Biphosphinine rhodium and cobalt(-1) complexes

Article abstract of DOI:10.1021/om000279s

The 4,4′,5,5′-tetramethyl-2,2′-biphosphinine (tmbp) dianionic sodium salt 2 reacts with [M(acac)₃] (M = Co, Rh) precursors to yield the anionic [M(tmbp)₂]^- cobalt (3, M = Co) and rhodium (4, M = Rh) complexes. Trapping of

Full text of DOI:10.1021/om000279s

© Copyright 2000
Volume 19, Number 16, August 7, 2000
American Chemical Society
Communications
Bip h osp h in in e Rh od iu m a n d Coba lt(-1) Com p lexes
Nicolas Me´zailles, Patrick Rosa, Louis Ricard, Franc¸ois Mathey,* and
Pascal Le Floch*
Laboratoire “He´teroe´le´ments et Coordination”, UMR CNRS 7653, Ecole Polytechnique,
91128 Palaiseau Cedex, France
Received April 3, 2000
Ch a r t 1
Summary: The 4,4′,5,5′-tetramethyl-2,2′-biphosphinine
(tmbp) dianionic sodium salt 2 reacts with [M(acac)3]
(M ) Co, Rh) precursors to yield the anionic [M(tmbp)2]-
cobalt (3, M ) Co) and rhodium (4, M ) Rh) complexes.
Trapping of these two species with Ph3SnCl affords
[M(tmbp)SnPh3] complexes (5, M ) Co) and (6, M ) Rh).
For several years now, we have been interested in the
chemistry of 2,2′-biphosphinines, the phosphorus equiva-
lents of 2,2′-bipyridines. Our studies aim at developing
the use of these strong π-acceptor ligands for the
stabilization of highly reduced transition metal com-
plexes.1 In 1999, we reported on syntheses of the anion
radical and dianion of 4,4′,5,5′-tetramethyl-2,2′-biphos-
phinine (tmbp) and showed that their reactions with
halide salts of metals (W, Ru, and group 10 metals)
proved to be a convenient way to prepare the corre-
sponding zerovalent complexes.2 More recently, using
the same approach, we synthesized the first anionic
homoleptic biphosphinine complexes [M(tmbp)3]2- with
group 4 metals (M ) Ti, Zr, Hf) (Chart 1).3
complexes, we investigated the reactivity of these anions
toward Co and Rh precursors to see whether anionic
Co and Rh(-1) complexes could be obtained. In this
communication, we wish to report on these results.
Two strategies are available for the synthesis of the
Rh (-1) complex 4. The first one involves reaction of 2
equiv of the monoanion radical (M ) Li or Na) with 1
equiv of a Rh(I) precursor such as [Rh(COD)Cl]2. The
second requires the condensation of 2 equiv of dianion
2 with 1 equiv of a Rh(III) precursor, [Rh(acac)3]. This
latter method turned out to be the more successful and
was then subsequently transposed to the synthesis of
the Co(-1) complex, through the reaction of 2 with [Co-
(acac)3] (eq 1).4
As part of a continuing program aimed at expanding
this methodology to the synthesis of other anionic
(1) (a) Mathey, P.; Le Floch, P. Chem. Ber. 1996, 129, 263. (b) Rosa,
P.; Ricard, L.; Le Floch, P.; Mathey, F.; Sini, G.; Eisenstein, O. Inorg.
Chem. 1998, 37, 3154.
(2) Rosa, P.; Ricard, L.; Mathey, F.; Le Floch, P. Organometallics
1999, 18, 3348.
(3) Rosa, P.; Me´zailles, N.; Ricard, L.; Mathey, F.; Le Floch, P.
Angew. Chem., Int. Ed. 2000, 39, 1821.
10.1021/om000279s CCC: $19.00 © 2000 American Chemical Society
Publication on Web 07/06/2000

2942 Organometallics, Vol. 19, No. 16, 2000
Communications
(1)
It must be noted that 3 is the first example of a η1-
phosphinine cobalt complex. In both cases, the reduced
complexes were univocally formed and no side product
was detected in the 31P NMR spectra of the crude
mixture. Unfortunately, [Na(acac)] salts could not be
totally removed from the crude mixture by precipitation,
and 3 and 4 could not be recovered as analytically pure
1
substances. NMR experiments (31P, H, and 13C) were
carried out on crude mixtures in both cases. We found
that addition of the (2.2.2) cryptand resulted in nearly
quantitative precipitation of 3 and 4 as a powder
(contaminated by traces of acac salts). To gain more
structural information, X-ray crystallographic studies
were carried out. Suitable crystals were obtained by
heating poorly soluble [Na(2.2.2)] salts of 3 and 4 in
THF or DME overnight.5,8,9 Both complexes adopt a
nearly tetrahedral geometry as reported for other group
9 d10 complexes.5-7 Nevertheless the presence of differ-
ent conformations in the solid points toward a fluxional
behavior for 3 and 4 in solution. Thus, two independent
molecules (θ ) 78° and 83°), differing from each other
by the twist angle between the planes of the ligands,
are contained in the unit cell of the Co complex 38 and
three molecules (θ ) 59°, 63°, 87°) in the case of its Rh
counterpart 4.9 This situation is not maintained in
solution since the 31P NMR spectra of 4 (doublet at δ )
F igu r e 1. ORTEP drawing of one molecule of 4. Selected
bond distances (Å) and angles (deg): Co(1)-P(1) ) 2.1063-
(7), Co(1)-P(3) ) 2.0841(7), Co(1)-P(2) ) 2.0988(6), Co-
(1)-P(4) ) 2.1097(5), P(1)-C(1) ) 1.730(2), C(1)-C(2) )
1.391(2), C(2)-C(3) ) 1.414(2), C(3)-C(4) ) 1.391(2), C(4)-
C(5) ) 1.397(2), C(5)-C(6) ) 1.454(2), C(6)-P(2) ) 1.737-
(2); C(1)-P(1)-C(5) ) 101.91(7), P(1)-Co(1)-P(2) ) 83.82-
(2), P(2)-Co(1)-P(4) ) 122.32(2), P(1)-Co(1)-P(3) )
112.44(2), P(1)-Co(1)-P(4) ) 133.23(2), P(2)-Co(1)-P(3)
) 126.25(2).
is presented in Figure 1. In both cases a significant
electronic transfer from the metal to the π* LUMO of
the ligand is observed. This phenomenon is evidenced
by the shortening of the C-C bridge bond between each
phosphinine unit (average 1.456 vs 1.490(8) Å in cis-1)
and by the lengthening of the internal PdC bond
(average 1.763 vs 1.736(4) Å in cis-1), in good agreement
with the shape of the biphosphinine LUMO.1b Accord-
ingly, the Rh-P bond lengths in 4 appear to be rather
short (from average 2.219 Å) compared to values re-
ported for phosphinine Rh(+1) complexes (average 2.26
Å).10
1
194.1 ppm with J (31P-103Rh) ) 191 Hz) and 3 (broad
singlet at δ ) 209.4 ppm) show only a single resonance
pointing toward magnetic equivalence of the four P
atoms. An ORTEP view of one molecule of 3 (θ ) 78°)
(4) Preparation of 3: Biphosphinine 1 (0.1 g, 0.4 mmol) was reacted,
in a glovebox, at room temperature with excess sodium (0.23 g, 10
mmol) in THF or DME (10 mL). After 3 h, excess sodium was removed
and [Co(acac)3] (71 mg, 0.2 mmol) was added at -78 °C. The resulting
solution was then slowly warmed to room temperature. After 3 h, Na-
(acac) salts were separated by filtration (glovebox), and cryptand (2.2.2)
(75 mg, 0.2 mmol) was added to the filtrate to precipitate complex 3.
After drying, complex 3 was recovered as a very oxygen sensitive dark
red powder. Elemental data could not be obtained due to traces of Na-
(acac) salt. Preparation of 4: Synthesis of 4 was carried out following
the procedure described above for 3 using 1 (0.1 g, 0.4 mmol), Rh-
(acac)3 (70 mg, 0.2 mmol), and cryptand (2.2.2) (75 mg, 0.2 mmol). After
washing with hexanes, complex 4 was recovered as a very oxygen
sensitive black powder. Suitable crystals of 3 and 4 were obtained as
follows. In the glovebox, 15 mg of powder was placed in a glass tube
and was then subsequently covered with THF or DME. The tube was
sealed under vacuum and then heated at 80 °C overnight. The tube
was broken in the glovebox, and crystals were protected with para-
tone oil for handling and then submitted to X-ray diffraction anal-
ysis.
(5) For references on the synthesis of anionic group 9 complexes
incorporating alkene ligands, see: (a) J onas, K.; Mynott, R.; Kru¨ger,
C.; Sekulowski, J . C.; Tsay, Y.-H. Angew. Chem., Int. Ed. Engl. 1976,
15, 767. (b) J onas, K.; Schieferstein, L.; Kru¨ger, C.; Tsay, Y. H. Angew.
Chem., Int. Ed. Engl. 1979, 18, 550. (c) J onas, K.; Kru¨ger, C. Angew.
Chem., Int. Ed. Engl. 1980, 19, 520. (d) J onas, K. Pure Appl. Chem.
1984, 56, 63. (e) J onas, K. Angew. Chem., Int. Ed. Engl. 1985, 24, 295.
(6) For pertinent references on the synthesis of anionic group 9
complexes incorporating CO ligands and isonitriles, see: (a) Hieber,
W.; Schulten, H. Z. Anorg. Allg. Chem. 1937, 232, 17. (b) Devasaga-
yaraj, A.; Achyutha Rao, S.; Periasamy, M. J . Organomet. Chem. 1991,
387-391, 403. (c) Warnock, G. F.; Cooper, N. J . Organometallics 1989,
8, 1826. (d) Leach, P. A.; Geib, S. J .; Corella, J . A.; Warnock, G. F.;
Cooper, N. J . J . Am. Chem. Soc. 1994, 116, 8566. (e) Beck, W. Angew.
Chem., Int. Ed. Engl. 1991, 30, 168.
Though a significant part of the charge resides on
ligands, main-group electrophiles react at the metal
(7) For pertinent references on the synthesis of anionic group 9
complexes incorporating phosphine ligands, see: (a) Hieber, W.; Duch-
atsch, H. Chem. Ber. 1965, 98, 2933. (b) Kruck, Th.; Derner, N.; Lang,
W. Z. Naturforsch. 1966, 21b, 1020. (c) Scho¨nberg, H.; Boulmaaˆz, S.;
Wo¨rle, M.; Liesum, L.; Schweiger, A.; Gru¨tzmacher, H. Angew. Chem.,
Int. Ed. 1998, 37, 1423. (d) Boulmaaˆz, S.; Mlakar, M.; Loss, S.;
Scho¨nberg, H.; Deblon, S.; Wo¨rle, M.; Nesper, R.; Gru¨tzmacher, H. J .
Chem. Soc., Chem. Commun. 1998, 2623. (e) Collman, J . P.; Vastine,
F. D.; Roper, W. R. J . Am. Soc. 1966, 88, 5035. (f) Collman, J . P.;
Vastine, F. D.; Roper, W. R. J . Am. Chem. Soc. 1968, 90, 2282.
(8) Structure of 3: Deep red cubic crystals were grown from a hot
(80 °C) THF solution of the complex. Crystal data: C28H32P4Co‚
C18H36O6N2Na, triclinic, P1h, a ) 12.789(5) Å, b ) 18.760(5) Å, c )
20.143(5) Å, R ) 91.210(5)°, â ) 93.630(5)°, γ ) 93.530(5)°, V ) 4812-
(3) Å3, Z ) 4, Dcalcd ) 1.312 g cm-3, Mo KR radiation, λ ) 0.71069, T
) - 150.0 K, θmax ) 27.50°, 34 137 measured reflections, 21 921
independent reflections, 18 341 reflections used, Rint ) 0.0314 (>2σ),
wR2 ) 0.0788, R1 ) 0.0323, GOF ) 1.026, difference peak/hole )
0.400(0.049)/-0.322(0.049) e Å3.
(9) Structure of 4 : Deep red plates were grown from a hot (80 °C)
DME solution of the complex. Crystal data: C28H32P4Rh‚C18H36O6N2-
Na, triclinic, P1h, a ) 13.159(3) Å, b ) 13.579(3) Å, c ) 41.546(8) Å, R
) 81.428(1)°, â ) 85.187(1)°, γ ) 88.475(1)°, V ) 7314.1(3) Å3, Z ) 6,
Dcalcd ) 1.355 g cm-3, Mo KR radiation, λ ) 0.71069, T ) -150.0 K,
θmax ) 24.11°, 30 133 measured reflections, 22 243 independent reflec-
tions, 15 658 reflections used, Rint ) 0.0603 (>2σ), wR2 ) 0.1403, R1
) 0.0540, GOF ) 1.008, difference peak/hole ) 0.582(0.152)/-0.634-
(0.152) e Å3.

Communications
Organometallics, Vol. 19, No. 16, 2000 2943
center. Thus reaction of Ph3SnCl with 3 and 4, in THF
at room temperature, yielded the expected [M(tmbp)2-
(SnPh3)] complexes 5 (M ) Co) and 6 (M ) Rh),11
respectively, whose formulation was unambiguously
established on the basis of NMR and elemental analyses
data (eq 2).
(2)
Further information on the structure of complex 6 was
given by an X-ray structural study. An ORTEP view of
6 is presented in Figure 2 along with the more relevant
bond distances and angles.12 As generally observed for
penta-coordinated metal complexes, 6 shows a fluxional
behavior. Thus, whereas the 31P NMR signal of 6 attests
the presence of four equivalent P atoms (sharp doublet
F igu r e 2. ORTEP drawing of one molecule of 6. Selected
bond distances (Å) and angles (deg): Rh(1)-P(1) ) 2.243-
(2), Rh(1)-P(2) ) 2.236(2), Rh(1)-P(3) ) 2.240(2), Rh(1)-
P(4) ) 2.263(2), Rh(1)-Sn ) 2.6140(7), P(1)-C(1) )
1.716(7), C(1)-C(2) ) 1.38(1), C(2)-C(3) ) 1.40(1), C(3)-
C(4) ) 1.37(1), C(4)-C(5) ) 1.42(1), C(5)-P(1) ) 1.744(7),
C(5)-C(6) ) 1.452(8); C(1)-P(1)-C(5) ) 104.4(4), P(1)-
Rh(1)-P(2) ) 80.05(7), P(3)-Rh(1)-P(4) ) 80.81(6), P(1)-
Rh(1)-P(3) ) 170.72(6), P(2)-Rh(1)-P(4) ) 131.79(6),
P(1)-Rh(1)-P(4) ) 106.35(7), P(1)-Rh(1)-Sn ) 89.81(5),
P(3)-Rh(1)-Sn ) 83.30(5), P(2)-Rh(1)-Sn ) 130.63(5),
P(4)-Rh(1)-Sn ) 97.49(5).
1
of pseudo triplet at δ ) 196.3 with J (31P-103Rh) ) 142
Hz and 2J (31P-117Sn/119Sn) ) 66 Hz) even at low
temperature (-50 °C), 6 adopts a distorted trigonal
bipyramidal geometry in the solid state. The SnPh3
group and two P atoms of two different biphosphinines
(P2 and P4) are located on equatorial sites, while the
two others (P1 and P2) occupy axial sites.
In summary, we have established that the reaction
of biphosphinine dianion 3 with [M(acac)3] complexes
(M ) Co, Rh) provided the corresponding Co and Rh-
(-1) complexes as isolable species. Further investiga-
tions will now focus on the reactivity of these species
toward electrophiles as well as on the extension of
this approach to the synthesis of other reduced com-
plexes.
(10) For relevant references on Rh-phosphinine bond distances, see:
(a) Breit, B.; Winde, R.; Harms, K. J . Chem. Soc., Perkin Trans. 1997,
1, 2681. (b) Me´zailles, N.; Avarvari, N.; Ricard, L.; Mathey, F.; Le Floch,
P. Inorg. Chem. 1998, 37, 5313. (c) Avarvari, N.; Me´zailles, N.; Ricard,
L.; Le Floch, P.; Mathey, F. Science 1998, 8, 1587.
(11) Preparation of 5 : Triphenyltin chloride (77 mg, 0.2 mmol) was
added at room temperature to a solution of complex 3 prepared as
above (in THF) from 1 (0.1 g, 0.4 mmol) and [Co(acac)3] (71 mg, 0.2
mmol). The resulting mixture was stirred for 1 h and then taken to
dryness. Complex 5 was extracted in CH2Cl2 (20 mL) and filtrated.
After evaporation of the solvent complex 5 was recovered as a violet
powder. Yield: 91 mg (50%). Anal. Calcd for C46H47CoP4Sn: C, 61.29;
H, 5.26. Found: C, 60.96; H, 5.20. Preparation of 6: Synthesis of
complex 6 was carried out following the same procedure from 1 (0.1 g,
0.4 mmol), [Rh(acac)3] (70 mg, 0.2 mmol), and Ph3SnCl (77 mg, 0.2
mmol) in DME. Yield: 125 mg (65%). Anal. Calcd for C46H47P4RhSn‚
1/2 DME (performed on crystals): C, 58.21; H, 5.29. Found: C, 58.10;
H, 5.09.
(12) Structure of 6. Crystals were grown by slow diffusion of hexane
into a CHCl3 solution of the complex. Crystal data: C46H47P4RhSn‚1/
2DME, monoclinic, C2/c, a ) 32.9410(10) Å, b ) 12.4230(10) Å, c )
22.7740(10) Å, R ) 90.0000(10)°, â ) 107.740(10)°, γ ) 90.0000(10)°,
V ) 8876.5(9) Å3, Z ) 8, Dcalcd ) 1.482 g cm-3, Mo KR radiation, λ )
0.71069, T ) -150.0 K, θmax ) 22.21°, 12 582 measured reflections,
5450 independent reflections, 3982 reflections used, Rint ) 0.0889
(>2σ), wR2 ) 0.0865, R1 ) 0.0593, GOF ) 1.033, difference peak/hole
) 0.513(0.092)/-0.634(0.092) e Å3.
Ack n ow led gm en t. The authors thank the CNRS
and the Ecole Polytechnique for support of this
work.
Su p p or tin g In for m a tion Ava ila ble: Text giving experi-
mental details and characterization data for the compounds
prepared in this paper and tables of atomic coordinates and
equivalent isotropic displacement parameters, bond lengths
and bond angles, anisotropic displacement parameters, hy-
drogen coordinates, and equivalent isotropic parameters. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OM000279S