148906-52-9Relevant academic research and scientific papers
Kinetic studies of some substituted hexarhodium carbonyl clusters
Babij, Claudia,Farrar, David H.,Koshevoy, Igor O.,Poe, Anthony J.,Tunik, Sergey P.
, p. 116 - 122 (2007/10/03)
Reactions of the halides X- (X- = chloride, bromide or iodide) with the substituted cluster Rh6(CO)15(PPh 3) in oxygen-free chloroform lead to [Rh5(CO) 14(PPh3)]-, Rh(CO)2(PPh 3)2X and [Rh(CO)2X2]- in the molar ratios 2 : 1 : ～13, Oxidation by the solvent is assumed to lead to most of the Rh(I) product, and the stoichiometry for reactions with I - can be defined as 4Rh6(CO)15(PPh 3) + 27I- + 12CHCl3 → 2[Rh 5(CO)14(PPh3)]- + Rh(CO) 2(PPh3)2I + 13[Rh(CO)2I 2]- + 6C2H2Cl4 + 4CO + 12Cl-. This can be rationalized quite simply with the aid of a few generally justifiable assumptions. Rate constants for reactions with bromide increase to a limiting value with increasing [Br-] in a way that shows that breaking of one Rh-Rh bond, with an unusual closo to nido structural change, is rate determining. This opening of the cluster might be spontaneous or solvent induced. To complete the reaction, the bromide has to compete with the reverse nido to closo change. The same closo to nido change is also a major rate determining step for reactions with P(OPh)3 in oxygen-free solutions, and for reactions with bromide in oxygenated solutions in the presence of trifluoroacetic and some other acids. The limiting rates increase slightly with increasing basicity of the ligands P(p-XC6H 4)3 along the series X = F3C, Cl, F, H and MeO. Activation parameters for these reactions are reported.
31P and 13C NMR investigation of the system tetracarbonyldi-μ-chlorodirhodium(I)-tertiary phosphine
Rotondo, Enrico,Battaglia, Giovanni,Giordano, Giuseppe,Cusmano, Francesca Priolo
, p. 245 - 252 (2007/10/02)
13C and 31P NMR data at low temperature prompted us to characterize cis- (3) (3a, PR3 = PPh3; 3b, PR3 = PMe2Ph), as surprisingly stable products of the reaction between 2> (1) and tertiary phosphines in toluene (P : Rh = 1).Every attempt to isolate solid 3a led to the cis- and trans- halide-bridged dimers 2> (5a) and 6a which are formed from 3a by slow decarbonylation, a process which is greatly accelerated by the evaporation of the solvent under vacuum.The analogous reaction of 1 with dimethylphenylphosphinefollows a similar pathway; in this case, however, low temperature NMR spectra allowed us to characterize the pentacoordinated dinuclear species 2> (2b) as the unstable intermediate of the bridge-splitting process.The reaction of 3 with a second equivalent of phosphine (P : Rh = 2) leads, at room temperature, to the well known product trans- (8) accompanied by evolution of CO; however our data show that when the reaction is performed at 200 K, decarbonylation is prevented and spectroscopic evidence of trigonal bipyramidal pentacoordinate (7), stable only at low temperature, can be obtained.
