On the Nature of the Agostic Bond between Metal Centers and β-Hydrogen Atoms in Alkyl Complexes. An Analysis Based on the Extended Transition State Method and the Natural Orbitals for Chemical Valence Scheme (ETS-NOCV)

Publisher Summary This chapter discusses basic metal cluster reactions Addition or removal of electrons, the simplest type of chemical reaction, is much more common for transition metal than for main group element compounds Among the metal complexes, the clusters are predestined for this process Possible unidentate reagents are atomic cations and other simple electrophiles as well as atomic anions and other simple nucleophiles All cluster syntheses involve growth or fragmentation of metal atom aggregates But until very recently, the buildup of clusters or the use of clusters as fragment sources involved empirical approaches with little predictability The 18-electron rule generally governs the bonding in clusters with up to five metal atoms Clusters with five, six, and sometimes seven metal atoms can often be treated in terms of skeletal electron counting, describing the frameworks by the nido, closo, and capping formalisms A systematization of basic cluster reactions has been attempted based on the present status of knowledge The number of reactions reported is still relatively small for certain reaction types

Basic Metal Cluster Reactions

Publisher Summary This chapter discusses the electron-transfer reactions of polynuclear organotransition metal complexes The chemistry of polynuclear organometallic complexes has become increasingly important, particularly in aiding the understanding of the relationship among structure, bonding, and reactivity A great deal of effort has been devoted to the study of linked metallocene units to probe the redox properties of compounds containing two or more identical electron-transfer sites The imido-bridged complexes are reduced in a reversible one-electron process The monoanion (E = P), prepared by sodium naphthalenide reduction of the neutral compound and isolable as a sodium salt, has an electron spin resonance (ESR) spectrum consisting of 15 triplets There is very little information available on the redox properties of organometallic clusters of the early transition metals The trinuclear carbonyls and the mixed metal clusters undergo one-electron reduction Theoretical studies have shown that the monocations of both biferrocene and bis(fulvalene)diiron show some delocalization; the latter is much more delocalized than the former

The Electron-Transfer Reactions of Polynuclear Organotransition Metal Complexes

Measurement of the Barrier to β-Hydride Elimination in a β-Agostic Palladium−Ethyl Complex: A Model for the Energetics of Chain-Walking in (α-Diimine)PdR+ Olefin Polymerization Catalysts

Electron paramagnetic resonance studies of low-spin d5 transition metal complexes

η-Cycloheptatrienyl-molybdenum chemistry: Tertiary phosphine, alkyl, hydrido, halogeno and related derivatives

Protonation of Co(η-C5H4R)(η-C2H4)2, R = Me or Et with tetrafluoroboric acid gives the compounds [Co(η-C5Me4R)(η-C2H4)Et]Bf4, R = Me (1) or Et (2), in which a β-hydrogen of the Co–ethyl group forms a C–H⇀Co bridge via a two-electron, three-centre bond.

Two-electron, three-centre carbon–hydrogen–cobalt bonds in the compounds [Co(η-C5Me4R)(η-C2H4)(η-C2H4-µ-H)] BF4, R = Me and Et

The cation [Mo(η-C7H7)(η-C6H5R)]+ readily undergoes displacement of the arene ligand allowing the following compounds to be prepared: [Mo(η-C7H7)L3][PF6][L3=(MeCN)3, (MeCN)2(PPh3), (MeCN)(Ph2PCH2CH2PPh2), (PMe2Ph)3, (PMePh2)3, or (CO)(PMe2Ph)2]; [(η-C7H7)Mo(µ-X)3Mo(η-C7H7)]A (X = Cl, Br, OMe, or OEt; A = PF6, or BF4); and [(η-C7H7)Mo(µ-X)3Mo(η-C7H7)](X = Cl, Br, I, or OMe). The last neutral compounds are paramagnetic, and electronic, e.s.r., i.r., and photolectron spectral studies have been made. The new compounds K2[Mo(η-C7H7)(CN)3], [Mo(η5-C6H7)(η-C7H7)], [Mo(η-C7H7)(PPh3)(pd)](pd = pentane-2.4- dionate), and [Mo(η-C3H5)(η-C7H7)(PPh3)] are also described.

Some studies of η-cycloheptatrienylmolybdenum compounds

Tri-n-butyl(ethyltetramethylcyclopentadienyl)tin, Sn(etmcp)Bun3, reacts with cobalt(II) chloride to give, after treatment with chlorine, [{Co(etmcp)Cl(µ-Cl)}2] and [Co3(etmcp)2Cl6]. Using these compounds as precursors, many derivatives of the Co(η-etmcp) system have been prepared; examples are [(η-etmcp)Co(µ-Cl)3Co(η-etmcp)][FeCl4], [Co(η-etmcp)(PPh3)Cl2], [Co(η-etmcp)L2Cl][PF6][L2= Ph2P(CH2)2PPh2, or (PMe2Ph)2], [Co(η-etmcp)L3][PF6][L3=(NH3)3, (MeCN)3, (MeCN)2(Me2CNH), (CH2CHCN)3, η-benzene, or η-toluene], and [Co(η-etmcp)L2][L2=(η-C2H4)2, butadiene, or 1,5-C8H12].

Some chemistry of ethyltetramethylcyclopentadienylcobalt: arene, ethylene, butadiene, ammine, tertiary phosphine, and chloro-derivatives

Thermal decomposition of the known complex [Co(C5Me4Et)(C2H4)Me2] gives the intermediate species ‘Co(C5Me4Et)’ which reacts with [OS3(CO)10H2] to produce [Os3Co(CO)10(C5Me4Et)H2]. This complex crystallises in the triclinic space group P with a= 9.072(4), b= 10.477(5), c= 13.921(7)A, α= 95.80(3), β= 93.54(3), γ= 102.48(3)°, and Z= 2. The structure was solved by a combination of direct methods and Fourier-difference techniques and refined by blocked-cascade least squares to R= 0.039 for 3 084 diffractometer data. The Co(C5Me4Et) fragment caps the Os3 triangle. Each Os atom is also co-ordinated to three terminal carbonyl groups while the tenth carbonyl bridges an Os–Co bond. The complex [Os3Co(CO)10(C5Me4Et)H2] reacts with hydrogen to give [Os3Co(CO)9(C5Me4Et)H4], and both clusters react with carbon monoxide under fairly mild conditions to yield [Os3(CO)12] and [Co(CO)2(C5Me4Et)].

Richard B. A. Pardy

Papers

η-Cycloheptatrienyl-molybdenum chemistry: Tertiary phosphine, alkyl, hydrido, halogeno and related derivatives

Two-electron, three-centre carbon–hydrogen–cobalt bonds in the compounds [Co(η-C5Me4R)(η-C2H4)(η-C2H4-µ-H)] BF4, R = Me and Et

Some studies of η-cycloheptatrienylmolybdenum compounds

Some chemistry of ethyltetramethylcyclopentadienylcobalt: arene, ethylene, butadiene, ammine, tertiary phosphine, and chloro-derivatives

Synthesis of new cobalt–osmium mixed-metal clusters using a novel reactive cobalt species; X-ray crystal structure of [Os3Co(CO)10(C5Me4Et)H2]