Double isocyanide insertion and C,C-coupling reaction of [(C5Me4)SiMe2(N-t-Bu)]ZrMe2. Structural characterization of the two 1,4-diaza-5-zirconacyclopentene ring Conformations for [(C5Me4)SiMe2(N-t-Bu)]Zr[N(R)C(Me)=C(Me)N(R)] complexes

Article abstract of DOI:10.1021/om9610760

The reactions of 2 equiv of CNR (R = (a) tert-butyl, (b) 2,6-xylyl, (c) Me) with [(C₅Me₄)SiMe₂(N-t-Bu)]ZrMe₂, 1, proceed sequentially with isocyanide insertion into both Zr-C(methyl) bonds of this 14-electron complex to give the corresponding η²-iminoacyl Zr complexes [(C₅Me₄)SiMe₂(N-t-Bu)]ZrMe[η ²-C(Me)NR], 2, and [(C₅Me₄)SiMe₂(N-t-Bu)]Zr[η ²-C(Me)NR]₂, 3. Subsequent thermolysis of 3 leads to C,C-coupling of the two η²-iminoacyl units and proceeds solely with formation of the enediamidate derivative [(C₅Me₄)SiMe₂(N-t-Bu)]Zr[N(R)C(Me)=C(Me)N(R)], 4. Compounds 2a, 3a-c, and 4a-c have been observed and characterized by solution NMR measurements, and the molecular structures of 3a, 3b, 4a, and 4b have been confirmed by crystallographic methods. The nonplanar 1,4-diaza-5-zirconacyclopentene rings of 4a and 4b are folded by ca. 50° in opposite directions along the corresponding N?N line segment and adopt the prone and supine conformations, respectively. The activation parameters for the first-order intramolecular C,C-coupling reaction leading to the conversion of 3a → 4a are ΔH? = 24.6(2) kcal/mol and ΔS? = -11.3(7) eu and of 3b → 4b are ΔH? = 23.9(3) kcal/mol and ΔS? = -10.4(8) eu.

Full text of DOI:10.1021/om9610760

3548
Organometallics 1997, 16, 3548-3556
Dou ble Isocya n id e In ser tion a n d C,C-Cou p lin g Rea ction
of [(C5Me4)SiMe2(N-t-Bu )]Zr Me2. Str u ctu r a l
Ch a r a cter iza tion of th e Tw o
1,4-Dia za -5-zir con a cyclop en ten e Rin g Con for m a tion s for
[(C5Me4)SiMe2(N-t-Bu )]Zr [N(R)C(Me)dC(Me)N(R)]
Com p lexes
Lioba Kloppenburg and J effrey L. Petersen*
Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506-6045
Received December 18, 1996X
The reactions of 2 equiv of CNR (R ) (a ) tert-butyl, (b) 2,6-xylyl, (c) Me) with
[(C5Me4)SiMe2(N-t-Bu)]ZrMe2, 1, proceed sequentially with isocyanide insertion into both
Zr-C(methyl) bonds of this 14-electron complex to give the corresponding η2-iminoacyl Zr
complexes [(C5Me4)SiMe2(N-t-Bu)]ZrMe[η2-C(Me)NR], 2, and [(C5Me4)SiMe2(N-t-Bu)]Zr[η2-
C(Me)NR]2, 3. Subsequent thermolysis of 3 leads to C,C-coupling of the two η2-iminoacyl
units and proceeds solely with formation of the enediamidate derivative [(C5Me4)SiMe2(N-
t-Bu)]Zr[N(R)C(Me)dC(Me)N(R)], 4. Compounds 2a , 3a -c, and 4a -c have been observed
and characterized by solution NMR measurements, and the molecular structures of 3a , 3b,
4a , and 4b have been confirmed by crystallographic methods. The nonplanar 1,4-diaza-5-
zirconacyclopentene rings of 4a and 4b are folded by ca. 50° in opposite directions along the
corresponding N‚‚‚N line segment and adopt the prone and supine conformations, respec-
tively. The activation parameters for the first-order intramolecular C,C-coupling reaction
leading to the conversion of 3a f 4a are ∆Hq ) 24.6(2) kcal/mol and ∆Sq ) -11.3(7) eu and
of 3b f 4b are ∆Hq ) 23.9(3) kcal/mol and ∆Sq ) -10.4(8) eu.
In tr od u ction
that this reaction proceeds via an unusual double
insertion reaction that involves the participation of η2-
iminoacyl and η2-iminoacyl imine intermediates (eq 2).
Reactivity studies of the transition-metal-mediated
reductive coupling of isocyanides by an electrophilic
group 4 metal complex have uncovered two primary
reaction mechanisms associated with this C-C bond
forming reaction. From their studies of a series of
bis(η2-iminoacyl)aryloxide complexes, M(OAr)2[η2-C-
(R′)NR]2 (M ) Ti, Zr, Hf), Rothwell and co-workers1
observed that these compounds upon thermolysis un-
dergo an intramolecular coupling of the two η2-iminoacyl
groups to produce the cyclic enediamidate complexes,
M(OAr)2[N(R)C(R′)dC(R′)N(R)] (eq 1). Our investiga-
(2)
In the former case an isocyanide inserts sequentially
into both M-C(alkyl) bonds, whereas in the latter case
the electrophilic character of the η2-iminoacyl carbon
promotes nucleophilic attack of the second isocyanide
(1)
(1) (a) McMullen, A. K.; Rothwell, I. P.; Huffman, J . C. J . Am. Chem.
Soc. 1985, 107, 1072. (b) Chamberlain, L. R.; Durfee, L. D.; Fanwick,
P. E.; Kobriger, L. M.; Latesky, S. L.; McMullen, A. K.; Steffey, B. D.;
Rothwell, I. P.; Folting, K.; Huffman, J . C. J . Am. Chem. Soc. 1987,
109, 6068. (c) Durfee, L. D.; Rothwell, I. P. Chem. Rev. 1988, 88, 1059
and references cited therein.
(2) (a) Berg, F. J .; Petersen, J . L. Organometallics 1989, 8, 2461.
(b) Berg, F. J .; Petersen, J . L. Organometallics 1991, 10, 1599. (c) Berg,
F. J .; Petersen, J . L. Tetrahedron 1992, 48, 4749. (d) Valero, C.; Grehl,
M.; Wingbermu¨hle, D.; Kloppenburg, L.; Carpenetti, D.; Erker, G.;
Petersen, J . L. Organometallics 1994, 13, 415.
tions of the reductive coupling of isocyanides by “sta-
bilized” group 4 metallacyclobutane complexes, (C5R5)2-
M(CH2SiMe2CH2) (M ) Zr,2 Hf;3 R ) H, Me) revealed
(3) (a) Berg, F. J .; Petersen, J . L. Organometallics 1993, 12, 3890.
(b) Kloppenburg, L.; Petersen, J . L. Polyhedron 1995, 14, 69.
X Abstract published in Advance ACS Abstracts, J uly 1, 1997.
S0276-7333(96)01076-X CCC: $14.00 © 1997 American Chemical Society

Reaction of [(C5Me4)SiMe2(N-t-Bu)]ZrMe2
Organometallics, Vol. 16, No. 15, 1997 3549
at this carbenium-type4 carbon center. Isocyanide
insertion into the remaining metal-carbon bond of the
η2-iminoacyl intermediate is not observed. Similarly,
isocyanide insertion into only one metal-carbon bond
occurs for the related d0 Zr(IV) complexes (C5R5)2-
Zr(alkyl)2, R ) H, Me.5
The observed differences in these two C,C-coupling
pathways are primarily a consequence of the level of
coordinative unsaturation at the early transition metal
center in the 12-electron bis(aryloxide) complexes,
M(OAr)2R′2, and in the 16-electron (C5R5)2Zr(alkyl)2 and
corresponding bis(η2-iminoacyl) complexes [(C5Me4)Si-
Me2(N-t-Bu)]Zr[η2-C(Me)NR]2, 3, which upon thermoly-
sis rearrange to the enediamido isomer [(C5Me4)SiMe2(N-
t-Bu)]Zr[N(R)C(Me)dC(Me)N(R)], 4. Specific details
regarding the relevant kinetic and structural aspects
of the migratory insertion and intramolecular isocyanide
coupling reactions displayed by [(C5Me4)SiMe2(N-t-
Bu)]ZrMe2 are described herein.
Exp er im en ta l Section
Rea gen ts. Reagent grade hydrocarbon and ethereal sol-
vents were purified using standard methods and distilled
under nitrogen. Na/K alloy was used to dry pentane, toluene,
and tetrahydrofuran. These dried solvents were then trans-
ferred to storage flasks containing [(C5H5)2Ti(µ-Cl)2]2Zn10 and
were freshly distilled prior to use. Hexamethyldisiloxane and
diethyl ether were dried over CaH2. Chlorinated solvents were
distilled from P4O10. The deuterated solvents, C6H6-d6 (Ald-
rich, 99.5%) and CDCl3 (Aldrich, 99.8%), were dried over
activated 4 Å molecular sieves prior to use; tert-butyl isocya-
nide (Aldrich), t-butylamine (Aldrich), and SiMe2Cl2 (Hu¨ls)
were also stored over 4 Å molecular sieves and then introduced
by vacuum transfer. Methyllithium (Aldrich, 1.4 M in diethyl
ether) and 2,6-xylyl isocyanide (Fluka) were used as received,
(C5R5)2M(CH2SiMe2CH2) complexes. The presence of
only one vacant metal orbital in these 16-electron
complexes led us to hypothesize that a prerequisite for
the direct coupling of two iminoacyl fragments is the
availability of a minimum of two vacant orbitals at the
electrophilic d0 group 4 metal center.6
Several years ago, Bercaw and co-workers7 demon-
strated that the incorporation of the bifunctional ansa-
monocyclopentadienylamido ligand [(C5Me4)SiMe2(N-t-
Bu)]2- provides an effective strategy for enhancing the
Lewis acidity of d0 organoscandium complexes. Re-
placement of a permethylated cyclopentadienyl ring
with an appended amido functionality simultaneously
reduces steric crowding and lowers the metal’s formal
electron count by two, thus generating another vacant
metal orbital. Researchers at Dow Chemical Co. and
Exxon later independently found that the corresponding
d0 group 4 metal complexes [(η5-C5R4)SiR′2(η1-NR′′)]ML2
(M ) Ti, Zr, Hf; R ) H, alkyl; R′,R′′ ) alkyl, aryl; L )
Cl, Me) in the presence of excess methylalumoxane
provide commercially viable Ziegler-Natta catalysts for
the copolymerization of ethylene and 1-alkenes.8
12
whereas CNMe11 and [(C5Me4)SiMe2(N-t-Bu)]ZrCl2 were
prepared employing literature procedures.
Gen er a l Con sid er a tion s. All manipulations and reactions
were carried out on a double-manifold, high-vacuum line or
in a Vacuum Atmospheres glovebox equipped with a HE-493
Dri-Train. Air- and moisture-sensitive compounds were syn-
thesized using pressure equalizing filter frits equipped with
high-vacuum Teflon stopcocks. Nitrogen was purified by
passage over reduced BTS catalysts and activated 4 Å molec-
ular sieves. All glassware was thoroughly oven-dried or flame-
dried under vacuum prior to use. NMR sample tubes were
sealed under approximately 500 Torr of nitrogen. The NMR
spectra were acquired using procedures and instrumentation
that has been previously described.2b The NMR assignments
for the different methyl protons in 1, 3a , 3b, 4a , and 4b were
made on the basis of the cross peaks observed in the corre-
sponding HETCOR NMR spectrum. Elemental analyses were
performed either by Robertson Microlit Laboratories, Madison,
NJ (RML), or by E+R Microanalytical Laboratory, Corona, NY
(E+R).
Syn th esis of [(C5Me4)SiMe2(N-t-Bu )]Zr Me2, 1. A solu-
tion of [(C5Me4)SiMe2(N-t-Bu)]ZrCl2 (0.75 g, 1.82 mmol) in
diethyl ether (50 mL) was cooled down to -78 °C. Methyl-
lithium (3.0 mL, 4.20 mmol) was added dropwise via syringe
under a N2 flush. A white precipitate formed, and the reaction
mixture was stirred overnight at room temperature. The
solvent was replaced by an equal volume of pentane, and the
soluble product was separated from LiCl by filtration. After
removal of the pentane, sublimation (10-4 Torr, 60 °C) of the
Although the spotlight on 14-electron ansa-monocy-
clopentadienylamido group 4 metal complexes, such as
[(C5Me4)SiMe2(N-t-Bu)]ZrMe2, remains primarily fo-
cused on their industrial application, far less in known
about their reactivity with unsaturated substrates.9 To
provide an operational test of our working hypothesis,
we have undertaken an investigation of the migratory
insertion reaction of [(C5Me4)SiMe2(N-t-Bu)]ZrMe2, 1,
with various isocyanides. We have found that these
reactions indeed proceed with the formation of the
(4) Tatsumi, K.; Nakamura, A.; Hofmann, P.; Stauffert, P.; Hoff-
mann, R. J . Am. Chem. Soc. 1985, 107, 4440.
(5) (a) Lappert, M. F.; Luong-Thi, N. T.; Milne, C. R. C. J .
Organomet. Chem. 1979, 174, C35. (b) Wolczanski, P. T.; Bercaw, J .
E. J . Am. Chem. Soc. 1979, 101, 6450. (c) Lyszak, E. L.; O’Brien, J . P.;
Kort, D. A.; Hendges, S. K.; Redding, R. N.; Bush, T. L.; Hermen, M.
S.; Renkema, K. B.; Silver, M. E.; Huffman, J . C. Organometallics 1993,
12, 338.
(6) Notable examples of the C,C-coupling of isocyanides by an
electrophilic group 4 metal complex not involving the direct coupling
of two η2-iminoacyls include: (a) Bocarsly, J . R.; Floriani, C.; Chiesa-
Villa, A.; Guastini, C. Organometallics 1986, 5, 2380. (b) Hessen, B.;
Blenkers, J .; Teuben, J . H.; Helgesson, G.; J agner, S. Organometallics
1989, 8, 830. (c) Fandos, R.; Meetsma, A.; Teuben, J . H. Organome-
tallics 1991, 10, 2665.
(7) (a) Shapiro, P. J .; Bunel, E. E.; Schaefer, W. P.; Bercaw, J . E.
Organometallics 1990, 9, 867. (b) Piers, W. E.; Shapiro, P. J .; Bunel,
E. E.; Bercaw, J . E. Synlett 1990, 2, 74. (c) Shapiro, P. J .; Cotter, W.
D.; Schaefer, W. P.; Labinger, J . A.; Bercaw, J . E. J . Am. Chem. Soc.
1994, 116, 4623.
(8) (a) Canich, J . M. Eur. Pat. Appl. EP-420-436-A1, 1990. (b)
Canich, J . M. U.S. Patent 5,026,798, 1991. (c) Canich, J . M.; Hlatky,
G. G.; Turner, H. W. PCT Int. Appl. WO92-00333, 1992. (d) Stevens,
J . C.; Timmers, F. J .; Wilson, D. R.; Schmidt, G. F.; Nickias, P. N.;
Rosen, R. K.; Knight, G. W.; Lai, S. Eur. Pat. Appl. EP-416-815-A2,
1991. (e) Campbell, R. E., J r. U.S. Patent 5,066,741, 1991. (f) LaPointe,
R. E. European Patent 468651, 1991.
crude product yielded
a white semicrystalline material.
Yield: 0.45 g (76%). 1H NMR (C6H6-d6): δ 1.97, 1.91 (C5Me4,
s), 1.40 (NCMe3, s), 0.46 (SiMe2, s), -0.01 (ZrMe2, s); (CDCl3)
δ 2.08, 1.98 (C5Me4, s), 1.42 (NCMe3, s), 0.44 (SiMe2, s), -0.39
(ZrMe2, s). 13C NMR (C6H6-d6, mult., J CH in Hz): δ 130.2,
1
125.3 (proximal and distal carbons of C5Me4, s), 95.8 (bridge-
head carbon of C5Me4, s), 54.9 (NCMe3, s), 35.8 (ZrMe, q, 114),
34.4 (NCMe3, q, 125), 14.3, 11.3 (C5Me4, q, 127), 6.65 (SiMe2,
1
q, 118). The H and 13C NMR chemical shifts are comparable
to those reported in ref 8d. Anal. Calcd for C17H33NSiZr
(370.76): C, 55.07; H, 8.97; N, 3.78. Found: C, 55.19; H, 9.15;
N, 3.78 (E+R).
(10) Setukowski, D. G.; Stucky, G. D. Inorg. Chem. 1975, 14, 2192.
(11) Schuster, R. E.; Scott, J . E.; Casanova, J ., J r. Org. Synth. 1973,
5, 773.
(12) Carpenetti, D. W.; Kloppenburg, L.; Kupec, J . T.; Petersen, J .
L. Organometallics 1996, 15, 1572.
(9) Kloppenburg, L; Petersen, J . L. Organometallics 1996, 15, 7.

3550 Organometallics, Vol. 16, No. 15, 1997
Kloppenburg and Petersen
Syn th esis of [(C5Me4)SiMe2(N-t-Bu )]Zr [η2-C(Me)N(t-
Bu )]2, 3a . Initially, this reaction was performed in a sealed
NMR tube. Two equiv of tert-butyl isocyanide were added to
a solution of 1 (0.032 g, 0.086 mmol) in benzene-d6. Periodic
NMR measurements indicated that the reaction proceeds
initially with rapid insertion of 1 equiv of CN-t-Bu to give the
η2-iminoacyl adduct [(C5Me4)SiMe2(N-t-Bu)]ZrMe[η2-C(Me)N(t-
Bu)], 2a , and eventually the diinsertion product, 3a , by taking
up the second equivalent of CN-t-Bu after 1 day. Because this
double isocyanide insertion reaction yields a single product,
it was repeated on a larger scale. A 25 mL pentane solution
of 1 (0.90 g, 2.43 mmol) was charged with nearly 3 equiv of
CN-t-Bu (0.80 mL, 7.08 mmol). The yellow reaction mixture
was stirred at ambient temperature for 6 days. Following
solvent removal, the product was washed with hexamethyl-
disiloxane (2 × 5 mL). Slow removal of pentane from a
pentane solution of 3a yielded pale yellow crystals suitable
for an X-ray diffraction analysis. Isolated yield: 1.194 g (91%).
Monoinsertion product, 2a : 1H NMR (C6H6-d6) δ 2.45, 2.26,
1.89 (proximal and distal protons of C5Me4 and η2-CMe, s),
Yield: 0.984 g (80%). 1H NMR (CDCl3): δ 6.96-6.90 (meta
and para CH, m), 2.30, 1.97 (proximal and distal methyl
protons of C5Me4, s), 1.93, 1.63 (methyl protons of 2,6-xylyl
groups, s), 2.18 (η2-CMe, s), 0.96 (NCMe3, s), 0.51 (SiMe2, s).
1H NMR (C6H6-d6): δ 6.91-6.85 (meta and para CH, m), 2.37,
1.85 (proximal and distal methyl protons of C5Me4, s), 1.96,
1.66 (methyl protons of 2,6-xylyl groups, s), 2.02 (η2-CMe, s),
1.21 (NCMe3, s), 0.79 (SiMe2, s). 13C NMR (CDCl3, mult., 1J CH
in Hz): δ 251.8 (η2-C, s), 147.2 (NC, s), 129.2, 128.6 (xylyl-
CMe, s), 127.9, 127.7, 124.3 (meta and para CH, d, 156, 156,
160), 123.5, 122.8 (proximal and distal carbons of C5Me4, s),
104.8 (bridgehead carbon of C5Me4, s), 55.0 (NCMe3, s), 35.5
(NCMe3, q, 124), 23.8 (η2-CMe, q, 126), 19.7, 17.6 (xylyl-CMe,
q, 127), 14.6, 11.6 (C5Me4, q, 126), 8.09 (SiMe2, q, 118). Anal.
Calcd for C35H51N3SiZr (633.12): C, 66.40; H, 8.12; N, 6.64.
Found: C, 66.48; H, 8.22; N, 6.60 (E+R).
Syn th esis of [(C5Me4)SiMe2(N-t-Bu )]Zr [N(2,6-xylyl)C-
(Me)dC(Me)N(2,6-xylyl)], 4b. A NMR tube containing the
solution of 3b in deuterated chloroform was heated in an oil
bath at 75 °C. Periodic 1H NMR measurements revealed that
3b rearranges solely to 4b. On a larger scale, a cylindrical
reaction tube equipped with a high-vacuum adapter was
charged with 3b (0.235 g, 0.371 mmol) and toluene (10 mL).
The solution was stirred at 70 °C for 2 days. After the solvent
was removed, the product residue was washed with pentane
(5 mL). Yellow single crystals of 4b suitable for X-ray
diffraction studies were obtained by slow removal of the solvent
from a saturated toluene solution. Yield: 0.167 g (71%). 1H
NMR (CDCl3): δ 7.12-6.92 (meta and para CH, m), 2.37
(dCMe, s), 1.97, 1.36 (C5Me4, s), 1.88, 1.68 (xylyl-CMe, s), 1.07
1.19, 1.09 (NCMe3, s), 0.69, 0.70 (SiMe2, s), 0.04 (ZrMe, s). 13
C
NMR (C6H6-d6, mult., J CH in Hz): δ 247.9 (η2-C, s), 122.3,
121.8 (proximal and distal carbons of C5Me4, s), 100.2 (bridge-
head carbon of C5Me4, s), 62.4 (ZrNCMe3, s), 54.5 (SiNCMe3,
s), 34.3 (SiNCMe3, q, 126), 30.3 (ZrNCMe3, q, 126), 23.0 (η2-
CMe, q, 127), 20.2 (ZrMe, q, 113), 14.8, 11.3 (C5Me4, q, 126),
7.43, 7.28 (SiMe2, q, 118).
1
Diinsertion product, 3a : 1H NMR (C6H6-d6) δ 2.36, 1.76
(proximal and distal protons of C5Me4), 2.35 (η2-CMe, s), 1.34
(SiNCMe3, s), 1.22 (ZrNCMe3, s), 0.79 (SiMe2, s). 13C NMR
1
(C6H6-d6, mult., J CH in Hz): δ 246.0 (η2-C, s), 123.8, 122.4
1
(NCMe3, s), 0.62 (SiMe2, s). 13C NMR (CDCl3, mult., J CH in
(proximal and distal carbons of C5Me4, s), 104.0 (bridgehead
carbon of C5Me4, s), 58.9 (ZrNCMe3, s), 53.8 (SiNCMe3, s), 36.1
(SiNCMe3, q, 126), 30.7 (ZrNCMe3, q, 126), 23.4 (η2-CMe, q,
126), 15.2, 12.0 (C5Me4, q, 126), 8.94 (SiMe2, q, 118). Anal.
Calcd for C27H51N3SiZr (537.03): C, 60.39; H, 9.57; N, 7.82.
Found: C, 60.39; H, 9.59; N, 7.67 (E+R).
Hz): δ 148.3 (xylyl-NC, s), 134.5, 132.9 (xylyl-CMe, s), 128.6,
128.2 (proximal and distal carbons of C5Me4, s), 128.0, 127.6,
123.6 (meta and para CH, d, 156, 154, 160), 112.8 (dC, s), 100.1
(bridgehead carbon of C5Me4, s), 55.6 (NCMe3, s), 34.4 (NCMe3,
q, 125), 21.8 (dCMe, q, 126), 19.4, 17.0 (xylyl-CMe, q, 127),
13.6, 9.56 (C5Me4, q, 127), 8.34 (SiMe2, q, 118). Anal. Calcd
for C35H51N3SiZr (633.12): C, 66.40; H, 8.12; N, 6.64. Found:
C, 66.34; H, 8.22; N, 6.59 (E+R).
Red u ctive Cou p lin g of CNMe. A NMR sample tube
equipped with a calibrated gas bulb was charged with 1 (0.030
g, 0.081 mmol) and benzene-d6. Two equivalents of methyl
isocyanide were then introduced. The reaction mixture turned
dark brown after a few hours. NMR measurements confirmed
the formation of the bis(η2-iminoacyl) product 3c, which gives
a characteristic downfield 13C NMR resonance at δ 242.2. 1H
NMR (C6H6-d6): δ 2.79 (NMe, s), 2.28, 1.97, 1.79 (proximal
and distal methyl protons of C5Me4 and η2-CMe, s), 1.37
(NCMe3, s), 0.77 (SiMe2, s). 13C{1H} NMR (C6H6-d6): δ 242.2
(η2-C), 124.0, 123.3 (proximal and distal carbons of C5Me4),
90.1 (bridgehead carbon of C5Me4), 54.1 (NCMe3), 35.8 (NC-
Me3), 35.6 (NMe), 19.6 (η2-CMe), 14.4, 11.6 (C5Me4), 8.96
(SiMe2). Upon heating the NMR sample tube containing 3c
to 65 °C, the proton NMR resonances of the η2-iminoacyl
product 3c diminished with the formation of the enediamido
isomer, 4c. 1H NMR (C6H6-d6): δ 3.16 (NMe, s), 2.29, 1.88,
1.71 (proximal and distal protons of C5Me4 and dCMe, s), 1.09
(NCMe3, s), 0.73 (SiMe2, s).
Syn th esis of [(C5Me4)SiMe2(N-t-Bu )]Zr [N(t-Bu )C(Me)d
C(Me)N(t-Bu )], 4a . A sample of 3a (0.035 g, 0.065 mmol)
was added to a NMR tube and dissolved in benzene-d6.
Periodic 1H NMR measurements indicated that 3a upon
heating rearranges solely to 4a . On a larger scale, a cylindrical
reaction tube equipped with a high-vacuum adapter was
charged with 3a (0.232 g, 0.43 mmol) and 10 mL of toluene.
The solution was heated to 70 °C for 9 days. The solvent was
removed, and the product was extracted with pentane to give
a yellow crystalline material. Slow removal of pentane from
a saturated pentane solution of 4a afforded single crystals
suitable for X-ray structural analysis. Yield: 0.227 g (98%).
1H NMR (C6H6-d6): δ 2.37, 1.53 (proximal and distal methyl
protons of C5Me4, s), 1.95 (dCMe, s), 1.37 (ZrNCMe3, s), 1.34
1
(SiNCMe3, s), 0.80 (SiMe2, s). 13C NMR (C6H6-d6, mult., J CH
in Hz): δ 125.0, 122.5 (proximal and distal carbons of C5Me4,
s), 109.0 (dC, s), 104.2 (bridgehead carbon of C5Me4, s), 55.9
(ZrNCMe3, s), 55.7 (SiNCMe3, s), 35.3 (SiNCMe3, q, 124), 34.2
(ZrNCMe3, q, 125), 19.9 (dCMe, q, 126), 15.4, 11.5 (C5Me4, q,
126), 8.81 (SiMe2, q, 118). Anal. Calcd for C27H51N3SiZr
(537.03): C, 60.39; H, 9.57; N, 7.82. Found: C, 60.18; H, 9.66;
N, 7.63 (RML).
Syn th esis of [(C5Me4)SiMe2(N-t-Bu )]Zr [η2-C(Me)N(2,6-
xylyl)]2, 3b. A NMR tube was charged with 1 (0.030 g, 0.081
mmol) and 2,6-xylyl isocyanide (0.027 g, 0.206 mmol). The
solids were dissolved in deuterated chloroform. 1H NMR
measurements indicate that the isocyanide insertion reaction
proceeds at ambient temperature with formation of 3b. On a
larger scale, a 25 mL pentane solution of 1 (0.72 g, 1.94 mmol)
and 2,6-xylyl isocyanide (0.60 g, 4.57 mmol) was stirred at
ambient temperature for 9 days. The solvent was filtered, and
the product was washed with pentane (2 × 25 mL), yielding
3b as a white powder. Slow removal of solvent from a toluene
solution yielded single crystals suitable for X-ray analysis.
Kin etic Mea su r em en ts. The first-order thermal rear-
rangements of 3a f 4a and of 3b f 4b were followed by
1
monitoring the loss of the intensity of the H NMR resonance
corresponding to the t-Bu substituents of the η2-iminoacyl
ligands located at δ 1.22 for 3a and the t-Bu substituent of
the appended amido at δ 1.21 for 3b. Two standard solutions
were prepared by dissolving 0.537g of 3a and 0.186 g of
ferrocene in 8.773 g of C6D6 (0.108 M) and by adding 0.3168 g
of 3b and 0.0931 g of ferrocene to 8.332 g of C6D6 (0.0571 M).
Appropriate aliquots taken from each solution were sealed in
a
series of NMR tubes. A typical kinetic run involved
submerging the NMR tube in an oil bath set at an appropriate
temperature (within the range 70-120 °C) maintained to (0.1

Reaction of [(C5Me4)SiMe2(N-t-Bu)]ZrMe2
Organometallics, Vol. 16, No. 15, 1997 3551
Ta ble 1. Ra te Con sta n ts for th e In tr a m olecu la r
Rea r r a n gem en t of 3a f 4a a n d 3b f 4b
T, °C
k, s-1
t1/2, min
3a f 4a
5.21(4) × 10-6
1.54(1) × 10-5
4.40(4) × 10-5
1.09(2) × 10-4
2.53(2) × 10-4
5.95(11) × 10-4
70.0
80.0
90.0
100.0
110.0
120.0
2215(17)
750(5)
262(2)
106(2)
45.7(4)
19.4(4)
3b f 4b
2.26(6) × 10-5
6.60(8) × 10-5
1.67(2) × 10-4
4.26(8) × 10-4
1.06(2) × 10-3
2.16(6) × 10-3
70.0
80.0
90.0
100.0
110.0
120.0
511(14)
175(2)
69.4(8)
27.1(5)
10.9(2)
5.3(2)
°C with a Fisher Scientific model 730 isotemp immersion
circulator. The NMR tube was removed from the oil bath at
a predetermined time and then immediately cooled in an ice-
water slush bath to quench the rearrangement reaction. Each
1H NMR spectrum was measured three times with a pulse
delay of 20 s in order to obtain reliable peak integrations. The
integrated intensity for the tert-butyl proton resonance ob-
tained for these three spectra was reproducible to within 5%;
the averaged integrated peak intensity for each run was used
in the determination of the rate constant k at each tempera-
ture. The sample was then returned to the constant-temper-
ature oil bath, and the process was repeated for a total time
corresponding to a minimum of at least three half-lives. The
concentrations of 3a and 3b were calculated from the expres-
sions:
F igu r e 1. Eyring plots for the first-order intramolecular
rearrangements of 3a to 4a and 3b to 4b.
reflections at 22 °C. The refined lattice parameters and other
pertinent crystallographic information are summarized in
Table 2.
Intensity data were measured with graphite-monochro-
mated Mo KR radiation (λ ) 0.710 73 Å) and variable ω scans.
Background counts were measured at the beginning and at
the end of each scan with the crystal and counter kept
stationary. The intensities of three standard reflections were
measured after every 100 reflections. The intensity data were
corrected for Lorentz-polarization and crystal decay (when
appropriate). An empirical absorption correction (when ap-
plied) was based upon ψ scans measured for a minimum of
eight reflections with ø ≈ (90° and 2θ ranging from 5° to 45°.
The structure solution in each case was provided by the first
E-map calculated on the basis of the phase assignments made
by the SHELXTL direct methods structure solution software.
The coordinates of all remaining non-hydrogen atoms that
were not revealed on the initial E-map were located in the
subsequent difference Fourier map. All hydrogen atoms were
idealized with isotropic temperature factors set at 1.2 times
that of the adjacent carbon. The positions of all the methyl
hydrogens were optimized by a rigid rotating group refinement
with idealized tetrahedral angles. Full-matrix least-squares
10(area of iminoacyl t-Bu resonance of 3a )
[3a ] )
[Cp2Fe]
18(area of Cp resonance of Cp2Fe)
and
[3b] )
10(area of appended amido t-Bu resonance of 3b)
[Cp2Fe]
9(area of Cp resonance of Cp2Fe)
The experimentally determined rate constants and t1/2
values for the rearrangements 3a f 4a and 3b f 4b are
summarized in Table 1. The values of the activation param-
eters, ∆Hq and ∆Sq, were calculated from the least-squares
determined slope (∆Hq/R) and the y-intercept (-∆Sq/R -
23.76), respectively, of the corresponding plot of -ln(k/T) vs
1/T, assuming a transmission coefficient of unity in the Eyring
equation ∆Gq(T) ) RTln(κkBT/kh), Figure 1. The standard
errors, which are given in parentheses for the activation
parameters, correspond to the errors calculated from the
regression analysis.13
X-r a y Da ta Collection a n d Str u ctu r a l An a lyses of 3a ,
3b, 4a , a n d 4b. The molecular structures of 3a , 3b, 4a , and
4b were determined following the same general procedure for
each X-ray structural analysis. A suitable crystal was sealed
in a capillary tube under a nitrogen atmosphere and then
optically aligned on the goniostat of a Siemens P4 automated
X-ray diffractometer. The unit cell dimensions were initially
determined by indexing a set of reflections whose angular
coordinates were obtained either from a rotation photograph
or with the automatic peak search routine provided with
XSCANS.14 The corresponding unit cell parameters and
orientation matrix were determined from a nonlinear least-
squares fit of the orientation angles of at least 20 higher order
2
2 2
refinement, based upon the minimization of ∑wi|Fo - Fc | ,
with wi-1 ) [σ2(Fo2) + (aP)2 + bP] where P ) (Max(Fo2,0) +
2Fc2)/3, was performed with SHELXL-9315 operating on a
Silicon Graphics Iris Indigo workstation. The final values of
the discrepancy indices are provided in Table 2. Their values
were calculated from the expressions R1 ) ∑||Fo| - |Fc||/∑|Fo|
2
and wR2 ) [∑(wi(Fo - Fc2)2)/∑(wi(Fo2)2)]1/2, and the standard
deviation of an observation of unit weight σ1 is equal to
2
[∑(wi(Fo - Fc2)2)/(n - p)]1/2, where n is the number of
reflections and p is the number of parameters varied during
the last refinement cycle.
Selected interatomic distances and bond angles for the
bis(η2-iminoacyl) compounds, 3a and 3b, and for the cyclic
enediamidate complexes, 4a and 4b, are compared in Tables
3 and 4, respectively.
Discu ssion of Resu lts
Migr a tor y Isocya n id e In ser tion a n d C,C-Cou -
p lin g Rea ction s. The reactions of 2 equiv of CNR (R
(14) XSCANS (version 2.0) is
a diffractometer control system
developed by Siemens Analytical X-ray Instruments, Madison, WI.
(15) SHELXL-93 is a FORTRAN-77 program developed by Professor
G. Sheldrick (Institut fu¨r Anorganische Chemie, University of Go¨ttin-
gen, D-37077 Go¨ttingen, Germany) for single-crystal X-ray structural
analyses.
(13) Skoog, D. A.; West , D. M.; Holler, F. J . Analytical Chemistry,
an Introduction, 6th ed.; Saunders College Publishing: Philadelphia,
PA, 1994; Appendix 6.

3552 Organometallics, Vol. 16, No. 15, 1997
Kloppenburg and Petersen
Ta ble 2. Cr ysta llogr a p h ic Da ta for th e X-r a y Str u ctu r a l An a lyses of [(C5Me4)SiMe2(N-t-Bu )]Zr [η2-C(Me)NR]2
(R ) ter t-Bu tyl (3a ), 2,6-Xylyl (3b), a n d [(C5Me4)SiMe2(N-t-Bu )]Zr [NRC(Me)dC(Me)NR] (R ) ter t-Bu tyl (4a ),
2,6-Xylyl (4b))
A. Crystal Data
compound
emp form
dimens, mm
cryst syst
space group
a, Å
3a
3b
4a
4b
C
27H51N3SiZr
C35H51N3SiZr
0.36 × 0.40 × 0.48
triclinic
P1h
11.4096(8)
12.0530(9)
13.2952(10)
83.642(6)
79.413(6)
72.010(6)
1706.5(2)
2
C27H51N3SiZr
C35H51N3SiZr
0.20 × 0.30 × 0.42
monoclinic
P21/c
16.282(1)
10.611(1)
19.544(1)
90
93.352(7)
90
3370.8(4)
4
0.20 × 0.40 × 0.60
0.20 × 0.30 × 0.54
orthorhombic
Pbca
orthorhombic
Pbca
16.957(1)
11.979(1)
30.469(3)
90
90
90
11.968(1)
17.738(1)
27.679(2)
90
90
90
b, Å
c, Å
R, deg
â, deg
γ, deg
volume, Å3
Z
6189.1(7)
8
5875.9(8)
8
fw
537.03
1.153
4.11
633.12
1.232
3.84
672
537.03
1.214
4.33
633.12
1.248
3.88
1344
density, g/cm3
µ, cm-1
F(000)
2304
2304
B. Data Collection and Structural Analyses
scan type
ω, variable
ω, variable
ω, variable
ω, variable
2.0-10.0
scan rate, deg/min
2θ range, deg
reflns sampled
2.0-10.0
2.0-10.0
3.0-10.0
3.0-50.0
3.0-50.0
3.0-50.0
3.0-50.0
h (-1 e h e 20)
k (-1 e k e 14)
l (-36 e l e 1)
6636
h (-13 e h e 12)
k (-14 e k e 0)
l (-15 e l e 15)
6308
h (-1 e h e 14)
k (-1 e k e 21)
l (-1 e l e 32)
6294
h (0 e h e 19)
k (0 e k e 12)
l (-23 e l e 23)
6097
no. of reflns
no. of unique data
agreement factor
no. of data (I > 2σ(I))
abs corr
5433
Rint ) 0.0375
4601
empirical
R1 ) 0.0497
wR2 ) 0.0904
R1 ) 0.1182
wR2 ) 0.1155
1.032
5990
Rint ) 0.0180
5711
empirical
R1 ) 0.0328
wR2 ) 0.0750
R1 ) 0.0453
wR2 ) 0.0809
1.026
5137
Rint ) 0.0429
4330
5879
Rint ) 0.0226
5295
empirical
R1 ) 0.0420
wR2 ) 0.0812
R1 ) 0.0808
wR2 ) 0.0964
1.001
none
R indices (I > 2σ(I))
R1 ) 0.0517
wR2 ) 0.0860
R1 ) 0.1257
wR2 ) 0.1097
1.006
R indices for all data
σ1, GOF
values of a and b
no. of variables
0.0437, 0.0
307
0.0384, 0.67
376
0.0338, 0.0
307
0.0411, 0.0
376
data to parameter ratio
largest diff peak and hole
17.7:1
0.254, -0.284
15.2:1
0.232, -0.209
16.7:1
0.336, -0.279
14.1:1
0.241, -0.217
) (a ) tert-butyl, (b) 2,6-xylyl, (c) Me) with [(C5Me4)-
SiMe2(N-t-Bu)]ZrMe2, 1, similarly proceed at 25 °C with
the sequential migratory insertion of an equivalent of
isocyanide into each Zr-C(Me) bond (eq 3) to afford the
mono(η2-iminoacyl) and bis(η2-iminoacyl) complexes
[(C5Me4)SiMe2(N-t-Bu)]ZrMe[η2-C(Me)NR], 2, and [(C5-
Me4)SiMe2(N-t-Bu)]Zr[η2-C(Me)NR]2, 3. For tert-butyl
solution by the presence of a characteristic downfield
13C NMR resonance for the η2-iminoacyl carbon nucleus
at δ 247.9. Whereas two resolved 1H and 13C NMR
resonances for the diastereotopic methyl groups of the
SiMe2 linkage are observed for 2a , only two rather than
the expected four 1H and 13C NMR resonances are
observed for the proximal and distal methyl groups and
the ring carbon atoms. This latter observation may
reflect the presence of a dynamic process involving the
methyl and η2-iminoacyl ligands of 2a . The bis(η2-
iminoacyl) species 3a -c also exhibit a single downfield
13C NMR resonance in solution for the two η2-iminoacyl
carbons, consistent either with a Cs-symmetric static
structure in which both iminoacyls adopt the sterically
more favorable N-outside orientation or with a dynamic
structure that has the N-inside and N-outside confor-
mations rapidly interconverting on the NMR time scale.
The results of the X-ray structure determinations
performed on 3a and 3b (vide infra) indicate that the
two η2-iminoacyl ligands do not adopt the Cs-symmetric
structure in the solid state.
(3)
Upon thermolysis, the bis(η2-iminoacyl) complexes
3a -c rearrange via an intramolecular reaction that
involves C,C-coupling of the two iminoacyl ligands to
afford solely the cyclic enediamido complexes, 4a -c,
respectively (eq 4). These reactions proceed with con-
comitant disappearance of the downfield η2-iminoacyl
carbon resonance of 3a -c. The activation parameters
for the first-order conversions of 3a f 4a and 3b f 4b
isocyanide, this insertion reaction proceeds sufficiently
slow to observe the formation of the intermediate mono
(η2-iminoacyl) complex, 2a , which was identified in

Reaction of [(C5Me4)SiMe2(N-t-Bu)]ZrMe2
Organometallics, Vol. 16, No. 15, 1997 3553
Ta ble 3. Selected In ter a tom ic Dista n ces (Å) a n d
Bon d An gles (d eg) for th e
Ta ble 4. Selected In ter a tom ic Dista n ces (Å) a n d
Bon d An gles (d eg) for th e Zir con iu m
Bis(η2-im in oa cyl)zir con iu m Com p lexes 3a a n d 3ba ,b
En ed ia m id a te Com p lexes 4a a n d 4ba
3a
3b
4a
4b
A. Interatomic Distances
A. Interatomic Distances
Zr-Cp(c)
Zr-N(1)
2.231
Zr-Cp(c)
2.236
Zr-Cp(c)
Zr-N(1)
2.244
Zr-Cp(c)
2.211
2.184(3)
2.235(4)
2.304(4)
2.218(5)
2.242(5)
1.863(5)
1.711(4)
1.485(5)
1.276(6)
1.259(6)
1.504(6)
1.508(6)
Zr-N(1)
2.174(2)
2.316(2)
2.268(2)
2.258(3)
2.237(3)
1.871(3)
1.716(2)
1.485(3)
1.282(3)
1.276(3)
1.434(3)
1.434(3)
2.138(4)
2.068(4)
2.064(4)
2.564(5)
2.563(5)
1.860(5)
1.733(4)
1.501(6)
1.405(6)
1.400(6)
1.491(6)
1.483(6)
1.388(7)
Zr-N(1)
2.149(3)
2.071(3)
2.069(3)
2.603(4)
2.595(4)
1.870(4)
1.723(3)
1.487(5)
1.413(5)
1.417(5)
1.436(5)
1.423(5)
1.373(5)
Zr-N(2)
Zr-N(2)
Zr-N(3)
Zr-N(2)
Zr-N(2)
Zr-N(3)
Zr-N(3)
Zr-N(3)
Zr-C(16)
Zr-C(22)
Si-C(1)
Zr-C(16)
Zr-C(26)
Si-C(1)
Zr‚‚‚C(16)
Zr‚‚‚C(17)
Si-C(1)
Zr‚‚‚C(16)
Zr‚‚‚C(27)
Si-C(1)
Si-N(1)
Si-N(1)
Si-N(1)
Si-N(1)
N(1)-C(12)
N(2)-C(16)
N(3)-C(22)
N(2)-C(18)
N(3)-C(24)
N(1)-C(12)
N(2)-C(16)
N(3)-C(26)
N(2)-C(18)
N(3)-C(28)
N(1)-C(12)
N(2)-C(16)
N(3)-C(17)
N(2)-C(20)
N(3)-C(24)
C(16)-C(17)
N(1)-C(12)
N(2)-C(16)
N(3)-C(17)
N(2)-C(20)
N(3)-C(28)
C(16)-C(17)
B. Bond Angles
Cp(c)-Zr-N(1)
Cp(c)-Zr-Im(1)
Cp(c)-Zr-Im(2)
N(1)-Zr-Im(1)
N(1)-Zr-Im(2)
Im(1)-Zr-Im(2)
N(1)-Zr-N(2)
N(1)-Zr-N(3)
N(1)-Zr-C(16)
N(1)-Zr-C(22)
N(2)-Zr-N(3)
N(2)-Zr-C(16)
N(3)-Zr-C(22)
N(3)-Zr-C(16)
N(3)-Zr-C(22)
C(16)-Zr-C(22)
N(1)-Si-C(1)
Si-N(1)-Zr
99.2
Cp(c)-Zr-N(1)
Cp(c)-Zr-Im(1)
Cp(c)-Zr-Im(2)
N(1)-Zr-Im(1)
N(1)-Zr-Im(2)
Im(1)-Zr-Im(2)
99.5
121.0
115.4
105.6
111.9
103.1
91.26(7)
121.13(8)
119.96(9)
101.34(9)
88.53(7)
32.52(8)
116.62(8)
86.29(8)
32.90(8)
119.17(9)
95.08(11)
104.48(6)
125.5(2)
129.4(2)
B. Bond Angles
125.0
110.4
101.7
113.7
106.4
Cp(c)-Zr-N(1)
Cp(c)-Zr-N(2)
Cp(c)-Zr-N(3)
N(1)-Zr-N(2)
N(1)-Zr-N(3)
N(2)-Zr-N(3)
N(1)-Si-C(1)
Si-N(1)-Zr
100.5
123.6
123.3
Cp(c)-Zr-N(1)
Cp(c)-Zr-N(2)
Cp(c)-Zr-N(3)
101.5
115.1
116.0
120.33(12)
119.84(12)
84.81(12)
95.9(2)
103.3(2)
123.3(3)
133.4(2)
110.94(14) N(1)-Zr-N(2)
113.2(2)
85.6(2)
N(1)-Zr-N(3)
N(2)-Zr-N(3)
N(1)-Si-C(1)
Si-N(1)-Zr
102.61(14) N(1)-Zr-N(2)
98.03(14)
99.7(2)
129.8(2)
97.1(2)
33.3(2)
85.1(2)
130.0(2)
32.1(2)
111.0(2)
96.3(2)
104.2(2)
124.4(3)
131.3(3)
N(1)-Zr-N(3)
N(1)-Zr-C(16)
N(1)-Zr-C(26)
N(2)-Zr-N(3)
N(2)-Zr-C(16)
N(2)-Zr-C(26)
N(3)-Zr-C(16)
N(3)-Zr-C(26)
C(16)-Zr-C(26)
N(1)-Si-C(1)
Si-N(1)-Zr
96.2(2)
103.9(2)
124.2(3)
131.9(3)
C(12)-N(1)-Si
C(12)-N(1)-Zr
C(12)-N(1)-Si
C(12)-N(1)-Zr
C(16)-N(2)-C(20) 123.6(4)
C(16)-N(2)-C(20) 120.6(3)
C(16)-N(2)-Zr
C(20)-N(2)-Zr
93.2(3)
141.6(3)
C(16)-N(2)-Zr
C(20)-N(2)-Zr
94.8(2)
142.1(2)
C(17)-N(3)-C(24) 122.1(4)
C(17)-N(3)-C(28) 119.2(3)
C(17)-N(3)-Zr
C(24)-N(3)-Zr
C(5)-C(1)-C(2)
C(2)-C(1)-Si
C(5)-C(1)-Si
93.5(3)
C(17)-N(3)-Zr
C(28)-N(3)-Zr
C(5)-C(1)-C(2)
C(2)-C(1)-Si
C(5)-C(1)-Si
94.4(2)
144.0(3)
105.8(5)
122.1(4)
124.5(3)
145.5(3)
105.6(4)
122.5(3)
124.3(3)
C(12)-N(1)-Si
C(12)-N(1)-Zr
C(12)-N(1)-Si
C(12)-N(1)-Zr
C(16)-N(2)-C(18) 128.3(4)
C(16)-N(2)-C(18) 125.0(2)
N(2)-C(16)-C(17) 120.4(4)
N(2)-C(16)-C(18) 119.9(5)
C(17)-C(16)-C(18) 119.4(5)
N(3)-C(17)-C(16) 120.4(5)
N(3)-C(17)-C(19) 120.4(5)
C(16)-C(17)-C(19) 118.5(5)
N(2)-C(16)-C(17) 119.8(3)
N(2)-C(16)-C(18) 117.7(3)
C(17)-C(16)-C(18) 122.3(3)
N(3)-C(17)-C(16) 120.4(3)
N(3)-C(17)-C(19) 117.7(3)
C(16)-C(17)-C(19) 121.7(4)
C(16)-N(2)-Zr
C(18)-N(2)-Zr
72.6(3)
158.5(4)
C(16)-N(2)-Zr
C(18)-N(2)-Zr
71.23(14)
163.8(2)
C(22)-N(3)-C(24) 131.4(4)
C(26)-N(3)-C(28) 128.8(2)
C(22)-N(3)-Zr
C(24)-N(3)-Zr
C(5)-C(1)-C(2)
C(2)-C(1)-Si
C(5)-C(1)-Si
71.2(3)
C(26)-N(3)-Zr
C(28)-N(3)-Zr
C(5)-C(1)-C(2)
C(2)-C(1)-Si
C(5)-C(1)-Si
72.19(14)
158.9(2)
105.7(2)
121.4(3)
125.6(2)
157.3(3)
105.1(4)
125.5(3)
121.4(4)
a
Cp(c) is the centroid of the permethylated cyclopentadienyl
ring containing atoms C(1), C(2), C(3), C(4), and C(5).
N(2)-C(16)-C(17) 128.8(5)
N(2)-C(16)-C(17) 122.2(2)
mol and ∆Sq ) -10.4(8) eu for 3b f 4b fall within the
∆Hq range (21.0-25.0 kcal/mol) and ∆Sq range (-2 to
-16 eu) reported by Rothwell and co-workers16 for the
analogous intramolecular C,C-coupling reaction ob-
served for Zr(OAr)2[η2-C(Me)NR]2 complexes, where OAr
) 2,6-di-tert-butylphenoxide and R ) meta- or para
substituted phenyl substituent. The negative entropy
of activation is consistent with a mechanism that
proceeds toward a more symmetric transition state,16
and the positive enthalpy of activation presumably
reflects the collective energy needed to rotate the two
η2-iminoacyl groups toward mutually-similar N-outside
orientations as well as weaken the two Zr-C(iminoacyl)
bonds.
N(2)-C(16)-Zr
C(17)-C(16)-Zr
74.1(3)
156.8(4)
N(2)-C(16)-Zr
C(17)-C(16)-Zr
76.25(14)
161.3(2)
N(3)-C(22)-C(23) 127.7(7)
N(3)-C(26)-C(27) 124.9(2)
N(3)-C(22)-Zr
C(23)-C(22)-Zr
76.6(3)
155.4(3)
N(3)-C(26)-Zr
C(27)-C(26)-Zr
74.90(14)
159.9(2)
a
Cp(c) is the centroid of the permethylated cyclopentadienyl
b
ring containing atoms C(1), C(2), C(3), C(4), and C(5). Im(1) and
Im(2) designate the midpoints of the N(2)-C(16) bond and the
N(3)-C bond of the two η2-iminoacyl ligands, respectively.
(4)
The NMR spectra for the three enediamidate com-
plexes, 4a -c, are consistent with the presence of a
mirror plane of symmetry passing through the bridge-
head C, Si, and Zr atoms and bisecting the N-Zr-N
angle of the 1,4-diaza-5-zirconacyclopentene ring. Each
pair of distal and proximal methyl substituents on the
permethylated cyclopentadienyl ring, the two methyl
groups of the SiMe2 linkage, and the pair of cis methyl
were obtained from an evaluation of the temperature
dependence of the rate constant in each case. The
corresponding rate constants within the temperature
range of 70-120 °C are tabulated in Table 1. The
activation parameters of ∆Hq ) 24.6(2) kcal/mol and ∆Sq
) -11.3(7) eu for 3a f 4a and of ∆Hq ) 23.9(3) kcal/
(16) Durfee, L. D.; McMullen, A. K.; Rothwell, I. P. J . Am. Chem.
Soc. 1988, 110, 1463.

3554 Organometallics, Vol. 16, No. 15, 1997
Kloppenburg and Petersen
1
groups on the CdC bond exhibit one characteristic H
and one 13C NMR resonance. As expected, the carbon
resonance for the bridgehead carbon12 of the cyclopen-
tadienyl ring is positioned ca. 20 ppm upfield from the
corresponding pair of signals for the distal and proximal
ring carbons.
The results of our X-ray structural analysis of 4a and
4b (vide infra) reveal that their five-membered ZrN2C2
rings are significantly folded along the N‚‚‚N line
segment, thereby suggesting the possibility of observing
in solution a dynamic equilibrium between two in-
equivalent folded ring conformations. Rothwell and co-
workers1b estimated that the activation energy for the
corresponding degenerate process in Zr(OAr′)2[N(2,6-
xylyl)C(Me)dC(Me)N(2,6-xylyl)], where OAr′ is 2,6-di-
tert-butylphenoxide, is 14.5 (5) kcal/mol at 0 °C. We
subsequently found that the activation barrier and
coalescence temperature for the analogous process in
the related bicyclic enediamidate group 4 metallocene
complexes, (C5R′5)2M[N(R)C(CH2SiMe2CH2)dCN(R)], are
highly variable and depend on the substituents R and
R′ and the metal M.17 In contrast, upon lowering the
temperature of the NMR solutions containing 4a or 4b,
no noticeable broadening or reduction in the intensities
of the 1H NMR resonances was observed, thereby
suggesting either that the activation barrier for this
interconversion is small (i.e., ,10 kcal/mol) or that the
ring conformations associated with the molecular struc-
tures of 4a and 4b remain rigid in solution.
F igu r e 2. Molecular structure of 3a with the non-
hydrogen atom labeling scheme. The thermal ellipsoids are
scaled to enclose 30% probability.
Str u ctu r a l Ch a r a cter iza tion of th e Bis(η2-im i-
n oa cyl) Com p lexes, 3a a n d 3b. Perspective views of
the molecular structures of 3a and 3b with the corre-
sponding atom labeling schemes are depicted in Figures
2 and 3, respectively. The pseudotetrahedral coordina-
tion spheres about the Zr atoms in these complexes are
analogous, consisting of a permethylated cyclopentadi-
enyl ring with an appended t-butylamido ligand and two
η2-bound iminoacyl groups. The angle between the two
vectors extending from Zr to the midpoints Im(1) and
Im(2) of the two iminoacyl C)N bonds (106.4° (3a ) and
103.1° (3b)) compares well with the Cl-Zr-Cl bond
angle of 104.92(4)° in [(C5Me4)SiMe2(N-t-Bu)]ZrCl2.12
The Zr-N(1) and Cp(c)-Zr distances of 2.184(3) and
2.231 Å in 3a and of 2.174(2) and 2.236 Å in 3b are
significantly longer than the corresponding distances of
2.052(2) and 2.163 Å in the 14-electron dichloride
derivative. Similar elongations of the Zr-N distance
and the Zr-Cp(c) separation are observed in {[(C5Me4)-
SiMe2(N-t-Bu)]Zr(η2-O2CMe)(µ-O2CMe)}2,9 which con-
tains a coordinatively saturated ligand environment at
each 18-electron Zr(IV) center. By utilizing two ad-
ditional metal orbitals for bonding, the two 4-electron
donating η2-iminoacyl ligands in 3a and 3b reduce the
electrophilicity at Zr, thereby diminishing the magni-
tude of the π-donating interaction of the appended
amido functionality. The crowded metal coordination
environment in 3a and 3b is further accompanied by a
F igu r e 3. Molecular structure of 3b with the non-
hydrogen atom labeling scheme. The thermal ellipsoids are
scaled to enclose 30% probability.
modest decrease12 in the Cp(c)-Zr-N(amido) angle to
99.2° and 99.5°, respectively.
The structural parameters, such as the C)N distance
and the internal angles within the three-membered
ZrCN rings, are consistent with those reported for other
organozirconium compounds containing one,18 two,19 or
three19 η2-iminoacyl ligands. Normally, one finds that
(18) (a) Reger, D. L.; Tarquini, M. E.; Lebioda, L. Organometallics
1983, 2, 1763. (b) Erker, G.; Korek, U.; Petersen, J . L. J . Organomet.
Chem. 1988, 355, 121. (c) Bristow, G. S.; Lappert, M. F.; Atwood, J .
L.; Hunter, W. E. Unpublished results described in Chemistry of
Organozirconium and Hafnium Compounds; Cardin, D. F., Lappert,
M. F., Raston, C. L., Eds.; Wiley, New York, 1986.
(19) 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.
(17) The activation barrier and coalescence temperature for the
degenerate interconversion of the five-membered ZrN2C2 ring in (C5-
Me5)2Zr[N(Me)C(CH2SiMe2CH2)dCN(Me)],2c Cp2Zr[N(CMe3)C(CH2Si-
Me2CH2)dCN(CMe3)],2b Cp2Hf[N(CMe3)C(CH2SiMe2CH2)dCN(CMe3)],3a
and Cp2Zr[N(2,6-xylyl)C(CH2SiMe2CH2)dCN(CMe3)]2b are ∆Gq(est.)
, 10 kcal/mol, Tc < -110 °C; ∆Gq ) 19.5(5) kcal/mol, Tc ) 142 °C;
∆Gq ) 16.9(5) kcal/mol, Tc ) 85 °C; and ∆Gq(est.) >> 20 kcal/mol, Tc
. 150 °C, respectively.

Reaction of [(C5Me4)SiMe2(N-t-Bu)]ZrMe2
Organometallics, Vol. 16, No. 15, 1997 3555
F igu r e 5. Molecular structure of 4b with the non-
hydrogen atom labeling scheme. The thermal ellipsoids are
scaled to enclose 30% probability.
F igu r e 4. Molecular structure of 4a with the non-
hydrogen atom labeling scheme. The thermal ellipsoids are
scaled to enclose 30% probability.
corresponding Zr-N(2) and Zr-N(3) distances which
range from 2.06-2.07 Å in 4a and 4b. These latter
distances are comparable to the Zr-N distances of
2.060(5) and 2.064(4) Å for the terminal dialkylamido
ligands in [(C5Me4)SiMe2(N-t-Bu)]Zr(NMe2)212 and many
other zirconium amido complexes20 in which an ap-
preciable N π-donation to an electrophilic d0 Zr center
exists. These Zr-N distances for the enediamido ligands
of 4a and 4b are essentially identical to the values of
2.060(6) and 2.061(6) Å in Zr(OAr)2[N(2,6-xylyl)C-
(Me)dC(Me)N(2,6-xylyl)]1b but are noticeably shorter
than the Zr-N distances of 2.111(8), 2.104(6) Å in
for these Zr η2-iminoacyl complexes, the Zr-N bond
distance is typically equal to or less than the Zr-C bond
distance within the same η2-iminoacyl ligand. However,
the opposite trend is observed in 3a and 3b. Here, the
Zr-N distance in each three-membered ZrCN ring is
ca. 0.02-0.06 Å longer than the corresponding Zr-C
distance. The magnitude of ∆d (dZr-N - dZr-C) cor-
relates directly with the relative orientation of the
iminoacyl group with respect to the plane defined by
Zr, Im(1), and Im(2). For 3a , the acute dihedral angles
between the planes containing Zr, N(2), C(16) and Zr,
N(3), C(22) with the Zr, Im(1), Im(2) plane are 24.3° and
61.1°, respectively, with N(2) and N(3) positioned inside
and outside of the wedge defined by the Zr-Im(1) and
Zr-Im(2) directions. For 3b, the acute dihedral angles
between the planes containing Zr, N(2), C(16) and Zr,
N(3), C(26) with the corresponding Zr, Im(1), Im(2)
plane are 90.0° and 14.5°, respectively, with N(3)
occupying an inside position. For N(2) in 3a and N(3)
in 3b, which adopt a nearly N-inside orientation, ∆d is
0.017 and 0.031 Å, respectively. In contrast, for the
remaining iminoacyl ligand containing N(3) in 3a and
N(2) in 3b, the respective ∆d values of 0.062 and 0.058
Å are considerably larger. The relatively long Zr-N(3)
distance of 2.304(4) Å in 3a and the Zr-N(2) distance
of 2.316(2) Å in 3b probably reflect a poorer orbital
match between the available Zr-valence and N-donor
orbitals, both of which are directed toward one another
from below the Zr, Im(1), Im(2) plane.
Str u ctu r a l Ch a r a cter iza tion of th e Cyclic En e-
d ia m id a te Com p lexes, 4a a n d 4b. The molecular
structures of 4a and 4b have also been determined by
X-ray crystallography, and perspective views of these
two enediamidate complexes with their atom labeling
schemes are shown in Figures 4 and 5, respectively. The
pseudotetrahedral coordination sphere about the Zr
atom in both compounds consists of the permethylated
cyclopentadienyl ring, the appended amido N, and the
two N-donors of a symmetrically-chelating enediamidate
ligand generated by the intramolecular C,C-coupling of
the two η2-iminoacyl groups of 3a and 3b, respectively.
The Zr-N(1) distances of 2.138(4) Å in 4a and 2.149(3)
Å in 4b correspond to the appended t-butylamido
functionality and are substantially longer than the
Cp2Zr[N(CMe3)C(CH2SiMe2CH2)dCN(CMe3)];2b 2.110(6),
2.112(7) Å in Cp*2Zr[N(Me)C(CH2SiMe2CH2)dCN(Me)];2c
and 2.100(4), 2.123(5) Å in Cp2Zr[N(Ph)C(Ph)dC(Ph)N-
(Ph)].21
The structural parameters within the 1,4-diaza-5-
zirconacylopentene rings of 4a and 4b are consistent
with a dianionic enediamido ligand donating to a d0
Zr(IV) center. The C(16)-C(17) bonds of 1.388(7) (4a )
and 1.373(5) Å (4b ) fall well within the range 1.35-
1.42 Å observed for the CdC double bond in related
enamidolate,1 enediamidate,1,2,6a and butadiene com-
plexes22 that also conform to the metallacyclopentene
resonance structure. The N(2)-C(16) and N(3)-C(17)
distances of 1.405(6) and 1.400(6) in 4a and 1.413(5) and
1.417(5) in 4b are consistent with C-N single bonds.
A notable structural feature associated with the
molecular structures of these compounds is the folding
(20) Some representative Zr-N bond distances for Zr(IV) amide
complexes: (a) 2.07 Å, Zr(NMe2)4 (electron diffraction); Hagen, K.;
Holwill, C. J .; Rice, D. A.; Runnacles, J . D. Inorg. Chem. 1988, 27,
2032. (b) 2.06 Å, (Me2N)2Zr(µ-N-t-Bu)2Zr(NMe2)2; Nugent, W. A.;
Harlow, R. L. Inorg. Chem. 1979, 18, 2030. (c) 2.06 Å, rac-[C2H4-
(C9H6)2]Zr(NMe2)2; Diamond, G. M.; J ordan, R. F.; Petersen, J . L. J .
Am. Chem. Soc. 1996, 118, 8024. (d) 2.07 Å, rac-[SiMe2(C9H6)2]Zr(NMe2)2;
2.04 Å, [µ-SiMe2(C9H6)2]Zr2(NMe2)6; Christopher, J . N.; Diamond, G.
M.; J ordan, R. F.; Petersen, J . L. Organometallics 1996, 15, 4038. (e)
2.07 Å, Zr[N(SiMe3)2]3Cl; 2.08 Å, Zr[N(SiMe3)2]3Me; Bradley, D. C.;
Chudzynska, H.; Backer-Dirks, J . D. J .; Hursthouse, M. B.; Ibrahim,
A. A.; Montevalli, M.; Sullivan, A. C. Polyhedron 1990, 9, 1423. (f) 2.00
Å, (C5Me5)Zr[N(i-Pr)2]Cl2; Pupi, R. M.; Coalter, J . N.; Petersen, J . L.
J . Organomet. Chem. 1995, 497, 17.
(21) Scholz, J .; Dlikan, M.; Stro¨hl, D.; Dietrich, A.; Schumann, H.;
Thiele, K.-H. Chem. Ber. 1990, 123, 2279.
(22) Erker, G.; Kru¨ger, C.; Mu¨ller, G. Adv. Organomet. Chem. 1985,
24, 1 and references cited therein.

3556 Organometallics, Vol. 16, No. 15, 1997
Kloppenburg and Petersen
of the 1,4-diaza-5-zirconacyclopentene ring along the
N‚‚‚N line segment. For Zr(OAr)2[N(R)C(Me)dC(Me)-
N(R)],1 Cp2Zr[N(Ph)C(Ph)dC(Ph)N(Ph)],21 and Cp2Zr-
type of π-interaction is probably not a major factor in
determining the relative stability and conformational
preference of the nonplanar prone and supine structures
in 4a and 4b, respectively.
[N(R)C(CH2SiMe2CH2)dCN(R)],2 the two possible folded
conformations represent degenerate structures, and
thus only one conformational structure is observed in
the solid state. In contrast, the presence of the bifunc-
tional ansa-monocyclopentadienylamido ligand in 4a
and 4b offers the possibility of observing two inequiva-
lent conformations for the folded 1,4-diaza-5-zirconacy-
clopentene ring. If we adopt the analogous nomencla-
ture recently used to define the conformational geometry
of the coordinated diene in [(C5Me4)SiMe2(N-t-Bu)]Ti-
(diene) complexes,23 then the ring conformer with the
1,4-diaza-5-zirconacyclopentene ring folded up toward
the cyclopentadienyl ring corresponds to the prone
structure because the open end of the cup defined by
atoms N(2), C(16), C(17), and N(3) is oriented away from
the cyclopentadienyl ring. The other ring conformer
corresponds to the supine structure because the opening
of the cup is directed toward the cyclopentadienyl ring.
On the basis of this nomenclature, the 1,4-diaza-5-
zirconacyclopentene ring of 4a exhibits the prone struc-
ture with the acute dihedral angle between the planes
containing Zr, N(2), N(3) and N(2), C(16), C(17), N(3)
being 50.5° and the corresponding five-membered ring
of 4b adopts the alternative supine structure with the
dihedral angle being 49.0°. Given that these folding
angles are comparable in magnitude, one might expect
that the prone structure should be sterically less favor-
able. However, the dihedral angle between the plane
of the cyclopentadienyl ring and the plane containing
Zr, N(2), N(3) of 53.0° for the prone structure is ca. 12°
greater than the corresponding dihedral angle of 41.1°
associated with the supine structure of 4b. This struc-
tural alteration apparently compensates for the steric
interactions imposed by the prone conformation.
The bending of these five-membered rings is more
likely a consequence of the presence of the tert-butyl or
2,6-xylyl substituent at each N atom of the enediamido
ligand. Folding along the N(2)‚‚‚N(3) line segment (in
either direction) enhances the overlap of the pπ-orbital
at each N with the same laterally disposed vacant metal
orbital and thus helps account for the observed reduc-
tion in the Zr-N(2) and Zr-N(3) distances mentioned
earlier. However, because the magnitude of the ring
folding is comparable for 4a and 4b, the degree of
π-stabilization associated with these Zr-N bonds is
expected to be similar and, thus, explains why the Zr-N
distances are essentially equal for the prone and supine
conformations.
In view of the similar electronic features displayed
by these folded metallacylic rings, why do the 1,4-diaza-
5-zirconacyclopentene rings of 4a and 4b adopt different
conformational structures? The explanation apparently
lies in considering the steric features imposed by the
different size and shape of the substituents at N(2) and
N(3) of the folded ZrN2C2 rings. In 4a , the prone
structure directs the bulky tert-butyl substituents away
from the methyl substituents at C(2) and C(5) of the
cyclopentadienyl ring. In contrast, the supine structure
of 4b allows both planar 2,6-xylyl groups to lie parallel
to the plane of the cyclopentadienyl ring. By minimizing
the steric interactions between the methyl substituents
of the 2,6-xylyl and cyclopentadienyl rings, this ar-
rangement reinforces the structural preference for the
supine conformation observed for 4b.
Ack n ow led gm en t. Financial support for this re-
search was provided by the National Science Foundation
(Grant No. CHE-9113097). J .L.P. gratefully acknowl-
edges the support provided by the Chemical Instrumen-
tation Program of the National Science Foundation
(Grant No. CHE 9120098) to acquire a Siemens P4
X-ray diffractometer in the Department of Chemistry
at West Virginia University.
In both 4a and 4b, ring folding moves the internal
carbons, C(16) and C(17), of the 1,4-diaza-5-zirconacy-
clopentene ring closer to the electrophilic Zr center. The
corresponding Zr-C(16) and Zr-C(17) distances of
2.564(5) and 2.563(5) Å in 4a and 2.603(4) and 2.595(4)
Å in 4b imply that both conformers could experience
some stabilization from a weak attractive interaction
between the filled π-orbital of the CdC double bond and
an empty metal orbital that is directed above and below
the Zr, N(2), N(3) plane. However, the absence of any
significant elongation or notable difference in the C(16)-
C(17) bond distances in 4a and 4b suggests that this
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data and structure refinement, atomic coordinates, interatomic
distances and bond angles, anisotropic displacement param-
eters, and hydrogen coordinates for 3a , 3b, 4a , and 4b (29
pages). Ordering information is given on any current mast-
head page. Structure factor tables for these four compounds
are available from the authors upon written request.
(23) Devore, D. D.; Timmers, F. J .; Hasha, D. L.; Rosen, R. K.;
Marks, T. J .; Deck, P. A.; Stern, C. L. Organometallics 1995, 14, 3132.
OM9610760