Metalloborane derivatives

Metalloborane Derivatives with Ligand-Metal Single Bonds... 

This paper reviews the chemistry of metalloborane derivatives that contain borane or heteroatom borane groups which function as monohapto ligands. These compounds can be divided into three classes according to the number of electrons formally donated by the borane ligand to the metal. The electron pair acceptor class, represented by the compound Na[(OC)5Mn BHg], has received little attention thus far. The one-electron donor class, exemplified by the complex, l,2-(CH3)2-3- (C5H5)Fe(CO)2]-BioC2Ho, has a rich chemistry of metal-carbon and metal-boron derivatives. The third class includes two-electron donor derivatives that are represented by the compound (CHs)f,N[7,8-BoHioCHP - CrfCO),]. 

Another route to metalloborane derivatives with metal-boron single bonds is the reaction of certain cationic transition metal compounds with borane anions (20). Addition of solid [(C5H5)Fe(CO)2(cyclohexene)]-PFe to an ether solution of NaBioHia at room temperature formed yellow 6-[(C5Hr>)Fe(CO)2]BioHi3 in 50% yield. The pattern of the B NMR spectrum of this derivative was very similar to other 6-substituted deca-borane derivatives, and on this basis it was proposed that an iron-boron single bond had been formed at B(6) of the decaborane cage as illus-... 

FIGURE 25 Structure of B4HsFe(CO)3. The metalloborane derived from the isolobal replacement of B—H by Fe(CO)3. 

Professor Greenwood has provided routes to metalloboranes which are derived from the noble metals Pt and Ir and the nido-B9H12 ", arachno-B9H1A, and closo-BioH102 ions. We wish to make note of some new reactions of Ir and Rh complexes with the arachno-B< H9 ion and compare these results with his observations of arachno-B9H14. ... 

In constrast to the previous section, the literature in this area over the period of the review was dominated by metalloheteroborane (mainly metallocar-borane) chemistry, narrowly focussed on charge-compensated carbollide C2B9H10L derivatives, with relatively few examples of metalloboranes. In... 

By no means do all metallocarboranes have the metal atoms occupying vertices of the basic polyhedra. Apart from many derivatives in which o-bonded metal residues occupy exo sites attached to particular skeletal atoms, several metalloboranes and -carboranes are known in which the metal occupies an edge-bridging site, effectively replacing a bridging hydrogen atom of the parent borane. Many are nido species related to BeHio, for example, the /x-silyl and /i-germyl carboranes. 

In addn to these methods the Grignard reaction can be employed. For example, decaborane will react with a methyl Grignard and produce the product expected or it will react with double Grignard reagents to produce a cyclic deriv(Ref 28). Metalloboranes can be prepd from metal a-malgams, as illustrated by the following reactions (Ref 3) ... 

In addn to their uses as high energy fuels(HEF), boron hydrides and their org derivs are useful as diesel oil additives, as polymerization catalysts and as cetane improvers presumably because they increase the flame speed of fuel-air mixts. Many other possible applications are suggested for the metalloboranes and their derivs(Ref 36)... 

Borane Anions and Metallo-derivatives.—Greenwood and Ward have reviewed the synthesis and structures of metalloboranes, with a discussion of metal-boron bonding.29... 

Borane Anions and their Derivatives.—number of rules, analogous to the 18-electron rule of organo-transition-metal chemistry, have been proposed for metalloboranes. Thus, (i) a closo-, n-vertex polyhedral heteroborane with one transition-metal vertex requires 2n 4- 14 electrons, (ii) niWu-polyhedra of this type require 2 + 16 electrons, and (iii) c/ojo-polyhedra with two transition-metal vertices require 2n + 26 electrons. Further rules can also be derived for cowwo-compounds in which two c/ojo-polyhedra are fused at the metal atom. ... 

The metal carbonyl clusters - They have been characterized by X-ray diffraction with nuclearities up to the range 30 to 40, by the pioneering work of Chini. They are neutral or, mono-, di-, or trianionic, and these anions can be protonated to give respectively mono-, di- or trihydrides. They have been much studied by organometallic chemists who have used them as models of the Fischer-Tropsch reaction and replaced some carbonyls by unsaturated hydrocarbon ligands. Wade has compared them to metalloboranes, which allowed him to propose a new, correct electron count. Metallocarboranes, derived from the latter, were introduced by Hawthorne. 

The photolysis of Os(CO)5 in benzene has led to (n -C6H6)Os(CO)4 which is said to be similar to, but more reactive than, the iron analogue.The dimeric halide complexes [(arene)MX2]2 (M= Ru, Os) remain a useful entry into arene complex chemistry. The development of the ligand chemistry of these complexes continues.These substrates have also been used to make metalloborane complexes, used as catalysts for the coupling of furans and thiophenes and simple derivatives such as [ (p-cymene)20s2(0H)3] used for the catalytic oxidation of aldehydes to carboxylic acids. ... 

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