Tris(pyrazolyl)borate amidoborane complexes of the group 4 metals

Abstract

Treatment of the tris(pyrazolyl)borate metal triamides Tp'M(NMe(2))(3), where Tp' = (C(3)H(3)N(2))(3)BH (Tp) or (3,5-Me(2)C(3)HN(2))(3)BH (Tp*) and M = Ti, Zr and Hf, with the Brønsted acidic Lewis adduct (C(6)F(5))(3)B·NH(3) in toluene solution leads to the formation of Tp'M(NMe(2))(2){NH(2)B(C(6)F(5))(3)} complexes. The exception to this was the attempted preparation of Tp*Ti(NMe(2))(2){NH(2)B(C(6)F(5))(3)} which was unsuccessful. Where Tp' = Tp and M = Ti and Zr and where Tp' = Tp* and M = Zr the complexes have been characterized by single crystal X-ray diffraction methods, revealing the first examples of octahedral amidoborane complexes of the group 4 metals. Attempts to drive the reactions to completion resulted in competing preferential hydrolysis of the amidoborane group, regenerating (C(6)F(5))(3)B·NH(3).

Synthesis and Structure of Amido‐ and Imido(pentafluorophenyl)borane Zirconocene and Hafnocene Complexes: NH and BH Activation

“…The most striking feature of 5⋅ PhMe is the presence of two amidoborane ligands. Our previously characterised NH 2 B(C 6 F 5 ) 3 complexes were restricted to one amidoborane ligand 16–18. While examples are known for main group NH 2 BH 3 complexes,28 compound 5 is a rare instance of ligation by two substituted amidoborane ligands 29…”

“…Our previously Scheme 6. www.chemeurj.org 3 complexes were restricted to one amidoborane ligand. [16][17][18] While examples are known for main group NH 2 BH 3 complexes, [28] compound 5 is a rare instance of ligation by two substituted amidoborane ligands. [29] The two amidoborane ligands in 5·PhMe exhibit markedly different Zr À N À B angles 92.3(6) and 120.0(6), which coupled with the relatively short Zr···H contact of 2.294 does indicate an agostic interaction to one of the amidoborane ligands.…”

“…The [NHBA C H T U N G T R E N N U N G (C 6 F 5 ) 2 H] 2À ligand can be formally regarded as a Lewis acid stabilised terminal imido or imidoborane ligand, thus complementing the amidoborane and nitridoborane examples we have recently reported. [16][17][18][19][20][21] The coordination sphere of 9·PhMe is all the more remarkable, because imido zirconocene and hafnocene complexes have previously required stabilisation with bulky nitrogen substituents. Even then, such compounds could only be isolated with basic donor ligands occupying the coordination site taken by an agostic interaction in 9·PhMe.…”

“…In earlier work, we demonstrated the synthesis of amidoborane and ultimately nitridoborane complexes through sequential N À H activation of the adduct H 3 N·BA C H T U N G T R E N N U N G (C 6 F 5 ) 3 following the reaction with metal bases (Scheme 2). [16][17][18][19][20][21] Metallocene complexes of the [NH 2 BA C H T U N G T R E N N U N G (C 6 F 5 ) 3 ] À ligand were prepared through treatment of the electrophilic zwitterions [Cp 2 MMe- 3 ]. [16] This work has played an important role in illustrating N À H activation pathways, but BA C H T U N G T R E N N U N G (C 6 F 5 ) 3 derived ligands are of limited value as models for intermediates in the catalytic reactions, because of the absence of b-hydrides.…”

Boron, aluminium, gallium, indium and thallium

“…173 The direct reaction of the ammonia adduct with metal amide complexes has been shown to result in the formation of amidoborane complexes. 174 Similarly reactions of the H 2 O borane adduct result in the formation of anionic oxy-borate salts. 175 The topic of hydrogen storage and the development of amine-borane adducts and their derivatives has continued to be a topic of significant interest during 2011, and has attracted attention from researchers developing new B-N compounds [176][177][178][179][180][181] to those developing both Main Group [182][183][184][185] and transition metal dehydrogenation reagent catalysts [186][187][188][189][190] as well as those investigating mechanisms of dehydrogenation, both experimentally and computationally.…”