Insertions into azatitanacyclobutenes: New insights into three-component coupling reactions involving imidotitanium intermediates

Article abstract of DOI:10.1021/om8001203

Reaction of the titanium imido complexes [Ti(NR)(N₂ ^XylN_py)(L)] (N₂^XylN_py = MeC(2-C₅H₄N) {CH₂N(3,5-C₆H ₃Me₂)}₂)

Full text of DOI:10.1021/om8001203

2518
Organometallics 2008, 27, 2518–2528
Insertions into Azatitanacyclobutenes: New Insights into
Three-Component Coupling Reactions Involving Imidotitanium
Intermediates
Nadia Vujkovic,† Julio Lloret Fillol,† Benjamin D. Ward,† Hubert Wadepohl,†
Philip Mountford,*,‡ and Lutz H. Gade*,†
Anorganisch-Chemisches Institut, UniVersita¨t Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg,
Germany, and Chemistry Research Laboratory, UniVersity of Oxford, Mansfield Road,
Oxford, OX1 3TA, U.K.
ReceiVed February 11, 2008
Reaction of the titanium imido complexes [Ti(NR)(N2XylNpy)(L)] (N2XylNpy ) MeC(2-C5H4N){CH2N(3,5-
C6H3Me2)}2) with aryl acetylenes afforded the {2+2} cycloaddition products [Ti(N2 Npy){κ2-
Xyl
N(tBu)CHdCAr}] (Ar ) Ph: 1a, Tol: 1b (Tol ) 4-C6H4Me)). Complex 1a was found to insert sulfur
and selenium atoms into the Ti-C bond of the strained azatitanacyclobutene unit to give the five-membered
metallacyclic systems [Ti(N2 Npy){κ2-N(tBu)CHdC(Ph)E}] (E ) S: 2, Se: 3). Likewise, isonitriles
Xyl
Xyl
were found to insert into the Ti-C bonds to give [Ti(N2 Npy){κ2-N(tBu)CHdC(Ar)CdNR}] (Ar )
t
t
Ph, R ) xylyl: 4, Cy: 5, Bu: 6a; Ar ) C6H5Me, R ) Bu: 6b), one example of which (4) has been
characterized by X-ray crystallography. The latter species is thought to be a key intermediate in the
titanium-mediated three-component coupling of primary amines with acetylenes and isonitriles (“imi-
Xyl
noamination”). Reaction of [Ti(N2 Npy){κ2-N(tBu)CHdC(Ph)CdNR}] with tBuNH2 gave
tBuNdCHC(Ph)CHNHR, which have been previously identified as the major reaction products in the
catalytic aminoamination of alkynes.
Scheme 1. Catalytic Cycle for the Group 4 Metal Catalyzed
Hydroamination of Alkynes Originally Proposed by Bergman
et al.
Introduction
Azametallacyclobutenes of the Group 4 elements are key
intermediates in a range of stoichiometric and catalytic C-N
and C-C coupling reactions mediated by these metals.1,2 The
most intensely studied catalytic transformation involving such
species is the hydroamination of alkynes.3–8 The azametalla-
cycles have been identified as the {2+2} cycloaddition products
of Ti or Zr imidocomplexes with alkynes, the key step of this
catalytic cycle (Scheme 1).
* Corresponding authors. E-mail: philip.mountford@chem.ox.ac.uk;
lutz.gade@uni-hd.de.
† Universita¨t Heidelberg.
‡ University of Oxford.
(1) (a) Walsh, P. J.; Baranger, A. M.; Bergman, R. G. J. Am. Chem.
Soc. 1992, 114, 1708. (b) McGrane, P. L.; Jensen, M.; Livinghouse, T.
J. Am. Chem. Soc. 1992, 114, 5459. (c) Baranger, A. M.; Walsh, P. J.;
Bergman, R. G. J. Am. Chem. Soc. 1993, 115, 2753.
(2) (a) Zi, G.; Blosch, L. L.; Jia, L.; Andersen, R. A. Organometallics
2005, 24, 4602. (b) Duncan, A. P.; Bergman, R. G. Chem. Rec. 2002, 2,
431. (c) Poise, J. L.; Andersen, R. A.; Bergman, R. G. J. Am. Chem. Soc.
1998, 120–13405.
(3) (a) Pohlki, F.; Doye, S. Chem. Soc. ReV. 2003, 32, 104. (b)
Bytschkov, I.; Doye, S. Eur. J. Org. Chem. 2003, 935. (c) Hultzsch, K. C.
AdV. Synth. Catal. 2005, 347, 367. (d) Hong, S.; Marks, T. J. Acc. Chem.
Res. 2004, 37, 673. (e) Odom, A. L. Dalton Trans. 2005, 225. (f) Roesky,
P. W.; Mu¨ller, T. E. Angew. Chem., Int. Ed. 2003, 42, 2708. (g) Molander,
G. A.; Romero, J. A. C. Chem. ReV. 2002, 102, 2161. (h) Nobis, M.;
Driessen-Ho¨lscher, B. Angew. Chem., Int. Ed. 2001, 40, 3983. (i) Severin,
R.; Doye, S. Chem. Soc. ReV. 2007, 36, 1407.
The four-membered metallaheterocycle A is able to react
further with the primary amine, opening up to give an enamido
(4) (a) Cao, C.; Ciszewski, J. T.; Odom, A. L. Organometallics 2001,
20, 5011. (b) Cao, C.; Shi, Y.; Odom, A. L. Org. Lett. 2002, 4, 2853. (c)
Shi, Y.; Ciszewski, J. T.; Odom, A. L. Organometallics 2001, 20, 3967.
(d) Shi, Y.; Hall, C.; Ciszewski, J. T.; Cao, C.; Odom, A. L. Chem. Commun.
2003, 586.
(6) (a) Kim, J. Y.; Livinghouse, T. Org. Lett. 2005, 7, 1737. (b) Kim,
J. Y.; Livinghouse, T. Org. Lett. 2005, 7, 4391. (c) Kim, Y. K.; Livinghouse,
T. Angew. Chem., Int. Ed. 2002, 41, 3645. (d) Kim, Y. K.; Livinghouse,
T.; Horino, Y. J. Am. Chem. Soc. 2003, 125, 9560.
(5) (a) Li, C.; Thomson, R. K.; Gillon, B.; Patrick, B. O.; Schafer, L. L.
Chem. Commun. 2003, 2462. (b) Lauterwasser, F.; Hayes, P. G.; Bra¨se, S.;
Piers, W. E.; Schafer, L. L. Organometallics 2004, 23, 2234. (c) Bexrud,
J. A.; Beard, J. D.; Leitch, D. C.; Schafer, L. L. Org. Lett. 2005, 7, 1959.
(d) Zhang, Z.; Schafer, L. L. Org. Lett. 2003, 5, 4733.
(7) (a) Johnson, J. S.; Bergman, R. G. J. Am. Chem. Soc. 2001, 123,
2923. (b) Ackermann, L.; Bergman, R. G.; Loy, R. N. J. Am. Chem. Soc.
2003, 125, 11956. (c) Ackermann, L.; Bergman, R. G. Org. Lett. 2002, 4,
1475. (d) Ackermann, L. Organometallics 2003, 22, 4367.
10.1021/om8001203 CCC: $40.75
2008 American Chemical Society
Publication on Web 04/30/2008

Insertions into Azatitanacyclobutenes
Organometallics, Vol. 27, No. 11, 2008 2519
Scheme 2. Catalytic Cycle of the Iminoamination (left) and the Carboamination (right) of Alkynes. In the final step aminolysis
with R-NH2 occurs (not shown)
complex B, which rapidly eliminates the enamine to regenerate
the active imido catalyst. Alternatively, insertion of a third,
unsaturated substrate such as an isocyanide into the reactive
M-C bond has been thought to give a metallapentacycle C,
which has been postulated as an intermediate in the Ti-catalyzed
iminoamination of alkynes reported by Odom et al. (Scheme
2).9 A similar M-C insertion of an imine has been invoked by
Bergman and co-workers for the Zr-catalyzed carboamination
of alkynes with imines,10 a process extended to Ti-imides in
Mindiola’s group (Scheme 2).11
were able to demonstrate that such azatitanacyclobutenes act
as hydroamination catalysts, which allowed a detailed mecha-
nistic investigation of this process.16 The possibility to isolate
such species has led us to investigate their reactivity, in particular
with regard to insertions into the Ti-C bond. Starting with an
analysis of the bonding in these azatitanacyclobutenes, we report
in this work on the insertion of chalcogenide atoms as well as
isocyanides, the latter leading to the hitherto elusive intermediate
C in the Ti-catalyzed iminoamination of alkynes.
R
We introduced a tridentate diamido-pyridyl ligand [N2 Npy]2-
Results and Discusion
as a supporting ligand to early transition metal chemistry,12
a
Determination and Description of the Molecular Struc-
system that has been particularly suitable for the stabilization
of complexes containing reactive MdN bonds.13,14 We recently
reported the preparation and characterization of azatitanacy-
clobutene complexes supported by this ligand system.15 Using
tures of the Azatitanacyclobutenes [Ti(N2 Npy){K2-N(tBu)-
Xyl
CHdCPh}] (1a) and [Ti(N2 Npy){K2-N(tBu)CHdCTol}]
Xyl
(1b). The synthesis and spectroscopic characterization of
Xyl
azatitanacyclobutenes [Ti(N2 Npy){κ2-N(tBu)CHdCAr}] (Ar
Ar
the N-arylated derivatives [N2 Npy]2- as ancillary ligands, we
) Ph: 1a, Tol: 1b) have been previously described,16 and both
have been shown to be key intermediates in the catalytic
hydroamination of arylalkynes, which was chosen as the test
reaction. A first indication of the reactivity of their Ti-C bonds
was the insertion of a second equivalent of alkyne, leading to
azatitanacyclohexadienes. In order to analyze the structure and
bonding in 1a and 1b and the potential reactive behavior that
might result from it, single-crystal X-ray structure analyses of
both complexes have been carried out. These were thought to
provide the structural point of reference for subsequent theoreti-
cal modeling of the bonding in the metallacycles. Their closely
related molecular structures are depicted in Figure 1a,b and
confirm the previous structural proposal derived from the
NMR data. Moreover, they proved to be very similar to the
N-trimethylsilylated derivative previously characterized by
X-ray diffraction.15 Selected bond lengths and angles are
listed in Table 1.
(8) (a) Haak, E.; Bytschkov, I.; Doye, S. Angew. Chem., Int. Ed. 1999,
38, 3389. (b) Heutling, A.; Doye, S. J. Org. Chem. 2002, 67, 1961. (c)
Bytschkov, I.; Doye, S. Tetrahedron Lett. 2002, 43, 3715.
(9) Cao, C.; Shi, Y.; Odom, A. L. J. Am. Chem. Soc. 2003, 125, 2880.
(10) (a) Ruck, R. T.; Zuckerman, R. L.; Krska, S. W.; Bergman, R. G.
Angew. Chem., Int. Ed. 2004, 43, 5372. (b) Ruck, R. T.; Bergman, R. G.
Organometallics 2004, 23, 2231.
(11) (a) Basuli, F.; Aneetha, H.; Huffman, J. C.; Mindiola, D. J. J. Am.
Chem. Soc. 2005, 127, 17992. (b) Aneetha, H.; Basuli, F.; Bollinger, J.;
Huffman, J. C.; Mindiola, D. J. Organometallics 2006, 25, 2402.
(12) (a) Friedrich, S.; Schubart, M.; Gade, L. H.; Scowen, I. J.; Edwards,
A. J.; McPartlin, M. Chem. Ber./Recl. 1997, 130, 1751. (b) Gade, L. H.
Chem. Commun. 2000, 173.
(13) (a) Blake, A. J.; Collier, P. E.; Gade, L. H.; McPartlin, M.;
Mountford, P.; Schubart, M.; Scowen, I. J. Chem. Commun. 1997, 1555.
(b) Bashall, A.; Collier, P. E.; Gade, L. H.; McPartlin, M.; Mountford, P.;
Pugh, S. M.; Radojevic, S.; Schubart, M.; Scowen, I. J.; Tro¨sch, D. J. M.
Organometallics 2000, 19, 4784. (c) Blake, A. J.; Collier, P. E.; Gade, L. H.;
Mountford, P.; Pugh, S. M.; Schubart, M.; Tro¨sch, D. J. M. Inorg. Chem.
2001, 40, 870. (d) Tro¨sch, D. J. M.; Bashall, A.; Collier, P. E.; Gade, L. H.;
McPartlin, M.; Mountford, P. Organometallics 2001, 20, 3308. (e) Pugh,
S. M.; Tro¨sch, D. J. M.; Wilson, D. J.; Bashall, A.; Cloke, F. G. N.; Gade,
L. H.; Hitchcock, P. B.; McPartlin, M.; Nixon, J. F.; Mountford, P.
Organometallics 2000, 19, 3205. (f) Ward, B. D.; Orde, G.; Clot, E.;
Cowley, A. R.; Gade, L. H.; Mountford, P. Organometallics 2004, 23, 4444.
(g) Ward, B. D.; Orde, G.; Clot, E.; Cowley, A. R.; Gade, L. H.; Mountford,
P. Organometallics 2005, 24, 2368. (h) Herrmann, H.; Lloret Fillol, J.;
Wadepohl, H.; Gade, L. H. Angew. Chem., Int. Ed. 2007, 46, 8426. (i)
Herrmann, H.; Lloret Fillol, J.; Wadepohl, H.; Gade, L. H. Organometallics
2008, 27, 172.
(14) For a review of imido complexes containing this type of ligand
system, see: (a) Gade, L. H.; Mountford, P. Coord. Chem. ReV. 2001, 216/
217, 65. For a recent review of titanium imido chemistry in general see:
(b) Hazari, N.; Mountford, P., Acc. Chem. Res. 2005, 38, 839.
(15) Ward, B. D.; Maisse-Franc¸ois, A.; Mountford, P.; Gade, L. H.
Chem. Commun. 2004, 704.
(16) Vujkovic, N.; Ward, B. D.; Maisse-Franc¸ois, A.; Wadepohl, H.;
Mountford, P.; Gade, L. H. Organometallics 2007, 26, 5522.

2520 Organometallics, Vol. 27, No. 11, 2008
VujkoVic et al.
1.943(2); 1b: 1.929(2) Å) distances indicate sp2-type single
bonds to the metal center.
DFT Study of Compound 1a. In order to obtain insight into
the properties of the azametallacyclobutenes, compound 1a was
theoretically modeled using the DFT computational B3PW91
method with a 6.31G(d) basis set.17–20 Of particular interest were
the molecular orbitals (Cartesian (MO) as well as natural linear
molecular orbitals (NLMO)), involved in the C(2)-C(1)-N(4)
π-system of the azametallacyclobutene unit.20 The chemical
interpretation of the Cartesian molecular orbitals (CMOs) is
limited by the symmetry-imposed delocalization, while NLMOs
provide a more localized picture and interpretability of the
bonding. The semilocalized character of the NLMO offers direct
insight into the nature of the “delocalization tails”. The MO
orbitals contributing to the π-system (HOMO, HOMO-2,
HOMO-12) are depicted in Figure 2, and an alternative
representation of the π-bonding is provided by the NLMO
orbitals NLMOHOMO-15, NLMOHOMO-12, and NLMOHOMO-2
.
Furthermore, selected NPA charges of the Ti-bonded ligands
and the metallacycle are also provided. The Cartesian molecular
orbitals MOHOMO-12, MOHOMO-2, and MOHOMO depict the
π-bonding, nonbonding, and π C(2)-C(1)/π* C(1)-N(4) situ-
ation between C(2)-C(1)-N(4) atoms, respectively. It is evident
that the Ti-C(2)-C(1)-N(4) cycle is adequately described as
containing a C(2)-C(1) double bond and an amido-type N(4)
atom. In addition, the NLMO analysis indicates significant
delocalization of the lone electron pair of N(4) into the titanium
atom (ca. 10%), which is consistent with amide π-donation.16
Martins et al. have reported a combined experimental and
theoretical (DFT) study of the insertion of isocyanides into
titanium-carbon and titanium-nitrogen bonds in [Ti(η5-
Ind)(NMe2)2Me] and related complexes in which neither the
Ti-C nor the Ti-N bonds are part of strained structural units.21
Not unexpectedly, they found a clear preference of the insertion
into the Ti-C bond over insertion into the Ti-N bond, a
consequence of the difference in bond strength of the Ti-CH3
and Ti-NR2 bonds. NLMO analysis of complex 1a has
established a Ti-N bond (ENLMO(σ(Ti-N(4)) ) -10.3 eV) that is
more stable than the Ti-C bond (ENLMO(σ(Ti-C(1)) ) -8.4 eV)
Figure 1. (a) Molecular structure of [Ti(N2 Npy){κ2-N(tBu)CHd
Xyl
Xyl
CPh}] (1a). (b) Molecular structure of [Ti(N2 Npy){κ2-N(tBu)-
CHdCTol}] (1b). Thermal ellipsoids are drawn at 30% probability.
A comparative listing of selected bond lengths and angles of both
structures is provided in Table 1.
Table 1. Selected Bond Lengths (Å) and Angles (deg) for
Xyl
[Ti(N2
N
){K2-N(tBu)CHdCAr′}] (Ar′ ) Ph: 1a, 4-C6H4Me: 1b)
py
1a
1b
Ti-N(1)
1.912(2)
1.930(2)
2.231(2)
1.943(2)
2.091(2)
1.370(3)
1.380(3)
103.66(7)
82.90(7)
105.36(8)
127.21(8)
82.87(7)
103.73(8)
128.83(8)
167.53(7)
96.80(7)
70.80(8)
82.6(1)
1.960(2)
1.923(2)
2.232(2)
1.929(2)
2.097(2)
1.363(3)
1.393(2)
102.84(7)
83.40(6)
105.85(7)
128.35(7)
83.64(6)
104.64(7)
128.38(8)
165.47(6)
94.85(7)
70.63(7)
83.9(1)
Ti-N(2)
Ti-N(3)
Ti-N(4)
(17) M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A.
Robb, J. R. Cheeseman, J. A. Montgomery, Jr., T. Vreven, K. N. Kudin,
J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tomasi, V. Barone, B.
Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A. Petersson, H. Nakatsuji,
M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T.
Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox,
H. P. Hratchian, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R.
Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli,
J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J.
Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C. Strain,
O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman,
J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov,
G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T.
Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, M. Challacombe,
P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonzalez, J. A.
Pople Gaussian 03, ReVision D.02; Gaussian, Inc.: Wallingford, CT, 2004.
(18) (a) Carpenter, J. E.; Weinhold, F. J. Mol. Struct. (THEOCHEM)
1988, 169, 41. (b) Carpenter, J. E. Ph.D. Thesis, University of Wisconsin,
Madison, WI, 1987. (c) Foster, J. P.; Weinhold, F. J. Am. Chem. Soc. 1980,
102, 7211. (d) Reed, A. E.; Weinhold, F. J. Chem. Phys. 1983, 78, 4066.
(e) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. ReV. 1988, 88, 899.
(19) Dennington, R., II; Keith, T.; Millam, J.; Eppinnett, K.; Hovell,
W. L.; Gilliland, R. GaussView, Version 3.0; Semichem, Inc.: Shawnee
Mission, KS, 2003.
Ti-C(2)
C(1)-C(2)
C(1)-N(4)
N(1)-Ti-N(2)
N(1)-Ti-N(3)
N(1)-Ti-N(4)
N(1)-Ti-C(2)
N(2)-Ti-N(3)
N(2)-Ti-N(4)
N(2)-Ti-C(2)
N(3)-Ti-N(4)
N(3)-Ti-C(2)
N(4)-Ti-C(2)
Ti-C(2)-C(1)
C(2)-C(1)-N(4)
C(1)-N(4)-Ti
116.7(2)
88.2(1)
115.6(2)
89.8(1)
The titanium atom in both structures adopts a pentacoor-
dinate coordination geometry in which the diamidopyridyl
ligand is facially bound to the central metal atom, which itself
occupies a corner of the four-membered titanacycle. The bond
length between the two carbon atoms C(1)-C(2) of the
titanacycle is 1.370(3) Å for 1a (1.363(3) for 1b), which is
consistent with a CdC double bond. On the other hand, the
Ti-C(2) (1a: 2.091(2), 1b: 2.079(2) Å) and Ti-N(4) (1a:
(20) (a) Reed, A. E.; Weinhold, F. J. Chem. Phys. 1985, 83, 1736. (b)
Reed, A. E.; Weinstock, R. B.; Weinhold, F. J. Chem. Phys. 1985, 83,
735.
(21) Martins, A. M.; Ascenso, J. R.; Azevedo, C. G.; Dias, A. R.; Duarte,
M. T.; Silva, J. F.; Veiros, L. F.; Rodrigues, S. S. Organometallics 2003,
22, 4218.

Insertions into Azatitanacyclobutenes
Organometallics, Vol. 27, No. 11, 2008 2521
Figure 2. Molecular Kohn-Sham orbitals involved in the π-system of [Ti(N2 Npy){κ2-N(tBu)CHdCPh}] (1a) (left column) displayed
Xyl
along with an NLMO analysis (middle column). Selected NPA charges are shown in the line drawing on the right.
Figure 3. Lowest unoccupied Kohn-Sham molecular orbital (left). The corresponding LUMO, LUMO+1, and LUMO+2 NLMO orbitals
(right).
in the metallacycle, thus leading us to anticipate similar
reactivity to the system referred to above.
the chalcogen atom transfer reagent propylene sulfide13,22h or
Xyl
triphenylphosphine selenide13,23h gave the complexes [Ti(N2
-
Npy){κ2-N(tBu)CHdC(Ph)E}] (E ) S: 2, Se: 3) (Scheme 3).
1
Since the Cartesian and NLMO-LUMO orbitals are mainly
located on the titanium atom (Figure 3), it is reasonable to
assume that the inserting reagent first coordinates to the Ti atom,
giving a six-coordinate intermediate (or five-coodinate if the
pyridyl unit dissociates). Subsequently, the lower stability of
the σNLMO orbital representing the equatorial Ti-C(2) bond (E
) -8.4 eV) compared to the σNLMO (Ti(1)-N(4)) bond (E )
-10.3 eV) in the axial coordination site would explain the
observed selectivity (Vide infra).
The conversion was monitored by H NMR spectroscopy,
which indicated the formation of new titanium species, com-
(22) (a) Blum, S.; Rivera, V. A.; Ruck, R. T.; Michael, F. E.; Bergman,
R. G. Organometallics 2005, 24, 1647. (b) Mullins, S. M.; Duncan, A. P.;
Bergman, R. G.; Arnold, J. Inorg. Chem. 2001, 40, 6952.
(23) (a) Stuczynski, S. M.; Kwon, Y.-U.; Steigerwald, M. L. J.
Organomet. Chem. 1993, 449, 167. (b) Steigerwald, M. L.; Siegrist, T.;
Gyorgy, E. M.; Hessen, B.; Kwon, Y.-U.; Tanzler, S. M. Inorg. Chem.
1994, 33, 3389. (c) Adams, R. D.; Kwon, O.-S.; Sanyal, S. J. Organomet.
Chem. 2003, 681, 258. (d) Belleti, D.; Cauzzi, D.; Graiff, C.; Minarelli,
A.; Pattacini, R.; Predieri, G.; Tiripicchio, A. J. Chem. Soc., Dalton Trans.
2002, 3160.
Insertion of Chalcogen Atoms into Azatitanacyclobutene
(24) (a) Allen, F. H.; Kennard, O. Chem. Des. Autom. News 1993, 8,
1–31. (b) Fletcher, D. A.; McMeeking, R. F.; Parkin, D. J. Chem. Inf.
Comput. Sci. 1996, 36, 746.
Compound 1a. Reaction of the azatitanacyclobutene complex
[Ti(N2 Npy){κ2-N(tBu)CHdCPh}] (1a) with 1 molar equiv of
Xyl

2522 Organometallics, Vol. 27, No. 11, 2008
VujkoVic et al.
Scheme 3. Reaction of [Ti(N2 Npy){K2-N(tBu)CHdCPh}]
Xyl
(1a) with Chalcogen-Atom Donors to Give Products 2 and 3.
Figure 4. Molecular structure of complex 2. Thermal ellipsoids
are drawn at 30% probability. Selected bond lengths (Å) and angles
(deg): Ti-S 2.3796(6), Ti-N(1) 1.9136(14), Ti-N(2) 1.9223(14),
Ti-N(3) 2.2355(15), Ti-N(4) 2.0019(15), S-C(2) 1.7521(18),
C(2)-C(1) 1.351(2), C(1)-N(4) 1.378(2), N(1)-Ti-S 126.44(5),
N(1)-Ti-N(2) 109.51(6), N(1)-Ti-N(3) 85.29(6), N(1)-Ti-N(4)
98.41(6),N(2)-Ti-S122.34(5),N(2)-Ti-N(3)85.53(6),N(2)-Ti-N(4)
104.00(6),N(3)-Ti-S86.17(4),N(3)-Ti-N(4)167.78(6),N(4)-Ti-S
82.27(4).
pounds 2 and 3, in both reactions as well as the concomitant
generation of the byproduct propene and triphenylphosphine,
respectively. Upon removal of the organic volatiles from the
Xyl
reaction with propylene sulfide in Vacuo, [Ti(N2 Npy){κ2-
N(tBu)CHdC(Ph)S}] (2) was isolated in quantitative yield. The
analytically pure selenacyclic complex [Ti(N2 Npy){κ2-
Xyl
N(tBu)CHdC(Ph)Se}] (3) was obtained through recrystallization
from a concentrated toluene solution at 10 °C.
The NMR data of complexes 2 and 3 are consistent with the
overall molecular Cs symmetry of the complexes depicted in
Scheme 3. f methyne proton is observed as a singlet at 7.5 for
2 and 7.7 ppm for 3 and thus at significantly higher field than
the corresponding signal in the azatitanacyclobutene complex
1a (10.0 ppm). On the other hand, the signal of the H6 pyridyl
proton of the N2Npy ligand is observed at lower field (10.1 ppm
for 2, 9.8 for 3 compared to 9.2 for 1a), which is consistent
with the pyridyl unit remaining coordinated to the Lewis acidic
Ti center. The 1H-1H NOESY NMR spectra of 2 and 3 indicate
that the tert-butyl resonance is in close proximity to the xylyl
groups of the N2Npy ligand, while the ortho-phenyl proton has
moved away from H6. The NMR data are thus consistent with
an S and Se insertion into the Ti-C bond.
Single-crystal X-ray structure analyses of both complexes 2
and 3 confirm the structural proposals derived from the NMR
data. Their molecular structures are depicted in Figures 4 and
5, respectively, along with the principal bond lengths and angles.
The titanium atom is pentacoordinate with the diamidopyridyl-
supporting ligand adopting facial tricoordination. The thia and
selena metallacycles incorporating the metal centers deviate
slightly from planarity. The C(1)-C(2) distance (1.351(2) Å
for 2 and 1.352(2) Å for 3) is consistent with there being a
double bond between these two carbon atoms in the metalla-
cycles, while the Ti-N(4) bond length indicates sp2-type single
bonding to the metal center. The Ti-S, Ti-Se, C-S, and Se-C
bond lengths were in the expected ranges on comparison with
the Cambridge Structural Database (Ti-S: 2.191-2.983 Å for
366 examples; Ti-Se: 2.369-2.796 Å, mean 2.569 Å for 36
examples; C-S: 1.218-2.178 Å for 12 736 examples; Se-C:
1.695-2.174 Å, mean 1.891 Å for 711 examples).24
Figure 5. Molecular structure of complex 3. Thermal ellipsoids
are drawn at 30% probability. Selected bond lengths (Å) and angles
(deg): Ti-Se 2.5019(4), Ti-N(1) 1.9148(13), Ti-N(2) 1.9265(13),
Ti-N(3) 2.2524(14), Ti-N(4) 2.0077(13), Se-C(2) 1.8986(16),
C(2)-C(1) 1.352(2), C(1)-N(4) 1.3810(19), N(1)-Ti-Se 126.27(4),
N(1)-Ti-N(2) 109.86(5), N(1)-Ti-N(3) 85.22(5), N(1)-Ti-N(4)
98.92(5),N(2)-Ti-Se121.82(4),N(2)-Ti-N(3)85.09(5),N(2)-Ti-N(4)
103.99(5), N(3)-Ti-Se 85.47(3), N(3)-Ti-N(4) 167.87(5),
N(4)-Ti-Se 82.89(4).
Insertion of Isocyanides into Azatitanacyclobutene Com-
plexes 1a and 1b. Treatment of [Ti(N2 Npy){κ2-N(tBu)CHd
Xyl
CAr}] (Ar ) Ph: 1a or Tol: 1b) with 1 molar equiv of CNR (R
t
)2,6-C6H3Me2, Cy, and Bu,) at room temperature selectively
gave the complexes [Ti(N2 Npy){κ2-N(tBu)CHdC(Ar)Cd
Xyl
N(R)}] (Ar ) Ph, R ) 2,6-C6H3Me2 (4), R ) Cy (5), or R )
t
tBu (6a); Ar ) Tol, R ) Bu (6b)) in quantitative yields
(Scheme 4).
The NMR data of the resulting complexes are consistent with
an insertion of the RNC group into the Ti-C bond similar to
the chalcogen atom insertion descibed above as well as the
1
previously observed insertion of a second alkyne. In the H
NMR spectra of 4-6a,b the metallacyclic CH proton resonance
1
is observed between 8.76 and 9.07 ppm. H NOESY spectra
established its position between the NtBu group and the C-Ph

Insertions into Azatitanacyclobutenes
Organometallics, Vol. 27, No. 11, 2008 2523
Scheme 4. Reaction of [Ti(N2 Npy){K2-N(tBu)CHdCAr}] 1a
Xyl
(Ar ) Ph) and 1b (Ar ) Tol) with Isonitriles to Give
Products [Ti(N2 Npy){K2-N(tBu)dCHC(Ar)dCNR}] (Ar )
Xyl
t
Ph) 4 (R ) 2,6-C6H3Me2), 5 (R ) Cy), or 6a (R ) Bu) and
t
(Ar ) Tol) 6b (R ) Bu)
Figure 7. Optimized structure of complex 4. (DFT calculation with
B3PW91 functional and 6-31G(d) basis set for all atoms.)
closer inspection of the bonding situation in the metallycyclic
insertion product, which proved to be particularly interesting.
The N(4)-C(1) and N(5)-C(3) distances of 1.310(1) and
1.292(1) Å, respectively, indicate substantial CdN double-bond
character, likewise with the C(2)-C(3) bond length of 1.382(1)
Å. This, along with the C(2)-C(3)-N(5) angle of 153.96(9)°,
renders this unit to some extent an η2-bonded heteroallene
(iminoketene). Notable is also the C(1)-C(2) distance of
1.431(1) Å, which also indicates some multiple-bond character
(bond order of ca. 1.5 due to conjugation of the adjacent double
bonds, Vide infra). The Ti-C(3) and Ti-N(5) distances of
2.0185(9) and 2.1399(8) Å lie in the range of alkyl-Ti and
amido-Ti single bonds, whereas the Ti-N(4) bond length of
2.3455(8) Å is in the range for an N-donor-acceptor interaction
of a ligand with the metal center as also observed for the pyridyl
bonding of the ancillary ligand in the trans axial position
[Ti-N(3) 2.2737(8) Å].13
Figure 6. Molecular structure of complex 4. Thermal ellipsoids
are drawn at 30% probability. Selected bond lengths (Å) and angles
(deg): Ti-N(1) 1.9521(8), Ti-N(2) 1.9550(8), Ti-N(3) 2.2737(8),
Ti-N(4) 2.3455(8), Ti-N(5) 2.1399(8), Ti-C(3) 2.0185(9),
N(5)-C(3)1.2916(11),C(3)-C(2)1.3816(12),C(2)-C(1)1.4314(13),
C(1)-N(4) 1.3101(12), N(1)-Ti-N(2) 104.28(3), N(1)-Ti-N(3)
82.74(3), N(1)-Ti-N(4) 91.47(3), N(1)-Ti-N(5) 124.05(3),
N(1)-Ti-C(3) 125.63(3), N(2)-Ti-N(3) 81.83(3), N(2)-Ti-N(4)
90.56(3), N(2)-Ti-N(5) 127.25(3), N(2)-Ti-C(3) 125.91(3),
N(3)-Ti-N(4) 168.96(3), N(3)-Ti-N(5) 84.40(3), N(3)-Ti-C(3)
120.39(3), N(4)-Ti-N(5) 106.61(3), N(4)-Ti-C(3) 70.59,
N(5)-Ti-C(3) 36.04(3), C(3)-N(5)-Ti 66.85(5), N(5)-C(3)-Ti
77.11(5), N(5)-C(3)-C(2) 153.96(9), C(3)-C(2)-C(1) 107.12(8),
C(2)-C(1)-N(4)121.72(8),C(1)-N(4)-Ti111.59(6),C(2)-C(3)-Ti
128.93(7).
DFT Study of [Ti(N2XylNpy){K2-N(tBu)CHdC(2,6-C6H3Me2)}]
(4). The metric parameters of the coupled organometallic
fragment ligated to the Ti center discussed in the previous
section raised the question of the overall bonding situation and
the interpretation of the resulting bond lengths. Similar to the
chosenapproachforcomplex1a,theinsertionproduct[Ti(N2XylNpy){κ2-
N(tBu)CHdC(Ph)CdN(2,6-C6H3Me2)}] (4) has been modeled
by DFT methods using the B3PW91 functional and a 6-31G(d)
basis set for all atoms.17–19 The optimized structure of complex
4 represented in Figure 7 is in good agreement with the
experimental X-ray data, as is shown in Table 2 for selected
bond lengths and angles.
The average difference of the calculated and experimental
Ti-N and Ti-C bond lengths is less than 0.02 Å, with the
exception of the axial pyridyl N(3)-Ti distance, for which the
calculated and experimental values deviate by 0.049 Å, which
we have noticed in previous modeling studies of related systems.
The excellent agreement between theory and experiment for the
κ2-N(tBu)CHC(Ph)CN(2,6-C6H3Me2) fragment of complex 4
(deviations of <0.003 Å, well within typical error limits for
X-ray crystallographic analyses) allowed a closer inspection of
its bonding.
group and thus proved the regiochemistry of the insertion
indicated in Scheme 4. Moreover, the NOE cross-peaks between
the signals of the isocyanide substituent R and the resonances
of the C-Ph group as well as the H6 pyridyl proton of the
ancillary ligand is explained by the orientation of the metally-
1
cycle represented in Scheme 4. Finally, the characteristic H
NMR chemical shift of the H6 proton of the pyridyl donor of
the N2Npy ligand is observed between 9.00 and 9.31 ppm,
indicating the coordination of the pyridyl donor to the metal
center.
Since the physical (particularly magnetic) properties of
complex 4 are consistent with a formal oxidation state of TiIV
for the central atom, the κ2-N(tBu)CHC(Ph)CN(2,6-C6H3Me2)
unit is supposed to be formally dianionic. However, as for many
other organometallic complexes such formal oxidation states
do not necessarily reflect the partial charges calculated for the
respective atoms or molecular fragments. The entire N(tBu)CH-
Additional proof of the connectivity in the metallacycles has
beenobtainedbyanX-raycrystallographicstudyof[Ti(N2XylNpy){κ2-
N(tBu)CHdC(Ph)CdN(2,6-C6H3Me2)}] (4). Its molecular struc-
ture is depicted in Figure 6 along with the principal bond lengths
and angles. The establishment of the structural details allowed

2524 Organometallics, Vol. 27, No. 11, 2008
VujkoVic et al.
Figure 8. Resonance structures describing the bonding situation in [Ti(N2 Npy){κ2-N(tBu)dCHC(Ph)dCN(2,6-C6H3Me2)}] (4).
Xyl
Table 2. Selected Experimental and Theoretical Angles (deg) and Distances (Å) for Compounds 1a and 4
1a
4
exptl
calcd
exptl
calcd
d(Ti-N(1))
d(Ti-N(2))
d(Ti-N(3))
d(Ti-N(4))
1.912
1.930
2.231
1.943
1.941
1.953
2.275
1.942
1.952
1.955
2.274
2.346
2.140
2.019
1.310
1.431
1.382
1.292
1.940
1.958
2.323
2.358
2.136
2.001
1.309
1.432
1.384
1.294
d(Ti-N(5))
d(Ti-C(3))
d(Ti-C(2))
d(N(4)-C(1))
d(C(1)-C(2))
2.091
1.380
1.370
2.069
1.382
1.375
d(C(2)-C(3))
d(C(3)-N(5))
R(N(1)-Ti-N(2))
R(N(4)-C(1)-C(2))
103.7
116.7
104.1
116.8
104.3
154.0
105.4
153.4
R(C(2)-C(3)-N(5))
C(Ph)CN(2,6-C6H3Me2) fragment is planar, suggesting a highly
delocalized π-system spread across the five atoms. It is
instructive to begin an analysis of the data in terms of the
limiting resonance structures A-C depicted in Figure 8.
Given the way in which complex 4 was formed, i.e., as an
insertion product of an isocyanide and an azatitanacyclobutene,
resonance structure A appears reasonable. However, the bond
length pattern described above, with short C(2)-C(3) and
N(4)-C(1) as well as a longer C(1)-C(2) distances, does not
agree with this resonance form. The alternative resonance
structure B appears to reflect the metric parameters better, as
does the formulation of the side-on bound cumulene unit in
resonance form C. The latter, however, implies the formulation
of N(tBu)CHC(Ph)CN(2,6-C6H3Me2) as a neutral fragment and
thus the Ti center as formally divalent. A natural population
analysis (NPA) performed for 4 established the partial charge
pattern represented in Figure 9.
Notable is the low partial charge at titanium, which may be
explained by the high degree of covalency of the metal-ligand
bonding in this complex and, in particular, the alternating charge
distribution pattern in N(tBu)CHC(Ph)CNR, with the highest
electron density being located in the middle (C(2)) and at
extreme ends (N(4), N(5)) of the chain. This is very similar to
the charge distribution in a pentadienyl monoanion, and this
analogy is also apparent in an analysis of the conjugated
π-system in the metallacyclic fragment.
In Figure 10 an orbital analysis of the π-bonding in the
pentadienide reference system (column a) as well as the
metallacyclic unit (columns b and c) is provided. An all in-
phase conjugated π-bonding of the NC3N fragment is evident
in HOMO-20, whereas HOMO-14 clearly represents the
π-bonding interaction between N(5)-C(3) and N(4)-C(1). The
HOMO itself represents the third nonbonding combination (with
some constructive overlap reinforcing the C(2)-C(3) bond).
Calculation of the Wiberg indices, which provide a semiquan-
titative measure of the bond multiplicity,25 for the bonds within
this fragment revealed a higher bond order between the atoms
C(2)-C(3) (1.35) than between carbons C(1)-C(2) (1.21), while
the bond orders between N-C atoms are significantly greater
than unity (1.50 and 1.60) (Table 3).
Three-Component Coupling to Generate r,ꢀ-Unsatur-
ated ꢀ-Iminoamines. Compounds 4-6a,b are models for the
key intermediate of the catalytic cycle for the three-component
coupling of alkynes, isocyanides, and amines to generate R,ꢀ-
unsaturated ꢀ-iminoamines, which has been reported by Odom
and co-workers.9 In order to determine whether compounds
4-6a reported in this work do in fact display the reactivity
postulated for this type of intermediate, we investigated their
reaction with tert-butylamine (Scheme 5).
Compounds 4-6a were reacted with 2 molar equiv of tert-
butylamine at room temperature to give a titanium imido species
along with the respective three-component iminoamination
coupling products 7a-c. This reaction represents the final step
1
in the catalytic cycle. The H NMR spectra of the reaction
mixture showed the characteristic signals from the previously
described titanium imido complex stabilized by tert-butylamine
[Ti(NtBu)(N2 Npy)(NH2 Bu)] (8).16 After filtration through
silica, the crude reaction mixtures were analyzed by GC-MS,
HR-MS, and NMR spectroscopy. For each reaction, the three-
component coupling products have been identified as sole
reaction products according to high-resolution mass spectrometry.
Attempts to develop the sequence of stoichiometric reactions
described in this work into a catalytic process failed. We
Xyl
t
Figure 9. Selected NPA charges in [Ti(N2 Npy){κ2-
Xyl
N(tBu)dCHC(Ph)dCN(2,6-C6H3Me2)}] (4).
(25) Wiberg, K. B. Tetrahedron 1968, 2, 4–1083.

Insertions into Azatitanacyclobutenes
Organometallics, Vol. 27, No. 11, 2008 2525
Figure 10. Schematic π orbitals in CH2(CH)3CH2 and in the Ti-κ2-N(tBu)dCHC(Ph)dCN(2,6-C6H3Me3) fragment of complex 4 (columns
a and b, respectively). Molecular orbitals of complex 4 involving the π-system in the κ2-N(tBu)dCHC(Ph)dCN(2,6-C6H3Me3) fragment
are presented in column c.
Table 3. Bond Orders (WI)a and Bond Lengths of the π-System
Experimental Section
N(tBu)CHdC(2,6-C6H3Me2) in Complex 4
General Experimental Procedures. All manipulations of air-
N(4)-C(1)
C(1)-C(2)
C(2)-C(3)
C(3)-N(5)
and moisture-sensitive materials were performed under an inert
atmosphere of dry argon using standard Schlenk techniques or by
working in a glovebox. Toluene was dried over sodium, distilled,
and degassed prior to use. C6D6 was dried over potassium, vacuum
distilled, and stored in Teflon valve ampules under argon. Samples
for NMR spectroscopy were prepared under argon in 5 mm Wilmad
tubes equipped with J. Young Teflon valves. 1H, 13C, 15N, and
77Se spectra were recorded on Bruker Avance 200, 400, and 600
NMR spectrometers and were referenced using the residual protio
solvent (1H) or solvent (13C) resonances or externally to 15NH3
and 77SeMe2. Mass spectra and elemental analyses were recorded
by the analytical service of the Heidelberg Chemistry Department.
WI
d (Å)
1.50
1.294
1.21
1.432
1.35
1.384
1.60
1.309
a The Wiberg indices (WI) are used as a measure of the bond order.25
tentatively attribute this to the more rapid imido-isocyanide
coupling as compared to the essential {2+2} cycloaddition of
the imide with the alkyne. We have studied such rapid (multiple)
reactions with isonitriles previously in some detail for a closely
related imidotitanium complex.13a,13b However, in the case at
hand, we were unable to identify such products unambiguously.
Xyl
The azametallacyclobutenes [Ti(N2 Npy){κ2-N(tBu)CHdCAr′}]
(Ar′ ) Ph: 1a 4-C6H4Me: 1b) were prepared according to published
procedures.16 All other reagents were obtained from commercial
sources and used as received unless explicitly stated otherwise.
Conclusion
The stable azatitanocyclobutene complexes 1a and 1b have
been shown to readily undergo Ti-C bond insertion reactions.
This has allowed us to synthesize and fully characterize the
intermediates of the three-component iminoamination of alkynes
to give R,ꢀ-unsaturated ꢀ-iminoamines. Furthermore, a DFT
study has provided some insight into the bonding in a previously
postulated but unobserved key intermediate of this process along
with the qualitative rationalization of the observed Ti-C
selectivity in the insertion reaction step converting compounds
1a and 1b to 2-6a,b.
Xyl
Preparation of the Compounds. [Ti(N2 Npy){K2-N(tBu)CHd
C(Ph)S}] (2). To a solution of [Ti(N2 Npy){κ2-N(tBu)CHdCPh}]
Xyl
(211 mg, 0.36 mmol) in toluene (10 mL) was added an equimolar
amount of propenesulfide (28 µL, 0.36 mmol) via syringe. The
resulting dark green solution was stirred overnight before removing
the solvent in Vacuo to yield the title compound as a dark green
solid. Quantitative yield. Diffraction-quality single crystals were
grown from a saturated toluene solution at 10 °C. 1H NMR (C6D6,
600.1 MHz, 296 K): δ 1.10 (3 H, s, Me of N2Npy), 1.17 (9 H, s,
3
CMe3), 2.19 (12 H, s, C6H3Me2), 3.13 (2 H, d, CHH, J ) 12.6

2526 Organometallics, Vol. 27, No. 11, 2008
VujkoVic et al.
t
Scheme 5. Formation of r,ꢀ-Unsaturated ꢀ-Iminoamines (R ) Cy, 2,6-C6H3Me2, or Bu)
1
Hz), 4.75 (2 H, d, CHH, 3J ) 12.6 Hz), 6.46 (1 H, ddd, H5,
3J(H4H5) ) 7.5 Hz, 3J(H6H5) ) 5.5 Hz, 4J(H3H5) ) 1.2 Hz), 6.51
(2 H, s, p-C6H3Me2), 6.71 (1 H, d, H3, 3J ) 7.6 Hz), 6.91 (1 H, td,
H4, 3J(H3H4H5) ) 7.9 Hz, 4J(H4H6) ) 1.7 Hz), 6.94 (4 H, s,
saturated toluene solution at 10 °C. H NMR (C6D6, 600.1 MHz,
296 K): δ 1.01 (9 H, s, CMe3), 1.27 (3 H, s, Me of N2Npy), 2.15 (6
H, s, 2,6-C6H3Me2), 2.21 (12 H, s, C6H3Me2), 3.22 (2 H, d, CHH,
3J ) 12.7 Hz), 3.76 (2 H, d, CHH, 3J ) 12.7 Hz), 6.35 (1 H, ddd,
H5, 3J(H4H5) ) 7.4 Hz, 3J(H6H5) ) 5.5 Hz, 4J(H3H5) ) 1.2 Hz),
6.41 (4 H, s, o-C6H3Me2), 6.44 (2 H, s, p-C6H3Me2), 6.84 (1 H, d,
3
4
o-C6H3Me2), 7.07 (1 H, tt, p-C6H5, J ) 7.3 Hz, J ) 1.2 Hz),
7.37 (2 H, app. t, m-C6H5, J ) 7.4 Hz), 7.47 (1 H, s, CdCH), 8.01
3
4
(2 H, dd, o-C6H5, J ) 8.1 Hz, J ) 1.2 Hz), 10.07 (1 H, dd, H6,
3J(H5H6) ) 5.5 Hz, 4J(H4H6) ) 1.6 Hz) ppm. 13C{1H} NMR
(C6D6, 150.9 MHz, 296 K): δ 21.7 (C6H3Me2), 25.4 (Me of N2Npy),
31.7 (CMe3), 42.1 [C(CH2NXyl)2], 62.3 (CMe3), 62.8 [(CH2NXyl)2],
107.0 (CdCH), 114.7 (o-C6H3Me2), 120.5 (C3), 123.1 (C5), 123.7
(p-C6H3Me2), 123.8 (p-C6H5), 126.0 (o-C6H5), 128.5 (m-C6H5),
135.6 (CdCH), 137.9 (m-C6H3Me2), 139.3 (C4), 142.3 (ipso-C6H5),
149.6 (C6), 153.5 (ipso-C6H3Me2), 159.9 (C2) ppm. 15N{1H} NMR
(C6D6, 60.8 MHz, 296 K): δ 261.0 (N2Npy), 280.4 (N2Npy), 314.2
(NtBu) ppm. Anal. Found (calcd) (%) for C37H44N4STi: C 71.5
(71.1); H 7.1 (7.1); N 8.6 (9.0).
H3, J ) 7.9 Hz), 6.90 (1 H, app. t, p-C6H5) 7.94 (1 H, td, H4,
3
3J(H3H4H5) ) 7.6 Hz, J(H4H6) ) 1.6 Hz), 7.05 (3 H, m, 2,6-
4
C6H3Me2), 7.13 (2 H, app. t, m-C6H5, J ) 7.8 Hz), 7.18 (2 H, dd,
o-C6H5, 3J ) 8.3 Hz, 4J ) 1.1 Hz), 9.07 (1 H, s, NdCH), 9.31 (1
H, dd, H6, 3J(H5H6) ) 5.5 Hz, 4J(H4H6) ) 1.6 Hz) ppm. 13C{1H}
NMR (C6D6, 150.9 MHz, 296 K): δ 19.1 (2,6-C6H3Me2), 21.6
(C6H3Me2), 24.7 (Me of N2Npy), 31.6 (CMe3), 43.3 [C(CH2NXyl)2],
57.4 (CMe3), 61.7 [(CH2NXyl)2], 93.7 (C-CH), 112.3 (o-C6H3Me2),
119.1 (C3), 120.7 (p-C6H3Me2), 122.1 (C5), 122.8 (p-C6H5), 124.2
(o-C6H5), 125.0 (o/p-2,6-C6H3Me2), 128.5 (m-C6H5), 128.6 (o/p-
2,6-C6H3Me2), 132.7 (m-2,6-C6H3Me2), 137.5 (m-C6H3Me2), 137.6
(ipso-C6H5), 138.2 (C4), 148.3 (ipso-2,6-C6H3Me2), 149.0 (C6),
153.5 (ipso-C6H3Me2), 162.0 (C2), 175.8 (C-CH), 199.2 (C-N) ppm.
15N{1H} NMR (C6D6, 60.8 MHz, 296 K): δ 193.8 (CNC6H3Me2),
252.6 (N2Npy), 259.8 (NtBu), 290.3 (N2Npy) ppm. Anal. Found
(calcd) (%) for C46H53N5Ti (+C7H8): C 77.8 (78.0); H 7.7 (7.5); N
8.7 (8.6).
Xyl
[Ti(N2 Npy){K2-N(tBu)CHdC(Ph)Se}] (3). To a solution of
[Ti(N2 Npy){κ2-N(tBu)CHdCPh}] (185 mg, 0.27 mmol) in
Xyl
toluene (10 mL) was added an equimolar amount of triphenylphos-
phine selenide (91 mg, 0.27 mmol). The resulting dark green
solution was stirred overnight. Removing the volatiles under reduced
pressure produced a dark green waxy solid, which was redisolved
into toluene (5 mL). After 2 days at 10 °C, the title compound was
formed as a black crystalline solid. Yield: 38 mg (21%). Diffraction-
quality single crystals were grown from a saturated toluene solution
at 10 °C. 1H NMR (C6D6, 600.1 MHz, 296 K): δ 1.09 (3 H, s, Me
of N2Npy), 1.14 (9 H, s, CMe3), 2.21 (12 H, s, C6H3Me2), 3.12 (2
[Ti(N2 Npy){K2-N(tBu)CHdC(Ph)CdN(Cy)}] (5). To a solu-
Xyl
tion of [Ti(N2 Npy){κ2-N(tBu)CHdCPh}] (215 mg, 0.36 mmol)
Xyl
in toluene (10 mL) was added an equimolar amount of cyclohexyl
isocyanide (45 µL, 0.36 mmol) via syringe. The resulting dark green
solution was stirred overnight before removing the solvent in Vacuo
to yield the title compound as a brown solid. Quantitative yield.
1H NMR (C6D6, 600.1 MHz, 296 K): δ 0.90 (1 H, m, p-C6H11),
1.01 (2 H, m obscured by CMe3, m-C6H11), 1.02 (9 H, s, CMe3),
1.29 (3 H, s, Me of N2Npy), 1.33 (1 H, app. d, p-C6H11, 3J ) 11.7
3
3
H, d, CHH, J ) 12.5 Hz), 3.71 (2 H, d, CHH, J ) 12.5 Hz),
6.41 (1 H, ddd, H5, 3J(H4H5) ) 7.2 Hz, 3J(H6H5) ) 5.6 Hz,
4J(H3H5) ) 1.2 Hz), 6.53 (2 H, s, p-C6H3Me2), 6.71 (1 H, d, H3,
3
4
3J ) 7.9 Hz), 6.90 (1 H, td, H4, J(H3H4H5) ) 7.8 Hz, J(H4H6)
) 1.6 Hz), 7.03 (5 H, m, o-C6H3Me2 and p-C6H5), 7.34 (2 H, app.
t, m-C6H5, J ) 7.5 Hz), 7.71 (1 H, s, CdCH), 7.99 (2 H, app. d,
o-C6H5, 3J ) 8.3 Hz), 9.85 (1 H, dd, H6, 3J(H5H6) ) 5.5 Hz,
4J(H4H6) ) 1.2 Hz) ppm. 13C{1H} NMR (C6D6, 150.9 MHz, 296
K): δ 21.7 (C6H3Me2), 25.7 (Me of N2Npy), 31.8 (CMe3), 41.9
[C(CH2NXyl)2], 62.5 (CMe3), 62.7 [(CH2NXyl)2], 104.2 (CdCH),
114.4 (o-C6H3Me2), 120.3 (C3), 122.8 (C5), 123.7 (p-C6H3Me2),
123.9 (p-C6H5), 126.4 (o-C6H5), 128.4 (m-C6H5), 137.6 (m-
C6H3Me2), 138.0 (CdCH), 138.9 (C4), 143.4 (ipso-C6H5), 150.1
(C6), 152.7 (ipso-C6H3Me2), 159.7 (C2) ppm. 15N{1H} NMR (C6D6,
60.8 MHz, 296 K): δ 265.1 (N2Npy), 281.0 (N2Npy), 314.2 (NtBu)
ppm. 77Se NMR (76 MHz, C6D6, 296 K): δ 926.2 ppm. Anal. Found
(calcd) (%) for C37H44N4SeTi (+C7H8): C 68.8 (69.2); H 6.8 (6.9);
N 7.3 (7.3).
3
Hz), 1.49 (2 H, app. d, m-C6H11, J ) 13.5 Hz), 1.64 (2 H, app.
3
dq, o-C6H11), 2.04 (2 H, app. d, o-C6H11, J ) 12.5 Hz), 2.25 (12
3
H, s, C6H3Me2), 3.24 (2 H, d, CHH, J ) 12.6 Hz), 3.71 (2 H, d,
CHH, 3J ) 12.6 Hz), 3.86 (1 H, app. tt, ispo-C6H11), 6.38 (4 H, s,
o-C6H3Me2), 6.45 (2 H, s, p-C6H3Me2), 6.69 (1 H, ddd, H5,
3J(H4H5) ) 7.4 Hz, 3J(H6H5) ) 5.5 Hz, 4J(H3H5) ) 1.2 Hz), 6.93
(1 H, d, H3, J ) 7.9 Hz), 7.12 (2 H, m, H4 and p-C6H5), 7.39 (2
3
3
H, app. t, m-C6H5, J ) 7.7 Hz), 7.68 (2 H, dd, o-C6H5, J ) 8.2
Hz, 4J ) 1.2 Hz), 8.82 (1 H, s, NdCH), 9.27 (1 H, dd, H6, 3J(H5H6)
) 5.4 Hz, 4J(H4H6) ) 1.2 Hz) ppm. 13C{1H} NMR (C6D6, 150.9
MHz, 296 K): δ 21.7 (C6H3Me2), 24.6 (Me of N2Npy), 27.7 (p-
C6H11), 25.9 (m-C6H11), 31.7 (CMe3), 33.6 (o-C6H11), 43.5
[C(CH2NXyl)2], 57.6 (CMe3), 61.9 [(CH2NXyl)2], 63.8 (ipso-
C6H11), 95.9 (C-CH), 112.2 (o-C6H3Me2), 119.3 (C3), 120.4 (p-
C6H3Me2), 121.2 (C5), 123.2 (p-C6H5), 126.4 (o-C6H5), 128.7 (m-
C6H5), 137.3 (m-C6H3Me2), 138.1 (C4), 140.1 (ipso-C6H5), 149.6
(C6), 154.2 (ipso-C6H3Me2), 162.1 (C2), 173.6 (C-CH), 206.4 (C-
N) ppm. 15N{1H} NMR (C6D6, 60.8 MHz, 296 K): δ 212.6 (CNCy),
242.0 (N2Npy), 254.5 (NtBu), 291.1 (N2Npy) ppm. Anal. Found
(calcd) (%) for C44H55N5Ti: C 75.4 (75.3); H 8.1 (7.9); N 9.9 (10.0).
Xyl
[Ti(N2 Npy){K2-N(tBu)CHdC(Ph)CdN(2,6-C6H3Me2)}] (4).
To a solution of [Ti(N2 Npy){κ2-N(tBu)CHdCPh}] (229 mg, 0.39
Xyl
mmol) in toluene (10 mL) was added an equimolar amount of 2,6-
dimethylphenyl isocyanide (50 mg, 0.39 mmol). The resulting dark
red solution was stirred overnight before removing the solvent in
Vacuo to yield the title compound as a brown solid. Quantitative
yield. Diffraction-quality single crystals were grown from a

Insertions into Azatitanacyclobutenes
Organometallics, Vol. 27, No. 11, 2008 2527
Table 4. Details of the Crystal Structure Determinations of the Complexes 1a, 1b, 2a, 3, and 4
1a
37H44N4Ti
1b
2a
3
4
formula
cryst syst
space group
C
C
38H46N4Ti
C
37H44N4STi · 0.5C7H8
C
37H44N4SSeTi · 0.5C7H8
C53H61N5Ti
orthorhombic
monoclinic
P21/c
triclinic
P1
j
Pbca
a /Å
b/Å
c/Å
20.6472(16)
12.203(1)
25.668(2)
21.266(4)
12.788(2)
24.435(4)
11.1455(13)
12.2427(15)
25.737(3)
11.210(1)
12.180(1)
25.940(3)
11.434(2)
14.483(3)
14.939(3)
95.761(4)
103.409(4)
108.459(3)
2241.9(8)
2
R/deg
ꢀ/deg
97.782(2)
3479.5(7)
97.311(2)
3513.0(7)
γ/deg
V/Å3
6467.3(9)
6645(2)
Z
8
4
Mr
592.66
1.217
2528
0.296
0.7464, 0.6898
2.1 to 27.9
-27 ... 0, 0 ... 16,
-33 ... 0
131 850
7701, 0.0970
5369
606.69
1.213
2592
0.289
0.7464, 0.6499
1.9 to 29.1
-29 ... 0, 0 ... 17,
-33 ... 0
148 273
8936, 0.0992
6032
670.79
1.281
1428
0.341
0.0514, 0.1128
2.3 to 30.5
-15 ... 15, 0 ... 17,
0 ... 36
84 423
10622, 0.0946
7602
717.69
1.357
1500
1.314
0.6700, 0.7464
1.8 to 32.3
-16 ... 16, 0 ... 18,
0 ... 38
88 720
11743, 0.0547
8927
815.97
1.209
872
0.232
0.7464, 0.6850
2.0 to 32.1
-16 ... 15, -20 ... 20,
0 ... 22
55 273
14532, 0.0274
12817
dc/Mg · m-3
F000
µ(Mo KR) /mm-1
max., min. transmn factors
range/deg
index ranges (indep set)h,k,l
no. of reflns measd
unique, Rint
observed [I2σ(I)]
no. of params refined
R indices [F > 4σ(F)] R(F),
wR(F2)
389
453
435
438
582
0.0545, 0.1411
0.0509, 0.1229
0.0514, 0.1128
0.0390, 0.1005
0.0377, 0.1081
R indices (all data) R(F),
0.0828, 0.1549
0.0877, 0.1370
0.0824, 0.1239
0.0583, 0.1071
0.0433, 0.1127
wR(F2)
GooF on F2
1.09
0.429, -0.802
1.08
0.412, -0.464
1.07
0.506, -0.441
1.10
0.921, -0.510
1.10
0.560, -0.3
largest residual peaks/e · Å-3
[Ti(N2 Npy){K2-N(tBu)CHdC(Ph)CdN(tBu)}] (6a). To a
Xyl
7.54 (2 H, d, o-C6H4Me, 3J ) 8.0 Hz), 8.76 (1 H, s, NdCH), 9.01
(1 H, dd, H6, 3J(H5H6) ) 5.3 Hz, 4J(H4H6) ) 1.2 Hz) ppm.
13C{1H} NMR (C6D6, 150.9 MHz, 296 K): δ 21.2 (C6H4Me), 21.8
(C6H3Me2), 24.8 (Me of N2Npy), 30.2 (CN(CMe3)), 31.8 (CMe3),
43.8 [C(CH2NXyl)2], 57.9 (CMe3), 61.3 (CN(CMe3)), 62.1
[(CH2NXyl)2], 98.3 (C-CH), 112.5 (o-C6H3Me2), 119.5 (C3), 120.6
(p-C6H3Me2), 120.7 (C5), 125.6 (p-C6H4Me), 126.4 (o-C6H4Me),
129.7 (m-C6H4Me), 132.3 (ipso-C6H4Me), 137.4 (m-C6H3Me2),
138.1 (C4), 149.3 (C6), 154.7 (ipso-C6H3Me2), 161.9 (C2), 171.9
(C-CH), 210.7 (C-N) ppm. 15N{1H} NMR (C6D6, 60.8 MHz, 296
K): δ 228.4 (CNtBu), 238.1 (N2Npy), 254.0 (NtBu), 290.4 (N2Npy)
ppm. Anal. Found (calcd) (%) for C43H55N5Ti: C 74.9 (74.9); H
8.1 (8.0); N 9.6 (10.1).
solution of [Ti(N2 Npy){κ2-N(tBu)CHdCPh}] (190 mg, 0.27
Xyl
mmol) in toluene (10 mL) was added an equimolar amount of tert-
butyl isocyanide (30 µL, 0.27 mmol) via syringe. The resulting
dark red solution was stirred overnight before removing the solvent
in Vacuo to yield the title compound as a brown solid. Quantitative
yield. 1H NMR (C6D6, 600.1 MHz, 296 K): δ 1.08 (9 H, s, CMe3),
1.25 (9 H, s, CN(CMe3)), 1.28 (3 H, s, Me of N2Npy), 2.24 (12 H,
s, C6H3Me2), 3.28 (2 H, d, CHH, 3J ) 12.6 Hz), 3.65 (2 H, d,
CHH, 3J ) 12.6 Hz), 6.43 (2 H, s, p-C6H3Me2), 6.46 (4 H, s,
o-C6H3Me2), 6.54 (1 H, ddd, H5, 3J(H4H5) ) 7.4 Hz, 3J(H6H5) )
5.6 Hz, 4J(H3H5) ) 1.2 Hz), 6.89 (1 H, d, H3, 3J ) 7.9 Hz), 7.06
3
4
(1 H, td, H4, J(H3H4H5) ) 7.7 Hz, J(H4H6) ) 1.7 Hz), 7.11 (1
H, app. t, p-C6H5), 7.39 (2 H, app. t, m-C6H5, J ) 7.8 Hz), 7.61 (2
H, dd, o-C6H5, J ) 7.1 Hz, J ) 1.0 Hz), 8.78 (1 H, s, NdCH),
General Procedure for the Preparation of Three-Component
3
4
Xyl
Iminoamination Products. To a solution of [Ti(N2 Npy){κ2-
3
4
9.00 (1 H, dd, H6, J(H5H6) ) 5.3 Hz, J(H4H6) ) 1.2 Hz) ppm.
13C{1H} NMR (C6D6, 150.9 MHz, 296 K): δ 21.6 (C6H3Me2), 24.6
(Me of N2Npy), 30.0 (CN(CMe3)), 31.6 (CMe3), 43.6
[C(CH2NXyl)2], 57.8 (CMe3), 61.2 (CN(CMe3)), 61.9
[(CH2NXyl)2], 98.4 (C-CH), 112.3 (o-C6H3Me2), 119.3 (C3), 120.4
(p-C6H3Me2), 120.5 (C5), 123.1 (p-C6H5), 126.0 (o-C6H5), 128.7
(m-C6H5), 137.3 (m-C6H3Me2), 137.9 (C4), 140.7 (ipso-C6H5), 149.1
(C6), 154.4 (ipso-C6H3Me2), 161.7 (C2), 171.6 (C-CH), 211.1 (C-
N) ppm. 15N{1H} NMR (C6D6, 60.8 MHz, 296 K): δ 229.4
(CNtBu), 238.6 (N2Npy), 254.7 (NtBu), 290.3 (N2Npy) ppm. Anal.
Found (calcd) (%) for C42H53N5Ti: C 74.9 (74.7); H 7.7 (7.9); N
10.2 (10.4).
N(tBu)dCHC(Ph)dCN(R)}] (0.025 mmol) in toluene (0.5 mL) was
added 2 equiv of tert-butylamine (0.05 mmol) via syringe. The
reaction mixture was stirred overnight at room temperature,
affording an orange solution, which was filtered through silica. 7a:
1H NMR (CD2Cl2, 600.1 MHz, 296 K): δ 1.39 (9 H, s, CMe3),
2.23 (6 H, s, 2,6-C6H3Me2), 6.89 (1 H, t, p-2,6-C6H3Me2, 3J ) 7.5
3
Hz), 7.06 (2 H, d, m-2,6-C6H3Me2, J ) 7.5 Hz), 7.12 (1 H, app.
t, p-C6H5, 3J ) 7.0 Hz), 7.25-7.30 (4 H, m, o-C6H5 and m-C6H5),
7.38 (1 H, d, 3J ) 3.0 Hz), 8.10 (1 H, d, 3J ) 3.0 Hz) 11.04 (1 H,
br s, NH). 13C{1H} NMR (CD2Cl2, 150.9 MHz, 296 K): δ 18.6
(2,6-C6H3Me2), 30.1 (CMe3), 52.0 (CMe3), 104.3 (Cb), 122.7 (p-
2,6-C6H3Me2), 124.1 (p-C6H5), 124.9 (C6H5), 128.0 (m-2,6-
C6H3Me2), 128.3 (o-2,6-C6H3Me2), 128.5 (C6H5), 141.4 (ipso-C6H5),
143.7, 151.8 (ipso-2,6-C6H3Me2), 162.2. HRMS (EI): m/z (%) calcd
for C21H26N2 [M+] 306.2096, found: 306.2115 (100). 7b: 1H NMR
(CD2Cl2, 600.1 MHz, 296 K): δ 1.30 (9 H, s, HaNCMe3), 1.39 (9
H, s, HcNCMe3), 7.26-7.37 (6 H, m, Ha and C6H5), 9.47 (1 H, d,
Hc, 3J ) 3.8 Hz), 10.87 (1 H, br s, NH). HRMS (EI): m/z (%)
calcd for C17H26N2 [M+] 258.2096, found 258.2096 (100). 7c: 1H
NMR (CD2Cl2, 600.1 MHz, 296 K): δ 1.30 (9 H, s, HaNCMe3),
1.39 (9 H, s, HcNCMe3), 7.26-7.37 (6 H, m, Ha and C6H5), 9.47
(1 H, d, Hc, 3J ) 3.8 Hz), 10.87 (1 H, br s, NH). HRMS (EI): m/z
(%) calcd for C19H28N2 [M+] 284.2252, found 284.2269 (100).
X-ray Crystal Structure Structure Determinations. Crystal
data and details of the structure determinations are listed in Table
4. Intensity data were collected at 100(2) K with a Bruker AXS
Xyl
[Ti(N2 Npy){K2-N(tBu)CHdC(Tol)CdN(tBu)}] (6b). To a
solution of [Ti(N2 Npy){κ2-N(tBu)CHdCTol}] (175 mg, 0.29
Xyl
mmol) in toluene (10 mL) was added an equimolar amount of tert-
butyl isocyanide (33 µL, 0.29 mmol) via syringe. The resulting
dark green solution was stirred overnight before removing the
solvent in Vacuo to yield the title compound as a brown solid.
Quantitative yield. 1H NMR (C6D6, 600.1 MHz, 296 K): δ 1.08 (9
H, s, CMe3), 1.26 (9 H, s, C-NCMe3), 1.28 (3 H, s, Me of N2Npy),
2.26 (12 H, s, C6H3Me2), 2.28 (3 H, s, C6H4Me), 3.28 (2 H, d,
3
3
CHH, J ) 12.6 Hz), 3.66 (2 H, d, CHH, J ) 12.6 Hz), 6.42 (2
H, s, p-C6H3Me2), 6.46 (4 H, s, o-C6H3Me2), 6.54 (1 H, ddd, H5,
3J(H4H5) ) 7.4 Hz, 3J(H6H5) ) 5.4 Hz, 4J(H3H5) ) 1.1 Hz), 6.89
3
3
(1 H, d, H3, J ) 8.0 Hz), 7.06 (1 H, td, H4, J(H3H4H5) ) 7.7
Hz, J(H4H6) ) 1.7 Hz), 7.20 (2 H, d, m-C6H4Me, J ) 7.7 Hz),
4
3

2528 Organometallics, Vol. 27, No. 11, 2008
VujkoVic et al.
Smart 1000 CCD diffractometer (Mo KR radiation, graphite
monochromator, λ ) 0.71073 Å). Data were corrected for Lorentz,
polarization, and absorption effects (semiempirical, SADABS).26
The structures were solved by the heavy atom method combined
with structure expansion by direct methods applied to difference
structure factors27 and refined by full-matrix least-squares methods
based on F2.28 All non-hydrogen atoms were given anisotropic
displacement parameters. Hydrogen atoms were generally input at
calculated positions and refined with a riding model. When justified
by the quality of the data, the positions of some hydrogen atoms
were taken from difference Fourier syntheses and refined.
Gaussian 03. In particular, linear natural molecular orbitals (NLMO)
(“delocalization tails”) as well as natural population analysis (NPA)
(charge distribution) were determined and analyzed. As a semi-
quantitative measure of the bond order, the Wiberg bond index was
used. All the orbital visualizations have been obtained with
GaussView19 and MOLEKEL29 programs. The molecular structures
were optimized starting from X-ray diffraction data. Following
geometry optimization, frequency calculations were performed on
all calculated structures to ensure that there were no imaginary
frequencies and thus confirm their character as that of energy
minima.
Computational Methods. All the calculations have been carried
out with the Gaussian 03 program.17 DFT calculations with the
nonlocal hybrid B3PW91 functional and 6-31G(d) basis set for all
atoms were performed. This approach is widely used for compu-
tational studies of transition metal complexes, yielding consistent
results. The electronic structures were studied using natural bond
orbital (NBO) analysis, with the NBO 3.0 facilities built into
Acknowledgment. We thank the Deutsche Forschungs-
gemeinschaft for funding, the MEC (Spain) for a postdoctoral
fellowship (to J.L.F.), and the EU for the award of a Marie
Curie EIF fellowship to B.D.W. Continuous support by
BASF (Ludwigshafen) is gratefully acknowledged.
Supporting Information Available: Crystallographic informa-
tion in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
(26) Sheldrick, G. M. SADABS; Bruker AXS, 2004-2007.
(27) Beurskens, P. T. In Crystallographic Computing 3; Sheldrick, G. M.,
Kru¨ger, C., Goddard, R., Eds.; Clarendon Press: Oxford, UK, 1985; p 216.
Beurskens, P. T., Beurskens, de Gelder, G. R., Smits, J. M. M., Garcia-
Granda, S., Gould, R. O. DIRDIF-2007; Raboud University: Nijmegen, The
Netherlands, 2007(b) Sheldrick, G. M. SHELXS; University of Go¨ttingen,
1986.
OM8001203
(28) Sheldrick, G. M., SHELXL-97; University of Go¨ttingen, 1997; Acta
Crystallogr. 2008, A64, 112.
(29) Flu¨kiger, P.; Lu¨thi, H. P.; Portmann; Weber, S. J. MOLEKEL 4.0;
Swiss National Supercomputing Centre CSCS: Manno (Switzerland), 2000.