Technetium(I) Carbonyl Chemistry with Small Inorganic Ligands

Abstract

[Tc­(OH2)­(CO)3(PPh3)2]­(BF4) has been used as a synthon for reactions with small inorganic ligands with relevance for the treatment of nuclear waste solutions such as nitrate, nitrite, pseudohalides, permetalates (M = Mn, Tc, Re), and BH4 –. The formation of bond isomers and/or a distinct reactivity has been observed for most of the products. [Tc­(NCO)­(CO)3(PPh3)2], [Tc­(NCS)­(CO)3(PPh3)2], [Tc­(CN)­(CO)3(PPh3)2], [Tc­(N3)­(CO)3(PPh3)2], [Tc­(NCO)­(OH2)­(CO)2(PPh3)2], [Tc­(η2-OON)­(CO)2(PPh3)2], [Tc­(η1-NO2)­(CO)3(PPh3)2], [Tc­(η2-OONO)­(CO)2(PPh3)2], [Tc­(η1-ONO2)­(CO)3(PPh3)2], [Tc­(η2-OO­(CCH3))­(CO)2(PPh3)2], [Tc­(η2-SSC­(SCH3))­(CO)2(PPh3)2], [Tc­(η2-SSC­(OCH3))­(CO)2(PPh3)2], [Tc­(η2-SSC­(CH3))­(CO)2(PPh3)2], [Tc­(η2-SS­(CH))­(CO)2(PPh3)2], [Tc­(OTcO3)­(acetone)­(CO)2(PPh3)2], [Tc­(OTcO3)­(CO)3(PPh3)2], and [Tc­(η2-HHBH2)­(CO)2(PPh3)2] have been isolated in crystalline form and studied by X-ray crystallography. Additionally, the typical reactivity patterns (isomerization, thermal decomposition, hydrolysis, or decarbonylation) of the products have been studied by spectroscopic methods. 99Tc NMR spectroscopy has proved to be a particularly useful tool for the evaluation of such reactions of the diamagnetic technetium­(I) compounds in solution.

Unlocking Air- and Water-Stable Technetium Acetylides and Other Organometallic Complexes

“…Other carbon donors such as carbonyls bind more tightly to technetium. The Tc–C bond lengths in [Tc­(CO) 4 (PPh 3 ) 2 ] + are approximately 1.94–2.04 Å; the isonitrile ligands in [Tc­(CN–R)­(CO) 3 (PPh 3 ) 2 ] + (R = cyclohexyl or C 6 H 2 F­(C 6 H 3 (CF 3 ) 2 ) 2 ) form ∼2.1 Å bonds, and the anionic cyanido ligand in [Tc­(CN)­(CO) 3 (PPh 3 ) 2 ] forms a 2.14 Å bond in the trans -position to a carbonyl ligand. , …”

“…The general structures of 3 and 4 are similar to those of other octahedral complexes containing the mer,trans -{Tc­(CO) 3 (PPh 3 ) 2 } + unit. − Three carbonyl ligands are bound in the equatorial plane, which is completed by the methyl or phenyl ligands. The axial positions are occupied by two PPh 3 ligands.…”

“…The broad and highly shielded 99 Tc resonances are observed at −2053 ppm (ν 1/2 = 7885 Hz) for the methyl derivative and at −1806 ppm (ν 1/2 = 12238 Hz) for the phenyl derivative. This is in the range in which the signal of the hydrido complex [TcH­(CO) 3 (PPh 3 ) 2 ] (−2208 ppm) and those of the [Tc­(L)­(CO) 3 (PPh 3 ) 2 ] 0/+ complexes with other carbon donor ligands (L = CN – , CO, or isonitriles) also appear. − …”

“…The 99 Tc NMR resonances of the products are found between −1914 and −2056 ppm and have half-widths between 8 and 12 kHz. The chemical shifts are similar to those found for the other [Tc­(L)­(CO) 3 (PPh 3 ) 2 ] 0/+ complexes, where L represents a ligand with a carbon donor atom and differs significantly from those of related complexes having ligands with other donor atoms (e.g., nitrogen donor ligands at approximately −1300 to −1500 ppm). , …”

“…In comparison, both the asymmetric and the symmetric CO bands in the IR spectra of the complexes show red-shifts in the order CN–R, NC–R, and CC–R with similar wavenumbers for the complexes of types 9 and 10 and much lower wavenumbers for the acetylide complexes (red-shift of ∼30 cm –1 ). Especially upon comparison of them with the carbonyl frequencies observed in the cyanido complex [Tc­(CN)­(CO) 3 (PPh 3 ) 2 ], where the symmetric stretching vibration was found at 2054 cm –1 , and the tetracarbonyl cation [Tc­(CO) 4 (PPh 3 ) 2 ] + , which shows only one carbonyl vibration at 2012 cm –1 , , it becomes obvious that the underlying electronic differences are complex and do not follow trivial trends. Similar findings have been reported for a number of isonitrile complexes of technetium and rhenium, where it became evident that isonitriles cannot simply be regarded as electronic surrogates for carbonyl ligands and the related IR frequencies are no simple measures for π back-donation, but the oxidation state of the metal ions and particularly the organic residues of the isocyanides play a critical role. ,,, …”