Tantalacyclobutane complexes containing the potentially C,N,N′ -coordinating ligand [C6H4(CH2N(Me)CH2 CH2NMe2)-2]- (CNN) and their reactivity with carbon monoxide and tert-butyl isocyanide. X-ray molecular structures of [Ta{CH2 CH(Me)CH2-1,3}(CNN)(O-t-Bu)2]

Article abstract of DOI:10.1021/om960808l

From the reactions of the unsubstituted tantalacyclobutane complex [Ta{(CH₂)₃-1,3}(CNN)-(O-t-Bu)₂] (CNN = [C₆H₄(CH₂N(Me)CH₂CH ₂NMe₂)-2]^-) (1) with propene and styrene have been isolated in good yields the substituted tantalacyclobutane complexes [TaJCH₂CH(Me)-CH₂-1,3}(CNN)(O-t-Bu)₂] (2) and [Ta{CH₂CH(Ph)CH₂-1,3}(CNN)(O-t-Bu)₂] (3), respectively. The X-ray molecular structures of 2 and 3 show them to be seven-coordinate pentagonal bipyramidal species in which the meridional ligation comprises C,N,N′-bonding of the aryldiamine ligand CNN and σ-bonding of two carbons of the metallacycle; the two alkoxide groups occupy the apical positions. The organyl substituent of the metallacycle is positioned on the β-carbon. Complexes 2 and 3 can both be converted back into 1 by reacting them in Et₂O with ethene. The reaction of 1 with carbon monoxide yields the oxytantalacyclopropane complex [Ta{C(O)((CH₂)₃-1,3)}(CNN)(O-t-Bu)₂] (4), which has been isolated as an air-stable white solid in 59% yield. The X-ray molecular structure of 4 reveals that the carbon and oxygen atoms of the C=O function are ligated in the meridional plane with further η³-C,N,N′-ligation of CNN and the two alkoxides as found in 2 and 3. Reaction of the tantalacyclobutane complexes 2-4 with 1 equiv of t-BuNC affords the 1:1 insertion products [Ta{C(=N-t-Bu)-CH₂CH(R)CH₂-1,4}(CNN)(O-t-Bu)₂] (R = H (5), Me (6), and Ph (7), respectively). Complexes 5 and 7 have been isolated as yellow solids (yields: 5, 62%; 7, 50%), while 6 has been prepared and characterized in situ. ¹H and ¹³C NMR spectroscopy of 6 and 7 indicate for each complex the presence of two isomers in solution. The X-ray molecular structure of 7 shows η²-C,N-bonding of the CNN ligand through the aryl C_ipso atom and the N(Me) donor atom and, most importantly, the presence of two tantalacyclic rings of different sizes that have a common Ta-C bond. The smaller three-membered ring comprises the metal center with the nitrogen and the α-carbon atom of the η²-bonded iminoacyl fragment, while the larger five-membered ring is a metallacylopentane system comprising the metal center and four carbon atoms.

Full text of DOI:10.1021/om960808l

168
Organometallics 1997, 16, 168-177
Ta n ta la cyclobu ta n e Com p lexes Con ta in in g th e
P oten tia lly C,N,N′-Coor d in a tin g Liga n d
[C6H4(CH2N(Me)CH2CH2NMe2)-2]- (CNN) a n d Th eir
Rea ctivity w ith Ca r bon Mon oxid e a n d ter t-Bu tyl
Isocya n id e. X-r a y Molecu la r Str u ctu r es of
[Ta {CH2CH(Me)CH2-1,3}(CNN)(O-t-Bu )2],
[Ta {CH2CH(P h )CH2-1,3}(CNN)(O-t-Bu )2],
[Ta {C(O)((CH2)3-1,3)}(CNN)(O-t-Bu )2], a n d
[Ta {C(dN-t-Bu )CH2CH(P h )CH2-1,4}(CNN)(O-t-Bu )2]|
Marco H. P. Rietveld,† Henk Hagen,† Leon van de Water,† David M. Grove,†
Huub Kooijman,‡ Nora Veldman,‡ Anthony L. Spek,‡,§ and Gerard van Koten*,†
Debye Institute, Department of Metal-Mediated Synthesis, and Bijvoet Center for Biomolecular
Research, Department of Crystal and Structural Chemistry, Utrecht University,
Padualaan 8, 3584 CH Utrecht, The Netherlands
Received September 23, 1996X
From the reactions of the unsubstituted tantalacyclobutane complex [Ta{(CH2)3-1,3}(CNN)-
(O-t-Bu)2] (CNN ) [C6H4(CH2N(Me)CH2CH2NMe2)-2]-) (1) with propene and styrene have
been isolated in good yields the substituted tantalacyclobutane complexes [Ta{CH2CH(Me)-
CH2-1,3}(CNN)(O-t-Bu)2] (2) and [Ta{CH2CH(Ph)CH2-1,3}(CNN)(O-t-Bu)2] (3), respectively.
The X-ray molecular structures of 2 and 3 show them to be seven-coordinate pentagonal
bipyramidal species in which the meridional ligation comprises C,N,N′-bonding of the
aryldiamine ligand CNN and σ-bonding of two carbons of the metallacycle; the two alkoxide
groups occupy the apical positions. The organyl substituent of the metallacycle is positioned
on the â-carbon. Complexes 2 and 3 can both be converted back into 1 by reacting them in
Et2O with ethene. The reaction of 1 with carbon monoxide yields the oxytantalacyclopropane
complex [Ta{C(O)((CH2)3-1,3)}(CNN)(O-t-Bu)2] (4), which has been isolated as an air-stable
white solid in 59% yield. The X-ray molecular structure of 4 reveals that the carbon and
oxygen atoms of the CdO function are ligated in the meridional plane with further η3-C,N,N′-
ligation of CNN and the two alkoxides as found in 2 and 3. Reaction of the tantalacyclobutane
complexes 2-4 with 1 equiv of t-BuNC affords the 1:1 insertion products [Ta{C(dN-t-Bu)-
CH2CH(R)CH2-1,4}(CNN)(O-t-Bu)2] (R ) H (5), Me (6), and Ph (7), respectively). Complexes
5 and 7 have been isolated as yellow solids (yields: 5, 62%; 7, 50%), while 6 has been prepared
and characterized in situ. 1H and 13C NMR spectroscopy of 6 and 7 indicate for each complex
the presence of two isomers in solution. The X-ray molecular structure of 7 shows η2-C,N-
bonding of the CNN ligand through the aryl Cipso atom and the N(Me) donor atom and, most
importantly, the presence of two tantalacyclic rings of different sizes that have a common
Ta-C bond. The smaller three-membered ring comprises the metal center with the nitrogen
and the R-carbon atom of the η2-bonded iminoacyl fragment, while the larger five-membered
ring is a metallacylopentane system comprising the metal center and four carbon atoms.
In tr od u ction
t-Bu, CMe2Ph) in which CNN functions as a chelating
system.1 In the dichloride complex (X ) Cl) the CNN
ligand is η3-C,N,N′ pseudofacially-bonded to the metal
by the aryl Cipso carbon atom and the N(Me) and NMe2
nitrogen donors both in solution and in the solid state.
In solution at room temperature the dialkoxide com-
plexes (X ) O-t-Bu) have the CNN ligand only η2-C,N-
bonded to the metal by the aryl Cipso carbon atom and
the N(Me) nitrogen donor. Apparently the dialkoxide
complexes, compared to the dichloride species, have a
In a recent paper we reported that the anionic
aryldiamine ligand [C6H4(CH2N(Me)CH2CH2NMe2)-2]-
(CNN), which has a single ortho substituent, can be used
to synthesize new tantalum alkylidene complexes [Ta-
(dCHR)(CNN)X2] (X ) Cl, R ) t-Bu; X ) O-t-Bu, R )
* To whom correspondence should be addressed.
† Debye Institute.
‡ Bijvoet Center for Biomolecular Research.
§ Address correspondence pertaining to crystallographic studies to
this author.
| This work was reported at the 11th International Symposium on
Olefin Metathesis and Related Chemistry, Durham, England, J uly,
1995: van Koten G. Application of Well-Defined Transition Metal
Alkylidenes in Olefin Metathesis. ISOM abstract book L23.
X Abstract published in Advance ACS Abstracts, December 15, 1996.
(1) Rietveld, M. H. P.; Teunissen, W.; Hagen, H.; van de Water, L;
Grove, D. M.; van der Schaaf, P. A.; Mu¨hlebach, A.; Kooijman, H.;
Smeets, W. J . J ; Veldman, N.; Spek, A. L.; van Koten, G. Organome-
tallics, in press.
S0276-7333(96)00808-4 CCC: $14.00 © 1997 American Chemical Society

Tantalacyclobutane Complexes
Organometallics, Vol. 16, No. 2, 1997 169
Sch em e 1. Syn th esis of th e Câ-Su bstitu ted
Ta n ta la cyclobu ta n e Com p lexesa
lower Lewis acidity of the metal center due to pπ f dπ
electron donation of the alkoxide lone pairs to the metal
center.2 This difference in bonding of CNN between the
dialkoxide and the dichloride species is also reflected
in their reactivity. The dichloride complex does not
react with ethene and does not show ring-opening
metathesis polymerization (ROMP) reactivity with nor-
bornene, whereas the dialkoxide neopentylidene and
neophylidene complexes react at room temperature with
ethene to form the tantalacyclobutane complex [Ta-
{(CH2)3-1,3}(CNN)(O-t-Bu)2], 1. Interestingly, reaction
of the dialkoxide neophylidene complex and ethene at
69 °C affords the ethene adduct complex [Ta(H2CdCH2)-
(CNN)(O-t-Bu)2].1 The X-ray molecular structures of the
tantalacyclobutane complex 1 and the ethene adduct
complex show the CNN ligand to be η3-C,N,N′-bonded
to the metal in a meridional fashion. The five-
coordinate alkylidene complex [Ta(dCH-t-Bu)(C6H4CH2-
NMe2-2)(O-t-Bu)2], which contains an η2-C,N chelating
arylamine, also reacts with ethene, but a mixture of
unstable products results.1 The tantalum CNN di-
alkoxide complex [Ta(dCHCMe2Ph)(CNN)(O-t-Bu)2] and
1 are active ROMP catalysts for the polymerization of
norbornene and dicyclopentadiene, and though the rate
of their reactivity with these strained cyclic olefins is
low at room temperature, it is greatly increased at 70
°C. In the case of norbornene polymers are obtained
with approximately 90% trans-vinylene bonds. In con-
trast, the reaction of norbornene with the five-coordinate
neophylidene complex [TaCl(dCHCMe2Ph)(O-t-Bu)2-
(PMe3)] at room temperature is extremely rapid and
affords a polymer with 70% trans-vinylene double
bonds.1
a
Reaction conditions: i, +C2H3R′, -C2H4, Et2O, RT (room
temperature); ii, +C2H4, -C2H3R′, Et2O, RT.
stable isolable species containing oxytantalacyclopro-
pane and tantalum η2-iminoacyl moieties, respectively.
Resu lts a n d Discu ssion
Rea ctivity of 1 w ith P r op en e a n d Styr en e. Reac-
tion of a saturated diethyl ether solution of the known
tantalacyclobutane complex [Ta{(CH2)3-1,3}(CNN)(O-t-
Bu)2] (CNN ) [C6H4(CH2N(Me)CH2CH2NMe2)-2]-) (1)1
with propene affords the methyl-substituted tantala-
cyclobutane complex [Ta{CH2CH(Me)CH2-1,3}(CNN)-
(O-t-Bu)2] (2), which has been isolated as a white air-
sensitive solid in 84% yield (Scheme 1). In the same
way reaction of 1 with 1 equiv of styrene affords the
phenyl-substituted tantalacyclobutane complex [Ta-
{CH2CH(Ph)CH2-1,3}(CNN)(O-t-Bu)2] (3), which has
been isolated as a white solid in 65% yield (Scheme 1).
The methyl- and the phenyl-substituted tantalacyclo-
butane complexes 2 and 3, respectively, can both be
converted back into the unsubstituted tantalacyclo-
butane 1 by dissolving them in diethyl ether and then
saturating the solution with ethene; i.e., it is obvious
that these substitution reactions are reversible (vide
infra). Complexes 2 and 3 are soluble in benzene,
toluene, and diethyl ether but are insoluble in pentane
or hexane. Needle-shaped colorless crystals of 2 and 3
can be obtained by recrystallization from a saturated
diethyl ether solution at -30 °C. The solid powdered
tantalacyclobutane complexes 1-3 decompose in less
than 5 min on exposure to air forming a sticky yellowish
mass, but they can be stored intact under a nitrogen
atmosphere for months. In solution at room tempera-
ture 1-3 slowly decompose liberating ethene, propene,
and styrene, respectively, together with C6H5CH2N-
(Me)CH2CH2NMe2, i.e. protonated CNN.
We conclude from these results that the outer NMe2
nitrogen donor of the CNN ligand, even when it is only
weakly bonded, hampers approach of an alkene to the
alkylidene function. However, the CNN ligand can
stabilize reaction products and intermediates, like tan-
talacyclobutane species and ethene adducts, and is
therefore an ideal ligand for the study of elementary
reaction processes.
In this paper we report first on reaction of the
tantalacyclobutane complex 1 with terminal olefins that
affords new isolable â-substituted tantalacyclobutanes.
Second, we have investigated insertion reactions of
small molecules, i.e. CO and t-BuNC, into the metal-
carbon bonds of such species. Although much is known
concerning the reactions of metal-carbon bonds with
CO3 and isocyanides,4 the literature concerning metal-
lacycles is comparatively limited.3a-g,4a-e We now show
that CNN tantalacylobutane complexes undergo inser-
tion reactions with CO and t-BuNC to afford interesting
Solid -Sta te Str u ctu r es of 2 a n d 3. The molecular
structures of 2 and 3 together with the adopted num-
(4) (a) Berg, F. J .; Petersen, J . L. Organometallics 1993, 12, 3890.
(b) Berg, F. J .; Petersen, J . L. Organometallics 1989, 8, 2461. (c) Berg,
F. J .; Peterson, J . L. Organometallics 1991, 10, 1599. (d) Berg, F. J .;
Peterson, J . L. Tetrahedron 1992, 23, 4749. (e) Valero, C.; Grehl, M.;
Wingbermu¨hle, D.; Kloppenburg, L.; Carpenetti, D.; Erker, G.; Peter-
son, J . L. Organometallics 1994, 13, 415. (f) Martin, A.; Mena, M.;
Pellinghelli, M. A.; Royo, P.; Serrano, R.; Tiripicchio, A. J .Chem. Soc.,
Dalton Trans. 1993, 2117. (g) Curtis, M. D.; Real, J .; Hirpo, W.; Butler,
W. M. Organometallics 1990, 9, 66. (h) Filippou, A. C.; Gru¨nleiter, W.;
Vo¨lkl, C.; Kiprof, P. J . Organomet. Chem. 1991, 413, 181. (i) Filippou,
A. C.; Gru¨nleiter, W.; Fischer, E. O.; Imhof, W.; Huttner, G. J .
Organomet. Chem. 1991, 413, 165. (j) Chamberlain, L. R.; Rothwell, I.
P; Huffman, J . C. J . Chem. Soc., Chem. Commun. 1986, 1203. (k) Klei,
E.; Teuben, J . H. J . Organomet. Chem. 1981, 209, 297. (l) Bazan, G.
C.; Donnelly, S. J .; Rodriguez, G. J . Am. Chem. Soc. 1995, 117, 2671.
(m) Pizzano, A.; Sa´nchez, L. Altmann, M.; Monge, A.; Ruiz, C.;
Carmona, E. J . Am. Chem. Soc. 1995, 117, 1759. (n) Durfee, L. D.;
Hill, J . E.; Fanwick, P. E.; Rothwell Organometallics 1990, 9, 75. (o)
Chiu, K. W.; J ones, R. A.; Wilkinson, G.; Galas, A. M. R.; Hursthouse,
M. B. J . Chem. Soc., Dalton Trans. 1981, 2088. (p) Chiu, K. W.; J ones,
R. A.; Wilkinson, G.; Galas, A. M. R.; Hursthouse, M. B. J . Am. Chem.
Soc. 1980, 102, 7979.
(2) Coffindaffer, I. W.; Rothwell, I. P.; Huffmann, J . Inorg. Chem.
1983, 22, 2906.
(3) (a) Arnold, J .; Tilley, T. D.; Rheingold, A. L.; Geib, S. J .; Arif, A.
M. J . Am. Chem. Soc. 1984, 111, 149. (b) Meinhart, J . D.; Santarsiero,
B. D.; Grubbs, R. H. J . Am. Chem. Soc. 1986, 108, 3318. (c) Grubbs,
R. H.; Miyashi, A.; Liu, M.; Burk, P. J . Am. Chem. Soc. 1978, 100,
2418. (d) McDermott, J . X.; Wilson, M. E.; Whiteside, G. M. J . Am.
Chem. Soc. 1976, 98, 6529. (e) McDermott, J . X.; Whiteside, G. M. J .
Am. Chem. Soc. 1974, 96, 947. (f) Manriquez, J . M.; McAlister, D. R.;
Sanner, R. D.; Bercaw, J . E. J . Am. Chem. Soc. 1978, 100, 2716. (g)
Peterson, J . L.; Egan, J . W. Organometallics 1987, 6, 2007. (h) Durfee,
L. D.; Rothwell, I. P. Chem. Rev. 1988, 88, 1059 and references therein.
(i) Erker, G. Acc. Chem. Res. 1984, 17, 103. (j) Wood, C. D.; Schrock,
R. R. J . Am. Chem. Soc. 1979, 101, 5431. (k) Meyer, T. Y.; Garner, L.
R.; Baenziger, J .; Tilley, T. D.; Messerle, L. Inorg. Chem. 1990, 29,
4045.

170 Organometallics, Vol. 16, No. 2, 1997
Rietveld et al.
Ta ble 1. Bon d Dista n ces (Å) a n d An gles (d eg) for 2
a n d 3
2
3
Ta(1)-O(1)
Ta(1)-O(2)
Ta(1)-C(1)
Ta(1)‚‚‚C(14)
Ta(1)-N(1)
Ta(1)-N(2)
Ta(1)-C(13)
Ta(1)-C(15)
C(13)-C(14)
C(14)-C(15)
C(14)-C(24)
1.890(3)
1.896(3)
2.307(5)
2.894(5)
2.425(4)
2.506(4)
2.264(5)
2.238(5)
1.517(8)
1.529(7)
1.524(7)
1.892(5)
1.895(5)
2.287(7)
2.880(6)
2.398(6)
2.482(7)
2.244(7)
2.271(6)
1.499(9)
1.543(10)
1.518(9)
O(1)-Ta(1)-O(2)
O(1)-Ta(1)-C(13)
O(1)-Ta(1)-C(15)
O(1)-Ta(1)-C(1)
O(1)-Ta(1)-N(1)
O(1)-Ta(1)-N(2)
N(1)-Ta(1)-C(1)
N(1)-Ta(1)-C(15)
N(1)-Ta(1)-C(13)
N(1)-Ta(1)-N(2)
Ta(1)-O(1)-C(16)
Ta(1)-O(2)-C(20)
Ta(1)-C(13)-C(14)
Ta(1)-C(15)-C(14)
C(13)-C(14)-C(15)
C(13)-Ta(1)-C(15)
168.82(15)
92.95(16)
95.61(17)
92.77(17)
86.25(14)
85.62(14)
70.80(17)
147.90(17)
151.44(18)
72.37(14)
159.5(3)
169.9(2)
94.6(2)
91.8(2)
94.6(2)
88.0(2)
85.8(2)
70.3(3)
151.6(3)
147.4(2)
73.1(2)
161.9(4)
160.6(5)
98.6(5)
96.2(4)
97.7(5)
61.0(3)
159.5(3)
97.9(3)
98.6(3)
96.5(4)
60.63(19)
ent on C(14) is in an equatorial position with the H atom
positioned on the side of the meridional plane opposite
to that of the methyl group of the inner N(Me) unit.
Solutions of 2 and 3 do show the presence of the second
possible diastereoisomer (vide infra).
The Ta- -Câ distances of 2.894(5) and 2.880(6) Å in
complexes 2 and 3, respectively, compare favorably with
those of 2.846(19) and 2.868(7) Å found in the two
crystal modifications of complex 1.1 Within the metal-
lacycle the dihedral angle between the planes C(13)-
Ta(1)-C(15) and C(13)-C(14)-C(15) in 2 (25.1(4)°) and
3 (25.7(6)°) are also similar to the corresponding angles
found for complex 1 (26.8(6) and 23.1(17)°).1 In both 2
and 3 the Ta-O distances have values of approximately
1.89 Å.
F igu r e 1. ORTEP thermal motion ellipsoid plot19 (drawn
at 30% probability level) of (a) [Ta{CH2CH(Me)CH2-
1,3}(CNN)(O-t-Bu)2] (2) and (b) [Ta{CH2CH(Ph)CH2-1,3}-
(CNN)(O-t-Bu)2] (3) together with adopted numbering
scheme. Hydrogen atoms have been omitted for clarity.
NMR Sp ectr oscop y of th e Ta n ta la cyclobu ta n e
1
Com p lexes 2 a n d 3. The H NMR spectra of 2 and 3
show characteristic resonance patterns associated with
the pentagonal bipyramidal structures as shown in
Figure 1 (vide supra). For example, both 2 and 3 afford
two Me resonances for the NMe2 unit, and the ArCH2N-
(Me) protons give rise to a well-resolved AB pattern. A
complication in the NMR spectra of both 2 and 3 is that
there are signals for two diastereoisomers in a 1:10 and
1:12 molar ratio, respectively. These diastereoisomers
are due to the presence of two chiral centers, i.e. the
ArCH2NMe nitrogen donor and the CH(R) carbon atom
of the metallacyle; the major diastereoisomer is that in
which the N(Me) unit has an S configuration and the
â-substituent is in equatorial position. Due to severe
overlap of the signals of the major isomer with the minor
isomer in 2 and 3 only the signals of the major isomer
bering scheme are shown in Figure 1. The bond
distances and angles for 2 and 3 are given in Table 1.
Complexes 2 and 3 are mononuclear pentagonal bi-
pyramidal tantalum(V) species with the aryl Cipso
carbon, the inner N(Me), and the outer NMe2 nitrogen
donor atoms of the CNN ligand together with the
σ-bonded carbons of the metallacycle forming the me-
ridional plane, while the two alkoxide groups are in the
apical positions. Overall, both structures show great
similarity to the structure of the parent tantalacyclo-
butane complex 1.1 In both 2 and 3 coordination of the
inner N(Me) nitrogen donor of CNN makes this nitrogen
donor a stereogenic center; Figure 1 shows the S
configuration, but both enantiomers are present in the
unit cell. Furthermore, the metallacycle Ta-C(13)-
C(14)-C(15) in 2 and 3 has an organyl substituent (Me
and Ph, respectively) on the â-carbon (C(14)) of the ring.
Accordingly this CH(R) carbon atom is a stable chiral
center and each complex can exist in two diastereoiso-
meric forms. The X-ray structures of both 2 and 3
represent the diastereoisomer in which the R substitu-
1
have been fully assigned. The H and 13C NMR data
for the metallacyclic ring of 1-3 are listed in Table 2.
These data, and in particular the characteristic positions
of the protons on the CR carbon atom (HR) of the
metallacyclic ring that are at higher field than those of
the Câ protons (Hâ), underline the structural similarity
of complexes 1-3 in solution. The 13C chemical shift

Tantalacyclobutane Complexes
Organometallics, Vol. 16, No. 2, 1997 171
Ta ble 2. Releva n t 1H (200.13 MHz) a n d 13C (50.32 MHz) NMR Da ta for th e Meta lla cycles of 1-3a
b
b
complex
HR
Hâ
CR
Câ
1c
2
3
0.61, 0.76, 0.87, 1.58
0.29, 0.96, 1.68, 1.95
0.77, 1.12, 1.44, 2.18
3.75, 4.69
3.20
4.33
23.7 (121), 36.7 (120)
36.9 (124), 49.3 (125)
34.7 (124), 46.7 (122)
25.0 (123)
37.1 (129)
41.3 (128)
a
Measured in C6D6 at 298 K. Chemical shifts (δ, ppm) referenced to SiMe4. b 1J (C,H) in Hz in parentheses. c Data from ref 1.
Sch em e 2. P ostu la ted Mech a n ism for th e
F or m a tion of Com p lexes 2 a n d 3 (*Ta )
{Ta (CNN)(O-t-Bu )2})a
Sch em e 3. Syn th esis of Com p lexes 4-7a
a
Reaction conditions: i, +C2H4; ii, -C2H4; iii, +C2H3R; iv,
-C2H3R.
values for CR and Câ fall in the range 20-50 ppm, and
the 1J (C,H) values of approximately 125 Hz indicate
that the carbon atoms of the metallacycle have more
aliphatic (sp3) than olefinic (sp2) character. In each
complex the absolute differences in chemical shift
between the CR and Câ atoms, i.e. |δ(CR) - δ(Câ)|, is
relatively small (∼10 ppm) and similar small values for
|δ(CR) - δ(Câ)| were also found by Schrock and co-
workers for square-pyramidal tantala- and tungstacy-
clobutane complexes which contain small CR-M-CR
angles (∼60°) and relative long M- - -Câ distances (∼2.8
Å). In contrast trigonal-bipyramidal tantala- and tung-
stacyclobutane complexes which contain large CR-M-
CR angles (∼80°) and short M- - -Câ distances (∼2.3 Å)
show a relatively large value for |δ(CR) - δ(Câ)|, and it
was therefore concluded that there is a direct correlation
between |δ(CR) - δ(Câ)| and the M- - -Câ distance.5
The molecular structures of the pentagonal-bipyra-
midal tantalacyclobutane complexes described in this
paper and in a previous paper1 are comparable to the
square-pyramidal tantalum tungsten complexes men-
tioned earlier; i.e., they have small CR-M-CR angles
and long M- - -Câ distances (vide supra) and, consistent
with earlier reports, they show small differences in
chemical shift values between CR and Câ.
Mech a n ism for th e F or m a tion of 2 a n d 3. The
formation of complexes 2 and 3 from 1 and an alkene is
a process which can be reversed by reaction with excess
ethene (vide supra). On the basis of the experimental
observations, we propose a mechanism for the formation
of 2 and 3 which is shown in Scheme 2. The first step
in this mechanism involves a rearrangement of a
metallacyclic complex into an “alkylidene/olefin” inter-
mediate5a from which loss of ethene results in the
formation of a methylene intermediate (Scheme 2).
Schrock and co-workers were able to trap the meth-
ylene intermediate [W(dCH2)(NAr){OCMe2(CF3)}(PMe3)]
by addition of PMe3 to a solution of the tungstacyclo-
a
Reaction conditions: i (1), CO, 1 atm, Et2O, RT, 48 h. ii
(1-3): + t-BuNC, Et2O, RT, 1 h.
butane complex [W{(CH2)3-1,3}(NAr){OCMe2(CF3)}].5a
Related kinetic studies on the reaction of [W{CH2CH-
(t-Bu)CH2-1,3}(NAr)(OAr)2] with ethene, which gives
the unsubstituted tungstacyclobutane complex
[W{(CH2)3-1,3}(NAr){OCMe2(CF3)}], showed this reac-
tion to be independent of the ethene concentration; i.e.,
the methylene intermediate forms by a dissociative
mechanism as is shown in Scheme 2.5 In earlier work
from our group we proposed that the methylene inter-
mediate as shown in Scheme 2 is involved in the
formation of complex 1 from the reaction of alkylidene
complexes [Ta(dCHR)(CNN)(O-t-Bu)2] (R ) t-Bu, CMe2-
Ph) with ethene.1
In the second step of the proposed mechanism the
methylene intermediate can react either with ethene to
re-form 1 or in the forward direction with propene or
styrene to form 2 or 3, respectively. In practice because
of loss of ethene from the solution the equilibrium shifts
completely to the side of the substituted tantalacyclo-
butane complexes 2 and 3. Probably for steric reasons
the organyl substituent of the olefin becomes located in
the products 2 and 3 on the â carbon atom of the
metallacyle as far away from the bulky groups attached
to the metal center as possible (Scheme 2).
Rea ctivity of Com p lexes 1-3 w ith CO. The
unsubstituted tantalacyclobutane 1 reacts with CO at
room temperature to afford the oxytantalacyclopropane
complex [Ta{C(O)((CH2)3-1,3)}(CNN)(O-t-Bu)2] (4), which
has been isolated as a white air-stable solid in 59% yield
(Scheme 3). Complex 4 is soluble in benzene, toluene,
and diethyl ether, but it is insoluble in pentane and
hexane. Needle-shaped colorless crystals of 4 were
obtained by slow cooling of a saturated diethyl ether
solution from +25 to -30 °C. In contrast to the
unsubstituted tantalacyclobutane complex 1, the meth-
yl- and phenyl-substituted tantalacyclobutane com-
plexes 2 and 3, respectively, react only slowly with CO
in benzene-d6 and after 2 days NMR spectroscopy
(5) (a) Feldman, J .; Davis, W. M.; Thomas, J . K.; Schrock, R. R.
Organometallics 1990, 9, 2535 and references therein. (b) Wallace, K.
C.; Liu, A. H.; Dewan, J . C.; Schrock, R. R. J . Am. Chem. Soc. 1988,
110, 4964. (c) Feldman, J .; Schrock, R. R. Prog. Inorg. Chem. 1991,
39, 1.

172 Organometallics, Vol. 16, No. 2, 1997
Rietveld et al.
showed the formation of a mixture of products from
which no stable organometallic product could be iso-
lated. In the 13C NMR spectrum of this in situ mixture
no signals in the region around 100 ppm, indicative for
an oxymetallacyclopropane CO carbon,6a-e were found.
The 1H NMR spectrum of 4 shows this complex to
exist as two isomers in a 10:1 molar ratio. The major
product has the aromatic Hortho signal of the CNN ligand
at 9.06 ppm whereas the minor product has an aromatic
Hortho signal at 9.33 ppm. Unfortunately, most of the
resonances of this minor product could not be assigned
accurately due to overlap with those of the major
product. We believe the two species are mutual isomers
which differ in orientation of the oxytantalacyclopropane
1
unit. Overall the H spectrum of the major isomer of 4
is in accordance with a pentagonal bipyramidal struc-
ture with the two O-t-Bu groups occupying the apical
positions as found in the solid-state molecular structure
(vide infra) illustrated in Figure 4. This spectrum
shows, for example, two Me signals for a diastereotopic
NMe2 unit and a well-resolved AB pattern for the
ArCH2N protons. The 13C NMR (50 MHz, C6D6, 25 °C)
spectrum of 4 shows a signal for the CO carbon atom
at 100.6 ppm and CH2 signals for the cyclobutanone ring
are present at 16.79, 49.59 and 51.56 ppm. The
“acetone-coordinated” complex [Ta(Me)2(η5-C5Me5){η2-
C(O)Me2}] described by Schrock and co-workers has a
similar characteristic high-field CO carbon resonance
at 111 ppm;2j in other oxymetallacyclopropane com-
plexes this resonance falls in the range 80-120 ppm.6a-e
The IR spectrum (KBr) of 4 shows a ν(C-O) value
F igu r e 2. ORTEP thermal motion ellipsoid plot19 (drawn
at 30% probability level) of [Ta(η2-C(O)(CH2)3)(CNN)(O-t-
Bu)2] (4) together with adopted numbering scheme. Hy-
drogen atoms have been omitted for clarity.
Sp ectr oscop ic Ch a r a cter iza tion of 5-7. Com-
plexes 5-7 have been (primarily) characterized by
spectroscopic techniques and a single-crystal structure
determination of 7. Both in the solid state and in
solution they are seven-coordinate complexes which
contain two tantalacycles of different sizes that share
a common Ta-C bond and which have only C,N-bonding
of the CNN ligand.
for the oxytantalacylopropane fragment at 1181 cm-1
,
1
The H NMR (300 MHz, C6D6, 25 °C) spectra of 5-7
and since noncoordinated cyclobutanone has a ν(C-O)
value of 1790 cm-1,7 this value indicates that in 4 there
is strong overlap of the CdO π* acceptor orbital with
the occupied frontier orbitals of the [Ta(CNN)(O-t-Bu)]
fragment. The “acetone-coordinated” complexes [Ta-
(Me)2(η5-C5Me5){C(O)Me2}] and [WCl2{C(O)Me2)2(PMe2-
Ph)2) afford similar ν(C-O) values of 1200 and 1230
cm-1, respectively.3j,6d
Rea ctivity of Com p lexes 1-3 w ith t-Bu NC. Ad-
dition of 1 equiv of t-BuNC to diethyl ether solutions of
the tantalacyclobutane complexes 1-3 affords the
monoinsertion products [Ta{C(dN-t-Bu)(CH2CH(R)CH2-
1,4}(CNN)(O-t-Bu)2] (R ) H (5), Me (6), and Ph (7),
respectively), see Scheme 3, which contain an η2-bonded
acylamino unit. Complexes 5 (62% yield) and 7 (50%
yield) have been isolated as air-sensitive needle-shaped
yellow crystals by slow cooling of saturated solutions
in pentane and diethyl ether, respectively, from +25 to
-30 °C. Due to its high solubility in organic solvents
attempts to crystallize 6 from either pentane or diethyl
ether were unsuccessful, and this complex has therefore
been characterized in situ by NMR spectroscopy of a
benzene-d6 solution of 2 to which 1 equiv of t-BuNC had
been added. The η2-acylimino complexes 5-7 are
soluble in benzene, toluene, and diethyl ether.
show only one Me resonance for the NMe2 unit of the
CNN ligand, and this indicates that this outer NMe2
nitrogen donor is not coordinated to the metal center
in solution. As anticipated the ArCH2N(Me) protons
give rise to a well-resolved AB pattern. As a result of
the stereogenity of both the inner N(Me) nitrogen donor
and the CH(R) carbon atom of the five-membered
metallacyclic ring, two different NMR-distinguishable
diastereoisomers are theoretically possible, i.e. RR/ SS
and RS/ SR, and these isomers are indeed observed in
1
an approximate ratio of 1:1.2 in the H and 13C NMR
spectra of 6 and 7. In the 13C spectra (50 MHz, C6D6,
25 °C) of 5-7 the signal for the CdN carbon resonates
at approximately 230 ppm, and this result is in ac-
cordance with literature data for η2-coordinated imi-
noacyl carbon atoms.4b,g,h,j
The IR spectra (KBr) of complexes 5 and 7 show
ν(CdN) absorptions at 1721 and 1726 cm-1, respec-
tively, and these data are in agreement with literature
values for iminoacyl complexes.4i,m For noncoordinated
imines ν(CdN) is found between 1690 and 1640 cm-1 7
,
and these data for 5 and 7 in KBr indicate that there is
an interaction of the CdN π* acceptor orbital with the
occupied frontier orbitals of the [Ta(CNN)(O-t-Bu)2]
fragment.
(6) (a) Chisholm, M. H.; Folting, K.; Klang, J . A. Organometallics
1990, 9, 607. (b) Hill, J . E.; Fanwick, F. E.; Rothwell, I. P. Organo-
metallics 1992, 11, 1771. (c) Williams, D. S.; Schofield, M. H.; Schrock,
R. R. Organometallics 1993, 12, 4560. (d) Bryan, J . C.; Mayer, J . M. J .
Am. Chem. Soc. 1987, 109, 7213. (e) Klein, D. P.; Dalton, D. M.;
Me´ndez, N. Q.; Arif, A. M.; Gladysz, J . A. J . Organomet. Chem. 1991,
412, C7. (f) Alt, H. G.; Herrmann, G. S.; Thewalt, U. J . Organomet.
Chem. 1987, 327, 237.
Solid -Sta te Str u ctu r es of Com p lexes 4 a n d 7.
The molecular structures of 4 and 7 are shown in
Figures 2 and 3, respectively, and relevant bond dis-
tances and angles are given in Table 3. The molecular
structure of 4 shows it to be a mononuclear pentagonal
bipyramidal tantalum species with the aryl Cipso carbon,
the N(Me) and NMe2 nitrogen donors, and the carbon
and oxygen atoms of the CdO group (C(13)-O(1))
(7) Grasselli, J . G.; Ritchy, W. M. Atlas of Spectral Data and Physical
Constants for Organic Compounds, 2nd ed.; CRC Press: Cleveland,
OH, 1975; Vol. III, p 96.

Tantalacyclobutane Complexes
Organometallics, Vol. 16, No. 2, 1997 173
Sch em e 4. P ostu la ted Mech a n ism for th e
F or m a tion of Com p lexes 4-7 (*Ta )
{Ta (CNN)(O-t-Bu )2})a
F igu r e 3. ORTEP thermal motion ellipsoid plot19 (drawn
at 30% probability level) of [Ta{C(dN-t-Bu)CH2CH(Ph)-
CH2-1,4}(CNN)(O-t-Bu)2] (7) together with adopted num-
bering scheme. Hydrogen atoms and the minor disorder
component have been omitted for clarity.
a
Reaction conditions i 1: CO, R ) H. ii 1-3: + t-BuNC. iii
insertion. iv ring closure.
Ta ble 3. Bon d Dista n ces (Å) a n d An gles (d eg) for 4
a n d 7
between the planes described by C(15), C(13), and C(14)
and C(15), C(16), and C(14) having a value of 16(2)°.
4
7
The structure of 7 (Figure 3) shows it to be a seven-
coordinate tantalum(V) species with an overall pentago-
nal bipyramidal structure in which the O-t-Bu groups
occupy the apical positions. In the meridional plane the
tantalum center is η2-C,N-bonded by the CNN ligand
and, most importantly, η3-N,C,C bis-chelate bonded by
the C(dN-t-Bu)CH2CH(Ph)CH2-1,4 unit to form two
tantalacycles of different sizes which share a common
Ta-C bond. The smaller three-membered ring com-
prises the metal center with the nitrogen donor N(3)
and carbon atom C(30) of the η2-bonded iminoacyl
fragment, while the larger five-membered ring consists
of the metal center and the four carbon atoms C(30)-
C(15)-C(14)-C(13), i.e. it is a metallacylopentane
system. The geometric parameters of the tantalum η2-
iminoacyl unit are normal for early transition metal
complexes which contain a side-on-bonded isocyanide
substituent.3b,e,g,h,l,m In particular the small N(3)-
Ta(1)-C(3) bite angle of 31.64(16)° within the iminoacyl
fragment is comparable to those found by Peterson et
al. in the tert-butyl isocyanide mono- and di-insertion
products [Cp2Zr{(CdN-t-Bu)CH2SiMe2CH2-1,4}] and
[Cp2M{(CdN-t-Bu)(CdN-t-Bu)CH2SiMe2CH2-1,5}] (M )
Zr, Hf), respectively.4a-e
Ta(1)-O(2)
Ta(1)-O(3)
Ta(1)-C(1)
C(13)-O(1)
Ta(1)-N(1)
Ta(1)-N(2)
Ta(1)-O(1)
Ta(1)-C(13)
1.885(10) Ta(1)-O(1)
1.887(10) Ta(1)-O(2)
2.261(15) Ta(1)-C(1)
1.401(17) C(30)-N(3)
2.384(15) Ta(1)-N(1)
2.424(12) Ta(1)-C(13)
1.971(11) Ta(1)-C(30)
2.141(17) Ta(1)-N(3)
1.903(3)
1.890(3)
2.246(5)
1.236(6)
2.442(4)
2.265(5)
2.099(5)
2.348(4)
O(2)-Ta(1)-O(3)
O(2)-Ta(1)-C(13) 96.5(5)
O(2)-Ta(1)-O(1)
O(2)-Ta(1)-C(1)
O(2)-Ta(1)-N(1)
O(2)-Ta(1)-N(2)
N(1)-Ta(1)-C(1)
N(1)-Ta(1)-C(13) 160.4(5) N(1)-Ta(1)-C(13) 156.24(15)
N(1)-Ta(1)-O(1)
N(1)-Ta(1)-N(2)
166.0(5) O(1)-Ta(1)-O(2)
169.60(16)
O(2)-Ta(1)-C(30) 89.19(18)
95.6(5)
92.6(5)
86.1(5)
84.5(4)
71.6(5)
O(2)-Ta(1)-N(3)
O(2)-Ta(1)-N(1)
O(2)-Ta(1)-C(1)
87.05(15)
88.52(14)
91.48(17)
O(2)-Ta(1)-C(13) 96.14(16)
N(1)-Ta(1)-C(1) 74.50(15)
159.7(4) N(1)-Ta(1)-C(30) 133.38(16)
75.8(4) N(1)-Ta(1)-N(3) 101.75(13)
Ta(1)-O(2)-C(17) 165.3(11) N(3)-Ta(1)-C(30) 31.64(16)
Ta(1)-O(3)-C(21) 163.7(10) C(13)-Ta(1)-C(30) 70.14(18)
O(1)-Ta(1)-C(13) 39.6(5)
C(14)-C(13)-C(15) 90.5(12)
O(1)-C(13)-C(14) 117.7(12)
O(1)-C(13)-C(16) 142.2(13)
forming the meridional plane and with the alkoxide
groups occupying the axial positions. This structure
therefore bears analogy to that of 1,1 as well as those of
2 and 3 described above. In 4 the ArCH2N(Me) nitrogen
donor is a stereogenic center with a fixed configuration
because of its coordination to the metal center, and
Figure 2 shows the S configuration. The most interest-
ing aspect of the structure of 4 is the presence of a
cyclobutanone system with the keto function “side-on”
bonded to the metal center (Ta-C(13) ) 2.265(5) Å, Ta-
O(1) ) 1.903(3) Å). The C(13)-O(1) distance of
1.401(17) Å compares favorably with C-O distances in
other oxymetallacyclopropane complexes described in
literature that generally fall in the range 1.3-1.4 Å.6a-f
The four-membered cyclobutanone ring C(13)-C(14)-
C(16)-C(15) in 4 is slightly puckered with the angle
Mech a n ism s for t h e F or m a t ion of Com p lexes
4-7. The molecules CO and t-BuNC often have a
similar chemistry that is related to the isoelectronic
structure of CtO and -NtC units. It is therefore likely
that the formation of the oxytantalacyclopropane com-
plex 4 and the acylimino complexes 5-7 follow the same
mechanistic pathway, and we propose the most likely
pathway to be that shown in Scheme 4. This mecha-
nism involves: (i) a dissociation of the Ta-NMe2
coordination bond and subsequent coordination of a CO
or t-BuNC molecule to the metal, (ii) insertion of these
molecules into the metal-carbon bond to afford an acyl
intermediate in the case of CO or the iminoacyl com-
plexes 5-7 in the case of t-BuNC, and (iii) in the case

174 Organometallics, Vol. 16, No. 2, 1997
Rietveld et al.
Sch em e 5. P ostu la ted Mech a n ism for th e Rea ction
of Ta n ta la cyclobu ta n e Com p lexes w ith CO via a
Keten e In ter m ed ia te (*Ta ) {Ta (CNN)(O-t-Bu )2})a
which the CO bond of the carbonyl group is bonded in
a “edge-on” fashion to the titanium center. However,
attempted reaction of this ketene complex with ethene
does not give a monosubstituted oxytitanacyclopropane
complex as would be expected when a mechanism
similar to that shown in Scheme 5 is operative. Instead
they found that insertion of CO into the Ti-C bond takes
place to afford a bis(alkoxide) complex which contains
a 1-oxa-titanacyclopentane unit.10b
a
Reaction conditions: i, -C2H4; ii, +C2H4; iii, +CO; iv,
+C2H4.
The reason that carbon monoxide reacts differently
with the unsubstituted tantalacyclobutane complex 1
than with the substituted tantalacyclobutane complexes
2 and 3 is not clear. It was therefore very surprising
that 1-3 do react in exactly the same way with t-BuNC
to afford in all cases iminoacyl complexes. An important
aspect worthy of note is that the reactions of 1-3 with
CO are seen to be very slow (taking many hours) when
compared to the almost instantaneous reactions with
t-BuNC. An explanation for this behavior might be
found in the possible solution equilibrium between a
metallacyclic form and an “alkylidene/olefin” form of the
tantalacyclobutane. Loss of the olefin from the latter
would lead to a methylene species (Scheme 2; vide
supra). If this equilibrium is more shifted to the side
of the “alkylidene/olefin” for the substituted tantala-
cyclobutane complexes 2 and 3 than for unsubstituted
tantalacyclobutane 1 because of steric hinderance of the
substituent on the olefin, then complexes 2 and 3 will
show more alkylidene character and are therefore more
likely to react with CO as shown in Scheme 5 to give a
ketene species. For complex 1 it is likely that this
equilibrium is shifted more to the metallacyclic side so
that reaction with CO, as shown in Scheme 4, affords
the oxytantalacyclopropane complex 4. However, with-
out spectroscopic evidence supporting a mechanism as
shown in Scheme 5 this explanation for the difference
in reactivity of the tantalacylobutane complexes 1-3
with CO is only speculative.
of the acyl intermediate a ring closure to afford the
oxytantalacyclopropane complex 4.
Hoffmann and co-workers found by extended Hu¨ckel
calculations that an iminoacyl complex8 is thermo-
dynamically more stable than an acyl complex, and this
result was further supported by experimental findings
of Sanchez and co-workers.4m The reason why the acyl
complex does not undergo ring closure in the case of the
iminoacyl complex (Scheme 4) might be explained by
these earlier results. Finally, further support for the
mechanism of Scheme 4 is provided by insertion reac-
tions of CO into the M-C bond of four- and five-
membered metallacyclic complexes which afford cyclo-
butanone9a-c and cyclopentanone.3d,e,9d-f
Alter n a tive Mech a n ism for th e F or m a tion of
Com p lex 4. On the basis of literature reports,9c,d,e an
alternative mechanism for the formation of 4 from 1 and
CO is possible, and this involves a ketene intermediate
as shown in Scheme 5. This mechanism involves
formation of a methylene intermediate via rearrange-
ment of the metallacycle of 1 into an “alkylidene/olefin”
intermediate and subsequent loss of the coordinated
ethene as described earlier in the mechanism for the
formation of the substituted tantalacyclobutanes 2 and
3. A ketene intermediate is then formed through a
reaction of this methylene intermediate with CO.10ab
Reaction of ethene, which was initially lost from the
“alkylidene/olefin” intermediate but which is still present
in solution, with this ketene intermediate gives complex
4. Although this alternative mechanism (Scheme 5) is
possible, it seems less likely as we have not observed
the presence of such a ketene intermediate by NMR
spectroscopy in the formation of 4. Futhermore, the
synthesis of the complexes 5-7, which can be considered
to be the acylimino analogs of the acyl intermediate in
the formation of 4, favors the first mechanism (Scheme
4). Results reported by Van der Heiden and co-workers
working with systems similar to ours also oppose this
alternative mechanism.10b When they reacted CO with
the titanium neopentylidene complex [Ti(Cp)(dCH-t-
Bu)(PMe2CH2CO)(CMe2-o-C6H4CMe2)], which contains
a bulky phosphinoalkoxide ancillary ligand, they ob-
tained a mixture of two isomeric ketene complexes in
Str u ctu r a l Com p a r ison of th e Bon d in g in th e
CNN Ta n ta lu m Com p lexes. In this and a previous
paper1 we have reported a series of pentagonal bipyra-
midal tantalum complexes which show a great struc-
tural similarity; i.e. the CNN ligand is meridionally η3-
C,N,N′-bonded to the metal with two alkoxide groups
in the apical positions. In the case of the iminoacyl
complex [Ta{C(dN-t-Bu)(CH2CH(Ph)CH2-1,4}(CNN)(O-
t-Bu)2] (7), the position that is occupied by the NMe2
nitrogen donor of CNN in the other species is now
occupied by the nitrogen donor of the imine group and,
thus, it too bears a direct structural analogy to these
other complexes. The structural similarity of these
species finds its origin in the filled frontier orbital of
the [Ta(CNN)(O-t-Bu)2] fragment. This orbital is posi-
tioned in the meridional plane of the pentagonal bi-
pyramidal structure and is available for binding to
substrates either in a η2- or in a σ-fashion and in so
doing affords bite angles varying from 70° in the η2-
iminoacyl complex 7 (C-Ta-C) to ca. 40° for both the
ethene coordination complex [Ta(CNN)(O-t-Bu)2)-
(CH2dCH2)]1 (C-Ta-C) and the oxytantalacyclopro-
pane complex 4 (C-Ta-O). In this sense the [Ta(CNN)-
(O-t-Bu)2] fragment is isolobal to a CH2 fragment, and
on this basis, the structures of the different organo-
metallic complexes can be simplified to organic mol-
ecules, i.e. cyclopropane ([Ta(CNN′)(H2CdCH2)(O-t-
(8) Berke, H.; Hoffmann, R. J . Am. Chem. Soc. 1978, 100, 7224.
(9) (a) Fendrick, C. M.; Marks, T. J . J . Am. Chem. Soc. 1986, 108,
425. (b) Hidai, M.; Orisaku, M.; Uchida, Y. Chem. Lett. 1980, 753. (c)
Erker, G.; Czisch, P.; Schlund, R.; Angermund, K.; Kru¨ger, C. Angew.
Chem., Int. Ed. Engl. 1986, 98, 356. (d) Lindner, E.; Schauss, E.; Hiller,
W.; Fawzi, R. Angew. Chem., Int. Ed. Engl. 1984, 96, 727. (d) Lindner,
E.; Schauss, E.; Hiller, W.; Fawzi, R. Chem. Ber. 1985, 118, 3915. (e)
Lindner, E.; J anssen, R. M.; Hiller, W.; Fawzi, R. Chem. Ber. 1989,
122, 1403. (f) Diversi, P.; Ingrosso, G.; Lucherini, A.; Porzio, W.; Zocchi,
M. J . Chem. Soc., Dalton Trans. 1983, 967.
(10) (a) Schrock, R. R. Acc. Chem. Res. 1979, 12, 98. (b) van Doorn,
J . A.; van der Heijden, H.; Orpen, A. G. Organometallics 1995, 14, 1278.
(c) Miyashita, A.; Ohyoshi, M.; Shitara, H.; Nohira, H. J . Organomet.
Chem. 1988, 338, 103. (d) Miyashita, A.; Grubbs, R. H. Tetrahedron
Lett. 1981, 22, 1255. (e) Wulff, W. D.; Kaesler, R. W. Organometallics
1985, 4, 1461.

Tantalacyclobutane Complexes
Organometallics, Vol. 16, No. 2, 1997 175
0.96 (m, 1 H, CH2CH(Me)CH2), 1.10 (s, 9 H, OCMe3), 1.20 (s,
9 H, OCMe3), 1.68 (m, 2 H, NCH2CH2N), 1.73 (d, J (H,H) ) 4
Sch em e 6. Isoloba l Com p a r ison of th e F r on tier
Or bita ls of th e {Ta (CNN)(O-t-Bu )2} F r a gm en t in
th e Ta n ta lu m Com p lexes 1-7 w ith th e CH2
F r a gm en t
3
Hz, 3 H, CH2CH(Me)CH2), 1.95 (m, 1 H, CH2CH(Me)CH2), 2.08
(s, 3 H, NMe), 2.09 (m, 1 H, CH2CH(Me)CH2), 2.27 (s, 3 H,
NMe), 2.29 (s, 3 H, NMe), 2.45 (m, 1 H, NCH2CH2N), 2.76 (m,
1 H, NCH2CH2N), 3.18 (d, 2J (H,H) ) 12 Hz, 1 H, ArCH2N),
3.20 (m, 1 H, CH2CH(Me)CH2), 4.63 (d, 2J (H,H) ) 12 Hz, 1 H,
ArCH2N), 7.15-7.23 (m, 2 H, ArH), 7.38 (m, 1 H, ArH), 8.64
(d, 3J (H,H) ) 8 Hz, 1 H, ArH); 13C{1H} NMR (50.32 MHz, C6H6,
25 °C) δ 31.7 (OCMe3), 31.9 (OCMe3; CH2CH(Me)CH2), 36.9
(1J (C,H) ) 124 Hz, CH2CH(Me)CH2), 37.1 (1J (C,H) ) 129 Hz,
CH2CH(Me)CH2), 47.1 (NMe), 49.0 (NMe), 49.3 (1J (C,H) ) 125
Hz, CH2CH(Me)CH2), 50.3 (NMe), 56.6 (NCH2CH2N), 61.6
(NCH2CH2N), 70.3 (ArCH2N), 78.6 and 78.9 (OCMe3), 122.8,
124.6, 126.2, 138.2 and 148.7 (Ar), 191.0 (Cipso).
Bu)2]),1 cyclobutanes (1-3), cyclopentanes (5-7), and
an ethylene oxide derivative (4).
Con clu sion s
[Ta {CH2CH(P h )CH2-1,3}(CNN)(O-t-Bu )2] (3). To a pale
yellow solution of 1 (0.90 g, 1.61 mmol) in Et2O (70 mL) was
added H2CdCHPh (0.34 g, 3.23 mmol), and the solution was
stirred for 3 d. Removal of the solvent under reduced pressure
gave a yellow/white sticky solid which was subsequently
washed with cold pentane (3 × 10 mL) and dried under
reduced pressure giving 3 as a white solid; yield 0.67 g (65%).
The product can be recrystallized by cooling a saturated
solution in diethyl ether to -30 °C and is obtained as a mixture
of two isomers in a ratio of 10:1. Anal. Calcd for C29H47N2O2-
Ta: C, 54.71; H, 7.44; N, 4.40. Found: C, 54.61; H, 7.38; N,
4.32. Data for the major isomer: 1H NMR (300.13 MHz, C6H6,
25 °C) δ 0.77 (m, 1 H, CH2CH(Ph)CH2), 1.07 (s, 9 H, OCMe3),
1.12 (s + m, 10 H, OCMe3; CH2CH(Ph)CH2), 1.44 (m, 1 H, CH2-
CH(Ph)CH2), 1.64 (m, 2 H, NCH2CH2N), 2.09 (s, 3 H, NMe),
2.18 (m, 1 H, CH2CH(Ph)CH2), 2.27 (s, 3 H, NMe), 2.28 (s, 3
H, NMe), 2.40 (m, 1 H, NCH2CH2N), 2.76 (m, 1 H, NCH2CH2N),
3.17 (d, 2J (H,H) ) 12 Hz, 1 H, ArCH2N), 4.66 (d, 2J (H,H) ) 12
Hz, 1 H, ArCH2N), 4.33 (m, 1 H, CH2CH(Ph)CH2), 7.17-7.26
Our current investigations on the synthesis of Ta(V)
species with the ortho-chelating aryldiamine CNN
ligand have shown that the [Ta(CNN)] moiety in
combination with two alkoxide ligands, i.e. the [Ta-
(CNN)(O-t-Bu)2] fragment, which is isolobal with CH2,
provides an excellent fragment for binding of a variety
of (hetero)organyl fragments. The Ta-Cipso bond in the
[Ta(CNN)(O-t-Bu)2] fragment has considerable stability
as illustrated by the fact that CO and t-BuNC do not
insert in this bond but instead into the Ta-C bond of
the tantalacyclic unit. This makes the CNN ligand in
this Ta(V) chemistry a true spectator ligand; i.e., it does
not participate in reactions at the metal center, as is
generally found for the commonly used cyclopentadienyl
-
ligands C5H5 (Cp-) and its derivatives in transition
metal chemistry. It is interesting to note that a
comparison between the monoanionic CNN and Cp
ligands indicates that, from a stereochemical point of
view, the CNN ligand is much more versatile in its
bonding modes to tantalum. Whereas for Cp η5-bonding
to Ta is usually found we have established that CNN
can, in concert with the other ligands in the Ta
coordination sphere, bind either as η3-facial- or η3-
meridional-C,N,N′ as well as η2-C,N.
3
(m, 3 H, ArH), 7.37-7.48 (m, 3 H, ArH), 7.85 (d, J (H,H) ) 7
Hz, 2 H, Ph), 8.63 (t, 3J (H,H) ) 7 Hz, 1 H, C6H4). 13C{1H}
NMR (50.32 MHz, C6H6, 25 °C) δ 31.9 (OCMe3), 32.0 (OCMe3),
34.7 (1J (C,H) ) 124 Hz, CH2CH(Ph)CH2), 41.3 (1J (C,H) ) 128
Hz, CH2CH(Ph)CH2), 46.7 (1J (C,H) ) 122 Hz, CH2CH(Ph)CH2),
47.3 (NMe), 49.2 (NMe), 50.4 (NMe), 56.7 (NCH2CH2N), 61.7
(NCH2CH2N), 70.3 (ArCH2N), 78.9 (OCMe3), 79.0 (OCMe3),
123.0, 124.2, 124.7, 126.3, 126.4, 128.2, 138.3, 148.8 and 160.5
(Ar), 190.6 (Cipso).
[Ta {C(O)((CH2)3-1,3)}(CNN)(O-t-Bu )2] (4). A pale yellow
solution of 1 (1.26 g, 2.2 mmol) in Et2O (50 mL) was saturated
with carbon monoxide and stirred for 48 h. The pale yellow
solution was concentrated under reduced pressure to ca. 15
mL from which 4 crystallized overnight at -30 °C as needle-
shaped colorless crystals; yield 0.79 g (59%). Complex 4 is
obtained as a mixture of products, possibly two isomers (ratio
of major to minor product is 10:1). Anal. Calcd for C24H43N2O3-
Ta: C, 48,98; H, 7.36; N, 4.76. Found: C, 49.15; H, 7.31; N,
4.72. Data for the major product: 1H NMR (300.13 MHz, C6D6,
25 °C) δ 0.95 (s, 9 H, OCMe3), 1.08 (s, 9 H, OCMe3), 1.75 (m,
2 H, NCH2CH2N), 2.27 (s, 3 H, NMe), 2.42 (s, 3 H, NMe; m, 1
H, NCH2CH2N), 2.57 (s, 3 H, NMe; m, 2 H, CH2CH2CH2), 2.97
(m, 1 H, NCH2CH2N), 3.32 (d, 2J (H,H) ) 12 Hz, 1 H, ArCH2N),
Exp er im en ta l Section
Gen er a l Meth od s. All experiments were performed in a
dry nitrogen atmosphere using standard Schlenk techniques.
Solvents were stored over sodium benzophenone ketyl and
distilled prior to use. Elemental analyses were carried out by
Dornis und Kolbe, Microanalytisches Laboratorium, Mu¨lheim
a.d. Ruhr, Germany. 1H and 13C NMR spectra were recorded
on a Bruker AC200 or AC300 spectrometer; IR spectra were
recorded on
a Mattson Galaxy FTIR 5000 spectrometer.
Complex [Ta{(CH2)3-1,3}(CNN)(O-t-Bu)2}] (1) was prepared
according to a literature procedure.1 CH2dCHPh and t-BuNC
were obtained by Aldrich and dried on molecular sieves (4 Å).
High-purity ethene, propene, and carbon monoxide were
obtained from Aldrich and used as received; resublimed TaCl5
was obtained from Alfa.
[Ta {CH2CH(Me)CH2-1,3}(CNN)(O-t-Bu )2] (2). A pale
yellow solution of 1 (0.89 g, 1.59 mmol) in Et2O (70 mL) was
saturated with propene and stirred for 18 h. Removal of the
solvent under reduced pressure afforded an off-white solid
which was subsequently washed with cold pentane (3 × 10
mL) and dried under reduced pressure giving pure 2 as a white
solid; yield 0.77 g (84%). Small needle-shaped colorless
crystals of 2 can be obtained by slow cooling of a saturated
diethyl ether solution of 2 from +25 to -30 °C. Complex 2 is
obtained as a mixture of two isomers in a ratio of 10:1. Anal.
Calcd for C24H45N2O2Ta: C, 50.17; H, 7.89; N, 4.88. Found:
C, 49.88; H, 7.90; N, 4.93. Data for the major isomer: 1H NMR
(300.13 MHz, C6H6, 25 °C) δ 0.29 (m, 1 H, CH2CH(Me)CH2),
2
3.4-3.9 (m, 4 H, CH2CH2CH2), 4.62 (d, J (H,H) ) 12 Hz, 1 H,
ArCH2N), 7.30 (m, 2 H, ArH), 7.48 (m, 1 H, ArH), 9.06 (d,
3J (H,H) ) 7 Hz, 1H, ArH); 13C{1H} NMR (50.32 MHz, C6H6,
25 °C) δ 16.8 (CH2CH2CH2), 31.1 (OCMe3), 31.8 (OCMe3), 42.9
(NMe), 43.1 (NMe), 47.6 (NMe), 49.6 (CH2CH2CH2), 51.6
(CH2CH2CH2), 56.5 (NCH2CH2N), 60.2 (NCH2CH2N), 70.3
(ArCH2N), 77.7 (OCMe3), 77.9 (OCMe3), 100.6 (C(O)), 123.5,
125.0, 126.6, 142.5 and 148.9 (Ar), 184.7 (Cipso); IR (KBr) (cm-1
)
1181, ν(CdO).
[Ta {C(dN-t-Bu )(CH2)3-1,4}(CNN)(O-t-Bu )2] (5). To a
pale yellow solution of 1 (0.68 g, 1.2 mmol) in Et2O (50 mL)
was added within 1 min a solution of tert-butyl isocyanide (136
µL, 1.2 mmol) in Et2O (20 mL) which gave an immediate color
change to bright yellow. The solution was stirred for an
additional 1.5 h after which the solvent was removed in vacuo,

176 Organometallics, Vol. 16, No. 2, 1997
Ta ble 4. Cr ysta llogr a p h ic Da ta for 2-4 a n d 7
Rietveld et al.
2
3
4
7
Crystal Data
formula
mol wt
C24H45N2O2Ta
574.58
C29H47N2O2Ta
636.65
C24H43N2O3Ta
588.56
C34H56N3O2Ta
719.79
cryst system
space group
a (Å)
b (Å)
c (Å)
monoclinic
P21/c (No. 14)
17.1133(12)
16.128(2)
9.0213(6)
94.173(5)
2483.3(4)
1.537
monoclinic
P21/c (No. 14)
14.3964(12)
14.1155(8)
17.1913(8)
124.198(8)
2889.5(4)
1.463
monoclinic
P21/c (No. 14)
16.818(3)
9.520(4)
18.322(4)
122.55(2)
2472.7(14)
1.581
monoclinic
P21/c (No. 14)
9.4616(6)
9.4270(8)
38.962(3)
102.773(4)
3389.2(4)
1.411
â (deg)
V (Å3)
D
calc (g cm-3
)
Z
4
4
4
8
F(000)
1168
44.5 (Mo KR)
0.08 × 0.13 × 0.25
1296
1192
1480
µ (cm-1
)
37.8 (Mo KR)
0.5 × 0.5 × 0.5
44.2 (Mo KR)
0.4 × 0.4 × 0.4
32.8 (Mo KR)
0.10 × 0.18 x 0.23
cryst size (mm)
Data Collection
θ
min, θmax (deg)
1.2, 27.5
1.7, 27.5
11.16, 13.84 (25 reflcns)
1.4, 27.5
0.5, 27.5
SET4 θmin, θmax (deg)
10.32, 13.99 (25 reflcns)
ω/2θ
1.02 + 0.35 tan θ
11.86, 13.76 (21 reflcns) 11.43, 13.98 (24 reflcns)
scan type
∆ω (deg)
hor, ver aperture (mm) 3.65, 4.00
X-ray exposure (h)
linear decay (%)
ref reflcns
ω/2θ
ω/2θ
ω
0.62 + 0.35 tan θ
1.00 + 0.35 tan θ
0.88 + 0.35 tan θ
2.60, 4.00
3.00, 4.00
1.91 + 0.95 tan θ, 4.00
27
3
20
35
27
4
361, 7h31h
-21 to 19, -12 to 0,
-23 to 19
6202
16
2
502h, 4h22h, 2h33h
24h3, 5h23, 13h2
216, 02h9, 31h1h
-8 to 12, -12 to 0,
-50 to 49
data set
-22 to 22, 0 to 20, -11 to 9 -18 to 17, -18 to 0,
-22 to 17
tot. data
9863
9196
8910
tot. unique data
Rint
5661
0.036
6609
0.137
5655
0.068
7780
0.036
abs corr range
0.83, 1.36 (DIFABS)
0.70, 1.34 (DIFABS)
0.85, 1.32 (DIFABS)
0.33, 0.53 (PLATON)
Refinement
no. of refined params
final R1a
272
316
280
361
0.0386 [3931, I > 2σ(Ι)]
0.0623
0.0545 [5709, I > 2σ(Ι)]
0.0782 [3808, I > 2σ(I)] 0.0355 [6144, I > 2σ(I)]
0.1846
1.078
final wR2b
0.1496
1.083
0.0915
1.095
goodness of fit
1.022
w-1 c
σ2(F2) + (0.0179 P)2
σ2(F2) + (0.0950P)2 + 3.72P σ2(F2) + (0.0615P)2 +
71.91P
σ2(F2) + (0.0410P)2 +
6.20P
(∆/σ)av, (∆/σ)max
0.000, 0.004
0.000, 0.001
0.000, 0.001
0.000, 0.003
min and max
resid density (e Å-3
)
-0.86, 1.02 (near Ta)
-2.29, 4.04 (near Ta)
-2.62, 3.00 (near Ta)
-1.47, 2.40 (near Ta)
a
b
2
R1 ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) [∑[w(Fo - Fc2)2]/∑[w(Fo2)2]]1/2
.
c P ) (max(Fo2, 0) + 2Fc2)/3.
and the resulting a yellow oil was subsequently extracted with
pentane (75 mL). The combined extracts were concentrated
in vacuo to ca. 5 mL from which 5 crystallized overnight at
-30 °C as needle-shaped pale-yellow crystals; yield 0.48 g
(62%). 1H NMR (300.13 MHz, C6D6, 25 °C) δ 0.90 (s, 9 H,
OCMe3), 0.92 (s, 9 H, OCMe3), 1.33 (s, 9 H, NCMe3), 2.11 (s, 6
H, NMe2), 2.3-2.4 (m, 1 H, CH2CH2CH2), 2.4-2.7 (m, 1 H,
CH2CH2CH2); 2 H, NCH2CH2N), 2.71 (s, 3 H, NMe), 3.0-3.2
(m, 1 H, CH2CH2CH2), 3.2-3.3 (m, 1 H, CH2CH2CH2), 3.3-
3.5 (m, 1 H, CH2CH2CH2); 2 H, NCH2CH2N), 3.7-3.8 (m, 1 H,
CH2CH2CH2), 3.92 (d, 2J (H,H) ) 13 Hz, 1 H, ArCH2N), 4.38
(d, 2J (H,H) ) 13 Hz, 1 H, ArCH2N), 7.1-7.5 (m, 3 H, ArH),
2.40 (m, 1 H, CH2CH(Me)CH2; m, 2 H, NCH2CH2N), 2.40-
2.50 (m, 2 H, NCH2CH2N), 2.59 (s, 3 H, NMe; A), 2.80 (s, 3 H,
NMe; B), 2.90-3.10 (m, 1 H, CH2CH(Me)CH2), 3.15-3.30 (m,
1 H, CH2CH(Me)CH2), 3.40-3.60 (m, 2 H, NCH2CH2N), 3.73
(d, 2J (H,H) ) 13 Hz, 1 H, ArCH2N; A), 3.75-3.90 (m, 3 H,
CH2CH(Me)CH2), 4.10-4.20 (m, 1 H, CH2CH(Me)CH2); 1 H,
ArCH2N), 4.52 (d, 2J (H,H) ) 13 Hz, 1 H, ArCH2N), 7.10-7.25
(m, 3 H, ArH), 7.3-7.5 (m, 3 H, ArH), 8.52 (d, 3J (H,H) ) 7
3
Hz, 1 H, ArH), 8.62 (d, J (H,H) ) 7 Hz, 1 H, ArH). 13C{1H}
NMR (75.47 MHz, C6H6, 25 °C): δ 26.7 (CH2CH(Me)CH2), 30.1
(NCMe3), 30.1 (NCMe3), 31.8 (OCMe3), 31.9 (OCMe3), 32.1
(OCMe3), 32.2 (OCMe3), 46.0 (NMe2), 46.1 (NMe2), 46.2 (CH2CH-
(Me)CH2), 46.6 (CH2CH(Me)CH2), 47.2 (NMe), 47.2 (NMe), 48.8
(CH2CH(Me)CH2), 48.8 (CH2CH(Me)CH2), 52.7 (CH2CH(Me)-
CH2), 52.8 (CH2CH(Me)CH2), 56.1 (NCH2CH2N), 56.9 (NCH2-
CH2N), 58.3 (NCH2CH2N), 58.9 (NCH2CH2N), 61.5 (NCMe3),
61.6 (NCMe3), 65.3 (ArCH2N), 65.5 (ArCH2N), 77.2 (OCMe3),
77.3 (OCMe3), 124.0, 124.8, 125.9, 126.0, 138.1, 138.2, 147.7
and 147.7 (Ar), 188.8 (Cipso), 189.0 (Cipso), 234.3 (CdNCMe3),
234.4 (CdNCMe3).
[Ta{C(dN-t-Bu )CH2CH(P h )CH2-1,4}(CNN)(O-t-Bu )2] (7).
To a solution of 3 (0.67 g, 1.05 mmol) in Et2O (50 mL) was
added tert-butyl isocyanide (119 µL, 1.05 mmol) which gave
an immediate color change from pale to bright yellow. The
solution was stirred for 3 h after which the solution was
concentrated under reduced pressure to ca. 10 mL from which
7 crystallized overnight at -30 °C as needle-shaped yellow
crystals; yield 0.38 g (50%). Complex 7 is obtained as a
mixture of two isomers A and B in a ratio of 1.2:1. Anal. Calcd
for C34H56N3O2Ta: C, 56.74; H, 7.84; N, 5.84. Found: C, 56.62;
H, 7.73; N, 5.81. Where possible the data for the isomers A
3
8.74 (d, J (H,H) ) 8, 1 H, ArH). 13C{1H} NMR (50.32 MHz,
C6H6, 25 °C) δ 30.0 (NCMe3), 31.9 (OCMe3), 32.0 (OCMe3), 37.7
(CH2CH2CH2), 41.8 (CH2CH2CH2), 46.0 (NMe2), 46.3 (NMe),
52.7 (CH2CH2CH2), 55.1 (NCH2CH2N), 58.1 (NCH2CH2N), 61.5
(NCMe3), 65.1 (ArCH2N), 77.0 (two overlapping OCMe3 sig-
nals), 124.1, 125.0, 126.3, 138.3 and 147.8 (Ar), 188.9 (Cipso),
237.5 (CdNCMe3). IR (KBr) (cm-1) 1721, ν(CdN).
[Ta {C(dN-t-Bu )CH2CH(Me)CH2-1,4}(CNN)(O-t-Bu )2] (6)
(in Situ ). A 5 mm o.d. NMR tube was charged with a solution
of 2 (ca. 50 mg, 0.08 mmol) in C6D6 (1 mL) and 1 equiv (10 µL)
of tert-butyl isocyanide added with a microsyringe. 1H NMR
and 13C NMR showed that the product 6 is formed almost
instantly with two isomers A and B formed in a ratio of 1.2:1.
Where possible the signals for the two isomers formed have
been assigned. 1H NMR (300 MHz, C6D6, 25 °C): δ 0.88 (s, 9
H, OCMe3; A), 0.89 (s, 9 H, OCMe3; B), 0.92 (s, 9 H, OCMe3;
B), 0.93 (s, 9 H, OCMe3; A), 1.29 (s, 9 H, NCMe3; B), 1.32 (s, 9
3
H, NCMe3; A), 1.66 (d, J (H,H) ) 6 Hz, 6 H, CH2CH(Me)CH2;
A + B), 2.06 (s, 6 H, NMe2); A), 2.13 (s, 6 H, NMe2; B), 2.30-

Tantalacyclobutane Complexes
Organometallics, Vol. 16, No. 2, 1997 177
and B are assigned. 1H NMR (300.13 MHz, C6H6, 25 °C): δ
0.93 (s, 9 H, OCMe3; A), 0.95 (s, 9 H, OCMe3; B), 1.01 (s, 9 H,
OCMe3; B), 1.05 (s, 9 H, OCMe3; A), 1.31 (s, 9 H, NCMe3; B),
1.33 (s, 9 H, NCMe3; A), 2.08 (s, 6 H, NMe2; B), 2.13 (s, 6 H,
NMe2; A), 2.25-2.40 (m, 2 H, NCH2CH2N), 2.40-2.55 (m, 2
H, NCH2CH2N; 2 H, CH2CH(Ph)CH2; A + B), 2.62 (s, 3 H,
NMe; A), 2.83 (s, 3 H, NMe; B), 3.06-3.10 (m, 2 H, NCH2CH2N),
3.15-3.30 (m, 2 H, NCH2CH2N; 1 H, ArCH2N; B), 3.45-3.60
(m, 2 H, CH2CH(Ph)CH2), 3.74 (d, 2J (H,H) ) 13 Hz, 1 H,
ArCH2N; A), 3.80-3.95 (m, 1 H, CH2CH(Ph)CH2; A), 4.10-
4.20 (m, 5 H, CH2CH(Ph)CH2; A + B; 1 H, ArCH2N ; B), 4.56
(d, 2J (H,H) ) 13 Hz, ArCH2N; A), 7.1-7.4 (m, 12 H, ArH; A +
B), 7.71 (d, 3J (H,H) ) 7.2 Hz, 4 H, ArH; A + B), 8.58 (d, 3J (H,H)
complex 7 and SHELXL-9317 for the other complexes); no
observance criterion was applied during refinement.
Hydrogen atoms were included in the refinement on calcu-
lated positions, riding on their carrier atoms. All methyl
hydrogen atoms were refined in a rigid group, allowing for
rotation around the C-C or N-C bonds. The C(14)H(Ph)
group bonded to C(13) and C(15) is disordered over two
positions, approximately related to each other by a local mirror
plane through Ta(1), C(13), and C(15). The site occupancy
parameter of the major disorder component refined to
0.767(9).
The non-hydrogen atoms were refined with anisotropic
thermal parameters, except for the disorder atoms of 7. The
thermal parameters of the minor disorder component atoms
were equivalenced to the individually refined isotropic dis-
placement parameters of the major disorder component atoms.
The hydrogen atoms were refined with a fixed isotropic
thermal parameter related to the value of the equivalent
isotropic displacement parameter of their carrier atoms by a
factor of 1.5 for the methyl hydrogen atoms and a factor of 1.2
for all other hydrogen atoms.
3
) 7 Hz, 1 H, C6H4; A), 8.62 (d, J (H,H) ) 7.1 Hz, 1 H, C6H4;
B). 13C{1H} NMR (50.32 MHz, C6H6, 25 °C): δ 30.0 (NCMe3),
30.1 (NCMe3), 31.9 (ÃCMe3), 31.9 (ÃCMe3), 32.2 (ÃCMe3), 32.3
(ÃCMe3), 46.0 (NMe2), 46.6 (NMe), 46.4 (NMe), 47.9 (CH2CH-
(Ph)CH2), 47.8 (CH2CH(Ph)CH2), 52.6 (CH2CH(Ph)CH2), 52.8
(CH2CH(Ph)CH2), 57.0 (NCH2CH2N), 57.9 (NCH2CH2N), 58.0
(NCH2CH2N), 59.0 (NCH2CH2N), 61.6 (NCMe3), 61.7 (NCMe3),
64.6 (CH2CH(Ph)CH2), 64.4 (CH2CH(Ph)CH2), 65.3 (ArCH2N),
77.1 (ÃCMe3), 77.5 (ÃCMe3), 77.6 (ÃCMe3), 124.1, 125.0, 125.7,
126.2, 127.1, 127.5, 128.4, 128.7, 138.4, 138.3, 147.6 and 151.6
(Ar), 188.8 and 188.6 (Cipso), 233.4 and 233.3 (CdNCMe3). IR
(KBr) (cm-1) 1726, ν(CdN).
Neutral atom scattering factors and anomalous dispersion
correction were taken from ref 18. Geometrical calculations
and illustrations were performed with PLATON;19 all calcula-
tions were performed on a DECstation 5000 cluster.
X-r a y Str u ctu r e Deter m in a tion s of 2-4 a n d 7. Crystals
suitable for X-ray diffraction were mounted on the tip of a glass
fiber and were placed in the cold nitrogen stream on an Enraf-
Nonius CAD4-T diffractometer on rotating anode (T ) 150 K,
Mo KR radiation, graphite monochromator, λ ) 0.710 73 Å).
Accurate unit-cell parameters and an orientation matrix were
determined by least-squares fitting of the setting angles of a
set of well-centered reflections (SET4).11 Reduced-cell calcula-
tions did not indicate higher lattice symmetry.12 Crystal data
and details on data collection and refinement are presented
in Table 4. Data were corrected for Lp effects and for the
observed linear decay of the reference reflections. An analyti-
cal absorption correction,13 as implemented in PLATON,19 was
applied for complex 7; empirical absorption correction was
applied for the other compounds (DIFABS).14
Ack n ow led gm en t. This work was supported in part
(A.L.S., N.V.) by the Netherlands Foundation for Chemi-
cal Research (SON) with financial aid from the Neth-
erlands Organization for Scientific Research (NWO).
Su p p or tin g In for m a tion Ava ila ble: Further details of
the structure determinations, including tables of X-ray pa-
rameters, atomic coordinates, bond lengths and angles, and
thermal parameters (26 pages). Ordering information is given
on any current masthead page.
OM960808L
(15) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.;
Garc´ıa-Granda, S.; Gould, R. O.; Smits, J . M. M.; Smykalla, C. The
DIRDIF program system. Technical report of the Crystallography
Laboratory, University of Nijmegen, The Netherlands, 1992.
(16) Sheldrick, G. M. SHELXL-96 Program for crystal structure
refinement. Beta test version. University of Go¨ttingen, Germany, 1996.
(17) Sheldrick, G. M. SHELXL-93 Program for crystal structure
refinement. University of Go¨ttingen, Germany, 1993.
The structures of all complexes were solved by automated
Patterson methods and subsequent difference Fourier tech-
niques (DIRDIF-92).15 The structures were refined on F2,
using full-matrix least-squares techniques (SHELXL-9616 for
(11) Boer, J . L. de; Duisenberg, A. J . M. Acta Crystallogr. 1984, A40,
C410.
(12) Spek, A. L., J . Appl. Crystallogr. 1988, 21, 578.
(13) Alcock, N. W. Cryst. Comput. 1990, 271.
(14) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 158.
(18) Wilson, A. J . C., Ed. International Tables for Crystallography;
Kluwer Academic Publisher: Dordrecht, The Netherlands, 1992; Vol.
C.
(19) Spek, A. L. Acta Crystallogr. 1990, A46, C34.