Remarkable Stability of (η⁵-C₅H₅)Re(CO)₂L (L = n-Heptane, Xe, and Kr):  A Time-Resolved Infrared Spectroscopic Study of (η⁵-C₅H₅)Re(CO)₃ in Conventional and Supercritical Fluid Solution

Abstract

Employing fast time-resolved infrared (TRIR) spectroscopy we have characterized CpRe(CO)2(n-heptane), CpRe(CO)2(Xe), and CpRe(CO)2(Kr) (Cp = η5-C5H5) at or above room temperature in n-heptane, supercritical Xe, and Kr solution. The reactivity of CpRe(CO)2(n-heptane) with CO (k 2 = 2.1 (±0.5) × 103 mol-1 dm3 s-1) shows this complex to be the least reactive of the reported organometallic alkane complexes. We report a trend in reactivity of the early transition metal alkane complexes. CpRe(CO)2(Xe) and CpRe(CO)2(Kr) are also shown to have significant stability. CpRe(CO)2(Xe) is less reactive toward CO than all of the reported alkane complexes except CpRe(CO)2(n-heptane).

Evidence for Alkane Coordination to an Electron-Rich Uranium Center

“…Most known examples of transition metal-alkane complexes to date have been detected in gas phases, matrices, and solutions in situ. 2 In virtually all reported cases, the metal-alkane adducts were identified spectroscopically as fleeting intermediates at cryogenic temperatures.Noteworthy exceptions were recently reported by George et al 3 and Geftakis and Ball. 4 The latter group generated a cyclopentane adduct, [(Cp)Re(CO) 2 (C 5 H 10 )], via photolysis of [(Cp)Re(CO) 3 ] that was detected NMR-spectroscopically as an intermediate in neat cyclopentane solution at -93°C.…”

“…4 The latter group generated a cyclopentane adduct, [(Cp)Re(CO) 2 (C 5 H 10 )], via photolysis of [(Cp)Re(CO) 3 ] that was detected NMR-spectroscopically as an intermediate in neat cyclopentane solution at -93°C. On the basis of a comparison of the experimentally determined 13 C and 1 H coupling constants and chemical shifts with those of structurally closely related, -agostic bonded C-H moieties, an η 2 -H,C metal-alkane interaction was proposed (see below).…”

Time-resolved infrared (TRIR) study on the formation and reactivity of organometallic methane and ethane complexes in room temperature solution

“…Time-resolved infrared (TRIR) spectroscopy has proved to be a powerful tool for the study of metal carbonyl alkane complexes. Their reactivity decreases on going both across and down groups 5,6, and 7 (10)(11)(12), and these observations led to the identification of a very long-lived alkane complex, Re(Cp)(CO) 2 (nheptane) (Cp ϭ 5 OC 5 H 5 ), which has a lifetime of Ϸ25 ms at room temperature (13). The relative stability of Re(Cp)(CO) 2 (alkane) complexes allowed Re(Cp)(CO) 2 (C 5 H 10 ) to be observed at 180 K by NMR spectroscopy (14), and subsequent NMR studies have been carried out to determine the binding modes of a series of related alkanes to the Re(CpЈ)(CO) 2 moiety (15,16).…”

“…Clearly, there is a significant WOCH 4 interaction in solution at room temperature. We previously have shown that Re(Cp)(CO) 2 (heptane) is Ϸ700 times longer-lived than W(CO) 5 (heptane) is (13). In an attempt to produce long-lived complexes of the lighter alkanes, we have investigated the photochemistry of M(Cp)(CO) 3 (M ϭ Mn or Re) in scCH 4 and liqC 2 H 6 .…”

Characterization of an organometallic xenon complex using NMR and IR spectroscopy

“…Re(Cp)(CO) 2 Xe (Cp ϭ 5 -C 5 H 5 ) was shown by using time-resolved IR (TRIR) spectroscopy to be long-lived at room temperature in supercritical Xe (scXe) solution (17). Re(Cp)(CO) 2 Xe was shown to have a lifetime of up to 3.5 min at 170 K in lXe, leading to the prediction that it was a realistic goal to observe such complexes by NMR spectroscopy (18).…”