Reactions of tungsten(VI) dialkyl complexes with tBuNC: Synthesis and characterization of new square pyramidal and trigonal bipyramidal tungsten (VI) complexes

Article abstract of DOI:10.1021/om960773p

The complexes [(TMS)₂pda](NPh)WR₂ ((TMS)₂pda = o-(Me₃SiN)₂C₆H₄}^2-; R = CH₃ (1), CH₂-CMe₃ (4)) react with ^tBuNC to form the octahedral monoadducts [(TMS)₂pda](NPh)WR₂(CN^t-Bu) (Ia and 4a). Ia is observed only at low temperature, while 4a can be isolated. Both Ia and 4a react with ^tBuNC to form the corresponding trigonal bipyramidal bis(η²-imino-acyl) species [(TMS)₂pda](NPh)W[η²-(^tBu)NCR]₂ (R = CH₃ (2), CH₂CMe₃ (5)), which have been isolated and characterized. Compound 2 isomerizes upon heating to the square pyramidal metallacycle [(TMS)₂pda](NPh)W[(^tBu)NC(CH₃)=C(CH ₃)N(tBu)] (3), which has been isolated as a red solid. X-ray crystal structures have been obtained for compounds 2 and 3. Crystals of 2 are orthorhombic, space group P2₁2₁2₁, with α= 9.1175(3) A?, b = 17.9587(5) A?, c = 20.9435(6) A?, and Z = 4. Compound 2 has trigonal bipyramidal geometry with the imido N and one amido N in axial positions. Crystals of 3 are monoclinic, space group C2/c, with α = 35.1302(9) A?, b = 12.6459(2) A?, c = 16.2386(6) A?, β= 112.021(3)°, and Z = 8. 3 has distorted square pyramidal geometry with the imido moiety in the apical position.

Full text of DOI:10.1021/om960773p

Organometallics 1997, 16, 1779-1785
1779
Rea ction s of Tu n gsten (VI) Dia lk yl Com p lexes w ith
tBu NC: Syn th esis a n d Ch a r a cter iza tion of New Squ a r e
P yr a m id a l a n d Tr igon a l Bip yr a m id a l Tu n gsten (VI)
Com p lexes
R. Leigh Huff, Shu-Yu S. Wang, Khalil A. Abboud, and J ames M. Boncella*
Department of Chemistry and Center for Catalysis, University of Florida,
Gainesville, Florida 32611-7200
Received September 9, 1996X
The complexes [(TMS)2pda](NPh)WR2 ((TMS)2pda ) o-(Me3SiN)2C6H4}2-; R ) CH3 (1), CH2-
t
CMe3 (4)) react with BuNC to form the octahedral monoadducts [(TMS)2pda](NPh)WR2(CNt-
Bu) (1a and 4a ). 1a is observed only at low temperature, while 4a can be isolated. Both 1a
t
and 4a react with BuNC to form the corresponding trigonal bipyramidal bis(η2-imino-acyl)
species [(TMS)2pda](NPh)W[η2-(tBu)NCR]2 (R ) CH3 (2), CH2CMe3 (5)), which have been
isolated and characterized. Compound 2 isomerizes upon heating to the square pyramidal
metallacycle [(TMS)2pda](NPh)W[(tBu)NC(CH3)dC(CH3)N(tBu)] (3), which has been isolated
as a red solid. X-ray crystal structures have been obtained for compounds 2 and 3. Crystals
of 2 are orthorhombic, space group P212121, with a ) 9.1175(3) Å, b ) 17.9587(5) Å, c )
20.9435(6) Å, and Z ) 4. Compound 2 has trigonal bipyramidal geometry with the imido N
and one amido N in axial positions. Crystals of 3 are monoclinic, space group C2/c, with a
) 35.1302(9) Å, b ) 12.6459(2) Å, c ) 16.2386(6) Å, â ) 112.021(3)°, and Z ) 8. 3 has
distorted square pyramidal geometry with the imido moiety in the apical position.
In tr od u ction
functionality often adopts an η2 structure involving
coordination through both the carbon and oxygen atoms.
The structure, spectroscopic properties, and reactivities
of these η2-acyls have been widely reported.5,6 They are
proposed to possess a significant amount of oxycarbene
character,3ef,7 supported by their ability to undergo both
intra- and intermolecular coupling to make ene-
diolates.4a,7b,8 We report here the syntheses, charac-
terizations, and X-ray crystal structures of several
W(VI) η2-imino-acyl complexes and the subsequent
formation of diamide ligands through C-C coupling
reactions of the η2-imino-acyl groups.
Recent work in our group has focused on the use of
the chelating disubstituted phenylenediamide group {o-
(Me3SiN)2C6H4}2- [(TMS)2pda] as an ancillary ligand for
high-oxidation-state metal centers such as W(VI) and
Mo(VI).1,2 The facile, high yield synthesis of several
W(VI) dialkyl complexes of formula [(TMS)2pda](NPh)-
2
WR2 has provided us with the opportunity to investi-
gate the chemistry of these d0 dialkyl compounds. Until
now, our efforts have been concentrated on the conver-
sion of bulky, â-H-free dialkyls into alkylidene com-
plexes and the subsequent use of the alkylidenes as
olefin metathesis catalysts. We now report the reac-
tivities of the dimethyl and dineopentyl complexes with
isocyanides.
Resu lts a n d Discu ssion
Rea ction of [(TMS)2p d a ](NP h )W(CH3)2 (1) w ith
tBu NC. When 2 equiv of tBuNC is added to a solution
of 1, the golden-brown mixture immediately turns
The reaction of alkyl isocyanides (RNC) with coordi-
natively unsaturated, electrophilic early transition metal
alkyls typically results in the insertion of the isocyanide
moiety into the metal-alkyl bond, frequently forming
η2-imino-acyl ligands.3,4 These reactions are closely
related to the reactions of CO with alkyl complexes that
lead to the formation of metal acyls.5,6 In the case of
electrophilic metal centers like W, Mo, and Ta, the acyl
(5) (a) Calderazzo, F. Angew. Chem., Int. Ed. Engl. 1977, 16, 299.
(b) Kuhlmann, K. J .; Alexander, J . J . Coord. Chem. Rev. 1980, 33, 195.
(c) Wojcicki, A. Adv. Organomet. Chem. 1973, 11, 87. (d) Erker, G. Acc.
Chem. Res. 1984, 17, 103. (e) Tatsumi, K.; Nakamura, A.; Hofmann,
P.; Stauffert, P.; Hoffman, R. J . Am. Chem. Soc. 1985, 107, 4440. (f)
Wolczanski, P. T.; Bercaw, J . E. Acc. Chem. Res. 1980, 13, 121.
(6) (a) Manriquez, J . M.; McAlister, D. R.; Sanner, R. D.; Bercaw,
J . E. J . Am. Chem. Soc. 1978, 100, 2716. (b) Tatsumi, K.; Nakamura,
A.; Hofmann, P.; Hoffman, R.; Moloy, K. G.; Marks, T. J . J . Am. Chem.
Soc. 1986, 108, 4467.
(7) (a) Chamberlain, L. R.; Durfee, L. D.; Fanwick, P. E.; Kobriger,
L.; Latesky, S. L.; McMullen, A. K.; Rothwell, I. P.; Folting, K.;
Huffman, J . C.; Streib, W. E.; Wang, R. J . Am. Chem. Soc. 1987, 109,
390. (b) Bochmann, M.; Wilson, L. M.; Hursthouse, M. B.; Short, R. L.
Organometallics 1987, 6, 2556. (c) Filippou, A. C.; Vo¨lkl, C.; Kiprof, P.
J . Organomet. Chem. 1991, 415, 375.
X Abstract published in Advance ACS Abstracts, March 1, 1997.
(1) (a) Vanderlende, D. D.; Abboud, K. A.; Boncella, J . M. Organo-
metallics 1994, 13, 3378. (b) Vaughan, W. M.; Abboud, K. A.; Boncella,
J . M. J . Am. Chem. Soc. 1995, 117, 11015. (c) Ortiz, C. G.; Boncella, J .
M. unpublished results.
(2) Boncella, J . M.; Wang, S.; Vanderlende, D. D.; Huff, R. L.;
Vaughan, W. M.; Abboud, K. A. J . Organomet. Chem., in press.
(3) For a thorough review, see: Durfee, L. D.; Rothwell, I. P. Chem.
Rev. 1988, 88, 1059.
(4) (a) Chiu, K. W.; J ones, R. A.; Wilkinson, G.; Galas, A. M. R.;
Hursthouse, M. B. J . Chem. Soc., Dalton Trans. 1981, 2090. (b) Valero,
C.; Grehl, M.; Wingbermu¨hle, D.; Kloppenburg, L.; Carpenetti, D.;
Erker, G.; Petersen, J . L. Organometallics 1994, 13, 415.
(8) (a) Manriquez, J . M.; McAlister, D. R.; Sanner, R. D.; Bercaw,
J . E. J . Am. Chem. Soc. 1976, 98, 6733. (b) Marks, T. J .; Day, V. W. In
Fundamental and Technological Aspects of Organo-f-Element Chem-
istry; Marks, T. J ., Fragala, I. L., Eds.; Kluwer: Dordrecht, Holland,
1986. (c) Tatsumi, K.; Nakamura, A.; Hoffmann, R. Organometallics
1985, 4, 404.
S0276-7333(96)00773-X CCC: $14.00 © 1997 American Chemical Society

1780 Organometallics, Vol. 16, No. 8, 1997
Huff et al.
Ta ble 1. 1H NMR Da ta
compound
δ, ppm
0.56
mult
s
J , Hz
int
9
assnmt
W(NPh)[(TMS)2pda](CH3)2
-SiMe3
(CNtBu) (1a ) at -60 °C in C7D8
0.62
0.64
0.81
1.38
6.60-7.50
0.15
s
s
9
9
-CNCMe3
-SiMe3
tBuNC
-CH3
aromatic
-SiMe3
br s
s
6
9
W(NPh)[(TMS)2pda][η2-(tBu)
NCCH3]2 (2) in C6D6
s
0.69
1.21
2.69
6.60-7.40
0.45
s
s
s
9
18
6
9
18
-SiMe3
-CMe3
-CH3
aromatic
-SiMe3
W[N(tBu)C(CH3)dC(CH3)N(tBu)]
[(TMS)2pda](NPh) (3) in C6D6
s
1.26
1.53
6.74
6.79
6.87
7.14
7.40
0.68
s
s
m
t
m
t
18
6
2
1
2
2
2
18
-CMe3
-CH3
aromatic
p-H
aromatic
m-H
t
s
o-H
-SiMe3
W(NPh)[(TMS)2pda](CH2CMe3)2
(CNtBu) (4a ) in C6D6
0.76
1.15
1.84
2.73
6.75-7.70
0.68
0.70
0.73
1.17
1.78
2.78
6.7-7.7
0.27
s
s
d
d
9
18
2
2
9
9
9
9
18
2
-CNCMe3
-CMe3
-CH2CMe3
-CH2CMe3
aromatic
-CNCMe3
-SiMe3
-SiMe3
-CMe3
-CH2CMe3
-CH2CMe3
aromatic
-SiMe3
12.6
12.6
spectrum taken at -40 °C in C7D8
s
s
s
s
d
d
12.6
12.6
2
9
9
W(NPh)[(TMS)2pda][η2-(tBu)
NCCH2CMe3]2 (5) in C6D6
s
0.65
1.06
1.43
3.31
3.82
6.60-7.40
s
s
s
d
d
9
-SiMe3
18
18
2
2
9
-CMe3
-NCMe3
-CH2CMe3
-CH2CMe3
aromatic
12.9
12.9
black. Concentration and cooling of this solution
afford a black solid, 2, which is extremely soluble in
hydrocarbon solvents and ethers (eq 1). Compound
The 13C NMR spectrum in C6D6 (see Table 2) displays
inequivalent TMS groups and equivalent tert-butyl
and methyl groups. Additionally, a single peak at
210.48 ppm is consistent with the presence of an η2-
imino-acyl moiety.6 The NMR data for compound 2 indi-
cate that it is the trigonal bipyramidal bis(η2-imino-acyl)
complex [(TMS)2pda](NPh)W[η2-(tBu)NC(CH3)]2, in which
one (TMS)2pda nitrogen and the imido N occupy axial
positions. This formulation has been confirmed by the
solid state structure of 2, as will be discussed below.
If left at room temperature for a period of weeks, a
solution of 2 begins to take on a red color. Heating 2 to
80 °C for 24 h hastens the conversion of 2 to a new
complex, 3, which can be isolated as a deep red, air- and
moisture-sensitive, crystalline solid (eq 2). Compound
2 is air- and moisture-sensitive but is indefinitely
stable in the solid state under an inert atmosphere.
1
The H NMR spectrum of 2 in C6D6 (Table 1) reveals
peaks at 0.15 ppm (9H) and 0.69 ppm (9H), identified
as inequivalent trimethylsilyl groups. A singlet at
1.21 ppm (18H) is assigned to equivalent tert-butyl
groups, shifted downfield from free tBuNC (0.94
ppm). A singlet at 2.69 ppm (6 H) is identified as
two equivalent methyl groups, while overlapping mul-
tiplets in the aromatic region integrate to a total of 9
protons.

t
Reactions of W(VI) Dialkyl Complexes with BuNC
Organometallics, Vol. 16, No. 8, 1997 1781
Ta ble 2. 13C NMR Da ta
starting material (1) and the bis(η2-imino-acyl) (2).
When a sample of 1 and tBuNC was prepared and
analyzed at -70 °C, the red monoadduct (1a ) was indeed
observed to form before insertion occurred. As for
[(TMS)2pda](NPh)WCl2(L) (L ) PMe3, THF, 3-picoline,
tBuNC, CH3CN) and the PMe3 adduct of 1,2 we expected
the isocyanide to coordinate in the vacant site trans to
the imido moiety and cis to the methyl groups. How-
ever, coordination trans to the imido group is not
δ,
J ,
compound
ppm mult Hz int
assnmt
W(NPh)[(TMS)2pda][η2-(tBu)
NCCH3]2 (2) in C6D6
4.12
s
-SiMe3
5.25
21.84
29.54
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
-SiMe3
-CMe3
-CMe3
-CH3
60.22
116.09
116.27
117.71
117.79
124.35
125.24
150.26
152.88
156.21
210.48
3.39
aromatic
1
observed. Instead, the H NMR of 1a at -60°C in C7D8
reveals two TMS peaks at 0.56 ppm (9H) and 0.64 ppm
(9H). The coordinated isocyanide appears at 0.62 ppm
(9H), while free isocyanide appears at 0.81 ppm. Equiva-
lent methyl groups appear as a singlet at 1.38 ppm (6H).
These data reveal that complex 1a has a pseudoocta-
hedral structure with trans CH3 groups, as shown in
eq 3.
(tBu)NCMe
-SiMe3
W[N(tBu)C(CH3)C(CH3)N(tBu)]
[(TMS)2pda](NPh) (3) in C6D6
16.28
31.69
59.91
s
s
s
s
s
s
s
s
s
s
s
s
CdC-CH3
-CMe3
-CMe3
118.77
118.93
119.78
125.96
128.47
128.60
148.97
157.14
4.64
aromatic
CdC
aromatic
W(NPh)[(TMS)2pda][η2-(tBu)
NCCH2CMe3]2 (5) in C6D6
-SiMe3
6.41
30.97
31.84
32.96
47.02
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
-SiMe3
CH2CMe3
NCMe3
CH2CMe3
CH2CMe3
NCMe3
There are three possible explanations for this some-
what surprising result. One possibility arises from the
fact that even though the vacant coordination site on 1
is trans to the imido group, the LUMO of the complex
is most likely the dxy orbital (the WdN bond axis being
defined as the z axis of the molecule).12 This being the
case, a Lewis base might be expected to attack the
molecule at the LUMO and could generate the observed
adduct directly. A second possibility is that the initial
adduct that is formed has the isocyanide ligand coor-
dinated trans to the imido group, but this rapidly
rearranges to the observed product. A third possibility
might be that 1 exists in solution as a rapidly equili-
brating mixture of square pyramidal and trigonal bi-
pyramidal isomers at all temperatures that have been
probed via 1H NMR (-80 to +25 °C). Assuming a
trigonal bipyramidal structure akin to the observed
structure of [(TMS)2pda](NPh)W(CH2CMe3)2 which has
the alkyl groups in the equatorial positions, preferential
coordination between the alkyl groups would then
generate the observed product.
62.95
115.95
116.54
118.32
118.82
125.53
150.36
152.84
155.50
213.28
aromatic
-NCCH2-
3 is extremely soluble in both hydrocarbon solvents and
a variety of ethers and is indefinitely stable both in solid
form and in solution at room temperature. The 1H NMR
spectrum of 3 in C6D6 displays a singlet at 0.45 ppm
(18H), attributed to equivalent TMS groups, and a
singlet at 1.26 ppm (18H) which is assigned to equiva-
lent tert-butyl groups. An additional singlet at 1.53 ppm
(6H) is assigned to equivalent methyl groups. The 13C-
{1H} NMR spectrum displays peaks assigned to the
equivalent TMS, tert-butyl, and methyl groups and a
singlet at 125.96 ppm that corresponds to the carbons
of a C-C double bond. The NMR spectra of 3 are
consistent with square pyramidal geometry about the
W atom. The presence of the C-C double bond suggests
that 3 is a metallacycle of formula [(TMS)2pda](NPh)W-
[(tBu)NC(CH3)dC(CH3)N(tBu)], with the imido moiety
in the apical position (eq 2). This structural assignment
has been confirmed by the crystal structure of 3.
Rea ction of [(TMS)2p d a ](NP h )W(CH2CMe3)2 (4)
t
t
w ith Bu NC. When excess BuNC is added to a golden-
brown solution of 4, the color of the solution changes to
bright red. Concentration and cooling of this solution
yield an air- and moisture-sensitive orange-red solid (4a )
which is soluble in hydrocarbon solvents and diethyl
ether and is only slightly soluble in diisopropyl ether
(9) (a) McDade, C.; Bercaw, J . E. J . Organomet. Chem. 1985, 279,
281. (b) Gambarotta, S.; Floriani, C.; Chiesi-Villa, A.; Guastini, C. J .
Am. Chem. Soc. 1983, 105, 1690. (c) Evans, W. J .; Grate, J . W.;
Doedens, R. J . J . Am. Chem. Soc. 1985, 107, 1671.
(10) McMullen, A. K.; Rothwell, I. P.; Huffman, J . C. J . Am. Chem
Soc. 1985, 107, 1072.
(11) Sandstro¨m, J . Dynamic NMR Spectroscopy; Academic Press:
New York, 1982.
(12) (a) Nugent, W. A.; Mayer, J . M. Metal-Ligand Multiple Bonds;
Wiley: New York, 1988. (b) Wigley, D. E. Prog. Inorg. Chem. 1994,
42, 239.
The fact that 1 is both electronically and coordina-
tively unsaturated suggests that the mono(isocyanide)
adduct of 1 might be observable prior to insertion. This
adduct is not observed at ambient temperature; the
addition of 1 equiv of BuNC to a solution of 1 in C6D6
at room temperature produces a clean 1:1 mixture of
t

1782 Organometallics, Vol. 16, No. 8, 1997
Huff et al.
(eq 4). Complex 4a begins to decompose to insoluble,
unidentified products after only a few hours in solution
at room temperature, which prevented the acquisition
of 13C NMR data for this compound. When stored in
solid form under an inert atmosphere at room temper-
ature, complex 4a displays considerable decomposition
after approximately 2 weeks.
The 1H NMR spectrum of 4a at room temperature
shows a singlet at 0.68 ppm (18H), assigned to equiva-
lent TMS groups. Another singlet at 0.76 ppm (9H) is
attributed to 1 equiv of coordinated isocyanide. A peak
at 1.15 ppm (18H) is assigned to equivalent tert-butyl
groups on the neopentyl ligands. Two doublets at 1.84
ppm (2H) and 2.73 ppm (2H) (J C-H ) 12.6 Hz) are
identified as the methylene protons on the R-carbons of
the neopentyl groups. These data indicate that 4a is
the isocyanide adduct of the dineopentyl complex but
do not uniquely identify the structure of the adduct.
Low-temperature (-40 °C) 1H NMR studies of 4a
display inequivalent TMS peaks, each integrating to 9
protons, which coalesce to a single peak at 13 °C. The
two-site exchange approximation11 allows us to estimate
that ∆Gq for this process is 15.2 kcal/mol. These low-
temperature NMR studies show that, like the mono-
(isocyanide) adduct of the dimethyl species, complex 4a
has a pseudooctahedral structure with the alkyl groups
trans to one another. At this time, we do not know
whether the fluxional process is an intramolecular
nance at 213.28 ppm. From these data, we have
identified compound 5 as the trigonal bipyramidal bis-
(imino-acyl) insertion product of the dineopentyl com-
plex, [(TMS)2pda](NPh)W[η2-(tBu)NCCH2CMe3]2, analo-
gous to complex 2. Like complex 2, compound 5 is
expected to have η2 coordination for each imino-acyl
group, both groups being in the N-out position.
The formation of 5 from 4 requires the presence of
excess tBuNC to give a clean product. When the
reaction between 4 and 2 equiv of tBuNC was monitored
by 1H NMR spectroscopy at 25 °C, the initial formation
of 4a was observed, followed by incomplete conversion
to a new species that we tentatively assign as the mono-
(imino-acyl)-mononeopentyl complex 6.7a After the
mixture is heated to 80 °C for 24 h, a complex mixture
that contains unreacted starting material as well as
compounds 5 and 6, and other unidentified materials
is formed. These data suggest that it is likely that the
formation of 5 occurs in a stepwise fashion and that the
t
t
presence of excess BuNC is necessary to prevent other
rearrangement or involves dissociation of the BuNC
unidentified modes of reaction from occurring. Contin-
ued thermolysis of 5 does not result in isomerization to
a metallacyclic diamide structure that would be analo-
gous to 3. It is possible that the further coupling of the
imino-acyl groups is prevented by the steric bulk of the
neopentyl groups.
ligand.
Unlike 1, the dineopentyl species, 4, has trigonal
bipyramidal geometry about the W atom in the solid
state.2 In solution at room temperature, however, only
one TMS peak is observed in its H NMR spectrum. At
low temperature, the H NMR spectrum of 4 displays
1
1
The generation of the enediamidate ligand in com-
pound 3 is similar the reactions of other early transition
metal alkyls with isocyanides or CO. Migratory inser-
tion reactions involving formation of bis(acyl) or bis-
(imino-acyl) ligands are well-known.3e,6 Additionally,
several examples of acyl-acyl and acyl-imino-acyl
coupling to form metallacycles have been reported,5c,9b,10
for example, the reaction of CO and (η5-C5Me5)2Zr(CH3)2
to produce the bis(acyl), which isomerizes to the ene-
diolate complex Cp*2Zr[O(CH3)CdC(CH3)O].4a Similar
reactions have been reported for Cp*2AnR2 and CO (An
) actinide).4b
Str u ctu r a l Stu d ies. Single-crystal X-ray diffraction
studies were performed on compounds 2 and 3. The
crystal structure of complex 1 was reported previously,2
and that structure will be referenced for comparison.
Thermal ellipsoid plots of complexes 2 and 3 are found
in Figures 1 and 2, respectively, while selected bond
two Me3Si resonances, consistent with the solid state
structure. It is likely that coordination of BuNC to 4
occurs between the neopentyl groups (at the site of the
LUMO) of the trigonal bipyramidal complex, giving the
observed six-coordinate adduct, 4a .
t
When heated to 70 °C for 18 h with 4 equiv of tBuNC,
the brownish-orange solution becomes emerald green.
Upon concentration and cooling, a green solid, 5 (eq 5),
can be isolated, which is soluble in hydrocarbon solvents
and ethers and can be stored indefinitely under an inert
atmosphere. The 1H NMR spectrum of 5 in C6D6 shows
two inequivalent TMS peaks at 0.27 ppm (9H) and 0.65
ppm (9H), a tert-butyl methyl peak from the neopentyl
groups at 1.06 ppm (18H), and a tert-butyl peak from
the isocyanide at 1.43 ppm (18H). The two doublets
from the methylene protons on the neopentyl groups
split farther apart and move downfield (Table 1). The
13C NMR spectrum reveals one imino-acyl carbon reso-

t
Reactions of W(VI) Dialkyl Complexes with BuNC
Organometallics, Vol. 16, No. 8, 1997 1783
Ta ble 4. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 3
1
2
3
1-2
1-2-3
N1
N1
N1
N1
C1
C1
C2
N2
N2
N2
N2
N2
N3
N3
N3
N3
N4
N4
N4
N5
N5
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
N2
N3
N4
N5
N1
C2
N1
N3
N4
N5
C1
C2
N4
N5
C1
C2
N5
C1
C2
C1
C2
1.957(3)
81.77(12)
91.09(12)
125.22(11)
112.97(13)
34.01(11)
32.56(11)
62.12(11)
157.89(11)
89.55(12)
103.08(12)
62.26(11)
33.10(11)
77.48(11)
98.97(12)
100.75(11)
125.87(11)
121.67(12)
95.28(11)
81.90(11)
141.09(13)
134.01(12)
2.482(3)
2.531(3)
2.025(3)
2.117(3)
2.051(3)
1.749(3)
F igu r e 1. Thermal ellipsoid plot of 2.
Ta ble 5. Cr ysta llogr a p h ic Da ta a
2
3
A. Crystal Data (173 K)
a, Å
b, Å
c, Å
9.1175(3)
17.9587(5)
20.9435(6)
90.0
3451.8(2)
1.389
35.1302(9)
12.6459(2)
16.2386(6)
112.021(3)
6687.8(3)
1.434
â, deg
V, Å3
d
calc, g cm-3
empirical formula
fw
cryst syst
space group
Z
C
30H51N5Si2W
C30H51N5Si2W
721.79
monoclinic
C2/c
721.79
orthorhombic
P212121
4
8
F(000), electrons
1472
2944
B. Structure Refinement
refinement method
S, goodness-of-fit
R1/reflns
full-matrix least-squares on F2
1.081
1.035
1.99/6592 > 2σ(I)
4.81/6711
3.61
2.66/5226 > 2σ(I)
6.16/5744
3.76
F igu r e 2. Thermal ellipsoid plot of 3.
wR2/reflns
R
int, %
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 2
a
R1 ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) [∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]]1/2
.
S ) [∑[w(Fo - Fc2)2]/(n - p)]1/2
. +
w ) 1/[σ2(Fo2) + (0.0370p)2
2
1
2
3
1-2
1-2-3
0.31p]; p ) [max(Fo2,0) + 2Fc2]/3.
N1
N1
N1
N1
C1
C1
C2
N2
N2
N2
N2
N2
N3
N3
N3
N3
N4
N4
N4
N5
N5
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
N2
N3
N4
N5
N1
C2
N1
N3
N4
N5
C1
C2
N4
N5
C1
C2
N5
C1
C2
C1
C2
2.157(3)
162.14(11)
82.88(11)
94.30(11)
92.45(12)
34.47(13)
96.7(2)
W-N-Ph angles (174.7(3) and 175.2(2)°, respectively)
that are close to linear, as is consistent with the
presence of W-N triple bonds.12 Regardless of geom-
etry, the phenylenediamide ligand retains a N-W-N
angle of under 80°. Each of these angles (77.66° for 2
and 77.48° for 3) reflects a decrease from that of the
dimethyl complex (82.55°) possibly due to the increased
steric congestion around the metal center.
Solid Sta te Str u ctu r e of 2. Complex 2 has trigonal
bipyramidal geometry about the W center with both
imino-acyls in the equatorial plane. The phenylenedia-
mido ligand adopts an axial-equatorial coordination
with one N trans to the imido moiety. A substantial
trans influence is observed when the two amido W-N
bond lengths are compared; the equatorial W-N bond
is 2.101(3) Å, while the axial W-N bond (trans to the
imido moiety) is longer, 2.179(3) Å. The solid state
structure of 2 confirms η2 coordination for both imino-
acyl ligands. Both C-N distances are 1.265(5) Å, well
within the range for the C-N double bond of a coordi-
nated imino-acyl.3 Additionally, the W-C1, W-C2,
W-N1, and W-N2 bond lengths of the imino-acyls are
consistent with reported bond lengths for η2-imino-acyls
2.112(4)
2.110(4)
2.149(3)
131.12(14)
87.17(11)
98.03(11)
98.05(12)
129.81(13)
34.55(14)
77.66(10)
174.57(12)
84.28(12)
93.01(12)
100.01(11)
127.74(13)
132.50(13)
93.46(13)
92.15(13)
2.179(3)
2.101(3)
1.773(3)
lengths and angles are found in Tables 3 and 4.
Abbreviated crystal data for both 2 and 3 are listed in
Table 5.
Some general comments about these structures are
warranted. Both compounds have short W-N(imido)
bond lengths (1.773(3) and 1.749(3) Å, respectively) and

1784 Organometallics, Vol. 16, No. 8, 1997
Huff et al.
on early transition metal centers.7a,b,3 The W-C-N
angles for each imino-acyl (74.7(2)° for N1-C1-W and
74.4(2)° for N2-C2-W) are also similar to published
data.3 Both imino-acyls bond in an N-out fashion with
their bulky tert-butyl groups directed away from the
metal center. This geometry is perfectly disposed to
allow coupling of the imino-acyl carbon atoms to occur
to generate the new diamido ligand in 3.
However, there is no doubt that the same adduct isomer
forms when either 4 or 1 interacts with BuNC. The
t
isocyanide adducts react with additional isocyanide to
generate new trigonal bipyramidal bis(η2-imino-acyl)
complexes. Coupling of the imino-acyl ligands is pos-
sible, if the size of the carbon substituents permit, giving
an enediamidate ligand. Further studies are underway
to identify why the trigonal bipyramidal geometry
appears to produce greater reactivity and to study how
more hindered dialkyls such as metallacycles interact
with isocyanide.
Solid St a t e St r u ct u r e of 3. The structure of
compound 3 reveals that the imino-acyl carbon atoms
of 2 have coupled to generate a new enediamidate
ligand. The compound has a distorted square pyramidal
geometry about the metal center with the phenylimido
moiety in the apical position. All four amido N’s are in
the equatorial plane. Although there is no crystal-
lographic plane of symmetry that equates the ends of
the amido groups, the librational motion of the bis-
(amido) chelate ligands about a plane of symmetry
containing the phenylimido ligand and bisecting the
N1-W-N2 and N3-W-N4 angles results in the equiva-
lence of the tBu and SiMe3 groups in the ambient-
temperature 1H NMR spectrum of 3. The distorted
square pyramidal structure is similar to that of (NPh)W-
(NMe2)4,13 which adopts an intermediate structure
between a square pyramid and a trigonal bipyramid at
low temperature which also equilibrates in solution at
room temperature.
Exp er im en ta l Section
Ma ter ia ls a n d Meth od s. All syntheses were carried out
under dry argon atmospheres using standard Schlenk tech-
niques. [(TMS)2pda](NPh)WMe2 (1) and [(TMS)2pda](NPh)W-
(CH2CMe3)2 (4) were synthesized according to published
procedures.2 tBuNC was purchased from Aldrich and used as
received. Diethyl ether (Et2O) and diisopropyl ether (iPr2O)
were distilled from sodium benzophenone ketyl. Pentane,
hexanes, and toluene were distilled from sodium. NMR
solvents were stored over molecular sieves and degassed prior
to use. NMR spectra were acquired on either a General
Electric QE-300, a Gemini 300, or a Varian VXR-300 spec-
trometer. 1H and 13C chemical shifts are referenced to residual
protons in deuterated solvents and are reported relative to
TMS. Elemental analyses were performed by Atlantic Micro-
labs, Inc., Norcross, GA.
t
The bond lengths within the Bu-NC(Me)C(Me)N-
[(TMS)2p d a ](NP h )W[η2-(tBu )NCCH3]2 (2). tBuNC (0.29
mL, 2.56 mmol) was added via syringe to a 15 mL pentane
solution of [(TMS)2pda](NPh)W(CH3)2 (705 mg, 1.27 mmol).
The resulting black solution was stirred for 1 h at room
temperature. Subsequent concentration and cooling to -78
°C for 1 h resulted in a black solid, which was isolated by
filtration and dried under reduced pressure for 30 min.
Crystals suitable for an X-ray diffraction study were grown
from a concentrated diisopropyl ether solution at -20 °C
over a period of 2 days. Yield: 662 mg (72%). Anal. Calcd
for C30H51N5Si2W: C, 49.92; H, 7.14; N, 9.71. Found: C, 48.37;
H, 7.01; N, 9.61.
[(TMS)2p d a ](NP h )W[(tBu )NC(CH3)dC(CH3)N(tBu )] (3).
A 10 mL toluene solution of 2 (620 mg, 0.859 mmol) in a round-
bottom ampule was heated to 80 °C for 24 h. The resulting
red solution was concentrated and cooled to -78 °C for 1 h.
The resulting red solid was isolated by filtration and dried
under reduced pressure for 1 h. Crystals of 3 suitable for an
tBu ligand are consistent with this group being a bis-
(amido) ligand and not a diazabutadiene ligand. The
N1-C1 and N2-C2 bond lengths are 1.392 and 1.386
Å, respectively, and are considerably longer than the
related N-C bond lengths that are found in diazabuta-
diene ligands of ca. 1.27-1.30 Å.14 Additionally, the
C1-C2 bond distance (1.406(5) Å) in compound 3 is
shorter than the corresponding bond lengths found
in diazabutadiene complexes (ca. 1.44-1.46 Å), as is
more consistent with a C-C double bond.14 Thus, the
structural details of 3 are consistent with a W(VI) bis-
(amide) complex and not a W(IV) diazabutadiene com-
plex as might be expected given the relative stability of
W(VI). It is likely that the bulk of the bis(amide)
ligands in 3 causes the observed twisting of the both
the newly formed metallacycle (W-N1-C1 ) 94.2(2)°)
and (TMS)2pda (W-N3-C11 ) 104.2(2)°) from the
equatorial plane to accommodate the steric bulk of the
tert-butyl and trimethylsilyl groups, respectively.
X-ray diffraction study were grown from
a concentrated
diisopropyl ether solution at -20 °C over a period of 2 days.
Yield: 350 mg (56%). Anal. Calcd for C30H51N5Si2W: C, 49.92;
H, 7.14; N, 9.71. Found: C, 48.49; H, 7.06; N, 9.69.
[(TMS)2p d a ](NP h )W(CH2CMe3)2(CNtBu ) (4a ). tBuNC
(0.34 mL, 3.0 mmol) was added via syringe to a 10 mL
diisopropyl ether solution of [(TMS)2pda](NPh)W(CH2CMe3)2
(495 mg, 0.74 mmol). The resulting orange-red solution was
stirred for 10 min at room temperature. Concentration and
cooling to -78 °C for 1 h produced an orange-red solid, which
was isolated by filtration and dried under reduced pressure
for 45 min. Yield: 430 mg (77%). Anal. Calcd for C33H58N4-
Si2W: C, 52.78; H, 7.80; N, 7.46. Found: C, 52.53; H, 7.85;
N, 7.45.
[(TMS)2p d a ](NP h )W[η2-(tBu )NCCH2CMe3]2 (5). tBuNC
(0.34 mL, 3.0 mmol) was added via syringe to a 15 mL
diisopropyl ether solution of [(TMS)2pda](NPh)W(CH2CMe3)2
(500 mg, 0.75 mmol) in an ampule. The resulting solution
was stirred for 24 h at 70°C, producing a green solution,
which was allowed to cool to ambient temperature. Subse-
quent concentration and cooling to -78 °C for 1 h afforded a
green solid, which was isolated by filtration and dried under
reduced pressure for 1 h. Yield: 300 mg (48%). Anal. Calcd
Su m m a r y a n d Con clu sion s
t
From our work with these dialkyl complexes and -
BuNC, we have seen that complexes which contain
bulky alkyl groups (compound 4) undergo rapid inter-
conversion between square pyramidal and trigonal
bipyramidal isomers.2 The dominant geometry is dic-
tated by the steric bulk of the alkyl groups. In the case
of bulky alkyl groups, isocyanide may react preferen-
tially with the trigonal bipyramidal isomer, producing
an octahedral adduct with one N atom of the (TMS)2pda
ligand occupying a position trans to the imido ligand.
The NMR properties of the less sterically hindered
dimethyl complex, 1, do not allow us to assess whether
it undergoes a fluxional process similar to that of 4.
(13) Berg, D. M.; Sharp, P. R. Inorg. Chem. 1987, 26, 2959.
(14) van Koten, G.; Vrieze, K. Adv. Organomet. Chem. 1982, 21, 151.

t
Reactions of W(VI) Dialkyl Complexes with BuNC
Organometallics, Vol. 16, No. 8, 1997 1785
for C38H67N5Si2W: C, 54.72; H, 8.11; N, 8.40. Found: C, 54.52;
H, 8.06; N, 8.35.
tropic thermal parameters except for the disordered C atoms.
All of the H atoms were included in the final cycle of
refinement and were allowed to ride on the atoms to which
they were bonded.
X-r a y Cr ysta l Str u ctu r es. Data for both compounds were
collected at 173 K on a Siemens CCD SMART PLATFORM
equipped with a CCD area detector and a graphite monochro-
mator utilizing Mo KR radiation (λ ) 0.710 73 Å). Cell
parameters were refined using 8192 reflections from each data
set. A hemisphere of data (1381 frames) was collected using
the ω-scan method (0.3° frame width). The first 50 frames
were remeasured at the end of data collection to monitor
instrument and crystal stability (maximum correction on I was
<1%). Absorption corrections were applied using the psi scan
data and the entire data set.
Ack n ow led gm en t. We thank the National Science
Foundation (Grant CHE-9523279) for support of this
work. R.L.H. wishes to acknowledge the University of
Florida for a National Merit Scholarship. We also wish
to acknowledge the National Science Foundation for
funding the purchase of the X-ray equipment.
Both structures were solved by the direct methods in
SHELXTL15 and refined using full-matrix least-squares cal-
culations on F2. The non-H atoms were refined with aniso-
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data and structure refinement details, bond lengths and
angles, and positional and thermal parameters (18 pages).
Ordering information is given on any current masthead page.
(15) Sheldrick, G. M. SHELXTL; Nicolet XRD Corp.: Madison, WI,
1995.
OM960773P