Addition and metathesis reactions of zirconium and hafnium imido complexes

Article abstract of DOI:10.1021/ic9910007

The zirconium and hafnium imido metalloporphyrin complexes (TTP)M=NAr(i(Pr)) (TTP = meso-5,10,15,20-tetra-p-tolylporphyrinato dianion; M = Zr (1), Hf; Ar(i(Pr)) = 2,6-diisopropylphenyl) were used to mediate addition reactions of carbonyl species and metat

Full text of DOI:10.1021/ic9910007

2344
Inorg. Chem. 2000, 39, 2344-2351
Addition and Metathesis Reactions of Zirconium and Hafnium Imido Complexes
Joseph L. Thorman,† Ilia A. Guzei,† Victor G. Young, Jr.,‡ and L. Keith Woo*,†
Departments of Chemistry, Iowa State University, Ames, Iowa 50011-3111, and
University of Minnesota, Minneapolis, Minnesota 55455
ReceiVed August 18, 1999
The zirconium and hafnium imido metalloporphyrin complexes (TTP)MdNAriPr (TTP ) meso-5,10,15,20-tetra-
p-tolylporphyrinato dianion; M ) Zr (1), Hf; AriPr ) 2,6-diisopropylphenyl) were used to mediate addition reactions
of carbonyl species and metathesis of nitroso compounds. The imido complexes react in a stepwise manner in the
presence of 2 equiv of pinacolone to form the enediolate products (TTP)M[OC(tBu)CHC(tBu)(Me)O] (M ) Zr
(2), Hf (3)), with elimination of H2NAriPr. The bis(µ-oxo) complex [(TTP)ZrO]2 (4) is formed upon reaction of
(TTP)ZrdNAriPr with PhNO. Treatment of compound 4 with water or treatment of compound 2 with acetone
produced the (µ-oxo)bis(µ-hydroxo)-bridged dimer [(TTP)Zr]2(µ-O)(µ-OH)2 (5). Compounds 2, 4, and 5 were
structurally characterized by single-crystal X-ray diffraction.
Hf), and (TTP)Zr(η2-NAriPrC(dNtBu)O) compounds were prepared
Introduction
according to literature procedures.7 Pinacolone was purchased from
The preparation of group 4 chalcogenido complexes is an
Aldrich, vacuum-transferred, and dried by passage through a plug of
attractive goal in light of the high reactivity of metallocene and
tetraazaannulene analogues described in a number of reports.1-3
Notable examples include C-H bond activation, cycloaddition,
and enolate formation. Toward this end, we have developed
nitrene group and chalcogenido atom transfer routes with
titanium metalloporphyrin complexes. Efforts to extend this
methodology to the heavier congeners has now become an area
of attention. In an ongoing investigation of group 4 metallopor-
phyrin imido complexes, we have found a number of novel
reactivity properties.4-6 We demonstrated previously that the
imido complexes (TTP)MdNAriPr (M ) Zr, Hf) exhibit
reactivity with heterocumulenes to form [2 + 2] cycloaddition
products.7 Further reactivity has been explored with other
unsaturated substrates. Among these are pinacolone and PhNO,
for which we now describe results found for their reactions with
zirconium and hafnium imido complexes.
activated neutral alumina. Pinacolone-d12 was prepared according to a
literature procedure.8 1H and 13C NMR data were acquired on Varian
VXR (300 MHz, 20 °C) and Bruker DRX (400 MHz, 25 °C)
spectrometers. Chemical shifts (ppm) are referenced to proton solvent
impurities (δ 7.15, C6D5H). UV-vis data were recorded on a HP8452A
diode array spectrophotometer and are reported as λmax in nm (log ꢀ).
Elemental analyses (C, H, N) were performed by Iowa State University
Instrument Services. GCMS studies were performed on a Varian gas
chromatograph coupled to an ITS 40 ion trap mass spectrometer
(capillary column DB-5MS).
(TTP)Zr(NHAriPr)[OC(tBu)(dCH2)], 2a. This complex was formed
within minutes by treatment of the imido complex, 1, with 1 equiv of
pinacolone in toluene or benzene. Although complex 2a is stable in its
mother liquor for days at ambient temperature and at 80 °C, it could
not be isolated in an analytically pure form. 1H NMR (C6D6, 400
MHz): 9.18 (s, 8H, â-H), 8.55 (d, 4H, 3JH-H ) 7 Hz, meso-C6H4CH3),
3
3
7.85 (d, 4H, JH-H ) 7 Hz, meso-C6H4CH3), 7.33 (d, 4H, JH-H ) 8
Hz, meso-C6H4CH3), 7.23 (d, 4H, 3JH-H ) 8 Hz, meso-C6H4CH3), 6.22
(m, 3H, m,p-NHAriPr), 3.02 (s, 1H, OC(dCH2)tBu), 2.40 (s, 12H, meso-
C6H4CH3), 1.35 (s, 1H, OC(dCH2)tBu), 0.96 (s, 1H, NHAriPr), 0.46
Experimental Section
General Procedures. All manipulations were performed under a
nitrogen atmosphere using a Vacuum Atmospheres glovebox equipped
with a model MO40-1 Dri-Train gas purifier. Benzene, benzene-d6,
toluene, THF, and hexane were freshly distilled from purple solutions
of sodium benzophenone and brought into the drybox without exposure
to air. The dichloro, (TTP)MCl2, imido, (TTP)MdNAriPr (M ) Zr,
3
3
(d, 6H, JH-H ) 8.9 Hz, 2,6-(CH(CH3)2)2C6H4), 0.32 (d, 6H, JH-H
)
8.6 Hz, 2,6-(CH(CH3)2)2C6H4), -0.22 (m, 2H, 2,6-(CH(CH3)2)2C6H4),
-0.50 (s, 9H, OC(dCH2)tBu). 13C NMR (C6D6): 170.7 (OC(dCH2)t-
Bu), 150.6, 148.6, 139.8, 137.1, 135.2 (o-tolyl), 134.2 (o-tolyl), 132.5
(â-pyrrole), 128.5 (m-tolyl), 125.6, 125.4, 121.2 (m,p-AriPr), 119.7 (m,p-
AriPr), 83.3 (OC(dCH2)tBu), 34.1, 29.0 (CH(Me)2), 27.3 (OC(dCH2)-
(C(CH3)3), 24.6 (CH(Me)2), 22.0 (CH(Me)2), 21.4 (CH3-tolyl).
† Iowa State University.
(TTP)Zr[OC(tBu)CHC(tBu)(Me)O], 2. A solution of (TTP)Zrd
NAriPr (237 mg, 0.253 mmol) and pinacolone (200 µL, 1.60 mmol) in
benzene (ca. 15 mL) was stirred at 25 °C for 40 h. This dark blue
solution was filtered, and the filtrate was evaporated to dryness in vacuo
to yield blue 2 (204 mg, 84% yield). UV/vis (toluene): 548 (4.55),
‡ University of Minnesota.
(1) Carney, M. J.; Walsh, P. J.; Hollander, F. J.; Bergman, R. G.
Organometallics 1992, 11, 761 and references therein.
(2) Howard, W. A.; Trnka, T. M.; Waters, M.; Parkin, G. J. Organomet.
Chem. 1997, 528, 95 and references therein.
(3) 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.
(4) Berreau, L. M.; Young, V. G., Jr.; Woo, L. K. Inorg. Chem. 1995,
34, 527.
(5) Gray, S. D.; Thorman, J. L.; Berreau, L. M.; Woo, L. K. Inorg. Chem.
1997, 36, 278.
1
425 (5.66), 405 (shoulder, 3.23). H NMR (C6D6, 300 MHz): 9.21
3
(m, 8H, â-H), 8.47 (d, 4H, JH-H ) 7 Hz, meso-C6H4CH3), 7.93 (d,
4H, 3JH-H ) 7 Hz, meso-C6H4CH3), 7.36 (d, 4H, 3JH-H ) 8 Hz, meso-
3
C6H4CH3), 7.25 (d, 4H, JH-H ) 8 Hz, meso-C6H4CH3), 3.00 (s, 1H,
OC(tBu)CHC(tBu)(Me)O), 2.40 (s, 12H, meso-C6H4CH3), 0.04 (s, 9H,
OC(tBu)CHC(tBu)(Me)O), -0.46 (s, 9H, OC(tBu)CHC(tBu)(Me)O),
(6) Gray, S. D.; Thorman, J. L.; Adamian, V.; Kadish, K. M.; Woo, L.
K. Inorg. Chem. 1998, 37, 1.
(7) Thorman, J. L.; Guzei, I. A.; Young, V. G., Jr.; Woo, L. K. Inorg.
Chem. 1999, 38, 3814.
(8) Gilman, H. Organic Syntheses; John Wiley & Sons: New York, 1932;
Collect. Vol. I, pp 48-452.
10.1021/ic9910007 CCC: $19.00 © 2000 American Chemical Society
Published on Web 05/04/2000

Zirconium and Hafnium Imido Complexes
Inorganic Chemistry, Vol. 39, No. 11, 2000 2345
-0.69 (s, 3H, OC(tBu)CHC(tBu)(Me)O); 13C NMR (C6D6): 159.5 (OC-
(dCH)(tBu)), 150.4 (R-pyrrole), 150.1 (R-pyrrole), 140.0, 137.4, 135.2
(o-tolyl), 134.5 (o-tolyl), 132.61 (â-pyrrole), 132.56 (â-pyrrole), 127.9
(m-tolyl, obscured by solvent), 127.8 (m-tolyl, obscured by solvent),
124.7, 97.6 (OC(dCH)(tBu)), 80.0 (OC(Me)(tBu)), 37.2, 34.8, 27.4
(OC(dCH)CMe3), 24.3 (OC(Me)CMe3), 23.7 (OC(Me)(tBu)), 21.4
(CH3-tolyl). Anal. Calcd (found) for C60H58N4O2Zr: C, 75.20 (75.35);
H, 6.10 (6.19); N, 5.85 (5.59).
and H2NAriPr), -0.26 (s, 9H, OC(dCH2)tBu). Addition of 2 equiv of
pinacolone led to the formation of complex 2 within 15 min.
Reaction of Complex 2a with 2-Octanone. An NMR tube equipped
with a Teflon stopcock was charged with (TTP)ZrdNAriPr (15.6 mg,
16.7 µmol), Ph3CH (93.0 µL, 0.1397 M in C6D6, 13.0 µmol), pinacolone
(2.3 µL, 18.4 µmol), and C6D6 (ca. 0.6 mL). Allowing the tube to stand
at 20 °C for 16 h afforded 2a in quantitative yield, at which time
2-octanone (7.0 µL, 44.7 µmol) was added. Allowing this reaction
mixture to stand at 20 °C for 23 h afforded (TTP)Zr(OC(tBu)CHC-
(hexyl)(Me)O) (15.0 µmol, 90% NMR yield). Complex 2 was not
observed at any time during this reaction. Treatment of the final reaction
mixture with water produced the enone as one of the many decomposi-
tion products. 1H NMR (C6D6, 300 MHz): 9.21 (s, 8H, â-H), 8.41 (d,
4H, 3JH-H ) 7 Hz, meso-C6H4CH3), 7.91 (d, 4H, 3JH-H ) 7 Hz, meso-
(TTP)Hf(NHAriPr)[OC(tBu)(dCH2)], 3a. The formation of complex
3a was observed in an NMR tube experiment. An NMR tube equipped
with a Teflon stopcock was charged with (TTP)HfdNAriPr (11.7 mg,
11.5 µmol), Ph3CH (91.0 µL, 0.1439 M in C6D6, 13.0 µmol), pinacolone
(6.7 µL, 53.6 µmol), and C6D6 (ca. 0.6 mL). Complex 3a (11.5 µmol,
100% NMR yield) was formed after 17 h at 25 °C. Complex 3 (11.4
µmol, 99% NMR yield) was formed after heating this solution for 25
3
C6H4CH3), 7.37 (d, 4H, JH-H ) 8 Hz, meso-C6H4CH3), 7.24 (d, 4H,
1
h at 85 °C. H NMR (C6D6, 400 MHz): 9.20 (s, 8H, â-H), 8.55 (d,
3JH-H ) 8 Hz, meso-C6H4CH3), 2.84 (s, 1H, OC(tBu)CHC(hexyl)-
(Me)O), 2.40 (s, 12H, meso-C6H4CH3), 1.2-0.6 (m, OC(tBu)CHC-
(hexyl)(Me)O, obscured by H2NAriPr, pinacolone, and 2-octanone), 0.05
(s, 9H, OC(tBu)CHC(hexyl)(Me)O), -0.29 (m, 2H, OC(tBu)CHC-
(CH2(CH2)4CH3)(Me)O), -0.72 (s, 3H, OC(tBu)CHC(hexyl)(Me)O.
GC/MS (2,2,5-trimethyl-4-undecen-3-one, C14H26O), m/z, calcd
(found): [M+] 210.36 (211).
4H, 3JH-H ) 7 Hz, meso-C6H4CH3), 7.85 (d, 4H, 3JH-H ) 7 Hz, meso-
3
C6H4CH3), 7.33 (d, 4H, JH-H ) 8 Hz, meso-C6H4CH3), 7.23 (d, 4H,
3JH-H ) 8 Hz, meso-C6H4CH3), 6.22 (m, 3H, m,p-NHAriPr), 2.91 (s,
1H, OC(dCH2)tBu), 2.40 (s, 12H, meso-C6H4CH3), 1.18 (s, 1H, OC-
(dCH2)tBu), 0.88 (s, NHAriPr, obscured by pinacolone), 0.48 (d, 6H,
3
3JH-H ) 6.9 Hz, 2,6-(CH(CH3)2)2C6H4), 0.31 (d, 6H, JH-H ) 6.7 Hz,
Reaction of (TTP)Zr(η2-NAriPrC(dNtBu)O) with Pinacolone. An
NMR tube equipped with a Teflon stopcock was charged with (TTP)-
Zr(η2-NAriPrC(dNtBu)O) (13.1 mg, 12.68 µmol), Ph3CH (91.5 µL,
0.1455 M in C6D6, 13.3 µmol), pinacolone (7.0 µL, 56.0 µmol), and
C6D6 (ca. 0.6 mL). Allowing the tube to stand at 20 °C for 15 h afforded
2 (11.5 µmol, 90% NMR yield) and AriPrNHC(O)NHtBu (9.2 µmol,
72% NMR yield). GC/MS (C17H28N2O), m/z, calcd (found): [M-]
2,6-(CH(CH3)2)2C6H4), -0.17 (m, 2H, 2,6-(CH(CH3)2)2C6H4), -0.50
(s, 9H, OC(dCH2)tBu).
(TTP)Hf[OC(tBu)CHC(tBu)(Me)O], 3. A solution of (TTP)Hfd
NAriPr (128 mg, 0.125 mmol) and pinacolone (90 µL, 0.72 mmol) in
toluene (ca. 10 mL) was stirred at 25 °C for 140 h. The reaction had
not reached completion at this time, and the mixture was subsequently
heated for 26 h at 80 °C. This dark blue solution was filtered, and the
filtrate was evaporated to dryness in vacuo and recrystallized from a
toluene solution layered with hexanes at -25 °C overnight to yield
blue 3 (79 mg, 61% yield). UV/vis (toluene): 548, 425. 1H NMR (C6D6,
1
276.42 (277). H NMR (C6D6, 300 MHz): 7.16 (m,p-C6H3, obscured
by H2NAriPr), 7.08 (d, 2H, m-C6H3, obscured by H2NAriPr), 4.02 (s,
1H, NH), 3.57 (m, 2H, -CHMe2), 1.23 (d, 12H, -CHMe2), 1.18 (s,
9H, NCMe3).
3
300 MHz): 9.23 (m, 8H, â-H), 8.47 (d, 4H, JH-H ) 7 Hz, meso-
3
Structure Determinations of (TTP)Zr[OC(tBu)CHC(tBu)(Me)O]
(2), [(TTP)ZrO]2 (4), and [(TTP)Zr]2(µ-O)(µ-OH)2 (5). Crystal data
can be found in Table 1. Compound 5 was treated by attachment to a
glass fiber and mounting on a Siemens SMART system for data
collection at 173(2) K. An initial set of cell constants was calculated
from reflections harvested from three sets of 20 frames. These initial
sets of frames were oriented such that orthogonal wedges of reciprocal
space were surveyed. This produced orientation matrices determined
from 154 reflections for compound 5. Final cell constants were
calculated from a set of 4170 strong reflections from the actual data
collection. Three major swaths of frames were collected with 0.30°
steps in ω. The space group was determined on the basis of systematic
absences and intensity statistics, and a successful direct-methods
solution was calculated which provided most non-hydrogen atoms from
the E-map. Several full-matrix least squares/difference Fourier cycles
were performed which located the remainder of non-hydrogen atoms.
These were refined with anisotropic displacement parameters. Atom
O1 was located on the crystallographic 2-fold axis and appeared to be
a hydroxo ligand based on a long metal-oxygen bond length. The
proton attached to O1 was assumed to be in an sp3 geometry and
disordered over the two possible, partially occupied sites. The other
two oxygens, bridging hydroxide (O3) and oxo (O2), were equally
disordered over the crystallographic 2-fold axis and were refined with
restrained metal-oxygen distances. All hydrogen atoms were placed
in ideal positions and refined as riding atoms with relative isotropic
displacement parameters. There were 1.5 solvent molecules of benzene
per asymmetric unit. SHELXTL DELU and SAME restraints were
employed here to keep reasonable C-C distances and approximate
rigid-body anisotropic displacement parameters. There were 48 restraints
used altogether. Three bad reflections were omitted from the final least-
squares refinement. All calculations were performed using SGI INDY
R4400-SC or Pentium computers using the SHELXTL V5.0 program
suite.9
C6H4CH3), 7.91 (d, 4H, JH-H ) 7 Hz, meso-C6H4CH3), 7.35 (d, 4H,
3
3JH-H ) 8 Hz, meso-C6H4CH3), 7.24 (d, 4H, JH-H ) 8 Hz, meso-
C6H4CH3), 2.92 (s, 1H, OC(tBu)CHC(tBu)(Me)O), 2.40 (s, 12H, meso-
C6H4CH3), 0.04 (s, 9H, OC(tBu)CHC(tBu)(Me)O), -0.43 (s, 9H,
OC(tBu)CHC(tBu)(Me)O), -0.72 (s, 3H, OC(tBu)CHC(tBu)(Me)O.
[(TTP)ZrO]2, 4. A solution of (TTP)ZrdNAriPr (214 mg, 0.228
mmol) and PhNO (28.2 mg, 0.263 mmol) in toluene (ca. 15 mL) was
stirred at 25 °C for 1.5 h. This dark blue solution was filtered, and the
filtrate was evaporated to dryness in vacuo to yield blue 4 (99 mg,
56% yield). UV/vis (toluene): 548 (4.38), 511 (4.51), 473 (4.40), 420
1
(5.56), 364 (4.41). H NMR (CDCl3, 300 MHz): 8.44 (s, 8H, â-H),
7.58 (m, 8H, meso-C6H4CH3), 7.40 (m, 8H, meso-C6H4CH3), 2.71 (s,
12H, meso-C6H4CH3). 13C NMR (CDCl3): 148.0, 139.3, 136.8, 135.7
(meso-C6H4CH3), 132.9 (meso-C6H4CH3), 130.6 (â-pyrrole), 127.0
(meso-C6H4CH3), 122.5, 21.5 (meso-C6H4CH3). GC/MS (AriPrNdNPh),
m/z, calcd (found): 266.39 (266). Anal. Calcd (found) for C96H72N8O2-
Zr2: C, 74.29 (74.38); H, 4.68 (5.29); N, 7.22 (6.60).
[(TTP)Zr]2(µ-O)(µ-OH)2, 5. A solution of 2 (129 mg, 0.135 mmol)
and acetone (150 µL, 2.04 mmol) in toluene (ca. 10 mL) was refluxed
for 36 h. This dark blue solution was filtered, and the solid was washed
with toluene (3 × 2 mL) to yield blue 5 (92 mg, 43% yield). UV/vis
1
(CH2Cl2): 541 (4.64), 416 (5.75). H NMR (CDCl3, 300 MHz): 8.41
(s, 16H, â-H), 7.62 (bd, meso-C6H4CH3), 7.46 (bd, meso-C6H4CH3),
7.41 (bd, meso-C6H4CH3), 2.71 (s, 24H, meso-C6H4CH3), -8.27 (s,
2H, µ-OH). 13C NMR (CDCl3): 148.1, 139.2, 136.8, 130.4 (â-pyrrole),
129.0 (meso-C6H4CH3), 128.2, 127.0, 125.3, 21.5 (meso-C6H4CH3).
Anal. Calcd (found) for C96H74N8O3Zr2: C, 73.44 (73.99); H, 4.75
(4.91); N, 7.14 (6.48).
Reaction of Complex 2a with p-Toluidine. Complex 2a was
generated in situ in an NMR tube equipped with a Teflon stopcock.
Within minutes of adding approximately 6 equiv of H2N-tolyl, all
NHAriPr in 2a had been replaced by NH-tolyl to form (TTP)Zr(NH-
1
tolyl)(OC(tBu)(dCH2)), 2b. H NMR (C6D6, 300 MHz): 9.14 (s, 8H,
â-H), 8.46 (d, 4H, meso-C6H4CH3), 7.85 (d, 4H, meso-C6H4CH3), 7.35
(d, 4H, meso-C6H4CH3), 7.22 (d, 4H, meso-C6H4CH3), 6.29 (d, m-tolyl,
obscured by H2N-tolyl), 4.20 (d, 2H, o-tolyl), 3.00 (s, 1H, OC(dCH2)t-
Bu), 2.39 (s, 12H, meso-C6H4CH3), 1.87 (s, 6H, p-MeC6H4) (OC(d
CH2)tBu and NHAriPr signals were not observed, obscured by pinacolone
Crystals of 2 and 4 were treated in an analogous manner to that of
5. Systematic absences in the diffraction data were uniquely consistent
(9) SHELXTL-Plus V5.0; Siemens Industrial Automation, Inc.: Madison,
WI, 1997.

2346 Inorganic Chemistry, Vol. 39, No. 11, 2000
Table 1. Crystal Data and Structure Refinements
Thorman et al.
(TTP)Zr(OC(tBu)CHC(tBu)(Me)O)
[(TTP)ZrO]2
C110H88N8O2Zr2
1736.32
173(2)
[(TTP)Zr]2(µ-O)(µ-OH)2
empirical formula
fw
C76.50H84N4O2Zr
1182.70
173(2)
C114H92N8O3Zr2
1804.40
173(2)
temp, K
wavelength, Å
crystal system
space group
Unit cell dimens
a, Å
b, Å
c, Å
0.710 73
monoclinic
Cc
0.710 73
monoclinic
C2/c
0.710 73
monoclinic
C2/c
21.8318(8)
20.7139(8)
15.7878(8)
112.624(1)
6590.2(5)
4
1.192
0.215
31.8540(16)
16.7937(8)
18.8770(9)
117.254(1)
8977.1(8)
4
1.285
0.289
3600
0.21 × 0.40 × 0.42
2.48-28.32
-42 e h e 37
0 e k e 22
0 e l e 25
53 684
32.0930(7)
16.8621(3)
19.0706(4)
118.930(1)
9032.3(3)
4
1.327
0.291
â, deg
V, Å3
Z
density (calcd), Mg/m3
abs coeff, mm-1
F(000)
2508
3744
crystal size, mm3
θ range, deg
index ranges
0.30 × 0.30 × 0.30
0.35 × 0.26 × 0.13
1.41-21.97
1.41-25.07
-22 e h e 22
0 e k e 21
-38 e h e 33
0 e k e 20
-16 e l e 16
20 673
0 e l e 22
22 019
7894 (Rint ) 0.0434)
SADABS (Sheldrick, 1996)
1.000 and 0.716
full-matrix least-squares on F2
7891/48/583
no. of reflns collected
no. of indep reflns
abs cor
max and min transm
refinement method
data/restraints/params
goodness-of-fit on F2
final R Indices [I > 2σ(I)]a
R indices (all data)a
largest diff peak and hole, e Å-3
7601 (Rint ) 0.0337)
empirical with SADABS
0.9383 and 0.9383
full-matrix least-squares on F2
7601/233/544
1.065
R1 ) 0.0691, wR2 ) 0.1909
R1 ) 0.0828, wR2 ) 0.2084
1.292 and -0.690
10 734 (Rint ) 0.0687)
SADABS
full-matrix least-squares on F2
10734/0/488
1.007
R1 ) 0.0461, wR2 ) 0.1068
R1 ) 0.0848, wR2 ) 0.1133
0.587 and -0.435
1.030
R1 ) 0.0553, wR2 ) 0.1348
R1 ) 0.0840, wR2 ) 0.1526
0.855 and -0.828
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) [∑w(Fo2 - Fc2)2/∑w(Fo )2]0.5; w ) 1/[σ2(Fo ) + (XP)2 + (YP)] where P ) (max(Fo , 0) + 2Fc2)/3 and X and
2
2
2
Y are adjusted for each refinement.
and para AriPr protons, indicated that the NAriPr moiety had been
for space groups denoted in Table 1. The structures were solved using
direct methods, completed by subsequent difference Fourier synthesis,
and refined by full-matrix least-squares procedures. For complex 2,
all porphyrin non-hydrogen atoms and zirconium were refined with
retained in the product. This chemical shift is close to the upfield
signals found for the corresponding aryl protons of the imido
complex, 1, at 6.08 ppm. Additionally, the new AriPr isopropyl
anisotropic displacement coefficients. All other non-hydrogen atoms
proton chemical shifts, 0.46 (d, 6H), 0.32 (d, 6H), -0.23 (m,
were refined isotropically. The enediolate ligand exhibited high thermal
2H) ppm, remain significantly upfield of those of the free amine
activity and was refined with an idealized geometry. The crystal was
[2.63 (spt, 2H), 1.14 (d, 12H) ppm] and only slightly downfield
refined as a twin with a 52:48 ratio contribution from the two
from those found for complex 1 [0.18 (m, 2H), 0.00 (d, 12H)
ppm]. The NH amido proton was observed at 0.95 ppm, similar
to the chemical shifts reported for (TTP)Hf(NHPh)(NHAriPr).7
Signals at 3.02 (s, 1H), 1.35 (s, 1H), and -0.50 (s, 9H) ppm
signify the presence of a single bound pinacolone fragment. The
large variation in chemical shifts for the two geminal protons
(vide infra) was unusual but must arise because of differences
in position relative to the porphyrin ring current.
components. There were three severely disordered solvent molecules
also present in the asymmetric unit, which were identified and accounted
for as a hexane, toluene, and a half toluene molecule using the
SQUEEZE option in the PLATON10 program. PLATON calculated the
upper limit of volume that can be occupied by the solvent to be 2028.3
Å3, or 30.8% of the unit volume. The program calculated 512 electrons,
which corresponds to four hexane and six toluene molecules, in the
unit cell for the diffuse species. A similar treatment was applied to
two severely disordered toluene molecules that were identified and
refined in the asymmetric unit of complex 4. PLATON calculated the
upper limit of volume that could be occupied by the solvent to be 2016.5
Å3, or 22.5% of the unit volume. The program calculated 812 electrons,
corresponding to eight toluene molecules, in the unit cell for the diffuse
species. Note that all derived data in the following tables were based
on known contents. No data are given for the diffusely scattering solvent
molecules.
Three possible limiting isomers for this product, consistent
with the 1H NMR data, are shown in Figure 1. Distinctive 13
C
NMR resonances attributed to the bound pinacolone fragment,
but not due to the tert-butyl group, are found at 83.3 and 170.7
ppm. A HETCOR experiment revealed that the protons resonat-
ing at 3.02 and 1.35 ppm were both bound to the same carbon
atom (83.3 ppm), precluding isomer I. The proton resonating
at 3.02 ppm displayed a through-space interaction with the tert-
butyl group (-0.50 ppm) in a NOESY experiment. Conse-
quently, this proton must be cis to the tert-butyl group. The
13C NMR data are incompatible with isomer II because the peak
Results
Pinacolone Coupling Mediated by (TTP)ZrdNAriPr, 1.
Upon treatment of (TTP)ZrdNAriPr, 1, with 1 equiv of pina-
colone, a new species was observed within 5 min. Product
analysis was achieved by 1H NMR spectroscopy.11 The observa-
tion of a three-proton multiplet at 6.22 ppm, due to the meta
(11) The large ring current of the aromatic porphyrin macrocycle provides
a useful means for identifying metal-bound ligands through 1H NMR.
Upfield shifts of bound-ligand protons are commonly 1-4 ppm from
those of the free ligand. The ring current effects on the 13C nuclei of
metal-bound ligands of metalloporphyrin complexes are shifted to a
smaller degree, which allows comparison of these resonances to those
found in spectra of nonporphyrin metal analogues.
(10) All software and sources of the scattering factors are contained in the
SHELXTL V5.10 program library: G. Sheldrick, Siemens-AXS,
Madison, WI.

Zirconium and Hafnium Imido Complexes
Inorganic Chemistry, Vol. 39, No. 11, 2000 2347
bond coupling of the olefinic proton to only one carbon atom.
The chemical shifts of carbon 3 (160.0 ppm), carbon 4 (97.6
ppm), and carbon 5 (80.0 ppm) of the metallacycle backbone
were assigned by HETCOR and HMBC NMR experiments.
In addition to 2-D NMR results, support for the assignment
of the two tert-butyl groups in complex 2 was facilitated by
deuterium labeling. Treatment of the imido complex 1 with 1
equiv of pinacolone followed by excess pinacolone-d12 produced
complex 2 with a 9-proton singlet in the 1H NMR spectrum at
0.04 ppm. Conversely, treatment of complex 1 with 1 equiv of
pinacolone-d12 and then with excess pinacolone-d0 produced
enediolate complex 2 with a 9-proton singlet at -0.46 ppm and
a 3-proton singlet at -0.69 ppm. These experiments also
revealed that the source of the protons transferred to the imido
group was the methyl group of the first pinacolone consumed.
On the basis of the NMR structural analysis, the reaction
sequence for pinacolone condensation with complex 1 is shown
in eqs 1 and 2.
Figure 1. Possible isomers from the addition reaction between complex
1 and pinacolone.
Figure 2. Possible isomers of coupled-pinacolone derivatives consistent
1
with H NMR data.
at 83.3 ppm is too far downfield for a C-bound enolate.12
A
metallocene enolate complex, Cp*2Zr(OH)[η1-OC(dCH2)(tBu)],
possesses similar 13C NMR chemical shifts at 84.1 [OC(tBu)d
CH2] and 172.8 ppm [OC(dCH2)(tBu)].2 The NMR data for
the addition product are most consistent with an O-bound
enolate, isomer III. The enolato complex (TTP)Zr(NHAriPr)-
[OC(dCH2)(tBu)], 2a, could not be isolated in pure form
because of decomposition to intractable products during puri-
fication attempts.
Treatment of complex 2a with 1 equivalent of pinacolone
resulted in the elimination of H2NAriPr and formation of a
metalloporphyrin product, 2, containing two pinacolone frag-
1
ments. The H NMR integrations of the double-condensation
product were consistent with the overall loss of two hydrogens
from the two pinacolone molecules. A singlet at 3.00 ppm was
assigned to an olefinic proton that had been shifted upfield by
Complex 2 could also be synthesized by alternate routes.
Formation of the enediolate compound 2 occurred on treatment
of the ureato complex (TTP)Zr(η2-NAriPrC(dNtBu)O) with
excess pinacolone. The urea, NHAriPrC(dO)NHtBu, was a
byproduct of this process. Treatment of (TTP)ZrCl2 with excess
pinacolone in the presence of piperidine also resulted in the
formation of complex 2. Although this was a more direct
synthetic approach, it yielded impure product. A one-pot
synthesis that involved adding excess pinacolone to in situ
generated complex 1 produced complex 2 in a yield and purity
comparable to those found for the reaction with isolated imido
complex 1. Whereas the formation of complex 2 from enolate
species 2a required hours to reach completion, treatment of
complex 2b (the less bulky tolylamido analogue of 2a) with
pinacolone resulted in the rapid formation of the enediolate
compound.
t
the porphyrin ring current. Two Bu groups were observed as
singlets at 0.04 (9H) and -0.46 (9H) ppm, and a methyl singlet
appeared at -0.69 (3H) ppm. When a toluene-d8 solution of
complex 2 was cooled, broadening of the tert-butyl singlet at
-0.46 ppm was observed in the 1H NMR. At 234 K, this singlet
had nearly broadened into the baseline while the geminal methyl
signal (-0.69 ppm) remained sharp.13 An unusual feature of
complex 2 is the â-pyrrole proton resonance. This signal appears
3
as an AB quartet (9.21 ppm, JH-H ) 4.6 Hz, δν ) 4.8 Hz)
due to a stereogenic center in the product ligand. Two isomers
1
that are consistent with the 1-D H NMR data for the two
coupled pinacolone molecules are shown in Figure 2.
The position of the olefinic proton was established by a
NOESY experiment which showed through-space interactions
of this hydrogen with both tert-butyl groups and the methyl
group. Furthermore, the methyl group, which resonates at -0.69
ppm, was also close, spatially, to the tert-butyl unit with the
signal at -0.46 ppm. Isomer IV was consistent with the NOESY
experiment, while isomer V would exhibit an NOE interaction
of the olefinic proton with only one tBu group. The connectivity
of the hydrocarbon backbone was definitively established by a
HMBC experiment that showed two-bond coupling interactions
between the olefinic proton and both carbon 3 and carbon 5
(see Figure 2 for numbering). Isomer V would contain a two-
The preceding investigation also employed hafnium in place
of zirconium. Due to similarities of the two series of compounds,
1
only the latter was addressed. The largest difference in the H
NMR data of the amido/enolato congeners was found for the
methylene resonances. The geminal CH2 resonances for 3a
(2.91, 1.18 ppm) were slightly upfield of those for 2a (3.02,
1.35 ppm). Similarly, the olefinic resonance in the enediolate
complex was upfield for the hafnium derivative (2.92 ppm)
relative to that for the zirconium complex (3.00 ppm). Reaction
times were observed to be somewhat longer for the heavier
congener, as observed previously for other Hf and Zr metal-
loporphyrin complexes.7 Under identical reaction conditions,
treatment of the respective imido complex, (TTP)MdNAriPr (M
) Zr, Hf), with excess pinacolone produced the amide/enolate
complex within minutes for zirconium and 1 h for hafnium.
(12) (a) Stack, J. G.; Doney, J. J.; Bergman, R. G.; Heathcock, C. H.
Organometallics 1990, 9, 453 and references therein. (b) Wanat, R.
A.; Collum, D. B. Organometallics 1986, 5, 120.
(13) Conformational changes of the six-membered ring may serve as a
possible source of disorder in the metallacycle as observed in the X-ray
structure analysis.

2348 Inorganic Chemistry, Vol. 39, No. 11, 2000
Thorman et al.
Table 2. Selected Bond Distances (Å) For Complexes 2, 4, and 5
Formation of Oxygen-Bridged Dimers 4 and 5. The bis-
(µ-oxo) complex [(TTP)ZrO]2, 4, was initially observed in the
thermal decomposition of the N,O-bound ureato complexes
(TTP)Zr[η2-NAriPrC(dNtBu)O] and (TTP)Zr[η2-NtBuC(dNAriPr)-
O].7,14 A more facile route to complex 4 was found from the
metathesis reaction between complex 1 and PhNO (eq 3). The
2
4
5
Zr-O1 1.963(6)
Zr-O2 1.945(7)
Zr1-O1 1.9719(16) Zr1-O1 2.166(3)
Zr1-O2 1.9791(16) Zr1-O2 1.988(4)
Zr1-O3 2.171(5)
Zr-N1 2.254(8)
Zr1-N1 2.246(2)
Zr1-N1 2.291(3)
Zr1-N2 2.279(3)
Zr1-N3 2.266(3)
Zr1-N4 2.286(3)
1.04
Zr-N2 2.290(10) Zr1-N2 2.280(2)
Zr-N3 2.177(9)
Zr-N4 2.295(9)
Zr1-N3 2.241(2)
Zr1-N4 2.280(2)
0.97
a
Zr-N4 0.98
a Zr displacement from N4 plane.
with the results of spectroscopic experiments. A representation
of complex 2 is given in Figure 3. The Zr-O bond distances
of 1.963(6) [Zr-O1] and 1.945(7) Å [Zr-O2] compare well
with those in alkoxido compounds16 but are considerably shorter
than the single bonds observed in the four-atom metallacycles
(TTP)Zr(η2-NAriPrC(dNtBu)O) [2.0677(12) Å] and (TTP)Zr-
(η2-NtBuC(dNAriPr)O) [2.066(3) Å].7 Atom O1 eclipses the Zr-
N2 bond within 2.0°, while atom O2 is staggered in relation to
the Zr-N3 and Zr-N4 bonds by 62.5 and 26.5°, respectively.
The Zr-N2 [2.290(10) Å] and Zr-N4 [2.295(9) Å] bonds are
long compared to Zr-N3 [2.177(9) Å] and Zr-N1 [2.254(8)
Å] distances. These differences are likely due to contributions
from nitrogen-oxygen repulsions [N2-O1 ) 2.717(2) Å; N4-
O2 ) 2.721(2) Å].17
Compound 4 (Figure 4) results from the formal dimerization
of two (TTP)ZrdO units. The metal-oxygen bond distances,
1.9719(16) and 1.9791(16) Å [Zr1-O1 and Zr1-O2], are
elongated compared to those of known oxo-bridged analogues
but still suggest the presence of multiple bonding.18 The oxygen
atoms in complex 4 are staggered with respect to the Zr-Npyrrole
bonds. The O2-Zr1-Zr1A-N4A torsion angle is 33.8° and
that of O2-Zr1-Zr1A-N3A is 57.3°. The positions of the
bridging oxygen atoms lying closer to the N2 and N4 atoms
may explain the variation in the Zr-Npyrrole bond distances
dimer was formed in moderate yield along with the diazene
PhNdNAriPr. The 1H NMR spectrum of the bis(µ-oxo) species
exhibited signals typical of zirconium metalloporphyrin com-
plexes. The exception was an upfield shift of the â-pyrrole signal
to 8.44 ppm due to the face-to-face orientation of the two
porphyrin rings. The â-pyrrole signal remained as a singlet at
223 K in CDCl3, indicating fast rotation of the porphyrin rings
relative to one another. Complex 4 readily undergoes hydrolysis
upon exposure to water to produce the (µ-oxo)bis(µ-hydroxo)
dimer, complex 5 (eq 4). The most facile preparation of
compound 5 was found from heating a toluene solution of
complex 2 in the presence of excess acetone. The hydroxyl
protons at -8.27 ppm (s, 2H) were found to be upfield of those
reported for the tetraphenylporphyrin analogue (-6.73 ppm, s,
2H).15b
(16) Pertinent complexes with Zr-O bonds (Zr-O bond distance (Å); Zr-
O-Zr bond angle (deg)) are as follows. (a) Cp2Zr(OC(Me)2C(TMS)C-
(TMS)] (1.936(2)): Rosenthal, U.; Ohff, A.; Baumann, W.; Tillack,
A.; Gorls, H.; Burlakov, V. V.; Shur, V. B. J. Organomet. Chem.
1994, 484, 203. (b) Cp*2Zr(OCH2CH2CH2) (2.008(13)): Mashima,
K.; Yamakawa, M.; Takaya, H. J. Chem. Soc., Dalton Trans. 1991,
2851. (c) (Me4taen)Zr(OtBu)2 (1.947 average): Black, D. G.; Jordan,
R. F.; Rogers, R. D. Inorg. Chem. 1997, 36, 103. (d) Cp2Zr(OPh)2
(2.008(14) average): Howard, W. A.; Trnka, T. M.; Parkin, G. Inorg.
Chem. 1995, 34, 5900. (e) (OEP)Zr(OtBu)2 (1.948 average): ref 14b.
(f) Cp*2Zr(OH)(OC(tBu)(CH2)) (2.001(6) for OH, 2.006(5) for eno-
late): ref 2. (g) Cp*2Zr(OH)(OC(Ph)(CH2)) (2.010(2) for OH, 1.993-
(2) for enolate): Howard, W. A.; Parkin, G. J. Am. Chem. Soc. 1994,
116, 606. (h) Cp′2Zr(O)(py) (1.804(4)): Howard, W. A.; Waters, M.;
Parkin, G. J. Am. Chem. Soc. 1993, 115, 4917. (i) [Cp2ZrO]3 (1.959-
(3), 142.5(2)): Fachinetti, G.; Floriani, C.; Chiesi-Villa, A.; Guastini,
C. J. Am. Chem. Soc. 1979, 101, 1767. (j) [Cp2ZrMe]2O (1.948(1),
174.1): Hunter, W. E.; Hrncir, D. C.; Vann Bynum, R.; Penttila, R.
A.; Atwood, J. L. Organometallics 1983, 2, 750. (k) [Cp2ZrCl]2O
(1.94(5), 168.9(8)): Clarke, J. F.; Drew, M. G. B. Acta Crystallogr.
B 1974, 30, 2267. (l) [((TMS)2N)2ZrMe]2O (1.950, 180.0): Planalp,
R. P.; Andersen, R. A. J. Am. Chem. Soc. 1983, 105, 7774. (m) [Cp2-
Zr(C(TMS)CH(TMS))]2O (1.973(1)): Rosenthal, U.; Ohff, A.; Micha-
lik, M.; Gorls, H.; Burlakov, V. V.; Shur, V. B. Organometallics 1993,
12, 5016. (n) [Cp2Zr(triflate)]2O (1.946(1), 175.6(5)): Calderazzo, F.;
Englert, U.; Pampaloni, G.; Tripepi, G. J. Organomet. Chem. 1998,
555, 49. (o) [Cp2Zr(SPh)]2O (1.968(3), 165.8(2)): Petersen, J. L. J.
Organomet. Chem. 1979, 166, 179. (p) [Cp2Zr(NCO)]2O (1.946(3),
165.7(2)): Klouras, N.; Tzavellas, N.; Raptopoulou, C. P. Z. Anorg.
Allg. Chem. 1997, 623, 1027.
Crystal Structures of (TTP)Zr(OC(tBu)CHC(tBu)(Me)O)
(2), [(TTP)ZrO]2 (4), and [(TTP)Zr]2(µ-O)(µ-OH)2 (5). The
crystallographic data for complexes 2, 4, and 5 are presented
in Table 1, and selected metrical parameters are collected in
Tables 2 and 3. All of the molecules exhibit typical out-of-
plane displacements of the zirconium from the mean 4-Npyrrole
plane for six- and seven-coordinate metals. In the case of
complex 2, acquisition of high-quality crystals was not possible,
despite numerous recrystallizations. These difficulties were
attributed to the solvent-dependent nature of the crystals and
volatile solvent molecules packed in the voids of the lattice.
While extensive disorder in the enediolate ligand precluded
anisotropic refinement of the carbon backbone, the oxygen atom
identities were unequivocally established and were consistent
(14) (a) The bis(µ-oxo) complex was reported previously, but no details
on characterization were provided: Sewchok, M. G.; Haushalter, R.
C.; Merola, J. S. Inorg. Chim. Acta 1988, 144, 47. (b) The unisolated
octaethylporphyrin analogue of complex 4 has been characterized by
1H NMR: Brand, H.; Arnold, J. Organometallics 1993, 12, 3655.
(15) (a) Huhmann, J. L.; Corey, J. Y.; Rath, N. P.; Campana, C. F. J.
Organomet. Chem. 1996, 513, 17. (b) Kim, H. J.; Whang, D.; Do, Y.;
Kim, K. Chem. Lett. 1993, 807. (c) Kim, H.; Whang, D.; Kim, K.;
Do, Y. Inorg. Chem. 1993, 32, 360. (d) Ryu, S.; Whang, D.; Kim, J.;
Yeo, W.; Kim, K. J. Chem. Soc., Dalton Trans. 1993, 205. (e) Ryu,
S.; Kim, J.; Yeo, H.; Kim, K. Inorg. Chim. Acta 1995, 228, 233.
(17) van der Waals radii: O (1.52 Å), N (1.55 Å); Porterfield, W. W.
Inorganic Chemistry; 2nd ed.; Academic Press: San Deigo, CA, 1998;
p 214.
(18) Covalent radii estimates (Å): (a) O ) 0.66; Jolly, W. L. Modern
Inorganic Chemistry; McGraw-Hill: New York, 1984; p 52. (b) Zr
) 1.48, O ) 0.73; ref 17.

Zirconium and Hafnium Imido Complexes
Inorganic Chemistry, Vol. 39, No. 11, 2000 2349
Table 3. Selected Bond Angles (deg) for Complexes 2, 4, and 5
2
4
5
O1-Zr-O2
76.9(3)
O1-Zr1-O2
Zr-O-Zr
78.56(8)
O1-Zr1-O2
O1-Zr1-O3
O2-Zr1-O3
Zr-O1-Zr
76.1(2)
66.6(2)
74.0(2)
89.91(14)
100.6(3)
89.7(2)
125.83(11)
125.60(11)
101.64(12) av
Zr-O2-Zr
Zr-O3-Zr
N1-Zr1-N3
N2-Zr1-N4
N1-Zr-N3
N2-Zr-N4
131.97(18)
124.85(19)
N1-Zr1-N3
N2-Zr1-N4
130.35(8)
127.86(7)
Figure 3. Ball and stick representation of complex 2, (TTP)Zr[OC-
(tBu)CHC(tBu)(Me)O].
resulting from O-N interactions. The Zr1-Zr1A (3.0584(5)
Å) and the O-O distances (2.5014 Å) are similar to those of
previously described bridging zirconium porphyrin complexes.15a,b
Three common distortions from planarity of the porphyrin
macrocycle were observed in complex 4.19 The doming effect
was readily perceived in the deviations of the four pyrrole
nitrogens from the 24-atom porphyrin plane [11 (N1), 7 (N2),
17 (N3), and 9 (N4) pm]. The meso carbon atoms alternate
above and below the mean 24-atom plane [15 (C5), -12 (C10),
16 (C15), and -12 (C20) pm] in a ruffling deformation.
Although the saddle deformation of the porphyrin ring is
perturbed by the presence of the other two distortions, it is
observed in the deviations of the â-pyrrole atoms above and
below the core porphyrin plane [-24 (C2), -15 (C3), 10 (C7),
1 (C8), -29 (C12), -19 (C13), 8 (C17), 2 (C18) pm].
The samples of [(TTP)Zr]2(µ-O)(µ-OH)2, 5, produced in this
work are closely related to the previously described tetraphe-
nylporphyrin derivatives [(TPP)Zr(µ-OH)2]215a and [(TPP)Zr]2-
(µ-O)(µ-OH)2.15b However, the OH proton resonance in complex
5 (-8.27 ppm) was significantly shifted from those of the
tetrahydroxy- (-6.79 ppm) and the tetraphenylporphyrin dihy-
droxy analogues (-6.73 ppm). Consequently, compound 5 was
examined in a single-crystal X-ray diffraction study. The
zirconium coordination environment and metrical parameters
are unremarkable from those previously described by Kim and
co-workers for [(TPP)Zr]2(µ-O)(µ-OH)2. However, the presence
of staggered porphyrin rings in complex 5 (Figure 5) is in
marked contrast to the other structurally characterized oxygen-
bridged Zr and Hf metalloporphyrin species.15 The most acute
torsion angle present in complex 5 involving a Zr-Npyrrole bond
is 22.2° (N3-Zr1-Zr1A-N2A), whereas the corresponding
angle in the TPP species is only 7.8°. The intramolecular
Figure 4. Molecular structure of [(TTP)ZrO]2 (4). Thermal ellipsoids
are drawn at the 30% probability level: (a) side view; (b) top view.
distance between the two 20-carbon atom mean planes of the
porphyrins is equivalent for complexes 4 and 5 [5.3(2) Å].
Discussion
Coupling of Pinacolone by (TTP)MdNAriPr (M ) Zr, Hf).
The reactivity of the nitrene group in terminal zirconium and
hafnium imido complexes has been documented in a number
of studies.7,20 A comparable example of a ZrdX moiety reacting
with a ketone occurs with Cp*2Zr(dO)(py) and acetophenone,
(20) (a) Walsh, P. J.; Hollander, F. J.; Bergman, R. G. J. Am. Chem. Soc.
1988, 110, 8729. (b) Cummins, C. C.; Baxter, S. M.; Wolczanski, P.
T. J. Am. Chem. Soc. 1988, 110, 8731. (c) Walsh, P. J.; Hollander, F.
J.; Bergman, R. G. Organometallics 1993, 12, 3705. (d) Blake, A. J.;
Mountford, P.; Nikonov, G. I.; Swallow, D. J. Chem. Soc., Chem.
Commun. 1996, 1835.
(19) Jentzen, W.; Simpson, M. C.; Hobbs, J. D.; Song, X.; Ema, T.; Nelson,
N. Y.; Medforth, C. J.; Smith, K. M.; Veyrat, M.; Mazzanti, M.;
Ramasseul, R.; Marchon, J.-C.; Takeuchi, T.; Goddard, W. A., III.;
Shelnutt, J. A. J. Am. Chem. Soc. 1995, 117, 11085.

2350 Inorganic Chemistry, Vol. 39, No. 11, 2000
Thorman et al.
with aldehydes or ketones generally results in the formation of
η1- or η2-bound â-hydroxy ketone complexes.22 However, as
shown in Scheme 2, deprotonation of the η2-hydroxy ketone
complex by the strong base NHAr- results in the formation of
a unique chelated enediolate product.23
Intractable mixtures were obtained from the addition of
acetone to 1 or 2a. However, the reaction between (TTP)Zr-
(NHAriPr)[OC(dCH2)(tBu)], 2a, and 2-octanone resulted in a
new enediolate complex, (TTP)Zr[OC(tBu)CHC(hexyl)(Me)O].
Thus, this synthetic methodology may be extended to other
ketones.
Bridging Oxo Complexes. An atom transfer route for the
preparation of terminal oxo species of titanium porphyrin
complexes was extended to Zr for the production of complex
4.24 Thus, the metathesis reaction between (TTP)ZrdNAriPr and
nitrosobenzene cleanly produced the µ-oxo dimer 4. The
postulated transient monomeric oxo species (TTP)ZrdO could
not be trapped in the presence of excess THF or pyridine.
t
Compound 4 is unreactive toward BuNCO, ketones, amines,
and alcohols, including phenol. This lack of reactivity appears
to be based, in part, on steric factors, since compound 4 is
quickly hydrolyzed to compound 5. Further reactivity of
complex 5 was not observed in the presence of phenol, tert-
butylamine, aniline, or ZnEt2. A comparison of the structurally
characterized oxygen-bridged complexes [(TPP)Hf]2(µ-OH)2-
(µ-O),15e [(TPP)Zr]2(µ-OH)2(µ-O),15b and {[(OEP)Zr]2(µ-OH)3}-
(7,8-C2B9H12)15b shows near-eclipsing of an M-O bond with
an M-N bond and the presence of eclipsed porphyrin rings.
This has been attributed to pπ-dπ orbital interaction between
the oxygen and the metal. Complex 5 does not possess eclipsed
porphyrin rings. As the intramolecular steric properties of
tetraphenylporphyrin are expected to be equivalent to those of
tetratolylporphyrin, dπ-pπ interactions between the Zr and O
atoms in complexes 4 and 5 are not readily apparent.25
Figure 5. Top view of complex 5, [(TTP)Zr]2(µ-O)(µ-OH)2. Thermal
ellipsoids are drawn at the 50% probability level.
Scheme 1
It is interesting to note the structure of the only other known
six-coordinate zirconium metalloporphyrin complex containing
two O-bound ligands, (OEP)Zr(OtBu)2.14b First, the O-Zr-O
angle of 90.08(9)° is rather large for this class of molecules.26
Second, the zirconium out-of-plane distance of 1.06 Å is the
largest value reported for six-coordinate zirconium metallopor-
phyrin complexes. Although these features were attributed
primarily to the steric bulk of the OtBu ligands, Zr-O π-bonding
would most likely be enhanced by such an arrangement.27
Zirconium lies further toward the porphyrin plane and contains
an O1-Zr1-O2 angle of 78.56(8)° in complex 4. The presence
of dπ-pπ interactions is expected in complex 4, albeit
somewhat diminished, as evident in the metrical parameters
described above.
Scheme 2
producing the hydroxo/enolato derivative.16g An amido/O-bound
enolato species, 2a, was found upon treatment of the imido
complex 1 with 1 equiv of pinacolone. This enolate complex,
2a, was inert in the presence of PhCtCH, acetophenone,
(TMS)Cl, or MeI at 80 °C in C6D6. The zirconium coordination
sphere in 2a appears to be sterically congested, as indicated by
two observations. First, the ortho isopropyl groups of the NAriPr
moiety are diastereotopic as a result of hindered rotation around
the N-Cipso bond. Second, the bulky H2NAriPr group is readily
ejected on treatment with H2N-tolyl to form (TTP)Zr(NH-tolyl)-
[OC(dCH2)(tBu)], 2b. As expected, the reduced steric conges-
tion of the tolyl amido/enolate species, 2b, facilitates the
formation of complex 2 in a substantially shorter time period
(Scheme 1). The formation of complex 2 presumably involves
a variation of the generally accepted aldol reaction mechanism
(Scheme 2).21 The reaction of transition metal enolate complexes
Conclusion
New examples of the novel reactivity possessed by zirconium
and hafnium imido metalloporphyrin complexes have been
demonstrated. These complexes mediate the stepwise coupling
(22) (a) Veya, P.; Cozzi, P. G.; Floriani, C.; Rotzinger, F. P.; Chiesi-Villa,
A.; Rizzoli, C. Organometallics 1995, 14, 4101. (b) Veya, P.; Floriani,
C.; Chiesi-Villa, A.; Rizzoli, C. Organometallics 1994, 13, 208.
(23) Aldol condensation reactions utilizing zirconium enolates have been
well studied: Cozzi, P. G.; Veya, P.; Floriani, C.; Rotzinger, F. P.;
Chiesi-Villa, A.; Rizzoli, C. Organometallics 1995, 14, 4092 and
references therein.
(24) Thorman, J. L.; Woo, L. K. Inorg. Chem. 2000, 39, 1301.
(25) Bottomley, F.; Sutin, L. AdV. Organomet. Chem. 1988, 28, 339.
(26) Brand, H.; Arnold, J. Coord. Chem. ReV. 1995, 140, 137.
(27) Tatsumi, K.; Hoffmann, R. J. Am. Chem. Soc. 1981, 103, 3328.
(21) Yamago, S.; Machii, D.; Nakamura, E. J. Org. Chem. 1991, 56, 2098.

Zirconium and Hafnium Imido Complexes
Inorganic Chemistry, Vol. 39, No. 11, 2000 2351
of pinacolone in the formation of an enediolate compound.
Mixed-ketone condensation products are also possible. More-
over, we have developed direct synthetic routes to zirconium
metalloporphyrin complexes containing bridging oxygen ligands.
(TTP)ZrdNAriPr undergoes metathesis with nitrosobenzene to
produce the µ-oxo-bridged dimer, [(TTP)ZrO]2, 4. The bis(µ-
hydroxo)(µ-oxo) dimer [(TTP)Zr]2(µ-OH)2(µ-O), 5, is a hy-
drolysis product of complex 4. Also of interest is the unique
structural characteristic of staggered porphyrin rings found for
complexes 4 and 5. This is in marked contrast to the eclipsed
conformers known for other Zr and Hf analogues.
Acknowledgment. We are grateful for financial support from
the Camille and Henry Dreyfus Foundation.
Supporting Information Available: X-ray crystallographic files
in CIF format, for 2, 4, and 5. This material is available free of charge
via the Internet at http://pubs.acs.org.
IC9910007