Isocyanide insertion reactions with organometallic group 4 tropocoronand complexes: Formation of η2-iminoacyl, enediamido, η2-imine, and μ-imido products

Article abstract of DOI:10.1021/om9706830

The reactivity of the tropocoronand complexes [M(TC-3,n)R₂] (M = Zr(IV), Hf(IV); n = 3, 5; R = CH₂Ph, Ph) with aryl and alkyl isocyanides is described. Alkyl isocyanides induced migration of both benzyl groups to afford the bis(iminoacyl) species [Hf(TC-3,n){n²-(R)N=C(CH₂Ph)}₂] (n = 5, R = Cy(1), n-Bu (2); n = 3, R = Cy(3)). Different products were isolated with aryl isocyanides, depending on the rate of substrate addition. Treatment of [M(TC-3,n)(CH₂Ph)₂] with excess 2,6-dimethylphenyl isocyanide (ArNC) generated the enediamido compounds [(TC-3,3)MN(Ar)C(CH₂Ph)=C(CH₂Ph)N(Ar)] (M = Zr (4), Hf (5)) via coupling of two bis(iminoacyl) groups, whereas slow step-wise addition produced [(TC-3,n)-MN(Ar)C(CH₂Ph)₂C(=NAr)] (M = Zr, n = 3 (6); M = Hf, n = 3 (7), n = 5 (8)). The η²-imine complex [(TC-3,5)HfN(Ar)C(CH₂Ph)₂] (9), an intermediate in the formation of 7, was isolated and characterized, but the corresponding zirconium species was unstable in solution, decomposing to form the imido-bridged compound {[Zr(TC-3,3)]₂(μ-NAr)₂} (10). Altering the nature of the carbon donor ligands also influenced the reactivity. Addition of both aryl and alkyl isocyanides to solutions of [Zr(TC-3,3)Ph₂] (11) afforded the η²-imine complexes [(TC-3,3)ZrN(R)C(Ph)₂] R = Cy (12), Ar (13)), the stability of which may be due in part to interactions between the metal center and a phenyl ring. Electron-withdrawing R substituents enhance this effect. All new compounds were characterized by X-ray crystallography, and plausible mechanisms for the migration reactions are outlined.

Full text of DOI:10.1021/om9706830

Organometallics 1997, 16, 5857-5868
5857
Isocya n id e In ser tion Rea ction s w ith Or ga n om eta llic
Gr ou p 4 Tr op ocor on a n d Com p lexes: F or m a tion of
η2-Im in oa cyl, En ed ia m id o, η2-Im in e, a n d µ-Im id o
P r od u cts
Michael J . Scott and Stephen J . Lippard*
Department of Chemistry, Massachusetts Institute of Technology,
Cambridge, Massachusetts 02139
Received August 5, 1997X
The reactivity of the tropocoronand complexes [M(TC-3,n)R2] (M ) Zr(IV), Hf(IV); n ) 3,
5; R ) CH2Ph, Ph) with aryl and alkyl isocyanides is described. Alkyl isocyanides induced
migration of both benzyl groups to afford the bis(iminoacyl) species [Hf(TC-3,n){η2-
(R)NdC(CH2Ph)}2] (n ) 5, R ) Cy (1), n-Bu (2); n ) 3, R ) Cy (3)). Different products were
isolated with aryl isocyanides, depending on the rate of substrate addition. Treatment of
[M(TC-3,n)(CH2Ph)2] with excess 2,6-dimethylphenyl isocyanide (ArNC) generated the
enediamido compounds [(TC-3,3)MN(Ar)C(CH2Ph)dC(CH2Ph)N(Ar)] (M ) Zr (4), Hf (5)) via
coupling of two bis(iminoacyl) groups, whereas slow step-wise addition produced [(TC-3,n)-
MN(Ar)C(CH2Ph)2C(dNAr)] (M ) Zr, n ) 3 (6); M ) Hf, n ) 3 (7), n ) 5 (8)). The η2-imine
complex [(TC-3,5)HfN(Ar)C(CH2Ph)2] (9), an intermediate in the formation of 7, was isolated
and characterized, but the corresponding zirconium species was unstable in solution,
decomposing to form the imido-bridged compound {[Zr(TC-3,3)]2(µ-NAr)2} (10). Altering the
nature of the carbon donor ligands also influenced the reactivity. Addition of both aryl and
alkyl isocyanides to solutions of [Zr(TC-3,3)Ph2] (11) afforded the η2-imine complexes [(TC-
3,3)ZrN(R)C(Ph)2] R ) Cy (12), Ar (13)), the stability of which may be due in part to
interactions between the metal center and a phenyl ring. Electron-withdrawing R substit-
uents enhance this effect. All new compounds were characterized by X-ray crystallography,
and plausible mechanisms for the migration reactions are outlined.
In tr od u ction
distinct from those of the more traditional cyclopenta-
dienyl ancillary ligands.11-13 In our work with group 4
organometallic complexes of the tetraazamacrocylic
tropocoronand ligand {TC-n,m}2-, several unusual reac-
tions with extrinsic substrates were encountered, in-
cluding the tendency to insert carbon monoxide into
both metal-alkyl bonds of [M(TC-n,m)R2] complexes
forming η2-ketone species.14
Much attention has been devoted to the development
of methodology for the formation of complicated con-
structs from simple starting materials such as CO and
isocyanides.1-3 Group 4 metals are especially adept at
incorporating small substrates into larger organic
molecules.4-7 Until recently, most of the work in this
field has involved the metallocene fragment {Cp2M}2+
,
but lately the potential of macrocyclic ligand systems
to induce coupling reactions has been explored.8-10
Macrocycles endow group 4 metals with many properties
X Abstract published in Advance ACS Abstracts, December 1, 1997.
(1) Applied Homogenous Catalysis with Organometallic Complexes;
Cornils, B., Hermann, W. A., Ed.; VCH: Weinheim, Germany, 1996.
(2) Catalytic Activation of Carbon Monoxide; Ford, P. C., Ed.;
American Chemical Society: Washington, DC, 1981.
(3) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987.
Unless subjected to forcing conditions, [Cp2MR2] (M
) Zr, Hf) typically insert CO into a single metal-carbon
bond.15,16 The relatively electron-rich tropocoronand
ligands alter the electrophilicity at the metal center,
(4) Reetz, M. T. Organotitanium Reagents in Organic Synthesis;
Springer-Verlag: Berlin, Germany, 1986.
(5) Wailes, P. C.; Coutts, R. P.; Weigold, H. Organometallic Chem-
istry of Titanium, Zirconium and Hafnium; Academic Press: New
York, 1974.
(6) Fu¨rstner, A.; Bogdanovic, B. Angew. Chem., Int. Ed. Engl. 1996,
35, 2442-2469 and references therin.
(7) Erker, G. Angew. Chem., Int. Ed. Engl. 1989, 28, 397.
(8) Giannini, L.; Solari, E.; De Angelis, S.; Ward, T. R.; Floriani, C.;
Chiesi-Villa, A.; Rizzoli, C. J . Am. Chem. Soc. 1995, 117, 5801-5811.
(9) Uhrhammer, R.; Black, D. G.; Gardner, T. G.; Olsen, J . D.;
J ordan, R. F. J . Am. Chem. Soc. 1993, 115, 8493-8494.
(10) Black, D. G.; Swenson, D. C.; J ordan, R. F.; Rogers, R. D.
Organometallics 1995, 14, 3539-3550.
(11) Black, D. G.; J ordan, R. F.; Rogers, R. D. Inorg. Chem. 1997,
36, 103-108.
(12) Brand, H.; Arnold, J . Angew. Chem., Int. Ed. Engl. 1994, 33,
95-96.
(13) Lee, L.; Berg, D. J .; Bushnell, G. W. Organometallics 1997, 16,
2556-2561.
(14) Scott, M. J .; Lippard, S. J . J . Am. Chem. Soc. 1997, 119, 3411-
3412.
(15) Hofmann, P.; Stauffert, P.; Frede, M.; Tatsumi, K. Chem. Ber.
1989, 122, 1559-1577 and references therein.
(16) Erker, G.; Dorf, U.; Czisch, P.; Petersen, J . L. Organometallics
1986, 5, 668-676.
S0276-7333(97)00683-3 CCC: $14.00 © 1997 American Chemical Society

5858 Organometallics, Vol. 16, No. 26, 1997
Scott and Lippard
at δ 255.01, consistent with an η2-iminoacyl ligand, was
detected in the 13C{1H} NMR spectrum. IR (KBr, cm-1): 3024
w, 2924 s, 2848 m, 1589 s, 1562 m, 1508 s, 1500 s, 1469 m,
1448 w, 1432 m, 1425 w, 1414 w, 1388 m, 1359 w, 1322 w,
1263 m, 1226 w, 1203 w, 1081 w, 1020 m, 975 w, 930 w, 888
w, 837 w, 816 w, 747 m, 713 m, 695 m, 542 w, 466 w, 442 vw,
428 vw. Samples sent for elemental analysis consistently
analyzed low in carbon, possibly due to gradual decomposition
at room temperature.19
[Hf(TC-3,5){η2-(n -Bu )NdC(CH2P h )}2] (2). As described
above for 1, a dichloromethane solution containing 30 mg
(0.042 mmol) of [Hf(TC-3,5)(CH2Ph)2] was treated with 17.7
µL (0.170 mmol) of n-butyl isocyanide to afford 6 mg (16%) of
crystalline product. Owing to the extreme thermal sensitivity
and low yield of the material, the complex was characterized
only by CCA.
affecting the reactivity. In comparison to metallocenes,
the enhanced carbenoid character of the acyl group
formed upon insertion of CO into the first M-C bond
of a [M(TC-n,m)R2] complex favors migration of the
second alkyl substituent to afford an η2-ketone. These
complexes further react with extrinsic substrates, among
them enones, ketones, azides, isocyanides, isocyanates,
and diazamethanes, incorporating CO into a wide
variety of fragments.
In the present article, we describe our studies with
the isoelectronic substrate R-NtC, which further
exemplify the ability of organometallic group 4 tropo-
coronand complexes to undergo migratory insertion
reactions. In accord with the reactivity trends previ-
ously observed with carbon monoxide, isocyanides pro-
mote the migration of alkyl or aryl ligands affording η2-
imine, η2-iminoacyl, and µ-imido products as well as a
new metallacycle incorporating an iminoacyl functional-
ity. Although insertion and coupling reactions involving
isocyanides have been well-studied,17,18 the tropocoro-
nand complexes induce transformations by what appear
to be uncommon reaction pathways. The ready avail-
ability of substituted alkyl and aryl isocyanides facili-
tates elaboration of this chemistry, providing method-
ology for the construction of sophisticated molecules
from simple, readily available starting materials.
[Hf(TC-3,3){η2-(Cy)NdC(CH2P h )}2] (3). Following the
procedure outlined above for 1, small red crystals of 3 were
manually separated from the reaction mixture and character-
1
ized by CCA. The H NMR spectrum of the reaction mixture
was complicated by the presence of multiple products, and all
attempts to optimize the synthesis of 3 were unsuccessful.
[(TC-3,3)Zr N(Ar )C(CH2P h )dC(CH2P h )N(Ar )] (4). At
room temperature, a rapidly stirred solution of 40 mg (0.068
mmol) of [Zr(TC-3,3)(CH2Ph)2] in 1.5 mL of dichloromethane
was treated with 50 mg (0.381 mmol) of solid 2,6-dimethyl-
phenyl isocyanide in one portion. The color of the mixture
immediately turned dark brown, and after 15 min the solution
was filtered through Celite. Over the course of several days,
ether was diffused into the filtrate at -30 °C, yielding dark
red-brown platelike crystals. The material was collected from
the reaction mixture, washed with ether and pentane, and
dried to afford 27 mg (47%) of product. 1H NMR (CD2Cl2): 7.08
(m, 6H), 6.86 (m, 8H), 6.50 (m, 4H), 6.42 (m, 4H), 6.26 (d, 4H),
3.77 (m, 4H), 3.26 (s, 4H), 3.02 (t, 4H), 2.82 (m, 2H), 2.34 (m,
2H), 1.86 (s, 12H). 13C{1H} NMR (CD2Cl2): δ 163.11, 152.71,
143.96, 134.75, 134.60, 134.43, 129.35, 127.98, 127.12, 125.12,
125.30, 122.04, 120.66, 115.43, 113.83, 51.78, 35.68, 19.18. IR
(KBr, cm-1): 3022 w, 2997 w, 2927 m, 2844 w, 1637 w, 1588
s, 1506 s, 1471 m, 1451 w, 1437 m, 1416 m, 1387 w 1378 m,
1363 m, 1344 w, 1273 m, 1230 m, 1212 w, 1196 w, 1186 w,
1140 w, 1101 m, 1088 w, 1033 m, 994 m, 948 w, 887 m, 872 w,
852 w, 834 w, 754 m, 722 s, 696 m, 475 m. CCA revealed
single crystals containing one dichloromethane molecule per
three molecules of 4. Analytical data indicated only partial
removal of the solvate in vacuo. Anal. Calcd for C52H54N6-
Zr‚1/6CH2Cl2 (C52.167H54.33N6Cl0.33Zr): C, 72.15; H, 6.31; N, 9.68.
Found: C, 72.32; H, 6.51; N, 9.68.
Exp er im en ta l Section
P r ep a r a tion of Com p ou n d s. The complexes [M(TC-3,n)-
(CH2Ph)2] (M ) Zr(IV), Hf(IV); n ) 3, 5) were prepared as
previously described.19 All operations, excluding ligand prepa-
rations, were conducted under a pure dinitrogen or argon
atmosphere using standard Schlenk and glovebox techniques.
Solvents were dried according to established protocols and
degassed prior to use. Unless otherwise specified, reagents
were obtained from commercial suppliers and thoroughly
degassed and dried before use. 1H NMR spectra were recorded
on a Bruker AM-250 and 13C{1H} NMR spectra on a Varian
Unity 300. Due to the limited solubility of the complexes in
the solvents used, data were collected at room temperature.
Chemical shifts are referenced with respect to the residual
solvent peak. FTIR spectra were recorded on a BioRad FTS-
135 FTIR spectrometer. All compounds were characterized
by crystallographic chemical analysis (CCA), and elemental
analyses were obtained on representative species. Several
samples sent for elemental analysis contained solvent mol-
ecules in the crystal lattice, but the limited thermal stability
of the complexes precluded heating them under vacuum.
[Hf(TC-3,5){η2-(Cy)NdC(CH2P h )}2] (1). Upon addition of
34.4 µL (0.277 mmol) of cyclohexyl isocyanide, an orange
solution of 47.0 mg (0.069 mmol) of [Hf(TC-3,5)(CH2Ph)2] in 1
mL of dichloromethane at -30 °C rapidly turned dark red-
orange. The solution was warmed to room temperature and
filtered, and several volume equivalents of ether were diffused
into the reaction mixture at -30 °C. After 72 h, the resulting
orange-yellow crystalline mass was collected, washed with
ether, and dried to afford 17 mg (27%) of product. 1H NMR
(CD2Cl2): δ 7.30 (m, 8H), 7.12 (m, 2H), 6.83 (m, 4H), 6.30 (d,
2H), 6.00 (m, 4H), 4.83 (m, 1H), 4.52 (m, 1H), 4.13 (m, 2H),
3.93 (m, 3H), 3.73 (m, 1H), 3.47 (m, br, 5H), 2.99 (m, 2H), 2.31
(m, H), 1.76 (m, 5H), 1.50 (m, br, 6H), 1.21 (m, br, 6H).
Although the material decomposes over the course of a few
hours at room temperature in dichloromethane, a resonance
[(TC-3,3)HfN(Ar )C(CH2P h )dC(CH2P h )N(Ar )] (5). Fol-
lowing the procedure outlined for the preparation of 4, a
portion of 50 mg (0.381 mmol) of solid 2,6-dimethylphenyl
isocyanide was added to 40 mg (0.059 mmol) of [Hf(TC-3,3)-
(CH2Ph)2] in dichloromethane. Slow diffusion of ether into the
saturated solution yielded a mixture of small red and dark
red-brown crystals. The crude material was redissolved in
toluene and filtered, and several volume equivalents of pen-
tane were diffused into the filtrate at -30 °C. Although the
product was still contaminated with a small amount of the
red crystalline material, the large dark red-brown crystals
were collected manually and characterized by CCA.
[(TC-3,3)Zr N(Ar )C(CH2P h )2C(dNAr )] (6). Over the course
of 15 min, 15.7 mg (0.120 mmol) of solid 2,6-dimethylphenyl
isocyanide was slowly added in small portions to a rapidly
stirred solution of 35 mg (0.059 mmol) of [Zr(TC-3,3)(CH2Ph)2]
in 1.5 mL of dichloromethane at -30 °C. After the mixture
was warmed to room temperature, the dark red solution was
filtered through Celite and several volume equivalents of ether
were slowly diffused into the filtrate at -30 °C, producing
large, irregularly shaped red crystals. The crystals were
collected, washed with ether, and dried to afford 17 mg (34%)
(17) Durfee, L. D.; Rothwell, I. P. Chem. Rev. 1988, 88, 1059-1079.
(18) Carnahan, E. M.; Protasiewicz, J . D.; Lippard, S. J . Acc. Chem.
Res. 1993, 26, 90-97.
(19) Scott, M. J .; Lippard, S. J . Inorg. Chim. Acta 1997, 263, 287-
299.

Reactions with Group 4 Tropocoronand Complexes
Organometallics, Vol. 16, No. 26, 1997 5859
of product. 1H NMR (CD2Cl2): 7.12 (t, 4H), 6.78 (m, 13H),
6.56 (m, 2H), 6.47 (m, 6H), 6.28 (t, 1H), 3.63 (m, 2H), 3.42 (m,
6H), 3.14 (m, 6H), 2.25 (s, 6H), 2.11 (m, 2H), 2.00 (s, 6H).
13C{1H} NMR (CD2Cl2): 163.58, 154.99, 153.39, 141.52, 136.54,
135.89, 131.08, 128.81, 127.83, 127.31, 126.18, 124.78, 123.06,
122.21, 121.11, 114.79, 88.71, 51.37, 45.63, 27.02, 21.89, 19.92.
IR (KBr, cm-1): 3055 w, 1999 w, 2918 w, 2878 m, 1592 s, 1574
m, 1509 s, 1471 m, 1449 m, 1431 w, 1418 m, 1395 m, 1367 w,
1340 m, 1275 m, 1230 s, 1206 w, 1190 m, 1138 m, 1105 m,
1091 w, 1032 w, 993 m, 979 w, 942 m, 909 w, 882 m, 859 w,
848 w, 836 w, 824 w, 778 w, 756 w, 733 s, 745 w, 707 w, 694
m, 641 w, 586 w, 529 w, 481 s, 474 m. From the structural
analysis as well as 1H NMR spectra, single crystals were
observed to contain a dichloromethane molecule. Analytical
data indicated the solvate molecule to be removed only
partially in vacuo. Anal. Calcd for C52H54N6Zr‚0.5CH2Cl2
(C52.5H55N6ClZr): C, 70.32; H, 6.18; N, 9.37. Found: C, 70.84;
H, 6.17; N, 9.35.
(0.059 mmol) of [Zr(TC-3,3)(CH2Ph)2] in 1.5 mL of toluene at
-30 °C. After the mixture was warmed to room temperature,
the dark red solution was filtered through Celite and the
solution was cooled to -30 °C. Over the course of 24 h, several
volume equivalents of ether were diffused into the filtrate,
producing a color change to green brown and depositing long,
platelike light green-brown crystals. The solid was collected,
washed with ether, and dried to afford 13 mg (42%) of product.
1H NMR (CD2Cl2): δ 6.90 (t, 8H), 6.49 (d, 4H), 6.28 (t, 4H),
6.16 (m, 10H), 3.55 (m, 8H), 3.29 (m, 8H), 2.14 (m, 4H), 1.94
(s, 12H), 1.78 (m, 4H). 13C{1H} NMR (CD2Cl2): 163.13, 160.60,
134.67, 127.50, 125.11, 118.87, 116.65, 112.78, 50.36, 28.50,
19.89. IR (KBr, cm-1): 2924 m, 2848 m, 1590 s, 1567 m, 1507
s, 1471 w, 1452 w, 1421 m, 1399 w, 1375 m, 1344 w, 1332 w,
1271 m, 1229 s, 1199 s, 1134 w, 1102 m, 1078 w, 1026 w, 992
m, 953 w, 925 w, 887 w, 855 m, 833 w, 817 m, 746 m, 725 s,
694 w, 579 s, 504 m, 463 s. Although 1H NMR spectroscopy,
CCA, as well as visual inspection of the crystalline material
confirmed the identity of the material, compound 10 consis-
tently analyzed with both low nitrogen and carbon content.
Anal. Calcd for C56H62N10Zr2: C, 63.60; H, 5.91; N, 13.24.
Found: C, 62.43; H, 5.70; N, 11.41. In an alternative
procedure, a mixture of 9.06 µL (0.073 mmol) of 2,6-dimeth-
ylaniline and 43 mg (0.073 mmol) of [Zr(TC-3,3)(CH2Ph)2] in
2 mL of dichloromethane was stirred at room temperature for
8 h. The brown solution was filtered, and ether was slowly
diffused into the filtrate at -30 °C yielding 22 mg (57%) green-
brown crystals of 10. A unit cell determination as well as a
1H NMR spectrum confirmed the identity of the material.
[(TC-3,3)HfN(Ar )C(CH2P h )2C(dNAr )] (7). By utilizing
a procedure similar to the one outlined above for 6, 14.4 mg
(0.110 mmol) of 2,6-dimethylphenyl isocyanide was added to
a slurry of 35 mg (0.052 mmol) of [Hf(TC-3,3)(CH2Ph)2] in 1
mL of toluene at -30 °C. When the mixture was warmed to
room temperature, the solution became bright red and ho-
mogenous, and after an additional 15 min, a brick-red pre-
cipitate deposited from the reaction mixture. The solid was
collected by filtration, washed with ether and pentane, and
dried to afford 18 mg (37%) of crude product. Large bright-
red crystals of 7 were obtained after recrystallization from
dichloromethane/ether. 1H NMR (CD2Cl2): 7.15 (d of t, 4H),
6.87 (t, 11H), 6.82 (m, 2H), 6.60 (t, 2H), 6.46 (m, 6H), 6.24 (t,
1H), 3.61 (m, 2H), 3.52 (m, 6H), 3.24 (m, 6H), 2.24 (s, 6H),
2.03 (m, br, 2H), 1.98 (s, 6H). 13C{1H} NMR (CD2Cl2): 163.77,
155.71, 153.51, 141.65, 137.43, 136.00, 131.05, 128.82, 127.82,
127.29, 125.96, 124.73, 123.06, 122.41, 121.05, 115.43, 87.61,
51.49, 45.94, 26.92, 21.81, 19.89. IR (KBr, cm-1): 3059 w, 3018
w, 2918 m, 2882 w, 2843 w, 1592 s, 1577 m, 1510 s, 1472 m,
1451 w, 1431 m, 1421 m, 1396 m, 1363 w, 1340 m, 1278 m,
1231 s, 1208 w, 1191 w, 1140 w, 1109 m, 1034 w, 998 m, 945
w, 886 m, 759 w, 733 m, 694 w, 477 m.
[M(TC-3,3)P h 2] (M ) Zr (11), Hf). A slurry of 276.5 mg
(0.487 mmol) of [Hf(TC-3,3)Cl2] in 10 mL of toluene at -30 °C
was treated with 0.974 mL of a 1.0 M solution of PhMgBr in
THF. The mixture was allowed to warm to room temperature,
and after several minutes, 5 mL of tetrahydrofuran and 3 mL
of dioxane were added. After an additional 10 min of stirring,
the solution was filtered through Celite and the filtrate was
evaporated in vacuo. The orange-red residue was redissolved
in dichloromethane, filtered through Celite, and evaporated
to dryness. The crude product was collected, washed with
ether and pentane, and dried to afford 302 mg (62%) of [Hf-
(TC-3,3)Ph2]. Recrystallization from a dichloromethane/ether
mixture yielded long red needle-like crystals. 1H NMR (CD2-
Cl2): δ 7.40 (t, 4H), 7.19 (d, 4H), 6.95 (m, 8H), 6.77 (m, 4H),
3.97 (m, 8H), 2.45 (m, 2H), 1.78 (m, 2H). From the structural
analysis, single crystals of [Hf(TC-3,3)Ph2] were found to
contain a dichloromethane molecule, and elemental analysis
indicated the solvate molecule was only partially removed in
vacuo. Anal. Calcd for C32H32N4Hf.0.5CH2Cl2 (C32.5H33N4-
HfCl): C, 56.28; H, 4.80; N, 8.08. Found: C, 56.66; H, 5.15;
N, 8.03. Following an analogous procedure, [Zr(TC-3,3)Ph2]
was isolated in 53-62% yield. [Zr(TC-3,3)Ph2] 1H NMR (CD2-
Cl2): δ 7.30 (t, 4H), 7.17 (m, 4H), 6.88 (m, 10H), 6.69 (t, 2H),
3.99 (m, 4H), 3.77 (m, 4H), 2.58 (m, 2H), 2.01 (m, 2H). 13C{1H}
NMR (CD2Cl2): δ 194.65, 163.25, 135.93, 134.22, 126.74,
124.94, 122.07, 114.31, 51.24.
[(TC-3,5)HfN(Ar )C(CH2P h )2C(dNAr )] (8). Following the
procedure outlined above for the preparation of 6, the product
was isolated in 32% yield. Single crystals were obtained from
dichloromethane/ether solutions. 1H NMR (CD2Cl2): 7.18 (m,
4H), 6.83 (m, 12H), 6.60 (m, 4H), 6.54 (m, 3H), 6.34 (m, 1H),
4.21 (m, 2H), 3.60 (m, 2H), 3.41 (m, 8H), 3.01 (m, 2H), 2.12 (s,
6H), 2.08 (m, 2H), 1.85 (s, 6H), 1.29 (m, 2H), 0.93 (m, 2H).
13C{1H} NMR (CD2Cl2): 164.89, 164.78, 155.15, 153.39, 141.81,
137.58, 135.91, 135.74, 131.19, 128.68, 127.69, 127.40, 125.80,
124.81, 123.38, 122.51, 120.54, 115.88, 84.51, 52.72, 47.05,
45.93, 28.31, 27.80, 21.57, 19.77, 18.04. IR (KBr, cm-1): 3053
w, 2923 m, 2852 w, 1594 s, 1577 m, 1508 s, 1470 m, 1447 w,
1423 m, 1392 w, 1360 w, 1345 w, 1334 w, 1314 m, 1279 m,
1245 m, 1227 m, 1191 m, 1138 w, 1105 m, 1025 m, 978 w, 938
w, 884 m, 860 w, 846 w, 760 w, 730 m, 716 w, 701 m, 586 w,
471 m.
[(TC-3,3)Zr N(Cy)C(P h )2] (12). At -30 °C, the addition
of 4.6 µL (0.037 mmol) of cyclohexyl isocyanide to a solution
of 21 mg (0.037 mmol) of 11 in 1 mL of toluene induced an
immediate color change. After the mixture was warmed to
room temperature, the dark brown solution was filtered
through Celite and several volume equivalents of pentane were
diffused into the filtrate over 72 h, yielding red-brown crystals.
The filtrate was decanted away from the material, and after
pentane and ether washings, 17 mg (68%) of product was
isolated. 1H NMR (CD2Cl2): δ 7.09 (m, 8H), 6.90 (m, 4H), 6.51
(m, 6H), 6.36 (t of t, 2H), 3.72 (d of t, 4H), 3.09 (t, 4H), 2.78
(m, br, 3H), 2.15 (m, 2H), 1.48 (m, br, 3H), 1.22 (m, 2H), 1.02
(m, br, 3H). 13C{1H} NMR (CD2Cl2): δ 164.26, 145.01, 135.53,
129.13, 122.58, 120.42, 119.23, 114.15, 50.81, 37.41, 27.20,
26.90, 26.77. IR (KBr, cm-1): 2921 m, 2849 w, 1589 s, 1507
s, 1472 m, 1428 m, 1415 m, 1388 m, 1349 w, 1271 m, 1229 m,
[(TC-3,3)HfN(Ar )C(CH2P h )2] (9). A rapidly stirred slurry
of 35 mg (0.052 mmol) of [Hf(TC-3,3)(CH2Ph)2] in 1 mL of
toluene at -30 °C was treated with 6.6 mg (0.050 mmol) of
2,6-dimethylphenyl isocyanide in several small portions over
the course of several minutes. After the addition of isocyanide
was complete, the dark red solution was warmed to room
temperature and filtered and pentane was slowly diffused into
the filtrate over 72 h yielding small, red crystals of 7 in
addition to large blocklike crystals of 9. Single crystals of 9
were manually separated from the mixture and characterized
by CCA.
{[Zr (TC-3,3)]2(µ-NAr )2} (10). In a procedure identical to
the one described for 9, a 7.2 mg (0.055 mmol) portion of 2,6-
dimethylphenyl isocyanide was added to a slurry of 35 mg

5860 Organometallics, Vol. 16, No. 26, 1997
Scott and Lippard
Ta ble 1. Cr ysta llogr a p h ic a n d Selected Metr ic
P a r a m eter s for P r od u cts fr om th e Rea ction of
[Hf(TC-3,n )(CH2P h )2] w ith Cycloh exyl Isocya n id e
{1 (n ) 5), 3 (n ) 3)} a n d n -Bu tyl Isocya n id e
{2 (n ) 5)}
1137 w, 1100 w, 1029 w, 995 w, 939 w, 886 w, 742 w, 723 m,
694 w, 476 m. Single crystals of compound 12 contain one
toluene molecule per two Zr complexes, and analytical data
were consistent with partial loss of this solvate under vacuo.
Anal. Calcd for C39H43N5Zr‚1/4C7H8 (C40.75H45N5Zr): C, 70.32;
H, 6.52; N, 10.06. Found: C, 69.80; H, 6.29; N, 9.56.
compound
formula
fw
1
2
3‚CH2Cl2
C49H60Cl2HfN6
982.42
C50H62HfN6
925.55
C46H58HfN6
873.47
[(TC-3,3)MN(Ar )C(P h )2] (M ) Zr (13), Hf). Compound
13 and its Hf analog were prepared following identical
procedures. In a typical reaction, a 5.5 mg (0.042 mmol)
portion of solid 2,6-dimethylphenyl isocyanide was added to a
rapidly stirred solution of 23.5 mg (0.042 mmol) of 11 in 1.5
mL of dichloromethane. After 30 min, the dark red-brown
solution was filtered and the filtrate was cooled to -30 °C.
Over the course of several days, ether was slowly diffused into
the reaction mixture, resulting in the formation of several
feathery crystalline masses. The solid was collected, washed
cryst system triclinic
triclinic
P1h
monoclinic
C2/c
14.5490(4)
23.2915(5)
13.5525(4)
space group P1h
a (Å)
10.3461(4)
10.5664(2)
13.3583(2)
15.0730(1)
98.844(1)
103.481(1)
94.316(1)
2030.61(5)
2
b (Å)
c (Å)
14.0599(5)
15.6630(6)
103.386(1)
95.368(1)
102.411(1)
2139.96(14)
2
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
101.241(1)
4504.4(2)
4
1
with pentane, and dried to afford 15 mg (52%) of product. H
T, K
188(2)
3.52
7.00
2.28(1)
188(2)
3.62
6.38
2.28(1)
188(2)
3.76
7.17
R (%)a
wR2 (%)b
Hf-Ntrop
NMR (CD2Cl2) for 13: 7.08 (m, 8H), 6.92 (t, 4H), 6.69 (d, 2H),
6.54 (m, 6H), 6.44 (t, 1H), 6.37 (t of t, 2H), 3.65 (d of t, 4H),
3.14 (t of d, 4H), 2.44 (m, 2H), 2.06 (m, 2H), 2.01 (s, 6H).
13C{1H} NMR (CD2Cl2): δ 163.94, 142.66, 135.83, 129.63,
129.40, 122.39, 120.83, 120.21, 119.44, 114.63, 51.08, 25.96,
25.54. IR (KBr, cm-1): 3047 w, 2918 w, 2872 m, 2826 w, 1589
s, 1507 s, 1471 m, 1429 m, 1416 m, 1387 m, 1346 w, 1271 m,
1230 s, 1172 w, 1137 w, 1101 m, 1030 m, 994 m, 943 w, 886
2.28(5)
(average)
Hf-N(5/3)
2.206(5)
2.217(4)
2.201(5)
2.215(4)
2.201(4)
Hf-N(6)
Hf-Ciminoacyl 2.268(5),2.269(6) 2.252(6),2.263(6) 2.264(5)
(C-N)iminoacyl 1.272(7),1.275(7) 1.291(6),1.292(6) 1.275(7)
a
R ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) {∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]}1/2
.
w, 849 w, 745 w, 725 m, 695 w, 611 w, 477 m. [(TC-3,3)HfN-
(Ar)C(Ph)2] 1H NMR (CD2Cl2): δ 7.18 (m, 8H), 6.84 (t, 4H),
6.72 (d, 2H), 6.61 (m, 6H), 6.41 (d, 1H), 6.30 (m, 2H), 3.70 (d
of t, 4H), 3.25 (t of d, 4H), 2.85 (m, 2H), 2.09 (m, 2H), 2.04 (s,
6H). Anal. Calcd for C41H41N5Hf: C, 62.95; H, 5.28; N, 8.95.
Found: C, 62.64; H, 5.37; N, 8.51.
Collection a n d Red u ction of X-r a y Da ta . Crystals were
typically obtained by vapor diffusion of ether or pentane into
a saturated solution of the complexes at -30 °C as described
above. Single crystals were coated with Paratone-N oil,
selected under a microscope, attached to a glass fiber, and
transferred rapidly to the -85 °C cold stream of a Siemens
CCD X-ray diffraction system controlled by a Pentium-based
PC running the SMART software package.20 The program
SADABS21 was used to correct the data for absorption and
decay. Data were collected by following standard procedures
reported in detail elsewhere.22
The structures were solved by direct methods using SIR-
9223 or SHELXS and refined by full-matrix least-squares and
Fourier techniques with the SHELXTL-PLUS program pack-
age.24 Space groups were determined from an examination of
the systematic absences in the data and confirmed by the
successful solution and refinement of the structures. Except
in cases where disorder was apparent, all non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were normally
assigned idealized locations and given a thermal parameter
equal to 1.2 times that of the carbon atom to which it was
attached, unless otherwise noted.
The asymmetric units of compounds 1, 2, 6, and 7 all contain
one complete metal complex, but in 3, the Hf as well as a
dichloromethane molecule lie on 2-fold symmetry positions.
The structure of compound 4 contains one metal complex in
addition to one-half of both a metal species and a dichlo-
romethane solvate molecule. On the 2-fold symmetry element,
the metal complex exhibits two orientations for the Ar and
phenyl groups. The site occupancy factors for the phenyl group
positions were fixed at 0.5, while the factors for the Ar moiety
refined to values of 0.53 and 0.47, respectively. Crystals of 5
contain two symmetry inequivalent complexes together with
a pentane solvate. Since the carbon atoms exhibited a high
degree of thermal motion, the pentane was refined isotropically
and hydrogen atoms were omitted from this molecule. In the
unit cell of 8, a highly disordered dichloromethane molecule
crystallizes near a mirror plane with an overall site occupancy
of 0.5. The disorder was modeled with several partially
occupied carbon and chlorine atoms. After the refinement had
converged, a large difference Fourier peak (1.4 e-/Å3) was
located on the mirror-plane midway between two areas of
disordered solvent. The asymmetric unit of 9 contains a metal
complex as well as a toluene molecule disordered across a
2-fold symmetry position. The toluene atoms were refined
isotropically, and hydrogen atoms were not included in the
refinement of this molecule. In the structure of 10, both the
dinuclear complex and a toluene solvate molecule are well-
ordered on general symmetry positions. The Zr metal center
resides on a 2-fold symmetry position in crystals of 11, which
also contain an additional dichloromethane. The solvate
molecules were refined anisotropically without inclusion of
hydrogen atoms. Compound 12 contained a toluene solvate
molecule besides the two symmetry inequivalent metal com-
plexes in the asymmetric unit. One of the two dichlo-
romethane molecules in 13 exhibited two orientations for one
chlorine atom. The two positions were refined with site
occupancy factors of 0.76 and 0.24, respectively. All of the
solvate atoms were refined anisotropically, but hydrogen atoms
were not included on the disordered molecule. In the final
stages of refinement, a spurious difference Fourier peak (1.55
e-/Å3) was located on a 3-fold symmetry position. Even at
partial occupancy on this position, a carbon atom refined to
unreasonably high thermal parameter and no further attempt
was made to assign an atom to this electron density. Crystal-
lographic data and selected metrical parameters are reported
in Tables 1-5, and additional experimental details are avail-
able as Supporting Information.
(20) SMART: Version 4.0; Siemens Industrial Automation, Inc.:
Madison, WI, 1994.
(21) Flack, H. D. Acta Crystallogr. 1983, A39, 876-881.
(22) Feig, A. L.; Bautista, M. T.; Lippard, S. J . Inorg. Chem. 1996,
35, 6892-6898.
Resu lts a n d Discu ssion
Bis(η2-im in oa cyl) Com p lexes. Isocyanides typi-
cally insert into group 4 metal-carbon bonds producing
η2-iminoacyl functionalities.17 Aryloxide, metallocene,
and tetraazamacrocylic8 complexes all react similarly,
(23) Burla, M. C.; Camalli, M.; Cascarano, G.; Giacovozza, C.;
Polidori, G.; Spagna, R.; Viterbo, D. J . Appl. Crystallogr. 1989, 22, 389-
393.
(24) SHELXTL: Structure Analysis Program; Siemens Industrial
Automation, Inc.: Madison, WI, 1995.

Reactions with Group 4 Tropocoronand Complexes
Organometallics, Vol. 16, No. 26, 1997 5861
Ta ble 2. Cr ysta llogr a p h ic a n d Selected Metr ica
P a r a m eter s of P r od u cts of [(TC-3,3)-
Ta ble 4. Cr ysta llogr a p h ic a n d Selected Metr ic
P a r a m eter s for {[Zr (TC-3,3)]2(µ-NAr )2}
compound
formula
fw
cryst system
space group
a (Å)
b (Å)
10‚C7H8
MN(Ar )C(CH2P h )C(CH2)N(Ar )] (M ) Zr (4), Hf (5))
C63H70N10Zr2
1149.73
compound
formula
fw
4‚1/3CH2Cl2
C52.33H54.67Cl0.67N6Zr
882.54
5‚1/2C5H12
C54.5H60HfN6
977.57
monoclinic
C2/c
37.3596(5)
12.3296(3)
25.4789(6)
113.1210(1)
10793.6(4)
8
188
4.11
cryst system
space group
a (Å)
b (Å)
c (Å)
monoclinic
C2/c
monoclinic
P21/n
32.2663(5)
17.3947(2)
26.0130(3)
115.644(1)
13162.0(3)
12
12.2697(2)
17.7686(3)
44.5468(1)
94.278(1)
9664.8(2)
8
c (Å)
â (deg)
V (Å3)
â (deg)
Z
V (Å3)
T, K
R (%)a
Z
wR2 (%)b
10.41
T, K
188
6.58
188
4.80
R (%)b
Zr(1)-Ntrop (range, average)
Zr(2)-Ntrop (range, average)
Zr(1)-N(9),N(10)
Zr(2)-N(9),N(10)
Zr(1)-N(9),N(10)-Zr(2)
N(9)-Zr(1),Zr(2)-N(10)
2.180(2)-2.362(2), 2.27(9)
2.228(2)-2.243(2), 2.236(8)
2.110(2),2.099(2)
2.169(2),2.162(2)
101.14(9),101.72(9)
79.90(9),77.22(8)
wR2 (%)c
M(1)-Ntrop (average)
M(1)-N(5)
M(1)-N(6)
N(5)-C(29)
N(6)-C(37)
C(29)-C(37)
13.47
8.00
2.216(5)
2.185(3)
2.178(3)
1.413(4)
1.416(5)
1.347(5)
2.198(3)
2.155(3)
2.170(3)
1.412(5)
1.405(5)
1.363(6)
a
R ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) {∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]}1/2
.
a
Metric data from one of the complexes in the asymmetric unit.
R ) ∑||Fo| - |Fc||/∑|Fo|. c wR2 ) {∑[w(Fo - Fc2)2]/∑[w(Fo2)2]}1/2
.
b
2
Ta ble 5. Cr ysta llogr a p h ic a n d Selected Metr ic
P a r a m eter s for [Zr (TC-3,3)P h 2] (11) a n d
Ta ble 3. Cr ysta llogr a p h ic a n d Selected Metr ic
[(TC-3,3)Zr N(R)C(P h )2] (R ) Cy (12), Ar (13))
P a r a m eter s for [(TC-3,n )-
compound
formula
11‚2CH2Cl2
12‚1/2C7H8
13‚2CH2Cl2
C34H36Cl4N4Zr C42.5H47N5Zr C41H47Cl4N5Zr
MN(Ar )C(CH2P h )2C(dNAr )] (n ) 3, M ) Zr (6), Hf
fw
733.69
719.07
842.86
cryst system
space group
a (Å)
b (Å)
c (Å)
monoclinic
C2/c
monoclinic
P21/n
rhombohedral
R3h
(7); n ) 5, M ) Hf (8)) a n d [(TC-3,3)HfN(Ar )C-
(CH2P h )2] (9)
18.6816(2)
11.3684(2)
16.1775(2)
107.856(1)
3270.27(8)
4
188(2)
3.74
9.92
2.20(2)
12.9863(1)
17.9911(4)
30.4661(4)
90.238(1)
7118.0(2)
8
188(2)
7.46
12.19
2.21(2)
37.0719(13)
compound
formula
fw
6
7
8‚1/2CH2Cl2
C52H54N6Zr C52H54HfN6 C54.5H59ClHfN6 C46.5H49HfN5
854.23 941.50 1012.02 856.40
9‚1/2C7H8
15.8829(8)
â (deg)
cryst system monoclinic monoclinic orthorhombic monoclinic
V (Å3)
18903.8(13)
18
188(2)
6.73
17.15
2.22(2)
space group P21/c
P21/c
Pbcn
C2/c
Z
a (Å)
b (Å)
c (Å)
â (deg)
V (Å3)
Z
15.0969(4) 15.0344(5) 32.412(2)
10.7570(3) 10.7267(4) 18.5853(12)
26.5236(7) 26.4832(9) 16.6215(11)
100.909(1) 101.139(1)
33.3770(5)
13.5048(3)
17.0047(3)
93.833(1)
7647.7(2)
8
T, K
R (%)a
wR2 (%)b
Zr(1)-Ntrop
(average)
Zr(1)-N(5)
Zr(1)-Ph
Zr(1)-C(21)
Zr(1)-C(22)
Zr(1)-C(23)
N(5)-C(21)
Zr(1)-C(21)-C(22)
N(5)-M-C(21)
4229.5(2)
4
4190.5(3)
4
10012.6(11)
8
2.033(5)
2.079(3)
T, K
188(2)
3.80
8.54
188(2)
3.52
6.82
188(2)
5.70
10.26
188(2)
2.70
6.03
2.19(2)
R (%)a
wR2 (%)b
M-Ntrop
2.353(2)
2.373(6)
2.721(6)
2.396(4)
2.645(4)
2.652(4)
1.441(5)
83.6(2)
2.21(3)
2.19(3)
2.20(5)
(average)
M-N(5)
2.154(2)
2.367(2)
1.521(2)
2.137(4)
2.336(5)
1.527(6)
2.134(6)
2.348(8)
1.511(9)
2.020(3)
2.260(4)
1.486(5)
1.451(8)
87.4(4)
37.5(2)
M-C
N(5)-
36.71(12)
C(29/C31)c
a
R ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) {∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]}1/2
.
N(5)-M-C
58.27(7)
59.1(2)
59.8(2)
40.14(12)
R ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) {∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]}1/2
.
a
c 6, 7, 9-C(29); 8-C(31).
exhibits resonances at 251.66 and 239.81 ppm in its 13C
NMR spectrum, consistent with the formation of two
distinct compounds containing η2-iminoacyl moieties.
Attempts to optimize the formation of [M(TC-3,3){η2-
(R)NdC(CH2Ph)}2] (M ) Zr, Hf; R ) alkyl) were
unsuccessful. Nevertheless, with the larger TC-3,5
macrocycle, favorable solubility properties permitted
isolation of the predominant product, either in moderate
yield for [Hf(TC-3,5){η2-(Cy)NdC(CH2Ph)}2] (1) or in low
yield for [Hf(TC-3,5){η2-(n-Bu)NdC(CH2Ph)}2] (2). Single
crystals of [Hf(TC-3,3){η2-(Cy)NdC(CH2Ph)}2] (3) could
also be obtained in some instances.
The structures of all three complexes are presented
in Figure 1, and selected crystallographic information
is contained in Table 1. The geometry of the iminoacyl
groups is unremarkable and essentially indistinguish-
able from that in a related macrocyclic complex [Zr-
(tmtaa){η2-(t-Bu)NdC(CH2Ph)}2].8,27 In this tmtaa com-
although in some instances η2-imine25 and η2-imino26
complexes can be isolated. Following this trend, the
tropocoronand complexes [M(TC-3,n)(CH2Ph)2] (M )
Zr(IV)/Hf(IV); n ) 3, 5) rapidly react at low temperature
with alkyl isocyanides such as cyclohexyl and n-butyl
isocyanide, primarily generating the bis(η2-iminoacyl)
compounds [M(TC-3,n){η2-(R)NdC(CH2Ph)}2]. Several
additional, unidentified species are present, as judged
1
by H and 13C NMR spectra of the reaction mixtures,
particularly with Zr and the smaller macrocycle TC-3,3.
For example, the crude mixture from the reaction of
[Zr(TC-3,3)(CH2Ph)2] and cyclohexyl isocyanide (CyNC)27
(25) Durfee, L. D.; Hill, J . E.; Fanwick, P. E.; Rothwell, I. P.
Organometallics 1990, 9, 75-80.
(26) Valero, C.; Grehl, M.; Wingbermu¨hle, D.; Kloppenburg, L.;
Carpenetti, D.; Erker, G.; Petersen, J . L. Organometallics 1994, 13,
415-417.

5862 Organometallics, Vol. 16, No. 26, 1997
Scott and Lippard
F igu r e 1. ORTEP diagrams of [Hf(TC-3,5){η2-(Cy)NdC(CH2Ph)}2] (1), [Hf(TC-3,5){η2-(n-Bu)NdC(CH2Ph)}2] (2), and
[Hf(TC-3,3){η2-(Cy)NdC(CH2Ph)}2] (3) showing 50% ellipsoids and atom-labeling scheme. Primed and unprimed atoms
are related by a 2-fold symmetry operation. Selected distances and angles are contained in Table 1.
Sch em e 1
plex, the metal center is significantly displaced from the
mean plane of this ligand and the average M-N
distance has increased over that in the dibenzyl starting
material by 0.13 Å, presumably due to severe steric
congestion at the metal center. The average Hf-N
tropocoronand distances in 1-3, on the other hand, are
only marginally larger than the average distance of
2.21(2) Å in the starting material, perhaps because the
ligand can distort away from the η2-iminoacyl ligands.
Although able to alleviate unfavorable intramolecular
steric interactions, the enhanced flexibility of TC-3,5
makes the complexes less stable in solution. Over the
course of several hours at room temperature, the central
methylene linker chain carbon atom reacts with the
metal center, a common decomposition pathway with
larger tropocoronands and group 4 metal centers.19
Although a characteristic η2-iminoacyl resonance was
detected at δ 255.01,17 the insolubility of the product at
low temperature precluded complete characterization by
13C{1H} NMR spectroscopy. Compound 1 exhibits a
stretch at 1562 cm-1 in the infrared spectrum, well
within the normal range for group 4 η2-iminoacyls.17
En ed ia m id o Com p lexes. In contrast to the reactiv-
ity of the alkyl isocyanides, addition of a large excess of
2,6-dimethylphenyl isocyanide (ArNC)27 to solutions
containing [M(TC-3,3)(CH2Ph)2] (M ) Zr(IV)/Hf(IV))
rapidly yielded the new metallacyclic compounds [(TC-
tramolecular coupling and formation of enediamido
ligands.28,29 Lowering the energy of the π*CN orbital
with electron-withdrawing substituents facilitates this
transformation, and aryl-substituted isocyanides nor-
mally couple significantly more rapidly than alkyl
isocyanides.17 In comparison to complexes of other
ligand systems, the relatively electron-rich metal center
in [M(TC-3,3)(CH2Ph)2] may lower the energy of the
π*CN orbitals even further, rendering the isolation of bis-
(η2-iminoacyl) complexes more difficult. With the judi-
cious choice of ligands, however, stable bis(η2-iminoacyl)
compounds could be prepared with the TC-3,X macro-
cycle and CH2SiMe3 alkyl groups.30 This result indi-
(28) 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, 6068-6076.
(29) Berg, F. J .; Petersen, J . L. Tetrahedron 1992, 48, 4749-4756.
(30) The reaction of [Hf(TC-3,X)(CH2SiMe3)2] (X ) xylyl) with 2,6-
dimethylphenyl isocyanide affords the bis(iminoacyl) product [Hf(TC-
3,X){η2-(Ar)NdC(CH2SiMe)2)}], as revealed by X-ray crystallography.
P21/c, Z ) 4, a ) 16.9878(8) Å, b ) 11.3387(5) Å, c ) 28.7841(13) Å, â
) 102.070(1)°.
3,3)MN(Ar)C(CH2Ph)dC(CH2Ph)N(Ar)] (M ) Zr (4), Hf
(5)), (Scheme 1). Mild thermolysis of bis(η2-iminoacyl)
group 4 or 5 metal complexes sometimes induces in-
(27) Abbreviations used: tmtaa, tetramethyltetraazadibenzo[14]-
annulene; CyNC, cyclohexyl isocyanide; ArNC, 2,6-dimethylphenyl
isocyanide.

Reactions with Group 4 Tropocoronand Complexes
Organometallics, Vol. 16, No. 26, 1997 5863
folded conformations of these planes in solution, how-
ever, is generally low (∆Gq < 20 kcal/mol).28,33,35 Mo-
lecular-orbital calculations and experimental studies on
similar zirconocene enediolate species indicate the fold-
ing lowers the energy of the HOMO (π) orbital of the
CdC bond, significantly enhancing the orbital overlap
between the olefin and the electron-deficient metal
center.36 With enediamido complexes, the angle be-
tween the two planes can vary from 37.8° in [(OPh-2,6-
t-Bu)2ZrN(Ar)C(CH3)dC(CH3)N(Ar)]28 to anywhere from
35.7° to 52.1° in zirconocenes.33,34 In contrast, the five-
membered metallacycles in 4 and 5 are essentially
planar, the dihedral angles in the two crystallographi-
cally independent metal complexes in 4 being 0.1° and
0.5°. Because there is no π-interaction with the metal
center, the olefin stretching frequency in 4 increases by
comparison to that of similar group 4 enediamido
species. The absence of metal-olefin orbital overlap in
4 and 5 further emphasizes the decreased Lewis acidity
of the metal center compared to complexes of other
ligand systems.
F igu r e 2. ORTEP diagram of [(TC-3,3)HfN(Ar)C(CH2-
Ph)dC(CH2Ph)N(Ar)] (5) showing 30% ellipsoids and the
atom labeling scheme. Selected distances and angles are
contained in Table 2.
cates that the coupling reaction (Scheme 1) is driven
by electronic and not steric factors.
When two iminoacyl groups couple, the resulting
ligand can adopt either the enediamido or diazadiene
resonance forms depicted below. The structural data
η2-Im in es a n d In ser tion P r od u cts. Although 4
can be prepared in moderate yield, the reaction mixtures
often contained a second species, the insolubility of
which complicated the preparations of pure 5. At
reduced temperature, slow addition of the solid ArNC
to [M(TC-3,3)(CH2Ph)2] (M ) Zr(IV)/Hf(IV)) enhanced
the formation of these compounds. In nonpolar solvents,
their insolubility allowed them to be isolated and
characterized as the new metallacyclic species [(TC-3,3)-
MN(Ar)C(CH2Ph)2C(dNAr)] (M ) Zr (6), Hf (7)). The
same synthetic strategy was used to prepare [(TC-3,5)-
HfN(Ar)C(CH2Ph)2C(dNAr)] (8). These results can be
rationalized by assuming that an equivalent of isocya-
nide first inserts into one metal-alkyl bond of [M(TC-
3,n)(CH2Ph)2] (n ) 3, 5), generating a mono(iminoacyl)
intermediate. If addition of isocyanide is slow, the
remaining benzyl ligand migrates to the iminoacyl
group before a second equivalent can react. When the
concentration of isocyanide is high, however, a second
insertion involving an external isocyanide occurs before
the alkyl group can migrate, producing the bis(imino-
acyl) precursors to compounds 4 and 5 (Scheme 2).
Analogous reactions of mono(iminoacyl) ligands can be
induced either thermally37 or with hydride transfer38
in zirconocenes or through the addition of an external
base to bis(aryloxy)titanium25 complexes. The de-
creased electrophilic character of the metal in the
tropocoronand complex allows an electron-deficient iso-
cyanide ligand to induce this transformation. Attempts
to prepare comparable products with alkyl isocyanides
consistently afforded bis(iminoacyl) species. Further
support for the mechanism depicted in Scheme 2 is the
presented in Table 2 indicate that the metallacycles in
4 and 5 have essentially identical metric parameters
which are consistent with the features of the enediamido
form of the ligand. An ORTEP diagram of 5 is pre-
sented in Figure 2. The metal-nitrogen amido distances
of 2.185(3) and 2.178(3) Å in compound 4 are typical of
Zr-N single bonds and only marginally longer then the
metal-nitrogen distances of 2.156(4) and 2.139(4) Å in
the bis(amido) complex [Zr(TC-3,3)(NH-Ph-4-t-Bu)2].31
In addition, the CdC distance of 1.347(5) Å and the
N-C distances of 1.413(4) and 1.416(5) Å deviate
considerably from the respective values in free 1,4-
diaza-1,3-butadiene32 and are well within the normal
ranges for double and single bonds, respectively.
Additional evidence for a CdC double bond in the
enediamido ligand of 4 is a weak stretch at 1637 cm-1
in the infrared spectrum. This value is higher in
frequency than those for similar zirconocene enediamido
species, which range from 1535 to 1610 cm-1 33,34
Often,
.
in the solid state structures of group 4 enediamido
complexes, a significant fold develops at the angle
between the N-Zr-N and N-CdC-N planes. The
energy barrier for interconverting the two possible
isolation of the complex [(TC-3,5)HfN(Ar)C(CH2Ph)2] (9)
from mixtures containing 7. This material is an inter-
mediate in the formation of 7, since insertion of a second
aryl isocyanide ligand in a 1,1-fashion into 9 can produce
(31) Treatment of [Zr(TC-3,3)(CH2Ph)2] with
2 equiv of 4-tert-
butylaniline affords [Zr(TC-3,3)(NH-Ph-4-t-Bu)2]. The complex cystal-
lizes together with one-half of a dme solvate molecule in the ortho-
rhombic space group Pbca with Z ) 8, a ) 23.4496(8) Å, b ) 13.3184(4)
Å, c ) 25.0602(8) Å, V ) 7826.6(4) Å3, R ) 6.72%, and wR2 ) 15.21%.
(32) Van Koten, G.; Vrieze, A. Adv. Organomet. Chem. 1982, 21,
153.
(35) Scholz, J .; Dlikan, M.; Stro¨hl, D.; Dietrich, A.; Schumann, H.;
Thiele, K.-H. Chem. Ber. 1990, 123, 2279-2285.
(36) Hoffman, P.; Frede, M.; Stauffert, P.; Lasser, W.; Thewalt, U.
Angew. Chem., Int. Ed. Engl. 1985, 24, 712-713.
(37) Davis, J .; Whitby, R. J .; J axa-Chamiec, A. Tetrahedron Lett.
1992, 33, 5655-5658.
(33) Berg, F. J .; Petersen, J . L. Organometallics 1991, 10, 1599-
1607.
(38) Wolczanski, P. T.; Bercaw, J . E. J . Am. Chem. Soc. 1979, 101,
6450-6452.
(34) Berg, F. J .; Petersen, J . L. Organometallics 1989, 8, 2461-2470.

5864 Organometallics, Vol. 16, No. 26, 1997
Scott and Lippard
Sch em e 2
7. Zirconocene η2-imine complexes are similarly sus-
ceptible to attack by external substrates, including
ketones and nitriles, but in these systems 1,2-insertion
reactions are more typical.39-43
The structures of 6 and 8 are presented in Figures 3
and 4; selected crystallographic information for 6, 7, and
8 is contained in Table 3. The geometric parameters of
the metallacycles in all three complexes are essentially
indistinguishable, with an iminoacyl group adopting an
η1-bonding mode, an uncommon motif in zirconocene
complexes.44 In compound 6, the Zr-N distance of
2.154(2) Å and Zr-C distance of 2.367(2) Å are compa-
rable to the Zr-O (2.194(1) Å) and Zr-C distances
(2.374(1) Å) in the metalloxirane unit of a related
dinuclear zirconocene species [Cp2ZrOCH2C(dNR)]2,
which also contains an iminoacyl moiety.45 In this
dimer, the oxygen atom of the metalloxirane unit
bridges two metal centers and stabilizes the electrophilic
Zr atom. With the tropocoronand ligand, the relatively
F igu r e 3. ORTEP diagram of [(TC-3,3)ZrN(Ar)C(CH2-
Ph)2C(dNAr)] (6) showing 30% ellipsoids and atom-labeling
scheme. Selected distances and angles are contained in
Table 3.
(39) Coles, N.; Harris, M. C. J .; Whitby, R. J .; Blagg, J . Organome-
tallics 1994, 13, 190-199.
electron-rich metal center remains mononuclear while
still preferring to adopt an η1-binding mode. In the
zirconocene complex, the iminoacyl carbon exhibits a
resonance at δ 220.2 in the 13C NMR spectrum, margin-
ally upfield from the typical range for η2-iminoacyl
ligands. Despite repeated attempts, no signal was
detectable in this region in the 13C NMR spectrum of
compounds 6, 7, or 8, possibly owing to the slow
decomposition of the complexes in the polar solvent
media required to dissolve them. Nevertheless, a
(40) Buchwald, S. L.; Watson, B. T.; Wannamaker, M. W.; Dewan,
J . C. J . Am. Chem. Soc. 1989, 111, 4486-4494.
(41) Grossman, R. B.; Davis, W. M.; Buchwald, S. L. J . Am. Chem.
Soc. 1991, 113, 2321-2322.
(42) Gately, D. A.; Norton, J . R.; Goodson, P. A. J . Am. Chem. Soc.
1995, 117, 986-996.
(43) Gately, D. A.; Norton, J . R. J . Am. Chem. Soc. 1996, 118, 3479-
3489.
(44) J ubb, J .; Song, J .; Richeson, D.; Gambarotta, S. In Comprehen-
sive Organometallic Chemistry; M. F. Lappert, Ed.; Pergamon Press:
Oxford, U.K., 1995; Vol. 4; pp 582-585.
(45) Erker, G.; Mena, M.; Kru¨ger, C.; Noe, R. Organometallics 1991,
10, 1201-1203.

Reactions with Group 4 Tropocoronand Complexes
Organometallics, Vol. 16, No. 26, 1997 5865
F igu r e 6. ORTEP diagram of {[Zr(TC-3,3)]2(µ-NAr)2} (10)
showing 30% ellipsoids and atom-labeling scheme. Selected
distances and angles are contained in Table 4.
F igu r e 4. ORTEP diagram of [(TC-3,5)HfN(Ar)C(CH2-
Ph)2C(dNAr)] (8) showing 50% ellipsoids and atom-labeling
scheme. Selected distances and angles are contained in
Table 3.
metallacycle in the η2-imine zirconocene complex [Cp2-
(THF)ZrC(Ph)N(SiMe3)].40 Once again reflecting the
different donating ability of the ligands, the isolation
of this zirconocene species requires the stabilizing
influence of a THF ligand.
A Di(µ-im id o) Com p lex. Much like the formation
of 9, [Zr(TC-3,3)(CH2Ph)2] reacts rapidly with 1 equiv
of ArNC yielding a dark red-brown solution. Over the
course of several hours at -30 °C, however, the color of
the solution changes and green-brown crystals of the
imido-bridged complex {[Zr(TC-3,3)]2(µ-NAr)2} (10, Fig-
ure 6) are obtained in moderate yield from these
mixtures. Selected metrical parameters are contained
in Table 4, from which the asymmetry in imido bridges
can readily be identified. In particular, the Zr(1)-Nimido
distances of 2.099(2) and 2.110(2) Å are shorter than
the Zr(2)-Nimido distances, 2.162(2) and 2.169(2) Å.
Accompanying the shorter distances to Zr(1) are two
anomalously long Zr(1)-N tropocoronand bonds of 2.328(2)
and 2.362(2) Å. In addition, the tropocoronand macro-
cycles are rotated by 59.0° from the eclipsed conforma-
tion, and the two phenylimido ligands are slightly
canted away from the perpendicular to the plane defined
by C(24)-Zr(2)-C34, the angles being 13.9° and 37.2°.
The tropocoronand ligand bound to Zr(1) is significantly
rotated with respect to the aryl imido ligands as well
as the other macrocycle. Packing interactions in the
crystal lattice may perhaps induce strain in the coor-
dination sphere of Zr(1) with the concomitant increase
in two Zr-N tropocoronand distances. The Zr(1)-Nimido
distances in 10 are indistinguishable from those in (Cp2-
Zr)2[µ-N(Ph-4-t-Bu)]2,46 but the obtuse Zr-N-Zr angles
in the former cause a significant increase in the metal-
metal separation, which is 3.198(1) Å in the zirconocene
complex but 3.3055(4) Å in 10. This metal-metal
separation is also significantly greater then the distance
of 3.1575(6) Å in [(Me4taa)Zr(µ-N-t-Bu)2Zr(NH-t-Bu)2].47
The only product identifiable by GC/MS in the reac-
tion mixture used to prepare 10 was 1-methyl-2-(2-
phenylethenyl)benzene, suggesting that the product
may form via the mechanism outlined in Scheme 3.
After undergoing a retro [1 + 2] cycloaddition, the
F igu r e 5. ORTEP diagram of [(TC-3,5)HfN(Ar)C(CH2Ph)2]
(9) showing 50% ellipsoids and atom-labeling scheme.
Selected distances and angles are contained in Table 3.
characteristic CdN stretch is evident in the infrared
spectra at 1574 cm-1 in 6 and 1577 cm-1 in 7 and 8.
These values lie well within the typical range for η2-
iminoacyls but somewhat lower in energy then the
iminoacyl group in [Cp2ZrOCH2C(dNR)]2 (1596 cm-1).
Finally, comparison of the 13C NMR spectra does reveal
one resonance which differs perceptibly among the three
complexes, ranging from δ 88.71 in 6 to δ 84.51 in 8.
We tentatively assign the resonance to the quarternary
carbon atom of the M-N-C-C metallacycle.
The Hf-N and Hf-C distances of 2.020(3) and
2.260(4) Å, respectively in the structure of the η2-imine
complex 9 (Figure 5; Table 3) are noticeably shorter then
the distances in compound 7, but the mean Hf-
tropocoronand nitrogen distance remains the same.
Increasing the Hf-Nimine distances while maintaining
the N-C single bond distance of 1.486(5) Å would
further strain an already acute N-Hf-C angle of
40.14(12)°, which perhaps explains this result. The
geometric parameters of the metallacycle in 9 are
virtually indistinguishable from those of the analogous
(46) Walsh, P. J .; Hollander, F. J .; Bergman, R. G. Organometallics
1993, 12, 3705-3712.
(47) Nikonov, G. I.; Blake, A. J .; Mountford, P. Inorg. Chem. 1997,
36, 1107-1112.

5866 Organometallics, Vol. 16, No. 26, 1997
Scott and Lippard
Sch em e 3
Sch em e 4
F igu r e 7. ORTEP diagram of [Zr(TC-3,3)Ph2] (11) showing
50% ellipsoids and atom-labeling scheme. Primed and
unprimed atoms are related by a 2-fold symmetry opera-
tion. Selected distances and angles are contained in Table
5.
terminal imido intermediate might rapidly dimerize in
the absence of trapping agents to form 10. Ziroconcene
imido complexes, such as [CpZr(NAr)], also typically
form dinuclear species. Once eliminated, the reactive
carbene moiety can either attack the ortho position of
a phenyl ring or dimerize to form tetrabenzylethylene.
The kinetic inertness of Hf with respect to Zr would
retard this chemistry, facilitating the isolation of 9.
Although inconsistent with the formation of 1-methyl-
2-(2-phenylethenyl)benzene, other potentially parallel
reactions for the formation of 10 can be envisioned. In
the presence of acetone, the isoelectronic complex [Hf-
(TC-3,5)(η2-OC(CH2Ph)2)] appears to undergo a â-hy-
drogen transfer reaction generating a transient metal-
hydride/enolate.48 An equivalent transformation in the
present system would afford a metal-hydride and a
vinyl amide identical to an intermediate in the forma-
tion of [(OAr)2Ta(dNAr){N(Ar)(CH2CH2Ph)}].49 Sub-
sequent intramolecular rearrangement of this Ta com-
plex transfers a hydride to a η2-imine ligand and
generates a metallacyclobutene. In the tropocoronand
system, attack of the terminal hydride on the vinyl
olefin could eliminate dihydrogen and produce a met-
allacyclobutene. As is often the case with zirconocene
metallacyclobutenes, such as the Ta example just
discussed, this metallacycle could undergo a retro [2 +
2] cycloaddition to afford the terminal imido product and
1 equiv of alkyne. The inability to detect an alkyne in
reaction mixtures containing 10 discredits this mecha-
nism.
P h en yl-Su bstitu ted η2-Im in es. To further explore
the influence of the ancillary ligands on the insertion
chemistry, the complexes [M(TC-3,3)Ph2] (M ) Zr (11),
Hf) were prepared. The structure of 11 is depicted in
Figure 7. As illustrated in Table 5, replacement of alkyl
with aryl ligands has little influence on the M-C and
M-N bond lengths. The Zr-R distances decrease
minimally from 2.374(3) Å in [Zr(TC-3,3)(CH2Ph)2]19 to
2.353(2) Å in 11, and the average Zr-N distances are
identical, 2.19(1) and 2.20(2) Å, respectively. Altering
the R-groups has a profound effect on the reactivity of
the complexes, however. Addition of isocyanides to
solutions containing 11 or its Hf analog afforded the η2-
imine complexes, [(TC-3,3)MN(R)C(Ph)2], irrespective of
the nature of the substituents on the isocyanide. The
structures of the products from reactions of 11 with
CyNC (12) and ArNC (13) are displayed in Figure 8
(Scheme 4). Selected metrical parameters are contained
(48) Scott, M. J .; Lippard, S. J . 1997, submitted for publication.
(49) Chamberlain, L. R.; Steffey, B. D.; Rothwell, I. P.; Huffman, J .
C. Polyhedron 1989, 8, 341-349.

Reactions with Group 4 Tropocoronand Complexes
Organometallics, Vol. 16, No. 26, 1997 5867
F igu r e 8. ORTEP diagrams of [(TC-3,3)ZrN(Cy)C(Ph)2] (12) and [(TC-3,3)ZrN(Ar)C(PH)2] (13) showing 50% ellipsoids
and atom labeling scheme. Selected distances and angles are contained in Table 5.
in Table 5, from which the presence of a N(5)-C(21)
single bond can be identified. Although the structures
of 12 and 13 are similar, the different electronic proper-
ties of the CyNC and ArNC substrates are evident in
the geometric parameters of the resulting metallacycles.
With the more electron-withdrawing aryl isocyanide
ligand, the Zr-N(5) and Zr-C(21) bond lengths in 13
(2.079(3, 2.396(4) Å) have increased slightly relative to
those in 12 (2.033(5), 2.373(6) Å). The distances in both
complexes are significantly longer then the equivalent
bond lengths of 2.020(3) and 2.260(4) Å in 9, reflecting
the decrease in the donating ability of the diphenyl-
substituted η2-imine fragment. The distances in 12 and
13 also differ from those in related zirconocene. The
are acute, being 87.4(4)° in 12 and 83.6(2)° in 13, and
although dissimilar, the Zr-C(21) distances are within
the typical range for Zr-ipso-carbon interactions, 2.721(6)
and 2.645(4) Å, respectively.50 For comparison, the
angles at the benzyl carbon atoms in 9 are normal,
120.6(3)° and 118.9(3)°. In 13, a further twist in the
Zr(1)-C(21)-C(22)-C(23) torsion angle provides some
overlap between the metal center and the π electrons
of the aromatic ring, as indicated by the Zr(1)-C(22)
and Zr(1)-C(23) distances of 2.645(4) and 2.652(4) Å,
respectively. These features are not manifested in the
13C NMR spectra of the two complexes, however, which
are symmetric and suggest the fluxional behavior in
solution.
In contrast to most metallaaziridines39-43 including
9, the metallacycles in 12 and 13 are unreactive toward
extrinsic substrates, even in the presence of excess
isocyanide. Attempts thermally to induce insertion of
a second equivalent of isocyanide to afford products
comparable to 6-8 resulted in complex mixtures. This
stability of the ligand in the presence of extrinsic
substrates reinforces the description of the imine bond-
ing in 12 and 13, as previously deduced from their
geometric and spectroscopic properties. In particular,
the ligand has significant η1 character which is stabi-
lized by π interaction with the phenyl substituents.
Zr-N distances in [(THF)Cp2ZrN(SiMe3)CH(Ph)]40 and
[(THF)Cp2ZrN(Ph)CH(Ph)]42 of 2.11(1) and 2.113(4) Å,
respectively, are longer than those in 12 and 13, but
the metal-carbon bonds are significantly shorter. Al-
though the geometric parameters and reactivity of these
zirconocenes are in agreement with the metallaaziridine
bonding formalism depicted below, the metallacycles in
12 and 13 may have some η1-imine character. This
Con clu sion s
A diverse set of products are obtained from migratory
insertion reactions of isocyanides and group 4 tropo-
coronand alkyl and aryl complexes, reflecting the elec-
tronic properties of the substrate as well as the carbon-
donor ligands. By comparison to zirconocene analogs,
the tropocoronand ligand is more electron-releasing and
the reactivity of the complexes is affected by the
decreased electrophilicity of the metal center. Addition
of alkyl isocyanides to [M(TC-3,3)(CH2Ph)2] affords bis-
(η2-iminoacyl) complexes. Aryl isocyanides react simi-
larly but, in certain instances, induce coupling of the
bis(η2-iminoacyl) ligands to afford enediamido ligands.
Migration of alkyl groups to the iminoacyl functionality
is facile in these systems, and slow addition of aryl
property is suggested by the 13C NMR resonances for
C(21), δ 145.01 in 12 and δ 142.66 in 13 which are
shifted significantly downfield from the analogous reso-
nance at δ 95 in [(OPh-2,6-i-Pr)2(py-4-Et)TiN(t-Bu)C-
(CH2Ph)2].25
The diminished electron-releasing character of the
phenyl substituents on the imine ligand in 12 and 13
renders the metal centers more electron deficient. As
a consequence, distortions occur which allow the metal
center to acquire additional electron density from the
phenyl rings. The Zr(1)-C(21)-C(22) angles (Figure 8)
(50) J ordan, R. F.; LaPointe, R. E.; Baenziger, N.; Hinch, G. D.
Organometallics 1990, 9, 1539-1545 and references therein.

5868 Organometallics, Vol. 16, No. 26, 1997
Scott and Lippard
isocyanide produces η2-imino groups. Formation of the
latter is enhanced by replacement of the benzyl ligands
with aryl ligands in the precursor complex, the relative
electron-withdrawing character of which deactivates the
first insertion product toward further insertion chem-
istry. With benzyl groups, the η2-imine moiety can
decompose to form µ-imido complexes and also insert a
second equivalent of isocyanide in a 1,1-fashion. In
migratory insertion reactions of these tropocoronand
complexes, subtle alterations in the electronic character
of the system allow for the construction of complex
organic fragments from readily available starting ma-
terials.
Ack n ow led gm en t. This work was supported by a
grant from the National Science Foundation. M.J .S. is
grateful to the National Institute of General Medical
Science for a postdoctoral fellowship.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data and structure refinement results, atomic coordinates,
anisotropic thermal parameters, hydrogen atom parameters,
and complete bond distances and angles for 1, 2, 3‚CH2Cl2,
4‚1/3CH2Cl2, 5‚1/2C5H12, 6, 7, 8‚1/2CH2Cl2, 9‚1/2C7H8, 10‚C7H8,
11‚2CH2Cl2, 12‚1/2C7H8, and 13‚2CH2Cl2 (145 pages). Ordering
information is given on any current masthead page.
OM9706830