Assembly of triangular trimetallic complexes by triamidophosphine ligands: Spin-frustrated Mn2+ plaquettes and diamagnetic Mg2+ analogues with a combined through-space, through-bond pathway for 31P-31P spin-spin coupling

Article abstract of DOI:10.1021/ja065597i

The reactions of 2 equiv of the ligand precursor P(CH₂NHPh) ₃ or P[CH₂NH-3,5-(CF₃)₂C ₆H₃]₃ with 3 equiv of Mn[N(SiMe ₃)₂]₂ provide high-yielding routes to the triangular trinuclear Mn(II) complexes [P(CH₂NPh)₃] ₂Mn₃(THF)₃·1.5THF and [P(CH ₂N-3,5-(CF₃)₂C₆H₃) ₃]₂Mn₃(THF)₃. The solid-state structures of these paramagnetic complexes have approximate C₃ symmetry. The magnetic moments from 300 to 1.8 K could be fit as a magnetic Jahn-Teller distorted isosceles triangle. These complexes exhibit spin frustration and possess an S = 1/2 ground state, as revealed by a plot of magnetization versus field at 1.8 K; at fields above 3.8 T, the occupation of an excited state with S = 3/2 becomes significant. The diamagnetic magnesium analogues were prepared by the reaction of the ligand precursor P(CH ₂NHPh)₃, P[CH₂NH-3,5-(CF₃) ₂C₆H₃]₃, or P(CH₂NH-3,5- Me₂C₆H₃)₃ with ⁿBu ₂Mg. The solid-state structures of [P(CH₂NPh) ₃]₂Mg₃(THF)₃·1.5THF and [P(CH₂N-3,5-(CF₃)₂C₆H ₃)₃]₂Mg₃(THF)₃ were determined. Solution ¹H NMR spectroscopy was used to demonstrate that the solid-state structures are maintained in solution. The aryl group of the terminal amido donor exhibits slow rotation on the NMR time scale, and this was found to be an electronic effect. Solution ³¹P{¹H} NMR spectroscopy revealed an unexpected 15 Hz coupling between phosphorus nuclei in these complexes. Calculations on a model complex using density functional theory demonstrates that this coupling occurs via a combined through-space, through-bond pathway.

Full text of DOI:10.1021/ja065597i

Published on Web 11/01/2006
Assembly of Triangular Trimetallic Complexes by
Triamidophosphine Ligands: Spin-Frustrated Mn2+ Plaquettes
and Diamagnetic Mg2+ Analogues with a Combined
Through-Space, Through-Bond Pathway for
31P-31P Spin-Spin Coupling
Jillian A. Hatnean,† Ritu Raturi,† Julie Lefebvre,‡ Daniel B. Leznoff,‡
Gavin Lawes,§ and Samuel A. Johnson*,†
Contribution from the Department of Chemistry & Biochemistry, UniVersity of Windsor,
Windsor, Ontario, Canada N9B 3P4, Department of Chemistry, Simon Fraser UniVersity, British
Columbia, Canada V5A 1S6, and Department of Physics, Wayne State UniVersity,
Detroit, Michigan 48202
Received August 2, 2006; E-mail: sjohnson@uwindsor.ca
Abstract: The reactions of 2 equiv of the ligand precursor P(CH2NHPh)3 or P[CH2NH-3,5-(CF3)2C6H3]3
with 3 equiv of Mn[N(SiMe3)2]2 provide high-yielding routes to the triangular trinuclear Mn(II) complexes
[P(CH2NPh)3]2Mn3(THF)3‚1.5THF and [P(CH2N-3,5-(CF3)2C6H3)3]2Mn3(THF)3. The solid-state structures of
these paramagnetic complexes have approximate C3 symmetry. The magnetic moments from 300 to 1.8
K could be fit as a magnetic Jahn-Teller distorted isosceles triangle. These complexes exhibit spin frustration
and possess an S ) 1/2 ground state, as revealed by a plot of magnetization versus field at 1.8 K; at fields
above 3.8 T, the occupation of an excited state with S ) 3/2 becomes significant. The diamagnetic magnesium
analogues were prepared by the reaction of the ligand precursor P(CH2NHPh)3, P[CH2NH-3,5-(CF3)2C6H3]3,
or P(CH2NH-3,5-Me2C6H3)3 with nBu2Mg. The solid-state structures of [P(CH2NPh)3]2Mg3(THF)3‚1.5THF
1
and [P(CH2N-3,5-(CF3)2C6H3)3]2Mg3(THF)3 were determined. Solution H NMR spectroscopy was used to
demonstrate that the solid-state structures are maintained in solution. The aryl group of the terminal amido
donor exhibits slow rotation on the NMR time scale, and this was found to be an electronic effect. Solution
31P{1H} NMR spectroscopy revealed an unexpected 15 Hz coupling between phosphorus nuclei in these
complexes. Calculations on a model complex using density functional theory demonstrates that this coupling
occurs via a combined through-space, through-bond pathway.
Geometric spin frustration1 in paramagnetic species is of
current interest due to its influence on desirable physical
properties2 such as spin-mediated superconductivity.3 The
simplest examples of spin-frustrated species are antiferromag-
netically coupled triangular complexes, where the topology of
the complex or lattice prevents all pairwise interactions between
unpaired spins from being simultaneously satisfied. The most
ubiquitous of these are the oxo-centered carboxylate complexes,4
and interest in the magnetic behavior of trinuclear complexes
has recently been renewed.5 The need for new synthetic
approaches to multidimensional assemblies based on spin-
frustrated plaquettes has been noted,6 and a molecular ap-
proach7,8 where the constituent building blocks are robust and
retain triangular bonding motifs in the solid state as well as in
solution would be advantageous.
The ability of amido ligands to provide bimetallic9 or larger
Mn(II) complexes10 is known. Our studies have utilized the
trianionic triamidophosphine donors P(CH2NArR)3, where ArR
(6) (a) Harrison, A. J. Phys.: Condens. Matter 2004, 16, S553-S572. (b)
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M., Eds. Magnetism: Molecules to Materials; Wiley-VCH: New York,
2005.
† University of Windsor.
‡ Simon Fraser University.
§ Wayne State University.
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J. AM. CHEM. SOC. 2006, 128, 14992-14999
10.1021/ja065597i CCC: $33.50 © 2006 American Chemical Society

Assembly of Triangular Trimetallic Complexes
A R T I C L E S
represents a variety of aryl substituents, to assemble heterobi-
metallic11 and polynuclear12 complexes. Unlike other triamido13
and amidophosphine14 ligands, the P(CH2NArR)3 ligands cannot
chelate all of their donor atoms to a single metal.11,12 Herein
we show how trimetallic Mn2+ spin-frustrated phosphines can
be assembled using these ligands, and how their diamagnetic
Mg2+ analogues maintain their trimetallic structures in solution.
Results and Discussion
Synthesis of Trinuclear Manganese(II) Complexes. The
synthesis of complexes of manganese using the ligand precursors
P(CH2NHPh)3 (1a) and P[CH2NH-3,5-(CF3)2C6H3]3 (1b) proved
to be facile. The reaction of 2 equiv of 1a with 3 equiv of Mn-
[N(SiMe3)2]2 in THF produced [P(CH2NPh)3]2Mn3(THF)3‚
1.5THF (2a) as a pale yellow crystalline precipitate over the
course of 36 h, as shown in eq 1. Analogously, the reaction of
Figure 1. Solid-state molecular structure of 2a as determined by X-ray
crystallography. Only the ipso carbons of the phenyl substituents on nitrogen
are shown, and the hydrogen atoms are omitted for clarity. The short contacts
between P(1) and the Mn ions are shown as dashed lines. Selected bond
lengths or distances (Å): Mn(1)‚‚‚Mn(2), 3.353(1); Mn(1)-N(1), 2.048-
(2); Mn(1)-N(6), 2.157(2); Mn(1)-N(5), 2.185(2); Mn(1)-O(1), 2.209-
(2); Mn(3)‚‚‚P(1), 2.9122(8); Mn(1)‚‚‚P(1), 2.978(1); Mn(2)‚‚‚P(1), 2.976(1).
Selected angles in degrees: N(1)-Mn(1)-N(6), 119.38(9); N(1)-Mn(1)-
N(5), 127.78(9); N(6)-Mn(1)-N(5), 103.10(9); N(1)-Mn(1)-O(1), 104.25-
(9); N(6)-Mn(1)-O(1), 105.17(8); N(5)-Mn(1)-O(1), 91.31(8).
The crystals isolated from the synthesis of 2a proved suitable
for X-ray diffraction, and an ORTEP depiction of the solid-
state molecular structure is shown in Figure 1. The complex
has no crystallographic symmetry, but approximate C3 sym-
metry, and contains a trinuclear manganese core supported by
two P(CH2NPh)3 moieties. The average Mn-Mn distance of
3.359(1) Å is approximately twice the van der Waals radius of
manganese.
2 equiv of 1b with 3 equiv of Mn[N(SiMe3)2]2 in THF for 72
h produced [P(CH2N-3,5-(CF3)2C6H3)3]2Mn3(THF)3, which was
isolated as a pale yellow crystalline solid by slow evaporation
of a concentrated benzene solution. Attempts to react P[CH2-
NH-3,5-Me2C6H3]3 (1c) with Mn[N(SiMe3)2]2 produced a
material which could not be recrystallized, and thus was not
further characterized. The 77 K X-band EPR spectra of powder
samples of 2a and 2b both display a broad resonance at g )
2.0, with poorly resolved hyperfine couplings, which is typical
for paramagnetic triangular systems.4,15 Much weaker broad
transitions are also observed at 1300 and 2300 G. Although
2a,b do not have any resolved 1H or 31P{1H} NMR resonances,
two broad and shifted 19F resonances are observed for 2b. Cyclic
The P(CH2NHPh)3 ligand moieties in 2a adopt two different
conformations. The lone pair of P(1) is directed toward the inside
of the triangle of Mn2+ ions, and the amido donors associated
with this ligand fragment are each bound terminally to a Mn
center, with an average Mn-N distance of 2.060(3) Å. The
second ligand fragment has the lone pair of P(2) pointing away
from the manganese atoms, and the associated amido donors
bridge between Mn atoms, with an average Mn-N distance of
2.169(5) Å. The Mn2+ ions attain four-coordinate geometries
by binding to one THF molecule each, but they are considerably
distorted from a tetrahedral geometry, with the angles to the
oxygen donor less than typical tetrahedral angles. The bond
angles between the bridging amido donors are also acute, with
a N(5)-Mn(1)-N(6) angle of 98.76(10)°, whereas the bond
angles between the terminal amido donor and the bridging
amides are considerably larger, with N(1)-Mn(1)-N(6) and
N(1)-Mn(1)-N(5) angles of 128.26(10) and 120.48(11)°,
respectively. The average of the sum of N-Mn-N angles for
Mn(1-3) is 351°, which is close to the value expected for a
planar arrangement of amido donors. Although the lone pair of
P(1) is not properly oriented to bond with a single manganese
ion, the distance between P(1) and the Mn2+ ions indicates some
interaction is probable. The shortest of these is the P(1)-Mn-
(3) distance of 2.9122(8) Å, which is only ∼5% longer than
other comparable P-Mn(II) bonds.16 For largely ionic bonds,
imperfect orbital overlap does not always greatly affect bond
strength.17 The P(1)-Mn(1)-O(1-3) angles range from 160.23-
n
-
voltammetry of complexes 2a,b in THF using BuN+PF6 as
an electrolyte revealed no reversible oxidation or reduction
processes.
(10) (a) Alvarez, C. S.; Bond, A. D.; Cave, D.; Mosquera, M. E. G.; Harron, E.
A.; Layfield, R. A.; McPartlin, M.; Rawson, J. M.; Wood, P. T.; Wright,
D. S. Chem. Commun. 2002, 2980-2981. (b) Alvarez, C. S.; Bashall, A.;
Bond, A. D.; Cave, D.; Harron, E. A.; Layfield, R. A.; Mosquera, M. E.
G.; McPartlin, M.; Rawson, J. M.; Wood, P. T.; Wright, D. S. J. Chem.
Soc., Dalton Trans. 2003, 3002-3008. (c) Crewdson, P.; Gambarotta, S.;
Yap, G. P. A.; Thompson, L. K. Inorg. Chem. 2003, 42, 8579-8584.
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(12) Keen, A. L.; Doster, M.; Han, H.; Johnson, S. A. Chem. Commun. 2006,
1221-1223.
(13) (a) Turculet, L.; Tilley, T. D. Organometallics 2002, 21, 3961-3972. (b)
Jia, L.; Ding, E.; Rheingold, A. L.; Rhatigan, B. Organometallics 2000,
19, 963-965. (c) Gade, L. H. Acc. Chem. Res. 2002, 35, 575-582. (d)
Gade, L. H. J. Organomet. Chem. 2002, 661, 85-94.
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D.; Johnson, S. A.; Rettig, S. J. J. Am. Chem. Soc. 1998, 120, 11024-
11025. (c) Fryzuk, M. D.; Love, J. B.; Rettig, S. J. Chem. Commun. 1996,
2783-2784. (d) Harkins, S. B.; Peters, J. C. J. Am. Chem. Soc. 2005, 127,
2030-2031. (e) Liang, L.-C.; Lin, J.-M.; Hung, C.-H. Organometallics
2003, 22, 3007-3009.
(15) (a) Boudalis, A. K.; Sanakis, Y.; Dahan, F.; Hendrich, M.; Tuchagues, J.-
P. Inorg. Chem. 2006, 45, 443-453. (b) Boudalis, A. K.; Sanakis, Y.;
Raptopoulou, C. P.; Terzis, A.; Tuchagues, J.-P.; Perlepes, S. P. Polyhedron
2005, 24, 1540-1548. (c) Kessissoglou, D. P. Coord. Chem. ReV. 1999,
185-186, 837-858.
(16) (a) Godfrey, S. M.; McAuliffe, C. A.; Pritchard, R. G. J. Chem. Soc., Dalton
Trans. 1993, 371-375. (b) Hitchcock, P. B.; Lappert, M. F.; Leung, W.
P.; Buttrus, N. H. J. Organomet. Chem. 1990, 394, 57-67.
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9
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A R T I C L E S
Hatnean et al.
2 and 3, and a second value, J13, to describe the unique coupling
between centers 1 and 3, as shown in eq 2.21
Hˆ ex ) -2J[S1‚S2 + S2‚S3] - 2J13S3‚S1
(2)
The energy levels for the states described by S′ and S* for this
Hamiltonian are given in eq 3.4
E(S′,S*) ) -J[S′(S′ + 1) - S*(S* + 1) - 35/4] -
J13[S*(S* + 1) - 35/2] (3)
Here, S′ ) S1 + S2 + S3 and can take on values from (15/2 to
(1/2 in integer steps, and S* ) S1 + S3 and can take values
from (5 to 0.
Using this equation, it is possible to calculate the energy levels
for any pair of J and J13 values. The resultant magnetic
susceptibilities can then be determined from the degeneracy of
the states, Ω(S′,S*), provided in the Supporting Information,
and their Boltzmann populations at any given temperature, as
shown in eq 4.
Figure 2. Plot of ømT versus temperature obtained at 10 000 Oe for complex
2b (0), with the modeled fit shown as a solid line.
(6) to 169.63(6)°, and when these phosphorus-manganese
interactions are included, the geometry about the manganese
centers is approximately trigonal bipyramidal.
Complex 2b crystallizes from benzene/hexamethyldisiloxane
in both monoclinic and trigonal space groups. In both cases,
the connectivity was analogous to that observed for 2a. Both
structures of 2b suffer from rotational disorder of the CF3
substituents, and disordered cocrystallized solvent molecules
further complicate the trigonal structure. Full details are provided
in the Supporting Information.
S′(S′ + 1)(2S′ + 1)Ω(S′,S*) e-E(S′,S*)/kT
∑
Nâ2g2 S′,S*
øm )
3kT
(2S′ + 1)Ω(S′,S*) e-E(S′,S*)/kT
Magnetic Measurements. The temperature dependence of
the molar magnetic susceptibility, øm, of 2a and 2b was studied
over the temperature range of 300-1.8 K. A plot of the product
of the susceptibility with the temperature, ømT, versus temper-
ature for complex 2b is shown in Figure 2. At room temperature,
ømT is 8.39 cm3‚K‚mol-1. This is less than the value of 13.13
cm3‚K‚mol-1 expected for three uncoupled Mn(II) centers with
five unpaired electrons each, and indicative of antiferromagnetic
coupling between the metal centers. The values of ømT steadily
decrease down to a minimum of 0.386 cm3‚K‚mol-1 at 1.8 K;
∑
S′,S*
(4)
Here, N is Avogadro’s number, â is the Bohr magneton, k is
the Boltzmann constant, and the electron proportionality constant
g is assumed to be 2.0 for this isotropic Mn(II) system.
The data for 2b can be fit in this manner using J ) -9.2 and
J13 ) -7.0 cm-1, and the fit is shown as a solid line in Figure
2. An equivalent fit can also be obtained with J ) -7.5 and J13
) -10.5 cm-1. The magnetic susceptibility of compound 2a
a spin 1/2 system has an expected value of 0.375 cm3‚K‚mol-1
.
can be modeled using J ) -11.0 and J13 ) -7.8 cm-1
.
The data for 2a are provided in the Supporting Information and
are similar, with only a slightly lower value of ømT (7.64
cm3‚K‚mol-1) at 300 K. Comparable magnetic susceptibilities
were obtained for these complexes in solution. Toluene solutions
of 2a,b at 300 K were determined by Evans’s method to have
ømT values of 6.7 and 7.3 cm3‚K‚mol-1, respectively.
Despite the approximate C3 symmetry of these complexes,
the solid-state variable-temperature magnetic susceptibility data
are poorly fit by the model predicted from the Heisenberg-
Dirac-Van Vleck Hamiltonian for an equilateral triangle, which
assumes equal J couplings between all three metal centers. This
phenomenon has been the source of considerable debate in the
literature,18 and it has been postulated in related triangular
systems that the magnetically degenerate ground state is split
by a magnetic Jahn-Teller effect.19,20 Here we use the static
model to fit the observed data to the Hamiltonian appropriate
for an isosceles triangle,21 which uses one value of J to describe
the coupling between metal centers labeled 1 and 2 as well as
Compounds 2a,b display magnetic coupling that is stronger than
that observed in the three examples of related Mn(II) triangular
complexes based on carboxylate ligands, whose magnetic
properties have been modeled, with reported J values ranging
from -0.588 to -2.36 cm-1 22
.
This model predicts a ground-state spin of 1/2, which is
characteristic of triangular trimetallic spin-frustrated systems
comprised of metals with noninteger spins. This is corroborated
by the observed value of ømT at 1.8 K. A plot of the
magnetization of 2b at different field strengths at 1.8 K is shown
in Figure 3. The data fit well to the Brillouin function for S )
1/2 up to 3 T. At higher fields, the plateau of 1 Nâ predicted
1
from the spin /2 Brillouin function, shown as a dashed line in
Figure 3, is not observed.
It proved possible to model this deviation from the Brillouin
function. As a first approximation, the energy of the states in
an applied field, E(H,S′,S*), can be expressed as shown in eq
5.7
(18) (a) Uryu, N.; Friedberg, S. A. Phys. ReV. A 1965, 140, 1803-1811. (b)
Sorai, M.; Tachiki, M.; Suga, H.; Seki, S. J. Phys. Soc. Jpn. 1971, 30,
750-759. (c) Wrobleski, J. T.; Dziobkowski, C. T.; Brown, D. B. Inorg.
Chem. 1981, 20, 684-686. (d) Rakitin, Y. V.; Zhemchuzhnikova, T. A.;
Zelentsov, V. V. Inorg. Chim. Acta 1977, 23, 145-148. (e) Dubicki, L.;
Day, P. Inorg. Chem. 1972, 11, 1868-1875. (f) Jones, D. H.; Sams, J. R.;
Thompson, R. C. J. Chem. Phys. 1984, 81, 440-447. (g) Gu¨del, H. U. J.
Chem. Phys. 1985, 82, 2510-2511.
E(H,S′,S*) ) E(S′,S*) + S′gâH
(5)
An examination of the energy levels predicted from the values
of J used to fit the variable-temperature magnetic susceptibility
(22) (a) Reynolds, R. A., III; Yu, W. O.; Dunham, W. R.; Coucouvanis, D.
Inorg. Chem. 1996, 35, 2721-2722. (b) Christian, P.; Rajaraman, G.;
Harrison, A.; Helliwell, M.; McDouall, J. J. W.; Raftery, J.; Winpenny, R.
E. P. J. Chem. Soc., Dalton Trans. 2004, 2550-2555. (c) Lin, W.; Evans,
O. R.; Yee, G. T. J. Solid State Chem. 2000, 152, 152-158.
(19) For the static model, the anticipated distortion has been calculated to be
approximately 0.01 Å: Murao, T. Phys. Lett. A 1974, 49A, 33-35.
(20) Kahn, O. Chem. Phys. Lett. 1997, 265, 109-114.
(21) Kambe, K. J. Phys. Soc. Jpn. 1950, 5, 48-51.
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Assembly of Triangular Trimetallic Complexes
A R T I C L E S
or THF. Complex 3a prepared in this manner analyzes as the
trinuclear magnesium complex [P(CH2NPh)3]2Mg3(THF)3‚
1.5THF and was isolated in greater than 70% yield by this
simple approach. Crystals suitable for X-ray diffraction were
obtained from the reaction of P(CH2NHPh)3 with (C5H5)2Mg-
(THF)2 in benzene, and sufficiently large crystals formed from
the undisturbed reaction mixture.
The solid-state molecular structure of 3a exhibits the same
connectivity as the Mn(II) analogue 2a. The average Mg-Mg
distance of 3.411(1) Å is slightly larger than the average Mn-
Mn distance in 2a of 3.359(1) Å. The average terminal Mg-N
bond length of 2.049(3) Å is identical, within error, to the
comparable average terminal Mn-N bond length observed for
2a, whereas the average bridging Mg-N bond distance of 2.146-
(3) Å is 0.023 Å shorter. These distances are typical of
previously structurally characterized Mg amido compounds.23
The average P(1)-Mg distance is 2.973(1) Å. This is only 0.2-
0.3 Å longer than in the few crystallographically characterized
magnesium phosphine complexes, which contain Mg-P bond
lengths of 2.65-2.77 Å.24
Complex 3b was crystallized from a benzene/hexamethyl-
disiloxane solution and characterized by X-ray crystallography.
Complex 3b crystallized as two polymorphs, one monoclinic
and one hexagonal, both isomorphous to those observed for 2b.
Full details regarding the structures of 3b are included in the
Supporting Information.
Figure 3. Magnetization versus applied field at 1.8 K for complex 2b (]),
the Brillouin function for a S ) 1/2 system (- - -), and the modeled fit (s).
data reveals a low-lying spin 3/2 state 10 cm-1 higher in energy
than the spin 1/2 ground state in the absence of an applied field.
In an applied field, the spin -3/2 state decreases in energy faster
1
than the spin
/ ground state, and its occupancy becomes
2
significant at higher fields. At 1.8 K and in a field of 3.8 T,
only 1% of the sample is predicted to be in this spin -3/2 state,
whereas at an applied field of 7 T, 10% of the sample should
be in this state. At fields greater than 10 T, the S ) -3/2 state
is the predicted ground state. No other states are low enough in
energy to have significant populations at 1.8 K under these
applied fields. By using the calculated populations of these two
states, it is possible to determine a function for the magnetization
at any given field in these systems. The modeled field
dependency of the magnetization at 1.8 K, determined using J
) -9.24 and J13 ) -7.04 cm-1, is shown in Figure 3 as a
solid line and adequately reproduces the observed data. The
modeled fit is very sensitive to both the ratio and values of J
and J13.
The complex [P(CH2N-3,5-Me2C6H3)3]2Mg3(THF)3 (3c) was
obtained as an analytically pure solid via removal of the THF
solvent from the reaction mixture under vacuum; however, the
growth of X-ray-quality crystals has so far proven impossible.
Solution Structure. The 1H NMR spectra of 3a-c are
consistent with C3V-symmetric species with two ligand environ-
ments, and thus they provide verification that the solution
structures of these complexes are the same as those determined
in the solid state. For each of 3a-c, there are two methylene
proton environments associated with each of the two chemically
unique triamidophosphine moieties. In the case of complex 3a,
which was isolated cocrystallized with THF, both free and bound
THF resonances were observed at room temperature. At higher
temperatures these resonances broadened and coalesced, and
an activation energy of 57 kJ/mol could be estimated for THF
Based on these analyses, complexes 2a,b behave as spin-
1
frustrated building blocks with spin
/ ground states. The
2
magnetic data can only be suitably fit by assuming that a
magnetic Jahn-Teller effect splits the ground-state degeneracy,
3
which yields a low-lying spin /2 state as the lowest energy
excited state.
Synthesis of Diamagnetic Magnesium Analogues. To serve
as useful building blocks for magnetic materials, complexes 2a,b
must maintain their trinuclear structures in solution. To dem-
onstrate that these complexes persist in solution, the Mg(II)
analogues were prepared; the ionic radius of Mg(II) is nearly
identical to that of Mn(II), and thus similar properties were
1
exchange. For complexes 3a and 3c, the room-temperature H
n
NMR spectra exhibit broad resonances, indicative of slow
anticipated. The addition of 3 equiv of Bu2Mg to 2 equiv of
the ligand precursors 1a-c in tetrahydrofuran provided 3a-c,
as shown in eq 6. Analyses of the crude reaction mixtures via
1H and 31P{1H} NMR spectroscopy revealed that no significant
side products were formed.
(23) (a) Tang, Y.; Zakharov, L. N.; Rheingold, A. L.; Kemp, R. A. Organo-
metallics 2005, 24, 836-841. (b) Bartlett, R. A.; Olmstead, M. M.; Power,
P. P. Inorg. Chem. 1994, 33, 4800-4803. (c) Bradley, D. C.; Hursthouse,
M. B.; Ibrahim, A. A.; Abdul Malik, K. M.; Motevalli, M.; Moseler, R.;
Powell, H.; Runnacles, J. D.; Sullivan, A. C. Polyhedron 1990, 9, 2959-
2964. (d) Clegg, W.; Frank, M.; Mulvey, R. E.; O’Neil, P. A. J. Chem.
Soc., Chem. Commun. 1994, 97-98. (e) Dozzi, G.; Del Piero, G.; Cesari,
M.; Cucinella, S. J. Organomet. Chem. 1980, 190, 229-236. (f) Duff, A.
W.; Hitchcock, P. B.; Lappert, M. F.; Taylor, R. G.; Segal, J. A. J.
Organomet. Chem. 1985, 293, 271-283. (g) Han, R.; Parkin, G. Organo-
metallics 1991, 10, 1010-1020. (h) Henderson, K. W.; Mulvey, R. E.;
Glegg, W.; O’Neil, P. A. J. Organomet. Chem. 1992, 439, 237-250. (i)
Henderson, K. W.; Mulvey, R. E.; Clegg, W.; O’Neil, P. A. Polyhedron
1993, 12, 2535-2538. (j) Her, T. Y.; Chang, C. C.; Liu, L. K. Inorg. Chem.
1992, 31, 2291-2294. (k) Holloway, C. E.; Melnik, M. J. Organomet.
Chem. 1994, 465, 1-63. (l) Kennedy, A. R.; Mulvey, R. E.; Schulte, J. H.
Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 2001, C57, 1288-
1289. (m) Magnuson, V. R.; Stucky, G. D. Inorg. Chem. 1969, 8, 1427-
1433. (n) Sebestl, J. L.; Nadasdi, T. T.; Heeg, M. J.; Winter, C. H. Inorg.
Chem. 1998, 37, 1289-1294. (o) Vargas, W.; Englich, U.; Ruhlandt-Senge,
K. Inorg. Chem. 2002, 41, 5602-5608. (p) Westerhausen, M. Inorg. Chem.
1991, 30, 96-101.
These reactions proceed faster than the formation of 2a,b,
and as a result, X-ray-quality crystals of 3a could not be obtained
directly from the reaction mixture. Instead, the product precipi-
tated as a white powder that is only slightly soluble in benzene
(24) (a) Pape, A.; Lutz, M.; Mueller, G. Angew. Chem., Int. Ed. Engl. 1994,
33, 2281-2284. (b) Gindelberger, D. E.; Arnold, J. Inorg. Chem. 1994,
33, 6293-6299.
9
J. AM. CHEM. SOC. VOL. 128, NO. 46, 2006 14995

A R T I C L E S
Hatnean et al.
rotation of one of the two chemically distinct aromatic substit-
uents on the amido groups. For 3b, this fluxional process is
slow enough at room temperature that three ortho proton
environments are resolved in the 1H NMR spectrum, in a 2:1:1
ratio, and likewise three fluorine environments are seen in the
coupling is transmitted by a bonding interaction, though no
formal bond exists because the antibonding combination of
orbitals is also occupied. This mechanism of coupling has been
found to display an inverse exponential dependence on the
distance between nuclei.29 Although small couplings have been
observed at distances slightly greater than twice the van der
Waals radii of the coupled nuclei, coupling constants rapidly
drop to zero at greater distances.30
From an examination of the structure of 3a, it is clear that
the requirements for traditional through-space spin-spin cou-
pling directly between the phosphorus nuclei are not met. The
lone pair of P(1) is directed toward P(2), but the lone pair of
P(2) is directed away from P(1). Furthermore, the van der Waals
radius of phosphorus is 1.8 Å, and the 5.298 Å distance between
P(1) and P(2) is nearly 3 times are large, and approximately 1
Å farther than the maximum predicted distance at which
through-space P-P spin-spin coupling should be observable.30
Although alternate orbital interactions between the phosphorus
nuclei could be postulated, such as the interaction of the lone
pair on P(1) with a higher lying vacant orbital on P(2), the
distance between the nuclei still seems to prohibit any significant
direct through-space interaction.
This hypothesis was tested by computational methods using
density functional theory and the B3LYP method in Gaussian
03. The simplest relevant model system, two PH3 molecules
arranged in space in an identical manner to the phosphorus
nuclei in 3a, failed to exhibit any significant coupling when
studied using the aug-cc-pVTZ basis set available in Gaussian
03. An examination of each of the Fermi contact, paramagnetic
spin-orbit, diamagnetic spin-orbit, and spin-dipole contribu-
tions to the coupling constant demonstrated that they were all
less than 0.1 Hz.
To provide an explanation for the coupling observed in 3a-
c, calculations were performed on the model complex [P(CH2-
NH)3]2Mg3, where the THF molecule has been omitted and the
aryl substituent on nitrogen is replaced with a hydrogen atom.
The geometry from 3a was maintained, but with a N-H distance
of 1.1 Å. Although this system is far too simplified for us to
hope to quantitatively reproduce the experimentally observed
coupling, it proved sufficient to gain qualitative insight into the
mechanism of spin-spin coupling between phosphorus nuclei.
With this simplified model and a minimal 3-21G basis set, a
31P-31P coupling constant of 10.7 Hz was calculated. When
the larger aug-cc-pVTZ basis set was utilized for the phosphorus
atoms, a 22.1 Hz 31P-31P coupling was calculated for the same
geometry; the approximate magnitude of the 31P-31P coupling
is well predicted, even with modest basis sets.
1
19F NMR spectrum. By modeling the variable-temperature H
NMR spectra, the activation energies for these ring rotations
were determined to be 76, 97, and 73 kJ/mol for 3a-c,
respectively. This trend is consistent with an electronic rather
than a steric barrier to rotation, with the largest activation energy
for the electron-withdrawing trifluoromethyl-substituted aryl
rings and the lowest barrier for the electron-donating methyl-
substituted aromatics. It can be concluded that this fluxional
process involves the aromatic substituents on the terminal amido
donors, whose lone pair is not involved in σ-bonding, and can
thus be delocalized over the aromatic system. This assignment
1
was confirmed by H-1H NOESY; the ortho protons of the
aromatic substituents associated with the bridging amido exhibit
cross-peaks with both sets of ligand methylene protons, whereas
the ortho protons of the slowly rotating terminal amido donor
substituents exhibit a single cross-peak. These results are
consistent with the solid-state structures of 3a-c. There is also
evidence for the delocalization of the lone pair over the aromatic
substituents from the structural parameters of 3a,b. In 3a, the
terminal amido-ipso carbon distances N(1)-C(4), N(2)-C(10),
and N(3)-C(16) are considerably shorter than the bridging
amido-ipso carbon distances N(4)-C(25), N(5)-C(31), and
N(6)-C(37); their average distances are 1.379(4) and 1.431(4)
Å, respectively, a difference of 0.05 Å. This could be ascribed
to partial double bond character in the terminal amido bonds,
due to delocalization of the nonbonding amido lone pair over
the aromatic substituents,25 and similar bond lengths have been
observed in a related magnesium complex containing both
bridging and terminal amido donors.26
Through-Space 31P-31P Coupling. Irrespective of temper-
ature, there are two phosphorus environments in the 31P{1H}
NMR spectra for each complex, 3a-c, as anticipated from the
X-ray structures of 3a and 3b. Unexpectedly, the two phos-
phorus resonances features 15 Hz couplings between phosphorus
nuclei; the 31P nuclei are separated by six bonds, two of which
are largely ionic in character, and should not readily transmit
spin-spin coupling via a Fermi contact term.
Through-space spin-spin coupling is well documented, and
most commonly observed with fluorine, although a few
examples of 31P-31P through-space coupling are known.27 The
accepted explanation28 for through-space coupling of nuclear
spins is that the overlap of the lone pairs of two adjacent nuclei
transmits spin-spin coupling via a Fermi contact term. The
The Fermi contact term dominates the coupling for calcula-
tions using either basis set; the paramagnetic spin-orbit,
diamagnetic spin-orbit, and spin-dipole contributions were all
less than (0.02 Hz. An examination of the molecular orbitals
predicted from the DFT calculation using the 3-21G basis set
showed that only the HOMO-15 had significant bonding
interactions that extended from P(1) to P(2), which is a
requirement for a Fermi contact contribution. A depiction of
(25) The shortened bonds could also be construed as being due to the sp2 versus
sp3 hybridization of the orbitals participating in the N-C bond. Comparison
with the methylene N-C bonds, where no delocalization of the lone pair
can occur, allows for an approximate contribution to the difference in bond
length that can be attributed to the difference in hybridization. The N(1-
3)-C(1-3) bonds are on average 1.459(4) Å, whereas the N(4-6)-C(22-
24) bond lengths are on average 1.481(4) Å, a difference of only 0.02 Å;
this supports the partial double bond character of the terminal amido-ipso
carbon bond.
(26) Clegg, W.; Horsburgh, L.; Mulvey, R. E.; Ross, M. J.; Rowlings, R. B.;
Wilson, V. Polyhedron 1998, 17, 1923-1930.
(27) (a) Pastor, S. D.; Shum, S. P.; Rodebaugh, R. K.; Debellis, A. D.; Clarke,
F. H. HelV. Chim. Acta 1993, 76, 900-914. (b) Hierso, J.-C.; Fihri, A.;
Ivanov, V. V.; Hanquet, B.; Pirio, N.; Donnadieu, B.; Rebiere, B.; Amardeil,
R.; Meunier, P. J. Am. Chem. Soc. 2004, 126, 11077-11087. (c) Kaupp,
M.; Patrakov, A.; Reviakine, R.; Malkina, O. L. Chem.sEur. J. 2005, 11,
2773-2782.
(29) Mallory, F. B.; Mallory, C. W.; Butler, K. E.; Lewis, M. B.; Xia, A. Q.;
Luzik, E. D., Jr.; Fredenburgh, L. E.; Ramanjulu, M. M.; Van, Q. N.; Francl,
M. M.; Freed, D. A.; Wray, C. C.; Hann, C.; Nerz-Stormes, M.; Carroll,
P. J.; Chirlian, L. E. J. Am. Chem. Soc. 2000, 122, 4108-4116.
(30) (a) Alkorta, I.; Elguero, J. Int. J. Mol. Sci. 2003, 4, 64-92. (b) Diz, A. C.;
Contreras, R. H.; Natiello, M. A.; Gavarini, H. O. J. Comput. Chem. 1985,
6, 647-651.
(28) Mallory, F. B. J. Am. Chem. Soc. 1973, 95, 7747-7752.
9
14996 J. AM. CHEM. SOC. VOL. 128, NO. 46, 2006

Assembly of Triangular Trimetallic Complexes
A R T I C L E S
complexes, should allow for extended structures to be derived
from these spin-frustrated building blocks.
Experimental Section
General Procedures. Unless otherwise stated, all manipulations were
performed under an inert atmosphere of nitrogen using either standard
Schlenk techniques or an MBraun glovebox. Dry, oxygen-free solvents
were employed throughout. Anhydrous pentane, toluene, diethyl ether,
and THF were purchased from Aldrich, sparged with dinitrogen, and
passed through activated alumina under a positive pressure of nitrogen
gas; toluene and hexanes were further deoxygenated using Ridox
catalyst columns.32 Deuterated benzene was dried by heating at reflux
with sodium/potassium alloy in a sealed vessel under partial pressure
and then trap-to-trap distilled and freeze-pump-thaw degassed three
times. Deuterated toluene was purified in an analogous manner by
heating at reflux over Na. NMR spectra were recorded on a Bruker
AMX 300 MHz or 500 MHz spectrometer. All chemical shifts are
reported in parts per million , and all coupling constants are in hertz.
For 19F{1H} NMR spectra, trifluoroacetic acid was used as the external
Figure 4. Isosurface of the HOMO-15 in the model complex [P(CH2-
NH)3]2Mg3, and a simplified depiction of the orbital interactions as they
pertain to 3a.
an isosurface of the orbital generated using Molden31 is shown
in Figure 4. The bonding occurs through space between the lone
pair on P(1) and an in-phase combination of an sp2-hybridized
orbitals on each bridging amido donor; however, the coupling
is not solely transmitted through space. The nitrogen-based
orbital also overlaps with a CH2 carbon-based p-orbital, which
likewise overlaps with an orbital on P(2). A simplification of
this interaction, depicted on only one of the three ligand arms,
is also shown in Figure 4. The fact that there are three identical
coupling pathways presumably plays a role in the magnitude
of the coupling constant. At higher energy there is a similar
orbital exhibiting antibonding interactions between P(1) and the
in-phase combination of sp2-hybridized orbitals on each bridging
amido donor; as expected, no net N-P bonding exists. The
contribution of the phosphine lone pair to an orbital that is
primarily a component of the ionic amido-magnesium bonds
supports a weak bonding interaction between the metals and
this phosphine donor.
The observation of 31P-31P coupling in these molecules
indicates that significant delocalization of σ-bonding occurs over
the ligand framework. The transfer of spin information from
nitrogen to the phosphorus nuclei in 3a-c suggests that, in
complexes 2a-c, significant coupling of electron spins might
occur between the Mn3 fragment and paramagnetic metal centers
attached to the phosphine lone pair directed away from the
trimetallic core. These complexes could therefore act as spin-
frustrated phosphine donors.
1
reference at 0.00 ppm. H NMR spectra were referenced to residual
protons (C6D5H, δ 7.15; C7D7H, δ 2.09; CDHCl2, δ 5.32) with respect
to tetramethylsilane at δ 0.00. 31P{1H} NMR spectra were referenced
to external 85% H3PO4 at δ 0.0. 13C{1H} NMR spectra were referenced
to solvent resonances (C6D6, δ 128.0; C7D8, δ 20.4; CD2Cl2, δ 53.8).
EPR spectra were collected using an X-band Bruker ESR 300E
spectrometer. Unless otherwise noted, magnetizations were measured
at 10 000 Oe with a Quantum Design Evercool MPMS-XL7 system.
Corrections for the diamagnetic contributions of compounds were made
using Pascal’s constants. Samples were run both in vacuum-dried gelatin
capsules mounted in low-background diamagnetic straws and in a PVC
holder specially designed to possess a constant cross-sectional area,
with no difference between the two data sets. Cyclic voltammetry was
performed using a Bioanalytical Systems 100B/W electrochemical
analyzer. Elemental analyses were performed by the Centre for Catalysis
and Materials Research (CCMR, Windsor, Ontario, Canada). The
compounds tris(hydroxylmethyl)phosphine, aniline, 3,5-dimethylaniline,
3,5-bis(trifluoromethyl)aniline, and 1.0 M dibutylmagnesium in heptane
were purchased from Aldrich and used as received. The ligand
precursors 1a-c11 and Mn[N(SiMe3)2]233 were prepared as previously
reported. Bis(cyclopentadienyl)bis(tetrahydrofuran)magnesium was pre-
pared via the literature method,34 but in our hands it was soluble in
hydrocarbon solvents.
Synthesis of [P(CH2NPh)3]2Mn3(THF)3‚1.5THF (2a). A solution
of P(CH2NHC6H5)3 (500 mg, 1.43 mmol, 2 equiv) and Mn[N(SiMe3)2]2
(806 mg, 2.14 mmol, 3 equiv) was dissolved in 5 mL of THF and left
undisturbed for 36 h. A crystalline solid containing 1.5 equiv of
cocrystallized THF slowly precipitated. The solid was filtered and
washed with pentane and 1 mL of THF. The crystalline yellow solid
was dried under vacuum (526 mg, 64% yield). A second crop (148
mg, 18%) was obtained by cooling the mother liquor, providing a total
yield of 82%. Anal. Calcd for C60H78Mn3N6O4.5P2: C, 60.15; H, 6.56;
N, 7.01. Found: C, 59.82 H, 6.79; N, 7.08.
Conclusions
The triamidophosphine ligands P(CH2NArR)3, where ArR is
an aryl substitutent, readily assemble trinuclear clusters with
divalent Mn and Mg. The manganese complexes have a
1
degenerate S ) /2 ground state due to spin frustration, with J
values that are significantly larger than those for the related
trinuclear carboxylate systems. Solution NMR studies show that
the diamagnetic magnesium clusters are robust in solution and
feature a 15 Hz coupling between 31P nuclei that occurs via a
combined through-space, through-bond pathway. This coupling
requires extended delocalization of the σ-bonds from the
bridging amido donors to the external phosphine. Investigations
into the reactivities and use of these clusters as building blocks
for molecular magnetic materials are underway. Both the use
of the external phosphine as a donor ligand11 to additional
paramagnetic transition metal complexes, and the replacement
of the THF donors with donors capable of bridging the trinuclear
Synthesis of [P(CH2N-3,5-(CF3)2C6H3)3]2Mn3(THF)3 (2b). To a
stirred solution of P(CH2NH-3,5-(CF3)2C6H3)3 (5.0 g, 6.6 mmol, 2
equiv) in 25 mL of THF was added Mn[N(SiMe3)2]2 (3.72 g, 9.9 mmol,
3 equiv). The solution was stirred for 72 h. The solvent was evacuated,
leaving a tan solid. The product was washed with pentane and dried in
vacuo (4.68 g, 75% yield). Pale yellow X-ray-quality crystals containing
1 equiv of benzene were obtained by slow evaporation of an undisturbed
solution (2.1 g, 44.9% yield). The cocrytallized benzene could be
(32) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.; Timmers,
F. J. Organometallics 1996, 15, 1518-1520.
(33) (a) Andersen, R. A.; Faegri, K., Jr.; Green, J. C.; Haaland, A.; Lappert, M.
F.; Leung, W. P.; Rypdal, K. Inorg. Chem. 1988, 27, 1782-1786. (b)
Buerger, H.; Wannagat, U. Monatsh. Chem. 1964, 95, 1099-1102.
(34) Jaenschke, A.; Paap, J.; Behrens, U. Organometallics 2003, 22, 1167-
1169.
(31) Schaftenaar, G. CAOS/CAMM Center; The University of Nijmegen:
Nijmegen, The Netherlands, 1991.
9
J. AM. CHEM. SOC. VOL. 128, NO. 46, 2006 14997

A R T I C L E S
Hatnean et al.
trigonal
Table 1. Crystallographic Data for Compounds 2a, 2b, 3a, and 3b
2b
3b
2a
monoclinic
trigonal
3a
monoclinic
empirical formula
formula weight
crystal system
a, Å
b, Å
c, Å
C60H78Mn3N6O4.50P2
1182.04
triclinic
C72H60F36Mn3N6O3P2
1968.02
trigonal
C69H81Mg3N6O3P2
1177.27
monoclinic
26.882(4)
9.5933(13)
25.776(3)
90
108.937(2)
90
6287.4(14)
P2(1)/c
C72H60F36Mg3N6O3P2
1876.13
monoclinic
16.2034(17)
21.886(2)
22.723(2)
90
monoclinic
trigonal
24.1481(11)
24.1481(11)
54.053(5)
90
9.8336(10)
13.3050(13)
22.388(2)
86.3530(10)
81.8870(10)
84.5170(10)
2882.8(5)
P1h
24.1780(16)
24.1780(16)
54.747(8)
90
16.1671(19)
21.732(3)
22.771(3)
90
R, °
â, °
90.1720(10)
90
90
120
90.6540(10)
90
90
120
γ, °
volume, Å3
space group
Z
8058.2(15)
P2(1)/c
27716(5)
R3h
12
7999.9(16)
P2(1)/c
4
27297(3)
R3h
12
2
4
4
µ (mm-1
)
0.755
173(2)
32 597
12 815
[Rint ) 0.025]
0.062, 0.156
0.636
0.555
0.151
173(2)
58 371
11 073
[Rint ) 0.0737]
0.094, 0.140
0.212
133(2)
88 776
18 033
0.187
143(2)
temperature (K)
total reflns
143(2)
76 431
14 174
[Rint ) 0.038]
0.068, 0.146
133(2)
89 234
10 839
[Rint ) 0.051]
0.082, 0.176
87 852
10 690
[Rint ) 0.0449]
0.122, 0.313
no. unique
[Rint ) 0.0298]
0.077, 0.175
residuals: R1, wR2
removed under vacuum. 19F{1H} NMR (tol, 282.5 MHz, 20 °C): δ
5.8 (br), 10.1 (br). Anal. Calcd for C66H54F36Mn3N6O3P2: C, 41.94; H,
2.88; N, 4.45. Found: C, 41.71; H, 2.84; N, 4.30.
Ph p-C), 114 (s, Ph m-C), 114.9 (s, Ph m-C), 120.4 (s, Ph o-C), 122.8
(s, Ph o-C), 132 and 134.5 (m, Ph-CF3, J ) 46.11 Hz), 156.3 (s, ipso-
C), 158.9 (s, ipso-C). 19F{1H} NMR (CD2Cl2, 25 °C, 282.5 MHz): δ
13.89 (s, 9F, Ph-CF3), 14.06 (s, 18F, Ph-CF3), 14.18 (s, 9F, Ph-CF3).
Anal. Calcd for C66H54F36Mg3N6O3P2: C, 44.09; H, 3.03; N, 4.67.
Found: C, 44.48; H, 3.48; N, 4.28.
Synthesis of [P(CH2NPh)3]2Mg3(THF)3‚1.5THF (3a). To a stirred
solution of P(CH2NHPh)3 (1.5 g, 4.29 mmol, 2 equiv) in 10 mL of
n
THF was added a 1.0 M heptane solution of Bu2Mg (6.44 mL, 6.44
mmol, 3 equiv). The solution was stirred for 4 h at room temperature,
over which time a white powder precipitated. The solvent was removed,
and the solid was dried under vacuum for 30 min. The product was
rinsed with pentane and dried in vacuo (1.616 g, 76.6% yield).
Additional product was also recovered from the pentane fraction (246
mg, 11.7% yield) for an overall yield of 88.3%. The microcrystalline
sample obtained in this manner contained 1.5 equiv of cocrystallized
THF, which could not be removed under vacuum. X-ray-quality crystals
were obtained by performing the analogous reaction at room temper-
ature in benzene using (η5-C5H5)2Mg(THF)2 in lieu of nBu2Mg. Large
colorless crystals containing 2.5 equiv of cocrystallized benzene slowly
precipitated from an undisturbed solution; the complex has only slight
Synthesis of [P(CH2N-3,5-Me2C6H3)3]2Mg3(THF)3 (3c). To a stirred
solution of P(CH2N-3,5-Me2C6H3)3H3 (1.0 g, 2.306 mmol, 2 equiv) in
15 mL of THF was added a 1.0 M heptane solution of nBu2Mg (3.46,
3.46 mmol, 3 equiv). The solution was stirred for 4 h at room
temperature. The solvent was evacuated, leaving a white solid. The
product was rinsed with pentane and dried in vacuo (1.08 g, 81.2%
1
yield). H NMR (toluene-d8, 25 °C, 300.13 MHz): δ 0.92 (s, 12H,
MgOCH2CH2), 2.01 (s, 9H, Ph-CH3), 2.15 (s, 18H, Ph-CH3), 2.18 (s,
9H, Ph-CH3), 3.0 (s, 12H, MgOCH2), 3.8 (s, 6H, PCH2), 4.25 (s, 6H,
PCH2), 5.85 (s, 6H, Ph o-H), 6.2 (s, 3H, Ph p-H), 6.42 (s, 3H, Ph p-H),
6.63 (br, 3H, Ph o-H), 7.8 (br, 3H, Ph o-H). 31P{1H} NMR (toluene-
d8, 25 °C, 121.5 MHz): δ -22.7 (d, JPP ) 15 Hz), -34.3 (d, JPP ) 15
Hz). 13C{1H} NMR (toluene-d8, -60 °C, 75.48 MHz): δ 21.4 (s, 3C,
Ph-CH3), 22.2 (s, 6C, Ph-CH3), 23.1 (s, 3C, Ph-CH3), 24.7 (s,
1
solubility in benzene. H NMR (CD2Cl2, 25 °C, 500.13 MHz): δ 1.5
(m, 12H, MgOCH2CH2), 1.8 (m, 6H, cocrystallized THF), 3.0 (s, 12H,
MgOCH2), 3.68 (m, 6H, cocrystallized THF), 3.75 (d, 6H, PCH2, J )
6.7 Hz), 3.96 (s, 6H, PCH2), 5.95 (d, 6H, Ph o-H, J ) 8.8 Hz), 6.18 (t,
3H, Ph p-H, J ) 8.8 Hz), 6.7 (t, 3H, Ph p-H, J ) 8.3 Hz), 6.75 (dd,
MgOCH2CH2), 46.7 (d, PCH2, JPC ) 15.6 Hz), 47.9 (d, PCH2, JPC
)
24.2 Hz), 70.5 (s, MgOCH2), 114.2 (br, Ph p-C), 114.5 (s, Ph p-C),
119.2 (s, Ph m-C), 120.8 (s, Ph m-C), 136.5 (s, Ph o-C), 139.4 (s, Ph
o-C), 156.3 (s, Ph ipso-C), 159.6 (d, Ph ipso-C, J ) 24.15 Hz). Anal.
Calcd for C66H90Mg3N6O3P2: C, 68.91; H, 7.89; N, 7.31. Found: C,
68.40; H, 7.87; N, 7.31.
2
6H, Ph m-H, J ) 7.3 Hz, J ) 14.7 Hz), 7.1 (br, 6H, Ph o-H and
m-H), 7.6 (br, 3H, Ph o-H). 31P{1H} NMR (CD2Cl2, 25 °C, 202.46
MHz): δ -22.1 (d, JPP ) 15.0 Hz), -32.0 (d, JPP ) 15.0 Hz). 13C-
{1H} NMR (C6D6, 25 °C, 75.48 MHz): δ 25.1 (s, MgOCH2CH2), 25.9
(s, cocrystallized THF), 40.9 (s, PCH2), 42.1 (s, PCH2), 67.5 (s,
MgOCH2), 68.0 (s, cocrystallized THF), 113.8 (s, Ph o-C), 116.5 (s,
Ph m-C), 118.5 (s, Ph p-C). Anal. Calcd for C60H78Mg3N6O4.5P2: C,
65.15; H, 7.11; N, 7.60. Found: C, 64.81; H, 7.10; N, 7.83.
X-ray Crystallography. X-ray structures of 2a, 2b, 3a, and 3b were
obtained at low temperature, with each crystal covered in Paratone and
placed rapidly into the cold N2 stream of the Kryo-Flex low-temperature
device. Two different polymorphs of 2b and 3b were identified. The
data were collected using SMART35 software on a Bruker APEX CCD
diffractometer, using a graphite monochromator with Mo KR radiation
(λ ) 0.71073 Å). A hemisphere of data was collected using a counting
time of 10-30 s per frame. Details of crystal data, data collection, and
structure refinement are listed in Table 1. Data reductions were
performed using the SAINT36 software, and the data were corrected
for absorption using SADABS.37 The structures were solved by direct
Synthesis of [P(CH2N-3,5-(CF3)2C6H3)3]2Mg3(THF)3 (3b). To a
stirred solution of P(CH2NH-3,5-(CF3)2C6H3)3H3 (1.5 g, 1.98 mmol, 2
equiv) in 15 mL of THF was added a 1.0 M heptane solution of nBu2-
Mg (2.97 mL, 2.97 mmol, 3 equiv). The solution was stirred for 2 h at
room temperature. The solvent was evacuated, leaving an off-white
solid. The product was washed with pentane and dried in vacuo (1.43
1
g, 80% yield). H NMR (CD2Cl2, 25 °C, 300.13 MHz): δ 1.58 (s,
12H, MgOCH2CH2), 3.08 (s, 12H, MgOCH2), 3.9 (d, 6H, PCH2, J )
6.4 Hz), 4.12 (d, 6H, PCH2, J ) 3.2 Hz), 6.1 (s, 6H, Ph o-H), 6.76 (s,
3H, Ph p-H), 7.33 (s, 3H, Ph o-H), 7.5 (s, 3H, Ph p-H), 7.98 (s, 3H, Ph
o-H). 31P{1H} NMR (CD2Cl2, 25 °C, 300 MHz): δ -17.8 (d, J )
14.8 Hz), -33.5 (d, J ) 14.6 Hz). 13C{1H} NMR (C6D6, 25 °C, 75.48
MHz): δ 24.5 (s, MgOCH2CH2), 46.2 (d, PCH2, J ) 24.2 Hz), 48.1
(d, PCH2, J ) 26.4 Hz), 71.4 (s, MgOCH2), 107 (s, Ph p-C), 112 (s,
(35) SMART, Molecular analysis research tool; Bruker AXS Inc.: Madison,
WI, 2001.
(36) SAINTPlus, Data reduction and correction program; Bruker AXS Inc.:
Madison, WI, 2001.
(37) SADABS, An empirical absorption correction program; Bruker AXS Inc.:
Madison, WI, 2001.
9
14998 J. AM. CHEM. SOC. VOL. 128, NO. 46, 2006

Assembly of Triangular Trimetallic Complexes
A R T I C L E S
methods using SIR9738 and refined by full-matrix least-squares on F 2,
and anisotropic displacement parameters for the non-H atoms, with
the exception of some highly disordered solvent molecules, were
determined using SHELXL-9739 and the WinGX40 software package.
The structure of 2a features a two-fold disordered THF moiety that
shows disorder and is refined isotropically, along with a second
cocrystallized THF moiety. The monoclinic structure of 3a features a
residual electron density maximum of 1.21 e/Å3 that is within 0.85 Å
of Mg(1). The monoclinic structure of 3b features a residual electron
density maximum of 1.96 e/Å3 that is within 1.339 Å of F(25), and is
associated with a poorly resolved rotational disorder of the CF3 group.
The trigonal structures of 2b and 3b suffer from rotational disorder of
the CF3 substituents, disorder of some of the coordinated THF
molecules, possible twinning, and disordered cocrystallized solvent
molecules that could not be adequately modeled, and they were treated
with the SQUEEZE option of PLATON.41 Hydrogen atoms were
excluded on a further disordered cocrystallized benzene molecule in
these trigonal structures, as well as on some of the carbons associated
with the disordered THF moieties. Thermal ellipsoid plots were
produced using ORTEP32.42
Calculations. Ab initio DFT calculations were performed using the
hybrid functional B3LYP43 method with the Gaussian 03 package.44
The basis functions used were the aug-cc-pVTZ and 6-21G set, provided
in the Gaussian 03 program.
Acknowledgment is made to the National Sciences and
Engineering Research Council (NSERC) of Canada and the
Ontario Research and Development Challenge Fund (ORDCF)
for their financial support.
Supporting Information Available: Complete ref 44; EPR
spectrum for 2a; ømT versus temperature plot for 2a; tables of
crystallographic data; crystallographic information in CIF format
for 2a, 2b, 3a, and 3b. This material is available free of charge
via the Internet at http://pubs.acs.org.
(38) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giacovazzo,
C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. Appl.
Crystallogr. 1999, 32, 115-119.
JA065597I
(39) Sheldrick, G. M. SHELXL-97; Universitat Gottingen: Gottingen, 1997.
(40) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837-838.
(41) Van der Sluis, P.; Spek, A. L. Acta Crystallogr., Sect. A: Found.
Crystallogr. 1990, A46, 194-201.
(43) Becke, A. D. J. Chem. Phys. 1993, 98, 5648-5652.
(44) Frisch, M. J.; et al. Gaussian 03, revision C.01; Gaussian, Inc.: Wallingford,
CT, 2004.
(42) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
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