Synthesis, characterization, and crystal structures of {Me2Al(μ-i-Pr2N)2Mg[(R)NC(Me)N(R)]} (R = i-Pr, t-Bu): Insertion of a carbodiimide (RNCNR) into a Mg-C bond

Article abstract of DOI:10.1021/om9508703

A series of amidino-bridged mixed-metal aluminum-magnesium complexes, {[R₂Al(μ-R′₂N) ₂Mg-[(R″)NC(R)N(R″)]} (R = Me, R′ = i-Pr, R″ = i-Pr, 1a; R = Me, R′ = i-Pr, R″ = t-Bu, 1b; R = Me, R′ = i-Pr, R″ = p-tolyl, 1c; R = Me, R′ = Et, R″ = i-Pr, 2a; R = Me, R′ = Et, R″ = t-Bu, 2b; R = Et, R′ = i-Pr, R″ = i-Pr, 3a; R = Et, R′ = i-Pr, R″ = t-Bu), were prepared by insertion reactions of the aluminum-magnesium complexes [R₂-Al(μ-R′₂N)₂Mg(μ-R)]_n (R = Me, Et; R′ = Et, i-Pr) (n = 2, 4) with various substituted carbodiimides and characterized by mass spectra, IR spectra, elemental analysis, and ¹H and ¹³C NMR data. The structures of two of the compounds 1a,b have been determined by single-crystal X-ray diffraction analysis. The structural data show that the bonding of the two nitrogens of the carbodiimide to the magnesium atom is (σ, σ) symmetric and indicate a weak interaction between Mg and C(15).

Full text of DOI:10.1021/om9508703

Organometallics 1996, 15, 2571-2574
2571
Syn th esis, Ch a r a cter iza tion , a n d Cr ysta l Str u ctu r es of
{Me2Al(µ-i-P r 2N)2Mg[(R)NC(Me)N(R)]} (R ) i-P r , t-Bu ):
In ser tion of a Ca r bod iim id e (RNCNR) in to a Mg-C Bon d
Mung-Dar Li,† Chung-Cheng Chang,*,† Yu Wang,‡ and Gene-Hsiang Lee‡
Departments of Chemistry, National Sun Yat-sen University, Kaohsiung, Taiwan, ROC, and
National Taiwan University, Taipei, Taiwan, ROC
Received November 6, 1995X
Summary: A series of amidino-bridged mixed-metal
aluminum-magnesium complexes, {[R2Al(µ-R′2N)2Mg-
[(R′′)NC(R)N(R′′)]} (R ) Me, R′ ) i-Pr, R′′ ) i-Pr, 1a ; R
) Me, R′ ) i-Pr, R′′ ) t-Bu, 1b; R ) Me, R′ ) i-Pr, R′′
) p-tolyl, 1c; R ) Me, R′ ) Et, R′′ ) i-Pr, 2a ; R ) Me,
R′ ) Et, R′′ ) t-Bu, 2b; R ) Et, R′ ) i-Pr, R′′ ) i-Pr, 3a ;
R ) Et, R′ ) i-Pr, R′′ ) t-Bu), were prepared by insertion
reactions of the aluminum-magnesium complexes [R2-
Al(µ-R′2N)2Mg(µ-R)]n (R ) Me, Et; R′ ) Et, i-Pr) (n ) 2,
4) with various substituted carbodiimides and charac-
terized by mass spectra, IR spectra, elemental analysis,
and 1H and 13C NMR data. The structures of two of
the compounds 1a ,b have been determined by single-
crystal X-ray diffraction analysis. The structural data
show that the bonding of the two nitrogens of the
carbodiimide to the magnesium atom is (σ, σ) symmetric
and indicate a weak interaction between Mg and C(15).
been reported.12,13 Here we present the synthesis and
characterization of a series of amidino-bridged mixed-
metal aluminum-magnesium complexes: {[R2Al(µ-
R′2N)2Mg[(R′′)NC(R)N(R′′)]} (R ) Me, R′ ) i-Pr, R′′ )
i-Pr, 1a ; R ) Me, R′ ) i-Pr, R′′ ) t-Bu, 1b; R ) Me, R′
) i-Pr, R′′ ) p-tolyl, 1c; R ) Me, R′ ) Et, R′′ ) i-Pr, 2a ;
R ) Me, R′ ) Et, R′′ ) t-Bu, 2b; R ) Et, R′ ) i-Pr, R′′
) i-Pr, 3a ; R ) Et, R′ ) i-Pr, R′′ ) t-Bu). The structures
of two of the complexes 1a ,b were determined by X-ray
diffraction analysis. The carbodiimide acts as a biden-
tate ligand forming two Mg-N σ bonds. Pyrolysis of
these compounds was also examined.
Exp er im en ta l Section
Ap p a r a tu s a n d Ma ter ia ls. All manipulations were car-
ried out in a N2-flushed glovebag, drybox, or vacuum system.
1
Solvents were distilled and degassed prior to use. All H and
13C NMR spectra were measured on
a Varian VXR-300
spectrometer. Chemical shifts are referenced relative to either
TMS (1H), benzene-d6 (1H, δ 7.16; 13C{1H}, δ 128.00), or
toluene-d8 (1H, δ 7.09 (m), 7.00 (br), 6.98 (m), 2.09 (quint); 13C-
{1H}, δ 137.5 (s), 128.9 (t), 128.0 (t), 125.2 (t) 20.4 (sep)). Mass
spectral data were obtained on a VG-7025 GC/MS/MS spec-
trometer. IR spectra were recorded at Nujol mulls between
KBr disks on a FT-IR spectrometer. Elemental analyses (C,
H, N) were performed at the Analytische Laboratorien, Lind-
lar, Germany. Deviations from the calculated values in the
elemental analyses were attributed to the extremely air-
sensitive and hygroscopic nature of these compounds. The
starting material, {R2Al(µ-NR′2)2Mg(µ-R)}n, was prepared by
following the method previously described by us.7
Syn th esis of th e Com p lexes. In a generalized procedure,
an ether solution (50 mL) of {R2Al(µ-NR′2)2Mg(µ-R)}n was
added dropwise to a stirred ether solution of carbodiimide (1:n
molar ratio) at room temperature under a nitrogen atmo-
sphere. The reaction took place immediately. Pure com-
pounds of 1a -3b were obtained either by recrystallization or
by distillation of the crude products.
In tr od u ction
Over the past several decades, there are several
reports on the synthesis of organo-aluminum-magne-
sium complexes.1-8 Recently we reported on the inter-
esting chemical properties of the aluminum-magne-
sium complexes including carbon dioxide fixation.9-11
Reactions of carbon dioxide with {Me2Al(µ-NR2)2MgR′}
(R ) Et, i-Pr; R′ ) CH3, C6H5, C6H4-p-CH3) occurred
with insertion at metal-carbon and metal-nitrogen
bonds. The high reactivity of the four-coordinated
magnesium atom in these aluminum-magnesium-
bridged complexes is believed to be due to its stronger
electrophilicities. In this work, carbodiimides (RNCNR),
the molecules isoelectronic with CO2, are used to react
with Mg-C in aluminum-magnesium complexes. Simi-
lar insertion reaction of carbodiimides with transition
metal complexes (e.g. Zr, Nb, Mo, Ru, Ta, W, etc.) have
(12) (a) Gambarotta, S.; Strologo, S.; Floriani, C.; Chiesi-Villa, A.;
Guastini, C. J . Am. Chem. Soc. 1985, 107, 6278. (b) Gambarotta, S.;
Strologo, S.; Floriani, C.; Chiesi-Villa, A.; Guastini, C. Inorg. Chem.
1985, 24, 654.
† National Sun Yat-sen University.
‡ National Taiwan University.
X Abstract published in Advance ACS Abstracts, April 1, 1996.
(1) Ziegler, K.; Holzkamp, Z. J ustus Liebigs Ann. Chem. 1957, 605,
93.
(13) (a) Baker, J .; Kilner, M. Coord. Chem. Rev. 1994, 133, 219. (b)
Bycroft, B. M.; Cotton, J . D. J . Chem. Soc., Dalton Trans. 1973, 1867.
(c) Wilkins, J . D. J . Organomet. Chem. 1974, 80, 349. (d) Drew, M. G.
B.; Wilkins, J . D. J . Chem. Soc., Dalton Trans. 1974, 1579. (e) Drew,
M. G. B.; Wilkins, J . D. Acta Crystallogr., Sect. B 1975, 31, 177. (f)
Drew, M. G. B.; Wilkins, J . D. J . Chem. Soc., Dalton Trans. 1975, 2611.
(g) Drew, M. G. B.; Wilkins, J . D. Acta Crystallogr., Sect. B 1975, 31,
2642. (h) Barker, J .; Kilner, M. J . Chem. Soc., Dalton Trans. 1973,
1867. (i) Inglis, T.; Kilner, M.; Reynoldson, T.; Robertson, E. E. J .
Chem. Soc., Dalton Trans. 1975, 924. (j) Westerhausen, M.; Schwarz,
W. Z. Anorg. Allg. Chem. 1992, 609, 39. (k) Ergezinger, C.; Weller,
F.; Denhnicke, K. Z. Naturforsch., B 1988, 43, 1621. (l) Shapiro, P.
J .; Henling, L. M.; Marsh, R. E.; Bercaw, J . E. Inorg. Chem. 1990, 29,
4560. (m) Gambarotta, S.; Floriani, C.; Villa, A. C.; Guastini, C. J .
Am. Chem. Soc. 1982, 104, 1918. (n) Dick, D. G.; Duchateau, R.;
Edema, J . J . H.; Gambarotta, S. Inorg. Chem. 1993, 32, 1959.
(14) Ibers, J . A., Hamilton, W. C., Eds. International Tables for X-ray
Crystallography; Kynoch Press: Birmingham, England, 1974; Vol. IV,
Tables 2.2B and 2.3.1.
(2) Atwood, J . L.; Stucky, G. D. J . Organomet. Chem. 1968, 3, 53.
(3) Atwood, J . L.; Stucky, G. D. J . Am. Chem. Soc. 1969, 85, 2538.
(4) Malpass, D. B.; Ammin, L. W. J . Organomet. Chem. 1975, 93, 1.
(5) Veith, M.; Frand, W.; Toner, F.; Lange, H. J . Organomet. Chem.
1987, 326, 315.
(6) Meese-Markscheffel, J . A.; Cramer, R. E.; Gilje, J . W. Polyhedron
1994, 13, 1045.
(7) Her, T. Y.; Chang, C. C.; Liu, L. K. Inorg. Chem. 1992, 31, 2219.
(8) Her, T. Y.; Chang, C. C.; Lee, G. H.; Peng, S. M.; Wang, Y. Inorg.
Chem. 1994, 33, 99.
(9) Chang, C. C.; Her, T. Y.; Li, M. D.; Lee, G. H.; Peng, S. M.; Wang,
Y. Inorg. Chem. 1995, 34, 4296.
(10) Chang, C. C.; Lee, W. H.; Her, T. Y.; Lee, G. H.; Peng, S. M.;
Wang, Y. J . Chem. Soc., Dalton Trans. 1994, 315.
(11) Chang, C. C.; Srinivas, B.; Wu, M. L.; Chiang, W. H.; Chiang,
M. Y.; Hsiung, C. S. Organometallics 1995, 14, 5150.
S0276-7333(95)00870-3 CCC: $12.00 © 1996 American Chemical Society

2572 Organometallics, Vol. 15, No. 10, 1996
Ta ble 1. 1H NMR Sp ectr a l Da ta (δ (p p m ))
Notes
compd (solvent)
AlR2
NR′2
(R′′N)C(R)(NR′′)
(R′′N)C(R)(NR′′)
1a (d8-toluene)
-0.28 (s), Me
1.29 (d), Me of iPr;a 3.65 (sep),
CH of iPra
1.07 (d), Me of iPr;b 3.44 (sep),
CH of iPrb
1.63 (s), Me
1.97 (s), Me
1.69 (s), Me
1.58 (s), Me
1.91 (s), Me
1b (d6-benzene) -0.29 (s), Me
1c (d6-benzene) -0.30 (s), Me
1.35 (d), Me of iPr;c 3.72 (sep),
CH of iPrc
1.24 (s), Me of tBu
1.22, 1.30 (d), Me of iPr;d 3.51
(sep), CH of iPrd
6.82, 6.86, 7.02, 7.06 (s), aryl H
of tolyl; 2.16 (s), Me of tolyl
1.00 (d), Me of iPr;f 3.31 (sep),
CH of iPrf
2a (d8-toluene)
2b (d8-toluene)
-0.43 (s), Me
-0.45 (s), Me
1.04, 1.06 (t), Me of Et;e 2.94,
2.96 (q), CH2 of Ete
1.02 (t), Me of Et;g 2.94, 2.96 (q),
CH2 of Etg
1.17 (d), Me of tBu
3a (d6-benzene) 0.46 (q), CH2 of Et;h
1.56 (t), CH3 of Eth
1.31, 1.35 (d), Me of iPr;i
3.64 (sep), CH of iPri
1.37, 1.41 (d), Me of iPr;m
3.70 (sep), CH of iPrm
1.11 (d), Me of iPr;j 3.48 (sep),
CH of iPrj
0.91 (t), CH3 of Et;k
2.11 (q), CH2 of Etk
1.22 (t), CH3 of Et;n
2.41 (q), CH2 of Etn
3b (d6-benzene) 0.44 (q), CH2 of Et;l
1.55 (t), CH3 of Etl
1.27 (s), Me of tBu
a
b 3
c 3
d
3
e 3
f 3
g 3
h 3
3J H-H ) 6.9 Hz.
J
) 6.3 Hz.
J
) 6.7 Hz. J H-H ) 6.7 Hz.
J
) 6.6 Hz.
J
) 6.6 Hz.
J
) 6.6 Hz. J H-H
H-H
H-H
H-H
H-H
H-H
i 3
j 3
k 3
l 3
m
n 3
) 7.8 Hz.
J
) 6.9 Hz.
J
) 6.3 Hz.
J
) 7.8 Hz.
J
) 7.8 Hz. 3J H-H ) 6.9 Hz. J H-H ) 7.8 Hz.
H-H
H-H
H-H
H-H
The complex {Me2Al(µ-i-Pr2N)2Mg[(i-Pr)NC(Me)N(i-Pr)]}
(1a ) (colorless solid) was purified by recrystallization from
toluene: mp, 143-144 °C; yield, 72%. IR (Nujol mull): 2950
(s), 2916 (s), 2863 (s), 2733 (m), 1654 (m), 1462 (s), 1379 (s),
1269 (br), 1181 (m), 1128 (m), 1025 (m), 977 (m), 921 (s), 809
(m), 692 cm-1 (br). Anal. Calcd: C, 62.5; H, 11.9; N, 13.3.
Found: C, 62.6; H, 11.7; N, 13.1. The 10 most intense peaks
of the mass spectral data (30 eV) are m/z (relative intensity,
ion formula tentatively assigned) 407 (42, [M - Me]+), 322
(100, [M - (i-Pr)2N]+), 307 (33, [M - (i-Pr)2N - MeH]+), 265
(16, [MeAlMg(i-Pr2N)2 - H]+), 250 (44, [AlMg(i-Pr2N)2 - H]+),
165 (12, [MeAlMg(i-Pr2N) - H]+), 142 (19, [MeC(i-PrN)2H]+),
86 (21, [HAl(i-Pr)NH]+), 58 (28, [(i-Pr)NH]+), and 44 (72, [(i-
Pr)H]+), with a molecular ion peak at 422 (2, [M]+). The 1H
NMR data for all the complexes are listed in Table 1.
tentatively assigned) 58 (100, [(i-Pr)NH]+), 69 (67, [(i-Pr)NC]+),
142 (34, [MeC(i-PrN)2 + H]+), 43 (33, [(i-Pr)]+), 85 (22,
[HAlNEt2 - Me]+), 99 (22, [AlNEt2]+), 111 (18, [C((i-Pr)N)2 -
Me]+), 127 (15, [C(N(i-Pr))2 + H]+), 351 (10, [M - Me]+), and
294 (7, [M - NEt2]+), with a molecular ion peak at 366 (5,
[M]+).
The complex {Me2Al(µ-Et2N)2Mg[(t-Bu)NC(Me)N(t-Bu)]} (2b)
(colorless liquid) was purified by distillation at 72 °C, 10-3 Torr
(yield, 61%). IR (Nujol mull): 2969 (s), 2921 (s), 2876 (s), 2725
(m), 1657 (m), 1463 (s), 1410 (s), 1380 (s), 1265 (m), 1200 (m),
1175 (m), 1105 (br), 1035 (br), 959 (m), 922 (m), 810 (m), 729
(m), 670 cm-1 (br). Anal. Calcd: C, 60.8; H, 12.0; N, 14.2.
Found: C, 60.1; H, 11.5; N, 12.8. The 10 most intense peaks
of the mass spectral data of compound 2b (70 eV) are m/z
(relative intensity, ion formula tentantively assigned) 379 (7,
[M - Me]+), 365 (5, [M - Et]+), 322 (6, [M - (Et2N)]+), 211
(15, [Me2Al(Et2N)2Mg - Me + H]+), 170 (27, [MeC(t-BuN)2 +
H]+), 155 (22, [C(t-BuN)2H]+), 99 (62, [Al(Et2N)]+), 98 (100, [Al-
(Et2N) - H]+), 58 (67, [HAlMe2]+), and 42 (51, [AlMe]+), with
a molecular ion peak at 394 (3, [M]+).
The complex {Et2Al(µ-i-Pr2N)2Mg[(i-Pr)NC(Et)N(i-Pr)]} (3a )
(colorless liquid) was purified by distillation at 77 °C, 10-3 Torr
(yield, 75%). IR (Nujol mull): 2964 (s), 2926 (s), 2869 (s), 2727
(m), 1657 (m), 1471 (s), 1410 (m), 1380 (s), 1280 (m), 1207 (m),
1104 (br), 1032 (br), 974 (m), 918 (m), 802 (m), 730 (m), 671
cm-1 (br). The 10 most intense peaks of the mass spectral data
of compound 3a (30 eV) are m/z (relative intensity, ion formula
tentatively assigned) 351 (10, [M - Me]+), 294 (7, [M - Et2N]+),
142 (34, [MeC((i-Pr)N)2 + H]+), 127 (15, [C((i-Pr)N)2 + H]+),
111 (18, [C((i-Pr)N)2 - Me]+), 99 (22, [Al(Et2N)]+), 85 (22, [HAl-
(Et2N) - Me]+), 69 (67, [(i-Pr)NC]+), 58 (100, [(i-Pr)NH]+), and
43 (33, [(i-Pr)]+), with a molecular ion peak at 366 (5, [M]+).
The complex {Et2Al(µ-i-Pr2N)2Mg[(t-Bu)NC(Et)N(t-Bu)]} (3b)
(colorless liquid) was purified by distillation at 87 °C, 10-3 Torr
(yield 51%). IR (Nujol mull): 2969 (s), 2921 (s), 2876 (s), 2725
(m), 1657 (m), 1463 (s), 1410 (s), 1380 (s), 1265 (m), 1200 (m),
1175 (m), 1105 (br), 1035 (br), 959 (m), 922 (m), 810 (m), 729
(m), 670 cm-1 (br). The 10 most intense peaks of the mass
spectral data of compound 3b (70 eV) are m/z (relative
intensity, ion formula tentatively assigned) 379 (7, [M - Me]+),
365 (5, [M - Et]+), 322 (6, [M - (Et2N)]+), 211 (15, [Me2Al-
(Et2N)2Mg - Me + H]+), 170 (27, [MeC((t-Bu)N)2 + H]+), 155
(22, [C(t-BuN)2H]+), 99 (62, [Al(Et2N)]+), 84 (100, [AlEt2 - H]+),
56 (42, [(t-Bu) - H]+), and 42 (51, [AlMe]+), with a molecular
ion peak at 394 (3, [M]+).
The complex {Me2Al(µ-i-Pr2N)2Mg[(t-Bu)NC(Me)N(t-Bu)]}
(1b ) (colorless solid) was purified by recrystallization from
toluene: mp, 121-122 °C; yield 81%. IR (Nujol mull): 2955
(s), 2926 (s), 2871 (s), 2753 (m), 1655 (m), 1466 (s), 1377 (s),
1254 (br), 1094 (m), 1027 (m), 969 (m), 917 (s), 805 (m), 666
cm-1 (br). Anal. Calcd: C, 63.9; H, 12.3; N, 12.4. Found: C,
62.1; H, 11.1; N, 11.3. The 10 most intense peaks of the mass
spectral data of compound 1b (30 eV) are m/z (relative
intensity, ion formula tentatively assigned) 435 (13, [M -
Me]+), 350 (49, [M - (i-Pr)2N]+), 334 (13, [M - (i-Pr)2N-
MeH]+), 292 (12, [MeC((t-Bu)N)2Mg(i-Pr)2N+H]+), 278 (19,
[MeC(t-BuN)2Mg(i-Pr)2N - MeH]+), 170 (25, [MeC(t-BuN)2H]+),
142 (41, [HAlMe(i-Pr)2N]+), 99 (44, [(i-Pr)2N - H]+), 86 (63,
[HAl(i-Pr)NH]+), and 58 (100, [(i-Pr)NH]+), with a molecular
ion peak at 450 (2, [M]+).
The complex {Me2Al(µ-i-Pr2N)2Mg[(p-tolyl)NC(Me)N(p-tolyl)]}
(1c) (colorless solid) was purified by recrystallization from
toluene: mp, 164-165 °C; yield, 78%. IR (Nujol mull): 2963
(s), 2917 (s), 2859 (s), 2732 (m), 1670 (m), 1650 (m), 1613 (m),
1516 (s), 1472 (s), 1429 (s), 1381 (br), 1300 (w), 1225 (m), 1182
(w), 1114 (m), 1020 (w), 981 (m), 923 (w), 969 (m), 868 (m),
808 (w), 727 (m), 687 cm-1 (br). Anal. Calcd: C, 69.4; H, 9.9;
N, 10.8. Found: C, 69.6; H, 9.7; N, 10.7. The 10 most intense
peaks of the mass spectral data of compound 1c (70 eV) are
m/z (relative intensity, ion formula tentatively assigned) 249
(8, [Al(i-Pr2N)2Mg - 2H]+), 235 (32, [Al(i-Pr2N)2Mg - Me]+),
123 (32, [Mg(i-Pr)2N - H]+), 109 (43, [Mg(i-Pr)2N - Me]+), 91
(17, [C7H8]+), 84 (100, [(i-Pr)2N - MeH]+), 72 (68, [(i-Pr)2N -
2Me + 2H]+), 69 (57, [(i-Pr)2N - 2Me - H]+), 57 (72,
[(i-Pr)N]+), and 43 (52, [HAlMe]+), with a molecular ion peak
at 518 (1, [M]+).
Str u ctu r e Deter m in a tion . Suitable single crystals of
compounds 1a ,b for X-ray measurements were sealed in glass
capillaries. Preliminary examination and intensity data col-
lection were carried out with an Enraf-Nonius CAD-4 auto-
matic diffractometer using graphite-monochromated Mo KR
radiation (λ ) 0.710 73 Å). Intensity data were collected by
using the θ-2θ scan mode for 2θ e 45° and corrected for
absorption and decay. Both structures were solved by MUL-
The complex {Me2Al(µ-Et2N)2Mg[(i-Pr)NC(Me)N(i-Pr)]} (2a )
(colorless liquid) was purified by distillation at 60 °C, 10-3 Torr
(yield, 52%). IR (Nujol mull): 2964 (s), 2926 (s), 2869 (s), 2727
(m), 1657 (m), 1471 (s), 1410 (m), 1380 (s), 1280 (m), 1207 (m),
1104 (br), 1032 (br), 974 (m), 918 (m), 802 (m), 730 (m), 671
cm-1 (br). The 10 most intense peaks of the mass spectral data
of compound 2a (30 eV) are m/z (relative intensity, ion formula

Notes
Ta ble 2. Cr ysta llogr a p h ic Da ta Refin em en t
Organometallics, Vol. 15, No. 10, 1996 2573
Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p ou n d s 1a ,b
Deta ils for Com p ou n d s 1a ,b
compd
1a
1b
1a
1b
Distances
formula
fw
a, Å
b, Å
c, Å
C22H51N4AlMg
422.96
10.648(4)
22.149(6)
12.038(3)
92.83(3)
2836(2)
monoclinic
P21/n
C24H55N4AlMg
451.01
9.912(5)
19.648(4)
15.296(4)
92.19(3)
2977(2)
monoclinic
P21/n
Al‚‚‚Mg
2.848(4)
Al‚‚‚Mg
2.865(3)
1.950(6)
1.974(5)
1.98(1)
1.95(1)
2.174(5)
2.163(5)
2.064(5)
2.063(5)
2.45(1)
1.49(1)
1.32(1)
1.32(1)
1.46(1)
1.47(1)
1.54(1)
Al-N(1)
1.945(8)
1.958(8)
1.96(1)
1.97(1)
2.155(7)
2.152(8)
2.062(8)
2.079(8)
2.44(1)
1.49(1)
1.32(1)
1.32(1)
1.46(1)
1.44(1)
1.54(2)
Al-N(1)
Al-N(2)
Al-N(2)
Al-C(1)
Al-C(1)
Al-C(2)
Al-C(2)
â, deg
Mg-N(1)
Mg-N(2)
Mg-N(3)
Mg-N(4)
Mg‚‚‚C(15)
N(1)-C(3)
N(3)-C(15)
N(4)-C(15)
N(3)-C(17)
N(4)-C(20)
C(15)-C(16)
Mg-N(1)
Mg-N(2)
Mg-N(3)
Mg-N(4)
Mg‚‚‚C(15)
N(1)-C(3)
N(3)-C(15)
N(4)-C(15)
N(3)-C(17)
N(4)-C(21)
C(15)-C(16)
V, Å3
cryst system
space group
2θ range, deg
cryst size, mm
Z
14.00-23.10
17.10-24.68
0.50 × 0.50 × 0.50 0.30 × 0.50 × 0.50
4
4
D
calc, g‚cm-3
0.991
1.025
0.710 70
3721
3687
1.006
1.009
0.710 70
3881
3881
1808
µ, cm-1
λ, Å
no. of rflns measd
no. of unique rflns
no. of rflns I0 > 2.0σ(I0) 1488
transm factors
(min, max)
RF
RW
GoF
max ∆/σ
radiation
Angles
49.1(2)
49.0(2)
96.6(3)
43.0(2)
43.4(2)
85.1(3)
87.9(3)
Mg‚‚‚Al-N(1)
Mg‚‚‚Al-N(2)
Mg‚‚‚Al-N(1)
Mg‚‚‚Al-N(2)
49.3(2)
48.9(2)
96.5(2)
42.9(2)
43.5(1)
85.0(2)
87.8(2)
87.6(2)
106.5(4)
111.2(4)
163.1(2)
131.3(2)
164.0(2)
65.6(2)
0.975, 1.000
0.803, 1.000
N(1)-Al-N(2)
Al‚‚‚Mg-N(1)
N(1)-Al-N(2)
Al‚‚‚Mg-N(1)
0.079
0.079
1.38
0.0037
Mo KR
0.060
0.058
1.40
0.0097
Mo KR
Al‚‚‚Mg-N(2)
Al‚‚‚Mg-N(2)
N(1)-Mg-N(2)
Al-N(1)-Mg
N(1)-Mg-N(2)
Al-N(1)-Mg
Al-N(2)-Mg
87.6(3)
Al-N(2)-Mg
Al-N(1)-C(3)
115.9(6)
118.6(7)
165.1(3)
131.3(2)
129.2(2)
65.6(3)
Al-N(1)-C(3)
TAN and refined by full-matrix least-squares analyses on F
with w ) 1.0/[σ2(Fo) + 0.0001Fo2]. One isopropyl group of
compound 1a is disordered. Site occupancy of 50% was
assigned for each of the disordered carbon atoms (C8 and C8′)
and subsequently refined anisotropically. Scattering factors
for the neutral atoms and anomalous scattering coefficients
for non-hydrogen atoms were taken from the literature.15 All
calculations were carried out with a Micro Vax 3600 computer
using the NRC VAX program package.16 A summary of data
collected on the crystal structures is given in Table 2. Selected
bond distances and angles are listed in Table 3.
Al-N(1)-C(6)
Al-N(1)-C(6)
Al‚‚‚Mg-N(3)
Al‚‚‚Mg-N(3)
Al‚‚‚Mg-N(4)
Al‚‚‚Mg-N(4)
Al‚‚‚Mg‚‚‚C(15)
N(3)-Mg-N(4)
N(3)-Mg‚‚‚C(15)
N(4)-Mg‚‚‚C(15)
N(1)-Mg-N(3)
N(1)-Mg-N(4)
N(1)-Mg‚‚‚C(15)
N(2)-Mg-N(3)
N(2)-Mg-N(4)
N(2)-Mg‚‚‚C(15)
Mg-N(3)-C(15)
Mg-N(4)-C(15)
N(3)-C(15)-N(4)
N(3)-C(15)-C(16)
N(4)-C(15)-C(16)
Mg-N(3)-C(17)
Mg-N(4)-C(20)
C(15)-N(3)-C(17)
C(15)-N(4)-C(20)
Al‚‚‚Mg‚‚‚C(15)
N(3)-Mg-N(4)
N(3)-Mg‚‚‚C(15)
N(4)-Mg‚‚‚C(15)
N(1)-Mg-N(3)
N(1)-Mg-N(4)
N(1)-Mg‚‚‚C(15)
N(2)-Mg-N(3)
N(2)-Mg-N(4)
N(2)-Mg‚‚‚C(15)
Mg-N(3)-C(15)
Mg-N(4)-C(15)
N(3)-C(15)-N(4)
N(3)-C(15)-C(16)
N(4)-C(15)-C(16)
Mg-N(3)-C(17)
Mg-N(4)-C(21)
C(15)-N(3)-C(17)
C(15)-N(4)-C(21)
32.9(3)
32.7(3)
32.9(2)
32.8(2)
131.4(3)
126.0(2)
136.5(3)
134.0(3)
122.9(3)
136.6(3)
89.4(6)
130.9(2)
126.0(2)
138.2(2)
132.6(2)
122.6(2)
135.8(2)
89.6(4)
Resu lts a n d Discu ssion
88.8(5)
89.8(4)
116.2(8)
121.6(9)
122.2(9)
148.7(7)
149.5(6)
121.8(8)
121.6(8)
115.0(5)
122.3(6)
122.7(6)
144.8(5)
144.1(4)
125.5(6)
126.1(5)
Syn th esis a n d Ch a r a cter iza tion of Am id in e-
Br id ged Com p lexes. The precursor complexes 1-3
were allowed to react with carbodiimide in a 1:n molar
ratio giving the amidino-bridged complexes {R2Al(µ-
NR′2)2Mg[(R′′N)C(R)(NR′′)]} (eq 1). These precursor
{R2Al(µ-(R′2N)2)Mg(µ-R)}n + nR′′NdCdNR′′ f
n{R2Al(µ-(R′2N)2)Mg[(R′′N)C(R)(NR′′)]} (1)
stituents of the [(R′′)NC(Me)N(R′′)] groups. ORTEP
views of the complexes 1a ,b are shown in Figures 1 and
2, respectively. Selected bond distances and bond
angles are listed in Table 3. The molecular structure
of 1b is refined by considering a disorder for C8(2/3) and
C8′(1/3). The two molecules, 1a ,b, both exist as mono-
mers possessing two coplanar heterocyclic four-mem-
bered rings AlN(1)N(2)Mg and MgN(4)C(15)N(3). The
average distances of the bridged Mg-N of 2.154(8) Å
in 1a and 2.167 (5) Å in 1b are normal for a σ bond.
Interestingly, the Mg-N distance of the AlN2Mg moiety
is ca. 0.08 Å longer than that of the MgCN2 moiety in
compounds 1a ,b, which suggests that the chelating
ligand (amidino) was more nucleophilic than the bridg-
ing ligand (amido). Also, the Mg-C(15) distance of
2.44(1) Å is longer than expected for a σ bond (2.0-2.2
Å) indicating a weak interaction between Mg and C(15).
The distances of N(3)-C(15) and N(4)-C(15) are the
same (1.32(1) Å) indicating the partial double-bond
character. Hence the C(15) has an sp2 structure, as do
N(3) and N(4). The unusual bond length of d(C(6)-C(8))
R ) Me, R′ ) i-Pr, R′′ ) i-Pr (1a ), R′′ ) t-Bu (1b),
R′′ ) p-tolyl (1c); R ) Me, R′ ) Et, R′′ ) i-Pr (2a ),
R′′ ) t-Bu (2b); R ) Et, R′ ) i-Pr, R′′ ) i-Pr (3a ),
R′′ ) t-Bu (3b)
complexes and products are extremely air-sensitive and
hygroscopic. The structures of two of the complexes
1a ,b were determined by single-crystal X-ray diffraction
techniques, and the other amido complexes are consis-
1
tent with the data obtained from H and 13C NMR and
mass spectra and elemental analyses.
Descr ip tion of th e Str u ctu r es. Compounds 1a ,b
possess similar structural features except for the sub-
(15) Gabe, E. J .; Lee, F. L.; Le Page, Y. In Crystallographic
Computering 3: Data Collection, Structure Determination, Proteins, and
Databases; Sheldrick, G. M., Krueger, C., Goddard, R., Eds.; Claren-
don: Oxford, U.K., 1985; p 167.
(16) Barker, J .; Kilner, M. J . Chem. Soc., Dalton Trans. 1987, 2687.

2574 Organometallics, Vol. 15, No. 10, 1996
Notes
1
spectra, which show the monomeric ion peak. The H
NMR spectral data were in good agreement with the
1
X-ray data. For compound 1a , the H NMR spectrum
(toluene-d8) showed two sets of doublets and septets at
δ ) 1.29 (24H), 1.07 (12H) and at δ ) 3.65 (4H), 3.44
(2H), respectively, which are due to the methyl protons
and methine protons of the isopropyl groups. The
chemical shifts at δ ) -0.28 (s, 6H) and 1.63 (s, 3H)
are due to the methyl protons attached to the aluminum
atom and the migrated methyl protons, respectively. For
compound 1b, the 1H NMR spectrum (benzene-d6)
showed a doublet at δ ) 1.37 (24H) and a septet at δ )
3.73 (4H) which are due to the methyl protons and
methine protons of the isopropyl groups, respectively.
The chemical shifts at δ ) -0.19 (s, 6H), 1.19 (s, 18H),
and 1.97 (s, 3H) are due to the methyl protons attached
to the aluminum atom, the methyl protons in tert-butyl
groups, and the migrated methyl protons, respectively.
F igu r e 1. ORTEP view of the complex {Me2Al(µ-i-Pr2N)2-
Mg[(i-Pr)NC(Me)N(i-Pr)]}, 1a . Thermal ellipsoids are
drawn at 50% probability level.
1
The H NMR spectra of the other complexes are well in
agreement with the carbodiimide insertion products.
The 1H NMR spectral assignments for all the complexes
are listed in Table 1.
P yr olysis of Alu m in u m -Ma gn esiu m Am id in e
Com p lexes. The reactions of {R2Al(µ-NR′2)2Mg(µ-R)}n
with carbodiimide in a 1:n ratio give the amidine-
bridged complexes {R2Al(µ-NR′2)2Mg[(R′′)NC(R)N(R′′)]}.
When subjected to pyrolysis, a dialuminum amido
complex and some unisolated species were obtained. We
believe that the dialuminum complexes [R2Al(µ-NR′2)]2
were obtained from the thermal decomposition of alu-
minum-magnesium amidine complexes, and when
heated to 80 °C, 1a ,c produce [Me2Al(µ-i-Pr2N)]2. When
heated to 110 °C, 2a ,b produce [Me2Al(µ-EtN2)]2, and
when heated to 130 °C, 3a ,b produce [Et2Al(µ-i-Pr2N)]2
and some unisolated species as shown in eq 2. The
unisolated species could be a polymer of MeMg(Et2N)
which is insoluble in organic solvents and which would
be difficult to isolate and purify.
F igu r e 2. ORTEP view of the complex {Me2Al(µ-i-Pr2N)2-
Mg[(t-Bu)NC(Me)N(t-Bu)]}, 1b. Thermal ellipsoids are
drawn at 50% probability level.
) 1.34(2) Å and d(C(20)-C(22)) ) 1.39(2) Å probably
results from the disorder of the isopropyl of the bridged
i-Pr2N moiety in 1a , and likewise, d(C(6)-C(8′)) )
1.35(2) Å in 1b.
Sp ectr a l Da ta . With the carbodiimide insertion, the
NdCdN moiety appears with partial double-bond char-
acter N - -C - -N in the organoaluminum amidinomag-
nesium complexes. Their 13C NMR spectra display
chemical shifts in the range δ ) 174-182 ppm assigned
to the sp2-hybridization carbon of [(R′′)NC(R)N(R′′)]
moiety, similar to that of [Pt{(R′)NC(R)N(R′)}2].18 In-
frared spectra show absorptions in the range 1650-1660
cm-1 assigned to the stretching frequency of
N - -C - -N of the [(R′′)NC(R)N(R′′)] moiety.14 The ten-
tative assignments were used to support the character-
ization of these amidino complexes as well as their mass
Ack n ow led gm en t. We thank the National Science
Council, Taiwan, ROC, for financial support.
Su p p or tin g In for m a tion Ava ila ble: Tables of 13C NMR
data, X-ray parameters, anisotropic displacement coefficients
for non-hydrogen atoms, complete fractional coordinates and
isotropic displacement coefficients, and complete bond dis-
tances and angles and an ORTEP diagram (15 pages). Order-
ing information is given on any current masthead page.
A
list of structure factors (41 pages) is available from the authors
upon request.
OM9508703