Warren R. Roper

Platinum group metals in the formation of metal–carbon multiple bonds

Existence de nombreux composes de Ru(II), Os(II), Ir(III), Ru(0), Os(0) et Ir(I) qui font intervenir des doubles ou des triples liaisons entre metal et C. Types structuraux

Metallacyclohexatrienes or ‘metallabenzenes.’ Synthesis of osmabenzene derivatives and X-ray crystal structure of [Os(CSCHCHCHCH)(CO)(PPh3)2]

The first metallabenzene,[O[graphic omitted]H)(CO)(PPh3)2] has been prepared from [Os(Co)(CS)(PPh3)3] and ethyen; X- ray crystal structure determination reveals a planar six-membered ring with no significant alternation of C–C bond lengths thus supporting the idea of electron delocalization within the ring.

Oxidative-Addition Reactions of d8 Complexes

Publisher Summary The rapid development of organo-transition-metal chemistry over the past decade has been dominated by considerations of bonding and structure. The reactions of such organo-metallic compounds have been discussed to a lesser extent and usually in the context of a particular metal or ligand. The apparent parallel between oxidative addition of covalent molecules to unsaturated d complexes and chemisorption of these molecules to the latent valences on transition metal surfaces may be significant. Several organic reactions that are homogeneously catalyzed by unsaturated d8 complexes involve oxidative addition FS a key step in the mechanism. An alternative pathway for five-coordinate complexes to undergo oxidative additions is through prior dissociation of a ligand to form a more reactive four-coordinate complex. Labilization of a ligand may be brought about by heating or irradiating a five-coordinate complex. The tendency for d complexes to undergo oxidative additions depends markedly on the nature of the central metal ion and the ligands attached to it.

Carbene and Carbyne Complexes of Ruthenium, Osmium, and Iridium

Publisher Summary This chapter discusses the carbene and carbyne complexes of ruthenium, osmium, and iridium. The importance of transition-metal carbene complexes and of transition-metal carbyne complexes is now well appreciated. The wealth of empirical information collected for transition-metal carbene and carbyne complexes may be best interpreted within the framework of sound theoretical models for these compounds. Theoretical studies of metal–carbene complexes have been undertaken by several groups. The chemistry of transition metal–carbyne complexes is rather less developed than the chemistry of carbene complexes. The development of the chemistry of carbene complexes of the Group 8A metals, Ru, Os, and Ir, parallels chemistry realized initially with transition metals from Groups 6 and 7. Although transition-metal alkylidene complexes––that is, carbene complexes––containing only hydrogen or carbon-based substituents were first recognized over 15 years ago, it is only relatively recently that Ru, Os, and Ir alkylidene complexes have been characterized. In 1980, a stable dichlorocarbene complex of osmium (II) was described, and since then a large number of dihalocarbene complexes of ruthenium, osmium, and iridium has been prepared. Transition-metal carbyne complexes are still relatively uncommon as only a few synthetic approaches to these compounds have proved generally applicable. M=C and M=C bonds are now well-established features of the chemistry of Ru, Os, and Ir. Many exciting possibilities exist for using these functions in further reactions.

Stepwise reduction of the thiocarbonyl ligand: hydride transfer to CS: thioformyl, thioformaldehyde, methylthiolato, secondary carbene, formyl and iminoformyl complexes of osmium

Abstract The complexes OsHX(CS)L(PPh3)2 (X  Cl, Br; L  CO and X  Cl; L  CN-p-tolyl), which contain mutually cis hydrido and thiocarbonyl ligands, undergo transfer of the hydrido ligand to CS when treated with CO to give blue complexes containing the thioformyl ligand [OsCHS]. OsCl(CHS)(CO)2(PPh3)2 reacts with borohydride to give the first metal complex of the thioformaldehyde monomer, viz. Os(η2-CH2S)(CO)2(PPh3)2, which reacts rapidly with HCl to give OsCl(SCH3)(CO)2(PPh3)2 and then, by a slower reaction, OsCl2(CO)2(PPh3)2 and CH3SH. The ligands produced in this stepwise reduction have possible relevance as models for postulated intermediates in the Fischer—Tropsch synthesis. Synthetic routes to formyl [OsCHO], iminoformyl [OsCHNMe] and secondary carbene complexes [OsCHSMe, OsCHNMe2, OsCHOMe] are also demonstrated.

Synthesis, structure and reactions of a dihapto-formaldehyde complex, Os(η2-CH2O)(CO)2(PPh3)2

Abstract Os(η 2 -CH 2 O)(CO) 2 (PPh 3 ) 2 results from direct reaction of formaldehyde with the zerovalent complex, Os(CO) 2 (PPh 3 ) 3 . The structure of Os(η 2 -CH 2 O)(CO) 2 (PPh 3 ) 2 was determined by X-ray crystallography. The crystals are triclinic, space group P 1 , a 18.739(2), b 11.157(1), c 9.986(1) A, α 116.70(1), β 93.20(1), γ 107.93(1)°, V 1727.69 A 3 , Z = 2, D m 1.55(2), D c 1.57 g cm −3 . Refinement of atomic parameters was by full-matrix least-squares methods, employing anisotropic thermal parameters for all non-hydrogen atoms except for the carbon atoms of the phenyl rings. The formaldehyde hydrogen atoms were located from difference electron density maps, other hydrogens were included in calculated positions. Final residuals were R = 0.047 and R w = 0.061 for 3508 unique observed reflections measured on an automatic diffractometer. The complex itself is monomeric, although interstices in the crystal lattice are occupied by hydrogen-bonded water dimers which fulfil a purely space-filling role. The osmium is bonded to two mutually trans triphenylphosphines, two carbonyls, and the η 5 -formaldehyde, in an arrangement which is best described as distorted octahedral. The geometry of the coordinated formaldehyde is characterised by OsO 2.039(7), OsC 2.186(8) and CO 1.584(11) A. The OsP bonds are equivalent at 2.372(2) and 2.378(2) A but the OsCO bond trans to the formaldehyde carbon 1.931(7) A is longer than that trans to the formaldehyde oxygen 1.907(7) A. Os(η 2 -CH 2 O)(CO) 2 (PPh 3 ) 3 has proved to be a useful synthetic precursor for stable formyl, hydroxymethyl, methoxymethyl, and halomethyl (CH 2 X, X  Cl, Br, I) complexes. The compounds Os(CHO)H(CO) 2 (PPh 3 ) 2 , Os(CH 2 OH)H(CO) 2 (PPh 3 ) 2 , Os(CH 2 OMe)Cl(CO) 2 (PPh 3 ) 2 and Os(CH 2 Cl)Cl(CO) 2 (PPh 3 ) 2 are illustrative of the many compounds which have been characterised. A general synthetic route to neutral formyl osmium complexes, Os(CHO)X(CO) 2 (PPh 3 ) 2 (X = halide or alkyl) has been developed from reaction of the cations [OsX(CO) 3 (PPh 3 ) 2 ] + with BH 4 − . Acetaldehyde also reacts with Os(CO) 2 (PPh 3 ) 3 forming Os(η 1 -C[O]CH 3 )H(CO) 2 (PPh 3 ) 2 . No reaction was observed with benzaldehyde, and trichloroacetaldehyde affords the cation, [OsCl(CO) 2 (PPh 3 ) 3 ] + .

Reaction between the thiocarbonyl complex, Os(CS)(CO)(PPh3)3, and propyne: crystal structure of a new sulfur-substituted osmabenzene

Abstract Reaction between Os(CS)(CO)(PPh 3 ) 3 and propyne gives a complex mixture of products from which can be isolated the simple oxidative addition product Os(CCMe)H(CS)(CO)(PPh 3 ) 2 ( 1 ) and the osmabenzene Os(η 2 -C[S]CMeCHCHC Me)(CO)(PPh 3 ) 2 ( 2 ), where the two propyne molecules in the osmabenzene ring have linked tail-to-tail. Treatment of 1 with HCl gives, as the ultimate product, the propenylthioacyl complex, Os(η 2 -C[S]CHCHMe)Cl(CO)(PPh 3 ) 2 ( 3 ). The crystal structures of compounds 1 – 3 have been determined.

Reactions of osmium coordinated formaldehyde. Synthesis of complexes of selenoformaldehyde and telluroformaldehyde

Abstract Os(η 2 -CH 2 O)(CO) 2 (PPh 3 ) 2 reacts with CSe 2 to form a metallacycle O s(CH 2 OC[Se ]Se)(CO) 2 (PPh 3 ) 2 . This compound breaks down to Os(η 2 -CH 2 Se)(CO) 2 (PPh 3 ) 2 with probable loss of COSe. An alternative route to Os(η 2 -CH 2 Se)(CO) 2 (PPh 3 ) 2 and also Os(η 2 -CH 2 Te)(CO) 2 (PPh 3 ) 2 is through reaction of Os(CH 2 I)I(CO) 2 (PPh 3 ) 2 with SeH − and TeH − , respectively. HCl with Os(η 2 -CH 2 E)(CO) 2 (PPh 3 ) 2 (E = Se or Te) gives OsCl(EMe)(CO) 2 (PPh 3 ) 2 while methyl iodide gives [Os(η 2 -CH 2 EMe)(CO) 2 - (PPh 3 ) 2 ] I. BH 4 − reacts with these cations to cleave the CE bond and form Os(CH 3 )(EMe)(CO) 2 (PPh 3 ) 2 .

Bromination and nitration reactions of metallated (Ru and Os) multiaromatic ligands and crystal structures of selected products

Abstract Three nitrogen-containing aromatic heterocycles, 2-(1′-naphthyl)pyridine, 2-phenylquinoline, and 2,3-diphenylquinoxaline, have been mercurated in the naphthyl or phenyl ring 2-position and then symmetrised to form the mercury compounds Ar2Hg (Ar=Nppy (3), Phqn (1) or Dpqx (5), respectively). These reagents are suitable for trans-metallation and reaction with MHCl(CO)(PPh3)3 affords the complexes M(η2-C,NAr)Cl(CO)(PPh3)2, (6, M=Ru, Ar=Nppy; 7, M=Os, Ar=Nppy; 8, M=Ru, Ar=Phqn; 9, M=Os, Ar=Phqn; 10, M=Ru, Ar=Dpqx; 11, M=Os, Ar=Dpqx) in which each product features an aryl ligand that forms a strongly chelated five-membered ring through coordination of the heterocyclic N atom. The chloride ligand in each of the complexes 6–11 can be replaced by dimethyl dithiocarbamate to give ultimately the mono-triphenylphosphine complexes, M(η2-Ar)(η2-S2CNMe2)(CO)(PPh3) (12, M=Ru, Ar=Nppy; 13, M=Os, Ar=Nppy; 14, M=Ru, Ar=Phqn; 15, M=Os, Ar=Phqn; 16, M=Ru, Ar=Dpqx; 17, M=Os, Ar=Dpqx). Similarly, compound 10 when treated with Na(acac) gives Ru(η2-Dpqx)(η2-acac)(CO)(PPh3) (18), while treatment with trifluoroacetic acid gives Ru(η2-Dpqx)(O2CCF3)(CO)(PPh3)2 (19). Many of these complexes were found to be very robust, making them suitable for electrophilic aromatic substitution reactions under harsh conditions. In each case, the presence of the metal had both an activating and a directing effect on the aryl ring to which it was bonded. Bromination or nitration reactions, both of which are not normally possible with organometallic substrates, were carried out successfully, giving rise to monobrominated or dinitrated products, respectively. The following compounds were characterised, M(η2-Ar-4-Br)Cl(CO)(PPh3)2 (20, M=Ru, Ar=Phqn; 21, M=Os, Ar=Phqn; 22, M=Ru, Ar=Dpqx; 24, M=Os, Ar=Dpqx), M(η2-Dpqx-4-Br)(η2-S2CNMe2)(CO)(PPh3) (23, M=Ru; 25, M=Os), Os(η2-Ar)Cl(CO)(PPh3)2 (26, Ar=Nppy-6,8-(NO2)2; 27, Ar=Phqn-4,6-(NO2)2). Crystal structures of compounds 7, 12, 15, 18, 19, 21, 23 and 25 have been determined.

Trifluoromethyl, difluorocarbene and tetrafluoroethylene complexes of iridium and the crystal structures of IrI(CH3)(CF3)(CO)(PPh3)2, Ir(CF3)(C2F4)(CO)(PPh3)2 and Ir(CF3)(CF2)(CO)(PPh3)2

Abstract A trifluoromethyl iridium(I) complex Ir(CF3)(CO)2(PPh3)2 (1 has been prepared by the reaction of Hg(CF3)2 with IrH(CO)2(PPh3)2, or by thermal decomposition of Ir(COCF3)(CO)2(PPh3)2 (3), which is produced from (CF3CO)2O and a reduced iridium(−I) species. Either the reaction of IrH(CO)(PPh3)3 with Hg(CF3)2 or the reversible thermal decarbonylation of 1 yields the coordinatively unsaturated complex Ir(CF3)(CO)(PPh3)2 (2). Derivatives Ir(CF3)L(CO)(PPh3)2 (L = C2F4 (4), L = C2H4 (5), L = O2 (6)) result from treatment of 1 with tetrafluoroethylene, or 2 with ethylene or oxygen, respectively. Both 1 and 2 undergo oxidative addition of Cl2, I2, HCl, H2 and CH3I to give trifluoromethyl iridium(III) complexes IrCl2(CF3)(CO)(PPh3)2 (7), IrI2 (CF3)(CO)(PPh3)2 (8), IrHCl(CF3)(CO)(PPh3)2 (9), cis-IrH2(CF3)(CO)(PPh3)2 (10) and IrI(CH3)(CF3)(CO)(PPh3)2 (11), respectively. The iodo ligand in 11 is labile and can be replaced by an acetonitrile ligand to yield [Ir(CH3)(CF3)(L)(CO)(PPh3)2]ClO4 (L = CH3CN (12)). This ligand can in turn be replaced by p-tolylisocyanide (L = CN-p-C6H4CH3 (13)) or Cl− to give IrCl(CH3)(CF3)(CO)(PPh3)2 (14). Complexes 1 and 9 each react with AlCl3 to give the difluoromethyl species IrCl2(CF2H)(CO)(PPh3)2 (15). A difluorocarbene iridium(I) complex, IrCl(CF2)(CO)(PPh3)2 (16), has been prepared by thermal decarbonylation of Ir(COCF2Cl)(CO)2(PPh3)2 (18), and a complex containing both CF3 and CF2 ligands, Ir(CF2)(CF3)(CO)(PPh3)2 (17), has been made by treatment of either IrCl(CO)(PPh3)2, 2 or 16 with Cd(CF3)2 · glyme. Both 16 and 17 are hydrolysed to give carbonyl species IrCl(CO)2(PPh3)2 and 1, respectively, while 16 reacts with t-butylamine to give an isocyanide complex, IrCl(CN-t-C4H9)(CO)(PPh3)2 (20). Addition of HCl to 16 or 17 produces 15 or 9, respectively. Complexes 4, 11 and 17 have been characterised by X-ray diffraction studies.