Resurgence of Organomanganese(I) Chemistry. Bidentate Manganese(I) Phosphine–Phenol(ate) Complexes

As part of the United Nations 2019 celebration of the periodic table of elements, we are privileged to present our studies with the element manganese in this Forum Article series. Catalysis with organomanganese­(I) complexes has recently emerged as an important area with the discovery that pincer manganese­(I) complexes that can activate substrates through metal–ligand cooperative mechanisms are active (de)­hydrogenation catalysts. However, this rapidly growing field faces several challenges, and we identify these in this Forum Article. Some of our efforts in addressing these challenges include using alternative precursors to Mn­(CO)5Br to prepare manganese­(I) dicarbonyl complexes, the latter of which is usually a component of active catalysts. Specifically, the synthesis of a new bidentate phosphine–phenol ligand along with its corresponding coordination chemistry of five new manganese­(I) complexes is described. The complexes having two phenol–phenolate moieties interact with the secondary coordination sphere to enable facile loss of the bromido ligand and even one of the CO ligands to afford manganese­(I) dicarbonyl centers

Activation of H₂ with Dinuclear Manganese(I)-Phosphido Complexes

There are few reports of activation of H2 across metal–phosphido linkages, and all of the first-row metal examples use N-heterocyclic phosphido donors. In this report, we highlight the discovery of H2 activation using first-row transition-metal phosphido complexes with alkyl and aryl substituents. The complex [Mn­(CO)4(μ-PPh2)]2 (1) was treated with H2 (125 °C, 33 h), affording [{Mn­(CO)4}­(μ-H)­(μ-PPh2)­{Mn­(CO)3(Ph2PH)}] (2). Treating 2 with Mn2(CO)10 leads to PH bond activation and formation of [{Mn­(CO)4}­(μ-H)­(μ-PPh2)­{Mn­(CO)4}] (3). The interconversion of 1 to 3 is reversible, as indicated by the treatment of 3 with free Ph2PH, giving 2 at 80 °C or 1 and H2 at 120 °C. The isopropyl analogue of 1, [Mn­(CO)4(μ-P­(iPr)2)]2 (5), was synthesized by the oxidative addition of [(iPr)2PP­(iPr)2] (4) with Mn2(CO)10. The reactivity of 5 is analogous to that of 1, forming [{Mn­(CO)4}­(μ-H)­(μ-P­(iPr)2)­{Mn­(CO)3((iPr)2PH}] (6) on treatment with H2, which in turn reacts with Mn2(CO)10, quantitatively affording [{Mn­(CO)4}­(μ-H)­(μ-P­(iPr)2)­{Mn­(CO)4}] (7). The chemistry diverges upon use of the tBu substituent. Treating Na­[Mn­(CO)5] with Cl­(tBu)2P results in formation of the bis-(tBu2P) hexacarbonyl complex [Mn­(CO)3(μ-PtBu2)]2 (8), a dark green compound with a formal M–M double bond (2.5983(5) Å). 8 reacts sluggishly with H2 to form free tBu2PH and [MnH­(CO)4(HPtBu2)] (10). The activation of H2 with 1 is incomplete even at high temperatures. In contrast, facile activation of H2 occurs with [{Mn­(CO)3(μ-PPh2)}2(μ-CO)] (1-CO) to yield 2 (84%, 70 °C, 10 h), implicating thermally demanding CO dissociation from 1 as the first step in the H2 activation. PCl bond activation under hydrogenative conditions was also examined. The reactions between Mn2(CO)10 and ClPh2P or Cl­(iPr)2P under 1 atm of H2 gave 3 (R = Ph) or 7 (R = iPr) in 50–60% yield, indicating the intermediacy of bisphosphido compounds. When Cl­(tBu)2P was used instead, the compounds cis-[Mn­(CO)4(H)­((tBu2)­P)2H)] (10), [Mn­(CO)3(H)­((tBu2)­P)2H] (11), and diaxial-[Mn­(CO)4((tBu2)­PH)]2 (12) were isolated, indicating PCl bond hydrogenation to phosphines using H2 and Mn2(CO)10

Resurgence of Organomanganese(I) Chemistry. Bidentate Manganese(I) Phosphine–Phenol(ate) Complexes

As part of the United Nations 2019 celebration of the periodic table of elements, we are privileged to present our studies with the element manganese in this Forum Article series. Catalysis with organomanganese­(I) complexes has recently emerged as an important area with the discovery that pincer manganese­(I) complexes that can activate substrates through metal–ligand cooperative mechanisms are active (de)­hydrogenation catalysts. However, this rapidly growing field faces several challenges, and we identify these in this Forum Article. Some of our efforts in addressing these challenges include using alternative precursors to Mn­(CO)5Br to prepare manganese­(I) dicarbonyl complexes, the latter of which is usually a component of active catalysts. Specifically, the synthesis of a new bidentate phosphine–phenol ligand along with its corresponding coordination chemistry of five new manganese­(I) complexes is described. The complexes having two phenol–phenolate moieties interact with the secondary coordination sphere to enable facile loss of the bromido ligand and even one of the CO ligands to afford manganese­(I) dicarbonyl centers

Resurgence of Organomanganese(I) Chemistry. Bidentate Manganese(I) Phosphine–Phenol(ate) Complexes

As part of the United Nations 2019 celebration of the periodic table of elements, we are privileged to present our studies with the element manganese in this Forum Article series. Catalysis with organomanganese­(I) complexes has recently emerged as an important area with the discovery that pincer manganese­(I) complexes that can activate substrates through metal–ligand cooperative mechanisms are active (de)­hydrogenation catalysts. However, this rapidly growing field faces several challenges, and we identify these in this Forum Article. Some of our efforts in addressing these challenges include using alternative precursors to Mn­(CO)5Br to prepare manganese­(I) dicarbonyl complexes, the latter of which is usually a component of active catalysts. Specifically, the synthesis of a new bidentate phosphine–phenol ligand along with its corresponding coordination chemistry of five new manganese­(I) complexes is described. The complexes having two phenol–phenolate moieties interact with the secondary coordination sphere to enable facile loss of the bromido ligand and even one of the CO ligands to afford manganese­(I) dicarbonyl centers

Propellanes as Drop-In ROMP Initiators

Addition of 1.1.1-propellane (111P) to (Ph3P)3MCl2 (M = Ru, Os) afforded 3-exo-methylenecycloalkylidene complexes (Ph3P)2Cl2M(cC4H4)CH2 (M = Ru, 1-PPh3; M = Os, 4-PPh3) via electrophilic ring opening. When they were combined in situ or when they were isolated, both 1-PPh3 and 4-PPh3 were competent at the ROMP of norbornene. Phosphine substitution of 1-PPh3 with PcHex3 generated (cHex3P)2Cl2Ru(cC4H4)CH2 (1-PcHex3), which was competent at norbornene ROMP and ring-closing metathesis. Similar in situ addition of tetracyclo­[3.3.1.13,7.01,3]­decane (i.e., 1,3-dehydroadamantane, AdP) to (Ph3P)3RuCl2 yielded (Ph3P)2Cl2RuC­{C9H14) (3-PPh3), a cyclohexylidene derivative with related reactivity. Self-metathesis of 1-PPh3 produced (Ph3P)2Cl2Ru(cC4H4)RuCl2(PPh3) (2-PPh3), which was structurally characterized. The use of 13C-labeled 111P* enabled identification of several alkylidene resonances in 13C NMR spectra

Resurgence of Organomanganese(I) Chemistry. Bidentate Manganese(I) Phosphine–Phenol(ate) Complexes

As part of the United Nations 2019 celebration of the periodic table of elements, we are privileged to present our studies with the element manganese in this Forum Article series. Catalysis with organomanganese­(I) complexes has recently emerged as an important area with the discovery that pincer manganese­(I) complexes that can activate substrates through metal–ligand cooperative mechanisms are active (de)­hydrogenation catalysts. However, this rapidly growing field faces several challenges, and we identify these in this Forum Article. Some of our efforts in addressing these challenges include using alternative precursors to Mn­(CO)5Br to prepare manganese­(I) dicarbonyl complexes, the latter of which is usually a component of active catalysts. Specifically, the synthesis of a new bidentate phosphine–phenol ligand along with its corresponding coordination chemistry of five new manganese­(I) complexes is described. The complexes having two phenol–phenolate moieties interact with the secondary coordination sphere to enable facile loss of the bromido ligand and even one of the CO ligands to afford manganese­(I) dicarbonyl centers

Resurgence of Organomanganese(I) Chemistry. Bidentate Manganese(I) Phosphine–Phenol(ate) Complexes

As part of the United Nations 2019 celebration of the periodic table of elements, we are privileged to present our studies with the element manganese in this Forum Article series. Catalysis with organomanganese­(I) complexes has recently emerged as an important area with the discovery that pincer manganese­(I) complexes that can activate substrates through metal–ligand cooperative mechanisms are active (de)­hydrogenation catalysts. However, this rapidly growing field faces several challenges, and we identify these in this Forum Article. Some of our efforts in addressing these challenges include using alternative precursors to Mn­(CO)5Br to prepare manganese­(I) dicarbonyl complexes, the latter of which is usually a component of active catalysts. Specifically, the synthesis of a new bidentate phosphine–phenol ligand along with its corresponding coordination chemistry of five new manganese­(I) complexes is described. The complexes having two phenol–phenolate moieties interact with the secondary coordination sphere to enable facile loss of the bromido ligand and even one of the CO ligands to afford manganese­(I) dicarbonyl centers

Rapid Dissolution of BaSO₄ by Macropa, an 18-Membered Macrocycle with High Affinity for Ba²⁺

Insoluble BaSO4 scale is a costly and time-consuming problem in the petroleum industry. Clearance of BaSO4-impeded pipelines requires chelating agents that can efficiently bind Ba2+, the largest nonradioactive +2 metal ion. Due to the poor affinity of currently available chelating agents for Ba2+, however, the dissolution of BaSO4 remains inefficient, requiring very basic solutions of ligands. In this study, we investigated three diaza-18-crown-6 macrocycles bearing different pendent arms for the chelation of Ba2+ and assessed their potential for dissolving BaSO4 scale. Remarkably, the bis-picolinate ligand macropa exhibits the highest affinity reported to date for Ba2+ at pH 7.4 (log K′ = 10.74), forming a complex of significant kinetic stability with this large metal ion. Furthermore, the BaSO4 dissolution properties of macropa dramatically surpass those of the state-of-the-art ligands DTPA and DOTA. Using macropa, complete dissolution of a molar equivalent of BaSO4 is reached within 30 min at room temperature in pH 8 buffer, conditions under which DTPA and DOTA only achieve 40% dissolution of BaSO4. When further applied for the dissolution of natural barite, macropa also outperforms DTPA, showing that this ligand is potentially valuable for industrial processes. Collectively, this work demonstrates that macropa is a highly effective chelator for Ba2+ that can be applied for the remediation of BaSO4 scale