Spectroscopic characterization of molybdenum dinitrogen complexes containing a combination of di- and triphosphine coligands: 31P NMR analysis of five-spin systems

The three molybdenum-N2 complexes [Mo(N2)(dpepp)(depe)] (1), [Mo(N2)(dpepp)(dppe)] (2), and [Mo(N2)(dpepp)(1,2-dppp)] (3), all of which contain a combination of a bi- and a tridentate phosphine ligand, were prepared and investigated by vibrational and (31)P NMR spectroscopy. As a tridentate ligand bis(2-diphenylphosphinoethyl)phenylphosphine (dpepp) has been employed. The three different bidentate ligands are 1,2-bis(diethylphosphino)ethane (depe), 1,2-bis(diphenylphosphino)ethane (dppe), and R-(+)-1,2-bis(diphenylphosphino)propane (1,2-dppp). N-N as well as metal-N vibrations of 1-3 are identified and interpreted in terms of the geometric and electronic structures of the complexes. (31)P NMR spectra are recorded and fully analyzed. Moreover, correlation spectroscopy (COSY)-45 measurements are performed to determine the relative signs of coupling constants. Special attention is directed to a detection of different isomers and their (31)P NMR, as well as vibrational spectroscopic properties. The implications of the results for the area of synthetic nitrogen fixation with phosphine complexes are discussed.     

Synthesis, structure and photoluminescence of [Cu(acac)(dppe)]n with novel 1D zigzag chain-like motif

A novel complex [Cu(acac)(dppe)]_n (1) [acac = acetylacetone; dppe = 1,2-bis(diphenylphosphino)ethane] was obtained by solution reactions and structurally characterized by X-ray diffraction. The crystal structure analysis indicates that the title complex is characteristic of a polymeric chain formed by the dppe ligands bridging neighboring copper centers. The copper atom is in a distorted tetrahedral geometry. Photoluminescent investigation reveals that the title complex displays a strong emission in bluelight region.     

Importance of out-of-state spin-orbit coupling for slow magnetic relaxation in mononuclear Fe(II) complexes

Two mononuclear high-spin Fe(II) complexes with trigonal planar ([Fe(II)(N(TMS)(2))(2)(PCy(3))] (1) and distorted tetrahedral ([Fe(II)(N(TMS)(2))(2)(depe)] (2) geometries are reported (TMS = SiMe(3), Cy = cyclohexyl, depe = 1,2-bis(diethylphosphino)ethane). The magnetic properties of 1 and 2 reveal the profound effect of out-of-state spin-orbit coupling (SOC) on slow magnetic relaxation. Complex 1 exhibits slow relaxation of the magnetization under an applied optimal dc field of 600 Oe due to the presence of low-lying electronic excited states that mix with the ground electronic state. This mixing re-introduces orbital angular momentum into the electronic ground state via SOC, and 1 thus behaves as a field-induced single-molecule magnet. In complex 2, the lowest-energy excited states have higher energy due to the ligand field of the distorted tetrahedral geometry. This higher energy gap minimizes out-of-state SOC mixing and zero-field splitting, thus precluding slow relaxation of the magnetization for 2.     

1H,1H,2H,2H-perfluoroalkyl-functionalization of Ni(II), Pd(II), and Pt(II) mono- and diphosphine complexes: minimizing the electronic consequences for the metal center

A series of fluorous derivatives of group 10 complexes MCl(2)(dppe) and [M(dppe)(2)](BF(4))(2) (M = Ni, Pd or Pt; dppe = 1,2-bis(diphenylphosphino)ethane) and cis-PtCl(2)(PPh(3))(2) was synthesized. The influence of para-(1H,1H,2H,2H-perfluoroalkyl)dimethylsilyl-functionalization of the phosphine phenyl groups of these complexes, as studied by NMR spectroscopy, cyclovoltammetry (CV), XPS analyses, as well as DFT calculations, points to a weak steric and no significant inductive electronic effect. The steric effect is most pronounced for M = Ni and leads in the case of NiCl(2)(1c) (3c) and [Ni(1c)(2)](BF(4))(2) (7c) (1c = [CH(2)P[C(6)H(4)(SiMe(2)CH(2)CH(2)C(6)F(13))-4](2)](2)) to a tetrahedral distortion from the expected square planar geometry. The solubility behavior of NiCl(2)[CH(2)P[C(6)H(4)(SiMe(3-b)(CH(2)CH(2)C(x)F(2x+1)b)-4](2)](2) (3: b = 1-3; x = 6, 8) in THF, toluene, and c-C(6)F(11)CF(3) was found to follow the same trends as those observed for the free fluorous ligands 1. A similar correlation between the partition coefficient (P) of complexes 3 and free 1 was observed in fluorous biphasic solvent systems, with a maximum value obtained for 3f (b = 3, x = 6, P = 23 in favor of the fluorous phase).     

Hypervalent, low-coordinate phosphorus(III) centers in complexes of the phosphadiazonium cation with chelate ligands

Trifluoromethylsulfonyloxy-(2,4,6-tri-tert-butylphenylimino)phosphine, Mes*NPOTf (Mes = 2,4,6-tri-tert-butylphenyl, OTf = trifluoromethanesulfonate, triflate) reacts quantitatively with the multifunctional ligands 2,2'-bipyridine (2,2'-BIPY), N,N,N',N'-tetramethylethylenediamine (TMEDA), 1,2-bis(diethylphosphino)ethane (DEPE), 1,2-bis(diphenylphosphino)ethane (DIPHOS), and N,N,N',N' ',N' '-pentamethyldiethylenetriamine (PMDETA) to give the Lewis acid-base complexes [Mes*NP(2,2'-BIPY)][OTf], [Mes*NP(TMEDA)][OTf], [Mes*NP(DIPHOS)][OTf], [Mes*NP(DEPE)][OTf], and [Mes*NP(PMDETA)][OTf], respectively. Single-crystal X-ray diffraction studies indicate that the closest contact of the ligand donor atoms occurs at phosphorus in all cases, affecting significant displacement of the OTf anion. The resulting cations [Mes*NP(L)]+ are best described as complexes of a neutral chelating ligand on a phosphadiazonium Lewis acceptor, and highlight the potential for electron-rich centers to behave as Lewis acids despite the presence of a lone pair of electrons at the acceptor site. More importantly, the new complexes represent rare examples of systems containing hypervalent, low-coordinate phosphorus(III) centers.     

Initial structure modification of tetrahedral to planar nickel(II) in a nickel-iron-sulfur cluster related to the C-cluster of carbon monoxide dehydrogenase

A method has been devised that creates a planar Ni(II) site from a tetrahedral site in a NiFe(3)S(4) cubane-type cluster. Reaction of [(Ph(3)P)NiFe(3)S(4)(LS(3))](2)(-) (2) with 1,2-bis(dimethylphosphino)ethane affords [(dmpe)NiFe(3)S(4)(LS(3))](2)(-) (3), isolated in ca. 45% yield as (Et(4)N)(2)[3a].2.5MeCN and (Et(4)N)(2)[3b].0.25MeCN, both of which occur in triclinic space group P. Each crystalline form contains two crystallographically inequivalent clusters with the same overall structure but slightly different dimensions. The cluster is bound by three thiolate terminal ligands to semirigid cavitand ligand LS(3). The NiFe(3)S(4) core contains three tetrahedral sites, one Fe(micro(3)-S)(3)(SR) and two Fe(micro(3)-S)(2)(micro(2)-S)(SR) with normal metric features, and one distorted square planar Ni(micro(3)-S)(2)P(2) site in a Ni(micro(3)-S)(2)Fe face with mean bond lengths Ni-P = 2.147(9) A and Ni-S = 2.29(2) A. The opposite Fe(2)(micro(3)-S)(micro(2)-S) face places the micro(2)-S atom at nonbonding and variable distances (2.60-2.90 A) above the nickel atom. Binding of the strong-field ligand dmpe results in a planar Ni(II) site and deconstruction of the full cubane geometry. The structure approximates that established crystallographically in the C-cluster of C. hydrogenoformans carbon monoxide dehydrogenase whose NiFe(4)S(4) core contains a planar NiS(4) site and three tetrahedral FeS(4) sites in a fragment that is bridged by sulfide atoms to an exo iron atom. M?ssbauer studies of polycrystalline samples containing both clusters 3a and 3b reveal the presence of at least two cluster types. The spectroscopically best defined cluster accounts for ca. 54% of total iron and exhibits hyperfine interactions quite similar to those reported for the S = (5)/(2) state of the protein-bound cubane-type cluster [ZnFe(3)S(4)](1+), whose M?ssbauer spectrum revealed the presence of a high-spin Fe(2+) site and a delocalized Fe(2.5+)Fe(2.5+) pair. Development of reactions leading to a planar nickel and a sulfide-bridged iron atom is requisite to attainment of a synthetic analogue of this complex protein-bound cluster. This work demonstrates a tetrahedral (2) --> planar (3) Ni(II) stereochemical conversion can be effected by binding of ligands that generate a sufficiently strong in-plane ligand field (dmpe = 1,2-bis(dimethylphosphino)ethane, LS(3) = 1,3,5-tris((4,6-dimethyl-3-mercaptophenyl)thio)-2,4,6-tris(p-tolylthio)benzene(3-)).     

含硫过渡金属基元的反应 2: 双膦及双齿巯基混合配位钴, 镍化合物的合成和结构特征

双膦(P-P)和1, 2-双齿巯基(S-X)混合与MCl2(M=Co, Ni)反应,得到通式为M(S-X)(P-P)的产物。晶体结构测定表明, 配合物Co(bdt)(dppe)(1), Ni(tdt)(dppm)(2)和Ni(tsal)(dppe)(3)中的金属均为SXP2配位的四方平面构型, S, X, P原子分别来自二种双齿配体, 各形成四、五或六元螯合配位环。文中总结了结构特征, 探讨了基元配合物稳定的原因。     

Functionalised trimethylsilyl reagents in cluster synthesis: reactions of Ph2P(S)SSiMe3 with group 11 salts

A series of complexes, ranging from the small cluster 1/infinity[Ag(Ph2PS2)(dppe)](infinity) [dppe=1,2-bis(diphenylphosphino)ethane] to [Cu48S20(O(t)Bu)2(Ph2PS2)2(dppm-)4(dppm)4][dppm=1,2-bis(diphenylphosphino)methane] (the largest Cu cluster containing phosphinodithioato ligands), has been synthesised. The structural evidence presented here indicates that in these reactions initially small cyclic aggregates or one-dimensional coordination polymers are formed. The growth of these intermediates to larger aggregates can take up to several months and could proceed via cationic intermediates.     

Active-site models for the nickel-iron hydrogenases: effects of ligands on reactivity and catalytic properties

Described are new derivatives of the type [HNiFe(SR)(2)(diphosphine)(CO)(3)](+), which feature a Ni(diphosphine) group linked to a Fe(CO)(3) group by two bridging thiolate ligands. Previous work had described [HNiFe(pdt)(dppe)(CO)(3)](+) ([1H](+)) and its activity as a catalyst for the reduction of protons (J. Am. Chem. Soc. 2010, 132, 14877). Work described in this paper focuses on the effects on properties of NiFe model complexes of the diphosphine attached to nickel as well as the dithiolate bridge, 1,3-propanedithiolate (pdt) vs 1,2-ethanedithiolate (edt). A new synthetic route to these Ni-Fe dithiolates is described, involving reaction of Ni(SR)(2)(diphosphine) with FeI(2)(CO)(4) followed by in situ reduction with cobaltocene. Evidence is presented that this route proceeds via a metastable μ-iodo derivative. Attempted isolation of such species led to the crystallization of NiFe(Me(2)pdt)(dppe)I(2), which features tetrahedral Fe(II) and square planar Ni(II) centers (H(2)Me(2)pdt = 2,2-dimethylpropanedithiol). The new tricarbonyls prepared in this work are NiFe(pdt)(dcpe)(CO)(3) (2, dcpe = 1,2-bis(dicyclohexylphosphino)ethane), NiFe(edt)(dppe)(CO)(3) (3), and NiFe(edt)(dcpe)(CO)(3) (4). Attempted preparation of a phenylthiolate-bridged complex via the FeI(2)(CO)(4) + Ni(SPh)(2)(dppe) route gave the tetrametallic species [(CO)(2)Fe(SPh)(2)Ni(CO)](2)(μ-dppe)(2). Crystallographic analysis of the edt-dcpe compund [2H]BF(4) and the edt-dppe compound [3H]BF(4) verified their close resemblance. Each features pseudo-octahedral Fe and square pyramidal Ni centers. Starting from [3H]BF(4) we prepared the PPh(3) derivative [HNiFe(edt)(dppe)(PPh(3))(CO)(2)]BF(4) ([5H]BF(4)), which was obtained as a ～2:1 mixture of unsymmetrical and symmetrical isomers. Acid-base measurements indicate that changing from Ni(dppe) (dppe = Ph(2)PCH(2)CH(2)PPh(2)) to Ni(dcpe) decreases the acidity of the cationic hydride complexes by 2.5 pK(a)(PhCN) units, from ～11 to ～13.5 (previous work showed that substitution at Fe leads to more dramatic effects). The redox potentials are more strongly affected by the change from dppe to dcpe, for example the [2](0/+) couple occurs at E(1/2) = -820 for [2](0/+) vs -574 mV (vs Fc(+/0)) for [1](0/+). Changes in the dithiolate do not affect the acidity or the reduction potentials of the hydrides. The acid-independent rate of reduction of CH(2)ClCO(2)H by [2H](+) is about 50 s(-1) (25 °C), twice that of [1H](+). The edt-dppe complex [2H](+) proved to be the most active catalyst, with an acid-independent rate of 300 s(-1).     

Synthesis and structure of singly bridged and doubly bridged [MoFe(3)S(4)] double cubanes with bidentate phosphine ligands

The reactions of the (Et(4)N)(2)[(Cl(4)-cat)(MeCN)MoFe(3)S(4)Cl(3)] (I) cluster with Fe(pp)(2)Cl(2) (pp = depe (bis(1,2-diethylphosphino)ethane) or dmpe (bis(1,2-dimethylphosphino)ethane)) produced the [(Cl(4)-cat)MoFe(3)S(4)(pp)(2)Cl](2)(mu-pp) (pp = depe (III) or dmpe (V)) singly bridged double cubanes. The reactions of I with the same bidentate phosphine ligands in the presence of NaBPh(4) also produced III and the [(Cl(4)-cat)MoFe(3)S(4)(dmpe)(2)](2)(mu-S)(mu-dmpe) (VI) doubly bridged double cubane, respectively. The byproduct (BPh(4))[Fe(dmpe)(2)(MeCN)Cl] (VII) has been isolated from the reaction mixture and crystallographically characterized. The depe analogue of VI, [(Cl(4)-cat)MoFe(3)S(4)(depe)(2)](2)(mu-S)(mu-depe) (IV), has been successfully prepared from III in the presence of excess Li(2)S. Similar reactions with (Et(4)N)(2)[Fe(4)S(4)(SPh)(4)] (VIII) have resulted in the formation of the neutral Fe(4)S(4)(depe)(2)(SPh)(2) (IX) cluster. The chloride analogue of IX, Fe(4)S(4)(depe)(2)Cl(2) (XI), has been obtained by a reaction of IX with benzoyl chloride. The crystal and molecular structures of III, VI, VII, and XI have been determined by single-crystal X-ray crystallography. The electrochemical and spectroscopic properties, including the Mossbauer spectra of the new clusters, have been determined and analyzed.     

Synthesis and Ligand Substitution Reactions of a Mesitylphosphido-Bridged Platinum(II) Dimer

The stable primary phosphine complexes trans-M(PH(2)Mes)(2)Cl(2) (1, M = Pd; 2, M = Pt; Mes = 2,4,6-(t-Bu)(3)C(6)H(2)) were prepared from Pd(PhCN)(2)Cl(2) and K(2)PtCl(4), respectively. Reaction of Pt(COD)Cl(2) (COD = 1,5-cyclooctadiene) with less bulky arylphosphines gives the unstable cis-Pt(PH(2)Ar)(2)Cl(2) (3, Ar = Is = 2,4,6-(i-Pr)(3)C(6)H(2); 4, Ar = Mes = 2,4,6-Me(3)C(6)H(2)). Spontaneous dehydrochlorination of 4 or direct reaction of K(2)PtCl(4) with 2 equiv of PH(2)Mes gives the insoluble primary phosphido-bridged dimer [Pt(PH(2)Mes)(&mgr;-PHMes)Cl](2) (5), which was characterized spectroscopically, including solid-state (31)P NMR studies. The reversible reaction of 5 with PH(2)Mes gives [Pt(PH(2)Mes)(2)(&mgr;-PHMes)](2)[Cl](2) (6), while PEt(3) yields [Pt(PEt(3))(2)(&mgr;-PHMes)](2)[Cl](2) (7), which on recrystallization forms [Pt(PEt(3))(&mgr;-PHMes)Cl](2) (8). Complex 5 and PPh(3) afford [Pt(PPh(3))(&mgr;-PHMes)Cl](2) (9). Addition of 1,2-bis(diphenylphosphino)ethane (dppe) to 5 gives the dicationic [Pt(dppe)(&mgr;-PHMes)](2)[Cl](2) (10-Cl), which was also obtained as the tetrafluoroborate salt 10-BF(4)() by deprotonation of [Pt(dppe)(PH(2)Mes)Cl][BF(4)] (11) with Et(3)N or by reaction of [Pt(dppe)(&mgr;-OH)](2)[BF(4)](2) with 2 equiv of PH(2)Mes. Complexes 8, 9, and 10-Cl.2CH(2)Cl(2).2H(2)O were characterized crystallographically.     

Synthesis and ligand exchange reactions of P2Pd(II) and P2Pt(II) salicylaldimates

Reaction of (dppe)MCl(2)(dppe = 1,2-bis(diphenylphosphino)ethane) with 2-(N-phenyliminomethyl)phenol leads to air-stable (dppe)M(N,O) chelates (M = Pd, 1a; M = Pt, 1b). The N-4-methylphenyl derivative of 1a has been characterized by X-ray analysis. The N,O ligands are kinetically labile and exchange occurs in solution in the presence of other salicylaldimines. In the presence of anilines, a metal-mediated imine exchange process occurs. Hammett analysis reveals that the platinum complexes are sensitive to the electronics at N but not at O. Electron donating groups on the N-aryl ring stabilize the metal complex.     

Cobalt (iron) thiolato complexes containing the Co-ligand phosphine and reaction products of the structural fragment ML 2 L′ (L = 1,2-bidentate thiolate,L′= tertiary phosphine)

Mono-, di-, tri-, and tetra-nuclear cobalt (iron) complexes containing co-ligands phosphine and thiolate are presented according to the classification by combination of different dentates of the two ligands. Emphasis is being put on the triand tetranuclear cluster complexes of monodentate phosphines and 1,2-bidentate thiolates. These complexes are considered to be constructed based on the general structural fragment (or building block) ML ₂L (L=1,2-bidentate thiolate,L=tertiary phosphine). Structural regularities are presented in Tables I, III, IV, and V and discussed. FAB mass spectroscopic data showed the possible fragmentation patterns. Synergism of the cluster skeletons is proposed to explain the occurrence of the distinct structural modes.Abbreviations Bu _n ³ P tri-n-butylphosphine - dmpe 1,2-bis(dimethylphosphino)ethane - dmpm 1,2-bis(dimethylphosphino)methane - dppe 1,2-bis(diphenylphosphino)ethane - dppep bis(2-diphenylphosphinoethyl)phenylphosphine - dppm 1,1-bis(diphenylphosphino)methane - dppp 1,3-bis(diphenylphosphino)propane - Et₃P triethylphosphine - Ph₃P triphenylphosphine - tepme 1,1,1-tris(diethylphosphinomethyl)ethane - tppme 1,1,1-tris(diphenylphosphinomethyl)ethane - H₂bdt 1,2-benzenedithiol - H₂edt 1,2-ethanedithiol - Hmbt 2-mercaptobenzothiazole - H₂mp 2-mercaptophenol - Hmp 2-hydroxythiophenolate - Hmpo 2-mercaptopyridine-N-oxide - H₂mpp 2-mercapto-3-hydroxypyridine - Hmpp 3-hydroxy-2-pyridinothiolate - H₂pdt 1,2-propanedithiol - HSPh thiophenol - H₂tdt 4-methyl-1,2-benzenedithiol(4-toluenedithiol) - R₂dtc dialkyldithiocarbamate - (RO)₂dtp dialkyldithiophosphate     

Extended-chain, multinuclear transition metal complexes bridged by cyanodiazenido(1-), [N=N-C[triple bond, length as m-dash]N]-, ligands

Extended-chain complexes containing multiple transition metal centres linked by conjugated micro-cyanodiazenido(1-) ligands [N=N-C[triple bond, length as m-dash]N]- have been obtained by reaction of trans-[BrW(dppe)2(N2CN)], , [dppe=1,2-bis(diphenylphosphino)ethane] with dirhodium(II) tetra-acetate, bis(benzonitrile)palladium(II) dichloride, and bis(aqua)M(II) bis(hexafluoroacetylacetonate) (M=Mn, Ni, Cu, Zn): stronger Lewis acids such as tetrakis(acetonitrile)palladium(II) tetrafluoroborate and boron trifluoride promote hydrolysis of complex , leading to the isolation of a novel carbamoylhydrazido(2-) complex, trans-[BrW(dppe)2(N2HC=ONH2)]+[BF4]-.     

Meso-porphyrinylphosphine oxides: mono- and bidentate ligands for supramolecular chemistry and the crystal structures of monomeric {[10,20-diphenylporphyrinatonickel(II)-5,15-diyl]-bis-[P(O)Ph(2)] and polymeric self-coordinated {[10,20-diphenylporphyrinatozinc(II)-5,15-diyl]-bis-[P(O)Ph(2)]}

A series of porphyrins substituted in one or two meso positions by diphenylphosphine oxide groups has been prepared by the palladium-catalyzed reaction of diphenylphosphine or its oxide with the corresponding bromoporphyrins. Compounds {MDPP-[P(O)Ph2]n} (M = H2, Ni, Zn; H2DPP = 5,15-diphenylporphyrin; n = 1, 2) were isolated in yields of 60-95%. The reaction is believed to proceed via the conventional oxidative addition, phosphination, and reductive elimination steps, as the stoichiometric reaction of eta(1)-palladio(II) porphyrin [PdBr(H2DPP)(dppe)] (H2DPP = 5,15-diphenylporphyrin; dppe = 1,2-bis(diphenylphosphino)ethane) with diphenylphosphine oxide also results in the desired mono-porphyrinylphosphine oxide [H2DPP-P(O)Ph2]. Attempts to isolate the tertiary phosphines failed due to their extreme air-sensitivity. Variable-temperature 1H NMR studies of [H2DPP-P(O)Ph2] revealed an intrinsic lack of symmetry, while fluorescence spectroscopy showed that the phosphine oxide group does not behave as a "heavy atom" quencher. The electron-withdrawing effect of the phosphine oxide group was confirmed by voltammetry. The ligands were characterized by multinuclear NMR and UV-visible spectroscopy, as well as mass spectrometry. Single-crystal X-ray crystallography showed that the bis(phosphine oxide) nickel(II) complex {[NiDPP-[P(O)Ph2]2} is monomeric in the solid state, with a ruffled porphyrin core and the two P=O fragments on the same side of the average plane of the molecule. On the other hand, the corresponding zinc(II) complex formed infinite chains through coordination of one Ph2PO substituent to the neighboring zinc porphyrin through an almost linear P=O...Zn unit, leaving the other Ph2PO group facing into a parallel channel filled with disordered water molecules. These new phosphine oxides are attractive ligands for supramolecular porphyrin chemistry.     

SYNTHESIS AND STRUCTURE OF 1,2-BIS(DIPHENYLPHOSPHINO)ETHANE COMPLEXES OF COPPER(I) ACETATE. CATALYSTS FOR THE DECARBOXYLATION OF CARBOXYLIC ACIDS

Abstract

Several dimeric complexes of copper(I) acetate with bidentate phosphine ligands have been synthesized. The solid-state structure of one of these derivatives, dppe(CuO₂CCH₃)₂, where dppe = 1,2-bis(diphenylphosphino)ethane, has been determined. The complex is shown to exist in the solid-state as a polymeric chain of dimeric copper(I) units containing a dppe and two acetate ligands, with the dimers being linked together via weaker Cu-O interactions. The Cu-Cu bond length in the dimeric units is considerably longer, at 2.712(2) Å, than that observed in copper(I) acetate of 2.556(2) Å. The use of these derivatives as catalyst precursors for the catalytic decarboxylation of cyanoacetic acid to acetonitrile and carbon dioxide is discussed. Crystal data for dppe(CuO₂CCH₃)₂: space group P2_i/n,a = 14.976(6) Å, b = 11.676(3) Å, c = 16.999(6) Å, β = 107.59(3)°, Z = 4, R = 7.33%     

A new series of luminescent phosphine stabilised platinum ethynyl complexes

A series of cis-platinum ethynyl complexes with the general formula cis-[Pt(dppe)(C[triple bond]CR)2](dppe = 1,2-bis(diphenylphosphino)ethane; R = C6H4-p-NO2 1, C6H4-p-CH3 2, C6H4-p-C[triple bond]CH 3 and C6H4-p-C6H4-p-C[triple bond]CH 4) have been prepared by the coupling reaction of cis-[Pt(dppe)Cl2] with two equivalents of the appropriate alkyne. The new complexes have been fully characterized by spectroscopic techniques, and the cis square planar arrangement at the platinum centre has been confirmed by single-crystal X-ray diffraction studies of complexes 1, 2 and 4. The absorption spectra of the complexes 1-4 are dominated by a pi-->pi* band that contains some platinum (n + 1) p orbital character. The position of the band is dependent on the electron donating or withdrawing properties of the ethynyl substituents, R. Complex 1 displays a triplet emission in the green, at room temperature, while complexes 2-4, display singlet emissions in the blue. Again, the difference can be attributed to the nature of the R substituents.     

Organosilicon backbone containing pyridyl/quinolyl ligands: Synthesis, complexation reactions and single crystal structures of metallamacrocyclic Pd(II) and Cu(II) complexes

Organosilicon backbone containing ligands 1,2-bis(dimethyl(2-pyridyl)silyl)ethane (L¹) and 1,2-bis(dimethyl(3-quinolyl)silyl) ethane (L²) have been synthesized by treating 2-bromopyridine and 3-bromoquinoline with n-butyllithium and reacting the resulting lithiated products with 1,2-bis(chlorodimethylsilyl)ethane. The ligation of L¹ and L² with Pd(II), Ag(I) and Cu(II) has been investigated. The single crystal structures of L², [Pd(L¹)Cl₂] (1), [Cu(L¹)Br₂] (3) and [PdCl₂(L²)]₂ (4) have been solved. All the three complexes are metallamacrocyclic in nature. The last one is 22-membered and the first example which has ligands containing organosilicon backbone. The geometry of Pd as well as Cu is very close to square planar. The Pd–N, Pd–Cl, Cu–N and Cu–Br bond distances (2.010(1)–2.027(3), 2.3063(10)–2.3114(4), 2.004(4)–2.018(5) and 2.4137(10)–2.4172(10) Å) are very close to sum of covalent radii, indicating strong ligation of L¹ and L² with the metal ions.     

Homoleptic pnictogen-chalcogen coordination complexes

The synthesis and structural characterization of dicationic selenium and tellurium analogues of the carbodiphosphorane and triphosphenium families of compounds are reported. These complexes, [Ch(dppe)][OTf](2) [Ch = Se, Te; dppe = 1,2-bis(diphenylphosphino)ethane; OTf = trifluoromethanesulfonate], are formed using [Ch](2+) reagents via a ligand-exchange protocol and represent extremely rare examples of homoleptic pnictogen → chalcogen coordination complexes. The corresponding arsenic compounds were also prepared, [Ch(dpAse)][OTf](2) [Ch = Se, Te; dpAse = 1,2-bis(diphenylarsino)ethane], exhibiting the first instance of an arsenic → chalcogen dative bond. The electronic structures of these unique compounds were determined and compared to previously reported chalcogen dications.     

Palladium complexes of perylene diimides: strong fluorescence despite direct attachment of late transition metals to organic dyes

We prepared the first sigma-bonded metal complexes of widely utilized organic dyes, perylene tetracarboxylic acid diimides (PDIs). These 1,7-dipalladium PDI complexes were synthesized by C-Br oxidative addition of 1,7-dibromo-N,N'-dicyclohexyl PDI (Br2PDI) to Pd(0) phosphine complexes bearing triphenylphosphine and bischelating 1,2-bis(diphenylphosphino)ethane (dppe). The structures of Pd-PDI complexes were elucidated by single-crystal X-ray analysis. Surprisingly, despite direct attachement of two late transition metal centers, Pd-PDI systems are highly fluorescent (Phi=0.65 and 0.22 for triphenylphosphine and dppe systems, respectively). This is rationalized in terms of weak electronic interactions between the metal centers and PDI pi-system, as revealed by TD-DFT calculations.