Magnesium(II) complexes of 2,4-N,N′-disubstituted 1,3,5-triazapentadienyl ligands: Synthesis and characterization of [N(Dipp)C(NMe2)NC(NMe2)N(SiMe3)MgBr] 2 and [N(R)C(R′)NC(R′)N(SiMe3)]2Mg

Article abstract of DOI:10.1021/ic102401w

Treatment of the appropriate lithium or sodium 2,4-N,N′-disubstituted 1,3,5-triazapentadienate [RNC(R′)NC(R′)N(SiMe₃)M] ₂ (R = Ph, 2,6-ⁱPr₂-C₆H ₃(Dipp) or SiMe₃; R′ = NMe₂

Full text of DOI:10.1021/ic102401w

1926 Inorg. Chem. 2011, 50, 1926–1930
DOI: 10.1021/ic102401w
Magnesium(II) Complexes of 2,4-N,N0-Disubstituted 1,3,5-Triazapentadienyl
Ligands: Synthesis and Characterization of
[N(Dipp)C(NMe2)NC(NMe2)N(SiMe3)MgBr]2 and [N(R)C(R0)NC(R0)N(SiMe3)]2Mg
(Dipp = 2,6-iPr2-C6H3, R = Ph, SiMe3; R0 = NMe2, 1-piperidino)
Meisu Zhou,* Tao Gong, Xiaoli Qiao, Hongbo Tong, Jianping Guo, and Diansheng Liu
Institute of Applied Chemistry, Shanxi University, Taiyuan 030006, People’s Republic of China,
Received December 1, 2010
Treatment of the appropriate lithium or sodium 2,4-N,N0-disubstituted 1,3,5-triazapentadienate [RNC(R0)NC(R0)-
N(SiMe3)M]2 (R = Ph, 2,6-iPr2-C6H3(Dipp) or SiMe3; R0 = NMe2 or 1-piperidino; M = Li or Na) with one or half
equivalent portion of MgBr2(THF)2 in Et2O under mild conditions furnishes in good yield the first structurally
characterized molecular magnesium 2,4-N,N0-disubstituted 1,3,5-triazapentadienates [DippNC(NMe2)NC(NMe2)N-
(SiMe3)MgBr]2 (1), [{RNC(R0)NC(R0)N(SiMe3)}2Mg] (R = Ph, R0 = NMe2 2; R = Ph, R0 = 1-piperidino 3; R = SiMe3,
R0 = 1-piperidino 4). The solid-state structure of 1 is dimeric and those of 2, 3, and 4 are monomeric. The ligand
backbone NCNCN in 1 adopts a W-shaped configuration, while in 2, 3 and 4 adopts a U-shaped configuration.
Introduction
5-triazapentadienyl ligands are rare. The perfluoraoalkyl-
substituted chelating 1,3,5-triazapentadienyl [C3F7-C(NPh)-
N-C(NPh)-C3F7]2Mg was the only such example in the
literature, which was prepared from the corresponding ligand
C3F7-C(dNPh)-NdC(PhNH)-C3F7 and (C5H5)2Mg in
toluene.11 Other monoanionic nitrogen-chelating magnesium-
(II) complexessuchasβ-diketiminates,12,13 symmetric and asym-
metric amidinates,14,15 and guanidinates16 are well-known. The
magnesium(II) boratahetero-amidinates including bis-
(organomagnesium) complexes {[PhB(μ3-NtBu)2](MgtBu)2-
(μ3-Cl)Li(OEt2)3}, {[PhB(μ3-NtBu)2](MgR)2(THF)2} (R =
iPr or Ph) and mononuclear {[PhB(μ-NDipp)2]Mg(OEt2)2}
were reported.17 Several chelating magnesium(I) derivatives
[{N(Dipp)C(Me)}2CH]2Mg2 and [N(Dipp)C(N(iPr)2)N-
(Dipp)]2Mg2 (Dipp = 2,6-(iPr)2C6H3) were also described.13,18
We have recently synthesized some main-group and transition
metal complexes bearing 2,4-N,N0-disubstituted 1,3,5-tria-
1,3,5-triazapentadienyl ligand frameworks containing do-
nor nitrogen atoms have turned out to be the most promising
ligands since the powerful ligands not only coordinate to a
remarkably wide range of metal ions, but also show a rich
variety of coordination modes.1-4 On the basis of their
structural characters, the easy tuning of their steric and
electronic properties by variation of the substituents at the
nitrogen atoms makes these ligands very attractive for the
synthesis of main group and transition metal complexes of
this system.5-7 Recently, the utilities of some fluorinated
1,3,5-triazapentadienato or 2,4-alkoxy-1,3,5-triazapentadie-
nato metal complexes as catalysts were investigated.8-10 The
structurally characterized magnesium(II) adducts of 1, 3,
*To whom correspondence should be addressed. Tel: þ86-351-7010722.
Fax: þ86-351-7016048. E-mail: mszhou@sxu.edu.cn.
(1) Dias, H. A. R.; Singh, S. Dalton Trans. 2006, 1995–2000.
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2
(3) Dias, H. A. R.; Singh, S. Inorg. Chem. 2004, 43, 7396–7402.
(4) Dias, H. A. R.; Singh, S. Inorg. Chem. 2004, 43, 5786–5788.
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J. R. F.; Pombeiro, A. J. L. Chem. Commun. 2010, 46, 2766–2768.
(11) Siedle, A. R.; Webb, R. J.; Behr, F. E.; Newmark, R. A.; Weil, D. A.;
Erickson, K.; Naujok, R.; Brostrom, M.; Mueller, M.; Chou, S.-H.; Young,
V. G. Inorg. Chem. 2003, 42, 932–934.
(12) Caro, C. F.; Hitchcock, P. B.; Lappert, M. F. Chem. Commun. 1999,
1433–1434.
(13) Green, S. P.; Jones, C.; Stasch, A. Science 2007, 318, 1754–1757.
(14) Lee, H.-K.; Lam, T. S.; Lam, C.-K.; Li, H.-W.; Fung, S.-M. New. J.
Chem. 2003, 27, 1310–1318.
ꢀ
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r
pubs.acs.org/IC
Published on Web 01/28/2011
2011 American Chemical Society

Article
Inorganic Chemistry, Vol. 50, No. 5, 2011 1927
R0 = NMe2) and [N(Ar)C(NMe2)NC(NMe2)N(R)]-2 (Ar =
Ph, 2,6-iPr2-C6H3; R = H, SiMe3),19,20 closely related analo-
gues of the popular 1,5-diazapentadienyl systems, which have
been widely investigated.21-25 As part of a broader study of
the coordination chemistry of triazapentadienyl ligands, we
report here on the 2,4-N,N0-disubstituted 1,3,5-triazapenta-
dienyl ligands in magnesium(II) chemistry: the synthesis and
molecular structures of dimeric [DippNC(NMe2)NC(NMe2)-
N(SiMe3)MgBr]2 1, and monomeric [{RNC(R0)NC(R0)N-
(SiMe3)}2Mg] (R = Ph, R0 = NMe2 2; R =Ph, R0 = 1-
piperidino 3; R = SiMe3, R0 = 1-piperidino 4). The NCNCN
ligands backbone in dimeric 1 adopted W-shaped configura-
tion, bridging two metal centers with three N-centers of each
coordinated to two Mg atoms, while in homoleptic com-
plexes 2-4 NCNCN backbone adopted U-shaped config-
uration, chelating the Mg center via the terminal nitrogen
atoms. Five-coordinate Mg(II) atom in complex 1 featured a
much distorted trigonal bipyramidal environment, while in
2-4 tetrahedral or distorted tetrahedral structures were found.
solution was allowed to warm to room temperature (rt) and was
stirred overnight. Then MgBr2(THF)2 (0.61 g, 1.85 mmol) was
added slowly to the above solution at -78 °C. The resultant
mixture was allowed to warm to rt and stirred for overnight. The
volatiles were removed in vacuo, and the residue was extracted
with dichloromethane and filtered. The filtrate was concentrated
in vacuo to ca. 15 cm3, yielding colorless crystals of 1 (0.85 g,
36%). Mp 240-242 °C. (Found: C, 48.44; H, 7.31, N, 12.88%.
C43H78Br2Cl2Mg2N10Si2 requires C, 48.24; H, 7.34, N, 13.08%.
1H NMR (C5D5N): δ 0.72 (s, 18 H, Si(CH3)3), 1.16-1.18 (d, 24
H, CH(CH3)2), 2.62-2.91 (m, 24 H, N(CH3)2), 3.02-3.16 (m, 4
H, PhCH(CH3)2), 7.38-7.59 (m, 6 H, Ph), 4.20 (s, 2 H, CH2Cl2).
13C NMR (C5D5N): δ 3.06 Si(CH3)3, 24.86, 25.86 (CH(CH3)2),
29.55 CH(CH3)2), 38.00, 38.61, 39.91, 40.79 (N(CH3)2), 121.99
(p-CAr), 129.58 (m-CAr), 140.45 (o-CAr), 156.34 (Cipso),161.61
(Me3SiNCN), 184.00 (ArNCN), 56.13 (CH2Cl2).
[{RNC(R0)NC(R0)N(SiMe3)}2Mg] (R = Ph, R0 = NMe2) (2).
N,N-dimethylcyanamide (0.58 mL, 7.18 mmol) was added
slowly to a solution of compound PhN(Li)SiMe3 (0.67 g, 3.59
mmol) in Et2O (30 mL) at -78 °C. The resultant pale-yellow
solution was allowed to warm to rt and was stirred overnight.
Then MgBr2(THF)2 (1.18 g, 3.59 mmol) was added slowly to the
above solution at -78 °C. The resultant white solution was also
allowed to warm to rt and was stirred overnight. The solvent was
removed in vacuo. The residue was dissolved in CH2Cl2 and
filtered. The filtrate was concentrated and crystallized at rt to
give colorless crystals of 2 (0.35 g, 30%). Mp 227-229 °C.
(Found: C, 56.74; H, 8.18, N, 22.28%. C30H52MgN10Si2 re-
Experimental Section
General Procedures. All manipulations were carried out
under an atmosphere of argon using standard Schlenk techni-
ques. Solvents were purchased from commercial sources. Deut-
erated solvents C5D5N, CDCl3 were dried over activated
˚
molecular sieves (4 A) and vacuum transferred before use.
Diethyl ether was dried and distilled from sodium/benzophe-
none and stored over a sodium mirror under argon. Dichloro-
1
quires: C, 56.90; H, 8.28 N, 22.12%). H NMR (C5D5N): δ
0.20-0.37 (m, 18 H, Si(CH3)3), 2.78, 2.94 (d, 24 H, N(CH3)2),
6.78-7.21 (m, 10 H, Ph). 13C NMR (C5D5N): δ 0.96 (Si(CH3)3),
37.88, 38.39, 40.08, 40.34 (N(CH3)2), 122.05 (p-CPh), 123.62 (m-
CPh), 128.14 (o-CPh), 150.2 (Cipso), 158.57, 160.65 (NCN).
[{RNC(R0)NC(R0)N(SiMe3)}2Mg] (R=Ph, R0 =1-piperidino)
(3). 1-Piperidinecarbonitrile (0.57 mL, 4.88 mmol) was added to a
solution of PhN(Na)SiMe3 (0.46 g, 2.44 mmol) in Et2O (30 cm3) at
-78 °C. The resulting mixturewas warmed to ca. 25°Candstirred
for overnight. MgBr2(THF)2 (0.40 g, 1.22 mmol) was added at
-78 °C. The resulting white mixture was warmed to ca. 25 °C,
stirred overnight, and then filtered. The filtrate was concentrated
in vacuo to ca. 15 cm3 and cooled at -25 °C for several days,
yielding colorless crystals of 3 (0.37 g, 38%). Mp 200-202 °C.
(Found: C, 64.10; H, 8.96, N, 17.28%. C42H68MgN10Si2 requires:
C, 63.57; H, 8.64 N, 17.65%). 1H NMR (CDCl3): δ 0.12 (s, 18 H,
Si(CH3)3, 1.32-1.55 (m, 24 H, (CH2)3), 3.04-3.12 (m, 16 H,
N(CH2)), 6.68-7.26 (m, 10 H, Ph). 13C NMR (CDCl3): δ 2.12
(Si(CH3)3), 24.67, 24.92, 25.85 ((CH2)3), 48.09, 51.15 (N(CH2)2),
119.12 (p-CPh), 121.64 (m-CPh), 128.65 (o-CPh), 151.40 (Cipso),
161.12, 169.67 (NCN).
[{RNC(R0)NC(R0)N(SiMe3)}2Mg] (R = SiMe3, R0 = 1-piper-
idino) (4). 1-Piperidinecarbonitrile (0.45 mL, 3.88 mmol) was
added to a solution of LiN(SiMe3)2 (0.32 g, 1.94 mmol) in Et2O
(30 cm3) at -78 °C. The resulting mixture was warmed to ca.
25 °C and stirred for overnight. MgBr2(THF)2 (0.414 g, 1.26
mmol) was added at -78 °C. The resulting white mixture was
warmed to ca. 25 °C, stirred overnight, and then filtered. The
filtrate was concentrated in vacuo to ca. 10 cm3 and left at room
temperature for 3 d to to give colorless crystals of 4 (0.48 g, 58%).
Mp 125-127 °C. (Found: C, 55.24; H, 9.52, N, 16.57%. C40H86-
MgN10OSi4 requires: C, 55.88; H, 10.08 N, 16.29%). 1H NMR
(CDCl3): δ 0.04-0.08 (m, 36 H, Si(CH3)3, 1.49 (s, 24 H, (CH2)3),
3.04 (s, 16 H, CN(CH2)), 1.16-1.20 (t, 6 H, OCH2CH3), 3.44-
3.46 (q, 4 H, OCH2CH3). 13C NMR (CDCl3): δ 2.59 (Si(CH3)3),
24.24, 25.44 ((CH2)3), 45.14-48.01 (N(CH2)2), 14.60 (OCH2CH3),
65.20 (OCH2CH3), 166.01 (NCN).
˚
methane was distilled from activated molecular sieves (4 A) or
CaH2. The compounds (Dipp)N(Li)SiMe3 and PhN(Li)SiMe3
were obtained according to published procedures.14,26-28 PhN-
(Na)SiMe3 was prepared in situ by direct transmatallation in
hexane of PhN(Li)SiMe3 with Na(OBut). The lithium amide
LiN(SiMe3)2 was easily accessible via the lithiation of 1,1,1,
3,3,3-hexamethyldisilazane with LiBun in hexane. Glassware
was oven-dried at 150 °C overnight. The NMR spectra were
recorded on a Bruker DRX-300 instrument, and solvent reso-
1
nances were used as the internal references for H spectra and
13C spectra. Melting points were measured in sealed capillaries
and are uncorrected. Elemental analyses were carried out using a
Vario EL-III analyzer (Germany).
Preparations. [DippNC(NMe2)NC(NMe2)N(SiMe3)MgBr]2
(1). N,N-dimethylcyanamide (0.36 mL, 4.4 mmol) was added
slowly to a solution of compound (Dipp)N(Li)SiMe3 (0.56 g, 2.2
mmol) in Et2O (30 mL) at -78 °C. The resultant pale-yellow
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Weng, L.-H.; Liu, D.-S. Inorg. Chem. 2008, 47, 1886–1888.
(20) Zhou, M.-S.; Song, Y.-P.; Gong, T.; Tong, H.-B.; Guo, J.-P.; Weng,
L.-H.; Liu, D.-S. Inorg. Chem. 2008, 47, 6692–6700.
(21) Bourget-Merle, L.; Lappert, M. F.; Severn, J. R. Chem. Rev. 2002,
102, 3031–3066.
(22) Hitchcock, P. B.; Lappert, M. F.; Linnolahti, M.; Sablong, R.;
Severn, J. R. J. Organomet. Chem. 2009, 694, 667–676.
(23) (a) Hitchcock, P. B.; Lappert, M. F.; Liu, D.-S. J. Chem. Soc., Chem.
Commun. 1994, 1699–1700. (b) Hitchcock, P. B.; Lappert, M. F.; Liu, D.-S. J.
Chem. Soc., Chem. Commun. 1994, 2637–2638. (c) Lappert, M. F.; Liu, D.-S. J.
Organomet. Chem. 1995, 500, 203–217.
(24) (a) Annibale, V. T.; Lund, L. M.; Song, D. -T. Chem. Commun. 2010,
46, 8261–8263. (b) Hadzovic, A.; Song, D.-T. Inorg. Chem. 2008, 47, 12010–
12017.
(25) (a) Panda, A; Stender, M; Wright, R. J; Olmstead, M. M.; Klavins,
P.; Power, P. P. Inorg. Chem. 2002, 41, 3909–3916. (b) Wright, R. J; Power, P. P;
Scott, B. L; Kiplinger, J. L. Organometallics 2004, 23, 4801–4803.
(26) Bezombes, J.-P.; Hitchcock, P. B.; Lappert, M. F.; Merle, P. G. J.
Chem. Soc., Dalton Trans. 2001, 816–821.
(27) Hitchcock, P. B.; Lappert, M. F.; Merle, P. G. Dalton Trans. 2007,
585–594.
X-ray Crystallography. X-ray diffraction data for each of 1, 2,
and 4 were collected on an Bruker SMART APEX diffracto-
meter/CCD area detector using monochromated Mo-KR ra-
(28) Antolini, F.; Hitchcock, P. B.; Lappert, M. F.; Merle, P. G. Chem.
Commun. 2000, 1301–1302.
˚
diation, λ = 0.71073 A. Crystals were coated in oil and then

1928 Inorganic Chemistry, Vol. 50, No. 5, 2011
Table 1. Crystal and Refinement Data for 1, 2, and 4
compound
Zhou et al.
1
2
4
formula
M
C43H78Br2Cl2Mg2N10Si2
1070.67
triclinic
C30H52MgN10Si2
633.31
triclinic
C40H86MgN10OSi4
859.86
crystal system
space group
monoclinic
P21/c (No.14)
15.188(4)
28.697(7)
11.888(3)
90.00
100.801(3)
90.00
5090(2)
4
0.168
8707, 0.0395
6367
P1 (No.2)
12.3170(8)
13.8217(9)
17.1073(11)
73.8230(10)
82.7830(10)
76.2170(10)
2711.0(3)
2
1.700
9387, 0.0126
7904
P1 (No.2)
11.175(3)
11.979(4)
16.136(5)
90.077(4)
107.705(4)
115.707(4)
1831.6(10)
2
˚
a/A
˚
b/A
˚
c/A
R°
β °
γ °
3
˚
U/A
Z
absorption coeff (mm-1
unique reflections, Rint
)
0.148
6227, 0.0279
5064
reflections with I > 2σ(I)
final R indices [ I > 2σ(I) ] R1, wR2
R indices (all data) R1, wR2
0.0337, 0.0893
0.0419, 0.0940
0.0723, 0.1916
0.0946, 0.2350
0.0558, 0.1534
0.0787, 0.1833
o
o
˚
˚
Table 2. Selected Bond Lengths (A) and Angles ( ) for 1
Table 4. Selected Bond Lengths (A) and Angles ( ) for 4
Mg1-Br1
2.4622(7)
2.1429(19)
1.361(3)
1.406(3)
1.311(3)
63.69(7)
113.16(19)
118.59(19)
127.35(19)
Mg1-N3
N1-C13
N3-C13
N4-C16
2.1757(18)
1.308(3)
1.388(3)
1.349(3)
Mg-N1
2.082(2)
2.073(2)
1.320(4)
1.338(4)
1.443(4)
1.330(3)
1.346(4)
1.435(4)
95.08(10)
116.02(18)
128.3(2)
116.84(18)
128.4(2)
117.35(18)
Mg-N5
Mg-N10
C1-N2
2.062(2)
2.058(3)
1.403(4)
1.327(4)
1.311(4)
1.390(4)
1.321(4)
1.326(4)
94.84(10)
127.5(2)
129.1(2)
126.7(2)
128.8(3)
116.47(19)
Mg1-N5
Mg-N6
N2-C13
C1-N1
N3-C16
C1-N3
C2-N3
N5-C16
C2-N4
C2-N5
N3-Mg1-N5
N1-C13-N3
N3-C16-N4
N4-C16-N5
N1-C13-N2
N2-C13-N3
N3-C16-N5
C13-N3-C16
127.4(2)
C19-N6
C19-N7
C20-N8
C20-N10
119.41(19)
113.92(18)
122.49(17)
C19-N8
C20-N9
N1-Mg-N5
Mg-N1-C1
C1-N3-C2
Mg-N5-C2
C19-N8-C20
Mg-N6-C19
N6-Mg-N10
N1-C1-N3
N3-C2-N5
N6-C19-N8
N8-C20-N10
Mg-N10-C20
o
˚
Table 3. Selected Bond Lengths (A) and Angles ( ) for 2
Mg-N1
2.040(3)
2.049(3)
2.052(3)
2.039(3)
1.365(4)
94.20(12)
119.3(2)
122.8(3)
127.9(3)
C1-N2
1.330(4)
1.330(4)
1.331(4)
1.376(5)
1.329(4)
94.19(12)
113.0(2)
126.8(3)
Mg-N5
C1-N3
Mg-N6
C2-N3
Mg-N10
C1-N1
C2-N4
C2-N5
Scheme 1. Synthetic Routes to Complexes 1-4
N1-Mg-N5
Mg-N1-C1
N1-C1-N3
C1-N3-C2
N6-Mg-N10
Mg-N5-C2
N3-C2-N5
directly mounted on the diffractometer under a stream of cold
nitrogen gas. A total of N reflections were collected by using ω
scan mode. Corrections were applied for Lorentz and polariza-
tion effects as well as absorption using multiscans (SADABS).29
The structure was solved by direct method (SHELXS-97).30
Then the remaining non-hydrogen atoms were obtained from
the successive difference Fourier map. All non-H atoms were
refined with anisotropic displacement parameters, while the H
atoms were constrained to parent sites, using riding modes
(SHELXTL).31 Crystal data and details of data collection and
refinements for 1, 2 and 4 are summarized in Table 1. Selected
bond distances and bond angles are listed in Tables 2-4.
Compounds 2, 3, and 4 were obtained similarly to the
procesure of complex 1 at the ratio of 2:1 by treatment of
lithium or sodium (for 3) 1,3,5-triazapentadienate, and
crystallization from dichloromethane for 2, and from
Et2O for 3 and 4 (Scheme 1). The colorless, sharp melting,
crystalline 2,4-N,N0-disubstituted 1,3,5-triazapentadienyl
compounds 1-4 gave satisfactory 1H NMR, 13C NMR,
microanalyses as well as single crystal X-ray (1, 2, and 4)
data.
Crystal Structures. Structure of 1. The X-ray structu-
rally characterized crystalline 1 (Figure 1) shows that
there are two independent molecules in one unit cell.
For each molecule, it is a head-to-tail dimer built around
a planar MgNMgN ring; the angles at the magnesium
atoms [87.69(7), 87.69(7)°] are narrower than those at the
nitrogen atoms [92.31(7), 92.31(7)°]. Each magnesium
Results and Discussion
Synthesis and Characterization. The starting materials
for the synthesis of 1-4 were [RNC(R0)NC(R0)N(SiMe3)-
M]2 (R = Ph, 2,6-iPr2-C6H3(Dipp) or SiMe3; R0 = NMe2
or 1-piperidino; M = Li or Na).19,20 Complexes 1 was ob-
tained in 36% yield by treatment of corresponding lithium
1,3,5-triazapentadienate with magnesium bromide at the
ratio of 1:1 in Et2O and crystallization from CH2Cl2.
€
(29) Sheldrick, G. M. Correction Software; University of Gottinggen:
Germany, 1996.
(30) Sheldrick, G. M. Program for the Solution of Crystal Structures;
€
University of Gottinggen: Germany, 1997.
(31) Program for Crystal Structure Refinement; Bruker Analytical X-ray
Instruments Inc.: Madison, WI, 1998.

Article
Inorganic Chemistry, Vol. 50, No. 5, 2011 1929
Figure 1. Molecular structure of 1.
Figure 2. Molecular structure of 2.
atom is coordinated with four nitrogen atoms from two
ligands and one bromide atom in a much distorted
trigonal bipyramidal environment with the fifth position
being occupied by the bromide. Each ligand NCNCN
backbone adopts a twisted W-shaped conformation. The
dihedral angles between the two MgNCN moieties linked
by N3 and Mg1 are 61.9 and 119.1°, respectively. The
molecule has two fused tricyclic ladder motifs comprising
a central plane Mg1N3Mg10N30 ring flanked by parallel
planes Mg1N3C16N5 and Mg10N30C160N50, Mg10N1-
C13N3, and Mg1N10C130N30, respectively. The dihedral
angle between the core Mg1N3Mg10N30 and the adjacent
four-membered rings Mg1N10C130N30 and Mg1N3C-
16N5 are 46.7 and 40.0°. The bond distances N1-C13,
C13-N3, N3-C16, and C16-N5 are 1.308(3), 1.388(3),
˚
1.406(3), and 1.311(3) A, respectively, indicating an ob-
Figure 3. Molecular structure of 4.
vious short-long-long-short pattern of C-N bond
lengths in the NCNCN backbone. The C=N and C-N
bonding is consistent with previously reported dimeric
W-shaped triazapentadienyl lithium complexes [(SiMe3)-
nearly rigorously tetrahedral environment defined by the
four nitrogen atoms from the two bidentate 1,3,5-triaza-
pentadienato ligands with dihedral angle of 90.4° between
planes N1MgN5 and N6MgN10. Each of the bidentate
1,3,5-triazapentadieno ligand forms a planar six-mem-
bered metallacycle MgNCNCN with a mean deviation of
NC(NMe2)NC(NMe2)N(SiMe3)]- 19 and [N(Dipp)C-
2
20
.
(NMe2)NC(NMe2)N(SiMe3)]-
The coordination
2
mode that the ligands to bridge two metal centers with
three N-centers of each coordinated to two Mg atoms in
complex 1 is quite similar to that in the corresponding
triazapentadienyl lithium complexes19,20 because Liþ and
Mg2þ have closer sizes, and there is a well-known diagonal
periodicity between these two ions (ionic radii for Liþ =
˚
0.13 A. The Mg-N bond distances are 2.040(3) [Mg-
˚
N1], 2.049(3) [Mg-N5], 2.052(3) [Mg-N6], and 2.039(3) A
[Mg-N10], respectively. The bond angles N1-Mg-N5
and N6-Mg-N10 are 94.20(12) and 94.19(12)°, respec-
tively. Within the 1,3,5-triazapentadieno ligand, the bond
2þ
˚
˚
˚
˚
0.60 A, Mg = 0.65 A).
For the CN3 (C13N3 and C16N3) frameworks in 1, the
C-N bond distances are in the range of 1.308(3)
distances N1-C1[1.365(4) A], C1-N3 [1.330(4) A],
˚
˚
N3-C2 [1.331(4)] A], and C2-N5 [1.329(4) A] are almost
identical, suggesting delocalization in the ligand backbone.
Bond angles N1-C1-N3, C1-N3-C2, and N3-C2-N5
are 122.8(3), 127.9(3) and 126.8(3)°, respectively.
˚
∼1.406(3) A, and the dihedral angles between N1C13N3
and C14N2C15, N3C16N5 and C17N4C18 are 21.7 and
9.9°, respectively, indicating the presence of delocalized CN3
fragments to some extent. This is related to the structural
nature of guanidinate complexes and sp2 hybridization ne-
cessary for conjugation.
Complex 4 (Figure 3) crystallizes in the monoclinic
space P21/c. The coordination mode of central metal
magnesium in complex 4 is similar to that in magnesium
complex 2. Complex 4 contains two η2-chelating 1,3,5-
triazapentadieno ligands around the magnesium center,
adopting a highly distorted tetrahedral coordination
geometry, with a dihedral angle of 73.3° between planes
N1MgN5 and N6MgN10. Very similar structures to
complexes 2 and 4 were found in the previously reported
transition metal Mn(II), Fe(II), and Co(II) 2,4-N,N0-
disubstituted 1,3,5-triazapentadienyl complexes20 and
the related magnesium β-diketiminate complex [Mg-
({N(R)C(Ph)}2CH)2].12 All of the analogues featured
Structures of 2, 3 and 4. The monomeric structures of
complexes 2-4 with tetrahedral Mg(II) centers are very
similar. Although crystals of 3 have not yet proved suitable
for X-ray crystallographic studies, the X-ray data is en-
ough to confirm the outline of the molecule. Crystals of 2
and 4 yielded a good data set that upon refinementgavethe
structures presented in Figures 2 and 3, respectively.
The low-temperature X-ray diffraction analysis reveals
that in molecule 2 (Figure 2) the magnesium atom is in a

1930 Inorganic Chemistry, Vol. 50, No. 5, 2011
Zhou et al.
˚
Table 5. Selected Bond Lengths [A] and Angles [°] of 2, 4 and Their Four-
NCy}2ZrCl2] [86.3°], or [{CyNC[N(SiMe3)2]NCy}2HfCl2]
[85.8°],32 again indicating stronger or a little π-bonding
interactions between NCN and NR2 moieties in 2 or 4.
The dimeric and monomeric structures of complexes
1-4 seem to be the result of the two modes of coordina-
tion exhibited by the ligand. A comparison of the struc-
tural features of complexes 1-4 suggests that the dimeric
structure for complex 1 will be sterically favored due to
the presence of the bulky diisopropylphenyl substitution
at the nitrogen atom. And the W- form should be the
preferred conformer that is free of steric strain and the
electron density is distributed over a maximum distance.
Whereas in less bulky complexes 2-4, the magnesium
atomic radii allowed the NCNCN backbone to span from
one terminus of the 1,3,5-triazapentadienyl moiety to the
other provided the latter coils up to adopt the U shape.
This was also found in pentadienyl species and substi-
tuted 1,3-diphenylallyllithium species.33,34
In conclusion, 1,3,5-triazapentadienyl ligands have
proven to be useful in the preparation of a family of
2,4-N,N0-disubstituted 1,3,5-triazapentadienyl magne-
sium complexes [DippNC(NMe2)NC(NMe2)N(SiMe3)-
MgBr]2 1, [{RNC(R0)NC(R0)N(SiMe3)}2Mg] (R = Ph,
R0 = NMe2 2; R = Ph, R0 = 1-piperidino 3; R = SiMe3,
R0 = 1-piperidino 4). From these results, it is clear that
the ligands bridge two metal centers with three N-centers
of each coordinated to two Mg atoms in complex 1,
whereas in homoleptic compounds 2-4, the ligands
chelate the Mg center via the terminal nitrogen atoms of
NCNCN. Conjugation occurs in the ligand backbone
NCNCN of 2-4, and a partial delocalization is observed
in 1. The orientation of the NR2 substituents at 2- and 4-
positions to its adjacent NCN planes in 1, 2, and 4 result in
guanidinate structural features for the ligand system. The
first structurally characterized 2,4-N,N0-disubstituted
1,3,5-triazapentadienyl magnesium(II) complexes 1-4
represent a novel class of lighter alkaline-earth metal
complexes having NCNCN ligand system. Our continu-
ing investigations are focus on the use of the reported
magnesium(II) complexes and the steric and electronic
features that influence the coordination chemistry and the
properties of alkaline-earth metal 2,4-N,N0-disubstituted
1,3,5-triazapentadienyl complexes.
Coordinate Analogues
parameters
2
4
I
II
III
˚
a/A
2.040(3)
2.049(3)
1.365(4)
1.329(4)
1.330(4)
1.331(4)
2.082(2)
2.063(2)
1.320(4)
1.311(4)
1.338(4)
1.327(4)
2.096(8)
2.068(8)
1.299(11)
1.318(11)
1.432(13)
1.403(13)
1.996(5)
2.027(4)
1.296(3)
1.305(3)
1.356(3)
1.342(3)
2.014(2)
2.038(2)
1.330(4)
1.358(4)
1.338(4)
1.346(3)
˚
b/A
˚
c/A
˚
d/A
˚
e/A
˚
f/A
R/°
β/°
94.20(12) 95.08(10) 99.7(3)
127.9(3) 128.3(2) 131.5(9)
92.58(18) 94.57(8)
123.4(2) 127.3(2)
η2-bonded ligands with a U-shaped ligand backbone and
gave planar six-membered MNCCCN metallacycles. A
comparison of some of the relevant bond lengths and
angles for complexes 2 and 4 with those of several other
known N,N0 chelating four-coordinate monoanionic com-
plexes such as magnesium β-diketiminate [{N(SiMe3)-
C(Ph)}2CH]2Mg (I),12 lithium fluorinated 1,3,5-triaza-
pentadienate N{(C3F7)C(Mes)N}2Li(THF)2 (Mes =
2,4,6-trimethylphenyl) (II)9 and transition metal 2, 4-N,
N0-disubstituted 1,3,5-triazapentadienate [N(Ph)C(NMe2)-
NC(NMe2)N(SiMe3)]2Fe (III)20 is presented in Table 5.
The bond distances of Mg-N in 4 are in the range of
˚
2.058(3)∼2.082(2) A, slightly longer than those in 2
˚
[2.039(3)∼2.052(3) A], Li-N in II and Fe-N in III,
comparable to the Mg-N bond distances in I. Both the
bite angles N-Mg-N in 4 [95.08(10) and 94.84(10) °] and
in 2 [94.19(12) and 94.20(12) °] are comparable to those in
other 1,3,5- triazapentadienyl metal systems such as II
and III, narrower than that in the 1,5-diazapentadienyl
system I. Although there are minor differences among the
N-C bond lengths in those complexes, all of them are
falling in the normal range for π-delocalization in each
ligand NCNCN backbone.22 In 4, the metallacycle
MgNCNCN is almost planar with a mean deviation of
˚
0.09 A. The bond angle at central nitrogen atom of
NCNCN backbone in 4 is similar to that in other 2,4-N,
N0-disubstituted 1,3,5-triazapentadienyl systems 2 and
III, wider than that in four-coordinate fluorinated 1,3,5-
triazapentadienato lithium complex II, but narrower than
that at the central carbon atom of NCCCN of its 1,5-
diazapentadienyl analogue I.
The dihedral angles formed by the planar NR2 (2-,
4- positions) functions and their adjacent NCN planes
[between N1C1N3 and C3N2C7; N3C2N5 and C8N4-
C12] are 16.0 and 26.4° in 2, 48.8 and 69.7° in 4, respectively.
They are much smaller than those nearly perpendicular
orientation moieties found in guanidinato complexes iPrNC-
[N(SiMe3)2]NiPr}2ZrCl2] [88.2°], [{CyNC[N(SiMe3)2]-
Acknowledgment. The authors acknowledge the finan-
cial support of the Natural Science Foundation of China
(No.20672070, 20772074), and Shanxi Scholarship Coun-
cil of China (No. 201012, M.S.Z.).
Supporting Information Available: X-ray crystallographic
data for 1, 2, and 4 (CCDC reference numbers 710048,
710049, and 716179). This material is available free of charge
via the Internet at http://pubs.acs.org.
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