Colin M. Archer

Development of new technetium cores containing technetium—nitrogen multiple bonds. Synthesis and characterization of some diazenido-, hydrazido- and imido- complexes of technetium

Abstract The syntheses of several novel diazenido-, hydrazido- and imido- complexes of technetium are described. These precursors which contain technetium—nitrogen multiple bonds are derived directly from the appropriate organohydrazine or amine in good yield. Some of the chemistry has been extended to the metastable isotope 99mTc (γ, t 1 2 = 6 h) in highly dilute aqueous media to give single species in high radiochemical purity. These preparations are applicable to the synthesis of new technetium radiopharmaceuticals and should provide for the development of a whole new range of technetium-based diagnostic agents in nuclear medicine.

The preparation and electrochemistry of technetium and rhenium complexes of 2-(diphenylphosphino)benzenethiol. The crystal and molecular structures of [Re(2-Ph2PC6H4S)3] and [Tc(2-Ph2PC6H4S)3]

Abstract Reaction of a variety of rhenium(III) or (V) precursors with the bidentate (1−) mixed phosphino-thiol ligand 2-(diphenylphosphino)benzenethiol (DPPBTH) in mildly alkaline methanol leads to the formation of the 16-electron complex [Re(DPPBT)3] (I). With technetium [Tc(DPPBT)3] (II), [TcOCl(DPPBT)2] (III) or [TcN(DPPBT)2] (IV) may be obtained depending on the conditions and starting material. The X-ray crystal and molecular structures of I and II show very similar distortions from ideal geometry due to intraligand interactions. The complexes have been further studied by cyclic voltammetry and UV-vis spectroscopy.

Technetium diazenido complexes. Part 1. Syntheses and structures of [TcCl(NNC6H4Cl-4)2(PPh3)2] and [TcCl(NNPh)(Ph2PCH2CH2PPh2)2][PF6]·H2O

Reaction of [NBu4][TcOCl4] with monosubstituted organohydrazines RNHNH2(R = aryl) in methanol leads to red solutions of technetium diazenido species. These species may be derivatised with the monotertiary phosphine PPh3 to give the khaki to orange bis(diazenido) complexes [TcCl(NNR)2(PPh3)2](R = Ph 1, C6H4Cl-4 2 or C6H4Me-4 3) and the lime-green monodiazenido complex [TcCl2(NNC6H4NO2-4)(PPh3)2]4. These triphenylphosphine derivatives are also easily prepared directly from [NH4][TcO4]. An X-ray crystal structure of one of the bis(diazenido) complexes [TcCl(NNC6H4Cl-4)2(PPh3)2] shows the Tc to be trigonal bipyramidal with axial PPh3 ligands. Derivatisation of the red technetium diazenido containing solutions with the bidentate ditertiary phosphine ligand Ph2PCH2CH2PPh2(dppe) gives the orange cationic complexes [TcCl(NNR)(dppe)2]+(R = Ph 5, C6H4Cl-4 6 or C6H4NO2-4 7) isolated as hexafluorophosphate or tetraphenylborate salts in good yield. These cationic monodiazenido complexes may also be prepared by substitution reactions of complexes 1–4 with dppe, or directly from [NH4][TcO4]. X-Ray structure details for 5: monoclinic, space group C2/c with Z= 4 in a unit cell of dimensions a= 23.808(5), b= 13.830(3), c= 17.452(4)A, β= 92.53(2)°. Complex 5 has slightly distorted trans octahedral geometry with two co-ordinated dppe ligands surrounding both axial phenyldiazenido and chloride ligands. The angle at the α nitrogen Tc–N(1)–N(2) is 163(2)° with Tc–N(1) 1.917(19) and N(1)–N(2) 1.25(4)A. The phenyldiazenido(1–) ligand therefore bonds formally as a singly bent three-electron donor giving complex 5 an overall valence electron count of eighteen. A most important development of this work is that these technetium complexes are directly accessible from ammonium pertechnetate [NH4][TcO4], the chemical form of technetium used in preparation of radiopharmaceuticals.

The preparation and characterization of some imido- and diazenido-rhenium complexes of maltol. The x-ray crystal structure of [Re(maltol)2(NPh)(PPh3)][BPh4]

Abstract The imido complex [ReCl3(NPh)(PPh3)2] reacts with excess maltol to give the green complex [Re(maltol)2(NPh)(PPh3)][BPh4] (1). Under analogous conditions, [ReCl2(N2COPh)(PPh3)2] gives [ReCl(maltol)(N2COPh)(PPh3)2] (2). An X-ray crystal structure of complex 1 revealed a distorted octahedral structure with cis-maltol ligands. Preliminary X-ray data on a poorly diffracting crystal of complex 2 has confirmed the formulation and stereochemistry. The possible structures of products from other precursors are discussed together with their redox and spectroscopic properties.

Mono- and bis-diazenido complexes of rhenium(III) containing bidentate ditertiary phosphine ligands. The crystal and molecular structures of [Re(NNC6H4Me-4)2(Ph2PCH2CH2PPh2)2][PF6]·2dmf, [Re(NNC6H4Cl-4)2(Me2PCH2CH2PMe2)2][PF6] and [ReCl(NNC6H4Me-4)(Me2PCH2CH2PMe2)2][PF6]

Reaction of the ReIII bis-diazenido starting materials [ReCl(NNC6H4X-4)2(PPh3)2](X = Cl 1 or Me 2) with excess dppe (Ph2PCH2CH2PPh2) in methanol–toluene under reflux gave the novel orange-brown, formally 20-electron ReIII bis-diazenido cations [Re(NNC6H4X-4)2(dppe)2]+(X = Cl or Me) in good yield by addition of a suitable anion to the cooled reaction mixture. Reaction of 1 and 2 with the more reducing dmpe (Me2PCH2CH2PMe2) ligand gave the formally 20-electron bis-diazenido cation [Re(NNC6H4X-4)2(dmpe)2]+ for X = Cl but the 18-electron mono-diazenido cation [ReCl(NNC6H4X-4)(dmpe)2]+ for X = Me. The structures of complexes [Re(NNC6H4Me-4)2(dppe)2][PF6]·2dmf (dmf = dimethylformamide)5, [Re(NNC6H4Cl-4)2(dmpe)2][PF6]6 and [ReCl(NNC6H4Me-4)(dmpe)2][PF6]7 have been determined: 5, triclinic, space group P, a= 13.046(3), b= 13.250(3), c= 12.233(4)A, α= 110.74(2), β= 95.86(2), γ= 115.83(2)°, Z= 1, R= 0.040; 6 monoclinic, space group P21/c, a= 8.992(2), b= 21.947(2), c= 18.982(2)A, β= 91.45(1)°, Z= 4, R= 0.056; 7 orthorhombic, space group Pnma, a= 19.298(2), b= 11.327(2), c= 13.960(2)A, α=β=γ= 90°, Z= 4, R= 0.042. All three complexes have pseudo-octahedral co-ordination with four P donors in a planar equatorial array. The M–N–N angle of the diazenide ligands is found to be dependent on the steric requirements of the diphosphine ligands, the smaller dmpe ligand permitting the M–N–N angles in 6 to decrease to 147.3(5) and 149.0(4)° compared to values of around 162.7(2)° for the dppe complex 5. Reaction of [NH4][ReO4] with the arylhydrazine hydrochloride 4-MeC6H4NHNH2·HCl in CH2Cl2 in the presence of SiMe3Cl and pyridine (py) gave the new hydrazide [ReCl3{NN(SiMe3)C6H4Me-4}2(py)]. Subsequent reaction with PPh3 in MeOH gave the ReIII diazenide [Re(OMe)(NNC6H4Me-4)2(PPh3)2], and overall this provides a route for the synthesis of Re diazenides directly from perrhenate.

New technetium complexes with metal−nitrogen bonds

Abstract The optimal nuclear characteristics of technetium make it an ideal radionuclide for diagnostic medical imaging. However, the development of new imaging agents requires the prior development of technetium coordination chemistry to generate appropriate new complexes and their precursors. Here we report the synthesis of some new technetium complexes containing metal-nitrogen bonds and their coordination chemistry.

The synthesis and reactivity of a new technetium(III) precursor. The crystal structures of [TcCl3(MeCN){P(C6H4Me-3)3}2] and [Tc(bipy)3]2+ (bipy=2,2'-bipyridine)

The reduction of [TcCl4(PPh3)2] with zinc metal in acetonitrile in the presence of triphenylphosphine gives the orange crystalline technetium(III) complex [TcCl3(MeCN)(PPh3)2]1 in good yield. Suitable crystals of 1 were grown, but the crystal structure could not be determined satisfactorily due to pseudo-symmetry in the crystal lattice. To overcome this problem the crystal and molecular structure of the tri-m-tolylphosphine analogue [TcCl3(MeCN){P(C6H4Me-3)3}2]1a was determined. Crystals of 1a are triclinic, space group P with Z= 2 in a unit cell of dimensions a= 10.157(2), b= 10.302(2), c= 22.073(2)A, α= 87.27(2), β= 86.66(1) and γ= 66.87(1)°. The structure was refined based on 5636 reflections converging to R= 0.039. Complex 1a exhibits a distorted pseudo-octahedral geometry with two trans P(C6H4Me-3)3 groups, three meridionally disposed chloride groups, and a linear terminally N-bound acetonitrile ligand. The reaction of 1 with the aromatic imines 2,2′-bipyridine (bipy), 1,10-phenanthroline (phen), and 2,2′:6′2″-terpyridine (terpy) gives the blue-black technetium(II) dicationic complexes [Tc(bipy)3]2+, [Tc(phen)3]2+ and [Tc(terpy)2]2+ isolated as their [BPh4]– or [PF6]– salts. The crystal and molecular structure of one of these novel technetium(II) complexes, [Tc(bipy)3][PF6]22a, has been determined. Crystals of 2a are trigonal, space group Pc1 (no. 165) with Z= 2 in a unit cell of dimensions a= 10.847(2) and c= 16.299(3)A. The structure was refined based on 414 unique reflections converging to R= 0.0525. The monomeric complex 2a exhibits exact D3 symmetry with the Tc–N bonds [2.077(10)A] equivalent by symmetry. The electrochemical behaviour of complexes 1, 2 and 3 has been investigated.

Radiopharmaceuticals for Imaging Hypoxia

The purpose of this article is to briefly review recent research on radiolabeled agents designed for the purpose of imaging tissue hypoxia in vivo. The text of this article will present a broad brush summary of the subject matter with more detailed information contained in the literature sources referenced. Another review of this subject area has recently been published elsewhere and may offer the reader the chance to gain additional insights into work performed in this area of research [1].

Technetium diazenido-complexes. Part 2. Substitution chemistry of [TcCl(NNC6H4Cl-4)2(PPh3)2] and the synthesis of technetium diazenido-complexes directly from [NH4][TcO4]

The bis(diazenido)technetium(III) complex [TcCl(NNR)2(PPh3)2](R = C6H4Cl-4) reacted with bidentate ligands L with loss of one diazenide ligand to give [Tc(NNR)L2(PPh3)](L = S2CNR2) and [TcCl(NNR)L(PPh3)2](HL = maltol) in high yield. With dianionic tetradentate ligands L′ complexes of the type cis-[Tc(NNR)L′(PPh3)][L′= dianion of N,N′-bis(salicylidene)ethane-1,2-diamine (salen), S(CH2)2NMe(CH2)2NMe(CH2)2S or O2S(CH2)2NMe(CH2)2NMe(CH2)2SO2] were obtained. The crystal structure of the complex with L′= salen has been determined. It shows pseudo-octahedral co-ordination about the Tc with the NNR and PPh3 ligands cis. Direct reaction of [TcO4]– with arylhydrazine hydrochlorides generated a diazenide species in situ which reacts with S2CNR2 to give [TcCl(NNR)2(S2CNR2)2] and 2,2′-bipyridine (bipy) to give [TcCl(NNR)(bipy)2]+ isolated as a BPh4– salt.

Synthesis of technetium-99 nitrido complexes with chelating diphosphine and diimine ligands

The reaction of [TcNCl4]– with bidentate diphosphines P–P gives the cationic complexes [TcNCl(P–P)2]+[A]–[P–P = Ph2PCH2CH2PPh2 or Me2PCH2CH2PMe2(dmpe), A = BPh4 or PF6] in good yield. An analogous complex was prepared with Me2PCH2CH2NMe(CH2)3NMeCH2CH2PMe2 whereas the bulky Pri2PCH2CH2PPRi2(dippe) gave a binuclear complex [Tc2N2Cl4(dippe)2] which on the basis of 31P NMR spectroscopy has bridging chloride groups. An X-ray crystal structure of [TcNCl(dmpe)2][BPh4] revealed a distorted trans-octahedral geometry about technetium with an exceptionally long TcN bond distance of 1.853(6)A. Reaction of [TcNBr4]– with 2,2′-bipyridyl (bipy) in ethanol gives [TcNBr(bipy)2]2[TcBr4]. An X-ray crystal structure revealed a cis-octahedral structure for the nitrido-cation [TcN 1.621(20)A] with the novel tetrahedral tetrabromotechnetate(II) dianion.