Uranium-carbon multiple bonding: Facile access to the pentavalent uranium carbene [U{C(PPh2NSiMe3)2}(Cl)2(I)] and comparison of UV=C and UIV=C bonds

Article abstract of DOI:10.1002/anie.201007675

(Chemical Equation Presented) A straightforward oxidation strategy affords the first pentavalent uranium carbene complex, 2. Owing to the structural similarity of 1 and 2, it was possible for the first time to directly probe the differences in U=C bonding on oxidation of U^IV to U^V.

Full text of DOI:10.1002/anie.201007675

DOI: 10.1002/anie.201007675
Uranium Carbene Complexes
Uranium–Carbon Multiple Bonding: Facile Access to the Pentavalent
Uranium Carbene [U{C(PPh2NSiMe3)2}(Cl)2(I)] and Comparison of
V
IV
=
=
U C and U C Bonds**
Oliver J. Cooper, David P. Mills, Jonathan McMaster, Fabrizio Moro, E. Stephen Davies,
William Lewis, Alexander J. Blake, and Stephen T. Liddle*
Compared to the extensive investigations of d-block metal–
ligand multiple bonding and reactivity,[1] the corresponding
field of f-block chemistry is underdeveloped.[2,3] For uranium,
imido and oxo complexes dominate, yet there is a paucity of
uranium carbenes that do not derive from neutral free
carbenes.[3]
The first uranium carbenes, [U(h5-C5H5)3(CHPMe2R)]
(R = Ph, I; Me, II), were reported by Gilje et al.[4] Uranium
carbenes have been detected in matrix isolation experi-
ments,[5] and implicated in reactions of ketones with UCl4/
Scheme 1. Synthesis of 2 and 3.
Li(Hg).[6] Recently, Ephritikhine et al. reported a range of
uranium carbenes, exemplified by [U{C(PPh2S)2}(BH4)2-
(THF)2],[7] and, as part of a program studying f-block
carbenes,[8] we reported the homoleptic uranium carbene
[U{C(PPh2NMes)2}2] (1, Mes = 2,4,6-trimethylphenyl).[9]
ꢀ
To date, all uranium carbenes with U C multiple bonds
incorporate uranium(IV). Higher-valence analogues are
notable for their absence, which contrasts to the dominance
of high-oxidation-state uranium oxo and imido complexes.[3,10]
However, pentavalent uranium chemistry has been revital-
ized recently,[10] and encouraged by this and the absence of
any uranium(V) carbenes we targeted a pentavalent uranium
carbene by an oxidation strategy. Herein, we report the facile
synthesis, structure, and reactivity of the first pentavalent
uranium carbene, which permits direct comparisons between
IV
UV C and U C bonds for the first time.
=
=
Complex 1 was prepared from a disproportionation
reaction between [UI3(thf)4] and [Li4{C(PPh2NMes)2}2].[9]
We therefore employed [UCl4(thf)3] and treated it with
[Li4{C(PPh2NSiMe3)2}2][11] in toluene/Et2O (Scheme 1). The
uranium(IV) carbene [U{C(PPh2NSiMe3)2}(Cl)(m-Cl)2Li-
(thf)2] (2) was isolated as yellow plates in 62% yield following
workup and recrystallization from THF.[12]
The molecular structure of 2, as determined by X-ray
crystallography, is shown in Figure 1a with selected bond
[*] O. J. Cooper, Dr. D. P. Mills, Dr. J. McMaster, Dr. F. Moro,
Dr. E. S. Davies, Dr. W. Lewis, Prof. A. J. Blake, Dr. S. T. Liddle
School of Chemistry, University of Nottingham
University Park, Nottingham, NG7 2RD (UK)
Fax: (+44)115-951-3563
Figure 1. Molecular structures of a) 2 and b) 3. Displacement ellip-
soids set at 30% probability; hydrogen atoms and minor disorder
components omitted for clarity. Selected bond lengths [ꢀ] and angles
[8] for 2: U(1)–C(1) 2.310(4), U(1)–N(1) 2.371(4), U(1)–N(2) 2.374(4),
U(1)–Cl(1) 2.6249(13), U(1)–Cl(2) 2.7041(14), U(1)–Cl(3) 2.7453(13),
C(1)–P(1) 1.649(4), C(1)–P(2) 1.661(4), P(1)–N(1) 1.630(4), P(2)–N(2)
1.635(4); P(1)-C(1)-P(2) 164.8(3); 3: U(1)–C(1) 2.268(10), U(1)–N(1)
2.282(7), U(1)–N(2) 2.268(8), U(1)–Cl(1) 2.711(2), U(1)–Cl(2)
2.710(2), U(1)–I(1) 2.9845(7), C(1)–P(1) 1.676(11), C(1)–P(2)
1.701(10), P(1)–N(1) 1.636(7), P(2)–N(2) 1.648(8); P(1)-C(1)-P(2)
154.5(6).
E-mail: stephen.liddle@nottingham.ac.uk
[**] We thank the Royal Society, the Engineering and Physical Sciences
Research Council, the European Research Council, the University of
Nottingham, and the UK National Nuclear Laboratory for funding
this work.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201007675.
Angew. Chem. Int. Ed. 2011, 50, 2383 –2386
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Table 1: Selected experimental and computed data for 2 and 3.[a]
[h]
[h]
=
=
U C p-component
Bond lengths and indices
Atomic spin densities
and charges
U C s-component
[b]
[c]
[e]
[f]
[g]
BI[d]
mU
qU
qC
C [%]
U [%]
U 6d/5f
C [%]
U [%]
U 6d/5f
ꢀ
ꢀ
U C
U C
2
3
2.310(4)
2.268(10)
2.313
2.267
1.43
1.54
2.24
1.25
2.30
2.53
ꢀ2.00
ꢀ1.85
82.4
74.2
17.6
25.8
20.0:79.4
10.3:89.4
82.2
74.3
17.8
25.7
15.8:84.2
9.8:90.0
ꢀ
[a] Both molecules geometry-optimized without symmetry constraints at the spin-unrestricted BP TZP/ZORA level. [b] Experimental U C distance [ꢀ].
ꢀ
[c] Calculated U C distance [ꢀ]. [d] Nalewajski–Mrozek bond indices. [e] MDC-m a-spin density on uranium. [f] MDC-q charge on uranium. [g] MDC-q
charge on carbene. [h] Natural bond orbital (NBO) analysis.
lengths and angles.[13] Complex 2 is monomeric and occludes a
{ClLi(thf)2} fragment. The uranium center adopts a distorted
octahedral geometry, the carbene is close to planar T-shaped
[ꢀ] = 357.9(3)8],[14] and the CP2N2U ring is essentially flat.
observed NIR extinction coefficients of 35mꢀ1 cmꢀ1 are
comparable to Oh UBr6 (22mꢀ1 cmꢀ1),[19] which is signifi-
ꢀ
cantly lower than observed for the approximately Cs-sym-
metric metallocenes [(h5-C5Me5)2U(X)(NAr)] (X = halide;
Ar= bulky aryl; e = 200–400mꢀ1 cmꢀ1).[16c,d] This suggests an
effective Oh local symmetry at uranium in 3, and reduction of
peak intensity by efficient coupling of the A1g vibrational
mode to electronic transitions. The energetic similarity of the
ꢀ
The U(1) C(1) bond of 2.310(4) ꢀ is short, and longer only
than those in I and II [I = 2.293(2); II = 2.274(8) ꢀ].[4]
We interrogated 2 with cyclic voltammetry in the potential
range of ꢀ1.0 to + 0.4 V vs. Fc+/Fc and observed two
oxidation processes at Epa = ꢀ0.5 V and Epa = + 0.27 V.[12]
The position of the first oxidation process, which has an
ꢀ
bands observed for 3 to UX6 ions suggests that spin–orbit
coupling is similar (ca. 2000 cmꢀ1).[16a]
c
associated reduction wave at Ep = ꢀ0.9 V, suggested that
Complexes 2 and 3 both possess octahedral geometry at
uranium comprising the same chelating carbene ligand and
meridional halide ligands. Thus, 2 and 3 present the first
iodine would be capable of effecting the oxidation of
tetravalent 2 to a potential pentavalent derivative, but also
that it would be unable to oxidize 2 to a potentially hexavalent
state.[15]
meaningful opportunity to directly compare UV C and
=
UIV C bonds. Complexes I and II were not investigated
=
Straightforward addition of half a molar equivalent of
iodine to 2 effected one-electron oxidation to afford the first
pentavalent uranium carbene [U{C(PPh2NSiMe3)2}(Cl)2(I)]
(3) as red crystals in 45% yield after workup and recrystal-
lization from toluene. The characterization data support this
formulation.[12] In particular, variable-temperature magnetic
moment measurements on pentavalent 3 showed it to have a
magnetic moment of 2.16 mB at 300 K that decreases to 0.9 mB
at 1.8 K.[16] In contrast, the magnetic moment of 2 is 2.62 mB at
300 K, and this decreases to 0.34 mB at 1.8 K and clearly tends
towards zero as expected for tetravalent uranium which has a
singlet magnetic ground state.[16]
computationally because the presence of only one carbene
phosphorus substituent and cyclopentadienyl, rather than
halide, co-ligands renders these systems incompatible for
direct comparison to 2 and 3. We therefore carried out
unrestricted DFT calculations on 2 and 3 and pertinent data
are compiled in Table 1.[12] The HOMO and HOMOꢀ1 of 2
and the HOMO of 3 are each singularly occupied and are
nonbonding, essentially pure f-orbitals. The computed ura-
nium spin densities and Mulliken charges support the 3H4 and
2F5/2 formulations of 2 and 3, respectively, and show significant
charge donation from the carbene ligands to uranium in 2 and
3. The calculated carbene charges are high, consistent with
To confirm the formulation of 3 we determined the
structure by X-ray diffraction and this is illustrated in
Figure 1b with selected bond lengths and angles.[12,13,17]
Complex 3 is monomeric and the uranium center adopts a
formally dianionic centers. The a-spin Kohn–Sham orbitals[12]
[12]
=
show s- and p-components of the U C bonds in 2 and 3,
and the Nalewajski–Mrozek bond indices show significant
multiple bond character,[20] with the value for 3 greater than
for 2.
The valence molecular orbitals of 2 and 3 are delocalized
over the complexes. To obtain a localized and more chemi-
ꢀ
distorted octahedral geometry. The U(1) C(1) bond of
2.268(10) ꢀ is very short compared to all other uranium
carbenes,[4,7,9,18] but it is essentially invariant to II and 2 which
reflects the fact that an electron of essentially nonbonding f-
=
cally relevant description of the U C bonds, we performed
ꢀ
character is removed on oxidation. The U N bonds in 3 are
natural bond orbital (NBO) analyses which show polarized
=
contracted by 0.1 ꢀ compared to 2; however, the U Cl bonds
U C bonds in each case. Upon oxidation from UIV to UV, the
ꢀ
ꢀ
=
are 0.09 ꢀ longer than the terminal U Cl bond in 2, perhaps
uranium character in the U C bond increases by 8% in both
reflecting greater steric congestion in 3. This is also suggested
by the geometry of the carbene center in 3 which is now
slightly pyramidalized [ꢀ] = 345.7(5)8].
The electronic absorption spectrum of 3 is dominated by
charge transfer in the UV/Vis/NIR regions and exhibits peaks
characteristic of UV.[12,16] A sharp peak at 6650 cmꢀ1 is
assigned as the pure electronic G7!G7’ transition and broad
peaks at 8420–9400 cmꢀ1 are assigned as vibronic transi-
tions.[16a] Although 3 has approximately Cs symmetry which
should enhance transition intensities compared to Oh, the
the s- and p-components. Within the uranium contribution, a
50% reduction in 6d character in the s- and p-components
occurs with a concomitant increase in 5f orbital participation.
Thus, although the 6d orbitals are radially more expansive
compared to the 5f orbitals, oxidation from UIV to UV
apparently results in the 5f orbitals being better suited to
the energetic and angular overlaps required to construct the
=
U C bond in 3. It should be noted that the 5f orbital
percentages in 2 and 3 are high compared to the 40% 6d and
=
60% 5f character of the 18% uranium components of the U
2384
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Angew. Chem. Int. Ed. 2011, 50, 2383 –2386

C bonds in [UIV{C(PPh2S)2}(BH4)2(thf)2].[7] This shows that
the carbene substituents, as well as the formal oxidation state
of uranium, profoundly affects the extent of 6d and 5f orbital
participation with ligand orbitals.
A preliminary investigation of the reactivity of 3 and 2
showed metallo-Wittig reactivity with 9-anthracene carbox-
aldehyde to quantitatively afford the yellow alkene
Experimental Section
2: Diethyl ether (20 mL) and toluene (20 mL) were added to a pre-
cooled (ꢀ788C) mixture of [UCl4(thf)3] (2.98 g, 5.00 mmol) and
=
[Li2{C(PPh2 NSiMe3)2}]2 (2.85 g, 2.50 mmol). The reaction mixture
was allowed to warm to room temperature and was stirred for 72 h to
give a brown suspension. Volatiles were removed in vacuo and the
residue was recrystallized from THF (5 mL) layered with diethyl
ether (5 mL) to afford 2 as yellow crystals. Several crops were
obtained. Combined yield: 3.35 g, 62%. Elemental analysis calcd for
C39H54Cl3LiN2O2P2Si2U: C 44.51, H 5.17, N 2.66; found: C 41.93, H
5.15, N 2.68. 1H NMR ([D8]THF, 400.2 MHz, 298 K): d = ꢀ14.33 (br,
18H, Si(CH3)3), 1.79 (m, 8H, OCH2CH2), 3.64 (m, 8H, OCH2CH2),
8.78 (br, 4H, p-Ar-H), 9.18 (br, 8H, m-Ar-H), 14.55 ppm (br, 8H, o-
Ar-H). 7Li{1H} NMR ([D8]THF, 155.5 MHz, 298 K): d = 6.93 ppm.
=
(Me3SiNPPh2)2C C(H)R (4, R = 9-anthracene, Figure 2a) in
~
FTIR (Nujol): n = 1587 (w), 1344 (m), 1245 (m), 1109 (m), 1042 (br, s),
834 (s), 771 (m) 753 (m), 716 (m), 693 (m), 640 (m), 606 (m), 525 (m),
510 cmꢀ1 (m).
3: Toluene (20 mL) was added to a precooled (ꢀ788C) mixture of
2 (1.05 g, 1.00 mmol). Iodine (0.13 g, 1.00 mmol) was then added and
the mixture was allowed to slowly warm to room temperature with
stirring over 18 h to afford a deep red solution. Volatiles were
removed in vacuo and the resulting red solid was dissolved in toluene.
Storage at 58C overnight gave a small crop (< 3% yield) of the
compound identified as 3a by X-ray diffraction. The mother liquor
was decanted and stored at ꢀ308C to afford 3 as red crystals.
Figure 2. Molecular structures of a) 4 and b) 5. Displacement ellip-
soids set at 30% probability; hydrogen atoms and minor disorder
components omitted for clarity. Selected bond lengths [ꢀ] and angles
[8] for 4: C(1)–C(32) 1.346(3), C(1)–P(1) 1.821(2), C(1)–P(2) 1.848(2),
P(1)–N(1) 1.528(2), P(2)–N(2) 1.525(2); P(1)-C(1)-P(2) 121.58(11); 5:
U(1)–C(1) 2.613(8), U(1)–N(1) 2.425(7), U(1)–N(2) 2.360(7), U(1)–
Cl(1) 2.732(2), U(1)–Cl(2) 2.583(3), U(1)–I(1) 3.077(3), U(1)···I(2)
3.345(2) C(1)–P(1) 1.775(8), C(1)–P(2) 1.791(8), P(1)–N(1) 1.611(7),
P(2)–N(2) 1.617(8); P(1)-C(1)-P(2) 125.3(5).
Yield:
0.49 g,
45%.
Elemental
analysis
calcd
for
C31H38Cl2IN2P2Si2U·1= C7H8: C 39.89, H 4.08, N 2.70; found: C
2
38.92, H 4.06, N 2.63. 1H NMR ([D6]benzene, 400.2 MHz, 298 K): d =
1.77 (s, 8H, Ar-H), 1.09 (s, 4H, p-Ar-H), 0.10 (s, 8H, Ar-H),
~
ꢀ0.07 ppm (s, 18H, Si(CH3)3). FTIR (Nujol): n = 1589 (w), 1402 (m),
1260 (m), 1109 (m), 1049 (m), 1024 (s), 842 (s), 736 cmꢀ1 (m).
4: Toluene (30 mL) was added to a precooled (ꢀ788C) mixture of
9-anthracene carboxaldehyde (0.21 g, 1.00 mmol) and
2 or 3
(1.00 mmol). The reaction mixture was allowed to slowly warm to
room temperature with stirring over 16 h, forming a cloudy red
reaction mixture. Volatiles were removed in vacuo and recrystalliza-
tion from pyridine (2 mL) afforded 4 as yellow crystals (0.31 g, 42%).
Elemental analysis calcd for C46H48N2P2Si2: C 73.96, H 6.48, N 3.75;
41% yield.[12,13] This parallels other reports of uranium
carbene reactivity,[7a] and confirms the UV nature of 3. In
agreement with the cyclic voltammetric study of 2, addition of
half a molar equivalent of iodine to 3 does not afford
oxidation of uranium to a hexavalent state and we are
investigating the reactivity of stronger oxidants towards 2 and
3. Instead, the uranium center in 3 is formally reduced to give
tetravalent [U{C(I)(PPh2NSiMe3)2}(Cl)2.5(I)0.5] (5; Figure 2b)
as yellow plates in 35% crystalline yield.[12,13] Addition of one
molar equivalent of iodine to 2 also affords 5, which suggests
the reaction from 2 to 5 involves stepwise oxidation then
reduction with 3 as an intermediate. However, we could not
observe any intermediates when these reactions were moni-
tored by 1H NMR spectroscopy and 2 does not react with 5 to
give 3. Therefore, we can not rule out a concerted 1,2-addition
1
found: C 73.87, H 6.57, N 3.69. H NMR ([D6]benzene, 400.2 MHz,
298 K): d = 0.09 (s, 9H, Si(CH3)3), 0.40 (s, 9H, Si(CH3)3), 6.58 (m, 4H,
m-Ph-H), 6.67 (m, 2H, Ar-H-3,6), 7.08 (m, 2H, Ar-H-2,7), 7.14–7.20
(m, 6H, m- and p-Ph-H), 7.29–7.39 (m, 6H, o- and p-Ph-H), 7.59 (d,
J
HH = 8.80 Hz, 2H, Ar-H-4,5), 7.77 (s, 1H, Ar-H-10), 8.20 (d, JHH
=
3
9.20 Hz, 2H, Ar-H-1,8), 8.23 (m, 4H, o-Ph-H), 9.09 ppm (dd, JPH
=
39.62 Hz and 27.61 Hz, 1H, ArCH CP2). 13C{1H} NMR
([D6]benzene, 100.6 MHz, 298 K): d = 3.95 (d, JPC = 3.02 Hz, Si-
(CH3)3), 4.18 (d, JPC = 3.02 Hz, Si(CH3)3), 125.00, (d, JPC = 26.67 Hz,
o-Ph-CH), 126.31, (d, JPC = 26.67 Hz, o-Ph-CH), 126.56 (Ar-CH-1,8),
126.89 (Ar-CH-3,6), 127.46 (Ar-CH-2,7), 127.55 (Ar-CH-4,5), 128.33
(Ar-CH-10), 128.40 (Ar-C-12,13), 129.69 (d, 4JPC = 3.02 Hz, p-Ph-CH)
=
4
130.51 (d, JPC = 3.02 Hz, p-Ph-CH), 131.08 (Ar-C-11,14), 131.20 (d,
2JPC = 11.07 Hz, m-Ph-CH), 132.90 (d, 2JPC = 11.07 Hz, m-Ph-CH),
141.69 (d, 1JPC = 73.97 Hz, ipso-Ph-CH), 142.42 (d, 1JPC = 73.97 Hz,
=
=
ipso-Ph-CH), 156.15 (m, CH CP2), 191.26 ppm (br, CH CP2). Ar-C-9
of iodine across the UIV C bond when the reaction is
=
was not observed. 31P{1H} NMR ([D6]benzene, 162.0 MHz, 298 K):
conducted in one-pot.
d = ꢀ4.35 (d, 2JPP = 36.45 Hz, C CP2), 3.9 ppm (d, JPP = 36.45 Hz, C
CP2). 29Si{1H} NMR ([D6]benzene, 79.5 MHz, 298 K): d = ꢀ13.36 (d,
2JPSi = 22.34 Hz, NSi(CH3)3), ꢀ12.47 ppm (d, 2JPSi = 23.22 Hz, NSi-
2
=
=
To conclude, we have prepared and characterized the first
uranium(V) carbene by a simple oxidation strategy, and have
confirmed its formulation by spectroscopic and reactivity
=
~
(CH3)3). FTIR (Nujol): n = 1615 (C C, m), 1560 (w), 1261 (m), 1240
(m), 1100 (br, s), 1020 (m), 854 (m), 823 (m), 801 (m), 719 (m),
698 cmꢀ1 (m).
studies. The isolation of structurally similar 2 and 3 has
V
permitted a meaningful comparison of UIV C and U
C
=
=
5: Toluene (20 mL) was added to a precooled (ꢀ788C) mixture of
2 (1.05 g, 1.00 mmol). Iodine (0.26 g, 1.00 mmol) was then added and
the mixture was allowed to slowly warm to room temperature with
stirring over 18 h to afford a brown solution. Volatiles were removed
in vacuo and the resulting brown solid was recrystallized from toluene
(10 mL) to afford 5 as yellow crystals. Yield 0.39 g, 35%. Elemental
bonds for the first time. Computational analyses show that
=
upon oxidation: 1) the uranium character of the U C bond
increases; 2) the 6d orbital contribution to the uranium
=
component of the U C bond halves; 3) the 5f character of
the uranium component increases to compensate.
Angew. Chem. Int. Ed. 2011, 50, 2383 –2386
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
2385

Communications
analysis calcd for C31H38Cl2.5I1.5N2P2Si2U: C 34.67, H 3.57, N 2.61;
found: C 34.04, H 3.96, N 2.35. H NMR ([D6]benzene, 400.2 MHz,
Rint = 0.062, q < 67.58) Data were collected on a Oxford Dif-
1
fraction SuperNova Atlas CCD diffractometer and were cor-
rected for absorption (transmission 0.19–0.81).The structure was
solved by direct methods and refined by full-matrix least-squares
on F2 values of all to give wR2 = 0.1560, conventional R = 0.0544
for F values of 6640 with Fo2 > 2s(Fo2), S = 1.050 for 428
parameters. Residual electron density extrema were 3.06 and
ꢀ2.77 eꢀꢀ3. Crystal data for 4: C46H48N2P2Si2, Mr = 746.98, space
group P21/n, a = 10.2019(11), b = 22.108(2), c = 18.280(2), b =
100.901(2), V= 4048.5(8) ꢀ3, Z = 4, 1calcd = 1.226 gcmꢀ3; MoKa
radiation, l = 0.71073 ꢀ, m = 0.201 mmꢀ1, T= 90 K. 24918 data
(9235 unique, Rint = 0.048, q < 258) Data were collected on a
Bruker SMART APEX CCD diffractometer and were corrected
for absorption (transmission 0.61–0.75).The structure was solved
by direct methods and refined by full-matrix least-squares on F2
values of all to give wR2 = 0.1260, conventional R = 0.0516 for F
values of 6497 with Fo2 > 2s(Fo2), S = 1.020 for 475 parameters.
298 K): d = 1.77 (s, 8H, Ar-H), 1.10 (s, 8H, Ar-H), ꢀ0.07 (s, 4H, p-Ar-
H), ꢀ1.67 (s, 9H, Si(CH3)3, ꢀ1.78 ppm (s, 9H, Si(CH3)3). FTIR
~
(Nujol): n = 1588 (w), 1438 (m), 1257 (m), 1161 (w), 1108 (s), 1049
(m), 1024 (m), 999 (m), 843 (s), 772 cmꢀ1 (m).
Received: December 7, 2010
Revised: January 6, 2011
Published online: February 14, 2011
Keywords: carbene ligands · f-block elements ·
.
metallo-Wittig reactivity · multiple bonding · uranium complexes
[1] W. A. Nugent, J. M. Mayer, Metal-Ligand Multiple Bonds, Wiley,
New York, 1988.
Residual electron density extrema were 0.57 and ꢀ0.31 eꢀꢀ3
.
[2] G. R. Giesbrecht, J. C. Gordon, Dalton Trans. 2004, 2387.
[3] T. W. Hayton, Dalton Trans. 2010, 39, 1145.
[4] a) R. E. Cramer, R. B. Maynard, J. C. Paw, J. W. Gilje, J. Am.
Chem. Soc. 1981, 103, 3598; b) R. E. Cramer, M. A. Bruck, F.
Edelmann, D. Afzal, J. W. Gilje, H. Schmidbaur, Chem. Ber.
1988, 121, 417.
Crystal data for 5: C41.50H50Cl2.50I1.50N2P2Si2U, Mr = 1212.42,
ꢁ
space group P1, a = 11.938(2), b = 11.975(2), c = 17.611(3), a =
81.020(3), b = 71.561(3), g = 74.175(3), V= 2291.0(8) ꢀ3, Z = 2,
1calcd = 1.758 gcmꢀ3
;
MoKa radiation, l = 0.71073 ꢀ, m =
4.855 mmꢀ1, T= 90 K. 18089 data (10202 unique, Rint = 0.045,
q < 258). Data were collected on a Bruker SMART APEX CCD
diffractometer and were corrected for absorption (transmission
0.66–0.77). The structure was solved by direct methods and
refined by full-matrix least-squares on F2 values of all to give
wR2 = 0.1835, conventional R = 0.0684 for F values of 7047 with
Fo2 > 2s(Fo2), S = 0.957 for 459 parameters. Residual electron
density extrema were 4.56 and ꢀ3.77 eꢀꢀ3. CCDC 803695(2),
803696 (3), 803697 (3a), 803698 (4), and 803699 (5) contain the
supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
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[12] Full details can be found in the Supporting Information.
[13] Crystal data for 2: C39H54Cl3LiN2O2P2Si2U, Mr = 1052.28, space
group P21/n, a = 12.6786(2), b = 21.0589(3), c = 17.1111(2), b =
95.2915(11), V= 4549.16(9) ꢀ3, Z = 4, 1calcd = 1.536 gcmꢀ3; CuKa
radiation, l = 1.5418 ꢀ, m = 13.094 mmꢀ1, T= 90 K. 24272 data
(8207 unique, Rint = 0.046, q < 67.58). Data were collected on a
Oxford Diffraction SuperNova Atlas CCD diffractometer and
were corrected for absorption (transmission 0.22–0.69). The
structure was solved by direct methods and refined by full-matrix
least-squares on F2 values of all to give wR2 = {ꢀ[w(Fo2ꢀFc2)2]/
ꢀ[w(Fo2)2]}1/2 = 0.0843, conventional R = 0.0331 for F values of
7085 with Fo2 > 2s(Fo2), S = 1.030 for 485 parameters. Residual
electron density extrema were 3.16 and ꢀ1.20 eꢀꢀ3. Crystal data
for 3: C38H46Cl2IN2P2Si2U, Mr = 1084.72, space group P21/c, a =
16.3721(3), b = 11.6050(2), c = 22.8223(4), b = 98.1607(16), V=
4292.29(13) ꢀ3, Z = 4, 1calcd = 1.679 gcmꢀ3; CuKa radiation, l =
1.5418 ꢀ, m = 0.143 mmꢀ1, T= 90 K. 15074 data (7159 unique,
[15] The formal potential for I2 in acetonitrile is ꢀ0.14 V vs. Fc+/Fc,
see: N. G. Connelly, W. E. Geiger, Chem. Rev. 1996, 96, 877.
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T. W. Hayton, J. Am. Chem. Soc. 2010, 132, 6888.
[17] Yellow
crystals
of
[U{CH(PPh2NSiMe3)2}(m-Cl)(Cl)-
(Cl)0.69(I)0.31
]
(3a, < 3% yield) were also isolated from the
2
reaction that produced 3, which supports the carbene assignment
of 3. See Ref. [12] for full details.
[18] As evidenced from a search of the Cambridge Structural
Database (CSD version 1.11, date: 29/10/2010): a) F. H. Allen,
Acta Crystallogr. Sect. B 2002, 58, 380.
[19] J. L. Ryan, J. Inorg. Nucl. Chem. 1971, 33, 153.
[20] Nalewajski–Mrozek bond indices incorporate ionic and covalent
components, see: A. Michalak, R. L. DeKock, T. Ziegler, J. Phys.
Chem. A 2008, 112, 7256.
2386
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