A new and versatile diamide-diamine donor ligand set in early transition metal chemistry

Article abstract of DOI:10.1039/b002455o

Straightforward, multigram synthesis of the new diamidediamine proligand H₂N₂NN' [N₂NN' = (2-NC₅H₄)-CH₂N(CH₂CH₂NSiMe₃)₂] is described along with a preliminary survey of the five- and six-coordinate, neutral and cationic, single- and multiply-bonded complexes of groups 3, 4 and 5 that it can support; the related bis(alkoxide)-diamine proligand H₂O₂NN' is also described where H₂O₂NN' = (2-NC₅H₄)CH₂N(CH₂CMe₂OH)₂.

Full text of DOI:10.1039/b002455o

A new and versatile diamide–diamine donor ligand set in early transition metal
chemistry†
Michael E. G. Skinner, David A. Cowhig and Philip Mountford*
Inorganic Chemistry Laboratory, South Parks Road, Oxford, UK OX1 3QR.
E-mail: philip.mountford@chemistry.oxford.ac.uk
Received (in Cambridge, UK) 28th March 2000, Accepted 22nd May 2000
Straightforward, multigram synthesis of the new diamide–
diamine proligand H2N2NNA [N2NNA
=
(2-NC5H4)-
CH2N(CH2CH2NSiMe3)2] is described along with a prelimi-
nary survey of the five- and six-coordinate, neutral and
cationic, single- and multiply-bonded complexes of groups 3,
4 and 5 that it can support; the related bis(alkoxide)–
diamine proligand H2O2NNA is also described where
H2O2NNA = (2-NC5H4)CH2N(CH2CMe2OH)2.
The bis(cyclopentadienyl) ligand set has been the dianionic
environment par excellence for organotransition metal chem-
istry for ca. four decades.1 Driven by the search for new
fundamental and catalytic chemistry, the last ten years in
particular have established the importance of polydentate di-
and tri-anionic N-donor ligands as environments for early- to
mid-transition metal coordination and organometallic com-
plexes.2
Scheme 1 Reagents and yields: i, N-tosylaziridine (74% for this step) then
conc. H2SO4 83% (61% overall); ii, 2 Me3SiCl, 4 Et3N, 75%; iii, 2.2 BunLi,
57%; iv, 3-isobutylene oxide, 25%.
rated into a wide range of transition, lanthanide and main group
metal derivatives. Thus reaction of Li2N2NNA 2-Li2 with
[Ti(NAr)Cl2(py)3]6a (Ar
=
C6H3Pri2-2,6) or [Ta(NBut)-
Among the tetradentate ‘N4’ donor ligands, the porphyrins2b
and tetraaza[14]annulenes2c are probably the best established
dianionic ligands. They provide a really quite rigid, square-base
donor environment. In contrast, the trianionic triamidoamine
‘tren’ systems generally provide four vertices of a trigonal
bipyramid or octahedron. Such ligands have been extremely
successful in developing p-block, early-mid transition metal,
lanthanide and actinide chemistry.2d,3 Despite these successes,
however, as a trianionic species the versatility of this ligand is
hampered in certain regards for developing new lanthanide, and
groups 3 and 4 chemistry in particular since there is only one
(group 4) or no (lanthanide, group 3) metal electrons remaining
for binding additional anionic ligands. Dianionic ‘N4’ ana-
logues of the tren systems will help advance early transition
metal and lanthanide chemistry, and compliment the extensive
studies of tridentate diamido-donor systems.2a Indeed, it was
recently reported that addition of an extra donor arm to
bis(alkoxide)-donor systems can lead to enhanced ethylene
polymerisation capability.4
Cl3(py)2]6b gives the five- and six-coordinate imides, [Ti-
(NAr)(N2NNA)] 4 and [Ta(NBut)Cl(N2NNA)] 5, respectively.
Transition metal imides continue to attract considerable inter-
est,7 and those of group 4 with p-donor coligands can have a
particularly rich reaction chemistry.2a,7,8 Reaction of 2-Li2 with
YCl3 in pyridine affords the ‘ate’ complex 6, formulated as
‘[YCl(N2NNA)(py)]·1.5LiCl’ on the basis of elemental analyses
and 7Li NMR spectroscopy. Nonetheless, preliminary reactivity
studies of 6 show that it behaves as though it were simply
[YCl(N2NNA)(py)], and that it is a useful synthon with the Y-
bound Cl ligand being readily substituted by bulky monoanionic
donors.
The straightforward syntheses of the new proligands
H2N2NNA 2-H2 and H2O2NNA 3-H2 are shown in Scheme 1.‡
The intermediate tetra-amine 1 has been previously described,5
but we have found that the alternative synthesis shown from
2-aminomethylpyridine is more convenient on a large scale.
The proligand 2-H2 is conveniently converted (BunLi) to its
lithiated derivative Li2N2NNA 2-Li2. The new proligands can all
be prepared in multigram quantities: e.g. 5.4 g of 1 yields 7.1 g
(75%) of 2-H2 and lithiation of this gives 4.2 g (57%) of
Li2N2NNA 2-Li2.
The ready availability of H2N2NNA 2-H2 and Li2N2NNA 2-Li2
has allowed us to develop a representative range of new five-
and six-coordinate, neutral and cationic, single- and multiply-
bonded complexes of groups 3, 4 and 5 (Scheme 2). They are
formed by salt- (for 4–6), and alkane- or amine- (for 7 and 8)
elimination reactions; the applicability of a range of such
protocols will clearly permit these new ligands to be incorpo-
Scheme 2 Reagents and yields: i, (with 2-Li2) [Ta(NBut)Cl3(py)2], 36 h,
29%; ii, (with 2-Li2) [Ti(NC6H3Pri2-2,6)Cl2(py)3], 58%; iii, (with 2-Li2)
YCl3, 71%; iv, (with 2-H2) for 7: [ZrCl2(CH2SiMe3)2·2Et2O], 87%; for 8:
[Zr(NMe2)4], 55%; v, PhCH2MgCl, 87%; vi, LiMe (2 equiv.), 88%; vii,
B(C6F5)3, 61% [counter ion = B(CH2Ph)(C6F5)32]; viii, B(C6F5)3, 60%
[counter ion = BMe(C6F5)32].
† Electronic supplementary information (ESI) available: experimental
details and characterisation. See http://www.rsc.org/suppdata/cc/b0/
b002455o/
DOI: 10.1039/b002455o
Chem. Commun., 2000, 1167–1168
This journal is © The Royal Society of Chemistry 2000
1167

Ziegler–Natta olefin polymerisation catalysts.10 Treatment of
12 with B(C6F5)3 or [CPh3][B(C6F5)4], however, affords the
TMS-metallated cation 13 with counter anion [MeB(C6F5)3]2
or [B(C6F5)4]2; there is no evidence for interaction between 13
and the [MeB(C6F5)3]2 anion in solution. The [MeB(C6F5)3]2
salt of 13 is thermally stable at r.t. in both the solid state and
CD2Cl2 solution, and has been fully characterised by NMR and
elemental analysis. Cation 13 presumably forms via an
intermediate cation [ZrMe(N2NNA)]+ (not observed) followed
by s-bond metathesis with one of the SiMe3 C–H bonds. Similar
reactions have been seen in group 4 triamidoamine chemistry,11
but can, in principle, be circumvented by use of alternative
amide N-substituents: such protocols are well established.2a,12
Indirect evidence for a five-coordinate cationic intermediate
comes from the formation of the cation [ZrCl(N2NNA)]+ 14 from
the monobenzyl complex [Zr(CH2Ph)Cl(N2NNA)] 11 and
B(C6F5)3. Salts of the cation 13 react sluggishly with ethylene
(1 atm), but work is in progress to develop analogues of
H2N2NNA with other, more robust amide N-substituents.
In summary, we have described the new diamido–diamine
ligand H2N2NNA and a survey of its versatile complexation
chemistry.
Fig. 1 Displacement ellipsoid plot of [Ti(N2NNA)(NC6H3Pri2-2,6)] 4.
This work was supported by the EPSRC and Royal Society.
We thank Dr G. A. Vaughan (Exxon Chemical Co.) for a gift of
[Zr(NMe2)4] and Dr D. J. Watkin for help with the X-ray data
collection.
Notes and references
‡ Full spectroscopic data and elemental analyses have been obtained as far
as possible for all the new compounds.
§ Crystal data for 4: C28H49N5Si2Ti, M = 559.80, orthorhombic, space
group Pbcm, a = 9.8632(4), b = 18.413(1), c = 17.507(1) Å, U =
3179.4(8) A3, Z = 4, T = 170 K, m = 0.36 mm21, 3688 independent
reflections (Rmerge = 0.035), 3240 with I > 3s(I) used in refinement, final
Fig. 2 Displacement ellipsoid plot of [Zr(N2NNA)Cl2] 7.
The group 4 compounds [Zr(X)2(N2NNA)] (X = Cl 7 or
NMe2 8) are readily obtained from 2-H2 and [Zr(CH2Si-
Me3)2Cl2·2Et2O]9 or [Zr(NMe2)4], respectively. Such cis-X2
complexes are of great importance in the study of new
stoichiometric and catalytic group 4 reaction chemistry.10 The
bis(alkoxide) analogues of 7 and 8, namely [Zr(X)2(O2NNA)] [X
= Cl 9 or NMe2 10, eqn. (1)] can be similarly prepared from
R
indices:
R
=
0.0574, Rw
=
0.0434. For 7·0.5C6H6:
C16H32Cl2N4Si2Zr·0.5C6H6, M = 537.81, monoclinic, space group P21/n, a
= 8.4280(1), b = 14.3380(4), c = 21.5020(6) Å, b = 93.295(2)°, U =
2594.0 Å3, T = 150 K, m = 0.73 mm21, 5550 independent reflections
(Rmerge = 0.030), 4506 with I > 3s(I) used in refinement, final R indices:
R = 0.0278, Rw = 0.0269. CCDC 182/1648. See http://www.rsc.org/
suppdata/cc/b0/b002455o/ for crystallographic files in .cif format.
1 Metallocenes: synthesis, reactivity, applications, ed. A. Togni and R. L.
Halterman, Wiley-VCH, New York, 1998, vol. 1 & 2.
2 Recent reviews: (a) diamide-donors in general; L. H. Gade, Chem.
Commun., 2000, 173 (Feature Article); (b) porphyrins: H. Brand and J.
Arnold, Coord. Chem. Rev., 1995, 140, 137; (c) tetraaza[14]annulenes:
P. Mountford, Chem. Soc. Rev., 1998, 27, 105; (d) triamidoamines: R. R.
Schrock, Acc. Chem. Res., 1997, 30, 9; J. G. Verkade, Acc. Chem. Res.,
1993, 26, 483.
3 P. Roussel, N. W. Alcock and P. Scott, Chem. Commun., 1998, 801; P.
Roussel, N. W. Alcock, R. Boaretto, A. Kingsley, I. J. Munslow, C. P.
Sanders and P. Scott, Inorg. Chem., 1999, 38, 3651 and references
therein.
(1)
H2O2NNA 3-H2. The compounds 9 and 10 will provide
interesting comparisons with their more sterically-shielded
7 and 8, and with very recent
bis(phenoxide)–diamine ligands that are active ethylene poly-
tetraaza homologues
merisation catalysts.4
We have structurally confirmed that the N2NNA ligand can
readily accommodate both five- and six-coordinate metal
centres. Views of the X-ray structures of [Ti(NAr)(N2NNA] 4
and [ZrCl2(N2NNA)] 7 are shown in Fig. 1 and 2, respectively.§
The structure of 4 reveals an approximately trigonal bipyr-
amidal geometry at the five-coordinate Ti centre. The structure
of 7 reveals an approximately octahedral Zr centre; the chloride
ligands are mutually cis. In both 4 and 7, and indeed in all the
derivatives to date of the N2NNA ligand, including the crowded
bis(dimethylamide) complex 8, the pyridyl donor is firmly
bound to the metal centre and establishes a well defined
coordination environment.
4 E. Y. Tshuva, I. Goldberg, M. Kol, H. Weitman and Z. Goldschmidt,
Chem. Commun., 2000, 379.
5 H. Adams, N. A. Bailey, W. D. Carlisle, D. E. Fenton and G. Rossi,
J. Chem. Soc., Dalton Trans., 1990, 1271.
6 (a) A. J. Blake, P. E. Collier, S. C. Dunn, W.-S. Li, P. Mountford and
O. V. Shishkin, J. Chem. Soc., Dalton Trans., 1997, 1549; (b) J.
Sundermeyer, J. Putterlik, M. Foth, J. S. Field and N. Ramesar, Chem.
Ber., 1994, 127, 1201.
7 D. E. Wigley, Prog. Inorg. Chem., 1994, 42, 239; P. Mountford, Chem.
Commun., 1997, 2127 (Feature Article).
8 J. L. Bennett and P. T. Wolczanski, J. Am. Chem. Soc., 1997, 119,
10 696 and references therein.
9 H. Brand, J. A. Capriotti and J. Arnold, Organometallics, 1994, 13,
4469.
10 G. J. P. Britovsek, V. C. Gibson and D. F. Wass, Angew. Chem., Int. Ed.,
1999, 38, 429 and references therein.
11 C. Morton, N. W. Alcock and P. Scott, Organometallics, 1999, 18,
4608; C. C. Cummins, R. R. Schrock and W. M. Davis, Organo-
metallics, 1992, 11, 1452.
One or both chloride ligands in [ZrCl2(N2NNA)] 7 can be
substituted using organo-magnesium or -lithium reagents
forming
the
mono-
and
di-alkyl
derivatives
[Zr(CH2Ph)Cl(N2NNA)] 11 and [ZrMe2(N2NNA)] 12 in ca. 90%
yield. There is no evidence in any of the reaction chemistry
herein for metallation or other attack at the pyridyl donor group.
cis-Dialkyl compounds such as 12 are potential precursors to
12 G. E. Greco, A. I. Popa and R. R. Schrock, Organometallics, 1998, 17,
5591.
1168
Chem. Commun., 2000, 1167–1168