Synthetic and Structural Study of the Coordination Chemistry of a <i>peri</i>-Backbone-Supported Phosphino-Phosphonium Salt

Coordination chemistry of an acenaphthene <i>peri</i>-backbone-supported phosphino-phosphonium chloride (<b>1</b>) was investigated, revealing three distinct modes of reactivity. The reaction of <b>1</b> with Mo­(CO)₄(nor) gives the Mo(0) complex [(<b>1</b>)­Mo­(CO)₄Cl] (<b>2</b>), in which the ligand <b>1</b> exhibits monodentate coordination through the phosphine donor and the P–P bond is retained. PtCl₂(cod) reacts with the chloride and triflate salts of <b>1</b> to form a mononuclear complex [(<b>1</b>Cl)­PtCl₂] (<b>3</b>) and a binuclear complex [((<b>1</b>Cl)­PtCl)₂]­[2TfO] (<b>4</b>), respectively. In both of these complexes, the platinum center adds across the P–P bond, and subsequent chloride transfer to the phosphenium center results in phosphine-chlorophosphine bidentate coordination. [((<b>1</b>)­PdCl)₂] (<b>5</b>) was isolated from the reaction of <b>1</b> and Pd₂(dba)₃ (dba = dibenzylideneacetone). Oxidative addition to palladium(0) results in a heteroleptic phosphine bridging phosphide coordination to the Pd­(II) center. In addition, reaction of <b>1</b> with BH₃·SMe₂ leads to the bis­(borane) adduct of the corresponding mixed tertiary/secondary phosphine (<b>6</b>), with BH₃ acting as both a reducing agent and a Lewis acid. The new compounds were fully characterized, including X-ray diffraction. The ligand properties of <b>1</b> and related bonding issues are discussed with help of DFT computations

Synthetic, Structural, NMR, and Computational Study of a Geminally Bis(<i>peri</i>-substituted) Tridentate Phosphine and Its Chalcogenides and Transition-Metal Complexes

Coupling of two acenaphthene backbones through a phosphorus atom in a geminal fashion gives the first geminally bis­(<i>peri</i>-substituted) tridentate phosphine <b>1</b>. The rigid nature of the aromatic backbone and overall crowding of the molecule result in a rather inflexible ligand, with the three phosphorus atoms forming a relatively compact triangular cluster. Phosphine <b>1</b> displays restricted dynamics on an NMR time scale, which leads to the anisochronicity of all three phosphorus nuclei at low temperatures. Strained bis- and tris­(sulfides) <b>2</b> and <b>3</b> and the bis­(selenide) <b>4</b> have been isolated from the reaction of <b>1</b> with sulfur and selenium, respectively. These chalcogeno derivatives display pronounced in-plane and out-of-plane distortions of the aromatic backbones, indicating the limits of their angular distortions. In addition, we report metal complexes with tetrahedral [(<b>1</b>)­Cu­(MeCN)]­[BF₄] (<b>5</b>), square planar [(<b>1</b>)­PtCl]­[Cl] (<b>6</b>), trigonal bipyramidal [(<b>1</b>)­FeCl₂] (<b>7</b>), and octahedral <i>fac</i>-[(<b>1</b>)­Mo­(CO)₃] (<b>8</b>) geometries. In all of these complexes the tris­(phosphine) backbone is distorted, however to a significantly smaller extent than that in the mentioned chalcogenides <b>2</b>–<b>4</b>. Complexes <b>5</b> and <b>8</b> show fluxionality in ³¹P and ¹H NMR. All new compounds <b>1</b>–<b>8</b> were fully characterized, and their crystal structures are reported. Conclusions from dynamic NMR observations were augmented by DFT calculations

Synthetic, Structural, NMR, and Computational Study of a Geminally Bis(<i>peri</i>-substituted) Tridentate Phosphine and Its Chalcogenides and Transition-Metal Complexes

Coupling of two acenaphthene backbones through a phosphorus atom in a geminal fashion gives the first geminally bis­(<i>peri</i>-substituted) tridentate phosphine <b>1</b>. The rigid nature of the aromatic backbone and overall crowding of the molecule result in a rather inflexible ligand, with the three phosphorus atoms forming a relatively compact triangular cluster. Phosphine <b>1</b> displays restricted dynamics on an NMR time scale, which leads to the anisochronicity of all three phosphorus nuclei at low temperatures. Strained bis- and tris­(sulfides) <b>2</b> and <b>3</b> and the bis­(selenide) <b>4</b> have been isolated from the reaction of <b>1</b> with sulfur and selenium, respectively. These chalcogeno derivatives display pronounced in-plane and out-of-plane distortions of the aromatic backbones, indicating the limits of their angular distortions. In addition, we report metal complexes with tetrahedral [(<b>1</b>)­Cu­(MeCN)]­[BF₄] (<b>5</b>), square planar [(<b>1</b>)­PtCl]­[Cl] (<b>6</b>), trigonal bipyramidal [(<b>1</b>)­FeCl₂] (<b>7</b>), and octahedral <i>fac</i>-[(<b>1</b>)­Mo­(CO)₃] (<b>8</b>) geometries. In all of these complexes the tris­(phosphine) backbone is distorted, however to a significantly smaller extent than that in the mentioned chalcogenides <b>2</b>–<b>4</b>. Complexes <b>5</b> and <b>8</b> show fluxionality in ³¹P and ¹H NMR. All new compounds <b>1</b>–<b>8</b> were fully characterized, and their crystal structures are reported. Conclusions from dynamic NMR observations were augmented by DFT calculations

Sterically Crowded Tin Acenaphthenes

The synthesis of crowded <i>peri</i>-5-bromo-6-(organostannyl)­acenaphthenes is described. Reaction of 5,6-dibromoacenaphthene with 1 equiv of <i>n</i>-BuLi at −40 °C in diethyl ether followed by addition of the appropriate organotin reagent at 0 °C gave 5-bromo-6-(triphenylstannyl)­acenaphthene (<b>1</b>), 5-bromo-6-(chlorodiphenylstannyl)­acenaphthene (<b>2</b>), bis­(6-bromoacenaphthen-5-yl)­diphenylstannane (<b>3</b>), bis­(6-bromoacenaphthen-5-yl)­dibenzylstannane (<b>4</b>), bis­(6-bromoacenaphthen-5-yl)­dibutylstannane (<b>6</b>), and bis­(6-bromoacenaphthen-5-yl)­dichlorostannane (<b>7</b>) in low to medium yields (10–56%). <b>4</b> was converted into 5-iodo-6-bromoacenaphthene (<b>5</b>) by stirring overnight in the presence of a large excess of iodine. The new compounds were fully characterized spectroscopically. ¹¹⁹Sn NMR spectra suggest and interaction between the tin atoms and the neighboring peri halogen atoms. Single-crystal X-ray studies on <b>1</b>–<b>4</b> and <b>6</b>–<b>8</b> revealed Sn···X distances which are significantly less than the sum of the van der Waals radii, while DFT calculations indicate Wiberg bond indices of up to 0.11. Furthermore, there is evidence of the onset of 3c–4e bonding, though according to natural population analysis, the charge on tin is close to +2 in all compounds studied. Electrostatic interactions may thus be another important driving force for the close Br···Sn interactions, along with the small covalent (donor–acceptor) contributions

Sterically Encumbered Tin and Phosphorus <i>peri-</i>Substituted Acenaphthenes

A group of sterically encumbered <i>peri</i>-substituted acenaphthenes have been prepared, containing tin moieties at the 5,6-positions in <b>1</b>–<b>3</b> ([Acenap­(SnR₃)₂], Acenap = acenaphthene-5,6-diyl; R₃ = Ph₃ (<b>1</b>), Me₃ (<b>2</b>); [(Acenap)₂(SnMe₂)₂] (<b>3</b>)) and phosphorus functional groups at the proximal <i>peri</i>-positions in <b>4</b> and <b>5</b> ([Acenap­(PR₂)­(P^<i>i</i>Pr₂)] R₂ = Ph₂ (<b>4</b>), Ph­(^<i>i</i>Pr) (<b>5</b>)). Bis­(stannane) structures <b>1</b>–<b>3</b> are dominated by repulsive interactions between the bulky tin groups, leading to <i>peri</i>-distances approaching the sum of van der Waals radii. Conversely, the <i>quasi</i>-linear C_Ph-P···P three-body fragments found in bis­(phosphine) <b>4</b> suggest the presence of a lp­(P)−σ*­(P–C) donor–acceptor 3c-4e type interaction, supported by a notably short intramolecular P···P distance and notably large <i>J</i>_PP through-space coupling (180 Hz). Severely strained bis­(sulfides) <b>4-S</b> and <b>5-S</b>, experiencing pronounced in-plane and out-of-plane displacements of the exocyclic <i>peri</i>-bonds, have also been isolated following treatment of <b>4</b> and <b>5</b> with sulfur. The resulting nonbonded intramolecular P···P distances, ∼4.05 Å and ∼12% longer than twice the van der Waals radii of P (3.60 Å), are among the largest ever reported <i>peri</i>-separations, independent of the heteroatoms involved, and comparable to the distance found in <b>1</b> containing the larger Sn atoms (4.07 Å). In addition we report two metal complexes with square planar [(<b>4</b>)­PtCl₂] (<b>4-Pt</b>) and octahedral <i>cis</i>-[(<b>4</b>)­Mo­(CO)₄] (<b>4-Mo</b>) geometries. In both complexes the bis­(phosphine) backbone is distorted, but notably less so than in bis­(sulfide) <b>4-S</b>. All compounds were fully characterized, and except for bis­(phosphine) <b>5</b>, crystal structures were determined

Sterically Crowded Tin Acenaphthenes

The synthesis of crowded <i>peri</i>-5-bromo-6-(organostannyl)­acenaphthenes is described. Reaction of 5,6-dibromoacenaphthene with 1 equiv of <i>n</i>-BuLi at −40 °C in diethyl ether followed by addition of the appropriate organotin reagent at 0 °C gave 5-bromo-6-(triphenylstannyl)­acenaphthene (<b>1</b>), 5-bromo-6-(chlorodiphenylstannyl)­acenaphthene (<b>2</b>), bis­(6-bromoacenaphthen-5-yl)­diphenylstannane (<b>3</b>), bis­(6-bromoacenaphthen-5-yl)­dibenzylstannane (<b>4</b>), bis­(6-bromoacenaphthen-5-yl)­dibutylstannane (<b>6</b>), and bis­(6-bromoacenaphthen-5-yl)­dichlorostannane (<b>7</b>) in low to medium yields (10–56%). <b>4</b> was converted into 5-iodo-6-bromoacenaphthene (<b>5</b>) by stirring overnight in the presence of a large excess of iodine. The new compounds were fully characterized spectroscopically. ¹¹⁹Sn NMR spectra suggest and interaction between the tin atoms and the neighboring peri halogen atoms. Single-crystal X-ray studies on <b>1</b>–<b>4</b> and <b>6</b>–<b>8</b> revealed Sn···X distances which are significantly less than the sum of the van der Waals radii, while DFT calculations indicate Wiberg bond indices of up to 0.11. Furthermore, there is evidence of the onset of 3c–4e bonding, though according to natural population analysis, the charge on tin is close to +2 in all compounds studied. Electrostatic interactions may thus be another important driving force for the close Br···Sn interactions, along with the small covalent (donor–acceptor) contributions

Unusual Intermolecular “Through-Space” <i>J</i> Couplings in P–Se Heterocycles

Solid-state NMR spectra of new P–Se heterocycles based on <i>peri</i>-substituted naphthalene motifs show the presence of unusual <i>J</i> couplings between Se and P. These couplings are between atoms in adjacent molecules and occur “through space”, rather than through conventional covalent bonds. Experimental measurements are supported by relativistic DFT calculations, which confirm the presence of couplings between nonbonded atoms, and provide information on the pathway of the interaction. This observation improves the understanding of <i>J</i> couplings and offers insight into the factors that affect crystal packing in solids, for future synthetic exploitation

Unusual Intermolecular “Through-Space” <i>J</i> Couplings in P–Se Heterocycles

Solid-state NMR spectra of new P–Se heterocycles based on <i>peri</i>-substituted naphthalene motifs show the presence of unusual <i>J</i> couplings between Se and P. These couplings are between atoms in adjacent molecules and occur “through space”, rather than through conventional covalent bonds. Experimental measurements are supported by relativistic DFT calculations, which confirm the presence of couplings between nonbonded atoms, and provide information on the pathway of the interaction. This observation improves the understanding of <i>J</i> couplings and offers insight into the factors that affect crystal packing in solids, for future synthetic exploitation

Spin-State Patterning in an Iron(II) Tripodal Spin-Crossover Complex

A mononuclear iron­(II) complex that displays a gradual two-step spin-crossover (SCO) transition is reported. The intermediate plateau (IP) occurs between HS^0.40LS^0.60 and HS^0.30LS^0.70 (HS = high spin; LS = low spin) ratios over the region of ca. 190–170 K. A phase change occurs at the IP, breaking the symmetry, resulting in six independent SCO sites compared to one at the 100% HS and LS plateau regions, respectively. Variable-temperature X-ray photoelectron spectroscopy shows that the SCO behavior is completely reversible among the HS, IP, and LS regions. The results both confirm and extend the related results for the above system described by Halcrow et al. (Kulmaczewski, R.; Cespedes, O.; Halcrow, M. A. Gradual Thermal Spin-Crossover Mediated By a Reentrant <i>Z</i>′ = 1 → <i>Z</i>′ = 6 → <i>Z</i>′ = 1 Phase Transition, Inorg. Chem. 2017, 56, 3144−3148) in a recent report