One- and two-step [2 + 2] cycloaddition reactions of group 4 imides with the phosphaalkyne Bu(t)CP. Crystal and molecular structures of [Zr(η5-C5H5)2(PCBu(t)NC6H3Me2-2,6)] and [T

Article abstract of DOI:10.1039/a900648f

The structures of novel complexes resulting from one- and two-step [2 + 2] cycloaddition reactions of four group 4 imides with the phosphaalkyne Bu(t)CP are described.

Full text of DOI:10.1039/a900648f

One- and two-step [2 + 2] cycloaddition reactions of group 4 imides with the
phosphaalkyne ButCP. Crystal and molecular structures of
5
[Zr(h -C5H5)2(PCButNC6H3Me2-2,6)] and [TiCl2(P2C2But2NBut)(py)] (py) =
pyridine)
F. Geoffrey N. Cloke,*a Peter B. Hitchcock,a John F. Nixon,*a D. James Wilsona and Philip Mountfordb
a School of Chemistry, Physics and Environmental Science, University of Sussex, Brighton, Sussex, UK BN1 9QJ.
E-mail: J.Nixon@sussex.ac.uk
b Inorganic Chemistry Laboratory, South Parks Road, Oxford, UK OX1 3QR
Received (in Cambridge, UK) 25th January 1999, Accepted 4th March 1999
The structures of novel complexes resulting from one- and
two-step [2 + 2] cycloaddition reactions of four group 4
imides with the phosphaalkyne ButCP are described.
Regitz and coworkers1 have recently reported novel reactions of
the phosphaalkyne ButCP with vanadium(v) imido complexes
to afford either 3-aza-1,2,4,6-tetraphosphaquadricyclanes B or
1,3,5-triphosphabenzenes A, the products critically depending
on reaction conditions (Scheme 1). They proposed a mechanism
for the formation of A and B which involves an initial [2 + 2]
cycloaddition step of the vanadium imide with the phosphaalk-
yne, but no metal containing complexes have been charac-
terised.
In order to better understand this interesting type of reaction,
we now describe the first fully structurally characterised
complexes of Zr(iv) and Ti(iv) resulting from one- and two-step
Fig. 1 Molecular structure of [(C5H5)2Zr(PCButNC6H3Me2-2.6)] 5. Se-
lected distances (Å) and angles (°): Zr–N 2.101(4), P–N 1.729(4), P–C(1)
1.692(5), Zr–C(1) 2.188(5); Zr–N–P 91.0(2), C(1)–P–N 102.8(2), P–C(1)–
Zr 89.1(2), N(1)–Zr–C(1) 77.1(2)°. Displacement elipsoids are shown at
5
[2 + 2] cycloaddition reactions of ButCP with ‘[Zr(h -
C5H5)2(NC6H3Me2-2,6)]’ 12 and [TiCl2(NBut)(py)3] 23,4 re-
spectively. In addition we report the NMR spectroscopically
5
characterised [2 + 2] phosphaalkyne adducts of ‘[Zr(h -
50% probability level.
C5H5)2(NBut)]’
32,
and
[Ti{(SiMe3)N[CH2CH2N(Si-
Me3)2]}(NBut)(py)]5 4.
The investigation of this type of addition was subsequently
extended to the sterically encumbered titanium imide 4.
Treatment of 4 with an excess of ButCP at room temperature in
toluene, yielded an orange oil after work up. NMR spectro-
scopic data were found to be very similar to that of 5 indicative
Treatment of the transient imide complex 1 (prepared from
5
the thermolysis of [Zr(h -C5H5)2(NHC6H3Me2-2,6)2])2 with an
excess of ButCP in toluene at 100 °C for 48 h yielded the orange
5
crystalline complex [Zr(h -C5H5)2(PCButNC6H3Me2-2,6)] 5 in
45% yield.† A single crystal X-ray diffraction study on 5‡
of formation of the [2
+ 2] cycloadduct [Ti{N(Si-
established that its molecular structure (Fig. 1) contains the four
Me3)[CH2CH2N(SiMe3)]2}(PCButNBut)] 7¶ (Scheme 2).
Since the reactivity presumably results from release of steric
strain, complex 2 was reacted with an excess of ButCP in
toluene at 55 °C for 72 h to yield the dark-red crystalline
complex [TiCl2(P2C2But2NBut)(py)] 8 (61% yield).∑** The
corresponding pyridine free complex [TiCl2(P2C2But2NBut)]
8a can be obtained (25%) by subliming 8 in vacuo at 110 °C. A
single crystal X-ray diffraction study was carried out on 8‡ and
its molecular structure, (Fig. 2 ), reveals a TiC2P2N core in
which the Ti(iv) centre is in an unsymmetrical environment
resulting from being capped by a puckered 1,3-diphosphacyclo-
butadiene unit, whose P(1) atom is s-bonded to the nitrogen of
the imide function [interplanar angle between C(1)P(2)C(2) and
C(1)P(1)P(2), 23.3°]. One representation of the bonding to the
membered planar metallacycle (Sinternal angles
= 360 °C)
resulting from the [2 + 2] phosphaalkyne–imide cycloaddition,
in which the phosphorus is bonded to the nitrogen of the imide
function, consistent with the bond polarity of the unsaturated
reactive sites. This geometry is similar to that observed for the
addition of internal alkynes to 1.2 The Zr–N–C(6) bond angle in
5 (147.8°) is typical of double bond character of the metal–
nitrogen linkage. A similar adduct [Zr(C5H5)2(PCButNBut)] 6
5
can also be prepared from ‘[Zr(h -C5H5)2(NBut)]’ (generated in
5
situ by thermolysis of [Zr(h -C5H5)2(NHBut)2])2, as determined
by NMR spectroscopy.§
But
V=NBut Cl3
4 P CBut
P
P
3
Ti centre involves an h -interaction with the 2-phosphaallyl
Toluene
-78
25 o
fragment of the C2P2 ring which is augmented by interaction
But
But
C
P
A
SiMe3
But
SiMe3
N
N
But
N
P
[ 2 + 2]
Benzene, 48 h
N
V=NButCl3•dme
Toluene
P
N
+
Ti
C
N
P
Ti NBut
Py
P
C
Me3Si
Me3Si
4 P CBut
Me3Si
Me3Si
P
N
But
N
But
But
-78
25 o
C
t
Bu
B
7
4
Scheme 1
Scheme 2
Chem. Commun., 1999, 661–662
661

Notes and references
† 5: NMR (d6-benzene, 295 K), 1H d 7.16, 7.09 (m, 3H, C6H3), 5.69 [(s,
10H, C5H5)], 2.28 [s , 6H, C6H3(CH3)2], 1.52 [s, 9H, PCC(CH3)3] 31P{1H}
d 81.7. EI-MS m/z (%): 439 (20) [M]+, 339 (100) [M 2 PCCMe3]+.
Elemental analysis: Calc. for C23H28NPZr; C, 62.69; H, 6.40, N, 3.18.
Found: C, 62.41; H, 6.37, N, 3.12%.
‡ Crystal data: 5: C23H28NPZr, M = 440.6, monoclinic space group P21/c,
a = 11.622(3), b = 21.830(8), c = 8.389(4) Å, b = 107.01(3), U =
2035.3(13) Å3, Z = 4, Dc = 1.44 Mg m23, crystal dimensions 0.40 3 0.30
3 0.02 mm, T = 173(2) K, Mo-Ka, radiation l = 0.71073 Å. Data were
collected on an Enraf-Nonius CAD4 diffractometer and of the total 3811
reflections measured, 3563 unique (Rint = 0.042). Refinement on F2, wR2
= 0.138 (all data), R1 = 0.048 [for 2651 reflections with I > 2s(I)].
7: C19H32Cl2N2P2Ti, M = 469.2, monoclinic, space group P21/n, a =
12.728 (2), b = 12.170(1), c = 15.596(1) Å, b = 97.5(1)°, U = 2395.1(5)
Å3, Z = 4, Dc = 1.3 Mg m23, T = 173(2) K, Mo-Ka, radiation l =
0.71073 Å. Data were collected on an Enraf-Nonius CAD4 diffractometer
and of the total 7242 reflections measured, 6969 unique (Rint = 0.017).
Refinement on F2, wR2 = 0.095 (all data), R1 = 0.040 [for 5271 reflections
with I > 2s(I)]. CCDC 182/1184. See http:/www rsc.org/suppdata/cc/
1999/661/ for crystallographic files in .cif format.
Fig. 2 Molecular structure of [Ti{NButPCButPCBut}Cl2(py)]8. Selected
distances (Å) and angles (°): P(1)–N(2) 1.727(2), Ti–N(2) 1.880(2), P1–
C(1) 1.825(2), P(2)–C(1) 1.735(2), P(2)–C(2) 1.768(2), C(2)–P(1) 1.847(2),
Ti–N(1) 2.394(2), Ti–P(2) 2.784(2), Ti–C(2) 2.221(2), Ti–P(1) 2.442(1),
Ti–C(1) 2.439(2); Ti–N(2)–C(11) 148.31(14), Cl(2)–Ti–Cl(1) 109.57(2),
C(2)–P(1)–C(1) 80.86(8), C(1)–P(2)–C(2) 85.65(8). Displacement elip-
soids are shown at 50% probability level.
§ 6: NMR (d6-benzene, 295 K), 1H d 5.68 (s, 10H, C5H5), 1.31 [s , 9H,
NC(CH3)], 1.52 [s, 9H, PCC(CH3)3]. 31P{1H} d 64.1. EI-MS m/z (%): 391
(30) [M]+, 376 (20) [M 2 Me]+, 276 (55) [M 2 Me 2 PCCMe3]+.
¶ 7: NMR (d6-benzene, 295 K), 1H d 4.12, 3.8, 2.81 (3 3 m, 8H, CH2CH2),
1.5 [s, 9H, NC(CH3)], 1.48 [s, 9H, PC(CH3)], 0.2 (s, 9H, NSiMe3), 0.09 (s,
18H, NSiMe3). 13C{1H d 53.7, 51.6 (CH2CH2), 35.2 [d, NC(CH3), 3JPC 12.2
with the N, two Cl ions, P lone pair and the pyridine. As
expected the Ti–N(2) bond length [1.880(2) Å] in 8 is
considerably elongated when compared with the starting imide
complex 2 [1.705(3) Å] and the Ti–N(pyridine) bond length
[2.394(2) Å] is very long. The Ti–N–C(a) bond angle in 8
(148.3°) is typical for a metal–nitrogen double bond.
3
Hz], 34.4 [d, PCC(CH3)3, JPC 8 Hz] 2.5 [SiC(CH3)], 0.2 [SiC(CH3)].
31P{1H} d 209.4. EI-MS m/z (%): 536 (20) [M]+ , 436 (45) [M 2 (PCBut)]+.
The oily nature of this compound precluded satisfactory microanalysis.
∑ 8: NMR (d6-benzene, 295 K), 1H d 9.5, 6.78, 6.53 (m, 5H, NC5H5), 1.46
[s, 9H, NC(CH3)3], 1.32, 1.30 [s 3 2, 18H, PC(CH3)3]. 13C{1H} (d8-
toluene, 295 K): 198.3 (dd, PCP, 1JPC 61.95, 2JPC 29.9 Hz), 151.1, 123.2 (m,
Although no reaction intermediates have been spectroscop-
ically characterised, the formation of the TiC2P2N core in 8 is
presumed to proceed by sequential [2 + 2] cycloaddition of
ButCP with (i) the titanium–nitrogen double bond and (ii) the
resulting PNC double bond (Scheme 3).
2
NC5H5), 68.89 [d, NC(CH3)3, JPC 8.10 Hz], 41.33 [pseudo-t,
2
3
{PCC(CH3)3}2, JPC 6.50 Hz], 33.96 [pseudo-t, {PCC(CH3)3}2, JPC 4.97
Hz], 32.37 [d, NC(CH3)3, JPC 6.03 Hz]. 31P{1H} (d6-benzene, 295 K) d
3
296.5, 2139.5 (d 3 2, 2JPP 40.5 Hz). EI-MS m/z (%): 465 (85) [M]+, 389
(10) [M 2 py]+, 333 (12) [M 2 Py 2But)]+
.
** Similarly [Ti(h -C8H8)(NBut)] readily reacted with ButCP in toluene at
8
But
room temp. to afford, after recrystallisation from pentane, dark brown
Toluene 55 °C But
P
8
crystals of [Ti(h -C8H8)(P2C2But2NBut)] 9 in 71% yield. Although not
52 h
[2+2]
[Ti(NBut)Cl2(py)3]
P
N
P
But
But
N
shown here, the molecular structure of 9 has also recently been obtained and
reveals a common TiC2P2N core comfirming its structural significance for
this type of reaction.
ButCP
Ti
Lx'
[2+2]
2
But
Ti
+
Py
Cl
Cl
ButCP
8
1 F. Tabellion, A. Nachbauer, S. Leininger, C. Peters and M. Regitz,
Angew. Chem., Int. Ed., 1998, 37, 1233.
Scheme 3
2 P. A. Walsh, A. M. Baranger and R. G. Bergman, J. Am. Chem. Soc.,
1992, 114, 1708.
3 For a review of titanium imido chemistry, see: P. Mountford, Chem.
Commun., 1997, 2127 and references therein (Feature Article).
4 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.
5 P. Mountford and F. G. N. Cloke, unpublished work.
6 A. J. Blake, S. C. Dunn, J. C. Green, N. M. Jones, A G. Moody and P.
Mountford, Chem. Commun., 1998, 1235.
7 F. G. N. Cloke, P. B. Hitchcock, J. F. Nixon, L. Nyulaszi, M. Regitz and
D. J. Wilson, unpublished work.
Interestingly, the course of the reactions involving complexes
of type 2 is also affected by the nature of the imido N-
substituent. Thus treatment of [Ti(NR)Cl2(py)3] (R = Ph, p-
MeC6H4, p-NO2C6H4 or Pri) with ButCP gave the previously
unknown 1,2,4-azadiphospholes P2C2But2NR. The molecular
structure of P2C2But2NPh has been determined and this new
class of heteroaromatic ring systems will be the subject of a
separate publication.6 The range of products obtained with
different metal and N-substituents indicates the possibility for a
rich and diverse derivative chemistry.
Philip Mountford is the Royal Society of Chemistry Sir
Edward Frankland Fellow for 1998–9.
Communication 9/00648F
662
Chem. Commun., 1999, 661–662
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