. Chim. Acta 1982, 57, 1. (d)
Booth, B. L.; Smith, K. G. J. Organomet. Chem. 1981, 220, 229. (e)
Pierpont, C. G.; Downs, H. H.; Itoh, K.; Nishiyama, H.; Ishii, Y. J.
Organomet. Chem. 1976, 124, 93. (f) Hirai, M.-F.; Miyasaka, M.; Itoh, K.;
Ishii, Y. J. Organomet. Chem. 1979, 165, 391. (g) Hirai, M.-F.; Miyasaka,
M.; Itoh, K.; Ishii, Y. J. Chem. Soc., Dalton Trans. 1979, 1200. (h) Tresoldi,
G.; Faraone, F.; Piraino, P.; Bottino, F. A. J. Organomet. Chem. 1982, 231,
265. (i) Holy, N, L.; Baenziger, N, C.; Flynn, R. M.; Swenson, D. C. J.
Am. Chem. Soc. 1976, 98, 7823. (j) Roberts, R. M. G. Tetrahedron 1980,
36, 3295.
(6) (a) Nalesnik, T.; Warfield, L.; Holy, N.; Layton, J.; Smith, S. Inorg.
Nucl. Chem. Lett. 1977, 13, 523. (b) Holy, N. L.; Nalesnik, T. E.; Warfield,
L. T. Inorg. Nucl. Chem. Lett. 1977, 13, 569. (c) Holy, N. L.; Nalesnik, T.
E.; Warfield, L.; Mojesky, M. J. Coord. Chem. 1983, 12, 157.
(7) See, for instance: (a) Metallocenes: Synthesis, ReactiVity, Applica-
tions; Togni, A., Halterman, R. L., Eds.; Wiley: New York, 1998; Vols. 1
and 2. (b) Severin, K. Chem. Commun. 2006, 3859. (c) Metallocenes in
Regio- and StereoselectiVe Synthesis; Topics in Organometallic Chemistry
8; Takahashi, T., Ed.; Springer-Verlag: Berlin, Heidelberg, Germany, 2005.
(8) Black, insoluble substances are generally obtained, presumably
containing polymeric materials.
(9) Mathey, F.; Lampin, J.-P. Tetrahedron 1975, 31, 2685.
(10) (a) Bruker AXS Crystal Structure Analysis Package, Version 5.10
(SMART NT (Version 5.053), SAINT-Plus (Version 6.01), SHELXTL
(Version 5.1)); Bruker AXS Inc., Madison, WI, 1999. (b) Cromer, D. T.;
Waber, J. T. International Tables for X-ray Crystallography; Kynoch
Press: Birmingham, U.K., 1974; Vol. 4, Table 2.2 A.

New Complexes of C5H4PMePh2
Organometallics, Vol. 26, No. 6, 2007 1435
ground, and Lorentz and polarization effects) to structure amplitudes
and their esds using the program SAINT, which corrects for Lp
and decay. Absorption corrections were applied using the program
SADABS. All non-hydrogen atoms were refined anistropically. The
positions for all hydrogen atoms were calculated (unless otherwise
stated), and their contributions were included in the structure factors
and calculations.
Found: C, 62.51; H, 4.17. Calcd: C, 63.01; H, 4.28. IR (CH2Cl2):
1915, 1812 cm-1
.
The compound (η5-C5H4PMePh2)Mo(CO)3 (IV) was prepared
and purified similarly using 0.40 g of II (1.5 × 10-3 mol) and
1.21 g of Mo(CO)6 (4.6 × 10-3 mol). The yellow product was
1
obtained in 60% yield (0.41 g). H NMR (CD2Cl2, 500 MHz): δ
3
7.77 (2H, t, JH-H ) 7.1 Hz, Ph), 7.71-7.62 (8H, m, Ph), 5.48
(2H, m, PCCHCH), 5.29 (2H, m, PCCHCH), 2.55 (3H, d, 2JH-P
)
Synthesis of C5H4PMePh2 (II). A suspension of 20.0 g of TlCp
(0.074 mol) in 200 mL of ether was treated dropwise with 13.3
mL of Ph2PCl (0.073 mol). As the reaction proceeded, the flask
warmed and the solution turned slightly yellow. After it was stirred
for 1 h, the reaction mixture was filtered to remove TlCl, and the
phosphine, P(C5H5)Ph2, was immediately treated in situ with 4.5
mL of MeI (0.072 mol). As the alkylation reaction proceeded, a
white product precipitated. The reaction mixture was stirred for 3
h, and 22.9 g of the white phosphonium salt ([PMe(C5H5)Ph2]I)
was collected by filtration in 81% yield. The product was impure
(NMR), but attempts to purify it proved fruitless and the salt was
therefore used as obtained in the next step.
13.6 Hz, Me). 13C NMR (CD2Cl2, 125 MHz): δ 231.2 (Mo-CO),
4
135.0 (d, JP-C ) 2.9 Hz, p-Ph), 133.4 (d, JP-C ) 10.6 Hz, Ph),
1
130.2 (d, JP-C ) 12.5 Hz, Ph), 122.5 (d, JP-C ) 90.2 Hz, ipso-
2
3
Ph), 94.5 (d, JP-C ) 14.4 Hz, PCCHCH), 92.1 (d, JP-C ) 12.5
1
1
Hz, PCCHCH), 71.8 (d, JP-C ) 109.4 Hz, PC), 14.4 (d, JP-C
)
66.2 Hz, Me). 31P NMR (CD2Cl2, 121 MHz): δ 18.25. Anal.
Found: C, 56.81; H, 3.76. Calcd: C, 56.77; H, 3.86. IR (CH2Cl2):
1918, 1812 cm-1
.
The tungsten analogue (η5-C5H4PMePh2)W(CO)3 (V) was pre-
pared by reacting 0.11 g of II (4.1 × 10-4 mol) and 0.40 g of
W(MeCN)3(CO)3 (1.0 × 10-3 mol) in 20 mL of diglyme at 110
°C for 40 h. The solution turned a black-green color, and a black
precipitate formed. The reaction mixture was cooled, the solvent
was removed under reduced pressure, and the resulting gray-green
solid was dissolved in degassed CHCl3 and passed through an
alumina column under an argon atmosphere. The yellow band was
collected, and the solvent was removed in vacuo to yield 0.15 g
(70%) of yellow product. X-ray-quality crystals were obtained by
crystallization from CH2Cl2 at -30 °C by layering with hexanes,
but several attempts to recrystallize the bulk product failed to
To prepare II, a suspension of 10.1 g of [PMe(C5H5)Ph2]I (0.26
mol) in 150 mL of THF was cooled in an ice bath and treated
dropwise with 17.7 mL of 1.6 M n-BuLi in hexanes (0.028 mol).
As the n-BuLi was added, the solution warmed and the solid
disappeared, generating a deep orange-red solution. The reaction
was stirred until no solid remained, at which point the reaction
was hydrolyzed by the addition of 20 mL of H2O. This caused the
formation of a white solid, while the solution turned yellow. The
organic layer was decanted, and the aqueous layer was washed with
3 × 75 mL of toluene. The organic layers were combined, and the
solvent was removed in vacuo to yield an orange solid which was
extracted with 200 mL of ethyl acetate and passed through a silica
column using ethyl acetate as the eluent. The yellow band was
collected, and the solvent was removed under reduced pressure to
yield 2.1 g (30% based upon phosphonium salt) of C5H4PMePh2
(II) as a yellow powder. X-ray-quality crystals and analytically pure
material were obtained by crystallization from CH2Cl2 solution at
-30 °C by layering with hexanes. This procedure has been repeated
1
remove a small amount of impurity, which exhibited a similar H
1
NMR spectrum and similar solubility properties. H NMR (CD2-
3
Cl2, 500 MHz): δ 7.78 (2H, t, JH-H ) 7.0 Hz, Ph), 7.71-7.62
(8H, m, Ph), 5.46 (2H, m, PCCHCH), 5.21 (2H, m, PCCHCH),
2.56 (3H, d, 2JH-P ) 13.6 Hz, Me). 13C NMR (CD2Cl2, 125 MHz):
δ 221.1 (W-CO), 135.1 (d, 4JP-C ) 2.1 Hz, p-Ph), 133.6 (d, JP-C
) 10.7 Hz, Ph), 130.3 (d, JP-C ) 12.9 Hz, Ph), 121.9 (d, 1JP-C
)
2
90.3 Hz, ipso-Ph), 91.4 (d, JP-C ) 14.0 Hz, PCCHCH), 89.6 (d,
3JP-C ) 11.8 Hz, PCCHCH), 70.5 (d, 1JP-C ) 109.6 Hz, PC), 14.5
(d, 1JP-C ) 65.5 Hz, Me). 31P NMR (CD2Cl2, 121 MHz): δ 18.58.
Anal. Found: C, 48.34; H, 3.14. Calcd: C, 47.40; H, 3.22. IR (CH2-
1
many times with yields ranging from 20 to 35%. H NMR of II
Cl2): 1912, 1808 cm-1
.
(CDCl3, 500 MHz): δ 7.64-7.59 (6H, m, Ph), 7.52-7.49 (4H, m,
Ph), 6.44 (2H, m, PCCHCH), 6.29 (2H, m, PCCHCH), 2.37 (3H,
Synthesis of [(η5-C5H4PMePh2)Mo(CO)3I][I] (VI). A solution
of 0.040 g of I2 (1.6 × 10-4 mol) in 10 mL of CH2Cl2 was slowly
added to a solution of 0.070 g of IV (1.6 × 10-4 mol) in 10 mL of
CH2Cl2; on addition of the I2, the yellow solution became bright
orange. The reaction mixture was stirred for 30 min and then
filtered, and the solvent was removed from the filtrate in vacuo to
give 0.059 g of red product (54%). X-ray-quality crystals and
analytically pure material were obtained by crystallization from CH2-
2
d, JH-P ) 13.2 Hz, Me). 13C NMR (CDCl3, 125 MHz): δ 132.6
(d, 4JP-C ) 2.1 Hz, p-Ph), 132.3 (d, JP-C ) 10.6 Hz, Ph), 129.0 (d,
1
JP-C ) 11.5 Hz, Ph), 127.5 (d, JP-C ) 88.3 Hz, ipso-Ph), 114.9
2
3
(d, JP-C ) 16.3 Hz, PCCHCH), 114.3 (d, JP-C ) 17.3 Hz,
PCCHCH), 79.2 (d, 1JP-C ) 114.2 Hz, PC), 12.6 (d, 1JP-C ) 63.3
Hz, Me). 31P NMR (CDCl3, 121 MHz): δ 7.95. Anal. Found: C,
80.76; H, 6.56. Calcd: C, 81.80; H, 6.48.
1
Synthesis of (η5-C5H4PMePh2)Cr(CO)3 (III). A solution of 0.39
g of II (1.5 × 10-3 mol) and 0.96 g of Cr(CO)6 (4.4 × 10-3 mol)
in 30 mL of diglyme was refluxed under argon for 3 h, during
which time the solution developed a black-green color. The reaction
mixture was cooled and filtered, and the solid residue was washed
with 3 × 10 mL of diglyme. The resulting filtrate was then treated
with 200 mL of hexanes to precipitate a yellow solid that was
collected and washed with hexanes (3 × 10 mL). The solid was
dried in vacuo to yield 0.35 g (61%) of yellow product. X-ray-
quality crystals and analytically pure material were obtained by
crystallization from CH2Cl2 solution at -30 °C by layering with
Cl2 solution at -30 °C by layering with hexanes. H NMR (CD2-
Cl2, 300 MHz): δ 7.87-7.67 (10H, m, Ph), 6.43 (2H, m,
2
PCCHCH), 6.04 (2H, m, PCCHCH), 3.12 (3H, d, JH-P ) 13.6
Hz, Me). 13C NMR (CD2Cl2, 125 MHz): δ 229.3 (Mo-CO), 216.3
(Mo-CO), 136.4 (d, 4JP-C ) 3.8 Hz, p-Ph), 133.5 (d, JP-C ) 11.5
Hz, Ph), 131.2 (d, JP-C ) 13.4 Hz, Ph), 119.6 (d, 1JP-C ) 91.1 Hz,
2
3
ipso-Ph), 104.1 (d, JP-C ) 11.5 Hz, PCCHCH), 97.5 (d, JP-C
)
1
1
8.6 Hz, PCCHCH), 87.0 (d, JP-C ) 95.0 Hz, PC), 11.7 (d, JP-C
) 58.5 Hz, Me). 31P NMR (CD2Cl2, 121 MHz): δ 21.08. Anal.
Found: C, 35.58; H, 3.12. Calcd: C, 36.13; H, 2.45. IR (CH2Cl2):
2055, 1979 cm-1
.
1
Attempted Reactions of IV with MeI and H2. To a solution
of 0.24 g of IV (5.3 × 10-4 mol) in 20 mL of THF was added
0.75 g of MeI (5.3 × 10-4 mol). The solution was stirred for 22 h,
with neither color change nor change in the IR spectrum being
observed. Similarly, no reaction was observed on bubbling H2
through a solution of IV in THF for 6 h.
hexanes. H NMR (CD2Cl2, 500 MHz): δ 7.75-7.63 (10H, m,
Ph), 4.90 (2H, br, PCCHCH), 4.71 (2H, br, PCCHCH), 2.55 (3H,
d, 2JH-P ) 13.2 Hz, Me). 13C NMR (CD2Cl2, 125 MHz): δ 241.8
(Cr-CO), 134.8 (d, 4JP-C ) 2.2 Hz, p-Ph), 133.3 (d, JP-C ) 11.1
Hz, Ph), 130.2 (d, JP-C ) 12.3 Hz, Ph), 123.1 (d, 1JP-C ) 90.2 Hz,
2
3
ipso-Ph), 89.9 (d, JP-C ) 13.4 Hz, PCCHCH), 87.5 (d, JP-C
)
13.4 Hz, PCCHCH), 65.8 (d, 1JP-C ) 111.4 Hz, PC), 12.8 (d, 1JP-C
) 65.7 Hz, Me). 31P NMR (CD2Cl2, 121 MHz): δ 19.54. Anal.
Attempted Thermal and Photochemical Reactions of III and
IV with PPh3. Solutions of either III or IV and 1 equiv of PPh3 in

1436 Organometallics, Vol. 26, No. 6, 2007
Table 1. Selected NMR Data for the Compounds II-VIa
III (CD2Cl2) IV (CD2Cl2) V (CD2Cl2)
1H NMR
Brownie et al.
position
II (CDCl3)
VI (CD2Cl2)
6.04 (m)
2, 5
3, 4
Me
6.29 (m)
4.71 (m)
5.29 (m)
5.21 (m)
6.44 (m)
4.90 (m)
5.48 (m)
5.46 (m)
6.43 (m)
2.37 (d, 2JP-H ) 13.2)
2.55 (d, 2JP-H ) 13.2)
2.55 (d, 2JP-H ) 13.6)
2.56 (d, 2JP-H ) 13.6)
3.12 (d, 2JP-H ) 13.6)
13C NMR
1
79.2 (d, 1JP-C ) 114.2)
114.9 (d, 2JP-C ) 16.3)
114.3 (d, 3JP-C ) 17.3)
12.6 (d, 1JP-C ) 63.3)
65.8 (d, 1JP-C ) 111.4)
89.9 (d, 2JP-C ) 13.4)
87.5 (d, 3JP-C ) 13.4)
12.8 (d, 1JP-C ) 65.7)
71.8 (d, 1JP-C ) 109.4)
94.5 (d, 2JP-C ) 14.4)
92.1 (d, 3JP-C ) 12.5)
14.4 (d, 1JP-C ) 66.2)
70.5 (d, 1JP-C ) 109.6)
91.4 (d, 2JP-C ) 14.0)
89.6 (d, 3JP-C ) 11.8)
14.5 (d, 1JP-C ) 65.5)
87.0 (d, 1JP-C ) 95.0)
104.1 (d, 2JP-C ) 11.5)
97.5 (d, 3JP-C ) 8.6)
11.7 (d, 1JP-C ) 58.5)
2, 5
3, 4
Me
31P NMR
18.25
7.95
19.54
18.58
21.08
a δ values are given in ppm and J values in Hz. Full listings of NMR data are given in the Experimental Section. Refer to A for the atom-labeling scheme.
Scheme 1. Synthesis of C5H4PMePh2 (II)
20 mL of THF were refluxed for 20 h while being monitored by
IR spectroscopy. Similarly, solutions of IV and either 1 or 3.5 equiv
of PPh3 in 20 mL of CH2Cl2 were photolyzed with UV light from
a Hanovia lamp for 20 h, during which time the experiments were
monitored by IR. No changes in the IR spectra were observed. A
similar photochemical experiment with 1 equiv of PMe3 had the
same result.
Photochemical Reaction of IV with 3.5 Equiv of PMe3. A
solution of IV and 3.5 equiv of PMe3 in 20 mL of CH2Cl2 was
photolyzed with UV light from a Hanovia lamp while being
monitored by IR spectroscopy. After 18 h, the IR spectrum showed
we then obtained further results at three levels of computation,
B3LYP, restricted Hartee-Fock (RHF), and second-order Møller-
Plesset perturbation theory (MP2), as well as in two basis sets, the
“split valence” 6-31G* basis, and Dunning’s correlation consistent
double-ú basis12i,j with the chromium atom represented in a
that the peaks of IV had disappeared and had been replaced by
new peaks at 1830 and 1930 cm-1. After removal of the solvent,
1
the residue was dissolved in CD2Cl2 and the H and 31P NMR
Wachters-Hay basis.12k,l
spectra were recorded. Free ligand peaks of II were observed in
1
both the H and 31P NMR spectra, while a new peak in the 31P
Results and Discussion
NMR spectrum corresponds to the resonance of the previously
reported complex fac-Mo(PMe3)3(CO)3 (δ -17 ppm).11
Synthesis, Structure, and Spectroscopic Properties of II.
Ab Initio Calculations. To gain information on the electronic
Ligand II was synthesized using a procedure very similar to
structures of C5H4PMePh2 (II) and (η5-C5H4)PMePh2Cr(CO)3 (III),
that of Mathey and Lampin,9 who had previously reported only
and also to compare the ylide-metal bonding in III with the (η6-
1
its H NMR spectrum (Scheme 1). As part of our study, we
C6H6)-metal bonding in (η6-C6H6)Cr(CO)3, a series of ab initio
1
have now characterized this ligand by H, 31P, and 13C{1H}
calculations was performed on II and III, employing the Gaussian
03 suite of programs.12a Using the crystal structures as initial starting
points, optimized structures were obtained with the B3LYP12b-d
functional on a self-consistent hybrid-DFT level of calculation in
a standard “split valence” 6-31G* basis.12e-h Using these structures,
NMR spectroscopy, elemental analyses, and X-ray crystal-
lography. The 1H and 13C{1H} NMR data are presented in Table
1 and will be discussed below. Note that all spectral and
structural parameters of free and coordinated cyclopentadi-
enylidenes are presented in terms of the general labeling scheme,
shown as A. To facilitate comparisons, the atom numbering for
(11) Mathieu, R.; Lenzi, M.; Poilblanc, R. Inorg. Chem. 1970, 9, 2030.
(12) (a) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin,
K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;
Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.;
Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,
X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich,
S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A.
D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A.
G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.;
Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham,
M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian
03, revision B.04; Gaussian, Inc.: Wallingford, CT, 2004. (b) Becke, A.
D. J. Chem. Phys. 1993, 98, 5648. (c) Lee, C.; Yang, W.; Parr, R. G. Phys.
ReV. B 1988, 37, 785. (d) Miehlich, B.; Savin, A.; Stoll, H.; Preuss, H.
Chem. Phys. Lett. 1989, 15, 7200. (e) Hehre, W. J.; Ditchfield, R.; Pople,
J. A. J. Chem. Phys. 1972, 56, 2257. (f) Francl, M. M.; Pietro, W. J.; Hehre,
W. J.; Binkley, J. S.; Gordon, M. S.; DeFrees, D. J.; Pople, J. A. J. Chem.
Phys. 1982, 77, 3654. (g) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta
1973, 28, 213. (h) Rassolov, V. A.; Pople, J. A.; Ratner, M. A.; Windus, T.
L. J. Chem. Phys. 1998, 109, 1223. (i) Dunning, T. H., Jr. J. Chem. Phys.
1989, 90, 1007. (j) Woon, D. E.; Dunning, T. H., Jr. J. Chem. Phys. 1993,
98, 1358. (k) Wachters, A. J. H. J. Chem. Phys. 1970, 52, 1033. (l) Hay,
P. J. J. Chem. Phys. 1977, 66, 4377.
the carbon and hydrogen atoms of the C5H4 ring corresponds
to the crystallographic labeling schemes.
The crystal structure of II was obtained for purposes of
comparison with that of I, which was reported previously.1g The
structure of II contains two independent molecules (molecules
1 and 2) in the unit cell (Figure 1), and selected bond lengths
and angles for I and II are given in Table 2. Crystallographic
data for II and the coordination complexes, prepared here and
to be discussed below, are given in Table 3; complete tables of
bond lengths and angles may be found in the Supporting
Information.
The most important structural parameters for assessing the
relative contributions of the resonance structures IIa and IIb

New Complexes of C5H4PMePh2
Organometallics, Vol. 26, No. 6, 2007 1437
Table 2. Selected Bond Distances and Angles for I and IIa
II (molecule 1)
II (molecule 2)
I1g
Bond Lengths (Å)
P(1)-C(1)
P-Me
1.7277(17)
1.799(2)
1.810
1.429(3)
1.414(3)
1.374(3)
1.384(3)
1.405(3)
1.7268(17)
1.7921(19)
1.802
1.413(2)
1.429(2)
1.384(2)
1.383(3)
1.407(3)
1.718(2)
P-Ph (av)
C(1)-C(2)
C(1)-C(5)
C(2)-C(3)
C(4)-C(5)
C(3)-C(4)
1.806
1.430(3)
1.419(3)
1.392(4)
1.376(4)
1.401(4)
Bond Angles (deg)
C(1)-P(1)-Me
C(1)-P-Ph (av)
Me-P-Ph (av)
Ph(1)-P(1)-Ph(2)
C(1)-C(2)-C(3)
C(2)-C(3)-C(4)
C(3)-C(4)-C(5)
C(4)-C(5)-C(1)
C(5)-C(1)-C(2)
111.46(9)
111.44
106.96
108.37(8)
107.42(19)
108.85(18)
108.74(18)
107.47(18)
107.51(16)
111.96(9)
110.64
108.44
106.55(7)
108.36(16)
108.16(18)
108.87(15)
107.50(17)
107.11(16)
Figure 1. Molecular structures of the two molecules in the unit
cell of C5H4PMePh2.
111.4
107.5 (av)
106.8(2)
108.9(2)
108.8(2)
108.0(2)
107.4(2)
the P-Ph bonds in I and II (which fall within the typical range
for this type of C-P single bond in phenyl phosphonium
ylides13) but significantly longer than the PdCH2 bond in Ph3Pd
CH2 (1.66 Å).13 The latter compound is a typical example of a
non-resonance-stabilized ylide, and its PdCH2 bond is believed
to contain considerable double-bond character.13a Thus, the
P-C5H4 bond lengths of I and II are consistent with very
significant contribution from both the uncharged and zwitterionic
resonance structures Ia, Ib, IIa, IIb.
a Refer to A for the atom-labeling scheme.
to the overall electronic structure involve the bond lengths and
angles of the P-C5H4 moiety. The P-C5H4 bond length of I is
Interestingly, although the C-C-C bond angles within the
five-membered rings of both ylides are all very close to the
108° of a regular pentagon, the C-C bond lengths seemingly
also provide evidence for a degree of localization of π bond
electron density. Thus, while the structures of both molecules
exhibit long (C1-C2), short (C2-C3), long (C3-C4), short (C4-
C5), long (C5-C1) alternating patterns of bond lengths, as in Ia
and IIa, the “long” bonds are much shorter than a C-C typical
single-bond length and all bonds are similar to those of, e.g.,
benzene (1.3894 Å).13b Thus, again there is evidence for a very
1.718(2) Å,1g while those of the two molecules of II are 1.7277-
(17) and 1.7268(17) Å. The slight elongation of the P-C5H4
bond distances in II may be the result of having substituted a
phenyl group for the better donating methyl group, but more to
the point, these P-C5H4 bonds are all significantly shorter than
Table 3. Crystallographic Data
II
III
IV
V
VI
empirical formula
fw
C
18H17
P
C21H17CrO3P
400.32
180(2)
C21H17MoO3P
444.26
180(2)
C21H17WO3P
532.17
180(2)
0.710 73
monoclinic
P21/c
9.6818(12)
14.5322(17)
14.1153(17)
90
108.514(2)
90
1883.2(4)
4
1.877
6.236
C21.50H18ClI2MoO3P
740.52
180(2)
0.710 73
triclinic
P1h
9.3488(10)
16.5390(18)
16.6312(18)
94.800(2)
103.058(2)
90.427(2)
2495.3(5)
4
264.29
180(2)
0.710 73
triclinic
P1h
9.2856(8)
10.8254(9)
15.0721(13)
89.602(2)
83.260(2)
75.6430(10)
1457.2(2)
4
temp (K)
wavelength (Å)
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
0.710 73
monoclinic
P21/c
9.738(2)
14.410(3)
13.927(3)
90
108.742(4)
90
1850.8(6)
4
0.710 73
monoclinic
P21/c
9.6728(7)
14.5246(10)
14.1801(10)
90
108.3930(10)
90
1890.4(2)
4
γ (deg)
V (Å3)
Z
F(calcd) (g/cm3)
1.205
0.172
560
1.437
0.722
824
1.561
0.795
896
1.971
3.191
1404
µ (mm-1
F(000)
)
1024
cryst size (mm3)
θ range (deg)
index ranges
0.40 × 0.20 × 0.10
0.30 × 0.15 × 0.05
0.30 × 0.15 × 0.08
0.35 × 0.25 × 0.05
0.35 × 0.10 × 0.06
2.28-25.00
2.09-25.00
2.06-25.00
2.22-25.00
1.69-25.00
-10 e h e 11,
-12 e k e 11,
-17 e l e 17
-11 e h e 10,
-17 e k e 15,
-16 e l e 16
-11 e h e 11,
-17 e k e 17,
-15 e l e 16
-11 e h e 11,
-17 e k e 16,
-16 e l e 16
-10 e h e 11,
-18 e k e 19,
-19 e l e 19
no. of rflns collected
no. of indep rflns
8642
5090 (R(int) )
0.0171)
10 657
3263 (R(int) )
0.0373)
10 967
3334 (R(int) )
0.0283)
10 698
3319 (R(int) )
0.0540)
14 730
8747 (R(int) )
0.0384)
completeness to θ ) 25.00° (%)
max, min transmission
no. of data/restraints/params
goodness of fit on F2
99.50
100
100
99.90
99.40
1.0000, 0.7520
5090/0/343
1.000
1.0000, 0.8567
3263/0/235
1.000
1.0000, 0.8555
3334/0/235
1.000
0.5984, 0.2118
3319/0/235
1.000
1.0000, 0.6904
8747/0/532
1.000
final R indices (I > 2σ(I))
R1 ) 0.0377,
wR2 ) 0.1015
R1 ) 0.0374,
wR2 ) 0.0672
R1 ) 0.0253,
wR2 ) 0.0470
R1 ) 0.0270,
wR2 ) 0.0849
R1 ) 0.0489,
wR2 ) 0.0996
R indices (all data)
R1 ) 0.0509,
wR2 ) 0.1080
0.327, -0.299
R1 ) 0.0613,
wR2 ) 0.0710
0.443, -0.355
R1 ) 0.0381,
wR2 ) 0.0491
0.370, -0.267
R1 ) 0.0295,
wR2 ) 0.0864
0.923, -0.796
R1 ) 0.0832,
wR2 ) 0.1062
1.641, -1.349
largest diff peak, hole (e Å-3
)

1438 Organometallics, Vol. 26, No. 6, 2007
Brownie et al.
Scheme 2. Syntheses of (η5-C5H4PMePh2)M(CO)3 (M ) Cr,
Table 5. Selected Bond Lengths and Angles of Complexes
a,2g
III-V and (η5-C5H4PPh3)Cr(CO)3
Mo, W)
(η5-C5H4PPh3)Cr(CO)3
III
IV
V
molecule 1 molecule 2
Bond Lengths (Å)
P(1)-C(1)
P-Me
1.759(3) 1.759(3) 1.765(4) 1.751(5) 1.755(6)
1.789(3) 1.785(2) 1.786(4)
P-Ph (av)
M-C5 centroid
C(1)-C(2)
C(1)-C(5)
C(2)-C(3)
C(4)-C(5)
C(3)-C(4)
C(1)-metal
C(2)-metal
C(3)-metal
C(4)-metal
C(5)-metal
1.796
1.848
1.790
2.044
1.793
2.033
1.798
1.862
1.799
1.872
1.427(4) 1.434(3) 1.435(6) 1.431(8) 1.443(8)
1.429(4) 1.430(3) 1.438(6) 1.430(8) 1.441(8)
1.392(4) 1.403(3) 1.405(7) 1.452(9) 1.403(8)
1.397(4) 1.400(3) 1.393(7) 1.422(9) 1.386(9)
1.422(4) 1.417(3) 1.402(7) 1.394(10) 1.443(9)
2.185(2) 2.350(2) 2.342(4) 2.183(5) 2.192(6)
2.204(2) 2.352(2) 2.349(4) 2.201(6) 2.226(6)
2.226(3) 2.385(2) 2.371(4) 2.248(7) 2.257(6)
2.217(3) 2.403(3) 2.380(5) 2.249(7) 2.238(7)
2.191(3) 2.375(2) 2.367(5) 2.229(6) 2.230(6)
Table 4. Carbonyl Stretching Frequencies for the
Compounds III-V (in CH2Cl2), for the Neutral Arene
Compounds (η5-C6H6)M(CO)3 (M ) Cr, Mo, W; in
CH2Cl2),14a and for the Anionic Complexes
[(η5-C5H5)M(CO)3]- (M ) Cr, Mo, W; in THF)14b
ν(CO) (cm-1
)
M
(η5-C5H4PMePh2)M(CO)3 (η5-C6H6)M(CO)3 [(η5-C5H5)M(CO)3]-
Bond Angles (deg)
Cr
1915 (s), 1812 (s)
1971, 1892
1972, 1891
1971, 1887
1895, 1778
1898, 1781
1894, 1779
C(1)-P-Me
C(1)-P-Ph (av)
Me-P-Ph (av)
Ph-P-Ph
111.08(13) 110.91(12) 111.2(2)
Mo 1918 (s), 1812 (s)
1912 (s), 1808 (s)
109.78
109.38
109.48
109.36
109.19 110.3
109.35
109.4
W
107.37(12) 108.35(11) 108.4(2) 108.6
178.0 178.5 173.4
109.7
169.0
P-C(1)-C5 centroid 178.9
significant contribution from both the uncharged and the
zwitterionic resonance structures of I and II.
C(1)-C(2)-C(3)
C(2)-C(3)-C(4)
C(3)-C(4)-C(5)
C(4)-C(5)-C(1)
C(5)-C(1)-C(2)
108.3(3) 108.1(2) 107.4(4) 107.4(6) 107.7(6)
108.3(3) 108.1(2) 108.8(4) 108.4(6) 108.3(6)
108.3(3) 108.7(2) 109.1(4) 108.3(6) 108.4(6)
108.0(3) 108.0(2) 107.6(4) 108.8(6) 108.4(6)
107.1(2) 107.1(2) 107.1(4) 107.0(6) 107.2(6)
Syntheses, Structures, and Spectroscopic Properties of
Group 6 Complexes of II. The group 6 tricarbonyl complexes
III-V were synthesized using procedures similar to those
reported by Kotz et al. in the syntheses of the corresponding
complexes of I.2b An excess (2-3 equiv) of M(CO)6 (M ) Cr,
Mo) was refluxed in diglyme with II to give the resulting
chromium and molybdenum complexes in ∼60% yield for both
complexes (Scheme 2); however, the tungsten derivative
required the use of W(CO)3(CH3CN)3 to ensure ligand
substitution.2b An excess of W(CO)3(CH3CN)3 was heated with
II in diglyme to 110 °C to provide the tungsten complex in
70% yield.
The IR spectra (CH2Cl2, Table 4) of the complexes exhibit
two strong carbonyl stretching bands, consistent with an
essentially 3-fold -M(CO)3 moiety at frequencies nearly
identical with those reported for the corresponding complexes
of I.2b For purposes of comparison the ν(CO) values of the
analogous η6-benzene14a and anionic η5-C5H514b complexes are
also shown in Table 4, and it is clear that the donor properties
of II lie between those of benzene and Cp-, but possibly closer
to the latter. (The data for the Cp- complexes are believed to
be for the free ions, as the spectra were run in the presence of
ligands thought to coordinate to the countercations).14b These
data provide further evidence that the neutral ylides contain
significant negative charge on the C5H4 rings.
Selected 1H NMR data for III-V are given in Table 1, where
it is shown that coordination of II to a metal results in the two
multiplet C5H4 ring resonances shifting upfield relative to those
of the free ligand, while the P-Me 1H resonances shift
downfield for the three complexes. Compound III shows the
greatest change in the C5H4 ring proton resonances, which shift
upfield by ∼1.6 ppm upon complexation of II. The C5H4 proton
resonances for IV and V exhibit very similar chemical shifts
and are downfield of complex III by ∼0.6 ppm. Similar changes
are observed for the group 6 complexes of I.2b
a Refer to A for the atom-labeling scheme.
correlation between the resonance at δ 6.29 and both the Me
and the Ph resonances. Thus, the resonance at δ 6.29 is to be
assigned to the proton attached to carbon 2,5 (refer to A for
labeling scheme), since the proton of carbons 3 and 4 would
be expected to exhibit much less significant NOE correlations.
Carbon assignments were made in part via an HSQC experiment.
The resonances of the ipso and para carbons of the phenyl ring
were assigned on the basis of their carbon-phosphorus coupling
constants, although the corresponding ortho and meta carbon
resonances could not be assigned unambiguously because of
1
overlap in the H NMR spectrum. Assignment of these by use
of the P-C coupling constants was also impossible because of
the similarity in magnitudes of the two coupling constants, 10.6
and 11.5 Hz. Where feasible, assignments of the NMR spectra
of III-V were made similarly.
The 31P resonance of II shifts downfield some 10-12 ppm
on coordination in compounds III-V, but the differences among
the three coordination compounds are relatively small. No spin-
spin coupling to 183W was observed in the 31P spectrum of V.
On the other hand, the 13C NMR spectra exhibit significant
changes in the C5H4 ring carbon resonances on going from the
free ligand to complexes III-V. Thus, the resonance of C(1)
shifts from δ 79.2 in II to δ 65.8 ppm in III, δ 71.8 in IV, and
δ 70.5 in V, while much more dramatic shifts are observed for
the resonances of C(2) and C(3), which shift to higher field by
over 20 ppm.
X-ray structures of all three complexes III-V were obtained;
selected bond lengths and angles are given in Table 5 (see the
Supporting Information for full listings) and crystallographic
data in Table 3. Included in Table 5 are the literature data for
(η5-C5H4PPh3)Cr(CO)3, in which there are two independent
molecules in the unit cell (molecules 1 and 2).2g The structure
of (η5-C5H4PPh3)Cr(CO)3 offers a good structural comparison
with that of III and also allows for a general appraisal of
structural changes in this type of ligand on coordination. The
molecular structure of III is shown in Figure 2; since the crystals
of III-V are all isomorphous, the structures of the latter two
Assignments of the C5H4 proton resonances of II were made
via a NOESY experiment, which showed a strong NOE
(13) (a) Bart, J. C. J. J. Chem. Soc. B 1969, 350. (b) Pl´ıva, J.; Johns, J.
W. C.; Goodman, L. J. Mol. Spectrosc. 1990, 140, 214.
(14) (a) Brown, D. A.; Hughes, F. J. J. Chem. Soc. A 1968, 1519. (b)
Darensbourg, M. Y.; Jimenez, P.; Sackett, J. R.; Hanckel, J. M.; Kump, R.
L. J. Am. Chem. Soc. 1982, 104, 1521.

New Complexes of C5H4PMePh2
Organometallics, Vol. 26, No. 6, 2007 1439
as indicated in Scheme 3. Conformation 1 is increasingly
populated at lower temperatures, as indicated by significant
temperature dependence of the time-averaged chemical shift of
the edge hydrogen atom Ho, the observed chemical shift of Ho
moving to increasingly higher field as the temperature is lowered
because of ring current shielding arising in the close edge-
face association of Conformation 1.
The origin of the ring-edge attractive force is believed to
be largely electrostatic,15 the aromatic π electrons interacting
with a slightly positive Ho. In view of the apparent significance
of resonance structure IIb and in accord with DFT calculations
to be discussed below, it appears that the C5H4 rings of II and
its coordination complexes are not only aromatic in character
but also carry a significant partial negative charge, while the
MePh2P- moieties carry a partial positive charge. In addition,
for each of the compounds II-V, the distance between one of
the phenyl ortho C-H groups and C(1) of the C5H4 ring falls
well within the range of distances observed in the previously
reported compounds in which attractive edge-face interactions
have been established,15 and one would anticipate relatively
strong attractive interactions in compounds II-V. To seek
evidence for the phenomenon in solution, we ran a series of
Figure 2. Molecular structure of (η5-C5H4PMePh2)Cr(CO)3.
Scheme 3. Representation of On-Off Equilibrium for
Edge-Face Aromatic Ring Interactions
1
low-temperature H NMR experiments with II (to 213 K) and
IV (to 190 K). Unfortunately, no change in the 1H NMR
spectrum of either was observed, and thus although edge-face
interactions seem to be important in the solid state, no evidence
for them has been obtained in solution. However, we note that
the apparent electrostatic interactions in compounds II-V are
between phenyl ortho C-H groups and C(1) of the C5H4 rings
rather than with the centroids of the C5H4 rings. Thus, it is
possible that the ortho hydrogen atoms do not actually lie in
the region of ring-current-induced enhanced shielding.
Reactions of IV: Synthesis, Characterization, and Struc-
ture of [(η5-C5H4PMePh2)Mo(CO)3I][I]. As part of this study,
and to expand on the chemistry of the group 6 tricarbonyl ylide
complexes, we have carried out an investigation of the reac-
tivities of III and IV. Two classes of reactions were studied,
ligand substitution and oxidative addition.
are shown only in the Supporting Information. To our knowl-
edge, the structures of the Mo and W complexes are the first
reported crystallographically determined structures for these
metals with this class of ligand.
Compounds III-V all assume near-tetrahedral geometries
around the phosphorus atoms, similar to that seen for (η5-C5H4-
PPh3)Cr(CO)3.2g The C5H4PMePh2 is coordinated, as expected,
in an η5 fashion in all three complexes, with little difference in
the five C5H4-Cr distances. The ring carbon atoms C(2) and
C(5) essentially eclipse two of the carbonyl ligands, C(19) and
C(20), respectively, and thus the third carbonyl ligand assumes
a staggered orientation relative to C(3) and C(4). The P-C5H4
bond is elongated on coordination to all three metals. The same
We initially began the study of ligand substitution using PPh3,
with a view to substituting CO ligands of III and IV. To this
end, solutions of III or IV with 1 equiv of PPh3 were refluxed
in THF for up to 22 h while the reactions were monitored by
IR spectroscopy. No changes in the IR spectra were apparent
after this reaction time. We also attempted photochemical CO
substitution reactions of IV, but after 18 h of photolyzing a
CH2Cl2 solution of the metal complex and 1 equiv of phosphine,
no change in the IR spectrum was observed. We also attempted
CO substitution using PMe3, anticipating that the use of this
smaller, better donor would promote the ligand exchange. As
with the PPh3 experiment, however, no reaction occurred with
1 equiv of PMe3 after 18 h of photolysis. However, when 3.5
equiv of PMe3 was used in a photochemical reaction, the ν-
(CO) band of IV disappeared as a new set of peaks in the
carbonyl region grew in at 1830 and 1930 cm-1, very similar
to the literature values for fac-Mo(CO)3(PMe3)3.11 Consistent
degree of elongation is observed in (η5-C5H4PPh3)Cr(CO)3
2g
and probably indicates an increase in the contribution of the
zwitterionic structure on coordination: i.e., an increase in the
aromatic character in the C5H4 ring on coordination. The P(1)-
C(1)-C5(centroid) angle is essentially linear in III-V, the
greatest deviation from linearity being ∼2.1°. This is in contrast
to the case for both free ligands I and II, for which the P-C5H4
bonds are bent significantly out of the C5H4 ring planes. The
C5H4 ring bond lengths of II are slightly elongated in III-V,
as is observed in (η5-C5H4PPh3)Cr(CO)3,2g and the ring bond
angles are all very close to those of a regular pentagon (108°).
The PMePh2 moieties of compounds II-V are oriented such
that one of the phenyl rings not only eclipses the C5H4 ring but
is oriented toward it in an edge-on fashion in spite of the
apparently greater congestion in this conformation. Interestingly,
intramolecular edge-face orientations involving interactions of
aromatic hydrogen atoms with aromatic π systems have well-
established precedent in conformationally flexible compounds,
for which equilibria of the type shown generically in Scheme 3
can be established.15 In these cases, edge-face interactions are
sufficiently attractive that the molecules assume Conformation
1 in the solid state, although on-off equilibria exist in solution,
1
with this conclusion, H and 31P NMR spectra of the crude
reaction mixture clearly indicated that the ylide had been cleaved
from the metal, and in addition there appeared in the 31P NMR
spectrum a new peak at δ -17.2, also attributable to fac-Mo-
(CO)3(PMe3)3.11 The displacement by phosphines of η6-arenes
(15) (a) Desiraju, G. R. Crystal Engineering; Elsevier: Amsterdam, 1989;
pp 92-95. (b) Jennings, W. B.; Farrell, B. M.; Malone, J. F. Acc. Chem.
Res. 2001, 34, 885. (c) Carver, F. J.; Hunter, C. A.; Livingstone, D. J.;
McCabe, J. F.; Seward, E. M. Chem. Eur. J. 2002, 8, 2847. (d) Ercolani,
G.; Mencarelli, P. J. Org. Chem. 2003, 68, 6470.

1440 Organometallics, Vol. 26, No. 6, 2007
Brownie et al.
Table 6. Selected Bond Lengths and Angles of the Two
Molecules of VIa
molecule 1
molecule 2
Bond Lengths (Å)
1.780(8)
1.777(8)
1.792
P(1)-C(1)
P-Me
1.775(9)
1.789(8)
1.782
P-Ph (av)
M-C5 centroid
C(1)-C(2)
C(1)-C(5)
C(2)-C(3)
C(4)-C(5)
C(3)-C(4)
Mo-I(1)
1.997
1.994
1.436(10)
1.440(10)
1.428(11)
1.385(11)
1.401(11)
2.8355(9)
2.310(7)
2.301(8)
2.324(8)
2.360(8)
2.370(8)
1.437(11)
1.412(11)
1.418(12)
1.415(11)
1.386(12)
2.8176(10)
2.318(8)
2.292(8)
2.312(8)
2.361(9)
2.356(8)
C(1)-Mo
C(2)-Mo
C(3)-Mo
C(4)-Mo
C(5)-Mo
Bond Angles (deg)
108.1(4)
110.8
C(1)-P-Me
108.5(4)
109.6
111.0
107.1(4)
172.7
108.1(8)
108.3(8)
108.5(8)
108.9(8)
106.2(8)
Figure 3. Molecular structure of [(η5-C5H4PMePh2)Mo(CO)3I]I,
C(1)-P-Ph (av)
Me-P-Ph (av)
Ph-P-Ph
showing one of the independent molecules in the unit cell.
110.0
106.9(4)
170.2
107.0(8)
108.1(7)
109.7(8)
107.9(7)
107.2(7)
P-C(1)-C5 centroid
C(1)-C(2)-C(3)
C(2)-C(3)-C(4)
C(3)-C(4)-C(5)
C(4)-C(5)-C(1)
C(5)-C(1)-C(2)
of group 6 metal tricarbonyl complexes is known to give fac
isomers,11 and we believe this is occurring here. When the
photochemical reaction (18 h) was attempted using 3.5 equiv
of PPh3, no reaction occurred. This may be due to the large
size of PPh3 versus that of PMe3. In general, therefore, IV
appears to be relatively inert with respect to ligand exchange.
Reactions of the electrophilic reagents I2, MeI, and H2 with
IV were also investigated. The reaction of I2 with (η5-C5H4-
PPh3)Mo(CO)3 had been previously reported to give the Mo-
(II) complex [(η5-C5H4PPh3)Mo(CO)3I][PF6], but only IR and
elemental analysis data were reported.2d On the addition of 1
equiv of I2 to a solution of IV, the color of the solution changed
instantly to orange and, on workup, we isolated the crystalline
product [(η5-C5H4PMePh2)Mo(CO)3I]I. NMR data are given in
Table 1 and are consistent with this formulation. As anticipated,
the P-Me and C5H4 1H resonances are all significantly
deshielded relative to the precursor, IV; the C5H4 ring 13C
resonances are also significantly deshielded, but not the 13C
resonance of the P-Me group. The IR spectrum (CH2Cl2
solution) of VI exhibited two strong ν(CO) bands at 2055 and
1979 cm-1, as expected at higher frequencies than is the case
for IV but similar to the reported ν(CO) values for [(η5-C5H4-
PPh3)Mo(CO)3I][PF6] (2052, 1997, and 1976 cm-1; run as a
KBr disk).2d
a Refer to A for the atom-labeling scheme.
bonds are bent out of the plane of the C5H4 ring and away from
the metals in the two molecules by ∼9.8 and ∼7.3°.
The P-C5H4 bond lengths of the two molecules of VI are
slightly longer (1.780(8), 1.775(9) Å) than is the case with IV
(1.759(2) Å), while the C-C distances in the C5H4 ring lose
the alternating bond lengths found in II and IV. Both of these
factors are consistent with an increase in aromatic character in
the C5H4 ring on oxidation of the metal. The metal-C5H4 ring
centroid distance decreases (1.997 and 1.994 Å) on oxidation,
as is to be expected, but the individual Mo-C bond distances
vary somewhat irregularly, with the distances to C(4) and C(5)
being somewhat longer than those to C(1), C(2) and C(3).
Reaction of IV with MeI was attempted as a test of
nucleophilicity of IV. The analogous [(η5-C5H5)Mo(CO)3]-
reacts readily with MeI to give (η5-C5H5)Mo(CO)3Me,17 but IV
was found to be inert to MeI. There was also no reaction of IV
with H2.
Electronic Structures of C5H4PMePh2 (II) and (η5-C5H4)-
PMePh2Cr(CO)3 (III). Geometry optimizations of II and III
were carried out using B3LYP12b-d in a 6-31G* basis set.12e-h
The geometries obtained in this way were kept fixed in all
subsequent computations. Bond lengths and angles obtained in
the DFT-optimized structures for C5H4PMePh2 (II) and (η5-
C5H4)PMePh2Cr(CO)3 (III) are shown in Table 7, together with
the crystallographic data for II and III. As can be seen, the
calculated bond lengths and angles are generally in reasonable
agreement with the experimental data for both the free and
coordinated ylide ligand, and in particular the same trends are
observed. Thus, the P(1)-C(1) bonds of both compounds are
calculated to be significantly shorter than the averages of the
P-phenyl bonds, consistent with the calculated partial double-
bond character in the former; the Mulliken-Mayer bond index
for the P(1)-C(1) bond is about 1.2, as opposed to 0.9 for the
P-phenyl bonds. In addition, the experimentally observed
lengthening of the P(1)-C(1) bond on coordination is also
Crystals suitable for X-ray crystallography were grown, and
the crystal structure of VI is shown in Figure 3. Selected bond
distances and angles are given in Table 6 (see the Supporting
Information for full listings) and crystallographic data in Table
3. The crystal structure contains two independent molecules in
the unit cell, molecules 1 and 2, and one molecule of CH2Cl2.
As with III-V, the molecules assume piano-stool-type struc-
tures about the metal atoms and an ortho hydrogen atom of a
phenyl group is positioned relatively closely to C(1) of the C5H4
ring. Perhaps because of this, the coordinated iodine atoms are
oriented relatively closely to the phosphorus atoms, with the
P(1)-C(1)-Mo(1)-I(1) torsional angles being 47.0(5) and
59.7(5)° for molecules 1 and 2, respectively. Observation that
the phosphorus atoms are in close proximity to the coordinated
iodines seems surprising, but no covalent bonding interaction
is present, as the interatomic distances (4.474 and 4.325 Å)
exceed the sum of the van der Waals radii.16 Indeed, the P-C5H4
(16) Emsley, J. The Elements, 2nd ed.; Clarendon Press: Oxford, U.K.,
1991.
(17) Jolly, W. L. Inorg. Synth. 1968, 11, 116.

New Complexes of C5H4PMePh2
Organometallics, Vol. 26, No. 6, 2007 1441
Table 7. Calculated (6-31G* B3LYP) and Experimental
Bond Lengths and Angles of C5H4PMePh2 (II) and of
(η5-C5H4PMePh2)Cr(CO)3 (III)a
which they are bound, and even more so if one looks only at
the overall groups (C5H4 ring, phenyl rings, methyl). In this
case we find that the C5H4 ring of the free ligand carries a charge
of about -0.5 independent of the type of calculation, the phenyl
rings and the methyl group are near neutral, and the charge on
phosphorus is between +0.4 and +0.7, depending on the level
and basis set. Somewhat similar results have been reported
recently for I.1i
II
III
exptl
calcd
exptl
calcd
Bond Lengths (Å)
1.7277(17), 1.7268(17) 1.717
P(1)-C(1)
P-Me
1.759(3)
1.789(3)
1.796
1.427(4)
1.429(4)
1.392(4)
1.397(4)
1.422(4)
1.757
1.825
1.822
1.449
1.443
1.409
1.413
1.430
1.799(2), 1.7921(19)
1.810, 1.802
1.429(3), 1.413(2)
1.414(3), 1.429(2)
1.374(3), 1.384(2)
1.384(3), 1.383(3)
1.405(3), 1.407(3)
1.835
1.836
1.439
1.441
1.387
1.388
1.426
P-Ph (av)
C(1)-C(2)
C(1)-C(5)
C(2)-C(3)
C(4)-C(5)
C(3)-C(4)
In the case of the chromium complex III, calculations based
on all of the basis sets suggest that the C5H4 ring is less negative
than is the case in the free ligand, as anticipated, and that the
overall charge of the Cr(CO)3 group is negative, with the
negative charge largely delocalized onto the CO ligands. Again
the phosphorus atom carries a positive charge, while the methyl
and phenyl groups are essentially neutral.
Bond Angles (deg)
C(1)-P(1)-Me
111.46(9), 111.96(9)
110.47 111.08(13) 110.14
113.29 109.78
106.17 109.38
C(1)-P-Ph (av) 111.44, 110.64
111.95
107.45
Me-P-Ph (av)
Ph-P-Ph
106.96, 108.44
108.37(8), 106.55(7)
106.97 107.37(12) 107.64
We have also calculated the ylide-Cr(CO)3 bond dissociation
energy and have compared this with the analogous ring-metal
bond dissociation energy of (η6-C6H6)Cr(CO)3.18 The calcula-
tions were based on the B3LYP/6-31G* gas-phase geometries:
i.e., without reoptimization. Values of the calculated ylide-
Cr(CO)3 and C6H6-Cr(CO)3 bond dissociation energies varied
considerably, being consistently greater for MP2 than for
Hartree-Fock, as well as greater for the smaller basis set.
Interestingly, however, the ratio of the ylide-Cr(CO)3 to the
C6H6-Cr(CO)3 bond dissociation energy was consistently about
1.3, and thus the ylide-Cr(CO)3 bond dissociation energy
appears to be about 30% stronger than the C6H6-Cr(CO)3 bond
dissociation energy.
C(1)-C(2)-C(3) 107.42(19), 108.36(16) 107.36 108.3(3)
C(2)-C(3)-C(4) 108.85(18), 108.16(18) 108.88 108.3(3)
C(3)-C(4)-C(5) 108.74(18), 108.87(15) 108.89 108.3(3)
C(4)-C(5)-C(1) 107.47(18), 107.50(17) 107.24 108.0(3)
C(5)-C(1)-C(2) 107.51(16), 107.11(16) 107.61 107.1(2)
107.6
109.0
108.2
108.1
107.2
a Refer to A for the atom-labeling scheme.
reflected in the calculations. The alternating bond lengths of
the C5H4 rings of both free and coordinated ylide, noted above,
are also reproduced in the calculated geometries, as well as in
the bond indices (typically 1.2 for long and 1.5 for short bonds).
This finding lends further credence to our conclusion of
significant delocalization of the π system of the C5H4 rings.
The Mulliken charges for the free ligand II were computed
at the B3LYP, RHF, and MP2 levels of computation, both in
the Pople split-valence (6-31G*) and the Dunning double-ú (cc-
pVDZ) basis sets. While the charges calculated for individual
atoms are very basis set dependent, they become more consistent
if the hydrogen atoms are combined with the heavy atoms to
Contour plots of the HOMO and HOMO-1 of free C5H4-
PMePh2 are shown in Figure 4A,B, respectively. These differ
by only 6 kcal/mol and, as can be seen, correspond closely to
the doubly degenerate HOMO (E1 symmetry) of the free (D5h)
cyclopentadienyl anion.19 That they are not degenerate reflects
Figure 4. Contour plots of the HOMO (A), HOMO-1 (B), and HOMO-6 (C) of free C5H4PMePh2. The contour values are (0.05.

1442 Organometallics, Vol. 26, No. 6, 2007
Brownie et al.
Figure 5. Contour plots of the primary η5-C5H4-Cr interactions in (η5-C5H4PMePh2)Cr(CO)3, involving the dxz (A, HOMO-4) and dyz (B,
HOMO-3) orbitals on Cr. The contour values are (0.05.
5
2
2
Figure 6. Contour plots showing the interactions between the CO ligands and the d orbitals of (η -C5H4PMePh2)Cr(CO)3: (A) the dx -y
2
orbital (HOMO); (B) the dxy orbital (HOMO-1); (C) the dz orbital (HOMO-2). The contour values are (0.05.
the lack of symmetry in the molecule. The LUMO and
LUMO+1, as well as HOMO-2 to HOMO-5 of free C5H4-
PMePh2, are all essentially localized on the phenyl rings and
hence are not of interest here. However, Figure 4C shows the
HOMO-6 orbital, which is the low-energy, almost fully sym-
metric bonding MO of the C5H4 ring, corresponding to the fully
symmetric bonding A1 MO of the cyclopentadienyl anion.19
Interestingly, there appears to be little π-type interaction of any
of the orbitals shown in Figure 4 with an orbital on the
phosphorus atom, consistent with a lack of significant π
conjugation of the phosphorus atom with the C5H4 ring and
suggesting that the zwitterionic resonance structure IIb may
well be the better representation of the electronic structure of
II.
orbitals of the metal. If Cartesian axes are chosen as in Figure
5, then the receptor orbitals are the dxz and dyz orbitals, as shown
in the contour plots of parts A and B of Figure 5, respectively.
5
2
2
Orbitals of (η -C5H4PMePh2)Cr(CO)3 which are largely dx -y
2
(HOMO), dxy (HOMO-1), and dz (HOMO-2) in character but
which contribute to bonding with the CO ligands are shown in
parts A-C of Figure 6, respectively.
Summary. Methyldiphenylphosphonium cyclopentadienylide,
C5H4PMePh2 (II), has been synthesized and characterized
spectroscopically (1H, 13C{1H}, and 31P{1H} NMR) and crys-
tallographically, and its electronic structure has been investigated
via ab initio methodologies. The best representation of II appears
to be the zwitterionic structure IIb, and it is found that the
HOMO and HOMO-1 orbitals of II are near-degenerate and
exhibit symmetries very similar to those of the corresponding,
doubly degenerate HOMO (E1 symmetry) of the free (D5h)
cyclopentadienyl anion. There is also, at a lower energy, an
As with cyclopentadienyl complexes,19b the primary η5-
C5H4-Cr interaction involves donation from the near-degener-
ate, filled orbitals shown in Figure 4A,B into the appropriate d

New Complexes of C5H4PMePh2
Organometallics, Vol. 26, No. 6, 2007 1443
almost fully symmetric orbital which corresponds to the fully
symmetric bonding A1 MO of the cyclopentadienyl anion. In
none of these three orbitals do there appear to be significant π
interactions with an orbital on the phosphorus atom, again
consistent with the zwitterionic resonance structure IIb. Ob-
servations that II forms the stable coordination compounds (η5-
C5H4PMePh2)M(CO)3 (M ) Cr, Mo, W) also demonstrate that
the implied aromatic cyclopentadienyl anion-like structure is
of major significance. The three group 6 metal complexes have
Aspects of the chemistry of the compounds (η5-C5H4-
PMePh2)M(CO)3 (M ) Cr, Mo) have been investigated.
Thermal and photochemical substitution of the CO ligands by
equimolar amounts of PMe3 and PPh3 was not observed, but
the ylide is displaced photochemically from (η5-C5H4PMePh2)-
Mo(CO)3 by excess PMe3 to form fac-Mo(CO)3(PMe3)3. The
compound (η5-C5H4PMePh2)Mo(CO)3 does not react with MeI
or H2, but it does react with I2 to form [(η5-C5H4PMePh2)Mo-
(CO)3I]I, which has been characterized spectroscopically (IR,
1H, 13C{1H}, and 31P{1H} NMR) and crystallographically. An
interesting and unanticipated feature of the crystal structures
of the free ylide and all four of its coordination complexes is
that one of the ylide phenyl rings not only eclipses the C5H4
ring but also is oriented toward it in an edge-on fashion. The
intramolecular edge-face orientations involve interactions of
one aromatic hydrogen atom with the C5H4 aromatic π systems
and are rationalized in terms of electrostatic attractive forces
between the slightly positive phenyl hydrogen atom and the
negatively charged C5H4 ring.
1
been investigated by spectroscopy (IR and H, 13C{1H}, and
31P{1H} NMR), crystallography, and ab initio calculations. In
all cases the metal-carbon bond distances are very similar,
consistent with a cyclopentadienyl-like structure, while com-
parisons of ν(CO) values of the complexes (η5-C5H4PMePh2)M-
(CO)3 (M ) Cr, Mo, W) with those of the isoelectronic
complexes (η6-C6H6)M(CO)3 and [(η5-C5H5)M(CO)3]- suggest
that the electron-donating ability of the ylide is less than that
of the cyclopentadienyl anion but much greater than that of
benzene. The primary bonding interaction of the ylide with the
Cr(CO)3 moiety involves donation of the HOMO and HOMO-1
orbitals into the metal dxz and dyz orbitals, and the calculated
ylide-Cr(CO)3 bond dissociation energy is about 30% higher
than the analogous ring-metal bond dissociation energy of (η6-
C6H6)Cr(CO)3.
Acknowledgment. We thank the Government of Ontario
(Ontario Graduate Scholarship to J.H.B.), Queen’s University
(Queen’s Graduate Award to J.H.B.) and the Natural Sciences
and Engineering Research Council (Research Grant to M.C.B.)
for funding this research.
Supporting Information Available: Crystallographic details,
including figures of C5H4PMePh2, (η5-C5H4PMePh2)Cr(CO)3, (η5-
C5H4PMePh2)Mo(CO)3, (η5-C5H4PMePh2)W(CO)3 and [(η5-C5H4-
PMePh2)Mo(CO)3I]I, showing complete numbering schemes and
thermal ellipsoid figures, tables of positional and thermal parameters
and bond lengths and angles, and CIF files. This material is available
free of charge via the Internet at http://pubs.acs.org.
(18) Stoddart, M. W.; Brownie, J. H.; Schmider, H. L.; Baird, M. C. J.
Organomet. Chem. 2005, 690, 3440.
(19) (a) Jorgensen, W. L.; Salem, L. The Organic Chemist’s Book of
Orbitals; Academic Press: New York, 1973; p 237. (b) Albright, T. A.;
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