Electronic structure and coordination chemistry of phenanthridine ligand in first‐row transition metal complexes: A DFT study

The geometric parameters, electronic structures, and haptotropic migration of a series of hypothetical compounds of general formula CpM(C₁₃H₉N) and (CO)₃M(C₁₃H₉N) (M = fist row transition metal, Cp = C₅H₅, and C₁₃H₉N = phenanthridine ligand) are investigated by means of the density functional theory. The phenanthridine ligand can bind to the metal through η¹ to η⁶ coordination mode, in agreement with the electron count and the nature of the metal, showing its capability to adapt itself to the electronic demand of the metal as well as to the polycyclic aromatic hydrocarbons. In the investigated species, the most favored closed‐shell count is 18‐electron except for the Ti and V models which are deficient open‐shell 16‐electron configuration. This study has shown the difference in coordination ability of this heteropolycyclic ligand: the coordination of the central C₅N ring is less favored than the terminal C₆ rings, in agreement with the π‐electron density localization. Most of the investigated complexes are expected to exhibit a rich fluxional behavior. This flexibility favors the possibility for the existence of several isomers as well as their interconversion through haptotropic shifts. © 2012 Wiley Periodicals, Inc.     

η4‐HBCC‐σ,π‐Borataallyl Complexes of Ruthenium Comprising an Agostic Interaction

Thermolysis of [Cp*Ru(PPh₂(CH₂)PPh₂)BH₂(L₂)] 1 (Cp*=η⁵‐C₅Me₅; L=C₇H₄NS₂), with terminal alkynes led to the formation of η⁴‐σ,π‐borataallyl complexes [Cp*Ru(μ‐H)B{R‐C=CH₂}(L)₂] ( 2 a – c ) and η²‐vinylborane complexes [Cp*Ru(R‐C=CH₂)BH(L)₂] ( 3 a – c ) ( 2 a , 3 a : R=Ph; 2 b , 3 b : R=COOCH₃; 2 c , 3 c : R=p‐CH₃‐C₆H₄; L=C₇H₄NS₂) through hydroboration reaction. Ruthenium and the HBCC unit of the vinylborane moiety in 2 a – c are linked by a unique η⁴‐interaction. Conversions of 1 into 3 a – c proceed through the formation of intermediates 2 a – c . Furthermore, in an attempt to expand the library of these novel complexes, chemistry of σ‐borane complex [Cp*RuCO(μ‐H)BH₂L] 4 (L=C₇H₄NS₂) was investigated with both internal and terminal alkynes. Interestingly, under photolytic conditions, 4 reacts with methyl propiolate to generate the η⁴‐σ,π‐borataallyl complexes [Cp*Ru(μ‐H)BH{R‐C=CH₂}(L)] 5 and [Cp*Ru(μ‐H)BH{HC=CH‐R}(L)] 6 (R=COOCH₃; L=C₇H₄NS₂) by Markovnikov and anti‐Markovnikov hydroboration. In an extension, photolysis of 4 in the presence of dimethyl acetylenedicarboxylate yielded η⁴‐σ,π‐borataallyl complex [Cp*Ru(μ‐H)BH{R‐C=CH‐R}(L)] 7 (R=COOCH₃; L=C₇H₄NS₂). An agostic interaction was also found to be present in 2 a – c and 5 – 7 , which is rare among the borataallyl complexes. All the new compounds have been characterized in solution by IR, ¹H, ¹¹B, ¹³C NMR spectroscopy, mass spectrometry and the structural types were unequivocally established by crystallographic analysis of 2 b , 3 a – c and 5 – 7 . DFT calculations were performed to evaluate possible bonding and electronic structures of the new compounds.     

Synthesis and Reactivity of Six‐Membered Oxa‐Nickelacycles: A Ring‐Opening Reaction of Cyclopropyl Ketones

Cyclopropanecarboxaldehyde ( 1 a ), cyclopropyl methyl ketone ( 1 b ), and cyclopropyl phenyl ketone ( 1 c ) were reacted with [Ni(cod)₂] (cod=1,5‐cyclooctadiene) and PBu₃ at 100 °C to give η²‐enonenickel complexes ( 2 a – c ). In the presence of PCy₃ (Cy=cyclohexyl), 1 a and 1 b reacted with [Ni(cod)₂] to give the corresponding μ‐η²:η¹‐enonenickel complexes ( 3 a , 3 b ). However, the reaction of 1 c under the same reaction conditions gave a mixture of 3 c and cyclopentane derivatives ( 4 c , 4 c′ ), that is, a [3+2] cycloaddition product of 1 c with (E)‐1‐phenylbut‐2‐en‐1‐one, an isomer of 1 c . In the presence of a catalytic amount of [Ni(cod)₂] and PCy₃, [3+2] homo‐cycloaddition proceeded to give a mixture of 4 c (76 %) and 4 c′ (17 %). At room temperature, a possible intermediate, 6 c , was observed and isolated by reprecipitation at ?20 °C. In the presence of 1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene (IPr), both 1 a and 1 c rapidly underwent oxidative addition to nickel(0) to give the corresponding six‐membered oxa‐nickelacycles ( 6 ai , 6 ci ). On the other hand, 1 b reacted with nickel(0) to give the corresponding μ‐η²:η¹‐enonenickel complex ( 3 bi ). The molecular structures of 6 ai and 6 ci were confirmed by X‐ray crystallography. The molecular structure of 6 ai shows a dimeric η¹‐nickelenolate structure. However, the molecular structure of 6 ci shows a monomeric η¹‐nickelenolate structure, and the nickel(II) 14‐electron center is regarded as having “an unusual T‐shaped planar” coordination geometry. The insertion of enones into monomeric η¹‐nickelenolate complexes 6 c and 6 ci occurred at room temperature to generate η³‐oxa‐allylnickel complexes ( 8 , 9 ), whereas insertion into dimeric η¹‐nickelenolate complex 6 ai did not take place. The diastereoselectivity of the insertion of an enone into 6 c having PCy₃ as a ligand differs from that into 6 ci having IPr as a ligand. In addition, the stereochemistry of η³‐oxa‐allylnickel complexes having IPr as a ligand is retained during reductive elimination to yield the corresponding [3+2] cycloaddition product, which is consistent with the diastereoselectivity observed in Ni⁰/IPr‐catalyzed [3+2] cycloaddition reactions of cyclopropyl ketones with enones. In contrast, reductive elimination from the η³‐oxa‐allylnickel having PCy₃ as a ligand proceeds with inversion of stereochemistry. This is probably due to rapid isomerization between syn and anti isomers prior to reductive elimination.     

A halide‐free pyridinium‐substituted η3‐cycloheptatrienide–Pd complex

We report the synthesis and characterization of a novel 4‐(dimethylamino)pyridinium‐substituted η³‐cycloheptatrienide–Pd complex which is free of halide ligands. Diacetonitrile{η³‐[4‐(dimethylamino)pyridinium‐1‐yl]cycloheptatrienido}palladium(II) bis(tetrafluoroborate), [Pd(C₂H₃N)₂(C₁₄H₁₆N₂)](BF₄)₂, was prepared by the exchange of two bromide ligands for noncoordinating anions, which results in the empty coordination sites being occupied by acetonitrile ligands. As described previously, exchange of only one bromide leads to a dimeric complex, di‐μ‐bromido‐bis({η³‐[4‐(dimethylamino)pyridinium‐1‐yl]cycloheptatrienido}palladium(II)) bis(tetrafluoroborate) acetonitrile disolvate, [Pd₂Br₂(C₁₄H₁₆N₂)₂](BF₄)₂·2CH₃CN, with bridging bromide ligands, and the crystal structure of this compound is also reported here. The structures of the cycloheptatrienide ligands of both complexes are analogous to the dibromide derivative, showing the allyl bond in the β‐position with respect to the pyridinium substituent. This indicates that, unlike a previous interpretation, the main reason for the formation of the β‐isomer cannot be internal hydrogen bonding between the cationic substituents and bromide ligands.     

Study of 1,3‐Dipolar Cycloaddition and Ring Contraction of New 1,4‐Phenylene‐bis[1,5]benzothiazepine Derivatives

Some 1,4‐phenylene‐bis[1,2,4]oxadiazolo‐[5,4‐d][1,5]benzothiazepine derivatives ( 4a , 4b , 4c ) were synthesized by 1,3‐dipolar cycloaddition reaction of benzohydroximinoyl chloride with 1,4‐phenylene‐bis(4‐aryl)‐2,3‐dihydro[1,5]benzothiazepine ( 2a , 2b , 2c ); meanwhile, compounds 2a , 2b , 2c also occurred ring contraction under acylating condition to obtain bis[2‐aryl‐2′‐(β‐1,4‐phenylenevinyl)‐3‐acetyl]‐2,3‐dihydro[1,5]benzothiazoles ( 3a , 3b , 3c ). The structures of some novel compounds were confirmed by IR, ¹H‐NMR, elemental, and X‐ray crystallographic analysis.     

Polymerization of 3‐ethynylthiophene with homogeneous and heterogeneous Rh catalysts

3‐Ethynylthiophene (3ETh) was polymerized with Rh(I) complexes: [Rh(cod)acac], [Rh(nbd)acac], [Rh(cod)Cl]₂, and [Rh(nbd)Cl]₂ (cod is η²:η²‐cycloocta‐1,5‐diene and nbd η²:η²‐norborna‐2,5‐diene), used as homogeneous catalysts and with the last two complexes anchored on mesoporous polybenzimidazole (PBI) beads: [Rh(cod)Cl]₂/PBI and [Rh(nbd)Cl]₂/PBI used as heterogeneous catalysts. All tested catalyst systems give high‐cis poly(3ETh). In situ NMR study of homogeneous polymerizations induced with [Rh(cod)acac] and [Rh(nbd)acac] complexes has revealed: (i) a transformation of acac ligands into free acetylacetone (Hacac) occurring since the early stage of polymerization, which suggests that this reaction is part of the initiation, (ii) that the initiation is rather slow in both of these polymerization systems, and (iii) a release of cod ligand from [Rh(cod)acac] complex but no release of nbd ligand from [Rh(nbd)acac] complex during the polymerization. The stability of diene ligand binding to Rh‐atom in [Rh(diene)acac] catalysts remarkably affects only the molecular weight but not the yield of poly(3ETh). The heterogeneous catalyst systems also provide high‐cis poly(3ETh), which is of very low contamination with catalyst residues since a leaching of anchored Rh complexes is negligible. The course of heterogeneous polymerizations is somewhat affected by limitations arising from the diffusion of monomer inside catalyst beads. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2776–2787, 2008     

Modular Synthesis and Dynamics of a Variety of Donor–Acceptor Interlocked Compounds Prepared by Click Chemistry

A series of donor–acceptor [2]‐, [3]‐, and [4]rotaxanes and self‐complexes ([1]rotaxanes) have been synthesized by a threading‐followed‐by‐stoppering approach, in which the precursor pseudorotaxanes are fixed by using Cu^I‐catalyzed Huisgen 1,3‐dipolar cycloaddition to attach the required stoppers. This alternative approach to forming rotaxanes of the donor–acceptor type, in which the donor is a 1,5‐dioxynaphthalene unit and the acceptor is the tetracationic cyclophane cyclobis(paraquat‐p‐phenylene), proceeds with enhanced yields relative to the tried and tested synthetic strategies, which involve the clipping of the cyclophane around a preformed dumbbell containing π‐electron‐donating recognition sites. The new synthetic approach is amenable to application to highly convergent sequences. To extend the scope of this reaction, we constructed [2]rotaxanes in which one of the phenylene rings of the tetracationic cyclophane is perfluorinated, a feature which significantly weakens its association with π‐electron‐rich guests. The activation barrier for the shuttling of the cyclophane over a spacer containing two triazole rings was determined to be (15.5±0.1) kcal mol^?1 for a degenerate two‐station [2]rotaxane, a value similar to that previously measured for analogous degenerate compounds containing aromatic or ethylene glycol spacers. The triazole rings do not seem to perturb the shuttling process significantly; this property bodes well for their future incorporation into bistable molecular switches.     

Variable Bonding Modes of Pyrimidine‐2‐thione in PdII/PtII Complexes [M(η2‐N,S‐pymS)(η1‐S‐pymS)(PPh3)] and [M(η1‐S‐pymS)2(L‐L)] (L‐L = dppm,dppe)

Reactions of pyrimidine‐2‐thione (HpymS) with Pd^II/Pt^IV salts in the presence of triphenyl phosphine and bis(diphenylphosphino)alkanes, Ph₂P‐(CH₂)_m‐PPh₂ (m = 1, 2) have yielded two types of complexes, viz. a) [M(η²‐N, S‐ pymS)(η¹‐S‐ pymS)(PPh₃)] (M = Pd, 1 ; Pt, 2 ), and (b) [M(η¹‐S‐pymS)₂(L‐L)] {L‐L, M = dppm (m = 1) Pd, 3 ; Pt, 4 ; dppe (m = 2), Pd, 5 ; Pt, 6 }. Complexes have been characterized by elemental analysis (C, H, N), NMR spectroscopy (¹H, ¹³C, ³¹P), and single crystal X‐ray crystallography ( 1 , 2 , 4 , and 5 ). Complexes 1 and 2 have terminal η¹‐S and chelating η²‐N, S‐modes of pymS⁻, while other Pd/Pt complexes have only terminal η¹‐S modes. The solution state ³¹P NMR spectral data reveal dynamic equilibrium for the complexes 3 , 5 and 6 , whereas the complexes 1 , 2 and 4 are static in solution state.     

A Density Functional Theory Investigation of the Cobalt‐Mediated η5‐Pentadienyl/Alkyne [5+2] Cycloaddition Reaction: Mechanistic Insight and Substituent Effects

Alkyl‐substituted η⁵‐pentadienyl half‐sandwich complexes of cobalt have been reported to undergo [5+2] cycloaddition reactions with alkynes to provide η²,η³‐cycloheptadienyl complexes under kinetic control. DFT studies have been used to elucidate the mechanism of the cyclization reaction as well as that of the subsequent isomerization to the final η⁵‐cycloheptadienyl product. The initial cyclization is a stepwise process of olefin decoordination/alkyne capture, C? C bond formation, olefin arm capture, and a second C? C bond formation; the initial decoordination/capture step is rate‐limiting. Once the η²,η³‐cycloheptadienyl complex has been formed, isomerization to η⁵‐cycloheptadienyl again involves several steps: olefin decoordination, β‐hydride elimination, reinsertion, and olefin coordination; also here the initial decoordination step is rate limiting. Substituents strongly affect the ease of reaction. Pentadienyl substituents in the 1‐ and 5‐positions assist pentadienyl opening and hence accelerate the reaction, while substituents at the 3‐position have a strongly retarding effect on the same step. Substituents at the alkyne (2‐butyne vs. ethyne) result in much faster isomerization due to easier olefin decoordination. Paths involving triplet states do not appear to be competitive.     

Reaction of “Non‐Symmetrical” 1,2,4‐Trithiolanes with [(phosphane)Pt0(η2‐nbe)] Complexes

Two unsymmetrical 1,2,4‐trithiolanes ( 1d and 1e ) were reacted with [Pt⁰(PPh₃)₂(η²‐nbe)] ( 6 ; nbe=norborn‐2‐ene) and [Pt⁰(dppn)(η²‐nbe)] ( 11 ; dppn=1,8‐bis(diphenylphosphanyl)naphthalene)), respectively. Their treatment with compound 6 resulted in the formation of six‐membered platinacycles of type 7 , which selectively underwent fragmentation into dithiolato complexes and thiobenzophenone ( 4b ). The isolation of the first stable C‐substituted member of this class of compounds (i.e., compound 7e ) permitted kinetic studies of this process by using UV/Vis spectroscopy. These results, together with DFT calculations, allowed us to propose a mechanism for the reactions of compound 6 with 1,2,4‐trithiolanes. In contrast, similar treatment of compound 11 with compounds 1d and 1e at room temperature did not result in any reaction. Heating the appropriate samples to 110 °C led to the formation of dithiolato complexes and η²‐thioketone compounds, thus pointing to a thermally induced [3+2]‐cycloreversion of the heterocycles as an initial step of the reaction.     

Mechanistic Aspects of Aryl–Halide Oxidative Addition,Coordination Chemistry,and Ring‐Walking by Palladium

This contribution describes the reactivity of a zero‐valent palladium phosphine complex with substrates that contain both an aryl halide moiety and an unsaturated carbon–carbon bond. Although η²‐coordination of the metal center to a C?C or C?C unit is kinetically favored, aryl halide bond activation is favored thermodynamically. These quantitative transformations proceed under mild reaction conditions in solution or in the solid state. Kinetic measurements indicate that formation of η²‐coordination complexes are not nonproductive side‐equilibria, but observable (and in several cases even isolated) intermediates en route to aryl halide bond cleavage. At the same time, DFT calculations show that the reaction with palladium may proceed through a dissociation–oxidative addition mechanism rather than through a haptotropic intramolecular process (i.e., ring walking). Furthermore, the transition state involves coordination of a third phosphine to the palladium center, which is lost during the oxidative addition as the C?halide bond is being broken. Interestingly, selective activation of aryl halides has been demonstrated by adding reactive aryl halides to the η²‐coordination complexes. The product distribution can be controlled by the concentration of the reactants and/or the presence of excess phosphine.     

N‐Heterocyclic Carbene Stabilized Dicarbondiphosphides: Strong Neutral Four‐Membered Heterocyclic 6π‐Electron Donors

In contrast to cyclic π‐conjugated hydrocarbons, the coordination chemistry of inorganic heterocycles is less developed. Dicarbondiphosphides stabilized by N‐heterocyclic carbenes (NHCs) NHC→C₂P₂←NHC ( 1 a , b ) (NHC=IPr or SIPr) contain a four‐membered C₂P₂ ring with an aromatic 6π‐electron configuration. These heterocycles coordinate to a variety of complex fragments with metals from groups 6, 9, and 10, namely [M⁰(CO)₃] (M=Cr, Mo), [Co^I(CO)₂]⁺, or [Ni^IIBr₂], through an η⁴‐coordination mode, leading to complexes 2 a , b , 3 a , b , 5 a , b , and 6 a , b , respectively. These complexes were characterized by X‐ray diffraction methods using single crystals, IR spectroscopy, and DFT calculations. In combination these methods indicate that 1 a , b behave as exceptionally strong 6π‐electron donors.     

Proton Order–Disorder Phenomena in a Hydrogen‐Bonded Rhodium–η5‐Semiquinone Complex: A Possible Dielectric Response Mechanism

A newly synthesized one‐dimensional (1D) hydrogen‐bonded (H‐bonded) rhodium(II)–η⁵‐semiquinone complex, [Cp*Rh(η⁵‐p‐HSQ‐Me₄)]PF₆ ([ 1 ]PF₆; Cp*=1,2,3,4,5‐pentamethylcyclopentadienyl; HSQ=semiquinone) exhibits a paraelectric–antiferroelectric second‐order phase transition at 237.1 K. Neutron and X‐ray crystal structure analyses reveal that the H‐bonded proton is disordered over two sites in the room‐temperature (RT) phase. The phase transition would arise from this proton disorder together with rotation or libration of the Cp* ring and PF₆^? ion. The relative permittivity ε_b′ along the H‐bonded chains reaches relatively high values (ca., 130) in the RT phase. The temperature dependence of ¹³C CP/MAS NMR spectra demonstrates that the proton is dynamically disordered in the RT phase and that the proton exchange has already occurred in the low‐temperature (LT) phase. Rate constants for the proton exchange are estimated to be 10^?4–10^?6 s in the temperature range of 240–270 K. DFT calculations predict that the protonation/deprotonation of [ 1 ]⁺ leads to interesting hapticity changes of the semiquinone ligand accompanied by reduction/oxidation by the π‐bonded rhodium fragment, producing the stable η⁶‐hydroquinone complex, [Cp*Rh³⁺(η⁶‐p‐H₂Q‐Me₄)]²⁺ ([ 2 ]²⁺), and η⁴‐benzoquinone complex, [Cp*Rh⁺(η⁴‐p‐BQ‐Me₄)] ([ 3 ]), respectively. Possible mechanisms leading to the dielectric response are discussed on the basis of the migration of the protonic solitons comprising of [ 2 ]²⁺ and [ 3 ], which would be generated in the H‐bonded chain.     

The syndiospecific polymerization of styrene in the presence of fluorine‐containing half‐sandwich metallocenes

The syndiospecific polymerization of styrene was investigated with the fluorine‐containing half‐sandwich complexes η⁵‐pentamethylcyclopentadienyl titanium bis(trifluoroacetate) dimer, η⁵‐octahydrofluorenyl titanium tristrifluoro‐acetate, η⁵‐octahydrofluorenyl titanium dimethoxymonotrifluoroacetate, and η⁵‐octahydrofluorenyl titanium tris(pentafluorobenzoate) in comparison to known chloride and methoxide complexes in the presence of relatively low amounts of methylalumoxane and triisobutylaluminum. After the selection of effective reaction conditions for a solvent‐free polymerization, the following orders of decreasing polymerization activity of the titanium complexes can be observed: for pentamethylcyclopentadienyl compounds, Cp*Ti(OMe)₃ > [Cp*Ti(OCOCF₃)₂]₂O ≈ Cp*TiCl₃, and for octahydrofluorenyl compounds, [656]Ti(OMe)₃ > [656]Ti(OCOC₆F₅)₃ > [656]Ti(OCH₃)₂(OCOCF₃) > [656]Ti (OCOCF₃)₃. The [656]Ti complexes, showing the highest polymerization conversions at 70 °C and in comparison with the Cp* Ti compounds, turned out to be highly efficient catalysts for the syndiospecific styrene polymerization. The fluorine‐containing Cp* and [656]Ti complexes lead to much higher molecular weights than the chloride and methoxide compounds because of a reduction in chain‐limiting transfer reactions. The introduction of only one fluorine‐containing ligand into the coordination sphere of the metal compound is obviously sufficient for a significant increase in molecular weight. The active polymerization sites of the [656]Ti complexes with methylalumoxane and triisobutylaluminum are extremely stable during storage at room temperature in regard to their polymerization activity. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2428–2439, 2000     

Flexible Structural Features of Pentafulvene Titanium Derivatives: Isolation and Characterization of NHC Complexes

The reaction of η⁵,η¹‐pentafulvene titanium complexes with the strong N‐heterocyclic carbene (NHC) donor 1,3,4,5‐tetramethylimidazole‐2‐ylidene, leads to the formation of isolable NHC titanium adducts, featuring a haptotropic shift of the pentafulvene ligand, proved by single crystal X‐ray diffraction as well as NMR spectroscopy studies.     

Efficient Preparation of 2, 2′‐Disubstituted‐3, 3′‐(1, 4‐phenylene)bis‐thienopyrimidin‐4‐ones Based on an aza‐Wittig Reaction

Tandem aza‐Wittig reaction of iminophosphorane with 1, 4‐phenylene diisocyanate followed by intramolecular heteroconjugate addition annulation after addition of a nucleophilic reagent (amine, phenol, and alcohol), in the presence of catalytic K₂CO₃ or NaOR, gives selectively the functionalized substituted 2, 2′‐di(alkylamino, aryloxy)‐3, 3′‐(1, 4‐phenylene)bis(thieno[3, 2‐d]pyrimidin‐4(3H)‐ones) and 2, 2′‐di(alkylamino or alkoxy)‐3, 3′‐(1, 4‐phenylene)bis(3, 5, 6, 7‐tetrahydro‐4H‐cyclopenta[4, 5]thieno[2, 3‐d]pyrimidin‐4‐ones).     

Metallkomplexe mit N2O2S2‐Koordinationssphäre. Synthese und Charakterisierung der Cobalt(II)‐, Nickel(II)‐ und Kupfer(II)‐Komplexe eines 15‐ und eines 16‐gliedrigen N,N′‐bis(2‐hydroxyethyl)‐funktionalisierten makrocyclischen Liganden

Metal Complexes with N₂O₂S₂ Donor Set. Synthesis and Characterization of the Cobalt(II), Nickel(II), and Copper(II) Complexes of a 15‐ and a 16‐Membered Bis(2‐hydroxyethyl) Pendant Macrocyclic Ligand The macrocyclic ligands 6, 10‐bis(2‐hydroxyethyl)‐7, 8, 9, 11, 17, 18‐hexahydro‐dibenzo‐[e, n][1, 4, 8, 12]‐dithiadiaza‐cyclopentadecine ( 1 ) (L¹) and 5, 13‐bis(2‐hydroxyethyl)‐7, 8, 9, 10, 16, 17, 18, 19, 20‐nonahydro‐dibenzo‐[g, o][1, 9, 5, 13]‐dithiadiaza‐cyclohexadecine (L⁴) have been prepared. They form the stable complexes [CoL¹(‐H)CoL¹](ClO₄)₃ ( 2 ), [NiL¹](ClO₄)₂·MeOH ( 3 ), Λ‐[CuL¹](ClO₄)₂·MeOH ( 4a ) and rac‐[CuL¹](ClO₄)₂·MeOH ( 4b ), [NiL⁴](ClO₄)₂ ( 5 ), and [CuL⁴](ClO₄)₂ ( 6 ). The compounds 1 to 6 have been characterized by standard methods and single‐crystal X‐ray diffraction. In the complexes 2 to 6 the metal atoms are octahedrally coordinated by the N₂O₂S₂ donor set of the ligands. L¹ and L⁴ are folded herein along the N···M···S‐ and the N···M···N′‐axes, respectively. This results at the metal atom in a all‐cis‐configuration for the complexes of L¹ and a trans‐N₂‐cis‐O₂‐cis‐S₂‐configuration for the complexes of L⁴. The cobalt(II) complex 2 is a dimer, bridged by a rather short hydrogen bridge of 2.402(12)Å length. The copper(II) complexes of L¹ and L⁴ differ with respect to the Jahn‐Teller‐distortion.     

Cationic Platinum(II) σ‐SiH Complexes in Carbon Dioxide Hydrosilation

The low‐electron‐count cationic platinum complex [Pt(ItBu’)(ItBu)][BAr^F], 1 , interacts with primary and secondary silanes to form the corresponding σ‐SiH complexes. According to DFT calculations, the most stable coordination mode is the uncommon η¹‐SiH. The reaction of 1 with Et₂SiH₂ leads to the X‐ray structurally characterized 14‐electron Pt^II species [Pt(SiEt₂H)(ItBu)₂][BAr^F], 2 , which is stabilized by an agostic interaction. Complexes 1 , 2 , and the hydride [Pt(H)(ItBu)₂][BAr^F], 3 , catalyze the hydrosilation of CO₂, leading to the exclusive formation of the corresponding silyl formates at room temperature.     

Bis(4,4′‐dimethyl‐2,2′‐bipyridine) ruthenium (II) Complexes Containing 2‐Arylimidazo‐ [4,5‐f] [1,10] phenanthroline: Syntheses,Characterization and Third‐order Nonlinear Optical Properties

Four novel mononuclear ruthenium(II) complexes [Ru(dmb)₂L]²⁺ [dmb = 4,4′‐dimethyl‐2,2′‐bipyridine, L = imidazo‐[4,5‐f][1,10]phenanthroline (IP), 2‐phenylimidazo‐[4,5‐f][1,10]phenanthroline (PIP), 2‐(4′‐hydroxyphenyl)imidazo‐[4,5‐f] [1,10] phenanthroline (HOP), 2‐(4′‐dimethylaminophenyl) imidazo‐[4, 5‐f] [1,10] phenanthroline (DMNP)] were synthesized and characterized by ES‐MS, ¹H NMR, UV‐vis and electrochemistry. The nonlinear optical properties of the ruthenium(II) complexes were investigated by Z‐scan techniques with 12 ns laser pulse at 540 nm, and all of them exhibit both nonlinear optical (NLO) absorption and self‐defocusing effect. The corresponding effective NLO susceptibility |x³| of the complexes is in the range of 2.68 × 10^?12‐4.57 × 10^?12 esu.     

Synthesis,Reactivity, and Crystal Structure of the η2‐Thiocarbamoyl Palladium Complex [Pd(PPh3)2(η2‐SCNMe2)][PF6]

The η¹‐thiocarbamoyl palladium complexes [Pd(PPh₃)(η¹‐SCNMe₂)(η²‐S₂R)] (R = P(OEt)₂, 2 ; CNEt₂, 3 ) and trans‐[Pd(PPh₃)₂(η¹‐SCNMe₂)(η¹‐Spy)], 4 , (pyS: pyridine‐2‐thionate) are prepared by reacting the η²‐thiocarbamoyl palladium complex [Pd(PPh₃)₂(η²‐SCNMe₂)][PF₆], 1 with (EtO)₂PS₂NH₄, Et₂NCS₂Na, and pySK in methanol at room temperature, respectively. Treatment of 1 with dppm (dppm: bis(diphenylphosphino)methane) in dichloromethane at room temperature gives complex [Pd(PPh₃)(η¹‐SCNMe₂)(η²‐dppm)] [PF₆], 5 . All of the complexes are identified by spectroscopic methods and complex 1 is determined by single‐crystal X‐ray diffraction.