The reaction of mixtures of [Rh4(CO)12] and triphenylphosphite with carbon monoxide or syngas as studied by high-resolution, high-pressure NMR spectroscopy.
The fragmentation and redistribution reactions of [Rh4(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, [Rh4(CO)9{P(OPh)3}3] fragments to give mainly [Rh2(CO)6{P(OPh)3}2]; [Rh4(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[Rh4(CO)10{P(OPh)3}2] is found to be pressure-dependent giving predominantly [Rh2(CO)6{P(OPh)3}2] at low CO pressure (1-40 bar), and increasing amounts of [Rh2(CO)7{P(OPh)3}] at higher (40-80 bar) pressure. Using Syngas (CO : H2 (1 : 1)) instead of CO in the above fragmentations, homolytic addition of H2 to the dimer [Rh2(CO)6{P(OPh)3}2] to give [RhH(CO)3{P(OPh3}] 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.
Department of Chemistry, University of Liverpool, Oxford Street, Liverpool L69 7ZD, England, UK.
Gillian
G
Overend
Jonathan A
JA
Iggo
Brian T
BT
Heaton
Robin
R
Whyman
D002248:Carbon Monoxide / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D009942:Organometallic Compounds / Q000737:chemistry; D017905:Phosphites / Q000737:chemistry*; D011312:Pressure; D012238:Rhodium / Q000737:chemistry*
D009942:Organometallic Compounds; D017905:Phosphites; D002248:Carbon Monoxide; D012238:Rhodium