Borinato complexes

A broad synthetic approach to borinato complexes ( 6.5.3.3) via alkali-metal borinates has been developed. Treatment of 1-boracyclohexadiene with t-BuLi leads to the anionic borinato ligand ... 

Another elegant synthesis route to borinato ligands and sandwich complexes uses cyanide degradation of otherwise prepared borinato complexes ( 6.5.3.3). The reactions proceed quantitatively to yield borinato ligands and insoluble metal cyanides ... 

A third route to borinato complexes (70) involves thermal reaction of 4,4-dimethyl-l-phenyl-l-bora-2,5-cyclohexadiene with Mn2(CO)10 and Re2(CO)10, yielding 56 (M = Mn, Re). Upon heating the boracyclohex-adiene complex 57, bis(4-methyl-l-phenylborinato)iron (55b R = H) is obtained by elimination of CH3, CO, and iron. In addition, higher methylated borinato complexes (e.g., 55c, R = CH3) have been isolated from the reaction mixture (70). 

Reaction products of borinato complexes with pyridine and cyanide. 

Cyclic voltammetry of (borinato)cyclopentadienyliron and of bis(borinato) complexes of iron, chromium, and vanadium revealed oxi-... 

Cyclic voltammetry studies of borabenzene cobalt complexes, (borinato)-cyclopentadienyliron, and bis(borinato) complexes of iron, chromium, and vanadium have appeared. The electrochemical behaviour and e.s.r. spectroscopy of heterocyclic organoboron compounds (60) have been studied. ... 

Cobaltocene is partially oxidized and in part undergoes insertion of a borylene group, RB. The borinato ligands derive from the unknown borabenzene ( 6.5.3.4). Some porphyrinatoindium and thallium complexes ( 6.5.2.2) can also be synthesized via oxidative addition reactions (TPP)InCl is added oxidatively to Co2(CO)g and Mn2(CO) to give (TPP)In—Co(CO)4 and (TPP)ln — Mn(CO)j, respectively, and (oep)InCl is added to CojfCOg to yield (oep)ln— 0(00)4. 

Comparable reactions between cyclic divinyl boranes and metal carbonyls lead to borinato (borabenzene) complexes... 

Ferrous chloride reacts with the borinato anion to give sandwich complexes ... 

The filtered solutions of the borinato salts are used directly to synthesize such different complexes as Fe(C5H5BR>2, RufCjHjBRlj, Os(C5H5BR)2, (COD)Rh-(C5H5BR), Me,Pt(C5HsBR)2 or Crt(CsH5BR2) (R = Me, Ph) . 

Alkali metal 1-methyl- and 1-phenyl-borinates are also available from bis(borinato)cobalt complexes (see below) on treatment with sodium or potassium cyanide in an aprotic solvent like acetonitrile. Cobalt cyanide precipitates and the alkali borinate remains in solution. After addition of thallium(I) chloride to some complexes, thallium 1-methyl- or 1-phenyl-borinate could be isolated as pale yellow solids, the only main group borinates isolated hitherto. They are insoluble in most organic solvents but readily soluble in pyridine and DMSO. The solids are stable on treatment with water and aqueous potassium hydride, but are decomposed by acids <78JOM(153)265). 

The first borinate-transition metal complex to be prepared was actually the first known derivative of borin. Bis(cyclopentadienide)cobalt (94) reacts with organic halides and was analogously found to react with boron halides in a redox reaction to give (95), followed by an insertion to yield (cyclopentadienide)(borinato)cobalt (97) (72CB3413). The product composition depends on the ratio of reactants. Compound (97) is the main product (80% yield when R = Ph, X = Br) when the molar ratio between (94) and the boron halide is 2.5 1. A second and slower insertion occurs to give (28) when (97) is treated with another equivalent of the boron halide (Scheme 13). Compounds (28), (29) and (97) have one electron more than predicted by the 187r-electron rule for transition metal complexes. They are red in colour and, of course, paramagnetic. The mixed complexes (97) are thermally labile, in contrast to (28) and (29), which can be heated to 180 °C and sublimed at 90 °C. Their ionization potentials are low and the complexes are sensitive to air. 

In the paramagnetic electron-rich bis(borinato)coba t complexes, the labilized metal-ligand interaction allows ligand exchange and transfer to other metals. The phenyl derivative of complex 52 reacts in boiling... 

Fig. 17. Dinuclear complexes having borinato, thia-, and azadiborolene ligands.

Reaction of the bis(borinato)cobaIt complexes Co(C5H5BR)2 (R = Ph or Me) with iron carbonyls gives the complexes (41). Pyrolysis of these at 230 °C produces (42). 

G. E. Herberich, W. Koch, and H. Lueken, J. Organometallic Chem., 1978, 160, 17. Bis-(borinato) cobalt ions - a new class of stable 20 electron sandwich complexes. 

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