Structural systematics of the {ReO}3+ core with ‘3+2’ ligand donor sets

N-Centered Tripodal Phosphine Re(V) and Tc(V) Oxo Complexes: Revisiting a [3 + 2] Mixed-Ligand Approach

N-Triphos derivatives (NP₃^R, R = alkyl, aryl) and asymmetric variants (NP₂^RX^R′, R′ = alkyl, aryl, X = OH, NR₂, NRR′) are an underexplored class of tuneable, tripodal ligands in relation to the coordination chemistry of Re and Tc for biomedical applications. Mixed-ligand approaches are a flexible synthetic route to obtain Tc complexes of differing core structures and physicochemical properties. Reaction of the NP₃^Ph ligand with the Re(V) oxo precursor [ReOCl₃(PPh₃)₂] generated the bidentate complex [ReOCl₃(κ²-NP₂^PhOH^Ar)], which possesses an unusual AA’BB’XX’ spin system with a characteristic second-order NMR lineshape that is sensitive to the bi- or tridentate nature of the coordinating diphosphine unit. The use of the asymmetric NP₂^PhOH^Ar ligand resulted in the formation of both bidentate and tridentate products depending on the presence of base. The tridentate Re(V) complex [ReOCl₂(κ³-NP₂^PhO^Ar)] has provided the basis of a new reactive “metal-fragment” for further functionalization in [3 + 2] mixed-ligand complexes. The synthesis of [3 + 2] complexes with catechol-based π-donors could also be achieved under one-pot, single-step conditions from Re(V) oxo precursors. Analogous complexes can also be synthesized from suitable ⁹⁹Tc(V) precursors, and these complexes have been shown to exhibit highly similar structural properties through spectroscopic and chromatographic analysis. However, a tendency for the {M^VO}³⁺ core to undergo hydrolysis to the {M^VO₂}⁺ core has been observed both in the case of M = Re and markedly for M = ⁹⁹Tc complexes. It is likely that controlling this pathway will be critical to the generation of further stable Tc(V) derivatives.

An N-centered tripodal heterofunctionalized phosphine ligand was used to generate a reactive “metal-fragment” based on the {M^VO}³⁺ (M = Re, ⁹⁹Tc) core for the formation of mixed-ligand [3 + 2] complexes. Characteristic lineshapes arising from an AA’BB’XX’ spin system are diagnostic of bidentate vs tridentate coordination modes of the ligand.

Rhenium versus cadmium: an alternative structure for a thermally stable cadmium carbonyl compound

An alternative description is provided for the previously reported novel tetranuclear cadmium carbonyl compound, [Cd(CO)3(C6H3Cl)]4. Specifically, consideration of single crystal X-ray diffraction data indicates that the compound is better formulated as the rhenium compound, [Re(CO)3(C4N2H3S)]4. Furthermore, density functional theory calculations predict that, if it were to exist, [Cd(CO)3(C6H3Cl)]4 would have a very different structure to that reported. While it is well known that X-ray diffraction may not reliably distinguish between atoms of similar atomic number (e.g. N/C and Cl/S), it is not generally recognized that two atoms with very different atomic numbers could be misassigned. The misidentification of two elements as diverse as Re and Cd (ΔZ = 27) is unexpected and serves as an important caveat for structure determinations.

Aminoalcohols and benzoates-friends or foes? Tuning nuclearity of Cu(ii) complexes, studies of their structures, magnetism, and catecholase-like activities as well as performing DFT and TDDFT studies

The Cu(ii) complexes of varying nuclearity are synthesized, characterized and assessed for catecholase activities.

Schiff base chemistry of the rhenium(V)-oxo core with '3+2' ligand donor sets

Reactions of [ReOCl(3)(PPh(3))(2)] with the bidentate ligands 2-(2-hydroxyphenyl) benzoxazole and (2'-hydroxyphenyl)-2-thiazoline resulted in the isolation of the complexes [ReOCl(2)(OC(6)H(4)-2-C=NC(6)H(4)-2-O)(PPh(3))] (1) and [ReOCl(2)(OC(6)H(4)-2-C=NCH(2)CH(2)S)(PPh(3))] (2). Reactions of 1 with the tridentate Schiff base ligands salicylaldehyde 2-hydroxyanil (H(2)L(1b)), salicylaldehyde 2-mercaptoanil (H(2)L(2b)) afnd S-benzyl-2-[(2-hydroxyphenyl)methylene] dithiocarbazate (H(2)L(3b)) yielded the '3+2' rhenium(V) oxo species [ReO(OC(6)H(4)-2-C=NC(6)H(4)O) (OC(6)H(4)CH=NC(6)H(4)O)] (3), [ReO(OC(6)H(4)-2-C=NC(6)H(4)O)-(OC(6)H(4)CH=NC(6)H(4)S)] (4) and [ReO(OC(6)H(4)-2-C=NC(6)H(4)O){OC(6)H(4)CH=N-N=C(SCH(2)C(6)H(5))S}] (5). Similarly, the reactions of [ReOCl(2)(OC(6)H(4)-2-C=NC(6)H(4)S)(PPh(3))] (2) with H(2)L(2b), H(2)L(3b) and 2-[(2-hydroxyphenyl) methylene]-N-phenyl-hydrazinecarbothioamide (H(2)L(4b)) were exploited to prepare [ReO(OC(6)H(4)-2-C=NC(6)H(4)S)(OC(6)H(4)CH=NC(6)H(4)O)] (6), [ReO(OC(6)H(4)C=NC(6)H(4)S){OC(6)H(4)CH=N-N=C (SCH(2)C(6)H(5))S}] (7) and [ReO(OC(6)H(4)-2-C=NC(6)H(4)S){OC(6)H(4)CH=N-N=C(NHC(6)H(5))}] (8), respectively.

Schiff base chemistry of the {ReO} core: structural characterization of the unusual '3 + 2' complex [ReO(eta-OC(6)H(4)-CH=NC(6)H(4)-2-S)(eta-OC(6)H(4))]

The reaction of [ReOCl(3)(PPh(3))(2)] with salicylaldehyde-2-mercaptoanil (1) in methanol yields [ReO(OCH(3))(PPh(3))(eta(3)-OC(6)H(4)CH=NC(6)H(4)S)] (3). Reaction of 3 with 2-(2-hydroxyphenyl)benzothiazole (2) produces [ReO(eta(3)-OC(6)H(4)CH=NC(6)H(4)S)( eta(2)-OC(6)H(4))] (4) in good yield. Compound 4 may also be prepared directly from the reaction of [ReOCl(3)(PPh(3))(2)] with excess 1, after prolonged reaction times in the presence of atmospheric oxygen. The structure of 3 exhibits a distorted octahedral Re(V) center coordinated to a terminal oxo-group, a methoxy ligand, a triphenylphosphine ligand, and the N, O and S donors of the tridentate Schiff base ligand. The octahedral geometry of 4 is defined by the terminal oxo-group, the N, O and S donors of the tridentate Schiff base ligand, and the N and O donors of the bidentate 2-(2-hydroxophenyl)benzothiazole ligand. Oxidation and cyclization of the Schiff base salicylaldehyde-2-mercaptoanil to produce 2-(2-hydroxyphenyl)benzothiazole is precedented and in this instance may be driven by the formation of the robust '3+2' complex 4.

Investigations of the {ReO} core: A '2+2' complex from bidentate and potentially trident ligands: [ReO(η-HOC(6)H(4)-2-CH(2)NC(6)H(4)S)(η-SC(5)H(4)N)(PPh(3))]

The reaction of [ReOCl(3)(PPh(3))(2)] with N-(2-hydroxybenzyl)-2-mercaptoaniline (H(3)hbma) (2) and 2-mercaptopyridine in hot CHCl yields [ReO(η(2)-HOC(6)H(4)-2-CH(2)NC(6)H(4)S)(η(2)-SC(5)H(4)N)(PPh(3))] (3). The structure of 3 consists of distorted octahedral Re(V) monomers. The coordination geometry at the rhenium is defined by a terminal oxo-group, the nitrogen and sulfur donors of the chelating mercaptopyridine, the nitrogen and sulfur donors of a bidentate (Hhbma)(2-) ligand, and the phosphorus of the PPh(3) group. The -C(6)H(4)OH arm of (Hhbma)(2-) is pendant, and the coordinated nitrogen of this ligand is present as a deprotonated amido nitrogen.

Structural characterizations of an Re(IV) complex [ReCl(4)(OPPh(3))(2)] and of an imino species [ReOCl(2)(PPh(3))(eta-OC(6)H(4)-2-CH=NH)] prepared from the reaction of [ReOCl(3)(PPh(3))(2)] with salicylaldoxime

The reaction of [ReOCl(3)(PPh(3))(2)] with salicylaldoxime unexpectedly yields [ReCl(4)(OPPh(3))(2)] (1) and [ReOCl(2)(PPh(3))(eta(2)-OC(6)H(4)-2-CH=NH)] (2). The crystal structure of the Re(IV) complex 1 consists of discrete mononuclear units. The Re site is bound to four chlorides and two trans oxygens of the OPPh(3) groups. The crystal structure of 2 is also mononuclear with the geometry of the Re(V) center defined by a terminal oxo-group, two cis chlorides, the phosphorus of the PPh(3), and the nitrogen and oxygen donors of the phenoxyimino ligand [OC(6)H(4)-2-CH=NH](-).