(2-(Dimethylammonium)ethyl)cyclopentadienyltricarbonyl-metalates: Group VI metal zwitterions. Attenuation of the bronsted basicity and nucleophilicity of formally anionic metal centers

Article abstract of DOI:10.1021/om050484d

Protonation of (2-(dimethylamino)ethyl)cyclopentadienyl (Cp^N) group VI metal carbonyl anions with acetic acid proceeds at the amine to provide zwitterionic (2-(dimethylammonium)- ethyl)cyclopentadienyltricarbonylmetalates, M(CO)₃(η⁵-Cp^NH) (M = Cr (1), Mo (2), W (3)). Few zwitterionic organometalates with anionic metal centers and positive charges that cannot be delocalized have been reported to date. The impact of the intramolecular charge separation on the structures and reactivity of zwitterionic organometalates is of current interest. The M(CO)₃ units of structurally characterized 1-3 are significantly perturbed in solution and the solid state due to ion-pairing between the pendant ammonium cation and anionic metal center. The concentration and solvent dependence of the ¹H NMR ammonium hydrogen chemical shifts of 1-3 and the intramolecular N...M separations of these zwitterions in the solid state are consistent with three-center-four-electron N - H...M hydrogen bonding. One other hydrogen bond with a zerovalent group VI metal acceptor has been characterized to date. The intramolecular charge separation attenuates the reactivity of the anionic metal centers of 1-3 relative to that of [M(CO) ₃(η⁵-Cp)]^-. Structurally characterized [WH(CO)₃- (η⁵-Cp^NH)]Cl (4) was the only isolable salt obtained from protonation of 1-3; the Cr and Mo analogues are unstable relative to 1 and 2, respectively. Structurally characterized [M(AuPPh₃)(CO)₃(η⁵-Cp^NH)]Cl (M = Mo (5), W(6)) were synthesized via reactions of 2 and 3, respectively, with Ph₃PAuCl and protonation of M(AuPPh₃)(CO) ₃(η⁵-Cp^N) (M = Mo (8), W (9)) with HCl. Pure samples of the analogous chromium salt were inaccessible from either 1 or structurally characterized Cr(AuPPh₃)(CO)₃(η ⁵-Cp^N) (7).

Full text of DOI:10.1021/om050484d

5116
Organometallics 2005, 24, 5116-5126
(2-(Dimethylammonium)ethyl)cyclopentadienyltricarbonyl-
metalates: Group VI Metal Zwitterions. Attenuation of
the Brønsted Basicity and Nucleophilicity of Formally
Anionic Metal Centers
Paul J. Fischer,*,† Kristina M. Krohn,† Edward T. Mwenda,† and
Victor G. Young, Jr.‡
Department of Chemistry, Macalester College, Saint Paul, Minnesota 55105-1899, and
Department of Chemistry, X-ray Crystallographic Laboratory, University of Minnesota,
Minneapolis, Minnesota 55455-0431
Received June 11, 2005
Protonation of (2-(dimethylamino)ethyl)cyclopentadienyl (CpN) group VI metal carbonyl
anions with acetic acid proceeds at the amine to provide zwitterionic (2-(dimethylammonium)-
ethyl)cyclopentadienyltricarbonylmetalates, M(CO)3(η5-CpNH) (M ) Cr (1), Mo (2), W (3)).
Few zwitterionic organometalates with anionic metal centers and positive charges that cannot
be delocalized have been reported to date. The impact of the intramolecular charge separation
on the structures and reactivity of zwitterionic organometalates is of current interest. The
M(CO)3 units of structurally characterized 1-3 are significantly perturbed in solution and
the solid state due to ion-pairing between the pendant ammonium cation and anionic metal
1
center. The concentration and solvent dependence of the H NMR ammonium hydrogen
chemical shifts of 1-3 and the intramolecular N‚‚‚M separations of these zwitterions in the
solid state are consistent with three-center-four-electron N-H‚‚‚M hydrogen bonding. One
other hydrogen bond with a zerovalent group VI metal acceptor has been characterized to
date. The intramolecular charge separation attenuates the reactivity of the anionic metal
centers of 1-3 relative to that of [M(CO)3(η5-Cp)]-. Structurally characterized [WH(CO)3-
(η5-CpNH)]Cl (4) was the only isolable salt obtained from protonation of 1-3; the Cr and Mo
analogues are unstable relative to 1 and 2, respectively. Structurally characterized
[M(AuPPh3)(CO)3(η5-CpNH)]Cl (M ) Mo (5), W(6)) were synthesized via reactions of 2 and 3,
respectively, with Ph3PAuCl and protonation of M(AuPPh3)(CO)3(η5-CpN) (M ) Mo (8), W
(9)) with HCl. Pure samples of the analogous chromium salt were inaccessible from either
1 or structurally characterized Cr(AuPPh3)(CO)3(η5-CpN) (7).
Introduction
metal centers have received relatively less attention to
date despite speculation that specifically designed in-
tramolecular dative-electrostatic interactions in the
coordination sphere of reduced metal centers could
govern catalyst activity or selectivity.1,3 Among these
zwitterions with a single metal, many feature conju-
gated ligands that allow negative charge delocaliza-
Zwitterionic organometalates exhibit interesting struc-
tures and reactivity due to the electronic impact of their
formal charge separation.1 Consideration of zwitter-
ions is important in transition metal catalyst design.
The catalytic activity of bis(cyclopentadienyl) com-
plexes with cationic group IV metal centers and in-
tramolecular anionic functions (e.g., Cp*2Zr(m-C6H4-
BPh3),2a (Cp*)(C5Me4CH2B(C6F5)3)Zr(C6H5)2b) depends
on the interaction between the opposite charges per-
mitted by the structure.2c-h Zwitterions with anionic
tion (e.g., W(CO)5{CdC(Ph)CH(Ph)CHdCHN(iPr)dC-
(OEt)},4a-c MoO(SC6H2iPr3-2,4,6)3{dC(Ph)CHdC(Ph)-
CH2PMe2Ph}4d). The incorporation of an sp3 carbon
between group VI metal pentacarbonyl units and con-
jugated systems (e.g., W(CO)5{CHN(nPr)dC(OMe)CHd
C(Ph)NCHdCHCHdC}4e) allows delocalization of posi-
* To whom correspondence should be addressed. E-mail: fischer@
macalester.edu.
† Macalester College.
‡ University of Minnesota.
(1) Chauvin, R. Eur. J. Inorg. Chem. 2000, 577.
(3) (a) Brunet, J.-J.; Chauvin, R.; Commenges, G.; Donnadieu, B.;
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10.1021/om050484d CCC: $30.25 © 2005 American Chemical Society
Publication on Web 09/16/2005

Group VI Metal Zwitterions
Organometallics, Vol. 24, No. 21, 2005 5117
through a column of activated Aceto Corp. catalyst R3-11 and
10 Å molecular sieves. The plumbing components of the gas
purification systems were made of glass and copper. Ultra-
Torr and Swagelock fittings were employed to provide con-
nections between glass and copper tubing that are imperme-
able to air. Solutions were routinely transferred via stainless
steel cannulas. Gastight syringes equipped with stainless steel
three-way stopcocks and needles were used to transfer solu-
tions when necessary. Standard Schlenk techniques were
employed with double manifold vacuum lines.12 Solids were
handled in a glovebox. Solvents were purified by standard
procedures and stored under argon. Literature procedures
were employed to prepare NaCpN and triphenylphosphinegold-
(I) chloride.13,14 The reagents M(CO)6 (M ) Cr, Mo, W),
concentrated aqueous HCl, trifluoroacetic acid, phosphoric
acid, and glacial acetic acid were used as received (Aldrich).
Solution infrared spectra were acquired on a Nicolet Magna
550 FTIR spectrometer with samples sealed in 0.1 mm gastight
NaCl cells. Nujol (mineral oil) mulls for IR spectra were
prepared in the glovebox. NMR samples were sealed under
argon into 5 mm tubes and were analyzed on a Varian Gemini
tive charge but permits retention of anionic metal
fragments in all resonance structures.4f Zwitterionic
organometalates that feature a single anionic metal and
a positive charge that cannot be delocalized are rare,
and these complexes exhibit fascinating properties.
Despite the formal negative charge on tungsten in the
zwitterionic olefin-coordinated imine complex W(CO)2-
(η2-(Z)-(Me2NdC(Me))CHdCHCOOH)(η5-Cp), the metal
neither deprotonates the carboxylic acid nor can be
methylated by CH3I.5 Zwitterionic HFe(CO)3(PPh2OCH-
(Ph)CH(Me)NMe3) exhibits an unexpected cis H-Fe-P
+
geometry to permit close contact between NMe3 and
[HFe]- in the vicinity of the hydride.3a
Zwitterionic organometalates have played an impor-
tant role in establishing the existence of hydrogen bonds
where transition metals function as acceptors.6 The
negatively charged platinum and dimethylammonium
substituent of PtBr(C,N-8-C10H6NMe2)(C-8-C10H6NMe2H)
participate in a N-H‚‚‚Pt hydrogen bond.7 Many three-
center-four-electron X-H‚‚‚M hydrogen bonds have
been characterized with electron-rich d8 and d10 metal
centers.6 Only one hydrogen bond involving a zerovalent
group VI metal acceptor has been reported to date. An
intramolecular O-H‚‚‚Mo hydrogen bond in the η6-
arene complex Mo(PMe3)3(η6-C6H5C6H3(Ph)OH) was
confirmed by Parkin in both solution and the solid
state.8
Our research group is exploring the chemistry of (2-
(dimethylamino)ethyl)cyclopentadienyl (CpN) metal car-
bonyl anions. The reactivity of transition metal CpN
complexes in which both the pendant amine and metal
center are susceptible to electrophilic attack is an area
of current interest.9 The lack of constraints on the amine
is not conducive to an intramolecular N-Sn interaction
in the tin(IV) derivatives M′(SnR3)(CO)3(η5-CpN) (M′ )
Mo, W; R ) Ph, cyclohexyl).10 The basicities of [M(CO)3-
(η5-Cp)]- (M ) Cr, Mo, W) determined by Norton and
Jordan11 suggested that protonation of the group VI
metal anions [M(CO)3(η5-CpN)]- 10 would occur at the
tertiary amine and provide zwitterionic organometalates
M(CO)3(η5-CpNH). We have synthesized and character-
ized these zwitterions in solution and the solid state.
The surprisingly unreactive tungsten center of W(CO)2-
(η2-(Z)-(Me2NdC(Me))CHdCHCOOH)(η5-Cp) prompted
us to explore the metal-based reactivity of these zwit-
terions toward protonation and electrophilic addition
with triphenylphosphinegold(I) chloride.
1
300 MHz FT-NMR spectrometer at ambient temperature. H
and 13C chemical shifts are reported in parts per million (δ)
1
and are given with reference to residual H and 13C solvent
references relative to TMS. Melting points (uncorrected) were
determined under argon in sealed capillary tubes on a Labora-
tory Devices Mel-Temp apparatus. Microanalyses were carried
out by H. Malissa and G. Reuter Analytische Laboratorien,
Lindlar, Germany.
Similar procedures were conducted to synthesize 1-3, 5-6,
and 7-9, respectively. Representative procedures for 1, 5, and
7 are provided below. Complete experimental details for 2, 3,
6, 8, and 9 are given in the Supporting Information.
Cr(CO)3(η5-CpNH) (1). CH3CN (70 mL) was added to Cr-
(CO)6 (0.754 g, 3.43 mmol) and NaCpN (0.600 g, 3.77 mmol).
The pale yellow solution was refluxed for 52 h. The CH3CN
was removed in vacuo, and THF (70 mL) was added to provide
a red-orange solution. Addition of a 20% v/v glacial acetic acid/
THF solution (1.20 mL containing 0.252 g, 4.19 mmol of
HC2H3O2) at ambient temperature resulted in a dark orange
suspension; the [Cr(CO)3(η5-CpN)]- was consumed within 15
min. The suspension was filtered through Celite. The filtrate
was concentrated in vacuo until ∼3 mL remained. An orange
solid precipitated upon addition of Et2O (70 mL). The nearly
colorless supernatant was removed. The solid was washed with
Et2O (2 × 50 mL) and dried in vacuo. Recrystallization from
CH3CN/Et2O provided orange, air-sensitive microcrystals (0.634
g, 68%). Anal. Calcd for C12H15CrNO3: C, 52.75; H, 5.53; N,
5.13. Found: C, 52.55; H, 5.52; N, 5.31. Mp: 204-205 °C (dec).
IR (CH3CN) ν(CO): 1906 (s), 1805 (m), 1782 (s) cm-1; (THF)
ν(CO): 1910 (s), 1814 (s), 1784 (s) cm-1; (CH2Cl2) ν(CO): 1908
(s), 1811 (s), 1778 (s) cm-1; (Nujol) ν(CO): 1896 (s), 1801 (s),
1789 (s, sh) cm-1. 1H NMR (CD3CN, 300 MHz): δ 10.34 (s, br,
1H, NH), 4.65 (app t, J ) 2.1 Hz, 2H, Cp), 4.41 (app t, J ) 2.1
Hz, 2H, Cp), 3.07 (t, J ) 6.0 Hz, 2H, CH2CH2N), 2.91 (s, 6H,
CH3), 2.65 (t, J ) 6.0 Hz, 2H, CH2CH2N). 13C{1H} NMR (CD3-
CN, 75 MHz): δ 244.1 (s, CO), 92.1 (s, quaternary C, Cp), 86.2
(s, Cp), 81.8 (s, Cp), 57.6 (s, CH2CH2N), 43.9 (s, CH3), 23.3 (s,
Experimental Section
General Procedures. All operations were performed under
an atmosphere of 99.5% argon further purified by passage
(5) (a) Butters, C.; Carr, N.; Deeth, R. J.; Green, M.; Green, S. M.;
Mahon, M. F. J. Chem. Soc., Dalton Trans. 1996, 2299. (b) Lee, L.;
Chen, D.-J.; Lin, Y.-C.; Lo, Y.-H.; Lin, C. H.; Lee, G.-H.; Wang, Y.
Organometallics 1997, 16, 4636.
(6) (a) Brammer, L. J. Chem. Soc., Dalton Trans. 2003, 3145, and
references therein. (b) Mart´ın, A. J. Chem. Educ. 1999, 76, 578, and
references therein.
(7) Wehman-Ooyevaar, I. C. M.; Grove, D. M.; Kooijman, H.; van
der Sluis, P.; Spek, A. L.; van Koten, G. J. Am. Chem. Soc. 1992, 114,
9916.
1
CH2CH2N). H NMR (C4D8O, 300 MHz): δ 11.79 (s, br, 1H,
NH). 13C{1H} NMR (C4D8O, 75 MHz): δ 243.3 (s, CO). 1H NMR
(CD2Cl2, 300 MHz): δ 12.15 (s, br, 1H, NH). 13C{1H} NMR
(CD2Cl2, 75 MHz): δ 243.1 (s, CO).
(12) (a) Shriver, D. F.; Drezdon, M. A. The Manipulation of Air-
Sensitive Compounds, 2nd ed.; Wiley-Interscience: New York, 1986.
(b) Ellis, J. E. ACS Symp. Ser. 1987, No. 357, 34.
(13) NaCpN: (a) Bradley, S.; Corradi, M. M.; Camm, K. D.; Furtado,
S. J.; McGowan, P. C.; Mumtaz, R.; Thornton-Pett, M. J. Organomet.
Chem. 2002, 656, 49. (b) Rees, W. S, Jr.; Dippel, K. A. Org. Prep. Proc.
Int. 1992, 24, 527.
(8) Hascall, T.; Baik, M.-H.; Bridgewater, B. M.; Shin, J. H.;
Churchill, D. G.; Friesner, R. A.; Parkin, G. Chem. Commun. 2002,
2644.
(9) Esteruelas, M. A.; Lo´pez, A. M.; On˜ate, E.; Royo, E. Inorg. Chem.
2005, 44, 4094.
(10) Fischer, P. J.; Krohn, K. M.; Mwenda, E. T.; Young, V. G., Jr.
Organometallics 2005, 24, 1776.
(14) Ph3PAuCl: Braunstein, P.; Lehner, H.; Matt, D. Inorg. Synth.
1990, 27, 218.
(11) Jordan, R. F.; Norton, J. R. J. Am. Chem. Soc. 1982, 104, 1255.

5118 Organometallics, Vol. 24, No. 21, 2005
Fischer et al.
Mo(CO)3(η5-CpNH) (2). Yield: 76%. Anal. Calcd for C12H15-
MoNO3: C, 45.44; H, 4.77; N, 4.42. Found: C, 45.25; H, 4.78;
N, 4.50. Mp: 221-222 °C (dec). IR (CH3CN) ν(CO): 1911 (s),
1809 (s), 1788 (s) cm-1; (THF) ν(CO): 1915 (s), 1819 (s), 1790
AuClMoNO3P: C, 44.38; H, 3.72; N, 1.73. Found: C, 44.30;
H, 3.71; N, 1.88. Mp: 192-193 °C (dec). IR (CH3CN) ν(CO):
1947 (s), 1910 (vw), 1857 (m, sh), 1837 (s) cm-1; (THF) ν(CO):
1948 (s), 1917 (w), 1864 (m, sh), 1843 (s) cm-1; (Nujol) ν(CO):
(s) cm-1; (CH2Cl2) ν(CO): 1913 (s), 1815 (s), 1784 (s) cm-1
;
1948 (s), 1864 (m), 1813 (s) cm-1 1H NMR (CD3CN, 300
.
(Nujol) ν(CO): 1900 (s), 1798 (s), 1771 (s) cm-1. 1H NMR (CD3-
CN, 300 MHz): δ 9.20 (s, br, 1H, NH), 5.25 (app t, J ) 2.1 Hz,
2H, Cp), 5.03 (app t, J ) 2.1 Hz, 2H, Cp), 3.02 (t, J ) 6.3 Hz,
2H, CH2CH2N), 2.85 (s, 6H, CH3), 2.74 (t, J ) 6.3 Hz, 2H, CH2-
CH2N). 13C{1H} NMR (CD3CN, 75 MHz): δ 234.0 (s, CO), 96.8
(s, quaternary C, Cp), 90.4 (s, Cp), 85.9 (s, Cp), 57.7 (s,
CH2CH2N), 43.7 (s, CH3), 23.5 (s, CH2CH2N). 1H NMR (C4D8O,
300 MHz): 1H δ 11.48 (s, br, 1H, NH). 13C{1H} NMR (C4D8O,
75 MHz): δ 232.9 (s, CO). 1H NMR (CD2Cl2, 300 MHz): δ 11.90
(s, br, 1H, NH). 13C{1H} NMR (CD2Cl2, 75 MHz): δ 232.6 (s,
CO).
MHz): δ 7.62-7.52 (m, 15H, AuPPh3), 5.48 (app t, J ) 2.1
Hz, 2H, Cp), 5.27 (app t, J ) 2.1 Hz, 2H, Cp), 2.82-2.65 (m,
4H, CH2CH2), 2.37 (s, 6H, CH3). 13C{1H} NMR (CD3CN, 75
2
MHz): δ 232.2 (s, CO), 134.8 (d, JPC ) 14.2 Hz, ortho C,
4
AuPPh3), 132.5 (d, JPC ) 2.4 Hz, para C, AuPPh3), 131.2 (d,
1JPC ) 51.2 Hz, ipso C, AuPPh3), 130.3 (d, 3JPC ) 10.7 Hz, meta
C, AuPPh3), 93.4 (s, quaternary C, Cp), 88.9 (s, Cp), 87.8 (s,
Cp), 60.2 (s, CH2CH2N), 44.0 (s, CH3), 26.2 (s, CH2CH2N).
[W(AuPPh3)(CO)3(η5-CpNH)]Cl (6). Yield: 61%. Anal.
Calcd for C30H30AuClNO3PW: C, 40.04; H, 3.36; N, 1.56.
Found: C, 40.09; H, 3.39; N, 1.61. Mp: 209-210 °C (dec). IR
(CH3CN) ν(CO): 1943 (s), 1850 (m, sh), 1831 (s) cm-1; (Nujol)
W(CO)3(η5-CpNH) (3). Yield: 60%. Anal. Calcd for C12H15-
NO3W: C, 35.58; H, 3.73; N, 3.46. Found: C, 35.41; H, 3.68;
N, 3.47. Mp: 203-204 °C (dec). IR (CH3CN) ν(CO): 1904 (s),
1803 (s), 1782 (s) cm-1; (THF) ν(CO): 2015 (m), 1920 (s), 1909
(s), 1813 (s), 1785 (s) cm-1; (CH2Cl2) ν(CO): 2017 (m), 1920 (s,
sh), 1907 (s), 1809 (s), 1779 (s) cm-1; (Nujol) ν(CO): 1905 (s,
1
ν(CO): 1944 (s), 1861 (m), 1808 (s) cm-1. H NMR (CD3CN,
300 MHz): δ 7.62-7.50 (m, 15H, AuPPh3), 5.57 (app t, J )
2.1 Hz, 2H, Cp), 5.35 (app t, J ) 2.1 Hz, 2H, Cp), 2.66 (s, br,
4H, CH2CH2N), 2.25 (s, 6H, CH3). 13C{1H} NMR (CD3CN, 75
2
MHz): δ 221.8 (s, CO), 134.8 (d, JPC ) 14.6 Hz, ortho C,
4
1
sh), 1894 (s), 1791 (s), 1763 (s) cm-1. H NMR (CD3CN, 300
AuPPh3), 132.5 (d, JPC ) 2.4 Hz, para C, AuPPh3), 131.5 (d,
1JPC ) 50.2 Hz, ipso C, AuPPh3), 130.3 (d, 3JPC ) 11.2 Hz, meta
C, AuPPh3), 93.4 (s, quaternary C, Cp), 87.8 (s, Cp), 86.4 (s,
Cp), 60.9 (s, CH2CH2N), 44.5 (s, CH3), 26.8 (s, CH2CH2N).
Cr(AuPPh3)(CO)3(η5-CpN) (7). CH3CN (100 mL) was
added to Cr(CO)6 (0.377 g, 1.71 mmol) and NaCpN (0.300 g,
1.88 mmol). The pale yellow solution was refluxed for 50 h.
The CH3CN was removed in vacuo; the residue was dissolved
in THF (60 mL) to provide an orange solution. A solution of
triphenylphosphinegold(I) chloride (0.847 g, 1.71 mmol) was
added, resulting in a bright yellow solution; the [Cr(CO)3(η5-
CpN)]- was consumed within 10 min. The solution was filtered
through alumina. The filtrate was concentrated in vacuo. The
resulting red oil was dissolved in Et2O (70 mL) and filtered.
The filtrate was concentrated in vacuo until ∼3 mL remained.
The addition of pentane (100 mL) precipitated a red-orange
oil. Trituration converted this oil into a yellow solid, which
was isolated by filtration, washed with pentane (3 × 10 mL),
and dried in vacuo. Recrystallization from Et2O/pentane
resulted in a brownish yellow, air-stable powder (0.700 g, 56%).
Anal. Calcd for C30H29AuCrNO3P: C, 49.26; H, 4.00; N, 1.91.
Found: C, 49.34; H, 3.96; N, 2.04. Mp: 97-98 °C (dec). IR
(THF) ν(CO): 1935 (s), 1856 (m, sh), 1828 (s) cm-1; (Et2O) ν-
(CO): 1940 (s), 1861 (m), 1833 (s) cm-1; (Nujol) ν(CO): 2002
MHz): δ 8.80 (s, br, 1H, NH), 5.27 (app t, J ) 2.4 Hz, 2H,
Cp), 5.06 (app t, J ) 2.4 Hz, 2H, Cp), 3.01 (t, J ) 6.3 Hz, 2H,
CH2CH2N), 2.83 (s, 6H, CH3), 2.81 (t, J ) 6.3 Hz, 2H, CH2-
CH2N). 13C{1H} NMR (CD3CN, 75 MHz): δ 224.6 (s, CO,
(
183W-13C satellites: 226.54, 224.00, 1JWC ) 192 Hz)), 96.8 (s,
quaternary C, Cp), 89.1 (s, Cp), 84.9 (s, Cp), 58.4 (s, CH2CH2N),
44.4 (s, CH3), 24.1 (s, CH2CH2N). 13C{1H} NMR (C4D8O, 75
MHz): δ 221.4 (s, CO). 13C{1H} NMR (CD2Cl2, 75 MHz): δ
221.0 (s, CO).
[WH(CO)3(η5-CpNH)]Cl (4). A 5% v/v concentrated aqueous
HCl/CH3CN solution (2.40 mL containing 0.053 g, 1.46 mmol
of HCl) was added to a pale yellow solution of W(CO)3(η5-CpNH
)
(0.500 g, 1.23 mmol) in CH3CN (50 mL). The solution im-
mediately became colorless; the W(CO)3(η5-CpNH) was con-
sumed within 5 min. The solution was filtered through Celite,
and the filtrate was concentrated in vacuo until ∼4 mL
remained. Dilution with Et2O (80 mL) resulted in the precipi-
tation of a white solid. The supernatant was removed. The
solid was washed with Et2O (3 × 30 mL) and dried in vacuo.
Recrystallization from CH3CN/Et2O provided white, moder-
ately air-sensitive microcrystals (0.380 g, 70%). Anal. Calcd
for C12H16NO3ClW: C, 32.64; H, 3.65; N, 3.17. Found: C, 32.78;
H, 3.70; N, 3.20. Mp: 168-169 °C (dec). IR (CH3CN) ν(CO):
1
(w), 1924 (s), 1869 (w), 1832 (s, sh), 1814 (s) cm-1. H NMR
2019 (s), 1923 (s) cm-1; (CH3OH) ν(CO): 2021 (s), 1929 (s) cm-1
;
(Nujol) ν(CO): 2026 (s), 1947 (s), 1889 (s) cm-1. 1H NMR (CD3-
CN, 300 MHz): δ 12.29 (s, br, 1H, NH), 5.65 (s, br, 2H, Cp),
5.46 (s, br, 2H, Cp), 3.12-2.90 (m, 4H, CH2CH2), 2.72 (s, 6H,
(CD2Cl2, 300 MHz): δ 7.62-7.44 (m, 15H, AuPPh3), 4.85 (app
t, J ) 2.1 Hz, 2H, Cp), 4.71 (app t, J ) 2.1 Hz, 2H, Cp), 2.41
(m, 4H, CH2CH2N), 2.12 (s, 6H, CH3). 13C{1H} NMR (CD2Cl2,
2
1
75 MHz): δ 240.2 (s, CO), 134.6 (d, JPC ) 14.2 Hz, ortho C,
CH3), -7.25 (s, br, 1H, WH). H NMR (CD3OD, 300 MHz): δ
1
AuPPh3), 131.9 (s, br, para C, AuPPh3), 130.7 (d, JPC ) 50.8
NH not observed due to exchange with solvent, 5.80 (app t, J
) 2.1 Hz, 2H, Cp), 5.57 (app t, J ) 2.10 Hz, 2H, Cp), 3.35-
3.25 (s, 4H, CH2CH2), 2.93 (s, 6H, CH3), -7.23 (s, integrates
to <1H due to exchange with solvent, WH (183W-1H satellites:
Hz, ipso C, AuPPh3), 129.7 (d, 3JPC ) 11.2 Hz, meta C, AuPPh3),
106.1 (s, quaternary C, Cp), 84.1 (s, Cp), 83.1 (s, Cp), 61.2 (s,
CH2CH2N), 45.7 (s, CH3), 27.9 (s, CH2CH2N).
1
-7.17, -7.30, JWH ) 39 Hz)). 13C{1H} NMR (CD3OD, 75
Mo(AuPPh3)(CO)3(η5-CpN) (8). Yield: 45%. Anal. Calcd
for C30H29AuMoNO3P: C, 46.47; H, 3.77; N, 1.81. Found: C,
46.57; H, 3.75; N, 1.85. Mp: 87-88 °C (dec). IR (THF) ν(CO):
1947 (s), 1862 (m, sh), 1840 (s) cm-1; (Nujol) ν(CO): 1944 (s),
MHz): δ 218.4 (s, br, CO), 109.0 (s, quaternary C, Cp), 91.2
(s, Cp), 89.2 (s, Cp), 60.3 (s, CH2CH2N), 43.8 (s, CH3), 25.2 (s,
CH2CH2N).
1843 (s, sh), 1824 (s) cm-1 1H NMR (CD2Cl2, 300 MHz): δ
.
[Mo(AuPPh3)(CO)3(η5-CpNH)]Cl (5). A solution of triph-
enylphosphinegold(I) chloride (0.319 g, 0.645 mmol) in CH3-
CN (125 mL) was added to a yellow solution of Mo(CO)3(η5-
CpNH) (0.205 g, 0.646 mmol) in CH3CN (10 mL). The Mo(CO)3(η5-
CpNH) was consumed within 10 min. The solution was filtered
through Celite. CH3CN was removed in vacuo from the filtrate
until ∼5 mL remained and a pale yellow, microcrystalline solid
had precipitated. Dilution with Et2O (60 mL) resulted in
additional precipitation. The supernatant was removed. The
solid was washed with Et2O (3 × 50 mL) and dried in vacuo.
Recrystallization from CH3CN/Et2O provided pale yellow, air-
sensitive microcrystals (0.315 g, 60%). Anal. Calcd for C30H30-
7.62-7.44 (m, 15H, AuPPh3), 5.83 (app t, J ) 2.1 Hz, 2H, Cp),
5.21 (app t, J ) 2.1 Hz, 2H, Cp), 2.52-2.34 (m, 4H, CH2CH2N),
2.11 (s, 6H, CH3). 13C{1H} NMR (CD2Cl2, 75 MHz): δ 231.8
2
(s, CO), 134.6 (d, JPC ) 14.6 Hz, ortho C, AuPPh3), 131.8 (d,
4JPC ) 2.5 Hz, para C, AuPPh3), 131.0 (d, 1JPC ) 50.8 Hz, ipso
C, AuPPh3), 129.6 (d, 3JPC ) 11.2 Hz, meta C, AuPPh3), 112.1
(s, quaternary C, Cp), 88.2 (s, Cp), 86.8 (s, Cp), 61.9 (s,
CH2CH2N), 45.9 (s, CH3), 28.1 (s, CH2CH2N).
W(AuPPh3)(CO)3(η5-CpN) (9). Yield: 49%. Anal. Calcd for
C30H29AuNO3PW: C, 41.74; H, 3.39; N, 1.62. Found: C, 41.62;
H, 3.34; N, 1.53. Mp: 99-100 °C (dec). IR (DME) ν(CO): 1943

Group VI Metal Zwitterions
Organometallics, Vol. 24, No. 21, 2005 5119
Table 1. Crystal Data, Data Collection, Solution, and Refinement for 1-4
1
2
3
4
empirical formula
fw
C
12H15CrNO3
C
12H15MoNO3
C
12H15NO3W
C12H16ClNO3W
441.56
273.25
317.19
405.10
cryst color
morphology
cryst size (mm)
cryst syst
space group
a (Å)
yellow
colorless
block
0.22 × 0.20 × 0.08
monoclinic
P21/n
colorless
block
0.15 × 0.12 × 0.08
monoclinic
P21/n
colorless
plate
pyramid
0.20 × 0.20 × 0.20
monoclinic
P21/n
0.16 × 0.12 × 0.03
orthorhombic
Pnma
7.0927(8)
13.3643(14)
12.5749(13)
90
7.1688(8)
13.5094(14)
12.6905(13)
90
7.1578(6)
13.4710(12)
12.6744(11)
90
26.028(4)
8.0667(11)
6.9001(10)
90
b (Å)
c (Å)
R (deg)
â (deg)
91.057(2)
90
93.127(2)
90
92.8780(10)
90
90
90
γ (deg)
V (Å3)
1191.8(2)
4
1227.2(2)
4
1220.56(18)
4
1448.8(4)
4
Z
F(calc) (Mg m-3
)
1.523
1.717
2.205
2.024
µ (mm-1
F(000)
)
0.955
1.064
9.459
8.157
568
640
768
840
θ range (deg)
2.22-27.51
-9 e h e 9
0 e k e 17
0 e l e 16
9901
2.20-27.52
-9 e h e 9
0 e k e 17
0 e l e 16
14 940
2.21-27.51
-9 e h e 9
0 e k e 17
0 e l e 16
14 901
1.56-27.49
-33 e h e 32
-10 e k e 10
-8 e l e 8
13 448
index ranges
no. of rflns collected
no. of indep rflns
R(int)a
2719
2830
2809
1776
0.0261
0.0466
0.0381
0.0685
no. of obsd rflns
max./min. transmn
no. of data/restraints/params
R1;b wR2c (I > 2σ(I)
GOF on F2
2394
2518
2566
1362
0.8320/0.8320
2719/0/156
0.0332; 0.0756
1.089
0.9197/0.7996
2830/0/156
0.0224; 0.0567
1.070
0.5183/0.3311
2809/0/156
0.0182; 0.0465
1.074
0.7919/0.3552
1776/2/107
0.0363; 0.0780
1.048
largest diff peak/hole (e Å-3
)
0.328/-0.346
0.463/-0.266
1.253/-0.462
1.365/-1.703
2
2
2
2
2
a R(int) ) ∑|Fo - Fc |/∑|Fo |. b R1 ) ∑||Fo| - |Fc||/∑|Fo|. c wR2 ) [∑[w(Fo - Fc )2]/∑[w(Fo2)2]]1/2
.
(s), 1856 (m, sh), 1835 (s) cm-1; (THF) ν(CO): 1943 (s), 1857
non-merohedral twin with twin law [1 0 0/0 -1 0/0.564 0 -1],
an 180° rotation about the [100] axis in reciprocal space. Out
of 194 reflections, 43 indexed uniquely to component 1, 43
indexed uniquely to component 2, 148 were common to both,
and no reflections were left unindexed. During data collection
a randomly oriented region of reciprocal space was surveyed
to the extent of one sphere to a resolution of 0.77 Å (1-7) or
0.84 Å (8). Four major sections of frames were collected with
0.30° steps in ω. Final cell constants were calculated from the
actual data collection after integration (SAINT).15a The inten-
sity data were corrected for absorption and decay by the
SADABS16 (1-5, 7) or TWINABS15b,16b (6, 8) program. The
Strip Redundant V13 program15c removed redundant reflec-
tions from the data of 8. Reflections involving systematic
absences were removed from the data of 8 with the SysAb-
sFilterV13 program.15c Space groups were determined on the
basis of systematic absences and intensity statistics. Successful
direct-methods solutions were calculated, which provided most
non-hydrogen atoms from the E-maps. Several full-matrix
least-squares/difference Fourier cycles were performed to
locate the remainder of the non-hydrogen atoms. All non-
hydrogen atoms were refined with anisotropic displacement
parameters. All hydrogen atoms, except the hydride of 4, were
placed in ideal positions and refined as riding atoms with
relative isotropic displacement parameters. The tungsten
hydride of 4 was found from the difference map and refined
accordingly. For 3, the largest difference Fourier peak is in
the vicinity of the W atom. The unit cell of 8 features a small
void (34 Å3) that water may occupy; there is no peak in the
difference Fourier to suggest any solvent. For 8, the ratio of
twin components is 0.606:0.394. All calculations were per-
formed on Pentium computers using the SHELXTL V6.14 suite
of programs.15a Crystal data, data collection, solution, and
refinement information for 1-4 and 5-8 are provided in
Tables 1 and 2, respectively.
(m, sh), 1836 (s) cm-1; (Nujol) ν(CO): 1932 (s), 1818 (s) cm-1
.
1H NMR (CD2Cl2, 300 MHz): δ 7.60-7.42 (m, 15H, AuPPh3),
5.47 (app t, J ) 2.1 Hz, 2H, Cp), 5.28 (app t, J ) 2.1 Hz, 2H,
Cp), 2.58-2.36 (m, 4H, CH2CH2N), 2.11 (s, 6H, CH3). 13C{1H}
NMR (CD2Cl2, 75 MHz): δ 221.3 (s, CO, (183W-13C satellites:
222.42, 220.21, 1JWC ) 167 Hz)), 134.6 (d, 2JPC ) 14.6 Hz, ortho
3
C, AuPPh3), 131.8 (s, br, para C, AuPPh3), 129.6 (d, JPC
)
11.2 Hz, meta C, AuPPh3), 110.3 (s, quaternary C, Cp), 87.1
(s, Cp), 85.5 (s, Cp), 61.9 (s, CH2CH2N), 45.7 (s, CH3), 28.0 (s,
CH2CH2N).
X-ray Crystallographic Characterization of 1-8. X-ray
quality crystals of 1-6 were obtained by diffusion of Et2O into
a CH3CN solution of each compound. Crystals of 7 were
obtained by evaporation of an 80% v/v pentane/Et2O solution.
Crystals of 8 were obtained by evaporation of a pentane
solution. All manipulations with the crystals of 1-6 were
conducted in a N2-filled glovebag; these crystals were selected
from the mother liquor. Crystals of 7 and 8 were dried in vacuo
and selected in air. A selected crystal was coated with viscous
oil, placed onto the tip of a 0.1 mm diameter glass capillary,
and mounted on a Bruker SMART Platform CCD diffracto-
meter for data collection (Mo KR radiation with λ ) 0.71073
Å) at 173(2) K. For 1-5, 7, and 8, a preliminary set of cell
constants was calculated from reflections harvested from three
sets of 20 frames; four sets of 30 frames were used for 6. The
SMART program15a indexed the non-twins 1-5 and 7. The
CellNow program15b indexed 6 as a two-component non-
merohedral twin; of the 424 reflections used, 303 indexed
exclusively to twin component 1, 121 indexed exclusively to
twin component 2, and 167 were common to both. The twin
law for 6 is best described as an 180° rotation in reciprocal
space about the [1h01] axis. The twin law matrix by rows is
[0.233 0.000 -0.766/0.000 -1.000 0.000/-1.234 0.000 -0.233].
The CellNow program15b also indexed 8 as a two-component
(15) (a) SMART V5.054 2001, SAINT+ V6.45 2003, SHELXTL V6.14
2000; Bruker Analytical X-ray Systems: Madison, WI. (b) CellNow,
TWINABS; G. M. Sheldrick, 2003. (c) Strip Redundant V13, SysAb-
sFilterV13; W. W. Brennessel, V. G. Young, Jr., 2003, unpublished
programs.
(16) (a) SADABS (Siemens Area Detector Absorption correction
program); G. M. Sheldrick, 1996. (b) Blessing, R. Acta Crystallogr.
1995, A51, 33.

5120 Organometallics, Vol. 24, No. 21, 2005
Table 2. Crystal Data, Data Collection, Solution, and Refinement for 5-8
Fischer et al.
5
6
7
8
empirical formula
fw
C
30H30AuClMoNO3P
C30H30AuClNO3PW
899.79
C30H29AuCrNO3P
731.48
C30H29AuMoNO3P
775.42
811.88
cryst color
morphology
cryst size (mm)
cryst syst
space group
a (Å)
colorless
needle
0.13 × 0.07 × 0.06
monoclinic
P21/n
colorless
needle
colorless
needle
colorless
needle
0.30 × 0.10 × 0.08
monoclinic
P21/c
0.40 × 0.05 × 0.05
monoclinic
P21/c
0.35 × 0.05 × 0.04
monoclinic
P21/c
8.9559(9)
23.828(2)
14.0808(14)
90
15.541(2)
23.874(3)
17.795(3)
90
11.169(4)
19.417(8)
13.637(5)
90
11.8991(16)
18.567(3)
13.8647(19)
90
b (Å)
c (Å)
R (deg)
â (deg)
97.029(2)
90
115.381(2)
90
106.889(6)
90
109.127(2)
90
γ (deg)
V (Å3)
2982.3(5)
4
5965.1(15)
8
2829.9(19)
4
2894.1(7)
4
Z
F(calc) (Mg m-3
)
1.808
2.004
1.717
1.780
µ (mm-1
F(000)
)
5.508
8.941
5.650
5.582
1576
3408
1432
1504
θ range (deg)
1.69-27.51
-11 e h e 11
0 e k e 30
0 e l e 18
35 927
1.45-27.53
-20 e h e 18
0 e k e 31
0 e l e 23
117 682
1.88-27.49
-14 e h e 14
-25 e k e 24
-17 e l e 16
25 554
1.81-25.03
-14 e h e 13
0 e k e 22
0 e l e 16
46 807
index ranges
no. of rflns collected
no. of indep rflns
R(int)a
6850
13 682
6456
5113
0.0596
0.0900
0.0584
0.0760
no. of obsd rflns
Max./min. transmn
no. of data/restraints/params
R1;b wR2c (I > 2σ(I)
GOF on F2
5221
10158
4593
3941
0.7334/0.5345
6850/0/345
0.0350; 0.0728
1.106
0.5348/0.1745
13 682/0/690
0.0328; 0.0584
0.990
0.7654/0.2109
6456/0/336
0.0394; 0.0682
1.039
0.8076/0.2454
5113/0/337
0.0318; 0.0441
0.995
largest diff peak/hole (e Å-3
)
1.809/-0.627
1.501/-0.972
0.824/-1.429
1.084/-0.785
2
2
2
2
2
a R(int) ) ∑|Fo - Fc |/∑|Fo |. b R1 ) ∑||Fo| - |Fc||/∑|Fo|. c wR2 ) [∑[w(Fo - Fc )2]/∑[w(Fo2)2]]1/2
.
Table 3. ν(CO) IR Data (cm-1) for M(CO)3(η5-CpNH) and [PPN][M(CO)3(η5-CpN)]
complex
CH3CN
THF
1
1906 (s), 1805 (m), 1782 (s)
1889 (s), 1771 (s)
1910 (s), 1814 (s), 1784 (s)
1890 (m), 1776 (s)
[PPN][Cr(CO)3(η5-CpN)] (10)
2
1911 (s), 1809 (s), 1788 (s)
1893 (s), 1775 (s)
1915 (s), 1819 (s), 1790 (s)
1894 (s), 1779 (s)
[PPN][Mo(CO)3(η5-CpN)] (11)
3
1904 (s), 1803 (s), 1782 (s)
1887 (s), 1770 (s)
2015 (m), 1920 (s), 1909 (s), 1813 (s), 1785 (s)
1888 (s), 1774 (s)
[PPN][W(CO)3(η5-CpN)] (12)
Scheme 1
suggest cation penetration into the coordination sphere,
giving Cs ion pairs with reduced electron density at the
metal center relative to 10-12. The lowest and highest
energy ν(CO) absorptions of 1-3 are shifted higher by
approximately 12 and 16 cm-1, respectively, relative to
the corresponding absorptions of 10-12. This contrasts
the ν(CO) IR spectra of [NMe4][M′(CO)3(η5-Cp)] (M′ )
Cr, Mo) in THF, which suggest contact ion-pairing
between the cation and CO ligands.17 The ν(CO) IR
spectrum of 3 in THF suggests that a second, even
tighter ion-pair persists in this solvent. Although the
additional carbonyl absorptions are strikingly similar
to those of WH(CO)3(η5-Cp)11 and 4, no spectroscopic
evidence could be obtained to support proton transfer
to tungsten in THF, consistent with the stability of [Et3-
NH][W(CO)3(η5-Cp)].11 Tight ion-pairing is also evident
in hydrogen-bonding solvents. Complexes 1-3 are spar-
ingly soluble in methanol and pyridine; the ν(CO) IR
spectra in these solvents are similar to those in CH3-
Results and Discussion
Synthesis of M(CO)3(η5-CpNH) and Characteriza-
tion in Solution. Reactions of M(CO)6 and NaCpN
followed by protonation with acetic acid afforded M(CO)3-
(η5-CpNH) (Scheme 1). These zwitterions engage in tight
ion-pairing; the positive charge is completely localized
at the ammonium nitrogen and the tethered substituent
is sufficiently flexible to permit its approach toward the
anionic metal center. Comparison of the ν(CO) IR
spectra of 1-3 with those of [PPN][M(CO)3(η5-CpN)]10
indicates that the M(CO)3 units of 1-3 are significantly
perturbed in solution (Table 3). The perturbation in
CH3CN is noteworthy since alkali metal salts of [M(CO)3-
(η5-Cp)]- display spectra indicative of a symmetrical
solvent field about the anions in this solvent but engage
in ion-pairing in THF.17 The infrared spectra for 1-3
CN. The ν(CO) IR spectra of 1-3 in THF do not change
13
upon addition of excess acetic acid (3 equiv). The δ
-
CO of 1-3 in CD3CN are upfield those of 10-12 in this
solvent by 2.9, 3.3, and 3.5 ppm, respectively (Table 4).
These chemical shifts for 1-3 are solvent dependent;
the 13CO resonances of 1, 2, and 3 in CD2Cl2 are shifted
upfield 1.0, 1.4, and 3.6 ppm, respectively, relative to
those in CD3CN. The ν(CO) IR and 13CO NMR spectral
data suggest that 3 exhibits the tightest ion-pairing
(17) Darensbourg, M. Y.; Jimenez, P.; Sackett, J. R.; Hanckel, J.
M.; Kump, R. L. J. Am. Chem. Soc. 1982, 104, 1521.

Group VI Metal Zwitterions
Organometallics, Vol. 24, No. 21, 2005 5121
Table 4. 13C NMR 13CO Chemical Shifts (ppm) of
companied by significant irregularity in the (O)C-M-
C(O) angles of 1-3. The C(12)-M-C(10) angles are
larger than the corresponding C(12)-M-C(11) angles
by approximately 7.5°, 6.8°, and 6.6° in 1-3, respec-
tively. Compression of C(12)-M-C(11) primarily ac-
commodates C(12)-M-C(10) expansion; the M(10)-M-
C(11) angles of 1-3 are statistically indistinguishable
from the average (O)C-M-C(O) angles of 10-12,
respectively. Important average structural parameters
for the M(CO)3 units of 1-3 (1: Cr-C(O), 1.820(7) Å;
C-O, 1.169(6) Å; O-C-Cr, 178.2(5)°; 2: Mo-C(O),
1.946(11) Å; C-O, 1.16(1) Å; O-C-Mo, 177.8(9)°; 3:
W-C(O), 1.944(9) Å; C-O, 1.171(8) Å; O-C-W, 177.2-
(9)°) are statistically identical to those of 10-12, re-
spectively. However, the slight elongation of average
M-C(O) lengths (∼1-2σ) and contraction of average
C-O lengths (∼1σ) in 1-3 are consistent with less
electron rich metal centers than found in 10-12.
Although the average M-C(dienyl) lengths of 1-3 (1,
2.217(5) Å; 2, 2.379(4) Å; 3, 2.367(5) Å) are statistically
indistinguishable from those of 10-12, the minor ring
slippage in 10-12, attributed to steric hindrance be-
tween the 2-(dimethylamino)ethyl substituent and
M(CO)3 fragment, is not observed in the unambiguously
η5-Cp complexes 1-3. The approach of the pendant
cation toward M(CO)3 draws C(1) closer to the metal
and results in nearly uniform M-C(dienyl) lengths.
M(CO)3(η5-CpNH) and [PPN][M(CO)3(η5-CpN)]
complex
CD3CN
C4D8O
243.3
CD2Cl2
243.1
1
10
2
11
3
12
244.1
247.0
234.0
237.3
224.6
228.1
232.9
221.4
232.6
221.0
among these zwitterions. This is consistent with [W(CO)3-
(η5-Cp)]- being the most basic among its group VI
analogues.
The possibility that N-H‚‚‚M hydrogen bonds ac-
company the tight ion-pairing of 1-3 in solution cannot
1
be ruled out. Downfield shifts of the H NMR bridging
hydrogen atom resonance are diagnostic of hydrogen
bonding. The δ NH of 1-3 is solvent and concentration
dependent; the limited solubility of 2 and 3 permitted
evaluation of only dilute solutions of these complexes
(Table 5). The ammonium hydrogen of [Et3NH][Co(CO)4]
exhibits a resonance at δ 8.31 in C6D6.18 In Mo(PMe3)3-
(η6-C6H5C6H3(Ph)OH) (13), the bridging hydroxylic hy-
drogen is coupled to the three phosphorus nuclei and
exhibits a resonance at δ 8.2.8 Deshielding of the
bridging hydrogen as solute concentration increases is
a general condition associated with hydrogen bonding.
The concentration dependence of δ NH appears to be
independent of solution composition; a CD3CN solution
containing equimolar quantities of 1-3 (total conc 0.165
M) exhibited a single NH resonance at δ 9.81, nearly
identical to that of a 0.17 M solution of 1. Further NH
deshielding as solvent polarity decreases (C4D8O, CD2-
Cl2) is consistent with enhanced hydrogen bonding due
to even tighter ion-pairing.
Structural Characterization of M(CO)3(η5-CpNH).
Complexes 1-3 were characterized by single-crystal
X-ray crystallography to examine the ion-pairing inter-
action in the solid state. The three-legged piano-stool
structures of 1-3 are shown in Figures 1-3, respec-
tively. The N‚‚‚M distances 3.5479(15), 3.6068(16), and
3.613(2) Å in 1-3, respectively, are similar to the O‚‚‚
Mo separation in 13 (3.571(2) Å)8 and the intermolecular
N‚‚‚Co length of [Et3NH][Co(CO)4] (3.667(2) Å),18 con-
sistent with hydrogen bonding in the solid state. The
NH hydrogen atoms of 1-3 were not located, so H‚‚‚M
lengths and N-H-M angles for 1-3 were calculated
(Supporting Information) on the basis of the N-H
length (1.033 Å) expected from neutron diffraction.19
Although these calculated parameters are also consis-
tent with hydrogen-bonding interactions involving tran-
sition metal acceptors, the elongated neutron diffraction
N-H distance in [Et3NH][Co(CO)4] (1.054(1) Å)18 indi-
cates that accurate determination of NH hydrogen
coordinates is required to unambiguously characterize
these intramolecular interactions as hydrogen bonds.
The electrostatic attraction between the anionic metal
centers and the ammonium ion results in marked
structural differences in 1-3 relative to their conjugate
bases 10-12.10 Approach of the pendant cation toward
M(CO)3 units causes widening of C(12)-M-C(10) ac-
Protonation of M(CO)3(η5-CpNH). The Brønsted
basicity of the formally anionic metal centers of 1-3 is
reduced relative to that of [M(CO)3(η5-Cp)]-. Addition
of excess acetic acid to 1-3 did not protonate the metal
centers of these zwitterions even though this acid reacts
with Na[M(CO)3(η5-Cp)] to provide MH(CO)3(η5-Cp).20
While strong acids stoichiometrically react with [M(CO)3-
(η5-Cp)]- to provide these hydrides, attempts to isolate
pure salts containing [M′H(CO)3(η5-CpNH)]+ (M′ ) Cr,
Mo) were uniformly unsuccessful. Reactions of 1 and 2
with 1 equiv of phosphoric acid, concentrated hydro-
chloric acid, or trifluoroacetic acid in THF resulted in a
mixture of metal hydride and starting zwitterion on the
basis of IR spectroscopy; the product ν(CO) absorptions
were very similar to those of M′H(CO)3(η5-Cp).11 Excess
strong acid (5-10 equiv) was required to completely
protonate 1 and 2 in solution. However, attempts to
isolate the metal hydride products, with removal of the
excess acid, resulted in formation of 1 and 2. Protonation
of 1 with these acids in CH3CN provided the same
outcome. Reaction of 2 with 1 equiv of these acids in
CH3CN at -10 °C resulted in instantaneous production
of Mo(CO)3(CH3CN)3 via reductive elimination. The
hydride MoH(CO)3(η5-Cp) decomposes in acetonitrile to
provide Mo(CO)3(CH3CN)3, but the reaction was found
sufficiently slow at 0 °C to permit experimentation with
the hydride at that temperature.11,21 Pure [WH(CO)3-
(η5-CpNH)]Cl (4) was obtained from the reaction of 3 and
hydrochloric acid (Scheme 2). The lower and higher
energy ν(CO) absorptions of 4 in CH3CN are shifted
higher by 8 and 11 cm-1, respectively, relative to those
1
of WH(CO)3(η5-Cp) (14) in CH3CN.11 A H NMR reso-
nance at δ -7.25 for the tungsten hydride of 4 in CD3-
(18) Brammer, L.; McCann, M. C.; Morris Bullock, R.; McMullan,
R. K.; Sherwood, P. Organometallics 1992, 11, 2339.
(19) International Tables for Crystallography; Kluwer: Dordrecht,
1992; Vol. C, Table 9.5.1.1, p 703.
(20) Haines, R. J.; Nyholm, R. S.; Stiddard, M. H. B. J. Chem. Soc.
(A) 1968, 46.
(21) Kubas, G. J.; Kiss, G.; Hoff, C. D. Organometallics 1991, 10,
2870.

5122 Organometallics, Vol. 24, No. 21, 2005
Table 5. 1H NMR NH Chemical Shifts (ppm) of M(CO)3(η5-CpNH
Fischer et al.
)
solvent
CD3CN
CD3CN
CD3CN
CD3CN
CD3CN
CD3CN
CD3CN
C4D8O
CD2Cl2
conc (M)
0.067
8.46
8.02
7.83
0.10
8.92
8.68
8.40
0.13
9.41
9.15
0.17
9.78
0.20
10.07
0.27
10.27
sat.
sat.
sat.
1
2
3
10.34a
9.20b
8.80c
11.79d
11.48e
h
12.15f
11.90g
h
Sat. conc (M): a 0.29. b 0.15. c 0.12. d 0.07. e 0.05. f 0.06. g 0.04. h Resonance not observed.
Figure 3. Molecular structure of 3 (50% thermal el-
lipsoids). Selected bond lengths (Å) and angles (deg):
W-C(1) ) 2.374(3), W-C(2) ) 2.365(3), W-C(3) ) 2.361-
(3), W-C(4) ) 2.372(3), W-C(5) ) 2.365(3), W-C(10) )
1.948(3), W-C(11) ) 1.950(3), W-C(12) ) 1.934(3), C(10)-
O(1) ) 1.167(4), C(11)-O(2) ) 1.165(4), C(12)-O(3) )
1.180(4), C(12)-W-C(10) ) 91.26(13), C(12)-W-C(11) )
84.70(13), C(10)-W-C(11) ) 86.74(13), O(1)-C(10)-W )
176.6(3), O(2)-C(11)-W ) 178.3(3), O(3)-C(12)-W )
176.8(3).
Figure 1. Molecular structure of 1 (50% thermal el-
lipsoids). Selected bond lengths (Å) and angles (deg): Cr-
C(1) ) 2.2224(17), Cr-C(2) ) 2.2111(18), Cr-C(3) )
2.214(2), Cr-C(4) ) 2.2203(19), Cr-C(5) ) 2.2184(17), Cr-
C(10) ) 1.8239(19), Cr-C(11) ) 1.8238(19), Cr-C(12) )
1.8122(19), C(10)-O(1) ) 1.167(2), C(11)-O(2) ) 1.165-
(2), C(12)-O(3) ) 1.176(2), C(12)-Cr-C(10) ) 93.47(8),
C(12)-Cr-C(11) ) 85.96(8), C(10)-Cr-C(11) ) 88.43(8),
O(1)-C(10)-Cr ) 177.90(17), O(2)-C(11)-Cr ) 178.75-
(16), O(3)-C(12)-Cr ) 178.00(18).
Scheme 2
shown in Figure 4. Complex 4 lies on a crystallographic
mirror plane. Four pendant group atoms (C(4-7)) are
disordered 50:50 over this plane. The related MoH(CO)3-
(η5-Cp) (16) also adopts an approximate Cs molecular
symmetry.23 The configuration of 4, in which the car-
bonyl trans to the hydride is staggered with respect to
C-H bonds of the Cp ring, while the hydride and two
carbonyl ligands are oriented in a nearly eclipsed
orientation, is consistent with the structures of 1522 and
16. It is noteworthy that the hydride of 4 was located
and refined since this was not possible with 1424 and
15, previous WH(CO)3(η5-C5HxR5-x) complexes charac-
terized by X-ray crystallography. The W-H distance of
4 is statistically indistinguishable from that determined
for gas phase 14 (1.79(2) Å) (microwave spectroscopy)25
and the Mo-H distance in MoH(CO)3(η5-C5Me5) (1.789-
(7) Å) (neutron diffraction).23 In 4, the η5-Cp ring is
Figure 2. Molecular structure of 2 (50% thermal el-
lipsoids). Selected bond lengths (Å) and angles (deg): Mo-
C(1) ) 2.3833(18), Mo-C(2) ) 2.3744(19), Mo-C(3) )
2.377(2), Mo-C(4) ) 2.3833(19), Mo-C(5) ) 2.3752(19),
Mo-C(10) ) 1.945(2), Mo-C(11) ) 1.958(2), Mo-C(12) )
1.936(2), C(10)-O(1) ) 1.166(2), C(11)-O(2) ) 1.154(2),
C(12)-O(3) ) 1.174(2), C(12)-Mo-C(10) ) 91.05(8), C(12)-
Mo-C(11) ) 84.21(8), C(10)-Mo-C(11) ) 86.36(8), O(1)-
C(10)-Mo ) 177.26(17), O(2)-C(11)-Mo ) 178.78(18),
O(3)-C(12)-Mo ) 177.22(18).
CN is intermediate that of 14 (δ -7.40)11 and WH(CO)3-
(η5-C5H4CO2H) (15) (δ -7.03)22 in this solvent.
Structural Characterization of [WH(CO)3(η5-Cp-
NH)]Cl. Complex 4 was characterized by single-crystal
X-ray crystallography, and its molecular structure is
(23) Brammer, L.; Zhao, D.; Morris Bullock, R.; McMullan, R. K.
Inorg. Chem. 1993, 32, 4819.
(24) Johnson, P. L. Diss. Abstr. B 1968, 2905, 1626.
(22) Shafiq, F.; Szalda, D. J.; Creutz, C.; Morris Bullock, R. Orga-
nometallics 2000, 19, 824.

Group VI Metal Zwitterions
Organometallics, Vol. 24, No. 21, 2005 5123
Scheme 3
Figure 4. Molecular structure of 4 (50% thermal el-
lipsoids). Selected bond lengths (Å) and angles (deg):
W-H(1W) ) 1.75(9), W-C(1) ) 2.373(9), W-C(2) ) 2.345-
(6), W-C(2A) ) 2.346(6), W-C(3/3A) ) 2.306(7), W-C(8/
8A) ) 1.971(7), W-C(9) ) 1.969(10), C(8/8A)-O(1/1A) )
1.147(8), C(9)-O(2) ) 1.173(12), N‚‚‚Cl ) 3.066(7), C(8A)-
W-C(8) ) 106.5(4), C(9)-W-C(8/8A) ) 80.6(3), O(1/1A)-
C(8/8A)-W ) 178.3(7), O(2)-C(9)-W ) 178.0(10).
Characterization of Cr(AuPPh3)(CO)3(η5-CpN).
The spectroscopic data for 7 are consistent with CpN
being the strongest donor ligand among related Cr-
(AuPPh3)(CO)3(η5-C5HxR5-x) complexes. The ν(CO) IR
absorptions of 7 are shifted to lower energies than the
corresponding absorptions of Cr(AuPPh3)(CO)3(η5-Cp),20
Cr(AuPPh3)(CO)3(η5-C5H4CHO) (17),26 and [(CO)3Cr-
(µ,η5-C5H4PPh2)Au]2;27 the δ 13CO of 7 (240.2) is also
downfield that of 17 (δ 236.6). Although AuPR3 ligands
are ubiquitous, 7 is only the fourth complex containing
a Cr-AuPR3 unit to be characterized by X-ray crystal-
lography and the second containing a structurally
characterized unsupported bond of this type. The four-
legged piano-stool structure of 7 is displayed in Figure
5. The Au-Cr length of 7 (2.6291(11) Å) is statistically
identical to those of 17 (2.632(2) Å)26 and [n-Bu4N][Au-
(Cr(CO)3(η5-Cp))2] (2.641(9), 2.635(8) Å)28 and shorter
than the supported Au-Cr bonds in (Ph3PAu)(µ-H)Cr-
(CO)5 (2.770(2) Å)29 and cis-{η2-(Ph3PAu)2}Cr(CO)4-
(PPh3) (2.7038(7), 2.6932(6) Å).30 Important average
structural parameters of 7 (Cr-C(O), 1.84(1) Å; C-O,
1.168(9) Å; M-C(dienyl), 2.19(1) Å) and the angles that
define its AuCr(CO)3 geometry are statistically indis-
tinguishable from those of 17. Semibridging carbonyl-
gold interactions were claimed in 17 on the basis of the
distances between Au and its adjacent CO carbons
(2.429(13), 2.494(15) Å) and modest deviation from
linearity in the O-C-Cr angles for these ligands (171.3-
(12)°, 171.8(12)°). Although 7 exhibits nearly identical
structural features, other expected changes in the
bridging CO ligands associated with this type of inter-
action are imperceptible and emphasize that these
alleged interactions are exceedingly weak. Specifically,
elongation in C-O lengths for the semibridging carbo-
nyls relative to the trans C-O distance is statistically
indistinguishable. Structural parameters associated
with the Au atom and the closer CO defined by C(10)
in 7 are very similar to those in Mo(AuPPh3)(CO)3(η5-
C10H9BNiPr2) (18) (Au-C(O), 2.485(3) Å; C-O, 1.171-
oriented such that the tethered group occupies space
above the hydride and between symmetrically equiva-
lent CO ligands defined by C(8) and C(8A). In 15, the
carboxylic acid function and the assumed location of the
hydride are between different sets of carbonyl ligands.
The impact of Cp substituent orientation on the (O)C-
W-C(O) angle that accommodates the hydride appears
minimal, as this angle in 4 (106.5(4)°) is only slightly
larger than that of 15 (105.1(4)°). Important average
structural parameters of 4 (W-C(O), 1.970(1) Å; W-C(di-
enyl), 2.34(3) Å; C-O, 1.16(2) Å; O-C-W, 178.2(2)°) are
statistically identical to those of 15. However, the
W-C(O) distances of 4 are significantly more uniform
than in 15 (av 1.96(2) Å), where the carbonyl trans to
the hydride has the longest W-C(O) length. The η5-Cp
of 4 engages in minor tilting; the W-C(1) distance is
0.067 Å longer (∼7σ) than the uniform W-C(3/3A)
distances due to steric influence of the substituent.
Reactions of M(CO)3(η5-CpNH) with Triphenyl-
phosphinegold(I) Chloride. An investigation into the
metal-based nucleophilicity of 1-3 was initiated with
reactions of the zwitterions and Ph3PAuCl due to the
AuPPh3+/H+ isolobal analogy. Reactions of 1 and Ph3-
PAuCl in THF and CH3CN were reminiscent of the
unsuccessful protonation attempts of 1. Excess Ph3-
PAuCl (3 equiv) was required to completely convert 1
to [Cr(AuPPh3)(CO)3(η5-CpNH)]Cl in solution on the basis
of IR spectroscopy; its ν(CO) IR spectrum was nearly
identical with that of Cr(AuPPh3)(CO)3(η5-CpN) (7).
Subsequent removal of excess Ph3PAuCl resulted in
formation of 1; pure samples of [Cr(AuPPh3)(CO)3(η5-
CpNH)]Cl could not be obtained. Pure salts [M(AuPPh3)-
(CO)3(η5-CpNH)]Cl (M ) Mo (5), W (6)) were isolated
from reactions of 2 and 3, respectively, with Ph3PAuCl.
Complexes 5 and 6 were also accessible via protonation
of M(AuPPh3)(CO)3(η5-CpN) (M ) Mo (8), W (9)) with
concentrated HCl (1 equiv). Reactions of M(CO)6 and
NaCpN, followed by addition of Ph3PAuCl, afforded
complexes 7-9 (Scheme 3). Concentrated HCl (1 equiv)
reacted with 7 to provide 1.
(26) Edelmann, F.; To¨fke, S.; Behrens, U. J. Organomet. Chem. 1986,
309, 87.
(27) Brumas-Soula, B.; Dahan, F.; Poilblanc, R. New J. Chem. 1998,
1067.
(28) Braunstein, P.; Schubert, U.; Burgard, M. Inorg. Chem. 1984,
23, 4057.
(25) (a) Tanjaroon, C.; Karunatilaka, C.; Keck, K. S.; Kukolich, S.
G. Organometallics 2005, 24, 2848. (b) Tanjaroon, C.; Keck, K. S.;
Sebonia, M. M.; Karunatilaka, C.; Kukolich, S. G. J. Chem. Phys. 2004,
121, 1449.
(29) Green, M.; Orpen, A. G.; Salter, I. D.; Stone, F. G. A. J. Chem.
Soc., Chem. Commun. 1982, 813.
(30) Esterhuysen, M. W.; Raubenheimer, H. G. Acta Crystallogr.
2003, C59, m286.

5124 Organometallics, Vol. 24, No. 21, 2005
Fischer et al.
Figure 6. Molecular structure of 5 (50% thermal el-
lipsoids). Selected bond lengths (Å) and angles (deg): Au-
Mo ) 2.7063(5), Au-C(10) ) 2.540(6), Au-C(12) ) 2.613-
(6), Mo-C(1) ) 2.357(6), Mo-C(2) ) 2.320(6), Mo-C(3) )
2.314(6), Mo-C(4) ) 2.350(7), Mo-C(5) ) 2.391(6), Mo-
C(10) ) 1.966(6), Mo-C(11) ) 1.954(6), Mo-C(12) ) 1.969-
(7), O(1)-C(10) ) 1.159(7), O(2)-C(11) ) 1.158(7), O(3)-
C(12) ) 1.163(7), N‚‚‚Cl ) 2.976(5), P-Au-Mo ) 174.47(4),
C(10)-Mo-C(12) ) 105.8(2), C(10)-Mo-C(11) ) 80.4(2),
C(11)-Mo-C(12) ) 82.7(2), C(11)-Mo-Au ) 120.70(17),
C(10)-Mo-Au ) 63.57(17), C(12)-Mo-Au ) 65.76(16),
O(1)-C(10)-Mo ) 171.6(5), O(2)-C(11)-Mo ) 179.5(6),
O(3)-C(12)-Mo ) 172.9(5).
Figure 5. Molecular structure of 7 (50% thermal el-
lipsoids). Selected bond lengths (Å) and angles (deg): Au-
Cr ) 2.6291(11), Au-C(10) ) 2.461(5), Au-C(12) ) 2.493-
(5), Cr-C(1) ) 2.217(5), Cr-C(2) ) 2.193(5), Cr-C(3) )
2.184(5), Cr-C(4) ) 2.179(5), Cr-C(5) ) 2.192(5), Cr-
C(10) ) 1.841(6), Cr-C(11) ) 1.821(5), Cr-C(12) ) 1.848-
(6), O(1)-C(10) ) 1.176(6), O(2)-C(11) ) 1.159(6), O(3)-
C(12) ) 1.168(6), P-Au-Cr ) 177.59(4), C(10)-Cr-C(12)
) 109.3(2), C(10)-Cr-C(11) ) 82.0(2), C(11)-Cr-C(12) )
85.9(2), C(11)-Cr-Au ) 121.31(17), C(10)-Cr-Au )
63.99(16), C(12)-Cr-Au ) 64.98(16), O(1)-C(10)-Cr )
172.1(4), O(2)-C(11)-Cr ) 177.2(5), O(3)-C(12)-Cr )
171.9(5).
(CO)3(η5-Cp) (21).20 Complexes 5, 6, and 8 were char-
acterized by single-crystal X-ray crystallography; the
four-legged piano-stool structures of these substances
are shown in Figures 6-8, respectively. The structure
of 6 differs from that of 5 by doubling the contents of
the unit cell to one with Z ) 8/Z′ ) 2 in P21/c (5 was
found in P21/n); the two unique cation/anion pairs of 6
were found with a pseudoinversion relationship.33 The
Au-M distances of 5 (2.7063(5) Å), 6 (2.7060(5), 2.7121-
(5) Å), 8 (2.7208(6) Å), 19 (2.710(1) Å),34 20 (2.7121(5)
Å),32 and 21 (2.698(3) Å)35 are nearly uniform. Important
average distances (Å) such as M-C(dienyl) (5, 2.35(3);
6, 2.34(3); 8, 2.33(3) Å), M-C(O) (5, 1.963(8); 6, 1.958-
(7); 8, 1.947(1) Å), and C-O (5, 1.160(3); 6, 1.17(1); 8,
1.167(12) Å) are statistically identical, as expected. In
each complex, the η5-Cp engages in minor tilting away
from the AuPPh3 ligand; the pendant group exerts no
perceptible steric impact on metal-Cp binding. For
example, in 5, C(5) is ∼0.077 Å (∼13σ) farther from Mo
than C(3); the M-C(1) and M-C(4) distances are nearly
uniform. The AuM(CO)3 geometries of 5, 6, and 8 are
very similar; the structural parameter that exhibits the
largest variation is the trans C(11)-M-Au angle.
However, the largest difference in this angle among
these complexes is only ∼6.2°, between that of 6 (cation
Table 6. ν(CO) IR and 13CO NMR Data of
[M(AuPPh3)(CO)3(η5-CpNH)]Cl and
M(AuPPh3)(CO)3(η5-CpN) (M ) Mo, W)
complex
ν(CO) IR (cm-1
)
δ 13CO (ppm)
5
1947 (s), 1910 (vw), 1857 (m, sh),
1837 (s)a
232.2b
8
6
9
1947 (s), 1862 (m, sh), 1840 (s)c
1943 (s), 1850 (m, sh), 1831 (s)a
1943 (s), 1857 (m, sh), 1836 (s)c
231.8d
221.8b
221.3d
a CH3CN. b CD3CN. c THF. d CD2Cl2
(3) Å; O-C-Mo, 171.5(2)°), where a semibridging
interaction was ruled out.31
Characterization of [M(AuPPh3)(CO)3(η5-CpNH)]-
Cl and M(AuPPh3)(CO)3(η5-CpN) (M ) Mo, W). The
ν(CO) IR and 13CO NMR spectral data of 5, 8 and 6, 9,
respectively, are virtually identical (Table 6); protona-
tion of the pendant amine has no apparent electronic
impact on the M(CO)3 units of these complexes. The ν-
(CO) IR absorptions of 5 and 8 are shifted to slightly
lower energies than those of Mo(AuPPh3)(CO)3(η5-Cp)
(19),20 Mo(AuPPh3)(CO)3(η5-C5H4CHO) (20),32 and [(CO)3-
Mo(µ,η5-C5H4PPh2)Au]2.27 These absorptions of 6 and 9
are similarly shifted lower than those of W(AuPPh3)-
(33) In order for this doubling to occur, half of the inversion centers
become general sites. On the basis of the W atom positions the
pseudoinversion center is located at (0.2426 0.4948 0.2378). The x and
y coordinates of this pseudoinversion center are sufficiently far from
the 1/4 fractional coordinates as to not hamper the least-squares
refinement of 6. Drawings that compare the unit cells of 5 and 6 are
in the Supporting Information.
(34) Pethe, J.; Maichle-Mo¨ssmer, C.; Stra¨hle, J. Z. Anorg. Allg.
Chem. 1997, 623, 1413.
(35) Wilford, J. B.; Powell, H. M. J. Chem. Soc. (A) 1969, 8.
(31) Braunstein, P.; Cura, E.; Herberich, G. E. J. Chem. Soc., Dalton
Trans. 2001, 1754.
(32) Strunin, B. N.; Grandberg, K. I.; Andrianov, V. G.; Setkina, V.
N.; Perevalova, E. G.; Struchkov, Y. T.; Kursanov, D. N. Dokl. Akad.
Nauk SSSR 1985, 281, 599.

Group VI Metal Zwitterions
Organometallics, Vol. 24, No. 21, 2005 5125
Figure 7. Molecular structure of the unique cation/anion pairs of 6 (50% thermal ellipsoids). Selected bond lengths (Å)
and angles (deg): Au-W(A) ) 2.7121(5), Au-W(B) ) 2.7060(5), Au-C(10A) ) 2.553(7), Au-C(12A) ) 2.660(7), Au-
C(10B) ) 2.560(7), Au-C(12B) ) 2.659(7), W(A)-C(dienyl) (av) ) 2.35(3), W(B)-C(dienyl) (av) ) 2.34(3), W(A)-C(O) (av)
) 1.957(5), W(B)-C(O) (av) ) 1.96(1), C(A)-O (av) ) 1.16(1), C(B)-O (av) 1.17(2), N(A)‚‚‚Cl(A) ) 2.978(6), N(B)‚‚‚Cl(B) )
2.987(6), P-Au-W(A) ) 171.89(5), P-Au-W(B) ) 174.37(4), Au-W(A)-C(11A) ) 121.8(2), Au-W(B)-C(11B) ) 123.64-
(19), C(10A)-W-C(11A) ) 81.2(3), C(10B)-W-C(11B) ) 80.7(3), C(11A)-W-C(12A) ) 81.8(3), C(11B)-W-C(12B) )
82.5(3), C(12A)-W-C(10A) ) 106.6(3), C(12B)-W-C(10B) ) 105.1(3), O(1A)-C(10A)-W ) 171.8(6), O(1B)-C(10B)-W
) 173.6(6), O(2A)-C(11A)-W ) 178.5(7), O(2B)-C(11B)-W ) 179.6(6), O(3A)-C(12A)-W ) 175.6(6), O(3B)-C(12B)-W
) 174.5(6).
mity of M-C(O) and C-O distances, and O-C-M
angles such as those in 18, rule out significant carbo-
nyl-Au semibridging interactions in 5, 6, and 8. The
relatively acute O(1)-C(10)-Mo angle of 8 (169.4(5)°)
is similar to that found for a semibridging carbonyl
ligand in [Ti(AuPEt3)(CO)6]- (169.45(6)°).36 Crystal-
packing forces are responsible for this angle in 8, as O1
and its symmetry equivalent have a close contact of 2.85
Å.
Concluding Remarks
Reactions of acetic acid and in situ Na[M(CO)3(η5-
CpN)] afford zwitterionic organometalates 1-3 that
engage in tight ion-pairing interactions. These zwitte-
rions exhibit spectroscopic and structural features
consistent with N-H‚‚‚M hydrogen bonding in solution
and the solid state. In this regard, complexes 1-3 join
13 as the only substances containing hydrogen bonds
with zerovalent group VI metal acceptors prepared to
date. The interaction between the separated charges in
1-3 lowers the electronic ground state of these zwitte-
rions, rendering the formally negatively charged metal
centers less Brønsted basic and nucelophilic relative to
[M(CO)3(η5-Cp)]-. This attenuation was examined by
investigating reactions of 1-3 with strong acids and
triphenylphosphinegold(I) chloride. The only isolable
salt from reactions of these zwitterions and hydrochloric
acid was 4, consistent with metal carbonyl anion Brøn-
sted basicity increasing down a column. Complexes 5
and 6 were accessible by reactions of 2 and 3 with Ph3-
PAuCl and 8 and 9 with hydrochloric acid. The analo-
gous Cr salt could not be obtained despite the existence
Figure 8. Molecular structure of 8 (50% thermal el-
lipsoids). Selected bond lengths (Å) and angles (deg): Au-
Mo ) 2.7208(6), Au-C(10) ) 2.547(6), Au-C(12) ) 2.524-
(6), Mo-C(1) ) 2.345(6), Mo-C(2) ) 2.362(6), Mo-C(3) )
2.351(6), Mo-C(4) ) 2.308(7), Mo-C(5) ) 2.302(6), Mo-
C(10) ) 1.947(6), Mo-C(11) ) 1.946(7), Mo-C(12) ) 1.947-
(7), O(1)-C(10) ) 1.176(6), O(2)-C(11) ) 1.171(7), O(3)-
C(12) ) 1.153(7), P-Au-Mo ) 171.25(4), C(10)-Mo-C(12)
) 107.4(3), C(10)-Mo-C(11) ) 83.1(3), C(11)-Mo-C(12)
) 81.5(3), C(11)-Mo-Au ) 117.45(19), C(10)-Mo-Au )
63.62(17), C(12)-Mo-Au ) 62.93(18), O(1)-C(10)-Mo )
169.4(5), O(2)-C(11)-Mo ) 179.0(6), O(3)-C(12)-Mo )
170.3(6).
B) and 8. The influence of crystal-packing forces on
AuM(CO)3 fragment geometry cannot be discounted, as
the C(11)-W-Au angles of the unique cations of 6 are
significantly different (1.84°, ∼9σ). The Au to adjacent
CO carbon distances range from 2.524(6) to 2.660(7) Å
in 5, 6, and 8. These lengths, coupled with the unifor-
(36) Fischer, P. J.; Young, V. G., Jr.; Ellis, J. E. Chem. Commun.
1997, 1249.

5126 Organometallics, Vol. 24, No. 21, 2005
Fischer et al.
of neutral 7. This study emphasizes the importance of
salt elimination as a contribution to the driving force
for formation of MH(CO)3(η5-Cp) and M(AuPPh3)(CO)3-
(η5-Cp) complexes. Reactions of Na[M(CO)3(η5-Cp)] and
RX are commonly employed to synthesize complexes
containing M-R bonds with concurrent formation of
insoluble NaX. Precipitation of alkali metal salts does
not accompany these reactions of 1-3. This study
provides more examples of metal centers with modu-
lated reactivity due to an intramolecular charge separa-
tion. Further studies of metal carbonyl anions contain-
ing CpN and related ligands are underway in this
laboratory.
cal Society (ACS PRF 39928-GB3), and an award from
Research Corp. (CC5932) supported this research. We
are grateful to these agencies and Macalester College.
We are indebted to Benjamin E. Kucera and William
W. Brennessel (Crystallographic Laboratory). P.J.F.
thanks Professors Robert Angelici and Gerard Parkin
for helpful discussions.
Supporting Information Available: Text giving ad-
ditional experimental details, unit cell drawings of 5 and 6,
and crystallographic data for 1-8 compiled in tables; these
data are also given as CIF files. This material is available free
of charge via the Internet at http://pubs.acs.org.
Acknowledgment. The donors of the Petroleum
Research Fund, administered by the American Chemi-
OM050484D