Phosphanylphosphido and phosphanylphosphinidene complexes of zirconium(IV) supported by bidentate N,N ligands

Article abstract of DOI:10.1016/j.poly.2016.12.005

Phosphanylphosphido complexes of zirconium, [NacNacZrCl₂(η²-R₂P–PSiMe₃)] (R?=?t-Bu, i-Pr), were synthesized in the reaction of R₂P–P(SiMe₃)Li·nTHF (R?=?t-Bu, i-Pr) with a β-diketiminate complex, [NacNacZrCl₃], in toluene. Elimination of Me₃SiCl from [NacNacZrCl₂(η²-R₂P–PSiMe₃)] provided the phosphanylphosphinidene complexes [NacNacZrCl(η²-R₂P–P)] (R?=?t-Bu, i-Pr). Moreover, the reaction of [NacNacZrCl₂(η²-R₂P–PSiMe₃)] with R₂P–P(SiMe₃)Li·nTHF yielded the phosphanylphosphinidenoid complexes [NacNacZrCl₂(η²-R₂P–PLi)] (R?=?t-Bu, i-Pr). The same reaction, but in the presence of 12-crown-4, gave rise to the phosphanylphosphinidene complexes [NacNacZrCl(η²-R₂P–P)]. The X-ray structures of [NacNacZrCl₂(η²-i-Pr₂P–PSiMe₃)] and [NacNacZrCl(η²-t-Bu₂P–P)] revealed that the R₂P-P ligands exhibit side-on coordination to the metal center. From the reaction of i-Pr₂P–P(SiMe₃)Li·3THF with [{PhN(CH₂)₃NPh)}ZrCl₂], a triple-core, anionic, phosphanylphosphinidene complex, [{PhN(CH₂)₃NPh)}Zr₃Cl₂(μ²-Cl)(μ²-i-Pr₂P–P)₂(μ³-i-Pr₂P–P)₂]^?[Li(DME)₃]⁺, was obtained in which the i-Pr₂P–P ligands exhibit bridging coordination.

Full text of DOI:10.1016/j.poly.2016.12.005

Accepted Manuscript
Phosphanylphosphido and phosphanylphosphinidene complexes of zirconi-
um(IV) supported by bidentate N,N ligands.
Mateusz Zauliczny, Rafał Grubba, Łukasz Ponikiewski, Jerzy Pikies
PII:
S0277-5387(16)30656-8
DOI:
http://dx.doi.org/10.1016/j.poly.2016.12.005
POLY 12363
Reference:
Polyhedron
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Revised Date:
Accepted Date:
17 October 2016
30 November 2016
1 December 2016
Please cite this article as: M. Zauliczny, R. Grubba, L. Ponikiewski, J. Pikies, Phosphanylphosphido and
phosphanylphosphinidene complexes of zirconium(IV) supported by bidentate N,N ligands., Polyhedron (2016),
doi: http://dx.doi.org/10.1016/j.poly.2016.12.005
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Phosphanylphosphido and phosphanylphosphinidene complexes of
zirconium(IV) supported by bidentate N,N ligands.
Mateusz Zauliczny, Rafał Grubba*, Łukasz Ponikiewski and Jerzy Pikies
Chemical Faculty, Department of Inorganic Chemistry, Gdansk University of Technology,
G. Narutowicza St. 11/12. Pl-80-233 Gdansk (Poland)
*To whom correspondence should be addressed: Email: grubba@pg.gda.pl
Abstract
Phosphanylphosphido complexes of zirconium, [NacNacZrCl2(η2-R2P–PSiMe3)] (R = t-Bu, i-
Pr), were synthesized in the reaction of R2P–P(SiMe3)Li·nTHF (R = t-Bu, i-Pr) with a β-
diketiminate complex, [NacNacZrCl3], in toluene. Elimination of Me3SiCl from
[NacNacZrCl2(η2-R2P–PSiMe3)] provided the phosphanylphosphinidene complexes
[NacNacZrCl(η2-R2P–P)] (R = t-Bu, i-Pr). Moreover, the reaction of [NacNacZrCl2(η2-R2P–
PSiMe3)] with R2P–P(SiMe3)Li·nTHF yielded the phosphanylphosphinidenoid complexes
[NacNacZrCl2(η2-R2P–PLi)] (R = t-Bu, i-Pr). The same reaction, but in the presence of 12-
crown-4, gave rise to the phosphanylphosphinidene complexes [NacNacZrCl(η2-R2P–P)]. The
X-ray structures of [NacNacZrCl2(η2-i-Pr2P–PSiMe3)] and [NacNacZrCl(η2-t-Bu2P–P)]
revealed that the R2P-P ligands exhibit side-on coordination to the metal center. From the
reaction of i-Pr2P–P(SiMe3)Li·3THF with [{PhN(CH2)3NPh)}ZrCl2], a triple-core, anionic,
phosphanylphosphinidene complex, [{PhN(CH2)3NPh)}Zr3Cl2(µ2-Cl)(µ2-i-Pr2P–P)2(µ3-i-
Pr2P–P)2]-[Li(DME)3]+, was obtained in which the i-Pr2P–P ligands exhibit bridging
coordination.
Keywords: coordination chemistry; zirconium complexes; P-donor ligands; phosphido
ligands; phosphinidene ligands.

Introduction
The lithium diphosphides R2P-P(SiMe3)Li (R = t-Bu, i-Pr, Et2N and i-Pr2N) display
fascinating diverse reactivity towards transition metal complexes. These diphosphorus
compounds
are
precursors
of
phosphanylphosphido
(R2P-P-SiMe3)1
and
phosphanylphosphinidene (R2P-P) ligands1a,2a-2d in the synthesis of transition metal
complexes. The reactions of R2P-P(SiMe3)Li and [L2MCl2] (M = Zr, Hf; L = Cp, indenyl) in
pentane or toluene give the terminal phosphanylphosphido complexes [L2MCl(Me3SiP-
PR2)].1a,1b Moreover the reactions of Cp2W and Cp2Mo metal centers with the R2P-P-SiMe3
anion lead to the formation of a new H4C5-P–Pt-Bu2 ligand and migration of an H atom or
SiMe3 group onto the Mo or W atom.1c,1d
The family of phosphanylphosphinidene (R2P-P) complexes exhibit great structural diversity
and can be divided into three main types of compounds. Firstly, side-on complexes have been
distinguished for platinum compounds [(η2-R2P=P)ML2] (M = Pt, L = tertiary phosphine)2b ,
anionic tungsten and molybdenum complexes [(2,6-i-Pr2C6H3N)2M(Cl)(η2-P=PR2)]- (M =
Mo, W)2c,2d, niobium complexes [(η2-P=PR2)Nb{N(3,5-Me2C6H3)Np}3]2e-2h and a tungsten
cationic complex [(η2-P=PR2)W{N(3,5-Me2C6H3)i-Pr}3]+ 2i, these and are derived from the
corresponding phosphido complexes and R2PCl. Moreover, until now only one example of a
µ2-bridging complex, [Cp2Zr{µ2-PP(NEt2)2}2ZrCp2]1a, and one terminal complex,
[{Zr(PPhMe2)Cp2}(η1-P–Pt-Bu2)]2a, are known. Recently Bertrand and co-workers have
opened a new chapter in the chemistry of phosphinidenes, showing the synthesis of free
phosphanylphosphinidene (other name phosphinophosphinidene) which is stable at room
temperature, being stabilized by a very bulky and π-electron donating substituents.3
In contrast to the chemistry of phosphanylphosphido complexes of zirconium, the chemistry
of phosphido complexes of zirconium(IV) with Cp (η5-C5H5) or Cp-derivatives as ancillary
ligands is well developed. The metathesis reactions of [Cp2ZrCl2] with R2PLi, where R is a
medium-size or voluminous substituent, yield mainly the desired [Cp2Zr(PR2)2]4a,4b. Reactions
of [Cp2ZrCl2] with lithiated primary phosphines4c-4i or lithiated trimethylsilyl phosphines1b, 3j-
3l
yield disubstituted or monosubstituted phosphido zirconium(IV) complexes, depending on
the steric properties of the R group and the reaction conditions. Complexes with a hydrogen
atom or a trimethylsilyl group in the phosphido ligand provide access to stable nucleophilic
phosphinidene2a, 4c, 4d, 5, 6 Zr(IV) complexes via elimination reactions. These compounds were
studied mainly because of the high oxo- and halogenophilicity of their metal centers, which
implies significant Wittig-like reactivity.

The chemistry of zirconium β-diketiminate complexes bearing intended functionalities at the
metal center is underdeveloped. No zirconium complexes containing phosphido or
phosphinidene groups with β-diketiminates as auxiliary ligands have been reported.
Conversely, the chemistry of carbene, nitrene and phosphinidene Ti(IV) complexes with
relatively robust and sterically demanding β-diketiminate groups7a-7c or pincer PNP ligands7d
is relatively well developed, mainly by Mindiola’s group. These ligands render substantial
stability to the resulting Ti(IV) phosphinidene complexes.
We recently began to study the reactivity of [NacNacTiCl2] and [NacNacTiCl3] towards
lithium derivatives of diphosphanes, R2P-P(SiMe3)Li (R = t-Bu, i-Pr), and demonstrated the
formation of side-on-bonded Ti(III) phosphanylphosphido and side-on-bonded Ti(IV)
phosphanylphosphinidene complexes.8 Now, we extend our efforts to the related zirconium
complexes with nitrogen-based auxiliary ligands and describe the reactivity of zirconium(IV)
complexes supported by bidentate diimido ligands, [{PhN(CH2)3NPh}ZrCl2], and β-
diketiminate ligands, [NacNacZrCl3], towards R2P-P(SiMe3)Li (R = t-Bu, i-Pr) in order to
compare this chemistry with the known reaction starting from [Cp2ZrCl2]1b, 2a and also to
compare the results to those with their Ti(IV) and Ti(III) counterparts.8
Results and discussion
The reaction of equimolar amounts of a β-diketiminate zirconium(IV) complex,
[NacNacZrCl3], with lithium phosphanylphosphides, R2P–P(SiMe3)Li, in toluene led to the
formation of rare Zr(IV) compounds containing phosphanylphosphido ligands (Scheme 1).
R
SiMe3
Cl
Zr
R
P
P
Cl
Cl
N
Cl Zr Cl
R2P-P(SiMe3)Li
Ar
N
Ar
+
Ar
N
N
Ar
-LiCl
R= i-Pr (1a), t-Bu (1b)
Ar= 2,6-i-Pr2C6H3
1a, 1b
Scheme 1 Syntheses of phosphanylphosphido complexes 1a and 1b.
The complex [NacNacZrCl2(η2-i-Pr2P–PSiMe3)] (1a) was isolated in high yield via
crystallization from a concentrated pentane solution at low temperature. Intensive red crystals
of 1a were sensitive towards moisture and oxygen, but could be stored at ambient temperature
for a relatively long time. The 31P{1H} NMR spectrum of a freshly prepared solution of 1a in
C6D6 displayed a set of two doublets at δ 32.9 and -54.1 ppm, which were assigned to i-Pr2P

1
and PSiMe3 groups, respectively. The absolute value of the coupling constant JPP = 432 Hz
was relatively large. A comparison of the 31P NMR data of 1a with the corresponding data of
the only known Zr(IV) complex with a terminal phosphanylphosphido ligand, [Cp2ZrCl(i-
1
Pr2P–PSiMe3-κP1)] (δ 35.1 (d, i-Pr2P) and 2.9 ppm (d, PSiMe3), JPP = 427 Hz),1b indicates
very similar δ values for the phosphanyl-P atoms, but the signal of the PSiMe3 group in the
terminal complex [Cp2ZrCl(η1-i-Pr2P–PSiMe3)] is shifted downfield compared to 1a because
of a partial double Zr-P bond in this complex, indicating the presence of a P→Zr π-donor
interaction in this case.9 On the other hand, the upfield shift of the PSiMe3 group in 1a
suggests single-bond character of the metal-phosphorus bond. X-ray structure analysis of
crystals of 1a confirmed the NMR results. The solid-state structure of 1a is shown in Figure 1.
Figure 1 X-ray structure of 1a showing the atom-numbering scheme. Ellipsoids are drawn at the 50%
probability level; H atoms have been omitted for clarity. Important bond lengths (Å) and bond angles
(°): Zr-P1 2.6686(8), Zr-P2 2.6800(6), P1-P2 2.143(1), P1-Si 2.2564(9), Zr-N1 2.260(2), Zr-N2
2.217(2), Zr-Cl1 2.4303(7), Zr-Cl2 2.4348(6), P1-Zr-P2 47.24(2), Zr-P1-P2 66.66(3), Zr-P2-P1
66.10(3), Zr-P1-Si 133.77(4), N1-Zr-N2 84.31(8), C1-Zr-Cl2 144.21(3), N1-Zr-P1 164.03(6), N2-Zr-
P2 132.47(6), ΣP1 310.43, ΣP2 338.13.
The zirconium atom is pentacoordinated, and the distorted bipyramid consists of Cl1, Cl2 and
N2atoms as a basal triangle with the N1 atom and the P1-P2 bond in vertical positions. This is
the first example of a zirconium complex with an η2-coordinated phosphanylphosphido
ligand. The side-on bonding of the phosphorus ligand strongly impacts the geometries at the P
atoms. The terminal phosphanylphosphido complex [Cp2ZrCl(i-Pr2P2-P1SiMe3-κP1)]
possesses relatively short Zr-P1 and P-P bonds; moreover, the i-Pr2P group is pyramidal (sum

of angles Σ = 313.11°), but the geometry around the terminal P1 atom exhibits a high degree
of planarity (Σ = 348.57°).1b For 1a, the Zr-P1 distance is significantly longer than in the
terminal complex (2.6686(8) vs. 2.583(1) Å), which indicates single-bond character.
Moreover, opposite to [Cp2ZrCl(i-Pr2P–PSiMe3-κP1)], the geometry around the P1 atom is
significantly pyramidal (Σ = 310.43°), but more planar (Σ = 338.13°) around the P atom of the
i-Pr2P group. Furthermore, the P-P distance in 1a is slightly shorter in comparison to the
terminal phosphanylphosphido complex (2.143(1) vs. 2.187(2) Å). Thus, these structural
differences in the side-on vs. terminal phosphanylphosphido zirconium complexes can be
rationalized according to the Lewis structures presented in Scheme 2.
R
R
SiMe3
SiMe3
R
P
R
P
P
P
Cl Zr Cl
Cl Zr Cl
Ar
N
N
Ar
Ar
N
N
Ar
side-on
R
SiMe3
R
SiMe3
R
P
P
R
P
P
Cp
Cp
Zr
Zr
Cl
Cp
Cl
Cp
terminal
Scheme 2 Comparison of the Lewis structures of the side-on and terminal phosphanylphosphido
zirconium(IV) complexes.
The stability of 1a in solution was tested by NMR spectroscopy. Crystals of 1a were
dissolved in C6D6 and stored in a flame-sealed NMR tube for a few weeks at room
31
temperature. The P{1H} NMR spectrum reveals the formation of only one new phosphorus
compound (2a), which exhibits a strong downfield resonance of an unsubstituted phosphorus
atom at δ 412.1 ppm and a resonance of the i-Pr2P group at δ 93.2 ppm with a coupling
1
1
constant of JPP= 435 Hz. Moreover, a strong signal from Me3SiCl appeared in the H
spectrum, that suggests elimination of this molecule from 1a. These findings indicate that the
newly formed compound 2a is a side-on phosphanylphosphinidene zirconium complex
(Scheme 3).

R
R
SiMe3
R
P
P
R
P
P
Zr Cl
Cl Zr Cl
Ar
N
N
Ar
Ar
N
N
Ar
- Me3SiCl
2a, 2b
R= i-Pr (1a, 2a); t-Bu (1b, 2b)
1a, 1b
Ar= 2,6-i-Pr2C6H3
Scheme 3 Transformations of the phosphanylphosphido complexes 1a and 1b into
phosphanylphosphinidene complexes 2a and 2b.
The molar ratio of 1a:2a in solution was 8:5, based on the integration of the signals of 1a and
1
2a in the H NMR spectrum, and this ratio did not change with time. Furthermore, an
equimolar amount of Me3SiCl relative to 2a was formed. Attempts to isolate 2a in the
crystalline form were unsuccessful because of its high solubility in hydrocarbons.
Importantly, an analogous reaction leading to phosphanylphosphinidene zirconium complexes
via elimination of Me3SiCl was not observed for the terminal complex [Cp2ZrCl(i-Pr2P–
PSiMe3-κP1)].1b We have also performed DFT calculations to better understand the structures
and reactivity of phosphanylphosphido and phoshanylphosphinidene zirconium complexes
supported by the NacNac ligand (for details see the supplementary materials). Hirshfeld
Population Analysis of 1a showed that the P-SiMe3 bond is polarized with a negative charge
on the phosphorus atom (-0.110) and a high positive charge on the silicon atom (0.348). This
feature of 1a can facilitate the elimination of Me3SiCl and formation of the
phosphanylphosphinidene complex 2a. The DFT-optimized structure of 2a shows that the i-
Pr2P-P group exhibits the η2 bonding mode (Figure S1, supplementary materials). Moreover,
the calculated 31P{1H} NMR spectrum of 2a revealed a low-field resonance of a
phosphinidene P-atom that is consistent with the experimental value (Table 1). Notably, the
low-field resonances of the phosphinidene P atoms are not necessarily connected with
phosphinidene “bent” complexes, i.e. side-on [NacNacTi(Cl)(η2-P–P-t-Bu2)] has an AX
pattern of δ 843.8, 143.6 ppm and 1JP-P = 457.8 Hz. 8
Table 1 Experimental and calculated 31P{1H} NMR data for complexes 1a-3b.
No. Experimental values
Calculated values
δP1
δP2
1JP1P2
[Hz]
432
δP1
δP2
1JP1P2
[Hz]
-463
[ppm]
-54.1
[ppm]
32.9
[ppm]
-46.7
[ppm]
25.7
1a

412.1
267.2
214.6
-62.8
432.7
283.2
93.2
49.7
45.7
29.8
117.1
76.2
435
436
436
482
441
443
514.8
287.5
65.7
72.9
-402
-424
2a
3a
3a’
1b
2b
3b
447.5
129.6
-414
The reactivity of 1a towards i-Pr2P-P(SiMe3)Li·3THF was investigated. 31P NMR analysis
revealed that the reaction of 1a with i-Pr2P-P(SiMe3)Li·3THF in a molar ratio of 1:1 in
pentane or THF led to the formation of new complexes, 3a or 3a’, together with i-Pr2P–
P(SiMe3)2 and small amounts of i-Pr2P–P(SiMe3)H and i-Pr2PH. A possible outcome of the
reaction of 1a with i-Pr2P-P(SiMe3)Li·3THF is presented in Scheme 4.
R
R
SiMe3
R
P
P
Li(thf)n
Ar
R
P
P
Cl Zr Cl
Cl Zr Cl
R2P-P(SiMe3)Li
Ar
N
N
Ar
N
N
Ar
- R2P-P(SiMe3)2
1a, 1b
R= i-Pr (1a, 3a, 3a'), t-Bu (1b, 3b)
3a, 3a', 3b
Ar= 2,6-i-Pr2C6H3
Scheme 4 Synthesis of the phosphanylphosphinidenoid complexes 3a, 3a’ and 3b.
This result clearly indicates that R2P–P(SiMe3)Li acts as a lithiation agent. The Me3Si group
of the phosphanylphosphido ligand is lithiated by 1 equivalent of phosphanylphosphide, with
the simultaneous formation of the phosphanylphosphinidenoid complexes 3 and disililated
diphosphane R2P–P(SiMe3)2. Activation of the P-Si bond was also observed by us during the
formation of the phosphanylphosphinidene complexes involving R2P–P(SiMe3)Li and
dichloride compounds of Zr,1a, 2a Mo2c, W2d and Pt2b supported by cyclopentadienyl, imido
and phosphine ligands. In the case of these reactions R2P–P(SiMe3)2 was also formed as a
second product, however the corresponding phosphanylphosphinidenoid complexes were only
postulated as a transient species on the way to the phosphanylphosphinidene complexes. In
contrast to these results, the reaction presented in Scheme 4 occurs even in non-donor
solvents, such as pentane, and stops at the stage of phosphanylphosphinidenoid complex
formation.
Depending on the reaction medium, complex 3a (pentane) or 3a’ (THF) can be formed. 3a
and 3a’ differ only in the chemical shift of the PLi group in 31P{1H} NMR spectra (Table 1).

This difference results from the different number of molecules of donor solvent that can
coordinate to the lithium atom. The resonance of the P1 atom in 3a is upfield shifted by
approximately 150 ppm compared to the resonance of the P1 atom in
phosphanylphosphinidene complex 2a. Zirconium complexes bearing an RPLi group were
31
previously identified in solution by Stephan3c and Protasiewicz.10 The P{1H} NMR spectra
of [Cp*2Zr(Cl){MesPLi}(DME)]3c and [Cp2Zr{dmpPLi}(dmpPH)]10 exhibit signals from an
RPLi group at δ 537.6 and 496.0 ppm, respectively, which are high-field shifted compared to
the parent phosphinidene ZrIV complexes supported by Cp ligands (δ 792.4 and 771.0
ppm).3c,5b The calculated 31P{1H} NMR spectrum of 3a is in good agreement with the
experimental results (see Table 1), which additionally confirms our findings. The DFT-
calculated structure of 3a is shown in Figure 2.
Figure 2 DFT-optimized structure of 3a. Important bond lengths (Å) and bond angles (°): Zr-P1
2.600, Zr-P2 2.623, P1-P2 2.132, P1-Li 2.497, Zr-N1 2.336, Zr-N2 2.297, Zr-Cl1 2.558, Zr-Cl2 2.459,
Cl1-Li 2.332, P1-Zr-P2 48.17, Zr-P1-P2 66.47, Zr-P2-P1 65.36, N1-Zr-N2 81.02, N1-Zr-P1 157.75,
N2-Zr-P2 129.17, ΣP1 244.5, ΣP2 335.7.
DFT calculations indicate that the phosphinidenoid complex 3a has an i-Pr2P–P ligand that
coordinates in an η2 fashion to the zirconium center and the P1 atom is additionally bonded to
the Li1 atom. One of the chlorido ligands (Cl1) forms a bridge between the zirconium and
lithium atoms and closes the distorted ring, Zr-P1-Li-Cl1. The Zr-P1, Zr-P2 and P1-P2
distances in 3a are slightly shorter than the corresponding bonds in 1a. Moreover, similar to
1a, the geometry around the P2 atom is flattened, but geometry of the P1 atom is more

pyramidal with respect to the phosphanylphosphido complex 1a. Compound 3a is additionally
stabilized by coordination of additional THF molecules to the lithium atom.
When the equimolar reaction of zirconium complex 1a with i-Pr2P–P(SiMe3)Li·3THF was
carried out in the presence of 12-crown-4 in THF, the 31P{1H} NMR spectrum of the reaction
mixture revealed the formation of phosphanylphosphinidene complex 2a, in addition to 3a’
and i-Pr2P–P(SiMe3)2. The molar ratio of these products was 2:3:5, based on integration of the
31
signals from the i-Pr2P groups in the P NMR spectrum. These observations suggest that the
addition of 12-crown-4 causes elimination of LiCl from 3a’ through the strong complexation
of the lithium cation, resulting in the formation of 2a and [Li(12-crown-4)]Cl (Scheme 5).
R
R
R
P
P
Zr Cl
N
R
P
P
Li(thf)n
Ar
Cl Zr Cl
12-crown-4
Ar
N
Ar
Ar
N
N
- [Li(12-crown-4)]Cl
2a, 2b
Ar= 2,6-i-Pr2C6H3
3a', 3b
R= i-Pr (2a, 3a'), t-Bu (2b, 3b)
Scheme 5 Reactions of phosphinidenoid complexes 3a’ and 3b with 12-crown-4.
t-Bu2P–P(SiMe3)Li·2.5THF reacted in toluene (molar ratio of 1:1) with [NacNacZrCl3],
similar to i-Pr2P–P(SiMe3)Li·3THF, yielding the phosphanylphosphido complex 1b (Scheme
1), which could further eliminate Me3SiCl with formation the phosphanylphosphinidene
zirconium complex 2b with a t-Bu2P-P ligand (Scheme 3). In the reactions with t-Bu2P–
P(SiMe3)Li·2.5THF, the contribution of radical side reactions was greater and significant
amounts of t-Bu2P-P(SiMe3)H were identified in all reaction mixtures.
The phoshanylphosphinidenoid complex 3b was derived from the reaction of t-Bu2P–
P(SiMe3)Li·2.5THF with [NacNacZrCl3] (DME, molar ratio 2:1, Scheme 4). The same
reaction, but in the presence of two equivalents of 12-crown-4, gave rise to 2b (Scheme 5).
Compounds 1b, 2b and 3b exhibited similar 31P{1H} NMR data as those of complexes 1a, 2a
and 3a/3a’, respectively (see Table 1).
Compounds 1b, 2b and 3b displayed very good solubility in hydrocarbons. Despite this fact,
complex 2b was isolated from a pentane solution in the reaction of [NacNacZrCl3] with t-
Bu2P–P(SiMe3)Li·2.5THF and 12-crown-4 (molar ratio of 1:2:2 in DME). Crystallization
from a pentane solution gave small red crystals of 2b, which slightly melted over -30°C;
therefore, all manipulation for the separation of 2b must be conducted below this temperature.

The procedure for the preparation of crystals of 2b for XRD is provided in the supplementary
materials. The molecular structure of 2b is shown in Figure 3.
Figure 3 X-ray structure of 2b showing the atom-numbering scheme. Ellipsoids are drawn at the 50%
probability level; H atoms have been omitted for clarity. Important bond lengths (Å) and bond angles
(°): Zr-P1 2.456(2), Zr-P2 2.640(2), P1-P2 2.104(2), Zr-N1 2.159(5), Zr-N2 2.187(5), Zr-Cl1 2.424(1),
P1-Zr-P2, Zr-P1-P2 70.27(6), Zr-P2-P1 61.12(6), N1-Zr-N2 90.1(2), N1-Zr-P1 88.1(1), N2-Zr-P2
104.7(1), ΣP2 330.8.
Importantly, the metric parameters of 2b are very similar to the DFT-optimized structure of
the analogous complex 2a (Figure S1). The geometry of the zirconium atom in 2b can be
described as distorted pseudotetrahedral, taking into account ligation by the P1-P2 bond and
the N1, N2 and Cl1 atoms. This is the first zirconium complex in which the
phosphanylphosphinidene ligand R2P–P exhibits side-on coordination. The most striking
features of 2b are the very short P1-P2 and Zr-P1 distances. The P1-P2 distance of 2.104(2) Å
is almost identical to that in the Ti (IV) analogue,8 similar to the P-P distances in tungsten and
molybdenum complexes2c,2d, 2i, 11 with R2P-P groups and nitrogen-based ancillary ligands, but
slightly longer than in phosphanylphosphinidene Pt(0) complexes.1b, 15 The P2 atom possesses
a substantially flattened pyramidal geometry. These features suggest a substantial π-bonding
contribution in the P-P and Zr-P1 bonds. DFT calculations indicate a positive charge on the
phosphanyl t-Bu2P group and a high negative charge on the phosphinidene P atom, which
supports the nucleophilic properties of 2b. The Zr-P1 bond length of 2.456(2) Å is very short,
shorter than in the terminal complex [{Zr(PPhMe2)Cp2}(P–Pt-Bu2)] (2.488(3) Å)1a and within
the range of Zr-P double bonds. Moreover, the highest occupied molecular orbital (HOMO) is

localized on a triangle of bonds, Zr1-P1-P2, with the center on the phosphinidene P1 atom.
The Zr-N1 and Zr-N2 distances are as expected for zirconium β-diketiminate complexes. The
Zr atom does not lie in the NacNac plane, with an average Zr-CCH3(NacNac) distance of
2.884 Å, which can indicate weak Zr-C interactions. Scheme 6 depicts the possible Lewis
structures for phosphanylphoshinidene complexes 1b and 2b.
R
R
R
P
P
R
P
P
Zr Cl
Zr Cl
Ar
N
N
Ar
Ar
N
N
Ar
Scheme 6 Possible Lewis structures of the side-on phosphanylphosphinidene zirconium(IV)
complexes.
The outcome of the reactions of [NacNacZrCl3] with the lithium salts of diphosphanes
strongly differs from the analogous reactions involving [NacNacTiCl3]. The reactions of
(R2P-PSiMe3)Li with β-diketiminate Ti(IV) complexes are dominated by redox reactions
which lead to the Ti(III) complex [NacNacTiCl2] and tetraphosphanes as products of the
oxidative dimerization of the phosphorus substrate.8 Ti(IV) phosphanylphosphido complexes
were not formed in these reactions, as was observed for the β-diketiminate complexes of
Zr(IV) compounds, and phosphanylphosphinidene Ti(IV) complexes were formed in low
yield due to the parallel dimerization of the R2P-PSiMe3 groups. Complexes with the R2P-
PSiMe3 ligand can only be obtained as Ti(III) paramagnetic compounds.
We have expanded our reactivity studies on the diamido Zr(IV) complex
[{PhN(CH2)3NPh}ZrCl2], which reacted with R2P–P(SiMe3)Li·3THF (R= i-Pr, t-Bu) to yield
mainly [{PhN(CH2)3NPh}2Zr] and insoluble products. However, the triple-core anionic
phosphanylphosphinidene
complex
4
together
with
i-Pr2P–P(SiMe3)2
and
[{PhN(CH2)3NPh}2Zr] were obtained from the reaction of i-Pr2P–P(SiMe3)Li·3THF with
[(PhN(CH2)3NPh)ZrCl2]. The proposed stoichiometry for the reaction path leading to
4·[Li(DME)3] is presented in Scheme 7.

Cl
Zr
Cl
N
N
O
O
5
+
8 i-Pr2P-P(SiMe3)Li
- 2 [(PhN(CH2)3NPh)2Zr]
- 4 i-Pr2P-P(SiMe3)2
- 7 LiCl
Cl
Cl
Zr
Cl
Li(DME)3
Zr
i-Pr2P
Pi-Pr2
P
P
Pi-Pr2
i-Pr2P
P
P
Zr
N
N
4
Scheme 7 Synthesis of phosphanylphosphinidene complex 4.
Single crystals of 4·[Li(DME)3] were grown slowly from a pentane/toluene mixture at room
temperature. The isolated crystals of 4·[Li(DME)3] were very moisture sensitive and
decomposed immediately during dissolution in C6D6 with the formation of insoluble products.
Figure 4 displays the X-ray structure of the anion 4. The zirconium atoms form a triangle with
an average Zr-Zr distance of 3.527 Å. The Zr1 atom displays a distorted octahedral geometry,
in which the N1 and N2 atoms of the diimido ligand and the four bridging phosphinidene P
atoms of the four different i-Pr2P–P ligands (P1, P3, P5, P7) are bonded to the metal center.
Atoms Zr2 and Zr3 display a distorted pseudo-trigonal-bipyramidal geometry, in which the P-
P bond of the i-Pr2P–P ligand, the i-Pr2P group of the other phosphorus ligand and two Cl
atoms coordinate to the metal centers. Two phosphanylphosphinidene ligands form a bridge
between the two Zr-atoms, whereas two other phosphorus ligands link all three metal atoms.

The i-Pr2P-Zr distances range from 2.656(2) to 2.684(3) Å, corresponding to single Zr-P
bonds.
Figure 4 X-ray structure of the anion 4 showing the atom-numbering scheme. Ellipsoids are drawn at
the 50% probability level; H atoms have been omitted for clarity. Important bond lengths (Å) and
bond angles (°): Zr1-P1 2.684(3), Zr1-P3 2.812(2), Zr1-P5 2.768(2), Zr1-P7 2.698(2), Zr1-N1
2.163(7), Zr1-N2 2.168(7), Zr2-P1 2.584(2), Zr2-P2 2.684(3), Zr2-P4 2.656(2), Zr2-P5 2.611(2), Zr2-
Cl1 2.479(3), Zr2-Cl2 2.642(2), Zr3-P3 2.594(2), Zr3-P6 2.660(3), Zr3-P7 2.589(3), Zr3-P8 2.677(3),
Zr3-Cl2 2.613(2), Zr3-Cl3 2.480(2), P1-P2 2.138(3), P3-P4 2.177(3), P5-P6 2.170(3), P7-P8 2.144(3),
N1-Zr1-N2 86.8(3), ΣP1 262.0, ΣP2 329.2, ΣP3 320.9, ΣP4 322.0, ΣP5 317.9, ΣP6 324.2, ΣP7 261.0,
ΣP8 331.7.
The Zr-P(phosphinidene) bonds lengths cover a wide range, 2.584(2)-2.812(2) Å. The
geometries around the P atoms are flattened pyramidal, except for the geometries around
atoms P1 and P7, that are pyramidal. The P-P distances vary from 2.138(3) to 2.177(3) Å,
which are significantly longer than the corresponding distance in 2b; however, these data still
indicate a moderate contribution of π-bonding.
The
syntheses
of
phosphanylphosphido,
phosphanylphosphinidenoid
and
phosphanylphosphinidene zirconium compounds 1-4 suggest stabilization of these
diphosphorus complexes by amido and NacNac spectator ligands. These two ligands are
powerful σ and π donors, thus they stabilize the high oxidation states of the metal complexes.
Moreover, these spectator ligands drive the binding of the R2P–P–SiMe3, R2P–P–Li and R2P–
P moieties into the side-on mode. A similar phenomenon was also established for phosphanyl-
2i
phosphinidene complexes of tungsten,2d,
molybdenium2c and niobium2e-2h containing
strongly electron donating amido and imido ligands. Furthermore these observations are in

strong contrast with the reactivity of Cp2ZrCl2 towards R2P–P(SiMe3)Li, where terminal
coordination of the diphoshorus ligands was observed in the resulting phosphanylphosphido
and phosphinidene complexes. This difference in reactivity can be explained by the weaker
electron donating properties of the cyclopentadienyl spectator ligand in comparison to amido,
imido and NacNac ligands.17 The side-on coordination of a R2P–P or R2P–P(SiMe3) ligand is
stabilized by π-backbonding from the metal center to the phosphorous ligands and thus high
electron density at the metal center seems to be crucial.
A comparison of the reactivity of lithium phosphanylphosphides with that of lithium
phosphides towards [NacNacZrCl3] indicates significant differences. To our surprise, the
reaction of R2PLi (R = t-Bu, Cy, Ph) with [NacNacZrCl3] in DME or toluene did not yield
zirconium complexes with phosphido ligands. 31P{1H} NMR analysis of the reaction mixtures
indicated only resonances from R2PH and R2P–PR2. The phosphides probably reduce the
starting Zr(IV) complex to form [NacNacZrCl2]·Ln and R2P radicals, which can further
dimerize or react with the solvent to yield R2PH (Scheme 8).
Ph2P-PPh2
Zr(IV)
Zr(III)
Ar
N
Ar
Cl
N
Cl
Cl
Ph2PLi
-LiCl
Zr Cl
Cl
Zr
N
Ph2P
+
N
Ar
Ar
solvent
Ar= 2,6-i-Pr2C6H3
Ph2PH
Scheme 8 Reaction of [NacNacZrCl3] with lithium phosphide.
The difference in reactivity of R2P–P(SiMe3)Li and R2PLi can be explained by the distinct
structural features of the phosphanylphosphido and phosphido anions. Based on the X-ray
analysis of the lithium salts R2P–P(SiMe3)Li·nL (R = i-Pr, t-Bu, i-Pr2N, Ph; L = THF, DME,
TMEDA, 12-crown-4), the significant shortening of the P–P distances compared to the
corresponding diphosphanes suggests partial P–P multiple-bond character.18 Considering
these observations, the structure of the phosphanylphosphido anion can be described by two
possible resonance structures (Scheme 9).

SiMe3
SiMe3
R
R
R
R
R
R
P
P
P
P
P
phosphido
phoshanylphosphido
Scheme 9 Comparison of the Lewis structures of the phosphido and phosphanylphosphido anions.
Delocalization of the free electron pairs on the phosphorus atoms in R2P–P(SiMe3)- weakens
the reducing ability of this anion. This delocalization is in contrast to the phosphido ligand, in
which the electron density is located mainly around one phosphorus atom, which is
manifested as the stronger reducing properties of the R2P- anion.
Materials and methods
THF and DME were dried over K/benzophenone and distilled under argon. Toluene was dried
over Na/benzophenone and distilled under argon. Pentane was dried over
Na/benzophenone/diglyme and distilled under argon. All manipulations were performed in
flame-dried Schlenk-type glassware on a vacuum line. Solution 31P, 13C and 1H NMR spectra
were recorded on Bruker Avance III HD 400 MHz spectrometer (external standard TMS for
13
1H, C; 85% H3PO4 for 31P) at ambient temperature. We have determined the composition of
the reaction solutions by integration of the R2P signals in the 31P{1H} NMR spectra.
Literature methods were used to prepare t-Bu2P-P(SiMe3)Li·2.5THF, i-Pr2P-
P(SiMe3)Li·3THF,18 [NacNacZrCl3]19 and [{PhN(CH2)3NPh}ZrCl2]. 20
Reaction of [NacNacZrCl3] with i-Pr2P-P(SiMe3)Li·3THF in toluene (molar ratio 1:1).
Synthesis of [NacNacZrCl2(η2-i-Pr2P–PSiMe3)] (1a).
A solution of i-Pr2P-P(SiMe3)Li·3THF (167 mg, 0.375 mmol) in 2 mL of toluene was added
dropwise to a solution of [NacNacZrCl3·0.42DME] (245 mg, 0.375 mmol) in 2 mL of toluene
at -30 °C. During the reaction, the color of the solution changed from yellow to red. The
mixture was then warmed up to ambient temperature. The volume of the mixture was reduced
31
to one half under reduced pressure and the remaining solution was analyzed by 31P{1H}, P
1
and H NMR spectroscopy. The solvent was then evaporated under reduced pressure and the
residue was extracted with 10 mL of pentane. The pentane extract was concentrated to 3 mL
and stored at -30 °C for a few days. After this time, red crystals of 1a·pentane precipitated.
Isolated crystals lose pentane under reduced pressure and after evacuation of the crystalline

material; 250 mg of 1a (yield 76%) was obtained. Elemental analysis, found %: C 57.09, H
8.05, N 3.43 calc. % for C43H76Cl2N2P2SiZr: C 56.97, H 8.05, N 3.50.
1a·pentane: 31P{1H} NMR (C6D6) δ: 32.9 (d, 1JPP = 431.9 Hz, i-Pr2P), -54.1 (d, 1JPP = 431.9
Hz, PSiMe3).
1H NMR (C6D6) δ: 7.10-7.18 (m, 6H, C6H3CH(CH3)2, overlapped with solvent signal), 5.36
3
(s, 1H, CH3C(NAr)CHC(NAr)CH3), 3.49 (m, 4 H, C6H3CH(CH3)2), 2.62 (dsept, JHH = 7.3
2
Hz, JPH = 8.2 Hz, 2H, PCH(CH3)2), 1.53 (s, 6 H, CH3C(NAr)CHC(NAr)CH3, overlapped),
3
3
3
1.52 (d, JHH = 6.5 Hz, 12H, C6H3CH(CH3)2), 1.35 (dd, JHH = 7.3 Hz, JPH = 18.0 Hz, 6H,
3
3
PCH(CH3)2), 1.28 (dd, JHH = 7.3 Hz, JPH = 18.0 Hz, 6H, PCH(CH3)2), 1.23 (m,
3
3
CH3(CH2)3CH3, pentane), 1.20 (d, JHH = 6.9 Hz, 12H, C6H3(CH(CH3)2); 0.87 (t, JHH = 6.5
Hz, CH3(CH2)3CH3, pentane), 0.09 (d, 3JPH = 4.0 Hz, 9H, PSi(CH3)3).
13C{1H} NMR (C6D6) δ: 166.0 (CH3C(NAr)CHC(NAr)CH3), 142.4, 142.0, 126.6, 125.5,
124.2, 123.2 (C H3CH(CH3)2), 103.8 (CH3C(NAr)CHC(NAr)CH3) 34.1 (CH3(CH2)3CH3,
6
pentane), 29.9 (m, PCH(CH3)2), 28.7 (C6H3CH(CH3)2, 26.4, 24.3 (C6H3CH(CH3)2), 24.3
(CH3C(NAr)CHC(NAr)CH3), 24.1, 23.1 (PCH(CH3)2), 22.4 (CH3(CH2)2CH3, pentane), 13.9
(CH3(CH2)2CH3, pentane), 3.6 (d, 2JPC = 11.7 Hz, PSi(CH3)3).
The decay of 1a·pentane in C6D6 solution was monitored by NMR spectroscopy over a few
weeks. 30 mg of crystalline 1a·pentane was dissolved in 0.7 mL of C6D6 and stored in a
1
13
31
13
flame-sealed NMR tube. This solution was analyzed by 31P, H, C, P HMBC, C HMQC
31
1
13
and 13 HMBC NMR spectroscopy. Results of examination of the P{1H}-NMR, H and C
NMR spectra of a C6D6 solution of 1a·pentane after a one week at room temperature: 1a
(44%), 2a (28%), Me3SiCl (28%) and t-Bu2PH (observed before in spectra of freshly
dissolved 1·pentane).
2a: 31P{1H} δ: 412.1 (d, 1JPP = 435.4 Hz, P); 93.2 (d, 1JPP = 435.4 Hz, i-Pr2P).
1H NMR (C6D6) δ: 7.15 (m, 6H, C6H3CH(CH3)2, overlapped with solvent signal), 4.86 (s, 1H,
3
CH3C(NAr)CHC(NAr)CH3), 3.32, (sept, JHH = 7.0 Hz, 2 H, C6H3CH(CH3)2), 3.30 (sept,
3
2
3JHH = 7.0 Hz, 2 H, C6H3CH(CH3)2), 1.90 (dsept, JHH = 3.3 Hz, JPH = 7.0 Hz, 2H,
3
PCH(CH3)2), 1.69 (d, JHH = 6.5 Hz, 6H, C6H3CH(CH3)2), 1.66 (s, 3 H,
CH3C(NAr)CHC(NAr)CH3), 1.21 (m, 6H, PCH(CH3)2), 1.17 (s,
3
H,

3
3
CH3C(NAr)CHC(NAr)CH3), 1.15 (d, JHH = 6.5 Hz, 6H, C6H3CH(CH3)2), 0.95 (dd, JHH
7.0 Hz, 3JPH = 15.0 Hz, 6H, PCH(CH3)2), 1.03 (d, 3JHH = 7 Hz, 12H, C6H3(CH(CH3)2).
=
13C{1H} NMR (C6D6) δ: 161.2 (CH3C(NAr)CHC(NAr)CH3), 145.7, 140.9, 127.0, 124.4
1
(C H3CH(CH3)2), 94.0 (CH3C(NAr)CHC(NAr)CH3), 28.8 (C6H3CH(CH3)2, 28.4 (d, JPC
=
6
11.0 Hz, PCH(CH3)2), 24.4, 21.0 (PCH(CH3)2), 24.6, 23.4 (C6H3CH(CH3)2), 24.3, 20.4
(CH3C(NAr)CHC(NAr)CH3).
Reaction of [NacNacZrCl(η2-i-Pr2P–PSiMe3)] (1) with i-Pr2P-P(SiMe3)Li · 3THF.
A solution of i-Pr2P-P(SiMe3)Li·3THF (43 mg, 0.097 mmol) in 2 mL of pentane was added
dropwise to a solution of crystals of [NacNacZrCl(η2-i-Pr2P–PSiMe3)] (1) (80 mg, 0.092
mmol) in 3 mL of pentane at -30 °C. The mixture was then warmed up to ambient
temperature. The solvent was then evaporated under reduced pressure, and the residue was
31
31
1
dissolved with 1 mL of C6D6 and the solution was analyzed by P{1H}, P, and H NMR
spectra.
The results of the examination of the 31P{1H} NMR spectrum of the reaction solution: 3a
(29%), i-Pr2P-P(SiMe3)2 (24%), i-Pr2P-P(SiMe3)Li (12%), i-Pr2P-P(SiMe3)H (29%), i-Pr2PH
(6%).
3a: 31P{1H} δ: 267.2 (d, 1JPP = 436.0 Hz, PLi), 49.7 (d, 1JPP = 436.0 Hz, i-Pr2P).
Reaction of [NacNacZrCl2(η2-i-Pr2P–PSiMe3)] (1) with i-Pr2P-P(SiMe3)Li·3THF and 12-
crown-4.
A mixture of i-Pr2P-P(SiMe3)Li·3THF (55 mg, 0.124 mmol) and 12-crown-4 (22,6 µL, 0.130
mmol) in 1 mL of THF was added dropwise to a solution of the crystals of [NacNacZrCl(η2-i-
Pr2P–PSiMe3)] (1) (102 mg, 0.117 mmol) in 1.5 mL of THF at -30 °C. The mixture was
warmed up to ambient temperature. The solvent was then evaporated under reduced pressure,
31
the residue was dissolved with 1 mL of C6D6 and the solution was analyzed by 31P{1H}, P
and 1H NMR spectroscopy.

The results of the examination of the 31P{1H} NMR spectrum of the reaction solution: 2a
(13%), 3a’ (21%), i-Pr2P-P(SiMe3)2 (34%), i-Pr2P-P(SiMe3)H (9%), i-Pr2PH (11%), i-PrPCl2
(12%).
3a’: 31P{1H} δ: 214.6 (d, 1JPP = 436.0 Hz, PLi), 45.7 (d, 1JPP = 436.0 Hz, i-Pr2P).
Reaction of [NacNacZrCl3] with t-Bu2P-P(SiMe3)Li·2.5THF in toluene (molar ratio 1:1).
Formation of [NacNacZrCl2(η2-t-Bu2P–PSiMe3)] (1b).
A solution of t-Bu2P-P(SiMe3)Li·2.5THF (164 mg, 0.375 mmol) in 2 mL of toluene was
added dropwise to a solution of [NacNacZrCl3·0.42DME] (245 mg, 0.375 mmol) in 2 mL of
toluene at -30 °C. During the reaction, the color of the solution changed from yellow to red.
The mixture was then warmed up to ambient temperature. The volume of the mixture was
reduced to one half under reduced pressure and the remaining solution was analyzed by
31P{1H}, 31P and 1H NMR spectroscopy.
Results of the examination of the 31P{1H} NMR spectrum of the reaction solution: 1b (13%),
2b (32%), t-Bu2PP(SiMe3)2 (33%), t-Bu2PH (22%).
1b: 31P{1H} δ: 29.8 (d, 1JPP = 482 Hz, t-Bu2P), -62.8 (d, 1JPP = 482 Hz, P-SiMe3).
1H NMR (C6D6) δ: 7.00-7.20 (m, 6H, C6H3CH(CH3)2, overlapped with solvent signal), 5.47
3
(s, 1H, CH3C(NAr)CHC(NAr)CH3), 3.57 (sept, JHH = 6.6 Hz, 4 H, C6H3CH(CH3)2), 1.86 (s,
6 H, CH3C(NAr)CHC(NAr)CH3), 1.53 (d, 3JHH = 6.6 Hz, 12H, C6H3CH(CH3)2), 1.46 (d, 3JHH
3
3
= JPH = 15.0 Hz, 18H, PC(CH3)2), 1.14 (d, JHH = 6.9 Hz, 12H, C6H3(CH(CH3)2), 0.49 (d,
3JPH = 6.0 Hz, 9H, PSi(CH3)3).
2b: 31P{1H} δ: 432.7 (d, 1JPP = 441.0 Hz, P). 117.1 (d, 1JPP = 441.0 Hz, t-Bu2P).
1H NMR (C6D6) δ: 7.00-7.20 (m, 6H, C6H3CH(CH3)2, overlapped with solvent signal), 4.92
(s, 1H, CH3C(NAr)CHC(NAr)CH3), 3.38, (sept, 3JHH = 7.0 Hz, 4 H, C6H3CH(CH3)2), 1.70 (s,
3
6 H, CH3C(NAr)CHC(NAr)CH3), 1.28 (d, JHH = 6.9 Hz, 12H, C6H3(CH(CH3)2), 1.20 (d,
3JPH = 16.0 Hz, 18H, PC(CH3)3), 1.17 (d, 3JHH = 6.9 Hz, 12H, C6H3CH(CH3)2).
Reaction of [NacNacZrCl3] with t-Bu2P-P(SiMe3)Li·2.5THF in DME (molar ratio 1:2).
Formation of [NacNacZrCl2(η2-t-Bu2P–PLi)] (3b).

A solution of t-Bu2P-P(SiMe3)Li·2.5THF (327 mg, 0.750 mmol) in 2 mL of DME was added
dropwise to a suspension of [NacNacZrCl3·0.42DME] (245 mg, 0.375 mmol) in 2 mL of
DME at -30 °C. During the reaction, the color of the solution changed from yellow to red.
The mixture was then warmed up to ambient temperature. The volume of the mixture was
reduced to one half under reduced pressure and the remaining solution was analyzed by
31P{1H}, 31P and 1H NMR spectroscopy.
Results of the examination of the 31P{1H} NMR spectra of the reaction solution: 3b (15%), t-
Bu2P-P(SiMe3)2 (30%), t-Bu2P-P(SiMe3)Li (7%), t-Bu2P-P(SiMe3)H (48%).
3b: 31P{1H} δ: 283.2 (d, 1JPP = 443.2 Hz, PLi), 76.2 (d, 1JPP = 443.2 Hz, t-Bu2P).
Reaction of [NacNacZrCl3] with t-Bu2P-P(SiMe3)Li·2.5THF and 12-crown-4. Synthesis
of [NacNacZrCl(η2-t-Bu2P–P)] (2b).
A mixture of t-Bu2P-P(SiMe3)Li·2.5THF (436 mg, 1 mmol) and 12-crown-4 (160 µL, 1
mmol) in 3 mL of THF was added dropwise to a solution of [NacNacZrCl3·0.42DME]
(325 mg, 0.5 mmol) in 7 mL of THF at -30 °C. During the reaction, the color of the solution
changed from yellow to red. The mixture was then warmed up to ambient temperature. The
volume of the mixture was reduced to one half under reduced pressure and 5 mL of pentane
was layered over the THF solution. After a few weeks, small red crystals of 2b·pentane
precipitated. Crystals of 2b·pentane melt on warming up over -30 °C.
The results of the examination of the 31P{1H} NMR spectrum of the supernatant solution: 2b
(7%), t-Bu2P-P(SiMe3)2 (52%), t-Bu2P-P(SiMe3)H (39%), t-BuPCl2 (2%).
Reaction of [{PhN(CH2)3NPh}ZrCl2] with i-Pr2P-P(SiMe3)Li·3THF in DME (molar ratio
1:1).
Synthesis
of
[{(PhN(CH2)3NPh)Zr}(ZrCl)2(µ-Cl)(η2-i-Pr2P–P)4][Li(DME)3]
(4·[Li(DME)3]).
A solution of i-Pr2P-P(SiMe3)Li·3THF (167 mg, 0.375 mmol) in 2 mL DME was added
dropwise to a solution of [(PhN(CH2)3NPh)ZrCl2] (145 mg, 0.375 mmol) in 2 mL DME at -30
°C. The mixture was then warmed up to ambient temperature. The solvent was evaporated
under reduced pressure and the residue dissolved in 3 mL of toluene. 3 mL of pentane was
then layered over the toluene solution. After few days at room temperature, a small quantity
of black crystals of 4·[Li(DME)3] was deposited (60 mg; yield 35%).

Reaction of [NacNacZrCl3] with Ph2PLi.
A solution of Ph2PLi (96 mg, 0.5 mmol) in 3 mL of DME was added dropwise to a solution of
[NacNacZrCl3·0.42DME] (325 mg, 0.5 mmol) in 7 mL of DME at -30 °C. The mixture was
then warmed up to ambient temperature. The volume of the mixture was reduced to one half
1
under reduced pressure and the remaining solution was analyzed by 31P{1H}, 31P and H
NMR spectroscopy.
31
The results of the examination of the P{1H}NMR spectrum of the reaction solution: Ph2PH,
Ph2P-PPh2.
Conclusions
Studies of the reactivity of [NacNacZrCl3] towards R2P–P(SiMe3)Li (R = t-Bu, i-Pr) showed
that β-diketiminate spectator ligands drive the binding of the diphosphorus ligands R2P–
PSiMe3 or R2P-P into a side-on coordination mode. This coordination mode is in contrast to
the reactivity of the corresponding complexes of early transition metals possessing cyclo-
pentadienyl anions as co-ligands, for which terminal and bridging coordination of R2P–P or
R2P–PSiMe3 to the metal center was observed. Furthermore, the direct transformation of the
phosphanylphosphido complex (R2P–PSiMe3) into a phosphanylphosphinidene complex
(R2P–P) via elimination of Me3SiCl has not been previously observed for transition metal
complexes with R2P–P-SiMe3 ligands. The phosphanylphosphinidene complex
[NacNacZrCl(η2-t-Bu2P–P)] exhibits unusual structural features, such as very short P-P and
simultaneously very short Zr-P bonds. A short multiple Zr-P bond has only previously been
observed in terminal, bent phosphinidene complexes. The presence of a phosphanyl group in
the R2P–P-SiMe3 moiety influences not only the coordination mode of the ligand but also its
reactivity. The possible formation of a P-P double bond and thus delocalization of the
negative charge via resonance weakens the reducing properties of [R2P–P-SiMe3]- compared
to [R2P]-, which is manifested by the substitution of a chlorido ligand in [NacNacZrCl3], but
not by the reduction of this complex.
Appendix A. Supplementary data
CCDC 1493784, 1493783 and 1493786 contains the supplementary crystallographic data for
1a, 2b and 4. These data can be obtained free of charge via

http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
Acknowledgements
We thank the National Centre of Science NCN (Grant Harmonia, no. 2012/06/M/ST5/00472)
for financial support.
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Studies of the reactivity of [NacNacZrCl3] towards R2P–P(SiMe3)Li showed that β-
diketiminate spectator ligands drive the binding of the diphosphorus ligands R2P–PSiMe3 or
R2P-P into
a
side-on coordination mode. The direct transformation of the
phosphanylphosphido complex into a phosphanylphosphinidene complex via elimination of
Me3SiCl was observed.

R
SiMe3
R
Li
P
R
P
P
R
P
Cl Zr Cl
Cl Zr Cl
Phosphanyl...
...phosphido
...phosphinidenoid
R
i-Pr
i-Pr
R
P
P
=
i-Pr
i-Pr
Cl Zr
R = t-Bu, i-Pr
...phosphinidene