NOTE pubs.acs.org/Organometallics
Improved Syntheses for the Compounds [(1,5-COD)M(μ-O2C8H15)]2 (M = Ir, Rh) Kuang-Hway Yih,† William M. Alley,‡ and Richard G. Finke*,‡ † ‡
Department of Applied Cosmetology, Hungkuang University, Taichung, Taiwan 433 Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, United States
bS Supporting Information ABSTRACT: An improved synthesis procedure is reported for the compounds [(1,5-COD)M(μ-O2C8H15)]2 (COD = cyclooctadiene, M = Ir (1), Rh (2), O2C8H15 = 2-ethylhexanoate); that procedure provides a more effective method of product isolation resulting in easier crystallization, and 76% and 85% yields of pure, crystalline 1 and 2, respectively. The improved synthesis and simplified crystallization of high-purity 1 and 2 are significant, not only because 1 is useful as a model for industrial Ziegler-type hydrogenation precatalysts, but also because 1 and 2 are potentially useful in a variety of other areas.
recent paper1 describes the synthesis and characterization of the compounds [(1,5-COD)M(μ-O2C8H15)]2 (COD = cyclooctadiene, M = Ir (1), Rh (2), O2C8H15 = 2-ethylhexanoate) as models of industrial Co and Ni Ziegler-type hydrogenation precatalysts.1 3 For that work, it is important to have definitively characterized, high-purity precatalyst materials readily available— characterization of 1 and 2 previously included single-crystal X-ray crystallographic structure determinations (Figure 1). Additionally, it was noted therein1 that both 1 and 2 have potential in other areas,4 including film deposition on semiconductor devices, for which the synthesis and preliminary characterization of 1 was described previously.5 In a broader sense, complexes 1 and 2 are valuable members of the class of alkanoate complexes of M(1,5COD)+ (M = Ir, Rh) typified by the classic acetate prototypes [(1,5-COD)Ir(μ-OAc)]2 and [(1,5-COD)Rh(μ-OAc)]2.6 Herein we report improved synthetic procedures for 1 and 2 and the resulting simplification in isolating 1 and 2 in pure crystalline form. In addition, the improved synthesis procedure has led to an improved yield of 1: 76% versus the 61% yield achieved via the previous synthetic approach.1 The improved synthesis and simplified crystallization procedures are significant, not only because of the demonstrated usefulness of 1 as a model for study of the industrial Ziegler-type hydrogenation catalysts,3 but also because of the potential usefulness of both 1 and 2 in other areas and in important industrial applications.4,5
A
’ RESULTS AND DISCUSSION The prior synthetic approach for [(1,5-COD)Ir(μ-O2C8H15)]2 involved an extensive air-free hexane/water extraction to remove Bu3NHCl, after the initial combination of [(1, 5-COD)Ir(μ-Cl)]2 starting material and a mixture of Bu3N and 2-ethylhexanoic acid in acetone.1,5 If the air-free hexane/water extraction is not rigorously performed, residual Bu3NHCl prevents easy crystallization. 1 Furthermore, even when the r 2011 American Chemical Society
air-free hexane/water extraction is performed rigorously, crystallization still requires careful, extremely slow cooling over dry ice, giving a 61% yield of 1 in pure, crystalline form. 1 The syntheses described herein for both 1 and 2 involve reacting the [(1,5-COD)M(μ-Cl)]2 starting material (M = Ir, Rh) with sodium 2-ethylhexanoate (Scheme 1). The crude product in powdered form is then collected by filtration and washed with water to remove NaCl and residual sodium 2-ethylhexanoate. The improved syntheses are described in detail in the Experimental Section. The yield of the pure products as powders is 97% for both 1 and 2. Overall, the synthesis and isolation of 1 and 2 is simplified and more effective, which in turn facilitates crystallization of 1 and 2 and results in overall yields of 76% and 85% for crystalline 1 and 2, respectively. Characterization of 1 and 2 synthesized according to the improved procedure is accomplished by 1H and 13C NMR and mass spectrometry (see the Supporting Information for spectra). Crystal space group and lattice parameter determinations via singlecrystal X-ray diffractometry further confirm the identities of 1 and 2 (Table 1). In short, these characterization results verify that the improved syntheses reported herein do indeed give the target compounds, [(1,5-COD)M(μ-O2C8H15)]2 (M = Ir, Rh). In short, improved syntheses, isolation and crystallization procedures for the preparation of pure forms of the valuable synthons 1 and 2 have been reported. In that sense, the primary purpose of this Note is to provide the detailed synthetic procedures which follow.
’ EXPERIMENTAL SECTION General Procedures. Many of the experimental considerations are the same as those reported previously.1 Specifically, all air-free Received: April 16, 2011 Published: August 23, 2011 5068
dx.doi.org/10.1021/om2003249 | Organometallics 2011, 30, 5068–5070
Organometallics
NOTE
Figure 1. Single -crystal X-ray structures determined previously for 1 and 2. Thermal ellipsoids are shown at 30% probability (hydrogen atoms are not shown). Reproduced from ref 1 with permission, copyright 2009 American Chemical Society.
Scheme 1. Improved Synthesis and Crystallization Procedure for [(1,5-COD)M(μ-O2C8H15)]2 (M = Ir (1), Rh (2))
Table 1. Crystal Space Group and Lattice Parameters of Compounds 1 and 2 Obtained from the Synthesis Procedure Reported in Ref 1 (Previous) and from the Improved Synthesis Procedure Reported Herein (Current) compd,
space
synthesis
group
a (Å)
b (Å)
c (Å)
β (deg) 108.408(2)
1, previous
P21/n
15.7748(5)
9.8962(3)
20.8847(7)
1, current
P21/n
15.786(10)
9.918(7)
20.874(14)
108.301(12)
2, previous
P21/n
15.7608(4)
9.9032(3)
20.8259(5)
108.527(1)
2, current
P21/n
15.784(10)
9.938(7)
20.887(15)
108.381(14)
manipulations were performed either under N2 in a Vacuum Atmospheres drybox, where oxygen levels were monitored by a Vacuum Atmospheres O2-level monitor and maintained at e5 ppm, or under Ar (General Air, 99.985%) on a Schlenk line. All glassware was oven-dried at 160 °C before use and cooled either under vacuum or under N2 in the drybox. Solvents, compounds, and glassware were stored in the drybox. The starting materials [(1,5-COD)M(μ-Cl)]2, where M = Ir, Rh (Strem Chemicals; Ir 99%, Rh 98%), and sodium 2-ethylhexanoate (Aldrich, 97%) were used as received. Prior to storage in the drybox, acetone (Burdick and Jackson, water content
