A new synthetic entry to phosphinophosphinidene complexes. Synthesis and structural characterisation of the first side-on bonded and the first terminally bonded phosphinophosphinidene zirconium complexes [μ-(1,2:2-η- tBu2P=P){Zr(Cl)Cp2}2] and [{Zr(PPhMe2)Cp2}(η1-P-PtBu 2)]

Article abstract of DOI:10.1039/b409673h

The reactions of lithiated diphosphanes with transition metal chlorides constitute a new general entry to phosphinophosphinidene complexes: the reaction of Cp₂ZrCl₂ (Cp = C₅H₅) with ^tBu₂P-P(SiMe₃)Li (molar ratio ?1:1) yields [μ-(1,2:2-η-^tBu₂P=P){Zr(Cl)Cp₂} ₂]; the reaction of Cp₂ZrCl₂ with ^tBu₂P-P(SiMe₃)Li (molar ratio ?1:2) and an excess of PPhMe₂ in DME yields the first terminally bonded phosphinophosphinidene complex, [(Zr(PPhMe₂)Cp₂) (η¹-P-P^tBu₂)].

Full text of DOI:10.1039/b409673h

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A new synthetic entry to phosphinophosphinidene complexes. Synthesis
and structural characterisation of the first side-on bonded and the first
terminally bonded phosphinophosphinidene zirconium complexes
[m-(1,2:2-g-tBu2PLP){Zr(Cl)Cp2}2] and [{Zr(PPhMe2)Cp2}(g1-P–
PtBu2)]{
Jerzy Pikies,*b Elke Baum,a Eberhard Matern,a Jarosław Chojnacki,b Rafał Grubbab and
Andrzej Robaszkiewiczb
a Institut fu¨r Anorganische Chemie der Universita¨t (TH), Engesserstr. 15 Geb. Nr. 30.45, D-76128
Karlsruhe, Germany
b
´
Chemical Faculty, Gdansk University of Technology, ul. Narutowicza 11/12, 80-952 Gdansk, Poland.
E-mail: pikies@chem.pg.gda.pl; Fax: 148 58 3472694; Tel: 148 58 3472622
´
Received (in Cambridge, UK) 25th June 2004, Accepted 12th August 2004
First published as an Advance Article on the web 16th September 2004
The reactions of lithiated diphosphanes with transition metal
chlorides constitute a new general entry to phosphinopho-
sphinidene complexes: the reaction of Cp2ZrCl2 (Cp = C5H5)
yields [m-(1,2:2-g-tBu2PLP){Zr(Cl)Cp2}2] (1) in 32% yield (eqn. 1)
t
together with Bu2P–P(SiMe3)2 and other compounds which we
were not able to isolate, but which could be characterised by 31P
NMR spectroscopy. 1 is only for a limited time stable in THF
solution. 31P{1H} NMR data of 1: P2 21.2 ppm (d), P1 93.9 ppm
t
with Bu2P–P(SiMe3)Li (molar ratio y1 : 1) yields [m-(1,2:2-
g-tBu2PLP){Zr(Cl)Cp2}2]; the reaction of Cp2ZrCl2 with
tBu2P–P(SiMe3)Li (molar ratio y1 : 2) and an excess of
PPhMe2 in DME yields the first terminally bonded phosphi-
nophosphinidene complex, [{Zr(PPhMe2)Cp2}(g1-P–PtBu2)].
1
(d), J(P–P) 2520.6 Hz.
t
t
2 [Cp2ZrCl2] 1 2 Bu2P–P(SiMe3)Li A Bu2P–P(SiMe3)2
(1)
1 2 LiCl 1 [m-(1,2:2-g-tBu2PLP){Zr(Cl)Cp2}2] (1)
The chemistry of the phosphinophosphinidene ligand tBu2P–P was
established by the group of Prof. Gerhard Fritz, mainly starting
The structure of
1 (Fig. 1){ reveals a pseudo five-fold
phosphinophosphinidene-s4-phosphoranes
tBu2P–
coordination sphere of the ligands around Zr1. Zr2 adopts a
pseudo tetrahedral coordination sphere with two g5-Cp rings, a Cl
and the P1 atom. The tBu2P–P ligand exhibits a side-on
coordination to Zr1 with a short P–P distance of 211.28(6) pm,
just in the range of side-on bonded phosphinophosphinidene
complexes.2,4 This is shorter than the P–P bond in [(g2-
MesPLPMes)ZrCpu2], Cpu ~ C5H4Et (218.8 pm) with an g2-
bonded diphosphene ligand10 but is almost the same as in the
from
t
PLP(X)tBu2 (X = Me, Br) as a source of the Bu2P–P moiety.1,2
The g2-coordination was found to be essential to stabilise the
tBu2P–P ligand, and up to 2004 only d10 ML2 Pt(0) metal centres
were found to be able to stabilise this ligand as a two electron donor
without additional g1-coordination of a second metal centre at the
phosphinidene P atom.3 Very recently Cummins has shown
another synthetic access to phosphinophosphinidene complexes
with the synthesis of the first such complex of Nb(III).4 Our current
investigations on the reactivity of lithium and trimethylsilyl
derivatives of di- and triphosphanes towards transition metal
halides presented us with the up to now most general and simplest
entry into this unique class of compounds. Using lithiated
diphosphanes R2P–P(SiMe3)Li rather than R2P–PLPR’3 as pre-
cursors of the R2P–P group offers substantial advantages:
i. The synthesis of R2P–P(SiMe3)Li is simpler5 than the relatively
tedious one of R2P–PLPR’3.6
similar complex [m-(1,2:2-g-tBu2PLP){Mo(CO)2Cpt}2] (Cpt
~
t
C5H4 Bu) – 211.4 pm.11
The Zr1–P2 bond length of 283.9(4) pm is very large whereas the
Zr1–P1 distance of 267.9 pm is similar to the Zr–P distance
(265.0 pm) in [(g2-MesPLPMes)ZrCpu2].10 The bond length P1–
Zr2 of 255.97(5) pm is in the same range as in [Cp2(Cl)ZrP(SiMe3)2]
(254.7 pm),12 thus it provides the evidence of a moderate degree of
Zr2–P1 p bonding in 1. The geometry around P1 is not planar. The
ii. The range of well-characterized and easily accessible
phosphinophosphinidene-s4-phosphoranes R2P–PLPR’3 is limited
and some compounds of this type (R = Et2N, SiMe3) are not
obtainable in the known way.7
iii. The reaction of R2P–P(SiMe3)Li with [L2PtCl2] (L ~ tertiary
phosphine) yields complexes [L2Pt{g2-(R2PLP)}] with new side-on
bonded phosphinophosphinidene ligands R2PLP (R = Ph, Et2N,
i
iPr2N, Pr), which were not available in the known way, together
with the previously known [L2Pt{g2-(tBu2PLP)}].8
Now we extend our investigations to the reactivity of lithiated di-
and triphosphanes towards titanocene and zirconocene dichlorides.
Whereas the Ti(III) centre shows only a very low tendency to
coordinate the tBu2P–P ligand,9 the chemistry of this ligand bonded
to Zr(III) and Zr(II) centres is very rich. Herein we report some of
our latest results on the reaction of [Cp2ZrCl2] (Cp = C5H5) with
tBu2P–P(SiMe3)Li.
Fig. 1 Solid-state structure of 1 showing the atom labelling scheme,
hydrogen atoms are omitted for simplicity. Selected bond distances (pm)
and angles (u): Zr1–P1 267.98(5), Zr1–P2 283.9(4), Zr2–P1 255.97(5), P1–
P2 211.28(6), P2–C21 191.0(2), P2–C25 191.04(18), P2–P1–Zr2 135.71(2),
P2–P1–Zr1 71.549(18), Zr2–P1–Zr1 142.487(18), C21–P2–C25 109.06(8),
Cl1–Zr1–P1 124.696(16), Cl2–Zr2–P1 99.338(16). Thermal ellipsoids at
35% probability.
t
The reaction of the lithiated diphosphane Bu2P–P(SiMe3)Li
with [Cp2ZrCl2] in a molar ratio of about 1 : 1 in THF or DME
{ Electronic supplementary information (ESI) available: experimental,
NMR, crystallographic. See http://www.rsc.org/suppdata/cc/b4/b409673h/
2 4 7 8
C h e m . C o m m u n . , 2 0 0 4 , 2 4 7 8 – 2 4 7 9
T h i s j o u r n a l i s ß T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

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P2–P1–Zr2 angle of 135.71(2)u and the torsion angle Zr2–P1–P2–
t
Zr1 of 148.8(2)u both suggest that Bu2P–P adopts the distorted
geometry of 1,1-di-tert-butyldiphosphene, with a visible steric effect
of an inert electron pair on P1 in this complex (Fig. 2, 1 and Fig. 3,
A). The fragment (tBu)2PLP–ZrCp2Cl in 1 can be seen as related to
the phosphanyl phosphenium ion13 with a double P–P bond and an
inert electron pair. The large value of 1J(P–P) ~ 2520.6 Hz
additionally indicates the multiple bond character of P1–P2 in 1.
Surprisingly, the unusual zirconium complex 1 is more stable
than the hypothetical symmetric one [(m2-tBu2P–P){Cp2ZrCl}2]
(Fig. 2, 1a) which is similar to the known [(m2-PMes){Cp2ZrCl}2]
(Fig. 2, 3) (Mes = 2,4,6-Me3C6H2).14
The special geometry of 1 (Fig. 2) only can be realised due to the
conjugation between P2 with a free electron pair and the
phosphinidene atom P1 (Fig. 3, A). This is not possible for 3.
The geometry of 1 cannot be explained in terms of an additional
coordination of P2 to Zr1 in 1a because this would not lead to the
observed significant shortening of the P1–P2 bond, which is in the
range of a side-on bonded short double bond.
The possible terminal coordination of H2P–P to various metal
centers was discussed,15 however no compound with R2P–P
bonded only via the phosphinidene P atom to a metal center
became known. Terminally bonded nucleophilic phosphinidene
R–P complexes are rare and their stability is achieved by steric
protection due to a bulky group R (R is not able to conjugate with
the electron deficient P atom).16 Recently, complexes of the
electrophilic aminophosphinidene iPr2N–P were synthesized and in
some cases the X-ray structures determined.17,18
Fig. 4 Solid-state structure of 2, showing the atom labelling scheme. Only
one of two independent molecules in the asymmetric unit is shown.
Hydrogen atoms are omitted for simplicity. Selected bond lengths (pm) and
angles (u): Zr1–P1 248.8(3), Zr1–P3 273.4(3), P1–P2 220.0(4), P2–C19
194.9(13), P2–C23 190.9(12), P2–P1–Zr1 115.53(16), C19–P2–C23
108.3(5), P1–Zr1–P3 88.49(10), P1–P2–C23 104.1(4), P1–P2–C19
100.5(4). Thermal ellipsoids drawn at 25% probability. The data on the
second molecule are given in the supplementary material.
group does not conjugate with the electron deficient phosphinidene
atom P1. This is in strong contrast to the side-on bonded
phosphinophosphinidene ligand, e.g. in [(R3P)2Pt{g2-(R2PLP)}]2
t
or in 1, where the Bu2PLP ligand adopts a 1,1-di-tert-butyl-
diphosphene geometry. Thus our ligand in 2 may be regarded as
similar to structure B (Fig. 3). DFT calculations to elucidate the
bondings in these systems and the stabilisation effect of the
Now we report our successful synthesis of the first metal complex
containing a terminally bonded R2P–P ligand. The reaction of
tBu2P–P(SiMe3)Li?2THF with a solution of Cp2ZrCl2 and PPhMe2
(molar ratio 1 : 2 : 10) in DME and crystallization from pentane
yields [{Zr(PPhMe2)Cp2}(g-P–PtBu2)] (2), the zirconium complex
with a terminally bonded tBu2P–P ligand in 44% yield together with
t
relatively small Bu2P group are currently in progress.
J.P. and A.R. thank the Polish State Committee of Scientific
Research (project No. 4 T09A 028 22 – phosphinophosphinidene
R2P–P, a novel p electron ligand) for financial support. We thank
Prof. Dr H. Schno¨ckel (Institut fu¨r Anorganische Chemie der
Universita¨t Karlsruhe) for generous support and for providing the
Stoe IPDS diffractometer time.
tBu2P–P(SiMe3)2 and other products which were identified by 31
NMR spectroscopy.
P
[Cp2ZrCl2] 1 2 tBu2P–P(SiMe3)Li 1 PPhMe2 A tBu2P–P(SiMe3)2
1 [{Zr(PPhMe2)Cp2}(g1-P–PtBu2)] (2) 1 2 LiCl
(2)
Notes and references
Although solutions of 2 in DME are indefinitely stable in the
presence of an excess of PPhMe2 at ambient temperature, an
attempt to dissolve 2 in THF-d8 resulted in a partial decomposition
of this compound. The 31P{1H} NMR spectrum clearly reflects the
geometry of 2 in solution. The low field resonance of P1 is typical
for terminal ‘‘bent’’ phosphinidene complexes.19,20 The small
{ CCDC 225538. See http://www.rsc.org/suppdata/cc/b4/b409673h/ for
crystallographic data in .cif or other electronic format.
§ CCDC 232586. See http://www.rsc.org/suppdata/cc/b4/b409673h/ for
crystallographic data in .cif or other electronic format.
1
1 G. Fritz and P. Scheer, Chem. Rev., 2000, 100, 3341.
2 J. Olkowska-Oetzel and J. Pikies, Appl. Organomet. Chem., 2003, 17, 28.
3 E. Matern, J. Pikies and G. Fritz, Z. Anorg. Allg. Chem., 2001, 627, 999.
4 J. S. Figueroa and C. C. Cummins, Angew. Chem., 2004, 116, 1002.
5 G. Fritz, T. Vaahs and J. Ha¨rer, Z. Anorg. Allg. Chem., 1987, 552, 11.
6 I. Kovacs, V. Balema, A. Bassowa, E. Matern, E. Sattler, G. Fritz,
H. Borrmann, K. Bauernschmitt and R. Ahlrichs, Z. Anorg. Allg.
Chem., 1994, 620, 2033.
coupling J(P1–P2) of 2283.7 Hz in 2 indicates a single bond
character of the P–P bond within the Bu2P–P ligand.
t
The X-ray structure determination§ of 2 (one of the two
independent molecules in the asymmetric unit is shown in Fig. 4)
fully confirms the NMR results. The distance of 248.8(3) pm
suggests a double bond character for Zr1–P1 and lies in the typical
region of Zr–P distances of terminal phosphinidene zirconium
complexes.18,19 TherelativelylongP1–P2distanceof220.0(4)pmand
the Zr1–P1–P2 angle of 115.52(16)uconfirm the NMR observations.
Apparently, in [{Zr(PPhMe2)Cp2}(g1-P–PtBu2)] the PtBu2
7 I. Kovacs, E. Matern and G. Fritz, Z. Anorg. Allg. Chem., 1996, 622,
935.
´
8 J. Chojnacki, W. Domanska, E. Matern and J. Pikies (in preparation).
9 E. Baum, E. Matern, J. Pikies and A. Robaszkiewicz, Z. Anorg. Allg.
Chem., 2004, 630, 1090.
10 S. Kurz and E. Hey-Hawkins, J. Organomet. Chem., 1993, 462, 203.
11 H. Krautscheid, E. Matern, J. Olkowska-Oetzel, J. Pikies and G. Fritz,
Z. Anorg. Allg. Chem., 2001, 627, 1505.
12 E. Hey-Hawkins, Chem. Rev., 1994, 94, 1661.
13 S. Loss, C. Windauer and H. Gru¨tzmacher, Angew. Chem., Int. Ed.,
1999, 38, 3329.
14 J. Ho and D. W. Stephan, Organometallics, 1991, 10, 3001.
15 G. Trinquier and G. Bertrand, Inorg. Chem., 1985, 24, 3842.
16 K. Lammertsma, Top. Curr. Chem., 2003, 229, 95.
17 J. B. M. Wit, G. T. van Eijkel, M. Schakel and K. Lammertsma,
Tetrahedron, 2000, 56, 13718.
Fig. 2 Geometries of 1, 1a and 3.
18 J. Sanches-Nieves, B. T. Sterenberg, K. A. Udachin and A. J. Carty,
J. Am. Chem. Soc., 2003, 125, 2404 and refs. cited therein.
19 Z. Hou, T. L. Breen and D. W. Stephan, Organometallics, 1993, 12, 3158.
20 E. Urnezius, K-C. Lam, A. L. Rheingold and J. D. Protasiewicz,
J. Organomet. Chem., 2001, 630, 193.
t
Fig. 3 Possible Lewis structures of the Bu2P–P group.
C h e m . C o m m u n . , 2 0 0 4 , 2 4 7 8 – 2 4 7 9
2 4 7 9