Synthesis and characterization of two novel cobalt (II) phosphine complexes: crystal structures of [CoCl 3 ( 2 CH 2 2 H)] and [Co(N 3 ) 2 ( 2 CH 2 2 )]. = cyclohexyl, C 6 H 11 ax ajireck, Charles Kriley (Sigma Xi advisor), Jacob Tobolewski, Luke Kelvington, Stephan Cumming, Stefan Hershberger, Jason Link, Anthony Silverio, hillip Fanwick, Ian Rothwell ABSTRACT: The compound [CoCl 3 ( 2 CH 2 2 H)] was synthesized by the reaction of CoCl 2. 6H 2 plus dcpm (dcpm = bis(dicyclo-hexylphosphino)methane) and subsequently characterized by ER, UV-Vis, microanalysis, and X-ray crystallography to reveal a monomeric, four coordinate, thermochromic, and paramagnetic complex with a pseudo-tetrahedral geometry around the cobalt atom. f particular significance is the formation of a zwitterion in which the dangling phosphine adds a hydrogen atom to give the phosphorous atom a +1 formal charge; the first recorded example of a self-contained zwitterion of a cobalt complex. [Co(N 3 ) 2 ( 2 CH 2 2 )] The compound [Co(N 3 ) 2 ( 2 CH 2 2 )] was synthesized by the reaction of Co(N 3 ) 2. 6H 2 plus dcpm in a toluene/ methanol/methylene chloride mixture to yield a similar complex with a pseudo-octahedral geometry around the cobalt atom. INTRDUCTIN Various cyclohexyl phosphines (di-, tri-, and poly-), have in the past been either unavailable or difficult to synthesis. With the advent of advanced methods in chemical synthesis of cyclohexyl phosphines comes the possibility of an increased development of dinuclear transition metal chemistry. revious research by our group has shown dcpm, in particular, to be an effective ligand when added to nickle (II) chloride, forming the [NiCl 2 (dcpm)] complex in which the phosphine is bound in a bidentate fashion to the nickel center. Unlike its nickel counterpart, the cobalt complex [CoCl 3 ( 2 CH 2 2 H)] binds dcpm in a monodentate fashion to the cobalt center, leaving a dangling phosphine which then adds a hydrogen to give the phosphorous atom a +1 formal charge. nly a few complexes similar to [(Co(N 3 ) 2 ( 2 CH 2 2 )] have been found in the literature. Figure 1. The bonding modes of dcpm ligand to metal.
ATERIALS AND ETHDS reparation of [CoCl 3 ( 2 CH 2 2 H)]: To 50 ml of a methanol solution of CoCl 2. 6H 2 (0.246 g, 1.11 mmol) was added 50 ml of a toluene solution of dcpm (0.50 g, 1.22 mmol), stirred for 12 h and then stripped to dryness and dissolved in degassed methylene chloride (Scheme 1). The resulting blue solution was then placed in a freezer, which resulted in the formation of large blue blocks of pure product in high yield (0.5538 g, 99.2%). Scheme 1. Synthesis of [CoCl 3 ( 2 CH 2 2 H)] from CoCl 2. H 2 and dcpm. CoCl. dcpm/toluene 2 6H 2 methanol Cl Co Cl Cl H Analysis of [CoCl 3 ( 2 CH 2 2 H)]: The structure of [CoCl 3 ( 2 CH 2 2 H)] is of a cobalt d 7, +2 oxidation state with C s symmetry (Figure 2). UV-Vis studies of [CoCl 3 ( 2 CH 2 2 H)] show the concentration and thermal dependence of the complex in relation to the solutions absorbance (Figure 3). Uv-Vis temperature experiments of a 1:5 ratio of methanol to methylene chloride solution of [CoCl 3 ( 2 CH 2 2 H)] shows a reversible hypochromic/hyperchromic system. The relevant absorption occurs in the 500-750 nm run range where the spectral pattern is characteristic of that for a pseudo-tetrahedral Co(II) complex. The IR spectrum of [CoCl 3 ( 2 CH 2 2 H)] shows strong bands at 736 and 1127 cm -1, indicative of a tetracoordinated phosphine.
Figure 2. olecular structure of [CoCl 3 ( 2 CH 2 2 H)] with selected bond distances (Ǻ) and angles ( )
Absorbance Figure 3. Spectrum of methylene chloride solutions prepared from 0.01 [CoCl 3 ( 2 CH 2 2 H)] and varying solution temperatures 269 K (blue), 290.5 K (black), and 303 K (red) 2.50 2.00 1.50 1.00 0.50 0.00 500 550 600 650 700 750 800 Wavelength (nm) Table 1. Elemental analysis of C 22.5 H 49 Cl 5 Co 2 [CoCl 3 ( 2 CH 2 2 H)]. 1/2CH 2 Cl 2 %C %H %Cl % Anal. Calc. 49.54 7.84 22.97 10.02 Found 50.67 7.8 22.48 9.09
reparation of [Co(N 3 ) 2 ( 2 CH 2 2 )]: To 50 ml of a methanol solution of Co(N 3 ) 2. 6H 2 (0.234 g, 0.80 mmol) was added 50 ml of a toluene solution of dcpm (0.50 g, 1.22 mmol) then 10 ml of degased methylene chloride (Scheme 2). The solution was stirred for 12 hr, stripped to dryness, dissolved in methylene chloride and allowed to slowly evaporate to yield a small purple chunk of pure product in high yield (0.6024 g, 89.4%). Scheme 2. Synthesis of [Co(N 3 ) 2 ( 2 CH 2 2 )] from Co(N 3 ) 2. 6H 2 and dcpm. Co(N 3 ) 2. 6H 2 dcpm/toluene/ch 2 Cl 2 methanol N Co N Figure 4. olecular structure of [Co(N 3 ) 2 ( 2 CH 2 2 )] with selected bond distances (Ǻ) and angles ( )
Analysis of [Co(N 3 ) 2 ( 2 CH 2 2 )] The structure of[co(n 3 ) 2 ( 2 CH 2 2 )] is paramagnetic and contains a pseudo-octahedral geometry around the Co 5 core, the cobalt is a d 7 with a +2 oxidation state, and the point group symmetry is C s (Figure 4). The IR spectrum of [Co(N 3 ) 2 ( 2 CH 2 2 )] shows two strong bands at 724 and 1038 cm-1, indicative of a tetracoordinated phosphine. Two bands are seen due to the N= stretching vibrations consisting of a broad band at 1323 and 1623 cm -1. Table 2. Elemental analysis of C 25 H 46 CoN 2 7 2 [Co(N 3 ) 2 ( 2 CH 2 2 )]
DISCUSSIN AND CNCLUSINS A search through the literature seems to support our theory that the quaternization reaction between phosphine and methylene chloride provides the extra chlorine ion to the cobalt center in [CoCl 3 ( 2 CH 2 2 H)]. Since dcpm is a bidentate phosphine, the qauternization reaction between phosphine and methylene chloride will be both the source of the chloride ion and of the counter ion making the complex zwitterion. The complex [CoCl 3 ( 2 CH 2 2 H)] has been found to react with multiple reducing agents, though no products have been isolated as of yet. Further reactivity of [Co(N 3 ) 2 ( 2 CH 2 2 )] has yet to be investigated. FUTURE RJECTS Figure 5. Reactivity of other ligands dcpme Co(N 3 ) 2. 6H 2 NiCl 2. 6H 2 etallic brown crystals range crystals dcpme = CH 3 ACKNWLEDGEENTS I would like to thank Dr. Kriley for allowing me to be involved in all aspects of his research projects, and for 4 years of his patience and encouragement both in and out of academics. Thank you to Dave Richardson for both his lab work and for keeping research fun. I would like to express sincere gratitude to Dr. Rothwell for his generous input. Thanks also goes to the Grove City College Department of Chemistry and urdue University Department of Chemistry for the extensive use of their facilities.