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1. Conformationally Rigid Cyclic Tungsten Bis-Alkyne Complexes Derived from 1,1’-Dialkynylferrocenes

   https://doi.org/10.1016/j.jorganchem.2017.05.048  

   Curran, T. P.; Lawrence, A. P.; Murtaugh, T. S.; Ji, W.; Pokharel, N.; Gober, C. B.; Suitor, J. (October 2017, Journal of organometallic chemistry)

   In exploring the conformational behavior of cyclic tungsten bis-alkyne complexes, two dialkynylamides (14a and 14c) and two dialkynylesters (14b and 14d) derived from 1,1’-ferrocenedicarboxylic acid were prepared. They were subsequently reacted with W(CO)3(dmtc)2 to yield the desired cyclic tungsten bis-alkyne complexes 8-11. In the cyclization of 14a to yield 8 a dimeric macrocyclic complex, 15, featuring two tungsten bis-alkyne complexes in the ring, also was isolated. The conformational behavior of these complexes was assessed by analysis of the 1H NMR resonances for the alkyne hydrogens, which appear around 11 ppm. The spectra for complexes 10, 11 and 15 show multiple singlets of varying integrations for these protons, while the spectra for complexes 8 and 9 show only two resonances of equal integration for the alkyne hydrogens. The spectra for 8 and 9 changed very little when examined at higher temperatures, indicating that the solution conformation is robust. A ROESY spectrum was obtained for 8. It did not show any crosspeaks between the two alkyne hydrogens. The NMR data shows that the alkyne ligands in 10, 11 and 15 are able to rotate about the tungsten-alkyne bond; these complexes adopted several different solution conformations relating to syn and anti arrangements of the alkyne ligands. In contrast, complexes 8 and 9 adopt only one solution conformation, and the alkyne ligands in these species do not rotate about the tungsten-alkyne bond. The NMR spectra for 8 and 9 also show that these complexes are asymmetric. The 1H NMR spectra for 8 and 9 show that each hydrogen atom has its own unique resonance in the 1H NMR spectrum. There are 8 resonances for the 8 Cp protons, 4 resonances for the methylene protons, 2 resonances for the alkyne protons, and in the case of 8, 2 resonances for the NH protons. The two NH protons on complex 8 were found to have widely different chemical shifts. A DMSO titration was performed and it showed that one of the two NH protons in 8 is involved in an intramolecular hydrogen bond. Given that the diester 9 adopts a similar conformation as the diamide 8, this intramolecular hydrogen bond appears to result from the conformation imposed by cyclization of the ring system. Overall, the data show that the ring system for 8 and 9 provides a unique, rigid, robust, and air stable cyclic molecule where the alkyne ligands are limited to one orientation, presumably the syn orientation. The lack of mobility for the alkyne ligands limits the cyclic molecule to only one solution conformation. Complexes 8 and 9 are the first reported examples of cyclic tungsten bis-alkyne complexes that only adopt a single, robust conformation in solution. 

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2. Introducing the Bis(mesitoyl)phosphide Ligand into Dinuclear Trivalent Rare Earth Metal Coordination Chemistry

   https://doi.org/10.1002/cplu.202400311  

   Deshapriya, Saroshan; Delano, IV, Francis; Demir, Selvan (August 2024, ChemPlusChem)

   Abstract Anionic ancillary ligands play a critical role in the construction of rare earth (RE) metal complexes due to the large influence on the stability of the molecule and engendering emergent electronic properties that are of interest in a plethora of applications. Supporting ligands comprising oxygen donor atoms are highly pursued in RE chemistry owing to the high oxophilicity innate to these ions. The scarcely employed bis(acyl)phosphide (BAP) ligands feature oxygen coordination sites and contain a phosphide backbone rendering it attractive for RE‐coordination chemistry. Here, we integrate bis(mesitoyl)phosphide (^mesBAP) as an ancillary ligand into RE^IIIchemistry to generate the first dinuclear trivalent RE complexes containing BAP ligands; [{^mesBAP}₂RE(THF)(μ‐Cl)]₂(RE=Y, (1), Gd (2), and Dy (3); THF=tetrahydrofuran). Each RE center is ligated to two monoanionic^mesBAP ligands, one THF molecule and one chloride ion. All three molecules were characterized through single‐crystal X‐ray diffraction,³¹P NMR, IR and UV‐Vis spectroscopy.³¹P,¹H and¹³C NMR on the diamagnetic yttrium congener1confirm asymmetric ligand coordination. DFT calculations conducted on2provided insight into the electronic structure. The magnetic properties of2and3were investigated via SQUID magnetometry. The Gd^IIIions exhibit weak antiferromagnetic coupling, corroborated by DFT results. 

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3. Synthesis of phosphiranes via organoiron-catalyzed phosphinidene transfer to electron-deficient olefins

   https://doi.org/10.1039/d2sc05011k  

   Xin, Tiansi; Geeson, Michael B.; Zhu, Hui; Qu, Zheng-Wang; Grimme, Stefan; Cummins, Christopher C. (November 2022, Chemical Science)

   Herein is reported the structural characterization and scalable preparation of the elusive iron–phosphido complex FpP( t Bu)(F) (2-F, Fp = (Fe(η 5 -C 5 H 5 )(CO) 2 )) and its precursor FpP( t Bu)(Cl) (2-Cl) in 51% and 71% yields, respectively. These phosphide complexes are proposed to be relevant to an organoiron catalytic cycle for phosphinidene transfer to electron-deficient alkenes. Examination of their properties led to the discovery of a more efficient catalytic system involving the simple, commercially available organoiron catalyst Fp 2 . This improved catalysis also enabled the preparation of new phosphiranes with high yields ( t BuPCH 2 CHR; R = CO 2 Me, 41%; R = CN, 83%; R = 4-biphenyl, 73%; R = SO 2 Ph, 71%; R = POPh 2 , 70%; R = 4-pyridyl, 82%; R = 2-pyridyl, 67%; R = PPh 3 + , 64%) and good diastereoselectivity, demonstrating the feasibility of the phosphinidene group-transfer strategy in synthetic chemistry. Experimental and theoretical studies suggest that the original catalysis involves 2-X as the nucleophile, while for the new Fp 2 -catalyzed reaction they implicate a diiron–phosphido complex Fp 2 (P t Bu), 4, as the nucleophile which attacks the electron-deficient olefin in the key first P–C bond-forming step. In both systems, the initial nucleophilic attack may be accompanied by favorable five-membered ring formation involving a carbonyl ligand, a (reversible) pathway competitive with formation of the three-membered ring found in the phosphirane product. A novel radical mechanism is suggested for the new Fp 2 -catalyzed system. 

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4. Molecular Mimics of Heterogeneous Metal Phosphides: Thermochemistry, Hydride‐Proton Isomerism, and HER Reactivity

   https://doi.org/10.1002/anie.201808307  

   Buss, Joshua A.; Hirahara, Masanari; Ueda, Yohei; Agapie, Theodor (November 2018, Angewandte Chemie International Edition)

   Abstract A new series of low‐valent dinuclear molybdenum complexes bearing phosphido or phosphinidene bridging ligands was synthesized as a structural model of heterogeneous metal phosphide catalysts. Addition of acid to a monocationic Mo₂‐μ‐P complex results in phosphide protonation, affording a dicationic Mo₂‐μ‐PH species. Alternatively, reaction of an isoelectronic Mo₂‐μ‐P precursor with LiBEt₃H gives a Mo₂H‐μ‐P complex. Mixing these species, one bearing a Mo−H and the other a P−H bond, results in facile H₂production at room temperature. 

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5. P-H/Ru-Cl migration by triphosphine pincer-ruthenium complexes

   Mandal, Souvik; Malakar, Santanu; Emge, Thomas J; Hughes, Russell Profit; Goldman, Alan S (August 2023, American Chemical Society)

   Metal ligand cooperativity (MLC) has revealed a plethora of unusual reactivity in catalysis in the last couple of decades. Since Milstein's report of aromatization-dearomatization of the pincer backbone of pyridine-based-pincer complexes, ruthenium has played a partic ularly important role in the develo pment of M LC. We have recently reported a (H- P3 )Ir complex which is the fastest known catalyst for alkane-transfer dehydrogenation. The active species results from P- to-Ir migration of H in this system. We further explored the possib ility of MLC in an analogous Ru system. Surprisingly, when metalating the same H-P3 ligand with a RuCl2 precursor we only isolated a (Cl-P3 )Ru(H)Cl complex where H had migrated to Ru from P, and Cl to P from Ru ("P- H/M-X exchange"). We have demonstrated that the thermodynamically favored direction of such exchanges depends strongly on the ancillary ligands, with particular driving force for formation of 5-coordinate (pincer)MHCl complexes (M = d6 metal center) . However, for 6- coordinate Ru complexes (H- pincer)MXYL, the electronic nature of L appears to determine if P-H/M-X exchange occurs. Strongly pi-accepting ligands promote P-X/M-H exchange with the reaction observed for L = CO, xylylisonitrile and N O+ , but not for L = N2 , C H3 CN, or PMe3 . While exchange at 5- coordinate (16e- ) Ru centers appears to proceed through initial P-to-Ru migration of X or H, to give a phosphide interme diate, in the case of 6- coordinate (18e- ) Ru centers exchange is believed to proceed through phosphoranyl intermediates. DFT and intrinsic bond orbital anal. has been used to better understand this reactivity. 

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