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

The complex [Pd2Cl2(dmp)2][dmp = 2-(dimethylaminomethyl)phenyl] reacts with 1H-pyridine-2-thione (pySH) or with the 6-methyl substituted derivative (mpySH) in the presence of triethylamine to generate the dinuclear complexes [Pd2(dmp)2(pyS)2] and [Pd2(dmp)2(mpyS)2]. These exist as head-to-tail isomers with folded conformations so that the palladium co-ordination planes are approximately parallel. Fluxional enantiomerisation of the mpyS-bridged compound leading to N-methyl group exchange has been studied. These bridged dimers behave as cyclic bidentate sulphur ligands. [Pd2(dmp)2(pyS)2] reacts with [Pd(dmp)(solvent)2]+ to give [Pd3(dmp)3(pyS)2]+; the X-ray structure of [Pd3(dmp)3(pyS)2][BF4] is reported. The cation contains a cage of three palladium atoms linked by two triply-bridging pyS ligands. Related η3-2-methylallyl trimers and mixed-ligand trimers have also been synthesised by the same method.

Di- and tri-nuclear complexes of palladium(II) containing doubly- and triply-bridging pyridine-2-thionato (pyS) ligands: crystal structure of [Pd3(C6H4CH2NMe2)3(pyS)2][BF4]

Some studies on a μ3-indyne complex of triosmium relating to alkyne rotation in M3C2 clusters

Thermal and photochemical reactions of diphenyl-2-thienylphosphine (L) with [Mn2(CO)10] gave simple substitution products [Mn2(CO)10 – nLn] 1 (n = 1) and 2 (n = 2) with ligand L co-ordinated through the phosphorus atom. Under forcing conditions (refluxing xylene) oxidative addition with P–C cleavage occurred to give the µ-2-thienyl complex [Mn2(CO)6(µ-PPh2)(µ-η1∶η5-C4H3S)] 3. Loss of CO and P–C bond cleavage do not occur so easily in the case of [Re2(CO)10]. UV Treatment of the rhenium carbonyl with L gave [Re2(CO)8(µ-P,S-Ph2PC4H3S)] 4, in which the ligand L is bridging through the two heteroatoms. Oxidative addition occurs internally at about 180° in decane with rupture of a P–C bond to produce an isomer of 4, [Re2(CO)8(µ-PPh2)(µ-η1∶η1-C,S-C4H3S)] 5. Crystal structures revealed a novel form of bridging of L co-ordinated through P and S in 4 and two different modes of 2-thienyl bridge (µ-η2∶η5 and µ-η1∶η1-C,S) in 3 and 5 respectively. With the previously known µ-η1∶η2-bridging form of thienyl, these new compounds 3 and 5 provide three distinct type of thienyl bridge. The type of bridge which is formed depends upon the electronic requirements of the metal atoms and the span between them.

Two different types of 2-thienyl bridge in dinuclear manganese and rhenium compounds

The diyne clusters [Os3(µ3,η2-RCCCCR)(CO)10](R = Me, Et, Ph, But, SiMe3) in hydrocarbon solvent at 120 °C decarbonylate to give the nonacarbonyl clusters [Os3(µ3,η2-C2R)(µ-C2R)(CO)9] when R = Ph, But, or SiMe3, [Os3H(µ3,σ,η2,η2-EtCC–CCCHMe)(CO)9] when R = Et, and [Os3(C4Me2)(CO)9] of known structure when R = Me; the µ-C2Ph ligand in [Os3(µ3, η2-C2Ph)(µ-C2Ph)(CO)9](X-ray structure) is unusual in bridging unsymmetrically through only one carbon atom.

Oxidative addition of 1,3-diynes at triosmium clusters with cleavage of the central carbon–carbon bond: X-ray crystal structure of [Os3(µ3,η2-C2Ph)(µ-C2Ph)(CO)9] derived from 1,4-diphenylbuta-1,3-diyne

Synthesis and structures of two isomers of [Re3Ru(S)(C5H4N)(C5H4NS)2(CO)11] which differ in the distribution of pyridine-2-thionato ligands between doubly- and triply-bridging positions

Antony J. Deeming

Papers

Di- and tri-nuclear complexes of palladium(II) containing doubly- and triply-bridging pyridine-2-thionato (pyS) ligands: crystal structure of [Pd3(C6H4CH2NMe2)3(pyS)2][BF4]

Some studies on a μ3-indyne complex of triosmium relating to alkyne rotation in M3C2 clusters

Two different types of 2-thienyl bridge in dinuclear manganese and rhenium compounds

Oxidative addition of 1,3-diynes at triosmium clusters with cleavage of the central carbon–carbon bond: X-ray crystal structure of [Os3(µ3,η2-C2Ph)(µ-C2Ph)(CO)9] derived from 1,4-diphenylbuta-1,3-diyne

Synthesis and structures of two isomers of [Re3Ru(S)(C5H4N)(C5H4NS)2(CO)11] which differ in the distribution of pyridine-2-thionato ligands between doubly- and triply-bridging positions