Heteroleptic [M(CH2C6H5) 2(I)(THF)3] complexes (M = y or Er): Remarkably stable precursors to yttrium and erbium T-shaped carbenes

Article abstract of DOI:10.1021/om9007949

mHeteroleptic dibenzyl yttrium and erbium iodides [Ln(Bn) ₂(I)(THF)₃] [Ln = Y (1), Er (2); Bn = CH₂C ₆H₅] were prepared in high yields and are remarkable for their thermal stability and inertness towa

Full text of DOI:10.1021/om9007949

Organometallics 2009, 28, 6771–6776 6771
DOI: 10.1021/om9007949
Heteroleptic [M(CH2C6H5)2(I)(THF)3] Complexes (M = Y or Er):
Remarkably Stable Precursors to Yttrium and Erbium T-Shaped
Carbenes
David P. Mills, Ashley J. Wooles, Jonathan McMaster, William Lewis, Alexander J. Blake,
and Stephen T. Liddle*
School of Chemistry, University of Nottingham, University Park, Nottingham, NG7 2RD U.K.
Received September 11, 2009
Heteroleptic dibenzyl yttrium and erbium iodides [Ln(Bn)2(I)(THF)3] [Ln = Y (1), Er (2); Bn =
CH2C6H5] were prepared in high yields and are remarkable for their thermal stability and inertness
toward ligand scrambling in Schlenk-type equilibria. A variable-temperature study of 1 revealed a
dynamic process in solution attributed to the presence of three isomers, namely, cis-fac, cis-mer, and
trans-mer, which were observed in a 0.11:1:0.05 ratio at 298 K, respectively. Only the isomer
attributed as cis-mer was observed at 313 K. The synthetic utility of 1 and 2, which combines the
potential benefits of protonolysis and salt elimination chemistry, was demonstrated by the facile
synthesis of phosphorus-stabilized yttrium and erbium carbenes [Ln(BIPM)(I)(THF)2] [Ln = Y (3);
Er (4); BIPM = {C(PPh2NSiMe3)}2-], which each contain unusual T-shaped carbene centers. DFT
calculations on 3, BIPM, and Ph3PdCdPPh3 showed very similar frontier orbital compositions in all
three examples. Although 3 and 4 are classified as carbene complexes, and NBO analysis is consistent
with the BIPM ligand adopting the dipolar N--Pþ-C2--Pþ-N- resonance form, the possibility of
categorizing 3 and 4 as captodative carbon(0) complexes of yttrium and erbium cannot be ruled out.
Complexes 1-4 have been variously characterized by X-ray crystallography, multinuclear NMR
spectroscopy, FTIR spectroscopy, room-temperature Evans method solution magnetic moments,
and CHN microanalyses.
Introduction
sterically demanding But group results in “ate” complexes,
e.g., [Ln(But)4]-.4 Even the bulky (Me3Si)2CH- group forms
“ate” complexes when salt elimination methods are used,
e.g., [LiClLn{CH(SiMe3)2}3],5 although the homoleptic
[Ln{CH(SiMe3)2}3] complexes are available from rare earth
aryloxides.6 Rare earth complexes of Trisyl, e.g., (Me3Si)2-
(Me2XSi)C- (X = Me, OMe, NMe2),7 are known but they
are not usually employed as starting materials, as several
steps are required to prepare them. Generally, the Me3-
The synthesis of organo-rare earth complexes continues to
be of significant interest due to their high reactivities in
synthetic transformations.1 Salt elimination represents a
convenient method to introduce ligands into the coordina-
tion sphere of rare earth metals, but it may be complicated by
ligand redistribution reactions and alkali metal occlusion.2
An attractive alternative to avoid such difficulties is to
employ rare earth alkyls as starting materials. However,
large coordination spheres, high Lewis acidities, and highly
polar and labile rare earth-ligand bonds render the selective
synthesis of rare earth alkyls a challenge.
Consequently, the synthesis of rare earth alkyls that are
simple enough to be regarded as convenient starting materi-
als is not always straightforward. For example, reaction of
LnCl3 salts with MeLi results in the formation of mixed-
metal aggregates, e.g., [Ln(Me)6Li3].3 Use of the more
-
SiCH2 group has risen to greater prominence,8 and even
cationic species have been reported, but they are often
(4) Wayda, A. L.; Evans, W. J. J. Am. Chem. Soc. 1978, 100, 7119.
(5) Atwood, J. L.; Lappert, M. F.; Zhang, H. J. Chem. Soc., Chem.
Commun. 1988, 1308.
(6) (a) Avent, A. G.; Caro, C. F.; Hitchcock, P. B.; Lappert, M. F.; Li,
Z.; Wei, X.-H. Dalton Trans. 2004, 1567. (b) Hitchcock, P. B.; Lappert, M.
F.; Smith, R. G.; Bartlett, R. A.; Power, P. P. J. Chem. Soc., Chem. Commun.
1988, 1007.
(7) Representative examples: (a) Bowman, L. J.; Izod, K.; Clegg, W.;
Harrington, R. W. Organometallics 2007, 26, 2646. (b) Bowman, L. J.;
Izod, K.; Clegg, W.; Harrington, R. W. J. Organomet. Chem. 2007, 692, 806.
(c) Bowman, L. J.; Izod, K.; Clegg, W.; Harrington, R. W. Organometallics
2006, 25, 2999. (d) Clegg, W.; Eaborn, C.; Izod, K.; O'Shaughnessy, P.;
Smith, J. D. Angew. Chem., Int. Ed. Engl. 1997, 36, 2815. (e) Eaborn, C.;
Hitchcock, P. B.; Izod, K.; Smith, J. D. J. Am. Chem. Soc. 1994, 116, 12071.
(8) (a) Schumann, H.; Freckmann, D. M. M.; Dechert, S. Z. Anorg.
Allg. Chem. 2002, 628, 2422. (b) Hultzsch, K. C.; Voth, P.; Beckerle, K.;
Spaniol, T. P.; Okuda, J. Organometallics 2000, 19, 228. (c) Schumann, H.;
M€uller, J. J. Organomet. Chem. 1978, 146, C5. (d) Lappert, M. F.; Pearce, R.
J. Chem. Soc., Chem. Commun. 1973, 126.
*Corresponding author. E-mail: stephen.liddle@nottingham.ac.uk.
(1) For a general review of the use of organo-rare earth metals in
catalysis see: Molander, G.; Romero, J. A. C. Chem. Rev. 2002, 102,
2161.
(2) Piers, W. E.; Emslie, D. J. H. Coord. Chem. Rev. 2002, 233-234,
131.
€
(3) (a) Schumann, H.; Muller, J.; Bruncks, N.; Lauke, H.; Pickardt, J.
Organometallics 1984, 3, 69. (b) Schumann, H.; M€uller, J. Angew. Chem.,
Int. Ed. Engl. 1981, 20, 120. (c) Schumann, H.; M€uller, J. Angew. Chem.,
Int. Ed. Engl. 1978, 17, 276.
r
2009 American Chemical Society
Published on Web 10/06/2009
pubs.acs.org/Organometallics

6772 Organometallics, Vol. 28, No. 23, 2009
Mills et al.
stabilized with crown ethers, which may limit their applica-
tions.9 A simple one-step oxidative preparation of YbR3
complexes (R = CH2SiMe3 or CH2But) was reported, but
this is currently limited to ytterbium.10
Scheme 1. Synthesis of 1-4
More recently, straightforward tribenzyls of Y,11 La,12
Sc,13 and Lu13a have been reported, and they have already
provided new synthetic routes to organo-rare earth com-
plexes.14 These reports prompted us to report our improved
synthesis of [Y(Bn)3(THF)3] (1, Bn = CH2C6H5),15 and we
have subsequently extended this methodology across the rare
earth series.16 We have used these and related trialkyls to
prepare phosphorus-stabilized rare earth carbenes from
H2C(PPh2NSiMe3)2 (H2BIPM) and have investigated their
reactivity, but while the desired complexes were isolated in
good yields for yttrium and erbium (I and II),15-17 the
presence of an alkyl group limits the options for further
synthetic transformations. The optimum scenario is repre-
sented by III, where a halide ligand provides maximum
synthetic flexibility for derivatization. This is exemplified
by our recent report of the first yttrium-gallium bond
(IV).18 Complex IV was prepared by reacting [Ga(NAr-
CH)2]K(tmeda)19 (Ar=2,6-diisopropylphenyl) with the pro-
duct (III) of the in situ reaction between [K(Bn)]20 and
[Y(HBIPM)(I)2(THF)].18 Since preparation of the latter
compound is surprisingly tedious, but double deprotonation
of H2BIPM by rare earth alkyls is facile, we targeted a
heteroleptic dialkyl metal iodide, as this would bring the
benefits of protonolysis chemistry but retain a halide ligand
for maximum synthetic flexibility. Herein, we report the
synthesis of dibenzyl yttrium and erbium iodides, which
are remarkably stable, and demonstrate their synthetic
utility by their reactions with H2BIPM, which generates
phosphorus-stabilized rare earth carbenes that exhibit unu-
sual T-shaped carbene centers.
Results and Discussion
We chose [Y(I)3(THF)3.5]
21 and [K(Bn)]20 as reagents for
the preparation of a dibenzyl complex because they are easy
to prepare and the potassium iodide byproduct is too large to
be occluded. Treatment of [Y(I)3(THF)3.5] with 2 equiv of
[K(Bn)] in THF at 0 ꢀC for 4 h affords the anticipated
potassium iodide precipitate. Filtration and removal of
volatiles affords a brown oil in 62% yield, which was shown
1
by H NMR spectroscopy to be essentially pure and of the
composition [Y(Bn)2(I)(THF)3] (1) (Scheme 1). Complex 1
can be obtained as a microcrystalline solid by stirring the oil
in hexane, or it can be recrystallized from THF. Complex 1 is
thermally stable and surprisingly inert to ligand redistribu-
tion. Although the benzylic proton resonance of 1 is com-
pletely obscured by the β-methylene THF resonance in the
1H NMR spectrum, the benzylic carbon, tentatively assigned
as the cis-mer isomer V on the basis of the solid state structure
(vide infra), is clearly observed in the 13C{1H} NMR spec-
trum at 55.10 ppm (JYC = 34.3 Hz). Interestingly, 13C{1H}
NMR spectra of recrystallized or crude samples of 1 often
exhibit two minor sets of resonances (∼10 and ∼5%) at
298 K, consistent with presence of the cis-fac VI and trans-
mer VII isomers in solution with those benzylic carbons
resonating at 58.71 ppm (JYC = 32.2 Hz) and 54.10 ppm
(JYC = 33.2 Hz). The presence of tribenzyl yttrium from
Schlenk-type equilibria in solution was ruled out by careful
comparison with an authentic sample.15 A variable-tempera-
ture 13C{1H} NMR study of 1 in d8-THF showed a cis-fac:
cis-mer:trans-mer isomer ratio of 0.11:1:0.05 at 298 K and
only the cis-mer isomer at 313 K, which returns to the
(9) Zeimentz, P. M.; Arndt, S.; Elvidge, B. R.; Okuda, J. Chem. Rev.
2006, 106, 2404.
(10) Niemeyer, M. Z. Anorg. Allg. Chem. 2000, 626, 1027.
(11) (a) Carver, C. T.; Diaconescu, P. L. J. Am. Chem. Soc. 2008, 130,
7558. (b) Harder, S.; Ruspic, C.; Bhriain, N. N.; Berkermann, F.; Sch€urmann,
M. Z. Naturforsch. B 2008, 63b, 267. (c) Zhang, W. -X.; Nishiura, M.;
Mashiko, T.; Hou, Z. Chem.;Eur. J. 2008, 14, 2167. (d) Harder, S.
Organometallics 2005, 24, 373.
(12) Bambirra, S.; Meetsma, A.; Hessen, B. Organometallics 2006, 25,
3454.
(13) (a) Meyer, N.; Roesky, P. W.; Bambirra, S.; Meetsma, A.;
Hessen, B.; Saliu, K.; Takats, J. Organometallics 2008, 27, 1501. (b)
Carver, C. T.; Monreal, M. J.; Diaconescu, P. L. Organometallics 2008, 27,
363.
(14) Bambirra, S.; Perazzolo, F.; Boot, S. J.; Sciarone, T. J. J.;
Meetsma, A.; Hessen, B. Organometallics 2008, 27, 704.
(15) Mills, D. P.; Cooper, O. J.; McMaster, J.; Lewis, W.; Liddle, S. T.
Dalton Trans. 2009, 4547.
(16) Wooles, A. J.; Mills, D. P.; Lewis, W.; Blake, A. J.; Liddle, S. T.
Dalton Trans. 2009, DOI: 10.1039/b911717b.
(17) Liddle, S. T.; McMaster, J.; Green, J. C.; Arnold, P. L. Chem.
Commun. 2008, 1747.
(18) Liddle, S. T.; Mills, D. P.; Gardner, B. M.; McMaster, J.; Jones,
C.; Woodul, W. D. Inorg. Chem. 2009, 48, 3520.
(19) Baker, R. J.; Farley, R. D.; Jones, C.; Kloth, M.; Murphy, D. M.
J. Chem. Soc., Dalton Trans. 2002, 3844.
(20) Schlosser, M.; Hartmann, J. Angew. Chem., Int. Ed. Engl. 1973,
12, 508.
(21) Izod, K.; Liddle, S. T.; Clegg, W. Inorg. Chem. 2004, 43, 214.

Article
Organometallics, Vol. 28, No. 23, 2009 6773
Figure 1. Molecular structure of 1 (30% probability ellipsoids);
hydrogen atoms and disordered THF components omitted for
clarity. The molecular structure of 2 is very similar.
Figure 2. Molecular structure of 3 (30% probability ellipsoids).
Hydrogen atoms and disordered THF components are omitted
for clarity. The structure of 4 is very similar.
Table 1. Selected Bond Lengths and Angles for 1-4
1
Y(1)-C(1)
Y(1)-I(1)
Y(1)-O(2)
2.431(3)
3.0981(3)
2.4723(17)
Y(1)-C(8)
Y(1)-O(1)
Y(1)-O(3)
2.461(3)
2.3303(16)
2.3178(18)
2
3
Er(1)-C(1)
Er(1)-I(1)
Er(1)-O(2)
2.440(4)
3.0821(3)
2.309(2)
Er(1)-C(8)
Er(1)-O(1)
Er(1)-O(3)
2.413(4)
2.308(2)
2.461(2)
Y(1)-C(1)
2.356(3)
2.382(3)
1.641(3)
1.620(3)
172.5(2)
93.34(15)
Y(1)-I(1)
Y(1)-N(2)
C(1)-P(2)
P(2)-N(2)
Y(1)-C(1)-P(1)
3.0667(4)
2.367(3)
1.640(3)
1.623(3)
93.55(14)
Y(1)-N(1)
C(1)-P(1)
P(1)-N(1)
P(1)-C(1)-P(2)
Y(1)-C(1)-P(2)
4
Er(1)-C(1)
2.322(2)
2.3636(17)
1.640(2)
1.6240(19)
171.72(15)
94.37(10)
Er(1)-I(1)
Er(1)-N(2)
C(1)-P(2)
P(2)-N(2)
Er(1)-C(1)-P(1)
3.0737(2)
2.3794(18)
1.640(2)
1.6221(18)
93.42(10)
Er(1)-N(1)
C(1)-P(1)
P(1)-N(1)
P(1)-C(1)-P(2)
Er(1)-C(1)-P(2)
isomeric mixture on cooling back to 298 K. Unfortunately,
no definite conclusions could be drawn from EXSY spectra
because of the low quantities of VI and VII present coupled
with the low isotopic abundance of 13C and the relatively
small temperature window of 15 K; consequently, and
because numerical line shape analysis was not practical, it
is not realistic to extract thermodynamic parameters. How-
ever, a comparison of 0.02 and 0.04 M solutions showed
almost identical isomer ratios and dynamic behavior, which
implies the exchange is unimolecular in nature. The observa-
tion of isomers in solution, even on samples recrystallized
several times, is noteworthy, as this is seldom observed in
rare earth chemistry.22
Figure 3. Kohn-Sham orbital representations of (a) HOMO
of 3; (b) HOMO-1 of 3; (c) HOMO of 5; (d) HOMO-1 of 5;
(e) HOMO of 6; (f) HOMO-1 of 6.
˚
2.431(3) and 2.461(3) A, respectively, are at the lower and
higher end of the range of reported yttrium-benzyl bond
distances,23 and the difference between them may reflect a
trans-effect from the iodide ligand. The Y(1)-I(1) bond
21
˚
distance of 3.0981(3) A is unremarkable.
Encouraged by the successful and straightforward pre-
paration of 1, we sought to extend the synthetic protocol to a
heavier rare earth metal. The erbium analogue [Er(Bn)2-
Colorless crystals of 1 were grown from a solution in THF.
The molecular structure is illustrated in Figure 1, and
selected bond lengths are listed in Table 1. The yttrium center
adopts a distorted octahedral cis-mer geometry. Multihapto
yttrium-benzyl interactions are not observed in the solid
(I)(THF)3] (2) was prepared from [Er(I)3(THF)3.5]
21 and [K-
(Bn)]20 as a microcrystalline solid in 85% yield (Scheme 1).
Pink single crystals of 2 were grown from a solution in THF
layered with hexane and were found to be isostructural to 1;
˚
state [Y(1) C(2) and Y(1) C(9) = 3.177 and 3.273 A,
3 3 3
3 3 3
respectively]. The Y(1)-C(1) and Y(1)-C(8) bond lengths of
(23) As evidenced from a search of the Cambridge Structural Data-
base (CSD version 1.11, date 07/08/2009): (a) Allen, F. H. Acta
Crystallogr. Sect. B 2002, 58, 380. (b) Allen, F. H.; Kennard, O. Chem.
Des. Autom. News 1993, 8, 31.
(22) (a) Jones, C.; Stasch, A.; Woodul, W. D. Chem. Commun. 2009,
113. (b) Beaini, S.; Deacon, G. B.; Delbridge, E. E.; Junk, P. C.; Skelton, B.
W.; White, A. H. Eur. J. Inorg. Chem. 2008, 4586.

6774 Organometallics, Vol. 28, No. 23, 2009
Mills et al.
Table 2. Crystallographic Data for 1-4
1
2
3
4
formula
fw
C26H38IO3Y
614.37
C26H38ErIO3
692.72
C44.25H60IN2O2P2Si2Y
985.87
C39H54ErIN2O2P2Si2
995.12
cryst size, mm
cryst syst
space group
0.81 ꢀ 0.27 ꢀ 0.25
monoclinic
P21/n
8.4422(5)
21.3091(13)
14.9695(9)
104.035(2)
2612.6(3)
4
0.52 ꢀ 0.45 ꢀ 0.42
monoclinic
P21/n
8.4244(6)
21.3331(14)
14.9588(10)
104.078(2)
2607.6(3)
4
0.33 ꢀ 0.11 ꢀ 0.06
monoclinic
P21/c
22.2321(15)
10.4676(7)
22.5947(15)
101.744(2)
5148.1(6)
4
0.27 ꢀ 0.26 ꢀ 0.20
monoclinic
P21/c
12.6861(4)
17.9166(5)
19.2882(6)
96.902(2)
4352.3(2)
4
˚
a, A
˚
b, A
˚
c, A
β, deg
3
˚
V, A
Z
F
calcd, g cm-3
1.562
3.437
1.765
4.426
1.272
1.874
1.519
2.799
μ, mm-1
no. of reflections measd
no. of unique reflns, Rint
no. of reflns with F2 > 2σ(F2)
transmn coeff range
R, Rwa (F2 > 2σ)
R, Rwa (all data)
Sa
15 963
4590, 0.0190
4169
0.42-0.24
0.0291, 0.0631
0.0252, 0.0648
1.036
16 106
5975, 0.0316
5769
0.24-0.20
0.0303, 0.0804
0.0314, 0.0811
1.113
25 216
9030, 0.0370
6635
0.90-0.57
0.0409, 0.0929
0.0595, 0.0987
0.980
27 317
9946, 0.0197
8763
0.58-0.49
0.0211, 0.0511
0.0274, 0.0546
1.026
parameters
max., min. diff map, e A
298
0.57, -0.43
281
2.01, -1.91
P
496
0.74, -0.59
448
0.93, -0.48
-3
˚
P
P
P
P
a Conventional R = ||Fo| - |Fc||/ |Fo|; Rw = [ w(Fo2 - Fc2)2/ w(Fo2)2]1/2; S = [ w(Fo2 - Fc2)2/no. data - no. params)]1/2 for all data.
selected bond lengths are compiled in Table 1. With 1 and 2 in
hand, we tested their synthetic utility in reactions with
H2BIPM.
and 4 bind in-plane, the potential for C-Y π-bonding is
maxmized. We therefore carried out DFT calculations on the
full structure of 3 and, for comparison, the BIPM dianion (5)
and the carbodiphosphorane Ph3PCPPh3 (6) (see Supporting
Information for further details). The latter was included due
to the similarity of the valid heteroallene resonance forms
R3Pþ-C2--PþR3 T R3Pþ-C-dPR3 T R3PdCdPR3 for 3, 5,
and 6. In each case the key features of the available X-ray
structures are reproduced well by the calculations with bond
Compounds 1 and 2 react smoothly with H2BIPM at
room temperature to give facile access to the doubly de-
protonated carbene complexes [Ln(BIPM)(I)(THF)2] (Ln =
Y, 3; Er, 4) as colorless and pink crystals in 68% and 81%
yields, respectively (Scheme 1). The 31P{1H} NMR spec-
trum of 3 exhibits a doublet at 3.48 ppm (2JYP = 12.96 Hz)
and the 13C{1H} NMR spectrum of 3 exhibits a triplet
of doublets at 60.28 ppm (JPC = 207.30; JYC = 5.03 Hz),
which is similar to that observed in related yttrium-BIPM
complexes.15-18
26
˚
lengths typically overestimated by 0.03 A.
The natures of the HOMO and HOMO-1 Kohn-Sham
orbitals for each calculation (Figure 3) show little change in
the gross nature of the two carbon-based frontier orbitals.
The orbitals are composed as follows: 3, HOMO 53.7% Cp,
2% Y, 5.9% P, HOMO-1 58.0% Cp, 3.2% Y, 2% P; 5,
HOMO 60.3% Cp, 12.6% P, HOMO-1 56.1% Cp, 13.2% P;
6, HOMO 60.7% Cp, 16.7% P, HOMO-1 51.2% Cp, 10.1%
Cs, 13.8% P. The trends from the NBO analyses for 3, 5, and
6 (see Supporting Information) are clear-cut: (i) the central
carbon atom of the carbene ligand carries a negative charge
between -1.32 and -1.58; (ii) the phosphorus centers carry a
positive charge between þ1.32 and þ1.61; (iii) the nitrogen
atoms in 3 and 5 possess a negative charge between -1.48
and -1.56. The P-C and P-N bond orders are consistently
>1, which reflects a polarization of the central carbon and
nitrogen lone pairs toward phosphorus, although true multi-
ple bonds are clearly not manifested. NBO analyses show
C-P σ-bonds with ∼60% carbon 2sp and ∼40% phos-
phorus 3sp3 character and frontier orbitals of π-symmetry
with ∼90% carbon 2p and ∼10% phosphorus 3pd
compositions for 3, 5, and 6. The latter values indicate
that negative hyperconjugation is minimal in these sys-
tems.27 NBO analysis of the Y-C interaction reveals a
highly polarized interaction with 95% carbon 2p and 5%
yttrium 4d contributions to this bond. This is consistent with
Crystalline samples of 3 and 4 suitable for X-ray diffrac-
tion were obtained from toluene. The molecular structure of
3 is illustrated in Figure 2, and selected bond lengths and
angles for 3 and 4 are tabulated in Table 1. Since the struc-
tures of 3 and 4 are very similar, we confine our discussion to
3. The yttrium center is distorted from an octahedral geo-
metry by the bite angle of the BIPM ligand [133.86(9)ꢀ]. Of
principal interest is the nearly perfect T-shaped geometry at
P
C(1) ( — = 359.4(2)ꢀ); indeed the YN2P2C ring adopts a
rare, essentially planar geometry, whereas a boat conforma-
tion is more usual for BIPM.24 We suggest this is due to the
softer iodide rendering the yttrium center more Lewis acidic
than in the corresponding alkyls (I and II), so the carbene is
drawn closer to the yttrium center, resulting in the planar
˚
configuration. The Y(1)-C(1) bond length of 2.356(3) A is
˚
∼0.05 A shorter than in I, and, while short, it is not the
shortest reported to date (range of 2.339-2.632 A).23 In 3 the
˚
P-N and endocyclic P-C bonds are longer and shorter,
respectively, compared to H2BIPM,25 and the exocyclic P-C
˚
bonds are ∼0.01 A longer.
DFT studies of I and II showed that the carbene centers
contain a nonbonding pair of electrons due to the YN2P2C
ring boat conformation.15,17 Since the carbene centers in 3
(26) (a) Hardy, G. E.; Kaska, W. C.; Chandra, B. P.; Zink, J. I. J. Am.
Chem. Soc. 1981, 103, 1074. (b) Hardy, G. E.; Zink, J. I.; Kaska, W. C.;
Baldwin, J. C. J. Am. Chem. Soc. 1978, 100, 8001. (c) Vincent, A. T.;
Wheatley, P. J. J. Chem. Soc., Dalton Trans. 1972, 617.
(27) Tonner, R.; Oxler, F.; Neumuller, B.; Petz, W.; Frenking, G.
Angew. Chem., Int. Ed. 2006, 45, 8038.
ꢀ
(24) (a) Cantat, T.; Mezailles, N.; Auffrant, A.; Le Floch, P. Dalton
Trans. 2008, 1957. (b) Jones, N. D.; Cavell, R. G. J. Organomet. Chem.
2005, 690, 5485. (c) Cavell, R. G.; Kamalesh Babu, R. P.; Aparna, K. J.
Organomet. Chem. 2001, 617-618, 158.
€
€
(25) Appel, R.; Ruppert, I. Z. Anorg. Allg. Chem. 1974, 406, 131.

Article
Organometallics, Vol. 28, No. 23, 2009 6775
Coulombic attraction between these centers within the BIPM
ligand in the dipolar N--Pþ-C2--Pþ-N- resonance form,
which has now emerged as the most accurate description of
the bonding within other early metal BIPM complexes.15,17,24,28
However, given the close similarity between the frontier
orbitals and atomic charges of 3 and 6, the intriguing possibility
of categorizing 3 and 4 as captodative carbon(0) complexes of
yttrium and erbium should not be dissmissed.29
(OCH2CH2), 55.10 (d, 1JYC = 34.3 Hz, CH2Ph), 67.61 (OCH2-
CH2), 115.88 (Ar-C), 123.62 (Ar-C), 127.61 (Ar-C) and 153.22
(ipso-Ar-C). IR ν/cm-1 (Nujol): 1586 (m), 1213 (m), 1014 (m),
904 (m), 852 (br, m), 794 (m), 745 (m), 703 (w), 675 (w).
Preparation of [Er(Bn)2(I)(THF)3] (2). This was prepared by
the same general method as 1, with PhCH2K (0.78 g, 6.00 mmol)
and [ErI3(THF)3.5] (2.40 g, 3.00 mmol), and was isolated as an
orange-pink microcrystalline solid. Yield: 1.77 g, 85%. Pink
crystals were grown at 5 ꢀC overnight from a THF solution
layered with hexane. Yield: 0.53 g, 26%. Anal. Calcd for
C26H38IO3Er: C, 45.08; H, 5.53. Found: C, 44.99; H, 5.46. μeff
(Evans method, 298 K, THF): 9.34 μB. IR ν/cm-1 (Nujol): 1586
(s), 1297 (w), 1260 (w), 1212 (s), 1177 (m), 1014 (m), 910 (br, s),
855 (br, s), 795 (m), 746 (m), 703 (m), 536 (w).
Summary and Conclusions
In summary, utilizing readily available reagents we have
prepared heteroleptic dibenzyl yttrium (1) and erbium (2)
iodides. Both 1 and 2 are accessible as thermally stable
crystalline solids in high yields, and they each exhibit re-
markable stability with respect to ligand scrambling. The
potential widespread utility of 1 and 2 in rare earth chemistry
was demonstrated by their successful use in the synthesis of
yttrium (3) and erbium (4) carbene derivatives that exhibit
unusual T-shaped carbon geometries. We are currently
seeking to extend the synthesis of 1 and 2 across the whole
rare earth series and are investigating the reactivity of 3 and
4, and we will describe these experiments in subsequent
publications.
Preparation of [Y(BIPM)(I)(THF)2] (3). A solution of H2C-
(PPh2NSiMe3)2 (1.12 g, 2.00 mmol) in toluene (15 mL) was
added dropwise to a suspension of 1 (1.23 g, 2.00 mmol) in
toluene (15 mL) at -78 ꢀC. The mixture was allowed to slowly
warm to room temperature with stirring over 18 h. Volatiles
were removed in vacuo, and the resulting pale yellow solid was
recrystallized from toluene (1.50 mL) to afford 3 as colorless
crystals. Yield: 1.13 g, 68%. Anal. Calcd for C39H54IN2O2P2-
Si2Y: C, 51.09; H, 5.94; N, 3.06. Found: C, 51.07; H, 5.78; N,
1
3.13. H NMR (d8-THF, 298 K): δ 0.12 (s, 18H, NSi(CH3)3),
1.82 (m, 8H, OCH2CH2), 3.68 (m, 8H, OCH2CH2), 7.21 (t, 3JHH
= 7.20 Hz, 8H, m-Ar-CH), 7.31 (t, 3JHH = 7.20 Hz, 4H, p-Ar-
3
CH) and 7.48 (dd, JHH = 7.20 Hz, 8H, o-Ar-CH). 13C{1H}
NMR (d8-THF, 298 K): δ 3.91 (NSi(CH3)3), 25.43 (OCH2CH2),
60.28 (td, JPC = 207.30 Hz, JYC = 5.03 Hz, YCP2), 67.39
(OCH2CH2), 127.07 (Ar-C), 129.12 (Ar-C), 131.09 (Ar-C) and
Experimental Section
1
1
General Procedures. All manipulations were carried out using
standard Schlenk techniques, or an MBraun UniLab glovebox,
under an atmosphere of dry nitrogen. Solvents were dried by
passage through activated alumina towers and degassed before
use. All solvents were stored over potassium mirrors (with the
1
141.81 (t, JPC = 47.80 Hz, i-Ar-C). 31P{1H} NMR (d8-THF,
2
298 K): δ 3.48 (d, JYP = 12.96 Hz, NPC). 29Si{1H} NMR
2
(d8-THF, 298 K): δ -3.05 (virtual t, JPSi = 3.98 Hz, NSi-
(CH3)3). IR ν/cm-1 (Nujol): 1260 (w), 1241 (w), 1105 (s), 1088
(m), 1066 (s), 832 (s), 725 (m), 521 (m).
˚
exception of THF, which was stored over activated 4 A molec-
Preparation of [Er(BIPM)(I)(THF)2] (4). This compound was
prepared by the same general method as 3, with 2 (1.83 g, 2.64
mmol) and H2C(PPh2NSiMe3)2 (1.48 g, 2.64 mmol), and was
isolated as pink crystals. Yield: 1.82 g, 81%. Anal. Calcd for
C39H54ErIN2O2 P2Si2Er: C, 47.07; H, 5.47; N, 2.82. Found: C,
46.97; H, 5.54; N, 2.73. μeff (Evans method, 298 K, THF):
7.18 μB. IR ν/cm-1 (Nujol): 2360 (w), 1261 (m), 1081 (br, m),
1022 (m), 800 (m), 691 (w), 667 (w).
ular sieves). Deuterated solvents were distilled from potassium,
degassed by three freeze-pump-thaw cycles, and stored under
nitrogen. The compounds [LnI3(THF)n],21 [K(Bn)],20 and H2-
BIPM25 were prepared according to published procedures.
1H, 13C, 31P, and 29Si NMR spectra were recorded on a
Bruker 400 spectrometer operating at 400.2, 100.6, 162.0, and
79.5 MHz, respectively; chemical shifts are quoted in ppm and
are relative to TMS (1H, 13C, and 29Si) and external 85% H3PO4
(31P). FTIR spectra were recorded on a Bruker Tensor
27 spectrometer. Elemental microanalyses were carried out by
Stephen Boyer at the Microanalysis Service, London Metropo-
litan University, UK.
X-ray Crystallography. Crystal data for compounds 1-4 are
given in Table 2, and further details of the structure determina-
tions are in the Supporting Information. Bond lengths and
angles are listed in Table 1. Crystals were examined variously
on Bruker AXS SMART 1000 or APEX CCD area detector
diffractometers using graphite-monochromated Mo KR radia-
Preparation of [Y(Bn)2(I)(THF)3] (1). THF (30 mL) was
added to a precooled (0 ꢀC) mixture of PhCH2K (1.30 g, 10.00
mmol) and [YI3(THF)3.5] (3.61 g, 5.00 mmol), and the resultant
beige mixture was stirred at this temperature for 4 h. The
mixture was filtered and volatiles were removed in vacuo to
afford 1 as a brown oil of sufficient purity for further reaction.
A pale beige powder was obtained by stirring the oil in hexane
(30 mL) overnight, followed by filtration of the supernatant
solution and drying in vacuo. Yield: 1.60 g, 62%. Colorless
crystals were grown at 5 ꢀC overnight from a saturated THF
solution. Yield: 1.17 g, 45%. Anal. Calcd for C26H38IO3Y: C,
50.83; H, 6.23. Found: C, 50.71; H, 6.22. 1H NMR (d8-THF, 298
K): δ 1.81 (m, 12H, OCH2CH2 and CH2Ph), 3.66 (m, 8H,
˚
tion (λ = 0.71073 A). Intensities were integrated from a sphere
of data recorded on narrow (0.3ꢀ) frames by ω rotation. Cell
parameters were refined from the observed positions of all
strong reflections in each data set. Semiempirical absorption
corrections based on symmetry-equivalent and repeat reflec-
tions were applied. The structures were solved variously by
direct methods and were refined by full-matrix least-squares
on all unique F2 values, with anisotropic displacement para-
meters for all non-hydrogen atoms, and with constrained riding
hydrogen geometries; Uiso(H) was set at 1.2 (1.5 for methyl
groups) times Ueq of the parent atom. The largest features in
final difference syntheses were close to heavy atoms and were of
no chemical significance. Highly disordered solvent molecules
of crystallization in 3 could not be modeled and were treated
with the Platon SQUEEZE procedure.30 Programs were Bruker
AXS SMART (control) and SAINT (integration),31 and
3
OCH2CH2), 6.44 (t, JHH = 6.80 Hz, 2H, p-Ar-CH), 6.88 (m,
3JHH = 7.20 Hz, 6H, m-Ar-CH) and 6.93 (d, 3JHH = 7.20 Hz,
4H, o-Ar-CH). 13C{1H} NMR (d8-THF, 298 K): δ 25.40
(28) (a) Orzechowski, L.; Jansen, G.; Lutz, M.; Harder, S. Dalton
Trans. 2009, 2958. (b) Orzechowski, L.; Harder, S. Organometallics 2007,
26, 2144. (c) Orzechowski, L.; Jansen, G.; Harder, S. J. Am. Chem. Soc.
2006, 128, 14676.
(30) Spek, A. L. Platon SQUEEZE; University of Utrecht: The
Netherlands, 2000.
(31) Bruker SMART and SAINT; Bruker AXS Inc.: Madison, WI,
€
(29) Alcarazo, M.; Lehmann, C. W.; Anoop, A.; Thiel, W.; Furster,
A. Nat. Chem. 2009, 1, 295.
2001.

6776 Organometallics, Vol. 28, No. 23, 2009
Mills et al.
SHELXTL was employed for structure solution and refinement
and for molecular graphics.32
support of this work, and the UK NSCCS for compu-
tational time.
Supporting Information Available:
Variable-temperature
Acknowledgment. We thank the Royal Society for
a University Research Fellowship (S.T.L.), the UK
EPSRC and University of Nottingham for generous
NMR study of 1, details of the DFT calculations, including
calculated coordinates and energies of 3, 5, and 6, and X-ray
crystallography of 1-4. This material is available free of charge via
the Internet at http://pubs.acs.org. Observed and calculated struc-
ture factor details are available from the authors upon request.
(32) Sheldrick, G. M. SHELXTL. Acta Crystallogr., Sect. A 2008, 64, 112.