Formation of P-C bonds under unexpectedly mild conditions. Phosphoryl migration and metal coordination of diphenylphosphinomethyl-oxazolines and -thiazolines

Article abstract of DOI:10.1021/ic800934h

The heterocycles 2-methyl-2-oxazoline (mox) and 2-methyl-2-thiazoline (mth) react with Ph₂PCl under mild conditions, in the presence of NEt ₃ which promotes their phosphorylation by stabilization of their enamino tautomers mox_e and mth_e, respectively, and which also behaves as HCl scavenger. Depending on the reaction conditions, three different phosphine ligands were obtained in good yields from mox: the monophosphine Ph₂PCH₂C=NCH₂CH₂O (1_ox) and the isomeric diphosphines Ph₂PCH=COCH ₂CH₂NPPh₂ (2_ox) (X-ray structure) and (Ph₂P)₂CHC=NCH₂CH₂O (3 _ox). The formation of these ligands involves phosphoryl migration reactions, which were studied by NMR spectroscopy. The synthesis and the X-ray structures of the corresponding diphenylphosphinothiazolines Ph ₂PCH₂C=NCH₂CH₂S (1_th) and Ph₂CH=CSCH₂CH₂NPPh₂ (2 _th) are also reported but the thiazoline analog of the geminal diphosphine 3_ox was not observed. The metal complexes [Pt(3 _ox-H)₂]·4CH₂Cl₂ (4·4CH₂Cl₂), [Pt(Me)I(1_ox)] (5), [Pt(Me)₂(1_ox)] (7), [Pd(dmba-C,N)(1_th)] OTf·0.25Et₂O (8·0.25Et₂O), [Pd(dmba-C,N)(1_th-H)] (9), and [9·{Pd(dmba-C,N)Cl}]·2. 5C₆H₆ (10·2.5C₆H₆) have been prepared and structurally characterized by X-ray diffraction.

Full text of DOI:10.1021/ic800934h

Inorg. Chem. 2008, 47, 9886-9897
Formation of P-C Bonds under Unexpectedly Mild Conditions.
Phosphoryl Migration and Metal Coordination of
Diphenylphosphinomethyl-oxazolines and -thiazolines
Roberto Pattacini, Gu¨nter Margraf, Abdelatif Messaoudi, Nicola Oberbeckmann-Winter,
and Pierre Braunstein*
Laboratoire de Chimie de Coordination, Institut de Chimie (UMR 7177 CNRS), UniVersite´ Louis
Pasteur, 4 rue Blaise Pascal, F-67070 Strasbourg Cedex, France, Fax: (+33) (0)3 90 24 13 22
Received May 22, 2008
The heterocycles 2-methyl-2-oxazoline (mox) and 2-methyl-2-thiazoline (mth) react with Ph2PCl under mild conditions,
in the presence of NEt3 which promotes their phosphorylation by stabilization of their enamino tautomers moxe and
mthe, respectively, and which also behaves as HCl scavenger. Depending on the reaction conditions, three different
phosphine ligands were obtained in good yields from mox: the monophosphine Ph2PCH2CdNCH2CH2O (1ox) and
the isomeric diphosphines Ph2PCHdCOCH2CH2NPPh2 (2ox) (X-ray structure) and (Ph2P)2CHCdNCH2CH2O (3ox).
The formation of these ligands involves phosphoryl migration reactions, which were studied by NMR spectroscopy.
The synthesis and the X-ray structures of the corresponding diphenylphosphinothiazolines Ph2PCH2CdNCH2CH2S
(1th) and Ph2CHdCSCH2CH2NPPh2 (2th) are also reported but the thiazoline analog of the geminal diphosphine
3ox was not observed. The metal complexes [Pt(3ox-H)2] · 4CH2Cl2 (4· 4CH2Cl2), [Pt(Me)I(1ox)] (5), [Pt(Me)2(1ox)] (7),
[Pd(dmba-C,N)(1th)]OTf · 0.25Et2O (8· 0.25Et2O), [Pd(dmba-C,N)(1th-H)] (9), and [9· {Pd(dmba-C,N)Cl}] · 2.5C6H6
(10· 2.5C6H6) have been prepared and structurally characterized by X-ray diffraction.
Scheme 1
Introduction
The synthesis of chelating P,N ligands and their applica-
tions in coordination chemistry are attracting much attention.1
The introduction of an alkyl-phosphine moiety in a ligand
generally requires delicate reaction conditions (alkyllithium
compounds, amide bases at low temperatures), when com-
pared to those used for the preparation of other classes of
organophosphorus compounds, such as phosphinites or
aminophosphines. In the latter cases, chlorophosphines (e.g.,
Ph2PCl) are generally reacted with the parent alcohol or
amine, respectively, in a one step reaction involving the use
of NEt3 as HCl scavenger. Although such reactions usually
simply involve a H/PPh2 exchange, a nontrivial reaction
pathway was recently discovered for the reaction of Ph2PCl
with 2-amino-2-thiazoline in the presence of NEt3, as
depicted in Scheme 1.2
* To whom correspondence should be addressed. E-mail: braunstein@
chimie.u-strasbg.fr.
(1) For example, see: (a) Benito-Garagorri, D.; Kirchner, K. Acc. Chem.
Res. 2008, 41, 201–213. (b) Roseblade, S. J.; Pfaltz, A. Acc. Chem.
Res. 2007, 40, 1402–1411. (c) Braunstein, P. Chem. ReV. 2006, 106,
134–159. (d) Braunstein, P. J. Organomet. Chem. 2004, 689, 3953–
3967. (e) Guiry, P. J.; Saunders, C. P. AdV. Synth. Catal. 2004, 346,
497–537. (f) Chelucci, G.; Orru, G.; Pinna, G. A. Tetrahedron 2003,
59, 9471–9515. (g) Pfaltz, A.; Blankenstein, J.; Hilgraf, R.; Hormann,
E.; McIntyre, S.; Menges, F.; Schonleber, M.; Smidt, S. P.; Wuste-
nberg, B.; Zimmermann, N. AdV. Synth. Catal. 2003, 345, 33–44. (h)
Braunstein, P.; Naud, F. Angew. Chem., Int. Ed. 2001, 40, 680–699.
(i) Helmchen, G.; Pfaltz, A. Acc. Chem. Res. 2000, 33, 336–345. (j)
Slone, C. S.; Weinberger, D. A.; Mirkin, C. A. Prog. Inorg. Chem.
1999, 48, 233–350. (k) Espinet, P.; Soulantica, K. Coord. Chem. ReV.
1999, 193-195, 499–556.
This reaction proceeds by fast double phosphorylation of
2-amino-2-thiazoline, leading first to diphosphine a, which
then reacts more slowly with the imino-form of the 2-amino-
(2) Margraf, G.; Pattacini, R.; Messaoudi, A.; Braunstein, P. Chem.
Commun. 2006, 3098–3100.
9886 Inorganic Chemistry, Vol. 47, No. 21, 2008
10.1021/ic800934h CCC: $40.75  2008 American Chemical Society
Published on Web 10/03/2008

Formation of P-C Bonds
standards, with downfield shifts reported as positive. All NMR
spectra were measured at 298 K, unless otherwise specified. The
assignment of the signals was made by 1H,1H-COSY, and 1H,13C-
HMQC experiments. Elemental C, H, and N analyses were
performed by the ”Service de microanalyses”, Universite´ Louis
Pasteur, Strasbourg. [Pd(dmba)(µ-Cl)]2,6 [PtCl2(NCPh)2],7
[PtCl2(cod)],8 [PtMe2(cod)],9 [PtCl(Me)(cod)],10 and [PtI(Me)-
(cod)]10 (cod ) 1,5 cyclooctadiene) were prepared according to
literature procedures. Ph2PCl and NEt3 were freshly distilled before
use. Other chemicals were commercially available and were used
as received.
2-thiazoline, to yield the monophosphine b as the final
product. The reaction is under kinetic control, with the attack
of Ph2PCl on 2-amino-2-thiazoline to give a being signifi-
cantly faster than the a f b transformation.
We became interested in investigating whether these mild
reaction conditions could be applied to isoelectronic, mixed
alkyl-aryl phosphines (2-oxazoline-2-ylmethyl)diphenylphos-
phine (1ox) and (2-thiazoline-2-ylmethyl)diphenylphosphine
(1th).
Preparation of Ph2PCH2CdNCH2CH2O (1ox). To a solution
of 2-methyl-2-oxazoline (1.00 mL, 11.7 mmol) in toluene (150 mL)
were added NEt3 (1.62 mL, 11.7 mmol) and pure Ph2PCl (2.15
mL, 11.7 mmol). The reaction mixture turned cloudy and was stirred
for one week at room temperature, whereupon a voluminous white
precipitate formed. The solid was removed by filtration, and the
filtrate was taken to dryness in vacuo to afford 1ox as a pale yellow
paste (2.93 g, 10.81 mmol, 93%). Because of the instability of the
The former ligand3 and its substituted derivatives4 have
been successfully applied in several catalytic processes and
are usually obtained by multistep reactions involving (i)
lithiation of 2-methyl-2-oxazoline (mox), usually with n-BuLi
as a base, (ii) silylation with Me3SiCl, and (iii) phosphory-
lation with Ph2PCl. This protocol has been recently followed
for the preparation of 1th.5 The corresponding mononuclear
square-planar Ni(II) complexes [NiCl2(L)] (L ) 1ox or 1th)
were found to be in equilibrium with a paramagnetic
tetramer, which undergoes in the solid state an irreversible
pressure-induced fragmentation into the monomer.5 We shall
see below that 1ox and 1th can be more conveniently
synthesized in one-pot reactions from the corresponding
substrates and chlorophosphine in the presence of triethy-
lamine at room temperature, following nontrivial pathways
that involve stable intermediates. We shall also see that these
ligands, as well as their rearrangement products, readily form
a number of Pd(II) and Pt(II) complexes which have been
structurally characterized by X-ray diffraction.
reaction intermediate Ph2PCHd COCH2CH2NPPh2 (2ox) and the
very slow speed of the overall reaction described here, the
previously reported method, although featuring a multistep ma-
nipulation, is to be preferred for the synthesis of 1ox, and it yields
the ligand in a more reproducible manner.3f The spectroscopic data
of 1ox have been reported elsewhere.3f
Preparation and Spectroscopic Data for Ph2PCHd
COCH2CH2NPPh2 (2ox). To a solution of 2-methyl-2-oxazoline
(1.00 mL, 11.7 mmol) in toluene (150 mL) were added NEt3 (8.12
mL, 58.5 mmol) and pure Ph2PCl (4.30 mL, 22.4 mmol). The
reaction mixture turned cloudy and was stirred for 12 h at room
temperature, whereupon a voluminous white precipitate formed.
The reaction mixture was filtered, and the filtrate was taken to
dryness in vacuo at 38 °C (oil bath temperature) to afford a colorless
solid that was washed with Et2O (20 mL). Evaporation of the
volatiles afforded 2ox as a colorless solid (3.34 g, 7.4 mmol, 63%).
Single crystals of 2ox were obtained by layering pentane on its
saturated solution in toluene. In CH2Cl2, 2ox was found to
spontaneously and quickly isomerize to give (Ph2P)2-
Experimental Section
CHCdNCH2CH2O (3ox). This should be taken into account when
manipulating 2ox. Exposure of 2ox to alcohols should be avoided
because it quantitatively undergoes alcoholysis, with formation of
General Considerations. All manipulations were carried out
under inert dinitrogen atmosphere, using standard Schlenk-line
conditions and dried and freshly distilled solvents. Unless otherwise
1
stated, the H, 13C{1H}, and 31P{1H} NMR spectra were recorded
Ph2PCH2CdNCH2CH2O (1ox) and phosphinites. For similar reasons,
exposure of 2ox to moisture quickly results in the formation of 1ox
and Ph2P(O)PPh2. 1H NMR (C6D6): δ 3.29 (t, 2H, 3JH-H ) 7.2 Hz,
on a Bruker Avance 300 instrument at 300.13, 75.47, and 121.49
MHz, respectively, using TMS or H3PO4 (85% in D2O) as external
3
2
NCH2), 4.24 (t, 2H, JH-H ) 7.2 Hz, OCH2), 4.63 (dd, 1H, JH-P
(3) (a) Jie, S.; Agostinho, M.; Kermagoret, A.; Cazin, C. S. J.; Braunstein,
P. Dalton Trans. 2007, 4472–4482. (b) Braunstein, P.; Clerc, G.;
Morise, X.; Welter, R.; Mantovani, G. Dalton Trans. 2003, 1601–
1605. (c) Braunstein, P.; Clerc, G.; Morise, X. New. J. Chem. 2003,
27, 68–72. (d) Braunstein, P.; Naud, F.; Rettig, S. J. New. J. Chem.
2001, 25, 32–39. (e) Braunstein, P.; Graiff, C.; Naud, F.; Pfaltz, A.;
Tiripicchio, A. Inorg. Chem. 2000, 39, 4468–4475. (f) Braunstein,
P.; Fryzuk, M. D.; Le Dall, M.; Naud, F.; Rettig, S. J.; Speiser, F.
Dalton Trans. 2000, 1067–1074.
4
) 5.3 Hz, JH-P ) 3.1 Hz, PCH), 7.20-7.55 (m, 20H, aromatic).
31P{1H} NMR (C6D6): δ -27.1 (s, PC), 38.4 (s, PN). The 13C{1H}
spectrum of 2ox is not reported because under the conditions
necessary to record good quality spectra, 2ox was found to rapidly
isomerize to 3ox. Anal. Calcd for C28H25NOP2 (453.45): C, 74.16;
H, 5.56; N, 3.09. Found: C, 73.93; H, 5.50; N, 2.89.
(4) (a) Schrems, M. G.; Neumann, E.; Pfaltz, A. Angew. Chem., Int. Ed.
2007, 46, 8274–8276. (b) Speiser, F.; Braunstein, P.; Saussine, L.
Organometallics 2004, 23, 2633–2640. (c) Speiser, F.; Braunstein,
P.; Saussine, L.; Welter, R. Organometallics 2004, 23, 2613–2624.
(d) Braunstein, P.; Naud, F.; Graiff, C.; Tiripicchio, A. Chem. Commun.
2000, 897–898. (e) Lloyd-Jones, G. C.; Pfaltz, A. Z. Naturforsch., B:
Chem. Sci. 1995, 50, 361–367. (f) Sprinz, J.; Helmchen, G. Tetrahe-
dron Lett. 1993, 34, 1769–1772.
(6) Cope, A. C.; Friedrich, E. C. J. Am. Chem. Soc. 1968, 90, 909.
(7) (a) Hartley, F. R. The Chemistry of Platinum and Palladium; Applied
Science Publishers: London, 1973. (b) Braunstein, P.; Bender, R.; Jud,
J.-M. Inorg. Synth. 1989, 26, 341–350.
(8) Drew, D.; Doyle, J. R. Inorg. Synth 1990, 28, 346–349.
(9) Clark, H. C.; Manzer, L. E. J. Organomet. Chem. 1973, 59, 411–428.
(10) Dekker, G. P. C. M.; Buijs, A.; Elsevier, C. J.; Vrieze, K.; van
Leeuwen, P. W. N. M.; Smeets, W. J. J.; Spek, A. L.; Wang, Y. F.;
Stam, C. H. Organometallics 1992, 11, 1937–1948.
(5) Kermagoret, A.; Pattacini, R.; Vasquez, P. C.; Rogez, G.; Welter, R.;
Braunstein, P. Angew. Chem., Int. Ed. 2007, 119, 6558–6561.
Inorganic Chemistry, Vol. 47, No. 21, 2008 9887

Pattacini et al.
Preparation and Spectroscopic Data for (Ph2P)2-
by layering hexane onto a solution of 4 in CH2Cl2 (0.33 g, 0.30
mmol, 68% based on Pt). 1H NMR (CDCl3): δ 3.52 (second order
CHCdNCH2CH2O (3ox). Solid 2ox was dissolved in a minimum
amount of CH2Cl2. The colorless solution was stirred overnight
under nitrogen. The volatiles were removed under vacuum, afford-
ing 3ox as a colorless oil (NMR yield: 97%). 1H NMR (CDCl3): δ
3
t, 4H, simulated JH-H ) 8.4, NCH2), 3.81 (second order t, 4H,
simulated 3JH-H ) 8.4 Hz, OCH2), 7.05-7.50 (m, 20H, aromatic).
1
31P{1H} NMR (CDCl3): δ -33.7 (s, with 195Pt satellites, JP-Pt
)
1940 Hz). 13C{1H} NMR (CDCl3): δ 31.0 (s, P-C-P), 52.5 (s,
br, NCH2), 66.3 (s, OCH2), 128.0-133.0 (m, aromatic), 167.7 (s,
3
3.34 (second order t, 2H, simulated JH-H ) 9.0 Hz, NCH2), 3.45
3
(second order t, 2H, simulated JH-H ) 9.0 Hz, OCH2), 4.39 (s,
with 195Pt satellites, JC-Pt ) 39.4 Hz, C)N). Anal. Calcd for
3
1H, PCH), 7.10-7.70 (m, 10H, aromatic). 31P{1H} NMR (CDCl3):
C56H48N2O2P4Pt (1099.97): C, 61.15; H, 4.40; N, 2.55. Found: C,
60.89; H, 4.12; N, 2.18.
2
δ -9.25 (s). 13C{1H} NMR (CDCl3): δ 37.9 (t, JP-C ) 28.3 Hz,
3 +
PCHP), 54.1 (s, NCH2), 66.9 (s, OCH2), 128.0 (virtual triplet,
3 + 5
Preparation and Spectroscopic Data for [PtI(Me)(1ox)] (5).
To a solution of [PtI(Me)(cod)] (0.150 g, 0.34 mmol) in CH2Cl2
(20 mL) was added 1ox (0.091 g, 0.34 mmol), and the mixture was
stirred for 2 h. The pale yellow solution turned colorless, and after
it was concentrated under reduced pressure, pentane was added to
precipitate a colorless powder. The crude product was washed with
pentane and dried in vacuo to afford 5 (0.196 g, 0.32 mmol, 95%).
Single crystals suitable for X-ray analysis were obtained at room
temperature by slow diffusion of heptane into a solution of 5 in
5JP-C ) 6.7 Hz, m-Ph), 128.3 (virtual triplet,
J
) 7.5 Hz,
P-C
2
+
m-Ph), 129.1 (s, p-Ph), 129.3 (s, p-Ph), 133.9 (virtual triplet,
2 + 4
4JP-C ) 21.5 Hz, o-Ph), 134.2 (virtual triplet,
J
) 22.8 Hz,
P-C
1
+
o-Ph), 135.9 (virtual triplet,
3JP-C ) 9.8 Hz, ipso-Ph), 136.8
1 + 3
(virtual triplet,
J
P-C
) 8.8 Hz, ipso-Ph), 164.9 (t, 2JP-C ) 3.5
Hz, CdN). The oily nature of 3ox and its sensitivity toward
hydrolysis prevented obtention of satisfactory elemental analyses.
1
Its purity was checked by 31P, H, and 13C NMR spectroscopic
methods.
1
toluene. H NMR (CD2Cl2): δ 0.75 (d, with 195Pt satellites, 3H,
Preparation and Spectroscopic Data for Ph2PCH2-
2
3JH-P ) 4.0 Hz, JH-Pt ) 75.4 Hz, CH3), 3.29 (dt, with 195Pt
CdNCH2CH2S (1th). To a solution of 2-methyl-2-thiazoline (0.40
mL, 4.16 mmol) in toluene (100 mL) was added NEt3 (0.58 mL,
4.16 mmol), and the clear solution was stirred for 5 min. After
addition of Ph2PCl (0.76 mL, 4.16 mmol), the reaction mixture
turned cloudy and was further stirred for 1 h at room temperature,
whereupon a voluminous white precipitate formed. The mixture
was filtered off, and the filtrate was taken to dryness in vacuo. The
oily, crude product was dissolved in a minimum amount of toluene,
and this solution was added dropwise to stirred, cold pentane to
afford a pale yellow powder that was collected by filtration and
dried in vacuo to afford 1th (0.950 g, 3.33 mmol, 80%). Single
crystals of 1th suitable for X-ray diffraction were obtained upon
storing the crude product under N2. The spectroscopic data of 2th
have been published elsewhere.5 Anal. Calcd for C16H16NPS
(285.34): C, 67.35; H, 5.65; N, 4.91. Found: C, 67.27; H, 5.33; N,
4.41.
satellites, 2H, 2JH-P ) 10.1 Hz, 5JH-H ) 2.0 Hz, 3JH-Pt ) 25.1 Hz,
PCH2), 4.21 (tt, 2H, 3JH-H ) 9.7 Hz, 5JH-H ) 2.0 Hz, NCH2), 4.60
3
(t, 2H, JH-H ) 9.7 Hz, OCH2), 7.40-7.79 (m, 10H, aromatic).
13C{1H} NMR (CDCl3): δ -25.0 (d, with 195Pt satellites, 1JC-Pt
)
606 Hz, 2JC-P ) 5.3 Hz, CH3), 31.5 (d, with 195Pt satellites, 2JC-Pt
1
) 14.4 Hz, JP-C ) 38.0 Hz, PCH2), 56.0 (s, with 195Pt satellites,
3
2JC-Pt ) 15.9 Hz, NCH2), 73.5 (s, with 195Pt satellites, JC-Pt
)
12.9 Hz, OCH2), 128.0-134.0 (m, aromatic, PPh2), 176.2 (s, with
195Pt satellites, 2JP-C ) 14.7 Hz, CdN). 31P{1H} NMR (CDCl3): δ
1
12.0 (s, with 195Pt satellites, JP-Pt ) 4423 Hz). Anal. Calcd for
C17H19INOPPt (606.29): C, 33.68; H, 3.16; N, 2.31. Found: C,
33.31; H, 3.01; N, 2.20.
Preparation and Spectroscopic Data for [PtCl(Me)(1ox)]
(6). To a solution of [PtCl(Me)(cod)] (0.120 g, 0.340 mmol) in
CH2Cl2 (20 mL) was added 1ox (0.091 g, 0.34 mmol), and the
mixture was stirred for 2 h. The pale yellow solution turned
colorless, and after it was concentrated under reduced pressure,
pentane was added to precipitate a colorless powder. The crude
product was washed with pentane and dried in vacuo to afford 6
(0.160 g, 0.31 mmol, 92%). Single crystals suitable for X-ray
analysis were obtained at room temperature by slow diffusion of
heptane into a solution of 6 in benzene. 1H NMR (CD2Cl2): δ 0.49
Preparation and Spectroscopic Data for Ph2PCHd
CSCH2CH2NPPh2 (2th). To a stirred solution of 1th (0.450 g, 1.58
mmol) in THF (10 mL) were added successively NEt3 (0.22 mL,
1.58 mmol) and Ph2PCl (0.29 mL, 1.58 mmol), whereupon the
initially clear yellow solution turned cloudy. After it was stirred
for 1 h at room temperature, the reaction mixture was filtered
through a Schlenk frit directly into a Schlenk flask containing cold
pentane (200 mL). Ligand 2th was collected in two crops, filtered,
and dried in vacuo (0.497 g, 1.06 mmol, 67%). 1H NMR (CDCl3):
δ 2.96 (t, 2H, 3JH-H ) 6.5 Hz, SCH2), 3.49 (tdd, 2H, 3JH-H ) 6.5
Hz, 5JP-H ) 2.4 Hz, 5JH-H ) 0.4 Hz, NCH2), 5.75 (ddt, 1H, 2JP-H
) 5.0 or 4.5 Hz, 4JP-H ) 4.5 or 5.0 Hz, 5JH-H ) 0.4 Hz, simulated,
PCH), 7.24-7.47 (m, 20H, aromatic). 31P{1H} NMR (CDCl3): δ
-13.2 (s, PC), 41.4 (s, PN). Anal. Calcd for C28H25NP2S (M )
469.52): C, 71.63; H, 5.37; N, 2.98. Found: C, 71.67; H, 5.86; N,
2.42.
Preparation and Spectroscopic Data for [Pt(3ox-H)2] (4). Pure
NEt3 (0.30 mL, 2.14 mmol) was added to a solution of freshly
prepared 3ox (0.45 g, 1.00 mmol), in dry acetonitrile (20 mL). After
addition of [PtCl2(NCPh)2] (0.21 g, 0.44 mmol), the reaction mixture
was stirred for 3 h, during which the formation of a yellow
precipitate was observed. The yellow solid 4 was collected by
filtration, washed with MeCN (3 × 5 mL), and dried under vacuum.
Complex 4 can be recrystallized by slow evaporation from a
saturated 1:1 CH2Cl2/hexane solution, affording 4·4CH2Cl2. Single
crystals of 4·4CH2Cl2 suitable for X-ray analysis were obtained
3
2
(d, with 195Pt satellites, 3H, JH-P ) 3.2 Hz, JH-Pt ) 74.1 Hz,
CH3), 3.26 (d, with 195Pt satellites, 2H, 2JH-P ) 10.0 Hz, 3JH-Pt
)
25.0 Hz, PCH2), 4.07 (t, 2H, 3JH-H ) 9.8 Hz, NCH2), 4.14 (t, 2H,
3JH-H ) 9.8 Hz, OCH2), 7.40-7.75 (m, 10H, aromatic). 13C{1H}
NMR (CDCl3): δ -20.9 (d, with 195Pt satellites, JC-P ) 6.2 Hz,
2
1JC-Pt ) 639 Hz, CH3), 31.5 (d, with 195Pt satellites, 1JP-C ) 39.6
Hz, JC-Pt ) 12 Hz, PCH2), 52.1 (s, with 195Pt satellites, JC-Pt
)
2
2
12 Hz, NCH2), 72.9 (s, with 195Pt satellites, 3JC-Pt ) 11 Hz, OCH2),
128.0-133.7 (m, aromatic, PPh2), 175.2 (d, with 195Pt satellites,
2JP-C ) 14.3 Hz, JP-Pt ) 94 Hz, C)N). 31P{1H} NMR (CDCl3):
2
δ 13.36 (s, with 195Pt satellites, 1JP-Pt ) 4573 Hz). Anal. Calcd for
C17H19ClNOPPt (514.84): C, 39.66; H, 3.72; N, 2.72. Found: C,
39.40; H, 3.79; N, 2.65.
Preparation and Spectroscopic Data for [PtMe2(1ox)] (7). To
a solution of [PtMe2(cod)] (0.200 g, 0.60 mmol) in CH2Cl2 (20
mL) was added 1ox (0.162 g, 0.60 mmol), and the mixture was
stirred for 2 h. The pale yellow solution turned colorless, and after
it was concentrated under reduced pressure, pentane was added to
precipitate a colorless powder. The crude product was washed with
pentane and dried in vacuo to afford 7 (0.258 g, 0.522 mmol, 87%).
9888 Inorganic Chemistry, Vol. 47, No. 21, 2008

Formation of P-C Bonds
Single crystals suitable for X-ray analysis were obtained at room
temperature by slow diffusion of heptane into a solution of 7 in
toluene. 1H NMR (C6D6): δ 1.44 (d, with 195Pt satellites, 3H, 3JH-P
125.1 (d, JP-C ) 5.1 Hz, aryl, dmba), 128.1-133.3 (m, aromatic,
PPh2), 135.6 (d, 1JP-C ) 54.0 Hz, ipso-aryl), 138.0 (d, JP-C ) 10.3
Hz, aryl, dmba), 148.7 (s, Cq-dmba), 150.1 (s, Cq-dmba), 175.0 (d,
2JP-C ) 27.9 Hz, CN). 13C{1H} NMR (C6D6): δ 34.9 (s, SCH2),
49.4 (s, N(CH3)2, dmba), 57.4 (d, 1JP-C ) 66.9 Hz, PCH), 59.6 (s,
NCH2), 73.2 (s, NCH2, dmba), 122.5 (s, aryl, dmba), 123.7 (s, aryl,
dmba), 125.5 (d, JP-C ) 5.1 Hz, aryl, dmba), 129.3-133.5 (m,
2
) 8.2 Hz, JH-Pt ) 71.0 Hz, trans-CH3-Pt-P), 1.60 (d, with 195Pt
3
2
satellites, 3H, JH-P ) 7.5 Hz, JH-Pt ) 89.3 Hz, cis-CH3-Pt-P),
2
3.29 (d, 2H, JH-P ) 8.4 Hz, PCH2), 3.35 (m, 4H, SCH2, NCH2),
6.90-7.69 (m, 10H, aromatic). 13C{1H} NMR (C6D6): δ -22.6
(d, with 195Pt satellites, 1JC-Pt ) 761 Hz, 2JC-P ) 4.9 Hz, cis-CH3-
Pt-P), -7.4 (d, with 195Pt satellites, 1JC-Pt ) 695 Hz, 2JC-P ) 112.8
1
aromatic, PPh2), 135.9 (d, JP-C ) 54.3 Hz, ipso-aryl), 138.4 (d,
JP-C ) 9.7 Hz, aryl, dmba), 148.4 (s, Cq-dmba), 150.7 (d, JP-C
)
1
Hz, trans-CH3-Pt-P), 30.2 (d, JP-C ) 25.6 Hz, PCH2), 51.6 (d,
2.8 Hz, Cq-dmba), 175.5 (d, 2JP-C ) 27.9 Hz, C)N). 31P{1H} NMR
(CD2Cl2): δ 38.1 (s); 31P{1H} NMR (C6D6): δ 37.7 (s). Anal. Calcd
for C25H27N2PPdS (524.95): C, 57.20; H, 5.18; N, 5.34. Found: C,
57.51; H, 4.86; N, 5.34.
with 195Pt satellites, JC-P ) 2.1 Hz, JC-Pt ) 24.0 Hz, NCH2),
3
2
70.6 (s, with 195Pt satellites, 4JC-Pt ) 12.3 Hz, OCH2), 127.5-134.0
(m, aromatic, PPh2), 177.1 (d, JP-C ) 24.7 Hz, CdN). 31P{1H}
2
1
NMR (C6D6): δ 19.6 (s, with 195Pt satellites, JP-Pt ) 1871 Hz).
Preparation and Spectroscopic Data for [9 ·{Pd(dmba-
C,N)Cl}] (10). To a solution of 10 (0.098 g, 0.187 mmol) in THF
(20 mL) was added [Pd(dmba-C,N)(µ-Cl)]2 (0.051 g, 0.093 mmol),
and the mixture was stirred overnight. The red-brown solution
turned orange, and after it was concentrated under reduced pressure,
pentane was added to precipitate a beige brown powder. The crude
product was washed with pentane and dried in vacuo to afford 10
(0.140 g, 0.175 mmol, 93.5%). Single crystals suitable for X-ray
analysis were obtained at room temperature by slow diffusion of
Anal. Calcd for C18H22NOPPt (494.4): C, 43.73; H, 4.48; N, 2.83.
Found: C,43.95; H, 4.40; N, 2.76.
Preparation and Spectroscopic Data for [Pd(dmba-C,N)-
(1th)]OTf (8). A solution prepared by addition of solid AgSO3CF3
(0.643 g, 2.50 mmol) to a solution of [Pd(dmba)(µ-Cl)]2 (0.690 g,
1.25 mmol) in THF (50 mL), was filtered via cannula into a solution
of 1th (0.855 g, 3.00 mmol) in THF (30 mL). The yellow solution
was stirred overnight at room temperature, whereupon its color
changed to orange. The volume of the solution was reduced under
vacuum to about 5 mL. The addition of pentane led to the
precipitation of an orange solid, which was washed with pentane
and dried in vacuo (1.550 g, 2.30 mmol, 92% based on Pd). Single
crystals suitable for X-ray analysis were obtained at room temper-
ature by slow diffusion of diethyl ether into a CHCl3 solution of
1
heptane into a solution of 10 in benzene (NMR tube). H NMR
(CD2Cl2): δ 2.28 (s, 3H, NCH3, dmba Pd1), 2.46 (s, 3H, NCH3,
4
dmba Pd1), 2.64 (d, JP-H ) 1.4 Hz, 3H, NCH3, dmba Pd2), 3.09
4
(d, 3H, JP-H ) 3.1 Hz, NCH3, dmba Pd2), 3.32-3.47 (m, 6H,
3JH-H ) 2.4 Hz, 3 CH2), 4.05 (m, 2H, CH2), 4.75 (d, 1H, 2JP-H
)
1
4
13.0 Hz, PCHPd2), 6.50-7.95 (m, 18H, aryl). 31P{1H} NMR
(C6D6): δ 56.1 (s). Anal. Calcd for C34H39ClN3PPd2S (801.03): C,
50.98; H, 4.91; N, 5.25. Found: C, 49.26; H, 4.92; N, 4.43.
the complex. H NMR (CDCl3): δ 2.95 (d, 6H, JP-H ) 3.0 Hz,
N(CH3)2), 3.65 (t, 2H, 3JH-H ) 8.7 Hz, SCH2), 3.74 (d, 2H, 2JP-H
4
) 11.1 Hz, PCH2), 4.06 (d, 2H, JP-H ) 1.8 Hz, NCH2, dmba),
3
4.49 (t, 2H, JH-H ) 8.7 Hz, NCH2), 6.46-7.04 (m, 4H, aryls,
X-ray Data Collection, Structure Solution, and Refinement
for All Compounds. Suitable crystals for the X-ray analysis of
compounds 1th, 2ox, 2th, 4·4CH2Cl2, 5, 7, 8·0.25C4H10O, 9, and
10·2.5C6H6 were obtained as described above. The intensity data
was collected at 173(2) K on a Kappa CCD diffractometer11
(graphite-monochromated Mo KR radiation, λ ) 0.71073 Å).
Crystallographic and experimental details for the structures are
summarized in Tables 1 and 2. The structures were solved by direct
methods (SHELXS-97) and refined by full-matrix least-squares
procedures (based on F2, SHELXL-97)12 with anisotropic thermal
parameters for all the non-hydrogen atoms. The hydrogen atoms
were introduced into the geometrically calculated positions (SHELXS-
97 procedures) and refined riding on the corresponding parent
atoms. For 2ox, a residual difference electron density peak of 2.43 e
Å-3 was located at ∼1.38 Å from P1. Although the lone pair of P2
gave rise to a well localized electron density peak too, the latter
was very weak when compared to that close to P1. The model has
therefore been refined as a 0.7/0.3 mixture of 2ox and its mono-
oxide, respectively. An ORTEP plot, also displaying the oxygen
ellipsoid is reported in the Supporting Information for this paper.
CCDC 687225 (1th), 699172 (2ox), 687226 (2th), 687227
(4·4CH2Cl2), 687228 (5), 687229 (7), 687230 (8·0.25C4H10O),
687231 (9), and 687232 (10·2.5C6H6) contain the crystallographic
data for this paper that can be obtained free of charge from the
Cambridge Crystallographic Data Center via www.ccdc.cam.ac.uk/
datarequest/cif.
dmba), 7.47-7.79 (m, 10H, aryls, PPh2). 13C{1H} NMR (CDCl3):
δ 35.2 (s, SCH2), 39.3 (d, 1JP-C ) 28.8 Hz, PCH2), 51.1 (s, N(CH3)2,
3
dmba), 63.5 (s, NCH2), 72.6 (d, JP-C ) 2.6 Hz, NCH2, dmba),
123.3 (s, aryl, dmba), 125.3 (s, aryl, dmba), 126.2 (d, 1JP-C ) 50.8
Hz, ipso-aryl), 126.4 (d, JP-C ) 6.6 Hz, aryl, dmba), 129.6 (d, 3JP-C
) 11.3 Hz, m-aryls), 132.6 (d, 4JP-C ) 2.4 Hz, p-aryls), 133.9 (d,
2JP-C ) 12.5 Hz, o-aryls), 138.2 (d, JP-C ) 13.3 Hz, aryl, dmba),
145.6 (s, Cq-dmba), 148.1 (s, Cq-dmba), 181.5 (d, 2JP-C ) 6.8 Hz,
C)N). 19F{1H} NMR (CDCl3): δ -78.5 (s, SO3CF3). 31P{1H} NMR
(CDCl3): δ 45.8 (s). Anal. Calcd for C26H28F3N2O3PPdS2 (675.03):
C, 46.26; H, 4.18; N, 4.15. Found: C, 46.97; H, 4.45; N, 3.64.
Preparation and Spectroscopic Data for [Pd(dmba-C,N)-
(1th-H)] (9). To a solution of 8 (0.635 g, 0.94 mmol) in THF (100
mL) was added t-BuOK (0.267 g, 2.38 mmol), and the mixture
was stirred overnight. The red-brown solution was filtered, and the
filtrate was taken to dryness in vacuo. The resulting solid was
extracted with toluene. The extract was concentrated under vacuum,
and pentane was added to precipitate a beige powder (0.482 g, 0.92
mmol, 97.7%). Single crystals suitable for X-ray analysis were
obtained at room temperature by slow diffusion of heptane into a
benzene solution of 9. 1H NMR (CD2Cl2): δ 2.84 (d, 6H, 4JP-H
)
3.6 Hz, N(CH3)2, dmba), 3.34 (t, 2H, 3JH-H ) 6.9 Hz, SCH2), 3.37
(d, 1H, 2JP-H ) 3.6 Hz, PCH), 3.97 (t, 2H, 3JH-H ) 6.9 Hz, NCH2),
3.98 (s, 2H, NCH2, dmba), 6.61-7.10 (m, 4H, aryl, dmba),
1
7.34-7.74 (m, 10H, aromatic). H NMR (C6D6): δ 2.07 (d, 6H,
3
4JP-H ) 2.4 Hz, N(CH3)2), 3.04 (t, 2H, JH-H ) 6.9 Hz, SCH2),
3
3.37 (bs, 2H, NCH2, dmba), 3.56 (t, 2H, JH-H ) 6.9 Hz, NCH2),
2
3.79 (d, 1H, JP-H ) 3.9 Hz, PCH), 6.78-7.92 (m, 14H, aryl).
(11) Bruker-Nonius. Kappa CCD Reference Manual; Nonius BV: Delft:
The Netherlands, 1998.
(12) Sheldrick., M.; SHELXL-97, Program for Crystal Structure Refinement;
University of Go¨ttingen: Go¨ttingen, Germany, 1997.
13C{1H} NMR (CD2Cl2): δ 34.9 (s, SCH2), 50.4 (s, N(CH3)2, dmba),
57.4 (d, 1JP-C ) 65.7 Hz, PCH), 59.6 (s, NCH2), 73.4 (d, 3JP-C
)
2.5 Hz, NCH2, dmba), 122.5 (s, aryl, dmba), 123.6 (s, aryl, dmba),
Inorganic Chemistry, Vol. 47, No. 21, 2008 9889

Pattacini et al.
Table 1. Data Collection and Refinement Parameters for 1th, 2th, 4·4CH2Cl2, and 5
compound
formula
Mr
cell setting
space group
a (Å)
b (Å)
c (Å)
R (deg)
ꢁ (deg)
γ (deg)
V (Å3)
1th
2th
2ox
4·4CH2Cl2
5
C16H16NPS
285.33
monoclinic
P21/c
11.6510(4)
8.0670(3)
16.3080(7)
90
109.814(2)
90
1442.0(1)
4
C28H25NP2S
469.49
triclinic
C28H25NP2O
461.43
C56H48N2O2P4Pt·4(CH2Cl2)
C17H19INOPPt
606.29
triclinic
1439.64
triclinic
triclinic
j
j
j
j
P1
P1
P1
P1
10.0750 (5)
10.2980 (5)
12.5970 (9)
72.097(2)
77.206(2)
79.831(4)
1204.49 (12)
2
8.712(1)
11.500(1)
12.651(1)
80.151(6)
76.242(7)
77.920(5)
1194.0(2)
2
9.8628(1)
12.5690(2)
13.3269(2)
75.749(1)
73.261(1)
74.076(1)
1496.0(4)
1
11.7825(4)
12.2252(5)
12.8954(5)
92.310(2)
94.819(2)
105.997(2)
1775.35(12)
4
Z
Dx (Mg m-3
)
1.314
0.32
1.295
0.28
1.283
0.20
1.598
2.85
2.268
9.73
µ (mm-1
)
cryst size (mm)
measured reflns
independent reflns
obsd reflns
Rint
0.11 × 0.09 × 0.08
0.12 × 0.1 × 0.08
0.1 × 0.06 × 0.01
0.05 × 0.05 × 0.04
16 852
6853
6780
0.042
0.04 × 0.04 × 0.03
6126
7581
6272
21 754
3861
2818
0.041
4997
2648
0.057
4218
2607
0.045
10 312
7858
0.053
θmax (deg)
R[F2 > 2σ(F2)]
Rw(F2)
29.2
0.062
0.106
26.5
0.064
0.133
25.05
0.072
0.130
27.5
0.026
0.060
30.0
0.044
0.112
S
1.06
0.98
1.105
1.05
1.08
params
172
289
299
349
399
Table 2. Data Collection and Refinement Parameters for 7, 8·0.25C4H10O, 9, and 10·2.5C6H6
compound
formula
Mr
cell setting
space group
a (Å)
b (Å)
c (Å)
R (deg)
ꢁ (deg)
γ (deg)
V (Å3)
7
8·0.25C4H10O
9
10·2.5C6H6
C18H22NOPPt
494.43
monoclinic
P21
11.5550(4)
12.4293(4)
12.1149(5)
90
97.721(2)
90
1724.17(11)
4
4(C25H28N2PPdS)·4(CF3O3S)·C4H10O
C25H27N2PPdS
524.92
triclinic
C34H39ClN3PPd2S·2.5(C6H6)
1387.05
triclinic
996.23
triclinic
j
j
j
P1
P1
P1
9.6076(1)
12.7675(1)
25.3804(4)
96.3772(4)
92.9540(4)
107.7705(7)
2934.37(6)
2
9.661(1)
10.901(2)
12.780(2)
111.414(1)
110.096(1)
90.230(1)
1163.75(3)
2
11.3551(1)
13.7549(2)
16.4871(2)
101.481(1)
104.670(1)
107.821(1)
2262.18(5)
2
Z
Dx (Mg m-3
)
1.905
8.23
1.570
0.88
1.498
0.97
1.463
0.97
µ (mm-1
)
cryst size (mm)
measured reflns
independent reflns
obsd reflns
Rint
0.04 × 0.03 × 0.03
13 581
9287
8639
0.055
0.07 × 0.07 × 0.03
0.05 × 0.05 × 0.05
0.10 × 0.10 × 0.10
31 900
9969
20 839
12 127
9078
0.045
6784
6147
0.017
13 105
9381
0.032
θmax (deg°)
R[F2 > 2σ(F2)]
Rw(F2)
30.0
0.047
0.120
26.5
0.045
0.140
30.1
0.027
0.064
30.0
0.041
0.093
S
1.00
1.07
1.05
1.04
params
401
739
273
518
Computational Details. All calculations were done using the
program system TURBOMOLE.13 If not mentioned explicitly
otherwise, we used the DFT method with the Becke-Perdew
functional (BP86).14 The Coulomb terms were treated by the RI-J
approximation.15 For the structure optimizations, we used SV(P)
basis sets16 (single-ꢀ for core orbitals, double-ꢀ for the valence
shells and one set of polarization functions for all centers except
hydrogen). Single-point energies were calculated with larger triple-ꢀ
valence plus polarization basis sets (TZVP).17 The Cartesian
coordinates of the optimized models and the total energies,
computed with BP86/SV(P) and BP86/TZVP methods/bases are
reported in the Supporting Information. The absolute and relative
energies correspond to the most stable conformations.
Results and Discussion
Ligand Synthesis. In an attempt to develop simple access
to the phosphine ligand Ph2PCH2CdNCH2CH2O (1ox) and
its analogous thiazoline derivative Ph2PCH2CdNCH2CH2S
(1th), mox, and 2-methyl-2-thiazoline (mth) were reacted in
toluene with Ph2PCl in the presence of NEt3. The products
of these reactions are depicted in Scheme 2.
Surprisingly, even when mox and Ph2PCl were reacted in
a 1:1 ratio, in the presence of NEt3, the diphosphine ligand
(13) Ahlrichs, R.; Ba¨r, M.; Ha¨ser, M.; Horn, H.; Ko¨lmel, C. Chem. Phys.
Lett. 1989, 162, 165–169.
(14) Becke, A. D. Phys. ReV. 1988, A38, 3098–3100.
(15) Eichkorn, K.; Treutler, O.; Ohm, H.; Ha¨ser, M.; Ahlrichs, R. Chem.
Phys. Lett. 1995, 240, 283–290.
(16) Scha¨fer, A.; Horn, H.; Ahlrichs, R. J. Chem. Phys. 1992, 97, 2571–
2577.
Ph2PCHdCOCH2CH2NPPh2 (2ox) was observed as the major
(17) Scha¨fer, A.; Huber, C.; Ahlrichs, R. J. Chem. Phys. 1994, 100, 5829–
5835.
(18) (a) Kondoh, A.; Yorimitsu, H.; Oshima, K. Org. Lett. 2007, 9, 1383.
(b) Morise, X.; Braunstein, P.; Welter, R. Inorg. Chem. 2003, 42, 7752.
9890 Inorganic Chemistry, Vol. 47, No. 21, 2008

Formation of P-C Bonds
Scheme 2
product of the reaction after 12 h reaction time, instead of
Figure 1. ORTEP plot of the molecular structures of compound 2ox. H
atoms omitted for clarity. Displacement parameters include 50% of the
electron density. Selected bond distances (Å) and angles (deg): N1-C1,
1.472(5); C2-O1, 1.445(5); C3-C4, 1.332(5); N1-C3, 1.391(5); C3-O1,
1.363(4); P1-C4, 1.784(4); P2-N1, 1.718(3); C3-N1-C1, 109.8(3);
C3-N1-P2, 122.5(3); C1-N1-P2, 126.1(3); C3-O1-C2, 109.6(3);
C(3)-C(4)-P(1), 122.7(3); C(4)-C(3)-O(1), 121.1(3); N(1)-C(3)-C(4),
129.9(4); N(1)-C(3)-O(1), 109.1(3).
the expected monophosphine Ph2PCH2CdNCH2CH2O (1ox).
This is also the case when a deficiency of Ph2PCl was used.
When the reaction between mox, Ph2PCl, and NEt3 was
carried out in a 1:1:1 ratio, it proceeded over 1 week to give
1ox in high yield. It was shown independently that diphos-
phine 2ox slowly reacts with mox to form two molecules of
1ox.
When, in the same reaction, Ph2PCl was added dropwise
to a large excess of mox, formation of 2ox and traces of the
monophosphine 1ox were observed by in situ 31P{1H} NMR
spectroscopy, suggesting that under these conditions, the
reaction is under kinetic control. The reaction of a second
equivalent of Ph2PCl with 1ox is much faster than the reaction
of mox with Ph2PCl. Similar observations were made with
the thiazoline system, although in this case the reaction
leading to 2th is faster (vide infra).
Diphosphine 2ox was prepared in good yields by a 2:1
reaction of Ph2PCl with mox or by reaction of 1ox with
Ph2PCl, under the conditions described above. Ligand 2ox
rapidly degrades when exposed to traces of water or alcohols
to form Ph2P(dO)PPh2 and phosphinites, respectively, along
with 1ox. Moreover, when dissolved in chlorinated solvents
such as CH2Cl2 or CHCl3, 2ox rapidly isomerizes to the
geminal diphosphine 3ox.
The reaction of mth with Ph2PCl proceeds similarly to that
of mox, although in this case the rearrangement leading to
a geminal diphosphine similar to 3ox was not observed. The
crystal structures of 2ox, 2th, and 1th have been determined
by single-crystal X-ray diffraction (Figures 1-3).
The bonding parameters in these molecules are as ex-
pected, with the P2-N1 distances in anti-diphosphines 2ox
and 2th (1.718(3) and 1.718(2) Å, respectively) being shorter
than the P1-C4 ones (P1-C4 1.784(4), 1.771(3), and
1.862(2) Å for 2ox, 2th, and 1th, respectively). This may
suggest a contribution of the lone pair on N1 to the bonding
with P2. Diphosphines 2ox and 2th adopt slightly different
conformations, the P1 atom being closer to the chalcogen in
Figure 2. ORTEP plot of the molecular structures of compound 2th. H
atoms omitted for clarity. Displacement parameters include 50% of the
electron density. Selected bond distances (Å) and angles (deg): C(1)-N(1),
1.453(4); C(2)-S(1), 1.770(3); C(3)-C(4), 1.342(4); C(3)-N(1), 1.378(3);
C(3)-S(1), 1.749(3); C(4)-P(1), 1.771(3); N(1)-P(2), 1.718(2); C(1)-
N(1)-C(3), 114.9(2); C(3)-N(1)-P(2), 117.5(2); C(1)-N(1)-P(2), 126.8(2);
C(2)-S(1)-C(3), 92.5(1); C(3)-C(4)-P(1), 122.7(2); C(4)-C(3)-S(1),
123.1(2); N(1)-C(3)-C(4), 126.6(3); N(1)-C(3)-S(1), 110.3(2).
hydrogen atom on C4 in 2ox than in 2th (P2-C4 distances,
3.199(5) and 3.015(2) Å for 2ox and 2th, respectively). As a
consequence, the P2 lone pair of 2ox is deviated outside the
C4-C3-N1 plane (C3-N1-P2-C23 torsion angle, 132.2(4)°
in 2ox and 177.7(3)° in 2th).
2ox than in 2th (P1 · · ·O1 distance in 2ox, 3.023(3) Å; P1 · · ·S1
distance in 2th, 3.258(1) Å). Moreover, P2 is closer to the
Inorganic Chemistry, Vol. 47, No. 21, 2008 9891

Pattacini et al.
of 1 by a fast H/PPh2 exchange on a sp3 carbon, without
prior deprotonation, is an unreasonable hypothesis. Two
possible alternative mechanisms are proposed in Scheme 3
and discussed below: (a) an electrophilic attack of Ph2PCl
could occur first at the nitrogen, with intermediate formation
of the unobserved aminophosphines iox and ith, which would
then undergo a second attack of the chlorophosphine, to give
2ox and 2th, respectively; (b) the enamine forms moxe and
mthe could be phosphorylated on the exocyclic carbon,
forming 1ox and 1th, which rapidly react with Ph2PCl to give
the two respective diphosphines.
Mechanism 3a is similar to that proposed for the reaction
between mox and acid chlorides ClC(O)R (R ) alkyl), which
afforded diacyl derivatives of the general formula RC(dO)-
CHdCOCH2CH2NC(dO)R.20 Mechanism 3b would imply
that NEt3, prior to HCl scavenging, promotes the presence
of the more reactive enamino tautomers of mox and mth
(moxe and mthe, respectively, Scheme 3). Although mech-
anism 3a cannot be ruled out, some observations are more
in favor of pathway 3b: (i) No reaction was observed between
2-methyl-2-benzoxazole and Ph2PCl in the presence of NEt3.
In this case, the enamino tautomer is too disfavored by the
decreased basicity of the endocyclic nitrogen. (ii) The
hypothetical aminophosphines iox and ith were not observed
in the reaction mixture. (iii) When mox and Ph2PCl were
stirred in the absence of a base, no trace of cationic
aminophosphine was detected. The last step of mechanism
3b was independently achieved, with monophosphines 1ox
and 1th rapidly reacting with Ph2PCl to afford 2ox and 2th,
respectively. When pyridine was used instead of NEt3, no
reaction was observed. Although pyridine itself is an efficient
HCl scavenger, its lower Lewis basicity, when compared to
that of NEt3, is probably not sufficient for the formation of
the enamino tautomers in mechanism 3b. However, it may
also not be sufficient to achieve the deprotonation step in
mechanism 3a.
Figure 3. ORTEP plot of the molecular structures of compound 1th. H
atoms omitted for clarity. Displacement parameters include 50% of the
electron density. Selected bond distances (Å) and angles (deg): C(1)-C(2),
1.518(3); C(1)-N(1), 1.469(3); C(2)-S(1), 1.785(3); C(3)-C(4), 1.492(3);
C(3)-N(1), 1.264(2); C(3)-S(1), 1.774(2); C(4)-P(1), 1.862(2); C(1)-
N(1)-C(3), 112.4(2); C(2)-S(1)-C(3), 90.6(1); C(3)-C(4)-P(1), 112.7(2);
C(4)-C(3)-S(1), 117.8(2); N(1)-C(3)-C(4), 124.3(2); (1)-C(3)-S(1),
117.9(2).
These slight geometric differences result, in solution, in
dissimilar NMR data. The 31P{1H} NMR signal at -27.1
ppm for the Ph2P-CHdC phosphorus is typical for alkenyl
diphenylphosphines,18 but is upfield shifted when compared
to that in 2th (-13.2 ppm). This indicates the influence of
the chalcogen, the P1 nucleus of 2th being deshielded because
of the different mutal orientation of the lone pairs. Similar
steric influences in the chemical shifts of tertiary phosphines
were reported for alkenyl phosphines.19 Moreover, the H
1
NMR spectrum of 2th displays a 2J(HC4,31P) coupling constant
of 9 Hz, larger than that observed for 2ox (4 Hz).
Because, in the absence of NEt3, mox and mth do not
undergo phosphoryl attack on the exocyclic carbon, it is
reasonable to assume that the enamino tautomers moxe and
mthe are not available in solution under these conditions.
As reported in Figure 4 (DFT BP86/TZVP calculations),
these tautomers are greatly disfavored with respect to the
The reactions mox + 2 Ph2PCl f 2ox and mth + 2 Ph2PCl
f 2th largely depend on the amount of NEt3 present in the
reaction mixture (e.g., 48 h reaction time for the overall
reaction mox + 2 Ph2PCl f 2ox when performed with a 1:1
Ph2PCl/NEt3 ratio vs 1 h with a 1:20 ratio). Direct formation
Scheme 3
9892 Inorganic Chemistry, Vol. 47, No. 21, 2008

Formation of P-C Bonds
Scheme 4
Figure 4. Relative energy diagrams for mox, moxe, moxe · NMe3,
moxe ·pyridine and mth, mthe, mthe ·NMe3.
Scheme 5
As mentioned above, under certain conditions, 2ox and 2th
further react with mox and mth when these are available in
solution. However, when the mox + Ph2PCl + NEt3 f 2ox
reaction was carried out in the presence of a large excess of
NEt3 with respect to Ph2PCl, formation of 1ox was not
observed. Instead, the latter was formed when the base was
added in a stoichiometric amount, implying that excess
triethylamine inhibits the conversion 2ox + mox f 2 1ox. If
NEt3 is not available in solution, the equilibrium reported in
Scheme 4 is established, as demonstrated independently by
stirring a suspension of Et3N · HCl in a solution of 2ox in
toluene and in situ 31P{1H} NMR monitoring. The resulting
diphenylchlorophosphine can, then, attack 1ox (backward
reaction) or react with mox, more slowly, although the latter
is present in large excess with respect to Ph2PCl. These two
reactions thus compete. Although poorly soluble in toluene,
traces of Et3N · HCl were detected after filtration. This may
be the reason for the sensitivity in solution of 2ox toward
humidity because of the regeneration of Ph2PCl. The
formation of R2PCl (R ) alkyl, aryl) from aminophosphines
and HCl has been described before.21 The ammonium
chloride Et3N · HCl could then be seen as an HCl carrier,
the latter being responsible of the P-N bond cleavage
reaction. The ammonium chloride is finally regenerated upon
formation of 1ox.
Figure 5. Orbital plot depicting the HOMO of moxe. In the DFT
calculations, NEt3 was replaced with NMe3 to avoid issues related to the
alkyl chains conformation.
imino forms. However, hydrogen bonding with NEt3 would
make moxe and mthe available in solution, because of the
significantly decreased energy gap. This gap is significantly
larger in the case of pyridine, in agreement with its inability
to promote the reaction. These results should be regarded as
semiquantitative because the calculations refer to the gas
phase and also because of the role played by entropy in the
formation of the Me3N · · · mox complexes. However, the
order of magnitude of the stabilization indicates that a
trialkylamine can provide the necessary access to the reactive
species that undergoes the first phosphorylation. A plot
depicting the highest-occupied molecular orbital 2MOe is
reported in Figure 5. The HOMO is mainly localized over
the CdCH2 group and the nitrogen atom, consistent with
both mechanisms 3a and 3b.
The reaction 2ox + mox f 1ox is reminiscent of that
observed with 2-amino-2-thiazoline in which the monophos-
(19) For example, see: (a) Verkade, J. G.; Quin, L. D. Phosphorus-31 NMR
Spectroscopy in Stereochemical Analysis; Verlag Chemie: Weinheim,
Germany, 1987. (b) Grim, S. O.; Molenda, R. P.; Mitchell, J. D. J.
Org. Chem. 1980, 45, 250–252.
phine Ph2PNHCdNCH2CH2S was found to be the thermo-
dynamic product of a multistep reaction, featuring the
intermediacy of Ph2PNdCSCH2CH2NPPh2 (Scheme 5).2
(20) Zhou, A.; Pittman, C. U., Jr. Tetrahedron Lett. 2004, 45, 8899–8903.
Inorganic Chemistry, Vol. 47, No. 21, 2008 9893

Pattacini et al.
Scheme 6
Scheme 7
is much faster than that on the carbon R to the phosphorus
of the hypothetical enamino tautomer of 1ox. Related double
phosphorylation reactions leading to functional dppm-type
ligands have been observed before but resulted from a
different sequence of steps.24
The gas-phase energy profiles reported in Figure 6 were
obtained by optimizing several conformers for each ligand,
and then choosing those displaying the lower energies. Their
Cartesian coordinates are available as Supporting Informa-
tion. The DFT calculations indicate that in the gas phase
the geminal diphosphines 3ox and 3th are slightly disfavored
with respect to the parent C,N diphosphines, but this energy
gap is smaller for 3ox than for 3th, which is consistent with
a destabilizing steric effect of the sulfur atom. In solution,
this small 5 kJ/mol 2ox/3ox gap may be readily overcome,
allowing the formation of the geminal diphosphine. As
mentioned before, the solvent plays indeed an important role
in the 2ox f 3ox rearrangement.
Metal Complexation. Preliminary attempts to obtain Pt(II)
or Pd(II) complexes featuring 2ox as ligand were unsuccessful.
Only species containing chelating 1ox (vide infra) were
detected in the crude reaction mixtures. Their stability and
the lability of the P-N bond in 2ox are probably the reasons
for this reactivity pattern.
The reaction of diphosphine 3ox with [PtCl2(NCPh)2] in
the presence of NEt3 yielded the square-planar complex
[Pt(3ox-H)2] (4) (Scheme 7). Deprotonation of the PCHP
moiety was performed in situ, by addition of the base together
with the platinum complex and an excess of ligand.
Compound 4 is remarkably stable and its purification takes
advantage of its poor solubility in acetonitrile. An ORTEP
view of its molecular structure in 4 · 4CH2Cl2 is depicted in
Figure 7.
In the planar, centrosymmetric structure of complex 4, two
molecules of deprotonated 3ox P,P-chelate the metal center
with P-M-P angles of 70.42(2)°. The N1-C3 separation
of 1.299(3) Å is consistent with a double bond character but
However, at variance with the case reported herein, it was
concluded that the diphosphine f monophosphine conver-
sion was the result of a direct intermolecular phosphoryl
migration from the exocyclic nitrogen of the diphosphine to
the imine of the less stable tautomer of 2-amino-2-thiazole,
without the intermediacy of Ph2PCl (Scheme 5).
The isomerization of 2ox f 3ox observed in chlorinated
solvents was monitored by 31P{1H} NMR and found to be
concentration dependent, suggesting an intermolecular mech-
anism. This reaction is incomplete even after one week under
the conditions used for the preparation of 2ox, but it is fast
in chlorinated solvents (minutes). A concerted mechanism
is shown in Scheme 6a, which bears similarities with that in
Scheme 5. However, the good solubility of residual
Et3N · HCl in chlorinated solvents may facilitate a reaction
pathway similar to that of Scheme 3, in which reformed
Ph2PCl may be subject to the nucleophilic attack of the
enamino tautomer of 1ox possibly present in solution under
these conditions (Scheme 6b). This is currently under study
by means of variable temperature NMR and DFT calcula-
tions.
The geminal diphosphine 3ox represents a new function-
alized dppm ligand,22 and features similarities with 2-py-
ridylbis(diphenylphosphino)methane, whose P,N and P,P
chelating properties and relevance to homogeneous catalysis
have been extensively explored.23 Formation of 3ox from 1ox
and Ph2PCl in the presence of NEt3 was not observed in
toluene, for two possible reasons: (i) the enamino tautomer
of 1ox similar to moxe is not available in solution or (ii) under
these conditions, attack of the nitrogen atom of 1ox on Ph2PCl
Figure 6. Relative energy diagrams for 2ox, 3ox and 2th, 3th.
9894 Inorganic Chemistry, Vol. 47, No. 21, 2008

Formation of P-C Bonds
Figure 7. ORTEP view of the molecular structure of complex 4 in
4 · 4CH2Cl2. Solvent molecules and hydrogen atoms omitted for clarity.
Thermal ellipsoids are depicted at 50% level. Symmetry operation generating
equivalent atoms (′): -x, -y, -z. Selected bond distances (Å) and angles
(deg): Pt(1)-P(1), 2.3293(6); Pt(1)-P(2), 2.3164(6); P(1)-C(4), 1.745(3);
P(2)-C(4), 1.751(2); C(3)-C(4), 1.432(3); N(1)-C(3), 1.299(3); O(1)-C(3),
1.356(3); P(1)-Pt(1)-P(2), 70.42(2); P(1)-Pt(1)-P(2)′, 109.58(2); P(1)-
C(4)-P(2), 100.0(2); C(3)-C(4)-P(1), 130.8 (2); C(3)-C(4)-P(2), 129.0(2);
C(4)-P(1)-Pt(1), 94.17(8); C(4)-P(2)-Pt(1), 94.46(9).
Figure 8. ORTEP plot of the molecular structure of compound 5. H atoms
omitted for clarity. Selected distances and angles are reported in Table 3.
One of the two crystallographically independent molecules is depicted.
Scheme 8
Figure 9. ORTEP plot of the molecular structure of compound 7. H atoms
omitted for clarity. Selected distances and angles are reported in Table 3.
One of the two crystallographically independent molecules is depicted.
oxazoline ring with other metal centers offers the potential
to generate new heterometallic complexes, and this reactivity
is currently under study.
The products of the reactions of ligand 1ox with [Pt(I)Me-
(cod)], [Pt(Cl)Me(cod)], and [PtMe2(cod)] are reported in
Scheme 8.
Single crystals of complexes 5 and 7 were obtained and
studied by X-ray diffraction for comparative purpose. The
ORTEP plots of their molecular structures are reported in
Figures 8 and 9, respectively. Selected bond distances and
angles are compared to those of 4 in Table 3.
the P-C bond lengths [P1-C4, 1.745(3) Å; P2-C4, 1.751(2)
Å], shorter than those typically found in tertiary phosphine
complexes and the C3-C4 distance [1.432(3) Å] indicate
that the double bond is delocalized over the P1, P2, C3, C4,
N1 atoms, rather than solely over the C4-C3-N1 moiety.
The geometry around the sp2-hybridized C4 carbon atom is
planar, the sum of the P-C-P and P-C-C angles being
359.69(2)°. These structural features are similar to those
found in related metal complexes containing the chelating
diphosphine obtained by deprotonation of (Ph2P)2CHPy or
its substituted analogues.23a,25 N-functionalization on the
(23) (a) Mague, J. T.; Krinsky, J. L. Inorg. Chem. 2001, 40, 1962–1971.
(b) Mague, J. T.; Hawbaker, S. W. J. Chem. Crystallogr. 1997, 27,
603-608; Mattson, B. M.; Ito, L. N. Organometallics 1989, 8,
391-395. (c) McNair, R. J.; Pignolet, L. H. Inorg. Chem. 1986, 25,
4717–4723. (d) Anderson, M. P.; Mattson, B. M.; Pignolet, L. H. Inorg.
Chem. 1983, 22, 2644–2647. (e) Anderson, M. P.; Tso, C. C.; Mattson,
B. M.; Pignolet, L. H. Inorg. Chem. 1983, 22, 3267–3275.
(24) Andrieu, J.; Braunstein, P.; Tiripicchio, A.; Ugozzoli, F. Inorg. Chem.
1996, 35, 5975–5985.
(21) For example, see: Imamura, Y.; Mizuta, T.; Miyoshi, K. Organome-
tallics 2006, 25, 882–886.
(22) For recent examples, see: (a) Braun, L.; Liptau, P.; Kehr, G.; Ugolotti,
J.; Froehlich, R.; Erker, G. Dalton Trans. 2007, 1409–1415. (b)
Piestert, F.; Fetouaki, R.; Bogza, M.; Oeser, T.; Blu¨mel, J. Chem.
Commun. 2005, 1481–1483.
Inorganic Chemistry, Vol. 47, No. 21, 2008 9895

Pattacini et al.
Table 3. Comparison between Selected Bond Distances (Å) and Angles
(deg) in Compounds 4·4CH2Cl2, 5, and 7a
4·4CH2Cl2
5
7
Pt1-N1
Pt1-P1
Pt1-C5
Pt1-I1
Pt1-C6
Pt1-Cl1
N1-C3
P1-C4
C3-C4
C3-O1
C5-O2
P1-Pt1-N1
2.128(5), 2.119(5)
2.192(2), 2.191(2)
2.095(6), 2.100(6)
2.6501(5), 2.6459(5)
2.111(7), 2.086(8)
2.258(2), 2.251(2)
2.042(9), 2.051(9)
2.3293(6)
2.072(8), 2.161(9)
1.299(3)
1.745(3)
1.432(3)
1.356(3)
1.276(7), 1.284(8)
1.858(6), 1.833(5)
1.472(9), 1.480(8)
1.346(7), 1.339(7)
1.28(1), 1.29(1)
1.862(9), 1.870(9)
1.48(1), 1.51(1)
1.338(9), 1.34(1)
83.5 (1), 82.2(1)
81.5(2), 83.2(2)
P1-Pt1-P2 70.42(2)
a Two crystallographically independent molecules were present in the
crystals of 5 and 7.
Scheme 9
Figure 10. ORTEP plot of the molecular structure of the cation of
compound 8 in 8·0.25Et2O. H atoms omitted for clarity. Selected distances
and angles are reported in Table 4. One of the two crystallographic
independent molecules is depicted.
Table 4. Comparison between Selected Bond Distances (Å) and Angles
a
(deg) in Compounds 8 in 8·0.25Et2O, 9, and 10 in 10·2.5C6H6
8·0.25Et2O
9
10·2.5C6H6
Pd1-N1
Pd1-P1
Pd1-C5
Pd1-N2
Pd2-C4
Pd2-N3
Pd2-C26
Pd2-Cl1
N1-C3
2.163(3), 2.154(3)
2.218(1), 2.228(1)
1.993(4), 2.002(4)
2.152(3), 2.154(3)
2.117(1)
2.2410(5)
2.010(2)
2.181(1)
2.140(2)
2.2299(7)
2.006(3)
2.162(2)
2.082(2)
2.150(2)
1.988(2)
2.4178(7)
1.286(3)
1.824(2)
1.464(4)
1.766(2)
81.01(6)
81.8(1)
1.273(5), 1.285(5)
1.834(4), 1.845(4)
1.478(5), 1.493(6)
1.747(4), 1.744(4)
82.29(9), 79.61(9)
82.5(2), 82.2(2)
1.330(2)
1.749(2)
1.375(2)
1.780(2)
82.74(4)
81.43(6)
P1-C4
C3-C4
C3-S1
P1-Pd1-N1
C5-Pd1-N2
As expected, the phosphine 1ox chelates the metal center
in complexes 5-7 through the P and N donor atoms. In 5,
the iodide and the methyl group are in trans position with
respect to the phosphorus and nitrogen atoms, respectively,
as observed in related complexes.26 The ligand geometrical
parameters remain almost the same in 5 and 7, but the trans
influence of the methyl group slightly elongates the Pt-P
bond in 7. Several crystal structures of variously substituted
phosphino-methyl-oxazoline Pt and Pd complexes have been
reported in the literature.27 Since the bonding parameters of
5 and 7 are similar to those reported for other Pt(II)
complexes bearing 1ox,27c we shall not discuss them in detail,
but their comparison with those for 4 is interesting and
consistent with the delocalization of the double bond over
the P1, P2, C3, C4, N1 atoms in the latter. The N1-C3 bond
in 4 is only slightly longer than the corresponding bonds in
5 and 7, while the P-C4 and C3-C4 bonds are significantly
shorter. The P-Pt bonds of 4 are longer than those in 5 and
7, as a result of the mutual trans influence of the phosphines
and, probably, of the aforementioned electronic delocalization.
The reaction of 1th with the solvent-stabilized complex
[Pd(dmba)(THF)n]OTf prepared in situ (dmbaH ) N,N-
dimethylbenzylamine; OTf ) CF3SO3) afforded [Pd(dmba-
a Two crystallographically independent molecules were present in the
crystals of 8.
C,N)(1th)]OTf (8) in almost quantitative yield. Complex 8
was deprotonated with t-BuOK to yield [Pd(dmba-C,N)(1th-
H)] (9) (Scheme 9). The deprotonation occurs selectively at
the PCH2 group of 8, as indicated by 1H NMR. The 31P{1H}
(25) Mosquera, M. E. G.; Ruiz, J.; Garcia, G.; Marquinez, F. Chem.sEur.
J. 2006, 12, 7706–7716.
(26) (a) Agostinho, M.; Braunstein, P. C. R. Chim. 2007, 10, 666–676. (b)
Agostinho, M.; Braunstein, P.; Welter, R. Dalton Trans. 2007, 759–
770.
Figure 11. ORTEP plot of the molecular structure of compound 9. H
atoms omitted for clarity. Selected bond distances and angles are reported
in Table 4.
9896 Inorganic Chemistry, Vol. 47, No. 21, 2008

Formation of P-C Bonds
C,N)Cl through the carbon atom C4. The geometry around
C4 is slightly distorted tetrahedral, the sum of the three angles
involving C4, P1, C3, and Pd(2) being 328.4(2)°. The
geometrical parameters of the P,N ligand are more similar
to those of 8 than to those of 9 (for example, C3-C4 for
10, 1.464(4) Å vs 1.375(2) for 9 and an average of 1.485(5)
Å for 8). Complex 10 features strong similarities with the
analogous compound obtained with 1ox,27e and its formation
extends the use of neutral, stable metal complexes with a
ligand-centered nucleophilicity as building blocks in poly-
nuclear chemistry.
Conclusion
The mild reaction conditions used for the preparation of
ligands such as 1ox and 1th may be extended to other imines
susceptible to tautomerisation. The study of their formation
and isomerization mechanisms suggests that the phosphoryl
migrations reported herein could be more frequent than
originally anticipated, since we observed similar reactivities
in alkyl-phosphine (as 1ox) and amino-phosphine systems
(such as diphenylphosphino-2-amino-2-thiazoline). Subtle but
sometimes significant differences were observed between the
oxazoline and thiazoline-based systems. Moreover, complex
4 represents a new example of functionalized metalloligand.
Its reactivity toward further metal centers is under study,
with promising preliminary results.
Figure 12. ORTEP plot of the molecular structure of the dinuclear complex
10 in 10·2.5C6H6. H atoms omitted for clarity. Selected bond distances
and angles are reported in Table 4.
NMR signal shifts from 45.8 (8) to 38.1 ppm (9). Both
complexes were crystallized, and their molecular structures
were determined by single crystal X-ray diffraction (Figures
10 and 11 and Table 4).
The ligand 1th chelates the metal center in 8 through the
P and N atoms. A C,N-chelating dmba anion completes the
metal coordination sphere. The chelation geometry is similar
to that found for 1ox, although the chelating five-membered
ring of one of the two independent molecules is significantly
less planar [P1-C4-C3-N1 torsion angle: 33.2(3)° (mol-
ecule B of 8) compared, for example, to the 8.4(1)° torsion
angle in molecule A of 5]. The deprotonation results, as
expected, in a shortening of the C3-C4 bond of 9 and in a
slight elongation of the C3-S1 and C3-N1 bonds. The
P1-C4 bond is also significantly shortened, similarly to what
was encountered in 4. A certain electronic delocalization is
thus established over the P1-C4-C3-N1 moiety of 9, in
contrast to the more localized nature of the CdN double
bond of 8.
Acknowledgment. Support from the Centre National de
la Recherche Scientifique, the Ministe`re de l’Enseignement
Supe´rieur et de la Recherche, the French Embassy in Berlin,
the DFG (Bonn), and the European Commission (Marie
Curie fellowship HPMF-CT-2002-01659 and COST D-17
Action) is gratefully acknowledged. We thank Dr. A. DeCian
(ULP Strasbourg) for the crystal structure data collection and
Prof. R. Welter (ULP Strasbourg) for the refinement of the
crystal structures of compounds 5, 7, 8, 9, and 10.
The nucleophilic sp2 carbon atom C4 of 9 can regiospe-
cifically attack further metal centers. Thus, reaction of 9 with
[Pd(dmba-C,N)(µ-Cl)]2 afforded [9·{Pd(dmba-C,N)Cl}] (10)
(Scheme 9), of which the molecular structure was established
by X-ray diffraction (Figure 12). Upon reaction, the C4
carbon becomes a stereogenic sp3-hybridized center, and both
enantiomers are present in the centrosymmetric unit cell, at
variance with a similar complex bearing 1ox.27e
Supporting Information Available: Listings of output Cartesian
coordinates of the DFT calculations. This material is available free
of charge via the Internet at http://pubs.acs.org.
IC800934H
(27) (a) Agostinho, M.; Braunstein, P. Chem. Commun. 2007, 58–60. (b)
Danjo, H.; Higuchi, M.; Yada, M.; Imamoto, T. Tetrahedron Lett.
2004, 45, 603–606. (c) Oberbeckmann-Winter, N.; Braunstein, P.;
Welter, R. Organometallics 2004, 23, 6311–6318. (d) Thoumazet, C.;
Melaimi, M.; Ricard, L.; Le Floch, P. C. R. Chim. 2004, 7, 823–832.
(e) Apfelbacher, A.; Braunstein, P.; Brissieux, L.; Welter, R. Dalton
Trans. 2003, 1669–1674.
In the dinuclear, zwitterionic complex 10, the component
9 behaves as a metalloligand toward the fragment Pd(dmba-
Inorganic Chemistry, Vol. 47, No. 21, 2008 9897