On the reactivity of platina‐β‐diketones: a straightforward synthesis of trans‐acetylchlorobis(phosphine)platinum(II) complexes and their reactivity

The platina‐β‐diketone [Pt₂{(COMe)₂H}₂(µ‐Cl)₂] ( 1 ) was found to react with monodentate phosphines to yield acetyl(chloro)platinum(II) complexes trans‐[Pt(COMe)Cl(PR₃)₂] (PR₃ = PPh₃, 2a ; P(4‐FC₆H₄)₃, 2b ; PMePh₂, 2c ; PMe₂Ph, 2d ; P(n‐Bu)₃, 2e ; P(o‐tol)₃, 2f ; P(m‐tol)₃, 2g ; P(p‐tol)₃, 2h ). In the reaction with P(o‐tol)₃ the methyl(carbonyl)platinum(II) complex [Pt(Me)Cl(CO){P(o‐tol)₃}] ( 3a ) was found to be an intermediate. On the other hand, treating 1 with P(C₆F₅)₃ led to the formation of [Pt(Me)Cl(CO){P(C₆F₅)₃}] ( 3b ), even in excess of the phosphine. Phosphine ligands with a lower donor capability in complexes 2 and the arsine ligand in trans‐[Pt(COMe)Cl(AsPh₃)₂] ( 2i ) proved to be subject to substitution by stronger donating phosphine ligands, thus forming complexes trans‐[Pt(COMe)Cl(L)L′] (L/L′ = AsPh₃/PPh₃, 4a ; PPh₃/P(n‐Bu)₃, 4b ) and cis‐[Pt(COMe)Cl(dppe)] ( 4c ). Furthermore, in boiling benzene, complexes 2a – 2c and 2i underwent decarbonylation yielding quantitatively methyl(chloro)platinum(II) complexes trans‐[Pt(Me)Cl(L)₂] (L = PPh₃, 5a ; P(4‐FC₆H₄)₃, 5b ; PMePh₂, 5c ; AsPh₃, 5d ). The identities of all complexes were confirmed by ¹H, ¹³C and ³¹P NMR spectroscopy. Single‐crystal X‐ray diffraction analyses of 2a ·2CHCl₃, 2f and 5b showed that the platinum atom is square‐planar coordinated by two phosphine ligands (PPh₃, 2a ; P(o‐tol)₃, 2f ; P(4F‐C₆H₄)₃, 5b ) in mutual trans position as well as by an acetyl ligand ( 2a, 2f ) and a methyl ligand ( 5b ), respectively, trans to a chloro ligand. Single‐crystal X‐ray diffraction analysis of 3b exhibited a square‐planar platinum complex with the two π‐acceptor ligands CO and P(C₆F₅)₃ in mutual cis position (configuration index: SP‐4‐3). Copyright © 2005 John Wiley & Sons, Ltd.     

Alternative Synthesis and Structures of C‐monoacetylenic Phosphaalkenes

An alternative synthesis of C‐monoacetylenic phosphaalkenes trans‐Mes*P=C(Me)(C≡CR) (Mes* = 2, 4, 6‐^tBu₃Ph, R = Ph, SiMe₃) from C‐bromophosphaalkenes cis‐Mes*P=C(Me)Br using standard Sonogashira coupling conditions is described. Crystallographic studies confirm cis‐trans isomerization of the P=C double bond during Pd‐catalyzed cross coupling, leading exclusively to trans‐acetylenic phosphaalkenes. Crystallographic studies of all synthesized compounds reveal the extend of π‐conjugation over the acetylene and P=C π‐systems.     

Theoretical study of the red‐ and blue‐shifted hydrogen bonds of nitroxyl and acetylene dimers

Ab initio molecular orbital and density functional theory (DFT) in conjunction with different basis sets calculations were performed to study the C? H…O red‐shifted and N? H…π blue‐shifted hydrogen bonds in HNO? C₂H₂ dimers. The geometric structures, vibrational frequencies and interaction energies were calculated by both standard and counterpoise (CP)‐corrected methods. In addition, the G3B3 method was employed to calculate the interaction energies. The topological and natural bond orbital (NBO) analysis were investigated the origin of N? H…π blue‐shifted hydrogen bond. From the NBO analysis, the electron density decrease in the σ* (N? H) is due to the significant electron density redistribution effect. The blue shifts of the N? H stretching frequency are attributed to a cooperative effect between the rehybridization and electron density redistribution. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Probing long‐range spin–spin coupling constants in 2‐halo‐substituted cyclohexanones and cyclohexanethiones: The role of solvent and stereoelectronic effects

Earlier studies with 2‐bromocyclohexanone demonstrated a measurable long‐range coupling constant (⁴J_H2,H6) for the equatorial conformer, although ⁴J_H2,H4 and ⁴J_H4,H6 were not observed; as a consequence, it is inferred that the carbonyl group plays an important role particularly due to hyperconjugative interactions σ_C2H2→π*_C═O and σ_C6H6→π*_C═O. In the present study, NBO analysis and coupling constant calculations were performed to cyclohexanone and cyclohexanethione alpha substituted with F, Cl, and Br, aiming to evaluate the halogen effect and acceptor character of the π* orbital on the long‐range coupling pathway. The σ_C2H2→π*_C1═Y and σ_C6H6→π*_C1═Y (Y═O and S) hyperconjugative interactions for the equatorial conformer indeed contribute for the ⁴J_H2,H6 transmission mechanism_. Surprisingly, the ⁴J_H2,H6 value is higher for the carbonyl compounds, although the interactions σ_C2H2→π*_C═Y and σ_C6H6→π*_C═Y are more efficient for the thiocarbonyl compounds. Accordingly, the Fermi contact (FC) contribution for the thiocarbonyl compounds decays deeper than in ketones, thus reducing more the ⁴J_H2,H6 values. Moreover, both π_C═S→σ*_C─X and π_C═S→σ*_C─H interactions seem to be stronger in thiocarbonyl than in carbonylic compounds. The implicit solvent effect (DMSO and water) on the coupling constant values was negligible when compared with the gas phase. On the other hand, an explicit solvent effect was found and ⁴J_H2,H6 for the thiocarbonyl compounds appeared to be more sensitive than for the cyclohexanones.     

Density functional theory study of calix[4]arene‐N‐azacrown‐5, calix[4]arene‐N‐phenyl‐azacrown‐5, and their complexes with alkali‐metal cations: Na+, K+, and Rb+

Theoretical studies of 1,3‐alternate‐25,27‐bis(1‐methoxyethyl)calix[4]arene‐azacrown‐5 ( L₁ ), 1,3‐alternate‐25,27‐bis(1‐methoxyethyl)calix[4]arene‐N‐phenyl‐azacrown‐5 ( L₂ ), and the corresponding complexes M⁺/ L of L₁ and L₂ with the alkali‐metal cations: Na⁺, K⁺, and Rb⁺ have been performed using density functional theory (DFT) at B3LYP/6‐31G* level. The optimized geometric structures obtained from DFT calculations are used to perform natural bond orbital (NBO) analysis. The two main types of driving force metal–ligand and cation–π interactions are investigated. The results indicate that intermolecular electrostatic interactions are dominant and the electron‐donating oxygen offer lone pair electrons to the contacting RY* (1‐center Rydberg) or LP* (1‐center valence antibond lone pair) orbitals of M⁺ (Na⁺, K⁺, and Rb⁺). What's more, the cation–π interactions between the metal ion and π‐orbitals of the two rotated benzene rings play a minor role. For all the structures, the most pronounced changes in geometric parameters upon interaction are observed in the calix[4]arene molecule. In addition, an extra pendant phenyl group attached to nitrogen can promote metal complexation by 3D encapsulation greatly. In addition, the enthalpies of complexation reaction and hydrated cation exchange reaction had been studied by the calculated thermodynamic data. The calculated results of hydrated cation exchange reaction are in a good agreement with the experimental data for the complexes. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

Photo‐physical Properties of N‐methyl‐3,4‐fulleropyrrolidine and Its Derivatives: A DFT and TD‐DFT Investigation

A series of N‐methyl‐3,4‐fulleropyrrolidine (NMFP) derivatives were designed by selecting different π‐conjugated linkers and electron‐donating groups as D‐π‐A and D‐A systems. The optimised structures and photo‐physical properties of NMFP and its derivatives have been determined using density functional theory (DFT) and time‐dependent density functional theory (TD‐DFT) methods with the B3LYP functional and the 6‐31G basis set. According to the computation analysis, both the π‐conjugated linkers and the electron‐donating groups can influence the electronic and photo‐physical properties of the NMFP derivatives. Our calculated results demonstrated that the electron‐donating groups, with significant electron‐donating ability, had the tendency to increase the highest occupied molecular orbital (HOMO) energy. The π‐conjugated linkers with lower resonance energy decreased the lowest occupied molecular orbital (LUMO) energy and caused a significant decrease in the energy gap (E_g) between the E_HOMO and E_LUMO. A Natural Bond Orbital (NBO) analysis examines the effect of the electron‐donating group, π conjugated linker, and electron‐withdrawing group for these NMFP derivatives. For the NMFP derivatives, a projected density of state (PDOS) analysis demonstrated that the electron density of HOMO and LUMO are concentrated on the electron‐donating group and the π‐conjugated linker, respectively. A TD‐DFT/B3LYP calculation was performed to calculate the electronic absorption spectra of these NMFP derivatives. Both the electron‐donating group and the π‐conjugated linker contribute to the major absorption peaks, which are assigned as HOMO to LUMO transitions and are red‐shifted relative to those of non‐substituted NMFP.     

The Pi‐Nature of Methyl Obtained by the Natural Bond Orbital Method: Orbital‐Based Rationalizations of Site‐Dependent Substitution Effects on Fine Color‐Tuning of Luminescence

Both C‐H bonding and antibonding (σ_CH and σ*_CH) of a methyl group would contribute to the highest occupied or lowest unoccupied molecular orbitals (HOMO or LUMO) in methylated derivatives of Ir(ppz)₂ 3 iq (ppz = 1‐phenylpyrazole and 3iq = isoquinoline‐3‐carboxylate). This is found by analysis of HOMO (or LUMO) formed by linear combination of bond orbitals using the natural bond orbital (NBO) method. The elevated level of HOMO (or LUMO) uniformly found for each methylated derivative, indicating the σ_CH‐destabilization outweighs the σ*_CH‐stabilization. To broaden the HOMO‐LUMO gap, methylation at a carbon having smaller contribution to HOMO and/or larger contribution to LUMO is suggested.     

Deprotonation of Coordinated Phosphanes in a Rhenium Complex: CC Coupling with Diimine Coligands

The reaction of fac‐[Re(bipy)(CO)₃(PMe₃)][OTf] (bipy=2,2′‐bipyridine) with KN(SiMe₃)₂ affords two neutral products: cis,trans‐[Re(bipy)(CO)₂(CN)(PMe₃)], and a thermally unstable compound, which features a new C?C bond between a P‐bonded methylene group (from methyl group deprotonation) and the C6 position of bipy. The solid‐state structures of more stable 1,2‐bis[(2,6‐diisopropylphenyl)imino]acenaphthene analogs, resulting from the deprotonation of PMe₃, PPhMe₂, and PPh₂Me ligands, are determined by X‐ray diffraction.     

Transition‐Metal Complexes [(PMe3)2Cl2M(E)] and [(PMe3)2(CO)2M(E)] with Naked Group 14 Atoms (E=C–Sn) as Ligands; Part 1: Parent Compounds

The equilibrium geometries and bond dissociation energies of 16‐valence‐electron(VE) complexes [(PMe₃)₂Cl₂M(E)] and 18‐VE complexes [(PMe₃)₂(CO)₂M(E)] with M=Fe, Ru, Os and E=C, Si, Ge, Sn were calculated by using density functional theory at the BP86/TZ2P level. The nature of the M? E bond was analyzed with the NBO charge decomposition analysis and the EDA energy‐decomposition analysis. The theoretical results predict that the heavier Group 14 complexes [(PMe₃)₂Cl₂M(E)] and [(PMe₃)₂(CO)₂M(E)] with E=Si, Ge, Sn have C_2v equilibrium geometries in which the PMe₃ ligands are in the axial positions. The complexes have strong M? E bonds which are slightly stronger in the 16‐VE species 1ME than in the 18‐VE complexes 2ME . The calculated bond dissociation energies show that the M? E bonds become weaker in both series in the order C>Si>Ge>Sn; the bond strength increases in the order Fe<Ru<Os for 1ME , whereas a U‐shaped trend Ru<Os<Fe is found for 2ME . The M? E bonding analysis suggests that the 16‐VE complexes 1ME have two electron‐sharing bonds with σ and π symmetry and one donor–acceptor π bond like the carbon complex. Thus, the bonding situation is intermediate between a typical Fischer complex and a Schrock complex. In contrast, the 18‐VE complexes 2ME have donor–acceptor bonds, as suggested by the Dewar–Chatt–Duncanson model, with one M←E σ donor bond and two M→E π‐acceptor bonds, which are not degenerate. The shape of the frontier orbitals reveals that the HOMO?2 σ MO and the LUMO and LUMO+1 π* MOs of 1ME are very similar to the frontier orbitals of CO.     

Molecular design of a “molecular syringe” mimic for metal cations using a 1,3‐alternate calix[4]arene cavity

The chemically switchable actions well imitate the function of a “molecular syringe,” has been studied in theory using the 1,3‐alternate calix [4]arene bearing a nitrogen‐containing crown cap at one side and a bis(ethoxyethoxy) group at another side by the π‐basic calixtube as a pipette and the crown ring as a rubber cap. The model is characterized by geometry optimization using density functional theory (DFT) at B3LYP/6‐31G level. The obtained optimized structures are used to perform natural bond orbital (NBO) and frequency analysis. The electron‐donating heteroatoms: O and N offer lone pair electrons to the contacting RY* (1‐center Rydberg) or LP* (1‐center valence antibond lone pair) orbitals of K⁺, Ag⁺. The results indicate that when the nitrogen atom in the crown ring is protonated, K⁺ and Ag⁺ will be pushed out to the bis(ethoxyethoxy) side through a π‐basic calixtube. When the nitrogen·H⁺ in the crown ring is deprotonated, K⁺ and Ag⁺ are sucked back to the crown‐capped side again. In the course of the coordination, both the intermolecular electrostatic interactions and the cation‐π interactions between the metal ion and π‐orbitals of the two pairs facing inverted benzene rings play a significant role. It is believed that this prototype of a “molecular syringe” is a novel molecular architecture for the action of metal cations. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010     

Novel P‐Stereogenic PCP Pincer‐Aryl Ruthenium(II) Complexes and Their Use in the Asymmetric Hydrogen Transfer Reaction of Acetophenone

Achiral P‐donor pincer‐aryl ruthenium complexes ([RuCl(PCP)(PPh₃)]) 4c , d were synthesized via transcyclometalation reactions by mixing equivalent amounts of [1,3‐phenylenebis(methylene)]bis[diisopropylphosphine] ( 2c ) or [1,3‐phenylenebis(methylene)]bis[diphenylphosphine] ( 2d ) and the N‐donor pincer‐aryl complex [RuCl{2,6‐(Me₂NCH₂)₂C₆H₃}(PPh₃)], ( 3 ; Scheme 2). The same synthetic procedure was successfully applied for the preparation of novel chiral P‐donor pincer‐aryl ruthenium complexes [RuCl(P*CP*)(PPh₃)] 4a , b by reacting P‐stereogenic pincer‐arenes (S,S)‐[1,3‐phenylenebis(methylene)]bis[(alkyl)(phenyl)phosphines] 2a , b (alkyl=ⁱPr or ^tBu, P*CHP*) and the complex [RuCl{2,6‐(Me₂NCH₂)₂C₆H₃}(PPh₃)], ( 3 ; Scheme 3). The crystal structures of achiral [RuCl(equation/tex2gif-sup-3.gifPCP)(PPh₃)] 4c and of chiral (S,S)‐[RuCl(equation/tex2gif-sup-6.gifPCP)(PPh₃)] 4a were determined by X‐ray diffraction (Fig. 3). Achiral [RuCl(PCP)(PPh₃)] complexes and chiral [RuCl(P*CP*)(PPh₃)] complexes were tested as catalyst in the H‐transfer reduction of acetophenone with propan‐2‐ol. With the chiral complexes, a modest enantioselectivity was obtained.     

The σ‐donating and π‐accepting properties of ortho‐Si(CH3)3 phosphinine macrocycles

A theoretical investigation of both the ortho‐Si(CH₃)₃ phosphinine and some silacalix[n]phosphinines was performed. The optimized geometries agree well with those reported from X‐ray analysis and other structural studies. The silacalix[n]phosphinine macrocyle is very flexible because of the C Si C bridges. This, in turn, makes possible the formation of strained configurations in solid packed structures. In the silacalix[3]phosphinine, a P P bonding interaction that is presumably responsible for its structural and electronic features seems to exist. The molecular orbital calculations corroborate that both the π‐accepting properties and the σ‐donating capacities of the phosphinine unit may be enhanced by ortho‐Si(CH₃)₃ substitution. These features satisfy the proposal of the synthesizers as regards the production of macrocyclic phosphorus compounds, with good π‐accepting properties and strong σ‐donating capacities, which are sufficiently flexible as to encapsulate metals with coordination spheres of different geometries. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:160–169, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10118     

Osmium Complexes with Tridentate 6‐Pyrazol‐3‐yl 2,2′‐Bipyridine Ligands: Coarse Tuning of Phosphorescence from the Red to the Near‐Infrared Region

We have prepared and characterized a series of osmium complexes [Os₂(CO)₄(fpbpy)₂] ( 1 ), [Os(CO)(fpbpy)₂] ( 2 ), and [Os(fpbpy)₂] ( 3 ) with tridentate 6‐pyrazol‐3‐yl 2,2′‐bipyridine chelating ligands. Upon the transformation of complex 2 into 3 through the elimination of the CO ligand, an extremely large change in the phosphorescence wavelength from 655 to 935 nm was observed. The results are rationalized qualitatively by the strong π‐accepting character of CO, which lowers the energy of the osmium d_π orbital, in combination with the lower degree of π conjugation in 2 owing to the absence of one possible pyridine‐binding site. As a result, the energy gap for both intraligand π–π* charge transfer (ILCT) and metal‐to‐ligand charge transfer (MLCT) is significantly greater in 2 . Firm support for this explanation was also provided by the time‐dependent DFT approach, the results of which led to the conclusion that the S₀→T₁ transition mainly involves MLCT between the osmium center and bipyridine in combination with pyrazolate‐to‐bipyridine ³π–π* ILCT. The relatively weak near‐infrared emission can be rationalized tentatively by the energy‐gap law, according to which the radiationless deactivation may be governed by certain low‐frequency motions with a high density of states. The information provided should allow the successful design of other emissive tridentate metal complexes, the physical properties of which could be significantly different from those of complexes with only a bidentate chromophore.     

A Boryl‐Substituted Diphosphene: Synthesis,Structure, and Reaction with n‐Butyllithium To Form a Stabilized Adduct by pπ‐pπ Interaction

A boryl‐substituted diphosphene was synthesized through the nucleophilic borylation of PCl₃ with a borylzinc reagent, followed by a reduction with Mg. A combined analysis of the resulting diboryldiphosphene by single‐crystal X‐ray diffraction, DFT calculations, and UV/Vis spectroscopy revealed a σ‐electron‐donating effect for the boryl substituent that was slightly weaker than that of the 2,4,6‐tri‐tert‐butylphenyl (Mes*) ligand. The reaction of this diboryldiphosphene with ⁿBuLi afforded a boryl‐substituted phosphinophosphide that was, in comparison with the thermally unstable Mes*‐substituted diaryldiphosphene, stabilized by a π‐electron‐accepting effect of the boryl substituent.     

On the Reactivity of Platina‐β‐diketones – Synthesis and Characterization of Acylplatinum(II) Complexes

The platina‐β‐diketones [Pt₂{(COR)₂H}₂(μ‐Cl)₂] ( 1 , R = Me a , Et b ) react with phosphines L in a molar ratio of 1 : 4 through cleavage of acetaldehyde to give acylplatinum(II) complexes trans‐[Pt(COR)Cl(L)₂] ( 2 ) (R/L = Me/P(p‐FC₆H₄)₃ a , Me/P(p‐CH₂=CHC₆H₄)Ph₂ b , Me/P(n‐Bu)₃ c , Et/P(p‐MeOC₆H₄)₃ d ). 1 a reacts with Ph₂As(CH₂)₂PPh₂ (dadpe) in a molar ratio of 1 : 2 through cleavage of acetaldehyde yielding [Pt(COMe)Cl(dadpe)] ( 3 a ) (configuration index: SP‐4‐4) and [Pt(COMe)Cl(dadpe)] (configuration index: SP‐4‐2) ( 3 b ) in a ratio of about 9 : 1. All acyl complexes were characterized by ¹H, ¹³C and ³¹P NMR spectroscopy. The molecular structures of 2 a and 3 a were determined by single‐crystal X‐ray diffraction. The geometries at the platinum centers are close to square planar. In both complexes the plane of the acyl ligand is nearly perpendicular to the plane of the complex (88(2)° 2 a , 81.2(5)° 3 a ).     

A Boryl‐Substituted Diphosphene: Synthesis,Structure, and Reaction with n‐Butyllithium To Form a Stabilized Adduct by pπ‐pπ Interaction

A boryl‐substituted diphosphene was synthesized through the nucleophilic borylation of PCl₃ with a borylzinc reagent, followed by a reduction with Mg. A combined analysis of the resulting diboryldiphosphene by single‐crystal X‐ray diffraction, DFT calculations, and UV/Vis spectroscopy revealed a σ‐electron‐donating effect for the boryl substituent that was slightly weaker than that of the 2,4,6‐tri‐tert‐butylphenyl (Mes*) ligand. The reaction of this diboryldiphosphene with ⁿBuLi afforded a boryl‐substituted phosphinophosphide that was, in comparison with the thermally unstable Mes*‐substituted diaryldiphosphene, stabilized by a π‐electron‐accepting effect of the boryl substituent.     

2,6‐Diphospha‐s‐indacene‐1,3,5,7(2 H,6 H)‐tetraone: A Phosphorus Analogue of Aromatic Diimides with the Minimal Core Exhibiting High Electron‐Accepting Ability

Phosphorus analogues of pyrromellitic diimides (PyDIs), which represent a family of privileged electron‐accepting organic compounds, have been successfully synthesized as novel electron‐accepting π‐conjugated molecules. Investigation into their physicochemical properties uncovered their prominent electron‐accepting abilities over the corresponding PyDI. Furthermore, theoretical studies revealed the significant contribution of σ*–π* hyperconjugation in stabilizing the LUMO+1.     

Zum Einfluß der PR3‐Liganden auf Bildung und Eigenschaften der Phosphinophosphiniden‐Komplexe [{η2‐tBu2P–P}Pt(PR3)2] und [{η2‐tBu2P1–P2}Pt(P3R3)(P4R′3)]

Coordination Chemistry of P‐rich Phosphanes and Silylphosphanes XXI The Influence of the PR₃ Ligands on Formation and Properties of the Phosphinophosphinidene Complexes [{η²‐^tBu₂P–P}Pt(PR₃)₂] and [{η²‐^tBu₂P¹–P²}Pt(P³R₃)(P⁴R′₃)] (R₃P)₂PtCl₂ and C₂H₄ yield the compounds [{η²‐C₂H₄}Pt(PR₃)₂] (PR₃ = PMe₃, PEt₃, PPhEt₂, PPh₂Et, PPh₂Me, PPh₂ⁱPr, PPh₂^tBu and P(p‐Tol)₃); which react with ^tBu₂P–P=PMe^tBu₂ to give the phosphinophosphinidene complexes [{η²‐^tBu₂P–P}Pt(PMe₃)₂], [{η²‐^tBu₂P–P}Pt(PEt₃)₂], [{η²‐^tBu₂P–P}Pt(PPhEt₂)₂], [{η²‐^tBu₂P–P}Pt(PPh₂Et)₂], [{η²‐^tBu₂P–P}Pt(PPh₂Me)₂], [{η²‐^tBu₂P–P}Pt(PPh₂ⁱPr], [{η²‐^tBu₂P–P}Pt(PPh₂^tBu)₂] and [{η²‐^tBu₂P–P}Pt(P(p‐Tol)₃)₂]. [{η²‐^tBu₂P–P}Pt(PPh₃)₂] reacts with PMe₃ and PEt₃ as well as with ^tBu₂PMe, PⁱPr₃ and P(c‐Hex)₃ by substituting one PPh₃ ligand to give [{η²‐^tBu₂P¹–P²}Pt(P³Me₃)(P⁴Ph₃)], [{η²‐^tBu₂P¹–P²}Pt(P³Ph₃)(P⁴Me₃)], [{η²‐^tBu₂P¹–P²}Pt(P³Et₃)(P⁴Ph₃)], [{η²‐^tBu₂P¹–P²}Pt(P³Me^tBu₂)(P⁴Ph₃)], [{η²‐^tBu₂P¹–P²}Pt(P³ⁱPr₃)(P⁴Ph₃)] and [{η²‐^tBu₂P¹–P²}Pt(P³(c‐Hex)₃)(P⁴Ph₃)]. With ^tBu₂PMe, [{η²‐^tBu₂P–P}Pt(P(p‐Tol)₃)₂] forms [{η²‐^tBu₂P¹–P²}Pt(P³Me^tBu₂)(P⁴(p‐Tol)₃)]. The NMR data of the compounds are given and discussed with respect to the influence of the PR₃ ligands.     

Synthesis,Characterization and Optical Properties of a Novel Si‐Containing σ‐π‐Conjugated Hyperbranched Polymer

The polymerization of bis(4‐ethynylphenyl)methylsilane catalyzed by RhI(PPh₃)₃ afforded a regio‐ and stereoregular hyperbranched polymer, hb‐poly[(methylsilylene)bis(1,4‐phenylene‐trans‐vinylene)] (poly( 1 )), containing 95% trans‐vinylene moieties. The weight loss of this polymer at 900°C in N₂ was 9%. Poly( 1 ) displayed an absorption due to π‐π* transition around 275 nm as a shoulder and a weak absorption around 330 nm due to π‐to‐σ charge transfer, which was hardly seen in the corresponding linear polymer.     

Kinetic Study and NBO Analysis of the Dehydrogenation Mechanism of Five‐membered Ring Heterocyclic 2,5‐Dihydro‐[furan,thiophene, selenophene

The theoretical study of the dehydrogenation of 2,5‐dihydro‐[furan ( 1 ), thiophene ( 2 ), and selenophene ( 3 )] was carried out using ab initio molecular orbital (MO) and density functional theory (DFT) methods at the B3LYP/6‐311G**//B3LYP/6‐311G** and MP2/6‐311G**//B3LYP/6‐311G** levels of theory. Among the used methods in this study, the obtained results show that B3LYP/6‐311G** method is in good agreement with the available experimental values. Based on the optimized ground state geometries using B3LYP/6‐311G** method, the natural bond orbital (NBO) analysis of donor‐acceptor (bond‐antibond) interactions revealed that the stabilization energies associated with the electronic delocalization from non‐bonding lone‐pair orbitals [LP(e)_X3] to δ*_{C(1)  H(2)} antibonding orbital, decrease from compounds 1 to 3 . The LP(e)_X3→δ*_{C(1)  H(2)} resonance energies for compounds 1 – 3 are 23.37, 16.05 and 12.46 kJ/mol, respectively. Also, the LP(e)_X3→δ*_{C(1)  H(2)} delocalizations could fairly explain the decrease of occupancies of LP(e)_X3 non‐bonding orbitals in ring of compounds 1 – 3 ( 3 > 2 > 1 ). The electronic delocalization from LP(e)_X3 non‐bonding orbitals to δ*_{C(1)  H(2)} antibonding orbital increases the ground state structure stability, Therefore, the decrease of LP(e)_X3→δ*_{C(1)  H(2)} delocalizations could fairly explain the kinetic of the dehydrogenation reactions of compounds 1 – 3 (k ₁ >k ₂ >k ₃ ). Also, the donor‐acceptor interactions, as obtained from NBO analysis, revealed that the (_C(4)C(7)→δ*_{C(1)  H(2)} resonance energies decrease from compounds 1 to 3 . Further, the results showed that the energy gaps between (_C(4)C(7) bonding and δ*_{C(1)  H(2)} antibonding orbitals decrease from compounds 1 to 3 . The results suggest also that in compounds 1 – 3 , the hydrogen eliminations are controlled by LP(e)→δ* resonance energies. Analysis of bond order, natural bond orbital charges, bond indexes, synchronicity parameters, and IRC calculations indicate that these reactions are occurring through a concerted and synchronous six‐membered cyclic transition state type of mechanism.