The reaction of mixtures of [Rh 4 (CO) 12 ] and triphenylphosphite with carbon monoxide or syngas as studied by high‐resolution, high‐pressure NMR spectroscopy

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. Copyright © 2008 John Wiley & Sons, Ltd.