Actinide metals with multiple bonds to carbon: Synthesis, characterization, and reactivity of U(IV) and Th(IV) bis(iminophosphorano)methandiide pincer carbene complexes

Article abstract of DOI:10.1021/ic102537q

Treatment of ThCl₄(DME)₂ or UCl₄ with 1 equiv of dilithiumbis(iminophosphorano) methandiide, [Li₂C(Ph ₂P=NSiMe₃)₂] (1), afforded the chloro actinide carbene complexes [Cl₂M(C(Ph₂P=NSiMe₃) ₂)] (2 (M = Th) and 3 (M = U)) in situ. Stable PCP metal-carbene complexes [Cp₂Th(C(Ph₂P=NSiMe₃)₂)] (4), [Cp₂U(C(Ph₂P=NSiMe₃)₂)] (5), [TpTh(C(Ph₂P=NSiMe₃)₂)Cl] (6), and [TpU(C(Ph₂P=NSiMe₃)₂)Cl] (7) were generated from 2 or 3 by further reaction with 2 equiv of thallium(I) cyclopentadienide (CpTl) in THF to yield 4 or 5 or with 1 equiv of potassium hydrotris(pyrazol-1- yl) borate (TpK) also in THF to give 6 or 7, respectively. The derivative complexes were isolated, and their crystal structures were determined by X-ray diffraction. All of these U (or Th)-carbene complexes (4-7) possess a very short M (Th or U)=carbene bond with evidence for multiple bond character. Gaussian 03 DFT calculations indicate that the M=C double bond is constructed by interaction of the 5f and 6d orbitals of the actinide metal with carbene 2p orbitals of both π and σ character. Complex 3 reacted with acetonitrile or benzonitrile to cyclo-add C≡N to the U=carbon double bond, thereby forming a new C-C bond in a new chelated quadridentate ligand in the bridged dimetallic complexes (9 and 10). A single carbon-U bond is retained. The newly coordinated uranium complex dimerizes with one equivalent of unconverted 3 using two chlorides and the newly formed imine derived from the nitrile as three connecting bridges. In addition, a new crystal structure of [CpUCl ₃(THF)₂] (8) was determined by X-ray diffraction.

Full text of DOI:10.1021/ic102537q

ARTICLE
pubs.acs.org/IC
Actinide Metals with Multiple Bonds to Carbon: Synthesis, Characterization,
and Reactivity of U(IV) and Th(IV) Bis(iminophosphorano)methandiide
Pincer Carbene Complexes
Guibin Ma, Michael J. Ferguson,† Robert McDonald,† and Ronald G. Cavell*
Department of Chemistry and †X-ray Structure Determination Laboratory, University of Alberta, Edmonton, Alberta, Canada T6G 2G2
S Supporting Information
b
ABSTRACT: Treatment of ThCl4(DME)2 or UCl4 with
1 equiv of dilithiumbis(iminophosphorano) methandiide,
[Li2C(Ph2PdNSiMe3)2] (1), afforded the chloro actinide
carbene complexes [Cl2M(C(Ph2PdNSiMe3)2)] (2 (M =
Th) and 3 (M = U)) in situ. Stable PCP metalꢀcarbene
complexes [Cp2Th(C(Ph2PdNSiMe3)2)] (4), [Cp2U(C-
(Ph2PdNSiMe3)2)] (5), [TpTh(C(Ph2PdNSiMe3)2)Cl]
(6), and [TpU(C(Ph2PdNSiMe3)2)Cl] (7) were generated
from 2 or 3 by further reaction with 2 equiv of thallium(I) cyclopentadienide (CpTl) in THF to yield 4 or 5 or with 1 equiv of
potassium hydrotris(pyrazol-1-yl) borate (TpK) also in THF to give 6 or 7, respectively. The derivative complexes were isolated,
and their crystal structures were determined by X-ray diffraction. All of these U (or Th)ꢀcarbene complexes (4ꢀ7) possess a very
short M (Th or U)dcarbene bond with evidence for multiple bond character. Gaussian 03 DFT calculations indicate that the MdC
double bond is constructed by interaction of the 5f and 6d orbitals of the actinide metal with carbene 2p orbitals of both π and σ
character. Complex 3 reacted with acetonitrile or benzonitrile to cyclo-add CtN to the Udcarbon double bond, thereby forming a
new CꢀC bond in a new chelated quadridentate ligand in the bridged dimetallic complexes (9 and 10). A single carbonꢀU bond is
retained. The newly coordinated uranium complex dimerizes with one equivalent of unconverted 3 using two chlorides and the
newly formed imine derived from the nitrile as three connecting bridges. In addition, a new crystal structure of [CpUCl3(THF)2]
(8) was determined by X-ray diffraction.
’ INTRODUCTION
and it is thought that the intrinsic electronic properties of these
metals does not allow stabilization of the carbene center.5 A few
species of the form [M]dCH2 (M = Ce, Nd, Th, U) have been
detected by IR spectroscopy in reactions of excited metal atoms
with methane or methyl halides in solid argon.6 Carbenoid
[U]dCR2 nucleophilic species were suggested in McMurry type
reactions of sterically hindered ketones in the UCl4/Li(Hg)
system.7 We have undertaken an exploration of our bis-
(iminophosphorano)methandiide system with lanthanides and
actinides with a view of establishing whether involvement of 4f
and 5f orbitals and development of MꢀC multiple bonds could
be established with these elements. Very recently, several ur-
anium nucleophilic carbene complexes with the related SCS
(SCS = (Ph2PdS)2C2ꢀ) ligand and alternatively substituted
NPCPN2ꢀ methandiide pincer carbene complexes were ob-
tained and structurally characterized.8
Binding of two-electron carbene donors to metal ions to form
complexes with carbonꢀmetal bonds plays a central role in
catalytic organometallic chemistry,1 and for many main-group
and d-block elements, this chemistry has reached an advanced
stage of development.2 However, the development of actinide (5f)
carbene complexes has not been extensively pursued. In pioneering
work, Gilje et al. prepared uranium phosphoylide carbene com-
pounds such as (η5-C5H5)3UdCHP(CH3)2(C6H5) and several
relatives thereof which were the first actinide carbenes to be
structurally characterized.3f,g No thorium carbene complexes
have been reported in the literature. Recently, adducts of neutral
N-heterocyclic carbene (NHCs) to the UO22þ and UI2þ ions and
to Cp*2UI have been prepared, yielding complexes such as UO2-
4a
Cl2L2 (L = 1,3-dimesitylimidazole-2-ylidene (IMes) or 1,3-
4b
dimesityl-4,5-dichloroimidazole-2-ylidene (IMesCl2)), UIL3
(L=OCMe2CH2[1-C(NCHCHNiPr)],U(C5Me5)2I(C3Me4N2))4c
and U(C5H4But)3(C3Me4N2).4c In contrast to these relatively
sparse examples, uranium complexes with organoimido or
hydrocarbyl ligands are fairly numerous.3 The N-heterocyclic
carbene (NHC) ligands are well-known to be strong σ-donor
ligands, so formation of these NHCꢀmetal complexes are con-
sidered to be simple Lewis base adducts possessing a single CꢀM
bond with no significant multiple carbeneꢀmetal bond character,
We developed the bis(iminophosphorano)methandiide pin-
cer carbene ligand system by means of double deprotonation of a
neutral bis(iminophosphorane) through dilithiation of the ligand
followed by metathetical lithium halide elimination or by reacting
the ligand with appropriate metal precursors to eliminate alkyls
Received: December 20, 2010
Published: June 13, 2011
r
2011 American Chemical Society
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|

Inorganic Chemistry
ARTICLE
Scheme 1. Synthesis of Complexes
Figure 1. Perspective view of the [(η5-C5H5)2Th{κ3-C(Ph2Pd
NSiMe3)2}] (4) molecule showing the atom labeling scheme. Only the
ipso carbons of the phenyl rings are shown. Non-hydrogen atoms are
represented by Gaussian ellipsoids at the 20% probability level. Hydrogen
atoms are not shown. The structure of the analogous, isostructural uranium
complex (5) is given in the Supporting Information.
or other protonated species, and an interesting body of chemistry
for transition, main group, and noble metals has emerged.9
Previously, the only reported lanthanide metal complex of this
carbene ligand was the Sm(III) carbene double bond complex
[SmdC(Ph2PdNSiMe3)2(NCy)]9g; however, others have re-
cently prepared additional examples of the lanthanide complexes
with the Mes-substituted bis(iminophosphorano)methandiide
analog.9r We have now extended our studies of metal complexes
of this system to the 5f actinide group, specifically Th and U,
thereby providing new extensions to the examples of doubly
bound carbeneꢀactinide metal complexes of the dianionic methan-
diide ligand system derived from [Li2C(Ph2PdNSiMe3)2]2 (1).10
identities of 2 and 3. The result of the reactions of 3 with nitriles
described below is also supportive of the identity and formulation
of 3. Interestingly, initial attempts to prepare the analogous
SPPh2CPPh2S dianionic complex (SCS2ꢀ) directly from UCl4
and Li2(SCS) by others was not successful due to solubility
problems and interfering ligand and solvent interactions, and
accordingly alternate routes were necessary.8a In this case, success-
ful syntheses of a series of uranium(IV) complexes were achieved
using a U(BH4)4 precursor. Three complexes (two containing
three SCS ligands and one pincer monomer complex) were
obtained.8a Later, this group successfully prepared pincer SCS
complexes (including a bis(carbene)) with both Cl or Cp substit-
uents directly from UCl4.8b Others have used the methylene
backbone NMe’s analog of 1 to obtain a uranium(IV) complex
containing two NCN pincer substituents (as a bis(carbene)) by a
substitutionꢀdisproportionation reaction from UI3.8c
’ RESULTS AND DISCUSSION
Synthesis of the Complexes. A red, air-sensitive, presumably
monomeric, crystalline solid complex of Th(IV), [Cp2Th{C-
(Ph2PdNSiMe3)2}], 4, was obtained when 1 equiv of dimeric
[Li2C(Ph2PdNSiMe3)2]2 (1)10 was added to a THF solution of
2 equiv of ThCl4(DME)2 under an argon atmosphere. Ulti-
mately, because 2 could not be crystallized, we then added,
directly, two equivalents of solid thallium(I) cyclopentadienide,
TlCp, per equivalent of 2 to give 4. Successful Cp substitution
was indicated by the generation of white, insoluble, solid TlCl.
Complex 4 crystallized nicely and was fully structurally and
analytically characterized. As an alternative to Cp substitution,
we also converted the dichloride complex, 2, to the pyrazolyl
borate complex, [{HB(pyrazolyl)3}Th{C(Ph2PdNSiMe3)2}Cl]
(6), with 1 equiv of TpK (Scheme 1), which provided good
crystals. Similarly, two U(IV) complexes were prepared as green
air-sensitive crystalline solids. The first, [Cp2U{C(Ph2Pd
NSiMe3)2}] (5), was prepared from UCl4 and 1 followed by
treatment with TlCp in an exactly parallel fashion to the
preparation of 4 and the second, [{HB(pyrazolyl)3}U{C-
(Ph2PdNSiMe3)2}Cl] (7), by treatment of intermediate 3 with
1 equiv of TpK. These derivatized complexes also crystallized
nicely and were fully analytically and structurally characterized.
Although we did not succeed in crystallizing the chloro com-
pounds 2 and 3 from the reaction solutions, the derivatizations
to the fully characterized species 4ꢀ7 clearly established the
The NMR spectra of the diamagnetic complexes 4 and 6 were
normal with all chemical shifts in the predicted regions. Multi-
plicities expected from the presence of two 31P nuclei were
observed. Complexes 5 and 7 are paramagnetic, so NMR
resonances are broad and display paramagnetic shifts; the 31P
NMR spectra of 5 and 7 each consisted of one broad singlet at
361.62 and ꢀ381.7 ppm, respectively. The signal for 5 is down-
field shifted by 347.2 ppm with respect to the 31P shift value for
compound 1 (14.4 ppm), and that for 7 is upfield shifted by 396.1
ppm. The proton NMR for complex 5, showed downfield shifts
for phenyl protons and upfield shifts for the ꢀSi(CH3)3 and Cp
protons. No signal was observed in the 13C{1H} NMR spectrum
for the quaternary backbone carbon for these complexes, fairly
typical behavior for these carbene centers.9j
Crystal Structures and Bond Lengths in the Com-
plexes. The molecular structures of [(η5-C5H5)2Th{κ3-C-
(Ph2PdNSiMe3)2}] (4), [(η5-C5H5)2U{κ3-C(Ph2PdNSiMe3)2}]
(5), [{HB(pyrazolyl)3}Th{κ3-C(Ph2PdNSiMe3)2}(Cl)] (6), and
[{HB(pyrazolyl)3}U{κ3-C(Ph2PdNSiMe3)2}(Cl)] (7) were con-
firmed by X-ray crystallography. Perspective views of thorium com-
plexes (4 and 6) are shown in Figures 1 and 2. The isostructural
uranium complexes (5and 7) are given in the Supporting Information.
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Inorganic Chemistry
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Table 1. Selected Bond Lengths (Å) and Angles (deg) for
Complexes 4 and 5
complex 4
bond lengths (Å)
ThꢀC(1)
ThꢀN(1)
ThꢀN(2)
ThꢀC(50)
ThꢀC(51)
ThꢀC(52)
ThꢀC(53)
ThꢀC(54)
ThꢀC(55)
2.436(4)
2.508(3)
2.501(3)
2.813(5)
2.849(5)
2.868(5)
2.846(5)
2.813(5)
2.800(5)
ThꢀC(56)
ThꢀC(57)
ThꢀC(58)
ThꢀC(59)
P(1)ꢀC(1)
P(1)ꢀN(1)
P(2)ꢀC(1)
P(2)ꢀN(2)
2.814(5)
2.828(5)
2.830(5)
2.816(5)
1.654(4)
1.635(3)
1.664(4)
1.631(4)
Figure 2. Perspective view of the [{HB(pyrazolyl)3}Th{C(Ph2PdN-
SiMe3)2}Cl] (6) molecule showing the atom labeling scheme. Only the
ipso carbons of the phenyl rings are shown. Non-hydrogen atoms are
represented by Gaussian ellipsoids at the 20% probability level. The
hydrogen atom of the BꢀH group is shown with an arbitrarily small
thermal parameter; the remaining hydrogen atoms are not shown. The
structure of the analogous, isostructural uranium complex (7) is given in
the Supporting Information.
angles (deg)
N(1)ꢀThꢀN(2)
N(1)ꢀThꢀC(1)
N(2)ꢀThꢀC(1)
125.09(11)
62.93(12)
63.46(12)
N(2)ꢀP(2)ꢀC(1)
P(1)ꢀC(1)ꢀP(2)
104.06(19)
150.5(3)
complex 5
bond lengths (Å)
2.351(2)
UꢀC(1)
UꢀN(1)
UꢀN(2)
UꢀC(50)
UꢀC(51)
UꢀC(52)
UꢀC(53)
UꢀC(54)
UꢀC(55)
The selected bond lengths and bond angles are shown in Tables 1 and
2. The core structures of 4ꢀ7 are similar, consisting of two nearly
planar, fused, four-membered rings with a common MꢀC(1) (M =
Th, U) shared edge. The two planes in 4 and 5 have small dihedral
angles (7.65(14)° for 4 and 7.62(8)° for 5), but the planes in
structures 6 and 7, defined by the two four-membered rings (plane
1: M, N(1), P(1), and C(10) and plane 2: M, N(2), P(2), and
C(10)), have somewhat bigger dihedral angles (32.76(9)° for 6 and
34.24(6)° for 7). Foldings in this methandiide system have previously
been found to range from about 30° to 0°,9a,b,fꢀi,l and it seems that the
bonding is flexible with regard to this axis. The extent of bending is
probably determined by intramolecular interactions. Intramolecular
chelation of the two trimethylsilylimine units in the ligand completes
the pincer carbene structure. The two η5-Cp rings complete the
coordination around the thorium(IV) and uranium(IV) in 4 and 5.
The two Cp planes are disposed symmetrically above and below this
axial (MdC) bis(chelate) pair of planes of fused four-membered rings
with dihedral angles of 59.3(2)° in 4and 59.32(10)° in 5, respectively.
In 6 and 7, which are forced to functional 7 coordination by the
requirements of the tridentate (three N atoms) Tp ligand and the
bound Cl substituent, the Tp is sitting on the opposite side of the
chloride with respect to the axial (folded) plane along the MdC axis.
One of the coordinated N atoms (N(52)) is located opposite the
carbeneC(10) withaN(52)ꢀMꢀC(10) bond angle of 166.18(11)°
for 6 and 168.28(8)° for 7. The uranium to carbon bond distances
UꢀC(1) = 2.351(2) Å (5) andUꢀC(10) = 2.376(3) Å (7) areboth
considerably shorter (15%) than the average Uꢀcarbene (NHC)
distances4 {average 2.694 Å, a range of 2.609(4)∼2.799(3) Å};
however, these lengths are slightly longer (3%) than the shortest
known multiple UꢀCbonddistanceintheUꢀphosphoylide, 2.29(3)
Å,3f,g and indeed they are compatible with the three recently studied
uranium SCS pincer carbene complexes containing a UdC double
bond (UꢀC = 2.327(3), 2.444(4), and 2.484(3) Å, respectively).8a
All of these distances are shorter than those found for UꢀC single
bonds. Typical recent examples of UꢀC single bonds are the pincer-
like complex (which bears some resemblance to the present system)
tris(1,2-dimethoxyethane)-lithium-μ2-chloro-(μ2-4-oxybutyl)-
1,2-dimethoxyethane)-(2,6-bis(N-(2,6diisopropylanilino)ethen-1-
2.4896(18)
2.4775(18)
2.747(2)
2.781(2)
2.807(3)
2.789(2)
2.757(2)
2.744(2)
UꢀC(56)
UꢀC(57)
UꢀC(58)
UꢀC(59)
P(1)ꢀC(1)
P(1)ꢀN(1)
P(2)ꢀC(1)
P(2)ꢀN(2)
2.756(2)
2.771(3)
2.770(3)
2.762(3)
1.667(2)
1.6288(18)
1.667(2)
1.6253(19)
angles (deg)
N(1)ꢀUꢀN(2)
N(1)ꢀUꢀC(1)
127.14(6)
64.13(7)
N(1)ꢀP(1)ꢀC(1)
P(1)ꢀC(1)ꢀP(2)
102.59(10)
149.83(14)
yl)benzene)-lithiumꢀuranium with a UꢀC(phenyl) single bond
length of 2.476 Å.3j Our UꢀC(methine) bond in 9 (see below) is
2.660(7) Å. A dimethyl-tetramethyl EDTA U(IV) complex with
a six coordinate structure has UꢀC(methyl) bond lengths of
2.47ꢀ2.48 Å.3k A large number of Cp and Cp* uranium(IV)
examples have been reported which show UꢀC single bond
lengths ranging around from 2.33 to 2.43 Å depending on the
electronegativity of the substituent (see, for example, ref 3l and
references therein). These Cp, Cp*, and related complexes are
however more open than our pincers, and this may allow for
shorter bonds. No Thꢀcarbene bond data are available for
comparison; however, the ThꢀC distances in 4 {2.436(4) Å}
and in 6 {2.469(3) Å} are also obviously shorter (9%) than the
ThꢀC bond distances found for previously reported hydrocarbyl
thorium complexes {2.641(5) Å11a and 2.617(5)∼2.892(5)
Å}.11b These bond lengths suggest multiple bond character
between the metals (U or Th) and the central ligand carbon
atom for complexes 4ꢀ7.
The bond distances (PꢀC and PꢀN) within the ligand frame-
work in these complexes are also considerably altered in comparison
with the related values in the free bis(iminophosphorano)methane
ligand12 and the dilithium dianionic methanide salt 1.10 The PdN
bond distances are elongated, and the endocyclic PꢀC bond
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Table 2. Selected Bond Lengths (Å) and Angles (deg) for
Complexes 6 and 7
Scheme 2. Reactivity of the UdC Double Bond with Nitriles,
RꢀCtN
complex 6
bond lengths (Å)
ThꢀC(10)
ThꢀN(1)
ThꢀN(2)
ThꢀN(52)
ThꢀN(62)
ThꢀN(72)
2.469(3)
2.430(3) ThꢀCl
2.457(3) P(1)ꢀC(10)
2.654(3) P(1)ꢀN(1)
2.650(3) P(2)ꢀC(10)
2.621(3) P(2)ꢀN(2)
2.7264(10)
1.683(4)
1.633(3)
1.668(4)
1.640(3)
angles (deg)
ClꢀThꢀN(1)
ClꢀThꢀN(2)
ClꢀThꢀN(52)
ClꢀThꢀN(62)
ClꢀThꢀN(72)
88.78(8)
83.79(8)
80.94(8)
134.50(8)
137.26(8)
ClꢀThꢀC(10)
112.53(8)
Reactivity of the Uranium Complexes. Many years ago, Gilje
et al. studied the reactivity of the phospholide uraniumꢀcarbon
multiple bond in the system Cp3UdCHPR3 toward CO,14a
isonitrile, or nitrile,14b which resulted in insertion reactions to
the UdC double bond and the formation of new ligands in the
uranium coordination sphere. The new ligands replaced the UdC
bond with a bond between C and also O of the reactant. Recently,
Mꢀezailles et al. studied the reactivity of their UdC (SCS) carbene
complexes toward molecules containing a carbonyl function such
as ketones and aldehydes.8a In these cases, the CdO center added
to the carbene center, and a tetrasubstituted olefin was eliminated
to break the MdC bond and the pincer structure. Presumably, a
metal oxo complex was also formed, as the eliminated organic
products contained no oxygen.
The chemical reactivity of the UdC multiple bond in the
intermediate 3 was explored with a solution study of reactivity
with nitriles (acetonitrile and benzonitrile). In these cases, the
CtN triple bond suffered a 1,2 cycloaddition to the carbonꢀmetal
bond to form a new CꢀC bond and build a new tetradentate
ligand (with three imine centers which coordinate to the U while
maintaining a single UꢀC bond), as shown in Scheme 2. Thus,
reactions of either acetonitrile or benzonitrile with 1 equiv of 3
in situ (THF) at room temperature (about 25 °C) formed
complexes 9 and 10, respectively, in almost quantitative yields,
and only 1/2 of the quantity of 3 was transformed. The newly
formed (carbon) imine center joins with two of the chlorides to
form a bridged complex with the remaining half of the starting
complex, 3. The reaction pathways demonstrated by the present
uranium methandiide complex provide a contrast with the
behavior of UdC centers reported by previous workers.8a,14
The crystal structure of 9 was solved by X-ray diffraction. The
molecular structure is shown in Figure 3a, and the selected bond
distances and angles are listed in Table 3. The structure has two
separated (and different) pincer carbon complexed uranium
metal centers linked to each other by two chlorides and one
nitrogen atom (a carbon imine center derived from the insertion
of the nitrile into one of the UdC bonds). As a result, one pincer
unit contains a uranium methandiide (UdC) center; the other
pincer U center is formed with a uraniumꢀmethine carbon center.
Both PCP pincer units are bound by the aforementioned bridges
such that each metal achieves seven coordination. The Ud
C(methandiide) bond is shorter (distance U(1)ꢀC(1) = 2.337(7)
Å) than similar bonds in 5 (bond distance UꢀC(1) = 2.351(2)
Å) and 7 (bond distance UꢀC(2) = 2.376(3) Å). The other has a
UꢀC single bond (distance U(2)ꢀC(2) = 2.660(7) Å). The
difference in bond lengths (the UꢀC (2) distance is 13% longer
than the UdC(1) distance) is consistent with a reduction in
bond order in one case from a formal metalꢀcarbon double bond
P(1)ꢀC(10)ꢀP(2) 139.1(2)
N(1)ꢀThꢀN(2)
N(1)ꢀThꢀN(52)
N(1)ꢀThꢀN(62)
120.32(10)
120.80(10)
77.85(11)
133.87(11)
N(1)ꢀP(1)ꢀC(10) 104.25(16) N(1)ꢀThꢀN(72)
complex 7
bond lengths (Å)
UꢀC(10)
UꢀN(1)
UꢀN(2)
UꢀN(52)
UꢀN(62)
UꢀN(72)
2.376(3)
2.389(2) UꢀCl
2.6840(7)
1.687(3)
1.628(2)
1.681(3)
1.633(2)
2.405(2) P(1)ꢀC(10)
2.599(2) P(1)ꢀN(1)
2.609(2) P(2)ꢀC(10)
2.574(2) P(2)ꢀN(2)
angles (deg)
ClꢀUꢀN(1)
ClꢀUꢀN(2)
ClꢀUꢀN(52)
ClꢀUꢀN(62)
ClꢀUꢀN(72)
86.88(6)
83.34(6)
79.89(6)
133.58(6)
137.69(6)
ClꢀUꢀC(10)
P(1)ꢀC(10)ꢀP(2) 138.49(17)
N(1)ꢀUꢀN(2)
N(1)ꢀUꢀN(52)
N(1)ꢀUꢀN(62)
111.54(7)
122.58(8)
118.90(8)
76.92(8)
N(1)ꢀP(1)ꢀC(10) 102.94(11) N(1)ꢀUꢀN(72)
135.28(8)
distances are significantly shorter. However, the exocyclic PꢀC
distances are unaffected. The PꢀCꢀP bond angles 150.55(11)°-
(4), 149.84(14)° (5), 139.1(2)° (6), and 138.49(17)° (7) are
considerably widened compared to the corresponding values in
CH3CH{Ph2PdN(p-tolyl)}2 (112.39(19)°)12a and in H2C{Cy2-
PdNSiMe3}2 (117.41(12)°)12b and are also remarkably widened
compared to [Li2C(Ph2PdNSiMe3)2]2 (132.6(3)°)10 and
[Sm{C(Ph2PdNSiMe3)2}(NCy2) (THF)] (138.0(3)°).9g These
factors suggest that there is a delocalization of π electron density
within each of the four-membered metallocyclic rings, via conjuga-
tion of MdC (M = Th, U) and PdN bonds. That the two four-
membered metallocyclic rings are nearly coplanar is an indication of
strong carbene to actinide metal and π electron delocalization
interactions.
During the course of precursor preparation, we isolated com-
pound 8 (CpUCl3(THF)2) as deep green crystals from the
reaction mixture of UCl4 with 1 equiv of CpTl in THF. Although
previously synthesized,13a,b no structure was reported. We have
structurally characterized this interesting precursor, and the results
are given in the Supporting Information. The structure is quite
similar to that of MeCpUCl3(THF)2, which was reported some-
time later than the original syntheses of the original relatives.13c
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Table 3. Selected Bond Lengths (Å) and Angles (deg) for
Complex 9
bond lengths (Å)
U(1)ꢀC(1)
U(1)ꢀN(1)
U(1)ꢀN(2)
U(1)ꢀN(5)
U(1)ꢀCl(1)
U(1)ꢀCl(2)
U(1)ꢀCl(3)
P(1)ꢀC(1)
P(2)ꢀC(1)
P(1)ꢀN(1)
P(2)ꢀN(2)
2.337(7)
2.465(6)
2.432(6)
2.412(6)
2.9313(18)
2.8941(17)
2.660(2)
1.674(7)
1.681(7)
1.635(6)
1.605(6)
U(2)ꢀC(2)
U(2)ꢀN(3)
U(2)ꢀN(4)
U(2)ꢀN(5)
U(2)ꢀCl(1)
U(2)ꢀCl(2)
U(2)ꢀCl(4)
P(3)ꢀC(2)
P(4)ꢀC(2)
P(3)ꢀN(3)
P(4)ꢀN(4)
C(2)ꢀC(3)
N(5)ꢀC(3)
C(3)ꢀC(4)
2.660(7)
2.456(6)
2.354(7)
2.383(6)
2.7717(18)
2.782(2)
2.522(5)
1.729(6)
1.754(7)
1.617(6)
1.615(7)
1.570(9)
1.268(9)
1.490(10)
angles (deg)
P(1)ꢀC(1)ꢀP(2)
U(1)ꢀN(5)ꢀU(2)
U(1)ꢀCl(1)ꢀU(2)
U(1)ꢀCl(2)ꢀU(2)
Cl(2)ꢀU(1)ꢀCl(3)
Cl(2)ꢀU(2)ꢀCl(4)
144.4(4)
108.7(3)
86.14(5)
86.67(5)
95.40(6)
87.81(11)
P(3)ꢀC(2)ꢀP(4)
P(3)ꢀC(2)ꢀC(3)
P(4)ꢀC(2)ꢀC(3)
C(2)ꢀC(3)ꢀC(4)
N(5)ꢀC(3)ꢀC(2)
N(5)ꢀC(3)ꢀC(4)
126.1(4)
114.7(5)
118.2(4)
118.4(6)
116.9(6)
124.7(6)
using as models [Cp2Th{C(Me2PdNSiH3)2}] (4a), [Cp2-
U{C(Me2PdNSiH3)2}] (5a), [TpTh{C(Me2PdNSiH3)2}Cl]
(6a), and [TpU{C(Me2PdNSiH3)2}Cl] (7a) to probe the
nature of the core structure. We performed closed shell Hartreeꢀ
Fock calculations on all model systems (4aꢀ7a); however,
because the two U(IV) compounds (5a and 7a) possess a 5f2
electron configuration with two unpaired electrons, we also per-
formed restricted open shell HartreeꢀFock calculations
(ROHF) on 5a and 7a as well. The result was an additional
energy stabilization of approximately 25.0 kcal/mol for (5a and
7a) compared to the closed shell results (for details, see the
Supporting Information). Overall, bonding pictures are not
substantially affected by the open shell configuration, which
shows a double bonding interaction between the metal (Th or U)
and the carbene centers.
For thorium compound 4a, the highest occupied molecular
orbitals (HOMOs; MO = 110, E = ꢀ0.190 au) and the HOMOꢀ1
(MO = 109, E = ꢀ0.200 au) show individual π and σ multiple
bond components between the carbene center and the metal
thorium center (Figure 4, top). The molecular orbital coefficients
indicate that this molecular orbital (HOMO, MOꢀ110) is
formed by interaction between the carbene pz atomic orbital
and (mainly) part of the Th 6d orbital, with two electrons of the
carbene pz providing a π lone pair donation to the Th 6d orbital
to form a π bond. HOMOꢀ1 (MOꢀ109) is formed between the
py carbene orbital (which is best described as one σ component
of an approximately sp2 set) and part of the Th 6d. Two electrons
of this σ component provided as a σ lone pair donation to the Th
6d orbital to form a σ bond. A natural bond orbital (NBO)
analysis of 4a also reveals the double carbene metal bonds (CꢀTh)
with 5.7% Th and 94.3% carbene (NBO orbitals in Figure 4,
bottom; for details, see the Supporting Information). This indicates
Figure 3. (a) Perspective view of the [{(Me3SiNdPPh2)2C}ClU
(μ-Cl)2UCl{NC(Me)C(Ph2PdNSiMe3)2}] (9) molecule showing
the atom labeling scheme. Non-hydrogen atoms are represented by
Gaussian ellipsoids at the 20% probability level. Only the ipso carbon
atoms attached to phosphorus are shown. Hydrogen atoms attached to
C(4) are shown with arbitrarily small thermal parameters and are not
numerically designated; all other hydrogen atoms are not shown. (b)
View of the trigonal bipyramid formed by the two uranium centers and
the three bridging atoms.
to a single metalꢀcarbon bond with the insertion of the nitrile
CN unit. As shown in Figure 3b, the three bridging atoms Cl(1),
Cl(2), and N(5) define a plane with the two uranium metals
sitting above and below the plane. This core adopts a trigonal
bipyramidal shape. Uranium(2), which is coordinated by three
nitrogen atoms and one carbon atom of the tetradentate ligand,
forms a set of three planes jointly sharing the axis defined by U(2)
and C(2) atoms, with a dihedral angle of approximately 120°.
The uranium-bound terminal chlorides show shorter UꢀCl
bond distances (2.522(5) Å or 2.660(2) Å) compared to those
to the chlorides which bridge the uranium atoms (2.8941(17) Å
or 2.9313(18) Å). In addition, the bond angle of P(1)ꢀC(1)ꢀ
P(2) (144.4(4)° incorporating the UdC double bond in U(1))
is slightly smaller than that in 5 (149.84(14)°) and larger than
that in 7 (138.49(17)°)). This angle is larger than the P(3)ꢀ
C(2)ꢀP(4) (126.1(4)°) based on the UꢀC single bond to U(2).
Theoretical Calculations. The most interesting feature of
these Th(IV) and U(IV) PCP methanediide structures is the
presence of short metalꢀcarbon bond distances. In order to fully
understand the nature of this metalꢀcarbene bond interaction,
we have carried out DFT calculations with Gaussian 0315,11b
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Figure 4. (a) HOMO (MOꢀ110) and HOMOꢀ1 (MOꢀ109) of
[Cp2Th{C(Me2PdNSiH3)2}] (4a), which represent individual double
bonding CdTh components. (b) NBO of C(carbene)ꢀTh double
bond in 4a (π and σ bonds).
Figure 5. (a) HOMO (MOꢀ112), HOMOꢀ1 (MOꢀ111), HOMOꢀ2
(MOꢀ110), and HOMOꢀ3 (MOꢀ109) of [Cp2U{C(Me2PdNSiH3)2}]
(5a). HOMOꢀ2 and HOMOꢀ3 represent individual double bonding
CdU components. (b) NBO of C(carbene)ꢀU double bond components
in 5a (π and σ bonds).
the main contribution to the double bond from the carbene
center, and it is consistent with dianion carbene character.
For the uranium compound 5a, the highest occupied molec-
ular orbitals HOMO (MOꢀ112, E = ꢀ0.058 au) and HOMOꢀ
1 (MOꢀ111, E = ꢀ0.062 au) have almost pure 5f atomic orbital
(AO) character (with also a small bonding interaction with the carbons
of the two Cp ligands), while HOMOꢀ2 (110, E = ꢀ0.193 au)
and HOMOꢀ3 (109, E = ꢀ0.207 au) are the individual π and
σ multiple bond components formed between the diide carbon
and the metal (U) orbital components (Figure 5a). The molec-
ular orbital coefficients indicate that in 5a the formation of the
σ bond involves one lobe (which is dominated by the p character:
16% s and 84% p) of the carbene center σ hybrid overlapping
with a mix of the 6s0.09, 6d0.22, and 5f0.68 uranium orbitals, dominated
by the latter. A second (π) bond is formed by the pz carbene orbital
(which is 100% p) overlapped with a metal 6d0.185f0.88 orbital
combination. A natural bond orbital (NBO) analysis of 5a reveals
the double carbene metal bond character (CꢀU) with 12.0% U and
88.0% carbene in 5a (Figure 5b, for details, see the Supporting
Information). Wiberg bond indices are 0.4582 and 0.6619 for CdTh
and CdU, respectively, indicating that the CdU bond is stronger
than the CdTh bond, which is consistent with the relative CꢀTh
and CꢀU bond distances in 4 and 5. When compared to Wiberg
bond indices of NꢀTh (4: 0.258) and NꢀU (5: 0.300) bonds, it is
clear that the MdC binding in 4 and 5 has an order higher than one.
The very wide P(1)ꢀC(1)ꢀP(2) angle suggests that the σstructure
about C(1) is not a true sp2 hybrid.
σ bond and the carbene pz orbitals are used to form the π bond
between the carbene center and the Th and U metal 6d and 5f
orbitals. Overall, the core MdC bond structures of 6a and 7a are
very similar to those of 4a and 5a despite the differences in
coordination geometry. A natural bond orbital (NBO) analysis of
6a and 7a reveals the carbene metal bonds (CꢀTh or CꢀU)
with approximately 7.0% Th and 93.0% carbene in 6a and 12.8%
U and 87.2% carbene in 7a in character (Supporting In-
formation). We suspect that the multiple M (thorium and
uranium)ꢀcarbon bonds in 4ꢀ7 are stabilized by balanced,
strong coordination to the Cp and Tp ligands and by the
chelating imine donation. It is interesting that the core carbe-
neꢀmetal orbitals may appear either as the HOMO and next
lowest frontier orbital or, in other cases, somewhat below the
frontier levels, which one would think would perturb the potential
reactivity. This appears to arise through the subtle interplay between
the metal and the other ligand (e g. Cp or Tp) orbitals and the core
pincer (NPCPN) structure. What influence this has on the reactivity
of each complex particularly with respect to overall nucleophilicity of
the MdC center needs to be further explored.
DFT calculations for related carbene complexes of uranium
with the geminal dianion SCS2ꢀ carbene were reported recently
in the literature.8a,16 In principle, our NPCPN carbene has the
same central coordination properties as SCS2ꢀ, and the ligand
systems belong to the same methandiide family, so it is not
surprising to see very similar actinide MdC double bond bonding
The DFT calculations reveal that the bond structures of 6a and
7a are similar; the HOMOꢀ2 (137, E = ꢀ0.127 au) and
HOMOꢀ1 (138, E = ꢀ0.108 au) of 6a and the HOMOꢀ
4 (137, E = ꢀ0.231 au) and HOMOꢀ3 (138, E = ꢀ0.209 au) of
7a show that carbene px orbitals are used for formation of a
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Scheme 3. Formation of a MdC Double Bond upon Coor-
dination of the Carbene Dianion to an Electron Deficient
Metal Center
indicated electron transfer from the carbon to the metal center.
The DFT calculations show that the components of the MdC
double bond involve the 5f and 6d orbitals of the actinide metal
and the carbene 2p orbitals, as both π bond and σ bond
components. The chemical reactivity of the multiple UdC
double bond in 3 with either acetonitrile or benzonitrile sub-
strates was established. The nitrile cycloadds to the MdC bond
to form a new CꢀC bond building a new tetradentate chelating
ligand with a carbon imine center which subsequently coordi-
nates and binds through this new imine nitrogen with another
equivalent of untransformed carbene to form a dimeric, dime-
tallic complex. The cycloaddition reduces the MdC bond to a
MꢀC bond; thus, the final dimetallic complex contains two
Uꢀcarbon bond types with the expected difference in bond
lengths.
Some contrasting reactivity between the imino NCN2ꢀ and
thiophosphoryl SCS2ꢀ 8a systems was observed, and additional
studies of these systems warrant further investigation. Our work
on imino coordinated systems continues.
’ EXPERIMENTAL SECTION
General Methods. All experimental manipulations were per-
formed under rigorously anaerobic conditions using Schlenk techniques
or an argon-filled glovebox. Solvents used (special THF, toluene, and
ether) were dried over appropriate drying agents and degassed by three
1
freezeꢀpumpꢀthaw cycles prior to use. The H, 13C, and 31P NMR
spectra were recorded on a Varian I400 spectrometer operating at
400.13, 100.6, and 161.9 MHz, respectively. The H and 13C NMR
1
structures in both complexes. Overall, all results demonstrate
that ligand 1 behaves as a dianionic carbene center through the
donation of two carbon electron pairs on the dianion (a π(pz)
and a σ(py) NꢀPꢀCꢀPꢀN framework set (made up of py and
px and s components) to metal-centered vacant orbitals, which
results in the formation of an MdC double bond (Scheme 3).
We also show the Mulliken charges in Scheme 3, which
(although not completely accurate) reflect a zwitterionic delo-
calization throughtout the core structure.
Interestingly, complexes 4 (5) and 6 (7) show very similar
thorium (uranium) to carbon bonding, but 6 and 7 differ from 4
and 5 in that a chloride is also bound to the actinide metal, forcing
an increase in coordination to 7 in the 6 and 7 pair. In addition,
the Tp ligand imposes smaller steric constraints than Cp, so it will
be interesting to see if the Th and U centers in 6 and 7 can be
further functionalized.
spectra are referenced internally using the residual proton solvent
resonances, which were referenced to SiMe4 (δ = 0). 31P NMR chemical
shifts are given relative to an 85% H3PO4 external reference. Elemental
analyses and IR spectra were carried out at the Analytical and Instru-
mentation Laboratory, Department of Chemistry, University of Alberta.
The organolithium compound [Li2L]2 (1) was prepared according to
our published procedures.10a,17 ThCl4(dme)2 and UCl4, which had been
prepared according to published procedures,18 were donated by Prof.
Josef Takats, Department of Chemistry, University of Alberta. All other
chemicals were purchased from either Strem or Aldrich.
Crystal Structure Determination. Suitable crystals of 4ꢀ9 were
mounted on glass fibers by means of mineral oil, and data were collected
using graphite-monochromated Mo KR radiation (0.71073 Å) on a
Bruker PLATFORM/SMART 1000 CCD diffractometer. The struc-
tures were solved by direct methods using SHELXL-8619a and refined
using full-matrix least-squares on F2(SHELXL-93).19b All of the non-
hydrogen atoms in the structure compound were refined with aniso-
tropic displacement parameters. Selected crystal data and structure
refinement details for all of the compounds are listed in Table 4.
Synthesis of [Cp2Th{C(Ph2PdNSiMe3)2}] (4). To a colorless
THF (5 mL) solution of ThCl4(DME)2 (0.111 g, 0.2 mmol) was added
solid [Li2C(Ph2PdNSiMe3)2]2 (0.115 g, 0.1 mmol) with stirring at
room temperature. The reaction mixture was stirred at room tempera-
ture for 2 h, providing a brown-orange solution, to which was added
solid, brown-red, thallium(I) cyclopentadienide, TlCp (0.108 g, 0.4
mmol). The reaction mixture was kept overnight at room temperature
while maintaining vigorous stirring. The white precipitate of TlCl was
decanted by centrifugation. The THF solvent was removed under
vacuum conditions, and the remaining powder was dissolved in 10 mL
of ether. The insoluble solid LiCl was decanted by centrifugation. The
resultant red solution was reduced to half of the volume under vacuum
conditions and put inside a ꢀ20 °C freezer for two days. A red crystalline
solid was obtained. The product was filtered and dried under vacuum
conditions. Yield: 0.103 g, 56.0%. IR data (Nujol mull): 3057 m, 2949s,
’ SUMMARY AND CONCLUSION
Treating uranium or thorium tetrachloride with dilithium-
bis(iminophosphorano)methandiide gave U or Th metal car-
bene complexes which were derivatized for crystallinity. These
four complexes (4ꢀ7) represent additional extensions of actinides
bound to a dianionic carbene bis(iminophosphorano)methandiide
ligand system, which exhibits bonding properties similar to those of
the analogous actinide dianionic bis(thiophosphoryl)methandiide.
The complexes 4 and 6 are the first examples of Th complexes of this
system.
All complexes present short MꢀC bond distances. The
planarity at the carbene center favors the donation of the σ
and π structures of the carbon to the actinide (U or Th) center,
leading to formation of a “double” bond with marked shortening
of the Uꢀcarbene distance. Gaussian 03 DFT calculations clearly
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Table 4. Crystal Data and Structure Refinement Details for Complexes 4ꢀ9
empirical formula
C41H48N2-
P2Si2Th (4)
918.97
C
41H48N2-
C
40H48BClN8-
C
40H48BClN8-
C
13H21Cl3O2U (8)
C76H107Cl4N5-
P4Si4U2 (9)
1944.77
P2Si2U6 (5)
P2Si2Th (6)
P2Si2U (7)
fw
924.96
1037.28
1043.27
553.68
cryst syst
triclinic
triclinic
P (No. 2)
orthorhombic
P212121 (No. 19)
orthorhombic
P212121 (No. 19)
monoclinic
P21/c (No. 14)
trigonal
space group
unit cell parameters
a (Å)
P (No. 2)
R3c (No. 161)
10.263(2)
11.750(3)
17.920(4)
74.871(3)
76.889(3)
76.480(3)
1996.3(8)
2
10.2290(6)
11.7512(7)
17.8708(10)
74.6909(7)
76.9568(7)
76.4559(7)
1983.3(2)
2
10.5465(6)
18.4379(11)
22.7463(13)
10.5116 (9)
18.3976 (15)
22.7622 (19)
8.3657 (9)
45.586 (4)
b (Å)
13.3438 (14)
15.4265 (16)
c (Å)
21.7302 (14)
R (deg)
β (deg)
101.9790(10)
γ (deg)
volume (Å3)
4401.9 (6)
4
1684.6 (3)
4
39107 (5)
18
Z
4
calculated density (g cmꢀ3
temperature, K
)
1.529
1.549
1.558
1.574
1.574
1.486
193.2(1)
3.905
193.2(1)
4.264
193.2(1)
3.597
193.2(1)
3.914
193.2(1)
10.10
193.2(1)
4.015
μ (Mo KR) (mmꢀ1
independent reflns
observed reflns
)
8988
9044
10088
9498
10014
3845
19943
7926
8507
9521
3633
14958
data/restraints/params
goodness of fit on F2
final R indices
8988/0/433
1.056
9044/0/433
1.078
10088/0/496
1.090
10014/0/496
1.020
3845/0/181
1.154
19943/0/749
0.959
[F02 g 2σ(F0)]
R1 = 0.0299
wR2 = 0.0879
ꢀ0.766 and
2.164 e/Å3
R1 = 0.0200
wR2 = 0.0503
ꢀ0.343 and
1.244 e/Å3
R1 = 0.0222
wR2 = 0.0578
ꢀ0.516 and
1.106 e/Å3
R1 = 0.0196
wR2 = 0.0437
ꢀ0.403 and
1.203 e/Å3
R1 = 0.0212
wR2 = 0.0538
ꢀ1.115 and
1.081 e/Å3
R1 = 0.0444
wR2 = 0.106
ꢀ0.683 and
3.187 e/Å3
wR2 [F02 g ꢀ3σ(F02)]
large difference peak
and hole
2894w, 1438s, 1298, 1275s, 1240s, 1159 m, 1114s, 1014 m, 830s, 746s,
694s. 1H NMR (THF-d8): δ 7.37 (m, phenyl, 8H), 7.26 (t, phenyl, 4H),
7.15 (t, phenyl, 8H), 6.41 (s, C5H5, 10H), ꢀ0.02 (s, Si(CH3)3, 18H).
13C{1H} NMR (THF-d8): δ 139.55 (d, phenyl), 131.70 (t, phenyl),
130.34 (s, phenyl), 128.41 (t, phenyl), 117.18 (s, C5H5), 4.32 (s,
Si(CH3)3). 31P{1H} NMR (THF-d8): δ 4.0 (s). Anal. Calcd for
C41H48N2P2Si2Th: C, 53.58; H, 5.26; N, 3.05. Found: C, 53.13; H,
5.33; N, 3.00.
Synthesis of [Cp2U{C(Ph2PdNSiMe3)2}] (5). A similar proce-
dure to that for 4 was used. Yield: 0.113 g, 61.1%. IR data (Nujol mull): 3058
m, 2953s, 1438s, 1313w, 1241 m, 1124s, 1070 m, 1016 m, 882s, 743s, 691s.
1H NMR (THF-d8): δ 14.27 (s, phenyl, 8H), 9.16 (t, phenyl, 8H), 8.31
(t, phenyl, 4H), ꢀ14.21 (s, ꢀSi(CH3)3, 18H), ꢀ14.79 (s, C5H5, 10H).
13C{1H} NMR (THF-d8): δ 142.11 (br, s, phenyl), 133.51 (br. s, phenyl),
131.56 (br. s, phenyl), 130.60 (s, C5H5),128.04(s,phenyl),3.40(s,Si(CH3)3.
31P{1H} NMR (THF-d8):δ361.62 (br. s). Anal. Calcd for C41H48N2P2Si2U:
C, 53.24; H, 5.23; N, 3.03. Found: C, 53.21; H, 5.29; N, 3.03.
Synthesis of [{HB(pyrazolyl)3}U{C(Ph2PdNSiMe3)2}(Cl)]
(7). A similar procedure to that for 4 was used. Yield: 0.110 g, 53%. IR
data (Nujol mull): 3056 m, 2949s, 2892 m, 2456s 1501s, 1436s, 1401w,
1386w, 1299s, 1273w, 1240 m, 1216 m, 1116s, 1048s, 975 m, 920 m, 860
m, 829 m, 741s, 724 m, 692 m. 1H NMR (THF-d8): δ 15.15 (d, phenyl,
8H), 9.49 (t, phenyl, 8H), 8.96 (t, phenyl, 4H), 5.39 (t, pyrazolyl, 3H), 5.09
(s, ꢀSi(CH3)3, 18H), 4.22 (br. t, pyrazolyl, 3H), ꢀ2.00 (very br. pyrazolyl,
3H). As above, the BꢀH signal was not observed in 1H NMR, and in this
case the paramagnetic broadening will likely obscure this signal. However,
the IR peak at 2456 cmꢀ1 and the crystal structure confirm the presence of
BꢀH. 13C{1H} NMR (THF-d8): δ 149.96 (d, pyrazolyl), 138.52 (br. s,
phenyl), 135.79 (s, pyrazolyl), 133.65 (s, phenyl), 130.12 (s, phenyl),
123.56 (s, phenyl), 102.65 (s, pyrazolyl), ꢀ1.38 (s, Si(CH3)3). 31P{1H}
NMR (THF-d8): δ ꢀ382.0 (br. s). Anal. Calcd for C40H48BClN8P2Si2U-
(THF): C, 47.38; H, 5.06; N, 10.05. Found: C, 47.10; H, 4.95; N, 10.05.
Synthesis of [CpUCl3(THF)2] (8). To a green THF (5 mL) solution
of UCl4 (0.076 g, 0.2 mmol) was added solid, brown-red thallium(I)
cyclopentadienide TlCp (0.074 g, 0.2 mmol) with stirring at room tempera-
ture. The reaction mixture was kept overnight at room temperature with
vigorous stirring. The white precipitate of TlCl was decanted by centrifuga-
tion. The THF solvent was evaporated slowly for a few days, and deep green
solid brick crystals were collected. Yield: 0.085 g, 77%. The IR, element
analysis, and 1H NMR were carried out in the previous works.13b
Synthesis of [{HB(pyrazolyl)3}Th{C(Ph2PdNSiMe3)2}(Cl)]
(6). A similar procedure to that for 4 was used, except that 1 equiv of
TpK was added in the second step in place of TlCp. Yield: 0.125 g,
60.3%. IR data (Nujol mull): 3056 m, 2925 m, 2447s 1590s, 1573s, 1500
m, 1482w, 1436w, 1296 m, 1110s, 1043s, 965s, 926 m, 876 m, 828 m,
747s, 703s, 693 m. 1H NMR (THF-d8): δ 7.71 (m, pyrazolyl, 3H), 7.56
(m, pyrazolyl, 3H), 7.32 (m, phenyl, 8H), 7.29 (m, phenyl, 4H), 7.19
(t, phenyl, 8H), 6.00 (t, pyrazolyl, 3H), ꢀ0.15 (s, Si(CH3)3, 18H). The
Computational Details. DFT calculations of core structures of 4a,
5a, 6a, and 7a were performed with Gaussian 0315 using the closed shell
HartreeꢀFock and therestrictedopen shell HartreeꢀFock (ROHF) with
B3PW91 functionalfor Thand U compounds, respectively;theSDD basis
set of MWB60 on Th and U; the 6-311G basis set on P and N; and 6-31G
onSi, C, and H. The phenylring onphosphorus was replaced withmethyl,
and methyl on silicon was replaced with H. The SDD basis is constructed
with a quasirelativistic effective core potential that allows the incorpora-
tion of scalar relativistic effects in nonrelativistic calculations.11b
1
BꢀH signal was not observed in H NMR, as it is frequently broad;
however, the IR peak at 2447 cmꢀ1 and the crystal structure confirm the
presence of BꢀH. 13C{1H} NMR (THF-d8): δ 142.51 (s, pyrazolyl),
139.51 (s, phenyl), 137.56 (s, pyrazolyl), 132.11 (s, phenyl), 131.11 (s,
phenyl), 128.03 (s, phenyl), 103.63 (s, pyrazolyl), 4.32 (s, Si(CH3)3).31P{1H}
NMR (THF-d8): δ 17.7 (s). Anal. Calcd for C40H48BClN8P2Si2Th: C,
46.31; H, 4.66; N, 10.80. Found: C, 46.16; H, 4.75; N, 10.78.
6507
dx.doi.org/10.1021/ic102537q |Inorg. Chem. 2011, 50, 6500–6508

Inorganic Chemistry
ARTICLE
’ ASSOCIATED CONTENT
(6) (a) Andrews, L.; Cho, H. G. Organometallics2006, 25, 4040–4053.
(b) Lyon, J. T.; Andrews, L.; Hu, H. S.; Li, J. Inorg. Chem. 2008,
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S
Supporting Information. Atomic positions and displace-
b
(7) (a) Villiers, C.; Ephritikhine, M. Chem.—Eur. J. 2001, 7 (14),
3043–3051. (b) Villiers, C.; Vandais, A.; Ephritikhine, M. J. Organomet.
Chem. 2001, 617ꢀ618, 744–747.
ment parameters, anisotropic displacement parameters, bond lengths
and bond angles in CIF format. Table of crystal structural data and
computed input files for all the calculated model compounds (4a, 5a,
6a, and 7a). This material is available free of charge via the Internet at
http://pubs.acs.org.
(8) (a) Cantat, T.; Arliguie, T.; Noel, A.; Thuery, P.; Ephritikhine,
M.; Le Floch, P.; Mꢀezailles, N. J. Am. Chem. Soc. 2009, 131, 963–972. (b)
Tourneux, J.-C.; Berthet, J.-C.; Thuery, P.; Mezailles, N.; Floch, P. L.;
Ephritikhine, M. Dalton Trans. 2010, 39, 2494–2496. (c) Cooper, O. J.;
McMaster, J.; Lewis, W.; Blake, A. J.; Liddle, S. T. Dalton Trans. 2010,
39, 5074–5076.
’ AUTHOR INFORMATION
Corresponding Author
*Telephone 780-492-5310. Fax 780-492-8231. E-mail: ron.cavell@
ualberta.ca.
(9) (a) Cavell, R. G.; Kamalesh Babu, R. P.; Kasani, A.; McDonald, R.
J. Am. Chem. Soc. 1999, 121, 5805–5806. (b) Kamalesh Babu, R. P.;
McDonald, R.; Decker, S. A.; Klobukowski, M.; Cavell, R. G. Organo-
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’ ACKNOWLEDGMENT
We thank the Natural Sciences and Engineering Research
Council of Canada and the University of Alberta for financial
support. The authors also thank Prof. Josef Takats for kindly
donating the Th and U precursors and the University of Alberta
for supporting the X-ray Crystallography, NMR, and Analytical
and Instrumentation laboratories at the Department of Chemistry.
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