Acetylene-linked bis(germaethenes): The first molecules with conjugated germanium-carbon double bonds

Article abstract of DOI:10.1021/om000284w

In solution, the digermene Ar₂Ge double bond GeAr₂ (Ar = 2-tBu-4,5,6-Me₃C₆H) partly dissociates into two molecules of the germylene Ar₂Ge:. The reaction of this digermene with some 1,3-diynes (RC triple bond C-)₂ leads to the formation of the acetylene-linked bis(germaethenes) Ar₂-Ge double bond C(R)C triple bond C(R)C double bond GeAr₂ (R = n-C₄H₉ (6a), C₆H₅ (6b)). The conjugation between the two Ge double bond C units is reflected by the positions of the UV/vis absorptions at longest wavelengths of 518 (6a) and 595 (6b) nm. An X-ray structure analysis of 6a reveals a nearly linear C₄ skeleton and short Ge double bond C bond lengths of 1.819(2) angstroms.

Full text of DOI:10.1021/om000284w

Organometallics 2000, 19, 2835-2836
2835
Acetylen e-Lin k ed Bis(ger m a eth en es): Th e F ir st
Molecu les w ith Con ju ga ted Ger m a n iu m -Ca r bon Dou ble
Bon d s1
Frank Meiners, Wolfgang Saak, and Manfred Weidenbruch*
Fachbereich Chemie, Universita¨t Oldenburg, D-26111 Oldenburg, Germany
Received April 3, 2000
Sch em e 1
Summary: In solution, the digermene Ar2GedGeAr2 (Ar
) 2-tBu-4,5,6-Me3C6H) partly dissociates into two mol-
ecules of the germylene Ar2Ge:. The reaction of this
digermene with some 1,3-diynes (RCtC-)2 leads to the
formation of the acetylene-linked bis(germaethenes) Ar2-
GedC(R)CtC(R)CdGeAr2 (R ) n-C4H9 (6a ), C6H5 (6b)).
The conjugation between the two GedC units is reflected
by the positions of the UV/ vis absorptions at longest
wavelengths of 518 (6a ) and 595 (6b) nm. An X-ray
structure analysis of 6a reveals a nearly linear C4
skeleton and short GedC bond lengths of 1.819(2) Å.
immediate formation of a red solution from which dark
red crystals were isolated. The analytical and spectral
data of this compound are indicative of a 2:1 adduct of
the germylene and the diyne. The intense color and
extreme air sensitivity of the compound clearly show
that it is not a germanium analogue of the colorless
silicon compounds 1 and 2. The UV/vis absorption at
longest wavelength of 518 nm is bathochromically
shifted by about 100 nm in comparison to those of the
yellow or pale orange germaethenes2-5 and is thus
rather suggestive of the molecule 6a 11 with conjugated
Ge-C double bonds. Inadequate shielding of these
double bonds then would be responsible for the in-
creased reactivity to atmospheric oxygen (Scheme 2).
An X-ray crystallographic analysis12 (Figure 1) not
only confirmed the proposed constitution of 6a but also
revealed some interesting features. The molecules of 6a
have a C2 symmetry axis which passes through the
central C-C triple bond and an almost linear C4
skeleton with CCtC angles of 178.1(4)° each. The Ge-C
Since the discovery of thermally stable germaethenes
(germenes) in 1987, the structures of four representa-
tives have been unambiguously elucidated.2-5 Common
features of these compounds are the short Ge-C double
bond lengths of between 1.77 and 1.84 Å and the
shielding of the two participating atoms by bulky
substituents that effectively prevents further reactions
of the multiple-bond system.6
We recently investigated the reactions of some 1,3-
diynes R′CtCCtCR′ with photolytically generated si-
lylenes and found that the product pattern obtained
depends strongly on the nature of the substituents R
and R′.7,8 When R is an alkyl group, the isolable bis-
(silirene) 1 is formed initially but undergoes rearrange-
ment to the bicyclohexadiene derivative 2 upon longer
photolysis (Scheme 1). We then addressed the question
as to whether a change from silicon to germanium would
lead to different products and now report on the
observed unusual mode of reactivity.
(10) Della Bona, M. A.; Cassani, M. C.; Keates, J . M.; Lawless, G.
A.; Lappert, M. F.; Stu¨rmann, M.; Weidenbruch, M. J . Chem. Soc.,
Dalton Trans. 1998, 1187.
(11) Dodeca-5,7-diyne (0.165 g, 1 mmol) was added at room tem-
perature to a suspension of 3 (0.354 g, 0.42 mmol) in n-hexane (40
mL). The mixture was stirred for 5 days at room temperature, excess
3 was filtered off, and the red solution was kept at -20 °C to deposit
dark red crystals of 6a : yield 0.096 g, 23%; mp 160 °C dec. 1H NMR
(C6D6): δ 0.72 (m, 6 H), 0.89 (m, 4 H), 1.21 (m, 4 H), 1.41 (s, 18 H),
1.45 (s, 18 H), 1.72 (m, 4 H), 2.06 (s, 6 H), 2.09 (s, 6 H), 2.16 (s, 6 H),
2.24 (s, 6 H), 3.08 (s, 6 H), 3.26 (s, 6 H), 7.20 (s, 4 H). 13C NMR (C6D6):
δ 14.26, 16.70, 16.79, 21.18, 21.28, 22.87, 22.99, 23.99, 25.19, 25.78,
32.41, 32.85, 32.91, 35.40, 36.78, 111.34, 123.66, 133.21, 133.51, 136.77,
137.19, 138.49, 139.36, 142.40, 151.88, 152.36. UV/vis (toluene): λmax
518 nm. Because of the sensitivity of 6a in solution the ꢀ value could
not be determined. Anal. Calcd for C64H94Ge2: C, 76.21; H, 9.39.
Found: C, 75.79; H, 9.22.
As the germanium component we chose the di-
germene 3,9 which partially dissociates in solution into
the germylene molecules 4.10 The reaction of 4 with
dodeca-5,7-diyne at room temperature resulted in the
(1) Compounds of Germanium, Tin, and Lead. 36. Part 35: Scha¨fer,
H.; Saak, W.; Weidenbruch, M. J . Organomet. Chem., in press.
(2) Lazraq, M.; Escudie´, J .; Couret, C.; Satge´, J .; Dra¨ger, M.;
Dammel, R. Angew. Chem. 1988, 100, 885; Angew. Chem., Int. Ed.
Engl. 1988, 27, 828.
(3) Meyer, H.; Baum, G.; Massa, W.; Berndt, A. Angew. Chem. 1987,
99, 790; Angew. Chem., Int. Ed. Engl. 1987, 26, 798.
(4) Tokitoh, N.; Kishikawa, K.; Okazaki, R. J . Chem. Soc., Chem.
Commun. 1995, 1425.
(5) Stu¨rmann, M.; Saak, W.; Weidenbruch, M.; Berndt, A.; Schesch-
kewitz, D. Heteroat. Chem. 1999, 10, 554.
(6) Reviews: (a) Baines, K. M.; Stibbs, W. G. Adv. Organomet. Chem.
1996, 39, 275. (b) Escudie´, J .; Couret, C.; Ranaivonjatovo, H. Coord.
Chem. Rev. 1998, 178-180, 565.
(7) Kirmaier, L.; Weidenbruch, M.; Marsmann, H.; Peters, K.; von
Schnering, H. G. Organometallics 1998, 17, 1237.
(8) Ostendorf, D.; Kirmaier, L.; Saak, W.; Weidenbruch, M.; Mars-
mann, H. Eur. J . Inorg. Chem. 1999, 2301.
(9) Weidenbruch, M.; Stu¨rmann, M.; Kilian, H.; Pohl, S.; Saak, W.
Chem. Ber. 1997, 130, 735.
(12) Crystal data for 6a ‚C6H14: C70H108Ge2, fw 1094.74, monoclinic,
a ) 26.886(1) Å, b ) 9.8551(3) Å, c ) 25.168(1) Å, â ) 101.254(5)°, V
) 6540.4(4) Å3, space group C2/c, Mo KR radiation, λ ) 0.71073 Å, Z
) 4, crystal dimensions 0.90 × 0.27 × 0.18 mm3, µ ) 0.956 mm-1
,
Stoe IPDS area detector, T ) 193(2) K, 24 350 reflections collected,
5982 unique reflections, 4509 observed reflections (I > 2σ(I)). The
structure was solved by direct phase determination and refined by full-
matrix least-squares techniques against F2 with the SHELXL program
system.14 Hydrogen atoms were placed in the calculated positions, and
all other atoms were refined anisotropically. R1(I > 2σ(I)) ) 0.0350,
wR2 ) 0.0850, R1(all data) ) 0.0519, wR2 ) 0.0905 for 325 parameters,
and GOF (F2) ) 0.931. The data have been deposited with the
Cambridge Crystallographic Data Centre (reference no. CCDC-141
238).
10.1021/om000284w CCC: $19.00 © 2000 American Chemical Society
Publication on Web 06/22/2000

2836 Organometallics, Vol. 19, No. 15, 2000
Communications
Sch em e 2
between the Ge-C double bonds. The angles between
the respective germanium atom and the ipso-C atoms
of the aryl substituents of 130.74(9)° are considerably
opened and are even slightly larger than the corre-
sponding angles in digermene 3 (128.0°).9
The mechanism of formation of 6a is not known with
certainty. In analogy to the reactions of silylenes,8 one
possible sequence could involve the formation of the bis-
(germirene) 5, which would then undergo rearrange-
ment via the cleavage and new formation of two bonds
to afford the isolated product.
To define the scope of the formation of the bis-
(germaethenes), we have also carried out the reaction
of 1,4-diphenylbuta-1,3-diyne with germylene 4 and,
after 4 days at room temperature, obtained a dark blue-
violet solution from which a violet powder was isolated
in 96% yield. Although we have not yet been able to
grow a single crystal of this compound, its analytical
and spectral data, especially its color together with the
UV/vis absorption at longest wavelength at 595 nm,
strongly suggest that it is the diaryl analogue 6b of the
dialkyl compound 6a .13 Other buta-1,3-diynes appear
to react in a similar manner with the germylene 4.
However, we have not yet been able to isolate any pure
compounds.
Ack n ow led gm en t. Financial support of our work
by the Deutsche Forschungsgemeinschaft and the Fonds
der Chemischen Industrie is gratefully acknowledged.
Su p p or t in g In for m a t ion Ava ila b le: Listing of atomic
coordinates, anisotropic displacement parameters, and bond
lengths and angles for 6a . This material is available free of
charge via the Internet at http://pubs.acs.org.
F igu r e 1. Molecule of 6a in the crystal (hydrogen atoms
omitted). Ellipsoids are drawn at 50% probability. Selected
bond lengths (Å) and bond angles (deg): Ge(1)-C(2) )
1.819(2), C(1)-C(2) ) 1.407(3), C(1)-C(1a) ) 1.200(5), Ge-
(1)-C(7) ) 1.991(2), Ge(1)-C(20) ) 1.991(2); C(2)-C(1)-
C(1a) ) 178.1(4), C(7)-Ge(1)-C(20) ) 130.74(9), C(7)-
Ge(1)-C(2) ) 113.70(9), C(20)-Ge(1)-C(2) ) 115.49(9).
OM000284W
(13) A solution of 1,4-diphenylbuta-1,3-diyne (66 mg, 0.33 mmol) in
n-hexane (10 mL) was added dropwise to a suspension of 3 (0.278 g,
0.33 mmol) in n-hexane (20 mL). The mixture was stirred for 4 days
at room temperature. From the dark blue solution a violet powder of
6b was isolated by filtration: yield 0.330 g, 96%; mp 130-135 °C dec.
1H NMR (C6D6): δ 1.36 (s, 18 H), 1.38 (s, 18 H), 1.78 (s, 6 H), 1.89 (s,
6 H), 2.03 (s, 6 H), 2.10 (s, 6 H), 2.64 (s, 6 H), 3.30 (s, 6 H), 6.74 (m, 4
H), 6.85 (m, 4 H), 7.24 (m, 6 H); 13C NMR (C6D6): δ 16.30, 16.41, 21.18,
21.40, 24.15, 32.88, 32.94, 36.54, 36.65, 107.73, 123.20, 125.87, 134.17,
134.53, 137.46, 137.74, 138.14, 140.28, 141.76, 142.53, 143.86, 151.75,
152.28, UV/vis (toluene): λmax 595 nm, minor absorptions at 750 and
850 nm. Anal. Calcd for C68H86Ge2: C, 77.89; H, 8.27. Found: C, 77.70;
H, 8.08.
double-bond lengths of 1.819(2) Å are in the same range
as those of the simple germenes. Although the C-C
triple-bond length of 1.200(5) Å is typical for such
systems, the formal C(1)-C(2) single-bond lengths of
1.407(3) Å between the sp- and the sp2-hybridized
carbon atoms are remarkably short and can be consid-
ered as further evidence in support of the conjugation
(14) Sheldrick, G. M. SHELXL-97: Program for Crystal Structure
Refinement; Universita¨t Go¨ttingen, Go¨ttingen, Germany, 1997.