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.

Dehydrohalogenation of fac-Mn­(κ2-N,P-PicP)­(CO)3Br (1 H ) and fac-Mn­(κ2-N,P-LutP)­(CO)3Br (1 Me ) with equimolar K­[N­(SiMe3)]2 afforded the reactive, aromatized 18-electron complexes fac-Mn­(κ3-N,C,P-PicP)­(CO)3 (2 H ) and fac-Mn­(κ3-N,C,P-LutP)­(CO)3 (2 Me ), respectively, with atypical binding modes. 2 H and 2 Me activate H2 across the Mn­(I)–C bond to furnish hydride complexes fac-Mn­(κ2-N,P-PicP)­(CO)3H (4 H ) and fac-Mn­(κ2-N,P-LutP)­(CO)3H (4 Me ), respectively. Both 2 H and 2 Me were observed to produce dearomatized 18-electron complexes Mn­(κ2-N,P-PicP*)­(CO)4 (3 H ) and Mn­(κ2-N,P-LutP*)­(CO)4 (3 Me ), respectively, when reacted with CO. The reactive Mn­(I)–C moiety of 2 H and 2 Me reacts with a variety of electrophiles: benzyl cyanide to form fac-Mn­(κ3-N,N′,P-(LutP-BnCN))­(CO)3 (6), E-chalcone to form fac-Mn­(κ3-N,C,P-LutP-chalcone)­(CO)3 (7), and AlCl3 to form fac-Mn­(κ3-N,Cl,P-PicP-AlCl3)­(CO)3 (8 H ) and fac-Mn­(κ3 -N,Cl,P-LutP-AlCl3)­(CO)3 (8 Me ) featuring a rare intramolecular Mn-(μ-Cl)-Al moiety. Mn­(I)-catalyzed Michael addition was explored. Dehydrohalogenation of 1 H with alkoxides afforded the substituted complex fac-Mn­(κ2-N,P-PicP)­(OR)­(CO)3 (10 H ) that was also reactive toward H2 forming 4 H . Under identical conditions with alkoxide bases, 1 Me affords 2 Me demonstrating dichotomous behavior. We also explored the iPr-substituted analogues of 1 H and 1 Me (11 H and 11 Me , respectively) and found them to be essentially identical in behavior. Complexes 1 R and 11 R were found to be excellent catalysts for styrene hydrogenation. The relevance of the κ3-N,C,P binding mode discovered herein to catalysis is briefly discussed.

Herein, we report a new tripodal tris‐benzimidazole ligand (Tbim) that structurally mimics the 3‐His coordination environment of certain nonheme mononuclear iron oxygenases. The coordination chemistry of Tbim was explored with iron(II) revealing a diverse set of coordination modes. The aerobic oxidation of biomimetic model substrate diethyl‐2‐phenylmalonate was studied using the Tbim−Fe and Fe(OTf)2.

Dinuclear manganese hydride complexes of the form [Mn2(CO)8(μ‐H)(μ‐PR2)] (R=Ph, 1; R=iPr, 2) were used in E‐selective alkyne semi‐hydrogenation (E‐SASH) catalysis. Catalyst speciation studies revealed rich coordination chemistry and the complexes thus formed were isolated and in turn tested as catalysts; the results underscore the importance of dinuclearity in engendering the observed E‐selectivity and provide insights into the nature of the active catalyst. The insertion product obtained from treating 2 with (cyclopropylethynyl)benzene contains a cis‐alkenyl bridging ligand with the cyclopropyl ring being intact. Treatment of this complex with H2 affords exclusively trans‐(2‐cyclopropylvinyl)benzene. These results, in addition to other control experiments, indicate a non‐radical mechanism for E‐SASH, which is highly unusual for Mn−H catalysts. The catalytically active species are virtually inactive towards cis to trans alkene isomerization indicating that the E‐selective process is intrinsic and dinuclear complexes play a critical role. A reaction mechanism is proposed accounting for the observed reactivity which is fully consistent with a kinetic analysis of the rate limiting step and is further supported by DFT computations.

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This work describes the synthesis and characterization of new ligands and iron complexes for mononuclear nonheme iron oxygenase structural models.

Metal-ligand cooperativity (MLC) predominantly occurs across transition-metal amido moieties. In contrast, there are few reports of activation of H2 or substrate across metal-phosphido linkages, and all of the first-row metal examples use N-heterocyclic phosphido donors. In this report, we highlight a discovery of the first MLC dihydrogen activation with first-row transition metal M-PR2 (R = alkyl or aryl) complexes using dinuclear Mn(I)-bisphosphido complexes. In addition, we demonstrate that oxidative addition of P-Cl bond leads to the same Mn(I)-bisphosphido complexes at elevated temperatures, enabling a simple and versatile strategy for in-situ reduction of phosphine chlorides to phosphine using dihydrogen, a process that appears general having success with both diaryl-and dialkyl-phosphines.

A class of organomanganese hydrogenation catalysts was recently rediscovered. These are simple dinuclear Mn(I) carbonyl compounds with phosphido (PR 2 À ) and hydrido (H À ) bridges. This class of compounds has been known since the 1960's, and they have rich coordination chemistry and reactivity. Given their recently discovered potential for catalytic applications, a fresh look at this class of compounds was necessary. Hence, this Review comprehensively covers the synthesis, reactivity, and catalysis of this interesting class of molecules.