Reactivity of terminal electrophilic phosphinidene complexes: Synthesis of the first rhenium phosphinidene, [Re(CO)5(η1-PN iPr2)][AlCl4], and novel reactions with azobenzene

Article abstract of DOI:10.1021/om0401307

The first terminal rhenium phosphinidene complex, [Re(CO) ₃(η¹-PNⁱPr₂)][AlCl₄], has been synthesized by chloride abstraction from [Re(CO)₅{P(Cl)- (NⁱPr₂)}]. The electr

Full text of DOI:10.1021/om0401307

Organometallics 2005, 24, 2023-2026
2023
Reactivity of Terminal Electrophilic Phosphinidene
Complexes: Synthesis of the First Rhenium
Phosphinidene, [Re(CO)5(η1-PNiPr2)][AlCl4], and Novel
Reactions with Azobenzene
Todd W. Graham, Renan P.-Y. Cariou, Javier Sa´nchez-Nieves, Anna E. Allen,
Konstantin A. Udachin, Rachid Regragui, and Arthur J. Carty*
Steacie Institute for Molecular Sciences, National Research Council of Canada,
100 Sussex Drive, Ottawa, Ontario, Canada K1A 0R6, and The Ottawa-Carleton Chemistry
Institute, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5
Received November 19, 2004
Summary: The first terminal rhenium phosphinidene
complex, [Re(CO)5(η1-PNiPr2)][AlCl4], has been synthe-
sized by chloride abstraction from [Re(CO)5{P(Cl)-
(NiPr2)}]. The electrophilic character of the terminal
phosphinidene ligand is demonstrated by phosphine
addition at the unsaturated phosphorus center and by
novel reactions with azobenzene, PhNdNPh, which
generate, via C-H activation and P-N and P-C bond
formation, coordinated benzodiazaphosphole ligands.
The cations [Re(CO)5P(PPh3)NiPr2]+ and [Re(CO)5-
{P(PhNNHC6H4)NiPr2}]+ have been crystallographically
reactive toward unsaturated substrates such as olefins
and alkynes, affording cyclic phosphiranes or phos-
phirenes via phosphinidene group transfer3 or cycload-
dition at the coordinated phosphinidene.3,4 An extensive
chemistry of adducts of these η1-PR complexes is also
developing.10
In this communication we describe, inter alia, the
synthesis and characterization of the first η1-phosphin-
idene complex of rhenium, [Re(CO)5(η1-PNiPr2)][AlCl4],
and unprecedented reactions of this compound and the
related cobalt complex [Co(CO)3(PPh3)(η1-PNiPr2)][AlCl4]4
with the unsaturated nitrogen-containing species azoben-
zene, PhNdNPh, which afford, via aryl C-H activation
and PN2C2 ring formation, new coordinated benzodi-
azaphospholes. These results are in contrast with the
only other reported reaction of azobenzene with the
transient [(OC)5WdPR] complex, generated in situ,
which afforded o-phosphino azobenzene derivatives.11
This suggests that the chemistry of stable η1-phosphin-
idenes may differ from that of their transient rela-
tives.9,11
-
characterized as their AlCl4 salts. The corresponding
late-metal terminal phosphinidene complexes [Co(CO)3-
(PR3)(η1-PNiPr2)][AlCl4] (R ) Ph, Et) also afford coor-
dinated benzodiazaphospholes via reaction with PhNd
NPh.
Since the isolation and structural characterization of
the first terminal electrophilic phosphinidene complexes
in 2001,1,2 interest in the chemistry of these unsaturated
phosphorus analogues of Fischer carbene complexes has
expanded considerably.3-5 Both late-metal compounds,
exemplified by (dtbpe)NidP(dmp),3 [Co(CO)3(PPh3)-
(η1-PNiPr2)][AlCl4],4 [(η6-Ar)LMdPMes*] (M ) Ru, Os),5
[Cp*M(CO)2dPNiPr2]AlCl4 (M ) Fe, Ru, Os),6 and
CpR(L)MdPAr (M ) Co, Rh, Ir),7 and complexes of the
group 6 metals1 have been stabilized and isolated.
Although their chemistry has not been extensively
explored, unlike that of transient species such as
[(OC)4FedPR]8 and [(OC)5WdPR],9 there is evidence
that the phosphorus center in these compounds is
The phosphido complex [Re(CO)5P(Cl)NiPr2] (1)12 was
readily prepared by the reaction of Na[Re(CO)5] with
Cl2PNiPr2. In solution 1, like its counterpart [Cp*Mo-
1
(CO)3(P(Cl)NiPr2)], is dynamic, with H and 31P NMR
data1 indicating restricted rotation about the P-N bond
and inversion at the stereogenic phosphorus center. The
subsequent addition of AlCl3 to 1 resulted in chloride
abstraction and quantitative formation of the Re-
phosphinidene species [Re(CO)5(η1-PNiPr2)][AlCl4]13 (2),
as shown in Scheme 1.
* To whom correspondence should be addressed. E-mail: acarty@
pco-bcp.gc.ca. Tel: (613) 948-6666. Fax: (613) 948-6667.
(1) Sterenberg, B. T.; Carty, A. J. J. Organomet. Chem. 2001, 617,
696.
(2) Sterenberg, B. T.; Udachin, K. A.; Carty, A. J. Organometallics
2001, 20, 2657.
(3) (a) Waterman, R.; Hillhouse, G. L. J. Am. Chem. Soc. 2003, 125,
13350. (b) Waterman, R.; Hillhouse, G. L. Organometallics 2003, 22,
5182.
(4) Sa´nchez-Nieves, J.; Sterenberg, B. T.; Udachin, K. A.; Carty, A.
J. J. Am. Chem. Soc. 2003, 125, 2404.
(5) Termaten, A. T.; Nijbacker, T.; Schakel, M.; Lutz, M.; Spek, A.
L.; Lammertsma, K. Chem. Eur. J. 2003, 9, 2200.
(6) Sterenberg, B. T.; Udachin, K. A.; Carty, A. J. Organometallics
2003, 22, 3927.
(7) Termaten, A. T.; Aktas, H.; Schakel, M.; Ehlers, A. W.; Lutz,
M.; Spek, A. L.; Lammertsma, K. Organometallics 2003, 22, 1827.
(8) (a) Wit, J. B. M.; van Eijkel, G. T.; Schakel, M.; Lammertsma, K
Tetrahedron 2000, 56, 137. (b) Wit, J. B. M.; van Eijkel, G. T.; de
Kanter, F. J. J.; Schakel, M.; Ehlers, A. W.; Lutz, M.; Spek, A. L.;
Lammertsma, K. Angew. Chem., Int. Ed. 1999, 38, 2596.
(9) (a) Marinetti, A.; Mathey, F. Organometallics 1984, 3, 456. (b)
Marinetti, A.; Mathey, F. J. Am. Chem. Soc. 1982, 104, 4484. (c) Hung,
J.-T.; Yang, S.-W.; Chand, P.; Gray, G. M.; Lammertsma, K. J. Am.
Chem. Soc. 1994, 116, 10966. (d) Tran Huy, N. H.; Ricard, L.; Mathey,
F. Heteroat. Chem. 1998, 9, 597. (e) Tran Huy, N. H.; Mathey, F. J.
Org. Chem. 2000, 65, 652. (f) For an extensive review of the chemistry
of these compounds see: Dillon, K. B.; Mathey, F.; Nixon, J. F.
Phosphorus: The Carbon Copy; Wiley: Chichester, U.K., 1998. Lam-
mertsma, K. Top. Curr. Chem. 2003, 229, 95. Mathey, F.; Tran Huy,
N. H.; Marinetti, A. Helv. Chim. Acta 2001, 84, 2938.
(10) Sterenberg, B. T.; Udachin, K. A.; Carty, A. J. Organometallics
2001, 20, 4463.
(11) Tran Huy, N. H.; Ricard, L.; Mathey, F. New J. Chem. 1998,
23, 75.
(12) Data for [Re(CO)5(P(Cl)NiPr2)] (1) are as follows. Yield: 55%.
IR (νCO, cm-1, hexane solution): 2165 (w), 2060 (w), 2022 (s), 1998 (s).
1H NMR (CDCl3, 25 °C): δ 1.22 (d, 6H, CH(CH3)2), 1.40 (bs, 6H, CH-
(CH3)2), 3.59 (bs, 1H, CH(CH3)2), 3.90 (bs, 1H, CH(CH3)2). 31P NMR
(CDCl3, 25 °C): δ 214.2. Anal. Calcd for C11H14O5PNClRe: C, 26.82;
H, 2.84; N, 2.84. Found: C, 26.83; H, 2.89; N, 2.82.
10.1021/om0401307 CCC: $30.25 © 2005 American Chemical Society
Publication on Web 03/22/2005

2024 Organometallics, Vol. 24, No. 9, 2005
Communications
Figure 1. ORTEP diagram of the cations of [Re(CO)5(P(NiPr2)(PPh3))][AlCl4] (3) and [Re(CO)5{P(PhNNHPh)(NiPr2)}]-
[AlCl4] (4). Hydrogen atoms have been eliminated for clarity, and thermal ellipsoids are shown at the 50% probability
level.
Scheme 1
phosphorus resonance and the large one-bond P-P
coupling suggests that nucleophilic addition of the
phosphine has occurred at the phosphinidene ligand.
This was confirmed by a single-crystal X-ray diffraction
experiment, which showed that a species with an
unusual P-donor/P-acceptor moiety had formed. The
molecular structure of 3 is shown in Figure 1. Com-
pound 3 has a pseudooctahedral ligand arrangement
about the rhenium center with five carbonyls and one
phosphine ligand bound to the metal. The Re-P(1)
separation of 2.5771(7) Å is longer than the Re-P(1)
distance in 2 (2.446(3) Å) and corresponds to a single
bond;15 the coordination of PPh3 to the phosphinidene
phosphorus atom P(1) has resulted in a distinctly
pyramidalized rhenium-bound phosphorus. The P-P
separation of 2.235(1) Å is slightly elongated compared
to a typical P-P single bond (e.g. 2.2149(9) Å in [Cp*Mo-
(CO)2(η2-P(NiPr2)PMe2CH2CH2PMe2)][AlCl4]),10 and this
likely reflects steric interactions between the bulky PPh3
group and both the NiPr2 and Re(CO)5 moieties. Sur-
prisingly, while P(1) is pyramidal and the P-N distance
(1.678(2) Å) is significantly longer than in η1-phosphin-
idene complexes,6 N(1) is planar. This may suggest
residual π-character in the P-N bond or, more likely,
steric resistance to pyramidalization at nitrogen.
The 31P NMR spectrum of complex 2 has a singlet at
δ 956, with a downfield chemical shift characteristic for
terminal phosphinidene ligands.1-7 The 1H NMR spec-
trum shows two well-resolved doublets for the iPr
methyl groups at δ 1.54 and 1.76, with the methine
resonances appearing as septets at δ 5.26 and 5.06. The
sharpness of these signals indicates severely restricted
rotation about the P-N bond, suggesting a significant
π interaction between the P and N atoms. A single-
crystal X-ray study confirmed the structural identity of
2 as a terminal η1-phosphinidene complex, and the Re-
(1)-P(1) (2.446(3) Å) and P(1)-N(1) (1.634(6) Å) bond
lengths are comparable to the analogous separations in
the related tungsten complex [Cp*W(CO)3(η1-PNiPr2)]-
[AlCl4] (W(1)-P(1) ) 2.4503(6) Å; P(1)-N(1) ) 1.629-
(2) Å).2 Complex 2 is the first η1-phosphinidene of the
d7 metals to be reported.
Both complex 2 and [Co(CO)3(PPh3)(η1-PNiPr2][AlCl4]
readily react with azobenzene. This results in the
conversion of the phosphinidene fragment to a coordi-
nated phosphine ligand via nitrogen binding to phos-
phorus and subsequent C-H activation of an ortho
hydrogen, affording the novel benzodiazaphosphole
(14) Data for [Re(CO)5{P(NiPr2)(PPh3)}][AlCl4] (3) are as follows.
Yield: 80%. IR (νCO, cm-1, CH2Cl2 solution): 2164 (w), 2140 (w), 2063
(s), 2032 (s) cm-1. 1H NMR (CDCl3, 0 °C): δ 7.83-7.70 (m, 18H, C6H5),
3.34 (s, 2H, CH), 1.05 (s, 6H, CH(CH3)2), 0.67 (s, 6H, CH(CH3)2). 31P
The addition of PPh3 to complex 2 results in a rapid
reaction, affording a species with two 31P NMR reso-
nances appearing as an AB quartet centered at δ 19.4
(1JPP ) 609 Hz).14 The upfield shift of the Re-bound
1
NMR (CDCl3, 0 °C): δ 20.3 (AB quartet, JPP ) 609 Hz). Anal. Calcd
for C29.5H30AlCl5NO5P2Re (contains 0.5 equiv of cocrystallized CH2-
Cl2): C, 37.42; H, 3.16; N 1.18. Found: C, 36.71; H, 2.92; N, 1.39. Mass
spectrum: calcd M+, m/z 720.1; found, m/z 720.7. X-ray data: triclinic,
P1h, a ) 9.7056(5) Å, b ) 12.8757(7) Å, c ) 15.5502(9) Å, R ) 89.1760-
(10)°, â ) 79.1640(10)°, γ ) 71.8490(10)°, V ) 1811.60(17) Å3, Z ) 2,
Dcalcd ) 1.707 Mg/m3, T ) 125(2) K, 9958 independent reflections
(R(int) ) 0.0275), R1 ) 0.0280, wR2 ) 0.0666.
(13) Data for [Re(CO)5(η1-PNiPr2)][AlCl4] (2) are as follows. Yield:
94%. IR (νCO, cm-1, CH2Cl2 solution): 2164 (w), 2060 (s), 2014 (w) cm-1
.
1H NMR (CD2Cl2, 25 °C): δ 1.54 (d, 6H, CH(CH3)2), 1.76 (d, 6H, CH-
(CH3)2), 5.26 (sept, 1H, CH(CH3)2), 5.06 (m, 1H, CH(CH3)2). 31P NMR
(CDCl3, 25 °C): δ 956.1. Anal. Calcd for C11H14O5PNCl4AlRe: C, 21.15;
H, 2.25; N, 2.24. Found: C, 20.63; H, 2.48; N, 1.98.
(15) Buhro, W. E.; Zwick, B. D.; Savas, G.; Hutchinson, J. P.;
Gladysz, J. A. J. Am. Chem. Soc. 1988, 110, 2427.

Communications
Organometallics, Vol. 24, No. 9, 2005 2025
Scheme 2
Scheme 3
complexes [Re(CO)5{P(PhNNHC6H4)(NiPr2)}][AlCl4] (4)
and [Co(CO)3(PPh3){P(PhNNHC6H4)(NiPr2)}][AlCl4] (5)
(Scheme 2).
Complexes 4 and 5 have been characterized via X-ray
crystallography.16,17 The structure of 416 (Figure 1)
shows the expected pseudooctahedral ligand environ-
ment around the rhenium center and a benzodiazaphos-
phole ligand that is staggered with respect to the metal-
bound carbonyl ligands.
The Re-C(3) distance of 1.986(2) Å is considerably
shorter than the M-C bonds of all other carbonyl
ligands in the complex (2.005(2), 2.020(2), 2.023(2), and
2.024(2) Å), indicating greater π-back-donation to this
CO as a result of the trans tertiary phosphine ligand.
As in compound 3, the phosphorus center is highly
pyramidalized and the Re-P bond length of 2.5016(5)
Å corresponds to a single bond. The elongated P(1)-
N(1) distance (1.712(2) Å) compared to P(1)-N(3) (1.652-
(2) Å) may be due to strain imposed by the five-
membered ring. The geometry about N(3) is planar, as
[AlCl4] to a coordinated benzodiazaphosphole in 5. The
31P NMR spectrum17 of this complex shows the expected
two doublets at δ 100.3 and 54.3, with the latter signal
belonging to the PPh3 ligand. The 123 Hz coupling is
as expected for trans phosphines. The analogous PEt3
complex [Co(CO)3(PEt3)(P{PhNNHC6H4}NiPr2][AlCl4]
(6) can be synthesized similarly.18-20 Complex 6 has a
31P NMR chemical shift identical with that for the
benzodiazaphosphole ligand in 5 suggesting the same
structure as 5. To the best of our knowledge, there is
no precedent for the synthesis of benzodiazaphosphole
ligands as in 4-6 from terminal phosphinidenes, and
indeed such ligands are rare.
By analogy with the recently reported reactivity of
electrophilic phosphinidenes with phosphines,10 the
initial site of attack by a nitrogen donor atom of
azobenzene is likely at the phosphinidene phosphorus.
This should result in activation of an ortho carbon to
nucleophilic attack due to resonance structure II, shown
in Scheme 3. In the final step, proton migration occurs
from the six-membered ring to the adjacent azobenzene
nitrogen atom.
1
expected from the H NMR spectrum16 of this species,
in which the two isopropyl methyl resonances appear
as sharp doublets at δ 1.18 and 1.29, apparently a result
of severely restricted rotation about the P-N bond. The
N-H signal of the coordinated phosphine ligand ap-
pears as a broad resonance centered at δ 7.11.
The X-ray structure of compound 5 resembles that of
4, and so only a few features will be described. The
coordination geometry at cobalt is approximately trigo-
nal bipyramidal, with the two phosphine ligands in a
trans disposition and the carbonyl groups located in the
trigonal plane. The two Co-P bond lengths are very
similar (2.2374(4) and 2.2359(4) Å for Co-P(1) and Co-
P(2), respectively), a result of the conversion of the
phosphinidene fragment in [Co(PPh3)(CO)3(η1-PNiPr2)]-
(18) Data for [Co(CO)3(PEt3){P(Cl)NiPr2}] (6) are as follows. Yield:
38%. IR (νCO, cm-1, ether solution): 1972 (s), 1959 (s), 1923 (w). 1H
NMR (CD2Cl2, -80 °C): δ 1.13 (m, 15H, CH2CH3 and CH(CH3)2), 1.24
(d, 3H, CH(CH3)2, 3J(HH) ) 6.5 Hz), 1.39 (d, 3H, CH(CH3)2, 3J(HH) )
6.6 Hz), 1.82 (sept, 6H, CH2CH3, 3J(HH) ) 7.7 Hz), 3.57 (sept, 1H,
CH(CH3)2, 3J(HH) ) 6.5 Hz), 4.42 (sept, 1H, CH(CH3)2, 3J(HH) ) 6.4
Hz). 31P NMR (CDCl3, 25 °C): δ 49.3 (d, PEt3, 2J(PP) ) 17.2 Hz), 284.6
(d, P(Cl)NiPr2, 2J(PP) ) 18.8 Hz). Anal. Calcd for C15H29O3P2NClCo:
C, 42.12; H, 6.83; N, 3.28. Found: C, 42.14; H, 7.12; N, 3.44.
(19) Data for [Co(CO)3(PEt3)(PNiPr2)][AlCl4] (7) are as follows.
IR (νCO, cm-1, CH2Cl2 solution): 2068 (w), 2015 (s), 1999 (s). 1H NMR
(CDCl3, 25 °C): δ 1.25 (m, 9H, CH2CH3), 1.53 (d, 6H, CH(CH3)2,
3J(HH) ) 6.0 Hz), 1.63 (d, 6H, CH(CH3)2, 3J(HH) ) 6.2 Hz), 2.05 (sept,
6H, CH2CH3, 3J(HH) ) 7.0 Hz), 4.74 (bm, 1H, CH(CH3)2), 5.58 (sept,
1H, CH(CH3)2, 3J(HH) ) 7.0 Hz). 31P NMR (CDCl3, 25 °C): δ 50.2 (s,
PEt3), 882.0 (bs, PNiPr2). Note: this complex decomposes upon
attempted isolation.
(16) Data for [Re(CO)5{P(PhNNHC6H4)(NiPr2)}][AlCl4] (4) are as
follows. Yield: 60%. IR (νCO, cm-1, CH2Cl2 solution): 2155 (w), 2093
(w), 2051 (s), 2009 (w) cm-1 1H NMR (CD2Cl2, 25 °C): δ 1.18 (d, 6Η,
.
CH(CH3)2, 3J(HH) ) 6.7 Hz), 1.29 (d, 6H, CH(CH3)2, 3J(HH) ) 6.6 Hz),
3.81 (m, 2H, CH(CH3)2), 7.11 (s, 1H, NH), 7.42 (m, 9H, Ar). 31P NMR
(CD2Cl2 25 °C): δ 48.3. Anal. Calcd for C23H24O5PN3Cl4AlRe: C, 34.23;
H, 2.98; N, 5.21. Found: C, 34.16; H, 3.05; N, 5.18. X-ray data:
monoclinic, P21/c, a ) 14.5701(8) Å, b ) 14.3060(8) Å, c ) 15.6888(9)
Å, R ) 90°, â ) 111.192(1)°, γ ) 90°, V ) 3049.0(3) Å3, Z ) 4, Dcalcd
)
1.761 Mg/m3, T ) 125(2) K, 7567 independent reflections, R1 ) 0.0182,
wR2 ) 0.0448.
(17) Data for [Co(CO)3(PPh3){P(PhNNHC6H4)(NiPr2)}][AlCl4] (5) are
as follows. Yield: 89%. IR (νCO, cm-1, CH2Cl2 solution): 2155 (w), 2093
(w), 2051 (s), 2009 (w) cm-1 1H NMR (CD2Cl2, 25 °C): δ 1.18 (d, 6Η,
.
CH(CH3)2, 3J(HH) ) 6.7 Hz), 1.29 (d, 6H, CH(CH3)2, 3J(HH) ) 6.6 Hz),
3.81 (m, 2H, CH(CH3)2), 7.11 (s, 1H, NH), 7.42 (m, 9H, Ar). 31P NMR
(CD2Cl2, 25 °C): δ 48.3. Anal. Calcd for C23H24O5PN3Cl4AlRe: C, 34.23;
H, 2.98; N, 5.21. Found: C, 34.16; H, 3.05; N, 5.18. X-ray data:
monoclinic, P21/c, a ) 16.5189(8) Å, b ) 13.5147(6) Å, c ) 22.8441(8)
(20) Data for [Co(CO)3(PEt3){P(PhNNHC6H4)(NiPr2)}][AlCl4] (8) are
as follows. Yield: 84%. IR (νCO, cm-1, CH2Cl2 solution): 2068 (w), 2006
(s), 1994 (s). 1H NMR (CDCl3, 25 °C): δ 1.04 (bs, 9H, CH2CH3), 1.19
(bs, 6H, CH(CH3)2), 1.40 (bs, 6H, CH(CH3)2), 1.95 (bs, 6H, CH2CH3),
4.07 (bs, 2H, CH(CH3)2), 7.50 (bm, 10H, PhNNHPh). 31P NMR (CDCl3,
25 °C): δ 61.0 (d, 2J(PP) ) 107.6 Hz), 100.3 (d, 2J(PP) ) 107.4 Hz).
Anal. Calcd for C39H39O3P2N2AlCl4Co: C, 43.63; H, 5.29; N, 5.65.
Found: C, 43.10; H, 5.77; N, 6.07.
Å, R ) 90°, â ) 122.642(2) °, γ ) 90°, V ) 4294.4(3) Å3, Z ) 4, Dcalcd
)
1.373 Mg/m3, T ) 125(3) K, 12 025 independent reflections, R1 )
0.0326, wR2 ) 0.0808.

2026 Organometallics, Vol. 24, No. 9, 2005
Communications
Mathey and co-workers have reported the reaction of
transient [(OC)5WdPR] complexes with azobenzene.11
In this case, however, generation of the phosphinidene
in the presence of azobenzene resulted in the formation
of an ortho-phosphinated metal complex (7 in Scheme
chemistry driven by nucleophilic and oxidative addition
at the highly unsaturated phosphorus center.
Acknowledgment. This work was supported by the
National Research Council of Canada and the Natural
Sciences and Engineering Research Council of Canada
(to A.J.C.).
3). While the origins of these differences in reactivity
+
between the two metal fragments W(CO)5 and Re(CO)5
,
which are isoelectronic, may relate to higher N-P bond
strengths in the cationic intermediates to 4 and 5
(Scheme 3), it is clear that these reactions may lead to
synthetically useful and complementary methods for the
synthesis of new phosphine ligands. These results add
to a growing body of evidence that stable, electrophilic
η1-phosphinidene complexes possess a versatile reaction
Supporting Information Available: Text and tables
giving synthetic procedures and analytical, spectroscopic, and
crystallographic data for compounds 3-5. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM0401307