PI and PIII Ions Supported by BZIMPY Ligands.

We report a class of compounds in which both PIII -X and PI forms featuring the same ligand are stable and readily cycled with each other. A series of PIII -X (X=Cl, Br, I) dicationic triflate salts supported by benzyl- and allyl-substituted 2,6-bis(benzimidazole-2-yl)pyridine (BZIMPY) ligands is synthesized. Surprisingly, treatment of these with R3 PO (R=Et, Oct) results in reduction to BZIMPY-ligated PI monocationic triflate salts while treatment with Ph3 P reduces but also substitutes the compound to produce Ph3 P-BZIMPY-ligated PI dicationic triflate salts. The mechanisms of these surprising reductions are probed experimentally and rationalized computationally. The PIII -X dications are shown to be strong Lewis acids both experimentally and computationally and to readily behave as X+ , PX, and P+ transfer agents in reactions with phosphines, NHCs, and diazabutadienes. The PI mono- and dications are shown to be very effective P+ transfer agents when treated similarly. Oxidation from a monocationic PI salt back to the dicationic PIII -X (X=Cl, Br) salt was achieved by treatment with N-chlorosuccinimide (NCS) or N-bromosuccinimide (NBS). Full characterization is reported using multinuclear nuclear magnetic resonance spectroscopy, elemental analysis, and single-crystal X-ray diffractometry where suitable crystals were isolated.

A remarkably stable acyclic phosphamethine cyanine dye.

While cyanine dyes enjoy a multitude of uses in science and technology, their phosphorus analogues, phosphamethine cyanine dyes, have not yet found benchtop applications primarily because of their sensitivity to air and moisture. We are excited to report full characterization of an extraordinarily stable acyclic phosphamethine cyanine dye. Nitrile substituents on the N-heterocyclic framework afford air and water stability as well as resistance to methylation and sulfuration even under forcing conditions. Cyclic voltammetry confirms a high oxidation potential of the compound and computational investigations reveal stabilized orbitals. The unusual orbital stability appears to render the normally electron-rich PI site an extremely poor nucleophile and difficult to oxidize. From a practical perspective, this dye is prepared in a one-pot method under mild conditions.

Triphosphenium salts: air-stable precursors for phosphorus(I) chemistry.

The chemistry of low-coordinate phosphorus-containing species is an area of intense interest in modern main group chemistry. While typical routes for accessing such species include pyrophoric phosphorus-centered precursors or harsh reducing agents, triphosphenium cations represent a more convenient and safer alternative. This Perspective summarizes the use of air- and moisture-stable triphosphenium salts of [dppeP]+ as a source of P+ ions for the generation of a variety of new and/or useful low-coordinate phosphorus-containing species. These range from phosphorus-rich oligomers to phosphamethine cyanine dyes. Special emphasis is placed on the electronic structure of the newly generated species as well as their subsequent reactivity.

Oxidative addition of tetrathiocins to palladium(0) and platinum(0): a route to dithiolate coordination complexes.

The preparation of a series of 4,4',5,5'-substituted benzo-fused 1,2,5,6-tetrathiocins X2C6H2S4C6H2X2 (1a-1g) were prepared from the reaction of S2Cl2 with 1,2-C6H4X2 (X = OMe, OEt; X2 = OCH2O, OCH2CH2O, OCH2CH2CH2O, MeNC([double bond, length as m-dash]O)NMe, O(CH2CH2O)4). The oxidative addition of 1a-1g to zero-valent Pd2dba3 or Pt2dba3 (dba = dibenzylideneacetone) in the presence of bis (diphenylphosphino)ethane (dppe) resulted in formation of the substituted mononuclear benzenedithiolate complexes M(L)(dppe) [L = dithiolate ligand; 2a-2g (M = Pd) and 3a-3g (M = Pt)] in 37-89% yield based on recrystallized material. Representative examples of M(L)(dppf) [dppf = bis-diphenylphosphinoferrocene; 4a, 4g (M = Pd) and 5g (M = Pt)] were prepared in a similar fashion. The structures of all derivatives were determined by X-ray diffraction, multinuclear NMR and elemental analysis. The reactivity of the two crown ether dithiolate complexes, 2g and 4g, with 1 equivalent of NaBPh4 led to isolation of the 1 : 1 complexes in which the Na+ cation is bound in the macrocyclic crown, [Na(2g)(MeOH)2][BPh4] and [Na(4g)][BPh4] whose structures were determined by X-ray diffraction. Electrochemical studies supported through DFT calculations on the crown ether derivatives revealed a series of ligand-based oxidation waves corresponding to the dithiolate ligand (and dppf for 4g and 5g) whose redox potentials were shifted by ca. +0.1 V on binding to Na+.

Heavy Metals Make a Chain: A Catenated Bismuth Compound.

Catenation is common for the light main-group elements whereas it is rare for the heavy elements. Herein, we report the first example of a neutral molecule containing a Bi4 chain. It is prepared in a one-step reaction between bismuth trichloride and bis(diisopropylphosphino)amine in methanol suspension. The same reaction carried out in dichloromethane gives quite different products. All products have been characterized spectroscopically and using single-crystal X-ray analysis.

The phosphinoboration of acyl chlorides.

This investigation examines the reactivity of phosphinoboronate esters Ph2PBpin (pin = 1,2-O2C2Me4) and Ph2PBcat (cat = 1,2-O2C6H4), as well as other phosphinoboron species, with various aryl and aliphatic acyl chlorides. These reactions proceed smoothly to give acyl phosphines of the type RC(O)PR'2 along with loss of a boron-chloride compound. In some cases, a second equivalent of the phosphinoboron species can add to the C[double bond, length as m-dash]O double bond at elevated temperatures to give the corresponding diphosphines RC(OBR''2)(PR'2)2. These ambiphilic diphosphines behave like substituted (1,1-bis(diphenylphosphino)methane) derivatives in a reaction of PhC(OBpin)(PPh2)2 (2a) with (η5-C9H7)Rh(η2-coe)2 (coe = cis-cyclooctene) affording the indenyl rhodium complex (η5-C9H7)Rh(PhC(OBpin)(PPh2)2) (3a) where the phosphines are bound to the metal centre in a κ2-P,P bidentate manner.

A Comprehensive Investigation of a Zwitterionic GeI Dimer with a 1,2-Dicationic Core.

The reductive dehalogenation of a zwitterionic GeII species to make a zwitterionic GeI dimer with a 1,2-dicationic core is reported herein. To the root of the stability of this compound, the molecular and electronic structures were comprehensively characterized and investigated using crystallographic, spectroscopic, and computational methods. It was determined that the Ge centers are attracted because they are both electron-rich and positively charged. A comparison to the electronic structure in triphosphenium cations revealed varying degrees of covalent bonding and that this difference can be distinguished spectroscopically.

2,6-Bis(benzimidazol-2-yl)pyridine complexes of group 14 elements.

Treatment of MCl2 (M = Ge or Sn) with 2,6-bis(benzimidazol-2-yl)pyridine (G-BZIMPY, G = NBn, N(3,5-CF3)Bn, NAllyl and O) yielded the self-ionization products [G-BZIMPYMCl][MCl3] (1-6) in high yields (75-98%). Reduction reactions are examined and the nickel complexes 8 and 9 ([(NBn-BZIMPY)2Ni][MCl3]2) are isolated from the reaction of Ni(COD)2 with 1 and 2 respectively. [NBn-BZIMPYSnCl][SnCl3] shows a significantly stronger MLCT band in the UV-vis absorption spectrum than its germanium counterparts, with germanium complexes exhibiting negative solvatochromism that is not observed in tin complexes.

Halogen and Sulfur Oxidation of Germanium and Tin Dications.

Herein we present the oxidation of base-stabilized tetrelII dications [LM][OTf]2 [L = BIMEt3 = tris(1-ethyl-benzoimidazol-2-ylmethyl)amine and M = Ge, Sn] with PCl5, SeCl4, Br2, and I2 to access dicationic dihalides [LMX2][OTf]2. The addition of oxygen-rich donor molecules (picoline N-oxide, OPEt3) to dications [LM][OTf]2 yielded donor-acceptor complexes bearing a tetrel(II) dication adjacent to a pnictogen(V) moiety. The addition of elemental sulfur to [LGe][OTf]2 yielded [(LGeS)2][OTf]4 containing a dimeric tetracation.

2,6-Bis(benzimidazol-2-yl)pyridines as more electron-rich and sterically accessible alternatives to 2,6-bis(imino)pyridine for group 13 coordination chemistry.

Treatment of GaCl3 with 2,6-bis(benzimidazol-2-yl)pyridine (G-BZIMPY, G = NBz, N(3,5-CF3)Bz, N-allyl and O) yielded the autoionization products [G-BZIMPYGaCl2][GaCl4] (1-4) in great yields. The Ga(iii) complex 1 was reduced to Ga(i) using K2[Fe(CO)4], resulting in the complex [(NBzBZIMPY)(Cl)Ga-Fe(CO)4] (7). GaCl3 and AlCl3 were complexed by the structurally similar bis(imino)pyridine (DIMPY) and the resulting complexes are compared to those of G-BZIMPY.

Diphosphoniodiphosphene Formation by Transition Metal Insertion into a Triphosphenium Zwitterion.

Treatment of two equivalents of the triphosphenium zwitterion L with sources of Ni0 and Pd0 form the mononuclear η2 -diphosphoniodiphosphene complexes 1 and 2. The reaction between L and [FeCp(CO)2 ]2 results in the binuclear µ-η1 :η1 -diphosphoniodiphosphene iron complex 3, which features an alternative bonding motif of the diphosphoniodiphosphene unit. The formation of these species has been confirmed by spectroscopic methods and single-crystal X-ray diffraction analysis, and their electronic structures have been elucidated using computational methods.

Synthesis, characterization and mass-spectrometric analysis of [LSn(IV)F4-x]x+ salts [L = tris ((1-ethyl-benzoimidazol-2-yl)methyl)amine, x = 1-4].

A series of complexes with the formulae [(BIMEt3)SnF4-x][OTf]x with x = 1-4 has been synthesized by successive fluoride abstraction from SnF4 with TMSOTf in the presence of the tetradentate nitrogen donor BIMEt3 (tris ((1-ethyl-benzoimidazol-2-yl)methyl)amine). Single crystal X-ray diffraction and heteronuclear NMR spectroscopic analysis provided insight into these new main group cations. Electrospray ionization mass spectrometric analysis on solutions containing the different salts allowed for successful detection of the cations [(BIMEt3)SnF]3+, [(BIMEt3)SnF2]2+ and [(BIMEt3)SnF3]+.

Synthesis of Heteroleptic Phosphorus(I) Cations by P+ Transfer.

Reported are general synthetic approaches for the syntheses of asymmetrically substituted phosphorus(I) cations by P+ transfer from [dppeP]+ (dppe = 1,2-bis(diphenylphosphino)ethane). The first method grants access to acyclic derivatives and is accomplished by the sequential substitution of dppe using first a sterically encumbered ligand which cannot form a stable homoleptic complex, followed by a second equivalent of a less sterically demanding ligand. The second method grants access to cyclic derivatives and utilizes asymmetric hybrid phosphine/N-heterocyclic carbene ligands. Interplay between the different ligand types and their stoichiometries relative to those of [dppeP]+ also allows for the isolation of symmetrical derivatives with pendant phosphines.

Synthesis of Heavy Dicyanamide Homologues from Air-Stable Precursors.

A convenient synthesis of dicyanophosphide and dicyanoarsenide anions is reported. These heavy homologues of the long-known and fundamentally important dicyanamide anion were formed through the nucleophilic displacement of bis(diphenylphosphino)ethane (dppe) from the pnictogen+ transfer agents [dppePn][BPh4 ] (Pn=P, As) by exposure to cyanide salts. The protocol requires three synthetic steps from commercially available materials and the [dppePn][BPh4 ] salts are remarkably temperature, air, and moisture stable. All products have been fully characterized by spectroscopic methods and by single-crystal X-ray diffraction, and the electronic structures of the DCPn anions have been assessed computationally.

Tris(benzoimidazol)amine (L) complexes of pnictogen(iii) and pnictogen(v) cations and assessment of the [LP]3+/[LPF2]3+ redox couple.

A series of cationic complexes involving a pnictogen(iii) (Pn = P, As, Sb) centre and the tetradentate ligand tris((1-ethyl-benzoimidazol-2-yl)methyl)amine (BIMEt3) have been synthesized and comprehensively characterized. Oxidation of [P(BIMEt3)]3+ with XeF2 provides access to [PF2(BIMEt3)]3+ representing the first structurally characterized example of a phosphorus(v) centred trication.

Oxidation of a germanium(ii) dication to access cationic germanium(iv) fluorides.

The synthesis and characterization of the tris(1-ethyl-benzoimidazol-2-ylmethyl)amine (BIMEt3 = L) complex of Ge(ii)2+ is described. Oxidation of [LGe]2+ with Selectfluor gives [LGeF2]2+, in a process that is envisaged to involve a tricationic complex [LGeF]3+ as an intermediate, which has been isolated by fluoride ion abstraction from [LGeF2]2+.

Phosphonium-Templated Iodoplumbates.

A new family of iodoplumbates based on phosphonium cations have been synthesized and characterized via X-ray crystallography. Thermogravimetric analysis demonstrates that these materials have a remarkably high thermal stability and show potential for applications as organic-inorganic hybrid semiconductors. We also present the synthesis of three novel phosphonium salts and the crystallographic elucidation of these compounds.

Addressing the Nature of Phosphinidene Sulfides via the Synthesis of P-S Heterocycles.

The phosphorus-sulfur heterocycles 1,2-thiaphosphetenes and phosphirene sulfides have been prepared, and represent the first structurally characterized derivatives for either class of compound. These strained P-S ring systems are formed by the reaction of a phosphinidene sulfide and alkyne. Using an internal alkyne, only the 3-membered PV , phosphirene sulfide was produced, whereas a terminal alkyne yielded a mixture of phosphirene sulfide and 1,2-thiaphosphetene (PIII ). Detailed computational analysis revealed that for numerous derivatives of alkynes, the corresponding 4-membered rings are always more stable than the 3-membered isomers. The electronic nature of "free" phosphinidene sulfides (R-P=S) is discussed based on computational results.

Assessing the Ligand Properties of NHC-Stabilised Phosphorus(I) Cations.

The isolation and full characterisation of a series of cationic metal-carbonyl complexes bearing an N-heterocyclic carbene stabilised phosphorus(I) ligand are reported. Specifically, the mononuclear coordination complexes [LM(CO)5 ][BPh4 ] (M=Cr, Mo, W), [LFe(CO)4 ][BPh4 ] and the dinuclear complexes [LMn2 (CO)8 ][BPh4 ] and [LCo2 (CO)6 ][BPh4 ], in which L=[bis(1,3,4,5-tetramethylimidazol-2-ylidene)phosphanide]+ , have all been isolated in the solid state and structurally confirmed by single-crystal X-ray diffraction. The dicationic platinum complex trans-[L2 PtCl2 ][BPh4 ]2 is also reported and fully characterised. The donor ability of [L]+ has been assessed by IR spectroscopy of its metal-carbonyl complexes and by using DFT calculations. The results suggest that [L]+ is a weak π-acceptor with moderate donor strength and thus it bridges the gap that exists between phosphines and amines in terms of ligand properties. Collectively, these molecules represent the first crystallographically characterised cationic metal-carbonyl derivatives of a PI -centred ligand and are a rare collection of cationic metal-carbonyl complexes.

Accessing multimetallic complexes with a phosphorus(i) zwitterion.

We present the synthesis of a zwitterionic triphosphenium molecule, tBu(C5H2)(PPh2)2PI (L), which can act as a single- or multidentate ligand with group 6, 7, 8 and 9 metal carbonyl complexes. Group 6, [M(CO)5L] complexes are formed under photolytic conditions, where the metal is bound at the P(i) center. In the case of Mo(CO)6, the bimetallic complex [M(CO)5LMo(CO)3] is generated, which features bonds to both the phosphorus(i) center and the cyclopentadienyl moiety of the molecule. Interestingly, group 7 and 9 metal carbonyl dimers generate bimetallic complexes in the form [M2(CO)nL], where both metal centers are bound at the phosphorus(i) center. A detailed analysis of these molecules is provided, including X-ray diffraction, multinuclear NMR, infrared spectroscopy and computational investigations.