Binding of π-acceptor ligands to (triamine)iron(II) complexes

Article abstract of DOI:10.1021/ic9912629

A series of (Me₃TACN)Fe(II) derivatives with soft coligands have been investigated, where Me₃TACN is N,N',N''-trimethyl-1,4,7-triazacyclononane. Treatment of Me₃TACN with FeCl₂ afforded a compound with the empir

Full text of DOI:10.1021/ic9912629

Inorg. Chem. 2000, 39, 3029-3036
3029
Binding of π-Acceptor Ligands to (Triamine)iron(II) Complexes
Andrew C. Moreland and Thomas B. Rauchfuss*
School of Chemical Sciences, University of Illinois, Urbana, Illinois 61801
ReceiVed October 26, 1999
A series of (Me3TACN)FeII derivatives with soft coligands have been investigated, where Me3TACN is N,N′,N′′-
trimethyl-1,4,7-triazacyclononane. Treatment of Me3TACN with FeCl2 afforded a compound with the empirical
formula (Me3TACN)FeCl2 (1). Compound 1, which is a versatile precursor reagent, was shown by single-crystal
X-ray diffraction to be the salt [(Me3TACN)2Fe2Cl3][(Me3TACN)FeCl3], containing isolated [(Me3TACN)2Fe2-
Cl3]+ and [(Me3TACN)FeCl3]- subunits. Treatment of 1 with NaBPh4 gave the known [(Me3TACN)2Fe2Cl3]-
BPh4, while the addition of Me3TACN to FeCl4 gave [(Me3TACN)FeCl3]-. Oxygenation of 1 afforded
2-
[(Me3TACN)FeCl2]2(µ-O), which was shown crystallographically to be centrosymmetric with a pair of distorted
octahedral Fe centers. The Fe-N bond trans to the Fe-O bond is elongated by 0.2 Å relative to the other Fe-N
distances. Solutions of 1 and thiolates absorb CO to give [(Me3TACN)Fe(SPh)(CO)2]BPh4 and (Me3TACN)Fe-
(S2C2H4)(CO) (νCO ) 1896 cm-1). Treatment of 1 with excess CN- afforded [(Me3TACN)Fe(CN)3]-, isolated as
its PPh4+ salt 5. Crystallographic and spectroscopic studies show that 5 is low spin with a C3V structure; its Fe-N
distances contracted by 0.23 Å relative to those in [(Me3TACN)FeCl3]-. Aqueous solutions of 1 bind CO upon
the addition of CN- to produce (Me3TACN)Fe(CN)2(CO) (6). Analogous to 6 is (Me3TACN)Fe(CN)2(CNMe),
prepared by methylation of 5. The metastable dicarbonyl [(Me3TACN)FeI(CO)2]I was prepared by treatment of
-
FeI2(CO)4 with Me3TACN and was crystallographically characterized as its BPh4 salt. Values of E1/2 for
[(Me3TACN)FeCl3]-, 5, and 6 are -0.409, -0.640, and 0.533 V vs Fc/Fc+, respectively.
Introduction
ing and reactivity of which demonstrated the potential of the
(TACN)Fe unit as a π-donor center.
Recent years have witnessed increased interest in the binding
of π-acid ligands to metal centers bearing classical ligands such
as amines. To some extent, this theme is rooted in very old
chemistry. Copper and ruthenium ammine complexes of π-acid
ligands have been fruitfully investigated since the 1960s.1-3
Ruthenium-ammine chemistry cannot be extended to Fe
compounds because the FeII-NH3 linkage is typically labile.
In this investigation of the ligand-binding properties of
amine-FeII centers, we have focused on the R3TACN family
of facially coordinating tridentate ligands, where TACN is 1,4,7-
triazacyclononane and Me3TACN is the bulkier N,N′N′′-
trimethyl derivative thereof.4,5 The R3TACN class of facially
coordinating amine ligands has been employed extensively to
probe the role of metal centers in biological systems. TACN
complexes have proven particularly useful in the characterization
of metals involved in dioxygen activation, as illustrated by the
studies of Wieghardt3,4 and Tolman.5,6 These successes are due
to the kinetic resilience of the M-R3TACN interaction as well
as to the highly basic nature of the mesocyclic ligand. In contrast
to unidentate NH3-Fe derivatives, the Fe(R3TACN) fragment
is robust and tolerates the introduction of diverse and reactive
coligands. For example, our first foray into (TACN)Fe chemistry
uncovered the exceptional species (TACN)2Fe2(S2)3,7 the bond-
We were especially interested in the ability of the R3TACN-
Fe system to support CO coligands. Studies of non-heme Fe-
CO compounds provide insights into the electronic features that
allow one to bind still more challenging substrates to Fe, such
as N2 and alkenes, as implicated in Fe-catalyzed nitrogen
fixation and alkene polymerization catalysis,8 respectively. It
is now known that FeII-CO complexes are common to all
metallohydrogenases;9-11 thus expertise with FeII-CO systems
should guide the preparation of active-site analogues. Other
enzymes featuring non-heme Fe centers with soft donor ligands
(thiolates, cyanide) include nitrile hydratase12,13 and possibly
nitrogenase.14
The binding of CO to amine-FeII complexes has been of
intermittent interest since the 1970s. Noteworthy early results
are those of Karlin and Lippard15 and Marko´ et al.,16 who
isolated Fe[SC2H4N(Me)C2H4N(Me)C2H4S](CO)2 and Fe(SPh)2-
(7) Moreland, A. C.; Rauchfuss, T. B. J. Am. Chem. Soc. 1998, 120,
9376-7.
(8) Britovsek, G. J. P.; Gibson, V. C.; Kimberley, B. S.; Maddox, P. J.;
McTavish, S. J.; Solan, G. A.; White, A. J. P.; Williams, D. J. Chem.
Commun. 1998, 849-50.
(9) Thauer, R. K.; Klein, A. R.; Hartmann, G. C. Chem. ReV. 1996, 96,
3031-42.
(10) Peters, J. W.; Lanzilotta, W. N.; Lemon, B. J.; Seefeldt, L. C. Science
1998, 282, 1853-8.
(1) Taube, H. Pure Appl. Chem. 1979, 51, 901-12.
(2) Hidai, M.; Mizobe, Y. Chem. ReV. 1995, 95, 1115-33.
(3) Schneider, R.; Ju¨stel, T.; Wieghardt, K.; Nuber, B. Z. Naturforsch.
1994, 49B, 330.
(11) Cammack, R. Nature 1999, 397, 214-5.
(12) Nagashima, S.; Nakasako, M.; Dohmae, N.; Tsujimura, M.; Takio,
K.; Odaka, M.; Yohda, M.; Kamiya, N.; Endo, I. Nature Struct. Biol.
1998, 5, 347-52.
(4) Chaudhuri, P.; Wieghardt, K. Prog. Inorg. Chem. 1988, 35, 329-
(13) Marlin, D. S.; Olmstead, M. M.; Mascharak, P. K. Inorg. Chem. 1999,
38, 3258-60.
436.
(5) Halfen, J. A.; Tolman, W. B. Inorg. Synth. 1998, 32, 75-81.
(6) Halfen, J. A.; Mahapatra, S.; Wilkinson, E. C.; Kaderli, S.; Young,
V. G.; Que, L.; Zuberbuhler, A. D.; Tolman, W. B. Science 1996,
271, 1397-400.
(14) Burgess, B. K.; Lowe, D. J. Chem. ReV. 1996, 96, 2983-3011.
(15) Karlin, K. D.; Lippard, S. J. J. Am. Chem. Soc. 1976, 98, 6951-7.
(16) Taka´cs, J.; Soo´s, E.; Nagy-Magos, Z.; Marko´, L.; Gervasio, G.;
Hoffmann, T. Inorg. Chim. Acta 1989, 166, 39-46.
10.1021/ic9912629 CCC: $19.00 © 2000 American Chemical Society
Published on Web 06/16/2000

3030 Inorganic Chemistry, Vol. 39, No. 14, 2000
Moreland and Rauchfuss
Scheme 1
(CO)2(en), respectively. Study of Fe-amine-CO species has
been reinvigorated in recent years.17-23 For example, in pursuing
the relationship between the electronic structure and catalytic
mechanism of nitrile hydratase,17,24 Kovacs has reported the CO
adduct of an Fe(diimino-amino-dithiolato) species. In contrast
to the known amine-FeII-CO complexes, well-characterized
FeII-N2 complexes all feature tertiary phosphine coligands.25-30
The principal compounds prepared in this project are sum-
marized in Scheme 1.
Results
The principal precursor to the new (Me3TACN)FeII com-
pounds results from the treatment of Me3TACN with FeCl2.
This reaction afforded a tan solid analyzed as (Me3TACN)FeCl2
(1). Crystals grown from MeCN/Et2O were examined by X-ray
diffraction and shown to be the salt [(Me3TACN)2Fe2(µ-Cl)3+]-
[(Me3TACN)FeCl3-] (eq 1). The cation [(Me3TACN)2Fe2(µ-
(17) Ellison, J. J.; Nienstedt, A.; Shoner, S. C.; Barnhart, D.; Cowen, J.
A.; Kovacs, J. A. J. Am. Chem. Soc. 1998, 120, 5691-700.
(18) Sellmann, D.; Mahr, G.; Knoch, F.; Moll, M. Inorg. Chim. Acta 1994,
224, 45-59.
(19) Sellmann, D.; Sutter, J. Acc. Chem. Res. 1997, 30, 460-9. Sellmann,
D. New J. Chem. 1997, 21, 681-9.
3FeCl2 + 3Me3TACN f
+
-
[(Me3TACN)2Fe2(µ-Cl)3 ][(Me3TACN)FeCl3 ] (1)
(20) Davies, S. C.; Hughes, D. L.; Richards, R. L.; Sanders, J. R. Chem.
Commun. 1998, 2699-700. Davies, S. C.; Evans, D. J.; Hughes, D.
L.; Longhurst, S.; Sanders, J. R. Chem. Commun. 1999, 1935-6.
(21) Hsu, H.-F.; Koch, S. A.; Popescu, C. V.; Mu¨nck, E. J. Am. Chem.
Soc. 1997, 119, 8371-2.
Cl)3]+ was previously characterized by Wieghardt et al. as its
BPh4 derivative (Figure 1).31 This is a face-sharing biocta-
-
(22) Mauro, A. E.; Casagrande, O. L., Jr.; Nogueira, V. M.; Santos, R. H.
A.; Gambardella, M. T. P.; Lechat, J. R.; Filho, M. F. J. Polyhedron
1993, 12, 297-301.
hedral species with a nonbonding Fe‚‚‚Fe separation of 3.008
Å. The metrical details for the cation in 1 (see Table 1) are
-
(23) Liaw, W.-F.; Chen, C.-H.; Lee, G.-H.; Peng, S.-M. Organometallics
1998, 17, 2370-2372.
virtually identical to those of the BPh4 salt.31 The anion
[FeCl3(Me3TACN)]- is new. This species has idealized C3V
symmetry. The Fe-Cl distances in the anion (2.4467(9)-
(24) Marini, P. J.; Murray, K. S.; West, B. O. J. Chem. Soc., Dalton Trans.
1983, 143-51.
(25) Hills, A.; Hughes, D. L.; Jimenez-Tenorio, M.; Leigh, G. J.; Rowley,
A. T. J. Chem. Soc., Dalton Trans. 1993, 3041-9.
(26) Ghilardi, C. A.; Midollini, S.; Sacconi, L.; Stoppioni, P. J. Organomet.
Chem. 1981, 205, C193-202.
(29) Buys, I. E.; Field, L. D.; Hambley, T. W.; McQueen, A. E. D. Acta
Crystallogr. 1993, C49, 1056-9.
(30) de la J. Leal, A.; Jime´nez-Tenorio, M.; Puerta, M. C.; Valerga, P.
Organometallics 1995, 14, 3839-47.
(27) Hughes, D. L.; Leigh, J.; Jimenez-Tenorio, M.; Rowley, A. T. J. Chem.
Soc., Dalton Trans. 1993, 75-82.
(31) Bossek, U.; Nu¨hlen, D.; Bill, E.; Glaser, T.; Krebs, C.; Weyhermu¨ller,
T.; Wieghardt, K.; Lengen, M.; Trautwein, A. X. Inorg. Chem. 1997,
36, 2834-43.
(28) Wiesler, B. E.; Lehnert, N.; Tuczek, F.; Neuhausen, J.; Tremel, W.
Angew. Chem., Int. Ed. Engl. 1998, 37, 815-6.

(Triamine)iron(II) Complexes
Inorganic Chemistry, Vol. 39, No. 14, 2000 3031
Table 2. Selected Bond Distances (Å) and Angles (deg) for 2
Fe(1)-O(1)
Fe(1)-N(1)
Fe(1)-N(2)
1.8190(7)
2.237(4)
2.414(4)
Fe(1)-N(3)
Fe(1)-Cl(1)
Fe(1)-Cl(2)
2.258(4)
2.3426(15)
2.3789(14)
O(1)-Fe(1)-N(1)
O(1)-Fe(1)-N(3)
N(1)-Fe(1)-N(3)
92.98(11) N(3)-Fe(1)-Cl(2)
97.91(11) Cl(1)-Fe(1)-Cl(2)
78.56(15) O(1)-Fe(1)-N(2)
88.88(11)
93.25(5)
167.28(11)
75.34(15)
75.14(15)
85.42(11)
88.47(11)
O(1)-Fe(1)-Cl(1) 100.68(4)
N(1)-Fe(1)-N(2)
N(1)-Fe(1)-Cl(1) 94.21(11) N(3)-Fe(1)-N(2)
N(3)-Fe(1)-Cl(1) 160.39(11) Cl(1)-Fe(1)-N(2)
O(1)-Fe(1)-N(1)
O(1)-Fe(1)-N(3)
Figure 1. Structures of the anion and cation in “(Me3TACN)FeCl2”
(1), with thermal ellipsoids drawn at the 50% level.
92.98(11) Cl(2)-Fe(1)-N(2)
97.91(11) Fe(1)-O(1)-Fe(1)#1 180.00(5)
Table 1. Selected Bond Distances (Å) and Angles (deg) for 1
Fe(1)-N(1)
Fe(1)-N(2)
Fe(1)-N(3)
Fe(1)-Cl(3)
Fe(1)-Cl(1)
Fe(1)-Cl(2)
Fe(2)-N(6)
Fe(2)-N(4)
Fe(2)-N(5)
2.307(3)
2.321(3)
2.327(3)
2.4467(9)
2.4486(9)
2.4589(9)
2.197(3)
2.212(3)
2.207(3)
Fe(2)-Cl(6)
Fe(2)-Cl(5)
Fe(2)-Cl(4)
Fe(3)-N(9)
Fe(3)-N(8)
Fe(3)-N(7)
Fe(3)-Cl(5)
Fe(3)-Cl(4)
Fe(3)-Cl(6)
2.4729(9)
2.4921(9)
2.5197(9)
2.193(3)
2.194(3)
2.210(3)
2.4820(9)
2.4913(9)
2.5129(9)
ligands in [(Me3TACN)FeCl3]- are kinetically labile. We were
unable to convert 1 into PPh4[(Me3TACN)FeCl3] by the reaction
of 1 with an excess of PPh4Cl. On the other hand, the
observation of [(Me3TACN)FeCl3]- in solutions of 1 shows that
the anion is not spontaneously unstable with respect to the
dinuclear cation, implying that the nonreaction of Cl- and [(Me3-
TACN)2Fe2Cl3]+ is due to kinetic factors, e.g., slow cleavage
1
of the Fe(µ-Cl)3Fe bridge. H NMR analysis did confirm that
Cl(3)-Fe(1)-Cl(1)
Cl(3)-Fe(1)-Cl(2)
Cl(1)-Fe(1)-Cl(2)
Cl(6)-Fe(2)-Cl(4)
Cl(5)-Fe(2)-Cl(4)
97.67(3)
97.94(3)
97.27(3)
87.85(3)
86.56(3)
Cl(5)-Fe(3)-Cl(6)
Cl(4)-Fe(3)-Cl(6)
Fe(3)-Cl(4)-Fe(2)
Fe(3)-Cl(5)-Fe(2)
Fe(2)-Cl(6)-Fe(3)
87.25(3)
87.60(3)
73.77(3)
74.41(2)
74.40(3)
(PPh4)2[FeCl4] and Me3TACN react to give exclusively
[(Me3TACN)FeCl3]- (Chart 1). Interestingly, D2O solutions of
1 feature only three signals, suggesting a rather simple structure.
Chart 1. Equilibria Related to the (Me3TACN)FeII-Cl System
2LFeCl2 u [L2Fe2Cl3]+ + [LFeCl3]-
2[LFeCl3]- U [L2Fe2Cl3]+ 3Cl-
-
3NaBPh4 + 2[LFeCl3]- u [L2Fe2Cl3+]BPh4
+
-
2NaCl + 2BPh4
[FeCl4]2- + L f [LFeCl3]- + Cl-
The cyclic voltammograms of solutions of 1 showed a
reversible event at -0.409 V vs Fc+/Fc, which is not present
in solutions of [(Me3TACN)2Fe2Cl3]BPh4. This redox process,
which is a reduction, is assigned to the [(Me3TACN)FeCl3]0/-
couple. This assignment was confirmed by electrochemical
measurements on independently prepared (Me3TACN)FeCl3.34
Aerobic oxidation of solutions of 1 afforded orange crystals
of [(Me3TACN)FeCl2]2(µ-O) (2). The new compound is soluble
in water and only slightly soluble in polar organic solvents such
as MeOH and MeCN. Like other high-spin d5 complexes, such
Figure 2. Structure of [(Me3TACN)FeCl2]2(µ-O) (2), with thermal
ellipsoids drawn at the 50% level.
2.4589(9) Å) are significantly longer than those in (Me3TACN)-
FeIIICl3 (2.300(1)-2.309(1) Å).32 The Fe-N distances are also
elongated, but less dramatically so: 2.307(3)-2.327(3) Å for
FeII vs 2.232(2)-2.264(2) Å for FeIII.32 When compared to those
of other FeII(Me3TACN) species, for example, [(Me3TACN)-
Fe(NCS)2]2 (2.25(1)-2.27(2) Å),33 the Fe-N distances are
slightly longer as well, perhaps due to the effect of negative
charge. Acetonitrile solutions of 1 exhibit a conductivity of 133
Ω-1 cm-1, which is independent of concentration over the range
0.50-5.0 mM.
1
as (Me3TACN)FeCl3, compound 2 exhibits no detectable H
NMR spectrum.
Compound 2 was further characterized by single-crystal X-ray
diffraction. The complex is described as a corner-shared
bioctahedral species, each Fe center being held in an OCl2N3
coordination sphere. The Fe-O-Fe angle is constrained at 180°
by the crystallographically imposed centrosymmetry (Figure 2,
Table 2). A similar compound, [(Me3TACN)Fe(acac)]2(µ-O)-
(ClO4)2, which has no crystallographically imposed symmetry,
has an Fe-O-Fe angle of 158.6(3)°.35 In both compounds, the
Fe-N bond trans to oxygen is longer than the other metal-
ligand distances. In 2, the length of the Fe-N bond trans to
Fe-O is 2.414(4) Å and the cis Fe-N distances are 2.237(4)-
2.258(4) Å, while in [(Me3TACN)Fe(acac)]2(µ-O)(ClO4)2, the
Fe-N distances are 2.161(6) and 2.229(6) Å for the bonds cis
1
The H NMR spectrum of 1 shows five signals in MeCN
solution. Three of these signals are assigned to [(Me3TACN)2Fe2-
Cl3]+, as seen for an independently prepared sample (see below).
One of these three signals has double the expected intensity
and is the result of accidental degeneracy. One of the coinci-
dental signals and the other two signals are assigned to the anion
[(Me3TACN)FeCl3]-. In CD3OD solution, all six signals are
resolved. Treatment of methanolic solutions of 1 with NaBPh4
afforded a 77% yield of [(Me3TACN)2Fe2Cl3]BPh4, thus
confirming the relationship of 1 to Wieghardt’s derivative. The
facility and efficiency of this conversion suggest that the Cl-
(34) Chaudhuri, P.; Winter, M.; Wieghardt, K.; Gehring, S.; Haase, W.;
Nuber, B.; Weiss, J. Inorg. Chem. 1988, 27, 1564-9.
(35) Wieghardt, K.; Pohl, K.; Bossek, U.; Nuber, B.; Weiss, J. Z.
Naturforsch. 1988, 43B, 1184-94.
(32) Silver, G. C.; Trogler, W. C. J. Am. Chem. Soc. 1995, 117, 3983-93.
(33) Pohl, K.; Wieghardt, K.; Nuber, B.; Weiss, J. J. Chem. Soc., Dalton
Trans. 1987, 187.

3032 Inorganic Chemistry, Vol. 39, No. 14, 2000
Moreland and Rauchfuss
1
Table 3. Selected IR and H NMR Data (Obtained in CH3CN or
CD3CN Solutions)
compound
ν
CX (cm-1
)
δMe (rel intens)
[(Me3TACN)Fe(SPh)(CO)2]BPh4 (3)
2040
1988
1896
3.29 (2)
2.88 (1)
3.33 (1)
2.61 (2)
2.99 (3)
(Me3TACN)Fe(S2C2H4)(CO) (4)
PPh4[(Me3TACN)Fe(CN)3] (5)
(Me3TACN)Fe(CN)2CO (6)
2052
2035
2097
2092
1960
2131
2068
2037
2051
3.35 (1)
2.92 (2)
(Me3TACN)Fe(CN)2(CNMe) (7)
[(Me3TACN)FeI(CO)2]BPh4 (8)
3.56 (1, CNMe)
3.30 (1)
2.96 (2)
3.55 (2)
Figure 3. Structure of the anion [(Me3TACN)Fe(CN)3]- in 5, with
2.85 (1)
thermal ellipsoids drawn at the 50% level.
and trans to the terminal oxo ligand, the overall contraction of
Fe-N distances in the cationic species being attributable to
electrostatic effects. The Fe-Cl distances in 2 are 2.3789(14)
and 2.3426(15) Å, which are slightly longer than those in (Me3-
TACN)FeCl3 (2.300(1)-2.309(1) Å).32 Also related to 2 is the
mixed-valence anion [(Me3TACN)Fe(dbm)]2(µ-O)- (dbm is the
â-ketoenolate dibenzoylmethanide).36 In this case, the Fe-N
distances are for N trans to oxide 0.1 Å longer than the other
Fe-N distances.
(Me3TACN)Fe-SR-CO Derivatives. Compound 1 is a
useful precursor to the series (Me3TACN)Fe-SR-CO, which
allowed us to assess the influence of thiolato ligands on CO
binding. The simple derivative [(Me3TACN)Fe(SPh)(CO)2]+
was generated by treatment of a methanolic solution of 1 with
NaSPh to afford a brown intermediate, which was not further
characterized. This solution absorbed CO gas to give a red
derivative, which was isolated by precipitation as its BPh4- salt.
The new compound, [(Me3TACN)Fe(SPh)(CO)2]BPh4 (3), was
isolated in ∼75% yield. 1H NMR spectroscopic characterization
indicates that 3 is a diamagnetic species with an Me resonance
pattern consistent with the Cs symmetry. As will be illustrated
for other compounds discussed below, the chemical shifts for
the NMe groups trans to CO are observed in the region δ 3.25-
3.55 (Table 3). The IR spectrum of 3 in the CO region exhibits
two intense signals at 2040 and 1988 cm-1. The CO ligands in
3 were not displaced by an N2 purge, unlike the situation for
[(Me3TACN)FeI(CO)2]+ (see below). We obtained 3 even when
the reaction was conducted with a 2-fold excess of PhSNa:
(Me3TACN)Fe(SPh)2(CO) was not observed (see contrasting
situation for (Me3TACN)Fe(CN)2(CO), below).
Table 4. Selected Bond Distances (Å) and Angles (deg) for 5
Fe(1)-C(11)
Fe(1)-C(12)
Fe(1)-C(10)
Fe(1)-N(2)
Fe(1)-N(3)
1.868(9)
1.877(9)
1.882(6)
2.082(6)
2.087(6)
Fe(1)-N(1)
C(10)-N(4)
C(11)-N(5)
C(12)-N(6)
2.089(4)
1.169(7)
1.175(10)
1.174(10)
C(11)-Fe(1)-C(12)
C(11)-Fe(1)-C(10)
C(12)-Fe(1)-C(10)
C(11)-Fe(1)-N(2)
C(12)-Fe(1)-N(2)
C(10)-Fe(1)-N(2)
C(11)-Fe(1)-N(3)
C(12)-Fe(1)-N(3)
C(10)-Fe(1)-N(3)
90.6(3) N(2)-Fe(1)-N(3)
89.5(4) C(11)-Fe(1)-N(1)
89.0(4) C(12)-Fe(1)-N(1)
84.2(2)
92.1(5)
95.3(4)
175.1(6) C(10)-Fe(1)-N(1) 175.4(3)
92.2(7) N(2)-Fe(1)-N(1)
94.5(3) N(3)-Fe(1)-N(1)
92.9(7) N(4)-C(10)-Fe(1) 179.3(7)
176.1(7) N(5)-C(11)-Fe(1) 172(2)
92.7(3) N(6)-C(12)-Fe(1) 176.0(17)
83.7(2)
82.9(2)
unexceptional and fully consistent with the C3V symmetry.
Microanalysis indicates that the product crystallizes as the
monohydrate. The 13CN-labeled complex was prepared similarly
using K13CN. The isotopic shift for νCN in the infrared spectrum
is 44 cm-1 (2052 and 2035 cm-1 for 12CN; 2008 and 1991 cm-1
for 13CN).
Cyclic voltammetry studies demonstrate that the potential of
the couple [(Me3TACN)Fe(CN)3]0/- occurs at -0.640 V vs Fc/
Fc+ in MeCN. For comparison, the redox potential of
[Fe(CN)6]4-/3- is -0.921 V vs Fc+/Fc in MeCN. However, the
ferrocyanide potential can vary by >1 V depending on solvent,
with values of +0.079 V in H2O to -0.971 V in DMF.37
A
similar compound, [Fe(CN)4(diamine)]-/2- has an E1/2 value of
+0.058 V in H2O,38-40 which is closer to that of aqueous
[Fe(CN)6]3-/4-, but solvent effects were not investigated for this
diamine derivative. The effect of solvent on the redox potential
for 5 was evaluated. The potentials of the redox couple,
[(Me3TACN)-
To investigate the influence of two thiolato ligands on the
CO-binding properties of the FeII center, we undertook the
synthesis of an ethanedithiolato derivative of 1. A solution of 1
was treated with methanolic Na2S2C2H4 followed by CO to give
a red-violet species. The product, (Me3TACN)Fe(S2C2H4)(CO)
(4), was purified by extraction into CH2Cl2 followed by
precipitation with Et2O. The NMR data indicate that 4 is
diamagnetic with Cs symmetry. The IR spectrum shows that
νCO ) 1896 cm-1, more than 100 cm-1 lower frequency than
the average of the νCO bands for 3.
Fe(CN)3]0/-, are -0.240 V in H2O, -0.297 V in MeOH, and
-0.640 V in MeCN, all vs Fc/Fc+. The trend of redox potential
increase reflects the fact that polar, hydrogen-bonding solvents
stabilize the ferrous state. This trend is similar to that seen for
ferrocyanide but less dramatic.
X-ray crystallographic analysis of 5 revealed that Fe is
octahedral in an N3C3 coordination sphere (Figure 3, Table 4).
The Fe-N distances in 5 (2.082(6)-2.089(4) Å) are dramati-
cally shorter than those in high-spin FeII(Me3TACN) com-
[(Me3TACN)Fe(CN)3]-. The simple tricyano derivative
[(Me3TACN)Fe(CN)3]- was readily prepared by treatment of
a methanolic solution of 1 with slightly greater than three equiv
of KCN. Addition of PPh4Cl to the reaction mixture afforded
orange microcrystals of PPh4[(Me3TACN)Fe(CN)3] (5) in
excellent yield. The NMR and IR spectra for this species are
(37) Mascharak, P. K. Inorg. Chem. 1986, 25, 245-7.
(38) Goto, M.; Takeshita, M.; Kanda, N.; Sakai, T.; Goedken, V. L. Inorg.
Chem. 1985, 24, 582-7.
(39) Goedken, V. L. J. Chem. Soc., Chem. Commun. 1972, 207-8.
(40) Kuroda, Y.; Tanaka, N.; Goto, M.; Sakai, T. Inorg. Chem. 1989, 28,
2163-9.
(36) Mu¨ller, M.; Bill, E.; Weyhermu¨ller, T.; Wieghardt, K. Chem. Commun.
1997, 705-6.

(Triamine)iron(II) Complexes
Inorganic Chemistry, Vol. 39, No. 14, 2000 3033
-
plexes: the Fe-N distances in [(Me3TACN)FeCl3 (average
2.32 Å) are >0.2 Å longer than those in 5. The Fe-CN distances
in 5 (1.868(9)-1.882(6) Å) are slightly shorter than those in
[Fe(CN)6]4- (1.896(6)-1.909(6) Å).41 Other Fe-CN-amine
complexes have been known for many years, e.g., [Fe(CN)4-
(en)]2-, but have not been subject to structural studies.39,40
Known examples of complexes with the basic formula
(TACN)M(CN)3 include those for M ) Cr42 and Co.43
(Me3TACN)Fe(CN)2(CO). The preparation of the mixed
CO-CN- derivative (Me3TACN)Fe(CN)2(CO) (6) was modeled
on the procedure used for the thiolato carbonyl 3. The synthesis
of 6 proved, however, to be particularly challenging. Carbon-
ylation of solutions of 1 in the presence of 2 equiv of Et4NCN
indeed generated CO-containing products, but it was difficult
to purify the products because of the comparable solubilities of
Et4NCl, Et4NCN, and 6. An improved method for the prepara-
tion of 6 involved the reaction of aqueous 1 with 2 equiv of
KCN under an atmosphere of CO (eq 2).
Figure 4. Structure of the cation [(Me3TACN)FeI(CO)2]+ in 8, with
thermal ellipsoids drawn at the 35% level.
Table 5. Selected Bond Distance (Å) and Angles (deg) for 8
(Me3TACN)FeCl2 + 2CN- + CO f
(Me3TACN)Fe(CN)2(CO) + 2Cl- (2)
I(1)-Fe(1)
Fe(1)-C(1)
Fe(1)-C(2)
Fe(1)-N(1)
2.6509(10)
1.791(9)
1.792(9)
2.028(5)
Fe(1)-N(3)
Fe(1)-N(2)
O(1)-C(1)
O(2)-C(2)
2.069(5)
2.072(5)
1.146(9)
1.133(8)
The crude product contained 6 together with some 5 as well
as other unidentified species. Charge-neutral 6 was purified by
extraction into CH2Cl2; evaporation of this solution gave an
orange solid that was spectroscopically and analytically pure.
In this synthesis, CO intercepts intermediate cyano species,
perhaps oligomers with µ-CN ligands.44 Characterization of 6
relied on its straightforward and informative IR and NMR
properties (Table 1). The 1H NMR data confirm the Cs
symmetry, and the shift patterns are consistent with one NMe
group trans to CO and two NMe groups trans to CN. Solid
samples of 6 are stable under a nitrogen atmosphere. Cyclic
voltammetry studies show that 6 undergoes quasi-reversible
oxidation at the relatively high potential of 0.533 V vs Fc/Fc+.
This can be compared with the value of -0.640 V for
[(Me3TACN)Fe(CN)3]0/-, as discussed above.
C(1)-Fe(1)-C(2)
C(1)-Fe(1)-N(1)
C(2)-Fe(1)-N(1)
C(1)-Fe(1)-N(3)
C(2)-Fe(1)-N(3)
N(1)-Fe(1)-N(3)
C(1)-Fe(1)-N(2)
C(2)-Fe(1)-N(2)
89.6(3)
94.7(3)
95.9(3)
93.9(3)
176.3(3)
85.2(2)
178.0(3)
92.3(3)
N(1)-Fe(1)-N(2)
N(3)-Fe(1)-N(2)
C(1)-Fe(1)-I(1)
C(2)-Fe(1)-I(1)
N(1)-Fe(1)-I(1)
N(3)-Fe(1)-I(1)
N(2)-Fe(1)-I(1)
N(1)-Fe(1)-N(2)
84.4(2)
84.2(2)
83.1(2)
83.9(2)
177.76(15)
95.19(14)
97.79(13)
84.4(2)
spectrum shows three νCN bands assigned respectively to cyano
(2068, 2037 cm-1) and isocyano ligands (2131 cm-1).
[(Me3TACN)FeI(CO)2]+. An alternative route to (Me3-
TACN)Fe-CO complexes involved the reaction of Fe(CO)4I2
with Me3TACN. Vigorous CO evolution occurred as the red-
violet precursor was converted to pink [(Me3TACN)FeI(CO)2]I
1
(eq 3). The H NMR spectrum of this salt shows the expected
We investigated the possible carbonylation of 5 as a possible
route to 6. IR spectroscopic measurements show that MeCN
solutions of 5 rapidly react with CO gas at room temperature
to afford a small amount of a new complex with νCO ) 2023,
1994 cm-1. The identity of these new bands as νCO was
confirmed by the carbonylation of [(Me3TACN)Fe(13CN)3]-,
which produced the same IR signature as that of the new species.
Using 6 as a standard for the relative intensities of νCN and
FeI2(CO)4 + Me3TACN f
[(Me3TACN)FeI(CO)2]I + 2CO (3)
2:1 pattern for the NMe groups, the more intense signal being
at δ 3.55, consistent with methyl trans to CO. The IR spectrum
also indicates a dicarbonyl with a pair of νCO bands (2051, 2003
cm-1), which are of ∼15 cm-1 higher energy than those of the
analogous (SPh)(CO)2 species 3. In contrast to those in the other
carbonyl complexes prepared in this work, the CO ligands in
this species are labile, although the complex is stable under a
CO atmosphere. The loss of CO is accompanied by a bleaching
of the solution color. The progress of decarbonylation can be
observed by UV-vis spectroscopy, monitoring the decrease in
intensity of the bands at 338 and 512 nm. The change obeys
isobestic behavior, and the kinetics are approximately first order
(k ) 5.68 × 10-4 s-1, t1/2 ) 1220 s at 22 °C).
νCO, the concentration of the new species was estimated to be
e10% of the total Fe concentration. Note that signals for 6 were
not observed. Upon evaporation, these carbonylated solutions
yielded spectroscopically pure 5, indicating that the CO is
kinetically labile. It has been known for some years that
[Fe(CN)6]4- can be carbonylated at high pressures to give
[Fe(CN)5(CO)]3- 45
.
The isocyanide analogue of 6 was prepared by exploiting the
nucleophilic character of the FeCN units in 5. Thus (Me3-
TACN)Fe(CN)2(CNMe) (7) was obtained by addition of the
methylating agent MeOTf to an MeCN solution of 5. 1H NMR
measurements indicate that 7 has Cs symmetry, and the infrared
Treatment of methanolic [(Me3TACN)FeI(CO)2]I with NaB-
Ph4 precipitated pink [(Me3TACN)FeI(CO)2]BPh4 (8). Crystal-
lographic analysis reveals an octahedral species (Figure 4, Table
5). The FeI(CO)2 unit resembles that in (C5Me5)FeI(CO)2,46 e.g.,
in the Fe-I distances (2.6509(10) Å for Me3TACN vs 2.6077-
(9) Å for the Cp* compound) and Fe-CO distances (1.792(9)
Å for Me3TACN vs 1.774(5) Å for the Cp* compound). In both
(41) Meyer, H.-J.; Pickardt, J. Z. Anorg. Allg. Chem. 1988, 560, 185-90.
(42) Kirk, A. D.; Namasivayam, C. Inorg. Chem. 1988, 27, 1095-9.
(43) Heinrich, J. L.; Berseth, P. A.; Long, J. R. Chem. Commun. 1998,
1231-2.
(44) Vahrenkamp, H.; Geiss, A.; Richardson, G. N. J. Chem. Soc., Dalton
Trans. 1997, 3643-51.
(45) Cotton, F. A.; Monchamp, R. R.; Henry, R. J. M.; Young, R. C. J.
Inorg. Nucl. Chem. 1959, 10, 28.
(46) Akita, M.; Terada, M.; Tanaka, M.; Moro-Oka, Y. J. Organomet.
Chem. 1996, 510, 255-61.

3034 Inorganic Chemistry, Vol. 39, No. 14, 2000
Moreland and Rauchfuss
cases, the bond distances are slightly longer for the Me3TACN
compound, perhaps as a consequence of steric crowding. The
Fe-N distances are, on average, slightly shorter still than those
in the other low-spin FeII compound, 5 (averages: 2.056(5) vs
2.086(6) Å for 5). The Fe-N distance trans to I is 0.04 Å shorter
than the Fe-N distances trans to CO. Qualitative experiments
confirm that 8 can be converted to the other carbonyl complexes
3 and 6 by treatment with SPh- and CN-, respectively.
It is also significant that (Me3TACN)Fe(CN)2(CO) is sus-
ceptible to oxidation, albeit at the relatively high potential of
0.533 V vs Fc+/Fc. Very few FeIICO complexes undergo
chemically reversible oxidation, as summarized by Koch, who
described a complex of the type FeIII(CN)(SR)3(PR3)(CO)2-
.
The shift in potential of ∼1.2 V for [(Me3TACN)Fe(CN)2(CO)]+/0
vs [(Me3TACN)Fe(CN)3]0/- is substantial. Though some of the
change in redox potential can be attributed to charge effects, a
large part of the 1.2 V shift is attributed to the differing donor
properties of CO and CN-. On the basis of the νCO bands for
the complexes reported in this work, it is clear that electron-
rich iron complexes can be generated using classical ligand
sets.
Discussion
In our investigation of CO derivatives of the amine-FeII
systems, we have focused on the Me3TACN derivatives for
reasons of stoichiometric control: less bulky triamines, e.g.,
Similarly, the lability of the CO correlates with the νCO
values: the derivative with high values of νCO (i.e., [(Me3-
TACN)Fe(CO)2I]+) is labile, while (Me3TACN)Fe(CN)2(CO)
and (Me3TACN)Fe(S2C2H4)(CO) are stable with respect to the
loss of CO. Kovacs has reported an iron complex which νCO
value of ∼1900 cm-1 but which is also labile;17 however, this
lability may reflect the ability of the coligand to adopt a trigonal
bipyramidal coordination geometry after decarbonylation.
n+
TACN itself, often form complexes of the type Fe(triamine)2
,
which are unsuitable for ligand substitution.47 An additional
reason for using Me3TACN instead of TACN is that unmethyl-
ated (TACN)FeCl3 is very poorly soluble. A drawback of the
high basicity of Me3TACN, however, is the stabilization of ionic
derivatives such as [(Me3TACN)2Fe2(µ-Cl)3+][(Me3TACN)-
FeCl3-] (1), not simple monomeric or dimeric derivatives, [(Me3-
TACN)FeCl2]x. We had hoped to obtain [(Me3TACN)FeCl2]2,
which would serve as an analogue of such well-known species
as [(ring)MCl2]2 (where (ring)M ) (arene)Ru and (C5Me5)Rh).
Nonetheless, compound 1 generally behaves as an equivalent
of (Me3TACN)FeCl2 and appears to be versatile, even beyond
the immediate theme of amine-Fe-CO compounds. We note
that Wieghardt has in fact reported [(Me3TACN)FeX2]2 (X- )
NCO-, SCN-).33
Experimental Section
Materials and Methods. Solvent purifications and spectroscopic
measurements were conducted as previously described.50 The following
compounds were prepared using literature procedures: FeCl2,51 FeI2-
(CO)4,52 and Me3TACN.4,53 All manipulations were carried out under
an atmosphere of purified nitrogen using either Schlenk techniques or
an inert-atmosphere glovebox. Redox potentials were measured relative
to Ag/AgCl (saturated KCl) or Ag/AgPF6 (0.1 M Bu4NPF6 in MeCN).
The reported potentials are referenced to ferrocene by comparing the
potential to E1/2 of Fc measured under similar conditions (0.434 V vs
Ag/AgCl, (saturated KCl), 0.115 V vs Ag/AgPF6 (0.1 M Bu4NPF6 in
MeCN)).
Parallel to studies on 1, we examined the synthetic utility of
the “precarbonylated” species [(Me3TACN)FeI(CO)2]I, which
is prepared from the readily available FeI2(CO)4. The inability
of 1 to bind CO is consistent with the tendency of [(Me3TACN)-
FeI(CO)2]+ to expel CO. The important and relatively subtle
role of the coligand L in controlling the π-basicity of [(Me3-
TACN)FeLn]+ (n e 2; L ) I-, CN-, SPh-) is demonstrated by
the binding of CO to thiolato and cyanido derivatives of 1.
All metallohydrogenases feature Fe(CN)n(CO) units as part
of a bimetallic active site.11 This fact led us to examine Me3-
TACN-Fe-CO-CN derivatives in order to learn more about
the electronic characteristics of this subunit and to elucidate
some facts that may ultimately be relevant to the biosynthesis
of the Fe-CN-CO subunit. The desired (Me3TACN)Fe(CN)2-
(CO) compound was prepared via two routes: (i) treatment of
[(Me3TACN)FeI(CO)2]+ with CN- and (ii) treatment of “(Me3-
TACN)FeCl2” sources with CN- under an atmosphere of CO.
The latter method presumably involves the carbonylation of an
intermediate dicyano derivative. Previous examples of LnFe-
(CN)2(CO) species are the cyclopentadienyl derivatives [(C5R5)-
Fe(CN)2(CO)]-. In selected solvents, IR spectra of [(C5R5)-
Fe(CN)2(CO)]- match those of the hydrogenase enzymes in the
[(Me3TACN)2Fe2Cl3][(Me3TACN)FeCl3] (1). A stirred slurry of
0.317 g (2.50 mmol) of anhydrous FeCl2 in 20 mL of MeCN was treated
with 0.50 mL (2.58 mmol) of Me3TACN. After 2 h, the yellow solution
was filtered to remove traces of unreacted FeCl2. The filtrate was
reduced in volume to 5 mL; addition of 50 mL of Et2O precipitated
the product. Yield: 0.664 g (89%). X-ray-quality crystals were grown
by diffusion of Et2O vapors into a MeCN solution of 1. 1H NMR (CD3-
CN): δ 121.6 (12H, CH2, cation), 103.2 (24H, Me, cation, and CH2,
anion), 53.2 (12H, CH2, cation), 46.2 (9H, Me, anion), 39.7 (6H, CH2,
1
anion). H NMR (CD3OD): δ 122.3 (12H, CH2, cation), 111.5 (6H,
CH2, anion), 103.6 (18H, Me, cation), 69.1 (12H, CH2, cation), 53.1
(9H, Me, anion), 41.3 (6H, CH2, anion). 1H NMR (D2O): δ 117.5 (6H,
CH2), 83.2 (9H, Me), 41.5 (6H, CH2). Anal. Calcd for C27H63N9Cl6Fe3
(found): C, 36.27 (36.08); H, 7.10 (7.13); N, 14.10 (13.94).
Solution Conductivity of [(Me3TACN)2Fe2Cl3][(Me3TACN)FeCl3]
(1). The solution conductivity was measured on 0.50-5.0 mM solutions
of 1 in an inert-atmosphere glovebox, employing a model 31A
conductance bridge and a model 3403 cell (cell constant k ) 1.0/cm),
both from Yellow Springs Instrument Co., Yellow Springs, OH.
In Situ Generation of [(Me3TACN)FeCl3]-. A slurry of 6.0 mg
(0.047 mmol) of FeCl2 in 1 mL of CD3CN was treated with 35 mg
(0.093 mmol) of PPh4Cl, and the mixture was stirred until all solids
dissolved. The resulting solution of (PPh4)2[FeCl4]54 was treated with
ν
CO and νCN regions.48,49 Koch21 has reported related complexes
of the type Fe(PR3)(SR)3(CO)(CN)2-. Our principal observation
on the Me3TACN-Fe-CO-CN system is that CO binding to
FeII is enhanced by the presence of CN- coligands relative to
halide coligands. This enhancement indicates the synergy arising
from the strong donor properties of the CN- ligands that
stabilize the π-interaction between FeII and CO. This view is
supported by trends in the vibrational data (see Table 1).
1
9.0 µL (0.047 mmol) of Me3TACN, and the H NMR spectrum was
recorded within minutes. 1H NMR: δ 104.7 (6H, CH2), 42.2 (9H, Me),
(50) Pafford, R. J.; Chou, J.-H.; Rauchfuss, T. B. Inorg. Chem. 1999, 38,
3779-86.
(51) Kovacic, P.; Brace, N. O. Inorg. Synth. 1960, 6, 172-3.
(52) Brunner, H.; Herrmann, W. A. Anorganisch-Chemisches Praktikum
fu¨r Fortgeschrittene: Metallorganische Chemie; Fachbereich Chemie
und Pharmazie, Universita¨t Regensburg: Regensburg, Germany, 1979.
(53) Wieghardt, K.; Chaudhuri, P.; Nuber, B.; Weiss, J. Inorg. Chem. 1982,
21, 3086-90.
(47) Wu, L. P.; Yamagiwa, Y.; Ino, I.; Sugimoto, K.; Kuroda-Sowa, T.;
Kamikawa, T.; Munakata, M. Polyhedron 1999, 18, 2047-53.
(48) Lai, C.-H.; Lee, W.-Z.; Miller, M. L.; Reibenspies, J. H.; Darensbourg,
D. J.; Darensbourg, M. Y. J. Am. Chem. Soc. 1998, 120, 10103-14.
(49) Pierik, A. J.; Roseboom, W.; Happe, R. P.; Bagley, K. A.; Albracht,
S. P. J. J. Biol. Chem. 1999, 274, 3331-7.
(54) Gill, N. S.; Taylor, F. B. Inorg. Synth. 1967, 9, 136-42.

(Triamine)iron(II) Complexes
Inorganic Chemistry, Vol. 39, No. 14, 2000 3035
39.0 (6H, CH2). Attempts to generate [(Me3TACN)FeCl3]- by the
Anal. Calcd for C36H41N6FeP‚0.5H2O (found): C, 66.16 (66.01); H,
6.48 (6.20); N, 12.86 (12.27).
addition of up to a 10-fold excess of PPh4Cl to solutions of 1 in CD3-
1
CN resulted in no reaction over the course of 24 h, as judged by H
(Me3TACN)Fe(CN)2(CO) (6). A solution of 81 mg (0.27 mmol)
of 1 in 5 mL of CO-degassed H2O was placed under a CO atmosphere.
IR measurements indicated that no reaction had occurred. While CO
was flowing through the apparatus, a solution of 27 mg (0.56 mmol)
of NaCN in 5 mL of H2O was added dropwise to give an orange
solution, after which the solvent was removed in vacuo. Under an
atmosphere of N2, the crude product was extracted into 5 mL of CH2-
Cl2 and the undissolved NaCl was removed by filtration. A yellow-
orange powder was precipitated by the addition of Et2O. The product
was filtered off, washed with Et2O, and dried under N2. Yield: 58 mg
NMR analysis.
[(Me3TACN)2Fe2Cl3][BPh4]. To a solution of 50 mg 1 (0.056 mmol)
in 5 mL of MeCN was added a stirred solution of NaBPh4 (29 mg,
0.085 mmol) in 5 mL of MeCN. After 1 h, a white precipitate (NaCl)
as well as a lightening in color was observed. The NaCl was removed
by filtration, and the colorless product was precipitated from the filtrate
by the addition of 50 mL of Et2O. Yield: 58 mg (77%).
Alternatively, the product could be synthesized in higher purity by
the addition of a solution of 80 mg (0.23 mmol) of NaBPh4 in 5 mL of
MeOH to a solution of 62 mg (0.21 mmol) of 1 in 5 mL of MeOH.
The product precipitated in analytical purity. Yield: 72 mg (78%). 1H
NMR (CD3CN): δ 121.6 (12H, CH2), 103.2 (18H, Me), 53.2 (12H,
CH2), 7.27 (8H, BPh4), 6.99 (8H, BPh4), 6.83 (4H, BPh4). Anal. Calcd
for C42H62N6BCl3Fe2 (found): C, 57.33 (57.32); H, 7.10 (6.97); N, 9.55
(9.47).
[(Me3TACN)FeCl2]2(µ-O) (2). Dry O2 was bubbled at a rate of ca.
5 bubbles/s into a solution of 50 mg (0.168 mmol) of 1 in 15 mL of
MeCN. The solution color changed quickly from pale yellow to green,
immediately followed by the precipitation of orange microcrystals. The
reaction mixture was filtered, and the solid was washed with Et2O.
Yield: 25 mg (49%). The yield was low because of the partial solubility
of the product in MeCN. Anal. Calcd for C18H42N6Cl4Fe2O (found):
C, 35.32 (35.73); H, 6.92 (6.91); N, 13.73 (13.34).
[(Me3TACN)Fe(SPh)(CO)2]BPh4 (3). A solution of NaOMe was
prepared by dissolving 6.7 mg (0.17 mmol) of a 60% dispersion (hexane
washed) of NaH in 20 mL of MeOH. To the NaOMe solution was
added 17 µL (0.17 mmol) of PhSH, and the mixture was transferred
via cannula to a solution of 50 mg (0.17 mmol) of 1 in 10 mL of MeOH.
A color change to yellow-brown occurred. The homogeneous solution
was treated with CO delivered through a needle at a rate of ∼5 bubbles/
s, and the color of the solution changed to red. After 15 min, the
carbonylation was discontinued, and a solution of 68 mg (0.20 mmol)
of NaBPh4 in 10 mL of MeOH was added. The resulting brown
precipitate was filtered off and washed with MeOH and Et2O. Yield:
87 mg (72%). 1H NMR (CD3CN): δ 3.29 (6H, 2 Me), 2.88 (3H, Me),
3.27 (2H, CH2), 3.12 (2H, CH2), 3.05 (2H, CH2), 2.95 (2H, CH2), 2.84
(2H, CH2), 2.77 (2H, CH2), 7.53 (2H, SPh), 7.16 (2H, SPh), 7.26 (9H,
SPh and BPh4), 6.98 (8H, BPh4), 6.83 (4H, BPh4). IR (CH3CN): 2040,
1988 cm-1. Anal. Calcd for C41H46N3BFeO2S‚0.5MeOH (found): C,
68.51, (68.54); H, 6.65 (6.42); N, 5.78 (5.51).
1
(69%). H NMR (CD3CN): δ 3.35 (3H, Me), 2.92 (6H, 2 Me), 3.54
(2H, CH2), 2.96 (2H, CH2), 2.87 (2H, CH2), 2.70 (2H, CH2), 2.53 (4H,
CH2). IR (CH3CN): 2097, 2092 (νCN), 1960 (νCO) cm-1. Anal. Calcd
for C12H21N5FeO‚H2O (found): C, 44.32 (44.20); H, 7.13 (7.11); N,
21.10 (21.54).
(Me3TACN)Fe(CN)2(CNMe) (7). A solution of 63 mg (98 µmol)
of PPh4[(Me3TACN)Fe(CN)3] in 15 mL of MeCN was treated with 11
µL (0.095 mmol) of MeO3SCF3. A color change from orange to yellow
was observed. Solvent was removed in vacuo, and the residue was
extracted into 5 mL of CH2Cl2. The product precipitated upon addition
of Et2O; the solid was filtered off, washed with Et2O, and dried under
N2. No attempts were made to remove PPh4(O3SCF3), which copre-
1
cipitated with the product. H NMR (CD3CN): δ 3.56 (3H, CNMe),
3.30 (3H, NMe), 3.24 (2H, CH2), 3.05 (2H, CH2), 2.96 (6H, 2 NMe),
2.65 (8H, CH2). IR (CH3CN): 2131 (νCNMe), 2068, 2037 cm-1 (νCN).
[(Me3TACN)FeI(CO)2]I. To a solution of 0.660 g (1.57 mmol) of
FeI2(CO)4 in 15 mL of CH2Cl2 was added 0.32 mL (1.64 mmol) of
Me3TACN. Vigorous CO evolution occurred as the red-violet solution
turned brown and then pink. After 30 min, the product was precipitated
from the homogeneous solution by the addition of 50 mL of Et2O.
Filtration followed by drying under nitrogen afforded a light red solid.
1
Yield: 0.755 g (90%). H NMR (CD3CN): δ 3.55 (6H, 2 Me), 2.85
(3H, Me), 3.41 (4H, CH2), 3.26 (4H, CH2), 2.82 (2H, CH2), 2.71 (2H,
CH2). IR (CH3CN): 2051, 2003 cm-1. Anal. Calcd for C11H21N3FeI2O2
(found): C, 24.61 (24.95); H, 3.94 (4.22); N, 7.83 (8.17). A stirred
solution of 82 mg (0.15 mmol) of [(Me3TACN)FeI(CO)2]I in 10 mL
of MeCN was monitored by UV-vis spectroscopy. After 2 h at 25 °C,
the solution had become colorless and the band at 512 nm had
disappeared. The IR spectrum of the solution was featureless in the
1900-2200 cm-1 region. A solution of 0.122 g (0.227 mmol) of [(Me3-
TACN)FeI(CO)2]I in 5 mL of MeOH was treated with a solution of
0.120 g (0.346 mmol) of NaBPh4 in 5 mL of MeOH. The pink
precipitate (8) that formed immediately was filtered off and washed
(Me3TACN)Fe(S2C2H4)(CO) (4). A solution of Na2(S2C2H4) was
prepared using 12 mg (0.31 mmol) of 60% NaH and 13 µL (0.15 mmol)
of HSCH2CH2SH in 10 mL of MeOH. This solution was transferred
via cannula to a solution of 46 mg (0.15 mmol) of 1 in 5 mL of MeOH.
The resulting pale red solution was purged with CO gas for 5 min,
causing a color change to red-violet. The carbonylation was discon-
tinued, and the solvent was removed in vacuo. The crude product was
extracted into 5 mL of CH2Cl2, followed by filtration to remove NaCl.
The product was precipitated from the filtrate by the addition of 30
mL of Et2O and was washed with Et2O. Yield: 38 mg (72%). 1H NMR
(CD3CN): δ 3.33 (3H, Me), 2.61 (6H, 2 Me), 3.39 (2H, CH2), 2.99
(2H, CH2), 2.55 (8H, CH2), 2.28 (2H, S2C2H4), 1.84 (2H, S2C2H4). IR
(CH3CN): 1896 cm-1. Anal. Calcd for C12H25N3FeOS2‚0.3CH2Cl2
(found): C, 39.63 (39.65); H, 6.92 (6.87); N, 11.27 (11.07).
[PPh4][(Me3TACN)Fe(CN)3] (5). A mixture of 0.200 g (0.67 mmol)
of 1 and 0.219 g (3.36 mmol) of KCN was dissolved in 10 mL of
MeOH. An immediate change occurred, giving a dark brown color,
which lightened to orange over 2 h at 25 °C. The orange solution was
treated with 0.252 g (0.67 mmol) of PPh4Cl, resulting in partial
precipitation of the product. The mixture was evaporated to dryness,
and the resulting residue was extracted into 75 mL of CH2Cl2, followed
by filtration through Celite to remove undissolved KCl and excess KCN.
The CH2Cl2 solution was concentrated to 15 mL, and the product was
precipitated as an orange solid by the addition of 100 mL of Et2O.
Yield: 0.314 g (73%). X-ray-quality crystals were grown by diffusion
of Et2O vapors into an MeCN solution of the product. 1H NMR (CD2-
Cl2): δ 2.99 (9H, 3 Me), 2.95 (6H, CH2), 2.51 (6H, CH2), 7.95 (8H,
1
with MeOH and Et2O. Yield: 0.132 g (80%). H NMR (CD3CN): δ
3.53 (6H, 2 Me), 2.83 (3H, Me), 3.39 (4H, CH2), 3.20 (4H, CH2), 2.84
(2H, CH2), 2.69 (2H, CH2), 7.27 (8H, BPh4), 6.99 (8H, BPh4), 6.84
(4H, BPh4). IR (CH3CN): 2051, 2003 cm-1
.
Crystallographic Analysis of (C9H21N3)3Fe3Cl6‚CH3CN (1). Color-
less prismatic crystals of (C9H21N3)3Fe3Cl6‚CH3CN were grown from
MeCN/Et2O solutions at 25 °C. A crystal for analysis was attached to
a thin glass fiber with Paratone-N oil (Exxon). The data crystal was
bound by the (001h), (001), (111h), (1h02), (011), (01h1), and (011h) faces.
Distances from the crystal center to these facial boundaries were 0.130,
0.130, 0.240, 0.200, 0.170, 0.140, and 0.170 mm, respectively. Data
were collected at 198 K on a Siemens CCD diffractometer. Crystal
and refinement details are given in Table 6. Systematic conditions
suggested the unambiguous space group Pbca. The structure was solved
by Direct Methods; correct positions for Cl, Fe, and N were deduced
from an E map. Subsequent cycles of isotropic least-squares refinement
followed by an unweighted difference Fourier synthesis revealed
positions for all C atoms. H atom U’s were assigned as 1.2 times the
Ueq’s of adjacent C atoms. Non-H atoms were refined with anisotropic
thermal coefficients. Successful convergence of the full-matrix least-
squares refinement of F2 was indicated by the maximum shift/error
for the last cycle.
Crystallographic Analysis of [(C9H21N3)Fe]2O‚CH2Cl2 (2). Orange
needlelike crystals of [(C9H21N3)Fe]2O‚CH2Cl2 were grown from MeCN
solutions at 22 °C. A crystal for analysis was attached to a thin glass
fiber with Paratone-N oil (Exxon). The data crystal was bound by the
PPh4), 7.78 (8H, PPh4), 7.64 (4H, PPh4). IR (KBr): 2053, 2036 cm-1
.

3036 Inorganic Chemistry, Vol. 39, No. 14, 2000
Moreland and Rauchfuss
Table 6. Crystal Data and Structural Refinement Details for 1, 2, 5, and 8
(Me3TACN)3Fe3Cl6‚
CH3CN (1)
[(Me3TACN)FeCl2]2O‚
CH2Cl2 (2)
PPh4[(Me3TACN)Fe(CN)3]‚
0.5H2O (5)
[(Me3TACN)FeI(CO)2]BPh4
(8)
empirical formula
f w
crystal system
space group
a (Å)
b (Å)
c (Å)
C29H66Cl6Fe3N10
935.17
orthorhombic
Pbca
12.1837(2)
21.4868(3)
34.1478(7)
90, 90, 90
8939.5(3)
8
C19H44Cl6Fe2N6O
694.99
orthorhombic
Pbcn
13.8095(3)
13.5150(3)
16.0125(2)
90, 90, 90
2988.50(10)
4
C36H42FeN6O0.50
653.58
orthorhombic
Imm2
20.7970(14)
22.6904(17)
7.1678(5)
90, 90, 90
3382.4(4)
4
P
C35H41BFeIN3O2
729.27
monoclinic
P21/n
10.3651(5)
21.0670(10)
15.0224(7)
90, 90.5540(10), 90
3280.2(3)
4
R, â, γ, (deg)
V (Å3)
Z
F
calc (Mg m-3
)
1.390
1.352
198(2)
1.545
1.532
198(2)
1.283
0.529
173(2)
1.477
1.436
193(2)
µ (mm-1
T (K)
)
λ, Å
0.710 73
1.90-28.27
3920
0.717 03
2.11-28.27
1440
0.717 03
1.79-25.07
1380
0.717 03
1.66-28.26
1488
θ range for collcn (deg)
F(000)
no. of reflns collected
no. of indep reflns (Rint)a
R index (I > 2σ)
54 211
17 895
3663 (0.1299)
0.0666
0.1257, 0.1975
1.90 × 0.04 × 0.04
3663/0/156
1.141
9076
3143 (0.0532)
0.0416
21 473
21 473 (0.0814)
0.1163
0.2300, 0.3506
0.24 × 0.30 × 0.50
21 473/0/389
2.043
10 835 (0.0433)a
0.0496
R indices (all data): R1, wR2
crystal size (mm)
0.0822, 0.1412
0.26 × 0.34 × 0.44
10 835/1/444
0.948
0.0743, 0.0833
0.05 × 0.05 × 0.64
3143/172/310
1.115
data/restraints/params
goodness of fit on F2
largest peak and hole (e/Å3)
1.094 and -0.618
0.780 and -0.551
0.284 and -0.300
4.070 and -2.001
a Rint ) ∑|Fo - Fo (mean)|/∑Fo .
2
2
2
(1h10), (11h0), (110), (1h1h0), (001), and (001h) faces. Distances from
the crystal center to these facial boundaries were 0.020, 0.020, 0.020,
0.020, 0.095, and 0.095 mm, respectively. Data were collected at
198 K on a Siemens CCD diffractometer. Crystal and refinement de-
tails are given in Table 6. Systematic conditions suggested the
unambiguous space group Pbcn. The structure was solved by Direct
Methods; correct positions for Cl, Fe, N, O, and C were deduced from
an E map. H atom U’s were assigned as 1.2 times the Ueq’s of adjacent
C atoms. Non-H atoms were refined with anisotropic thermal coef-
ficients. Successful convergence of the full-matrix least-squares re-
finement of F2 was indicated by the maximum shift/error for the last
cycle.
Crystallographic Analysis of Ph4P[(C9H21N3)Fe(CN)3]‚0.5H2O (5).
Yellow needlelike crystals of Ph4P[(C9H21N3)Fe(CN)3]‚0.5H2O were
grown from MeCN/Et2O solutions at 25 °C. A crystal for analysis was
attached to a thin glass fiber with Paratone-N oil (Exxon). The data
crystal was bound by the (011h), (01h1), (011), (01h1h), (100), and (1h00)
faces. Distances from the crystal center to these facial boundaries were
0.025, 0.025, 0.025, 0.025, 0.320, and 0.320 mm, respectively. Data
were collected at 173 K on a Siemens CCD diffractometer. Crystal
and refinement details are given in Table 6. Systematic conditions
suggested the space group Imm2. The structure was solved by Direct
Methods; correct positions for Fe, P, and N were deduced from an E
map. Subsequent cycles of isotropic least-squares refinement followed
by an unweighted difference Fourier synthesis revealed positions for
all C atoms. H atom U’s were assigned as 1.2 times the Ueq’s of adjacent
C atoms. Non-H atoms were refined with anisotropic thermal coef-
ficients. Successful convergence of the full-matrix least-squares re-
finement of F2 was indicated by the maximum shift/error for the last
cycle.
Crystallographic Analysis of [(C9H21N3)FeI(CO)2]BPh4 (8). Red
prismatic crystals of [(C9H21N3)FeI(CO)2]BPh4 were grown from
MeCN/Et2O solutions at -30 °C in the dark. A crystal for analysis
was attached to a thin glass fiber with Paratone-N oil (Exxon). The
data crystal was bound by the (01h0), (010), (111), (1h1h0), (0 01h), and
(111h) faces. Distances from the crystal center to these facial boundaries
were 0.120, 0.120, 0.150, 0.200, 0.200, and 0.170 mm, respectively.
Data were collected at 193 K on a Siemens CCD diffractometer. Crystal
and refinement details are given in Table 6. Systematic conditions
suggested the unambiguous space group P21/n. The best available
crystals was severely twinned. The structure was solved by Direct
Methods; correct positions for I, Fe, and B were deduced from a vector
map. Subsequent cycles of isotropic least-squares refinement followed
by an unweighted difference Fourier synthesis revealed positions for
all N, O, and C atoms. H atom U’s were assigned as 1.2 times the
Ueq’s of adjacent C atoms. Non-H atoms were refined with anisotropic
thermal coefficients. Successful convergence of the full-matrix least-
squares refinement of F2 was indicated by the maximum shift/error
for the last cycle. The highest residual electron density in the final
difference Fourier map was in the vicinity of I(1). Efforts to model the
twinning condition were unsuccessful.
Acknowledgment. This research was funded by the National
Science Foundation and the U.S. Department of Energy.
Supporting Information Available: Listings of X-ray experimental
details, atomic coordinates, bond distances and angles, and thermal
parameters for compounds 1, 2, 5, and 8. This material is available
free of charge via the Internet at http://pubs.acs.org.
IC9912629