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An unexpected nitro group displacement during a nitro-Mannich reaction led to the one-pot formation of the octahydro-2H-pyrazino[1,2-a]pyrazine core, representing the shortest access to date to this pharmacologically relevant heterobicyclic system. A mechanistic hypothesis is suggested and supported by specific experiments and HRMS analysis of reaction mixtures. [ABSTRACT FROM AUTHOR]

The rich coordination chemistry of lanthanoid ions (Ln3+) is currently exploited in a vast and continuously expanding array of applications. Chelating agents are central in the development of Ln3+-complexes and in tuning their physical and chemical properties. Most chelators for Ln3+-complexation are derived from the macrocyclic DOTA or from linear DTPA platforms, both of which arise from fossil-based starting materials. Herein, we report a green and efficient approach to a chelating agent (EHDTA), derived from cheap and largely available furfurylamine. The oxygenated heterocycle of the latter is converted to a stereochemically defined and rigid heptadentate chelator, which shows good affinity towards Ln3+ ions. A combination of NMR, relaxometric, potentiometric and spectrophotometric techniques allows us to shed light on the interesting coordination chemistry of Ln3+–EHDTA complexes, unveiling a promising ligand for the chelation of this important family of metal ions. [ABSTRACT FROM AUTHOR]

The reaction of cyclopentaphosphine cyclo‐(P5Ph5) (1) with ketones (acetone and cyclooctanone) in the presence of [Mo(CO)4(cod)] (cod=cycloocta‐1,5‐diene) led to air‐stable trinuclear complexes in which the bis‐phosphanido ligands (PPh−PPh−PPh−PPh−CMe2O−PPh)2− (complex 2) and (PPh−PPh−PPh−PPh−C(CH2)7O−PPh)2− (complex 3) bridge a Mo(CO)3−Mo(CO)3 unit. This extends the reaction of 1 with transition metal carbonyl complexes to further substrates and represents the first examples of insertion of carbonyl compounds into the P−P bond of cyclic oligophosphorus compounds. Complexes 2 and 3 have been characterized by 31P NMR spectroscopy and single crystal X‐ray diffraction. Furthermore, the thermal properties of the obtained complexes have been studied by differential scanning calorimetry (DSC) and fast scanning calorimetry (FSC). [ABSTRACT FROM AUTHOR]

The cyclo-(P4tBu3) synthon [Li{cyclo-(P4tBu3)}(thf)(tmeda)] (1) (thf = tetrahydrofuran, tmeda = N,N,N′,N′-tetramethylethane-1,2-diamine) is readily accessible in a one-pot synthesis from P4 and LitBu. The use of 1 as a cyclo-(P4tBu3) building block enables the rational synthesis of cyclo-(P4tBu3)-containing oligophosphanes, namely {cyclo-(P4tBu3)}2 (2), {cyclo-(P4tBu3)}2PtBu (3) and {cyclo-(P4tBu3)}2CH2 (4), C3v-symmetric pnictaphosphanes E{cyclo-(P4tBu3)}3 (E = Bi, Sb, As; 5–7) as well as AsCl{cyclo-(P4tBu3)}2 (8). Compounds 5 and 6 represent the first neutral homoleptic bismuthane and stibane that contain only bonds to phosphorus. All new compounds were isolated in moderate to good yields and fully characterised. The 31P{1H} NMR spectral data of 1, 2, 4, and 8 have been determined by automated line-shape analysis. [ABSTRACT FROM AUTHOR]

Octaphosphane {cyclo‐(P4tBu3)}2 (1) undergoes an unexpected isomerization reaction to the constitutional isomer 2,2′,2′′,2′′′,3,3′‐hexa‐tert‐butyl‐bicyclo[3.3.0]octaphosphane (2) in the presence of Lewis acidic metal salts. The mechanism of this reaction is discussed and elucidated with DFT calculations. The results underline the fascinating similarity between phosphorus‐rich and isolobal carbon compounds. The new bicyclic octaphosphane 2 shows a dynamic behavior in solution and reacts with [AuCl(tht)] (tht=tetrahydrothiophene) to give a mono‐ ([AuCl(2‐κP3)], 3) and a dinuclear complex ([(AuCl)2(2‐κP3,κP3′)], 4). With cis‐[PdCl2(cod)] (cod=1,5‐cyclooctadiene), the chelate complex ([PdCl2(2‐κ2P2,P2′)], 5) with a different coordination mode of the ligand was obtained. [ABSTRACT FROM AUTHOR]

Group 6 metal (Cr, Mo, W) carbonyl complexes react with cyclo-(P5Ph5) to afford the phosphorus-rich complexes [Cr(CO)5{cyclo-(P5Ph5)-κP1}] (1), [{Cr(CO)5}2{μ-cyclo-(P5Ph5)-κP1,P3}] (2), [M(CO)4{cyclo-(P5Ph5)-κP1,P3}] (with M=Cr (3), Mo (4), W (exo-5, endo-5)) depending on the reaction conditions. Complexes 1–5 were characterised by 31P{1H} NMR and IR spectroscopy, elemental analysis, and X-ray crystallography. The cyclopentaphosphane remains intact and acts as monodentate (1), bridging (2) or bidentate (3–5) ligand. Compounds exo-5 and endo-5 are configurational isomers and essentially differ in the orientations adopted by the phenyl rings attached to the uncoordinated phosphorus atoms. The 31P{1H} NMR spectra show five multiplets for an ABCDE spin system. Theoretical calculations showed that exo-5 and endo-5 are practically isoenergetic, which is in good agreement with the observed equilibrium in solution between exo-5 and endo-5. The thermal properties of the complexes have also been evaluated. [ABSTRACT FROM AUTHOR]

Group 6 metal (Cr, Mo, W) carbonyl complexes react with cyclo-(P5Ph5) to afford the phosphorus-rich complexes [Cr(CO)5{cyclo-(P5Ph5)-κP1}] (1), [{Cr(CO)5}2{μ-cyclo-(P5Ph5)-κP1,P3}] (2), [M(CO)4{cyclo-(P5Ph5)-κP1,P3}] (with M=Cr (3), Mo (4), W (exo-5, endo-5)) depending on the reaction conditions. Complexes 1–5 were characterised by 31P{1H} NMR and IR spectroscopy, elemental analysis, and X-ray crystallography. The cyclopentaphosphane remains intact and acts as monodentate (1), bridging (2) or bidentate (3–5) ligand. Compounds exo-5 and endo-5 are configurational isomers and essentially differ in the orientations adopted by the phenyl rings attached to the uncoordinated phosphorus atoms. The 31P{1H} NMR spectra show five multiplets for an ABCDE spin system. Theoretical calculations showed that exo-5 and endo-5 are practically isoenergetic, which is in good agreement with the observed equilibrium in solution between exo-5 and endo-5. The thermal properties of the complexes have also been evaluated. [ABSTRACT FROM AUTHOR]

The reaction of [M(CO)4Lx] {M = Cr, W, L = MeCN, x = 2; M = Mo, L = 2,5‐norbornadiene (nbd), x = 1} with cyclo‐(P5Ph5) led to an unusual transformation reaction including the oxidative addition of a P–P bond to the Group 6 metal carbonyl, the insertion of MeCN into a P–P bond, and the formation of an M–M bond. The products were characterized by IR and 31P{1H} NMR spectroscopy, ESI mass spectrometry and single crystal X‐ray crystallography. The complexes contain a metal–metal unit bridged by two terminal phosphanido groups of the novel ligand, (PPh‐PPh‐PPh‐PPh‐CMe=N‐PPh)2–. The 31P{1H} NMR spectrum shows an ABCDE spin system consistent with the molecular structure observed in the solid state. Furthermore, the thermal properties of the complexes were evaluated. A novel route to complexes that contain a dinuclear metal core bridged by the two terminal phosphanido groups of the novel ligand (PPh‐PPh‐PPh‐PPh‐CMe=N‐PPh)2– is reported. The products are formed via oxidative addition of a P–P bond at a metal carbonyl fragment and transition metal‐assisted insertion of MeCN into a P–P bond. [ABSTRACT FROM AUTHOR]

In contrast to their mostly unstable isolobal carbon counterparts, oligophosphanide anions, such as M(cyclo-P5tBu4) (M=Li, Na) and M2(P4R4) [M=Na, K; R=Ph, tBu, 2,4,6-Me3C6H2 (Mes)], have unique features, depending on their composition and structure, and are highly suitable building blocks for the synthesis of phosphorus-rich metal compounds. However, alkali metal oligophosphanediides are highly reactive and highly reducing, and a major problem is their tendency for disproportionation in reactions with electrophiles. This, however, can also give rise to a fascinating chemistry of making and breaking of P–P bonds. On the other hand, neutral cyclooligophosphines, such as cyclo-(P5Ph5), are suitable stable ligands for the formation of phosphorus-rich metal complexes. [ABSTRACT FROM AUTHOR]

Abstract: Carborane‐substituted 1,2‐diphosphetanes (Ia,b) react with elemental lithium in THF with cleavage of the P−P bond to give a deep red solution from which, in the case of Ia, red crystals of a lithiated intermediate, [{1‐Li(THF)PtBu‐6‐PtBu‐4,1,6‐closo‐Li(THF)C2B10H10}{Li(THF)3}]2⋅2 THF (2 a), are obtained. The compound is dimeric, C2‐symmetric and contains six lithium and four phosphorus atoms. Two lithium atoms cap the six‐membered C2B4 faces, resulting in two 13‐vertex closo‐clusters (according to Wade's rules) with docosahedral geometry. The addition of methyl iodide resulted in the formation of zwitterionic bis‐phosphonium‐nido‐carborates 7,10‐bis(tert‐butyldimethylphosphonium)dodecahydro‐7,10‐dicarba‐nido‐dodecaborate(2−) (1 a) and 7,10‐bis(N,N‐diisopropylaminodimethylphosphonium)dodecahydro‐7,10‐dicarba‐nido‐dodecaborate(2−) (1 b) in moderate to good yields. Compounds 1 a and 1 b exhibit short Ccluster−P bonds and large Ccluster⋅⋅⋅Ccluster distances in the solid state. Further insight into the ring opening and reduction potential of the alkyl halide was obtained from methylation reactions of different 1,2‐bis‐phosphinocarboranes. The reaction of rac‐/meso‐1,2‐bis(tert‐butylmethylphosphino)‐1,2‐dicarba‐closo‐dodecaborane(12) (3 a) with two equivalents of methyl iodide also resulted in the formation of 1 a (as shown by NMR spectroscopy), whereas the reaction of 1,2‐bis(diphenylphosphino)‐1,2‐dicarba‐closo‐dodecaborane(12) with methyl triflate afforded the phosphonium salt 1‐methyl‐diphenylphosphonium‐2‐diphenylphosphino‐1,2‐dicarba‐closo‐dodecaborane(12) triflate (4) without reduction of the cluster. [ABSTRACT FROM AUTHOR]