Reactions of Rhenium and Technetium Nitrido Complexes with ER₃ Fragments (E = B, Ga, Al, C, P; R = H, Alkyl, Aryl)

Abstract

Terminal ‘N3—’ ligands in rhenium and technetium nitrido complexes are sufficiently nucleophilic to react with Lewis acids under formation of nitrido‐bridged compounds. The reactivity of the nucleophilic centre and the nature of the formed compounds are strongly dependent on the Lewis acid and the composition of the metal complex used. Air‐stable compounds with Re≡N‐ER3 bridges are formed when ER3 is BR3 (R = H, Cl, Br, Ethyl, Phenyl, C6F5), BCl2Ph, GaCl3, CPh3+, or PPh3. The six‐co‐ordinate rhenium(V) complexes [ReNX2(PMe2Ph)3] (X = Cl, Br), [ReN(X)(Et2dtc)(PMe2Ph)2] (Et2dtc— = diethyldithiocarbamate) and [ReN(Et2dtc)2(PMe2Ph)] have been proved to be excellent starting materials for this type of reactions, whereas the five‐co‐ordinate precursors [ReNCl2(PPh3)2], [ReN(Et2dtc)2], [ReN{Ph2P(S)NP(S)Ph2}2] or [ReNCl4]— only react with the most reactive Lewis bases of the examples mentioned above such as BCl2Ph or B(C6F5)3. The rhenium‐nitrido bond lengths remain almost unchanged by the adduct formation, whereas a significant decrease of the trans‐influence of the nitrido complexes has been observed as can be seen by a shortening of the corresponding bond lengths or dimerization of five‐co‐ordinate precursors. Electrophilic attack of the Lewis acid to a donor atom of the equatorial co‐ordination sphere of the rhenium complex results in the formation of ‘underco‐ordinate’ metal centres which resemble to di‐, tri or tetrameric units with asymmetric nitrido bridges between each two rhenium atoms. EPR spectroscopy is an excellent tool to reflect the formation of nitrido bridges at the paramagnetic (d1) [ReNX4]— core (X = F, Cl, Br, NCS). The spectral parameters derived for the products of reactions of [ReNCl4]— with various boron compounds indicate an increase of the covalency of the equatorial Re‐L bonds as a consequence of the formation of a nitrido bridge. The tendency for the formation of nitrido bridges with Lewis acids is significantly lower for technetium compounds compared to their rhenium analogues. Only a few examples with BH3 and BPhCl2 have been established.

New Water‐Soluble Rhenium Complexes with 1,3,5‐Triaza‐7‐phosphaadamantane (PTA) – X‐ray Crystal Structures of [ReNCl2(PTA)3], [ReO2Cl(PTA)3], [ReCl3­(PTA)2(PPh3)], and [Re2N2Cl3(Et2dtc)­(PTA)4]

“…of N , N ‐diethyldithiocarbamate ligand in methanol25 or when the complex [ReN(Et 2 dtc) 2 (Me 2 PhP)] reacted with SbCl 3 26. Detailed studies of these reactions have been described by Abram and co‐workers and some of the complexes were structurally characterized 27…”

“…This substitution is followed by a rearrangement with migration of the remaining Cl – trans to the nitrido ion. Thus, a second molecule of dithiocarbamate substitutes one phosphane and the trans ‐Cl – 27. More recently Dilworth and co‐workers have reported diazenide‐rhenium complexes with dithiocarbamate ligands of the formula [ReNNC 6 H 4 ‐4‐OCH 3 (dtc) 2 (PPh 3 )]30 in which the position trans to the diazenide ligand is occupied by a sulfur atom of one of the dithiocarbamate ligands.…”

Rhenium mixed-ligand complexes with S,N,S-tridentate thiosemicarbazone/thiosemicarbazide ligands

“…A band at 1028 cm −1 can be assigned to the ν (ReuN) vibration. 33,34 The decomposition of nitrido ligands or other nitrogen-containing ligands with final formation of nitrido complexes has been described for many examples, [35][36][37] and particularly the decomposition of azido compounds is a convenient approach, e.g. to prepare the common nitrido precursor (NBu 4 )-[ReNCl 4 ].…”

Tetrameric rhenium complexes with a glycine-thiourea derivative

“…Selected bond lengths are summarized in Table 1. The nitrido bridges are asymmetric and show slightly lengthened Re"N triple bonds of 1.699(8) and 1.717(9) Å in comparison to terminal nitrido ligands in Re(V) compounds (commonly between 1.60 and 1.65 Å) [10], while the single bonds of 1.988(9) and 2.049(8) Å are in the expected range. The two PPhMe 2 ligands direct to opposite directions with respect to the plane of the metallacycle and, thus, the product represents the anti isomer of the tetrameric complex.…”

“…The formation of bi-, tri-or tetranuclear rhenium(V) complexes with asymmetric nitrido bridges is not without precedent and frequently happens when 'undercoordinated' nitridorhenium units are formed during the course of a reaction. Such fragments are stabilized by a bond between the lone pair of the nitrido ligand and the neighbouring metal ion [10]. Four more tetranuclear compounds with a similar square arrangement of a central {Re 4 N 4 } 8À units have been described containing phosphine and dithiocarbamate ligands [12,13].…”