Germanium and tin analogues of alkynes and their reduction products

Article abstract of DOI:10.1021/ja035711m

The reduction of terphenylgermanium(II) or terphenyltin(II) chlorides with alkali metals was investigated. Treatment of Ar′GeCl or Ar*GeCl (Ar′ = C₆H₃-2,6-Dipp₂, Dipp = C ₆H₃-2,6-Prⁱ₂; Ar* = C ₆H₃-2,6-Trip₂, Trip = C₆H ₂-2,4,6-Prⁱ₃) with lithium, sodium, or potassium afforded the neutral alkyne analogues Ar′GeGeAr′, 1, Ar*GeGeAr*, 2, the singly reduced radical species NaAr*GeGeAr*, 3, or KAr′GeGeAr′, 4, or the doubly reduced compounds Li₂Ar′GeGeAr′, 5, Na ₂Ar*GeGeAr*, 6, or K₂Ar*GeGeAr*, 7. Similarly, reduction of Ar′SnCl or Ar*SnCl afforded the neutral Ar′SnSnAr′, 8, or Ar*SnSnAr*, 9, the radical anions [(THF)₃Na{Ar*SnSnAr*}], 10, [K(THF) ₆][Ar′SnSnAr′], 11, [K(THF)₆][Ar* SnSnAr*], 12, [K(18-crown- 6)(THF)₂] [Ar*SnSnAr*], 13, or the doubly reduced Na₂Ar*SnSnAr*, 14, K ₂Ar′SnSnAr′, 15, or K₂Ar*SnSnAr*, 16. The compounds were characterized by UV-vis, ¹H and ¹³C NMR or EPR spectroscopy. The X-ray crystal structures of all compounds were determined except those of 2 and 9. The neutral 1 and 8 displayed planar, trans-bent CMMC (M = Ge and Sn) cores with M-M-C angles of 128.67(8) and 125.24(7)°, respectively. The M-M bond lengths, 2.2850(6) and 2.6675(4)A, indicated considerable multiple character and a bond order approaching two. Single and double reduction of the neutral species resulted in the narrowing of the M-M-C angles by ca. 12-32° and changes in the Ge-Ge and Sn-Sn bond lengths. One-electron reduction afforded a slight (ca. 0.03-0.05A) lengthening of the Ge-Ge bonds in the case of germanium species 3 and 4 and a greater lengthening (ca. 0.13-0.15A) for the Sn-Sn bonds in the tin compounds 10-13. The addition of another electron yielded salts of the formal dianions [Ar′MMAr′]^2- and [Ar*MMAr*]^2- which are isoelectronic to the corresponding doubly bonded, neutral arsenic and antimony derivatives. All the dianion salts were obtained as contact ion triples with two alkali metal cations complexed between aryl rings. The Ge-Ge bonds in the dianions of 5-7 were longer, whereas the Sn-Sn distances in the dianions in 14, 15, and 16 were shorter than those in the monoanions. Unusually, the Li₂Ar′ GeGeAr′ salt, 5, displayed a longer Ge-Ge bond (by ca. 0.06A) than those of its Na⁺ or K⁺ analogue salts which was attributed to the greater polarizing power of Li⁺. It was concluded that the M-M bond lengths in 3-7 and 10-16 are dependent on several factors that include M-M-C angle, Coulombic repulsion, alkali metal cation size, and the character of the molecular energy levels. The M-M bonding in the neutral compounds was accounted for in terms of a second-order Jahn-Teller mixing of σ*- and a π-orbital which afforded bond orders near two for the neutral compounds, 1, 2, 8, and 9. Calculations on MeMMMe (M = Ge or Sn) model species showed that the LUMO corresponded to an orbital that had n₊ lone pair character. The slight Ge-Ge bond length increase upon one-electron reduction is consistent with these results, and the further bond lengthening upon double reduction is consistent with increased Coulombic repulsion. The greater Sn-Sn bond length increase seen for one-electron reduction of the tin species is probably due to the increased p-character of orbitals comprising the Sn-Sn σ-bond when the Sn-Sn-C angle is decreased by ca. 30°. Upon further reduction, the slight decrease in the Sn-Sn bond is probably a result of the reduced importance of Coulombic repulsion due to the larger size of tin and a widening of the Sn-Sn-C angles which may shorten the Sn-Sn σ-bond.

Full text of DOI:10.1021/ja035711m

Published on Web 08/30/2003
Germanium and Tin Analogues of Alkynes and Their
Reduction Products
Lihung Pu, Andrew D. Phillips, Anne F. Richards, Matthias Stender,
Richard S. Simons, Marilyn M. Olmstead, and Philip P. Power*
Contribution from the Department of Chemistry, UniVersity of California, DaVis,
One Shields AVenue, DaVis, California 95616
Received April 18, 2003; E-mail: pppower@ucdavis.edu
Abstract: The reduction of terphenylgermanium(II) or terphenyltin(II) chlorides with alkali metals was
investigated. Treatment of Ar′GeCl or Ar*GeCl (Ar′ ) C6H3-2,6-Dipp2, Dipp ) C6H3-2,6-Pri2; Ar* ) C6H3-
2,6-Trip2, Trip ) C6H2-2,4,6-Pri3) with lithium, sodium, or potassium afforded the neutral alkyne analogues
Ar′GeGeAr′, 1, Ar*GeGeAr*, 2, the singly reduced radical species NaAr*GeGeAr*, 3, or KAr′GeGeAr′, 4,
or the doubly reduced compounds Li2Ar′GeGeAr′, 5, Na2Ar*GeGeAr*, 6, or K2Ar*GeGeAr*, 7. Similarly,
reduction of Ar′SnCl or Ar*SnCl afforded the neutral Ar′SnSnAr′, 8, or Ar*SnSnAr*, 9, the radical anions
[(THF)3Na{Ar*SnSnAr*}], 10, [K(THF)6][Ar′SnSnAr′], 11, [K(THF)6][Ar*SnSnAr*], 12, [K(18-crown-6)(THF)2]
[Ar*SnSnAr*], 13, or the doubly reduced Na2Ar*SnSnAr*, 14, K2Ar′SnSnAr′, 15, or K2Ar*SnSnAr*, 16. The
compounds were characterized by UV-vis, 1H and 13C NMR or EPR spectroscopy. The X-ray crystal
structures of all compounds were determined except those of 2 and 9. The neutral 1 and 8 displayed
planar, trans-bent CMMC (M ) Ge and Sn) cores with M-M-C angles of 128.67(8) and 125.24(7)°,
respectively. The M-M bond lengths, 2.2850(6) and 2.6675(4)Å, indicated considerable multiple character
and a bond order approaching two. Single and double reduction of the neutral species resulted in the
narrowing of the M-M-C angles by ca. 12-32° and changes in the Ge-Ge and Sn-Sn bond lengths.
One-electron reduction afforded a slight (ca. 0.03-0.05Å) lengthening of the Ge-Ge bonds in the case of
germanium species 3 and 4 and a greater lengthening (ca. 0.13-0.15Å) for the Sn-Sn bonds in the tin
compounds 10-13. The addition of another electron yielded salts of the formal dianions [Ar′MMAr′]2- and
[Ar*MMAr*]2- which are isoelectronic to the corresponding doubly bonded, neutral arsenic and antimony
derivatives. All the dianion salts were obtained as contact ion triples with two alkali metal cations complexed
between aryl rings. The Ge-Ge bonds in the dianions of 5-7 were longer, whereas the Sn-Sn distances
in the dianions in 14, 15, and 16 were shorter than those in the monoanions. Unusually, the Li2Ar′GeGeAr′
salt, 5, displayed a longer Ge-Ge bond (by ca. 0.06Å) than those of its Na+ or K+ analogue salts which
was attributed to the greater polarizing power of Li+. It was concluded that the M-M bond lengths in 3-7
and 10-16 are dependent on several factors that include M-M-C angle, Coulombic repulsion, alkali metal
cation size, and the character of the molecular energy levels. The M-M bonding in the neutral compounds
was accounted for in terms of a second-order Jahn-Teller mixing of σ*- and a π-orbital which afforded
bond orders near two for the neutral compounds, 1, 2, 8, and 9. Calculations on MeMMMe (M ) Ge or Sn)
model species showed that the LUMO corresponded to an orbital that had n+ lone pair character. The
slight Ge-Ge bond length increase upon one-electron reduction is consistent with these results, and the
further bond lengthening upon double reduction is consistent with increased Coulombic repulsion. The
greater Sn-Sn bond length increase seen for one-electron reduction of the tin species is probably due to
the increased p-character of orbitals comprising the Sn-Sn σ-bond when the Sn-Sn-C angle is decreased
by ca. 30°. Upon further reduction, the slight decrease in the Sn-Sn bond is probably a result of the reduced
importance of Coulombic repulsion due to the larger size of tin and a widening of the Sn-Sn-C angles
which may shorten the Sn-Sn σ-bond.
Introduction
characterization of such compounds is of fundamental impor-
tance because of the enhanced understanding they provide on
the bonding among such elements. In particular, the availability
of stable heavier group 14 alkyne analogues allows the
differences between the bonding in carbon and the heavier
elements to be explored experimentally in a novel way. These
The synthesis of stable heavier group 14 element analogues
of alkynes has proven to be a considerable synthetic challenge1,2
that has been partially overcome recently by the synthesis of
germanium,3 tin,4 and lead5 derivatives.6 The synthesis and
(1) Jutzi, P. Angew. Chem., Int. Ed. 2000, 39, 3797.
(2) Weidenbruch, M. J. Organomet. Chem. 2002, 646, 39.
(3) Stender, M.; Phillips, A. D.; Wright, R. J.; Power, P. P. Angew. Chem.,
Int. Ed. 2002, 41, 1785.
(4) Phillips, A. D.; Wright, R. J.; Olmstead, M. M.; Power, P. P. J. Am. Chem.
Soc. 2002, 124, 5930.
(5) Pu, L.; Twamley, B.; Power, P. P. J. Am. Chem. Soc. 2000, 122, 3524.
9
11626
J. AM. CHEM. SOC. 2003, 125, 11626-11636
10.1021/ja035711m CCC: $25.00 © 2003 American Chemical Society

Ge and Sn Analogues of Alkynes and Reduction Products
A R T I C L E S
from molten Na/K alloy and degassed 3 times prior to use. The
differences, which have their origin in the changing electronic
structure of the atoms, are manifested in molecular energy
patterns and structures that differ considerably from their lighter
counterparts. Initial work in the area resulted in the synthesis
of the singly reduced salts [K(THF)6][Ar*SnSnAr*], 12, and
[K(18-crown-6)(THF)2][Ar*SnSnAr*], 13, by reduction of
Ar*SnCl with potassium.7 The bulky terphenyl Ar* substituent
(Ar* ) C6H3-2,6-Trip2; Trip ) C6H2-2,4,6-Pri3)8 was employed
to stabilize both compounds. Later, the doubly reduced species
Na2Ar*GeGeAr*, 6, and K2Ar*SnSnAr*, 16, were obtained by
reaction of Ar*GeCl or Ar*SnCl for longer periods with excess
alkali metal.9 Both the singly and doubly reduced species
featured a planar, trans-bent CMMC (M ) Ge or Sn) core with
M-M-C angles that did not exceed 107.50(14)°. Further work
showed that the desired neutral species Ar*GeGeAr*, 2,10 and
Ar*SnSnAr*, 9, could also be isolated from these mixtures.
Unfortunately, crystals of these compounds proved unsuitable
for X-ray crystallography. Several different terphenyl ligands
were investigated in order to overcome these crystallographic
problems. Eventually, it was shown that use of the related Ar′
terphenyl substituent (Ar′ ) C6H3-2,6-Dipp2; Dipp ) C6H3-
2,6-Pri2) permitted a detailed examination of the structure of
the first stable germanium and tin alkyne analogues Ar′GeGeAr′,
1, and Ar′SnSnAr′, 8.3,4 We now present a more extensive and
systematic examination of all three classes of compound in
which we compare the effects of the ligands, alkali metal, and
group 14 element on the M-M bonding. The bonding in the
neutral alkyne analogues can be interpreted in terms of second-
order Jahn-Teller σ*-π-orbital mixing11,12 which results in a
diminution of the Ge-Ge and Sn-Sn bond orders from triple
in an idealized linear geometry to approximately double in the
more stable trans-bent geometries that are observed experimen-
tally. The addition of one or two electrons to the neutral
compounds to give singly or doubly reduced species results in
relatively large changes to the trans-bending angles and M-M
bond lengths. Different structural trends are found in the
germanium and tin species which can be explained on the basis
of the larger size and more electropositive character of the tin
atom.
compounds LiAr′,13 Ar*GeCl,14 and Ar*SnCl7,15 were prepared as
1
previously described. H, 13C, and 119Sn NMR spectra were recorded
on Varian 300 and 400 spectrometers and referenced to known
standards. UV-vis data were recorded on a Hitachi-1200 spectrometer,
while infrared data were recorded as Nujol mulls using a Perkin-Elmer
1430 instrument. The EPR spectra 3 and 4 were obtained with use of
a Bruker CWX band spectrometer operating near 9.6 GHz. Melting
points were recorded using a Meltemp apparatus and are uncorrected.
(Ar′GeCl)2 and {Ar′Sn(µ-Cl)}2. To a well stirred ether solution of
GeCl2(dioxane) (0.23 g, 1 mmol) at 0 °C was added LiAr′ (0.404 g, 1
mmol) in ether. The solution was allowed to warm to ambient
temperature during which time it developed an orange color. Stirring
was maintained for 12 h, after which time the solvents were removed
under reduced pressure. The resultant orange powder was extracted
into toluene and filtered. Storage of the solution at ca. -30 °C for 16
h afforded large orange crystals of (Ar′GeCl)2 which were dried under
reduced pressure. Yield: 74%, mp 150-155 °C (dec). 1H NMR (399.8
3
MHz, 25 °C, C6D6): δ 0.99 (d, JHH ) 6.81 Hz, 6H, o-CH(CH3)2),
3
3
1.29 (d, JHH ) 6.81 Hz, 6H, o-CH(CH3)2), 2.72 (sept, JHH ) 6.81
Hz, 8H, o-CH(CH3)2), 7.0-7.25 broad signal, aryl ring hydrogens. 13C-
{1H} NMR (100.5 MHz, 25 °C, C6D6): δ 22.72 (o-CH(CH3)2), 26.15
(o-CH(CH3)2), 31.02 (o-CH(CH3)2), 123.84 (m-Dipp), 128.59 (p-C6H3),
129.88 (m-C6H3), 130.85 (i-Dipp), 142.92 (p-Dipp), 145.97 (o-Dipp),
147.52 (o-C6H3), 167.54 (i-C6H3). In a similar manner, LiAr′ (4.85 g,
12 mmol) in Et2O (40 mL) was added dropwise to a well stirred
suspension of SnCl2 (3.27 g, 17 mmol) in Et2O (20 mL) with cooling
in an ice bath. The reaction mixture became orange. Workup as above
afforded orange crystals of the product {Ar′Sn(µ-Cl)}2 from toluene
(50 mL) at ca. -25 °C. Yield: 5.75 g, 87%, mp 156-159 °C. 1H NMR
3
(399.8 MHz, 25 °C, C6D6): δ 1.03 (d, JHH ) 6.80 Hz, 6H, o-CH-
(CH3)2), 1.31 (d, 3JHH ) 6.80 Hz, 6H, o-CH(CH3)2), 3.06 (sept, 3JHH
)
6.80 Hz, 4H, o-CH(CH3)2), 7.15 (s, 4H, m-Dipp), 7.24 (m, 4H, p-Dipp,
m-C6H3), 7.27 (m, 1H, p-C6H3). 13C{1H} NMR (100.5 MHz, 25°C,
C6D6): δ 23.47 (o-CH(CH3)2), 26.62 (o-CH(CH3)2), 31.54 (o-CH-
(CH3)2), 124.36 (m-Dipp), 128.18 (p-C6H3), 129.98 (m-C6H3), 131.08
(i-Dipp), 137.72 (p-Dipp), 145.76 (o-Dipp), 148.15 (o-C6H3), 181.95
(i-C6H3). 119Sn{1H} NMR (149.18 MHz, 25 °C, C6D6): δ 817.
Ar′GeGeAr′ (1) and Ar*GeGeAr* (2). At ambient temperature, a
solution of Ar′GeCl (0.79 g, 1.56 mmol) in THF (10 mL) was added
dropwise to finely divided potassium suspended in THF (30 mL) under
vigorous stirring. After ca. 2 h, the reaction mixture began to turn red,
and upon stirring for 56 h, the solution had become deep red. The THF
was removed under reduced pressure, and the red solid residue was
redissolved in hexane (30 mL). The potassium chloride precipitate and
any remaining potassium was allowed to settle whereupon the
supernatant solution was removed by decantation. The deep red solution
was then concentrated to incipient crystallization (ca. 15 mL). Storage
at 5 °C for 12 h yielded the product 1 as carmine/red-orange crystals.
Yield: 0.28 g, 0.3 mmol, 39%, mp 214-216 °C (turns dark red/black
after melting). 1H NMR (C6D6, 399.77 MHz, 25 °C): δ 1.05 (d, 3JH,H
Experimental Section
General Procedures. All manipulations were carried out by using
modified Schlenk techniques under an atmosphere of argon or N2 or
in a Vacuum Atmospheres HE-43 drybox. All solvents were distilled
(6) The existence of alkyne-like transient species such as MeSiSiMe,a 2,6-
Mes2H3C6SiSiC6H3-2,6-Mes2,b R*SiSiR* (R* ) SiBut3),c (R2*MeSi)SiSi-
f
(SiMeR2*),d HCSiX (X ) F or Cl),e and Me3SiCGeC6H3-2,6(CH2NPri2)2
has been indicated by several experiments. In addition, the mono and di-
3
hydrogen bridged species HSi(µ-H)Sig and Si(µ-H)2Sih have been structur-
ally characterized by submillimeter spectroscopy. (a) Sekiguchi, A.; Zigler,
S. S.; West, R. J. Am. Chem. Soc. 1986, 108, 4241. (b) Pietschnig, R.;
West, R.; Powell, D. R. Organometallics 2000, 19, 2724. (c) Wiberg, N.;
Finger, C. M. M.; Polborn, K. Angew. Chem., Int. Ed. Engl. 1993, 32,
1054. (d) Wiberg, N.; Niedermayer, W.; Fischer, G.; No¨th, H.; Sutin, M.
Eur. J. Inorg. Chem. 2002, 1066. (e) Karni, M.; Apeloig, Y.; Schro¨der,
D.; Zummack, W.; Rabezzana, R.; Schwarz, H. Angew. Chem., Int. Ed.
1999, 38, 332. (f) Bibal, C.; Mazieres, S.; Gornitzka, C.; Couret, C. Angew.
Chem., Int. Ed. 2001, 40, 952. (g) Cordonnier, M.; Bogey, M.; Demuynck,
C.; Destombes, J. L. J. Chem. Phys. 1992, 97, 7984. (h) Bogey, M.; Bolvin,
H.; Demuynck, C.; Destombes, J. L. Phys. ReV. Lett. 1991, 66, 413.
(7) Olmstead, M. M.; Simons, R. S.; Power, P. P. J. Am. Chem. Soc. 1997,
119, 11705.
(8) Twamley, B.; Haubrich, S. T.; Power, P. P. AdV. Organomet. Chem. 1999,
441. Clyburne, J. A. C.; McMullen, N. Coord. Chem. ReV. 2000, 210, 73.
(9) Pu, L.; Senge, M. O.; Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc.
1998, 120, 12682.
(10) Stender, M.; Phillips, A. D.; Power, P. P. Chem. Commun. 2002, 1312.
(11) Bader, R. F. W. Can. J. Chem. 1962, 40, 1164.
(12) Grev, R. S. AdV. Organomet. Chem. 1991, 33, 125.
) 6.8 Hz, 24H, o-CH(CH3)2), 1.30 (d, JH,H ) 6.8 Hz, 24H, o-CH-
(CH3)2), 2.72 (sept, 3JH,H ) 6.8 Hz, 8H, o-CH(CH3)2), 6.91 (d, 3JH,H
)
3
7.2 Hz, 4H, m-C6H3), 7.09 (d, JH,H ) 8.0 Hz, 8H, m-Dipp), 7.18 (t,
3JH,H ) 7.2 Hz, 2H, p-C6H3), 7.29 (t, 3JH,H ) 8.0 Hz, 4H, p-Dipp). 13
C
{1H} NMR (C6D6, 100.59 MHz, 25 °C): δ ) 25.59 (o-CH(CH3)2),
26.06 (o-CH(CH3)2), 31.59 (o-CH(CH3)2), 124.58 (m-Dipp), 127.28 (p-
C6H3), 130.024 (m-C6H3), 141.36 (p-Dipp), 145.67 (i-Dipp), 146.81
(i-C6H3), 147.29 (o-Dipp), 158.76 (o-C6H3). IR (Nujol): 1925(w), 1885-
(w), 1590(w), 1570(2), 1550(w), 1325(sh), 1055(m), 750(m), 450(w),
320(w) cm-1. UV-vis (hexanes): λmax, (ε, L mol-1 cm-1): 501 nm
(7500), 371 nm (34 000, sh), 280 nm (28000). In a similar manner,
(13) Schiemenz, B.; Power, P. P. Angew. Chem., Int. Ed. Engl. 1996, 35, 2150.
(14) Pu, L.; Olmstead, M. M.; Power, P. P.; Schiemenz, B. Organometallics
1998, 17, 5602.
(15) Eichler, B. E.; Pu, L.; Stender, M.; Power, P. P. Polyhedron 2001, 20,
556.
9
J. AM. CHEM. SOC. VOL. 125, NO. 38, 2003 11627

A R T I C L E S
Pu et al.
reduction of Ar*GeCl (1.68 g, 2.85 mmol) in THF (60 mL) with
potassium 0.112 g (2.85 mmol) at room temperature for 56 h, followed
by standard work and recrystallization from hexane, afforded
Ar*GeGeAr* 2 as red crystals. Yield: 0.55 g, 35%, 0.5 mmol, mp
244-246 °C (darkens above 200 °C, remains glassy after melting and
cooling). Anal. Calcd for C36H49Ge: C 70.00, H 8.91. Found: C 78.36,
Yield: 0.38 g, 0.33 mmol, 30.1%, mp 234-236 °C. 1H NMR (C6D6):
δ 1.11 (d, 24H, 3JHH ) 6.9 Hz, p-CH(CH3)2), 1.29 (d, 48H, 3JHH ) 6.9
Hz, o-CH(CH3)2), 2.92 (sept, 4H, JHH ) 6.9 Hz, p-CH(CH3)2), 3.60
3
(sept, 8H, 3JHH ) 6.9 Hz, o-CH(CH3)2), 6.93 (m, 6H, p-C6H3, overlap),
7.04 (s, 8H, m-Trip). 13C{1H} NMR (C6D6): δ 23.67 (o-CH(CH3)2),
24.17 (p-CH(CH3)2), 25.56 (o-CH(CH3)2), 30.810 (o-CH(CH3)2), 34.15
(p-CH(CH3)2), 120.58 (m-Trip), 121.50 (m-C6H3), 128.52 (o-C6H3),
142.09 (i-Trip), 145.38 (p-C6H3), 147.27 (p-Trip), 148.32 (o-Trip),
176.16 (i-C6H3). λmax (ε, L mol-1 cm-1): 601 (1900), 464 (4200).
1
H 8.80. H NMR (C6D6): δ (ppm) 6.93 (s, 8H, m-Trip), 2.95 (sept,
3
3
4H, p-CH(CH3)2, J ) 6.8 Hz), 2.75 (sept, 4H, o-CH(CH3)2, J ) 6.8
3
Hz), 1.38 (d, 12H, o-CH(CH3)2, J ) 7.2 Hz), 1.30 (d, 12H, o-CH-
(CH3)2, J ) 7.2 Hz), 1.09 (d, 12H, p-CH(CH3)2, J ) 7.2 Hz). 13C
NMR (C6D6): δ (ppm) 156.8 (i-C6H3), 148.6 (o-C6H3), 146.1 (o-Trip),
139.1 (p-Trip), 128.6 (i-Trip), 128.2 (m-C6H3), 127.5 (p-C6H3), 121.7
(m-Trip), 34.6 (p-CH(CH3)2), 31.3 (o-CH(CH3)2), 25.7 (o-CH(CH3)2),
25.4 (o-CH(CH3)2), 24.4 (o-CH(CH3)2); UV-vis (toluene): λmax, nm
(ε, L mol-1 cm-1) ) 365 (31 000, sh), 490 (5500).
3
3
K2Ar*GeGeAr* (7). Ar*GeCl (1.00 g, 1.70 mmol) in benzene (20
mL) was added to finely divided potassium (0.35 g, 8.95 mmol) in
benzene (10 mL) at room temperature with stirring. The reaction
mixture was stirred for an additional 24 h, and the resulting deep
greenish-red solution was filtered. The filtrate was reduced to incipient
crystallization (ca. 12 mL) and stored in a ca. 6 °C refrigerator to yield
7 as red crystals. Yield: 0.48 g, 0.40 mmol, 47%, mp 232-233 °C.
NaAr*GeGeAr* (3). An ice cold, green solution of sodium (0.042
g, 1.83 mmol) and naphthalene (0.24 g, 1.87 mmol) in THF (25 mL)
was added dropwise to a rapidly stirred solution of Ar*GeCl (0.78 g,
1.32 mmol) in THF (10 mL) with cooling in a dry ice bath. The reaction
mixture became red and was allowed to warm to room temperature.
Upon stirring for 24 h, the solvent was stripped off and the residue
was warmed (40 °C) under reduced pressure in the presence of a
coldfinger to remove the naphthalene. The remaining solid was extracted
with hexane (40 mL). The solution was allowed to settle, and the
supernatant liquid was decanted. Reduction of the volume to ca. 20
mL under reduced pressure, and storage of the solution in a 6 °C
refrigerator for several days, afforded the product 3 as orange-red
crystals. Yield: 0.99 g, 0.58 mmol, 64%, mp 223-225 °C. Anal. Calcd
for C72H88Ge2Na: C, 76.41; H, 8.72. Found: C, 76.89; H, 8.98. UV-
vis(hexane) λmax, nm (ε, L mol-1 cm-1): 703 (1400), 598 (1500).
KAr′GeGeAr′ (4). At room temperature, a THF (30 mL) solution
of Ar′GeCl (1 mmol, 0.506 g) was added dropwise to a THF suspension
of molten potassium (0.059 g, 1.5 mmol). Stirring was maintained until
all the potassium was consumed, after which time the THF was removed
under reduced pressure. The deep red colored powder was extracted
into hexanes (50 mL), and the resultant dark red solution was filtered.
Storage at ca. -20 °C for 24 h afforded the product 4 as red crystals
suitable for X-ray crystallography. Anal. Calcd for C60H74Ge2K: C
73.57, H 7.60. Found: C 72.1, H 7.61. UV-vis (benzene): λmax, nm
(ε, L mol-1 cm-1): 698 (1500), 590 (1300). Yield: 0.152 g, 0.15 mmol,
31%, mp 74-76 °C.
3
1H NMR (C6D6): δ 1.13 (d, 24H, JHH ) 6.8 Hz, o-CH(CH3)2), 1.17
3
3
(d, 24H, JHH ) 6.8 Hz, o-CH(CH3)2), 1.32 (d, 24H, JHH ) 6.8 Hz,
p-CH(CH3)2) , 2.68 (sept, 4H, 3JHH ) 6.8 Hz, p-CH(CH3)2), 3.78 (sept,
8H, JHH ) 6.8 Hz, o-CH(CH3)2), 6.85-6.95 (mult, 6H, m, p-C6H3),
3
6.96 (s, 8H, m-Trip). 13C {1H} NMR (C6D6): δ 24.26 (o-CH(CH3)2),
24.61 (p-CH(CH3)2), 25.00 (o-CH(CH3)2), 30.85 (o-CH(CH3)2), 34.49
(p-CH(CH3)2), 120.64 (m-Trip), 120.81 (m-C6H3), 129.15 (o-C6H3),
142.68 (i-Trip), 147.44 (p-C6H3), 147.54 (p-Trip), 149.65 (o-Trip),
177.63 (i-C6H3). UV-vis (hexane) λmax (ε, L mol-1 cm-1): 605 (1700),
470 (4600).
Ar′SnSnAr′ (8) and Ar*SnSnAr* (9). A benzene solution (50 mL)
of Ar′SnCl (1.21 g, 2.2 mmol) was added dropwise to finely divided
potassium (0.086 g, 2.2 mmol) in benzene (10 mL) at room temperature.
The reaction mixture was stirred for 3 days, after which time the
precipitate was allowed to settle for 4 h. The intensely dark blue-green
solution was decanted from the precipitated solid. The volume of the
solution was reduced to incipient crystallization and stored in a ca. 6
°C refrigerator to give the product 1 as purple crystals. Yield: 0.31 g,
0.30 mmol, 32.2%. mp 208-10 °C (dec). UV-vis (hexanes) λmax (ε,
L mol-1 cm-1) 410 (2000), 597 (1700). 1H NMR (C6D6, 399.77 MHz,
3
3
25 °C): δ 1.13 (d, 24H, J ) 6.0 Hz, o-CH(CH3)2), 1.39 (d, 24H, J
3
) 6.0 Hz, o-CH(CH3)2), 2.87 (sept, 8H, J ) 6.0 Hz, o-CH(CH3)2),
6.22 (t, 2H, 3J ) 7.2 Hz, p-C6H3), 7.05 (d, 8H, 3J ) 7.2 Hz, m-Dipp),
7.19 (t, 4H, 3J ) 7.2 Hz, p-Dipp), 7.51 (d, 4H, 3J ) 7.2 Hz, m-C6H3).
13C {1H} NMR (C6D6, 100.53 MHz, 25 °C): δ 27.44 (o-CH(CH3)2),
32.67 (o-CH(CH3)2), 34.98 (o-CH(CH3)2), 124.55 (p-C6H3), 125.94 (m-
Dipp), 130.65 (m-C6H3), 131.68 (i-Dipp), 141.72 (p-Dipp), 150.84 (o-
Dipp), 153.98 (i-C6H3), 159.02 (o-C6H3). 119Sn NMR (C6D6, 149.00
MHz, 25 °C): δ no signal observed. In a similar manner, Ar*SnCl
(1.202 g, 1.89 mmol) in toluene (50 mL) was added to a stirred
suspension of finely divided potassium (0.078 g, 2 mmol) in toluene
(25 mL) at room temperature. The solution was stirred for 3 d during
which time the color changed to dark greenish blue. The mother liquor
was decanted from the settled precipitates, and the volume was reduced
to ca. 20 mL. Storage of the solution at -25 °C for 1 week resulted in
deposition of very air and moisture sensitive dark blue-green crystals
of 9. Anal. Calcd for C36H49Sn: C, 72.00; H, 8.22. Found: C, 72.91;
H, 8.41. Yield: 42%, 0.480 g, 0.40 mmol,, mp 134-138 °C (dec) to
red solid. UV-vis (hexane) λmax (ε, L mol-1 cm-1) 409 (1800), 593
(1400). 1H NMR (399.8 MHz, 25 °C, C6D6) δ 1.14 (d, 3JHH ) 6.4 Hz,
Li2Ar′GeGeAr′ (5). To a suspension of lithium powder (0.07 g, 10
mmol) in diethyl ether (10 mL) was added dropwise an ether solution
of Ar′GeCl (0.54 g, 1 mmol) at room temperature. Immediately, the
solution assumed a red color. After stirring for 16 h, the solution
developed a deep brown color. Removal of the excess lithium by
filtration and concentration of the ether solution afforded large dark
red, almost black crystals of 5. Yield: 0.10 g, 0.11 mmol, 21%, mp
171-173 °C. 1H NMR (C6D6, 399.7 MHz, 25 °C): δ 1.052 (d, 3JHH
6.8 Hz, 24H, o-CH(CH3)2), 1.241 (d, 3JHH ) 6.8 Hz, 24H, o-CH(CH3)2),
)
3
3
2.824 (sept, JHH ) 6.8 Hz, 18H, o-CH(CH3)2), 6.967 (d, JHH ) 7.2
3
3
Hz, 4H, m-C6H3), 7.11 (d, JHH ) 8.0 Hz, 8H, m-Dipp), 7.15 (t, JHH
) 7.2 Hz, 4H, p-C6H3), 7.233 (t, JHH ) 8.0 Hz, 4H, p-Dipp). 13C {1H}
NMR (C6D6, 100.59 MHz, 25 °C) δ 24.157 (o-CH(CH3)2), 23.271 (o-
CH(CH3)2), 30.567 (o-CH(CH3)2), 122.667 (m-Dipp), 126.517 (p-C6H3),
131.251 (m-C6H3), 139.509 (p-Dipp), 146.610 (i-Dipp), 146.693 (o-
Dipp), 148.292 (o-C6H3) (i-C6H3 carbon was not observed). Li {1H}
NMR (C6D6), δ -2.206 (s). UV-vis (benzene): λmax, nm (ε, L mol-1
cm-1): 430 (3400), 570 (1500).
7
3
3
o-CH(CH3)2), 1.15 (d, JHH ) 6.4 Hz, o-CH(CH3)2), 1.23 (d, JHH
)
6.4 Hz, o-CH(CH3)2), 1.30 (d, 3JHH ) 6.2 Hz, p-CH(CH3)2), 2.84 (sept,
3JHH ) 6.4 Hz, o-CH(CH3)2), 2.96 (sept, 3JHH ) 6.4 Hz, o-CH(CH3)2),
3.05 (sept, 3JHH ) 6.2 Hz, p-CH(CH3)2), 3.97 (t, 3JHH ) 7.6 Hz, p-C6H3),
7.00 (s, m-Trip), 8.65 (d, 3JHH ) 7.6 Hz, m-C6H3). 13C{1H} NMR (100.5
MHz, 25°C, C6D6) δ 23.06 (o-CH(CH3)2), 24.66 (o-CH(CH3)2), 28.05
(p-CH(CH3)2), 29.45 (p-CH(CH3)2), 32.49 (o-CH(CH3)2), 112.54 (p-
C6H3), 119.35 (m-C6H3), 122.84 (m-Trip), 145.45 (o-C6H3), 147.02 (i-
Trip), 149.80 (o-Trip), 155.96 (p-Trip), 188.84 (i-Trip), 188.84 (i-C6H3).
119Sn{1H} NMR (149.51 MHz, 25 °C, C6D6) δ no signal observed.
Na2Ar*GeGeAr* (6). Ar*GeCl (1.29 g, 2.19 mmol) in benzene (20
mL) was added to finely divided sodium (0.30 g, 13.05 mmol) in
benzene (10 mL) at room temperature with stirring. The reaction
mixture was stirred for an additional 24 h at room temperature, and
the resulting deep red solution was filtered. The filtrate was reduced
to incipient crystallization (ca. 12 mL) under reduced pressure and
stored in a ca. 6 °C refrigerator to yield the product 6 as red crystals.
9
11628 J. AM. CHEM. SOC. VOL. 125, NO. 38, 2003

Ge and Sn Analogues of Alkynes and Reduction Products
A R T I C L E S
[(THF)3Na{Ar*SnSnAr*}] (10). An ice-cold, blue solution of
sodium (0.031 g, 1.35 mmol) and anthracene (1.35 mmol, 0.178 g) in
THF (35 mL) was added dropwise to a rapidly stirred solution of
Ar*SnCl (0.84 g, 1.32 mmol) in THF (20 mL) which was cooled in a
dry ice bath. The reaction mixture became orange-brown and was
allowed to warm to room temperature. Upon stirring for 24 h, the
solvents were stripped off and the residue was warmed (50 °C) under
reduced pressure for 20 h in the presence of a coldfinger to remove
the anthracene. The remaining material was extracted with pentane (40
mL). The solution was allowed to settle and the supernatant liquid was
filtered through Celite. Reduction of the volume to ca. 20 mL under
reduced pressure, and storage of the solution in a ca. -20 °C freezer
for several days afforded the product 2 as orange-red crystals. Yield:
0.35 g, 36%. Calcd for C84H122NaO3Sn2: C, 70.05, H, 8.54. Found: C
) 70.96, H ) 8.19. UV-vis(hexane) λmax, nm (ε, L mol-1 cm-1): 709
(140).
Hz, 4H, m-C6H3), 7.15 (t, 3JHH ) 7.60 Hz, 4H, p-Dipp). 13C{1H} NMR
(100.5 MHz, 25 °C, C6D6): δ 24.18 (o-CH(CH3)2), 24.30 (o-CH(CH3)2),
30.60 (o-CH(CH3)2), 122.71 (m-Dipp), 128.26 (p-Dipp), 133.28 (m-
C6H3), 134.24 (p-C6H3), 139.54 (i-Dipp), 140.93 (o-C6H3), 146.71 (o-
Dipp), not observed (i-C6H3). 119Sn{1H} NMR (149.53 MHz, 25 °C,
C6H6): δ no signal observed. In a manner similar to the synthesis of
15, 7 (1.2 g, 1.9 mmol) in benzene (20 mL) was added to finely divided
potassium (0.45 g, 11.4 mmol) in benzene (10 mL) at room temperature
and stirred for 16 h. The dark red solution was evaporated to dryness,
and the residue was extracted with toluene (40 mL) and filtered. The
filtrate was reduced to incipient crystallization (ca. 15 mL) and stored
in a ca. 6 °C refrigerator to yield 16 as dark red crystals. Yield: 0.43
g, 30%, mp 228-230 °C. 1H NMR (C6D6, 60 °C): δ 1.02 (d, 6H, 3JHH
3
) 6.9 Hz, p-CH(CH3)2), 1.11 (d, 6H, JHH ) 6.9 Hz, p-CH(CH3)2),
1.16 (d, 6H, 3JHH ) 6.9 Hz, p-CH(CH3)2), 1.19 (d, 6H, 3JHH ) 6.6 Hz,
3
o-CH(CH3)2), 1.30 (d, 6H, JHH ) 6.9 Hz, o-CH(CH3)2), 1.41 (d, 6H,
3
3JHH ) 6.9 Hz, o-CH(CH3)2), 2.76 (sept, 1H, JHH ) 6.9 Hz,
[K(THF)6][Ar′SnSnAr′] (11). A dark green solution of Ar′SnSnAr′
(8) (1.033 g, 1 mmol) in THF (50 mL) was added to a suspension of
finely divided potassium (0.196 g, 5 mmol). The solution was stirred
for 2 d by which time the color had darkened slightly. The suspended
excess potassium and KCl were allowed to settle, and the solution was
decanted and reduced in volume to incipient crystallization. Storage in
a ca. -25 °C freezer yielded the product 11‚THF as highly air and
moisture sensitive dichroic green-orange crystals. Yield: 0.504 g, 0.32
mmol, 32%, mp 152-164 °C (dec). Anal. Calcd for C84H122KO6Sn2:
C, 67.06; H 8.18. Found: C, 68.01; H 8.23. UV-vis (THF) λmax, nm
(ε, L mol-1 cm-1): 461 (1900).
o-CH(CH3)2), 2.89 (sept, 1H, 3JHH ) 6.9 Hz, o-CH(CH3)2), 2.92 (sept,
3
3
2H, JHH ) 6.9 Hz, p-CH(CH3)2), 3.06 (sept, 1H, JHH ) 6.9 Hz,
3
o-CH(CH3)2), 3.24 (sept, 1H, JHH ) 6.9 Hz, o-CH(CH3)2), 6.82 (t,
3
1H, JHH ) 3.2 Hz, p-C6H3). 13C {1H} NMR (C6D6): δ 23.83 (o-CH-
(CH3)2), 24.43 (p-CH(CH3)2), 24.57 (o-CH(CH3)2), 25.75 (p-CH(CH3)2),
30.63 (o-CH(CH3)2), 34.24 (p-CH(CH3)2), 34.98 (o-CH(CH3)2), 120.49
(m-Trip), 130.42, 132.22 (m-C6H3), 141.45, 141.51 (o-C6H3), 146.62,
146.98 (i-Trip), 147.07, 147.22 (p-C6H3), 148.35, 148.44 (o-Trip),
150.18 (p-C6H3), 169.80 (i-C6H3). UV-vis (toluene) λmax, nm (ε, L
mol-1 cm-1): 552 (3200), 412 (4200).
X-ray Crystallographic Studies. The samples were prepared by
removing the crystal from the Schlenk tube under a rapid flow of Argon
and immediately submerging it in hydrocarbon oil. A suitable crystal
was selected, mounted on a glass fiber attached to a copper pin, and
rapidly placed in the cold stream of N2 of the diffractometer for data
collection.16 Data were collected at 90 K (Ar′GeCl, Ar′SnCl, 4, 5, 15)
on a Bruker SMART 1000 diffractometer or at 140 K (11 and 14) on
a Simens R3m/V with use of Mo KR (λ ) 0.710 73Å) radiation and a
CCD area detector. Data for 3 and 7 were collected at 130 K on a
Siemens R3m/V diffractometer with Cu KR (λ ) 1.541 78Å) radiation.
Empirical absorption corrections were applied using SADABS17a or
XABS (3, 7, 11, 14).17b The crystal structures were solved with use of
either direct methods or the Patterson option in SHELXS18 and refined
by the full-matrix least-squares procedure in SHELXL.18 All non-
hydrogen atoms were refined anisotropically while hydrogens were
placed at calculated positions and included in the refinement using a
riding model. A number of the structures, (Ar′GeCl)2‚PhMe, 3‚
0.5hexane, 11‚2THF, 14‚3C6H6, and 15‚1.5C6H6 contained disordered
solvent molecules which could be satisfactorily refined with use of
partial occupancies. Hydrogen atoms were not added to these molecules.
Some details of the data collection and refinement are given in Table
1. Further details are in the Supporting Information.
[K(THF)6][Ar*SnSnAr*] (12) and [K(12-crown-6)(THF)2][Ar*-
SnSnAr*] (13). Ar*SnCl (1.00 g, 1.57 mmol) and KC8 (0.21 g, 1.54
mmol) in THF (20 mL) were stirred rapidly at room temperature for 2
h. All volatile materials were removed under reduced pressure, and
the residue was extracted with a THF/toluene, 3:1 mixture (30 mL)
and rapidly filtered through Celite. The dark red solution was
concentrated to incipient crystallization and stored in a ca. -20 °C
freezer for 2 days to afford the product 12 as orange-green dichroic
crystals. Yield: 0.36 g, 0.22 mmol, 27%, mp 120 °C (dec). Anal. Calcd
for C96H146KO6Sn2: C, 68.92; H, 8.80. Found C, 68.13; H, 8.97. The
compound 13‚2THF was obtained similarly except that dibenzo-18-
crown-6 was included in the reaction mixture. The product 13‚2THF
was obtained in 22% yield, mp 125 °C (dec).
Na2Ar*SnSnAr* (14). In a manner similar to the preparation of 6,
Ar*SnCl (2.00 g, 3.14 mmol) in benzene (40 mL) was added to finely
divided sodium (0.50 g, 21.75 mmol) in benzene (10 mL). The solution
was stirred for 24 h and filtered to afford a dark red, almost black
solution which was reduced to incipient crystallization (ca. 25 mL).
Storage in a ca. 6 °C refrigerator for 24 h afforded 14 as red crystals.
1
3
Yield: 1.65 g, 37.1%. H NMR (C6D6, 17.6 °C): δ 1.13 (d, 6H, JHH
3
) 6.6 Hz, o-CH(CH3)2), 1.19 (d, 6H, JHH ) 4.5 Hz, o-CH(CH3)2),
3
3
1.21 (d, 6H, JHH ) 4.5 Hz, o-CH(CH3)2), 1.28 (d, 12H, JHH ) 6.9
Hz, p-CH(CH3)2), 1.35 (d, 6H, 3JHH ) 6.9 Hz, o-CH(CH3)2), 2.97 (sept,
Results and Discussion
3
8H, JHH ) 7.2 Hz, o-CH(CH3)2), 3.59 (br, 4H, p-CH(CH3)2), 6.91-
Precursors. Ar′MCl (M ) Ge or Sn). All compounds
discussed in this paper are derivatives of the sterically crowded
terphenyl ligands Ar′ and Ar* as illustrated by
7.20 (mult, 10H, aromatic region).
K2Ar′SnSnAr′ (15) and K2Ar*SnSnAr* (16). A solution of
Ar′SnSnAr′ (8) (1.033 g, 1 mmol) in benzene (30 mL) was added
dropwise to a suspension of finely divided potassium (0.469 g, 12
mmol). The solution was stirred for 5 days, by which time the color
had changed from dark green to dark red. The suspended solids were
allowed to settle, and the supernatant solution was decanted and reduced
in volume to incipient crystallization. Storage at room temperature for
4 h yielded the product as highly air and moisture sensitive dark red
crystals. Yield: 26%, 0.289 g, 0.26 mmol, mp 141-163 °C (dec). UV-
vis(benzene) λmax, nm (ε, L mol-1 cm-1): 408 (3900), 556 (2200), 875
1
3
(152). H (399.8 MHz, 25 °C, C6D6): δ 0.970 (d, JHH ) 6.80 Hz,
12H, o-CH(CH3)2), 0.984 (d, 3JHH ) 6.80 Hz, 12H, o-CH(CH3)2), 2.75
(sept, 3JHH ) 6.80 Hz, 4H, o-CH(CH3)2), 6.91 (d, 3JHH ) 7.60 Hz, 8H,
3
3
m-Dipp), 7.02 (t, JHH ) 8.00 Hz, 2H, p-C6H3), 7.06 (d, JHH ) 8.00
9
J. AM. CHEM. SOC. VOL. 125, NO. 38, 2003 11629

A R T I C L E S
Pu et al.
The synthesis of compounds 1-16 involved the reduction
of the aryl element halide precursors Ar′MCl or Ar*MCl (M )
Ge or Sn) with an alkali metal. The synthesis and properties of
the precursors Ar*MCl (M ) Ge14 or Sn15) have been described
previously. The Ar′MCl species were synthesized in a similar
manner by the straightforward reaction of 1 equiv of LiAr′13
with GeCl2‚dioxane or SnCl2. They were isolated as orange
crystals and have physical properties similar to their Ar*
substituted analogues. Their structures, however, show unex-
pected differences which can be attributed to the slightly smaller
size of the Ar′ ligand. Ar′GeCl crystallizes from toluene as Ge-
Ge bonded dimers (Ar′GeCl)2 as illustrated in Figure 1. The
structure has a centrosymmetric, trans-pyramidal ClCGeGeCCl
core with Ge(1)-Ge(1A), Ge(1)-C(1), and Ge(1)-Cl(1) dis-
tances of 2.4624(4), 1.976(2), and 2.2167(5) Å, respectively.
The Ge-Ge bond length may be compared with those previ-
ously published for (Ar*GeCl)2 (Ge-Ge ) 2.363(2) Å)14 and
(2,6-Mes2H3C6GeCl)2 (Ge-Ge ) 2.443(2) Å).19 Unexpectedly,
the Ge-Ge distance in the Ar′GeCl dimer is the longest of the
three compounds. Furthermore, the coordination geometry at
germanium is the most pyramidal (Σ° Ge ) 327.82°), and the
out-of-plane angle (38.8°, i.e., the angle between the Ge-Ge
bond and the GeCCl plane) is very similar to the 39.0° in the
least crowded derivative 2,6-Mes2H3C6GeCl. As in the structure
of 2,6-Mes2H3C6GeCl,19 part of the explanation of the long Ge-
Ge distance lies in the relatively close contacts between
germanium and a flanking aryl ring (e.g., C(6) (2.822 Å), C(7)
(2.984 Å)) which effectively increase the germanium coordina-
tion number. Such interactions can occur in aryl group 14
element(II) halide derivatives owing to less crowding Ar′ and
C6H3-2,6-Mes2 5 ligands and enhanced Lewis acidity conferred
by the halogen coligand. The interactions are prevented in
(Ar*GeCl)2 by the para Pri groups on the flanking rings which
cause steric conflict that disfavors close Ge‚‚C approaches. The
unusual circumstance whereby para-Pri substituents can exert a
steric effect may also be understood from structures such as 8
and 11 (Figure 1) where, because of configuration of the
terphenyl groups within the molecules, para Pri groups, if they
were present, would be oriented toward each other (see also
the structures of the lithium salts of Ar′ and Ar* for structural
differences due to the absence of para Pri groups).13,14
The Ar′SnCl precursor also has a dimeric structure, {Ar′Sn-
(µ-Cl)]2, which, like {Ar*Sn(µ-Cl)}2, has tins that are bridged
by chlorines. However, the bridging distances in [Ar′Sn(µ-Cl)]2
are significantly longer than those observed for {Ar*Sn(µ-Cl)}2.
The latter has almost equal Sn-Cl distances (2.5768(6) and
2.5978(7) Å) in the Sn2Cl2 core, whereas the corresponding
distances in {Ar′Sn(µ-Cl)}2 are significantly longer at 2.651(1)
and 2.967(1) Å. As in the germanium structure, part of the
explanation for the weaker association of the Ar′SnCl monomers
in close contacts between the tin and carbons (e.g., C(7) (2.999-
(6) Å) and C(2) (3.014(6) Å)) of a flanking aryl ring which
effectively increase the tin coordination number and weaken
the already feeble association even further. The compound exists
as a monomer in hydrocarbon solution as indicated by the 119Sn
(16) Hope, H. Prog. Inorg. Chem. 1995, 41, 1.
(17) (a) SADABS: Area-Detector Absorption Corrections; Bruker AXS Inc.:
Madison, WI, 1996. (b) XABS: Parkin, S.; Moezzi, B.; Hope, H. J. Appl.
Crystallogr. 1995, 28, 53.
1.
(18) SHELXLPC, version 5.03; Bruker AXS Inc.: Madison, WI, 1994.
(19) Simons, R. S.; Pu, L.; Olmstead, M. M.; Power, P. P. Organometallics
1997, 16, 1920.
Table
9
11630 J. AM. CHEM. SOC. VOL. 125, NO. 38, 2003

Ge and Sn Analogues of Alkynes and Reduction Products
A R T I C L E S
Figure 1. Thermal ellipsoid (30%) drawings of the representative structures (Ar′GeCl)2, KAr′GeGeAr′ (4), Li2Ar′GeGeAr′ (5), Ar′SnSnAr′ (8),
[K(THF)6][Ar′SnSnAr′] (11), K2Ar′SnSnAr′ (15). Selected bond distances and angles for these compounds and {Ar′Sn(µ-Cl)}2, 1, 3, 6, 7, 10, 12-14, and
16 are given in Tables 2, 4, and 5.
NMR chemical shift of 817 ppm which is very similar to the
793.4 ppm observed for Ar*SnCl.15
can be minimized, and almost eliminated, by the use of exactly
stoichiometric quantities of alkali metal and stirring for extended
periods (2-3 days). In this way, the desired neutral germanium
and tin alkyne analogues 1, 2, 8, and 9 could be crystallized.
At first, all experiments were carried out with use of the Ar*
substituent,20 and X-ray quality crystals of Ar* substituted
derivatives could be obtained for the mono- and dianions in a
relatively straightfoward manner. But the neutral Ar*GeGeAr*,
2,10 and Ar*SnSnAr*, 9,4 although they appeared to crystallize
well, displayed poor diffraction characteristics and did not
extinguish under polarized light. Experiments with various bulky
terphenyl ligands showed that the use of the related Ar′ ligand,
which differs from Ar* only in that it does not carry para-Pri
Neutral Ar′MMAr′ and Ar*MMAr* (M ) Ge or Sn). The
original objective in the reduction of the Ar′MCl and Ar*MCl
(M ) Ge or Sn) aryl element halides by alkali metals was the
isolation of stable germanium and tin analogues of alkynes.
Initially, however, salts containing the tin radical monoanion
[Ar*SnSnAr*]•- were crystallized with several different coun-
tercations (see below),7 and later, the doubly reduced dianionic
salts K2Ar*GeGeAr*, 7, and Na2Ar*SnSnAr*, 16, were iso-
lated.8 Experiments with stoichiometric quantities of alkali metal
reductant (i.e., a 1:1 ratio of alkali metal:Ar*MCl) showed that
the “overreduced” mono- and dianions were produced in
addition to the neutral species, especially if short (<ca. 4 h)
reaction times were used. The amounts of the charged species
(20) Schiemenz, B.; Power, P. P. Organometallics 1996, 15, 958.
9
J. AM. CHEM. SOC. VOL. 125, NO. 38, 2003 11631

A R T I C L E S
Pu et al.
Table 2. Selected Bond Distances (Å) and Angles (deg) for
(Ar′GeCl)2, {Ar′Sn(µ-Cl)}2, Ar′GeGeAr′ (1), and Ar′SnSnAr′ (8)
that the relatively wide M-M-C angles at germanium and tin
(128.67(8)° and 125.24(7)°) afford a changed σ-hybridization
which could also be a significant factor in shortening the M-C
bonds.
{Ar′GeCl}2
{Ar′Sn(µ-Cl)}2
Ge(1)-Ge(1A)
Ge(1)-C(1)
Ge(1)-Cl(1)
2.4624(4)
1.9758(17)
2.2167(5)
Sn(1)-C(1)
2.225(6)
2.650(1)
2.967(1)
Sn(1)-Cl(1)
The most important structural parameters are, of course, the
trans-bending angles and the M-M distances. The M-M
distances suggest the existence of considerable multiple char-
acter because they are shorter than those expected for normal
single bonds between these elements (cf. 2.44 Å for germanium
and 2.81 Å for tin).24 The Ge-Ge bond length, 2.2850(6) Å,
lies in the lower half of the known range (2.21-2.46 Å) for
digermenes, the digermanium analogues of alkenes.25 It is
shorter than the 2.3173(3) Å observed in the digermene Ar′-
(Me)GeGe(Me)Ar′ 26 which has a similar degree of crowding
to 1. On the basis of the structural evidence, it can be argued
that the bond order in 1 is approximately two. In contrast, the
Sn-Sn bond length in 8, 2.6675(4)Å, is less than the shortest
known Sn-Sn distance in a distannene (i.e., 2.702 Å in
R*(Mes)SnSn(Mes)R* (R* ) Si(SiMe3)3)).27 This should not
be interpreted to imply an Sn-Sn bond order in 8 that is greater
than two because most Sn-Sn bonds in distannenes are known
to be quite weak, and dissociation to monomers is usually
observed in hydrocarbon solutions at room temperature.28 The
Sn-Sn bond distance in 8 is slightly shorter than the 2.68(1) Å
Sn(1)-Cl(1A)
C(1)-Ge(1)-Cl(1)
C(1)-Ge(1)-Ge(1A)
Cl(1)-Ge(1)-Ge(1A)
Ge(1)-C(1)-C(6)
Ge(1)-C(1)-C(6)
C(2)-C(1)-C(6)
102.51(5)
119.51(5)
105.80(2)
111.7(1)
128.5(1)
119.8(2)
C(1)-Sn(1)-Cl(1)
Sn(1)-C(1)-C(2)
Sn(1)-C(1)-C(6)
C(2)-C(1)-C(6)
91.14(7)
109.9(5)
131.6(5)
118.5(6)
Ar′GeGeAr′ (1)
Ar′SnSnAr′ (8)
Ge(1)-Ge(1A)
Ge(1)-C(1)
2.2850(8) Sn(1)-Sn(1A)
1.996(3) Sn(1)-C(1)
2.6675(4)
2.191(3)
Ge(1)-Ge(1A)-C(1A) 128.67(8) Sn(1)-Sn(1A)-C(1A) 125.24(7)
Ge(1)-C(1)-C(2)
Ge(1)-C(1)-C(6)
C(1)-C(2)-C(6)
116.9(2)
124.6(2)
118.5(3)
Sn(1)-C(1)-C(2)
Sn(1)-C(1)-C(6)
C(1)-C(2)-C(6)
124.9(2)
115.8(2)
119.3(2)
groups on the flanking aryl rings, produced similar steric
protection and also afforded crystals that diffracted X-rays
readily. All four neutral compounds (ie., 1, 2, 8, and 9) displayed
considerable thermal stability. The germanium compounds are
a red-orange color, whereas the tin analogues form dark blue-
green solutions and crystals that may also appear purple under
intense illumination. The color of the compounds undergoes
no apparent change when dissolved in hydrocarbons.21 The
UV-visible spectra of the germanium species feature absor-
bances at 371, 501 (1) and 365, 490 nm (2), whereas the
corresponding wavelengths for the tin species 8 and 9 and 410,
597 and 409, 593 nm, respectively. The shift to longer
wavelengths absorptions on descending a group is common in
the electronic spectra of element-element bonded main group
species.22 A disappointing feature of the spectroscopic studies
of the tin species 8 and 9 (and of the dianions 14-16) has been
our inability to detect 119Sn NMR signals. Despite numerous
attempts to record spectra, with use of a variety of parameters,
no signals have been detected so far. We account for this in
terms of the unsymmetric electron environment at tin which
may cause rapid relaxation through the anisotropy of the
chemical shift tensor.23
Data for the structures of 1 and 8 are provided in Table 2.
The structure of 8 is illustrated in Figure 1. In contrast to the
usually linear structure of alkynes, they possess trans-bent planar
CGeGeC or CSnSnC core arrays. It can also be seen that, apart
from the changed M-M distances and M-M-C angles, the
structures are very similar. This similarity extends to the very
low torsion angles between the central phenyl rings of the ligand
and the CMMC array, only 0.4° for the germanium compound
and 3.5° for the tin species. Thus, overlap of the ring orbitals
of π-symmetry and a π-orbital on the dimetal units is allowed
by symmetry in both cases. The Ge-C and Sn-C bond lengths,
however, are not particularly short in comparison to other
terphenyl substituted species. In addition, even if significantly
shortened M-C bonds had been observed, it could be argued
found in the tristannaallene Sn{Sn(SiBut3)2}2 and is longer
29
than the Sn-Sn double bond (2.59(1) Å) in the cyclotristannene
(But3Si)2SnSn(SiBut3)Sn(SiBut3).29 On the basis of these com-
parisons, a bond order between 1.5 and 2.0 can be estimated
for the Sn-Sn bond in 8.
The lower bond orders in 1, 2, 8, and 9 may be accounted
for in terms of a second-order Jahn-Teller effect involving the
mixing of a σ* orbital and the in plane π-orbital upon trans-
bending of the linear skeleton.11,12 This can occur in heavier
element compounds because the bonds are weaker, and hence,
the energy separations between the bonding and antibonding
levels are smaller. In this way, one of the π-orbitals associated
with the M-M bonding in an idealized linear structure becomes
nonbonding by mixing with a σ* orbital upon bending the
geometry, and the bond order is reduced from three to
approximately two. The estimates of the bond orders and the
measured structural parameters may be compared with those
calculated by Bridgeman,30 Nagase31 and co-workers for the
simple model species RMMR (M ) Ge or Sn, R ) H, Me, or
Ph) (Table 3). For the germanium species, the Ge-Ge distance
and Ge-Ge-R angle vary from 2.22 to 2.25 Å and 124°-
118°, and the bond order varies from 2.32 to 1.74. For tin, the
corresponding numbers are 2.65-2.67 Å, 122°-119°, and a
bond order of 1.87-1.73. An independent calculation for
MeGeGeMe afforded the parameters 2.197 Å, 129.7°, and a
(24) Wells, A. F. Structural Inorganic Chemistry, 5th ed.; Clarendon: Oxford,
1984; p 1279.
(25) Escudie, J.; Ranaivonjatovo, H. AdV. Organomet. 1999, 44, 113. Power,
P. P. Chem. ReV. 1999, 99, 3463.
(26) Stender, M.; Pu, L.; Power, P. P. Organometallics 2001, 20, 1820.
(27) Klinkhammer, K. W. Polyhedron 2002, 21, 587. It is not known if
R*(Mes)SnSn(Mes)R* is dissociated in solution however.
(28) Goldberg, D. E.; Hitchcock, P. B.; Lappert, M. F.; Thomas, K. M.; Fjelberg,
T.; Haaland, A.; Schilling, B. E. R. Dalton Trans. 1986, 2387. Zilm, K.
W.; Lawless, G. A.; Merrill, R. M.; Millar, J. M.; Webb, G. G. J. Am.
Chem. Soc. 1987, 109, 7236.
(21) This behavior may be contrasted with that of the group 13 species
Ar′GaGaAr′ which dissociates readily in solution: Hardman, N. J.; Wright,
R. J.; Phillips, A. D.; Power, P. P. J. Am. Chem. Soc. 2003, 125, 2667.
(22) Tokitoh, N.; Arai, T.; Sasamori, T.; Okazaki, R.; Nagase, S.; Uekusa, H.;
Okashi, Y. J. Am. Chem. Soc. 1998, 120, 443.
(23) Eichler, B. E.; Phillips, B. L.; Power, P. P.; Augustine, M. P. Inorg. Chem.
2000, 32, 5444.
(29) Wiberg, N.; Lerner, H.-W.; Vasisht, S.-K.; Wagner, S.; Karaghiosoff, K.;
No¨th, H.; Ponikwar, W. Eur. J. Inorg. Chem. 1999, 1211.
(30) Bridgeman, A. J.; Ireland, L. R. Polyhedron 2001, 20, 2841.
(31) Takagi, N.; Nagase, S. Organometallics 2001, 20, 5498.
9
11632 J. AM. CHEM. SOC. VOL. 125, NO. 38, 2003

Ge and Sn Analogues of Alkynes and Reduction Products
A R T I C L E S
Table 3. Calculated Structural Parameters (DFT) and Bond
Orders for RMMR (M ) Ge or Sn; R ) H, Me, Ph, or Ar*)30,31
Table 4. Selected Bond Distances (Å) and Angles (deg) for the
Radical, Monoanion Salts NaAr*GeGeAr* (3), KAr′GeGeAr′ (4),
(THF)3Na{Ar*SnSnAr*} (10), [K(THF)6][Ar′SnSnAr′] (11),
[K(THF)6][Ar*SnSnAr*] (12), and
H
Me
Ph
Ar*
[K(18-crown-6)(THF)2][Ar*SnSnAr*] (13)
Ge-Ge
2.22
124
2.32
2.24
127
2.10
2.25
118
1.74
2.277
123.2
Ge-Ge-R
bond order
NaAr*GeGeAr* (3)
KAr′GeGeAr′ (4)
Ge(1)-Ge(2)
2.3089(8)
2.014(4)
2.005(4)
1596(15)
1391(15)
2.822(4)-
2.981(4)
Ge(1)-Ge(2)
2.3331(4)
2.033(2)
2.036(2)
3.5326(6)
3.6091(6)
3.029(3)-
3.302(2)
Sn-Sn
Sn-Sn-R
bond order
2.65
122
1.87
2.66
124
1.84
2.67
119
1.73
2.900
111.0
Ge(1)-C(1)
Ge(2)-C(37)
Ge(1)-Na(1)
Ge(2)-Na(1)
Na-C (range)
Ge(1)-C(1)
Ge(2)-C(1)
Ge(1)-K(1)
Ge(2)-K(1)
K-C (range)
bond order of 2.017.32 Bearing in mind the very large size
difference between the model ligands and those used experi-
mentally, we find the calculated parameters are in good
agreement with the measured values and support the lower bond
order implied by the trans-bent geometries. Calculations have
also been carried out on the compounds Ar*MMAr* and
TbtMMTbt (M ) Ge or Sn, Tbt ) C6H2-2,4,6-{CH(SiMe3)2}3).31
The calculated values for Ar*GeGeAr* (Table 3) approach the
measured values for Ar′GeGeAr′ closely. For Ar*SnSnAr*
however, the calculated values differ considerably. In contrast,
the calculated values for TbtGeGeTbt (Ge-Ge ) 2.231Å, Ge-
Ge-C ) 121.8°) and TbtSnSnTbt (Sn-Sn ) 2.659Å, Sn-
Sn-C ) 122°) are both in reasonably good agreement with
those found for 1 and 8.
Monoanionic Radical Compounds. Two germanium (3 and
4) and four tin (10-13) derivatives containing four different
monoanions have been isolated as crystalline species. Some
details of their structures are given in Table 4. Representative
examples of the structures are provided by the germanium
compound NaAr*GeGeAr*, 3, and the tin derivative [K(THF)6]-
[Ar′SnSnAr′], 11, which are illustrated in Figure 1. The planarity
of the core and the trans-bent geometry seen in the neutral
precursors 1 and 8 are preserved in all cases. This behavior
may be contrasted with that of diarylacetylenes, which, upon
reduction, dimerize to form tetraarylbutadiene dianionic salts.33
It seems likely that dimerization of the terphenyl substituted
derivatives is prevented by steric effects. Within each series,
the Ge-Ge and Sn-Sn distances are remarkably uniform
averaging 2.32(1) Å for the germanium compounds and 2.81-
(1) Å for the tin species. These distances are ca. 0.03 and 0.14
Å longer than the 2.2850(6) and 2.6675(4) Å observed in neutral
1 and 8. The other main structural change that occurs on
reduction is a narrowing of the M-M-C angles. The extent of
the narrowing is greatest (ca. 30°) for the tin species where an
Sn-Sn-C range of 93.6(4)°-98.1(4)° is observed, cf. 125.24-
(7)° in the neutral Ar′SnSnAr′. For the two germanium salts 3
and 4, the Ge-Ge-C angles are in the range 112.60(5)°-
115.32(12)°, cf. 128.67(8)° in Ar′GeGeAr′, so that the amount
of the closure of the Ge-Ge-C angle is less than half that seen
in the tin series.
C(1)-Ge(1)-Ge(2)
114.2(1)
C(37)-Ge(2)-Ge(1) 115.3(1)
C(1)-Ge(1)-Ge(2)
C(31)-Ge(2)-Ge(1) 112.59(5)
115.55(5)
Ge(1)-C(1)-C(2)
Ge(1)-C(1)-C(6)
C(2)-C(1)-C(6)
Ge(2)-C(37)-C(38) 117.2(3)
Ge(2)-C(37)-C(42) 125.0(3)
C(38)-C(37)-C(42) 116.7(4)
124.8(3)
117.5(3)
116.8(4)
Ge(1)-C(1)-C(2)
Ge(1)-C(1)-C(6)
C(2)-C(1)-C(6)
Ge(2)-C(31)-C(36) 124.09(17)
Ge(2)-C(31)-C(36) 119.55(17)
C(32)-C(31)-C(36) 115.9(2)
120.18(16)
122.96(15)
116.24(19)
[K(THF)6][Ar′SnSnAr′] (11)
[K(THF)6][Ar*SnSnAr*] (12)
Sn(1)-Sn(1A)
Sn(1)-C(1)
K(1)-O(1)
K(1)-O(2)
2.8081(9) Sn(1)-Sn(1A)
2.8123(9)
2.249(6)
2.623(7)
2.703(9)
Sn(1)-C(1)
K(1)-O(1)
K(1)-O(2)
K(1)-O(3)
2.236(5)
2.684(7)
2.7003(6)
2.684(7)
C(1)-Sn(1)-Sn(1A) 97.91(16) C(1)-Sn(1)-Sn(1A) 95.20(13)
Sn(1)-C(1)-C(2)
C(2)-C(1)-C(2A)
120.9(3)
117.5(6)
Sn(1)-C(1)-C(2)
Sn(1)-C(1)-C(6)
Sn(1)-C(2)-C(6)
120.2(4)
123.0(4)
116.6(5)
[(THF)3Na{Ar*SnSnAr*}] (10)
[K(18-crown-6)(THF)2][Ar*SnSnAr*] (13)
Sn(1)-Sn(2)
Sn(1)-C(1)
Sn(2)-C(37)
Na(1)-Sn(1)
Na(1)-O(1)
Na(1)-O(2)
Na(1)-O(3)
2.8107(13) Sn(1)-Sn(1A)
2.782(1)
2.29(1)
2.824(1)
2.226(7)
95.0(4)
2.22(2)
2.19(1)
3.240(7)
2.26(2)
2.35(2)
2.47(2)
Sn(1)-C(1)
Sn(2)-Sn(2A)
Sn(2)-C(2)
C(1)-Sn(1)-Sn(1A)
C(1A)-Sn(1)-Sn(1A) 93.6(4)
C(37)-Sn(2)-Sn(2A)
97.3(2)
C(1)-Sn(1)-Sn(2)
97.9(3)
C(37)-Sn(2)-Sn(1) 98.0(4)
C(1)-Sn(1)-Na(1)
Sn(2)-Sn(1)-Na(1) 130.4(2)
131.3(4)
Sn(1)-C(1)-C(2)
Sn(1)-C(1)-C(6)
C(2)-C(1)-C(6)
121(1)
125(1)
114(1)
observed in previously reported species with Na-Sn interac-
tions.27,34 Also, the data for germanium and tin series indicate
that there are only minor differences between the structures of
the Ar′ and Ar* derivatives. The bond length and angular
changes are therefore associated with changes in the internal
electronic structure that take place upon reduction of the M2
unit. In the absence of detailed calculations on model radical
species, such changes can be accounted for only in general
terms. The changes probably arise from the fact that the addition
of an electron to the M2 unit effectively increases the electro-
positive character of the element. As a result, the electronega-
tivity of the ligands relative to the central element is increased.
By using orbital considerations and arguments similar to those
used elsewhere35,36 for the explanation of barriers to inversion
or linearization in a variety of main group compounds, it can
be predicted that barriers to linearization will be increased, and
The extent of the angular change is surprising, and in the
case of the tin compounds, it cannot be attributed to the effects
of alkali metal countercations since similar Sn-Sn-C angles
are obtained whether the alkali metal is in contact with the anion
(as in 10) or not (as in 11-13). It has to be said, however, that
the Na-Sn interaction in 10 is probably quite weak since the
Na-Sn distance, 3.240(7) Å, is 0.14-0.17 Å longer than those
(32) Allen, T. L.; Fink, W. H.; Power, P. P. J. Chem. Soc., Dalton Trans. 2000,
407.
(33) Schlenk, W.; Bergman, E. Justus Liebigs Ann. Chem. 1928, 463, 71. Smith.
L. I.; Hoehn, H. H. J. Am. Chem. Soc. 1941, 61, 1184.
(34) Klinkhammer, K. W. Chem.sEur. J. 1999, 3, 1418. Wiberg, N.; Lerner,
H.-W.; Wagner, S.; No¨th, H.; Seifert, T. Z. Naturforsch 1999, 54b, 877.
(35) Levin, C. C. J. Am. Chem. Soc. 1975, 97, 5649.
(36) Gilheany, D. G. Chem. ReV. 1994, 94, 1339.
9
J. AM. CHEM. SOC. VOL. 125, NO. 38, 2003 11633

A R T I C L E S
Pu et al.
Figure 2. EPR spectrum of a ca. 0.1 mM solution of [K(THF)6][Ar*SnSnAr*] in THF at 296 K.
the interligand angles decreased, by the addition of an electron
to the M2 unit. This effect is greatest in tin since the
electronegativity differences between the metal and ligand are
larger. The narrower M-M-C angles in the radicals probably
also give rise to an increase in the p-character of the σ-bonds.37
This is expected to lead to longer bond lengths as a result of
the greater average radius of the p-orbitals vis-a`-vis s-orbitals.
The longer Ge-C, Sn-C, Ge-Ge, and Sn-Sn bonds experi-
mentally observed in the radicals are in agreement with this
hypothesis. In addition, the character of the orbital to which
the electron has been added is also of prime importance for the
M-M bond lengths. Calculations on the model germanium and
tin compounds MeGeGeMe32 and MeSnSnMe38 show that the
LUMO resembles an n+ lone pair combination and not the π*-
orbital observed for alkynes. The LUMO appears to be mainly
nonbonding in character (although it also has a small component
between the M nuclei) so that the addition of an electron to it
is expected to have a small effect on the M-M distance. These
results suggest that the lengthening of the M-M and C-C
bonds that occur on single-electron reduction is largely a result
of σ-bonding effects.
of these two p-orbitals is the LUMO, the addition of an electron
generates a π-bond of order 0.5 to yield an M-M bond of order
1.5. The Sn-Sn bonds in the reduced, monoanionic species 10-
13 are close to the Sn-Sn distance in elemental (gray) tin24
which suggests little multiple character. However, as discussed
above, it is probable that the multiple character and shortening
of the Sn-Sn bond be masked by the lengthening of the σ-bond
due to the closure of the Sn-Sn-C angle. This view receives
support from the structure of the neutral lead compound
Ar*PbPbAr*5,37 which has a Pb-Pb σ-bond, a Pb-Pb-C angle
of 94.26(4)°, and a “long” Pb-Pb bond length of 3.188(1) Å
which is ca. 0.30 Å longer than a “normal” Pb-Pb single bond
in R3PbPbR3 species (e.g., 2.844(4) Å in Ph3PbPbPh3).39
The EPR spectrum of 12 in THF at room temperature
displayed a strong signal near g ) 2.0691 with hyperfine
coupling to 117Sn (I ) /2, 7.68%) and 119Sn (I ) /2, 8.58%).
Simulation of the spectrum afforded a(117Sn) and a(119Sn)
couplings of 8.3 and 8.5 G (Figure 2), although the difference
between the couplings was not resolved in the experimental
spectrum. More recent work on the germanium radical 4
afforded a signal centered near g ) 2.003 82 with a hyperfine
1
1
9
coupling to 73Ge (I ) /2, 7.8%) of 7.5 G. The small coupling
The energy level order within the monoanions in 3, 4, and
10-13 or their model species is currently unknown, but the
near 90° Sn-Sn-C angle in the tin monoanions could be
accompanied by a change in the ordering of the energy levels
associated with the M2 unit. Thus, when the M-M-C bond
angle is narrowed from 180° to ca. 90°, the bonding is changed
from triple to approximately single as shown by the schematic
constants in both compounds suggest very low unpaired electron
density at the germanium or tin nuclei. Cyclic voltammetric
studies of 8 in THF revealed a facile, essentially reversible redox
cycle at -1.21 V versus SCE (Figure 3). On the other hand,
the germanium species 1 displayed an irreversible reduction
wave at ca. -1.38 V. No other reduction waves could be
observed until solvent breakdown occurred near -2.4 V.
Although 8 and 9 (like 1 and 2) can be doubly reduced, it seems
(37) It is not possible to deduce the extent of hybridization from bond angles.
However, in the related species Ar*PbPbAr*5 which has a Pb-Pb-C bond
angle that approaches 90°, the extent of hybridization is low: Chen, Y.;
Hartmann, M.; Diedenhofen, M.; Frenking, G. Angew. Chem., Int. Ed. 2001,
40, 2052.
This leaves an unused p-orbital at each M which lie perpen-
dicularly to the CMMC plane. If it is assumed that a combination
(38) Phillips, A. D.; Power, P. P. Unpublished work.
(39) Preut, H.; Huber, F. Z. Anorg. Allg. Chem. 1976, 419, 92-96.
9
11634 J. AM. CHEM. SOC. VOL. 125, NO. 38, 2003

Ge and Sn Analogues of Alkynes and Reduction Products
A R T I C L E S
Figure 3. Cyclic voltammogram of ca. 1 mM Ar′SnSnAr′ (8) in 0.1 M tetrabutylammonium perchlorate in THF referenced to SCE and scanned at 100 mV
s-1
.
Table 5. Selected Bond Distances (Å) and Angles (deg) for the Dianionic Salts Li2Ar′GeGeAr′ (5), Na2Ar*GeGeAr* (6), K2Ar*GeGeAr* (7),
Na2Ar*SnSnAr* (14), K2Ar′SnSnAr′ (15), and K2Ar*SnSnAr* (16)
Li2Ar′GeGeAr′ (5)
Na2Ar*GeGeAr* (6)
K Ar*GeGeAr* (7)
2
Ge(1)-Ge(1A)
Ge(1)-C(1)
Ge(1)-Li(1)
Ge(1)-Li(1A)
Li-C (range)
2.455(9)
2.060(3)
2.874(6)
2.892(7)
Ge(1)-Ge(1A)
Ge(1)-C(1)
Ge(1)-Na(1)
Ge(1)-Na(1A)
Na-C (range)
2.394(1)
2.065(3)
3.121(2)
3.074(3)
Ge(1)-Ge(1A)
Ge(1)-C(1)
Ge(1)-K(1)
2.3912(6)
2.077(3)
3.5573(8)
2.482(7)-2.759(7)
2.049(3)-2.831(3)
K(1)-C (range)
3.027(3)-3.179(3)
C(1)-Ge(1)-Ge(1A)
Ge(1)-C(1)-C(2)
Ge(1)-C(1)-C(6)
C(2)-C(1)-C(6)
102.97(9)
121.8(2)
122.3(2)
115.1(3)
C(1)-Ge(1)-Ge(1A)
Ge(1)-C(1)-C(2)
Ge(1)-C(1)-C(6)
C(2)-C(1)-C(6)
102.37(8)
122.5(2)
121.7(2)
114.9(2)
C(1)-Ge(1)-Ge(1A)
Ge(1)-C(1)-C(2)
Ge(1)-C(1)-C(6)
C(2)-C(1)-C(6)
112.14(7)
122.3(2)
120.7(2)
113.9(2)
Na2Ar*SnSnAr* (14)
K Ar′SnSnAr′ (15)
2
K Ar*SnSnAr* (16)
2
Sn-Sn′
2.789(1)
2.249(9)
3.298(5)
3.309(5)
Sn(1)-Sn(1A)
Sn-C(1)
K(1)-Sn(1)
K(1A)-Sn(1)
K-C (range)
2.7754(3)
2.282(2)
3.5947(5)
3.6383(5)
Sn-Sn′
2.7763(9)
2.274(6)
3.579(2)
3.591(2)
Sn-C(1)
Sn-C(1)
K(1)-Sn
K(2)-Sn
K-C (range)
Na(1)-Sn
Na(2)-Sn
Na-C (range)
2.934(9)-3.084(9)
3.097(2)-3.227(2)
3.076(7)-3.247(7)
Sn′-Sn-C(1)
104.8(2)
121.7(8)
120.8(8)
115.6(8)
Sn(1A)-Sn(1)-C(1)
Sn(1)-C(1)-C(2)
Sn(1)-C(1)-C(6)
C(2)-C(1)-C(6)
106.02(5)
121.3(1)
121.3(1)
115.1(2)
Sn′-Sn-C(1)
Sn-C(1)-C(2)
Sn-C(1)-C(6)
107.5(1)
120.9(5)
120.9(5)
115.6(5)
Sn-C(1)-C(2)
Sn-C(1)-C(6)
C(2)-C(1)-C(6)
C(2)-C(1)-C(6)
probable that the resultant dianion is only stable in the presence
of contact alkali metal cations. These cations are unavailable
in the CV solutions of neutral 1 or 8 in THF. The more facile
reduction of the tin compound supports the view that the LUMO
in this molecule lies lower than that in the germanium species
which is consistent with weaker bonding in the tin species.
Doubly Reduced Compounds. The reaction of Ar′MCl or
Ar*MCl (M ) Ge or Sn) with excess lithium, sodium, or
potassium for extended periods afforded the doubly reduced
compounds 5-7 and 14-16. The syntheses of 6 and 16 were
described in a preliminary publication.9 A range of compounds
with different alkali metals and aryl substituents was investigated
in order to gauge the effect of the various countercations and
the two aryl groups on the structures. The structural results are
summarized in Table 5. Trans-bent, planar CMMC cores were
observed in all cases. In addition, all the compounds are contact
ion triples in which the two alkali/metal countercations are
sandwiched between flanking aryl rings, each of which is drawn
from a different terphenyl group. The alkali metal cations bridge
the two germanium or tin atoms in an almost symmetric manner
and form a planar array with the germanium or tin atoms that
is perpendicular to the CMMC plane. It can be seen that the
use of sodium or potassium countercations affords structures
with Ge-Ge or Sn-Sn and Ge-C or Sn-C distances that are
9
J. AM. CHEM. SOC. VOL. 125, NO. 38, 2003 11635

A R T I C L E S
Pu et al.
very similar. The only notable differences between the sodium
and potassium salts, besides the alkali metal-germanium, tin,
or carbon distances, are the M-M-C angles. Wider M-M-C
angles are observed for the potassium derivatives, most notably
for the germanium species 6 and 7 where the difference is ca.
10°. The larger size of the K+ ions, which are complexed to
the aryl rings, probably causes the wider M-M-C angles. The
K-C distances in 7, 15, and 16 are comparable to each other,
but the Na-C distances in the germanium salt 6 are shorter
than those in its tin analogue 14 which suggests that Na+ is too
small for the cavity between the aryl rings in 14. The Na-Sn
distance in 14 is close to that observed in the monoanion 10.
Furthermore, the Na-Ge and K-Ge distances in 6 and 7 are
very similar to those in the monoanionic derivatives 3 and 4.
When the Ge-Ge distances in 5-7 and the Sn-Sn distances
in 14-16 are compared to those in the monoanions, it can be
seen that the Ge-Ge distances increase from ca. 2.32 to ca.
2.39 Å, whereas the Sn-Sn distances decrease slightly from
ca. 2.81 to ca. 2.78 Å. Furthermore, the Ge-Ge-C angles in 6
and 7 are narrower than those in the monoanions 3 and 4,
whereas the Sn-Sn-C angles in 14-16 are wider than those
in monoanions 10-13. The shorter Sn-Sn bond lengths,
although consistent with the addition of another electron to an
Sn-Sn π-orbital, can also be explained through the widening
of the Sn-Sn-C angle which could cause bond shortening by
σ-effects. Furthermore, the increase in Coulombic repulsion that
occurs upon the addition of the second electron may be not as
great as it is in the germanium system due to the relatively large
size of the tin. The Ge-Ge bond length increase that occurs
upon further reduction of the germanium compounds is con-
sistent with the addition of the second electron to the n+ LUMO.
The further narrowing of the Ge-Ge-C angle, owing to the
increasing relative electropositive character of the germanium,
combined with the increase in Coulombic repulsion, produces
a significant bond length increase to ca. 2.39 Å.
(12) Å, has been found in [(THF)3LiGe{N(Ph)SiMe2O}3-
SiBut].42 These data suggest a relatively weak interaction
between lithium and germanium. Despite this, the small size
and high polarizing power of the Li+ ion may cause the
lengthening in the Ge-Ge bond by attracting electron density
toward itself from the π-bonds. Calculations at the B3LYB/6-
31 level confirm longer Ge-Ge bonds with Li countercations.38
Such effects have been calculated for other systems that involve
alkali metal salts of dianionic systems.43,44 Finally, it is notable
that the dianions [Ar′MMAr′]2- and [Ar*MMAr*]2- (M ) Ge
or Sn) are isoelectronic to the corresponding neutral arsenic and
antimony species, Ar*PnPnAr* (Pn ) As or Sb), which have
As-As and Sb-Sb double bonds.45
Conclusions
It has been shown that large terphenyl ligands stabilize
germanium and tin analogues of alkynes. These have decreased
Ge-Ge and Sn-Sn bond orders that are less than three due to
the electronic properties of the Ge-Ge and Sn-Sn units which
permit mixing of a σ*- and a π-level and consequent transfor-
mation of a π-level into an n- lone pair combination. The
compounds can be easily reduced to mono- or dianionic species.
Reduction by one electron affords narrower trans-bending angles
and increased Ge-Ge and Sn-Sn bond lengths. The addition
of another electron further increases the Ge-Ge bond distance
but shortens the Sn-Sn bond slightly. These trends have been
rationalized on the basis of the character of the molecular orbitals
likely to be involved in M-M bonding. Further evidence of
the nature of the M-M bonds will come from the reaction
chemistry of the compounds themselves.
Acknowledgment. We are grateful to the National Science
Foundation (CHE-0096913) for financial support. We thank
Prof. T. L. Allen and W. H. Fink for useful discussions and
Prof. F. Osterloh for his essential help in recording the
electrochemical data.
Supporting Information Available: X-ray data (CIF) for
Ar′GeCl and Ar′SnCl, 3-5, 7, 11, 14, and 15. This material is
available free of charge via the Internet at http://pubs.acs.org.
The structure of the dilithium salt 5 resembles that of the
sodium salt 6 in having almost equal trans-bending angles and
Ge-C bond lengths. As expected, the Li-Ge and Li-C
distances are shorter than the corresponding Na-Ge and Na-C
distances owing to the smaller size of lithium. The Li-C
distances span an almost identical range to those seen in the
structures of (LiSC6H2-2,4,6-Ph3)4 and (LiSC6H3-2,6-Mes2)3.40
In contrast, the Ge-Ge bond length in 5 (2.457(2) Å), which
is ca. 0.06 Å longer than those observed for 6 and 7, was less
predictable. The Li-Ge distances (two shorter at ca. 2.83 Å
and two longer at ca. 2.94 Å) lie at the high end of the currently
known range.41,42 Normally, Li-Ge distances lie within ca.
2.55-2.75 Å,41 but an unusually long Li-Ge distance, 2.904-
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