Bis(diisopropylphosphino)pyridine iron dicarbonyl, dihydride, and silyl hydride complexes

Article abstract of DOI:10.1021/ic0608647

Treatment of the bis(diisopropylphosphino)pyridine iron dichloride, ( ^iPrPNP)FeCl₂ (^iPrPNP = 2,6-(ⁱPr ₂PCH₂)₂(C₅H₃N)), with 2 equiv of NaBEt₃H under an atmosphere of dinitrogen furnished the diamagnetic iron(II) dihydride dinitrogen complex, (^iPrPNP)FeH ₂(N₂). Addition of 1 equiv of PhSiH₃ to ( ^iPrPNP)FeH₂(N₂) resulted in exclusive substitution of the hydride trans to the pyridine to yield the silyl hydride dinitrogen compound, (^iPrPNP)FeH(SiH₂Ph)N₂, which has been characterized by X-ray diffraction. The solid-state structure established a distorted octahedral geometry where the hydride ligand distorts toward the iron silyl. Both (^iPrPNP)FeH₂(N₂) and (^iPrPNP)FeH(SiH₂Ph)N₂ form η²-dihydrogen complexes upon exposure to H₂. The iron hydrides and the η²-H₂ ligands are in rapid exchange in solution, consistent with the previously reported cis effect, arising from a dipole/induced dipole interaction between the two ligands. Taken together, the spectroscopic, structural, and reactivity studies highlight the relative electron-donating ability of this pincer ligand as compared to the redox-active aryl-substituted bis(imino)pyridines.

Full text of DOI:10.1021/ic0608647

Inorg. Chem. 2006, 45, 7252−7260
Bis(diisopropylphosphino)pyridine Iron Dicarbonyl, Dihydride, and Silyl
Hydride Complexes
Ryan J. Trovitch, Emil Lobkovsky, and Paul J. Chirik*
Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell UniVersity,
Ithaca, New York 14853
Received May 18, 2006
Treatment of the bis(diisopropylphosphino)pyridine iron dichloride, (iPrPNP)FeCl2 (iPrPNP
)
2,6-(iPr2PCH2)2(C5H3N)),
with 2 equiv of NaBEt3H under an atmosphere of dinitrogen furnished the diamagnetic iron(II) dihydride dinitrogen
complex, (iPrPNP)FeH2(N2). Addition of 1 equiv of PhSiH3 to (iPrPNP)FeH2(N2) resulted in exclusive substitution of
the hydride trans to the pyridine to yield the silyl hydride dinitrogen compound, (iPrPNP)FeH(SiH2Ph)N2, which has
been characterized by X-ray diffraction. The solid-state structure established a distorted octahedral geometry where
the hydride ligand distorts toward the iron silyl. Both (iPrPNP)FeH2(N2) and (iPrPNP)FeH(SiH2Ph)N2 form
η
2-dihydrogen
complexes upon exposure to H2. The iron hydrides and the
η
2-H2 ligands are in rapid exchange in solution, consistent
with the previously reported “cis” effect, arising from a dipole/induced dipole interaction between the two ligands.
Taken together, the spectroscopic, structural, and reactivity studies highlight the relative electron-donating ability of
this pincer ligand as compared to the redox-active aryl-substituted bis(imino)pyridines.
Introduction
our laboratory has described the synthesis of the bis(imino)-
pyridine iron bis(dinitrogen) complex, (iPrPDI)Fe(N2)2 (iPrPDI
) 2,6-(2,6-iPr2-C6H3NdCMe)2C5H3N) and its application
to catalytic olefin and alkyne hydrogenation and hydrosilation
reactions.2 Investigations into the electronic structure of
(iPrPDI)Fe(N2)2 by Mo¨ssbauer spectroscopy and DFT calcu-
lations have established an intermediate-spin ferrous iron
complexed by a bis(imino)pyridine dianion.7 A similar
electronic structure assignment has been suggested by
Gambarotta and co-workers for the square planar bis(imino)-
pyridine iron methyl anion, [(iPrPDI)FeMe]-.8
Aryl-substituted bis(imino)pyridine iron complexes have
emerged as a powerful class of catalysts for a host of
important bond-forming reactions including olefin polym-
erization,1 hydrogenation, and hydrosilation.2 It is also now
well-established that bis(imino)pyridines are both redox3 and
chemically active ligands,4 participating in electron transfer,
addition reactions, and deprotonation chemistry.5,6 Recently,
* To whom correspondence should be addressed. E-mail: pc92@
cornell.edu.
(1) (a) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. ReV. 2000, 100,
1169. (b) Small, B. L.; Brookhart, M.; Bennett, A. M. A. J. Am. Chem.
Soc. 1998, 120, 4049. (c) 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. (d) Britovsek, G. J. P.;
Bruce, M.; Gibson, V. C.; Kimberley, B. S.; Maddox, P. J.;
Mastroianni, S.; McTavish, S. J.; Redshaw, C.; Solan, G. A.;
Stro¨mberg, S.; White, A. J. P.; Williams, D. J. J. Am. Chem. Soc.
1999, 121, 8728. (e) Gibson, V. C.; Spitzmesser, S. K. Chem. ReV.
2003, 103, 283. (f) Bianchini, C.; Mantovani, G.; Meli, A.; Migliacci,
D.; Zanobini, F.; Laschi, F.; Sommazzi, A. Eur. J. Inorg. Chem. 2003,
1620. (f) Bouwkamp, M. W.; Lobkovsky, E.; Chirik, P. J. J. Am. Chem.
Soc. 2005, 127, 9660.
While the electronic structure of (iPrPDI)Fe(N2)2 has been
elucidated, one open question is the role, if any, that the
redox activity of the ligand plays in catalysis. Determining
(4) For examples see: (a) Clentsmith, G. K. B.; Gibson, V. C.; Hitchcock,
P. B.; Kimberely, B. S.; Rees, C. W. Chem. Commun. 2002, 1498.
(b) Korobkov, I.; Gambarotta, S.; Yap, G. P. A.; Budzelaar, P. H. M.
Organometallics 2002, 21, 3088. (c) Kooistra, T. M.; Hetterscheid,
D. G. H.; Schwartz, E.; Knijnenburg, Q.; Budzelaar, P. H. M.; Gal,
A. W. Inorg. Chim. Acta 2004, 357, 2945. (d) Blackmore, I. J.; Gibson,
V. C.; Hitchcock, P. B.; Rees, C. W.; Williams, D. J.; White, A. J. P.
J. Am. Chem. Soc. 2005, 127, 6012.
(5) Bouwkamp, M. W.; Lobkovsky, E.; Chirik, P. J. Inorg. Chem. 2006,
45, 2.
(6) Reardon, D.; Aharonian, G.; Gambarotta, S.; Yap, G. P. A.; Budzelaar,
P. H. M. J. Am. Chem. Soc. 2002, 124, 12268.
(2) Bart, S. C.; Lobkovsky, E.; Chirik, P. J. J. Am. Chem. Soc. 2004,
126, 13794.
(3) (a) de Bruin, B.; Bill, E.; Bothe, E.; Weyhermu¨ller, T.; Wieghardt, K.
Inorg. Chem. 2000, 39, 2936. (b) Budzelaar, P. H. M.; de Bruin, B.;
Gal, A. W.; Wieghardt, K.; van Lenthe, J. H. Inorg. Chem. 2001, 40,
4649. (c) Sugiyama, I.; Korobkov, I.; Gambarotta, S.; Mueller, A.;
Budzelaar, P. H. M. Inorg. Chem. 2004, 43, 5771. (d) Scott, J.;
Gambarotta, S.; Korobkov, I.; Knijnenburg, Q.; de Bruin, B.; Bud-
zelaar, P. H. M. J. Am. Chem. Soc. 2005, 127, 17204.
(7) Bart, S. C.; Chlopek, K.; Bill, E.; Bouwkamp, M. W.; Lobkovsky,
E.; Neese, F.; Weighardt, K.; Chirik, P. J. submitted.
(8) Scott, J.; Gambarotta, S.; Korobkov, I.; Budzelaar, P. H. M. Orga-
nometallics 2005, 24, 6298.
7252 Inorganic Chemistry, Vol. 45, No. 18, 2006
10.1021/ic0608647 CCC: $33.50
© 2006 American Chemical Society
Published on Web 08/05/2006

Bis(diisopropylphosphino)pyridine Iron Complexes
Figure 1. Comparison of redox-active bis(imino)pyridine to bis(phosphino)pyridine pincer ligands.
the answer to such a question is extremely challenging, as
many factors are often responsible for catalyst (in)activity.
Efforts are now underway in our laboratory aimed at
experimentally evaluating whether metal-ligand electron
transfer events are a prerequisite for catalytically active iron
centers and how these properties can be tuned for optimal
performance. To this end, we sought to modify the bis-
(imino)pyridine ligand core by replacing the unsaturated
imine donors with saturated dialkylphosphines (Figure 1),
thereby disrupting the conjugated π-system and increasing
the barrier for metal-ligand redox events.9 In this contribu-
tion, we report the synthesis, characterization, and evaluation
of the catalytic activity of bis(phosphino)pyridine iron
complexes and compare the structures, electronic properties,
and reactivity to established bis(imino)pyridine compounds.
Figure 2. Molecular structure of 1-(CO)2 depicted with 30% probability
ellipsoids. Hydrogen atoms omitted for clarity.
Results and Discussion
Table 1. Selected Bond Distances (Å) and Angles (deg) for 1-(CO)2
Synthesis of Bis(diisopropylphosphino)pyridine Iron
Dicarbonyl, Dihydride, and Silyl Hydride Compounds.
To gain insight into the relative electronic environments
imparted by the bis(phosphine) versus bis(imine) ligands,
the dicarbonyl complex, (iPrPNP)Fe(CO)2 (1-(CO)2) was
targeted. Milstein and co-workers have recently reported the
synthesis of (iPrPNP)FeCl2 (1-Cl2) by straightforward com-
plexation of the free ligand10 with ferrous dichloride.11
Stirring 1-Cl2 with an excess of 0.5% sodium amalgam in
the presence of 4 atm of carbon monoxide furnished a red
solid identified as 1-(CO)2, based on NMR and IR spec-
troscopies, combustion analysis, and single-crystal X-ray
diffraction (eq 1).
1-(CO)2
(iPrPDI)Fe(CO)2
Fe(1)-C(1)
1.7325(9)
1.7325(9)
2.1941(2)
2.0684(8)
1.1734(11)
1.3593(9)
165.990(12)
119.91(7)
82.995(6)
120.04(3)
1.7809(19) (apical)
1.7823(19) (basal)
-
1.8488(14)
1.147(2)
1.376(2)
-
97.01(9)
-
157.89(8)
Fe(1)-C(1A)
Fe(1)-P(1)
Fe(1)-N(1)
C(1)-O(1)
N(1)-C(3)
P(1)-Fe(1)-P(1A)
C(1)-Fe(1)-C(1A)
N(1)-Fe(1)-P(1)
C(1)-Fe(1)-N(1)
dramatic shift of the CO bands to lower frequencies is
consistent with a more reducing iron(0) center in 1-(CO)2
as compared to the more oxidized iron in (iPrPDI)Fe(CO)2.
Cooling a concentrated toluene solution of 1-(CO)2 to -35
°C produced single crystals suitable for X-ray diffraction.
The solid-state structure is presented in Figure 2, and selected
metrical parameters are reported in Table 1. The overall
geometry about the iron in 1-(CO)2 is best described as
idealized trigonal bipyramidal, in contrast to the distorted
square pyramidal structure observed for (iPrPDI)Fe(CO)2. In
1-(CO)2, the two carbonyl ligands and the pyridine nitrogen
define the equatorial plane with bond angles of 119.91(7)°
and 120.04(3)° for C(1)-Fe(1)-C(1A) and C(1)-Fe(1)-
N(1), respectively. The carbonyls and the phosphine sub-
stituents are related by symmetry. The pyridine ring is
slightly canted with respect to the iron-bis(phosphine) plane.
The only significant distortion observed is in the axial
phosphine ligands where the P(1)-Fe(1)-P(1A) bond angle
of 165.990(12)° is contracted toward the pyridine ring. The
bis(imino)pyridine iron dicarbonyl, (iPrPDI)Fe(CO)2, has a
more contracted C-Fe-C angle of 97.01(9)° between the
In the solid-state (KBr) infrared spectrum, two intense
carbonyl bands were observed at 1842 and 1794 cm-1,
substantially reduced from the peaks reported at 1950 and
1894 cm-1 for (iPrPDI)Fe(CO)2 in the same medium. The
(9) For a recent example of a singly reduced pincer ligand, see: Frech,
C. M.; Ben-David, Y.; Weiner, L.; Milstein, D. J. Am. Chem. Soc.
2006, 128, 7128.
(10) Jansen, A.; Pitter, S. Montasch. Chem. 1999, 130, 783.
(11) Zhang, J.; Gandelman, M.; Herrman, D.; Leitus, G.; Shimon, L. J.
W.; Ben-David, Y.; Milstein, D. Inorg. Chim. Acta 2006, 359, 1955.
Inorganic Chemistry, Vol. 45, No. 18, 2006 7253

Trovitch et al.
carbonyl ligands, consistent with a square pyramidal geom-
etry and reduced π-back-bonding.
symmetric isomer where the Fe-H ligands are in a trans
arrangement. This isomer is also disfavored due to the strong
trans influence of the hydride ligand.12 In addition, a single
31P resonance peak was observed at 108.28 ppm for the
equivalent phosphines. Coordination of the dinitrogen ligand
was confirmed by solid-state (KBr) infrared spectroscopy
with the observation of a strong NtN band centered at 2016
cm-1. This value is reduced compared to the corresponding
N2 stretching frequencies of 2124 and 2053 cm-1 reported
for (iPrPDI)Fe(N2)2, again highlighting a more reducing iron
center engendered by the iPrPNP ligand.
Assignment of 1-H2(N2) as an iron(II) dihydride rather
than an iron(0) dihydrogen complex is supported by T1(min)
measurements and the phosphorus-iron-hydride coupling
constant. A T1(min) value of 314 ms was measured at -25
°C in toluene-d8 at 500 MHz and in combination with the
2JP-H values of 52 and 60.5 Hz is consistent with the ferrous
dihydride formulation.13,14 While the iron-hydride peaks
appear as a sharp triplet of doublets at 23 °C, one-
dimensional EXSY NMR experiments indicate rapid ex-
change between the iron-hydride positions, demonstrating
that reductive coupling to form an iron(0) η2-dihydrogen
complex, followed by rapid η2-H2 rotation15 or N2 dissocia-
tion to form the five-coordinate iron(II) dihydride, is
competitive on the NMR time scale. This observation, along
with the H-H coupling constant of 21.5 Hz, suggest some
“stretched η2-dihydrogen” character.16
The formation of the iron(II) dihydride is interesting in
light of the observations with the corresponding bis(imino)-
pyridine compound. Treatment of (iPrPDI)FeCl2 with NaBEt3H
in the presence of N2 resulted in isolation of the bis-
(dinitrogen) complex, (iPrPDI)Fe(N2)2, presumably from rapid
reductive coupling of the two iron hydrides followed by
dissociation. Consistent with this hypothesis is the formation
of the iron dihydrogen complex, (iPrPDI)Fe(η2-H2), upon
exposure of (iPrPDI)Fe(N2)2 to 1 atm of H2. The instability
of (iPrPDI)Fe(η2-H2) was further demonstrated by the obser-
vation of rapid reversion to (iPrPDI)Fe(N2)2 upon exposure
to even trace amounts of dinitrogen. The relative stability
of the oxidative addition products, 1-H2(N2) versus the
putative “(iPrPDI)FeH2” is a consequence of the relative donor
abilities of the ligand and hence the reducing nature of the
iron center.2 In the iPrPNP case, the more electron donating,
redox innocent ligand engenders a more electron rich metal
center and stabilizes the iron(II) dihydride. In the bis(imino)-
pyridine compound, the “redox activity” of the ligand,
generating an [iPrPDI]2- chelate produces a more oxidizing
iron center where the requisite two electrons for H2 oxidative
addition are stored in the bis(imino)pyridine π-system. It is
also important to note that the redox properties of the two
The more reducing iron center in 1-(CO)2 as compared
to (iPrPDI)Fe(CO)2 is also evident in the bond distances of
the carbonyl ligands. In the phosphine-substituted compound,
1-(CO)2, contracted Fe-C bond distances of 1.7325(9) Å
are observed along with elongated C-O bond lengths of
1.1734(11) Å. By way of comparison, the corresponding
distances in (iPrPDI)Fe(CO)2 are 1.7809(19)/1.7823(19) and
1.147(2) Å, respectively, consistent with a more oxidized
iron center. Another interesting comparison are the structural
features of 1-(CO)2 and the corresponding ferrous dihalide.
For the latter class of compound, the only structurally
characterized example is the bis(tert-butyl)-substituted de-
rivative, (tBuPNP)FeCl2.11 The molecular geometry of the
dichloride compound is best described as distorted square
pyramidal with the iron atom raised out of the idealized basal
plane by 0.552 Å. Accordingly, the iron-pyridine bond
distance is elongated to 2.303(2) Å, as compared 2.0684(8)
Å in 1-(CO)2.
Attempts to synthesize a bis(phosphino)pyridine iron
dinitrogen complex analogous to (iPrPDI)Fe(N2)22 have been
unsuccessful. Stirring a pentane or toluene solution of 1-Cl2
or 1-Br2 with excess 0.5% sodium amalgam under N2
resulted in an intractable mixture of iron products and free
iPrPNP ligand. An alternative route to (iPrPDI)Fe(N2)2 involves
treatment of (iPrPDI)FeBr2 with 2 equiv of NaBEt3H under
a dinitrogen atmosphere. Presumably, the transient iron
dihydride undergoes reductive elimination of H2 and the
reduced iron fragment captures dinitrogen to furnish the
observed product. Treatment of a thawing ethereal slurry of
1-Cl2 with 2 equiv of NaBEt3H under an atmosphere of
dinitrogen resulted in isolation of a diamagnetic, red-orange
solid identified as (iPrPNP)FeH2(N2) (1-H2(N2)) (eq 2).
Unfortunately, 1-H2(N2) has proven extremely difficult to
handle, undergoing decomposition to free iPrPNP and in-
soluble iron products over the course of hours in benzene-
d6 solution at 23 °C. This unwanted side reaction complicates
characterization by 1H NMR spectroscopy, as small amounts
of decomposition (∼5-10%) significantly broaden spectra
to where peaks for 1-H2(N2) cannot be readily identified.
Collecting data immediately following purification allowed
characterization of 1-H2(N2) by multinuclear NMR spec-
(12) Jordan, R. B. In Reaction Mechanisms of Inorganic and Organome-
tallic Systems, 2nd ed.; Oxford University Press: New York, 1998;
pp 64-67.
(13) Desrosiers, P. J.; Cai, L.; Lin, Z.; Richards, R.; Halpern, J. J. Am.
Chem. Soc. 1991, 113, 4173.
(14) Kubas, G. J. Acc. Chem. Res. 1988, 21, 120.
(15) For studies describing the low rotational barriers of η2-H2 ligands,
see: Eckert, J.; Kubas, G. J. J. Phys. Chem. 1993, 97, 2378.
(16) Heinekey, D. M.; Lledos, A.; Lluch, J. M. Chem. Soc. ReV. 2004, 33,
175.
1
troscopy. In benzene-d6, the H NMR spectrum exhibited
the number of resonances expected for an idealized Cs-
symmetric molecule with the mirror plane containing the two
hydrides and the dinitrogen ligand. Two triplets of doublets
centered at -17.65 and -12.54 ppm were observed, diag-
nostic of inequivalent iron-hydride resonances. The appear-
ance of two inequivalent iron hydrides eliminates the C2V-
7254 Inorganic Chemistry, Vol. 45, No. 18, 2006

Bis(diisopropylphosphino)pyridine Iron Complexes
Figure 3. Molecular structure of the core of 1-H(Si)N2 depicted with 30% probability ellipsoids (left) and a view of the core of the molecule (right).
Hydrogen atoms, except for the iron-hydride and silicon hydrogens, omitted for clarity.
Table 2. Selected Bond Distances (Å) and Angles (deg) for 1-H(Si)N2
and 1-H(Si)CO
compounds are also attenuated by the ligand substituents.
The bis(imino)pyridine ligand contains relatively electron-
1-H(Si)N2
1-H(Si)CO
poor aryl groups, while the phosphines are substituted with
electron-donating alkyl substituents. Attempts to prepare the
corresponding iron compound bearing aryl-substituted PNP
ligands are currently under investigation in our laboratory.
Treatment of 1-H2(N2) with 1 equiv of PhSiH3 resulted
in replacement of one of the hydride ligands for the silyl to
yield solely one isomer of 1-H(Si)N2 (eq 3). This molecule
Fe(1)-H(1M)
1.512(19)
2.1823(5)
2.1817(5)
2.0370(15)
2.2718(6)
1.8002(17)
1.120(2)
2.420(17)
1.362(2)
161.12(2)
165.90(4)
173.3(7)
96.82(6)
97.04(5)
80.6(7)
1.522(15)
2.1780(5)
2.1827(4)
2.0605(13)
2.2689(5)
1.7541(16)
1.1635(19)
2.41(2)
1.359(2)
160.761(19)
167.02(4)
166.2(9)
102.36(6)
90.46(5)
81.8(9)
Fe(1)-P(1)
Fe(1)-P(2)
Fe(1)-N(1)
Fe(1)-Si(1)
Fe(1)-N(2)/C(26)
N(2)-N(3)/C(26)-O(1)
Si(1)-H(1M)
N(1)-C(2)
P(1)-Fe(1)-P(2)
N(1)-Fe(1)-Si(1)
H(1M)-Fe(1)-N(2)/C(26)
N(1)-Fe(1)-N(2)/C(26)
Si(1)-Fe(1)-N(2)/C(26)
H(1M)-Fe(1)-P(1)
H(1M)-Fe(1)-P(2)
H(1M)-Fe(1)-Si(1)
86.6(7)
76.6(7)
85.6(9)
75.9(9)
was also conveniently prepared by treatment of 1-Cl2 with
2 equiv of NaBEt3H in the presence of a stoichiometric
quantity of PhSiH3. A single iron hydride resonance was
observed at -13.12 ppm as a triplet (2JP-H ) 58 Hz) in the
benzene-d6 1H NMR spectrum, arising from coupling to two
equivalent phosphine ligands. The 31P NMR spectrum
exhibited a single peak at 96.85 ppm, shifted upfield from
the value observed for 1-H2(N2). Diastereotopic Si-H
value shifted to a significantly higher frequency than the N2
stretch observed in 1-H2(N2) (νNN ) 2016 cm-1), demon-
strating a more electropositive iron center upon replacing
hydride with silyl. Importantly, 1-H(Si)N2 was stable in
ambient temperature benzene-d6 solutions indefinitely, al-
lowing further characterization and reactivity studies.
The solid-state structure of 1-H(Si)N2 was determined by
single-crystal X-ray diffraction (Figure 3) and definitively
established the trans arrangement of the silyl and pyridine
nitrogen and the dinitrogen and iron-hydride, respectively.
The data were of sufficient quality such that all of the
hydrogens were located and refined. The metrical parameters
(Table 2) reveal an overall molecular geometry distorted from
idealized octahedral. The chelate-constrained P(1)-Fe(1)-
P(2) angle is 161.12(2)° and is also bent away from the
π-acidic dinitrogen ligand with H(1M)-Fe(1)-P(1) and
H(1M)-Fe(1)-P(2) angles of 80.6(7)° and 86.6(7)°, respec-
tively. Similar distortions have been observed in bis-
(diphosphino) iron hydride, dihydrogen cations, and trans-
[(P-P)2Fe(H)(η2-H2)]+ (P-P ) chelating bis(phosphine))
and are believed to hybridize the metal orbitals to increase
back-bonding to the π-acid.17 The iron hydride is also
1
resonances were observed by H NMR spectroscopy as
3
overlapping triplets centered at 4.94 ppm with JP-H ) 5.5
Hz. EXSY NMR spectroscopy (500 ms mixing time)
demonstrated that the iron-hydride and the silicon hydrogens
do not undergo exchange on the NMR time scale at 23 °C.
Moreover, the iron-hydride resonance has a T1(min) value
of 368 ms at -50 °C at 500 MHz. Taken together, these
data suggest that reductive coupling to form an iron-silane
σ-complex followed by rotation and oxidative addition has
a higher barrier than that associated process with the
corresponding η2-dihydrogen compound. These results again
highlight the electron-donating ability of the iPrPNP ligand
as compared to the bis(imino)pyridine where a bis(η2-silane)
complex has been crystallographically characterized.2
The presence of a coordinated dinitrogen ligand was
confirmed by solid-state (KBr) infrared spectroscopy with
the observation of a strong band centered at 2032 cm-1, a
(17) Maseras, F.; Duran, M.; Lledo˜s, A.; Bertra´n, J. J. Am. Chem. Soc.
1991, 113, 2879.
Inorganic Chemistry, Vol. 45, No. 18, 2006 7255

Trovitch et al.
directed toward the silyl ligand with an H(1M)-Fe(1)-Si(1)
bond angle of 76.6(7)°, suggestive of a weak interaction.
However, the distance between the iron-hydride and silicon
atom is 2.420(17) Å, well outside the sum of the covalent
radii for a silicon-hydrogen bond.
The iron-phosphorus bond distances (Table 2) of 2.1823(5)
and 2.1817(5) Å are comparable to those found in 1-(CO)2,
and the N(2)-N(3) distance of 1.120(2) Å is as expected
for a weakly activated dinitrogen ligand. The Fe(1)-H(1M)
distance of 1.512(19) Å is in agreement with iron-hydrides
characterized by neutron diffraction.18-20 The carbon-
nitrogen pyridine distance, N(1)-C(2), of 1.362(2) Å is
contracted as compared to the values of 1.37-1.39 Å
typically found in reduced bis(imino)pyridine ligands, dem-
onstrating that iPrPNP acts as a σ-donor ligand and is not
engaged in redox processes with the iron.
Figure 4. Hydride region of the 1H NMR spectrum of the hydrogenation
of 1-H(Si)N2 as a function of time.
Evaluation of Catalytic Activity and Ligand Substitu-
tion Reactions. With the ferrous dihydride, 1-H2(N2), and
silyl hydride, 1-H(Si)N2, in hand, the catalytic activity of
both compounds was assayed. The hydrogenation and
hydrosilation of simple, unactivated olefins such as 1-hexene
and cyclohexene were chosen as model reactions to compare
to the catalytic activity to the bis(imino)pyridine iron catalyst
precursor, (iPrPDI)Fe(N2)2.2 Hydrogenation of 1-hexene with
0.3 mol % of 1-H2(N2) and 4 atm of H2 in pentane solution
was complete (>98% conversion, GC) after stirring for 3 h
at 23 °C, substantially longer than the few minutes required
with (iPrPDI)Fe(N2)2. Attempts to hydrogenate cyclohexene
with 1-H2(N2) under identical conditions produced only
minimal conversion (∼10%) after 6 and 24 h, owing to
catalyst decomposition over the course of the reaction. The
ferrous silyl hydride, 1-H(Si)N2, was not effective for the
hydrosilation of 1-hexene or cyclohexene with PhSiH3.
dissociation followed by coordination of a molecule of
dihydrogen that is in rapid exchange with the iron hydride
(eq 4).
On the basis of the limited experimental data available,
we are unable to definitively assign the isomers of 1-H2(H2).
In addition to those depicted in eq 4, the isomer where the
dihydrogen ligand is trans to the pyridine nitrogen is also
possible but is most likely disfavored due to the strong trans
influence of the hydride ligands. Treatment of 1-H2(N2) with
D2 gas resulted in rapid isotopic exchange with the iron
hydride positions. In related experiments, exposure of either
1-H2(H2) or 1-D2(D2) to 1 atm of dinitrogen resulted in
displacement of the η2-dihydrogen or dideuterium ligand to
rapidly regenerate 1-H2(N2) or 1-D2(D2). Notably, the
reversion to 1-H2(N2) with 1 atm of N2 is faster than
formation of 1-H2(H2) with 4 atm of dihydrogen, demon-
strating N2 is a better ligand than H2.
The greater solution stability of 1-H(Si)N2, relative to
1-H2(N2), suggested that the corresponding dihydrogen
complexes could also be longer lived and allow more
thorough characterization. Addition of 4 atm of H2 to 1-H(Si)-
N2 resulted in gradual disappearance of the iron hydride
signal centered at -13.12 ppm with concomitant growth of
a new, broad signal at -9.37 ppm (Figure 4). This new
resonance integrates to three protons, consistent with forma-
tion of the dihydrogen complex, 1-H(Si)(H2) (eq 5). As with
The origin of the poor catalytic performance was studied
in more detail by evaluation of a series of stoichiometric
processes. Exposure of 1-H2(N2) to 4 atm of dihydrogen
resulted in gradual disappearance of the starting material with
concomitant growth of a new product over the course of 3
h at 23 °C. Importantly, iron hydride resonances for both
compounds were observed simultaneously. The product
exhibited a broad iron-hydride signal (∆ν1/2 ) 12 Hz)
centered at -11.17 ppm. Cooling the sample to -75 °C
resulted in gradual broadening of the peak (∆ν1/2 ) 46 Hz,
-75 °C) without resolution. On the basis of this observation
and results described below, we tentatively assign the product
as the iron hydride dihydrogen complex, 1-H2(H2). Definitive
characterization of this compound was again hampered by
competing decomposition processes involving loss of the
pincer ligand and formation of insoluble iron species.
However, the observation of a newly formed, single, broad
iron hydride resonance suggests that the N2 ligand undergoes
(18) Ricci, J. S.; Koetzle, T. F.; Bautista, M. T.; Hofstede, T. M.; Morris,
R. H.; Sawyer, J. F. J. Am. Chem. Soc. 1989, 111, 8823.
(19) Ho, N. N.; Bau, R.; Mason, S. A. J. Organomet. Chem. 2003, 676,
85.
(20) 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.
1-H2(H2), the observation of a single peak in the iron-hydride
region demonstrates rapid exchange between the Fe-H and
7256 Inorganic Chemistry, Vol. 45, No. 18, 2006

Bis(diisopropylphosphino)pyridine Iron Complexes
Figure 5. Proposed pathway for isotopic exchange in 1-H(Si)N2 upon treatment with D2 gas.
η2-H2 ligand. The benzene-d6 EXSY NMR spectrum (500
ms mixing time) established no exchange between the iron-
hydride/dihydrogen ligands and the silicon hydrogens on the
NMR time scale. Based on these observations, one of the
three possible isomers, the one in which the iron-hydride
and the η2-H2 are trans, was eliminated.
precursor. A neutral example, relevant to the compounds
reported in this work, is (Ph2EtP)3FeH2(H2), originally
prepared by Aresta and co-workers.30 Subsequent neutron
diffractions studies established an iron(II) dihydrogen-
dihydride complex where the η2-H2 ligand rapidly exchanges
with the iron-hydrides on the NMR time scale even at low
temperature.20 In cases where the hydride and η2-dihydrogen
are cis, the rapid exchange has been rationalized by a
phenomenon termed the “cis-effect” rather than by oxidation
to iron(IV).17,20,31,32 The rationale for this effect is an
electrostatic attraction between the iron-hydride and the η2-
dihydrogen ligand via a diplole/induced dipole interaction,
e.g., Fe-Hδ-‚‚‚Hδ+-Hδ-. Such an interaction is plausible
and would account for the rapid exchange observed in both
1-H2(H2) and 1-H(Si)(H2). To our knowledge, such an
interaction has not been computed for exchange with silane
ligands and oxidative addition to Fe(IV) may be required to
account for the slower isotopic exchange into the silyl ligand.
Simple ligand substitution reactions were also studied with
both 1-H2(N2) and 1-H(Si)N2. Addition of 4 atm of carbon
monoxide to 1-H2(N2) induced rapid reductive elimination
of H2 and formation of the dicarbonyl complex, 1-(CO)2 (eq
6). Performing the same experiment with 1-H(Si)N2 resulted
Observation of both 1-H(Si)N2 and 1-H(Si)(H2) again
suggests slow dissociation of N2 in the substitution of
dihydrogen for dinitrogen. Complete conversion to 1-H-
(Si)(H2) was not observed after multiple additions of 4 atm
of dihydrogen, demonstrating the affinity of the iron for N2
relative to H2. To probe if a silane σ-complex was accessible,
1-H(Si)N2 was treated with 4 atm of D2. As expected, the
iron-hydride resonance disappeared rapidly with concomitant
1
loss of H-D gas as evidenced by H NMR spectroscopy.
At slightly longer reaction times, disappearance of the silicon
hydride resonances was also observed, establishing the
intermediacy of a silane σ-complex (Figure 5). To account
for the observation of free H-D, dissociative substitution
of D2 for η2-H-D occurs, most likely from the isomer where
the σ ligand is trans to the silyl, a result of the strong trans
effect of silyl ligands.21 Isotopic exchange with benzene-d6
was not observed with either 1-H2(N2) or 1-H(Si)N2.
The rapid exchange of the hydride ligands in both
1-H2(H2) and 1-H(Si)(H2) is intriguing in light of results
concerning the structure and dynamics of iron hydride-
dihydrogen complexes where these two ligands are cis. The
majority of known iron hydride-dihydrogen compounds are
cationic bis(diphosphine) compounds where the Fe-H is
trans to the η2-H2 ligand.22-25 Other cationic examples where
the hydride and η2-dihydrogen are cis have been reported
with tetradentate phosphine chelates26-29 and are generally
prepared by protonation of the neutral iron dihydride
in substitution of the dinitrogen ligand with carbon monoxide
to form 1-H(Si)CO (eq 6). Extended thermolysis of 1-H-
(Si)CO at 95 °C for 1 week under excess CO produced
approximately 50% conversion to 1-(CO)2, establishing the
higher barrier for Si-H reductive coupling and dissociation
compared to H2.
The solid-state (KBr) infrared spectrum of 1-H(Si)CO
exhibited a strong carbonyl band centered at 1879 cm-1, a
higher frequency than those observed with 1-(CO)2, consis-
tent with an iron(II) center in the former. A diagnostic iron-
(21) Dioumaev, V. K.; Procopio, L. J.; Caroll, P. J.; Berry, D. H. J. Am.
Chem. Soc. 2003, 125, 8043.
(22) Gilbertson, J. D.; Szymczak, N. K.; Tyler, D. R. Inorg. Chem. 2004,
43, 3341.
(23) Morris, R. H.; Sawyer, J. F.; Shiralian, M.; Zubkowski, J. D. J. Am.
Chem. Soc. 1985, 107, 5581.
(24) Bautista, M.; Earl, K. A.; Morris, R. H.; Sella, A. J. Am. Chem. Soc.
1987, 109, 3780.
(25) Helleren, C. A.; Henderson, R. A.; Leigh, G. J. J. Chem. Soc., Dalton
Trans. 1999, 1213.
(26) Field, L. D.; Li, H. L.; Messerle, B. A.; Smernik, R. J.; Turner, P.
Dalton Trans. 2004, 1418.
(27) Bampos, N.; Field, L. D. Inorg. Chem. 1990, 29, 587.
(28) Jia, G.; Drouin, S. D.; Jessop, P. G.; Lough, A. J.; Morris, R. H.
Organometallics 1993, 12, 906.
(29) (a) Bianchini, C.; Peruzzini, M.; Polo, A.; Vacca, A.; Zanobini, F.
Gazz. Chim. Ital. 1991, 121, 543. (b) Bianchini, C.; Peruzzini, M.;
Zanobini, F. J. Organomet. Chem. 1988, 354, C19.
(30) Aresta, M.; Giannoccaro, P.; Rossi, M.; Sacco, A. Inorg. Chim. Acta
1971, 5, 115.
Inorganic Chemistry, Vol. 45, No. 18, 2006 7257

Trovitch et al.
Figure 6. (a) Molecular structure of 1-H(Si)CO depicted with 30% probability ellipsoids. (b) View of the core of the molecule highlighting the distortion
from idealized octahedral coordination. Hydrogen atoms, except for the iron-hydride and silicon hydrogens, omitted for clarity.
hydride resonance was observed at -6.41 ppm by 1H NMR
spectroscopy, and a single 31P peak was identified at 103.86
ppm. 1-H(Si)CO was also characterized by single-crystal
X-ray diffraction. A representation of the solid-state structure
is presented in Figure 6, and selected metrical parameters
are reported in Table 2. A similar distortion from idealized
octahedral geometry is observed with 1-H(Si)CO as was with
its dinitrogen congener. The P(1)-Fe(1)-P(2) and N(1)-
Fe(1)-Si(1) angles of 160.761(19)° and 167.02(4)° are
deviated from linearity as is the H(1M)-Fe(1)-C(26) angle
of 166.2(9)°. A slightly more pronounced silicon-iron
hydride interaction is evident in the carbonyl compound with
a Si(1)-Fe(1)-H(1) angle of 75.9(9)°.
The C(26)-O(1) bond length of 1.1635(19) Å is slightly
shorter than the corresponding values of 1.1734(11) Å found in
the iron(0) complex, 1-(CO)2. The distance between the iron-
hydride and the silyl ligand of 2.41(2) Å is comparable to the
dinitrogen complex, 1-H(Si)N2, and is outside the sum of the
covalent radii. In addition, a short N(1)-C(2) distance of
1.359(2) Å is found in the pyridine ring, indicating that the lig-
and is not involved in electron-transfer processes with the iron.
Treatment of 1-H(Si)N2 with 1 equiv of PMe3 produced
a similar outcome as carbon monoxide, resulting in substitu-
tion of the N2 by the phosphine (eq 7). Assignment of the
triplet of doublets centered at -9.97 ppm. Notably, the
coupling to the cis phosphines on the iPrPNP ligand is 67
Hz, larger than the value of 21.0 Hz determined for the
coupling to the “trans” PMe3 ligand. The origin of the
unusual magnitudes of the coupling constants is believed to
be a result of the distortion from idealized octahedral
geometry in analogy to the solid-state structures of 1-H(Si)N2
and 1-H(Si)CO. In this arrangement, the distortion of the
Me3P-Fe-H bond from linearity reduces the coupling
constant.
Because unusual coupling constants were observed with
1-H(Si)PMe3, the spin-spin coupling in molecules of known
stereochemistry was examined. The cis H-Fe-Si coupling
constants in 1-H(Si)N2 and 1-H(Si)CO are similar with
values of 28.0 and 25.0 Hz, respectively. A smaller coupling
constant of 12.5 Hz was measured for 1-H(Si)PMe3. The
isotopically labeled compound, 1-H(Si)13CO was prepared
in a straightforward manner by treatment of 1-H(Si)N2 with
13CO. The trans H-Fe-13C coupling constant of 10.5 Hz is
smaller than the cis P-Fe-13C coupling constant of 14.0
Hz. However, these values must be treated with caution as
the coupling to different atoms may not be compared directly
and previous work by Whitesides and Maglio has demon-
strated that H-M-13C coupling constants are not directly
related to stereochemistry.33
To gain additional insight about the poor performance of
1-H(Si)N2 in catalytic hydrosilation, reactions with olefins
and alkynes were explored. Addition of a large excess (>50
equiv) of 2-butyne to 1-H(Si)N2 resulted in immediate loss
of the iPrPNP ligand, as judged by 1H and 31P NMR
spectroscopy (eq 8). Analysis of the organic products by mass
stereochemistry of 1-H(Si)PMe3 was accomplished by two-
dimensional NOESY NMR spectroscopy. Cross-peaks were
observed between the iron hydride, the Si-H peaks, and the
ortho-phenyl of the silyl ligand. Notably, no cross-peaks were
observed between the phosphine ligand and the iron hydride,
suggesting a trans arrangement. The iron-hydride resonance
spectrometry and NMR spectroscopy revealed formation of
hexamethylbenzene and (Me(H)C ) (Me)C)2PhSiH. The iron
product(s) of the reaction has not been identified.
1
was observed by H NMR spectroscopy in benzene-d6 as a
7258 Inorganic Chemistry, Vol. 45, No. 18, 2006

Bis(diisopropylphosphino)pyridine Iron Complexes
respectively, using Inova 400 and 500 spectrometers. 1H and
{1H}13C NMR chemical shifts are reported in ppm downfield from
tetramethylsilane using 1H (residual) chemical shifts of the solvent
as a secondary standard. {1H}31P NMR and 31P chemical shifts are
reported downfield from H3PO4 and referenced to an external 85%
H3PO4 solution. Single crystals suitable for X-ray diffraction were
coated with polyisobutylene oil in a drybox and were quickly
transferred to the goniometer head of a Bruker ×8 APEX2 system
equipped with a molybdenum X-ray tube (λ ) 0.71073 A).
Preliminary data revealed the crystal system. A hemisphere routine
was used for data collection and determination of lattice constants.
The space group was identified and the data were processed using
the Bruker SAINT program and corrected for absorption using
SADABS. The structures were solved using direct methods
(SHELXS) completed by subsequent Fourier synthesis and refined
by full-matrix least-squares procedures. Elemental analyses were
performed at Robertson Microlit Laboratories, Inc. in Madison, NJ.
Similar experiments were conducted with olefins. Treat-
ment of 1-H(Si)N2 with a large excess (>50 equiv) of
1-hexene or cyclohexene produced no change in the 1H NMR
spectrum over the course of days at 23 °C. In contrast,
addition of a large excess of ethylene yielded (diethyl)-
phenylsilane, Et2PhSiH, along with a yellow powder that is
insoluble in most common organic solvents. While the exact
identity of this compound is unknown at this time, degrada-
tion experiments establish an iron compound containing
iPrPNP and ethylene-derived ligands. This material is unre-
active toward excess olefin and silanes, offering insight into
the inability of 1-H(Si)N2 to catalyze olefin hydrosilation.
Concluding Remarks
The studies described herein highlight the ability of
saturated bis(phosphino)pyridine ligands to engender more
reducing iron centers than aryl-substituted bis(imino)pyridine
chelates. In addition to more reduced carbonyl ligands, the
pincer-ligated compounds promote oxidative addition of
dihydrogen and phenyl silane forming observable ferrous
dihydride and silyl hydride compounds. Exposure of these
molecules to a dihydrogen atmosphere allowed observation
of dihydrogen σ-complexes where the iron-hydride and the
η2-dihydrogen ligands are in rapid exchange in solution.
These compounds, unlike the bis(imino)pyridine counter-
parts, do not engage in redox processes with the iron center
and hence are more prone to dissociation.
Preparation of [(2,6-iPr2PCH2)2C5H3N]Fe(CO)2 (1-(CO)2). A
thick-walled reaction vessel was charged with 0.500 g (0.901 mmol)
of 1-Br2 and ∼50 mL of pentane. A 0.5% sodium amalgam
prepared from 0.104 g (4.51 mmol) of sodium metal and 21.7 g
(901 mmol) of mercury was added to the vessel, and the resulting
slurry was frozen to liquid nitrogen temperature. On a high-vacuum
line, the vessel was evacuated and 1 atm of carbon monoxide was
added at -196 °C. The resulting reaction mixture was warmed to
ambient temperature and stirred for 48 h, over which time a royal
blue solution formed. The carbon monoxide was then removed from
the vessel, and the solution decanted away from the amalgam and
filtered through Celite. The filtrate was collected and the solvent
was removed in vacuo to yield 0.394 g (97%) of a red solid
identified as 1-(CO)2. Analysis for C21H35FeNO2P2: Calcd C, 55.89;
Experimental Section
1
H, 7.82; N 3.10. Found: C, 55.36; H, 7.65; N, 2.77. H NMR
General Considerations. All air- and moisture-sensitive ma-
nipulations were carried out using standard vacuum line, Schlenk,
and cannula techniques or in an MBraun inert atmosphere drybox
containing an atmosphere of purified nitrogen. The MBraun drybox
was equipped with a cold well designed for freezing samples in
liquid nitrogen. Solvents for air- and moisture-sensitive manipula-
tions were initially dried and deoxygenated using literature proce-
dures.34 Argon and hydrogen gas were purchased from Airgas
Incorporated and passed through a column containing manganese
oxide supported on vermiculite and 4 Å molecular sieves before
admission to the high-vacuum line. Benzene-d6 was purchased from
Cambridge Isotope Laboratories and distilled from 4 Å molecular
sieves under an atmosphere of argon and stored over 4 Å molecular
sieves and sodium metal. Carbon monoxide was purchased from
Aldrich and passed through a liquid nitrogen trap before use.
Ethylene was purchased from Aldrich, passed through a liquid-
nitrogen-cooled trap, and stored over a slurry of activated MAO in
toluene before use. Sodium triethylborohydride was obtained from
Aldrich in a 1.0 M solution in toluene and used as received.
Phenylsilane, 1-hexene, cyclohexene, trimethylphosphine, and 2-bu-
tyne were purchased from Acros or Aldrich and dried over activated
molecular sieves before use. The iron(II) dihalide complexes, 1-Cl2
and 1-Br2, were prepared as described previously.11
(benzene-d6): δ ) 1.17 (pseudo q, JHH ) 6.5 Hz, 12H, CH(CH3)2),
1.23 (pseudo q, JHH ) 6.5 Hz, 12H, CH(CH3)2), 2.16 (m, 4H,
CH(CH3)2), 2.79 (m, 4H, PCH2), 6.34 (d, JHH ) 7.0 Hz, 2H, 3,5
py-H), 6.55 (t, JHH ) 7.0 Hz, 1H, 4 py-H). 13C NMR (THF-d8): δ
) 18.72 (s, CH(CH3)2), 18.74 (s, CH(CH3)2), 28.80 (t, JPC ) 10.5
Hz, CH(CH3)2), 41.15 (t, JPC ) 8.5 Hz, PCH2), 119.28 (t, JPC
)
5.0 Hz, 3,5 py-C), 131.15 (s, 4 py-C), 162.49 (t, JPC ) 6.0 Hz, 2,6
py-C), 223.07 (t, JPC ) 27.0 Hz, Fe-CO). {1H}31P NMR (THF-d8):
δ ) 109.59 (s). IR (KBr): νCO ) 1794, 1842 cm-1
.
Preparation of [(2,6-iPr2PCH2)2C5H3N]FeH2(N2) (1-H2(N2)).
A 100 mL round-bottomed flask was charged with 1.00 g (2.16
mmol) of 1-Cl2 and ∼50 mL of diethyl ether. The resulting slurry
was frozen in a liquid-nitrogen-cooled cold well. To the thawing
slurry, 0.543 g (4.32 mmol) of NaBEt3H (from a 1.0 M solution in
toluene) was added dropwise to the flask. Immediately upon
addition, a dark purple solution formed. The reaction mixture was
stirred for 1 h and then filtered through Celite. The filtrate was
collected and the solvent removed in vacuo. The resulting residue
was washed three times with small portions of diethyl ether to yield
0.333 g (36%) of a red-orange solid identified as 1-H2(N2). Analysis
for C19H37FeN3P2: Calcd C, 53.66; H, 8.77; N 9.88. Found: C,
53.95; H, 8.46; N, 10.18. 1H NMR (benzene-d6): δ ) -17.65 (td,
JHH ) 21.5 Hz, JPH ) 52.0 Hz, 1H, Fe-H), -12.54 (td, JHH ) 21.5
Hz, JPH ) 60.5 Hz, 1H, Fe-H), 0.91 (pseudo q, JHH ) 7.0 Hz, 6H,
CH(CH3)2), 1.21 (pseudo q, JHH ) 7.0 Hz, 6H, CH(CH3)2), 1.31
(m, 12H, CH(CH3)2), 1.94 (m, 2H, CH(CH3)2), 2.29 (m, 2H,
CH(CH3)2), 2.90 (m, 2H, PCH2), 3.07 (m, 2H, PCH2), 6.48 (d, JHH
) 7.0 Hz, 2H, 3,5 py-H), 6.63 (t, JHH ) 7.0 Hz, 1H, 4 py-H). 13C
NMR (benzene-d6): δ ) 19.06 (s, CH(CH3)2), 19.22 (s, CH(CH3)2),
20.04 (s, CH(CH3)2), 20.15 (s, CH(CH3)2), 26.74 (t, JPC ) 14.0
Hz, CH(CH3)2), 27.77 (t, JPC ) 6.5 Hz, CH(CH3)2), 41.70 (t, JPC
1H, 13C, and 31P NMR spectra were recorded at 399.780 or
500.62, 101.535 or 125.893, and 161.833 or 202.648 MHz,
(31) Bianchini, C.; Masi, D.; Peruzzini, M.; Casarin, M.; Maccato, C.; Rizzi,
G. A. Inorg. Chem. 1997, 36, 1061.
(32) (a) Jackson, S. A.; Eisenstein, O. Inorg. Chem. 1990, 29, 3410. (b)
Riehl, J.-F.; Pe´lissier, M.; Eisenstein, O. Inorg. Chem. 1992, 31, 3344.
(33) Whitesides, G. M.; Maglio, G. J. Am. Chem. 1969, 91, 4980.
(34) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.
Inorganic Chemistry, Vol. 45, No. 18, 2006 7259

Trovitch et al.
) 5.5 Hz, PCH2), 118.07 (t, JPC ) 4.5 Hz, 3,5 py-C), 130.57 (s, 4
py-C), 164.47 (t, JPC ) 6.0 Hz, 2,6 py-C). {1H}31P NMR (benzene-
C), 162.86 (t, JPC ) 5.5 Hz, 2,6 py-C), 220.89 (t. JPC ) 14.0 Hz,
Fe-CO). {1H}31P NMR (benzene-d6): δ ) 103.86 (s). IR (KBr):
d6): δ ) 108.28 (s). 31P NMR (benzene-d6): δ ) 108.28 (t, JPH
)
νCO ) 1879 cm-1
.
52.0 Hz). IR (KBr): νNN ) 2016 cm-1
.
Preparation of [(2,6-iPr2PCH2)2C5H3N]FeH(SiH2Ph)(P(CH3)3)
(1-H(Si)PMe3). This compound was prepared in a manner similar
to that described for 1-H(Si)CO using 0.040 g (0.075 mmol) of
1-H(Si)N2 and 1 equiv of PMe3 yielding 0.035 g (80%) of a dark
purple solid identified as 1-H(Si)PMe3. Analysis for C28H52-
FeNOP3Si: Calcd C, 58.03; H, 9.04; N, 2.42. Found: C, 57.87;
H, 9.29; N, 2.31. 1H NMR (benzene-d6): δ ) -9.97 (td, JPH (PMe3)
) 21.0 Hz, JPH (PiPr2) ) 67.0 Hz, 1H, Fe-H), 0.97 (pseudo q, JHH
) 6.5 Hz, 6H, CH(CH3)2), 1.07 (pseudo q, JHH ) 6.5 Hz, 6H,
CH(CH3)2), 1.10 (d, JPH ) 5.5 Hz, 9H, P(CH3)3), 1.29 (pseudo q,
JHH ) 6.5 Hz, 6H, CH(CH3)2), 1.39 (pseudo q, JHH ) 6.5 Hz, 6H,
CH(CH3)2), 2.16 (m, 2H, CH(CH3)2), 2.43 (m, 2H, CH(CH3)2), 2.60
(m, 2H, PCH2), 3.03 (m, 2H, PCH2) 4.94 (q, JPH ) 7.0 Hz, 1H,
SiH2), 4.95 (q, JPH ) 7.0 Hz, 1H, SiH2), 6.41 (d, JHH ) 7.5 Hz,
Preparation of [(2,6-iPr2PCH2)2C5H3N]FeH(SiH2Ph)N2 (1-
H(Si)N2). A 100 mL round-bottomed flask was charged with 0.635
g (1.36 mmol) of 1-Cl2, 0.147 g (1.36 mmol) of phenylsilane and
∼60 mL of diethyl ether. After the solution was chilled in a liquid-
nitrogen-cooled cold well for 15 min, 0.332 g (2.73 mmol) of
NaBEt3H (from a 1.0 M solution in toluene) was slowly added
dropwise while stirring. After 3 h, the orange reaction mixture was
filtered through Celite and the solvent was removed in vacuo.
Recrystallization of the resulting residue from pentane at -35 °C
yielded 0.588 g (81%) of an orange solid identified as 1-H(Si)N2.
Analysis for C25H43FeN3P2Si: Calcd C, 56.49; H, 8.15; N 7.91.
1
Found: C, 56.53; H, 8.37; N, 7.64. H NMR (benzene-d6): δ )
-13.12 (t, JPH ) 57.5 Hz, 1H, Fe-H), 0.64 (pseudo q, JHH ) 7.0
Hz, 6H, CH(CH3)2), 0.94 (pseudo q, JHH ) 7.0 Hz, 6H, CH(CH3)2),
1.26 (m, 12H, CH(CH3)2), 2.16 (m, 2H, CH(CH3)2), 2.39 (m, 2H,
CH(CH3)2), 2.71 (m, 2H, PCH2), 2.97 (m, 2H, PCH2), 4.94 (t, JPH
) 5.5 Hz, 1H, SiH2), 4.95 (t, JPH ) 5.5 Hz, 1H, SiH2), 6.48 (d, JHH
) 7.5 Hz, 2H, 3,5 py-H), 6.68 (t, JHH ) 7.5 Hz, 1H, 4 py-H), 7.23
(m, 1H, 4 phenyl-H), 7.35 (m, 2H, 3,5 phenyl-H), 8.15 (m, 2H, 2,6
phenyl-H). 13C NMR (benzene-d6): δ ) 17.87 (s, CH(CH3)2), 18.32
(s, CH(CH3)2), 18.92 (s, CH(CH3)2), 19.20 (s, CH(CH3)2), 25.47
(t, JPC ) 14.0 Hz, CH(CH3)2), 27.48 (t, JPC ) 7.5 Hz, CH(CH3)2),
38.47 (t, JPC ) 5.0 Hz, PCH2), 118.84 (t, JPC ) 4.0 Hz, 3,5 py-C),
126.79 (s, 4 phenyl-C), 127.57 (s, 3,5 phenyl-C), 132.78 (s, 4 py-
C), 136.29 (s, 2,6 phenyl-C), 149.48 (s, 1 phenyl-C), 163.33 (t, JPC
) 5.5 Hz, 2,6 py-C). {1H}31P NMR (benzene-d6): δ ) 96.85 (s).
2H, 3,5 py-H), 6.53 (t, JHH ) 7.5 Hz, 1H, 4 py-H), 7.21 (t, JHH
)
7.5 Hz, 1H, 4 phenyl-H), 7.53 (t, JHH ) 7.5 Hz, 2H, 3,5 phenyl-
H), 8.32 (d, JHH ) 7.5 Hz, 2H, 2,6 phenyl-H). 13C NMR (benzene-
d6): δ ) 19.89 (s, CH(CH3)2), 20.11 (s, CH(CH3)2), 20.63 (s,
CH(CH3)2), 20.90 (s, CH(CH3)2), 22.15 (d, JPC ) 17.0 Hz, P(CH3)3),
28.94 (m, CH(CH3)2), 32.17 (m, CH(CH3)2), 44.26 (t, JPC ) 3.0
Hz, PCH2), 117.45 (t, JPC ) 5.0 Hz, 3,5 py-C), 126.48 (s, 4 phenyl-
C), 127.06 (s, 3,5 phenyl-C), 128.68 (s, 4 py-C), 137.66 (s, 2,6
phenyl-C), 150.78 (m, 1 phenyl-C), 164.13 (t, JPC ) 5.5 Hz, 2,6
py-C). {1H}31P NMR (benzene-d6): δ ) 9.83 (t, JPP ) 18.0 Hz,
PMe3), 86.49 (d, JPP ) 18.0 Hz, PiPr2). {CH}31P NMR (benzene-
d6): δ ) 9.83 (pseudo q, JPP ) 18.0 Hz, JPH ) 21.0 Hz, PMe3),
86.49 (dd, JPP ) 18.0 Hz, JPH ) 67.0 Hz, PiPr2).
IR (KBr): νNN ) 2032 cm-1
.
Observation of [(2,6-iPr2PCH2)2C5H3N]FeH(SiH2Ph)(H2) (1-
H(Si)(H2)). A J. Young tube was charged with 0.010 g (0.02 mmol)
of 1-H(Si)N2 and ∼0.5 mL of benzene-d6. The tube was submerged
in liquid nitrogen and evacuated on a high-vacuum line. At this
temperature, 1 atm of H2 was admitted and the tube sealed, thawed,
and shaken. Monitoring the reaction by multinuclear NMR spec-
troscopy established growth of 1-H(Si)(H2) over the course of hours
Preparation of [(2,6-iPr2PCH2)2C5H3N]FeH(SiH2Ph)CO (1-
H(Si)CO). A thick-walled reaction vessel was charged with 0.200
g (0.376 mmol) of 1-H(Si)N2 and ∼50 mL of pentane. The vessel
was submerged in liquid nitrogen and evacuated. At this temper-
ature, 1 atm of carbon monoxide was added. The resulting reaction
mixture was warmed to ambient temperature and stirred for 3 h,
forming a green solution. After 2 days of stirring, the vessel was
submerged in liquid nitrogen and evacuated. The solvent was
removed in vacuo and the resulting residue recrystallized from
diethyl ether at -35 °C to yield 0.117 g (56%) of an olive green
solid identified as 1-H(Si)CO. Analysis for C26H43FeNOP2Si: Calcd
C, 58.75; H, 8.15; N, 2.64. Found: C, 58.50; H, 8.03; N, 2.76. 1H
NMR (benzene-d6): δ ) -6.41 (t, JPH ) 55.0 Hz, 1H, Fe-H), 0.67
1
at 23 °C. H NMR (benzene-d6): δ ) -9.37 (br s, 3H, Fe-H),
0.94 (pseudo q, JHH ) 7.0 Hz, 12H, CH(CH3)2), 1.14 (pseudo q,
JHH ) 7.0 Hz, 12H, CH(CH3)2), 2.04 (m, 4H, CH(CH3)2), 2.84 (m,
4H, PCH2), 5.54 (m, 2H, SiH2), 6.45 (d, JHH ) 8.0 Hz, 2H, 3,5
py-H), 6.68 (t, JHH ) 8.0 Hz, 1H, 4 py-H), 7.21 (t, JHH ) 7.5 Hz,
1H, 4 phenyl-H), 7.33 (t, JHH ) 7.5 Hz, 2H, 3,5 phenyl-H), 8.23
(d, JHH ) 7.5 Hz, 2H, 2,6 phenyl-H). {1H}31P NMR (benzene-d6):
δ ) 108.36 (s).
(pseudo q, JHH ) 7.0 Hz, 6H, CH(CH3)2), 0.96 (pseudo q, JHH
)
7.0 Hz, 6H, CH(CH3)2), 1.26 (pseudo q, JHH ) 7.0 Hz, 6H,
CH(CH3)2), 1.35 (pseudo q, JHH ) 7.0 Hz, 6H, CH(CH3)2), 2.14
(m, 2H, CH(CH3)2), 2.24 (m, 2H, CH(CH3)2), 2.74 (m, 2H, PCH2),
2.88 (m, 2H, PCH2), 4.94 (t, JPH ) 5.0 Hz, 1H, SiH2), 4.95 (t, JPH
) 5.0 Hz, 1H, SiH2), 6.40 (d, JHH ) 7.5 Hz, 2H, 3,5 py-H), 6.66
(t, JHH ) 7.5 Hz, 1H, 4 py-H), 7.22 (t, JHH ) 7.5 Hz, 1H, 4 phenyl-
H), 7.33 (t, JHH ) 7.5 Hz, 2H, 3,5 phenyl-H), 8.21 (d, JHH ) 7.5
Hz, 2H, 2,6 phenyl-H). 13C NMR (benzene-d6): δ ) 17.63 (s,
CH(CH3)2), 18.03 (s, CH(CH3)2), 18.61 (s, CH(CH3)2), 19.18 (s,
Acknowledgment. We thank the David and Lucile
Packard Foundation for financial support. P.J.C. is a Cottrell
Scholar sponsored by the Research Corporation and a
Camille Dreyfus Teacher-Scholar. R.J.T. also thanks Cornell
University for partial support through a graduate fellowship.
Supporting Information Available: Crystallographic data for
1
1-(CO)2, 1-H(Si)N2, and 1-H(Si)CO as cif files and a sample H
CH(CH3)2), 25.39 (t, JPC ) 13.0 Hz, CH(CH3)2), 27.00 (t, JPC
)
NMR spectrum for 1-(CO)2. This material is available free of charge
via the Internet at http://pubs.acs.org.
10.0 Hz, CH(CH3)2), 39.50 (t, JPC ) 6.5 Hz, PCH2), 118.69 (t, JPC
) 4.5 Hz, 3,5 py-C), 126.13 (s, 4 phenyl-C), 127.52 (s, 3,5 phenyl-
C), 133.17 (s, 4 py-C), 136.38 (s, 2,6 phenyl-C), 149.37 (s, 1 phenyl-
IC0608647
7260 Inorganic Chemistry, Vol. 45, No. 18, 2006