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1. A surprise landing on the terra incognita of macrocyclic dibridgehead diorganoarsines: syntheses, structures, and reactivities

   https://doi.org/10.1039/d2cc03235j  

   Zarcone, Samuel R.; Verardi, Peter J.; Bhuvanesh, Nattamai; Gladysz, John A. (July 2022, Chemical Communications)

   Reactions of trans-[[upper bond 1 start]Fe(CO)2(NO)(As((CH2)n)3As[upper bond 1 end])]+ BF4− (n = 10, 12, 14) and Bu4N+ Cl− afford the title compounds As((CH2)n)3As, which upon reaction (n = 14) with MCl2 (M = Pt, Ni), Rh(CO)(Cl), and Fe(CO)3 sources reconstitute cage like complexes trans-[upper bond 1 start]MLn(As((CH2)14)3A[upper bond 1 end]s). Reactions with H2O2 and BH3 give the corresponding arsine oxides and boranes. Crystal structures of metal-free species reveal out,out isomers, but cage complex formation is proposed to entail homeomorphic isomerization to in,in isomers with endo directed lone pairs. 

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2. Platinum( ii ) alkyl complexes of chelating dibridgehead diphosphines P((CH ₂ ) _n ) ₃ P ( n = 14, 18, 22); facile cis / trans isomerizations interconverting gyroscope and parachute like adducts

   https://doi.org/10.1039/D1DT02321G  

   Zhu, Yun; Ehnbom, Andreas; Fiedler, Tobias; Shu, Yi; Bhuvanesh, Nattamai; Hall, Michael B.; Gladysz, John A. (September 2021, Dalton Transactions)

   The gyroscope like dichloride complexes trans -Pt(Cl) 2 (P((CH 2 ) n ) 3 P) ( trans -2; n = c, 14; e, 18; g, 22) and MeLi (2 equiv.) react to yield the parachute like dimethyl complexes cis -Pt(Me) 2 (P((CH 2 ) n ) 3 P) ( cis -4c,e,g, 70–91%). HCl (1 equiv.) and cis -4c react to give cis -Pt(Cl)(Me)(P((CH 2 ) 14 ) 3 P) ( cis -5c, 83%), which upon stirring with silica gel or crystallization affords trans -5c (89%). Similar reactions of HCl and cis -4e,g give cis / trans -5e,g mixtures that upon stirring with silica gel yield trans -5e,g. A parallel sequence with trans -2c/EtLi gives cis -Pt(Et) 2 (P((CH 2 ) 14 ) 3 P) ( cis -6c, 85%) but subsequent reaction with HCl affords trans -Pt(Cl)(Et)(P((CH 2 ) 14 ) 3 P) ( trans -7c, 45%) directly. When previously reported cis -Pt(Ph) 2 (P((CH 2 ) 14 ) 3 P) is treated with HCl (1 equiv.), cis - and trans -Pt(Cl)(Ph)(P((CH 2 ) 14 ) 3 P) are isolated (44%, 29%), with the former converting to the latter at 100 °C. Reactions of trans -5c and LiBr or NaI afford the halide complexes trans -Pt(X)(Me)(P((CH 2 ) 14 ) 3 P) ( trans -9c, 88%; trans -10c, 87%). Thermolyses and DFT calculations that include acyclic model compounds establish trans > cis stabilities for all except the dialkyl complexes, for which energies can be closely spaced. The σ donor strengths of the non-phosphine ligands are assigned key roles in the trends. The crystal structures of cis -4c, trans -5c, trans -7c, and trans -10c are determined and analyzed together with the computed structures. 

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3. Molecules that Turn Themselves Inside‐Out: Tuning in / out Equilibria and Homeomorphic Isomerization in Macrobicyclic Dibridgehead Diphosphines P((CH ₂ ) _n ) ₃ P Newly Accessible by Earth‐Abundant‐Metal Templates

   https://doi.org/10.1002/chem.202302200  

   Zarcone, Samuel R; Bhuvanesh, Nattamai; Gladysz, John A (December 2023, Chemistry – A European Journal)

   Photolyses of trans- Fe(CO)3(P((CH2)n)3P (n = 10 (a), 12 (b), 14 (c),16 (d), 18 (e)) in the presence of PMe3 provide the first economical and scalable route to macrobicyclic dibridgehead diphosphines P((CH2)n)3P (1). These are isolated as mixtures of in,in/out,out isomers that equilibrate with degenerate in,out/out,in isomers at 150 °C via pyramidal inversion at phosphorus. For the entire series, VT 31P NMR data establish or bound Keq rates, and activation parameters for a variety of phenomena, many of which involve homeomorphic isomerizations, topological processes by which certain molecules can turn themselve sinside out. This provides the first detailed mapping of such trends in homologous series of aliphatic bicyclic compounds XE((CH2)n)3EX with any type of bridgehead. Isomeric diborane adducts 1 a,d·2BH3 are also characterized. Crystal structures of out,out-1 a and in,in-1 a·2BH3 aid isomer assignments and reveal unusual cage conformations. 

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4. Synthesis, reactivity, structures, and dynamic properties of gyroscope like iron complexes with dibridgehead diphosphine cages: pre- vs. post-metathesis substitutions as routes to adducts with neutral dipolar Fe(CO)(NO)(X) rotors

   https://doi.org/10.1039/c6dt03258c  

   Lang, Georgette M.; Skaper, Dirk; Hampel, Frank; Gladysz, John A. (January 2016, Dalton Transactions)

   Three routes are explored to the title halide/cyanide complexes trans -Fe(CO)(NO)(X)(P((CH 2 ) 14 ) 3 P) ( 9c-X ; X = Cl/Br/I/CN), the Fe(CO)(NO)(X) moieties of which can rotate within the diphosphine cages (Δ H ‡ /Δ S ‡ (kcal mol −1 /eu −1 ) 5.9/−20.4 and 7.4/−23.9 for 9c-Cl and 9c-I from variable temperature 13 C NMR spectra). First, reactions of the known cationic complex trans -[Fe(CO) 2 (NO)(P((CH 2 ) 14 ) 3 P)] + BF 4 − and Bu 4 N + X − give 9c-Cl /- Br /- I /- CN (75–83%). Second, reactions of the acyclic complexes trans -Fe(CO)(NO)(X)(P((CH 2 ) m CHCH 2 ) 3 ) 2 and Grubbs’ catalyst afford the tris(cycloalkenes) trans -Fe(CO)(NO)(X)(P((CH 2 ) m CHCH(CH 2 ) m ) 3 P) ( m /X = 6/Cl,Br,I,CN, 7/Cl,Br, 8/Cl,Br) as mixtures of Z / E isomers (24–41%). Third, similar reactions of trans -[Fe(CO) 2 (NO)(P((CH 2 ) m CHCH 2 ) 3 ) 2 ] + BF 4 − and Grubbs’ catalyst afford crude trans -[Fe(CO) 2 (NO)P((CH 2 ) m CHCH(CH 2 ) m ) 3 P)] + BF 4 − ( m = 6, 8). However, the CC hydrogenations required to consummate routes 2 and 3 are problematic. Crystal structures of 9c-Cl /- Br /- CN are determined. Although the CO/NO/X ligands are disordered, the void space within the diphosphine cages is analyzed in terms of horizontal and vertical constraints upon Fe(CO)(NO)(X) rotation and the NMR data. The molecules pack in identical motifs with parallel P–Fe–P axes, and without intermolecular impediments to rotation in the solid state. 

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5. A Caged Neutral 17-Valence-Electron Iron(I) Radical [Fe(CO) ₂ (Cl)(P((CH ₂ ) ₁₀ ) ₃ P)] ^• : Synthetic, Structural, Spectroscopic, Redox, and Computational Studies

   https://doi.org/10.1021/acs.inorgchem.4c02275  

   Zarcone, Samuel R; Zhang, Zihan; Handunneththige, Suhashini; Ni, Zhen; Bhuvanesh, Nattamai; Nippe, Michael; Meyer, Karsten; Hall, Michael B; Gladysz, John A (September 2024, Inorganic Chemistry)

   UV irradiation of yellow CH2Cl2 solutions of trans-Fe(CO)3(P-((CH2)10)3P) (2a) and PMe3 (10 equiv) gives, in addition to the previously reported dibridgehead diphosphine P((CH2)10)3P (46%), a green paramagnetic complex that crystallography shows to be the trigonal-bipyramidal iron(I) radical trans-[Fe(CO)2(Cl)(P((CH2)10)3P)]• (1a•; 31% after workup). This is a rare example of an isolable species of the formula [Fe(CO)4−n(L)n(X)]• (n = 0−3, L =two-electron-donor ligand; X = one-electron-donor ligand). Analogous precursors with longer P(CH2)nP segments (n = 12, 14, 16, 18) give only the demetalated diphosphines, and a rationale is proposed. The magnetic susceptibility of 1a•,assayed by Evans’ method and SQUID measurements, indicates a spin (S) of 1/2. Cyclic voltammetry shows that 1a• undergoes a partially reversible one-electron oxidation, but no facile reduction. The UV−visible, EPR, and 57Fe Mössbauer spectra are analyzed in detail. Complex 2a is similarly studied, and, despite the extra valence electron, exhibits a comparable oxidation potential (ΔE1/2 ≤0.04 V). The crystal structure shows a cage conformation, solvation level, disorder motif, and unit cell parameters essentially identical to those of 1a•. DFT calculations provide much insight regarding the structural, redox, and spectroscopic properties. 

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