Zirconium-mediated synthesis of arsaalkene compounds from arsines and isocyanides

Article abstract of DOI:10.1021/ic4012058

An atom-economical synthesis of arsaalkenes via a net coupling of aryl arsines with aryl or alkyl isocyanides at zirconium is presented. Reaction of zirconium arsenido complexes (N₃N)ZrAsHAr [N₃N = N(CH ₂CH₂NSiM

Full text of DOI:10.1021/ic4012058

Article
pubs.acs.org/IC
Zirconium-Mediated Synthesis of Arsaalkene Compounds from
Arsines and Isocyanides
Annalese F. Maddox,† Jillian J. Davidson,† Tamila Shalumova,‡ Joseph M. Tanski,‡ and Rory Waterman*,†
†Department of Chemistry, University of Vermont, Burlington, Vermont 05405, United States
‡Department of Chemistry, Vassar College, Poughkeepsie, New York 12604, United States
S
* Supporting Information
ABSTRACT: An atom-economical synthesis of arsaalkenes
via a net coupling of aryl arsines with aryl or alkyl isocyanides
at zirconium is presented. Reaction of zirconium arsenido
3−
complexes (N3N)ZrAsHAr [N3N = N(CH2CH2NSiMe3)3
;
Ar = Ph, (2) Mes (3)] with aryl and alkyl isocyanides yields
arsaalkene products of the general form (N3N)Zr[NRC(H)
As(Ar)]. Two examples (5: R = Mes, Ar = Ph; 6: R = CH2Ph,
Ar = Mes) were structurally characterized. Observation of
intermediates in the reaction and structural characterization of
the previously reported 1,1-insertion product benzylisocyanide with (N3N)ZrAsPh2 (8), (N3N)Zr[η2-C(PPh2)=NCH2Ph] (9),
support the mechanistic hypothesis that these reactions occur via 1,1-insertion followed by rearrangement.
expansion of that reactivity to a synthesis of arsaalkenes is
presented. Metal-mediated syntheses of multiple bonds in the
main group are rare,1c,3c,6 and expansion of methods that
produce E−E multiply bonded species may represent a new
paradigm in inorganic synthesis.
INTRODUCTION
■
It is well-known that the development of low valent
organoarsenic chemistry has lagged behind that for phospho-
rus.1 In some instances, this lag has been attributed to less
developed synthetic methods associated with the heavier
congener.2 More commonly, the reduced stability of arsenic−
carbon multiple bonds as compared to their phosphorus
counterparts has hampered development.1a However, the
tremendous reaction chemistry exhibited by phosphaalkenes3
as well as their application in materials science4 argues for
continued exploration of arsaalkenes and potential applications.
Principal synthetic methods that produce phosphaalkenes
also apply to the preparation of arsaalkenes.3c,d These common
methods include condensation reactions, 1,2-elimination of
typically HCl, and 1,3-silyl migration.1a The drawback to all of
these methods is the amount of waste generated, but in some
cases, syntheses are dependent on the presence of specific
functional groups or exhibit limited functional group tolerance.
Recently, we have established a general synthetic route to
phosphaalkenes by reaction of zirconium phosphide complexes,
derived from primary phosphines, with isocyanides (eq 1).5
RESULTS AND DISCUSSION
■
It has been established that [κ5 -N,N,N,N,C-
(Me3SiNCH2CH2)2NCH2CH2NSiMe2CH2]Zr (1) is a con-
venient precursor to Zr−E bonds by E−H activation.7 Indeed
this is also true for arsines, and (N3N)ZrAsHPh (2) was
prepared by reaction of 1 with 1 equiv of phenylarsine and
isolated as analytically pure yellow crystals in 76% yield (eq 2).
The spectroscopic data for 2 mimic those of the previously
reported primary arsenido complex (N3N)ZrAsHMes (3, Mes
= 2,4,6-trimethylphenyl)8 and are similar to those of other
zirconium complexes featuring terminal arsenido ligands.9 The
diagnostic spectroscopic features of 2 include an arsenido
proton resonance at δ 3.42 in the 1H NMR spectrum and νAsH
= 2061 cm−1 in the infrared.
Both arsenido complexes 2 and 3 react readily with aryl and
alkyl isocyanides to give analytically pure arsaalkene products,
(N3N)Zr[N(R)CH=AsAr], that can be isolated in good to
The tolerance of the phosphaalkene synthesis toward
isocyanide substitution and the ability to use aryl and alkyl
phosphines argue that this method may have yet broader
promise, including the synthesis of arsaalkenes. Herein,
Received: May 14, 2013
© XXXX American Chemical Society
A
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Article
excellent yields (eq 3, Table 1). The reaction of arsenido
complexes with isocyanide proceeded smoothly to product, in
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
(N3N)Zr[N(Mes)CHAsPh] (5) and
(N3N)Zr[N(CH2Ph)CHAsMes] (6)
5
6
Bonds Length
Zr−N(1)
Zr−N(2)
Zr−N(3)
Zr−N(4)
Zr−N(5)
As−C(16)
2.089(3)
2.0831(14)
2.1016(13)
2.0824(14)
2.4467(14)
2.1629(13)
1.8419(16)
1.9735(16)
1.347(2)
2.072(3)
2.064(3)
2.517(3)
2.194(3)
1.845(4)
1.966(4)
1.359(5)
a
As−R
N(5)−C(16)
Table 1. Selected Spectroscopic Data for Arsaalkene
Products 4−7
a
Bond Angles
As−C(16)−N(5)
H(1)−C(16)−N(5)
As−C(16)−H(16)
113.2(2)
134.0(2)
112.8(3)
95.28(1)
127.5(1)
114.5(1)
118.0(1)
97.7(7)
cmpd
yield (%)
R
R′
AsCH (δ)
AsC (δ)
4
5
6
7
86
97
78
82
Ph
CH2Ph
Mes
11.46
11.54
10.95
11.01
251.4
214.3
273.5
262.2
b
Ph
C−As−C(16)
Mes
CH2Ph
a
b
Substituent at arsenic, C(21) for 5 and C(22) for 6. The “R−As−C
angle” where R is the arsenic substituent.
Mes
Mes
a
1H and 13C NMR spectroscopic data collected in benzene-d6 solution.
most cases, at ambient temperature. As a precaution, reactions
were performed in the absence of light. However, it was shown
for these examples, that similar yields to those noted can be
obtained under ambient lighting.
compounds is short (Table 2), as anticipated, and the values fit
neatly within the range of structurally characterized examples of
arsaalkenes.1,6a Of course arsenic substitution has substantial
effect on AsC bond length (i.e., normal vs inverse demand).
The AsC bonds of compounds 5 and 6 are similar to other
examples of monoamine substituted arsaalkenes including
Cp*Fe(CO)2AsC(Ph)NMe (AsC = 1.84.9 (7) Å),10 but
these bonds are still longer than the theoretical As−C π-bond
length of 1.79.11
As expected from steric arguments, the arsenic substituent is
syn to the crystallographically located arsaalkene hydrogen
atom. In both examples, the R−As−C angle is acute within the
range of structurally characterized arsaalkenes (Table 2). For 6,
this angle is slightly more obtuse than that for 5, which may be
a result of the steric demands of the mesityl substituent on
arsenic. There has not been a great deal of comment in the
literature regarding the R−As−C angle, which varies over not
less than 22° for reported examples.1a However, it has been
suggested for a variety of other multiply bonded systems that a
shallow R−E−E′ angle is consistent with greater s-character of
the lone pair at E.1c
The indicative spectroscopic features for these compounds
1
include arsaalkene H NMR and 13C NMR resonances (Table
1). The benzyl-substituted products 4 and 6 exhibit arsaalkene
resonances downfield as compared to those of the mesityl-
1
substituted derivatives 5 and 7 in the respective H NMR
spectra, while the reverse trend is observed in the 13C NMR
spectra. These trends suggest that the electronic influence of
the nitrogen substituent is likely the dominant factor in these
chemical shifts rather than ring current at the mesityl
substituent. In all instances, the 13C NMR resonances are
consistent with reported arsaalkenes.1,6a
Solid state structures of two arsaalkene derivatives, 5 and 6,
were determined by X-ray diffraction studies using crystals
grown from concentrated ethereal solutions cooled to −30 °C.
The compounds are as highly similar as is visually evident in
Figure 1 and are isostructural based on comparison of metrical
parameters (Table 2). The AsC bond length for both
Figure 1. Molecular structure of (N3N)Zr[N(Mes)CHAsPh] (5, left) and (N3N)Zr[N(CH2Ph)CHAsMes]·Et2O (6, right), with thermal
ellipsoids drawn at the 50% level. Hydrogen atoms, except those located on C(16), as well as solvent of crystallization for 6 are omitted for clarity.
B
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Perhaps the most striking feature of the solid state structures
of arsaalkene compounds 5 and 6 are that neither the As lone
pair nor AsC bond are associated with zirconium. This
stands in contrast with the known bonding modes of arsaalkene
ligands,1a yet the lack of interaction is consistent with highly
related phosphaalkene complexes prepared analogously.5 This
behavior may be these less a function of these ligands and more
of the (N3N)Zr platform, for which six-coordinate examples are
limited and involve stronger donors. For example, phosphine-
substituted iminato ligands bind exclusively in an η1 fashion,
whereas phosphaguanidinate ligands bind in an η2 fashion but
only through the nitrogen atoms.12
to the same reaction to form phosphaalkenes is a result of the
increased size of arsenic.1a Of course, the pivotal migration
herein is a 1,2-H shift, but the reverse of the trend seen for 1,3-
silyl migration is intriguing and suggests that atomic size may
not be the only factor governing the rate of migration. These
apparent disparities invite further study of migration reactions
between phosphorus and arsenic.
Despite the inability to isolate a 1,1-insertion intermediate,
some evidence to support this mechanistic hypothesis comes
from the reaction of secondary phosphines with isocyanides. As
previously reported, (N3N)ZrAsPh2 (8) reacts with benzyliso-
cyanide to give the 1,1-insertion product (N3N)Zr[C(AsPh2)-
N(CH2Ph)] (9). This is a general transformation. For
example, reaction of tert-butylisocyanide with 8 affords
analytically pure, yellow crystals of (N3N)Zr[C(AsPh2)-
N(CtBu)] (10) in 76% yield (eq 5). Compound 10 was
Complete conversion to product 5 required mild heating to
40 °C for approximately 20 min. Observation of the reaction of
2 with mesitylisocyanide by 1H NMR spectroscopy in benzene-
d6 solution revealed an intermediate with a new arsenic proton
resonance at δ 5.50 that is tentatively assigned as the 1,1-
insertion product based on the relative similarity of the arsenido
proton chemical shift to that of related phosphine-substituted
iminoacyl compounds.5 Formation of 5 is qualitatively slower
than generation of the intermediate, but sufficient concen-
trations of the intermediate could not be generated for more
thorough characterization. All efforts to isolate such inter-
mediates in any reaction of 2 or 3 with isocyanide failed.
Reaction of tert-butylisocyanide with arsenido complex 3
gave a mixture of products that is analytically the simple
combination of the two reagents (Anal. Calcd for
C29H60N5AsSi3Zr: C, 47.76; H, 8.29; N, 9.60. Found: C,
1
47.86; H, 8.08; N, 9.31). Observation of the mixture by H
NMR spectroscopy revealed a resonance at δ 10.92 that
accounted for all of the arsenic proton by mass balance. In the
13C NMR spectrum however, strong evidence for two products
is given by resonances at δ 265.5 and δ 142.8, where the former
is coupled to the aforementioned proton and the latter is not
characterized by the usual suite of techniques and gave similar
spectroscopic data to that of 9 and the products of related
insertion reactions involving phosphido derivatives.5,8
In the course of this study, single crystals of 9 were obtained
by cooling an ethereal solution to −30 °C for extended periods.
The molecular structure of 9 reveals an η2-bound iminoacyl
ligand, consistent with the infrared data (Figure 2). The bond
lengths are particularly important here. For 9, As−C(16) =
1
1
via an H-13C HMQC experiment. The H NMR data suggest
that neither compound is a 1,1-insertion product, and the
reaction may produce a mixture of the desired arsaalkene
product (N3N)Zr[N(tBu)CHAsMes] and the arsaamidinate
compound (N3N)Zr[N(tBu)C(H)AsMes], which is the
tautomer of the arsaalkene. Current data prohibits assignment
t
of a binding mode for the proposed BuNC(H)AsMes−
ligand, and the rich variety of binding for the phosphorus
derivative of these amidinate congeners suggests a range of
options are possible.13 Exclusive formation of the phospha-
formamidinate product (N3N)Zr[N,P:η2-N(tBu)C(H)PPh]
(i.e., the phosphaalkene tautomer) was seen in the reaction of
tert-butylisocyanide with (N3N)ZrPHPh, suggesting unique
reactivity associated with this particular isocyanide substrate.5b
Efforts to separate the two species failed, and subjecting the
reaction to more forcing conditions only resulted in eventual
decomposition.
The reaction of 2 with benzylisocyanide proceeded to
product 4 at ambient temperature without observation of an
intermediate by 1H NMR spectroscopy in benzene-d6 solution.
In the reaction of (N3N)ZrPHPh with benzylisocyanide, the
1,1-insertion product was isolated prior to formation of the
phosphaalkene (eq 4).5a That no intermediate is observed in
the reaction of arsenido derivative 2, an exact analogue to
(N3N)ZrPHPh, with benzylisocyanide suggests that rearrange-
ment to form phosphaalkenes is slower than that to form
arsaalkenes.
Figure 2. Molecular structure of (N3N)Zr[C(AsPh2)N(CH2Ph)]
(9) with thermal ellipsoids drawn at the 50% level. Hydrogen atoms
are omitted for clarity. Selected bond lengths (Å) and angles (deg):
Zr−N(1) = 2.1218(1), Zr−N(2) = 2.0923(2), Zr−N(3) = 2.4703(1),
Zr−N(4) = 2.2466(1), Zr−N(5) = 2.1186(1), C(16)−N(5) =
1.285(1), Zr−C(16) = 2.2840(2), C(16)−As = 1.974(2), Zr−
C(16)−N(5) = 71.94(9), Zr−N(5)−C(16) = 75.14(9), C(16)−Zr−
N(5) = 32.93(5), N(2)−C(16)−As = 128.7(1).
It has been proposed that the relative sluggishness of arsenic
to undergo 1,3-silyl migration to form arsaalkenes as compared
C
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was filtered and then concentrated until incipient crystallization under
reduced pressure. After gentle warming to redissolve the solids, the
solution was cooled to −30 °C for several days to afford orange
crystals (128 mg, 0.178 mmol, 86%). 1H (500 MHz): δ 11.46 (s, As
CH, 1 H), 7.93 (t, C6H5, 2 H), 7.53 (d, C6H5, 2 H), 7.24 (t, C6H5, 2
H), 7.19 (t, C6H5, 2 H), 7.08 (t, C6H5, 2 H), 5.15 (s, CH2, 2 H), 3.17
(t, CH2, 6 H), 2.25 (t, CH2, 6 H), 0.15 (s, CH3, 27 H). 13C{1H}
(125.8 MHz): δ 251.4 (s, AsC); 134.3 (s, C6H5), 133.3, (s, C6H5),
126.9 (s, C6H5), 126.2 (s, C6H5), 64.2 (s, CH2), 59.4 (s, CH2), 46.7 (s,
CH2), 1.24 (s, CH3). IR 3051 w, 2948 m, 2887 w, 2845 m, 1642 w,
1574 w, 1475 w, 1451 w, 1330 m, 1299 w, 1242 s, 1183 m, 1155 w,
1103 m, 1051 m, 1019 m, 996 s, 925 m, 825 s, 785 m, 744 m, 731 s,
689 m, 641 m, 622 m, 561 m, 456 m, 430 m, 408 m. Anal. Calcd for
C29H52N5AsSi3Zr: C, 48.30; H, 7.27; N, 9.71. Found: C, 47.92; H,
7.36; N, 9.44.
1.974(2) Å as well as the angles about arsenic are inconsistent
with As−C multiple bond character while C(16)−N(5) =
1.285(1) Å is consistent with an imine functionality.
Isocyanide 1,1-insertion reactions with group 4 arsenido
complexes are known. The first example was reaction of
phenylisocyanide with Cp′2HfCl[As(SiMe3)2] as reported by
Hey-Hawkins.9b The structural similarities of that hafnium
compound and 9 are high. More important, the prevalence of
these 1,1-insertion reactions argue for their intermediacy in the
formation of arsaalkenes at primary arsenido complexes.
CONCLUSIONS
■
Insertion of isocyanides into Zr−As bonds yields iminoacyl
products that are unstable with respect to rearrangement to
afford arsaalkene products for primary arsenide ligands. This
stands in contrast to literature examples of isocyanide insertion
into Zr−As bonds that yield stable iminoacyl products for
secondary arsines. Indeed this is a second example in which
zirconium arsenide chemistry significantly changes between
primary and secondary arsines. These observations imply that
rich reaction chemistry of M−As bonds may yet be available
upon further exploration. This reaction type, a net coupling of
arsines with isocyanides at zirconium, appears to be a general
transformation based on the examples provided and may
represent the basis for new, metal-mediated synthetic strategies
to multiple bonding in the main group.
(N3N)Zr[N(Mes)CHAsPh] (5). A 2 mL ethereal solution of
mesitylisocyanide (41 mg, 0.282 mmol) was added dropwise to a 5 mL
ethereal solution of 2 (170 mg, 0.281 mmol) cooled to −30 °C in the
dark. The resultant red-orange solution was heated to 40 °C for 20
min, filtered, then concentrated until incipient crystallization under
reduced pressure. After gentle warming to redissolve the solids, the
solution was cooled to −30 °C for several days to afford orange
crystals. Analytically pure material was given by dissolving the crystals
in benzene followed by filtration of the solution though Celite and
lyophylization, presumed to remove ether trapped in crystallization, to
1
afford a red-orange powder (205 mg, 0.274 mmol, 97%). H (500
MHz): δ 11.54 (s, AsCH, 1 H), 7.98 (d, C6H5, 2 H); 7.24 (t, C6H5,
2 H), 7.13 (m, obscured by solvent), 6.92 (s, C6Me3H2, 2 H), 3.19 (t,
CH2, 2 H), 2.63 (s, o-CH3, 6 H), 2.26 (t, CH2, 6 H), 2.17 (s, p-CH3, 3
H), 0.17 (s, CH3, 27 H). 13C{1H} (125.8 MHz): δ 214.3 (s, AsCH),
141.2 (s, Ar), 138.3 (s, Ar), 134.1 (s, Ar), 131.5 (s, Ar), 131.4 (s, Ar),
129.3 (s, Ar), 128.4 (s, Ar), 68.4 (s, CH2); 49.5 (s, CH2), 23.9 (s, o-
CH3), 23.8 (s, o-CH3), 13.8 (s, p-CH3), 0.08 (s, CH3). One aryl
resonance was not observed, presumably obscured by solvent. IR:
3059 w, 2949 w, 2893 w, 2850 w, 1476 w, 1395 w, 1348 w, 1309 w,
1246 m, 1183 w, 1146 w, 1125 m, 925 m, 891 m, 830 s, 782 s, 733 s,
674 m, 539 m, 471 m, 435 m. Anal. Calcd for C31H56N5AsSi3Zr: C,
49.70; H, 7.53; N, 9.35. Found: C, 50.30; H, 8.23; N, 9.00.
EXPERIMENTAL DETAILS
■
Reactions were performed under a purified nitrogen atmosphere using
dry, oxygen-free solvents in an M. Braun glovebox or by standard
Schlenk techniques. Celite-454 was heated to a temperature above 180
°C under dynamic vacuum for at least 8 h. Benzene-d6 was purchased
then degassed and dried over NaK alloy. Elemental analyses were
performed on an Elementar microCube. NMR spectra were recorded
with either a Bruker Avance III, Bruker ARX, or Varian 500 MHz
spectrometer in benzene-d6 and are reported with reference to residual
solvent resonances (δ = 7.16 and 128.0) unless otherwise noted.
Infrared spectra were collected on a Bruker Alpha FT-IR with an ATR
plate or a Perkin-Elmer System 2000 FT-IR spectrometer at a
resolution of 1 cm−1 with KBr plates.
(N3N)Zr[N(CH2Ph)CHAsMes] (6). A 2 mL solution of
benzylisocyanide (21 mg, 0.178 mmol) was cooled to −30 °C and
added to a 4 mL ethereal solution of 3 (112 mg, 0.174 mmol) at −30
°C in the dark. The reaction mixture was stirred in the dark while
warming to ambient temperature over 4 h. The resulting orange
solution was then filtered and concentrated to ∼2 mL before being
cooled to −30 °C for several days to afford orange-yellow crystals (103
Compounds 1, 3, and 8, and 9 were prepared using the literature
procedures.7,8 Mesitylisocyanide was prepared according to the
literature procedure for phenylisocyanide substituting 2,4,6-trimethy-
laniline.14 Diphenylarsine and mesitylarsine were prepared according
to literature procedure.8 Phenylarsine was prepared using a modified
version of that in the literature.15 All other chemicals were obtained
from commercial suppliers and dried or purified by conventional
means.
(N3N)ZrPhAsH (2). A −30 °C, 5 mL ethereal solution of PhAsH2
(197 mg, 1.28 mmol) was added dropwise to a 5 mL ethereal solution
of 1 (605 mg, 1.34 mmol) at −30 °C. The colorless solution was
stirred and allowed to warm to ambient temperature over 16.5 h. The
resulting red solution was filtered through Celite, concentrated to ∼2
mL, and then cooled to −30 °C for 24 h to afford yellow crystals (587
mg, 0.972 mmol, 76%). 1H (500 MHz): δ 7.91 (t, J = 7.05 Hz, C6H5, 1
H); 7.79 (d, J = 7.09 Hz, C6H5, 2 H); 7.11 (t, J = 7.44 Hz, C6H5, 2 H);
3.42 (s, AsH, 1 H); 3.17 (t, J = 5.00 Hz, CH2, 6 H); 2.09 (t, J = 5.00
Hz, CH2, 6 H); 0.27 (s, CH3, 27 H). 13C{1H} (125.8 MHz): δ 134.9
(s, C6H5); 128.5 (s, C6H5), 126.5 (s, C6H5), 123.9 (s, C6H5); 63.6 (s,
CH2); 47.5 (s, CH2); 0.9 (s, CH3). IR 2061 (νAsH) cm−1. Anal. Calcd
for C21H45N4AsSi3Zr: C, 41.76; H, 7.51; N, 9.28. Found: C, 41.41; H,
7.72; N, 9.23.
1
mg, 0.136 mmol, 78%). H (500 MHz): δ 10.95 (s, AsCH, 1 H),
7.60 (d, C6H6,2 H), 7.50 (t, C6H6, 2 H), 7.12 (d, C6H6, 2 H), 6.94 (s,
C6Me3H2, 2 H), 5.20 (s, CH2, 2 H), 3.11 (t, CH2, 2 H), 2.68 (s, CH3, 6
H), 2.34 (s, CH3, 3 H), 2.25 (t, CH2, 6 H), 0.11 (s, CH3, 27 H).
13C{1H} (125.8 MHz): δ 273.53 (s, AsC), 140.0 (s, Ar); 135.5 (s,
Ar), 135.0 (s, Ar), 134.8 (s, Ar), 131.6 (s, Ar), 129.1 (s, Ar), 128.3 (s,
Ar), 65.0 (s, CH2); 64.1 (s, CH2), 46.6 (s, CH2), 25.0 (s, o-CH3), 20.0
(s, p-CH3), 1.2 (s, CH3). One aryl resonance was not observed,
presumably obscured by solvent. IR: 3062 w, 2955 w, 2873 w, 1565 w,
1471 w, 1340 w, 1322 w, 1303 w, 1244 m, 1183 w, 1148 w, 1115 m,
925 m, 875 m, 828 s, 782 s, 732 s, 679 m, 531 m. Anal. Calcd for
C32H58N5AsSi3Zr: C, 50.36; H, 7.66; N, 9.18. Found: C, 50.51; H,
7.84; N, 9.02.
(N3N)Zr[N(Mes)CHAsMes] (7). A 2 mL solution of mesityliso-
cyanide (16 mg, 0.110 mmol) was cooled and added to a 3 mL
ethereal solution of 3 (68 mg, 0.105 mmol) at −30 °C in the dark. The
reaction mixture was stirred in the dark while warming to ambient
temperature over 5 h. The resulting yellow solution was then filtered
and concentrated to ∼2 mL before being cooled to −30 °C for 2 d to
1
afford yellow crystals (69 mg, 0.087 mmol, 82%). H (500 MHz): δ
11.01 (s, AsCH, 1 H); 6.96 (s, C6Me3H2, 2 H), 6.73 (s, C6Me3H2, 2
H), 3.21 (t, CH2, 2 H), 2.76 (s, CH3, 6 H), 2.71 (s, CH3, 6 H), 2.34 (s,
CH3, 3 H), 2.22 (t, CH2, 2 H); 2.17 (s, CH3, 3 H), 0.13 (s, CH3, 27
H). 13C{1H} (125.8 MHz): δ 262.2 (s, AsC) 144.6 (s, C6Me3H2),
143.2 (s, C6Me3H2), 138.7 (s, C6Me3H2), 137.1 (s, C6Me3H2), 134.5
(N3N)Zr[N(CH2Ph)CHAsPh] (4). A 2 mL ethereal solution of
benzylisocyanide (25 mg, 0.212 mmol) was added dropwise to a 5 mL
ethereal solution of 2 (125 mg, 0.207 mmol) cooled to −30 °C in the
dark and stirred for 2 h at ambient temperature. The resulting solution
D
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Table 3. Crystal Data and Structure Refinement Parameters for Compounds 5, 6, and 9
5
6
9
formula
M
C31H56AsN5Si3Zr
749.22
C34H63AsN5Si3ZrO0.5
800.30
C35H56AsN5Si3Zr
797.26
crystal syst.
a/Å
monoclinic
10.2583(1)
21.351(3)
17.623(2)
90
triclinic
monoclinic
11.3035(5)
19.5564(9)
19.0860(9)
90
11.3755(6)
12.1971(6)
16.5256(8)
84.972(1)
b/Å
c/Å
α/deg
β/deg
γ/deg
V/Å3
90.998(2)
90
72.278(1)
106.078(1)
90
70.593(1)
3859.4(9)
P21/n
2059.76(18)
4054.0(3)
P21/n
space group
Z
P1
̅
4
2
4
θ range/deg
μ/mm−1
N
2.20 to 23.98
1.255
1.29 to 28.33
1.181
1.52 to 29.20
1.199
33524
27250
55579
Nind
6025
10195
10961
Rint
0.0463
0.0229
0.0261
0.0640
1.077
0.0381
a
R1 (I > 2σ(I))
0.0406
0.0283
b
wR2 (I > 2σ(I))
0.1038
0.0635
Δρmax/e Å3
Δρmin/e Å3
GoF on R1
1.518
0.540
−0.610
1.063
−0.553
1.077
−0.483
1.020
a
b
2
2
R1 = ∑||Fo| − |Fc||/∑|Fo|. wR2 = {∑[w(Fo − Fc2)2]/∑[w(Fo )2]}1/2
.
(s, C6Me3H2), 131.0 (s, C6Me3H2), 129.3 (s, C6Me3H2), 128.0 (s,
C6Me3H2), 65.3 (s, CH2), 46.4 (s, CH2), 26.9 (s, o-CH3), 24.7 (s, o-
CH3), 20.9 (s, p-CH3), 20.7 (s, p-CH3), 0.99 (s, CH3). IR: 3045 w,
2943 m, 2884 w, 1576 w, 1473 w, 1456 w, 1328 m, 1298 w, 1238 s,
1183 m, 1158 w, 1101 m, 1048 m, 925 m, 867 s, 781 m, 739 m, 730 s,
684 m. Anal. Calcd for C34H62N5AsSi3Zr: C, 51.61; H, 7.90; N, 8.85.
Found: C, 51.74; H, 7.76; N, 8.58.
ASSOCIATED CONTENT
* Supporting Information
Crystallographic data for complexes 5, 6, and 9 (CIF). This
material is available free of charge via the Internet at http://
pubs.acs.org.
■
S
AUTHOR INFORMATION
Corresponding Author
*E-mail: rory.waterman@uvm.edu.
Notes
■
(N3N)Zr[C(AsPh2)NtBu] (10). A 2 mL ethereal solution of tert-
butylisocyanide (13 mg, 0.155 mmol) was added to a 5 mL ethereal
solution of 8 (104 mg, 0.153 mmol) cooled to −30 °C. After 3 h
stirring at ambient temperature, the yellow solution was filtered
through a bed of Celite then cooled to −30 °C. After 5 d, yellow
crystals formed and were collected by filtration and dried (89 mg,
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
1
■
0.116 mmol, 76%). H (500 MHz): δ 7.56 (d, C6H5, 4 H), 7.34 (t,
This work was supported by the U.S. National Science
Foundation (NSF, CHE-0747612 to R.W.). The NSF also
provided X-ray crystallographic (CHE-0521237 to J.M.T. and
CHE-1039436 to R.W.) and NMR (CHE-1126265) facilities.
C6H5, 4 H), 7.10 (t, C6H5, 2 H), 3.31 (t, CH2, 6 H), 2.43 (t, CH2, 6
H), 1.16 (s, CH3, 9 H); 0.42 (s, CH3, 27 H). 13C{1H} (125.8 MHz): δ
145.2 (s, CN); 136.1 (s, C6H5); 129.9 (s, C6H5); 129.8 (s, C6H5);
128.5 (s, C6H5); 62.64 (s, CH2); 48.9 (s, CH2); 33.5 (s, C(CH3)3),
30.3 (s, CH3), 3.6 (s, CH3). IR (Nujol): 2924 w, 2116 w, 1614 s (νCN),
1583 m, 1461 m, 1377 s, 1089 m, 1018 m, 950 m, 909 w, 837 m, 734 s,
690 m. Anal. Calcd. for C34H60N5AsSi3Zr: C, 50.36; H, 7.66; N, 9.18.
Found: C, 49.98; H, 7.38; N, 8.91.
X-ray Structure Determinations. X-ray diffraction data were
collected on a Bruker APEX 2 CCD platform diffractometer (MoKα, λ
= 0.71073 Å) at set temperature of 125 K. Suitable crystals of each
compounds 5, 6, and 9 were mounted in a nylon loop under Paratone-
N cryoprotectant oil. Direct methods and standard difference map
techniques were used for solution structure followed by refinement
using full-matrix least-squares procedures on F2 via SHELXTL
(version 6.14).16 Non-hydrogen atoms were refined anisotropically.
Hydrogen atoms on carbon were included in calculated positions and
were refined using a riding model. The hydrogen atoms on the
arsaalkene carbon atom of each 5 and 6, H(1), were located in the
Fourier difference map and refined semifreely using a distance
restraint. Crystallographic data for compounds 5, 6, and 9 can be
found in Table 3.
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