First kinetic data of the CO substitution in fac-[Re(L,L′-Bid)(CO)3(X)] complexes (L,L′-Bid = acacetylacetonate or tropolonate) by tertiary phosphines PTA and PPh3: Synthesis and crystal structures of water-soluble rhenium(I) tri- and dicarbonyl complexes with 1,3,5-triaza-7-phosphaadamantane (PTA)

Abstract

fac-[Re(OH2)3(CO)3]+ reacts with acetylacetone (AcacH) at room temperature to yield fac-[Re(Acac)(CO)3(OH2)] (1) under aqueous conditions 1 was isolated and reacted with the monodentate ligand, 1,3,5-triaza-7-phosphaadamantane (PTA), to form fac-[Re(Acac)(CO)3(PTA)] (2) in a 9:1 ratio of water and methanol. The isolated complex 2 was further reacted with an excess of PTA ligand in a 9:1 ratio of water and methanol to yield the highly soluble cis-trans-[Re(Acac)(CO)2(PTA)2] (3). The complexes have been characterized by spectroscopic techniques IR, 1H, 13C and 31P NMR, as well as single crystal X-ray crystallography for 2 and 3. From the crystallographic results of 3, the formation of the cis-trans conformation was confirmed, while the 31P NMR results further established 3 as the sole product formed. A 31P NMR kinetic study, involving the methanol substitution of fac-[Re(CO)3(Acac)(CH3OH)] (4) and fac-[Re(CO)3(Trop)(CH3OH)] (TropH = tropolone) with PTA as entering monodentate ligand was also undertaken. The second-order rate constants (k1) for the forward reactions at 25.0 °C were respectively obtained as (35.9 ± 0.2) x 10−3 M−1 s−1 and (25.1 ± 0.8) M−1 min−1. In a preliminary 31P NMR kinetic investigation of the carbonyl substitution in fac-[Re(Acac)(CO)3(PPh3)] by PPh3, an estimated equilibrium constant (Kest) of ≈ 5.09 was calculated for the reversible reaction.