Neutral N-pyrazolyl radicals [3,5-R2pz]• as reactive intermediates were generated by one-electron oxidization of the corresponding 3,5-disubstituted pyrazolato anions [3,5-R2pz]− (R = tBu, Ph) with BiCl3 and trapped by the use of 5,5-dimethyl-1-pyrroline-N-oxide as a spin trap, which was confirmed by electron paramagnetic resonance spectral analysis. With dimerization of the postulated pyrazolato low-valent BiII radical species, two novel paddlewheel pyrazolatodibismuthanes [L2(Bi–Bi)L2] [L = η1,η1-3,5-R2pz; R = tBu (5α, 5β, and 5γ), Ph (6)] were isolated and structurally characterized.

Two 1,2-diaza-4-phosphaferrocenes [(η5-3,5-R2dp)Fe(η5-CpMe5)] (R = tBu (3), Ph (4)) with a single η5 ring containing two nitrogen atoms are prepared. Mössbauer spectroscopic, electrochemical, and density functional theory (DFT) studies have provided a more detailed understanding of the electronic structures and stabilities of these complexes.

A few heteroleptic, charge-separated heterobimetallic, and polymeric alkali metalate complexes of 1,2,4-diazaphospholide lanthanum(III), cerium(III), neodymium(III), praseodymium(III), and samarium(III) were simply prepared via the metathesis reaction of MCl3 (THF)m (m = 1–2) and K[3,5-R2dp] ([3,5-R2dp]− = 3,5-di-substituent-1,2,4-diazaphospholide; R = tBu, Ph) in a varied ratio (1:3, 1:4, and 1:5, respectively) at room temperature in tetrahydrofuran. All the complexes were fully characterized by 1H, 13C{1H}, 31P{1H}, IR, and X-ray single crystal diffraction analysis despite their paramagnetism (excluding La(III) complexes). The structures of the complexes were found to feature varied coordination modes. The magnetic properties of several compounds were studied by magnetic susceptibility, and the complexes presented the magnetic moments close to or lower than the theoretical values for the free ions in the trivalent oxidation states (Pr3+, Nd3+).

The oxidation of 1,2,4-diazaphospholide potassium (K+[2−]) produces a neutral 1,2,4-diazaphospholyl radical (2˙) which can subsequently afford the 2(N)–2(P) dimer involving a N–P linkage.

One-electron oxidation of the 1,2,4-diazaphospholide anion [3,5-R2dp]− by BiCl3 generated several remarkable paddlewheel dibismuthanes [L2(Bi−Bi)L2] (L = η1,η1-3,5-R2dp, R = tBu, iPr, or Ph) with very short Bi–Bi single bond lengths (2.7964(4)–2.8873(3) Å).

•A family of new bis(N-1,2,4-diazaphosphol-1-yl)methanes (bdpm) were prepared.•It has been demonstrated that bdpm can be used as ligands for preparation of metal complexes.•Copper and cobalt complexes with bdpm ligand were studied by the EPR spectroscopy and magnetic susceptibility.Several novel derivatives of bis(N-1,2,4-diazaphosphol-1-yl)methane (bdpm) as well as the first bis(N-1,2,4-diazaphosphol-1-yl)methane metal complexes [Cu(bdpm)2(H2O)2]2+·2ClO4−, [(bdpm)Cu(μ-Cl)Cl]2, and [(bdpm)CoCl2] were prepared and structurally characterized. The complex [Cu(bdpm)2(H2O)2]2+·2ClO4− is with the higher local concentration of low-valent phosphorus(σ2λ3) on the periphery of the molecule. All compounds were characterized using 1H, 13C{1H}, 31P{1H} NMR, IR spectroscopy, and X-ray crystallography. The properties of compounds [Cu(bdpm)2(H2O)2]2+·2ClO4−, [Cu(bdpm)(μ-Cl)Cl], and [Co(bdpm)Cl2] were studied by the EPR spectroscopy and magnetic susceptibility.Bis(N-1,2,4-diazaphosphol-1-yl)methane (bdpm) and the related complexes [Cu(bdpm)2(H2O)2]2+·2ClO4−, [(bdpm)Cu(μ-Cl)Cl]2, and [(bdpm)CoCl2] were synthesized. The EPR and magnetic study showed that [Cu(bdpm)2(H2O)2]2+·2ClO4− with a dx2-y2dx2-y2 Cu(II) ion is paramagnetic.

Several novel derivatives of mono- and bis(1,2,4-diazaphosphol-1-yl)pyridine (or pyrazine) as well as the first 2,6-bis(1,2,4-diazaphosphol-1-yl)pyridine (bdppy) and 2,6-bis(1,2,4-diazaphosphol-1-yl)pyrazine (bdppz) metal complexes [Zn(bdppy)2]2+·2ClO4− and [(bdppz)Cu(NCMe)]2+·2ClO4− were prepared and structurally characterized. The complex [Zn(bdppy)2]2+·2ClO4− has a higher local concentration of low-valent phosphorus (σ2λ3) on the periphery of the molecule. All the compounds were characterized using 1H, 13C{1H}, 31P{1H} NMR and IR spectroscopy, and X-ray crystallography. The properties of the compound [(bdppz)Cu(NCMe)]2+·2ClO4− were studied using EPR spectroscopy and magnetic susceptibility measurements.Several novel derivatives of mono- and bis(1,2,4-diazaphosphol-1-yl)pyridine (or pyrazine) as well as the first 2,6-bis(1,2,4-diazaphosphol-1-yl)pyridine (bdppy) and 2,6-bis(1,2,4-diazaphosphol-1-yl)pyrazine (bdppz) metal complexes [Zn(bdppy)2]2+·2ClO4−, [(bdppz)Cu(NCMe)]2+·2ClO4− were prepared and structurally characterized. The complexes [Zn(bdppy)2]2+·2ClO4− is with the higher local concentration of low-valent phosphorus (σ2λ3) on the periphery of the molecule.

•Six 1H-1,2,4-diazaphospholes were prepared and structurally characterized.•All compounds are linked into oligomers via the bridges of NH⋯N hydrogen bonds in solid state.•The tetrameric feature represents a new motif of hydrogen-bonded 1H-1,2,4-diazaphospholes.A few 1H-1,2,4-diazaphospholes H[3,5-R2dp] (R = methyl (5a), p-tolyl (5b), 1-naphthyl (5c), 2-furanyl (5d), 2-thienyl (5e), and isopropyl (5f)) were prepared and structurally characterized by a substantial experimental modification of the synthetic protocol. The molecules of all compounds are linked into oligomers via the bridges of NH⋯N hydrogen bonds in solid state. The tetrameric feature of 5a, and 5d–f represents a new motif of hydrogen-bonded 1H-1,2,4-diazaphospholes in solid state. The DFT calculation at the B3LYP/6-311++G** level suggested the possible proton disorder with intermolecular solid state proton transfer (ISSPT) between 1H-1,2,4-diazaphosphole rings.Graphical abstract

The alkaline earth metal complexes [(η2-3,5-tBu2dp)(μ-Mg)(η1:η1-3,5-tBu2dp)]2 (2), {[(η2-3,5-tBu2dp)(μ-η2:η5-3,5-tBu2dp)(μ-η2:η1-3,5-tBu2dp)Ca]2(μ-Ca)} (3), [Sr(3,5-tBu2dp)2]m (4), [Ba(3,5-tBu2dp)2)]n (5), and [η1-{H(3,5-tBu2dp)}2Ca(η2-3,5-tBu2dp)2] (6), bearing bulky 1,2,4-diazaphospholide ligands [3,5-tBu2dp]− ([3,5-tBu2dp]− = 3,5-di-tert-butyl-1,2,4-diazaphospholide), were prepared. The structures of magnesium and calcium 1,2,4-diazaphospholide complexes represent homoleptic 1,2,4-diazaphospholide alkaline earth metal oligomers with a novel array of metal–ligand binding modes.

The [Ba(N(SiMe3)2)2]·2THF reacts with 1,2,4-triazole to afford an unusually polymeric 1,2,4-triazolato barium complex [trz2Ba(DMSO)2]∞ (trz = 1,2,4-triazolato) with a 2D coordination network, which consists of two-dimensional [trz2Ba]∞ sheets entrained within the stacked two-dimensional framework of [trz2Ba(DMSO)2]∞ polymer. Complex [trz2Ba(DMSO)2]∞ represents the first heavier alkaline earth 1,2,4-triazolato complex with an η2 and η1 bridging coordination.Graphical abstractOne new barium triazolato complex presents an unusual μ2-η2,η1 coordination mode. It is first layered polymeric planar azolato alkaline-earth metal complex. It has demonstrated that the 1,2,4-triazolato ligand has a tendency to join the metals in μ2-η1,η2 mode.Highlights► Complex (1) presents an unprecedented μ2-η2,η1 coordination mode. ► Complex 1 with solvated DMSO is first layered polymeric planar azolato alkaline-earth metal complex. ► Compound 1 demonstrates that the 1,2,4-triazolato ligand has a tendency to join the metals in μ2-η1,η2 mode.

A sandwich zwitterionic ruthenium complex (4) was prepared by an intramolecular 1,3-dipolar cycloaddition of the ruthenium azido isocyanide [CpMe5Ru(CNAr)2N3] (2). The reaction involved a formal 1,3-migration mechanism along a highly conjugated system linking to a cyanamido group.

A series of germylene, stannylene and plumbylene complexes [η2(N,N)-Me2Si(DippN)2Ge:] (3a), [η2(N,N)-Ph2Si(DippN)2Ge:] (3b), [η2(N,N)-Me2Si(DippN)2Sn:] (4), [η2(N,N)-Me2Si(DippN)2Pb:]2 (5a), and [η2(N,N)-Ph2Si(DippN)2Pb:] (5b) (Dipp = 2,6-iPr2C6H3) bearing bulky bis(amido)silane ligands were readily prepared either by the transamination of M[N(SiMe3)2]2 (M = Sn, Pb) and [Me2Si(DippNH)2] or by the metathesis reaction of bislithium bis(amido)silane [η1(N),η1(N)-R2Si(DippNLi)2] (R = Me, Ph) with the corresponding metal halides GeCl2(dioxane), SnCl2, and PbCl2, respectively. Preliminary atom-transfer chemistry involving [η2(N,N)-Me2Si(DippN)2Ge:] (3a) with oxygen yielded a dimeric oxo-bridged germanium complex [η2(N,N)-Me2Si(DippN)2Ge(μ-O)]2 (6). All complexes were characterized by 1H, 13C, 119Sn NMR, IR, and elemental analysis. X-ray single crystal diffraction analysis revealed that the metal centres in 3b, 4, and 5b are sterically protected to prevent interaction between the metal centre and the nitrogen donors of adjacent molecules while complex 5a shows a dimeric feature with a strong intermolecular Pb⋯N interaction.

The hydroalumination of the fused pentahydride aminocarbaaluminum species [(C6H3(iPr2-2,6)N(μ-AlH2)CH2)2(μ-AlH)NMe3] (1) with phenylacetylene resulted in the unexpected dimer [C6H3(iPr2-2,6)(*N)HCH2Al(CCPh)2]2 (2) with chiral centers at the nitrogen atoms. Compound 2 was characterized by X-ray structural analysis and contains geminal frustrated Lewis pairs.

Two 1,2,4-diazaphospholide complexes of [Ti(η2-3,5-Ph2dp)4] and paramagnetic [Ti(η2-3,5-tBu2dp)3] were prepared by the reaction of tetrakis(dimethylamido)titanium(IV) with 3,5-diphenyl-1,2,4-diazaphophole, H[3,5-Ph2dp], or by the treatment of 3,5-tert-butyl-1,2,4-diazaphopholide potassium, K[3,5-tBu2dp], with titanium trichloride. Complexes can be viewed as the core of P(σ2λ3)-functionalized metallodendrimers, in which the metal atoms are exclusively η2(N,N) bonding to the 1,2,4-diazaphospholides while P atoms (σ2λ3) with electron lone pairs are located on the periphery of the molecules.

Several of alkaline-earth-metal complexes [(η2:η2:μ(N):μ(N)-Li)+]2[{η2-Me2Si(DippN)2}2Mg]2– (4), [η2(N,N)-Me2Si(DippN)2Ca·3THF] (5), [η2(N,N)-Me2Si(DippN)2Sr·THF] (6), and [η2(N,N)-Me2Si(DippN)2Ba·4THF] (7) of a bulky bis(amido)silane ligand were readily prepared by the metathesis reaction of alkali-metal bis(amido)silane [Me2Si(DippNLi)2] (Dipp = 2,6-i-Pr2C6H3) and alkaline-earth-metal halides MX2 (M = Mg, X = Br; M = Ca, Sr, Ba, X = I). Alternatively, compounds 5–7 were synthesized either by transamination of M[N(SiMe3)2]2·2THF (M = Ca, Sr, Ba) and [Me2Si(DippNH)2] or by transmetalation of Sn[N(SiMe3)2]2, [Me2Si(DippNH)2], and metallic calcium, strontium, and barium in situ. The metathesis reaction of dilithium bis(amido)silane [Me2Si(DippNLi)2] and magnesium bromide in the presence of oxygen afforded, however, an unusual lithium oxo polyhedral complex {[(DippN(Me2Si)2)(μ-O)(Me2Si)]2(μ-Br)2[(μ3-Li)·THF]4(μ4-O)4(μ3-Li)2} (8) with a square-basket-shaped core Li6Br2O4 bearing a bis(aminolato)silane ligand. All complexes were characterized using 1H, 13C, and 7Li NMR and IR spectroscopy, in addition to X-ray crystallography.

A series of germylene, stannylene and plumbylene complexes [η2(N,N)-Me2Si(DippN)2Ge:] (3a), [η2(N,N)-Ph2Si(DippN)2Ge:] (3b), [η2(N,N)-Me2Si(DippN)2Sn:] (4), [η2(N,N)-Me2Si(DippN)2Pb:]2 (5a), and [η2(N,N)-Ph2Si(DippN)2Pb:] (5b) (Dipp = 2,6-iPr2C6H3) bearing bulky bis(amido)silane ligands were readily prepared either by the transamination of M[N(SiMe3)2]2 (M = Sn, Pb) and [Me2Si(DippNH)2] or by the metathesis reaction of bislithium bis(amido)silane [η1(N),η1(N)-R2Si(DippNLi)2] (R = Me, Ph) with the corresponding metal halides GeCl2(dioxane), SnCl2, and PbCl2, respectively. Preliminary atom-transfer chemistry involving [η2(N,N)-Me2Si(DippN)2Ge:] (3a) with oxygen yielded a dimeric oxo-bridged germanium complex [η2(N,N)-Me2Si(DippN)2Ge(μ-O)]2 (6). All complexes were characterized by 1H, 13C, 119Sn NMR, IR, and elemental analysis. X-ray single crystal diffraction analysis revealed that the metal centres in 3b, 4, and 5b are sterically protected to prevent interaction between the metal centre and the nitrogen donors of adjacent molecules while complex 5a shows a dimeric feature with a strong intermolecular Pb⋯N interaction.

A few heteroleptic, charge-separated heterobimetallic, and polymeric alkali metalate complexes of 1,2,4-diazaphospholide lanthanum(III), cerium(III), neodymium(III), praseodymium(III), and samarium(III) were simply prepared via the metathesis reaction of MCl3 (THF)m (m = 1–2) and K[3,5-R2dp] ([3,5-R2dp]− = 3,5-di-substituent-1,2,4-diazaphospholide; R = tBu, Ph) in a varied ratio (1:3, 1:4, and 1:5, respectively) at room temperature in tetrahydrofuran. All the complexes were fully characterized by 1H, 13C{1H}, 31P{1H}, IR, and X-ray single crystal diffraction analysis despite their paramagnetism (excluding La(III) complexes). The structures of the complexes were found to feature varied coordination modes. The magnetic properties of several compounds were studied by magnetic susceptibility, and the complexes presented the magnetic moments close to or lower than the theoretical values for the free ions in the trivalent oxidation states (Pr3+, Nd3+).

The oxidation of 1,2,4-diazaphospholide potassium (K+[2−]) produces a neutral 1,2,4-diazaphospholyl radical (2˙) which can subsequently afford the 2(N)–2(P) dimer involving a N–P linkage.

One-electron oxidation of the 1,2,4-diazaphospholide anion [3,5-R2dp]− by BiCl3 generated several remarkable paddlewheel dibismuthanes [L2(Bi−Bi)L2] (L = η1,η1-3,5-R2dp, R = tBu, iPr, or Ph) with very short Bi–Bi single bond lengths (2.7964(4)–2.8873(3) Å).

Two 1,2-diaza-4-phosphaferrocenes [(η5-3,5-R2dp)Fe(η5-CpMe5)] (R = tBu (3), Ph (4)) with a single η5 ring containing two nitrogen atoms are prepared. Mössbauer spectroscopic, electrochemical, and density functional theory (DFT) studies have provided a more detailed understanding of the electronic structures and stabilities of these complexes.