Coordination chemistry of [HFe(CN)2(CO)3]- and its derivatives: Toward a model for the iron subsite of the [NiFe]-hydrogenases

Article abstract of DOI:10.1021/ic900200s

The photoreaction of Fe(CO)5 and cyanide salts in MeCN solution affords the dianion [Fe(CN)₂(CO)₃]²-, conveniently isolated as [K(18-crown-6)]₂[Fe(CN)₂(CO)₃], Solutions of [Fe(CN)₂(CO)₃]₂- oxidize irreversibly at -600 mV (vs Ag/ AgCI) to give primarily [Fe(CN) ₃(CO)₃]-. Protonation of the dianion affords the hydride [K(18-crown-6)][HFe(CN)₂(CO)₃] with a pKa % 17 (MeCN). The ferrous hydride exhibits enhanced electrophilicity vs its dianionic precursor, which resists substitution. Treatment of [K(18-crown-6)][Fe(CN) ₂(CO)₃] with tertiary phosphines and phosphites gives isomeric mixtures of [HFe(CN)₂(CO)₂L]- (L = P(OPh)3 and PPh3). Carbonyl substitution on [1H(CO)₂]- by P(OPh)₃ is firstorder in both the phosphite and iron (k = 0.18 M-1 s-1 at 22 °C) with ΔH = 51.6 kJ mol-1 and ΔS= -83.0 J K-1 mol-1. These ligands are displaced under an atmosphere of CO. With CZs-Ph2PCH=CHPPh2 (dppv), we obtained the monocarbonyl, [HFe(CN)₂(CO)(dppv)]-, a highly basic hydride (pZCa > 23.3) that rearranges in solution to a single isomer. Treatment of [K(18-crown-6)][HFe(CN)₂(CO)₃] with Et4NCN resulted in rapid deprotonation to give [Fe(CN)₂(CO)₃]₂- and HCN. The tricyano hydride [HFe(CN)₃(CO)₂]_2- is prepared by the reaction of [HFe(CN)₂(CO)₂(PPh ₃)]_- and [K(18-crown-6)]CN. Similar to the phosphine and phosphite derivatives, [HFe(CN)₃(CO)₂]₂- exists as a mixture of all three possible isomers. Protonation of the hydrides [HFe(CN)₂(CO)(dppv)]- and [HFe(CN)₃(CO)₂]- in acetonitrile solutions releases H₂ and gives the corresponding acetonitrile complexes [K(18-crown-6)][Fe(CN)₃(NCMe)(CO)₂] and Fe(CN)₂(NCMe)(CO)(dppv). Alkylation of [K(18crown-6)] ₂[Fe(CN)₂(CO)₃] with MeOTf gives the thermally unstable [MeFe(CN)2(CO)3]-, which was characterized spectroscopically at -40°C. Reaction of dppv with [MeFe(CN)₂(CO)₃]- gives the acetyl complex, [Fe(CN)₂(COMe)(CO)(dppv)]-. Whereas [Fe(CN) ₂(CO)₃]^2- undergoes protonation and methylation at Fe, acid chlorides give the iron(O) /V-acylisocyanides [Fe(CN)(CO) ₃(CNCOR)]- (R = Ph, CH₃). The solid state structures of [K(18crown-6)][HFe(CN)₂(CO)(dppv)], Fe(CN)₂(NCMe)(CO) (dppv), and [K(18-crown-6)]₂[HFe(CN)₃(CO)₂] were confirmed crystallographically. In all three cases, the cyanide ligands are cis to the hydride or acetonitrile ligands.

Full text of DOI:10.1021/ic900200s

Inorg. Chem. 2009, 48, 4462-4469
Coordination Chemistry of [HFe(CN)2(CO)3]- and Its Derivatives: Toward
a Model for the Iron Subsite of the [NiFe]-Hydrogenases
C. Matthew Whaley, Thomas B. Rauchfuss,* and Scott R. Wilson
Department of Chemistry, UniVersity of Illinois at Urbana-Champaign, Urbana, Illinois 61801
Received January 31, 2009
The photoreaction of Fe(CO)5 and cyanide salts in MeCN solution affords the dianion [Fe(CN)2(CO)3]2-, conveniently
isolated as [K(18-crown-6)]2[Fe(CN)2(CO)3]. Solutions of [Fe(CN)2(CO)3]2- oxidize irreversibly at -600 mV (vs Ag/
AgCl) to give primarily [Fe(CN)3(CO)3]-. Protonation of the dianion affords the hydride [K(18-crown-6)][HFe(CN)2(CO)3]
with a pKa ≈ 17 (MeCN). The ferrous hydride exhibits enhanced electrophilicity vs its dianionic precursor, which
resists substitution. Treatment of [K(18-crown-6)][Fe(CN)2(CO)3] with tertiary phosphines and phosphites gives isomeric
mixtures of [HFe(CN)2(CO)2L]- (L ) P(OPh)3 and PPh3). Carbonyl substitution on [1H(CO)2]- by P(OPh)3 is first-
order in both the phosphite and iron (k ) 0.18 M-1 s-1 at 22 °C) with ∆H‡ ) 51.6 kJ mol-1 and ∆S‡ ) -83.0
J K-1 mol-1. These ligands are displaced under an atmosphere of CO. With cis-Ph2PCH)CHPPh2 (dppv), we
obtained the monocarbonyl, [HFe(CN)2(CO)(dppv)]-, a highly basic hydride (pKa > 23.3) that rearranges in solution
to a single isomer. Treatment of [K(18-crown-6)][HFe(CN)2(CO)3] with Et4NCN resulted in rapid deprotonation to
give [Fe(CN)2(CO)3]2- and HCN. The tricyano hydride [HFe(CN)3(CO)2]2- is prepared by the reaction of
[HFe(CN)2(CO)2(PPh3)]- and [K(18-crown-6)]CN. Similar to the phosphine and phosphite derivatives,
[HFe(CN)3(CO)2]2- exists as a mixture of all three possible isomers. Protonation of the hydrides
[HFe(CN)2(CO)(dppv)]- and [HFe(CN)3(CO)2]- in acetonitrile solutions releases H2 and gives the corresponding
acetonitrile complexes [K(18-crown-6)][Fe(CN)3(NCMe)(CO)2] and Fe(CN)2(NCMe)(CO)(dppv). Alkylation of [K(18-
crown-6)]2[Fe(CN)2(CO)3] with MeOTf gives the thermally unstable [MeFe(CN)2(CO)3]-, which was characterized
spectroscopically at -40 °C. Reaction of dppv with [MeFe(CN)2(CO)3]- gives the acetyl complex,
[Fe(CN)2(COMe)(CO)(dppv)]-. Whereas [Fe(CN)2(CO)3]2- undergoes protonation and methylation at Fe, acid chlorides
give the iron(0) N-acylisocyanides [Fe(CN)(CO)3(CNCOR)]- (R ) Ph, CH3). The solid state structures of [K(18-
crown-6)][HFe(CN)2(CO)(dppv)], Fe(CN)2(NCMe)(CO)(dppv), and [K(18-crown-6)]2[HFe(CN)3(CO)2] were confirmed
crystallographically. In all three cases, the cyanide ligands are cis to the hydride or acetonitrile ligands.
Introduction
The active site of [NiFe]-hydrogenase is composed of a
Ni center coordinated by two terminal and two bridging
cysteine thiolates in a highly distorted tetrahedral arrange-
ment and an octahedral Fe atom coordinated by two bridging
cysteine thiolates, two cyanides, and a terminal carbonyl.3
No bridging ligand has been observed crystallographically
in the catalytically relevant reduced forms of the active site;
however, a bridging hydride has been detected by ENDOR
and HYSCORE spectroscopies.4
Ferrous carbonyl cyanide complexes have aroused recent
interest because of their presence in [FeFe]- and [NiFe]-
hydrogenasessmetalloenzymes that are responsible for the
interconversion of dihydrogen to protons and electrons with high
catalytic efficiency.1 The active site of the [FeFe] enzyme
features Fe(CO)(CN) and Fe(CO)2(CN) sites, and the active
site of the [NiFe] enzyme features a Fe(CO)(CN)2 site.
Additionally, mutants of the [NiFe]-hydrogenases are proposed
to contain tricyano (Fe(CO)(CN)3-containing) centers.2
* To whom correspondence should be addressed. E-mail: rauchfuz@
uiuc.edu.
(1) Cammack, R.; Frey, M.; Robson, R. Hydrogen as a Fuel: Learning
from Nature; Taylor & Francis: London, 2001.
(2) Linden, E.; Burgdorf, T.; Bernhard, M.; Bleijlevens, B.; Friedrich,
B.; Albracht, S. J. Biol. Inorg. Chem. 2004, 9, 616–626.
(3) Fontecilla-Camps, J. C.; Volbeda, A.; Cavazza, C.; Nicolet, Y. Chem.
ReV. 2007, 107, 4273–4303.
4462 Inorganic Chemistry, Vol. 48, No. 10, 2009
10.1021/ic900200s CCC: $40.75  2009 American Chemical Society
Published on Web 04/17/2009

Coordination Chemistry of [HFe(CN)2(CO)3]- and DeriWatiWes
As indicated in the thorough review by Fehlhammer and
Fritz, metal cyanides are reactive toward a broad range of
electrophiles (e.g., HX, RX, RCOX), which attack almost
exclusively at cyanide.5 Such reactivity studies have em-
phasized midvalent metal cyanides, which are more widely
available, or low valent polycarbonyl cyanides wherein the
metal is only weakly basic. It seems likely that low-Valent
metal cyanides could display metal-centered reactivity,
competitive with the N-centered reactions. Indeed, complexes
of the type RhI(chel)CN (where chel ) N(CH2CH2PPh2)3
and P(CH2CH2PPh2)3) protonate at Rh.6 Similarly, proton-
ation of [FeI2(SR)2(CN)2(CO)4]2- and [FeI2(SR)2(CN)-
(CO)4(PMe3)]- occurs at the iron,7 not at FeCN, although in
these cases, the kinetic site of protonation may be FeCN.8
The alkylation of Ni(0) carbonyl cyanides implicates the
direct alkylation at nickel, not the cyanide ligands.9 In view
of this background, it is not surprising that [Fe(CN)2(CO)3]2-
undergoes protonation at iron, not FeCN, to give
[HFe(CN)2(CO)3]-, [1H(CO)2]-.10 In the present paper, we
examine the regiochemistry of reactions of [Fe(CN)2(CO)3]2-
with other electrophiles, including alkylating and acylating
agents.
conversion from Fe(CO)5 to [Fe(CN)2(CO)3]2- can be
effected in a one-pot process, although the second step is
slow apparently because of self-extinction. An intense
absorption band for [Fe(CN)2(CO)3]2- occurs at 230 nm
(ε ) 2 × 105 cm-1 M-1) and overlaps with the absorption
band of the precursor [Fe(CN)(CO)4]- at 210 nm (ε ) 8 ×
103 cm-1 M-1). Salts of [Fe(CN)2(CO)3]2- can also be
synthesized in water, but the conversion was slower and the
purification less efficient. Usually [Fe(CN)2(CO)3]2- was
isolated as the [K(18-crown-6)]+ salt because the product is
easily separated from [K(18-crown-6)][Fe(CN)(CO)4] and
[K(18-crown-6)]CN by a single reprecipitation. Other salts
were more difficult to purify.
The reaction of Fe(bda)(CO)3 and Et4NCN also gave
Et4N[Fe(CN)(CO)4] and (Et4N)2[Fe(CN)2(CO)3] by displace-
ment of bda (benzylideneacetone); however, the conversion
proceeds to completion only upon addition of 3 equiv of
Et4NCN because of the competing reaction between liberated
bda and unreacted cyanide, and the organic side-products
complicate workup.
Tetraethylammonium and [K(18-crown-6)]+ salts of
[Fe(CN)2(CO)3]2- readily dissolve in deoxygenated water.
The νCO band of [Fe(CN)2(CO)3]2- occurs 46 cm-1 higher
in energy in aqueous solution (1890 cm-1) as opposed to
MeCN solution (1844 cm-1). This type of solvent dependent
shift, which has been observed in other cyanocarbonyl
complexes of iron,13,14 reflects the tendency of the cyanide
ligands to engage in strong hydrogen bonds with protic
solvents.
The hydride, [1H(CO)2]-, features the HFe(CN)2(CO)
center that is found at the active site for certain states of
[NiFe]-hydrogenases.3 Numerous structural and functional
models for the [NiFe]-hydrogenase active site have been
reported featuring ferrous cyanide complexes,11,12 but few
studies have aimed at the hydride-containing Ni-C and
Ni-R states. With this background in mind, the present paper
describes the substitution chemistry of [1H(CO)2]- as a
prelude to the construction of bimetallic models.
The electron-rich character of [Fe(CN)2(CO)3]2- is indi-
cated by the ease with which it can be oxidized. The cyclic
voltammogram of [K(18-crown-6)]2[Fe(CN)2(CO)3] was
found to consist of a single irreversible oxidation at -600
mV (vs Ag/AgCl, MeCN solution). Treatment of a MeCN
Results and Discussion
Synthesis and Protonation of [Fe(CN)2(CO)3]2-. The
dianion [Fe(CN)2(CO)3]2- arises in good yields by the photo-
reaction of solutions of either preformed [Fe(CN)(CO)4]-
or Fe(CO)5 and cyanide salts in MeCN solution. The
solution of [Fe(CN)2(CO)3]2- with 2 equiv of FcPF6 (E1/2
)
517 mV vs Ag/AgCl) resulted in a color change to bright
yellow, and IR analysis of the resulting solution showed
numerous peaks in the range from 1800-2200 cm-1. The
only product identifiable by ESI-MS was [Fe(CN)3(CO)3]-.13
Aerobic oxidation of [Fe(CN)2(CO)3]2- is also complex, but
IR spectra show the formation of both [Fe(CN)5(CO)]3- and
trans-[Fe(CN)4(CO)2]2-.10
(4) Brecht, M.; van Gastel, M.; Buhrke, T.; Friedrich, B.; Lubitz, W. J. Am.
Chem. Soc. 2003, 125, 13075–13083.
(5) Fehlhammer, W. P.; Fritz, M. Chem. ReV. 1993, 93, 1243–1280.
(6) Bianchini, C.; Laschi, F.; Ottaviani, M. F.; Peruzzini, M.; Zanello,
P.; Zanobini, F. Organometallics 1989, 8, 893–899.
(7) Gloaguen, F.; Lawrence, J. D.; Rauchfuss, T. B. J. Am. Chem. Soc.
2001, 123, 9476–9477. Schmidt, M.; Contakes, S. M.; Rauchfuss, T. B.
J. Am. Chem. Soc. 1999, 121, 9736–9737.
(8) Boyke, C. A. Ph.D. Thesis, University of Illinois at Urbana-Champaign,
2006.
Protonation of [Fe(CN)2(CO)3]2-. Addition of 1 equiv
of strong acids to solutions of [K(18-crown-6)]2[Fe(CN)2-
(CO)3] resulted in immediate and quantitative protonation
of the iron complex. The resulting hydride [HFe(CN)2-
(CO)3]- ([1H(CO)2]-), which is extremely air-sensitive in
solution, was isolated as the salt [K(18-crown-6)][1H(CO)2].
Colorless CH2Cl2 or MeCN solutions of this complex become
bright yellow immediately upon exposure to air; however,
the products could not be identified by IR spectroscopy or
ESI-MS. Isolation of the hydride complex as an analytically
pure solid was complicated by the formation of salts (e.g.,
[K(18-crown-6)]Cl from HCl, [K(18-crown-6)]OTs from
(9) del Rosario, R.; Stuhl, L. S. Tetrahedron Lett. 1982, 23, 3999–4002.
Joo, F.; Alper, H. Organometallics 1985, 4, 1775–1778.
(10) Kayal, A.; Rauchfuss, T. B. Inorg. Chem. 2003, 42, 5046–5048.
(11) Ohki, Y.; Yasumura, K.; Kuge, K.; Tanino, S.; Ando, M.; Li, Z.;
Tatsumi, K. Proc. Natl. Acad. Sci. U.S.A. 2008, 105, 7652–7657. Liaw,
W.-F.; Tsai, W.-T.; Gau, H.-B.; Lee, C.-M.; Chou, S.-Y.; Chen, W.-
Y.; Lee, G.-H. Inorg. Chem. 2003, 42, 2783–2788. Liaw, W.; Lee, J.;
Gau, H.; Chen, C.; Jung, S.; Hung, C.; Chen, W.; Hu, C.; Lee, G.
J. Am. Chem. Soc. 2002, 124, 1680–1688. Liaw, W.; Lee, N.; Chen,
C.; Lee, C.; Lee, G.; Peng, S. J. Am. Chem. Soc. 2000, 122, 488–494.
Pal, S.; Ohki, Y.; Kuge, K.; Tatsumi, K. Chem.sAsian J. 2009, 2,
457. Li, Z.; Ohki, Y.; Tatsumi, K. J. Am. Chem. Soc. 2005, 127, 8950–
8951. van der Vlugt, J. I.; Meyer, F. In Met. Ions Life Sci.; Sigel, A.,
Sigel, H., Sigel, R. K. O., Eds.; J. Wiley: London, 2007; Vol. 2, pp
181-240. Ogo, S.; Kabe, T.; Uehara, K.; Kure, B.; Nishimura, T.;
Menon, S. C.; Harada, R.; Fukuzumi, S. Science 2007, 316, 585–8.
(12) Chen, C.; Chang, Y.; Yang, C.; Chen, T.; Lee, C.; Liaw, W. Dalton
Trans. 2004, 137–143.
(13) Jiang, J.; Koch, S. A. Inorg. Chem. 2002, 41, 158–160.
(14) Jiang, J.; Koch, S. A. Angew. Chem., Int. Ed. 2001, 40, 2629–2631.
Jiang, J.; Acunzo, A.; Koch, S. A. J. Am. Chem. Soc. 2001, 123,
12109–12110.
Inorganic Chemistry, Vol. 48, No. 10, 2009 4463

Whaley et al.
Scheme 1. Main reactions described in this paper
toluenesulfonic acid) with solubilities similar to that of the
complex, but this problem was solved by using
In contrast to the situation for monophosphines and
phosphites, 1 equiv of the chelating diphosphine cis-Ph2-
PCH)CHPPh2 (dppv) was found to displace two CO ligands
from [1H(CO)2]-, rapidly generating [HFe(CN)2(CO)-
(dppv)]- ([1H(dppv)]-). The solution IR spectrum of [K(18-
crown-6)][1H(dppv)] in MeCN consisted of a single νCO band
at 1936 cm-1 and two νCN bands at 2087 and 2080 cm-1.
The IR spectrum of [1H(dppv)]- closely resembles that of
[CpFe(CN)2(CO)]-.17 Unlike the aforementioned cases of
[1H(CO)(PR3)] (R ) Ph, OPh), solutions of [1H(dppv)]-
were unaffected by CO. Upon standing in solution,
[1H-(dppv)]- was found to convert to a mixture containing
>90% of a single isomer over the course of hours at room
temperature, although the IR spectra of the isomers were
apparently indistinguishable. Thus, seconds after adding dppv
to a CD3CN solution of [1H(CO)2]-, the 1H NMR spectrum
exhibited a triplet and two doublets of doublets (see
Supporting Information). Within minutes, these signals
diminished, concomitant with the appearance of a new triplet
-
[H(OEt2)2][BArF ] (BArF ) B[C6H2-3,5-CF3)2]4 ), which
4
4
allowed for the removal of the co-formed salts, which are
soluble in ether.
The basicity of [1H(CO)2]- in MeCN solution was semi-
quantified by monitoring changes in its IR spectrum. Pro-
tonation is fully effected using NH4PF6 (pKa ) 16.46), and
[1H(CO)2]- can be fully deprotonated by 1 equiv of
2-aminoethanol (pKa ) 17.53), indicating a pKa ∼ 17. All
pKa values are for compounds dissolved in MeCN unless
otherwise specified. Solutions of [1H(CO)2]- in CD2Cl2
undergo rapid H/D exchange with D2O to give the corre-
sponding deuteride complex, [DFe(CN)2(CO)3]-, while such
solutions of [1H(CO)2]- do not undergo H/D exchange with
D2 (Scheme 1).
Derivatives of [HFe(CN)2(CO)3]-. The ferrous hydride
[1H(CO)2]- exhibits enhanced electrophilicity relative to its
dianionic precursor, which resists substitution reactions.
Treatment of [K(18-crown-6)][1H(CO)2] with tertiary phos-
phines or phosphites in MeCN solution resulted in rapid
evolution of CO and formation of [K(18-crown-6)][HFe(CN)2-
(CO)2L] (L ) P(OPh)3 and PPh3), [K(18-crown-6)][1H(CO)-
L]. These complexes exhibit two νCO bands, consistent with
cis carbonyl ligands. 1H- and 31P NMR spectra show multiple
stable isomers as also observed for [1H(CO)2]-. The reaction
of [1H(CO)2]- with phosphorus donor ligands is an equi-
librium process. Upon placing a MeCN solution of [K(18-
crown-6)][1H(CO)(PPh3)] under an atmosphere of CO, a
mixture of [1H(CO)2]-, [1H(CO)(PPh3)]-, and PPh3 was
observed by 1H- and 31P NMR spectroscopy. Purging these
solutions with N2 gave [1H(CO)(PPh3)]-. The P(OPh)3
complex formed analogously. Treatment of [1H(CO)-
{P(OPh)3}]- with 1 equiv of PPh3 gave [1H(CO)(PPh3)]-.
The phosphine ligand in PPN[HFe(CO)3(PPh3)] is known
to be reversibly displaceable by CO.15
The introduction of the phosphorus ligand significantly
affects the acidity of the hydride. Whereas the pKa of
[1H(CO)2]- is ∼17 in MeCN, [1H(CO)L]- (L ) PPh3,
P(OPh)3) resisted deprotonation by tetramethylguanidine (pKa
) 23.3 in MeCN). Such decreases in acidity are precedented
in the case of HCo(CO)4-x(PPh3)x (x ) 1, 0) where the Ka
of the phosphine adduct was 107 greater for the tetracarbo-
nyl.16 The P(OPh)3- and PPh3-substituted complexes do not
undergo further substitution by these phosphorus ligands even
in refluxing solvent.
2
(δ -8.64; JP-H ) 58 Hz). A singlet (δ 103.7) in the 31P
NMR spectrum indicated of the unique Cs-symmetrical
isomer. This thermodynamic product can be described as
having the cyanides and dppv in the equatorial plane with
the hydride and CO along the axis.
We also attemped the substitution of CO by sulfur ligands,
since the coordination sphere about Fe in the [NiFe]-
hydrogenases is FeH(CN)2(CO)(SR)2. The hydride [1H-
(CO)2]- was deprotonated by NaSPh. We observed no
reaction between [1H(CO)L]- (L ) PPh3, P(OPh)3) and
Me2S, NaS2CNEt2, NaSPh, and MeSCH2CH2SMe. No reac-
tion was also observed between [1H(CO)2]- and olefins such
as styrene or norbornene.
Kinetics of Carbonyl Substitution. The rate of substitu-
tion of CO in [1H(CO)2]- by P(OPh)3 was examined under
conditions of excess phosphite (Figure 1). Upon varying the
amount of P(OPh)3 from 10 to 40 equiv, the rate increased
by a factor of 4, indicating a first-order dependence upon
the incoming ligand; the rate was also first-order in
[1H(CO)2]-, consistent with a second-order rate law. Rates
were evaluated over a temperature range of 22 to -29 °C
(see Supporting Information) to give the following activation
(15) Ash, C. E.; Delord, T.; Simmons, D.; Darensbourg, M. Y. Organo-
metallics 1986, 5, 17–25.
(16) Moore, E. J.; Sullivan, J. M.; Norton, J. R. J. Am. Chem. Soc. 1986,
108, 2257–2263.
(17) Lai, C.-H.; Lee, W.-Z.; Miller, M. L.; Reibenspies, J. H.; Darensbourg,
D. J.; Darensbourg, M. Y. J. Am. Chem. Soc. 1998, 120, 10103–10114.
4464 Inorganic Chemistry, Vol. 48, No. 10, 2009

Coordination Chemistry of [HFe(CN)2(CO)3]- and DeriWatiWes
Figure 1. IR spectra (νCO region only) for the reaction of [K(18-crown-
6)][1H(CO)2] with 10 equiv of P(OPh)3 in MeCN solution at 20 °C.
Figure 2. Molecular structure of the anion [HFe(CN)2(dppv)(CO)]- with
thermal ellipsoids set at the 35% probability level. Cation, solvates, and
nonhydride hydrogen atoms were omitted for clarity.
parameters: ∆H‡ ) 51.6 kJ mol-1 and ∆S‡ ) -83 J K-1
mol-1.
[HFe(CN)3(CO)2]2-. Substitution of CO in [1H(CO)2]-
is limited by the Brønsted basicity of the attacking ligand
since highly basic reagents deprotonate the complex. Con-
sistent with this pattern, treatment of [K(18-crown-
6)][1H(CO)2] with Et4NCN resulted in rapid deprotonation
of the hydride to cleanly regenerate [Fe(CN)2(CO)3]2-, as
indicated by in situ IR spectroscopy. The facility of the
deprotonation is consistent with the low acidity of HCN, with
a pKa ) 18.1.18 An indirect route to the tricyanide was
therefore undertaken, bearing in mind the decreased acidity
and convenient lability of [1H(CO)(PPh3)]- and the lability
of PPh3. Treatment of a MeCN solution of [1H(CO)(PPh3)]-
with 1 equiv Et4NCN was found to rapidly generate the
targeted hydrido tricyanide complex [HFe(CN)3(CO)2]2-
([1H(CN)(CO)]2-) concomitant with displacement of PPh3.
The analogous phosphite complex [1H(CO){P(OPh)3}]- was
found to react similarly. Excess cyanide does not result in
further substitution. The IR spectrum of [1H(CN)(CO)]2-
showed the expected two-band νCO pattern at approximately
the release of H2. The IR spectrum of this solution showed
one νCO peak at 2003 cm-1 and a broadened νCN band. The
31P NMR spectrum showed a singlet. Upon dissolving this
product into MeCN, the νCO band shifted to 1993 cm-1, and
the νCN sharpened. We hypothesize that protonation generates
a labile H2 ligand that is displaced by FeCN on another
molecule of Fe(CN)2(CO)(dppv) to give the polymer
[Fe(CN)2(CO)(dppv)]n. In MeCN solution, this species
depolymerizes to give 1(NCMe)(dppv).
Similarly, protonation of the tricyanide [K(18-crown-
6)]2[1H(CN)(CO)] with an MeCN solution of HCl resulted
in the immediate release of H2 and the formation of [K(18-
crown-6)][Fe(CN)3(NCMe)(CO)2]. The formation of
[Fe(CN)3(NCMe)(CO)2]- is evidenced by an approximately
60 cm-1 shift to higher energy for νCO, similar to the shift
seen upon formation of 1(NCMe)(dppv) from [K(18-crown-
6)][1H(dppv)]. Liaw and co-workers had previously obtained
[Fe(CN)3(NCMe)(CO)2]- in low yield from the reactions of
PPN[FeBr(CN)2(CO)3] as well as (PPN)2[FeBr(CN)3-
(CO)2].20 No reaction between [1(CN)(NCMe)(CO)]- and
cyanide was observed.
Structural Studies of Ferrous Cyanide Complexes. The
structure of [K(18-crown-6)][1H(dppv)], determined by
single-crystal X-ray diffraction (Figure 2), is consistent with
the IR and NMR data. The hydride was located in the
difference map with a Fe-H distance of 1.51(6) Å. The
cyanide and carbonyl ligands were distinguished by their
Fe-C bond lengths (Table 1). The [K(18-crown-6)]+ cation
lies in close proximity to the cis-cyanide ligands; the resulting
interaction is such that the potassium ion is removed from
the center of the crown ether toward the cyanides.
The complex 1(NCMe)(dppv) was also characterized by
single crystal X-ray diffraction (see Supporting Information).
The molecular structure is consistent with retention of stereo-
chemistry of the precursor [1H(dppv)]- upon protonolysis.
Crystallographic analysis of the tricyanide [K(18-crown-
6)]2[1H(CN)(CO)] (Figure 3) failed to locate the hydride
ligand; however, an unoccupied coordination site is indicated
1
20 cm-1 lower energy than for [1H(CO)(PPh3)]-. The H
NMR spectrum showed the presence of three hydride signals,
reflecting the presence of the three possible isomers in a ratio
of ∼10:6:0.5. The isomer ratio in CD3CN solution was found
to be unchanged upon sitting for days at room temperature.
Protonation of Ferrous Hydride Complexes. The basic-
ity of the new iron hydrides is highly dependent upon the
coligands, as expected.19 Treatment of a MeCN solution of
[1H(dppv)]- with 1 equiv of [H(OEt2)2]BArF4 resulted in the
slow crystallization of a yellow product along with the
evolution of H2 (1H NMR spectrum: δ4.56). The IR spectrum
of the precipitated yellow solid exhibited a νCO band 1993
cm-1 (vs 1934 cm-1 for [1H(dppv)]-). Elemental analysis
and NMR measurements indicated that this reaction produced
Fe(CN)2(NCMe)(CO)(dppv), 1(NCMe)(dppv). This species
is formed as a single isomer as evidenced by a singlet at δ
83.7 in the 31P NMR spectrum. Protonation of CH2Cl2
solutions of [1H(dppv)]- with [H(OEt2)][BArF4] resulted in
(18) Augustin-Nowacka, D.; Chmurzyn˜ski, L. Anal. Chim. Acta 1999, 381,
215–220.
(19) Kristjansdottir, S. S.; Moody, A. E.; Weberg, R. T.; Norton, J. R.
Organometallics 1988, 7, 1983–1987.
(20) Chen, C.-H.; Chang, Y.-S.; Yang, C.-Y.; Chen, T.-N.; Lee, C.-M.;
Liaw, W.-F. Dalton Trans. 2004, 137–143.
Inorganic Chemistry, Vol. 48, No. 10, 2009 4465

Whaley et al.
Table 1. Bond Lengths (Å) for [K(18-crown-6)][1H(dppv)] and
1(NCMe)(dppv)
[1H(dppv)]-
1(NCMe)(dppv)
Fe(1)-P(1)
2.169(2)
2.169(2)
1.770(10)
1.915(8)
1.914(9)
1.51(6)
1.154(9)
1.162(8)
1.161(9)
Fe(1)-P(1)
2.2563(9)
2.2563(9)
1.748(4)
1.938(3)
1.938(3)
1.980(4)
1.156(5)
1.153(4)
1.153(4)
Fe(1)-P(2)
Fe(1)-C(27)
Fe(1)-C(28)
Fe(1)-C(29)
Fe(1)-H(1A)
C(27)-O(1)
C(28)-N(1)
C(29)-N(2)
Fe(1)-P(1A)
Fe(1)-C(2)
Fe(1)-C(3)
Fe(1)-C(3A)
Fe(1)-N(2)
C(2)-O(1)
C(3)-N(1)
C(3A)-N(1A)
in an otherwise five-coordinate square pyramidal complex.
The presence of a pair of [K(18-crown-6)]+ counter-cations
and a non-coordinating acetonitrile solvate imply the pres-
ence of a hydride ligand. The three cyanide ligands reside
in the equatorial plane with one carbonyl: the hydride and
the remaining carbonyl occupy axial positions. The potassium
atoms in the [K(18-crown-6)]+ cations are located within
close proximity to the trans cyanide ligands.
Figure 4. Solution (MeCN) IR spectra of [K(18-crown-6)][HFe(CN)2(CO)3]
(bottom) and [K(18-crown-6)][MeFe(CN)2(CO)3] (top).
slower rearrangement to the hydride tautomer. We have
observed this pattern of N- followed by Fe-protonation in
studies of [Fe2(S2C2H4)(CN)2(CO)4]2-.8
Alkylation and Acylation of [Fe(CN)2(CO)3]2-. To test
the scope of its nucleophilic reactivity, [Fe(CN)2(CO)3]2- was
treated with a selection of organic electrophiles. Combining
a MeCN solution of [K(18-crown-6)]2[Fe(CN)2(CO)3] with
1 equiv of MeOTf resulted in a rapid reaction, as indicated
by changes in the IR spectra. The IR spectrum of the resulting
solution resembled that for [K(18-crown-6)][1H(CO)2].
Figure 4, consistent with alkylation at Fe, that is, the
formation of [K(18-crown-6)][MeFe(CN)2(CO)3], [K(18-
crown-6)][1Me(CO)2]. The formula was confirmed by ESI-
MS of the reaction mixture. At -40 °C, solutions of this
alkylated derivative are stable for hours. The same IR spectra
were obtained when the reaction was performed using MeI
or [Me3O]BF4 as the methylating agents; in each case,
however, the product decomposed upon attempted isolation.
For reference, we examined the methylation of K[Fe-
(CN)(CO)4] with MeOTf in MeCN solution. The exclusive
product, identified by IR spectroscopy, was Fe(CO)4-
(CNMe).21 We had earlier reported that the protonation of
the monocyanide [Fe(CN)(CO)4]- reacts with HCl to give a
mixture of Fe(CO)4(CNH) (major) and HFe(CN)(CO)4
(minor).10 The methylation result suggests that protonation
may also occur at FeCN, the likely kinetic site, followed by
MeCN solutions of [1Me(CO)2]-, which are unstable, were
found to react with dppv to give a robust derivative. Upon
addition of dppv to the complex, gas evolution was observed.
In the IR spectrum, a band at 1937 cm-1 appeared as seen
for the hydride [K(18-crown-6)][1H(dppv)] and a band of
medium intensity was observed at 1592 cm-1, consistent with
ν
CdO of an acetyl complex. The 1H NMR spectrum exhibited
a singlet for an acetyl group at δ 2.60, and the ESI-mass
spectrum confirmed that the complex was indeed the acetyl,
[1Ac(dppv)]-. Cardaci and co-workers observed similar spectral
features in Fe(COMe)(CN)(CO)2(PMe3)2, which they prepared
from cyanation of [Fe(Me)(CO)3(PMe3)2]+.22 Acetyl complex
[1Ac(dppv)]- exhibited no tendency to decarbonylateseven in
refluxing MeCN.
Whereas [Fe(CN)2(CO)3]2- was found to protonate and
alkylate at the metal, acid chlorides (MeCOCl, PhCOCl) gave
N-acyl isocyanide complexes [Fe(CN)(CO)3(CNCOR)]- (R
) Me, Ph), which were readily obtained in analytical purity.
As expected,23 the IR spectra in the νCO region are similar
for [Fe(CN)(CO)3(CNCOR)]- and [Fe(CN)(CO)4]- (see
Supporting Information). The acyl derivatives were charac-
terized by a new νCO band at ∼1660 cm-1 for the RC(O)NC
ligand.
Summary
In this work, we have developed the H-CN-CO-Fe system.
Two members of the series are now well characterized,
[HFe(CN)3(CO)2]2- and [HFe(CN)2(CO)3]-. The species
[HFe(CN)5]4- and [HFe(CN)4(CO)]3- remain unknown,
(21) Albers, M. O.; Coville, N. J.; Singleton, E. J. Chem. Soc., Dalton
Trans. 1982, 1069–1079.
(22) Cardaci, G.; Reichenbach, G.; Bellachioma, G. Inorg. Chem. 1984,
23, 2936–2940.
(23) Simonneaux, G.; Lemaux, P.; Jaouen, G.; Dabard, R. Inorg. Chem.
1979, 18, 3167–3170. Carter, S. J.; Foxman, B. M.; Stuhl, L. S.
Organometallics 1986, 5, 1918–1920.
Figure 3. Molecular structure of the anion [HFe(CN)3(CO)2] with thermal
ellipsoids set at the 35% probability level. [K(18-crown-6)]+ cations and
acetonitrile solvate was omitted for clarity.
4466 Inorganic Chemistry, Vol. 48, No. 10, 2009

Coordination Chemistry of [HFe(CN)2(CO)3]- and DeriWatiWes
pKa(MeCN) of 16.6 (see Supporting Information). For
comparison, [1H(CO)2]- has pKa(MeCN) of about 17.
Similar comparability of pKa values has been observed in
dinuclear complexes, as well, with [Fe2(S2C3H6)(µ-
H)(CO)4(PMe3)2]+ and [Fe2(S2C3H6)(µ-H)(CN)2(CO)4]-, both
having pKa values between 10.4 and 11.3.8,26
Neutral complexes of the type Fe(CO)3L2 (L ) P(OPh)3,
PPh3, PPh2Me, P(NMe2)3) undergo reversible one-electron
oxidation in a range from 0.73 to 0.19 V versus Ag/AgCl,
and the diphosphine complex Fe(CO)3(dppe) oxidizes at 0.15
V versus Ag/AgCl. The products in these cases are the
corresponding five-coordinate (17e) derivatives.30 These
neutral Fe(CO)3L2 complexes are all much more difficult to
oxidize than [Fe(CN)2(CO)3]2- (-600 mV, irreversible).
Protonation of metal cyanides most often occurs at cyanide
to give complexes containing the CNH ligand.5 Depending
on their degree of substitution, the cyanocarbonyls of Fe(0)
protonate either mainly at cyanide or at Fe to give a hydride
complex. The regiochemistry of protonation in such com-
plexes depends on the basicity of the respective sites. For
example, the low temperature (-30 °C) protonation of
[Fe(CN)(CO)4]- results in the formation of a mixture of
mainly Fe(CO)4(CNH) as well as HFe(CN)(CO)4 prior to
decomposition by loss of HCN.10 Consistent with this result,
methylation on the monocyanide gives Fe(CO)4(CNMe). The
dicyanide, [Fe(CN)2(CO)3]2-, is significantly more basic at
Fe, and no CNH and CNMe species are observed. The
substitution of CO for CN-, in this case, has the effect of
elevating the nucleophilicity of the Fe(0) center above that
of the FeCN centers.
Figure 5. Fe site of the Ni-R and Ni-C states in the [NiFe]-hydrogenases
(A) and [1H(dppv)]- (B).
although related hydridocyanocobaltates are known.24 This
series of complexes complements the ferrous cyanide car-
bonyl complexes of the type [Fe(CN)x(CO)6-x
]
2-x (x ) 3, 4,
5).13,14,25
The compound [K(18-crown-6)][1H(dppv)] is a rare example
of a hydrido iron carbonyl cyanide. Another example is the
bimetallic species Fe2(S2C3H6)(µ-H)(CN)(CO)4(PMe3).26 Morris
has reported HFe(CN)(R2PCH2CH2PR2)2 (R ) Et, Ph, p-tol),
wherein the regiochemistry of protonation (hydride vs. cyanide)
depends upon the basicity of the diphosphine ligand.26b Spec-
troscopically and structurally, [1H(dppv)]- is a reasonable
structural model for the Fe site of the [NiFe]-hydrogenases
(Figure 5). The similarity extends to the IR spectra in the νCO
and νCN regions.27
Whereas [Fe(CN)2(CO)3]2- resists substitution, its proto-
nated derivative [1H(CO)2]- is readily monosubstituted by
soft ligands such as phosphines and phosphites. Substitution
by P(OPh)3 was examined in some detail, and the negative
activation entropy and bimolecular rate law point to an
associative mechanism. For the related reaction of a variety
of metal hydride complexes (e.g., [HFe(CO)4(PPh3)]+, HCo-
(CO)4), Pearson has suggested that the nucleophile induces
migration of the hydride to a carbonyl ligand followed by
rapid deinsertion with loss of CO (Scheme 2).28 A similar
mechanism is expected for the substitution of chelating
diphosphines. Thus, a stable acetyl species forms upon
addition of dppv to [1Me(CO)2]-, whereas the corresponding
formyl species is apparently less stable, resulting in decar-
bonylation to give the hydride complex.
The influence of the coligands on the basicity of the Fe
versus the CN centers is relevant to understanding the
regiochemistry of protonation reactions. Angelici has as-
sessed the basicity of series of Fe(CO)3(phosphine)2 and
Fe(CO)3(diphosphine) complexes and has shown that the
enthalpies of protonation correlates with pKa.29 For example,
Fe(CO)3(PMe3)2, has a heat of protonation (-∆HHM) of 23.3
kcal/mol. We estimate that [Fe(CO)3(PMe3)2]+ has a
Whereas the coligands slightly affect the acidity of the
MCNH center,31 the acidity of the MH is highly sensitive
to the nature of the ligand set. This effect can be seen when
comparing the difference in heats of protonation (∆∆HH+
)
of complexes of the type CpRu(PR3)2(CN) to those of
Fe(CO)3(PR3)2. In the first case, only protonation at cyanide
occurs, and ∆∆HH+ increases by only 1.9 kcal mol-1 upon
substituting PPh3 for PMe3.32 In the latter case, protonation
at Fe occurs, and ∆∆HH+ increases by 9.2 kcal mol-1 upon
substituting PPh3 for PMe3.33
Protonation of the dicyanoferrous hydrides described in
this work did not afford isolable complexes of H2. Proton-
ation of the hydride in [1H(CO)L]- would generate charge-
neutral products, whereas most stable H2 complexes are
cations.34 Consisting of six potentially anionic ligandssfour
thiolates and two cyanides, the active site of the [NiFe]-
hydrogenases (and the H2 adducts) would also be expected
to be anionic. The instability of such adducts may be
consistent with the high efficiency of [NiFe]-hydrogenase
(24) Guastalla, G.; Halpern, J.; Pribanic, M. J. Am. Chem. Soc. 1972, 94,
1575–1577. Halpern, J.; Guastalla, G.; Bercaw, J. Coord. Chem. ReV.
1972, 8, 167–173.
(25) Contakes, S. M.; Hsu, S. C. N.; Rauchfuss, T. B.; Wilson, S. R. Inorg.
Chem. 2002, 41, 1670–1678.
(26) (a) Gloaguen, F.; Lawrence, J. D.; Rauchfuss, T. B.; Be´nard, M.;
Rohmer, M.-M. Inorg. Chem. 2002, 41, 6573–6582. (b) Amrhein, P. I.;
Drouin, S. D.; Forde, C. E.; Lough, A. J.; Morris, R. H. J. Chem.
Soc., Chem. Commun. 1996, 1665-1666; Rocchini, E.; Rigo, P.;
Mezzetti, A.; Stephan, T.; Morris, R. H.; Lough, A. J.; Forde, C. E.;
Fong, T. P.; Drouin, S. D. J. Chem. Soc., Dalton Trans. 2000,
3591-3602.
(27) de Lacey, A. L.; Hatchikian, E. C.; Volbeda, A.; Frey, M.; Fontecilla-
Camps, J. C.; Fernandez, V. M. J. Am. Chem. Soc. 1997, 119, 7181–
7189.
(29) Sowa, J. R., Jr.; Zanotti, V.; Facchin, G.; Angelici, R. J. J. Am. Chem.
Soc. 1991, 113, 9185–9192.
(30) Connelly, N. G.; Somers, K. R. J. Organomet. Chem. 1976, 113,
C39-C41.
(31) Toma, H. E.; Malin, J. M. Inorg. Chem. 1973, 12, 1039–1045.
(32) Nataro, C.; Chen, J.; Angelici, R. J. Inorg. Chem. 1998, 37, 1868–
1875.
(33) Angelici, R. J. Acc. Chem. Res. 1995, 28, 51–60.
(34) Kubas, G. J. Metal Dihydrogen and σ-Bond Complexes; Kluwer
Academic/Plenum: New York, 2001.
(28) Pearson, R. G.; Walker, H. W.; Mauermann, H.; Ford, P. C. Inorg.
Chem. 1981, 20, 2741–2743.
Inorganic Chemistry, Vol. 48, No. 10, 2009 4467

Whaley et al.
Scheme 2
(H2 uptake: 1500 µmol H2 min-1 mg protein-1).35 It is known
that H2 formation by membrane-bound [NiFe]-hydrogenases
in Ralstonia species is inhibited by H2.36
was washed with 10 mL of Et2O to remove [K(18-crown-6)]BArF .
IR and H NMR spectra matched those previously reported.
4
10
1
[K(18-crown-6)][HFe(CN)2(CO)2(PPh3)],[K(18-crown-6)][1H(CO)(P-
Ph3)]. A solution of 0.387 g (0.485 mmol) of [K(18-crown-
6)]2[Fe(CN)2(CO)3] in 10 mL of MeCN was treated with 0.506 g
Experimental Section
(0.500 mmol) of [H(OEt2)2]BArF , resulting in an immediate change
4
Reactions were conducted as previously described using standard
Schlenk techniques or in an inert atmosphere glovebox under
dinitrogen. Solvents were dried via filtration through two 1 m
columns of alumina. CD3CN and CD2Cl2 were purchased from
Cambridge Isotopes and were dried with and distilled from CaH2.
from pale yellow to colorless. Addition of a solution of 0.13 g (0.50
mmol) of PPh3 in 5 mL of MeCN resulted in immediate gas
evolution and a slight yellowing of the solution. Solvent was
removed under vacuum to give a pale yellow powder. The powder
was washed with 50 mL of Et2O to extract the co-formed salt and
was dried under vacuum. Yield: 0.200 g (56%). IR (MeCN): νCN
[H(OEt2)2]BArF was prepared by literature methods.37 Other
4
1
reagents were purchased and used as received.
) 2111 (w), 2104 (w), 2092 (w); νCO ) 2011 (s), 1960 (s). H
[K(18-crown-6)]2[Fe(CN)2(CO)3]. A slurry of 0.25 g (3.8 mmol)
of KCN in MeCN was treated with 1.10 g (4.16 mmol) of 18-
crown-6 and stirred until the solids dissolved. Fe(CO)5 (0.25 mL,
1.9 mmol) was added to the solution, and the pale yellow reaction
mixture was photolyzed. Photolysis was continued until no more
significant changes were observed in the IR spectrum and no more
gas evolution was observed. The reaction mixture was filtered to
give a clear, very pale yellow solution. The product was precipitated
by concentrating the reaction solution to a volume of about 10 mL
and adding about 60 mL of EtOAc. The solid was isolated by
filtration and washed with 20 mL of Et2O. Yield: 0.835 g (55%).
Note: After 5 h of photolysis, an approximate 50:50 ratio of
[Fe(CN)2(CO)3]2-/[Fe(CN)(CO)4]- was observed. Continuing the
photolysis for another 17 h resulted in a negligible increase in that
ratio. Using MeOH as the reaction solvent resulted in the formation
of only [Fe(CN)(CO)4]-; no dicyanide was observed, possibly
because of overlap of the absorption bands of [Fe(CN)(CO)4]- and
the solvent (∼205 nm).
NMR (500 MHz, CD2Cl2): δ 7.35-7.75 (m, 15 H, PPh3), 3.61 (s,
24 H, 18-crown-6), -7.20 (d, 49 Hz), -9.90 (d, 52 Hz), -11.25
(d, 50 Hz). 31P NMR (202 MHz, CD2Cl2): δ 69.6 (s), 68.3 (s),
61.9 (s). ESI MS (MeCN): m/z 427 (HFe(CN)2(CO)2(PPh3)-).
[K(18-crown-6)][HFe(CN)2(CO)2{P(OPh)3}] · [K(18-crown-
6)]Cl, [K(18-crown-6)][1H(CO){P(OPh)3}] ·[K(18-crown-6)]Cl. A
solution of 0.066 g (0.083 mmol) of [K(18-crown-6)]2[Fe(CN)2-
(CO)3] in 10 mL of MeCN was treated with 0.085 mL of 1 M HCl
in Et2O, resulting in an immediate change from pale yellow to
colorless. Addition of a solution of 0.025 mL (0.095 mmol) of
P(OPh)3 in 5 mL of MeCN resulted in immediate gas evolution
and a slight yellowing of the solution. Solvent was removed under
vacuum to give a pale yellow powder and was dried under vacuum.
Yield: 0.073 g (79%). IR (MeCN): νCN ) 2118 (w), 2112 (w),
1
2101 (vw), 2080 (vw), 2086 (vw); νCO ) 2031 (s), 1983 (s). H
NMR (500 MHz, CD2Cl2): δ 7.7-7.0 (m, 18 H, P(OPh)3); 3.56 (s,
48 H, 18-crown-6); -8.13 (d, 70 Hz, Fe-H); -8.45 (d, 70 Hz, Fe-
H); -12.60 (d, 70 Hz, Fe-H). 31P NMR (202 MHz, CD2Cl2): δ
172.3 (s); 165.5 (s); 130.1 (s).
[K(18-crown-6)][HFe(CN)2(CO)3],[K(18-crown-6)][1H(CO)2]. A
solution of 0.050 g, (0.063 mmol) of [K(18-crown-6)]2[Fe(CN)2-
(CO)3] in 5 mL of MeCN was treated with a solution of 0.064 g
[K(18-crown-6)][HFe(CN)2(CO)(dppv)], [K(18-crown-6)][1H(d-
ppv)]. A solution of [K(18-crown-6)]2[Fe(CN)2(CO)3] (0.254 g, 0.318
mmol) in MeCN (10 mL) was treated with a solution of 0.329 g (0.325
(0.063 mmol) of [H(OEt2)2]BArF in 5 mL of MeCN, and the
4
mmol) of [H(OEt2)2]BArF in 10 mL of MeCN, resulting in an
solution immediately became colorless. The product precipitated
as a white powder upon addition of 40 mL of Et2O. The powder
4
immediate change from pale yellow to colorless. Addition of dppv
(0.143 g, 0.362 mmol) resulted in immediate gas evolution and a color
change to bright yellow. Solvent was removed under vacuum to give
a pale yellow powder. Addition of 100 mL of Et2O gave a cloudy
yellow solution. Upon concentrating the clear yellow filtrate by half
and storing in the freezer at -20 °C overnight, the product precipitated
as pale yellow microcrystals. The solid was filtered and dried under
vacuum. Yield: 0.218 g (82%). IR (MeCN): νCN ) 2087 (m), 2080
(m); νCO ) 1936 (s). 1H NMR (500 MHz, CD2Cl2): δ 7.33-7.91 (m,
(35) Fauque, G.; Peck, H. D., Jr.; Moura, J. J. G.; Huynh, B. H.; Berlier,
Y.; DerVartanian, D. V.; Teixeira, M.; Przybyla, A. E.; Lespinat, P. A.
FEMS Microbiol. ReV. 1988, 54, 299–344.
(36) Goldet, G.; Wait, A. F.; Cracknell, J. A.; Vincent, K. A.; Ludwig,
M.; Lenz, O.; Friedrich, B.; Armstrong, F. A. J. Am. Chem. Soc. 2008,
130, 11106–11113.
(37) Abdur-Rashid, K.; Fong, T. P.; Greaves, B.; Gusev, D. G.; Hinman,
J. G.; Landau, S. E.; Lough, A. J.; Morris, R. H. J. Am. Chem. Soc.
2000, 122, 9155–9171.
4468 Inorganic Chemistry, Vol. 48, No. 10, 2009

Coordination Chemistry of [HFe(CN)2(CO)3]- and DeriWatiWes
20 H, Ph), 3.59 (s, 24, 18-crown-6), 1.69 (br s, 2 H, Ph2PCHCHPPh2),
-8.64 (t, Fe-H, JHP ) 58 Hz), -14.02 (dd, Fe-H, JHP ) 59 Hz, JHP
) 49 Hz). 31P NMR (202 MHz, CD2Cl2): δ 108.2 (d), 103.7 (s), 97.2
(d). ESI MS (MeCN): m/z 533 (HFe(CN)2(CO)(dppv)-). Anal. Calcd
for C41H47FeKN2O7P2: C, 58.85; H, 5.66; N, 3.35. Found: C, 58.81;
H, 5.27; N, 3.65.
Protonation of [K(18-crown-6)][1(dppv)]. In MeCN: A solution
of [K(18-crown-6)][1H(dppv)] (0.102 g, 0.123 mmol) in 10 mL of
MeCN was treated with HCl (1.0 M in Et2O, 0.125 mL). Gas
evolution and a peak for free H2 at δ 4.56 in the 1H NMR spectrum
were observed. The product precipitated from solution as a yellow
powder. The solid was isolated by filtration and recrystallized from
5 mL of CH2Cl2 upon addition of 50 mL of hexane. Yield: 0.078
g (76%). IR (MeCN): νCN ) 2111 (w), 2104 (w sh); νCO ) 2004
(s). 1H NMR (500 MHz, CD2Cl2): δ 8.14 (s, 1H, CH); 8.03 (s, 1H,
CH); 8.0-7.3 (m, 20 H, Ph), 2.16 (s, 3H, NCCH3). 31P NMR (202
MHz, CDCl3): δ 84.1 (s˜) Anal. Calcd for C31H25FeN3OP2: C, 64.94;
H, 4.39; N, 7.33. Found: C, 64.12; H, 4.19; N, 8.01.
addition of 40 mL of Et2O. The bright yellow solid was washed
with 20 mL of benzene to remove a yellow impurity and dried
under vacuum. The solid was dissolved in 5 mL of CH2Cl2, and an
equal volume of water was added to extract Et4NI. The clear, yellow
CH2Cl2 layer was isolated and taken to dryness. Yield: 0.130 g
(48%). IR (MeCN): νCN ) 2077 (m); νCO ) 1936 (s), 1592 (m).
1H NMR (500 MHz, CD3CN): δ 7.9-7.0 (m, 22 H, dppv), 2.59 (s,
3 H, CH3). 31P NMR (202 MHz, CD3CN): δ 73.3 (br s), 72.1 (d,
3 Hz), 70.7 (br s), 69.9 (d, 3 Hz). ESI MS (MeCN): m/z 575
([Fe(CN)2(COMe)(CO)(dppv)]-). Anal. Calcd for C39H45FeN3O2P2:
C, 66.39; H, 6.43; N, 5.96. Found: C, 65.41; H, 6.37; N, 5.79. A
MeCN solution of the complex remained unchanged (no decarbo-
nylation) after heating at reflux for 12 h.
[K(18-crown-6)][Fe(CN)(CO)3(CNCOPh)]. A solution of [K(18-
crown-6)]2[Fe(CN)2(CO)3] (0.097 g, 0.12 mmol) in 3 mL of MeCN
was treated with PhCOCl (14 µL, 0.12 mmol), resulting in an
immediate change from pale yellow to deep red. Solvent was
removed under vacuum to give a dark red oil. The oil was extracted
with 30 mL of Et2O. The resulting solution was concentrated to
approximately 2 mL, and the product was precipitated upon addition
of 20 mL of hexane. The solid was isolated by filtration and dried
under vacuum. Yield: 30 mg (42%). IR (MeCN): νCN ) 2107 (w),
2035 (m); νCO ) 1947 (s, sh), 1932 (vs), 1661 (m). 1H NMR (500
MHz, CD3CN): δ 8.18 (d, 2 H, o-Ph), 7.67 (t, 1 H, p-Ph), 7.54 (t,
2 H, m-Ph), 3.56 (s, 24 H, 18-crown-6). ESI MS (MeCN): m/z 297
([Fe(CN)(CNCOPh)(CO)3]-). Anal. Calcd for C24H29FeKN2O10: C,
48.01; H, 4.87; N, 4.67. Found: C, 47.85; H, 4.90; N, 4.69. The
corresponding acetyl derivative was prepared similarly using
MeCOCl to give yellow solids with similar spectroscopic features.
Oxidation of [K(18-crown-6)]2[Fe(CN)2(CO)3]. A solution of
0.048 g (0.060 mmol) of [K(18-crown-6)]2[Fe(CN)2(CO)3] in 10
mL of MeCN was treated with a solution of 0.040 g (0.12 mmol)
of FcPF6 in 10 mL of MeCN, giving a clear, yellow solution. The
IR spectrum of the reaction mixture was difficult to interpret because
of a large number of overlapping peaks; however, ESI-MS of the
reaction mixture showed a significant signal for [Fe(CN)3(CO)3]-.
Crystallography. Crystals were mounted to a thin glass fiber
using Paratone-N oil (Exxon). Data, collected at 193 K on a Siemens
CCD diffractometer, were filtered to remove statistical outliers. The
integration software (SAINT) was used to test for crystal decay as
a bilinear function of X-ray exposure time and sin(θ). The data
were solved using SHELXTL (Table 2) by direct methods for
Fe(CN)2(NCMe)(CO)(dppv) and [K(18-crown-6)][HFe(CN)3-
(CO)2]·MeCN and by dual methods for [K(18-crown-6)][HFe(CN)2-
(CO)(dppv)]·MeCN·Et2O; atomic positions were deduced from an
E map or by an unweighted difference Fourier synthesis. Methyl
hydrogen atom U’s were assigned as 1.5 Ueq of the carrier atom;
remaining hydrogen atom U’s were assigned as 1.2 times carrier
Ueq. Metal hydride hydrogen atoms were surfaced in a late Fourier
difference map and were independently refined without restraints.
Non-hydrogen atoms were refined anisotropically. Successful
convergence of the full-matrix least-squares refinement of F2 was
indicated by the maximum shift/error for the final cycle.
In CH2Cl2: A solution of 0.050 g (0.060 mmol) of [K(18-crown-
6)][1H(dppv)] in 10 mL of CH2Cl2 was treated with a solution of
0.067 g (0.066 mmol) of [H(OEt2)2]BArF in 10 mL of CH2Cl2.
4
Gas evolution was observed. IR (CH2Cl2): νCN ) 2110 (w, br);
νCO ) 2004(s). Solvent was removed under vacuum to give a yellow
powder. Upon dissolving the yellow powder in 10 mL of MeCN,
the IR spectrum was indistinguishable from that of 1(NCMe)(dppv).
[K(18-crown-6)]2[HFe(CN)3(CO)2]·MeCN, [K(18-crown-6)]2[1H-
(CN)(CO)] ·MeCN. A solution of [K(18-crown-6)]2[Fe(CN)2(CO)3]
(0.0923 g, 0.116 mmol) in 5 mL of MeCN was treated with 60 µL
(0.12 mmol) of a 2.0 M solution of HCl in Et2O, giving a colorless
solution of the hydride. This solution was treated with PPh3 (0.0601
g, 0.229 mmol). When gas evolution ceased, a solution of 0.0083
g (0.13 mmol) KCN in ∼5 mL of MeOH was added to the reaction
mixture. After stirring for 30 min, the solvent was removed under
vacuum to give a pale yellow powder. The product was extracted
with 5 mL of MeCN, and the resulting pale yellow solution was
layered with 25 mL of Et2O. The pale yellow crystalline solid was
isolated by filtration and washed with 60 mL of Et2O to remove
PPh3. Yield: 0.045 g (49%). IR (MeCN): νCN ) 2098 (w), 2086
1
(w); νCO ) 1992 (s), 1935 (s). H NMR (500 MHz, CD2Cl2): δ
3.58 (s, 48 H, 18-crown-6), 2.09 (s, 3 H, CH3CN), -7.47 (s, Fe-
H), -11.65 (s, Fe-H), -13.04 (s, Fe-H). Anal. Calcd for
C29H49FeK2N3O14 ·C2H3N: C, 44.39; H, 6.25; N, 6.68. Found: C,
43.86; H, 5.96; N, 6.85.
Protonation of [K(18-crown-6)][HFe(CN)3(CO)2]. A solution of
[K(18-crown-6)]2[1H(CN)(CO)] (0.030 g, 0.038 mmol) in 5 mL
of MeCN was treated with 0.040 mL of 1 M HCl in Et2O. Gas
evolution was observed, and the solution became darker yellow.
Solvent was removed under vacuum to give a yellow solid. Yield:
0.028 g (84%). IR (MeCN): νCN ) 2133 (w), 2127 (w), 2118 (w);
νCO ) 2068 (s), 2023 (s). These data match those previously
reported by Liaw for (PPN)2[Fe(CN)3(NCMe)(CO)2].12
[K(18-crown-6)][MeFe(CN)2(CO)3], [K(18-crown-6)][1Me(CO)2]. A
solution of 0.086 g (0.11 mmol) of [K(18-crown-6)]2[Fe(CN)2(CO)3]
in 10 mL of CH2Cl2 was treated with 0.011 mL (0.10 mmol) of
MeOTf resulting in a color change from pale yellow to colorless.
IR (MeCN): νCN ) 2109 (w), 2083 (w), 2074 (w); νCO ) 2016 (s).
ESI MS (MeCN): m/z 207 ([MeFe(CN)2(CO)3]-).
(Et4N)[Fe(CN)2(COMe)(CO)(dppv)], Et4N[1Ac(dppv)]. A solu-
tion of 0.250 g (0.315 mmol) of (Et4N)2[Fe(CN)2(CO)3] in 20 mL
of CH2Cl2 was treated with 0.034 mL (0.31 mmol) of MeOTf.
Addition of 0.134 g (0.337 mmol) of dppv resulted in a color change
to light yellow-orange. The volume of the solution was reduced
by half, and the product was precipitated from solution upon
Acknowledgment. This research was sponsored by the NIH.
Supporting Information Available: Relevant spectra. Kinetic
plots and details of kinetics experiments. Crystallographic informa-
tion file (cif) for [K(18-crown-6)][1H(dppv)], 1(NCMe)(dppv), and
[K(18-crown-6)]2[1H(CN)(CO)]. This material is available free of
charge via the Internet at http://pubs.acs.org.
IC900200S
Inorganic Chemistry, Vol. 48, No. 10, 2009 4469