Platinum(II) and palladium(II) complexes of bisphosphine ligands bearing o-N,N-dimethylanilinyl substituants: A hint of catalytic olefin hydration

Article abstract of DOI:10.1021/ic048639h

Platinum(II) and palladium(II) complexes of the potentially hexadentate P,N-donor ligand family Ar₂P-X-PAr₂ (X = (CH ₂)₂ [dmape], cyclic-C₅H₈ [dmapcp]; Ar = o-N,N-dimethylanilinyl) are described. In CH₂Cl₂, the dmape complexes exist as equilibrium mixtures of MCl₂(P,P′,N- dmape) and [MCl(P,P′,N-dmape)]Cl isomers (M = Pd, Pt), governed by ΔH° = -19 ± 4 kJ mol^-1 and ΔS° = -100 ± 30 J mol^-1 K^-1 for M = Pt, and ΔH° = -11 ± 7 kJ mol^-1 and ΔS° = -60 ± 20 J mol^-1 K^-1 for M = Pd. The water-soluble dmapcp complexes exist solely in the [MCl(P,P′,N-dmapcp)]Cl form, but the free and coordinated anilinyl rings in these complexes are in slow diastereoselective exchange. X-ray crystal structures for MCl₂(P,P′-dmape) (M = Pd, Pt), and the [PdCl(P,P′,N-dmape)]⁺ and [PtCl-(P,P′,N- dmapcp)]⁺ cations, are presented. Some of the complexes show marginal activity in water for the catalyzed hydration of maleic to malic acid, giving about 6-7% conversion in 24 h at 100°C and substrate:catalyst loadings of 100:1. Attempts to synthesize a PdCl(P,P′,N-dmapm)⁺ species led instead to isolation of [Pd(μ-Cl)(P,P′-dmapm)]₂-[PF ₆]₂ (dmapm = Ar₂PCH₂Ar₂).

Full text of DOI:10.1021/ic048639h

Inorg. Chem. 2005, 44, 3290−3298
Platinum(II) and Palladium(II) Complexes of Bisphosphine Ligands
Bearing o-N,N-Dimethylanilinyl Substituents: A Hint of Catalytic Olefin
Hydration
Nathan D. Jones,† Patric Meessen, Udo Losehand, Brian O. Patrick, and Brian R. James*
Department of Chemistry, UniVersity of British Columbia, VancouVer, Canada V6T 1Z1
Received September 28, 2004
Platinum(II) and palladium(II) complexes of the potentially hexadentate P,N-donor ligand family Ar2P-X-PAr2 (X
)
(CH2)2 [dmape], cyclic-C5H8 [dmapcp]; Ar
) o-N,N-dimethylanilinyl) are described. In CH2Cl2, the dmape complexes
exist as equilibrium mixtures of MCl2(P,P
′
-dmape) and [MCl(P,P
′
,N-dmape)]Cl isomers (M
)
Pd, Pt), governed by
1
1
1
1
∆H° ) −19
±
±
4 kJ mol- and
∆
S
° ) −100
±
30 J mol- K- for M
)
Pt, and
∆H° ) −11
±
7 kJ mol- and
1
1
∆S° ) −60
20 J mol- K- for M
) Pd. The water-soluble dmapcp complexes exist solely in the [MCl(P,P′,N-
dmapcp)]Cl form, but the free and coordinated anilinyl rings in these complexes are in slow diastereoselective
exchange. X-ray crystal structures for MCl2(P,P -dmape) (M Pd, Pt), and the [PdCl(P,P
,N-dmape)]+ and [PtCl-
(P,P
,N-dmapcp)]+ cations, are presented. Some of the complexes show marginal activity in water for the catalyzed
hydration of maleic to malic acid, giving about 6 7% conversion in 24 h at 100 C and substrate:catalyst loadings
of 100:1. Attempts to synthesize a PdCl(P,P -Cl)(P,P -dmapm)]2-
,N-dmapm)+ species led instead to isolation of [Pd(
[PF6]2 (dmapm Ar2PCH2Ar2).
′
)
′
′
−
°
′
µ
′
)
Introduction
P-N ligands; they are attractive as homogeneous catalysts
because their “hard-soft” and hemilabile character permits
coordination to a variety of metals in a range of oxidation
states,12-15 and because the presence of N-atoms provides
strategies for water-solubilization.16-19
Recently, we reported the synthesis and characterization
of a family of bis(phosphine) ligands bearing two o-N,N-
dimethylanilinyl substituents at each P atom: 1,1-bis(di(o-
N,N-dimethylanilinyl)phosphino)methane (dmapm), 1,2-bis-
(di(o-N,N-dimethylanilinyl)phosphino)ethane (dmape), and
rac-1,2-bis(di(o-N,N-dimethylanilinyl)phosphino)cy-
clopentane (dmapcp), illustrated in Chart 1.8 Horner and
Simons20 reported in 1984 ligands akin to dmape but
Work in our laboratories over the last 15 years has pursued
the use of o-pyridyl-substituted1-6 and o-anilinyl-substituted7-11
mono-1-4,7 and bis(phosphine)4-6,8-11 ligands in platinum
group metal chemistry, one of the goals being to find water-
soluble transition metal catalysts for olefin hydration.1-3
More generally, there is a vast literature on complexes of
* To whom correspondence should be addressed. E-mail: brj@
chem.ubc.ca.
† Current address: Department of Chemistry, University of Western
Ontario, London, Ontario, Canada N6A 5B7.
(1) Xie, Y.; James, B. R. J. Organomet. Chem. 1991, 417, 277.
(2) Xie, Y.; Lee, C.-L.; Yang, Y.; Rettig, S. J.; James, B. R. Can. J. Chem.
1992, 70, 751.
(3) Xie, L. Y.; James, B. R. Inorg. Chim. Acta 1994, 217, 209.
(4) Baird, I. R.; Smith, M. B.; James, B. R. Inorg. Chim. Acta 1995, 235,
291.
(5) Jones, N. D.; Rettig, S. J.; James, B. R. J. Cluster Sci. 1998, 9, 243.
(6) Jones, N. D.; MacFarlane, K. S.; Smith, M. B.; Schutte, R. P.; Rettig,
S. J.; James, B. R. Inorg. Chem. 1999, 38, 3956.
(7) Mudalige, D. C.; Ma, E. S.; Rettig, S. J.; James, B. R.; Cullen, W. R.
Inorg. Chem. 1997, 36, 5426.
(8) Jones, N. D.; Meessen, P.; Smith, M. B.; Losehand, U.; Rettig, S. J.;
Patrick, B. O.; James, B. R. Can. J. Chem. 2002, 80, 1600.
(9) Jones, N. D.; James, B. R. AdV. Synth. Catal. 2002, 344, 1126.
(10) Jones, N. D.; Foo, S. J. L.; Patrick, B. O.; James, B. R. Inorg. Chem.
2004, 43, 4056.
(12) Guiry, P. J.; Saunders: C. P. AdV. Synth. Catal. 2004, 346, 497.
(13) Fache, F.; Schulz, E.; Tommasino, M. L.; Lemaire, M. Chem. ReV.
2000, 100, 2159. Newkome, G. R. Chem. ReV. 1993, 93, 2067.
(14) Espinet, P.; Soulantica, K. Coord. Chem. ReV. 1999, 193-195, 499.
(15) Braunstein, P.; Naud, F. Angew. Chem., Int. Ed. 2001, 40, 680.
Braunstein, P. J. Organomet. Chem. 2004, 689, 3953.
(16) Nagel, U.; Kinzel, E. Chem. Ber. 1986, 119, 1731.
(17) To´th, I.; Hanson, B. E. Tetrahedron: Asymmetry 1990, 1, 895. To´th,
I.; Hanson, B. E. Tetrahedron: Asymmetry 1990, 1, 913. To´th, I.;
Hanson, B. E.; Davis, M. E. J. Organomet. Chem. 1990, 396, 363.
To´th, I.; Hanson, B. E.; Davis, M. E. Catal. Lett. 1990, 5, 183.
(18) Lamouille, T.; Saluzzo, C.; ter Halle, R.; Guyader, F. L.; Lemaire,
M. Tetrahedron Lett. 2001, 42, 663.
(11) Foo, S. J. L.; Jones, N. D.; Patrick, B. O.; James, B. R. Chem. Commun.
2003, 988.
(19) Nuzzo, R. G.; Feitler, D.; Whitesides, G. M. J. Am. Chem. Soc. 1979,
101, 3683.
3290 Inorganic Chemistry, Vol. 44, No. 9, 2005
10.1021/ic048639h CCC: $30.25
© 2005 American Chemical Society
Published on Web 04/05/2005

Pt(II) and Pd(II) Complexes of Bisphosphine Ligands
Chart 1. Bisphosphine Ligands Bearing Two o-N,N-Dimethylanilinyl
Substituents at Each P-Atom
agents and distilled under N2 prior to use. Details on the measure-
ments of the NMR spectra, studied in CDCl3 at 300 K, unless
specified otherwise (s ) singlet, d ) doublet, t ) triplet, spt )
septet, m ) multiplet, br ) broad, p ) pseudo; J-values in Hz),
the UV-vis spectra (reported as λmax (( 2 nm) [ꢀ (M-1 cm-1)],
the conductivity data at 25 °C for 1 mM solutions (ΛM in Ω1-
mol-1 cm2), and the elemental analyses have been reported
recently.10 IR spectra (KBr disks) were recorded from 500 to 4000
cm-1 on a Bomem-Michelson MB-100 FTIR spectrometer, data
being reported in cm-1
.
Syntheses. [PtCl(P,P′,N-dmapcp)]Cl‚H2O, 2‚H2O. This com-
pound was made from either PtCl2 (via cis-PtCl2(MeCN)2) or PtCl2-
(cod). (a) From PtCl2. To a Schlenk tube containing PtCl2 (100
mg, 0.38 mmol) was added CH3CN (10 mL), and the slurry was
refluxed for 2 h to give a yellow solution. The dmapcp ligand (230
mg, 0.38 mmol) was then added to the hot solution that became
colorless. The solvent was removed in vacuo and the residue was
redissolved in minimum CH2Cl2. Addition of Et2O (20 mL) gave
a white powder that was isolated by filtration, washed with Et2O
and dried in vacuo at 78 °C. Yield: 240 mg (71%). (b) From PtCl2-
(cod). To a Schlenk tube charged with PtCl2(cod) (97 mg, 0.26
mmol) and dmapcp (160 mg, 0.26 mmol) was added 1,2-
dichloroethane (15 mL), and the resulting colorless solution was
refluxed for 17 h. The workup was the same as in method (a).
Yield: 150 mg (65%). Anal. Calcd for C37H48N4Cl2P2Pt‚H2O: C
containing only one o-substituted NR2 group at each P-atom
that was thus chiral; they subsequently used Rh complexes
of such ligands as precursors for asymmetric hydrogenation
of olefinic substrates.20 To´th and co-workers17 have made
related ligands bearing p-C6H4(NMe2) substituents, including
chiral derivatives with quaternized N-atoms for use in
catalytic asymmetric hydrogenation in water; with these
systems, simultaneous coordination to the same metal center
by the P- and N-atoms of the same ligand is not possible,
and there are no reports of bridging by these p-substituted
ligands. Our o-substituted ligands make the N-atoms avail-
able for coordination to the same metal as the P atoms, in
some cases generating water-soluble complexes (salts) by
displacement of halide from the metal coordination sphere.
This article builds upon our earlier reports of homo- and
heterobimetallic Pt and Pd complexes supported by a P,P′-
bridging, bis(P,N)-chelating coordination mode of dmapm.9-11
Here, we describe the synthesis and solution- and solid-state
characterization of monometallic PtII and PdII complexes of
the ligands shown in Chart 1. Details on solution fluxionality,
including thermodynamic parameters and stereochemical
considerations, are presented, as well as preliminary data on
the use of water-soluble species as precursors for the catalytic
hydration of the activated olefin, maleic acid, cis-CH-
(CO2H)dCH(CO2H); activated olefins have become standard
substrates for assays of catalytic hydration in water.1,21-23
1
49.7; H 5.6; N 6.3; Found: C 50.0; H 5.7; N 6.1. H{31P} NMR:
δ 1.32 (m, 1H, CH2), 1.55 (s, 2H, H2O), 1.70 (m, 1H, CH2), 1.90
(m, 2H, CH2), 2.26 (s, 6H, NCH3), 2.33 (br s, 6H, NCH3), 2.47
(m, 2H, CH2), 2.72 (s, 7H, NCH3 + 1 CH), 3.06 (s, 3H, NCH3,
3
3JHPt ) 22), 3.46 (s, 3H, NCH3, JHPt ) 17), 3.72 (m, 1H, CH),
6.74 (m, 2H, Ar), 7.09 (m, 1H, Ar), 7.3-7.9 (m, 11H, Ar), 8.35
1
(m, 1H, Ar), 9.37 (m, 1H, Ar). 31P{1H} NMR: δ 18.9 (d, JPPt
)
3490, 2JPP ) 12.3), 28.6 (d, 1JPPt ) 3400, 2JPP ) 12.3). ΛM (H2O):
150. X-ray diffraction quality crystals of 2‚CH2Cl2‚1.46H2O were
grown over 4 d by evaporation of a CH2Cl2 solution of the complex
onto which EtOH had been layered (CH2Cl2:EtOH 2:5 by vol).
[PtCl(P,P′,N-dmapcp)]PF6, 3. To a Schlenk tube charged with
2 (38 mg, 0.043 mmol) and NH4PF6 (7.0 mg, 0.043 mmol) was
added acetone (10 mL). The resulting white suspension was stirred
at room temperature (∼20 °C) for 1 h and then filtered through
Celite 545 that was washed with acetone (3 × 10 mL); the
combined filtrate was reduced in vacuo to ∼1 mL. The product
was afforded as a white powder by the addition of Et2O (20 mL),
isolated by filtration, washed with Et2O (3 × 3 mL), and dried in
vacuo at 100 °C. Yield: 21 mg (49%). Anal. Calcd for C37H48N4-
ClF6P3Pt: C 45.1; H 4.9; N 5.7. Found: C 44.8; H 4.9; N 5.6. The
Experimental Section
1
General. Unless otherwise noted, synthetic procedures were
performed using standard Schlenk techniques under dry Ar or N2.
The ligands8 dmapm, dmape, rac-dmapcp (see the Introduction,
Chart 1), and the precursors PtCl2(cod),24 trans-PdCl2(PhCN)2,25
and PdCl2(dmapm) (1)10 were made according to literature proce-
dures. All other reagents were purchased from commercial sources
and used as supplied. Solvents were dried over the appropriate
solution H NMR spectrum was essentially identical to that of 2.
31P{1H} NMR: δ 17.0 (d, 1JPPt ) 3510, 2JPP ) 13.7), 26.7 (d, 1JPPt
) 3390, JPP ) 13.7), -145 (spt, JPF ) 710, PF6-).
2
1
[PdCl(P,P′,N-dmapcp)]Cl, 4. To a Schlenk tube containing
trans-PdCl2(PhCN)2 (55 mg, 0.14 mmol) and dmapcp (86 mg, 0.14
mmol) was added CH2Cl2 (10 mL), and the initially orange solution
was stirred for 15 min when it became yellow. The volume was
reduced to ∼1 mL, and addition of Et2O (20 mL) gave the yellow
solid product that was isolated by filtration, washed with Et2O (3
× 3 mL), and dried in vacuo. Yield: 109 mg (98%). Anal. Calcd
for C37H48N4Cl2P2Pd: C 56.4; H 6.1; N 7.1. Found: C 56.1; H
6.3; N 7.0. 1H NMR: δ 1.42 (m, 1H, CH2), 1.65 (br m, 1H, CH2),
1.83 (br m, 1H, CH2), 2.15 (br m, 1H, CH2), 2.29 (s, 13H, NCH3,
and 1H, CH2), 2.45 (br m, 1H, CH2), 2.73 (s, 6H, NCH3), 2.93 (s,
3H, NCH3), 3.14 (br m, 1H, CH), 3.30 (s, 3H, NCH3), 4.05 (br m,
1H, CH), 6.73 (m, 1H, Ar), 6.82 (pt, 1H, Ar), 7.08 (pt, 1H, Ar),
7.58 (m, 11H, Ar), 8.21 (pt, 1H, Ar), 9.43 (m, 1H, Ar). 31P{1H}
(20) Horner, L.; Simons, G. Phosphorus, Sulfur Relat. Elem. 1984, 19, 65;
Z. Naturforsch. B: Chem. Sci. 1984, 39B, 512.
(21) Bzhasso, N. A.; Pyatnitskii, M. P. Zh. Prikl. Zhim. 1969, 42, 1610
(through Chem. Abstr. 71, 101239f). Xie, Y. Ph.D. Thesis, University
of British Columbia, Vancouver, 1990. Bennett, M. A.; Jin, H.; Lin,
S.; Redina, L. M.; Willis, A. J. Am. Chem. Soc. 1995, 117, 8335.
(22) Stewart, I. C.; Bergman, R. G.; Toste, F. D. J. Am. Chem. Soc. 2003,
125, 8696.
(23) Ganguly, S.; Roundhill, D. M. Organometallics 1993, 12, 4825.
(24) McDermott, J. X.; White, J. F.; Whitesides, G. M. J. Am. Chem. Soc.
1976, 98, 6521.
(25) Hartley, F. R. Organomet. ReV. (A) 1976, 6, 119.
Inorganic Chemistry, Vol. 44, No. 9, 2005 3291

Jones et al.
NMR: δ 48.7 (s), 49.6 (s) [2JPP not resolved]. UV-vis: 334 [6100]
(CH2Cl2); 378 [3900] (H2O). ΛM (H2O): 200. A crystal of 4 was
grown from a CH2Cl2 solution of the complex.
a yellow powder. Anal. Calcd for C34H44N4Cl2P2Pd: C 54.6; H
5.9; N 7.5; Found: C 54.6; H 5.9; N 7.6. The H NMR spectra
1
(CD2Cl2, 220-300 K) of an equilibrium mixture of the two isomers
9a and 9b were uninformative because the peaks were broad and
overlapped. PdCl2(P,P′-dmape), 9a: 31P{1H} NMR (CD2Cl2, 233
K): δ 66.4 (br s). [PdCl(P,P′,N-dmape)]Cl, 9b: 31P{1H} NMR
(CD2Cl2, 233 K): δ 60.5 (br s), 73.4 (br s). An X-ray quality crystal
of 9a ‚CH2Cl2 was grown from a CH2Cl2 solution of the complex
layered with Et2O.
[PdI(P,P′,N-dmapcp)]I, 5. To a Schlenk tube containing trans-
PdCl2(PhCN)2 (71 mg, 0.19 mmol) and dmapcp (110 mg, 0.18
mmol) was added CH2Cl2 (5 mL), and the resulting orange solution
was stirred for 0.5 h when it became yellow. To this was added
NaI (97 mg, 0.65 mmol) and acetone (5 mL). The solution
immediately became orange and turbid, and was stirred for a further
0.5 h, when the solvent was removed in vacuo. The residue was
taken up in CH2Cl2 (10 mL), and the mixture was filtered through
Celite 545. The filtrate volume was reduced to ∼2 mL, and addition
of Et2O (20 mL) precipitated the orange product that was collected
by filtration, washed with Et2O (3 × 3 mL), and dried in vacuo.
Yield: 130 mg (74%). Anal. Calcd for C37H48N4I2P2Pd: C, 45.8;
[PdCl(P,P′,N-dmape)]PF6, 10. This complex was prepared in
the same manner outlined for 6. Thus, reaction of 9 (83 mg, 0.11
mmol) and NH4PF6 (93 mg, 0.57 mmol) gave 60 mg (63%) of a
yellow powder. Anal. Calcd for C34H44N4ClF6P3Pd: C 47.6; H 5.2;
N 6.5. Found: C 47.4; H 5.4; N 6.4. 1H NMR: δ 2.6 (br s, ∼28H,
CH2 and NCH3), 6.8-8.0 (br m, 16H, Ar). 31P{1H} NMR (CD2-
1
-
Cl2): δ 60.5 (s), 73.4 (s) [2JPP not resolved], and spt of PF6
.
H, 5.0; N, 5.8. Found: C, 45.9; H, 5.1; N, 5.6. H NMR: δ 1.80
(br m, 2H, CH2), 2.35 (br s, ∼12H, NCH3), 2.70 (br s, ∼6H, NCH3),
3.05 (br s, ∼3H, NCH3), 3.70 (br s, ∼3H, NCH3), 3.95 (br m, 1H,
CH), 6.80 (br m, 1H, Ar), 7.05 (br m, 2H, Ar), 7.30-8.00 (br m,
11H, Ar), 8.20 (br m, 1H, Ar), 9.40 (br m, 1H, Ar). The peaks due
to the remaining CH2 and CH protons are obscured by the broad
NCH3 peaks. 31P{1H} NMR: δ 39.9 (s), 50.4 (s) [2JPP not resolved].
[PdCl(P,P′,N-dmapcp)]PF6, 6. This complex was made in a
manner corresponding to that given for 3, except that a 5-fold excess
of NH4PF6 was used. The acetone was removed at the pump and
the residue taken up in CH2Cl2 (10 mL) before filtration through
Celite 545. This removed unreacted NH4PF6 that is insoluble in
CH2Cl2. Thus, reaction of 4 (150 mg, 0.19 mmol) and NH4PF6 (157
mg, 0.97 mmol) gave 171 mg (100%) of a yellow powder. Anal.
Calcd for C37H48N4ClF6P3Pd: C 49.5; H 5.4; N 6.2. Found: C 49.7;
H 5.4; N 5.8. The 1H NMR spectrum of 6 was essentially the same
[PdCl(P,P′,N-dmape)]OTf, 11. To a CH2Cl2 solution (4 mL)
of 9 (50 mg, 0.067 mmol) was added MeOTf (23 µL, 0.20 mmol),
and the mixture was stirred at room temperature for 20 min.
Volatiles were removed in vacuo, and the residue was dissolved in
0.5 mL of CH2Cl2. Precipitation with hexanes (∼20 mL) yielded a
yellow, microcrystalline solid that was isolated, washed with Et2O,
and dried in vacuo. Yield: 31 mg (54%). Anal. Calcd for C35H44N4-
ClF3O3P2PdS: C, 48.8; H, 5.1; N, 6.5. Found: C, 48.9; H, 5.2; N,
6.4. 1H NMR (CD2Cl2): δ 1.68 (s, 4H, CH2), 2.63 (s, 18H, NCH3),
3.49 (s, 6H, NCH3), 7.34-7.82 (m, 16H, Ar). 31P{1H} NMR (CD2-
Cl2): δ 61.0 (s), 73.8 (s) [2JPP not resolved]. 19F NMR (CD2Cl2):
δ -78.6 (s). IR: νSO 1260. The triflate derivative was made because
an X-ray quality crystal of 11‚CH2Cl2 could be grown from a CH2-
Cl2 solution of the complex layered with Et2O.
[Pd(µ-Cl)(P,P′-dmapm)]2[PF6]2, 12. To a CH2Cl2 (4 mL)
solution containing PdCl2(dmapm) (1) (110 mg, 0.15 mmol) was
added acetone (6 mL) and NH4PF6 (220 mg, 1.3 mmol). The
resulting orange slurry was stirred at room temperature for 3 h and
then reduced in vacuo to a residue that was taken up in CH2Cl2
(∼5 mL), prior to filtration through Celite 545. The orange filtrate
was reduced to ∼1 mL, and EtOH (10 mL) was added to precipitate
the orange product. Addition of Et2O (10 mL) gave further product
that was isolated by filtration, washed with Et2O (3 × 3 mL), and
dried in vacuo. Yield: 77 mg (61%). Anal. Calcd for C66H84N8-
Cl2F12P6Pd2: C, 47.0; H, 5.0; N, 6.6. Found: C, 47.1; H, 5.0; N,
as that for 4, and the 31P{1H} NMR spectrum was similarly identical
-
save for the presence of the spt (δ -145) due to PF6
.
PtCl2(dmape), 7. This complex was synthesized by the corre-
sponding two routes detailed for 2. Thus, reaction of PtCl2 (105
mg, 0.40 mmol) and dmape (230 mg, 0.40 mmol) yielded 130 mg
(40%) of a white powder, while reaction of PtCl2(cod) (110 mg,
0.29 mmol) with dmape (160 mg, 0.28 mmol) gave 200 mg (85%)
of 7. However, elevated temperatures were not required for the
latter preparation that was conducted in CH2Cl2 at room temper-
ature. Anal. Calcd for C34H44N4Cl2P2Pt: C 48.8; H 5.3; N 6.7;
Found: C 48.5; H 5.3; N 6.5. PtCl2(P,P′-dmape), 7a: 31P{1H}
NMR (240 K): δ 46.0 (br s, 1JPPt ) 3750). The 1H NMR spectrum
of 7a was broad and uninformative, even at low temperature, and
could not be resolved from that of [PtCl(P,P′,N-dmape)]Cl (7b).
Resonances of the NCH3 and the CH2 protons fell in the range δ
2-4, and the aromatic protons gave peaks between δ 6.5-9. [PtCl-
(P,P′,N-dmape)]Cl, 7b: 31P{1H} NMR (240 K): δ 32.0 (br s, 1JPPt
) 3510), 53.0 (br s, 1JPPt ) 3460). Evaporation over 3 d of a CH2-
Cl2 solution of 7 onto which EtOH had been layered (CH2Cl2:EtOH
1:1 by vol) yielded colorless, X-ray diffraction quality crystals of
7a‚CH2Cl2.
1
6.6. UV-vis (CH2Cl2): 360 [14600]. H NMR: δ 2.56 (s, 48H,
2
NCH3), 4.91 (t, 4H, CH2, JHP ) 12.3), 7.32 (m, 16H, Ar), 7.57
(pt, 8H, Ar), 7.97 (m, 8H, Ar). 31P{1H} NMR: δ -52.0 (s), and
spt of PF6-. ΛM (MeNO2): 213.
X-ray Crystallographic Analyses. Measurements were made
on a Rigaku/ADSC CCD diffractometer at 180(1) K (for 2‚CH2-
Cl2‚1.46H2O, 4 and 7a‚CH2Cl2), or 173(1) K (for 9a‚CH2Cl2and
11‚CH2Cl2) using graphite monochromated Mo KR radiation (λ )
0.71069 Å). Some crystallographic data are shown in Table 1. The
data were collected and processed using the d*TREK program,26a
and the structures were solved using heavy- atom Patterson26b (for
[PtCl(P,P′,N-dmape)]PF6, 8. This compound was prepared in
the manner outlined for 6. Thus, reaction of 7 (92 mg, 0.11 mmol)
and NH4PF6 (42 mg, 0.26 mmol) gave 48 mg (47%) of a white
powder. Anal. Calcd for C34H44N4ClF6P3Pt: C 43.2; H 4.7; N 5.9.
Found: C 43.3; H 4.9; N 5.8.1H NMR: δ 2.2-3.6 (br m, 28H,
CH2 and NCH3), 7.10-7.80 (br m, 12H, Ar), 8.05 (m, 4H, Ar).
(26) (a) d*TREK: Area Detector Software; Molecular Structure Corpora-
tion: The Woodlands, TX, 1997. (b) Beurskens, P. T.; Admiraal, G.;
Beurskens, G.; Bosman, W. P.; Garcia-Granfa, S.; Gould, R. O.; Smits,
J. M. M.; Smykalla, C. The DIRDIF-PATTY-Program System;
Technical Report of the Crystallography Laboratory; University of
Nijmegen: Nijmegan, The Netherlands, 1992. (c) 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. (d) 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 Labora-
tory; University of Nijmegen: Nijmegan, The Netherlands, 1994.
1
1
31P{1H} NMR: δ 31.6 (s, JPPt ) 3540, 52.7 (s, JPPt ) 3446)
[2JPP not resolved], -145 (spt, JPF ) 710, PF6-).
1
PdCl2(dmape), 9. This complex was prepared in the same
manner given for 4. Thus, reaction of trans-PdCl2(PhCN)2 (56 mg,
0.15 mmol) and dmape (83 mg, 0.15 mmol) gave 88 mg (81%) of
3292 Inorganic Chemistry, Vol. 44, No. 9, 2005

Pt(II) and Pd(II) Complexes of Bisphosphine Ligands
Table 1. Crystallographic Data for 2·CH2Cl2·1.46H2O, 7a·CH2Cl2, 9a·CH2Cl2, and 11·CH2Cl2
2‚CH2Cl2‚1.46H2O
7a‚CH2Cl2
C35H46Cl4N4P2Pt
9a‚CH2Cl2
C35H46Cl4N4P2Pd
11a‚CH2Cl2
formula
fw
C38H52.92Cl4N4P2PtO1.46
987.99
C36H46Cl3N4O3F3P2SPd
946.55
921.62
832.93
cryst color, habit colorless, irregular
colorless, prism
0.15 × 0.20 × 0.25
P21 (#4)
12.3471(14)
11.8502(13)
12.9845(2)
-
yellow, block
0.50 × 0.40 × 0.20
P21 (#4)
12.3010(3)
11.8069(3)
12.9733(4)
-
colorless, plate
0.30 × 0.25 × 0.10
P1(bar) (#2)
9.9087(9)
11.2071(4)
20.076(1)
87.556(2)
86.209(2)
70.624(2)
2098.1(2)
2
cryst size (mm3)
space group
a (Å)
0.15 × 0.20 × 0.25
P1(bar) (#2)
10.6530(8)
14.115(2)
14.998(2)
71.471(4)
78.1136(14)
79.2564(13)
2074.5(4)
2
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
94.7052(4)
-
94.607(2)
-
1893.4(2)
2
40.88
14846
7628
1878.1(2)
2
8.95
16349
7915
Z
µ (cm-1
)
37.39
19383
8.12
18870
8457
0.040
total reflns
unique reflns
Rint
9355
0.046
0.021
0.035
no. variables
R1 (I > nσ(I))a
wR2b
499
414
414
456
0.032 (n ) 3, 6381 obsd reflns) 0.041(n ) 0, 7603 obsd reflns) 0.022 (n ) 3, 7647 obsd reflns) 0.038 (n ) 2, 6943 obsd reflns
0.054
1.05
0.046
1.24
0.062
1.09
0.096
1.06
GOF
a
2
2
2
R1 ) ∑||Fo| - |Fc||/∑|Fo| (observed data). b wR2 ) [∑(Fo - Fc )2/∑w(Fo )2]1/2 (all data).
2 and 7a) or direct26c (for 9a and 11) methods, and expanded using
Fourier techniques.26d
peaks defines a P,P′,N- coordination mode that is shown in
Chart 2 together with H NMR peak assignments. On the
1
Protocol for the Catalytic Hydration of Maleic Acid, cis-CH-
(CO2H)dCH(CO2H). To a combination of maleic acid (116 mg,
1.00 mmol) and a selected metal complex (0.01 mmol) in a 5 mm-
wall Schlenk tube (∼30 cm in length), topped with a Teflon Kontes
valve, and having a sidearm gas inlet and magnetic stir bar, was
added H2O (10 mL). The solution was degassed by shaking the
vessel under vacuum, and then Ar (1 atm) was admitted. The tube
was kept at 100 °C, and after 24 h, a 3 mL aliquot was withdrawn.
This was reduced to dryness on a rotatory evaporator and the residue
was ground to a powder sample (∼7 mg) that was dissolved in
Chart 2. Labeling of the NMe Groups in the Cation of 2
1
acetone-d6 (0.5 mL) to acquire a H NMR spectrum. The propor-
basis of integration, the two most downfield singlets (equiva-
lent to three protons each) are assigned unequivocally to Me
groups a and b associated with the Pt-bound N-atom: these
peaks show the largest coordination shifts from their (aver-
age) position in the free ligand (∆δ ) 0.83 and 0.51 ppm),
and they show three-bond 1H-195Pt coupling (17 and 22 Hz,
respectively).
tions of maleic, fumaric (the trans-isomer), and malic (the hydration
product, hydroxysuccinic) acids present were calculated using the
ratios of appropriate peak integrations (δ, acetone-d6: maleic, 6.40
s, cis-CH)CH; fumaric, 6.80 s, trans-CH)CH; malic, 4.52 dd,
CH(OH)CH2).
Results and Discussion
Complexes of dmapcp. Reaction of dmapcp with PtCl2
or PtCl2(cod) gives the white, air-stable, water-soluble
complex, [PtCl(P,P′,N-dmapcp)]Cl (2). The complex ana-
lyzed as a monohydrate, and 1H NMR confirmed the
presence of H2O; moreover, crystals of 2 contained 1.46H2O
per unit cell (see below). The number and relative integra-
tions of the singlets due to the NCH3 protons in the 1H NMR
spectra of anilinyldiphosphine complexes constitute an
invaluable diagnostic tool for determining the overall solution
structure of the molecule. In free dmapcp, the two anilinyl
substituents on each P-atom are diastereotopic, related to
those on the opposite P-atom by a C2 axis: the ligand bears
homotopic pairs of diastereotopic anilinyl rings, and the 1H
NMR spectrum shows two singlets for the NCH3 protons (δ
2.55 and 2.63).8 In the case of 2, the C2 symmetry is lifted,
and four sharp peaks due to NCH3 protons are apparent at δ
3.46, 3.06, 2.72, and 2.26 in a 1:1:2:2 ratio (i.e., 3:3:6:6
protons). The remaining six NCH3 protons are manifested
by a broad peak at δ 2.33 (Figure 1). This pattern of NCH3
1
Figure 1. The δ 1-4 region of the H{31P} NMR spectrum (121 MHz,
CDCl3, 300 K) of [PtCl(P,P′,N-dmapcp)]Cl (2); (*) and (#) indicate peaks
due to the CH2 and CH protons. Assignments (a-h) are discussed in the
text and shown in Chart 1. The singlet at δ 1.55 is due to H2O.
Inorganic Chemistry, Vol. 44, No. 9, 2005 3293

Jones et al.
Scheme 1. Exchange of Free and Coordinated Anilinyl Groups in the
Cation of [PtCl(P,P′,N-dmapcp)]Cl (2)a
Figure 2. ORTEP representation (50% ellipsoids) of the cation of [PtCl-
(P,P′,N-dmapcp)]Cl (2) showing the P,P′,N-coordination; H-atoms are
omitted for clarity.
Table 2. Selected Bond Distances and Angles for 2·CH2Cl2·1.46H2O
with Estimated Standard Deviations in Parentheses
Pt(1)-P(1)
2.2012(12) Pt(1)-P(2)
2.2646(10)
2.3642(13)
1.782(4)
1.848(4)
1.829(4)
1.490(6)
1.452(6)
1.449(6)
94.08(4)
94.53(11)
109.1(2)
Pt(1)-N(1)
2.184(3)
1.822(4)
1.814(5)
1.819(5)
1.481(6)
1.496(6)
1.500(6)
84.07(11)
87.43(4)
112.1(2)
115.9(2)
108.3(4)
Pt(1)-Cl(1)
a For clarity only bonding anilinyl rings are shown; the pendant rings
are omitted, as well as the cation +1 charge.
P(1)-C(1)
P(1)-C(6)
P(1)-C(14)
P(2)-C(2)
P(2)-C(22)
P(2)-C(30)
be in exchange with the NMe protons of the corresponding
pseudoequatorial anilinyl ring on the other P-atom. This is
clearly demonstrated by the EXSY NMR spectrum: a and
b are in chemical exchange with g,h only, while c,d and e,f
are mutually exchanging. If an associative mechanism is
assumed for the d8 square planar metal center, the data can
be interpreted via the exchange pathways illustrated in
Scheme 1. Only one diastereomer (I) of the postulated five-
coordinate P,P′,N,N′-intermediate, arising from coordination
of N(4) (Figure 2), can lead to the exchange of P-atoms.
Inspection of the crystal structure shows no obvious reason
why the “nonproductive” diastereomer (II) should not also
form; however, this cannot decay to 2, probably for reasons
N(1)-C(7)
N(1)-C(12)
N(1)-C(13)
N(2)-C(15)
N(2)-C(20)
N(2)-C(21)
P(1)-Pt(1)-N(1)
P(1)-Pt(1)-P(2)
C(1)-P(1)-C(6)
C(6)-P(1)-C(14)
C(7)-N(1)-C(12)
P(2)-Pt(1)-Cl(1)
Cl(1)-Pt(1)-N(1)
C(1)-P(1)-C(14)
C(12)-N(1)-C(13) 109.8(3)
C(7)-N(1)-C(13) 109.2(4)
C(20)-N(2)-C(21) 109.5(4)
C(20)-N(2)-C(15) 114.6(4)
C(15)-N(2)-C(21) 109.9(4)
C(5)-C(4)-C(3)
P(1)-C(1)-C(5)
C(1)-C(5)-C(4)
C(4)-C(3)-C(2)
P(2)-C(2)-C(3)
99.3(4)
105.8(4)
123.8(3)
106.2(4)
125.4(3)
The structure of the cation component of 2‚CH2Cl2‚1.46H2O
is shown in Figure 2, and selected bond distances and angles
are given in Table 2. The metal coordination sphere is
approximately square planar and, in agreement with the
solution NMR data, the ligand adopts a P,P′,N-configuration
in the solid state. The absolute configurations of P(1) and
the methine C-atoms C(1) and C(2) are R,S,S, respectively,
and the five-membered chelate ring is in the δ-configuration.
As the space group is P1(bar) and Z ) 2, the mirror image
is present in the unit cell, but the diastereomeric R,R,R and
S,S,S forms are absent. This is consistent with the fact that
the substituents on the P-atoms of a chiral C2-symmetric
ligand are present as pseudoaxial and pseudoequatorial pairs,
and the hypothesis that only the equatorial type are sterically
available for binding to a square planar metal center. That
the R,R,R and S,S,S forms of 2 cannot arise was shown by
a 2D 1H EXSY experiment [see Figure S1 in the Supporting
Information (SI)]. If the “pendant” and bound N-atoms were
in free chemical exchange, the stereogenic P-atoms would
be racemized. If, however, only pseudoequatorial anilinyl
rings are able to bind to the Pt, then the NMe groups a and
b cannot exchange with c and d, i.e., the NMe groups
associated with the other (pseudoaxial) anilinyl group at-
tached to the same (bound) P-atom. Rather, a and b can only
1
of steric strain at the P(2)-atom. The broadened H NMR
peak due to the e,f groups is tentatively attributed to the rapid
equilibrium formation of II, i.e., to the reversible binding
of N(3) (Figure 2).
Complexes bearing P,P,N-chelating ligands, in which the
N-donor is pendant from one of the P-donors, are known,6
including P,N,P-pincer27 and P,P,N-tripod28 type systems.
An example relevant to this paper is the five-coordinate Rh-
(I) compound meso-[Rh(cod)(P,P′,N-Ph2P{CH(py)}2PPh2)]+
(py ) o-pyridyl), in which there is slow interchange of
coordinated and noncoordinated pyridyl rings,29 very much
like the exchange seen in 2. A key difference between the
Rh system and 2 is that, in the former, exchange of the bound
and free N-atoms results in the conversion of one enantiomer
into the other, while in 2, it results in self-exchange. The
inability of the P-atom to epimerize during the fluxional
(27) Melaimi, M.; Thoumazet, C.; Ricard, L.; LeFloch, P. J. Organomet.
Chem. 2004, 689, 2988 and refs. therein.
(28) Liu, C.-Y.; Cheng, M.-C.; Peng, S.-M.; Liu, S.-T. Organometallics
1994, 13, 4294.
(29) Bookham, J. L.; Smithies, D. M.; Thornton Pett, M. J. Chem. Soc.,
Dalton Trans. 2000, 975.
3294 Inorganic Chemistry, Vol. 44, No. 9, 2005

Pt(II) and Pd(II) Complexes of Bisphosphine Ligands
Scheme 2. MCl2(P,P′-dmape) h [MCl(P,P′,N-dmape)][Cl] Equilibria
for 7a,b (M ) Pt) and 9a,b (M ) Pd)
process is obviously of importance for potential asymmetric
catalysis using ligands such as dmapcp. A detailed under-
standing of the stereochemical implications of fluxional
processes in chiral complexes is becoming increasingly
important in light of recent discoveries that both chiral30 and
achiral31 hemilabile ligand groups may act to enhance
enantioselectivities in metal-catalyzed asymmetric reactions.
The aqueous conductivity of 2 is 150 ohm-1 mol-1 cm2,
consistent with a 1:1 electrolyte,32 and the Cl- anion is easily
replaced by PF6- on reaction with NH4PF6 in acetone at room
temperature to give [PtCl(P,P′,N-dmapcp)]PF6 (3). Even in
the presence of excess NH4PF6, only the ionic chloride of 2
is replaced under these conditions.
observed by Stelzer and co-workers37 for the compound
[PdCl(P,P′,N-py(CH2)2P(Me)(CH2)3P(Me)(CH2)2py)]Cl (py
) o-pyridyl), which gives two 31P{1H} singlets at δ 13.7
and 15.5; and just as 2 gives the AX pattern, the analogous
Pt complex of Stelzer gives two separated signals for the
chemically inequivalent P-atoms at δ -6.2 and -12.9.
Reaction of 4 with excess NaI gives [PdI(P,P′,N-dmapcp)]I
(5) and with NH4PF6 gives [PdCl(P,P′,N-dmapcp)]PF6 (6).
In water, the molar conductivity of 4 is 200 ohm-1 cm2
mol-1, perhaps indicating further chloride dissociation to
generate [Pd(OH2)(P,P′,N-dmapcp)]Cl2; the bathochromic
shift in λmax on going from CH2Cl2 (334 nm) to H2O (378
nm) also suggests a change in inner-sphere coordination on
dissolution of 4 in H2O.
Complexes of dmape. The isolated product 7 from the
1:1 reaction between dmape and PtCl2(cod) exists in CDCl3
solution as a mixture of PtCl2(P,P′-dmape) (7a) and [PtCl-
(P,P′,N-dmape)]Cl (7b). At room temperature, the 31P{1H}
NMR spectrum consists of several broad, ill-defined peaks
in the range δ 15-70; however, below ∼ 250 K, this resolves
into three singlets and their associated Pt satellites (Figure
S4). The peaks at δ 32 and 53 correspond to the inequivalent
P-atoms of 7b, as shown by room temperature 31P{1H} data
(δ 31.6 and 52.7) for [PtCl(P,P′,N-dmape)]PF6 (8), made
from 7 by treatment with NH4PF6. As for the dmapcp
analogues 4 and 6, 2JPP coupling was not observed for 7b or
8. The remaining singlet (δ 46) at 240 K corresponds to the
C2-symmetric complex 7a. No evidence was obtained for
formation of [Pt(P,P′,N,N′-dmape)]Cl2.
The dmapcp ligand reacts in an analogous fashion with
trans-PdCl2(PhCN)2 to give the yellow, air-stable, water-
soluble complex, [PdCl(P,P′,N-dmapcp)]Cl (4). Olefin-free
Pd precursors are preferable to PdX2(diolefin) (X ) halogen)
for the syntheses of the Pd complexes because the o-anil-
inyldiphosphine ligands tend to react with coordinated olefin,
most probably via nucleophilic attack by either the P-atom33,34
or N-atom.35 Thus, dmapcp reacts with PdCl2(cod) at room
temperature to give not only 4, but also another product (A)
with an AX pattern in the 31P{1H} NMR spectrum: δA 36.5
2
(d), δX 47.8 (d), JPP ) 8.8 Hz. As the 31P{1H} NMR
spectrum of A depends both on the nature of the diolefin,
1
and the H NMR shows peaks of coordinated olefin (mul-
tiplets at δ 5.23, 5.65),36 A must be an organometallic species
bearing both the diolefin moiety and the anilinyldiphosphine
ligand; a plausible suggestion for the structure of A is given
in the Supporting Information (Chart S1). Further studies
are needed to substantiate this organometallic chemistry.
1
The H NMR spectrum of 4 is reminiscent of that of 2,
but shows only four NCH3 peaks in a 1:1:2:4 ratio. The
difference arises from overlap of peaks due to the e,f and
g,h groups of NCH3 protons in 4. A P,P′,N coordination
mode of dmapcp is indicated, and this was confirmed by
some crystallographic data; these are not good enough for
publication, but at least the atom connectivity is established
(Figure S2 shows a PLUTO representation of the structure,
while a well determined structure of the [PdCl(P,P′,N-
dmape)]+ cation in 11 is discussed below). However, the
31P{1H} spectrum shows two closely separated singlets at δ
48.7 and 49.6 instead of the anticipated AX pattern (as seen
The Pd product (9) from reaction of dmape and trans-
PdCl2(PhCN)2 exhibited NMR behavior analogous to that
of 7. The room temperature 31P{1H} spectrum showed a
single broad peak centered at δ 66.4 that below ∼250 K di-
minished in intensity with 2 new singlets at δ 60.5 and 73.4
appearing, these corresponding to the resonances of the sep-
arately synthesized [PdCl(P,P′,N-dmape)]PF6 (10). Thus, the
δ 66.4 singlet is assigned to PdCl2(P,P′-dmape) (9a), and
those at δ 60.5 and 73.4 to the inequivalent P-atoms of [PdCl-
1
for the Pt analogue, 2; see Figure S3). The 2D H EXSY
spectrum of 4 is similar to that of 2, implying similar
exchange between coordinated and free anilinyl N-atoms.
The 31P{1H} data suggest that the P-atoms are undergoing
exchange. Such exchange between P-atoms whose pendant
N-containing “arms” are either coordinated or free has been
2
(P,P′,N-dmape)]Cl (9b) (where again JPP is unresolved).
Variable temperature, reversible 31P{1H} NMR spectra of
7 and 9 in CD2Cl2 showed that the P,P′- (a) and P,P′,N-
isomers (b) are in thermal equilibrium (Scheme 2), and
equilibrium constants (K) were determined for both systems
from the spectra over the temperature range 210-250 K;
the resulting van’t Hoff plots appear in Figure S5. The
determined thermodynamic parameters are ∆H° ) -19 (
(30) Zhang, A.; Rajanbabu, T. V. Org. Lett. 2004, 6, 1515.
(31) Goldfuss, B.; Lo¨schmann, T.; Rominger, F. Chem. Eur. J. 2004, 10,
5422.
(32) Geary, W. J. Coord. Chem. ReV. 1971, 7, 81.
(33) Fallis, S.; Anderson, G. K.; Rath, N. P. Organometallics 1991, 10,
3180.
(34) Huang, C.-C.; Duan, J.-P.; Wu, M.-Y.; Liao, F.-L.; Wang, S.-L.; Cheng,
C.-H. Organometallics 1998, 17, 676.
(35) Panunzi, A.; Renzi, A. D.; Paiaro, G. J. Am. Chem. Soc. 1970, 92,
3488.
(36) Jones, N. D.; James, B. R. Can. J. Chem. In press.
(37) Hessler, A.; Fischer, J.; Kucken, S.; Stelzer, O. Chem. Ber. 1994, 127,
481.
Inorganic Chemistry, Vol. 44, No. 9, 2005 3295

Jones et al.
4 kJ mol-1 and ∆S° ) -100 ( 30 J mol-1 K-1 for 7, and
∆H° ) -11 ( 7 kJ mol-1 and ∆S° ) -60 ( 20 J mol-1
K-1 for 9. The entropy decrease likely results from solvent
ordering about the charged species, and the exothermicity
presumably reflects the formation of strong M-N bonds (vs
M-Cl) with that for Pt being stronger than for Pd.
Because of the equilibria between the neutral dichloro and
cationic monochloro species, the 1H NMR resonances (partic-
ularly of the CH2 protons) were broadened and difficult to
assign.
More generally, studies on hemilabile ligands (that can
make available a coordination site as needed) remain highly
topical, because of their ability to confer on metal complexes
the balance between stability and a reactivity needed for a
catalytic system.15 Hemilability has been assessed historically
in terms of rates of intramolecular exchange between coor-
dinated and pendant groups, studied usually by variable tem-
perature NMR line-shape analysis;38 such kinetic data often
refer to exchange between identical or enantiomeric com-
plexes (“Type II” hemilability as defined by Braunstein and
Naud15). Equilibria thermodynamic data of the kind shown
in Scheme 2, where there is competition for a metal center
between a hemilabile group and an incoming (intermolecular)
ligand, are rare,39 although many processes of this type (Type
III)15 have been observed40 and are especially relevant to
catalysis in terms of designing hemilabile ligands. Of note,
the hemilabile nature of the dmape systems (Scheme 2) is
quite different from that of the dmapm ones, which is
governed by the strain energy of the four-membered metal-
chelate ring10 (see below).
The X-ray crystallographic structure of 7a‚CH2Cl2 (Figure
3, Table 3) reveals the expected, close to square planar
coordination at the metal. Bond distances and angles are
similar to those of other PtII complexes with bis(phosphine)
ligands.41 All four anilinyl groups are involved in short
intramolecular C-H‚‚‚N contacts involving the ligand CH2
protons, these interactions being reminiscent of those seen
in the free ligands.8 The Pd analogue, 9a‚CH2Cl2 (Figure 4,
Table 4), is isostructural with 7a‚CH2Cl2, the bond lengths
and angles being within 0.015 Å and 3.0°, respectively, of
those of the Pt system. Distances of ∼3.65 Å between the
metal atom and the N-atom of a noncoordinating dimethy-
lanilinyl group in the structures of 7a (Pt-N(1)) and 9a (Pd-
N(3)) are slightly less than the sum of the van der Waals
radii of the metal and N-atom (3.85 Å)42 and presumably
this weak interaction assists in the loss of coordinated
chloride to form 7b and 9b, respectively.
Figure 3. ORTEP representation (50% ellipsoids) of PtCl2(P,P′-dmape)
(7a). The C-H‚‚‚N contacts involving the CH2 protons are shown; other
H-atoms are omitted.
Table 3. Selected Bond Distances and Angles for 7a·CH2Cl2 with
Estimated Standard Deviations Parentheses
Pt(1)-P(1)
2.2317(13)
2.3728(12)
1.8819(5)
1.818(7)
1.844(7)
92.74(5)
86.07(5)
109.2(2)
109.2(3)
105.7(3)
Pt(1)-P(2)
2.2355(13)
2.3776(13)
1.810(4)
1.833(5)
1.813(4)
91.25(5)
90.99(5)
105.5(3)
106.2(3)
110.2(2)
Pt(1)-Cl(1)
Pt(1)-Cl(2)
P(1)-C(1)
P(1)-C(3)
P(1)-C(11)
P(2)-C(2)
P(2)-C(19)
P(2)-C(27)
P(1)-Pt(1)-Cl(2)
P(1)-Pt(1)-P(2)
C(1)-P(1)-C(3)
C(11)-P(1)-C(1)
C(19)-P(2)-C(27)
P(2)-Pt(1)-Cl(1)
Cl(1)-Pt(1)-Cl(2)
C(3)-P(1)-C(11)
C(2)-P(2)-C(19)
C(2)-P(2)-C(27)
A suitable crystal to substantiate the structure of the cation
in 9b was obtained from a CH2Cl2 solution of the triflate
salt, [PdCl(P,P′,N-dmape)]OTf (11), this being readily
(38) For example: Lindner, E.; Mo¨ckel, A.; Mayer, H. A.; Ku¨hbauch, H.;
Fawzi, R.; Steimann, M. Inorg. Chem. 1993, 32, 1266.
(39) We have been unable to find a report showing such thermodynamic
data; the closest system is our own work (ref 10) that involves the
intramolecular ligand system PdCl2(P, P-dmapm) h PdCl2(P, N-
dmapm).
(40) For P, N-systems, see for example: Braunstein, P.; Naud, F.; Dedieu,
A.; Rohmer, M.-M.; DeCian, A.; Rettig, S. J. Organometallics 2001,
20, 2966. Braunstein, P.; Naud, F.; Rettig, S. J. New J. Chem. 2001,
25, 32. Cadierno, V.; D´ıez, J.; Garc´ıa-Garrido, S. E.; Garc´ıa-Granda,
S.; Gimeno, J. J. Chem. Soc., Dalton Trans. 2002, 1465.
(41) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson, D.
G. J. Chem. Soc., Dalton Trans. 1989, S1.
Figure 4. ORTEP representation (50% ellipsoids) of PdCl2(P,P′-dmape)
(9a); H-atoms are omitted for clarity.
(42) Bondi, A. J. Phys. Chem. 1964, 68, 441.
3296 Inorganic Chemistry, Vol. 44, No. 9, 2005

Pt(II) and Pd(II) Complexes of Bisphosphine Ligands
Chart 3. Hydration of Maleic to Malic Acid
Table 4. Selected Bond Distances and Angles for 9a·CH2Cl2 with
Estimated Standard Deviations Parentheses
Pd(1)-P(1)
2.2507(5)
2.3690(5)
1.836(2)
1.833(2)
1.813(2)
90.42(2)
85.13(2)
106.5(1)
105.9(1)
105.7(1)
Pd(1)-P(2)
2.2471(5)
2.3783(5)
1.815(2)
1.830(2)
1.836(2)
92.16(2)
93.43(2)
105.9(1)
108.79(9)
109.2(1)
Pd(1)-Cl(1)
Pd(1)-Cl(2)
P(1)-C(1)
P(1)-C(3)
P(1)-C(11)
P(2)-C(2)
Table 6. Product Distributions for Catalytic Hydration of Maleic Acida
P(2)-C(19)
P(2)-C(27)
P(1)-Pd(1)-Cl(1)
P(1)-Pd(1)-P(2)
C(1)-P(1)-C(11)
C(11)-P(1)-C(3)
C(19)-P(2)-C(27)
P(2)-Pd(1)-Cl(2)
Cl(1)-Pd(1)-Cl(2)
C(3)-P(1)-C(11)
C(2)-P(2)-C(19)
C(2)-P(2)-C(27)
maleic acid fumaric acid malic acid
catalyst precursor
(%)
(%)
(%)
none
HCl (1.2 M)
[PtCl(P,P′,N-dmapcp)]Cl (2)
[PdCl(P,P′,N-dmapcp)]Cl (4)
[PdI(P,P′,N-dmapcp)]I (5)
PdCl2(dmape) (9)
95
78
91
88
93
92
3
16
4
6
4
2
6
5
6
3
2
Table 5. Selected Bond Distances and Angles for 11·CH2Cl2 with
Estimated Standard Deviations Parentheses
6
Pd(1)-P(1)
2.1833(8)
2.191(2)
1.825(3)
1.797(3)
1.804(3)
1.472(4)
1.481(4)
1.470(4)
85.90(7)
83.17(3)
Pd(1)-P(2)
2.2457(8)
2.3578(8)
1.808(3)
1.850(3)
1.839(3)
1.501(4)
1.437(4)
1.466(4)
96.59(3)
94.83(7)
106.68(13)
108.9(3)
108.9(2)
Pd(1)-N(1)
Pd(1)-Cl(1)
P(1)-C(9)
a [Maleic acid] ) 0.1 M in water at 100 °C (substrate: catalyst ) 100:
1); % conversion ( 1 (TON) after 24 h.
P(1)-C(17)
P(1)-C(1)
P(2)-C(18)
P(2)-C(19A)
N(1)-C(8)
N(2)-C(10)
N(2)-C(15)
P(2)-Pd(1)-Cl(1)
Cl(1)-Pd(1)-N(1)
P(2)-C(27)
N(1)-C(2)
cation is the same as that for the cation of 9b (see above),
N(1)-C(7)
1
while the H spectrum shows broad singlets at δ 3.49 and
N(2)-C(16)
2.63 for the Me protons of the coordinated and pendant
groups NMe2, respectively (for the free ligand,8 the Me
resonance is seen at δ 2.62). Exchange behavior similar to
that shown in Scheme 1 for complex 2 must occur, but the
EXSY NMR spectrum was not investigated. The 19F NMR
resonance at δ - 78.6 and the ν(SO) stretch at 1260 cm-1
confirm the presence of a noncoordinated triflate anion.43
Thus, only the P,P′,N-coordination mode is observed for
dmapcp within the chloro-Pt and chloro-Pd species, while
the corresponding dmape systems generated isomeric mix-
tures of the neutral, dichloro-P,P′ and cationic monochloro-
P,P′,N species, and the latter could be isolated by abstraction
of the chloride. Presumably, the difference between the
dmapcp and dmape systems is dictated by the higher rigidity
of the former ligand imposed by the cyclic-C5H8 ring, while
the four intramolecular C-H‚‚‚N interactions present in the
P,P-bound isomer of the dmape complexes could also play
a role.
P(1)-Pd(1)-N(1)
P(1)-Pd(1)-P(2)
C(17)-P(1)-C(1)
C(1)-P(1)-C(9)
C(2)-N(1)-C(7)
112.80(13) C(17)-P(1)-C(9)
110.48(13) C(7)-N(1)-C(8)
110.9(2)
C(2)-N(1)-C(8)
C(15)-N(2)-C(16) 108.9(3)
C(15)-N(2)-C(10) 112.9(3)
C(16)-N(2)-C(10) 110.3(3)
formed by treatment of 9 (the isomeric mixture) with MeOTf.
As in the case of Cl- abstraction with NH4PF6, only one
Cl- is removed by excess (∼3-fold) MeOTf. The structure
of 11 (Figure 5, Table 5) is very similar to that of 2 and
shows the P,P′,N-coordination with distortion from square
planarity at the metal (one of the anilinyl rings at P(2) is
disordered in two orientations). For the structure shown in
Figure 5, the absolute configuration of P(1) is R, and the
five-membered chelate ring is again in the δ-configuration,
but the P1(bar) space group with Z ) 2 implies again that
the mirror image molecule (where the configuration of P(1)
is S) is also present in the unit cell. Complex 11 is soluble
in chlorinated solvents and acetone and is slightly soluble
in water. The unresolved 31P{1H} NMR spectrum for the
The [Pd(µ-Cl)(P,P′-dmapm)]2[PF6]2 Complex. The tri-
dentate coordination could not be induced in the case of
dmapm. Our previously reported complex PdCl2(dmapm)
(1),10 which exists in CHCl3 as an equilibrium mixture of
neutral, dichloro-P,P′and dichloro-P,N-bound isomers, reacts
with NH4PF6 in acetone to give [Pd(µ-Cl)(P,P′-dmapm)]2-
[PF6]2 (12).The NMR spectra show a singlet at δH 2.56 for
the 24 equivalent NCH3 protons, and an upfield δP singlet
at -52.0 that is indicative of equivalent P-atoms involved
in a four-membered metallacycle.10 The conductivity in
MeNO2 confirms the presence of a 2:1 electrolyte.32
Hydration of Maleic Acid in Water. Complexes 2, 4, 5,
and 9 were assayed as potential catalysts for the homoge-
neous hydration of maleic acid, cis-CH(CO2H)dCH(CO2H),
to malic acid in water at 100 °C (Chart 3), but the data (Table
6) reveal marginal activity that in the cases of 2 and 4 was
comparable to that of dilute HCl. However, these cationic
Pt- and Pd-dmapcp precursors (that both contain a P,P′,N-
ligand bonding mode) give less isomerization to fumaric acid
than does the HCl, and give better turn-over numbers than
2+
did Ganguly and Roundhill’s [(P-P)Pd(µ-OH)]2 com-
Figure 5. ORTEP representation (50% ellipsoids) of the cation of [PdCl-
(P,P′,N-dmape)]OTf (11); H-atoms are omitted for clarity.
plexes for the hydration of diethylmaleate in THF/H2O (for
Inorganic Chemistry, Vol. 44, No. 9, 2005 3297

Jones et al.
example, with the P-P ) Ph2P(CH2)2PPh2 system, they
report < 1.0 and 2.6 diethylmalate/mol catalyst after 30 h at
100 and 120 °C, respectively).23 The nature of the species
present in the aqueous solution at 100 °C in our systems is
unknown, but it is worth noting that the chloro precursor 4
is more active than the iodo analogue, 5. Itaconic acid
(CH2dC(CO2H)CH2CO2H) was also tested as a substrate
with 4 as catalyst, but no hydration was observed, implying
that the “internal position” of the double bond as in maleic
acid is not the limiting factor in the catalyzed reactions. In
attempts to synthesize bridged-hydroxo complexes of the
well-known type44 used by Ganguly and Roundhill,23 the
isomeric mixture of PdCl2(dmape) (9) was reacted with KOH
in an aqueous/CH2Cl2 medium; however, the product pre-
cipitated with NH4PF6 was the remarkable dimer [PdCl(µ-
N,P,O-dmapeO)]2[PF6]2, where dmapeO is Ar2P(CH2)2P(O)-
Ar2 (Ar ) o-N,N-dimethylanilinyl), the monooxide of
dmape.36 Details on the characterization of this dimer, and
related oxidation chemistry of these dimethylanilinyl ligands,36
will be published elsewhere.
nature of the fluxionality depending principally on the ligand
“backbone” and to a lesser extent on the metal. Thus, dmapm
shows P,P′- to P,N′-coordination exchange in chloro-Pd(II)
complexes and solely P,P′-coordination within chloro-Pt(II)
species;10 dmape shows P,P′ to P,P′,N exchange in com-
plexes of both metals; and dmapcp gives solely P,P′,N-
coordination, again with both metals. In the last case, there
is slow, diastereoselective exchange between bound and free
anilinyl rings. The cationic Pd(II) and Pt(II) species contain-
ing P,N-bound dmapcp show marginal activity as catalytic
precursors for the hydration of maleic to malic acid; the
activity is comparable to that of general acid catalysis, but
the selectivity (relatively less isomerization to fumaric acid)
suggests a role for the metal.
Acknowledgment. We thank the Natural Sciences and
Engineering Research Council of Canada (NSERC) for
financial support, and the University of British Columbia
for a University Graduate Fellowship (N.D.J.).
More generally, development of effective, transition metal
catalysts for hydration of olefins remains elusive; the his-
tory of the topic can be traced through some relevant
literature,1,2,21-23,45 which includes the notable, metal-free
phosphine systems reported recently.22
Supporting Information Available: X-ray crystallographic data
for the structures of 2, 7a, 9a, and 11 in CIF format. The δ 2-4
1
range of the 2D H EXSY spectrum of 2 (Figure S1), a PLUTO
representation of the structure of 4 (Figure S2), the 31P{1H} spectra
of 2 and 4 (Figure S3), the 31P{1H} NMR spectrum of an
equilibirum mixture of PtCl2(P,P′-dmape) (7a) (*) and [PtCl(P,P′,N-
dmape)]Cl (7b) (#) (Figure S4), the van’t Hoff plots for the
equilibria between 7a and 7b, and between 9a and 19b (Figure
S5), and a possible structure for A (Chart S1). This information is
available free of charge from http://pubs.acs.org.
Conclusions
Tetra(o-anilinyl)bis(phosphine) ligands give rise to a range
of fluxional coordination modes with Pt(II) and Pd(II), the
(43) Lawrence, G. A. Chem. ReV. 1986, 86, 17.
(44) Ruiz, J.; Vicente, C.; Marti, J. M.; Cutillas, N.; Garcia, G.; Lopez, G.
J. Organomet. Chem. 1993, 460, 241. Pieri, G.; Pasquali, M.; Leoni,
P.; Englert, U. J. Organomet. Chem. 1995, 491, 27.
(45) Sanford, M. S.; Groves, J. T.Angew. Chem., Int. Ed. 2004, 43, 588.
IC048639H
3298 Inorganic Chemistry, Vol. 44, No. 9, 2005