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1. Lung parenchyma transverse relaxation rates at 0.55 T

   https://doi.org/10.1002/mrm.29541  

   Li, Bochao; Lee, Nam G; Cui, Sophia X; Nayak, Krishna S (April 2023, Magnetic Resonance in Medicine)

   PurposeTo determineR₂and transverse relaxation rates in healthy lung parenchyma at 0.55 T. This is important in that it informs the design and optimization of new imaging methods for 0.55T lung MRI. MethodsExperiments were performed in 3 healthy adult volunteers on a prototype whole‐body 0.55T MRI, using a custom free‐breathing electrocardiogram‐triggered, single‐slice echo‐shifted multi‐echo spin echo (ES‐MCSE) pulse sequence with respiratory navigation. Transverse relaxation ratesR₂and and off‐resonance ∆fwere jointly estimated using nonlinear least‐squares estimation. These measurements were compared againstR₂estimates from T₂‐prepared balanced SSFP (T₂‐Prep bSSFP) and estimates from multi‐echo gradient echo, which are used widely but prone to error due to different subvoxel weighting. ResultsThe meanR₂and values of lung parenchyma obtained from ES‐MCSE were 17.3 ± 0.7 Hz and 127.5 ± 16.4 Hz (T₂ = 61.6 ± 1.7 ms;  = 9.5 ms ± 1.6 ms), respectively. The off‐resonance estimates ranged from −60 to 30 Hz. TheR₂from T₂‐Prep bSSFP was 15.7 ± 1.7 Hz (T₂ = 68.6 ± 8.6 ms) and from multi‐echo gradient echo was 131.2 ± 30.4 Hz ( = 8.0 ± 2.5 ms). Paired t‐test indicated that there is a significant difference between the proposed and reference methods (p < 0.05). The meanR₂estimate from T₂‐Prep bSSFP was slightly smaller than that from ES‐MCSE, whereas the mean and estimates from ES‐MCSE and multi‐echo gradient echo were similar to each other across all subjects. ConclusionsJoint estimation of transverse relaxation rates and off‐resonance is feasible at 0.55 T with a free‐breathing electrocardiogram‐gated and navigator‐gated ES‐MCSE sequence. At 0.55 T, the meanR₂of 17.3 Hz is similar to the reported meanR₂of 16.7 Hz at 1.5 T, but the mean of 127.5 Hz is about 5–10 times smaller than that reported at 1.5 T. 

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2. Isolation of an Elusive Phosphametallacyclobutadiene and Its Role in Reversible Carbon−Carbon Bond Cleavage

   https://doi.org/10.1002/anie.202203073  

   Jakhar, Vineet K.; Esper, Alec M.; Ghiviriga, Ion; Abboud, Khalil A.; Ehm, Christian; Veige, Adam S. (June 2022, Angewandte Chemie International Edition)

   Abstract The reactivity of phosphaalkynes, the isolobal and isoelectronic congeners to alkynes, with metal alkylidyne complexes is explored in this work. Treating the tungsten alkylidyne [^tBuOCO]W≡C^tBu(THF)₂(1) with phosphaalkyne (10) results in the formation of [O₂C(^tBuC=)W{η²‐(P,C)−P≡C−Ad}(THF)] (13‐^tBu_THF) and [O₂C(AdC=)W{η²‐(P,C)−P≡C−^tBu}(THF)] (13‐Ad_THF); derived from the formal reductive migratory insertion of the alkylidyne moiety into a W−C_arenebond. Analogous to alkyne metathesis, a stable phosphametallacyclobutadiene complex [^tBuOCO]W[κ²‐C(^tBu)PC(Ad)] (14) forms upon loss of THF from the coordination sphere of either13‐^tBu_THFor13‐Ad_THF. Remarkably, the C−C bonds reversibly form/cleave with the addition or removal of THF from the coordination sphere of the formal tungsten(VI) metal center, permitting unprecedented control over the transformation of a tetraanionic pincer to a trianionic pincer and back. Computational analysis offers thermodynamic and electronic reasoning for the reversible equilibrium between13‐^tBu/Ad_THFand14. 

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3. Heteroleptic Square Planar Cobalt(I/II) Complexes

   https://doi.org/10.1002/ejic.202200675  

   Gao, Yafei; Lee, Wei‐Tsung; Carta, Veronica; Chen, Chun‐Hsing; Telser, Joshua; Smith, Jeremy_M (January 2023, European Journal of Inorganic Chemistry)

   Abstract Reduction of the cobalt(II) chloride complex, Ph₂B(^tBuIm)₂Co(THF)Cl (1) in the presence of^tBuN≡C affords the diamagnetic, square planar cobalt(I) complex Ph₂B(^tBuIm)₂Co(C≡N^tBu)₂(2). This is a rare example of a 16‐electron cobalt(I) complex that is structurally related to square planar noble metal complexes. Accordingly, the electronic structure of2, as calculated by DFT, reveals that the HOMO is largely d_z²in character. Complex2is readily oxidized to its cobalt(II) congener [Ph₂B(^tBuIm)₂Co(C=N^tBu)₂]BPh₄(3‐BPh₄), whose EPR spectral parameters are characteristic of low‐spin d⁷with an unpaired electron in an orbital of d_z²parentage. This is also consistent with the results of DFT calculations. Despite its 16‐electron configuration and the d_z²parentage of the HOMO, the only tractable reactions of2involve one electron oxidation to afford3. 

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4. Metal‐Ligand Cooperativity to Assemble a Neutral and Terminal Niobium Phosphorus Triple Bond (Nb≡P)

   https://doi.org/10.1002/anie.202212488  

   Senthil, Shuruthi; Kwon, Seongyeon; Fehn, Dominik; Im, Hoyoung; Gau, Michael R.; Carroll, Patrick J.; Baik, Mu‐Hyun; Meyer, Karsten; Mindiola, Daniel J. (November 2022, Angewandte Chemie International Edition)

   Abstract Decarbonylation along with P‐atom transfer from the phosphaethynolate anion, PCO⁻, to the Nb^IVcomplex [(PNP)NbCl₂(N^tBuAr)] (1) (PNP=N[2‐PⁱPr₂‐4‐methylphenyl]₂⁻; Ar=3,5‐Me₂C₆H₃) results in its coupling with one of the phosphine arms of the pincer ligand to produce a phosphanylidene phosphorane complex [(PNPP)NbCl(N^tBuAr)] (2). Reduction of2with CoCp*₂cleaves the P−P bond to form the first neutral and terminal phosphido complex of a group 5 transition metal, namely, [(PNP)Nb≡P(N^tBuAr)] (3). Theoretical studies have been used to understand both the coupling of the P‐atom and the reductive cleavage of the P−P bond. Reaction of3with a two‐electron oxidant such as ethylene sulfide results in a diamagnetic sulfido complex having a P−P coupled ligand, namely [(PNPP)Nb=S(N^tBuAr)] (4). 

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5. Dinitrogen activation at chromium by photochemically induced Cr^II–C bond homolysis

   https://doi.org/10.1039/d4cc02387k  

   Duletski, Olivia L; Platz, Duncan; Pollock, Charlie J; Mosquera, Martín A; Arulsamy, Navamoney; Mock, Michael T (June 2024, Chemical Communications)

   Exposure of (POCOP^tBu)Cr(Bn) to 427 nm blue light under 1 atm N₂ promoted Cr–C_Bn bond homolysis and led to N₂ activation forming [(POCOP^tBu)Cr]₂(μ-N₂). 

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