Derivatives Containing Transition Metals

4 Derivatives Containing Transition Metals.- 1993 has been a relatively quiet year for this area. Soluble catalysts for the polymerisation of dialkenes have been obtained from mixtures of (MeAlO)n and CpTiCl3. 0 and nmr data on the products of reactions between (Me3SiCH2)3AI and V(0)(CH2SiMe3) (0SiPh3)3-  

Co(CO)3(PPh3), Ni(CO)Cp], have also been prepared. Stable, volatile derivatives [L(CO) M]In[(CH2)3NMe2]2 [L(CO)nM = Fp, Mn(C0)5, Co(CO)4, Ni(CO)Cp] can also be prepared, and their stability is a result of the two chelating groups which protect the indium centre. The In-N bonds in these species are typically 10 - 20 pm shorter than in BrGa[(CH2)3NR 2] and are very unsymmetrical [Fp derivative, In-N 264.3(5), 272.6(5) In-Fe  

93(8)pm], features which BHMO calculations suggest have their origin in d-electron transfer to a (In-N) bonds. In support of this, photolysis of Fpin[(CH2)3NM62]2 yields 

5 Matarial Science.- Relevant review articles are the use of metalorganic precursors for vapour phase epitaxy, precursor requirements for the growth of GaAs and AlGaAs by chemical beam epitaxy,and the use of aluminium-nitrogen compounds for AIN deposition.203 

Laser pyrolysis of the mixture containing Et3Ga results in P-elimination to give Et2GaH and EtGaH2- The stabilty of Me3ln on the Si (100) surfaces has been reported. 

4 Derivatives Containing Transition Metals.-This Section can be conveniently divided into species with a direct bond to a transition metal (TM) and heterobimetallic species which lack this interaction. There seems a noticable shift in emphasis away from the latter grouping, for so long driven by the relevance of such species to homogeneous catalysis, towards MOCVD applications and the former class. 

A novel molecular species containing an Al-Ni bond has been prepared from (Cp Al)4 and Cp2Ni. The product, (CpNi)2(Cp Al)2, which adopts a butterfly arrangement with each aluminium bridging a Ni-Ni bond, represents the first crystallographic characterisation of the Al-Ni bond in a discrete species. 

The gallacyclopentadiene (Mes )Ga(C4Me4) forms a sandwich compound with CpCo(C2H4) after loss of ethene, in which the gallium heterocycle changes from a planar to an envelope conformation. A Co(NO)2Ga heterocycle is present in (py)EtCo-(dmgH)[(dmg)GaEt2], formed from hydrolysis of (py)EtCo[(dmg)- 

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Three other pentamethylcyclopentadienyl ytterbium derivatives containing transition metals in the same molecule have been prepared by Tilley and Andersen (1981a, 1982). (C5Me5)2Yb (Et20) splits the cobalt-cobalt bond in Co2(CO)g with forma-... 

The first pentamethylcyclopentadienyl lanthanide derivative containing transition metals in the same molecule to be synthesized was Cp2Yb(p,-OC)Co(CO)3-THF (Evans et al. 1988f). The structural characterization of the compound (by X-rays) shows the two coordination tetrahedra around each metal ion (Yb or Co) connected via a CO bridge. 

Additional tetraorganotin derivatives containing transition metals may be found in Chapters 2 3 and 2.6.5 ... 

Compounds containing transition metals bonded to main-group elements, such as Hg and Sn, react with Au derivatives to form metal-metal bonds with the elimination of R3MCI ... 

In the unusually effective reducing medium of sodium-hexamethylphos-phoramide (HMPA), [Mn(CO)5] underwent facile reduction to form a golden yellow to yellow brown solution. On the basis mainly of derivative chemistry and infrared spectra, the major soluble component was formulated as Na3[Mn(CO)4] (14). Once this materia] was in hand it was evident that similar binary carbonyl trianions should be possible for other rf-block transition elements of odd atomic number. Since 1976, syntheses of mononuclear binary carbonyl trianions of V, Nb, Ta, Re, Co, Rh, and Ir have also been reported from this laboratory (vide infra). Because these substances contain transition metals in their lowest known oxidation states, they have often been referred to as superreduced species (15). 

The development of new types of reagents for the formation of perfluoroalkyl derivatives of metals is of interest since, as discussed below (Section II), the types of trifluoromethyl complexes which could be prepared until quite recently have been severely limited by the synthetic methods that have been historically available. Virtually all of the trifluoromethyl-containing transition metal species prepared prior to the 1980s arose from only two types of reactions thermal decarbonylations of trifluoroacetyl complexes or oxidative additions of CF3I. 

The interest in coordination compounds containing transition metal-main group element bonds led to the preparation of tellurium derivatives, in which a bare tellurium atom is bonded to and bridges transition metal atoms such as Zr, Ilf, V, Cr, Mo, W, Mn, Re, Fe, Os, Co,... 

Although a considerable volume of work on fluoroaromatic derivatives of transition metals has been reported in the period under review (see, e.g. ref. 186), comparatively few reports contain any mention of 19F NMR parameters. 

Volume 7 contains two reviews which update previous chapters by the same authors in Volume 5B. Dr. Fields has devoted his 19F NMR review to fluoroalkyl and fluoroaryl derivatives of transition metals, while Dr. Witanowski and his co-authors have covered all of the literature, pertaining to nitrogen NMR, which appeared between 1972 and 1976. A valuable contribution of spin-spin coupling interactions between carbon and first row nuclei has been provided by Dr. Wasylishen. 

Good examples of small polaron transport are the glasses containing transition metal ions in two valence states such as (V, V ), (Fe, Fe ), (Cu, Cu ) and (Mo ", Mo ). In all of them, when the electron jumps from the lower valent ion to the higher valent ion, the lattice distortion also moves along with the electron. Mott derived an expression for the polaronic d.c. electrical conductivity of glasses containing transition metal ions. 

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