Preparation and Reactivity of Mixed-Ligand Iron(II) Hydride Complexes with Phosphites and Polypyridyls

Article abstract of DOI:10.1021/ic0348190

Hydride complexes [FeH(N-N)P₃]BPh₄ (1, 2) [N-N = 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen); P = P(OEt) ₃, PPh(OEt)₂, and PPh₂OEt] were prepared by allowing FeCl₂(N-N) to react wi

Full text of DOI:10.1021/ic0348190

Inorg. Chem. 2004, 43, 1328−1335
Preparation and Reactivity of Mixed-Ligand Iron(II) Hydride Complexes
with Phosphites and Polypyridyls
Gabriele Albertin,* Stefano Antoniutti, and Marco Bortoluzzi
Dipartimento di Chimica, UniVersita` Ca’ Foscari di Venezia,
Dorsoduro, 2137, 30123 Venezia, Italy
Received July 14, 2003
Hydride complexes [FeH(N-N)P ]BPh4 (1, 2) [N-N ) 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen); P )
3
P(OEt)3, PPh(OEt)2, and PPh2OEt] were prepared by allowing FeCl2(N-N) to react with phosphite in the presence
of NaBH . The hydrides [FeH(bpy)2P]BPh4 (3) [P ) P(OEt)3 and PPh(OEt)2] were prepared by reacting the tris-
4
(2,2′-bipyridine) [Fe(bpy)3]Cl2‚5H O complex with the appropriate phosphite in the presence of NaBH . The protonation
2
4
reaction of 1 and 2 with acid was studied and led to thermally unstable (above −20 °C) dihydrogen [Fe(η2-H )-
2
(N-N)P ]2+ (4, 5) derivatives. The presence of the H ligand is indicated by short T1min values (3.1−3.6 ms) and by
3
2
JHD measurements (31.2−32.5 Hz) of the partially deuterated derivatives. Carbonyl [Fe(CO)(bpy){P(OEt)3}3](BPh4)2
(6) and nitrile [Fe(CH CN)(N-N)P ](BPh4)2 (7, 8) [N-N ) bpy, phen; P ) P(OEt)3 and PPh(OEt)2] complexes were
3
3
prepared by substituting the H ligand in the η2-H 4, 5 derivatives. Aryldiazene complexes [Fe(ArNdNH)(N-N)-
2
2
P ](BPh4)2 (9, 10, 11) (Ar ) C H , 4-CH C H ) were also obtained by allowing hydride [FeH(N-N)P ]BPh4 derivatives
3
6
5
3
6
4
3
to react with aryldiazonium cations in CH Cl2 at low temperature.
2
Introduction
knowledge, no iron(II) hydride complexes containing poly-
pyridyl or mixed-ligand polypyridyl-phosphine as supporting
ligands have ever been reported.
The chemistry of iron(II) classical and nonclassical hydride
complexes has developed considerably in the last 30 years,
highlighting the syntheses of a number of complexes with
interesting properties.1,2 The ancillary ligands used in this
chemistry involve mainly π-acceptors such as tertiary phos-
phine, carbon monoxide, and cyclopentadienyl ligands, which
are associated with classical neutral FeH2P4, FeH2(CO)2P2,
FeHXP4 (X ) Cl, CN), FeH(CO)2(η5-C5H5), and FeHP2(η5-
C5H5) [P ) mono- to tetradentate phosphorus ligands] as
well as classical or nonclassical cationic [FeH3P4]+, [FeH-
(η2-H2)P4]+, [FeH(CO)P4]+, [FeHP5]+, [Fe(η2-H2)(CO)P4]2+,
or neutral FeH4P3 hydride derivatives.1-5
(3) (a) Tebbe, F. N.; Meakin, P.; Jesson, J. P.; Muetterties, E. L. J. Am.
Chem. Soc. 1970, 92, 1068-1070. (b) Morris, R. H.; Sawyer, J. F.;
Shiralian, M., Zubkowski, J. D. J. Am. Chem. Soc. 1985, 107, 5581-
5582. (c) Baker, M. V.; Field, L. D.; Young, D. J. J. Chem. Soc.,
Chem. Commun. 1988, 546-548. (d) Pankowski, M.; Samuel, E.;
Bigorgne, M. J. Organomet. Chem. 1975, 97, 105-108. (e) Cappellani,
E. P.; Drowin, S. D.; Jia, G.; Maltby, P. A.; Morris, R. H.; Schweitzer,
C. T. J. Am. Chem. Soc. 1994, 116, 3375-3388.
(4) (a) Bancroft, G. M.; Mays, M. J.; Prater, E. B.; Stefanini, F. P. J.
Chem. Soc. A 1970, 2146-2149. (b) Dapporto, P.; Midollini, S.;
Sacconi, L. Inorg. Chem. 1975, 14, 1643-1650. (c) Sanders, J. R. J.
Chem. Soc., Dalton Trans. 1972, 1333-1336. (d) Brunet, J. J.; Kindela,
F. B.; Labrowe, D.; Neibecker, D. Inorg. Chem. 1990, 29, 4152-
4153. (e) Albertin, G.; Antoniutti, S.; Lanfranchi, M.; Pelizzi, G.;
Bordignon, E. Inorg. Chem. 1986, 25, 950-957. (f) Bampos, N.; Field,
L. D. Inorg. Chem. 1990, 29, 587-588. (g) Bianchini, C.; Peruzzini,
M.; Polo, A.; Vacca, A.; Zanobini, F. Gazz. Chim. Ital. 1991, 121,
543. (h) Gusev, D. G.; Hu¨bener, R.; Burger, P.; Orama, O.; Berke, H.
J. Am. Chem. Soc. 1997, 119, 3716-3731. (i) Field, L. D.; Messerle,
B. A.; Smernik, R. J.; Hambley, T. W.; Turner, P. Inorg. Chem. 1997,
36, 2884-2892. (j) Forde, C. E.; Landau, S. E.; Morris, R. H. J. Chem.
Soc., Dalton Trans. 1997, 1663-1664. (k) Bianchini, C.; Masi, D.;
Peruzzini, M.; Casarin, M.; Maccato, C.; Rizzi, G. A. Inorg. Chem.
1997, 36, 1061-1069.
Less attention, however, has been devoted to the use of
nitrogen-donor ancillary ligands, and, to the best of our
* Author to whom correspondence should be addressed. E-mail: albertin@
unive.it.
(1) (a) Muetterties, E. L. Transition Metal Hydrides; Dekker, M., Ed.;
New York, 1971. (b) Dedieu, A. Transition Metal Hydrides; Wiley-
VCH: New York, 1992. (c) Peruzzini, M.; Poli, R. Recent AdVances
in Hydride Chemistry; Elsevier: Amsterdam, 2001. (d) Sabo-Etienne,
S.; Chaudret, B. Chem. ReV. 1998, 98, 2077-2091.
(2) (a) Kubas, G. J. Acc. Chem. Res. 1988, 21, 120-128. (b) Jessop, P.
G.; Morris, R. H. Coord. Chem. ReV. 1992, 121, 155-284. (c)
Heinekey, D. M.; Oldham, W. J., Jr. Chem. ReV. 1993, 93, 913-926.
(d) Crabtree, R. H. Angew. Chem., Int. Ed. Engl. 1993, 32, 789-805.
(e) Esteruelas, M. A.; Oro, L. A. Chem. ReV. 1998, 98, 577-588.
(5) (a) Aresta, M.; Giannoccaro, P.; Rossi, M.; Sacco, A. Inorg. Chim.
Acta 1971, 5, 115-118. (b) Van Der Sluys, L. S.; Eckert, J., Eisenstein,
O.; Hall, J. H.; Huffman, J. C.; Jackson, S. A.; Koetzle, T. F.; Kubas,
G. J.; Vergamini, P. J.; Caulton, K. G. J. Am. Chem. Soc. 1990, 112,
4831-4841.
1328 Inorganic Chemistry, Vol. 43, No. 4, 2004
10.1021/ic0348190 CCC: $27.50 © 2004 American Chemical Society
Published on Web 01/30/2004

Mixed-Ligand Iron(II) Hydride Complexes
on a Nicolet Magna 750 FT-IR spectrophotometer. NMR spectra
(1H, 13C, 31P, 15N) were obtained on a Bruker AC200 or an
AVANCE 300 spectrometer at temperatures varying between +30
and -90 °C, unless otherwise noted. 1H and 13C spectra are referred
to internal tetramethylsilane. 31P{1H} chemical shifts are reported
with respect to 85% H3PO4, while 15N shifts are referred to external
CH315NO2, in both cases with downfield shifts considered positive.
The COSY, HMQC, and HMBC NMR experiments were performed
using their standard programs. The SwaN-MR software package11
was used in treating the NMR data. Proton T1 values were measured
in CD2Cl2 at 200 MHz by the inversion-recovery method between
+30 and -90 °C with a standard 180°-τ-90° pulse sequence.
The conductivity of 10-3 mol dm-3 solutions of the complexes in
CH3NO2 at 25 °C was measured with a Radiometer CDM 83
instrument. Elemental analyses were determined in the Microana-
lytical Laboratory of the Dipartimento di Scienze Farmaceutiche
of the University of Padova (Italy).
Synthesis of Complexes. Both the red12,13a and the orange13b
isomers of FeCl2(bpy) were prepared following the method previ-
ously reported. Also the FeCl2(phen) was obtained using the same
method.12,13 The tris(2,2′-bipyridine) [Fe(bpy)3]Cl2‚5H2O complex
was prepared by a procedure previously described.14 The spectro-
scopic data (IR and NMR) of the new complexes are reported in
Tables 1 and 2.
Changes in the nature of the ancillary ligands may greatly
change both the reactivity of the M-H bond and the
properties of the M-(η2-H2) group. In dihydrogen com-
plexes, for example, the following are important: stability
regarding the loss of H2, the bonding mode which may make
η2-H2 stretched or unstretched, and the acidity of the η2-H2
ligand. These properties have been raised in recently
reported6 dicationic dihydrogen such as [Fe(η2-H2)(CO)-
(dppe)2]2+, [Os(η2-H2)(dppe)2(NCCH3)]2+ (dppe ) 1,2-bis-
(diphenylphosphino)ethane), [Os(η2-H2)(PiPr3)2(NCCH3)3]2+,
[M(η2-H2)(dppp)(CO)]2+ [M ) Ru, Os; dppp ) 1,3-bis-
(diphenylphosphino)propane], and [Os(η2-H2)(PR3)2(CO)-
i
(bpy)]2+ (R ) Ph, Pr).
For several years we have developed the chemistry of
classical and nonclassical metal hydride complexes of the
iron7 and manganese8 triads of the [MH(η2-H2)P4]+, [MX-
(η2-H2)P4]+ (M ) Fe, Ru, Os; X- ) Cl-, Br-, I-),
MH(CO)nP5-n, and [M(η2-H2)(CO)nP5-n]+ (M ) Mn, Re; n
) 1-4) types using phosphites as ancillary ligands. We have
now extended these studies with the aim of introducing
nitrogen-donor ligands such as 2,2′-bipyridine and 1,10-
phenanthroline in the iron hydride chemistry. The results of
these studies, which allow the synthesis and reactivity of
the unprecedented mixed-ligand iron(II) hydrides and dica-
tionic η2-H2 derivatives with phosphites and polypyridyls,
are reported here.
[FeH(bpy)P3]BPh4 (1) [P ) P(OEt)3 (1a), PPh(OEt)2 (1b),
PPh2OEt (1c)]. In a 50-mL three-necked round-bottomed flask were
placed 0.500 g (1.8 mmol) of FeCl2(bpy) (orange isomer), 15 mL
of ethanol, and an excess of the appropriate phosphite (8 mmol).
An excess of NaBH4 (10 mmol, 0.38 g) in 20 mL of ethanol was
slowly added, and the reaction mixture was stirred at room
temperature for 150 min. The resulting red-brown solution was
filtered through silica gel (TLC standard grade) and the solvent
removed under reduced pressure to give a brown oil. The addition
of an excess of NaBPh4 (0.68 g, 2 mmol) in 5 mL of ethanol caused
the separation of a red-brown solid, which was filtered and
crystallized from CH2Cl2 and ethanol; g55%. Anal. Calcd for
C52H74BFeN2O9P3 (1a): C, 60.59; H, 7.24; N, 2.72. Found: C,
60.40; H, 7.35; N, 2.79. ΛM ) 53.6 Ω-1 mol-1 cm2. Calcd for
C64H74BFeN2O6P3 (1b): C, 68.22; H, 6.62; N, 2.49. Found: C,
68.01; H, 6.57; N, 2.43. ΛM ) 55.8 Ω-1 mol-1 cm2. Calcd for
C76H74BFeN2O3P3 (1c): C, 74.64; H, 6.10; N, 2.29. Found: C,
74.86; H, 6.19; N, 2.25. ΛM ) 49.8 Ω-1 mol-1 cm2.
[FeH(bpy)P3]CF3SO3 (1-CF3SO3) [P ) P(OEt)3 (1a-CF3SO3),
PPh(OEt)2 (1b-CF3SO3), PPh2OEt (1c-CF3SO3)]. In a 50-mL
three-necked round-bottomed flask were placed 0.500 g (1.8 mmol)
of FeCl2(bpy) (orange isomer), 15 mL of ethanol, and an excess of
the appropriate phosphite (8 mmol). An excess of NaBH4 (10 mmol,
0.38 g) in 20 mL of ethanol was slowly added, and the reaction
mixture was stirred at room temperature for 150 min. The solvent
was removed under reduced pressure to give an oil, from which
the hydride [FeH(bpy)P3]Cl was extracted with three 10-mL
portions of CH2Cl2. The extracts were evaporated to dryness to
give an oil, which was treated with an excess of LiCF3SO3 (7 mmol,
1.1 g) in 4 mL of ethanol. The resulting solution was stirred for 1
h and then the solvent removed under reduced pressure to give a
red-brown oil, from which the complex was extracted with three
5-mL portions of diethyl ether. By cooling to -25 °C of the
Experimental Section
All synthetic work was carried out under an appropriate
atmosphere (Ar, H2) using standard Schlenk techniques or a
Vacuum Atmospheres drybox. Once isolated, the complexes were
found to be relatively stable in air, but were stored under an inert
atmosphere at -25 °C. All solvents were dried over appropriate
drying agents, degassed on a vacuum line, and distilled into vacuum-
tight storage flasks. Triethyl phosphite was an Aldrich product,
purified by distillation under nitrogen, while the phosphines PPh-
(OEt)2 and PPh2OEt were prepared by the method of Rabinowitz
and Pellon.9 Diazonium salts were obtained in the usual way.10
Labeled diazonium tetrafluoroborates (C6H5Nt15N)BF4 were pre-
pared from Na15NO2 (99% enriched, CIL) and aniline. 2,2′-
Bipyridine (bpy) and 1,10-phenanthroline (phen), HBF4‚Et2O (54%
solution in Et2O), CF3SO3H, and CF3SO3D were Aldrich products,
used without any further purification. Infrared spectra were recorded
(6) (a) Schlaf, M.; Lough, A. J.; Maltby, P. A.; Morris, R. H. Organo-
metallics 1996, 15, 2270-2278. (b) Rocchini, E.; Mezzetti, A.;
Ru¨egger, H.; Burckhardt, U.; Gramlich, V.; Del Zotto, A.; Martinuzzi,
P.; Rigo, P. Inorg. Chem. 1997, 36, 711-720. (c) Luther, T. A.;
Heinekey, D. M. Inorg. Chem. 1998, 37, 127-132. (d) Landau, S.
E.; Morris R. H.; Lough, A. J. Inorg. Chem. 1999, 38, 6060-6068.
(e) Smith, K. T.; Tilset, M.; Kuhlman, R.; Caulton, K. G. J. Am. Chem.
Soc. 1995, 117, 9473-9480.
(7) (a) Albertin, G.; Antoniutti, S.; Bordignon, E. J. Am. Chem. Soc. 1989,
111, 2072-2077. (b) Amendola, P.; Antoniutti, S.; Albertin, G.;
Bordignon, E. Inorg. Chem. 1990, 29, 318-324. (c) Albertin, G.;
Antoniutti, S.; Baldan, D.; Bordignon, E. Inorg. Chem. 1995, 34,
6205-6210. (d) Albertin, G.; Antoniutti, S.; Bordignon, E.; Pegoraro,
M. J. Chem. Soc., Dalton Trans. 2000, 3575-3584.
(8) (a) Albertin, G.; Antoniutti, S.; Garcia-Fonta´n, S.; Carballo, R.; Padoan,
F. J. Chem. Soc., Dalton Trans. 1998, 2071-2081. (b) Albertin, G.;
Antoniutti, S.; Bettiol, M.; Bordignon, E.; Busatto, F. Organometallics
1997, 16, 4959-4969.
(9) Rabinowitz, R.; Pellon, J. J. Org. Chem. 1961, 26, 4623-4626.
(10) Vogel, A. I. Practical Organic Chemistry, 3rd ed.; Longmans, Green
and Co.: New York, 1956.
(11) Balacco, G. J. Chem. Inf. Comput. Sci. 1994, 34, 1235-1241.
(12) Broomhead, J. A.; Dwyer, F. P. Aust. J. Chem. 1961, 14, 250-252.
(13) (a) Reiff, W. M.; Dockum, B.; Weber, M. A.; Frankel, R. B. Inorg.
Chem. 1975, 14, 800-806. (b) Charron, F. F., Jr.; Reiff, W. M. Inorg.
Chem. 1986, 25, 2786-2790.
(14) Sato, H.; Tominaga, T. Bull. Chem. Soc. Jpn. 1976, 49, 697-700.
Inorganic Chemistry, Vol. 43, No. 4, 2004 1329

Albertin et al.
Table 1. Selected IR and NMR Data for Iron Complexes
31P{1H}
NMRb,d
(ppm; J, Hz)
31P{1H}
NMRb,d
(ppm; J, Hz)
IRa
1H NMRb,c
(ppm; J, Hz)
spin
syst
IRa
1H NMRb,c
assgnt (ppm; J, Hz)
spin
syst
(cm-1
)
assgnt
assgnt
(cm-1
)
assgnt
[FeH(bpy){P(OEt)3}3]BPh4 (1a)
[Fe(η2-H2)(bpy){PPh2OEt}3]2+ (4c)
f
e
1857 w νFeH
4.04 me
3.67 m
3.46 m
1.28 t
CH2
AB2
δ
A 179.4
B 161.3
3.5 bre
CH2
CH3
AB2
δ
δ
A 156.8
B 154.1
δ
0.80 br
0.50 br
-13.3 br
JAB ) 129.7
JAB ) 57.1
CH3
η2-H2
0.94 t
[Fe(η2-H2)(phen){P(OEt)3}3]2+ (5a)
e
AB2X
H hydride
4.15 qnte
3.82 m
1.30 t
CH2
AB2
δ
δ
A 152.9
B 140.5
δX -18.34
JAX ) 70
JBX ) 56
CH3
JAB ) 128.0
0.84 t
[FeH(bpy){PPh(OEt)2}3]BPh4 (1b)
-15.7 br
η2-H2
1886 w νFeH
3.87 m
CH2
AB2
δ
δ
A 204.1
B 187.2
[Fe(η2-H2)(phen){PPh(OEt)2}3]2+ (5b)
e
3.64 m
3.44 m
3.73 me
1.35 t
CH2
CH3
AB2
δ
δ
A 181.3
B 172.8
JAB ) 94.0
1.32 t
CH3
1.24 t
JAB ) 99.0
1.05 t
AB2X
δX -18.01
JAX ) JBX ) 62
[FeH(bpy){PPh2OEt}3]BPh4 (1c)
3.29 m
3.02 m
0.70 t
0.75 t
H hydride
-16.2 br
η2-H2
[Fe(CO)(bpy){P(OEt)3}3](BPh4)2g (6a)
2033 s νCO
4.20 m
3.59 m
1.41 t
CH2
A2B
δ
δ
A 147.0
B 129.2
1863 w νFeH
CH2
AB2
δ
A 177.0
B 167.0
CH3
JAB ) 148.0
δ
1.02 t
CH3
JAB ) 74.0
[Fe(CH3CN)(bpy){P(OEt)3}3](BPh4)2 (7a)
0.47 t
AB2X
δX -16.87
JAX ) JBX ) 56
4.25 qnt
3.72 m
2.07 s
1.42 t
CH2
AB2
δ
δ
A 153.4
B 137.0
H hydride
CH3CN
CH3 phos
JAB ) 133.6
[FeH(phen){P(OEt)3}3]BPh4 (2a)
1.01 t
1890 w νFeH
4.21 qnt
3.69 m
3.45 m
1.42 t
0.90 t
CH2
AB2
δ
A 180.3
B 160.0
[Fe(CH3CN)(bpy){PPh(OEt)2}3](BPh4)2 (7b)
δ
4.30 m
3.84 m
1.34 s
1.49 t
1.23 t
0.98 t
CH2
AB2
δ
δ
A 191.5
B 170.1
JAB ) 100.0
JAB ) 130.0
CH3
CH3CN
CH3 phos
AB2X
H hydride
δX -17.95
JAX ) 70
JBX ) 56
[FeH(phen){PPh(OEt)2}3]BPh4 (2b)
3.98 m
3.50 m
1.38 t
0.97 t
[Fe(CH3CN)(phen){PPh(OEt)2}3](BPh4)2h (8b)
4.30 m
3.70 m
1.42 s
1.56 t
1.17 t
0.89 t
CH2
AB2
δ
δ
A 190.8
B 170.2
1887 w νFeH
CH2
AB2
δ
δ
A 205.9
B 187.9
CH3CN
CH3phos
JAB ) 97.2
CH3
JAB ) 95.0
AB2X
H hydride
[Fe(C6H5NdNH)(bpy){P(OEt)3}3](BPh4)2 (9a)
δX -17.74
13.88 s, br
4.19 m
3.69 m
1.35 t
NH
CH2
AB2
δ
δ
A 148.1
B 134.2
JAB ) 136.9
JAX ) JBX ) 62
[FeH(bpy)2{P(OEt)3}]BPh4 (3a)
3.65 qnt
1.00 t
-13.13 d
JPH ) 116
[FeH(bpy)2{PPh(OEt)2}]BPh4 (3b)
3.85 m
1.18 t
1782 w νFeH
CH2
CH3
H hydride
168.6 s
193.8 s
CH3
1.01 t
[Fe(C6H5Nd15NH)(bpy){P(OEt)3}3](BPh4)2i (9a-15N)
13.87 d
NH
AB2Y
δ
δ
A 147.9
B 134.2
1
J
NH ) 68
(Y ) 15N)
15
1798 w νFeH
CH2
CH3
4.18 m
3.69 m
1.32 t
0.99 t
CH2
CH3
JAB ) 136.8
JAY ) 8.6
JBY ) 8.4
1.04 t
-12.86 d
H hydride
JPH ) 102
[Fe(4-CH3C6H4NdNH)(bpy){P(OEt)3}3](BPh4)2 (10a)
[Fe(η2-H2)(bpy){P(OEt)3}3]2+ (4a)
13.68 s, br
4.20 m
3.70 m
2.49 s
1.35 t
1.01 t
NH
CH2
AB2
δ
δ
A 148.6
B 134.6
f
3.96 me
3.44 m
1.33 br
1.00 br
-15.7 br
CH2
AB2
δA 151.8
δB 140.4
JAB ) 136.6
CH3
JAB ) 127.5
CH3 p-tolyl
CH3 phos
η2-H2
[Fe(η2-H2)(bpy){PPh(OEt)2}3]2+ (4b)
[Fe(4-CH3C6H4NdNH)(bpy){PPh(OEt)2}3](BPh4)2 (10b)
f
3.88 me
3.66 m
3.41 m
1.29 t
CH2
AB2
δA 179.8
δB 172.3
13.37 s, br
4.20 m
3.78 m
2.50 s
NH
CH2
AB2
δ
δ
A 181.6
B 168.7
JAB ) 99.7
JAB ) 104.6
CH3
CH3 p-tolyl
1.17 t
1.51 t
CH3 phos
1.14 t
-16.3 br
1.14 t
η2-H2
1330 Inorganic Chemistry, Vol. 43, No. 4, 2004

Mixed-Ligand Iron(II) Hydride Complexes
Table 1. Continued
31P{1H}
NMRb,d
(ppm; J, Hz)
31P{1H}
NMRb,d
(ppm; J, Hz)
IRa
1H NMRb,c
(ppm; J, Hz)
spin
syst
IRa
1H NMRb,c
(ppm; J, Hz)
spin
syst
(cm-1
)
assgnt
assgnt
(cm-1
)
assgnt
assgnt
[Fe(4-CH3C6H4NdNH)(phen){P(OEt)3}3](BPh4)2 (11a)
[Fe(4-CH3C6H4NdNH)(phen){PPh(OEt)2}3](BPh4)2 (11b)
13.85 s, br
4.26 m
3.53 m
2.51 s
NH
CH2
AB2
δ
A 130.2
B 115.3
13.77 s, br
4.32 m
3.58 m
2.55 s
NH
CH2
AB2
δ
A 181.3
B 168.9
δ
δ
JAB ) 136.5
JAB ) 105.0
CH3 p-tolyl
CH3 p-tolyl
1.41 t
CH3 phos
1.61 t
CH3 phos
0.82 t
1.19 t
a In KBr pellets. b In CD2Cl2 at 25 °C unless otherwise noted. c Phenyl proton resonances omitted; for the OC2H5 group of the phosphine JHH ) 7 Hz.
d Positive shifts downfield from 85% H3PO4. e At -70 °C. f At -30 °C. g 13C NMR (CD2Cl2, 25 °C): 207.8 (dt, CO, JCP ) JCP ) 55 Hz), 165-122 (m,
cis
Ph + bpy), 65.9 (m, CH2), 16.2 (m, CH3). h 13C NMR (CD2Cl2, 25 °C): 165-122 (m, Ph + phen), 137.8 (s, CH3CN), 67.2 (m,trCansH2), 17.1 (m, CH3 phos),
3.65 (s, CH3CN). i 15N NMR (CD2Cl2, 25 °C; δ from CH315NO2): AB2Y spin system. δY 17.6, JAY ) 8.6, JBY ) 8.4 Hz.
Table 2. T1min (200 MHz) and JHD NMR Data for Some Dihydrogen and Hydride Complexes and Calculated H-H Distances
rH-H (Å)
compound
T (K)
δ
T1min (ms)
JHD (Hz)
4a
4b
5a
5b
1a
[Fe(η2-H2)(bpy){P(OEt)3}3]2+
[Fe(η2-H2)(bpy){PPh(OEt)2}3]2+
[Fe(η2-H2)(phen){P(OEt)3}3]2+
[Fe(η2-H2)(phen){PPh(OEt)2}3]2+
FeH(bpy){P(OEt)3}3]+
210
218
213
225
193
-15.7 br
-16.3 br
-15.7 br
-16.2 br
-18.34 dt
3.1
3.6
3.3
3.1
196
31.5
32.5
31.2
32.0
0.92a
0.94
0.93
0.92
0.73b
0.75
0.74
0.73
0.91c
0.89
0.92
0.90
a,b The H-H distances were calculated18,20 from the T1min values for fast rotationb or static regimesa of the H2 ligand. c H-H distances calculated from
the JHD values for HD complexes using the equation6c,8 rH-H ) 1.44-0.0168 (JHD).
exctracts, red-brown microcrystals of the product separated out,
which were filtered and dried under vacuum; yield g15%. Anal.
Calcd for C29H54F3FeN2O12P3S (1a-CF3SO3): C, 40.48; H, 6.32;
N, 3.26. Found: C, 40.63; H, 6.25; N, 3.20. ΛM ) 76.8 Ω-1 mol-1
cm2. IR (KBr): 1890 w [ν(FeH)] cm-1. 1H NMR [CD2Cl2, 25 °C;
δ]: 9.58-7.28 (m, 8 H, bpy), 4.00 qnt, 3.65 m, 3.47 m (18 H,
CH2), 1.23, 0.90 (t, 27 H, CH3), spin system AB2X (X ) H), δX
-18.41 (1 H, Fe-H, JAX ) 70, JBX ) 58 Hz). 31P{1H} NMR [CD2-
Cl2, 25 °C; δ]: spin system AB2, δA 178.9, δB 160.1, JAB ) 127.9
Hz. 13C{1H} NMR [CD2Cl2, 25 °C; δ]: 159-117 (m, bpy), 120.5
(q, CF3, 1JCF ) 319 Hz), 61.9 d, 60.7 t (CH2), 16.2 d, 16.0 t (CH3).
Calcd for C41H54F3FeN2O9P3S (1b-CF3SO3): C, 51.47; H, 5.69;
N, 2.93. Found: C, 51.28; H, 5.55; N, 3.02. ΛM ) 80.4 Ω-1 mol-1
cm2. IR (KBr): 1886 w [ν(FeH)] cm-1. 1H NMR [CD2Cl2, 25 °C;
δ]: 9.21-7.12 (m, 15 H, Ph and 8 H, bpy), 3.86, 3.61, 3.38 (m,
12 H, CH2), 1.30, 1.05, 1.03 (t, 18 H, CH3), spin system AB2X (X
) H), δX -18.04 (1 H, Fe-H, JAX ) JBX ) 62 Hz). 31P{1H} NMR
C31H54F3FeN2O12P3S: C, 42.09; H, 6.15; N, 3.17. Found: C, 42.27;
H, 6.25; N, 3.10. ΛM ) 82.5 Ω-1 mol-1 cm2. IR (KBr): 1890 w
[ν(FeH)] cm-1. 1H NMR [CD2Cl2, 25 °C; δ]: 9.11-7.05 (m, 8 H,
phen), 4.25 qnt, 3.55 m (18 H, CH2), 1.47, 0.90 (t, 27 H, CH3),
spin system AB2X (X ) H), δX -17.91 (1 H, Fe-H, JAX ) 70,
JBX ) 56 Hz). 31P{1H} NMR [CD2Cl2, 25 °C; δ]: spin system
AB2, δA 180.5, δB 159.8, JAB ) 130.5 Hz.
[FeH(bpy)2P]BPh4 (3) [P ) P(OEt)3 (3a), PPh(OEt)2 (3b)].
To a solution of [Fe(bpy)3]Cl2‚5H2O (1 g, 1.46 mmol) in 15 mL of
ethanol were added first an excess of the appropriate phosphite (2
mmol) and then an excess of NaBH4 (10 mmol, 0.38 g) in 10 mL
of ethanol. The reaction mixture was stirred at room temperature
for 2 h, and then the resulting red-brown solution was filtered
through silica gel (TLC standard grade). The solvent was removed
under reduced pressure to give an oil, which was triturated at 0 °C
with ethanol (5 mL) containing an excess of NaBPh4 (2.5 mmol,
0.86 g). A red-brown solid slowly separated out, which was filtered
and crystallized from CH2Cl2 and ethanol; yield g50%. Anal. Calcd
for C50H52BFeN4O3P (3a): C, 70.27; H, 6.13; N, 6.56. Found: C,
70.02; H, 6.10; N, 6.49. ΛM ) 54.3 Ω-1 mol-1 cm2. Calcd for
C54H52BFeN4O2P (3b): C, 73.15; H, 5.91; N, 6.32. Found: C,
72.96; H, 6.00; N, 6.25. ΛM ) 48.6 Ω-1 mol-1 cm2.
[CD2Cl2, 25 °C; δ]: spin system AB2, δA 204.0, δB 187.2, JAB
)
93.5 Hz. Calcd for C53H54F3FeN2O6P3S (1c-CF3SO3): C, 60.46;
H, 5.17; N, 2.66. Found: C, 60.28; H, 5.29; N, 2.55. ΛM ) 78.8
Ω-1 mol-1 cm2. IR (KBr): 1865 w [ν(FeH)] cm-1. 1H NMR [CD2-
Cl2, 25 °C; δ]: 9.32-7.05 (m, 30 H, Ph and 8 H, bpy), 3.32 m,
2.99 qnt (6 H, CH2), 0.72, 0.47 (t, 9 H, CH3), spin system AB2X
(X ) H), δX -16.86 (1 H, Fe-H, JAX ) JBX ) 56.2 Hz). 31P{1H}
NMR [CD2Cl2, 25 °C; δ]: spin system AB2, δA 177.5, δB 167.0,
JAB ) 74.0 Hz.
[FeH(phen)P3]BPh4 (2) [P ) P(OEt)3 (2a), PPh(OEt)2 (2b)].
These red-brown complexes were prepared exactly like the related
bipyridine complexes 1 starting from the FeCl2(phen) precursor;
yield g45%. Anal. Calcd for C54H74BFeN2O9P3 (2a): C, 61.49;
H, 7.07; N, 2.66. Found: C, 61.35; H, 6.95; N, 2.54. ΛM ) 56.0
Ω-1 mol-1 cm2. Calcd for C66H74BFeN2O6P3 (2b): C, 68.88; H,
6.48; N, 2.43. Found: C, 68.97; H, 6.56; N, 2.49. ΛM ) 51.8 Ω-1
mol-1 cm2.
[Fe(η2-H2)(bpy)P3]2+Y2- (4), [Fe(η2-H2)(phen)P3]2+Y2- (5) [P
) P(OEt)3 (4a, 5a), PPh(OEt)2 (4b), PPh2OEt (4c); Y )
2CF3SO3-] and [Fe(η2-H2){PPh(OEt)2}3(phen)]2+Y2- (5b) (Y2-
-
) BPh4 and CF3SO3-). These complexes were prepared in
solution in an NMR tube at a temperature below -20 °C. A typical
experiment involves the preparation of a solution of the appropriate
hydride (0.04 mmol) in CD2Cl2 (0.5 mL) in an NMR tube which
was cooled to -80 °C. An excess (0.08 mmol, 7.1 µL) of triflic
acid was added and the tube transferred into the probe of the NMR
instrument, precooled to -80 °C. The progress of the reaction was
1
monitored by H and 31P{1H} spectra recorded from -80 to 20
°C.
[FeH(phen){P(OEt)3}3]CF3SO3 (2a-CF3SO3). This complex
was prepared like the related triflate complex 1a-CF3SO3 using
LiCF3SO3 as precipitating agent; yield g15%. Anal. Calcd for
[Fe(CO)(bpy){P(OEt)3}3](BPh4)2 (6a). An excess of HBF4‚Et2O
(0.6 mmol, 86 µL of a 54% solution in Et2O) was added to a
Inorganic Chemistry, Vol. 43, No. 4, 2004 1331

Albertin et al.
solution of [FeH(bpy){P(OEt)3}3]BPh4 (0.200 g, 0.19 mmol) in 10
mL of CH2Cl2 cooled to -80 °C and placed under a CO atmosphere
(1 atm). The reaction mixture was allowed to reach room temper-
ature overnight with stirring. The solvent was removed under
reduced pressure to give an oil, which was triturated with ethanol
(3 mL) containing an excess of NaBPh4 (0.4 mmol, 0.137 g). An
orange solid slowly separated out from the resulting solution, which
was filtered and crystallized from CH2Cl2 and ethanol; yield g60%.
Anal. Calcd for C77H93B2FeN2O10P3: C, 67.17; H, 6.81; N, 2.03.
Found: C, 67.32; H, 6.88; N, 1.95. ΛM ) 119.5 Ω-1 mol-1 cm2.
[Fe(CH3CN)(bpy)P3](BPh4)2 (7) [P ) P(OEt)3 (7a), PPh(OEt)2
(7b)]. To a solution of the appropriate hydride (0.19 mmol) in 10
mL of CH3CN cooled to -80 °C was added an excess of HBF4‚
Et2O (0.6 mmol, 86 µL of a 54% solution in Et2O), and the reaction
mixture was allowed to reach room temperature and stirred for 2
h. The solvent was removed under reduced pressure to give an oil,
which was treated with ethanol (3 mL) containing an excess of
NaBPh4 (0.4 mmol, 0.137 g). An orange solid slowly separated
out, which was filtered and crystallized from CH2Cl2 and ethanol;
yield g65%. Anal. Calcd for C78H96B2FeN3O9P3 (7a): C, 67.40;
H, 6.96; N, 3.02. Found: C, 67.21; H, 7.04; N, 2.93. ΛM ) 124.0
Ω-1 mol-1 cm2. Calcd for C90H96B2FeN3O6P3 (7b): C, 72.74; H,
6.51; N, 2.83. Found: C, 72.93; H, 6.60; N, 2.87. ΛM ) 119.7
Ω-1 mol-1 cm2.
31P spectra using a delay time of 10 s between pulses. A typical
experiment involved the addition of 30-40 mg (0.03-0.04 mmol)
of the appropriate hydride [FeH(N-N)P3]CF3SO3 in a screw-cap
NMR tube placed in a Vacuum Atmospheres drybox. CD2Cl2 (0.5
mL) was added, the solid was dissolved and the tube was sealed
by the screw-cap. After standard NMR measurements, incremental
amounts of CF3SO3H were added (from 0.5 to 4 equiv) by a
microsyringe to the NMR tube cooled to -80 °C and then
transferred into the probe precooled to -80 °C. Approximately 1.5
equiv of CF3SO3H is required to completely generate the [Fe(η2-
H2)(N-N)P3]2+ dicationic species for all the hydrides 1 and 2.
Results and Discussion
Preparation of Hydride Complexes. Dichloro complexes
FeCl2(bpy) and FeCl2(phen) react with phosphites in the
presence of NaBH4 to give the mixed-ligand hydride cations
[FeH(bpy)P3]+ (1) and [FeH(phen)P3]+ (2), which were
isolated as BPh4 or CF3SO3 salts and characterized (eq 1).
excess P, excess NaBH4
+
FeCl2(N-N)
8
(1)
[FeH(N-N)P3]
EtOH
1, 2
N-N ) bpy (1), phen (2); P ) P(OEt)3 (a),
[Fe(CH3CN)(phen){PPh(OEt)2}3](BPh4)2 (8b). This orange
complex was prepared exactly like the related bipyridine complexes
7; yield g60%. Anal. Calcd for C92H96B2FeN3O6P3: C, 73.17; H,
6.41; N, 2.78. Found: C, 73.04; H, 6.50; N, 2.69. ΛM ) 112.6
Ω-1 mol-1 cm2.
PPh(OEt)2 (b), PPh2OEt (c)
Studies on the reaction course showed that both the
isomers of FeCl2(N-N) compounds, which were reported to
be a chain polymer containing either a six-coordinated (red
isomer) or a five-coordinated (orange isomer) iron(II) unit,13
did not react with phosphites in ethanol, and only the addition
of NaBH4 led the reaction to proceed yielding the final
species 1 or 2. These compounds, however, were the only
hydrides we isolated from the reaction, and changes in the
experimental conditions, i.e. change of the ratio among the
reagents, addition of free bpy or phen, or the lowering of
the reaction temperature, resulted only in a lowering of the
yield of the final complexes 1 and 2.
[Fe(ArNdNH)(bpy)P3](BPh4)2 (9, 10) [Ar ) C6H5 (9),
4-CH3C6H4 (10); P ) P(OEt)3 (a), PPh(OEt)2 (b)]. In a 25-mL
three-necked round-bottomed flask were placed solid samples of
the appropriate hydride (0.34 mmol) and an excess of the appropri-
ate aryldiazonium salt (1 mmol), and the flask was cooled to -196
°C. Dichloromethane (10 mL) was slowly added, and the reaction
mixture was allowed to reach room temperature and stirred for 2
h. The solvent was removed under reduced pressure to give an oil,
which was treated with ethanol (3 mL) containing an excess of
NaBPh4 (0.88 mmol, 0.30 g). A yellow-orange solid slowly
separated out from the resulting solution, which was filtered and
crystallized from CH2Cl2 and ethanol; yield g70%. Anal. Calcd
for C82H99B2FeN4O9P3 (9a): C, 67.69; H, 6.86; N, 3.85. Found:
C, 67.89; H, 6.95; N, 4.02. ΛM ) 118.7 Ω-1 mol-1 cm2. Calcd for
C83H101B2FeN4O9P3 (10a): C, 67.86; H, 6.93; N, 3.81. Found: C,
67.80; H, 7.02; N, 3.74. ΛM ) 126.6 Ω-1 mol-1 cm2. Calcd for
C95H101B2FeN4O6P3 (10b): C, 72.90; H, 6.50; N, 3.58. Found: C,
72.68; H, 6.55; N, 3.51. ΛM ) 119.9 Ω-1 mol-1 cm2.
The tris(bipyridine) complex [Fe(bpy)3]Cl2‚5H2O also
reacted with NaBH4 in the presence of phosphites and gave
the bis(bipyridine) [FeH(bpy)2P]+ (3) hydride cations, which
were isolated as BPh4 salts and characterized (eq 2). The
excess P, excess NaBH4
[Fe(bpy)3]2+
8
(2)
+
[FeH(bpy)2P]
EtOH
3
[Fe(C6H5Nd15NH)(bpy){P(OEt)3}3](BPh4)2 (9a-15N). This com-
pound was prepared exactly like the related unlabeled complex 9a
using the [C6H5Nt15N]BF4 as a reagent; yield g65%.
[Fe(4-CH3C6H4NdNH)(phen)P3](BPh4)2 (11) [P ) P(OEt)3
(11a), PPh(OEt)2 (11b)]. These orange complexes were prepared
following the method used for the related bipyridine derivatives
10; yield g65%. Anal. Calcd for C85H101B2FeN4O9P3 (11a): C,
P ) P(OEt)3 (a), PPh(OEt)2 (b)
reaction of the related phenanthroline [Fe(phen)3]2+ cation,
instead, gave under all conditions the tris(phosphite) com-
plexes [FeH(phen)P3]+ (2), isolable either in pure form or
as a mixture containing the starting [Fe(phen)3]2+ derivative.
The new hydrides 1-3 are red-brown solids moderately
stable in air and in a solution of polar organic solvents, where
they behave as 1:1 electrolytes.15 The analytical and spec-
troscopic data (Table 1) support the proposed formulation,
and a geometry in solution was also established. The IR
spectra show a weak band at 1890-1782 cm-1 attributed to
the ν(FeH) of the hydride ligand. Its presence is confirmed
68.37; H, 6.82; N, 3.75. Found: C, 68.44; H, 6.91; N, 3.88. ΛM
)
121.0 Ω-1 mol-1 cm2. Calcd for C97H101B2FeN4O6P3 (11b): C,
73.31; H, 6.41; N, 3.53. Found: C, 73.08; H, 6.54; N, 3.49. ΛM
115.8 Ω-1 mol-1 cm2.
)
Acidity Measurements. The protonation of [FeH(N-N)P3]CF3-
SO3 complexes 1-CF3SO3 and 2-CF3SO3 was studied in an NMR
1
tube by 31P and H NMR mesurements in CD2Cl2 at low temper-
ature. The concentrations of [FeH(N-N)P3]+ and [Fe(η2-H2)(N-N)-
P3]2+ were determined by integration of the inverse-gated decoupled
(15) Geary, W. J. Coord. Chem. ReV. 1971, 7, 81-122.
1332 Inorganic Chemistry, Vol. 43, No. 4, 2004

Mixed-Ligand Iron(II) Hydride Complexes
measurement of the JHD values of the isotopomer [Fe(η2-
HD)(N-N)P3]2+ derivatives. These HD complexes were
prepared by the addition of deuterated triflic acid CF3SO3D
to the hydrides 1, 2 in CD2Cl2. Their 1H NMR spectra exhibit,
in the hydride region, a relatively sharp triplet of doublets
of intensity ratio 1:1.3:1. The increased intensity of the center
peak of the triplet of the HD resonances is due to the presence
of a small amount of H2 species, resulting from the incom-
plete deuteration of the triflic acid, while the doubling of
each signal of the triplet is attributable to the coupling with
Chart 1
by the 1H NMR spectra which show the characteristic low-
frequency multiplet between -12 and -19 ppm. This pattern
appears as an AB2X (X ) H) multiplet for the [FeH(N-N)-
P3]+ (1, 2) cations, due to the coupling with the phosphorus
nuclei. A simulation of the spectra can be obtained with the
parameters reported in Table 1, which show that the values
of the two JPH are equal in some cases or comparable in
magnitude (i.e. 70 and 56 Hz) in the others, suggesting that
the hydride should occupy the same mutual position with
all the phosphite ligands. Taking into account that in the
temperature range between +20 and -80 °C the 31P{1H}
NMR spectra appear as an AB2 multiplet, a mer geometry
of type I (Chart 1) can reasonably be proposed for the tris-
(phosphite) 1, 2 derivatives.
Support for this proposal comes from the X-ray crystal
structure determination16 of the related ruthenium complex
[RuH(bpy){P(OEt)3}3]BPh4, whose spectroscopic data are
very similar, and a mer geometry was established.
The hydride signals for the bis(bipyridine) [FeH(bpy)2P]+
complexes 3a and 3b each appear as a doublet (at -13.13
and at -12.86 ppm) with JPH values of 116 and 102 Hz.
These values are somewhat higher than those observed in
the related [FeH(N-N)P3]+ complexes (1, 2) and may suggest
a mutually trans position of the hydride and phosphite ligands
as in a type II geometry (Chart 1).
2
the phosphorus nuclei of the phosphites with JPH of 12
HD
Hz for 4a, 4b and 14 Hz for 5a. From this triplet a value
between 31.5 and 32.5 Hz for JHD was measured, which
confirms the formation of the dihydrogen derivatives. From
the JHD values the H-H distances18 were calculated, and they
are reported in Table 2. Values between 0.89 and 0.92 Å
were observed for our η2-H2 complexes 4, 5, which fall in
the range found in the previously reported dicationic dihy-
drogen derivatives6 of iron and ruthenium. The presence of
the poor π-acceptor bpy or phen ligands does not seem to
have a strong influence on the H-H distances of dicationic
η2-H2 complexes. The H-H bond length in the H2 ligand
can also be calculated19 from the T1min values. The results
for our complexes (Table 2) show that there is a general
agreement between the distance calculated from the JHD
values and those determined by the T1 method using a static
rotation model. For a fast rotation of H2, instead, the observed
T1min values give rather short H-H lengths, which are also
not comparable with the known dihydrogen derivatives. An
analysis of JHD and T1min data of known dihydrogen
complexes that have JHD values g25 Hz has been recently
reported20 and shows as in only a few cases, namely those
with general formula trans-[MH(η2-H2)(P-P)2]+ (M ) Fe,
Ru; P-P ) chelating phosphine) it is necessary to invoke
the fast-rotation model to produce a reasonable H-H distance
in the H2 ligand. In general, the H-H distances should be
calculated from T1min data using a static rotation model, as
observed in our case. However, the dicationic dihydrogen
complex [Fe(η2-H2)(CO)(dppe)2]2+ [dppe ) 1,2-bis(diphen-
ylphosphinoethane)] recently reported by Morris and co-
workers6d shows that the H-H distances obtained from the
Protonation Reactions. Hydride [FeH(N-N)P3]+ (1, 2)
complexes react with the Brønsted acid CF3SO3H (or HBF4)
at low temperature to give the dihydrogen [Fe(η2-H2)(N-N)-
P3]2+ (4, 5) derivatives, as shown in eq 3. The protonation
CF SO H8
(3)
3
3
[FeH(N-N)P3]+
[Fe(η2-H2)(N-N)P3]2+
4, 5
1, 2
N-N ) bpy (1, 4), phen (2, 5); P ) P(OEt)3 (a),
PPh(OEt)2 (b), PPh2OEt (c)
JHD are consistent with those calculated from T1min data using
a fast-spinning model. Our mixed-ligand dicationic dihy-
drogen complexes 4 and 5 differ from that of Morris in this
aspect.
reaction was carried out at variable temperatures and was
monitored by 1H and 31P NMR spectra. The addition of the
Brønsted acid to 1 or 2 caused the disappearance of the
hydride multiplet and the appearance of a broad signal (half-
height width of about 200 Hz) between -13 and -17 ppm
attributed to the η2-H2 ligand. Measurements of T1 on these
signals gave a T1min value of about 3 ms (Table 2) in agree-
ment17 with the presence of a dihydrogen derivative. Further
support for the presence of the η2-H2 ligand came from the
In the temperature range between -80 and -20 °C the
31P{1H} NMR spectra of η2-H2 complexes 4 and 5 appear
1
as an AB2 multiplet. Taking into account that the H NMR
spectra of the isotopomers [Fe(η2-HD)(N-N)P3]2+ recorded
(18) (a) Heinekey, D. M.; Luther, T. A. Inorg. Chem. 1996, 35, 4396-
4399. (b) Maltby, P. A.; Schlaf, M.; Steinbeck, M.; Lough, A. J.;
Morris, R. H.; Klooster, W. T.; Koetzle, T. F.; Srivastava, R. C. J.
Am. Chem. Soc. 1996, 118, 5396-5407. (c) King, W. A.; Luo, X.-L.;
Scott, B. L.; Kubas, G. J.; Zilm, K. W. J. Am. Chem. Soc. 1996, 118,
6782-6783.
(19) Earl, K. A.; Jia, G.; Maltby, P. A.; Morris, R. H. J. Am. Chem. Soc.
1991, 113, 3027-3039.
(20) Gusev, D. G.; Kuhlman, R. L.; Renkema, K. B.; Eisenstein, O.;
Caulton, K. G. Inorg. Chem. 1996, 35, 6775-6783.
(16) Albertin, G.; Antoniutti, S.; Bacchi, A.; D’Este, C.; Pelizzi, G. Inorg.
Chem. 2004, 43, 1336-1349.
(17) (a) Hamilton, D. G.; Crabtree, R. H. J. Am. Chem. Soc. 1988, 110,
4126-4136. (b) Bautista, M. T.; Earl, K. A.; Maltby, P. A.; Morris,
R. H.; Schweitzer, C. T.; Sella, A. J. Am. Chem. Soc. 1988, 110, 7031-
7036. (c) Desrosiers, P. J.; Cai, L.; Lin, Z.; Richards, R.; Halpern, J.
J. Am. Chem. Soc. 1991, 113, 4173-4184.
Inorganic Chemistry, Vol. 43, No. 4, 2004 1333

Albertin et al.
Chart 2
Scheme 1a
a P ) P(OEt)3, N-N ) bpy (6a, 7a); P ) PPh(OEt)2, N-N ) phen (7b,
8b).
at -40 °C show a strong coupling (2JHP of 12 and 14 Hz)
between HD and one phosphorus nucleus suggesting a
mutually trans position between the hydrogen and one
phosphite ligand, a fac geometry III (Chart 2) can reasonably
be proposed for our derivatives 4 and 5. The protonation of
the hydrides 1 and 2, therefore, involves an isomerization
as well, giving a final complex containing the H2 trans to
the π-acceptor phosphite ligand.
The variable-temperature 1H NMR spectra of 4 and 5 also
show that the complexes are thermally unstable and, already
at -20 °C, the signal of free H2 at 4.6 ppm appears in the
proton spectra. Unfortunately, this thermal instability prevents
the isolation of the complexes 4 and 5 in the solid state.
This instability, however, is somewhat unexpected in light
of the relatively long H-H distances and of the behavior of
the comparable [Fe(η2-H2)(CO)(P-P)2]2+ dicationic complex,6d
which does not lose H2 in solution at room temperature.
Probably, either the trans influence of the phosphite ligand
in our compounds 4 and 5 as compared to CO in [Fe(η2-
H2)(CO)(P-P)2]2+ derivative, or the nature of the Fe(N-N)P3
fragment makes the [Fe(η2-H2)(N-N)P3]2+ derivative unstable
toward the loss of H2.
We have also studied the protonation of the mono-
phosphite [FeH(bpy)2P]+ (3) at low temperatures with both
CF3SO3H and HBF4‚Et2O, but in this case no formation of
η2-H2 species was detected by 1H NMR spectra. The addition
of the Brønsted acid at low temperature causes a color change
of the solution followed by the separation of solid products
indicating that decomposition takes place. It seems therefore
that only complexes containing three phosphites and one
bipyridine or phenanthroline like 1, 2 can stabilize the η2-
H2 derivatives, at least at low temperature.
Reactivity. The lability of the η2-H2 ligand in complexes
4, 5 prompted us to test the substitution reaction with several
ligands, and the results are summarized in Scheme 1.
Although the reaction proceeds easily with CO, phosphite,
isocyanide, H2O, CH3CN, etc., only the carbonyl 6a and the
nitrile 7, 8 complexes were obtained in pure form. In the
other cases, mixtures of products were obtained from which
the detected complexes were not separated.
The new iron(II) complexes 6-8 were isolated as BPh4
salts and are orange solids stable in the air and in a solution
of polar organic solvents in which they behave as 2:1
electrolytes.15 Analytical and spectroscopic data (Table 1)
support their formulation. The IR spectrum of the carbonyl
Studies on the protonation of the [FeH(N-N)P3]+ com-
plexes indicated that less than 1.5 equiv of CF3SO3H is
required to completely generate the [Fe(η2-H2)(N-N)P3]2+ (4,
5) species. This result indicates that our dicationic dihydrogen
complexes 4 and 5 are less acidic than the related dicationic
η2-H2 derivatives6b,d such as [Os(η2-H2)(CO)(dppe)2]2+ and
[Fe(η2-H2)(CO)(dppe)2]2+, which require at least 10 equiv
of CF3SO3H for their preparation. The relatively low acidity
observed in our complexes 4, 5 is probably due to the
presence of the bpy or phen ligands, which can delocalize
the total charge of the complexes making the η2-H2 ligand
less acidic. However, all the compared complexes contain
CO as a ligand, whose π-acceptor properties in those M(CO)-
(dppe)2 fragments should lead to a strong acidity of the η2-
H2 ligand. A qualitative comparison can also be made with
-
complex 6a shows, besides the absorptions of the BPh4
anion and of the bpy and P(OEt)3 ligands, one strong band
at 2033 cm-1 attributed to the ν(CO) of the carbonyl group.
The 13C{1H} NMR spectrum confirms the presence of the
CO ligand showing one doublet of triplets at 207.8 ppm due
to the carbonyl carbon atom coupled with the phosphorus
2
nuclei of the phosphites. The two JCP have the same value
of 55 Hz, suggesting that the carbonyl ligand should occupy
the same mutual position with all the phosphite ligands. In
the temperature range between +20 and -80 °C the 31P-
{1H} NMR spectrum appears as an A2B multiplet. On this
basis a mer geometry IV can be reasonably proposed for
the carbonyl complex 6a.
6a
[Os(η2-H2)(CH3CN)(dppe)2](BF4)2 and [M(η2-H2)(PR3)2-
The IR spectra of the nitrile complexes 7, 8 do not show
any band attributable to ν(CN) probably owing to their very
low intensity.22 However, the presence of this ligand is
(bpy)(CO)]2+ (M ) Ru, Os),6c whose formation from the
monohydride required a large excess of HBF4‚Et2O for the
former and 4 equiv of CF3SO3H for the latter, suggesting
that the mixed-ligand iron(II) dihydrogen complexes [Fe-
(η2-H2)(N-N)P3]2+ (4, 5) can be estimated as the least acidic
among the above-reported6 dicationic dihydrogen derivatives.
Only the dicationic21 [Os(η2-H2)(NH3)5]2+ is less acidic than
our 4 and 5 derivatives, probably owing to the presence of
the σ-donor NH3 ligands, which make the amino complex
stable toward base.
1
confirmed by the H NMR spectra which show a singlet at
1.34-2.07 ppm of the methyl group of the CH3CN. The 13C-
{1H} NMR spectra of 8b further support the presence of the
nitrile showing a singlet at 3.65 ppm due to the methyl carbon
resonance and a singlet at 137.8 ppm of the CtN carbon
atom. The HMQC and HMBC experiments confirm this
attribution showing the correlation between the methyl proton
signal at 1.42 ppm of CH3CN with the 13C signal at 3.65
(21) Harman, W. D.; Taube, H. J. Am. Chem. Soc. 1990, 112, 2261-2263.
1334 Inorganic Chemistry, Vol. 43, No. 4, 2004
(22) Rouschias, G.; Wilkinson, G. J. Chem. Soc. A 1967, 993-1000.

Mixed-Ligand Iron(II) Hydride Complexes
Chart 3
Chart 4
spectra of the labeled [Fe(C6H5Nd15NH)(bpy){P(OEt)3}3]-
(BPh4)2 (9a-15N) complex, which appear as an AB2Y
multiplet (Y ) 15N) due to the coupling with the phosphorus
ppm in HMQC and with those at 137.8 ppm in HMBC, in
agreement with the proposed formulation.
In the temperature range between +30 and -80 °C the
31P{1H} NMR spectra of the nitrile complexes 7, 8 appear
as AB2 multiplets which were simulated with the parameters
reported in Table 1. These data, however, do not allow us
to unambiguously assign a geometry in solution to these
complexes, although by analogy with the carbonyl 6a, a mer
type V (Chart 3) may be tentatively proposed.
2
nuclei. The two coupling constants JNP show very similar
values (8.4 and 8.6 Hz) as expected for a diazene ligand
which is in the same mutual position with all the phosphite
ligands. On this basis a geometry of type VI (Chart 4) can
be reasonably proposed for the aryldiazene derivatives 9-11.
Aryldiazene complexes of iron(II) are known,23,25 but
contain exclusively phosphites as supporting ligands. The
synthesis of complexes 9-11 shows that also polypyridyls
such as phen and bpy are able to stabilize aryldiazene iron-
(II) derivatives.
Reactivity studies on the new hydrides [FeH(N-N)P3]BPh4
(1, 2) and [FeH(N-N)2P]BPh4 (3) were devoted also to an
insertion reaction into the Fe-H bond. Several unsaturated
molecules were tested such as terminal alkynes, heteroallenes
(CO2, CS2, ArNCS) and aryldiazonium cations. The results
+
showed that only aryldiazonium cations ArN2 react with
Conclusions
[FeH(N-N)P3]BPh4 to give isolable aryldiazene23 [Fe(ArNd
NH)(N-N)P3](BPh4)2 (9, 10, 11) derivatives (eq 4). Decom-
position products were obtained with the other reagents in
the reaction with the mixed-ligand hydrides 1-3, except with
carbon dioxide, which does not react with either tris-
(phosphite) [FeH(N-N)P3]+ or the mono(phosphite) [FeH-
(bpy)2P]+ hydride derivative.
An easy route for the synthesis of the first iron(II) hydride
complexes containing both polypyridyl and phosphite as
supporting ligands of the [FeH(N-N)P3]BPh4 and [FeH-
(bpy)2P]BPh4 type is described. Mixed-ligand dihydrogen
complexes [Fe(η2-H2)(N-N)P3]2+ were obtained by protona-
tion of the [FeH(N-N)P3]BPh4 hydride precursors with
Brønsted acid. Measurements of T1min and JHD values give
information on the H-H distances of the η2-H2 ligand, while
protonation studies suggests a strong acidic character of the
dihydrogen ligand. However, the presence of the polypyridyl
ligand makes the [Fe(η2-H2)(N-N)P3]2+ complexes among
the least acidic of the known dicationic dihydrogen deriva-
tives. New polypyridyl iron(II) complexes can also be
prepared using both classical and nonclassical hydride
complexes as precursors. Thus, carbonyl [Fe(CO)(bpy)-
{P(OEt)3}3](BPh4)2, nitrile [Fe(CH3CN)(N-N)P3](BPh4)2, and
aryldiazene [Fe(ArNdNH)(N-N)P3](BPh4)2 complexes were
obtained.
+
ArN2
[FeH(N-N)P3]+
8
(4)
2+
[Fe(ArNdNH)(N-N)P3]
9, 10, 11
N-N ) bpy (9, 10), phen (11); P ) P(OEt)3 (a),
PPh(OEt)2 (b); Ar ) C6H5 (9), 4-CH3C6H4 (10, 11)
Good analytical data were obtained for aryldiazene
complexes 9, 10, 11, which are orange solids stable in air
and in a solution of polar organic solvents where they behave
as 2:1 electrolytes.15 The spectroscopic data (Table 1) support
the proposed formulation, and a geometry in solution was
also established. Diagnostic for the presence of the diazene
ligand are the 1H NMR spectra which show the characteristic
slightly broad NH signal between 13 and 14 ppm. Support
for this attribution comes from the 1H spectra of the labeled
9a-15N complex which shows the 15NH resonance as a high
Acknowledgment. The financial support of MIUR (Rome),
PRIN 2002, is gratefully acknowledged. We thank Daniela
Baldan for technical assistance.
1
frequency doublet at 13.87 ppm with JNH of 68 Hz in
Supporting Information Available: Observed and calculated
31P{1H} NMR spectra of compound 5b (Figure S1). The hydride
part of the proton spectrum of compound 1a (Figure S2). This
material is available free of charge via the Internet at http://pubs.
acs.org.
agreement23,24 with the presence of the diazene ligand. In
the proton spectra the signals of the phosphite, the polypyri-
dyl ligand, and the BPh4 anion are also present, while the
31P spectra appear as an AB2 multiplet suggesting that two
phosphites are magnetically equivalent and different from
the third. Furthermore, we also recorded the 15N{1H} NMR
IC0348190
(23) (a) Kisch, H.; Holzmeier, P. AdV. Organomet. Chem. 1992, 34, 67-
109. (b) Sutton, D. Chem. ReV. 1993, 93, 995-1022.
(24) (a) Laing, K. R.; Robinson, S. D.; Uttley, M. F. J. Chem. Soc., Dalton
Trans. 1973, 2713-2722. (b) Carrol, J. A.; Sutton, A.; Xiaoheng, Z.
J. Organomet. Chem. 1983, 244, 73-86.
(25) (a) Albertin, G.; Antoniutti, S.; Lanfranchi, M.; Pelizzi, G.; Bordignon,
E. Inorg. Chem. 1986, 25, 950-957. (b) Albertin, G.; Antoniutti, S.;
Pelizzi, G.; Vitali, F.; Bordignon, E. J. Am. Chem. Soc. 1986, 108,
6627-6634. (c) Albertin, G.; Antoniutti, S.; Bacchi, A.; Bordignon,
E.; Pelizzi, G.; Ugo, P. Inorg. Chem. 1996, 35, 6245-6253.
Inorganic Chemistry, Vol. 43, No. 4, 2004 1335