Rhodium physical constants

Tertiary phosphine analogs have been prepared from [Rh(NO)2Cl]x.1301 Nitrosyltris(phosphorus trifluoride)rhodium has been prepared from both rhodium(—I) and rhodium(I) complexes (equations 294-296).1297 Their physical properties are listed in Table 90. The triphenylphosphine complex is quite reactive (Scheme 42). Both electronic1312 and 31P NMR spectrometry show the equilibrium constant for the reaction (297) to be of the order of 10-4moldm3 in dichloromethane, benzene1312,1313 or THF,1313 so the reactivity of the complex cannot arise from the facile loss of a... 

Butadiene is polymerized by rhodium compounds in aqueous or alcoholic solution [178]. It is generally accepted that the active species is a TT-allyl rhodium complex of low valency [28, 179] which is not rapidly terminated by reaction with water or alcohol. No clear kinetic pattern was observed in the earlier papers but a recent investigation [180] has shown the rate and molecular weight data to be accommodated by a scheme involving monomer transfer and physical immobilization of the active centres in precipitated polymer. In the initial stages the polymerization is first order in rhodium and, at constant monomer concentration, is (pseudo) zero order E = 14.8 kcal mole" ). This is followed by a declining rate which is almost independent of temperature. Molecular weights rise slowly to a maximum value with time (ca. 4000 after 22 h at 70°C). 

Deuteroethane distributions have been interpreted in terms of a parameter P, which is the quotient of the rate constants for ethyl to ethene and ethyl reverting to ethane. For molybdenum, tantalum, rhodium and palladium films, a single value of P (respectively 0.25, 0.25, 18 and 28) sufficed to reproduce the observed distribution, assuming that a further deuterium atom is acquired at every opportunity. With other metals, however, two simultaneous values of P appeared to operate, one contributing 30 to 50% of the reaction having a high P value (13.5-18) and another having a much lower P value (0.36-2). This analysis has not however been accorded an interpretation in terms of the metals physical properties or of ensemble sizes and structures responsible for each participant. 

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