Low-coordinate organoyttrium complexes supported by β-diketiminato ligands

Article abstract of DOI:10.1021/om900082d

Several organoyttrium complexes stabilized by β-diketiminato ligands (Ar)NC(R)CHC(R)N(Ar) (Ar = 2,6-tPr₂CoH₃; R = CH ₃ (ligand a), R = ^tBu (ligand b)) have been prepared. Ligand-supported yttrium diiodides LYI₂(THF)_n were alkylated with organolithium or potassium reagents, yielding low-coordinate bis-alkyl derivatives. Several of these compounds have been characterized by X-ray crystallography, and a discussion of these structures in comparison to similar scandium complexes is presented. An out-ofplane bonding mode is observed in the solid state, analogous to that seen in scandium bis-alkyls, and spectroscopic studies reveal that fluxional behavior in solution is also comparable to that observed for the scandium species. The bis-alkyls LYR ₂ are susceptible to metalative alkane elimination at room temperature in solution. Activation of (Liga)YR₂ with [HNMe ₂Ph][B(C₆F₅)₄] generates alkyl cations stabilized with η⁶-arene-bound NMe₂Ph. This unique coordination mode was studied via ID ¹H, ¹³C, and ¹⁵N NMR and 2D ROESY spectroscopy and appears to stabilize the alkyl cations against metalative alkane elimination.

Full text of DOI:10.1021/om900082d

3012
Organometallics 2009, 28, 3012–3020
Low-Coordinate Organoyttrium Complexes Supported by
ꢀ-Diketiminato Ligands
Alyson L. Kenward, Warren E. Piers,* and Masood Parvez
Department of Chemistry, UniVersity of Calgary, 2500 UniVersity DriVe NW, Calgary,
Alberta, T2N 1N4, Canada
ReceiVed February 3, 2009
Several organoyttrium complexes stabilized by ꢀ-diketiminato ligands (Ar)NC(R)CHC(R)N(Ar) (Ar
) 2,6-iPr2C6H3; R ) CH3 (ligand a), R ) iBu (ligand b)) have been prepared. Ligand-supported yttrium
diiodides LYI2(THF)n were alkylated with organolithium or potassium reagents, yielding low-coordinate
bis-alkyl derivatives. Several of these compounds have been characterized by X-ray crystallography, and
a discussion of these structures in comparison to similar scandium complexes is presented. An out-of-
plane bonding mode is observed in the solid state, analogous to that seen in scandium bis-alkyls, and
spectroscopic studies reveal that fluxional behavior in solution is also comparable to that observed for
the scandium species. The bis-alkyls LYR2 are susceptible to metalative alkane elimination at room
temperature in solution. Activation of (Liga)YR2 with [HNMe2Ph][B(C6F5)4] generates alkyl cations
stabilized with η6-arene-bound NMe2Ph. This unique coordination mode was studied via 1D 1H, 13C, and
15N NMR and 2D ROESY spectroscopy and appears to stabilize the alkyl cations against metalative
alkane elimination.
ization.6 While the bis-cyclopentadienyl framework has been
Introduction
exploited extensively in group 3 chemistry,3a,7 in recent years
Low-coordinate, base-free group 3 alkyl complexes are of
current interest for their utility as highly active catalysts for
olefin polymerization,1,2 hydroamination,3-5 and alkyne dimer-
there has been considerable focus on the design and use of
monoanionic ancillary ligands. The design of sterically bulky
and chelating ligands that afford complexes of the type LMR2
(M ) Sc, Y) are of particular interest because they provide a
synthetic avenue into group 3 alkyl cations that can be compared
to metallocenium group 4 cationic polymerization catalysts.8
* Corresponding author. E-mail: wpiers@ucalgary.ca.
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10.1021/om900082d CCC: $40.75
2009 American Chemical Society
Publication on Web 04/21/2009

Low-Coordinate Organoyttrium Complexes
Organometallics, Vol. 28, No. 10, 2009 3013
Scheme 1
The ꢀ-diketiminato, or “nacnac”, ligand is an attractive choice
for stabilizing numerous transition metal and main group
complexes9 because it exhibits both steric and electronic10
tunability and its successful application in scandium chemistry,11
such as in I, makes it an obvious choice for investigating
analogous yttrium complexes.12 Given the considerable size
differential between scandium and yttrium (ionic radii for Sc3+
) 0.745 Å, Y3+ ) 0.90 Å), the propensity for complex
dimerization, ligand redistribution, and the formation of “ate”
complexes is typically of greater concern in organoyttrium
chemistry, and thus ꢀ-diketiminato yttrium complexes of
monohapto alkyls have previously eluded isolation.
Herein we describe the synthesis of a series of neutral and
cationic organoyttrium complexes supported by the bulky
ꢀ-diketiminate ligands. The two ligands employed have 2,6-
iPr2C6H3 aryl groups on nitrogen and either CH3 (a series) or
tBu (b series) as backbone substituents. Although decomposition
via ligand metalation has been observed with this ligand
ancillary,10a many of the complexes reported here exhibit
remarkable thermal stability and represent examples of low-
coordinate base-free organoyttrium compounds.
Arnold.11b In contrast, the bulkier ArNC(tBu)CHC(tBu)NAr
ligand required more forcing conditions for installation onto
yttrium, where reaction of the potassium salt of the ligand15
with YI3(THF)3.5 for 1.5 h at 90 °C in toluene gave 1b in 87%
1
yield. The H and 13C NMR spectra of 1a reveal that one
molecule of THF remains coordinated to yttrium, whereas the
backbone tBu groups in 1b force greater steric bulk toward the
metal center and consequently discourage THF retention in this
compound.16 Both 1a and 1b display an otherwise symmetrical
pattern in the 1H NMR spectrum, which suggests these
complexes are fluxional at room temperature, similar to
analogous ꢀ-diketiminato scandium dichloride complexes,10a
although here the dynamic behavior was not probed further.
The solid-state structure of 1b (Figure S1) reveals the dimeric
nature of this complex in the solid state.
Results and Discussion
Neutral Yttrium Bis-alkyls. In order to access yttrium
complexes supported by the ꢀ-diketiminate ligand framework,
a salt metathesis approach was employed for ligand attachment;
YI3(THF)3.5 was used exclusively, as it exhibits greater solubility
in common organic solvents. Furthermore, in order to avoid
complications arising from persistent lithium iodide,13 potassium
salts of two nacnac ligands,11b prepared by reaction of proteo-
ligands with excess KH, were used as starting materials.
Reaction of the potassium reagent {ArNC(CH3)CHC(CH3)-
NAr}K, where Ar ) 2,6-iPr2C6H3, with a stoichiometric amount
Contrary to what was reported by Liddle and Arnold, we
found that these ꢀ-diketiminato yttrium diiodide complexes can
conveniently be alkylated with organolithium or potassium
reagents to give yttrium bis-alkyl complexes (Scheme 1). Key
to their isolation is a timely workup prior to product losses
through metalative loss of alkane.
14
of YI3(THF)3.5 overnight in THF affords 1a in 63% yield
(Scheme 1), analogous results to those reported by Liddle and
When the backbone substituent is the less bulkyl methyl
group, as in series “a”, THF can remain coordinated at the metal
center upon alkylation. For example, reaction of 1a with 2 equiv
of benzyl potassium in THF yields dibenzyl complex 2a, in
which 1 equiv of THF is retained. X-ray quality crystals of 2a
were grown from a cold toluene solution, and the structure is
shown in Figure 1. Moderate steric crowding around the metal
center causes the yttrium center to tilt 0.735(3) Å out of the
ligand plane, resulting in a distorted trigonal bipyramidal
geometry at yttrium. Furthermore, one benzyl ligand is coor-
dinatedinanη2-bindingfashion(Vidainfra),withaY-C(1)-C(32)
bond angle of 92.27(16)° and Y-C(1) and Y-C(32) bond
lengths of 2.454(3) and 2.903(13) Å, respectively. The Y-O(1)
bond length (2.3973(19) Å) is within the range of known THF
adducts of similar yttrium bis-alkyl complexes,11c,17 but it is
toward the longer end of this group.
(8) For reviews see: (a) Piers, W. E.; Emslie, D. J. H. Coord. Chem.
ReV. 2002, 233, 131. (b) Edelmann, F. T.; Freckmann, D. M. M.; Schumann,
H. Chem. ReV. 2002, 102, 1851. (c) Mountford, P.; Ward, B. D. Chem.
Commun. 2003, 1797.
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J. Am. Chem. Soc. 2002, 124, 14284. (b) Laitar, D. S.; Mathison, C. J. N.;
Davis, W. M.; Sadighi, J. P. Inorg. Chem. 2003, 42, 7354.
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Hayes, P. G.; Piers, W. E.; McDonald, R. J. Am. Chem. Soc. 2002, 124,
2132. (c) Hayes, P. G.; Piers, W. E.; Parvez, M. J. Am. Chem. Soc. 2003,
125, 5622. (d) Basuli, F.; Tomaszewski, J.; Huffman, J. C.; Mindiola, D. J.
Organometallics 2003, 22, 4705. (e) Neculai, A. M.; Roesky, H. W.;
Neculai, D.; Magull, J. Organometallics 2001, 20, 5501.
(12) (a) Sa´nchez-Barba, L. F.; Hughes, D. L.; Humphrey, S. M.;
Bochmann, M. Organometallics 2005, 24, 3792. (b) Liddle, S. T.; Arnold,
P. L. Dalton Trans. 2007, 3305. (c) Hayes, P. G.; Welch, G. C.; Emslie,
D. J. H.; Noack, C. L.; Piers, W. E.; Parvez, M. Organometallics 2003, 22,
1577. (d) Shang, X. M.; Liu, X. L.; Cui, D. M. J. Polym. Sci., Part A:
Polym. Chem. 2007, 45, 5662. (e) Zhang, Z.; Cui, D.; Liu, X. J. Polym.
Sci., Part A: Polym. Chem. 2008, 46, 6810.
(15) See Supporting Information for experimental details and X-ray
structure of 1b.
(16) Budzelaar, P. H. M.; van Oort, A. B.; Orpen, A. G. Eur. J. Inorg.
Chem. 1998, 1485.
(17) Emslie, D. J. H.; Piers, W. E.; Parvez, M.; McDonald, R.
Organometallics 2002, 21, 4226.
(13) Cloke, F. G. N.; Elvidge, B. R.; Hitchcock, P. B.; Lamarche,
V. M. E. Dalton Trans. 2002, 2413.
(14) Izod, K.; Liddle, S. T.; Clegg, W. Inorg. Chem. 2004, 43, 214.

3014 Organometallics, Vol. 28, No. 10, 2009
Kenward et al.
Figure 1. Solid-state structure of 2a shown as 50% ellipsoids.
Hydrogen atoms are omitted for clarity. Selected bond lengths
(Å): Y(1)-N(1), 2.408(2); Y(1)-N(2), 2.333(2); Y(1)-O(1),
2.3973(19);Y(1)-C(1),2.454(3);Y(1)-C(2),2.450(3);Y(1)-C(32),
2.903(3); Y(1)-N2C3 plane, 0.735(3). Selected bond angles
(deg): C(1)-Y(1)-C(2), 128.94(10); N(1)-Y(1)-C(1), 93.14(9);
N(1)-Y(1)-C(2), 96.12(9); N(2)-Y(1)-C(1), 115.00(8); N(2)-
Y(1)-C(2), 116.05(9); N(1)-Y(1)-N(2), 80.65(7); N(1)-Y(1)-
O(1), 175.71(6); Y(1)-C(1)-C(32), 92.27(16); Y(1)-C(2)-C(38),
107.43(17).
Figure 2. Solid-state structure of 2b shown as 50% ellipsoids.
Hydrogen atoms are omitted for clarity. Selected bond lengths (Å):
Y(1)-N(1), 2.273(3); Y(1)-N(2), 2.258(3); Y(1)-C(1), 2.392(4);
C(1)-Y(1)-C(2), 124.29(15); N(1)-Y(1)-C(1), 107.51(14); N(1)-
Y(1)-C(2), 124.82(1); N(2)-Y(1)-C(1), 95.21(13); N(2)-Y(1)-
C(2), 103.63(11); N(1)-Y(1)-N(2), 88.03(10); Y(1)-C(1)-C(38),
91.4(2).
In contrast, dibenzyl complex 2b, derived from reaction of
1b and benzyl potassium, remains free of coordinating base,
even when THF is the reaction solvent. The monomeric and
base-free nature of 2b attests to the more pronounced steric
protection afforded by the tert-butyl ligand. Single-crystal X-ray
diffraction of 2b (Figure 2) indicates that the metal lies 1.309(4)
Å outside the ligand plane, rendering the benzyl substituents
diastereotopic. The endo benzyl group, which lies down and
under the ligand plane,11a coordinates only through the benzylic
carbon, whereas the exo benzyl group, directed up and out from
the ligand, is coordinated through an η2-binding interaction. The
acute Y-C(1)-C(38) bond angle (91.4(2)°) and short Y-C(1)
and Y-C(38) bond distances of 2.391(4) and 2.823(4) Å,
respectively, are comparable to those found in known lanthanide
complexes containing η2-bound benzyl ligands,18,19 while the
long Y-C(39) ortho bond distance of 3.225(5) Å is outside
the accepted range for η3-bound benzyl ligands.15,20 In previ-
ously reported scandium mixed bis-alkyl complexes, the larger
substituent preferentially occupied the more open exo position,10a
so the position of the η2-bound benzyl ligand in 2b is in
agreement with this previous work. Interestingly, however, the
scandium congener of 2b does not display any mulit-hapto
binding of either benzyl group; the larger yttrium ionic radius
is believed to be responsible for the extra coordination in the
present case.
While the solid-state structure of 2b demonstrates out-of-
plane bonding of yttrium to the ligand, room-temperature
solution NMR spectra are consistent with a symmetrical in-
plane C2V solution structure, indicative of the fluxional out-of-
plane exchange elucidated for known ꢀ-diketiminato scandium
alkyl complexes.11a At lower temperatures, this “ligand-flip”
process can be slowed sufficiently so that the less symmetrical
(Cs) species identified in the solid state can be observed on the
NMR time scale, where the diastereotopic alkyl groups can be
distinguished. The barrier for this exchange for 2b at 243 K is
11.4(3) kcal mol-1. The yttrium bis-alkyls reported here have
barriers for “ligand-flip” that are slightly smaller than those
previously determined for the scandium bis-alkyls.11a This
observation is rationalized on the basis of the larger ionic radius
for yttrium; as a consequence, the metal sits further from the
ligand, facilitating exchange through a congested planar (C2V)
intermediate.
In 2b, the benzyl methylene 13C NMR resonance found at
56.4 ppm (1JCH ) 122 Hz) suggests that both benzyl ligands
exhibit average η1-binding in solution.16 Variable-temperature
experiments were conducted below the coalescence temperature
of ligand-flip in order to evaluate the possibility of significant
η2-binding of a benzyl group at lower temperatures in solution.
At 203 K in toluene-d8, in the slow-exchange regime for ligand-
flip, two distinct 13C NMR resonances are found, at 57.6 ppm
(1JCH) 125 Hz) and 52.3 ppm (1JCH ) 122 Hz), which indicates
that even at reduced temperatures the dominant mode of benzyl
coordination in solution is likely via η1-interactions.
(18) For examples of η2-bound benzyl ligands to Ln: Bambirra, S.;
Meetsma, A.; Hessen, B. Organometallics 2006, 25, 3454.
(19) For examples of η2-bound benzyl ligands to Zr: (a) Latesky, S. L.;
McMullen, A. K.; Niccolai, G. P.; Rothwell, I. P.; Huffman, J. C.
Organometallics 1985, 4, 902. (b) Jordan, R. F.; Lapointe, R. E.; Bajgur,
C. S.; Echols, S. F.; Willett, R. J. Am. Chem. Soc. 1987, 109, 4111. (c)
Jordan, R. F.; Lapoint, R. E.; Baenziger, N.; Hinch, G. D. Organometallics
1990, 9, 1539. (d) Bochmann, M.; Lancaster, S. J. Organometallics 1993,
12, 633.
Diiodide 1a can also be reacted with LiCH2SiMe2Ph to form
bis-alkyl 3a, and here the sizable alkyl groups preclude THF
coordination. The solid-state structure of 3a is shown in Figure
3 and is a member of a rare class2i of four-coordinate yttrium
bis-alkyl complexes unsupported by multihapto or agostic
binding. The geometry at yttrium is only slightly distorted from
(20) For examples of η3-bound benzyl ligands to Ln, see: (a) Booij,
M.; Meetsma, A.; Teuben, J. H. Organometallics 1991, 10, 3246. (b) Evans,
W. J.; Perotti, J. M.; Ziller, J. W. J. Am. Chem. Soc. 2005, 127, 3894. (c)
Bambirra, S.; Brandsma, M. J. R.; Brussee, E. A. C.; Meetsma, A.; Hessen,
B.; Teuben, J. H. Organometallics 2000, 19, 3197.

Low-Coordinate Organoyttrium Complexes
Organometallics, Vol. 28, No. 10, 2009 3015
Figure 4. Partial 1H NMR spectra of 4a (300 MHz, 243 K) in d8-
toluene depicting the Y-CH2 region.
in 3a the yttrium atom sits 1.240(4) Å out of the ligand plane,
the nearly planar configuration of the N-C-C-C-N ligand
backbone and the lack of puckering of C(5) toward the metal
suggests that σ-donation from N(1) and N(2) is the only
significant electronic contribution from the ligand. This is in
agreement with the analysis of known ꢀ-diketiminato scandium
complexes,11a and thus in these yttrium complexes the position-
ing of the metal outside of the ligand plane is instead driven by
steric interactions of the N-aryl groups with the alkyl substituents.
Although bis-alkyl 3b was observed when 1b was reacted
with 2 equiv of LiCH2SiMe2Ph on the NMR scale, it was not
isolable upon scale-up due to its rapid decomposition via
metalative decay (Vida infra), which is driven by the increased
steric congestion imposed by the ligand.11a,25,26
Figure 3. Solid-state structure of 3a shown as 50% ellipsoids.
Hydrogen atoms are omitted for clarity. Selected bond lengths (Å):
Y(1)-N(1), 2.272(2); Y(1)-N(2), 2.274(2); Y(1)-C(1), 2.365(3);
Y(1)-C(2), 2.396(3); Y(1)-N2C3 plane, 1.240(4). Selected bond
angles (deg): C(1)-Y(1)-C(2), 116.01(10); N(1)-Y(1)-C(1),
104.15(10); N(1)-Y(1)-C(2), 117.00(10); N(2)-Y(1)-C(1),
109.56(10); N(2)-Y(1)-C(2), 119.07(10); N(1)-Y(1)-N(2),
86.13(9); Y(1)-C(1)-Si(1), 129.46(16).
Diiodide complexes 1 have also been alkylated with methyl
potassium in order to generate yttrium dimethyl complexes 4
(Scheme 1). Although solid-state structural analyses of 4 have
yet to be obtained, the solution NMR studies (1H and 13C NMR)
presented herein, along with elemental analysis, corroborate the
proposed structures of both 4a and 4b.
tetrahedral, and there is no evidence of any ꢀ-Si-C interaction,
as indicated by the 29Si NMR resonance at -7.2 ppm;21
furthermore, the closest of the ꢀ-Si-C contacts, Y(1)-C(33),
is 4.241(4) Å, and this is too long to be considered for any
electronic stabilization.
Variable-temperature 1H NMR experiments revealed that 4a
is dimeric, as the broad Y-CH3 resonance at -0.12 ppm splits
into one doublet (2JYH ) 2.10 Hz) and one triplet (2JYH ) 2.45
Hz) at 243 K, indicating that there are two terminal methyl
groups and two bridging methyl groups within the dimer,
respectively (see Figure 4). This dimeric structure again brings
to light the ligand scaffold’s steric influence on the molecular
structure. Although THF coordination is precluded in 4a, unlike
in 2a, the open coordination sphere around the metal center
(along with the relatively smaller methyl functionality) facilitates
dimerization. Interestingly, even at low temperatures, only one
isomer of dimer 4a is observed in solution, which contrasts the
behavior observed in dimeric ꢀ-diketiminato scandium telluro-
lates, where endo-endo, endo-exo, and exo-endo dimeric isomers
were characterized in solution.27 While it appears that 4a exists
as only one isomer, it is also possible that ligand-flip to exchange
isomers is still facile in the temperature regime monitored.
At room temperature, dimethyl complex 4b exhibits a broad
resonance at -0.37 ppm for the Y-CH3 protons, and this signal
does not sharpen even as the temperature is lowered to -30
°C, and the 13C NMR spectrum at this temperature also reveals
a broad peak for Y-CH3. With this ambiguous NMR data and
lack of X-ray analysis, the monomeric nature of 4b cannot be
confirmed; however, the high solubility of this complex at room
Although the ꢀ-diketiminato ligand can potentially donate
up to 10 electrons to the metal center, according to DFT
investigations by Tolman and Solomon,22 most of the bonding
interactions take place through in-plane σ-bonding via the
nitrogen lone pairs. Although examples of further donation from
the ligand backbone in an κ3-manner are known for Ti and Zr,23
as well as Cr24 complexes, these manifest in significant
puckering of the backbone carbon (C5) toward the metal. While
(21) (a) Bolton, P. D.; Clot, E.; Adams, N.; Dubberley, S. R.; Cowley,
A. R.; Mountford, P. Organometallics 2006, 25, 2806. (b) Klooster, W. T.;
Brammer, L.; Shaverien, C. J.; Budzelaar, P. H. M. J. Am. Chem. Soc.
1999, 121, 1381. (c) Clot, E.; Eisenstein, O. Struct. Bonding 2004, 113, 1.
(d) Tredget, C. S.; Clot, E.; Mountford, P. Organometallics 2008, 27, 3458.
(e) Eisch, J. J.; Piotrowski, A. M.; Brownstein, S. K.; Gabe, E. J.; Lee,
F. L. J. Am. Chem. Soc. 1985, 107, 7219. (f) Horton, A. D.; Orpen, A. G.
Organometallics 1991, 10, 3910. (g) Clark, D. L.; Gordon, J. C.; Hay, P. J.;
Martin, R. L.; Poli, R. Organometallics 2002, 21, 5000. (h) Brady, E. D.;
Clark, D. L.; Gordon, J. C.; Hay, P. J.; Keogh, D. W.; Poli, R.; Scott, B. L.;
Watkin, J. G. Inorg. Chem. 2003, 42, 6682. (i) Perrin, L.; Maron, L.;
Eisenstein, O.; Lappert, M. F. New J. Chem. 2003, 43, 1782. (j) Scherer,
W.; McGrady, G. S. Angew. Chem., Int. Ed. 2003, 43, 1782. (k) Nikonov,
G. J. Organomet. Chem. 2001, 635, 24.
(22) Randall, D. W.; DeBeer George, S.; Holland, P. L.; Hedman, B.;
Hodgson, K. O.; Tolman, W. B.; Solomon, E. L. J. Am. Chem. Soc. 2000,
122, 11632.
(23) (a) Kakaliou, L.; Scanlon, W. J.; Qian, B.; Back, S. W.; Smith,
M. R., III.; Motry, D. H. Inorg. Chem. 1999, 38, 5964. (b) Rahim, M.;
Taylor, N. J.; Xin, S.; Collins, S. Organometallics 1998, 17, 1315. (c)
Hitchcock, P. B.; Lappert, M. F.; Liu, D.-S. J. Chem. Soc., Chem. Commun.
1994, 2637. (d) Lappert, M. F.; Liu, D. S. J. Organomet. Chem. 1995, 500,
203. (e) Vollmerhaus, R.; Rahim, M.; Tomaszewski, R.; Xin, S.; Taylor,
N. J.; Collins, S. Organometallics 2000, 19, 2161.
(25) (a) Constable, E. Polyhedron 1984, 3, 1037. (b) Ibers, J. A.;
DiCosimo, R.; Whitesides, G. M. Organometallics 1982, 1, 13.
(26) Conroy, K. D.; Piers, W. E.; Parvez, M. J. Organomet. Chem. 2008,
693, 834.
(24) MacAdams, L. A.; Kim, W.-K.; Liable-Sands, L. M.; Guzei, I. A.;
Rheingold, A.; Theopold, K. H. Organometallics 2002, 21, 952.
(27) Knight, L. K.; Piers, W. E.; McDonald, R. Chem.sEur. J. 2000,
6, 4322.

3016 Organometallics, Vol. 28, No. 10, 2009
Kenward et al.
Table 1. Half-Lives and kobsd(calculated) for Comparable Metalation
Scheme 2
Reactions
temperature and its propensity to metalation support the
assignment that the structure is indeed monomeric.
complex
temperature (K)
t1/2 (h)
kobsd (s-1
)
3a
2b
4b
320
298
298
377
333
333
7.33
6.90
0.28
5.46
11.7
0.53
1.89(4) × 10-3
1.98(4) × 10-3
4.90(2) × 10-2
2.54(2) × 10-3
1.65 × 10-5
While this new family of yttrium bis-alkyl complexes exhibits
moderate thermal stability in aromatic solvents, they are
susceptible to intramolecular metalative alkane elimination
whereby one alkyl moiety is lost via σ-bond metathesis with
one of the C-H bonds of the N-aryl isopropyl methyl groups,
producing a C1 symmetric yttrium alkyl product with a tridentate
ligand structure (Scheme 2). This mode of clean decomposition
is a well-documented process for ꢀ-diketiminato scandium
complexes,10a although the yttrium complexes decompose more
readily.
LMeSc(CH2SiMe3)2
LtBuSc(CH2Ph)2
LtBuSc(CH3)2
3.59 × 10-4
For example, while 3a remains largely unaffected (5%
metalation) overnight at room temperature in solution, at
elevated temperatures it cleanly eliminates Me3SiPh to form 5a.
The dimeric structure of metalate 5a (Figure 5) is unique among
ꢀ-diketiminato cyclometalated species. Intramolecular C-H
i
activation occurs at one of the Pr-CH3 N-aryl groups, and the
resulting exo methylene group bridges two yttrium centers. The
“intermolecular” Y(1)-C(28′) bond length (2.474(2) Å) is
shorter than the intramolecular bond distance, where Y(1)-C(28)
is 2.573(2) Å. While this is longer than the Y(1)-C(1) bond at
2.374(2) Å, they are still within the reasonable bonding range
for this type of molecule. Within the Y(1)-C(28)-Y(1′)-C(28′)
metallacyle, the C-Y-C bond angle is 91.86(7)°, while the
Y-C-Y bond angle is 88.13(7)°. Looking at the asymmetric
unit of the 5a dimer, Figure 5, the large open face at the metal
center reveals the propensity for this metalated product to
dimerize.
1
The H NMR spectrum of 5a in d8-THF (where the dimeric
Figure 5. Solid-state structure of 5a shown as 50% ellipsoids.
Hydrogen atoms, noncyclometalated N-aryl groups, and -SiMe2Ph
fragments are removed for clarity. Selected bond lengths (Å):
Y(1)-N(1), 2.3756(19); Y(1)-N(2), 2.2960(19); Y(1)-C(1),
2.374(2); Y(1)-C(28), 2.573(2); Y(1)-C(28′), 2.474(2). Selected
bond angles (deg): N(1)-Y(1)-N(2), 80.46(7); N(1)-Y(1)-C(1),
106.13(8); N(2)-Y(1)-C(1), 127.90(8); N(1)-Y(1)-C(28), 163.34-
(7); N(1)-Y(1)-C(28′), 87.66(7); N(2)-Y(1)-C(28), 86.14(7);
N(2)-Y(1)-C(28), 124.54(8); Y(1)-C(1)-Si(1), 137.77(13).
structure has been disrupted) reveals the C1 symmetry of this
i
molecule (Figure S10); four distinct Pr-methine septet signals
are observed, along with seven iPr-methyl doublet resonances.
The now diastereotopic protons, HA and HB, on the remaining
silylalkane moiety appear as two doublets of doublets (3JHH
)
11.3 Hz, 2JYH ) 3.6 Hz), while the Y-CH2CHCH3 resonances
appear as multiplets at 0.25 and -0.24 ppm. Further indication
of the monomeric asymmetric structure is found in the 13C NMR
spectrum of 5a, where the newly formed methylene carbon
resonance is split into a doublet (1JYC ) 47 Hz) rather than a
triplet.
isolable as solids that can be stored indefinitely at -35 °C. With
these complexes in hand, our attention turned to investigating
the activation of these bis-alkyl complexes in hopes of preparing
well-characterized cationic yttrium alkyl complexes.
Similar to known organoscandium ꢀ-diketiminato complexes,
the yttrium compounds described here exhibit metalation rates
that are dependent on both ligand bulk and alkyl group.
Specifically, the b series, such as 2b and 4b, exhibit moderate
metalation rates at room temperature, while 3a is more robust
under these conditions and requires heating to reach a similar
rate of metalation (Table 1). Other complexes of the a series
do not cleanly eliminate alkane to produce one metalate product,
although they do decompose at elevated temperatures. It is also
of note that the yttrium complexes described above undergo
metalative alkane elimination more rapidly than known orga-
noscandium ꢀ-diketiminate complexes, again owing to the larger
metal ionic radius.
Cationic Yttrium Alkyl Complexes. Reactions of neutral
bis-alkyls 2-4 with typical protonolysis and alkide abstraction
reagents were investigated in order to study the potential for
isolating monomeric yttrium alkyl cations. Reaction of 3a with
1 equiv of the Brønstead acid [NHMe2Ph][B(C6F5)4] in toluene
results in the formation of an orange oil. However, when the
reaction was performed in bromobenzene, the clean formation
of ion pair 6a was observed, along with free silane, CH3SiPh
(Scheme 3). Although there are a number of known cationic
group 4 complexes that coordinate the NMe2Ph base upon
reaction with this activator (Table 4),28 typical coordination is
through a nitrogen-based dative interaction. In the case of 6a,
however, the significant upfield shift of the ortho- and para-
phenyl resonances, as observed in the 1H NMR spectrum (Hpara
Despite the susceptibility of 2-4 to metalation or decomposi-
tion at elevated temperatures, these bis-alkyls are nevertheless

Low-Coordinate Organoyttrium Complexes
Organometallics, Vol. 28, No. 10, 2009 3017
coupling between 89Y and 15N (2-16 Hz),33 but the reaction of
3a with labeled activator exhibits a singlet in the 15N NMR
spectrum at 75.4 ppm (free aniline at 45.3 ppm) with ν1/2 ) 3.2
Hz, which suggests that there is no direct one-bond dative
interaction between the yttrium metal and the aniline nitrogen.
Although the arene 13C NMR chemical shifts of the NMe2Ph
moiety are not unusually upfield (Cmeta ) 131.8 ppm, Cpara
)
112.1 ppm, Cortho ) 110.6 ppm) and appear as singlets, literature
examples of this η6-arene binding in d0 metal complexes do
not exhibit any indicative changes in 13C chemical shift.29
Previous reports of scandium alkyl cations describe exchange
between various arene moieties, where more electron-rich arenes
exhibit preferential binding.28 While 6a and 7a did not exhibit
exchange with other arenes, such as bromobenzene and toluene,
there was observable exchange between free and coordinated
aniline, as determined by 2D EXSY spectroscopy.
Figure 6. 400 MHz 1H NMR spectrum of 6a in d5-bromobenzene
at 298 K.
Scheme 3
Although cations 6a and 7a exhibit remarkable thermal
stability, with metalation rates that are slower that those of the
parent neutral bis-alkyls, attempts to generate stable yttrium
cations of the b series were largely unsuccessful. Treatment of
dibenzyl 2b with B(C6F5)3 at -40 °C led to the formation of
ion pair 8, which undergoes rapid metalation at room temper-
ature (Scheme 4). Furthermore, reaction of 2b and 4b with
[CPh3][B(C6F5)3] at low temperatures generates cationic products
that rapidly decompose above 0 °C. Once again, the bulkier
tert-butyl ligand appears to influence the overall stability of the
yttrium alkyl products. In addition, the increased stability of
6a and 7a suggests that the coordinated arene impedes otherwise
facile reactions from taking place at the metal center.
Summary and Conclusions. The ꢀ-diketiminato ligand has
been employed to prepare a series of yttrium bis-alkyl com-
plexes. Equipped with bulky 2,6-iPr2C6H3 N-aryl groups, these
ligands provide an ideal scaffold for supporting these low-
coordinate and electronically unsaturated compounds, similar
to that observed in previously reported organoscandium chem-
istry. Ligand backbone substitution influences both the coordi-
nation number and the overall stability of the bis-alkyls, as
observed through structure determination of many of the
complexes and solution 1H NMR studies. These yttrium
complexes are susceptible to thermal alkane elimination ac-
cording to a well-established metalation process;11a it is a more
rapid process here than for known scandium compounds. Stable
yttrium alkyl cations supported by η6-arene coordination of N,N-
dimethylaniline have also been prepared, and this unique binding
mode has been studied spectroscopically. The coordinatively
unsaturated and highly electrophilic nature of these new
organoyttrium complexes makes them interesting candidates for
catalytic studies, and work investigating this potential is
currently underway.
) 5.79 ppm, Hortho ) 6.11 ppm), relative to free aniline (Hpara
) 6.74 ppm, Hortho ) 6.60 ppm), is instead suggestive of η6-
arene coordination of aniline (Figure 6). Similar reactivity was
observed when 4a was reacted with [HNMe2Ph][B(C6F5)4],
producing metal cation 7a. To date there has only been one
other report of a cationic metal complex with η6-coordinated
dimethylaniline.29 However, recent reports of scandium methyl
cations that coordinate aromatic solvent molecules with η6-
hapticity,30 along with the identification of a dinuclear yttrium
η6-biphenyl complex,31 make the postulated structure of 6a
plausible.32
Although crystals of 6a and 7a suitable for X-ray diffraction
were not obtained, extensive spectroscopic characterization
provides further evidence for arene binding. For example, a 2D
ROESY NMR experiment was utilized to analyze any relevant
NOE in 6a and 7a between the ligand and the NMe2Ph moiety.
The spectrum of 7a reveals distinct cross-peaks between each
of the ortho-, meta-, and para-hydrogens of the coordinated
NMe2Ph moiety and the iPr-CH3 groups from the ligand (Figure
7). These correlations indicate the close coordination of the
arene, and assuming that the NMe2Ph occupies the less
congested exo position (in agreement with previous work
investigating mixed bis-alkyl scandium complexes),11a the
ROESY NMR spectrum suggests that the NMe2 group is
oriented downward and out away from the ligand, with the para-
hydrogens pointed up, above the ligand plane.
As further proof of the η6-arene coordination of NMe2Ph in
6a, bis-alkyl 3a was treated with [15NHMe2Ph][B(C6F5)4].
Literature precedent exists for the observation of one-bond
Experimental Section
General Procedures. All operations were performed under a
purified argon atmosphere using glovebox or vacuum-line tech-
niques. Toluene, hexanes, and THF solvents were dried and purified
by passing through activated alumina and Q5 columns.34 Pentane
and bromobenzene were dried over Na, with a benzophenone
indicator. Deuterated NMR solvents were dried according to their
respective standard procedures. 1H, 13C{1H}, HMQC, 15N, and
29Si-1H HMBC NMR experiments were performed on a Bruker
(28) NMe2Ph bound to group 4 complexes: (a) Grossman, R. B.; Doyle,
R. A.; Buchwald, S. L. Organometallics 1991, 10, 1501. (b) Horton, A. D.;
de With, J. Organometallics 1997, 16, 5424. (c) Tjaden, E. B.; Swenson,
D. C.; Jordan, R. F. Organometallics 1995, 14, 371.
(29) Yu, N.; Nishiura, M.; Li, X.; Xi, Z.; Hou, Z. Chem. Asian J. 2008,
3, 1406.
(30) (a) Hayes, P. G.; Piers, W. E.; Parvez, M. J. Am. Chem. Soc. 2003,
125, 5622. (b) Hayes, P. G.; Piers, W. E.; Parvez, M. Chem.sEur. J. 2007,
13, 2632.
(31) (a) Fryzuk, M. D.; Love, J. B.; Rettig, S. J. J. Am. Chem. Soc.
1997, 119, 9071. (b) Fryzuk, M. D.; Jafarpour, L.; Kerton, F. M.; Love,
J. B.; Patrick, B. O.; Rettig, S. J. Organometallics 2001, 20, 1387.
(32) Bochkarev, M. N. Chem. ReV. 2002, 102, 2089.
(33) (a) Lee, S. G. Bull. Korean Chem. Soc. 1996, 17, 589. (b) Fratiello,
A.; Kubo-Anderson, V.; Bolanos, E. L.; Haigh, D.; Laghaei, F.; Perrigan,
R. D. J. Magn. Reson. 1994, 107, 56.
(34) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.

3018 Organometallics, Vol. 28, No. 10, 2009
Kenward et al.
Figure 7. 2D ROESY NMR spectrum of 7a at 298 K.
Scheme 4
temperature overnight, and then the solvent was removed in Vacuo.
The resultant yellow powder was slurried in toluene (40 mL) and
filtered. The remaining KI was washed again with toluene (10 mL).
Toluene was removed in Vacuo, and the residue was triturated with
pentane to give 1a as a pale beige solid in 63% yield (1.054 mg,
1
1.323 mmol). H NMR (C7D8): δ 7.13-6.96 (m, 6H; C6H3), 5.14
(s, 1H; CH), 3.51(sp, 4H; CHMe2, 2JH-H ) 6.9 Hz), 3.41 (br, 4H;
2
OCH2CH3), 1.63 (s, 6H; NCMe), 1.45 (d, 12H; CHMe2, JH-H
)
6.9 Hz), 1.17 (ov m, 16 H; CHMe2, OCH2CH2). 13C{1H} NMR
(CD2Cl2): δ 168.1 (NCMe), 143.6 (Cipso) 143.5, 127.1, 124.7 (C6H3),
99.2 (d, JY-H ) 10.0 Hz; CH), 71.8 (OCH2CH2), 29.1 (CHMe2),
4
AMX-300 and WH-400, and data are given in ppm relative to
solvent signals for 1H and 13C signals, NH3 for 15N, and SiMe4 for
29Si spectra. Elemental analyses were performed by Mrs. Dorothy
Fox and Mr. Jianjun Li of this department. Yttrium-containing
complexes were regularly found to be low in carbon, possibly as a
result of metal-catalyzed silicon carbide formation, leading to
25.0 (NCMe), 24.9 (CHMe2), 24.8 (OCH2CH2). Anal. Calcd for
C33H49N2O2I2Y: C, 47.54; H, 5.92; N, 3.36. Found: C, 46.44; H,
6.27; C, 2.99.
Preparation of [ArNC(tBu)CHC(tBu)NAr]YI2, 1b. A 100 mL
round-bottom flask was charged with KLtBu (1.000 g, 1.848 mmol)
and YI3(THF)3.5 (1.456 g, 2.001 mmmol), to which toluene (90
mL) was added. The reaction mixture was warmed to 90 °C and
stirred for 75 min, after which it was filtered and washed with more
toluene (2 × 10 mL), and the solvent was removed in Vacuo to
afford a sticky yellow solid. Hexanes (20 mL) was added, and the
reaction mixture was sonicated for 5 min, filtered, and washed (3
× 10 mL). Removal of hexanes under reduced pressure gave 1b
incomplete combustion;35 relevant H and 13C NMR spectra can
1
be viewed in the Supporting Information. The ligands HL (L)
ArNC(R)CHC(R)NAr, where Ar ) 2,6-iPr2C6H3 and R ) CH3,
tBu),14 KCH2Ph,36 LiCH2SiMe2Ph,15 and KCH3 were prepared
37
according to literature procedures. YI3 was purchased from Alfa
Aesar and converted to YI3(THF)3.5 by stirring in THF solvent at
room temperature for 1 h. All other materials were obtained from
Sigma-Aldrich and purified according to standard procedures.
Preparation of [ArNC(CH3)CH(CH3)NAr]YI2(THF), 1a. A
100 mL round-bottom flask was charged with KLMe (966 mg, 2.115
mmol) and YI3(THF)3.5 (1.527 g, 2.115 mmol), and THF (75 mL)
was condensed into the flask. The solution was stirred at room
1
as a bright yellow solid in 87% yield (1.345 g, 1.620 mmol). H
NMR (C7D8, 343 K): δ 6.99-6.69 (m, 6H; C6H3), 5.82 (s, 1H;
CH), 3.05 (sp, 4H; CHMe2, JHH ) 6.7 Hz), 1.44 (d, 12H, CHMe2,
JHH ) 6.7 Hz), 1.26 (d, 12H, CHMe2, JH-H ) 6.Hz), 1.13 (s, 18H;
NCCMe3). 13C{1H} NMR (C7D8, 343K): δ 173.2 (NCCMe3), 143.1
(Cipso), 140.6, 126.9, 124.4 (C6H3) 88.0 (CH), 45.1 (NCC(CH3)3),
32.2 (NCC(CH3)3), 30.3 (CHMe2), 24.0 (CHMe2). Anal. Calcd for
C35H53N2I2Y: C, 49.71; H, 6.32; N, 3.31. Found: C, 49.17; H, 6.44;
N, 3.07.
(35) Fryzuk, M. D.; Giesbrecht, G. R.; Rettig, S. J. Organometallics
1996, 15, 3329.
(36) Schlosser, M.; Hartmann, J. Angew. Chem., Int. Ed. 1973, 12, 508.
(37) Weiss, E.; Sauermann, G. Angew. Chem., Int. Ed. 1968, 7, 133.

Low-Coordinate Organoyttrium Complexes
Organometallics, Vol. 28, No. 10, 2009 3019
Preparation of [ArNC(tBu)CHC(tBu)NAr]Y(CH2C6H5)2 · THF,
2a. Toluene (45 mL) was condensed into a flask charged with 1a
(240 mg, 0.301 mmol) and then warmed to room temperature. Solid
KCH2C6H5 (94 mg, 0.723 mmol) was added to the stirring solution
over 30 min. The resulting solution was stirred for 1 h, during which
time the color changed from orange to yellow. The solution was
then filtered and toluene removed in Vacuo. Hexanes (10 mL) was
condensed into flask at -78 °C, which was then sonicated until an
orange precipitate formed. The resulting orange powder was filtered
and washed with another portion of hexanes (5 mL), yielding 2a
3 h. THF was removed in Vacuo, and the mixture was then filtered
in 30 mL of toluene to remove KI. The volatiles were removed,
and then the resultant off-white powder was washed with pentane
(3 × 5 mL) and dried under vacuum for 1 h (0.317 mmol, 50.5%
yield). 1H NMR (C6D6, 298 K): δ 7.01-7.11 (m, 6H; C6H3), 5.03
2
(s, 1H; CH), 3.29 (sp, 4H; CHMe2, JH-H ) 6.8 Hz), 1.72 (s, 6H;
2
NCCH3), 1.36 (d, 12H; CHMe2, JH-H ) 6.8 Hz), 1.23 (d, 12H;
CHMe2, 2JHH ) 6.8 Hz), -0.27 (br s, 6H; YMe2). 1H NMR (C7D8,
240 K): δ 7.00-7.14 (m, 6H; C6H3), 4.85 (s, 1H; CH), 3.16 (sp,
4H; CHMe2, 2JH-H ) 6.7 Hz), 1.63 (s, 6H; NCCH3), 1.28 (d, 12H;
CHMe2, 2JH-H ) 6.7 Hz), 1.18 (d, 12H; CHMe2, 2JH-H ) 6.7 Hz),
1
(36 mg, 0.047 mmol) in 16% yield. H NMR (C6D6, 298 K): δ
2
2
7.24 (b, 6H, C6H3), 7.04 (t, 4H, m-C6H5, JHH ) 7.5 Hz), 6.77 (d,
-0.09 (d, 3H; terminal Y-CH3, JY-H ) 2.10 Hz), -0.13 (t, 3H;
4H, o-C6H5, 2JHH ) 7.5 Hz), 6.77 (t, 2H, p-C6H5, 2JHH ) 7.5 Hz),
5.13 (s, 1H, NCCH), 3.19 (sp, 4H, iPrCH, 2JHH ) 6.8 Hz), 3.09 (b,
bridging Y-CH3, JY-H ) 2.45 Hz). 13C{1H} NMR (C6D6, 298
2
K): δ 167.8 (NC(CH3)), 147.2 (NArCipso), 142.8 (NArC), 126.3
(NArC), 124.8 (NArC), 97.2 (CH), 35.3 (Y-CH3, broad), 28.8
(NC(CH3)), 26.0 (iPrCH), 25.6, 25.1 (iPrCH3). Anal. Calcd for
C31H47N2Y: C, 69.38; H, 8.83; N, 5.22. Found: C, 67.00; H, 8.44;
N, 5.25.
2
4H, OCH2), 1.96 (d, 4H, YCH2, JYH ) 2.8 Hz), 1.71 (s, 6H,
i
2
NCCH3), 1.36 (b, 4H, OCCH2), 1.32, 1.20 (d, 24H, PrCH3, JHH
) 6.8 Hz). 13C{1H} NMR (C6D6, 298 K): δ 167.6 (NC(CH3)), 152.5
(BnCipso), 145.2 (NArCipso), 142.8 (NArC), 130.4 (BnC), 126.6
(BnC), 124.7 (NArC), 123.3 (NArC), 118.7 (BnC), 95.9 (NCCCN),
Preparation of [ArNC(tBu)CHC(tBu)NAr]Y(CH3)2, 4b. THF
(30 mL) was condensed into a 50 mL round-bottom flask charged
with 1b (300 mg, 0.360 mmol) and KMe (58 mg, 1.08 mmol).
The reaction was stirred at room temperature for 1 h before the
THF was removed in Vacuo. Toluene (25 mL) was added to the
flask, and the solution was filtered to remove KI before solvent
was again removed in Vacuo. Pentane (15 mL) was added to the
flask, which was then sonicated for 10 min, over which time the
product precipitated. The mixture was filtered, washed with pentane
(5 mL), and then isolated as an orange powder in 79% yield (177
1
70.0 (OCH2), 58.2 (d, YC, JYC ) 33.3 Hz), 36.0 (OCCH2), 29.2
(NC(CH3)), 25.5, 25.2 (iPrC).
Preparation of [ArNC(tBu)CHC(tBu)NAr]Y(CH2C6H5)2, 2b.
Solid KCH2C6H5 (56 mg, 0.430 mmol) was slowly added into a
stirring solution of 1b (174 mg, 0.210 mmol) in toluene (30 mL).
The reaction mixture was stirred at room temperature for 5 h and
then filtered. Solvent was removed in Vacuo, yielding an orange-
yellow solid. Pentane (15 mL) was added, and the mixture was
sonicated before filtering and washing with pentane (2 × 5 mL),
1
1
mg, 0.285 mmol), which was stored at -30 °C. H NMR (C7D8,
affording 101 mg of the desired product (0.129 mmol, 61%). H
243 K): δ 6.99 (b, 6H, C6H3), 5.79 (s, 1H, CH), 3.21(b, 4H, iPrCH),
1.30 (d, 24H, iPrCCH3, 2JHH ) 6.4 Hz), 1.12 (s, 18H, NCC(CH3)3),
-0.27 (b, 6H, Y-CH3). 13C{1H} NMR (C7D8, 243 K): δ 172.4
(NCC(CH3)3), 145.1 (NArCipso), 139.0 (NArC), 124.0 (NArC), 122.8
(NArC), 94.2 (CH), 44.0 (NCC(CH3)3), 31.4 (NCC(CH3)3), 28.9
(iPrCH), 25.2 (YCH3), 24.0 (iPrCH3). Anal. Calcd for C31H47N2Y:
C, 71.59; H, 9.58; N, 4.51. Found: C, 69.20; H, 9.31; N, 4.31.
NMR (C7D8, 298 K): δ 7.01-6.98 (m, 6H, -C6H3), 6.93, (m, 4H,
m-C6H5) 6.50 (m, 6H, o,p-C6H5) 5.71 (s, 1H, NCCH), 2.97 (sp,
2
2
4H, CHMe2, JHH ) 6.7 Hz), 1.75 (d, 4H, YCH2, JYH ) 2.9 Hz),
1.21 (d, 12H, CHMe2, 2JHH ) 6.7 Hz), 1.15 (d, 12H, CHMe2, 2JHH
) 6.7 Hz), 1.09 (s, 18H, NCCMe3). 13C{1H} NMR (C7D8, 298 K):
171.1 (NC(C(CH3)3)), 150.8 (BnCipso), 143.6 (NArCipso), 140.7
(NArC), 130.5 (BnC), 125.5 (NArC), 123.9 (NArC), 123.2 (BnC),
1
118.5 (BnC), 91.4 (NCCCN), 56.4 (d, YC, JYC ) 43.3 Hz), 44.6
Preparation of K3-[ArNC(CH3)CHC(CH3)N-iPr-C6H3]YCH2-
SiMe2Ph, 5a. An NMR tube containing 3a (27.5 mg, 0.042 mmol)
and toluene (0.6 mL) was sealed and heated at 60 °C overnight,
(NCC(CH3)3), 31.9 (NCC(CH3)3), 28.7, 26.0, 23.9 (iPrC). Anal.
Calcd for C49H63N2OY: C, 76.14; H, 8.74; N, 3.62. Found: C, 75.82;
H, 8.83; N, 3.53.
1
during which time crystals were observed to form. H NMR (d8-
THF, 298 K): δ 7.31-7.05 (m, 11H, ArCH), 5.07 (s, 1H, CH),
Preparation of [ArNC(CH3)CHC(CH3)NAr]Y(CH2SiMe2Ph)2,
3a. A 100 mL round-bottom flask was charged with 1a (700 mg,
0.879 mmol) and LiCH2SiMe2Ph (275 mg, 1.76 mmol), and toluene
(50 mL) was condensed into the flask at -78 °C. The flask was
allowed to slowly warm to room temperature and stirred for 3 h.
The toluene solution was filtered, and the remaining LiI was washed
once with toluene (5 mL). The toluene was removed from the filtrant
in Vacuo, leaving a crude yellow solid. Hexanes (10 mL) was added,
and the mixture was sonicated for 5 min, cooled to -78 °C, cold
filtered, and washed with cold pentane (2 × 5 mL), yielding 253
3
3
3.23 (sp, 2H, CHMe2, JHH ) 7.2 Hz) 3.05 (sp, 1H, CHMe2, JHH
) 7.2 Hz), 2.94 (m, 1H, Y-CCHMe2) 1.75 (s, 3H, NCCH), 1.71
(s, 3H, NCMe), 1.31 (d, 3H; CHCH3, 3JHH ) 7.2 Hz), 1.29 (d, 3H;
3
3
CHCH3, JHH ) 7.2 Hz), 1.25 (d, 3H; CHCH3, JHH ) 7.2 Hz),
1.24 (d, 3H; CHCH3, 3JHH ) 7.2 Hz), 1.22 (d, 3H; CHCH3, 3JHH
7.2 Hz), 1.14 (d, 3H; CHCH3, 3JHH ) 7.2 Hz), 1.07 (d, 3H; CHCH3,
)
3JHH ) 7.2 Hz), 0.14 (dd, 1H, YCH2CHMe, JHH ) 12.2 Hz, JYH
2
2
2
2
) 2.8 Hz), -0.21 (dd, 1H, YCH2CHMe, JHH ) 12.2 Hz, JYH
)
2.5 Hz), -0.27 (s, 3H, SiCH3), -0.32 (s, 3H, SiCH3), -0.99 (ddd,
2
2
1
1H, Y-CH2SiMe2Ph, JYH ) 3.6 Hz, JHH ) 11.3 Hz), -1.092
mg of pale yellow powder (0.314 mmol, 36% yield). H NMR
2
2
(ddd, 1H, Y-CH2SiMe2Ph, JYH ) 3.6 Hz, JHH ) 11.3 Hz).
13C{1H} NMR (d8-THF) δ 166.1, 165.8 (NCCH3), 145.9, 145.3,
144.5, 144.0, 143.1, 141.5, 141.0 (ArCquat), 134.3 (SiPhCortho), 129.7,
128.6, 127.9, 126.8, 126.0, 125.5, 125.1, 124.0, 123.6, 123.2, 122.8
(C7D8, 298 K): δ 7.52 (m, 4H, m-C6H5), 7.23 (m, 6H, o,p-C6H5)
7.00-6.98 (m, 6H, C6H3), 5.01 (s, 1H, CH), 3.08 (sp, 4H, CHMe2,
2
2JHH ) 6.7 Hz), 1.61 (s, 6H, NCMe), 1.28 (d, 12H, CHMe2, JHH
2
) 6.7 Hz), 1.09 (d, 12H, CHMe2, JHH ) 6.7 Hz), 0.19 (s, 12H,
1
2
SiMe2), -0.23 (d, 4H, YCH2, JYH ) 3.0 Hz). 13C (C7D8, 298 K):
(ArCH), 98.0 (NCCCN), 58.6 (d, YCH2CHMe, JYC ) 47.3 Hz),
38.6 (YCH2CHMe), 29.8 (iPrCH), 29.7 (d, YCH2SiMe2Ph, 1JYC
)
δ 167.1 (NCCH3), 146.7 (SiCipso), 144.8 (NArCipso), 142.7 (NArC),
133.7 (SiPhC), 127.8 (SiPhC), 127.4 (SiPhC), 126.3, (NArC), 124.5
42 Hz), 28.7 (iPrCH), 27.5, 26.1, 25.8, 25.2, 25.1, 24.8, 24.2
(iPrCH3), 3.2, 2.3 (SiCH3).
1
(NArC), 96.2 (NCCCN), 34.7 (d, YCH2, JYC ) 40.3 Hz), 28.7
(NCCH3), 25.3 (iPrCH), 24.8 (iPrCH3), 2.9 (SiCH3). 29Si NMR
(C7D8, 298 K): δ -7.2 (1H-29Si HMBC). Anal. Calcd for
C47H67N2Si2Y: C, 70.11; H, 8.39; N, 3.48. Found: C, 68.30; H,
8.52; N, 3.32.
Preparation of {[ArNC(CH3)CHC(CH3)NAr]Y(CH2SiMe2Ph)-
(NMe2Ph)}{B(C6F5)4}, 6a. An NMR tube was charged with 3a (25
mg, 0.031 mmol) dissolved in toluene (0.4 mL). Solid [HNMe2Ph]-
[B(C6F5)4] (24 mg, 0.030 mmol) was added to the solution, and
the tube was shaken vigorously and then left to sit at room
temperature for 10 min. The resultant orange oil was extracted from
Preparation of [ArNC(CH3)CHC(CH3)NAr]Y(CH3)2, 4a. THF
(30 mL) was added to a 50 mL round-bottom flask containing 1a
(500 mg, 0.628 mmol) and KMe (100 mg, 1.88 mmol). The mixture
was sonicated for 10 min and then stirred at room temperature for
1
the toluene and dissolved in C6D5Br. H NMR, 13C NMR, and
HMQC experiments were performed and confirm there is one

3020 Organometallics, Vol. 28, No. 10, 2009
Kenward et al.
isomer of 6a and that aniline remains coordinated. 1H NMR
(C6D5Br, 298 K): δ 7.26-7.14 (m, 6H; C6H3), 6.66 (t, 2H;
Synthesis of {[ArNC(tBu)CHC(tBu)NAr]Y(CH2Ph)}{PhCH2B-
(C6F5)3}, 8. A 1 dram vial was charged with 2b (50 mg, 0.0647 mmol)
and hexane (2.0 mL). In a second vial, B(C6F5)3 (33 mg, 0.647 mmol)
was suspended in hexane (2 mL), and both vials were cooled to -32
°C in the glovebox freezer. After 30 min, the B(C6F5)3 mixture was
added dropwise to the stirring solution of 2b. The orange precipitate
of 8 immediately precipitated, and the solution was stored overnight
at -32 °C to allow the solid to settle. The supernatant was removed
via syringe, and the solid was dried briefly under vacuum to afford an
orange solid of 8 (52 mg, 0.0401 mmol, 62% yield). 1H NMR (C6D5Br/
C7D8, 223 K): δ 7.18-6.98 (m, 14H; C6H3, C6H5CH2), 6.18 (b, 3H;
m,p-C6H5CH2B), 5.50 (s, 1H; CH), 3.38 (b, 2H; B-CH2), 2.36 (sp,
2H; iPrCH), 2.20 (sp, 2H; iPrCH), 1.54 (b, 2H; Y-CH2), 1.13 (d, 6H;
3
3
m-C6H5NMe2, JHH ) 7.6 Hz), 6.11 (d, 2H; o-C6H5NMe2, JHH
)
7.6 Hz), 5.79 (t, 1H; p-C6H5NMe2), 5.18 (s, 1H; CH), 2.57 (sp,
2H; iPrCH, 3JHH ) 6.8 Hz), 2.46 (sp, 2H; iPrCH3, 3JHH ) 6.8 Hz),
2.26 (s, 6H; N(CH3)2), 1.66 (s, 6H; NC(CH3)), 1.24 (d, 6H; iPrCH3,
3JHH ) 6.8 Hz), 1.06 (d, 12H; iPrCH3, 3JHH ) 6.8 Hz), 0.84 (d, 6H;
3
iPrCH3, JHH ) 6.8 Hz), 0.20 (s, 6H; Si(CH3)2), -0.76 (d, 2H;
2
YCH2, JYH ) 2.8 Hz). 13C{1H} NMR (C6D5Br, 298 K): δ 166.7
(NCCH3), 150.5 (ipso-C6H5NMe2), 140.4 (C6H3, Cipso), 139.8, 139.2
(C6H3), 131.8 (m-C6H5NMe2), 127.4, 126.5, 123.3 (C6H3), 112.1
(p-C6H5NMe2), 110.6 (o-C6H5NMe2), 91.9 (CH), 37.5
1
(C6H5N(CH3)2), 35.4 (d, Y-CH3, JYC ) 37.8 Hz), 27.2, 26.8
(iPrCH), 24.5, 23.5, 23.0, 21.7 (iPrCH3), -2.5 (SiMe2Ph). 19F NMR
iPrCH3), 1.04 (d, 6H; PrCH3), 0.96 (d, 6H; PrCH3), 0.94 (d, 6H;
iPrCH3), 0.87 (s, 18H; NCC(CH3)). 13C{1H} NMR (C6D5Br/C7D8, 223
K): δ 175.4 (NC(CH3)), 149.3 (ipso-C6H3), 147.0 (ipso-C6H5CH2Y),
143.4 (ipso-C6H5CH2B), 139.8, 139.5, 139.0, 135.7, 133.6, 132.2,
130.3, 129.8, 125.8, 124.4 (C6H3, C6H5CH2), 86.1 (NCCH), 57.2 (b,
Y-CH2), 35.2 (B-CH2), 33.6, 31.8 (iPrCH), 32.4, 31.3, (iPrCH3), 28.8
(NC(CH3), 25.1, 24.5. 19F NMR (C6D5Br, 273 K): δ -131.6 (o-F),
-165.0 (p-F), -167.8 (m-F). 11B NMR (C6D5Br, 223 K): δ -12.7.
i
i
3
(C6D5Br, 298 K): δ -131.9 (d, JFF ) 19 Hz, Fortho), -162.1 (t,
3
3JFF ) 19 Hz, Fmeta), -166.1 (t, JFF ) 19 Hz, Fpara). 11B NMR
(C6D5Br, 298 K): δ -16.5.
Preparation of {[ArNC(CH3)CHC(CH3)NAr]Y(CH3)(NMe2Ph)}-
{B(C6F5)4}, 7a. An NMR tube was charged with 4a (15 mg, 0.031
mmoles) and [HNMe2Ph][B(C6F5)4] (19 mg, 0.030 mmol), to which
C6D5Br was added. The tube was sonicated for 10 min and then
1
left to sit at room temperature for 10 min. H NMR (C6D5Br, 298
3
K): δ 7.29-7.01 (m, 6H; NArC), 6.56 (t, 2H; m-C6H5NMe2, JHH
Acknowledgment. This work was generously supported
by NSERC of Canada in the form of a Discovery Grant to
W.E.P. and a Postgraduate PGS-D Award to A.L.K. The
authors would like to thank Dr. Paul G. Hayes, who
performed preliminary experiments in the preparation of
diiodide 1b.
) 7.2 Hz), 6.08 (d, 2H; o-C6H5NMe2, 3JHH ) 7.2 Hz), 5.71 (t, 1H;
3
p-C6H5NMe2, JHH ) 7.2 Hz), 5.04 (s, 1H; CH), 2.67 (sp, 2H;
3
3
CHCH3, JHH ) 7.2 Hz), 2.51 (sp, 2H; CHCH3, JHH ) 7.2 Hz),
2.31 (s, 6H; NCH3), 1.56 (s, 6H; NCCH3), 1.23 (d, 6H; CHCH3,
3JHH ) 7.2 Hz), 1.08 (d, 6H; CHCH3, 3JHH ) 7.2 Hz), 1.07 (d, 6H;
3
2
CHCH3, JHH ) 7.2 Hz), -0.63 (d, 3H; YCH3 ) JYH ) 2.0 Hz).
13C{1H} NMR (C6D5Br, 298 K, C6F5 resonances not reported): δ
168.5 (NCCH3), 151.6 (ipso-C6H5NMe2), 143.5 (NArCipso), 141.5,
139.3 (NArC), 133.1 (m-C6H5NMe2), 128.1, 125.1, 124.6 (C6H3),
113.0 (p-C6H5NMe2), 112.0 (o-C6H5NMe2), 96.9 (NCCCN), 39.0
Supporting Information Available: Crystallographic data for
compounds 1b, 2a, 2b, 3a, and 5a, including ORTEP diagrams
1
and crystallographic information (CIF). H and 13C NMR spectra
1
((CH3)2NPh), 29.2 (NCCH3), 28.4 (d, Y-CH3, JYC ) 33.6 Hz),
1
of 2-4. H NMR spectra of 5a. Table of known NMe2Ph-bound
28.2, 26.2 (iPrCH), 24.3, 24.2, 24.08, 23.1 (iPrCH3). 19F NMR
metal cations. This material is available free of charge via the
Internet at http://pubs.acs.org.
3
(C6D5Br, 298 K): δ -131.4 (d, JFF ) 22.6 Hz, Fortho), -161.9 (t,
3JFF ) 22.6 Hz, Fmeta), -165.7 (t, 3JFF ) 22.6 Hz, Fpara). 11B NMR
(C6D5Br, 298 K): δ -16.5.
OM900082D