Chalcogen-substituted carbenes: a density functional study of structure, stability, and donor ability.

Chalcogen-substituted carbenes are examined computationally using density functional theory. Several approaches are used to assess the stability and reactivity of chalcogenazol-2-ylidene carbenes (NEHCs; E = O, S, Se, Te). The known unsaturated species 1,3-dimethylimidazol-2-ylidene is studied at the same level of theory as the NEHC molecules, as a reference. Electronic structures, stability towards dimerization, and ligand properties are discussed. The results highlight the NEHCs as potentially valuable ancillary ligands for stabilizing low-valent metals or paramagnetic main group molecules. A simple, effective computational method for evaluating σ donor ability and π acidity of carbenes is presented.

Crystal structure and computational study of an oxo-bridged bis-titanium(III) complex.

The solid-state structure of the new compound µ-oxido-bis[dichloridotris(tetrahydrofuran-κO)titanium(III)], [Ti2Cl4O(C4H8O)6], at 150 K has been determined. The crystal has monoclinic (C2/c) symmetry and the complex features C2 symmetry about the bridging O atom. Positional disorder is evident in one of the three tetrahydrofuran environments. A post-Hartree-Fock computational analysis indicates that the complex has nearly degenerate triplet and singlet spin states, with the former favoured slightly by ca 2 kJ mol-1.

A new polymorph of phenylselenium trichloride.

A second polymorph of phenylselenium trichloride, PhSeCl3 or C6H5Cl3Se, is disclosed, which is comprised of asymmetric chlorine-bridged noncovalent dimer units rather than polymeric chains. These dimers are each weakly bound to an adjacent dimer through noncovalent Se...Cl bonding interactions. Phenyl rings within each dimer are oriented in a syn fashion. Density functional theory (DFT) calculations reveal that the putative anti isomer is within 5 kJ mol-1 of the experimentally observed form. This structure represents the first additional polymorph discovered for an organoselenium trihalide compound.

A structural study of 2,4-di-methyl-aniline derivatives.

Crystallographic studies of nitro-gen-containing small mol-ecules aid in the elucidation of their structure-activity relationships and modes of aggregation. In this study, two previously synthesized mol-ecules are crystallographically characterized for the first time. Reaction of 2,4-di-methyl-aniline with N-bromo-succinimide affords the ortho-brominated derivative 2-bromo-4,6-di-methyl-aniline (1; C8H10BrN), which sublimates in vacuo to afford crystals featuring hydrogen-bonded chains as well as Type I halogen-halogen inter-actions. Conversely, alkyl-ation of two equivalents of 2,4-di-methyl-aniline with 1,2-di-bromo-ethane affords a separable mixture of N,N'-bis-(2,4-di-methyl-phen-yl)piperazine (2; C20H26N2), which was crystallographically characterized, as well as N,N'-bis-(2,4-di-methyl-phen-yl)ethyl-enedi-amine (3).

Diverse silver(i) coordination chemistry with cyclic selenourea ligands.

The coordination chemistry of two selenourea ligands (SeIMes and SeIPr) towards silver(i) triflate and silver(i) nitrate was investigated. Two aggregation modes were observed in the solid state, strongly influenced by the size of the aromatic substituents on the ligand. With mesityl groups, selenium-bridged bimetallic motifs [AgX(SeIMes)]2 were obtained, while for the bulkier diisopropylphenyl groups ion-separated species of formulae [Ag(SeIPr)2]+[X]- were obtained. Recrystallization of [Ag(NO3)(SeIMes)]2 from hot methanol resulted in the formation of a unique coordination polymer featuring three silver environments. Characterization of the complexes by NMR spectroscopy and mass spectrometry suggested all complexes adopt the ionic aggregation mode in methanol solution.

A Selenium-Containing Diarylamido Pincer Ligand: Synthesis and Coordination Chemistry with Group 10 Metals.

The synthesis of new bifunctional organoselenium diarylamine compounds RN(4-Me-2-SeMe-C6H3)2 (R = Me: 1; R = tert-butoxycarbonyl (Boc): 2; R = H: 3-H) via aryllithium chemistry is disclosed. Compound 1 serves as a Se,Se-bidentate neutral ligand toward Pd(II), forming the coordination complex {PdCl2[MeN(4-Me-2-SeMe-C6H3)2-κ(2)Se)]} (1-Pd) in reaction with [PdCl2(COD)] (COD = 1,5-cyclooctadiene), while the protio ligand 3-H forms tridentate pincer complexes [MCl(N(4-Me-2-SeMe-C6H3)2)] (M = Pd: 3-Pd; M = Pt: 3-Pt) with [MCl2(COD)] (M = Pd, Pt) in the presence of triethylamine. Complex 1-Pd does not undergo N-C cleavage at high temperature, unlike related alkylphosphine-bearing complexes. All compounds have been characterized by multinuclear ((1)H, (13)C, (77)Se) NMR spectroscopy, and crystal structures of 1, 1-Pd, 3-Pd, and 3-Pt are reported. Additionally, density functional theory calculations have been performed on the pincer complexes to contrast them with well-known analogues containing phosphine donor groups.

A square-planar tellurium(II) complex with Te,Te'-chelating ligands.

While exploring the chemistry of tellurium-containing dichalcogenidoimidodiphosphinate ligands, the first all-tellurium member of a series of related square-planar E(II)(E')4 complexes (E and E' are group 16 elements), namely bis(P,P,P',P'-tetraphenylditelluridoimidodiphosphinato-κ(2)Te,Te')tellurium(II) (systematic name: 2,2,4,4,8,8,10,10-octaphenyl-1λ(3),5,6λ(4),7λ(3),11-pentatellura-3,9-diaza-2λ(5),4λ(5),8λ(5),10λ(5)-tetraphosphaspiro[5.5]undeca-1,3,7,9-tetraene), C48H40N2P4Te5, was obtained unexpectedly. The formally Te(II) centre is situated on a crystallographic inversion centre and is Te,Te'-chelated to two anionic [(TePPh2)2N](-) ligands in an anti conformation. The central Te(II)(Te)4 unit is approximately square planar [Te-Te-Te = 93.51 (3) and 86.49 (3)°], with Te-Te bond lengths of 2.9806 (6) and 2.9978 (9) Å.

Crystal structure of 1-bromo-2-(phenyl-selen-yl)benzene.

In the title compound, C12H9BrSe, the Se atom exhibits a bent geometry, with a C-Se-C bond angle of 99.19 (6)°. The ortho Se and Br atoms are slightly displaced from opposite faces of the mean plane of the benzene ring [by 0.129 (2) and 0.052 (2) Å, respectively]. The planes of the benzene and phenyl rings form a dihedral angle of 72.69 (5)°. In the crystal, π-stacking inter-actions between inversion-related phenyl rings are observed, with a centroid-centroid distance of 3.630 (1) Å.

Secondary diphosphine and diphosphido ligands: synthesis, characterisation and group 1 coordination compounds.

Two types of secondary diphosphines, 1,8-(ArPH)2C14H8 (1a: Ar = Tripp, 2,4,6-triisopropylphenyl; 1b: Ar = Mes, 2,4,6-trimethylphenyl) and 1,3-((t)BuPHCH2)2C6H4 (2), based on rigid 1,8-anthracene and flexible m-xylyl frameworks, respectively, have been synthesized using different strategies. Compounds 1a and 1b were formed by nucleophilic aromatic substitution of a potassium organophosphido salt onto 1,8-difluoroanthracene, while compound 2 was obtained by addition of the Grignard reagent [1,3-(ClMgCH2)2C6H4]x to a dichloroorganophosphine, followed by reduction to the diphosphine. These compounds were isolated as ca. 1 : 1 mixtures of rac and meso diastereomers as determined by multinuclear NMR spectroscopy. Borane and selenide derivatives of 2, 1,3-((t)BuPH(BH3)CH2)2C6H4 (3) and 1,3-((t)BuPH(Se)CH2)2C6H4 (4), were obtained. Preferential crystallization of one diastereomer of 3 and 4 was observed; X-ray crystallographic studies identified this as the rac isomer for diselenide 4. Metallation studies of compounds 1a and 2 yielded several alkali metal salts. The reaction of KH or K metal with 1a yielded the compounds 1,8-(TrippPK)2C14H8·xTHF (5) and 1,8-(TrippPK)2C14H10·xTHF (6), respectively; in complex 6 the central aromatic ring has been reduced to yield a bent dihydroanthracene backbone. A crown ether derivative of 6, [K(18-crown-6)(THF)2]2[1,8-(TrippP)2C14H10] (7), was characterised crystallographically. Double deprotonation of compound 2 with (n)BuLi/TMEDA (TMEDA = N,N,N',N'-tetramethylethylenediamine) afforded the yellow dilithium complex 1,3-((t)BuPLiCH2)2C6H4·TMEDA (8), which crystallized as a dimer featuring lithium-arene π interactions.

Thermally stable rare earth dialkyl complexes supported by a novel bis(phosphinimine)pyrrole ligand.

A novel bis(phosphinimine)pyrrole based ligand (HL) and its synthesis are reported. Rare earth dialkyl complexes of the ligand, LLn(CH(2)SiMe(3))(2) (Ln = Er, Lu, Sc), have been prepared and found to exhibit high thermal stability in solution. The protio-ligand and dialkyl lanthanide complexes (Ln = Er, Lu) have been characterised by single crystal X-ray diffraction studies.

Ring-opening polymerisation of rac-lactide mediated by cationic zinc complexes featuring P-stereogenic bisphosphinimine ligands.

The diastereomerically pure P-stereogenic bis(phosphinimine) ligands 4,6-(ArN[double bond, length as m-dash]PMePh)(2)dbf [Ar = 4-isopropylphenyl (Pipp): rac-4, meso-4; Ar = 2,6-diisopropylphenyl (Dipp): rac-4a; dbf = dibenzofuran] were synthesised and complexed to zinc using a protonation-alkane elimination strategy. The cationic alkylzinc complexes thus obtained, RZn[4,6-(ArN[double bond, length as m-dash]PMePh)(2)dbf][B(Ar')(4)] [Ar = Pipp, Ar' = C(6)H(3)(CF(3))(2): rac-6 (R = Et), meso-6 (R = Et), rac-7 (R = Me) meso-7 (R = Me); Ar = Dipp: rac-6a (R = Et, Ar' = C(6)H(3)(CF(3))(2)), rac-6b (R = Et, Ar' = C(6)F(5))] were investigated for their competency as initiators for the ring-opening polymerisation of rac-lactide. The formation of polylactide was achieved under relatively mild conditions (40 °C, 2-4 h) and the microstructures of the resulting polymers exhibited a slight heterotactic bias [polymer tacticity (P(r)) = 0.51-0.63].

Toward stereoselective lactide polymerization catalysts: cationic zinc complexes supported by a chiral phosphinimine scaffold.

The P-stereogenic phosphinimine ligands (dbf)MePhP═NAr (7: Ar = Dipp; 8: Ar = Mes; dbf = dibenzofuran, Dipp = 2,6-diisopropylphenyl, Mes = 2,4,6-trimethylphenyl) were synthesized as racemates via reactions of the parent phosphines (rac)-(dbf)MePhP (6) with organoazides. The ligands 7 and 8 were protonated by Brønsted acids to afford the aminophosphonium borate salts [(7)-H][BAr(4)] (9: Ar = C(6)F(5); 11: Ar = Ph) and [(8)-H][BAr(4)] (10: Ar = C(6)F(5); 12: Ar = Ph). The protonated ligands 9 and 10 were active toward alkane elimination reactions with diethylzinc and ethyl-[methyl-(S)-lactate]zinc to give the heteroleptic complexes [{(dbf)MePhP═NAr}ZnR][B(C(6)F(5))(4)] (Ar = Dipp, 13: R = Et; 15: R = methyl-(S)-lactate; Ar = Mes, 14: R = Et; 16: R = methyl-(S)-lactate). By contrast, reaction of the tetraphenylborate derivative 11 with diethylzinc yielded a phenyl transfer product, [(dbf)MePhP═NDipp]ZnPh(2) (17). Complex 15 was found to catalyze the ring-opening polymerization of rac-lactide.

A sulfur(II) complex of a dithioimidodiphosphinate.

The structure of bis[P,P-di-tert-butyl-N-(di-tert-butylphosphorothioyl)phosphinimidothioato-κS]sulfur(II) toluene solvate (systematic name: 5,13-dibutyl-7,7,11,11-tetramethyl-8,9,10-trithia-6,12-diaza-5λ(5),7λ(5),11λ(5),13λ(5)-tetraphosphaheptadeca-6,11-diene-5,13-dithione toluene solvate), C(32)H(72)N(2)P(4)S(5)·C(7)H(8), at 173 K has monoclinic (C2/c) symmetry. The S(II) centre of (SP(t)Bu(2)NP(t)Bu(2)PS-)(2)S is coordinated in an S-monodentate fashion to two [(SP(t)Bu(2))(2)N](-) monoanions. The molecule resides on a twofold axis which bisects the central S atom. The internal P-S distance is ca 0.19 Šlonger than the terminal P=S bond and there is a compensating alternation in P-N bond distances. The central S-S-S angle is 106.79 (8)°. The toluene solvent molecule is disordered about a twofold axis.

Thallium(I) complexes of dichalcogenido imidodiphosphinates {Tl[(EP(i)Pr(2))(2)N]}(n) (E = Te, Se, S): Synthesis, NMR spectra and a structural comparison.

The homoleptic thallium(i) complexes {Tl[(EP(i)Pr(2))(2)N]}(n) (, E = Te; , E = Se; , E = S) have been obtained in 70-86% yields from the reaction of TlOEt with (TMEDA)Na[(EP(i)Pr(2))(2)N] in CH(2)Cl(2) or Et(2)O. Complexes were structurally characterised in the solid state by single crystal X-ray diffraction and in solution by multinuclear NMR spectroscopy ((31)P, (77)Se, and (125)Te). The solid-state structures of , and are comprised of one-dimensional coordination polymers. In and there are two distinct environments for both the thallium centres and the [(EP(i)Pr(2))(2)N](-) ligands. The denticities of the selenium centres in the ligands of differ significantly from those of tellurium donor atoms in giving rise to different coordination geometries at the chalcogen atoms in these two complexes; however, both possess edge-sharing Tl(2)E(4) octahedra as structural units. By contrast, the sulfur analogue exhibits only one ligand environment with trigonal pyramidal geometries for both sulfur centres and a distorted tetrahedral geometry for thallium generating vertex-sharing four-membered Tl(2)S(2) rings.

Epitaxial CdTe rods on Au/Si islands from a molecular compound.

Formation of unusual CdTe rods on Si/SiO(2) and gold coated Si/SiO(2) surfaces is reported from chemical vapor deposition of Cd[(TeP(i)Pr(2))(2)N](2).

New insights into the chemistry of imidodiphosphinates from investigations of tellurium-centered systems.

Dichalcogenido-imidodiphosphinates, [N(PR(2)E)(2)](-) (R = alkyl, aryl), are chelating ligands that readily form cyclic complexes with main group metals, transition metals, lanthanides, and actinides. Since their discovery in the early 1960s, researchers have studied the structural chemistry of the resulting metal complexes (where E = O, S, Se) extensively and identified a variety of potential applications, including as NMR shift reagents, luminescent complexes in photonic devices, or single-source precursors for metal sulfides or selenides. In 2002, a suitable synthesis of the tellurium analogs [N(PR(2)Te)(2)](-) was developed. In this Account, we describe comprehensive investigations of the chemistry of these tellurium-centered anions, and related mixed chalcogen systems, which have revealed unanticipated features of their fundamental structure and reactivity. An exhaustive examination of previously unrecognized redox behavior has uncovered a variety of novel dimeric arrangements of these ligands, as well as an extensive series of cyclic cations. In combination with calculations using density functional theory, these new structural frameworks have provided new insights into the nature of chalcogen-chalcogen bonding. Studies of metal complexes of the ditellurido ligands [N(PR(2)Te)(2)](-) have revealed unprecedented structural and reaction chemistry. The large tellurium donor sites confer greater flexibility, which can lead to unique structures in which the tellurium-centered ligand bridges two metal centers. The relatively weak P-Te bonds facilitate metal-insertion reactions (intramolecular oxidative-addition) to give new metal-tellurium ring systems for some group 11 and 13 metals. Metal tellurides have potential applications as low band gap semiconductor materials in solar cells, thermoelectric devices, and in telecommunications. Practically, some of these telluride ligands could be applied in these industries. For example, certain metal complexes of the isopropyl-substituted anion [N(P(i)Pr(2)Te)(2)](-) serve as suitable single-source precursors for pure metal telluride thin films or novel nanomaterials, for example, CdTe, PbTe, In(2)Te(3), and Sb(2)Te(3).

Synthesis, multinuclear NMR spectra, and X-ray structures of tBu2PNP(I)tBu2 and EPR2NP(I)R2 (E = Se, Te; R = iPr, tBu).

Two synthetic routes to bifunctional P(V)/P(V) compounds of the type EPR(2)NP(I)R(2) have been developed. The reaction of Li[EP(i)Pr(2)NP(i)Pr(2)] with one molar equivalent of I(2) produces EP(i)Pr(2)NP(I)(i)Pr(2) (3a-I, E = Se; 3b-I, E = Te). Alternatively, the oxidation of Na[N(P(t)Bu(2))(2)] with I(2) in tetrahydrofuran (THF) generates the P(III)/P(V) compound (t)Bu(2)PNP(I)(t)Bu(2) (6'-I) which, on treatment with elemental selenium or tellurium in THF, yields EP(t)Bu(2)NP(I)(t)Bu(2) (3a'-I, E = Se; 3b'-I, E = Te). The acyclic compounds 3a-I, 3a'-I, 3b-I, 3b'-I, and 6'-I have been characterized in solution by multinuclear ((1)H, (31)P, (77)Se, and (125)Te) NMR spectroscopy and in the solid state by X-ray structural determinations.

Synthesis, structures, and multinuclear NMR spectra of tin(II) and lead(II) complexes of tellurium-containing imidodiphosphinate ligands: preparation of two morphologies of phase-pure PbTe from a single-source precursor.

Group 14 metal complexes of heavy chalcogen-centered anions, M[(TeP(i)Pr(2))(2)N](2) (5, M = Sn; 6, M = Pb) and M(TeP(i)Pr(2)NP(i)Pr(2)Se)(2) (7, M = Sn; 8, M = Pb), were synthesized in 64-89% yields by metathesis of alkali-metal salts of the ligands with group 14 metal dihalides. Crystallographic characterization of the complexes revealed that 5, 6, and 8 engage in metal...chalcogen secondary bonds to generate dimers, whereas 7 is monomeric in the solid state. Multinuclear ((1)H, (31)P, (77)Se, and (125)Te) solution NMR data for these homoleptic complexes evinced dynamic behavior leading to the equivalence of the two ligand environments. The Pb(II) complex 6 was utilized as a single-source precursor to micrometer-scale lead telluride particles via two divergent techniques: aerosol-assisted chemical vapor deposition of the complex in THF/CH(2)Cl(2) solution onto glass substrates yielded rectangular prisms, while solution injection of 6 in tri-n-octylphosphine onto Si/SiO(2)(100) substrates heated to 200-220 degrees C resulted in the formation of wires. PXRD and EDX analysis of the products confirmed the phase purity of the PbTe materials.

Palladium and platinum complexes of tellurium-containing imidodiphosphinate ligands: nucleophilic attack of Li[(P(i)Pr2)(TeP(i)Pr2)N] on coordinated 1,5-cyclooctadiene.

Homoleptic group 10 complexes of ditellurido PNP (PNP = imidodiphosphinate), heterodichalcogenido PNP and monotellurido PNP ligands, M[(TeP(i)Pr2)2N]2 (1: M = Pd; 2: M = Pt), M[(EP(i)Pr2)(TeP(i)Pr2)N]2 (3: M = Pd, E = Se; 4: M = Pt, E = Se; 5: M = Pd, E = S; 6: M = Pt, E = S) and M[(P(i)Pr2)(TeP(i)Pr2)N]2 (7: M = Pd; 8: M = Pt), respectively, were prepared by metathesis between alkali-metal derivatives of the appropriate ligand and MCl2(COD) in THF. Complexes 1-8 were characterised in solution by multinuclear (31P, 77Se, 125Te and 195Pt) NMR spectroscopy and, in the case of 1, 2, trans-7, cis-7 and trans-8, in the solid state by X-ray crystallography. The square-planar complexes 3-6 are formed as a mixture of cis- and trans-isomers on the basis of NMR data. The cis and trans isomers of 7 were separated by crystallisation from different solvents. In addition to trans-8, the reaction of Li[(P(i)Pr2)(TeP(i)Pr2)N] with MCl2(COD) produced the heteroleptic complex Pt[(P(i)Pr2)(TeP(i)Pr2)N][sigma:eta2-C8H12(P(i)Pr2NP(i)Pr2Te)] (9) resulting from nucleophilic attack on coordinated 1,5-cyclooctadiene. Complex 9 was identified by multinuclear (13C, 31P, 125Te and 195Pt) NMR spectroscopy, which revealed a mixture of geometric isomers, and by X-ray crystallography.

Group 11 complexes of the P,Te-centered ligand [TeP(i)Pr2NP(i)Pr2]-: synthesis, structures, and insertion reactions of the copper(I) complex with chalcogens.

The lithium reagent [LiTeP(i)Pr(2)NP(i)Pr(2)] undergoes metathetical reactions with group 11 chlorides to give the complexes {M(TeP(i)Pr(2)NP(i)Pr(2))}(3) (6: M = Cu; 7: M = Ag) and (Ph(3)P)Au(TeP(i)Pr(2)NP(i)Pr(2)) (8) as yellow crystalline solids. These new complexes were characterized by single crystal X-ray diffraction and multinuclear NMR spectroscopy. The tellurium atoms in the trimeric complexes 6 and 7 occupy bridging positions to give a Cu(3)Te(3) ring in a twist-boat conformation with short M...M contacts (M = Cu, Ag). Variable temperature (31)P NMR and ESI-MS spectra for 6 and 7 give evidence for the formation of several oligomers in tetrahydrofuran solution. The reactions of 6 with dioxygen (or Me(3)NO), elemental sulfur, or red selenium generate the chalcogen-insertion products {Cu(TeP(i)Pr(2)NP(i)Pr(2)E)}(3) (9: E = O; 10: E = S; 11: E = Se), which were also structurally characterized by single crystal X-ray diffraction and multinuclear NMR spectroscopy. The lighter chalcogens are two-coordinate while the tellurium centers occupy bridging positions in the trimeric complexes 9-11 giving rise to Cu(3)Te(3) rings in a chairlike conformation.