Reactivity of the coordinated η2-ketone in the tropocoronand complex [Hf(TC-3,5)(η2-OC(CH2Ph)2)]: N-C coupling, C-C coupling, and insertion into the C-O bond

Article abstract of DOI:10.1021/om971040n

The reactions of [Hf(TC-3,5)(η²-OC(CH₂Ph)₂)] (1) with a variety of substrates are described. Molecules containing conjugated terminal nitrogen atoms, specifically arylazides and diazoalkanes, insert into the metalloxirane unit in a 1,1-fashion to form four-membered chelate rings Hf-O-C-N via N-C coupling. Enones and phenyl-substituted ketones react by C-C, pinacolic-type coupling to give the 1,2-addition product of the ketone moiety across the metal-carbon bond, Hf-O-C-C-O. Reaction of 1 with simple ketones is notably more complex. With acetone, the product contains a six-membered Hf-O-C=C-C-O chelate ring, possibly derived by a β-hydrogen transfer from the η²-ketone to form the metal hydride, which reacts with substrate to achieve C-C coupling accompanied by loss of H₂. Substrates containing nitro groups insert a single oxygen atom into the metalloxirane unit, forming an equivalent of nitrosoalkane or nitrosoarene. In the presence of nitrosoarenes, the resulting four-membered oxametallacycle can react further, undergoing a retro [2 + 2] cycloaddition to generate an unusual μ-η²:η² nitrosoarene-bridged dinuclear species. Phenyl isocyanate attacks the C-O bond of the η²-ketone ligand in 1 giving rise to a coordinated carbamate, perhaps by means of a [2 + 2] cycloaddition. The products of the reactions were characterized by X-ray crystallography, and plausible mechanisms are suggested for all the coupling reactions.

Full text of DOI:10.1021/om971040n

466
Organometallics 1998, 17, 466-474
Rea ctivity of th e Coor d in a ted η2-Keton e in th e
Tr op ocor on a n d Com p lex [Hf(TC-3,5)(η2-OC(CH2P h )2)]:
N-C Cou p lin g, C-C Cou p lin g, a n d In ser tion in to th e
C-O Bon d
Michael J . Scott and Stephen J . Lippard*
Department of Chemistry, Massachusetts Institute of Technology,
Cambridge, Massachusetts 02139
Received November 25, 1997
The reactions of [Hf(TC-3,5)(η2-OC(CH2Ph)2)] (1) with a variety of substrates are described.
Molecules containing conjugated terminal nitrogen atoms, specifically arylazides and
diazoalkanes, insert into the metalloxirane unit in a 1,1-fashion to form four-membered
chelate rings Hf-O-C-N via N-C coupling. Enones and phenyl-substituted ketones react
by C-C, pinacolic-type coupling to give the 1,2-addition product of the ketone moiety across
the metal-carbon bond, Hf-O-C-C-O. Reaction of 1 with simple ketones is notably more
complex. With acetone, the product contains a six-membered Hf-O-CdC-C-O chelate
ring, possibly derived by a â-hydrogen transfer from the η2-ketone to form the metal hydride,
which reacts with substrate to achieve C-C coupling accompanied by loss of H2. Substrates
containing nitro groups insert a single oxygen atom into the metalloxirane unit, forming an
equivalent of nitrosoalkane or nitrosoarene. In the presence of nitrosoarenes, the resulting
four-membered oxametallacycle can react further, undergoing a retro [2 + 2] cycloaddition
to generate an unusual µ-η2:η2 nitrosoarene-bridged dinuclear species. Phenyl isocyanate
attacks the C-O bond of the η2-ketone ligand in 1 giving rise to a coordinated carbamate,
perhaps by means of a [2 + 2] cycloaddition. The products of the reactions were characterized
by X-ray crystallography, and plausible mechanisms are suggested for all the coupling
reactions.
In tr od u ction
insertion and coupling reactions of the metalloxirane
core of [Hf(TC-3,5)(η2-OC(CH2Ph)2)] (1), where TC-3,5
is the tetraazamacrocylic tropocoronand depicted below.
With the continual improvement of exploration and
extraction technologies, the supply of hydrocarbons
today is considerably greater than in the “gas crisis” era
of the early 1970s.1 As a consequence, research into the
organometallic chemistry of readily available precursors
such as CO and CO2 has waned in recent years.
Nevertheless, the reactions of these C1 substrates
remains of fundamental interest for many reasons,
among them being the need to delineate how they are
incorporated as synthons for biomolecules.2,3 Moreover,
the rate of human consumption of hydrocarbons will
inevitably exceed that supplied by fossil fuels,1 and
strategies will be required for the manufacture of larger
constructs from such simple starting materials. Of
particular interest from a synthetic point of view are
insertion, coupling, and ligand-migration reactions in-
volving carbon monoxide.4,5
Compound 1 forms in nearly quantitative yield by
insertion of a single molecule of CO into the two metal-
alkyl bonds of [Hf(TC-3,5)(CH2Ph)2]. As described
previously, dichloromethane, isocyanides, and enones
attack the coordinated ketone in 1 to afford a variety of
organic fragments (Scheme 1).6 Further elaboration of
this chemistry, described here, includes some remark-
able and unprecedented examples of an η2-ketone ligand
In the present article, we have investigated several
(1) A summary of the supply and regulation of petroleum products
in the United States is available on the Internet from Petroleum Supply
Monthly at http://eiainfo.eia.doe.gov/oil gas/psm/psm.html, and a pro-
file of energy consumption can be found at http://www.eia.doe.gov/
fueloverview.html.
(2) Holm, R. H.; Kennepohl, P.; Solomon, E. I. Chem. Rev. 1996,
96, 2239-2314 and references therein.
(3) Lippard, S. J .; Berg, J . M. Principles of Bioinorganic Chemistry;
University Science Books: Mill Valley, CA, 1994.
(4) Applied Homogenous Catalysis with Organometallic Complexes;
Cornils, B., Hermann, W. A., Eds.; VCH: Weinheim, Germany, 1996.
(5) Collmann, 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.
(6) Scott, M. J .; Lippard, S. J . J . Am. Chem. Soc. 1997, 119, 3411-
3412.
S0276-7333(97)01040-6 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 01/16/1998

Reactivity in the Tropocoronand Complex
Organometallics, Vol. 17, No. 3, 1998 467
ane was added dropwise to a solution of 30 mg (0.041 mmol)
of 1 in 1.5 mL of chlorobenzene. As the temperature was
raised to 35 °C, the color of the solution slowly turned from
red-brown to orange-yellow, and after 30 min the mixture was
filtered through Celite. Several volume equivalents of ether
were diffused into the filtrate over 48 h at -30 °C, yielding
long, feathery crystals. The solid was collected, washed with
ether, and dried to afford 14 mg (40%) of product. 1H NMR
(CD2Cl2): δ 7.18 (m, 4H), 6.99 (m, 4H), 6.85 (s, 1H, N2CHSi),
6.71 (m, 4H), 6.53 (m, 8H), 4.81 (d of t, J ) 3.8, 14.7 Hz, 2H),
3.35 (m, 8H), 2.64 (d, J ) 12.9 Hz, 2H, CH2Ph), 2.09 (m, 4H),
1.42 (m, 2H), 0.98 (m, 2H), 0.22 (s, 9H, SiCH3). IR (KBr, cm-1):
2931 m, 1592 vs, 1509 vs, 1472 w, 1437 w, 1423 m, 1389 m,
1346 w, 1328 w, 1275 s, 1229 s, 1186 m, 1112 w, 1028 m, 992
w, 979 w, 934 m, 903 w, 887 w, 846 m, 833 m, 767 w, 723 s,
699 m, 658 w, 613 w, 518 w, 473 m. Anal. Calcd for C41H50N6-
HfOSi: C, 57.97; H, 5.93; N, 9.89. Found: C, 58.27; H, 5.50;
N, 9.36.
Sch em e 1
[(TC-3,5)HfOC(CH2P h )2N(NdNP h )] (3). A rapidly stirred
solution of 40 mg (0.054 mmol) of 1 in dichloromethane was
treated with 19.3 mg (0.162 mmol) of phenylazide. Upon
heating to 35 °C, the color of the solution gradually turned
yellow and the temperature was maintained for 1 h. After
the mixture was cooled to room temperature, the solution was
filtered and ether was diffused into the saturated solution at
-30 °C over the course of several days. The product was
collected from the reaction mixture and washed with ether and
pentane to afford 11 mg (24%) of yellow needle-like crystals.
1H NMR (CD2Cl2): δ 7.57 (m, 1H), 7.40 (t, J ) 7.5 Hz, 1H),
7.22 (m, 8H), 6.90 (m, 6H), 6.63 (m, 2H), 6.52 (m, 6H), 6.28 (t,
J ) 7.4 Hz, 1H), 4.86 (d of t, J ) 3.7, 14.0 Hz, 2H), 4.17 (d, J
) 12.5 Hz, 1H), 3.74 (m, 3H), 3.54 (m, 4H), 3.19 (m, 1H), 2.85
(d, J ) 12.5 Hz, 1H), 2.61 (d, J ) 12.5 Hz, 2H), 2.06 (m, 2H),
1.43 (m, 2H), 0.96 (m, 2H). IR (KBr, cm-1): 2931 m, 1593 vs,
1511 vs, 1471 w, 1438 w, 1424 m, 1387 w, 1375 w, 1341 w,
1327 w, 1304 w, 1276 m, 1239 m, 1207 w, 1137 w, 1114 w,
1082 w, 1044, 1029 m, 979 w, 936 w, 887 w, 865 w, 766 m,
741 m, 720 m, 700 m, 473 m.
Sch em e 2
[(TC-3,5)HfOC(CH2P h )2C(Cy)(P h )O] (4). A solution of
30 mg (0.0408 mmol) of 1 in 1.5 mL of dichloromethane was
treated with 15.4 mg (0.0817 mmol) of solid cyclohexyl phenyl
ketone at -30 °C. The solution rapidly turned from red-brown
to bright yellow, and the mixture was allowed to warm to room
temperature. The reaction was filtered, and several volume
equivalents of ether were diffused into the filtrate at -30 °C
over the course of several days. The resulting yellow material
was collected, washed with ether, and dried to afford of 11 mg
(29%) of blocklike crystals of 4. 1H NMR (CD2Cl2): δ 7.34 (t,
J ) 7.4 Hz, 2H), 7.25 (m, 4H), 7.01 (s, br, 5H), 6.88 (m, 2H),
6.80 (m, 4H), 6.60 (m, 2H), 6.55 (m, 2H), 6.51 (m, 2H), 5.70
(m, 1H), 5.24 (m, 1H), 4.24 (m, 1H), 3.90 (d, J ) 16 Hz, 2H),
3.62 (m, 6H), 2.97 (d, J ) 14.1 Hz, 1H), 2.67 (d, J ) 13.4 Hz,
1H), 2.51 (m, br, 1H) 2.10 (m, br, 2H), 1.86 (m, br, 3H), 1.67
(m, br, 2H), 1.43 (m, br, 2H), 1.23 (m, br, 2H) 0.99 (m, br, 2H),
0.82 (m, br, 2H), 0.53 (m, br, 2H). IR (KBr, cm-1): 3079 w,
3054 w, 3023 w, 2921 m, 2847 m, 2593 s, 1509 s, 1472 m, 1425
s, 1381 m, 1355 m, 1337 w, 1318 m, 1277 m, 1229 m, 1206 w,
1168 w, 1137 w, 1096 m, 1066 w, 1026 m, 995 w, 978 w, 934
w, 887 w, 823 w, 748 w, 729 m, 707 m, 627 w, 611 w, 565 w,
546 w, 465 m. Anal. Calcd for C50H56N4HfO2: C, 65.03; H,
6.11; N, 6.07. Found: C, 65.11; H, 6.04; N, 6.34.
coupling to acetone, isocyanates, and nitro groups.
Scheme 2 depicts the newly obtained fragments and the
numbering scheme adopted in this paper.
Exp er im en ta l Section
Gen er a l P r oced u r es. The ligand H2(TC-3,5)7 and starting
material 16 were prepared as described. All manipulations,
excluding ligand preparations, were conducted under a pure
dinitrogen or argon atmosphere using standard Schlenk and
glovebox techniques. Solvents were dried according to estab-
lished protocols and were degassed prior to use. Unless
otherwise specified, all reagents were obtained from com-
mercial suppliers and were thoroughly degassed and dried
before use. NMR spectra were recorded on a Bruker AM-250
at room temperature. Owing to the thermal instability of the
tropocoronand complexes in solution at room temperature and
their sparing solubility at low temperatures, 13C NMR data
could not be obtained. All compounds were characterized by
crystallographic chemical analysis (CCA), and elemental analy-
ses were obtained on representative species. Product yields
are reported for the isolated, crystalline materials and were
not optimized.
[(TC-3,5)HfOC(CH2P h )dC(P h )C(Me)2O] (5). At -30 °C,
a red-brown slurry of 75 mg (0.102 mmol) of 1 in 2 mL of
tetrahydrofuran was treated with 15 µL (0.204 mmol) of
acetone and allowed to warm to room temperature. Over the
course of several minutes, the solution became bright yellow
and homogenous. After 30 min, the mixture was filtered and
several volume equivalents of pentane were diffused into the
solution at -30 °C resulting in the formation of large,
[(TC-3,5)HfOC(CH 2P h )2N(NdCHSiMe3)] (2). A 2 M
solution of (trimethylsilyl)diazomethane (0.200 mmol) in hex-
(7) Zask, A.; Gonnella, N.; Nakanishi, K.; Turner, C. J .; Imajo, S.;
Nozoe, T. Inorg. Chem. 1986, 25, 3400-3406.

468 Organometallics, Vol. 17, No. 3, 1998
Scott and Lippard
irregularly shaped yellow crystals. The crystals were collected,
washed with ether, and dried to afford 31 mg (39%) of product.
The crystals contained two tetrahydrofuran solvate molecules,
as confirmed by 1H NMR spectroscopy, elemental analysis, and
CCA. 1H NMR (CD2Cl2): δ 7.18 (m, 8H), 6.72 (d, br, J ) 11.3
Hz, 8H), 6.50 (t, J ) 9.2 Hz, 4H), 4.7 (s, br, 2H), 3.84 (m, br,
4H), 3.50 (m, br, 4H), 3.14 (s, 2H), 2.16 (s, br, 2H), 1.35 (s, br,
2H), 1.20 (s, 6H, CH3), 0.95 (s, br, 2H). IR (KBr, cm-1): 2968
m, 2919 m, 2854 m, 1609 m, 1592 vs, 1509 vs, 1471 w, 1438
m, 1426 m, 1383 m, 1351 w, 1321 w, 1278 m, 1244 w, 1229 w,
1198 w, 1113 w, 1067 w, 1027 w, 1003 w, 978 w, 962 w, 937
w, 887 w, 826 w, 718 s, 650 w, 611 w, 564 w, 536 w, 469 m.
Anal. Calcd for C48H60N4HfO4: C, 61.63; H, 6.46; N, 5.99.
Found: C, 61.69, H, 6.41; N, 6.15.
at -30 °C. After several days, a fine yellow powder and large
orange crystals formed in the reaction vessel. The single
orange crystals of 8 were manually separated from the mixture
and characterized by CCA. Since multiple products were
formed in the reaction media, no attempt was made to optimize
the synthesis of 8.
[(TC-3,5)HfOC(dO)N(P h )C(CH2P h )2] (9). In 2 mL of
chlorobenzene a red-brown slurry of 107 mg (0.146 mmol) of
1 and 32 µL (0.294 mmol) of phenyl isocyanate was stirred at
35 °C for 30 min, and the resulting orange-brown solution was
filtered through Celite. Over the course of several days,
pentane was diffused into the filtrate at -30 °C. The
subsequent orange crystalline mass was collected, washed with
pentane, and dried to afford 39 mg (31%) of product. 1H NMR
(CD2Cl2): δ 7.24 (m, 11H), 7.06 (m, 2H), 6.88 (d, J ) 11.6 Hz,
2H), 6.75 (m, 6H), 6.49 (t, J ) 7.3 Hz, 2H), 6.36 (d, J ) 11.3
Hz, 2H), 5.56 (m, 2H), 4.05 (d, br, 2H), 3.57 (m, br, 6H), 3.00
(m, 1H), 2.75 (d, J ) 17.5 Hz, 2H), 2.34 (m, br, 1H), 2.05 (m,
br, 2H), 1.58 (m, br, 2H), 0.91 (m, br, 2H). IR (KBr, cm-1):
2931 m, 1645 vs, 1592 vs, 1509 vs, 1492 w, 1472 w, 1443 w,
1424 m, 1378 m, 1364 w, 1349 m, 1336 w, 1318 w, 1281 m,
1274 m, 1131 m, 1116 w, 1086 w, 1026 m, 983 w, 936 m, 886
w, 859 w, 826 w, 784 w, 759 w, 725 s, 694 m, 520 w, 469 m.
Anal. Calcd for C44H45N5HfO2: C, 61.86; H, 5.31; N, 8.20.
Found: C, 61.32; H, 5.53; N, 8.07.
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 a Siemens CCD X-ray diffraction system
controlled by a Pentium-based PC running the SMART
software package.10 The program SADABS11 was utilized for
absorption corrections. Data were collected by following the
standard procedures reported in detail elsewhere.12
[(TC-3,5)HfOC(CH 2P h )2O] (6). Upon addition of 12 µL
(0.099 mmol) of nitrocyclohexane, a red-brown solution of 35
mg (0.048 mmol) of 1 in 1.5 mL of dichloromethane rapidly
turned bright yellow and a precipitate formed. The mixture
was filtered through Celite, and ether was diffused into the
solution over 48 h. The solid was collected and washed with
ether and pentane, and the product was isolated as large
yellow-orange blocklike crystals (17 mg, 47%). The crystalline
material contained one ether solvate molecule, as confirmed
by elemental analysis and CCA. 1H NMR (CD2Cl2): δ 7.16
(m, 4H), 7.07 (m, 4H), 6.68 (t, J ) 7.45 Hz, 4H), 6.53 (m, 4H),
6.41(m, 4H), 4.58 (d of t, J ) 4.1, 14.7 Hz, 2H), 3.85 (m, 2H),
3.58 (m, 2H), 3.42 (m, 4H), 2.87 (s, 4H, CH2Ph), 2.14 (m, br,
2H), 1.46 (m, br, 2H), 0.98 (m, 2H). IR (KBr, cm-1): 2029 m,
1592 s, 1511 s, 1495 w, 1472 w, 1451 w, 1438 w, 1422 m, 1389
m, 1354 w, 1340 w, 1321 w, 1300 w, 1276 s, 1229 m, 1141 m,
1114 m, 1089 w, 1054 w, 1044 w, 1028 m, 980 w, 937 w, 887
w, 857 w, 822 w, 798 w, 768 w, 725 m, 706 s, 699 m, 661 w,
517 w, 475 m. Anal. Calcd for C41H50N4HfO3: C, 59.66; H,
6.11; N, 6.79. Found: C, 59.80; H, 6.19; N, 6.28.
[Hf(TC-3,5)]2(µ,η2:η2-ONP h )(µ-O) (7). A mixture of 26 µL
(0.252 mmol) of nitrobenzene and 92 mg (0.125 mmol) of 1 in
2 mL of dichloromethane was stirred at room temperature for
15 min. Addition of an additional 27 mg (0.252 mmol) of PhNO
induced a further color change from yellow to yellow-orange.
After 30 min of additional stirring, the mixture was filtered
and several volume equivalents of ether were diffused into the
filtrate over the course of 48 h at -30 °C. The product was
collected by filtration, washed with ether and pentane, and
dried to afford 12 mg (21%) of material. In an alternative
procedure, 11.7 µL (0.114 mmol) of nitrobenzene added to a
dichloromethane solution of 40 mg (0.057 mmol) of [Hf(TC-
3,5)(CH2Ph)2]8 induced a rapid color change from red-orange
to orange yellow. Several volume equivalents of ether were
diffused into the solution over 72 h at -30 °C to afford 8 mg
(27%) of orange blocks. The material was isolated by removal
of the supernatant followed by washing with copious amounts
of ether. 1H NMR (CD2Cl2): δ 7.05 (m, br, 4H), 6.86 (m, 2H),
6.64 (m, vbr, 6H), 6.34 (m, br, 4H), 6.01 (m, br, 6H), 5.50 (m,
1H), 5.01 (m, 2H), 4.37 (m, 2H), 4.14 (m, 2H), 3.50 (m, vbr,
6H), 3.14 (m, 2H), 2.56 (m, 2H), 2.08 (m, 2H), 1.51 (m, br, 6H),
1.0 (m, br, 2H). IR (KBr, cm-1): 2918 m, 2855 m, 1591 vs,
1508 vs, 1472 m, 1427 d, 1385 m, 1352 w, 1337 w, 1319 wm
1273 m, 1228 m, 1113 w, 1026 m, 978 w, 938 w, 887 w, 823 w,
724 s, 630 s, 519 w, 473 m.
The structures were solved by direct methods using SIR-
9213 or SHELXS and refined by full-matrix least-squares and
Fourier techniques using the SHELXTL-PLUS program pack-
age.14 Space groups were determined from an examination of
the systematic absences in the data confirmed by the success-
ful solution and refinement of the structures. When a complex
crystallized in a polar space group, both enantiomers were
refined, and the structure presented is that yielding the lowest-
weighted residual and smaller value for the Flack parameter.15
Except in the cases where disorder was apparent, all non-
hydrogen atoms were refined anisotropically. Hydrogen atoms
were assigned idealized locations and given a thermal param-
eter equal to 1.2 times that of the carbon atom to which it
was attached.
The asymmetric units of both 2 and 4 contain one complete
complex; in compound 3 the Hf atom lies on a mirror plane.
The phenyl group derived from the azide substrate is disor-
dered across this mirror plane. The azide nitrogen atoms, the
ipso carbon atom, and one meta carbon atom all lie on the
mirror plane, but the phenyl ring is canted approximately 30°
with respect to this plane in two orientations, each having a
site occupancy of 0.5. The disordered carbon atoms were
refined isotropically, and the hydrogen atoms on the ring were
omitted from the final refinement. Compound 5 crystallized
[(TC-3,3)Zr OC(p-tol)2C(p-tol)2O] (8). Addition of 7 µL
(0.068 mmol) of nitrobenzene to a red solution of 20 mg (0.034
mmol) of [Zr(TC-3,3)(η2-OC(p-tol)2)]9 in dichloromethane in-
duced a rapid color change to orange. The mixture was stirred
for 15 min and filtered through Celite, and several volume
equivalents of ether were diffused into the reaction mixture
(10) SMART: Version 4.0; Siemens Industrial Automation, Inc.:
Madison, WI, 1994.
(11) SADABS was obtained from Prof. George Sheldrick at the
University of Go¨ttingen. The program corrects data collected on
Siemens CCD and Multiwire detectors for absorption and decay.
(12) Feig, A. L.; Bautista, M. T.; Lippard, S. J . Inorg. Chem. 1996,
35, 6892-6898.
(13) Burla, M. C.; Camalli, M.; Cascarano, G.; Giacovozza, C.;
Polidori, G.; Spagna, R.; Viterbo, D. J . Appl. Crystallogr. 1989, 22, 389-
393.
(8) Scott, M. J .; Lippard, S. J . Inorg. Chim. Acta 1997, 263, 287-
299.
(14) SHELXTL: Structure Analysis Program; Siemens Industrial
Automation, Inc.: Madison, WI, 1995.
(15) Flack, H. D. Acta Crystallogr. 1983, A39, 876-881.
(9) [Zr(TC-3,3)(η2-OC(p-tol)2)] was prepared from [Zr(TC-3,3)(p-tol)2]
(ref 8) following the procedures outlined for the formation of 1 (ref 6).

Reactivity in the Tropocoronand Complex
Organometallics, Vol. 17, No. 3, 1998 469
Ta ble 1. Cr ysta llogr a p h ic a n d Selected Metr ic
P a r a m eter s of P r od u cts fr om th e Rea ction of 1
w ith TMSCHN2 (2) a n d P h N3 (3)
Ta ble 2. Cr ysta llogr a p h ic a n d Selected Metr ic
P a r a m eter s of th e P r od u cts fr om th e Rea ction of 1
w ith CyP h CO (4) a n d Aceton e (5)
compound
formula
fw
2
C
3
compound
formula
fw
4
C
5‚2C4H8O
C48H60HfN4O4
935.49
41H50HfN6OSi
C43H45HfN7O
854.35
50H56HfN4O2
849.45
923.48
cryst syst
space group
a (Å)
orthorhombic
Pca21
orthorhombic
Cmc21
cryst syst
space group
a (Å)
b (Å)
c (Å)
triclinic
P1h
Triclinic
P1h
26.8228(8)
13.8639(4)
10.2644(3)
3817.0(2)
4
188
5.68
6.65
18.0841(5)
20.7913(5)
10.0864(2)
3792.4(2)
4
188
3.36
7.59
11.0942(8)
13.0632(10)
15.1685(11)
78.5990(10)
75.885(2)
72.773(2)
2017.5(3)
2
10.9645(4)
11.7043(4)
18.4183(6)
87.9380(10)
89.2560(10)
65.5680(10)
2150.60(13)
2
b (Å)
c (Å)
V (Å3)
R (deg)
Z
â (deg)
T, K
γ (deg)
R (%)a
V (Å3)
wR2 (%)b
Z
Hf(1)-O(1) Å
Hf(1)-N(1) Å
Hf(1)-N(2) Å
Hf(1)-N(3) Å
Hf(1)-N(4) Å
Hf(1)-N(5) Å
Hf(1)-N-N (deg)
O(1)-Hf(1)-N(5) (deg)
O(1)-Hf(1)-N(3) (deg)
1.998(4)
2.190(6)
2.211(6)
2.202(5)
2.201(6)
2.151(6)
140.5(6)
63.9(2)
62.8(3)
2.005(6)
2.193(6)
2.181(6)
2.195(7)
T, K
188
6.95
9.71
188
4.69
7.76
R (%)a
wR2 (%)b
Hf(1)-O(1) Å
Hf(1)-O(2) Å
Hf(1)-N(1) Å
Hf(1)-N(2) Å
Hf(1)-N(3) Å
Hf(1)-N(4) Å
O(1)-C(23) Å
O(2)-C(38) Å
C(23)-C(31) Å
C(23)-C(38) Å
C(31)-C(38) Å
O(1)-Hf(1)-O(2) (deg)
2.001(5)
2.038(5)
2.244(6)
2.206(6)
2.253(6)
2.166(6)
1.406(8)
1.408(9)
1.962(3)
2.039(3)
2.185(4)
2.238(4)
2.212(4)
2.230(4)
1.354(6)
1.404(5)
1.335(6)c
141.1(6)
R ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) {∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]}1/2
.
a
with two tetrahydrofuran solvent molecules, which were
refined anisotropically despite their high degree of thermal
motion. Compound 6 was well-ordered on a mirror plane, but
the ether solvate molecule exhibited a large amount of thermal
motion across this symmetry element. Since the structure
refined to a low residual value, no attempt was made to model
the disorder rigorously and hydrogen atoms on the disordered
carbon atoms were omitted. In the structure of 7, both
bridging ligands lie in the mirror plane as do two dichlo-
romethane solvate molecules, one of which had one chlorine
atom disordered across this plane. An additional dichlo-
romethane molecule crystallized on a general position in two
orientations with site occupancies of 0.75 and 0.25, respec-
tively. These atoms were refined isotropically, and hydrogen
atoms were not included in the refinement of the solvate
molecules. The asymmetric units of both 8 and 9 contain one
1.612(10)
76.0(2)
1.545(6)
80.91(13)
R ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) {∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]}1/2
.
a
c The angles (deg) at C(23) and C(31) are as follows: C(31)-C(23)-
O(1), 125.0(4); C(31)-C(23)-C(24), 123.6(4); O(1)-C(23)-C(24),
111.3(4); C(23)-C(31)-C(32), 120.6(4); C(23)-C(31)-C(38), 123.4(4);
C(23)-C(31)-C(38), 115.8(4).
Sch em e 3
complete complex, but 8 also crystallized with
a dichlo-
romethane molecule in the lattice. The ether was badly
disordered, and its electron density was modeled with partially
occupied carbon atoms. Crystallographic data and selected
metrical parameters are reported in Tables 1-4, and ad-
ditional experimental details are available as Supporting
Information.
plexes, although 1,1-additions occur, [Cp*2Zr(η2-C2Ph2)]
inserting both p-tolylazide and diazoalkanes via this
pathway.20 In the latter systems, the steric require-
ments of the Cp* ligand were suggested to block
coordination of a second nitrogen atom from the incom-
ing substrate. In both 2 and 3, the coordination sphere
of the metal is relatively unencumbered. Instead, the
strongly electron-donating tropocoronand ligand reduces
the electrophilicity of the Hf atom, reducing its ability
to bind a second nitrogen atom. Attempts to extrude
dinitrogen from 2 and 3 at elevated temperatures
resulted in the formation of complex product mixtures.
1,2-In ser tion s F or m in g C-C Bon d s. As described
previously, enones add across the metal-carbon bond of
1 in a 1,2-fashion forming five-membered metallacycles
(Scheme 1).6 Although simple ketones attack the met-
alloxirane unit in 1, the reaction is more complicated
and slow, even at elevated temperatures. When a
Resu lts a n d Discu ssion
1,1-In ser tion s F or m in g C-N Bon d s. At 35 °C,
(trimethylsilyl)diazomethane and phenylazide both re-
act with 1 by formal 1,1-insertion into the Hf-C bond
to afford 2 and 3, respectively (Scheme 3). ORTEP
diagrams of the products from these reactions are
displayed in Figures 1 and 2, and selected geometric
parameters are available in Table 1. The Hf-O bond
lengths of 1.998(4) Å in 2 and 2.005(6) Å in 3 are
indistinguishable from the analogous distance of
1.993(5) Å in 1, and the two Hf-N distances are
marginally inequivalent, 2.151(6) and 2.195 (7) Å,
respectively. These substrates typically insert into
group 4 metal-hydride or metal-carbon bonds to afford
either η2-hydrazonato6,16,17 or η2-triazenido18,19 com-
(18) Hillhouse, G. L.; Bercaw, J . E. Organometallics 1982, 1, 1026-
1029.
(16) Gambarotta, S.; Basso-Bert, M.; Floriani, C.; Guastini, C. J .
Chem. Soc., Chem. Commun. 1982, 374-375.
(17) Gambarotta, S.; Floriani, C.; Chiesi-Villa, A.; Guastini, C. Inorg.
Chem. 1983, 22, 2029-2034.
(19) Chiu, K. W.; Wilkinson, G.; Thornton-Pett, M.; Hursthouse, M.
B. Polyhedron 1984, 3, 79-85.
(20) Vaughan, G. A.; Hillhouse, G. L.; Rheingold, A. L. J . Am. Chem.
Soc. 1990, 112, 7994-8001.

470 Organometallics, Vol. 17, No. 3, 1998
Scott and Lippard
Ta ble 3. 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 CyNO2 (6)
a n d P h NO2 (7) w ith 1 a n d [Zr (TC-3,3)(η2-OC(P h )2)] w ith P h NO2 (8)
compound
formula
fw
cryst syst
space group
a (Å)
6‚Et2O
7‚4CH2Cl2
C54H65Cl8Hf2N9O2
1512.73
orthorhombic
Pnma
14.9933(2)
21.6572(5)
18.1929(4)
5907.5(2)
4
8‚CH2Cl2
C51H52Cl2N4O3Zr
931.09
orthorhombic
P212121
9.7421(2)
20.4331(5)
23.7925(1)
4736.2(2)
4
C41H50HfN4O3
825.34
orthorhombic
Cmc21
17.4362(4)
21.7256(4)
9.7862(2)
3707.13(13)
4
b (Å)
c (Å)
V (Å3)
Z
T, K
188
1.66
3.62
188
3.55
9.19
188
7.40
15.47
R (%)a
wR2 (%)b
M-O(1) Å
M-O(2) Å
M-Ntrop (avg) Å
M-N(5) Å
O(1)-M-O(2) (deg)
O(1)-N(5) Å
Hf(1)-O(1)-Hf(1′) (deg)
Hf(1)-N(5)-Hf(1′) (deg)
Hf(1)-O(2)-Hf(1′) (deg)
C(21)-C(36) Å
2.018(2)
2.045(2)
2.203(5)
2.161(3)
1.975(3)
2.24(2)
2.218(4)
78.92(13)
1.500(7)
93.7(2)
2.024(5)
2.043(5)
2.21(2)
67.37(9)
75.3(2)
90.7(2)
106.1(2)
1.627(12)
R ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) {∑[w(Fo - Fc2)2]/∑[w(Fo2)2]}1/2
.
a
b
2
Ta ble 4. 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 1
w ith P h NCO (9)
compound
formula
9
C
44H45HfN5O2
fw
854.34
cryst syst
space group
a (Å)
orthorhombic
Pbca
12.1883(2)
14.9260(2)
38.7591(3)
7051.2(2)
8
b (Å)
c (Å)
V (Å3)
Z
T, K
193
4.20
R (%)a
wR2 (%)b
Hf(1)-O(1) Å
Hf(1)-N(4) Å
Hf(1)-N(1) Å
Hf(1)-N(2) Å
Hf(1)-N(3) Å
Hf(1)-C(23) Å
O(1)-C(44) Å
O(2)-C(44) Å
7.26
2.050(3)
2.200(4)
2.207(4)
2.210(4)
2.214(3)
2.439(4)
1.306(5)
1.222(5)
F igu r e 1. ORTEP diagram of 2 showing 50% ellipsoids
and atom-labeling scheme. Selected distances and angles
are contained in Table 1.
R ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) {∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]}1/2
.
a
illustrated in Figure 3 and selected crystallographic
parameters are contained in Table 2. This transforma-
tion is general for tropocoronand complexes with dispar-
ate macrocycles and auxiliary groups, as illustrated by
the reaction of [Zr(TC-3,3)(η2-OC(p-tol)2)] outlined be-
low.
phenyl group is present, the reactivity is enhanced and
a 1,2-insertion into the metalloxirane occurs, as depicted
in Scheme 4.
Coupling reactions of this type are common with
group 4 metal centers, as illustrated by the insertion of
acetophenone into [Cp2Zr(η2-CO(CH3)2(µ-Cl)Al(CH3)2].21
Moreover, treatment of reduced cyclopentadienyl-ligated
group 4 metal centers with either ketones or aldehydes
will afford saturated diolate complexes, but typically,
in these systems, two equivalent substrates are coupled
to give a symmetric ligand.22,23 With the tropocoronand
complexes, however, asymmetric diolate complexes can
be prepared in a stepwise manner (Scheme 4). The
Whereas both enones and phenyl-substituted ketones
react with 1 in a manner analogous to pinacol coupling,22
acetone induces the formation of a diolato product
having distinctive characteristics, including a new ole-
finic stretch in the infrared spectrum at 1609 cm-1
.
Figure 4 depicts the structure of the product, 5, isolated
from the reaction mixture upon recrystallization. Se-
lected metrical parameters are contained in Table 2,
from which the C(23)dC(31) bond can be identified. The
two Hf-O bond lengths are inequivalent (2.039(3),
1.962(3) Å) and span the values of 1.999(7) and
2.009(7) Å observed in the diolato product obtained from
the reaction of 1 with cyclohexenone (1.999(7) and
2.009(7) Å).6 This result is ascribed to the presence of
structure of [(TC-3,5)HfOC(CH2Ph)2C(Cy)(Ph)O] (4) is
(21) Waymouth, R. M.; Clauser, K. R.; Grubbs, R. H. J . Am. Chem.
Soc. 1986, 108, 6385-6387.
(22) McMurry, J . E. Acc. Chem. Res. 1983, 16, 405-411.
(23) Fu¨rstner, A.; Bogdanovic, B. Angew. Chem., Int. Ed. Engl. 1996,
35, 2442-2469 and references therin.

Reactivity in the Tropocoronand Complex
Organometallics, Vol. 17, No. 3, 1998 471
F igu r e 2. ORTEP diagram of 3 showing 30% ellipsoids,
atom-labeling scheme, and both orientations of the disor-
dered phenyl group. Primed and unprimed atoms are
related by an mirror plane. Selected distances and angles
are contained in Table 1.
F igu r e 4. ORTEP diagram of 5 showing 30% ellipsoids
and atom-labeling scheme. Selected distances and angles
are contained in Table 2.
Addition of acetone to the resulting enolate with the
accompanying rearrangement and loss of dihydrogen
would afford 5, as illustrated in Scheme 5.
O-Atom Tr a n sfer fr om Nitr oa lk a n es. The met-
alloxirane unit in 1 reacts rapidly with nitroalkanes,
excising one of the N-O bonds to afford the diolato-
ligated tropocoronand complex [(TC-3,5)HfOC(CH2-
Ph)2O] (6). The structure is illustrated in Figure 5 and
selected geometric information is contained in Table 3.
Concomitant with the formation of 6, 1 equiv of ni-
trosoalkane would be generated, but attempts to detect
this material in the reaction were unsuccessful. In 6,
the resulting four-membered chelate ring has a O-Hf-O
angle of 67.37(9)°, smaller than that in 4, and shorter
Hf-O distances of 2.018(2) and 2.045(2) Å, which reflect
the greater charge accumulation. Although reagents
such as [TiCl2(O-i-Pr)2] can catalyze the cycloaddition
of olefins and nitroalkanes,26 evidently little attention
has been paid to the interaction of nitroalkanes with
group 4 metals. Hydrolysis of 6 affords dibenzyl ketone
and the di(µ-oxo) complex [Hf(TC-3,5)(µ-O)]2,27,28 pre-
sumably through dimerization of transient terminal oxo
species.29
F igu r e 3. ORTEP diagram of 4 showing 30% ellipsoids
and atom-labeling scheme. Selected distances and angles
are contained in Table 2.
Sch em e 4
For m a l Retr ocycloa d d ition Ch em istr y. Nitroare-
nes also react with 1 to afford complex reaction mixtures
having 1H NMR spectra revealing several species present
in solution. Nevertheless, after careful purification by
recrystallization, the dominant product 7, a dinuclear
complex in which two Hf atoms are bridged by both oxo
and a η2:η2-nitroso groups, was isolated. Addition of
the double bond. The spectroscopic and structural data
indicate that, during the formation 5, two hydrogen
atoms were lost from one benzylic position of the
coordinated η2-ketone, a reaction accomplished by for-
mation of a bond to the central carbon atom of the
acetone substrate. Group 4 metal centers can abstract
â-hydrogen atoms from coordinated transient η2-ketone
ligands to form metal-hydride/enolate species,24,25 sug-
gesting that 5 may form through such an intermediate.
(25) Hessen, B.; Blenkers, J .; Teuben, J . H.; Helgesson, G.; J agner,
S. Organometallics 1989, 8, 2809-2812.
(26) Denmark, S. E.; Thorarensen, A. Chem. Rev. 1996, 96, 137-
165.
(27) [Hf(TC-3,5)(µ-O)]2: C2/c, a ) 15.9674(5) Å, b ) 19.0350(6) Å, c
) 14.7935(3) Å, â ) 97.644(1)°, Z ) 4, R ) 3.05%, wR2 ) 6.74%.
Relevant distances: Hf-O 1.971(4), 1.983(4) Å. Complete structural
details are available in the Supporting Information.
(28) Dibenzylketone was detected in the reaction mixture by GC/
MS.
(24) Manriquez, J . M.; McAlister, D. R.; Sanner, R. D.; Bercaw, J .
E. J . Am. Chem. Soc. 1978, 100, 2716-2724.
(29) Hey-Hawkins, E. Chem. Rev. 1994, 94, 1661-1717 and refer-
ences therein.

472 Organometallics, Vol. 17, No. 3, 1998
Scott and Lippard
Sch em e 5
F igu r e 5. ORTEP diagram of 6 showing 50% ellipsoids
and atom-labeling scheme. Primed and unprimed atoms
are related by an mirror plane. Selected distances and
angles are contained in Table 3.
F igu r e 6. ORTEP diagram of 7 showing 30% ellipsoids
and atom-labeling scheme. Primed and unprimed atoms
are related by an mirror plane. Selected distances and
angles are contained in Table 3.
excess nitrosobenzene to the crude reaction mixture
increases the yield of 7. Figure 6 presents an ORTEP
diagram of the product, and Table 3 contains selected
geometric information. Compound 7 is a rare example
of the η2:η2-nitrosoarene bridging motif,30 in which the
nitrogen and oxygen atoms link the two metal centers
with elongated metal-ligand distances of 2.218(4) and
2.161(3) Å, respectively. The N-O distance of
1.500(7) Å in the nitrosoarene bridge is markedly longer
than the comparable distance of 1.422(4) Å in the only
other structurally characterized example of the µ-η2:η2
bonding mode, [(Cp*Rh)2(µ-Cl)(µ,η2-η2-ONPh)](BF4),30
indicating significant reduction in bond order. The
Hf-O distance of 1.975(3) Å in the (µ-oxo)dihafnium-
(IV) is normal.27
Sch em e 6
On the basis of the products isolated, we suggest that
the nitrosobenzene generated by excision of oxygen from
nitrobenzene (vide supra) may induce 6 to react further,
probably by a retro [2 + 2] cycloaddition, as depicted in
Scheme 6. Such a reaction would afford a transient
terminal oxo complex and 1 equiv of dibenzyl ketone.
(30) Hoard, D. W.; Sharp, P. R. Inorg. Chem. 1993, 32, 612-620.

Reactivity in the Tropocoronand Complex
Organometallics, Vol. 17, No. 3, 1998 473
Sch em e 7
Sch em e 8
Although the µ-η2:η2 binding of nitrosoarenes is
exceedingly uncommon, such a motif readily assembles
with group 4 tropocoronand complexes. Most dialkyl-
substituted Zr(IV) and Hf(IV) tropocoronand complexes
react with nitrobenzene as well as other nitroalkanes
to afford either µ-η2:η2-nitrosoarene- or -nitrosoalkane-
bridged compounds in moderate yield. Several ex-
amples have been structurally characterized from re-
action mixtures containing nitromethane,32 nitro-
propane,33 and nitrotoluene.34 In comparison to 1, the
mechanism by which this structural type forms from
dialkyl complexes could be more complicated, perhaps
involving protonation of the nitroalkane substrate by
the nitronic acid tautomer.26
C-O Bon d Scission w ith P h en yl Isocya n a te a n d
th e η2-Keton e. In contrast to reactions of 1 discussed
above, phenyl isocyanate does not attack the Hf-C bond
of the metalloxirane unit. Rather unexpectedly, this
substrate preferentially inserts into the carbon-oxygen
bond, generating the carbamate moiety 9 (Figure 8;
Table 4). This reaction differs dramatically from that
of (η2-formaldehyde)zirconocene, which reacts by 1,2-
addition to insert the C-O fragment from isocyanates
into the metal-carbon bond, forming a five-membered
metallacycle.35,36 A simple [2 + 2] cycloaddition reaction
between the N-C bond of the phenyl isocyanate and
the C-O bond of the η2-ketone in 1 would account for
the observed carbamate functionality (Scheme 9), but
other mechanisms are possible.
F igu r e 7. ORTEP diagram of 8 showing 50% ellipsoids
and atom-labeling scheme. Primed and unprimed atoms
are related by an mirror plane. Selected distances and
angles are contained in Table 3.
The latter was detected in the reaction mixture by GC-
MS. In the presence of unreacted 1, the terminal oxo
complex can react with nitrosoarene to afford 7, as
pictured in Scheme 7.
Several observations lend credence to this proposal.
Electron-deficient ketones undergo reversible cyclo-
additions with oxotitanium tetraazaannulene com-
plexes.31 Addition of PhNO to the reaction mixture
increased the yield of 7, consistent with the postulated
mechanism. Finally, the diolate complex [(TC-3,3)-
ZrOC(p-tol)2C(p-tol)2O] (8) (Figure 7; Table 3) was
isolated from the reaction of [Zr(TC-3,3)(η2-OC(p-tol)2)]
with PhNO2, albeit from a mixture complicated by the
presence of multiple products. The manner by which 8
might form would be consistent with the postulated
mechanism for 7 formation. With p-tol substituents, the
ketone liberated by a retro [2 + 2] cycloaddition (Scheme
6) is activated by the phenyl rings. It could, in turn,
attack unreacted [Zr(TC-3,3)(η2-OC(p-tol)2)], as outlined
in Scheme 8, presumably by a mechanism similar to
that postulated for the formation of 4 (Scheme 4). As
indicated previously,6 enones form coupled products in
this manner. In reactions of 1, the released dibenzyl
ketone is inert, preventing such coupling chemistry and
allowing isolation of the bridged nitrosoarene complex
7.
Without any perceptible alteration in the Hf-N
distances, the metal-carbon distance in 9 has increased
considerably to 2.439(4) Å. The Hf-O distance of
(32) [Hf(TC-3,5)]2{µ-η2:η2-ON(CH2CH2Ph)}(µ-O): P21/ c, Z ) 4, a )
23.5409(4) Å, b ) 11.9600(2) Å, c ) 19.3407(3) Å, â ) 109.709(1)°, V )
5126.35(8) Å3.
(33) [Zr(TC-3,3)]2{µ-η2:η2-ON(i-Pr)}(µ-O): Pnma,
Z ) 4, a )
10.0703(9) Å, b ) 24.146(2) Å, c ) 17.8020(16) Å, V ) 4328(1) Å3.
(34) [Zr(TC-3,5)]2{µ-η2:η2-ON(o-MePh)}(µ-O): Pnma, Z ) 4, a )
14.811(6) Å, b ) 21.96(1) Å, c ) 18.143(9) Å, V ) 5903(2) Å3.
(35) Erker, G.; Mena, M.; Werner, S.; Kru¨ger, C. J . Organomet.
Chem. 1990, 390, 323-331.
(36) Schmuck, S.; Erker, G.; Kotila, S. J . Organomet. Chem. 1995,
502, 75-86.
(31) Housmekerides, C. E.; Ramage, D. L.; Kretz, C. M.; Shontz, J .
T.; Pilato, R. S.; Geoffroy, G. L.; Rheingold, A. L.; Haggerty, B. S. Inorg.
Chem. 1992, 31, 4453-4468.

474 Organometallics, Vol. 17, No. 3, 1998
Scott and Lippard
plex.37 Attempts to isolate products from the reaction
of 1 with substrates comparable to phenyl isocyanate,
among them PhCH2NCO and PhNCS, were unsuccess-
ful. In the polar solvent media required for these
reactions, compound 1 slowly decomposed at elevated
temperatures, forming [Hf(TC-3,5)(OCH(CH2Ph)2)Cl]6
as well as other unidentified species.
Con clu sion s
The coordinated η2-ketone ligand in the tropocoronand
complex 1 reacts with several substrates to afford
interesting organic moieties. Metal-mediated transfor-
mations include 1,1-additions, pinacolic coupling, and
C-H and C-O bond scission from which a variety of
complicated constructs have been assembled incorporat-
ing one of the simplest of starting materials, carbon
monoxide. As exemplified by the insertion of phenyl
isocyanate into a C-O bond derived from carbon
monoxide, these metal-mediated conversions can pro-
ceed through unprecedented pathways. These bond-
forming reactions allow for the incorporation of isoto-
pically labeled substrates into larger molecules and
potentially could contribute to synthetic organic meth-
odology. During the course of this research, metal
complexes with a diverse set of organic ligands have
been isolated (Scheme 2), which, following hydrolysis,
could be detached. The reactivity described here is due
at least in part to the electronic and steric properties of
the (TC-n,m)2- tetraazamacrocycle compared to more
conventional organometallic ligands such as cyclopen-
tadienyl.
F igu r e 8. ORTEP diagram of 9 showing 50% ellipsoids
and atom-labeling scheme. Selected distances and angles
are contained in Table 4.
Sch em e 9
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. We thank Profes-
sor G. C. Fu for helpful discussions.
2.050(3) Å is not unusually short, despite differences
in the bound (1.306(5) Å) and terminal (1.222(5) Å) C-O
bond lengths, which implies some delocalization of the
carbamate double bond, potentially contributing ad-
ditional electron density to the metal center. The
carbamate ligand exhibits a single C-O stretching band
at 1645 cm-1 in the infrared spectrum, slightly lower
in energy compared to the values of 1660 and 1651 cm-1
in a somewhat related dinuclear zirconafuranone com-
Su p p or tin g In for m a tion Ava ila ble: Tables of anisotro-
pic thermal parameters, hydrogen atom parameters, and
complete bond distances and angles and ORTEP diagrams for
all compounds (81 pages). Ordering information is given on
any current masthead page.
OM971040N
(37) Rosenthal, U.; Ohff, A.; Baumann, W.; Kempe, R.; Tillack, A.;
Burlakov, V. V. Angew. Chem., Int. Ed. Engl. 1994, 33, 1850-1852.