Electrophilic activation of alkynes promoted by a cationic alkylidene complex of Pt(II).

Pt(II) alkylidene 1a has been reacted with terminal alkynes to afford ylide complexes 3a-d, resulting from electrophilic activation of the CC bond and its insertion into the platinacyclic fragment of 1a that contains the carbene functionality. DFT calculations indicate that the observed regioselectivity is determined by the nucleophilic attack of the alkyne to the alkylidene carbon.

Dinuclear Cu(I) Halides with Terphenyl Phosphines: Synthesis, Photophysical Studies, and Catalytic Applications in CuAAC Reactions.

Several dinuclear terphenyl phosphine copper(I) halide complexes of composition [CuX(PR2Ar')]2 (X = Cl, Br, I; R = hydrocarbyl, Ar' = 2,6-diarylterphenyl radical), 1-5, have been isolated from the reaction of CuX with 1 equiv of the phosphine ligand. Most of them have been characterized by X-ray diffraction studies in the solid state, thus allowing comparative discussions of different structural parameters, namely, Cu···Cu and Cu···Aryl separations, conformations adopted by coordinated phosphines, and planarity of the Cu2X2 cores. Centrosymmetric complexes [CuI(PMe2ArXyl2)]2, 1c, and [CuI(PEt2ArMes2)]2, 3c, despite their similar structures, show very distinct photoluminescence (PL) in powder form at room temperature. The photophysical behavior of these compounds in liquid solution, solid-solid Zeonex solution and powder samples at room temperature and 77 K have been investigated and supported by DFT calculation. Identification of vibronic coupling modes, done by group theory calculations and the technique of projection operators, shows that the manifestation of these modes is conditioned by crystal packing. Complexes [CuI(PMe2ArXyl2)]2, 1c, and [CuI(PEt2ArMes2)]2, 3c, display remarkable activity in copper-catalyzed azide-alkyne cycloaddition reactions involving preformed and in situ-made azides. Reactions are performed in H2O, under aerobic conditions, with low catalyst loadings and tolerate the use of iodoalkynes as substrates.

Steerable-Discrete-Cosine-Transform (SDCT): Hardware Implementation and Performance Analysis.

In the last years, the need for new efficient video compression methods grown rapidly as frame resolution has increased dramatically. The Joint Collaborative Team on Video Coding (JCT-VC) effort produced in 2013 the H.265/High Efficiency Video Coding (HEVC) standard, which represents the state of the art in video coding standards. Nevertheless, in the last years, new algorithms and techniques to improve coding efficiency have been proposed. One promising approach relies on embedding direction capabilities into the transform stage. Recently, the Steerable Discrete Cosine Transform (SDCT) has been proposed to exploit directional DCT using a basis having different orientation angles. The SDCT leads to a sparser representation, which translates to improved coding efficiency. Preliminary results show that the SDCT can be embedded into the HEVC standard, providing better compression ratios. This paper presents a hardware architecture for the SDCT, which is able to work at a frequency of 188 M Hz , reaching a throughput of 3.00 GSample/s. In particular, this architecture supports 8k UltraHigh Definition (UHD) (7680 × 4320) with a frame rate of 60 Hz , which is one of the best resolutions supported by HEVC.

Synthesis, Structure and Nickel Carbonyl Complexes of Dialkylterphenyl Phosphines.

The experimental and computational characterization of a series of dialkylterphenyl phosphines, PR2 Ar' is described. The new P-donors comprise five compounds of general formula PR2 Ar Dtbp 2 (R=Me, Et, iPr, c-C5 H9 and c-C6 H11 ); Ar Dtbp 2 = 2,6-C6 H3 -(3,5-C6 H3 -(CMe3 )2 )2 ), and another five PR2 Ar' phosphines containing the bulky alkyl groups iPr, c-C5 H9 or c-C6 H11 , in combination with Ar'=Ar Xyl 2 , Ar Xyl ' 2 , or Ar Ph 2 (L1-L10). Steric and electronic parameters have been determined computationally and from IR and X-ray data obtained for the phosphines and for some derivatives, including tricarbonyl and dicarbonyl nickel complexes, Ni(CO)3 (PR2 Ar') and Ni(CO)2 (PR2 Ar'). In the solid state, the free phosphines PR2 Ar' adopt one of the three possible structures formally related by rotation around the Cipso -P bond. Details on their relative energies and on the influence of the free phosphine structure on its coordination chemistry towards Ni(CO)n (n = 2, 3) fragments has been obtained by experimental and computational methods.

A Cationic Unsaturated Platinum(II) Complex that Promotes the Tautomerization of Acetylene to Vinylidene.

Complex [PtMe2 (PMe2 ArDipp2 )] (1), which contains a tethered terphenyl phosphine (ArDipp2 =2,6-(2,6-i Pr2 C6 H3 )2 C6 H3 ), reacts with [H(Et2 O)2 ]BArF (BArF- =B[3,5-(CF3 )2 C6 H3 ]4- ) to give the solvent (S) complex [PtMe(S)(PMe2 ArDipp2 )]+ (2⋅S). Although the solvent molecule is easily displaced by a Lewis base (e.g., CO or C2 H4 ) to afford the corresponding adducts, treatment of 2⋅S with C2 H2 yielded instead the allyl complex [Pt(η3 -C3 H5 )(PMe2 ArDipp2 )]+ (6) via the alkyne intermediate [PtMe(η2 -C2 H2 )(PMe2 ArDipp2 )]+ (5). Deuteration experiments with C2 D2 , and kinetic and theoretical investigations demonstrated that the conversion of 5 into 6 involves a PtII -promoted HC≡CH to :C=CH2 tautomerization in preference over acetylene migratory insertion into the Pt-Me bond.

Methyl Complexes of the Transition Metals.

Organometallic chemistry can be considered as a wide area of knowledge that combines concepts of classic organic chemistry, that is, based essentially on carbon, with molecular inorganic chemistry, especially with coordination compounds. Transition-metal methyl complexes probably represent the simplest and most fundamental way to view how these two major areas of chemistry combine and merge into novel species with intriguing features in terms of reactivity, structure, and bonding. Citing more than 500 bibliographic references, this review aims to offer a concise view of recent advances in the field of transition-metal complexes containing M-CH3 fragments. Taking into account the impressive amount of data that are continuously provided by organometallic chemists in this area, this review is mainly focused on results of the last five years. After a panoramic overview on M-CH3 compounds of Groups 3 to 11, which includes the most recent landmark findings in this area, two further sections are dedicated to methyl-bridged complexes and reactivity.

Platinum(0) olefin complexes of a bulky terphenylphosphine ligand. Synthetic, structural and reactivity studies.

A novel terphenylphosphine PMe2Ar(Dipp2) () (Dipp = 2,6-(i)Pr2C6H3) forms stable Pt(0) complexes with ethene and 3,3-dimethylbut-1-ene that behave as sources of the reactive Pt(PMe2Ar(Dipp2)) fragment. The complexes are efficient catalysts for the selective hydrosilylation of terminal alkynes.

Lithium Di- and trimethyl dimolybdenum(II) complexes with Mo-Mo quadruple bonds and bridging methyl groups.

New dimolybdenum complexes of composition [Mo2{µ-Me}2Li(S)}(µ-X)(µ-N^N)2] (3a-3c), where S = THF or Et2O and N^N represents a bidentate aminopyridinate or amidinate ligand that bridges the quadruply bonded molybdenum atoms, were prepared from the reaction of the appropriate [Mo2{µ-O2CMe}2(µ-N^N)2] precursors and LiMe. For complex 3a, X = MeCO2, while in 3b and 3c, X = Me. Solution NMR studies in C6D6 solvent support formulation of the complexes as contact ion pairs with weak agostic Mo-CH3···Li interactions, which were also evidenced by X-ray crystallography in the solid-state structures of the molecules of 3a and 3b. Samples of 3c enriched in (13)C (99%) at the metal-bonded methyl sites were also prepared and investigated by NMR spectroscopy employing C6D6 and THF-d8 solvents. Crystallization of 3c from toluene:tetrahydrofuran mixtures provided single crystals of the solvent separated ion pair complex [Li(THF)4] [Mo2(Me)2(µ-Me){µ-HC(NDipp)2}2] (4c), where Dipp stands for 2,6-iPr2C6H3. A computational analysis of the Mo2(µ-Me)2Li core of complexes 3a and 3b has been developed, which is consistent with a small but non-negligible electron-density sharing between the C and Li atoms of the mainly ionic CH3···Li interactions.

Reactivity of cationic agostic and carbene structures derived from platinum(II) metallacycles.

This paper describes the formation of new platinacyclic complexes derived from the phosphine ligands PiPr2 Xyl, PMeXyl2 , and PMe2 Ar Xyl 2 (Xyl=2,6-Me2 C6 H3 and Ar Xyl 2=2,6-(2,6-Me2 C6 H3 )2 -C6 H3 ) as well as reactivity studies of the trans-[Pt(C^P)2 ] bis-metallacyclic complex 1 a derived from PiPr2 Xyl. Protonation of compound 1 a with [H(OEt2 )2 ][BArF ] (BArF =B[3,5-(CF3 )2 C6 H3 ]4 ) forms a cationic δ-agostic structure 4 a, whereas α-hydride abstraction employing [Ph3 C][PF6 ] produces a cationic platinum carbene trans-[Pt{PiPr2 (2,6-CH(Me)C6 H3 }{PiPr2 (2,6-CH2 (Me)C6 H3 }][PF6 ] (8). Compounds 4 a and 8 react with H2 to yield the same 1:3 equilibrium mixture of 4 a and trans-[PtH(PiPr2 Xyl)2 ][BArF ] (6), in which one of the phosphine ligands participates in a δ-agostic interaction. DFT calculations reveal that H2 activation by 8 occurs at the highly electrophilic alkylidene terminus with no participation of the metal. The two compounds 4 a and 8 experience C-C coupling reactions of a different nature. Thus, 4 a gives rise to complex trans-[PtH{(E)-1,2-bis(2-(PiPr2 )-3-MeC6 H3 )CHCH}] (7) that contains a tridentate diphosphine-alkene ligand, through agostic CH oxidative cleavage and C-C reductive coupling steps, whereas the C-C coupling reaction in 8 involves classical migratory insertion of its [PtCH] and [PtCH2 ] bonds promoted by platinum coordination of CO or CNXyl. The mechanisms of the CC bond-forming reactions have also been investigated by computational methods.

Experimental and computational studies of the molybdenum-flanking arene interaction in quadruply bonded dimolybdenum complexes with terphenyl ligands.

To clarify the nature of the Mo-Carene interaction in terphenyl complexes with quadruple Mo-Mo bonds, ether adducts of composition [Mo2 (Ar')(I)(O2 CR)2 (OEt2)] have been prepared and characterized (Ar'=Ar(Xyl) 2 , R=Me; Ar'=ArMes2, R=Me; Ar'=Ar(Xyl2), R=CF3) (Mes=mesityl; Xyl=2,6-Me2 C6 H3, from now on xylyl) and their reactivity toward different neutral Lewis bases investigated. PMe3 , P(OMe)3 and PiPr3 were chosen as P-donors and the reactivity studies complemented with the use of the C-donors CNXyl and CN2 C2 Me4 (1,3,4,5-tetramethylimidazol-2-ylidene). New compounds of general formula [Mo2 (Ar')(I)(O2 CR)2 (L)] were obtained, except for the imidazol-2-ylidene ligand that yielded a salt-like compound of composition [Mo2 (Ar(Xyl2))(O2 CMe)2 (CN2 C2 Me4)2]I. The Mo-Carene interaction in these complexes has been analyzed with the aid of X-ray data and computational studies. This interaction compensates the coordinative and electronic unsaturation of one of the Mo atoms in the above complexes, but it seems to be weak in terms of sharing of electron density between the Mo and Carene atoms and appears to have no appreciable effect in the length of the Mo-Mo, Mo-X, and Mo-L bonds present in these molecules.

Terphenyl complexes of molybdenum and tungsten with quadruple metal-metal bonds and bridging carboxylate ligands.

Mono- and bis-terphenyl complexes of molybdenum and tungsten with general composition M2(Ar')(O2CR)3 and M2(Ar')2(O2CR)2, respectively (Ar' = terphenyl ligand), that contain carboxylate groups bridging the quadruply bonded metal atoms, have been prepared and structurally characterized. The new compounds stem from the reactions of the dimetal tetracarboxylates, M2(O2CR)4 (M = Mo, R = H, Me, CF3; M = W, R = CF3) with the lithium salts of the appropriate terphenyl groups (Ar' = Ar(Xyl2), Ar(Mes2), Ar(Dipp2), and Ar(Trip2)). Substitution of one bidentate carboxylate by a monodentate terphenyl forms a M-C σ bond and creates a coordination unsaturation at the other metal atom. Hence in M2(Ar')2(O2CR)2 complexes the two metal atoms have formally a low coordination number and an also low electron count. However, the unsaturation seems to be compensated by a weak M-C(arene) bonding interaction that implicates one of the aryl substituents of the terphenyl central aryl ring, as revealed by X-ray studies performed with some of these complexes and by theoretical calculations.

Experimental and theoretical studies on arene-bridged metal-metal-bonded dimolybdenum complexes.

The bis(hydride) dimolybdenum complex, [Mo2(H)2{HC(N-2,6-iPr2C6H3)2}2(thf)2], 2, which possesses a quadruply bonded Mo2(II) core, undergoes light-induced (365 nm) reductive elimination of H2 and arene coordination in benzene and toluene solutions, with formation of the Mo(I)2 complexes [Mo2{HC(N-2,6-iPr2C6H3)2}2(arene)], 3⋅C6H6 and 3⋅C6H5Me, respectively. The analogous C6H5OMe, p-C6H4Me2, C6H5F, and p-C6H4F2 derivatives have also been prepared by thermal or photochemical methods, which nevertheless employ different Mo2 complex precursors. X-ray crystallography and solution NMR studies demonstrate that the molecule of the arene bridges the molybdenum atoms of the Mo(I)2 core, coordinating to each in an η(2) fashion. In solution, the arene rotates fast on the NMR timescale around the Mo2-arene axis. For the substituted aromatic hydrocarbons, the NMR data are consistent with the existence of a major rotamer in which the metal atoms are coordinated to the more electron-rich C-C bonds.

Quadruply bonded dimolybdenum complexes with highly unusual geometries and vacant coordination sites.

New quadruply bonded dimolybdenum complexes of the terphenyl ligand Ar(Xyl(2)) (Ar(Xyl(2)) = C(6)H(3)-2,6-(C(6)H(3)-2,6-Me(2))(2)) have been prepared and structurally characterized. The steric hindrance exerted by the Ar(Xyl(2)) groups causes the Mo atoms to feature unsaturated four-coordinate structures and a formal fourteen-electron count.

Chemical reactivity and electrochemistry of metal-metal-bonded zincocenes.

Attempts to prepare mixed-ligand zinc-zinc-bonded compounds that contain bulky C(5)Me(5) and terphenyl groups, [Zn(2)(C(5)Me(5))(Ar')], lead to disproportionation. The resulting half-sandwich Zn(II) complexes [(η(5)-C(5)Me(5))ZnAr'] (Ar' = 2,6-(2,6-(i)Pr(2)C(6)H(3))(2)-C(6)H(3), 2; 2,6-(2,6-Me(2)C(6)H(3))(2)-C(6)H(3), 3) can also be obtained from the reaction of [Zn(C(5)Me(5))(2)] with the corresponding LiAr'. In the presence of pyr-py (4-pyrrolidinopyridine) or DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), [Zn(2)(η(5)-C(5)Me(5))(2)] reacts with C(5)Me(5)OH to afford the tetrametallic complexes [Zn(2)(η(5)-C(5)Me(5))L(µ-OC(5)Me(5))](2) (L = pyr-py, 6; DBU, 8), respectively. The bulkier terphenyloxide Ar(Mes)O(-) group (Ar(Mes) = 2,6-(2,4,6-Me(3)C(6)H(2))(2)-C(6)H(3)) gives instead the dimetallic compound [Zn(2)(η(5)-C(5)Me(5))(OAr(Mes))(pyr-py)(2)], 7, that features a terminal Zn-OAr(Mes) bond. DFT calculations on models of 6-8 and also on the Zn-Zn-bonded complexes [Zn(2)(η(5)-C(5)H(5))(OC(5)H(5))(py)(2)] and [(η(5)-C(5)H(5))ZnZn(py)(3)](+) have been performed and reveal the nonsymmetric nature of the Zn-Zn bond with lower charge and higher participation of the s orbital of the zinc atom coordinated to the cyclopentadienyl ligand with respect to the metal within the pseudo-ZnL(3) fragment. Cyclic voltammetric studies on [Zn(2)(η(5)-C(5)Me(5))(2)] have been also carried out and the results compared with the behavior of [Zn(C(5)Me(5))(2)] and related magnesium and calcium metallocenes.

Electrophilic activation and the formation of an unusual Tl+/Cr3+ tetranuclear ion-complex adduct.

Reaction of TlPF(6) with the Cr(III) complex fac-[CrCl(3)(NPN)] (NPN = bis(2-picolyl)phenyl phosphine) did not lead to precipitation of TlCl but rather to addition of the Tl(+) cation to the CrCl(3) moiety, which resulted in a pseudo-dimeric adduct which has an unusual tetranuclear centrosymmetric structure in the solid state.

Palladium and iridium complexes with a N,P,N-bis(pyridine)phenylphosphine ligand.

A variety of Pd(II) complexes containing the neutral N,P,N-ligand bis(2-picolyl)phenylphosphine (N(py)PN(py)) have been synthesised and characterized by IR and NMR spectroscopy and X-ray diffraction. The neutral complex [PdCl(2)(N(py)PN(py)-N,P)] (1) has been selectively obtained in high yield by reaction of [PdCl(2)(NCPh)(2)] with the ligand in dichloromethane. The cationic complexes [PdCl(N(py)PN(py)-N,P,N)]PF(6) (2) and [Pd(N(py)PN(py)-N,P,N)(NCMe)](PF(6))(2) (5) have been prepared from the same reagents by addition to the reaction mixture of one or two equivalents of TlPF(6), respectively. It was found that dynamic exchange of the pyridine rings of 1 occurs on the NMR time-scale and possible mechanisms are discussed. As a by-product of the synthesis of 2, the unexpected dinuclear complex [Pd(2)Cl(2)(mu-N(py)PN(py))(2)](PF(6))(2) (3) has been isolated in 10% yield. Its molecular structure in the solid state reveals the presence of two N(py)PN(py) chelating/bridging ligands. The cationic complex [Pd(2)Cl(2)(mu-N(py)PN(py))(2)](2+) was then selectively obtained by reaction of cis-[Pd(N(py)PN(py)-N,P)(2)](BF(4))(2) (4) with [PdCl(2)(cod)]. (1)H- and (31)P{(1)H} NMR studies have demonstrated that 3 converts slowly into 2 in DMSO solution. The Ir(I) complexes [IrCl(cod)(N(py)PN(py))] (6) and [Ir(cod)(N(py)PN(py)-N,P,N)]BAr(F) (7) have also been prepared, the latter exhibits a trigonal bipyramidal structure with the ligand displaying a facial coordination mode. Compound 7 represents a rare example of an Ir(I) complex bearing a N,P,N-chelating ligand.

Structure and reactivity of new iridium complexes with bis(oxazoline)-phosphonito ligands.

The synthesis and characterization of novel iridium(I) complexes bearing a neutral bis(oxazoline)phosphonite ligand, NOPON(Me(2)) (I), are reported. Numerous Ir(I) complexes have been isolated in high yields and characterized by spectroscopy and X-ray diffraction. [Ir(mu-Cl)(cod)](2) (cod = 1,5-cyclooctadiene) reacted with I to give the air-sensitive complex [IrCl(cod)(NOPON(Me(2)))] (1), which shows broad (1)H and (13)C{(1)H} NMR signals due to dynamic exchange equilibria involving the cod and the NOPON(Me(2)) ligands. Reaction between a solution of 1 and CO afforded the carbonyl complex [IrCl(CO)(NOPON(Me(2)))] (2), whose solid-state structure has been determined by X-ray diffraction. Cationic complexes have been obtained by using NaBAr(F) (BAr(F) = B[3,5-(CF(3))(2)C(6)H(3)](4)) as a chloride abstractor. The complex [Ir(cod)(NOPON(Me(2)))]BAr(F) (3) displays a mononuclear structure in the solid state with ligand I acting as a bidentate P,N chelating ligand. This complex is a precatalyst for the hydrogenation of alkenes. Oxidative addition of H(2) to 3 occurred either in solution or in the solid-state and this reaction allowed the isolation of the 32 electron, dinuclear dihydrido-bridged iridium(III) complex [IrH(mu-H)(NOPON(Me(2)))](2)(BAr(F))(2) (4), in which the NOPON(Me(2)) ligands exhibit a facial coordination mode. It contains only hydrides as bridging ligands and the Ir(2)(mu-H)(2) unit can be viewed as containing a formal Ir-Ir double bond or two 3c-2e bonds. Complex 3 has also been reacted with CO in solution and in the solid state, and this yielded the dicarbonyl derivative [Ir(CO)(2)(NOPON(Me(2)))]BAr(F) (5). A transmetalation reaction between 3 and [PdCl(2)(NCPh)(2)] afforded the cationic Pd(II) complex [PdCl(NOPON(Me(2)))]BAr(F) (6), which has been structurally characterized.