The first coordination of an (α-diazo)phosphine to a transition-metal center

Article abstract of DOI:10.1021/om0210558

The first coordination of an (α-Diazo)phosphine to a transition-metal center is discussed. X-ray diffraction studies demonstrate that the coordination occurs via the phosphorus lone pair with retention of the diazo moiety in both complexes. The coordination of the compound via the phosphorus lone pair in preference to reaction at the diazo fragments is also observed.

Full text of DOI:10.1021/om0210558

1358
Organometallics 2003, 22, 1358-1360
Th e F ir st Coor d in a tion of a n (r-Dia zo)p h osp h in e to a
Tr a n sition -Meta l Cen ter
Emmanuelle Despagnet-Ayoub,† Heinz Gornitzka,† J ohn Fawcett,‡
Philip W. Dyer,*,‡ Didier Bourissou,*,† and Guy Bertrand*,†,§,|
Laboratoire d’He´te´rochimie Fondamentale et Applique´e du CNRS (UMR 5069), Universite´
Paul Sabatier, 118, route de Narbonne, 31062 Toulouse Cedex 04, France, Department of
Chemistry, University of Leicester, University Road, Leicester LE1 7RH, U.K., and UCR-CNRS
J oint Research Chemistry Laboratory (UMR 2282), Department of Chemistry, University of
California, Riverside, California 92521-0403
Received December 30, 2002
Ch a r t 1. Str u ctu r es of (P h osp h in o)ca r ben es A
Summary: Reaction of [o-(trifluoromethyl)phenyl][bis-
(diisopropylamino)phosphino]diazomethane (1) with tet-
racarbonylbis(µ-chloro)dirhodium(I) ([Rh(CO)2(µ-Cl)]2)
affords the monometallic complex 2 at low temperature
and the dinuclear complex 3 upon warming to 0 °C.
X-ray diffraction studies demonstrate that the coordina-
tion occurs via the phosphorus lone pair with retention
of the diazo moiety in both complexes.
a n d (r-Dia zo)p h osp h in es B
(phosphino)(aryl)carbene.10 Since all the (phosphino)-
carbenes are extremely moisture sensitive, we became
interested in using their considerably more robust diazo
precursors B11 as potential synthons for the preparation
of (phosphino)carbene complexes. Indeed, ever since the
pioneeringwork ofYates,12a Werner,12b-d andHermann,12e-g
diazo compounds have routinely been used to prepare
transition-metal carbene complexes. Here, we report
that, surprisingly, (R-diazo)phosphines B coordinate13
to rhodium(I) via the phosphorus lone pair, with reten-
tion of the diazo moiety. The resulting mono- and
dinuclear complexes 2 and 3 are the first rhodium(I)
cis-chloro dicarbonyl phosphine and dinuclear mono-
substituted complexes, respectively, to be structurally
characterized.
The (R-diazo)phosphine 1,10c featuring the o-(trifluo-
romethyl)phenyl substituent, and tetracarbonylbis(µ-
chloro)dirhodium(I) were chosen because both fragments
afford an interesting compromise between stability and
reactivity. Irrespective of the temperature, addition of
1/2 equiv of [Rh(CO)2(µ-Cl)]2 to 1 in diethyl ether led to
a mixture of starting material 1 and the P-coordinated
complex 2, as deduced from the 31P NMR chemical shift
Over the last 10 years, N-heterocyclic carbenes (NHCs)
have become commonplace ligands, finding applications
as scaffolds in a broad range of transition-metal-
mediated transformations.1 Despite the availability of
NHCs as free, stable species,2 many of the catalytically
relevant metal complexes are prepared from masked
forms (such as conjugated acids,3 dimers,4 alcohol ad-
ducts,5 etc.).
In contrast, the coordination chemistry of the other
family of stable carbenes, namely (phosphino)carbenes
A, has been somewhat overlooked (Chart 1).6-8 The first
(phosphino)carbene complexes were prepared (in poor
yields) either by coupling a metal-bound carbyne ligand
with a phosphorus fragment or, alternatively, by C-H
activation of PMe3.6 We have recently shown that direct
complexation is also feasible,9 both η1- as well as η2-
rhodium(I) complexes being obtained from a stable
† Universite´ Paul Sabatier.
‡ University of Leicester.
§ University of California.
| E-mail: gbertran@mail.ucr.edu.
(1) (a) J afarpour, L.; Nolan, S. P. Adv. Organomet. Chem. 2001, 46,
181. (b) Herrmann, W. A.; Weskamp, T.; Bohm, V. P. W. Adv.
Organomet. Chem. 2002, 48, 1. (c) Herrmann, W. A. Angew. Chem.,
Int. Ed. 2002, 41, 1290.
(9) Despagnet, E.; Miqueu, K.; Gornitzka, H.; Dyer, P. W.; Bourissou,
D.; Bertrand G. J . Am. Chem. Soc. 2002, 124, 11834.
(2) (a) Bourissou, D.; Guerret, O.; Gabba¨ı F. P.; Bertrand, G. Chem.
Rev. 2000, 100, 39. (b) Arduengo, A. J ., III. Acc. Chem. Res. 1999, 32,
913.
(3) (a) Ko¨cher, C.; Herrmann, W. A. J . Organomet. Chem. 1997, 532,
261. (b) Herrmann, W. A.; Elison, M.; Fischer, J .; Ko¨cher, C.; Artus,
G. R. J . Angew. Chem., Int. Ed. Engl. 1995, 34, 2371. (c) Herrmann,
W. A.; Reisinger, C. P.; Spiegler, M. J . Organomet. Chem. 1998, 557,
93.
(10) (a) Buron, C.; Gornitzka, H.; Romanenko, V.; Bertrand, B.
Science 2000, 288, 834. (b) Despagnet, E.; Gornitzka, H.; Rozhenko,
A. B.; Schoeller, W. W.; Bourissou, D.; Bertrand, G. Angew. Chem.
2002, 114, 2959; Angew. Chem., Int. Ed. 2002, 41, 2835. (c) Despagnet-
Ayoub, E.; Sole´, S.; Gornitzka, H.; Rozhenko, A. B.; Schoeller, W. W.;
Bourissou, D.; Bertrand, G. J . Am. Chem. Soc. 2003, 125, 124.
(11) Baceiredo, A.; Bertrand, G.; Sicard, G. J . Am. Chem. Soc. 1985,
107, 4781.
(4) Lappert, M. F. J . Organomet. Chem. 1988, 358, 185.
(5) (a) Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H. Org. Lett. 1999,
1, 953. (b) Denk, K.; Sirsch, P.; Herrmann, W. A. J . Organomet. Chem.
2002, 649, 219.
(6) Bourissou, D.; Bertrand, G. Adv. Organomet. Chem. 1999, 44,
175.
(7) For attempted coordination of an anionic bis(phosphino)carbene,
see: Fuchs, A.; Gudat, D.; Nieger, M.; Schmidt, O.; Sebastian, M.;
Nyulaszi, L.; Niecke, E. Chem. Eur. J . 2002, 8, 2188.
(8) For theoretical investigations of (phosphino)carbene complexes,
see: (a) Schoeller, W. W.; Eisner, D.; Grigoleit, S.; Rozhenko, A. J . B.;
Alijah, A. J . Am. Chem. Soc. 2000, 122, 10115. (b) Schoeller, W. W.;
Rozhenko, A. J . B.; Alijah, A. J . Organomet. Chem. 2001, 617, 435.
(12) (a) Yates, P. J . Am. Chem. Soc. 1952, 74, 5376. (b) Werner, H.;
Richards, J . H. J . Am. Chem. Soc. 1968, 90, 4976. (c) Wolf, J .; Brandt,
L.; Fries, A.; Werner, H. Angew. Chem., Int. Ed. Engl. 1990, 29, 510.
(d) Schwab, P.; Mahr, N.; Wolf, J .; Werner, H. Angew. Chem., Int. Ed.
Engl. 1993, 32, 1480. (e) Herrmann, W. A. Angew. Chem., Int. Ed. Engl.
1974, 13, 599. (f) Herrmann, W. A.; Reiter, B.; Biersack, H. J .
Organomet. Chem. 1975, 97, 245. (g) Herrmann, W. A. Angew. Chem.,
Int. Ed. Engl. 1978, 17, 800.
(13) End-on coordination of the terminal diazo nitrogen was postu-
lated in the reaction of the lithium salt of the [bis(diisopropylamino)-
phosphino]diazomethane with Rh(PMe3)4Cl: Menu, M. J .; Crocco, G.;
Dartiguenave, M.; Dartiguenave, Y.; Bertrand, G. Organometallics
1988, 7, 2231.
10.1021/om0210558 CCC: $25.00 © 2003 American Chemical Society
Publication on Web 02/25/2003

Communications
Sch em e 1. Syn th esis of Com p lexes 2 a n d 3
Organometallics, Vol. 22, No. 7, 2003 1359
F igu r e 1. Molecular structure of 2 in the solid state. For
clarity the hydrogen atoms are omitted and the isopropyl
groups are simplified. Selected bond lengths (Å) and angles
(deg): P1-C1 ) 1.818(7), P1-Rh1 ) 2.367(2), Rh1-C22
) 1.824(9), Rh1-C21 ) 1.895(8), P1-N3 ) 1.691(5), P1-
N4 ) 1.674(5), Rh1-Cl1 ) 2.364(2), Rh1-C21 ) 1.895(8),
Rh1-C22 ) 1.824(9); P1-C1-N1 ) 115.8(4), P1-C1-C2
) 126.6(4), N1-C1-C2 ) 117.2(5), C1-P1-N3 ) 100.7-
(3), C1-P1-N4 ) 105.8(3), C1-P1-Rh1 ) 112.7(2), P1-
Rh1-Cl1 ) 90.46(7), P1-Rh1-C21 ) 175.7(2), P1-Rh1-
C22 ) 95.6(2).
(118.1 ppm) and the magnitude of the J PRh coupling
constant (162 Hz). To achieve complete conversion of 1,
an excess of [Rh(CO)2(µ-Cl)]2 was required.14 Complex
2 is indefinitely stable in solution at -50 °C but evolves
over a period of a few hours at 0 °C to afford the new
P-coordinated complex 3, as a 4/1 mixture of the two
NMR-distinguishable conformers 3a and 3b (31P NMR
126.8 and 127.8 ppm) (Scheme 1). Complex 3 is also
stable for days at -50 °C but decomposes within the
space of a few hours at room temperature, leading to a
complex mixture of products. No trace of the desired
(phosphino)carbene complex could be detected. Com-
plexes 216 and 317 were characterized at low tempera-
ture by multinuclear NMR spectroscopy18 as well as
through X-ray diffraction studies.19
The rhodium center adopts a slightly distorted square
planar geometry (∑angles ) 360.26°), with the phospho-
rus-rhodium bond distance (2.367(2) Å) being at the
longer end of the range typical for P-Rh single bonds.21
A significant inequivalence of the Rh-C bond distances
for the two carbonyl ligands (Rh-CO(cis to P) ) 1.824(9)
Å and Rh-CO(trans to P) ) 1.895(8) Å) is observed,
something that is consistent with the different trans
influences of phosphine and chloride. Complex 2 is the
first rhodium(I) cis-chloro dicarbonyl phosphine complex
to be structurally characterized. Until recently, such
complexes had only been identified spectroscopically in
solution,20 as in general they evolve to dimeric com-
plexes of the type [Rh(µ-Cl)(CO)(phosphine)]2 with loss
of CO. The stability of 2 probably results from the
The monometallic structure and cis geometry of 2
were suggested by the presence of two carbonyl reso-
2
nances in the 13C NMR spectrum that exhibit J PC
coupling constants of 16 and 155 Hz, respectively.20a
These structural features were confirmed by an X-ray
analysis19 performed on single crystals obtained from a
saturated diethyl ether solution of 2 at -80 °C. The
molecular structure of 2 is shown in Figure 1 along with
the pertinent metric parameters.
(14) The propensity of bis(diisopropylamino)phosphines to react with
[Rh(CO)2(µ-Cl)]2 strongly depends on the steric constraints of the third
substituent of the phosphorus.15 An excess of rhodium complex allows
the coordination equilibration to be displaced and, thus, to complete
the conversion of 1.
(15) Dyer, P. W.; Fawcett, J .; Hanton, M. J .; Kemmitt, R. D. W.;
Padda, R.; Singh, N. J . Chem. Soc., Dalton Trans. 2003, 104.
(16) To an ether solution (5 mL) of [o-(trifluoromethyl)phenyl][bis-
(diisopropylamino)phosphino]diazomethane (1; 0.12 mmol) was added
an ether solution (2 mL) of tetracarbonylbis(µ-chloro)dirhodium(I) ([Rh-
(CO)2(µ-Cl)]2; 0.12 mmol) at -50 °C. After the mixture was stirred for
30 min at this temperature, complex 2 was obtained in quantitative
yield (according to 31P NMR spectroscopy). Orange crystals of 2 (38
mg, 52%) were obtained by cooling the ether solution to -80 °C. Mp:
75 °C dec.
(19) Crystal data for 2 and 3 are as follows. 2: orthorhombic, space
group P212121; T ) 173 K; a ) 11.377(2) Å, b ) 11.556(2) Å, c )
20.805(3) Å, V ) 2735.2(6) Å3, Z ) 4, R1 (I > 2σ(Ι)) ) 0.0439, wR2 (all
data) ) 0.0755 for 3930 unique reflections, 316 parameters, GOF )
0.999. 3: triclinic, space group P1h; T ) 173 K; a ) 9.046(2) Å, b )
9.341(2) Å, c ) 21.629(4) Å, R ) 80.909(3)°, â ) 83.124(4)°, γ )
82.532(4)°, V ) 1780.2(5) Å3, Z ) 2, R1 (I > 2σ(Ι)) ) 0.0530, wR2 (all
data) ) 0.1181 for 5049 unique reflections, 491 parameters, GOF )
0.984. Data for both structures were collected at low temperatures
using an oil-coated shock-cooled crystal on a Bruker-AXS CCD 1000
diffractometer with graphite-monochromated Mo KR (λ ) 0.710 73 Å)
radiation. The structures were solved by direct methods using SHELXS-
9726 and refined with all data on F2 using SHELXL-97.27 All non-
hydrogen atoms were treated anisotropically. The hydrogen atoms were
geometrically idealized and refined using a riding model. Crystal-
lographic data (excluding structure factors) have been deposited with
the Cambridge Crystallographic Data Centre as Supplementary
Publication Nos. CCDC-203087 (2), 203088 (3), and 203089 (3′). Copies
of the data can be obtained free of charge on application to the CCDC,
12 Union Road, Cambridge CB2 1 EZ, U.K. (fax, (+44)1223-336-033;
email, deposit@ccdc.cam.ac.uk).
(20) (a) Rotondo, E.; Battaglia, G.; Giordano, G.; Cusmano, F. P. J .
Organomet. Chem. 1993, 450, 245. (b) Uguagliati, P.; Deganello, G.;
Belluco, U. Inorg. Chim. Acta 1974, 9, 203. (c) Steele, D. F.; Stephenson,
T. A. J . Chem. Soc., Dalton Trans. 1972, 2161.
(21) (a) Orpen, A. G.; Brammer, B.; Allen, F. H.; Kennard, O.;
Watson, D. G.; Taylor, R. J . Chem. Soc., Dalton Trans. 1989, S1. (b)
Allen, F. H.; Kennard, O. 3D Search and Research Using the
Cambridge Structural Database. Chem. Design Automation News 1993,
8(1), 1, 31-37. (c) Dyer, P. W.; Fawcett, J .; Hanton, M. J . Unpublished
results.
(17) To an ether solution (5 mL) of [o-(trifluoromethyl)phenyl][bis-
(diisopropylamino)phosphino]diazomethane (1; 0.12 mmol) was added
an ether solution (2 mL) of tetracarbonylbis(µ-chloro)dirhodium(I) ([Rh-
(CO)2(µ-Cl)]2; 0.12 mmol) at room temperature. After the mixture was
stirred for 30 min at this temperature, 1 mL of pentane was added
and yellow crystals of 3 (60 mg, 64%) were obtained by cooling the
solution to -20 °C. Mp: 63 °C dec.
(18) Selected spectroscopic data are as follows. For 2: 19F (376.5
MHz, C7D8, 223 K) δ 17.3; 31P (162 MHz, C7D8, 223 K) δ 118.1 (d, 1J PRh
1
) 162 Hz); 13C{1H} (100.6 MHz, C7D8, 223 K) δ 51.2 (dd, J PC ) 32
2
2
1
Hz, J CRh ) 7 Hz, CN2), 181.8 (dd, J PC ) 155 Hz, J CRh ) 71 Hz, CO),
181.8 (dd, J PC ) 16 Hz, J CRh ) 71 Hz, CO). For 3a : 31P (162 MHz,
2
1
C7D8, 223 K) δ 126.8 (d, J PRh ) 220 Hz); 13C{1H} (100.6 MHz, C7D8,
1
1
2
1
223 K) δ 52.5 (dd, J PC ) 6 Hz, J CRh ) 10 Hz, CN2), 179.4 (d, J CRh
)
1
2
76 Hz, CO), 180.1 (d, J CRh ) 76 Hz, CO), 183.8 (dd, J PC ) 16 Hz,
1J CRh ) 87 Hz, CO). For 3b: 31P (162 MHz, C7D8, 223 K) δ 127.8 (d,
1J PRh ) 224 Hz).

1360 Organometallics, Vol. 22, No. 7, 2003
Communications
shortened compared to that determined for 2 (3, 2.237(2)
Å; 2, 2.367(2) Å); the two Rh1-Cl bond distances are
inequivalent, as expected (Rh-Cl(cis to P) ) 2.408(2)
Å and Rh-Cl(trans to P) ) 2.435(2) Å). As in 2, the aryl
ring of the ligand is orientated perpendicularly to the
square coordination plane of Rh1. Thus, it seems
reasonable to suggest that the bulky o-trifluoromethyl
group might impede rotation around the Cipso-Cdiazo
bond, giving rise to two conformers which differ as a
consequence of syn and anti orientations of this CF3
group toward the coordination plane about the second
rhodium center. Although dinuclear monophosphine
complexes analogous to 3 have been postulated as
transient intermediates in the reaction of phosphines
with tetracarbonylbis(µ-chloro)dirhodium(I), their struc-
tures have not been unambiguously determined.20a
The incorporation of 1 into the coordination sphere
of rhodium without diazo decomposition is contrary to
the reactivity often associated between diazo compounds
and transition-metal salts. In many cases, even a
catalytic amount of a transition-metal complex induces
dinitrogen elimination,23 only a very few complexes
featuring an intact diazo moiety having been isolated.24
The coordination of the (R-diazo)phosphine 1 via the
phosphorus lone pair in preference to reaction at the
diazo fragment is even more surprising, considering the
presence of the bulky diisopropylamino groups.25 Fur-
ther studies into the coordination of (R-diazo)phosphines
and on the use of the ensuing complexes as precursors
for (phosphino)carbene complexes are currently in
progress.
F igu r e 2. Molecular structure of 3 in the solid state. For
clarity the hydrogen atoms are omitted and the isopropyl
groups are simplified. Selected bond lengths (Å) and angles
(deg): P1-C1 ) 1.831(7), P1-Rh1 ) 2.237(2), P1-N3 )
1.689(6), P1-N4 ) 1.686(6), Rh1-Cl1 ) 2.435(2), Rh1-
Cl2 ) 2.408(2), Rh1-C21 ) 1.817(8); P1-C1-N1 ) 115.5(5),
P1-C1-C2 ) 125.7(5), N1-C1-C2 ) 118.3(6), C1-P1-
N3 ) 104.6(3), C1-P1-N4 ) 100.2(3), C1-P1-Rh1 )
115.0(2), P1-Rh1-Cl1 )175.75(8), P1-Rh1-Cl2 )93.86(8),
P1-Rh1-C21 ) 94.1(2).
elevated basicity and poor π-acceptance of the phospho
rus center of the bis(dialkylamino)phosphine moiety
bound to rhodium.15 Significantly, there is no interaction
between the metal center and the diazo moiety.
The observation of three sets of signals for the
carbonyl groups in the 13C NMR spectrum for the major
conformer of 3 was in favor of a dinuclear complex. The
exact structure of both conformers was revealed by an
X-ray diffraction study carried out on single crystals
obtained from a diethyl ether/pentane solution of 3 at
-20 °C. Complex 3 is a dinuclear rhodium(I) complex
with two bridging chlorine atoms and a single coordi-
nated (R-diazo)phosphine (Figure 2).22
Ack n ow led gm en t. Thanks are due to the Centre
National de la Recherche Scientifique, Universite´ Paul
Sabatier, the University of Leicester, and the University
of California at Riverside for financial support of this
work.
Su p p or tin g In for m a tion Ava ila ble: Text giving selected
spectroscopic data for 2 and 3 and tables giving X-ray crystal-
lographic data for 2 and 3. This material is available free of
charge via the Internet at http://pubs.acs.org.
The low-temperature 31P NMR spectrum of a single
crystal of 3 revealed that the same 4/1 ratio of conform-
ers was present in the solid state and in solution. The
two conformers differ in the geometry associated with
the Rh1-Cl1-Cl2-Rh2 plane, with the major con-
former adopting a “butterfly” arrangement about the
Cl1-Cl2 vector, while for the minor conformer Rh1, Cl1,
Cl2, and Rh2′ are near coplanar. As for 2, the Rh1 center
of 3 adopts a distorted-square-planar geometry (∑angles
) 366.16°), the Rh1-P bond distance in 3 being slightly
OM0210558
(23) Doyle, M. P.; McKervey, M. A. and Ye, T. Modern Catalytic
Methods for Organic Synthesis with Diazo Compounds; Wiley: New
York, 1998; Chapter 2, pp 61-111.
(24) (a) Sutton, D. Chem. Rev. 1993, 93, 995. (b) Mizobi, Y.; Ishii,
Y.; Hidai, M. Coord. Chem. Rev. 1995, 139, 281. (c) Dartiguenave, M.;
Menu, M. J .; Deydier, E.; Dartiguenave, Y.; Siebald, H. Coord. Chem.
Rev. 1998, 178-180, 623.
(25) Diazo compounds react with transition-metal fragments either
by the carbon or by the terminal nitrogen atoms, with or without
nitrogen elimination: Diazo Chemistry; Zollinger, H., Ed.; VCH:
Weinheim, Germany, 1995; Vol. 2, pp 439-454.
(26) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467.
(27) Sheldrick, G. M. SHELXL-97: Program for Crystal Structure
Refinement; University of Go¨ttingen, Go¨ttingen, Germany, 1997.
(22) An investigation of the molecular structure of the mesityl
analogue of 3 has been undertaken, and all relevant crystallographic
data are reported in the Supporting Information. An geometry identical
with that observed for 3 was determined. It should be noted that the
mesityl derivative 3′ was considerably more reactive than 3, making
its characterization much more difficult.