SUBSTITUTION REACTIONS OF MOLYBDENUM HEXACARBONYL AND THE USE OF INFRARED SPECTROSCOPY AS A STRUCTURAL TOOL
Substitution Reactions of Molybdenum Hexacarbonyl and the Use of Infrared Spectroscopy as a Structural Tool
01-09-2011
Abstract
A variety of metal carbonyl derivatives can be synthesized by substitution reactions. In this experiment two geometric [Mo(CO)4(PPh3)2] isomers A and B were synthesized and their molecular geometries were determined by means of infrared spectroscopy. Isomer A was synthesized first by reacting [Mo(CO)6] with sodium borohydride employed as a reducing agent and triphenylphosphine. A satisfactory 90 % yield was obtained for this isomer. From Isomer A produced, 0.502 g was taken and then used to synthesize Isomer B which was obtained at a yield of 50 %. The infrared spectra measured showed an active CO bands with frequencies: 1866, 1888, 1920 and 2025 cm-1. In Isomer B only one υ(CO) mode was observed with frequency of 1880 cm-1, hence Isomer can considered as a cis-isomer and isomer B a trans-isomer.
Results
Isomer A
Isomer B
Isomer A was obtained as a very fine, light yellow, crystalline powder.
Mass of Isomer A Produced: 1.155 g
Mass of [Mo(CO)6] Used: 0.5020 g n = m/Mr = 0.5020 g /264.00 g/mol = 1.890×10-3 mol
Reaction 1: Synthesis of cis-Mo(CO)4(PPh3)2
Mo(CO)6 + 2 PPh3 → cis-Mo(CO)4(PPh3)2+2 CO
[Mo(CO)6] reacts with PPh3 in a ratio of 1:2. Thus [Mo(CO)6] is the Limiting reagent.
[Mo(CO)6] reacts with Mo(CO)4(PPh3)2 in a 1:1 Stoichiometric ratio. Thus:
Expected /Theoretical Yield of Isomer A: n= 1.890×10-3 mol m = n×Mr = 1.890×10-3 X 732.5569 =1.385 g
% Yield = (Mass Produced/Theoretical Mass) × 100 = (1.155 g ÷ 1.358 g) × 100 = 90 %
Isomer B was obtained as a fine, pale yellow powder.
Mass of Isomer B Produced: 0.147 g
Mo(CO)4(PPh3)2 (Isomer A) → Mo(CO)4(PPh3)2 (Isomer B)
Since isomer A and B are geometric isomers, the data from isomer A can be used for isomer B. Isomer A and B react in
01-09-2011
Abstract
A variety of metal carbonyl derivatives can be synthesized by substitution reactions. In this experiment two geometric [Mo(CO)4(PPh3)2] isomers A and B were synthesized and their molecular geometries were determined by means of infrared spectroscopy. Isomer A was synthesized first by reacting [Mo(CO)6] with sodium borohydride employed as a reducing agent and triphenylphosphine. A satisfactory 90 % yield was obtained for this isomer. From Isomer A produced, 0.502 g was taken and then used to synthesize Isomer B which was obtained at a yield of 50 %. The infrared spectra measured showed an active CO bands with frequencies: 1866, 1888, 1920 and 2025 cm-1. In Isomer B only one υ(CO) mode was observed with frequency of 1880 cm-1, hence Isomer can considered as a cis-isomer and isomer B a trans-isomer.
Results
Isomer A
Isomer B
Isomer A was obtained as a very fine, light yellow, crystalline powder.
Mass of Isomer A Produced: 1.155 g
Mass of [Mo(CO)6] Used: 0.5020 g n = m/Mr = 0.5020 g /264.00 g/mol = 1.890×10-3 mol
Reaction 1: Synthesis of cis-Mo(CO)4(PPh3)2
Mo(CO)6 + 2 PPh3 → cis-Mo(CO)4(PPh3)2+2 CO
[Mo(CO)6] reacts with PPh3 in a ratio of 1:2. Thus [Mo(CO)6] is the Limiting reagent.
[Mo(CO)6] reacts with Mo(CO)4(PPh3)2 in a 1:1 Stoichiometric ratio. Thus:
Expected /Theoretical Yield of Isomer A: n= 1.890×10-3 mol m = n×Mr = 1.890×10-3 X 732.5569 =1.385 g
% Yield = (Mass Produced/Theoretical Mass) × 100 = (1.155 g ÷ 1.358 g) × 100 = 90 %
Isomer B was obtained as a fine, pale yellow powder.
Mass of Isomer B Produced: 0.147 g
Mo(CO)4(PPh3)2 (Isomer A) → Mo(CO)4(PPh3)2 (Isomer B)
Since isomer A and B are geometric isomers, the data from isomer A can be used for isomer B. Isomer A and B react in
References: 1. G.I Brown “Introduction to Inoganic Chemistry”; Longman Press, 4th edition. 2. “Vogel’s Qualitative Inorganic Analysis” Longman Press, 6th edition.