31P and 13C NMR investigation of the system tetracarbonyldi-μ-chlorodirhodium(I)-tertiary phosphine

Article abstract of DOI:10.1016/0022-328X(93)80163-6

13C and 31P<1H> 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.