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Stable Cyclic Germanediyls (УCyclogermylenesФ) Synthesis Structure Metal Complexes and Thermolyses.

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CAS Registry numbers:
N, 34727-11-2; C, 344017-98-1; 11, 144041-54-3; 112. 144017-99-2: cis[Pt(NH,),(H,O),lZ+ .2NO;, 52241-26-6; cis-[PtCI(NH,), ,(H,O)]+, 5386142-0.
A. Laoui, J. Kozelka, J. C. Chottard, h o r g . Chem. 1988, 27, 2751 -2753.
A. Eastman, Biochemistry 1983, 22, 3927-3933.
A. Eastman, Biochemistry 1985, 24, 5027-5032.
A. Eastman, M. A. Barry, Biochemistr~.1987, 26, 3303-3307.
[S] A. Eastman, N. Schulte, Biochemistry 1988. 27, 4730-4734.
161 A. M. J. Fichtinger-Schepman, P. H. M. Lohmdn. J. Reedijk, Nucleic
Acids Res. 1982, 10, 5345-5356.
[7] A. M. J. Fichtinger-Schepman. J. L. Van der Veer, J. H. J. Den Hartog,
P. H. M. Lohman, J. Reedijk, Biochemis~ry1985, 24, 707-713.
(81 A. Pullman, C. Zakrzewska, D. Perahia. Int. J. Quanrum Chem. 1979, 16.
191 The modeled species was, in fact, the pentacoordinated intermediate, since
the assumption was made that the structure of the transition state would
not be very different.
[lo] This value was approximated as czs4{d(TGG)}% &254(dT)
2&,,,{d(pG)); EZ5,(dT) and c,,,{d(pG)) were measured on Sigma products, and their analytically determined water content taken into account
as 5850 ~ - ‘ c m - ’and 8160 ~ - ‘ c m - ’ , respectively.
[Ill Y. N. Kukushkin. S. C. Dhara, hdian J. Chem. 1970, 8 , 184-185.
1121 I t is essential to allow the monoaqua products (I, X = H,O) to convert to
monochloro species (I, X = Cl-). otherwise the chelation reactions proceed during HPLC analysis, leading to smearing of the peaks. The minimum time necessary at 293 K is 1.75 min. Longer incubations should be
avoided, since the chelation reactions are not sufficiently inhibited at this
[I31 K. Inagaki, Y Kidani, Inorg. Chim. Arta 1985, 106, 187-191.
1141 J. A. McCammon, S. C. Harvey, Dynamics ofproteins and nucleic acrds,
Cambridge University Press, Cambridge, 1987, p. 48.
Scheme 1. a) [(CH,),Si],NLi; -[(CH,),Si],NH,
L = 1,4-dioxane.
-LiH; THF, 2h, 60°C.
Stable Cyclic Germanediyls (“Cyclogermylenes”):
Synthesis, Structure, Metal Complexes,
and Thermolyses**
By Wolfgang A . Herrmann,* Michael Denk, Joachim Behm,
Wolfgang Scherer, Franz-Robert Klingan, Hans Bock,
Bahman Solouki, and Matthias Wagner
Substituted ethylenediamine 2 a and its derivatives form
volatile, spirocyclic titanium amides, which precipitate from
the gas phase (produced thermally or plasma-induced) as
titanium carbonitrides.“] We discovered that this type of
ligand is generally suited for the stabilization of main group
and subgroup elements with unusual valencies and report
here on new applications in the chemistry of germanium.
The cyclic germanium(1v) diamide 3aIZ1was formed in
almost quantitative yields from GeCl, ( l a ) and diamine 2 a
in the presence of triethylamine. Reductive dehalogenation
of 3a then provided the new germanediyl (“germylene”) 3 b
(Scheme l).13]In another approach to 3 b the dilithium salt
2 b was allowed to react with germanium dichloride. 1,4dioxane (1 b). Surprisingly, the CC-unsaturated germanediyl
3 c obtained by a formal dehydrogenation was isolated as a
side product (Scheme 1). Compound 3 c can be prepared
[*] Prof. Dr. W A. Herrmann, Dr. M. Denk. Dr. J. Behm, W. Scherer,
F.-R. Klingan
Anorganisch-chemisches Institut der Technischen Universitat Miinchen
Lichtenbergstrasse 4, D-W-8046 Garching (FRG)
Prof. Dr. H. Bock, Dr. B. Solouki
Anorganisch-chemisches Institut der Universitat Frankfurt
Dr. M. Wagner
Anorganisch-chemisches Institut der Universitdt Munchen
[**I Cyclic Metal Amides, Part 2. This research was supported by the Bundesministerium fur Forschung und Technologie. Part 1: ref. [lh].
Angew. Chem. Int. Ed. Engl. 1992, 31, N o . 11
C Ib
Fig. 1. Top: Crystal structure of 3b at -70°C (ORTEP, without hydrogen
atoms, thermal ellipsoids at the SO% probability level). Middle: Model of the
disorder in 3b (SCHAKAL, see text). Selected distances [pm] and angles I”]:
Ge-NI 183.3(2),N1-CI 145.9(4),CI-Cla 157.1(7), N1-C2 146.7(4);Nl,Ge,Nl’
88.0(1), NI,CI,Cla 105.7(2), Ge,Nl,Cl 113.1(2), C2,Nl,Ge 128.2(2); shortest
Ge-Ge distance: 643 pm. Bottom: Crystal structure of 3c at -50°C. Selected
distances[pm]and angles[“]: Ge-NI 185.6(1), NI-CI 138.4(1), Ct-Cl’ 136.4(1),
Nl-C10 149.3(1); Nl,Ge,Nl‘ 84.8(1), Nl,Cl,CI‘ 144.3(1), Ge,Nl,Cl 113.3(1);
shortest Ge-Ge distance: 641 pm.
Verlagsgesellschaji mbH, W-6940 Weinheim, 1992
cleanly from treatment of the dilithium salt 2 c with l b
Both germanediyls are infinitely stable at 25 "C under inert
gas. The extraordinarily volatile compounds (both sublime
at 45°C and 1 Torr; 3b: m.p. 4 5 T , 3 c : m.p. 51 "C) are
highly prone to hydrolysis. Compared to 3b, compound 3 c
is less reactive, thermally more stable, and can even be handled briefly in air in the crystalline state. Cermanediyls 3 b
and 3 c are monomeric not only in solution (osmometry) and
in the gas phase (CI-MS, electron diffra~tion[~"]),
but also in
the solid state (Fig. l), and thus belong to a rare class of
compounds.f6IMerely replacing the t-butyl groups on the N
atom with methyl groups leads to dimerization or trimerization.[61The tin derivative analogous to 3 b is d i m e r i ~ . ~ ~ ~ '
According to the X-ray structure analysis of 3b,I7"] the
atoms of the C,N,Ge five-membered ring appear to lie in a
mirror plane, which could imply a planar framework. However, the large vibration ellipsoids of C1 and C1' (view parallel to the mirror plane, Fig. 1 top) cannot be rationalized
completely in terms of thermal vibrations. In addition, the
C1-C1' bond is too short (142.8(7)pm) for a CC single
bond. These features can be explained by a model in which
the disorder is caused by two superimposed twist conformations (Fig. l middle).[7a]The refinement of this model provides the same R values,[71but leads to a CC bond length
(157.1 (7) pm) reasonable for a single bond. Calculations also
predict that 3 b should have a twist conformation in the
ground state.['0a1 In contrast, 3 c is planar (Fig. 1 bottom);'7b1the bond lengths and bond angles at germanium
differ only marginally from those of 3 b and give no evidence
of electronic differences between the two molecules.
[Ni(CO),] reacts with 3 b to furnish the monogermanediyl
complex 4a, and with excess 3 b to give the bis(germanediy1)
complex 5 a (Scheme 2). The structure of fiat8] was deter-
Scheme 2
mined by X-ray diffraction (Fig. 2). The zero-valent metal
atom has an almost ideal tetrahedral coordination geometry,
the respective carbonyl and germanediyl ligands are
nonequivalent, and the GeN,C, five-membered rings are
nonplanar, as in the free ligand 3b. Their CC bonds thus
appear to be shortened, but this effect is caused once again
by a twist disorder of the ethylene bridge. The angles at N,
Ce, and N' are almost identical to those in 3b. Germanium
has trigonal-planar coordination (sum of the angles is ca.
360"). Each N,GeNi plane is coplanar with a carbonyl
group. The resulting nonequivalence of the two tert-butyl
groups of each germanediyl ligand is also evident in solu1486
VCH VerfagsgeselischaftmbH, W-6940 Weinheim, 1992
Fig. 2. Crystal structure of 5a (ORTEP, without hydrogen atoms, thermal
ellipsoids at the 50% probability level). Selected distances Ipm] and angles I"]:
Gel-Ni 229.69(4), Ge2-Ni 229.13(3), Cl-Ni 177.2(3), C2-Ni 176.9(2), C1-01
113.1(2), C2-02 113.3(2), Ge-N1 182.6(2), Gel-N2 181.9(1), Ge2-N3 183.0(1),
Ge2-N4 181.3(2); Gel,Ni,Ge2 106.67(1), Cl,Ni,C2 111.6(1). Gel,Ni,Cl
113.71(8), Gel,Ni.C2 106.3(1), Ni,C1,01 176.4(3), NiC2.02 176.3(2).
NI,Gel,N2 88.62(7), N3,Ge2,N4 89.22(7), Gel,Nl,C5 112.2(1), Gel,Nl,C11
129.3(1), CS,Nl,ClI 118.3(2). Gel,N2,C6 11 1.8(1), Gel,N2.C21 129.8(1),
C6,N2,C21 118.1(2).
tion ['H/13C NMR; coalescence temperature + 65 "C (13C
NMR)]. The Ni-Ge distances (ca. 230 pm) are not
shorter than the single bonds in the few known germylnickel c o m p l e x e ~ .As
~ ~ ]the "N NMR and IR data ( v C 0 )
show, the nickel atom (d orbitals) cannot compete effectively with N-Ge backbonding: [Ni(CO),] 2057 (T,),
5a 2003 (All/
"~(CO),{P(C~H~),)ZI2000 (A1)/1941
1945 (B,) cm-'; the corresponding force constants for CO
stretching have the following respective values K = 17.9,
14.1, and 14.2 Ncm-'. Thus,germanediyl3bisaligandwith
relatively good o-donor and poor n-acceptor qualities, and
in this respect is similar to triphenylphosphine.
Ab initio calculations of the model compound (NH,),Ge:
(planar ground state, symmetry point group C,J showed
unexpectedly strong Ge-N backbonding. The barrier to rotation about the first Ge-N bond with pyramidalization is
12.8 kcalmol-', about the second 21.8 kcalmol-'. The second NH, group apparently provides some of the charge
density which the Ge atom loses when the first NH, group
is orthogonal.[l0]
The reaction of 3b with [Ni(l,S-cod),] (cod = cyclooctadiene), furnished the extremely air- and moisture-sensitive tris(germanediy1)complex 6 a (Scheme 2), which crystallized as brick-red crystals from n-hexane. The NMR spectra
('H, 13C, "N) indicate that the compound has D,, symmetry.
Investigations of the chemical vapor deposition (CVD) to
[Gel, or [Ge/GeH], were conducted in a flow tube under
controlled conditions;["". b] the gas was analyzed by photoelectron (PE) spectroscopy. Surprisingly, the thermolysis
of 3b,c gave rise to isobutene and HCN; H, could not be
detected. Besides the ionization pattern of isobutene,[' IC1 the
region of contourless bands between 11 - 16 eV presumably
also contains the one of isobutane. The thermolyses analyzed
by PE spectroscopy suggest the following reaction sequence
for the extrusion of [Gel, or [Ge/GeH], (Scheme 3). At
470 K 3 b decomposes to 3 c and 2 a. At 900 K 3 b and 3 c give
identical PE spectra in which isobutene and HCN can be
identified by their characteristic ionization peaks besides
residual 3 c . These results indicate that the CVD decomposition of 3 b,c may be optimized for the preparation of (hydrogen-containing) germanium layers.
The different thermal stabilities of the saturated and unsaturated cyclogermanediyls were approximated by ab initio
0570-0833/9211111-1486 $3.50+.25/0
Angew. Chem. hi.Ed. Engl. 1992, 31, No. I 1
5 470 K
which upon sublimation (1 Torr, 40°C) provided analytlcally pure 3 b in the
form of colorless needles (750 mg, 75 %). Occasionally a small amount of a
yellow, volatile impurity was observed which could be removed by sublimation.
3c: A solution of N,N'-bis(tert-hutyl)-1,4-diazabutadiene (59.4 mmol,
1 molequiv) in THF (200 mL) was treated with Li granules (830 mg, 0.12 gatom, 2 molequiv) and stirred overnight (reaction mixture turned red). A solution of l b (13.8 g) in T H F (50 mL) was added dropwise at 25 "C over lOmin
(reaction mixture turned brown and warmed to 30-40°C). The solvent was
removed under vacuum after 1 h, the residue stirred with n-pentane (100 mL),
and the mixture filtered (G3 or G4 Schlenk frit). The solvent was evaporated,
and sublimation provided 3c as dull colorless needles (11.5 g, 80%). Correct
complete analysis.
4 a : [Ni(CO),] ( 5 mL, excess) was added dropwise to a stirred solution of 3 b
(900 mg. 3.705 mmol) in T H F ( 5 mL) at 25 "C. After a short induction period,
a vigorous evolution of gas began and lasted ca. 3min (reaction mixture turned
pale yellow). After 1 h at 25 " C , the solvent was removed under vacuum, the
orange-yellow, clear, glasslike residue taken up in n-pentane (10 mL). and the
solution stored at -25 "C (1 d) and - 78 "C (1 d). 4 a was obtained as colorless
crystals with a slightly gray tinge (1.17 g, 82%). 'H NMR (270 MHz. C,D,.
25°C): 6 = 1.23 (s, CH,); 3.08(s, CH,); 13C NMR(100.54 MHz,C,D,, 25°C):
6 = 32.2(q, 'J(C.H) = 125 Hz; CH3),48.7(t, 'J(C,H) = 136 Hz; CH,), 55.5 (s;
C(CH,),), 195.9(s; CO): " 0 NMR (36.64 MHz, [DJtoluene, 25 "C, D,O standard): 6 = -197.1 ( s ; CO); "NNMR (40.51 MHz, C,D,, 25°C. CH,NO,
standard): 6 = - 226.1 (s).
Scheme 3.
calculations[' Oal of the hydrogenation enthalpies of the model compounds 3b' and 3c' [isodesmic Eqs. (a) and (b)].
The unsaturated cyclogermanediyl3c' is 41 kJmol- lower
in energy than the saturated compound 3b' (RHF/
LANLl DZ//RHF/LANLl DZ); when electron correlation
is included (MP2/LANLlDZ//RHF/LANLIDZ),
3 c' is
54 kJ mol - more stable than 3b'." Oal The optimized geometry is in excellent agreement with the structural data (Fig. 1).
In the triplet state, in which seven electrons occupy the IT
molecular orbitals of 3c', there is no significant difference
between the hydrogenation
enthalpies of the model compounds and those of the hypothetical germane derivatives
[Eqs. (a) and (b)].
5 a : To a solution of 3 b (900 mg, 3.705 mmol) in n-hexane ( 5 mL) was added
[Ni(CO),] (161 pL, 0.212 g. 1.235 mmol). After a short induction period, a
vigorous evolution of gas began and lasted ca. 3min. The solvent was removed
by distillation under vacuum and the residue heated at 90 "C (oil bath temperature) in a sublimation apparatus under high vacuum for 1d. The clear, glassy
remaining material was taken up in n-pentane (10 mL) and crystals formed at
-25 "C. Yellow, transparent prisms were obtained (830 mg, 75%). IR (Nujol,
CsI): v(C0) = 2003 (s), 1945 (s) cm-' ; 'H NMR (400 MHz, C,D,, 25 'C):
6 =1.41, 1.48 ( s ; CH,), 3.09 (s; CH,); I3C NMR (100.54 MHz, [D,]toluene,
25°C): 6 = 31.9, 32.2 (q, 'J(C,H) = I 2 5 Hz; CH,), 48.6, 48.7 (t,
'J(C,H) =136 Hz; CH,), 55.4 (s, C(CH,),). 195.7 (s; CO); " 0 NMR
(36.64 MHz, C,D,, 2 5 T , D,O standard): 6 = 207.7 (s); l5N NMR
(40.51 MHz, C6D6. 25 "C, CH,NO, standard): 6 = - 222.2 (s). Correct complete analysis.
6a:Asolutionof3b(840 mg,3,46mmol)inTHF(5mL)at -78"Cwastredted
with [Ni(iS-cod),] (317 mg, 1.15 mmol) (reaction mixture turned red immediately). The reaction mixture was allowed to warm to 25"C, and the volatiles
were removed by distillation. The remaining material was heated at 60 "C (oil
bath temperature) for 2h under argon and then 8h under vacuum. The redbrown crystalline residue was dissolved in n-hexane (10 mL) and cooled to
-30°C for ca. 15d to provide deep red needles (810 mg, 89%). 'H NMR
(400MH2, C,D6, 25°C): 6 =1.45 ( s ; CH,), 3.24 ( s ; CH,); 13CNMR
(100.54 MHz, [DJtoluene, 25°C): 6 = 32.4 (q, 'J(C,H) = 125 Hz; CH,), 48.6
(t. 'J(C,H) = 135 Hz; CH,), 54.5 (s; C(CH,),); 15NNMR (40.51 MHz.
[D,]toluene, 25'C, CH,NO, standard): 6 = - 234.7 (s); CI-MS (isohutene.
positive ions): m / z 242 (LGe", 100%); CI-MS (isobutene, negative ions): m / i
749 (6a"
3CH,. 42%), 394(30), 315(23), 279(10), 208(9), 149(100).Correct
complete analysis.
Received: June 22, 1992
Revised: August 25, 1992 [Z 5432IEl
German version: Angew. Chem. 1992, 104, 1489
CAS Registry numbers:
1b, 28595-67-7; 2a, 4062-60-6; 3a, 143970-59-6,3b, 143970-60-9;3c, 14397061-0; 4a, 143970-63-2;5a, 144000-21-5;6a, 143970-64-3;[Ni(cod),], 1295-358; [Ni(CO),], 13463-39-3; N,N'-Bis(tert-butyl)-1,4-diazabutadiene, 14397062-1.
The theoretical and experimental results (planarity, 'H/
reduced reactivity) can best be explained by assuming a cyclic delocalization of the x electrons
in 3 c in the ground state. In light of the results reported here,
as well as the work of Arduengo et al.["] on the structurally
analogous carbenes (C instead of Ge), the corresponding
silanediyls should also be stable.
Experimental Procedure
3b: A solution of 3a (1.29 g, 4.12 mmol) in THF ( 5 mL) was treated with Li
granules (57 mg) (the reaction mixture turned brown). After 5-6h the solvent
was removed under vacuum and replaced with n-pentane (10 mL). Filtration
(G3 Schlenk frit) and evaporation of the solvent gave a thick, light yellow oil,
Angen. Cliem. l n t . Ed. Engl. 1992, 31, No. 11
[l] a) W. A. Herrmann, M. Denk, S. Vepiek, unpublished results, 1991/1992;
b) W. A. Herrmann, M. Denk, R. W. Albach, J. Behm, E. Herdtweck,
Chem. Ber. 1990, f24,683-689.
[21 3a: 'H NMR (270 MHz, C,D,, 25°C): 6 =1.21 (s, 18H; CH,), 2.75 (s;
(67.94MH2, C,D,,
25°C): 6 = 29.3 (9,
'J(C,H) = 126 Hz; CH,), 43.6 (t, 'J(C,H) = 139 Hz; CH,), 54.0 (s;
C(CH,),); "N NMR (40.51 MHz, C6D,. 25°C. Standard CH,NO,):
6 = - 302.5 (s; C(CH,),); El-MS (70eV. positive ions): m/z 318 ( M +,
1"A).299 ( M ' + - CH,, 100). Correct complete analysis.
[3] 3b: 'HNMR (C,D,, 270 MHz, 25°C): 6 =1.28 (s, 9 H ; CH,), 3.27(s, 2 H ;
CH,); 13CNMR (C6D,, 67.9 MHz, 25°C): 6 = 32.1 (4, 'J(C,H) =
125 Hz; CH,), 54.3 ( s , C(CH,),), 49.7 (t, 'J(C,H) =135 Hz, 'J(C,H) =
3 Hz; CH,); 15N NMR (C,D,, 40.51 MHz, 20°C. CH,NO, standard):
6 = - 207.3 ( s ) ; CI-MS (isobutene, positive ions): m / z 242 (65%), 229(28),
173(100). Correct complete analysis.
[4] 3c: 'H NMR (270 MHz, C,D,, 25°C): 6 =1.43 ( s , 18H; CH,), 7.05 (s,
2 H ; CH); l3C NMR (67.94 MHz, C,D,, 25 "C): 6 = 33 ' 2 (4, 'J(C,H) =
125.1 Hz; CH,), 55.7 (s, C(CH,),), 121.4 (dd. 'J(C,H) = 173.0 Hz,
Verlagsgesehchafl mbH, W-6940 Weinheim,1992
f f 1-f 487 S 3.50+ .25/0
'J(C,H) =11.0 Hz; CH); "N NMR (C,D,, 40.51 MHz, 2 5 T , CH,NO,
standard): 6 = -136.3 (s); CI-MS (isobutene, positive ions): m / i 242
(60%), 194(47), 169(100). Correct complete analysis.
[5] a) A. Haaland, P. Kiprof, W. A. Herrmann, M. Denk, unpublished; b) M.
Denk, Dissertation, Technische Universitat Miinchen, 1992.
[6] a) M. F. Lappert, M. J. Slade, J. L. Atwood, J. Chem. Soc. Chem. Commun.
1980, 621-622; b) J. Pfeiffer, W. Maringgele, M. Noltemeyer, A. Meller,
Chem. Ber. 1989, 122. 245-252; c) R. A. Bartlett, P. P. Power, J. Am.
Chem. Soc. 1990, f12,3660-3662; d) M. Veith, L. Stahl, V. Huch. J. Chem.
SOC.Chem. Commun. 1990, 359-361.
[7] a) X-ray structure analysis of 3b (C,,H,,GeN,): Irregular fragment of a
crystdl obtained by sublimation. Systematic extinctions hOO (h = 2n + 1)
and OkO ( k = 2n +I). space group P-Z2,m (no. 113), a = 998.09(4),
c = 643.12(5) pm, V = 640. 106 pm3, Z = 2, p.,,. = 1.259 gcm-', EnrafNonius CAD4, I =71.07 pm (Mo,., graphite monochromator), T = - 70
(f3)"C, range of measurement 1.0" < 0 < 25.0', w-scan. scan width
(1.2 0.25 tan0)" (f25 %) before and after each reflection to determine
the background, I,,, = 60s. empirical absorption correction based on Pscan data, p = 23.2 cm-', no decomposition, direct structure determination, difference Fourier technique, 620 independent reflections, of which
620 had I > 0.01a(I), 67 parameters refined by full-matrix least-squares.
reflection/parameter relationship 9.25, all six heavy atoms except C1 with
anisotropic thermal motion parameters, all hydrogen atoms found and
independently refined, anomalous dispersions accounted for, shift/
error < 0.001, residual electron density 0.20 A e , k 3 (105 pm off the Ge
atom) and -0.31 A e , k ' , R = Z(ilF,I - ~ & ~ ~ ) / Z=~ 0.017.
F o / R, =
[Zw(IFol - lF,l)'/~~~lFol2]"'
= 0.019. The refinement of the other enantiomer gave a larger R value (0.0263). Three additional sets of data were
collected from another crystal between -35 and -110°C for further
support the model of disorder. All four measurements confirm the model
of disorder and thus the nonplanarity of the C,N,Ge ring, since the large
vibration ellipsoids were shown to be temperature invariant and best rationalized by disorder. The structure refinement provided almost identical
behavior for the main axes of the thermal parameters. b) X-ray structure
analysis of 3c (C,,H,,GeN,):
a =1378.40(4), b =1403.12(3), c =
641.45(1) pm, V = 1240-10' pm', measurement at - 50 "C, p,,,, =
1.289 gcm-3, p = 30.2cm". 2 = 4, orthorhombic crystal system, space
group Pmmn, Enraf-Nonius CAD4, 1 = 154.184 pm, Cu,,, graphite
monochromator), 4 2 0-scan, 4635 measured reflections, ( - h, f k , fI) of
which 1143 were independent, structure determination with Patterson
methods and difference Fourier syntheses, empirical absorption correction, transmission coefficients 0.8592-0.999, 118 refined parameters,
R=X(IIFoI - l ~ l l ) / Z I F o=~0.035,RW =[Zl~(lF,l - IF,))*/Z.M.IF~~]'!'
0.029, residual electron density 0.68, -0.76 A e , k 3 . c) Further details
of the crystal structure investigation may be obtained from the Fachinformationszentrum Karlsruhe, Gesellschaft fur wissenschaftlich-technische
Information mbH, D-W-7514 Eggenstein-Leopoldshafen 2 (FRG), on
quoting the depository number CSD-56578, the names of the authors, and
the journal citation.
[8] X-ray structure analysis of 5 a (C,,H,,Ge,N,NiO,):
a = 965.1(1),
h=1671.8(2), c=1811.5(2)pm, ~ = l O 1 . 5 1 " , V=2864.10'pm3, measurementat25'C,pC,,, = 1 . 3 9 g ~ m - ~ =33.8cm~',F,,,
monoclinic crystal system, space group P2,/c, Enraf-Nonius CAD4,
1= 154.184 pm (Cu,,, graphite monochromator), w/tQ-scan, 5288 measured reflections (fh,-k, + I), 4651 of which were independent, 4645 used
for refinement. structure solution with Patterson methods and difference
Fourier syntheses, empirical absorption correction, transmission coefficients 0.939-0.999, 280 refined parameters. R = Z( llFol- l&ll)/Z~Fol=
0.052, R , = [Zw(lF,I - l&1)'/ZwlF1']''' = 0.049, residual electron density 0.98, - 0 . 7 4 A e k 3 . See also ref. [7c].
[9] Cf. for example F. Clocking, A. McGregor, M. L. Schneider, H. M. M.
Shearer, J. Inorg. Nucl. Chem. 1970, 32. 3101. Few metal complexes of
stable germane- and stannanediyls have been reported previously; see for
example W. P. Neumann, Chem. Rev. 1991.91,311, and references therein;
M. S. Holt, W. L. Wilson, J. H. Nelson, ibid. 1989, 89, 11.
[lo] a) The calculations were conducted on a Cray vector computer with the
GAUSSIAN-90 program package; cf. W J. Hehre, C. Radom. P. von R.
Schleyer, J. A. Pople, A h lnitro Molecular Orbital The0r.y. Wiley, New
York, 1986; T. Clark, A Handbook of Conipulaiional Chemistry, Wiley,
New York, 1985. Geometries were optimized at the RHF (singlet states) or
the U H F level (triplet states) within the given symmetry restrictions with
the LANLIDZ basis set. The frequencies were calculated in the same way
for the determination of local minima. The energies listed were obtained
from single-point calculations on the RHFILANLI DZ geometries with up
to second-order perturbation theory (MP2); cf. P. J. Hay, W. R. Wadt, J.
Cheni. Phys. 1985, 82, 270-283, 284-298, 299-310. b) For rr-electron
delocalization cf. S. S. Shatk, P. C. Hiberty, J.-M. Lefour, G. Ohanessian,
J. Am. Chem. Soc. 1987, 109. 363.
[ l l ] a) H. Bock, B. Solouki, H. S. Aygen, M. Bankmann, 0. Breuer, R.
Dammel, J. Darr, M. Hann, D. Jaculi, J. Mintzer, S. Mohumand, H.
Miiller, P. Rosmus, B. Roth, J. Wittmann, H.-P. Wolf, J. Mol. Struct. 1988,
173,31; H. Bock, M. Kremer. H. Schmidbaur, J. Organomet. Chem. 1992,
429, I . b) Quartz tube (40 x 1.5 cm) with three plugs of quartz wool each
Verlagsgesellschafi mhH, W-6940 Weinheim. 1992
1.5 cm long in a 30-cm tubular oven connected to a Leybold Heraeus UPG
200 PE spectrometer (resolution ca. 20 meV, 2000 countss-I). The spectra
were recorded at a pressure of 10-4mbar and calibrated with Ar
(zP3!2)= 15.76 eV. c) Cf. for example K. Kimura, S. Katsumata, Y. Achiba,
T. Yamazaki, S. Iwata. Handbook of He-I Photoelectron Spectra ofFundumental Organic Molecules, Halstedd Press, New York, 1981. d) The assignment of the PE spectra of 3b and 3c following Koopman's correlation
IE: = with MNDO eigenvalues was not reliable, since in the
optimization of the parameters for Ge (M. J. S. Dewar. G. L Grady, E. F.
Healy, Organometallics 1987,6,186-189) MeGeNMe, was the only nitrogen compound considered. Under C,, symmetry, the order of the first
three bands should ben,- (a,) < N,, ( a , ) 2 n N ( h , )is expected qualitatively; the bands of the last M ' + states overlap.
[I21 a) A. J. Arduengo 111, R. L. Harlow, M. Kline, J. Am. Chem. Soc. 1991,
113, 361; b) A. J. Arduengo 111. H. V. Rasika Dias, R. L. Harlow, M.
Kline. ibid. 1992. 114. 5530; c) D. A. Dixon, A. J. Arduengo 111, J. Phys.
Chem. 1991, 95, 4180.
Quest for Higher Ladderanes:
Oligomerization of a Cyclobutadiene Derivative**
By Goverdhan Mehta,* M . Balaji Viswanath,
G. Narahari Sastry, Eluvathingal D. Jemmis,*
D. Sivakumar K . Reddy, and Ajit C. Kunwar*
The name [n]-ladderane has been given to novel molecular
arrays composed entirely of linearly concatenated cyclobutanes for example, l.[ll Thus, cyclobutane, bicyclo[2.2.0]hexane, and tricycl0[]octane
are [I]-, [2]-, and [3]ladderane, respectively. These multifused, cyclobutanoid
systems hold great promise as spacers in view of the latitude
they offer in terms of rigidity, distal variation, steric disposition, and an accommodating CJ framework. However, only
[2]-ladderanes have been exploited as spacers thus far.[']
Ladderanes with n 2 11, which possess functional groups at
the terminal rings [e.g., 2 (x 2 9)], have been considered as
precursors of configurational isomers of higher [n]-prismanes for example, israelane 3 and helvetane 4.[3*41However, to our knowledge, the ladderane route to the fascinating hydrocarbons 3 and 4 has never progressed beyond the
realm of fanciful ideas.[4% The major impediment in the
exploitation of the potentially rich chemistry of ladderanes
has been their inaccessibility. It has not yet been possible to
assemble a linear array of more than four cyclobutane rings,
and only a handful of [4]-ladderanes are
we report a new approach for the rapid assembly of higher
ladderanes, and describe the characteristics of [5]- and [7]ladderane derivatives.
The simplest and shortest approach to the higher ladderanes 1/2 (x > 3) would be by the controlled oligomerization
of a cyclobutadiene. However, cyclobutadiene and its
derivatives are known to dimerize only.[71If we can understand why the oligomerization of cyclobutadiene does not
proceed beyond the dimer stage, it should be possible to
design cyclobutadiene derivatives that may exhibit enhanced
Prof. G . Mehta, M. B. Viswanath, G. N. Sastry. Prof. E. D. Jemmis
School of Chemistry
University of Hyderabad
Hyderabad 500 134 (India)
Dr. D. S. K. Reddy
ARDEC, Picatinny Arsenal, NJ (USA)
Dr. A. C. Kunwar
Indian Institute of Chemical Technology
Hyderabad 500007 (India)
This work was supported, in part, by the Council of Scientific and Industrial Research, New Delhi (Research Fellowships for MBV and
Angew. Chem. Ini. Ed. Engl. 1992, 31, No. 1 1
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