Metal-assisted synthesis of new and highly functionalized diphosphines

Article abstract of DOI:10.1021/om980448x

The coupling of coordinated isocyanide with a fragment diphosphinocarbene in the complexes fac-[Mn(CO)₃(CNR){(PPh₂)₂CI}] (3a, R = Ph; 3b, R = ^tBu) leads to the formation of 4a,b, which contain the new ketenimines [(PPh₂)₂C=C=NR] (5a,b). The N-phenylketenimine in 4a undergoes a [4 + 1] cycloaddition by treatment with phenyl isocyanide to give 6, a neutral complex containing a unique 2-(diphosphinomethylidene)-3-imino-2,3-dihydroindole ligand.

Full text of DOI:10.1021/om980448x

Organometallics 1998, 17, 3835-3837
3835
Meta l-Assisted Syn th esis of New a n d High ly
F u n ction a lized Dip h osp h in es
J avier Ruiz, V´ıctor Riera,* and Maril´ın Vivanco
Departamento de Quı´mica Orga´nica e Inorga´nica, Instituto de Qu´ımica Organometa´lica
EM/ CSIC, Universidad de Oviedo, 33071 Oviedo, Spain
Maurizio Lanfranchi and Antonio Tiripicchio
Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica,
Centro di Studio per la Strutturistica Diffrattometrica del CNR, Universita` di Parma,
Viale delle Scienze 78, I-43100 Parma, Italy
Received J une 2, 1998
Sch em e 1
Summary: The coupling of coordinated isocyanide with
a fragment diphosphinocarbene in the complexes fac-
[Mn(CO)3(CNR){(PPh2)2CI}] (3a , R ) Ph; 3b, R ) tBu)
leads to the formation of 4a ,b, which contain the new
ketenimines [(PPh2)2CdCdNR] (5a ,b). The N-phe-
nylketenimine in 4a undergoes a [4 + 1] cycloaddition
by treatment with phenyl isocyanide to give 6, a neutral
complex containing a unique 2-(diphosphinomethylidene)-
3-imino-2,3-dihydroindole ligand.
Diphosphine ligands play a crucial role in coordina-
tion and organometallic chemistry, owing to their ability
to stabilize a great variety of metal complexes in a
number of oxidation states1 as well as to their applica-
tion in homogeneous catalysis.2 Even more, the design
of new transition-metal catalysts strongly depends on
the availability of new types of diphosphines; notably,
it has been shown that functionalization of tertiary
phosphine and diphosphine ligands improves the selec-
tivity of some catalytic processes.3 In view of this, we
describe herein a metal-assisted synthesis of new diphos-
phinoketenimines of the type [(PPh2)2CdCdNR] (5a , R
t
) Ph; 5b, R ) Bu), derived from one of the simplest
and most readily available diphosphines, dppm (bis-
(diphenylphosphino)methane). We also report herein
some preliminary results on the reactivity of these
ligands.
As shown in Scheme 1, dppm coordinated to manga-
nese(I) in the cationic complex 1 is deprotonated by
KOH, in CH2Cl2 as solvent, to give the diphosphino-
methanide derivative 2,4 which further reacts with I2
and KOH to afford 3, a neutral complex containing the
anionic ligand [(PPh2)2CI]-.5,6 In a sense, which is
useful for the understanding of the present reaction
pathway, this ligand can be described as being formed
by a diphosphinocarbene fragment [(PPh2)2C:] and the
anion I- (see below). 3 is quantitatively converted to
the ketenimine derivative 4,5,7 either by standing in
CH2Cl2 at room temperature (R ) Ph) or by refluxing
(1) (a) Puddephatt, R. J . Chem. Soc. Rev. 1983, 12, 99. (b) Chaudret,
B.; Delavaux, B.; Poilblanc, R. Coord. Chem. Rev. 1988, 86, 191. (c)
Cotton, F. A.; Hong, B. Prog. Inorg. Chem. 1992, 40, 179.
(2) Pignolet, L. H. Homogeneous Catalysis with Metal Phosphine
Complexes; Plenum Press: New York, 1983.
(3) (a) See ref 2, p 239, and references therein. (b) Hayashi, T.;
Kanehira, K.; Tsuchiya, H.; Kumada, M. J . Chem. Soc., Chem.
Commun. 1982, 1162. (c) Hayashi, T.; Kanehira, K.; Hagihara, T.;
Kumada, M. J . Org. Chem. 1988, 53, 113. (d) Sawamura, M.; Nagata,
H.; Sakamoto, H., Ito, Y. J . Am. Chem. Soc. 1992, 114, 2586.
(4) The synthesis of complexes of type 1 and 2 has been described
in: Ruiz, J .; Riera, V.; Vivanco, M.; Garc´ıa-Granda, S.; Garc´ıa-
Ferna´ndez, A. Organometallics 1992, 11, 4077.
t
in toluene (R ) Bu). A possible mechanism for this
interesting transformation is included in Scheme 1.
First, we propose that 3 undergoes a change in the
coordination mode of the ligand [(PPh2)2CI]- from η2-
(P,P′) to η2(P,C) to give intermediate I; this type of
bonding for diphosphinomethanides is well-documented
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3836 Organometallics, Vol. 17, No. 18, 1998
Communications
in the literature.8 The second step involves dissociation
of iodide, affording the η2(P,C)-diphosphinocarbene
intermediate II.9 Finally, the coupling of this carbene
with coordinated isocyanide would form the new diphos-
phinoketenimine, with I- completing the octahedral
coordination around manganese to yield 4. The coupling
of carbenes and isocyanides, either free or coordinated
to a metal center, is a well-established method of
generating ketenimines,10 and this knowledge offers
support for the above proposal, although neither I nor
II have been detected in the reaction mixture. Owing
to the presence of CO and CNR groups in these
complexes, major information is gained by monitoring
(5) Typical synthetic procedures are as follows. 3b: a solution of
2b (0.30 g, 0.49 mmol) in 20 mL of CH2Cl2 was added dropwise to a
stirred solution of iodine (0.19 g, 0.74 mmol) in 5 mL of CH2Cl2. The
resulting mixture was vigorously stirred with an excess of KOH (1 g,
18 mmol) for 1 h. The solution was then filtered off, and the solvent
was evaporated to dryness, affording a yellow solid. Yield: 0.33 g, 90%.
Anal. Calcd for C33H29IMnNO3P2: C, 54.19; H, 4.00; N, 1.91. Found:
C, 53.95; H, 3.99; N, 1.94. 4b: a suspension of 3b (0.40 g, 0.54 mmol)
in 25 mL of toluene was refluxed for 10 min. After this time, an orange
solution was formed which was concentrated under vacuum to about
7 mL and cooled to -15 °C to obtain orange needles of 4b. Yield: 0.36
g, 90%. Anal. Calcd for C33H29IMnNO3P2: C, 54.19; H, 4.00; N, 1.91.
Found: C, 54.03; H, 3.86; N, 1.72. Suitable crystals for X-ray analysis
were obtained from a dichloromethane solution layered with hexane.
5b: a solution of 0.3 g of 4b (0.41 mmol) in 25 mL of toluene was
irradiated with visible-UV light at 10 °C for 3 h. The solvent was
then removed under vacuum and the remaining solid chromatographed
through an alumina column (activity III) prepared in hexane. Elution
with toluene/hexane (1/2) gave a colorless fraction, which was evapo-
rated to dryness, giving a white solid. This was recrystallized from
hexane at -20 °C. Yield: 63 mg, 33%. Mp: 118 °C. Anal. Calcd for
F igu r e 1. ORTEP view of the molecular structure of the
complex [MnI(CO)3[(PPh2)2CdCdNtBu] (4b), together with
the atomic numbering scheme. The ellipsoids for the atoms
are drawn at the 30% probability level. The I1 atom and
the trans carbonyl C3-O3 are partially interchanged.
Important bond distances (Å) and angles (deg): Mn1-I1
) 2.617(2), Mn1-P1 ) 2.338(3), Mn1-P2 ) 2.339(3), P1-
C28 ) 1.811(10), P2-C28 ) 1.819(9), C28-C29 ) 1.305-
(15), N-C29 ) 1.194(14), N-C30 ) 1.489(15); P1-Mn-
P2 ) 72.6(1), P1-C28-P2 ) 99.3(4), C28-C29-N )
175.0(12), C29-N-C30 ) 131.3(10).
C
30H29NP2: C, 77.40; H, 6.38; N, 3.01. Found: C, 77.27; H, 6.20; N,
3.02. 6: to a solution of 4a (0.30 g, 0.40 mmol) in 20 mL of CH2Cl2
was added phenyl isocyanide (50 mg, 0.48 mmol). After the mixture
was stirred at room temperature for 12 h, the color of the solution
changed from orange to dark red. The solvent was evaporated to
dryness and the residue washed with hexane (3 × 10 mL) to provide
the reactions by IR spectroscopy;5,7 of note is the
disappearance of the ν(CN) band of the coordinated
isocyanide at 2172 (3a ) and 2148 cm-1 (3b) on going
from 3 to 4. The structure of 4b was definitively
established by an X-ray diffraction study.11 The struc-
ture is shown in Figure 1, together with the most
important bond distances and angles. The Mn atom is
in an octahedral arrangement with the diphosphi-
a
dark red solid. Yield: 0.31 g, 90%. Anal. Calcd for C42H30-
IMnN2O3P2: C, 59.04; H, 3.54; N, 3.28. Found: C, 58.83; H, 3.62; N,
3.15. Suitable crystals for X-ray analysis were obtained from
a
saturated solution of 6 in a mixture of THF/toluene/hexane. Detailed
synthetic procedures for all compounds and additional characterization
data are provided in the Supporting Information.
(6) The synthesis of the closely related complex [Mn(CO)4{(PPh2)2-
CI}] has been reported elsewhere: Ruiz, J .; Arau´z, R.; Riera, V.;
Vivanco, M.; Garc´ıa-Granda, S.; Mene´ndez-Vela´zquez, A. Organome-
tallics 1994, 13, 4162.
(7) Key spectroscopic and analytical data are as follows. 4a : FTIR
(CH2Cl2) ν(CO) 2015 (vs), 1954 (s), 1920 (s) cm-1
;
13C NMR (75.5 MHz,
1
2
CD2Cl2) δ 52.6 (t, J C-P ) 26 Hz, CdCdNPh), 154.8 (t, J C-P ) 8 Hz,
CdC)NPh); 31P{1H} NMR (121.5 MHz, CD2Cl2) δ 22.2 (s). Anal. Calcd
for C35H25NIO3P2Mn: C, 55.95; H, 3.35; N, 1.86. Found: C, 56.23; H,
3.46; N, 2.01. 4b: FTIR (CH2Cl2) ν(CO) 2016 (vs), 1950 (s), 1917 (s)
cm-1; 1H NMR (300 MHz, CD2Cl2) δ 1.32 (s, C(CH3)3); 13C NMR (CD2-
(11) Crystal data for C33H29IMnNO3P2 (4b) at 22 °C: monoclinic,
space group P21/n, a ) 11.629(3) Å, b ) 20.177(5) Å, c ) 14.134(4) Å,
â ) 94.68(2)°, Z ) 4, Fcalcd ) 1.470 g cm-3, µ(Mo KR) ) 14.62 cm-1
;
diffractometer, Philips PW 1100; radiation, graphite-monochromated
Mo KR (λ ) 0.710 73 Å). A total of 7186 reflections were collected in
the range 3 < θ < 27° ((h,k,l). Of these, 2265 having I > 2σ(I) were
used in the structure solution. R ) 0.0567, Rw ) 0.0664, w ) 0.661/
[σ2(Fo) + 0.0018Fo2]. The I1 atom and the trans carbonyl C3-O3 have
been found to be partially interchanged (refined occupancy factor 0.68).
All non-hydrogen atoms, except those of the disordered carbonyl C3-
O3, were refined anisotropically. All hydrogen atoms were placed at
their calculated positions and refined “riding” on the corresponding
parent atoms. Crystal data for C42H30IMnN2O3P2‚2.5C4H8O (6) at 22
°C: monoclinic, space group P21/c, a ) 12.540(3) Å, b ) 21.717(5) Å, c
) 37.098(7) Å, â ) 95.81(2)°, Z ) 8, Fcalcd ) 1.368 g cm-3, µ(Mo KR) )
9.88 cm-1; diffractometer, Philips PW 1100; radiation, graphite-
monochromated Mo KR (λ ) 0.710 73 Å). A total of 29 394 reflections
were collected in the range 3 < θ < 30° ((h,k,l). Of these, 8317 having
I > 2σ(I) were used in the structure solution. R ) 0.0766, Rw ) 0.0832,
unit weights in all stages of refinement. Two crystallographically
independent, even if very similar, complexes (A and B) are present.
Moreover, five THF molecules of solvation have been found. The I1
atom and the trans carbonyl C3-O3 have been found partially
interchanged (refined occupancy factor 0.83 for complex A and 0.64
for complex B). All non-hydrogen atoms, except C3B, O3B, C3B′, O3B′,
C13B-C18B, and C13C-C18C (this phenyl was found disordered and
distributed in two positions of equal occupancy factor) and the atoms
of the THF molecules, were refined anisotropically. All hydrogen atoms
(except those of the disordered phenyl group and of the THF molecules)
were placed at their calculated positions and refined “riding” on the
corresponding parent atoms.
1
2
Cl2) δ 47.6 (t, J C-P ) 29 Hz, CdCdNtBu), 144.6 (t, J C-P ) 7 Hz,
CdC)NtBu); 31P{1H} NMR (CD2Cl2) δ 18.5 (s). Anal. Calcd for C33H29
-
NIO3P2Mn: C, 54.19; H, 4.00; N, 1.91. Found: C, 54.59; H, 4.19; N,
1.82. 5a : FTIR (Nujol) ν(CCN) 1997 cm-1 (m); 13C NMR (toluene/D2O)
1
2
δ 50.4 (t, J C-P ) 39 Hz, CdCdNPh), 174.72 (t, J C-P ) 7 Hz,
CdC)NPh); 31P{1H} NMR (CD2Cl2) δ -9.8 (s). 5b: FTIR (Nujol) ν-
(CCN) 2002 cm-1 (s); 1H NMR (CD2Cl2) δ 0.74 (s, C(CH3)3); 13C NMR
(CD2Cl2) δ 47.5 (t, 1J C-P ) 34 Hz, CdCdNtBu), 167.5 (t, 2J C-P ) 5 Hz,
CdCdNtBu), 30.1 (s, C(CH3)3), 58.8 (s, C(CH3)3); 31P{1H} NMR (CD2-
Cl2) δ -10.5 (s). Anal. Calcd for C30H29NP2: C, 77.40; H, 6, 38; N, 3.01.
Found: C, 77.29; H, 6.20; N, 3.20. 6: FTIR (CH2Cl2) ν(CO) 2013 (vs),
1948 (s), 1916 (s) cm-1
;
13C NMR (CD2Cl2) δ 98.4 (dd, J C-P ) 28 Hz,
1
2
2
1J C-P ) 23 Hz, P2CdC), 146.2 (dd, J C-P ) 6 Hz, J C-P ) 4 Hz, P2Cd
C), 156.1 (dd, 3J C-P ) 7 Hz, 3J C-P ) 4 Hz, CdNPh); 31P{1H} NMR (CD2-
2
2
Cl2) δ 29.9 (d, J P-P ) 10 Hz), 18.4 (d, J P-P ) 10 Hz). Anal. Calcd for
C
42H30N2IO3P2Mn: C, 59.04; H, 3.54; N, 3.28. Found: C, 59.28; H, 3.37;
N, 3.15.
(8) Karsch, H. H.; Grauvogl, G.; Deubelly, B.; Mu¨ller, G. Organo-
metallics 1992, 11, 4238 and references therein.
(9) A similar coordination mode for a diphosphinocarbene has been
found in the complex [Cp2Zr{C(PMe2)2}]2: Karsch, H. H.; Grauvogl,
G.; Kawecki, M.; Bissinger, P. Organometallics 1993, 12, 2757.
(10) (a) Aumann, R. Angew. Chem., Int. Ed. Engl. 1988, 27, 1456.
(b) Moloy, K. G.; Fagan, P. J .; Manriquez, J . M.; Marks, T. J . J . Am.
Chem. Soc. 1986, 108, 56. (c) Igau, A.; Baceiredo, A.; Trinquier, G.;
Bertrand, G. Angew. Chem., Int. Ed. Engl. 1989, 28, 621.

Communications
Organometallics, Vol. 17, No. 18, 1998 3837
diphosphines. A preliminary result which anticipates
the rich chemistry of these ligands is provided by the
reaction of 4a with phenyl isocyanide resulting in a [4
+ 1] cycloaddition, followed by migration of the ortho
hydrogen to nitrogen to give 6,5 a neutral complex
containing a unique 2-(diphosphinomethylidene)-3-
imino-2,3-dihydroindole ligand (see Scheme 1).14 The
analytical and spectroscopic data for 6 were in ac-
cordance with this formulation,7 but in order to fully
structurally characterize the new ligand, an X-ray
diffraction study of complex 6 was carried out.11 A view
of the structure is shown in Figure 2, together with the
most important bond distances and angles.
It must be noted that so far we have not been able to
isolate the above diphosphinoindole as a free ligand,
because, on trying to remove this from the metal,
degradation of the molecule invariably occurs, giving a
complex mixture of species from which only the known
tetraphosphine [(PPh2)2CdC(PPh2)2]15 and free phenyl
isocyanide appear to be spectroscopically recognized.
This result is not very surprising, because the diphos-
phinoindole in 6 is formally assembled by coupling of 2
equiv of CNPh with the carbene [(PPh2)2C:].
It is expected that the synthetic methodology de-
scribed herein can be extended to a number of cationic
dppm-manganese(I) complexes bearing two-electron
ligands other than isocyanide in that axial position (CO,
PR3, NCR, etc.). This may allow the metal-assisted
synthesis of a variety of diphosphines functionalized at
the central carbon atom (ketenes, ylides, azirines, etc.).
Furthermore, we must emphasized the importance of
the ligands [(PPh2)2CdCdNR] themselves, not only
because they are rare examples of ketenimines but also
because they are highly reactive molecules which show
promise in for the preparation of other functionalized
diphosphines.
F igu r e 2. ORTEP view of the molecular structure of one
of the two crystallographically independent complexes
[MnI(CO)3[(PPh2)2CdC-C(dNPh)(o-C6H4)NH] (6A), to-
gether with the atomic numbering scheme. The ellipsoids
for the atoms are drawn at the 30% probability level. The
I1 atom and the trans carbonyl C3-O3 are partially
interchanged. Important bond distances (Å) and angles
(deg): Mn1-I1 ) 2.687(2) [2.752(3)], Mn-P1 ) 2.329(4)
[2.328(4)], Mn-P2 ) 2.329(3) [2.321(3)], P1-C4 ) 1.810-
(9) [1.805(10)], P2-C4 ) 1.805(10), [1.822(11)], C4-C5 )
1.361(14) [1.355(15)], N1-C5 ) 1.401(12) [1.430(14)]; P1-
Mn-P2 ) 72.1(1) [72.4(1)], P1-C4-P2 ) 98.6(4) [98.4(5)].
The values in brackets refer to complex 6B.
noketenimine ligand chelating through the P atoms. The
bond lengths and angles along the C28-C29-N-C30
skeleton are similar to those found in most free keten-
imines,12 indicating that there is not a substantial
change in these structural parameters on coordination.
The ligands [(PPh2)2CdCdNR] (5a ,b) could be re-
moved from the metal by irradiation of toluene solutions
of 4a ,b with visible-UV light. Upon workup, the free
diphosphines were isolated as a pale yellow oil (5a ) and
a white microcrystalline solid (5b) in 30-40% yield.5,7
Ketenimines and other heterocumulenes are among the
most reactive organic functionalities,13 and this feature
makes the diphosphinoketenimines 5a ,b promising
substrates for the synthesis of new functionalized
Ack n ow led gm en t. We thank the Spanish DGICYT
(Project PB91-0678) for financial support.
Su p p or tin g In for m a tion Ava ila ble: Text giving detailed
experimental procedures and spectroscopic and analytical data
for 3-6 and tables of atomic coordinates and thermal param-
eters, all bond distances and angles, and experimental data
for the X-ray diffraction studies (Tables SI-IX) for complexes
4b and 6 (17 pages). Ordering information is given on any
current masthead page.
OM980448X
(12) Wolf, R.; Wong, M. W.; Kennard, C. H. L.; Wentrup, C. J . Am.
Chem. Soc. 1995, 117, 6789 and references therein.
(13) Tennant, G. In Comprehensive Organic Chemistry; Sutherland,
I. O., Ed.; Pergamon Press: Oxford, U.K., 1979; Vol. 2, pp 513-590.
(14) For other [4 + 1] cycloaddition reactions of N-arylketenimines
and isocyanides, see for instance ref 9a.
(15) Anderson, D. M.; Hitchcock, P. B.; Lappert, M. F. J . Organomet.
Chem. 1989, 363, C7.