Oxygen atom transfer from Re(v)O to tertiary diphosphines: Spacer length and chemical differentiation of products

Article abstract of DOI:10.1039/b004565i

The reaction of mer-[ReL(O)Cl₃], [L = 2-(p-chlorophenyl-azo)-1-methylimidazole] with Ph₂P(CH₂)(n)PPh₂ (abbreviated PnP) affords [ReL(OP1P)Cl₃] 2a, [ReL(OP1PO)Cl₃] 4 and [ReL(OP2P)Cl₃

Full text of DOI:10.1039/b004565i

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Oxygen atom transfer from RevO to tertiary diphosphines: spacer length and
chemical differentiation of products
Sibaprasad Bhattacharyya, Indranil Chakraborty, Bimal Kumar Dirghangi and Animesh Chakravorty*
Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Calcutta 700 032, India.
E-mail: icac@mahendra.iacs.res.in
Received (in Cambridge, UK) 7th June 2000, Accepted 16th August 2000
The reaction of mer-[ReL(O)Cl3], [L = 2-(p-chlorophenyl-
azo)-1-methylimidazole] with Ph2P(CH2)nPPh2 (abbrevi-
ated PnP) affords [ReL(OP1P)Cl3] 2a, [ReL(OP1PO)Cl3] 4
and [ReL(OP2P)Cl3] 2b, [Cl3LRe(OP2PO)ReLCl3] 5, all
having mer geometry; unlike 2b which is stable in solution,
2a spontaneously isomerizes to fac-[ReL(P1PO)Cl3] via an
associative pathway; the origin of the observed differ-
entiation (2a vs. 2b and 4 vs. 5) is scrutinized in terms of
structures and reaction models.
Tertiary phosphines are model oxygen atom acceptors from oxo
moieties such as ReVO.1,2 Chelation by the p-acidic azoimida-
zole L as in 1, facilitates the transfer process.3 This work
Fig. 2 Perspective view of fac-[ReIIIL(P1PO)Cl3] 3. Selected bond
distances (Å) and angles (°): Re–N(1) 2.050(8), Re–N(4) 2.055(8), Re–
Cl(2) 2.351(3), Re–Cl(1) 2.372(3), Re–Cl(3) 2.401(3), Re–P(1) 2.476(3);
N(1)–Re–Cl(2) 176.7(2), N(4)–Re–Cl(1) 162.9(2), Cl(3)–Re–P(1)
174.9(1).
concerns the species 2–5 formed from 1 and Ph2P(CH2)nPPh2
(abbreviated PnP, n = 1, 2)4 directly or via subsequent
transformations. The differentiation referred to in the title
relates to the pairs 2a, 2b and 4, 5 in which the length of the
spacer –(CH2)n– varies.
With PnP in excess, stereoretentive one-atom transfer [eqn.
(1)] afforded† 2a and 2b (Fig. 1).‡ Both are stable in the solid
state and 2b is also stable in solution. In contrast, 2a undergoes
spontaneous linkage-cum-geometrical isomerization [eqn. (2)]
in solution furnishing† 3 (Fig. 2).‡
The reaction follows§ the rate law of eqn. (3). Variable
temperature rate constants (103 k/min21: 308 K, 5.30; 313 K,
7.78; 318 K, 10.06; 323 K, 12.75) correspond to the activation
parameters DH,‡ 12.3 kcal mol21 and DS,‡ 238.2 cal K21
mol21. The reaction is thus intramolecular and strongly
associative in nature.
k
2a ææÆ3 : rate = k[2a]
(3)
Oxygen atom transfer to the pendent phosphine function of 2
occurs† upon reacting it with an excess of 1 [eqn. (4) and (5)].
While 2a furnishes 4 (Fig. 3),‡ 2b yields insoluble 5 in which
both the phosphine oxide functions are coordinated, the metal
atoms presumably having mer geometry.5
R·O + PnP ? Re–OPnP
Re–OP1P ? Re–P1PO
(1)
(2)
Fig. 1 Perspective view of mer-[ReIIIL(OP2P)Cl3] 2b. Selected bond
distances (Å) and angles (°): Re–N(1) 2.000(6), Re–N(4) 2.002(7), Re–O(1)
2.048(5), Re–Cl(3) 2.355(2), Re–Cl(2) 2.372(2), Re–Cl(1) 2.375(2); N(1)–
Re–O(1) 173.9(2), Cl(3)–Re–Cl(2) 174.67(8), N(4)–Re–Cl(1) 166.9(2),
P(1)–O(1)–Re 164.0(4).
Fig. 3 Perspective view of mer-[ReIIIL(OP1PO)Cl3] 4. Selected bond
distances (Å) and angles (°): Re–N(4) 1.985(10), Re–N(1) 1.993(11), Re–
O(1) 2.033(7), Re–Cl(3) 2.356(4), Re–Cl(2) 2.370(4), Re–Cl(1) 2.377(4),
P(1)–O(1) 1.523(8), P(2)–O(2) 1.459(8); N(1)–Re–O(1) 172.7(4), Cl(3)–
Re–Cl(2) 174.4(1), N(4)–Re–Cl(1) 168.0(3), P(1)–O(1)–Re 147.5(5).
DOI: 10.1039/b004565i
Chem. Commun., 2000, 1813–1814
This journal is © The Royal Society of Chemistry 2000
1813

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Re–OP1P + Re·O ? Re–OP1PO
(4)
(5)
Notes and references
† 2a was prepared from P1P (0.6 mmol) and 1 (0.2 mmol) in CH2Cl2
solution followed by rapid solvent removal, washing with hexane and
drying; 2b was similarly prepared; 3 was made by leaving 2a in C6H6 for 8
h and 4 was prepared from 2a (0.1 mmol) and 1 (0.2 mmol) in C6H6; for
each, purification was carried out by chromatography on a silica gel column
using C6H6–MeCN mixtures as eluents. Reaction of 2b (0.1 mmol) and 1
(0.1 mmol) in C6H6 afforded insoluble 5. The yields in all cases were in the
range 75–85% and satisfactory elemental analyses were obtained for all.
Selected spectral data: UV–VIS (C6H6): lmax/nm (e/dm3 mol21 cm21): 2a,
660(610), 454(5680), 355(7570); 2b, 658(450), 460(3550), 348(4970); 3,
660(840), 468(5530), 362(9510); 4, 655(510), 450(5230), 358(6910). IR
(KBr, cm21): 2a, 300, 310 (Re–Cl), 1120 (O–P), 1330 (NNN); 2b, 310, 320
(Re–Cl), 1120 (O–P), 1330 (NNN); 3, 310, 320 (Re–Cl), 1190 (P–O), 1325
(NNN); 4, 310, 320 (Re–Cl), 1120 (O–P), 1200 (P–O), 1335 (NNN); 5, 300,
320 (Re–Cl), 1120 (O–P), 1335 (NNN).
Re–OP2P + Re·O ? Re–OP2PO–Re
The remarkable double isomerization of 2a can be ration-
alized. 2a did not afford single crystals but the structure of 4
provides a credible geometrical model in which the pendent
P(1)C(23)P(2) fragment is positioned near the Cl(1)Cl(2)O(1)
face. A simple rotation around the P(1)–C(23) bond brings the
P(2) atom to within 2.6 Å of the face as in 6 which is a plausible
‡ Crystal data for 2b·1.5C6H6: C45H42Cl4N4OP2Re, M
= 1044.77,
¯
triclinic, space group P1, a = 11.957(4), b = 12.383(3), c = 17.046(6) Å,
a = 88.36(2), b = 74.21(2), g = 84.10(2)°, U = 2415.8(12) Å3, Z = 2, T
= 293 K, m(Mo-Ka) = 2.84 mm21, 7237 reflections measured, 7109
unique, 5904 observed [I
> 2s(I)], R1 = 0.0467, wR2 = 0.1273;
¯
3·1.5C6H6: C44H40Cl4N4OP2Re, M = 1030.74, triclinic, space group P1, a
= 10.110(6), b = 10.668(5), c = 20.760(7) Å, a = 89.47(3), b = 80.08(4),
g = 81.41(4)°, U = 2181(2) Å3, Z = 2, T = 293 K, m(Mo-Ka) = 3.143
mm21, 6515 reflections measured, 6424 unique, 5198 observed [I > 2s(I)],
R1 = 0.0542, wR2 = 0.1279; 4: C35H31Cl4N4O2P2Re, M = 929.58,
model for the associative transition state of the reaction. The
attack by P(2) can progress via edge displacement6 of a chloride
ligand with concomitant Re–OP(1) bond cleavage leading to 3,
[eqn. (6)]. The fac geometry of 3 is sustained by concerted
monoclinic, space group C2/c, a
= 35.353(11), b = 12.730(6), c =
16.840(7) Å, b = 104.68(3)°, U = 7332(5) Å3, Z = 8, T = 293 K, m(Mo-
Ka) = 3.73 mm21, 5705 reflections measured, 5422 unique, 3386 observed
[I > 2s(I)], R1 = 0.0585, wR2 = 0.1060. CCDC 182/1746. See http://
www.rsc.org/suppdata/cc/b0/b004565i/ for crystallographic files in .cif
format.
§ UV–VIS spectra of thermostatted isomerizing benzene solutions of 2a
displayed well defined isosbestic points at 482, 422 and 307 nm. The rate
was followed at 360 nm. The first order rate constants were obtained from
the slope of linear plot of 2ln(A∞ 2 At) vs. time t where At is the absorbance
at time t and A∞ is the absorbance at the completion of reaction (after 24
h).
(6)
1 S. Banerjee, S. Bhattacharyya, B. K. Dirghangi, M. Menon and A.
Chakravorty, Inorg. Chem., 2000, 39, 6; B. K. Dirghangi, M. Menon, A.
Pramanik and A. Chakravorty, Inorg. Chem., 1997, 36, 1095; S. B.
Seymore and S. N. Brown, Inorg. Chem., 2000, 39, 325; R. R. Conry and
J. M. Mayer, Inorg. Chem., 1990, 29, 4862; R. Rossi, A. Duatti, L.
Magon, V. Casellato, R. Graziani and L. Toniolo, J. Chem. Soc., Dalton
Trans., 1982, 1949; J. F. Rowbottom and G. Wilkinson, J. Chem. Soc.,
Dalton Trans., 1972, 826.
2 J. R. Dilworth, D. V. Griffiths, S. J. Parrott and Y. Zheng, J. Chem. Soc.,
Dalton Trans., 1997, 2931; X. L. R. Fontaine, E. H. Fowles, T. P. Layzell,
B. L. Shaw and M. Thornton-Pett, J. Chem. Soc., Dalton Trans., 1991,
1519; X.-L. Luo and R. H. Crabtree, J. Am. Chem. Soc., 1990, 112,
4813.
Re–L and Re–P back-bonding as in fac-[ReL(PPh3)Cl3].3 In 2b
the PCH2CH2P fragment has the anti conformation 7. The
potentially reactive gauche conformation is not accessible due
to the bulk of PPh2, and accordingly 2b fails to isomerize.
The conformation 7 is, however, ideally suited for sustaining
binucleation as in 5.5 On the other hand only the dangling
phosphine oxide function is preserved in 4 as a vestige of
transient binucleation. The environment of the O(2) atom in 4 is
crowded [O(2)…P(1) 3.57 Å, O(2)…C(11) 3.55 Å] and model
building has confirmed that the n = 1 analog of 5 is not
sterically viable.
In summary, there is a strong chemical differentiation
between the n = 1 and 2 products formed in both one-atom (2a,
2b) and two-atom (4, 5) transfer from 1 to PnP. The
applicability of the observed structural and dynamical features
to other systems is under scrutiny.
We thank the Indian National Science Academy, the
Department of Science and Technology and the Council of
Scientific and Industrial Research for financial support. Affilia-
tion with the Jawaharlal Nehru Centre for Advanced Scientific
Research, Bangalore, India, is acknowledged.
3 I. Chakraborty, S. Bhattacharyya, S. Banerjee, B. K. Dirghangi and A.
Chakravorty, J. Chem. Soc., Dalton Trans., 1999, 3744.
4 The n = 1–3 cases have been examined but only n = 1, 2 are reported
here as n = 2, 3 constitute a similar pair.
5 The similarly prepared binuclear complex [Cl3LARe(OP2PO)ReLACl3],
where LA is the Schiff base of pyridine-2-carbaldehyde and p-toluidine
has been structurally characterized. It is centrosymmetric with the
PCH2CH2P fragment having anti and the metals having mer geometry. S.
Bhattacharyya, I. Chakraborty, B. K. Dirghangi and A. Chakravorty,
unpublished work.
6 N. Serpone and D. G. Bickley, Prog. Inorg. Chem., 1972, 17, 391.
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Chem. Commun., 2000, 1813–1814