First catalytic dihydroamination of a phosphaalkyne. Crystal and molecular structure of trans-[PdCl2{P(iPrNH)2CH2tBu}2]

Article abstract of DOI:10.1039/b007512o

Treatment of a dichloromethane solution of tBuCP, containing a catalytic amount of TiCl4, with an excess of the primary amines RNH2 (R = iPr, tBu) quantitatively affords the corresponding bis-dialkylaminophosphine P(tBuNH)2-CH2tBu, P(iPrNH)2CH2tBu is structurally characterised by a single crystal X-ray diffraction study of its bis-trans-PdCl2 complex.

Full text of DOI:10.1039/b007512o

First catalytic dihydroamination of a phosphaalkyne. Crystal and molecular
structure of trans-[PdCl2{P(PriNH)2CH2But}2]
F. Geoffrey N. Cloke,* Peter B. Hitchcock, John F. Nixon* and D. James Wilson
School of Chemistry, Physics and Environmental Science, University of Sussex, Brighton, Sussex, UK BN1 9QJ.
E-mail: J.Nixon@sussex.ac.uk
Received (in Cambridge, UK) 18th September 2000, Accepted 25th October 2000
First published as an Advance Article on the web
Treatment of a dichloromethane solution of ButCP, contain-
ing a catalytic amount of TiCl4, with an excess of the primary
amines RNH2 (R = Pri, But) quantitatively affords the
corresponding bis-dialkylaminophosphine P(ButNH)2-
CH2But. P(PriNH)2CH2But is structurally characterised by a
single crystal X-ray diffraction study of its bis-trans-PdCl2
complex.
During the course of this work we have discovered that the
reaction of catalytic amounts of TiCl4 with the primary amines
RNH2 (R = But, Pri) followed by the addition of PCBut yields
the dialkyldiaminophosphines P(NHR)2CH2But (R = Pri 5,†
But 6†) in near quantitative yields (90–95%) (Scheme 2). No
reaction occurs in the absence of TiCl4.
The direct addition of nucleophiles HNR2 to alkenes and
alkynes has been shown to be kinetically unfavourable due to
high activation barriers caused by unfavourable approach of the
substrates.1 Catalysis is therefore of fundamental importance
for the amination of alkynes, by providing alternative lower
energy kinetic pathways. A survey of the literature in this area
reveals a stronger precedence for catalytic intra-molecular
hydroamination of alkynes employing complexes of titanium,2
nickel,3 palladium,4 gold5 and lanthanides.6 In contrast, cata-
lytic inter-molecular hydroamination of alkynes appears much
more difficult and these reactions are often hampered by low
turnover numbers. The use of HgII reagents appears to be the
most general route for the hydroamination of alkenes and
alkynes7,8 and examples of thallium,9 lanthanides,10 uranium
and thorium11 containing catalysts exist.
Scheme 2
Compounds 5 and 6 are colourless oils which can be easily
purified from the crude reaction mixtures by sublimation in
vacuo on to a cold finger (liquid nitrogen, 60–70 °C, 1022 mbar,
yield 95%). The 1H NMR spectrum of 5 displays the expected
five signals. The septet at d 3.16 and two doublets at d 1.40, 1.31
are assigned to the methine, methylene and NH protons
respectively, the NH resonance being broadened by 14N
quadrupolar coupling. The singlet at d 1.1 is attributed to the
tert-butyl protons, and the doublet of doublets at d 1.03 is
assigned to the diastereotopic methyl groups of the isopropyl
units which are further coupled to the methine protons. The 31P-
{1H} NMR spectrum displays a singlet at d 57.2. In order to
unambiguosly assign the connectivity of 5, the bis-diamino-
phosphine complex trans-[PdCl2{P(PriNH)2CH2(But)}2] 7†
was prepared from the reaction of [PdCl2(NCPh)2] 8 and 2
equiv. 5 in acetone. Crystals suitable for X-ray analysis were
grown from a concentrated toluene solution cooled to 250 °C
and the molecular structure is depicted below together with
relevant bond lengths and angles (Fig. 1).‡ The structure is
unremarkable, but serves to confirm the dihydroamination of
the phosphaalkyne. The bis-aminophosphine units adopt a
Recently, Bergman et al.12 have demonstrated the utility of
5
the zirconocene diamide [Zr(h -C5H5)2(NHC6H3-Me2)2] 1 for
the stoichiometric and catalytic addition of amines to internal
alkynes and allenes, yielding enamines and imines respectively.
The thermolysis (a-elimination) of 1 yields the transient imide
5
‘[Zr(h -C5H5)2(NC6H3-Me2)]’ 2 which catalyses the addition
of alkynes (RCCR, R = Me, Ph) to 2,6-dimethylaniline.
Although intermediates have not been observed during the
catalytic cycle, the proposed intermediate metallacyclobutene
5
complex [Zr(h -C5H5){N(C6H3-Me2)(Ph)CC(Ph)}] 3, formed
from a stoichiometric [2 + 2] addition of diphenyl acetylene to
the metal nitrogen unsaturated bond of 2, has been prepared and
structurally characterised (see Scheme 1).
Scheme 1
Although phosphaalkynes, RCP, contain a slightly polarised
bond13 their similarity in reactivity to alkynes is now very well
established.14 However, although nucleophilic, trans-metal-
lations and 1,2-additions have been described,13 there are no
examples to date of hydroaminations of this class of unsaturated
molecule. Recently we have been interested in the cycloaddition
chemistry of the phosphaalkyne ButCP with Ti and Zr imides.15
The reaction of ButCP with the transient imide ‘[Cp2ZrN(C6H3-
Me2)]’ 2 affords the azaphosphacyclobutadiene complex
[Cp2ZrN(C6H5-Me2)PC(But)] 4 which is isostructural with 3.
Fig. 1 Molecular structure of [PdCl2{(NHPri)2PCH2(But)}] 7. Selected
distances (Å) and angles (°): Pd–P 2.313(1), P–C(1) 1.829(3), P–N(1)
1.667(2), P–N(2) 1.662(2), Å. P–Pd–ClA 87.19(4), N(2)–P–N(1) 103.8(1)
P–Pd–Cl 92.81(4) N(1)–P–C(1) 110.0(1), N(2)–P–Pd 116.32(9), N(1)–P–
Pd 112.26(8), C(1)–P–Pd 114.49(9)°. Displacement ellipsoids are shown at
50% probability level. Hydrogen atoms are omitted for clarity.
The MNPC fragment in 4 is in agreement with the expected
bond polarity of the unsaturated reactive sites.
DOI: 10.1039/b007512o
Chem. Commun., 2000, 2387–2388
This journal is © The Royal Society of Chemistry 2000
2387

[PdCl2{P(NH2Pri)2CH2But}2] 7 1H NMR (d6-benzene, 295 K): d 3.5 [s,
3
br, 2H, NH], 2.8 [sept., 2H, CH(CH3)2, J(HH) 7.1 Hz], 1.8 [d, 4H, CH2P,
2J(HP) 3.92 Hz], 1.39 [s, 9H, C(CH3)3, ], 1.05 [d, 12H, CH(CH3)2, 3J(HH) 4.1
3
Hz] 1.19 [d, 12H, CH(CH3)2, J(HH) 4.1 Hz]. 13C-{1H} NMR+d 44.3
[C(CH3)3], 41.1 [pseudo-t, PCH2, 1J(PC) 22 Hz], 32.6 [br, C(CH3)3], 31.09
[NCH], 26.1, 25.6 [d, CH(CH3)2]. 31P-{1H} NMR d 64.8. EI-MS m/z (%):
614 (25) [M]+ , 543 (5) [M 2 (CC(CH3)3]+. Analysis calculated for
C22H54Cl2N4P2Pd: C, 43.04; H, 8.87. Found: C, 43.00; H, 8.90%.
Scheme 3
‡ Crystal data for C36H66Cl2N4P2Pd 7: M = 794.2, triclinic, a = 7.869(3),
b = 10.919(3), c = 12.754(5) Å, a = 90.44(3), b = 103.26(3), g =
¯
95.81(3)°, U = 1060.6(6) Å3, T = 173(2) K, space group P1 (no. 2), Z =
trans-orientation in 7 and the phosphorus atoms display a
tetrahedral coordination geometry.
1, l(Mo-Ka) = 0.71073 Å, 5107 reflections measured which were used in
all calculations. Final R indices for [I > 2s(I)] with 4563 reflections was R1
= 0.038. Single crystals of [PdCl2{P(NH2Pri)2CH2(But)}2] were grown
from a saturated toluene solution (253 °C), mounted in inert oil and
transferred to the cold gas stream of the diffractometer. The structure was
solved using direct methods and refined by full-matrix least-squares on F2.
CCDC 182/1830. See http://www.rsc.org/suppdata/cc/b0/b007512o/ for
crystallographic files in .cif format.
Surprisingly, a survey of the literature shows a relative
paucity of structural information on diaminophosphines and
only P(Ar*NH)2Ar (Ar* = C6H2But3-2,4,6)16 and P(ArfN-
H)2Ar* (Arf
=
C6H2(CF3)3-2,4,6)17 have been crystallo-
graphically characterised. A few complexes of the group 6
metals have also been reported.18
The mechanism of formation of the diaminophosphine has
not been fully determined, however Winter et al.19 reported that
treatment of TiCl4 with an excess of primary amines affords
imido complexes of type [TiCl2(NR)(NH2R)x)] 9 which clearly
are likely candidates for the active catalytic species. Fur-
thermore, in unpublished results Regitz and Asmus20 have
1 R. Tauber, in Applied Homogeneous Catalysis with Organometallic
Compounds, ed. B. Cornils and W. A. Herrmann, VCH, Weinheim,
1996, vol. 1, p. 507.
2 P. L. McGrane, M. Jensen and T. Livinghouse, J. Am. Chem. Soc., 1992,
114, 5459.
3 E. M. Campi and W. R. Jackson, J. Organomet. Chem., 1996, 523,
205.
5
recently shown that the reaction of [Ti(h -C5H5)Cl3] with
5
ButNH2
and
PCBut
in
toluene
yields
[Ti(h -
4 K. Utimoto, Pure Appl. Chem., 1983, 55, 1845.
5 Y. Fukuda, K. Utimoto and H. Nozaki, Heterocycles, 1987, 25, 297.
6 Y. Li, P. F. Fu and T. J. Marks, Organometallics, 1994, 13, 439.
7 J. Barluenga and F. Azar, Synthesis, 1975, 704.
8 F. Esser, Synthesis, 1987, 5, 460; R. C. Larock, Angew. Chem., Int. Ed.
Engl., 1978, 17, 27.
9 J. Barluenga and F. Aznar, Synthesis, 1977, 195.
10 Y. Li and T.J. Marks, J. Am. Chem. Soc., 1996, 118, 707.
11 A. Haskel, T. Straub and M. S. Eisen, Organometallics, 1996, 15,
3773.
12 P. J. Walsh, A. M. Baranger and R. G. Bergman, J. Am Chem. Soc.,
1992, 114, 1708.
13 M. Regitz and P. Binger, in Multiple bonds and Low Coordination in
Phosphorus Chemistry, ed. M. Regitz and O. J. Scherer, Thieme,
Stuttgart, 1990 and references cited therein.
C5H5)Cl{PNBut(NHBut)CHBut}] 10, (probably via a [2 + 2]
addition of PCBut to the intermediate titanium imide
[Ti(C5H5)Cl(NBut)], followed by a 1,2 addition of NH2But
across the activated PNC bond) (Scheme 3).
The mechanism of formation of the diaminophosphines 5 and
6 by di-hydroamination of PCBut probably proceeds via the
intermediacy
of
[TiCl2(NR)(NH2R)x)]
9
and
[TiCl2(NR)P(NHR)CHBut] which is analogous to 10, the
excess [NH3ButCl] formed subsequently removing the resulting
substrate ‘{PNR(NHR)CHBut}’ via a double protonation
step.
We thank the EPSRC for financial support (D. J. W.) and
Professor Manfred Regitz for unpublished results cited in ref.
20.
14 K. B. Dillon, F. Mathey and J. F. Nixon, in Phosphorus the Carbon
Copy, John Wiley and Sons, Chichester, 1998.
15 F. G. N. Cloke, P. B. Hitchcock, J. F. Nixon, D. J. Wilson and P.
Mountford, Chem. Commun., 1999, 661.
16 E. G. Bent, R. Schaeffer, R. C. Haltiwanger and A. D. Norman, Inorg.
Chem., 1990, 29, 2608; P. B. Hitchcock, H. A. Jasim, M. F. Lappert and
H. D. Williams, J. Chem. Soc., Chem. Commun., 1986, 1634.
17 J. T. Ahlemann, H. W. Roesky, R. Murugavel, E. Parsini, M.
Noltemeyer, H. G. Smidt, O. Muller, R. Herbst-Irmer, L. N. Markovskii
and Y. G. Shermolovich, Chem. Ber., 1997, 130, 1113.
18 E. Lindner, H. Rauleder and W. Hiller, Z. Naturforsch., 1983, 38B,
417.
19 T. S. Lewkebandara, P. H. Sheridan, M. J. Heeg, A. L. Rheingold and
C. H. Winter, Inorg. Chem., 1994, 33, 5879.
20 S. M. F. Asmus, Ph.D. Thesis, University of Kaiserslautern, 1999. M.
Regitz, personal communication.
Notes and references
t
† Characterisation data for: P(NHPri)2CH2 Bu 5: 1H NMR (d6-benzene,
295 K) d 2.36 [sept, 1H, CH, 3J(HH) 6.4 Hz], 1.4 [d, 2H, CH2, 2J(HP) 2.5 Hz],
1.31 [d, 2H, NHC(CH3)3, 3J(HH) 7.14 Hz], 1.11 [s, PCH2C(CH3)3], 1.05, 1.0
[d 3 2, 12H, CH(CH3)2]. 31P-{1H} NMR d 57.16.
P(NHBut)2CH2But 6: 1H NMR (d6-benzene, 295 K): d 1.19 [s, 18H,
CH2C(CH3)3], 1.09 [s, 9H, C(CH3)3], 1.27 [d, br, 2H, CH2]. 13C-{1H} NMR
d 55.9 [d, C(CH3)3, 2J(CP) 6.83 Hz], 50.97 [d, PC, 1J(CP) 14 Hz], 32.69 [d,
NHC(CH3)3, 3J(CP) 8.93 Hz], 31.80 [d, CH2C(CH3)3, 2J(CP) 9.03 Hz], 31.1
[d, NHC(CH3)3, 2J(CP) 12.28 Hz] 31P-{1H}: NMR d 40.88. EI-MS m/z (%):
246 (30) [M]+, 233 (13) [M 2 (Me)]+, 175 (80) [M 2 (NHBut) 2 (Me)].
2388
Chem. Commun., 2000, 2387–2388