Tuning the potential of redox-active diphosphine ligands based on the alkyne complexes [Tp*W(CO)L{η2-C2(PPh2)2}].

Eleven complexes with the general formula [Tp*W(CO)L{η2-C2(PPh2)2}]n+ {Tp* = hydridotris(3,4,5-trimethylpyrazolyl)-borate, L = F-, Cl-, Br-, I-, MeS-, PhS-, pyCH2S-, CN- and TfO-; n = 0 and L = CH3CN and pyridine; n = 1} have been synthesized and fully characterized. Depending on L, the oxidation process from W(II) to W(III) is detected between -0.28 and +0.55 V vs. Fc/Fc+ and the spectroscopic properties (X-ray, IR, and NMR) are influenced according to the electron-rich or electron-poor character of the central metal. The basicity of the alkyne complex-based phosphine groups was estimated by the 31P/77Se coupling method of the corresponding diselenides. Selected examples of the dppa-complex ligands were converted into the corresponding κ2-PdCl2 chelate complexes and employed in a Sonogashira reaction in order to estimate the effect of L on the catalytic behaviour of the dinuclear complexes. While the spectroscopic properties show a good correlation with the redox potential in a mostly linear fashion, catalytic activity is influenced only slightly. The effect of PdCl2 coordination on the alkyne complex is evident from the W(II)/W(III) redox potentials measured by cyclic voltammetry supported by a change of the CO stretching frequency in IR. A comparison of the molecular structures of the alkyne complexes with terminal phosphine groups and the PdCl2 chelate complexes all determined by XRD shows the essential flexibility of the bend-back angles in the alkyne complex moiety.

Synthesis and coordination behaviour of 1H-1,2,3-triazole-4,5-dithiolates.

The preparative access to and first group 10 metal complexes of novel 1H-1,2,3-triazole-4,5-dithiolate ligands (tazdt2-) are reported. A set of S-protected 1H-1,2,3-triazole-4,5-dithiol derivatives with R1 = 2,6-dimethylphenyl (Xy) or benzyl (Bn) at N1 and with R2 = Bn or trimethylsilylethyl (TMS-ethyl) at both S atoms were synthesized by a 1,3-dipolar cycloaddition catalysed by either Ru(II) or Cu(I). Extensive investigations on the removal of the protective groups resulted the reductive removal of benzyl groups to be superior in isolating the free 4,5-dithiols of R1N3C2(SH)2 with R1 = Xy (H2-8) or Bn (H2-9). Coordination of these ligands led to the formation of the metal complexes [(η5-C5H5)2Ti(8)], [Ni(dppe)(8)], [Ni(dppe)(9)], [Pd(dppe)(9)] {dppe = bis(diphenylphosphanyl)ethane} and homoleptic (NBu4)n[Ni(8)2] (n = 1, 2). All complexes were fully characterized including structure determination by single crystal XRD. The electronic properties of the Ni and Pd complexes were determined by cyclic voltammetry, UV/vis and EPR spectroscopy supported by DFT calculations. According to the spectral and electrochemical data, the tazdt2- complexes resemble the corresponding benzene-1,2-dithiolate (bdt2-) type compounds reflecting the restricted influence of the electron-withdrawing N3 moiety in the backbone. DSC-TGA measurements with [(η5-C5H5)2Ti(8)] and [Ni(dppe)(8)] indicate a well-defined thermal process involving simultaneous elimination of both N2 and CS.

Development and application of redox-active cyclometallating ligands based on W(II) alkyne complexes.

The assembly of dinuclear complexes with the ultimate smallest ditopic ligands based on side-on complexes of methyl substituted alkynes is presented. In fact, the coordination of Ru(II) and Ir(III) by a W alkyne complex based cyclometallating metalla-ligand causes close intermetallic electronic cooperation, which substantially changes the electrochemical and photophysical properties of the single isolated moieties.

Migratory insertion of isocyanide into a ketenyl-tungsten bond as key step in cyclization reactions.

Treatment of the side-on tungsten alkyne complex of ethinylethyl ether [Tp*W(CO)2(η2-C,C'-HCCOCH2CH3)]+ {Tp* = hydridotris(3,4,5-trimethylpyrazolyl)borate} (2a) with n-Bu4NI afforded the end-on ketenyl complex [Tp*W(CO)2(κ1-HCCO)] (4a). This formal 16 ve complex bearing the prototype of a ketenyl ligand is surprisingly stable and converts only under activation by UV light or heat to form a dinuclear complex [Tp*2W2(CO)4(µ-CCH2)] (6). The ketenyl ligand in complex 4a underwent a metal template controlled cyclization reaction upon addition of isocyanides. The oxametallacycles [Tp*W(CO)2{κ2-C,O-C(NHXy)C(H)C(Nu)O}] {Nu = OMe (7), OEt (8), N(i-Pr)2 (9), OH (10), O1/2 (11)} were formed by coordination of Xy-NC (Xy = 2,6-dimethylphenyl) at 4a and subsequent migratory insertion (MI) into the W-ketenyl bond. The resulting intermediate is susceptible to addition reactions with protic nucleophiles. Compounds 2a-PF6, 4a/b, and 7-11 were fully characterized including XRD analysis. The cyclization mechanism has been confirmed both experimentally and by DFT calculations. In cyclic voltammetry, complexes 7-9 are characterized by a reversible W(ii)/W(iii) redox process. The dinuclear complex 11 however shows two separated redox events. Based on cyclic voltammetry measurements with different conducting electrolytes and IR spectroelectrochemical (SEC) measurements the W(ii)/W(iii) mixed valent complex 11+ is assigned to class II in terms of the Robin-Day classification.

Metal/Metal Redox Isomerism Governed by Configuration.

A pair of diastereomeric dinuclear complexes, [Tp'(CO)BrW{µ-η2 -C,C'-κ2 -S,P-C2 (PPh2 )S}Ru(η5 -C5 H5 )(PPh3 )], in which W and Ru are bridged by a phosphinyl(thiolato)alkyne in a side-on carbon P,S-chelate coordination mode, were synthesized, separated and fully characterized. Even though the isomers are similar in their spectroscopic properties and redox potentials, the like-isomer is oxidized at W while the unlike-isomer is oxidized at Ru, which is proven by IR, NIR and EPR-spectroscopy supported by spectro-electrochemistry and computational methods. The second oxidation of the complexes was shown to take place at the metal left unaffected in the first redox step. Finally, the tipping point could be realized in the unlike isomer of the electronically tuned thiophenolate congener [Tp'(CO)(PhS)W{µ-η2 -C,C'-κ2 -S,P-C2 (PPh2 )S}Ru(η5 -C5 H5 )-(PPh3 )], in which valence trapped WIII /RuII and WII /RuIII cationic species are at equilibrium.

Facile Synthesis of a Stable Side-on Phosphinyne Complex by Redox Driven Intramolecular Cyclisation.

Alkyne complexes with vicinal substitution by a Lewis acid and a Lewis base at the coordinated alkyne are prospective frustrated Lewis pairs exhibiting a particular mutual distance and, hence, a specific activation potential. In this contribution, investigations on the generation of a WII alkyne complex bearing a phosphine as Lewis base and a carbenium group as Lewis acid are presented. Independently on potential substrates added, an intramolecular cyclisation product was always isolated. A subsequent deprotonation step led to an unprecedented side-on λ5 -phosphinyne complex, which is interpreted as highly zwitterionic according to visible absorption spectroscopy supported by TD-DFT. Low-temperature 31 P NMR and EPR spectroscopic measurements combined with time-dependent IR-spectroscopic monitoring provided insights in the mechanism of the cyclisation reaction. Decomposition of the multicomponent IR spectra by multivariate curve resolution and a kinetic hard-modelling approach allowed the derivation of kinetic parameters. Assignment of the individual IR spectra to potential intermediates was provided by DFT calculations.

Pathways to Polynuclear Complexes with α-S,N-Substituted Alkynes as Bridging Ligands.

Recently, alkyne complexes with terminal thiolate/amide substitution have been shown to act as S,N-chelate ligands in dinuclear complexes. In this study, the detailed synthesis and reactivity of W(II) alkyne complexes bearing different amino groups in the α-position are reported. The preparative scheme starts with cationic alkyne complexes [Tp'W(CO)2-η2-C,C'-C2Br(SR)]PF6 {Tp' = hydridotris(3,5-dimethylpyrazolyl)borate, R = benzyl (Bn), C2H4SiMe3}, which are obtained by applying free bromo alkynes. Subsequent nucleophilic substitution of the bromine substituent led to unsymmetrical substituted alkyne complexes [Tp'W(CO)2-η2-C,C'-C2(SR)(NHBn)]PF6 with S,N substitution in the α position of the coordinated alkyne. Depending on the base used, deprotonation of the secondary amine resulted in either neutral iminoketenyl complexes [Tp'W(CO)2-η2-C,C'-C2(SR)(NBn)] or a zwitterionic PF5 adduct. Reductive removal of the benzyl protective group was primarily observed at the imine substituent, causing a side-on/end-on rearrangement to the cyanide substituted carbene complex K[Tp'W(CO)2-η1-C(CN)(SBn)]. The reversibility of the rearrangement was proven with HBF4/Et2O, because double protonation led to [Tp'W(CO)2-η2-C,C'-C2(SR)(NH2)]BF4 exhibiting an unprecedented primary amine substitution at the coordinated alkyne. The reaction sequence starting with the thiol SC2H4SiMe3 derivative leading to the desired [Tp'W(CO)2-η2-C,C'-C2S(NHBn)] with a terminal S atom as well as the bonding situation in those complexes is discussed based on full spectroscopic characterization including X-ray structure analyses. Finally, a trinuclear complex assembled by homoleptic coordination of Pd(II) by two anionic S,N-chelates [Tp'W(CO)2-η2-C,C'-C2S(NBn)]- is presented.

Ultrafast Energy Transfer in Dinuclear Complexes with Bridging 1,10-Phenanthroline-5,6-Dithiolate.

We report herein the preparation and characterization of dinuclear complexes with the bridging ligand 1,10-phenanthroline-5,6-dithiolate (phendt2-) bearing Ru(bpy)2 or Ir(ppy)2 at the diimine moiety and Ni(dppe), Ni(dppf), CoCp, RhCp*, and Ru( p-Me-iPr-benzene) at the dithiolate unit. In comparison with the mononuclear precursors used in the synthesis, all dinuclear complexes were characterized by absorption and photoluminescence spectroscopy as well as cyclic voltammetry. Because of the beneficial spectral and electrochemical properties of the Ir/Co complex for a light-driven charge separation, this complex was investigated in detail by time-resolved luminescence {nanosecond (ns)-resolution} and transient absorption spectroscopy {femtosecond (fs)-resolution}. All measurements supported by DFT calculations show that the observed effective luminescence quenching by the dithiolate coordinated metal is caused by an ultrafast singlet-singlet Dexter energy transfer.

Sterically encumbered metalla-diphosphines: unlocking alkyne rotation by PtII coordination.

We present the synthesis and coordination chemistry of a series of WII alkyne complexes with symmetric and asymmetric acetylene diphosphines. Chelate-like P,P'-coordination of PtCl2 cause a drastic potential change of the W centered oxidation proving intermetallic cooperativity. The choice of peripheric P-substituents has a measurable influence on the potential itself as well on the respective potential change upon coordination. The enlarged deviation of the diphosphino alkyne from linearity in the dinuclear complexes unlock alkyne rotation making different isomers accessible.

Synthesis and activation potential of an open shell diphosphine.

A paramagnetic WIII alkyne complex bearing free terminal diphenylphosphino groups at the side-on coordinated alkyne was synthesized using a stepwise template strategy. This moderately stable metal supported open shell diphosphine shows an unprecedented spontaneous splitting of nitric oxide providing a WII-η2-C2{P(NH2)Ph2}{P(O)Ph2}+ complex featuring an amino phosphonium and a phosphine oxide substituent.

Minimalistic Ditopic Ligands: An α-S,N-Donor-Substituted Alkyne as Effective Intermetallic Conjugation Linker.

The capability of donor-substituted alkynes to link different metal ions in a side-on carbon donor-chelate coordination mode is extended from the donor centers S and P to the second period element N. The complex [Tp'W(CO)2 {η(2) -C2 (S)(NHBn)}] (Tp'=hydrido-tris(3,5-dimethylpyrazolyl)borate, Bn=benzyl) bearing a terminal sulfur atom and a secondary amine substituent is accessible by a metal-template synthesis. Subsequent deprotonation allowed the formation of remarkably stable heterobimetallic complexes with the [(η(5) -C5 H5 )Ru(PPh3 )] and the [Ir(ppy)2 ] moiety. Electrochemical and spectroscopic investigations (cyclic voltammetry, IR, UV/Vis, luminescence, EPR), as well as DFT calculations, and X-ray structure determinations of the W-Ru complex in two oxidation states reveal a strong metal-metal coupling but also a limited delocalization of excited states.

Dual nucleophilic substitution at a W(ii) η(2)-coordinated diiodo acetylene leading to an amidinium carbyne complex.

The synthesis and reactivity of a W(ii) C2I2 complex towards various nucleophiles are described. Soft, aprotic nucleophiles like 4-dimethylaminopyridine (DMAP) lead to substitution of one CO at tungsten, whereas reaction with an excess of benzylamine results in a dual nucleophilic substitution at the alkyne moiety involving the rearrangement to a novel cationic amidinium carbyne complex.

Understanding the Excited State Behavior of Cyclometalated Bis(tridentate)ruthenium(II) Complexes: A Combined Experimental and Theoretical Study.

The synthesis and characterization of the donor-acceptor substituted cyclometalated ruthenium(II) polypyridine complex isomers [Ru(dpb-NHCOMe)(tpy-COOEt)](PF6) 1(PF6) and [Ru(dpb-COOEt)(tpy-NHCOMe)](PF6) 2(PF6) (dpbH = 1,3-dipyridin-2-ylbenzene, tpy = 2,2';6,2"-terpyridine) with inverted functional group pattern are described. A combination of resonance Raman spectroscopic and computational techniques shows that all intense visible range absorption bands arise from mixed Ru → tpy/Ru → dpb metal-to-ligand charge transfer (MLCT) excitations. 2(PF6) is weakly phosphorescent at room temperature in fluid solution and strongly emissive at 77 K in solid butyronitrile matrix, which is typical for ruthenium(II) polypyridine complexes. Density functional theory calculations revealed that the weak emission of 2(PF6) arises from a (3)MLCT state that is efficiently thermally depopulated via metal-centered ((3)MC) excited states. The activation barrier for the deactivation process was estimated experimentally from variable-temperature emission spectroscopic measurements as 11 kJ mol(-1). In contrast, 1(PF6) is nonemissive at room temperature in fluid solution and at 77 K in solid butyronitrile matrix. Examination of the electronic excited states of 1(PF6) revealed a ligand-to-ligand charge-transfer ((3)LL'CT) as lowest-energy triplet state due to the very strong push-pull effect across the metal center. Because of the orthogonality of the participating ligands, emission from the (3)LL'CT is symmetry-forbidden. Hence, in this type of complex a stronger push-pull effect does not increase the phosphorescence quantum yields but completely quenches the emission.

A new class of azadipnictiridines generated by an unusual rearrangement reaction.

Dipnictadiazanediyls, [E(µ-NR)]2 (E = P, As), the pnictogen analogues of cyclobutandiyl, were found to react readily with alkynes forming [2.1.1]bicyclic structures. These, in turn, rearrange in an unprecedented reaction to [3.1.o]bicycles leading to the isolation of the first azadiarsiridine and the determination of its solid-state structure. All new species were comprehensively characterized, and the reaction pathways and bonding situations were computationally studied.

Dinuclear Ru/Ni, Ir/Ni, and Ir/Pt complexes with bridging phenanthroline-5,6-dithiolate: synthesis, structure, and electrochemical and photophysical behavior.

We report the synthesis and full characterization of dinuclear complexes with the bridging ligand phenanthroline-5,6-dithiolate (phendt(2-)) featuring the [Ru(bpy)2](2+) or Ir(ppy)2](+) fragment at the diimine donor center and the [Ni(dppe)](2+) or [Pt(phen)](2+) complex moiety at the dithiolate group. The molecular structures of the mononuclear complexes [(C5H5)2Ti(S,S'-phendt)] and [(ppy)2Ir{N,N'-phendt-(C2H4CN)2}](PF6) as well as the dinuclear complex [(C5H5)(PPh3)Ru(phendt)Ni(dppe)](PF6) determined by X-ray diffraction (XRD) studies are compared. Photophysical studies with mononuclear [(bpy)2Ru{phendt-(C2H4CN)2}](2+) and [(ppy)2Ir{phendt-(C2H4CN)2}](+) as well as dinuclear [(bpy)2Ru(phendt)Ni(dppe)](2+) and [(ppy)2Ir(phendt)Ni(dppe)](+) uncovered an effective luminescence quenching in the dinuclear complexes. Lifetime measurements at room temperature, steady-state measurements at low temperature, electrochemical investigations, and DFT calculations provide evidence for a very efficient energy transfer from the Ru/Ir to the Ni complex moiety with a rate constant k > 5 × 10(9) s(-1). In comparison, the [Ru]phendt[Ni] complex displays a higher quenching efficiency with reduced excited state lifetime, whereas the [Ir]phendt[Ni] complex is characterized by an unaltered lifetime of the thermally equilibrated excited state.

Acetylene dithiolate linking up the [Tp'W(CO)(CN)] moiety with Ru(II) or Pd(II.).

A series of heterodinuclear complexes with acetylene dithiolate (acdt(2-) ) as the bridging moiety were synthesised by a facile one-pot procedure that avoided use of the highly elusive acetylene dithiol. Generation of the W-Ru complex [Tp'W(CN)(CO)(C2 S2 )Ru(η(5) -C5 H5 )(PPh3 )] (Tp'=hydrotris(3,5-dimethylpyrazolyl)borate) and the W-Pd complexes [Tp'W(CN)(CO)(C2 S2 )Pd(dppe)] and [Tp'W(CO)2 (C2 S2 )Pd(dppe)][PF6 ] (dppe=1,2-bis(diphenylphoshino)ethane), which exhibit a [W(η(2) -κ(2) -C2 S2 )M] core (M=Ru, Pd), was accomplished by using a transition-metal-assisted solvolytical removal of the Me3 Si-ethyl thiol protecting groups. All intermediate species of the reaction have been fully characterised. The highly coloured W-Ru complex [Tp'W(CN)(CO)(C2 S2 )Ru(η(5) -C5 H5 )(PPh3 )] shows reversible redox chemistry, as does the prototype complex [Tp'W(CO)2 (C2 S2 )Ru(η(5) -C5 H5 )(PPh3 )][PF6 ]. Single crystal X-ray diffraction and IR, EPR and UV/Vis spectroscopic studies in conjunction with DFT calculations prove the high electronic delocalisation of states over the acdt(2-) linker. Comparative studies revealed a higher donor strength and more pronounced dithiolate character of acdt(2-) in [Tp'W(CN)(CO)(C2 S2 )Ru(η(5) -C5 H5 )(PPh3 )] relative to [Tp'W(CO)2 (C2 S2 )Ru(η(5) -C5 H5 )(PPh3 )](+) . In addition, the influence of the overall complex charge on the metric parameters was investigated by single-crystal X-ray diffraction studies with the W-Pd complexes [Tp'WL2 (C2 S2 )Pd(dppe)] (L=(CN(-) )(CO) or (CO)2 ). The central [W(C2 S2 )Pd] units exhibit high structural similarity, which indicates the extensive delocalisation of charge over both metals.

Ethenedithione (S=C=C=S): trapping and isomerization in a cobalt complex.

Swing bridge: The triplet species ethenedithione has been generated within the coordination sphere of cobalt, leading to a dinuclear µ-η(2)-η(2)-C(2)S(2) complex (see picture: C gray, Co blue, P purple, S yellow). Depending on the solvent, the C(2)S(2) moiety displays a transoid or a cisoid geometry. This isomerization step changes the sign of the magnetic coupling between the cobalt centers.

Acetylenedithiolate as directional bridging ligand in cobalt(I) alkyne platinum dithiolato bimetallic complexes.

The eta(2)-C,C-acetylenedithiolate (acdt2-) complex K[(triphos)Co(acdt)], K-5, {triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane} was obtained by consecutive removal of S-protection groups in [(triphos)Co(1)]PF6, 3-PF6 (1 = 1-Trimethylsilyl-7-phenyl-3,6-dithiahept-4-ine). Reaction of K-5 with selected Pt(II) salts resulted in the formation of the new heterobimetallic complexes [(phen)Pt(5)]BPh4, 6-BPh4, (phen = 1,10-phenanthroline) and [(dppe)Pt(5)]BPh4, 7-BPh4, {dppe = 1,2-bis(diphenylphosphino)ethane}, which were fully characterized. X-ray diffraction studies showed that Co and Pt are linked by acdt2- in the eta(2)-C,C-2-S,S-bridging mode. The electronic structure of 6-BPh4 and 7-BPh4 was investigated by electronic absorption spectroscopy, cyclic voltammetry and X-band EPR spectroscopy of neutral 7. In addition, NMR spectroscopy, X-ray diffraction and reactivity studies with the alkyne complexes [(PMe3)3Co(1)]-PF6, 2-PF6, with 3-PF6 and the intermediate product [(triphos)Co{eta(2)-(S)C2(SCH2Ph)}], 4, uncovered the flexibility of the CoC2S2-moiety within the persisting complex scaffold throughout the synthetic scheme.