Triamidoamine-uranium(IV)-stabilized terminal parent phosphide and phosphinidene complexes

Article abstract of DOI:10.1002/anie.201400798

Reaction of [U(Tren^TIPS)(THF)][BPh₄] (1; Tren ^TIPS=N{CH₂CH₂NSi(iPr)₃} ₃) with NaPH₂ afforded the novel f-block terminal parent phosphide complex [U(Tren^TIPS)(PH₂)] (2; U-P=2.883(2)?A). Treatment of 2 with one equivalent of KCH ₂C₆H₅ and two equivalents of benzo-15-crown-5 ether (B15C5) afforded the unprecedented metal-stabilized terminal parent phosphinidene complex [U(Tren^TIPS)(PH)][K(B15C5)₂] (4; UP=2.613(2)?A). DFT calculations reveal a polarized-covalent UP bond with a Mayer bond order of 1.92. Straightforward deprotonation of the first f-block terminal parent phosphide complex and potassium abstraction results in the isolation of an unprecedented structurally authenticated metal-stabilized terminal parent phosphinidene complex. B15C5=benzo-15-crown-5 ether.

Full text of DOI:10.1002/anie.201400798

.
Angewandte
Communications
DOI: 10.1002/anie.201400798
Metal Phosphinidenes
Triamidoamine–Uranium(IV)-Stabilized Terminal Parent Phosphide
and Phosphinidene Complexes**
Benedict M. Gardner, Gꢀbor Balꢀzs, Manfred Scheer,* Floriana Tuna, Eric J. L. McInnes,
Jonathan McMaster, William Lewis, Alexander J. Blake, and Stephen T. Liddle*
Abstract: Reaction of [U(TrenTIPS)(THF)][BPh4] (1;
TrenTIPS = N{CH2CH2NSi(iPr)3}3) with NaPH2 afforded the
novel f-block terminal parent phosphide complex [U-
(TrenTIPS)(PH2)] (2; U–P = 2.883(2) ꢁ). Treatment of 2 with
one equivalent of KCH2C6H5 and two equivalents of benzo-15-
crown-5 ether (B15C5) afforded the unprecedented metal-
stabilized terminal parent phosphinidene complex [U-
Indeed, there is a paucity of well-defined compounds
containing a terminal PH group and structurally elucidated
examples are confined to the p-block, where the bonding
descriptions are open to interpretation, for example, NHC–
phosphinidene vs. phosphaalkene.[10]
Herein, we describe the straightforward synthesis and
characterization of the first example of a metal-stabilized
terminal parent phosphinidene complex. This is only the
second actinide terminal phosphinidene complex,[11,12] and
was prepared from the first example of an f-block parent
terminal phosphide complex; terminal phosphide complexes
are rare, as the sterically unencumbered PH2 group often
bridges metal centers.[13]
(TrenTIPS)(PH)][K(B15C5)2] (4; U P = 2.613(2) ꢁ). DFT
=
=
calculations reveal a polarized-covalent U P bond with
a Mayer bond order of 1.92.
=
T
erminal metal phosphinidene complexes (LnM PR) are,
despite continued interest, far less developed than their
isolobal metal imide and alkylidene counterparts.[1] Although
In order to prepare a triplet-PH-derived metal-stabilized
terminal parent phosphinidene, we reasoned that a high-
=
the first LnM PR complex was reported over a quarter of
a century ago,[2] sterically demanding R-groups are required,
oxidation-state metal would be required to engage in a formal
[14]
=
=
as M PR linkages are reactive and require kinetic stabiliza-
M PH bonding interaction. We also noted that, as PH is
tion.[3] Certainly, free phosphinidenes (PR) are usually very
reactive owing to their triplet ground states and unsaturated
valence shells.[4] Although stabilization of a triplet PR group
sterically unencumbered, a sterically demanding metal–ligand
fragment would be required to compensate for the lack of
kinetic protection at phosphorus. Given our success in
stabilizing terminal uranium–nitrides,[15] we identified the
[U(TrenTIPS)]n+ (TrenTIPS = N{CH2CH2NSi(iPr)3}3) unit as an
ideal metal fragment, and NaPH2 as the ideal PH precursor
transfer group. Initial attempts to install PH2 at uranium using
NaPH2 and [U(TrenTIPS)(Cl)] failed, presumably because the
phosphide cannot displace a strongly bound chloride from
uranium. Thus, we utilized [U(TrenTIPS)(THF)][BPh4] (1),[16]
=
by a triplet metal fragment to generate a formal M P bond is
=
an attractive strategy, unlike the well-known LnM NH and
LnM CH2 linkages,[5] there has never been a structurally
=
authenticated report of a d-/f-block metal-stabilized terminal
[6,7]
=
parent phosphinidene LnM PH,
and studies of such
species are limited to computational investigations.[8] This
paucity is underscored by a triplet-singlet energy gap of
22 kcalmolꢀ1 for free PH,[4b] which has only been observed
transiently in the gas phase or low temperature matrices.[4a,9]
as the THF and BPh4 groups are labile.[17] Treatment of
ꢀ
1 with NaPH2 afforded, after work-up and recrystallization
from iso-hexane, yellow crystals of the uranium(IV) parent
terminal phosphide complex [U(TrenTIPS)(PH2)] (2) in 89%
yield (Scheme 1). The characterization data for 2 support the
proposed formulation.[16] Notably, the 31P NMR spectrum of 2
exhibits a triplet centered at 595 ppm (JPH = 160 Hz), which
confirms the presence of PH2. The solid-state structure of 2
was determined by X-ray diffraction (Figure 1), which
revealed a monomeric structure with a terminal PH2 unit.
[*] Dr. B. M. Gardner, Dr. J. McMaster, Dr. W. Lewis, Prof. A. J. Blake,
Prof. S. T. Liddle
School of Chemistry, University of Nottingham
University Park, Nottingham, NG7 2RD (UK)
E-mail: stephen.liddle@nottingham.ac.uk
Dr. G. Balꢀzs, Prof. Dr. M. Scheer
Institut of Inorganic Chemistry, University of Regensburg
Universitaetsstr.31, Regensburg, 93053 (Germany)
E-mail: manfred.scheer@chemie.uni-r.de
ꢀ
The U P bond length of 2.883(2) ꢀ is slightly longer than the
sum of the single bond covalent radii of uranium and
phosphorus (2.81 ꢀ),[18] and compares to a U P bond length
ꢀ
Dr. F. Tuna, Prof. E. J. L. McInnes
School of Chemistry and Photon Science Institute, University of
Manchester, Oxford Road, Manchester, M13 9PL (UK)
of 2.789(4) ꢀ in the less encumbered uranium(IV) complex
[U(C5Me5)2{P(SiMe3)2}(Cl)].[19]
[**] We thank the Royal Society, the European Research Council, the
Engineering and Physical Sciences Research Council, the University
of Nottingham, the University of Manchester, the UK National
Nuclear Laboratory, and COST Action CM1006 for generously
supporting this work; we also thank the EPSRC UK National EPR
Facility.
We treated 2 with benzyl potassium and 2,2,2-cryptand to
afford [U(TrenTIPS)(PH)(K-2,2,2-cryptand)] (3) in 80% yield
as black crystals after work-up and recrystallization from iso-
hexane (Scheme 1). The characterization data for 3 support
the proposed formulation,[16] and the 31P NMR spectrum
exhibits a broad resonance at 2460 ppm (fwhm = 440 Hz, JPH
not resolved). To determine whether the phosphinidene in 3
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201400798.
4484
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 4484 –4488

Angewandte
Chemie
Figure 1. Molecular structures of [U(TrenTIPS)(PH2)] (2, left), one of the four independent molecules in the asymmetric unit of [U(TrenTIPS)(PH)(K-
2,2,2-cryptand)] (3, center), and the anionic component of [U(TrenTIPS)(PH)][K(B15C5)2] (4, right). Displacement ellipsoids set at 50% probability.
Non-phosphorus-bound hydrogen atoms and minor disorder components are omitted for clarity. Selected bond lengths [ꢁ]: 2, U1–P1 2.883(2),
U1–N1 2.241(4), U1–N2 2.259(3), U1–N3 2.233(3), U1–N4 2.633(3); 3, U1–P1 2.661(2), U1–N1 2.312(3), U1–N2 2.287(3), U1–N3 2.310(3),
U1–N4 2.716(3), K1–P1 3.575(2); 4, U1–P1 2.613(2), U1–N1 2.326(3), U1–N2 2.320(3), U1–N3 2.320(3), U1–N4 2.692(3).
=
firmed the identity of 4 (Figure 1). The U P distance of
=
2.613(2) ꢀ is ca. 0.05 ꢀ shorter than the U P distance in 3,
perhaps reflecting the weak P–K interaction in 3. It is
germane to note that the sum of the double bond covalent
radii of uranium and phosphorus is 2.36 ꢀ,[21] thus the U P
=
distance in 4 lies midway between the sum of the covalent
single and double bond radii values. For comparison, ura-
nium–phosphorus distances of 2.743(1) and 2.562(3) ꢀ were
observed in [{U(C5Me5)2(OMe)}2(m-PH)],[12] and [U-
(C5Me5)2(P-2,4,6-tBu3C6H2)(OPMe3)],[11] respectively. The
U–N distances are consistent with the uranium(IV) formula-
tion.[22] The phosphinidene hydrogen atom in 4 could be
located in the difference electron density map revealing a U-
=
P-H angle of 118.8(9)8, which suggests a formal U P bond, as
would be expected.
Unlike 2 and 3, complex 4 is silent in the 31P NMR
spectrum, presumably because of a stronger uranium–phos-
phorus interaction resulting in paramagnetic line-broadening.
The 1H NMR spectrum of 4 spans the range of + 46 to
ꢀ10 ppm, and exhibits four Tren-ligand resonances, which is
consistent with C3v symmetry on the NMR timescale. The
FTIR spectrum of 4 exhibits an absorption at 2360 cmꢀ1,
which we attribute to a terminal PH stretch. The UV/Vis/NIR
electronic absorption spectrum of 4 exhibits broad absorp-
Scheme 1. Synthesis of 2–4. B15C5=benzo-15-crown-5 ether.
was terminal, we analyzed the structure by X-ray diffraction
(Figure 1). However, although the potassium ion is coordi-
nated by the cryptand, it is not sequestrated from the
tions in the range 25000–10000 cmꢀ1 [16]
which accounts for its
,
=
phosphinidene. The U P distance was found to be
black color and weak (e ꢁ 25mꢀ1 cmꢀ1) bands in the 10000–
5000 cmꢀ1 region that are characteristic of uranium(IV).[23]
The solution magnetic moment of 4 in C6D6 at 298 K is
2.98 mB. The solid-state magnetic moment of 4 at 298 K
measured by SQUID magnetometry is 2.45 mB,[16] which is
consistent with the solution-phase magnetic data. The mag-
netic moment decreases smoothly with decreasing temper-
ature to 1.04 mB at 1.8 K and tending to zero; this is consistent
with uranium(IV), which is a magnetic singlet at low temper-
ature. The data are similar to those of 2 and 3, which is
commensurate with the formal uranium oxidation state of + 4
for all these complexes.
2.661(2) ꢀ, which is ca. 0.22 ꢀ shorter than the U–P distance
in 2. The long P–K distance of 3.575(2) ꢀ must be regarded as
a weak interaction.
The failure of 2,2,2-cryptand to abstract the potassium ion
in 3 is surprising, but the long P–K distance suggested that
a separated ion pair might be feasible. Noting the prior
success of a conjugate acid deprotonation method to afford
a terminal molybdenum carbide,[20] we treated 2 with benzyl
potassium and two equivalents of benzo-15-crown-5 ether
(B15C5) and, after work-up and recrystallization from
toluene, isolated the uranium(IV) terminal parent phosphi-
nidene complex [U(TrenTIPS)(PH)][K(B15C5)2] (4) in 89%
yield as black crystals.[16] An X-ray diffraction study con-
=
In order to probe the nature of the U PH linkages in 3
and 4, we conducted single-point energy calculations on the
Angew. Chem. Int. Ed. 2014, 53, 4484 –4488
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
4485

.
Angewandte
Communications
Table 1: Selected computed DFT, NBO, and QTAIM data for 2–4.
Bond lengths Atomic spin densities
NBO s-component[g]
and indices and charges
Entry[a] U–P[b] BI[c] mU
NBO p-component[g]
QTAIM[h]
[d]
[e]
[f]
2
qU
qP
P [%] U [%] U 7s/7p/5f/6d P [%] U [%] U 7s/7p/5f/6d 1(r) 5 1(r) H(r)
e(r)
2
3
4
2.9250 0.84 2.31
2.6718 1.61 2.36
2.6209 1.92 2.41
2.61
2.53
2.32
ꢀ0.54
ꢀ1.18
ꢀ1.16
87.4
82.8
75.9
12.6
17.2
24.1
2:2:45:51
2:0:48:50
0:0:80:20
–
–
–
0.05 0.04
0.07 0.07
0.08 0.07
ꢀ0.01 0.01
ꢀ0.02 0.22
ꢀ0.03 0.20
79.1 20.9
72.1 27.9
0:1:62:37
0:1:69:30
[a] All molecules geometry optimized without symmetry constraints at the spin-unrestricted LDA VWN BP TZP/ZORA level. [b] Calculated U–P
distances [ꢁ]. [c] Mayer bond indices. [d] MDC-m a-spin densities on uranium. [e] MDC-q charges on uranium. [f] MDC-q charges on phosphorus.
2
[g] Natural Bond Orbital (NBO) analyses. [h] QTAIM topological electron density [1(r)], Laplacian [5 1(r)], electronic energy density [H(r)], and
ellipticity [e(r)] bond critical point data.
geometry optimized structures of 3 and the anion component
of 4 (Table 1). The calculated bond lengths and angles are
within 0.05 ꢀ and 28 of the experimentally determined
structures, and therefore we conclude that the calculated
structures represent qualitative models of the electronic
structures of 3 and 4. For comparison, we calculated the
electronic structure of 2 (Table 1). The calculated MDCq
charges for uranium (2.32–2.61) are typical of Tren–uraniu-
m(IV) complexes.[24] The phosphorus charges reflect the
changes from mono-anionic phosphide in 2 to dianionic
phosphinidenes in 3 and 4. The uranium spin densities span
2.31–2.41 and together with the charges support the notion of
increased donation of electron density from the ligands in the
order 4 > 3 > 2, as would be expected from the progression of
terminal phosphinidene to pseudo-bridging phosphinidene to
phosphide. The calculated Mayer bond order for 4 is 1.92,
which is consistent with a double bond interaction (cf. bond
orders of 1.61 for 3 and 0.84 for 2). The HOMO and HOMO-
1 of 2–4 are each singly occupied and of essentially pure 5f
character, as expected for 3H4 uranium centers. For 3 and 4 the
HOMO-2 and HOMO-3 represent the principal p- and s-
bonding, as observed in uranium–nitrides[14] and uranium–
carbenes.[25] Although the K–P distance in 3 is long, it is
=
evident from a comparison of the U P bond data in Table 1
that coordination of potassium to the phosphinidene perturbs
=
the U P bond through the polarization of electron density
towards the potassium center.
To gain further insight into the uranium-phosphorus
linkages in 2–4 we employed Baderꢁs Atoms in Molecules
(QTAIM) to analyze the topological electron density [1(r)],
2
the Laplacian of the electron density [5 1(r)], and the
electronic energy density H(r) of the charge distribution
(defined as H(r) = G(r) + V(r) where G(r) is the kinetic
energy density and V(r) is the potential energy). In each case,
a 3,ꢀ1 bond critical point (BCP) was identified (Table 1).
These BCP data are consistent with predominantly electro-
static bonding with modest covalent contributions, and are
consistent with greater bonding interactions for the formal
=
U P bonds in 3 and 4 compared to the formal single bond in 2.
=
The calculated ellipticity parameters [e(r)] for the U P bonds
in 3 and 4 confirm the presence of double-bonding inter-
actions. Specifically, for a cylindrical s-bond the ellipticity is 0,
and for a bond with a p-contribution the ellipticity is > 0. The
=
components, respectively, of the U P bond, which for 4 are
=
ꢀ
illustrated in Figure 2. In order to exclusively probe the U P
ellipticity values for the C C bonds in ethane, benzene, and
linkages, we studied them with Natural Bond Orbital (NBO)
analysis, which identified s- and p-bonding interactions. For 4,
the s-bond comprises 24% uranium and 76% phosphorus
character and the p-bond is composed of 72% phosphorus
and 28% uranium character. It is notable that the NBO data
suggest a dominance of 5f orbital contributions in the
ethene are calculated to be 0.0, 0.23, and 0.45, respectively.[26]
+
ꢀ
ꢀ
Although it should be recognized that the dipolar U P(H)
resonance form will contribute to the electronic structure of
=
the U PH linkages, the ellipticity values for 3 and 4 are
similar to that of benzene and the calculated bond order is
close to two. This suggests that the uranium–phosphorus
bonds in 3 and 4 are composed of s- and p-components, and
=
that the U PH bond resonance form may dominate. Lastly,
we note a surprising, given the differences in covalency of 4f
and early 5f complexes, similarity of the computational data
for 5f 3 and 4 compared to our recently reported 4f
cerium(IV)–carbene
complex
[Ce{C(PPh2NSiMe3)2}-
=
(ODipp)2] (Dipp = 2,6-iPr2C6H3), which exhibits a Ce C
bond.[27]
To conclude, we have reported the straightforward syn-
thesis and characterization of the first structurally authenti-
cated metal-stabilized terminal parent phosphinidene com-
=
plex, thus extending the range of metal–parent imide LnM
=
=
NH and alkylidene LnM CH2 complexes to include the LnM
PH linkage. This complex is only the second example of an
actinide terminal phosphinidene complex, and was prepared
from the first example of an f-block parent terminal
phosphide complex. Complex 4 is potentially a precursor to
Figure 2. a-spin Kohn Sham orbitals that represent the principal
=
components of the U P bond in 4. Left: HOMO-2 (225a, ꢀ0.608 eV);
Right: HOMO-3 (224a, ꢀ0.692 eV).
4486 www.angewandte.org
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 4484 –4488

Angewandte
Chemie
ꢂ
[9] a) J. J. Harrison, B. E. Williamson, J. Phys. Chem. A 2005, 109,
the uranium terminal phosphido U P linkage, which has only
been experimentally observed in matrix isolation experiments
1343; b) G. Bucher, M. L. G. Borst, A. W. Ehlers, K. Lam-
mertsma, S. Ceola, M. Huber, D. Grote, W. Sander, Angew.
Chem. 2005, 117, 3353; Angew. Chem. Int. Ed. 2005, 44, 3289;
c) J. Glatthaar, G. Maier, Angew. Chem. 2004, 116, 1314; Angew.
Chem. Int. Ed. 2004, 43, 1294.
and probed computationally,[28] and this work suggests that
heavier pnictide LnU EH linkages (E = As, Sb) may also be
accessible. Studies to these ends are ongoing in our labora-
tories.
=
[10] a) K. Hansen, T. Szilvꢂsi, B. Blom, E. Irran, M. Driess, Chem.
Eur. J. 2014, 20, 1947; b) K. Hansen, T. Szilvꢂsi, B. Blom, S.
Inoue, J. Epping, M. Driess, J. Am. Chem. Soc. 2013, 135, 11795;
c) Y. Wang, Y. Xie, M. Y. Abraham, R. J. Gilliard, Jr., P. Wei,
H. F. Schaefer III, P. v. R. Schleyer, G. H. Robinson, Organo-
metallics 2010, 29, 4778; d) M. Driess, S. Block, M. Brym, M. T.
Gamer, Angew. Chem. 2006, 118, 2351; Angew. Chem. Int. Ed.
2006, 45, 2293; e) K. Issleib, E. Leissring, M. Riemer, H. Oehme,
Z. Chem. 1983, 23, 99.
Received: January 24, 2014
Published online: March 18, 2014
Keywords: density functional calculations · multiple bonds ·
phosphides · phosphinidene · uranium
.
[11] D. S. J. Arney, R. C. Schnabel, B. C. Scott, C. J. Burns, J. Am.
Chem. Soc. 1996, 118, 6780.
[1] a) H. Aktas¸, J. C. Slootweg, K. Lammertsma, Angew. Chem.
2010, 122, 2148; Angew. Chem. Int. Ed. 2010, 49, 2102; b) R.
Waterman, Dalton Trans. 2009, 18; c) B. P. Johnson, G. Balꢂzs,
M. Scheer, Coord. Chem. Rev. 2006, 250, 1178; d) C. C.
Cummins, Angew. Chem. 2006, 118, 876; Angew. Chem. Int.
Ed. 2006, 45, 862; e) F. Garcꢃa, M. L. Stead, D. S. Wright, J.
Omet. Chem. 2006, 691, 1673; f) F. Mathey, Angew. Chem. 2003,
115, 1616; Angew. Chem. Int. Ed. 2003, 42, 1578; g) K.
Lammertsma, M. J. M. Vlaar, Eur. J. Org. Chem. 2002, 1127;
h) F. Mathey, N. H. T. Huy, A. Marinetti, Helv. Chim. Acta 2001,
84, 2938; i) A. D. Hopkins, J. A. Wood, D. S. Wright, Coord.
Chem. Rev. 2001, 216 – 217, 155; j) M. Scheer, Coord. Chem. Rev.
1997, 163, 271; k) A. H. Cowley, Acc. Chem. Res. 1997, 30, 445;
l) A. H. Cowley, Acc. Chem. Res. 1988, 21, 81; m) F. Mathey,
Angew. Chem. 1987, 99, 285; Angew. Chem. Int. Ed. Engl. 1987,
26, 275; n) G. Huttner, K. Evertz, Acc. Chem. Res. 1986, 19, 406.
[2] a) P. B. Hitchcock, M. F. Lappert, W. P. Leung, J. Chem. Soc.
Chem. Commun. 1987, 1282; b) R. Bohra, P. B. Hitchcock, M. F.
Lappert, W. P. Leung, Polyhedron 1989, 8, 1884.
[3] Selected examples: a) R. Waterman, T. D. Tilley, Chem. Sci.
2011, 2, 1320; b) G. Zhao, F. Basuli, U. J. Kilgore, H. Fan, H.
Aneetha, J. C. Huffman, G. Wu, D. J. Mindiola, J. Am. Chem.
Soc. 2006, 128, 13575; c) B. C. Bailey, J. C. Huffman, D. J.
Mindiola, W. Weng, O. V. Ozerov, Organometallics 2005, 24,
1390; d) F. Basuli, J. Tomaszewski, J. C. Huffman, D. J. Mindiola,
J. Am. Chem. Soc. 2003, 125, 10170; e) J. B. Bonanno, P. T.
Wolczanski, E. B. Lobkovsky, J. Am. Chem. Soc. 1994, 116,
11159; f) Z. Hou, T. L. Breen, D. W. Stephan, Organometallics
1993, 12, 3158; g) C. C. Cummins, R. R. Schrock, W. M. Davis,
Angew. Chem. 1993, 105, 758; Angew. Chem. Int. Ed. Engl. 1993,
32, 756; h) A. H. Cowley, B. Pellerin, J. L. Atwood, S. G. Bott, J.
Am. Chem. Soc. 1990, 112, 6734.
[12] A bridging phosphinidiide with a U-P(H)-U core has been
reported: M. R. Duttera, V. W. Day, T. J. Marks, J. Am. Chem.
Soc. 1984, 106, 2907.
[13] A search of the cambridge structural database (January 15, 2014,
version 1.15) reveals 9 structurally characterized examples of
terminal PH2 groups bound to metal centers.
[14] With the combination of formal uranium(IV) and [PH]2ꢀ units,
the term phosphanediide could be invoked. However, in the
present context we prefer phosphinidene to emphasize the ene
=
multiple bond nature of a terminal U PH linkage, and use
phosphinidiide to refer to bridging M-P(H)-M species.
[15] a) D. M. King, F. Tuna, E. J. L. McInnes, J. McMaster, W. Lewis,
A. J. Blake, S. T. Liddle, Nat. Chem. 2013, 5, 482; b) D. M. King,
F. Tuna, E. J. L. McInnes, J. McMaster, W. Lewis, A. J. Blake,
S. T. Liddle, Science 2012, 337, 717.
[16] Full details can be found in the Supporting Information.
[17] a) B. M. Gardner, W. Lewis, A. J. Blake, S. T. Liddle, Inorg.
Chem. 2011, 50, 9631; b) B. M. Gardner, J. McMaster, W. Lewis,
A. J. Blake, S. T. Liddle, J. Am. Chem. Soc. 2009, 131, 10388.
[18] P. Pyykkç, M. Atsumi, Chem. Eur. J. 2009, 15, 186.
[19] S. W. Hall, J. C. Huffman, M. M. Miller, L. R. Avens, C. J. Burns,
A. P. Sattelberger, D. S. J. Arney, A. F. England, Organometal-
lics 1993, 12, 752.
[20] J. C. Peters, A. L. Odom, C. C. Cummins, Chem. Commun. 1997,
1995.
[21] P. Pyykkç, M. Atsumi, Chem. Eur. J. 2009, 15, 12770.
[22] J. C. Berthet, M. Ephritikhine, Coord. Chem. Rev. 1998, 178 –
180, 83.
[23] D. P. Mills, F. Moro, J. McMaster, J. van Slageren, W. Lewis, A. J.
Blake, S. T. Liddle, Nat. Chem. 2011, 3, 454.
[24] a) B. M. Gardner, J. C. Stewart, A. L. Davis, J. McMaster, W.
Lewis, A. J. Blake, S. T. Liddle, Proc. Natl. Acad. Sci. USA 2012,
109, 9265; b) B. M. Gardner, D. Patel, W. Lewis, A. J. Blake, S. T.
Liddle, Angew. Chem. 2011, 123, 10624; Angew. Chem. Int. Ed.
2011, 50, 10440; c) B. M. Gardner, D. Patel, A. D. Cornish, J.
McMaster, W. Lewis, A. J. Blake, S. T. Liddle, Chem. Eur. J.
2011, 17, 11266; d) B. M. Gardner, J. McMaster, F. Moro, W.
Lewis, A. J. Blake, S. T. Liddle, Chem. Eur. J. 2011, 17, 6909;
e) S. T. Liddle, J. McMaster, D. P. Mills, A. J. Blake, C. Jones,
W. D. Woodul, Angew. Chem. 2009, 121, 1097; Angew. Chem. Int.
Ed. 2009, 48, 1077; f) B. M. Gardner, J. McMaster, W. Lewis, S. T.
Liddle, Chem. Commun. 2009, 2851.
[4] a) X. Li, S. I. Weissman, T. S. Lin, P. P. Gaspar, J. Am. Chem. Soc.
1994, 116, 7899; b) P. F. Zittel, W. C. Lineberger, J. Chem. Phys.
1976, 65, 1236.
[5] A search of the Cambridge structural database (January 15,
=
=
2014, version 1.15) reveals 18 LnM NH and 20 LnM CH2
structurally characterized complexes.
[6] A triamidoamine tantalum – phosphinidene phenyl complex
=
undergoes cleavage of the P – phenyl bond to afford a Ta PLi
linkage, but although this could be quenched with carbon- and
=
silicon-based electrophiles, attempts to prepare the parent Ta
PH linkage were not successful: J. S. Freundlich, R. R. Schrock,
[25] a) O. J. Cooper, D. P. Mills, J. McMaster, F. Tuna, E. J. L.
McInnes, W. Lewis, A. J. Blake, S. T. Liddle, Chem. Eur. J.
2013, 19, 7071; b) D. P. Mills, O. J. Cooper, F. Tuna, E. J. L.
McInnes, E. S. Davies, J. McMaster, F. Moro, W. Lewis, A. J.
Blake, S. T. Liddle, J. Am. Chem. Soc. 2012, 134, 10047; c) O. J.
Cooper, D. P. Mills, J. McMaster, F. Moro, E. S. Davies, W. Lewis,
A. J. Blake, S. T. Liddle, Angew. Chem. 2011, 123, 2431; Angew.
Chem. Int. Ed. 2011, 50, 2383.
W. M. Davis, J. Am. Chem. Soc. 1996, 118, 3643.
=
[7] Formation of a Nb PH linkage is mentioned in a reactivity study
of a niobium phosphine complex but the only structurally
characterized complex in that report is a bridging phosphinidiide
complex exhibiting a Nb-P(H)-Nb core: K. F. Hirsekorn, A. S.
Veige, P. T. Wolczanski, J. Am. Chem. Soc. 2006, 128, 2192.
[8] A. W. Ehlers, E. J. Baerends, K. Lammertsma, J. Am. Chem. Soc.
2002, 124, 2831.
Angew. Chem. Int. Ed. 2014, 53, 4484 –4488
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org 4487

.
Angewandte
Communications
[26] R. F. W. Bader, T. S. Slee, D. Cremer, E. Kraka, J. Am. Chem.
Soc. 1983, 105, 5061.
[27] M. Gregson, E. Lu, J. McMaster, W. Lewis, A. J. Blake, S. T.
Liddle, Angew. Chem. 2013, 125, 13254; Angew. Chem. Int. Ed.
2013, 52, 13016.
[28] [PUF3] has been characterized in matrix isolation experiments
and computationally: a) D. M. King, S. T. Liddle, Coord. Chem.
Rev. 2014, 266 – 267, 2; b) B. Vlaisavljevich, L. Gagliardi, Inorg.
Chem. 2010, 49, 9230; c) L. Andrews, X. Wang, R. Lindh, B. O.
Roos, C. J. Marsden, Angew. Chem. 2008, 120, 5446; Angew.
Chem. Int. Ed. 2008, 47, 5366.
4488 www.angewandte.org
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 4484 –4488