ion. The oxidative addition mechanism was originally proposed22i because of the lack of a strong rate dependence on polar factors and on the acidity of the medium. Later, however, the electrophilic substitution mechanism also was proposed. Recently, the oxidative addition mechanism was confirmed by investigations into the decomposition and protonolysis of alkylplatinum complexes, which are the reverse of alkane activation. There are two routes which operate in the decomposition of the dimethylplatinum(IV) complex Cs2Pt(CH3)2Cl4. The first route leads to chloride-induced reductive elimination and produces methyl chloride and methane. The second route leads to the formation of ethane. There is strong kinetic evidence that the ethane is produced by the decomposition of an ethylhydridoplatinum(IV) complex formed from the initial dimethylplatinum(IV) complex. In D2O-DCl, the ethane which is formed contains several D atoms and has practically the same multiple exchange parameter and distribution as does an ethane which has undergone platinum(II)-catalyzed H-D exchange with D2O. Moreover, ethyl chloride is formed competitively with H-D exchange in the presence of platinum(IV). From the principle of microscopic reversibility it follows that the same ethylhydridoplatinum(IV) complex is the intermediate in the reaction of ethane with platinum(II). Important results were obtained by Labinger and Bercaw62c in the investigation of the protonolysis mechanism of several alkylplatinum(II) complexes at low temperatures. These reactions are important because they could model the microscopic reverse of C-H activation by platinum(II) complexes. Alkylhydridoplatinum(IV) complexes were observed as intermediates in certain cases, such as when the complex (tmeda)Pt(CH2Ph)Cl or (tmeda)PtMe2 (tmeda ) N,N,N′,N′-tetramethylenediamine) was treated with HCl in CD2Cl2 or CD3OD, respectively. In some cases H-D exchange took place between the methyl groups on platinum and the, CD3OD prior to methane loss. On the basis of the kinetic results, a common mechanism was proposed to operate in all the reactions: (1) protonation of Pt(II) to generate an alkylhydridoplatinum(IV) intermediate, (2) dissociation of solvent or chloride to generate a cationic, fivecoordinate platinum(IV) species, (3) reductive C-H bond formation, producing a platinum(II) alkane σ-complex, and (4) loss of the alkane either through an associative or dissociative substitution pathway. These results implicate the presence of both alkane σ-complexes and alkylhydridoplatinum(IV) complexes as intermediates in the Pt(II)-induced C-H activation reactions. Thus, the first step in the alkane activation reaction is formation of a σ-complex with the alkane, which then undergoes oxidative addition to produce an alkylhydrido complex. Reversible interconversion of these intermediates, together with reversible deprotonation of the alkylhydridoplatinum(IV) complexes, leads to multiple H-D exchange

Activation of c-h bonds by metal complexes

Ru-, Rh-, and Pd-Catalyzed C-C Bond Formation Involving C-H Activation and Addition on Unsaturated Substrates: Reactions and Mechanistic Aspects

The synthesis, electrochemistry, and photophysics of a series of square planar Pt(II) complexes are reported. The complexes have the general structure C∧NPt(O∧O),where C∧N is a monoanionic cyclometalating ligand (e.g., 2-phenylpyridyl, 2-(2‘-thienyl)pyridyl, 2-(4,6-difluorophenyl)pyridyl, etc.) and O∧O is a β-diketonato ligand. Reaction of K2PtCl4 with a HC∧N ligand precursor forms the chloride-bridged dimer, C∧NPt(μ-Cl)2PtC∧N, which is cleaved with β-diketones such as acetyl acetone (acacH) and dipivaloylmethane (dpmH) to give the corresponding monomeric C∧NPt(O∧O) complex. The thpyPt(dpm) (thpy = 2-(2‘-thienyl)pyridyl) complex has been characterized using X-ray crystallography. The bond lengths and angles for this complex are similar to those of related cyclometalated Pt complexes. There are two independent molecular dimers in the asymmetric unit, with intermolecular spacings of 3.45 and 3.56 A, consistent with moderate π−π interactions and no evident Pt−Pt interactions. Most of the C∧NPt(O∧O) complexes...

Synthesis and characterization of phosphorescent cyclometalated platinum complexes.

Publisher Summary This is one of two articles in this volume that is concerned with the borane-carborane structural pattern. In the other, Williams has shown how the pattern reflects the coordination number preferences of the various atoms involved. The purpose of the present article is to note some bonding implications of the pattern, and to show its relevance to a wide range of other compounds, including metal clusters, metal-hydrocarbon 7∼ complexes, and various neutral or charged hydrocarbons. Boranes and carboranes may be regarded as cluster compounds in the sense defined by Cotton; they contain a finite group or skeleton of atoms held together entirely, mainly, or at least to a significant extent by bonding directly between those atoms, even though some other atoms may be associated intimately with the cluster. Examples of their structural pattern, however, can be found far beyond the confines of what is normally regarded as cluster chemistry, so this survey includes many systems not commonly referred to as clusters.

Structural and Bonding Patterns in Cluster Chemistry

The potential of palladacycles: more than just precatalysts

Addition reactions of a polynuclear osmium hydrido compound leading to associative carbonyl substitution and catalytic alkene isomerisation

Acetylene and substituted acetylenes react with [H2Os3(CO)10] without CO loss at room temperature to give vinyl derivatives of type [HOs3(CR1:CHR2)(CO)10](R1= R2= H or Ph; R1= H, R2= Me or Ph), alkenylene complexes [Os3(CR1:CR2)(CO)10](R1= R2= H or Me; R1= H, R2= Me), and the phenylethynyl complex [HOs3(C2Ph)(CO)10], while other derivatives containing coupled alkynes are formed in low yield, if at all, at room temperature. On heating these complexes in hydrocarbon solvents, hydrogen transfer and CO loss occur to give [H2Os3(C2R2)(CO)9](R = H, Me, or Ph), [HOs3(C2R)(CO)9](R = H or Me), and [HOs3(MeC3H2)(CO)9][in two isomeric forms (A) or (B)]. The dihydrido-complexes may also be prepared by hydrogenation of [Os3-(CR1:CR2)(CO)10](R1= H or Me, R2= Me). Structures are proposed on spectroscopic evidence. The significance of these results to the reactivity of olefins with Os3(CO)12 is discussed.

Reactions of acetylene, methyl- and phenyl-substituted acetylenes, and ethylene with 1,1,1,1,2,2,2,3,3,3-decacarbonyl-2,3-di-µ-hydrido-triangulo-triosmium

Benzo[h]quinoline (bquin) does not cleave the chloride bridge of [{Pd(dmp)Cl}2][dmp = 2-(dimethylaminomethyl)phenyl-N], 8-methylquinoline (8Me-quin) does so if in large excess, while other ligands L (pyridine, 2-methylpyridine, or 7-methylquinoline) give monomeric [Pd(dmp)Cl(L)] quantitatively. Measured equilibrium constants for the bridge-cleavage reaction indicate that the Pd⋯H–C interactions in bquin and 8Me-quin complexes are strongly destabilising. Rotations about the Pd–N bonds in [Pd(dmp)Cl(L)] are slow and no faster than equilibria involving dissociation to [{Pd(dmp)Cl}2]. Stable complexes of bquin and of 8Me-quin can, however, be readily formed if the strongly bridging chloride ligands are replaced by nitrate or perchlorate. For example, stoicheiometric addition of bquin to an acetone solution derived by addition of Ag[ClO4] to [{Pd(dmp)Cl}2] gives the title complex, [Pd(dmp)(bquin)(OH2)][ClO4], the crystal and molecular structure of which has been determined by single-crystal X-ray diffraction. The crystals are triclinic, a= 11.050(4), b= 9.808(4), c= 11.412(5)A, α= 77.04(4), β= 110.90(4), γ= 97.00(3)°, and Z= 2, space group P. The structure was solved by standard heavy-atom methods and refined by least squares, using 1976 observed data, to R 0.053. The co-ordination is essentially square planar with mutually trans nitrogen atoms. The most notable feature is the short H10(bquin)⋯Pd distance [2.09(6)A], but consistent with this being a non-bonding interaction is the ca. 10° tilt of the bquin (Pd–N–C 111 and 131°) in a direction that lessens this clash. From a comparison of 1,10-phenanthroline and other authentic bidentate ligands with 8Me-quin and bquin, it is concluded that the latter ligands are unidentate.

Comparison of 8-methylquinoline and benzo[h]quinoline complexes of palladium(II) with those of related ligands. Crystal and molecular structure of aqua(benzo[h]quinoline)[2-(dimethylaminomethyl)phenyl-N]palladium(II) perchlorate

Palladation behaviour of 8-methyl-, 8-ethyl-, and 8-isopropyl-quinolines and some of their 2-substituted derivatives

A new type of pyridine-2-thionato bridge: X-ray crystal structure of the complex [Re2(MepyS)2(CO)6] where MepyS is the 6-methylpyridine-2-thionato ligand

Antony J. Deeming

Papers

Addition reactions of a polynuclear osmium hydrido compound leading to associative carbonyl substitution and catalytic alkene isomerisation

Reactions of acetylene, methyl- and phenyl-substituted acetylenes, and ethylene with 1,1,1,1,2,2,2,3,3,3-decacarbonyl-2,3-di-µ-hydrido-triangulo-triosmium

Comparison of 8-methylquinoline and benzo[h]quinoline complexes of palladium(II) with those of related ligands. Crystal and molecular structure of aqua(benzo[h]quinoline)[2-(dimethylaminomethyl)phenyl-N]palladium(II) perchlorate

Palladation behaviour of 8-methyl-, 8-ethyl-, and 8-isopropyl-quinolines and some of their 2-substituted derivatives

A new type of pyridine-2-thionato bridge: X-ray crystal structure of the complex [Re2(MepyS)2(CO)6] where MepyS is the 6-methylpyridine-2-thionato ligand