Organometallics 2001, 20, 481-484
481
Rea ction of Dia zoa lk a n es w ith Ir on P h osp h in e
Com p lexes Affor d s Novel P h osp h a zin e Com p lexes
J anis Louie and Robert H. Grubbs*
The Arnold and Mabel Beckman Laboratories of Chemical Synthesis,
Division of Chemistry and Chemical Engineering, California Institute of Technology,
Pasadena, California 91125
Received J uly 10, 2000
The crystal structures of novel products from the insertion of various diazoalkanes into
the iron-phosphorus bond in FeCl2L2 (L ) phosphine) complexes are presented. Specifically,
ethyl diazoacetate and diphenyldiazomethane reacted with FeCl2(PMe2Ph)2 to afford
FeCl2[N(PMe2Ph)NC(H)CO2Et]2 (1) and FeCl2[N(PMe2Ph)NCPh2] (2). Interestingly, ethyl
diazoacetate inserted into both iron phosphine bonds of FeCl2(dippe)2 to afford the seven-
membered metallacycle FeCl2{N[NC(H)CO2Et]P(iPr)2CH2CH2P(iPr)2N[NC(H)CO2Et]}2 (3).
In tr od u ction
complex 1, although in reduced yield. A characteristic
absorption at 1560 cm-1, indicative of a ν(CdN) stretch,
was observed in the infrared spectrum (KBr pellet) of
1. Crystals suitable for X-ray analysis were obtained by
slow diffusion of pentane into a saturated solution of 1
in benzene at room temperature (Figure 1; crystal-
lographic data and selected bond distances and angles
are given in Tables 1 and 2, respectively). The crystal
structure unambiguously indicated that the ethyl di-
azoacetate inserted into both iron-phosphine bonds.
Analysis of the structure revealed two geometries for
1; each structure differed only by a slight rotation of
the ethyl group. Complex 1 adopted a distorted-
tetrahedral geometry with angles ranging from 100.32-
(10) to 120.63(5)°. Notably, the Cl1-Fe-Cl2 angle in 1
(120.63(5)°) is substantially larger than it is in FeCl2-
(PtBu2Me)2 (110.97(3)°),7 which may be due to the
increased steric bulk of the PtBu2Me ligands relative to
the phosphazine ligands. The Cl1-Fe-Cl2 angle re-
sembles the Br-Fe-Br angle in FeBr2(PEt3)2 (121.9-
(1)°).8 Fe-N bond lengths (2.088(4) Å) are as expected
for a single bond, indicating that a dative bond formed
between the N1 and the metal center. As expected, the
N1-N2-C1 linkage adopted a geometry similar to a
free phosphazine rather than a free diazoacetate. First,
the N-N bond (1.391(5) Å) resembles the N-N bond in
benzophenone triphenylphosphazine (1.390 Å)9 and is
considerably longer than the N-N bond in a free diazo
compound (1.12 Å).1 Second, the N-N-C angle is bent
(116.0(3)°) rather than linear, as it is in free diazo
compounds. In classical η1-bound diazo complexes, the
M-N-N angle deviates only marginally from linearity
(153-177°).1 In complex 1, however, this angle is much
smaller (127.6(3)°), suggesting the hybridization of N1
changed from sp to sp2.
Diazoalkanes have proven to be important synthetic
reagents in organometallic chemistry.1,2 While diazoal-
kanes are known to coordinate to the metal center in
either an η1 or η2 fashion,3 in many cases the R-carbon
of the diazoalkane undergoes nucleophilic attack by the
metal center. Subsequent release of dinitrogen leads to
the formation of a transition-metal carbene complex.
The metal alkylidene may be generated as a transient
intermediate along a reaction pathway or may be
formed as a stable and isolable complex.4 In our at-
tempts to synthesize an iron analogue to the metathesis
catalyst PCy3Cl2RudCHPh, we examined the reactivity
of diazoalkanes with iron chlorides. To our surprise, the
diazoalkane inserted into the iron-phosphine bond
instead of releasing dinitrogen and forming the expected
iron alkylidene. While few examples of diazoalkanes
inserting into various metal-ligand systems exist,2 only
one report involves insertion into a metal-phosphide
bond to provide a zirconocene phosphamine complex.5
To the best of our knowledge, this is the first example
of the formation of a phosphazine complex via insertion
of a diazoalkane. In fact, metal phosphazine complexes
are rather scarce, although phosphazines have been
known for some time.6 Herein we report a series of
insertion products and their structural characterization.
Resu lts a n d Discu ssion
Treatment of FeCl2(PMe2Ph)2 with 2 equiv of ethyl
diazoacetate in benzene afforded FeCl2[N(PMe2Ph)NC-
(H)CO2Et]2 (1) in 82% yield. Addition of only 1 equiv of
ethyl diazoacetate to FeCl2(PMePh2)2 still produced
(1) Putala, M.; Lemenovskii, D. A. Russ. Chem. Rev. (Engl. Transl.)
1994, 63, 197.
(2) Mizobe, Y.; Ishii, Y.; Hidai, M. Coord. Chem. Rev. 1995, 139, 281.
(3) Dartiguenave, M.; Menu, M. J .; Deydier, E.; Dartiguenave, Y.;
Siebald, H. Coord. Chem. Rev. 1998, 178-180, 623.
(4) Doyle, M. P. 5.1 Transition Metal Carbene Complexes: Cyclo-
propanation. In Comprehensive Organometallic Chemistry II; Elsevi-
er: New York, 1995; Vol. 12, pp 388-419, and references therein.
(5) Hey, E.; Weller, F. Chem. Ber. 1988, 121, 1207.
In analogy to the formation of complex 1, reaction of
FeCl2(PMe2Ph)2 with 1 equiv of diphenyldiazomethane
(7) Renkema, K. B.; Ogasawara, M.; Streib, W. E.; Huffman, J . C.;
Caulton, K. G. Inorg. Chim. Acta 1999, 317, 226.
(8) Snyder, B. S.; Holm, R. H. Inorg. Chem. 1988, 27, 2339.
(9) Bethell, D.; Brown, M. P.; Harding, M. M.; Herbert, C. A.;
Khodaei, M. M.; Rios, M. I.; Woolstencro, K. Acta Crystallogr., Sect. B
1992, 48, 683.
(6) Staudinger, H.; Meyer, J . Helv. Chim. Acta 1919, 2, 619.
10.1021/om000586y CCC: $20.00 © 2001 American Chemical Society
Publication on Web 01/06/2001
Louie, Janis
