The reaction of mixtures of [Rh4(CO)12] and triphenylphosphite with carbon monoxide or syngas as studied by high-resolution, high-pressure NMR spectroscopy
✍ Scribed by Gillian Overend; Jonathan A. Iggo; Brian T. Heaton; Robin Whyman
- Publisher
- John Wiley and Sons
- Year
- 2008
- Tongue
- English
- Weight
- 186 KB
- Volume
- 46
- Category
- Article
- ISSN
- 0749-1581
- DOI
- 10.1002/mrc.2314
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✦ Synopsis
The fragmentation and redistribution reactions of [Rh 4 (CO) 12-x {P(OPh) 3 } x ] (x = 1-4) with carbon monoxide have been studied using high-resolution, high-pressure NMR spectroscopy. Under the conditions of efficient gas mixing in a high-pressure NMR bubble column, [Rh 4 (CO) 9 {P(OPh) 3 } 3 ] fragments to give mainly [Rh 2 (CO) 6 {P(OPh) 3 } 2 ]; [Rh 4 (CO) 11 {P(OPh) 3 }] is also observed, implying redistribution of the phosphite ligand and/or recombination of the dimers to tetrameric clusters. Fragmentation of [Rh 4 (CO) 10 {P(OPh) 3 } 2 ] is found to be pressure-dependent giving predominantly [Rh 2 (CO) 6 {P(OPh) 3 } 2 ] at low CO pressure (1-40 bar), and increasing amounts of [Rh 2 (CO) 7 {P(OPh) 3 }] at higher (40-80 bar) pressure. Using Syngas (CO : H 2 (1 : 1)) instead of CO in the above fragmentations, homolytic addition of H 2 to the dimer [Rh 2 (CO) 6 {P(OPh) 3 } 2 ] to give [RhH(CO) 3 {P(OPh 3 }] and [RhH(CO) 2 {P(OPh) 3 } 2 ] is observed. The distribution of tetrameric species obtained is similar to that obtained under the same partial pressure of CO. On depressurisation/out-gassing of the sample, the original mixture of tetrameric clusters is obtained.