A Caged Neutral 17-Valence-Electron Iron(I) Radical [Fe(CO)2(Cl)(P((CH2)10)3P)]•: Synthetic, Structural, Spectroscopic, Redox, and Computational Studies

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.

Molecules that Turn Themselves Inside-Out: Tuning in/out Equilibria and Homeomorphic Isomerization in Macrobicyclic Dibridgehead Diphosphines P((CH2 )n )3 P Newly Accessible by Earth-Abundant-Metal Templates

Photolyses of trans-Fe(CO)3 (P((CH2 )n )3 P) (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 )3 P (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 31 P 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 themselves inside out (e. g., in,in⇌out,out). This provides the first detailed mapping of such trends in homologous series of aliphatic bicyclic compounds XE((CH2 )n )3 EX 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.

Square-Planar and Octahedral Gyroscope-Like Metal Complexes Consisting of Dipolar Rotators Encased in Dibridgehead Di(triaryl)phosphine Stators: Syntheses, Structures, Dynamic Properties, and Reactivity

For a variety of purposes, it is of interest to embed metals in cagelike trans-spanning di(triaryl)phosphine ligands. Toward this end, a combination of P(p-C₆H₄O(CH₂)_mCH═CH₂)₃ [3; m = 4 (a), 5 (b), 6 (c), and 7 (d)], [Rh(COD)(μ-Cl)]₂, and CO gives square-planar trans-Rh(CO)(Cl)[P(p-C₆H₄O(CH₂)_mCH═CH₂)₃]₂ (4a-4d). Reactions of 4b-4d with Grubbs' catalyst (first generation) and then H₂ (catalyst PtO₂) yield the title compounds trans-Rh(CO)(Cl)[P(p-C₆H₄O(CH₂)_nO-p-C₆H₄)₃P] (n = 2m + 2, 6b-6d; 26-41% from 4b-4d). Two are crystallographically characterized. The Cl-Rh-CO moieties rapidly rotate on the NMR time scale at -120 °C, per the ample clearance provided by the (CH₂)_n segments. Steric interactions with the PC₆H₄O linkages are analyzed. LiC≡CAr displaces the chloride ligand from 6b to give RhC≡CAr adducts (Ar = C₆H₅/p-C₆H₄CH₃, 7b/8b). The ArC≡C-Rh-CO rotator of 7b rapidly rotates on the NMR time scale (-70 °C), but with 8b, the longer p-CH₃C₆H₄C≡C group is confined between two (CH₂)₁₂ bridges, even at 120 °C. Reactions of Re(CO)₅(X) and 3c (140 °C) give octahedral mer,trans-Re(CO)₃(X)[P(p-C₆H₄O(CH₂)₆CH═CH₂)₃]₂ (X = Cl/Br), and metathesis/hydrogenation sequences yield mer,trans-Re(CO)₃(X)[P(p-C₆H₄O(CH₂)₁₄O-p-C₆H₄)₃P]. Reactions of 6c and 6d and excess PMe₃ give the free diphosphines P(p-C₆H₄O(CH₂)_nO-p-C₆H₄)₃P (14c and 14d, 83-75%). The addition of 14d to [Rh(CO)₂(μ-Cl)]₂ reconstitutes 6d (87%). Both in,in and out,out isomers of 14c and 14d are possible, but low-temperature NMR spectra show one set of signals, consistent with rapid homeomorphic isomerizations that turn the molecules inside out. Thermolyses (C₆D₅Br, 140 °C) effect phosphorus inversion to give in,out isomers.

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

Reactions of trans-[Fe(CO)₂(NO)(As((CH₂)_n)₃As)]⁺ 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-ML_n(As((CH₂)₁₄)₃A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.

Platinum(II) alkyl complexes of chelating dibridgehead diphosphines P((CH2)n)3P (n = 14, 18, 22); facile cis/trans isomerizations interconverting gyroscope and parachute like adducts

The gyroscope like dichloride complexes trans-Pt(Cl)₂(P((CH₂)_n)₃P) (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((CH₂)_n)₃P) (cis-4c,e,g, 70-91%). HCl (1 equiv.) and cis-4c react to give cis-Pt(Cl)(Me)(P((CH₂)₁₄)₃P) (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((CH₂)₁₄)₃P) (cis-6c, 85%) but subsequent reaction with HCl affords trans-Pt(Cl)(Et)(P((CH₂)₁₄)₃P) (trans-7c, 45%) directly. When previously reported cis-Pt(Ph)₂(P((CH₂)₁₄)₃P) is treated with HCl (1 equiv.), cis- and trans-Pt(Cl)(Ph)(P((CH₂)₁₄)₃P) 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((CH₂)₁₄)₃P) (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.

Toward Frameworks with Multiple Aligned and Interactive Fe(CO)3 Rotators: Syntheses and Structures of Diiron Complexes Linked by Two trans-Diaxial α,ω-Diphosphine Ligands Ar2P(CH2)nPAr2

Reactions of (η⁴-benzylideneacetone)Fe(CO)₃ and the α,ω-diphosphines Ar₂P(CH₂)_nPAr₂ afford the trigonal bipyramidal diiron tetraphosphorus complexes trans,trans-(CO)₃Fe[Ar₂P(CH₂)_nPAr₂]₂Fe(CO)₃ (n/Ar = 3/Ph 3, 4/Ph 4a, 4/p-tol 4b; 56-19%). Crystal structures establish essentially parallel P-Fe-P axes, iron-iron distances of 5.894(9)-5.782(1) Å (3) and 6.403(1)-6.466(1) Å (4a,b), and van der Waals radii of 4.45 Å for the Fe(CO)₃ rotators, the planes of which are offset by 0.029-1.665 Å. Analogous reactions of Ph₂P(CH₂)₆PPh₂ yield the square pyramidal monoiron complex trans-(CO)₃Fe[Ph₂P(CH₂)₆PPh₂] (6', 31%), a rare case where a diphosphine spans trans basal positions (∠P-Fe-P 147.4(2)°). Both 3 and 6' exhibit two CO ¹³C NMR signals at room temperature, indicating slow exchange on the NMR time scale, which in the former could entail Fe(CO)₃/Fe(CO)₃ gearing. Under analogous conditions, 4a,b exhibit one signal. Previously reported adducts of Fe(CO)₃ and Ph₂P(CH₂)_nPPh₂ are surveyed (1:1, n = 1-5; 2:2, n = 5), and the IR ν_C≡O band patterns and energies of all complexes analyzed with the aid of DFT calculations. The diiron complexes are preferred thermodynamically. Attention is given to limiting types of Fe(CO)₃/Fe(CO)₃ interactions in the diiron complexes.

Non-metal-templated approaches to bis(borane) derivatives of macrocyclic dibridgehead diphosphines via alkene metathesis

Two routes to the title compounds are evaluated. First, a ca. 0.01 M CH₂Cl₂ solution of H₃B·P((CH₂)₆CH=CH₂)₃ (1·BH₃) is treated with 5 mol % of Grubbs' first generation catalyst (0 °C to reflux), followed by H₂ (5 bar) and Wilkinson's catalyst (55 °C). Column chromatography affords H₃B·P(n-C₈H₁₇)₃ (1%), H₃B·P((CH₂)₁₃CH₂)(n-C₈H₁₇) (8%; see text for tie bars that indicate additional phosphorus–carbon linkages, which are coded in the abstract with italics), H₃B·P((CH₂)₁₃CH₂)((CH₂)₁₄)P((CH₂)₁₃CH₂)·BH₃ (6·2BH₃, 10%), in,out-H₃B·P((CH₂)₁₄)₃P·BH₃ (in,out-2·2BH₃, 4%) and the stereoisomer (in,in/out,out)-2·2BH₃ (2%). Four of these structures are verified by independent syntheses. Second, 1,14-tetradecanedioic acid is converted (reduction, bromination, Arbuzov reaction, LiAlH₄) to H₂P((CH₂)₁₄)PH₂ (10; 76% overall yield). The reaction with H₃B·SMe₂ gives 10·2BH₃, which is treated with n-BuLi (4.4 equiv) and Br(CH₂)₆CH=CH₂ (4.0 equiv) to afford the tetraalkenyl precursor (H₂C=CH(CH₂)₆)₂(H₃B)P((CH₂)₁₄)P(BH₃)((CH₂)₆CH=CH₂)₂ (11·2BH₃; 18%). Alternative approaches to 11·2BH₃ (e.g., via 11) were unsuccessful. An analogous metathesis/hydrogenation/chromatography sequence with 11·2BH₃ (0.0010 M in CH₂Cl₂) gives 6·2BH₃ (5%), in,out-2·2BH₃ (6%), and (in,in/out,out)-2·2BH₃ (7%). Despite the doubled yield of 2·2BH₃, the longer synthesis of 11·2BH₃ vs 1·BH₃ renders the two routes a toss-up; neither compares favorably with precious metal templated syntheses.

A Nontemplated Route to Macrocyclic Dibridgehead Diphosphorus Compounds: Crystallographic Characterization of a "Crossed-Chain" Variant of in/out Stereoisomers

Reactions of (O=)PH(OCH2 CH3 )2 and BrMg(CH2 )m CH=CH2 (4.9-3.2 equiv; m=4 (a), 5 (b), 6 (c)) give the dialkylphosphine oxides (O=)PH[(CH2 )m CH=CH2 ]2 (2 a-c; 77-81 % after workup), which are treated with NaH and then α,ω-dibromides Br(CH2 )n Br (0.49-0.32 equiv; n=8 (a'), 10 (b'), 12 (c'), 14 (d')) to yield the bis(trialkylphosphine oxides) [H2 C=CH(CH2 )m ]2 P(=O)(CH2 )n (O=)P[(CH2 )m CH=CH2 ]2 (3 ab', 3 bc', 3 cd', 3 ca'; 79-84 %). Reactions of 3 bc' and 3 ca' with Grubbs' first-generation catalyst and then H2 /PtO2 afford the dibridgehead diphosphine dioxides (4 bc', 4 ca'; 14-19 %, n'=2m+2); 31 P NMR spectra show two stereoisomeric species (ca. 70:30). Crystal structures of two isomers of the latter are obtained, out,out-4 ca' and a conformer of in,out-4 ca' that features crossed chains, such that the (O=)P vectors appear out,out. Whereas 4 bc' resists crystallization, a byproduct derived from an alternative metathesis mode, (CH2 )12 P(=O)(CH2 )12 (O=)P(CH2 )12 , as well as 3 ab' and 3 bc', are structurally characterized. The efficiencies of other routes to dibridgehead diphosphorus compounds are compared.

A crystalline molecular gyrotop with a biphenylene dirotor and its temperature-dependent birefringence

A crystalline molecular gyrotop with a biphenylene dirotor showed a reduction in the birefringence with increasing temperature.