Aminoborylene complexes

In agreement with these findings aminoborylene complexes of the type [p-BR2 (p5-C5H5)Mn(CO)2 2] (1) proved to be inert toward air and water and to undergo nucleophilic substitutions at the boron center with retention of the electronically stabilized Mn2B-skeleton vide supra). 

The reactivity of the aminoborylene complexes 1 and 2 under thermal conditions leads to the formation of semi-bridged borylene or bis-borylene complexes (vide infra). The photochemical transfer of the borylene ligand is useful for the preparation of borirenes [23], turned out to be an alternative for the synthesis of 1, and was also used for the synthesis of the first half-sandwich borylene complex [(775-C5H5)(OC)3V=B=N(SiMe3)2] (5) [24] (Scheme 4). In the crystal, the borylene ligand adopts the expected linear geometry (V-B-N 177.9(4)°) and the B-N bond (137.8(7) pm) is... 

Due to the formation of two metal-boron bonds, the compounds 23a,b-26a,b show characteristically deshielded nB-NMR signals in solution. In the case of aminoborylene complexes, resonances in the range of S = 100-120 are observed. For the tert-butylborylene complex 26a an even more deshielded signal is found at 8= 170.0. The observed CO stretching frequencies of 23a,b-26a,b are comparable to those of the related /x-methylene complexes [48-50]... 

It has been found that the aminoborylene complexes 23a,b-25 display extremely low reactivity towards nucleophilic substitution at the boron center. Consequently, they show high stability against both air and moisture for long periods (vide supra). Treatment of 23b with an excess of HCl, however, provided the corresponding chloroborylene complex [(/x-BCl) ( 5-C5H4Me)Mn(CO)2 2] (34). The weakly 7r-stabilized complex 34 undergoes a number of substitution reactions at the boron center with protic reagents (Scheme 15) [46,60]. Reaction of 34 with pyridine in the presence of H[BF4] results in the formation of the aminoborylene complex 41 via formal 1,4-hydroboration of pyridine [61,62]. 

The photochemistry of bridging borylene complexes differs significantly from that of their terminal counterparts. The aminoborylene complex 23a,b proved to be entirely unreactive under photolytic conditions, which is in sharp contrast to the terminal aminoborylene complexes 1 and 2. The chloro derivative 34, however, yielded upon irradiation in the presence of a CO donor (i.e. M(CO)6> M = Cr, Mo, W) the dimetalla-mdo-tetraborane [B2Cl2 ( 75-C5R5)Mn(CO)2 2] (43) as shown in Scheme 17 [64]. The reaction provides a direct synthetic link between electron-precise borylene complexes and electron-deficient metallaboranes. 

Aminoborylene Complexes of Group 6 Elements and Iron A Synthetic, Structural and Quantum Chemical Study [83] ... 

Cationic Terminal Aminoborylene Complexes Controlled Stepwise Insertion into M=B and B=N Double Bonds [91] ... 

Blank B, Colling-Hendelkens M, Kollann C, Radacki K, Rais D, Uttinger K, Whittell GR, Braunschweig H (2007) Aminoborylene complexes of group 6 elements and iron a synthetic, structural, and quantum chemical study. Chem Eur J 13 4770... 

---