Jamie S. Ritch

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.

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, 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.

Chemical vapour deposition of II–VI semiconductor thin films using M[(TePiPr2)2N]2 (M = Cd, Hg) as single-source precursors

The aerosol-assisted chemical vapour deposition (AACVD) of CdTe has been carried out using Cd[(TePiPr2)2N]2 at substrate temperatures between 375 and 475 °C. XRD shows the formation of cubic CdTe between 425 and 475 °C. At low deposition temperature (375 °C), a mixture of hexagonal tellurium and cubic cadmium telluride is observed. SEM images reveal that the growth temperatures do not have a profound effect on the morphologies of films. Surface analysis by XPS of films deposited at 475 °C showed the growth of Te-rich films. The AACVD of Hg[(TePiPr2)2N]2 resulted in deposition of hexagonal tellurium.

Group 11 Complexes of the P,Te-Centered Ligand [TePiPr2NPiPr2]−: 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.

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).

Palladium and platinum complexes of tellurium-containing imidodiphosphinate ligands: nucleophilic attack of Li[(PiPr2)(TePiPr2)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.

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 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 Å longer 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.