Bidentate coordination of pyrazolate in low-coordinate iron(II) and nickel(II) complexes

Article abstract of DOI:10.1002/anie.200503535

(Chemical Equation Presented) The first Fe^II and Ni^II complexes with bidentate pyrazolate ligands have been prepared (see scheme; M = Fe^II, Ni^II; R = tBu, Me; Ar = 2,6-iPr₂C ₆H₃;

Full text of DOI:10.1002/anie.200503535

Angewandte
Chemie
Coordination Modes
The endo-bidentate (h2-pyrazolate) coordination mode
(Figure 1b) was long thought to be prevented by the opposing
directionality of the two pyrazolate nitrogen lone pairs. More
recently, h2-pyrazolate coordination has been established for
the lanthanides, actinides, alkali and alkaline earth metals,
and early transition metals in high oxidation states.[11–13] h2-
Pyrazolate coordination to transition-metal ions with partially
filled d shells is rare[11] and is limited to a few well-
characterized examples with TiIII (d1),[14] VIII(d2),[15] MoIV
(d2),[8] CrIII (d3),[16] MoII (d4),[17] and FeIII (d5).[16]
DOI: 10.1002/anie.200503535
Bidentate Coordination of Pyrazolate in Low-
Coordinate Iron(ii) and Nickel(ii) Complexes**
Javier Vela, Sridhar Vaddadi, Savariraj Kingsley,
Christine J. Flaschenriem, Rene J. Lachicotte,
Thomas R. Cundari,* and PatrickL. Holland*
Bulky b-diketiminate ancillary ligands have enabled the
isolation and study of late, first-row transition-metal com-
plexes with coordination numbers three and four.[18–20]
Herein, it is shown that the steric protection of a b-
diketiminate stabilizes the first h2-pyrazolate complexes
with d6 and d8 electron configurations, and these show
different coordination geometries. Interestingly, a bridging
pyrazolate binding mode is also accessible in the complexes,
and the balance between the different pyrazolate coordina-
tion modes is explored through solution spectroscopic meth-
ods.
Pyrazolate ligands have rich coordination chemistry
(Figure 1) that includes exo-bidentate bridging (m-h1:h1,
Treatment of [LtBuMCl] (LtBu = 2,2,6,6-tetramethyl-3,5-
bis(2,6-diisopropylphenylimino)hept-4-yl; M = Fe, Ni)[19]
with a freshly prepared solution of potassium 3,5-dimethyl-
pyrazolate (Kdmp) in tetrahydrofuran (THF) affords the
complexes [LtBuFe(h2-dmp)] and [LtBuNi(h2-dmp)] in 89 and
72% yields, respectively (Scheme 1a).[21] The monomeric
nature and endo-bidentate ligation of the dmp ligand in these
complexes was confirmed by X-ray diffraction studies
(Figure 2).
Figure 1. Typical coordination modes of pyrazolate ligands (R=H,
alkyl, or aryl) towards metal ions (M, M’). a) exo-bidentate; b) endo-
bidentate; c) monodentate; d) pentadentate.
Figure 1a, most commonly observed),[1,2] endo-bidentate (h2,
Figure 1b), terminal monodentate (h1, Figure 1c), and side-
on, pentadentate (h5, Figure 1d) coordination modes.[3,4]
Because of this diversity in coordination modes, pyrazolates
are potentially useful in devising synthetically useful process-
es in which the presence of a hemilabile ligand is required, as
well as in the construction of metal architectures for
catalysis,[5–8] luminescent materials,[9] and chemical vapor
deposition.[10]
[*] S. Vaddadi, Prof. T. R. Cundari
Department of Chemistry
University of North Texas
Denton, TX 76203 (USA)
Fax: (+1)940-565-4318
E-mail: tomc@unt.edu
Dr. J. Vela, Dr. S. Kingsley, C. J. Flaschenriem, Dr. R. J. Lachicotte,
Prof. P. L. Holland
Department of Chemistry
University of Rochester
Scheme 1.
Rochester, NY 14627 (USA)
Fax: (+1)585-276-0205
The coordination geometry around the iron center in the
14-electron complex [LtBuFe(h2-dmp)] is intermediate
between tetrahedral and square planar; the twist angle
between the pyrazolato and diketiminato (C3N2Fe) planes is
E-mail: holland@chem.rochester.edu
[**] The authors acknowledge funding from the Petroleum Research
Fund (38275-G; P.L.H.), the A. P. Sloan Foundation (P.L.H.), the
University of Rochester (Messersmith Fellowship; J.V.), and the US
Departments of Education and Energy (DOE-FG02-97ER14811;
T.R.C.). A portion of the calculations were performed on the UNT
computational chemistry resource, for which S.V. and T.R.C.
acknowledge the NSF for support through grant CHE-0342824. J.V.
thanks Sandip Sur for help with DEPT and 2D NMR experiments
and Dr. Azwana R. Sadique for advice on synthetic procedures.
À
35.62(7)8 (Figure 2a). The pyrazolate Fe N bonds (2.031(1)
À
and 2.048(1) Š) are longer than the diketiminate Fe N bonds
À
(1.988(1) and 2.001(1) Š). They are also longer than the Fe N
bonds reported for the homoleptic complex tris(3,5-di-tert-
butylpyrazolato)iron(iii) (2.009 Š).[16] The 1H NMR spectrum
shows paramagnetically shifted resonances, which have been
assigned on the basis of relative integrations (see the
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
Angew. Chem. Int. Ed. 2006, 45, 1607 –1611
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1607

Communications
Figure 3. B3LYP/SBKJC(d)-optimized geometries of singlet C2v-symmet-
ric [L’Ni(h2-pz)] (top) and quintet C2-symmetric [L’Fe(h2-pz)] (bottom).
All geometries correspond to energy minima. Bond lengths are in Š;
bond angles are in degrees. The twist angle is 08 in the nickel
compound and 908 in the iron compound.
Figure 2. Molecular structures of iron(ii) (a, c) and nickel(ii) (b, d)
diketiminate complexes containing either endo-bidentate (h2) (a, b) or
exo-bidentate (m-(h1:h1)) (c, d) 3,5-dimethylpyrazolato coordination.
Thermal ellipsoids drawn at 50% probability; hydrogen atoms omitted
for clarity.
Supporting Information). The solution magnetic moment is
5.1 mB, which is consistent with a high-spin iron(ii) center
having four unpaired electrons and a spin state of S = 2.
In the 16-electron complex [LtBuNi(h2-dmp)], the four
nitrogen atoms and the nickel(ii) center are roughly situated
within a plane (Figure 2b). This is evidenced by a sum of
angles around the metal center of 360.1(6)8, and there is only
a small twist angle of 4.8(1)8 between the pyrazolato and
not suffer from steric obstructions, we infer that the planar
geometry around the nickel center is determined electroni-
cally, whereas the geometry observed for the iron complex is
probably dominated by steric factors.[26]
Treating [LMeM(m-Cl)2Li(thf)2] (M = Fe, Ni)[18,19]—analo-
gous complexes with the slightly smaller diketiminate ligand
LMe
(2,4-bis(2,6-diisopropylphenylimino)pent-3-yl)—with
Kdmp in THF gives the bridged complexes [LMeFe{m-
(h1:h1)-dmp}(m-Cl)Li(thf)2] and [LMeNi{m-(h1:h1)-dmp}(m-
Cl)Li(thf)2] in 85and 76% yields, respectively (Scheme 1a).
The bridging, exo-bidentate nature of the dmp ligand in these
complexes was confirmed by X-ray diffraction studies
(Figure 2).
À
diketiminato (C3N2Ni) planes. The pyrazolate Ni N bond
lengths (1.901(1) and 1.906(1) Š) are again longer than the
À
diketiminate Ni N bond lengths (1.851(1) and 1.852(1) Š).
The 1H NMR spectrum indicates a diamagnetic complex with
well-defined proton resonances and coupling constants, and
the complex has no measurable solution magnetic moment.
Thus, the h2-pyrazolate iron(ii) complex is nonplanar, and
its nickel(ii) analogue is planar. To understand whether this
geometric difference arises from a steric or electronic effect,
we performed density functional theory (DFT) calculations
(B3LYP[22] in conjunction with both double- and triple-zeta-
plus-polarization pseudopotential[23] and all-electron[24] basis
sets) on C2v-symmetric models [L’Fe(h2-pz)] and [L’Ni(h2-pz)]
(L’ represents the truncated b-diketiminate C3N2H5À, and pz
Both the iron(ii) and nickel(ii) heterobridged complexes
À
are tetrahedral (Figure 2). The pyrazolate Fe N (2.033(1) Š)
À
and Ni N (1.959(1) Š) bond lengths are elongated with
respect to those in the endo-bidentate complexes (see above).
The H NMR spectrum of each complex shows broad and
1
paramagnetically shifted resonances. The solution magnetic
moment for the iron(ii) complex is 5.2 mB and is consistent
with a high-spin d6 configuration with four unpaired electrons
and a spin state of S = 2. The nickel(ii) complex has a
magnetic moment of 3.1 mB, which is consistent with a high-
spin d8 configuration (S = 1).
À
represents the parent pyrazolate C3N2H3 ). The geometries
(Figure 3) of the molecules were optimized in the quintet (Fe)
and singlet (Ni) states. A parallel (i.e., square-planar)
coordination geometry is greatly preferred for the nickel
complex (32.2 kcalmolÀ1 at the B3LYP/SBKJC(d) level),
whereas the parallel and perpendicular conformers are
closer in energy for the iron complex (3.8 kcalmolÀ1 at the
B3LYP/SBKJC(d) level), with the perpendicular conformer
slightly preferred. The latter inference was confirmed by
multiconfiguration self-consistent field (MCSCF)[25] geometry
optimization on the [L’Fe(pz)] model complex, which showed
the lowest-energy 5A1 and 5A2 states of the parallel and
perpendicular conformations to be essentially at the same
energy. As the truncated models used in the calculations do
The tert-butyl substituents in LtBu consistently push the
aryl rings closer to the metal center than in the LMe complex
and increase the steric crowding around the metal center.[18,19]
Thus, the different balance between bridging and h2-pyrazo-
late ligation can be rationalized by the different steric
requirements of the two diketiminate ligands used—the
{Li(Cl)(dmp)} “ligand” is more sterically hindering than
dmp itself, thus the bridging pyrazolate complex is forced to
assume the more sterically accessible tetrahedral geometry.
Interestingly, the h2 and bridging forms of the pyrazolate
ligand interconvert in the nickel complexes of the smaller
diketiminate ligand (Scheme 1b). Green solutions of [LMeNi-
1608 www.angewandte.org
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2006, 45, 1607 –1611

Angewandte
Chemie
{m-(h1:h1)-dmp}(m-Cl)Li(thf)2] quickly become pink and form
a white precipitate upon exposure to toluene. Filtration of this
pink solution followed by evaporation of the solvent leads to a
diamagnetic solid ([LMeNi(h2-dmp)]) whose 1H NMR and
electronic spectra are reminiscent of those displayed by
[LtBuNi(h2-dmp)]. Each complex has a band between 522 and
547 nm (e = 440mÀ1 cmÀ1) that is typical of square-planar d8
complexes,[27,28] along with a weaker band at 731–778 nm (e =
150mÀ1 cmÀ1; see Supporting Information). Treatment with a
slight excess of LiCl in THF returned the compound to the
green tetrahedral form. Therefore, we conclude that uptake
and release of the alkali halide by the nickel(ii) pyrazolate
complexes are reversible, solvent-dependent processes. Tol-
uene favors formation of the h2-pyrazolate complex by
decreasing the solubility of LiCl in the organic phase, thus
promoting salt extrusion from the heterobridged species.
Considering that three-coordinate nickel and iron com-
plexes of these bulky diketiminates have been synthesized,[18]
it is surprising that h1-pyrazolate ligands collapse so easily to
the h2 form in the absence of LiCl. DFT calculations of the
nickel complexes were used to evaluate the cause of this
phenomenon. Several different conformations of h1-pyrazo-
late species of truncated [L’Ni(pz)] and full [LtBuNi(dmp)]
were constructed manually from the calculated or experi-
mental h2-pyrazolate structures. The truncated complex was
studied with density functional (B3LYP/SBKJC(d)) methods
and the full complex was studied with hybrid quantum
mechanics/molecular
mechanics
(ONIOM(B3LYP/6-
31G(d):UFF))[29] calculations. In all cases, h1-pyrazolate
complexes relaxed upon geometry optimization either back
to the h2 structures found previously or, in the case of the L’
models, to a higher-energy structure in which the noncoordi-
nated pyrazolate nitrogen atom hydrogen bonds to one of the
1
À
N H bonds of L’. Hence, h -pyrazolate coordination in the
nickel complex is disfavored with respect to h2-pyrazolate
coordination.
As the [L’Ni(h1-pz)] structure does not correspond to a
stable stationary point, the geometry was constructed by
constraining one Ni-Npz-Cpz angle and one Npz-Ni-NL’ angle
while performing B3LYP/SBKJC(d) geometry optimization
of all other degrees of freedom. Analysis of the frontier
molecular orbitals (Figure 4) for the h2-pz (left) and h1-pz
(right) geometry minima of [L’Ni(pz)] at the B3LYP/
SBKJC(d) level reveals that the symmetric (in-phase) and
antisymmetric (out-of-phase) combinations of the pyrazolate
nitrogen lone pairs interact with the appropriate-symmetry Ni
d orbitals. These “s” frontier orbitals decrease in energy upon
coordinating the second nitrogen atom, as described by
Schlegel, Winter, and co-workers for early transition-metal
pyrazolate complexes.[12b,15,16] Whereas the changes in fron-
tier-orbital energies indicate a preference for h2-pz bonding
from the s orbitals (top three orbitals in Figure 4), the frontier
orbitals made up of Ni dp orbitals and p electrons in the
pyrazolate and L’ rings (bottom three orbitals in Figure 4)
predominantly favor h1-pz bonding. In the complexes de-
scribed herein, the preference of the s orbitals for h2-pz
bonding more than counterbalances the preference of the
p orbitals for h1-pz bonding, as can be inferred from the
changes in the frontier-orbital energies. We speculate that the
Figure 4. Changes in s and p frontier orbitals upon transforming
[L’Ni(h1-pz)] (right) into [L’Ni(h2-pz)] (left).
balance between h1 and h2 binding modes could be tuned
through appropriate manipulation of these opposing elec-
tronic effects.
In summary, we have shown the first examples of h2-
pyrazolate complexes of d6 and d8 metal ions. The high d-
electron count of the late transition metals does not exclude
this binding mode. Depending on the steric crowding imposed
by the diketiminate ancillary ligand used, both h2 and h1
coordination to iron(ii) and nickel(ii) can be observed. The
nickel(ii) complexes show solvent-dependent behavior and
Angew. Chem. Int. Ed. 2006, 45, 1607 –1611
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org 1609

Communications
[15] K. R. Gust, J. E. Knox, M. J. Heeg, H. B. Schlegel, C. H. Winter,
Eur. J. Inorg. Chem. 2002, 2327 – 2334.
[16] K. R. Gust, J. E. Knox, M. J. Heeg, H. B. Schlegel, C. H. Winter,
Angew. Chem. 2002, 114, 1661 – 1664; Angew. Chem. Int. Ed.
2002, 41, 1591 – 1594.
adopt either high-spin tetrahedral or diamagnetic square-
planar configurations.
Received: October 5, 2005
[17] G. Zhu, J. M. Tanski, G. Parkin, Polyhedron 2003, 22, 199 – 203.
[18] Recent references: a) N. A. Eckert, E. M. Bones, R. J. Lachi-
cotte, P. L. Holland, Inorg. Chem. 2003, 42, 1720 – 1725; b) N. A.
Eckert, J. M. Smith, R. J. Lachicotte, P. L. Holland, Inorg. Chem.
2004, 43, 3306 – 3321; c) J. Vela, S. Vaddadi, T. R. Cundari, J. M.
Smith, E. A. Gregory, R. J. Lachicotte, C. J. Flaschenriem, P. L.
Holland, Organometallics 2004, 23, 5226 – 5239; d) J. Vela, J. M.
Smith, Y. Yu, N. A. Ketterer, C. J. Flaschenriem, R. J. Lachi-
cotte, P. L. Holland, J. Am. Chem. Soc. 2005, 127, 7857 – 7870.
[19] a) J. M. Smith, R. J. Lachicotte, P. L. Holland, Chem. Commun.
2001, 1542 – 1543; b) P. L. Holland, T. R. Cundari, L. L. Perez,
N. A. Eckert, R. J. Lachicotte, J. Am. Chem. Soc. 2002, 124,
14416 – 14424.
[20] Selected references: a) E. Kogut, A. Zeller, T. H. Warren, T.
Strassner, J. Am. Chem. Soc. 2004, 126, 11984 – 11994; b) D. J. E.
Spencer, A. M. Reynolds, P. L. Holland, B. A. Jazdzewski, C.
Duboc-Toia, L. Le Pape, S. Yokota, Y. Tachi, S. Itoh, W. B.
Tolman, Inorg. Chem. 2002, 41, 6307 – 6321; c) A. Panda, M.
Stender, R. J. Wright, M. M. Olmstead, P. Klavins, P. P. Power,
Inorg. Chem. 2002, 41, 3909 – 3916.
Keywords: coordination modes · density functional
calculations · iron · N ligands · nickel
.
[1] a) A. P. Sadimenko, Adv. Heterocycl. Chem. 2001, 39, 157 – 240;
b) J. E. Cosgriff, G. B. Deacon, Angew. Chem. 1998, 110, 298 –
299; Angew. Chem. Int. Ed. 1998, 37, 286 – 287; c) G. La Monica,
G. A. Ardizzoia, Prog. Inorg. Chem. 1997, 46, 151 – 238; d) A. P.
Sadimenko, S. S. Basson, Coord. Chem. Rev. 1996, 147, 247 – 297;
e) S. Trofimenko, Prog. Inorg. Chem. 1986, 34, 115– 210.
[2] Bridging (exo-bidentate) pyrazolate ligation is formally present
in bis and tris(pyrazolyl)borate complexes: a) S. Trofimenko,
Polyhedron 2004, 23, 197 – 203; b) S. Trofimenko, Chem. Rev.
1993, 93, 943 – 980; c) S. Trofimenko, Chem. Rev. 1972, 72, 497 –
509.
[3] h5-Pyrazolate coordination in ruthenium(ii): J. R. Perera, M. J.
Heeg, H. B. Schlegel, C. H. Winter, J. Am. Chem. Soc. 1999, 121,
4536 – 4537.
[4] Other pyrazolate coordination modes: G. B. Deacon, C. M.
Forsyth, A. Gitlits, R. Harika, P. C. Junk, B. W. Skelton, A. H.
White, Angew. Chem. 2002, 114, 3383 – 3385; Angew. Chem. Int.
Ed. 2002, 41, 3249 – 3251.
[21] Full synthetic, spectroscopic, and crystallographic details are
given in the Supporting Information.
[22] a) A. D. Becke, Phys. Rev. A 1998, 38, 3098 – 3100; b) C. Lee, W.
Yang, R. G. Parr, Phys. Rev. B 1998, 37, 785– 789.
[23] The Stevens pseudopotentials and valence basis sets (W. J.
Stevens, M. Krauss, H. Basch, P. G. Jasien, Can. J. Chem. 1992,
70, 612 – 630) were employed, augmented with d polarization
functions for main-group elements within the GAMESS package
(M. W. Schmidt, K. K. Baldridge, J. A. Boatz, S. T. Elbert, M. S.
Gordon, J. J. Jensen, S. Koseki, N. Matsunaga, K. A. Nguyen, S.
Su, T. L. Windus, M. Dupuis, J. A. Montgomery, J. Comput.
Chem. 1993, 14, 1347 – 1363). This basis-set combination is
referred to as SBKJC(d).
[24] All-electron calculations employed the 6-311G(d) basis set for
all atoms within the Gaussian03 suite of programs (Gaussian03
(RevisionB.03), M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E.
Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgomery, Jr.,
T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar,
J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N.
Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y.
Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P.
Hratchian, J. B. Cross, C. Adamo, J. Jaramillo, R. Gomperts,
R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli,
J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P.
Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D.
Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K.
Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul,
S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P.
Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A.
Al-Laham, C. Y. Peng, A. Nanayakkara, M. Challacombe,
P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonzalez,
J. A. Pople, Gaussian, Inc., Pittsburgh, PA, 2003).
[5] Initial studies suggest that the mechanism of oxo transfer in a Mo
system involves switching from h2- to h1-pyrazolate ligation: K.
Most, J. Hoßbach, D. Vidovic, J. Magull, N. C. Mösch-Zanetti,
Adv. Synth. Catal. 2005, 347, 463 – 472.
[6] N. C. Mösch-Zanetti, A. Sachse, R. Pfoh, D. Vidovic, J. Magull,
Dalton Trans. 2005, 2124 – 2129.
[7] P. J. Baricelli, R. Santos, A. J. Pardey, J. Mol. Catal. A 2004, 207,
81 – 87.
[8] K. Most, N. C. Mösch-Zanetti, D. Vidovic, J. Magull, Organo-
metallics 2003, 22, 5485 – 5490.
[9] a) H. V. Rasika Dias, H. V. K. Diyabalanage, M. G. Eldabaja, O.
Elbjeirami, M. A. Rawashdeh-Omary, M. A. Omary, J. Am.
Chem. Soc. 2005, 127, 7489 – 7501; b) T. R. Cundari, H. V.
Rasika Dias, H. V. K. Diyabalanage, O. Elbjeirami, M. A.
Gonzer, T. Grimes, M. A. Omary, M. Rawashdeh-Omary,
Inorg. Chem. 2005, 44, 8200 – 8210.
[10] a) H. M. El-Kaderi, M. J. Heeg, C. H. Winter, Eur. J. Inorg.
Chem. 2005, 2081 – 2088; b) H. M. El-Kaderi, M. J. Heeg, C. H.
Winter, Polyhedron 2005, 24, 645– 653.
[11] a) C. W. Eigenbrot, Jr., K. N. Raymond, Inorg. Chem. 1981, 20,
1553 – 1556; b) C. W. Eigenbrot, Jr., K. N. Raymond, Inorg.
Chem. 1982, 21, 2653 – 2660.
[12] Initial examples of h2-pyrazolate coordination to transition
metals, (e.g. [ZrCp2(h2-pz)(thf)][BPh4]; Cp = cyclopentadienyl)
were explained in terms of their need to attain an 18-electron
configuration: a) D. Röttger, G. Erker, M. Grehl, R. Fröhlich,
Organometallics 1994, 13, 3897 – 3902; b) I. A. Guzei, A. G.
Baboul, G. P. A. Yap, A. L. Rheingold, C. H. Schlegel, C. H.
Winter, J. Am. Chem. Soc. 1997, 119, 3387 – 3388; c) I. A. Guzei,
G. P. A. Yap, C. H. Winter, Inorg. Chem. 1997, 36, 1738 – 1739.
[13] A search of the CSD revealed 55 structures with h2-pyrazolate
coordination to f-block elements, 13 with alkali and alkaline-
earth metals, 40 with d0 early transition-metal ions, and only 8
with h2-pyrazolate coordination to a metal ion with a partially
filled d shell: Cambridge Structural Database, ConQuest version
1.7, November 2004 release, May 2005.
[25] For the MCSCF calculations, the five 3d orbitals of iron(ii),
subtending the irreducible representations 2a1 + a2 + b1 + b2,
and the six electrons contained within this orbital manifold
comprised the active space. Geometry optimizations were
5
5
5
5
carried out for the A1, A2, B1, and B2 states. The latter two
states were found to be much higher in energy (> 6 kcalmolÀ1
)
for both parallel and perpendicular conformations of [L’Fe(pz)].
MCSCF calculations employed the GAMESS package (see
reference 23) and the SBKJC(d) basis set.
[14] N. C. Mösch-Zanetti, R. Krꢀtzner, C. Lehmann, T. R. Schneider,
I. Usꢁn, Eur. J. Inorg. Chem. 2000, 13 – 16.
1610
www.angewandte.org
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2006, 45, 1607 –1611

Angewandte
Chemie
[26] Calculations on full models with the PM3(tm) Hamiltonian gave
similar results, that is, a nearly planar geometry for [LtBuNi(h2-
dmp)] and a nonplanar geometry for [LtBuFe(h2-dmp)].
[27] a) N. N. Greenwood, A. Earnshaw, Chemistry of the Elements,
2nd ed., Butterworth Heinemann, Oxford, 1997, pp. 1091 – 1097,
1156 – 1166; b) R. L. Carter, Molecular Symmetry and Group
Theory, Wiley, New York, 1998, pp. 201 – 214.
[28] A. B. P. Lever, Inorganic Electronic Spectroscopy, 2nd ed.,
Elsevier, Amsterdam, 1984, pp. 507 – 611.
[29] The ONIOM methodology is described in M. Svensson, S.
Humbel, R. D. J. Froese, T. Matsubara, S. Sieber, K. Morokuma,
J. Phys. Chem. 1996, 100, 19357 – 19363. The UFF force field is
described in A. K. Rappꢂ, C. J. Casewit, K. S. Colwell, W. A.
Goddard III, W. M. Skiff, J. Am. Chem. Soc. 1992, 114, 10024 –
10035. In our calculations, the MM region included the aryl and
tert-butyl substituents of LtBu and the methyl groups of dmp.
Angew. Chem. Int. Ed. 2006, 45, 1607 –1611
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
1611