Interaction of the bulky alane (H2AlC6H3-2,6-Mes2)2 (Mes = -C6H3-2,4,6-Me3) with H2EPh (E = N, P or As)

Article abstract of DOI:10.1039/a803431a

The reactions of the bulky primary alane (H₂AlC₆H₃-2,6-Mes₂)₂ (Mes = -C₆H₂-2,4,6-Me₃) with H₂EPh (E = N, P or As) are described. With aniline, H₂

Full text of DOI:10.1039/a803431a

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Interaction of the bulky alane (H AlC H -2,6-Mes )
6 3 2 2
(Mes = wC H -2,4,6-Me ) with H EPh (E = N, P or As)
6 3
2
3
2
Rudolf J. Wehmschulte and Philip P. Power*
Department of Chemistry, University of California, Davis, California 95616, USA
The reactions of the bulky primary alane (H AlC H -2,6-Mes ) (Mes \ wC H -2,4,6-Me ) with H EPh
2
6
3
2 2
6
2
3
2
(E \ N, P or As) are described. With aniline, H NPh, the dimeric products 2,6-Mes H C MPh(H)NNAlMl-
2
2
3 6
N(H)PhN Al(H)C H -2,6-Mes (1) and [2,6-Mes H C (H)AlMl-N(H)PhN] (2) are obtained. The structures of
3 6
2
6
3
2
6
2
2
both 1 and 2 feature two wC H -2,6-Mes substituted aluminums bridged by two wN(H)Ph groups. In 2 each
aluminum is also bound to a terminal hydrogen whereas in 1 one of these hydrogens is replaced by a terminal
wN(H)Ph substituent. The structure of the wP(H)Ph derivative [2,6-Mes H C (H)AlMl-P(H)PhN] (3) is very
similar to that of 2 (and presumably the arsenido derivative 4) and features bridging phosphido groups and
four-coordinate aluminums. The arsenido dimer 4 is cleaved by ether to give the ether adduct 2,6-
Mes H C (H)AlMAs(H)PhN(OEt ) for which a partial X-ray structure was determined. Thermolysis of 2, 3 and 4
led to decomposition. However, heating (H AlC H -2,6-Mes ) with excess H AsPh led to the unique cluster (2,
2 2
6-Mes H C Al) Ml-As(H)PhN (l-PhAsAsPh) which has a basket-type Al As core.
3 6
3
2
2
3 6
2
2
3 6
2
2
6
3
2
2
2
2
2
4
Interest in neutral hydride derivatives of heavier main group
13 elements has undergone rapid growth over the last
decade.1 The variety of such compounds is large and it
includes numerous types of Lewis base stabilized2 and uncom-
plexed metallanes.3 The latter are characterized by strong
hydride bridging unless other strongly bridging ligands such
Syntheses
2,6-Mes H C {Ph(H)N}Al{l-N(H)Ph} Al(H)C H -2,6-
2
3 6
2
6 3
Mes (1) and [2,6-Mes H C (H)Al{l-N(H)Ph} ] (2). Aniline
2
2
3 6
2
(0.137 mL, 1.5 mmol, 0.14 g) was added slowly via syringe to a
solution of (H AlC H -2,6-Mes ) [prepared in situ by heat-
2
6
3
2 2
ing (Et O)H AlC H -2,6-Mes (0.62 g, 1.5 mmol) to 115 ¡C
as wOR or wNR are present.4 Hydride bridging can also be
2
2
6
3
2
under reduced pressure for 30 min] in toluene (30 mL) at
2
prevented by the use of bulky substituent groups, and a
room temperature. Intensive gas evolution (H ) commenced
immediately and ceased a few minutes after the addition was
number of unassociated alanes and gallanes featuring only ter-
minally bound hydrogens have been synthesized. Examples of
2
completed. After 1 h at room temperature the colorless, clear
solution was concentrated to 5 mL and cooled to [20 ¡C
overnight. As no crystals had formed, the solution was con-
centrated further to ca. 3 mL and 2 mL of n-hexane were
added; cooling to ]6 ¡C for 3 days gave a few, small crystals.
The solution was then cooled in a [20 ¡C freezer for a week
to give ca. 60 mg of small colorless crystals of a mixture of 1
and 2 and some unidentiÐed products. From this batch the
crystal used for the X-ray structure determination of 1 was
chosen. Further concentration of the mother liquor and
cooling to [20 ¡C for 3 days gave 0.37 g of small colorless
crystals, which consisted mostly of 2. Recrystallization from
tolueneÈn-hexane (2 mL : 4 mL) at [20 ¡C a†orded 0.21 g of
2 in the form of large colorless blocks (B1 mm on a side). It
crystallizes as a toluene solvate of formula 2 É 0.5 PhMe. The
toluene may be removed by prolonged pumping at room tem-
perature. Yield: 30.6%. Mp: softens at 160 ¡C, melts with gas
stable compounds include the monomeric species H GaMes*5
2
(Mes* \ wC H -2,4,6-tert-Bu ), HMMes* (M \ Al6 or Ga7)
6
2
3
2
and HAl(Mes*)N(SiMe ) .8 A further advantage of the use of
3 2
sterically crowding groups is that it stabilizes primary metal-
lane derivatives toward rearrangement reactions of the type
described by eqn. (1):
2 H AlR ] HAlR ] H Al
(1)
2
2
3
The stability of a primary metallane such as (H AlMes*) has
2
2
permitted its use in the synthesis of a variety of compounds
that are often not readily accessible by other routes.9 This
work is now extended to the reactions of the primary alane
(H AlC H -2,6-Mes ) 10 (Mes \ wC H -2,4,6-Me ) and a
2
6
3
2 2
6
2
3
range of reactions of this compound with H EPh, (E \ N, P
2
or As) are described. It is shown that they are quite di†erent
from the corresponding reactions of (H AlMes*) with the
2
2
same substrates.
evolution at 165È170 ¡C. IR: m \ 3275(w), 3260(w), m
\
NH
AlH
1902(st), 1859(st) cm~1. 1H NMR (C D ): 7.16 (t, p-H, 2H,
6
6
Experimental
General procedures
3J \ 7.5 Hz), 6.82 [m, m-H(NPh), 4H], 6.76 (d, m-H, 4H),
HH
6.60 [s, m-H(Mes), 8H], 6.58 [m, o-, p-H(NPh), 6H], 4.09
(br, s, AlwH, 2H), 2.50 (s, NwH, 2H), 2.10 (s, p-CH , 12H),
3
All reactions were performed under N by using either modi-
1.93 (s, o-CH , 24H). 13CM1HN NMR (C D ): 151.1 (o-C),
2
3
6 6
Ðed Schlenk techniques or a Vacuum Atmospheres HE43-2
142.7 [i-C(NPh)], 141.6 [i-C(Mes)], 136.1 [p-C(Mes)], 135.7
[o-C(Mes)], 129.3 (p-C), 129.1 [m-C(Mes)], 127.9 [m-C or
m-C(NPh)], 122.8 [o-C(NPh)], 122.5 [p-C(NPh)], 21.7
(o-CH ), 21.2 (p-CH ).
dry box. Solvents were freshly distilled from sodiumÈ
potassium alloy and degassed twice before use. (H AlC H -
2
6 3
2,6-Mes ) ,10 H PPh11 and H AsPh12 were synthesized by
2 2
2
2
3
3
literature methods. Aniline was obtained from a commercial
supplier and dried by standard procedures. 1H, 13C and 31P
NMR spectra were recorded in C D or C D solutions by
using a General Electric QE-300 spectrometer. IR spectra
were recorded as a Nujol mull between CsI plates using a
PerkinÈElmer PE-1430 spectrometer.
[2,6-Mes H C (H)Al{l-P(H)Ph} ] (3). H PPh (0.22 mL,
2
3 6
2
2
2.0 mmol, 0.22 g) was added via syringe to Ðnely ground
6
6
7 8
[H AlC H -2,6-Mes ] (0.48 g, 0.7 mmol) at room tem-
2
6
3
2 2
perature to give a paste. After 5 min the Ñask was placed into
a 150 ¡C oil bath for 5 min during which time the excess
New J. Chem., 1998, Pages 1125È1130
1125

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Table 1 Crystallographic data for 1 É 0.25 hexane, 2 É 0.5 toluene, 3 and 6 É 2Et O
2
1 É 0.25 hexane
2 É 0.5 toluene
3
C
6 É 2Et O
2
Formula
FW
Space group
a/A
b/A
c/A
C
979.75
H
Al N
C
913.16
C2/c
H
Al N
H
Al P
C H Al As O
67.5 72.5
2
3
63.5 68
2
2
60 64 2 2
80 92
2
4 2
901.01
Pbca
13.718(4)
20.923(10)
35.886(7)
È
1439.18
P2 /n
P2 /c
1
1
13.873(6)
21.996(6)
13.089(3)
36.376(6)
96.38(2)
10408(4)
8
13.880(8)
23.343(5)
18.733(6)
107.48(3)
5786(3)
4
45.59(2)
12.100(5)
112.20(3)
7089(6)
4
b/¡
U/A
Z
Ž
3
10300(6)
8
T /K
k/A
130(2)
1.54178
1.125
0.766
8.49
130(2)
1.54178
1.166
0.810
6.14
130(2)
1.54178
1.162
1.370
7.35
130(2)
1.54178
1.349
2.791
7.13
d
/g cm~3
calcd
l/mm~1
R /%
1
wR /%
23.98
12.51
16.58
17.33
2
R \ &pF [ F p/& o F o; wR \ M&[w(F2 [ F2)2]/&[w(F2)2]N1@2
1
o
c
o
2
o
c
o
H PPh distils to the cooler part of the Ñask. After being held
at room temperature for ca. 30 min the sticky, colorless solid
was heated to 160 ¡C for 15 min, cooled to room temperature
128.4 [o- or m-C(AsPh)], 127.4 [p-C(AsPh)], 126.7 (m-C), 21.2
2
(o- and p-CH ).
3
2,6-Mes C H (H)Al{As(H)Ph}(OEt ) (5). H AsPh (0.34
and the excess H PPh was removed under reduced pressure.
2 6
3
2
2
2
mL, 3.0 mmol, 0.46 g) was added via syringe to 1.5 mmol of
Ðnely ground (H AlC H -2,6-Mes ) [prepared in situ from
No gas evolution was apparent during the reaction. The
remaining colorless solid was dissolved in warm toluene (20
mL) and crystallized at [20 ¡C for 2 days to a†ord 0.40 g of
small colorless crystals. Concentration of the supernatant
liquid to 2È3 mL followed by cooling to [20 ¡C overnight
gave another 0.08 g of product. Total yield: 76%. X-ray
quality crystals were grown from benzene (0.2 g in 10 mL) at 6
¡C for one week. Mp: turns yellow at ca. 230 ¡C, melts with
gas evolution at 235È6 ¡C. IR: m \ 2355(w), m \ 1812(st),
2
6
3
2 2
0.64 g of 2,6-Mes H C AlH É (OEt )] at room temperature to
2
3 6
2
2
form a colorless paste. After ca. 5 min a smooth gas evolution
commenced and after a further 10 min the paste solidiÐed and
the gas evolution ceased. The volatile material was removed
30 min later under reduced pressure (1.5 h) and the remaining
colorless solid was dissolved into Et O (30 mL). Concentra-
2
tion to ca. 5 mL and subsequent cooling to [20 ¡C for 5 days
PH
AlH
a†orded 0.53 g of colorless needles. Recrystallization from
1797(st) cm~1. 1H NMR (C D ): 7.23 (t, p-H, 2H, 3J \ 7.5
6
6
HH
Et OÈhexane (25 mL : 5 mL) at [20 ¡C for 2 days gave X-ray
Hz), 7.23 [br, s, m-H(PPh), 4H], 6.95 [br, s, o-, p-H(PPh), 6H],
6.86 (d, m-H, 4H), 6.62 [s, m-H(Mes), 8H], 4.03 (br, s, AlwH,
2H), 2.61 (center of AA@XX@ multiplet, PwH, 2H, 3 of 10 pos-
sible lines observed: 3.07, 2.74, 2.29; absorption at 3.07 split
2
quality crystals of 5. An X-ray data set of 5 was collected and
could be solved. Subsequent reÐnement showed disorder that
could not be modeled successfully to give a R value of \0.2.
1
Nevertheless, the identity of 5 was conÐrmed. Mp: turns
into three lines due to coupling to AlwH, 3J \ 7.5 Hz), 2.15
HH
opaque at 119È122 ¡C (desolvation), gradually changes color
(s, p-CH , 12 H), 1.92 (s, o-CH , 24H). 13CM1HN NMR
3
3
to orange, melts with gas evolution and color change to red at
(C D ): 151.3 (owC), 142.4 [i-C(Mes)], 136.0 [o-C(Mes)],
6
6
168È175 ¡C. IR: m
NMR spectrum (C D ) displayed a mixture of compounds
indicating an equilibrium between 5 and 4 and free Et O in
solution. Heating to 80 ¡C drives the equilibrium almost com-
2088(m), m
1805(m, br) cm~1. The 1H
135.9 [p-C(Mes)], 132.8 [“tÏ (AA@X), o- or m-C(PPh), *m \ 5.6
Hz], 129.7 (p-C), 128.7 [m-C(Mes)], 128.0 [“tÏ (AA@X), o- or
m-C(PPh), *m \ 5.5 Hz], 127.5 [p-C(PPh)], 126.6 (m-C), 22.2
(p- and m-CH ). 31PM1HN NMR (C D ): [116 (s, w B 17
AsH
6
AlH
6
2
3
6
6
1@2
pletely to 4 and free Et O. The room temperature spectrum of
Hz). 31P NMR (C D ): [116 [six-line multiplet (AA@XX@):
[113.1, [115.3, [116.1, [117.2, [118.0, [120.2, rel. inten-
2
6
6
5 was identical with a spectrum of a C D solution of 4 to
6
6
which 1 equiv. Et O per aluminum was added.
sity: 1 : 5 : 4.3 : 4.3 : 5 : 1].
2
(2,6-Mes H C Al) [l-As(H)Ph] (l-PhAsAsPh) (6). H AsPh
2
3 6
2
2
2
[2,6-Mes H C (H)Al{l-As(H)Ph} ] (4). Finely ground
(0.48 mL, 4.2 mmol, 0.65 g) was added via syringe to 0.71 g
2
3 6
2
(H AlC H -2,6-Mes ) (0.48 g, 0.7 mmol) was treated with
(2.1 mmol) of Ðnely ground (H AlC H -2,6-Mes ) at room
2
6
3
2 2
2
6
3
2 2
H AsPh (0.23 mL, 2.0 mmol, 0.31 g) at room temperature to
temperature. After ca. 10 min the colorless paste solidiÐed into
a sticky solid. After 1 h, the Ñask was placed into a 100È110
¡C oil bath for 10 min, after which the solid turned pale
yellow. The Ñask was then heated to 150È160 ¡C for about 5
min to complete the reaction. The orange solid was cooled to
room temperature and then placed under reduced pressure at
60 ¡C for 1 h to remove all volatile materials. Upon cooling,
2
form a paste. After ca. 2È3 min a weak gas evolution com-
menced and within ca. 10 min the paste solidiÐed and 10 min
later excess H AsPh was removed under reduced pressure.
2
Crystallization from toluene (5È7 mL) at [20 ¡C for one week
a†orded 0.11 g of colorless, microcrystalline 4. Concentration
of the mother liquor to 2 mL and subsequent cooling to [20
¡C for one week a†orded another 0.03 g of 4. Total yield:
20%. Mp: turns yellow at 140 ¡C, orange at 160 ¡C and melts
with gas evolution and color change to red-orange at 175È178
Et O (20 mL) was added. Concentration to ca. 5 mL and
2
cooling in a [20 ¡C freezer for 10 days gave a small amount
(\100 mg) of colorless needles of 5, which were separated. A
¡C. IR: m
2175(w), m
1812(st), 1797(sh) cm~1. 1H NMR
mixture of Et OÈhexane (20 mL : 20 mL) was added to the
AsH
AlH
2
(C D ): 7.24 [m, m-H(AsPh), 4H], 7.23 (t, p-H, 2H, 3J \ 7.5
pale yellow supernatant, insoluble material was separated and
6
6
HH
Hz), 6.97 [m, o-, p-H(AsPh), 6H], 6.86 (d, m-H, 4H), 6.62 [s,
the remaining solution was concentrated to 15 mL and cooled
m-H(Mes), 8H], 4.13 (br, s, AlwH, 2H), 2.13 (s, p-CH , 12H),
in a [20 ¡C freezer for 5 days to give ca. 20 mg of X-ray
3
1.96 (s, o-CH , 24H). 13CM1HN NMR (C D ): 151.3 (o-C),
quality crystals (yellow plates) of 6 É 2Et O. Concentration of
3
6
6
2
142.2 [i-C(Mes)], 136.2 [o- and p-C(Mes)], 133.3 [o- or m-
C(AsPh)], 131.2 [i-C(AsPh)], 129.8 (p-C), 128.7 [m-C(Mes)],
the supernatant to ca. 4 mL and crystallization in a [20 ¡C
freezer for 2 weeks gave 6 É hexane (0.32 g) in the form of pale
1126
New J. Chem., 1998, Pages 1125È1130

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X-ray structure determinations
Table 2 Selected bond distances (A) and angles (¡) for 1È3 and 6
Crystals of 1 É 0.25 hexane, 2 É 0.5 toluene, 3 and 6 É 2Et O were
2
removed from the Schlenk tube under a stream of N and
2
1
Al(1)wN(1)
1.833(6)
1.969(5)
1.963(5)
1.975(5)
86.3(2)
115.4(2)
110.1(2)
107.8(2)
111.5(2)
87.0(2)
Al(2)wN(3)
1.983(5)
2.001(5)
1.998(6)
1.516(10)
122.4(2)
108.5(2)
113.6(2)
93.0(2)
immediately covered with a layer of hydrocarbon oil.13 A suit-
Al(1)wN(2)
Al(1)wC(1)
able crystal was selected, attached to a glass Ðber, and imme-
diately placed in the low temperature nitrogen stream as
described in ref. 13. The data for 1 É 0.25 hexane were collected
at 130 K with a Siemens P4-RA di†ractometer (nickel foil
monochromator) and the data for 2 É 0.5 toluene, 3 and
6 É 2Et O at 130 K with a Syntex P2 di†ractometer (graphite
Al(1)wN(3)
Al(2)wC(37)
Al(2)wN(2)
Al(2)wH(2)
N(2)wAl(2)wN(3)
N(2)wAl(2)wC(37)
N(3)wAl(2)wC(37)
N(1)wAl(1)wN(2)
N(1)wAl(1)wN(3)
N(2)wAl(1)wN(3)
N(1)wAl(1)wC(1)
N(2)wAl(1)wC(1)
N(3)wAl(1)wC(1)
Al(1)wN(2)wAl(2)
Al(1)wN(3)wAl(2)
2
1
93.0(2)
monochromator) using CuKa (k \ 1.54178 A) radiation.
Crystallographic programs used for the structure solutions
were those of the SHELXTL Version 5.03 (Siemens, 1994)
program package. Scattering factors were obtained from ref.
14. Absorption corrections were applied by using the method
described in ref. 15. Some details of the data collections and
reÐnements are given in Table 1 and selected bond distances
and angles are given in Table 2. Further details are provided
in the supplementary material, CCDC reference number 440/
061. The structures were solved by direct methods and reÐned
by full-matrix least-squares procedures. All non-hydrogen
atoms were reÐned anisotropically except for the disordered
2
Al(1)wN(1)
1.973(2)
1.987(2)
1.985(3)
1.51(3)
Al(2)wN(1)
Al(2)wN(2)
Al(2)wC(25)
Al(2)wH(2)
1.961(2)
1.978(2)
1.991(3)
1.47(3)
122.17(10)
116.7(11)
84.35(9)
101.6(11)
104.9(11)
89.36(10)
88.48(9)
Al(1)wN(2)
Al(1)wC(1)
Al(1)wH(1)
C(1)wAl(1)wN(1)
C(1)wAl(1)wN(2)
C(1)wAl(1)wH(1)
N(1)wAl(1)wN(2)
N(1)wAl(1)wH(1)
N(2)wAl(1)wH(1)
C(25)wAl(2)wN(1)
118.89(10) C(25)wAl(2)wN(2)
117.31(10) C(25)wAl(2)wH(2)
115.6(10)
83.83(9)
N(2)wAl(2)wN(1)
N(2)wAl(2)wH(2)
N(1)wAl(2)wH(2)
Al(1)wN(1)wAl(2)
109.7(11)
107.2(10)
121.34(11) Al(1)wN(2)wAl(2)
solvent molecules in 1 É 0.25 hexane and 6 É 2Et O (for details
see supplementary material). Hydrogen-atoms attached to the
2
3
Al(1)wP(1)
2.428(2)
2.442(2)
1.43(6)
1.980(5)
82.93(7)
110(2)
122.1(2)
106(2)
121.0(2)
111(2)
Al(2)wP(1)
2.436(2)
2.425(2)
1.49(6)
1.981(5)
120.1(2)
97(2)
123.8(2)
100(2)
123(2)
carbons were included in the reÐnement at calculated posi-
tions using a riding model. Heteroatom-bound hydrogen
atoms were generally located in the Fourier maps and reÐned
freely with Ðxed thermal isotropic parameters except for H(2)
and H(1N) in 1 É 0.25 hexane whose Al(2)wH(2) and
N(1)wH(1N) distances were also restrained.
Al(1)wP(2)
Al(2)wP(2)
Al(1)wH(1)
Al(2)wH(2)
Al(1)wC(1)
Al(2)wC(31)
P(1)wAl(1)wP(2)
P(1)wAl(1)wH(1)
P(1)wAl(1)wC(1)
P(2)wAl(1)wH(1)
P(2)wAl(1)wC(1)
C(1)wAl(1)wH(1)
P(1)wAl(2)wP(2)
P(1)wAl(2)wC(31)
P(1)wAl(2)wH(2)
P(2)wAl(2)wC(31)
P(2)wAl(2)wH(2)
C(31)wAl(2)wH(2)
Al(1)wP(1)wAl(2)
Al(1)wP(2)wAl(2)
91.44(8)
91.38(8)
83.13(7)
Results
6
Al(1)wC(1)
Al(1)wAs(2)
Al(1)wAs(3)
Al(1)wAs(4)
Al(2)wC(25)
1.985(8)
2.455(3)
2.516(3)
2.539(3)
1.983(8)
Aa(1)wAl(2)wC(25) 120.0(3)
Syntheses
Al(2)wAs(1)
Al(2)wAs(3)
Al(2)wAs(4)
As(1)wAs(2)
2.463(3)
2.541(3)
2.512(3)
2.4453(14)
101.01(9)
The reaction of (H AlC H -2,6-Mes ) with H NPh (aniline)
2
6
3
2 2
2
at room temperature in toluene a†orded a small amount of
the asymmetric product 1 in addition to the expected product
2. The formation of 1 may be rationalized by the presence of a
small excess of aniline. In contrast, reaction of (H AlC H -
As(3)wAl(1)wAs(2) 101.35(10) As(1)wAl(2)wAs(4)
As(3)wAl(1)wAs(4)
As(3)wAl(1)wC(1)
As(2)wAl(1)wC(1)
76.53(7)
123.5(2)
120.3(2)
As(4)wAl(2)wC(25) 125.0(3)
Al(1)wAs(3)wAl(2)
Al(1)wAs(4)wAl(2)
88.25(8)
88.39(9)
96.2(2)
98.1(2)
97.1(2)
2
6 3
2,6-Mes ) with excess H PPh at 150 ¡C gave only the mixed
2 2
2
aluminum hydride-phosphide 3 with elimination of H . Sig-
As(2)wAl(1)wAs(4) 102.18(10) C(49)wAs(1)wAs(2)
2
As(4)wAl(1)wC(1)
As(3)wAl(2)wAs(1) 101.70(9)
As(3)wAl(2)wAs(4) 76.58(7)
As(3)wAl(2)wC(25) 123.0(3)
123.5(3)
C(49)wAs(1)wAl(2)
C(55)wAs(2)wAs(1)
niÐcantly, no reaction was observed at room temperature.
Heating of 3 to its melting point (235È6 ¡C) did not lead to
C(55)wAs(2)wAl(1) 100.4(2)
the elimination of a further equivalent of H but to the loss of
2
H PPh with decomposition. Heating of an NMR sample of 3
2
As(1)wAs(2)wAl(1)
102.39(7)
to 85 ¡C did not change the coupling pattern in the 31P spec-
trum, indicating little or no dissociation in solution at this
temperature. In contrast to H PPh, H AsPh reacts with the
2
2
yellow microcrystals. The hexane or ether solvents of crys-
tallization may be removed completely by pumping under
reduced pressure (ca. 0.01 mm Hg for ca. 4 h). Yield: 21%. Mp
alane at room temperature to give 4, which was identiÐed by
IR and NMR spectroscopy. In the presence of Et O the
2
adduct 5 is formed, for which only a relatively low quality
(6 É 2Et O): turns red at 160 ¡C, melts with gas evolution at
X-ray data set could be obtained. A 1H NMR spectrum of 5
2
185È7 ¡C to form a dark red liquid. Spectroscopic data for
indicates loss of Et O in solution and formation of 4 [eqn.
2
6 É 2Et O: IR: m \ 2148(w) cm~1. 1H NMR (C D ): 7.85
(2)]:
2
AsH
6 6
(m, AsPh, 4H), 7.21 (t, p-H, 2H, 3J \ 7.5 Hz), 6.95, 6.94 [s,
HH
m-H(Mes), 4H each], 6.95 (m, AsPh, 4H), 6.88 (d, m-H, 4H),
2,6-Mes H C (H)AlAs(H)Ph É OEt H
2
3 6
2
6.78 (t, AsPh, 4H, J \ 7.5 Hz), 6.53 (d, AsPh, 4H, J \ 7.8 Hz),
5
6.37 (br, s, AsPh, 4H), 3.25 (q, CH O, 8H, 3J \ 6.6 Hz),
2
HH
2.29, 2.15, 1.59 [s, CH (Mes), 12H each], 1.11 (t, OCH CH ,
1/2 [2,6-Mes H C Al(H)Ml-As(H)PhN] ] Et O (2)
3 6
3
2
3
2
2
2
12H). 13CM1HN NMR: 152.0, 144.7, 142.7, 136.4, 136.2, 130.4
(quaternary carbons), 136.8, 134.9, 130.2, 129.7, 129.3, 128.0,
4
127.9, 127.8, 127.4, 126.0 (aromatic CwH), 65.9 (OCH ), 21.8,
Addition of ca. one equiv. Et O to a solution of 4 in C D
2
2
6 6
21.2, 21.1 [CH (Mes)], 15.6 (OCH CH ).
gave an NMR spectrum very similar to that of 5 in C D .
3
2
3
6 6
Heating of the mixture to 160 ¡C for 3È5 min until it begins
to turn orange appears to be essential for the formation of 6.
In a separate experiment, in which the reaction mixture was
heated to only 110È120 ¡C for 20 min, 6 was isolated in only
4% yield.
Attempted elimination of a further equivalent of H , by
2
heating the reaction mixture of (H AlC H -2,6-Mes ) and
excess H AsPh to 150È160 ¡C, gave the unusual cage com-
pound 6 É 2Et O, featuring an AswAs bond in the As Al core
2
6
3
2 2
2
2
4 2
in which all the aluminum hydrogens have been eliminated.
New J. Chem., 1998, Pages 1125È1130
1127

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Structures
1 Æ 0.25 hexane. The structure of 1 (Fig. 1) is composed of
dimeric molecules in which the four-coordinate aluminum
centers are bridged by two wN(H)Ph groups to form an
almost perfectly planar Al N core. Each aluminum is also
2
2
bound to a wC H -2,6-Mes substituent. However, the alu-
6
3
2
minum coordination is completed by bonding to terminal
hydride for Al(2) and to terminal amide wN(H)Ph for Al(1).
The coordination of the metals is thus distorted tetrahedral in
each case. Within the Al N core the AlwN distances are
2
2
in the range 1.963(5)È1.983(5) A. The internal angles at Al(1)
and Al(2) are 87.0(2)¡ and 86.3(2)¡ and those at N(2) and N(3)
are both 93.0(2)¡. The AlwC distances are essentially identical
and average 2.000(5) A; the Al(2)wH(2) distance is 1.52(1) A.
The terminal Al(1)wN(1) distance is 1.833(6) A and there is
approximately planar coordination at N(1). Other selected
bond distances and angles may be found in Table 2.
2 Æ 0.5 PhMe. The structure of 2 (Fig. 2) has many simi-
larities to that of 1. The major di†erences are that in 2 both
aluminums are bound to a terminal hydride ligand and the
Al N core is folded with a fold angle along the Al(1)wAl(2)
Fig. 2 Computer generated drawing of 2. Important bond distances
and angles are given in Table 2
2
2
axis of 139.5¡. The AlwN bond lengths [range 1.961(2)È
1.987(2) A] within the Al N unit are almost identical to those
2
2
in 1. The AlwC and AlwH distances average 1.988(4) and
1.49(3) A, respectively. The wC H -2,6-Mes aluminum sub-
6
3
2
stituents adopt a cis orientation across the Al N core, as do
2
2
the two nitrogen phenyl substituents.
3. The structure of the bridged phosphido derivative 3 (Fig.
3) is very similar in its overall conÐguration to that of 2 in
that the two pairs of wC H -2,6-Mes and Ph substituents
6
3
2
each have mutually cis orientations but are trans with respect
to each other. The Al P unit, like its Al N counterpart in 2,
2 2
2 2
also is folded in a similar manner with a fold angle of 143.3¡
along the Al(1)wAl(2) vector. The internal ring angles at alu-
minum and phosphorus average 83.03(10) and 91.41(3)¡. The
AlwP and AlwC distances average 2.433(5) and 1.981(5) A.
The AlwH distances of 1.43(6) and 1.49(6) A are comparable
to those in 1 and 2 and the PwH distances are both 1.31(6) A.
6 Æ 2Et O. The structure of 6 (Fig. 4) has a number of fea-
2
tures in common with that of 3. First, the cyclic [Al(C H -2,6-
6
3
Mes )As(H)Ph] unit is quite similar to the overall structure
2
2
Fig. 3 Computer generated drawing of 3. Important bond distances
and angles are given in Table 2
of 3 since there is the same cis-trans relationship involving the
wC H -2,6-Mes and Ph substituents. Moreover, the Al As
6
3
2
2
2
Fig. 1 Computer generated drawing of 1. Important bond distances
and angles are given in Table 2
Fig. 4 Computer generated drawing of 6. Important bond distances
and angles are given in Table 2
1128
New J. Chem., 1998, Pages 1125È1130

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core is folded in a similar manner although the amount of
folding (fold angle of 119.4¡) is substantially more than that in
The structural parameters for 1 and 2 are within normal
ranges. For instance, the terminal Al(1)wN(1) distance in 1,
1.833(6) A, is very close to the reference value (1.81 A) for a
normal AlwN bond to four-coordinate aluminum.19 The
bridging AlwN distances in both 1 and 2 are close to the 1.96
A observed in the dimers (Me AlNMe ) 20 or the 1.97 A in
3. The structure of
6 is completed by the “diarseneÏ
PhAs(1)As(2)Ph unit in which each arsenic is bound to a
single aluminum atom. The internal angles within the
Al(1)Al(2)As(3)As(4) ring may average 76.55(8)¡ at aluminum
and 88.32(9)¡ at arsenic and the AlwAs distances average
2.53(1) A. The AlwAs bonds to the PhAsAsPh moiety average
slightly shorter than 2.459(5) A. These arsenics possess dis-
torted trigonal pyramidal coordination with &¡ As(1) \ 297.1¡
and &¡ As(2) \ 299.9¡. The AswAs bond length is 2.4453(14)
A.
2
2 2
MAl(NMe ) N .21 The AlwC and AlwH distances are also
2 3 2
very similar to those previously reported for (H AlC H -2,6-
2
6 3
Mes ) .10 Both 1 and 2 have the same arrangement of
2 2
(bridging) amide phenyl and aluminum wC H -2,6-Mes sub-
6
3
2
stituents whereby the two amide phenyls are on one side of
the Al N core and the two wC H -2,6-Mes are on the
2
2
6
3
2
opposite side. Their relative orientation is seen to best advan-
tage in Fig. 2. It is apparent that the wC H -2,6-Mes groups
Discussion
6
3
2
are oriented essentially perpendicular to each other. The
folding of the Al N unit is also readily apparent as is the
The following compounds are the focus of this discussion:
2
2
2,6-Mes H C MPh(H)NNAlMl-N(H)PhN Al(H)C H -2,6-Mes
orientation of the wN(H)Ph phenyls perpendicular to the
core. It can be seen in Fig. 2 that the wN(H)Ph phenyl rings
to some extent eclipse and sterically interact with the ortho-
mesityl groups of the C(1)wC H -2,6-Mes ligand. This is
2
3 6
2
6
3
2
[2,6-
(1),
[2,6-Mes H C (H)AlMl-N(H)PhN]
(2),
2
3 6
Mes H C (H)AlMl-P(H)PhN]
3 6
As(H)PhN] (4), 2,6-Mes H C (H)AlMAs(H)PhN(OEt ) (5) and
3 6
(2,6-Mes H C Al) Ml-As(H)PhN (l-PhAsAsPh) (6). Previous
2
(3), [2,6-Mes H C (H)Al(l-
2
2
2
3 6
2
3 6
2
2
6
3
2
reÑected in the asymmetry of the Al(1)wNwC and
Al(2)wNwC angles, which di†er by ca. 14¡.
2
2
2
work in a number of areas has shown that large terphenyl
groups can often stabilize compounds with coordination
numbers or bonding that are not known with other currently
available ligands. A recent example is provided by the group
13 metal derivative InC H -2,6-Trip (Trip \ wC H -2,4,6-
The phosphido complex 3 has a structure very similar to
that of 2 in that the wPh and wC H -2,6-Mes substituents
6
3
2
have similar orientations with respect to the dimeric core unit.
The average AlwP distance of 2.433(5) A is very close to the
predicted value, 2.43 A,19 for these type of bonds and to the
average AlwP distances in complexes such as
(Me AlPMe ) ,22 (2.43 A) or M(Me Si) AlPPh N (2.452 A).23
6
3
2
6 3
iso-Pr ),16 which features a one-coordinate metal in the solid,
3
whereas
the
corresponding
wC(SiMe )
derivative
3 3
[InMC(SiMe ) N] is tetrameric with an In tetrahedrane struc-
3 3
4
4
2
2 3
3
2
2 2
ture.17 In the context of group 13 metal hydride chemistry it
has been shown that the reaction of (H AlMes*) 18 with
The length of the AlwP bonds in comparison to the AlwN
bond lengths in 2 allows a more sterically relaxed structure
and this is reÑected in the almost equal AlwPwC angles,
which di†er only by 4.8¡ for P(1) and by 1.6¡ for P(2).
2 2
or As) led to the monomer
H EPh (E \ N,
P
2
MPh(H)NN AlMes* and the ring compounds (PhNAlMes*) ,
2
2
(PhPAlMes*) and (PhAsAlMes*) .9 It has also been demon-
strated that the aluminum halide or hydride derivatives of the
The arsenido complex 4 could be isolated in poor yield
3
3
from the reaction of H AsPh with (H AlC H -2,6-Mes ) .
2
2
6
3
2 2
Mes* ligand and those of terphenyl ligands such as wC H -
This reaction takes place at room temperature in contrast to
6
2
2,4,6-Ph , wC H -2,6-Mes or wC H -2,6-Trip 10 have dif-
the corresponding reaction with H PPh which requires
3
6
3
2
6
3
2
2
ferent structures and reactivity. We now extend these investi-
gations to the interaction of these terphenyl alanes with
heating to ca. 150 ¡C to obtain 3. Unfortunately, crystals of 4
of sufficient size for an X-ray structure determination have not
H EPh (E \ N, P or As) species.
been obtained. If 4 is synthesized in the presence of Et O,
2
2
Interaction of H NPh with (H AlC H -2,6-Mes ) in an
however, the adduct 5 is produced, which may also be synthe-
2
2
6
3
2 2
approximate 2 : 1 ratio led to the products 1 and 2. Only small
amounts of 1 were observed, however, and the major product
of the reaction is the symmetrical amide-hydride dimer 2. The
stability of 2 may be contrasted with the corresponding Mes*
derivative.9 When H NPh is reacted with (H AlMes*) in a
sized by the simple addition of Et O to 4. 1H NMR studies of
2
5 indicate an equilibrium in accordance with eqn. (2) in which
the ether is lost to a†ord 4. A good quality X-ray data di†rac-
tion set was not obtained for 5 owing to deterioration of
crystal quality, which is probably a result of desolvation and
disorder problems. However, sufficient data were obtained to
2
2
2
2 : 1 ratio the only product isolated was the bisamide
MPh(H)NN AlMes*, in addition to some unreacted
conÐrm that the aluminum was bound to OEt (AlwO \ 1.89
2
2
(H AlMes*) . The structures of both 1 and 2 thus provide
A), wAs(H)Ph (AlwAs \ 2.48 A) and wC H -2,6-Mes
2
2
6
3
2
unique instances of stable group 13 compounds with geminal
hydrido and primary amide groups. Such compounds are
(AlwC \ 2.01 A) with the remaining tetrahedral site occupied
by a hydrogen that was not located.
prone to a rearrangement reaction as seen in the H NPh
] (H AlMes* ) or hydrogen elimination reactions.9 Appar-
Heating the reaction mixture of (H AlC H -2,6-Mes ) and
2
2
6
3
2 2
excess H AsPh to 150È160 ¡C gives the cage species 6. This
2
2 2
2
ently, the wC H -2,6-Mes substituent has the appropriate
unique compound, which is the Ðrst structurally characterized
6
3
2
steric requirements to stabilize the compounds against these
reaction pathways. Moreover, since previous work has indi-
cated that a single wC H -2,6-Mes substituent is not as
aluminum arsenic cluster, is related to the galliumÈarsenic
cluster 7,24 which also features an AswAs bond. The latter is
formed by the reaction in eqn. (3):
6
3
2
e†ective as wMes* at preventing further coordination at alu-
minum,10 it seems probable that the stability of 1 and 2 is a
result of their dimerized conÐgurations in which the metals
are four-coordinate and less prone to further reaction than a
putatively monomeric species such as HAlMN(H)PhNMes*.
The symmetric dimer 2 readily undergoes hydrogen elimi-
nation at its melting point of 162 ¡C. This process eventually
results in pale yellow glassy material, which dissolves in
hydrocarbon solvent. The 1H NMR revealed a 1 : 1 ratio of
Ph and wC H -2,6-Mes with no AlwH resonances being
GaR ] H AsPh ][(PhAsH)(R Ga)(PhAs) (RGa) ] (3)
3
2
2
6
4
7
where R is wCH SiMe . It has a Ga As core composed of
2
3
5
7
two di†ering, nonplanar, Ðve-membered rings linked by three
GawAs bonds. In contrast, the As Al basket-like core in 6
4
2
has a less complicated structure with the AswAs moiety
acting as the “handleÏ for the Al(1)Al(2)As(3)As(4) “basketÏ.
Within the “basketÏ the AlwAl distances of 2.53(1) A are very
similar to those in other compounds involving arsenide
ligands bridging four-coordinate aluminum centers.25 The
shorter (by ca. 0.07 A) aluminumÈarsenic bonds to the As(1)
6
3
2
observed. The IR spectrum also shows no AlwH stretching
absorptions. Possibly, the glassy material contains an imide of
formula (PhNAlC H -2,6-Mes ) .
6
3
2 n
New J. Chem., 1998, Pages 1125È1130
1129

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7 R. J. Wehmschulte, J. J. Ellison, K. Ruhlandt-Senge and P. P.
Power, Inorg. Chem., 1994, 33, 6300.
8 R. J. Wehmschulte and P. P. Power, Inorg. Chem., 1998, 37, 2106.
9 R. J. Wehmschulte and P. P. Power, J. Am. Chem. Soc., 1996, 118,
791.
and As(2) atoms are attributable to their lower (i.e., three)
coordination number. The AswAs distance of 2.4453(14) A is
normal for an AswAs single bond.26
10 R. J. Wehmschulte, W. J. Grigsby, B. Schiemenz, R. A. Bartlett
and P. P. Power, Inorg. Chem., 1996, 35, 6694.
Conclusions
11 R. J. Horvat and A. Furst, J. Am. Chem. Soc., 1952, 74, 562.
12 C. S. Palmer and R. Adams, J. Am. Chem. Soc., 1922, 44, 1356.
13 H. Hope, in Experimental Organometallic Chemistry, ed. A. L.
Wayda and M. Y Daresbourg, ACS Symposium Series 357, Amer-
ican Chemical Society, Washington, D.C., 1987, ch. 10.
14 International T ables for Crystallography, Reidel Publishing, Dor-
drecht, 1993, vol. C.
The reactions between (H AlC H -2,6-Mes ) and H EPh
2
6
3
2 2
2
(E \ N, P or As) di†er from the corresponding reactions with
the bulky primary alane (H AlMes*) . Essentially, elimination
2
2
of the second equivalent of hydrogen to give rings featuring
three-coordinate metals is not observed for the terphenyl sub-
stituted compounds. Instead, either thermal decomposition or
the substitution of some or all of the remaining hydrogens
15 S. R. Parkin, B. Moezzi and H. Hope, J. Appl. Crystallogr., 1995,
28, 53.
(e.g., in 1 or 6) in the presence of an excess of H EPh is
2
16 S. T. Haubrich and P. P. Power, J. Am. Chem. Soc., 1998, 120,
2202.
observed. The stability of the compounds toward elimination
of the second equivalent of H is attributed to the dimer-
17 R. D. Schluter, A. H. Cowley, D. A. Atwood, R. A. Jones and J. L.
Atwood, J. Coord. Chem., 1993, 30, 215; W. Uhl, R. Graupen, M.
Layh and U. Schutz, J. Organomet. Chem., 1995, 493, C1.
18 R. J. Wehmschulte and P. P. Power, Inorg. Chem., 1994, 33, 5611.
19 A. Haaland, in Coordination Chemistry of Aluminum, ed. G. H.
Robinson, VCH, New York, 1993, ch. 1.
2
ization of the amide, phosphide and arsenide derivatives,
which gives four-coordinate metal species that are especially
stable.
20 H. Hess, A. Hinderer and S. Z. Steinhausen, Z. Anorg. Allg. Chem.,
1970, 377, 1; K. Gosling, G. M. McLaughlin, G. A. Sim and J. D.
Smith, J. Chem. Soc., Dalton T rans, 1972, 2719.
Acknowledgements
We thank the National Science Foundation and the Donors
of the Petroleum Research Fund for Ðnancial support.
21 K. M. Waggoner, M. M. Olmstead and P. P. Power, Polyhedron,
1990, 9, 257.
22 A. Haaland, J. Hougen, H. V. Volden, G. H. Hanika and H. H.
Karsch, J. Organomet. Chem., 1987, 322, C24.
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Received in New Haven, CT , USA, 9th April 1998;
Paper 8/03431A
1130
New J. Chem., 1998, Pages 1125È1130