Well-defined soluble P3--containing rare-earth-metal compounds

Article abstract of DOI:10.1002/anie.201105378

A rare find: Soluble P^3--containing rare-earth-metal coordination compounds have been synthesized. A P^3--containing polymetallic yttrium iodide was obtained through P-Si (or H) and P-C bond cleavage, and this compound can be transferred into other P^3-- containing yttrium coordination compounds by metathesis reactions. Copyright

Full text of DOI:10.1002/anie.201105378

DOI: 10.1002/anie.201105378
Rare-Earth-Metal Complexes
Well-Defined Soluble P3À-Containing Rare-Earth-Metal Compounds**
Yingdong Lv, Xin Xu, Yaofeng Chen,* Xuebing Leng, and Maxim V. Borzov
Transition-metal–phosphorus coordination compounds have
attracted intense attention and been extensively studied in the
past half century.[1–6] Such coordination compounds not only
have a fundamental bearing on the theory of coordination
chemistry, but also are known to have important applications,
especially in the area of synthetic chemistry. A great number
in 71% yield. Compound 1 was characterized by NMR
spectroscopy, elemental analysis, and X-ray crystallography
(see the Supporting Information). Reaction of 1 with
1 equivalent of K[P(H)C6H3-(2,6-iPr2)] in toluene resulted
in a new compound (2; Scheme 1). The NMR spectral data for
2 in C6D6 are intriguing and disagree with what was expected
of transition-metal–phosphorus coordination compounds,
À
including PRnH3Àn (n = 1–3),[2] [PRnH2Àn
]
(n = 1–2),[2]
[PR]2À,[5] and P3À containing species,[6] have been synthesized.
One exception is those with rare-earth-metal ions. Rare-
earth-metal ions are among the hardest Lewis acids, whereas
phosphines and phosphides are soft Lewis bases; thus,
according to Pearsonꢀs hard and soft acids and bases
(HSAB) principle, rare-earth-metal–phosphorus coordina-
tion is a mismatch.[7,8] Up to now, only a handful of examples
[9]
[10]
À
À
of Ln PR3 and Ln PR2 (Ln = rare-earth metal) coordi-
À
nation compounds have been reported, and examples of Ln
PR coordination compounds are even more sparse and have
been reported just recently.[11,12] The synthesis of soluble rare-
earth-metal coordination compounds containing a P3À ligand
remains a challenging task primarily because the substituent-
free phosphido has a strong tendency to assemble into an
oligo-phosphorous one. Reduction of white phosphorus (P4)
with the low-valent rare-earth-metal compound [(h5-
C5Me5)2Sm] produces the polyphosphido compound [{(h5-
C5Me5)2Sm}4P8].[13] P3À containing rare-earth-metal com-
pounds are only precedent in solid-state chemistry, where
the LnP compounds possess rock salt (NaCl) type struc-
tures,[2] which provides high lattice energy for the stabilization
of P3À. Herein, we report the synthesis and characterization of
well-defined soluble P3À containing rare-earth-metal coordi-
nation compounds.
Scheme 1. Synthesis of 2 from 1.
for yttrium diphosphido iodide [Y{P(SiMe3)C6H3-(2,6-
iPr2)}{P(H)C6H3-(2,6-iPr2)}I(thf)n].
For
example,
the
31P NMR spectrum of 2 reveals two signals at d = 347.4 and
154.7 ppm, which are dramatically downfield from that
observed for 1 (d = À62.5 ppm) and other reported yttrium
phosphido compounds: [Y{P(SiMe3)2}3]2 (d = À107.8 ppm),[14]
[Cp*2Y{P(H)Ph}]2 (d = À107 ppm)[15] and [Y{P(H)C6H2-
2,4,6-Me3}Cl2(thf)3]2 (d = À18.9 ppm).[16] The signal at d =
154.7 ppm is comparable to that reported for the bridging
phosphinidene unit in
a lutetium phosphinidene [{2-
(R2P)C6H4}2NLu(m-PMes)]2 (d = 186.7 ppm).[11] Moreover, in
the 1H NMR spectrum, the signals for the -SiMe3 group of the
[P(SiMe3)C6H3-(2,6-iPr2)]À ligand and for the -PH group of
the [P(H)C6H3-(2,6-iPr2)]À ligand were not observed.
Reaction of YI3(THF)3.5 with 1 equivalent of K[P-
(SiMe3)C6H3-(2,6-iPr2)] in toluene gave the desired yttrium
phosphido diiodide [Y{P(SiMe3)C6H3-(2,6-iPr2)}I2(thf)3] (1)
Single crystals of 2 suitable for X-ray diffraction analysis
were obtained from a solution in toluene. Compound 2
(Figure 1) is a polymetallic yttrium phosphinidene phosphide
(33% yield). The signals at d = 347.4 and 154.7 ppm in the
[*] Y. D. Lv, X. Xu, Prof. Dr. Y. F. Chen, Dr. X. B. Leng
State Key Laboratory of Organometallic Chemistry
Shanghai Institute of Organic Chemistry
Chinese Academy of Sciences
345 Lingling Road, Shanghai 200032 (P.R. China)
E-mail: yaofchen@mail.sioc.ac.cn
Prof. Dr. M. V. Borzov
College of Chemistry and Material Science
The North-West University of Xi’an
229 Taibai Bei Road, Xi’an, Shaanxi prov. 710069 (P.R. China)
[**] This work was supported by the National Natural Science
Foundation of China (grant Nos. 20872164 and 20821002), the
State Key Basic Research & Development Program (grant No.
2011CB808705), Shanghai Municipal Committee of Science and
Technology (10DJ1400104), and Chinese Academy of Sciences.
Figure 1. Two views of molecular structure of 2. Isopropyl groups on
the Ar rings, hydrocarbon fragments of thf molecules, all hydrogen
atoms, and solvents in the lattice are omitted for clarity.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201105378.
Angew. Chem. Int. Ed. 2011, 50, 11227 –11229
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
11227

Communications
31P NMR spectrum of 2 are, thus, assigned to P3À and [PR]2À
ligands, respectively. Compound 2 has some rather remark-
able structural features. In general, the total structure adopts
a pseudo-C4v point group symmetry. Five Y3+ centers occupy
the vertices of a square pyramid while the four m3-[PR]2À
ligands cap the side faces of this pyramid. The basal and apical
Y3+ centers are in strikingly different environments; each of
the four basal centers form bonds to the unique m6-P3À ligand
(2.7770(4) ꢁ), two m3-[PR]2À ligands, one m-IÀ ligand, and a thf
ligand, while the apical center is coordinated by the m6-P3À
ligand (2.8850(19) ꢁ), four m3-[PR]2À ligands, and a terminal
IÀ ligand. The distances from the P atoms of [PR]2À ligands to
the basal Y1 atoms are 2.6720(11) and 2.7100(11) ꢁ, while
those to the apical Y2 atom are significantly longer
(2.9801(10) ꢁ). A K+ center closes the open face of the
heavy atom core, forming four bonds to four m-IÀ ligands and
a contact with the m6-P3À ligand. A disordered toluene
molecule complements the coordination sphere of the K+
À
center to a pseudooctahedron and K C distances range from
3.18 to 3.25 ꢁ. It is noteworthy that the P3À ligand in this
soluble coordination compound has an octahedral coordina-
tion environment, which is similar to those observed in solid-
state LnP compounds.[2]
Consistent with the formation of 2, two by-products
HP(Si(CH3)3)C6H3-(2,6-iPr2) [1H NMR (C6D6): d = 0.12 ppm
(d, 3JPH = 4.4 Hz, 9H, Si(CH3)3), 3.62 ppm (d, 1JPH = 206.0 Hz,
PH); 31P NMR (C6D6): d = À164.2 ppm] and (1,3-iPr2)-C6H4
[1H NMR (C6D6): d = 2.76 ppm (sept, 3JHH = 6.8 Hz, CH-
(CH3)2)] were observed in the mother liquor. The formation
Scheme 2. Syntheses of 3–6.
À
À
of 2 apparently involves P Si(or H) and P C bonds
cleavage.[12,17] Monitoring of the reaction by 31P NMR spec-
troscopy in C6D6 revealed a reaction intermediate formed
after the first 10 min of the run. This intermediate exhibited
2
one dd type signal at d = À62.2 ppm (1JYP = 142.9 Hz, JPP
=
10.7 Hz) and one ddt type signal at d = À95.5 ppm (1JPH
=
181.8 Hz, 1JYP = 65.9 Hz, 2JPP = 10.7 Hz), and was suggestively
assigned
iPr2)}2{P(H)C6H3-(2,6-iPr2)}]. The assignment was further
supported by monitoring of reaction of [Y{P(Si-
a
structure
of
[Y{P(Si(CH3)3)C6H3-(2,6-
Figure 2. Molecular structures of 3 (left) and 4 (right). Isopropyl
groups on the Ar rings, hydrocarbon fragments of thf molecules, all
hydrogen atoms, and solvents in the lattice are omitted for clarity.
a
(CH3)3)C6H3-(2,6-iPr2)}2I(thf)3] with K[P(H)C6H3-(2,6-iPr2)].
Along with the reaction progress of 1 with K[P(H)C6H3-(2,6-
iPr2)], the intensities of the signals related to the intermediate
decreased, while those related to 2 and HP(Si(CH3)3)C6H3-
(2,6-iPr2) increased. Mechanistic details of how [Y{P(Si-
(CH3)3)C6H3-(2,6-iPr2)}2{P(H)C6H3-(2,6-iPr2)}] reacts with
other species in the reaction mixture to give the final product
2 are presently unclear.
Treatment of 2 with THF provided two other polymetallic
yttrium phosphinidene phophides 3 and 4 (Scheme 2). The
structure of 3 resembles that of 2, with the coordinated
toluene replaced by a THF molecule (Figure 2). Unlike
pseudo-C4v-symmetrical 2 and 3, 4 possesses only a pseudo-Cs
point group symmetry as a result of the loss of KI; one of the
IÀ ligands links two Y3+ centers in m-mode (Figure 2). In 4, the
P3À ligand adopts an unusual rectangular pyramid coordina-
tion mode, and is positioned 0.30 ꢁ below the base of a
rectangular pyramid defined by five Y3+ centers.
(NCH2CH2NMe2)] (Ar= 2,6-iPr2C6H3) (KL) to give yttrium
phosphinidene phophide 5 in a 76% yield (Scheme 2). During
the reaction, the two IÀ ligands coordinate to the Y3+ centers
of 2 at the pyramid base plane are replaced with two L ligands.
Compound 5 crystallizes in a rare trigonal space group R3c (a
racemic twin). The core of 5 is a positively charged
pentanuclear yttrium phosphinidene phosphide composed
of five Y3+ centers, one m5-P3À ligand, four m3-[PR]2À ligands,
three terminal IÀ ligands, and two thf ligands (Figure 3). The
b-diketiminato backbone of L displays a delocalized elec-
tronic structure and adopts a rare W-conjugated conforma-
tion.[18] Ligand L coordinates to a Y3+ center through a
ketiminato nitrogen donor and an amine nitrogen donor at
one end, and to a K+ ion through the remaining ketiminato
nitrogen atom at the other end. With K+ ions as linkages, the
compound is concatenated into helical chains as shown in
Figure 3.
Compound 2 reacted with a potassium salt of b-diketimi-
nato based tridentate ligand K[MeC(NAr)CHC(Me)-
11228 www.angewandte.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2011, 50, 11227 –11229

compounds display two kinds of coordination modes: octa-
hedral and rectangular pyramidal. The results reported herein
extend the P3À coordination chemistry to the rare-earth-metal
series and fill in the gap between coordination compounds
and solid-state inorganic compounds of the rare-earth metal
containing P3À ligand.
Received: July 30, 2011
Published online: September 28, 2011
Keywords: coordination modes · helical structures ·
.
phosphorus · rare-earth metals · solid-state structures
Figure 3. Molecular structure of 5. Isopropyl groups on the Ar rings,
hydrocarbon fragments of thf molecules, all hydrogen atoms, and
solvents in the lattice are omitted for clarity.
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52% yield (Scheme 2), which shows remarkable structural
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centers occupy the vertices of a pyramid as observed in 2–5;
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IÀ ligand and three m3-phosphinidene ligands instead of four
m3-phosphinidene ligands in 2–5 (Figure 4).[19] The apical Y1
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contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
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Figure 4. Molecular structure of 6. Isopropyl groups on the Ar rings,
hydrocarbon fragments of thf molecules, and all hydrogen atoms are
omitted for clarity.
centers exhibit three types of coordination environment. The
Y2 and Y4 centers are coordinated by one m6-P3À ligand, two
m3-[PR]2À ligands, two m3-IÀ ligands, and one thf ligand; the Y3
center is coordinated by one m6-P3À ligand, three m3-[PR]2À
ligands, one m3-IÀ ligand, and one thf ligand; the Y5 center is
coordinated by one m6-P3À ligand, one m3-[PR]2À ligand, three
m3-IÀ ligands, and one h5-[Cp*]À ligand. A K+ center
coordinates to one m6-P3À ligand, one m3-[PR]2À ligand, three
m3-IÀ ligands, and one thf ligand, and adopts a pseudooctahe-
dral coordination environment.
In summary, the first soluble P3À containing rare-earth-
metal coordination compounds were synthesized and struc-
turally characterized. The P3À ligands in these coordination
Angew. Chem. Int. Ed. 2011, 50, 11227 –11229
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