Metal-metal bonded homo- and heterobimetallic compounds of Pt(I) and Pd(I) supported by a bridging-N,P:N′,P′ moiety of a potentially hexadentate ligand

Article abstract of DOI:10.1021/ic040019t

Reactions of metal-metal bonded homobimetallic (Pd₂) and heterobimetallic (PtPd) complexes, supported by a P,P′-bridging-bis(P,N- chelating) coordination mode of the potentially hexadentate ligand 1,1-bis[di(o-N,N-dimethylanilinyl)phosphino]methane (dmapm), with CO, diethylacetylenedicarboxylate (DEAD), and thiols (RSH) in CH₂Cl ₂ are described. At room temperature, rac-Pd₂Cl ₂(μ-N,P:P′,N′-dmapm) gives the stable complexes Pd₂Cl₂(μ-CO)₂-(μ-P.P′-dmapm) and PdCl(η²-DEAD)(μ-P:P′,N-dmapm)PdCl (which is fluxional in solution), while rac-PtPdCl₂(μ-N,P:P′,N′-dmapm) disproportionates to PtCl₂(P,P′-dmapm) and Pd metal, although at low temperature intermediate carbonyl species are detected in the CO reaction. The reactions with thiols in the presence of triflic acid (HOTf) generate rac-[MPdCl₂(μ-SR)μ-N,P:P′,N′-dmapm)][OTf] and H₂ for both M = Pt and Pd. In CH₂Cl₂, PdX₂(dmapm) species (X = halide or CN) exist as equilibrium mixtures of P,P′- and P,N-ligated forms. For X = Cl, the P,P′-P,N equilibrium is governed by ΔH° = -5.5 ± 0.5 kJ mol^-1 and ΔS° = 10 ± 1 J mol^-1 K^-1, and the ring-strain energy within the P,P′-isomer is ～32 kJ mol^-1; the equilibrium increasingly favors the P,N-form with X = CN ? I > Br > Cl. The solid-state structures of rac-[PtPdCl₂(μ-SEt)(μ-N,P: P′,N′-NP:P′,N-dmapm)][OTf] and PdCl₂(P,N-dmapm) are presented; the latter contains both bound and free N- and P-atoms of identical types in the same molecule and permits an assessment of σ- and π-bonding between these atoms and Pd.

Full text of DOI:10.1021/ic040019t

Inorg. Chem. 2004, 43, 4056−4063
Metal−Metal Bonded Homo- and Heterobimetallic Compounds of Pt(I)
and Pd(I) Supported by a Bridging-N,P:N′,P′ Moiety of a Potentially
Hexadentate Ligand
Nathan D. Jones,† S. Jo Ling Foo, Brian O. Patrick, and Brian R. James*
Department of Chemistry, The UniVersity of British Columbia, VancouVer,
British Columbia, Canada V6T 1Z1
Received February 9, 2004
Reactions of metal−metal bonded homobimetallic (Pd2) and heterobimetallic (PtPd) complexes, supported by a
P,P′-bridging-bis(P,N-chelating) coordination mode of the potentially hexadentate ligand 1,1-bis[di(o-N,N-dimethyl-
anilinyl)phosphino]methane (dmapm), with CO, diethylacetylenedicarboxylate (DEAD), and thiols (RSH) in CH Cl2
2
are described. At room temperature, rac-Pd2Cl2(µ-N,P:P′,N′-dmapm) gives the stable complexes Pd2Cl2(µ-CO)2-
(µ-P:P′-dmapm) and PdCl(η2-DEAD)(µ-P:P′,N-dmapm)PdCl (which is fluxional in solution), while rac-PtPdCl2(µ-
N,P:P′,N′-dmapm) disproportionates to PtCl2(P,P′-dmapm) and Pd metal, although at low temperature intermediate
carbonyl species are detected in the CO reaction. The reactions with thiols in the presence of triflic acid (HOTf)
generate rac-[MPdCl2(µ-SR)(µ-N,P:P′,N′-dmapm)][OTf] and H for both M ) Pt and Pd. In CH Cl2, PdX (dmapm)
2
2
2
species (X ) halide or CN) exist as equilibrium mixtures of P,P′- and P,N-ligated forms. For X ) Cl, the P,P′-P,N
equilibrium is governed by ∆H° ) −5.5 ± 0.5 kJ mol-1 and ∆S° ) 10 ± 1 J mol-1 K-1, and the ring-strain energy
within the P,P′-isomer is ∼32 kJ mol-1; the equilibrium increasingly favors the P,N-form with X ) CN . I > Br
> Cl. The solid-state structures of rac-[PtPdCl2(µ-SEt)(µ-N,P:P′,N′-dmapm)][OTf] and PdCl2(P,N-dmapm) are
presented; the latter contains both bound and free N- and P-atoms of identical types in the same molecule and
permits an assessment of σ- and π-bonding between these atoms and Pd.
Introduction
ligands have rarely been used in catalysis,11-14 even though
their stoichiometric chemistry continues to expand.15,16 The
dearth of catalytic applications has been attributed2 to the
geometries of the complexes that typically forbid the cis
juxtaposition of incoming ligands (L in Chart 1A), which is
generally essential for elementary catalytic steps.
We note, however, that chair-shaped Pt2 complexes
bridged by two cis-P-P ligands do exist and these can
accommodate cis L ligands,17-19 and also that elevated
In a search for bimetallic complexes in which both metals
act cooperatively during a catalytic cycle,1 the choice of
bridging ligand remains crucial. Tsukada et al.2 have recently
pointed out that Pd2,3,4 Pt2,5-7 and Pt-Pd8-10 complexes
bridged by two diphosphine (PP) or 2-pyridylphosphine (PN)
* To whom correspondence should be addressed. E-mail: brj@
chem.ubc.ca.
† Current address: Department of Chemistry, University of Alberta,
Edmonton, Alberta, Canada T6G 2G2.
(11) Ishii, H.; Goyal, M.; Ueda, M.; Takeuchi, K.; Asai, M. J. Mol. Catal.
A: Chem. 1999, 148, 289.
(12) Ishii, H.; Ueda, M.; Takeuchi, K.; Asai, M. J. Mol. Catal. A: Chem.
1999, 144, 477.
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1995, 34, 2278.
(14) Wong, T. Y. H.; James, B. R.; Wong, P. C.; Mitchell, K. A. R. J.
Mol. Catal. A: Chem. 1999, 139, 159.
(1) Rowlands, G. Tetrahedron 2001, 57, 1865.
(2) Tsukada, N.; Tamura, O.; Inoue, Y. Organometallics 2002, 21, 2521.
(3) Pamplin, C. B.; Rettig, S. J.; Patrick, B. O.; James, B. R. Inorg. Chem.
2003, 42, 4117.
(4) Stockland, R. A.; Anderson, G. K.; Rath, N. P. J. Am. Chem. Soc.
1999, 121, 7945.
(5) Janka, M.; Anderson, G. K.; Rath, N. P. Organometallics 2000, 19,
5071.
(6) Irwin, M. J.; Gia, G.; Vittal, J. J.; Puddephatt, R. J. Organometallics
1996, 15, 5321.
(7) Toronto, D. V.; Balch, A. L. Inorg. Chem. 1994, 33, 6132.
(8) Xu, C.; Anderson, G. K. Organometallics 1996, 15, 1760.
(9) Xu, C.; Anderson, G. K. Organometallics 1994, 13, 3981.
(10) Fallis, K. A.; Xu, C.; Anderson, G. K. Organometallics 1993, 12, 2243.
(15) Chaudret, B.; Delavaux, B.; Poilblanc, R. Coord. Chem. ReV. 1988,
86, 191.
(16) Puddephatt, R. J. Chem. Soc. ReV. 1983, 12, 99.
(17) Azam, K. A.; Ferguson, G.; Ling, S. S. M.; Parvez, M.; Puddephatt,
R. J.; Srokowski, D. Inorg. Chem. 1985, 24, 2799.
(18) Manojlovic-Muir, L.; Muir, K. W.; Frew, A. A.; Ling, S. S. M.;
Thomson, M. A.; Puddephatt, R. J. Organometallics 1984, 3, 1637.
4056 Inorganic Chemistry, Vol. 43, No. 13, 2004
10.1021/ic040019t CCC: $27.50 © 2004 American Chemical Society
Published on Web 05/21/2004

Metal-Metal Bonded Pt(I) and Pd(I) Compounds
Chart 1. Typical Structures of Bimetallic Complexes Supported by
Scheme 1. Bimetallic dmapm Complexes and Their Reaction with
Bridging-Bidentate and by Bridging-Chelating Tetradentate Ligandsa
Thiolsa
a Ar ) o-C6H4NMe2. For M ) Pt, products are rac-10 (R ) Et) and
n
rac-11 (R ) Pr). See text.
We have reported on the synthesis of the metal-metal
bonded PdI2 complex, rac-Pd2Cl2(µ-N,P:P′,N′-dmapm)25 (1,
Scheme 1), and the non-metal-metal bonded MIIPdII species
MPdCl4(µ-N,P:P′,N′-dmapm)26 (M ) Pd, Pt; Chart 2), the
last two complexes being effective catalyst precursors for
aerobic, aqueous Heck reactions, but not via intermetallic
cooperative pathways.26 Further, we have noted that 1, unlike
Pd2Cl2(µ-P:P′-dppm)2 (dppm ) Ph2PCH2PPh2), reacts with
thiols (RSH), in the presence or absence of added acid, to
give the bridged-thiolate complex cations, rac-[Pd2Cl2(µ-SR)-
(µ-N,P:P′,N′-dmapm)]+, and H2, via a novel oxidative
addition of RS-H across a phosphine-bridged PdI-PdI bond
(Scheme 1).25 We are not aware of other reports describing
reactions of small molecules with metal-metal bonded
complexes supported by tetradentate ligands. In this article,
we describe reactions of 1 and its heterobimetallic analogue,
rac-PtPdCl2(µ-N,P:P′,N′-dmapm) (2, Scheme 1), with CO
and with diethylacetylenedicarboxylate (DEAD), and the
a D ) donor atom (typically P or N), L ) other ligand, M ) metal
(typically Pt or Pd); adapted from ref 2.
Chart 2. Structural Diagrams of dmapm and MPdCl4(µ-N,P:P′,N′-
dmapm) Complexes (M ) Pt, Pd)
temperatures can invert “A”-frame complexes (Chart 1A)
via transition structures with mutually cis (i.e., “W”-like)
orientations of the three L ligands.4 Nevertheless, edge-
sharing “A”-frame and face-to-face complexes that permit
naturally a cis orientation of L ligands and/or vacant sites
should favor catalytic activity. Thus, tetradentate ligands that
may form simultaneously both bridges and chelates are
attractive scaffolds for bimetallic “cooperative” catalysts,
(Chart 1B) and indeed, effective Rh2 hydroformylation
catalysts, based on such a (tetraphosphine) ligand, have been
developed by Stanley’s group.20
n
reaction of 2 with RSH (R ) Et, Pr) in the presence of
triflic acid (HOTf). We show that indeed the architecture
afforded by the potentially hexadentate, but functionally
tetradentate, dmapm ligand gives rise to stoichiometric reac-
tion pathways that are different from those undergone by
the analogous bis(P-P)- and bis(P-N)-bridged complexes
in the same reactions. In addition, we demonstrate that the
incorporation of hemilabile N-donors can give rise to
dynamic coordination modes, previously unknown within
phosphine-bridged Pd and Pt bimetallic chemistry. The solid-
state structure and solution fluxional behavior of PdX2-
(dmapm) (X ) Cl (3), Br (4), I (5) and CN (6)), are also
described; 3 is used in the synthesis of 1.
Our group has recently reported some diphosphine ligands
that bear two o-N,N-dimethylanilinyl groups on each P-
atom.21 One of these, 1,1-bis[di(o-N,N-dimethylanilinyl)-
phosphino]methane (dmapm), illustrated in Chart 2, shows
a tendency both to bridge metals, given that the P donors
are separated by a single CH2 group, and to form five-
membered P,N-chelate rings [note that P,N-coordination of
dmapm induces chirality at the P-atom]. The only other
ligand that spans two metals in this way is the bis(2-
pyridylphosphine), py(Ph)PCH2P(Ph)py, reported by Bud-
Experimental Section
zelaar et al.22 We have made face-to-face PtII complexes
2
General. Unless otherwise noted, synthetic procedures were
performed at room temperature (rt, ∼20 °C) using standard Schlenk
techniques under an atmosphere of dry Ar or N2. The dmapm
ligand,21 PtCl2(cod),27 trans-PdCl2(PhCN)2,28 and 125 were made
according to literature procedures. Other reagents were purchased
from commercial sources and used as supplied. Solvents were dried
containing two P,P′-chelating-bis(P,N-bridging), py2P(CH2)2-
Ppy2 ligands,23 and PdII and PtII complexes supported by
2
2
tetradentate ligands that form an N,N′-bridge and two N,P-
chelate rings are also known.2,24
(19) Radecka-Paryzek, W.; McLennan, A. J.; Puddephatt, R. J. Inorg. Chem.
1986, 25, 3097.
(20) (a) Broussard, M. E.; Juma, B.; Train, S. G.; Peng, W.-J.; Laneman,
S. A.; Stanley, G. G. Science 1993, 260, 1784. (b) Aubry, D. A.;
Bridges, N. N.; Ezell, K.; Stanley, G. G. J. Am. Chem. Soc. 2003,
125, 11180.
(21) Jones, N. D.; Meessen, P.; Smith, M. B.; Losehand, U.; Rettig, S. J.;
James, B. R. Can. J. Chem. 2002, 80, 1600.
(24) Ligtenbarg, A. G.; van der Beukin, E. K.; Veldman, A. M.; Smeets,
W. J. J.; Spek, A. L.; Feringa, B. L. J. Chem. Soc., Dalton Trans.
1998, 263.
(25) Foo, S. J. L.; Jones, N. D.; Patrick, B. O.; James, B. R. Chem. Commun.
2003, 988.
(26) Jones, N. D.; James, B. R. AdV. Synth. Catal. 2002, 344, 1126.
(27) McDermott, J. X.; White, J. F.; Whitesides, G. M. J. Am. Chem. Soc.
1976, 98, 6521.
(22) Budzelaar, P. H. M.; Frijns, J. H. G.; Orpen, A. G. Organometallics
1990, 9, 1222.
(23) Jones, N. D.; Rettig, S. J.; James, B. R. J. Cluster Sci. 1998, 9, 243.
(28) Hartley, F. R. J. Organomet. Chem. ReV., Sect. A 1970, 6, 119.
Inorganic Chemistry, Vol. 43, No. 13, 2004 4057

Jones et al.
2
over the appropriate agents and distilled under N2 prior to use. NMR
spectra were recorded in CDCl3 solution on Varian AV300 (121
MHz for 31P, 282 MHz for 19F) or AV400 (162 MHz for 31P)
spectrometers at 300 K, unless otherwise specified. Residual solvent
proton (1H, relative to external SiMe4 δ 0.00) and external P(OMe)3
(31P{1H}, δ 141.00 vs external 85% aq H3PO4) were used as
references; s ) singlet, d ) doublet, t ) triplet, m ) multiplet, br
) broad, p ) pseudo. All J-values are given in Hertz. UV-vis
spectra were recorded on a Hewlett-Packard 8452A diode array
spectrophotometer and are reported as λmax ((2 nm) [ꢀ (M-1 cm-1)].
Conductivity measurements at 25 °C (reported as ΛM in Ω-1 mol-1
cm2 ) were obtained on 1 mM solutions of the complexes using a
Thomas Serfass conductance bridge model RCM151B1 (Arthur H.
Thomas Co. Ltd.) connected to a 3404 cell (Yellow Springs
Instrument Co.). Mass spectra were measured in LSIMS mode
(Kratos Concept IIHQ instrument) with 3-nitrobenzyl alcohol as
matrix and are reported as m/z peaks. Elemental analyses were done
in the department here by Mr. P. Borda using a Carlo Erba 1108
analyzer.
35.4 (d, JPP ) 88.9). X-ray quality crystals of 3b were grown by
slow evaporation from a CDCl3 solution.
PdBr2(dmapm), 4. To 1 (77 mg, 0.10 mmol) and NaBr (170
mg, 1.7 mmol) were added acetone (10 mL) and H2O (2 mL). The
yellow slurry was stirred for 2 h before evaporation to dryness.
The residue was taken up in CH2Cl2 (10 mL) and the mixture
filtered through Celite 545. The filtrate volume was reduced in
vacuo to ∼1 mL, and Et2O (20 mL) was added to give a yellow
powder that was collected, washed with Et2O (3 × 3 mL), and
dried under vacuum. Yield: 55 mg (64%). Anal. Calcd for
C33H42N4Br2P2Pd: C, 48.2; H, 5.1; N, 6.8. Found: C, 48.1; H, 5.1;
N, 6.6. UV-vis (CH2Cl2): 378 [4310]. Data follow for PdBr2(P,P′-
dmapm), 4a. 1H NMR (250 K): δ 2.30 (br s, 24H, NCH3), 5.41 (t,
2H, CH2, 2JHP ) 12.0). The aromatic 1H signals of the two isomers
again overlap (δ 6.3-7.9). 31P{1H} NMR (250 K): δ -58.5 (s).
Data follow for PdBr2(P,N-dmapm), 4b. 1H NMR (250 K): δ 1.61
(br s, 3H, NCH3), 2.45 (s, 6H, NCH3), 2.92 (s, 9H, NCH3), 3.01
(pt, 1H, CH2), 3.51 (s, 3H, NCH3), 3.82 (s, 3H, NCH3), 3.97 (pt,
1H, CH2). 31P{1H} NMR (250 K): δ -40.4 (d, JPP ) 112), 33.3
(d, JPP ) 112).
2
2
Syntheses. rac-PtPdCl2(µ-N,P:N′,P′-dmapm)‚H2O, 2‚H2O. To
trans-PdCl2(PhCN)2 (130 mg, 0.33 mmol) and dmapm (190 mg,
0.33 mmol) in a Schlenk tube was added CH2Cl2 (7 mL). The
initially orange solution rapidly turned yellow. The solvent was
removed, and EtOH (10 mL) was added, followed by an aqueous
solution (5 mL) containing K2PtCl4 (140 mg, 0.33 mmol). The
orange slurry was heated to 70 °C for 1 h when it turned yellow.
An ethanolic solution containing KOH (13 mL, 70 mmol L-1) was
added over 3 min and the resulting brown solution stirred at 70 °C
for an additional 0.5 h. The solvents were then removed in vacuo,
the residue, dried overnight, was partially dissolved in warm C6H6
(30 mL), and then the mixture was filtered through a plug of Celite
545 and MgSO4. The brown filtrate was shown by NMR spectros-
copy to contain unreacted PtPdCl4(µ-N,P:P′,N′-dmapm), formed
in situ,26 and 2. The Celite-trapped solid was then eluted with
CH2Cl2 (10 mL), and the brown-red filtrate was concentrated to
∼1 mL. Addition of Et2O (25 mL) gave the green-brown product
that was isolated by filtration, washed with Et2O (3 × 3 mL), and
dried in vacuo. Yield: 99 mg (32%). Anal. Calcd for C33H44N4-
Cl2OP2PdPt: C, 41.9; H, 4.7; N, 5.9. Found: C, 41.5; H, 4.6; N,
5.7. 1H NMR: δ 2.36 (s, 6H, NCH3), 2.45 (s, 6H, NCH3), 2.78 (s,
3H, NCH3), 3.02 (s, 3H, NCH3), 3.07 (s, 3H, NCH3), 3.19 (s, 3H,
NCH3), 3.54 (ddd, 1H, CH2, 2JHH ) 15.9, 2JHP ) 7.77), 3.93 (ddd,
PdI2(dmapm), 5. To trans-PdCl2(PhCN)2 (91 mg, 0.24 mmol),
dmapm (130 mg, 0.23 mmol), and NaI (190 mg, 1.3 mmol) was
added CH2Cl2 (5 mL), followed after 5 min by acetone (10 mL)
which caused a rapid color change from yellow to deep orange.
The slurry was stirred for 2 h at rt before reduction to dryness in
vacuo. The workup was the same as that for 2. Yield: 180 mg
(83%). Anal. Calcd for C33H42N4I2P2Pd: C, 43.2; H, 4.6; N, 6.1.
Found: C, 43.4; H, 4.7; N, 6.0. UV-vis (CH2Cl2): 304 [16100],
430 [4010]. Data follow for PdI2(P,P′-dmapm), 5a. 1H NMR (250
K): δ 2.26 (br s, 24H, NCH3), 5.58 (t, 2H, CH2, 2JHP ) 12.4). The
aromatic 1H signals of 5a and 5b again overlap (δ 6.3-8.0).
31P{1H} NMR: δ -65.6 (s). Data follow for PdI2(P,N-dmapm),
5b. 1H NMR (250 K): δ 1.55 (br s, 3H, NCH3), 2.46 (s, 6H, NCH3),
2.80 (br s, 3H, NCH3), 2.88 (s, 6H, NCH3), 3.22 (pt, 1H, CH2),
3.55 (s, 3H, NCH3), 3.84 (s, 3H, NCH3), 3.93 (pt, 1H, CH2). 31P-
2
2
{1H} NMR: δ -40.8 (d, JPP ) 98), 27.3 (d, JPP ) 98).
Pd(CN)2(P,N-dmapm), 6b. To a yellow slurry of 1 (46 mg,
0.063 mmol) and KCN (8.3 mg, 0.013 mmol) in EtOH (5 mL)
was added H2O (2 mL), whereupon a colorless solution formed.
The solvent was removed in vacuo after 10 min, and the residue
was taken up in CH2Cl2 (10 mL); this was filtered through Celite
545/MgSO4, and the filtrate was reduced to ∼1 mL. Addition of
Et2O (10 mL) gave the product as a white powder that was isolated
by filtration, washed with Et2O (3 × 3 mL), and dried under
vacuum. Yield: 24 mg (54%). Anal. Calcd for C35H42N6P2Pd: C,
2
2
3
1H, CH2, JHH ) 15.9, JHP ) 7.77), 6.94 (ddd, 1H, Ar, JHH
)
3
4
6.4, JHP ) 8.0, JHP ) 1.3), 7.01 (pt, 1H, Ar), 7.13 (pt, 1H, Ar),
7.24 (m, 4H, Ar), 7.41 (m, 4H, Ar), 7.53 (m, 4H, Ar), 8.18 (dd,
1H, Ar, 3JHH ) 7.5, 3JHP ) 14.2). 31P{1H} NMR: δ -23.0 (d, 2JPP
1
58.8; H, 5.9; N, 11.8. Found: C, 58.9; H, 6.0; N, 11.5. H NMR
2
2
1
) 21.9, JPPt ) 260, P-Pd), -31.7 (d, JPP ) 21.9, JPPt ) 4200,
P-Pt).
(233 K): δ 1.57 (s, 3H, NCH3), 2.33 (s, 6H, NCH3), 2.74 (s, 3H,
NCH3), 2.96 (s, 6H, NCH3), 3.11 (pt, 1H, CH2), 3.41 (s, 3H, NCH3),
3.61 (pt, 1H, CH2), 3.77 (s, 3H, NCH3), 6.39 (pt, 1H, Ar), 6.66
(m, 2H, Ar), 6.96 (m, 3H, Ar), 7.15 (pt, 1H, Ar), 7.22 (pt, 1H, Ar),
6.39 (pt, 1H, Ar), 7.32 (m, 5H, Ar), 7.48 (m, 2H, Ar), 7.72 (pt,
1H, Ar). 31P{1H} NMR (233 K): δ 21.1 (d, 2JPP ) 130), -41.6 (d,
2JPP ) 130).
PdCl2(dmpam), 3. To trans-PdCl2(PhCN)2 (31 mg, 0.081 mmol)
and dmapm (48 mg, 0.086 mmol) was added CH2Cl2 (5 mL). After
the solution was stirred for 5 min, the volume was reduced in vacuo
to ∼1 mL, and Et2O (20 mL) was added to give a yellow powder
that was collected, washed with Et2O (3 × 3 mL), and dried under
vacuum. Yield: 54 mg (92%). Anal. Calcd for C33H42N4Cl2P2Pd:
C, 54.0; H, 5.8; N, 7.6. Found: C, 53.8; H, 5.9; N, 7.4. UV-vis
(CH2Cl2): 360 [3870]. Data follow for PdCl2(P,P′-dmapm), 3a.
1H NMR: δ 2.35 (s, 24H, NCH3), 5.31 (t, 2H, CH2, 2JHP ) 12.1).
PtCl2(P,P′-dmapm), 7. The synthesis was identical in principle
to that of 3. Thus, PtCl2(cod) (58 mg, 0.15 mmol) and dmapm (86
mg, 0.16 mmol) gave 83 mg (66%) of an off-white powder. Anal.
Calcd for C33H42N4Cl2P2Pt: C, 48.2; H, 5.2; N, 6.8. Found: C,
1
1
48.5; H, 5.4; N, 6.7. H NMR: δ 2.24 (s, 24H, NCH3), 5.77 (t,
The aromatic H signals of 3a and 3b overlap (δ 6.4-8.2) and
2H, CH2, 2JHP ) 12.9, 3JHPt ) 60), 7.17 (pt, 4H, Ar), 7.25 (pd, 4H,
could not be resolved. 31P{1H} NMR: δ -56.8 (s). Data follow
for PdCl2(P,N-dmapm), 3b. 1H NMR (240 K): δ 1.61 (s, 3H,
NCH3), 2.43 (s, 6H, NCH3), 2.87 (pt, 1H, CH2), 2.91 (s, 3H, NCH3),
2.97 (s, 6H, NCH3), 3.46 (s, 3H, NCH3), 3.79 (s, 3H, NCH3), 4.01
Ar), 7.44 (pt, 4H, Ar), 7.17 (br m, 4H, Ar). 31P{1H} NMR: δ -65.6
1
(s, JPPt ) 3084).
Pd2Cl2(µ-CO)2(µ-P:P′-dmapm), 8. To a Schlenk tube contain-
ing 1 (31 mg, 0.037 mmol) was admitted CO (1 atm), followed by
2
(pt, 1H, CH2). 31P{1H} NMR (215 K): δ -39.8 (d, JPP ) 88.9),
4058 Inorganic Chemistry, Vol. 43, No. 13, 2004

Metal-Metal Bonded Pt(I) and Pd(I) Compounds
Table 1. Crystallographic Data for 3b and rac-10
Et2O (10 mL) and CH2Cl2 (2 mL). The orange slurry on being
stirred overnight became blue-purple. The solid was collected,
washed with Et2O, and dried in vacuo. Yield: 21 mg (64%). Anal.
Calcd for C35H42N4Cl2O2P2Pd2: C, 46.9; H, 4.7; N, 6.2. Found:
C, 46.4; H, 4.8; N, 6.3. 1H NMR (under 1 atm CO): δ 2.67 (t, 2H,
3b
rac-10
formula
fw
C33H42N4Cl2P2Pd
733.98
C36H47N4Cl2F3O3P2PdPtS2
1139.25
cryst color, habit yellow, block
yellow, platelet
0.30 × 0.15 × 0.03
C2/c (No. 15)
39.621(2)
11.7466(5)
17.8781(8)
89.228(3)
8320.0(6)
41.38
38644
9662
2
CH2, JHP ) 12.0 Hz), 2.72 (s, 24H, NCH3), 7.12 (m, 8H, Ar),
cryst size (mm3)
space group
a (Å)
0.30 × 0.15 × 0.15
7.45 (m, 8H, Ar). 31P{1H} NMR (under 1 atm CO): δ 43.0 (s). IR
(KBr pellet): νCO: 1798 [s].
P21/n (No. 14)
11.6675(4)
19.8387(6)
14.9924(7)
99.291(3)
3424.7(2)
8.20
29535
7350
0.055
b (Å)
c (Å)
PdCl(η2-DEAD)(µ-P:P′,N-dmapm)PdCl‚H2O, 9‚H2O. To a
CH2Cl2 (5 mL) solution of 1 (63 mg, 0.075 mmol) was added
DEAD (0.020 mL, 0.13 mmol). Over 10 h, the solution changed
from red to yellow, and some decomposition to Pd metal occurred.
After filtration through Celite 545, the solution was reduced in
vacuo to ∼1 mL, and Et2O (20 mL) was added to give the product
as a fine yellow precipitate that was collected, washed with Et2O
(3 × 3 mL), and dried under vacuum. Yield: 44 mg (58%). Anal.
Calcd for C41H54N4Cl2O5P2Pd2: C, 47.9; H, 5.3; N, 5.4. Found:
C, 47.8; H, 5.4; N, 5.4. 1H NMR (325 K): δ 1.47 (t, 6H, CH2CH3,
3JHH ) 6.9), 1.78 (s, 2H, H2O), 2.32 (s, 12H, NCH3), 2.84 (s, 6H,
â (deg)
V (Å3)
µ (cm-1
)
total reflns
unique reflns
Rint
0.067
no. variables
R1 (I > 3σ(I))a
wR2b
379
489
0.027 (5198 observns) 0.030 (5755 observns)
0.080
0.86
0.076
0.93
GOF
a R1 ) ∑||Fo| - |Fc||/∑|Fo| (observed data). b wR2 ) [∑(Fo - Fc )2/
2
2
∑w(Fo )2]1/2 (all data).
2
2
2
NCH3), 2.89 (s, 6H, NCH3), 3.19 (dt, 1H, PCH2P, JHH ) JHP
)
14.0), 3.70 (m, 5H, PCH2P and CH2CH3), 6.90 (pt, 2H, Ar), 7.05
(m, 2H, Ar), 7.35 (m, 8H, Ar), 7.50 (pt, 2H, Ar), 8.55 (m, 2H, Ar).
31P{1H} NMR (325 K): δ 31.6 (s).
Scheme 2. Solution Equilibrium Behavior of PdCl2(dmapm) in
CDCl3
rac-[PdPtCl2(µ-N,P:P′,N′-dmapm)(µ-SEt)][OTf], rac-10. Ex-
cess EtSH (0.044, mL, 0.54 mmol) and 1 equiv of TfOH (0.005
mL, 0.054 mmol) were added to a solution containing 2 (50 mg,
0.059 mmol) in CH2Cl2 (5 mL). The solution was stirred for 24 h
and filtered through Celite 545/MgSO4. The volume of the red
filtrate was reduced in vacuo to ∼1 mL, and Et2O (20 mL) was
added to give the yellow product that was collected, washed with
Et2O (3 × 3 mL), and dried in vacuo. Yield: 32 mg (51%). Anal.
Calcd for PdPtCl2P2N4C36H47S2O3F3: C 38.0, H, 4.1, N 4.8.
The non-hydrogen atoms were refined anisotropically, and the H
atoms were included but not refined. In rac-10, there was some
disorder at both metal atoms: the electron density at Pd was greater
than expected (but less than for one Pt), and at Pt was less than
expected (but greater than for one Pd), so the populations at Pd
and Pt were refined with values of 0.82 and 1.28, respectively, to
fit better the total electron density at each site.
1
Found: C 37.8, H 4.1, N 4.8. H NMR (CD3OD): δ 1.01 (t, 3H,
CH3CH2, 2JHH ) 7.3), 2.15 (q, 2H, CH2S), 2.20 (br s, 12 H, NCH3),
2.47 (s, 3H, NCH3), 3.43 (m, 1H, CH2) 3.55 (s, 3H, NCH3), 3.60
(s, 3H, NCH3), 3.66 (s, 3H, NCH3), 3.94 (m, 1H, CH2), 7.24-8.08
2
(m, 16H, Ar). 31P{1H} NMR (CD3OD): δ 23.4 (d, JPP ) 43.2,
2
2
1JPPt ) 3900, P-Pt), 48.9 (d, JPP ) 43.2, JPPt ) 260, P-Pd).
19F{1H} NMR (CD3OD): δ -3.5 (s). ΛM (MeOH): 84. MS: 991
[M+]. Single crystals suitable for X-ray analysis were obtained by
slow diffusion of Et2O into a methanolic solution of the complex.
rac-[PdPtCl2(µ-N,P:P′,N′-dmapm)(µ-SnPr)][OTf], rac-11. The
synthesis was performed in a manner similar to that for rac-10.
Results and Discussion
Solution Behavior and Structure of Monometallic
Complexes. The isolated product 3 from the 1:1 reaction
between dmapm and trans-PdCl2(PhCN)2 exists in CDCl3
as a mixture of PdCl2(P,P′-dmapm) (3a) and PdCl2(P,N-
dmapm) (3b) that show, respectively, a singlet and an AB
doublet of doublets in their 31P{1H} NMR spectra (see
Experimental Section). Varying the temperature reversibly
alters the relative peak intensities, showing that 3a and 3b
are in thermal equilibrium (Scheme 2); 3b becomes increas-
ingly dominant at lower temperatures.
n
Thus, an excess PrSH (0.044, mL, 0.54 mmol) and 1 equiv of
TfOH (0.005 mL, 0.054 mmol) and 2 (50 mg, 0.059 mmol) gave
1
40.9 mg (66%) of a yellow powder. H NMR: δ 0.66 (t, 3H,
CH3CH2, 2JHH ) 7.3), 1.38 (sp, 2H, CH2CH2S), 2.12 (q, 2H, CH2S),
2.22 (br s, 12 H, NCH3), 2.91 (m, 2H, CH2) 3.46 (s, 3H, NCH3),
3.54 (s, 3H, NCH3), 3.59 (s, 3H, NCH3), 3.66 (s, 3H, NCH3), 7.27
(pt, 1H, Ar), 7.44 (m, 4H, Ar), 7.60 (pt, 2H, Ar), 7.74 (m, 4H, Ar),
3
3
8.03 (m, 4H, Ar), 8.26 (dd, 1H Ar, JHH ) 9.5, JHP ) 12.2).
2
1
31P{1H} NMR (CD3OD): δ 23.1 (d, JPP ) 43.0, JPPt ) 3940,
P-Pt), 48.6 (d, JPP ) 43.5, JPPt ) 300, P-Pd). 19F{1H} NMR
2
2
(CD3OD): δ -3.5 (s). MS: 1003 [M+].
(29) d*TREK: Area Detector Software; Molecular Structure Corporation:
The Woodlands, TX, 1997.
X-ray Crystallographic Analyses. Measurements were made
at 173(1) K on a Rigaku/ADSC CCD area detector with graphite
monochromated Mo KR radiation (0.71069 Å). Some crystal-
lographic data for 3b and rac-10 are shown in Table 1. The final
unit cell parameters were based on 24451 reflections for 3b and
21322 reflections for rac-10 with 2θ ) 4.1-55.8°. The data were
collected and processed using the d*TREK program,29 and the
structures were solved using direct (for 3b) or heavy-atom Patterson
(for rac-10) methods,30 and expanded using Fourier techniques.31
(30) (a) Altomare, A.; Burla. M. C.; Cammalli, G.; Cascarano, M.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.;
Spagna, A. J. Appl. Crystallogr. 1999, 32, 115. (b) Beurskens, P. T.;
Admiraal, G.; Beurskens, G.; Bosman, W. P.; Garcia-Granda. S.;
Gould, R. O.; Smits, J. M. M.; Smykalla, C. The DIRDIF-PATTY-
Program System; Technical Report of the Crystallography Laboratory;
University of Nijmegen: Nijmegen, The Netherlands, 1992.
(31) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; de
Gelder, R.; Israel, R.; Smits, J. M. M. The DIRDIF-94 Program
System; Technical Report of the Crystallography Laboratory; Univer-
sity of Nijmegen: Nijmegen, The Netherlands, 1994.
Inorganic Chemistry, Vol. 43, No. 13, 2004 4059

Jones et al.
In contrast to the linkage isomerism of 3, the Pt analogue,
made from PtCl2(cod) and dmapm, exists solely as PtCl2-
(P,P′-dmapm) (7). The thermodynamic stability of 7 has
important ramifications for the reactivity of mixed-metal
complex 2 (vide infra).
1
The number and relative integrations of the H NMR
singlets due to the NCH3 protons of dmapm complexes are
informative about their molecular structures (for free dmapm,
this signal appears at δ 2.68). In the 1H NMR spectrum (300
K) of 3, five singlets due to NCH3 protons are seen at δ
3.70, 3.47, 2.85, 2.49, and 2.35 with relative integrations of
1:1:2:2:3, respectively. These represent all 24 NMe protons
associated with 3a (δ 2.35) and 18 of the 24 corresponding
protons of 3b. The remaining 6 NMe protons of 3b give
signals that are broadened into the baseline. At 240 K, these
“missing” protons appear as singlets at δ 1.61 and 2.91, while
the peak due to 3a diminishes (see Supporting Information
(SI), Figure S1.) The two new peaks likely correspond to
the two Me groups on the free anilinyl ring associated with
the Pd-bound P-atom. In the solid-state structure of 3b (vide
infra), the N(2)-atom of this ring is oriented towards the Pd
center with which it shows a close contact (3.32 Å; the sum
of the van der Waals radii of Pd and N ) 3.18 Å). The
broadened peaks at 300 K likely result from the rapid,
reversible coordination of this anilinyl ring.
Figure 1. ORTEP diagram of 3b, with 50% probability ellipsoids.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 3b
Pd(1)-P(1)
Pd(1)-N(1)
Pd(1)-Cl(1)
Pd(1)-Cl(2)
P(1)-C(1)
2.1798(6)
2.132(2)
2.3041(6)
2.3812(6)
1.801(2)
1.806(2)
1.824(2)
1.873(2)
P(2)-C(18)
P(2)-C(26)
N(1)-C(6)
N(1)-C(7)
N(1)-C(8)
N(3)-C(23)
N(3)-C(24)
N(3)-C(25)
1.847(2)
1.845(2)
1.481(3)
1.492(4)
1.490(3)
1.425(3)
1.467(3)
1.453(3)
P(1)-C(9)
P(1)-C(17)
P(2)-C(17)
From the relative intensities of the peaks at δ 2.35 and
3.70 (which shift marginally downfield with decreasing
temperature), equilibrium constants (K’s) for the 3a,b
isomerization from 215 to 300 K have been calculated, and
the corresponding van’t Hoff plot yielded ∆H° ) -5.5 (
0.5 kJ mol-1 and ∆S° ) -10 ( 1 J K-1 mol-1 (see SI, Figure
S2.). Thermochemical data for the substitution of the PhCN
of trans-PdCl2(PhCN)2 by PPh3 and pyridine (py) have
shown previously that the Pd-PPh3 bond is stronger than
the Pd-py bond by 27 kJ mol-1,32 and we have used this
value for the energy difference between the Pd-P bond in
3a and the Pd-N bond in 3b. If ∆H° for the 3a,b equilibrium
is assumed to be the sum of the enthalpic penalty for breaking
the Pd-P bond and the combined gain from the formation
of the Pd-N bond and alleviation of the four-membered ring
strain, and, if the five-membered P,N ring in 3b is assumed
to be strain-free, then the four-membered ring strain energy
in 3a can be estimated to be ∼32 kJ mol-1. The ring strain
energy values associated with the binding of chelated dppm
to “(C5R5)RuCl” (R ) H, Me), estimated by comparison of
the heats of reaction for the substitution of cod by dppm
and PPh2Me in (C5R5)Ru(cod)Cl, are 42 and 56 kJ mol-1
for R ) H and R ) Me, respectively.33,34 Our lower value
is consistent with weaker Pd-P bonding relative to that of
Ru-P.
P(1)-Pd(1)-N(1)
Cl(1)-Pd(1)-Cl(2)
P(1)-C(17)-P(2)
C-P(2)-C
86.10(6)
92.63(2)
108.4(1)
100.5 (av)
P(1)-Pd(1)-Cl(1)
N(1)-Pd(1)-Cl(2)
C-P(1)-C
87.93(2)
93.54(6)
107.4 (av)
isomers. The a,b equilibrium constants at 250 K for 3, 4,
and 5 are 4.1, 4.8, and 6.3, respectively. Pringle and Shaw
discovered that PdCl2(P,P′-dppm) reacts with NaCN to give
the face-to-face species [trans-Pd(CN)2(µ-P:P′-dppm)]2.35 In
contrast, 3 reacts with 2 equiv of KCN to give exclusively
Pd(CN)2(P,N-dmapm) (6b); 6a is not detected at 215 K,
implying that K > 100 for the 6a,b equilibrium. Thus, the
magnitudes of K for the a,b equilibria correlate with the
position of X in the trans effect series (Cl < Br < I , CN);36
as P-donors also show a strong trans effect, PdX2(P,N-
dmapm) (b) should be progressively more stable than PdX2-
(P,P′-dmapm) (a) as the trans effect of X increases.
The crystal structure of 3b is shown in Figure 1, and
relevant bond distances and angles are given in Table 2. Of
importance, the structure allows for a direct comparison
between both bound and free N- and P-atoms of identical
type in the same molecule and, thus, permits an assessment
of the relative degrees of σ- and π-bonding between these
atoms and the metal. The variations in P-C bond lengths
on coordination of dmapm to Pd(II) can be rationalized in
light of the hypothesis, supported by calculations by
Marynick37 and Xiao et al.,38 that P-based π-acceptor orbitals
Bromo (4) and iodo (5) complexes are readily made by
reaction of 3 with excess NaX (X ) Br, I), and these also
exist in CDCl3 as equilibrium mixtures of the P,P′- and P,N-
(35) Pringle, P. G.; Shaw, B. L. J. Chem. Soc., Chem. Commun. 1982,
956.
(32) Partenheimer, W.; Hoy, E. F. Inorg. Chem. 1973, 12, 2805.
(33) Luo, L.; Zhu, N.; Zhu, N.-J.; Stevens, E. D.; Nolan, S. P.; Fagan, P.
J. Organometallics 1994, 13, 669.
(34) Li, C.; Cucullu, M. E.; McIntyre, R. A.; Stevens, E. D.; Nolan, S. P.
Organometallics 1994, 13, 3621.
(36) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. ReV. 1973,
10, 335.
(37) Marynick, D. S. J. Am. Chem. Soc. 1984, 106, 4064.
(38) Xiao, S.-X.; Trogler, W. C.; Ellis, D. E.; Berkovich-Yellin, Z. J. Am.
Chem. Soc. 1983, 105, 5.
4060 Inorganic Chemistry, Vol. 43, No. 13, 2004

Metal-Metal Bonded Pt(I) and Pd(I) Compounds
(the LUMOs) are not purely 3d but have significant 3p
character and local σ* symmetry with respect to the P-C
bonds. In addition, Orpen and Connelly propose that when
the potential for π-back-bonding exists, a phosphine ligand
responds to give a lower overall energy by adopting a more
pyramidal geometry, enabling better overlap between the P
3d and P-C σ* orbitals that together constitute the π-ac-
ceptor LUMOs.39 This leads to a compression of the C-P-C
angles and a lengthening of the P-C bonds. Conversely,
when a phosphine acts predominantly as a σ-donor, the ligand
adopts a more trigonal planar geometry with larger C-P-C
angles giving better overlap for P-C σ-bonding and shorter
P-C bonds. This latter case is observed in the solid-state
structure of 3b: the P-C bond lengths involving the bound
P(1)-atom, both for P-C(aromatic) (av 1.804 Å) and
P-C(aliphatic) (1.824 Å), are significantly shorter than those
involving the free P(2)-atom (av 1.846 and 1.873 Å,
respectively); in addition, the angles surrounding P(1)
average 107.4°, larger than those found at P(2) (av 100.5 °).
It is thus reasonable to rationalize the Pd-P bonding in 3b
in terms of a dominant PfPd σ-contribution; this conforms
to the observation that the relative importance of π- with
respect to σ-bonding decreases on going from left to right
across the transition series (as metal d-electrons become
increasingly tightly bound).40 In addition, the N-C bonds
at the bound N-atom, N-C(aromatic) (1.481 Å) and
N-C(aliphatic) (av 1.491 Å), are longer than those involving
the free N-atoms (av 1.430 and 1.463 Å, respectively). As
nitrogen has no d-orbitals available for bonding, the observed
increase in N-C bond lengths upon coordination suggests
that the so-called N-based “sp3 nonbonding lone pair” has
some N-C σ-character; depopulation of this orbital on
coordination would induce a lengthening of the N-C bonds.
The Pd(1)-Cl(1) bond of 3b is shorter than the Pd(1)-
Cl(2) bond because of the higher trans influence of P with
respect to N.36 The Pd(1)-P(1) bond (2.1798 Å) is unusually
short, as judged by the mean Pd-P distances for PMe3, PPh3,
PPhMe2, dppe, and dppm complexes of 2.287, 2.308, 2.253,
2.260, and 2.258 Å, respectively, calculated by Orpen et al.41
The P(1)-C(17)-P(2) angle of 107.4 ° is intermediate
between the compressed P-C-P angles found in four-
membered P,P′-metallacycles (e.g., 93.0° for PdCl2(dppm)42)
and those found in complexes containing η1-dppm (e.g.,
118.9° for trans-Ru(η1-dppm)2(N,O-quin)2; quin ) 2-quinal-
dinate anion43). The P(1)-Pd(1)-N(1) “bite” angle is 86.1°,
similar to those found in Ru(II) complexes of 2-(diphen-
ylphosphino)-N,N-dimethylaniline, which are 80-83° within
both five- and six-coordinate complexes.44
N,P:P′,N′-dmapm) complex (1), containing dmapm in a P,P′-
bridging-bis(P,N)-chelating coordination mode, was made by
the conproportionation reaction of 3 and Pd2(dba)3 (dba )
dibenzylideneacetone).25 Although several reducing agents
have been used in attempted syntheses of group 10, MI-MI
bonded complexes,45 the conproportionation route involving
MII and M0 complexes in the presence of a bridging ligand
tends to give the best results.46 The mixed-metal complex
PtPdCl2(µ-P:P′-dppm)2 was first made by such a route using
in situ PtCl2(NCtBu)2/dppm and Pd(PPh3)4/dppm systems as
precursors,47 and corresponding complexes containing bridg-
ing 2-pyridylphosphine ligands have been made similarly.48
However, our attempts to make PtPdCl2(µ-N,P:P′,N′-dmapm)
(2) from 3 and Pt(dba)2 were unsuccessful; 2 was made
instead via the 2-electron reduction of in situ formed PtPdCl4-
(µ-N,P:P′,N′-dmapm)26 by hot ethanolic KOH. Reduction of
PtII salts by ethanolic KOH is well-known (e.g., in the
synthesis of Pt(PPh3)4 from K2PtCl4),49 but to our knowledge,
the synthesis of 2 represents the first time that the method
has been used to make a MI-MI complex from the
corresponding MII compound.
2
The 31P{1H} data for 2 reveal inequivalent P-atoms, the
higher field resonance showing 1J coupling to Pt, while the
P-atom at the Pd shows 2J coupling to Pt. The NMe groups
1
are manifest as 6 singlets in the H NMR with relative
intensities of 2:2:1:1:1:1. By virtue of their similar positions
in the spectrum of 1,25 the singlets at δ 3.07 and 2.78, and
2.45 are assigned to the 2 diastereotopic NMe groups of the
Pd-bound N-atom and the 2 equivalent NMe groups of the
free N-atom associated with the Pd-bound P-atom, respec-
tively. The remaining peaks at δ 3.19, 3.02, and 2.36
correspond to the analogous NMe protons on the “Pt-side”
of the molecule.
Exposure of an orange CDCl3 solution of 1 to 1 atm of
CO resulted in a rapid color change to intense purple. The
in situ 31P{1H} NMR spectrum showed a singlet at δP 43.0
for the product (8), and the δP -29.9 singlet of unreacted 1,
1
in a ratio of ∼6:1. The H NMR spectrum showed that all
24 NMe protons of 8 were equivalent, implying that the
coordinated N-atoms of 1 had been displaced by CO.
Conducting three freeze-pump-thaw cycles on the product
solution regenerated 1 quantitatively. The isolated, purple
solid 8 revealed a single, strong IR band at 1798 cm-1,
attributed to µ-CO, and analyzed correctly for Pd2Cl2(CO)2-
(dmapm). Its proposed structure (Scheme 3) contains a
µ-P:P′-dmapm ligand, and bridged CO ligands on both sides
of a Pd-Pd bond that maintain a 16 e- requirement. The
ν
sym(CO) would be IR-invisible. The CO reaction has
Synthesis and Reactivity of Bimetallic Complexes. Our
recently reported, structurally characterized Pd2Cl2(µ-
analogies to that of Pd2Cl2[µ-P:N-PPh2(2-pyridyl)]2, but here,
the pyridyl N-donors are replaced by terminal CO ligands
(νCO: 1994, 2019 cm-1).50 In contrast, Pd2Cl2(µ-P,P′-dppm)2
(39) Orpen, A. G.; Connelly, N. G. Organometallics 1990, 9, 1206.
(40) Dunne, B. J.; Morris, R. B.; Orpen, A. G. J. Chem. Soc., Dalton Trans.
1991, 653.
(41) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson, D.
G. J. Chem. Soc., Dalton Trans. 1989, S1.
(42) Steffen, W. L.; Palenik, G. J. Inorg. Chem. 1976, 15, 2432.
(43) Barral, M. C.; Jime´nez-Aparicio, R.; Royer, E. C.; Saucedo, M. J.;
Urbanos, F. A. Inorg. Chim. Acta 1993, 209, 105.
(44) Mudalige, D. C.; Ma, E. S.; Rettig, S. J.; James, B. R.; Cullen, W. R.
Inorg. Chem. 1997, 36, 5426.
(45) Pringle, P. G.; Shaw, B. L. J. Chem. Soc., Dalton Trans. 1983, 889.
(46) Balch, A. L.; Benner, L. S. Inorg. Synth. 1982, 21, 47.
(47) Pringle, P. G.; Shaw, B. L. J. Chem. Soc., Chem. Commun. 1982, 81.
(48) Xie, Y.; Lee, C.-L.; Yang, Y. P.; Rettig, S. J.; James, B. R. Inorg.
Chim. Acta 1994, 217, 209.
(49) Ugo, R.; Cariati, F.; Monica, G. L. Inorg. Synth. 1968, 11, 105.
(50) Maisonnat, A.; Farr, J. P.; Balch, A. L. Inorg. Chim. Acta 1981, 53,
L217.
Inorganic Chemistry, Vol. 43, No. 13, 2004 4061

Jones et al.
Scheme 3. Reversible Reaction of 1 with CO to Give 8
Chart 3. Possible Structure of Intermediate I
2
no JPPt coupling is observed for the non-metal-metal
bonded, PtIIPdII complex shown in Chart 2 26), thus likely
ruling out a species with a single bridged CO. Initial sub-
stitution of one N-atom donor by a terminal CO gives the
most reasonable formulation for I (Chart 3); substitution at
the more labile Pd atom is shown, but similar reactivity at
the Pt cannot be ruled out (a Pt-CO bond is more stable
than a corresponding Pd-CO bond).53 For intermediate II,
Scheme 4. Proposed Fluxionality of Complex 9 (R ) CO2Et)
1
2
data were the following: δP 25.6 (d, JPPt ) 5120, JPP
)
173 Hz, P-Pt), 46.9 (d, 2JPPt ) 1270, 2JPP ) 173 Hz, P-Pd);
the large downfield shifts of peaks relative to shifts of 2 (δP
-31.7 and -23.0) are comparable to that for 8 (δP 43.0)
relative to that of 1 (δP -29.9), and a structure such as 8
with two bridging carbonyls (Scheme 3), but with mixed
metals, seems feasible for II. That the downfield shifts for
I are much smaller than those of II (vs shifts for 2) perhaps
supports a less dramatic structural change in forming I versus
II. Intermediates I and II appeared after ∼30 min at 233 K
and increased in concentration as 2 was consumed; at 263
K, 7 (δP -65.2) appeared and at 300 K was the sole
P-containing product. It is not obvious how reaction of 2
with CO (or DEAD) leads to disproportionation to Pd0 and
PtII; the incoming unsaturated ligand clearly promotes
electron transfer between the PdI and PtI states via (in the
CO system) intermediates such as I or II.
reversibly binds 1 equiv of CO to give the “A-frame” product
Pd2Cl2(µ-CO)(µ-P,P′-dppm)2 (νCO: 1705 cm-1).51
Complex 1 also reacted with the electron deficient alkyne,
DEAD, to give a product (9) of formula Pd2Cl2(DEAD)-
(dmapm). At 325 K, the 31P{1H} NMR spectrum in CDCl3
shows just a slightly broadened singlet (δP 31.6) that at 220
2
K becomes two doublets (δP 19.3 and 44.3; JPP ) 68 Hz)
(SI, Figure S3). One possible interpretation is illustrated in
Scheme 4 (R ) CO2Et), where reversible coordination of
an N-atom causes the acetylene to shuttle between the Pd
atoms, the two species in equilibrium being enantiomers of
PdCl(η2-DEAD)(µ-P:P′,N-dmapm)PdCl (9). In a “frozen”
state at low temperature, the two P-atoms become inequiva-
lent, while at higher temperatures, the P-atoms are rendered
equivalent by rapid exchange. More typically, acetylenes
react with PdI2-complexes to generate species in which the
unsaturated ligand acts as a µ-η1:η1 donor lying parallel to
the Pd-Pd axis;52 such a structure, i.e., Pd2Cl2(µ-η1:η1-
DEAD)(µ-N,P:N′,P′-dmapm), would provide an appropriate
transition state for the shuttling mechanism. A 2D 31P EXSY
measurement at 220 K confirmed that the P-atoms of 9 are
indeed in chemical exchange. The Me groups appear in the
1H NMR at 325 K as 3 singlets with relative integrations
1:1:2, corresponding to 2 diastereotopic sets of Me groups
on the Pd-bound N-atoms, and one set of equivalent Me
groups of the free N-atoms.25
The reaction of 2 and thiols (RSH) in the presence of triflic
acid (HOTf) generated the bridged-thiolate complexes rac-
[PtPd(µ-SR)(µ-N,P:P′,N′-dmapm)][OTf] (R ) Et (rac-10),
nPr (rac-11)) and H2 (Scheme 1, M ) Pt); we have reported
recently25 on the corrresponding reaction of the homobime-
n
tallic complex 1 and PrSH (including its mechanism) that
gave rac-[Pd2(µ-SnPr)(µ-N,P:P′,N′-dmapm)][OTf] (rac-12).
The molecular structure of rac-10 (Figure 2, with selected
bond lengths and angles in Table 3) is very similar to that
of rac-12, although the P(1)-C(17)-P(2) angle in this
(115.6(3)°) is slightly more open than in the homobimetallic
case (112.9(1)°). rac-10 consists of two corner-sharing square
planes that are not in the typical “A”-frame orientation
because of the constraint imposed by the chirality of the
P-atoms that, in Figure 2, both have S absolute configuration
(the C2/c space group necessitates that the R,R-enantiomer
is also present in equal abundance in the unit cell). In
classical “A”-frame complexes such as Pd2Cl2(µ-S)(µ-P:P′-
dppm)2, the P-Pd-P axes are approximately parallel, and
both P-atoms of each dppm ligand are on the same side of
the plane defined by the Pd- and S-atoms.54 The analogous
P-Pd-Cl and P-Pt-Cl axes in rac-10 cannot be parallel
In contrast to the reactions of CO and DEAD with 1, which
gave the stable products 8 and 9, analogous reactions with
2 at rt resulted in disproportionation of 2 to Pd metal and
PtCl2(P,P′-dmapm) (7). At 233 K, however, 31P{1H} data
revealed the presence of two intermediates in the CO
reaction, although the corresponding 1H spectra revealed only
broad and uninformative resonances. Data for the first
observed intermediate I were the following: δP -18.4 (d,
2
2
1JPPt ) 3060, JPP ) 23.3 Hz, P-Pt), -8.3 (d, JPPt ) 300,
2JPP ) 23.3 Hz, P-Pd). The observation of the JPPt coup-
2
ling requires that the Pd-Pt bond remains intact (cf. the
2
31P{1H} data for 2, where JPPt )260 Hz, and the fact that
(51) Benner, L. S.; Balch, A. L. J. Am. Chem. Soc. 1978, 100, 6099.
(52) Xie, L. Y.; James, B. R. Inorg. Chim. Acta 1994, 217, 209.
(53) Calderazzo, F.; Dell’Amico, D. B. Pure Appl. Chem. 1986, 58, 56.
(54) James, B. R. Pure Appl. Chem. 1997, 69, 2213.
4062 Inorganic Chemistry, Vol. 43, No. 13, 2004

Metal-Metal Bonded Pt(I) and Pd(I) Compounds
containing a related tetraphosphine ligand (R ) R′ ) Ph).55
Both tetraphosphine systems required physical separation of
the two diastereomers. With the dmapm-bridged metal-
metal bonded species, however, the rac-diastereomer is
formed selectively, and no separation is necessary. In
addition, the diastereoselection appears to be fixed at this
stage and is conserved in subsequent reaction with thiols (and
perhaps other small molecules). The preferred rac-coordina-
tion (vs meso) within the tetraphosphine systems has also
been noted.56
Conclusions
The dmapm ligand is a versatile scaffold for the synthesis
of metal-metal bonded homobimetallic (Pd2) and heterobi-
metallic (PtPd) complexes in which it adopts a P,P′-bridging-
bis(P,N-chelating) coordination mode. Only the rac-MPdCl2-
(µ-N,P:P′,N′-dmapm) diastereomer is formed, and this
selectivity is conserved on reaction of these with thiols. This
preference may make metal catalysts based on dmapm more
attractive than those based on P4-donors, which require
separation of meso and rac forms. Hopefully, systems can
be found that circumvent the problem of fragmentation of
the catalyst.20,26
Figure 2. ORTEP diagram of the cation of rac-10, with 50% probability
ellipsoids.
Table 3. Selected Bond Distances (Å) and Angles (deg) for rac-10
Pd(1)-S(1)
Pd(1)-P(2)
Pd(1)-Cl(2)
Pd(1)-N(3)
2.288(1)
2.186(1)
2.370(1)
2.164(2)
Pt(1)-S(1)
Pt(1)-P(1)
Pt(1)-Cl(1)
Pt(1)-N(1)
2.306(1)
2.189(1)
2.377(1)
2.162(4)
Reactions of small molecules with bis(P-P)-bridged
bimetallic complexes are characterized by single insertions
into the metal-metal bonds. By contrast, rac-Pd2Cl2(µ-N,P:
P′,N′-dmapm) gives not only such insertion products (e.g.,
with RSH), but also doubly bridged adducts (e.g., with CO),
and fluxional species involving exchange of bound and free
anilinyl rings (e.g., with DEAD). Again, the extended range
of coordination modes available to dmapm-bridged com-
plexes may make them more useful as catalysts than those
based on P-P-type ligands.
Pd(1)-S(1)-Pt(1)
P(2)-Pd(1)-N(3)
P(2)-Pd(1)-S(1)
P(2)-Pd(1)-Cl(2)
N(3)-Pd(1)-S(1)
121.61(5)
85.0(1)
91.01(5)
173.76(6)
174.5(1)
P(1)-C(17)-P(2)
P(1)-Pt(1)-N(1)
P(1)-Pt(1)-S(1)
P(1)-Pt(1)-Cl(1)
N(1)-Pt(1)-S(1)
115.6(3)
85.9(1)
96.55(5)
177.28(5)
176.6(1)
because the Cl-atoms fall on either side of the plane defined
by the metal- and S-atoms as a result of the P-atoms having
the same configuration. A putative meso-10 could attain a
classical “A”-frame structure. The solution 31P{1H} NMR
spectrum of the isolated 10, or of an in situ reaction mixture
of 2 and EtSH (which is similar to that of 2, but shifted
downfield), showed no evidence for diastereomers (i.e., no
doubling of the resonances), and thus, rac-10 must be formed
diastereoselectively. This is presumably because the precursor
2 is also formed diastereoselectively (i.e., the N-atoms do
not exchange, or exchange only in a concerted manner),
during the reaction of 2 and EtSH. Identical findings were
seen for formation of rac-12 from 1.25 The sets of 1H NMR
signals seen for the NMe protons of 10 and 11 are similar
to those seen for 2, although the 2 sets for the free N-atoms
overlap to give a broad signal integrating for 12 protons.
Stereochemical considerations are pertinent for bimetallic
catalysts. In hydroformylations catalyzed by Stanley’s dirhod-
ium complexes, which are based on the ligand R2P(CH2)2-
PR′CH2PR′(CH2)2PR2 (R ) Et, R′ ) Ph), the rac-form is
much more active than the meso-form.20 Anderson and co-
workers have recently reported PtII and PdII complexes
Acknowledgment. We thank the Natural Sciences and
Engineering Council of Canada for financial support and the
University of British Columbia for a University Graduate
Fellowship (N.D.J.).
Supporting Information Available: X-ray crystallographic data
for the structures of the 3b and rac-10 in CIF format. Variable
temperature 1H NMR spectra of an equilibrium mixture of 3a and
3b (Figure S1), the van’t Hoff plot for this equilibrium (Figure
S2), and 31P{1H} NMR spectra for 9 at 325 and 220 K (Figure
S3). This information is available free of charge via the Internet at
http://pubs.acs.org.
IC040019T
(55) Nair, P.; Anderson, G. K.; Rath, N. P. Inorg. Chem. Commun. 2002,
5, 653.
(56) (a) Aubry, D. A.; Laneman, S. A.; Fronczek, F. R.; Stanley, G. G.
Inorg. Chem. 2001, 40, 5036. (b) Hunt, C. H.; Fronczek, F. R.;
Billodeaux, D. R.; Stanley, G. G. Inorg. Chem. 2001, 40, 5192.
2
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Inorganic Chemistry, Vol. 43, No. 13, 2004 4063