Selective C-Cl versus P-Cl activation - Syntheses of complexes with P-Cl functional phosphinomethyl bridges η2,μ2-{P(R)Cl-CH2}

Article abstract of DOI:10.1016/S0022-328X(97)00717-1

On reaction of chloromethylchlorophosphines Cl(R)P-CH₂-Cl with Pd(Ph₃P)₄ the C-Cl bond is selectively activated by oxidative addition to Pd(0), unusual dipalladium complexes with P-Cl functional η²,μ₂-{CH₂-P(R)Cl} bridges being formed with high diastereoselectivity. The X-ray structure of 3a (R=tBu) reveals a chair-shaped Pd₂P₂C₂ six-membered ring system with the substituents (Cl, tBu) at the two m₂-P atoms in cis-position.

Full text of DOI:10.1016/S0022-328X(97)00717-1

Journal of Organometallic Chemistry 554 (1998) 207–210
Preliminary communication
Selective C–Cl versus P–Cl activation-syntheses of complexes with
P–Cl functional phosphinomethyl bridges p2,v2-{P(R)Cl–CH2}
Peter Machnitzki a, Othmar Stelzer a,*, William S. Sheldrick b, Claudia Landgrafe b
a Fachbereich 9, Anorganische Chemie, Bergische Uni6ersita¨t-GH Wuppertal, Gaußstraße 20, D-42097, Wuppertal, Germany
b Lehrstuhl fu¨r Analytische Chemie, Ruhr-Uni6ersita¨t Bochum, Uni6ersita¨tsstraße 150, D-44780, Bochum, Germany
Received 14 October 1997
Abstract
On reaction of chloromethylchlorophosphines Cl(R)P–CH2–Cl with Pd(Ph3P)4 the C–Cl bond is selectively activated by
oxidative addition to Pd(0), unusual dipalladium complexes with P–Cl functional p2,v2-{CH2-P(R)Cl} bridges being formed with
high diastereoselectivity. The X-ray structure of 3a (R=tBu) reveals a chair-shaped Pd2P2C2 six-membered ring system with the
substituents (Cl, tBu) at the two m2-P atoms in cis-position. © 1998 Elsevier Science S.A. All rights reserved.
Keywords: Chloromethylchlorophosphines; Selective C–Cl activation; p2,v2-Phosphinomethyl bridges; Palladium; X-ray structure
bis-v2-phosphido complex (X=PRR%) has been ob-
tained on reaction of Cl2P–CH2–Cl with Fe2(CO)9 [3]
1. Introduction
Chloromethylchlorophosphines Cl(R)P–CH2–Cl [1–
3] are multifunctional building blocks of great synthetic
potential. The prototype of this class of chlorophosphi-
nes, Cl2P–CH2–Cl, has been employed for the synthe-
ses of novel phosphorus containing heterocycles, e.g.
1,3,4-diazaphospholes A, by [3+2]-cyclocondensation
reactions with amidine type compounds. Metal assisted
reductive 1,2-dehalogenation of the derivatives Cl(R)P–
CH2–Cl with Fe2(CO)9 or Fe3(CO)12 leads to phos-
phaalkenes stabilized by incorporation into cluster
frameworks B [3,4] or bimetallic complexes C [3]. By
analogy with the reductive dehalogenation of alkyl or
arylchlorophosphines RR’PCl with transition metal
carbonyls or carbonylates [5] v2-phosphido complexes,
In context of a program aimed at the syntheses of
mono- and bicyclic phosphines by template assisted
transformations of reactive metal stabilized phos-
phaalkenes we were interested in a further development
of the synthetic procedure leading to clusters or com-
plexes of type B or C containing transition metals other
than iron, e.g. palladium.
e.g.
(CO)3Fe(v2-PRR%)(v2-X)Fe(CO)3
(X=Cl,
PRR%·R=Cl·R%=CH2–Cl), are assumed to be
formed as intermediates by oxidative addition of the
P–Cl bonds to the low valent transition metal. The
2. Results and discussion
Reaction of the chloromethylchlorophosphine
* Corresponding author. Fax: +49 202439291.
tBu(Cl)P–CH2–Cl (1a) [3,4] with an equimolar amount
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(97)00717-1

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P. Machnitzki et al. / Journal of Organometallic Chemistry 554 (1998) 207–210
Fig. 1. (a) 31P{1H} NMR spectrum of 3a (CDCl3, 303 K), *=impurity. (b) Extended high-field part.
of Pd(Ph3P)4 [6] in toluene at ambient temperature
yields yellow colored complex of composition
of the reaction product for which structure 2a was
assumed initially were calculated using iterative tech-
niques (J(AA%)=42.1, J(AX)=517.1, J(AX%)= −2.7,
J(XX%)=3.7 Hz). The coupling constants J(AA%) and
J(AX%) obtained for the structurally related v2-phos-
phido complexes of type D are significantly greater,
however (J(AA%)=289.5, J(AX)=405.9, J(AX%)=
31.9, J(XX%)=2.9 Hz). Taking into account the un-
usual lP values for the phosphido bridges and the
pattern of the P–P coupling constants the unusual
structure 3a had to be assigned to the reaction product
of composition {Pd(Ph3P)1a}. Insertion of CH2 groups
between the P and Pd atoms reduces J(AA%) and
J(AX%) while low-field 31P{1H} NMR resonances
should be expected for the h-metalated chlorophos-
phine bridges v2-{CH2–P(tBu)Cl} in 3a. The dipalla-
dium complex 3a with two asymmetrically substituted
phosphorus atoms is formed with a high degree of
diastereoselectivity the line pattern of only one AA%XX%
spin system being observed in the 31P{1H} NMR spec-
trum. This is in agreement with the 13C{1H} NMR data
which show only one higher-order triplet (X-part of
ABNMX spin system; A, B=v2-P; N, M=P(Ph3P)) at
lC=9.6 for the CH2(P) group. As a consequence of
the lower electronegativity of Pd versus Cl it is shifted
to a high field compared with the lC value of the
CH2–Cl moiety in the starting material 1a (lC=41.9)
[3]. 13C{1H} NMR signals at lC=42.4 and 26.8 were
assigned to the tertiary carbon and the Me groups of
the tBu substituents using DEPT spectra and the 13C–
1H coupling fine structure in the 13C NMR spectra.
a
{Pd(Ph3P)1a}. Triphenylphosphine being formed could
be separated by extraction of the crude reaction
product remaining after all volatiles had been removed
in vacuo. The molecular mass of the reaction product
determined by osmometry on CH2Cl2 solutions (1070)
indicated a dimeric structure [{Pd(Ph3P)1a}]2 for which
a value of 1083.4 g mol−1 had to be expected. A
product of identical composition was obtained, if 1a
was reacted with excess Pd(Ph3P)4 at ambient or higher
temperature. In the 31P{1H} NMR spectrum of the
reaction product (Fig. 1) the line pattern of an AA%XX%
spin system (indication of the P atoms see formula) is
observed, compatible with a phosphine substituted
phosphido-bridged dipalladium complex of structure
2a.
Its formation may be explained by oxidative addition
of the P–Cl bond of 1a to Pd(0) and subsequent
dimerization of the intermediate E with elimination of
Ph3P (Eqs. (1a) and (2a)). By comparison of the lP
values with those of cis- or trans-PdCl2L2 (L e.g.
Ph2PR; R=Me, Et, nBu) [7] the high field part (lP=
26.6) of the 31P{1H} NMR AA%XX% spin system may be
assigned to the Ph3P ligands coordinated to Pd(II)
(PXX%). The strong deshielding of the central P atoms
(PAA%, lP=138.3) was, however, not compatible with
structure 2a proposed for the reaction product.
v2-Phosphido complexes of this type, e.g. D, have
been investigated [8]. For the v2-phosphido bridges
in these complexes the lP values are in the range
between −120 and −180. The P–P coupling constants

P. Machnitzki et al. / Journal of Organometallic Chemistry 554 (1998) 207–210
209
˚
Fig. 2. Molecular structure of 3a. The hydrogen atoms have been omitted for clarity. Selected bond lengths (A) and angles (°): Pd(1)–C(1)
2.051(12), Pd(1)–P(11) 2.284(4), Pd(1)–P(12) 2.356(4), Pd(1)–Cl(1) 2.383(4), Pd(2)–C(2) 2.075(11), Pd(2)–P(21) 2.287(4), Pd(2)–P(22) 2.359(4),
Pd(2)–Cl(2) 2.379(4), Cl(11)–P(11) 2.049(5), Cl(21)–P(21) 2.040(5), C(1)–Pd(1)–P(11) 85.2(4), C(1)–Pd(1)–P(12) 91.5(4), P(11)–Pd(1)–P(12)
167.2(2), C(1)–Pd(1)–Cl(1) 176.4(4), P(11)–Pd(1)–Cl(1) 94.07(14), P(12)–Pd(1)–Cl(1) 89.98(13), C(2)–P(11)–C(130) 105.8(6), C(130)–P(11)–
Cl(11) 102.9(5), C(2)–P(11)–Cl(11) 100.1(5), C(2)–P(11)–Pd(1) 120.3(5).
reaction between 1a and Pd(Ph3P)4 product formation
is possibly controlled by the shielding effect of the
bulky tBu group directing the attack of the transition
metal nucleophile towards the C–Cl bond at the pe-
riphery of the chlorophosphine.
Diethylaminochloromethylchlorophosphine 1b re-
acted with Pd(Ph3P)4 in an analogous manner as 1a.
Based on the similarity of the 31P{1H} NMR spectra
and the pertinent data (lP(PAA%)=132.28, lP(PXX%)=
27.06, N=ꢀJ(AX)+J(AX%)ꢀ=568.2, J(AA%)=116 Hz)
a structure analogous to that of 3a may be assigned to
the product 3b formed concommitantly with Ph3P. Due
to the formation of side products which could not be
separated from 3b the product of this reaction could
not be obtained analytically pure.
Crystals of composition 3a·2.5CHCl3 ·2H2O ob-
tained by recrystallization of 3a from chloroform con-
taining small amounts of water were used for a single
crystal X-ray diffraction study. The asymmetric unit
contains two independent molecules 3a their structure
being consistent with that derived from the analysis of
the NMR spectra. As shown in Fig. 2 the Pd atoms and
the the h-metalated chlorophosphine bridges, p2,v2-
{CH2–P(tBu)Cl}, form a chair shaped Pd2P2C2 six-
membered ring. In both cystallographically independent
molecules in the asymmetric unit the substituents at the
v2-phosphorus atoms P(11) and P(21) are in cis-posi-
tion. The coordination geometry at the Pd atoms is
distorted square planar. While the Pd–P distance
The formation of the dipalladium complex 3a is quite
surprising. It may be explained by a selective activation
of the C–Cl bond in the chlorophosphine 1a by
Pd(Ph3P)4 (Eq. (1b)). Dimerization of the intermediate
F involving elimination of Ph3P yields the reaction
product 3a (Eq. (2b)). Activation of C–Cl bonds may
be achieved under mild conditions (ambient tempera-
ture) by electron rich Pd(0) complexes, e.g.
Pd(tBu2PH)3 [9](a) or Pd(Cy3P)2(dba) (dba=dibenzyli-
dene acetone) [9](b), even in CH2Cl2. In case of the

210
P. Machnitzki et al. / Journal of Organometallic Chemistry 554 (1998) 207–210
˚
(Pd(1)–P(11)=2.284(4), Pd(2)–P(21)=2.287(4) A) in
3a is significantly shorter than in trans-Cl2Pd[Cl(tBu)–
3.2. X-ray structure analysis of 3a
˚
CH2–Cl]2 (G) [10] (Pd(1)–P(1)=2.3172(10) A), the
Empirical formula: 3a·2.5CHCl3 ·2H2O, crystal size
0.52×0.44×0.30 mm, space group monoclinic, P21/n
opposite is true for the Pd–Cl and P–Cl bond lengths
(Pd(1)–Cl(1)/Pd(2)–Cl(2)=2.383(4)/2.379(4) or P(11)–
Cl(11)/P(21)–Cl(21)=2.049(5)/2.040(5) A) in 3a versus
Pd(1)–Cl(1)=2.2898(10) or P(1)–Cl(2)=2.0347(11) in
˚
(Nr. 14), a=19.283(7), b=31.641(9), c=21.811(5) A,
3
˚
˚
i=94.81(2)°, V=13261(7) A , Z=8, F(000)=5704,
D
calc=1.420 g×cm−3, v(MoKh)=1.135 mm−1. Data
G.
collection was performed on a Siemens P4 Diffractome-
ter, T=293 K, ꢀ-scan, 17206 independent reflections
with q522.51°, R1=0.080 for 7875 reflections with
ꢀF2ꢀ\2|(F2), wR2=0.199, S=0.896. The structure
was refined by full matrix least square techniques using
the SHELXL-93 program system [11]. Hydrogen atoms
were placed in calculated positions and all other atoms
were refined anisotropically with exception of the oxy-
gen atoms of the water molecules. Full details of data
collection, structure refinement, thermal parameters
and bond lengths and angles have been deposited with
the Cambridge Crystallographic Data Centre [12].
3. Experimental section
All reactions were performed in an oxygen-free atmo-
sphere using standard Schlenk technique. H, 13C{1H}
1
and 31P{1H} NMR spectra were recorded at 400.1,
100.6 and 162.0 MHz on a Bruker AC 400 instrument.
The chloromethylchlorophosphines 1a and 1b were pre-
pared by reaction of tBuMgCl or Et2N–SiMe3 with
Cl2P–CH2–Cl as reported earlier by us [3,4].
Acknowledgements
3.1. Preparation of {Cl(Ph3P)Pd[p2,v2-CH2–P(tBu)
Cl]}2 (3a)
Financial support of this work from the Deutsche
Forschungsgemeinschaft, Fonds der Chemischen Indu-
strie and Hoechst AG is gratefully acknowledged.
To a suspension of 9.71 g (8.4 mmol) Pd(Ph3P)4 in 50
ml of toluene 1.45
g
(8.4 mmol) of t-butyl-
chloromethylchlorophosphine 1a were added with mag-
netic stirring at ambient temperature. After 1 h the
solvent was removed in vacuo and the remaining
residue was dissolved in 10 ml of dichloromethane. The
solution obtained was poured into 250 ml of petrolether
40/60 a yellow colored precipitate being formed. After
filtration with a Schlenk frit the remaining yellow solid
was washed with three aliquots of 5 ml of petrolether
and dried in vacuo. The filtrate contained all the Ph3P
formed during the reaction. For a further purifcation
3a was recrystallized from chloroform. Yield: 3.35 g
(73.6%).
References
[1] A.A. Prishchenko, E.S. Novikova, I.F. Lutsenko, Zh. Obshch.
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Sheldrick, J. Organomet. Chem. 462 (1993) 111.
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[7] (a) S.O. Grim, R.L. Keiter, Inorg. Chim. Acta 4 (1970) 56. (b)
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Ph2PEt (30.2/19.3).
[8] R. Glaser, D.J. Kountz, R.D. Waid, J.C. Gallucci, D.W. Meek,
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[12] Copies of these data may be obtained under the deposit number
100356 free of charge on application to the Director, CCDC, 12
Union Road, Cambridge CB2, 1EZ, UK (Fax: int. code +
44(0)1223/336-033, e-mail: deposit @ chemcrys.cam.uk).
3.1.1. Spectroscopic and analytical data of 3a
31P{1H} NMR (CDCl3, 303 K): [ppm] lP(A,A%)=
138.3; lP(XX%)=26.6; J(AA%)=42.1, J(AX)=517.1,
J(AX%)= −2.7, J(XX%)=3.7; −13C{1H} NMR
(CDCl3, 303 K): [ppm] lC=9.6 (t, CH2); 26.8 (m,
CH3(tBu)); 42.4 (s, C(tBu)); 128.5 (d, 10.2 Hz, C3-aryl);
130.5 (s, C4-aryl); 131,0 (d, 39.7 Hz, C1-aryl); 135.6 (d,
11.2 Hz, C2-aryl); −1H NMR (CDCl3, 303 K):
[ppm]=0.9 (m, CH2, 2 H) 1.12 (d, 16.3 Hz. CH3(tBu),
9 H); 7.45 (m, Ph, 9 H), 7.78 (m, Ph, 6 H) (nJ(C,P) and
nJ(H,P) in parentheses). Analysis found: C, 50.85; H,
4.94; Cl, 13.34. C46H52Cl4P4Pd2 (1083.46). Calculation:
C, 50.99; H, 4.84; Cl, 13.09%.
.