First η1Migated 2,4,6-tri-fcrf-butyl-l,3,5-triphosphabenzene complexes

Article abstract of DOI:10.1039/a903745d

The first examples of ij'-complexes of 2,4,6-tri-tert-butyI1,3,5-triphosphabenzene are described, namely trans[PtCl₂(PR₃)(P₃C₃Bu ₃)] (PR₃ = PMe₃, PEt₃, PMe₂

Full text of DOI:10.1039/a903745d

1
First h -ligated 2,4,6-tri-tert-butyl-1,3,5-triphosphabenzene complexes and the
remarkable trihydration reaction of trans-[PtCl2(PMe3)(P3C3But3)] to
cis-[PtCl(PMe3)(P3O3C3H5But3)], containing the novel
CH(But)PH(O)C(But)PH(O)CH(But)P(O) ring system
Scott B. Clendenning, Peter B. Hitchcock and John F. Nixon*
School of Chemistry, Physics and Environmental Science, University of Sussex, Brighton, Sussex, UK BN1 9QJ
Received (in Cambridge, UK) 10th May 1999, Accepted 9th June 1999
1
The first examples of h -complexes of 2,4,6-tri-tert-butyl-
1,3,5-triphosphabenzene are described, namely trans-
[PtCl2(PR3)(P3C3But3)] (PR3 = PMe3, PEt3, PMe2Ph or
PMePh2) and their structures established by 31P and 195Pt
NMR spectroscopy. The unusual molecular structure of cis-
[PtCl(PMe3)(P3O3C3H5But3)], containing the novel CH-
(But)PH(O)C(But)PH(O)CH(But)P(O) ring system, which is
formed by the trihydration of trans-[PtCl2(PMe3)(P3-
C3But3)] is also reported.
by direct reaction with a variety of other metal halides such as
MCl4, (M = Ti or Zr), MCl5 (M = Nb or Ta), CuX (X = Cl or
I) were all unsuccessful as were ligand displacement reactions
involving [MCl2(NCPh)2] (M = Pd or Pt) and [RhClLn] (L =
cyclooctene, n = 2; L = PPh3, n = 3).
The 31P{1H} NMR spectrum of trans-[PtCl2(PMe3)
(P3C3But3)] 2, which is typical for all the complexes 2–5, is
shown in Fig. 1, and exhibits the characteristic coupling
constant data expected for the trans-isomer. The 195Pt NMR
spectrum exhibits the expected doublet of doublets pattern.†
Solution NMR data for the platinum complexes 3–5 containing
the bulkier phosphines showed that, unlike complex 2, there
was always a significant concentration of the starting
[PtCl2(PR3)]2 complex present as well as unreacted 1 and
several attempts to obtain crystalline complexes invariably led
to further disproportionation. Not surprisingly it proved im-
possible to attach more than one [PtCl2(PR3)] fragment to 1.
There is considerable current interest in the synthesis and
ligating properties of compounds containing P–C multiple
bonds.1–4 Very recently5,6 synthetic routes have been developed
to 2,4,6-tri-tert-butyl-1,3,5-triphosphabenzene 1 and its struc-
ture and PE spectrum have just been reported.7
6
Although h -arene transition metal complexes occupy a key
position in the development of contemporary organometallic
chemistry, heteroarenes of the type EC5R5 (E = N, P, As, Sb or
1
Bi) can also form h -ligated metal complexes unless bulky
substituents such as tert-butyl groups in the 2,6-positions
1
disfavour such interactions.8 To date, no examples of h -bonded
2,4,6-tri-tert-butyl-1,3,5-triphosphabenzene complexes have
6
been reported and only a handful of h -complexes of 1 are
Fig. 1 31P{1H} NMR spectrum of 2.
5
known such as the triple decker Sc(i) complex [Sc2(h -
6
P3C2But2)2 (h -P3C3But3)] the structure of which has been
It is interesting to compare the magnitude of the 1J(PtP)
coupling constant to the triphosphabenzene ring in 2 (2418 Hz)
with that of the trans ligated PMe3 (2901 Hz) indicating the
smaller s-character of the P-lone pair in the triphosphabenzene.
In the analogous 2,4,6-tri-tert-butyl-1-phosphabenzene11 com-
plex trans-[PtCl2(PMe3)(PC5H2But3)], synthesised in a similar
6
established by X-ray crystallography9 and [MLn(h -P3C3But3)],
5
[MLn = Mo(CO)3, W(CO)3, Mn(h -C5H5) or Ru(cod)],10
whose stuctures have been proposed on the basis of NMR
spectroscopic studies.
1
We now describe the first examples of h -bonded 2,4,6-tri-
tert-butyl-1,3,5-triphosphabenzene platinum(ii) complexes of
the type trans-[PtCl2(PR3)(S3C3But3)] (PR3 = PMe3 2, PEt3 3,
PMe2Ph 4 or PMePh2 5) which are formed by treatment of 1
1
manner, J(PtP) is 2548 Hz, indicating that the presence of
additional phosphorus atoms in the aromatic ring reduces the
s-character of the P-lone pair electrons.
1
It has been previously shown that h -ligation of phospha-
arenes can enhance their reactivity and we observe a remarkable
reaction when 2 was recrystallised from CH2Cl2 in the air at
room temperature. Addition of three water molecules to the
coordinated triphosphabenzene ring occurs, together with HCl
elimination, to afford the unusual complex [PtCl(PM3)-
(P3O3C3H5But3)] 6. The molecular structure of 6, which was
established by a single crystal X-ray diffraction study‡ and is
shown in Fig. 2, clearly results from addition of H2O across
each of the unsaturated P–C bonds in 2 in which the H adds to
carbon and the OH to phosphorus in accord with the expected
with the appropriate [PtCl2(PR3)]2 complex in CH2Cl2 or
CHCl3 at room temperature. Attempts to make complexes of 1
Chem. Commun., 1999, 1377–1378
1377

2.39 Å between O(2) and O(2)B; (iii) each individual molecule
is bisected by a mirror plane through Pt and the ring C and P
atoms to which it is bonded; (iv) the ring P–C bond lengths
(ranging between 1.78 and 1.84 Å) are elongated compared with
those in 1 and are typical for P–C single bonds; (v) the two
P(2)NO double bond distances [1.528(12) Å] are similar to that
of the formally single P(1)–O bond [1.479(15) Å] for the
phosphorus attached to platinum. The structure suggests that the
acidic H responsible for the dimeric structure of 6 may be
capable of replacement by other cations, or substituted by
organic groups, leading to significant structural changes (Fig. 3)
and this is currently under study along with other aspects of the
ligating behaviour of 1.
We thank NSERC for a scholarship (for S. B. C.) and EPSRC
for their continuing support (to J. F. N.) for phospha-
organometallic chemistry.
Notes and references
†
31P {1H} NMR data: 2: dPA 203.0, dPB 264.8, dPX 218.3; 1J(PtPA) 2418,
1J(PtPX) 2886, 2J(PAPB) 36.3, 2J(PAPX) 543.3 Hz. 3: dPA 207.1, dPB, 264.5,
dPX 12.1; 1J(PtPA) 2378, 1J(PtPX) 2884, 2J(PAPB) 36.4, 2J(PAPX) 508.5 Hz:
4: dPA, 202.5, dPB, 265.4, dPX 211.4; 1J(PtPA) 2487, 1J(PtPX) 2920,
2J(PAPB) 36.6, 2J(PAPX) 543.6 Hz. 5: dPA 200.4, dPB 267.0, dPX 1.3;
1J(PtPA) 2569, 1J(PtPX) 2961, 2J(PAPB) 37.0, 2J(PAPX) 545.5 Hz. 6: dPP(O)H
31.4 [d, 1J(PH) 552 Hz], dPP(OH) 20.6 [br, 1J(PtP) 3155 Hz] dP(PMe ), 10.1
3
[br, 1J(PtP) 3181 Hz].
Fig. 2 Molecular structure of 6. Selected distances (Å) and angles (°): Pt–
P(1) 2.224(6), Pt–Cl 2.416(5), Pt–P(3) 2.273(6), Pt–C(2) 2.24(2), P(1)–O(1)
1.479(15), P(2)–O(2) 1.528(12), P(1)–C(1) 1.843(16), P(2)–C(2) 1.777(12),
P(2)–C(1) 1.818(15); P(1)–Pt–C(2) 82.6(6), P(1)–Pt–P(3) 96.6(2), C(2)–
Pt–P(3) 179.2(6), P(1)–Pt–Cl 178.84(19), C(2)–Pt–Cl 98.6(6), P(3)–Pt–
Cl(1) 82.3(2), C(1)–P(1)–C(1)A 97.3(9), C(2)–P(2)–C(1) 109.3(8), P(2)–
C(2)–P(2)A 114.6(12) P(2)–C(1)–P(1) 105.6(7)
195Pt NMR data (rel. K2PtCl6): 2: dPt 23705; 3: dPt 23738; 4: dPt
23710; MS data (EI): 6: m/z 660 (M+).
‡ Crystal data: 6, C18H41ClO3P4Pt·2.5CH2Cl2, M = 872.2, orthorhombic,
space group Cmca (no. 64), a = 14.508(9), b = 15.924(9), c = 29.018(12)
Å, U = 6704(6) Å3, Z = 8, Dc = 1.73 Mg m23, crystal dimensions 0.3 3
0.2 3 0.05 mm, F(000) = 3464, T = 173(2) K, Mo-Ka radiation (l =
0.71073 Å). Data were collected on an Enraf-Nonius CAD4 diffractometer
and of the total 2428 independent reflections measured, 1951 having I >
2s(I), were used in the calculations. The final indices [I > 2s(I)] were R1
= 0.075, wR2 = 0.196. The complex lies on a crystallographic mirror plane
and forms H-bonded dimers across a twofold rotation axis. All non-H atoms
were anisotropic. H atoms were included in riding mode with Uiso(H) equal
to 1.2eq(C) or 1.5eq(C) for methyl groups. The H-bonded H atom lies on a
crystallographic twofold axis and was refined.
CCDC 182/1284. See http://www.rsc.org/suppdata/cc/1999/1377/ for
crystallographic files in .cif format.
1 K. B. Dillon, F. Mathey and J. F. Nixon, Phosphorus: The Carbon Copy,
John Wiley, Chichester, 1998, p. 366 and references therein.
2 J. F. Nixon, Coord. Chem. Rev., 1995, 145, 201.
3 J. F. Nixon, Chem. Rev., 1988, 88, 1327.
4 Multiple bonds and low coordination in phosphorus chemistry, ed. M.
Regitz and O. J. Scherer, Georg Thieme Verlag, 1990, p. 496 and
references therein.
Fig. 3 Dimeric structure of 6.
polarity of the bond. The resulting intermediate presumably
then undergoes Arbusov-type rearrangement at two of the newly
formed –P(OH)CHBut–centres to produce –PH(O)CHBut–ring
fragments with the rearrangement at the third phosphorus centre
unable to proceed because of ligation of the P atom to Pt. The
accompanying loss of HCl and formation of a Pt–C bond leads
to the observed product 6. Mathey, Venanzi and their cowork-
ers,12–14 have previously noted selective addition of water and
methanol to 2-pyridylphosphinines 7 and 2,2A-biphosphinines 8
coordinated to electrophilic metal centres as a result of the
partial dearomatisation of the ligand.
5 P. Binger, S. Leininger, J. Stannek, B. Gabor, R. Mynott, J. Bruckmann
and C. Kruger, Angew. Chem., Int. Edn. Engl., 1995, 34, 2227.
6 F. Tabellion, A. Nachbauer, S. Leininger, C. Peters, M. Regitz and F.
Preuss, Angew. Chem., Int. Edn., 1998, 37, 1233.
7 R. Gleiter, H. Lange, P. Binger, J. Stannek, C. Kru¨ger, J. Bruckmann, U.
Zenneck and S. Kummer, Eur. J. Inorg. Chem., 1998, 1619.
8 A. J. Ashe and J. C. Colburn, J. Am. Chem. Soc., 1977, 99, 8099. A. J.
Ashe, W. Butler, J. C. Colburn and S. Abu-Orabi, J. Organomet. Chem.,
1985, 282, 233.
9 P. L. Arnold, F. G. N. Cloke, P. B. Hitchcock and J. F. Nixon, J. Am.
Chem. Soc., 1996, 118, 7630.
10 P. Binger, S. Stutzmann, J. Stannek, B. Gabor and R. Mynott, Eur. J.
Inorg. Chem., 1999, 83.
11 K. Dimroth and W. Mach, Angew. Chem., Int. Edn. Engl., 1968, 7,
460.
12 B. Schmid, L. M. Venanzi, A. Albinati and F. Mathey, Inorg. Chem.,
1991, 30, 4693.
13 D. Carmichael, P. Le Floch and F. Mathey, Phosphorus, Sulphur, 1993,
77, 255.
14 P. Le Floch, S. Mansuy, L. Ricard, F. Mathey, A. Jutand and C.
Amatore, Organometallics, 1996, 15, 3267.
Complex 6 shows the following interesting features, (i) the
structure consists of a H-bonded dimer; (ii) this H atom lies on
a crystallographic twofold axis and was refined to a distance of
Communication 9/03745D
1378
Chem. Commun., 1999, 1377–1378