Properties of the [M(dppm) 2M′]2+ building blocks (M, M′ = Pd or Pt): site selectivity, emission features, and frontier orbital analysis

Article abstract of DOI:10.1021/ic8023315

The homodinuclear [ClIM(μ-dppm)₂MCI] complexes 1 (M = Pd) and 2 (M = Pt) react with RNC ligands (R = Ph, xylyl, p-tolyl, p-C ₆H₄/Pr) to provide the A-frame [ClPd(μ-dppm) ₂(μ C=N-R)PdCl] (R = Ph (5a), xylyl (5b))

Full text of DOI:10.1021/ic8023315

Inorg. Chem. 2009, 48, 4118-4133
Properties of the [M(dppm)2M′]2+ Building Blocks (M, M′ ) Pd or Pt):
Site Selectivity, Emission Features, and Frontier Orbital Analysis
Se´bastien Cle´ment,† Shawkat M. Aly,‡ Diana Bellows,‡ Daniel Fortin,‡ Carsten Strohmann,§
Laurent Guyard,† Alaa S. Abd-El-Aziz,| Michael Knorr,*,† and Pierre D. Harvey*,‡
Institut UTINAM UMR CNRS 6213, UniVersite´ de Franche-Comte´, 16 route de Gray, 25030
Besanc¸on, France, De´partement de Chimie, UniVersite´ de Sherbrooke, Sherbrooke, PQ,
Canada, J1K 2R1, Technische UniVersita¨t Dortmund, Anorganische Chemie Otto-Hahn-Str. 6,
D-44227 Dortmund, Germany, and Department of Chemistry, UniVersity of British Columbia
Okanagan, Kelowa, BC, Canada
Received December 5, 2008
The homodinuclear [ClM(µ-dppm)2MCl] complexes 1 (M ) Pd) and 2 (M ) Pt) react with RNC ligands (R ) Ph,
xylyl, p-tolyl, p-C6H4iPr) to provide the A-frame [ClPd(µ-dppm)2(µ-CdN-R)PdCl] (R ) Ph (5a), xylyl (5b)), [ClPt(µ-
dppm)2(µ-CdN-R)PtCl] (R ) p-tolyl (4a); p-C6H4iPr (4b)), and the d9-d9 M2-bonded [ClPt(µ-dppm)2Pt(CN-R)]Cl
(R ) xylyl (3a); p-C6H4iPr (3b)) complexes. The heterodinuclear [XPd(µ-dppm)2PtX] complexes 6a (X ) Cl) and
6b (X ) I) react with RNC (R ) o-anisyl) to form the A-frame [XPd(µ-dppm)2(µ-CdN-R)PtX] (X ) Cl (9); I
(10a)) and M2-bonded [ClPt(µ-dppm)2Pt(CN-R)]Cl (10b) complexes. The dangling ligand-containing complex [ClPd(µ-
dppm)2Pt(η1-dppmdO)](BF4) (7) reacts with xylyl-NC stoichiometrically to produce the dicationic salt [(xylyl-NC)Pd(µ-
dppm)2Pt(η1-dppmdO)](BF4)2 (8). Parameters ruling the coordination site terminal versus bridging are discussed.
The precursor 10a reacts with RNC (R ) o-anisyl, tBu) to form the heterobimetallic bis(isonitrile) [IPd(µ-dppm)2(µ-
CdN-o-anisyl)Pt(CN-R)]I complexes 11b and 12, respectively, demonstrating the site selectivity of the second
CNR ligand coordination, Pd versus Pt. The X-ray structures of 11b and 12 were obtained. Complex 12 is the first
example of an A-frame system of the Ni-triad bearing two different isocyanide ligands. Several d9-d9 terminal and
d8-d8 A-frame homo- and heterodinuclear complexes in 2-MeTHF at 77 K were studied by UV-vis and luminescence
spectroscopy. Assignments for the lowest energy absorption and emission bands are made on the basis of density
functional theory and time-dependent density functional theory computations.
Introduction
(Chart 1).5 Evidence for electronic communication along the
polymer backbone in the conjugated polymers was provided.
Concurrently, the electron-rich Pd-Pd and Pt-Pt bonds,
formally called d9-d9, are capable of oxidatively adding two-
electron donor substrates to form A-frame d8-d8 species
The M-containing macromolecules and polymers have gained
tremendous interest recently for their potential applications in
photonics and advanced materials.1 Among the transition metals,
one finds Pd and Pt occupying a major place in this wide
family,2,3 but very few works concerning M-M bond-contain-
ing oligomers and polymers.4 Recently, one of us (P.D.H.)
investigated in detail the physical properties of conjugated and
nonconjugated Pd-Pd and Pt-Pt bond-containing coordination
and organometallic polymers in the solid state and in solution
(1) (a) Abd-El-Aziz, A. S.; Carraher, C. E., Jr.; Pittman, C. U., Jr.; Sheats,
J. E.; Zeldin, M. Macromolecule Containing Metal and Metal-like
Elements; Wiley Interscience, John Wiley and Sons Inc.: New York,
2005; Vol. 5. (b) Frontiers in Transition Metal-Containing Polymers;
Abd-El-Aziz, A. S., Manners, I., Eds.; John Wiley and Sons: New
York, 2007. (c) Manners, I. Science 2001, 294, 1664–1666. (d)
Manners, I. Synthetic Metal-Containing Polymers; Wiley-VCH: Wein-
heim, Germany, 2004. (e) Newkome, G. R.; He, E.; Moorefield, C. N.
Chem. ReV. 1999, 99, 1689–1746. (f) Astruc, D.; Chardac, F. Chem.
ReV. 2001, 101, 2991–3023. (g) Abd-El-Aziz, A. S. Macromol. Symp.
2003, 196, 1. (h) Abd-El-Aziz, A. S.; Harvey, P. D. Macromol. Symp.
2004, 209, 1. (i) Wolf, M. O. AdV. Mater. 2001, 13, 545–553. (j)
Archer, R. D. Inorganic and Organometallic Polymers; John Wiley
& Sons Inc.,: New York, 2001.
* To whom correspondence should be addressed. E-mail: michael.knorr@
univ-fcomte.fr (M.K.); pierre.harvey@usherbrooke.ca (P.D.H.).
†
Universite´ de Franche-Comte´.
Universite´ de Sherbrooke.
Technische Universita¨t Dortmund.
University of British Columbia at Okanagan.
‡
§
|
4118 Inorganic Chemistry, Vol. 48, No. 9, 2009
10.1021/ic8023315 CCC: $40.75  2009 American Chemical Society
Published on Web 04/06/2009

[M(dppm)2M′]2+ Building Blocks
Chart 1
where no M-M bond exists.6 This feature is extremely
interesting since it was recently demonstrated that the
electronic communication was completely shut down when
the linear conjugated d9-d9 complex Pt2(dppm)2(Ct CFc)2
(Fc ) ferrocenyl) was reacted with different substrates,
including AuCl, to form the corresponding d8-d8 A-frame
complex.7 This feature opens the doors for potential applica-
tions in photonic materials, such as sensors, where the
stimulus is the reversible oxidative addition of a given
substrate onto the electron-rich M-M bond being part of a
conjugated backbone of a polymer. In principle, because the
conjugated polymer is long in comparison with a single
dinuclear complex, the amount of substrate does not need
to be large to affect the overall physical, optical, and
photophysical properties of the materials.
We now wish to report the chemical and structural
properties of a series of homo- and hetero-M-M bonded
complexes, as well as A-frame dimers, notably with respect
to site selectivity in heterobimetallic systems, and to their
photophysical behavior in comparison with other related
dinuclear compounds. A full understanding on what controls
terminal versus bridging coordination properties for various
CNR donors is crucial for the structural design of P- and
CNR-containing organometallic and coordination polymers.
The heterobimetallic systems are particularly interesting
because of the potential in building “head-to-tail” polymers
by making judicious choices of mixed-donor bidentate
ligands.
(2) Harvey, P. D. In Frontiers in Transition Metal-Containing Polymers;
Abd-El-Aziz, A., Manners, I., Eds.; Wiley Interscience: New York,
2006; pp 321-368.
(3) Wong, W.-Y. J. Inorg. Organomet. Polym. Mater. 2005, 15, 197–
219.
(4) (a) Fournier, E.; Sicard, S.; Decken, A.; Harvey, P. D. Inorg. Chem.
2004, 43, 1491–1501. (b) Irwin, M. J.; Jia, G.; Vittal, J. J.; Puddephatt,
R. J. Organometallics 1996, 15, 5321–5329. (c) Sicard, S.; Be´rube´,
J.-F.; Samar, D.; Messaoudi, A.; Fortin, D.; Lebrun, F.; Fortin, J.-F.;
Decken, A.; Harvey, P. D. Inorg. Chem. 2004, 43, 5321–5334. (d)
Tanase, T.; Goto, E.; Begum, R. A.; Hamaguchi, M.; Zhan, S.; Iida,
M.; Sakai, K. Organometallics 2004, 23, 5975–5988. (e) Zhang, T.;
Drouin, M.; Harvey, P. D. Inorg. Chem. 1999, 38, 1305–1315. (f)
Zhang, T.; Drouin, M.; Harvey, P. D. Inorg. Chem. 1999, 38, 957–
963. (g) Zhang, T.; Drouin, M.; Harvey, P. D. Inorg. Chem. 1999,
38, 4928–4936.
Experimental Section
Materials. All reactions were performed in Schlenk-tube flasks
under purified nitrogen. Compounds ClPd(µ-dppm)2PdCl (1),
ClPt(µ-dppm)2PtCl (2), ClPd(µ-dppm)2PtCl (6a), IPd(µ-dppm)2PtI
(6b), and [ClPd(µ-dppm)2Pt(η1-dppmdO)](BF4) (7) were prepared
according to literature methods.8,9,10a o-Anisylisocyanide was
prepared according to a procedure similar to one described for
p-anisylisocyanide.11 The following materials were purchased from
commercial suppliers: xylylisocyanide (Fluka) and tert-butyliso-
cyanide (Aldrich). All solvents were dried and distilled from
appropriate drying agents.
[ClPt(µ-dppm)2Pt(CNxylyl)](BF4) (3a′). Xylylisocyanide (0.013
g, 0.100 mmol), diluted in 2 mL of CH2Cl2, was added over 30
min to a stirred solution of 2 (0.123 g, 0.100 mmol) in 3 mL of
CH2Cl2. After one day, NaBF4 (0.110 g, 10 equiv) was added, and
stirring was continued for one week. After filtration, the volume
of the yellowish solution was reduced under a vacuum and layered
(5) Be´rube´, J.-F.; Gagnon, K.; Fortin, D.; Decken, A.; Harvey, P. D. Inorg.
Chem. 2006, 45, 2812–2823.
(6) (a) Evrard, D.; Groison, K.; Decken, A.; Mugnier, Y.; Harvey, P. D.
Inorg. Chim. Acta 2006, 359, 2608–2615. (b) Yip, J. H. K.; Wu, J.;
Wong, K.-Y.; Ho, K. P.; Koh, L. L.; Vittal, J. J. Eur. J. Inorg. Chem.
2004, 105, 6–1062. (c) Foch, I.; Besenyei, G.; Simandi, L. I. Inorg.
Chem. 1999, 38, 3944–3946. (d) Kluwe, C.; Mu¨ller, J.; Davies, J. A.
J. Organomet. Chem. 1996, 526, 385–387. (e) Besenyei, G.; Parkanyi,
L.; Simandi, L.; James, B. R. Inorg. Chem. 1995, 34, 6118–6123. (f)
Toronto, D. V.; Balch, A. L. Inorg. Chem. 1994, 33, 6132–6139. (g)
Neve, F.; Longeri, M.; Ghedini, M.; Crispini, A. Inorg. Chim. Acta
1993, 205, 15–22. (h) Neve, F.; Ghedini, M.; Tiripicchio, A.; Ugozzoli,
F. Organometallics 1992, 11, 795–801. (i) Uson, R.; Fornies, J.;
Navarro, R.; Tomas, M.; Fortuno, C.; Cebollada, J. I.; Welch, A. J.
Polyhedron 1989, 8, 1045–1052. (j) Davies, J. A.; Pinkerton, A. A.;
Syed, R.; Vilmer, M. J. Chem. Soc., Chem. Commun. 1988, 47–49.
(k) Arsenault, G. J.; Manojlovic-Muir, L.; Muir, K. W.; Puddephatt,
R. J.; Treurnicht, I. Angew. Chem., Int. Ed. Engl. 1987, 26, 86–87. (l)
Uson, R.; Fornies, J.; Navarro, R.; Cebollada, J. I. J. Organomet. Chem.
1986, 304, 381–390. (m) Uson, R.; Fornies, J.; Espinet, P.; Fortuno,
C. Inorg. Chim. Acta 1984, 87, 207–211. (n) Puddephatt, R. J.; Azam,
K. A.; Hill, R. H.; Brown, M. P.; Nelson, C. D.; Moulding, R. P.;
Seddon, K. R. J. Am. Chem. Soc. 1983, 105, 5642–5646. (o) Balch,
A. L.; Hunt, C. T.; Lee, C.-L.; Olmstead, M. M.; Farr, J. P. J. Am.
Chem. Soc. 1981, 103, 3764–3772. (p) Brown, M. P.; Fischer, J. R.;
Puddephat, R. J.; Seddon, K. R. Inorg. Chem. 1979, 18, 2808–2813.
(7) Yip, J. H.; Wu, J.; Wong, K.-Y.; Ho, K. P.; Pun, C. S.-N.; Vittal, J. J.
Organometallics 2002, 21, 5292–5300.
(8) Grossel, M. C.; Batson, J. R.; Moulding, R. P.; Seddon, K. R. J.
Organomet. Chem. 1986, 304, 391–423.
(9) Pringle, P. G.; Shaw, B. L. J. Chem. Soc., Dalton Trans. 1983, 5,
889–897.
(10) (a) Evrard, D.; Cle´ment, S.; Lucas, D.; Hanquet, B.; Knorr, M.;
Strohmann, C.; Decken, A.; Mugnier, Y.; Harvey, P. D. Inorg. Chem.
2006, 45, 1305–1315. (b) Clément, S.; Aly, S. M.; Fortin, D.; Guyard,
L.; Knorr, M.; Abd-El-Aziz, A. S.; Harvey, P. D. Inorg. Chem. 2008,
47, 10816–10824.
(11) Wagner, N. L.; Murphy, K. L.; Haworth, D. T.; Bennett, D. W. In
Inorganic Syntheses; Wiley-VCH: New York, 2004; Vol. 34, pp
24-29.
Inorganic Chemistry, Vol. 48, No. 9, 2009 4119

Cle´ment et al.
2+3
1
with diethyl ether. After several days, yellow needles were formed.
δ -8.9 (m, 2P, Pd-P,
J
Pt-P
) 52), -3.1 (m, 2P, Pt-P, JPt-P
1
Yield: 0.113 g (80%). IR (KBr): 2157 (s) (νCN) cm-1. H NMR
) 2590, N ) 80 Hz). 195Pt{1H} NMR (CDCl3/MeOH): δ -2758
(CDCl3): δ 6.76-8.00 (m, 43H, Ph), 4.59 (m, br, 4H, PCH2P, 3JPt-H
) 60), 1.70 (s, 6H, CH3) ppm. 31P{1H} NMR (CDCl3): δ 1.2 (m,
2P, 1JPt-P ) 2370, N ) 90), -1.7 (m, 2P, 1JPt-P ) 3070, N ) 90).
UV-vis (CH2Cl2) (λmax nm (ε)): 226 (62700), 348 (4500). Anal.
calcd for C59H53BClNF4P4Pt2 ·CH2Cl2: C, 48.12; H, 3.67. Found:
C, 47.88; H, 3.55.
(tt, 1JPt-P ) 2590,
J
) 50). 10a. IR (KBr): 1611 cm-1 (νCdN).
Pt-P
2+3
1H NMR (CDCl3): δ 3.53 (s, 3H, OCH3), 4.77 (t, 4H, PCH2P),
6.99-7.77 (m, 44H, Ph). 31P{1H} NMR (CDCl3): δ 10.8 (t, 2P,
1
3
Pt-P, JPt-P ) 3465, N ) 75 Hz), 12.3 (t, 2P, Pd-P, JPt-P
520). Anal. calcd for C58H51I2NOP4PdPt: C, 47.80; H, 3.53; N 1.05.
Found: C, 47.56; H, 3.53; N, 0.96.
)
[ClPt(µ-dppm)2(µ-CdN-C6H4-iPr)PtCl] (4b) and [ClPt(µ-
dppm)2Pt(CN-C6H4-iPr)]Cl (3b). 1-Isocyano-4-isopropylben-
zene (0.039 g, 0.268 mmol) in 2 mL of CH2Cl2 was added to a
stirred solution of 2 (0.330 g, 0.268 mmol) in 10 mL of CH2Cl2
over a period of 30 min. The orange solution was stirred for 1 h
and evaporated to dryness. The orange residue was then dissolved
in a minimum amount of CH2Cl2 and precipitated with hexane,
washed with ether (2 × 5 mL), and dried under a vacuum. Yield:
[XPd(µ-dppm)2(µ-CdN-C6H4-2-OCH3)Pt(CN-C6H4-2-
OCH3)]X (11a, X ) Cl; 11b, X ) I). o-Anisylisocyanide (0.027
g, 0.200 mmol), diluted in 2 mL of CH2Cl2, was added over a period
of 30 min to a stirred solution of 6a or 6b (0.100 mmol) in 3 mL
of CH2Cl2. After 2 h, the reddish solution was evaporated to dryness.
The orange residue was washed with 5 mL of Et2O and dried under
a vacuum. 11a. Yield: 93% (0.131 g). IR (KBr): 2171 (s) (νCN),
1
1621 (w) (νCdN) cm-1. H NMR (CDCl3): δ 5.98-7.95 (m, 48H,
1
0.270 g (73%). 4b. IR (KBr): 1616 (w) (νCdN) cm-1. H NMR
Ph), 3.51 (s, 3H, OCH3), 3.39 (m, br, 4H, PCH2P), 3.14 (s, 3H,
OCH3). 31P{1H} NMR (CDCl3): δ 16.1 (m, 2P, Pt-P(µ-dppm),
(CDCl3): δ 6.90-8.10 (m, 44H, Ph), 4.63 (m, br., 4H, PCH2P, 3JPt-H
) 60), 2.92 (h, 1H, CH(CH3)2, 3JH-H ) 6.8), 1.12 (d, 6H, CH(CH3)2,
3
1JPt-P ) 3210, N ) 80 Hz), 18.3 (m, 2P, Pd-P(µ-dppm), JPt-P
)
3JH-H ) 6.8) ppm. 31P{1H} NMR (CDCl3): δ 17.9 (s, 4P, 1JPt-P
)
302). 195Pt{1H} NMR (CDCl3): δ -2856 (tt, JPt-P ) 3210, JPt-P
) 302). UV (MeCN): λmax (ε) ) 224 (65800), 289 (36200), 384
(4100), 459 (2050). Anal. Calcd for C66H58Cl2N2O2P4PdPt·CH2Cl2:
C, 53.92; H, 4.03; N, 1.88, Found: C, 53.69; H, 4.09; N, 1.84. 11b.
1
3
3480). 3b. IR (CH2Cl2): 2162 (s) (νCN) cm-1 31P{1H} NMR
.
(CDCl3): δ 7.5 (m, 2P, 1JPt-P ) 3220), 3.4 (m, 2P, 1JPt-P ) 2980).
1H NMR (CDCl3): δ 6.55-8.10 (m, 44H, Ph), 3.83 (m, br, 4H,
PCH2P, 3JPt-H ) 60.2), 2.59 (h, 1H, CH(CH3)2, 3JH-H ) 7.4), 1.09
1
Yield: 0.135 g (80%). IR (KBr): 2174 (s) (νCN), 1630 (νCdN). H
3
(d, 6H, CH(CH3)2, JH-H
) 7.4) ppm. Anal. calcd for
NMR (CDCl3, 213 K): δ 6.10-7.90 (m, 48H, Ph), 3.63 (s, 3H,
OCH3), 3.46 (m, br, 4H, PCH2P), 3.17 (s, 3H, OCH3). 13C{1H}
NMR (CDCl3): 20.3 (2C, PCH2P), 55.9 (2C, OCH3), 112.0, 120.6
(Ph), 122.2 (2C, CN), 128.3-134.6 (Ph), 153 (dC-OMe). 31P{1H}
C60H55Cl2NP4Pt2 ·0.5 CH2Cl2: C, 51.27; H, 3.95; N, 0.99. Found:
C, 51.14; H, 3.82; N, 0.95.
[(xylylNC)Pd(µ-dppm)2Pt(η1-dppm)O)](BF4)2 (8). Xylyliso-
cyanide (0.011 g, 0.084 mmol), diluted in 1 mL of CH2Cl2, was
added within 30 min to a stirred solution of 7 (0.120 g, 0.076 mmol)
in 2 mL of CH2Cl2. After one day, NaBF4 (0.084 g, 10 equivalents)
was added, and stirring was continued for one week. The mixture
was filtered and evaporated to dryness. The resulting orange residue
was washed with diethyl ether and dried. Yield: 0.121 g (90%). IR
1
NMR (CDCl3): δ 15.0 (m, 2P, Pt-P, JPt-P ) 3225, N ) 85 Hz),
20.8 (m, 2P, Pd-P, 3JPt-P ) 300). 195Pt{1H} NMR (CDCl3): δ -2825
(tt, 1JPt-P ) 3225, 3JPt-P ) 300). UV-vis (CH2Cl2) (λmax nm (ε)):
245 (54200), 292 (20400), 406 (3560), 450 (4150). Anal. calcd for
C66H58I2N2O2P4PdPt·0.5CH2Cl2: C, 48.87; H, 3.61; N 1.71. Found:
C, 48.91; H, 3.65; N, 1.72.
1
(KBr): 2167(s) (νCN) cm-1. H NMR (CDCl3): δ 6.99-7.77 (m,
[IPd(µ-dppm)2Pt(µ-CdN-C6H4-OCH3)(CN-tBu)]I (12). Tert-
butylisocyanide (0.008 g, 0.100 mmol) dissolved in 1 mL of CH2Cl2
was added to a stirred solution of 9 (0.156 g, 0.100 mmol) in 3
mL of CH2Cl2 over a period of 30 min. The orange solution was
stirred for 1 h. Its volume was reduced under a vacuum and layered
with Et2O to afford X-ray-suitable orange crystals. Yield: 0.136 g
63H, Ph), 6.80 (m, 4H, PCH2P), 4.56 (m, br, 2H, PCH2P), 1.76 (s,
6H, CH3). 31P{1H} NMR (CDCl3): 25.6 (s, Pt-PCH2PdO), -0.98
(Pt-P(η1-dppm), 1JPt-P ) 2580, N ) 90 Hz), -3.98 (m, Pt-P(µ-
1
dppm), JPt-P ) 2450, N ) 80 Hz), -6.18 (m, Pd-P(µ-dppm)).
UV-vis (CH2Cl2) (λmax nm (ε)): 227 (57500), 270 (22400), 307
(13500), 375 nm (3100). Anal. calcd for C84H75B2F8NOP6PdPt ·
2CH2Cl2: C, 53.05; H, 4.06; N, 0.72. Found: C, 52.98; H, 4.03, N,
0.69.
1
(83%). H NMR (CDCl3): δ 6.10-7.90 (m, 44 H, Ph), 3.43 (s,
3H, OCH3), 3.16 (m, br, 4H, PCH2P), 0.86 (s, 9H, tBu). 31P{1H}
NMR (CDCl3): δ 14.9 (m, 2P, Pt-P(µ-dppm), 1JPt-P ) 3222, N )
81 Hz), 19.9 (m, 2P, Pd-P(µ-dppm), 3JPt-P ) 325). 195Pt{1H} NMR
[ClPd(µ-dppm)2(µ-CdN-C6H4-OCH3)PtCl] (9). o-Anisyl-
isocyanide (0.013 g, 0.100 mmol) in 2 mL of CH2Cl2 was added
slowly over a period of 30 min to a stirred solution of 6a (0.114 g,
0.100 mmol) in 3 mL of CH2Cl2. After 1 h, the yellowish solution
was evaporated to dryness. The orange residue was washed with 5
mL of Et2O and dried under a vacuum. Yield: 0.103 g (81%). IR
(KBr): 1616 (νCdN) cm-1. 1H NMR (CDCl3): δ 5.98-7.78 (m, 44H,
Ph), 3.54 (s, 3H, OCH3), 3.28 (m, br, 2H, PCH2P), 2.82 (m, br,
2H, PCH2P). 31P{1H} NMR (CDCl3): δ 12.1 (m, 4P, 1JPt-P ) 3560,
3JPt-P ) 495). UV-vis (MeCN) (λmax nm (ε)): 227 (51800), 267
(18900), 348 (2700). Anal. calcd for C58H51Cl2NOP4PdPt: C, 54.67;
H, 4.03; N, 1.10. Found: C, 54.49; H, 4.42; N, 1.00.
1
3
(CDCl3): δ -2860 (tt, JPt-P ) 3220, JPt-P ) 325). Mass FAB
(NBA-matrix) (rel. int.): 1328 (6%) PdPt(dppm)2I(CN-C6H4-OMe),
1196 (100%) PdPt(dppm)2I, 1068.0 (40%) PdPt(dppm)2. Anal. calcd
for C63H60I2N2OP4PdPt: C, 49.12; H, 3.92; N, 1.82. Found: C, 49.06;
H, 4.15; N, 1.83.
Apparatus. IR spectra have been recorded on a Nicolet Nexus
470 spectrometer. All NMR spectra were acquired with a Bruker
Avance 300 (1H 300.13 MHz, 13C 75.48 MHz and 31P 121.49 MHz)
using the solvent as the chemical shift standard, except for 31P NMR,
where the chemical shifts are relative to 85% H3PO4 in D2O. 195Pt
chemical shifts were measured on a Bruker ACP 200 instrument
(42.95 MHz) and externally referenced to K2PtCl4 in water with
downfield chemical shifts reported as positive. All of the chemical
shifts and coupling constants are reported in parts per million and
hertz, respectively. UV-vis spectra were recorded on a Varian Cary
50 spectrophotometer. Emission and excitation spectra were
obtained by using a double monochromator Fluorolog 2 instrument
from Spex. Fluorescence lifetimes were measured on a Timemaster
model TM-3/2003 apparatus from PTI. The source was a nitrogen
[IPd(µ-dppm)2Pt(CN-C6H4-OCH3)]I (10b) and [IPd(µ-
dppm)2Pt(µ-CdN-C6H4-OCH3)I] (10a). o-Anisylisocyanide
(0.013 g, 0.100 mmol) in 2 mL of CH2Cl2 was added to a stirred
solution of 6b (0.132 g, 0.100 mmol) in 3 mL of CH2Cl2 over a
period of 30 min. The reddish solution was stirred for 1 h and
evaporated to dryness. The orange residue was washed with 5 mL
of Et2O and dried in a vacuum. Yield: 0.125 g (86%). 10b. IR
(CH2Cl2/MeOH): 2175 cm-1 (νCN). 31P{1H} NMR (CDCl3/MeOH):
4120 Inorganic Chemistry, Vol. 48, No. 9, 2009

[M(dppm)2M′]2+ Building Blocks
laser equipped with a high-resolution dye laser (fwhm ∼ 1500 ps),
and the fluorescence lifetimes were obtained from deconvolution
and distribution lifetime analysis.
formed using the B3LYP method19 with the basis sets 6-21g20 for
all C, N, and H atoms, whereas basis sets and specific core electron
approximations were used for Pt, Pd, Cl, I, and P atoms.21 The
same basis sets were used to compute the electronic configuration
of the triplet states and the energy of the highest semioccupied
molecular orbitals (HSOMO) and the ground state (HOMO).22
Quantum Yield. The quantum yields were measured against
[Ru(bpy)3](Cl)2 (Φe ) 0.376 ( 0.036).12
X-Ray Crystallography. Single crystals of 11b and 12 were
coated with perfluoroalkyl ether oil (ABCR), mounted using a glass
fiber, and frozen in the cold nitrogen stream of the goniometer.
The data were collected on a Stoe IPDS diffractometer. The data
were reduced (Integrate in IPDS) and corrected for absorption
(FACEIT in IPDS). The structure was solved by direct methods
and refined by full-matrix least-squares on F2 (SHELXTL). Single
crystals of 4b were grown by slow vapor diffusion using methyl-
ethylketone as a good solvent and tert-butylmethylether at 298 K.
One single crystal of 0.50 × 0.10 × 0.10 mm3 was mounted using
a glass fiber on the goniometer at 298(2) K. Data were collected
on an Enraf-Nonius CAD-4 automatic diffractometer using ω scans.
The DIFRAC13 program was used for centering, indexing, and data
collection. Two standard reflections were measured every 200
reflections; no intensity decay was observed during data collection.
The data were corrected for absorption by empirical methods based
on ψ scans and reduced with the NRCVAX14 programs. All
structures were solved using SHELXS-9715 and refined by full-
matrix least-squares on F2 with SHELXL-97.15 The non-hydrogen
atoms were refined anisotropically. The hydrogen atoms were placed
at idealized calculated geometric positions and refined isotropically
using a riding model. The absolute structure of 4b was determined
by anomalous dispersion effect.16 Crystallographic data have been
deposited with the Cambridge Crystallographic Data Centre as
CCDC 711384 (4b), CCDC 711703 (11b), and CCDC 711702 (12).
Copies of the data can be obtained free of charge on application to
Cambridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, U.K. [fax: (+44) 1223-336-033; email:
deposit@ccdc.cam.ac.uk).
Results and Discussion
1. The d9-d9 Homo- and Heterobimetallic Systems. The
conclusion of our previous work on the reactivity of [ClM(µ-
dppm)2MCl] (M ) Pd, Pt) toward isocyanides10 urged us to
synthesize additional derivatives ligated by one or two CNR
ligands with diverging electronic and steric properties. A
systematic variation of the nature of R in CNR ligands, of
M, as well as of the halide ligands is necessary in order to
elucidate what controls the bridging versus terminal coor-
dination of the CNR ligands, as well as the photophysical
properties of these compounds. This section describes the
syntheses and characterization of some new isocyanide-
containing homo- and heterobimetallic systems and discusses
their structural features.
Grundy and Robertson previously demonstrated that treat-
ment of [ClPt(µ-dppm)2PtCl] (2) with p-tolylisocyanide in
a CH2Cl2 solution affords the A-frame compound [ClPt(µ-
dppm)2(µ-CdN-C6H4Me)PtCl] (4a), resulting from CNR
insertion on the Pt-Pt bond.23 Surprisingly, treatment of 2
with xylylisocyanide (xylyl ) 2,5-dimethylphenyl) in a 1:1
ratio under similar reaction conditions produces exclusively
the Pt-Pt-bonded monocationic species [ClPt(µ-dppm)2Pt-
(CNxylyl)]Cl (3a) bearing a terminal CNR ligand (Scheme
1). This terminal coordination mode can be inferred from
the IR spectra, which exhibits a strong ν(Ct N) absorption
at 2157 cm-1. The 31P{1H} NMR spectra of 3a give rise to
AA′BB′ spin systems consisting of two multiplets centered
Computational Details. Density functional theory (DFT) and
time-dependent density functional theory (TDDFT) were performed
with the commercial software Gaussian 0317 using the Super
Computer of the University of Sherbrooke (Mammouth MP) and
supported by the Re´seau Que´be´cois de Calcul de Haute Perfor-
mance. The TDDFT18a-c and DFT18d-g calculations were per-
1
at +1.2 and -1.7 ppm with JPt-P couplings of 2370 and
3070 Hz, respectively. These observations contrast with a
(18) (a) Stratmann, R. E.; Scuseria, G. E.; Frisch, M. J. J. Chem. Phys.
1998, 109, 8218–8224. (b) Bauernschmitt, R.; Ahlrichs, R. Chem.
Phys. Lett. 1996, 256, 454–464. (c) Casida, M. E.; Jamorski, C.;
Casida, K. C.; Salahub, D. R. J. Chem. Phys. 1998, 108, 4439–4449.
(d) Hohenberg, P.; Kohn, W. Phys. ReV. 1964, 136, B864-B871. (e)
Kohn, W.; Sham, L. J. Phys. ReV. 1965, 140, A1133-A1138. (f)
Salahub; D. R.; Zerner, M. C. The Challenge of d and f Electrons;
American Chemical Society: Washington DC, 1989. (g) Parr, R. G.;
Yang, W. Density-functional theory of atoms and molecules; Oxford
University Press: Oxford, U.K., 1989.
(19) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648–5652. (b) Lee, C.;
Yang, W.; Parr, R. G. Phys. ReV. B: Condens. Matter Mater. Phys.
1988, 785–789. (c) Miehlich, B.; Savin, A.; Stoll, H.; Preuss, H. Chem.
Phys. Lett. 1989, 157, 200–206.
(20) (a) Gordon, M. S.; Binkley, J. S.; Pople, J. A.; Pietro, W. J.; Hehre,
W. J. J. Am. Chem. Soc. 1982, 104, 2797–2803. (b) Pietro, W. J.;
Francl, M. M.; Hehre, W. J.; Defrees, D. J.; Pople, J. A.; Binkley,
J. S. J. Am. Chem. Soc. 1982, 104, 5039–5048. (c) Dobbs, K. D.;
Hehre, W. J. J. Comput. Chem. 1986, 7, 359–378. (d) Dobbs, K. D.;
Hehre, W. J. J. Comput. Chem. 1987, 8, 861–879. (e) Dobbs, K. D.;
Hehre, W. J. J. Comput. Chem. 1987, 8, 880–893.
(21) (a) Stevens, W. J.; Basch, H.; Krauss, M. J. Chem. Phys. 1984, 81,
6026–6033. (b) Stevens, W. J.; Krauss, M.; Basch, H.; Jasien, P. G.
Can. J. Chem. 1992, 70, 612–630. (c) Cundari, T. R.; Stevens, W. J.
J. Chem. Phys. 1993, 98, 5555–5565. (d) Binkley, J. S.; Pople, J. A.;
Hehre, W. J. J. Am. Chem. Soc. 1980, 102, 939–947.
(12) Demas, J. N.; Crosby, G. A. J. Am. Chem. Soc. 1971, 93, 2841–2847.
(13) Flack, H. D.; Blanc, E.; Schwarzenbach, D. J. Appl. Crystallogr. 1992,
25, 455–459.
(14) Gabe, E. J.; Le Page, Y.; Charland, J. P.; Lee, F. L.; White, P. S.
J. Appl. Crystallogr. 1989, 22, 384–387.
(15) Sheldrick, G. M. SHELXS 97, Release 97-2; Sheldrick, G. M.;
University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(16) Flack, H. D. Acta Crystallogr. 1983, A39, 876–881.
(17) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin,
K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone,
V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa,
J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene,
M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin,
A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.;
Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas,
O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.;
Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.;
Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen,
W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, revision
C.2; Gaussian, Inc.: Wallingford, CT, 2004.
(22) Lowry, M. S.; Hudson, W. R.; Pascal, R. A., Jr.; Bernhard, S. J. Am.
Chem. Soc. 2004, 126, 14129–14135.
(23) Grundy, K. R.; Robertson, K. N. Organometallics 1983, 2, 1736–
1742.
Inorganic Chemistry, Vol. 48, No. 9, 2009 4121

Cle´ment et al.
Scheme 1
Scheme 3
Scheme 2
forms. This dinuclear iodo complex is obtained by the
treatment of [IPd(µ-dppm)2PtI] (6b) with 1 equiv of o-
anisylisocyanide in CH2Cl2 or by halide metathesis with NaI
using [ClPd(µ-dppm)2(µ-CdN-o-anisyl)PtCl] (9) as a precur-
sor. This yellow compound prevails in the crystalline state
almost exclusively in the A-frame form [IPd(µ-dppm)2(µ-
CdN-o-anisyl)PtI] (10a), as deduced from the observed IR-
active ν(CdN) at 1611 cm-1. However, the IR spectrum of
10a in CH2Cl2 solution indicates the coexistence of an
appreciable percentage of the ionic form [IPd(µ-dppm)2Pt(CN-
o-anisyl)]I (10b) with a terminal coordinated CNR ligand.
This equilibrium is entirely shifted in a 1:1 MeOH/CH2Cl2
mixture toward the ionic isomer 10b. Owing to the increase
in solvent polarity, the dissociation of the iodo ligand is now
facilitated. Indeed, a single sharp ν(Ct N) band is detected
at 2175 cm-1 in the IR spectrum of 10b.
precedent report on the synthesis of [ClPd(µ-dppm)2(µ-
CdN-xylyl)PdCl] (5b) and [ClPd(µ-dppm)2(µ-CdN-
Ph)PdCl] (5a), spanned by a bridging CNR ligand.24 These
differences of behavior will be discussed later.
[ClPt(µ-dppm)2Pt(CNxylyl)][BF4]·CH2Cl2 (3a′) was pre-
pared from the counterion metathesis of the Cl- salt (3a)
with NaBF4. Single crystals suitable for an X-ray structure
analysis of this salt (3a′) were obtained, but because of the
poor crystal quality, little data could be collected. Neverthe-
less, the collected data unambiguously demonstrated the
conservation of the M-M bond (2.654 Å) and the terminal
coordination of a linear RNC ligand (R-N(1)-C(49) )
175.4°; d(Pt(1)-C(49)) ) 1.93 Å) at Pt(1) (Figure S2,
Supporting Information). These values compare favorably
tothoserecentlyreportedforthedicationicsalt[(iPrC6H4NC)Pt(µ-
dppm)2Pt(CNC6H4iPr)](BF4)2, having a Pt-Pt bond length
of 2.6453(3) Å and two linearly bonded CNR ligands with
mean Pt-C bond distances of 1.99 Å.5
The equilibrium in solution can also be monitored by
31P{1H} NMR spectroscopy. The spectra exhibit an ap-
proximate 50:50 distribution between 10a and 10b in a 1:1
CDCl3/CH2Cl2 mixture. However, in 1:1 CDCl3/MeOH as a
solvent medium, only a small amount of the A-frame isomer
10a remains detectable (Figure 1). The AA′BB′-type reso-
nances of 10b appear at strongly high-field regions at -3.1
(PPt) and -8.9 ppm (PPd) in comparison with those of the
µ-CNR isomer 10a (AA′BB′ type, 10.8 (P(Pt)) and 12.3 ppm
(PPd)). The Pt-Pd bond scission also causes a considerable
The cationic heterodinuclear complex [ClPd(µ-dppm)2Pt(η1-
dppmdO)](BF4) (7), coordinated by a dangling diphosphine
oxide, reacts with a stoichiometric amount of xylylisocyanide
to produce the dicationic salt [(xylylNC)Pd(µ-dppm)2Pt(η1-
dppmdO)](BF4)2 (8) after a metathesis reaction exchanging
the counterion Cl for BF4. (Scheme 2). The RNC terminal
coordination on Pd is readily deduced from the IR spectrum,
which exhibits a strong ν(Ct N) absorption at 2167 cm-1.
The 31P{1H} NMR spectrum of 8, which is similar to that
of precursor 7, is reported in the Supporting Information.
An interesting borderline case between RNC terminal
ligation in M-M connected d9-d9 systems and µ-CNR
coordination giving rise to d8-d8 A-frame bimetallics is
compound 10a (Scheme 3), which exists in two isomeric
1
increase of the JPt-P couplings going from 2590 to 3465
Hz. The 195Pt{1H} NMR spectrum of 10b consists of a
broadened triplet of triplets centered at -2758 ppm with
2+3
1JPt-P and
J
Pt-P
couplings of 2590 and 50 Hz, respectively.
The observation of isomers’ equilibrium, even in a less polar
medium such as CDCl3/CH2Cl2, suggests that the energetic
difference between bridging and terminal RNC bonding is quite
small in system 10. The solvent polarity dependence on the
CNR coordination mode was already noticed by others.25
Examples include the p-tolyl isocyanide adduct of [ClPt(µ-
(25) (a) Uson, R.; Fornies, J.; Espinet, P.; Fortuno, C. J. Chem. Soc., Dalton
Trans. 1986, 1849–1855. (b) Fornies, J.; Martinez, F.; Navarro, R.;
Redondo, A.; Tomas, M.; Welch, A. J. J. Organomet. Chem. 1986,
316, 351–366.
(24) (a) Khan, M. A.; McAlees, A. J. Inorg. Chim. Acta 1985, 104, 109–
114. (b) Benner, L. S.; Balch, A. L. J. Am. Chem. Soc. 1978, 100,
6099–6106.
4122 Inorganic Chemistry, Vol. 48, No. 9, 2009

[M(dppm)2M′]2+ Building Blocks
Figure 1. (a) 31P{1H} NMR spectrum of an isomeric mixture of 10a and 10b recorded in CDCl3/CH2Cl2. (b) 31P{1H} NMR spectrum of 10b recorded in
4
CDCl3/CH3OH (N ) |2J(PAPB) + J(PAPB′)|).
Scheme 4
dppm)2PtC6F5], which exists in benzene as the A-frame [ClPt(µ-
dppm)2(µ-CdN-p-tolyl)PtC6F5] but rearranges entirely in
CH2Cl2 to the ionic [(p-tolyl-Nt C)Pt(µ-dppm)2PtC6F5]Cl form.
The low, but definite, conductivity of the heterodinuclear
[ClPt(µ-dppm)2(µ-CdN-p-tolyl)PdC6F5] complex-containing
acetone solution was ascribed to a deinsertion-terminal coor-
dination equilibrium. All in all, system 10 represents the first
case where a coexistence of d8-d8 and d9-d9 isomers of the
Ni-triad in a noncoordinating solvent is established.
2. The d8-d8 A-Frame Homo- and Heterobimetallic
a singlet at 17.5 ppm. The shift and the types of resonances
obtained for 3b compare unambiguously with the data
Systems. In contrast with the stoichiometric reaction of 2
reported above for [ClPt(µ-dppm)2Pt(CNxylyl)]BF4 (3a′).
with xylylisocyanide affording the cationic complex [ClPt(µ-
Crystal Structure of 4b. In contrast with several reports
dppm)2Pt(CNxylyl)]Cl (3a), the treatment of 2 with 1-iso-
on the molecular structures of µ-CNR-containing d8-d8 Pd2
cyano-4-isopropylbenzene in CH2Cl2 yields, as previously,
A-frame systems, no crystallographic information on analogous
a mixture of the A-frame compound [ClPt(µ-dppm)2(µ-
Pt2 compounds was available until this work. The insertion of
CN-C6H4iPr into the Pt-Pt bond was corroborated by the
X-ray diffraction study (Figure 2, Table 2). The overall structure
CdN-C6H4iPr)PtCl] (4b) and the ionic compound [ClPt(µ-
dppm)2Pt(CNC6H4iPr)]Cl (3b) (Scheme 4; see Table 1 for
Crystal and Refinement Data).
The existence of these two isomeric forms can be deduced
of 4b resembles that of the corresponding Pd2 A-frame complex
[ClPd(µ-dppm)2(µ-CdN-Ph)PdCl].24a,26
from the IR (in CH2Cl2, ν(CdN) ) 1616; ν(Nt C) ) 2162
cm-1) and the 31P{1H} NMR spectra. The spectra exhibit an
approximate 50:50 distribution between 4b and 3b in CDCl3
at 298 K. The AA′BB′-type resonances of 3b appear at 3.4
and 7.5 ppm, whereas the resonance of µ-CNR isomer 4b is
Similarly to the previous complex (d(Pd· · ·Pd) ) 3.188(1)
Å),24a the insertion causes a considerable elongation of
M · · · M interactions (d(Pt · · · Pt) 3.2118(18) Å), and the
C)N-R angle is somewhat less acute (133.0(2) vs 129.3(9)°).
The coordination modes about the Pt atoms are square-planar
Inorganic Chemistry, Vol. 48, No. 9, 2009 4123

Cle´ment et al.
Table 1. Crystal and Refinement Data for 4b, 11b, and 12
4b
11b ·0.5CH2Cl2
12·CH2Cl2
empirical formula
fw
C60H55Cl2NP4Pt2
1375.01
C66.5H59ClI2N2O2P4PdPt
1632.78
C64H62Cl2I2OP4PdPt
1625.23
description
cryst size (mm)
temp (K)
cryst syst
space group
a (Å)
colorless
0.10 × 0.10 × 0.5
293(2)
tetragonal
P41
21.510(4)
21.510(4)
14.2270(13)
90
orange
orange
0.20 × 0.20 × 0.10
0.30 × 0.20 × 0.20
173(2)
173(2)
orthorhombic
Pbca
15.658(2)
24.377(4)
32.281(5)
90
monoclinic
P2(1)/c
21.703(4))
13.373(3)
24.493(5)
115.04(3)
6441(2)
b (Å)
c (Å)
ꢀ (deg
)
Vol (Å3)
6583(2)
12321(3)
Z
4
8
4
calcd. density (Mg/m3)
scan mode
1.387
ω
2688
1.760
ꢁ
6360
1.676
ꢁ
3168
F(000)
abs coeff (mm-1
θ range
)
9.747
3.756
3.631
4.11-69.98°
0 e h e 26
-26 e k e 0
-17 e l e 0
6385
1.26-25.00°
-18 e h e 26
-28 e k e 28
-38 e l e 38
229876
2.24-25.00°
-24 e h e 25
-15 e k e 15
-29 e l e 29
41644
limiting indices
reflns collected
independent reflns
6385
10851
11321
min./max.transmiss. ratio
data /restraints/ params
goodness-of-fit on F2
final R indices [I > 2σ(I)]a
0.4423/0.0848
3556/371/478
1.034
R1 ) 0.0880
wR2 ) 0.2308
R1 ) 0.1524
wR2 ) 0.2884
4
0.7052/0.5205
10851/2/727
1.081
R1 ) 0.0620
wR2 ) 0.1466
R1 ) 0.0842
wR2 ) 0.1550
0.5304/0.4089
11321/0/693
1.012
R1 ) 0.0848
wR2 ) 0.2447
R1 ) 0.0990
wR2 ) 0.2561
R indices (all data)
a
R1 ) ∑||Fo| - |Fc||/∑ |Fo|; wR2 ) (∑[w(Fo2 - Fc2)2]/∑[Fo ])1/2; weight ) 1/[σ2(Fo ) + (A·P)2 + (B·P)] where P ) (max (Fo ,0) + 2Fo )/3, A ) 0.0890
and B ) 11.4580 for 4b, A ) 0.0612 and B ) 161.0473 for 11b, and A ) 0.1686 and B ) 50.39 for 12.
2
2
2
Table 2. Selected Bond Distances (Å) and Angles (deg) for 4b
Pt(1)-C(3)
1.92(2)
1.97(2)
1.31(3)
Pt(1)-P(2)
Pt(1)-P(4)
Pt(2)-P(1)
Pt(2)-P(3)
C(4)-N(1)
2.290(9)
2.292(9)
2.289(8)
2.279(9)
1.41(3)
Pt(2)-C(3)
C(3)-N(1)
Pt(1)-Cl(2)
2.443(10)
2.446(8)
3.2118(18)
175.8(7)
176.8(7)
84.7(7)
171.0(4)
175.0(3)
110.9(11)
93.9(3)
Pt(2)-Cl(1)
Pt· · ·Pt
Cl(2)-Pt(1)-C(3)
Cl(1)-Pt(2)-C(3)
P(4)-Pt(1)-C(3)
P(4)-Pt(1)-P(2)
P(3)-Pt(2)-P(1)
Pt(1)-C(3)-Pt(2)
P(1)-Pt(2)-Cl(1)
P(2)-C(1)-P(1)
P(1)-Pt(2)-C(3)
P(3)-Pt(2)-C(3)
P(2)-Pt(1)-C(3)
P(2)-Pt(1)-Cl(2)
P(4)-Pt(1)-Cl(2)
P(3)-Pt(2)-Cl(1)
C(3)-N(1)-C(4)
P(3)-C(2)-P(4)
88.1(6)
86.9(6)
87.6(7)
93.03(3)
94.3(3)
91.1(3)
133.0(2)
114.6(17)
115.9(15)
the xylyl group, since in the case of the d8-d8 Pd · · ·Pd
system 5b, the xylylNC ligand adopts, without any steric
repulsion, a bridging position.
Figure 2. Thermal ellipsoid plot of 4b at the 30% probability level. The
H atoms are omitted for clarity. A colored ball-and-stick representation of
4b with the numbering scheme is available in the Supporting Information.
Hypothetically, electronic effects of the aryl substituent
R are likely responsible for the bonding mode of the ArNC
ligand. Theoretical studies on substituent effects on the
frontier MOs of o- and p-substituted ArNC illustrated that
(i) the substitution position (ortho vs para) does not ap-
preciably alter the electron density of the donor group; (ii)
phenyl ring substitution has a smaller effect on the σ-donat-
ing ability than it does on the π-accepting propensity of the
ArNC ligand; and (iii) the π-accepting abilities of the
isocyanide ligands increase in the order o-, p-CH3OC6H4NC;
o-, p-CH3C6H4NC; o-, p-C6H5NC; o-, p-FC6H4NC; o-,
p-CF3C6H4NC; o-, p-ClC6H4NC; and o-, p-NO2C6H4NC,
while the σ-donating ability decreases in this same order.27
The p-tolyl and xylylisocyanide ligands both exhibit methyl
substituents. On the basis of the above theoretical findings, the
and share bridging C(3), which spans in a symmetric manner
the two Pt centers. The Pt-C(3) bond lengths of 1.92(2)
and 1.97(2) Å resemble the Pd-µ-C distances in the Pd2
complex (1.99(1) and 1.96(1) Å). The Pt(1)-C(3)-Pt(2)
angle of 110.9(11)° is also close to the reported Pd(1)-C(3)-
Pd(2) angle of 107.5(5)° for [ClPd(µ-dppm)2(µ-CdN-Ph)-
PdCl].24a
The question now arises as to why the addition of
p-tolylisocyanide in a CH2Cl2 solution produces the A-frame
compounds 4a, whereas under analogous reaction conditions,
the treatment of 2 with xylylisocyanide leads to the d9-d9
salt 3a′. Steric effects are unlikely despite the bulkiness of
4124 Inorganic Chemistry, Vol. 48, No. 9, 2009

[M(dppm)2M′]2+ Building Blocks
Scheme 5
bridging is often associated with bending of the µ-CdN-R
angle, this structural feature is not so obvious. There are several
examples in the literature for di- and polynuclear clusters
exhibiting linear µ2-CNR ligands. One example is [(py)ClPd(µ-
CN-xylyl)2PdCl(py)], spanned by two isocyanides with C-N-C
angles of 175.2(13) and 157.9(9)°.28a The steric factors are not
important in determining the C-N-C angles since the more
linear ligand is associated with the less hindered position on
the dinuclear Pd2 complex. An electronic origin was also
suggested to explain the observed µ-CNR linearity (171.4(8)
and 168.4(7)°) in [Pd5(µ-SO2)3(µ-CdN-xylyl)2(CNxylyl)5].28b
Howell et al. computed the MeNC bonding properties and
predicted that, regardless of the molecular geometry, the CNR
σ-donor character remains essentially constant, but the π-ac-
ceptor capacity strongly depends on the CdN-R angle and
may even reach that of carbon monoxide, if the degree of
bending is significant enough.29
All A-frame complexes of the type [LM(µ-dppm)2(µ-
CdN-R)ML] contain four electron-donating bidentate phos-
phorus ligands. This donation in these electron-rich systems
could be, at least, partially compensated by back-bonding
in the µ-CNR ligand π* orbitals (push-pull). On the basis
of calculations,29 the CdN-R angle must be < 140° to
consider the isocyanide ligand as a good π-acceptor. This
may explain the marked bending observed in 4b, 11b, and
14 (see X-ray structures below). Packing effects may also
influence the degree of bending in the solid state.
Figure 3. (a) Thermal ellipsoid plot of 11b at the 30% probability level.
The H atoms are omitted for clarity. A colored ball-and-stick representation
with a numbering scheme is available in the Supporting Information. (b)
View of the core structure of 11b.
Table 3. Selected Bond Distances (Å) and Angles (deg) for 11b
The heterodinuclear complex [ClPd(µ-dppm)2(µ-CdN-o-
anisyl)PtCl] (9) results from the insertion of 1 equiv of
o-anisylisocyanide into the Pd-Pt bond of [ClPd(µ-
dppm)2PtCl] (6a). In contrast to its iodo analogue 10,
compound 9 exists in CH2Cl2 solution solely in the A-frame
form. This finding demonstrates that, apart from the solvent
polarity, the nature of the halide ligand also plays an
important role in the subtle balance between bridging and
terminal isocyanide bonding.
The iodo derivative 10a can also be used as precursor for
the synthesis of bis(isonitrile) heterobimetallics, allowing the
study of site selectivity in the second CNR ligand coordina-
tion, Pd versus Pt. Hence, upon the addition of 1 equiv of
o-anisylisocyanide, exclusive formation of [IPd(µ-dppm)2(µ-
CdN-o-anisyl)Pt(CN-o-anisyl)]I (11b; Figure 3, Table 3),
exhibiting both a µ-CNR and a Pt-bound terminal CNR
ligand, is observed (Scheme 5). This air-stable orange-red
salt was unambiguously identified by IR and multinuclear
NMR spectroscopy as well as by a single-crystal X-ray
diffraction study.
Pt-C(1)
2.014(10) Pt-P(3)
2.013(10) Pd-P(4)
1.264(12) Pd-P(2)
2.7213(11) Pt-P(1)
1.987(12) C(9)-N(2)
3.0273(9) C(10)-N(2)
2.323(3)
2.340(3)
2.336(2)
2.323(3)
1.123(14)
1.462(16)
83.9(3)
88.8(3)
97.6(3)
95.61(7)
93.74(8)
175.2(10)
Pd-C(1)
C(1)-N(1)
Pd-I(1)
Pt-C(9)
Pt· · ·Pd
C(9)-Pt-C(1)
I(1)-Pd-C(1)
P(1)-Pt-C(9)
P(1)-Pt-P(3)
P(2)-Pd-P(4)
Pd-C(1)-Pt
168.6(4)
177.3(3)
97.6(3)
P(1)-Pt-C(1)
P(3)-Pt-C(1)
P(1)-Pt-C(9)
158.87(9) P(2)-Pd-I(1)
175.57(9) P(4)-Pd-I(2)
97.5(4)
Pt-C(9)-N(2)
C(1)-N(1)-C(2) 122.8(8)
P(2)-C(29)-P(1) 117.4(5)
C(9)-N(2)-C(10)174.3(15)
P(3)-C(54)-P(4)
115.7(5)
relevant MO energies are affected little by the o- or p-
substitution with respect to the nature of the substituent.
Therefore, the subtle additional electron-donating effect of the
second methyl group of xylylisocyanide may cause a switching
of the CNR bonding mode from bridging to terminal (4a vs
3a). In 4b, the isopropyl substituent at the p-position likely
exerts a slightly stronger electron-donating induction effect than
methyl does, but in overall σ-donor/π-acceptor propensity,
xylylisocyanide seems to be a somewhat better donor ligand
than 1-isocyano-4-isopropylbenzene. In addition, one notes the
strong bending of the µ-CdN-R angle (123-135°) observed
for all homo- and heterodinuclear A-frame complexes. Although
The terminal ν(Ct N) and bridging ν(CdN) absorptions
of 11b in CH2Cl2 are observed at 2175 and 1627 cm-1,
respectively. In comparison with precursor 10, the 31P{1H}
NMR signals resonate downfield at 15.0 (PPt) and 20.8 (PPd)
Inorganic Chemistry, Vol. 48, No. 9, 2009 4125

Cle´ment et al.
302 Hz, respectively). Variable-temperature 1H NMR moni-
toring also showed a similar fluxional behavior, albeit at
higher temperatures (the fast exchange occurs at 313 K). The
exchange phenomenon of the isocyanide coordinations was
also previously noticed by Balch and Benner24 and Kubiak
and Kullberg30 for [(R-Nt C)]Pd(µ-“R2PCH2PR”2)2(µ-
CdN-R)Pd(Ct N-R)]2+ (R′ ) Me, Ph). Puddephatt and
collaborators also reported intramolecular terminal-bridge
isocyanide exchanges in Pt3(dppm)32+-type clusters, processes
believed to be due to small energy barriers.31
The salt [IPd(µ-dppm)2(µ-CdN-o-anisyl)Pt(Ct NtBu]I
(12) can also be isolated as an air-stable orange solid after
the addition of 1 equiv of tBuNC to 10 (Figure 4, Table 4).
As unambiguously confirmed by an X-ray diffraction study,
the additional terminal CNR is again coordinated at the Pt
site. The o-anisyl isocyanide occupies the bridging position,
since it is a better π acceptor compared to tBuNC. Indeed,
it can compensate more efficiently the electron donation
exerted by the two dppm ligands.32 To our knowledge, 12
is the first example of an A-frame system of the Ni-triad
bearing two different isocyanide ligands. As expected, the
pattern and couplings of the AA′BB′ 31P{1H} and 195Pt{1H}
NMR spectra resemble those of 11b. The 195Pt signal is
Figure 4. Thermal ellipsoid plot of 12 at the 30% probability level. The
H atoms are omitted for clarity. A colored ball-and-stick representation of
12 with a numbering scheme is available in the Supporting Information.
Table 4. Selected Bond Distances (Å) and Angles (deg) for 12
Pt-C(1)
2.010(13)
2.018(10)
1.277(17)
2.7116(18)
1.98(2)
3.2085(12)
179.6(6)
178.4(4)
93.3(4)
158.87(9)
175.57(9)
97.5(4)
124.0(11)
114.9(6)
Pt-P(3)
2.298(3)
2.366(3)
2.337(3)
2.321(3)
1.16(2)
1.511(19)
86.3(3)
85.4(3)
Pd-C(1)
Pd-P(4)
C(1)-N(1)
Pd-P(2)
1
Pd-I(1)
Pt-P(1)
somewhat high-field-shifted to -2860 ppm with JPt-P and
3JPt-P couplings of 3220 and 325 Hz, respectively. In the 1H
NMR spectrum at 295 K, the OCH3 and tert-butyl groups
give rise to sharp singlets at 3.43 and 0.86 ppm; however,
the CH2-dppm centered at 3.16 ppm is unresolved. The
question arises why the displacement reaction of X- by a
second CNR ligand takes place at platinum rather than
palladium. Substitution reactions at Pd are known to be much
faster than at Pt, but the positive charge of the resulting
cationic salts 11 and 12 is probably better stabilized on the
more electron-rich Pt(I) center. Furthermore, generation of
a new Pt-C bond instead of a Pd-C bond may also be more
favorable for thermodynamic reasons.
Pt-C(9)
C(9)-N(2)
Pt· · ·Pd
C(10)-N(2)
P(1)-Pt-C(1)
P(3)-Pt-C(1)
P(3)-Pt-C(9)
P(4)-Pd-I(1)
P(2)-Pd-I(1)
Pt-C(9)-N(2)
C(9)-N(2)-C(10)1
P(3)-C(51)-P(4)
C(9)-Pt-C(1)
I(1)-Pd-C(1)
P(1)-Pt-C(9)
P(1)-Pt-P(3)
P(2)-Pd-P(4)
Pd-C(1)-Pt
C(1)-N(1)-C(2)
P(2)-C(26)-P(1)
95.0(4)
88.48(7)
95.61(7)
178.0(18)
76.0(2)
115.0(6)
ppm. The 195Pt{1H} NMR of 11b contains a well-resolved
triplet of triplet resonance centered at -2825 ppm with 1JPt-P
3
and JPt-P couplings of 3225 and 300 Hz, respectively.
Despite the nonequivalence of the OCH3 groups, a single
sharp resonance is found at 55.9 ppm in the 13C{1H} NMR
spectrum (298 K). This fast CNR ligand exchange on the
NMR time scale is also concluded from the single resonance
Crystal Structures of 11b and 12. The X-ray structure
of 11b confirms the proposed A-frame structure of the
complex in solution at low temperatures (deduced from NMR
measurements). The coordination sphere about palladium and
platinum is nearly planar with the two squares connected at
one corner by the bridging CNR. The other coordination sites
in trans disposition relative to the µ-C atom are occupied by
a second CNR ligand and an I atom on the Pt and Pd metals,
respectively. The extreme inclination of the µ-CdN-o-anisyl
1
observed at 3.45 ppm in the H NMR spectrum at 273 K,
whereas the CH2-dppm (3.28 ppm) and the aromatic
hydrogens are quite large without any fine structure. Coa-
lescence occurs at about 243 K, since a broad hump including
the CH2-dppm and OCH3 groups is observed in the
3.65-3.15 ppm region. At 233 K, two new broad singlets
emerge at 3.60 and 3.21 ppm, which are attributed to two
distinct OCH3 groups. Progressive cooling to 213 K causes
a sharpening and splitting of the two OCH3 signals (3.63
and 3.17), whereas the CH2-dppm protons appear in the
form of an unstructured broad signal at 3.46 ppm.
(28) (a) Yamamoto, Y.; Yamazaki, H. Inorg. Chem. 1986, 25, 3327–3329.
(b) Burrows, A. D.; Fleischer, H.; Mingos, D. M. P. J. Organomet.
Chem. 1992, 433, 311–321.
(29) Howell, J. A. S.; Saillard, J. Y.; Le Beuze, A.; Jaouen, G. J. Chem.
Soc., Dalton Trans. 1982, 2533-2537.
(30) Kullberg, M. L.; Kubiak, C. P. Inorg. Chem. 1986, 25, 26–30.
(31) Bradford, A. M.; Kristof, E.; Rashidi, M.; Yang, D.-S.; Payne, N. C.;
Puddephatt, R. J. Inorg. Chem. 1994, 33, 2355–2363.
(32) (a) Knorr, M.; Braunstein, P.; Strohmann, C. Organometallics 1996,
15, 5653–5663. (b) Knorr, M.; Strohmann, C. Eur. J. Inorg. Chem.
1998, 49, 5–499. (c) Knorr, M.; Strohmann, C. Organometallics 1999,
18, 248–257. (d) Knorr, M.; Strohmann, C. Eur. J. Inorg. Chem. 2000,
24, 1–252. (e) Knorr, M.; Jourdain, I.; Lentz, D.; Willemsen, S.;
Strohmann, C. J. Organomet. Chem. 2003, 684, 216–229. (f) Knorr,
M. ReactiVity and actiVation of small molecules on heterobimetallic
complexes, Habilitation thesis, University of the Saarland, Saarbru¨cken,
Germany, 1996.
The Cl-analogue [ClPd(µ-dppm)2(µ-CdN-o-anisyl)Pt(Ct N-
o-anisyl)]Cl (11a) was also prepared (195Pt{1H}: triplet of
1
3
triplets at -2856 ppm with JPt-P and JPt-P of 3210 and
(26) (a) Hanson, A. W.; McAlees, A. J.; Taylor, A. J. Chem. Soc., Perkin
Trans. 1 1985, 441–446. (b) Olmstead, M. M.; Hope, H.; Benner,
L. S.; Balch, A. L. J. Am. Chem. Soc. 1977, 99, 5502–5503.
(27) (a) Johnston, R. F.; Cooper, J. C. THEOCHEM 1991, 236, 297–307.
(b) Csonka, I. P.; Szepes, L.; Modelli, A. J. Mass. Spectrom. 2004,
39, 1456–1466.
4126 Inorganic Chemistry, Vol. 48, No. 9, 2009

[M(dppm)2M′]2+ Building Blocks
Chart 2
Chart 3
Figure 5. Absorption (black), excitation (red), and emission (blue) spectra
of 3a′ in PrCN at 77 K. λexc ) 370 nm.
3096 and 390 Hz, respectively. The 195Pt{1H} NMR spectrum
exhibits quite a broad triplet-of-triplet resonance centered
at -2924 ppm. Complex 15 could not be isolated purely, as
mainly 11b was recovered after recrystallization. The facile
dissociation of the third CNR ligand was also noticed earlier
for[(RNC)Pt(µ-dppm)2(µ-CdN-R)Pt(CNR)]2+and[(RNC)Pd-
(µ-dppm)2(µ-CdN-R)Pd(CNR)]2+ (R ) Me, xylyl).23,30,34
3. Electronic Spectra and Photophysics. 3.1. Photo-
physical Properties of the d9-d9 Homo- and Heterobi-
metallic Systems. Many CNR-containing d9-d9 compounds,
such as 16 and 17 (Chart 3), exhibit luminescence at room
temperature in the solid state and at 77 K in frozen solution,5
while the binuclear complexes 1, 2, and 6a do not. Generally,
Pd-containing materials exhibit much less luminescence
intensity than the Pt-containing analogues. In addition, the
replacement of the two axial chloride ligands in 1 and 2 by
acetonitrile leads to the corresponding [(MeCN)M(µ-
dppm)2M(NCMe)]2+ complexes (M ) Pd, Pt), which are also
weakly emitting.5 This brings the question, what does it take
to render these d9-d9 Pd2- and Pt2(dppm)2-containing build-
ing blocks luminescent. Part of the answer lies in the presence
of luminescence of bisphosphine and bis(pyridine-like)-
containing d9-d9 “Pt(µ-dppm)Pt” complexes in solution at
room temperature.35
ligand of 122.8(8)° is much more pronounced than that of
4b, whereas the terminal CN-o-anisyl ligand is quite linear
with an angle C(9)-N(2)-C(10) of 174.1(15)°. Consistent
with a formal CdN double-bond character, the C(1)-N(1)
distance is markedly longer than the C(9)-N(2) triple bond
(1.264(12) vs 1.123(14) Å).
The terminal coordination of tBuNC at Pt is confirmed
by the structure determination of 12. In comparison with 11b,
the M · · · M′ separation has increased from 3.0273(9) to
3.2085(12) Å. As in 11b, the µ-CdN-R ligand is strongly
bent ((124.0(11)°), the anisyl ring being tilted toward the
PdP2I moiety. Again, the spanning of the two M centers is
almost symmetric with Pt-C(1) and Pd-C(1) bond distances
of 2.010(13) and 2.018(10) Å, respectively. The bond length
between Pt and the terminal tBuNC ligand (Pt-C(9) 1.98(2)
Å) is identical to that of [(OC)3Fe{Si(OMe)3}(µ-dpp-
m)Pt(CN-tBu){C(CdO)Me}] (1.989(8) Å).32a As in 4b, the
CH2-dppm groups of 11b and 12 are bent toward the µ-CNR
ligand, leading to a “boat” conformation of the M2P4C2 rings.
Complexes 11 and 12 are rare examples of heterobimetallic
MM′ complexes spanned by a µ-CNR ligand. The other
example is [ClPt(µ-dppm)2(µ-CdN-Me)Ni(CNMe)]Cl (13)
reported by Kubiak et al. via a transmetalation of [(CN-
Me)]Ni(µ-dppm)2(µ-CdN-Me)Ni(CNMe)] with [Cl2Pt-
(dppm)].33 Like in 11 and 12, the µ-CNR ligand is strongly
bent (132.3°), and the MeNC ligands are equivalent in
solution on the 1H NMR time scale, indicating fluxionality.
There are however some striking differences between the
Ni-Pt and Pd-Pt systems: (i) in 13 (Chart 2), the two M
centers are connected through a short Ni-Pt bond of
2.5892(9) Å, (ii) the terminal MeNC ligand is bonded to the
Ni center, whereas the halide ligand is coordinated on Pt,
and (iii) halide abstraction in the presence of 1 equiv of
MeNC produces the tris(isocyanide) compound 14 exhibiting
a penta-coordinated Ni center. In contrast, the addition of
an excess of o-anisylNC to 11b leads to the formation of
the A-frame dication 15. In comparison with 10 and 11b,
the 31P{1H} NMR signals also appear more downfield at 19.0
Dissymmetric compound 3a′, which contains one axially
substituted position by a xylyl-NC ligand, exhibits a weak
luminescence at 77 K (Figure 5). The excitation spectrum
superposes the absorption unambiguously, indicating that the
luminescence originates from compound 3a′ (and not an
impurity). Only two other examples of axially dissymmetric
Pt2-containing complex [ClPt(µ-dppm)2PtL]+ (L ) (4-
chlorophenyl)(4-pyridyl)acetylene, λmax ) 420 nm, τe ) 0.21
µs, Φe ) 0.0071 and L ) 2,4,6-trimethylpyridine, λmax
)
591 nm, τe ) 3.2 µs)35,36 were previously reported to be
emitting. The nature of the lowest-energy excited state
responsible for the emission was assigned to an intraligand
3ππ* state,35 while for the second, it was assigned to a
3dσdσ* state.36 The spectral and photophysical characteristics
are as follows: λmax ) 680 nm, τe ) 6.43 ( 0.1 µs, Φ )
1
3
(PPt) and 24.8 ppm (PPd) with JPt-P and JPt-P couplings of
(34) Rashidi, M.; Vittal, J. J.; Puddephatt, R. J. J. Chem. Soc., Dalton Trans.
1994, 1283–1289.
(35) Yip, H.-K.; Che, C.-M.; Peng, S.-M. J. Chem. Soc.; Dalton Trans.
1993, 179–187.
(33) Ratliff, K. S.; Fanwick, P. E.; Kubiak, C. P. Polyhedron 1990, 9, 2651–
2653.
Inorganic Chemistry, Vol. 48, No. 9, 2009 4127

Cle´ment et al.
Table 5. Photophysical Data for 3a′ and 8 at 77 K
and TDDFT results is made on the basis of the optimized
geometry computations for reasons of homogeneity.
compounds
solvent used
λ
em(nm)
τ (µs)
φ
The MO picture of the frontier MOs of compound 3b is
shown in Figure 6. It is reasonably assumed that the
conclusions drawn from this analysis are transferable to the
other d9-d9 species in this work, notably to the mixed-metal
Pd-Pt systems. This assumption is based upon the resem-
blance of the UV-vis spectra of [ClPt(µ-dppm)2PtCl] and
[ClPd(µ-dppm)2PtCl]. Moreover, the computations were
performed on compound 3b only. In this case, the aryliso-
cyanide group bears an isopropyl substituent. It is assumed
that the conclusions drawn from these calculations can also
be transposed to the case where the aryl group is modified
by substitution (e.g., xylyl and anisyl, for example). Again,
the argument is based on the resemblance of the UV-visible
spectra. The HOMO and HOMO-1 of 3b are composed of
the Pt(dxz)-Cl(px) and Pt(dyz)-Cl(py) components, where a
minor contribution is computed on the Pt atom that binds
the CNR ligand. In other words, for these two MOs, the
electronic density is placed primarily on the Pt-Cl fragment.
On the basis of symmetry and signs of the orbitals, this MO
is the equivalent of a dπ*. The LUMO is a π* orbital of the
aromatic-NC system with a minor component on the Pt
binding this RNC ligand. This diagram is also composed of
3a′
2-MeTHF
PrCN
solid
630
680
690
730
12.7 ( 0.467
6.43 ( 0.1
a
0.0033
8
PrCN
a
b
a Not measured. b Too weak to be measured accurately.
0.0033 (Table 5). These values compare very favorably with
the data reported earlier for the [(RNC)Pt(µ-dppm)2-
Pt(CNR)]2+ complexes (R ) p-C6H4iPr, tBu).5
The absorption spectrum of 3a′ (Figure 5) exhibits a
shoulder at about 350 nm (in acetonitrile; ε ) 4500 M-1
cm-1) and lower at 77 K in butyronitrile (∼360 nm), which
sharpens sensitively upon cooling. This band cannot readily
be assigned to the dσfdσ* transition typical for d9-d9 M2-
bonded complexes since the absorptivity is somewhat too
low.5 Something more is occurring.
In order to address this feature, DFT and TDDFT are used.
Since the X-ray structures are not always available, geometry
optimization was performed on the selected complexes. Prior
to analysis, the methodology was tested using the crystal-
lographically characterized complex [(tBuNC)Pt(µ-dppm)2Pt-
(CNtBu)]2+ containing a M-M bond,5 and the detail of the
comparison is placed in the Supporting Information. The reason
for this choice stems from the lower-quality data set of complex
3a′. On average, the Pt-C (X-ray ∼1.98 Å), Pt-P (X-ray
∼2.28 Å), and Pt-Pt (X-ray ∼ 2.64 Å) bond lengths are
computed to be 0.05, 0.06, and 0.07 Å longer than the those in
the experimental data, representing a lengthening of ∼2.5, ∼2.6,
and ∼2.7%, respectively. We find this comparison reasonable.
Results for geometry optimization for the complexes 3b, 4b,
11a, and 11b are presented in Scheme 6. The comparison of
the computed structural parameters with the X-ray data, notably
for complexes 4b and 11b, is similar to that described above,
except that the M-X bonds are calculated to be 0.1 Å longer
than those in the X-ray data, representing a difference of 4
(Pt-Cl) and 3.8% (Pd-I). The comparison of the MO schemes
two sets of bonding dσ orbitals (HOMO-2 and HOMO-3)
2
2
2
2
2
2
2
built upon Pt(dx -y )-Pt(dz ) and Pt(dx -y )-Pt(dx -y ) with
some bonding and antibonding Pt-Cl(n) interactions, re-
spectively. The LUMO+1 is an antibonding version of the
2
2
2
2
HOMO-3 (i.e., Pt(dx -y )-Pt(dx -y ). On the basis of TDDFT
computations, the lowest-energy electronic transition is
composed of three major components, HOMOfLUMO,
HOMO-2fLUMO+1, and HOMO-3fLUMO+1, with
relative weights of 0.57, 0.20, and 0.31, respectively. The
former transition is a metal/halide-to-ligand charger-transfer
(M/XLCT) process from the Pt-Cl fragment to the π* RNC
component, and the two latter ones are the dσ-dσ* ones
expected for the M2-bonded species. All in all, the lowest-
energy electronic transition is a mixture of M/XLCT and
Scheme 6. Geometry Optimization by DFT (P ) PPh2)
4128 Inorganic Chemistry, Vol. 48, No. 9, 2009

[M(dppm)2M′]2+ Building Blocks
Figure 7. Absorption spectra of 8 in PrCN at 77 K.
about 730 nm). Unfortunately, the harmonic of the excitation
light cluttered the emission band, so the photophysical data
could not be extracted. The fact that no vibronic structure is
observed in the emission band strongly suggests that the
emission does not arise from an intraligand ππ* state. Since
the emission maximum compares favorably to that reported
2+
for Pd2(dppm)2(CNtBu)2 (730 nm) and 3a′ (680 nm,
PrCN), we propose to assign the lowest energy-emitting
excited state as M/XLCT-dσfdσ* as well. Moreover, the
emission lifetimes (microsecond time scale; see Table 5) and
the large energy gap between the absorption and the emission
(Stoke shift, ∼12 000 cm-1) strongly suggest that the
emission arises from a triplet state, totally consistent with
the presence of heavy metals.
No emission was observed at room temperature for 3a′
and 8 in fluid solution, which is consistent with the known
facile photoinduced M-M bond cleavage in d9-d9 species.
In the solid state, a very weak emission centered at about
the same position was observed, but the intensity was too
weak to be exploited. This phenomenon is not uncommon
for such Pd-containing d9-d9 complexes.5
Figure 6. MO pictures of the frontier MOs of complex 3b. The MO
energies are in au units.
dσ-dσ*. The computed oscillator strength is 0.053, consis-
tent with the reported modest absorptivity, and may be a
consequence of the fact that the two contributing electronic
transitions are polarized along two different axes as well as
the presence of a dihedral angle of about 35°. The computed
position of this band is 387 nm when all three components
are used. Using simply the HOMO-LUMO gap, we compute
326 nm (Figure 6). Both values, 326 and 387 nm, are in the
same range as the experimental value (355 at room temper-
ature and 360 at 77 K).
We attempted to compute the position of the emission band
of 3b. First, the geometry of 3b in its triplet state was
optimized in order to extract the corresponding MO energies,
notably that of the highest semi-occupied molecular orbital
(HSOMO). Unfortunately, the geometry distorted drastically
where M-M and M-X bond dissociations were computed,
and strong angle deviations were noted. In other words, the
weakening of these bonds upon the dσfdσ* transition
induced a far too large excited-state distortion to render this
technique exploitable. This is consistent with the fact that
absence of emission is often noted for these complexes
notably in fluid solution at room temperature. In the solid
state or in frozen matrices, emission is observed, indicating
that, indeed, the matrix prevents major excited-state distortion
since the chromophore is trapped inside a rigid matrix. In
such a case, the ground-state geometry was used to compute
the HSOMO in the triplet state. For 3b, this energy gap was
-0.171 au, and a value of 414 nm was computed for the
position of the triplet emission. The conclusion is that some
excited-state distortion must occur, but we do not know a
At room temperature, the luminescence for 3a′ is not
detectable in fluid solution (PrCN) and is weak in the solid
state (not enough to extract τe) but exhibits about the same
emission maximum. In this respect, compound 3a′ behaves
the same way as compounds 16 and 17, for which emission
lifetimes were measured.5 Compound 8 is also interesting
since it exhibits a head-to-tail structure where the P donor
coordinates the Pt center and the RNC ligand occupies the
remaining Pd metal. This preferential site occupancy is based
on the observation that the P atom also coordinates the Pt
atom in 7, potentially leading to the synthesis of head-to-
tail organometallic and coordination polymers using dissym-
metric bidentate assembling ligand. The heterobinuclear
complex 8 exhibits a strikingly similar spectrum to that of
3a′ (Figure 7), allowing us to make the assignment for the
observed band at 365 nm the same transition, that is,
M/XLCT-dσfdσ* with M ) Pt and X ) P.
Compound 8 is also luminescent, as this was the case for
compounds 3a′ and 3b. It exhibits similar features to those
of the homobinuclear complex 3a′ (unresolved band, λmax at
Inorganic Chemistry, Vol. 48, No. 9, 2009 4129

Cle´ment et al.
Table 6. Photophysical Data for d8-d8 A-Frame Homo- and
Heterobimetallic Systems 4b, 9, 11a, 11b at 77 K
examples include ethynyl-containing d8-d8 species and an
A-frame triangular Pt2Au cluster.37 While compound 10 is
not luminescent, compounds 11a and 11b are at 77 K in
PrCN. The characteristics of these emissions are listed in
Table 6. The absorption spectra of 11a and 11b exhibit low-
energy bands (more red-shifted than that the d9-d9 M2-
bonded species discussed above), which are also better
resolved at 77 K in the 400-500 nm range (Figure 8).
Isocyanide insertion into the M-M leads to a breakdown
of the M-M bond and to a considerable elongation of the
M · · · M interaction (d(Pd · · · Pt) ) 3.0273(9) Å in 11b).
Consequently, a dσ*fdσ transition can be excluded. Several
studies on d8-d8 binuclear complexes assigned this low-
energy absorption band to a dσ*fpσ transition.38 In this
case, maximum wavelength absorption is related to the M-M
distance and to the nature of substituents ligated to the metal
centers.38
compounds
solvent used
λ
em(nm)a
τ (µs)
φ
4b
2-MeTHF
PrCN
solid
2-MeTHF
PrCN
solid
2-MeTHF
PrCN
2-MeTHF
PrCN
625
625
620
650
700
740
660
710
670
715
15.7 ( 0.13
8.6 ( 0.13
b
0.897 ( 0.01
0.516 ( 0.023
b
12.04 ( 1.029
3.06 ( 0.044
22 ( 1.64
12.7 ( 1.12
b
0.013
b
b
9
0.0027
b
b
11a
11b
0.0079
b
0.0043
a The large red shift of the emission band and decrease in τe by changing
the solvent from 2-MeTHF to PrCN could very likely be associated with a
halide dissociation in solution and its replacement by the nitrile. b Not
measured.
Similarly, as analyzed above, the nature of this low-energy
absorption is addressed by means of DFT and TDDFT.
Figure 9 presents the pictures of the relevant frontier MOs
of 11a and 11b, as computed by DFT. The HOMO and
LUMO exhibit complex atomic contributions. In both cases,
the HOMO is composed of in-plane atomic contributions:
the X(n) donor orbital interacting in an antibonding fashion
2
2
with the Pd(dx -y ) orbital, which interacts in a bonding
fashion with one of the sp2-hybridized n orbitals of the C
bridging atom, which interacts also in a bonding manner with
2
2
the Pt(dx -y ) one. This HOMO is also composed of the N(n)
orbital. Very minor contributions of the in-plane NC π*
system are also computed. The major contributions are
represented in a simple drawing in Scheme 7.
The LUMO (again in 11a and 11b) also exhibits a rather
complex series of atomic contributions. The contribution
from the halide atom and the µ-CNR is now very small. The
nature of the atomic contribution of the Pt atom is now
Figure 8. Absorption spectra of 11a and 11b in PrCN at 77 K.
way of finding out since it depends on the matrix that keeps
the complex together. All in all, this methodology cannot
be applied for this complex.
3.2. Photophysical Properties of the d8-d8 A-Frame
Homo- and Heterobimetallic Systems. Luminescent A-
frame complexes are extremely rare. The few known
2
primarily dz , and the electronic density on the CN π* system
has significantly augmented. Some modest contributions of
Figure 9. MO pictures of the LUMO, HOMO, HOMO-1, and HOMO-2 of 11a (right) and 11b (left).
4130 Inorganic Chemistry, Vol. 48, No. 9, 2009

[M(dppm)2M′]2+ Building Blocks
Scheme 7
the perpendicular P atoms are also computed and interact
with the Pt metal orbital in an antibonding fashion. The
HOMO-LUMO transitions are essentially a charge transfer
from the Pd/X center and µ-CNR to the terminal RNC π*
system. TDDFT computes that the lowest-energy electronic
transition is primarily the expected HOMOfLUMO for both
complexes. This computational conclusion comes from the
fact that both MOs are well isolated from other frontier MOs,
so little mixing occurs. The computed positions for this
transition by TDDFT are 496 and 519 nm, whereas the values
calculated from the HOMO and LUMO DFT energies are
411 and 434 nm (Scheme 7), for 11a and 11b, respectively.
Experimentally, the positions for these lower-energy features
are seen at 448 and 455 nm, respectively, which fall in the
middle of this window. All in all, this reasonable cor-
respondence between the computation and experimental
results provides support for the charge-transfer assignment.
It is also interesting to note that both dissymmetric d9-d9
M2-bonded and d8-d8 A-frame species exhibit a lowest-
energy charge-transfer character from the Pd moiety to the
RNC-Pt-containing fragment. For the A-frame complexes,
computations indicate that this process passes through the
central µ-CNR bridge.
Figure 10. Emission spectra of 11a (blue) and 11b (red) in PrCN at 77 K.
λexc ) 350 nm.
Figure 11. Absorption (black), excitation (red), and emission spectra (blue)
of 4b in PrCN at 77 K. λexc ) 440 nm.
Emission spectra in frozen butyronitrile (Figure 10) lead
to a broad unstructured band at λmax ) 710 nm (τe ) 3.06 (
0.044 µs, φ ) 0.0079) for 11a and at λmax ) 715 nm (τe )
12.7 ( 1.1 µs, φ ) 0.0043) for 11b. These values are
comparable with other A-frame d8-d8 systems based on
iridium and platinum metal centers.37a,c The λmax and the
nonradiative deactivation values of dinuclear complexes 11a
and 11b are in the order 11a < 11b, indicating that the nature
of the excited states is influenced by the nature of the halide.
This behavior has already been observed in other d8-d8
homo- and heterobimetallic A-frame polymers39 and is totally
consistent with the change in HOMO-LUMO gap computed
by DFT (Figure 9), where this gap is smaller for 11b (X )
I) versus 11a (X ) Cl).
luminescent at 77 K (Figure 11). Its absorption spectrum is
characterized by an absorption band at ∼350 nm, and a
weaker feature at ∼440 nm. The excitation spectrum (in red)
overlaps with the absorption, again illustrating that the
observed emission does not arise from an impurity. This
comparison is important because it refers to the equilibrium
between the two species illustrated in Scheme 4 between
the d8-d8 A-frame neutral species 4b and the d9-d9 M2-
bonded chloride salt, 3b. Upon cooling, the equilibrium
shifted toward the neutral species, preventing ligand dis-
sociation, but this does not necessarily preclude the pos-
sibility of having traces of the d9-d9 M2-bonded complex.
In this work, we had no spectroscopic evidence for this
species, as both the absorption and emission spectra are
different from that of 3a′ above.
The pseudosymmetric A-frame complex 4b (considering
the fluxion motion of the µ-CNR ligand) is also found to be
The analysis of the absorption spectrum was addressed in
a similar manner to that illustrated above. The picture of
selected relevant MOs of 4b is presented in Figure 12. The
(36) Hong, X.; Yip, H.-K.; Cheung, K.-K.; Che, C.-M. J. Chem. Soc.,
Dalton Trans. 1993, 815–816.
(37) (a) Marshall, J. L.; Hopkins, M. D.; Miskowski, V. M.; Gray, H. B.
Inorg. Chem. 1992, 31, 5034–5040. (b) Balch, A. L. J. Am. Chem.
Soc. 1976, 98, 8049–8054. (c) Che, C. M.; Yam, V. W.-W.; Wong,
W.-T.; Lai, T. F. Inorg. Chem. 1989, 28, 2908–2910.
(38) (a) Sacksteder, L.; Baralt, E.; DeGraff, B. A.; Lukehart, C. M.; Demas,
J. N. Inorg. Chem. 1991, 30, 3955–3957. (b) Nieuwenhuis, H. A.;
Stufkens, D. J.; Vicek, A., Jr. Inorg. Chem. 1995, 34, 3879–3886.
(39) Synthesis, characterization, photophysical properties of these polymeric
systems are described and published elsewhere: Clément, S.; Aly,
S. M.; Husson, J.; Fortin, D.; Strohmann, C.; Knorr, M.; Guyard, L.;
Abd-El-Aziz, A. S.; D. Harvey, P. D. Eur. J. Inorg. Chem. 2009, in
press.
2
2
HOMO is composed of Pt(dx -y ) in bonding interactions with
the in-plane µ-C(n) and in antibonding interactions with the
in-plane Cl(n). In-plane N(n) contribution is also computed,
which overall makes this MO bear a very close resemblance
to the corresponding HOMOs of 11a and 11b (Figure 9 and
Scheme 7). The presence of a bent static structure of the
µ-CNR group does not affect the relative amplitude of the
atomic contributions on the right- and left-hand sides. We
Inorganic Chemistry, Vol. 48, No. 9, 2009 4131

Cle´ment et al.
long emission lifetime (microsecond time scale), this lumi-
nescence is assigned to phosphorescence. We encountered
similar problems when attempting to optimize the geometry
of 4b in its triplet state. Pt-Cl bond dissociation was
calculated, and we could not address reliably the HSOMO
energy. On the other hand, by keeping the ground-state
structure for the triplet state calculations, which obviously
does not represent the real situation here but is used as an
approximation, a HSOMO energy of -0.079 au is computed.
This MO level is placed ∼0.093 au above the HOMO of 4b
(Figure 12), which would place the position of the phos-
phorescence at 490 nm. This value is strongly blue-shifted
with respect to the observed maximum (625 nm). By
considering that this methodology of estimating the position
of an emission from the HOMO-LUMO gap always
provides blue-shifted estimated values (see above), the this
490 nm value is not surprising. We propose that the observed
emission at 625 nm arises from a quasi d-d state, as
discussed above where the metal center is the Pt · · ·Pt unit
and the sets of ligands are the Cl’s and µ-CN on one hand
and the perpendicular P’s on the other.
In the solid state, a very weak emission centered at about
the same position as described below was observed for 4b,
9, 11a, and 11b, but the intensity was too weak to be
exploited. All photophysical data obtained for d9-d9 homo-
and heterobimetallic systems are summarized in Table 6.
Figure 12. MO pictures of the LUMO, HOMO, HOMO-1, and HOMO-2
of 4b.
can almost assess this MO as having a mirror plane on the
2
2
µ-CdN axis. The LUMO is composed of Pt(dx -y ) and a
minor contribution of in-plane Cl(n), but also of P(n) and
some phenyl π* orbitals of both the dppm and RNC ligand.
An electronic transition between the HOMO and the LUMO
would lead to a change in electronic density mostly located
in-plane, primarily on the Cl-Pt-C-Pt-Cl bent frame to
both almost perpendicularly placed P-Pt-P axes, reflecting
the typical d-d transition in square-planar complexes. This
quasi-perpendicular orientation of the electronic density shift
upon excitation suggests a lower overlap between the two
sets of orbitals. All in all, this means that this specific
transition would have a low probability.
Conclusion
This study provides a better understanding of coordination
properties for various CNR ligands in homo- and heterodi-
nuclear M-M bonded complexes, in particular, of what
controls the bridging versus terminal coordination mode.
Various subtle parameters influence the coordination mode:
(i) the π-acceptor propensity of the isocyanide ligand, (ii)
the nature of the M-X bond, and finally, (iii) the polarity
of the solvent. In the case of a bridging coordination, the
bending of the µ-CNR ligand is generally observed, allowing
the control of the electronic density on metal centers by back-
bonding. These findings help us to select the appropriate
assembling diisocyanide ligands to promote A-frame-
containing coordination polymers, avoiding the undesired
halide ligand dissociation. This would help us in addressing
the structure at all times.
We also find that the investigated complexes, which are
used as model compounds for the A-frame-containing
polymers, notably for complexes 11a and 11b, are most
currently modestly luminescent at 77 K in both the solid
state and in solution, leading to unstructured emission
bands in the 600-800 nm window. At the same time, this
work provides an insight into the nature of the lumines-
cence in both the dissymmetric M2-bonded chromophores
and the A-frame species. M/XLCT-dσfdσ* excited states
are predicted for the M2-bonded complexes, and M/XLCT-
states are also concluded for the A-frame species, in
particular for compounds 11a and 11b, on the basis of
DFT/TDDFT computations. The preparation and photo-
physical characterization of a series of corresponding
TDDFT computes that the lowest-energy electronic transi-
tion is indeed the expected HOMO-LUMO process with a
minor component of HOMO-LUMO+1. The relative con-
tributions of these two processes are 0.65 and 0.11, respec-
tively, so the second process is not analyzed here. The
position computed by TDDFT for this transition is 419 nm,
not too far away from the experimental value of 440 nm
(Figure 11). The HOMO-LUMO gap computed by DFT is
348 nm, a value that we consider far. The problem is that
the molecule must exhibit a large excited-state distortion that
is not taken into account in the computations. The modest
computed oscillator strength (0.15) is also consistent with
the observable low absorptivity (Figure 11). We could not
reliably calculate the experimental absorptivity value because
of the presence of two species in solution, as illustrated in
Scheme 4.
TDDFT coupled with DFT computations were also
performed in order to address the observed emission at ∼625
nm (Figure 11). Again, because of the large energy gap
between the absorption and emission (∼7000 cm-1) and the
4132 Inorganic Chemistry, Vol. 48, No. 9, 2009

[M(dppm)2M′]2+ Building Blocks
Supporting Information Available: 31P NMR spectrum of 8
in CDCl3. X-ray structure of 3a′. Absorption, excitation and
emission spectra in fluid solution at 77 K of 3a′, 4b, 11a, and
11b. Solid-state emission spectra of 4b at 77 K. Comparison
between the computed structure of [Pt2(dppm)2(CNtBu)2]2+
(DFT) and the experimental X-ray data from ref 5. Colored ball-
and-stick plots of 4b, 11b, and 12. 195Pt NMR spectrum of 11a
in CDCl3. This material is available free of charge via the Internet
at http://pubs.acs.org.
A-frame-containing polymers are underway and will be
reported shortly.39
Acknowledgment. P.D.H. thanks the Natural Sciences and
Engineering Research Council of Canada (NSERC), the
Fonds Que´be´cois sur la Recherche des Sciences de la Nature
et des Technologies (FQRNT) for a postdoctoral fellowship
´
for S.C., and the Centre d’Etudes sur les Mate´riaux Optiques
et Photoniques de l’Universite´ de Sherbrooke (CEMOPUS)
for funding. M.K. thanks the French Ministe`re de la
Recherche et de la Technologie for financial support and a
Ph.D. grant for S.C.
IC8023315
Inorganic Chemistry, Vol. 48, No. 9, 2009 4133