Sustainable Fertilizers: Publication Landscape on Wastes as Nutrient Sources, Wastewater Treatment Processes for Nutrient Recovery, Biorefineries, and Green Ammonia Synthesis.

The ability of modern agriculture to meet future food demand imposed by accelerating growth of the world's population is a major challenge, and fertilizers play a key role by replacing nutrients in agricultural soil. Given the need for fertilizers, their cost in nonrenewable resources and energy, and the consequences of the greenhouse gas emissions required to make them, people have begun to explore ways to make fertilizer manufacturing and use more sustainable. Using data from the CAS Content Collection, this review examines and analyzes the academic and patent literature on sustainable fertilizers from 2001 to 2021. The breakdown of journal and patent literature publication over time on this topic, country or region of publications, the substances included in published research, among other things allow us to understand the general progress in the field as well as the classes of materials and concepts driving innovation. We hope that this bibliometric analysis and literary review will assist researchers in relevant industries to discover and implement ways to supplement conventional fertilizers and nutrient sources while improving the efficiency and sustainability of waste management and ammonia production.

Aminolysis of bis[bis(trimethylsilyl)amido]-manganese, -iron, and -cobalt for the synthesis of mono- and bis-silylene complexes.

We report a method for the synthesis of amidinate stabilized silylene (NHSi) metal-halide complexes from M{N(SiMe3)2}2 (M = Mn, Fe, Co). The reported reactions can be used to make mono-silylene or bis-silylene complexes and the resulting products can be easily controlled by the reaction stoichiometry. Additionally, we apply this new synthetic protocol for the synthesis of a bis-iron complex derived from a bis-amidinate ligand having a terphenyl backbone.

Dimerization of terminal alkynes promoted by a heterobimetallic Zr/Co complex.

Enynes are important synthetic intermediates that are also found in a variety of natural products and other biologically relevant molecules. The most atom economical synthetic route to enynes is via the direct coupling of readily available terminal alkyne precursors. Towards this goal, we demonstrate the formation of 1,3-enynes from terminal alkynes facilitated by a reduced ZrIV/Co-I heterobimetallic complex. An intermediate is trapped as a tBuNC adduct, revealing that bimetallic activation of the terminal C-H bond of the alkyne is an essential mechanistic step.

Assessing the Metal-Metal Interactions in a Series of Heterobimetallic Nb/M Complexes (M = Fe, Co, Ni, Cu) and Their Effect on Multielectron Redox Properties.

A one-pot synthetic procedure for a series of bimetallic Nb/M complexes, Cl-Nb( iPrNPPh2)3M-X (M = Fe (2), Ni (4), Cu (5)), is described. A similar procedure aimed at synthesizing a Nb/Co analogue instead affords iPrN═Nb( iPrNPPh2)2(µ-PPh2)Co-I (3) through cleavage of one phosphinoamide P-N bond under reducing conditions. Complexes 4 and 5 are found to have short Nb-M distances, corresponding to unusual metal-metal bonds between Nb and these first row transition metals. For comparison, a series of heterobimetallic O≡Nb( iPrNPPh2)3M-X complexes (M = Fe (7), Co (8), Ni (9), Cu (10)) was synthesized. In these complexes, the NbV center is engaged in sufficient π-bonding to the terminal oxo ligand to remove the driving force for direct metal-metal interactions. A comparison of the cyclic voltammograms of 2 and 4-10 reveals that the presence of a second metal shifts the redox potentials of both Nb and the late metal center anodically, even when direct metal-metal interactions are not present.

Heterobimetallic Complexes Comprised of Nb and Fe: Isolation of a Coordinatively Unsaturated NbIII/Fe0 Bimetallic Complex Featuring a Nb≡Fe Triple Bond.

Heterometallic multiple bonds between niobium and other transition metals have not been reported to date, likely owing to the highly reactive nature of low-valent niobium centers. Herein, a C3-symmetric tris(phosphinoamide) ligand framework is used to construct a Nb/Fe heterobimetallic complex Cl-Nb(iPrNPPh2)3Fe-Br (2), which features a Fe→Nb dative bond with a metal-metal distance of 2.4269(4) Å. Reduction of 2 in the presence of PMe3 affords Nb(iPrNPPh2)3Fe-PMe3 (6), a compound with an unusual trigonal pyramidal geometry at a NbIII center, a Nb≡Fe triple bond, and the shortest bond distance (2.1446(8) Å) ever reported between Nb and any other transition metal. Complex 6 is thermally unstable and degrades via P-N bond cleavage to form a NbV═NR imide complex, iPrN═Nb(iPrNPPh2)3Fe-PMe3 (9). The heterobimetallic complexes iPrN═Nb(iPrNPPh2)3Fe-Br (8) and 9 are independently synthesized, revealing that the strongly π-bonding imido functionality prevents significant metal-metal interactions. The 57Fe Mössbauer spectra of 2, 6, 8, and 9 show a clear trend in isomer shift (δ), with a decrease in δ as metal-metal interactions become stronger and the Fe center is reduced. The electronic structure and metal-metal bonding of 2, 6, 8, and 9 are explored through computational studies, and cyclic voltammetry is used to better understand the effect of metal-metal interaction in early/late heterobimetallic complexes on the redox properties of the two metals involved.

Multi-electron redox processes at a Zr(iv) center facilitated by an appended redox-active cobalt-containing metalloligand.

The reactivity of a reduced heterobimetallic Co(-I)/Zr(IV) complex, ((t)BuNC)Co((i)Pr2PNMes)3Zr(THF) (), with a series of azido and diazo reagents is explored to demonstrate the feasibility of facilitating two-electron redox processes at a formally d(0) Zr(iv) center using the appended Co fragment exclusively as an electron-reservoir. Addition of mesityl or adamantyl azide to affords the terminal ((t)BuNC)Co((i)Pr2PNMes)3Zr[triple bond, length as m-dash]NMes () and bridging ((t)BuNC)Co((i)Pr2PNMes)2(µ-NAd)Zr((i)Pr2PNMes) () Co(I)/Zr(IV) imido products, respectively. Similarly, diphenyldiazomethane reacts with to afford the terminal Ph2CN2(2-)-bound product ((t)BuNC)Co((i)Pr2PNMes)3Zr[triple bond, length as m-dash]N-N[double bond, length as m-dash]CPh2 () via a two-electron oxidation of the Co center. Thermolysis of results in a structural rearrangement to the diazomethane-bridged isomer ((t)BuNC)Co((i)Pr2PNMes)2(µ-N2CPh2)Zr((i)Pr2PNMes) (). In contrast, treatment of with 0.5 equivalents of the conjugated diazo reagent ethyl diazoacetate affords a tetranuclear Zr(IV)/Co(0) complex, ((t)BuNC)Co((i)Pr2PNMes)3Zr(µ2-κ(1)-O-η(2)-N,N-OC(OEt)CHN2)Zr(MesNP(i)Pr2)3Co(CN(t)Bu) (), bridged through enolate and η(2)-bound diazo functionalities.

Assignment of the oxidation states of Zr and Co in a highly reactive heterobimetallic Zr/Co complex using X-ray absorption spectroscopy (XANES).

The reduced heterobimetallic complex (THF)Zr(MesNP(i)Pr2)3CoN2 (1) has been examined along with a series of structurally similar reference compounds using X-ray absorption near edge structure (XANES) spectroscopy. Complex 1 has been shown to be highly reactive, often via one-electron pathways that might be expected for a d(1) Zr(III) complex. However, the presence of two strongly interacting metals in complex 1 renders the assignment of oxidation states ambiguous. Both Zr and Co K-edge XANES spectra reveal that the most accurate description of complex 1 is that of a Zr(IV)/Co(-I) zwitterion. Electronic structure calculations support this assignment.

One-electron oxidation chemistry and subsequent reactivity of diiron imido complexes.

The chemical oxidation and subsequent group transfer activity of the unusual diiron imido complexes Fe((i)PrNPPh2)3Fe≡NR (R = tert-butyl ((t)Bu), 1; adamantyl, 2) was examined. Bulk chemical oxidation of 1 and 2 with Fc[PF6] (Fc = ferrocene) is accompanied by fluoride ion abstraction from PF6(-) by the iron center trans to the Fe≡NR functionality, forming F-Fe((i)PrNPPh2)3Fe≡NR ((i)Pr = isopropyl) (R = (t)Bu, 3; adamantyl, 4). Axial halide ligation in 3 and 4 significantly disrupts the Fe-Fe interaction in these complexes, as is evident by the >0.3 Å increase in the intermetallic distance in 3 and 4 compared to 1 and 2. Mössbauer spectroscopy suggests that each of the two pseudotetrahedral iron centers in 3 and 4 is best described as Fe(III) and that one-electron oxidation has occurred at the tris(amido)-ligated iron center. The absence of electron delocalization across the Fe-Fe≡NR chain in 3 and 4 allows these complexes to readily react with CO and (t)BuNC to generate the Fe(III)Fe(I) complexes F-Fe((i)PrNPPh2)3Fe(CO)2 (5) and F-Fe((i)PrNPPh2)3Fe((t)BuNC)2 (6), respectively. Computational methods are utilized to better understand the electronic structure and reactivity of oxidized complexes 3 and 4.

Metal-metal multiple bonding in C3-symmetric bimetallic complexes of the first row transition metals.

Metal-metal multiple bonds have been an intense area of focus in inorganic chemistry for many decades as a result of their fundamentally interesting bonding properties, as well as their potential applications in multielectron transfer and small molecule activation processes. Much of what is known in this field revolves around 2nd and 3rd row transition metals, with fundamental knowledge lacking in the area of bonds between elements of the first transition series. The smaller size and tendency of first row ions to adopt high-spin electron configurations weaken metal-metal interactions and serve to complicate the interpretation of the electronic structure and bonding in bimetallic species containing first row transition metals. Furthermore, traditional tetragonal "paddlewheel" complexes dominate the metal-metal multiple bond literature, and only recently have researchers begun to take advantage of the weaker ligand field in three-fold symmetric bimetallic complexes to encourage more favourable metal-metal bonding interactions. In the past 5 years, several research groups have exploited three-fold symmetric frameworks to investigate new trends in metal-metal bonding involving the first row transition metals. This feature article serves to highlight recent achievements in this area and to use C3-symmetric systems as a model to better understand the fundamental aspects of multiple bonds featuring first row transition metals.

Effect of ligand modification on the reactivity of phosphinoamide-bridged heterobimetallic Zr/Co complexes.

The effect of modifying the N-aryl substituent (aryl = mesityl vs. m-xylyl) of the phosphinoamide ligands linking Zr and Co in tris(phosphinoamide)-linked heterobimetallic complexes has been investigated. Treatment of the metalloligand ((i)Pr2PNXyl)3ZrCl (2) (Xyl = m-xylyl) with CoI2 affords the iodide-bridged product ICo((i)Pr2PNXyl)2(µ-I)Zr(η(2-i)Pr2PNXyl) (3) rather than the C3-symmetric isomer observed using the N-mesityl derivative, ICo((i)Pr2PNMes)3ZrCl. Upon two-electron reduction of complex 3, ligand rearrangement occurs to generate the three-fold symmetric reduced complex N2Co((i)Pr2PNXyl)3Zr(THF) (4). Comparison of 4 with the previously reported mesityl-substituted complex N2Co((i)Pr2PNMes)3Zr(THF) (1) reveals similar structural features but with a less sterically hindered Zr apical site in complex 4. An obvious electronic difference between these two complexes is also present based on the drastically different infrared N2 stretching frequencies of 1 and 4. These notable differences lend themselves to different reactivity in both stoichiometric and catalytic reactions. Alkyl halide addition to complex 4 results in homo-coupling products resulting from alkyl radicals rather than the alkyl-bridged or intramolecular C-H activation products formed upon addition of RX to 1. This difference in reactivity with alkyl halides renders complex 3 a less effective catalyst for the Kumada cross-coupling of alkyl halides with n-octylMgBr than ICo((i)Pr2PNMes)3ZrCl, as a greater proportion of homocoupling products are formed under catalytic conditions.

Synthesis, structure, and reactivity of an anionic Zr-oxo relevant to CO2 reduction by a Zr/Co heterobimetallic complex.

Oxidative addition of CO2 to the reduced Zr/Co complex (THF)Zr(MesNP(i)Pr2)3Co (1) followed by one-electron reduction leads to formation of an unusual terminal Zr-oxo anion [2][Na(THF)3] in low yield. To facilitate further study of this compound, an alternative high-yielding synthetic route has been devised. First, 1 is treated with CO to form (THF)Zr(MesNP(i)Pr2)3Co(CO) (3); then, addition of H2O to 3 leads to the Zr-hydroxide complex (HO)Zr(MesNP(i)Pr2)3Co(CO) (4). Deprotonation of 4 with Li(N(SiMe3)2) leads to the anionic Zr-oxo species [2][Li(THF)3] or [2][Li(12-c-4)] in the absence or presence of 12-crown-4, respectively. The coordination sphere of the Li(+) countercation is shown to lead to interesting structural differences between these two species. The anionic oxo fragment in complex [2][Li(12-c-4)] reacts with electrophiles such as MeOTf and Me3SiOTf to generate (MeO)Zr(MesNP(i)Pr2)3Co(CO) (5) and (Me3SiO)Zr(MesNP(i)Pr2)3Co(CO) (6), respectively, and addition of acetic anhydride generates (AcO)Zr(MesNP(i)Pr2)3Co(CO) (7). Complex [2][Li(12-c-4)] is also shown to bind CO2 to form a monoanionic Zr-carbonate, [(12-crown-4)Li][(κ(2)-CO3)Zr(MesNP(i)Pr2)3Co(CO)] ([8][Li(12-c-4)]). A more stable version of this compound [8][K(18-c-6)] is formed when a K(+) counteranion and 18-crown-6 are used. Binding of CO2 to [2][Li(12-c-4)] is shown to be reversible using isotopic labeling studies. In an effort to address methods by which these CO2-derived products could be turned over in a catalytic cycle, it is shown that the Zr-OMe bond in 5 can be cleaved using H(+) and the CO ligand can be released from Co under photolytic conditions in the presence of I2.

Development of more labile low electron count Co(I) sources: mild, catalytic functionalization of activated alkanes using a [(Cp*Co)2-µ-(η4:η4-arene)] complex.

Catalytic transfer dehydrogenation of silyl protected amines, requiring sp(3) C-H bond activation, is mediated by a bridging arene complex of the type [(Cp*Co)(2)-µ-(η(4):η(4)-arene)] under mild conditions. Mechanistic and qualitative rate studies establish the compound as a more reactive Co(I) source when compared to other known Cp*Co(I) complexes.

Activation of CO2 by a heterobimetallic Zr/Co complex.

At room temperature, the early/late heterobimetallic complex Co((i)Pr(2)PNMes)(3)Zr(THF) has been shown to oxidatively add CO(2), generating (OC)Co((i)Pr(2)PNMes)(2)(µ-O)Zr((i)Pr(2)PNMes). This compound can be further reduced under varying conditions to generate either the Zr oxoanion (THF)(3)Na-O-Zr(MesNP(i)Pr(2))(3)Co(CO) or the Zr carbonate complex (THF)(4)Na(2)(CO(3))-Zr(MesNP(i)Pr(2))(3)Co(CO). Additionally, reactivity of the CO(2)-derived product has been observed with PhSiH(3) to generate the Co-hydride/Zr-siloxide product (OC)(H)Co((i)Pr(2)PNMes)(3)ZrOSiH(2)Ph.