Formation of the unprecedented trilithio-capped heteroadamantanyl iminoalane anion [(HAI)4(NPh)6{Li(OEt2)}3]-: An open cage derived from a rhombododecahedron

Article abstract of DOI:10.1002/1521-3773(20001103)39:21<3879::AID-ANIE3879>3.0.CO;2-V

An Al/N adamantanyl frame with three of its Al₃N₃ faces capped by Li (see picture; E = NPh) forms the core of the title anion. Formation of the charge-separated species, and the unique arrangement adopted by the cage atoms is rationalized through analysis of its solid-state structure and by ab initio calculations.

Full text of DOI:10.1002/1521-3773(20001103)39:21<3879::AID-ANIE3879>3.0.CO;2-V

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NC6H11, NtBu, NC6H3=OMe)2, or PC6H11;[5] M ˆ GetBu, E ˆ
AsSiiPr3;[6] M ˆ SiR, E ˆ NR',[7] where R ˆ H, R' ˆ Me3Si;
R ˆ Me, tBu or Ph, R' ˆ Me3Si; R ˆ Me or Ph, R' ˆ tBu; R ˆ
Me or tBu, R' ˆ Me; M ˆ SiEt, E ˆ PSiiPr3), which all adopt
structures containing very similar 14-membered rhombodo-
decahedral cage cores =Lewis base complexants within the
compounds are ignored for simplicity). In contrast, we now
report the synthesis of the novel, charge-separated complex 1,
which though isovalent with the above compounds adopts a
unique molecular geometry.
[7] a) H. M. Sklenicka, R. P. Hsung, L.-L. Wei, M. J. McLaughlin, A. I.
Gerasyuto, S. J. Degen, J. A. Mulder, Organic Lett. 2000, 2, 1161;
b) R. P. Hsung, L.-L. Wei, H. M. Sklenicka, H. C. Shen, M. J.
McLaughlin, L. R. Zehnder in Advances in Cycloaddition =Ed.: M.
Harmata), JAI, Greenwich, 2000, in press.
[8] R. P. Hsung, L.-L. Wei, H. H. Sklenicka, C. J. Douglas, M. J.
McLaughlin, J. A. Mulder, L. J. Yao, Organic Lett. 1999, 1, 509.
[9] a) R. P. Hsung, H. C. Shen, C. J. Douglas, C. D. Morgan, S. J. Degen,
L. J. Yao, J. Org. Chem. 1999, 64, 690; b) L. R. Zehnder, J. W. Dahl,
R. P. Hsung, Tetrahedron Lett. 2000, 1901.
[10] C. J. Douglas, H. M. Sklenicka, H. C. Shen, G. M. Golding, D. S.
Mathias, S. J. Degen, C. D. Morgan, R. A. Shih, K. L. Mueller, L. H.
Seurer, E. W. Johnson, R. P. Hsung, Tetrahedron 1999, 55, 13683.
[11] M. Jonassohn, O. Sterner, H. Anke, Tetrahedron 1996, 52, 1473.
[12] a) K. C. Nicolaou, W. S. Li, J. Chem. Soc. Chem. Commun. 1985, 421;
For related approaches, see b) E. J. Corey, P. D. S. Jardine, J. C.
Rohloff, J. Am. Chem. Soc. 1988, 110, 3672; c) F. E. Ziegler, B. H.
Jaynes, M. T. Saindane, J. Am. Chem. Soc. 1987, 109, 8115; d) P. R.
Jenkins, K. A. Menear, P. Barraclough, M. S. Nobbs, J. Chem. Soc.
Chem. Commun. 1984, 1423.
‡
[Li=OEt2)3] [=HAl)4=NPh)6{Li=OEt2)}3]À
1
Complex 1 was originally prepared from the equimolar
reaction between the primary amidolithium PhN=H)Li and
the alane adduct H3Al ´ N=Me)C5H8 =where N=Me)C5H8 ˆ 1-
methyl-1,2,3,6-tetrahydropyridine)[8] in diethyl ether solution.
However, measurement of H2 evolution from the reaction has
established that the ideal stoichiometry for the preparation of
1 is that shown in Equation =1). Crystallographic analysis of 1
[13] B. Delpech, D. Calvo, R. Lett, Tetrahedron Lett. 1996, 1015.
[14] All new compounds are characterized by 1H NMR, 13C NMR, and FT-
IR spectroscopy, as well as mass spectrometry.
[15] a) L. E. Overman, M. H. Rabinowitz, J. Org. Chem. 1993, 58, 3235;
b) L. E. Overman, M. H. Rabinowitz, P. A. Renhowe, J. Am. Chem.
Soc. 1995, 117, 2657.
[16] For leading references on electrocyclic ring closures involving 1-oxa-
or 1-azatrienes, see a) T. Kametani, M. Kajiwara, K. Fukumoto,
Tetrahedron 1974, 30, 1053; b) K. Shishido, M. Ito, S.-I. Shimada, K.
Fukumoto, T. Kametani, Chem. Lett. 1984, 1943; c) D. F. Maynard,
W. H. Okamura, J. Org. Chem 1995, 60, 1763; d) W. H. Okamura,
A. R. de Lera, W. Reischl, J. Am. Chem. Soc. 1988, 110, 4462.
Et2
O
À!
6PhN=H)Li ‡ 4H3Al ´ N=Me)C5H8
1 ‡ 2LiH ‡ 6H
=1)
2
À4 MeNC5H8
revealed a remarkable structure consisting of a cage anion
=1a; Figure 1) and a solvent-separated countercation, withno
discernible close contacts between the two.[9]
Solution NMR data =27Al and low-temperature 7Li) appear
to be consistent withthe solid-state structure of 1, indicating
the presence of two distinct signals =apical/equatorial Al, and
cation/anion Li). However, a full understanding of the
Formation of the Unprecedented Trilithio-
Capped Heteroadamantanyl Iminoalane Anion
[ꢀHAl)4ꢀNPh)6{LiꢀOEt2)}3]À: An Open Cage
Derived from a Rhombododecahedron**
KennethW. Henderson,* Alan R. Kennedy,
Arlene E. McKeown, and Robert E. Mulvey
There is a great deal of current interest in the preparation of
organometallic compounds containing combinations of
p-block elements due to their uses in the electronics
industry,[1] in catalysis,[2] and in the search for new types of p
bonding.[3] As a result, a wide variety of heterodimetallic
species that adopt polyhedral cage frameworks have been
characterized, and structural patterns within their mixed-
metal cores are now emerging. A notable example exists for
the isovalent series of compounds with general formulas
M4E6Li4 =where M ˆ AlH, E ˆ AsSiiPr3; M ˆ AlMe or Sn,
E ˆ PC6H11)[4] or M2E6Li6 =where M ˆ Sb, E ˆ NCH2CH2Ph,
Figure 1. Molecular structure of 1a withhydrogen atoms omitted for
clarity. Selected bond lengths [Š] and angles [8]: Al1-N1 1.882=6), Al1-N3
1.901=7), Al1-N4 1.895=6), Al2-N1 1.914=6), Al2-N2 1.873=7), Al2-N5
1.881=7), Al3-N2 1.860=7), Al3-N3 1.918=6), Al3-N6 1.890=7), Al4-N4
1.924=6), Al4-N5 1.881=7), Al4-N6 1.868=7), Li1-O1 1.929=14), Li2-O2
1.950=14), Li3-O3 1.930=13), Li1-N1 2.205=15), Li1-N4 2.227=15), Li1-N5
2.106=14), Li2-N1 2.218=15), Li2-N2 2.059=14), Li2-N3 2.227=15), Li3-N3
2.225=14), Li3-N4 2.221=14), Li3-N6 2.069=13); N-Li-N 84.97 =mean),
N-Al1-N 104.17 =mean), N-Al2-N 105.40 =mean), N-Al3-N 105.40 =mean),
N-Al4-N 105.73 =mean).
[*] Dr. K. W. Henderson, Dr. A. R. Kennedy, A. E. McKeown,
Prof. R. E. Mulvey
Department of Pure and Applied Chemistry
University of Strathclyde
Glasgow, G1 1XL =UK)
Fax : =‡44)141-552-0876
E-mail: k.w.henderson@strath.ac.uk
[**] We thank the Royal Society for a University Research Fellowship
=K.W.H.) and BP Amoco for funding =A.E.M.).
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complex dynamic processes occurring in solution has yet to be
determined.
The fascinating feature of the ªmissingº vertex of the cage
can be explained in terms of the cavity size of the Al3N3 rings.
Analysis of the bond lengths within 1a indicate only small
where one rectangular plane of metals is composed of a
dimetallic M2Li2 ring. In contrast, 1a breaks withtihs
structural pattern by adopting a unique =HAl)4=NPh)6 hetero-
adamantanyl tetraanionic core, which has three of the four
six-membered Al3N3 rings capped by m3-Li centers. In theory,
placement of a fourthLi atom to make a closed cage structure
would result in two interpenetrating tetrahedra of metals, that
is an isomer of the related heterodimetallic complexes
=Scheme 1).
Ab initio molecular orbital calculations =HF/6-31G*) were
carried out for two isomers of the model complex
[=HAl)4=NH)6Li4]: 1) bisecting planes of metals =I) and 2)
interpenetrating tetrahedra of metals =II) =Scheme 2).[11]
À
differences for the Al N distances =range from 1.860=7) to
1.924=6) Š; mean 1.890 Š). These are consistent with the
distance of 1.888=5) Š found in bothof the related Li/Al
amide dimers 2 and 3.[10] Significantly, the Li N distances
À
[{Me2AlN=Ph)Li=thf)2}2]
2
[{iBu2AlN=Ph)Li=thf)}2]
3
show much greater variance, ranging from 2.059=14) to
2.227=15) Š, and the mean distance of 2.173 Š is much longer
than those found in 2 and 3 =2.023=12) and 1.980=17) Š,
respectively). EachLi center in 1a asymmetrically caps a
Al3N3 ring, with one relatively short contact to the nitrogen
atom on the open face of the cage =mean 2.078 Š), and two
long contacts, to the remaining nitrogen atoms =mean
2.220 Š). The overall effect is that the uncapped Al3N3 face
of the cage is more open =less puckered) than the three Li-
capped Al3N3 faces. Further evidence for this distortion is the
differences in the transannular N ´´´ N distances, which are
2.94 Š =mean) for the capped faces and 3.18 Š =mean) for the
open face. The widening of the fourth Al3N3 ring results in a
larger cavity, which can no longer accommodate =or trap) a Li
center, leading to the preferential formation of a charge-
separated complex.
Further examination of 1a reveals a surprising difference in
the arrangement of the atoms within the cage skeleton
compared to the previously mentioned isovalent 14-mem-
bered cage compounds.[4±7] These complexes, with the general
core formula M4E6Li4 =M ˆ Al, E ˆ As or P; M ˆ Sn, E ˆ P),
have almost identical frameworks. They consist of a pair of
dimeric M2E2 rings connected through two additional bridging
E ligands, leading to a tetraanionic polycycle =Scheme 1).
Another view is to consider the structures composed of two
orthogonal rectangular planes of metals, M4/Li4. This view can
be extended to include the compounds with the general core
formula M2E6Li6 =M ˆ Sb or Si, E ˆ N and M ˆ Ge, E ˆ As),
Scheme 2. Generalized view of the calculated molecules.
Interestingly, II was found to be more stable than I by
9.16 kcalmolÀ1, in agreement withteh ehteroadamantanyl
core found for 1a. This preference is due to an alleviation of
metal ± metal repulsions in the heteroadamantanyl isomer. In
I there are two short Al ´´´ Al and Li ´´´ Li distances of 2.656
and 2.345 Š =mean), respectively =transannular repulsions in
the M2N2 rings); however, in II the metals are separated by
3.357 and 3.889 Š =mean), respectively. Other distances in I
À
and II are similar =Li N 2.063 and 2.074 Š =mean), respec-
À
tively, and Al N 1.920 and 1.909 Š =mean), respectively).
Calculations on the related P-bridged model complexes
[=HAl)4=PH)6Li4] =III and IV) indicate that all the metal ±
metal separations are >3 Š for bothisomers as a consequence
of the larger bridging anion. Moreover, and consistent with
experimental data,[4b] the bridged dimers isomer III was found
to be favored over the heteroadamantanyl isomer IV by
8.67 kcalmolÀ1.
Therefore, the formation of the heteroadamantanyl core in
1a is driven principally by minimizing the metal ± metal
repulsions, while maintaining strong metal ± N interactions.
Furthermore, the factors governing the generation of the
charge-separated species are complex and include the aro-
matic nature of the phenyl groups attached to the imido
nitrogen atoms, the effect of solvation by Et2O, and the cavity
size of the Al3N3 rings.
Experimental Section
1: nBuLi =10 mmol, 5.9 mL of a 1.7m solution in hexanes) was added to a
Schlenk tube by syringe, and all solvent was removed in vacuo. The
resulting yellow oil was dissolved in Et2O =10 mL), the solution was cooled
to À788C, and aniline =10 mmol, 0.91 mL) was then added dropwise by
syringe. This solution was stirred at À788C for 30 min, then allowed to
warm to ambient temperature and stirred for a further 2 h. After dilution
withEt 2O =30 mL), the solution was recooled to À788C. H3Al ´ N=Me)C5H8
=10 mmol, 1.27 g; where N=Me)C5H8 ˆ 1-methyl-1,2,3,6-tetrahydropyri-
dine[8]) was added to the solution through a solids addition tube, and the
Scheme 1. Simplified view of the alternative cores in the dimetallic cages,
1) bridged dimers and 2) heteroadamantanyl.
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reaction mixture was stirred for 1 hbefore it was allowed to warm to
ambient temperature. After the mixture had been stirred for a further 24 h,
a cloudy yellow/brown solution was produced. The mixture was filtered
through Celite, cooled to À208C, and left to stand for 12 h, resulting in the
precipitation of small, colorless crystals of 1. Yield 60.5%; m.p. >3008C; IR
Crystallographic Data Centre as supplementary publication no.
CCDC-142922. Copies of the data can be obtained free of charge on
application to CCDC, 12 Union Road, Cambridge CB21EZ, UK =fax:
=‡44)1223-336-033; e-mail: deposit@ccdc.cam.ac.uk).
[10] a) D. A. Atwood, D. Rutherford, Organometallics 1996, 15, 436;
b) D. A. Atwood, D. Rutherford, J. Am. Chem. Soc. 1996, 118, 11535.
[11] Gaussian 94, revision E. 2. No constraints were used in any of the
calculations. M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill,
B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A.
Petersson, J. A. Montgomery, K. Raghavachari, M. A. Al-Laham,
V. G. Zakrzewski, J. V. Ortiz, J. B. Foresman, J. Cioslowski, B. B.
Stefanov, A. Nanayakkara, M. Challacombe, C. Y. Peng, P. Y. Ayala,
W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts,
R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J. P.
Stewart, M. Head-Gordon, C. Gonzalez, J. A. Pople, Gaussian Inc.,
PittsburghPA, 1995.
=Nujol): nĈ 1775 cmÀ1 =Al H); elemental analysis calcd for C60H94Al4Li4-
À
N6O6 =%): C 63.72, H 8.32, N 7.43; found: C 63.45, H 7.55, N 8.70; 1HNMR
=variable-temperature studies showed only one set of resonances =with
broadening) in the range 300 ± 193 K; 400.13 MHz, C6D6, 300 K): d ˆ 7.76
=d, 2H; o-H, Ph), 7.16 =t, 2H; m-H, Ph), 6.74 =t, 1H; p-H, Ph), 5.40 =v br.,
1H; AlH), 2.88 =q, 4H; OCH2), 0.60 =t, 6H; CH3); 13CNMR =100.62 MHz,
C6D6, 300 K): d ˆ 156.70 =i-C; Ph), 129.21 =m-C; Ph), 124.88 =o-C; Ph),
7
117.58 =p-C; Ph), 65.33 =OCH2), 13.66 =CH3); Li NMR =variable-temper-
ature studies showed only a single resonance in the range 300 ± 213 K but
the appearance of a second resonance at 193 K; 155.51 MHz, referenced to
LiCl in D2O, [D8]toluene, 193 K): d ˆ 6.75, d 6.58; 27Al NMR =C6D6, 298 K,
52.12 MHz, referenced to AlCl3 in D2O): d ˆ 131.30, 69.91.
Received: April 25, 2000 [Z15042]
[1] A. C. Jones, Chem. Soc. Rev. 1997, 101.
[2] a) H. Yamomoto in Organometallics in Synthesis =Ed.: M. Schlosser),
Wiley, Chichester, UK, 1994, chap. 7; b) Y. Koide, S. G. Bott, A. R.
Barron, J. Am. Chem. Soc. 1993, 115, 4971.
[3] M. A. Petrie, S. C. Shoner, H. V. R. Dias, P. P. Power, Angew. Chem.
1990, 102, 1061; Angew. Chem. Int. Ed. Engl. 1990, 29, 1033.
[4] a) M. Driess, S. Kuntz, K. Merz, H. Pritzkow, Chem. Eur. J. 1998, 4,
1628; b) R. E. Allan, M. A. Beswick, P. R. Raithby, A. Steiner, D. S.
Wright, J. Chem. Soc. Dalton Trans. 1996, 4153; c) R. E. Allan, M. A.
Beswick, N. L. Cromhout, M. A. Paver, P. R. Raithby, A. Steiner, M.
Trevithick, D. S. Wright, Chem. Commun. 1996, 1501.
[5] a) A. J. Edwards, M. A. Paver, P. R. Raithby, M.-A. Rennie, C. A.
Russell, D. S. Wright, Angew. Chem. 1994, 106, 1334; Angew. Chem.
Int. Ed. Engl. 1994, 33, 1277; b) M. A. Beswick, N. Choi, C. N. Harmer,
A. D. Hopkins, M. McPartlin, M. A. Paver, P. R. Raithby, A. Steiner,
M. Tombul, D. S. Wright, Inorg. Chem. 1998, 37, 2177; c) M. A.
Beswick, J. M. Goodman, C. N. Harmer, A. D. Hopkins, M. A. Paver,
P. R. Raithby, A. E. H. Wheatley, D. S. Wright, Chem. Commun. 1997,
1879.
New Fused Bicyclic Cyclotrigermanes from
Cycloaddition Reactions of Cyclotrigermene**
Norihisa Fukaya, Masaaki Ichinohe, and
Akira Sekiguchi*
The chemistry of three- and four-membered ring systems
consisting of Group 14 elements heavier than carbon is a
subject of considerable interest.[1] The thermal and photo-
chemical conversion of cyclotrigermanes into digermenes and
germylenes is well established and has been used for the
synthesis of a variety of novel germanium compounds.[2]
However, cyclotrigermane derivatives incorporating a bicyclic
system are completely unknown for synthetic reasons.[3, 4]
Most of the cyclotrigermane derivatives were synthesized by
the simple reductive coupling reaction of the corresponding
diorganodihalogermane with the appropriate reducing
agents.[1, 2] Recently, we succeeded in synthesizing a variety
of cyclotrigermene analogues of cyclopropene by reaction of
the cyclotrigermenium ion with nucleophiles.[5] The reactivity
of the cyclotrigermenes is of special interest, since cyclo-
[6] L. Zsolnai, G. Huttner, M. Driess, Angew. Chem. 1993, 105, 1549;
Angew. Chem. Int. Ed. Engl. 1993, 32, 1439.
[7] a) P. Kosse, E. Popowski, M. Veith, V. Huch, Chem. Ber. 1994, 127,
2103; b) D. J. Brauer, H. Bürger, G. R. Liewald, J. Wilke, J. Organo-
met. Chem. 1985, 287, 305; c) D. J. Brauer, H. Bürger, G. R. Liewald, J.
Organomet. Chem. 1986, 308, 119; d) G. Huber, A. Jockisch, H.
Schmidbaur, Z. Naturforsch. B 1999 54, 8; e) M. Veith, A. Spaniol, J.
Pöhlmann, F. Gross, V. Huch, Chem. Ber. 1993, 126, 2625; f) M. Driess,
G. Huttner, N. Knopf, H. Pritzkow, L. Zsolnai, Angew. Chem. 1995,
107, 354; Angew. Chem. Int. Ed. Engl. 1995, 34, 316.
ˆ
addition to the endocyclic Ge Ge bond could provide access
[8] J. L. Atwood, F. R. Bennett, F. M. Elms, C. Jones, C. L. Raston, K. D.
Robinson, J. Am. Chem. Soc. 1991, 113, 8183.
to new bicyclic compounds. We now report the synthesis of the
first bicyclic cyclotrigermane derivatives by the reaction of a
mesityl-substituted cyclotrigermene withisoprene, 2,3-di-
methyl-1,3-butadiene, and phenylacetylene.
[9] Crystal structure data for 1: C60H94Al4Li4N6O6, Mr ˆ 1131.1, colorless
plates, cut to approximately 0.60 Â 0.40 Â 0.20 mm. MoKa graphite-
monochromated radiation =l ˆ 0.71069 Š), Tˆ 123 K; monoclinic,
space group C2/c; a ˆ 22.035=6), b ˆ 12.818=3), c ˆ 46.487=6) Š; b ˆ
After the successful synthesis of tetrakis=tri-tert-butylsilyl)-
cyclotrigermene =tBu3Si)4Ge3 =1a)[6] and tetrakis=tri-tert-bu-
tylgermyl)cyclotrigermene =tBu3Ge)4Ge3 =1b)[6] by reaction
of GeCl2=dioxane) with tBu3SiNa or tBu3GeLi, we presumed
that the cyclotrigermenes should be suitable as precursors of
90.581=15)8; Vˆ 13129=5) Š3, Z ˆ 8, m ˆ 0.121 mmÀ1
,
1calcd
ˆ
1.144 MgmÀ3, 2qmax ˆ 468, 8786 reflections collected, 8509 unique
used =Rm ˆ 0.0650). The structure was solved and refined on F2 using
published programs and techniques =a) A. Altomare, M. C. Burla, M.
Camalli, G. Cascarano, C. Giacovazzo, A. Guagliardi, G. Polidori, J.
Appl. Crystallogr. 1994, 27, 435; b) G. M. Sheldrick, SHELXL-97.
University of Gottingen, Germany, 1997) to convergence at R1 ˆ
0.0917 =for 4592 reflections with I > 2s=I)), wR2 ˆ 0.2271 and S ˆ
1.064 for 777 parameters. Maximum residual electron density
0.505 eŠÀ3. Several factors combined to adversely affect the quality
of the solution. The crystals reacted with the oil used to mount them
and the large c axis gave overlapping reflections. Additionally the
ether groups of the cation were severely disordered over two sites
each. There was also some movement in the phenyl ring bonded to N6.
Crystallographic data =excluding structure factors) for the structure
reported in this paper have been deposited with the Cambridge
[*] Prof. Dr. A. Sekiguchi, Dipl.-Chem. N. Fukaya, Dr. M. Ichinohe
Department of Chemistry, University of Tsukuba
Tsukuba, Ibaraki 305-8571 =Japan)
Fax : =‡81)298-53-4314
E-mail: sekiguch@staff.chem.tsukuba.ac.jp
[**] This work was supported by a Grant-in-Aid for Scientific Research
=Nos. 10304051, 12020209, 12042213) from the Ministry of Education,
Science and Culture of Japan, and TARA =Tsukuba Advanced
ResearchAlliance) Fund.
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