Synthesis and characterization of four- and five-coordinate organoaluminum complexes incorporating the amido diphosphine ligand system N(SiMe2CH2PPri2)2

Article abstract of DOI:10.1021/om9604583

The preparation of new four- and five-coordinate aluminum amido diphosphine complexes is reported. The reaction of the potentially tridentate ligand precursor LiN(SiMe₂CH₂PPr₂ⁱ)₂ with AlCl₃ in toluene at 25°C leads to the formation of AlCl₂[N(SiMe₂CH₂PPr₂ ⁱ)₂]. The X-ray crystal structure shows it to be monomeric with a distorted-trigonal-bipyramidal geometry having the tridentate ligand meridionally bound. The solution NMR spectra are also consistent with this geometry. Addition of the alkyllithium reagents RLi (where R = Me, Et) or dialkyl magnesium reagents R₂Mg (R = Me, CH₂Ph) leads to the formation of bis-(hydrocarbyl) derivatives of the formula AIR₂[N(SiMe₂CH₂PPr₂ ⁱ)₂]. The X-ray structure of Al(CH₂Ph)₂[N(SiMe₂CH₂PPr ₂ⁱ)₂] shows that it is mononuclear in the solid state with a distorted-tetrahedral geometry in which coordination to only one phosphine is observed. Variable-temperature NMR studies are consistent with a rapidly fluxional molecule at ambient temperature. In solution, the NMR spectroscopic parameters of AlMe₂[N(SiMe₂CH₂PPr₂ ⁱ)₂] and AlEt₂[N(SiMe₂CH₂PPr₂ ⁱ)₂] are consistent with overall C_2v symmetry. These observations are supported by ²⁷Al NMR studies. Attempts to generate the monoalkyls Al(R)X[N(SiMe₂CH₂PPr₂ⁱ)₂] (R = Me, Et; X = Cl) by the addition of 1 equiv of the appropriate alkylating reagent results in equimolar mixtures of the corresponding dialkyl and dichloride; however, the reaction of the lithium salt LiN(SiMe₂CH₂PPr₂ⁱ)₂ with RAlCl₂ (R = Me, Et) produces mixtures containing predominantly Al(R)X[N(SiMe₂CH₂PPr₂ⁱ)₂] (R = Me, Et). Treatment of the monoethyl derivative with excess AlCl₃ affords AlCl₂[N(SiMe₂CH₂PPr₂ ⁱ)₂]. AlCl₃. The X-ray crystal structure of this compound shows it to be monomeric, with each phosphine bound to a tetrahedral Al center. Solution NMR studies are consistent with this geometry. This species is likely formed as the result of the coordination of an AlCl₃ molecule to the aluminum center, followed by coordination of a second molecule to a free phosphine and subsequent elimination OfEtAlCl₂. This species is also generated by the addition of 3 equiv AlCl₃ to the starting lithium salt LiN(SiMe₂CH₂PPr₂ⁱ)₂.

Full text of DOI:10.1021/om9604583

4832
Organometallics 1996, 15, 4832-4841
Syn th esis a n d Ch a r a cter iza tion of F ou r - a n d
F ive-Coor d in a te Or ga n oa lu m in u m Com p lexes
In cor p or a tin g th e Am id o Dip h osp h in e Liga n d System
N(SiMe2CH2P P r i )
2 2
Michael D. Fryzuk,* Garth R. Giesbrecht, Gunnar Olovsson,† and
Steven J . Rettig†
Department of Chemistry, University of British Columbia, 2036 Main Mall,
Vancouver, British Columbia, Canada V6T 1Z1
Received J une 7, 1996X
The preparation of new four- and five-coordinate aluminum amido diphosphine complexes
is reported. The reaction of the potentially tridentate ligand precursor LiN(SiMe2CH2PPri )
2 2
with AlCl3 in toluene at 25 °C leads to the formation of AlCl2[N(SiMe2CH2PPri ) ]. The X-ray
2 2
crystal structure shows it to be monomeric with a distorted-trigonal-bipyramidal geometry
having the tridentate ligand meridionally bound. The solution NMR spectra are also
consistent with this geometry. Addition of the alkyllithium reagents RLi (where R ) Me,
Et) or dialkyl magnesium reagents R2Mg (R ) Me, CH2Ph) leads to the formation of bis-
(hydrocarbyl) derivatives of the formula AlR2[N(SiMe2CH2PPri )2]. The X-ray structure of
2
Al(CH2Ph)2[N(SiMe2CH2PPri )2] shows that it is mononuclear in the solid state with a
2
distorted-tetrahedral geometry in which coordination to only one phosphine is observed.
Variable-temperature NMR studies are consistent with a rapidly fluxional molecule at
ambient temperature. In solution, the NMR spectroscopic parameters of AlMe2[N(SiMe2-
CH2PPri ) ] and AlEt2[N(SiMe2CH2PPri ) ] are consistent with overall C2v symmetry. These
2 2
2 2
observations are supported by 27Al NMR studies. Attempts to generate the monoalkyls
Al(R)X[N(SiMe2CH2PPri ) ] (R ) Me, Et; X ) Cl) by the addition of 1 equiv of the appropriate
2 2
alkylating reagent results in equimolar mixtures of the corresponding dialkyl and dichloride;
however, the reaction of the lithium salt LiN(SiMe2CH2PPri )2 with RAlCl2 (R ) Me, Et)
2
produces mixtures containing predominantly Al(R)X[N(SiMe2CH2PPri )2] (R ) Me, Et).
2
Treatment of the monoethyl derivative with excess AlCl3 affords AlCl2[N(SiMe2CH2PPri )2]‚
2
AlCl3. The X-ray crystal structure of this compound shows it to be monomeric, with each
phosphine bound to a tetrahedral Al center. Solution NMR studies are consistent with this
geometry. This species is likely formed as the result of the coordination of an AlCl3 molecule
to the aluminum center, followed by coordination of a second molecule to a free phosphine
and subsequent elimination of EtAlCl2. This species is also generated by the addition of 3
equiv AlCl3 to the starting lithium salt LiN(SiMe2CH2PPri )2.
2
In tr od u ction
achieved, along the way we did uncover some intriguing
results that are reported here.
Our previous studies on the coordination properties
of the potentially tridentate, mixed-donor ligand
-N(SiMe2CH2PR2)2 have centered on the transition
metals and the lanthanoids.1-3 In an effort to expand
the territory to which this ligand can be applied, we
have initiated a study of the coordination chemistry of
certain main-group elements. As a starting point we
began looking at complexes of aluminum using this
ligand, since both amide and phosphine type donors
have been used previously with this metal, although
never before at the same time. Our primary goal was
to try to use this ancillary ligand system to stabilize
cationic Al(III) alkyl systems4-14 of the formula {AlR-
[N(SiMe2CH2PR2)2]}+. While this has not yet been
Typically, Al(III) tends to form complexes that are
four- or five-coordinate. Simple adducts of AlCl3 or AlR3
(4) Robinson, G. H.; Zhang, H.; Atwood, J . L. Organometallics 1987,
6, 887.
(5) Robinson, G. H.; Sangokoya, S. A. J . Am. Chem. Soc. 1988, 110,
1494.
(6) Taghoif, M.; Heeg, M. J .; Bailey, M.; Dick, D. G.; Kumar, R.;
Hendershot, D. G.; Rahbarnoohi, H.; Oliver, J . P. Organometallics
1995, 14, 2903.
(7) Atwood, J . L.; Robinson, K. D.; J ones, C.; Raston, C. L. J . Chem.
Soc., Chem. Commun. 1991, 1697.
(8) Bott, S. G.; Alvanipour, A.; Morley, S. D.; Atwood, D. A.; Means,
C. M.; Coleman, A. W.; Atwood, J . L. Angew. Chem., Int. Ed. Engl.
1987, 26, 485.
(9) Atwood, J . L.; Bott, S. G.; Harvey, S.; J unk, P. C. Organometallics
1994, 13, 4151.
(10) Engelhardt, L. M.; Kynast, U.; Raston, C. L.; White, A. H.
Angew. Chem., Int. Ed. Engl. 1987, 26, 681.
(11) Bott, S. G.; Elgamal, H.; Atwood, J . L. J . Am. Chem. Soc. 1985,
107, 1796.
(12) Self, M. F.; Pennington, W. T.; Laske, J . A.; Robinson, G. H.
Organometallics 1991, 10, 36.
† UBC Structural Chemistry Laboratory.
X Abstract published in Advance ACS Abstracts, October 1, 1996.
(1) Fryzuk, M. D.; Haddad, T. S.; Berg, D. J . Coord. Chem. Rev. 1990,
99, 137.
(2) Fryzuk, M. D.; Haddad, T. S.; Berg, D. J .; Rettig, S. J . Pure Appl.
Chem. 1991, 63, 845.
(13) Knajazhansky, S. Y.; Nomerotsky, I. Y.; Bulychev, B. M.; Belsky,
V. K.; Soloveichik, G. L. Organometallics 1994, 13, 2075.
(14) Davidson, M. G.; Lambert, C.; Lopez-Solera, I.; Raithby, P. R.;
Snaith, R. Inorg. Chem. 1995, 34, 3765.
(3) Fryzuk, M. D. Can. J . Chem. 1992, 70, 2849.
S0276-7333(96)00458-X CCC: $12.00 © 1996 American Chemical Society

Four- and Five-Coordinate Organoaluminum Complexes
Organometallics, Vol. 15, No. 22, 1996 4833
with phosphines15-24 or amines10,14,25-35 tend to generate
four-coordinate species; chelating ligands can enforce
higher coordination numbers by virtue of the chelate
effect. With amido or imido type ligands, dimers,
trimers or cage structures can be obtained.26,36 Because
our mixed-donor system is potentially tridentate, we
anticipated that five-coordinate complexes of the general
formula AlX2[N(SiMe2CH2PR2)2] would result. While
this was generally found to be true, four-coordinate
derivatives were also found to form under certain
conditions.
Sch em e 1
Resu lts a n d Discu ssion
The reaction of the lithium salt of the ancillary ligand
that contains isopropyl substituents, LiN(SiMe2CH2-
starting lithium derivative. The broadness of the peak
is undoubtedly the result of coordination to the quad-
PPri ) ,37 with AlCl3 in toluene at 25 °C for 24 h
2 2
generates the monomeric starting dichloride AlCl2-
5
rupolar 27Al nucleus (27Al, I ) /2, 100% natural abun-
[N(SiMe2CH2PPri ) ] (1) in good yield (eq 1). The 1H
2 2
dance),38,39 while the upfield shift upon coordination is
in contrast to that found for other complexes of this
ligand system, for which a downfield shift is typical.40
Small upfield or negative shifts upon coordination have
been previously reported for the phosphorus-31 reso-
nances of phenyl- and benzylphosphines coordinated to
trimethylaluminum.17 Elemental analyses on 1 are
indicative of some LiCl incorporation that can be
removed by successive recrystallizations. This type of
behavior has been observed previously in aluminum
complexes29,32,36,41 and also during our investigations of
this ligand system with early transition metals.40,42
In typical metathesis fashion, the starting dichloride
1 reacts with lithium or magnesium alkyls to yield
monomeric aluminum hydrocarbyl complexes of the
(1)
NMR spectrum of the product is indicative of a C2v
symmetric complex: one observes resonances due to
equivalent silylmethyl protons (SiCH3), methylene (PCH2-
Si), isopropyl methyls (CH(CH3)2) and methines
(CH(CH3)2) at typical chemical shifts. The 31P{1H}
NMR spectrum of 1 consists of a single broad resonance
at -10.5 ppm, which is upfield as compared to the
general formula AlR2[N(SiMe2CH2PPri ) ] (R ) Me (2),
2 2
Et (3), CH2Ph (4)) with concomitant formation of the
appropriate metal-halide salt as a byproduct in each
case (Scheme 1). The reactions to form 2 and 3 were
carried out at 25 °C in toluene, whereas the metathesis
reaction to form the dibenzyl 4 proved to be more
successful at -60 °C using THF as the solvent. The
dimethyl complex 2 may also be generated via the
reaction of the starting lithium salt LiN(SiMe2CH2-
(15) Krannich, L. K.; Watkins, C. L.; Schauer, S. J . Organometallics
1995, 14, 3094.
(16) Sangokoya, S. A.; Pennington, W. T.; Robinson, G. H.; Hrncir,
D. C. J . Organomet. Chem. 1990, 385, 23.
(17) Muller, G.; Lachmann, J .; Rufinska, A. Organometallics 1992,
11, 2970.
(18) Schmidbaur, H.; Lauteschlager, S.; Muller, G. J . Organomet.
Chem. 1985, 281, 33.
(19) Wierda, D. A.; Barron, A. R. Polyhedron 1989, 8, 831.
(20) Wells, R. L.; McPhail, A. T.; Self, M. F.; Laske, J . A. Organo-
metallics 1993, 12, 3333.
(21) Sangokoya, S. A.; Lee, B.; Self, M. F.; Pennington, W. T.;
Robinson, G. H. Polyhedron 1989, 8, 1497.
(22) Bennet, F. R.; Elms, F. M.; Gardiner, M. G.; Koutsantonis, G.
A.; Raston, C. L.; Roberts, N. K. Organometallics 1992, 11, 1457.
(23) Barron, A. R. J . Chem. Soc., Dalton Trans. 1988, 3047.
(24) J anik, J . F.; Duesler, E. N.; McNamara, W. F.; Westerhausen,
M.; Paine, R. T. Organometallics 1989, 8, 506.
(25) Petrie, M. A.; Ruhlandt-Senge, K.; Power, P. P. Inorg. Chem.
1993, 32, 1135.
(26) Waggoner, K. M.; Power, P. P. J . Am. Chem. Soc. 1991, 113,
3385.
(27) Atwood, D. A.; Rutherford, D. Organometallics 1995, 14, 3988.
(28) Moise, F.; Pennington, W. T.; Robinson, G. H. J . Coord. Chem.
1991, 24, 93.
(29) Trepanier, S. J .; Wang, S. Organometallics 1994, 13, 2213.
(30) Steiner, A.; Stalke, D. Organometallics 1995, 14, 2422.
(31) van Vliet, M. R. P.; Buysingh, P.; van Koten, G.; Vrieze, K.;
Kojic-Prodic, B.; Spek, A. L. Organometallics 1985, 4, 1701.
(32) J anik, J . F.; Duesler, E. N.; Paine, R. T. Inorg. Chem. 1987,
26, 4341.
PPri ) with Me2AlCl at room temperature in hexanes.
2 2
All three dialkylaluminum compounds are isolated in
good yields either as colorless oils, as in the case of 2
and 3, or as pale yellow crystals, as found for 4. These
thermally stable derivatives are soluble in aromatic
solvents as well as THF; however, their solubility is
more limited in hydrocarbon solvents. As is the case
with 1, the elemental analysis of 4 is valid only if one
allows for the inclusion of salt, in this case MgCl2. All
three of these air- and moisture-sensitive hydrocarbyl
1
derivatives exhibit room-temperature H NMR spectra
indicative of highly symmetric environments. Interest-
ingly, and in contrast to that found for 1, the solution
31P{1H} NMR spectra of the dialkyl complexes 2-4 all
consist of sharp singlets in the range of -3.6 to -4.9
ppm, consistent with very weak phosphine coordination
(33) Sangokoya, S. A.; Moise, F.; Pennington, W. T.; Self, M. F.;
Robinson, G. H. Organometallics 1989, 8, 2584.
(34) Robinson, G. H.; Sangokoya, S. A. Organometallics 1988, 7,
1453.
(35) Healy, M. D.; Barron, A. R. J . Am. Chem. Soc. 1989, 111, 398.
(36) Choquette, D. M.; Timm, M. J .; Hobbs, J . L.; Rahim, M. M.;
Ahmed, K. J .; Planalp, R. P. Organometallics 1992, 11, 529.
(37) Fryzuk, M. D.; Carter, A.; Westerhaus, A. Inorg. Chem. 1985,
24, 642.
(38) Delpuech, J . J . NMR of Newly Accessible Nuclei; Academic
Press: New York, 1983; Vol. 2.
(39) Akitt, J . W. Prog. NMR Spectrosc. 1989, 21, 1.
(40) Fryzuk, M. D.; Giesbrecht, G. R.; Rettig, S. J . Organometallics
1996, 15, 3329.
(41) Sierra, M. L.; de Mel, V. S. J .; Oliver, J . P. Organometallics
1989, 8, 2313.
(42) Fryzuk, M. D.; Mylvaganam, M.; Zaworotko, M. J.; MacGillivray,
L. R. Polyhedron 1995, 15, 689.

4834 Organometallics, Vol. 15, No. 22, 1996
Ta ble 1. Cr ysta llogr a p h ic Da ta for 1, 4, a n d 7a
Fryzuk et al.
1
4
7
formula
fw
C18H44AlCl2NP2Si2
490.56
C32H58AlNP2Si2
601.92
C18H44Al2Cl5NP2Si2
623.90
color, habit
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
colorless, prism
monoclinic
P21/n
10.015(3)
16.132(5)
17.951(7)
90
101.41(3)
90
2842(1)
4
colorless, needle
triclinic
P1h
colorless, prism
monoclinic
P21/c
12.227(2)
17.388(2)
15.935(2)
90
102.987(8)
90
3301.0(6)
4
11.724(3)
18.649(4)
9.047(3)
98.38(2)
98.06(2)
73.92(2)
1870.0(9)
2
Z
F
calcd, g/cm3
1.146
1056
1.069
656
1.255
1312
F(000)
radiation
Mo
4.61
Mo
2.18
Cu
62.01
0.20 × 0.45 × 0.50
0.36-1.00
ω-2θ
µ, cm-1
cryst size, mm
transmissn factors
scan type
0.45 × 0.45 × 0.40
0.12 × 0.20 × 0.40
0.94-1.00
ω-2θ
ω-2θ
scan range, ω, deg
scan speed, deg min-1
data collected
2θmax, deg
cryst decay, %
total no. of rflns
no. of unique rflns
Rmerge
1.52 + 0.35 tan θ
8 (up to 9 scans)
+h,+k,(l
55
negligible
6048
1.15 + 0.35 tan θ
16 (up to 9 scans)
+h,(k,(l
50
6.3
6933
0.89 + 0.20 tan θ
16 (up to 9 scans)
+h,+k,(l
155
7.4
7300
5781
0.077
6574
0.045
6992
0.073
no. of rflns with I g 3σ(I)
no. of variables
R
1405
245
0.081
2569
343
0.056
3611
272
0.046
Rw
0.076
0.050
0.046
GOF
3.88
2.43
2.00
Max ∆/σ (final cycle)
0.07
-0.47 to +0.47
0.002
-0.28 to +0.28
0.0003
-0.28 to +0.30
residual density, e/Å3
a
Conditions: temperature 294 K, Rigaku AFC6S diffractometer, Mo KR (λ ) 0.710 69 Å) or Cu KR (λ ) 1.541 78 Å) radiation, graphite
monochromator, takeoff angle 6.0°, aperture 6.0 × 6.0 mm at a distance of 285 mm from the crystal, stationary background counts at
each end of the scan (scan/background time ratio 2:1), σ2(F2) ) [S2(C + 4B)]/Lp2 (S ) scan rate, C ) scan count, B ) normalized background
2
count), function minimized ∑w(|Fo| - |Fc|)2, where w ) 4Fo2/σ2(Fo2), R ) ∑||Fo| - |Fc||/∑|Fo|, Rw ) (∑w(|Fo| - |Fc|)2/∑w|Fo| )1/2, and GOF
) [∑w(|Fo| - |Fc|)2/(m - n)]1/2 (where m ) number of observations, n ) number of variables). Values given for R, Rw, and GOF are based
on those reflections with I g 3σ(I).
and/or rapid exchange. In an effort to probe these
aspects of phosphine ligation, we undertook some solid-
state structural analyses where possible.
Solid -St a t e St r u ct u r es of AlCl2[N(SiMe2CH 2-
P P r i )2] (1) a n d Al(CH2P h )2[N(SiMe2CH2P P r i )2] (4).
2
2
Slow evaporation of a saturated toluene solution of
AlCl2[N(SiMe2CH2PPri2)2] (1) resulted in colorless needles
that were suitable for single-crystal X-ray diffraction.
The molecular structure and numbering scheme are
illustrated in Figure 1. Complete details of the struc-
tural analyses of 1 and 4, as well as 7 (see later) are
presented in Table 1. The structural analysis confirms
the monomeric nature of 1 and illustrates the coordina-
tion geometry of the complex that is best described as
trigonal bipyramidal. The ancillary amido diphosphine
ligand is bound in a meridional fashion with the
phosphine donors occupying axial positions. The great-
est deviation from ideal trigonal-bipyramidal geometry
is evident in the P(1)-Al(1)-P(2) bond angle of 171.8(3)°.
The Cl(1)-Al(1)-Cl(2) bond angle of 118.2(3)° is close
to that expected (120°) and is complemented by Cl(1)-
Al(1)-N(1) and Cl(2)-Al(1)-N(1) bond angles of 121.3(5)
and 120.5(4)°, respectively. Presumably, the twist in
the backbone of the tridentate ligand is due to the
relatively small Al(III) radius; the dihedral angle be-
tween the AlNSi2 and AlNP2 planes is 37.8°. In addi-
tion, this twist may be necessary in order to maintain
a trigonal bipyramidal environment for the Al center,
the preferred geometry for five-coordinate alumi-
F igu r e 1. Molecular structure of AlCl2[N(SiMe2CH2-
PPri )2] (1), with 33% probability thermal ellipsoids. Hy-
2
drogen atoms and disorder are not shown for clarity.
num.43,44 This has been observed previously in early-
metal complexes that contain this same ancillary ligand
system40,45 and compares to values ranging from 34.4
(43) Robinson, G. H.; Sangokoya, S. J . Am. Chem. Soc. 1987, 109,
6852.
(44) Robinson, G. H.; Sangokoya, S. A.; Moise, F.; Pennington, W.
T. Organometallics 1988, 7, 1787.

Four- and Five-Coordinate Organoaluminum Complexes
Organometallics, Vol. 15, No. 22, 1996 4835
Ta ble 2. Selected Bon d An gles (d eg) for 1, 4, a n d 7
w ith Estim a ted Sta n d a r d Devia tion s in
P a r en th eses
Ta ble 3. Selected Bon d Len gth s (Å) for 1, 4, a n d 7
w ith Estim a ted Sta n d a r d Devia tion s in
P a r en th eses
Compound 1
Compound 1
Al(1)-P(1)-C(2)
Al(1)-P(1)-C(4)
Al(1)-P(1)-C(7)
C(2)-P(1)-C(4)
C(2)-P(1)-C(7)
C(4)-P(1)-C(7)
Al(1)-P(2)-C(12)
Al(1)-P(2)-C(13)
Al(1)-P(2)-C(16)
124.5(8) N(1)-Si(2)-C(12)
107.9(7)
Cl(1)-Al(1)
Cl(2)-Al(1)
P(1)-Al(1)
P(1)-C(2)
P(1)-C(4)
P(1)-C(7)
P(2)-Al(1)
P(2)-C(12)
P(2)-C(13)
P(2)-C(16)
2.183(6)
2.164(7)
2.542(7)
1.88(2)
1.81(2)
1.85(2)
2.509(7)
1.82(2)
1.90(2)
1.86(2)
Si(1)-N(1)
Si(1)-C(7)
Si(1)-C(8)
Si(1)-C(9)
Si(2)-N(1)
Si(2)-C(10)
Si(2)-C(11)
Si(2)-C(12)
Al(1)-N(1)
1.72(1)
1.89(2)
1.86(2)
1.80(2)
1.72(1)
1.90(2)
1.88(2)
1.84(2)
1.89(1)
116.7(7) C(10)-Si(2)-C(11) 107.4(9)
97.4(6) C(10)-Si(2)-C(12) 109.1(9)
102(1)
109.1(9) Cl(1)-Al(1)-Cl(2)
106(1) Cl(1)-Al(1)-P(1)
C(11)-Si(2)-C(12) 109.3(8)
118.2(3)
93.5(2)
89.3(2)
121.3(5)
89.8(2)
95.7(3)
120.5(4)
171.8(3)
84.6(4)
95.3(5) Cl(1)-Al(1)-P(2)
113.4(6) Cl(1)-Al(1)-N(1)
125.9(6) Cl(2)-Al(1)-P(1)
C(12)-P(2)-C(13) 104.7(9) Cl(2)-Al(1)-P(2)
C(12)-P(2)-C(16) 110.0(9) Cl(2)-Al(1)-N(1)
C(13)-P(2)-C(16) 105.4(9) P(1)-Al(1)-P(2)
Compound 4
P(1)-Al(1)
P(1)-C(1)
P(1)-C(7)
P(1)-C(8)
P(2)-C(2)
P(2)-C(13)
P(2)-C(14)
Si(1)-N(1)
Si(1)-C(1)
2.453(3)
1.835(6)
1.843(6)
1.846(7)
1.848(6)
1.846(8)
1.84(1)
Si(1)-C(3)
Si(1)-C(4)
Si(2)-N(1)
Si(2)-C(2)
Si(2)-C(5)
Si(2)-C(6)
Al(1)-N(1)
Al(1)-C(19)
Al(1)-C(26)
1.862(7)
1.867(7)
1.745(5)
1.881(7)
1.862(7)
1.876(7)
1.853(5)
1.991(7)
1.987(6)
N(1)-Si(1)-C(7)
N(1)-Si(1)-C(8)
N(1)-Si(1)-C(9)
C(7)-Si(1)-C(8)
C(7)-Si(1)-C(9)
C(8)-Si(1)-C(9)
N(1)-Si(2)-C(10)
N(1)-Si(2)-C(11)
107.9(7) P(1)-Al(1)-N(1)
111.3(8) P(2)-Al(1)-N(1)
114.5(8) Si(1)-N(1)-Si(2)
107.3(9) Si(1)-N(1)-Al(1)
87.4(4)
121.8(6)
119.3(6)
118.7(6)
108.3(7)
110.6(9)
108(1)
Si(2)-N(1)-Al(1)
108.0(9) P(1)-C(7)-Si(1)
110.4(7) P(2)-C(12)-Si(2)
112.7(7)
1.716(5)
1.882(7)
Compound 4
Compound 7
Al(1)-P(1)-C(1)
Al(1)-P(1)-C(7)
Al(1)-P(1)-C(8)
C(1)-P(1)-C(7)
C(1)-P(1)-C(8)
C(7)-P(1)-C(8)
C(2)-P(2)-C(13)
C(2)-P(2)-C(14)
97.2(2) N(1)-Si(2)-C(6)
123.6(2) C(2)-Si(2)-C(5)
114.9(2) C(2)-Si(2)-C(6)
106.9(3) C(5)-Si(2)-C(6)
107.4(3) P(1)-Al(1)-N(1)
105.4(3) P(1)-Al(1)-C(19)
105.3(3) P(1)-Al(1)-C(26)
102.5(4) N(1)-Al(1)-C(19)
112.1(3)
108.8(3)
108.5(3)
106.5(3)
92.1(2)
106.3(2)
110.4(2)
113.6(2)
117.5(3)
Cl(1)-Al(1)
Cl(2)-Al(1)
Cl(3)-Al(2)
Cl(4)-Al(2)
Cl(5)-Al(2)
P(1)-Al(1)
P(1)-C(1)
P(1)-C(7)
P(1)-C(10)
P(2)-Al(2)
P(2)-C(2)
2.132(2)
2.124(2)
2.115(2)
2.106(2)
2.112(2)
2.403(2)
1.807(5)
1.815(6)
1.832(5)
2.412(2)
1.808(4)
P(2)-C(13)
P(2)-C(16)
Si(1)-N(1)
Si(1)-C(1)
Si(1)-C(3)
Si(1)-C(4)
Si(2)-N(1)
Si(2)-C(2)
Si(2)-C(5)
Si(2)-C(6)
Al(1)-N(1)
1.833(5)
1.843(5)
1.727(3)
1.892(5)
1.860(6)
1.856(6)
1.729(3)
1.908(5)
1.854(5)
1.858(5)
1.828(3)
C(13)-P(2)-C(14) 100.6(5) N(1)-Al(1)-C(26)
N(1)-Si(1)-C(1)
N(1)-Si(1)-C(3)
N(1)-Si(1)-C(4)
C(1)-Si(1)-C(3)
C(1)-Si(1)-C(4)
C(3)-Si(1)-C(4)
N(1)-Si(2)-C(2)
N(1)-Si(2)-C(5)
108.1(3) C(19)-Al(1)-C(26) 114.1(3)
113.5(3) Si(1)-N(1)-Si(2)
115.6(3) Si(1)-N(1)-Al(1)
105.3(3) Si(2)-N(1)-Al(1)
106.5(3) P(1)-C(1)-Si(1)
107.1(3) P(2)-C(2)-Si(2)
121.7(3)
117.4(3)
120.9(3)
112.7(3)
117.2(3)
The aluminum-phosphorus bond lengths of 2.509(7)
and 2.542(7) Å are also common in terms of Al-P bond
distances for phosphine adducts of aluminum, which
usually span the range from ∼2.4 to 2.8 Å.17,22,49 The
intermediary solvation of the aluminum center by the
phosphine donors is further illustrated by comparison
to the bond lengths of 2.53 and 2.535 Å in Me3AlPMe3
and Me3AlPPh3, respectively.19 The aluminum-nitro-
gen bond distance of 1.89(1) Å falls well within the usual
range for aluminum-amide bonds.25,26,28-30,36,50 As is
expected, the amide bond present is slightly shorter
than for the N-donor amine adducts of aluminum
(∼2.0-2.2 Å)30,33,35 but is similar to the bond lengths
cited in structures retaining an Al2N2 or bridging
nitrogen core,12,26,32,36 in which a lower degree of dative
bonding is usually invoked. The Al-N bond distance
in 1 compares well with that in the similar amido
diamine compound Al(CH3)2[(NCH2CH2NEt2)2] (Al-
N(amido) ) 1.84(1) Å), which also exhibits a trigonal-
bipyramidal Al coordination geometry.29 It is unclear
to what extent this bond length, approximately 0.1 Å
shorter than the sum of the covalent radii, is indicative
of some degree of p-p π bonding.25 A partial list of bond
lengths for 1, 4, and 7 is presented in Table 3.
109.4(3) Al(1)-C(19)-C(20) 110.4(4)
111.3(3) Al(1)-C(26)-C(27) 116.2(4)
Compound 7
Al(1)-P(1)-C(1)
Al(1)-P(1)-C(7)
Al(1)-P(1)-C(10)
C(1)-P(1)-C(7)
C(1)-P(1)-C(10)
C(7)-P(1)-C(10)
Al(2)-P(2)-C(2)
Al(2)-P(2)-C(13)
Al(2)-P(2)-C(16)
C(2)-P(2)-C(13)
C(2)-P(2)-C(16)
98.6(2) C(2)-Si(2)-C(5)
113.1(2) C(2)-Si(2)-C(6)
120.8(2) C(5)-Si(2)-C(6)
107.3(3) Cl(1)-Al(1)-Cl(2)
109.1(2) Cl(1)-Al(1)-P(1)
107.0(3) Cl(1)-Al(1)-N(1)
115.0(2) Cl(2)-Al(1)-P(1)
109.2(2) Cl(2)-Al(1)-N(1)
106.3(2) P(1)-Al(1)-N(1)
108.3(2) Cl(3)-Al(2)-Cl(4)
107.6(2) Cl(3)-Al(2)-Cl(5)
110.0(2)
111.5(2)
106.8(2)
108.90(8)
110.02(7)
115.4(1)
110.29(8)
115.9(1)
95.5(1)
111.7(1)
110.30(9)
105.79(8)
112.1(1)
108.32(8)
108.42(9)
124.1(2)
116.7(2)
118.9(2)
113.8(2)
125.3(3)
C(13)-P(2)-C(16) 110.4(3) Cl(3)-Al(2)-P(2)
N(1)-Si(1)-C(1)
N(1)-Si(1)-C(3)
N(1)-Si(1)-C(4)
C(1)-Si(1)-C(3)
C(1)-Si(1)-C(4)
C(3)-Si(1)-C(4)
N(1)-Si(2)-C(2)
N(1)-Si(2)-C(5)
N(1)-Si(2)-C(6)
107.9(2) Cl(4)-Al(2)-Cl(5)
113.4(2) Cl(4)-Al(2)-P(2)
112.0(2) Cl(5)-Al(2)-P(2)
107.3(2) Si(1)-N(1)-Si(2)
106.3(3) Si(1)-N(1)-Al(1)
109.6(3) Si(2)-N(1)-Al(1)
105.6(2) P(1)-C(1)-Si(1)
110.9(2) P(2)-C(2)-Si(2)
112.1(2)
to 40.8° for similar compounds of scandium.40 Selected
bond angles for 1 can be found in Table 2.
The aluminum-chloride distances of 2.183(6) and
2.164(7) Å compare well with those previously reported
for terminal Al-Cl bonds,11,16,20,21,33,46 falling just out-
side the cited range of the longer bridging chlorides.47,48
Evaporation of a saturated toluene solution of Al(CH2-
Ph)2[N(SiMe2CH2PPri ) ] (4) resulted in the deposition
2 2
of pale yellow needles that were suitable for X-ray
diffraction. The molecular structure and numbering
(48) Lalama, M. S.; Kampf, J .; Dick, D. G.; Oliver, J . P. Organo-
metallics 1995, 14, 495.
(49) Atwood, J . L.; Butz, K. W.; Gardiner, M. G.; J ones, C.;
Koutsantonis, G. A.; Raston, C. L.; Robinson, K. D. Inorg. Chem. 1993,
32, 3482.
(45) Fryzuk, M. D.; Leznoff, D. B.; Rettig, S. J . Organometallics
1995, 14, 5193.
(46) Lewinski, J .; Pasynkiewicz, S.; Lipowski, J . Inorg. Chim. Acta
1990, 178, 113.
(47) Schonberg, P. R.; Paine, R. T.; Campana, C. F. J . Am. Chem.
Soc. 1979, 101, 7726.
(50) Heine, A.; Stalke, D. Angew. Chem., Int. Ed. Engl. 1992, 31,
854.

4836 Organometallics, Vol. 15, No. 22, 1996
Fryzuk et al.
116.2(4)°, were outside of the range normally found for
an η2 interaction. Furthermore, the Al-Cortho distances
of 3.589-3.924 Å were convincing evidence against an
η3 formulation of any type. The Cbenzylic-Cipso bond
lengths of 1.505(8) Å also fall within the desired range
for σ-bound benzyl groups devoid of any additional
interactions and are longer than that found in the
related chromium derivative.
31P a n d 27Al NMR St u d ies a n d Coor d in a t ion
Nu m ber . While the X-ray structure of dichloride 1 is
compatible with the solution 1H and 31P{1H} NMR
1
studies, the simple H NMR spectrum and single sharp
resonance in the 31P{1H} NMR spectrum of the dibenzyl
4 was at odds with the bidentate mode of coordination
of the ancillary ligand found in the solid state. Even
though we were unable to isolate either the dimethyl 2
or the diethyl 3 as solids, we were curious about their
solution structures. In the past, 27Al NMR spectroscopy
has proved helpful in correlating chemical shift with
coordination number,38,39 even at temperatures where
1
highly dynamic molecules show only averaged H and
F igu r e 2. Molecular structure of Al(CH2C6H5)2[N(SiMe2-
31P{1H} signals.17
CH2PPri )2] (4), with 33% probability thermal ellipsoids.
2
As already mentioned, the solution spectroscopic data
for dichloride 1 reinforces the results of the solid-state
Hydrogen atoms are omitted for clarity.
1
X-ray analysis. The H NMR spectrum is indicative of
scheme of this compound can be seen in Figure 2. The
structural study reveals 4 to be four-coordinate via
coordination to only one phosphine arm of the ancillary
a molecule with overall C2v symmetry, and the single
broad resonance in the 31P{1H} NMR spectrum at -10.5
ppm suggests some aluminum-phosphorus interaction.
The 31P{1H} NMR spectrum is temperature invariant
down to the solvent limit (-90 °C, d8-toluene). The 31P
and 27Al MAS NMR spectrum of a solid sample of
dichloride 1 is consistent with the same sort of Al-P
coupling that is present in solution. The solution 27Al
NMR spectrum contains a very broad peak at 65 ppm,
which is well within the typical range for five-coordinate
aluminum derivatives.38,39 Large peak widths appear
to be common when quadrupolar nuclei are observed
in heteroleptic environments.23,56 The dichloride 1 does
not form adducts with THF, pyridine, or acetonitrile in
solution. Presumably, the steric constraints of the
ancillary ligand system prevent the aluminum center
from attaining a higher coordination number, even in
the presence of excess donor molecules. Interestingly,
the addition of a strongly Lewis acidic moiety such as
AlCl3 to 1 results in the reduction of the aluminum
coordination number to 4, with a further AlCl3 interac-
tion being observed with a free phosphine (see later).
The 31P{1H} NMR spectrum of dimethyl 2 features a
much narrower peak than would be expected for a
compound harboring an Al-P interaction. The position
of this peak, -4.9 ppm, is also close to that of the
-N(SiMe2CH2PPri ) ligand. Presumably, the steric
2 2
repulsion between the aryl rings of the benzyl groups
and the isopropyl substituents on the phosphorus donors
is great enough to force one of the weakly bound
phosphines to dissociate, allowing the Al center to adopt
a distorted-tetrahedral geometry. This is the most
prevalent and preferred mode of coordination for
Al(III).51 The six tetrahedral angles, varying from
92.1(2) to 117.5(3)°, do indicate the extent of the
distortion from a pure tetrahedron with the most acute
angle, defined by the P(1), Al(1), and N(1) atoms, being
the result of the bidentate ligand “pinching back”.
The single aluminum-phosphorus bond measures
2.453(3) Å and is slightly shorter than the Al-P bond
lengths of 1. The aluminum-nitrogen bond is also
similar to that ascertained for 1, although the slightly
longer silicon-amide bond (1.745(5) vs 1.72(1) Å) coupled
with the marginally shorter Al-N bond (1.853(5) vs
1.89(1) Å) may point to a slightly higher degree of
π-donation from the amide lone pair to the metal.
Compound 4 also possesses unremarkable aluminum-
carbon bond lengths of 1.991(7) and 1.987(6) Å, which
are akin to those previously reported for terminal Al-C
bonds.10,25,48,52-54 The strongest similarity is with the
Al-C distances found in Al(CH2C6H5)3, for which aver-
age values of 1.989(6) Å were found.55
starting lithium salt LiN(SiMe2CH2PPri ) , which reso-
2 2
nates at -4.7 ppm and most likely does not experience
any sort of quadrupolar interaction. As the temperature
is lowered, the peak broadens slightly, but no evidence
of decoalescence behavior is observed even down to -90
°C. It is unclear whether this indicates a three-
coordinate structure or a rapidly fluxional process that
could not be frozen out. The solution 27Al NMR spec-
trum of 2, however, consists of a peak at 70 ppm,
indicating a geometry similar to that found in 1. In
addition, the equivalent methyl groups (AlMe2) appear
as a triplet in the 1H NMR spectrum, the result of
coupling to two equivalent phosphorus-31 nuclei. All
The recent X-ray structure of Cr(CH2C6H5)[N(SiMe2-
CH2PPh2)2],45 which possesses an η2-bound benzyl frag-
ment, prompted us to further examine the structure of
4. The Al-Cipso lengths of 2.883 and 2.974 Å, coupled
with Al-Cbenzylic-Cipso bond angles of 110.4(4) and
(51) Mole, T.; J effrey, E. A. Organoaluminum Compounds; Elsevi-
er: Amsterdam, 1972.
(52) de Mel, V. S. J .; Oliver, J . P. Organometallics 1989, 8, 827.
(53) J erius, J . J .; Hahn, J . M.; Rahman, A. F. M. M.; Mols, O.; Ilsley,
W. H.; Oliver, J . P. Organometallics 1986, 5, 1812.
(54) Fisher, J . D.; Wei, M. Y.; Willett, R.; Shapiro, P. J . Organo-
metallics 1994, 13, 3324.
(55) Rahman, A. F. M. M.; Siddiqui, K. F.; Oliver, J . P. Organo-
metallics 1982, 1, 881.
(56) Wehmshulte, R. J .; Power, P. P. Inorg. Chem. 1994, 33, 5611.

Four- and Five-Coordinate Organoaluminum Complexes
Organometallics, Vol. 15, No. 22, 1996 4837
the spectroscopic data taken together point to a highly
fluxional structure for 2, presumably a result of rapid
phosphine-arm dissociation and reassociation on the
NMR time scale.
these latter species; in addition, these derivatives might
be useful starting materials for cationic derivatives by
halide abstraction.8,9,11-14 Crown ether ligands have
been the most successful in this regard, although
nitrogen-based ancillary ligands have also been of some
use.7,10 Unfortunately, our attempts to selectively
Examination of the H and 31P{1H} NMR spectra of
1
diethyl 3 reveals properties similar to those found for
1
remove one alkyl group from the dialkyls 2 and 4 with
2. The H NMR spectrum is characteristic of a highly
57,58
the strong Lewis acid B(C6F5)3
or with Brookhart’s
symmetric molecule in which the methylene protons of
the ethyl groups (AlCH2CH3) appear as a quartet of
triplets due to coupling to two equivalent phosphines
as well as the terminal -CH3 protons of the ethyl group.
As in 2, the 31P{1H} NMR spectrum of 3 exhibits only a
single sharp resonance at -4.2 ppm, which broadens
but does not decoalesce as the temperature is lowered.
However, the 27Al NMR spectrum is shifted downfield
from that of 1 or 2 to 140 ppm, well within the range
normally associated with four-coordinate species.38,39
Again, the data point toward a rapidly fluxional struc-
ture; however, to account for the 27Al NMR spectral
result, one can suggest that diethyl 3 spends a com-
paratively greater amount of time in the dissociated
state as compared to dimethyl 2. That this is the case
can be rationalized on the similarity in size between the
-Cl and -CH3 groups in 1 and 2; the larger -CH2CH3
groups in 3 undoubtedly destabilize coordination by both
of the bulky isopropyl-substituted phosphine donors.
acid, HB(3,5-CF3(C6H3))4,59 resulted in a mixture of
intractable products.
When dichloride 1 was subjected to the slow addition
of 1 equiv of methyllithium or equivalent Grignard
1
reagent (i.e., MeMgBr, MeMgCl, or /2 equiv of Me2Mg),
equimolar mixtures of starting dichloride 1 and di-
methyl 2 were obtained. Similarly, addition of just 1
equiv of EtLi to 1 also produced a mixture of starting
dichloride 1 and diethyl 3 (eq 2). To account for this
(2)
behavior,41 we suggest that the monoalkyl intermediate
reacts faster than dichloro 1, because in the former
species, phosphine dissociation becomes more likely,
thus opening the coordination sphere to attack by
nucleophiles. However, we did find that the mixture
of dichloride 1 and dimethyl 2 could be induced to
equilibrate to a mixture that contained the monomethyl
The crystal structure of Al(CH2Ph)2[N(SiMe2CH2-
PPri ) ] (4) illustrates that, with large enough alkyl
2 2
groups, aluminum will reside in its preferred tetra-
1
hedral geometry. Once again, the H NMR spectrum
displays resonances indicative of a C2v-symmetric com-
plex, although instead of a triplet for the benzylic
protons, a broad peak at 3.50 ppm is observed. No
useful information could be garnered from variable-
derivative Al(Me)Cl[N(SiMe2CH2PPri ) ] (5) upon heat-
2 2
ing; it was found that after 1 week at 100 °C, the
exchange was approximately 85% complete, as moni-
tored by 1H NMR spectroscopy (eq 3). When the
1
temperature H NMR due to a systematic broadening
of all resonances with no obvious low-temperature limit.
However, the sharp singlet at -3.6 ppm in the 31P{1H}
NMR spectrum does display typical coalescence behav-
ior; the singlet broadened and shifted slightly upfield
as the temperature was lowered, and at -74 °C, two
singlets of equal intensity at -5.4 and -6.8 ppm were
evident. Unfortunately, the kinetic parameters, ∆Gq,
∆Hq, and ∆Sq, could not be derived due to the error
associated with a fluxional process such as this occur-
ring over such a limited temperature range (-63 to -74
°C). The solution 27Al NMR spectrum consists of a
broad peak at 54 ppm, both at room temperature and
at -74 °C. These data suggest that, at room temper-
ature in solution, 4 is rapidly fluxional through a five-
coordinate intermediate (associative pathway). That
dibenzyl 4 would be five-coordinate in solution, while
diethyl 3 would remain four-coordinate, is counter-
intuitive, on the basis of the relative sizes of the ethyl
and benzyl groups. In other words, one would expect
the solution 27Al NMR shift for dibenzyl 4 to be similar
to that for the diethyl 3 on the basis of the solid-state
structure of 4. It may be that, in the case of 4, the
correlation of 27Al NMR chemical shift and solution
coordination number breaks down.
(3)
equilibrium shown in eq 3 was monitored at tempera-
tures between 20 and 100 °C by H NMR spectroscopy,
1
the following thermodynamic data were calculated using
the van’t Hoff equation: ∆H° ) 106 ( 8 kJ mol-1 and
∆S° ) 311 ( 24 J mol-1 K-1
.
In an effort to obtain pure Al(Me)Cl[N(SiMe2CH2-
PPri ) ] (5), we studied the reaction of the starting
2 2
lithium salt LiN(SiMe2CH2PPri ) with MeAlCl2. Al-
2 2
though in this reaction we were able to prepare more
pure Al(Me)Cl[N(SiMe2CH2PPri ) ] (5), small quantities
2 2
of 1 and 2 were present, and these impurities persisted
even if the reaction was done under dilute conditions
at -78 °C. Given the equilibrium between 5 and
dichloro 1 and dimethyl 2, this last result is not
surprising.
As mentioned above, the reaction of 1 with 1 equiv of
EtLi produced an equimolar mixture of 1 and diethyl
3; however, in this case prolonged heating (2 weeks, 100
Syn th esis of th e Mon oa lk yl Der iva tives Al(R)-
Cl[N(SiMe2CH2P P r i )2] (R ) Me, Et). The difference
2
(57) Yang, X.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1991,
in structure between dichloride 1 and the dialkyls, 2-4
113, 3623.
(58) Yang, X.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1994,
prompted us to examine the preparation of the monoalkyl
116, 10015.
derivatives Al(R)Cl[N(SiMe2CH2PPri ) ]. It would stand
2 2
(59) Brookhart, M.; Grant, M.; Volpe, J . A. F. Organometallics 1992,
11, 3920.
to reason that intermediate behavior should obtain for

4838 Organometallics, Vol. 15, No. 22, 1996
Fryzuk et al.
°C) did not result in any observable exchange to produce
the monoethyl derivative, as monitored by 1H NMR
spectroscopy. As a result, we examined the reaction of
the lithium salt LiN(SiMe2CH2PPri ) with EtAlCl2, in
2 2
hopes of producing Al(Et)Cl[N(SiMe2CH2PPri2)2] (6). The
1H NMR spectrum of this reaction mixture indeed did
show predominantly 6, but small amounts (<5%) of 1
were invariably present, presumably due to contamina-
tion by AlCl3 in the starting AlEtCl2. The complete
absence of diethyl 3 is consistent with the lack of an
exchange equilibrium being present. In other words,
once the monoethyl complex 6 forms, it does not
disproportionate into 1 and 3, as was observed for the
monomethyl derivative 5.
Syn th esis of AlCl2[N(SiMe2CH2P P r i )2]‚AlCl3 (7).
2
Although we were unable to isolate pure monoalkyl
derivatives Al(R)Cl[N(SiMe2CH2PPri ) ], we decided to
2 2
attempt the formation of the cation {AlR[N(SiMe2CH2-
PPri ) ]}+ by reaction of the slightly impure monoethyl
2 2
F igu r e 3. Molecular structure of AlCl2[N(SiMe2CH2-
complex 6 with AlCl3. Upon addition of the solution of
6 to a slurry of AlCl3 in toluene (approximately 2.5
equiv), the solution turned slightly amber and most of
the AlCl3 was taken up into solution. Upon workup,
colorless crystals were isolated that displayed the fol-
lowing spectroscopic characteristics: the 31P{1H} NMR
spectrum consisted of two broad peaks at 0.0 and -11.8
ppm of roughly equal intensity, and the 1H NMR
spectrum indicated a single clean but unsymmetrical
product, with no resonances due to ethyl groups present.
The elemental analysis, coupled with the 31P{1H} and
1H NMR data, pointed toward an AlCl3 adduct of
PPri )2]‚AlCl3 (7), with 33% probability thermal ellipsoids.
2
Hydrogen atoms are omitted for clarity.
pair from the phosphine to the metal center. The
aluminum-chlorine bond lengths are all similar
(2.106(2)-2.132(2) Å) and unexceptional. The alumi-
num-phosphorus bond lengths of 2.403(2) Å (P(1)-
Al(1)) and 2.412(2) Å (P(2)-Al(2)) are both smaller than
those found in 1 and 4.
The 1H NMR spectrum of 7 is consistent with its
structure, in that a doubling of all ligand resonances is
seen as a result of the lack of symmetry. The 31P{1H}
NMR spectrum consists of two broad singlets, due to
the coordination of each phosphorus nucleus to a quad-
rupolar Al center. Also, the methylene protons associ-
ated with the “free” arm (C(2)) appear as a broad
doublet. Examination of the crystal structure reveals
a short intramolecular C(2)-H(3)‚‚‚Cl(2) distance of
3.082 Å. It appears this interaction slows the rotation
of the free arm on the NMR time scale, resulting in a
broadening of these protons. The molecule also has
three other short intramolecular contacts of note: two
protons on a silyl methyl group on the free side of the
ligand interact with chlorides on Al(1) and Al(2) (C(5)-
H(12)‚‚‚Cl(2) ) 3.623(5) Å, C(5)-H(13)‚‚‚Cl(5) ) 3.755(5)
Å), and a proton on an isopropyl group (C(11)-H(25))
interacts with a chloride (Cl(1)) associated with Al(1)
(3.750(7) Å). Finally, there is also an intermolecular
contact measuring 3.739(6) Å between C(12)-H(28) and
Cl(4) of an adjacent molecule of 7. No broadening of
the resonances associated with these further intra-
molecular contacts was observed.
dichloro 1, in which the -N(SiMe2CH2PPri ) ligand is
2 2
bound to an AlCl2 unit in a bidentate fashion via the
amide function and one phosphine donor, with the
remaining phosphine arm of the ancillary ligand coor-
dinated to an AlCl3 molecule (eq 4).
(4)
Str u ctu r e of AlCl2[N(SiMe2CH2P P r i )2]‚AlCl3 (7).
2
X-ray quality crystals of 7 were grown by slow evapora-
tion of a saturated toluene solution. The molecular
structure and numbering scheme are depicted in Figure
3. The most important feature of this molecule is that
two four-coordinate aluminum centers are present. One
Al is bound in a bidentate fashion to the tridentate
ligand, with the remaining phosphine arm coordinated
to the AlCl3 unit. We presume that the presence of this
coordinated AlCl3 unit in 7 serves the same function as
the large benzyl groups in 4, in that they both allow for
the central aluminum to retain a tetrahedral geometry.
The bond angles involving this aluminum range from
115.9(1) to 95.5(1)°. The smallest angle, as in 4, involves
chelation of the ligand to the metal (P(1)-Al(1)-N(1)).
The second aluminum also exhibits a four-coordinate,
tetrahedral geometry. The angles involving the phos-
phine in this case are slightly smaller (105.79(8)-
108.42(9)°) than those between the chlorides (110.30(9)-
112.1(1)°) and are the result of the donation of the lone
Polynuclear aluminum compounds are numerous in
the literature, although those incorporating amido
ligands are more rare. Complex 7 is one of only three
known polynuclear aluminum complexes with a triden-
tate amido ligand.29,60 Its asymmetric nature is similar
to that of Al3(CH3)8(Et2NCH2CH2NCH2CH2NEt2), al-
though ligation to the amide lone pair is not observed
in our case. Exposure of 7 to additional AlCl3 did not
result in any further rearrangement.
Mech a n ism of F or m a tion of AlCl2[N(SiMe2CH2-
P P r i2)2]‚AlCl3 (7). The most striking feature of the
structure of 7 is the absence of an ethyl group bound to
(60) Wannagat, U.; Blumenthal, T.; Brauer, D. J .; Burger, H. J .
Organomet. Chem. 1983, 249, 33.

Four- and Five-Coordinate Organoaluminum Complexes
Organometallics, Vol. 15, No. 22, 1996 4839
Sch em e 2
Thus, the addition of 2 equiv of AlCl3 to AlCl2[N(SiMe2-
CH2PPri ) ] also forms the AlCl3 adduct 7, although 1
2 2
equiv does not. This suggests that if the phosphine
arms of AlCl2[N(SiMe2CH2PPri ) ] were rapidly flux-
2 2
ional, and an AlCl3 molecule simply trapped a tran-
siently dangling phosphine arm, the addition of 1 equiv
of AlCl3 should be sufficient to form 7. The need for 2
equiv of AlCl3 supports our contention that the forma-
tion of a bridged species is necessary to dissociate one
phosphine arm, which is then trapped by the excess
AlCl3.
In an effort to track down the EtAlCl2 postulated to
be generated, we collected the volatiles from the reaction
and examined them by 1H NMR spectroscopy. Although
peaks at 0.93 (t) and 0.22 (q) ppm, corresponding to the
methyl and methylene protons of the Et group, respec-
tively, could be seen, the spectrum was further compli-
cated by additional resonances in the range 0-2 ppm.
In light of the 1H NMR results, it is difficult to
conclusively determine the presence or absence of the
desired aluminum alkyl halide. That EtAlCl2 is pro-
duced and then forms other products as the result of
exchange cannot be ruled out.
the central aluminum. It appears that monoethyl 6
undergoes two separate reactions with AlCl3 to form 7:
first, a ligand redistribution reaction at the central
aluminum to eliminate an ethyl group, and second,
ligation of a second AlCl3 molecule by a dissociated
phosphine arm. The ligand redistribution behavior of
mixed alkyl-halo aluminum compounds is well-docu-
mented and is most often called upon to explain a
deficiency of alkyl groups in organoaluminum com-
pounds.61 For example, redistribution of Et2AlCl to
generate EtAlCl2 and Et3Al has been suggested to occur
through the formation of the unsymmetrical dimer
Et2Al(µ-Cl)(µ-Et)AlEtCl. Such a process accounts for
the shortage of ethyl groups (relative to that expected)
for a number of organoaluminum compounds found
when Et2AlCl is added to ligand systems as varied as
crown ethers,12 macrocyclic and open-chain multiden-
tate amines,33,34 and aluminum-phosphorus dimers.16,20
A similar explanation has been invoked to account for
analogous results using Me2AlCl.21 As well, asymmetric
bridge cleavage has been implicated in the formation
of cationic species of crown ethers.12
It is possible that a similar type of process operates
in our system. As shown in Scheme 2, exposure of
monoethyl 6 to AlCl3 could result in the equilibrium
formation of a mixed ethyl-chloro-bridged species. For
this intermediate to form, dissociation of one phosphine
arm alleviates steric crowding that would otherwise
occur in a six-coordinate species. The dangling Lewis
basic phosphine then coordinates to a second equivalent
of AlCl3, effectively negating any further chance for
aluminum coordination. The transient alkyl-halo-
bridged dimer then eliminates EtAlCl2 to yield 7 (Scheme
2).
The analogous reaction of the methyl derivative
Al(Me)Cl[N(SiMe2CH2PPri ) ] (5) with AlCl3 provides a
2 2
mixture of products, among them a small amount of 7
(as observed by 1H NMR spectroscopy). The smaller
-CH3 group likely experiences a more facile exchange
and quickly forms other products as well. No attempt
to further characterize the products of this addition was
made.
Con clu sion s
Bis(hydrocarbyl)aluminum derivatives of the ancil-
lary, potentially tridentate ligand -N(SiMe2CH2PPri )
2 2
were synthesized via metathesis of the starting dichlo-
ride AlCl2[N(SiMe2CH2PPri ) ] with various alkylating
2 2
reagents. The solution structures of these compounds
are postulated to be highly fluxional on the basis of their
variable-temperature NMR spectroscopic properties. In
all cases, these compounds resisted attempts at chemi-
cal transformation. The aluminum alkyl halides could
be synthesized, upon addition of RAlCl2 (R ) Me, Et)
to the lithium salt LiN(SiMe2CH2PPri ) , but attempts
2 2
to abstract a chloride resulted in the formation of
AlCl2[N(SiMe2CH2PPri ) ]‚AlCl3, a compound retaining
2 2
two four-coordinate tetrahedral aluminum centers rather
than a cationic structure. It is postulated that an
exchange process is responsible for the lack of an alkyl
group in the final product. It appears that, even in the
presence of a tridentate anionic ligand, the aluminum
center will still tend to reside in a four-coordinate
environment if at all possible.
Some support for this mechanism comes from the
following observations. (i) The number of equivalents
of AlCl3 required for this reaction to ensue is 2. The
addition of 6 to a toluene slurry of 1 equiv of AlCl3 does
not result in the formation of 7. (ii) The trace amount
Exp er im en ta l Section
P r oced u r es. Unless otherwise stated, all manipulations
were performed under an atmosphere of dry, oxygen-free
dinitrogen or argon by means of standard Schlenk or glovebox
techniques. The glovebox used was a Vacuum Atmospheres
HE-553-2 model equipped with an MO-40-2H purification
system and a -40 °C freezer. 1H and 31P{1H} NMR spectros-
copy was performed on a Bruker AMX-500 instrument operat-
ing at 500.1 and 202.5 MHz, respectively. 27Al NMR spec-
troscopy was performed on a Varian XL-300 instrument
operating at 75.48 MHz. 27Al MAS and 31P MAS NMR
of AlCl2[N(SiMe2CH2PPri ) ] (1) present in starting
2 2
samples of AlEtCl[N(SiMe2CH2PPri ) ] (6) reacts in a
2 2
manner similar to that for 6, as no AlCl2[N(SiMe2CH2-
PPri ) ] can be found after the reaction with AlCl3.
2 2
(61) Ziegler, K. Organometallic Chemistry; Reinhold: New York,
1960.

4840 Organometallics, Vol. 15, No. 22, 1996
Fryzuk et al.
spectroscopy was performed on a Bruker MSL 400 instrument.
1H NMR spectra were referenced to internal C6D5H (7.15 ppm)
or C6D5CD2H (2.09 ppm). 31P{1H} NMR spectra were refer-
enced to external P(OMe)3 (141.0 ppm with respect to 85%
H3PO4 at 0.0 ppm). 27Al spectra were referenced to external
AlCl3 in D2O (0.0 ppm). Mass spectral studies were carried
out on a Kratos MS 50 using an EI source. Microanalyses (C,
H, N) were performed by Mr. P. Borda of this department.
with Celite to remove LiCl. The solvent was then removed in
vacuo to yield 2 as a clear colorless oil (140 mg; 58% yield). 1H
NMR (C6D6): δ 1.63 (d of sept, 4H, CHMe2, J H-H ) 7.5 Hz,
3
3
2J H-P ) 5.0 Hz), 0.99 and 0.97 (dd, 24H, CHMeMe′, J H-H
)
7.5 Hz, 3J H-P ) 10.0 Hz), 0.60 (d, 4H, CH2P, 2J H-P ) 10.0 Hz),
3
0.44 (s, 12H, SiMe2), -0.24 (t, 6H, AlMe2, J H-P ) 2.4 Hz).
31P{1H} NMR (C6D6): δ -4.9. 27Al NMR (C6D6): δ 70 (4.3 kHz
peak width at half-height).
Ma ter ia ls. LiN(SiMe2CH2PPri )2 was prepared by a pub-
2
Al(CH2CH3)2[N(SiMe2CH2P P r i2)2] (3). To a toluene solu-
lished procedure.37 MeLi (1.4 M solution in ether) and Me2AlCl
(1.0 M solution in hexanes) were purchased from Aldrich and
used as received. AlCl3 was purchased from Aldrich and
sublimed prior to use. MeAlCl2 (1.0 M solution in hexanes)
and EtAlCl2 (1.0 M solution in hexanes) were purchased from
Aldrich, crystallized, and used in the solid form. EtLi,
Mg(CH2Ph)2‚2THF and MgMe2‚dioxane were prepared accord-
ing to published procedures.62,63
tion (5 mL) of AlCl2[N(SiMe2CH2PPri )2] (200 mg; 0.408 mmol)
2
was added EtLi (30 mg; 0.83 mmol) in toluene (5 mL). The
reaction mixture was stirred overnight and then filtered
through a frit lined with Celite to remove LiCl, followed by
solvent removal in vacuo to yield a clear, colorless oil (144 mg;
74% yield). Purification by recrystallization was not possible
either due to the compound’s extreme solubility in hydrocarbon
solvents or because it was low melting; as a result, charac-
terization by mass spectrometry or elemental analysis was not
possible. 1H NMR (C6D6): δ 1.64 (d of sept, 4H, CHMe2, 3J H-H
Hexanes, toluene, THF, and Et2O were refluxed over CaH2
prior to a final distillation from either sodium metal or sodium
benzophenone ketyl under an Ar atmosphere. Deuterated
solvents were dried by distillation from sodium benzophenone
ketyl; oxygen was removed by three freeze-pump-thaw
cycles.
2
3
) 6.9 Hz, J H-P ) 3.5 Hz), 1.42 (t, 6H, AlCH2Me, J H-H ) 7.7
3
3
Hz), 0.99 and 0.98 (dd, 24H, CHMeMe′, J H-H ) 6.9 Hz, J H-P
2
) 6.3 Hz), 0.60 (d, 4H, CH2P, J H-P ) 7.7 Hz), 0.43 (s, 12H,
SiMe2), 0.34 (t of q, 4H, AlCH2Me, 3J H-H ) 8.4 Hz, 3J H-P ) 2.5
Hz). 31P{1H} NMR (C6D6): δ -4.2. 27Al NMR (C6D6): δ 140
(5.8 kHz peak width at half height).
AlCl2[N(SiMe2CH2P P r i2)2] (1). To a slurry of AlCl3 (650
mg; 4.88 mmol) in toluene (10 mL) was added a toluene
solution (10 mL) of LiN(SiMe2CH2PPri )2 (1.78 g; 4.47 mmol).
Al(CH2P h )2[N(SiMe2CH2P P r i )2] (4). A solution of Mg(CH2-
2
2
The mixture was then stirred for 12 h. The reaction mixture
was then passed through a frit lined with Celite to remove
LiCl. The solvent was then removed in vacuo to yield a white
waxy solid. The residue was taken up in a minimum amount
of toluene (approx 4 mL). Slow evaporation of the solvent
afforded large colorless needles (1.84 g; 84% yield). 1H NMR
Ph)2‚2THF (150 mg; 0.431 mmol) in THF (10 mL) was added
to a THF solution (15 mL) of AlCl2[N(SiMe2CH2PPri )2] (198
2
mg; 0.404 mmol) at -60 °C. The reaction mixture was warmed
to room temperature and stirred overnight, after which the
solvent was removed in vacuo. Toluene was then added to
the reaction vessel and the mixture filtered through a frit lined
with Celite to remove LiCl. The solvent was then reduced in
volume to approx 5 mL. Slow evaporation of the solvent
resulted in the formation of pale yellow needles (197 mg; 81%
(C6D6): δ 1.91 (d of sept, 4H, CHMe2, 3J H-H ) 7.0 Hz, 2J H-P
)
1.0 Hz), 1.21 and 1.11 (dd, 24H, CHMe2, 3J H-H ) 7.0 Hz, 3J H-P
2
) 7.0 Hz), 0.65 (d, 4H, CH2P, J H-P ) 9.0 Hz), 0.27 (s, 12H,
SiMe2). 31P{1H} NMR (C6D6): δ -10.5 (400 Hz peak width at
half-height). 27Al NMR (C6D6): δ 65 (900 Hz peak width at
half-height). MS: m/e 490 (M+). Anal. Calcd for
3
yield). 1H NMR (C6D6): δ 7.28 (d, 4H, o-Ph, J H-H ) 7.0 Hz),
3
3
7.20 (t, 2H, p-Ph, J H-H ) 3.5 Hz), 6.96 (t, 4H, m-Ph, J H-H
)
7.0 Hz), 3.50 (br s, 4H, AlCH2C6H5), 1.52 (d of sept, 4H, CHMe2,
2
3J H-H ) 7.0 Hz, J H-P ) 3.8 Hz), 0.89 and 0.85 (dd, 24H,
C
18H44Cl2NP2Si2‚0.34LiCl: C, 42.81; H, 8.78; N, 2.77. Found:
3
3
C, 42.84; H, 8.34; N, 2.48. Calcd after an additional recrys-
tallization for C18H44Cl2NP2Si2: C, 44.07; H, 9.04; N, 2.86.
Found: C, 44.08; H, 9.02; N, 2.66.
CHMeMe′, J H-H ) 7.0 Hz, J H-P ) 5.6), 0.39 (d, 4H, CH2P,
2J H-P ) 7.8 Hz), 0.33 (s, 12H, SiMe2). 31P{1H} NMR (C6D6): δ
-3.6. 27Al NMR (C6D6): δ 54 (5.6 kHz peak width at half-
Al(CH3)2[N(SiMe2CH2P P r i2)2] (2). Meth od 1. To a tolu-
height). MS: m/e 510 (M+
- Bz). Anal. Calcd for
ene solution (5 mL) of AlCl2[N(SiMe2CH2PPri )2] (500 mg; 1.02
.
2
C
32H58AlNP2Si2 0.39MgCl2: C, 60.14; H, 9.15; N, 2.19.
mmol) was added MeLi (1.50 mL of a 1.4 M Et2O solution,
diluted with 5 mL of ether; 2.08 mmol) dropwise. The reaction
mixture was then stirred for 3 h, after which time it was
filtered through a frit lined with Celite to remove LiCl. The
solvent was then removed in vacuo to yield 2 as a clear
colorless oil (398 mg; 87% yield). Purification by recrystalli-
zation was not possible either due to the compound’s extreme
solubility in hydrocarbon solvents or because it was low
melting; as a result, characterization by either mass spec-
trometry or elemental analysis was not possible.
Found: C, 60.11; H, 9.56; N, 1.94.
Al(CH3)Cl[N(SiMe2CH2P P r i2)2] (5). To a hexanes solution
(5 mL) of LiN(SiMe2CH2PPri )2 (204 mg; 0.511 mmol) was
2
added MeAlCl2 (69 mg; 0.61 mmol) in hexanes (5 mL) drop-
wise. The reaction mixture was then stirred overnight, after
which time it was filtered through a frit lined with Celite to
remove LiCl. The solvent was then removed in vacuo to yield
a clear colorless oil (144 mg; 59% yield). Purification by
crystallization was hampered by contamination of small
amounts of 1 and 2. 1H NMR (C6D6): δ 1.71 and 1.62 (d of
Meth od 2. To Me2AlCl (0.60 mL of a 1.0 M hexanes
solution, diluted with 10 mL of hexanes; 0.60 mmol) was added
3
2
sept, 4H, CHMe2, J H-H ) 6.6 Hz, J H-P ) 4.8 Hz), 1.05, 1.02,
3
3
0.95, and 0.92 (dd, 24H, CHMeMe′, J H-H ) 6.6 Hz, J H-P
)
LiN(SiMe2CH2PPri )2 (200 mg; 0.502 mmol) in 10 mL of
2
2
10.0 Hz), 0.68 and 0.61 (d, 4H, CH2P, J H-P ) 12.0 Hz), 0.48
and 0.40 (s, 12H, SiMe2), -0.05 (t, 3H, AlMe2, 3J H-P ) 2.8 Hz).
31P{1H} NMR (C6D6)SPCLN δ -6.6.
toluene. The reaction mixture was stirred overnight, after
which time it was filtered through a frit lined with Celite to
remove LiCl. The solvent was then removed in vacuo to yield
2 as a clear colorless oil (174 mg; 72% yield).
Al(CH2CH3)Cl[N(SiMe2CH2P P r i2)2] (6). To a hexanes
solution (5 mL) of LiN(SiMe2CH2PPri )2 (198 mg; 0.495 mmol)
2
Meth od 3. AlCl2[N(SiMe2CH2PPri )2] (250 mg; 0.51 mmol)
2
was added EtAlCl2 (70 mg; 0.55 mmol) in hexanes (5 mL)
dropwise. The reaction mixture was then stirred overnight,
after which time it was filtered through a frit lined with Celite
to remove LiCl. The solvent was then removed in vacuo to
yield a clear colorless oil (208 mg; 87% yield). Purification by
recrystallization was not possible, due to the persistence of
small amounts of 1 (<5%) in the reaction mixture. 1H NMR
was dissolved in 10 mL of THF. The solution was then cooled
to -60 °C and Me2Mg‚dioxane (3.7 mL of a 0.14 M THF/Et2O
solution; 0.52 mmol) added. The reaction mixture was then
warmed to room temperature and stirred overnight. The THF/
Et2O was removed under vacuum and toluene added to the
solution, after which time it was filtered through a frit lined
3
(C6D6): δ 1.70 and 1.64 (d of sept, 4H, CHMe2, J H-H ) 7.5
(62) Brookhart, M.; Green, M. L. H. J . Organomet. Chem. 1983, 250,
395.
(63) Dryden, N. H.; Legzdins, P.; Trotter, J .; Yee, V. C. Organo-
metallics 1991, 10, 2857.
2
3
Hz, J H-P ) 3.4 Hz), 1.41 (t, 3H, AlCH2Me, J H-H ) 8.7 Hz),
1.05, 1.02, 0.96, and 0.94 (dd, 24H, CHMeMe′, 3J H-H ) 7.5 Hz,
3J H-P ) 7.3 Hz), 0.67 and 0.65 (d, 4H, CH2P, J H-P ) 8.6 Hz),
2

Four- and Five-Coordinate Organoaluminum Complexes
Organometallics, Vol. 15, No. 22, 1996 4841
0.48 and 0.40 (s, 12H, SiMe2), 0.46 (t of q, 4H, AlCH2Me, 3J H-H
The structures were solved by direct methods. The struc-
ture analysis of 4 was initiated in the centrosymmetric space
group P1h on the basis of the E statistics. This choice was
confirmed by subsequent calculations. The isopropyl carbon
atom C(5) in 1 was modeled as disordered over two sites, C(5A)
and C(5B). The occupancy factors of the disordered carbon
atoms were adjusted as the refinement progressed to give
approximately equal thermal parameters. All non-hydrogen
atoms were refined with anisotropic thermal parameters.
Hydrogen atoms were fixed in calculated positions (C-H )
0.99 Å for 1, 0.98 Å for 4 and 7; BH ) 1.2Bbonded atom). Secondary
extinction corrections were applied for 1 and 7, the final values
of the extinction coefficients being [1.9(8)] × 10-7 and [3.75(13)]
× 10-6, respectively. Neutral atom scattering factors for all
atoms and anomalous dispersion corrections for the non-
hydrogen atoms were taken from ref 65. Crystals of 1 were
of poor quality, resulting in relatively high residuals and large
standard deviations for the derived geometric parameters. The
structure analysis of 1 is, however, sufficient to establish the
identity and geometry of this complex. Selected bond angles
and bond lengths appear in Tables 2 and 3, respectively.
Atomic parameters, anisotropic thermal parameters, bond
lengths, bond angles, torsion angles, intermolecular contacts,
and least-squares planes are included as Supporting Informa-
tion.
3
) 8.0 Hz, J H-P ) 1.6 Hz). 31P{1H} NMR (C6D6): δ -2.0.
AlCl2[N(SiMe2CH2P P r i2)2]‚AlCl3 (7). Meth od 1. To a
slurry of AlCl3 (88 mg; 0.66 mmol) in toluene (5 mL) was added
a 5 mL toluene solution of Al(Et)Cl[N(SiMe2CH2PPri )2] (150
2
mg; 0.310 mmol) dropwise. The reaction mixture turned
slightly amber and was then stirred overnight, after which
time it was filtered through a frit lined with Celite to remove
LiCl. The solvent was then removed in vacuo and the residue
taken up in a minimum amount of toluene (approx 5 mL). Slow
evaporation of the solvent resulted in the formation of colorless
plates (157 mg; 81% yield).
Met h od 2. To a slurry of AlCl3 (500 mg; 3.75 mmol) in
toluene (10 mL) was added a 10 mL toluene solution of LiN-
(SiMe2CH2PPri )2 (498 mg; 1.25 mmol) dropwise. The reaction
2
mixture was then stirred overnight, after which time it was
filtered through a frit lined with Celite to remove LiCl. The
solvent was then removed in vacuo and the residue taken up
in a minimum amount of toluene (approx 5 mL). Slow
evaporation of the solvent resulted in the formation of colorless
plates (615 mg; 78% yield). 1H NMR (C6D6): δ 2.11 and 1.48
3
2
(d of sept, 4H, CHMe2, J H-H ) 7.3 Hz, J H-P ) 2.0 Hz), 1.56
2
(br d, 2H, CH2P, J H-P ) 14.1 Hz), 1.09, 1.08, 0.86, and 0.81
(dd, 24H, CHMeMe′, 3J H-H ) 7.3 Hz, 3J H-P ) 7.5 Hz), 0.69 and
2
0.24 (s, 12H, SiMe2), 0.26 (d, 2H, CH2P, J H-P ) 13.5 Hz).
31P{1H} NMR (C6D6): δ 0.0 (800 Hz peak width at half-height)
and -11.8 (500 Hz peak width at half-height). MS: m/e 490
(M+ - AlCl3). Anal. Calcd for C14H36Al2Cl5NP2Si2: C, 34.65;
H, 7.11; N, 2.25. Found: C, 34.32; H, 7.26; N, 2.07.
Ack n ow led gm en t. Financial support was gener-
ously provided by the NSERC of Canada in the form of
grants to M.D.F. and a postgraduate scholarship to
G.R.G.
X-r a y Cr ysta llogr a p h ic An a lyses of AlCl2[N(SiMe2CH2-
P P r i2)2] (1), Al(CH2C6H5)2[N(SiMe2CH2P P r i2)2] (4), a n d
AlCl2[N(SiMe2CH2P P r i2)2]‚AlCl3 (7). Crystallographic data
appear in Table 1. The final unit-cell parameters were
obtained by least squares using the setting angles for 25
reflections with 2θ ) 23.2-31.0° for 1, 9.9-18.3° for 4, and
45.9-57.9° for 7. The intensities of 3 standard reflections,
measured every 200 reflections throughout the data collections,
decayed linearly by 6.3% for 4 and by 7.4% for 7 and showed
only small random fluctuations for 1. The data were proc-
essed64 and corrected for Lorentz and polarization effects,
decay (where appropriate), and absorption (empirical, based
on azimuthal scans for 4 and 7).
Su p p or tin g In for m a tion Ava ila ble: Complete tables of
bond lengths and bond angles, final atomic coordinates,
hydrogen atom parameters, anisotropic thermal parameters,
torsion angles, intermolecular contacts, and least-squares
planes for 1, 4, and 7 (59 pages). Ordering information is given
on any masthead page.
OM9604583
(65) (a) International Tables for X-Ray Crystallography; Kynoch
Press: Birmingham, U.K., 1974; Vol. IV, pp 99-102 (present distribu-
tor Kluwer Academic: Boston, MA). (b) International Tables for
Crystallography; Kluwer Academic: Boston, MA, 1992; Vol. C, pp 200-
206.
(64) teXsan: Crystal Structure Analysis Package; Molecular Struc-
ture Corp., The Woodlands, TX, 1985 and 1992.