Tetra diboron

The same reaction produced different alkenes 58-6563 (Scheme 13). These reactions were not catalyzed by rhodium(I) or palladium(0). Tetra(methoxo)- and bis(pinacolato)diboron(4) added to both terminal and internal alkynes in the presence of a catalytic amount of Pt(PPh3)4 to provide stereo defined pinacolato r/s-bis(boryl)alkenes 58-65 in excellent yields. Because reagents and reaction conditions were sufficiently mild,... 

Synthesis of diboron compound 164 via bisdiboranes has been demonstrated by Wrackmeyer and Kehr.103 Organoboration of tetra(alk-ynyl)stannanes leads to the spiro-cyclic compound in high yield, which reacts with MeBBr2, i-PrBBr2, and PhBCl2 in dichloromethane between —78... 

The reaction of the porphyrin ligand, TTP (tetra-p-tolylporphyrin) with BF3-OEt2 leads to the oxide fluoride complex, B2OF2(TTP) and the structure has been established using H, 13C, nB and 19F NMR spectroscopy and FAB mass spectrometry [9], The structure contains a B—O—B bridge in which each boron is bonded to fluorine and to a nitrogen of TTP. The structure of the diboron complex was confirmed by an X-ray crystal structure determination of the tetrakis-(p-chlorophenyl)porphyrin (TpCiPP) derivative. 

Ishiyama, T., Itoh, Y., Kitano, T., Miyaura, N. Synthesis of arylboronates via the palladium(0)-catalyzed cross-coupling reaction of tetra(alkoxo)diborons with aryl trifiates. Tetrahedron Lett. 1997, 38, 3447-3450. 

This method is an adaption of the U. S. Borax Research group s procedure that Illustrates a practical and efficient method for the synthesis of tetra(alkoxo)diborons. Several (alkoxo)diborons, such as tetra(methoxo)-,3 bis(catecholato)-, and bis(pinacolato)diboron (1). are synthesized from tetrakis(dimethylamino)diboron. The diborons are excellent reagents for the synthesis of various organoboronic esters via the transition metal-catalyzed addition and cross-coupling reactions. ... 

Ishiyama T, Itoh Y, Kitano T, Miyaura N (1997) Synthesis of Arylboronates via the Palladium(0)-Catalyzed Cross-Coupling Reaction of Tetra(alkoxo)diborons with Aryl Inflates. Tetrahedron Lett 38 3447... 

The palladiuin-catalyzed cross-coupling reaction of tetra(alkoxo)di-borons provides a method for direct boiylation of aryl iodides, bromides, or triflates (Eq. 13). Because bis(pinacolato)diboron is... 

Cataiyst Cu(I)Cl, 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (xantphos ligand), NaO Bu Keywords Alkynes, methyl iodide, bis(pinacolato)diboron [B2(pin)2], Cu(I)Cl, xantphos, tetrahydrofuran (THF), room temperature, regioselective carboboration of alkynes, tri-and tetra-substituted vinyl boronic esters... 

Tetra(2-thienyl)ethylene (TTE) derivatives 122 can be synthesized by Suzuki-Miyaura reactions of a c -boronic ester 121 with differently functionalized bromothiophenes 120 (Scheme 49, Table 27) [342]. F/c-bis(pinacolatoboryl)ethyl-ene 121 can be isolated from the reaction of di(2-thienyl)acetylene with bis-pinacolato-diboron beforehand, but is subsequently employed as crude intermediate... 

Figure 2 Relative Lewis acidity of CI2B-BCI2 and tetra(alkoxy)diboron compounds B2cat2 and B2pin2.

The same authors exhibited a comparative study on the activation of (MeO)2B-B(OMe)2 and (Me2N)2B-B(NMe2)2 vtith the platinum(O) complex [Pt(PPh3)4], and further application to the diboration of 1-octyne. The results clearly demonstrated that both the tetra(alkoxy) diboron performed in a similar way (quantitative conversion on the a s-l,2-diborated product, under 80 °C), but the tetrakis(dimethylamino) diboron was only added in 7% to the 1-octyne, even at 120 The oxidative addition of... 

To complement the activation study of tetra(alkoxy)diboron with Pt(0) complexes. Smith and Iverson disclosed their findings on the reactivity of B2cat2 with [Pt(ri -CH2=CH2)(PPh3)2], which resulted in the loss of ethylene, even at —80 °C, followed by oxidative addition of the B—B bond to give the bis(boryl) complex as-[Pt(Bcat)2(PPh3)2] (10b) (Scheme... 

Scheme 7 Multiple strategies to activate tetra alkoxy)diboron with Pt(0) and related...

Moving from the Pt to Pd and Ni complexes, it can be noted a progressive change on the activation mode of the tetra(alkoxy) diboron compounds from oxidative addition of the B—B within Pt(0) complexes to o-bond metathesis with Pd or Ni. Going further to the right of the periodic table, the activation of diboron by O-bond metathesis becomes more frequent. 

It seems that all the efforts to activate tetra(alkoxy)diboron compounds are justified since the model CI2B—BCI2 reagent, which develops borylation without metal activation, is too difficult to handle. However, the progress in this field has opened a new window toward the activation of tetra(alkoxy) diboron compounds in a metal-free context by the formation of Lewis add—base adducts and their addition to unsaturated substrates can be performed with total chemo-, regjo-, and stereoselectivity. 

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