Formation of germenes from bis(germavinylidene)

Article abstract of DOI:10.1021/om7002706

A series of germenes have been synthesized from the bis(germavinylidene) [(Me₃SiN=PPh₂)₂C= Ge→Ge=C(PPh ₂=NSiMe₃)₂] (1). The reaction of 1 with 2,2,6,6-tetramethylpiperidine N-oxide afforded [(Me₃SiN=PPh ₂)₂C=Ge(ONCMe₂C₃H ₆CMe₂)₂] (2). Germavinylidene, the dissociation derivative of 1, underwent [1+4] cycloaddition with azobenzene, followed by a 1,3-H shift to give [(Me₃SiN=PPh₂)₂C= Ge(o-C₆H₄NHNPh)] (3). Treatment of 1 with benzil afforded the [1 + 4] cycloaddition compound [(Me₃-SiN=PPh₂) ₂C=Ge{O(Ph)C=C(Ph)O}] (4). The results showed that the germavinylidene moiety dissociated from 1 acts as a synthon for the preparation of various germenes by addition to the germanium-(II) center. The molecular structures of 2-4 have been determined.

Full text of DOI:10.1021/om7002706

3802
Organometallics 2007, 26, 3802-3806
Formation of Germenes from Bis(germavinylidene)
Wing-Por Leung,* Kwok-Wai Kan, Cheuk-Wai So, and Thomas C. W. Mak
Department of Chemistry, The Chinese UniVersity of Hong Kong, Shatin, New Territories, Hong Kong,
People’s Republic of China
ReceiVed March 22, 2007
A series of germenes have been synthesized from the bis(germavinylidene) [(Me3SiNdPPh2)2Cd
GefGedC(PPh2dNSiMe3)2] (1). The reaction of 1 with 2,2,6,6-tetramethylpiperidine N-oxide afforded
[(Me3SiNdPPh2)2CdGe(ONCMe2C3H6CMe2)2] (2). Germavinylidene, the dissociation derivative of 1,
underwent [1 + 4] cycloaddition with azobenzene, followed by a 1,3-H shift to give [(Me3SiNdPPh2)2Cd
Ge(o-C6H4NHNPh)] (3). Treatment of 1 with benzil afforded the [1 + 4] cycloaddition compound [(Me3-
SiNdPPh2)2CdGe{O(Ph)CdC(Ph)O}] (4). The results showed that the germavinylidene moiety
dissociated from 1 acts as a synthon for the preparation of various germenes by addition to the germanium-
(II) center. The molecular structures of 2-4 have been determined.
The Lewis base property of germavinylidene toward transition
metals has been shown in the synthesis of [{(Me3SiNd
PPh2)2CdGe}2Ni(PPh3)2] and [(Me3SiNdPPh2)2CdGe(MX)]2
(MX ) AgCl and AuI).11 We anticipated that the bis(ger-
mavinylidene) 1 could be a potential source for the reactive
monomeric germavinylidene intermediate “:GedC(PPh2d
NSiMe3)2”, which may serve as a synthon for the synthesis of
germenes through its lone pair at the germanium(II) center.
Introduction
The chemistry of germenes (>GedC<) has attracted much
attention over the past few decades.1 It has been found that the
thermal stability of the GedC bond is intrinsically low. A
germene is usually treated as a reactive intermediate, and
transient germenes can be trapped in situ with simple compounds
such as alcohols, dienes, aldehydes, nitrones, and nitrosoben-
zene.2 Nevertheless, the germenes R2GedCR′2 can be stabilized
by incorporating sterically bulky substituents at both germanium
and carbon.3 For example, Mes2GedCR2 (Mes ) 2,4,6-
trimethylphenyl, CR2 ) fluorenylidene)4 and [{(Me3Si)2N}2Ged
C(BBut)2C(SiMe3)2]5 have been reported and structurally char-
acterized. The most common routes for the synthesis of a
germene are the dehydrohalogenation of a halogermane by a
organolithium compound and the germylene-carbene coupling
reaction. Novel methods such as the Peterson reaction6 and
germylene-CS2 coupling reactions have also been employed
in the synthesis of stable germenes.7 The reactivities of germene
such as 1,2-addition and [2 + n] cycloaddtion have been
extensively studied.8
Results and Discussion
Synthesis of Germenes. The reaction of 1 with 4 equiv of
2,2,6,6-tetramethylpiperidine N-oxide (TEMPO) in THF af-
forded [(Me3SiNdPPh2)2CdGe(ONCMe2C3H6CMe2)2] (2)
(Scheme 1). The X-ray structure of 2 showed that it contains a
germene moiety with iminophosphorano and alkoxy substituents
bonded to carbon and germanium atoms, respectively. The result
suggested that the bis(germavinylidene) 1 dissociated in solution
to give the germavinylidene [(Me3SiNdPPh2)2CdGe:] and
reacted with TEMPO via a radical intermediate (Scheme 2).
The lone-pair electron and the vacant orbital at the germanium
center play roles in this reaction. Similar radical reactions of a
germanium(II) complex toward TEMPO have also been reported
by Kira and co-workers.12
Recently, we reported the synthesis of the bis(germavi-
nylidene) [(Me3SiNdPPh2)2CdGefGedC(PPh2dNSiMe3)2]
(1).9 The existence of a monomeric germavinylidene intermedi-
ate in solution was demonstrated in the reaction of 1 with CpMn-
(CO)2THF to form [(Me3SiNdPPh2)2CdGefMn(CO)2Cp].10
Treatment of 1 with 2 equiv of azobenzene in THF gave
compound 3. The structure of 3 has been confirmed by X-ray
structure analysis. The first step of the reaction was probably
the formation of the five-membered-ring intermediate A via
* To whom correspondence should be addressed. E-mail: kevinleung@
cuhk.edu.hk.
(1) (a) Barrau, J.; Escudie´, J.; Satge´, J. Chem. ReV. 1990, 90, 283. (b)
Escudie´, J.; Ranaivonjatovo, H. AdV. Organomet. Chem. 1999, 44, 113.
(2) (a) Riviere, P.; Castel, A.; Satge´, J. J. Am. Chem. Soc. 1980, 102,
5413. (b) Toltl, N. P.; Leigh, W. J. J. Am. Chem. Soc. 1998, 120, 1172. (c)
Toltl, N. P.; Stradiotto, M.; Morkin, T. L.; Leigh, W. J. Organometallics
1999, 18, 5643. (d) Chaubon, M.-A.; Escudie´, J.; Ranaivonjatovo, H.; Satge´,
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Cretiu Nemes, G. Chem. Commun. 2003, 1662. (d) Ech-Cherif El Kettani,
S.; Lazraq, M.; Ranaivonjatovo, H.; Escudie´, J.; Couret, C.; Gornitzka, H.;
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S.; Lazraq, M.; Ranaivonjatovo, H.; Escudie´, J.; Couret, C.; Gornitzka, H.;
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(4) Couret, C.; Escudie´, J.; Satge´, J.; Lazraq, M. J. Am. Chem. Soc. 1987,
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Ed. Engl. 1987, 26, 798.
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Int. Ed. 2001, 40, 2501.
(10) Leung, W.-P.; So, C.-W.; Kan, K.-W.; Chan, H.-S.; Mak, T. C. W.
Inorg. Chem. 2005, 44, 7286.
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Zhivotovskii, D.; Bla¨ser, D.; Boese, R. J. Am. Chem. Soc. 1996, 118, 12228.
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10.1021/om7002706 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 06/14/2007

Formation of Germenes from Bis(germaVinylidene)
Organometallics, Vol. 26, No. 15, 2007 3803
Scheme 1
ylsilyl)methyl]phenyl; Tip ) 2,4,6-triisopropylphenyl),14 [{(Me3-
Si)2N}2Ge{O(Ph)CdC(Ph)O}],15 [(ArO)2Ge{O(Ph)CdC(Ph)O}]
(Ar ) 2,4,6-tris[(dimethylamino)methyl]phenyl),16 [Me2Si-
{N(But)}2Ge{O(Ph)CdC(Ph)O}],17and [Ge(OC6HPh4-2,3,5,6)2-
{O(Ph)CdC(Ph)O}]18 have been reported.
Scheme 2
Spectroscopic Properties. Compounds 2-4 have been
isolated as colorless (2) or yellow (3, 4) crystalline solids. They
are air-sensitive, soluble in THF, and sparingly soluble in Et2O.
They have been characterized by NMR spectroscopy and X-ray
structure analysis. The 31P NMR spectra of 2 and 3 displayed
two signals (δ 10.57, 49.94 ppm (2); δ 12.60, 30.04 ppm (3))
due to two different phosphorus environments, as found in the
solid-state structures. In contrast, the 31P NMR spectrum of 4
showed one singlet at δ 26.72 ppm. This does not correspond
to the X-ray structure. It may be due to the fluxional behavior
of the imino nitrogen atoms at the germanium center in solution.
At 238 K, as the fluxional coordination process slowed down,
the 31P NMR of 4 displayed two singlets at δ 5.56 and 53.77
ppm, consistent with the X-ray structure. It is suggested that
the sterically bulky substituents at the germanium centers in 2
and 3 prohibit their fluxional behavior.
Scheme 3
1
The H and 13C NMR spectra of 2 displayed signals due to
the bis(iminophosphorano)methanediide ligand and 2,2,6,6-
tetramethylpiperidyl groups. The 1H NMR spectrum of 3
exhibited one broad signal at δ 7.83 ppm, which is assigned to
the -PhNHNPh moiety. It also showed multiplet signals due
to the phenyl group in the normal range (δ 7-8 ppm). The 1H
and 13C spectra of 4 are normal. No 13C NMR signal could be
recorded for the methanediide carbons in 2-4. A similar
phenomenon has been reported by Cavell and co-workers for
some metal bis(iminophosphorano)methanediide complexes.19
X-ray Structures. Molecular structures with the atom-
numbering schemes for compounds 2-4 are shown in Figures
1-3, respectively. Selected bond distances (Å) and angles (deg)
of 2-4 are given in Tables 2-4, respectively.
[1 + 4] cycloaddition between the Ge(II) center and NdNCd
C moiety of azobenzene, followed by rearomatization via a
1,3-H shift (Scheme 3). Unlike a germene, the >CdGe: bond
of the germavinylidene was not involved in the cycloaddition.
This may be due to the delocalization between PdN and Cd
Ge bonds, which reduces the reactivity of the >CdGe: bond.13
Steric hindrance at the gemanium center may also contribute
to the lesser reactivity of the >CdGe: bond. To our knowledge,
compound 3 is the first example resulting from the cycloaddition
of a germanium(II) compound with azobenzene.
The bis(germavinylidene) 1 also underwent [1 + 4] cycload-
dition with 2 equiv of benzil in THF to form [(Me3SiNd
PPh2)2CdGe{O(Ph)CdC(Ph)O}] (4), as confirmed by X-ray
structure analysis. Similar 1,4-addition reactions of germanium-
(II) complexes with benzil have been documented. For example,
[(Tb)(Tip)Ge{O(Ph)CdC(Ph)O}] (Tb ) 2,4,6-tris[bis(trimeth-
(13) Lazraq, M.; Escudie´, J.; Couret, C.; Satge´, J.; Soufiaoui, M.
Organometallics 1991, 10, 1140.
(14) Tokitoh, N.; Manmaru, K.; Okazaki, R. Organometallics 1994, 13,
167.
(15) Litz, K. E.; Bender, J. E.; Sweeder, R. D.; Banaszak Holl, M. M.;
Kampf, J. W. Organometallics 2000, 19, 1186.
(16) Barrau, J.; Rima, G.; El Amraoui, T. Organometallics 1998, 17,
607.
(17) Billeb, G.; Bootz, K.; Neumann, W. P.; Steinhoff, G. J. Organomet.
Chem. 1991, 406, 303.
(18) Weinert, C. S.; Fenwick, A. E.; Fanwick, P. E.; Rothwell, I. P.
Dalton Trans. 2003, 532.
(19) (a) Jones, N. D.; Lin, G.; Gossage, R. A.; McDonald, R.; Cavell,
R. G. Organometallics 2003, 22, 2832. (b) Lin, G.; Jones, N. D.; Gossage,
R. A.; McDonald, R.; Cavell, R. G. Angew. Chem., Int. Ed. 2003, 42, 4054.

3804 Organometallics, Vol. 26, No. 15, 2007
Leung et al.
Figure 3. Molecular structure of 4.
The C(57)-C(67) bond distance of 1.336 Å in 4 is consistent
with a normal CdC double bond.
The C(61)-C(62) and N(4)-N(3) bond lengths of 1.399(7)
and 1.457(5) Å in 3 correspond to the CdC bond and N-N
bond, respectively. The Ge(1)-C(61) bond distance of 1.919-
(5) Å is similar to that of 1.989(5) Å in [GeCl{C6H3-2,6-Trip}]
(Trip ) C6H2-2,4,6-Pri3).22 The Ge(1)-N(3) bond distance of
1.878(4) Å in 3 is comparable with that of 1.920(2) Å in [Ge-
{N(SiMe3)C(Ph)C(SiMe3)(C5H4N-2)}Cl]23 and 1.988(2) Å in
[{HC(CMeNAr)2}GeCl].24 The Ge-N dative bond distance of
1.926(2) Å in 2, 1.941(4) Å in 3, and 1.892(3) Å in 4 are
comparable with those of 1.971(6) and 1.974(6) Å in 1.9
Figure 1. Molecular structure of 2.
Experimental Section
General Procedures. All manipulations were carried out under
an inert atmosphere of dinitrogen gas by standard Schlenk
techniques. Solvents were dried over and distilled from CaH2
(hexane) and/or Na (Et2O, toluene, and THF). The bis(germavi-
nylidene) [(Me3SiNdPPh2)2CdGefGedC(PPh2)NSiMe3)2] was
prepared by literature procedures.9 TEMPO, azobenzene, and benzil
were purchased from Aldrich Chemicals and used without further
1
purification. The H, 13C, and 31P NMR spectra were recorded on
Bru¨ker WM-300 and Varian 400 spectrometers. The NMR spectra
were recorded in THF-d8, and the chemical shifts δ are relative to
1
SiMe4 and 85% H3PO4 for H, 13C, and 31P, respectively.
Figure 2. Molecular structure of 3.
Reaction of 1 with TEMPO. A solution of 1 (0.57 g, 0.45
mmol) in THF (20 mL) was added slowly to TEMPO (0.28 g, 1.80
mmol) in THF (20 mL) at 0 °C. The resultant yellow solution was
raised to room temperature and stirred for 30 h. The volatiles were
removed under reduced pressure. The residue was extracted with
Et2O. After filtration and concentration of the filtrate, 2 was obtained
as colorless crystals. Yield: 0.53 g (63%). Mp: 157.2 °C dec. Anal.
Found: C, 62.19; H, 7.73; N, 5.64. Calcd for C49H74GeN4O2P2Si2:
The structures of compounds 2-4 are consistent with a
germene compound. The C-Ge bond distances of 1.859(1) Å
in 2, 1.852(1) Å in 3, and 1.850(4) Å in 4 are slightly longer
than that of 1.827(4) Å in [{(Me3Si)2N}2GedC(BBut)2C-
(SiMe3)2]5 and 1.803(4) Å in [Mes2GedCR2].20 This is probably
due to the delocalization of π electrons resulting from the
conjugation of PdN and CdGe bonds, which lengthens the
>CdGe< bond distance. However, the C-Ge distances of 2-4
are shorter than those of 1 (1.908(7), 1.905(8) Å),9 owing to
the higher oxidation state of germanium in 2-4. One imino
group of the ligand coordinates to the germanium(IV) center;
the other one remains uncoordinated. Thus, the geometry around
the germanium atom in 2-4 is tetrahedral. Compounds 2-4
are the first examples of germenes containing a four-coordinate
germanium center to be characterized by X-ray diffraction
methods. Other germenes reported display trigonal-planar
geometry at both germanium and carbon.
1
C, 62.48; H, 7.92; N, 5.92. H NMR (THF-d8): δ -0.33 (s, 9H,
SiMe3), -0.13 (s, 9H, SiMe3), 1.12 (s, 12H, CH3, tetramethylpi-
peridyl), 1.17 (s, 12H, CH3, tetramethylpiperidyl), 1.22-1.35 (m,
6H, CH2, tetramethylpiperidyl), 1.41-1.55 (m, 6H, CH2, tetram-
ethylpiperidyl), 7.21-7.27 (m, 6H, Ph), 7.29-7.37 (m, 6H, Ph),
7.55-7.68 (m, 8H, Ph). 13C{1H} NMR (THF-d8): δ 3.91, 4.54
(20) Lazraq, M.; Escudie´, J.; Couret, C.; Satge´, J.; Dra¨ger, M.; Dammel,
R. Angew. Chem., Int. Ed. 1998, 27, 828.
(21) Baines, K. M.; Stibbs, W. G. Coord. Chem. ReV. 1995, 145, 157.
(22) Pu, L.; Olmstead, M. M.; Power, P. P.; Schiemenz, B. Organome-
tallics 1998, 17, 5602.
(23) Leung, W.-P.; So, C.-W.; Wu, Y.-S.; Li, H.-W.; Mak, T. C. W.
Eur. J. Inorg. Chem. 2005, 513.
(24) Ding, Y.; Roesky, H. W.; Noltemeyer, M.; Schmidt, H.-S.; Power,
P. P. Organometallics 2001, 20, 1190.
The Ge-O bond distances in 2 and 4 (1.782(2), 1.772(2) Å
(2); 1.781(3), 1.794(3) Å (4)) are comparable to those of
compounds containing Ge-O single bonds (1.75-1.85 Å).21

Formation of Germenes from Bis(germaVinylidene)
Organometallics, Vol. 26, No. 15, 2007 3805
Table 1. Crystallographic Data for Compounds 2-4
2
3
4
formula
fw
C49H74GeN4O2P2Si2
941.83
C43H48GeN4P2Si2
811.56
C45H48GeN2O2P2Si2
839.56
cryst syst
space group
a (Å)
b (Å)
c (Å)
monoclinic
P21/c
13.2520(16)
12.4869(16)
32.041(4)
90
94.022(2)
90
5289.0(11)
4
monoclinic
P21/n
12.022(2)
19.184(4)
19.438(4)
90
90.00(3)
90
4482.9(15)
4
1.202
triclinic
P1h
11.492(2)
14.430(3)
15.903(3)
65.49(3)
74.47(3)
72.29(3)
2252.2(8)
2
1.236
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
d
calcd (g cm-3
)
1.183
0.724
2008
µ (mm-1
F(000)
)
0.841
1696
0.840
876
cryst size (mm)
2θ range (deg)
index ranges
0.50 × 0.40 × 0.40
1.27-28.33
-14 e h e 17
-16 e k e 16
-42 e l e 40
36 307
0.50 × 0.40 × 0.20
2.00-25.00
-13 e he 13
-22 e k e 0
-22 e l e 23
10 841
0.50 × 0.40 × 0.20
2.07-25.00
-13 e h e 13
-17 e k e 0
-18 e l e 17
8288
no. of rflns collected
no. of indep rflns
13 126
6453
7944
R1, wR2 (I > 2(σ)I)
0.0434, 0.1090
0.0762, 0.1295
1.012
0.0639, 0.1505
0.0782, 0.1610
1.144
0.0504, 0.1347
0.0952, 0.1534
1.032
R1, wR2 (all data)
goodness of fit, F2
no. of data/restraints/params
13 126/11/550
0.693/-0.672
6453/1/469
0.446/-0.670
7944/0/488
0.546/-0.489
largest diff peaks, e Å-3
Table 2. Selected Bond Distances (Å) and Angles (deg) for
Compound 2
Table 4. Selected Bond Distances (Å) and Angles (deg) for
Compound 4
C(1)-Ge(1)
Ge(1)-O(1)
Ge(1)-O(2)
Ge(1)-N(1)
1.859(1)
1.787(2)
1.772(2)
1.926(2)
P(1)-N(1)
P(2)-N(2)
C(1)-P(1)
C(1)-P(2)
1.649(2)
1.544(3)
1.722(3)
1.786(2)
C(4)-Ge(1)
Ge(1)-N(2)
P(2)-N(2)
P(1)-N(1)
C(4)-P(2)
C(4)-P(1)
1.850(4)
1.892(3)
1.660(3)
1.538(3)
1.719(4)
1.746(4)
Ge(1)-O(1)
Ge(1)-O(2)
O(1)-C(57)
O(2)-C(67)
C(57)-C(67)
1.781(3)
1.794(3)
1.401(4)
1.398(4)
1.336(5)
O(1)-Ge(1)-O(2)
O(1)-Ge(1)-N(1)
N(1)-Ge(1)-C(1)
C(1)-Ge(1)-O(2)
O(1)-Ge(1)-C(1)
102.9(8)
115.3(9)
82.1(1)
129.6(1)
122.6(9)
O(2)-Ge(1)-N(1)
Ge(1)-N(1)-P(1)
N(1)-P(1)-C(1)
P(1)-C(1)-P(2)
115.3(9)
91.1(9)
95.0(9)
131.7(9)
O(1)-Ge(1)-O(2)
O(2)-Ge(1)-C(4)
C(4)-Ge(1)-N(2)
N(2)-Ge(1)-O(1)
O(1)-Ge(1)-C(4)
O(2)-Ge(1)-N(2)
Ge(1)-N(2)-P(2)
91.4(1)
126.6(2)
83.5(2)
112.2(1)
128.5(2)
116.2(1)
91.0(2)
N(2)-P(2)-C(4)
P(2)-C(4)-Ge(1)
P(2)-C(4)-P(1)
Ge(1)-O(1)-C(57)
O(1)-C(57)-C(67)
C(57)-C(67)-O(2)
C(67)-O(2)-Ge(1)
94.9(2)
90.6(2)
131.9(2)
108.7(2)
115.3(3)
116.5(3)
107.9(2)
Table 3. Selected Bond Distances (Å) and Angles (deg) for
Compound 3
C(1)-Ge(1)
Ge(1)-N(2)
C(1)-P(1)
C(1)-P(2)
P(1)-N(1)
P(2)-N(2)
1.852(1)
1.941(4)
1.790(3)
1.722(4)
1.564(4)
1.664(4)
Ge(1)-C(61)
C(61)-C(62)
C(62)-N(4)
N(4)-N(3)
1.919(5)
1.399(7)
1.421(6)
1.457(5)
1.878(4)
1
GeN4P2Si2: C, 63.63; H, 5.96; N, 6.90. H NMR (THF-d8): δ
-0.43 (s, 9H, SiMe3), -0.33 (s, 9H, SiMe3), 6.66-6.74 (m, 2H,
Ph), 6.76-6.85 (m, 2H, Ph), 6.98-7.15 (m, 4H, Ph), 7.20-7.37
(m, 4H, Ph), 7.39-7.52 (m, 8H, Ph), 7.64-7.77 (m, 9H, Ph), 7.83
(s, 1H, NH). 13C{1H} NMR (THF-d8): δ 3.16, 5.14 (SiMe3), 115.99,
117.38, 119.46, 120.82, 122.92, 123.37, 125.03, 127.55, 128.75,
129.71, 131.39, 132.01, 133.37 (Ph). 31P{1H} NMR (THF-d8): δ
12.60, 30.04.
N(3)-Ge(1)
N(2)-Ge(1)-C(61)
C(61)-Ge(1)-N(3)
N(3)-Ge(1)-C(1)
C(1)-Ge(1)-N(2)
N(2)-Ge(1)-N(3)
C(1)-Ge(1)-C(61)
Ge(1)-N(2)-P(2)
116.5(2)
87.9(2)
126.4(2)
81.0(2)
116.1(2)
131.7(2)
92.2(2)
N(2)-P(2)-C(1)
P(2)-C(1)-Ge(1)
P(2)-C(1)-P(1)
Ge(1)-C(61)-C(62)
C(61)-C(62)-N(4)
C(62)-N(4)-N(3)
N(4)-N(3)-Ge(1)
93.3(1)
93.5(2)
122.9(1)
109.9(4)
117.8(4)
112.5(4)
111.8(3)
Reaction of 1 with Benzil. A solution of 1 (0.54 g, 0.43 mmol)
in THF (20 mL) was added slowly to benzil (0.18 g, 0.86 mmol)
in THF (20 mL) at 0 °C. The resultant yellow solution was raised
to room temperature and stirred for 42 h. The volatiles were
removed under reduced pressure. The residue was extracted with
Et2O. After filtration and concentration of the filtrate, 4 was obtained
as yellow crystals. Yield: 0.38 g (52%). Mp: 143-144 °C. Anal.
Found: C, 63.93; H, 5.48; N, 3.06. Calcd for C45H48GeN2O2P2Si2:
(SiMe3), 18.37, 18.59, 21.26 (CH3, tetramethylpiperidyl), 35.59,
40.98, 41.38, 41.99, 43.45, 44.90 (CH2, tetramethylpiperidyl), 61.40
(quaternary C, tetramethylpiperidyl), 128.39, 128.53, 129.05,
129.57, 130.12, 130.89, 131.54, 132.71, 133.02, 133.64, 134.34
(Ph). 31P{1H} NMR (THF-d8): δ 10.57, 49.94.
Reaction of 1 with Azobenzene. A solution of 1 (0.62 g, 0.49
mmol) in THF (20 mL) was added slowly to azobenzene (0.18 g,
0.98 mmol) in THF (20 mL) at 0 °C. The resultant orange solution
was raised to room temperature and stirred for 36 h. The volatiles
were removed under reduced pressure. The residue was extracted
with Et2O. After filtration and concentration of the filtrate, 3 was
obtained as yellow crystals. Yield: 0.37 g (46%). Mp: 133.5 °C
dec. Anal. Found: C, 63.37; H, 5.62; N, 6.78. Calcd for C43H48-
1
C, 64.37; H, 5.76; N, 3.34. H NMR (THF-d8): δ -0.19 (s, 18H,
SiMe3), 7.04-7.21 (m, 6H, Ph), 7.28-7.38 (m, 10H, Ph), 7.38-
7.43 (m, 6H, Ph), 7.73-7.79 (m, 8H, Ph). 13C{1H} NMR (THF-
d8): δ 3.28 (SiMe3), 126.55, 127.97, 128.22, 128.97, 129.02,
129.11, 129.28, 132.05, 132.71, 132.78, 133.04, 133.19, 133.91,
(25) Sheldrick, G. M. In Crystallographic Computing 3: Data Collection,
Structure Determination, Proteins, and Databases; Sheldrick, G. M., Kruger,
C., Goddard, R., Eds.; Oxford University Press: New York, 1985; p 175.

3806 Organometallics, Vol. 26, No. 15, 2007
Leung et al.
135.91, 135.74, 136.04, 137.37, 138.69 (Ph and PhCdCPh). 31P-
{1H} NMR (298 K, THF-d8): δ 26.72. 31P{1H} NMR (238 K, THF-
d8): δ 5.56, 53.77.
assigned isotropic temperature factor calculations. Full details of
the crystallographic analysis of 2-4 are given in the Supporting
Information.
X-ray Crystallography. Single crystals were sealed in Linde-
mann glass capillaries under nitrogen. X-ray data of 2-4 were
collected on a Rigaku R-AXIS II imaging plate using graphite-
monochromated Mo KR radiation (λ ) 0.710 73 Å) from a rotating-
anode generator operating at 50 kV and 90 mA. Crystal data for
2-4 are summarized in Table 1. The structures were solved by
direct phase determination using SHELXTL-PC25 and refined by
full-matrix least squares with anisotropic thermal parameters for
the non-hydrogen atoms. Hydrogen atoms were introduced in their
idealized positions and included in structure factor calculations with
Acknowledgment. This work was supported by the Hong
Kong Research Grants Council (Project No. CUHK 401404).
Supporting Information Available: Tables of crystal data and
structure refinement details, atomic coordinates, bond lengths and
angles, and anisotropic displacement parameters for 2-4. This ma-
terial is available free of charge via the Internet at http://pubs.acs.org.
OM7002706