Do early and late transition metal noble gas complexes react by different mechanisms? A room temperature time-resolved infrared study of (η5-C5R5)Rh(CO)2 (R = H or Me) in supercritical noble gas solution at room temperature

Abstract

Using fast time-resolved infrared spectroscopy, the late transition metal noble gas complexes CpRh(CO)(L) and Cp*Rh(CO)(L) (Cp = η 5 -C 5 H 5 ; Cp* = η 5 -C 5 Me 5 ; L = Xe and Kr) have been characterized at room temperature in supercritical noble gas solution. The krypton complexes are more reactive than the corresponding xenon compounds. There is a significant difference in reactivity with CO between CpRh(CO)(L) and Cp*Rh(CO)(L) with CpRh(CO)(Xe) (k CO = 6.7 × 10 5 dm 3 mol Ϫ1 s Ϫ1 ) being ca. 20 times less reactive than Cp*Rh(CO)(Xe) (k CO = 1.4 × 10 7 dm 3 mol Ϫ1 s Ϫ1 ). Similarly CpRh(CO)(Kr) (k CO = 1.3 × 10 8 dm 3 mol Ϫ1 s Ϫ1 ) is also less reactive than Cp*Rh(CO)(Kr) (k CO = 4.3 × 10 8 dm 3 mol Ϫ1 s Ϫ1 ). This should be contrasted to the early transition metal noble gas complexes, where for a given metal-noble gas complex, CpM(CO) 2 (L) and Cp*M(CO) 2 (L) (M = Mn or Re) have similar reactivity towards CO. The activation parameters for the reaction of CpRh(CO)(L) and Cp*Rh(CO)(L) with CO have been determined above room temperature, and suggest that the reaction proceeds by an associative mechanism.

Characterization of an organometallic xenon complex using NMR and IR spectroscopy

“…Location of the fluorine chemical shift. In the first instance, the new compounds were identified on the basis of a new doublet in the 19 F spectrum, which was directly detected by using standard pulse sequences. From this 1D spectrum, a 1 J PF value was extracted, and this value was used in subsequent experiments.…”

“…19 F-31 P heteronuclear single quantum coherence experiments were performed without refocusing and decoupling (21), and we used the States-time-proportional phase incrementation method to obtain pure phase spectra. Delays were optimized for a 1 J PF value of 1,220 Hz, with 90°pulse lengths of 8.3 and 10.5 s for 19 F and 31 P, respectively.…”

“…Xe, by comparison to the other noble gases, forms the most stable organometallic complexes. The reactivity of M(Cp)(CO) n Xe complexes, for instance, is in the order Re Ͻ Rh Ͻ Mn Ͻ Ta Ϸ Nb (19,20).…”

“…The compound is an organometallic Xe complex that has been characterized by using NMR spectroscopy and is shown to be longer-lived than other organometallic Xe complexes by IR spectroscopy. 19 …”

Energy of the quasi-free electron in xenon

“…Because of its chemical inertness and its relatively high critical temperature and low critical pressure, xenon is a popular supercritical solvent for probing density effects on electron mobility in highly polarizable fluids (see, for example, [1][2][3][4][5][6]) and for investigating pulse radiolysis reaction kinetics (see, for example, [6][7][8]). While xenon critical effects on electron mobility have been explored [9,10], an investigation of these effects on the quasi-free electron energy in xenon has not been performed.…”