Triphosphane formation from the terminal zirconium phosphinidene complex [Cp2Zr=PDmp(PMe3)] (Dmp=2,6-Mes2C6H3) and crystal structure of DmpP(PPh2)2

Article abstract of DOI:10.1016/S0022-328X(01)00863-4

The new terminal phosphinidene complex [Cp₂Zr=PDmp(PMe₃)] (Dmp=2,6-Mes₂C₆H₃; 1) was prepared in 81% yield by the reaction of [Li(Et₂O)][P(H)Dmp] with [Cp₂Zr(Me)Cl] in the presence of excess PMe₃. Compound 1 reacts with Ph₂PCl to produce selectively the sterically congested triphosphane DmpP(PPh₂)₂ (2) and [Cp₂ZrCl₂] in high yields. The structure of 2 obtained by X-ray diffraction analysis of a single crystal reveals phosphorus-phosphorus bond lengths of 2.251(2) and 2.234(2) ? and a PPP bond angle of 105.46(6)°.

Full text of DOI:10.1016/S0022-328X(01)00863-4

Journal of Organometallic Chemistry 630 (2001) 193–197
www.elsevier.com/locate/jorganchem
Triphosphane formation from the terminal zirconium
phosphinidene complex [Cp2ZrꢀPDmp(PMe3)]
(Dmp=2,6-Mes2C6H3) and crystal structure of DmpP(PPh2)2
Eugenijus Urnezius a, Kin-Chung Lam b, Arnold L. Rheingold b,
John D. Protasiewicz a,*
a Department of Chemistry, Case Western Reser6e Uni6ersity, 10900 Euclid A6enue, Cle6eland, OH 44106-7708, USA
b Department of Chemistry and Biochemistry, Uni6ersity of Delaware, Newark, DE 19716-2522, USA
Received 23 February 2001; received in revised form 25 April 2001; accepted 26 April 2001
Abstract
The new terminal phosphinidene complex [Cp2ZrꢀPDmp(PMe3)] (Dmp=2,6-Mes2C6H3; 1) was prepared in 81% yield by the
reaction of [Li(Et2O)][P(H)Dmp] with [Cp2Zr(Me)Cl] in the presence of excess PMe3. Compound 1 reacts with Ph2PCl to produce
selectively the sterically congested triphosphane DmpP(PPh2)2 (2) and [Cp2ZrCl2] in high yields. The structure of 2 obtained by
,
X-ray diffraction analysis of a single crystal reveals phosphorus–phosphorus bond lengths of 2.251(2) and 2.234(2) A and a PPP
bond angle of 105.46(6)°. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Phosphorus; Phosphinidene complexes; Triphosphane; Crystal structures; Electrophile addition
1. Introduction
Phosphinidene transfers using this reagent are also
equally effective for other phosphorus–heteroatom
bond forming processes using germanium, silicon, and
tin halides [2].
We are interested in developing zirconium-based
transfer chemistry for phosphinidenes bearing meta-ter-
phenyl [4,5] protected phosphorus centers [6–21]. In
particular, we sought new methods for constructing
phosphorus–phosphorus bonds that might utilize zirco-
nium phosphinidene complexes [13]. Herein we present
the synthesis of a terminal phosphinidene complex
bearing a meta-terphenyl ligand and its reaction with a
chlorophosphine to generate a novel triphosphane.
Organozirconium complexes have found widespread
use in the synthesis of new organophosphorus com-
pounds [1]. In particular, a number of fascinating mate-
rials have been prepared using the readily prepared
terminal phosphinidene complex [Cp2ZrꢀPMes*(PMe3)]
(Mes*=2,4,6-tBu3C6H2) to deliver the phosphinidene
‘PMes*’ [2,3]. The high oxo- and chlorophilicity of the
zirconium center in [Cp2ZrꢀPMes*(PMe3)] will readily
allow exchange of its phosphinidene unit for two chlo-
rine atoms or an oxygen atom of a substrate to form
either [Cp2ZrCl2] or [Cp2ZrO]n, respectively. For exam-
ple,
reaction
of
[Cp2ZrꢀPMes*(PMe3)]
with
dichloromethane affords a rapid and convenient syn-
thesis of the methylenephosphaalkene Mes*PꢀCH2 in
good yields (Eq. (1)).
2. Results and discussion
Stephan and Breen have illustrated that the terminal
phosphinidene complex [Cp2ZrꢀPMes*(PMe3)] is pro-
duced in high yields by reaction of [Li(THF)3]-
[P(H)Mes*] with [Cp2Zr(Me)Cl] in the presence of
excess PMe3 [2]. Accordingly, this method was chosen
for synthesis of the desired complex bearing the
meta-terphenyl Dmp (Dmp=2,6-Mes2C6H3) in place
[Cp2ZrꢀPMes*(PMe3)]+CH2Cl2
“[CP2ZrCl2]+Mes*PꢀCH2 (86%)
(1)
* Corresponding author. Tel.: +1-216-368-5060; fax: +1-216-368-
3006.
E-mail address: jdp5@po.cwru.edu (J.D. Protasiewicz).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)00863-4

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E. Urnezius et al. / Journal of Organometallic Chemistry 630 (2001) 193–197
31P{1H}-NMR of 1 is found at l 771.0 (d, JPP=23 Hz),
which can be compared to data for [Cp2ZrꢀPMes*
(PMe3)]: l 792.4 (d, JPP=23 Hz). Unfortunately, a high
quality X-ray structure of 1 could not be obtained. A
preliminary structure, however, confirmed the expected
of the supermesityl (Mes*) group. The new terminal
phosphinidene complex [Cp2ZrꢀPDmp(PMe3)] (1) was
thus isolated as a deep green crystalline material by
reaction of [Cp2Zr(Me)Cl] and [Li(Et2O)][P(H)Dmp] in
the presence of excess PMe3 in 81% yield (Eq. (2)).
(2)
gross structural features of 1. In particular, a short
Compound 1 is thermally stable in the absence of air or
water. The presumed precursor to 1, [Cp2Zr(Me)-
{P(H)Dmp}], can be isolated as a somewhat unstable
orange solid if the reaction is performed in the absence
of trialkylphosphine (31P-NMR (C6D6): l 33.3 (d,
,
ZrꢀP bond length of dZrꢀP=2.446(8) A (compare to
,
ZrꢀP=2.505(4) A for [Cp2ZrꢀPMes*(PMe3)]) and a
d
significantly bent zirconium phosphinidene array with a
ZrꢀPꢁC angle of 123.2(8)° could be ascertained.
We previously reported on the structural characteri-
zation of the stable phosphanido complexes [Cp2Zr(Cl)-
{P(H)Dmp}] and [Cp2Zr{P(H)Dmp}2] [20]. Although
Group 4 phosphanido complexes are well-known spe-
cies, species of the form [Cp2M(Cl){P(PR2)R}] are rare
or unknown [22]. Thus the reaction of 1 with Ph2PCl
was examined with the anticipation that [Cp2Zr(Cl)-
{P(PPh2)Dmp}] might be isolable (Eq. (3)).
J
PH=255 Hz)). However, attempts to purify this mate-
rial completely were unsuccessful. The 1H- and
31P{1H}-NMR spectra of 1 are in accord with the
previously characterized zirconium phosphinidene com-
plex [3]. For example, the phosphinidene signal in the
Table 1
Crystal data and structure refinement for DmpP(PPh2)2 (2)
Empirical formula
Formula weight
Temperature (K)
C48H45P3
714.75
173(2)
(3)
,
Wavelength (A)
0.71073
Monoclinic
P21/n
Crystal system
Space group
Reaction of equimolar amounts of 1 and Ph2PCl is
rapid and affords a single new organophosphorus spe-
cies. Surprisingly, the new species is not a zirconium
phosphanido complex but the novel triphosphane
DmpP(PPh2)2 (2; Eq. (4)). The triphosphane displays
very diagnostic 31P resonances at l −18.0 (d, JPP=221
Hz) and −52.3 (t, JPP=221 Hz). As expected for the
stoichiometry of the reaction, the 31P-NMR spectrum
of the reaction mixture shows remaining 1. If the
reaction is performed with two equivalents of Ph2PCl,
then 1 is consumed completely and the triphosphane 2
is produced in essentially quantitative yield (\95% by
1H-NMR).
Unit cell dimensions
,
a (A)
11.2205(2)
21.8735(4)
16.0223(3)
90
93.7125(8)
90
3924.14(17)
4
1.210
1.85
1512
0.45×0.25×0.15
2.04–24.00°
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
3
,
V (A )
Z
Dcalc (Mg m−3
)
Absorption coefficient (cm−1
F(000)
)
Crystal size (mm)
q Range for data collection
Index ranges
−11BhB12, −25BkB22,
−18BlB17
Reflections collected
Independent reflections
Refinement method
13 597
5620 [Rint=0.0599]
Full-matrix least-squares on
F2
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I\2|(I)]
R indices (all data)a,b
5620/0/460
2.103
R1=0.0784, wR2=0.1749
R1=0.1026, wR2=0.1860
0.442 and −0.441
(4)
Largest difference peak and hole
−3)
,
(e A
Crystals of 2 were grown from a THF–hexanes
mixture at −35°C and the results of a single-crystal
X-ray structure determination is presented in Fig. 1 and
Tables 1 and 2. Despite the severe steric crowding in
the molecule, the geometry at each phosphorus atom is
a R(F)=ꢀꢁꢁFoꢁ−ꢁFcꢁꢁ/ꢀꢁFoꢁ.
b Rw(F2)=[ꢀ{w(Fo2−Fc2)2}/ꢀ{w(Fo2)2}]0.5
;
w
−1=|2(Fo2)+
(aP)2+bP, where P=[Fo2+2Fc2]/3 and a and b are constants ad-
justed by the program.

E. Urnezius et al. / Journal of Organometallic Chemistry 630 (2001) 193–197
195
Table 2
Several other structural features of 2 merit comment.
First, two pairs of nearly coplanar aromatic rings can
be discerned (Fig. 1) that might suggest p stacking. The
pair of phenyl rings containing atoms C(31) and C(37)
deviate from coplanarity by only 18.9°, and have a
Selected bond lengths and bond angles for DmpP(PPh2)2 (2)
P(1)ꢁP(2)
P(1)ꢁP(3)
P(1)ꢁC(1)
P(2)ꢁC(25)
P(2)ꢁC(31)
P(3)ꢁC(37)
P(3)ꢁC(43)
2.2516(15)
2.2343(15)
1.859(5)
1.867(4)
1.846(5)
1.842(4)
1.844(4)
C(1)ꢁP(1)ꢁP(3)
C(1)ꢁP(1)ꢁP(2)
P(3)ꢁP(1)ꢁP(2)
C(2)ꢁC(1)ꢁP(1)
C(6)ꢁC(1)ꢁP(1)
C(31)ꢁP(2)ꢁC(25)
C(31)ꢁP(2)ꢁP(1)
C(25)ꢁP(2)ꢁP(1)
C(43)ꢁP(3)ꢁC(37)
C(43)ꢁP(3)ꢁP(1)
C(1)ꢁC(6)ꢁC(16)
C(3)ꢁC(2)ꢁC(7)
C(37)ꢁP(3)ꢁP(1)
102.96(13)
104.15(13)
105.46(6)
111.5(3)
128.9(3)
99.4(2)
95.84(14)
98.90(13)
101.68(19)
100.33(14)
124.3(4)
,
centroid–centroid distance of 4.02 A. The pair of aro-
matic rings involving atoms C(7) and C(43) are also
nearly coplanar (13.7°), but lie at a slightly greater
distance from one another (centroid–centroid distance
,
of 4.54 A). Second, the two PPh2 groups are directed
toward one of the two mesityl rings, and the resulting
steric clashes force the P(PPh2)2 unit further away from
this mesityl ring. This effect is evinced by a 17° dispar-
ity in the corresponding C(n)ꢁC(1)ꢁP(1) bond angles
(C(n) ꢀ C(2) and C(6)). Third, steric clashes between the
P(PPh2)2 unit and the Dmp group also force P(1) out of
120.5(4)
105.60(13)
,
the plane of the phenyl ring containing C(1) by 0.43 A.
The Dmp ligand also reacts to the steric pressures by
moving the mesityl rings away from the PPh2 unit, as
indicated by movement of the ipso-carbons of the
mesityl rings to the opposite side of the central phenyl
,
ring by 0.28 and 0.31 A for C(7) and C(16), respec-
tively. These structural distortions give rise to a
,
P(1)···C(7) ring centroid distance of 3.74 A, which is
longer than the Menshutkin-type interactions observed
in the related meta-terphenyls 2,6-Ar2ꢁC6H3ECl2 (Ar=
Mes or 2,4,6-iPr3C6H2; E=As, Bi or Sb; dE···centroid
ꢀ
,
3.4 A) [14].
reasonable pathway for the formation of
A
DmpP(PPh2)2 is outlined in Eq. (4). The putative inter-
mediate [Cp2Zr(Cl){P(PPh2)Dmp}], although not sta-
ble, finds precedent in the related reaction of
[Cp2ZrꢀPMes*(PMe3)] and Me2SiCl2. This reaction
produces Mes*P(SiMe2Cl)2, but if the reaction stoi-
chiometry is 0.5 [Cp2ZrꢀPMes*(PMe3)] to 1.0 Me2SiCl2,
the intermediate phosphanido complex [Cp2Zr(Cl)-
{P(Mes*)Si(Cl)Me2}] can be isolated in 71% yield [2].
The inability to isolate [Cp2Zr(Cl){P(Dmp)PPh2}] is
probably not a consequence of steric factors. Related
phosphanido complexes [Cp2Zr(Cl){P(H)Dmp}] and
[Cp2Zr{P(H)Dmp}2] have been prepared and character-
ized structurally [20]. The latter material is quite ther-
mally robust. Likewise, the extremely hindered
Fig. 1. Thermal ellipsoid plot for DmpP(PPh2)2.
mono-phosphanido
complex
[Cp2Zr(Cl){P(Mes*)-
essentially pyramidal. The PP bond lengths of 2.251(2)
SiMe3}] shows noteworthy thermal and photochemical
stability [26]. The failure to isolate [Cp2Zr(Cl){P(Dmp)-
PPh2}] probably lies in its enhanced reactivity with
Ph2PCl (relative to 1).
Alternative mechanisms for formation of 2 involving
radical intermediates (such as Ph2P ) are unlikely, as the
,
and 2.234(2) A and the PPP bond angle of 105.46(6)°
are comparable to values reported for two recent crys-
tallographically characterized silyltriphosphanes. For
i
example, in Pr3SiP(PPh2)2 the PP bond lengths are
,
2.243(1) and 2.217(1) A and the PPP bond angle is
’
100.0(1)° [23]. Likewise, Me3SiP(PtBu2)2 displays PP
reaction is exceptionally clean and Ph2PPPh2 (the antic-
ipated coupling product of two free Ph2P radicals) is
,
’
bond lengths of 2.1895(4) and 2.1964(4) A and a PPP
bond angle of 118.72(2)° [24]. All of the values are in
rough agreement with ab initio calculations (HF/6-
31G** level of theory) for hypothetical P3H5 that pre-
dict the most stable isomer to have PP bond lengths of
not detected. The reaction of DmpPCl2 with two equiv-
alents of LiPPh2 (or KPPh2) was investigated briefly as
an independent means for generating DmpP(PPh2)2.
This reaction gives multiple products, the major species
actually being Ph2PPPh2.
,
2.211 A and a PPP bond angle of 110.27° [25].

196
E. Urnezius et al. / Journal of Organometallic Chemistry 630 (2001) 193–197
3. Conclusions
reaction mixture was stirred for 30 min and then
filtered to afford 0.62 g of orange solid which was
ascertained to be predominantly [Cp2Zr(CH3)-
{P(H)Dmp}] (ca. 95%) by 1H- and 31P-NMR spec-
The terminal phosphinidene complex [Cp2ZrꢀPDmp-
(PMe3)] (1) was prepared and found to react cleanly
with Ph2PCl to produce the sterically congested triphos-
phane DmpP(PPh2)2 (2). The structure of 2 obtained by
single-crystal X-ray diffraction analysis confirms the
sterically congested nature of the central phosphorus
atom.
1
troscopy (crude yield 77%). H-NMR (C6D6): l 7.07
(m, 1H), 6.99 (m, 2H), 6.94 (s, 4H), 5.49 (s, 10H), 4.37
(d, 1H, JHP=255 Hz), 2.28 (s, 12H), 2.24 (s, 6H), 0.44
(d, 3H, 3JHP=8.3 Hz). 31P-NMR (C6D6): l 33.3 (d,
JHP=255 Hz).
4.4. Synthesis of DmpP(PPh2)2 (2)
4. Experimental
To a stirred solution of 1 (0.12 g, 0.18 mmol) in 6 ml
of benzene was added PPh2Cl (66.0 ml, 0.37 mmol) via
a microliter syringe. The reaction mixture gradually
turned pale yellow. After 30 min, the reaction mixture
was filtered through alumina plug and all volatiles were
removed in vacuo, affording 0.131 g (95% yield based
on 1H-NMR vs internal para-dimethoxybenzene) of
4.1. General procedures
All reactions, unless stated separately, were per-
formed in a Vacuum Atmospheres dry-box under dry
N2. All solvents were distilled from purple Na–ben-
zophenone solutions. DmpPH2 [6], [Li(Et2O)][P(H)-
Dmp] [20], and [Cp2Zr(Me)Cl] [27] were prepared as
reported. 1H-NMR spectra were recorded on Varian
Gemini 300 or 200 MHz instruments and referenced
using residual solvent proton signals. 31P-NMR spectra
were recorded on the Varian Gemini 300 MHz instru-
ment operating at 121.47 MHz and referenced to exter-
nal H3PO4 standard. Mass spectrometry was performed
at the CWRU departmental facility. Elemental analyses
were preformed by Oneida Research Services.
1
pale yellow DmpP(PPh2)2 (2). H-NMR (C6D6): l 7.04
(m, 9H), 6.93 (m, 2H), 6.83 (m, 16H), 2.31 (s, 6H), 2.15
(s, 12H). 31P{1H}-NMR (C6D6): l −18.0 (d, JPP=221
Hz), −52.3 (t, JPP=221 Hz). HRMS (EI) m/z Found:
714.2741. Calc. for C48H45P3: 714.2737. X-ray quality
crystals were obtained after slow crystallization from
hot THF–hexanes mixture (ca. 1:5) at −35°C.
4.5. X-ray crystallography for 2
4.2. Synthesis of [Cp2ZrꢀPDmp(PMe3)] (1)
The single-crystal X-ray diffraction experiment was
performed on a Siemens P4/CCD diffractometer for 2.
Systematic absences and diffraction symmetry for 2
were consistent with the monoclinic space group P21/n.
The structure was solved by direct methods, completed
by subsequent difference Fourier syntheses and refined
by full-matrix, least-squares procedures. All non-hydro-
gen atoms were refined with anisotropic coefficients and
all hydrogen atoms were treated as idealized
contributions.
[Li(Et2O)][P(H)Dmp] (1.40 g, 3.29 mmol) and
[Cp2Zr(Me)Cl] (0.87 g, 3.18 mmol) were dissolved in 20
ml of a 1.0 M toluene solution of PMe3 (20.0 mmol) at
room temperature. The solution turned orange–yellow
immediately upon dissolution and progressively turned
to a dark green solution over a period of 2 days. The
solution was filtered and the volume of the filtrate was
reduced in vacuo until substantial amounts of a dark
green solid had precipitated. The solid was filtered off,
washed with hexanes and dried in vacuo to afford 1.66
g of dark green 1a (81%). Analytical quality samples
were obtained by crystallization from hot toluene–hex-
anes (ca. 1:1) mixture. 1H-NMR (C6D6): l 7.15 (m,
3H), 6.82 (s, 4H), 5.43 (s, 5H), 5.42 (s, 5H), 2.43 (s,
12H), 2.23 (s, 6H), 0.41 (d, 9H, JHP=7.0 Hz). 31P{1H}-
NMR (C6D6): l 771.0 (d, JPP=23 Hz), −6.7 (d,
All software and sources of the scattering factors
were contained in the SHELXTL (5.03) program library
(G. Sheldrick, Siemens XRD, Madison, WI).
5. Supplementary material
JPP=23 Hz). Anal. Found: C, 69.44; H, 7.00. Calc. for
C37H44P2Zr: C, 69.23; H, 6.91%.
Crystallographic data for structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 158176 for 2. Copies of this
information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge CB2
1EZ, UK (Fax: +44-1223-336033; e-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
4.3. Synthesis of [Cp2Zr(CH3){P(H)Dmp}]
To a mixture of [Li(Et2O)][P(H)Dmp] (0.59 g, 1.38
mmol) and [Cp2Zr(CH3)Cl] (0.374 g, 1.375 mmol) was
added a mixture of toluene (4 ml)–Et2O (3 ml). The

E. Urnezius et al. / Journal of Organometallic Chemistry 630 (2001) 193–197
197
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Acknowledgements
[11] G.W. Rabe, S. Kheradmandan, L.M. Liable-Sands, I.A. Guzei,
A.L. Rheingold, Angew. Chem. Int. Ed. Engl. 37 (1998) 1404.
[12] G.W. Rabe, S. Kheradmandan, G.P.A. Yap, Inorg. Chem. 37
(1998) 6541.
We acknowledge the National Science Foundation
(CHE-9733412) for support of this research.
[13] E. Urnezius, S. Shah, J.D. Protasiewicz, Phosphorus, Sulfur,
Silicon Relat. Elem. 144–146 (1999) 137.
[14] B. Twamley, C.D. Sofield, M.M. Olmstead, P.P. Power, J. Am.
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