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

Dodecacarbonyltriosmium in refluxing aniline gives H2Os3(HNC6H4)(CO)8(H2NPh) which reacts successively with CO to give H2Os3(HNC6H4)(CO)9 and HOs3(HNPh)(CO)10. The decacarbonyl in refluxing nonane gives initially H2Os3(HNC6H4)(CO)9 which then isomerises to H2Os3(NPh)(CO)9 which is the main product on heating a hydrocarbon solution of the decacarbonyl in a sealed tube. Corresponding reactions with p-fluoro- and p-methyl-aniline are compared with those of aniline.

Metallation of aniline by reaction with dodecacarbonyltriosmium

Protonation of the µ-vinyloxy-ligand in [Os3H(µ-OCHCH2)(CO)10] with HX (X = Cl or CF3CO2) leads to the compounds [Os3H(X)(CO)10] with liberation of acetaldehyde (ethanal). Several intermediates including the addition species [Os3H(µ-OCHXCH3)(CO)10](X = Cl or CF3CO2) have been identified (and isolated for X = Cl). These addition compounds readily undergo β-elimination of acetaldehyde. This reaction has been exploited as a synthetic route to the known complexes [Os3H(X)(CO)10](X = Cl, Br, I, CF3CO2′ or OH) and the new compounds from potassium O-ethyl dithiocarbonate and NN-diethyldithiocarbamate, [Os3H(S2COEt)(CO)10](two isomers) and [Os3H(S2CNEt2)(CO)10]. The complex [Os3H(S2CNEt2)(CO)10] undergoes ready decarbonylation to [Os3H(S2CNEt2)(CO)9].

Acid-induced displacement of acetaldehyde from a µ-vinyloxy-triosmium cluster

Complexes of the new title ligand (mqp) have been synthesised which contain unidentate, bidentate, or 3-metallated modes of co-ordination as established by 1H and 13C n.m.r. data. The complex [PdCl2(mqp)2] contains unidentate mqp while [PdCl2(mqp)](as a CH2Cl2 solvate) contains bidentate mqp as shown by a single-crystal structure determination. Crystals are monoclinic, space group P21/c, with a= 12.936(3), b= 13.108(3), c= 15.085(3)A, β= 100.48(2)°, and Z= 4. The structure has been determined by Patterson and Fourier methods and refined by least squares to R 0.047 for 3 490 diffractometer data. In-plane bidentate co-ordination would require a considerable clash of mqp with one cis Cl, but distortions within the still essentially square-planar complex reduce this clash. A small pyramidal distortion at the co-ordinated nitrogen atom contributes to this reduction. This complex yields 3-metallated [Pd2Cl2(mqp-H3)2] in refluxing alcohols in the presence of lithium acetate, but in the absence of the latter the HCl formed leads to the quinolinium salt of the 3-metallated product. Various chlorocarbonyl derivatives of [Rh2Cl2(CO)4] are described, the most significant being [Rh2Cl2(CO)3(mqp)] which contains bidentate mqp and shows nuclear spin–spin coupling between the nuclei of the 8-Me group and the 103Rh and 31P nuclei, indicating a significant interaction between the non-metallated Me group and the metal atom. 3-Metallated mqp complexes of iridium(III) and of manganese(I) are also described.

Co-ordination chemistry of (8-methyl-2-quinolylmethyl)di-t-butyl-phosphine (mqp) with palladium, rhodium, iridium, and manganese: crystal structure of [PdCl2(mqp)]

Deprotonation of [Os3H(µ-PHPh)(CO)10]3 gives the anion [Os3H(µ-PPh)(CO)10]–4 containing a nucleophilic phosphorus centre which reacts with H+ to regenerate cluster 3 with the Ph group exo to the Os(CO)4 group as in the starting material. However, Mel reacts with anion 4 at the most accessible side of the µ-PPh ligand to give [Os3H(µ-PMePh)(CO)10]6(X-ray structure reported) which has the Ph group endo and the Me group exo to the Os(CO)4 group. Anion 4 reacts with [AuCl(PMe2Ph)] to give [Os3H(µ-PhPAuPMe2Ph)(CO)10]8(Ph probably endo) but the thermally generated isomer of 4, [Os3(µ-PHPh)(CO)10]–5, reacts by the attack of gold at osmium atoms to give [Os3(µ-AuPMe2Ph)(µ-PHPh)(CO)10]9(Ph probably endo) which is isomeric with 8. Compounds with P-Hg bonds are formed by the reaction of 4 with [HgCl(R)](R = Et, PhCH2 or ferrocenyl) or with HgX2(X = Cl, Br or I). The X-ray structure of the Hg-bridged product, [{Os3H(PPh)(CO)10}2Hg], formed from anion 4 and HgX2 or [Fe(C5H5)(C5H4HgCl)], is described. Although the co-ordination of the Hg atom is closely linear [P-Hg-P 171.8(2)°], there are fairly close approaches of O atoms of axial CO ligands to this atom (Hg ⋯ O 2.88 and 2.85 A). The conformations of the two µ3-PPh groups are different.

Reactions of the anionic phenylphosphinidene cluster [Os3-(µ-H)(µ-PPh)(CO)10]– and its phenylphosphido isomer [Os3-(µ-PHPh)(CO)10]– with electrophiles. Crystal structures of [Os3H(µ-PMePh)(CO)10] and [{Os3H(PPh)(CO)10}2Hg]

The trinuclear cluster [Os3(CO)11{(R)-BINAP}] 1 containing monodentate (R)-BINAP is formed by thermal treatment of [Os3(CO)12] with 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl, (R)-BINAP. This complex decarbonylates thermally to give the cluster [Os3(CO)10{(R)-BINAP}] 2, which was shown spectroscopically to contain chelating BINAP. On further thermal decarbonylation orthometallation at a phenyl group takes place to give [Os3(µ-H)(CO)8{µ3-(R)-BINAP – H}] 3. There is no evidence for restricted rotation about the P–Ph bonds within the PPh2 groups as we have previously observed for [Ru3(µ-OH)2(CO)8{µ-(R)-BINAP}]. This restricted rotation is an effect of crowding and appears to be a distinct property of µ-coordination rather than chelation of BINAP. However, both clusters 1 and 2 are fluxional, but as a result of different processes. Cluster 1 exists as two interconverting isomers 1A and 1B (31P NMR evidence) which we believe have different conformations within the monodentate (R)-BINAP ligand. Our observations are consistent with restricted rotations about the Ph2P–naphthyl bonds. The decacarbonyl cluster 2 has C2 symmetry and shows 13C NMR coalescences consistent with a dynamic merry-go-round motion at the two Os(CO)4 units but not at the Os(CO)2(BINAP) unit. Single-crystal structures of clusters 1 and 3 confirm these two new modes of BINAP coordination.

Antony J. Deeming

Papers

Metallation of aniline by reaction with dodecacarbonyltriosmium

Acid-induced displacement of acetaldehyde from a µ-vinyloxy-triosmium cluster

Co-ordination chemistry of (8-methyl-2-quinolylmethyl)di-t-butyl-phosphine (mqp) with palladium, rhodium, iridium, and manganese: crystal structure of [PdCl2(mqp)]

Reactions of the anionic phenylphosphinidene cluster [Os3-(µ-H)(µ-PPh)(CO)10]– and its phenylphosphido isomer [Os3-(µ-PHPh)(CO)10]– with electrophiles. Crystal structures of [Os3H(µ-PMePh)(CO)10] and [{Os3H(PPh)(CO)10}2Hg]

Trinuclear clusters of osmium containing monodentate, chelating and orthometallated forms of 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (BINAP)