Isolation and Computational Studies of a Series of Terphenyl Substituted Diplumbynes with Ligand Dependent Lead-Lead Multiple-Bonding Character.

A series of formally triply bonded diplumbyne analogues of alkynes of the general formula ArPbPbAr (Ar = terphenyl ligand with different steric properties) was synthesized by two routes. All diplumbyne products were synthesized by a simple reduction of the corresponding Pb(II) halide precursor ArPb(Br) by DIBAL-H with yields in the range 8-48%. For one of the diplumbynes ArPri4PbPbArPri4 (ArPri4 = C6H3-2,6-(C6H3-2,6-Pri2)2) it was shown that reduction of ArPri4Pb(Br) using a magnesium(I) beta-diketiminate afforded a much improved yield in comparison (29 vs 8%) to that obtained by reduction with DIBAL-H. The more sterically crowded diplumbyne ArPri8PbPbArPri8 (ArPri8 = C6H-3,5-Pri2-2,6-(C6H2-2,4,6-Pri3)2) displayed a shortened Pb-Pb bond with a length of 3.0382(5) Å and wide Pb-Pb-C angles of 114.73(7)° and 116.02(6)° consistent with multiple-bond character with a bond order of up to 1.5. The others displayed longer metal-metal distances and narrower Pb-Pb-C angles that were consistent with a lower bond order that approached one. Computational studies of the diplumbynes yielded detailed insight of the unusual bonding and explained their similar electronic spectra arising from the flexibility of the C-Pb-Pb-C core in solution. Furthermore, the importance of London dispersion interactions for the stabilization of the diplumbynes was demonstrated.

Convenient Preparation and Detailed Analysis of a Series of NHC-Stabilized Phosphorus(I) Dyes and Their Derivatives.

A safe, convenient, and P-atom-efficient synthesis of N-heterocyclic-carbene- (NHC-) stabilized phosphorus(I) bromide salts is reported that involves P(+) transfer from an easily prepared triphosphenium precursor. The resulting family of phosphamethine cyanine dyes featuring N,N'-dialkyl-substituted 4,5-dimethylimidazole-2-ylidenes ((R)NHC(Me)) and benzimidazole-2-ylidenes ((R)NHC(B)) (R = Me, Et, iPr) have been fully characterized. We found that increasing N-alkyl group size causes increased twisting of the carbene fragments from the C-P-C plane, which decreases the magnitude of hyperconjugation between the π-type lone pair on phosphorus and the carbene fragments. This decrease is manifested as changes in the (31)P NMR chemical shifts, magnitudes of the P-C coupling constants, and electronic spectra of the cations. The reactivities of these ions toward various oxidants are reported: Oxidation by sulfur generates dithiophosphinium salts, protonation or methylation gives dicationic phosphines, and coordination to 1 or 2 equiv of gold(I) chloride results in mono or bimetallic complexes, respectively.

Low-valent chemistry: an alternative approach to phosphorus-containing oligomers.

A convenient preparative approach to low-valent phosphorus-rich oligomers is presented. Ligand substitution reactions involving anionic diphosphine ligands of the form [(PR2)2N](-) and [(PPh2)2C5H3](-) and a triphosphenium bromide P(I) precursor result in the formation of phosphorus(I)-containing heterocycles, several of which are of types that have never been prepared before. The methodology described also allows for the preparation of the known heterocycle cyclo-[P(PPh2)N(PPh2)]2 in better yields and purity than the synthetic approach reported previously. Preliminary reactivity studies demonstrate the viability of such zwitterionic oligomers as multidentate ligands for transition metals.

1,1,1-Tris(di-methyl-amino)-2-[tris-(di-methyl-amino)-phospho-ranyl-idene]diphosphinium tetra-phenyl-borate tetra-hydro-furan monosolvate.

In the tetra-hydro-furan solvate of the title salt, C12H36N6P3 (+)·C24H20B(-)·C4H8O, the cation features short P-P bond lengths [2.1111 (11) and 2.1364 (10) Å] and a distinctly bent P-P-P angle [104.67 (4)°] that confirm that the mol-ecule is not allene-like. In the crystal, the solvent mol-ecule is linked to the cation via a weak C-H⋯O hydrogen bond.

Aza-Diels-Alder reaction between N-aryl-1-oxo-1H-isoindolium ions and tert-enamides: Steric effects on reaction outcome.

The synthesis of 5-substituted 6,6a-dihydroisoindolo[2,1-a]quinolin-11(5H)-ones via [4 + 2] imino-Diels-Alder cyclization from N-aryl-3-hydroxyisoindolinones and N-vinyl lactams under Lewis acid-catalysed anhydrous conditions is reported. Reactions of N-(2-substituted-aryl)-3-hydroxyisoindolinones with N-vinylpyrrolidone under identical conditions resulted in the formation of 2-(2-substitued-aryl)-3-(2-(2-oxopyrrolidin-1-yl)vinyl)isoindolin-1-one analogues indicating steric hinderance as the cause of deviation. The probable mechanism of the reaction based on the results from X-ray crystallography and molecular modelling is discussed.

Synthesis of zwitterionic triphosphenium transition metal complexes: a boron atom makes the difference.

A collection of zwitterionic phosphanide metal carbonyl coordination complexes has been synthesized and fully characterized, representing the first isolated series of metal complexes for the triphosphenium family of compounds. The dicoordinate phosphorus atom of the zwitterion is formally in the +1 oxidation state and can coordinate to one metal, 2M (M = Cr, Mo, W) and 2Fe, or two metals, a Co2(CO)6 fragment 4, depending on the starting reagents. All complexes have been isolated in greater than 80% yield, and structures were confirmed crystallographically. Metrical parameters are consistent with 1 being a weak donor and results in long metal-phosphorus bonds being observed in all cases. Unique bimetallic structures, 3M (M = Cr, Mo, W), consisting of a M(CO)5 fragment on phosphorus and a piano-stool M(CO)3 fragment on a boron phenyl group have been identified in the (31)P{(1)H} NMR spectra and confirmed using X-ray diffraction studies. Use of the borate backbone in 1, which renders the molecule zwitterionic, proves to be a determining factor in whether these metal complexes will form; the halide salt of a cationic triphosphenium ion, 6[Br], shows no evidence for formation of the analogous metal complexes by (31)P{(1)H} NMR spectroscopy, and tetraphenylborate salts, 6[BPh4] and 7[BPh4], produce complexes that are unstable.

Synthesis and characterization of the M(II) (M = Ge, Sn, or Pb) phosphinidene dimers {M(µ-PAr')}2 (Ar' = C6H3-2,6-(C6H3-2,6-Pr(i)2)2).

Reaction of M{N(SiMe(3))(2)}(2) (M = Ge, Sn, or Pb) with the sterically encumbered primary phosphine Ar'PH(2) (2), Ar' = C(6)H(3)-2,6-(C(6)H(3)-2,6-Pr(i)(2)), at ca. 200 °C afforded the highly colored phosphinidene dimers {M(µ-PAr')}(2), M = Ge(3), Sn(4), or Pb(5), with disilylamine elimination. The compounds were characterized by single-crystal X-ray crystallography and heteronuclear NMR spectroscopy. The structures of 3, 4, and 5 featured similar M(2)P(2) ring cores, of which 4 and 5 have 50/50 P atom disorder, consistent with either a planar four-membered M(2)P(2) arrangement with anti aryl groups or with an M(2)P(2) ring folded along the M-M axis with syn aryl groups. A syn-folded structure was resolved for the Ge(2)P(2) ring in compound 3. The M-P distances resembled those in M(II) phosphido complexes and are consistent with single bonding. The coordination geometries at the phosphorus atoms are pyramidal. DFT calculations on the gas phase models {M(µ-PMe)}(2) (M = Ge, Sn, Pb) agreed with the syn (M-M folded) structural interpretation of the X-ray data. The synthesis of the bulky phosphine Ar'PH(2) 2 with the use of the aryl transfer agent Ar'MgBr(THF)(2) is also reported. This route afforded a significantly higher yield of product than that which was obtained using LiAr', which tends to result in aryl halide elimination and the observation of insoluble red phosphorus.

Reaction of hydrogen or ammonia with unsaturated germanium or tin molecules under ambient conditions: oxidative addition versus arene elimination.

The reactions of hydrogen or ammonia with germylenes and stannylenes were investigated experimentally and theoretically. Treatment of the germylene GeAr(#)(2) (Ar(#) = C(6)H(3)-2,6-(C(6)H(2)-2,4,6-Me(3))(2)) with H(2) or NH(3) afforded the tetravalent products Ar(#)(2)GeH(2) (1) or Ar(#)(2)Ge(H)NH(2) (2) in high yield. The reaction of the more crowded GeAr'(2) (Ar' = C(6)H(3)-2,6-(C(6)H(3)-2,6-(i)Pr(2))(2)) with NH(3) also afforded a tetravalent amide Ar'(2)Ge(H)NH(2) (3), whereas with H(2) the tetravalent hydride Ar'GeH(3) (4) was obtained with Ar'H elimination. In contrast, the reactions with the divalent Sn(II) aryls did not lead to Sn(IV) products. Instead, arene eliminated Sn(II) species were obtained. SnAr(#)(2) reacted with NH(3) to give the Sn(II) amide {Ar(#)Sn(mu-NH(2))}(2) (5) and Ar(#)H elimination, whereas no reaction with H(2) could be observed up to 70 degrees C. The more crowded SnAr'(2) reacted readily with H(2), D(2), or NH(3) to give {Ar'Sn(mu-H)}(2) (6), {Ar'Sn(mu-D)}(2) (7), or {Ar'Sn(mu-NH(2))}(2) (8) all with arene elimination. The compounds were characterized by (1)H, (13)C, and (119)Sn NMR spectroscopy and by X-ray crystallography. DFT calculations revealed that the reactions of H(2) with EAr(2) (E = Ge or Sn; Ar = Ar(#) or Ar') initially proceed via interaction of the sigma orbital of H(2) with the 4p(Ge) or 5p(Sn) orbital, with back-donation from the Ge or Sn lone pair to the H(2) sigma* orbital. The subsequent reaction proceeds by either an oxidative addition or a concerted pathway. The experimental and computational results showed that bond strength differences between germanium and tin, as well as greater nonbonded electron pair stabilization for tin, are more important than steric factors in determining the product obtained. In the reactions of NH(3) with EAr(2) (E = Ge or Sn; Ar = Ar(#) or Ar'), the divalent ArENH(2) products were calculated to be the most stable for both Ge and Sn. However the tetravalent amido species Ar(2)Ge(H)NH(2) were obtained for kinetic reasons. The reactions with NH(3) proceed by a different pathway from the hydrogenation process and involve two ammonia molecules in which the lone pair of one NH(3) becomes associated with the empty 4p(Ge) or 5p(Sn) orbital while a second NH(3) solvates the complexed NH(3) via intermolecular N-H...N interactions.

Synthesis, characterization and real molecule DFT calculations for neutral organogallium(I) aryl dimers and monomers: weakness of gallium-gallium bonds in digallenes and digallynes.

A series of stable aryl gallium(I) terphenyl derivatives was synthesized and characterized spectroscopically, structurally and by density functional calculations. Dimeric structures with trans-bent planar CGaGaC core arrangements were observed for [(GaAr*-4-tBu)(2)] (7, Ar*-4-tBu = C(6)H(2)-2,6(C(6)H(2)-2,4,6-iPr(3))(2)-4-tBu) and [(GaAr*-4-CF(3))(2)] (8, Ar*-4-CF(3) = C(6)H(2)-2,6(C(6)H(2)-2,4,6-iPr(3))(2)-4-CF(3)), whereas monomeric structures featuring one coordinate gallium were observed for the more crowded complexes [:GaAr*-3,5-iPr(2)] (10, Ar*-3,5-iPr(2) = C(6)H-2,6(C(6)H(2)-2,4-6-iPr(3))(2)-3,5-iPr(2)) and [GaAr'-3,5-iPr(2)] (11, Ar'-3,5-iPr(2) = C(6)H-2,6(C(6)H(3)-2,6-iPr(2))(2)-3,5-iPr(2)). Complexes 7 and 8 dissociate to monomers in hydrocarbon solution and their electronic spectra closely resemble those of 10 and 11 as well as those of [Ar'GaGaAr'] (Ar' = C(6)H(3)-2,6(C(6)H(3)-2,6-iPr(3))(2)) and [(GaAr*)(n)] (Ar* = C(6)H(3)-2,6(C(6)H(2)-2,4,6-iPr(3))(2)). The calculations showed that the binding energies of the compounds are weak, resemble closed-shell interactions and average approximately 5 kcal mol(-1), as in [Ar*GaGaAr*] with a lowest value of approximately -2 kcal mol(-1) for monomeric 10 and a highest value approximately 9 kcal mol(-1) for the least crowded species [Ar'GaGaAr']. The weak bonding in the complexes supports the view that the GaGa bonding in the previously published doubly reduced Na(2)[Ar*GaGaAr*] and Na(2)[Ar'GaGaAr'] is also weak and is consistent with approximate single bonding.

Reactions of Ar'CrCrAr' with N2O or N3(1-Ad): complete cleavage of the Cr-Cr quintuple interaction.

Reaction of Ar'CrCrAr' (Ar' = C(6)H(3)-2,6-(C(6)H(3)-2,6-Pr(i)(2))(2)) with heterocumulene reagents N(2)O or N(3)(1-Ad) resulted in Ar'Cr(micro-O)(2)Cr(O)Ar' or Ar'Cr(micro(2):eta(1),eta(3)-N(3)(1-Ad))CrAr' which have no metal-metal bonding.

Diarylstannylene activation of hydrogen or ammonia with arene elimination.

Treatment of the stannylenes SnAr'2 (Ar' = C6H3-2,6(C6H3-2,6-Pri2)2), SnAr2# (Ar# = C6H3-2,6-(C6H2-2,4,6-Me3)2, or Sn{N(SiMe3)2}2 with H2, D2, or NH3 under identical, mild (1 atm, 65 degrees C) conditions showed that SnAr2' reacted readily to afford the products {Ar'Sn(mu-H)}2, {Ar'Sn(mu-D)}2, or {Ar'Sn(mu-NH2)}2 with elimination of Ar'H or Ar'D. The less crowded stannylenes SnAr2# and Sn{N(SiMe3)2}2 were recovered unreacted. The differences in reactivity were accounted for in terms of the n-p energy separations which is lowest in the case of AnAr2'. The low energy separation in SnAr' is consistent with enhanced singlet diradical character of the ground state which increases its reactivity.

Addition of H2 to distannynes under ambient conditions.

Dihydrogen reacts directly with a range of distannynes at ca. 25 degrees C under one atmosphere pressure to afford symmetric hydrogen bridged or unsymmetric stannylstannane products in high yield.

Univalent transition metal complexes of arenes stabilized by a bulky terphenyl ligand: differences in the stability of Cr(I), Mn(I) or Fe(I) complexes.

Two univalent transition metal complexes, (micro-eta6:eta6-C7H8){MnAr*-3,5-Pri2}2 () and (eta6-C6H6)FeAr*-3,5-Pri2 () (Ar*-3,5-Pri2=C6H-2,6-(C6H(2)-2,4,6-Pri3)(2)-3,5-Pri2), that have eta6 arene coordination were synthesized by reduction of the corresponding metal halides. The complexes are thermally stable in contrast to the corresponding Cri complexes of benzene or toluene which decompose at room temperature.

An arene-stabilized cobalt(I) aryl: reactions with CO and NO.

The half-sandwich cobalt(I) complex (eta (6)-C 7H 8)CoAr*-3,5- ( i )Pr 2 (Ar*-3,5- ( i )Pr 2 = -C 6H-2,6-(C 6H 2-2,4,6- ( i )Pr 3) 2-3,5- ( i )Pr 2) was synthesized by reduction of [3,5- ( i )Pr 2Ar*Co(mu-Cl)] 2 in toluene. It reacts with CO or NO to afford the unusual complexes [3,5- ( i )Pr 2Ar*C(O)Co(CO)] or [3,5- ( i )Pr 2Ar*N(NO)OCo(NO) 2].

The synthesis, characterisation and electronic structure of N-heterocyclic carbene adducts of P(I) cations.

Two different syntheses of N-heterocyclic carbene complexes of P(I) cations are presented; the structural features of these phosphamethine cyanine salts, in conjunction with the results of computational investigations, provide insight into the nature of the bonding of these heavy allene analogues.

Stabilised phosphorus(I) and arsenic(I) iodide: readily-synthesised reagents for low oxidation state main group chemistry.

Herein we report a surprisingly facile and clean synthesis of base-stabilised phosphorus(I) and arsenic(I) iodide salts, which are reagents that provide convenient access to new low oxidation state main group compounds.

Indium(I) trifluoromethanesulfonate and other soluble salts for univalent indium chemistry.

Herein we report the synthesis, structure and preliminary reactivity studies of a series of unusually soluble indium(i) salts that are improved alternatives to indium(i) halide reagents.

Synthesis and thermolytic behavior of tin(IV) formates: in search of recyclable metal-hydride systems.

The synthesis and characterization of the series of organotin formates together with their thermolytic behavior are described. The diformate Bu(n)(2)Sn{OC(O)H}(2) (1) was synthesized by the reaction of Bu(n)(2)SnH(2) with formic acid. The triorganotin monoformate compounds R(3)SnOC(O)H (R = Cy (cyclohexyl)) 3, Mes, (mesityl, 2,4,6-trimethylphenyl) 4, and Dmp (2,6-dimethylphenyl 5) were obtained by the reaction of R(3)SnOH with formic acid. Their X-ray crystal structures along with that of the previously reported formate (PhCH(2))(3)SnOC(O)H (2) were determined. The diformate 1 exhibits an extended two-dimensional polymeric structure in which six-coordinate tin centers are linked by formate bridges. The tribenzyltin formate (2) possesses a chain structure in which the five-coordinate Sn(CH(2)Ph)(3) units are bridged by formate ions. The cyclohexyl derivative 3 was observed to have a similar structure. In contrast, the Mes and Dmp derivatives 4 and 5 support monomeric structures in which the four-coordinate tin atom is bound to an oxygen of the formate ligand. Heating the compounds in various high boiling solvents produced no decomposition up to 120 °C in the case of 1 and refluxing a solution of 2 or 3 in mesitylene or diglyme left the starting material mostly unchanged, although 3 decomposed to an insoluble orange solid in refluxing decalin. In contrast, the heating of 4 and 5 in refluxing mesitylene led to elimination of CO to give the tin hydroxides. The results are in contrast to the known thermolytic behavior of R(3)SnOC(O)H (R = Pr(n) or Bu(n)) complexes, which eliminate CO(2) to generate R(3)SnH. Compounds 3-5 are rare examples of structurally characterized tin formates.

Recycle of tin thiolate compounds relevant to ammonia-borane regeneration.

The use of benzenedithiol as a digestant for ammonia-borane spent fuel has been shown to result in tin thiolate compounds which we demonstrate can be recycled, yielding Bu(3)SnH and ortho-benzenedithiol for reintroduction to the ammonia-borane regeneration scheme.