Synthesis and characterization of zinc complexes and reactivity with primary phosphines

Article abstract of DOI:10.1016/j.jorganchem.2011.10.008

Zinc complexes of chelating monoanionic N-donors and neutral diphosphine ligands were synthesized by reaction of diethylzinc with 1,3-diketimine, diazabutadiene, and diphosphine ligand precursors. These complexes were reacted with primary phosphines in an attempt to solicit phosphine dehydrocoupling reactivity. In most cases, insoluble zinc-containing precipitates were formed and ligands were liberated. For the most sterically encumbered complex, ( ^DippL)ZnEt (3, ^DippL = [(2,6-ⁱPrC ₆H₃)NC(CH₃)]₂CH^-), a product assigned as the zinc-phosphide (^DippL)ZnPHPh (6) was observed but could not be isolated as a pure compound. A new, less bulky β-diketiminate complex (^TolL)ZnEt (2, ^TolL = [(p-CH₃C₆H₄)NC(CH₃)] ₂CH^-) was reacted with primary phosphines to give a precipitate and the bis(β-diketiminate)zinc complex (^TolL) ₂Zn (5), an apparent product of comproportionation. ( ^MesAI)ZnEt (1, ^MesAI = MesNC(Me)(Et)C(Me) = NMes) and 2 were structurally characterized.

Full text of DOI:10.1016/j.jorganchem.2011.10.008

Journal of Organometallic Chemistry 696 (2012) 4327e4331
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and characterization of zinc complexes and reactivity with primary
phosphines
*
Benjamin A. Vaughan, Eliza M. Arsenault, Stephanie M. Chan, Rory Waterman
Department of Chemistry, University of Vermont, Burlington, VT 05405-0125, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Zinc complexes of chelating monoanionic N-donors and neutral diphosphine ligands were synthesized by
reaction of diethylzinc with 1,3-diketimine, diazabutadiene, and diphosphine ligand precursors. These
complexes were reacted with primary phosphines in an attempt to solicit phosphine dehydrocoupling
reactivity. In most cases, insoluble zinc-containing precipitates were formed and ligands were liberated.
For the most stericallyencumbered complex, (DippL)ZnEt (3, DippL ¼ [(2,6-iPrC6H3)NC(CH3)]2CHꢀ), a product
assigned as the zinc-phosphide (DippL)ZnPHPh (6) was observed but could not be isolated as a pure
Received 14 September 2011
Received in revised form
3 October 2011
Accepted 6 October 2011
Keywords:
Zinc
Phosphine
Phosphide
Dehydrocoupling
X-ray
compound. A new, less bulky
b
-diketiminate complex (TolL)ZnEt (2, TolL ¼ [(p-CH3C6H4)NC(CH3)]2CHꢀ) was
reacted with primary phosphines to give a precipitate and the bis(b
-diketiminate)zinc complex (TolL)2Zn
(5), an apparent product of comproportionation. (MesAI)ZnEt (1, MesAI ¼ MesNC(Me)(Et)C(Me) ¼ NMes) and
2 were structurally characterized.
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
are not viable catalysts due to the formation of insoluble ZneP
products, regardless of the nature of the ancillary ligand.
a key transformation in the
Dehydrocoupling catalysis is
synthesis of main-group materials [1e8]. However, the catalytic
dehydrocoupling of phosphines is less developed than related
transformations for elements such as silicon or for Lewis acid-base
adducts such as amine-boranes [2,4,6e7,9e10]. For phosphine
dehydrocoupling, the catalysts that have appeared in the literature
primarily use group 4 metals or rhodium [8]. In developing broad
synthetic applications for this transformation, it is attractive to use
inexpensive metal complexes as catalysts. Earth-abundant, first-row
transition metals are considered promising to displace conventional
coinage metal complexes in other catalytic transformations [11].
Zinc complexes have shown excellent reactivity in the copoly-
merization of carbon dioxide with epoxides [12e13]. Though zinc
complexes would not be expected to demonstrate the same kinds
of reactivity as formally d8 and d0 metal complexes, which are
demonstrated phosphine dehydrocoupling catalysts [8], the recent
report of a tin complex, Cp*2SnCl2, that is a catalyst for dehy-
drocoupling prompts the study of alternative metal species [14].
This report outlines efforts to solicit phosphine dehydrocou-
pling reactivity from a family of L’ZnEt2and LZnEt (L ¼ monoanionic
chelating ligand; L0 ¼ neutral chelating ligand) derivatives. These
reactions suggest that the simple zinc complexes reported herein
2. Results and discussion
2.1. Synthesis of zinc complexes
Simple ligands were selected to support zinc complexes as
potential catalysts based on prior observation of related zinc
complexes in stoichiometric or catalytic transformations. For
example, it was expected that
might afford reactivity with PeH bonds based on copolymerization
catalysis [15e16]. Zinc complexes with -aminoimine ligands have
not seen attention in catalysis since their discovery by van Koten
and coworkers [17e21], yet these ligands afford tunable steric and
electronic parameters in a way that is similar to b-diketiminate
b-diketiminate complexes of zinc
a
ligands. It was also anticipated that neutral ligands, like chelating
diphosphines, might promote different reactivites or stability over
anionic counterparts.
Reaction of diethylzinc with
a
mesityl-substitued dia-
zabutadiene in toluene solution gave analytically pure, orange
crystals of (MesAI)ZnEt (1, MesAI ¼ MesN ¼ C(Me)CEt(Me)NMes) in
81% yield upon crystallization from pentane (Eq. (1)). Complex 1 is
the product of a formal 1,2-insertion of one imine into the ZneC
bond of an ethyl ligand. Diagnostic spectral features of 1 include the
imine and amine resonances of the ligand backbone at
d
d 71.8 and
* Corresponding author. Tel.: þ1 802 656 0278; fax: þ1 802 656 8705.
E-mail address: rory.waterman@uvm.edu (R. Waterman).
191.1, respectively, in the 13C NMR spectrum. Two methyl
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.10.008

4328
B.A. Vaughan et al. / Journal of Organometallic Chemistry 696 (2012) 4327e4331
Fig. 1. Molecular structure of 1 with thermal ellipsoids drawn at the 50% probability
level. Hydrogen atoms have been omitted for clarity.
resonances were observed in the 1H NMR spectrum of 1 at
and 1.13. The transferred ethyl substituent resonances displayed
distinctive coupling and chemical shifts in the 1H NMR spectrum of
1 as well.
d
1.30
Fig. 2. Molecular structure of 2 with thermal ellipsoids drawn at the 50% probability
level. Hydrogen atoms have been omitted for clarity. Only one of two of independent
molecules in the unit cell are shown.
yield upon crystallization from pentane (Eq. (2)). This procedurewas
derived from that of
(
DippL)ZnEt (3, DippL
¼
[(2,6-iPrC6H3)
NC(CH3)]2CHꢀ), which was also prepared [22]. Key spectral features
in identifyingcomplex 2 includethe methineresonance at d4.90 and
the para-tolyl methyl resonance at
d
2.08 in the 1H NMR spectrum.
(1)
(2)
Structural characterization by X-ray crystallography confirmed
the identity of complex 1. Single crystals of 1 were grown from
pentane solution cooled to ꢀ30 ꢁC, and the molecular structure is
shown in Fig.1. The three-coordinate zinc is trigonal planar, featuring
an imine and amide functionality on the chelating ligand based on
C(4)eN(2) ¼ 1.283(2) Å and C(3)eN(1) ¼ 1.466(2) Å, respectively.
Selected bond lengths and angles are summarized in Table 1.
Van Koten and coworkers have investigated the use of the dia-
zabutadiene (DAB) bearing alkyl and aryl substituents as ligands
precursors for zinc complexes. Interestingly, a formal 1,1-insertion of
an imine from a DAB ligand into ZneC bonds was observed for
sterically unencumbered substituents, whereas formal 1,2-insertion
products resulted with DABs possessing bulky substituents such as
2,6-diisopropylphenyl [17,21]. It appears that the mesityl substitu-
ents possess sufficient bulk to promote the 1,2-insertion product.
Reaction of diethylzinc with one equiv. of para-tolyl substituted
1,3-diketimine in toluene solution gave analytically pure, yellow
crystals of (TolL)ZnEt (2, TolL ¼ [(p-CH3C6H4)NC(CH3)]2CHꢀ) in 78%
Single crystals of 2 were grown from cold pentane solution
and subjected to an X-ray diffraction study. The molecular struc-
ture, shown in Fig. 2, reveals a planar geometry around zinc. There
are two independent molecules in the unit cell, differing only in the
orientation of the ethyl ligand on zinc. In one molecule (Fig. 2),
N(2)eZneC(1) ¼ 127.49(8)ꢁ and C(1)eZneN(1) ¼ 135.26(8)ꢁ as
compared to the same angles of the other molecule, which are
129.93(8)ꢁ and 133.03(8)ꢁ, respectively. The remainder of bond
lengths and angles are consistent with other
complexes of zinc (Table 2).
b-diketiminate
A neutral ancillary ligand was also employed. Reaction of
diethylzinc with 1,2-bis(dimethylphosphino)ethane (dmpe) in
toluene solution gave analytically pure, colorless crystals of (dmpe)
ZnEt2 (4) in quantitative yield (Eq. (3)). Diagnostic spectral features
of 4 include the methylene resonance of the ligand backbone at
d
1.05 in the 1H NMR spectrum and the resonance at
d
ꢀ43 in the 31
P
NMR spectrum. Complex
4 is highly similar to the 1,2-
Table 1
Table 2
Selected bond lengths (Å) and angles (deg) for (MesAI)ZnEt (1).
Selected bond lengths (Å) and angles (deg) for (TolL)ZnEt (2).
ZneC(1)
ZneN(1)
ZneN(2)
1.951(2)
1.8725(16)
2.0950(17)
N(1)eC(3)
N(2)eC(4)
C(3)eC(4)
1.466(2)
1.283(2)
1.530(3)
ZneC(1)
ZneN(1)
ZneN(2)
1.970(2)
1.9758(17)
1.9633(17)
N(1)eC(3)
N(2)eC(5)
1.336(3)
1.326(3)
ZneN(1)eC(3)
ZneN(2)eC(4)
N(1)eC(3)eC(4)
N(2)eC(4)eC(3)
117.76(12)
112.11(13)
108.67(15)
118.51(17)
N(1)eZneC(1)
N(2)eZneC(1)
N(1)eZneN(2)
154.24(8)
123.13(8)
82.62(6)
ZneN(1)eC(3)
ZneN(2)eC(5)
N(1)eC(3)eC(4)
N(2)eC(5)eC(4)
122.31(13)
123.07(14)
123.46(19)
123.43(19)
N(1)eZneC(1)
N(2)eZneC(1)
N(1)eZneN(2)
135.26(8)
127.49(8)
97.22(7)

B.A. Vaughan et al. / Journal of Organometallic Chemistry 696 (2012) 4327e4331
4329
bis(diphenylphosphino)ethane derivative investigated by Noltes
and van den Hurk [23].
Working under the hypothesis that this new compound was in
fact the bis( -diketiminate) complex, a toluene solution of dieth-
b
ylzinc was added to p-tolyl 1,3-diketimine in toluene to give
analytically pure, colorless crystals of (TolL)2Zn (5) in 84% yield upon
consecutive crystallization from Et2O then pentane (Eq. (4)). Beside
the diagnostic resonance at
observed at 2.08 and
1.77 in the 1H NMR spectrum. Order of
addition was key in this transformation as addition of 1,3-
d 4.61, methyl resonances were
d
d
(3)
diketimine to
a
solution of diethylzinc gave
a
mixture of
complexes 2 and 5.
(4)
3. Reactions with phosphines
3.1. Attempted catalytic reactions
Initial investigations surrounded complex 4, which, when
reacted with 10 equiv. of phenyl- or cyclohexylphosphine at
ambient temperature in benzene-d6, yielded free dmpe and an
insoluble, colorless precipitate. Reaction of diethylzinc and phe-
nylphosphine under similar conditions gave the same result.
Treatment of 4 with one equiv. each of the same phosphines gave
a mixture of dmpe, precipitate, and unreacted 4 as in the attempted
catalyst. Precise stoichiometry to decompose 4 with phosphines
could not be determined.
Some indication of a new phosphide complex came from the
reaction of 3 with five equiv. of phenylphosphine in toluene solu-
tion (Eq (5)). The zinc-containing product was assigned to be (DippL)
ZnPHPh (6) based on spectroscopic data. In particular, a new 31P
NMR resonance at
d
d
ꢀ152 as well as a PH doublet (JPH ¼ 211 Hz) at
4.92 in the 1H NMR spectrum were observed. Unfortunately, the
These initial reactions prompted the investigation of zinc
complexes supported by monoanionic ancillary ligands to provide
greater stability. Reaction of five mol% of complex 1 with phenyl- or
optimum yield for complex 6 was obtained under these conditions,
and all other reactions and subsequent attempts to purify 6 could
not separate it from unreacted 3.
cyclohexylphosphine yielded
a colorless precipitate that was
insoluble in common solvents. Monitoring the reaction by 31P NMR
spectroscopy showed little to no conversion to dehydrocoupling
products, even upon extended heating.
(5)
The aromatized
b-diketiminate ligands were targeted as
potentially more stable anionic ancillary ligands. Heating benzene-
d6 solutions of phenyl- or cyclohexylphosphine with 10 mol % of
complex 3 for extended periods resulted in trace quantities of
dehydrocoupling products (PHPh)2 and (PCy)4, respectively. The
conversions were less than 10% as judged by integration in the 1H
and 31P NMR spectra and inconsistent between runs. It was
hypothesized that the steric bulk of the diisopropylphenyl
substituents was thwarting catalytic reactivity. This hypothesis
motivated the preparation of 5. However, treatment of phenyl-
phosphine with 5 mol % of 2 gave a precipitate, unreacted phos-
phine as observed in the 31P NMR spectrum, and a complex mixture
of products in the 1H NMR spectrum that included an unidentified
Treatment of complex
1
with phenyl- or cyclo-
hexylphosphine in toluene solution afforded analytically pure,
colorless crystals of the amine-substituted imine product (7) upon
filtration through silica and crystallization from pentane in greater
than 92% yield (Eq. (6)). The insoluble byproduct of the reaction,
presumed to be ZneP containing, could not be identified. Forma-
tion of 7 was also observed upon reaction of an NMR sample of 1
with water. Important spectral features of 7 include the aryl reso-
resonance at
(
d 4.61. This new resonance was consistent with a new
TolL)Zn complex, which was initially suspected to be a phosphide
nances around
d 6.8 and the methylene resonances at d 2.01 and
d
1.48 in the 1H NMR spectrum. Isolation of 7 allowed for the
derivative. To gain insight into these reactions, they were per-
formed stoichiometrically.
positive identification of the same complex in attempted catalytic
reactions involving 1. Formation of 7 is consistent with the reac-
tivity observed by Van Koten and coworkers for alcoholysis reac-
tions of related Zn complexes [17].
3.2. Stoichiometric reactions with phosphines
Treatment of complex 2 with one equiv. of phenylphosphine in
benzene-d6 showed loss of the ethyl ligand on zinc and complete
consumption of phenylphosphine. A new product was formed in
low conversion featuring the same d
4.61 resonance in the 1H NMR
spectrum as observed in the catalytic reaction. A precipitate was
also formed, and like the precipitate from the catalytic reactions, it
was insoluble in common solvents. Attempts to run this reaction at
(6)
larger scales gave the compound with the resonance at
purity and unreliable yield.
d 4.61 of low

4330
B.A. Vaughan et al. / Journal of Organometallic Chemistry 696 (2012) 4327e4331
In nearly every reaction described, the formation of an insoluble
Mes), 143.2 (s, Mes), 134.4 (s, Mes), 130.9 (s, Mes), 130.1 (s, Mes),
129.7 (s, Mes), 127.4 (s, Mes), 127.3 (s, Mes), 71.8 (s, NC), 25.1 (s,
CH2), 22.0 (s, CH3), 20.9 (s, CH3), 20.8 (s, CH3), 19.0 (s, CH3), 18.0 (s,
CH3), 16.4 (s, CH3), 12.2 (S, CH3), 10.0 (s, ZnCH2CH3), ꢀ1.7 (s,
ZnCH2CH3). IR: 2919 w, 2139 m, 1549 m, 1528 m, 1397 s, 1365 s,
1276 m, 1197 m, 1173 m, 1016 w, 859 w, 807 m, 763 m, 748 w, 711 m,
694 w, 626 m, 584 m, 571 w, 554 m, 432 m, 417 w. Anal. Calcd. for
C26H38N2Zn: C, 70.33; H, 8.63; N, 6.31. Found: C, 70.38; H, 8.31; N,
6.45.
precipitate was observed. Because some reactions led to the clean
liberation of ancillary ligands such as the formation of 7 (vide
supra), it is suspected that a zinc phosphinidene may have been
formed analogously to known zinc imido complexes [24,25]. Efforts
to isolate any putative phosphinidene complex by dissolution in
a wide variety of solvents as well as conducting some of these
reactions in alternative solvents (e.g., THF, a là Powers magnesium
imide [26]) have not produced a clean products. Thus, we have
accrued no evidence to support the formation of a zinc phosphi-
nidene but no evidence to discount it either.
(
TolL)ZnEt (2). To a stirring solution of diethylzinc (3.6 mL, 1.5 M
in toluene), a solution of TolLH (0.52 g, 1.9 mmol) in toluene (10 mL)
was added dropwise at ambient temperature causing an immediate
color change to orange. The solution was stirred for 18 h then dried
under reduced pressure. The residue was extracted into minimal
pentane, and the solution was filtered then cooled to ꢀ30 ꢁC
4. Conclusion
In this study, three new zinc ethyl complexes 1, 2, and 4 were
prepared, and complexes 1 and 2 were structurally characterized.
These and other zinc complexes were tested for catalytic reactivity
in the dehydrocoupling of phosphines. Unfortunately, these reac-
tions demonstrate that the complexes selected for this study are
ineffective catalysts for the dehydrocoupling of primary phos-
phines. Given that different types of ancillary ligands were
explored, it appears that the formation of insoluble ZneP products
is the main problem in these reactions. These difficulties are further
yielding 2 as yellow crystals (0.54 g, 1.5 mmol, 78%). 1H NMR:
d 6.92
(d, C6H4CH3, 4 H, J ¼ 7.9 Hz), 6.74 (d, C6H4CH3, 4 H, J ¼ 8.2 Hz), 4.90
(s, CH, 1 H), 2.08 (s, CH3, 6 H), 1.83 (s, CH3, 6 H), 1.14 (t, CH3, 3 H,
J ¼ 8.1 Hz), 0.40 (q, CH2, 2 H, J ¼ 8.1 Hz). 13C{1H} NMR:
d 166.2 (s, C]
CH), 147.9 (s, tol), 133.6 (s, tol), 129.7 (s, tol), 124.7 (s, tol), 97.0
(H3CC]CHCCH3), 23.2 (s, CH3), 20.8 (s, CH3), 12.7 (s, CH2), ꢀ1.8 (s,
CH3). IR: 2919 w, 1548 m, 1499 s, 1394 s, 1275 m, 1196 m, 1015 m,
937 w, 859 m, 805 m, 747 w, 626 w, 530 m, 500 w. Anal. Calcd. for
C21H26N2Zn: C, 67.83; H, 7.05; N, 7.53. Found: C, 68.12; H, 7.24;
N, 7.64.
compounded by the comproportionation of complex 2 to bis(
diketiminate) complex 5. However, the isolation of complex 6,
though impure, suggests that ZneP -bonds can be stabilized and
b-
s
(dmpe)ZnEt2 (4). To a stirring solution of diethylzinc (4.0 mL,
1.5 mL in toluene), a solution of dmpe (1.0 mL, 6.0 mmol) in toluene
(2 mL) was added dropwise. The solution was stirred for 15 h and
dried under reduced pressure yielding 4 as a colorless crystalline
that other systems may provide catalytic activity.
5. Experimental Section
solid (1.63 g, 5.9 mmol, 99%). 1H NMR:
d 1.62 (t, ZnCH2CH3, 6 H,
5.1. General considerations
J ¼ 8.1 Hz), 1.05 (m, PCH2, 4 H), 0.72 (br. s, P(CH3)2, 12 H), 0.52 (q,
ZnCH2CH3, 4 H, J ¼ 8.1 Hz). 13C{1H} NMR:
d 26.8 (t, PCH2,
All manipulations were performed under an atmosphere of dry
nitrogen using standard Schlenk or high vacuum techniques and/or
in an M. Braun glovebox. Dry, oxygen-free solvents were employed
throughout. All NMR spectra were collected in benzene-d6 that was
purchased from Cambridge Isotope Laboratories, degassed, and
dried over NaK alloy. Elemental analyses were collected using an
Elementar VarioMICRO micro-analyzer. Infrared spectra were
collected on a Bruker Alpha FT-IR spectrometer using an ATR head.
NMR spectra (1H, 13C, and 31P) were recorded on a Bruker ARX
500 MHz NMR spectrometer (1H, 500.1 HMz; 31P, 202.4 MHz; 13C,
125.8 MHz) and are reported with reference to residual solvent
JPC ¼ 6.6 Hz), 14.7 (s, CH3), 11.8 (br. s, PCH3), 2.4 (s, ZnCH2CH3). 31
P
NMR (202.4 MHz):
d
ꢀ42.96 (s). IR: 2835 s, 1423 s, 1297 m, 1281 m,
1180 w,1096 m, 989 w, 939 s, 887 s, 860 m, 720 s, 590 s, 484 s, 444 s.
Anal. Calcd. for C10H26P2Zn: C, 43.89; H, 9.58. Found: C, 43.39;
H, 9.02.
(
TolL)2Zn (5). To a stirring solution of 2 (0.51 g, 1.4 mmol) in
toluene (10 mL), diethylzinc (3.6 mL, 1.5 M in toluene) was added
dropwise yielding an immediate color change to yellow. The solu-
tion was stirred for 18 h and dried under reduced pressure. The
crude product was then dissolved in minimal ether, and the solu-
tion was then cooled to ꢀ30 ꢁC. The resulting solid was then dis-
solved in minimal pentane, the solution filtered, and then cooled
to ꢀ30 ꢁC to afford 5 as colorless crystals (0.48 g, 0.77 mmol, 84%).
resonances (C6HD5
d
7.16 and
d
128.0). 1,4-Bis(2,4,6-
trimethylphenyl)-2,3-dimethyl-1,4-diaza-1,3-butadiene, para-tolyl
1,3-diketimine (TolLH), and (DippL)ZnEt (3, DippL ¼ [(2,6-iPrC6H3)
NC(CH3)]2CHꢀ) were prepared according to literature protocols,
and toluidineꢂHCl was prepared using the method reported by
Barton and Young [22,27e29].
1H NMR:
d
6.97 (d, C6H4CH3, 8 H, J ¼ 8.1 Hz), 6.81 (d, C6H4CH3, 8 H,
J ¼ 8.2 Hz), 4.61 (s, CH, 2 H), 2.13 (s, C6H4CH3, 12 H), 1.77 (s, CH3,
12 H). 13C{1H} NMR:
165.8 (s, C]CH), 148.3 (s, tol), 132.2 (s, tol),
d
129.0 (s, tol), 124.6 (s, tol), 95.8 (s, C]CH), 22.9 (s, CH3), 20.6 (s,
CH3). IR: 3017 w, 2918 w, 2860 w, 1548 m, 1499 m, 1394 s, 1276 s,
1196 s, 1105 w, 1015 m, 938 m, 860 w, 806 m, 747 m, 626 m, 531 m,
500 w. Anal. Calcd. for C38H42N4Zn: C, 73.59; H, 6.83; N, 9.03.
Found: C, 73.39; H, 7.30; N, 9.02.
5.2. Synthetic procedures
(
MesAI)ZnEt (1). To a stirring solution of diethylzinc (2.5 mL,
1.5 M in toluene), a solution of diazabutadiene (1.1 g, 3.5 mmol) in
toluene (10 mL) was added dropwise at ambient temperature
causing an immediate color change to deep red. The solution was
stirred for an additional 10 min then dried under reduced pressure
The resulting oil was dissolved in minimal pentane and cooled
to ꢀ30 ꢁC yielding 1 as an orange solid (1.1 g, 2.5 mmol, 81%). 1H
(
DippL)ZnPHPh (6). A PTFE-valved reaction tube was charged
with 3 (137 mg, 0.267 mmol), approximately five equiv. of PhPH2
(146 mg, 1.327 mmol), and 5 mL of toluene. The vessel was sealed
and the pale orange solution was heated at 70 ꢁC for 8 h. The
volatile materials were removed under reduced pressure, and the
resultant yellow oil was dissolved in minimal Et2O. The solution
was filtered then cooled to ꢀ30 ꢁC to yield 161 mg of a colorless
crystalline solid that contained 6 (>80%) and starting 3. Data for 6
NMR:
d 7.05 (s, C6H2(CH3)3, 2 H), 6.73 (s, C6H2(CH3)3, 1 H), 6.72 (s,
C6H2(CH3)3, 1 H), 2.49 (s, CH3, 3 H), 2.46 (s, CH3, 3 H), 2.29 (s, CH3,
3 H), 2.12 (s, CH3, 3 H), 2.00 (s, CH3, 3 H), 1.94 (s, CH3, 3 H), 1.79 (m,
CH2,1 H),1.33 (s, CH3, 3 H),1.31 (m, CH2,1 H),1.20 (t, ZnCH2CH3, 3 H,
J ¼ 8.1 Hz), 1.13 (s, CH3, 3 H), 0.92 (t, CH3, 3 H, J ¼ 7.3 Hz), 0.51 (q,
1H NMR:
d
7.09 (d, Ar, 2 H, J ¼ 8 Hz), 6.73e6.63 (m, Ar, 9 H) 4.91 (s,
CH, 1 H), 4.92 (d, PH, 1 H, JPH ¼ 211) 3.11 (sept. CH, 2 H), 1.67 (s, CH3,
6 H), 1.55 (d, CH3, J ¼ 7 Hz), 1.11 (d, CH3, J ¼ 7 Hz). 31P NMR:
ZnCH2CH3, 2 H, J ¼ 8.1 Hz). 13C{1H} NMR:
d
191.1 (s, N]C), 149.5 (s,
d
ꢀ152.3 (s).

B.A. Vaughan et al. / Journal of Organometallic Chemistry 696 (2012) 4327e4331
4331
Table 3
The structures were solved using direct methods and standard
difference map techniques and were refined by full-matrix least-
squares procedures on F2 with SHELXTL (version 6.14) [30]. All non-
hydrogen atoms were refined anisotropically. Hydrogen atoms on
carbon were included in calculated positions and were refined
using a riding model. Crystal data and refinement details are pre-
sented in Table 3.
Crystal data and structure refinement parameters for 1 and 2.
1
2
Formula
M
Cryst syst
Color
a/Å
C26H38N2Zn
444.00
C42H52N4Zn2
743.62
Monoclinic
Colorless
7.9835(8)
23.309(2)
13.0485(13)
90.00
94.6350(10)
90.00
2420.2(4)
P21/n
Monoclinic
Colorless
12.2791(7)
22.4735(13)
13.9929(8)
90.00
99.0660(10)
90.00
3813.2(4)
P21/n
b/Å
c/Å
Appendix. Supplementary material
a/deg
b/deg
g/deg
Crystallographic data for complexes 1 and 2, CCDC 843858 and
843859, can be obtained free of charge from the Cambridge Crys-
tallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Unit cell vol/Å3
Space group
Z
4
4
q
m
range/deg
2.35 to 29.25
1.029
2.40 to 29.14
1.292
/mmꢀ1
Acknowledgments
N
30283
47641
Nind
Rint
6383
0.0261
0.0379
0.1058
10054
0.0222
0.0373
0.1077
This work was supported by the U. S. National Science Foun-
dation (NSF, CHE-0747612). X-ray facilities were provided by the
NSF (CHE-1039436). The authors thank Dr. David Newsham for the
synthesis of TolLH. EMA thanks UVM Office of Undergraduate
Research for a Summer Internship Award, and SMC thanks the
American Chemical Society Project SEED for summer support. RW
is a Sloan Research Fellow and a Cottrell Scholar.
R1a (I > 2
s
(I))
(I))
Drmin/e Å3
b
wR2 (I > 2
Drmax
GoF on R1
s
;
0.559; ꢀ0.509
0.687; ꢀ0.625
1.050
1.085
a
R1 ¼ jFoj e jFcj/SjFoj.
b
wR2 ¼ {S[w{F2o e F2c)2]/S[w(Fo2)2]}1/2
.
References
(E)-N-(3-(mesitylamino)-3-methylpentan-2-ylidene)-mesityla-
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Method C- Reaction with water. A solution of 1 (0.01 g,
0.02 mmol) in benzene-d6 (0.7 mL) was removed from the glove-
box. The cap was removed and the sample was exposed to air. The
reaction gave the organic product based on 1H NMR spectroscopy.
1H NMR:
d 6.85 (s, C6H2(CH3)3, 2 H), 6.83 (s, C6H2(CH3)3, 2H),
5.47 (s, NH, 1 H), 2.41 (s, C6H2(CH3)3, 6 H), 2.21 (d, C6H2(CH3)3, 3 H),
2.20 (s, C6H2(CH3)3, 3 H), 2.08 (s, C6H2(CH3)3, 3 H), 2.00 (m,
CCH2CH3, 1 H), 1.97 (s, C6H2(CH3)3, 3 H), 1.49 (m, CCH2CH3, 1 H), 1.41
(s, N]CCH3, 3 H), 1.06 (s, HNCCH3, 3 H), 1.04 (t, CCH2CH3, 3 H,
J ¼ 7.4 Hz). 13C{1H} NMR:
d 174.9 (s, N]C), 146.3 (s, Mes), 142.6 (s,
Mes), 135.0 (s, Mes), 132.0 (s, Mes), 129.8 (s, Mes), 129.3 (s, Mes),
126.1 (s, Mes), 125.0 (s, Mes), 65.1 (s, HNC), 32.5 (s, CH2), 24.5 (s,
CH3), 20.9 (s, CH3), 20.8 (s, CH3), 18.8 (s, CH3), 18.2 (s, CH3), 15.5 (s,
CH3), 9.2 (s, CH3). IR: 3314 s (nNH), 2971 m, 2950 m, 2916 m, 2855 m,
1646 s (nCN), 1470 s, 1446 m, 1301 w, 1227 s, 1182 m, 1147 m, 1121 m,
849 s, 788 s, 727 m, 670 m, 565 m, 463 m. Anal. Calcd. for C24H34N2:
C, 82.23; H, 9.78; N, 7.99. Found: C, 82.05; H, 9.70; N, 7.65.
X-ray Structure Determinations. X-ray diffraction data were
collected on a Bruker APEX 2 CCD platform diffractometer (Mo K
¼ 0.71073 Å) at 125 K. Suitable crystals of each complex 1 and 2
were mounted in a nylon loop with Paratone-N cryoprotectant oil.
a,
l
[30] G.M. Sheldrick, Acta Crystallogr. Sect. A: Found. Crystallogr. 64 (2008)
112e122.