Carbene and Isocyanide Ligation at Luminescent Cyclometalated 6-Phenyl-2,2′-bipyridyl Platinum(II) Complexes: Structural and Spectroscopic Studies

Article abstract of DOI:10.1021/om990256h

A series of luminescent cyclometalated platinum(II) diamino-carbene complexes, namely, [(CNN)Pt{C(NHR¹)(NHR²)}]⁺ (HCNN = 6-phenyl-2,2′-bipyridine; for R¹ = ^tBu, R² = Me (2), NH₂ (3), CH₂Ph (4); for R¹ = 2,6-Me₂C₆H₃ (Ar′), R² = Me (6), NH₂ (7), CH₂Ph (8)), are synthesized by nucleophilic attack of amines at the coordinated isocyanide ligands of [(CNN)-PtC≡NR¹]⁺ (R¹ = ^tBu (1), Ar′ (5)). The binuclear bridging bis(carbene) derivative [{(CNN)Pt}₂μ-{C(NH^tBu)(NH(CH₂) ₃)}₂NMe]²⁺ (9) is prepared by treatment of 1 with excess 3,3′-diamino-N-methyldipropylamine. The molecular structures of 2(ClO₄)?0.5H₂O, 3(ClO₄)? 0.5H₂O, 4(ClO₄), and 6(ClO₄) reveal Pt-C(carbene) distances of 1.997(7), 1.992(4), 1.989(6), and 1.996(8) A?, respectively. Short N-C(carbene) bond lengths (mean 1.332 A?) imply substantial p_π-p_π interactions within the N-C(carbene)-N fragment, and minimal π bonding in the Pt-C(carbene) moiety is inferred. Weak π-π stacking interactions between the CNN ligands are observed in the crystal lattice of 2-4 and 6 (range 3.5-3.6 A?). Complexes 1-9 display structureless emissions, with λ_max ranging from 528 to 558 nm in acetonitrile at 298 K, and they are assigned to ³MLCT excited states. The emissions of 1 and 5 exhibit noticeably higher quantum yields, which reflect the strong ligand field strength of the isocyanide auxiliaries. The 77 K emissions of 1-9 in frozen acetonitrile are blue-shifted and display well-resolved vibronic structures. At high concentrations (≥10^-5 M), 1 and 5 show an additional low-energy band at 627 (in butyronitrile) and 730 nm which are ascribed to π-π excimeric and MMLCT emissions, respectively. The solid-state emissions of complexes 1(ClO₄)-9(ClO₄)₂ (except 5(ClO₄)) at 298 K are red-shifted from solution to λ_max 553-579 nm with a shoulder at 595-612 nm. They are tentatively assigned to ³MLCT excited states with excimeric character due to weak CNN π-π interactions, as evident in the crystal structures. The remarkable low-energy luminescence of 5(ClO₄) in the solid state (λ_max 704 nm at 298 K; 781 nm at 77 K) is attributed to MMLCT transitions arising from solid-state intermolecular stacking interactions. Upon photolysis with UV-visible light, reaction between complex 2 and iodomethane in acetonitrile leads to decomposition of the diamino-carbene ligand and generation of the platinum(IV) diiodide cyanide derivative trans-[(CNN)-Pt(C≡N)I₂] (10).

Full text of DOI:10.1021/om990256h

Organometallics 1999, 18, 3327-3336
3327
Ca r ben e a n d Isocya n id e Liga tion a t Lu m in escen t
Cyclom eta la ted 6-P h en yl-2,2′-bip yr id yl P la tin u m (II)
Com p lexes: Str u ctu r a l a n d Sp ectr oscop ic Stu d ies
Siu-Wai Lai, Michael Chi-Wang Chan, Kung-Kai Cheung, and Chi-Ming Che*
Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong
Received April 12, 1999
A series of luminescent cyclometalated platinum(II) diamino-carbene complexes, namely,
[(CNN)Pt{C(NHR1)(NHR2)}]+ (HCNN ) 6-phenyl-2,2′-bipyridine; for R1 ) tBu, R2 ) Me (2),
NH2 (3), CH2Ph (4); for R1 ) 2,6-Me2C6H3 (Ar′), R2 ) Me (6), NH2 (7), CH2Ph (8)), are
synthesized by nucleophilic attack of amines at the coordinated isocyanide ligands of [(CNN)-
PtCtNR1]+ (R1
)
tBu (1), Ar′ (5)). The binuclear bridging bis(carbene) derivative
[{(CNN)Pt}2µ-{C(NHtBu)(NH(CH2)3)}2NMe]2+ (9) is prepared by treatment of 1 with excess
3,3′-diamino-N-methyldipropylamine. The molecular structures of 2(ClO4)‚0.5H2O, 3(ClO4)‚
0.5H2O, 4(ClO4), and 6(ClO4) reveal Pt-C(carbene) distances of 1.997(7), 1.992(4), 1.989(6),
and 1.996(8) Å, respectively. Short N-C(carbene) bond lengths (mean 1.332 Å) imply
substantial pπ-pπ interactions within the N-C(carbene)-N fragment, and minimal π bonding
in the Pt-C(carbene) moiety is inferred. Weak π-π stacking interactions between the CNN
ligands are observed in the crystal lattice of 2-4 and 6 (range 3.5-3.6 Å). Complexes 1-9
display structureless emissions, with λmax ranging from 528 to 558 nm in acetonitrile at 298
K, and they are assigned to 3MLCT excited states. The emissions of 1 and 5 exhibit noticeably
higher quantum yields, which reflect the strong ligand field strength of the isocyanide
auxiliaries. The 77 K emissions of 1-9 in frozen acetonitrile are blue-shifted and display
well-resolved vibronic structures. At high concentrations (g10-5 M), 1 and 5 show an
additional low-energy band at 627 (in butyronitrile) and 730 nm which are ascribed to π-π
excimeric and MMLCT emissions, respectively. The solid-state emissions of complexes
1(ClO4)-9(ClO4)2 (except 5(ClO4)) at 298 K are red-shifted from solution to λmax 553-579
nm with a shoulder at 595-612 nm. They are tentatively assigned to 3MLCT excited states
with excimeric character due to weak CNN π-π interactions, as evident in the crystal
structures. The remarkable low-energy luminescence of 5(ClO4) in the solid state (λmax 704
nm at 298 K; 781 nm at 77 K) is attributed to MMLCT transitions arising from solid-state
intermolecular stacking interactions. Upon photolysis with UV-visible light, reaction
between complex 2 and iodomethane in acetonitrile leads to decomposition of the diamino-
carbene ligand and generation of the platinum(IV) diiodide cyanide derivative trans-[(CNN)-
Pt(CtN)I2] (10).
In tr od u ction
are stabilized by at least one heteroatom, and isolation
of congeners without such heteroatoms is rare.5 Scant
attention, however, has been granted to their photo-
physical and photochemical properties, even though
photolysis can alter their intrinsic reactivity through
population of charge-transfer excited states. A pertinent
example of platinum(II) photocatalysis is the prolific
excited-state chemistry of [Pt2(µ-P2O5H2)4]4-, which can
mediate light-induced C-H and C-halogen bond acti-
vation and electron/atom transfer reactions.6 The first
observation of a metal f π*(carbene) charge transfer
excited state in solution was recently published for a
hexanuclear Pt(II) macrocycle with metallacyclic bis-
Reports regarding the generation and reactivity of
platinum carbene complexes have predominantly em-
phasized divalent species.1-4 The vast majority of these
* Fax: (852) 2857 1586. E-mail: cmche@hkucc.hku.hk.
(1) (a) Hartley, F. R. Comprehensive Organometallic Chemistry;
Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon: New York,
1982; Vol. 6, p 502. (b) Lappert, M. F. J . Organomet. Chem. 1988, 358,
185. (c) Cross, R. J . Comprehensive Organometallic Chemistry II;
Wilkinson, G., Stone, F. G. A., Abel, E. W., Puddephatt, R. J ., Eds.;
Pergamon: New York, 1995; Vol. 9, p 419.
(2) Recent examples: (a) Crociani, B.; Di Bianca, F.; Fontana, A.;
Forsellini, E.; Bombieri, G. J . Chem. Soc., Dalton Trans. 1994, 407.
(b) Zhang, S. W.; Kaharu, T.; Pirio, N.; Ishii, R.; Uno, M.; Takahashi,
S. J . Organomet. Chem. 1995, 489, C62. (c) Fehlhammer, W. P.;
Metzner, R.; Luger, P.; Dauter, Z. Chem. Ber. 1995, 128, 1061. (d)
Michelin, R. A.; Mozzon, M.; Vialetto, B.; Bertani, R.; Benetollo, F.;
Bombieri, G.; Angelici, R. J . Organometallics 1996, 15, 4096. (e)
Holtcamp, M. W.; Labinger, J . A.; Bercaw, J . E. J . Am. Chem. Soc.
1997, 119, 848. (f) Kernbach, U.; Lu¨gger, T.; Hahn, F. E.; Fehlhammer,
W. P. J . Organomet. Chem. 1997, 541, 51.
(4) Pt(IV) derivatives: (a) Rendina, L. M.; Vittal, J . J .; Puddephatt,
R. J . Organometallics 1995, 14, 1030, and references therein. (b) Zhang,
S. W.; Takahashi, S. Organometallics 1998, 17, 4757.
(5) (a) Lu, Z.; J ones, W. M.; Winchester, W. R. Organometallics 1993,
12, 1344. (b) Cave, G. W. V.; Hallett, A. J .; Errington, W.; Rourke, J .
P. Angew. Chem., Int. Ed. 1998, 37, 3270.
(3) Pt(0) derivatives: Arduengo, A. J ., III; Gamper, S. F.; Calabrese,
J . C.; Davidson, F. J . Am. Chem. Soc. 1994, 116, 4391.
(6) Roundhill, D. M.; Gray, H. B.; Che, C. M. Acc. Chem. Res. 1989,
22, 55.
10.1021/om990256h CCC: $18.00 © 1999 American Chemical Society
Publication on Web 08/16/1999

3328 Organometallics, Vol. 18, No. 17, 1999
Lai et al.
(carbene) ligands,7 and accounts of luminophores bear-
ing aminocarbene groups have also appeared.8 The
photochemistry of pentacarbonyl tungsten and chro-
mium Fischer carbene complexes has been extensively
studied.9,10
Academy of Sciences, Beijing. Infrared spectra were recorded
in Nujol on a BIO RAD FT-IR spectrometer. UV-vis spectra
were recorded on a Perkin-Elmer Lambda 19 UV/vis spectro-
photometer.
Em ission a n d Lifetim e Mea su r em en ts. Steady-state
emission spectra were recorded on a SPEX 1681 Fluorolog-2
series F111AI spectrophotometer. Low-temperature (77 K)
emission spectra for glasses and solid-state samples were
recorded in 5 mm diameter quartz tubes which were placed
in a liquid nitrogen Dewar equipped with quartz windows. The
emission spectra were corrected for monochromator and pho-
tomultiplier efficiency and for xenon lamp stability.
We and other researchers have been engaged in the
development of cyclometalated Pt(II) derivatives con-
taining substituted pyridyl and 2,2′-bipyridyl ligands
from a photochemical perspective.11-14 In particular,
complexes derived from 6-phenyl-2,2′-bipyridine (HCNN)
display low-lying metal-to-ligand charge transfer (MLCT)
excited states which generally exhibit improved photo-
physical properties compared to 2,2′:6′,2′′-terpyridine
(tpy) analogues.15,16 We now present the preparation,
molecular structures, and photophysical properties of
a series of cyclometalated platinum(II) diamino-car-
bene complexes and the corresponding isocyanide pre-
cursors. All new derivatives are photoluminescent at
room temperature in fluid solution. In addition, isolation
of a binuclear Pt(II) complex supported by an unusual
bidentate bis(carbene) bridge and the photochemical
reactivity of the carbene complexes with iodomethane
are described.
Sample and standard solutions were degassed with at least
three freeze-pump-thaw cycles. The emission quantum yield
was measured by the method of Demas and Crosby19 with [Ru-
(bpy)3](PF6)2 in degassed acetonitrile as the standard (Φr )
0.062) and calculated by Φs ) Φr(Br/Bs)(ns/nr)2(Ds/Dr), where
the subscripts s and r refer to sample and reference standard
solution respectively, n is the refractive index of the solvents,
D is the integrated intensity, and Φ is the luminescence
quantum yield. The quantity B is calculated by B ) 1 - 10-AL
,
where A is the absorbance at the excitation wavelength and L
is the optical path length.
Emission lifetime measurements were performed with a
Quanta Ray DCR-3 pulsed Nd:YAG laser system (pulse output
355 nm, 8 ns). The emission signals were detected by a
Hamamatsu R928 photomultiplier tube and recorded on a
Tektronix model 2430 digital oscilloscope. Errors for λ values
((1 nm), τ ((10%), and φ ((10%) are estimated.
Exp er im en ta l Section
Gen er a l P r oced u r es. All starting materials were used as
received from commercial sources. 6-Phenyl-2,2′-bipyridine
(HCNN)17 and [(CNN)PtCl]15 were prepared by literature
methods. (Ca u tion : perchlorate salts are potentially explosive
and should be handled with care and in small amounts.)
Acetonitrile for photophysical measurements was distilled over
potassium permanganate and calcium hydride. All other
solvents were of analytical grade and purified according to
conventional methods.18
Syn t h esis. [(CNN)P t (CtNt Bu )]ClO4, 1(ClO4). To an
orange suspension of [(CNN)PtCl] (0.10 g, 0.22 mmol) in
acetonitrile (20 mL) at room temperature was added excess
t
tert-butylisocyanide, BuNtC (0.5 mL, 4.4 mmol). Upon stir-
ring, the color of the mixture changed to cloudy orange-red,
then clear pale yellow after 30 min. Addition of excess LiClO4
in acetonitrile followed by diethyl ether yielded a yellow
precipitate, which was collected and dried. Recrystallization
by slow diffusion of diethyl ether into an acetonitrile solution
of the crude product afforded yellow crystals: yield 0.12 g, 91%.
Anal. Calcd for C21H20N3O4ClPt: C, 41.42; H, 3.31; N, 6.90.
Found: C, 41.65; H, 3.06; N, 6.62. FAB-MS: m/z 509 [M+],
426 [M+ - CtNtBu]. 1H NMR (CD3CN): 1.73 (s, 9H, tBu), 7.14
(m, 3H), 7.43 (m, 1H), 7.72 (m, 2H), 7.83 (d, 1H, J ) 7.8 Hz),
8.02 (t, 1H, J ) 8.0 Hz), 8.11 (d, 1H, J ) 7.9 Hz), 8.25 (t, 1H,
J ) 7.9 Hz), 8.57 (d, 1H, J ) 5.1 Hz). 13C{1H} NMR (CD3CN):
30.2 (CMe3), 61.5 (CMe3), 121.0, 121.4, 125.6, 127.0, 127.2,
130.3, 133.3, 138.1, 138.3, 142.6, 144.0, 148.0, 153.8, 156.2,
157.8, 165.9, Pt-CNtBu not resolved. IR (Nujol): ν ) 2207
Fast atom bombardment (FAB) mass spectra were obtained
1
on a Finnigan Mat 95 mass spectrometer. H (300 MHz) and
13C (126 MHz) spectra were recorded on DPX 300 and 500
Bruker FT-NMR spectrometers respectively with chemical
shifts (in ppm) relative to tetramethylsilane. Due to restricted
rotation about the C(carbene)-N bonds, multiple peaks for
each amino substituent are typically observed by NMR spec-
troscopy. In the 13C NMR spectra, all resolved peaks for
aliphatic carbons are recorded, while only the most intense
signals for aryl carbons are given. Elemental analysis was
performed by the Institute of Chemistry at the Chinese
(CtN), 1603 (CdN) cm-1
.
[(CNN)P t{C(NHtBu )(NHMe)}]ClO4, 2(ClO4). A stirred
solution of 1(ClO4) (0.10 g, 0.16 mmol) in acetonitrile (20 mL)
and excess MeNH2 (40 wt % solution in water, 0.5 mL, 5.8
mmol) was heated at reflux for 24 h. After cooling, the volume
of solution was reduced to ∼5 mL, and addition of excess
LiClO4 in acetonitrile gave an orange solid, which was collected
by filtration and dried. Recrystallization by slow diffusion of
diethyl ether into an acetonitrile solution yielded orange
crystals: yield 0.08 g, 76%. Anal. Calcd for C22H25N4O4ClPt:
C, 41.29; H, 3.94; N, 8.75. Found: C, 41.21; H, 4.26; N, 8.96.
(7) Lai, S. W.; Cheung, K. K.; Chan, M. C. W.; Che, C. M. Angew.
Chem., Int. Ed. 1998, 37, 182.
(8) (a) Xue, W. M.; Chan, M. C. W.; Su, Z. M.; Cheung, K. K.; Liu,
S. T.; Che, C. M. Organometallics 1998, 17, 1622. (b) Yam, V. W. W.;
Chu, B. W. K.; Cheung, K. K. Chem. Commun. 1998, 2261.
(9) Hegedus, L. S. Acc. Chem. Res. 1995, 28, 299.
(10) (a) Foley, H. C.; Strubinger, L. M.; Targos, T. S.; Geoffroy, G.
L. J . Am. Chem. Soc. 1983, 105, 3064. (b) Bell, S. E. J .; Gordon, K. C.;
McGarvey, J . J . J . Am. Chem. Soc. 1988, 110, 3107.
(11) (a) Chassot, L.; Mu¨ller, E.; von Zelewsky, A. Inorg. Chem. 1984,
23, 4249. (b) Sandrini, D.; Maestri, M.; Balzani, V.; Chassot, L.; von
Zelewsky, A. J . Am. Chem. Soc. 1987, 109, 7720.
(12) (a) Chan, C. W.; Lai, T. F.; Che, C. M.; Peng, S. M. J . Am. Chem.
Soc. 1993, 115, 11245. (b) Chan, C. W.; Cheng, L. K.; Che, C. M. Coord.
Chem. Rev. 1994, 132, 87.
(13) Tse, M. C.; Cheung, K. K.; Chan, M. C. W.; Che, C. M. Chem.
Commun. 1998, 2295.
(14) (a) Zheng, G. Y.; Rillema, D. P.; DePriest, J .; Woods, C. Inorg.
Chem. 1998, 37, 3588. (b) Zheng, G. Y.; Rillema, D. P. Inorg. Chem.
1998, 37, 1392.
(15) Cheung, T. C.; Cheung, K. K.; Peng, S. M.; Che, C. M. J . Chem.
Soc., Dalton Trans. 1996, 1645.
(16) Lai, S. W.; Chan, M. C. W.; Cheung, T. C.; Peng, S. M.; Che, C.
M. Inorg. Chem., in press.
(17) Kro¨hnke, F. Synthesis 1976, 1.
FAB-MS: m/z 540 [M+], 481 [M+ - Bu]. H NMR (CD3CN):
1.45, 1.50, 1.53 (3 singlets, 9H, tBu), 2.95, 3.19, 3.27 (3
doublets, 3H, 3J HH ) 4.8 Hz, NMe), 7.14 (m, 3H), 7.58 (m, 1H),
7.63 (m, 1H), 7.87 (m, 1H), 7.97 (m, 1H), 8.09 (m, 1H), 8.23
(m, 2H), 8.57 (m, 1H). 13C{1H} NMR (CD3CN): 29.5, 31.8, 31.9
(CMe3), 36.9, 37.1, 37.2 (NMe), 54.6, 54.8, 55.3 (CMe3), 120.4,
120.6, 125.2, 125.6, 126.2, 129.6, 132.4, 138.1, 138.6, 141.7,
142.3, 148.2, 153.5, 155.3, 159.0, 165.1, 193.7 (Pt-Ccarbene, 1J PtC
) 1363 Hz). IR (Nujol): ν ) 3383 (br, N-H), 1599, 1552
t
1
(CdN) cm-1
.
(18) Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of
Laboratory Chemicals, 2nd ed.; Pergamon: Oxford, 1980.
(19) Demas, J . N.; Crosby, G. A. J . Phys. Chem. 1971, 75, 991.

Carbene and Isocyanide Ligation
Organometallics, Vol. 18, No. 17, 1999 3329
3
[(CNN)P t{C(NHtBu )(NHNH2)}]ClO4, 3(ClO4). The pro-
cedure for 2(ClO4) was adopted using excess hydrazine hydrate
(0.3 mL, 9.6 mmol) to afford an orange crystalline solid: yield
0.07 g, 67%. Anal. Calcd for C21H24N5O4ClPt: C, 39.35; H, 3.77;
N, 10.93. Found: C, 39.44; H, 3.58; N, 10.68. FAB-MS: m/z
1H, J PtH ) 92 Hz, NH). 13C{1H} NMR (CD3CN): 19.9 (Me),
120.1, 120.4, 125.0, 125.6, 126.2, 127.9, 128.9, 129.2, 131.7,
132.3, 135.9, 138.1, 141.4, 142.1, 147.9, 153.0, 154.9, 158.4,
164.7, 187.0 (Pt-Ccarbene). IR (Nujol): ν ) 3320 (br, N-H),
1603, 1555 (CdN) cm-1
.
t
540 [M+]. 1H NMR (CD3CN): 1.50 (s, 9H, Bu), 4.01 (s, 2H,
[(CNN)P t{C(NHAr ′)(NHCH2P h )}]ClO4, 8(ClO4). The pro-
cedure for 6(ClO4) was adopted using excess benzylamine (0.5
mL, 4.6 mmol) to afford orange crystals: yield 0.08 g, 69%.
Anal. Calcd for C32H29N4O4ClPt: C, 50.30; H, 3.83; N, 7.33.
Found: C, 50.15; H, 3.98; N, 7.48. FAB-MS: m/z 664 [M+]. 1H
NMR (CD3CN): 2.37, 2.39 (2 singlets, 6H, Me), 4.67 (dd, 1H,
NH2), 7.16 (m, 2H), 7.58 (m, 1H), 7.68 (m, 1H), 7.86 (m, 1H),
7.96 (m, 2H), 8.09 (m, 1H), 8.25 (m, 2H), 8.57 (m, 1H). 13C-
{1H} NMR (CD3CN): 31.6 (CMe3), 53.6 (CMe3), 120.2, 120.5,
125.1, 125.5, 126.1, 129.4, 132.2, 138.4, 141.5, 141.9, 142.5,
148.1, 153.2, 155.1, 158.8, 164.9, 185.2 (Pt-Ccarbene
1274 Hz). IR (Nujol): ν ) 3369, 3291 (N-H), 1597, 1540
(CdN) cm-1
, )
1J PtC
2J HH ) 14.8 Hz, J HH ) 6.1 Hz, NCH2), 4.88 (dd, 1H, J HH
)
3
2
14.8 Hz, 3J HH ) 6.1 Hz, NCH2), 7.06 (d, 2H, J ) 6.5 Hz), 7.18-
7.32 (m, 7H), 7.42 (m, 1H), 7.58 (m, 2H), 7.89 (d, 1H, J ) 8.1
Hz), 7.96 (d, 1H, J ) 7.7 Hz), 8.09 (t, 1H, J ) 8.0 Hz), 8.21 (m,
2H), 8.32 (d, 1H, J ) 5.3 Hz), 8.55 (broad s, 1H, NH). 13C{1H}
NMR (CD3CN): 19.1, 19.3 (Me), 53.0 (NCH2), 120.4, 120.7,
125.3, 126.1, 126.6, 128.5, 129.1, 129.2, 129.5, 130.0, 130.3,
130.4, 132.4, 134.7, 137.1, 137.6, 137.8, 140.0, 140.1, 141.5,
142.5, 148.6, 152.8, 155.2, 158.6, 164.9, 189.4 (Pt-Ccarbene). IR
.
[(CNN)P t{C(NHtBu )(NHCH2P h )}]ClO4, 4(ClO4). The pro-
cedure for 2(ClO4) was adopted using excess benzylamine (0.5
mL, 4.6 mmol) to afford orange crystals: yield 0.09 g, 77%.
Anal. Calcd for C28H29N4O4ClPt: C, 46.96; H, 4.08; N, 7.82.
Found: C, 47.10; H, 4.17; N, 7.93. FAB-MS: m/z 616 [M+]. 1H
NMR (CD3CN):1.42, 1.45, 1.55 (3 singlets, 9H, tBu), 4.53-5.05
(m, 2H, NCH2), 7.01 (m, 2H), 7.18 (m, 5H), 7.45 (m, 2H), 7.60
(m, 1H), 7.88 (m, 2H), 8.09 (m, 4H). 13C{1H} NMR (CD3CN):
29.4, 31.7 (CMe3), 53.7 (NCH2), 54.8, 55.0 (CMe3), 120.3, 120.6,
124.8, 125.7, 126.3, 128.3, 128.9, 129.2, 132.5, 137.1, 138.2,
140.4, 141.1, 142.3, 148.1, 152.7, 153.6, 155.1, 158.4, 164.7,
194.0 (Pt-Ccarbene). IR (Nujol): ν ) 3388, 3313 (N-H), 1599,
(Nujol): ν ) 3340, 3264 (N-H), 1601, 1540 (CdN) cm-1
.
[{(CNN)P t }2µ-{C(NH t Bu )(NH (CH 2)3)}2NMe ](ClO4)2,
9(ClO4)2. A solution of 1(ClO4) (0.10 g, 0.16 mmol) and excess
3,3′-diamino-N-methyldipropylamine (CH3N(CH2CH2CH2NH2)2)
(0.1 mL, 0.62 mmol) in acetonitrile (20 mL) was heated at
reflux for 12 h. Upon cooling, the solution volume was reduced,
and addition of diethyl ether yielded an oily yellow solid, which
was washed repeatedly with n-hexane. Recrystallization by
slow diffusion of n-pentane into a CH2Cl2 solution afforded a
yellow solid: yield 0.07 g, 63%. FAB-MS: m/z (%) ) 1264 [M+
+ ClO4]. Anal. Calcd for C49H59N9O8Cl2Pt2: C, 43.18; H, 4.36;
N, 9.25. Found: C, 43.39; H, 4.13; N, 9.09. 1H NMR (CD3CN):
1.37-1.53 (m, CMe3), 1.7-3.8 (m, triamine), 7.14, 7.44-7.75,
7.86, 8.00, 8.09, 8.24, 8.59 (m, aryl H). 13C{1H} NMR (CD3-
CN): 28.6-31.7 (CMe3, triamine), 47.5-48.0, 54.6-55.1 (CMe3,
triamine), 120.5-120.7, 125.3-127.2, 129.9-130.3, 132.5-
133.2, 138.1-138.5, 141.7-144.0, 148.2, 152.8-155.2, 164.6,
172.0, 192.6 (Pt-Ccarbene). IR (Nujol): ν ) 3384 (br, N-H),
1551 (CdN) cm-1
.
[(CNN)P tCtNAr ′]ClO4, 5(ClO4). To an orange suspension
of [(CNN)PtCl] (0.10 g, 0.22 mmol) in acetonitrile (20 mL) was
added 2,6-dimethylphenyl (Ar′) isocyanide (0.03 g, 0.23 mmol).
The mixture was stirred for 10 min to yield a purple precipitate
and yellow solution. After addition of excess LiClO4 in aceto-
nitrile followed by diethyl ether, the resultant purple solid was
collected and dried. Recrystallization by slow diffusion of
diethyl ether into an acetonitrile solution afforded a purple
crystalline solid: yield 0.11 g, 77%. Anal. Calcd for C25H20N3O4-
ClPt: C, 45.70; H, 3.07; N, 6.40. Found: C, 45.84; H, 3.06; N,
6.26. FAB-MS: m/z 555 [M+], 423 [M+ - CNAr′]. 1H NMR
(CD3CN): 2.56 (s, 6H, Me), 7.15 (m, 2H), 7.32 (d, 2H, J ) 7.5
Hz), 7.43 (m, 2H), 7.52 (m, 1H), 7.74 (m, 1H), 7.82 (d, 1H, J )
8.2 Hz), 7.93 (d, 1H, J ) 8.0 Hz), 8.09 (m, 1H), 8.24 (m, 2H),
8.80 (d, 1H, J ) 5.6 Hz). The poor solubility of 5(ClO4) in
common deuterated solvents precluded its characterization by
13C NMR spectrum. IR (Nujol): ν ) 2169 (CtN), 1603 (CdN)
1630, 1568 (CdN) cm-1
.
tr a n s-[(CNN)P t(CtN)I2], 10. A solution of 2(ClO4) (0.10
g, 0.16 mmol) in dried and degassed acetonitrile (20 mL)
containing iodomethane (10 mL) was irradiated with UV-
visible light (RPR-100 Rayonet photochemical chamber reactor
equipped with 16 8-W RPR 3500 Å Hg lamps) for 12 h at room
temperature. An orange precipitate was obtained and collected
by filtration. Slow evaporation of a methanol/dimethylforma-
mide (v/v 1:1) solution of the crude product afforded orange
crystals: yield 0.08 g, 73%. Anal. Calcd for C17H11N3I2Pt: C,
28.91; H, 1.57; N, 5.95. Found: C, 28.99; H, 1.70; N, 5.74. FAB-
MS: m/z 707 [M+]. 1H NMR (DMSO-d6): 7.15 (m, 1H), 7.42
(d, 1H, J ) 6.3 Hz), 7.50 (d, 1H, J ) 7.3 Hz), 7.99 (m, 1H),
8.07 (d, 1H, J ) 7.4 Hz), 8.50 (m, 3H), 8.65 (d, 1H, J ) 7.0
Hz), 8.90 (d, 1H, J ) 7.7 Hz), 9.03 (m, 1H). 13C{1H} NMR
(DMSO-d6): 87.5 (CtN), 122.1, 122.2, 123.4, 125.9, 126.2,
126.9, 129.3, 133.0, 136.2, 141.8, 142.8, 144.6, 151.6, 151.9,
cm-1
.
[(CNN)P t{C(NHAr ′)(NHMe)}]ClO4, 6(ClO4). The proce-
dure for 2(ClO4) was adopted using 5(ClO4) (0.10 g, 0.15 mmol)
and excess MeNH2 (40 wt % solution in water, 0.5 mL, 5.8
mmol) to yield orange crystals: yield 0.07 g, 67%. Anal. Calcd
for C26H25N4O4ClPt: C, 45.39; H, 3.66; N, 8.14. Found: C,
45.65; H, 3.58; N, 7.82. FAB-MS: m/z 588 [M+]. 1H NMR (CD3-
CN): 2.38, 2.40 (2 singlets, 6H, Me2C6H3), 3.17 (d, 3H, J ) 4.7
Hz, NMe), 6.82 (s with 195Pt satellites, 1H, 3J PtH ) 91 Hz, NH),
7.19 (m, 2H), 7.28 (m, 3H), 7.36 (d, 1H, J ) 7.2 Hz), 7.63 (d,
1H, J ) 6.9 Hz), 7.76 (m, 1H), 7.89 (d, 1H, J ) 8.1 Hz), 7.99
(d, 1H, J ) 8.0 Hz), 8.11 (t, 1H, J ) 8.0 Hz), 8.28 (m, 2H),
8.75 (d, 1H, J ) 5.2 Hz). 13C{1H} NMR (CD3CN): 19.1, 19.3
(Me2C6H3), 36.3 (NMe), 120.5, 120.7, 125.6, 126.1, 126.6, 129.7,
129.9, 130.2, 130.3, 132.4, 134.7, 137.3, 137.6, 137.9, 139.9,
141.9, 142.5, 148.5, 153.0, 155.1, 158.9, 164.9, 188.4 (Pt-
155.7, 161.3. IR (Nujol): ν ) 2155 (CtN), 1598 (CdN) cm-1
.
X-r a y Cr ysta llogr a p h y. Crystals of 2(ClO4)‚0.5H2O (see
Supporting Information for all data), 3(ClO4)‚0.5H2O, 4(ClO4),
and 6(ClO4) were grown by slow diffusion of diethyl ether into
acetonitrile solutions. Crystals of 10 were obtained by slow
evaporation of methanol/dimethylformamide solution. Crystal
data and details of collection and refinement are summarized
in Table 1.
Diffraction experiments were performed at 301 K on a
Rigaku AFC7R (2(ClO4)‚0.5H2O and 4(ClO4)) or Nonius-Enraf
(3(ClO4)‚0.5H2O) diffractometer with graphite-monochroma-
tized Mo KR radiation (λ ) 0.71073 Å) using ω-2θ scans. For
6(ClO4) and 10, intensity data were collected on a MAR
diffractometer with graphite-monochromatized Mo KR radia-
tion (λ ) 0.71073 Å) using a 300 mm image plate detector.
For 2(ClO4)‚0.5H2O, 3(ClO4)‚0.5H2O, 4(ClO4), and 10, the
1
Ccarbene, J PtC ) 1321 Hz). IR (Nujol): ν ) 3336, 3300 (N-H),
1600, 1552 (CdN) cm-1
.
[(CNN)P t{C(NHAr ′)(NHNH2)}]ClO4, 7(ClO4). The pro-
cedure for 6(ClO4) was adopted using excess hydrazine hydrate
(0.3 mL, 9.6 mmol) to afford an orange-red crystalline solid:
yield 0.06 g, 57%. Anal. Calcd for C25H24N5O4ClPt: C, 43.58;
H, 3.51; N, 10.16. Found: C, 43.48; H, 3.33; N, 10.28. FAB-
1
MS: m/z 589 [M+]. H NMR (CD3CN): 2.39, 2.40 (2 singlets,
6H, Me), 4.38 (broad s, 2H, NH2), 6.88 (m, 3H), 6.99 (m, 2H),
7.08 (m, 1H), 7.26 (m, 2H), 7.55 (d, 1H, J ) 8.0 Hz), 7.67 (d,
1H, J ) 7.8 Hz), 7.88 (m, 2H), 8.08 (m, 1H), 8.47 (d, 1H, J )
4.6 Hz), 8.63 (broad s, 1H, NH), 9.72 (s with 195Pt satellites,

3330 Organometallics, Vol. 18, No. 17, 1999
3(ClO4)‚0.5H2O
Lai et al.
Ta ble 1. Cr ysta l Da ta
4(ClO4)
6(ClO4)
10
formula
fw
color
C
21H25N5O4.5ClPt
C28H29N4O4ClPt
716.10
orange
C26H25N4O4ClPt
688.05
yellow
C17H11N3I2Pt
706.19
red
650.00
yellow
crystal size, mm
crystal system
space group
a, Å
b, Å
c, Å
0.25 × 0.10 × 0.30
triclinic
P1h (No. 2)
11.866(4)
13.102(5)
8.392(2)
100.30(3)
97.50(4)
72.88(3)
1222.6(8)
2
0.30 × 0.10 × 0.07
triclinic
P1h (No. 2)
11.070(2)
11.216(2)
13.065(3)
111.29(1)
106.97(1)
101.67(1)
1356(1)
2
0.25 × 0.20 × 0.40
orthorhombic
Pbca (No. 61)
8.758(2)
21.560(3)
26.533(3)
0.25 × 0.15 × 0.10
monoclinic
P21/c (No. 14)
9.080(2)
22.843(3)
9.291(2)
R, deg
â, deg
116.43(2)
γ, deg
V, Å3
5010(1)
8
1.824
57.26
2688
1725.7(6)
4
2.718
116.80
1272
Z
Dc (g cm-3
)
1.766
58.63
634
1.753
52.91
704
µ, cm-1
F(000)
2θmax, deg
50
4272
3852
307
0.022
0.028
+0.85, -0.59
50
4786
3957
345
0.029
0.037
+0.90, -0.71
51
4799
2876
331
0.037
0.046
+0.86, -1.47
51
3172
2549
198
0.031
0.043
+1.03, -1.49
no. unique data
no. obsd data for I > 3σ(I)
no. variables
Ra
Rw
b
residual F, e Å-3
a
b
2
R ) ∑||Fo| - |Fc||/∑|Fo|. Rw ) [∑w(|Fo| - |Fc|)2/∑w|Fo| ]1/2
.
structures were solved by Patterson and Fourier methods
(PATTY)20a and refined by full-matrix least-squares using the
software package TeXsan21 on a Silicon Graphics Indy com-
puter. For 2(ClO4)‚0.5H2O, all 33 non-H atoms were refined
anisotropically. The H atoms bonded to N(3) and N(4) were
located in the difference Fourier synthesis, and their positional
parameters were refined. The O atom of the water molecule
is at special position, and the H atoms were not located. The
remaining 23 H atoms of the complex cation at calculated
positions with thermal parameters equal to 1.3 times that of
the attached C atoms were not refined. For 3(ClO4)‚0.5H2O,
all 33 non-H atoms were refined anisotropically. The 4 H atoms
bonded to N(3), N(4), and N(5) were located in the difference
Fourier synthesis, and their positional parameters were
refined. The O atom of the water molecule is at special position,
and the H atoms bonded to it were not located. Twenty H
atoms at calculated positions were not refined. For 4(ClO4),
there is positional disorder in N(2) and C(1), and C(1′) and
N(2′) were placed in the same sites and all four atoms were
given occupancy of 0.5. The O atoms of the perchlorate anion
were also disordered. In the least-squares refinement, 32
non-H atoms were refined anisotropically, N(2) and C(1) were
refined isotropically, and C(1′) and N(2′) constrained to N(2)
and C(1), respectively, were not refined. The positional pa-
rameters of H(1) and H(4) located in the difference Fourier
synthesis were refined, and 25 other H atoms at calculated
positions were not refined. For 10, there is positional disorder
in N(2) and C(1), and C(1′) and N(2′) were placed in the same
sites and all four atoms were given occupancy of 0.5. In the
least-squares refinement, C(1′) and N(2′) were constrained
respectively to N(2) and C(1), which were refined isotropically,
while the other 21 non-H atoms were refined anisotropically.
The other 11 H atoms at calculated positions were not refined.
For 6(ClO4), the structures were solved by direct methods
(SIR92),20b expanded by Fourier methods, and refined by full-
matrix least-squares using the software package TeXsan on a
Silicon Graphics Indy computer. All 36 non-H atoms were
refined anisotropically. The H atoms bonded to N(3) and N(4)
were located in difference Fourier synthesis, and their posi-
tional parameters were refined. The other 23 H atoms at
calculated positions were not refined.
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion . The facile dis-
placement of the chloride group from [(CNN)PtCl] by
excess tert-butyl and 2,6-dimethylphenyl (Ar′) isocyanide
yielded complexes 1 and 5 as yellow and purple solids,
respectively. The unusual color of the latter is discussed
below. Treatment of 1 and 5 with excess amine or
hydrazine afforded the diamino-carbene complexes 2-4
and 6-8 in moderate to high yields (Scheme 1). All
complexes are air- and moisture-stable at room tem-
perature. Generation of diamino-carbene derivatives
has been dominated by nucleophilic attack of amines
at coordinated isocyanides for decades.22 By employing
this methodology using 3,3′-diamino-N-methyldiprop-
ylamine with two isolated amine functionalities, we
have prepared the binuclear species 9, with the biden-
tate bis(carbene) moiety acting as a bridging ligand
(Scheme 1). The FAB mass spectrum of 9 reveals a
cluster around m/z 1264, the intensities of which are
comparable to the calculated isotope pattern of [M+
+
ClO4] (Figure 1). We have unsuccessfully attempted
analogous experiments using aliphatic and aromatic
diamines (H2N(CH2)nNH2 (n ) 2, 4), 1,4-diaminocyclo-
hexane, 9,10-diaminophenanthrene) where intractable
oily solids were afforded, while no reaction proceeded
upon treatment of the carbene complexes 3 and 7
(bearing NH2 groups) with corresponding isocyanide
derivatives. Although this synthetic route is presently
limited, we envisage that the bridging bidentate bis-
(carbene) motif will become an important ligand in the
(20) (a) PATTY: Beurskens, P. R.; Admiraal, G.; Bosman, W. P.;
Garcia-Granda, S.; Gould, R. O.; Smits, J . M. M.; Smykalla, C. The
DIRDIF program system, Technical Report of the Crystallography
Laboratory; University of Nijmegen: The Netherlands, 1992. (b)
SIR92: Altomare, A.; Cascarano, M.; Giacovazzo, C.; Guagliardi, A.;
Burla, M. C.; Polidori, G.; Camalli, M. J . Appl. Crystallogr. 1994, 27,
435.
coordination chemistry of binuclear complexes.23a,b
A
(22) (a) Badley, E. M.; Chatt, J .; Richards, R. L.; Sim, G. A. J . Chem.
Soc., Chem. Commun. 1969, 1322. (b) Belluco, U.; Crociani, B.;
Michelin, R.; Uguagliati, P. Pure Appl. Chem. 1983, 55, 47.
(21) TeXsan: Crystal Structure Analysis Package; Molecular Struc-
ture Corporation, 1985 and 1992.

Carbene and Isocyanide Ligation
Organometallics, Vol. 18, No. 17, 1999 3331
Sch em e 1
F igu r e 1. Calculated (top) and experimental (bottom)
isotopic distribution pattern of [M+ + ClO4] for 9.
Fischer carbene complexes.24 They are nevertheless
comparable with Pt(II) analogues, e.g., trans-[PtCl2-
(PnBu3){C(NMeCH2)2}] (196.5 ppm in CDCl3/C6F6)25 and
[PtH{C(NCH2CH2CH2)NH-p-MeOC6H4}(dppe)]BF4 (194.5
ppm in CD2Cl2),26 and Pt(IV) congeners, e.g., [PtClMe2-
(CClNMe2)(4,4′-tBu2bpy)]Cl (171.3 ppm in CD2Cl2)4a and
PtI2{C(NHPr)NH-3,4-(OMe)2C6H2}2 (185.2 ppm in ac-
tris(carbene) ligand generated by trialkylation followed
by deprotonation of tris(imidazolyl) borate and its
chelation at an Fe(III) center was recently reported.23c
The characteristic IR absorptions for the isocyanide
1
etone-d6).4b The carbene J PtC values are characteristic
complexes 1 and 5 (ν(CtN) 2207 and 2169 cm-1
,
for cationic Pt(II) diamino-carbene derivatives such as
[PtH{C(NCH2CH2CH2)NH-p-MeOC6H4}(dppe)]BF4 (1134
Hz in CD2Cl2),25 but are also surprisingly similar to that
for the Pt(IV) species [PtClMe2(CClNMe2)(4,4′-tBu2bpy)]-
Cl (1325 Hz in CD2Cl2).4a
respectively) disappear upon transformation to carbene
derivatives. For the latter, broad ν(N-H) bands at
3390-3260 cm-1 and multiple moderately intense ν(CN)
absorptions in the 1630-1540 cm-1 region are observed.
The 1H NMR spectra of the carbene compounds indicate
restricted rotation about the N-C(carbene) bonds,
which is typical for aminocarbene species. For example,
the spectrum of 2 in CD3CN contains three singlets at
1.45, 1.50, and 1.53 ppm (tBu) and three doublets at
P h otoch em ica l Rea ctivity. A prominent charac-
teristic of square-planar platinum(II) complexes is their
ability to undergo oxidative addition reactions which are
markedly dependent on the nature of ancillary ligands.
The platinum(II) diamino-carbene complexes in this
work are relatively unreactive in comparison with
Fischer carbene complexes of the early transition met-
als.1,24 Nevertheless, a photochemical reaction was ob-
served when a degassed acetonitrile solution of 2 con-
taining iodomethane was exposed to UV radiation for
12 h at room temperature. The reaction was moni-
tored by UV-vis spectroscopy, which depicted a gradual
decrease in absorbance at λmax 336 and 350 nm ac-
companied by growth of a band at λmax 367 nm. The new
band corresponds to the Pt(IV) cyanide complex trans-
[(CNN)Pt(CN)I2] (10), the structure of which was elu-
1
2.95, 3.19, and 3.27 ppm (3J HH 4.8 Hz, NMe). In the H
NMR spectrum of 7, two singlets at 2.39 and 2.40 ppm
(Me2C6H3) are observed, but only one broad resonance
at 4.38 ppm (NH2) is resolved due to peak broadening
by the quadrupolar 14N nuclei. The spectrum of 8 clearly
demonstrates that the methylene hydrogens in the
benzylamine moiety are diastereotopic: two doublet of
doublets are observed at 4.67 and 4.88 ppm (2J HH 14.8
3
Hz, J HH 6.1 Hz).
In the 13C NMR spectra, the carbene resonances for
2-4 and 6-8 (185.2-194.0 ppm), with attendant 195Pt
satellites (1J PtC 1274-1363 Hz), are upfield from typical
(24) Cardin, D. J .; Cetinkaya, B.; Lappert, M. F. Chem. Rev. 1972,
72, 545.
(25) Cardin, D. J .; Cetinkaya, B.; Cetinkaya, E.; Lappert, M. F.;
Randall, E. W.; Rosenberg, E. J . Chem. Soc., Dalton Trans. 1973, 1982.
(26) Michelin, R. A.; Bertani, R.; Mozzon, M.; Zanotto, L.; Benetollo,
F.; Bombieri, G. Organometallics 1990, 9, 1449.
(23) (a) Buil, M. L.; Esteruelas, M. A. Organometallics 1999, 18,
1798. (b) Hartbaum, C.; Mauz, E.; Roth, G.; Weissenbach, K.; Fischer,
H. Organometallics 1999, 18, 2619, and references therein. (c) Kern-
bach, U.; Ramm, M.; Luger, P.; Fehlhammer, W. P. Angew. Chem.,
Int. Ed. Engl. 1996, 35, 310.

3332 Organometallics, Vol. 18, No. 17, 1999
Lai et al.
F igu r e 2. Perspective view of the cation in 3(ClO4)‚0.5H2O
(50% probability ellipsoids).
F igu r e 4. Perspective view of the cation in 6(ClO4) (50%
probability ellipsoids).
F igu r e 3. Perspective view of the cation in 4(ClO4) (50%
probability ellipsoids, positional disorder exists for C(1) and
N(2)).
F igu r e 5. Perspective view of 10 (50% probability el-
lipsoids, positional disorder exists for C(1) and N(2)).
(C10H21N4)]6 (1.97(1)-2.01(1) Å),7 trans-[Pt{C(NEt2)(OC-
(O)Ph)}(PPh3)I2] (1.969(7) Å),27 trans-[PtMe{C(NMe2)Me}-
(PMe2Ph)2]PF6 (2.079(13) Å),28 [PtCl{η1-Ar2py}(µ-Cl)]2
(1.951(9) Å without heteroatom stabilization, Ar2py )
2,6-{2,4-(OC6H13)2C6H3}2C6H3N; carbene ligation at py-
ridyl C4),5b and the Pt(IV) derivatives [PtCl2Me(CH-
NMe2)(4,4′-tBu2bpy)]Cl (1.991(21) Å)4a and PtI2{C(NHPr)-
NH-3,4-(OMe)2C6H2}2 (2.039(6) and 2.037(6) Å).4b All
angles at the carbene carbon atoms in 2-4 and 6
approach 120°, which indicates sp2 hybridization, but
this does not necessarily amount to significant Pt-
C(carbene) π bonding. Intriguingly, the Pt-C(aryl) [Pt-
(1)-C(1) for 2-4 and 6: 2.001(8), 2.010(5), 2.068(5), and
2.033(9) Å, respectively] and Pt-C(carbene) distances
differ by less than 0.05 Å. The short N-C(carbene) bond
lengths (mean 1.332 Å) imply substantial pπ-pπ inter-
cidated by X-ray crystallography (see below). Hence
oxidation of the metal center and fragmentation of the
diamino-carbene ligand are apparent. We found that
heating an identical mixture at reflux resulted in
formation of a number of unidentifiable species (10 was
not detected by IR or FAB-MS).
Cr ysta l Str u ctu r es. Structural determinations of
2(ClO4)‚0.5H2O, 3(ClO4)‚0.5H2O, 4(ClO4), 6(ClO4), and
10 have been performed (Figures 2-5); selected bond
lengths and angles are listed in Table 2 (for 2(ClO4)‚
0.5H2O, see Supporting Information). The molecular
structure of each of the carbene complexes consists of a
distorted square-planar environment at the platinum
center, since the bite angle of the tridentate CNN ligand
deviates substantially from 180° (C(1)-Pt(1)-N(2) for
2-4 and 6: 159.6(3)°, 160.2(2)°, 159.2(2)°, and
159.0(3)°, respectively). The Pt(II)-C(carbene) distances
(1.997(7), 1.992(4), 1.989(6), and 1.996(8) Å for 2-4 and
6, respectively) are comparable to those in [Pt(CN)-
(27) Chen, J . T.; Tzeng, W. H.; Tsai, F. Y.; Cheng, M. C.; Wang, Y.
Organometallics 1991, 10, 3954.
(28) Stepaniak, R. F.; Payne, N. C. Inorg. Chem. 1974, 13, 797.

Carbene and Isocyanide Ligation
Organometallics, Vol. 18, No. 17, 1999 3333
formations for the tert-butyl groups in 2 and 3 and the
Z arrangement for the 2,6-dimethylphenyl unit in 6 may
be explained on steric grounds. The Z, Z configuration
in 4 is therefore unusual. Close inspection of the crystal
lattice reveals weak hydrogen bonds between the amino
hydrogens and the perchlorate groups (N-H‚‚‚O-Cl ca.
3.0 Å), which evidently stabilizes the lattice and com-
pensates for the deviation away from the normal Z, E
orientation. Weak π-π stacking interactions are appar-
ent in the packing diagrams of 2-4 and 6 (range 3.5-
3.6 Å). This has notable consequences for the emissive
properties of these luminophores, as is discussed in the
following section.
The platinum center in 10 adopts a distorted octahe-
dral geometry with coordination of tridentate cyclo-
metalated CNN, cyanide, and trans-diiodide ligands.
The short C(17)-N(3) bond distance of 1.14(1) Å is
consistent with a carbon-nitrogen triple bond. The Pt-
C(17) bond length of 1.988(9) Å closely resembles the
Pt-C(carbene) distances in this work (mean 1.994 Å).
Since the cyanide ligand is a strong σ-donor and weak
π-acid and minimal metal-cyanide π bonding is ex-
pected, this observation provides further support for the
notion that the Pt-C(carbene) interaction in diamino-
carbene complexes does not exhibit significant π char-
acter.
F igu r e 6. Resonance forms of the platinum(II) diamino-
carbene interaction (CNN ligand omitted for clarity).
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg)
[(CNN)Pt{C(NHtBu)(NHNH2)}]ClO4‚0.5H2O, 3(ClO4)‚0.5H2O
Pt(1)-N(1)
Pt(1)-N(2)
Pt(1)-C(1)
1.998(4)
2.109(4)
2.010(5)
Pt(1)-C(17)
C(17)-N(3)
C(17)-N(5)
1.992(4)
1.319(6)
1.327(6)
C(1)-Pt(1)-N(1)
C(1)-Pt(1)-N(2)
C(1)-Pt(1)-C(17)
81.4(2)
160.2(2)
98.0(2)
Pt(1)-C(17)-N(3)
Pt(1)-C(17)-N(5)
N(3)-C(17)-N(5)
116.2(3)
129.2(4)
114.6(4)
Absor p t ion a n d E m ission Sp ect r oscop y. The
UV-visible spectral data of complexes 1-10 in aceto-
nitrile are listed in Table 3 (see Figure 7 for 3). Like for
previously described Pt(II) complexes,12,15,16,30 the mod-
erately intense low-energy band with λmax in the range
[(CNN)Pt{C(NHtBu)(NHCH2Ph)}]ClO4, 4(ClO4)
Pt(1)-N(1)
Pt(1)-N(2)
Pt(1)-C(1)
1.999(5)
2.087(6)
2.068(5)
Pt(1)-C(17)
C(17)-N(3)
C(17)-N(4)
1.989(6)
1.343(7)
1.344(7)
1
C(1)-Pt(1)-N(1)
C(1)-Pt(1)-N(2)
C(1)-Pt(1)-C(17)
80.1(2)
159.2(2)
99.7(1)
Pt(1)-C(17)-N(3)
Pt(1)-C(17)-N(4)
N(3)-C(17)-N(4)
120.9(4)
126.5(4)
112.6(5)
386-401 nm is assigned to MLCT (5d)Pt f π*(CNN)
transitions, while the shoulder at λmax > 425 nm is
attributed to 3MLCT states. An increase in the electro-
philicity of the metal center is expected to result in a
blue-shift for these MLCT transitions. For example, the
singlet MLCT absorptions for the cations 1-9 appear
at higher energies than the neutral analogue [(CNN)-
PtCl] (420 nm in CH3CN),15 while the UV-vis spectrum
for the Pt(IV) derivative 10 reveals no absorptions at
λmax > 380 nm.
[(CNN)Pt{C(NHAr′)(NHMe)}]ClO4, 6(ClO4)
Pt(1)-N(1)
Pt(1)-N(2)
Pt(1)-C(1)
2.006(6)
2.110(8)
2.033(9)
Pt(1)-C(17)
C(17)-N(3)
C(17)-N(4)
1.996(8)
1.324(9)
1.328(9)
C(1)-Pt(1)-N(1)
C(1)-Pt(1)-N(2)
C(1)-Pt(1)-C(17)
80.8(3)
159.0(3)
100.4(3)
Pt(1)-C(17)-N(3)
Pt(1)-C(17)-N(4)
N(3)-C(17)-N(4)
121.5(6)
120.7(6)
117.5(7)
trans-[(CNN)Pt(CtN)I2], 10
Pt(1)-N(1)
Pt(1)-N(2)
Pt(1)-C(1)
2.005(6)
2.102(7)
2.086(5)
Pt(1)-I(1)
Pt(1)-I(2)
Pt(1)-C(17)
C(17)-N(3)
2.6490(5)
2.6718(6)
1.988(9)
1.14(1)
All isocyanide and carbene complexes in this study
are emissive in solution and solid states at room
temperature (Tables 4 and 5, respectively). With refer-
ence to earlier work on cyclometalated Pt(II) deriva-
tives,13,15,16 the structureless emissions of complexes
1-9 in CH3CN at 298 K are assigned as 3MLCT in
nature. Transformation of isocyanide ligands to di-
amino-carbene moieties results in red-shifts for the
emission maxima from 528/533 nm (for 5 and 1,
respectively) to 542-558 nm (for 2-4 and 6-8) (see
Figure 8 for 1 and 2). The emission maximum for the
binuclear bridging bis(carbene) complex 9 (λmax 545 nm)
falls within the range observed for the mononuclear
counterparts. This suggests that the two [(CNN)Pt]
moieties in 9 behave as discrete noninteracting frag-
ments from a spectroscopic perspective, since Pt(II)-
Pt(II) and/or ligand-ligand interactions would yield
MMLCT emission at λmax > 600 nm.15,16 Lifetimes
ranging from 0.18 and 0.30 µs (for 3 and 6, respectively)
up to 2.64 and 3.50 (for 2 and 9, respectively) µs are
detected. Self-quenching of the emissions are evident
I(1)-Pt(1)-N(1)
I(1)-Pt(1)-N(2)
I(1)-Pt(1)-C(1)
88.9(1)
91.6(2)
87.8(2)
I(1)-Pt(1)-I(2)
I(1)-Pt(1)-C(17)
Pt(1)-C(17)-N(3)
177.89(2)
89.7(2)
177.4(7)
actions within the N-C(carbene)-N fragment, and this
is clearly inferred from 1H NMR spectroscopy. The
resonance forms for Pt(II) diamino-carbene bonding are
shown in Figure 6. Based on structural and NMR data,
we suggest that forms A and C contribute noticeably
more to the hybrid structure than form D. A recent
experimental and theoretical study of platinum and
palladium bis(diamino-carbene) complexes found little
evidence for π bonding.29
The diamino groups of the carbene moieties in 2-4
and 6 are orientated out of the [(CNN)Pt] plane to
reduce steric repulsion. The Z, E arrangements of the
amino substituents in 2, 3, and 6 are expected for these
complexes, although the contrast between the E con-
(29) Green, J . C.; Scurr, R. G.; Arnold, P. L.; Cloke, F. G. N. Chem.
Commun. 1997, 1963.
(30) Houlding, V. H.; Miskowski, V. M. Coord. Chem. Rev. 1991,
111, 145.

3334 Organometallics, Vol. 18, No. 17, 1999
Lai et al.
Ta ble 3. UV-Vis Absor p tion Da ta in Aceton itr ile (ca r ben e com p lexes: [(CNN)P t{C(NHR1)NHR2}]ClO4)
complex
λ )
max/nm (ꢀ/dm3 mol-1 cm-1
[(CNN)Pt(CtNtBu)]ClO4, 1(ClO4)
2(ClO4): R1 ) tBu, R2 ) Me
250 (27800), 264 (26800), 333 (12800), 348 (12000), 398 (sh, 1000)
256 (27700), 269 (28800), 336 (12500), 350 (12700), 391 (1820), 435 (590),
469 (260)
234 (22000), 258 (25200), 266 (26000), 337 (11200), 350 (11200),
387 (1800), 429 (500), 465 (230)
3(ClO4): R1 ) tBu, R2 ) NH2
4(ClO4): R1 ) tBu, R2 ) CH2Ph
257 (27800), 267 (28300), 317 (10400), 336 (12000), 350 (12100),
388 (1800), 430 (750), 462 (470)
[(CNN)Pt(CtNAr′)]ClO4, 5(ClO4)
6(ClO4): R1 ) Ar′, R2 ) Me
248 (31000), 266 (28000), 330 (12400), 350 (12000), 401 (sh, 1000)
234 (27500), 255 (27700), 266 (29000), 311 (9000), 336 (12500),
350 (12700), 389 (1650), 433 (600), 468 (300)
234 (26500), 258 (25900), 267 (26900), 336 (10900), 350 (10600),
400 (1400), 470 (400)
254 (26700), 266 (26000), 309 (9900), 320 (10400), 336 (10800),
350 (11000), 389 (1400), 430 (470), 466 (200)
257 (19500), 266 (19600), 316 (7260), 351 (8280), 386 (1080), 430 (400)
7(ClO4): R1 ) Ar′, R2 ) NH2
8(ClO4): R1 ) Ar′, R2 ) CH2Ph
[{(CNN)Pt}2µ-{C(NHtBu)(NH(CH2)3)}2NMe](ClO4)2,
9(ClO4)2
trans-[(CNN)Pt(CtN)I2], 10
231 (34700), 260 (34000), 367 (7650)
Ta ble 4. Em ission Da ta in a ceton itr ile u n less oth er w ise sta ted , (com p lex con cen tr a tion ) 5 × 10-5 M,
ca r ben e com p lexes: [(CNN)P t{C(NHR1)(NHR2)}]ClO4)
298 K
77 K
complex
λ
max/nm; τï/µs; φï
λmax/nm
[(CNN)Pt(CtNtBu)]ClO4, 1(ClO4)
2(ClO4): R1 ) tBu, R2 ) Me
533; 1.12; 0.11
549; 2.64; 0.089
550; 0.18; 0.011
545; 1.17; 0.079
528; 1.18; 0.13
548; 0.30; 0.025
558; 0.56; 0.016
542; 1.14; 0.0025
545; 3.50; 0.090
505 (max), 538, 581 (sh) a
536 (max), 573, 625 (sh)
538 (max), 576, 624 (sh)
530 (max), 568, 612 (sh)
519 (max), 554, 598 (sh)
525 (max), 562, 611 (sh)
515 (max), 550, 600 (sh)a
532 (max), 570, 618 (sh)
529 (max), 560, 610 (sh)
3(ClO4): R1 ) tBu, R2 ) NH2
4(ClO4): R1 ) tBu, R2 ) CH2Ph
[(CNN)Pt(CtNAr′)]ClO4, 5(ClO4)
6(ClO4): R1 ) Ar′, R2 ) Me
7(ClO4): R1 ) Ar′, R2 ) NH2
8(ClO4): R1 ) Ar′, R2 ) CH2Ph
[{(CNN)Pt}2µ-{C(NHtBu)(NH(CH2)3)}2NMe](ClO4)2, 9(ClO4)2
a
Measured in butyronitrile.
Ta ble 5. Solid -Sta te Em ission Da ta (ca r ben e com p lexes: [(CNN)P t{C(NHR1)NHR2}]ClO4)
298 K
77 K
complex
λ
max/nm; τï/µs
λ
max/nm
[(CNN)Pt(CtNtBu)]ClO4, 1(ClO4)
2(ClO4): R1 ) tBu, R2 ) Me
579, 612 (sh); 2.60
572, 605 (sh); 1.76
568, 604 (sh); 2.04
563, 602 (sh); 1.69
704; 0.42
570, 599 (sh); 3.04
573; 1.72
553, 595 (sh); 2.49
568; 1.42
547 (sh), 568 (max), 610 (sh)
555 (max), 599, 650 (sh)
559 (max), 600, 652 (sh)
560 (max), 603, 655 (sh)
781
561 (max), 603, 660 (sh)
556 (max), 598, 654 (sh)
546 (max), 585, 635 (sh)
537 (max), 572, 627
3(ClO4): R1 ) tBu, R2 ) NH2
4(ClO4): R1 ) tBu, R2 ) CH2Ph
[(CNN)Pt(CtNAr′)]ClO4, 5(ClO4)
6(ClO4): R1 ) Ar′, R2 ) Me
7(ClO4): R1 ) Ar′, R2 ) NH2
8(ClO4): R1 ) Ar′, R2 ) CH2Ph
[{(CNN)Pt}2µ-{C(NHtBu)(NH(CH2)3)}2NMe](ClO4)2, 9(ClO4)2
F igu r e 7. UV-vis absorption spectra of 3 in acetonitrile
at 298 K.
F igu r e 8. Emission spectra of 1 and 2 in acetonitrile at
298 K (λex 350 nm, normalized intensities).
(e.g., kq ) 5.6 × 108 and 1.8 × 108 M-1 s-1 for 2 and 9,
respectively), where in each case a linear plot of 1/τ
versus complex concentration was obtained. Signifi-
cantly, high emission quantum yields on the order of
0.1 are observed for the isocyanide complexes 1 and 5.
This may be rationalized by the strong ligand field of
RNtC, which effects an increase in the energy of ligand-
field excited states so that radiationless decay is less

Carbene and Isocyanide Ligation
Organometallics, Vol. 18, No. 17, 1999 3335
F igu r e 9. Emission spectra of 1 at different concentrations
in butyronitrile at 77 K (λex 350 nm).
F igu r e 10. Solid-state emission spectra of 5(ClO4) and
6(ClO4) at 298 K (λex ) 350 nm, normalized intensities,
asterisk denotes instrumental artifact).
prevalent. According to reports by Gray and Miskowski,
the 3MLCT, 3IC, and 3dd states of Pt(II)-diimine
complexes are very close in energy,30 and nonradiative
decay via low-energy d-d excited states has been
proposed to be responsible for the low quantum yields
at 77 K (Table 5). The 627 nm band for 1 is tentatively
ascribed to excimeric intraligand emission arising from
weak π-stacking interaction of the CNN ligand, by
reference to previous studies on [Pt(tpy)Cl]+ (π-π
excimeric emission at 650 nm) by Gray and co-work-
ers.31 The shape and energy of the 730 nm band for 5 is
very similar to the 740 nm glassy emission of [Pt(tpy)-
Cl]+ at 77 K and can be attributed to MMLCT excited
states resulting from oligomerization of Pt(II) centers
in glassy solutions.31,36
3
of the MLCT emission of [Pt(tpy)Cl]+ complexes.31 We
also note that Pt(II) bpy and tpy complexes typically
exhibit very weak emission (φo on the order of 10-4
-
10-3) in solution at room temperature,32,33 whereas
derivatives bearing the cyclometalated 2-(2′-thienyl)-
pyridyl ligand can display large quantum yields of
magnitude similar to 1 and 5.34,35
The solid-state emissions of complexes 1(ClO4)-
9(ClO4)2 [except 5(ClO4)] at 298 K show poorly resolved
vibronic structures. They are red-shifted from solution
to λmax 553-579 nm with a shoulder at 595-612 nm
[see Figure 10 for 6(ClO4)], while at 77 K a blue-shift is
detected (Table 5). The emissions are tentatively as-
signed to 3MLCT excited states with excimeric character
due to weak CNN π-π interactions. As described in the
previous section, stacking interactions are evident in the
crystal lattice of these complexes (range 3.5-3.6 Å).
Similar emissive behavior has been observed for related
Pt(II)13 and transmetalated Au(III) species.37 The purple
color of 5(ClO4) in the solid state is striking and is
accredited to the propensity for these square-planar
Pt(II) species, like the established diimine relatives
reported by Miskowski and Houlding,30,38 to undergo
solid-state intermolecular stacking interactions which
yield low-energy MMLCT transitions. At 298 K, micro-
crystalline samples of 5(ClO4) emit at λmax 704 nm
(Figure 10). Upon cooling to 77 K, the bandwidth of the
emission decreases and the emission maximum red-
shifts to 781 nm, which is remarkably low for MMLCT
emissions of Pt(II) diimine solids. By comparison, the
The frozen emissions of 1-9 at 77 K have been
studied (Table 4). The 77 K emissions of 2-4 and 6-9
in acetonitrile are insensitive to the complex concentra-
tion in the range 10-6-10-3 M. Vibronically structured
emission bands are detected at λmax 515-538 nm which
are blue-shifted from 298 K. The vibrational spacings
of ca. 1200 cm-1 correspond to the skeletal stretching
of the free HCNN ligand. The most intense vibronic
component is ν′ ) 0 to ν′′ ) 0, indicating that these are
3MLCT emissions. The concentration-dependent emis-
sive behavior of 1 (Figure 9) and 5 in butyronitrile and
acetonitrile, respectively, at 77 K has been investigated.
A vibronic yellow emission at [in the order 1/5] λmax 505/
519 nm (vibronic progression ca. 1220 cm-1) is exhibited
at low concentrations (∼10-6 M). Dramatic changes in
the band shape are seen upon increasing the complex
concentration, where a new red emission centered at
627/730 nm develops at the expense of the yellow band.
The UV-vis absorption spectra of 1 and 5 for concen-
trations below 10-3 M follow Beer’s law and indicate
the absence of ground-state oligomerization processes.
For 1, emission from solid-state phases in frozen solu-
tion is discounted because this occurs at λmax 568 nm
3
solid-state MMLCT emission of [Pt(tpy)Cl]ClO4 at 298
(31) Bailey, J . A.; Hill, M. G.; Marsh, R. E.; Miskowski, V. M.;
Schaefer, W. P.; Gray, H. B. Inorg. Chem. 1995, 34, 4591.
(32) Cummings, S. D.; Eisenberg, R. J . Am. Chem. Soc. 1996, 118,
1949.
K appears at λmax 725 nm and blue-shifts to λmax 695
nm at 77 K.31
(33) Aldridge, T. K.; Stacy, E. M.; McMillin, D. R. Inorg. Chem. 1994,
33, 722.
(34) (a) Maestri, M.; Sandrini, D.; Balzani, V.; Chassot, L.; J olliet,
P.; von Zelewsky, A. Chem. Phys. Lett. 1985, 122, 375. (b) Kvam, P.-I.;
Puzyk, M. V.; Cotlyr, V. S.; Balashev, K. P.; Songstad, J . Acta Chem.
Scand. 1995, 49, 645.
(36) Yip, H. K.; Cheng, L. K.; Cheung K. K.; Che, C. M. J . Chem.
Soc., Dalton Trans. 1993, 2933.
(37) Wong, K. H.; Cheung, K. K.; Chan, M. C. W.; Che, C. M.
Organometallics 1998, 17, 3505.
(38) (38)(a) Miskowski, V. M.; Houlding, V. H. Inorg. Chem. 1989,
28, 1529. (b) Miskowski, V. M.; Houlding, V. H. Inorg. Chem. 1991,
30, 4446.
(35) Lai, S. W.; Chan, M. C. W.; Cheung, K. K.; Peng, S. M.; Che, C.
M. Organometallics, in press.

3336 Organometallics, Vol. 18, No. 17, 1999
Lai et al.
Con clu d in g Rem a r k s
blue-shifted from that of the carbene species, while
significantly higher emission quantum yields are dis-
played by 1 and 5. In future work, incorporation of
isocyanide ligands to improve the photophysical param-
eters of other classes of luminophores is anticipated. To
the best of our knowledge, the 77 K solid-state emission
of 5(ClO4) at λmax 781 nm is the lowest reported MMLCT
emission for square-planar platinum(II) diimine-type
solids.30,38
This account has described the convenient and ef-
ficient synthesis of cyclometalated platinum(II) isocya-
nide and carbene complexes. The bidentate bis(carbene)
moiety in complex 9 represents a novel class of bridging
ligand which may gain prominence in multinuclear
coordination chemistry. The crystal structures of the
1
diamino-carbene derivatives as well as H NMR data
reflect π-delocalization throughout the N-C(carbene)-N
fragment. Concurrently, the Pt-C(carbene) distances
are only slightly shorter (<0.05 Å) than the Pt-C(aryl)
contacts, and hence minimal π character in the
Pt-C(carbene) interaction is proposed.
Ack n ow led gm en t. We are grateful for support from
The University of Hong Kong and the Hong Kong
Research Grants Council.
All complexes display photoluminescence in solution
at room temperature. We suggest that the strong ligand
field strengths of the isocyanide ligands, which de-
creases the electrophilicity of Pt(II) and destabilizes
metal-centered transitions, have considerable impact
upon the emissive behavior of this system. Hence the
fluid emissions of the isocyanide derivatives 1 and 5 are
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data, atomic coordinates, calculated coordinates, anisotropic
displacement parameters, and bond lengths and angles for
2(ClO4)‚0.5H2O, 3(ClO4)‚0.5H2O, 4(ClO4), 6(ClO4), and 10. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OM990256H