Synthesis, structure and reductive dechlorination of the C-centred phosphorus(III) β-diketiminate PCl(Ph)L [L = C{C(Me)NC6H3Pri2-2,6} {C(Me)NHC6H3Pri2-2,6}]

Article abstract of DOI:10.1039/b301294h

Treatment of the β-diketimine HL with successively LiBuⁿ and PCl₂Ph gave the first C-centered monodentate β-diketiminate PCl(Ph)L 1; with C₈K 1 underwent reductive dechlorination yielding 2, a novel N-P^III-P

Full text of DOI:10.1039/b301294h

Synthesis, structure and reductive dechlorination of the C-centred
phosphorus(III) b-diketiminate PCl(Ph)L [L =
C{C(Me)NC6H3Pri2-2,6}{C(Me)NHC6H3Pri2-2,6}]
Peter B. Hitchcock, Michael F. Lappert* and Jacek E. Nycz
The Chemistry Laboratory, University of Sussex, Brighton, UK BN1 9QJ. E-mail: m.f.lappert@sussex.ac.uk
Received (in Cambridge, UK) 4th February 2003, Accepted 18th March 2003
First published as an Advance Article on the web 16th April 2003
Treatment of the b-diketimine HL with successively LiBun
and PCl2Ph gave the first C–centered monodentate b-
diketiminate PCl(Ph)L 1; with C8K 1 underwent reductive
dechlorination yielding 2, a novel N–PIII–PIII–CNC hetero-
cycle.
in Scheme 1) 2, as well as 3 and the meso- (4) and rac- (5)
diphosphines Ph(L)P–P(L)Ph [L
{N(C6H3Pri2-
2,6)C(Me)}2CH]. Colourless crystals of 1 ( > 60%) and 2 (ca.
10%) and the diketimine 3 (authentic14b X-ray structure) were
obtained by crystallisation from hexane; the yields have not
been optimised.
=
Each of 1 and 2 gave satisfactory microanalyses, multi-
nuclear NMR spectral solution and mass spectral data,† which
were consistent with the X-ray crystal structures,‡ illustrated in
Figs. 1 (1) and 2 (2); evidence for compounds 4 and 5 at present
rests solely on their NMR spectra: d[31P{1H}] 9.49 (4) and
223.44 (5) in C6D6 at 293 K. We suggest that reduction of 1
proceeds sequentially by dechlorination to afford the radical
·P(L)Ph, its coupling to yield 4/5 and elimination of LH, as
shown in 6.
The NCCCN bond lengths in crystalline 1 are closely similar
to those of 3,14b with the exception of the significantly longer
C2–C3 bond in 1. The parameters around the pyramidal
phosphorus atom are unexceptional.15
The role of b-diketiminates as supporting ligands for a wide
spectrum of metal complexes is rapidly growing.1 This may be
judged not only by the burgeoning literature (more than 50
papers in 2002), but also by the increasing range of their
applications as catalysts (a-olefin polymerisation,2 ring-open-
ing polymerisation of lactide3 or related monomers,4 and
5
copolymerisation of an epoxide and CO2 ), structural models
for a Type 1 Cu protein active site,6 and as spectator ligands for
unusual metal complexes, such as [Al(L)(NC6H3Pri2-2,6)]7 and
[{Fe(L)}2(µ-N2)]8 [L = {N(C6H3Pri2-2,6)C(Me)}2CH].
A variety of ligand-to-metal bonding modes has been
reported for metal b-diketiminates. The ligand may be terminal
or bridging, almost invariably (but see ref. 9) monoanionic,
often p-delocalised and for N,NA-chelated complexes the
metallacycle is planar or boat-shaped. b-Diketiminates are now
known of 42 elements, but there is only a single phosphorus
compound A.10 All examples to date, bar one B,11 have been of
N-, (N,NA)-, or (N,NA,C)-centred ligands (but see penultimate
paragraph).
The heterocyclic ring of crystalline 2 is non-planar (unlike
that of the almost planar cation of the phosphonium salt D12)
with the atom P 2 0.36(1) Å out-of-the almost planar
Scheme 1 Reagents and conditions: i, LiBun in C6H14, Et2O, 278 °C; ii,
PCl2Ph, 278 °C; iii C8K, Et2O, 20 °C (R = C6H3Pri2-2,6).
Our earlier work on b-diketiminates was on N,NA-bis-
(trimethylsilyl) ligands such as [{N(SiMe3)C(Ph)}2CH]2. We
chose not to use these in the present report on P(III) chemistry,
since from a 1-azaallyl precursor and a P(III) chloride there was
facile loss of SiClMe3, as in the formation of C from
Li{N(SiMe3)C(But)CHSiMe3} + PCl3.12
We now report the synthesis and structure of the crystalline
phosphorus(III) complex 1, which thus far is unique in being a
C-centred monodentate b-diketiminate (but see penultimate
paragraph). Furthermore, we find that its reductive dechlorina-
tion affords the crystalline, X-ray-authenticated novel13 hetero-
cycle 2.
Fig. 1 Molecular structure of crystalline 1. Selected bond lengths (Å) and
angles (°): P–Cl 2.129(2), P–C2 1.773(5), P–C30 1.828(6), C1–C2
1.398(7), C2–C3 1.488(7), C1–N1 1.329(7), C3–N2 1.302(6); C2–P–Cl
107.90(19), C2–P–C30 102.8(2), Cl–P–C30 100.2(2), C1–C2–C3 120.7(5),
C1–C2–P 114.6(4), C3–C2–P 124.3(4).
Thus, treatment of the b-diketimine 314 with successively
LiBun and phenyldichlorophosphine yielded (i, then ii, in
Scheme 1) 1, while the latter with potassium graphite gave (iii
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24.48 (s, CHCH3), 28.58 (s, CHCH3), 28.99 (s, CHCH3), 99.01 [d, 1J(13C–
31P) 41.5, CP], 123.86, 123.89, 126.43, 127.73, 127.79, 127.84, 128.84,
128.95, 129.05, 129.30, 139.73, 141.88 (aromatic), 143.78 [d, 1J(13C–31P)
33.2, ipso-C], 172.01 [d, 2J(13C–31P) 28.2 Hz, CCH3]; 31P{1H} NMR
(C6D6): d 94.12; MS (mz (%, assignment)): 561 (4, [1]+).
2 1H NMR (293 K, C6D6): d 0.39–1.15 (5d, 15 H, CHCH3), 1.21–1.25 (m,
4
9 H, CHCH3), 2.10 [d, J(1H–31P) 1.7, 3 H, CCH3], 2.33 (s, 3 H, CCH3),
3.09 (sept, 2 H, CHCH3), 3.24 (sept, 2 H, CHCH3), 7.06–7.22 (m, 12 H,
aromatic), 7.72–7.77 (m, 2 H, aromatic), 7.84–7.87 (m, 2 H, aromatic);
13C{1H} NMR (C6D6): d 19.24 [d, J(13C–31P) 2.2, CHCH3], 22.60 [d,
J(13C–31P) 7.7, CHCH3], 23.01 [d, 3J(13C–31P) 10.8, CCH3], 23.63 [d,
J(13C–31P) 3.4, CHCH3], 23.97 [d, 3J(13C–31P) 5.7, CCH3], 28.23 [d,
J(13C–31P) 3.6, CHCH3], 23.41, 23.53, 24.25, 28.75, 28.89 (5s),
108.89–147.83 (aromatic), 162.32 [s, C(CH3)N], 166.44 [d, 2J(13C–31P)
20.1 Hz, C(CH3)N]; 31P{1H} NMR (C6D6): d 58.89 [d, 1J(31P–31P) 229.5],
211.88 [d, 1J(31P–31P) 229.5 Hz]; MS (mz (%, assignment)): 633 (24,
[2]+).
‡
Crystal data: 1: C35H46ClN2P, M = 561.16, orthorhombic, space group
Pna21 (No.33), a = 14.5108(8), b = 25.9696(13), c = 8.4582(4) Å, U =
3187.4(3) Å3, Z = 4, µ(Mo–Ka) 0.20 mm21. Final residual was R1 = 0.056
for the 2746 reflections with I > 2s(I) and wR2 = 0.136 for all the 3317
reflections collected. CCDC 203507.
Fig. 2 Molecular structure of crystalline 2. Selected bond lengths (Å) and
angles (°): P1–P2 2.2036(8), P1–N1 1.756(2), P2–C2 1.828(2), N1–C1
1.384(2), C1–C2 1.366(3), C2–C3 1.463(3), C3–N2 1.290(3), C18–N1
1.449(3); N1–P1–P2 93.43(6), P1–P2–C2 90.66(7), P1–N1–C1 117.97(13),
N1–C1–C2 118.42(18), C1–C2–P2 117.09(15), P2–P1–C6 99.76(4), N1–
P1–C6 102.27(9), P1–P2–C2 90.66(7), P1–P2–C12 96.92(7), C2–P2–C12
102.02(9).
2 C41H50N2P2·C6H6, M
= 710.88, monoclinic, space group P21/n
(No.14), a = 14.5205(3), b = 19.8810(5), c = 15.4891(4) Å, b =
110.874(1)°, U = 4178.0(2) Å3, Z = 4, m(Mo–Ka) = 0.14 mm21. Final
residual was R1 = 0.048 for 5536 reflections with I > 2s(I) and wR2
=
0.109 for all the 6913 reflections collected. CCDC 203508. See http://
www.rsc.org/suppdata/cc/b3/b301294h/ for crystallographic files in .cif or
other electronic format.
1 L. Bourget-Merle, M. F. Lappert and J. R. Severn, Chem. Rev., 2002,
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2 E.g. [Zr{N(SiMe3)C(Ph)C(H)C(But)NiMe3}Cl3]: M. F. Lappert and D.-
S. Liu, Netherlands Pat., 1994, 9401515; Idem, J. Organomet.
Chem.1995, 500, , 203.
3 V. C. Gibson, E. L. Marshall, D. Navarro-Llobet, A. J. P. White and D.
J. Williams, J. Chem. Soc., Dalton Trans., 2002, 4321 and references
therein.
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Chem. Soc., 2002, 124, 15239 and references therein.
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1999, 580, 386.
P1N1C1C2 array. The geometrical parameters are appropriate
for the illustrated structure 2; for example, the P–P bond length
is in the normal range for a diphosphine.16
Compound 1 may well be the first of a family of C-centred b-
diketiminates. The fact that mononuclear P(III) compounds are
rarely four-coordinate (but see A10) is a pointer to new
experiments; those related to i and ii of Scheme 1 involving in
place of PClPh2 a non-metal chloride such as pivaloyl and
trimethylsilyl are in hand.
13 No N–PIII–PIII–CNC heterocycle is listed in the Beilstein database.
14 (a) J. Feldman, S. J. McLain, A. Parthasarathy, W. J. Marshall, J. C.
Calabrese and S. D. Arthur, Organometallics, 1997, 16, 1514; (b) M.
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references therein.
We thank the Royal Society for the award of an R.S./NATO
fellowship to J.E.N.
Note added to proof: In the proof stage, we became aware of
a paper (also received on 4th February 2003) reporting an
analogue of 2 in which the Cl atom of 2 was replaced by
Ph.17
Notes and references
1
†
Selected spectroscopic data: 1 H NMR (293 K, C6D6): d 1.04–1.22
(4d, 24 H, CHCH3), 2.12 (s, 6 H, CCH3), 3.07 (sept, 2 H, CHCH3), 3.18
(sept, 2 H, CHCH3), 6.99–7.15 (m, 9 H, aromatic), 7.75–7.80 (m, 2 H,
aromatic), 15.53 (s, 1 H, NH); 13C{1H} NMR (C6D6): d 20.99 (s, CCH3),
21.30 (s, CCH3), 23.37 (s, CHCH3), 23.46 (s, CHCH3), 24.25 (s, CHCH3),
17 P. J. Ragogna, N. Burford, M. D’eon and R. McDonald, Chem.
Commun., 2003, 1052.
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