The experiment intends to investigate the cis-trans isomerization that Mo(CO)4(PPh3)2. In stimulate to acquire these compounds, molybdenum hexacarbonyl is an initial reacted through piperidine (pip), which leads to the development of cis-Mo(CO)4(pip)2. The ligand exchange v triphenylphosphine at short temperature (40 oC, boil dichloromethane) affords the cis-Mo(CO)4(PPh3)2. At elevated temperature (110 oC, boiling toluene), this compound is converted into the trans-isomer. Thus, the cis isomer deserve to be pertained to as the kinetic product, when the trans isomer is the thermodynamic product. The infectious diseases worldwide isomer can additionally be derived directly through the reaction of Mo(CO)6 through two equivalents of triphenylphosphine in a microwave reaction, most likely since the reaction temperature is higher in the microwave reaction donate the thermodynamic product.

You are watching: Mo(co)4(pph3)2


*
*
*

cis-Mo(CO)4(pip)2
cis-Mo(CO)4(PPh3)2
trans-Mo(CO)4(PPh3)2

Kinetic studies have presented that the cis-Mo(CO)4(PR3)2 compounds shed the phosphine ligand at really different rates. When phosphine ligands with small cone angles space lost an extremely slowly, phosphine ligands with huge cone angles are lost an extremely fast. This step determines the in its entirety rate for the isomerization because the initial step appears to it is in the dissociation the the phosphine ligand leader to Mo(CO)4(PPh3). The mean Mo-P bond ranges seem to it is in a an excellent measure because that the dissociation kinetics together well.

PR3Cone angleAverage Mo-P distanceRate that PR3 loss native Mo(CO)4(PR3)295Mo-NMRshift
PPhMe2122o252.9 pmvery slowly-1637 ppm (cis, CH2Cl2)-1655 ppm (trans, CH2Cl2)
P(OPh)3128o244.3 pmvery slowly-1754 ppm (cis, CH2Cl2)-1792 ppm (trans, CH2Cl2)
P(n-Bu)3132o255.2 pmvery slowly-1742 ppm (cis, CH2Cl2)-1741 ppm (trans, toluene)
PPh3145o257.7 pmfast -1556 ppm (cis, CH2Cl2)
PCy2Ph~162overy fast
PCy3170o265.5 pm???-1765 ppm (trans, CH2Cl2)
Average Mo-N distance
Piperidine234.5 pm-1075 ppm (cis, CH2Cl2)
Pyrrolidine-1140 ppm (cis, CH2Cl2)
Pyridine~225 ppm-1046 ppm (cis, CH2Cl2)

Phosphite ligand (i.e., P(OPh)3) screen a stronger bond 보다 phosphine ligands (i.e., PPh3). The Mo-P bond ranges are much shorter and the Mo-P coupling constants are higher as well: cis-Mo(CO)4(P(OPh)3)2: 250 Hz; cis-Mo(CO)4(PPh3)2: 140 Hz.

Experiment

Safety: Molybdenum hexacarbonyl and also its derivative are very toxic and volatile. Make sure to take care of the compound in the hood. Toluene is flammable and also dichloromethane is a doubt carcinogen. Every procedures need to be carry out in the hood.

a. Cis-Mo(CO)4(pip)2

Note the the piperidine needs to be more than likely dried over potassium hydroxide first to remove the water and oxidation products.

While the is not really required, the reaction should be lugged out under the exemption of wait to alleviate the oxidation products. Throughout the reflux, a bright yellow precipitate will form. It is really important come filter the solution while the is still warm in order to store the Mo(CO)4(pip) in solution.

b. Cis-Mo(CO)4(PPh3)2

While the is no really required, the reaction have to be brought out under the exemption of waiting to reduce the oxidation products. Cis-Mo(CO)4(pip)2 is reacted through 2.2 equivalents the triphenylphosphine in dry, boiling dichloromethane. After ~ the refllux, the volume that the solution needs to be reduced to ~20 mL prior to methanol is added. Upon warehouse in one ice-bath, light yellow crystals form.

c. Trans-Mo(CO)4(PPh3)2

While the is not really required, the reaction have to be lugged out under the exclusion of air to mitigate the oxidation products. Cis-Mo(CO)4(PPh3)2 is refluxed in toluene for 30 minutes. After ~ cooling the mixture, chloroform is included to save the unreacted cis isomer in solution. The mixture is filtered and methanol is included to the filtrate. Top top cooling, the off-white (or an extremely pale yellow) heavy is formed.

Characterization

a. Infrared spectroscopy

The infrared spectrum room aquired top top the spectrometer in YH 6076 (ATR setup). Make sure to obtain an development of the carbonyl range.

See more: Trying Hard To Look Like Gary Cooper, If You'Re Dressed Like A

b. 13C- and also 31P-NMR spectrum

The solvent right here is CDCl3. Both measurements have the right to be collection up with each other on the 400 MHz autosampler because this spectrometer possesses a quad probe that have the right to measure 1H, 13C, 19Fand 31P-NMR spectra. Make certain to monitor the directions for preparing NMRsamples. Make certain to monitor the directions provided by the staff in the NMRlab (i.e., Dr. Strouse, Dr. Taylor, etc.).

c. 95Mo-NMR spectrum

The samples have to be a saturated equipment of the link in dry dichloromethane or dry toluene. Make sure to purge that the NMRtube is dry and purged v nitrogen or argon front placing the sample in it. The samples need to be prepared and measured automatically in bespeak to have actually a opportunity to watch a signal. The solution should be as focused as possible.

Hints come pre-lab questionsad 2: What governs how many signals and appear in the NMRspectrum?What determines how the signal appears?ad 4: How have the right to one rationalize various bond street in coordination compounds?ad 7: which geometric isomers are possible for MX3L3? What determines with of this isomers is favored?