Intra- and inter-molecular phosphoryl migration in phosphinothiazolines; precursors to polynuclear complexes and bimetallic coordination polymers

Article abstract of DOI:10.1039/b603495k

Two tautomers of the new phosphinoaminothiazoline Ph₂PNHC= NCH₂CH₂S (1), obtained from the reaction of 2-amino-2-thiazoline (ATHZ) with Ph₂PCl, have been structurally characterized and the intermediate formation

Full text of DOI:10.1039/b603495k

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Intra- and inter-molecular phosphoryl migration in
phosphinothiazolines; precursors to polynuclear complexes and
bimetallic coordination polymers{{
Gu¨nter Margraf, Roberto Pattacini, Abdelatif Messaoudi and Pierre Braunstein*
Received (in Cambridge, UK) 9th March 2006, Accepted 24th May 2006
First published as an Advance Article on the web 14th June 2006
DOI: 10.1039/b603495k
Two tautomers of the new phosphinoaminothiazoline
Ph2PNHCLNCH2CH2S (1), obtained from the reaction of
2-amino-2-thiazoline (ATHZ) with Ph2PCl, have been structu-
rally characterized and the intermediate formation of the
diphosphine Ph2PNLCN(PPh2)CH2CH2S (2) has been demon-
strated experimentally and by DFT calculations; 2 reacts with
[AuCl(THT)] to give [(AuCl)22] whereas the bidentate metallo-
ligand cis-[Pt(12H)2] reacts with AgOTf to form the Ag–Pt
coordination polymer [Ag‘[Pt(12H)2]‘](OTf)‘.
which is consistent with the endo-nitrogen atom being more
nucleophilic than the exo-nitrogen,4 was found to slowly and
quantitatively isomerize to 1. DFT studies§ suggest for this 1,3-
PPh2 migration an intramolecular mechanism in which the PPh2
group is transferred from the endocyclic to the exocyclic nitrogen
via transition state TS1 (Fig. 1a). Attempts to identify an
intermolecular Ph2P transfer were unsuccessful. The high energy
computed for TS1 (+126 kJ/mol) disfavours this reaction path. In
fact, when Ph2PCl is reacted with ATHZ in a 1 : 1 stoichiometry,
an alternative path is preferred. The exocyclic nitrogen of 3, being
more nucleophilic than the endo-nitrogen of ATHZ, rapidly
attacks Ph2PCl, to form 2. Isolated 2 was shown independently to
react with ATHZ to give first 1a, which rapidly equilibrates with
1b. Calculations showed that the reaction [2 + ATHZ A 2 1a] is
energetically favoured by 6.1 kJ/mol (Fig. 1b). We suggest a
concerted mechanism in which the Ph2P group is transferred
from the endocyclic nitrogen of 2 to the exocyclic nitrogen of the
ATHZ imino-tautomer while a proton transfer occurs in the
opposite direction (Fig. 1b). The calculated transition state TS2 is
The functionalization of phosphine ligands represents a major way
to fine-tune their stereoelectronic characteristics and coordination
properties as well as the dynamic behaviour and reactivity
(stoichiometric and catalytic) of their metal complexes.1 Increas-
ing the diversity of chemical functions present on such ligands
provides considerable opportunities for studying selectivity-related
problems. We have now found that when 2-amino-2-thiazoline
(ATHZ) is reacted with Ph2PCl in a 1 : 1 molar ratio, with
the original aim of preparing the monophosphine ligand
Ph2PNHCLNCH2CH2S (1a), corresponding to the most
stable tautomer of ATHZ,2 it is in fact the diphosphine
Ph2PNLCN(PPh2)CH2CH2S (2) that is isolated in almost
quantitative yield (based on phosphorus). This is rather surprising
in view of recent results obtained with a closely related system.3
However, when this reaction was performed in the presence of a
base like Et3N or n-BuLi, 1 was isolated in two tautomeric forms,
1a (favoured in non-polar solvents) and 1b, and 2 was found to be
a reaction intermediate (Scheme 1). It will be shown below that the
role of the base is to scavenge the HCl liberated in preference to
ATHZ. Another intermediate was formed prior to 2 and identified
as 3 (as confirmed by 31P NMR when reacting, at low
temperature, Ph2PCl with lithiated ATHZ in large excess, see
Supplementary Information), which results from nucleophilic
attack of the endo-nitrogen atom of ATHZ on Ph2PCl. This
kinetic product (+19.6 kJ/mol with respect to 1a), the formation of
Laboratoire de Chimie de Coordination, Universite´ Louis Pasteur
(UMR 7177 CNRS), Institut Le Bel, 4 rue Blaise Pascal, F-67070,
Strasbourg, France. E-mail: braunst@chimie.u-strasbg.fr;
Fax: +33390241322; Tel: +33390241308
{ Dedicated to Prof. A. Tiripicchio (Parma) on the occasion of his 70th
birthday, with our warmest wishes.
{ Electronic supplementary information (ESI) available: Computed
atomic coordinates and distances; complete sets of crystallographic
parameters; experimental procedures and spectroscopic characterizations.
See DOI: 10.1039/b603495k
Scheme 1
3098 | Chem. Commun., 2006, 3098–3100
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Scheme 2
tautomerism should occur via a head to tail transition state (TS3).
Although phosphine transamination represents a widely used
strategy for aminophosphine synthesis (e.g. P(NR2)3, R = Me, Et
as starting reagent), only a few examples concerning diaryl- or
dialkyl-aminophosphines have been reported.5 It is remarkable
that ATHZ plays a dual role, both as a substrate for Ph2PCl attack
and as a transamination reagent. To the best of our knowledge,
this kind of reactivity has never been reported in P(III) chemistry.
The P1–N1 bond distance in 2 is significantly longer than P2–N2,
consistent with the easier breaking of the endocyclic P–N bond. As
expected, the CLN double bond is localized between C1 and the
exocyclic N2 atom.
Fig. 1 Relative energy profiles for the intramolecular 1 A 3 tautomerism
(a) and the intermolecular ATHZ + 2 A 2 1 conversion (b).
+71.1 kJ/mol with respect to the reagents (ESI). Summarizing, two
pathways are available to form 1: the aforementioned (dis-
favoured) direct 1,3-PPh2 migration in 3 and the reaction of the
rapidly formed 2 with the ATHZ present in the reaction mixture
(Scheme 1). From the combined theoretical and experimental data,
we conclude that the two step conversion 3 A 2 A 1 is preferred to
the one step isomerization 3 A 1. The latter slowly occurs only if
Ph2PCl is unavailable in the reaction mixture, which then precludes
the intermediate formation of 2.
Alternative transition states for the ATHZ + 2 A 2 1 reaction
were computed (ESI). For instance, the conversion featuring the
amino-tautomer of ATHZ was found to be energetically
disfavoured (+181 kJ/mol), while an activated complex formed
by two molecules of ATHZ and one of 2 was calculated to be
energetically similar to TS2 but is entropically disfavoured.
Diphosphine 2 was isolated as the major product when ATHZ
was reacted with Ph2PCl in a 3 : 2 ratio, formation of ATHZ?HCl
preventing reaction of the free amine with 2 to give 1. The
molecular structures of 1 and 2" have been determined by X-ray
diffraction (Fig. 2).
When 2 was reacted with two equivalents of [AuCl(THT)] in
CH2Cl2, the dinuclear gold complex 4 was formed in quantitative
yield (Scheme 2). A view of its molecular structureI is shown in
Fig. 3.
Each metal centre is coordinated, in a slightly distorted linear
geometry, by a chlorine and a phosphorus atom. The coordinated
ligand retains a geometry similar to that found in 2. On the other
hand, both P–N distances shorten upon coordination. Reactions
of 2 with [PtCl2(NCMe)2] or [PdCl2(COD)] led to the formation of
poorly soluble precipitates, which are likely to be oligomeric
Tautomers 1a and 1b co-crystallized and adopt a head to tail
intermolecular arrangement, forming pseudo-dimers through two
…
N
H–N hydrogen bonds. Tautomer 1b was computed to be only
slightly more stable (0.95 kJ/mol) than 1a and this is consistent
with the ca. 1 : 1 mixture observed in the solid state. The
Fig. 3 ORTEP view of the crystal structure of compound 4 in 4?CHCl3.
Fig. 2 ORTEP views of the molecular structures of compounds 1 (left)
and 2 (right). Displacement parameters include 50% of the electron
density. For 1 only one of the two tautomers (1a) is shown. Owing to
crystallographic disorder, the bond parameters for this ligand are discussed
Displacement parameters include 50% of the electron density. Selected
˚
bond distances (A) and angles (u): Au(1)–P(1) 2.229(2), Au(2)–P(2)
2.2212(17), Au(2)–Cl(2) 2.2834(19), Au(1)–Cl(1) 2.299(2), P(1)–N(1)
1.675(6), P(2)–N(2) 1.713(6), N(2)–C(1) 1.379(8), N(1)–C(1) 1.294(8);
P(1)–Au(1)–Cl(1) 174.99(7), P(2)–Au(2)–Cl(2) 177.44(7), N(1)–P(1)–Au(1)
117.2(2), N(2)–P(2)–Au(2) 113.4(2), C(1)–N(1)–P(1) 124.8(5), C(1)–N(2)–
P(2) 117.7(4), C(1)–N(2)–C(2) 115.1(5), C(2)–N(2)–P(2) 126.3(5), N(1)–
C(1)–S(1) 128.7(5), N(2)–C(1)–S(1) 111.2(5), N(1)–C(1)–N(2) 120.1(6).
˚
in the Supplementary material. Bond distances (A) and angles (u) for 2:
S(1)–C(1) 1.7796(17), P(1)–N(1) 1.7511(15), P(2)–N(2) 1.7105(15), N(1)–
C(1) 1.364(2), N(2)–C(1) 1.280(2); C(1)–N(1)–C(3) 115.53(14), C(1)–N(1)–
P(1) 115.13(12), C(3)–N(1)–P(1) 129.32(12), C(1)–N(2)–P(2) 119.99(12).
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European Commission (COST D-17 Action) for support. We are
grateful to Prof. R. Welter and Dr A. DeCian (ULP Strasbourg)
forthecrystalstructuredeteminationsandtoProf.P.Hofmannand
Dr P. Deglmann (Heidelberg) for access to computing facilities.
Notes and references
§ All calculations were done using the program system TURBOMOLE.8a
If not mentioned explicitly otherwise, we used the DFT method with the
Becke–Perdew functional (BP86).8b The Coulomb terms were treated by
the RI-J approximation.8c For the structure optimizations we used SV(P)
basis sets8d (single zeta for core orbitals, double zeta for the valence shells
and one set of polarization functions for all centres except hydrogen).
Single point energies were calculated with larger triple zeta valence plus
polarization basis sets (TZVP).8e
" Crystal data for 1: C15H15N2PS, M = 286.32, monoclinic P21/c, a =
˚
15.5330(3), b = 11.8340(2), c = 16.1740(3) A, b = 105.3850(3)u, V =
3
2866.52(9) A , Z = 8, Dc = 1.327 g cm23, m(Mo-Ka) = 0.325 mm21
,
F(000) = 1200. A Nonius Kappa CCD diffractometer was employed for
˚
˚
the collection of 8350 unique reflections (Mo-Ka, l = 0.71073 A, T =
173 K). The structure was solved by direct methods and refined by a full
matrix least-squares technique based on F2 (SHELX977). The final R1 and
wR2 are 0.046 and 0.112, respectively, for 359 parameters and 5517
reflections [I . 2s(I)]. CCDC 601675. The same data collection and
refinement procedures were used for 2, 4?CHCl3 and 6?3CH2Cl2. Crystal
data for 2: C27H24N2P2S, M = 470.48, triclinic P-1, a = 9.1420(2),
Fig. 4 Views of the crystal structure of compound 6 in 6?3CH2Cl2.
Solvent molecules and OTf anions have been omitted for clarity. a)
Asymmetric unit (displacement parameters include 50% of the electron
density); b) two orthogonal projections of the polymer chain. Selected
˚
bond distances (A) and angles (u): Pt–N(4) 2.084(4), Pt–N(2) 2.096(4), Pt–
˚
b = 10.0760(2), c = 14.4330(4) A, a = 92.1400(9), b = 105.8700(9), c =
P(2) 2.2309(14), Pt–P(1) 2.2314(14), Ag(1)–N(3) 2.078(4), Ag(1)–N(1)
2.096(5), P(1)–N(1) 1.686(5), P(2)–N(3) 1.687(5), N(1)–C(1) 1.324(7),
N(2)–C(1) 1.307(7), N(4)–C(4) 1.319(7), N(3)–C(4) 1.339(7); N(4)–Pt–N(2)
100.04(18), N(4)–Pt–P(2) 80.95(13), N(2)–Pt–P(1) 80.49(13), P(2)–Pt–P(1)
98.51(5), N(3)–Ag–N(1) 172.08(19).
3
107.9900(12)u, V = 1205.47(5) A , Z = 2, Dc = 1.296 g cm23, m(Mo-Ka) =
˚
0.285 mm21, F(000) = 492. R1 and wR2 are 0.048 and 0.123, respectively,
for 289 parameters and 4950 reflections [I . 2s(I)] (7015 unique). CCDC
601676. For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b603495k
I Crystal data for 4?CHCl3: C27H24Au2Cl2N2P2S?CHCl3, M = 1054.68,
triclinic P-1, a = 9.610(1), b = 13.281(2), c = 13.769(2) A, a = 98.04(5), b =
˚
coordination compounds in which the diphosphine 2 would act as
a bridging ligand.
3
23
˚
101.87(5), c = 104.52(5)u, V = 1630.5(4) A , Z = 2, Dc = 2.148 g cm
,
m(Mo-Ka) = 9.582 mm21, F(000) = 992. The final R1 and wR2 are 0.041
and 0.11, respectively, for 361 parameters and 7031 reflections [I . 2s(I)]
(9536 unique). CCDC 601677. For crystallographic data in CIF or other
electronic format see DOI: 10.1039/b603495k
Ligand 1 reacted with t-BuLi and [PtCl2(NCPh)2] in a 2 : 2 : 1
ratio to afford the bidentate metalloligand cis-[Pt(12H)2] (5) which,
upon reaction with AgOTf, yielded quantitatively the new
bimetallic, cationic coordination polymer [Ag‘[Pt(12H)2]‘](OTf)‘
(6, Scheme 2). Views of the molecular structure of 6?3CH2Cl2**
are depicted in Fig. 4.
** Crystal data for 6?3CH2Cl2: C30H28AgN4P2PtS?3CH2Cl2?CF3O3S, M =
˚
1277.43, monoclinic P21/n, a = 9.185(3), b = 19.488(6), c = 25.892(9) A,
3
b = 99.74(2)u, V = 4568(3) A , Z = 4, Dc = 1.858 g cm23, m(Mo-Ka) =
˚
4.097 mm21, F(000) = 2488. R1 and wR2 are 0.050 and 0.112, respectively,
for 514 parameters and 10225 reflections [I . 2s(I)] (13265 unique). CCDC
601678. For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b603495k
The platinum coordination geometry is square planar, the four
L–Pt–L angles summing to 359.9(2)u, while the Ag atoms, which
are bound to the exocyclic N atoms of 5, adopt a slightly bent
geometry [N3–Ag–N1 172.08(19)u]. The CLN double bonds are
delocalized over the N1,C1,N2 and N3,C4,N4 atoms, respectively,
1 See e.g. (a) P. Braunstein, Chem. Rev., 2006, 106, 134; (b) P. Braunstein
and F. Naud, Angew. Chem., Int. Ed., 2001, 40, 680; (c) G. Helmchen and
A. Pfaltz, Acc. Chem. Res., 2000, 33, 336; (d) C. S. Slone,
D. A. Weinberger and C. A. Mirkin, Prog. Inorg. Chem., 1999, 48, 233.
2 Y. Xue, C. K. Kim, Y. Guo, D. Q. Xie and G. S. Yan, J. Comput.
Chem., 2005, 10, 994.
˚
the C–N distances ranging from 1.307(7) [N2–C1] to 1.339(7) A
[N3–C4].
The resulting infinite chains form a zig-zag and wave-like
arrangement (Fig. 4b); the silver atoms occupy the maximum and
3 H. L. Milton, M. V. Wheatley, A. M. Z. Slawin and J. D. Woollins,
Inorg. Chim. Acta, 2005, 358, 1393.
˚
theminimumpointsofthesinusoid,andareseparatedby9.899(3)A.
4 (a) M. Avalos, R. Babiano, P. Cintas, M. M. Chavero, F. J. Higes,
J. L. Jimenez, J. C. Palacios and G. Silvero, J. Org. Chem., 2000, 65,
8882; (b) G. Kaugars, S. E. Martin, S. J. Nelson and W. Watt,
Heterocycles, 1994, 12, 2593.
5 (a) N. V. Dubrovina, V. I. Tararov, Z. Kadyrova, A. Monsees and
A. Boerner, Synthesis, 2004, 12, 2047; (b) E. V. Bakhmutova, H. No¨th,
R. Contreras and B. Wrackmeyer, Z. Anorg. Allg. Chem., 2001, 627,
1846; (c) V. L. Foss, Y. A. Veits, T. E. Chernykh and I. F. Lutsenko, Zh.
Obshch. Khim., 1984, 54, 2670.
6 (a) P. Strickler, Helv. Chim. Acta, 1969, 52, 270; (b) I. B. Rother,
M. Willermann and B. Lippert, Supramol. Chem., 2002, 14, 189.
7 G. M. Sheldrick, SHELX-97, University of Go¨ttingen: Germany, 1997.
8 (a) R. Ahlrichs, M. Ba¨r, M. Ha¨ser, H. Horn and C. Ko¨lmel, Chem. Phys.
Lett., 1989, 162, 165; (b) A. D. Becke, Phys. Rev. A, 1988, 38, 3098; (c)
K. Eichkorn, O. Treutler, H. Ohm, M. Ha¨ser and R. Ahlrichs, Chem.
Phys. Lett., 1995, 240, 283; (d) A. Scha¨fer, H. Horn and R. Ahlrichs,
J. Chem. Phys., 1992, 97, 2571; (e) A. Scha¨fer, C. Huber and R. Ahlrichs,
J. Chem. Phys., 1994, 100, 5829.
To the best of our knowledge, only two examples of structurally
characterized Pt–Ag coordination polymers in which linear Ag
centres connect Pt metalloligands have been reported before.6
The full characterization of tautomers 1a,b and the intermediate
formation of the diphosphine ligand 2 in the course of their
synthesis emphasize the subtlety of the bonding in these systems
and are relevant to their use in coordination chemistry where ligand
interactions with one or many metal centres may profoundly affect
the nature of the reactive sites. Further studies with Cu(I), Ag(I)and
Au(I) are in progress to delineate the conditions for the formation
of new bimetallic coordination polymers.
We thank the Centre National de la Recherche Scientifique, the
Ministe`re de la Recherche, the French Embassy in Berlin and the
3100 | Chem. Commun., 2006, 3098–3100
This journal is ß The Royal Society of Chemistry 2006