Carbon-carbon bond formation using yttrium(III) and the lanthanide elements

Article abstract of DOI:10.1021/om000755e

The synthesis and characterization of a series of yttrium and lanthanide complexes that incorporate the macrocyclic bis(amidophosphine) ligand PhP(CH₂SiMe₂NSiMe₂CH₂)₂PP h, [P₂N₂], are described. The starting materials, {[P₂N₂]M}₂(μ-Cl)₂, (M = Y, Sm, Ho, Yb, Lu), are prepared by the reaction of syn-Li₂(dioxane)[P₂N₂] with MCl₃(THF)₃ in toluene. The reactivity of these complexes toward PhLi and other arylating agents is dependent on the size of the M³⁺ ion. M = Y and Ho undergo C-C bond formation reactions to give biphenyldiide compounds {[P₂N₂]M}₂ {μ-η⁶:η^6′ -(C₆ H₅)₂} and {[P₂N₂]Y}₂ {μ-η⁶:η^6′ -(C₆H₄-p-Ph)₂}. These have been structurally characterized and show the biphenyl dianion bridging two [P₂N₂]M fragments. These [P₂N₂]M fragments migrate over the bridging ligand's π-surface on the NMR time scale. M = Yb yields the paramagnetic monophenyl derivative [P₂N₂]Yb-(C₆H₅), where the Yb center is coordinatively unsaturated and resides in a distorted square-pyramidal environment. M = Lu results in a mixture of ate complexes of the formulation [P₂N₂]LuPh·LiCl , as evidenced by ⁷Li NMR. However, the biphenyl product {[P₂N₂]Lu}₂- {μ-η⁶:η^6′- (C₆H₅)₂} can be synthesized via a reductive route. The presence of THF was found to be deleterious to the coupling reaction; in this case, the THF adduct [P₂N₂]Y(C₆ H₄-p-Me)-(THF) was isolated and structurally characterized. The mechanism for the C-C bond formation reaction is described based on the isolation of these yttrium and lanthanide complexes.

Full text of DOI:10.1021/om000755e

Organometallics 2001, 20, 1387-1396
1387
Ca r bon -Ca r bon Bon d F or m a tion Usin g Yttr iu m (III) a n d
th e La n th a n id e Elem en ts
Michael D. Fryzuk,* Laleh J afarpour, Francesca M. Kerton, J ason B. Love,
Brian O. Patrick,† and Steven J . Rettig†
Department of Chemistry, University of British Columbia,
2036 Main Mall, Vancouver, B.C., Canada V6T 1Z1
Received August 30, 2000
The synthesis and characterization of a series of yttrium and lanthanide complexes that
incorporate the macrocyclic bis(amidophosphine) ligand PhP(CH2SiMe2NSiMe2CH2)2PPh,
[P2N2], are described. The starting materials, {[P2N2]M}2(µ-Cl)2, (M ) Y, Sm, Ho, Yb, Lu),
are prepared by the reaction of syn-Li2(dioxane)[P2N2] with MCl3(THF)3 in toluene. The
reactivity of these complexes toward PhLi and other arylating agents is dependent on the
size of the M3+ ion. M ) Y and Ho undergo C-C bond formation reactions to give
biphenyldiide compounds {[P2N2]M}2{µ-η6:η6′-(C6H5)2} and {[P2N2]Y}2{µ-η6:η6′-(C6H4-p-Ph)2}.
These have been structurally characterized and show the biphenyl dianion bridging two
[P2N2]M fragments. These [P2N2]M fragments migrate over the bridging ligand’s π-surface
on the NMR time scale. M ) Yb yields the paramagnetic monophenyl derivative [P2N2]Yb-
(C6H5), where the Yb center is coordinatively unsaturated and resides in a distorted square-
pyramidal environment. M ) Lu results in a mixture of “ate” complexes of the formulation
7
“[P2N2]LuPh‚LiCl”, as evidenced by Li NMR. However, the biphenyl product {[P2N2]Lu}2-
{µ-η6:η6′-(C6H5)2} can be synthesized via a reductive route. The presence of THF was found
to be deleterious to the coupling reaction; in this case, the THF adduct [P2N2]Y(C6H4-p-Me)-
(THF) was isolated and structurally characterized. The mechanism for the C-C bond forma-
tion reaction is described based on the isolation of these yttrium and lanthanide complexes.
Ch a r t 1
In tr od u ction
Because of the recent prominence of d0 metal com-
plexes as potential catalysts in a variety of processes,1-6
exploratory work on the discovery of new complexes of
the early transition elements and the lanthanides has
intensified. One particularly popular avenue has been
to move away from the traditional cyclopentadienyl-type
ligand systems to other donor sets.7-11 Our own work
has concentrated on developing mixed donor chelating
and macrocyclic ligands with amido and phosphine
donors in varying ratios.12-19 This has led to the design
† Professional Officers: UBC X-ray Structural Laboratory: S.J .R.
deceased October 27, 1998.
(1) Bochmann, M. J . Chem. Soc., Dalton Trans. 1996, 255.
(2) Grimmond, B. J .; Corey, J . Y. Organometallics 1999, 18, 2223.
(3) Gountchev, T. I.; Tilley, T. D. Organometallics 1999, 18, 5661.
(4) Tian, S.; Arredondo, V. M.; Stern, C. L.; Marks, T. J . Organo-
metallics 1999, 18, 2568.
(5) Douglass, M. R.; Marks, T. J . J . Am. Chem. Soc. 2000, 122, 1824.
(6) Alt, H. G.; Koppl, A. Chem. Rev. 2000, 100, 1205.
(7) Edelmann, F. T. Angew. Chem., Int. Ed. Engl. 1995, 34, 2466.
(8) Evans, W. J . New J . Chem. 1995, 19, 525.
(9) Britovsek, G. J . P.; Gibson, V. C.; Wass, D. F. Angew. Chem.,
Int. Ed. 1999, 38, 428.
(10) Gade, L. H. Chem. Commun. 2000, 173.
(11) Kempe, R. Angew. Chem., Int. Ed. 2000, 39, 468.
(12) Cohen, J . D.; Fryzuk, M. D.; Loehr, T. M.; Mylvaganam, M.;
Rettig, S. J . Inorg. Chem. 1998, 37, 112.
of three classes of ancillary ligands (PNP, NPN, and
P2N2, Chart 1) for which electronic and steric effects,
as well as overall charge, can be varied with consider-
able flexibility. As part of our efforts at exploring the
organometallic chemistry of the early transition ele-
ments and the lanthanides with the above ligand sets,
we were intrigued by the discovery of some deeply
(13) Fryzuk, M. D.; Giesbrecht, G.; Rettig, S. J . Organometallics
1996, 15, 3329.
(14) Fryzuk, M. D.; Love, J . B.; Rettig, S. J .; Young, V. G. Science
1997, 275, 1445.
(15) Fryzuk, M. D.; Love, J . B.; Rettig, S. J . Organometallics 1998,
17, 846.
(17) Fryzuk, M. D.; Leznoff, D. B.; Thompson, R. C.; Rettig, S. J . J .
Am. Chem. Soc. 1998, 120, 10126.
(18) Fryzuk, M. D.; Leznoff, D. B.; Ma, E. S. F.; Rettig, S. J .; Young,
V. G. Organometallics 1998, 17, 2313.
(16) Fryzuk, M. D.; J ohnson, S. A.; Rettig, S. J . J . Am. Chem. Soc.
1998, 120, 11024.
(19) Fryzuk, M. D.; J ohnson, S. A.; Rettig, S. J . Organometallics
1999, 18, 4059.
10.1021/om000755e CCC: $20.00 © 2001 American Chemical Society
Publication on Web 03/01/2001

1388 Organometallics, Vol. 20, No. 7, 2001
Fryzuk et al.
Ta ble 1. Cr ysta llogr a p h ic Da ta
1a
1e
3c
5
6
8
formula
fw
C48H84Cl2N4P4Si8Y2 C48H84Cl2N4P4Si8Lu2 C60H94N4P4Si8Ho2 C79H110N4P4Si8Y2 C37H62N2O1.50P2Si4Y C30H47N2P2Si4Yb
1314.52
1486.64
1549.87
1642.16
822.10
783.04
color, habit
cryst size, mm
cryst syst
space group
a, Å
colorless, irregular colorless, irregular
black, block
blue, needle
clear, needle
orange, block
0.20 × 0.20 × 0.30 0.20 × 0.25 × 0.45
0.50 × 0.35 × 0.25 0.15 × 0.20 × 0.45 0.15 × 0.25 × 0.50 0.60 × 0.40 × 0.40
orthorhombic
Pbca (no.61)
18.2743(9)
26.993(1)
27.782(2)
90
orthorhombic
Pbca (no.61)
18.167(1)
26.5525(4)
27.6449(2)
90
monoclinic
P21/c (no.14)
12.0991(3)
16.3568(3)
18.2721(5)
90
triclinic
P1h (no.2)
11.7461(9)
13.433(2)
15.608(2)
70.409(5)
87.346(3)
65.5352(13)
2099.5(4)
1
1.299
862.00
16.10
20 180
10 065
0.045
monoclinic
P21 (no.4)
11.1570(4)
21.4652(14)
19.3730(3)
90
104.9780(3)
90
4482.0(3)
4
1.218
1740.00
15.11
42 041
11 099
0.070
monoclinic
P21/c (no.14)
20.2123(5)
18.8132(4)
21.0448(4)
90
113.675(2)
90
7329.0(3)
8
1.419
3176.00
27.91
62 012
16 219
0.039
b, Å
c, Å
R, deg
â, deg
90
90
103.283(2)
90
3519.4(1)
2
1.462
1576.00
25.00
30 341
7754
0.035
γ, deg
90
90
V, Å3
13704(1)
8
13335.2(6)
8
Z
F
calcd, g cm-3
1.274
1.481
F(000)
5472.00
20.31
5984.00
32.97
µ(Mo, KR), cm-1
total no. of reflns
no. of unique reflns
Rint
114 732
23 388
0.078
122 553
17 131
0.048
reflns with I g 3σ(I)
no. of variables
R(F, I g 3σ(I))
Rw(F, I g 3σ(I))
R(F2, all data)
Rw(F2, all data)
gof
6235
613
0.060
0.056
0.106
0.125
1.91
8414
613
0.080
0.081
0.139
0.180
2.68
6375
352
0.023
0.030
0.043
0.066
1.26
5868
459
0.086
0.079
0.046
0.036
1.72
13 899
864
0.114
0.146
0.062
11 481
703
0.033
0.047
0.063
0.073
1.33
0.104
1.37
max ∆/σ (final cycle)
0.002
0.005
-5.25 to +11.18
(near Lu)
0.01
-1.19 to +1.62
0.06
-1.27 to +1.06
0.04
-2.53 to +4.93
0.06
-1.51 to +4.37
residual density, e Å-3 -1.14 to +2.57
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
colored complexes ofyttrium(III)[P2N2](P2N2 )PhP(CH2-
SiMe2NSiMe2CH2)2PPh) upon reaction with aryllithium
reagents.20 We have traced the origin of the color to the
formation of biphenyldiide derivatives via an intriguing
carbon-carbon bond coupling reaction that does not
require any change of formal oxidation state nor involve
any migratory insertion chemistry. In this paper we
detail our studies to understand these reactions, in
particular, to probe the effect of changing the metal from
yttrium(III) to other members of group 3 and to the
lanthanides. What becomes apparent is that the forma-
tion of carbon-carbon bonds via this process is very
dependent on the size of the metal ion.
(d eg) in {[P 2N2]Y}2(µ-Cl)2, 1a
Y(1)-N(1)
Y(1)-P(1)
Y(2)-N(3)
Y(2)-P(3)
Y(1)-Cl(1)
Y(2)-Cl(1)
2.270(3)
2.827(1)
2.255(3)
2.895(1)
2.697(1)
2.708(1)
Y(1)-N(2)
Y(1)-P(2)
Y(2)-N(4)
Y(2)-P(4)
Y(1)-Cl(2)
Y(2)-Cl(2)
2.283(3)
2.844(1)
2.274(3)
2.904(1)
2.707(1)
2.730(1)
Cl(1)-Y(1)-Cl(2)
Cl(1)-Y(1)-P(2)
Cl(1)-Y(1)-N(2)
Cl(2)-Y(1)-P(2)
Cl(2)-Y(1)-N(2)
P(1)-Y(1) -P(2)
77.05(3)
Cl(1)-Y(1)-P(1)
Cl(1)-Y(1)-N(1)
Cl(2)-Y(1)-P(1)
Cl(2)-Y(1)-N(1)
N(1)-Y(1) -N(2)
96.67(4)
91.90(9)
92.59(4)
92.59(4)
98.7(1)
98.35(4)
169.36(9)
103.00(4)
92.31(9)
160.38(4)
Cl(1)-Y(2)-Cl(2)
Cl(1)-Y(2)-P(4)
Cl(1)-Y(2)-N(4)
Cl(2)-Y(2)-P(4)
Cl(2)-Y(2)-N(4)
P(3)-Y(2)-P(4)
76.47(3)
130.45(4)
143.43(9)
86.76(4)
95.83(9)
136.69(4)
Cl(1)-Y(2)-P(3)
Cl(1)-Y(2)-N(3)
Cl(2)-Y(2)-P(3)
Cl(2)-Y(2)-N(3)
N(3)-Y(2)-N(4)
86.14(4)
98.07(9)
129.37(4)
147.38(9)
106.1(1)
Resu lts a n d Discu ssion
Syn t h esis a n d St r u ct u r e of {[P 2N2]M}2(µ-Cl)2
1a -e. The starting materials for all of the chemistry
described for these group 3 and lanthanide complexes
are the chloride-bridged dimers {[P2N2]M}2(µ-Cl)2 (M )
Y, Sm, Ho, Yb, Lu) 1a -e, which can be synthesized in
high to quantitative yields by the reaction of syn-Li2-
(dioxane)[P2N2] with MCl3(THF)3 in toluene at 85 °C.
They are isolated as colorless or pale-colored solids. For
1a and 1e, crystals suitable for X-ray diffraction were
grown; the molecular structure of 1a is shown in Figure
1; crystal data are given in Table 1 and selected bond
lengths and angles for 1a and 1e in Tables 2 and 3,
respectively. The complexes are isostructural and con-
tain two structurally different metal centers joined with
bridging chloride ligands; M1 resides in a distorted
trigonal prismatic environment, while the geometry of
M2 is distorted octahedral. In contrast to the solid-state
structures, the diamagnetic species 1a and 1e show
solution NMR spectra that indicate both ends of the
molecule are equivalent; thus the previously observed15
flexibility of the [P2N2] ligand framework allows ap-
proximately C2v symmetry in solution. In particular, two
1
silylmethyl environments are observed in the H NMR
spectrum, and in the 31P{1H} NMR spectrum, a single
phosphorus environment is observed: for 1a a doublet
at -33.8 ppm (J YP ) 84.0 Hz) and for 1e a singlet at
-26.0 ppm. The Sm, Ho, and Yb derivatives (1b-d ) are
paramagnetic species as anticipated; only broadened,
1
contact-shifted resonances are observed in the H NMR
spectrum, which could not be interpreted due to over-
lapping and missing resonances.
Ar yl Cou p lin g Rea ction s a t Yttr iu m . The impetus
for this project arose out of the observation of deep blue
solutions that resulted when the colorless yttrium(III)
alkyl complex [P2N2]Y(CH2SiMe3), 2a , was dissolved in
aromatic solvents such as benzene. Once the biphenyl-
diide complex {[P2N2]Y}2{µ-η6:η6′-(C6H5)2}, 3a, was struc-
turally characterized,20 we recognized that a more direct
route to these complexes was via the reaction of PhLi
(20) Fryzuk, M. D.; Love, J . B.; Rettig, S. J . J . Am. Chem. Soc. 1997,
119, 9071.

Carbon-Carbon Bond Formation Using Yttrium
Organometallics, Vol. 20, No. 7, 2001 1389
F igu r e 1. ORTEP representation of the solid state mo-
lecular structure of {[P2N2]Y}2(µ-Cl)2, 1a .
F igu r e 2. ORTEP representation of the solid state mo-
lecular structure of {[P2N2]Y}2{(µ-η6:η6-C6H4-p-Me)(C6H4-
p-Me)}, 4 (from ref 20).
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) in {[P 2N2]Lu }2(µ-Cl)2, 1e
to 3a using NMR spectroscopic data. The reaction of 1a
with p-tolyllithium gave a brown product whose struc-
ture showed the [P2N2]Y fragments bound to the same
ring (on opposite faces) with the remaining ring unco-
ordinated and retaining its aromaticity, Figure 2.20
Interestingly, the solution 1H NMR data for 4 are
inconsistent with this solid state structure, as reso-
nances for only one type of coordinated p-tolyl group are
observed at room temperature; therefore, the [P2N2]Y
fragments must be migrating across the π-surface of the
bi-p-tolyldiide moiety on the NMR time scale. In support
of this proposal, at -95 °C broad resonances for an
uncoordinated arene are observed between 6 and 7 ppm,
in addition to high-field-shifted resonances for the
sandwiched p-tolyl moiety; this suggests that the solid
state structure represents a low-temperature limiting
structure for this process. This type of dynamic behavior
probably occurs to some extent in all [P2N2]Y biaryldiide
complexes, even 3a ; however, we were unable to reach
a low-temperature limiting structure with 3a or any
other of these coupled diaryl products.
Lu(1)-N(1)
Lu(1)-P(1)
Lu(2)-N(3)
Lu(2)-P(3)
Lu(1)-Cl(1)
Lu(2)-Cl(1)
2.231(7)
2.785(2)
2.229(7)
2.855(2)
2.654(2)
2.671(2)
Lu(1)-N(2)
Lu(1)-P(2)
Lu(2)-N(4)
Lu(2)-P(4)
Lu(1)-Cl(2)
Lu(2)-Cl(2)
2.200(8)
2.795(2)
2.270(7)
2.847(2)
2.665(2)
2.692(2)
Cl(1)-Lu(1)-Cl(2)
Cl(1)-Lu(1)-P(2)
Cl(1)-Lu(1)-N(2)
Cl(2)-Lu(1)-P(2)
Cl(2)-Lu(1)-N(2)
P(1)-Lu(1) -P(2)
77.27(7) Cl(1)-Lu(1)-P(1)
95.20(8)
98.83(8) Cl(1)-Lu(1)-N(1) 168.2(2)
91.7(2)
Cl(2)-Lu(1)-P(1)
93.86(8)
90.9(2)
100.27(8) Cl(2)-Lu(1)-N(1)
168.6(2)
N(1)-Lu(1) -N(2) 100.1(3)
161.94(9)
Cl(1)-Lu(2)-Cl(2)
Cl(1)-Lu(2)-P(4)
Cl(1)-Lu(2)-N(4)
Cl(2)-Lu(2)-P(4)
Cl(2)-Lu(2)-N(4)
P(3)-Lu(2)-P(4)
76.52(7) Cl(1)-Lu(2)-P(3) 128.27(8)
86.26(7) Cl(1)-Lu(2)-N(3)
144.8(2) Cl(2)-Lu(2)-P(3)
96.3(2)
87.17(7)
127.35(8) Cl(2)-Lu(2)-N(3) 148.6(2)
95.2(2)
138.55(7)
N(3)-Lu(2)-N(4)
106.8(3)
with the chloride-bridged dimer 1a . Reaction of 2.2
equiv of aryllithium with 1a in toluene at -78 °C,
followed by additional stirring at room temperature,
affords blue solutions of the coupled diaryl complex (eq
1) in modest yields.
The above reactions of simple aryllithium reagents
(i.e., phenyllithium, m-tolyllithium, and p-tolyllithium)
1a show how small changes can affect the structure of
the coupled diaryl products.20 In an effort to examine
this further, other p-substituted-aryllithium reagents
were allowed to react with 1a ; p-tert-butylphenyllith-
ium, p-chlorophenyllithium, p-methoxyphenyllithium,
and p-trifluoromethylphenyllithium did not result in the
formation of any coupled diaryl derivatives. Analysis of
the crude products showed that mixtures of products
were formed that defied characterization; in addition,
no deep colors were observed indicative of coupled di-
aryls. However, one substituted aryllithium reagent was
eventually found to undergo this process. The reaction
of biphenyllithium (p-Ph-C6H4Li) with 1a generated
dark blue crystals of the bisbiphenyl-coupled product
5. X-ray structure analysis of 5 was undertaken and it
showed a bisbiphenyl moiety sandwiched by two [P2N2]Y
units that are η6-coordinated to the two middle rings.
The solid state molecular structure of {[P2N2]Y}2{µ-η6:
η6′-(C6H4-p-Ph)2} (5) is shown in Figure 3, and selected
bond lengths and bond angles are shown in Table 4. The
C-C bond distance between the two coordinated rings
is 1.396(6) Å, which indicates a double bond. The C-C
bond distances between the coordinated and the non-
The reaction of m-tolyllithium with 1a also produced
a dark blue complex, {[P2N2]Y}2{µ-η6:η6′-(C6H4-m-
Me)2},20 which although not structurally characterized,
was shown to be a π-biphenyl-bridged dimer by analogy

1390 Organometallics, Vol. 20, No. 7, 2001
Fryzuk et al.
Sch em e 1. F lu xion a l Beh a vior of 5
F igu r e 3. ORTEP representation of the solid state mo-
lecular structure of {[P2N2]Y}2{µ-η6:η6′-(C6H4-p-Ph)2}, 5.
Ta ble 4. Selected Bon d Len gth s (Å) a n d An gles
(d eg) in {[P 2N2]Y}2{µ-η6:η6′-(C6H4-p-P h )2}, 5
Y(1)-N(1)
2.304(2)
2.9267(10)
2.737(3)
2.716(3)
2.765(3)
1.396(6)
1.374(4)
1.444(4)
1.458(5)
1.420(5)
1.368(6)
1.382(5)
Y(1)-N(2)
2.299(2)
2.9075(10)
2.726(3)
2.705(3)
2.730(3)
1.474(4)
1.407(5)
1.370(4)
1.464(5)
1.379(5)
1.394(6)
1.400(5)
Y(1)-P(1)
Y(1)-P(2)
Y(1)-C(25)
Y(1)-C(27)
Y(1)-C(29)
C(25)-C(25)
C(26)-C(27)
C(28)-C(29)
C(25)-C(30)
C(31)-C(32)
C(33)-C(34)
C(35)-C(36)
Y(1)-C(26)
Y(1)-C(28)
Y(1)-C(30)
C(25)-C(26)
C(27)-C(28)
C(29)-C(30)
C(28)-C(31)
C(32)-C(33)
C(34)-C(35)
C(31)-C(36)
ture of a C7D8 solution of 5 was lowered, the signals
due to the bisbiphenyl moiety started to broaden and
gave rise to three resonances at 6.71, 5.90, and 5.47
ppm. At -15 °C a single broad resonance was observed
between 6.50 and 5.00 ppm, but there was no evidence
for less symmetric products despite cooling to -60 °C.
The 31P{1H} NMR spectra in the same temperature
range exhibited single broad resonances: -27.8 ppm
(ν1/2 ) 180 Hz, -15 °C) and -28.5 ppm (ν1/2 ) 400 Hz,
-30 °C).
In all of the reactions of 1a with aryllithiums that
have been discussed above, the solvent system of choice
was toluene, sometimes in the presence of diethyl ether.
To examine the effect of using a highly coordinating
solvent upon the course of reaction, 1a was allowed to
react with p-tolyllithium in a solvent mixture of toluene
and THF (eq 2). Evaporating the solvents caused no
color change, and a white microcrystalline solid, 6, was
isolated after workup. The 1H NMR spectrum of this
compound did not show any signals due to a π-coordi-
nated p-tolyl ring. Instead, a singlet due to the methyl
group of the p-tolyl moiety occurs at 2.40 ppm, and the
protons of the p-tolyl ring appear as a multiplet at
7.23 ppm. Two broad resonances due to the coordinated
THF are observed at 3.80 and 1.29 ppm. The 31P{1H}
N(1)-Y(1)-N(2)
101.97(9)
P(1)-Y(1)-P(2)
146.81(3)
coordinated rings are in the range of a single bond at
1.464(5) Å. The C-C bond distances in the coordinated
rings are inequivalent, but are similar to those shown
in the biphenyl analogue, 3a .20 The aromaticity is
preserved in the outer noncoordinated rings, as is
evident by the equivalent C-C bond lengths. The two
coordinated rings are coplanar, but each is twisted by
32.5° from its neighboring noncoordinated ring. There-
fore, the two inner rings can be considered as a biphenyl
dianion with each ring substituted by a phenyl ring at
the para-position. The average Y-C(ring) bond distance
is 2.730(3) Å, identical to that in 3a .
X-ray analysis clearly shows the presence of two types
of rings, one coordinated to the metal center and no
longer aromatic, and the other noncoordinated and aro-
1
matic. Five upfield-shifted resonances in the H NMR
NMR spectrum shows a doublet at -33.9 ppm (J YP
56 Hz).
)
spectrum were attributed to the π-bonded bisbiphenyl
protons at 6.50, 6.40, 6.20, 5.80, and 5.50 ppm, and no
resonances that correspond to uncoordinated phenyl
groups were observed. The room-temperature 31P{1H}
NMR spectrum exhibits a doublet at -26.87 ppm (J YP
) 84.1 Hz) that is consistent with equivalent phospho-
rus environments. The implication is that, in solution,
there is a fluxional process in which the two [P2N2]Y
units traverse the π-surfaces of all four of the rings, as
illustrated in Scheme 1. If such a process occurs rapidly
on the NMR time scale, one can anticipate that all four
rings will experience some upfield shielding due to the
presence of the coordinated yttrium center.
The X-ray crystal structure of 6 shows that the
complex is mononuclear with yttrium coordinated to a
[P2N2] moiety and a THF molecule and also σ-coordi-
nated to a p-tolyl group. The coordination geometry
around the yttrium center is distorted trigonal pris-
matic. The Y-C bond distance, 2.472(6) Å, is longer
This type of rapid fluxional process was also ob-
served for [P2N2]Ln cations coordinated to polyaromatic
ligands.21 As with those examples, attempts to freeze
out this process were unsuccessful. As the tempera-
(21) Fryzuk, M. D.; J afarpour, L.; Kerton, F. M.; Love, J . B.; Rettig,
S. J . Angew. Chem., Int. Ed. 2000, 39, 767.

Carbon-Carbon Bond Formation Using Yttrium
Organometallics, Vol. 20, No. 7, 2001 1391
and the reaction time did not change the outcome of
these reactions.
Ar yl Cou p lin g R ea ct ion s of t h e La n t h a n id es.
Having successfully obtained the [P2N2]Y-coupled diaryl
complexes by reacting 1a with phenyl, m-tolyl, p-tolyl,
and biphenyllithium reagents, we set out to prepare the
lutetium analogues by reaction with {[P2N2]Lu}2(µ-Cl)2,
1e. However, the formation of highly colored solutions
was not observed in any experiment, and only white
solids were isolated. These were only sparingly soluble
in hydrocarbon and aromatic solvents. Therefore at-
tempts to obtain NMR spectra in C6D6 or C7D8 were
futile. The noncoordinating polar solvent CD2Cl2 reacted
with the complex to afford the free ligand [P2N2D2] and
an insoluble white powder, presumably YCl3. Interpret-
able NMR spectra could be obtained from C4D8O solu-
tions. It is assumed that ate complexes are present, as
a single resonance at -0.7 ppm (ν1/2 ) 15 Hz, 27 °C) is
observed in the 7Li NMR spectrum of all samples in
saturated C4D8O solutions. The frequency compares well
with that reported for La(CH{SiMe3}2)3(µ-Cl)Li(pm-
deta), -0.2 ppm.24 Two anions are presumably present,
possibly {[P2N2]LuPh2}- and {[P2N2]LuCl2}-, as two
different 31P environments are observed at -18.7 and
-20.3 ppm in a ratio of 1:1 and for the p-tolyl derivative
-19.3 and -20.9 ppm. The presence of two anions is
also evident in the 1H NMR spectrum, where eight
SiMe2 environments are observed, along with many
overlapping multiplets in the aromatic region. No
change in appearance of the NMR spectra was observed
over a temperature range of -70 to 80 °C. Elemental
analysis of the white powder showed a lower level of C
and a higher level of N than expected; this is probably
due to incomplete combustion of the sample and is not
uncommon in organometallic lanthanide complexes.25,26
Attempts to isolate the Lu analogue of the THF adduct
6 upon performing the reaction in THF were unsuc-
cessful; removal of the solvent in vacuo afforded the
hydrocarbon-insoluble white powder identical to that
described above. Attempts to obtain crystals of these Lu
complexes have been frustrated by their low solubility.
However, their coloration when compared with 3a -c
and 5 and the lack of high-field-shifted arene protons
in the 1H NMR spectra indicate the formation of
σ-bonded complexes, and no evidence for C-C bond
formation is apparent. No reaction occurred when
PhMgBr was allowed to react with the lutetium chloro-
bridged dimer 1e even after 1 week.
F igu r e 4. ORTEP representation of the solid state mo-
lecular structure of [P2N2]Y(C6H4-p-Me)(THF), 6.
Ta ble 5. Selected Bon d Len gth s (Å) a n d An gles
(d eg) in [P 2N2]Y(C6H4-p-Me)(THF ), 6
Y(1)-N(1)
Y(1)-P(1)
Y(1)-O(1)
2.283(4)
2.9396(15)
2.401(4)
Y(1)-N(2)
Y(1)-P(2)
Y(1)-C(29)
2.321(5)
3.0391(15)
2.472(6)
N(1)-Y(1)-N(2)
109.8(2)
P(1)-Y(1)-P(2)
126.05(5)
than that of 2.394(6) Å found for the σ-bonded complex,
[P2N2]Y{CH(SiMe3)2},20 and shorter than the yttrium
to arene carbon bonds in 2a that range from 2.629(4)
to 2.699(4) Å. Therefore, the presence of a strongly
coordinating molecule such as THF blocks the C-C
bond coupling reaction. The solid state molecular struc-
ture of 6 is shown in Figure 4, and selected bond lengths
and angles are shown in Table 5.
If the coordinated THF molecule could be removed
from the coordination sphere of the Y center, it would
open up a coordination site that might facilitate the
formation of 3a via coupling. Cyclic ethers undergo
electrophilic attack with ring opening when treated with
trimethylsilyliodide.22 This property of Me3SiI was used
to remove the THF ligand from Cp*La[CH(SiMe3)2]2-
(THF).23 Reacting 6 with excess Me3SiI results in ring
opening of the coordinated THF, as seen in the 1H NMR
spectrum along with formation of {[P2N2]Y}2(µ-I)2 and
some intractable materials. Treating 6 with only 1 equiv
of Me3SiI did not result in THF ring opening. Attempts
to use Lewis acids such as AlPh3 and B(C6F5)3 to remove
the THF were unsuccessful; in these latter reactions,
no reaction occurred and the starting materials were
recovered.
When 1a was allowed to react with Grignard re-
agents such as PhMgBr, p-tolylMgBr, and p-biphen-
ylMgBr, the formation of white precipitates was not
observed, and the colorless reaction mixture did not
change color when the diethyl ether solvent was evapo-
rated; workup of these reactions produced white solids.
The 31P{1H} NMR spectra of these products were
identical for all three cases with three doublets at -33.3
(J YP ) 83.3 Hz), -33.45 (J YP ) 82.7), and -33.55 ppm
(J YP ) 83 Hz). The first doublet is the starting chloride
1a , and the other two are the products of halide
exchange, namely, {[P2N2]Y}2(µ-Cl)(µ-Br) and {[P2N2]Y}2-
(µ-Br)2, as shown in eq 3. Increasing the temperature
It had previously been shown by our group that
dinuclear [P2N2]Lu polycyclic aromatic π-complexes
could be prepared via a reductive route.21 This route is
successful for the preparation of {[P2N2]Lu}2{µ-η6:η6′-
(C6H5)2}, 3e, which can be isolated as a crystalline blue
(24) Atwood, J . L.; Lappert, M. F.; Smith, R. G.; Zhang, H. Chem.
Commun. 1988, 1308.
(25) Qian, C. T.; Nie, W. L.; Sun, J . J . Chem. Soc., Dalton Trans.
1999, 3283.
(26) Eppinger, J .; Spiegler, M.; Hieringer, W.; Herrmann, W. A.;
Anwander, R. J . Am. Chem. Soc. 2000, 122, 3080.
(22) Olah, G. A.; Narang, S. C. Tetrahedron 1982, 38, 2225.
(23) van der Heijden, H.; Schaverien, C. J . Organometallics 1989,
8, 255.

1392 Organometallics, Vol. 20, No. 7, 2001
Fryzuk et al.
solid in moderate yields via the reaction of 1e with
biphenyl in the presence of KC8 (eq 4).
F igu r e 5. ORTEP representation of the solid state mo-
lecular structure of [P2N2]YbPh, 8.
1
The H NMR spectrum of 3e contains three upfield-
Ta ble 6. Selected Bon d Len gth s (Å) a n d An gles
(d eg) in [P 2N2]Yb(C6H5), 8
shifted resonances, which are attributed to the π-bonded
biphenyl protons at 5.04, 4.41, and 4.03 ppm. The 31P-
{1H} NMR spectrum exhibits equivalent phosphorus
environments, with a singlet at -15.4 ppm. The solution
NMR data and the distinctive blue color of the material
are consistent with a structure that is identical to the
yttrium and holmium biphenyldiide complexes 3a and
3c. This reductive route could also be used to prepare
the yttrium analogue 3a , albeit in lower yields than
those obtained via the PhLi route.
Yb(1)-N(1)
Yb(2)-N(3)
Yb(1)-P(1)
Yb(2)-P(3)
Yb(1)-C(25)
2.220(4)
2.234(4)
2.810(1)
2.825(1)
2.336(5)
Yb(1)-N(2)
Yb(2)-N(4)
Yb(1)-P(2)
Yb(2)-P(4)
Yb(2)-C(55)
2.230(3)
2.240(4)
2.809(1)
2.804(1)
2.351(5)
N(1)-Yb(1)-N(2)
N(3)-Yb(2)-N(4)
N(1)-Yb(1)-C(25)
N(3)-Yb(2)-C(55)
P(1)-Yb(1)-C(25)
P(3)-Yb(2)-C(55)
110.0(1) P(1)-Yb(1)-P(2)
111.5(1) P(3)-Yb(2)-P(4)
124.4(2) N(2)-Yb(1)-C(25)
122.9(2) N(4)-Yb(2)-C(55)
109.9(1) P(2)-Yb(1)-C(25)
108.5(1) P(4)-Yb(2)-C(55)
145.65(3)
143.11(4)
125.5(2)
125.6(2)
104.4(1)
108.4(1)
The isolation of {[P2N2]Lu}2{µ-η6:η6′-(C6H5)2} via the
reaction of biphenyl under reducing conditions suggests
that the inability of the lutetium complex to undergo
the coupling reaction is a kinetic effect and not because
of any thermodynamic instability of the ultimate prod-
uct. The smaller size of lutetium(III) compared to
yttrium(III) may prevent the putative, but crucial
phenyl-bridged dimer formation that is suggested to be
necessary for aryl coupling (vide infra).
Reaction of PhLi with {[P2N2]Yb}2(µ-Cl)2 (1d ) in
toluene proceeded with a color change from yellow to
dark green. Extraction of the crude green product with
hexanes and cooling to -30 °C resulted in the isolation
of the mononuclear σ-phenyl complex [P2N2]Yb(C6H5)
(8) as orange crystals in modest yield. The green
byproduct could be the bridged biphenyl dimer, although
we were unable to confirm this experimentally. Heating
the mononuclear phenyl derivative 8 to 110 °C in
toluene for 48 h resulted in no color change and
therefore no coupling. The isolation of this mononuclear
σ-phenyl complex, which is unobtainable for the Y
series, indicates an increased stability for this species
possibly due to the smaller size of the metal.
Yb(1)-C(25)-C(26) 111.6(4) Yb(1)-C(25)-C(30) 134.3(5)
Yb(2)-C(55)-C(56) 118.9(4) Yb(2)-C(55)-C(60) 127.3(4)
(THF)3 and Ph2(THF)Yb(µ-Ph)3Yb(THF)3 have comparable
bond distances for their terminal phenyl groups, 2.39-
(1)-2.463(32) Å.28,29 Recently, the 2,6-dimesitylphenyl
ligand has been used successfully in the presence of
other ligands, but due to the steric demand of this
ligand, the Yb-C bond distances are significantly
longer, 2.403(4)-2.447(9) Å, than in our example.30,31
The intramolecular Yb-H bond distances for the ortho
protons of the phenyl groups are Yb(1)-H(43) 2.987 Å,
Yb(1)-H(47) 3.587 Å, Yb(2)-H(90) 3.202 Å, and Yb(2)-
H(96) 3.466 Å. Although not refined, there is clearly
some evidence of an agostic interaction in molecule 1,
namely, the C(26)-H(43) bond and Yb(1). This is also
evident when comparing bond angles around the Yb
bound C atoms: Yb(1)-C(25)-C(26) 111.6(4)° and
Yb(1)-C(25)-C(30) 134.3(5)°, Yb(2)-C(55)-C(56)
118.9(4)°, and Yb(2)-C(55)-C(60) 127.3(4)°; there is
clearly a tilt of the Ph ring toward one side of the
molecule away from the planes containing either the N
atoms and Yb or the P atoms and Yb.
The solid state molecular structure of 8 is shown in
Figure 5, and selected bond lengths and bond angles
are shown in Table 6.
The reaction of 1e, {[P2N2]Sm}2(µ-Cl)2, and also
{[P2N2]Ln}2(µ-I)2, Ln ) Sm, La, with PhLi in toluene
proceeded with a darkening of color to afford dark
purple/brown solutions. However, the hexanes extract
from these reactions afforded upon cooling colorless
crystals of Li2[P2N2]. The identity of the dark-colored
complexes are yet to be confirmed; however, one pos-
Two molecules are present in the asymmetric unit
cell; in both there is significant thermal motion associ-
ated with the Yb-bound phenyl ring. However, this
motion could not be well refined as simple static
disorder, and as such, the positions of the hydrogen
atoms could not be refined. In both molecules the Yb is
in a distorted square-pyramidal environment with the
four N and P atoms in the basal plane and C25 in the
apical position. The Yb-C bond distances are 2.336(5)
and 2.351(5) Å; only a limited number of Yb complexes,
or indeed crystallographically characterized Ln com-
plexes, with σ-bonded aryl ligands have been synthe-
sized to date.27 Homoleptic complexes such as Ph2Yb-
(27) Cotton, S. A. Coord. Chem. Rev. 1997, 160, 93.
(28) Bochkarev, M. N.; Khramenkov, V. V.; Rad’kov, Y. F.; Zakharov,
L. N.; Struchkov, Y. T. J . Organomet. Chem. 1992, 429, 27.
(29) Zakharov, L. N.; Struchkov, Y. T. J . Organomet. Chem. 1997,
536, 65.
(30) Rabe, G. W.; Strissel, C. S.; Liable-Sands, L. M.; Concolino, T.
E.; Rheingold, A. L. Inorg. Chem. 1999, 38, 3446.
(31) Niemeyer, M.; Hauber, S.-O. Z. Anorg. Allg. Chem. 1999, 625,
137.

Carbon-Carbon Bond Formation Using Yttrium
Organometallics, Vol. 20, No. 7, 2001 1393
Sch em e 2. P r op osed Mech a n ism for C-C Bon d
F or m a tion by [P 2N2]M F r a gm en ts
[P2N2]Ln fragments.21 The average Ho-C(ring) bond
distance is 2.708(2) Å, only slightly shorter than the
average Y-C(ring) distances in 3a .20
F igu r e 6. ORTEP representation of the solid state mo-
lecular structure of {[P2N2]Ho}2{µ-η6:η6′-(C6H5)2}, 3c.
Mech a n ism of C-C Bon d F or m a tion . In this
study, there is a bifurcation in product formation that
is clearly dependent on the central metal ion; for the
[P2N2]Y and [P2N2]Ho fragments, dinuclear coupled
diaryl units are formed, while for the [P2N2]Yb and
[P2N2]Lu moieties, only mononuclear products can be
isolated. What links these pairs of metal ions is their
size: the octahedral Y3+ ion has a radius of 1.04 Å,
identical to Ho3+ due to the well-known lanthanide
contraction;34 Yb3+ and Lu3+ have considerably smaller
but similar radii of 1.01 and 1.00 Å, respectively.
Some additional details are worth emphasizing; upon
addition of aryllithium solutions in ether to 3a in
toluene at -78 °C, a white precipitate immediately
forms and the solution remains colorless until the ether
is evaporated. Once all of the ether is evaporated, then
the solution turns dark blue. If performed solely in
toluene, the color change occurs without solvent re-
moval, simply upon stirring at room temperature. The
fact that no color change is observed before all of the
ether is removed in the former method, and the forma-
tion of the σ-bonded THF adduct of yttrium(III), 6,
suggests that the first step of the reaction involves
formation of an ether-solvated σ-bonded aryl complex,
[P2N2]M(σ-aryl)(OEt2). The existence of this monophenyl
intermediate is supported by isolation of the ether-free
Yb derivative, 8, and by SiMe4 generation in the
synthesis of 3a via σ-bond metathesis of the alkyl
Ta ble 7. Selected Bon d Len gth s (Å) a n d An gles
(d eg) in {[P 2N2]Ho}2{µ-η6:η6′-(C6H5)2}, 3c
Ho(1)-N(1)
Ho(1)-P(1)
Ho(1)-C(25)
Ho(1)-C(27)
Ho(1)-C(29)
C(25)-C(25)
C(26)-C(27)
C(28)-C(29)
C(25)-C(30)
2.313(2)
2.9229(6)
2.688(2)
2.731(2)
2.737(2)
1.403(5)
1.363(4)
1.418(4)
1.464(3)
Ho(1)-N(2)
Ho(1)-P(2)
Ho(1)-C(26)
Ho(1)-C(28)
Ho(1)-C(30)
C(25)-C(26)
C(27)-C(28)
C(29)-C(30)
2.322(2)
2.8000(6)
2.708(2)
2.666(2)
2.718(2)
1.460(4)
1.425(4)
1.375(4)
N(1)-Ho(1)-N(2)
99.42(8)
P(1)-Ho(1)-P(2)
149.19(2)
sibility is the formation of {MI2(THF)n}2{µ-η6:η6′-
(C6H5)2} or similar species. Several complexes of this
type have been previously reported:32,33 {LaI2(THF)3}2-
(µ-η4:η4-C10H8) and {LaI2(THF)3}2(µ-η4:η4-s-cis-PhCH-
CHCHCHPh).
The reaction of the holmium chloro-bridged dimer 1c
with PhLi in toluene proceeded with a color change from
colorless to blue, and from this reaction a mixture of
blue crystals of 3c could be isolated. 3c can also be
synthesized via a σ-bond metathesis reaction of ben-
zene and the trimethylsilylmethyl derivative [P2N2]Ho-
(CH2SiMe3), 2c, in the same way as that observed for
the Y analogue.20 The solid state molecular structure
of 3c is shown in Figure 6, and selected bond lengths
and bond angles are shown in Table 7; it is isostructural
with 3a .20The structure of 3c shows a bridging biphenyl
moiety sandwiched by two [P2N2]Ho units that are η6-
coordinated to each ring. The C-C bond distance
between the two coordinated rings is 1.403(5) Å, which
is shorter than a single bond and comparable with that
previously observed in 3a (1.393(8) Å).20 The C-C bond
distances in the coordinated rings are inequivalent
[1.363(4)-1.456(5) Å], but are similar to those shown
in the yttrium analogue, 3a .20 Therefore, the two planar
rings can be considered as a biphenyl dianion. The
planarity of the rings is worthy of note, as other
polyaromatics, such as naphthalene, have been found
to undergo puckering distortions upon coordination to
complex 2a . For those larger metal ions, Y3+ and Ho3+
,
the solvated ether is easily removed to generate coor-
dinatively unsaturated intermediates that undergo
dimerization to generate dinuclear species with bridging
phenyl groups; in the case where ether is not used,
direct replacement of the bridging chlorides with bridg-
ing aryl groups would generate the same intermediate;
this is summarized in Scheme 2.
Bridging alkyl complexes of yttrium(III) are known,
for example, (Cp2Y)2(µ-Me)2, whose solid state structure
has been determined and shows a dimer in which the
two metal centers are linked together via electron-
deficient methyl bridges.35,36 Bridging phenyl groups
(34) Shannon, R. D. Acta Crystallogr. Sect. A 1976, A32, 751.
(35) Holton, J .; Lappert, M. F.; Ballard, G. H.; Pearce, R.; Atwood,
J . L.; Hunter, W. E. J . Chem. Soc., Dalton Trans. 1979, 54.
(36) Holton, J .; Lappert, M. F.; Ballard, G. H.; Pearce, R.; Atwood,
J . L.; Hunter, W. E. J . Chem. Soc., Chem. Commun. 1976, 480.
(32) Fedushkin, I. L.; Bochkarev, M. N.; Schumann, H.; Esser, L.;
Kociok-Kohn, G. J . Organomet. Chem. 1995, 489, 145.
(33) Mashima, K.; Nakamura, A. J . Chem. Soc., Dalton Trans. 1999,
3899.

1394 Organometallics, Vol. 20, No. 7, 2001
Fryzuk et al.
have precedent in the ytterbium complex Ph2(THF)Yb(µ-
Ph)3Yb(THF)3.28
more complicated processes that are yet to be fully
understood.
These coupled diaryl complexes display fluxional
behavior that can be rationalized in terms of a rapid
migration of the [P2N2]M+ fragments over the π-surface
of the formally dianionic diaryl bridging unit. This
process is analogous to that observed recently in poly-
cyclic aromatic complexes using these same metal ions
and ligand systems.21
In Scheme 2, the bridged intermediate {[P2N2]M}2-
(µ-Ar)2 then presumably rearranges to give rise to the
coupled diaryl moiety sandwiched between two [P2N2]M
units. This last step is unprecedented and is therefore
not easily rationalized. However, it is worth noting that
the stability of the trivalent oxidation state of the group
3 elements and the lanthanides is well established, and
if one assumes that the bonding in these complexes is
largely ionic, then the diaryl coupling does allow a more
efficient interaction of the charge of the aryl groups with
the [P2N2]M+ units.
One further observation deserves mention. During the
whole process of metathesis, dimerization, and diaryl
coupling, no change in the formal oxidation state of the
central metal ion is required. Generally speaking,
carbon-carbon bond forming reactions occur via reduc-
tive elimination or via migratory insertion. The above
sequence involves neither of these well-established
processes and thus represents a new kind of C-C bond
forming reaction. There is considerable precedent for
lanthanide-assisted C-C bond formation via migratory
insertion of alkenes or acetylenes into the metal-carbon
or metal-hydride bonds.38-40 The only other example
of lanthanide-assisted C-C bond formation that in-
volves neither migratory insertion nor a redox process
is the coupling of lanthanide acetylide functionalities
to yield dinuclear complexes bridged by C4R2 moi-
eties.41,42 In these examples, two formally anionic,
acetylide ligands couple to form a C-C bond; there is
some evidence that suggests that these reactions are
also size dependent. Those systems that contain the
pentamethylcyclopentadienyl ligand have clearly shown
that there is a complicated mixture of steric and
electronic factors that lead to product variation in
lanthanide-based acetylene oligomerizations and C-C
bond formation reactions.40,41
Exp er im en ta l Section
All manipulations were performed under an atmosphere of
dry oxygen-free nitrogen or argon by means of standard
Schlenk or glovebox techniques (Vacuum Atmospheres HE-
553-2 glovebox equipped with a MO-40-2H purification system
and a -40 °C freezer). Hexanes and toluene were purchased
anhydrous from Aldrich and further dried by passage through
a tower of silica and degassed by passage through a tower of
Q-5 catalyst under positive pressure of nitrogen.43 Anhydrous
diethyl ether was stored over sieves and distilled from sodium
benzophenone ketyl under argon. Nitrogen and argon were
dried and deoxygenated by passing the gases through a column
containing molecular sieves and MnO. Deuterated benzene,
toluene, tetrahydrofuran, and cyclohexane were dried by
refluxing with molten sodium or potassium metal in a sealed
vessel under partial pressure, then trap-to-trap distilled, and
freeze-pump-thaw degassed three times. NMR spectra were
recorded on either a Bruker AC-200 instrument operating at
1
200.132 MHz for H spectra, or a Bruker AMX-500 instrument
operating at 500.132 MHz for 1H spectra, or a Bruker AVA-
1
400 instrument operating at 400.132 MHz for 1H spectra. H
NMR spectra were referenced to residual protons in the
deuterated solvent and 13C NMR spectra to the 13C atoms
therein. 31P{1H} and 7Li NMR spectra were referenced to
external P(OMe)3 (141.0 ppm with respect to 85% H3PO4 at
0.0 ppm) and external LiCl (1.0 M in D2O). UV-vis spectra
were recorded using a Hewlett-Packard 8454 UV-visible
spectrophotometer and quartz cuvettes with Teflon Kontes
valves. Elemental analyses were performed by Mr. P. Borda
of this department. The compounds syn-[P2N2]Li2‚C4H8O2 and
LiCH2SiMe3 were prepared according to literature procedures.
YCl3‚6H2O, LuCl3‚6H2O, HoCl3‚6H2O, SmCl3‚6H2O, and YbCl3‚
6H2O were purchased from Strem and used as received. YCl3-
(THF)3, LuCl3(THF)3, HoCl3(THF)3, SmCl3(THF)3, and YbCl3-
(THF)3 were synthesized according to a literature procedures.44
All organic materials were purchased from Aldrich. Phenyl-
bromide, p-tolylbromide, and p-bromobiphenyl were purified
by published procedures.45 Phenyllithium, p-tolyllithium, and
p-biphenyllithium were synthesized by dissolving the corre-
sponding aryl bromides in ether and dropwise addition of
n-BuLi to the reaction mixture. They were isolated as solids
or titrated following the literature methods.46
Syn th esis of {[P 2N2]M}2(µ-Cl)2, M ) Y, Sm , Ho, Yb, Lu ,
1a -e. To a mixture of syn-[P2N2]Li2‚C4H8O2 (1.90 g, 2.98
mmol) and MCl3(THF)3 (2.98 mmol) was added toluene (60
mL). The resulting suspension was stirred at 85 °C for 18 h.
Filtration through Celite and removal of the solvent in vacuo
produced colorless or pale-colored powders. Washing with
minimal hexanes allowed isolation of pale yellow 1a (1.92 g,
98%), pale yellow 1b (1.91 g, 89%), pale pink 1c (1.81 g, 83%),
yellow 1d (2.10 g, 95%), and white 1e (2.17 g, 98%). Crystals
could be obtained by slow evaporation of a toluene solution at
-40 °C.
Su m m a r y
It has been shown that Y and Ho derivatives of the
[P2N2] macrocyclic ligand are capable of coupling phenyl
units via two routes to give sandwiched biphenyl
complexes; neither redox nor radical chemistry is in-
volved, and the mechanism is proposed to proceed via
a monophenyl species, followed by dimerization and
finally C-C bond formation. The monophenyl interme-
diate is supported by the isolation of [P2N2]Yb(C6H5).
The importance of size becomes apparent when viewing
results using Lu; it is capable of forming a biphenyl
complex via reductive means but is unable to couple Ph
units. The availability of coordination sites is clearly
significant, as no coupling occurs in more basic solvents
such as THF, where monophenyl solvent adducts result.
Larger lanthanides such as Sm and La seem to undergo
(37) Cloke, F. G. N. Chem. Soc. Rev. 1993, 17.
(38) Nolan, S. P.; Stern, D.; Marks, T. J . J . Am. Chem. Soc. 1989,
111, 7844.
(39) Molander, G. A.; Hoberg, J . O. J . Am. Chem. Soc. 1992, 114,
3123.
(40) Heeres, H. J .; Teuben, J . H. Organometallics 1991, 10, 1980.
(41) Evans, W. J .; Keyer, R. A.; Ziller, J . W. Organometallics 1993,
12, 2618.
(42) Forsyth, C. M.; Nolan, S. P.; Stern, C. L.; Marks, T. J .;
Rheingold, A. L. Organometallics 1993, 12, 3618.
(43) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J . Organometallics 1996, 15, 1518.
(44) Piers, W. E.; Shapiro, P. J .; Bunel, E. E.; Bercaw, J . E. Synlett.
1990, 74.
(45) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 3 ed.; Butterworth-Heinemann Ltd.: Oxford, 1994.
(46) J uaristi, E.; Martinez-Richa, A.; Garcia-Rivera, A.; Cruz-
Sanchez, J . S. J . Org. Chem. 1983, 48, 2603.

Carbon-Carbon Bond Formation Using Yttrium
Organometallics, Vol. 20, No. 7, 2001 1395
1a : 1H NMR (200 MHz, C6D6, 25 °C) δ 7.90 (m, 4H, o-H,
phenyl), 6.90 (m, 6H, m/ p-H, phenyl), 1.43 (AB m’s, 4H, ring
CH2), 1.12 (AB m’s, 4H, ring CH2), 0.35 (s, 12H, ring SiMe2),
0.27 (s, 12H, ring SiMe2); 31P{1H} δ -33.8 (d, J YP ) 84.0 Hz)
Anal. Calcd for C24H42ClYN2P2Si4: C, 43.86; H, 6.44; N, 4.26.
Found: C, 44.24; H, 6.57; N, 4.21.
1b: Anal. Calcd for C24H42ClSmN2P2Si4: C, 40.11; H, 5.89;
N, 3.90. Found: C, 40.67; H, 6.14; N, 3.78.
1c: Anal. Calcd for C24H42ClHoN2P2Si4: C, 39.31; H, 5.77;
N, 3.82. Found: C, 39.62; H, 5.80; N, 3.77.
Me (82 mg, 0.84 mmol) was added a mixture of toluene (10
mL) and Et2O (5 mL) at room temperature. The colorless
mixture was stirred for 30 min, after which the solvents were
evaporated, causing a brown/orange color to develop. The
brown residues were extracted into toluene (2 × 5 mL), filtered
though Celite, and evaporated to ca. 1 mL The addition of
hexanes (5 mL) and cooling to -30 °C caused 4 to deposit as
dark brown prisms (0.17 g, 31%). 4: 1H NMR (200 MHz, C7D8,
25 °C) δ 7.05 (m, 8H, o/ p-H), 6.83 (m, 4H, m-H, phenyl), 4.15
(AB m’s, 4H, CH), 1.80 (AB m’s, 8H, ring CH2), 1.05 (overlap-
ping m, 7H, ring CH2 + tolyl- CH3), 0.70 (s, 12H, ring SiMe2),
0.04 (s, 12H, ring SiMe2); 31P{1H} NMR δ -20.1 (d, J YP 85.5
Hz); 13C{1H} NMR (C7D8) δ 139.7 (s, phenyl quat. C P2N2),
136.8 (s, ipso C, bi-p-tolyl), 133.0 (s, ipso C, bi-p-tolyl), 130.5
(m, CH P2N2 phenyl), 128.6 (m, CH P2N2 phenyl), 110.5 (br.s,
CH bi-p-tolyl), 104.0 (br s, CH bi-p-tolyl), 20.3 (s, CH3 bi-p-
tolyl), 19.7 (m, CH2 P2N2 ring), 7.60 (s, SiMe2 ring), 7.10 (s,
SiMe2 ring). Anal. Calcd for C62H98N4P4Si8Y2: C, 52.23; H, 6.93;
N, 3.93. Found: C, 51.95; H, 7.13; N, 3.83. UV-vis: λmax 465
(ꢀ0 >10 000 L mol-1 cm-1).
1d : Anal. Calcd for C24H42ClYbN2P2Si4: C, 38.88; H, 5.71;
N, 3.78. Found: C, 38.98; H, 5.53; N, 3.83.
1e: 1H NMR (200 MHz, C6D6, 25 °C) δ 7.80 (m, 4H, o-H,
phenyl), 6.80 (m, 6H, m/ p-H, phenyl), 1.50 (AB m’s, 4H, ring
CH2), 1.10 (AB m’s, 4H, ring CH2), 0.30 (s, 12H, ring SiMe2),
0.17 (s, 12H, ring SiMe2); 31P{1H} δ -26.0 Anal. Calcd for
C
24H42ClLuN2P2Si4: C, 38.78; H, 5.69; N, 3.77. Found: C,
38.74; H, 5.67; N, 3.57.
Syn th esis of [P 2N2]M(CH2SiMe3), M ) Y, Lu , Ho, a n d
Yb, 2a -d . To a slurry of {[P2N2]M}2(µ-Cl)2 (0.48 mmol) in
hexanes was added a hexanes solution of LiCH2SiMe3 (0.96
mmol). The resultant cloudy solution was stirred at room
temperature for 30 min and filtered through Celite, and the
solvent was removed in vacuo to yield 2a (0.68 g, 97%) as a
colorless oil, 2b (0.74 g, 97%) as a colorless oil that partially
solidified on standing, 2c (0.77 g, 97%) as a white crystalline
solid, and 2d (0. 67 g, 87%) as a pale orange solid.
Syn th esis of {[P 2N2]Y}2{µ-η6:η6′-(C6H4-p-P h )2}, 5. To a
solution of p-biphenyllithium in Et2O (1.9 mL, 0.1 M) was
added dropwise a stirred solution of 1a (0.50 g, 0.38 mmol) in
toluene at -78 °C. On warming, a colorless solid was deposited.
The mixture was then stirred for 2 h, during which time a
slight blue color developed, which intensified upon removal of
the solvents in vacuo. The residues were extracted into
hexanes (10 mL), filtered through Celite, evaporated to ca. 2
mL, and cooled to -30 °C, yielding 5 as dark blue blocks (0.37
g, 63%). 5: 1H NMR (200 MHz, C6D6, 25 °C) δ 7.40 (m, 8H,
o-H), 7.05 (m, 12H, m/ p-H, phenyl), 6.50 (m, 4H, bisbiphenyl),
6.40 (m, 4H, bisbiphenyl), 6.20 (m, 2H, p-H, bisbiphenyl), 5.80
(m, 4H, bisbiphenyl), 5.50 (m, 4H, bisbiphenyl), 1.20 (AB m’s,
8H, ring CH2), 0.95 (AB m’s, 8H, ring CH2), 0.35 (s, 24H, ring
SiMe2), 0.17 (s, 24H, ring SiMe2); 31P{1H} NMR δ -26.87 (d,
J YP 84.1 Hz). Anal. Calcd for C72H104N4P4Si8Y2‚(toluene): C,
57.71; H, 6.87; N, 3.41. Found: C, 57.97; H, 6.97; N, 3.55. UV-
2a : 1H NMR (200 MHz, C6D6, 25 °C) δ 7.66 (m, 4H, o-H,
phenyl), 7.10 (m, 6H, m/ p-H, phenyl), 1.30 (AB m’s, 4H, ring
CH2), 1.05 (AB m’s, 4H, ring CH2), 0.48 (s, 9H, alkyl SiMe3),
0.23 (s, 12H, ring SiMe2), 0.20 (s, 12H, ring SiMe2), 0.18 (d,
2H, J YH 2.4 Hz, Y-CH2); 31P{1H} NMR δ -32.1 (d, J YP 81.0
1
Hz); H NMR (200 MHz, C6D12, 25 °C) δ 7.63 (m, 4H, o-H,
phenyl), 7.28 (m, 6H, m/ p-H, phenyl), 1.14 (AB m’s, 4H, ring
CH2), 1.11 (AB m’s, 4H, ring CH2), 0.19 (s, 9H, alkyl SiMe3),
0.09 (s, 12H, ring SiMe2), 0.08 (s, 12H, ring SiMe2), -0.21 (d,
2H, J YH 2.5 Hz, Y-CH2); 31P{1H} NMR δ -27.8 (d, J YP 83.1
Hz).
vis: λmax 668, ꢀ0 7000 L mol-1 cm-1
.
1
2b: H NMR (200 MHz, C6D6, 25 °C) δ 7.70 (m, 4H, o-H),
Syn th esis of [P 2N2]Y(C6H4-p-Me)(THF ), 6. To a mixture
of 1a (0.30 g, 0.46 mmol) and LiC6H4-p-Me (0.25 g, 0.25 mmol)
was added a mixture of toluene (10 mL) and THF (5 mL) at
room temperature. The colorless mixture was stirred for 30
min, and then the solvents were removed in vacuo. The white
residues were extracted into toluene (2 × 5 mL), filtered
though Celite, and evaporated to ca. 1 mL. The addition of
hexanes (5 mL) and cooling to -30 °C caused 6 to deposit as
white needles (0.15 g, 85%). 6: 1H NMR (200 MHz, C6D6, 25
°C) δ 8.15 (m, 4H, tolyl ring), 7.23 (m, 4H, o-H), 7.12 (m, 6H,
m/ p-H, phenyl), 3.80 (b, 4H, THF), 2.40 (s, 3H, C6H4CH3), 1.40
(AB m’s, 4H, ring CH2), 1.29 (b, 4H, THF), 1.10 (AB m’s, 4H,
ring CH2), 0.30 (s, 12H, ring SiMe2), 0.10 (s, 12H, ring SiMe2);
7.05 (m, 6H, m/ p-H, phenyl), 1.40 (AB m’s, 4H, ring CH2), 1.05
(AB m’s, 4H, ring CH2), 0.40 (s, 9H, alkyl SiMe3), 0.30 (s, 2H,
Lu-CH2), 0.23 (s, 12H, ring SiMe2), 0.20 (s, 12H, ring SiMe2);
31P{1H} NMR δ -22.36.
2c: Anal. Calcd for C28H53HoN2P2Si5: C, 42.84; H, 6.80; N,
3.57. Found: C, 43.50; H, 7.12; N, 3.44.
2d : Anal. Calcd for C28H53N2P2Si5Yb: C, 42.40; H, 6.74; N,
3.53. Found: C, 43.07; H, 7.00; N, 3.42.
Syn t h esis of {[P 2N2]M}2{µ-η6:η6′-(C6H 5)2}, M ) Y, H o,
3a ,c. To a cooled suspension of 1a or 1c (0.66 mmol) in toluene
(30 mL) was added a toluene suspension of phenyllithium (2.89
mmol, 50 mL) at -78 °C. The mixture was stirred to room
temperature and allowed to react for a further 18 h, during
which time a pale blue color developed. The reaction mixture
was filtered though Celite and the solvent removed in vacuo.
The blue residues were extracted into hexanes (25 mL), and
cooling to -30 °C yielded 3a and 3c as dark blue cubes (0.42
g, 45% and 0.70 g, 69%, respectively).
31P{1H} NMR δ -33.90 (d, J YP ) 56 Hz). Anal. Calcd for C35H57
-
Cl2N2OP2Si4Y: C, 53.55; H, 7.32; N, 3.57. Found: C, 53.27;
H, 7.12; N, 3.63.
Syn th esis of [P 2N2]Lu (C6H5)‚LiCl, 7. To a mixture of 1e
(1.00 g, 0.67 mmol) and PhLi (0.12 g, 1.42 mmol) was added
toluene (50 mL) at -78 °C. After stirring for 1 h at this
temperature, the mixture was stirred for a further 36 h at
room temperature. The solvent was removed in vacuo to afford
an off-white oil. Extraction into hexanes (30 mL) and slow
evaporation yields 7 as a white microcrystalline solid (0.72 g,
65%). 7: 1H NMR (200 MHz, C4D8O, 25 °C) δ 7.8-6.7(m, 15H,
PPh/LuPh), 1.27 (m, 8H, ring CH2), 0.88 (m, 8H, ring CH2),
0.35 (s, 3H, SiMe2), 0.33(s, 3H, SiMe2), 0.23(s, 3H, SiMe2), 0.20-
(s, 3H, SiMe2), 0.16(s, 3H, SiMe2), 0.09(s, 3H, SiMe2), 0.06(s,
3H, SiMe2), 0.00(s, 3H, SiMe2); 31P{1H} NMR δ -18.7 (s), -20.3
(s); 7Li NMR δ -0.7 (br, ν1/2 ) 15 Hz). Anal. Calcd for
1
3a : H NMR (200 MHz, C7D8, 25 °C) δ 7.28 (m, 8H, o-H),
7.05 (m, 12H, m/ p-H, phenyl), 5.10 (dd, 4H, J HH 8.5 & 6.3 Hz,
m-H, biphenyl), 4.46 (d, 4H, J HH 8.5 Hz, o-H, biphenyl), 4.18
(t, 2H, J HH 6.0 Hz, p-H, biphenyl), 1.50 (AB m’s, 8H, ring CH2),
1.20 (AB m’s, 8H, ring CH2), 0.50 (s, 24H, ring SiMe2), 0.20 (s,
24H, ring SiMe2); 31P{1H} NMR δ -26.87 (d, J YP 84.1 Hz).
Anal. Calcd for C60H94N4P4Si8Y2‚0.15(toluene): C, 52.33; H,
6.82; N, 3.93. Found: C, 52.45; H, 6.90; N, 3.73. UV-vis: λmax
615, ꢀ0 13 000 L mol-1 cm-1
.
3c: Anal. Calcd for C60H94N4P4Si8Ho2: C, 46.50; H, 6.11; N,
3.62. Found: C, 46.40; H, 6.24; N, 3.61. UV-vis: λmax 618, ꢀ0
C
30H47N2P2Si4LuLiCl: C, 43.55; H, 5.73; N, 3.39. Found: C,
14 000 L mol-1 cm-1
.
40.19; H, 6.87; N, 3.67.
Syn th esis of {[P 2N2]Lu }2{µ-η6:η6-(C6H5)2}, 3e. To a mix-
ture of 1e (1.15 g, 0.78 mmol), KC8 (0.21 g, 1.64 mmol), and
Syn t h esis of {[P 2N2]Y}2{(µ-η6:η6-C6H 4-p -Me)(C6H 4-p -
Me)}, 4. To a mixture of 1a (0.5 g, 0.38 mmol) and LiC6H4-p-

1396 Organometallics, Vol. 20, No. 7, 2001
Fryzuk et al.
biphenyl (0.24 g, 1.60 mmol) was added toluene (60 mL) and
Et2O (20 mL). The mixture was stirred for 48 h and the solvent
removed in vacuo. The resulting dark blue mixture was
extracted with toluene (50 mL) and filtered through Celite.
Slow evaporation of the solvent initially led to the isolation of
colorless needles of biphenyl and eventually dark blue prisms
of 3e (0.63 g, 52%). 3e: 1H NMR (200 MHz, C7D8, 25 °C) δ
7.28 (m, 8H, o-H), 7.06 (m, 12H, m/ p-H, phenyl), 5.04 (br, 4H,
m-H, biphenyl), 4.41 (d, 4H, J HH 8.7 Hz, o-H, biphenyl), 4.03
(br, p-H, biphenyl), 1.49 (AB m’s, 8H, ring CH2), 1.22 (AB m’s,
8H, ring CH2), 0.54 (s, 24H, ring SiMe2), 0.20 (s, 24H, ring
SiMe2); 31P{1H} NMR δ -15.4 (s). Anal. Calcd for C60H94N4P4-
Si8Lu2: C, 45.90; H, 6.04; N, 3.57. Found: C, 46.20; H, 6.32;
processed47 and corrected by Lorentz and polarization effects
and absorption (empirical: based on a three-dimensional
analysis of a symmetry-equivalent data).
The structures were solved by heavy-atom Patterson meth-
ods (1a , 5), Fourier techniques (1b), and direct methods (3c,
6, 8). All non-hydrogen atoms were refined with anisotropic
thermal parameters. Hydrogen atoms were fixed in calculated
positions with C-H ) 0.98 Å and BH ) 1.2bonded atom. Unmodi-
fied statistical weights (w ) 1/σ2(Fo)2) were employed for all
six structures. Neutral atom scattering factors and anomalous
dispersion corrections were taken from the International
Tables for X-ray Crystallography.48-50
Selected bond lengths and bond angles appear in Tables
2-7. Tables of final atomic coordinates and equivalent isotropic
thermal parameters, anisotropic thermal parameters, bond
lengths and angles, torsion angles, intermolecular contacts,
and least-squares planes are included as Supporting Informa-
tion.
N, 3.55. UV-vis: λmax 603, ꢀ0 16 000 L mol-1 cm-1
.
Syn th esis of [P 2N2]Yb(C6H5), 8. To a mixture of 1d (1.60
g, 1.08 mmol) and phenyllithium (0.40 g, 4.82 mmol) at -78
°C was added cold toluene (40 mL). The mixture was stirred
at room temperature and allowed to react for a further 18 h,
during which time a pale green color developed. The reaction
mixture was filtered though Celite and the solvent removed
in vacuo. The green residues were extracted into hexanes (25
mL), and cooling to -30 °C yielded 8 as orange cubes (0.84 g,
50%) from the green mother liquor. 8: Anal. Calcd for
Ack n ow led gm en t. We thank NSERC of Canada for
generous financial support.
Su p p or tin g In for m a tion Ava ila ble: Complete X-ray
crystallographic experimental details and tables of final atomic
coordinates and equivalent isotropic thermal parameters,
anisotropic thermal parameters, bond lengths and angles,
torsion angles, intermolecular contacts, and least-squares
planes. This material is available free of charge via the
Internet at http://pubs.acs.org.
C
30H47N2P2Si4Yb: C, 46.02; H, 6.05; N, 3.58. Found: C, 46.12;
H, 6.23; N, 3.64. A green microcrystalline material obtained
from the mother liquor was similarly characterized: Anal.
Calcd for
C60H94N4P4Si8Yb2: C, 46.02; H, 6.05; N, 3.58.
Found: C, 45.95; H, 6.29; N, 3.38.
X-r a y Cr ysta llogr a p h ic An a lyses of {[P 2N2]Y}2(µ-Cl)2,
1a , {[P 2N2]Lu }2(µ-Cl)2, 1e, {[P 2N2]Ho}2{µ-η6:η6′-(C6H5)2}, 3c,
{[P 2N2]Y}2{µ-η6:η6′-(C6H4-p-P h )2}, 5, [P 2N2]Y(C6H4-p-Me)-
(THF ), 6, a n d [P 2N2]Yb(C6H5), 8. Crystallographic data were
collected on a Rigaku/ADSC CCD diffractometer and appear
in Table 1. The final unit cell parameters were obtained by
least squares on the setting angles for 20 107 reflections with
2θ ) 4.9-64.5°, 1a , 86 527 reflections with 2θ ) 4.0-60.1°,
1e, 20 751 reflections with 2θmax ) 55.8°, 3c, 12 205 reflections
with 2θ ) 4.0-63.7°, 5, 31 264 reflections with 2θ ) 4.0-60.2°,
6, and 35 557 reflections with 2θmax ) 55.8°, 8. The data were
OM000755E
(47) teXsan Crystal Structure Analysis Package, 1.8 ed.; Molecular
Structure Corp.: The Woodlands, TX, 1996.
(48) Cromer, D. T.; Waber, J . T. International Tables for X-ray
Crystallography; Kynoch Press: Birmingham, U.K., 1974; Vol. IV, p
99.
(49) Creagh, D. C., McAuley, W. J ., Wilson, A. J . C., Eds. Interna-
tional Tables for X-ray Crystallography; Kluwer Academic Publish-
ers: Boston, MA, 1992; Vol. C, p 200.
(50) Creagh, D. C., McAuley, W. J ., Wilson, A. J . C., Eds.; Interna-
tional Tables for X-ray Crystallography; Kluwer Academic Publish-
ers: Boston, MA, 1992; Vol. C, p 219.