Arene coordination to yttrium(III) via carbon-carbon bond formation

Full text of DOI:10.1021/ja9719743

J. Am. Chem. Soc. 1997, 119, 9071-9072
Scheme 1
9071
Arene Coordination to Yttrium(III) via
Carbon-Carbon Bond Formation
Michael D. Fryzuk,* Jason B. Love, and Steven J. Rettig†
Department of Chemistry, UniVersity of British Columbia
2036 Main Mall, VancouVer, British Columbia V6T 1Z1
ReceiVed June 16, 1997
The synthesis and structural elucidation of the prototypical
arene complex, bis(benzene)chromium, Cr(η6-C6H6)2, represents
a significant chapter in the development of organometallic
chemistry.1 However, even predating this work are the inves-
tigations described by Hein in the early 1920s and 1930s which
involved reaction of CrCl3 with excess phenyl-Grignard (Ph-
MgBr). The nature of these products was not unraveled until
the 1950s, and it is now generally accepted that the Hein
reactions produce bis(arene) Cr(I) derivatives by the transforma-
tion of an η1-aryl group to a coordinated η6-arene unit;2 two of
the major components of the Hein reactions were found to be
the Cr(I) biphenyl cations [Cr(η6-C6H6)(η6-C6H5-C6H5)]+ (A)
and [Cr(η6-C6H5-C6H5)2]+ (B), formed via an aryl coupling/
reduction sequence. In the course of examining some yttrium-
(III) alkyl chemistry, we discovered a series of highly colored
arene complexes of Y(III) that apparently involve C-H activa-
tion followed by carbon-carbon bond coupling. The fact that
[P2N2] ligand in the basal plane, and the CH(SiMe3)2 unit
apical.4-7 The utilization of the less sterically hindered alkyl
moiety CH2SiMe3 resulted in the yttrium neosilyl complex
Y(CH2SiMe3)[P2N2] (3), which could only be isolated as an oil
from hexanes. As with 2, the multiplicity of the methylene
protons of the CH2SiMe3 group in the 1H NMR spectrum
suggests that 3 is monomeric in solution.8 Addition of THF to
a solution of 3 in toluene results in the formation of the THF
adduct Y(CH2SiMe3)(THF)[P2N2] (3‚THF), isolated from hex-
anes as a colorless solid.
Although the bulkier yttrium alkyl derivative 2 was found to
be quite thermally robust in aromatic solvents, the THF-free
neosilyl complex 3 was less stable and prone to the formation
of deep blue solutions. When the reaction between 1 and LiCH2-
SiMe3 was monitored in a mixture of C6D6/C6H6 at ambient
temperature by 31P{1H} NMR spectroscopy, the immediately
formed neosilyl complex 3 (δP -32.1, d, 1JYP ) 81.0 Hz) slowly
1
transformed into a new product 4 (δP -25.2, d, JYP ) 84.9
Hz); solutions of 4 are intensely blue (λmax 616 nm, ꢀo 13 000
1
L mol-1 cm-1). From the H NMR spectrum of 4, it was
evident that SiMe4 had been eliminated, presumably via an
intermolecular σ-bond metathesis reaction9 with the benzene
solvent, with new resonances observed for one aryl group per
[P2N2]Y fragment, albeit dramatically shifted upfield to 5.10
(2H), 4.46 (2H), and 4.18 ppm (1H), a shift indicative of π-type
interaction with the yttrium.10 On the basis of the NMR
spectroscopic parameters and the microanalytical data, an
empirical formula for 4 as Y(C6H5)[P2N2] was supportable. This
formulation suggested that 4 should be accessible via the direct
reaction of the chloride-bridged dimer 1 with phenyllithium;
indeed, this is the case (Scheme 1).
An X-ray diffraction study was undertaken of the deep blue
crystals isolated from hexanes. The molecular structure of 4 is
shown in Figure 1 along with selected bond lengths and bond
angles.11 What becomes immediately obvious is that 4 is a
dinuclear complex having a biphenyl unit bridging two yttrium
[P2N2] fragments with each Y[P2N2] bound in an η6-fashion to
the opposite faces of the biphenyl moiety. The bonding in this
complex can be viewed simplistically as the interaction of two
an η1-aryl group attached to yttrium is undergoing a transforma-
tion to generate an η6-arene is reminiscent of the early Hein
work; however, the arene-type complexes of yttrium(III)
reported here are significantly different than the well-studied
arene complexes of the middle and late transition metals.
As part of our interest in the coordination chemistry of the
phosphorus-containing macrocycle, syn-[P2N2] ([P2N2] )
[PhP(CH2SiMe2NSiMe2CH2)2PPh]),3 we examined the prepara-
tion of yttrium(III) complexes incorporating this new ancillary
ligand system. The chloride-bridged dimer {[P2N2]Y}2(µ-Cl)2
(1), prepared in 95% yield by reaction of syn-Li2(THF)[P2N2]
with YCl3(THF)3 in tetrahydrofuran (THF), can be converted
to mononuclear alkyl species by straightforward metathesis using
alkyllithium reagents. Addition of the very bulky LiCH(SiMe3)2
to 1 leads to the formation of Y{CH(SiMe3)2}[P2N2] (2) in 92%
yield. Both the solution spectroscopic data4 and the X-ray
(5) Giardello, M. A.; Conticello, V. P.; Brard, L.; Sabat, M.; Rheingold,
A. L.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1994, 116, 10212.
(6) Duchateau, R.; Wee, C. T. v.; Meetsma, A.; Duijen, P. T. v.; Teuben,
J. H. Organometallics 1996, 15, 2279.
(7) Schaverien, C. J.; Orpen, A. G. Inorg. Chem. 1991, 30, 4968.
(8) Lee, L.; Berg, D. J.; Einstein, F. W.; Batchelor, R. J. Organometallics
1997, 16, 1819.
(9) Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, B. J.; Nolan,
M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J. E. J. Am. Chem.
Soc. 1987, 109, 203.
(10) Elschenbroich, C.; Salzer, A. Organometallics, a concise introduc-
tion; VCH Publishers, Inc.: New York, 1992.
crystal structure indicated that 2 is monomeric, with the yttrium
atom adopting a distorted square-based pyramidal geometry, the
(11) Crystal data for 4 [C60H94N4P4Si8Y2 (fw ) 1397.82)]: blue prism,
monoclinic P21/c (No. 14), a ) 12.154(1) Å, b ) 16.398(2) Å, c ) 18.478-
(1) Å, â ) 103.436(7)°, V ) 3581.7(6) Å3, Dcalcd ) 1.296 g/cm3 (Z ) 2),
R ) 0.039, GOF ) 1.87. All other details of the crystal structure are reported
in the Supporting Information. Crystal data for 6 [C69H106N4P4Si8Y2 (fw )
1518.01)]: brown prism, monoclinic P21/c (No. 14), a ) 13.0769(6) Å, b
) 26.9793(13) Å, c ) 23.6505(2) Å, â ) 104.0335(2)°, V ) 8095.0(4)
Å3, Dcalcd ) 1.245 g/cm3 (Z ) 4), R ) 0.046, GOF ) 2.00. All other details
of the crystal structure are reported in the Supporting Information.
† Professional Officer: UBC X-ray Structural Laboratory.
(1) Huheey, J. E. Inorganic Chemistry, 3rd ed.; Harper & Row: New
York, 1983.
(2) Zeiss, H. Organometallic Chemistry; ACS Monograph Series;
American Chemical Society: Washington, DC, 1960; Vol. 147, p 380.
(3) Fryzuk, M. D.; Love, J. B.; Rettig, S. J. Chem. Comm. 1996, 2783.
(4) Haan, K. H. d.; Boer, J. L. d.; Teuben, J. H.; Spek, A. L.; Kojic-
Prodic, B.; Hays, G. R.; Huis, R. Organometallics 1986, 5, 1726.
S0002-7863(97)01974-4 CCC: $14.00 © 1997 American Chemical Society

9072 J. Am. Chem. Soc., Vol. 119, No. 38, 1997
Communications to the Editor
Figure 1. The solid state structure of {[P2N2]Y}2{η6:η6′-(C6H5)2} 4.
Selected bond lengths (Å) and angles (deg): Y(1)-N(1) 2.313(3),
Y(1)-N(2) 2.328(3), Y(1)-P(1) 2.812(1), Y(1)-P(2) 2.931(1), Y(1)-
C(25) 2.699(4), Y(1)-C(26) 2.708(4), Y(1)-C(27) 2.733(4), Y(1)-
C(28) 2.675(4), Y(1)-C(29) 2.738(4), Y(1)-C(30) 2.722(4), C(25)-
C(26) 1.453(6), C(25)-C(25)* 1.393(8), C(25)-C(30) 1.456(5), C(26)-
C(27) 1.378(6), C(27)-C(28) 1.415(6), C(28)-C(29) 1.404(6), C(29)-
C(30) 1.359(6); N(1)-Y(1)-N(2) 99.2(1), P(1)-Y(1)-P(2) 149.29(4).
Figure 2. The solid state structure of {[P2N2]Y}2{η6:η6-C6H4Me-
4(C6H4Me-4′)} 6. Selected bond lengths (Å) and angles (deg): Y(1)-
N(1) 2.330(3), Y(1)-N(2) 2.353(3), Y(1)-P(1) 2.8750(11), Y(1)-P(2)
2.8513(11), Y(1)-C(49) 2.692(4), Y(1)-C(50) 2.661(4), Y(1)-C(51)
2.699(4), Y(1)-C(52) 2.693(4), Y(1)-C(53) 2.629(4), Y(1)-C(54)
2.680(4), Y(2)-Cav 2.699, C(49)-C(50) 1.399(5), C(49)-C(54) 1.431-
(5), C(49)-C(55) 1.481(5), C(50)-C(51) 1.508(5), C(51)-C(52) 1.414-
(5), C(52)-C(53) 1.394(5), C(53)-C(54) 1.508(5); C-Cav (uncoordi-
nated ring) 1.384(5); N(1)-Y(1)-N(2) 100.84(11), P(1)-Y(1)-P(2)
151.08(4); inter-ring twist angle 38.2°.
yttrium(III) [P2N2] fragments with a biphenyl dianion [Ph-
Ph]2-. The biphenyl dianion in 4 is essentially planar. The
bond distance between the two aryl groups (C25-C25*) is
1.393(8) Å, indicative of a C-C double bond; the other bond
lengths in the biphenyl unit clearly show short C-C bonds
except for those directly attached to the newly formed bond.
There is no evidence for ring slippage since all of the Y-C
bond distances are similar and range from 2.675(4) to 2.738(4)
Å. Also, there is a slight boat conformation in each aryl ring
of 4, although markedly less pronounced than the 25° deviation
presumed to be masked beneath the broadened ligand resonances
in the 0-2 ppm region. Thus, at low temperatures in solution,
a similar structure to that observed in the solid state is observed
but at higher temperatures, the two Y[P2N2] fragments migrate
from one p-tolyl group to the other on the NMR time scale.
Such a fluxional process is remarkable given the nature of the
different distortions in the biaryl unit observed in the solid state
structures of both 4 and 6, particularly since both structures are
presumably involved in this dynamic behavior.
In all three cases described above, a rearrangement from an
unobserved yttrium derivative having a σ-bound aryl group to
a dinuclear complex with both yttrium centers π-bound has
occurred. We speculate that the key intermediate is a dimer
with bridging aryl groups that couple to generate the observed
π-bound species. In contrast to the Hein chemistry discussed
above, the biaryl couplings reported here do not involve any
formal redox chemistry, since the yttrium center starts as Y(III)
and finishes in the same oxidation level. This contrasts other
lanthanoid arene systems that have been prepared via reductive
sequences14-16 or by metal vapor techniques.17 Phenyl groups
bridging lanthanoid metals are not well established;18 a few ex-
amples of mononuclear σ-aryl complexes are known for yttrium
but few have been structurally characterized.19-21 Reactivity
studies of these dinuclear bis(arene) complexes are underway.
2-
from planarity of the C6H6 ligand for the complex [K(18-
crown-6)][La{η5-1,3-C5H3(SiMe3)2}2)(C6H6)].12 The biphenyl
dianion has been previously structurally characterized in the
complex [(C5Me5)Fe]2(µ-η5:η5-biphenyl).13 Unlike 4, an η5-
coordination mode of the phenyl rings is adopted with a
significant 25° angle between the ring planes.
Other aryllithium reagents can be used; for example, the
reaction of m-tolyllithium with 1 also generates deep blue
solutions from which blue crystals of 5 could be isolated in
1
modest yield. The H NMR spectral data suggest an unsym-
metrical geometry, since all eight protons of the bi-m-tolyl
fragment are inequivalent; the UV-vis spectrum is virtually
identical to 4. However, the reaction of p-tolyllithium with 1
generated a dark orange-brown solution, from which dark brown
1
crystals of 6 could be isolated in good yield. The H NMR
spectrum indicated the presence of a π-bound p-Me-C6H4 unit
due to the upfield shift of these aromatic resonances: a tightly
coupled AB doublet of doublets was observed centred at 4.15
ppm. The solid state molecular structure (Figure 2) showed
that a bridging bi-p-tolyl unit was present; however, in this
complex both yttrium centers were found to be sandwiching
one tolyl group.11 The bond lengths in the sandwiched tolyl
group are indicative of a bis(allyl) distortion while the unco-
ordinated tolyl moiety is essentially unaffected by the presence
Acknowledgment. NSERC of Canada is gratefully acknowledged
for financial support of this work.
Supporting Information Available: Detailed experimental pro-
cedures, spectroscopic data, and X-ray structural details for 4 and 6
(49 pages). See any current masthead page for ordering and Internet
access instructions.
1
JA9719743
of the two proximate Y(III) centers. The aforementioned H
NMR spectral data are inconsistent with the solid state structure,
since only one type of p-tolyl group was observed; a fluxional
process was indicated since as the temperature was lowered,
broadening of all the signals was observed, and new broad peaks
grew in around 6-7 ppm at -95 °C suggestive of an uncoor-
dinated arene. The peaks due to the sandwiched arene are
(14) Cotton, F. A.; Schwotzer, W. J. Am. Chem. Soc. 1986, 108, 4657.
(15) Cotton, F. A.; Schwotzer, W. Organometallics 1987, 6, 1275.
(16) Deacon, J. B.; Shen, Q. J. Organomet. Chem. 1996, 511, 1.
(17) Cloke, F. G. N. Chem. Soc. ReV. 1993, 1993, 17.
(18) Schumann, H.; Meese-Markscheffel, J. A.; Esser, L. Chem. ReV.
1995, 95, 865.
(19) Booij, M.; Kiers, N. H.; Meetsma, A.; Teuben, J. H.; Smeets, W. J.
J.; Spek, A. L. Organometallics 1989, 8, 2454.
(12) Cassani, M. C.; Gun’ko, Y. K.; Hitchcock, P. B.; Lappert, M. F.
Chem. Commun. 1996, 1987.
(13) Lacoste, M.; Rabaa, H.; Astruc, D.; Ardoin, N.; Varret, F.; Saillard,
J.-Y. J. Am. Chem. Soc. 1990, 112, 9458.
(20) Booij, M.; Deelman, B.-J.; Duchateau, R.; Postma, D. S.; Meetsma,
A.; Teuben, J. H. Organometallics 1993, 12, 3531.
(21) Deelman, B.-J.; Stevels, W. M.; Teuben, J. H.; Lakin, M. T.; Spek,
A. L. Organometallics 1994, 13, 3881.