COMMUNICATION
Scheme 1
present work include the isolation of the mononuclear iron-
(II) and cobalt(II) methyl-arylamide complexes [M(L1)(Me)-
(tmeda)] [M ) Fe, Co; L1 ) N(SiMe3)(C6H3Me2-2,6)] and
the two-coordinate iron(II) bis(arylamide) [Fe(L2)2] [L2 )
N(CH2But)(C6H3Pri2-2,6)].
Figure 1. Molecular structure of 3 (30% thermal ellipsoid). Selected bond
lengths (Å) and angles (deg) with data for 4 in square brackets are as
follows: M ) Fe [Co], M-N1 1.965(4) [1.960(2)], M-C18 2.084(6)
[2.038(2)], N1-C1 1.423(6) [1.422(2)], N1-Si1 1.697(4) [1.715(2)]; M
) Fe [Co], C18-M-N1 127.4(2) [124.90(9)], C1-N1-Si1 118.7(3)
[118.5(1)], C1-N1-M 116.4(3) [116.4(1)], Si1-N1-M 122.6(2) [122.65-
(8)].
Our initial attempts to prepare iron(II) and cobalt(II) bis-
(amido) complexes of the L1 ligand via the reaction of 2
mol equiv of [Li(L1)(tmeda)] with anhydrous MCl2 (M )
Fe, Co) have been unsuccessful. In our hands, only the
monosubstituted iron(II) and cobalt(II) amides [M(L1)(Cl)-
(tmeda)] [M ) Fe (1), Co (2);17 (Scheme 1) were isolated,
despite the stoichiometry of the reagents and reaction
conditions (reaction temperature and solvent polarity) we
employed. Apparently, the steric stability of 1 and 2 prevents
them from undergoing further ligand metathesis reactions
to form the corresponding disubstituted derivatives.18 This
is consistent with our observations that both 1 and 2 were
unreactive toward the bulky [N(SiMe3)2]- ligand, notwith-
standing that they contain a terminal chloride ligand that may
allow further functionalization of the compounds. Accord-
ingly, we turned our attention to the reaction of 1 and 2 with
less hindered ligands. Toward this end, we chose a prototypi-
cal alkyl ligand in organometallic chemistry, namely, the least
hindered methyl ligand.
signals for the metal-bound methyl ligand could not be
observed, probably because of the broadness of the signals.
Figure 1 depicts the single-crystal X-ray structure of 3, which
is isomorphous with the CoII analogue 4 (see Figure S3 in
the Supporting Information).25 Complexes 3 and 4 exhibit a
distorted tetrahedral geometry. Compared to other four-
coordinate iron(II) and cobalt(II) methyl complexes, the Fe-
Me distance of 2.084(6) Å for 3 is comparable to that of
2.079(3) Å for [PhTptBu]FeMe20 but slightly longer than that
of 2.013(3) Å for [PhBPiPr3]FeMe.21 On the other hand, the
Co-Me distance of 2.038(2) Å for 4 is slightly shorter than
the corresponding distances of [TptBu]CoMe [Co-C ) 2.12-
(1) Å]22 and [PhTttBu]CoMe [Co-C ) 2.052(3) Å].23
However, they are longer than the Fe-Me and Co-Me
distances of 2.009(3) and 1.963(3) Å, respectively, in the
three-coordinate diketiminate complexes [LMMe] (L )
â-diketiminate; M ) Fe, Co).24 The M-N(amido) distances
of 1.965(4) and 1.960(2) Å in 3 and 4, respectively, are
slightly longer than the corresponding distances in the chloro
derivatives 1 [1.948(2) Å] and 2 [1.922(2) Å] (see the
Supporting Information). This structural difference may be
As shown in Scheme 1, treatment of 1 and 2 with
equimolar amounts of LiMe in toluene afforded the 14-
electron iron(II) and 15-electron cobalt(II) methyl-arylamide
complexes [M(L1)(Me)(tmeda)] [M ) Fe (3), Co (4)],
respectively. Both 3 and 4 are mononuclear high-spin
complexes with solution magnetic moments of 5.02 µB (for
3) and 4.12 µB (for 4).19 The 1H NMR spectra of the methyl
complexes showed well-resolved isotropically shifted reso-
nance signals due to L1 and tmeda (see the Supporting
Information). However, like other iron(II) alkyl complexes
recently reported in the literature (vide infra),20-24 resonance
(23) Schebler, P. J.; Mandimutsira, B. S.; Riordan, C. G.; Liable-Sands,
L. M.; Incarvito, C. D.; Rheingold, A. L. J. Am. Chem. Soc. 2001,
123, 331-332.
(24) Holland, P. L.; Cundari, T. R.; Perez, L. L.; Eckert, N. A.; Lachicotte,
R. J. J. Am. Chem. Soc. 2002, 124, 14416-14424.
(25) Data collection for 3: C18H37FeN3Si, Mr ) 379.45, crystal dimensions
0.4 × 0.3 × 0.2 mm3, triclinic (P1h), a ) 8.036(14) Å, b ) 10.296-
(16) Å, c ) 14.97(2) Å, R ) 75.74(3)°, â ) 76.18(3)°, γ ) 70.79-
(17) The molecular structures of 1 and 2 have been confirmed by X-ray
crystallography. See Figures S1 and S2 in the Supporting Information.
1 and 2 are isotypic, monomeric complexes with a distorted tetrahedral
geometry around the high-spin metal center (µeff ) 4.79 µB for 1 and
3.77 µB for 219). Detailed structural and spectroscopic characterization
of the complexes will be reported in a full article.
(18) In order to verify that 1 and 2 are not kinetic products of the reactions,
we have also examined the reaction of MCl2 (M ) Fe or Co) with 2
mol equiv of [Li(L1)(tmeda)] at a higher temperature (80 °C). Only
the monoamido complexes 1 and 2 were isolated under the latter
reaction conditions.
(19) Magnetic moments of the complexes were measured by the Evans
method in toluene at 298 K. Evans, D. F. J. Chem. Soc. 1959, 2003-
2005.
(20) Kisko, J. L.; Hascall, T.; Parkin, G. J. Am. Chem. Soc. 1998, 120,
10561-10562.
(21) Daida, E. J.; Peters, J. C. Inorg. Chem. 2004, 43, 7474-7485.
(22) Jewson, J. D.; Liable-Sands, L. M.; Yap, G. P. A.; Rheingold, A. L.;
Theopold, K. H. Organometallics 1999, 18, 300-305.
(3)°, V ) 1114(3) Å3, Z ) 2, Fcalcd ) 1.131 g/cm3, µ ) 0.734 mm-1
,
Mo KR radiation λ ) 0.710 73 Å, T ) 273(2) K, reflections measured
) 6817, independent reflections ) 4788 (Rint ) 0.0506), observed
reflections ) 2522 [I > 2σ(I)], final R indices R1 ) 0.0615 and wR2
) 0.1514. Data collection for 4: C18H37CoN3Si, Mr ) 382.53, crystal
dimensions 0.3 × 0.2 × 0.18 mm3, triclinic (P1h), a ) 8.0103(5) Å, b
) 10.2402(6) Å, c ) 15.1224(9) Å, R ) 76.1290(10)°, â ) 76.1650-
(10)°, γ ) 70.2830(10)°, V ) 1116.54(12) Å3, Z ) 2, Fcalcd ) 1.138
g/cm3, µ ) 0.826 mm-1, Mo KR radiation λ ) 0.710 73 Å, T ) 273-
(2) K, reflections measured ) 6019, independent reflections ) 4266
(Rint ) 0.0132), observed reflections ) 3786 [I > 2σ(I)], final R indices
R1 ) 0.0331 and wR2 ) 0.0945. Data collection for 5: C34H56FeN2,
Mr ) 548.66, crystal dimensions 0.4 × 0.3 × 0.2 mm3, monoclinic
(C2/c), a ) 20.236(3) Å, b ) 17.716(2) Å, c ) 9.7692(12) Å, R )
90°, â ) 100.340(3)°, γ ) 90°, V ) 3445.4(8) Å3, Z ) 4, Fcalcd
)
1.058 g/cm3, µ ) 0.459 mm-1, Mo KR radiation λ ) 0.710 73 Å, T
) 293(2) K, reflections measured ) 11 620, independent reflections
) 4163 (Rint ) 0.0663), observed reflections ) 1663 [I > 2σ(I)], final
R indices R1 ) 0.0528 and wR2 ) 0.1115.
7696 Inorganic Chemistry, Vol. 46, No. 19, 2007