Spontaneous multiple insertion of a bulky aromatic isocyanide into the palladium-hydride bond of trans-[Pd(H)Cl(PPh3)2], leading to formation of heterobicyclic and pyrrole compounds

Article abstract of DOI:10.1021/om950619n

The reaction of [PdCl₂(PPh₃)₂] (1) with an excess of 2,6-xylyl isocyanide (XylNC) and H₂SiMePh in refluxing toluene gave a mononuclear palladium complex of a polyimino ligand, [Pd{C(=NR)C(=NR)C(=NR)C(=NR)CH(=NR)}(C=NR)Cl]· 1/2C₆H₆ (3·1/2C₆H₆: R = Xyl, 30%), and a novel heterobicyclic compound, 2,6-(2′,6′-xylyl) ₂-3,7-(N-2′,6′-xylylimino) ₂-4,8-(N-2′,6′-xylylamino) ₂-2,6-diazabicyclo[3.3.0]octa-4,8-diene (4a, 15%), structures of which were determined by X-ray analyses. When the reaction was carried out in the presence of triethylamine, the yield of 4a increased up to 44%. The complex 3 involves a pentaimino moiety [-C(=NR){C(=NR)}₃CH(=NR)] derived from a successive insertion of isocyanide into the palladium-hydride bond of trans-[Pd(H)Cl(PPh₃)₂] (2), which was generated from the reaction of 1 and H₂SiMePh in situ. The pentaimino ligand attaches to the metal through the carbon atom of the α-imino group and the lone pair electron of the γ-imino nitrogen atom, resulting in a five-membered chelate ring. The reaction of 3 with XylNC in the presence of H₂SiMePh afforded the heterobicyclic compound 4a. Similar treatments of 3 with 2,4,6-mesityl isocyanide (MesNC) and carbon monoxide (～80 kg cm^-2) in the presence of H₂SiMePh gave 2,6-(2′,6′-xylyl) ₂-3-(2′,4′,6′-mesitylimino)-7-(2′,6′- xylylimino)-4,8-(2′,6′-xylylamino) ₂-2,6-diazabicyclo[3.3.0]octa-4,8-diene(5)and2,6-(2′,6′- xylyl) ₂-7-(2′,6′-xylylimino)-4,8-(2′,6′-xylylamino) ₂-2,6-diazabicyclo[3.3.0]octa-4,8-dien-3-one (6), respectively. The structure of 6 was confirmed by X-ray crystallography. When complex 3 was treated with HC=CPh, a pyrrole compound, 1-(2′,6′-xylylamino)-2-phenyl-4-R′-pyrrole (R′ = Ci=NR)-{C(=NR)}₂CH(=NR), R = Xyl) (7), was obtained. The structure of 7·C₆H₆ was confirmed by X-ray crystallography. Possible mechanisms for 4-7 were proposed.

Full text of DOI:10.1021/om950619n

3404
Organometallics 1996, 15, 3404-3411
Sp on ta n eou s Mu ltip le In ser tion of a Bu lk y Ar om a tic
Isocya n id e in to th e P a lla d iu m -Hyd r id e Bon d of
tr a n s-[P d (H)Cl(P P h 3)2], Lea d in g to F or m a tion of
Heter obicyclic a n d P yr r ole Com p ou n d s
Tomoaki Tanase,*,† Tetsuro Ohizumi,† Kimiko Kobayashi,‡ and
Yasuhiro Yamamoto*,†
Department of Chemistry, Faculty of Science, Toho University, Miyama 2-2-1,
Funabashi, Chiba 274, J apan, and RIKEN (The Institute of Physical and Chemical Research),
Wako, Saitama 350, J apan
Received August 8, 1995X
The reaction of [PdCl2(PPh3)2] (1) with an excess of 2,6-xylyl isocyanide (XylNC) and
H2SiMePh in refluxing toluene gave a mononuclear palladium complex of a polyimino ligand,
[Pd{C(dNR)C(dNR)C(dNR)C(dNR)CH(dNR)}(CtNR)Cl]‚ 1/2C6H6 (3‚1/2C6H6: R ) Xyl, 30%),
and a novel heterobicyclic compound, 2,6-(2′,6′-xylyl)2-3,7-(N-2′,6′-xylylimino)2-4,8-(N-2′,6′-
xylylamino)2-2,6-diazabicyclo[3.3.0]octa-4,8-diene (4a , 15%), structures of which were de-
termined by X-ray analyses. When the reaction was carried out in the presence of
triethylamine, the yield of 4a increased up to 44%. The complex 3 involves a pentaimino
moiety [-C(dNR){C(dNR)}3CH(dNR)] derived from a successive insertion of isocyanide into
the palladium-hydride bond of trans-[Pd(H)Cl(PPh3)2] (2), which was generated from the
reaction of 1 and H2SiMePh in situ. The pentaimino ligand attaches to the metal through
the carbon atom of the R-imino group and the lone pair electron of the γ-imino nitrogen
atom, resulting in a five-membered chelate ring. The reaction of 3 with XylNC in the
presence of H2SiMePh afforded the heterobicyclic compound 4a . Similar treatments of 3
with 2,4,6-mesityl isocyanide (MesNC) and carbon monoxide (∼80 kg cm-2) in the presence
of H2SiMePh gave 2,6-(2′,6′-xylyl)2-3-(2′,4′,6′-mesitylimino)-7-(2′,6′-xylylimino)-4,8-(2′,6′-
xylylamino)2-2,6-diazabicyclo[3.3.0]octa-4,8-diene (5) and 2,6-(2′,6′-xylyl)2-7-(2′,6′-xylylimino)-
4,8-(2′,6′-xylylamino)2-2,6-diazabicyclo[3.3.0]octa-4,8-dien-3-one (6), respectively. The struc-
ture of 6 was confirmed by X-ray crystallography. When complex 3 was treated with
HCtCPh, a pyrrole compound, 1-(2′,6′-xylylamino)-2-phenyl-4-R′-pyrrole (R′ ) C(dNR)-
{C(dNR)}2CH(dNR), R ) Xyl) (7), was obtained. The structure of 7‚C6H6 was confirmed
by X-ray crystallography. Possible mechanisms for 4-7 were proposed.
In tr od u ction
with the aim of elucidating the mechanistic aspects
of the catalytic hydrogenation of CO.3 Isolated exam-
ples were, however, limited to single insertion prod-
ucts such as [PtCl(η1-HCNR)(PEt3)2],8-10 [Ru(η1-HC-
NR)(CH3COO)(CO)(PPh3)2],11 [(η-C5H5)2Co2(µ-HCNR)-
(µ-PMe2)2](PF6) (C5H5 ) cyclopentadienyl),12 [Os3(µ-H)-
(µ-η2-HCNR)(CO)10],13 [Re2(µ-H)(µ-η2-HCNR)(dppm)-
(CO)6] (dppm ) 1,2-bis(diphenylphosphino)methane),14
[(η-C5Me5)2Zr(H)(η2-HCNR)] (C5Me5 ) pentamethyl-
cyclopentadienyl),15 and [(η-C5H5)2Y(µ-η2-HCNR)]2.16
Notably, the multiple insertion reaction of isocyanide
into a metal-hydride bond has not been reported thus
far.
Insertion reactions of carbon monoxide are of funda-
mental importance in organometallic chemistry and
play a key role in many homogeneous catalytic reactions
promoted by transition metal complexes.1-3 Since
isocyanide has an isoelectronic structure with car-
bon monoxide, its insertion reaction into metal-
carbon bonds has been extensively studied.4-7 Unlike
carbon monoxide, isocyanide readily undergoes multiple
insertion into various metal-carbon σ-bonds, providing
useful synthetic routes to nitrogen-containing organic
compounds.4-6 Recently, the insertion reactions of
isocyanide into metal-hydride bonds to produce η1-
and η2-formimidoyl complexes have also been reported,
(8) Christian, D. F.; Clark, H. C. J . Organomet. Chem. 1975, 85,
C9.
(9) Christian, D. F.; Clark, H. C.; Stepaniak, R. F. J . Organomet.
Chem. 1976, 112, 227.
(10) Christian, D. F.; Clark, H. C.; Stepaniak, R. F. J . Organomet.
Chem. 1976, 112, 209.
(11) Clark, G. R.; Waters, J . M.; Whittle, K. P. J . Chem. Soc., Dalton
Trans. 1975, 2446.
(12) Zolk, R.; Werner, H. Angew. Chem., Int. Ed. Engl. 1985, 24,
577.
(13) Adams, R. D.; Golembeski, N. M. J . Am. Chem. Soc. 1979, 101,
2579.
(14) Mays, M. J .; Prest, D. W.; Raithby, P. R. J . Chem. Soc., Chem.
Commun. 1980, 171.
(15) Wolcznski, P. T.; Bercaw, J . E. J . Am. Chem. Soc. 1979, 101,
6450.
† Toho University.
‡ The Institute of Physical and Chemical Research.
X Abstract published in Advance ACS Abstracts, J uly 1, 1996.
(1) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987.
(2) Kuhlmann, E. J .; Alexander, J . J . Coord. Chem. Rev. 1980, 33,
195.
(3) Durfee, L. D.; Rothwell, P. Chem. Rev. 1988, 88, 1059.
(4) Yamamoto, Y.; Yamazaki, H. Coord. Chem. Rev. 1972, 8, 225.
(5) Yamamoto, Y. Coord. Chem. Rev. 1980, 32, 193.
(6) Singleton, E.; Oosthuizen, H. E. Adv. Organomet. Chem. 1983,
22, 209.
(7) Motz, P. L.; Alexander, J . J .; Ho, D. M. Organometallics 1989,
8, 2589.
(16) Evans, W. J .; Meadows, J . H.; Hunter, W. E.; Atwood, J . L.
Organometallics 1983, 2, 1253.
S0276-7333(95)00619-4 CCC: $12.00 © 1996 American Chemical Society
+
+

Formation of Heterobicyclic and Pyrrole Compounds
Organometallics, Vol. 15, No. 15, 1996 3405
were prepared by the known methods. Complex 2 could also
be prepared by the procedure described below. All reactions
were carried out under a nitrogen atmosphere with standard
Schlenk and vacuum line techniques.
We have studied insertion reactions of isocyanides
into various transition metal-carbon bonds, where the
metals are Pt,17 Pd,18 Ni,19 Co,20 Fe,21 and Mo,22 with a
hope of establishing efficient synthetic routes to poly-
imino and/or nitrogen-containing compounds. Treat-
ments of Pd complexes of azobenzene with isocyanides
led to formation of 3-imino-2-phenylindazolines,18c and
those of [PdCl2(isocyanide)2] with phenyl-substituted
cyclopentadienyl groups, ketenimine compounds.23 The
reactions of Co2(isocyanide)8 with aromatic azo com-
pounds, malonic esters, and cyanoacetate gave the
corresponding indazoline and indazole derivatives20d
and cyclic polyimino compounds,20f and those with
carbon polyhalides, benzyl bromide, and 2-bromo ac-
etophenone afforded indolenine, tetraiminohexane, and
diiminofuran derivatives, respectively.20c,g-i The reac-
tion of diphenylacetylene complex, [CpCo(PhC2Ph)-
PPh3], with RNC gave triiminodiphenylcyclopentene.20b
Recently, we have reported a spontaneous multiple
insertion of bulky aromatic isocyanides, 2,6-xylyl (Xyl)
and 2,4,6-mesityl (Mes) isocyanides, into the palladium-
carbon σ-bond of [Pd(CH3)I(PPh3)2], leading to a triple
insertion product of [Pd{C(dNR)C(dNR)C(dNR)CH3}-
(RNC)I] (R ) Xyl or Mes).18e The spontaneous feature
of bulky aromatic isocyanides is interestingly contrasted
with aliphatic, tert-butyl, and cyclohexyl isocyanides
which underwent stepwise insertion.18b We wish to
describe, in this report, the formation of novel hetero-
bicyclic and pyrrole compounds via spontaneous mul-
tiple insertion of the sterically bulky isocyanides into a
palladium-hydride bond. A preliminary account of this
work has already appeared.24
Mea su r em en ts. 1H and 13C NMR spectra were measured
on a J EOL GX-400 instrument at 400 and 100 MHz, respec-
tively. Chemical shifts were calibrated to tetramethylsilane
as an external reference. Infrared and electronic absorption
spectra were recorded with J asco A-100 and Ubest-30 spec-
trometers, respectively. Mass spectra were measured on a
Hitachi M-80 spectrometer. High-resolution mass spectros-
copy was carried out on a J EOL DX300 spectrometer. HPLC
analysis was performed with a TSK-CCPM system (TOSO Co.
Ltd.) using an ODS-80TM reversed phase column (5 mm i.d.
× 100 mm) and a Model UV-8011 UV-vis detector. Methanol
was used as an eluent. Fractionation of organic compounds
was carried out on the same HPLC system using a large ODS
column (20 mm i.d. × 300 mm).
P r ep a r a t ion of tr a n s-[P d (H)Cl(P P h 3)2] (2). A 50 mL
benzene suspension containing [PdCl2(PPh3)2] (1) (200 mg,
0.285 mmol) and H2SiMePh (350 mg, 2.86 mmol) was incu-
bated at 70-80 °C for 1 h. The resultant red solution was
concentrated to ca. 10 mL, and an addition of hexane afforded
the off-white powder of trans-[Pd(H)Cl(PPh3)2] (2) in 54% yield
(103 mg). The spectroscopic data [IR (Nujol): ν(Pd-H) 2060sh,
2055 cm-1
.
1H NMR (CDCl3): δ -13.2 (br, Pd-H)] were in
accord with reported ones.27
P r epar ation of [P d{C(dNR)C(dNR)C(dNR)C(dNR)CH-
(dNR)}(CtNR)Cl]‚1/2C6H6 (3‚1/2C6H6) (R ) Xyl). A mixture
of [PdCl2(PPh3)2] (1) (500 mg, 0.712 mmol), XylNC (930 mg,
7.12 mmol), and H2SiMePh (870 mg, 7.12 mmol) was refluxed
in 50 mL of toluene for 1 h. The dark red reaction mixture
was concentrated to ca. 10 mL. Hexane (5 mL) was added to
the solution to give a dark red precipitate. Recrystallization
of the precipitate from a benzene/hexane mixed solvent af-
forded red prismatic crystals of [Pd{C(dNR)C(dNR)C(dNR)C-
(dNR)CH(dNR)}(CtNR)Cl]‚1/2C6H6 (3‚1/2C6H6) (R ) Xyl) (210
mg, 30% based on Pd). The mother liquor was used to isolate
an organic compound. Anal. Calcd for C57H58N6PdCl: C,
Exp er im en ta l Section
Toluene, benzene, and hexane were distilled over calcium
hydride and tetrahydrofuran and diethyl ether over lithium
aluminum hydride prior to use. Other reagents were of the
best commercial grade and were used as received. Isocya-
nides,25 [PdCl2(PPh3)2] (1),26 and trans-[Pd(H)Cl(PPh3)2] (2)27
1
70.65; H, 6.03; N, 8.67. Found: C, 70.42; H, 5.91; N, 8.65. H
NMR (CDCl3): δ 1.71 (br, 12H, o-Me), 1.99, 2.13, 2.17, 2.53
(s, 4 × 6H, o-Me), 6.3-7.1 (m, 18H, Ar), 7.52 (s, 1H, HCdN).
13C NMR (CDCl3): δ 18.03, 18.52, 18.68, 18.72, 19.52 (q, o-Me),
153.87 (d, CHdNR), 160.40, 168.44, 172.36, 173.60 (s, NtC,
(17) Yamamoto, Y.; Yamazaki, H. Bull. Chem. Soc. J pn. 1971, 44,
1873.
CdN). IR (Nujol): ν(NtC) 2192 s, ν(CdN) 1632, 1592 cm-1
.
UV-vis (in benzene): λmax (ꢀ) 319 nm (1.2 × 104 M-1 cm-1).
P r ep a r a tion of 2,6-(2′,6′-Xylyl)2-3,7-(2′,6′-xylylim in o)2-
4,8-(2′,6′-xylyla m in o)2-2,6-d ia za bicyclo[3.3.0]octa -4,8-d i-
en e (4a ). Meth od A. The mother liquor described above was
chromatographed on a silica gel column (10 mm i.d. × 120 mm)
eluted with a benzene/hexane (1:4) mixed solvent. The yellow
fraction was collected, concentrated to ca. 1 mL, and kept at
-25 °C. Yellow crystals of 2,6-(2′,6′-xylyl)2-3,7-(2′,6′-xylylimino)2-
4,8-(2′,6′-xylylamino)2-2,6-diazabicyclo[3.3.0]octa-4,8-diene (4a )
were obtained in 15% yield versus Pd (84 mg). 1H NMR
(CDCl3): δ 1.86, 2.15, 2.24 (s, 3 × 12H, o-Me), 3.99 (s, 2H,
NH), 6.6-6.9 (m, 18H, Ar). 13C NMR (CDCl3): δ 18.58, 18.91
(q, o-Me), 127.20, 129.39 (s, CdC), 135.10 (s, CdN). IR
(18) (a) Yamamoto, Y.; Yamazaki, H. Bull. Chem. Soc. J pn. 1970,
43, 2653. (b) Yamamoto, Y.; Yamazaki, H. Inorg. Chem. 1974, 13, 438.
(c) Yamamoto, Y.; Yamazaki, H. Synthesis 1976, 750. (d) Yamamoto,
Y.; Yamazaki, H. Inorg. Chim. Acta 1980, 41, 229. (e) Yamamoto, Y.;
Tanase, T.; Yanai, K.; Asano, T.; Kobayashi, K. J . Organomet. Chem.
1993, 456, 287.
(19) (a) Yamamoto, Y.; Yamazaki, H.; Hagihara, N. Bull. Chem. Soc.
J pn. 1968, 41, 532. (b) Yamamoto, Y.; Yamazaki, H. Bull. Chem. Soc.
J pn. 1975, 48, 3691.
(20) (a) Yamamoto, Y.; Yamazaki, H. Bull. Chem. Soc. J pn. 1969,
42, 2077. (b) Yamazaki, H.; Aoki, K.; Yamamoto, Y.; Wakatsuki, Y. J .
Am. Chem. Soc. 1975, 97, 3546. (c) Yamamoto, Y.; Yamazaki, H. J .
Organomet. Chem. 1977, 137, C31. (d) Yamamoto, Y.; Yamazaki, H.
J . Org. Chem. 1977, 42, 4136. (e) Yamamoto, Y.; Yamazaki, H. Inorg.
Chem. 1978, 17, 3111. (f) Yamamoto, Y.; Yamazaki, H. Bull. Chem.
Soc. J pn. 1981, 54, 787. (g) Yamamoto, Y.; Yamazaki, H. Organome-
tallics 1988, 7, 2411. (h) Sugano, K.; Tanase, T.; Kobayashi, K.;
Yamamoto, Y. Chem. Lett. 1991, 921. (i) Yamamoto, Y.; Tanase, T.;
Sugano, K. J . Organomet. Chem. 1995, 486, 21.
(21) (a) Yamamoto, Y.; Yamazaki, H. Inorg. Chem. 1972, 11, 211.
(b) Yamamoto, Y.; Aoki, K.; Yamazaki, H. J . Am. Chem. Soc. 1974,
96, 2647. (c) Yamamoto, Y.; Yamazaki, H. J . Organomet. Chem. 1975,
90, 329. (d) Aoki, K.; Yamamoto, Y. Inorg. Chem. 1976, 15, 48. (e)
Yamamoto, Y.; Yamazaki, H. Inorg. Chem. 1977, 16, 3182.
(22) Yamamoto, Y.; Yamazaki, H. J . Organomet. Chem. 1970, 24,
717.
(Nujol): ν(NH) 3398, ν(CdN, CdC) 1663, 1619, 1582 cm-1
.
UV-vis (CH2Cl2): λmax (ꢀ) 440 nm (2.27 × 105 M-1 cm-1).
MS: m/ z 789 (M+). High-resolution MS: Found 788.4530
(M+), calcd 788.4494.
Meth od B. Complex 3 (100 mg, 0.103 mmol), XylNC (95
mg, 0.721 mmol), and H2SiMePh (164 mg, 1.34 mmol) were
dissolved in 20 mL of toluene, and the solution was incubated
at 110 °C for 2 h. The resultant solution was concentrated
and passed through a short silica gel column (10 mm i.d. × 30
mm). The organic components were analyzed by HPLC. The
yield of 4a was 25% based on Pd.
(23) Tanase, T.; Fukushima, T.; Nomura, T.; Yamamoto, Y.; Koba-
yashi, K. Inorg. Chem. 1994, 33, 32.
(24) Tanase, T.; Ohizumi, T.; Yamamoto, Y.; Kobayashi, K. J . Chem.
Soc., Chem. Commun. 1992, 707.
(25) Walborsky, H. M.; Niznik, G. E. J . Org. Chem. 1972, 37, 187.
(26) Calvin, G.; Coates, G. E. J . Chem. Soc., Chem. Commun. 1960,
2008.
(27) Kudo, K.; Hidai, M.; Murayama, T.; Uchida, Y. J . Chem. Soc.,
Chem. Commun. 1970, 1701.
Meth od C. A mixture of [PdCl2(PPh3)2] (1) (27 mg, 0.038
mmol), XylNC (50 mg, 0.38 mmol), H2SiMePh (46 mg, 0.28
mmol), and triethylamine (193 mg, 1.91 mmol) was heated at
110 °C in toluene for 1 h. The reaction mixture was concen-
+
+

3406 Organometallics, Vol. 15, No. 15, 1996
Tanase et al.
trated and passed through a short silica gel column (10 mm
i.d. × 30 mm). The organic components were analyzed by
HPLC. The yield of 4a was 44% based on Pd. Some other Pd
complexes, amines, and silane derivatives were examined
instead of complex 1, triethylamine, and H2SiMePh, respec-
tively.
Rea ction of tr a n s-[P d (H)Cl(P P h 3)2] (2) w ith XylNC. A
20 mL benzene solution containing XylNC (394 mg, 3.00 mmol)
was added dropwise to a benzene solution of trans-[Pd(H)Cl-
(PPh3)2] (2) (200 mg, 0.300 mmol) at -10 °C. The mixture was
slowly warmed to room temperature and then refluxed in
benzene for 1 h. The resultant dark red solution was concen-
trated to ca. 10 mL, and addition of hexane gave a pale yellow
powder of [PdCl2(XylNC)(PPh3)] (79 mg, 46%), which was
filtered off. Hexane (5 mL) was added to the filtrate to yield
red crystals of 3 (64 mg, 22%). The mother liquor was
chromatographed on silica gel as described in method A to give
a small amount of 4a (5 mg, 2%).
crystals of 7 (20 mg, 22% vs Pd). Anal. Calcd for C62H62N8:
C, 83.56; H, 7.01; N, 9.43. Found: C, 83.19; H, 7.00; N, 9.33.
1H NMR (CDCl3): δ 1.42, 1.64, 1.89, 1.99, 2.05, 2.30 (s, 6 ×
6H, o-Me), 4.91 (s, 1H, NH), 6.7-7.2 (m, 23H, Ar). IR
(Nujol): ν(NH) 3348, ν(CdN, CdC) 1609, 1591, 1505 cm-1
.
UV-vis (CH2Cl2): λmax (ꢀ) 360 (1.67 × 104), 320 nm (1.47 ×
104 M-1 cm-1). MS: m/ z 891 (M+).
Cr yst a l Da t a a n d In t en sit y Mea su r em en t s for 3‚
1/2C6H6, 4a , 6, a n d 7‚C6H6. X-ray-quality crystals of 3‚1/2C6H6,
4a , 6, and 7‚C6H6 were obtained by recrystallizations from
benzene/hexane mixed solvents. Crystal data and experimen-
tal conditions are summarized in Table 1.
Str u ctu r e Solu tion a n d Refin em en t. The structure of
3 was solved by direct methods with MULTAN78.28 The
coordinates of all hydrogen atoms were determined by differ-
ence Fourier syntheses. The structure was refined with the
block-diagonal least-square techniques minimizing ∑w(|Fo| -
|Fc|)2. Final refinement with anisotropic thermal parameters
for non-hydrogen atoms and isotropic ones for hydrogen atoms
converged to R ) 0.067 and Rw ) 0.078 (w ) 1). The structure
of 4a was solved and refined by methods similar to those
described above to R ) 0.075 and Rw ) 0.071 (w ) 1). The
structures of 6 and 7‚C6H6 were solved by direct methods with
MITHRIL.29 The coordinates of all hydrogen atoms were
calculated at the ideal positions, taking the C-H distance as
being 0.95 Å, and were not refined. Final full-matrix least-
squares refinement with isotropic thermal parameters for non-
hydrogen atoms converged to R ) 0.093 and Rw ) 0.066 (w )
1/σ2(Fo)) for 6, and that with anisotropic temperature factors
for the N(1)-N(6) and C(1)-C(8) atoms and isotropic ones for
the other non-hydrogen atoms, to R ) 0.077 and Rw ) 0.083
(w ) 1/σ2(Fo)) for 7‚C6H6.
Atomic scattering factors and values of f ′ and f ′′ for Pd,
Cl, O, N, and C were taken from the literatures.30 All
calculations for 3 and 4a were carried out on a FACOM M-780
computer with the program system UNICS III,31 and those
for 6 and 7, on a Digital VAX Station 3100 with the TEXSAN
Program System.32 The perspective views were drawn by
using the programs ORTEP33 and PLUTO.34 Compilation of
final atomic parameters for all non-hydrogen atoms is supplied
as Supporting Information.
P r ep a r a tion of 2,6-(2′,6′-Mesityl)2-3,7-(2′,6′-m esitylim i-
n o)2-4,8-(2′,6′-m esityla m in o)2-2,6-d ia za bicyclo[3.3.0]octa -
4,8-d ien e (4b). A mixture of [PdCl2(PPh3)2] (1) (250 mg, 0.356
mmol), MesNC (515 mg, 3.56 mmol), and H2SiMePh (435 mg,
7.12 mmol) was refluxed in toluene for 1 h. The resultant
solution was chromatographed on a silica gel column (10 mm
i.d. × 120 mm) eluted with a benzene/hexane (1:4) mixed
solvent. The yellow fraction was collected, concentrated to ca.
1 mL, and kept at -25 °C. Yellow crystals of 2,6-(2′,6′-
mesityl)2-3,7-(2′,6′-mesitylimino)2-4,8-(2′,6′-mesitylamino)2-2,6-
diazabicyclo[3.3.0]octa-4,8-diene (4b) were obtained in 22%
yield vs Pd (68 mg). 1H NMR (CDCl3): δ 1.82, 2.09, 2.12, 2.17
(s, 4 × 12H, o,p-Me), 2.07 (s, 6H, p-Me), 4.01 (s, 2H, NH), 6.39,
6.48, 6.64 (s, 3 × 4H, Ar). IR (Nujol): ν(NH) 3380, ν(CdN,
CdC) 1658, 1609, 1575 cm-1. UV-vis (CH2Cl2): λmax (ꢀ) 439
nm (1.33 × 105 M-1 cm-1). MS: m/ z 873 (M+). High-
resolution MS: Found 872.5589 (M+), calcd 872.5505.
P r epar ation of 2,6-(2′,6′-Xylyl)2-3-(2′,4′,6′-m esitylim in o)-
7-(2′,6′-xylylim in o)-4,8-(2′,6′-xylylam in o)2-2,6-diazabicyclo-
[3.3.0]octa -4,8-d ien e (5). Complex 3 (100 mg, 0.103 mmol),
MesNC (105 mg, 0.721 mmol), and H2SiMePh (164 mg, 1.34
mmol) were dissolved in 20 mL of toluene, and the solution
was heated at 110 °C for 2 h. The reaction mixture was passed
through a silica gel short column (10 mm i.d. × 30 mm), and
compound 5 contained in the benzene eluate was purified by
HPLC. The fraction of 5 was collected and recrystallized from
hexane to afford yellow crystals (15 mg, 18% vs Pd). 1H NMR
(CDCl3): δ 1.85, 1.86, 2.11, 2.14, 2.23, 2.24 (s, 6 × 6H, o-Me),
2.09 (s, 3H, p-Me), 3.95, 4.07 (s, 2 × 1H, NH), 6.6-6.9 (m, 17H,
Ar). IR (Nujol): ν(NH) 3405, ν(CdN, CdC) 1677, 1628, 1610sh,
1596 cm-1. UV-vis (CH2Cl2): λmax (ꢀ) 441 nm (1.36 × 105 M-1
cm-1). MS: m/ z 803 (M+). High-resolution MS: Found
802.4632 (M+), calcd 802.4723.
P r ep a r a tion of 2,6-(2′,6′-Xylyl)2-7-(2′,6′-xylylim in o)-4,8-
(2′,6′-xylyla m in o)2-2,6-d ia za bicyclo[3.3.0]octa -4,8-d ien -3-
on e (6). Complex 3 (100 mg, 0.103 mmol) and H2SiMePh (183
mg, 1.34 mmol) were heated in toluene at 130 °C for 24 h under
a pressure of carbon monoxide (∼80 kg cm-2). The reaction
mixture was passed through a silica gel short column (10 mm
i.d. × 30 mm), and compound 6 contained in the benzene eluate
was purified by HPLC. The fraction of 6 was collected and
recrystallized from hexane to afford yellow crystals (12 mg,
17% vs Pd). 1H NMR (CDCl3): δ 1.88, 2.08, 2.09, 2.15, 2.21
(s, 5 × 6H, o-Me), 4.43, 4.82 (s, 2 × 1H, NH), 6.6-6.9 (m, 15H,
Ar). IR (Nujol): ν(NH) 3383, 3330, ν(CdN, CdC, CdO) 1708,
1672, 1641, 1586 cm-1. UV-vis (CH2Cl2): λmax (ꢀ) 421 nm (1.76
× 105 M-1 cm-1). MS: m/ z 686 (M+). High-resolution MS:
Found 685.3749 (M+), calcd 685.3717.
Resu lts a n d Discu ssion
P r ep a r a tion s of [P d {C(dNR)C(dNR)C(dNR)C-
(dNR )CH (dNR )}(CNR )Cl]‚1/2C6H 6 (3‚1/2C6H 6) a n d
2,6-(1-Xylyl)2-3,7-(1-xylylim in o)2-4,8-(N-1-xylyla m i-
n o)2-2,6-diazabicyclo[3.3.0]octa-4,8-dien e (4a). Com-
plex [PdCl2(PPh3)2] (1) was treated with excess amounts
of H2SiMePh and XylNC in toluene at 110 °C for 1 h.
The resultant dark red solution was concentrated, and
an addition of hexane gave a dark red precipitate.
Recrystallization of the precipitate from a benzene-
hexane mixed solvent gave red crystals formulated as
[PdCl(XylNC)6H]‚1/2C6H6 (3‚1/2C6H6) in 30% yield. By
chromatography of the filtrate on silica gel, a yellow
organic compound formulated as [(XylNC)6H2] (4a ) was
obtained in 15% yield based on Pd. Both compounds 3
and 4a were not obtained in the absence of H2SiMePh,
(28) Main, P.; Lessinger, L.; Woolfson, M. M.; Germain, G.; Declecq,
J . P. MULTAN78, Universities of York, U.K., and Louvain, Belgium,
1978.
(29) Gilmore, G. J . J . Appl. Crystallogr. 1984, 17, 42.
(30) (a) Cromer, D. T.; Waber, J . T. In International Tables for X-ray
Crystallography; Kynoch Press: Birmingham, England, 1974; Vol. IV.
(b) Cromer, D. T. Acta Crystallogr. 1965, 18, 17.
(31) Sakurai, T.; Kobayashi, K. Rikagaku Kenkyusho Hokoku 1979,
55, 69.
(32) TEXSAN Structure Analysis Package, Molecular Structure
Corp., The Woodlands, TX, 1985.
(33) J ohnson, C. K. ORTEP-II, Oak Ridge National Laboratory, Oak
Ridge, TN, 1976.
P r ep a r a t ion of 1-(2′,6′-Xylyla m in o)-2-p h en yl-4-R′-N′-
xylylp yr ole (R′ ) -C(dNXyl){C(dNXyl)}2CH(dNXyl)) (7).
Complex 3 (100 mg, 0.103 mmol) and phenylacetylene (105
mg, 1.03 mmol) were dissolved in 20 mL of toluene, and the
solution was incubated at 110 °C for 2 h. The reaction mixture
was passed through a silica gel short column (10 mm i.d. ×
30 mm), and the benzene eluate was concentrated to dryness.
The residue was crystallized from hexane to afford orange
(34) Motherwell, S.; Clegg, W. PLUTO: Program for Ploting Mo-
lecular and Crystal Structures, University of Cambridge, England,
1978.
+
+

Formation of Heterobicyclic and Pyrrole Compounds
Ta ble 1. Cr ysta llogr a p h ic a n d Exp er im en ta l Da ta for 3‚1/2C6H6, 4a , 6, a n d 7‚C6H6
compound
Organometallics, Vol. 15, No. 15, 1996 3407
3‚1/2C6H6
4a
6
7‚C6H6
C68H68N6
formula
fw
cryst size, mm
cryst system
space group
a, Å
C57H58N6PdCl
969.00
C54H56N6
C46H47N5
789.08
685.91
0.45 × 0.23 × 0.13
triclinic
P1h (No. 2)
12.804(3)
18.214(6)
8.301(2)
91.67(3)
98.36(2)
94.08(2)
1909
969.33
0.48 × 0.38 × 0.20
0.40 × 0.20 × 0.14
monoclinic
P21/a (No. 14)
21.195(7)
0.60 × 0.40 × 0.50
triclinic
P1h (No. 2)
11.688(2)
21.611(4)
11.222(3)
94.39(2)
94.83(2)
97.12(2)
2792
triclinic
P1h (No. 2)
14.312(5)
15.095(7)
13.303(7)
90.49(4)
97.30(3)
115.59(4)
2565
b, Å
c, Å
13.237(3)
8.422(4)
R, deg
â, deg
107.40(3)
γ, deg
V, Å3
2255
2
Z
2
2
2
T, °C
23
23
23
23
machine
CAD4
1.255
4.49
analytical method
ω (2θ < 30°), ω-2θ
(30 < 2θ < 55°)
55
AFC4
1.163
0.64
none
AFC5S
1.193
0.67
none
ω-2θ
AFC5S
1.153
1.07
ψ-scan method
ω-2θ
D
calcd, g cm-1
abs coeff, cm-1
abs corr
scan method
ω (2θ < 30°), ω-2θ
(30 < 2θ < 50°)
2θ max, deg
50
45
3598
849 (I > 3σ(I))
direct methods,
MITHRIL
209
4.06
0.093
0.066
0.35
45
4872
2005 (I > 3σ(I))
direct methods,
MITHRIL
367
5.46
0.077
0.083
0.29
no. of unique data
no. of obsd data
solution
9739
2203
8687 (I > 2.5σ(I))
direct methods,
MULTAN78
807
10.76
0.067
1810 (I > 1.5σ(I))
direct methods,
MULTAN78
384
4.71
0.075
no. of variables
data/param ratio
Ra
a
Rw
F
0.075
1.45 (around Pd)
0.071
0.31
max, e Å-3
a
2
R ) ∑||Fo| - |Fc||/∑|Fo|; Rw ) [∑w(|Fo| - |Fc|)2/∑w|Fo| ]1/2
.
nor by using SiMe2Ph2 instead of H2SiMePh. The IR
spectrum of 3 showed the absorptions corresponding to
NtC (2192 cm-1) and CdN groups (1632, 1592 cm-1).
The IR spectral pattern was comparable to that of [Pd-
{C(dNR)C(dNR)C(dNR)CH3}(RNC)I] (8) (R ) Xyl),
which involves a terminal isocyanide and a triimino
moiety derived from the multiple insertion of isocyanide
into a Pd-C σ-bond.18e The 1H NMR spectrum indi-
cated the presence of six xylyl units at δ 1.71, 1.99, 2.13,
2.17, and 2.53 with a 2:1:1:1:1 intensity ratio and one
formimidoyl residue (HCdN) at δ 7.52. The resonance
at δ 1.99 was assigned to a terminal isocyanide because
it showed a ligand exchange with free XylNC. The 13C
NMR spectrum of 3 also exhibited six methyl signals
at δ 18.03-19.52 and one doublet peak for the formim-
idoyl carbon at δ 153.87. A mononuclear palladium with
a terminal isocyanide, a chloride anion, and a polyimino
ligand, formed by multiple insertion of five isocyanide
molecules into a Pd-H bond, was inferred for a struc-
ture of 3 in the light of spectroscopic and analytical data.
An X-ray analysis of 3 confirmed the proposed structure
(vide infra).
spectrum of 4a , only three singlets assignable to the
o-methyl groups of xylyl units were observed at δ 1.86,
2.15, and 2.24 together with that to the amino protons
at δ 3.99, suggesting that the molecule 4a has a
symmetrical structure. The IR spectrum showed the
presence of amino groups at 3398 cm-1 (NH) and CdC
and CdN groups at 1663, 1619, and 1582 cm-1. By an
X-ray analysis, compound 4a was revealed to be a novel
heterobicyclic compound, 2,6-(1-xylyl)2-3,7-(1-xylylimino)2-
4,8-(N-1-xylylamino)2-2,6-diazabicyclo[3.3.0]octa-4,8-di-
ene (vide infra). Compound 4a was also prepared by
the reaction of complex 3 with excess XylNC and H2-
SiMePh in 25% yield. The yield of the bicyclic com-
pound 4a increased up to 44% (vs Pd) by an addition of
Et3N (Table 2, no. 1), though complex 3 was not obtained
at all. Other tertiary amines (nPr3N, nBu3N, and Me2-
PhN) and pyridine were also effective (18-39%), but
secondary and primary amines, Et2NH and nPr2NH,
suppressed the formation of 4a (0-5%) due to compli-
cated side reactions. H2SiMePh could be replaced by
HSiMe2Ph and H2SiPh2 in 31-34% yields, whereas H3-
SiPh, SiMe2Ph2, and (SiMe2Ph)2 were not effective. The
palladium complexes containing aliphatic tertiary phos-
phines, [PdCl2(PCy3)2], [PdCl2(PMe3)2], and [PdCl2-
(PnBu3)2], showed almost no activity for the formation
of 4a , and the use of [PdCl2(PMe2Ph)2] and [PdCl2-
(PMePh2)2] resulted in low yields. These results ten-
tatively suggested that dissociation of phosphine ligands
is an important step for the formation of 4a . The
chelating diphosphine complex, [PdCl2(dppe)], did not
have the activity, because it does not accommodate the
trans-[Pd(H)ClP 2] geometry. The analogous heterobi-
cyclic compound, 2,6-(1-mesityl)2-3,7-(1-mesitylimino)2-
4,8-(N-1-mesitylamino)2-2,6-diazabicyclo[3.3.0]octa-4,8-
diene (4b), was prepared by the reaction of [PdCl2(PPh3)2]
with MesNC and H2SiMePh in 22% yield.
When [PdCl2(PPh3)2] (1) was treated with an excess
amount of H2SiMePh in the absence of XylNC, the
palladium hydride complex, trans-[Pd(H)Cl(PPh3)2] (2),
was obtained in 54% yield. This procedure is more
convenient compared with the known method by using
the reaction of zerovalent palladium complex, [Pd-
(PPh3)4] or [Pd(PPh3)2(CO)], with HCl (32%).27 The
hydride complex 2 was transformed to 3 in 22% yield
by treatment with an excess of XylNC in refluxing
toluene.
The mass spectrum indicated that the organic com-
pound 4a was a co-oligomerization product of six iso-
cyanide molecules and two hydrogen atoms which were
seemingly derived from H2SiMePh. In the 1H NMR
+
+

3408 Organometallics, Vol. 15, No. 15, 1996
Tanase et al.
Ta ble 2. F or m a tion of 4a fr om th e Rea ction of
[P d Cl2P 2] w ith XylNC a n d Sila n es in th e P r esen ce
of Am in esa
Ta ble 3. Selected Bon d Dista n ces (Å) a n d
An gles (d eg) for 3a
Distances
yield of 4a , %b
Pd-Cl
2.376(2)
1.956(6)
1.271(8)
1.252(9)
1.260(9)
1.274(9)
1.272(9)
1.133(12)
1.547(11)
1.522(11)
0.97(8)
Pd-N(3)
2.100(6)
1.970(8)
1.437(11)
1.438(7)
1.435(7)
1.452(12)
1.417(9)
1.409(12)
1.482(8)
1.455(9)
no.
P ligand
silane
amine
Pd-C(1)
Pd-C(6)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
H2SiMePh
H2SiMePh
H2SiMePh
H2SiMePh
H2SiMePh
H2SiMePh
H2SiMePh
H2SiMePh
H2SiMePh
H2SiMePh
H2SiMePh
H2SiMePh
H2SiMePh
H2SiMePh
H2SiMePh
H2SiMePh
H2SiPh2
Et3N
44
39
29
22
18
5
N(1)-C(1)
N(2)-C(2)
N(3)-C(3)
N(4)-C(4)
N(5)-C(5)
N(6)-C(6)
C(1)-C(2)
C(3)-C(4)
C(5)-H(C5)
N(1)-C(11)
N(2)-C(21)
N(3)-C(31)
N(4)-C(41)
N(5)-C(51)
N(6)-C(61)
C(2)-C(3)
C(4)-C(5)
pyridine
Me2PhN
nPr3N
iBu3N
Et2NH
nPr2NH
Ph3N
none
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
5
trace
15
3
PPh3
PMe3
PMe2Ph
PMePh2
PnBu3
PCy3
7
Angles
20
trace
trace
0
Cl-Pd-N(3)
96.1(1)
84.1(2)
Cl-Pd-C(1)
177.1(2)
81.3(2)
98.6(3)
Cl-Pd-C(6)
N(3)-Pd-C(1)
C(1)-Pd-C(6)
C(2)-N(2)-C(21)
Pd-N(3)-C(31)
C(4)-N(4)-C(41)
C(6)-N(6)-C(61)
Pd-C(1)-C(2)
N(2)-C(2)-C(1)
C(1)-C(2)-C(3)
N(3)-C(3)-C(4)
N(4)-C(4)-C(3)
C(3)-C(4)-C(5)
N(5)-C(5)-H(C5)
Pd-C(6)-N(6)
N(3)-Pd-C(6)
C(1)-N(1)-C(11)
Pd-N(3)-C(3)
C(3)-N(3)-C(31)
C(5)-N(5)-C(51)
Pd-C(1)-N(1)
N(1)-C(1)-C(2)
N(2)-C(2)-C(3)
N(3)-C(3)-C(2)
C(2)-C(3)-C(4)
N(4)-C(4)-C(5)
N(5)-C(5)-C(4)
C(4)-C(5)-H(C5)
179.7(2)
122.0(6)
115.3(4)
123.4(6)
122.2(8)
134.9(6)
115.3(6)
118.9(7)
116.2(7)
118.9(6)
128.1(7)
118.2(7)
119(3)
dppec
no complex
PPh3
124.3(7)
121.2(5)
120.7(6)
171.8(6)
109.3(4)
129.8(5)
110.9(5)
124.6(5)
116.6(6)
115.4(6)
120(4)
0
34
31
trace
0
0
0
PPh3
PPh3
PPh3
PPh3
HSiMe2Ph
H3SiPh
SiMe2Ph2
(SiMe2Ph)2
none
PPh3
Et3N
a
A mixture of [PdCl2P 2] (0.038 mmol) and XylNC (0.38 mmol)
was incubated at 110 °C in toluene for 1 h in the presence of silane
b
(0.28 mmol) and amine (1.9 mmol). Determined by HPLC. c P 2
163.8(6)
) dppe (1,2-bis(diphenylphosphino)ethane).
a
Estimated standard deviations are given in parentheses. See
Figure 1 for atom labels. In this report, a systematic atomic
numbering is used for xylyl units shown as follows:
gauche conformation with the C(1) and C(2) atoms
significantly deviated from the best plane. The C(1) and
N(3) atoms occupy the coordination sites trans to the
chlorine and the terminal carbon atom of isocyanide,
respectively. The R- and â-imino groups are twisted
with a torsional angle of 43° (N(1)-C(1)-C(2)-N(2)).
A similar coordination geometry with five-membered
chelation of a polyimino moiety was also found in
complex 818e and [Ni{C(dNR)C(dNR)C(dNR)CH3}-
(RNC)Cl] (9, R ) tBu).35 The σ-bond distance between
the palladium and the imino carbon atoms in 3 is
F igu r e 1. ORTEP plot of [Pd{C(dNR)C(dNR)C(dNR)C-
(dNR)CH(dNR)}(CtNR)Cl] (3, R ) Xyl). Thermal el-
lipsoids are drawn at the 40% probability level, and
aromatic hydrogen atoms are omitted for clarity.
Str u ctu r e of [P d{C(dNR)C(dNR)C(dNR)C(dNR)-
CH(dNR)}(CNR)Cl]‚1/2C6H6 (3‚1/2C6H6). An X-ray
crystallographic analysis was carried out to clarify the
structure of complex 3. The unit cell contains two
discrete molecules of complex 3 and one lattice benzene
without the unusual contacts between them. A per-
spective drawing of complex 3 with the atomic number-
ing scheme is given in Figure 1, and some selected bond
distances and angles are listed in Table 3. The pal-
ladium atom is coordinated by a chlorine atom (Pd(1)-
Cl(1) ) 2.376(2) Å), a terminal XylNC (Pd(1)-C(6) )
1.970(8) Å), and a bidentate polyimino ligand in a
square planar geometry. The polyimino moiety consists
of four xylylimino groups and a terminal formimidoyl
unit (C(5)-H(1) ) 0.97(8) Å) and coordinates to the Pd
atom through the carbon atom of R-imino group (Pd-
C(1) ) 1.956(6) Å) and the lone pair electrons of the
γ-imino nitrogen atom (Pd-N(3) ) 2.100(6) Å), forming
a five-membered chelate ring (C(1)-Pd-N(3) ) 81.3-
(2)°). The chelate ring is no longer planar, taking a
shorter than the corresponding value (2.03(2) Å) of 8,
ascribable to the smaller trans effect of Cl- compared
to I-. The γ-imino and ꢀ-formimidoyl units are coplanar
to each other (torsion angle N(4)-C(4)-C(5)-N(5) )
175°) and are nearly perpendicular to the five-mem-
bered chelate ring (torsion angle N(3)-C(3)-C(4)-N(4)
) 81°), probably to avoid steric repulsions. The closely
related nickel complex involving a pentaimino moiety,
[Ni{C(dNR)C(dNR)C(dNR)C(dNR)C(dNR)COPh}-
(35) Carmona, E.; Marin, J . M.; Palma, P.; Poveda, M. L. J .
Organomet. Chem. 1989, 377, 157.
+
+

Formation of Heterobicyclic and Pyrrole Compounds
Organometallics, Vol. 15, No. 15, 1996 3409
Ta ble 4. Selected In ter a tom ic Dista n ces (Å) a n d
An gles (d eg) for 4a a
Distances
N(1)-C(1)
N(1)-C(11)
N(2)-C(21)
N(3)-C(31)
C(1)-C(1)′
N(3)-H(N3)
1.400(7)
1.443(6)
1.416(8)
1.418(9)
1.430(7)
0.98(7)
N(1)-C(2)
N(2)-C(2)
N(3)-C(3)
C(2)-C(3)
C(1)-C(3)′
1.421(7)
1.275(8)
1.382(8)
1.480(8)
1.327(8)
Angles
C(1)-N(1)-C(2)
C(2)-N(1)-C(11)
C(3)-N(3)-C(31)
N(2)-C(2)-C(3)
107.6(4)
121.7(5)
125.0(6)
107.6(5)
C(1)-N(1)-C(11)
C(2)-N(2)-C(21)
N(1)-C(2)-N(2)
N(3)-C(3)-C(2)
126.4(5)
122.2(5)
119.0(5)
121.6(5)
a
Estimated standard deviations are given in parentheses. See
Figure 2 for atom labels.
Sch em e 1a
F igu r e 2. ORTEP view of 2,6-(2′,6′-xylyl)2-3,7-(N-2′,6′-
xylylimino)2-4,8-(N-2′,6′-xylylamino)2-2,6-diazabicyclo[3.3.0]-
octa-4,8-diene (4a ). Thermal ellipsoids are drawn at the
40% probability level, and hydrogen atoms are omitted for
clarity.
(CNR)Cl] (R) tBu), has been prepared by the reaction
of Ni(tBuNC)4 with PhCOCl but has not been structur-
ally characterized.36,37 The molecular structure indi-
cated that complex 3 was derived from insertion of an
isocyanide molecule into a metal-hydride bond followed
by successive insertion of four isocyanides into a Pd-C
bond. To our knowledge, this is the first example of the
multiple insertion of isocyanide into metal-hydride
bonds.
a
L ) RNC, R ) Xyl.
six xylyl groups are nearly perpendicular to the ring
plane so as to release the steric repulsions.
Str u ctu r e of 2,6-(1-xylyl)2-3,7-(1-xylylim in o)2-4,8-
(N-1-xylyla m in o)2-2,6-d ia za b icyclo[3.3.0]oct a -4,8-
d ien e (4a ). A perspective drawing of compound 4a
Rea ction s of Com p lex 3 w ith Mesityl Isocya n id e
a n d Ca r b on Mon oxid e. The reaction of complex 3
with excess MesNC in the presence of H2SiMePh gave
a compound formulated as {(XylNC)5(MesNC)H2} (5,
18%) from a mass spectrum, with trace amounts of 4a ,b
(2-3%). The formation of 4a ,b implied decomposition
reactions of 3 including de-iminoacylation, and regen-
eration of Pd-H species took place as side reactions,
which may be responsible for the low yield of desired
compound. The IR spectrum of 5 showed the presence
of amino groups at 3405 cm-1 (NH) and CdC and CdN
groups at 1677, 1628, 1610sh, and 1596 cm-1. In the
1H NMR spectrum, seven methyl signals were observed
at δ 1.85, 1.86, 2.09, 2.11, 2.14, 2.23, and 2.24 with an
intensity ratio of 2:2:1:2:2:2:2 and two resonances for
amino protons at δ 3.95 and 4.07, consistent with the
asymmetric heterobicyclic structure as shown in Scheme
2. A similar reaction of 3 with CO (∼80 kg cm-2) also
afforded compound 6 formulated as {(XylNC)5(CO)H2}
in 17% yield. The IR spectrum showed absorptions due
to amino (3383, 3330 cm-1) and CdC, CdN (1672, 1641,
1586 cm-1), and CdO (1708 cm-1) groups. The 1H NMR
spectrum exhibited five resonances for methyl groups
of xylyl units at δ 1.88, 2.08, 2.09, 2.15, and 2.21 and
two peaks for amino groups at δ 4.43 and 4.82. The
UV-vis spectrum is similar to those of 4a ,b. The
structure of 6 was confirmed by X-ray crystallography
with the atomic numbering scheme is given in Figure
2, and some selected bond lengths and angles are listed
in Table 4. The molecule has a crystallographically
imposed inversion center at the middle of the C(1)-C(1)′
bond. The molecule comprises a planar [3.3.0] bicyclic
ring with two five-membered rings, each involving a
cyclic amino nitrogen atom (N(1)), an ene-amine unit
(C(1)′-C(3) ) 1.327(8) Å, C(3)-N(3) ) 1.382(8) Å), and
an imino group (C(2)-N(2) ) 1.275(8) Å). The bond
length between the two ring-junction carbons (C(1) and
C(1)′) is 1.430(7) Å. While the C(1)′-C(3) and C(2)-
N(2) bond distances correspond to typical values for
CdC and CdN double bonds, the other in-ring C-C and
C-N bonds show somewhat shorter values than those
for typical single bonds. These indicated that the
π-electrons in the rings are delocalized to some extent,
which is consistent with the upfield shift of CdN carbon
resonance (δ 135.10) in the 13C NMR spectrum. The
to have a heterobicyclic structure similar to 4a .
A
perspective drawing is illustrated in Figure 3, and some
selected bond angles and distances are listed in Table
5. One of the imino groups in 4a is replaced by a
carbonyl group in 6. The C(6)-O(1) bond distance of
1.20(1) Å is in the normal range for CdO double bonds.
(36) Otsuka, S.; Nakamura, A.; Yoshida, T. J . Am. Chem. Soc. 1969,
91, 7198.
(37) Otsuka, S.; Nakamura, A.; Yoshida, T.; Naruto, M.; Ataka, K.
J . Am. Chem. Soc. 1973, 95, 3180.
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3410 Organometallics, Vol. 15, No. 15, 1996
Tanase et al.
Sch em e 2a
Ta ble 5. Selected In ter a tom ic Dista n ces (Å) a n d
An gles (d eg) for 6a
Distances
O(1)-C(6)
N(1)-C(11)
N(2)-C(21)
N(3)-C(6)
N(4)-C(1)
N(4)-C(41)
N(5)-C(51)
C(2)-C(3)
C(4)-C(5)
1.20(3)
1.44(2)
1.44(3)
1.39(3)
1.41(2)
1.44(2)
1.41(2)
1.34(3)
1.35(3)
N(1)-C(1)
N(2)-C(2)
N(3)-C(3)
N(3)-C(31)
N(4)-C(4)
N(5)-C(5)
C(1)-C(2)
C(3)-C(4)
C(5)-C(6)
1.29(3)
1.35(2)
1.43(3)
1.48(2)
1.41(2)
1.38(2)
1.49(3)
1.45(2)
1.53(3)
Angles
C(1)-N(1)-C(11)
C(3)-N(3)-C(6)
C(6)-N(3)-C(31)
C(1)-N(4)-C(41)
C(5)-N(5)-C(51)
N(1)-C(1)-C(2)
N(2)-C(2)-C(1)
C(1)-C(2)-C(3)
N(3)-C(3)-C(4)
N(4)-C(4)-C(3)
C(3)-C(4)-C(5)
N(5)-C(5)-C(6)
O(1)-C(6)-N(3)
N(3)-C(6)-C(5)
129(2)
109(2)
122(2)
117(2)
121(2)
120(2)
113(2)
104(2)
105(2)
106(2)
114(2)
120(3)
128(3)
108(3)
C(2)-N(2)-C(21)
C(3)-N(3)-C(31)
C(1)-N(4)-C(4)
C(4)-N(4)-C(41)
N(1)-C(1)-N(4)
N(4)-C(1)-C(2)
N(2)-C(2)-C(3)
N(3)-C(3)-C(2)
C(2)-C(3)-C(4)
N(4)-C(4)-C(5)
N(5)-C(5)-C(4)
C(4)-C(5)-C(6)
O(1)-C(6)-C(5)
121(2)
129(2)
107(2)
117(2)
130(2)
109(2)
143(3)
141(3)
113(2)
140(2)
136(3)
104(2)
123(3)
a
a
L ) RNC, R ) Xyl.
Estimated standard deviations are given in parentheses. See
Figure 3 for atom labels.
F igu r e 4. PLUTO view of 1-(2′,6′-xylylamino)-2-phenyl-
4-R′-pyrole (R′ ) C(dNR){C(dNR)}2CH(dNR), R ) Xyl))
(7). Aromatic hydrogen atoms are omitted for clarity.
F igu r e 3. PLUTO diagram of 2,6-(2′,6′-xylyl)2-7-(2′,6′-
xylylimino)-4,8-(2′,6′-xylylamino)2-2,6-diazabicyclo[3.3.0]-
octa-4,8-dien-3-one (6). Hydrogen atoms are omitted for
clarity.
cm-1. In the 1H NMR spectrum, six singlets assignable
to the o-methyl groups of xylyl units were observed at
δ 1.42, 1.64, 1.89, 1.99, 2.05, and 2.30 with the same
intensity and one singlet assignable to an amino proton
was observed at δ 4.91; however, resonances for olefinic
and formimidoyl protons were not assigned owing to
overlap with aromatic signals. Compound 7‚C6H6 was
revealed by X-ray crystallography to be a pyrrole
derivative, 1-(2′,6′-xylylamino)-2-phenyl-4-R′-N′-xylyl-
pyrole (R′ ) -C(dNXyl){C(dNXyl)}2CH(dNXyl), as
shown in Figure 4. Some selected bond distances and
angles are summarized in Table 6. The pyrrole ring has
xylyl, xylylamino, phenyl, and polyimino substituents.
The polyimino side chain contained three internal imino
and a terminal formimidoyl moieties connected by C-C
single bonds; the average distances of C-N double and
C-C single bonds are 1.26 and 1.49 Å, respectively. The
CdNR groups in the side chain alternatively twisted
around the C-C single bonds; the torsion angles are
N(1)-C(1)-C(2)-N(2) ) -161°, N(2)-C(2)-C(3)-N(3)
) -133°, and N(3)-C(3)-C(4)-N(4) ) 51°.
Rea ction of Com p lex 3 w ith P h en yl Acetylen e.
When complex 3 was treated with an excess amount of
phenylacetylene in refluxing toluene, a red organic
compound, formulated as {(XylNC)6(PhC2H)H2} (7) from
the elemental analysis and the mass spectrum, was
obtained in 22% yield. The UV-vis spectral pattern of
7 is quite different (λmax 360, 320 nm) from those of the
heterobicyclic compounds 4-6 (λmax 420-440 nm). The
IR spectrum indicated the presence of NH group at 3348
cm-1 and CdN and CdC groups at 1609, 1591, and 1505
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Formation of Heterobicyclic and Pyrrole Compounds
Organometallics, Vol. 15, No. 15, 1996 3411
Sch em e 3a
Ta ble 6. Selected In ter a tom ic Dista n ces (Å) a n d
An gles (d eg) for 7a
Distances
N(1)-C(1)
N(2)-C(2)
N(3)-C(3)
N(4)-C(4)
N(5)-C(5)
N(5)-C(51)
N(6)-C(61)
C(2)-C(3)
C(4)-C(5)
C(6)-C(7)
1.23(2)
1.28(2)
1.27(1)
1.26(1)
1.41(1)
1.44(2)
1.45(2)
1.54(2)
1.44(2)
1.39(2)
N(1)-C(11)
N(2)-C(21)
N(3)-C(31)
N(4)-C(41)
N(5)-C(6)
N(6)-C(6)
C(1)-C(2)
C(3)-C(4)
C(5)-C(8)
C(7)-C(8)
1.43(2)
1.45(2)
1.44(2)
1.42(2)
1.37(1)
1.39(2)
1.49(2)
1.50(2)
1.39(2)
1.41(2)
Angles
C(1)-N(1)-C(11)
C(3)-N(3)-C(31)
C(5)-N(5)-C(51)
C(6)-N(5)-C(51)
N(1)-C(1)-C(2)
N(2)-C(2)-C(3)
N(3)-C(3)-C(2)
C(2)-C(3)-C(4)
N(4)-C(4)-C(5)
N(5)-C(5)-C(4)
C(4)-C(5)-C(8)
N(5)-C(6)-C(7)
C(6)-C(7)-C(8)
C(8)-C(7)-C(71)
119(1)
127(1)
125(1)
124(1)
124(1)
115(1)
124(1)
118(1)
120(1)
125(1)
128(1)
108(1)
107(1)
126(1)
C(2)-N(2)-C(21)
C(4)-N(4)-C(41)
C(5)-N(5)-C(6)
C(6)-N(6)-C(61)
N(2)-C(2)-C(1)
C(1)-C(2)-C(3)
N(3)-C(3)-C(4)
N(4)-C(4)-C(3)
C(3)-C(4)-C(5)
N(5)-C(5)-C(8)
N(5)-C(6)-N(6)
N(6)-C(6)-C(7)
C(6)-C(7)-C(71)
C(5)-C(8)-C(7)
121(1)
127(1)
110(1)
121(1)
122(1)
123(1)
118(1)
124(1)
116(1)
105(1)
118(1)
134(1)
129(1)
110(1)
a
L ) RNC, R ) Xyl.
a
Estimated standard deviations are given in parentheses. See
Figure 4 for atom labels.
abstraction of hydrogten atom, to give the bicyclic com-
pound 4a . The positions of the carbonyl and the mesityl
groups in 5 and 6 are consistent with this mechanism.
A plausible mechanism for 7 is depicted in Scheme
3. One phenylacetylene molecule is inserted into the
Pd-C σ-bond of 3 to give (E), which is followed by
insertion of an isocyanide molecule F. A nucleophilic
attack of the coordinated imino nitrogen atom onto the
R-imino carbon atom leads to a cyclization to form the
pyrrole ring G, and an abstraction of hydrogen atom
gives the pyrrole derivative 7. The differential reactiv-
ity of phenylacetylene toward 3, compared with RNC
and CO, resulted in the formation of different types of
heterocyclic compounds.
Mech a n ism . One of the possible mechanisms for
formation of the heterobicyclic compound 4a is depicted
in Schemes 1 and 2. The hydride complex, trans-[Pd-
(H)Cl(PPh3)2] (2), was assumed to be an incipient species
in the reaction of 1 with XylNC and H2SiMePh, on the
basis of the fact that [PdCl2(PPh3 )2] (1) was readily
transformed to 2 by treatment with H2SiMePh. Com-
plex 2 underwent multiple insertion of five isocyanide
molecules into the Pd-H bond to afford the stable
complex 3. While no intervening species between 2 and
3 was isolated in the present system, the reaction may
proceed through a successive fashion; a single insertion
of isocyanide generates the η1-formimidoyl compound,
which is further converted to double- and triple-inserted
compounds. The linear triimino species is stabilized by
forming a five-membered chelation of the triimino part
to afford complex A. A complex with a similar structure
has been obtained from the reaction of PdI(CH3)(PPh3)2
with XylNC.18e Complex A undergoes further insertion
of two XylNC molecules into the Pd-C bond under
vigorous conditions (reflux in toluene), leading to the
formation of complex 3. The successive insertion of
bulky XylNC was remarkably fast; reaction of 2 with 4
equiv of XylNC gave only complex 3 without isolation
of (A). Further, the reaction of 3 with XylNC in the
presence of H2SiMePh afforded the heterobicyclic com-
pound 4a (21% yield), suggesting that complex 3 is one
of the precursors of 4a . As to the steps between 3 and
4a , we speculated a plausible mechanism as shown in
Scheme 2. A nucleophilic attack of â-imino nitrogen
atom on the formimidoyl carbon in 3 leads to the first
cyclization, giving a Pd-containing [5.5]-membered bi-
cyclic compound B. The strained metalla-bicyclic struc-
ture might destabilize the [PdCCCN] five-membered
chelation and enhance the reactivity of the Pd-C
σ-bond. One more isocyanide is, then, inserted into the
Pd-C bond, resulting in a formation of [5.6]-membered
metalla-bicyclic complex C. The second cyclization takes
place by a nucleophilic attack of the δ imino nitrogen
atom on the R imino carbon atom, followed by an
Con clu sion
In the present study, we have successfully isolated
and characterized the palladium polyimino complex [Pd-
{C(dNR)C(dNR)C(dNR)C(dNR)CH(dNR)}(CNR)Cl] (3)
derived from multiple insertion of bulky XylNC into the
Pd-H bond of trans-[Pd(H)Cl(PPh3)2] (2). This is the
first structurally characterized example of multiple
isocyanide insertion products into Pd-H bonds. We also
demonstrated a self-cyclization of the polymino moiety
on the metal center leading to the formation of novel
heterobicyclic compounds (4). One of the imino groups
in the heterobicyclic ring can be modified by the reaction
of precursor 3 with MesNC and CO, providing asym-
metric compounds 5 and 6, respectively. The reaction
of 3 with phenylacetylene afforded the pyrrole derivative
7 instead of heterobicycles, suggesting that the products
of spontaneous oligomerization of isocyanides can be
controlled by utilizing stable intermediate complexes.
Ack n ow led gm en t. We thank Dr. Matsuzaka for
carrying out high-resolution mass spectroscopy.
Su p p or tin g In for m a tion Ava ila ble: Tables of complete
atomic positional parameters, anisotropic temperature factors,
and bond distances and angles for 3‚1/2C6H6, 4a , 6, and 7‚C6H6
(31 pages). Ordering information is given on any current
masthead page.
OM950619N
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