Synthesis, structure, and reactivity of zirconium and hafnium imido metalloporphyrins

Article abstract of DOI:10.1021/ic981399j

The zirconium and hafnium porphyrin imido complexes (TTP)M=NAr^iPr [TTP = meso-tetra-p-tolylporphyrinato dianion, M = Zr (1), Hf (2), Ar^iPr = 2,6-diisopropylphenyl] were synthesized from (TTP)MCl₂ and 2 equiv of LiNHAr^iPr. The zirconium imido complex, (TTP)Zr=NAr^iPr, was also obtained from the preformed imido complex Zr(NAr^iPr)Cl₂(THF)₂ and (TTP)Li₂(THF)₂. Treatment of (TTP)HfCl₂ with excess LiNH(p-MeC₆H₄) resulted in the formation of a bis(amido) complex, (TTP)Hf(NH-p-MeC₆H₄)₂ (3), instead of an imido complex. In the presence of excess aniline, 2 formed an equilibrium mixture of bis(amido) compounds, (TTP)Hf(NHPh)(NHAr^iPr) and (TTP)Hf(NHPh)₂. The nucleophilic character of the imido moiety is exhibited by its reaction with ₁BuNCO, producing isolable N,O-bound ureato metallacycles. The kinetic product obtained with zirconium, (TTP)Zr(η²-NAr^iPrC(=N^tBu)O) (4a), isomerized to (TTP)Zr(η²-N^tBuC(=NAr^iPr)O) (4b) in solution. Upon being heated to 80 °C, 4a produced the carbodiimide Ar^iPrN=C=N^tBu and a transient Zr(IV) oxo complex. The analogous hafnium complex (TTP)Hf(η²-NAr^iPrC(=N^tBu)O) (5a) did not eject the carbodiimide upon heating to 110 °C but isomerized to (TTP)Hf(η2-N^tBuC(=NAr^iPr)O) (5b). To support the formulation of 4a and 5a as N,O bound, the complex (TTP)Hf(η²-NAr^iPrC(=NAr^iPr)O) (6) was studied by variable-temperature NMR spectroscopy. The corresponding thio- and selenoureato metallacycles were not isolable in the reaction between 1 and 2 with ^tBuNCS and ^tBuNCSe. Concomitant formation of the metallacycle with decomposition to the carbodiimide, Ar^iPrN=C=N^tBu, reflects the lower C-Ch bond strength in the proposed N,Ch-bound metallacycles. Treatment of 2 with 1,3-diisopropylcarbodiimide resulted in the η²-guanidino complex (TTP)Hf(η²-NAr^iPrC(=NⁱPr)NⁱPr) (7a), which isomerized to the less sterically crowded isomer (TTP)Hf(η²-NⁱPrC(=NAr^iPr)NⁱPr) (7b). Complexes 1, 2, 4a, 4b, and 7a were characterized by X-ray crystallography. The monomeric terminal imido compounds, 1 and 2, are isomorphous: M-N_imido distances of 1.863(2) A? (Zr) and 1.859(2) A? (Hf); M-N_imido-C angles of 172.5(2)° (Zr) and 173.4(2)° (Hf). The structures of the ureato complexes 4a and 4b and the guanidino complex 7a exhibit typical alkoxido and amido bond distances (Zr-N = 2.1096(13) A? (4a), 2.137(3) A? (4b); Zr-O = 2.0677(12) A? (4a), 2.066(3) A? (4b); Hf-N = 2.087(2) A?, 2.151(2) A? (7a)).

Full text of DOI:10.1021/ic981399j

3814
Inorg. Chem. 1999, 38, 3814-3824
Synthesis, Structure, and Reactivity of Zirconium and Hafnium Imido Metalloporphyrins
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 December 7, 1998
The zirconium and hafnium porphyrin imido complexes (TTP)MdNAriPr [TTP ) meso-tetra-p-tolylporphyrinato
dianion, M ) Zr (1), Hf (2), AriPr ) 2,6-diisopropylphenyl] were synthesized from (TTP)MCl2 and 2 equiv of
LiNHAriPr. The zirconium imido complex, (TTP)ZrdNAriPr, was also obtained from the preformed imido complex
Zr(NAriPr)Cl2(THF)2 and (TTP)Li2(THF)2. Treatment of (TTP)HfCl2 with excess LiNH(p-MeC6H4) resulted in
the formation of a bis(amido) complex, (TTP)Hf(NH-p-MeC6H4)2 (3), instead of an imido complex. In the presence
of excess aniline, 2 formed an equilibrium mixture of bis(amido) compounds, (TTP)Hf(NHPh)(NHAriPr) and
t
(TTP)Hf(NHPh)2. The nucleophilic character of the imido moiety is exhibited by its reaction with BuNCO,
producing isolable N,O-bound ureato metallacycles. The kinetic product obtained with zirconium, (TTP)Zr(η2-
NAriPrC(dNtBu)O) (4a), isomerized to (TTP)Zr(η2-NtBuC(dNAriPr)O) (4b) in solution. Upon being heated to 80
°C, 4a produced the carbodiimide AriPrNdCdNtBu and a transient Zr(IV) oxo complex. The analogous hafnium
complex (TTP)Hf(η2-NAriPrC(dNtBu)O) (5a) did not eject the carbodiimide upon heating to 110 °C but isomerized
to (TTP)Hf(η2-NtBuC(dNAriPr)O) (5b). To support the formulation of 4a and 5a as N,O bound, the complex
(TTP)Hf(η2-NAriPrC(dNAriPr)O) (6) was studied by variable-temperature NMR spectroscopy. The corresponding
thio- and selenoureato metallacycles were not isolable in the reaction between 1 and 2 with tBuNCS and tBuNCSe.
Concomitant formation of the metallacycle with decomposition to the carbodiimide, AriPrNdCdNtBu, reflects
the lower C-Ch bond strength in the proposed N,Ch-bound metallacycles. Treatment of 2 with 1,3-
diisopropylcarbodiimide resulted in the η2-guanidino complex (TTP)Hf(η2-NAriPrC(dNiPr)NiPr) (7a), which
isomerized to the less sterically crowded isomer (TTP)Hf(η2-NiPrC(dNAriPr)NiPr) (7b). Complexes 1, 2, 4a, 4b,
and 7a were characterized by X-ray crystallography. The monomeric terminal imido compounds, 1 and 2, are
isomorphous: M-Nimido distances of 1.863(2) Å (Zr) and 1.859(2) Å (Hf); M-Nimido-C angles of 172.5(2)°
(Zr) and 173.4(2)° (Hf). The structures of the ureato complexes 4a and 4b and the guanidino complex 7a exhibit
typical alkoxido and amido bond distances (Zr-N ) 2.1096(13) Å (4a), 2.137(3) Å (4b); Zr-O ) 2.0677(12)
Å (4a), 2.066(3) Å (4b); Hf-N ) 2.087(2) Å, 2.151(2) Å (7a)).
Introduction
most studied of the group 4 compounds and have revealed novel
chemistry,11 including C-H bond activation,12 [2+2] cycload-
dition,9 and use in titanium nitride film deposition processes.13
The documented reactivity associated with the MdNR moiety
involving zirconium has been more varied. The nucleophilic
character of the imido nitrogen has been utilized in hydroami-
nation catalysis,14 dihydrogen activation,15 and the formation
of a wide variety of metallacycles with substrates ranging from
azidotrimethylsilane and benzaldehyde N-phenylimine8 to eth-
ylene.7 Alkynes, isocyanates, and isocyanides have produced
isolable [2+2] cycloaddition products as well (Scheme 1).1,7,9,16
Studies of hydroamination and hydrocarbon activation involving
The discovery of C-H bond activation by zirconium imido
complexes in 1988 prompted investigations of group 4 imido
complexes in a variety of supporting ligand environments.1,2
Cyclopentadienyl, bulky amido, tetraazaannulene, alkoxo, and
bis(amidophosphine) groups have been successfully employed
as ancillary ligands for isolable terminal Ti, Zr, and Hf imido
complexes.1-10 Titanium imido compounds rapidly became the
† Iowa State University.
‡ X-ray Crystallographic Laboratory, University of Minnesota.
(1) Walsh, P. J.; Hollander, F. J.; Bergman, R. G. J. Am. Chem. Soc.
1988, 110, 8729.
(2) Cummins, C. C.; Baxter, S. M.; Wolczanski, P. T. J. Am. Chem. Soc.
1988, 110, 8731.
(3) Profilet, R. D.; Zambrano, C. H.; Fanwick, P. E.; Nash, J. J.; Rothwell,
I. P. Inorg. Chem. 1990, 29, 4362.
(4) Bai, Y.; Roesky, H. W.; Noltemeyer, M.; Witt, M. Chem. Ber. 1992,
125, 825.
(5) Arney, D. J.; Bruck, M. A.; Huber, S. R.; Wigley, D. E. Inorg. Chem.
1992, 31, 3749.
(6) Zambrano, C. H.; Profilet, R. D.; Hill, J. E.; Fanwick, P. E.; Rothwell,
I. P. Polyhedron 1993, 12, 689.
(7) Walsh, P. J.; Hollander, F. J.; Bergman, R. G. Organometallics 1993,
12, 3705.
(10) Fryzuk, M. D.; Love, J. B.; Rettig, S. J. Organometallics 1998, 17,
846.
(11) (a) Wigley, D. E. Prog. Inorg. Chem. 1994, 42, 239. (b) Mountford,
P. J. Chem. Soc., Chem. Commun. 1997, 2127.
(12) Bennett, J. L.; Wolczanski, P. T. J. Am. Chem. Soc. 1994, 116, 2179
and references therein.
(13) Winter, C. H.; Lewkebandara, T. S.; Prosica, J. W.; Rheingold, A. L.
Inorg. Chem. 1994, 33, 1227.
(14) (a) Walsh, P. J.; Baranger, A. M.; Bergman, R. G. J. Am. Chem. Soc.
1992, 114, 1708. (b) Baranger, A. M.; Walsh, P. J.; Bergman, R. G.
J. Am. Chem. Soc. 1993, 115, 2753.
(8) Meyer, K. E.; Walsh, P. J.; Bergman, R. G. J. Am. Chem. Soc. 1995,
117, 974.
(9) Blake, A. J.; Mountford, P.; Nikonov, G. I.; Swallow, D. J. Chem.
Soc., Chem. Commun. 1996, 1835.
(15) Cummins, C. C.; Van Duyne, G. D.; Schaller, C. P.; Wolczanski, P.
T. Organometallics 1991, 10, 164.
(16) Meyer, K. E.; Walsh, P. J.; Bergman, R. G. J. Am. Chem. Soc. 1994,
116, 2669.
10.1021/ic981399j CCC: $18.00 © 1999 American Chemical Society
Published on Web 08/03/1999

Zirconium and Hafnium Imido Metalloporphyrins
Inorganic Chemistry, Vol. 38, No. 17, 1999 3815
Scheme 1
hafnium metalloporphyrin chemistry has been explored with a
wide variety of ligands, though all are limited to formal single
bonds between the metal and ligand.19 Herein we describe the
first isolation and reactivity of zirconium and hafnium metal-
loporphyrin imido complexes as well as the characterization of
N,O-bound ureato(2-) and guanidino(2-) derivatives.
Experimental Section
General Procedures. All manipulations were performed under an
inert atmosphere of nitrogen using a Vacuum Atmospheres glovebox
equipped with a model MO40-1 Dri-Train gas purifier. All solvents
were rigorously degassed and dried prior to use. Benzene-d6, toluene,
and hexane were freshly distilled from purple solutions of sodium
benzophenone and brought into the glovebox without exposure to air.
The dichloro complexes (TTP)ZrCl2 and (TTP)HfCl2 were prepared
according to published procedures21 but were recrystallized from CH2-
Cl2/hexane prior to use. Commercially purchased compounds, p-
toluidine, 2,6-diisopropylaniline, tBuNCO, and tBuNCS (Aldrich), were
dried over activated neutral alumina. The compounds Zr(AriPr)Cl2-
(THF)2,5 tBuNCSe,22 and LiNHAriPr 5 were prepared from literature
procedures. 1H NMR data were recorded at 20.0 °C, unless otherwise
stated, on either a Varian VXR (300 MHz) or a Bruker DRX (400
MHz) spectrometer. Chemical shifts were referenced to proton solvent
impurities (δ 7.15, C6D5H). UV-vis data were recorded on an
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.
Scheme 2
(TTP)ZrdNAriPr, 1. Method 1. To a toluene solution (ca. 20 mL)
of (TTP)ZrCl2 (353 mg, 0.424 mmol) at -25 °C was added a slurry of
LiNHAriPr (166 mg, 0.908 mmol) in toluene (ca. 6 mL). This solution
slowly darkened to a red color upon warming to 25 °C. After 2 h, the
solution was filtered over Celite. The filtrate was concentrated in vacuo
to a black oil. This residue was triturated with hexanes (ca. 12 mL),
the mixture was filtered, and the solid was dried in vacuo to afford
dark blue 1 (370 mg, 93% yield). Analytically pure crystalline samples
could be obtained by layering a toluene solution with hexanes (1:2
v/v), allowing the mixture to stand at -25 °C, filtering, and drying the
solid in vacuo. 1H NMR (C6D6, 300 MHz): δ 9.17 (s, 8H, â-H), 8.26
3
3
(d, 4H, JH-H ) 8 Hz, meso-C6H4CH3), 7.97 (d, 4H, JH-H ) 8 Hz,
3
meso-C6H4CH3), 7.28 (dd, 8H, JH-H ) 8 Hz, meso-C6H4CH3), 6.08
(s, 3H, m-, and p-C6H3), 2.42 (s, 12H, meso-C6H4CH3), 0.18 (m, 2H,
-CHMe2), 0.00 (d, 12H, JH-H ) 7 Hz, -CHMe2). 13C NMR (CD2-
3
Cl2, 400 MHz): δ 153.8, 144.3, 143.6, 142.8, 139.9, 138.9, 137.9, 133.8
(o-tolyl), 133.0 (o-tolyl), 132.6, 132.4 (â-pyrrole), 130.0, 129.4 (m-
tolyl), 124.3, 119.5 (m-AriPr), 115.0 (p-AriPr), 27.8 (-CHMe2), 26.1
(-CHMe2), 25.7 (p-MeC6H5). UV-vis (benzene): 544 (4.32), 439
(shoulder, 4.44), 420 (5.56), 398 (shoulder, 4.53). Anal. Calcd for
C60H53N5Zr: C, 77.05; H, 5.71; N, 7.49. Found: C, 76.66; H, 5.97; N,
7.02.
zirconium imido complexes illustrate the need for further
investigations utilizing different ancillary ligands.14,17
We recently explored the chemistry of tetravalent titanium
and tin metalloporphyrin complexes containing amido and imido
ligands (Scheme 2).18 The metals in the titanium and tin
hexacoordinate complexes reside in the plane of the porphyrin
and thus have the ancillary ligands situated in a trans config-
uration. In comparison, the larger congeners of group 4 have
the metal displaced substantially above the porphyrin by ∼1
Å. This generates a cis arrangement of unidentate substituents
which is slightly more sterically confined relative to that of
metallocene analogues.19 A similar coordination environment
is seen in the more flexible and less sterically demanding
tetramethyldibenzotetraaza[14]annulene (TMTAA) ligand. For
example, the imido complex of Zr(TMTAA) includes a bound
pyridine cis to the nitrene group.20 Monomeric zirconium and
Method 2. A round-bottom flask was charged with Zr(NAriPr)Cl2-
5
(THF)2 (172 mg, 0.357 mmol) and (TTP)Li2(THF)2 (119 mg, 0.173
mmol). Toluene (ca. 20 mL) was added, and the reaction mixture was
allowed to stir at ambient temperature for 18 h. The dark red solution
was filtered over Celite and the filtrate reduced to dryness in vacuo.
Recrystallization from toluene/hexanes at -25 °C afforded 1 (126 mg,
78% yield).
(TTP)HfdNAriPr, 2. To a rapidly stirred toluene solution (ca. 15
mL) of (TTP)HfCl2 (213 mg, 0.232 mmol) at -25 °C was added a
slurry of LiNHAriPr (90 mg, 0.489 mmol) in toluene (ca. 6 mL). The
solution became dark red upon warming to 25 °C over 2 h. The solution
was then filtered over Celite. The filtrate was concentrated in vacuo to
a black oil. This residue was triturated with hexanes (ca. 12 mL), the
mixture was filtered, and the solid was washed with hexanes (4 × 4
mL) and dried in vacuo to afford dark blue 2 (143 mg, 60% yield).
(17) Schaller, C. P.; Cummins, C. C.; Wolczanski, P. T. J. Am. Chem.
Soc. 1996, 118, 591.
(18) (a) Berreau, L. M.; Young, V. G., Jr.; Woo, L. K. Inorg. Chem. 1995,
34, 527. (b) Gray, S. D.; Thorman, J. L.; Berreau, L. M.; Woo, L. K.
Inorg. Chem. 1997, 36, 278. (c) Gray, S. D., Thorman, J. L.; Adamian,
V. A.; Kadish, K. M.; Woo, L. K. Inorg. Chem. 1998, 37, 1. (d) Chen,
J.; Woo, L. K. Inorg. Chem. 1998, 37, 3269.
(19) Brand, H.; Arnold, J. Coord. Chem. ReV. 1995, 140, 137.
(20) Blake, A. J.; McInnes, J. M.; Mountford, P.; Nikonov, G. I.; Swallow,
D.; Watkin, D. J. J. Chem. Soc., Dalton Trans. 1999, 379.
(21) (a) Kim, H.; Whang, D.; Kim, K.; Do, Y. Inorg. Chem. 1993, 32,
360. (b) Ryu, S.; Whang, D.; Kim, J.; Yeo, W.; Kim, K. J. Chem.
Soc., Dalton Trans. 1993, 205.
(22) Sonoda, N.; Yamamoto, G.; Tsutsum, S. Bull. Chem. Soc. Jpn. 1972,
45, 2937.

3816 Inorganic Chemistry, Vol. 38, No. 17, 1999
Thorman et al.
Crystals were grown analogously to 1. 1H NMR (C6D6, 300 MHz): δ
CH3), 7.86 (d, 4H, 3JH-H ) 7 Hz, meso-C6H4CH3), 7.29 (dd, 8H, 3JH-H
) 7 Hz, meso-C6H4CH3), 6.77 (t, 1H, p-C6H3), 6.62 (d, 2H, m-C6H3),
2.40 (s, 12H, meso-C6H4CH3), 0.84 (d, 6H, 3JH-H ) 7 Hz, -CHMe2),
0.43 (d, 6H, 3JH-H ) 7 Hz, -CHMe2), 0.34 (s, 9H, N-CMe3), -0.53
(m, 2H, -CHMe2). 13C NMR (C6D6, 400 MHz): δ 151.9, 149.7, 143.5,
140.4, 138.9, 138.0, 135.5 (o-tolyl), 133.6 (o-tolyl), 133.0 (â-pyrrole),
129-127 (solvent), 125.6, 123.5 (p-AriPr), 121.5 (m-AriPr), 50.3
(-CMe3), 30.4 (-CMe3), 26.9 (-CHMe2), 25.3 (-CHMe2), 24.4
(-CHMe2), 21.4 (p-MeC6H5). UV-vis (toluene): 549 (4.40), 416
(5.47). Anal. Calcd for C65H62N6OHf: C, 69.60; H, 5.57; N, 7.49.
Found: C, 69.20; H, 5.53; N, 7.30. Exposure to water resulted in rapid
decomposition to yield the urea AriPrNHC(O)NHtBu.
3
2
9.17 (s, 8H, â-H), 8.23 (dd, 4H, JH-H ) 8 Hz, JH-H ) 2 Hz, meso-
3
2
C6H4CH3), 7.97 (dd, 4H, JH-H ) 8 Hz, JH-H ) 2 Hz, meso-C6H4-
CH3), 7.31 (d, 4H, 3JH-H ) 8 Hz, meso-C6H4CH3), 7.25 (d, 4H, 3JH-H
) 8 Hz, meso-C6H4CH3), 6.16 (d, 2H, 3JH-H ) 8 Hz, m-C6H3), 6.04 (t,
3
1H, JH-H ) 8 Hz, p-C6H3), 2.41 (s, 12H, meso-C6H4CH3), 0.17 (m,
3
2H, -CHMe2), 0.00 (d, 12H, JH-H ) 7 Hz, -CHMe2). UV-vis
(benzene): 542 (4.52), 419 (5.67), 397 (shoulder, 4.80). Anal. Calcd
for C60H53N5Hf: C, 70.47; H, 5.22; N, 6.85. Found: C, 70.39; H, 5.25;
N, 6.54.
(TTP)Hf(NHC6H4-p-Me)2, 3. A slurry of (TTP)HfCl2 (253 mg,
0.275 mmol) and LiNH(p-MeC6H4) (68 mg, 0.60 mmol) in hexanes
(ca. 15 mL) was stirred for 10 h at 25 °C, at which time the dark red
suspension was filtered. The solid was transferred to a clean fritted
filter and washed through with CH2Cl2 (2 × 2 mL). The resulting
solution was taken to dryness to yield blue microcrystalline 3 (172
mg, 59% yield). 1H NMR (C6D6, 300 MHz): δ 9.17 (s, 8H, â-H), 8.24
(TTP)Hf(η2-NAriPrC(dNAriPr)O), 6. A solution of (TTP)HfdNAriPr
(291 mg, 0.284 mmol) and AriPrNCO (47 µL, 0.412 mmol) in toluene
(ca. 40 mL) was stirred for 10 h at 25 °C. The solution was filtered,
and the filtrate was reduced in volume (ca. 13 mL) in vacuo. The
concentrated solution was layered with hexanes (ca. 13 mL), and the
mixture was placed in a freezer at -25 °C overnight. This mixture
was filtered and the filtrate reduced to dryness in vacuo. The residue
was recrystallized from a toluene solution layered with hexanes at -25
°C overnight. Compound 6 was collected as a dark blue powder (81
mg, 25% yield). 1H NMR (C7D8, 400 MHz): δ 9.04 (s, 8H, â-H), 7.84
3
3
(d, 4H, JH-H ) 7 Hz, meso-C6H4CH3), 7.88 (d, 4H, JH-H ) 7 Hz,
3
meso-C6H4CH3), 7.28 (br, 8H, meso-C6H4CH3), 6.13 (d, 4H, JH-H
)
8 Hz, m-tolyl), 4.27 (d, 4H, 3JH-H ) 8 Hz, o-tolyl), 2.40 (s, 12H, meso-
C6H4CH3), 1.74 (s, 6H, p-MeC6H4), 0.96 (s, 2H, NH). UV-vis
(benzene): 544 (4.44), 418 (5.56), 398 (shoulder, 4.80).
(TTP)Zr(η2-NAriPrC(dNtBu)O), 4a. A solution of (TTP)ZrdNAriPr
3
3
(d, 4H, JH-H ) 7 Hz, meso-C6H4CH3), 7.79 (d, 4H, JH-H ) 7 Hz,
meso-C6H4CH3), 7.36 (d, 4H, 3JH-H ) 7 Hz, meso-C6H4CH3), 7.29 (d,
4H, JH-H ) 7 Hz, meso-C6H4CH3) 6.94 (t, 1H, p-C6H3), 6.84 (t, 1H,
t
(313 mg, 0.334 mmol) and BuNCO (250 µL, 2.19 mmol) in toluene
3
(ca. 15 mL) was stirred for 13 h and reduced to dryness in vacuo. The
residue was recrystallized from a toluene solution layered with heptane
at -25 °C for 1 day to yield microcrystalline dark blue 4a (112 mg,
32% yield). 1H NMR (C6D6, 300 MHz): δ 9.13 (s, 8H, â-H), 8.13 (d,
4H, 3JH-H ) 8 Hz, meso-C6H4CH3), 7.87 (d, 4H, 3JH-H ) 8 Hz, meso-
p-C6H3), 6.79 (d, 2H, m-C6H3), 6.61 (d, 2H, m-C6H3), 2.44 (s, 12H,
meso-C6H4CH3), 1.93 (m, 2H, -CHMe2), 0.62 (d, 6H, -CHMe2), 0.44
(d, 6H, -CHMe2), 0.33 (br s, 12H, -CHMe2), -0.07 (m, 2H,
-CHMe2). 13C NMR (C6D6, 400 MHz): δ 151.5, 149.6, 148.8, 144.1,
140.7, 138.7, 138.6, 138.1, 135.5, 132.9 (â-pyrrole), 132.7, 130-126
(solvent), 125.9, 123.9, 122.0, 121.7, 120.8, 26.9 (-CHMe2), 26.8
(-CHMe2), 26.5 (-CHMe2), 24.7 (-CHMe2), 23.8 (-CHMe2), 21.4
(p-MeC6H4). UV-vis (toluene): 549 (4.27), 415 (5.45). Anal. Calcd
for C73H70N6OHf: C, 71.52; H, 5.76; N, 6.86. Found: C, 69.20; H,
5.53; N, 7.30. This compound appeared pure by 1H NMR, but elemental
analyses were routinely low in carbon by 1% or more. Exposure to
water resulted in rapid decomposition to yield the urea AriPrNHC(O)-
NHAriPr.
3
C6H4CH3), 7.29 (dd, 8H, JH-H ) 8 Hz, meso-C6H4CH3), 6.79 (t, 1H,
3
3JH-H ) 8 Hz, p-C6H3), 6.60 (d, 2H, JH-H ) 8 Hz, m-C6H3), 2.40 (s,
12H, meso-C6H4CH3), 0.82 (d, 6H, 3JH-H ) 7 Hz, -CHMe2), 0.42 (d,
3
6H, JH-H ) 7 Hz, -CHMe2), 0.35 (s, 9H, NCMe3), -0.51 (m, 2H,
-CHMe2). 13C NMR (C6D6, 400 MHz): δ 152.5, 149.6, 142.7, 140.6,
139.0, 138.0, 135.5, 133.6, 132.8, 127-130 (C6D6), 125.6, 123.4, 121.6,
50.4, 30.4, 27.1, 25.2, 24.2, 21.4. UV-vis (toluene): 550 (4.65), 439
(shoulder, 4.94), 418 (5.73). Anal. Calcd for C65H62N6OZr: C, 75.47;
H, 6.04; N, 8.12. Found: C, 75.24; H, 6.14; N, 7.94. Exposure to water
resulted in rapid decomposition to yield the urea AriPrNHC(O)NHtBu,
as detected by GC/MS: m/z calcd (found) for C17H28N2O 276.42 (277).
1H NMR (C6D6, 300 MHz): δ 7.16 (m, 1H, p-C6H3), 7.08 (d, 2H,
m-C6H3), 4.02 (s, 1H, NH), 3.57 (m, 2H, -CHMe2), 1.23 (d, 12H,
-CHMe2), 1.18 (s, 9H, N-CMe3).
(TTP)Hf(η2-NAriPrC(dNiPr)NiPr), 7a. To a stirred solution of 2
(295 mg, 0.288 mmol) in toluene (ca. 12 mL) was added 1,3-
diisopropylcarbodiimide (69 µL, 0.441 mmol). The mixture was allowed
to stir at ambient temperature for 2 h. This dark red solution was filtered,
and the filtrate was reduced to dryness in vacuo. The residue was
washed with hexanes (2 × 6 mL) to afford dark blue 7a (147 mg,
44% yield). Crystals suitable for X-ray diffraction were obtained by
recrystallization from a toluene solution layered with hexanes at -25
(TTP)Zr(η2-NtBuC(dNAriPr)O), 4b. A solution of (TTP)ZrdNAriPr
(330 mg, 0.353 mmol) and ButNCO (250 µL, 2.19 mmol) in toluene
(ca. 15 mL) was stirred for 13 h and reduced to dryness in vacuo. The
residue was recrystallized from toluene/heptane at -25 °C over 17 days.
Filtration yielded microcrystalline red 4b, which was washed with 12
mL of toluene (105 mg, 29% yield). By 1H NMR, 0.5 equiv of toluene
was observed as a solvate. 1H NMR (C6D6, 400 MHz): δ 9.09 (s, 8H,
1
°C. H NMR (C6D6, 400 MHz): δ 9.13 (s, 8H, â-H), 8.22 (d, 4H,
3
3JH-H ) 8 Hz, meso-C6H4CH3), 7.76 (d, 4H, JH-H ) 8 Hz, meso-
3
C6H4CH3), 7.35 (d, 4H, JH-H ) 8 Hz, meso-C6H4CH3), 7.24 (d, 4H,
3
3JH-H ) 8 Hz, meso-C6H4CH3), 6.85 (t, 1H, JH-H ) 8 Hz, p-C6H3),
3
3
3
â-H), 8.23 (d, 4H, JH-H ) 6 Hz, meso-C6H4CH3), 7.83 (d, 4H, JH-H
6.68 (d, 2H, JH-H ) 8 Hz, m-C6H3), 2.40 (s, 12H, meso-C6H4CH3),
3
3
) 6 Hz, meso-C6H4CH3), 7.38 (d, 4H, 3JH-H ) 6 Hz, meso-C6H4CH3),
7.25 (d, 4H, JH-H ) 6 Hz, meso-C6H4CH3), 6.98 (m, 1H, p-C6H3),
6.91 (d, 2H, m-C6H3), 2.41 (s, 12H, meso-C6H4CH3), 1.84 (spt, 2H,
1.63 (m, 1H, JH-H ) 6 Hz, NCHMe2), 0.96 (d, 6H, JH-H ) 7 Hz,
C6H3CHMe2), 0.46 (dd, 12H, NCHMe2 and C6H3CHMe2), 0.13 (br d,
7H, 3JH-H ) 6 Hz, NCHMe2 and NCHMe2), -0.31 (m, 2H, 3JH-H ) 7
Hz, C6H3CHMe2). COSY was used to identify protons in overlapping
signals. The 2,6-diisopropyl resonances of the NAriPr fragment were
definitively assigned by HMBC. 13C NMR (C6D6, 200 MHz): δ 152.0,
150.3, 146.1, 142.3 (o-AriPr), 139.1, 137.9, 135.3 (o-tolyl), 133.7 (o-
tolyl), 132.8 (â-pyrrole), 130-126 (solvent), 125.3, 122.8 (p-AriPr),
122.7 (m-AriPr), 47.38, 26.8, 25.6, 24.5, 22.8, 21.4. UV-vis (toluene):
549 (4.32), 416 (5.42). 1H NMR showed that 1 equiv of toluene
remained after extended drying in vacuo. Anal. Calcd for C67H67N7-
Hf‚C7H8: C, 71.62; H. 6.09; N, 7.90. Found: C, 71.58; H, 6.23; N,
7.70. Exposure to water resulted in rapid decomposition to yield the
guanine AriPrNHC(dNiPr)NHiPr, as detected by GC/MS: calcd (found)
for C19H33N3 m/z 303.49 (305 [M + H+]).
3
3
3
-CHMe2), 0.78 (d, 6H, JH-H ) 7 Hz, -CHMe2), 0.31 (d, 6H, JH-H
) 7 Hz, -CHMe2), -0.14 (s, 9H, NCMe3). 13C NMR (C6D6, 400
MHz): δ 154.3, 150.1, 145.4, 139.6, 138.0, 137.8, 135.4 (o-tolyl), 133.6
(o-tolyl), 132.8 (â-pyrrole), 127-129 (solvent), 125.6 (m-tolyl), 121.4
(m-AriPr), 120.6 (p-AriPr), 53.0 (-CMe3), 29.0 (CMe3), 28.0 (-CHMe2),
23.6 (-CHMe2), 23.1 (-CHMe2), 21.4 (p-MeC6H5). UV-vis (tolu-
ene): 551 (4.31), 4.39 (shoulder, 4.57), 417 (5.46). Anal. Calcd for
C68.5H66N6OZr: C, 76.14; H, 6.16; N, 7.78. Found: C, 76.21; H, 6.37;
N, 7.32. Exposure to water resulted in rapid decomposition to yield
the urea AriPrNHC(O)NHtBu, as detected by GC/MS.
(TTP)Hf(η2-NAriPrC(dNtBu)O), 5a. A solution of (TTP)HfdNAriPr
t
(324 mg, 0.317 mmol) and BuNCO (54 µL, 0.473 mmol) in toluene
(ca. 10 mL) was stirred for 4.5 h at 25 °C. The solution was filtered,
and the filtrate was reduced in vacuo to produce an oily residue. The
residue was triturated with 10 mL of hexanes, and the mixture was
Reaction of 2 with Aniline. An NMR tube equipped with a Teflon
stopcock was charged with 2 (10.36 mg, 10.13 µmol), Ph3CH (88.5
µL, 0.1397 M, 12.36 µmol) as an internal standard, H2NPh (2.9 µL,
31.8 µmol), and C6D6 (ca. 0.6 mL). This solution was allowed to
equilibrate over 11 h at 25 °C, at which time there were present in
1
filtered to yield blue 5a (228 mg, 64% yield). H NMR (C6D6, 300
3
MHz): δ 9.16 (s, 8H, â-H), 8.12 (d, 4H, JH-H ) 7 Hz, meso-C6H4-

Zirconium and Hafnium Imido Metalloporphyrins
Inorganic Chemistry, Vol. 38, No. 17, 1999 3817
solution H2NAriPr (9.89 µmol), H2NPh (14.8 µmol), (TTP)Hf(NHAriPr)-
(NHPh) (1.5 µmol), and (TTP)Hf(NHPh)2 (7.32 µmol). K ) 3.3 (
0.3. 1H NMR (C6D6, 400 MHz): δ 9.16 (s, â-H, (TTP)Hf(NHPh)2 and
(TTP)Hf(NHPh)(NHAriPr)), 8.22 (br d, meso-C6H4CH3, (TTP)Hf-
(NHPh)2 and (TTP)Hf(NHPh)(NAriPr))2, 7.86 (br d, meso-C6H4CH3,
(TTP)Hf(NHPh)2 and (TTP)Hf(NHPh)(NAriPr)), 7.26 (br, meso-C6H4-
CH3, (TTP)Hf(NHPh)2 and (TTP)Hf(NHPh)(NAriPr)), 6.91 (t, p-H2NAriPr),
6.71 (t, p-H2NPh), 6.52 (t, p-C6H3, (TTP)Hf(NHPh)(NHAriPr)), 6.32
(m, m-H2NPh and m-NHPh, (TTP)Hf(NHPh)2), 6.06 (m, p-HNPh,
(TTP)Hf(NHPh)2 and (TTP)Hf(NHPh)(NHAriPr)), 4.24 (d, o-C6H5,
(TTP)Hf(NHPh)2), 4.06 (d, o-C6H5, (TTP)Hf(NHPh)(NHAriPr)), 3.16
(br s, H2NAriPr), 2.73 (br s, H2NPh), 2.62 (m, H2NAriPr), 2.39 (s, meso-
C6H4CH3), 1.13 (d, H2NAriPr), 0.93 (s, (TTP)Hf(NHPh)2 and (TTP)-
Hf(NHPh)(NHAriPr)), 0.38 (d, (TTP)Hf(NHPh)(NHAriPr), 0.14 (d,
(TTP)Hf(NHPh)(NHAriPr), -0.05 (m, (TTP)Hf(NHPh)(NHAriPr).
Decomposition of 4a. An NMR tube equipped with a Teflon
stopcock was charged with 4a (11.9 mg, 11.5 µmol), Ph3CH (87.5 µL,
0.1455 M, 12.73 µmol) as an internal standard, and C6D6 (ca. 0.6 mL).
After 238 h at 80 °C, 4a had been consumed and 4b (1.24 µmol),
[(TTP)ZrO]223 (0.42 µmol), and AriPrNdCdNtBu (9.5 µmol, 83% yield
by NMR) were detected. 1H NMR (C6D6, 300 MHz): δ (for
AriPrNdCdNtBu) 7.07 (m, 3H, m- and p-C6H3), 3.64 (spt, 2H,
-CHMe2), 1.24 (d, 12H, -CHMe2), 1.18 (s, 9H, N-tBu); δ (for [(TTP)-
ZrO]2) 8.74 (s, 8H, â-H), 7.95 (d, 4H, meso-C6H4CH3), 7.56 (d, 4H,
meso-C6H4CH3), 7.42 (d, 4H, meso-C6H4CH3), 2.45 (s, 12H, meso-
C6H4CH3).
δ (for [(TTP)HfS]2) 8.75 (s, 8H, â-H), 7.97 (d, 4H, meso-C6H4CH3),
7.55 (d, 4H, meso-C6H4CH3), 7.42 (d, 4H, meso-C6H4CH3), 2.45 (s,
12H, meso-C6H4CH3).
Reaction of 1 with tBuNCSe. An NMR tube equipped with a Teflon
stopcock was charged with 1 (19.32 mg, 20.66 µmol), Ph3CH (71 µL,
0.1397 M, 9.92 µmol) as an internal standard, tBuNCSe (7.5 mg, 46.27
µmol), and C6D6 (ca. 0.6 mL). After 8 h at 25 °C, 1 had been consumed
and a large amount of brown precipitate had formed. AriPrNdCdNtBu
(17.71 µmol) was produced in 86% yield (by NMR). No intermediates
were detected during this reaction.
Reaction of 2 with tBuNCSe. An NMR tube equipped with a Teflon
stopcock was charged with 2 (16.64 mg, 16.27 µmol), Ph3CH (85 µL,
t
0.1455 M, 12.37 µmol) as an internal standard, BuNCSe (10.1 mg,
62.3 µmol), and C6D6 (ca. 0.6 mL). After 109 h at 25 °C, AriPrNdCd
NtBu (13.59 µmol, 84% yield) had formed. No intermediates were
detected during this reaction.
Isomerization of 4a to 4b. An NMR tube equipped with a Teflon
stopcock was charged with 4a (23.2 mg, 22.45 µmol), Ph3CH (90 µL,
0.1397 M, 12.57 µmol), as an internal standard, and C6D6 (ca. 0.6 mL).
After 912 h at ambient temperature, the progress of the reaction had
slowed markedly and only a trace of 4a remained (0.70 µmol, 97%
consumption). Quantification of 4b was precluded by its insolubility.
However, X-ray diffraction quality crystals precipitated during the
reaction. No additional products or intermediates were observed
throughout this reaction; t1/2 ≈ 670 h.
Isomerization of 5a. An NMR tube equipped with a Teflon stopcock
was charged with 5a (16.86 mg, 15.03 µmol), Ph3CH (92.5 µL, 0.1397
M, 12.92 µmol), and C6D6 (ca. 0.6 mL). After 534 h at 80 °C, the
progress of the reaction had slowed markedly and only a trace of 5a
remained. The product, (TTP)Hf(η2-NtBuC(dNAriPr)O) (14.36 µmol),
was present in 94% yield. No additional products or intermediates were
Decomposition of 4b. An NMR tube equipped with a Teflon
stopcock was charged with 4b (7.32 mg, 7.58 µmol), Ph3CH (90.0 µL,
0.1455 M, 13.1 µmol) as an internal standard, and C7D8 (ca. 0.6 mL).
23
After 228.5 h at 110 °C, 4b had been consumed and [(TTP)ZrO]2
and AriPrNdCdNtBu (6.96 µmol, 92% yield by NMR) were produced.
1H NMR: δ (for AriPrNdCdNtBu) 3.60 (m, 2H, -CHMe2), 1.23 (d,
12H, -CHMe2), 1.20 (s, 9H, tBu), all other signals obscured by solvents;
δ (for [(TTP)ZrO]2) 8.69 (s, 16H, â-H), 7.81 (d, 8H, meso-C6H4CH3),
7.61 (d, 8H, meso-C6H4CH3), 7.43 (d, 8H, meso-C6H4CH3), 7.18 (d,
8H, meso-C6H4CH3), 2.51 (s, 24H, meso-C6H4CH3).
Reaction of 1 with tBuNCS. An NMR tube equipped with a Teflon
stopcock was charged with 1 (17.43 mg, 18.63 µmol), Ph3CH (92.0
µL, 0.1397 M, 12.85 µmol) as an internal standard, BuNCS (2.8 µL,
1
observed throughout this reaction; t1/2 ≈ 250 h. H NMR (C6D6, 300
MHz): δ 9.12 (s, 8H, â-H), 8.24 (br, 4H, meso-C6H4CH3), 7.83 (br,
4H, meso-C6H4CH3), 7.38 (br, 4H, meso-C6H4CH3), 7.26 (br, 4H, meso-
C6H4CH3), 6.93 (m, 3H, m- and p-C6H3), 2.41 (s, 12H, meso-C6H4CH3),
3
1.83 (m, 2H, -CHMe2), 0.78 (d, 6H, JH-H ) 7 Hz, -CHMe2), 0.32
3
(d, 6H, JH-H ) 7 Hz, -CHMe2), -0.14 (s, 9H, N-CMe3).
Isomerization of 7a. Complex 7a was synthesized in situ in an NMR
tube equipped with a Teflon stopcock. The tube was charged with 2
t
i
23.2 µmol), and C6D6 (ca. 0.6 mL). After 21 h at 25 °C, 1 had been
consumed and (TTP)Zr(η2-NAriPrC(dNtBu)S) (4.33 µmol), [(TTP)ZrS]2
(0.92 µmol), and AriPrNdCdNtBu (12.35 µmol) were produced. After
an additional 70 h at 25 °C, a large amount of brown precipitate was
present as well as [(TTP)ZrS]2 (0.21 µmol) and AriPrNdCdNtBu (16.91
µmol, 91% yield by NMR). 1H NMR (C6D6, 300 MHz): δ (for
AriPrNdCdNtBu) 7.07 (m, N-2,6-iPr2C6H3), 3.64 (m, N-2,6-iPr2C6H3),
1.24 (d, N-2,6-iPr2C6H3), 1.18 (s, N-tBu); δ (for [(TTP)Zr(η2-NAriPrC-
(dNtBu)S)]) 9.08 (s, 8H, â-H), 8.30 (d, 4H, meso-C6H4CH3), 7.69 (d,
4H, meso-C6H4CH3), 7.35 (d, 4H, meso-C6H4CH3), 7.21 (d, 4H, meso-
C6H4CH3), 6.96 (t, 1H, p-C6H3), 6.76 (d, 2H, m-C6H3), 2.39 (s, 12H,
meso-C6H4CH3), 1.02 (d, 6H, -CHMe2), 0.52 (s, 9H, NCMe3), 0.51
(d, 6H, -CHMe2), -0.13 (m, 2H, -CHMe2); δ (for [(TTP)ZrS]2) 8.74
(s, 8H, â-H), 7.95 (d, 4H, meso-C6H4CH3), 7.56 (d, 4H, meso-C6H4-
CH3), 7.42 (d, 4H, meso-C6H4CH3), 2.45 (s, 12H, meso-C6H4CH3).
Reaction of 2 with tBuNCS. An NMR tube equipped with a Teflon
stopcock was charged with 2 (13.88 mg, 13.57 µmol), Ph3CH (67 µL,
0.1397 M, 9.36 µmol) as an internal standard, tBuNCS (1.8 µL, 14.90
µmol), and C6D6 (ca. 0.6 mL). After 191 h at 25 °C, 2 was still present
(0.44 µmol), as well as (TTP)Hf(η2-NAriPrC(dNtBu)S) (9.47 µmol),
[(TTP)HfS]2 (1.56 µmol), and AriPrNdCdNtBu (2.75 µmol). The
temperature was subsequently raised to 80 °C for 21 h to yield a nearly
colorless solution containing [(TTP)HfS]2 (1.36 µmol) and AriPrNdCd
(12.38 mg, 12.10 µmol), PrNdCdNiPr (6.5 µL, 41.5 µmol), Ph3CH
(89 µL, 0.1455 M, 12.95 µmol), and C6D6 (ca. 0.6 mL). The formation
of 7a was complete in minutes. The sample was then heated at 80 °C
for 488 h; t1/2 ≈ 108 h. The product, (TTP)Hf(η2-NiPrC(dNAriPr)-
NiPr) (7b) (11.67 µmol), was produced in 96% yield (by NMR). No
additional products or intermediates were observed throughout this
1
reaction. H NMR (C6D6, 300 MHz): δ 9.12 (s, 8H, â-H), 8.59 (d,
4H, 3JH-H ) 7 Hz, meso-C6H4CH3), 7.76 (d, 4H, 3JH-H ) 7 Hz, meso-
3
C6H4CH3), 7.36 (d, 4H, JH-H ) 7 Hz, meso-C6H4CH3), 7.25 (d, 4H,
3JH-H ) 7 Hz, meso-C6H4CH3), 6.69 (d, 2H, m-C6H3), 6.59 (m, 1H,
p-C6H3), 2.40 (s, 14H, meso-C6H4CH3 and NCHMe2), 1.62 (spt, 2H,
3
C6H3(CHMe2)2), 0.70 (d, 12H, JH-H ) 7 Hz, C6H3(CHMe2)2), -0.18
(br, 12H, N-CHMe2). The methine proton resonance of the NiPr group
was found by COSY to overlap with the meso-C6H4CH3 signal at 2.40
ppm. The isopropyl groups were definitively assigned by HMBC.
Structure Determinations of (TTP)ZrdNAriPr (1), (TTP)Hfd
NAriPr (2), (TTP)Zr(NAriPrC(dN(tBu)O) (4a), (TTP)Zr(NtBuC(d
N(AriPr)O) (4b), and (TTP)Hf(NAriPrC(dNiPr)NiPr) (7a). Crystal
data are found in Table 1. Compounds 1 and 2 were treated similarly
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 208 and 218 reflections for compounds 1 and 2,
respectively. Final cell constants were calculated from sets of 7055
and 8028 strong reflections from the actual data collection, respectively,
for 1 and 2. Three major swaths of frames were collected with 0.30°
steps in ω. The data were merged into a unique set as indicated by the
data collection ranges. The space groups were determined on the basis
of systematic absences and intensity statistics, and a successful direct-
methods solution was calculated which provided most non-hydrogen
1
NtBu (12.17 µmol, 90% yield by NMR). H NMR (C6D6, 300 MHz):
δ (for [(TTP)Hf(η2-NAriPrC(dNtBu)S)]) 9.12 (s, 8H, â-H), 8.29 (d,
4H, meso-C6H4CH3), 7.69 (d, 4H, meso-C6H4CH3), 7.35 (d, 4H, meso-
C6H4CH3), 7.21 (d, 4H, meso-C6H4CH3), 6.94 (t, 1H, p-C6H3), 6.77 (d,
2H, m-C6H3), 2.39 (s, 12H, meso-C6H4CH3), 1.04 (d, 6H, -CHMe2),
0.52 (s, 9H, NCMe3), 0.51 (d, 6H, -CHMe2), -0.15 (m, 2H, -CHMe2);
(23) Thorman, J. L.; Guzei, I. A.; Young, V. G., Jr.; Woo, L. K. Manuscript
in submission.

3818 Inorganic Chemistry, Vol. 38, No. 17, 1999
Table 1. Crystal Data
Thorman et al.
compound
empirical formula
formula weight
crystal system
space group
a, Å
1
2
4a
4b
7a
C
70.50H69N5Zr
C70.50H69N5Hf
1164.80
monoclinic
P21/n
16.6081(2)
18.6360(3)
19.3910(1)
90
104.029(1)
90
5822.67(12)
4
C72H74N6OZr
1226.76
triclinic
C80H77N6OZr
1229.70
triclinic
C67H67N7Hf‚toluene
1274.96
monoclinic
P21/c
14.8756(8)
16.7514(9)
26.1874(15)
90
91.796(1)
90
1077.53
monoclinic
P21/n
16.6358(2)
18.7583(1)
19.4375(2)
90
103.970(1)
90
5886.24(10)
4
P1h
P1h
13.5421(10)
15.4623(11)
16.7239(12)
98.0192(14)
100.8337(14)
113.9894(11)
3050.0(4)
2
12.9237(8)
16.3912(10)
16.6590(10)
97.1371(11)
105.196(1)
100.532(1)
3292.6(3)
2
b, Å
c, Å
R, deg
â, deg
γ, deg
volume, Å3
Z
6522.4(6)
4
F, g/cm3
λ, Å
1.216
1.329
1.337
1.240
1.298
0.710 73
173(2)
1.646
2636
0.710 73
172(2)
0.710 73
173(2)
0.710 73
173(2)
0.710 73
173(2)
T, K
µ, mm-1
F(000)
0.233
2268
1.838
2396
0.229
1300
0.218
1294
θ range, deg
1.45-25.00
-19 e h 19
0 e k e 22
0 e l e 23
29 098
1.45-25.06
-19 e h e 19
0 e k e 22
0 e l e 23
32 323
1.69-28.86
-17 e h e 18
-20 e k e 20
-20 e l e 21
19 079
1.28-23.35
-13 e h e 14
-17 e k e 18
-18 e l e 17
15 220
1.37-28.34
-15 e h e 19
-21 e k e 21
-33 e l e 34
40 118
index ranges
no. of reflections collected
no. of independent reflections
Rint
10 237
0.0313
10 215
0.0270
13 540
0.0122
9395
0.0396
15 118
0.0352
data/restraints/parameters
R1
10 232/0/694
0.0403
10 215/0/694
0.0263
13 540/0/658
0.0340
9395/37/729
0.0547
15 115/0/676
0.0316
wR2
GooF
0.0984
0.977
0.305, -0.509
0.0573
1.055
0.444, -1.079
0.0910
0.999
0.491, -0.378
0.1457
0.995
1.032, -0.658
0.0814
1.027
1.414, -1.744
largest diff peak and hole, e Å-3
atoms from the E map. Several full-matrix least-squares/difference
Fourier cycles were performed that located the remainder of non-
hydrogen atoms, which were refined with anisotropic displacement
parameters. All hydrogen atoms were placed in ideal positions and
refined as riding atoms with relative isotropic displacement parameters.
Both complexes were found with one toluene and a half heptane in the
unit cell. The heptane was disordered over an inversion center such
that three carbons lie on one side and four on the other. Therefore, the
third and fourth carbon atoms are terminal methyl groups part of the
time. All calculations were performed with SGI INDY R4400-SC and
Pentium computers using the SHELXTL V5.0 program suite.24
Crystals of 4a, 4b, and 7a were treated in a manner analogous to
that for 1 and 2. Systematic absences in the diffraction data were
uniquely consistent for space groups denoted in Table 1. The structures
were solved using direct methods, completed by subsequent difference
Fourier syntheses and refined by full-matrix least-squares procedures.
All non-hydrogen atoms were refined with anisotropic displacement
coefficients unless otherwise specified. All hydrogen atoms were treated
as idealized contributions. The refinement of 7a revealed the presence
of several disordered solvent molecules. The SQUEEZE filter of the
program PLATON25 was applied to identify and account for 1.5 solvent
molecules of toluene present in the asymmetric unit of 7a along with
one molecule of the complex. In the case of 4b, there are 2.5 molecules
of benzene also present in the asymmetric unit. The half-molecule is a
part of a benzene molecule residing on an inversion center. The solvent
molecules were refined isotropically. The SQUEEZE filter was also
applied to 4a to identify and account for 0.5 toluene molecule and 0.5
heptane molecule present in the asymmetric unit.
tion of new terminal imido complexes (eq 1). Of these new
(TTP)ZrCl2 + 2LiNHR f
(TTP)ZrdNR + 2LiCl + NH2R (1)
imido compounds, the 2,6-diisopropylphenyl derivative (TTP)-
ZrdNAriPr, complex 1, was the most amenable to isolation and
purification. The analogous Hf complex, (TTP)HfdNAriPr,
complex 2, was also synthesized using the same metathesis
reaction. Complex 1 alternatively could be prepared by the
i
reaction of Zr(NArPr)Cl2(THF)2 with (TTP)Li2(THF)2. All of
5
these new imido complexes are moisture sensitive. In addition,
the Zr imido complexes with mesityl, 2,4,6-tri-tert-butylphenyl,
and 2,4,6-triphenylphenyl substituents decomposed over time,
precluding our ability to isolate analytically pure samples. The
rate of this decomposition qualitatively followed the steric bulk
of the substituent. However, with 2,6-diisopropylphenyl sub-
stituents, complexes 1 and 2 could be kept in the solid state at
ambient temperature under an N2 atmosphere for months. In
solution at ambient temperature, complex 2 decomposed to
uncharacterized diamagnetic species over a matter of weeks,
while 1 was stable in C6D6 at elevated temperatures (80 °C)
for several days.
1
The H NMR spectra of imido complexes 1 and 2 share the
same approximate characteristics. Particularly diagnostic is the
porphyrin ring current effect on the imido ligand protons.
Consequently, the meta and para aryl protons of the imido
groups exhibit upfield shifts of ∼0.90 ppm relative to that of
the free amine. The meta, and para protons of H2NAriPr appear
at 7.05 ppm (d) and 6.91 ppm (t), respectively. Thus, a well-
separated doublet (6.16 ppm, m-H) and triplet (6.04 ppm, p-H)
for complex 2 is observed. In comparison, complex 1 exhibits
a three-proton singlet at 6.08 ppm for the meta and para AriPr
protons. The resonances of the aryl isopropyl groups are also
shifted upfield relative to the corresponding free amine reso-
nances at 2.63 ppm (spt) and 1.14 ppm (d). For example, in
Results
Synthesis and Characterization of Imido Complexes.
Treatment of cis-(TTP)ZrCl2 with 2 equiv of bulky lithium
amide reagents, LiNHR (R ) 2,4,6-Me3C6H2, 2,4,6-tBu3C6H2,
2,4,6-Ph3C6H2, 2,6- iPr2C6H3), in toluene resulted in the forma-
(24) SHELXTL-Plus V5.0; Siemens Industrial Automation, Inc.: Madison,
WI, 1998.
(25) All software and sources of the scattering factors are contained in the
SHELXTL V5.10 program library. Sheldrick, G., Siemens XRD,
Madison, WI, 1998.

Zirconium and Hafnium Imido Metalloporphyrins
Inorganic Chemistry, Vol. 38, No. 17, 1999 3819
loporphyrin complexes exhibit coordination numbers from 6 to
8. The range of out-of-plane distances for hexacoordinated Zr-
(IV) and Hf(IV) porphyrin complexes is 0.84-1.06 Å.26 In
comparison to these examples, the metals in the five-coordinate
complexes 1 and 2 reside closer to the plane defined by the
four pyrrole nitrogens. The metal atoms in complexes 1 and 2
are located 0.75 and 0.71 Å above the N1-N2-N3-N4 plane,
respectively. The smaller value observed for complex 2 is
consistent with corresponding values for the congeners [(TPP)-
Zr(OH)2(O)]2, [(TPP)Hf(OH)2(O)]2 (1.057, 1.048 Å) and (TPP)-
Zr(O2CCH3)2, (TPP)Hf(O2CCH3)2 (1.036, 1.012 Å).21,27
A domed ruffling28 deformation of the porphyrin macrocycle,
a common phenomenon with relatively large metals, is observed
in both imido compounds, although to a lesser extent in complex
2. Deviations from the 24-atom porphyrin plane due to ruffling
in complex 1 are 11 (C5), -8 (C10), 19 (C15), and -10 (C20)
pm. The resultant dihedral angles in complex 1 of the pyrrole
rings containing N1, N2, N3, and N4 relative to the mean 24-
atom porphyrin plane are 5.0, -2.6, 5.5, and -8.5°, respectively.
Formation of Bis(amido) Complexes. Treatment of complex
2 with excess aniline results in the complete disappearance of
the starting imido complex. Two new bis(amido) complexes,
(TTP)Hf(NHPh)2 and (TTP)Hf(NHPh)(NHAriPr), are produced
as observed by 1H NMR. These two bis(amido) complexes are
in equilibrium with the free amines as shown in eq 2 (K ) 3.3
Figure 1. ORTEP representation of (TTP)ZrdNAriPr. Thermal el-
lipsoids are drawn at the 50% probability level.
(TTP)H(NHAriPr)(NHPh) + H2NPh h
(TTP)Hf(NHPh)2 + H2NAriPr (2)
( 0.3). The proton resonances of the coordinated arylamido
ligands are shifted upfield. For example, the o-H doublet of
aniline appears at 6.34 ppm whereas the corresponding ortho
protons of the amide in (TTP)Hf(NHPh)2 appear at 4.24 ppm.
The amide NH protons are found at 0.93 ppm. Thus, in the
presence of the less sterically demanding aniline, a bis(amido)
complex is produced with concomitant loss of the bulkier (2,6-
diisopropylphenyl)amine. Although no new imido complexes
were detected by 1H NMR during this reaction, decomposition
of the bis(amido) complexes to intractable products was
observed over days at ambient temperature. Bulky amines, H2-
NR (R ) 2,4,6-Me3C6H2, 2,4,6-tBu3C6H2, 2,4,6-Ph3C6H2), do
not react with complex 1 or 2. Treatment of (TTP)HfCl2 with
2 equiv of LiNH(C6H4-p-CH3) in hexanes affords the bis(amido)
complex (TTP)Hf(NHC6H4-p-CH3)2 (3). The amide NH protons
Figure 2. ORTEP representation of (TTP)HfdNAriPr. Thermal el-
lipsoids are drawn at the 50% probability level.
complex 1, the methine multiplet appears at 0.18 ppm and the
methyl doublet resonates at 0.00 ppm.
The crystal structures of compounds 1 (Figure 1) and 2
(Figure 2) are isomorphous. Each compound cocrystallizes with
one toluene and a half heptane per unit cell. As expected,
metrical parameters are similar due to the nearly equivalent sizes
of the metals. Most structurally characterized five-coordinate
Zr and Hf imido complexes have been described as possessing
a trigonal-bipyramidal arrangement of the ligands around the
metal. The geometry about the metals in complexes 1 and 2 is
best described as distorted square-pyramidal. The four pyrrole
nitrogens of the porphyrin form the basal plane with average
trans pyrrole Npor-M-Npor angles of 140 and 142°, respectively.
Metal-Nimido bond lengths are 1.863(2) and 1.859(2) Å for the
Zr and Hf complexes, respectively. These values are well within
the range of known alkyl- and aryl-substituted imido ligands
for Zr and Hf complexes. Typical M-Nimido distances are 1.826-
(4)-1.876(4) Å for zirconium1,3-6,12 and 1.850(3) Å for
hafnium.6 Only a small deviation from linearity is observed in
the M-N5-C49 angles, 172.5(2)° (complex 1) and 173.4(2)°
(complex 2). Similar metrical features have been reported for
the corresponding bond angles of other imido complexes
(164.5-179.5° for Zr1,3-6,12 and 174.4° for Hf 6). The metal
centers in other structurally characterized Zr and Hf metal-
1
are readily distinguishable in the H NMR spectrum at 0.96
ppm as a sharp singlet integrating as two protons. In free
p-toluidine the NH protons appear at 2.74 ppm (br s).
[2+2] Condensation Products of Complexes 1 and 2 with
t
R-NCO. Treatment of imido complex 1 with BuNCO at
ambient temperature resulted in the rapid appearance of a new
species, 4a, which was formulated as an addition product as
1
monitored by H NMR. The new compound retains the 2,6-
diisopropylphenyl fragment. It also exhibits a new nine-proton
singlet at 0.35 ppm consistent with a bound tert-butyl group.
Moreover, the isopropyl methyl substituents give rise to two
(26) (a) (OEP)ZrCl2, (OEP)Zr(OtBu)2, and (OEP)ZrMe2: Brand, H.;
Arnold, J. Organometallics 1993, 12, 3655. (b) (OEP)Zr(CH2-
SiMe3)2: Brand, H.; Arnold, J. J. Am. Chem. Soc. 1992, 114, 2266.
(c) (TPP)Hf(benzenedithiolato): Ryu, S.; Whang, D.; Yeo, H.; Kim,
K. Inorg. Chim. Acta 1994, 221, 51.
(27) Shannon, R. D. Acta Crystallogr. 1976, A32, 751.
(28) 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.

3820 Inorganic Chemistry, Vol. 38, No. 17, 1999
Thorman et al.
new doublets at 0.82 (6H) and 0.42 (6H) ppm. Heating a C6D6
solution of 4a in an NMR probe to 323 K resulted in no
broadening of the isopropyl signals. This observation suggested
that the isopropyl methyl groups are diastereotopic. Further
heating of compound 4a to 353 K in C6D6 for 238 h resulted in
the production of 1 equiv of the carbodiimide, tBuNdCdNAriPr.
The production of the carbodiimide suggests that compound 4a
can be formulated as an η2-ureato-N,O complex (eq 3). The
porphyrin ring than is its counterpart in complex 4a. Thus,
structure I is most likely the correct formulation for complex
4b. Moreover, heating 4b at 383 K for 228.5 h resulted in the
production of tBuNdCdNAriPr (92% by NMR). This reactivity
is also consistent with the N,O-bound isomer I. Final confirma-
tion of the correct structure for complex 4b was derived from
the synthesis of an analogue and by X-ray diffraction analysis
(vide infra).
Whereas complex 4a is formed within minutes at ambient
temperature from the reaction of 1 and tert-butyl isocyanate,
the isomerization of 4a to 4b (eq 5) requires ≈38 days at 298
(3)
remaining metal complex was observed transiently by 1H NMR
but eventually precipitated out of solution. Initially this complex
was formulated as a terminal oxo species, (TTP)ZrdO. How-
ever, this putative (TTP)ZrdO complex did not react with excess
tBuNCO to form (TTP)ZrdNtBu (eq 4).29 The metal byproduct
(5)
K in C6D6. The production of carbodiimide was not observed
during this transformation.
The analogous Hf imido complex 2 also forms a kinetic η2-
(4)
t
ureato-N,O complex, 5a, on treatment with BuNCO. The Hf
reaction is much slower than that of Zr and takes several hours
at 298 K. In addition, 5a isomerizes to a thermodynamic product,
5b, after heating at 353 K for 534 h in C6D6. Conversion of 5a
to 5b occurs cleanly with no formation of carbodiimide even
at 383 K. The kinetic isomers 4a and 5a both share similar
spectroscopic characteristics, as do the thermodynamic products
4b and 5b. All four complexes, 4a, 4b, 5a, and 5b, yield the
has been identified as the dimeric species [(TTP)Zr]2(µ-O)2.23,30
Over days at 298 K in C6D6, complex 4a isomerizes to a
new complex, 4b. The ureato ligand is still retained as indicated
by the presence of tert-butyl and isopropyl resonances in the
1H NMR spectrum. However, all proton signals of complex 4b
have shifted relative to those of complex 4a. For example, the
tert-butyl resonance of complex 4b has shifted upfield by 0.49
ppm to -0.14 ppm (s, 9H). The relative change on the isopropyl
methyl protons is less drastic. These now appear at 0.31 (d,
6H) and 0.78 ppm (d, 6H). However, a much stronger shift is
observed for the methine protons of the isopropyl groups. For
complex 4a, this signal appears at -0.51 ppm. The correspond-
ing resonance for complex 4b is shifted substantially downfield
to 1.84 ppm.
i
t
urea BuNHC(O)NHArPr upon hydrolysis.
Treatment of complex 2, (TTP)HfdNAriPr, with AriPrNCO
produced a new adduct, 6, containing two inequivalent AriPr
fragments. Diagnostic of the two different AriPr groups are the
two unique isopropyl methine signals at 1.93 (m, 2H) and -0.07
ppm (m, 2H). Clearly, complex 6 must be an η2-N,O-bound
ureato. An η2-N,N-bound ureato ligand would have equivalent
AriPr fragments. Heating complex 6 does not result in conversion
to a new isomer. This observation is consistent with all observed
isomers of 4 and 5 having N,O-bound ligands.
Two candidates serve as possible structures for complex 4b.
These are η2-N,O- and η2-N,N-bound ureatos I and II. The
The two AriPr groups of complex 6 exhibit different variable-
temperature behaviors. The methyl groups of one AriPr unit give
rise to a broad 12-proton signal at 0.33 ppm at 293 K in toluene-
d8. Upon cooling, this broad signal begins to decoalesce at 245
K and eventually sharpens into two new doublets (0.85 and
-0.03 ppm) at 234 K, as expected for diastereotopic isopropyl
methyl moieties. On warming to 323 K, the methyl signals for
this AriPr fragment sharpen into a single slightly broadened
doublet (12H) at 0.31 ppm. The other AriPr fragment exhibits
diastereotopic isopropyl methyl groups with doublets at 0.61
and 0.44 ppm throughout the temperature range from 234 to
323 K. The latter signals are assigned to the AriPr fragment which
is proximal to the porphyrin ligand. The distal AriPr group is
not sterically constrained by the porphyrin macrocycle and can
rotate about the N-Cipso bond. The free energy of activation
for this rotational process is 12 ( 0.3 kcal/mol.
strong downfield shift of the isopropyl methine signal suggests
that the N-bound aryl group in complex 4b is further from the
(29) (a) Bryan, J. C.; Burrell, A. K.; Miller, M. M.; Smith, W. H.; Burns,
C. J.; Sattelberger, A. P. Polyhedron 1993, 12, 1769. (b) Legzdins,
P.; Phillips, E. C.; Rettig, S. J.; Trotter, J.; Veltheer, J. E.; Yee, V. C.
Organometallics 1992, 11, 3104. (c) Jolly, M.; Mitchell, J. P.; Gibson,
V. C. J. Chem. Soc., Dalton Trans. 1992, 1329. (d) Michelman, R. I.;
Anderson, R. A.; Bergman, R. G. J. Am. Chem. Soc. 1991, 113, 5100.
(e) Leung, W. H.; Wilkinson, G.; Hussain-Bates, B.; Hursthouse, M.
B. J. Chem. Soc., Dalton Trans. 1991, 2791. (f) Herrmann, W. A.;
Weichselbaumer, G.; Paciello, R. A.; Fischer, R. A.; Herdtweck, E.;
Okuda, J.; Marz, D. W. Organometallics 1990, 9, 489. (g) Pilato, R.
S.; Housemekerides, C. E.; Jernakoff, P.; Rubin, D.; Geoffroy, G. L.;
Rheingold, A. L. Organometallics 1990, 8, 2333. For reviews of
RNCO, see: (h) Bruanstein, P.; Nobel, D. Chem. ReV. 1989, 89, 1927.
(i) Cenini, S.; LaMonica, G. Inorg. Chim. Acta 1976, 18, 279.
(30) Protonolysis of (OEP)Zr(CH2SiMe3)2 by 1 equiv of H2O in CDCl3
generates 2 equiv of SiMe4 and an unisolated complex formulated by
1H NMR as [(OEP)Zr]2(µ-O)2.26a
Synthesis and Isomerization of (TTP)Hf(η2-NAriPrC-
(dNiPr)NiPr). Reaction of complex 2 with a slight excess of
1,3-diisopropylcarbodiimide results in the formation of a new
guanidino complex, 7a. The two N-isopropyl groups of 7a are
inequivalent, as indicated by 1H NMR. The proton assignments
for this complex were confirmed by HMBC experiments. For
example, the methyl proton signal at 0.96 ppm is coupled to an
aromatic 13C resonance at 142.3 ppm. Thus, the 0.96 ppm peak

Zirconium and Hafnium Imido Metalloporphyrins
Inorganic Chemistry, Vol. 38, No. 17, 1999 3821
i
t
Table 2. Chemical Shifts of the NArPr and Bu Protons in the
N,Ch-Bound Ureato Derivatives
ppm
CHMe2, NAriPr from
reactant
tBuNdCdE metallacycle complexa
tBu
(TTP)ZrdNAriPr (1)
(TTP)HfdNAriPr (2)
(TTP)ZrdNAriPr (1)
(TTP)HfdNAriPr (2)
tBuNCO
tBuNCO
tBuNCS
tBuNCS
0.82 (d), 0.42 (d) (4a) 0.35 (s)
0.84 (d), 0.43 (d) (5a) 0.34 (s)
must be associated with an isopropyl fragment of the AriPr group.
The methine protons of these fragments appear at 1.63 (spt,
1H) and 0.13 (spt, 1H) ppm. The upfield methine proton
overlaps with one of the methyl signals of the N-iPr group at
0.13 ppm, but was identified by COSY. The N-iPr groups remain
inequivalent as the temperature is raised to 323 K. Complex 7a
is clearly an unsymmetrical N,N-bound guanidino species. Over
a period of approximately 3 weeks at 353 K in C6D6, a new
product, 7b, was formed with the concomitant loss of 7a. At
323 K, the 1H NMR spectrum (toluene-d8 solution) of 7b
exhibits a broad peak at -0.17 ppm for the methyl groups of
both proximal NiPr moieties. The distal NAriPr displays its
isopropyl resonances at 0.70 (d, 12H) and 1.62 (spt, 2H) ppm.
Unambiguous assignments for proton resonances were derived
from HMBC experiments. The proton peaks at 0.70 (d, 12H)
and 1.62 (spt, 2H) ppm are both coupled to an aromatic carbon
signal at 137.2 ppm. These two proton resonances correspond
to the isopropyl groups of the AriPr fragment. Consequently,
complex 7b is formulated as the symmetric guanidino complex
(TTP)Hf(η2-NiPrC(dNAriPr)NiPr).
1.02 (d), 0.51 (d)
1.04 (d), 0.51 (d)
0.52 (s)
0.52 (s)
a C6D6, 20 °C.
Figure 3. ORTEP representation of (TTP)Zr(η2-NAriPrC(dNtBu)O).
Thermal ellipsoids are drawn at the 30% probability level.
Reaction of Complexes 1 and 2 with tBuNCS and tBuNCSe.
t
Imido complexes 1 and 2 undergo reactions with BuNCS and
tBuNCSe at a slower rate than the analogous reactions with
rBuNCO. This reflects the greater electrophilic nature of the
t
t
t
carbon atom in BuNCO relative to BuNCS and BuNCSe. In
the reaction with tBuNCS, the loss of 1 occurred over 21 h. In
the reaction of tBuNCS with 2, the presence of the starting imido
Hf complex was detected even after 191 h. In both cases, a
transient complex assigned as the [2+2] cycloaddition product
was observable, but it decomposed simultaneously to the
i
t
carbodiimide BuNdCdNArPr and sparingly soluble [(TTP)-
Zr(µ-S)]2. Formulation of the zirconium product as a µ-sulfido-
1
bridged dimer was based on the similarity of its H NMR
spectrum to that of the oxygen analogue [(TTP)Zr(µ-O)]2. The
transient metallacycles were assigned by the similarity of the
1H NMR chemical shifts of the NAriPr and tBu groups to those
of the oxygen-containing analogues, 4a and 5a (Table 2). In
the presence of excess tBuNCSe, 1 and 2 are consumed without
the observation of intermediates during the formation of
Figure 4. ORTEP representation of (TTP)Zr(η2-NtBuC(dNAriPr)O).
Thermal ellipsoids are drawn at the 30% probability level.
i
t
carbodiimide, Bu-NdCdNArPr. Once again, the loss of the
zirconium imido (8 h) is faster than in the hafnium case (109
h).
porphyrin core exhibits a higher degree of ruffling and doming
in comparison to the core of the imido complex 1. Unexpectedly,
very little ruffling is observed in 4b. Instead, marked doming
and an appreciable saddle deformation are seen in the deviations
of the â-pyrrole carbon atoms from the 24-atom porphyrin core
[2 (C2), 3 (C3), -27 (C7), -26 (C8), 4 (C12), 8 (C13), -20
(C17), -25 (C18) pm]. The metallacycle fragments contain
obtuse N-C-O angles of 106.16(14) and 107.1(3)°, as well as
acute N-Zr-O angles of 63.62(5) and 63.13(11)°, in 4a and
4b, respectively.29 In comparison to Zr-N amide bond lengths
ranging from 2.027(7) to 2.159(3) Å,31 the Zr-N6 distance in
4a and the Zr-N5 bond length in 4b are somewhat elongated
with distances of 2.1096(13) and 2.137(3) Å, respectively (Table
2). These bond lengths are slightly shorter than those found for
Structures of (TTP)Zr(η2-NAriPrC(dNtBu)O), 4a, (TTP)-
Zr(η2-NtBuC(dNAriPr)O), 4b, and (TTP)Hf(η2-NAriPrC(d
NPri)NPri), 7a. The ureato ligand is bound to the zirconium in
both 4a (Figure 3) and 4b (Figure 4) through nitrogen and
oxygen. Both complexes 4a and 4b possess a slightly puckered
ureato metallacycle. This four-membered ring is nearly perpen-
dicular to the mean 24-atom porphyrin core, with dihedral angles
between planes of 91.1° (4a) and 101.2° (4b). The ureato
fragment is staggered with respect to the pyrrole nitrogens.
Representative torsional angles are 30.3° (N2-Zr-N6-C49)
and 34° (N4-Zr-O-C49) for 4a and 24.7° (N2-Zr-N5-
C49) and 7.7° (N4-Zr-O-C49) for 4b. The displacements of
the Zr atoms from the four-nitrogen pyrrole planes, 0.8891 Å
(4a) and 0.9069 Å (4b), are comparable to those of related six-
coordinate compounds (vide supra). For 4a, the 24-atom
(31) (a) Hagen, K.; Holwill, C. J.; Rice, D. A.; Runnacles, J. D. Inorg.
Chem. 1988, 27, 2032. (b) Cardin, D. J.; Lappert, M. F.; Raston, C.
L. Chemistry of Organ-Zirconium and -Hafnium Compounds; Ellis
Horwood Limited: West Sussex, U.K., 1986; p 101.

3822 Inorganic Chemistry, Vol. 38, No. 17, 1999
Thorman et al.
saddle deformation is observed, possibly due to the more
sterically demanding metallacycle. As expected, the hexacoor-
dinate hafnium center is further out of the N4 pyrrole plane
(0.9111 Å) compared to the five-coordinate hafnium center in
the imido complex 2 (out-of-plane distance of 0.7092 Å). The
coordination environments most closely resemble a distorted
trigonal prism with the metal ion displaced toward one of the
rectangular faces.33
Discussion
In continuing our work with titanium amido and imido
chemistry, we have expanded our efforts to zirconium and
hafnium. For hexacoordinate complexes, the large displacements
of Zr and Hf from the porphyrin planes confine the two ligands
to a cis geometry. This places further restrictions on the sizes
of the two mutually cis ligands. Thus, it is possible to prepare
cis-(TTP)M(NHC6H4-p-CH3)2 (M ) Zr, Hf) by simple meta-
thesis reactions of cis-(TTP)MCl2 with LiNHAr. However, when
ortho substituents are present on the amide reagent, formation
of a bis(amido) complex is not observed. Instead, a terminal
imido complex is produced. Presumably, ortho-substituted
arylamides are too bulky to form a cis-bis(amido) species.
Moreover, the kinetic stability of the final terminal imido
complexes is also a function of the size of the ortho substituent.
Varying the amide aryl group in the reaction of LiNHR (R )
2,4,6-Me3C6H2, 2,4,6-tBu3C6H2, 2,4,6-Ph3C6H2) with (TTP)-
MCl2 led to thermally unstable imido complexes, as observed
Figure 5. ORTEP representation of (TTP)Hf(η2-NAriPrC(dNiPr)NiPr).
Thermal ellipsoids are drawn at the 30% probability level.
Table 3. Selected Intramolecular Metallacycle Bond Distances (Å)
and Angles (deg) of 4a, 4b, and 7a
complex
Zr-O
2.0677(12) 2.1096(13) 1.401(2)
2.066(3) 2.137(3) 1.387(5)
M-Namide Namide-C49 NiminedC49 O-C49
4a
4b
7a
1.269(2) 1.349(5)
1.277(5) 1.3530(19)
1.282(4)
2.087(2), 1.391(3),
Hf-N6
N6-C49
2.151(2), 1.428(3),
Hf-N5
N5-C49
complex
O-Zr-N
N-Hf-N
E-C49-Namide
4a
4b
7a
63.62(5)
63.13(11)
106.16(14), E ) O
107.1(3), E ) O
104.0(2), E ) N
1
by H NMR. In these cases, analytically pure samples could
not be isolated.34 The 2,4,6-triphenyl derivative, (TTP)Hfd
NC6H2Ph3, was isolated as poorly diffracting crystals. A low-
resolution molecular structure confirmed the presence of an
imido ligand, but the complex was thermally unstable in solution
and in the solid state.35 The steric constraints in the related
tetraazaanulene complexes are less demanding. Thus, the
formation of a secondary bis(amido) complex, Zr(tmtaa)-
(HNAriPr)2,9 is possible.
63.21(8)
the N,N′-bound ureato ligand in [Zr(tmtaa)(η2-NAriPrC(dO)-
NtBu)]: Zr-NiPr ) 2.168(4) Å and Zr-NtBu ) 2.155(4) Å.9
No Zr-O π-bonding is suggested by the rather long bond
lengths of 2.0677(12) Å in 4a and 2.066(3) Å in 4b, along with
the acute C49-O-Zr angles of 96.76(10)° in 4a and 96.7(2)°
in 4b.31 Other intramolecular metallacycle distances are normal.
The kinetic product from the treatment of complex 2 with
1,3-diisopropylcarbodiimide yields the unsymmetric guanidino-
(2-) complex (TTP)Hf(η2-NAriPrC(dNiPr)NiPr), 7a. The slightly
puckered Hf(η2-NAriPrC(dNiPr)NiPr) metallacyle (Figure 5) is
perpendicular to the mean 24-atom porphyrin core, with a
dihedral angle between planes of 89.9°. The metallacycle is
staggered in relation to the pyrrole nitrogens to a lesser degree
than that of the ureato complexes. The torsional angles are 15.9°
(N1-Hf-N5-C49) and 5.4° (N3-Hf-N6-C49). The Hf-
NiPr distance (2.087(6) Å) is within known Hf-amido bond
distances (2.03-2.12 Å).32 However, the notably longer Hf-
NAriPr distance (2.151(2) Å) may be due to the steric bulk of
the AriPr group. Consequently, there is an irregularity in the Hf-
Npyrrole distances: Hf-N1 ) 2.251(2) Å, Hf-N2 ) 2.184(2)
Å, Hf-N3 ) 2.238(2) Å, and Hf-N4 ) 2.207(2) Å. The two
longer distances correspond to the nearly eclipsed nitrogens.
Intrametallacycle C-N single- and double-bond distances are
typical and are summarized in Table 3. As in complexes 4a
and 4b, the porphyrin macrocycle of 7a shows ruffling and
doming distortions. However, a somewhat more pronounced
Examples of isolated N,N′-bound ureato complexes formed
from imido complexes have been thoroughly studied.29 In
addition, the similar N,O-bound carbamates are well-known
reaction products from [2+2] cycloaddition of isocyantes to oxo
species.29 To the best of our knowledge, there are no examples
in the literature of an isolated transition metal N,O-bound ureato-
(2-) complex.36 This is somewhat of an anomaly, since early
transition metal M-O bonds are generally stronger than M-N
bonds.37 Nonetheless, the importance of N,O-bound forms has
been implicated in the catalytic condensation of phenyl isocy-
anate to N,N ′-diphenylcarbodiimide via a proposed vanadium
(33) For a leading reference pertaining to geometries of d° ML6 complexes,
see ref 32c.
(34) For example, during a recrystallization attempt of (TTP)Zr(dNMes*)
from toluene/hexanes at -25 °C, approximately 30% decomposed to
uncharacterized paramagnetic species.
(35) Thorman, J. L.; Woo, L. K. Unpublished results. R value ≈ 13%. At
ambient temperature, (TTP)Hf(NPh(Ph)3) crystals decomposed within
hours.
(36) (a) Examples of molybdenum and chromium complexes are as follows.
N,O-bound ureate(1-): Lam, H. W.; Wilkinson, G.; Hussain-Bates,
B.; Hursthouse, M. B. J. Chem. Soc., Dalton Trans. 1993, 781. (b)
Synthesis of ((Me3Si)2N)2Sn(NAriPrC(dNAriPr)O) from ((Me3-
Si)2N)2Sn(dNAriPr) and AriPrNCO: Ossig, G.; Meller, A.; Freitag,
S.; Herbst-Irmer, R.; Sheldrick, G. M. Chem. Ber. 1993, 126, 2247.
(37) (a) Ziegler, T.; Tschinke, V.; Versluis, L.; Baerends, E. J.; Ravenek,
W. Polyhedron 1988, 7, 1625. (b) Lappert, M. F.; Patil, D. S.; Pedley,
J. B. J. Chem. Soc., Chem. Commun. 1975, 830. (c) Schock, L. E.;
Marks, T. J. J. Am. Chem. Soc. 1988, 110, 7701.
(32) (a) 2.12 Å average: Hf(dNAriPr)(NH(AriPr)2(4-pyrrolidinylpyridine)2
(ref 6). (b) 2.03 Å: Cp*2Hf(H)(NHMe) (Hillhouse, G. L.; Bulls, A.
R.; Santarsiero, B. D.; Bercaw, J. E. Organometallics 1988, 7, 1309).
(c) 2.092 Å average: (Me4taen)Hf(NMe2)2 (Black, D. G.; Jordan, R.
F.; Rogers, R. D. Inorg. Chem. 1997, 36, 103). (d) Covalent radii
estimates: O ) 0.66, N ) 0.70 Å (Jolly, W. L. Modern Inorganic
Chemistry; McGraw-Hill: New York, 1984; p 52). Zr ) 1.48, Hf )
1.49, O ) 0.73, N ) 0.75 Å (Porterfield, W. W. Inorganic Chemistry,
2nd ed.; Academic Press: San Diego, CA, 1998; p 214).
(38) Birdwhistell, K. R.; Boucher, T.; Ensminger, M.; Harris, S.; Johnson,
M.; Toporek, S. Organometallics 1993, 12, 1023.

Zirconium and Hafnium Imido Metalloporphyrins
Inorganic Chemistry, Vol. 38, No. 17, 1999 3823
Scheme 3
cleavage of M-N and C-O σ-bonds and the formation of a
metal-oxygen π-bond and a carbon-nitrogen π-bond. Since
the C-O cleavage and CdN formation processes are equivalent
for both Zr and Hf, the difference in reactivity lies in the M-N
and MdO bonds. Because Hf forms stronger σ-bonds than Zr,41
5a does not eject carbodiimide. The weaker C-S and C-Se
bonds in tBuNCS and tBuNCSe are manifested in progressively
more reactive N,Ch-bound metallacycles with respect to loss
of carbodiimide.
t
t
In the reactions of 1 and 2 with BuNCS and BuNCSe, the
simultaneous presence of AriPrNdCdNtBu and the imido
complexes does not lead to a guanidino derivative, presumably
due to the steric bulk of the carbodiimide. In the presence of
i
the less sterically demanding PrNdCdNiPr, a kinetic [2+2]
condensation product, (TTP)Hf(η2-NAriPrC(dNiPr)NiPr), 7a, is
formed.42 As seen with the isocyanate [2+2] analogues, an
isomerization slowly occurs which leads to a thermodynamic
isomer with the bulky NAriPr moiety at the 3-position of the
metallacycle.
N,O-bound ureato intermediate.38 Two interesting examples
illustrating the reactivity of zirconium imido complexes with
tBuNCO are shown in Scheme 3. The first case involves the
implication of an N,O-bound ureate(2-) as an intermediate in
the reaction of Cp2Zr(NtBu) with tBu-NCO. The final products
are 1,3-di-tert-butylcarbodiimide and (Cp2ZrO)n.7 In the second
example, treatment of the tetraazaanulene derivative, (tmtaa)-
1
The variable-temperature H NMR spectra of the guanidino
complex 7b in toluene-d8 reveal the dynamic aspects involving
the imine nitrogen. At 223 K, two doublets for the diastereotopic
isopropyl methyl groups are observed for NAriPr at 0.79 and
0.73 ppm. In addition, a doublet is observed for the methyl
groups of each NiPr unit at 0.60 (d, 6H) and -0.82 (d, 6H)
ppm. The two resonances arise from a static structure in which
one of the NiPr groups is syn to the aryl fragment. The fact
that the syn- and anti-NiPr groups each exhibit a single doublet
indicates that the HfNCN four-membered metallacyclic ring
must, on the NMR time scale, have a time-averaged mirror plane
of symmetry which bisects the NiPr groups. Warming the sample
to 243 K results in coalescence of the NAriPr isopropyl groups
(∆Gq ) 11.8 ( 0.3 kcal/mol). This resonance subsequently
sharpens to a single doublet at temperatures above 253 K. At
283 K, the NiPr methyl signals have coalesced (∆Gq ) 12.1 (
0.3 kcal/mol) and reappear as a sharp doublet (-0.17 ppm) at
363 K. These two coalescence phenomena have equivalent
activation barriers and can be explained with a single process
involving inversion at the imine nitrogen. The transition state
for this process has C2V symmetry which results in NAriPr
isopropyl groups that are no longer diastereotopic on the NMR
i
ZrdNArPr, with BuNCO yields the N,N-bound ureate.9 The
latter demonstrates the smaller steric demands of the tetraaza-
annulene ligand in comparison to those of the porphyrin ureato
complexes 4a and 5a. Mean bond dissociation enthalpy data
collected for amido M(NR2)4 (M ) Zr, Hf; R ) Me, Et)
compounds indicate that Hf-NR2 bonds are generally stronger
than Zr bonds by ≈5%.39 We propose that the stronger bonds
of Hf explain the distinct conditions under which isomerization
and decomposition of the ureato complexes 4a and 5a occur.
Specifically, higher temperatures are required for the isomer-
ization of hafnium complex 5a (80 °C) versus the zirconium
analogue 4a (25 °C). Similarly, the ejection of carbodiimide
occurs for 4a at 80 °C but does not occur for 5a at 110 °C.
The anomalous preference of the N,O-binding motif of
complexes 4b and 5b is presumably a manifestation of steric
factors. The N,N′-form is likely to have unfavorable steric
interactions between the bulky AriPr group and the porphyrin.
The known N,N′-bound ureato complexes, where steric factors
appear not to be as critical, may be dictated by the resultant
stronger CdO bond versus the weaker CdN bond required in
a N,O-bound ureate.40 Kinetic products with the bulky AriPrN
group proximal to the porphyrin are converted to thermodynamic
t
time scale and equivalent NiPr groups. Rotation about the Cipso
-
Nimino bond can also rationalize the coalescence behavior of the
NAriPr isopropyl resonances. Although a rotational process does
not need to be invoked, it cannot be definitively ruled out. In
the related ureato complex 6, rotation about the Cipso-Nimino
bond of the distal NAriPr unit has an activation barrier of 12
kcal/mol.
t
complexes with the smaller proximal BuN group. This steric
influence also appears to occur in the isomerization of the
guanidino complex 7a. These isomerizations are readily detected
1
by H NMR spectroscopy since the substituents of the metal-
lacycle are strongly affected by the porphyrin ring current as a
function of proximity. Under identical reaction conditions, the
consumption of imido complexes 1 and 2 by tBuNCO was found
to be complete within minutes for Zr but required ≈90 min for
Hf. This difference may be attributed to the slightly more
confined coordination sphere due to a smaller out-of-plane
distance in 2 relative to the Zr imido analogue. Parallel behavior
is seen in the reactions of imido complexes 1 and 2 with tBuNCS
In a similar manner, the η2-ureato-N,O complex 6 also
1
exhibits dynamic H NMR features. However, only one of the
iPr
iPr
NAr groups exhibits fluxional behavior. Since the NAr
fragments proximal to the porphyrin in complexes 4a and 5a
iPr
exhibit no fluxionality, the distal NAr group in complex 6
must be involved in the dynamic process. Moreover, the only
motion that would collapse the diastereotopic iPr methyl signals
into a single resonance is rotation about the Cipso-Nimino bond.
The absence of an observable syn-anti isomerization for
t
and BuNCSe. For the [2+2] metallacycle products from
t
reaction of complexes 1 and 2 with BuNCdCh, the hafnium
complexes were found to be more stable toward elimination of
carbodiimide. The loss of carbodiimide from 4a involves the
(41) (a) Ziegler, T.; Tschinke, V.; Versluis, L.; Baerends, E. J.; Ravenek,
W. Polyhedron 1988, 7, 1625. (b) Lappert, M. F.; Patil, D. S.; Pedley,
J. B. J. Chem. Soc., Chem. Commun. 1975, 830. (c) Schock, L. E.;
Marks, T. J. J. Am. Chem. Soc. 1988, 110, 7701.
(42) Guanidino(2-): Tin, M. K. T.; Yap, G. P. A.; Richeson, D. S. Inorg.
Chem. 1998, 37, 6728. Guanidino(1-): Gazard, P. A.; Melvyn, K.;
Batsanov, A. S.; Howard, J. A. K. J. Chem. Soc., Dalton Trans. 1997,
4625.
(39) Dh(Zr-NMe2) ) 83.6 kcal/mol, Dh(Hf-NMe2) ) 88.4 kcal/mol:
Cardin, D. J.; Lappert, M. F.; Raston, C. L. Chemistry of Organo-
Zirconium and -Hafnium Compounds; Ellis Horwood Limited: West
Sussex, U.K., 1986; pp 16-22.
(40) March, J. AdVanced Organic Chemistry: Reactions, Mechanisms, and
Structure, 4th ed.; Wiley: New York, 1992; p 24.

3824 Inorganic Chemistry, Vol. 38, No. 17, 1999
Thorman et al.
i
complex 6 suggests two possibilities: (1) rapid inversion which
is not restricted at the lowest temperature observed (223 K);
(2) existence of only one isomer. However, syn-anti inversion
barriers of imine units are typically on the order of 10-20 kcal/
mol.43 Also, it is unlikely that the imine inversion barrier in
complex 7 is significantly lower than normal. Consequently,
the imine fragment in complex 6 must exist in one geometric
form. This is not unreasonable, as the two large AriPr substituents
should prefer to occupy mutually anti sites.
products from the reaction of RNCO and PrNdCdNiPr with
imido complexes 1 and 2 are formed with the NAriPr moiety
remaining bonded to the metal and the heterocumulene-derived
nitrene in the distal 3-position of the metallacycle. Distinct
isomerization conditions found for 4a and 5a illustrate the steric
interactions of the porphyrin macrocycle with substituents in
the R-position of the metallacycle ligand as well as bonding
characteristics between Zr-N and Hf-N. Steric factors appear
to be manifested in the conversion of the kinetic isomers to the
thermodynamic complexes. Differences in bond strengths
between the M-N(amide) bonds (M ) Zr, Hf) are exhibited in
the requirement of more forcing conditions for isomerization
of 5a relative to 4a.
The imido complexes also exhibit reactivity with a variety
of other heterocumulenes, aldehydes, and ketones. The chemistry
of an interesting pinacolone coupling product, (TTP)Zr(η2-
OC(tBu)(Me)CHdC(tBu)O), is currently under investigation.23
Conclusion
Acknowledgment. We are grateful for support from the
Camille and Henry Dreyfus Foundation.
In summary, we have found the rigid basil plane formed by
the porphyrin results in novel zirconium and hafnium imido
reaction products in comparison to known LnMdNR (M ) Zr,
Hf) complexes with other supporting ligand systems. Kinetic
Supporting Information Available: Five X-ray crystallographic
files, in CIF format, and tables of crystal data, structure solution and
refinement details, atomic coordinates, thermal parameters, and bond
distances and angles. This material is available free of charge via the
Internet at http://pubs.acs.org.
(43) (a) Patai, S. The Chemistry of the Carbon-Nitrogen Double Bond;
Interscience Publishers: London, 1970; Chapter 9. (b) Hartwig, J. F.;
Bergman, R. G.; Andersen, R. A. Organometallics 1991, 10, 3344.
(c) Knorr, R.; Ruhdorfer, J.; Mehlstaubl, J.; Bohrer, P.; Stephenson,
D. S. Chem. Ber. 1993, 126, 747.
IC981399J