Dimetal compounds preparation

Allylmetal compounds can be prepared by the Pd-catalysed allylation of dimetal compounds. The phenylallylboronate 195 is prepared by the reaction of 2-phenylallyl acetate with bis(pinacolate)diboron (194) catalysed by ligandless Pd in DMSO [95], A good synthetic route to the allylsilane 197 is the reaction of Me3SiSiMe3 with geranyl trifluoroacetate (196) catalysed by ligandless Pd via transmetallation of the n-allylpalladium intermediate at room temperature in DMF [96],... 

Allylstaimane 314 was prepared by the reaction of the allyl ester 313 with the very reactive hetero dimetal compound Bu3Sn-AIEt2 [115]. 

Scheme 5.20. Preparation of gem-dimetal compounds by carbometallation. n-CgHis MgBr...

Many novel cluster compounds have now been prepared in this way, including mixed metal clusters. Further routes involve the oxidative fusion of dicarbon metallacarborane anions to give dimetal tetracarbon clusters such as (103) and (104) O (jjg insertion of isonitriles into inetallaborane clusters to give monocarbon meiallacarboranes such as (105) and the reaction of small ii/t/o-carboranes with alane adducts such as Et3NAlH3 to give the commo species (106) ... 

The more elegant route—which we call for simplicity the method of [1 + l]-addition —may also be used to prepare other binuclear complexes containing either two allyl groups, or one allyl group and one halogen in the bridging positions. The results so far obtained are summarized in Eqs. (9) and (10). Compounds 45-47 are the first allyl-transition metal complexes in which not one metal atom but a dimetal unit is coordinated sandwich-like by two i73-bonded allylic ligands (75, 79). 

A few other examples of chain-forming coordination polymers are mentioned. A polymer 31 was obtained under inert conditions by the reaction of 4,4, 5,5 -tetramethyl-2,2 -bisphosphinine with naphthalene/Na in dimethoxy-ethane [85]. The bisphosphinine is reduced two-fold. In the deep purple oxygen-sensitive crystals the chain is held together by electrostatic interactions through alternation between three and one Na(I) cations. The reaction of pentaphosphaferrocene with CuX (X = Cl, Br, I) was used to prepare yellow-brown crystals of one- and two-dimensional poljmiers in which the phospha-ferrocene units are connected by CuX units [86]. One-, two- and three-dimensional tubes were prepared by employing dimetal building units [87]. For example, a one-dimensional tube was obtained from a Rh2 compound with malonic acid and linkers such as tra 5-l,2-bis(4-pyridyl)ethylene. 

In addition to homoleptic compounds, species with more than one ligand type can be prepared. For example, the reaction of M2(T PB)4 (M = Mo, W T PB = 2,4,6-triisopropylbenzoate) with 2equiv. of 2-thienylcarboxylic acid (02C-fh) yields fraMs-M2(T PB)2(02C-Th)2 [15]. Mixed carboxylate/amidinate compounds of form fraKs-M2(02CR)2(R NC R" NR )2 can also be prepared by the reaction of dimetal tetracarboxylate with the alkali metal salt of the ligand [16]. 

Two synthetic approaches have been prevalent in the preparation of these dinuclear coupled complexes. The first involves the reaction between a dimetal tetracarboxy-late and a bridging ligand that contains two active protons such as a dicarboxylic acid. This has been extensively used by the Chisholm group in the synthesis of dimers of dimers, compounds of type I [7,8], In reactions of this type the formation of the dimer of dimers is achieved by its preferential precipitation from solution. The most simple example of this type of reaction is seen in the reactions of oxalic acid with the dimetal pivalates shown in (2) (M = Mo or W). 

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