Mark A. Gallop

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.

Solid-phase synthesis of 1,5-benzodiazepin-2-ones

Abstract A solid-phase synthesis of polysubstituted 1,5-benzodiazepin-2-ones is described. Resin-bound 4-fluoro-3-nitrobenzoic acid was reacted with different β-amino acids, followed by nitro group reduction and formation of the seven-membered ring. Subsequent alkylations at N(5) and N(1) afforded the title compounds in high purities and yields.

Organometallic ‘helicopters.’ Characterisation of the non-rigid triosmium arene–alkene complexes [Os3(CO)8(η2-CH2CHR)(µ3-η2:η2:η2-C6H6)], (RH, Ph) and the X-ray crystal structure of [Os3(CO)8(η2-CH2CH2)(µ3-η2:η2:η2-C6H6)]

The cluster-alkene complexes [Os3(CO)8(η2-CH2CHR)(µ3-η2:η2:η2-C6H6)](RH, Ph) contain benzene ligands in a face-capping co-ordination mode, and the geometry of the ethylene derivative has been confirmed by a single-crystal X-ray analysis; the intramolecular dynamics of these complexes have been investigated in solution by n.m.r. spectroscopy and are discussed in terms of arene ring-whizzing and alkene rotation.

An α-diazoalkylosmium complex as carbyne-complex precursor. Synthesis and X-ray crystal structure of [OsCl(I)(NO)(PPh2C6H4CHCO2Et)(PPh3)], the product of an intramolecular carbyne insertion reaction

The α-diazoalkylosmium complex [OsCl(I)(NO)(CN2CO2Et)(PPh3)2] loses N2 to give the title complex and the formation of this metallacyclic compound, which has been structurally cahracterised by single crystal X-ray diffraction, is interpreted as arising from an intramolecular insertion reaction of an intermediate cationic carbyne complex, [OsCl(NO)(C–CO2Et)(PPh3)2]I.

Synthesis and structure of an ortho-metallated ketazine complex of osmium, OsH(CO)2[(C6H3-p-Me)(p-tolyl)CNNC(p-tolyl)2](PPh3)

Reaction of Os(CO)2(PPh3)2 with a two-fold excess of di-p-tolydiazomethane in benzene at reflux temperature affords the yellow OsH(CO)2[(C6H3-p-Me)(p-tolyl)CNNC(p-tolyl)2](PPh3) (A) in high yield. The structure of A has been determined by X-ray crystallography. The geometry about osmium is octahedral, with the hydride ligand trans to triphenylphosphine and the carbonyl ligands mutually cis. The ketazine ligand is bound to osmium through nitrogen and the ortho-carbon of a p-tolyl group. The Osue5f8N and Osue5f8C distances are 2.119(5) and 2.100(7) A, respectively.

An unusual nitrosyl-diazoalkane coupling reaction. Synthesis, structure and reactivity of the aldoxime-dinitrogen complex, OsCl2(N2)[N(OH)CHCO2Et](PPh3)2

Abstract Reaction of OsCl(NO)(PPh 3 ) 3 with IC(C 2 )CO 2 Et gives a purple species which, on treatment with HCl, affords OsCl 2 (N 2 )[N(OH)CHCO 2 Et] (PPh 3 ) 2 . This aldoxime-dinitrogen complex, structurally characterised by X-ray crystallography, is thought to arise from a coupling reaction of the diazoalkane with the nitrosyl ligand in the substrate. Dehydrating agents convert the osmium-bound aldoxime to a nitrile ligand.

Chemistry of triangulo and linear triosmium cyclopentadienyl cluster compounds: the X-ray structures of [OS3(CO)10(η5-C5H5)Cl] and [OS3(CO)8(η5-C5H5)(µ-Cl)]

The cationic triangulo-complex [Os3(CO)10(η5-C5H5)][BF4] reacts with X–(X = H, Cl) to afford linear triosmium cluster compounds, [Os3(CO)10(η5-C5H5)X], characterised by X-ray crystallography for X = Cl; on heating [Os3(CO)10-(η5-C5H5)Cl] is converted into the triangulo-cluster [OS3(CO)8(η5-C5H5)(µ-Cl)] which, on the basic of an X-ray analysis, contains an unusually short chloride-bridged osmium–osmium distance.

Benzene migration in an osmium cluster: the formation of Os3(CO)7(?6-C6H6)(3 : ?1 : ?2 : ?1-C2Me2) from Os3(CO)9(3 : ?2 : ?2 : ?2-C6H6). The crystal structure of Os3(CO)7(?6-C6H6)(3 : ?1 : ?2 : ?1-C2Me2)

The activated cluster [Os3(CO)7(C2H4)(µ3 : η2 : η2 : η2-C6H6)(MeCN)] reacts with alkynes RC2R′(R = R′= H, Ph or Me; R = H, R′= Ph; R = ME, R′= Et), to produce the new clusters [OS3(CO)7(η6-C6H6)(µ3 : η1 : η2 : η1-RC2R′)] in which the benzene is bonded to a single metal atom as shown by a single crystal X-ray structure determination of the C2Me2 derivative.

Metal cluster-induced electrophilicity of arenes

Hydride or carbanion attack on the triosmium cluster complexes [Os3(CO)9(µ3-η2:η2:η2-C6H5R)], R = H or Me, proceeds highly regio- and stereo-selectively at the face-capping arene ligands. The exo-addition products are anionic, triply bridging cyclohexadienyl complexes [Os3(CO)9(µ3-η2:σ:η2- C6H5RR′)]–, R′= H, Me, or Ph, that yield neutral compounds [Os3(CO)9(µ-E)(µ3-η2:σ:η2-C6H5RR′)] on reaction with electrophiles E = H+ or Au(PEt3)+.

Photoisomerisation of benzenetriosmium cluster complexes: a model for arene activation on flat metal surfaces

The photoinduced dimetallation of face-capping benzene ligands in triosmium carbonyl complexes is presented as a cluster analogue for benzene activation in adsorbate overlayers on transition metal surfaces.